1,691 research outputs found
Colloidal glass transition: Beyond mode-coupling theory
A new theory for dynamics of concentrated colloidal suspensions and the
colloidal glass transition is proposed. The starting point is the memory
function representation of the density correlation function. The memory
function can be expressed in terms of a time-dependent pair-density correlation
function. An exact, formal equation of motion for this function is derived and
a factorization approximation is applied to its evolution operator. In this way
a closed set of equations for the density correlation function and the memory
function is obtained. The theory predicts an ergodicity breaking transition
similar to that predicted by the mode-coupling theory, but at a higher density.Comment: to be published in PR
Anisotropic spatially heterogeneous dynamics in a model glass-forming binary mixture
We calculated a four-point correlation function G_4(k,r;t) and the
corresponding structure factor S_4(k,q;t) for a model glass-forming binary
mixture. These functions measure the spatial correlations of the relaxation of
different particles. We found that these four-point functions are anisotropic
and depend on the angle between vectors k and r (or q). The anisotropy is the
strongest for times somewhat longer than the beta relaxation time but it is
quite pronounced even for times comparable to the alpha relaxation time,
tau_alpha. At the lowest temperatures S_4(k,q;tau_alpha) is strongly
anisotropic even for the smallest wavevector q accessible in our simulation
GTP cyclohydrolase I gene polymorphisms are associated with endothelial dysfunction and oxidative stress in patients with type 2 diabetes mellitus
Background:
The genetic background of atherosclerosis in type 2 diabetes mellitus (T2DM) is complex and poorly understood. Studying genetic components of intermediate phenotypes, such as endothelial dysfunction and oxidative stress, may aid in identifying novel genetic components for atherosclerosis in diabetic patients.<p></p>
Methods:
Five polymorphisms forming two haplotype blocks within the GTP cyclohydrolase 1 gene, encoding a rate limiting enzyme in tetrahydrobiopterin synthesis, were studied in the context of flow and nitroglycerin mediated dilation (FMD and NMD), intima-media thickness (IMT), and plasma concentrations of von Willebrand factor (vWF) and malondialdehyde (MDA).<p></p>
Results:
Rs841 was associated with FMD (p = 0.01), while polymorphisms Rs10483639, Rs841, Rs3783641 (which form a single haplotype) were associated with both MDA (p = 0.012, p = 0.0015 and p = 0.003, respectively) and vWF concentrations (p = 0.016, p = 0.03 and p = 0.045, respectively). In addition, polymorphism Rs8007267 was also associated with MDA (p = 0.006). Haplotype analysis confirmed the association of both haplotypes with studied variables.<p></p>
Conclusions:
Genetic variation of the GCH1 gene is associated with endothelial dysfunction and oxidative stress in T2DM patients
Singular measures in circle dynamics
Critical circle homeomorphisms have an invariant measure totally singular
with respect to the Lebesgue measure. We prove that singularities of the
invariant measure are of Holder type. The Hausdorff dimension of the invariant
measure is less than 1 but greater than 0
The Bone-Vasculature Axis:Calcium Supplementation and the Role of Vitamin K
Calcium supplements are broadly prescribed to treat osteoporosis either as monotherapy or together with vitamin D to enhance calcium absorption. It is still unclear whether calcium supplementation significantly contributes to the reduction of bone fragility and fracture risk. Data suggest that supplementing post-menopausal women with high doses of calcium has a detrimental impact on cardiovascular morbidity and mortality. Chronic kidney disease (CKD) patients are prone to vascular calcification in part due to impaired phosphate excretion. Calcium-based phosphate binders further increase risk of vascular calcification progression. In both bone and vascular tissue, vitamin K-dependent processes play an important role in calcium homeostasis and it is tempting to speculate that vitamin K supplementation might protect from the potentially untoward effects of calcium supplementation. This review provides an update on current literature on calcium supplementation among post-menopausal women and CKD patients and discusses underlying molecular mechanisms of vascular calcification. We propose therapeutic strategies with vitamin K2 treatment to prevent or hold progression of vascular calcification as a consequence of excessive calcium intake
The Turbulent Warm Ionized Medium: Emission Measure Distribution and MHD Simulations
We present an analysis of the distribution of H-alpha emission measures for
the warm ionized medium (WIM) of the Galaxy using data from the Wisconsin
H-Alpha Mapper (WHAM) Northern Sky Survey. Our sample is restricted to Galactic
latitudes |b| > 10. We removed sightlines intersecting nineteen high-latititude
classical H II regions, leaving only sightlines that sample the diffuse WIM.
The distribution of EM sin |b| for the full sample is poorly characterized by a
single normal distribution, but is extraordinarily well fit by a lognormal
distribution, with = 0.146 +/- 0.001 and standard deviation
0.190 +/- 0.001. drops from 0.260 +/- 0.002 at Galactic
latitude 10<|b|<30 to 0.038 +/- 0.002 at Galactic latitude 60<|b|<90. The
distribution may widen slightly at low Galactic latitude. We compare the
observed EM distribution function to the predictions of three-dimensional
magnetohydrodynamic simulations of isothermal turbulence within a
non-stratified interstellar medium. We find that the distribution of EM sin |b|
is well described by models of mildy supersonic turbulence with a sonic Mach
number of ~1.4-2.4. The distribution is weakly sensitive to the magnetic field
strength. The model also successfully predicts the distribution of dispersion
measures of pulsars and H-alpha line profiles. In the best fitting model, the
turbulent WIM occupies a vertical path length of 400-500 pc within the 1.0-1.8
kpc scale height of the layer. The WIM gas has a lognormal distribution of
densities with a most probable electron density n_{pk} = 0.03 cm^{-3}. We also
discuss the implications of these results for interpreting the filling factor,
the power requirement, and the magnetic field of the WIM.Comment: 16 pages, 13 figures, ApJ in press. Replacement reflects version
accepted for publicatio
Discussion of the Electromotive Force Terms in the Model of Parker-unstable Galactic Disks with Cosmic Rays and Shear
We analyze the electromotive force (EMF) terms and basic assumptions of the
linear and nonlinear dynamo theories in our three-dimensional (3D) numerical
model of the Parker instability with cosmic rays and shear in a galactic disk.
We also apply the well known prescriptions of the EMF obtained by the nonlinear
dynamo theory (Blackman & Field 2002 and Kleeorin et al. 2003) to check if the
EMF reconstructed from their prescriptions corresponds to the EMF obtained
directly from our numerical models. We show that our modeled EMF is fully
nonlinear and it is not possible to apply any of the considered nonlinear
dynamo approximations due to the fact that the conditions for the scale
separation are not fulfilled.Comment: 15 pages, 12 figure
On the possibility of q-scaling in high energy production processes
It has been noticed recently that transverse momenta (p_T) distributions
observed in high energy production processes exhibit remarkably universal
scaling behaviour. This is the case when a suitable variable replaces the usual
p_T. On the other hand, it is also widely known that transverse momentum
distributions in general follow a power-like Tsallis distribution, rather than
an exponential Boltzmann-Gibbs, with a (generally energy dependent)
nonextensivity parameter q. Here we show that it is possible to choose a
suitable variable such that all the data can be fitted by the same Tsallis
distribution (with the same, energy independent value of the q-parameter). Thus
they exhibit q-scaling.Comment: Final version, accepted by J.Phys.
Spikes and diffusion waves in one-dimensional model of chemotaxis
We consider the one-dimensional initial value problem for the viscous
transport equation with nonlocal velocity with a given kernel . We show the existence
of global-in-time nonnegative solutions and we study their large time
asymptotics. Depending on , we obtain either linear diffusion waves ({\it
i.e.}~the fundamental solution of the heat equation) or nonlinear diffusion
waves (the fundamental solution of the viscous Burgers equation) in asymptotic
expansions of solutions as . Moreover, for certain aggregation
kernels, we show a concentration of solution on an initial time interval, which
resemble a phenomenon of the spike creation, typical in chemotaxis models
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