536 research outputs found
Plasma Relaxation and Topological Aspects in Hall Magnetohydrodynamics
Parker's formulation of isotopological plasma relaxation process in
magnetohydrodynamics (MHD) is extended to Hall MHD. The torsion coefficient
alpha in the Hall MHD Beltrami condition turns out now to be proportional to
the "potential vorticity." The Hall MHD Beltrami condition becomes equivalent
to the "potential vorticity" conservation equation in two-dimensional (2D)
hydrodynamics if the Hall MHD Lagrange multiplier beta is taken to be
proportional to the "potential vorticity" as well. The winding pattern of the
magnetic field lines in Hall MHD then appears to evolve in the same way as
"potential vorticity" lines in 2D hydrodynamics
Topological Black Holes in Lovelock-Born-Infeld Gravity
In this paper, we present topological black holes of third order Lovelock
gravity in the presence of cosmological constant and nonlinear electromagnetic
Born-Infeld field. Depending on the metric parameters, these solutions may be
interpreted as black hole solutions with inner and outer event horizons, an
extreme black hole or naked singularity. We investigate the thermodynamics of
asymptotically flat solutions and show that the thermodynamic and conserved
quantities of these black holes satisfy the first law of thermodynamic. We also
endow the Ricci flat solutions with a global rotation and calculate the finite
action and conserved quantities of these class of solutions by using the
counterterm method. We compute the entropy through the use of the Gibbs-Duhem
relation and find that the entropy obeys the area law. We obtain a Smarr-type
formula for the mass as a function of the entropy, the angular momenta, and the
charge, and compute temperature, angular velocities, and electric potential and
show that these thermodynamic quantities coincide with their values which are
computed through the use of geometry. Finally, we perform a stability analysis
for this class of solutions in both the canonical and the grand-canonical
ensemble and show that the presence of a nonlinear electromagnetic field and
higher curvature terms has no effect on the stability of the black branes, and
they are stable in the whole phase space.Comment: 14 page
Intercellular signaling as a cause of cell death in cyclically impacted cartilage explants
AbstractRecently, in vitro cartilage studies have shown that impact loading can produce structural damage and osteoarthritis-like changes, including tissue swelling, collagen denaturation, and cell death.Objective This study was to determine whether a signal for cell death moves through the cartilage matrix, resulting in the spread of cell death over time from impacted to unimpacted regions.Design Cyclic impacts were applied to the 2mm core of 4mm cartilage discs. Post-impact culturing extended for 3, 6 or 21 days and occurred in one of two ways. In one, discs were cultured intact. In the second, cores were removed immediately after cessation of impact and cores and rings cultured separately. Cells in apoptosis and later stage necrosis were monitored using the TUNEL assay.Results The extent of cell death in impacted samples increased with increased duration of post-impact culturing. At the early time, the majority of cell death was located in the regions of direct impact whereas after extended culture, the extent of cell death was similar in the surrounding unimpacted regions and in the impacted core region. However, the physical separation of the impacted core from the surrounding, non-impacted ring regions immediately after impact, and prior to independent culture, kept the level of cell death in the surrounding ring close to control levels, even after 21 days of incubation.Discussion These findings indicate that soluble intercellular signalling is involved in the spreading of cell death through the cartilage matrix, and that its effects can be prevented by physical isolation of the surrounding ring from the impacted core
Structured Random Matrices
Random matrix theory is a well-developed area of probability theory that has
numerous connections with other areas of mathematics and its applications. Much
of the literature in this area is concerned with matrices that possess many
exact or approximate symmetries, such as matrices with i.i.d. entries, for
which precise analytic results and limit theorems are available. Much less well
understood are matrices that are endowed with an arbitrary structure, such as
sparse Wigner matrices or matrices whose entries possess a given variance
pattern. The challenge in investigating such structured random matrices is to
understand how the given structure of the matrix is reflected in its spectral
properties. This chapter reviews a number of recent results, methods, and open
problems in this direction, with a particular emphasis on sharp spectral norm
inequalities for Gaussian random matrices.Comment: 46 pages; to appear in IMA Volume "Discrete Structures: Analysis and
Applications" (Springer
Evaluation of therapeutic enoxaparin in a pregnant population at a tertiary hospital
Therapeutic anticoagulation with enoxaparin in pregnancy is complex due to varying pharmacokinetics and the increasing prevalence of obesity. There is limited evidence to support current dosing and monitoring strategies of enoxaparin in this population.To describe the current practice in therapeutic anticoagulation in the pregnant population at a tertiary institution.A retrospective study of pregnant women on therapeutic enoxaparin between January 2007 and December 2011.Forty-four pregnant women requiring therapeutic anticoagulation were identified and divided into two groups, monitored with anti-factor Xa (AXA) concentrations and unmonitored. Fifty-five percent of monitored women were initiated on the recommended 1 mg/kg twice a day (bd) enoxaparin dose-strategy. Eighty-two percent of women were monitored; however, there was variability regarding the timing, frequency and subsequent dose adjustments from monitoring. Overall, as pregnancies progressed, there was both increasing dose adjustments and increasing frequency of monitoring. Fourteen women had a BMI over 30 kg/m(2) , and 13 of these women were monitored. Nine monitored obese women required doses less than 1 mg/kg/bd to maintain a therapeutic AXA level. Management appeared to be individualised. There were small numbers of toxicity events.Variation exists in dosing and monitoring practices for therapeutic enoxaparin in the pregnant population. Dosing obese patients using 1 mg/kg twice daily can lead to toxic AXA concentrations, and dose reductions are required to maintain a therapeutic range. A larger prospective study reviewing dose, AXA concentrations and outcome data is necessary to make dosing recommendations in this group
Impulse control disorders in non-treatment seeking hair pullers
Background and aims:
Hair pulling is a common body focused repetitive behavior. The purpose of this paper is to examine the prevalence of impulse control disorders (as defined in DSM-IV-TR) in a non-treatment seeking sample of hair pullers.
Methods:
1,717 college students with (n = 44) and without (n = 1673) hair pulling completed a mental health survey. The college students were sent an online survey assessing hair pulling behavior and other impulse control disorders using the Minnesota Impulsive Disorders Interview.
Results:
Students with hair pulling were significantly more likely to have a co-occurring impulse control disorder (20.5% vs. 8.9%, p = 0.009, OR = 2.71, CI = 1.28–5.75) and were significantly more likely to meet criteria for compulsive buying, compulsive sexual behavior and intermittent explosive disorder than students without hair pulling. Differences seemed to be moderated by the male gender among students with hair pulling.
Discussion and conclusions:
Hair pulling is often comorbid with another impulse control disorder, which suggests that elements of impulsivity may be important in our understanding of hair pulling. Furthermore, gender may moderate impulse control comorbidity in hair pulling disorder
Non-critical Heterotic Superstrings in Various Dimensions
We construct heterotic string theories on spacetimes of the form R^{d-1,1}
times N=2 linear dilaton, where d=6,4,2,0. There are two lines of
supersymmetric theories descending from the two supersymmetric ten-dimensional
heterotic theories. These have gauge groups which are lower rank subgroups of
E_{8} times E_{8} and SO(32). On turning on a (2,2) deformation which makes the
two dimensional part a smooth SL_{2}(R)/U(1) supercoset, the gauge groups get
broken further. In the deformed theories, there are non-trivial moduli which
are charged under the surviving gauge group in the case of d=6. We construct
the marginal operators on the worldsheet corresponding to these moduli.Comment: 27 pages, harvmac. v2 reference adde
Accelerated Expansion of the Universe in Gauss-Bonnet Gravity
We show that in Gauss-Bonnet gravity with negative Gauss-Bonnet coefficient
and without a cosmological constant, one can explain the acceleration of the
expanding Universe. We first introduce a solution of the Gauss-Bonnet gravity
with negative Gauss-Bonnet coefficient and no cosmological constant term in an
empty -dimensional bulk. This solution can generate a de Sitter
spacetime with curvature . We show that an
-dimensional brane embedded in this bulk can have an expanding feature
with acceleration. We also considered a 4-dimensional brane world in a
5-dimensional empty space with zero cosmological constant and obtain the
modified Friedmann equations. The solution of these modified equations in
matter-dominated era presents an expanding Universe with negative deceleration
and positive jerk which is consistent with the recent cosmological data. We
also find that for this solution, the derivative of the scale factor
with respect to time can be expressed only in terms of Hubble and deceleration
parameters.Comment: 12 pages, no figure, references added, typos corrected, Section 4
ammended, an appndix added, version to be appeared in Phys. Rev.
Asymptotically (anti)-de Sitter solutions in Gauss-Bonnet gravity without a cosmological constant
In this paper we show that one can have asymptotically de Sitter (dS),
anti-de Sitter (AdS) and flat solutions in Gauss-Bonnet gravity without any
need to a cosmological constant term in field equations. First, we introduce
static solutions whose 3-surfaces at fixed and have constant positive
(), negative (), or zero () curvature. We show that for
, one can have asymptotically dS, AdS and flat spacetimes, while for
the case of , one has only asymptotically AdS solutions. Some of these
solutions present naked singularities, while some others are black hole or
topological black hole solutions. We also find that the geometrical mass of
these 5-dimensional spacetimes is , which is different from
the geometrical mass, , of the solutions of Einstein gravity. This feature
occurs only for the 5-dimensional solutions, and is not repeated for the
solutions of Gauss-Bonnet gravity in higher dimensions. We also add angular
momentum to the static solutions with , and introduce the asymptotically
AdS charged rotating solutions of Gauss-Bonnet gravity. Finally, we introduce a
class of solutions which yields an asymptotically AdS spacetime with a
longitudinal magnetic field which presents a naked singularity, and generalize
it to the case of magnetic rotating solutions with two rotation parameters.Comment: 13 pages, no figur
TGF beta 1 and biglycan, decorin, and fibromodulin metabolism in canine cartilage
AbstractObjective: Small proteoglycans (PGs) may accumulate in late stage osteoarthritis even as aggrecan is lost. It is not clear what role transforming growth factor (TGF) beta has in this accumulation. Our goal was to investigate the ability of TGF beta 1 to modulate the synthesis and accumulation of decorin, biglycan, and fibromodulin in cartilage explants cultured under conditions in which aggrecan synthesis remains relatively constant.Design: Articular cartilage was cultured in the presence or absence of 4ng/ml TGF beta 1 for up to 16 days. Material extracted from cartilage was assayed for 35SO4-large and small PGs and for total endogenous decorin, biglycan and fibromodulin.Results: The synthesis of 35SO4-small PGs increased during the 16 days in culture in response to TGF beta 1, but declined in control cultures. The difference in 35SO4-decorin between TGF beta 1 and control samples reached nine-fold after 16 days, while the difference in total endogenous decorin was less than 1.5-fold. 35SO4-decorin, which was present in TGF beta 1-treated cultures had an identical core protein, but a longer glycosaminoglycan chain than that of decorin in control cultures. No significant differences in endogenous biglycan were detected, but accumulation of fibromodulin in TGF beta 1 explants exceeded fibromodulin in controls, on average, by 3.8-fold. Fibromodulin was present in cartilage in both keratan sulfate- and non-sulfated oligosaccharide-substituted forms.Conclusions: The accumulation of each of the three small PGs was affected to a different extent in response to TGF beta 1. Of the three, fibromodulin content was most rapidly augmented in response to TGF beta 1
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