731,579 research outputs found
Andersen-Tawil Syndrome
Andersen-Tawil syndrome (ATS) is a rare condition consisting of ventricular arrhythmias, periodic paralysis, and dysmorphic features. In 2001, mutations in KCNJ2, which encodes the α subunit of the potassium channel Kir2.1, were identified in patients with ATS. To date, KCNJ2 is the only gene implicated in ATS, accounting for approximately 60% of cases. ATS is a unique channelopathy, and represents the first link between cardiac and skeletal muscle excitability. The arrhythmias observed in ATS are distinctive; patients may be asymptomatic, or minimally symptomatic despite a high arrhythmia burden with frequent ventricular ectopy and bidirectional ventricular tachycardia. However, patients remain at risk for life-threatening arrhythmias, including torsades de pointes and ventricular fibrillation, albeit less commonly than observed in other genetic arrhythmia syndromes. The characteristic heterogeneity at both the genotypic and phenotypic levels contribute to the continued difficulties with appropriate diagnosis, risk stratification, and effective therapy. The initial recognition of a syndromic association of clinically diverse symptoms, and the subsequent identification of the underlying molecular genetic basis of ATS has enhanced both clinical care, and our understanding of the critical function of Kir2.1 on skeletal muscle excitability and cardiac action potentia
Symplectic algorithm for constant-pressure molecular dynamics using a Nose-Poincare thermostat
We present a new algorithm for isothermal-isobaric molecular-dynamics
simulation. The method uses an extended Hamiltonian with an Andersen piston
combined with the Nos'e-Poincar'e thermostat, recently developed by Bond,
Leimkuhler and Laird [J. Comp. Phys., 151, (1999)]. This
Nos'e-Poincar'e-Andersen (NPA) formulation has advantages over the
Nos'e-Hoover-Andersen approach in that the NPA is Hamiltonian and can take
advantage of symplectic integration schemes, which lead to enhanced stability
for long-time simulations. The equations of motion are integrated using a
Generalized Leapfrog Algorithm and the method is easy to implement, symplectic,
explicit and time reversible. To demonstrate the stability of the method we
show results for test simulations using a model for aluminum.Comment: 7 page
Is a "homogeneous" description of dynamic heterogeneities possible?
We study the simplest model of dynamic heterogeneities in glass forming
liquids: one-spin facilitated kinetic Ising model introduced by Fredrickson and
Andersen [G.H. Fredrickson and H.C. Andersen, Phys. Rev. Lett. 53, 1244 (1984);
J. Chem. Phys. 83, 5822 (1985)]. We show that the low-temperature, long-time
behavior of the density autocorrelation function predicted by a scaling
approach can be obtained from a self-consistent mode-coupling-like
approximation.Comment: accepted for publication in the Journal of Chemical Physic
Application of the Exact Muffin-Tin Orbitals Theory: the Spherical Cell Approximation
We present a self-consistent electronic structure calculation method based on
the {\it Exact Muffin-Tin Orbitals} (EMTO) Theory developed by O. K. Andersen,
O. Jepsen and G. Krier (in {\it Lectures on Methods of Electronic Structure
Calculations}, Ed. by V. Kumar, O.K. Andersen, A. Mookerjee, Word Scientific,
1994 pp. 63-124) and O. K. Andersen, C. Arcangeli, R. W. Tank, T.
Saha-Dasgupta, G. Krier, O. Jepsen, and I. Dasgupta, (in {\it Mat. Res. Soc.
Symp. Proc.} {\bf 491}, 1998 pp. 3-34). The EMTO Theory can be considered as an
{\it improved screened} KKR (Korringa-Kohn-Rostoker) method which is able to
treat large overlapping potential spheres. Within the present implementation of
the EMTO Theory the one electron equations are solved exactly using the Green's
function formalism, and the Poisson's equation is solved within the {\it
Spherical Cell Approximation} (SCA). To demonstrate the accuracy of the
SCA-EMTO method test calculations have been carried out.Comment: 20 pages, 10 figure
Andersen Filtration and Hard Lefschetz
On the space of homomorphisms from a Verma module to an indecomposable
tilting module of the BGG-category O we define a natural filtration following
Andersen and establish a formula expressing the dimensions of the filtration
steps in terms of coefficients of Kazhdan-Lusztig polynomials.Comment: English version of math.RT/0604589, v3 revised translatio
The Ellipticity of the Disks of Spiral Galaxies
The disks of spiral galaxies are generally elliptical rather than circular.
The distribution of ellipticities can be fit with a log-normal distribution.
For a sample of 12,764 galaxies from the Sloan Digital Sky Survey Data Release
1 (SDSS DR1), the distribution of apparent axis ratios in the i band is best
fit by a log-normal distribution of intrinsic ellipticities with ln epsilon =
-1.85 +/- 0.89. For a sample of nearly face-on spiral galaxies, analyzed by
Andersen and Bershady using both photometric and spectroscopic data, the best
fitting distribution of ellipticities has ln epsilon = -2.29 +/- 1.04. Given
the small size of the Andersen-Bershady sample, the two distribution are not
necessarily inconsistent. If the ellipticity of the potential were equal to
that of the light distribution of the SDSS DR1 galaxies, it would produce 1.0
magnitudes of scatter in the Tully-Fisher relation, greater than is observed.
The Andersen-Bershady results, however, are consistent with a scatter as small
as 0.25 magnitudes in the Tully-Fisher relation.Comment: 19 pages, 5 figures; ApJ, accepte
- …