635 research outputs found
Generalized quantum Fokker-Planck, diffusion and Smoluchowski equations with true probability distribution functions
Traditionally, the quantum Brownian motion is described by Fokker-Planck or
diffusion equations in terms of quasi-probability distribution functions, e.g.,
Wigner functions. These often become singular or negative in the full quantum
regime. In this paper a simple approach to non-Markovian theory of quantum
Brownian motion using {\it true probability distribution functions} is
presented. Based on an initial coherent state representation of the bath
oscillators and an equilibrium canonical distribution of the quantum mechanical
mean values of their co-ordinates and momenta we derive a generalized quantum
Langevin equation in -numbers and show that the latter is amenable to a
theoretical analysis in terms of the classical theory of non-Markovian
dynamics. The corresponding Fokker-Planck, diffusion and the Smoluchowski
equations are the {\it exact} quantum analogues of their classical
counterparts. The present work is {\it independent} of path integral
techniques. The theory as developed here is a natural extension of its
classical version and is valid for arbitrary temperature and friction
(Smoluchowski equation being considered in the overdamped limit).Comment: RevTex, 16 pages, 7 figures, To appear in Physical Review E (minor
revision
Kinetics of self-induced aggregation of Brownian particles: non-Markovian and non-Gaussian features
In this paper we have studied a model for self-induced aggregation in
Brownian particle incorporating the non-Markovian and non-Gaussian character of
the associated random noise process. In this model the time evolution of each
individual is guided by an over-damped Langevin equation of motion with a
non-local drift resulting from the local unbalance distributions of the other
individuals. Our simulation result shows that colored nose can induce the
cluster formation even at large noise strength. Another observation is that
critical noise strength grows very rapidly with increase of noise correlation
time for Gaussian noise than non Gaussian one. However, at long time limit the
cluster number in aggregation process decreases with time following a power
law. The exponent in the power law increases remarkable for switching from
Markovian to non Markovian noise process
Crossover of the high-energy spin fluctuations from collective triplons to localized magnetic excitations in doped Sr14-xCaxCu24O41 cuprate ladders
We studied the magnetic excitations in the quasi-one-dimensional (q-1D)
ladder subsystem of Sr_(14-x) Ca_x Cu_24 O_41(SCCO) using Cu L_3-edge resonant
inelastic X-ray scattering (RIXS). By comparing momentum-resolved RIXS spectra
with (x=12.2) and without (x=0) high Ca content, we track the evolution of the
magnetic excitations from collective two-triplon (2T) excitations (x=0) to
weakly-dispersive gapped modes at an energy of 280 meV (x=12.2). Density matrix
renormalization group (DMRG) calculations of the RIXS response in the doped
ladders suggest that the flat magnetic dispersion and damped excitation profile
observed at x=12.2 originates from enhanced hole localization. This
interpretation is supported by polarization-dependent RIXS measurements, where
we disentangle the spin-conserving {\Delta}S=0 scattering from the predominant
{\Delta}S=1 spin-flip signal in the RIXS spectra. The results show that the
low-energy weight in the {\Delta}S=0 channel is depleted when Sr is replaced by
Ca, consistent with a reduced carrier mobility. Our results demonstrate that
off-ladder impurities can affect both the low-energy magnetic excitations and
superconducting correlations in the CuO_4 plaquettes. Finally, our study
characterizes the magnetic and charge fluctuations in the phase from which
superconductivity emerges in SCCO at elevated pressures
Comparison of Gadoterate Meglumine and Gadobutrol in the MRI Diagnosis of Primary Brain Tumors: A Double-Blind Randomized Controlled Intraindividual Crossover Study (the REMIND Study)
ABSTRACT BACKGROUNDANDPURPOSE: Effective management of patients with brain tumors depends on accurate detection and characterization of lesions. This study aimed to demonstrate the noninferiority of gadoterate meglumine versus gadobutrol for overall visualization and characterization of primary brain tumors.
MATERIALS AND METHODS: This multicenter, double-blind, randomized, controlled intraindividual, crossover, noninferiority study included279patients.Bothcontrastagents(dose=0.1mmol/kgofbodyweight)wereassessedwith2identicalMRIsatatimeintervalof 2â14 days. The primary end point was overall lesion visualization and characterization, scored independently by 3 off-site readers on a 4-point scale, ranging from âpoorâ to âexcellent.â Secondary end points were qualitative assessments (lesion border delineation, internal morphology, degree of contrast enhancement, diagnostic conïŹdence), quantitative measurements (signal intensity), and safety (adverse events). All qualitative assessments were also performed on-site.
RESULTS: Forall3readers,imagesofmostpatients(>90%)werescoredgoodorexcellentforoveralllesionvisualizationandcharacterizationwitheithercontrastagent;andthenoninferiorityofgadoteratemeglumineversusgadobutrolwasstatisticallydemonstrated.No signiïŹcant differences were observed between the 2 contrast agents regarding qualitative end points despite quantitative mean lesion percentageenhancementbeinghigherwithgadobutrol(P81%ofthe patientswithbothcontrastagents.Similarpercentagesofpatientswithadverseeventsrelatedtothecontrastagentswereobservedwith gadoterate meglumine (7.8%) and gadobutrol (7.3%), mainly injection site pain.
CONCLUSIONS: Thenoninferiorityofgadoteratemeglumineversusgadobutrolforoverallvisualizationandcharacterizationofprimary brain tumors was demonstrated
Analytical and numerical investigation of escape rate for a noise driven bath
We consider a system-reservoir model where the reservoir is modulated by an
external noise. Both the internal noise of the reservoir and the external noise
are stationary, Gaussian and are characterized by arbitrary decaying
correlation functions. Based on a relation between the dissipation of the
system and the response function of the reservoir driven by external noise we
numerically examine the model using a full bistable potential to show that one
can recover the turn-over features of the usual Kramers' dynamics when the
external noise modulates the reservoir rather than the system directly. We
derive the generalized Kramers' rate for this nonequilibrium open system. The
theoretical results are verified by numerical simulation.Comment: Revtex, 25 pages, 5 figures. To appear in Phys. Rev.
Multifaceted Role of Neuropilins in the Immune System: Potential Targets for Immunotherapy.
Neuropilins (NRPs) are non-tyrosine kinase cell surface glycoproteins expressed in all vertebrates and widely conserved across species. The two isoforms, such as neuropilin-1 (NRP1) and neuropilin-2 (NRP2), mainly act as coreceptors for class III Semaphorins and for members of the vascular endothelial growth factor family of molecules and are widely known for their role in a wide array of physiological processes, such as cardiovascular, neuronal development and patterning, angiogenesis, lymphangiogenesis, as well as various clinical disorders. Intriguingly, additional roles for NRPs occur with myeloid and lymphoid cells, in normal physiological as well as different pathological conditions, including cancer, immunological disorders, and bone diseases. However, little is known concerning the molecular pathways that govern these functions. In addition, NRP1 expression has been characterized in different immune cellular phenotypes including macrophages, dendritic cells, and T cell subsets, especially regulatory T cell populations. By contrast, the functions of NRP2 in immune cells are less well known. In this review, we briefly summarize the genomic organization, structure, and binding partners of the NRPs and extensively discuss the recent advances in their role and function in different immune cell subsets and their clinical implications
The basic approval voting game
We survey results about Approval Voting obtained within the standard framework of game theory. Restricting the set of strategies to undominated and sincere ballots does not help to predict Approval Voting outcomes, which is also the case under strategic equilibrium concepts such as Nash equilibrium and its usual refinements. Strong Nash equilibrium in general does not exist but predicts the election of a Condorcet winner when one exists
Fetal loss and maternal serum levels of 2,2',4,4',5,5'-hexachlorbiphenyl (CB-153) and 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (p,p'-DDE) exposure: a cohort study in Greenland and two European populations
<p>Abstract</p> <p>Background</p> <p>In the present study, the aim is to examine the risk of fetal loss related to environmental 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153) or 1,1-dichloro-2,2-bis(<it>p</it>-chlorophenyl)ethylene (p,p'-DDE) exposure.</p> <p>Methods</p> <p>We related LC/MS/MS measurements of CB-153 and p,p'-DDE in serum samples to interview-data on previous fetal loss in populations of pregnant women from Poland, Ukraine and Greenland.</p> <p>Results</p> <p>In total, 1710 women were interviewed, and 678 of these had at least one previous pregnancy. The risk of ever experiencing a fetal loss increased at higher levels of CB-153 and p,p'-DDE exposure, with an adjusted odds ratio (OR) of 2.4; confidence interval (CI) (1.1-5.5) for CB-153>200 ng/g lipid compared to 0-25 ng CB-153/g lipid and OR of 2.5 CI (0.9-6.6) for p,p'-DDE>1500 ng/g lipid compared to 0-250 ng DDE/g lipid. However, no clear dose response associations were observed. The results further suggest that high level of organochlorine serum concentrations may be related to repeated loss.</p> <p>Conclusions</p> <p>The risk of fetal loss may increase at higher levels of CB-153 and p,p'-DDE exposure, although lack of dose response and inconsistencies between countries did not allow for firm conclusions.</p
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