657 results on '"Jacob, Peter"'
Search Results
352. Obituary William F. Morgan (23 December 1952-13 November 2015).
- Author
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Blettner, Maria, Jacob, Peter, Rühm, Werner, and Salomaa, Sisko
- Abstract
An obituary for William F. Morgan, a researcher specialized in radiation oncology, is presented.
- Published
- 2016
- Full Text
- View/download PDF
353. Mut zur Muße.
- Author
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Jacob, Peter
- Published
- 2018
- Full Text
- View/download PDF
354. Letters.
- Author
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BILBEY, IAN, TAYLOR, LINDSAY, BOITA, PETER, REID, MURRAY, HASSLINGER, CLAUS, FAVIER, RICHARD, Dixon, Mark, PERKINS, ROB, and JACOB, PETER
- Subjects
ANTIQUE & classic cars ,LOCOMOTIVES - Abstract
Several letters to the editor are presented in response different articles in previous issues of the periodical on topics including cars owned by British designer Sir Paul Smith, owning classic cars, and Garratt steam locomotives.
- Published
- 2015
355. Device Analysis--A System-Related Topic?
- Author
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Jacob, Peter
- Subjects
- *
SEMICONDUCTORS , *FAILURE analysis , *ELECTRICAL supplies , *ELECTRIC discharges , *ELECTROSTATIC induction , *AUTOMOBILE industry - Abstract
In this article, the author tells about the Eight-Disciplines (8D) requests for the semiconductor device failure. He states that 3 percent of electrical overstress (EOS) failures are related to electrostatic discharge (ESD) problems and others are mainly system-related. He adds that in modern cars, inductive responses generate pulses beyond the scope of chip internal protection, thus external protection circuitry must be considered.
- Published
- 2012
356. YOUR FEEDBACK.
- Author
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Rangel, Mark, Jacob, Peter, Harding, Walter, Cummings, Michael, Ziroli, Nick, and G. Y.
- Published
- 2017
357. Letters.
- Author
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Munk, Peter, O'Hagan, Kathleen, Roseth, Sigmund, Milne, Kelly, Jacob, Peter, and Leclair, Holly
- Subjects
LETTERS to the editor ,PUBLIC demonstrations ,PARENTHOOD ,PARENTING education for youth ,AFGHANS - Abstract
Several letters to the editor are presented in response to articles in previous issues including "The Question Remains" by Pasha Malla in the December 2010 issue, "On Deadbeat Dads" by Heather O'Neill in the December 2010 issue, and "Last Stand in Kandahar" by Matthieu Aikins in the December 2010 issue.
- Published
- 2011
358. The molecular basis for ER tubule formation
- Author
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Brady, Jacob Peter
- Subjects
- 572.8, Molecular biophysics (biochemistry) ; Endoplasmic reticulum ; Yop1p ; amphipathic helix ; reticulon ; tubular ER ; nuclear magnetic resonance ; membrane proteins
- Abstract
Integral membrane proteins of the DP1 and reticulon families are responsible for maintaining the high membrane curvature required for both smooth ER tubules and the edges of ER sheets. Mutations in these proteins lead to motor neurone diseases such as hereditary spastic paraplegia. Reticulon/DP1 proteins contain Reticulon Homology Domains (RHD) that have unusually long (≈30 aa) hydrophobic segments and are proposed to adopt intramembrane helical hairpins that stabilise membrane curvature. I have uncovered the secondary structure and dynamics of the DP1 protein Yop1p and identified a C-terminal conserved amphipathic helix that on its own interacts strongly with negatively charged membranes and is necessary for membrane tubule formation. Analyses of DP1 and reticulon family members indicate that most, if not all, contain C-terminal sequences capable of forming amphipathic helices. Together, these results indicate that amphipathic helices play a previously unrecognised role in RHD membrane curvature stabilisation. This work paves the way towards full structure determination of Yop1p by solution state NMR and marks the first high structural resolution study on an RHD protein.
- Published
- 2015
359. The System Challenge in Failure Analysis.
- Author
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Jacob, Peter
- Subjects
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ELECTRONIC circuit protection , *SEMICONDUCTOR defects , *PRINTED circuit manufacturing , *FAILURE analysis , *SYSTEM failures - Abstract
The author focuses on the issue of the printed circuit board (PCB) circuitry or system related failure analysis in electronics. Topics discussed include need to understand the passive components and PCB wiring for failure analysis, development in the semiconductor integration and failure-detection methods and localizing failures in nanostructures.
- Published
- 2014
360. Track Structures and Dose Distributions from Decays of 131I and 125I in and around Water Spheres Simulating Micrometastases of Differentiated Thyroid Cancer
- Author
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Li, Wei Bo, Friedland, Werner, Pomplun, Ekkehard, Jacob, Peter, Paretzke, Herwig G., Lassmann, Michael, and Reiners, Christoph
- Published
- 2001
- Full Text
- View/download PDF
361. Promoting Action of Radiation in the Atomic Bomb Survivor Cancer Incidence Data
- Author
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Jacob, Peter
- Published
- 2008
- Full Text
- View/download PDF
362. Investigations into long tract function following spinal cord injury and cell transplant therapy
- Author
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Griffin, Jacob Peter
- Subjects
- 617.4, R Medicine (General) ; RC Internal medicine
- Abstract
Traumatic spinal cord injury (SCI) leads to severe functional deficits for which there are currently no effective treatments. About 50% of SCIs are incomplete leaving varying numbers of spared axons intact whilst damaging the cells which ensheathe them. These spared fibres provide targets for therapeutic interventions which aim to maximise their potential for supporting residual functions. In preclinical studies, functional outcomes are most commonly assessed using behavioural approaches. However they are unable to provide information on the mechanisms of recovery or differentiate between mechanisms occurring in the spinal cord and compensatory mechanisms occurring in the brain. This study had two main aims: firstly to develop an electrophysiological protocol for assessing transmission in the ascending dorsal column pathway, to use this protocol to characterise the effects of contusion injuries of different severities and to investigate the time course of changes to long tract function following SCI. The second aim of this project was to use this protocol combined with behavioural testing to investigate the use of human lamina-propria mesenchymal stem cells (hLP-MSCs) as a potential therapy for spinal cord injury. An electrophysiological approach was used to investigate function in rats subjected to T9 contusion injuries of the dorsal columns. Changes in the function of this pathway were assessed by recording sensory evoked potentials (SEPs) from the surface of the exposed somatosensory cortex, following stimulation of the contralateral sciatic nerve. Functional effects of increasing injury severities were investigated in normal animals and animals 6 weeks after receiving contusion injuries of increasing severity. Maximum SEP amplitudes and isopotential plot areas were reduced with injury severity, and latency to sciatic SEP onset was seen to increase in a graded fashion with increasing injury severity. SEP mapping revealed that the region of cortex from which SEPs could be recorded at or greater than certain amplitudes remained focused in the same location with increasing injury severity. Animals were investigated at different time points from acute up to 6 months post injury. Acute investigation revealed that sciatic SEPs are ablated immediately following injury and after incomplete recovery stabilise within hours of injury. Maximum sciatic SEP amplitudes and cortical areas both show 2 phases of recovery: One at 2 weeks post injury and one at 6 months. Onset latencies are seen to increase initially before gradually returning nearer to normal levels by 6 months. SEP mapping revealed that the region of cortex from which SEPs could be recorded at or greater than certain amplitudes remained focused in the same location with increasing post injury survival time. Histological observations confirmed that the injury causes substantial damage to the dorsal columns. To assess the effects of potential therapeutic hLP-MSC transplants, the functional effects of T9 150 Kdyn contusion injuries were investigated in medium injected controls and 3 week delayed hLP-MSC transplanted Sprague Dawley rats, at 10 weeks post injury. Behavioural testing was performed throughout, with terminal electrophysiological and immunohistological investigations performed at the end of the study. Animals were behaviourally tested at pre- and post-operative time points for the duration of the experiment. Electrophysiological recordings suggest some recovery of function with time after injury. Two phases of recovery are seen, one at about 2 weeks after injury and the other at about 6 months after injury; however other measurements suggest hLP-MSC transplants had little or no effect on the functional integrity of the dorsal column pathway. Open field locomotor testing using the Basso, Beattie and Bresnahan (BBB) locomotor scale revealed no differences between the recoveries of cell transplanted and control groups. Gait analysis was performed using the Digigait™ Imaging System revealing a trend for earlier recovery of co-ordination between forelimbs and hindlimbs in hLP-MSC transplanted animals compared to control animals. Moreover the step sequence data also suggested a better recovery of co-ordinated stepping in transplanted compared to medium injected animals. Dynamic weight bearing apparatus (BIOSEB) was used to measure the percentage of body weight borne on the forepaws and hindpaws, this demonstrated no effect of transplanted cells on postural changes. hLP-MSC transplants did not increase indicators of neuropathic pain in our model suggesting they are unlikely to exacerbate neuropathic pain following spinal cord injury. At present there are no immunohistochemical (IHC) markers that can be used to differentiate axons which have been remyelinated with central-type myelination from those which survived the injury. Thus, the degree of peripheral-type myelination was investigated as a simple way of assessing remyelination. This suggested that there was a greater degree of remyelination in transplanted animals, and that this was specifically in areas where transplanted cells were located.
- Published
- 2013
363. Investigation into Utrafast Dynamics of Organometallic Compounds with Transient Resonance Infrared Spectroscopy and Growing String
- Author
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Schlegel, Jacob Peter
- Subjects
- Chemistry, Growing String, Organometallic, Triiron Dodecacarbonyl, Ultrafast Spectroscopy, Vanadium Hexacarbonyl
- Abstract
Two systems were studied using either a pump-probe spectroscopic technique or a density functional theory computational method. Ultrafast time-resolved infrared spectroscopy has been used to investigate the reactivity of V(CO)5, a doublet species, with silicon-hydrogen and carbon-hydrogen bonds. Using a ultraviolet pump pulse, a carbonyl was dissociated from V(CO)6 while dissolved in triethylsilane; subsequently, a broad bandwidth infrared pulse interrogated the system. On timescales less than 1 ns, vanadium pentacarbonyl does not appear to react. The second study used the Growing String Method incorporating density functional theory to examine the possible reaction mechanisms for the fluxional rearrangement of Fe3(CO)12 and Ru3(CO)12. Fluxional mechanisms have structurally identical reactants and products; the atoms swap positions with other atoms of the same element. The concerted bridge-opening, bridge-closing mechanism for the Fe3(CO)12 was calculated to have the lowest barrier of those tested at 0.777 kcal/mol; in this mechanism, all twelve carbonyl change position and the final structure is equivalent to the initial structure. At 4.285 kcal/mol, the next lowest energy barrier was calculated for the Cotton's Merry-Go-Round mechanism.
- Published
- 2012
364. Pulmonary diffusing capacity to nitric oxide and carbon monoxide during exercise and in the supine position: a test–retest reliability study.
- Author
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Madsen, Anna Christrup, Thomsen, Rie Skovly, Nymand, Stine B., Hartmann, Jacob Peter, Rasmussen, Iben E., Mohammad, Milan, Skovgaard, Lene Theil, Hanel, Birgitte, Jønck, Simon, Iepsen, Ulrik Winning, Chistensen, Regitse H., Mortensen, Jann, and Berg, Ronan M. G.
- Subjects
- *
SUPINE position , *STATISTICAL reliability , *CARBON monoxide , *NITRIC oxide , *MEASUREMENT errors - Abstract
New Findings: What is the central question in this study?How reliable is the combined measurement of the pulmonary diffusing capacity to carbon monoxide and nitric oxide (DLCO/NO) during exercise and in the resting supine position, respectively?What is the main finding and its importance?The DLCO/NO technique is reliable with a very low day‐to‐day variability both during exercise and in the resting supine position, and may thus provide a useful physiological outcome that reflects the alveolar–capillary reserve in humans. DLCO/NO, the combined single‐breath measurement of the diffusing capacity to carbon monoxide (DLCO) and nitric oxide (DLNO) measured either during exercise or in the resting supine position may be a useful physiological measure of alveolar–capillary reserve. In the present study, we investigated the between‐day test–retest reliability of DLCO/NO‐based metrics. Twenty healthy volunteers (10 males, 10 females; mean age 25 (SD 2) years) were randomized to repeated DLCO/NO measurements during upright rest followed by either exercise (n = 11) or resting in the supine position (n = 9). The measurements were repeated within 7 days. The smallest real difference (SRD), defined as the 95% confidence limit of the standard error of measurement (SEM), the coefficient of variance (CV), and intraclass correlation coefficients were used to assess test–retest reliability. SRD for DLNO was higher during upright rest (5.4 (95% CI: 4.1, 7.5) mmol/(min kPa)) than during exercise (2.7 (95% CI: 2.0, 3.9) mmol/(min kPa)) and in the supine position (3.0 (95% CI: 2.1, 4.8) mmol/(min kPa)). SRD for DLCOc was similar between conditions. CV values for DLNO were slightly lower than for DLCOc both during exercise (1.5 (95% CI: 1.2, 1.7) vs. 3.8 (95% CI: 3.2, 4.3)%) and in the supine position (2.2 (95% CI: 1.8, 2.5) vs. 4.8 (95% CI: 3.8, 5.4)%). DLNO increased by 12.3 (95% CI: 11.1, 13.4) and DLCOc by 3.3 (95% CI: 2.9, 3.7) mmol/(min kPa) from upright rest to exercise. The DLCO/NO technique provides reliable indices of alveolar–capillary reserve, both during exercise and in the supine position. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
365. Model validation for external doses due to environmental contaminations by the chernobyl accident
- Author
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Balonov, Michael, Jacob, Peter, Erkin, Viktor, and Golikov, Vladislav
- Subjects
DRUG dosage ,MODELING (Sculpture) ,THERMOLUMINESCENCE ,MODEL validation ,RADIATION exposure ,CESIUM - Abstract
The objective of the present paper is to validate the deterministic JSP5 model for external exposures to population groups living in the areas contaminated with radionuclides after the Chernobyl accident. For this purpose inhabitants of contaminated areas wore TL-dosimeters for about 1 mo in the spring/summer periods of the years 1989 to 1994. External doses due to the Chernobyl accident were determined from the dosimeter readings by subtracting the natural background. 2,342 results for rural inhabitants and 420 results for inhabitants of the town Novozybkov passed reliability checks. These data show that the average dose in inhabitants of a rural settlement predicted by the modelis in the range 0.69-1.55 of the measured values with a confidence level of 95%. Differences are attributed to settlement specific location factors, which are supported by the very good agreement of model and measurements in Novozybkov. In this case location factors of the model were obtained from Novozybkov directly." [ABSTRACT FROM AUTHOR]
- Published
- 1999
366. Effective doses due to external irradiation from the Chernobyl accident for different population groups of Ukraine
- Author
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Jacob, Peter, Kovgan, Lionella, Likhtariov, Ilya, Novak, Dmitriy, Paretzke, Herwig P., and Vavilov, Sergey
- Subjects
POPULATION ,MATHEMATICAL models ,CHERNOBYL Nuclear Accident, Chornobyl, Ukraine, 1986 ,CESIUM - Published
- 1996
367. Calculated DNA double-strand break and fragmentation yields after irradiation with He ions
- Author
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Friedland, Werner, Dingfelder, Michael, Jacob, Peter, and Paretzke, Herwig G.
- Subjects
- *
DNA , *GENES , *SOLUTION (Chemistry) , *NUCLEIC acids - Abstract
Abstract: Tracks of He ions with LET values ranging from 7.6 up to 210keV/μm were calculated by PARTRAC and radiation damage to DNA induced in human fibroblast cells was analysed using a higher-order DNA target model. Taking into account the resolution of experimental measurements of DNA fragmentation, the computed yields of DSBs relate to the experimentally observed LET dependence. Whereas the yields of total DSBs and of short DNA fragments continue to rise with increasing LET, the yields of intermediate DNA fragments (about 1–1000kbp) have a maximum around an LET value of 100keV/μm. A similar LET dependence in measured data for cell inactivation supports the hypothesis that multiple DSBs leading to fragments in this size region have an important role for this end point. [Copyright &y& Elsevier]
- Published
- 2005
- Full Text
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368. Toward an Optimal Definition of Hypoglycemia with Continuous Glucose Monitoring.
- Author
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Mahmoudi, Zeinab, Del Favero, Simone, Jacob, Peter, and Choudhary, Pratik
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MARKOV chain Monte Carlo , *HYPOGLYCEMIA , *TYPE 1 diabetes , *GLYCEMIC index , *MEDICAL research , *INSULIN aspart , *ALGORITHMS , *GLUCOSE - Abstract
• Data show that CGM identify many episodes of low interstitial glucose (LIG) that are not experience by patients • The aim is to design a parametric LIG definition that maximizes the detection of patient reported hypoglycemia (PRH) • The LIG parameters are a glycemic threshold (h) and a minimum duration (d) below the threshold. • Testing the algorithm using real CGM and simulated PRH events indicate the feasibility of the method to optimize LIG definition with respect to PRH detection As continuous glucose monitoring (CGM) becomes common in research and clinical practice, there is a need to understand how CGM-based hypoglycemia relates to hypoglycemia episodes defined conventionally as patient reported hypoglycemia (PRH). Data show that CGM identify many episodes of low interstitial glucose (LIG) that are not experienced by patients, and so the aim of this study is to use different PRH simulations to optimize CGM parameters of threshold (h) and duration (d) to provide the best PRH detection performance. The algorithm uses particle Markov chain Monte Carlo optimization to identify the optimal h and d which maximize an objective function for detecting PRH. We tested our algorithm by creating three different cases of PRH simulations. We added three types of simulated PRH events to 10 weeks of anonymized CGM data from 96 type 1 diabetes people to see if the algorithm can detect the optimal parameters set out in the simulations. In simulation 1, we changed the locations of PRHs with respect to LIG episodes in the CGM signal to simulate random optimal LIG parameters for every individual. In simulation 2, the PRHs are CGM glucose <3.9 mmol/L followed by at least 20 min of rise > 0.11 mmol/L/min. Simulation 3 is like simulation 2 but with glucose threshold of 3.0 mmol/L. The median [interquartile range] of deviation between the optimized (found by the algorithm) and the optimal (known) h and d are −0.07% [−0.4, 1.9] and −1.3% [−5.9, 6.8], respectively across the subjects for simulation 1. The mean [min max] of the optimized LIG parameters are h = 3.8 [3.7, 3.8] mmol/L and d = 12 [10, 14] min for simulation 2 and they are h = 3.0 [2.9, 3] mmol/L and d = 10 [8, 14] min for simulation 3 across a 10-fold cross validation. This work demonstrates the feasibility of the algorithm to find the best-fit definition of CGM-based hypoglycemia for PRH detection. In a prospective clinical study collecting CGM and PRH, the current algorithm will be used to optimize the definition of hypoglycemia with respect to PRH with the ambition of using the resulted definition as a surrogate for PRH in clinical practice. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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369. Rethink education.
- Author
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Jacob, Peter
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ARCHITECTURAL education ,ARCHITECTURE - Abstract
A letter to the editor is presented in response to articles published in the July 25, 2013 issue of the journal, which was devoted to the topic of architectural education in Great Britain.
- Published
- 2013
370. HELP IS NEEDED TO ENSURE SUPPLY OF ARCHITECTS.
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Jacob, Peter
- Subjects
LETTERS to the editor ,TRUSTS & trustees - Abstract
A letter to the editor about the Royal Institute of British Architects (RIBA) Education Trust Fund is presented.
- Published
- 2007
371. Hyponatraemia in primary care
- Author
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Jacob, Peter, Dow, Claire, Lasker, Shawarna S., Drake, William M., and Chowdhury, Tahseen A.
372. Dose-dependent expression of CLIP2 in post-Chernobyl papillary thyroid carcinomas.
- Author
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Selmansberger, Martin, Kaiser, Jan Christian, Hess, Julia, Güthlin, Denise, Likhtarev, I., Shpak, Victor, Tronko, Mykola, Brenner, Alina, Abend, Michael, Blettner, Maria, Unger, Kristian, Jacob, Peter, and Zitzelsberger, Horst
- Subjects
- *
GENE expression , *PAPILLARY carcinoma , *THYROID cancer , *CHERNOBYL Nuclear Accident, Chornobyl, Ukraine, 1986 , *MESSENGER RNA - Abstract
A previous study on papillary thyroid carcinomas (PTC) in young patients who were exposed to 131iodine from the Chernobyl fallout revealed an exclusive gain of chromosomal band 7q11.23 in exposed cases compared to an age-matched control cohort. CLIP2, a gene located within band 7q11.23 was shown to be differentially expressed between exposed and nonexposed cases at messenger RNA and protein level. Therefore, a standardized procedure for CLIP2 typing of PTCs has been developed in a follow-up study. Here we used CLIP2 typing data on 117 post-Chernobyl PTCs from two cohorts of exposed patients with individual dose estimates and 24 non-exposed controls to investigate a possible quantitative dose-response relationship of the CLIP2 marker. The 'Genrisk-T' cohort consisted of 45 PTCs and the 'UkrAm' cohort of 72 PTCs. Both cohorts differed in mean dose (0.59 Gy Genrisk-T, 1.2 Gy UkrAm) and mean age at exposure (AaE) (2 years Genrisk-T, 8 years UkrAm), whilst the median latency (16 years Genrisk-T, 18 years UkrAm) was comparable. We analyzed the association between the binary CLIP2 typing and continuous thyroid dose with logistic regression. A clear positive dose-response relationship was found for young PTC cases [age at operation (AaO) < 20 years, AaE < 5 years]. In the elder age group a higher proportion of sporadic tumors is assumed due to a negligible dose response, suggesting different molecular mechanisms in sporadic and radiation-induced cases. This is further supported by the association of elder patients (AaO > 20 years) with positivity for BRAF V600E mutation. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
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373. AGE DEPENDENCIES OF 90Sr INCORPORATION IN DENTAL TISSUES: COMPARATIVE ANALYSIS AND INTERPRETATION OF DIFFERENT KINDS OF MEASUREMENTS OBTAINED FOR RESIDENTS ON THE TECHA RIVER
- Author
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Jacob, Peter
- Published
- 2003
- Full Text
- View/download PDF
374. Role of DNA organisation and environmental scavenging capacity in the evolution of radiobiological damage: models and simulations
- Author
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Ballarini, Francesca, Friedland, Werner, Jacob, Peter, Ottolenghi, Andrea, Paretzke, Herwig G., Scannicchio, Domenico, and Valota, Andrea
- Subjects
- *
DNA , *RADIOBIOLOGY , *CHROMOSOMES , *NUCLEIC acids - Abstract
Summary: Background and purpose: Theoretical models and Monte Carlo simulations were developed, aimed to investigate the role played by the organisation of interphase DNA and the environmental scavenging capacity conditions in the induction of radiobiological damage. Methods: The induction of single- and double-strand breaks by gamma rays impinging on different DNA structures (e.g. linear DNA, SV40 minichromosome and cellular DNA) was simulated as a function of the environment scavenging capacity. Furthermore, yields of chromosome aberrations (CA) induced by gamma rays and light ions were simulated with a purposely developed MC code that explicitly takes into account the DNA higher-order organisation as chromosome territories. Results and Conclusions: Simulations performed with the PARTRAC code allowed quantification of the dependence of dsb and ssb both on the target structure, and on the scavenging capacity. The results relative to CA showed the importance of DNA damage complexity (nanometre scale) and interphase chromosome domains (micrometre scale) in the process of aberration formation. Very good agreement was found between the model predictions on ssb, dsb and CA and available experimental data. [Copyright &y& Elsevier]
- Published
- 2004
- Full Text
- View/download PDF
375. Journey to America
- Author
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Tocqueville, Alexis de, 1805-1859., Lawrence, George A. (George Alfred), 1827-1876., Mayer, J. P. (Jacob Peter), 1903-, and Tocqueville, Alexis de, 1805-1859.
- Published
- 1960
376. Συναρτήσεις Mittag-Leffler
- Author
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Κοκολογιαννάκη, Χρυσή, Rizos, Dimitrios, Παπαγεωργίου, Βασίλειος, and Van der Weele, Jacob Peter
- Subjects
Properties of functions ,Εφαρμογές συναρτήσεων ,Ιδιότητες συναρτήσεων ,Συναρτήσεις Mittag-Leffler ,Mittag-Leffler functions - Abstract
Οι συναρτήσεις Mittag-Leffler χρησιμοποιούνται στις κλασματικές διαφορικές εξισώσεις, διότι η λύση τους εκφράζεται με τις συναρτήσεις Mittag-Leffler και γενικεύσεις αυτών. Η εργασία αυτή αποτελεί ανασκόπηση για τις συναρτήσεις Mittag-Leffler και περιλαμβάνει εκτός από τους ορισμούς αυτών και των γενικεύσεών τους, ιδιότητες και αναδρομικές σχέσεις που ικανοποιούν. Εκφράζουμε γνωστές συναρτήσεις με τη βοήθεια των συναρτήσεων Mittag-Leffler. Βρίσκουμε το μετασχηματισμό Laplace αυτών και των γενικεύσεών τους, διότι ο μετασχηματισμός Laplace είναι μια μέθοδος επίλυσης των κλασματικών διαφορικών εξισώσεων. Τέλος, αναφέρουμε εφαρμογές και προβλήματα, που εκφράζονται μέσω κλασματικών διαφορικών εξισώσεων και δίνουμε τη λύση τους με μορφή συναρτήσεων Mittag-Leffler. The Mittag-Leffler functions are used in fractional differential equations, because their solution is expressed with the Mittag-Leffler functions and generalizations of them. This diploma thesis constitutes a review of the Mittag-Leffler functions and includes besides the definitions of them and their generalizations, some properties and recurrence relations that they satisfy. We express some acquaintances functions with the Mittag-Leffler functions. In addition, we calculate the Laplace transform of these functions and their generalizations, which is useful in deriving the solution of fractional differential equations. Finally, we present some applications and problems, which are expressed through fractional differential equations and we give their solution with terms of the Mittag-Leffler functions.
- Published
- 2010
377. Μαθηματικές μέθοδοι στα μικροοικονομικά και χρηματοοικονομικά
- Author
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Μπούντης, Αναστάσιος, Andriopoulos, Kostis, Τσουμπελής, Δημήτριος, Van der Weele, Jacob-Peter, Πνευματικός, Σπυρίδων, Παπαγεωργίου, Βασίλειος, Συριόπουλος, Κωνσταντίνος, and Παπαθεοδώρου, Θεόδωρος
- Subjects
Θεωρία παιγνίων ,338.5 ,Lie algebras ,Black-Scholes equation ,Εξίσωση Black-Scholes ,Συμμετρίες Lie ,Εξισώσεις Hamilton-Jacobi-Bellman ,Oligopoly theory ,Lie symmetries ,Θεωρία ολιγοπωλίων ,Pricing of commodities ,Άλγεβρες Lie ,Game theory - Abstract
Η διατριβή χωρίζεται σε δύο μέρη. Στο Μέρος Α' χρησιμοποιούνται μαθηματικές μέθοδοι της Θεωρίας Παιγνίων και των Δυναμικών Συστημάτων για να μελετηθεί η κανονική και χαοτική δυναμική διαφόρων μοντέλων της Μικροοικονομίας. Βασικά αποτελέσματα είναι η μετάβαση σε συνθήκες πλήρους ανταγωνισμού και η διαφοροποίηση του παραγόμενου προιόντος σε ένα δυοπώλιο-τριοπώλιο. Στο Μέρος Β', κύριος στόχος της έρευνας ήταν να συνδεθούν ορισμένες από τις πλέον γνωστές μερικές διαφορικές εξισώσεις (ΜΔΕ) που χρησιμοποιούνται στα Οικονομικά Μαθηματικά και Χρηματοοικονομικά, με την εξίσωση της θερμότητας της Μαθηματικής Φυσικής, εφαρμόζοντας την κατά Lie συμμετρίες ανάλυση. Επίσης η ανάλυση αυτή αποδείχθηκε ιδιαίτερα ισχυρή για την εύρεση αλγεβρικών δομών εξισώσεων που περιγράφουν την τιμολόγηση αγαθών. Έτσι, οδηγούμαστε με συστηματικό τρόπο όχι μόνο στην εύρεση νέων λύσεων αλλά και στην ανακάλυψη κομψών γενικεύσεων των εξισώσεων αυτών. The thesis is divided into two parts. In Part One we use the mathematical methods of Game Theory and Dynamical Systems to study the stable and chaotic dynamics of various models in Microeconomics. Some of our main results are the route to perfect competition and the differentiation of goods in a duopoly and in a triopoly. In Part Two, our main concern was to link some of the most well-known partial differential equations that are encountered in Economics and Financial Mathematics, with the heat equation of Mathematical Physics, using Lie symmetry analysis. More to that, this analysis proved extremely powerful to the finding of interesting algebraic properties for equations that describe the pricing of commodities. In such way, we succeed in presenting, in a systematic fashion, not only new solutions, but also elegant generalisations of the equations under investigation.
- Published
- 2010
378. Διαφορική θεωρία Galois και μη-ολοκληρωσιμότητα του ανισοτροπικού προβλήματος Stormer και του ισοσκελούς προβλήματος τριών σωμάτων
- Author
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Παπαγεωργίου, Βασίλειος, Nomikos, Dimitrios, Van der Weele, Jacob-Peter, Γκίκας, Δημήτριος, Κοκολογιαννάκη, Χρυσή, Μπούντης, Αναστάσιος, Πνευματικός, Σπυρίδων, and Τσουμπελής, Δημήτριος
- Subjects
Κανονικές ιδιομορφίες ,Anisotropic Stormer problem ,Διαφορική θεωρία Galois ,Ανισοτροπικό πρόβλημα Stormer ,Ισοσκελές πρόβλημα τριών σωμάτων ,Liouvillian solutions ,Differential Galois theory ,Linear algebraic groups ,Ολοκληρωσιμότητα συστημάτων Hamilton ,Isosceles three-body problem ,Regular singularities ,Variational equations ,Integrability of Hamiltonian systems ,Λύσεις Liouville ,Εξισώσεις μεταβολών ,515.39 ,Γραμμικές αλγεβρικές ομάδες - Abstract
Στην παρούσα διατριβή μελετήσαμε την ολοκληρωσιμότητα του ανισοτροπικού προβλήματος Størmer (ASP) και του ισοσκελούς προβλημάτος τριών σωμάτων (IP), με εφαρμογή της θεωρίας Morales-Ramis-Simó. Τα αποτελέσματα της μελέτης δημοσιεύθηκαν στο περιοδικό Physica D: Nonlinear Phenomena. Ένα σύστημα Hamilton SH, Ν βαθμών ελευθερίας, είναι ολοκληρώσιμο (κατά Liouville) όταν επιδέχεται Ν συναρτησιακώς ανεξάρτητα και σε ενέλιξη πρώτα ολοκληρώματα. Οι J.J. Morales-Ruiz, J.P. Ramis και C. Simó απέδειξαν ότι αν ένα SH είναι ολοκληρώσιμο, τότε η ταυτοτική συνιστώσα G0k της διαφορικής ομάδας Galois των εξισώσεων μεταβολών VE¬k τάξης k , που αντιστοιχούν σε μια ολοκληρωτική καμπύλη του SH, είναι αβελιανή. Το ASP μπορεί να θεωρηθεί ότι είναι ένα σύστημα Hamilton δυο βαθμών ελευθερίας που περιέχει τις παραμέτρους pφ και ν2>0, το οποίο περιγράφει την κίνηση ενός φορτισμένου σωματιδίου υπό την επίδραση του μαγνητικού πεδίου ενός διπόλου. Οι Α. Almeida, T. Stuchi είχαν αποδείξει ότι το ASP είναι μη-ολοκληρώσιμο για pφ≠0 και ν2>0, ενω για pφ=0 είχαν αποδείξει τη μη-ολοκληρωσιμότητα των περιπτώσεων που αντιστοιχούν στις τιμές ν2≠5/12, 2/3. Η δική μας διερεύνηση απέδειξε ότι το ASP με pφ=0 (ASP0) είναι, επίσης, μη-ολοκληρώσιμο για ν2=5/12, 2/3. Αρχικά, με χρήση της μεθόδου Yoshida, αναλύσαμε τις G01 των VE¬1, που αντιστοιχούν σε δύο ολοκληρωτικές καμπύλες του ASP0, καταλήγοντας ότι οι G01 είναι μη-αβελιανές για ν2≠2/3. Στη συνέχεια, ορίσαμε τις VE3 κατά μήκος μιας τρίτης ολοκληρωτικής καμπύλης του ASP0 και δείξαμε ότι η αντίστοιχη G03 είναι μη-αβελιανή για ν2=2/3. Σύμφωνα με τη θεωρία Morales-Ramis-Simó, τα προαναφερόμενα αποδεικνύουν τη μη-ολοκληρωσιμότητα του ASΡ για pφ=0 και ν2>0. Το ΙΡ είναι μια υποπερίπτωση του προβλήματος τριών σωμάτων και μπορεί να μελετηθεί ως ένα σύστημα Hamilton δύο βαθμών ελευθερίας με παραμέτρους pφ και m, m3>0. Η προγενέστερη ανάλυση του ΙΡ υπεδείκνυε τη μη-ολοκληρωσιμότητα του συστήματος, όμως είχε πραγματοποιηθεί με χρήση αριθμητικών μεθόδων. Βρίσκοντας από μια ολοκληρωτική καμπύλη για κάθε μια απο τις περιπτώσεις pφ=0, pφ≠0, ορίσαμε τις αντίστοιχες VE1 και αποδείξαμε τη μη-ολοκληρωσιμότητα του ΙΡ. Για pφ=0 χρησιμοποιήσαμε τη μέθοδο Yoshida για να μελετήσουμε την G01, ενώ για pφ≠0 εφαρμόσαμε τον αλγόριθμο Kovacic και ερευνητικά αποτελέσματα των D. Boucher, J.A. Weil για να διερευνήσουμε την αντίστοιχη G01. Οι G01 και στις δυο προαναφερόμενες περιπτώσεις είναι μη-αβελιανές, οπότε το ΙΡ είναι μη-ολοκληρώσιμο, σύμφωνα με τη θεωρία Morales-Ramis-Simó. In the present dissertation we studied the integrability of the anisotropic Stormer problem (ASP) and the isosceles three-body problem (IP), applying the Morales-Ramis-Simo theory. The results of our study were published by the journal Physica D: Nonlinear Phenomena. A Hamiltonian system SH, of N degrees of freedom, is integrable (in the Liouville sense) if it admits an involutive set of N functionally independent first integrals. J.J. Morales-Ruiz, J.P. Ramis and C. Simó proved that if an SH is integrable, then the identity component G0k of the differential Galois group of the variational equations VE¬k of order k that correspond to an integral curve of the SH, is abelian. The ASP can be considered as a Hamiltonian system of two degrees of freedom that contains the parameters pφ and ν2>0, which describes the motion of a charged particle under the influence of the magnetic field of a dipole. Α. Almeida, T. Stuchi had proved that the ASP is non-integrable for pφ≠0 and ν2>0, while for pφ=0 they had proved the non-integrability of the cases that correspond to ν2≠5/12, 2/3. Our study proved that the ASP with pφ=0 (ASP0) is, also, non-integrable for ν2=5/12, 2/3. Initially, using the Yoshida method, we analysed the G01 of the VE¬1, that correspond to two integrals curves of the ASP0, concluding that they are non-abelian for ν2≠2/3. Then, we defined the VE3 along a third integral curve of the ASP0 and indicated that the corresponding G03 is non-abelian for ν2=2/3. According to the Morales-Ramis-Simó theory, the aforementioned considerations prove the non-integrability of the ASP for pφ=0 and ν2>0. The IP is a special case of the three-body problem and it can be treated as a Hamiltonian system of two degrees of freedom that embodies the parameters pφ and m, m3>0. Previous analysis of the IP suggested the non-integrability of the system, but it was performed with the use of numerical methods. Finding an integral curve for each of the cases pφ=0, pφ≠0, we defined the corresponding VE1 and proved the non-integrability of the IP. For pφ=0 we used the Yoshida method to examine G01 , while for pφ≠0 we applied the Kovacic algorithm and some results of D. Boucher, J.A. Weil to investigate the corresponding G01 . In both of the aforementioned cases the G01 were non-abelian, yielding IP non-integrable, according to the Morales-Ramis-Simó theory.
- Published
- 2010
379. Μη γραμμικές εξισώσεις εξέλιξης : η μέθοδος ένδυσης
- Author
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Τσουμπελής, Δημήτριος, Roustemoglou, Ilia, Van der Weele, Jacob-Peter, and Μπούντης, Αναστάσιος
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Riemann-Hilbert problem ,Πρόβλημα Riemann-Hilbert ,D-bar problem ,Σολιτόνια ,Ζεύγη Lax ,Lax pairs ,Πρόβλημα d-bar ,515.353 ,Dressing method ,Μέθοδος ένδυσης ,Solitons - Abstract
Όπως μπορεί κανείς να καταλάβει και από τον τίτλο, η εργασία έχει να κάνει με μία μέθοδο επίλυσης μη γραμμικών μερικών διαφορικών εξισώσεων και, συγκεκριμένα, μιας οικογένειας τέτοιων εξισώσεων, που ονομάζονται εξισώσεις εξέλιξης. Πολλές από αυτές, μάλιστα, επιδέχονται ειδικού τύπου λύσεις που είναι γνωστές με το όνομα σολιτόνια (solitons). Αρχικά, μας απασχολεί η έννοια της ολοκληρωσιμότητας, για την οποία όμως δεν υπάρχει κάποιος σαφής ορισμός. Παρ' όλα αυτά, μπορούμε να πούμε ότι μία διαφορική εξίσωση καλείται ολοκληρώσιμη όταν μπορεί να γραμμικοποιηθεί άμεσα ή έμμεσα. Ο όρος έμμεση γραμμικοποίηση συνδέεται με την έννοια της ύπαρξης ζευγαριού Lax, την οποία εξηγούμε χρησιμοποιώντας εργαλεία της θεωρίας τελεστών. Για τις μη γραμμικές εξισώσεις εξέλιξης, έχει αναπτυχθεί πλέον πλήθος μεθόδων ανάλυσης, στα πλαίσια της ολοκληρωσιμότητας, και υπάρχει πλούσια σχετική βιβλιογραφία. Αναφέρουμε συνοπτικά μερικές από αυτές χρησιμοποιώντας κάποια παραδείγματα, ενώ επικεντρωνόμαστε στην αναλυτική περιγραφή μιας μεθόδου που πρώτοι παρουσίασαν οι Zakharov και Shabat το 1974. Η μέθοδος αυτή, η οποία αναπτύχθηκε λίγο μετά τη μέθοδο της αντίστροφης σκέδασης, ονομάζεται μέθοδος ένδυσης (dressing method) ή σχήμα των ZS. Για την παρουσίασή της, χρησιμοποιούμε μόνο τελεστές χωρίς να αναφερόμαστε πουθενά στα δεδομένα σκέδασης του προβλήματος. Εισάγουμε, με τη βοήθεια διαφορικών και ολοκληρωτικών τελεστών, το γυμνό (undressed) και το ντυμένο (dressed) τελεστή και, έπειτα, δείχνουμε πώς από αυτούς προκύπτει η γενικευμένη εξίσωση Lax. Παραθέτουμε κάποια παραδείγματα εξισώσεων στις οποίες εφαρμόζεται η μέθοδος και, τέλος, κατασκευάζουμε σολιτονικές λύσεις για τη μη γραμμική εξίσωση του Schrödinger, με τη βοήθεια της ολοκληρωτικής εξίσωσης των Gelfand-Levitan-Marchenko. Πέρα από την περιγραφή της μεθόδου ένδυσης στην αρχική της μορφή, βλέπουμε και πώς αυτή εμφανίζεται στη σύγχρονη βιβλιογραφία. Με την πάροδο του χρόνου εξελίχθηκε αρκετά και συνδέθηκε με προβλήματα της μιγαδικής ανάλυσης και, πιο συγκεκριμένα, με τα προβλήματα Riemann-Hilbert (RH) και dbar που, με τη σειρά τους, προκύπτουν σε πολλές εφαρμογές των μαθηματικών. Από ένα μεγάλο πλήθος πρόσφατα δημοσιευμένων άρθρων, παρουσιάζουμε αναλυτικότερα ένα, αυτό των Bogdanov και Zakharov (2002), που αφορά στην εξίσωση Boussinesq. Περιγράφουμε μια ειδικότερη μορφή της μεθόδου ένδυσης, η οποία ονομάζεται ένδυση dbar (dbar-dressing) και αναλύουμε, μέσω αυτής, τις σολιτονικές λύσεις και το συνεχές φάσμα της εξίσωσης Boussinesq. Οι σολιτονικές λύσεις της εξίσωσης παρουσιάζουν μία πολύ ιδιαίτερη συμπεριφορά, η οποία έρχεται σε αντίθεση με τον ευσταθή χαρακτήρα των σολιτονίων. As one can understand from the title, our main subject is a method for solving nonlinear partial differential equations and in particular a family of such equations, called evolution equations. Many of them admit a special kind of solutions, known as solitons. One of our basic interests is the integrability of a nonlinear evolution equation, although a specific definition for that does not exist in the bibliography. However, a partial differential equation is considered to be integrable when it can be linearized directly or indirectly. By indirect linearization we mean the existence of a Lax pair for the initial equation and this connection is explained in terms of operator theory. In the frame of integrability, a large number of methods dealing with the study and analysis of nonlinear evolution equations has been developed. We briefly mention some of them and present some examples, while we focus on the analytic description of a method which was introduced by Zakharov and Shabat, in 1974. This method was developed right after the Inverse Scattering Method and it is known as dressing method or ZS scheme. In order to present it, a dressed and undressed operator are introduced, by the use of operators only whithout refering to the scattering data. Based on those operators the generalized Lax equation is produced. Then we present a number of examples of evolution equations which can be solved via the dressing method and finally we constract soliton solutions for the nonlinear Schrödinger equation by solving the Gelfand-Levitan-Marchenko integral equation. Appart from the description of dressing method in its initial form, a quick review of recent papers and results is considered. The method evolved through time and was connected with some problems of complex analysis and specifically the Riemann-Hilbert (RH) and dbar problems. Those two problems arise in many mathematical and physical applications. From a wide range of recent published articles, we analytically present one which was written by Bogdanov and Zakharov (2002) and deals with Boussinesq equation. The continuous spectrum and soliton solutions are investigated, using a special form of dressind method called dbar-dressing. Soliton solutions for the Boussinesq equations demonstrate a quite extraordinary behaviour destroying the stereotype of usual solitons which are considered to be stable objects.
- Published
- 2009
380. The initial-boundary value problem for nonlinear evolution partial differential equations
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Τσουμπελής, Δημήτριος, Hitzazis, Iasonas, Van der Weele, Jacob-Peter, Δάσιος, Γεώργιος, Κοτσιώλης, Αθανάσιος, Μπούντης, Αναστάσιος, Παπαγεωργίου, Βασίλειος, and Σιαφαρίκας, Παναγιώτης
- Subjects
Εξελικτική ,Lax pair ,Evolution ,515.353 ,Nonlinear ,Πρόβλημα Riemann-HIilbert ,Partial differential equations ,Integrable ,Πρόβλημα αρχικών-συνοριακών τιμών ,Initial-boundary value problem ,Riemann-HIilbert problem ,Ζεύγος Lax ,Ολοκληρώσιμη ,Μη γραμμική ,Μερικές διαφορικές εξισώσεις - Abstract
Στην παρούσα διδακτορική διατριβή μελετά με το πρόβλημα αρχικών-συνοριακών τιμών (ΠΑΣΤ) για τη μη γραμμική εξελικτική μερική διαφορική εξίσωση των Korteweg-De Vries (KDV) σε ένα φραγμένο διάστημα της χωρικής μεταβλητής. Η μέθοδος που εφαρμόζουμε είναι γνωστή σαν μέθοδος του ενοποιημένου μετασχηματισμού. Η εφαρμογή της μεθόδου στο υπό θεώρηση ΠΑΣΤ συνίσταται στη λεγόμενη ταυτόχρονη φασματική ανάλυση του αντίστοιχου της εξίσωσης KDV ζεύγους Lax. Ένας βασικός ερευνητικός στόχος που επιτεύχθηκε στη συνεισφορά αυτή συνίσταται στην έκφραση, για μια αρκετά γενική κλάση αρχικών και συνοριακών συνθηκών, της λύσης του ΠΑΣΤ σαν μια ολοκληρωτική αναπαράσταση μέσω της λύσης ενός κατάλληλου προβλήματος Riemann-Hilbert (RH) στο μιγαδικό επίπεδο της φασματικής παραμέτρου. Μάλιστα, παρέχονται δύο εναλλακτικές ολοκληρωτικές αναπαραστάσεις για καθένα από δύο εναλλακτικά προβλήματα RH. Ένα δεύτερος ερευνητικός στόχος ο οποίος επιτυγχάνεται είναι η ανάπτυξη μιας διαδικασίας αναγωγής του ιδιόμορφου προβλήματος RH σε ένα ολόμορφο. Ένας τρίτος, τέλος, ερευνητικός στόχος ο οποίος επιτυγχάνεται είναι ο χαρακτηρισμός της λεγόμενης γενικευμένης απεικόνισης Dirichlet-to-Neumann, η έκφραση, δηλαδή, των αγνώστων συνοριακών συναρτήσεων μέσω των επιβεβλημένων αρχικών και συνοριακών συνθηκών. Η διατριβή διαρθρώνεται σε επτά κεφάλαια, εκ των οποίων το πρώτο είναι εισαγωγικού χαρακτήρα, ενώ τα υπόλοιπα έξι αποτελούν το πρωτότυπο μέρος της διατριβής. Αναλυτικά, το περιεχόμενο καθενός κεφαλαίου έχει ως ακολούθως. Στο πρώτο κεφάλαιο παρουσιάζεται, μεταξύ άλλων, το πρόβλημα RH, τη μέθοδο της αντίστροφης σκέδασης για την KDV, τη μέθοδο της ένδυσης για την KDV και τη μέθοδο της ταυτόχρονης φασματικής ανάλυσης του ζεύγους Lax. Στο κεφάλαιο 2 ξεκινάμε την εφαρμογή της μεθόδου στο υπό θεώρηση ΠΑΣΤ υποθέτοντας ότι η KDV επιδέχεται λύση στην αντίστοιχη χωροχρονική περιοχή. Η αντίστοιχη της περιοχής αυτής ταυτόχρονη φασματική ανάλυση του ζεύγους Lax οδηγεί στη διατύπωση ενός ιδιόμορφου ομογενούς προβλήματος RH. Αυτό ορίζεται μέσω μιας εξάδας φασματικών συναρτήσεων. Οι τελευταίες εκφράζονται μέσω των αρχικών τιμών της λύσης και των συνοριακών τιμών και εγκαρσίων συνοριακών της μέχρι και δεύτερης τάξης. Στο κεφάλαιο 3 ορίζουμε τις 6 φασματικές συναρτήσεις που αντιστοιχούν στις αρχικές και συνοριακές συνθήκες και δείχνουμε ότι η αντιστροφή των απεικονίσεων αυτών περιγράφεται μέσω καταλλήλων προβλημάτων RH. Δείχνουμε επίσης ότι ικανοποιείται μια εξίσωση που ονομάζεται ολική σχέση και χαρακτηρίζει τα αποδεκτά σύνολα αρχικών και συνοριακών συναρτήσεων. Στο κεφάλαιο 4 δείχνουμε ότι η ασυμπτωματική συμπεριφορά της λύσης του προβλήματος RH οδηγεί πράγματι σε μια λύση του ΠΑΣΤ. Στο κεφάλαιο 5 μελετάμε τη μονοσήμαντη επιλυσιμότητα του προβλήματος RH. Στο κεφάλαιο 6 παρουσιάζουμε έναν εναλλακτικό τρόπο διατύπωσης προβλήματος RH, αντικαθιστώντας του πόλους με καμπύλες ασυνέχειας. Στο κεφάλαιο 7 χρησιμοποιούμε την ολική σχέση για την κατασκευή της γενικευμένης απεικόνισης Dirichlet-to-Neumann, για το χαρακτηρισμό δηλαδή των αγνώστων συνοριακών συναρτήσεων (που εμφανίζονται στο πρόβλημα RH) μέσω των επιβεβλημένων αρχικών και συνοριακών συνθηκών. In the present PhD thesis we study the initial-boundary value problem for the nonlinear evolution partial diefferential equation of Korteweg-De Vries (KDV) posed on a finite interval of the spatial variable. The method we employ is known as unified transform method. The application of the method on the IBVP under consideration consists of the so-called simultaneous spectral analysis of the Lax pair associated to the KDV equation. The first aim achieved in this contribution, is the expression of the solution of the IBVP as an integral representation in terms of the solution an appropriate Riemann-Hilbert (RH) problem in the complex plane of the spectral parameter, for a sufficiently large class of initial and boundary conditions. In particular, we provide two different integral representations for each one of two different RH problems. A second aim achieved is the invention of a procedure for the reduction of the singular RH problem to a regular one. A third aim achieved is the caracterization of the so-called generalized Dirichlet-to_Neumann map, that is, the expression of the unknown boundary functions in terms of the prescribed initial and boundary conditions. The Phd thesis is divided in 7 chapters. The first chapter is of an introductory character, while the remaining six chapters consist of the original contribution of the thesis. Analytically, the content of each chapter has as follows. The first chapter presents, among other things, the RH problem, the inverse scattering method for KDV, the dressing method for KDV and the method of simultaneous spectral analysis of the Lax pair. Chapter 2 presents the first step of the application of the method upon the IBVP, under the assumption thet KDV is solvable in the corresponding space-time region. The simultaneous spectral analysis of the Lax pair leads to the formulation of a singular homogenous RH factorization problem, which is defined in terms of six spectral functions. The last ones are expressed in terms of the initial and boundary values of the solution and of its transverse boundary derivatives up to order two. In chapter 3 we define the six spectral functions that correspond to the initial and boundary conditions and show that the inversion of these mappings can be described through appropriate RH problems. Also an appropriate “global relation” is satisfied, which characterizes the admissible initial and boundary functions. In chapter 4 we show that the asymptotic behavior of the solution of the RH problem leads actually to a solution of the IBVP. In chapter 5 we study the unique solvability of the RH problem. In chapter 6 we present an alternative RH formulation, replacing the poles by discontinuity curves. In chapter 7 we present the global relation to construct the generalized Dirichlet-to-Neumann map, that is, the expression of the unknown boundary functions (appearing in the RH formulation) in terms of the prescribed initial and boundary conditions.
- Published
- 2009
381. Μοντέλα εξέλιξης πληθυσμών με περιοδικές διαταραχές : ευσταθής και χαοτική δυναμική
- Author
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Μπούντης, Αναστάσιος, Koutsokeras, Stavros, Van der Weele, Jacob-Peter, and Βραχάτης, Μιχαήλ
- Subjects
Chaotic dynamics ,Population ,Πληθυσμός ,577.880 151 ,Χαοτική δυναμική - Abstract
Όπως είναι γνωστό, οι μη γραμμικές συνήθεις διαφορικές εξισώσεις δυναμικών συστημάτων μιας ή περισσοτέρων μεταβλητών, αποτελούν σημαντικό εργαλείο για τους επιστήμονες, που προσπαθούν να δώσουν λύσεις σε ερωτήματα που αφορούν στην εξέλιξη των συστημάτων αυτών στον χρόνο. Ιδιαίτερο ενδιαφέρον παρουσιάζουν δυναμικά συστήματα που περιγράφουν προβλήματα της Φυσικής, της Βιολογίας, της Τεχνολογίας και των Οικονομικών Επιστημών. Στην παρούσα εργασία θα μελετήσουμε ορισμένα μη γραμμικά μοντέλα εξέλιξης πληθυσμών καθώς και διάφορες παραλλαγές αυτών που προκύπτουν από την προσθήκη μη γραμμικών όρων και περιοδικών συναρτήσεων. Πιο συγκεκριμένα, στο πρώτο κεφάλαιο θα κάνουμε μια εισαγωγή εξετάζοντας γνωστά μοντέλα μιας διάστασης, όπως το γραμμικό μοντέλο του Malthus, και το μη γραμμικό μοντέλο του Verhulst αναφέροντας κάποια παρατηρησιακά δεδομένα που επιβεβαιώνουν τη χρησιμότητα αλλά και τους περιορισμούς των μοντέλων αυτών. Θα αναφερθούμε επίσης στην εξίσωση του Verhulst υπό την επίδραση μιας εξωτερικής περιοδικής διαταραχής. Στο Κεφάλαιο 2, το οποίο αποτελεί και το κυρίως θέμα της παρούσας εργασίας, θα μελετήσουμε ένα μη γραμμικό σύστημα αλληλεπίδρασης δυο πληθυσμών διαφορετικών βιολογικών ειδών, που περιγράφεται από το σύστημα εξισώσεων Lotka-Volterra. Ξεκινώντας από την απλή περιοδική συμπεριφορά του αδιατάρακτου μοντέλου, προσθέτουμε επιπλέον όρους που περιγράφουν θανάτους λόγω ανταγωνισμού των μελών ενός είδους. Στη συνέχεια θα προχωρήσουμε στη μελέτη περιοδικώς διαταραγμένων συστημάτων τύπου Lotka-Volterra, η δυναμική των οποίων φανερώνει ένα μεγάλο μέρος της ομορφιάς της μη γραμμικής επιστήμης: Μπορούμε δηλαδή να δούμε απλά φαινόμενα όπως ένα ευσταθή οριακό κύκλο, εώς ένα πολύ εντυπωσιακό χαοτικό ελκυστή! Στη συνέχεια, θα εστιάσουμε τη μελέτη μας στο σύστημα Lotka-Volterra τριών μεταβλητών που είναι πολύ σημαντικό για την μελέτη πληθυσμών τριών διαφορετικών βιολογικών ειδών. Υπάρχουν για παράδειγμα περιπτώσεις οικοσυστημάτων όπου δυο διαφορετικοί κυνηγοί, ένας ισχυρότερος και ένας ασθενέστερος, τρέφονται με το ίδιο είδος θηραμάτων. Επίσης υπάρχει η περίπτωση που ένας ασθενής κυνηγός καταναλώνει ένα θήραμα και ο ίδιος καταναλώνεται από έναν ασθενέστερο. Αυτό είναι το λεγόμενο μοντέλο της τροφικής αλυσίδας. Έτσι, στις τρεις διαστάσεις θα δούμε φαινόμενα που ήδη παρατηρήσαμε στις δυο, αλλά θα αντιμετωπίσουμε και νέες ενδιαφέρουσες δυναμικές συμπεριφορές. Τέλος, στο τέταρτο κεφάλαιο θα αναφέρουμε κάποιες εφαρμογές που έχουν τα μοντέλα που εξετάσαμε. Θα δούμε δηλαδή πως το σύστημα Lotka-Volterra έχει εφαρμογή στην αλληλεπίδραση ιών και βακτηριοφάγων καθώς και πως βάσει της λογιστικής απεικόνισης μπορούμε να εκτιμήσουμε το μικρότερο δυνατό χρόνο που χρειάζεται ένας δρομέας για να διανύσει τα μέτρα.
- Published
- 2009
382. Μορφογένεση και οριακή ροή κοκκώδους υλικού σε δισδιάστατη κεκλιμένη πειραματική διάταξη
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Van der Weele, Jacob-Peter, Tsiavos, Christos, Καφούσιας, Νικόλαος, and Μπούντης, Αναστάσιος
- Subjects
Κοκκώδη υλικά ,Granular flow ,Κοκκώδης ροή ,Μορφογένεση ,620.43 ,Pattern formation ,Granular material - Abstract
Μελετάμε την ροή κοκκώδους σε κεκλιμένη πειραματική διάταξη δυο διαστάσεων, αποτελούμενη από Κ το πλήθος γραμμές και Μ το πλήθος στήλες δοχείων, τα οποία αναταράσσονται κάθετα. Η ροή του υλικού από δοχείο σε δοχείο περιγράφεται από ένα μοντέλο ροής [Eggers, 1999; Van der Weele, 2008]. Υποκινούμενοι από δυσλειτουργίες που παρουσιάζονται στις σύγχρονες βιομηχανικές μονάδες μεταφοράς (όπως είναι ο σχηματισμός συσσωματωμάτων), εισάγουμε σταθερή ποσότητα υλικού στην πρώτη γραμμή των δοχείων, και καθορίζουμε τις συνθήκες κάτω από τις οποίες η ροή παραμένει ομαλή και συνεχής μέχρι την τελευταία γραμμή. Ενώ στην περίπτωση μιας και μόνο σειράς δοχείων (Μ=1) η εκροή μηδενίζεται με την εμφάνιση ενός και μόνο συσσωματώματος [Κανελλόπουλος, 2008], για Μ>1 απαιτούνται περισσότερα συσσωματώματα για τον μηδενισμό της. Μελετάμε τον τρόπο με τον οποίο αυτά τα συσσωματώματα διατάσσονται στα δοχεία, ο οποίος πολλές φορές όπως βλέπουμε μπορεί να είναι ιδιαίτερα πολύπλοκος, αποτελώντας έτσι ένα εξαίρετο παράδειγμα μορφογένεσης σε δυναμικά συστήματα [Cross and Hohenberg, 1993]. Εντοπίζουμε τα βασικά χαρακτηριστικά αυτής της μορφογένεσης και εξηγούμε πως αυτά σχετίζονται με το μοντέλο ροής. Για την περαιτέρω μαθηματική και φυσική τους ερμηνεία προτείνουμε το συνεχές όριο του μοντέλου ροής, το οποίο θα αποτελέσει την απαρχή για μελλοντικές έρευνες [Van der Weele et al, 2008]. Αναφορές: •J. Eggers, Sand as Maxwell’s demon, Phys. Rev. Lett. 83, 5322 (1999). •K. van der Weele, Granular gas dynamics: How Maxwell’s demon rules in a nonequilibrium system, Contemporary Phys. 49, 157-175 (2008). •Γ. Κανελλόπουλος, Οριακή ροή κοκκώδους υλικού σε διάδρομο μεταφοράς, Διπλωματική Εργασία, Τμήμα Μαθηματικών, Πανεπιστήμιο Πατρών (2008). •M.C. Cross and P.C. Hohenberg, Pattern formation outside of equilibrium, Rev.Mod.Phys. 65, 851 (1993). •K. van der Weele, G. Kanellopoulos, C. Tsiavos, and D. van der Meer, Transient granular shock waves and upstream motion on a staircase (submitted, 2009). We study the dynamics of granular material in a 2-dimensional tilted setup, consisting of K rows and M columns of equal sized compartments, which is brought into motion by vertical shaking. Particles are inserted into the system along the upper row of compartments, then flow downwards, and eventually exit the system from the bottom row. Similar setups are encountered frequently in industrial transport machinery and are notorious for the tendency of the particles to form dense clusters, which obstruct the flow. We model the particle flow from box to box by a flux function and determine the maximal value of the inflow rate for which the flow remains steady. If the inflow rate exceeds this value, clusters are formed. The way in which these clusters are distributed over the KxM compartments is a fine example of spontaneous pattern formation. We analyze the main characteristics of this cluster formation, its dependence on the various parameters of the system, and its sensitivity to experimental fluctuations.
- Published
- 2009
383. Critical flow and pattern formation of granular matter on a conveyor belt
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Van der Weele, Jacob-Peter, Kanellopoulos, Giorgos, Καφούσιας, Νικόλαος, and Μπούντης, Αναστάσιος
- Subjects
532.051 ,Συσσωματώματα ,Granular flow ,Κοκκώδης ροή ,Clustering - Abstract
Εισάγουμε σταθερή εισροή υλικού στο πρώτο δοχείο με σκοπό να περιγράψουμε τις συνθήκες κάτω από τις οποίες η ροή θα είναι ομαλή και συνεχής μέχρι και το τελευταίο δοχείο. Σε αντίθεση με τα κανονικά ρευστά, τα κοκκώδη υλικά έχουν την τάση να δημιουργούν συσσωματώματα (λόγω της μη-ελαστικής σύγκρουσης των σωματιδίων τους [Goldhirsch and Zanetti, 1993]). Όταν συμβαίνει αυτό η ροή σταματά και η εκροή από το τελευταίο δοχείο μηδενίζεται. Δεδομένης της δύναμης ανατάραξης και των διαστάσεων του διαδρόμου, καθορίζουμε την οριακή τιμή της εισροής πέρα από την οποία η δημιουργία συσσωματωμάτων είναι αναπόφευκτη. Δείχνουμε ότι η κρίσιμη αυτή κατάσταση αναγγέλλεται εκ των προτέρων (ήδη πριν από την οριακή τιμή της εισροής) από την εμφάνιση ενός κυματιστού προφίλ πυκνότητας υλικού κατά μήκος του διαδρόμου. Η οριακή ροή καθώς και το κυματιστό προφίλ εξηγούνται σ΄αυτή την εργασία, τόσο ποιοτικά όσο και ποσοτικά, μέσω ενός μαθηματικού μοντέλου ροής [Eggers 1999, Van der Weele et al., 2001]. Τέλος, βασιζόμενοι σε αυτό το μοντέλο προτείνουμε πρακτικές λύσεις ώστε να βελτιωθεί σημαντικά η παροχή του διαδρόμου. We study the flow of granular material on a conveyor belt consisting of K connected, vertically vibrated compartments. A steady inflow is applied to the top compartment and our goal is to describe the conditions that ensure a continuous flow all the way down to the Kth compartment. In contrast to normal fluids, flowing granular matter has a tendency to form clusters (due to the inelasticity of the particle collisions [Goldhirsch and Zanetti, 1993]); when this happens the flow stops and the outflow from the Kth compartment vanishes. Given the dimensions of the conveyor belt and the vibration strength, we determine the critical value of the inflow beyond which cluster formation is inevitable. Fortunately, the clusters are announced in advance (already below the critical value of the inflow) by the appearance of a wavy density profile along the K compartments. The critical flow and the associated wavy profile are explained quantitatively in terms of a dynamical flux model [Eggers, 1999; Van der Weele et al., 2001]. This same model enables us to formulate a method to greatly increase the critical value of the inflow, improving the capacity of the conveyor belt by a factor two or even more.
- Published
- 2008
384. Μελέτη δυναμικού συστήματος διακριτού χρόνου με γραμμικό μέρος και ασυνέχεια
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Μπούντης, Αναστάσιος, Βραχάτης, Μιχαήλ, and Van der Weele, Jacob-Peter
- Subjects
Διάνυσμα ασυνέχειας ,515.39 ,Διακριτός χρόνος ,Χάος ,Linear parts ,Chaos ,Δυναμικά συστήματα ,Discrete time ,Γραμμικά μέρη ,Discontinuity ,Ασυνέχεια ,Dynamic systems ,Γραμμικός πίνακας στροφής φ - Abstract
Στην παρούσα εργασία εξετάζεται, αριθμητικά και αναλυτικά (όπου αυτό είναι εφικτό), η συμπεριφορά ενός 2-διάστατου διακριτού συστήματος, το οποίο συνθέτουν ένας γραμμικός πίνακας και ένα διάνυσμα ασυνέχειας. Παρόλη την απλότητα της έκφρασής του, η συμπεριφορά του χαρακτηρίζεται από ποικιλομορφία και πολυπλοκότητα. Αλλοιώνοντας το αρχικό αυτό σύστημα, με την παρουσία μιας παραμέτρου διαταραχής (όπως την ονομάζουμε), και στη συνέχεια φράσσοντας τις τιμές του με modulo, παράγουμε δύο συγγενή συστήματα με έντονα πολύπλοκη και απεριοδική συμπεριφορά. Οι απεριοδικές αλληλουχίες τιμών που παράγονται με αυτόν τον τρόπο δύνανται να μετατραπούν (μέσω διαφόρων κατάλληλων κωδικοποιήσεων) σε αποτελεσματικούς κρυπτογραφικούς κλειδάριθμους. In this paper, we present an application of the theory of symbolic dynamics to a class of discrete dynamical systems of interest to cryptography, which are composed of a linear part and a discontinuity. The irregular behavior of such systems is studied, in the sense of the existence of non-periodic orbits in certain areas of the configuration space. Some theorems are stated and proved, concerning the correspondence of such orbits with an infinite set of non-periodic symbolic series of infinite length. A specific dynamical system is used as an example, illustrating the remarkable patterns displayed by the dynamics of this class of systems. Keywords: Uncountably infinite, non-periodic symbolic series, disk of influence, eventually periodic orbit, pre-orbit point.
- Published
- 2008
385. Stapled versus hand-sewn anastomoses after bowel resection in patients with crohn disease.
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Lahes S, Fischer C, Igna D, Jacob P, and Glanemann M
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- Humans, Female, Male, Retrospective Studies, Adult, Middle Aged, Suture Techniques, Reoperation statistics & numerical data, Treatment Outcome, Length of Stay statistics & numerical data, Anastomotic Leak epidemiology, Anastomotic Leak etiology, Young Adult, Crohn Disease surgery, Anastomosis, Surgical methods, Surgical Stapling methods, Postoperative Complications epidemiology, Postoperative Complications etiology
- Abstract
Background: Anastomosis configuration is an essential step in treatment to restore continuity of the gastrointestinal tract following bowel resection in patients with Crohn's disease (CD). However, the association between anastomotic type and surgical outcome remains controversial. This retrospective study aimed to compare early postoperative complications and surgical outcome between stapler and handsewn anastomosis after bowel resection in Crohn's disease., Methods: Between 2001 and 2018, a total of 339 CD patients underwent bowel resection with anastomosis. Patient characteristics, intraoperative data, early postoperative complications, and outcomes were analyzed and compared between two groups of patients. Group 1 consisted of patients with stapler anastomosis and group 2 with handsewn anastomosis., Results: No significant difference was found in the incidence of postoperative surgical complications between the stapler and handsewn anastomosis groups (25% versus 24.4%, p = 1.000). Reoperation for complications and postoperative hospital stay were similar between the two groups., Conclusion: Our analysis showed that there were no differences in anastomotic leak, nor postoperative complications, mortality, reoperation for operative complications, or postoperative hospital stay between the stapler anastomosis and handsewn anastomosis groups., (© 2024. The Author(s).)
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- 2024
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386. Pulmonary blood volume measured by 82 Rb-PET in patients with chronic obstructive pulmonary disease: a retrospective cohort study.
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Hartmann JP, Lassen ML, Mohammad M, Iepsen UW, Mortensen J, Hasbak P, and Berg RMG
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- Humans, Male, Female, Retrospective Studies, Middle Aged, Aged, Lung physiopathology, Lung diagnostic imaging, Rubidium Radioisotopes, Myocardial Perfusion Imaging methods, Adenosine administration & dosage, Cardiac Output physiology, Pulmonary Disease, Chronic Obstructive physiopathology, Pulmonary Disease, Chronic Obstructive diagnostic imaging, Blood Volume physiology, Positron-Emission Tomography methods
- Abstract
In patients with chronic obstructive pulmonary disease (COPD), pulmonary vascular dysfunction and destruction are observable before the onset of detectable emphysema, but it is unknown whether this is associated with central hypovolemia. We investigated if patients with COPD have reduced pulmonary blood volume (PBV) evaluated by
82 Rb-positron emission tomography (PET) at rest and during adenosine-induced hyperemia. This single-center retrospective cohort study assessed 6,30182 Rb-PET myocardial perfusion imaging (MPI) examinations performed over a 6-yr period. We compared 77 patients with COPD with 44 healthy kidney donors (controls). Cardiac output ([Formula: see text]) and mean82 Rb bolus transit time (MBTT) were used to calculate PBV. [Formula: see text] was similar at rest (COPD: 3,649 ± 120 mL vs. control: 3,891 ± 160 mL, P = 0.368) but lower in patients with COPD compared with controls during adenosine infusion (COPD: 5,432 ± 124 mL vs. control: 6,185 ± 161 mL, P < 0.050). MBTT was shorter in patients with COPD compared with controls at rest (COPD: 8.7 ± 0.28 s vs. control: 11.4 ± 0.37 s, P < 0.001) and during adenosine infusion (COPD: 9.2 ± 0.28 s vs. control: 10.2 ± 0.37 s, P < 0.014). PBV was lower in patients with COPD, even after adjustment for body surface area, sex, and age at rest [COPD: 530 (29) mL vs. 708 (38) mL, P < 0.001] and during adenosine infusion [COPD: 826 (29) mL vs. 1,044 (38) mL, P < 0.001]. In conclusion, patients with COPD show evidence of central hypovolemia, but it remains to be determined whether this has any diagnostic or prognostic impact. NEW & NOTEWORTHY The present study demonstrated that patients with chronic obstructive pulmonary disease (COPD) exhibit central hypovolemia compared with healthy controls. Pulmonary blood volume may thus be a relevant physiological and/or clinical outcome measure in future COPD studies.- Published
- 2024
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387. Dual Test Gas Pulmonary Diffusing Capacity Measurement During Exercise in Humans Using the Single-Breath Method.
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Nymand SB, Hartmann JP, Hartmeyer HL, Rasmussen IE, Andersen AB, Mohammad M, Al-Atabi S, Hanel B, Iepsen UW, Mortensen J, and Berg RMG
- Subjects
- Humans, Reproducibility of Results, Lung, Carbon Monoxide, Nitric Oxide, Exercise Test, Pulmonary Diffusing Capacity, Exercise
- Abstract
The combined single-breath measurement of the diffusing capacity of carbon monoxide (DL,CO) and nitric oxide (DL,NO) is a useful technique to measure pulmonary alveolar-capillary reserve in both healthy and patient populations. The measurement provides an estimate of the participant's ability to recruit and distend pulmonary capillaries. The method has recently been reported to exhibit a high test-retest reliability in healthy volunteers during exercise of light to moderate intensity. Of note, this technique permits up to 12 repeated maneuvers and only requires a single breath with a relatively short breath-hold time of 5 s. Representative data are provided showing the gradual changes in DL,NO and DL,CO from rest to exercise at increasing intensities of up to 60% of maximal workload. The measurement of diffusing capacity and evaluation of alveolar-capillary reserve is a useful tool to evaluate the lung's ability to respond to exercise both in the healthy population as well as in patient populations such as those with chronic lung disease.
- Published
- 2024
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- View/download PDF
388. Doppler Ultrasound-Based Leg Blood Flow Assessment During Single-Leg Knee-Extensor Exercise in an Uncontrolled Setting.
- Author
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Hartmann JP, Krabek R, Nymand SB, Hartmeyer H, Gliemann L, Berg RMG, and Iepsen UW
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- Humans, Female, Male, Young Adult, Adult, Reproducibility of Results, Regional Blood Flow, Muscle, Skeletal, Ultrasonography, Doppler, Leg diagnostic imaging, Leg blood supply, Exercise physiology
- Abstract
Doppler ultrasound has revolutionized the assessment of organ blood flow and is widely used in research and clinical settings. While Doppler ultrasound-based assessment of contracting leg muscle blood flow is common in human studies, the reliability of this method requires further investigation. Therefore, this study aimed to investigate the within-day test-retest, between-day test-retest, and inter-rater reliability of Doppler ultrasound for assessing leg blood flow during rest and graded single-leg knee-extensions (0 W, 6 W, 12 W, and 18 W), with the ultrasound probe being removed between measurements. The study included thirty healthy subjects (age: 33 ± 9.3, male/female: 14/16) who visited the laboratory on two different experimental days separated by 10 days. The study did not control for major confounders such as nutritional state, time of day, or hormonal status. Across different exercise intensities, the results demonstrated high within-day reliability with a coefficient of variation (CV) ranging from 4.0% to 4.3%, acceptable between-day reliability with a CV ranging from 10.1% to 20.2%, and inter-rater reliability with a CV ranging from 17.9% to 26.8%. Therefore, in a real-life clinical scenario where controlling various environmental factors is challenging, Doppler ultrasound can be used to determine leg blood flow during submaximal single-leg knee-extensor exercise with high within-day reliability and acceptable between-day reliability when performed by the same sonographer.
- Published
- 2023
- Full Text
- View/download PDF
389. Pulmonary blood volume assessment from a standard cardiac rubidium-82 imaging protocol: impact of adenosine-induced hyperemia.
- Author
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Lassen ML, Byrne C, Hartmann JP, Kjaer A, Berg RMG, and Hasbak P
- Subjects
- Humans, Male, Female, Young Adult, Adult, Adenosine, Positron-Emission Tomography methods, Reproducibility of Results, Rubidium Radioisotopes, Blood Volume, Hyperemia diagnostic imaging, Myocardial Perfusion Imaging methods
- Abstract
Background: This study aimed to assess the feasibility of estimating the pulmonary blood volume noninvasively using standard Rubidium-82 myocardial perfusion imaging (MPI) and characterize the changes during adenosine-induced hyperemia., Methods: This study comprised 33 healthy volunteers (15 female, median age = 23 years), of which 25 underwent serial rest/adenosine stress Rubidium-82 MPI sessions. Mean bolus transit times (MBTT) were obtained by calculating the time delay from the Rubidium-82 bolus arrival in the pulmonary trunk to the arrival in the left myocardial atrium. Using the MBTT, in combination with stroke volume (SV) and heart rate (HR), we estimated pulmonary blood volume (PBV = (SV × HR) × MBTT). We report the empirically measured MBTT, HR, SV, and PBV, all stratified by sex [male (M) vs female (F)] as mean (SD). In addition, we report grouped repeatability measures using the within-subject repeatability coefficient., Results: Mean bolus transit times was shortened during adenosine stressing with sex-specific differences [(seconds); Rest: Female (F) = 12.4 (1.5), Male (M) = 14.8 (2.8); stress: F = 8.8 (1.7), M = 11.2 (3.0), all P ≤ 0.01]. HR and SV increased during stress MPI, with a concomitant increase in the PBV [mL]; Rest: F = 544 (98), M = 926 (105); Stress: F = 914 (182), M = 1458 (338), all P < 0.001. The following test-retest repeatability measures were observed for MBTT (Rest = 17.2%, Stress = 17.9%), HR (Rest = 9.1%, Stress = 7.5%), SV (Rest = 8.9%, Stress = 5.6%), and for PBV measures (Rest = 20.7%, Stress = 19.5%) CONCLUSION: Pulmonary blood volume can be extracted by cardiac rubidium-82 MPI with excellent test-retest reliability, both at rest and during adenosine-induced hyperemia., (© 2023. The Author(s).)
- Published
- 2023
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390. Discovery of a selective and biologically active low-molecular weight antagonist of human interleukin-1β.
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Hommel U, Hurth K, Rondeau JM, Vulpetti A, Ostermeier D, Boettcher A, Brady JP, Hediger M, Lehmann S, Koch E, Blechschmidt A, Yamamoto R, Tundo Dottorello V, Haenni-Holzinger S, Kaiser C, Lehr P, Lingel A, Mureddu L, Schleberger C, Blank J, Ramage P, Freuler F, Eder J, and Bornancin F
- Subjects
- Humans, Interleukin-1beta, Molecular Weight, Binding Sites, Biophysics, Cytokines, Thinness
- Abstract
Human interleukin-1β (hIL-1β) is a pro-inflammatory cytokine involved in many diseases. While hIL-1β directed antibodies have shown clinical benefit, an orally available low-molecular weight antagonist is still elusive, limiting the applications of hIL-1β-directed therapies. Here we describe the discovery of a low-molecular weight hIL-1β antagonist that blocks the interaction with the IL-1R1 receptor. Starting from a low affinity fragment-based screening hit 1, structure-based optimization resulted in a compound (S)-2 that binds and antagonizes hIL-1β with single-digit micromolar activity in biophysical, biochemical, and cellular assays. X-ray analysis reveals an allosteric mode of action that involves a hitherto unknown binding site in hIL-1β encompassing two loops involved in hIL-1R1/hIL-1β interactions. We show that residues of this binding site are part of a conformationally excited state of the mature cytokine. The compound antagonizes hIL-1β function in cells, including primary human fibroblasts, demonstrating the relevance of this discovery for future development of hIL-1β directed therapeutics., (© 2023. Springer Nature Limited.)
- Published
- 2023
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391. Physiolometrics and the puzzle of methodical acumen.
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Hartmann JP, Olsen MH, Rose G, Bailey DM, and Berg RMG
- Published
- 2023
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392. Assessment and management of chronic kidney disease in people living with obesity.
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Jacob P and McCafferty K
- Subjects
- Humans, Quality of Life, Obesity complications, Obesity epidemiology, Risk Factors, Diabetes Mellitus, Type 2 complications, Renal Insufficiency, Chronic complications, Renal Insufficiency, Chronic epidemiology, Renal Insufficiency, Chronic therapy, Kidney Failure, Chronic epidemiology, Kidney Failure, Chronic therapy, Kidney Failure, Chronic complications, Hypertension
- Abstract
Obesity and chronic kidney disease (CKD) are common and frequently coexisting medical conditions. Already well known to be a risk factor for type 2 diabetes mellitus (T2DM), ischaemic heart disease, stroke, hypertension, malignancy and premature death, obesity also predisposes to CKD. Elevated weight leads to declining renal function through several mechanisms, including established pathways via metabolic syndrome, hypertension and T2DM, but also through relatively recently understood glomerulosclerosis, directly related to obesity. Compared with non-obese comparators, people living with obesity and established CKD develop faster decline in glomerular filtration, progression to end-stage renal disease (ESRD) and death. Importantly, treatment of obesity can influence these crucial renal outcomes and significantly improve quality of life. Declining renal function also impacts the medical and surgical treatment options available to treat patients with overweight and obesity. In this article, we briefly outline the epidemiology of obesity and renal disease and review the pathological interactions between these diseases before focusing on considerations for assessment and evidence-based treatments for obesity and renal disease., (© Royal College of Physicians 2023. All rights reserved.)
- Published
- 2023
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- View/download PDF
393. Changes in attitudes to awareness of hypoglycaemia during a hypoglycaemia awareness restoration programme are associated with avoidance of further severe hypoglycaemia episodes within 24 months: the A2A in HypoCOMPaSS study.
- Author
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Sepúlveda E, Jacob P, Poínhos R, Carvalho D, Vicente SG, Smith EL, Shaw JAM, Speight J, Choudhary P, de Zoysa N, and Amiel SA
- Subjects
- Adult, Humans, Blood Glucose, Blood Glucose Self-Monitoring, Insulin therapeutic use, Awareness, Hypoglycemic Agents therapeutic use, Attitude, Diabetes Mellitus, Type 1 drug therapy, Hypoglycemia drug therapy, Hyperglycemia drug therapy
- Abstract
Aims/hypothesis: The aims of this study were to assess cognitions relating to hypoglycaemia in adults with type 1 diabetes and impaired awareness of hypoglycaemia before and after the multimodal HypoCOMPaSS intervention, and to determine cognitive predictors of incomplete response (one or more severe hypoglycaemic episodes over 24 months)., Methods: This analysis included 91 adults with type 1 diabetes and impaired awareness of hypoglycaemia who completed the Attitudes to Awareness of Hypoglycaemia (A2A) questionnaire before, 24 weeks and 24 months after the intervention, which comprised a short psycho-educational programme with optimisation of insulin therapy and glucose monitoring., Results: The age and diabetes duration of the participants were 48±12 and 29±12 years, respectively (mean±SD). At baseline, 91% reported one or more severe hypoglycaemic episodes over the preceding 12 months; this decreased to <20% at 24 weeks and after 24 months (p=0.001). The attitudinal barrier 'hyperglycaemia avoidance prioritised' (η
2 p =0.250, p=0.001) decreased from baseline to 24 weeks, and this decrease was maintained at 24 months (mean±SD=5.3±0.3 vs 4.3±0.3 vs 4.0±0.3). The decrease in 'asymptomatic hypoglycaemia normalised' from baseline (η2 p =0.113, p=0.045) was significant at 24 weeks (1.5±0.3 vs 0.8±0.2). Predictors of incomplete hypoglycaemia response (one or more further episodes of severe hypoglycaemia) were higher baseline rates of severe hypoglycaemia, higher baseline scores for 'asymptomatic hypoglycaemia normalised', reduced change in 'asymptomatic hypoglycaemia normalised' scores at 24 weeks, and lower baseline 'hypoglycaemia concern minimised' scores (all p<0.05)., Conclusions/interpretation: Participation in the HypoCOMPaSS RCT was associated with improvements in hypoglycaemia-associated cognitions, with 'hyperglycaemia avoidance prioritised' most prevalent. Incomplete prevention of subsequent severe hypoglycaemia episodes was associated with persistence of the cognition 'asymptomatic hypoglycaemia normalised'. Understanding and addressing cognitive barriers to hypoglycaemia avoidance is important in individuals prone to severe hypoglycaemia episodes., Clinical Trials Registration: www.isrctn.org : ISRCTN52164803 and https://eudract.ema.europa.eu : EudraCT2009-015396-27., (© 2022. The Author(s).)- Published
- 2023
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394. Role of biliary drainage before pancreatoduodenectomy for pancreatic adenocarcinoma: a retrospective study.
- Author
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Scherber PR, Gäbelein G, Spiliotis AE, Igna D, Holländer S, Jacob P, Hofmann J, and Glanemann M
- Subjects
- Humans, Pancreaticoduodenectomy adverse effects, Retrospective Studies, Pancreatic Fistula epidemiology, Preoperative Care adverse effects, Drainage adverse effects, Postoperative Complications epidemiology, Pancreatic Neoplasms, Pancreatic Neoplasms surgery, Jaundice, Obstructive etiology, Adenocarcinoma surgery, Carcinoma, Pancreatic Ductal surgery, Wound Infection complications
- Abstract
Background: Utilization of preoperative biliary drainage prior to pancreatoduodenectomy for patients with pancreatic ductal adenocarcinoma and obstructive jaundice remains controversial., Methods: All patients that underwent pancreatoduodenectomy for pancreatic ductal adenocarcinoma at the authors' institution were analyzed retrospectively to evaluate the effect of endoscopic biliary drainage on postoperative outcomes and long-term survival. Age, gender, ASA-Score, operative time, blood loss, intraoperative transfusion rate, and postoperative complications, including postoperative pancreatic fistula, delayed gastric emptying, bleeding, bile fistula, wound infections, sepsis, pulmonary and cardiac complications as well as the need for relaparotomy were analyzed., Results: Two hundred eighty-five patients with similar baseline characteristics underwent pancreatoduodenectomy, 151 patients with biliary drainage (group 1) and 134 without drainage (group 2). More than 60% of patients had one or more postoperative complications, without significant difference between the two groups (P=0.140). The overall incidence of pancreatic fistula was 21.75% in both groups (group 1: 19.87% vs. group 2: 23.88%, P=0.659). Wound healing impairment was the only postoperative complication that differed significantly between the two groups (group 1: 24.50% vs. group 2: 8.96%, P<0.001). In multivariate risk analysis, biliary drainage was the only independent risk factor for wound healing impairment (OR 4.126; 95% CI: 1.295-13.143; P=0.017). The median overall survival was similar in both groups., Conclusions: Preoperative endoscopic biliary drainage is associated with an increased risk for wound healing impairment and wound infections. Therefore, biliary drainage should not be used routinely in patients with obstructive jaundice prior to pancreatoduodenectomy.
- Published
- 2022
- Full Text
- View/download PDF
395. Regulation of the microvasculature during small muscle mass exercise in chronic obstructive pulmonary disease vs. chronic heart failure.
- Author
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Hartmann JP, Dahl RH, Nymand S, Munch GW, Ryrsø CK, Pedersen BK, Thaning P, Mortensen SP, Berg RMG, and Iepsen UW
- Abstract
Aim: Skeletal muscle convective and diffusive oxygen (O
2 ) transport are peripheral determinants of exercise capacity in both patients with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF). We hypothesised that differences in these peripheral determinants of performance between COPD and CHF patients are revealed during small muscle mass exercise, where the cardiorespiratory limitations to exercise are diminished. Methods: Eight patients with moderate to severe COPD, eight patients with CHF (NYHA II), and eight age- and sex-matched controls were studied. We measured leg blood flow (Q̇leg ) by Doppler ultrasound during submaximal one-legged knee-extensor exercise (KEE), while sampling arterio-venous variables across the leg. The capillary oxyhaemoglobin dissociation curve was reconstructed from paired femoral arterial-venous oxygen tensions and saturations, which enabled the estimation of O2 parameters at the microvascular level within skeletal muscle, so that skeletal muscle oxygen conductance (DSM O2 ) could be calculated and adjusted for flow (DSM O2 /Q̇leg ) to distinguish convective from diffusive oxygen transport. Results: During KEE, Q̇leg increased to a similar extent in CHF (2.0 (0.4) L/min) and controls (2.3 (0.3) L/min), but less in COPD patients (1.8 (0.3) L/min) ( p <0.03). There was no difference in resting DSM O2 between COPD and CHF and when adjusting for flow, the DSM O2 was higher in both groups compared to controls (COPD: 0.97 (0.23) vs. controls 0.63 (0.24) mM/kPa, p = 0.02; CHF 0.98 (0.11) mM/kPa vs. controls, p = 0.001). The Q̇-adjusted DSM O2 was not different in COPD and CHF during KEE (COPD: 1.19 (0.11) vs. CHF: 1.00 (0.18) mM/kPa; p = 0.24) but higher in COPD vs. controls: 0.87 (0.28) mM/kPa ( p = 0.02), and only CHF did not increase Q̇-adjusted DSM O2 from rest ( p = 0.2). Conclusion: Disease-specific factors may play a role in peripheral exercise limitation in patients with COPD compared with CHF. Thus, low convective O2 transport to contracting muscle seemed to predominate in COPD, whereas muscle diffusive O2 transport was unresponsive in CHF., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Hartmann, Dahl, Nymand, Munch, Ryrsø, Pedersen, Thaning, Mortensen, Berg and Iepsen.)- Published
- 2022
- Full Text
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396. Altered functional connectivity during hypoglycaemia in type 1 diabetes.
- Author
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Jacob P, Nwokolo M, Cordon SM, Macdonald IA, Zelaya FO, Amiel SA, O'Daly O, and Choudhary P
- Subjects
- Brain metabolism, Humans, Hypoglycemic Agents, Magnetic Resonance Imaging, Prefrontal Cortex, Diabetes Mellitus, Type 1, Hypoglycemia
- Abstract
Behavioural responses to hypoglycaemia require coordinated recruitment of broadly distributed networks of interacting brain regions. We investigated hypoglycaemia-related changes in brain connectivity in people without diabetes (ND) and with type 1 diabetes with normal (NAH) or impaired (IAH) hypoglycaemia awareness. Two-step hyperinsulinaemic hypoglycaemic clamps were performed in 14 ND, 15 NAH and 22 IAH participants. BOLD timeseries were acquired at euglycaemia (5.0 mmol/L) and hypoglycaemia (2.6 mmol/L), with symptom and counter-regulatory hormone measurements. We investigated hypoglycaemia-related connectivity changes using established seed regions for the default mode (DMN), salience (SN) and central executive (CEN) networks and regions whose activity is modulated by hypoglycaemia: the thalamus and right inferior frontal gyrus (RIFG). Hypoglycaemia-induced changes in the DMN, SN and CEN were evident in NAH (all p < 0.05), with no changes in ND or IAH. However, in IAH there was a reduction in connectivity between regions within the RIFG (p = 0.001), not evident in the ND or NAH groups. We conclude that hypoglycaemia induces coordinated recruitment of the DMN and SN in diabetes with preserved hypoglycaemia awareness which is absent in IAH and ND. Changes in connectivity in the RIFG, a region associated with attentional modulation, may be key in impaired hypoglycaemia awareness.
- Published
- 2022
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397. Characteristics of adults with type 1 diabetes and treatment-resistant problematic hypoglycaemia: a baseline analysis from the HARPdoc RCT.
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Jacob P, Potts L, Maclean RH, de Zoysa N, Rogers H, Gonder-Frederick L, Smith EL, Kariyawasam D, Brooks A, Heller S, Toschi E, Kendall M, Bakolis I, Choudhary P, Goldsmith K, and Amiel SA
- Subjects
- Adult, Cross-Sectional Studies, Fear psychology, Humans, Hypoglycemic Agents therapeutic use, Insulin therapeutic use, Diabetes Mellitus, Type 1 complications, Hypoglycemia complications
- Abstract
Aims/hypothesis: Problematic hypoglycaemia still complicates insulin therapy for some with type 1 diabetes. This study describes baseline emotional, cognitive and behavioural characteristics in participants in the HARPdoc trial, which evaluates a novel intervention for treatment-resistant problematic hypoglycaemia., Methods: We documented a cross-sectional baseline description of 99 adults with type 1 diabetes and problematic hypoglycaemia despite structured education in flexible insulin therapy. The following measures were included: Hypoglycaemia Fear Survey II (HFS-II); Attitudes to Awareness of Hypoglycaemia questionnaire (A2A); Hospital Anxiety and Depression Index; and Problem Areas In Diabetes. k-mean cluster analysis was applied to HFS-II and A2A factors. Data were compared with a peer group without problematic hypoglycaemia, propensity-matched for age, sex and diabetes duration (n = 81)., Results: The HARPdoc cohort had long-duration diabetes (mean ± SD 35.8 ± 15.4 years), mean ± SD Gold score 5.3 ± 1.2 and a median (IQR) of 5.0 (2.0-12.0) severe hypoglycaemia episodes in the previous year. Most individuals had been offered technology and 49.5% screened positive for anxiety (35.0% for depression and 31.3% for high diabetes distress). The cohort segregated into two clusters: in one (n = 68), people endorsed A2A cognitive barriers to hypoglycaemia avoidance, with low fear on HFS-II factors; in the other (n = 29), A2A factor scores were low and HFS-II high. Anxiety and depression scores were significantly lower in the comparator group., Conclusions/interpretation: The HARPdoc protocol successfully recruited people with treatment-resistant problematic hypoglycaemia. The participants had high anxiety and depression. Most of the cohort endorsed unhelpful health beliefs around hypoglycaemia, with low fear of hypoglycaemia, a combination that may contribute to persistence of problematic hypoglycaemia and may be a target for adjunctive psychological therapies., (© 2022. The Author(s).)
- Published
- 2022
- Full Text
- View/download PDF
398. A parallel randomised controlled trial of the Hypoglycaemia Awareness Restoration Programme for adults with type 1 diabetes and problematic hypoglycaemia despite optimised self-care (HARPdoc).
- Author
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Amiel SA, Potts L, Goldsmith K, Jacob P, Smith EL, Gonder-Frederick L, Heller S, Toschi E, Brooks A, Kariyawasam D, Choudhary P, Stadler M, Rogers H, Kendall M, Sevdalis N, Bakolis I, and de Zoysa N
- Subjects
- Adult, Blood Glucose, Humans, Insulin, Self Care, Diabetes Mellitus, Type 1 drug therapy, Hypoglycemia prevention & control
- Abstract
Impaired awareness of hypoglycaemia (IAH) is a major risk for severe hypoglycaemia in insulin treatment of type 1 diabetes (T1D). To explore the hypothesis that unhelpful health beliefs create barriers to regaining awareness, we conducted a multi-centre, randomised, parallel, two-arm trial (ClinicalTrials.gov NCT02940873) in adults with T1D and treatment-resistant IAH and severe hypoglycaemia, with blinded analysis of 12-month recall of severe hypoglycaemia at 12 and/or 24 months the primary outcome. Secondary outcomes included cognitive and emotional measures. Adults with T1D, IAH and severe hypoglycaemia despite structured education in insulin adjustment, +/- diabetes technologies, were randomised to the "Hypoglycaemia Awareness Restoration Programme despite optimised self-care" (HARPdoc, n = 49), a psychoeducation programme uniquely focussing on changing cognitive barriers to avoiding hypoglycaemia, or the evidence-based "Blood Glucose Awareness Training" (BGAT, n = 50), both delivered over six weeks. Median [IQR] severe hypoglycaemia at baseline was 5[2-12] per patient/year, 1[0-5] at 12 months and 0[0-2] at 24 months, with no superiority for HARPdoc (HARPdoc vs BGAT incident rate ratios [95% CI] 1.25[0.51, 3.09], p = 0.62 and 1.26[0.48, 3.35], p = 0.64 respectively), nor for changes in hypoglycaemia awareness scores or fear. Compared to BGAT, HARPdoc significantly reduced endorsement of unhelpful cognitions (Estimated Mean Difference for Attitudes to Awareness scores at 24 months, -2.07 [-3.37,-0.560], p = 0.01) and reduced scores for diabetes distress (-6.70[-12.50,-0.89], p = 0.02); depression (-1.86[-3.30, -0.43], p = 0.01) and anxiety (-1.89[-3.32, -0.47], p = 0.01). Despite positive impact on cognitive barriers around hypoglycaemia avoidance and on diabetes-related and general emotional distress scores, HARPdoc was not more effective than BGAT at reducing severe hypoglycaemia., (© 2022. The Author(s).)
- Published
- 2022
- Full Text
- View/download PDF
399. Hypoglycemia Subtypes in Type 1 Diabetes: An Exploration of the Hypoglycemia Fear Survey-II.
- Author
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Maclean RH, Jacob P, Choudhary P, Heller SR, Toschi E, Kariyawasam D, Brooks A, Kendall M, de Zoysa N, Gonder-Frederick LA, and Amiel SA
- Subjects
- Anxiety psychology, Fear psychology, Humans, Surveys and Questionnaires, Diabetes Mellitus, Type 1 psychology, Hypoglycemia epidemiology
- Abstract
Objective: The Hypoglycemia Fear Survey-II (HFS-II) is a well-validated measure of fear of hypoglycemia in people with type 1 diabetes. The aim of this study was to explore the relationships between hypoglycemia worries, behaviors, and cognitive barriers to hypoglycemia avoidance and hypoglycemia awareness status, severe hypoglycemia, and HbA1c., Research Design and Methods: Participants with type 1 diabetes (n = 178), with the study population enriched for people at risk for severe hypoglycemia (49%), completed questionnaires for assessing hypoglycemia fear (HFS-II), hyperglycemia avoidance (Hyperglycemia Avoidance Scale [HAS]), diabetes distress (Problem Areas In Diabetes [PAID]), and cognitive barriers to hypoglycemia avoidance (Attitudes to Awareness of Hypoglycemia [A2A]). Exploratory factor analysis was applied to the HFS-II. We sought to establish clusters based on HFS-II, A2A, Gold, HAS, and PAID using k-means clustering., Results: Four HFS-II factors were identified: Sought Safety, Restricted Activity, Ran High, and Worry. While Sought Safety, Restricted Activity, and Worry increased with progressively impaired awareness and recurrent severe hypoglycemia, Ran High did not. With cluster analysis we outlined four clusters: two clusters with preserved hypoglycemia awareness were differentiated by low fear/low cognitive barriers to hypoglycemia avoidance (cluster 1) versus high fear and distress and increased Ran High behaviors (cluster 2). Two clusters with impaired hypoglycemia awareness were differentiated by low fear/high cognitive barriers (cluster 3) as well as high fear/low cognitive barriers (cluster 4)., Conclusions: This is the first study to define clusters of hypoglycemia experience by worry, behaviors, and cognitive barriers to hypoglycemia avoidance. The resulting subtypes may be important in understanding and treating problematic hypoglycemia., (© 2022 by the American Diabetes Association.)
- Published
- 2022
- Full Text
- View/download PDF
400. Bi-allelic MCM10 variants associated with immune dysfunction and cardiomyopathy cause telomere shortening.
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Baxley RM, Leung W, Schmit MM, Matson JP, Yin L, Oram MK, Wang L, Taylor J, Hedberg J, Rogers CB, Harvey AJ, Basu D, Taylor JC, Pagnamenta AT, Dreau H, Craft J, Ormondroyd E, Watkins H, Hendrickson EA, Mace EM, Orange JS, Aihara H, Stewart GS, Blair E, Cook JG, and Bielinsky AK
- Subjects
- Cell Cycle Proteins metabolism, Cell Line, DNA Replication, DNA-Binding Proteins genetics, DNA-Binding Proteins metabolism, Endonucleases genetics, Endonucleases metabolism, Humans, Killer Cells, Natural, Alleles, Cardiomyopathies genetics, Minichromosome Maintenance Proteins genetics, Minichromosome Maintenance Proteins immunology, Telomere Shortening
- Abstract
Minichromosome maintenance protein 10 (MCM10) is essential for eukaryotic DNA replication. Here, we describe compound heterozygous MCM10 variants in patients with distinctive, but overlapping, clinical phenotypes: natural killer (NK) cell deficiency (NKD) and restrictive cardiomyopathy (RCM) with hypoplasia of the spleen and thymus. To understand the mechanism of MCM10-associated disease, we modeled these variants in human cell lines. MCM10 deficiency causes chronic replication stress that reduces cell viability due to increased genomic instability and telomere erosion. Our data suggest that loss of MCM10 function constrains telomerase activity by accumulating abnormal replication fork structures enriched with single-stranded DNA. Terminally-arrested replication forks in MCM10-deficient cells require endonucleolytic processing by MUS81, as MCM10:MUS81 double mutants display decreased viability and accelerated telomere shortening. We propose that these bi-allelic variants in MCM10 predispose specific cardiac and immune cell lineages to prematurely arrest during differentiation, causing the clinical phenotypes observed in both NKD and RCM patients.
- Published
- 2021
- Full Text
- View/download PDF
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