380 research outputs found
Non-equilibrium phase transition in a sheared granular mixture
The dynamics of an impurity (or tracer particle) immersed in a dilute
granular gas under uniform shear flow is investigated. A non-equilibrium phase
transition is identified from an exact solution of the inelastic Boltzmann
equation for a granular binary mixture in the tracer limit, where the impurity
carries either a vanishing (disordered phase) or a finite (ordered phase)
fraction of the total kinetic energy of the system. In the disordered phase,
the granular temperature ratio (impurity "temperature" over that of the host
fluid) is finite, while it diverges in the ordered phase. To correctly capture
this extreme violation of energy equipartition, we show that the picture of an
impurity enslaved to the host fluid is insufficient
Numerical Schemes for Multivalued Backward Stochastic Differential Systems
We define some approximation schemes for different kinds of generalized
backward stochastic differential systems, considered in the Markovian
framework. We propose a mixed approximation scheme for a decoupled system of
forward reflected SDE and backward stochastic variational inequality. We use an
Euler scheme type, combined with Yosida approximation techniques.Comment: 13 page
Diffusion Process in a Flow
We establish circumstances under which the dispersion of passive contaminants
in a forced, deterministic or random, flow can be consistently interpreted as a
Markovian diffusion process. In case of conservative forcing the repulsive case
only, with bounded from below, is
unquestionably admitted by the compatibility conditions. A class of diffusion
processes is exemplified, such that the attractive forcing is allowed as well,
due to an appropriate compensation coming from the "pressure" term. The
compressible Euler flows form their subclass, when regarded as stochastic
processes. We establish circumstances under which the dispersion of passive
contaminants in a forced, deterministic or random, flow can be consistently
interpreted as a Markovian diffusion process. In case of conservative forcing
the repulsive case only, with bounded
from below, is unquestionably admitted by the compatibility conditions. A class
of diffusion processes is exemplified, such that the attractive forcing is
allowed as well, due to an appropriate compensation coming from the "pressure"
term. The compressible Euler flows form their subclass, when regarded as
stochastic processes.Comment: 10 pages, Late
Broken symmetries and directed collective energy transport
We study the appearance of directed energy current in homogeneous spatially
extended systems coupled to a heat bath in the presence of an external ac field
E(t). The systems are described by nonlinear field equations. By making use of
a symmetry analysis we predict the right choice of E(t) and obtain directed
energy transport for systems with a nonzero topological charge Q. We
demonstrate that the symmetry properties of motion of topological solitons
(kinks and antikinks) are equivalent to the ones for the energy current.
Numerical simulations confirm the predictions of the symmetry analysis and,
moreover, show that the directed energy current drastically increases as the
dissipation parameter reduces. Our results generalize recent rigorous
theories of currents generated by broken time-space symmetries to the case of
interacting many-particle systems.Comment: 4 pages, 2 figure
Peritoneal and hemodialysis: I. Differences in patient characteristics at initiation
Peritoneal and hemodialysis: I. Differences in patient characteristics at initiation.BackgroundComparisons of mortality outcomes between peritoneal dialysis (PD) and hemodialysis (HD) patients have shown varying results, which may be caused by the unequally distributed clinical conditions of patients at initiation. To address this issue, we evaluated the clinical characteristics of 105,954 patients at the initiation of PD and HD, using the U.S. national incidence data on treated end-stage renal disease from the Medical Evidence Form, 1995 to 1997.MethodsA general linear model was used to analyze differences of age, albumin, creatinine, blood urea nitrogen (BUN), and hematocrit; categorical data analysis to evaluate body mass index (BMI), grouped into four categories: !19, 19–25 (!25), 25–30 (!30), and 30+; and logistic regression to assess the likelihood of initiating PD versus HD. Diabetics (DM) were analyzed separately from non-diabetics (NDM). Explanatory variables in the logistic regression included incidence year, race, gender, age, BMI, albumin, creatinine, BUN, and hematocrit. Race included white and black. Age was categorized into four groups: 20–44, 45–64, 65–74, and 75+.ResultsAt the initiation of dialysis PD patients were approximately 6 years younger (P ! 0.0001) than HD patients. PD patients also had higher (P ! 0.0001) albumin (+0.35 g/dL for DM and +0.23 g/dL for NDM) and hematocrit (+1.64% for DM and +1.71% for NDM) levels, and lower (P ! 0.04) BUN (-8.75 mg/dL for DM and -5.24 mg/dL for NDM) and creatinine (-0.51 mg/dL for DM and -0.23 mg/dL for NDM) levels than HD patients. Whites had a higher (P ! 0.0001) likelihood of starting PD than blacks, and patients with BMI !19 had a lower (P ! 0.0001) chance of beginning on PD.ConclusionPD patients had favorable clinical conditions at the initiation of dialysis, which should be taken into consideration when comparing dialysis outcomes between the two modalities
Primary spinal cord tumors of childhood: effects of clinical presentation, radiographic features, and pathology on survival
To determine the relationship between clinical presentation, radiographic features, pathology, and treatment on overall survival of newly diagnosed pediatric primary spinal cord tumors (PSCT). Retrospective analysis of all previously healthy children with newly diagnosed PSCT at a single institution from 1995 to present was performed. Twenty-five pediatric patients (15 boys, average 7.9 years) were diagnosed with PSCT. Presenting symptoms ranged from 0.25 to 60 months (average 7.8 months). Symptom duration was significantly shorter for high grade tumors (average 1.65 months) than low grade tumors (average 11.2 months) (P = 0.05). MRI revealed tumor (8 cervical, 17 thoracic, 7 lumbar, 7 sacral) volumes of 98–94,080 mm3 (average 19,474 mm3). Homogeneous gadolinium enhancement on MRI correlated with lower grade pathology (P = 0.003). There was no correlation between tumor grade and volume (P = 0.63) or edema (P = 0.36) by MRI analysis. Median survival was 53 months and was dependent on tumor grade (P = 0.05) and gross total resection (P = 0.01) but not on gender (P = 0.49), age of presentation (P = 0.82), duration of presenting symptoms (P = 0.33), or adjuvant therapies (P = 0.17). Stratified Kaplan–Meier analysis confirmed the association between degree of resection and survival after controlling for tumor grade (P = 0.01). MRI homogeneous gadolinium enhancement patterns may be helpful in distinguishing low grade from high grade spinal cord malignancies. While tumor grade and gross total resection rather than duration of symptoms correlated with survival in our series, greater than one-third of patients had reported symptoms greater than 6 months duration prior to diagnosis
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