233 research outputs found
Quarkonium states in a complex-valued potential
We calculate quarkonium binding energies using a realistic complex-valued
potential for both an isotropic and anisotropic quark-gluon plasma. We
determine the disassociation temperatures of the ground and first excited
states considering both the real and imaginary parts of the binding energy. We
show that the effect of momentum-space anisotropy is smaller on the imaginary
part of the binding energy than on the real part of the binding energy. In the
case that one assumes an isotropic plasma, we find disassociation temperatures
for the J/psi, Upsilon and chi_b of 1.6 T_c, 2.8 T_c, and 1.5 T_c,
respectively. We find that a finite oblate momentum-space anisotropy increases
the disassociation temperature for all states considered and results in a
splitting of the p-wave states associated with the chi_b first excited state of
bottomonium.Comment: 23 pages, 9 figures; v4: subtraction of V_infinity corrected to only
subtract Re[V_infinity
Topological Excitonic Superfluids in Three Dimensions
We study the equilibrium and non-equilibrium properties of topological
dipolar intersurface exciton condensates within time-reversal invariant
topological insulators in three spatial dimensions without a magnetic field. We
elucidate that, in order to correctly identify the proper pairing symmetry
within the condensate order parameter, the full three-dimensional Hamiltonian
must be considered. As a corollary, we demonstrate that only particles with
similar chirality play a significant role in condensate formation. Furthermore,
we find that the intersurface exciton condensation is not suppressed by the
interconnection of surfaces in three-dimensional topological insulators as the
intersurface polarizability vanishes in the condensed phase. This eliminates
the surface current flow leaving only intersurface current flow through the
bulk. We conclude by illustrating how the excitonic superfluidity may be
identified through an examination of the terminal currents above and below the
condensate critical current.Comment: 8 pages, 6 figure
Mineral and Bone Metabolism Disorders in Minority Incident ESRD Patients in an Inner-City Hemodialysis Unit
Background: Chronic kidney disease (CKD) predisposes patients to mineral and bone metabolism disorder (CKD- MBD), which is a well-known risk factor for increased mortality. Because Medical Evidence Form 2728 from the Centers for Medicare and Medicaid Services for incident end-stage renal disease (ESRD) patients does not require documentation of CKD-MBD markers, MBD status on incident patients remains unknown. Objective: Retrospective observational study to determine the prevalence of mineral and bone metabolism disorder in minority incident ESRD patients. Methods: We studied all incident ESRD patients in our hemodialysis unit between January 2000 and September 2008. Patients followed for less than three months were excluded. Target values for CKD stage 5 were defined as per 2003 Kidney Disease Outcome Quality Initiative guidelines. Results: One hundred seventy-four patients were stud- ied, with a mean age of 53.7±16.1 years, mean body mass index of 26.67±5.98 kg/m2, and mean estimated glomerular filtration rate of 6.7±4.03 mL/min/1.73m2. Mean lab values with one standard deviation were as follows: corrected calcium 8.5±1.3 mg/dL, serum albumin 3.05±0.77 g/dL, phosphorus 5.5±2.2 mg/dL, calcium-phosphorus product 46.7±18.5 mg2/dL2, and intact parathyroid hormone (iPTH) 440.9±397.8 pg/mL. Target values for cal- cium, phosphorus, calcium-phosphorus product, and iPTH were met in 34%, 42%, 72%, and 31% of the patients, respectively, while only 6% of the patients met all four target values. Conclusions: CKD-MBD is widely prevalent in minority incident dialysis patients at initiation of therapy. Its management continues to be a challenge and warrants early recognition and therapy in CKD patients.
Generalized Smoluchowski equation with correlation between clusters
In this paper we compute new reaction rates of the Smoluchowski equation
which takes into account correlations. The new rate K = KMF + KC is the sum of
two terms. The first term is the known Smoluchowski rate with the mean-field
approximation. The second takes into account a correlation between clusters.
For this purpose we introduce the average path of a cluster. We relate the
length of this path to the reaction rate of the Smoluchowski equation. We solve
the implicit dependence between the average path and the density of clusters.
We show that this correlation length is the same for all clusters. Our result
depends strongly on the spatial dimension d. The mean-field term KMFi,j = (Di +
Dj)(rj + ri)d-2, which vanishes for d = 1 and is valid up to logarithmic
correction for d = 2, is the usual rate found with the Smoluchowski model
without correlation (where ri is the radius and Di is the diffusion constant of
the cluster). We compute a new rate: the correlation rate K_{i,j}^{C}
(D_i+D_j)(r_j+r_i)^{d-1}M{\big(\frac{d-1}{d_f}}\big) is valid for d \leq
1(where M(\alpha) = \sum+\infty i=1i\alphaNi is the moment of the density of
clusters and df is the fractal dimension of the cluster). The result is valid
for a large class of diffusion processes and mass radius relations. This
approach confirms some analytical solutions in d 1 found with other methods. We
also show Monte Carlo simulations which illustrate some exact new solvable
models
Cooling Rates for Relativistic Electrons Undergoing Compton Scattering in Strong Magnetic Fields
For inner magnetospheric models of hard X-ray and gamma-ray emission in
high-field pulsars and magnetars, resonant Compton upscattering is anticipated
to be the most efficient process for generating continuum radiation. This is
due in part to the proximity of a hot soft photon bath from the stellar surface
to putative radiation dissipation regions in the inner magnetosphere. Moreover,
because the scattering process becomes resonant at the cyclotron frequency, the
effective cross section exceeds the classical Thomson value by over two orders
of magnitude, thereby enhancing the efficiency of continuum production and the
cooling of relativistic electrons. This paper presents computations of the
electron cooling rates for this process, which are needed for resonant Compton
models of non-thermal radiation from such highly-magnetized pulsars. The
computed rates extend previous calculations of magnetic Thomson cooling to the
domain of relativistic quantum effects, sampled near and above the quantum
critical magnetic field of 44.13 TeraGauss. This is the first exposition of
fully relativistic, quantum magnetic Compton cooling rates for electrons, and
it employs both the traditional Johnson and Lippman cross section, and a newer
Sokolov and Ternov (ST) formulation of Compton scattering in strong magnetic
fields. Such ST formalism is formally correct for treating spin-dependent
effects that are important in the cyclotron resonance, and has not been
addressed before in the context of cooling by Compton scattering. The QED
effects are observed to profoundly lower the rates below extrapolations of the
familiar magnetic Thomson results, as expected, when recoil and Klein-Nishina
reductions become important.Comment: 33 pages, 11 figures, accepted for publication in The Astrophysical
Journa
The Peculiar Motions of Early-Type Galaxies in Two Distant Regions VI: The Maximum Likelihood Gaussian Algorithm
The EFAR project is designed to measure the properties and peculiar motions
of early-type galaxies in two distant regions. Here we describe the maximum
likelihood algorithm we developed to investigate the correlations between the
parameters of the EFAR database. One-, two-, and three-dimensional gaussian
models are constructed to determine the mean value and intrinsic spread of the
parameters, and the slopes and intrinsic parallel and orthogonal spread of the
Mgb'-Mg2, Mg2-sigma, Mgb'-sigma relations, and the Fundamental Plane. In the
latter case, the cluster peculiar velocities are also determined. We show that
this method is superior to ``canonical'' approaches of least-squares type,
which give biased slopes and biased peculiar velocities. We test the algorithm
with Monte Carlo simulations of mock EFAR catalogues and derive the systematic
and random errors on the estimated parameters. We find that random errors are
always dominant. We estimate the influence of systematic errors due to the way
clusters were selected and the hard limits and uncertainties in the selection
function parameters for the galaxies. We explore the influence of uniform
distributions in the Fundamental Plane parameters and the errors. We conclude
that the mean peculiar motions of the EFAR clusters can be determined reliably.
In particular, the placement of the two EFAR sample regions relative to the
Lauer and Postman dipole allows us to strongly constrain the amplitude of the
bulk motion in this direction.Comment: 43 pages, 19 figures, accepted for publication in MNRA
Theoretical model for the formation of caveolae and similar membrane invaginations
We study a physical model for the formation of bud-like invaginations on fluid lipid membranes under tension, and apply this model to caveolae formation. We demonstrate that budding can be driven by membrane-bound proteins, provided that they exert asymmetric forces on the membrane that give rise to bending moments. In particular, caveolae formation does not necessarily require forces to be applied by the cytoskeleton. Our theoretical model is able to explain several features observed experimentally in caveolae, where proteins in the caveolin family are known to play a crucial role in the formation of caveolae buds. These include 1), the formation of caveolae buds with sizes in the 100-nm range and 2), that certain N- and C-termini deletion mutants result in vesicles that are an order-of-magnitude larger. Finally, we discuss the possible origin of the morphological striations that are observed on the surfaces of the caveolae
Effects of receptor clustering on ligand dissociation: Theory and simulations
Receptor-ligand binding is a critical first step in signal transduction and
the duration of the interaction can impact signal generation. In mammalian
cells, clustering of receptors may be facilitated by heterogeneous zones of
lipids, known as lipid rafts. In vitro experiments show that disruption of
rafts significantly alters the dissociation of fibroblast growth factor-2
(FGF-2) from heparan sulfate proteoglycans, co-receptors for FGF-2. In this
paper, we develop a continuum stochastic formalism in order to (i) study how
rebinding affects the dissociation of ligands from a planar substrate, and (ii)
address the question of how receptor clustering influences ligand rebinding. We
find that clusters reduce the effective dissociation rate dramatically when the
clusters are dense and the overall surface density of receptors is low. The
effect is much less pronounced in the case of high receptor density and shows
non-monotonic behavior with time. These predictions are verified via lattice
Monte Carlo simulations. Comparison with experimental results suggests that the
theory does not capture the complete biological system. We speculate that
additional co-operative mechanisms might be present in order to increase ligand
retention, and present one possible ``internal diffusion'' model.Comment: Expanded text and added figures, revised version to appear in
Biophys.
East Bay Coalition for the Homeless: Branding Study and Marketing Strategy
There are a number of potential positioning strategies. The two which make the most sense for the EBCH are to “position the EBCH away from others in the category” and to “position the EBCH as unique.” These strategies have the advantage of setting the EBCH apart from the other organizations that address homelessness. Occupying its own “position” in the minds of potential and current donors is not only an effective communications/marketing strategy but also a less costly one because it avoids head-to-head competition and comparisons
Prevalence of anogenital HPV infection, related disease and risk factors among HIV-infected men in inner-city Johannesburg, South Africa: baseline findings from a cohort study.
BACKGROUND: Persistent high-risk human papillomavirus (HR-HPV) infection is associated with the development of anogenital cancers, particularly in men living with HIV (MLWH). We describe the prevalence of anogenital HPV infection, abnormal anal cytology and anogenital warts (AGWs) in MLWH in Johannesburg, and explore whether HPV infection and receipt of antiretroviral treatment is associated with detection of abnormal anal cytology and AGWs. METHODS: We enrolled a cohort of 304 sexually-active MLWH ≥18 years, who completed a questionnaire and physical examination. Genital swabs were collected from all men and intra-anal swabs from 250 (82%). Swabs were tested for HPV DNA and genotypes, and anal smears graded using the Bethesda classification. Factors associated with anogenital disease were assessed by logistic regression models. RESULTS: Two thirds were receiving antiretroviral treatment, for a median 33 months (IQR = 15-58) and 54% were HIV-virologically suppressed. Only 5% reported ever having sex with men. Among 283 genital swabs with valid results, 79% had any HPV, 52% had HR-HPV and 27% had >1 HR-HPV infection. By comparison, 39% of the 227 valid intra-anal swabs had detectable HPV, 25% had any HR-HPV and 7% >1 HR infection. While most anal smears were normal (51%), 20% had ASCUS and 29% were LSIL. No cases had HSIL or cancer. Infection with >1 HR type (adjusted OR [aOR] = 2.39; 95%CI = 1.02-5.58) and alpha-9 types (aOR = 3.98; 95%CI = 1.42-11.16) were associated with having abnormal cytology. Prevalence of AGWs was 12%. Infection with any LR type (aOR = 41.28; 95%CI = 13.57-125.62), >1 LR type (aOR = 4.14; 95%CI = 1.60-10.69), being <6 months on antiretroviral treatment (aOR = 6.90; 95%CI = 1.63-29.20) and having a CD4+ count <200 cells/μL (aOR = 5.48; 95%CI: 1.60-18.78) were associated with having AGWs. CONCLUSIONS: In this population, anogenital HR-HPV infection and associated low-grade disease is common, but severe anal dysplasia was not detected. Findings reinforce the need for HPV vaccination in men for preventing both AGWs and HR-HPV infection. Given the absence of anal HSILs, however, the findings do not support the use of anal screening programmes in this population
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