355 results on '"Gray W"'
Search Results
2. Unwarranted variation and the goal of net zero for the NHS in England: exploring the link between efficiency working, patient outcomes and carbon footprint.
- Author
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van Hove, M., John, J. B., Ojelade, E., Ayyaz, F., Koris, J., Frame, J., Swart, M., Snowden, C., Briggs, T. W. R., and Gray, W. K.
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ECOLOGICAL impact ,PHYSICIAN practice patterns ,CARBON emissions ,DESFLURANE ,PATIENT care - Abstract
Summary: In 2020 the NHS in England set a target of reaching net zero carbon emissions by 2040. Progress has already been made towards this goal, with substantial reductions in the use of environmentally harmful anaesthetic gases, such as desflurane, in recent years. Where an effective replacement already exists, changing practice to use low carbon alternatives is relatively easy to achieve, but much greater challenges lie ahead. The Getting It Right First Time (GIRFT) programme is a clinically‐led, data‐driven clinical improvement initiative with a focus on reducing unwarranted variation in clinical practice and patient outcomes. Reducing unwarranted variation can improve patient care and service efficiency, and can also support the drive to net zero. In this article we set out what the GIRFT programme is doing to support sustainable healthcare in England, why it is uniquely positioned to support this goal and what the future challenges, barriers, enablers and opportunities are likely to be in the drive to net zero. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
3. Day-case and in-patient elective inguinal hernia repair surgery across England: an observational study of variation and outcomes.
- Author
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Joyner, J., Ayyaz, F. M., Cheetham, M., Briggs, T. W. R., and Gray, W. K.
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INGUINAL hernia ,HERNIA surgery ,MEDICAL personnel ,SURGERY ,HOSPITAL statistics ,ELECTIVE surgery - Abstract
Purpose: Elective primary inguinal hernia repair surgery is increasingly being conducted as a day-case procedure. However, in England there is evidence of wide variation in day-case rates across hospitals. Reducing the extent of this variation has the potential to support more efficient use of resources (e.g., clinician time, hospital beds) and help the recovery of elective surgical activity following the COVID-19 pandemic. The aims of this study were to explore the extent of variation in day-case rates across healthcare providers in England and to evaluate the safety of day-case elective primary inguinal hernia repair surgery. Methods: This was an exploratory, retrospective analysis of observational data from the Hospital Episode Statistics data set for England. All patients aged ≥ 17 years undergoing a first elective inguinal hernia repair between 1st April 2014 and 31st March 2022 were identified. The exposure of interest was day-case or in-patient stay, and the primary outcome of interest was 30-day emergency readmission with an overnight stay. For reporting, providers were aggregated to an Integrated Care Board (ICB) level. Results: A total of 413,059 elective primary inguinal hernia repairs were identified over the 8-year study period. Of these, 326,833 (79.1%) were day-case procedures. During the most recent financial year (2021–22), the highest day-case rate for an ICB was 93.8% and the lowest 66.1%. After adjusting for covariates, day-case surgery was associated with significantly lower rates of 30-day emergency readmission (odds ratio (OR) 0.61, 95% confidence interval (CI) 0.58–0.64, p < 0.001) and for the secondary outcomes 180-day mortality and haemorrhage, infection and pain at 30-day post-discharge. Rates of 30-day emergency readmission were significantly lower in ICBs with high rates of day-case surgery (OR 0.84, 95% CI 0.74–0.96, p < 0.001) than in ICBs with low rates of day-case surgery, although rates of post-procedural haemorrhage within 30 days of discharge were significantly higher in trusts with high day-case rates (OR 1.20, 95% CI 1.04–1.40, p = 0.015). Conclusions: For the outcomes studied, we found no consistent evidence that day-case elective inguinal hernia repair was unsafe for selected patients. Currently, there is substantial variation between ICBs in terms of delivering day-case surgery. Reducing this variability may help address the current pressures on the NHS in elective surgery. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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4. Revisiting Oxygen‐18 and Clumped Isotopes in Planktic and Benthic Foraminifera.
- Author
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Daëron, M. and Gray, W. R.
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FORAMINIFERA ,OCEAN temperature ,ISOTOPES ,PALEOCENE Epoch ,CENOZOIC Era ,CALCIFICATION - Abstract
Foraminiferal isotopes are widely used to study past oceans, with different species recording conditions at different depths. Their δ18O values record both seawater oxygen‐18 and temperature according to species‐specific fractionation factors, while their Δ47 signatures likely depend only on temperature. We describe an open‐source framework to collect/combine data relevant to foraminiferal isotopes, by constraining species‐specific oxygen‐18 fractionation factors (18α) based on culture experiments, stratified plankton tows or core‐top sediments; compiling stratified plankton tow constraints on living depths for planktic species; extracting seawater temperature, δ18O, and chemistry from existing databases for any latitude, longitude, and depth‐range; inferring calcification temperatures based on the above data. We find that although 18α differs between species, its temperature sensitivity remains indistinguishable from inorganic calcite. Based on > 2,600 observations we show that, although most planktic δ18O values are consistent with seawater temperature and δ18O over their expected living depths, a sizable minority (12%–24%) have heavier‐than‐predicted δ18O, best explained by calcification in deeper waters. We use this framework to revisit three recent Δ47 calibration studies of planktic/benthic foraminifera, confirming that planktic Δ47 varies systematically with oxygen‐18‐derived temperature estimates, even for samples whose δ18O disagrees with assumed climatological conditions, and demonstrating excellent agreement between planktic foraminifera and modern, largely inorganic Δ47 calibrations. Benthic foraminifera remain ambiguous: modern benthic Δ47 values appear offset from planktic ones, yet applying equilibrium Δ47 calibration to the Cenozoic benthic foraminifer record of Meckler et al. (2022, https://doi.org/10.1126/science.abk0604) largely reconciles it with δ18O‐derived temperatures, with discrete Δ47/δ18O discrepancies persisting in the Late Paleocene/Eocene/Plio‐Pleistocene. Key Points: We provide an open‐source, data‐driven framework to collect and combine data relevant to foraminifer isotope recordsΔ47 and δ18O thermometers agree well in planktics and indicate that calcification can sometimes occur below usually assumed living depthsPlanktic Δ47 follows I‐CDES calibrations, challenging prior Cenozoic Δ47 interpretations; benthics may differ and require new observations [ABSTRACT FROM AUTHOR]
- Published
- 2023
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5. Continuity of Formal Power Series Products in Nonlinear Control Theory.
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Gray, W. Steven, Palmstrøm, Mathias, and Schmeding, Alexander
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NONLINEAR control theory ,POWER series ,ADAPTIVE control systems ,LIE groups ,TRANSFORMATION groups - Abstract
Formal power series products appear in nonlinear control theory when systems modeled by Chen–Fliess series are interconnected to form new systems. In fields like adaptive control and learning systems, the coefficients of these formal power series are estimated sequentially with real-time data. The main goal is to prove the continuity and analyticity of such products with respect to several natural (locally convex) topologies on spaces of locally convergent formal power series in order to establish foundational properties behind these technologies. In addition, it is shown that a transformation group central to describing the output feedback connection is in fact an analytic Lie group in this setting with certain regularity properties. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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6. Formal power series approach to nonlinear systems with additive static feedback.
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Venkatesh, G. S. and Gray, W. Steven
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POWER series ,HOPF algebras ,NONLINEAR systems ,TRANSFORMATION groups ,CLOSED loop systems - Abstract
The goal of this paper is to compute the generating series of a closed-loop system when the plant is described in terms of a Chen–Fliess series and an additive static output feedback is applied. The first step is to consider the so-called Wiener-Fliess connection consisting of a Chen–Fliess series followed by a memoryless function. To explicitly compute the generating series, two Hopf algebras are needed: the existing output feedback Hopf algebra used to describe dynamic output feedback and the Hopf algebra of the shuffle group. These two combinatorial structures are combined to compute what will be called the Wiener–Fliess feedback product. It will be shown that this product has a natural interpretation as a transformation group acting on the plant and preserves the relative degree of the plant. The convergence of the Wiener–Fliess composition product and the additive static feedback product are characterised. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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- View/download PDF
7. Identifying drivers of breast cancer metastasis in progressively invasive subpopulations of zebrafish-xenografted MDA-MB-231.
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Jerry Xiao, McGill, Joseph R., Nasir, Apsra, Lekan, Alexander, Johnson, Bailey, Wilkins, Devan J., Pearson, Gray W., Tanner, Kandice, Goodarzi, Hani, Glasgow, Eric, Schlegel, Richard, and Agarwal, Seema
- Abstract
Cancer metastasis is the primary cause of the high mortality rate among human cancers. Efforts to identify therapeutic agents targeting cancer metastasis frequently fail to demonstrate efficacy in clinical trials despite strong preclinical evidence. Until recently, most preclinical studies used mouse models to evaluate anti-metastatic agents. Mouse models are time-consuming and expensive. In addition, an important drawback is that mouse models inadequately model the early stages of metastasis which plausibly leads to the poor correlation with clinical outcomes. Here, we report an in vivo model based on xenografted zebrafish embryos where we select for progressively invasive subpopulations of MDA-MB-231 breast cancer cells. A subpopulation analogous to circulating tumor cells found in human cancers was selected by injection of MDA-MB-231 cells into the yolk sacs of 2 days post-fertilized zebrafish embryos and selecting cells that migrated to the tail. The selected subpopulation derived from MDA-MB-231 cells were increasingly invasive in zebrafish. Isolation of these subpopulations and propagation in vitro revealed morphological changes consistent with activation of an epithelial-mesenchymal transition program. Differential gene analysis and knockdown of genes identified gene-candidates (DDIT4, MT1X, CTSD, and SERPINE1) as potential targets for anti-metastasis therapeutics. Furthermore, RNA-splicing analysis reinforced the importance of BIRC5 splice variants in breast cancer metastasis. This is the first report using zebrafish to isolate and expand progressively invasive populations of human cancer cells. The model has potential applications in understanding the metastatic process, identification and/or development of therapeutics that specifically target metastatic cells and formulating personalized treatment strategies for individual cancer patients. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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8. Social Participation's Association with Falls and Frailty in Malaysia: A Cross-Sectional Study.
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Risbridger, S., Walker, R., Gray, W. K., Kamaruzzaman, S. B., Ai-Vyrn, C., Hairi, N. N., Khoo, P. L., and Pin, Tan Maw
- Published
- 2022
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9. Safety of day‐case paediatric tonsillectomy in England: an analysis of administrative data for the Getting It Right First Time programme.
- Author
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Gray, W. K., Takhar, A. S., Navaratnam, A. V., Day, J., Swart, M., Snowden, C., Briggs, T. W. R., and Marshall, A.
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TONSILLECTOMY ,TONSILLITIS ,PEDIATRICS ,DATA analysis ,NUMERIC databases ,HOSPITAL statistics ,TREATMENT effectiveness - Abstract
Summary: We used the Hospital Episodes Statistics database to investigate unwarranted variation in the rates Trusts discharged children the same day after scheduled tonsillectomy and associations with adverse postoperative outcomes. We included children aged 2–18 years who underwent tonsillectomy between 1 April 2014 and 31 March 2019. We stratified analyses by category of Trust, non‐specialist or specialist, defined as without or with paediatric critical care facilities, respectively. We adjusted analyses for age, sex, year of surgery and aspects of presentation and procedure type. Of 101,180 children who underwent tonsillectomy at non‐specialist Trusts, 62,926 (62%) were discharged the same day, compared with 24,138/48,755 (50%) at specialist Trusts. The adjusted proportion of children discharged the same day as tonsillectomy ranged from 5% to 100% at non‐specialist Trusts and 9% to 88% at specialist Trusts. Same‐day discharge was not independently associated with an increased rate of 30‐day emergency re‐admission at non‐specialist Trusts but was associated with a modest rate increase at specialist Trusts; adjusted probability 8.0% vs 7.7%, odds ratio (95%CI) 1.14 (1.05–1.24). Rates of adverse postoperative outcomes were similar for Trusts that discharged >70% children the same day as tonsillectomy compared with Trusts that discharged <50% children the same day, for both non‐specialist and specialist Trust categories. We found no consistent evidence that day‐case tonsillectomy is associated with poorer outcomes. All Trusts, but particularly specialist centres, should explore reasons for low day‐case rates and should aim for rates >70%. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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10. Volume-outcome relationship for adrenalectomy: analysis of an administrative dataset for the Getting It Right First Time Programme.
- Author
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Gray, W. K., Day, J., Briggs, T. W. R., Wass, J. A. H., and Lansdown, M.
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MINIMALLY invasive procedures ,ADRENALECTOMY ,NUMERIC databases ,HOSPITAL statistics ,MULTILEVEL models - Abstract
Background: A minimum volume threshold of at least six procedures per annum per surgeon has been set in UK and European guidelines for adrenal surgery. The aim of this study was to investigate outcomes for adrenal surgery in England relative to annual surgeon and hospital trust volume. Methods: Data were extracted from the Hospital Episodes Statistics database for England. A 6-year period (January 2013 to December 2018 inclusive) for all adult admissions for unilateral adrenal surgery was used. The primary outcome measure was an emergency readmission within 30 days of discharge following surgery. Procedures were categorized as open or minimally invasive surgery for analysis. Multilevel modelling was used to adjust for hierarchy and potential confounders. Results: Data for 4189 adrenalectomies were identified. Only one third of surgeons (who operated on just over a half of all patients) performed at least six procedures in the year prior to the index procedure. For open surgery, emergency readmission rates fell significantly from 15.2 to 6.4 per cent for surgeons and from 13.2 to 6.1 per cent for trusts between the lowest- and highest-volume categories. Significant, but less dramatic falls were also seen for minimally invasive surgery. Conclusion: A volume-outcome effect was identified for adrenal surgery in England. Minimum volume thresholds should be set, although these may need to be more ambitious than the current threshold if outcomes are to be optimized. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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11. Numerical Modeling of Galactic Superwinds with Time-evolving Stellar Feedback.
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Danehkar, A., Oey, M. S., and Gray, W. J.
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MASS loss (Astrophysics) ,STELLAR mass ,HYDRODYNAMICS ,STARBURSTS ,SUPERGIANT stars - Abstract
Mass-loss and radiation feedback from evolving massive stars produce galactic-scale superwinds, sometimes surrounded by pressure-driven bubbles. Using the time-dependent stellar population typically seen in star-forming regions, we conduct hydrodynamic simulations of a starburst-driven superwind model coupled with radiative efficiency rates to investigate the formation of radiative cooling superwinds and bubbles. Our numerical simulations depict the parameter space where radiative cooling superwinds with or without bubbles occur. Moreover, we employ the physical properties and time-dependent ionization states to predict emission line profiles under the assumption of collisional ionization and non-equilibrium ionization caused by wind thermal feedback in addition to photoionization created by the radiation background. We see the dependence of non-equilibrium ionization structures on the time-evolving ionizing source, leading to a deviation from collisional ionization in radiative cooling wind regions over time. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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12. Disulfide HMGB1 acts via TLR2/4 receptors to reduce the numbers of oligodendrocyte progenitor cells after traumatic injury in vitro.
- Author
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Ved, R., Sharouf, F., Harari, B., Muzaffar, M., Manivannan, S., Ormonde, C., Gray, W. P., and Zaben, M.
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DISULFIDES ,OLIGODENDROGLIA ,PROGENITOR cells ,INFLAMMATION ,CLINICAL trials - Abstract
Traumatic brain injury (TBI) is associated with poor clinical outcomes; autopsy studies of TBI victims demonstrate significant oligodendrocyte progenitor cell (OPC) death post TBI; an observation, which may explain the lack of meaningful repair of injured axons. Whilst high-mobility group box-1 (HMGB1) and its key receptors TLR2/4 are identified as key initiators of neuroinflammation post-TBI, they have been identified as attractive targets for development of novel therapeutic approaches to improve post-TBI clinical outcomes. In this report we establish unequivocal evidence that HMGB1 released in vitro impairs OPC response to mechanical injury; an effect that is pharmacologically reversible. We show that needle scratch injury hyper-acutely induced microglial HMGB1 nucleus-to-cytoplasm translocation and subsequent release into culture medium. Application of injury-conditioned media resulted in significant decreases in OPC number through anti-proliferative effects. This effect was reversed by co-treatment with the TLR2/4 receptor antagonist BoxA. Furthermore, whilst injury conditioned medium drove OPCs towards an activated reactive morphology, this was also abolished after BoxA co-treatment. We conclude that HMGB1, through TLR2/4 dependant mechanisms, may be detrimental to OPC proliferation following injury in vitro, negatively affecting the potential for restoring a mature oligodendrocyte population, and subsequent axonal remyelination. Further study is required to assess how HMGB1-TLR signalling influences OPC maturation and myelination capacity. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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13. Uncovering a Role for the Dorsal Hippocampal Commissure in Recognition Memory.
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Postans, M, Parker, G D, Lundell, H, Ptito, M, Hamandi, K, Gray, W P, Aggleton, J P, Dyrby, T B, Jones, D K, and Winter, M
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- 2020
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14. PaCTS 1.0: A Crowdsourced Reporting Standard for Paleoclimate Data.
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Khider, D., Emile‐Geay, J., McKay, N. P., Gil, Y., Garijo, D., Ratnakar, V., Alonso‐Garcia, M., Bertrand, S., Bothe, O., Brewer, P., Bunn, A., Chevalier, M., Comas‐Bru, L., Csank, A., Dassié, E., DeLong, K., Felis, T., Francus, P., Frappier, A., and Gray, W.
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PALEOCLIMATOLOGY ,BIG data ,METADATA ,STANDARDS ,ATMOSPHERIC models ,TEAMS in the workplace - Abstract
The progress of science is tied to the standardization of measurements, instruments, and data. This is especially true in the Big Data age, where analyzing large data volumes critically hinges on the data being standardized. Accordingly, the lack of community‐sanctioned data standards in paleoclimatology has largely precluded the benefits of Big Data advances in the field. Building upon recent efforts to standardize the format and terminology of paleoclimate data, this article describes the Paleoclimate Community reporTing Standard (PaCTS), a crowdsourced reporting standard for such data. PaCTS captures which information should be included when reporting paleoclimate data, with the goal of maximizing the reuse value of paleoclimate data sets, particularly for synthesis work and comparison to climate model simulations. Initiated by the LinkedEarth project, the process to elicit a reporting standard involved an international workshop in 2016, various forms of digital community engagement over the next few years, and grassroots working groups. Participants in this process identified important properties across paleoclimate archives, in addition to the reporting of uncertainties and chronologies; they also identified archive‐specific properties and distinguished reporting standards for new versus legacy data sets. This work shows that at least 135 respondents overwhelmingly support a drastic increase in the amount of metadata accompanying paleoclimate data sets. Since such goals are at odds with present practices, we discuss a transparent path toward implementing or revising these recommendations in the near future, using both bottom‐up and top‐down approaches. Plain Language Summary: Standardizing the way data are described and shared is key to accelerating the progress of science. Building on recent advances in paleoceanography and paleoclimatology, we present the first community‐led reporting standard for such datasets. The Paleoclimate Community reporTing Standard (PaCTS) provides guidelines as to which information should be included when reporting data from various paleoclimate archives, as well as themes common to many fields, like uncertainty and other site‐specific information. The ultimate goal of this effort is to (1) make these datasets more re‐usable over the long term, and (2) provide a roadmap for implementing and revising the standard, as the field of paleoclimatology and its practitioners both evolve. The requirements are driven by the differing needs of data producers and the data consumers, who often have different goals in mind. Thus, agreeing on and writing up these requirements involves building consensus among the community to decide on their present and future goals. Key Points: First version of a crowdsourced reporting standard for paleoclimate dataThe standards arose through collective discussions, both in person and online, and via an innovative social platformThe standard helps meet the interoperability and reuse criteria of FAIR (Findable, Accessible, Interoperable, and Reusable) [ABSTRACT FROM AUTHOR]
- Published
- 2019
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15. Nonhysteretic Capillary Pressure in Two‐Fluid Porous Medium Systems: Definition, Evaluation, Validation, and Dynamics.
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Miller, C. T., Bruning, K., Talbot, C. L., McClure, J. E., and Gray, W. G.
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POROUS materials ,EQUATIONS of state ,EULER characteristic ,EULER equations - Abstract
A closure relation for capillary pressure plays an important role in the formulation of both traditional and evolving models of two‐fluid‐phase flow in porous medium systems. We review the traditional approaches to define capillary pressure, to describe it mathematically, to determine parameters for this relation, and to constrain the domain of applicability of this relation. In contrast to the traditional approach, we provide a rigorous, multiscale definition of capillary pressure, define the state domain of interest in practice, summarize computational and experimental approaches to investigate the system state, and apply the methods for two‐fluid states in a model ink bottle system, the classical Finney pack of spheres, and a synthetic sphere pack system. The results of these applications show that a state equation exists that describes capillary pressure without hysteresis. This state equation parameterizes a function that describes the nonwetting phase volume fraction in terms of the capillary pressure, the interfacial area, and the specific Euler characteristic of the nonwetting phase. Furthermore, this state equation applies over the complete range of conditions encountered in practice, and it applies under both equilibrium and dynamic conditions. This state equation involving capillary pressure forms an important foundation for the development of the next generation of macroscale two‐fluid‐phase flow models in porous medium systems. Key Points: A hysteretic‐free capillary pressure state equation is developedThe state equation is validated using both analytical and numerical simulation approachesThis state equation applies under both equilibrium and dynamic conditions [ABSTRACT FROM AUTHOR]
- Published
- 2019
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16. Musculoskeletal Outcomes from Chronic High-Speed High-Impact Resistive Exercise.
- Author
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Chen, L., Selimovic, E. A., Daunis, M., Bayers T., T. A., Vargas, L. J., O'Brien, I. T., McEnroe, C. B., Kozerski, A. E., Vanhoover, A. C., Gray, W. D., and Caruso, J. F.
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ISOMETRIC exercise ,SPACE biology ,PLYOMETRICS ,MUSCLE strength measurement ,MUSCLE strength ,ISOKINETIC exercise ,MOTOR unit ,HIP exercises - Published
- 2019
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17. Electromechanical stress analysis of transversely isotropic solenoids.
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Gray, W. H. and Ballou, J. K.
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- 1977
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18. A Microwave Study of the High Pressure Arc.
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Cobine, J. D., Cleary, E. P., and Gray, W. C.
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- 1950
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19. Modeling Nondilute Species Transport Using the Thermodynamically Constrained Averaging Theory.
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Weigand, T. M., Schultz, P. B., Crockett, A., Gray, W. G., Miller, C. T., Giffen, D. H., Kelley, C. T., and Farthing, M. W.
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POROUS materials ,HAZARDOUS substances - Abstract
Nondilute transport in porous media results in fronts that are much sharper in space and time than the corresponding transport of a conservative, nonreactive dilute species. A thermodynamically constrained averaging theory model for such situations is developed. A novel closure scheme is formulated, which is cross‐coupled between flow and transport in its most general form. Experiments are performed to investigate the effects of density, viscosity, and chemical activity. An adaptive numerical approximation method is developed to efficiently solve the formulated model. Parameter estimation is performed, and excellent agreement between laboratory data and model simulations is obtained. Accurate prediction of experimental data not used to estimate model parameters is found. It is also shown that chemical activity effects contribute to asymmetric breakthrough curves for nondilute transport in porous medium systems. Key Points: A TCAT approach is used to formulate a new closed model to describe nondilute species transport in porous mediaExperiments were run to investigate species transport for solutions that have a broad range of densities, viscosities, and activitiesResults show that the TCAT model improves upon both the description and prediction of laboratory data compared to extant approaches [ABSTRACT FROM AUTHOR]
- Published
- 2018
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20. Stability, performance and sensitivity analysis of I.I.D. jump linear systems.
- Author
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Chávez Fuentes, Jorge R., González, Oscar R., and Gray, W. Steven
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STABILITY of linear systems ,FAULT-tolerant control systems ,DIMENSIONAL analysis ,SENSITIVITY analysis ,DISTRIBUTION (Probability theory) - Abstract
This paper presents a symmetric Kronecker product analysis of independent and identically distributed jump linear systems to develop new, lower dimensional equations for the stability and performance analysis of this type of systems than what is currently available. In addition, new closed form expressions characterising multi-parameter relative sensitivity functions for performance metrics are introduced. The analysis technique is illustrated with a distributed fault-tolerant flight control example where the communication links are allowed to fail randomly. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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21. Discrete-time approximations of fliess operators.
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Gray, W. Steven, Duffaut Espinosa, Luis A., and Ebrahimi-Fard, Kurusch
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- 2016
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22. Discrete-time approximations of Fliess operators.
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Gray, W., Duffaut Espinosa, Luis, and Ebrahimi-Fard, Kurusch
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OPERATOR theory ,APPROXIMATION theory ,INPUT-output analysis ,ERROR analysis in mathematics ,ITERATIVE methods (Mathematics) ,DISCRETIZATION methods - Abstract
A convenient way to represent a nonlinear input-output system in control theory is via a Chen-Fliess functional expansion or Fliess operator. The general goal of this paper is to describe how to approximate Fliess operators with iterated sums and to provide accurate error estimates for two different scenarios, one where the series coefficients are growing at a local convergence rate, and the other where they are growing at a global convergence rate. In each case, it is shown that the error estimates are asymptotically achievable for certain worst case inputs. The paper then focuses on the special case where the operators are rational, i.e., they have rational generating series, and thus are realizable in terms of bilinear ordinary differential state equations. In particular, it is shown that a discretization of the state equation via a kind of Euler approximation coincides exactly with the discrete-time Fliess operator approximator of the continuous-time rational operator. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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23. Center Problem, Abel Equation and the Faà di Bruno Hopf Algebra for Output Feedback.
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Ebrahimi-Fard, Kurusch and Gray, W. Steven
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WORD problems (Mathematics) ,DIFFERENTIAL equations ,POLYNOMIALS ,HOPF algebras ,INTEGRALS - Abstract
A combinatorial interpretation is given of Devlin's word problem underlying the classical center problem of Poincaré for nonautonomous differential equations. It turns out that the canonical polynomials of Devlin are from the point of view of connected graded Hopf algebras the graded components of a Hopf algebra antipode applied to the formal power series of Ferfera. The link is made by applying control theory to the Abel equation, which can produce a center at the origin. The Abel equation is equivalent to an output feedback equation, and the Hopf algebra of output feedback is derived from the composition of iterated integrals rather than just the products of iterated integrals, which yields only the shuffle algebra. This means that the primary algebraic structure at play in Devlin's approach is actually not the shuffle algebra, but a Faà di Bruno type Hopf algebra, which is defined in terms of the unshuffle coproduct. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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24. SISO OUTPUT AFFINE FEEDBACK TRANSFORMATION GROUP AND ITS FAÀ DI BRUNO HOPF ALGEBRA.
- Author
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STEVEN GRAY, W. and EBRAHIMI-FARD, KURUSCH
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INTEGRATED circuit interconnections ,AFFINE transformations ,FEEDBACK control systems ,LIE algebras ,INVARIANT sets - Abstract
The general goal of this paper is to identify a transformation group that can be used to describe a class of feedback interconnections involving subsystems which are modeled solely in terms of Chen-Fliess functional expansions or Fliess operators and are independent of the existence of any state space models. This interconnection, called an output affine feedback connection, is distinguished from conventional output feedback by the presence of a multiplier in an outer loop. Once this transformation group is established, three basic questions are addressed. How can this transformation group be used to provide an explicit Fliess operator representation of such a closed-loop system? Is it possible to use this feedback scheme to do system inversion purely in an input-output setting? In particular, can feedback input-output linearization be posed and solved entirely in this framework, i.e., without the need for any state space realization? Last, what can be said about feedback invariants under this transformation group? A final objective of the paper is to describe the Lie algebra of infinitesimal characters associated with the group in terms of a pre-Lie product [ABSTRACT FROM AUTHOR]
- Published
- 2017
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25. Successful rescue therapy with venovenous extracorporeal membrane oxygenation for re-expansion pulmonary oedema in a patient with one lung.
- Author
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Gray, W Hampton, Hackmann, Amy E, Starnes, Vaughn A, and Kiankhooy, Armin
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EXTRACORPOREAL membrane oxygenation - Abstract
Re-expansion pulmonary oedema following the drainage of pleural fluid is rare. We report a patient with 1 lung who developed life-threatening re-expansion pulmonary oedema following thoracentesis and was rescued with venovenous (VV) extracorporeal membrane oxygenation (ECMO), surviving to discharge 28 days later. An aggressive early rescue therapy with VV ECMO should be pursued for all types of acute lung injury regardless of patient age, comorbidities or transplant candidacy, given the likelihood of native lung recovery following ECMO support. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
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26. Analytic left inversion of multivariable Lotka-Volterra models.
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Gray, W. Steven, Espinosa, Luis A. Duffaut, and Ebrahimi-Fard, Kurusch
- Published
- 2015
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27. Analytic left inversion of SISO Lotka-Volterra models.
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Gray, W. Steven, Espinosa, Luis A. Duffaut, and Ebrahimi-Fard, Kurusch
- Published
- 2015
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28. Fractional Fliess operators: Two approaches.
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Winter-Arboleda, Irina M., Gray, W. Steven, and Duffaut Espinosa, Luis A.
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- 2015
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29. On the Consistency of Scale Among Experiments, Theory, and Simulation.
- Author
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McClure, J., Dye, A., Miller, C., and Gray, W.
- Abstract
The career of Professor Eric F. Wood has focused on the resolution of problems of scale in hydrologic systems. Within this context, we consider an evolving approach known as the thermodynamically constrained averaging theory (TCAT), which has broad applicability to hydrology. Specifically, we consider the case of modeling of two-fluid-phase flow in porous media. Two-fluid flow processes in the subsurface are fundamentally important for a wide range of hydrologic processes, including the transport of water and air in the vadose zone and geological carbon sequestration. Mathematical models that describe these complex processes have long relied on empirical approaches that neglect important aspects of the system behavior. New data sources make it possible to access the true geometry of geologic materials and directly measure previously inaccessible quantities. This information can be exploited to support a new generation of theoretical models that are constructed based on rigorous multiscale principles for thermodynamics and continuum mechanics. The challenges to constructing a mature model are shown to involve issues of scale, consistency requirements, appropriate representation of operative physical mechanisms at the target scale of the model, and a robust structure to support model evaluation, validation, and refinement. We apply TCAT to perform physics-based data assimilation to understand how the internal behavior influences the macroscale state of two-fluid porous medium systems. Examples of a microfluidic experimental method and a lattice Boltzmann simulation method are used to examine a key deficiency associated with standard approaches. In a hydrologic process such as evaporation, the water content will ultimately be reduced below the irreducible wetting phase saturation determined from experiments. This is problematic since the derived closure relationships cannot predict the associated capillary pressures for these states. In this work, we demonstrate that the irreducible wetting-phase saturation is an artifact of the experimental design, caused by the fact that the boundary pressure difference does not approximate the true capillary pressure. Using averaging methods, we measure the true capillary pressure for fluid configurations at and below the irreducible wetting phase saturation. Results of our analysis include a state function for the capillary pressure expressed as a function of fluid saturation and interfacial area. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
30. Tracking interface and common curve dynamics for two-fluid flow in porous media.
- Author
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McClure, J. E., Berrill, M. A., Gray, W. G., and Miller, C. T.
- Subjects
POROUS materials ,MULTIPHASE flow ,LATTICE Boltzmann methods ,TWO-phase flow ,CONTACT angle - Abstract
The movements of fluid-fluid interfaces and the common curve are an important aspect of two-fluid-phase flow through porous media. The focus of this work is to develop, apply and evaluate methods to simulate two-fluid-phase flow in porous medium systems at the microscale and to demonstrate how these results can be used to support evolving macroscale models. Of particular concern is the problem of spurious velocities that confound the accurate representation of interfacial dynamics in such systems. To circumvent this problem, a combined level-set and lattice-Boltzmann method is advanced to simulate and track the dynamics of the fluid-fluid interface and of the common curve during simulations of two-fluid-phase flow in porous media. We demonstrate that the interface and common curve velocities can be determined accurately, even when spurious currents are generated in the vicinity of interfaces. Static and dynamic contact angles are computed and shown to agree with existing slip models. A resolution study is presented for dynamic drainage and imbibition in a sphere pack, demonstrating the sensitivity of averaged quantities to resolution. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
31. Case-fatality and disability in the Tanzanian Stroke Incidence Project cohort.
- Author
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Walker, R. W., Wakefield, K., Gray, W. K., Jusabani, A., Swai, M., and Mugusi, F.
- Subjects
STROKE-related mortality ,FOLLOW-up studies (Medicine) ,HEALTH outcome assessment ,COHORT analysis - Abstract
Objectives - The burden of stroke on healthcare services in sub-Saharan Africa (SSA) is increasing. However, long-term outcomes from stroke in SSA are not well described. We aimed to investigate case-fatality and health outcomes for stroke survivors at 7- to 10-year follow-up. Materials and methods - The Tanzanian Stroke Incidence Project (TSIP) recruited incidence stroke cases between 2003 and 2006. We followed up cases in 2013, recording date of death in those who had died. Results - Of 130 stroke cases included in this study, case-fatality and date of death data were available for 124 at 7- 10 years post-stroke. Of these, 102 (82.3%) had died by 7 years post-stroke. Functional disability, as measured by the Barthel index immediately post-stroke, was a significant predictor of case-fatality at seven-year follow-up with those with severe disability having an almost four-fold increase in the odds of death compared with those with no, mild or moderate disability. Conclusions - Case-fatality rates are higher than reported in high-income countries, with poststroke disability a significant predictor of death. Sustainable interventions to reduce post-stroke disability in this setting should be investigated. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
32. Dendriform-tree setting for fully non-commutative Fliess operators.
- Author
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Duffaut Espinosa, Luis A., Gray, W. Steven, and Ebrahimi-Fard, Kurusch
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- 2014
- Full Text
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33. Pre-Lie algebra characterization of SISO feedback invariants.
- Author
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Gray, W. Steven, Thitsa, Makhin, and Duffaut Espinosa, Luis A.
- Published
- 2014
- Full Text
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34. The prevalence and burden of behavioural and psychological symptoms of dementia in rural Tanzania.
- Author
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Paddick, S.‐M., Kisoli, A., Longdon, A., Dotchin, C., Gray, W. K., Chaote, P., Teodorczuk, A., and Walker, R.
- Subjects
DEMENTIA research ,SYMPTOMS ,HUMAN behavior research ,PSYCHOLOGICAL aspects of aging ,GERIATRIC psychiatry - Abstract
Objectives Behavioural and psychological symptoms (BPS) in dementia are common in high-income countries, but there are few data from sub-Saharan Africa. Our aim was to estimate the prevalence and pattern of BPS and associated caregiver distress in rural Tanzania. Methods Prevalent cases of dementia (aged 70 and over) were identified during a community-based door-to-door study in six rural villages in Tanzania. Following cognitive screening, a stratified sample (over-sampled for people with dementia) of cases underwent a detailed clinical assessment including the brief 12 item neuropsychiatric inventory (NPI-Q), which assesses BPS and associated caregiver distress over the preceding 30 days. Results Of 78 people with dementia, at least one current BPS was reported by 69 (88.4%), with 40 (51.3%) reporting 3 or more symptoms. In 172 people with no cognitive impairment, 110 (64.0%) reported at least one symptom and 48 (27.9%) reported 3 or more. In dementia cases, the most frequent symptoms reported were anxiety (47.4%), agitation/aggression (38.5%), night-time behavioural disturbance (34.6%), irritability (33.3%) and depression (33.3%). Conclusion The frequency of BPS in dementia in this rural Tanzanian population is high and comparable to that reported in prevalence studies from high income countries. Symptoms were also common, although to a lesser degree, amongst cognitively intact subjects. BPS are likely to have a significant impact on quality of life for elderly persons and their carers in low-income settings. Low-cost interventions, such as community-based therapy and education, are needed. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
35. On the dynamics and kinematics of two-fluid-phase flow in porous media.
- Author
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Gray, W. G., Dye, A. L., McClure, J. E., Pyrak-Nolte, L. J., and Miller, C. T.
- Subjects
POROUS materials ,MULTIPHASE flow ,WATER conservation ,KINEMATICS ,MICROFLUIDICS - Abstract
A model formulated in terms of both conservation and kinematic equations for phases and interfaces in two-fluid-phase flow in a porous medium system is summarized. Macroscale kinematic equations are derived as extensions of averaging theorems and do not rely on conservation principles. Models based on both conservation and kinematic equations can describe multiphase flow with varying fidelity. When only phase-based equations are considered, a model similar in form to the traditional model for two-fluid-phase flow results. When interface conservation and kinematic equations are also included, a novel formulation results that naturally includes evolution equations that express dynamic changes in fluid saturations, pressures, the capillary pressure, and the fluid-fluid interfacial area density in a two-fluid-system. This dynamic equation set is unique to this work, and the importance of the modeled physics is shown through both microfluidic experiments and high-resolution lattice Boltzmann simulations. The validation work shows that the relaxation of interface distribution and shape toward an equilibrium state is a slow process relative to the time scale typically allowed for a system to approach an apparent equilibrium state based upon observations of fluid saturations and external pressure measurements. Consequently, most pressure-saturation data intended to denote an equilibrium state are likely a sampling from a dynamic system undergoing changes of interfacial curvatures that are not typically monitored. The results confirm the importance of kinematic analysis in combination with conservation equations for faithful modeling of system physics. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
36. Functional Series Expansions for Continuous-Time Switched Systems.
- Author
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Duffaut Espinosa, Luis and Gray, W.
- Subjects
POISSON distribution ,MANIFOLDS (Mathematics) ,INTEGRALS ,POLYNOMIALS - Abstract
The main objective of this paper is to describe a class of functional series expansions, known as Fliess operators, which admit inputs from a ball in an L space as well as Poisson random processes. Conditions are given under which these functional series expansions converge absolutely in the mean. Then, it is shown that a continuous-time switched input-affine nonlinear system with a Poisson switching signal can be represented as a Fliess operator and that for certain cases a closed form solution can be obtained in terms of Poisson integrals. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
37. Feedback transformation group for nonlinear input-output systems.
- Author
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Gray, W. Steven and Espinosa, Luis A. Duffaut
- Published
- 2013
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38. System interconnections and combinatorial integer sequences.
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Gray, W. Steven and Thitsa, Makhin
- Published
- 2013
- Full Text
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39. Protecting patient privacy in distributed collaborative healthcare environments by retaining access control of shared information.
- Author
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Burnap, Peter R., Spasic, Irena, Gray, W. Alex, Hilton, Jeremy C., Rana, Omer F., and Elwyn, Glyn
- Abstract
Access control and privacy policies change during the course of collaboration. Information is often shared with collaborators outside of the traditional “perimeterized” organizational computer network. At this point the information owner (in the legal data protection sense) loses persistent control over their information. They cannot modify the policy that controls who accesses it, and have that enforced on the information wherever it resides. However, if patient consent is withdrawn or if the collaboration comes to an end naturally, or prematurely, the owner may be required to withdraw further access to their information. This paper presents a system that enhances the way access control technology is currently deployed so that information owners retain control of their access control and privacy policies, even after information has been shared. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
40. On the radius of convergence of mixed cascades of analytic nonlinear input-output systems.
- Author
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Thitsa, Makhin and Gray, W. Steven
- Abstract
The primary goal is to compute the radius of convergence of any cascade connection involving analytic functions and analytic integral operators, provided that the composite system is well defined and resides in one of these two classes. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
41. A Hopf algebra for product connections of analytic nonlinear input-output systems.
- Author
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Gray, W. Steven
- Abstract
A combinatorial Hopf algebra is described corresponding to a class of analytic nonlinear integral operators known as Fliess operators which are interconnected in a parallel fashion so that their outputs are multiplied componentwise. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
42. Volterra series analysis of semiconductor optical amplifiers.
- Author
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Thitsa, Makhin and Gray, W. Steven
- Abstract
Recently, semiconductor optical amplifiers (SOAs) have attracted much attention as potential candidates for active photonic circuits. In this paper, a Volterra series for the input-output map of such a device is derived using an existing nonlinear state space model. A second-order Volterra approximation is then compared in a specific instance against the full nonlinear model and a linearized model. It is shown that the Volterra model gives a more accurate estimate of gain and interchannel crosstalk than can a linearized model, especially when RMS power is used as the metric. The Volterra model is then employed to estimate the accuracy of the linearized model as a function of device length. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
43. Cascaded analytic nonlinear systems driven by rough paths.
- Author
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Duffaut Espinosa, Luis A., Gray, W. Steven, and Thitsa, Makhin
- Abstract
It was recently shown that the lack of a suitable probabilistic characterization of the input process for a system of interconnected analytic nonlinear input-output maps is an obstacle to well-posedness. For example, the cascade connection of two such systems is only known to be well-posed when a certain independence property is preserved by the first system in the connection. Hence, it appears that some alternative characterization of an input process is needed in this setting. One possibility is to employ T. Lyons' construction of a rough path. This concept employs the p-variation of a path and Chen's identity in order to extend the notion of integration with respect to paths having finite p-variation for p ≥ 1. The primary advantage of such an approach in the context of system interconnections is that independence is no longer needed for producing well-posed cascaded analytic nonlinear systems. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
- Full Text
- View/download PDF
44. A Faà di Bruno Hopf algebra for a group of Fliess operators with applications to feedback.
- Author
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Gray, W. Steven and Duffaut Espinosa, Luis A.
- Abstract
A Faà di Bruno type Hopf algebra is developed for a group of integral operators known as Fliess operators, where operator composition is the group product. The result is applied to analytic nonlinear feedback systems to produce an explicit formula for the feedback product, that is, the generating series for the Fliess operator representation of the closed-loop system written in terms of the generating series of the Fliess operator component systems. This formula is employed to provide a proof that local convergence is preserved under feedback. [ABSTRACT FROM PUBLISHER]
- Published
- 2011
- Full Text
- View/download PDF
45. On the radius of convergence of cascaded analytic nonlinear systems.
- Author
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Thitsa, Makhin and Gray, W. Steven
- Abstract
A complete analysis is presented of the radius of convergence of the cascade connection of two analytic nonlinear input-output systems represented as Fliess operators. Such operators are described by convergent functional series, which are indexed by words over a noncommutative alphabet. Their generating series are therefore specified in terms of noncommutative formal power series. Given growth conditions on the coefficients of the generating series for the component systems, the radius of convergence of the cascaded system is computed. [ABSTRACT FROM PUBLISHER]
- Published
- 2011
- Full Text
- View/download PDF
46. On the radius of convergence of self-excited feedback connected analytic nonlinear systems: The local case.
- Author
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Steven Gray, W. and Thitsa, M.
- Published
- 2009
- Full Text
- View/download PDF
47. Role Based Access to Support Collaboration in Healthcare.
- Author
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Skilton, Alysia, Gray, W. Alex, Allam, Omnia, Morry, Dave, and Bailey, Hazel
- Abstract
Traditional healthcare information systems have been developed and organized as silos. However, recent changes in healthcare delivery models have resulted in the widespread creation of MultiDisciplinary care Teams (MDTs). These teams consist of practitioners with a variety of specialties often sited at different locations [1, 2]. This collaborative approach has led to a significant shift in information needs. However, existing information systems are not designed to support this new level of collaboration and technical support for practitioners has not kept pace with changing needs [3]. As every case is different, one of the many information challenges of this new paradigm is that of providing appropriate views to practitioners based on the unique needs of the patient as well as the practitioner΄s role with that patient. This paper will describe an individualized role based approach to data views for healthcare providers using an independent system to access data stored in existing healthcare information systems. [ABSTRACT FROM AUTHOR]
- Published
- 2008
- Full Text
- View/download PDF
48. Supporting Collaborative Work through Wireless Technologies Support in Patient Centric Virtual Organizations (PCVOS).
- Author
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Mohyuddin, Gray, W. A., Bailey, Hazel, and Morrey, Dave
- Published
- 2007
- Full Text
- View/download PDF
49. Investigation of Semantic Similarity as a Tool for Comparative Genomics.
- Author
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Hutchison, David, Kanade, Takeo, Kittler, Josef, Kleinberg, Jon M., Mattern, Friedemann, Mitchell, John C., Naor, Moni, Nierstrasz, Oscar, Pandu Rangan, C., Steffen, Bernhard, Sudan, Madhu, Terzopoulos, Demetri, Tygar, Doug, Vardi, Moshe Y., Weikum, Gerhard, Wagner, Roland, Revell, Norman, Pernul, Günther, Welter, Danielle, and Gray, W. Alexander
- Abstract
The project sets out to investigate the concept of semantic similarity between individual and collections of gene products based on functional descriptors such as "Gene Ontology" (GO) annotations. Different existing concepts for quantifying semantic similarity are implemented into a basic "Semantic Similarity Calculator" and the resulting tool applied to assess its utility in different biological contexts. It is discussed what kinds of problems were encountered during the implementation of the prototype, and how these problems were addressed, or are planned to be addressed in the future. An overview over future work is given. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
50. A New Approach to Connecting Information Systems in Healthcare.
- Author
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Hutchison, David, Kanade, Takeo, Kittler, Josef, Kleinberg, Jon M., Mattern, Friedemann, Mitchell, John C., Naor, Moni, Nierstrasz, Oscar, Pandu Rangan, C., Steffen, Bernhard, Sudan, Madhu, Terzopoulos, Demetri, Tygar, Doug, Vardi, Moshe Y., Weikum, Gerhard, Cooper, Richard, Kennedy, Jessie, Skilton, Alysia, Gray, W. A., and Allam, Omnia
- Abstract
A novel approach to managing the information needed by healthcare practitioners working collaboratively to care for a patient is described. Traditionally, healthcare information systems have been disease focused, containing patient data related only to a specific function or concern, such as laboratory results or a particular disease. As healthcare is moving toward a collaborative, patient-centric approach which involves care teams comprising a range of health professionals with different needs, skills and working practices, they require up to date, reliable access to more comprehensive patient data; Data which is currently spread through databases at several treatment centres including hospitals, GP's surgeries and palliative care centres. Additionally, this information must be accessible without disrupting the current systems and services provided by each institution from these systems. A new approach to data sharing based on Virtual Organisations (VO) with a Service Oriented Architecture (SOA) which will allow patient-relevant data to be accessed from the diverse sources available is presented. Preliminary requirements and challenges that such an approach will need to meet are presented, and the approach is compared with existing approaches to illustrate its applicability to this domain. Finally, results and future work are covered. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
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