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702 results on '"Heiss, WD"'

1. An effective interaction at the Planck mass and Planck length

Author

Heiss, WD

Subjects
General Relativity and Quantum Cosmology
Abstract

A simple model is suggested by assuming an effective interaction at the crossing point of the two curves, the Schwarzschild radius and the Compton wave length, that is at the Planck length and Planck mass. It is argued that there would be a physical effect that may be measurable at, say, nucleon mass and size, while the Schwarzschild radius would remain unaffected for macroscopic lengths and masses., Comment: 4 pages, 1 figure

Published
2018

2. Chiral behaviour for three wave guides at an exceptional point of third order

Author

Heiss, WD and Wunner, G

Subjects
Physics - Optics
Abstract

A simple matrix model that has been used to describe essential features of a PT symmetric set-up of three coupled wave guides is investigated. The emphasis of the study lies on the occurrence of an exceptional point of third order. It is demonstrated that the eigenfunctions in close vicinity of the exceptional point have a distinctive chiral behaviour. Using data describing realistic situations it is argued that such chiral behaviour can be tested experimentally., Comment: 7 pages, 4 figures

Published
2017

3. Time behaviour near to spectral singularities

Author

Heiss, WD

Subjects
Quantum Physics
Abstract

Spectral singularities such as exceptional points invoke specific physical effects. The present paper focuses upon the time dependent solutions of the Schr\"odinger equation. In a simple model it is demonstrated that - depending on initial conditions - within close proximity of exceptional points the time behaviour of the wave function displays characteristic features such as very fast decay or the opposite, i.e. very long life time. At the exceptional point the wave function typically has a linear term in time besides the usual exponential behaviour., Comment: 5 pages, 3 figures to appear in EPJ D

Published
2010
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4. Time scales in nuclear giant resonances

Author

Heiss, WD, Nazmitdinov, RG, and Smit, FD

Subjects
Nuclear Theory
Abstract

We propose a general approach to characterise fluctuations of measured cross sections of nuclear giant resonances. Simulated cross sections are obtained from a particular, yet representative self-energy which contains all information about fragmentations. Using a wavelet analysis, we demonstrate the extraction of time scales of cascading decays into configurations of different complexity of the resonance. We argue that the spreading widths of collective excitations in nuclei are determined by the number of fragmentations as seen in the power spectrum. An analytic treatment of the wavelet analysis using a Fourier expansion of the cross section confirms this principle. A simple rule for the relative life times of states associated with hierarchies of different complexity is given., Comment: 5 pages, 4 figures

Published
2009
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5. On the Thermodynamic Limit of the Lipkin Model

Author

Heiss, WD

Subjects
Quantum Physics
Abstract

The thermodynamic limit of the Lipkin model is investigated. While the limit turns out to be rather elusive, the analysis gives strong indications that the limit yields two analytically dissociated operators, one for the normal and one for the deformed phase. While the Lipkin Hamiltonian is hermitian and has a second order phase transition in finite dimensions (finite particle number), both properties seem to be destroyed in the thermodynamic limit., Comment: 9 pages, 3 figures to appear in JPhysA

Published
2006
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6. Large N Scaling Behavior of the Lipkin-Meshkov-Glick Model

Author

Leyvraz, F and Heiss, WD

Subjects
Quantum Physics
Abstract

We introduce a novel semiclassical approach to the Lipkin model. In this way the well-known phase transition arising at the critical value of the coupling is intuitively understood. New results -- showing for strong couplings the existence of a threshold energy which separates deformed from undeformed states as well as the divergence of the density of states at the threshold energy -- are explained straightforwardly and in quantitative terms by the appearance of a double well structure in a classical system corresponding to the Lipkin model. Previously unnoticed features of the eigenstates near the threshold energy are also predicted and found to hold., Comment: 4 pages, 2 figures, to appear in PRL

Published
2005
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26. Positron emission tomography: present and future

Author

Heiss Wd

Subjects
Biomaterials, Nuclear magnetic resonance, medicine.diagnostic_test, business.industry, Positron emission tomography, Biomedical Engineering, Biophysics, Brain positron emission tomography, Medicine, Health Informatics, Bioengineering, business, Information Systems
Published
1996
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27. Thrombolysis with alteplase 3 to 4.5 hours after acute ischemic stroke

Author

Hacke, Werner, Kaste, Markku, Bluhmki, Erich, Brozman, Miroslav, Dávalos, Antoni, Guidetti, Donata, Larrue, Vincent, Lees, Kennedy R., Medeghri, Zakaria, Machnig, Thomas, Schneider, Dietmar, Von Kummer, Rüdiger, Wahlgren, Nils, Toni, Danilo, Hacke, W, Dávalos, A, Kaste, M, von Kummer, R, Larrue, V, Toni, D, Wahlgren, N, Lees, Kr, Heiss, Wd, Lesaffre, E, Orgogozo, Jm, Bastianello, S, Wardlaw, Jm, Peyrieux, Jc, Sauce, C, Medeghri, Z, Mazenc, R, Machnig, T, Bluhmki, E, Aichner, F, Alf, C, Baumhackl, U, Brainin, M, Eggers, C, Gruber, F, Ladurner, G, Niederkorn, K, Noistering, G, Willeit, J, Vanhooren, G, Blecic, S, Bruneel, B, Caekebeke, J, Laloux, P, Simons, Pj, Thijs, V, Bar, M, Dvorakova, H, Vaclavik, D, Boysen, G, Andersen, G, Iversen, Hk, Traberg-Kristensen, B, Marttila, R, Sivenius, J, Trouillas, P, Amarenco, P, Bouillat, J, Ducrocq, X, Giroud, M, Jaillard, A, Larrieu, Jm, Leys, D, Magne, C, Mahagne, Mh, Milhaud, D, Sablot, D, Saudeau, D, Busse, O, Berrouschot, J, Faiss, Jh, Glahn, J, Görtler, M, Grau, A, Grond, M, Haberl, R, Hamann, G, Hennerici, M, Koch, H, Krauseneck, P, Marx, J, Meves, S, Meyding-Lamadé, U, Ringleb, P, Schneider, D, Schwarz, A, Sobesky, J, Urban, P, Karageorgiou, K, Komnos, A, Csányi, A, Csiba, L, Valikovics, A, Agnelli, G, Billo, G, Bovi, P, Comi, G, Gigli, G, Guidetti, D, Inzitari, D, Marcello, N, Marini, C, Orlandi, G, Pratesi, M, Rasura, M, Semplicini, A, Serrati, C, Tassinari, T, Brouwers, Pj, Stam, J, Naess, H, Indredavik, B, Kloster, R, Czlonkowska, A, Kuczyńska-Zardzewialy, A, Nyka, W, Opala, G, Romanowicz, S, Cunha, L, Correia, C, Cruz, V, Pinho e Melo, T, Brozman, M, Dvorak, M, Garay, R, Krastev, G, Kurca, E, Alvarez-Sabin, J, Chamorro, A, del Mar Freijo Guerrero, M, Herrero, Ja, Gil-Peralta, A, Leira, R, Martí-Vilalta, Jl, Masjuan Vallejo, J, Millán, M, Molina, C, Mostacero, E, Segura, T, Serena, J, Vivancos Mora, J, Danielsson, E, Cederin, B, Von, Zweigberg, Wahlgren, Ng, Welin, L, Lyrer, P, Bogousslavsky, J, Hungerbühler, Hj, Weder, B, Ford, Ga, Jenkinson, D, Macleod, Mj, Macwalter, Rs, Markus, Hs, Muir, Kw, Sharma, Ak, Walters, Mr, Warburton, Ea, ACS - Amsterdam Cardiovascular Sciences, ANS - Amsterdam Neuroscience, and Neurology

Subjects
Adult, Male, Time Factors, medicine.medical_treatment, Placebo, Drug Administration Schedule, Brain Ischemia, Brain ischemia, Double-Blind Method, Fibrinolytic Agents, Modified Rankin Scale, medicine, Odds Ratio, Desmoteplase, Humans, Infusions, Intravenous, Stroke, Aged, business.industry, Cerebral infarction, Medicine (all), General Medicine, Thrombolysis, Middle Aged, medicine.disease, Logistic Models, Treatment Outcome, Anesthesia, Tissue Plasminogen Activator, Acute Disease, Female, business, Intracranial Hemorrhages, Fibrinolytic agent
Abstract

Background Intravenous thrombolysis with alteplase is the only approved treatment for acute ischemic stroke, but its efficacy and safety when administered more than 3 hours after the onset of symptoms have not been established. We tested the efficacy and safety of alteplase administered between 3 and 4.5 hours after the onset of a stroke. Methods After exclusion of patients with a brain hemorrhage or major infarction, as detected on a computed tomographic scan, we randomly assigned patients with acute ischemic stroke in a 1:1 double-blind fashion to receive treatment with intravenous alteplase (0.9 mg per kilogram of body weight) or placebo. The primary end point was disability at 90 days, dichotomized as a favorable outcome (a score of 0 or 1 on the modified Rankin scale, which has a range of 0 to 6, with 0 indicating no symptoms at all and 6 indicating death) or an unfavorable outcome (a score of 2 to 6 on the modified Rankin scale). The secondary end point was a global outcome analysis of four neurologic and disability scores combined. Safety end points included death, symptomatic intracranial hemorrhage, and other serious adverse events. Results We enrolled a total of 821 patients in the study and randomly assigned 418 to the alteplase group and 403 to the placebo group. The median time for the administration of alteplase was 3 hours 59 minutes. More patients had a favorable outcome with alte plase than with placebo (52.4% vs. 45.2%; odds ratio, 1.34; 95% confidence interval [CI], 1.02 to 1.76; P = 0.04). In the global analysis, the outcome was also improved with alteplase as compared with placebo (odds ratio, 1.28; 95% CI, 1.00 to 1.65; P

Published
2008

32. The ECAT HRRT: Performance and first clinical application of the new high resolution research tomograph

Author

UCL - MD/FSIO - Département de physiologie et pharmacologie, Wienhard, K., Schmand, M, Casey, ME, Baker, K., Bao, J, Eriksson, L., Jones, WF, Knoess, C, Lenox, M, Lercher, M, Luk, P, Michel, Caroline, Reed, JH, Richerzhagen, N, Treffert, J, Vollmar, S, Young, JW, Heiss, WD., Nutt, R, UCL - MD/FSIO - Département de physiologie et pharmacologie, Wienhard, K., Schmand, M, Casey, ME, Baker, K., Bao, J, Eriksson, L., Jones, WF, Knoess, C, Lenox, M, Lercher, M, Luk, P, Michel, Caroline, Reed, JH, Richerzhagen, N, Treffert, J, Vollmar, S, Young, JW, Heiss, WD., and Nutt, R

Abstract

The ECAT HRRT is a three-dimensional (3-D) only dedicated brain tomograph employing the new scintillator lutetium-oxy-orthosilicate (LSO) and using depth of interaction (DOI) information to achieve uniform isotropic resolution across a 20-cm diameter volume. With its unique technological innovations it represents the prototype of a new generation of high-resolution brain tomographs. The physical performance with respect to count rate, live time, scatter, sensitivity, and resolution was evaluated with phantom studies and measurements with a point source. The HRRTs imaging performance was tested with phantoms and fluorodeoxyglucose (FDG) scans performed in animal and human brains. We find that due to the significantly improved resolution and the large solid angle covered by the panel detectors, several Issues that have been adequately solved for older generation scanners demand new attention for the HRRT, like acquiring and handling large amounts of data effectively, strategies for optimal reconstruction, shielding, and correction of random coincidences.

Published
2002

33. Discrimination between Alzheimer dementia and controls by automated analysis of multicenter FDG PET

Author

Herholz, K, Salmon, E, Perani, D, Baron, J, Holthoff, V, Frolich, L, Schonknecht, P, Ito, K, Mielke, R, Kalbe, E, Zundorf, G, Delbeuck, X, Pelati, O, Anchisi, D, Fazio, F, Kerrouche, N, Desgranges, B, Eustache, F, Beuthien-Baumann, B, Menzel, C, Schroder, J, Kato, T, Arahata, Y, Henze, M, Heiss, W, Baron, JC, Heiss, WD, Herholz, K, Salmon, E, Perani, D, Baron, J, Holthoff, V, Frolich, L, Schonknecht, P, Ito, K, Mielke, R, Kalbe, E, Zundorf, G, Delbeuck, X, Pelati, O, Anchisi, D, Fazio, F, Kerrouche, N, Desgranges, B, Eustache, F, Beuthien-Baumann, B, Menzel, C, Schroder, J, Kato, T, Arahata, Y, Henze, M, Heiss, W, Baron, JC, and Heiss, WD

Abstract

A new diagnostic indicator of FDG PET scan abnormality, based on age-adjusted t statistics and an automated voxel-based procedure, is presented and validated in a large data set comprising 110 normal controls and 395 patients with probable Alzheimer's disease (AD) that were studied in eight participating centers. The effect of differences in spatial resolution of PET scanners was minimized effectively by filtering and masking. In controls FDG uptake declined significantly with age in anterior cingulate and frontolateral perisylvian cortex. In patients with probable AD decline of FDG uptake in posterior cingulate, temporoparietal, and prefrontal association cortex was related to dementia severity. These effects were clearly distinct from age effects in controls, suggesting that the disease process of AD is not related to normal aging. Women with probable AD had significantly more frontal metabolic impairment than men. The new indicator of metabolic abnormality in AD-related regions provided 93% sensitivity and specificity for distinction of mild to moderate probable AD from normals, and 84% sensitivity at 93% specificity for detection of very mild probable AD (defined by Mini Mental Score 24 or better). All regions related to AD severity were already affected in very mild AD, suggesting that all vulnerable areas are affected to a similar degree already at disease onset. Ventromedial frontal cortex was also abnormal. In conclusion, automated analysis of multicenter FDG PET is feasible, provides insights into AD pathophysiology, and can be used potentially as a sensitive biomarker for early AD diagnosis. (C) 2002 Elsevier Science (USA).

Published
2002

34. Random perturbation of systematic degeneracies and their Fourier transforms and periodic orbits

Author

Müller M and Heiss Wd

Subjects
Physics, symbols.namesake, Classical mechanics, Fourier transform, Chaotic systems, Degenerate energy levels, symbols, Periodic orbits, Perturbation (astronomy), Probability distribution, Random perturbation, Hamiltonian (quantum mechanics), Atomic and Molecular Physics, and Optics
Abstract

The effect of random perturbation is investigated for a Hamiltonian with systematic degeneracies. It turns out that the influence of the degeneracies remains significant under perturbation. The model simulates quantized versions of classically chaotic systems in that the Fourier transform of the level density shows the characteristic lines which would be associated with the periods of periodic orbits if the system had a classical analogy. The decaying magnitude of the recurring lines is related to the spread of the probability distribution under the influence of perturbation of the degenerate levels

Published
1993

41. Erkrankungsprogression bei Patienten mit idiopathischem Parkinson-Syndrom und STN-Stimulation – Eine 18-Fluorodopa-PET-Verlaufsstudie

Author

Hilker, R, primary, Portman, AT, additional, Voges, J, additional, Staal, MJ, additional, Burghaus, L, additional, van Laar, T, additional, Koulousakis, A, additional, Maguire, RP, additional, Pruim, J, additional, Herholz, K, additional, de Jong, BM, additional, Sturm, V, additional, Heiss, WD, additional, and Leenders, KL, additional

Published
2005
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