2,698 research outputs found
Towards a robust algorithm to determine topological domains from colocalization data
One of the most important tasks in understanding the complex spatial
organization of the genome consists in extracting information about this
spatial organization, the function and structure of chromatin topological
domains from existing experimental data, in particular, from genome
colocalization (Hi-C) matrices. Here we present an algorithm allowing to reveal
the underlying hierarchical domain structure of a polymer conformation from
analyzing the modularity of colocalization matrices. We also test this
algorithm on several model polymer structures: equilibrium globules, random
fractal globules and regular fractal (Peano) conformations. We define what we
call a spectrum of cluster borders, and show that these spectra behave
strikingly differently for equilibrium and fractal conformations, allowing us
to suggest an additional criterion to identify fractal polymer conformations
Role of Group and Phase Velocity in High-Energy Neutrino Observatories
Kuzmichev recently showed that use of phase velocity rather than group
velocity for Cherenkov light signals and pulses from calibration lasers in
high-energy neutrino telescopes leads to errors in track reconstruction and
distance measurement. We amplify on his remarks and show that errors for four
cases of interest to AMANDA, IceCube, and RICE (radio Cherenkov detector) are
negligibly small.Comment: To be published in Astroparticle Physics, 6 pages, uses elsart.st
Structure and mass distribution of spiral galaxies at intermediate redshifts
Using the HST archive WFPC2 observations and rotation curves measeured by Vogt et al. (1996), we constructed self-consistent light and mass distribution models for three disk galaxies at redshifts z = 0.15, 0.90 and 0.99. The models consist of three components: the bulge, the disk and the dark matter. Spatial density distribution parameters for the components were calculated. After applying k-corrections, mass-to-light ratios for galactic disks within the maximum disk assumption are M/L_B = 4.4, 1.2 and 1.2, respectively. Corresponding central densities of dark matter halos within a truncated isothermal model are 0.0092, 0.028 and 0.015 in units M_sol/pc^3. The light distribution of galaxies in outer parts is steeper than a simple exponential disk
Backward Tamm states in left-handed metamaterials
We study the electromagnetic surface waves localized at an interface
separating a one-dimensional photonic crystal and left-handed metamaterial, the
so-called surface Tamm states. We demonstrate that the metamaterial allows for
a flexible control of the dispersion properties of surface states, and can
support the Tamm states with a backward energy flow and a vortex-like
structure.Comment: 3 pages, 5 figure
When renormalizability is not sufficient: Coulomb problem for vector bosons
The Coulomb problem for vector bosons W incorporates a known difficulty; the
boson falls on the center. In QED the fermion vacuum polarization produces a
barrier at small distances which solves the problem. In a renormalizable SU(2)
theory containing vector triplet (W^+,W^-,gamma) and a heavy fermion doublet F
with mass M the W^- falls on F^+, to distances r ~ 1/M, where M can be made
arbitrary large. To prevent the collapse the theory needs additional light
fermions, which switch the ultraviolet behavior of the theory from the
asymptotic freedom to the Landau pole. Similar situation can take place in the
Standard Model. Thus, the renormalizability of a theory is not sufficient to
guarantee a reasonable behavior at small distances for non-perturbative
problems, such as a bound state problem.Comment: Four page
Influence of Different Alfalfa-Grass Mixtures and the Use of Additives on Nutritive Value and Fermentation of Silage
Legumes have a high nutritive value but they are known to be difficult to ensile and often result in poorly fermented silage. This is usually due to high buffering capacity and low available sugar concentration. However, the results have shown that silage quality can considerably be improved by using additives or when legume-grass mixtures are ensiled (Lättemäe & Tamm, 2002). Different legume-grass mixtures differ in their ensiling properties and also may affect the fermentation. The objective of this experiment was to study the effect of alfalfa-grass mixtures and the use of additives on nutritive value and fermentation of silage
Quantum Hall fractions for spinless Bosons
We study the Quantum Hall phases that appear in the fast rotation limit for
Bose-Einstein condensates of spinless bosonic atoms. We use exact
diagonalization in a spherical geometry to obtain low-lying states of a small
number of bosons as a function of the angular momentum. This allows to
understand or guess the physics at a given filling fraction nu, ratio of the
number of bosons to the number of vortices. This is also the filling factor of
the lowest Landau level. In addition to the well-known Bose Laughlin state at
nu =1/2 we give evidence for the Jain principal sequence of incompressible
states at nu =p/(p+- 1) for a few values of p. There is a collective mode in
these states whose phenomenology is in agreement with standard arguments coming
e.g. from the composite fermion picture. At filling factor one, the potential
Fermi sea of composite fermions is replaced by a paired state, the Moore-Read
state. This is most clearly seen from the half-flux nature of elementary
excitations. We find that the hierarchy picture does not extend up to the point
of transition towards a vortex lattice. While we cannot conclude, we
investigate the clustered Read-Rezayi states and show evidence for
incompressible states at the expected ratio of flux vs number of Bose
particles.Comment: RevTeX 4, 11 pages, 13 figure
Statistics of layered zigzags: a two-dimensional generalization of TASEP
A novel discrete growth model in 2+1 dimensions is presented in three
equivalent formulations: i) directed motion of zigzags on a cylinder, ii)
interacting interlaced TASEP layers, and iii) growing heap over 2D substrate
with a restricted minimal local height gradient. We demonstrate that the
coarse-grained behavior of this model is described by the two-dimensional
Kardar-Parisi-Zhang equation. The coefficients of different terms in this
hydrodynamic equation can be derived from the steady state flow-density curve,
the so called `fundamental' diagram. A conjecture concerning the analytical
form of this flow-density curve is presented and is verified numerically.Comment: 5 pages, 4 figure
Vacuum Cherenkov radiation
Within the classical Maxwell-Chern-Simons limit of the Standard-Model
Extension (SME), the emission of light by uniformly moving charges is studied
confirming the possibility of a Cherenkov-type effect. In this context, the
exact radiation rate for charged magnetic point dipoles is determined and found
in agreement with a phase-space estimate under certain assumptions.Comment: 4 pages, REVTeX
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