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Search Results: 1 - 10 of 197346 matches for " Jason D. Phillips "
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Exact Hausdorff Measure of Certain Non-Self-Similar Cantor Sets
Steen Pedersen,Jason D. Phillips
Mathematics , 2013,
Abstract: We establish a formula yielding the Hausdorff measure for a class of non-self-similar Cantor sets in terms of the canonical covers of the Cantor set.
On Intersections of Cantor Sets: Self-Similarity
Steen Pedersen,Jason D. Phillips
Mathematics , 2012,
Abstract: Let C be a Cantor set. For a real number t let C+t be the translate of C by t, We say two real numbers s,t are equivalent if the intersection of C and C+s is a translate of the intersection of C and C+t. We consider a class of Cantor sets determined by similarities with one fixed positive contraction ratio. For this class of Cantor set, we show that an "initial segment" of the intersection of C and C+t is a self-similar set with contraction ratios that are powers of the contraction ratio used to describe C as a self- similar set if and only if t is equivalent to a rational number. Our results are new even for the middle thirds Cantor set.
On Intersections of Cantor Sets: Hausdorff Measure
Steen Pedersen,Jason D. Phillips
Mathematics , 2012,
Abstract: We establish formulas for bounds on the Haudorff measure of the intersection of certain Cantor sets with their translates. As a consequence we obtain a formula for the Hausdorff dimensions of these intersections.
Intersections of certain deleted digits sets
Steen Pedersen,Jason Phillips
Mathematics , 2011, DOI: 10.1142/S0218348X11005518
Abstract: We consider some properties of the intersection of deleted digits Cantor sets with their translates. We investigate conditions on the set of digits such that, for any t between zero and the dimension of the deleted digits Cantor set itself, the set of translations such that the intersection has Hausdorff dimension equal to t is dense in the set F of translations such that the intersection is non-empty. We make some simple observations regarding properties of the set F, in particular, we characterize when F is an interval, in terms of conditions on the digit set.
Toward Patient-Specific, Biologically Optimized Radiation Therapy Plans for the Treatment of Glioblastoma
David Corwin, Clay Holdsworth, Russell C. Rockne, Andrew D. Trister, Maciej M. Mrugala, Jason K. Rockhill, Robert D. Stewart, Mark Phillips, Kristin R. Swanson
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0079115
Abstract: Purpose To demonstrate a method of generating patient-specific, biologically-guided radiotherapy dose plans and compare them to the standard-of-care protocol. Methods and Materials We integrated a patient-specific biomathematical model of glioma proliferation, invasion and radiotherapy with a multiobjective evolutionary algorithm for intensity-modulated radiation therapy optimization to construct individualized, biologically-guided plans for 11 glioblastoma patients. Patient-individualized, spherically-symmetric simulations of the standard-of-care and optimized plans were compared in terms of several biological metrics. Results The integrated model generated spatially non-uniform doses that, when compared to the standard-of-care protocol, resulted in a 67% to 93% decrease in equivalent uniform dose to normal tissue, while the therapeutic ratio, the ratio of tumor equivalent uniform dose to that of normal tissue, increased between 50% to 265%. Applying a novel metric of treatment response (Days Gained) to the patient-individualized simulation results predicted that the optimized plans would have a significant impact on delaying tumor progression, with increases from 21% to 105% for 9 of 11 patients. Conclusions Patient-individualized simulations using the combination of a biomathematical model with an optimization algorithm for radiation therapy generated biologically-guided doses that decreased normal tissue EUD and increased therapeutic ratio with the potential to improve survival outcomes for treatment of glioblastoma.
Surface Hardness as an Indicator of Soil Strength of Agricultural Soils  [PDF]
Gaius D. Eudoxie, Dennison Phillips, Raymond Springer
Open Journal of Soil Science (OJSS) , 2012, DOI: 10.4236/ojss.2012.24040
Abstract:

Soil strength is an important quality of agricultural soils prone to traffic. Surface hardness (SH) measured by the Clegg Impact Tester (CIT) was evaluated as an indicator for assessing soil strength. Proctor tests were performed on a diverse range of soils to examine the relationships between bulk density (BD), penetration resistance (PR), SH and water content. All three indices showed typical response curves with increasing water content, with notable differences among the soils. Maximum dry bulk density (MDBD), peak penetration resistance (PPR) and peak surface hardness (PSH) showed values of 1.98 Mg m-3, 8.2 MPa and 248 Cmax for Piarco, River Estate and Piarco respectively. Corresponding critical moisture contents (CMC) were much greater for MDBD compared to PPR and PSH. SH showed a significant positive correlation with PR, but not BD. Further divulgence into the relationships between SH and other soil properties as well as crop response will facilitate greater use of the CIT.

Functional Studies on the IBD Susceptibility Gene IL23R Implicate Reduced Receptor Function in the Protective Genetic Variant R381Q
Svetlana Pidasheva, Sara Trifari, Anne Phillips, Jason A. Hackney, Yan Ma, Ashley Smith, Sue J. Sohn, Hergen Spits, Randall D. Little, Timothy W. Behrens, Lee Honigberg, Nico Ghilardi, Hilary F. Clark
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0025038
Abstract: Genome-wide association studies (GWAS) in several populations have demonstrated significant association of the IL23R gene with IBD (Crohn's disease (CD) and ulcerative colitis (UC)) and psoriasis, suggesting that perturbation of the IL-23 signaling pathway is relevant to the pathophysiology of these diseases. One particular variant, R381Q (rs11209026), confers strong protection against development of CD. We investigated the effects of this variant in primary T cells from healthy donors carrying IL23RR381 and IL23RQ381 haplotypes. Using a proprietary anti-IL23R antibody, ELISA, flow cytometry, phosphoflow and real-time RT-PCR methods, we examined IL23R expression and STAT3 phosphorylation and activation in response to IL-23. IL23RQ381 was associated with reduced STAT3 phosphorylation upon stimulation with IL-23 and decreased number of IL-23 responsive T-cells. We also observed slightly reduced levels of proinflammatory cytokine secretion in IL23RQ381 positive donors. Our study shows conclusively that IL23RQ381 is a loss-of-function allele, further strengthening the implication from GWAS results that the IL-23 pathway is pathogenic in human disease. This data provides an explanation for the protective role of R381Q in CD and may lead to the development of improved therapeutics for autoimmune disorders like CD.
Factors Associated with D-Dimer Levels in HIV-Infected Individuals
álvaro H. Borges, Jemma L. O’Connor, Andrew N. Phillips, Jason V. Baker, Michael J. Vjecha, Marcelo H. Losso, Hartwig Klinker, Gustavo Lopardo, Ian Williams, Jens D. Lundgren, for the INSIGHT SMART and ESPRIT Study Groups and the SILCAAT Scientific Committee
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0090978
Abstract: Background Higher plasma D-dimer levels are strong predictors of mortality in HIV+ individuals. The factors associated with D-dimer levels during HIV infection, however, remain poorly understood. Methods In this cross-sectional study, participants in three randomized controlled trials with measured D-dimer levels were included (N = 9,848). Factors associated with D-dimer were identified by linear regression. Covariates investigated were: age, gender, race, body mass index, nadir and baseline CD4+ count, plasma HIV RNA levels, markers of inflammation (C-reactive protein [CRP], interleukin-6 [IL-6]), antiretroviral therapy (ART) use, ART regimens, co-morbidities (hepatitis B/C, diabetes mellitus, prior cardiovascular disease), smoking, renal function (estimated glomerular filtration rate [eGFR] and cystatin C) and cholesterol. Results Women from all age groups had higher D-dimer levels than men, though a steeper increase of D-dimer with age occurred in men. Hepatitis B/C co-infection was the only co-morbidity associated with higher D-dimer levels. In this subgroup, the degree of hepatic fibrosis, as demonstrated by higher hyaluronic acid levels, but not viral load of hepatitis viruses, was positively correlated with D-dimer. Other factors independently associated with higher D-dimer levels were black race, higher plasma HIV RNA levels, being off ART at baseline, and increased levels of CRP, IL-6 and cystatin C. In contrast, higher baseline CD4+ counts and higher high-density lipoprotein cholesterol were negatively correlated with D-dimer levels. Conclusions D-dimer levels increase with age in HIV+ men, but are already elevated in women at an early age due to reasons other than a higher burden of concomitant diseases. In hepatitis B/C co-infected individuals, hepatic fibrosis, but not hepatitis viral load, was associated with higher D-dimer levels.
What do you do for a living? Toward a more succinct definition of health services research
Charles D Phillips
BMC Health Services Research , 2006, DOI: 10.1186/1472-6963-6-117
Abstract: Discussing field definitions is usually the stuff of consensus conferences and boards of directors. This task is not usually the province of individual researchers, unless they find some reward in relatively thankless and often futile endeavors. That being said, I am, of course, now about to venture into that daunting area.I take this rather unusual step for two reasons. First, I have now taught the introductory, core courses in our doctoral program in health services research for a number of years. Like others who teach similar courses, one important part of the initial course meetings is familiarizing students with the various definitions of their chosen field. This task has always left me frustrated. I come away from those sessions thinking that the field of health services research is now well enough established that it deserves a more mature statement defining our field than we have heretofore enjoyed. By mature, I mean a statement about the field that has the simplicity and clarity found in the definitions of more long-established fields and disciplines.Second, with other members of the field in the United States, I participated in a recent meeting and series of exchanges supported by the U.S. Agency for Healthcare Research and Quality concerning the development of competencies for a doctoral degree in health services research. The definition of the field used in that effort was a "close cousin" to what is probably the most widely accepted definition of our field. This is the 2000 AcademyHealth definition of health services research [1]. From that definition, health services research is:"the multidisciplinary field of scientific investigation that studies how social factors, financing systems, organizational structures and processes, health technologies, and personal behaviors, affect access to health care, the quality and cost of health care, and ultimately our health and well-being. Its research domains are individuals, families, organizations, institutions,
Evolutionary geomorphology: thresholds and nonlinearity in landform response to environmental change
J. D. Phillips
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2006,
Abstract: Geomorphic systems are typically nonlinear, owing largely to their threshold-dominated nature (but due to other factors as well). Nonlinear geomorphic systems may exhibit complex behaviors not possible in linear systems, including dynamical instability and deterministic chaos. The latter are common in geomorphology, indicating that small, short-lived changes may produce disproportionately large and long-lived results; that evidence of geomorphic change may not reflect proportionally large external forcings; and that geomorphic systems may have multiple potential response trajectories or modes of adjustment to change. Instability and chaos do not preclude predictability, but do modify the context of predictability. The presence of chaotic dynamics inhibits or excludes some forms of predicability and prediction techniques, but does not preclude, and enables, others. These dynamics also make spatial and historical contingency inevitable: geography and history matter. Geomorphic systems are thus governed by a combination of "global" laws, generalizations and relationships that are largely (if not wholly) independent of time and place, and "local" place and/or time-contingent factors. The more factors incorporated in the representation of any geomorphic system, the more singular the results or description are. Generalization is enhanced by reducing rather than increasing the number of factors considered. Prediction of geomorphic responses calls for a recursive approach whereby global laws and local contingencies are used to constrain each other. More specifically a methodology whereby local details are embedded within simple but more highly general phenomenological models is advocated. As landscapes and landforms change in response to climate and other forcings, it cannot be assumed that geomorphic systems progress along any particular pathway. Geomorphic systems are evolutionary in the sense of being path dependent, and historically and geographically contingent. Assessing and predicting geomorphic responses obliges us to engage these contingencies, which often arise from nonlinear complexities. We are obliged, then, to practice evolutionary geomorphology: an approach to the study of surface processes and landforms which recognizes multiple possible historical pathways rather than an inexorable progression toward some equilbribrium state or along a cyclic pattern.
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