6,547 research outputs found
Second-order and Fluctuation-induced First-order Phase Transitions with Functional Renormalization Group Equations
We investigate phase transitions in scalar field theories using the
functional renormalization group (RG) equation. We analyze a system with
U(2)xU(2) symmetry, in which there is a parameter that controls the
strength of the first-order phase transition driven by fluctuations. In the
limit of \lambda_2\to0\epsilon$-expansion results. We compare results from the expansion and from
the full numerical calculation and find that the fourth-order expansion is only
of qualitative use and that the sixth-order expansion improves the quantitative
agreement.Comment: 15 pages, 10 figures, major revision; discussions on O(N) models
reduced, a summary section added after Introduction, references added; to
appear in PR
Ideal MHD theory of low-frequency Alfven waves in the H-1 Heliac
A part analytical, part numerical ideal MHD analysis of low-frequency Alfven
wave physics in the H-1 stellarator is given. The three-dimensional,
compressible ideal spectrum for H-1 is presented and it is found that despite
the low beta (approx. 10^-4) of H-1 plasmas, significant Alfven-acoustic
interactions occur at low frequencies. Several quasi-discrete modes are found
with the three-dimensional linearised ideal MHD eigenmode solver CAS3D,
including beta-induced Alfven eigenmode (BAE)- type modes in beta-induced gaps.
The strongly shaped, low-aspect ratio magnetic geometry of H-1 causes CAS3D
convergence difficulties requiring the inclusion of many Fourier harmonics for
the parallel component of the fluid displacement eigenvector even for shear
wave motions. The highest beta-induced gap reproduces large parts of the
observed configurational frequency dependencies in the presence of hollow
temperature profiles
Interpreting frequency responses to dose-conserved pulsatile input signals in simple cell signaling motifs.
This is the final version of the article. Available from PLoS via the DOI in this record.Many hormones are released in pulsatile patterns. This pattern can be modified, for instance by changing pulse frequency, to encode relevant physiological information. Often other properties of the pulse pattern will also change with frequency. How do signaling pathways of cells targeted by these hormones respond to different input patterns? In this study, we examine how a given dose of hormone can induce different outputs from the target system, depending on how this dose is distributed in time. We use simple mathematical models of feedforward signaling motifs to understand how the properties of the target system give rise to preferences in input pulse pattern. We frame these problems in terms of frequency responses to pulsatile inputs, where the amplitude or duration of the pulses is varied along with frequency to conserve input dose. We find that the form of the nonlinearity in the steady state input-output function of the system predicts the optimal input pattern. It does so by selecting an optimal input signal amplitude. Our results predict the behavior of common signaling motifs such as receptor binding with dimerization, and protein phosphorylation. The findings have implications for experiments aimed at studying the frequency response to pulsatile inputs, as well as for understanding how pulsatile patterns drive biological responses via feedforward signaling pathways.This work was partially supported by the National Science Foundation grant DMS-1220063 to R. Bertram and J. Tabak (http://www.nsf.gov) and by the
large-scale action REGATE (REgulation of the GonAdoTropE axis) to F. Clement and A. Vidal (https://www.rocq.inria.fr/sisyphe/reglo/regate.html). The funders had
no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Enhanced magnetization of ultrathin NiFeO films on SrTiO(001) related to cation disorder and anomalous strain
NiFeO thin films with varying thickness were grown on SrTiO(001)
by reactive molecular beam epitaxy. Soft and hard x-ray photoelectron
spectroscopy measurements reveal a homogeneous cation distribution throughout
the whole film with stoichiometric Ni:Fe ratios of 1:2 independent of the film
thickness. Low energy electron diffraction and high resolution (grazing
incidence) x-ray diffraction in addition to x-ray reflectivity experiments were
conducted to obtain information of the film surface and bulk structure,
respectively. For ultrathin films up to 7.3 nm, lateral tensile and vertical
compressive strain is observed, contradicting an adaption at the interface of
NiFeO film and substrate lattice. The applied strain is accompanied by
an increased lateral defect density, which is decaying for relaxed thicker
films and attributed to the growth of lateral grains. Determination of cationic
site occupancies in the inverse spinel structure by analysis of site sensitive
diffraction peaks reveals low tetrahedral occupancies for thin, strained
NiFeO films, resulting in partial presence of deficient rock salt like
structures. These structures are assumed to be responsible for the enhanced
magnetization of up to 250\% of the NiFeO bulk magnetization as
observed by superconducting quantum interference device magnetometry for
ultrathin films below 7.3 nm thickness.Comment: 11 pages, 9 figure
Abelian Yang-Mills theory on Real tori and Theta divisors of Klein surfaces
The purpose of this paper is to compute determinant index bundles of certain
families of Real Dirac type operators on Klein surfaces as elements in the
corresponding Grothendieck group of Real line bundles in the sense of Atiyah.
On a Klein surface these determinant index bundles have a natural holomorphic
description as theta line bundles. In particular we compute the first
Stiefel-Whitney classes of the corresponding fixed point bundles on the real
part of the Picard torus. The computation of these classes is important,
because they control to a large extent the orientability of certain moduli
spaces in Real gauge theory and Real algebraic geometry.Comment: LaTeX, 44 pages, to appear in Comm. Math. Phy
Alignment and preliminary outcomes of an ELT-size instrument to a very large telescope: LINC-NIRVANA at LBT
LINC-NIRVANA (LN) is a high resolution, near infrared imager that uses a
multiple field-of-view, layer-oriented, multi-conjugate AO system, consisting
of four multi-pyramid wavefront sensors (two for each arm of the Large
Binocular Telescope, each conjugated to a different altitude). The system
employs up to 40 star probes, looking at up to 20 natural guide stars
simultaneously. Its final goal is to perform Fizeau interferometric imaging,
thereby achieving ELT-like spatial resolution (22.8 m baseline resolution). For
this reason, LN is also equipped with a fringe tracker, a beam combiner and a
NIR science camera, for a total of more than 250 optical components and an
overall size of approximately 6x4x4.5 meters. This paper describes the
tradeoffs evaluated in order to achieve the alignment of the system to the
telescope. We note that LN is comparable in size to planned ELT
instrumentation. The impact of such alignment strategies will be compared and
the selected procedure, where the LBT telescope is, in fact, aligned to the
instrument, will be described. Furthermore, results coming from early
night-time commissioning of the system will be presented.Comment: 8 pages, 6 pages, AO4ELT5 Proceedings, 201
Theory of traveling filaments in bistable semiconductor structures
We present a generic nonlinear model for current filamentation in
semiconductor structures with S-shaped current-voltage characteristics. The
model accounts for Joule self-heating of a current density filament. It is
shown that the self-heating leads to a bifurcation from static to traveling
filament. Filaments start to travel when increase of the lattice temperature
has negative impact on the cathode-anode transport. Since the impact ionization
rate decreases with temperature, this occurs for a wide class of semiconductor
systems whose bistability is due to the avalanche impact ionization. We develop
an analytical theory of traveling filaments which reveals the mechanism of
filament motion, find the condition for bifurcation to traveling filament, and
determine the filament velocity.Comment: 13 pages, 5 figure
Growth and characterization of InGaN/GaN quantum dots for violet/blue applications
We report on plasma-assisted molecular beam epitaxy growth and characterization of InGaN/GaN quantum dots (QDs) for violet/blue applications
Transient hypertension and sustained tachycardia in mice housed individually in metabolism cages
The novel environment of a metabolic cage can be stressful for rodents, but few studies have attempted to quantify this stress response. Therefore, we determined the effects on mean arterial pressure (MAP) and heart rate (HR), of placing mice of both sexes in metabolism cages for 2 days. After surgical implantation of a carotid artery catheter mice recovered individually in standard cages for 5 days. Mice then spent 2 days in metabolism cages. MAP and HR were monitored in the standard cage on Day 5 and in metabolism cages on Days 6-7. MAP increased by 18±3 and 22±4 %, while HR increased by 27±4 and 27±6 %, in males and females, respectively, during the first hours after cage switch. MAP decreased to baseline in the fourth and eighth h following metabolism cage switch in males and females, respectively. However, HR remained significantly elevated in both sexes during the entire two-day period in metabolism cages. Females had lower MAP than males both pre- and postmetabolism cage switch, but there were no sex differences in HR. These results demonstrate sustained changes in cardiovascular function when mice are housed in metabolism cages, which could potentially affect renal function
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