7,087 research outputs found
Morphogenesis of defects and tactoids during isotropic-nematic phase transition in self-assembled lyotropic chromonic liquid crystals
We explore the structure of nuclei and topological defects in the first-order
phase transition between the nematic (N) and isotropic (I) phases in lyotropic
chromonic liquid crystals (LCLCs). The LCLCs are formed by self-assembled
molecular aggregates of various lengths and show a broad biphasic region. The
defects emerge as a result of two mechanisms. 1) Surface anisotropy mechanism
that endows each N nucleus (tactoid) with topological defects thanks to
preferential (tangential) orientation of the director at the closed I-N
interface, and 2) Kibble mechanism with defects forming when differently
oriented N tactoids merge with each other. Different scenarios of phase
transition involve positive (N-in-I) and negative (I-in-N) tactoids with
non-trivial topology of the director field and also multiply connected
tactoids-in-tactoids configurations. The closed I-N interface limiting a
tactoid shows a certain number of cusps; the lips of the interface on the
opposite sides of the cusp make an angle different from pi. The N side of each
cusp contains a point defect-boojum. The number of cusps shows how many times
the director becomes perpendicular to the I-N interface when one
circumnavigates the closed boundary of the tactoid. We derive conservation laws
that connect the number of cusps c to the topological strength m of defects in
the N part of the simply-connected and multiply-connected tactoids. We
demonstrate how the elastic anisotropy of the N phase results in non-circular
shape of the disclination cores. A generalized Wulff construction is used to
derive the shape of I and N tactoids as the function of I-N interfacial tension
anisotropy in the frozen director field of various topological charges m. The
complex shapes and structures of tactoids and topological defects demonstrate
an important role of surface anisotropy in morphogenesis of phase transitions
in liquid crystals.Comment: 31 pages, 13 figure
An animal experimental study on pubourethral ligament restoration with platelet rich plasma for the treatment of stress urinary incontinence.
Introduction: Minimally invasive methods for injured ligament and tendon restoration have been developed and gained popularity in recent years. Injury and relaxation of the pubourethral ligament (PUL) can lead to stress urinary incontinence (SUI). The aim of this study was to investigate the impact of injecting platelet rich plasma (PRP) into the PUL following its surgical transection resulting in SUI, confirmed by leak point pressure (LPP) measurements pre- and post-intervention in an experimental animal model. Material and methods: Twenty female adult Sprague-Dawley rats were assigned in 2 groups: 1) treatment group with transection of the PUL and application of PRP at the time of transection and at one month follow-up and 2) a control group, with transection of the PUL only. Leak point pressures (LPPs) were measured prior to transection, immediately following the transection and at 1 and 2 months in both groups. Results: The median LPPs for the control group were: LPP - preT: 35.6 (29.8-44.8) cmH2O, LPP - postT: 14.6 (5.8-19.0) cmH2O, LPP - 1 month: 27.3 (19.2-33.8) cmH2O, LPP - 2 months: 29.0 (27.0-34.0) cmH2O, whereas for the PRP group were: LPP-preT: 40.5 (33.2-46.3) cmH2O, LPP - postT: 15.7 (3.0-24.0) cmH2O, LPP - 1month: 31.6 (24.8-37.4) cmH2O, LPP - 2 months: 36.8 (32.5-45.4) cmH2O. PRP injections on transected PULs significantly increased LPPs at one month follow-up [31.6 cmH2O vs. 27.3 cmH2O, p = .043]. This effect was confirmed at two months [36.8 cmH2O vs. 29.0 cmH2O, p <.001]. Conclusions: Injection of PRP into transected PULs significantly improved LPPs at one and two months' follow-up. However, further experimental and clinical research is needed to evaluate the safety and efficacy of this treatment, in clinical practice
Continuous-wave phase-sensitive parametric image amplification
We study experimentally parametric amplification in the continuous regime
using a transverse-degenerate type-II Optical Parametric Oscillator operated
below threshold. We demonstrate that this device is able to amplify either in
the phase insensitive or phase sensitive way first a single mode beam, then a
multimode image. Furthermore the total intensities of the amplified image
projected on the signal and idler polarizations are shown to be correlated at
the quantum level.Comment: 14 pages, 7 figures, submitted to Journal of Modern Optics, Special
Issue on Quantum Imagin
Superconductivity from a non-Fermi liquid metal : Kondo fluctuation mechanism in the slave-fermion theory
We find new mechanism of superconductivity beyond the spin-fluctuation
theory, the standard model for unconventional superconductivity in the weak
coupling approach, where Kondo fluctuations result in multi-gap
superconductivity around an antiferromagnetic quantum critical point of the
slave-fermion theory. Fingerprints of the hybridization mechanism are two kinds
of resonance modes in not only spin but also charge fluctuations, originating
from pairing of conduction electrons and spinless holons,
respectively, thus differentiated from the spin-fluctuation mechanism. We show
that the ratio between each superconducting gap for conduction electrons
and holons and the transition temperature is
and , remarkably consistent with
Deconfinement in the presence of a Fermi surface
U(1) gauge theory of non-relativistic fermions interacting via compact U(1)
gauge fields in the presence of a Fermi surface appears as an effective field
theory in low dimensional quantum antiferromagnetism and heavy fermion liquids.
We investigate deconfinement of fermions near the Fermi surface in the
effective U(1) gauge theory. Our present analysis benchmarks the recent
investigation of quantum electrodynamics in two space and one time dimensions
() by Hermele et al. [Phys. Rev. B {\bf 70}, 214437 (2004)]. Utilizing a
renormalization group analysis, we show that the effective U(1) gauge theory
with a Fermi surface has a stable charged fixed point. Remarkably, the
renormalization group equation for an internal charge (the coupling
strength between non-relativistic fermions and U(1) gauge fields) reveals that
the conductivity of fermions near the Fermi surface plays the same
role as the flavor number of massless Dirac fermions in . This leads
us to the conclusion that if the conductivity of fermions is sufficiently
large, instanton excitations of U(1) gauge fields can be suppressed owing to
critical fluctuations of the non-relativistic fermions at the charged fixed
point. As a result a critical field theory of non-relativistic fermions
interacting via noncompact U(1) gauge fields is obtained at the charged fixed
point
Adaptive lattice bilinear filters
Journal ArticleAbstract-This paper presents two fast least squares lattice algorithms for adaptive nonlinear filters equipped with bilinear system models. Bilinear models are attractive for adaptive filtering applications because they can approximate a large class of nonlinear systems adequately, and usually with considerable parsimony in the number of coefficients required. The lattice filter formulation transforms the nonlinear filtering problem into an equivalent multichannel linear filtering problem and then uses multichannel lattice filtering algorithms to solve the nonlinear filtering problem. The lattice filters perform a Gram-Schmidt orthogonalization of the input data and have very good numerical properties. Furthermore, the computational complexity of the algorithms is an order of magnitude smaller than previously available methods. The first of the two approaches is an equation error algorithm that uses the measured desired response signal directly to compute the adaptive filter outputs. This method is conceptually very simple; however, it will result in biased system models in the presence of measurement noise. The second approach is an approximate least squares output error solution. In this case, the past samples of the output of the adaptive system itself are used to produce the filter output at the current time. Results of several experiments that demonstrate and compare the properties of the adaptive bilinear filters are also presented in this paper. These results indicate that the output error algorithm is less sensitive to output measurement noise than the equation error method
Adaptive algorithms for identifying recursive nonlinear systems
Journal ArticleABSTRACT This paper presents two fast least-squares lattice algorithms for adaptive non-linear filters equipped with system models involving nonlinear feedback. Such models can approximate a large class of non-linear systems adequately, and usually with considerable parsimony in the number of coefficients required. For simplicity of presentation, we consider the bilinear system model in the paper, even though the results are applicable to more general system models. The computational complexity of the algorithms is an order of magnitude smaller than previously available methods. Results of several experiments that demonstrate the properties of the adaptive bilinear filters as well as compare their performances with two other algorithms that are computationally more expensive are also presented in this paper
A criterion for the nature of the superconducting transition in strongly interacting field theories : Holographic approach
It is beyond the present techniques based on perturbation theory to reveal
the nature of phase transitions in strongly interacting field theories.
Recently, the holographic approach has provided us with an effective dual
description, mapping strongly coupled conformal field theories to classical
gravity theories. Resorting to the holographic superconductor model, we propose
a general criterion for the nature of the superconducting phase transition
based on effective interactions between vortices. We find "tricritical" points
in terms of the chemical potential for U(1) charges and an effective
Ginzburg-Landau parameter, where vortices do not interact to separate the
second order (repulsive) from the first order (attractive) transitions. We
interpret the first order transition as the Coleman-Weinberg mechanism, arguing
that it is relevant to superconducting instabilities around quantum
criticality.Comment: 7 pages, 7 figure
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