11,364 research outputs found
Spontaneously magnetized Tomonaga-Luttinger liquid in frustrated quantum antiferromagnets
We develop a theory of spontaneously magnetized Tomonaga-Luttinger liquid
(SMTLL) in geometrically frustrated quasi-one-dimensional quantum magnets by
taking an ferrimagnet on a union-jack lattice as an example. We show
that a strong frustration leads to a spontaneous magnetization because of the
ferrimagnetic nature of lattice. Due to the ferrimagnetic order, the local
magnetization has an incommensurate oscillation with the position. We show that
the spontaneously magnetized TLL is smoothly connected to the existence of a
Nambu-Goldstone boson in the canted ferrimagnetic phase of a two-dimensional
frustrated antiferromagnet
Topological transition between competing orders in quantum spin chains
We study quantum phase transitions between competing orders in
one-dimensional spin systems. We focus on systems that can be mapped to a
dual-field double sine-Gordon model as a bosonized effective field theory. This
model contains two pinning potential terms of dual fields that stabilize
competing orders and allows different types of quantum phase transition to
happen between two ordered phases. At the transition point, elementary
excitations change from the topological soliton of one of the dual fields to
that of the other, thus it can be characterized as a topological transition. We
compute the dynamical susceptibilities and the entanglement entropy, which
gives us access to the central charge, of the system using a numerical
technique of infinite time-evolving block decimation and characterize the
universality class of the transition as well as the nature of the order in each
phase. The possible realizations of such transitions in experimental systems
both for condensed matter and cold atomic gases are also discussed.Comment: 8 pages, 7 figure
Entropy estimates for a class of schemes for the euler equations
In this paper, we derive entropy estimates for a class of schemes for the
Euler equations which present the following features: they are based on the
internal energy equation (eventually with a positive corrective term at the
righ-hand-side so as to ensure consistency) and the possible upwinding is
performed with respect to the material velocity only. The implicit-in-time
first-order upwind scheme satisfies a local entropy inequality. A
generalization of the convection term is then introduced, which allows to limit
the scheme diffusion while ensuring a weaker property: the entropy inequality
is satisfied up to a remainder term which is shown to tend to zero with the
space and time steps, if the discrete solution is controlled in L and
BV norms. The explicit upwind variant also satisfies such a weaker property, at
the price of an estimate for the velocity which could be derived from the
introduction of a new stabilization term in the momentum balance. Still for the
explicit scheme, with the above-mentioned generalization of the convection
operator, the same result only holds if the ratio of the time to the space step
tends to zero
New analytical progress in the theory of vesicles under linear flow
Vesicles are becoming a quite popular model for the study of red blood cells
(RBCs). This is a free boundary problem which is rather difficult to handle
theoretically. Quantitative computational approaches constitute also a
challenge. In addition, with numerical studies, it is not easy to scan within a
reasonable time the whole parameter space. Therefore, having quantitative
analytical results is an essential advance that provides deeper understanding
of observed features and can be used to accompany and possibly guide further
numerical development. In this paper shape evolution equations for a vesicle in
a shear flow are derived analytically with precision being cubic (which is
quadratic in previous theories) with regard to the deformation of the vesicle
relative to a spherical shape. The phase diagram distinguishing regions of
parameters where different types of motion (tank-treading, tumbling and
vacillating-breathing) are manifested is presented. This theory reveals
unsuspected features: including higher order terms and harmonics (even if they
are not directly excited by the shear flow) is necessary, whatever the shape is
close to a sphere. Not only does this theory cure a quite large quantitative
discrepancy between previous theories and recent experiments and numerical
studies, but also it reveals a new phenomenon: the VB mode band in parameter
space, which is believed to saturate after a moderate shear rate, exhibits a
striking widening beyond a critical shear rate. The widening results from
excitation of fourth order harmonic. The obtained phase diagram is in a
remarkably good agreement with recent three dimensional numerical simulations
based on the boundary integral formulation. Comparison of our results with
experiments is systematically made.Comment: a tex file and 6 figure
Laboratory experiments on the generation of internal tidal beams over steep slopes
We designed a simple laboratory experiment to study internal tides
generation. We consider a steep continental shelf, for which the internal tide
is shown to be emitted from the critical point, which is clearly amphidromic.
We also discuss the dependence of the width of the emitted beam on the local
curvature of topography and on viscosity. Finally we derive the form of the
resulting internal tidal beam by drawing an analogy with an oscillating
cylinder in a static fluid
On transport in quantum Hall systems with constrictions
Motivated by recent experimental findings, we study transport in a simple
phenomenological model of a quantum Hall edge system with a gate-voltage
controlled constriction lowering the local filling factor. The current
backscattered from the constriction is seen to arise from the matching of the
properties of the edge-current excitations in the constriction () and
bulk () regions. We develop a hydrodynamic theory for bosonic edge
modes inspired by this model, finding that a competition between two tunneling
process, related by a quasiparticle-quasihole symmetry, determines the fate of
the low-bias transmission conductance. In this way, we find satisfactory
explanations for many recent puzzling experimental results.Comment: 4 pages, 4 figure
Transport through a molecular quantum dot in the polaron crossover regime
We consider resonant transport through a molecular quantum dot coupled to a
local vibration mode. Applying the non-equilibrium Green function technique in
the polaron representation, we develop a non-perturbative scheme to calculate
the electron spectral function of the molecule in the regime of intermediate
electron-phonon coupling. With increasing tunneling coupling to the leads,
correlations between polaron clouds become more important at relatively high
temperature leading to a strong sharpening of the peak structure in the
spectral function. The detection of such features in the current-voltage
characteristics is briefly discussed
Observation of thermally activated glassiness and memory dip in a-NbSi insulating thin films
We present electrical conductance measurements on amorphous NbSi insulating
thin films. These films display out-of equilibrium electronic features that are
markedly different from what has been reported so far in disordered insulators.
Like in the most studied systems (indium oxide and granular Al films), a slow
relaxation of the conductance is observed after a quench to liquid helium
temperature which gives rise to the growth of a memory dip in MOSFET devices.
But unlike in these systems, this memory dip and the related conductance
relaxations are still visible up to room temperature, with clear signatures of
a temperature dependent dynamics
The behavior of statically-indeterminate structural members and frames with cracks present
Arts et Métiers ParisTech, invitation en tant que professeur invité de Paul C. Paris au LAMEFIPCrack stability is discussed as affected by their presence in statically-indeterminate beams, frames, rings, etc. loaded into the plastic range. The stability of a crack in a section, which has become plastic, is analyzed with the remainder of the structure elastic and with subsequent additional plastic hinges occurring. The reduction of energy absorption characteristics for large deformations is also discussed. The methods of elastic–plastic tearing instability are incorporated to show that in many cases the fully plastic collapse mechanism must occur for complete failure.The authors acknowledge Arts et Metiers Paris Tech and Foundation Arts et Metiers for the financial support of the Prof. P.C. Paris’ stay at LAMEFIP in 2008 and 2009. The encouragement of Prof. Ivan Iordanoff, Director of LAMEFIP, is also acknowledged with thanks
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