446 research outputs found
The geometric order of stripes and Luttinger liquids
It is argued that the electron stripes as found in correlated oxides have to
do with an unrecognized form of order. The manifestation of this order is the
robust property that the charge stripes are at the same time anti-phase
boundaries in the spin system. We demonstrate that the quantity which is
ordering is sublattice parity, referring to the geometric property of a
bipartite lattice that it can be subdivided in two sublattices in two different
ways. Re-interpreting standard results of one dimensional physics, we
demonstrate that the same order is responsible for the phenomenon of
spin-charge separation in strongly interacting one dimensional electron
systems. In fact, the stripe phases can be seen from this perspective as the
precise generalization of the Luttinger liquid to higher dimensions. Most of
this paper is devoted to a detailed exposition of the mean-field theory of
sublattice parity order in 2+1 dimensions. Although the quantum-dynamics of the
spin- and charge degrees of freedom is fully taken into account, a perfect
sublattice parity order is imposed. Due to novel order-out-of-disorder physics,
the sublattice parity order gives rise to full stripe order at long wavelength.
This adds further credibility to the notion that stripes find their origin in
the microscopic quantum fluctuations and it suggests a novel viewpoint on the
relationship between stripes and high Tc superconductivity.Comment: 29 pages, 14 figures, 1 tabl
Spin motive forces due to magnetic vortices and domain walls
We study spin motive forces, i.e, spin-dependent forces, and voltages induced
by time-dependent magnetization textures, for moving magnetic vortices and
domain walls. First, we consider the voltage generated by a one-dimensional
field-driven domain wall. Next, we perform detailed calculations on
field-driven vortex domain walls. We find that the results for the voltage as a
function of magnetic field differ between the one-dimensional and vortex domain
wall. For the experimentally relevant case of a vortex domain wall, the
dependence of voltage on field around Walker breakdown depends qualitatively on
the ratio of the so-called -parameter to the Gilbert damping constant,
and thus provides a way to determine this ratio experimentally. We also
consider vortices on a magnetic disk in the presence of an AC magnetic field.
In this case, the phase difference between field and voltage on the edge is
determined by the parameter, providing another experimental method to
determine this quantity.Comment: 8 pages, 9 figures, submitted to PR
Systematic Density Expansion of the Lyapunov Exponents for a Two-dimensional Random Lorentz Gas
We study the Lyapunov exponents of a two-dimensional, random Lorentz gas at
low density. The positive Lyapunov exponent may be obtained either by a direct
analysis of the dynamics, or by the use of kinetic theory methods. To leading
orders in the density of scatterers it is of the form
, where and are
known constants and is the number density of scatterers expressed
in dimensionless units. In this paper, we find that through order
, the positive Lyapunov exponent is of the form
. Explicit numerical values of the new constants
and are obtained by means of a systematic analysis. This takes into
account, up to , the effects of {\it all\/} possible
trajectories in two versions of the model; in one version overlapping scatterer
configurations are allowed and in the other they are not.Comment: 12 pages, 9 figures, minor changes in this version, to appear in J.
Stat. Phy
Resonant Impurity States in the D-Density-Wave Phase
We study the electronic structure near impurities in the d-density-wave (DDW)
state, a possible candidate phase for the pseudo-gap region of the
high-temperature superconductors. We show that the local DOS near a
non-magnetic impurity in the DDW state is {\it qualitatively} different from
that in a superconductor with -symmetry. Since this result is a
robust feature of the DDW phase, it can help to identify the nature of the two
different phases recently observed by scanning tunneling microscopy experiments
in the superconducting state of underdoped Bi-2212 compounds
Cochrane corner: Is integrated disease management for patients with COPD effective?
Patients with COPD experience respiratory
symptoms, impairments of daily living and recurrent
exacerbations. The aim of integrated disease
management (IDM) is to establish a programme of
different components of care (ie, self-management,
exercise, nutrition) in which several healthcare providers
(ie, nurses, general practitioners, physiotherapists,
pulmonologists) collaborate to provide efficient and good
quality of care. The aim of this Cochrane systematic
review was to evaluate the effectiveness of IDM on
quality of life, exercise tolerance and exacerbation related
outcomes. Searches for all available evidence were
carried out in various databases. Included randomised
controlled trials (RCTs) consisted of interventions with
multidisciplinary (≥2 healthcare providers) and
multitreatment (≥2 components) IDM interventions with
duration of at least 3 months. Two reviewers
independently searched, assessed and extracted data of
all RCTs. A total of 26 RCTs were included, involving
2997 patients from 11 different countries with a followup
varying from 3 to 24 months. In all 68% of the
patients were men, with a mean age of 68 years and a
mean forced expiratory volume in 1 s (FEV1) predicted
value of 44.3%. Patients treated with an IDM
programme improved significantly on quality of life
scores and reported a clinically relevant improvement of
44 m on 6 min walking distance, compared to controls.
Furthermore, the number of patients with ≥1 respiratory
related hospital admission reduced from 27 to 20 per
100 patients. Duration of hospitalisation decreased
significantly by nearly 4 days
Influence of the interelectrode distance on the production of nanoparticles by means of atmospheric pressure inert gas DC glow discharge
This work is aimed at investigating the influence of the inter-electrode spacing on the production rate and size of nanoparticles generated by evaporating a cathode on an atmospheric pressure dc glow discharge. Experiments are conducted in the configuration of two vertically aligned cylindrical electrodes in upward coaxial flow with copper as a consumable cathode and nitrogen as a carrier gas. A constant current of 0.5 A is delivered to the electrodes and the inter-electrode distance spanned from 0.5 to 10 mm. Continuous stable nanoparticle production is attained by optimal coaxial flow convection cooling of the cathode. Both the particle production rate and the primary particle size increase with the inter-electrode spacing up to nearly 5 mm and strongly decrease with an increasing inter-electrode distance beyond 5 mm. Production rates in the range of 1 mg h-1 of very small nanoparticles
Field induced d_x^2-y^2+id_xy state in d-density-wave metals
We argue that the d_{xy} component of the order parameter can be generated to
form the d_x^2-y^2+id_xy-density wave state by the external magnetic field. The
driving force for this transition is the coupling of the magnetic field with
the orbital magnetism. The fully gapped particle spectrum and the magnetically
active collective mode of the condensate are discussed as a possible signature
of the d+id' density wave state.Comment: 5 pages, 2 color figure
Hidden order in bosonic gases confined in one dimensional optical lattices
We analyze the effective Hamiltonian arising from a suitable power series
expansion of the overlap integrals of Wannier functions for confined bosonic
atoms in a 1d optical lattice. For certain constraints between the coupling
constants, we construct an explicit relation between such an effective bosonic
Hamiltonian and the integrable spin- anisotropic Heisenberg model. Therefore
the former results to be integrable by construction. The field theory is
governed by an anisotropic non linear -model with singlet and triplet
massive excitations; such a result holds also in the generic non-integrable
cases. The criticality of the bosonic system is investigated. The schematic
phase diagram is drawn. Our study is shedding light on the hidden symmetry of
the Haldane type for one dimensional bosons.Comment: 5 pages; 1 eps figure. Revised version, to be published in New. J.
Phy
Geometry and the Hidden Order of Luttinger Liquids: the Universality of Squeezed Space
We present the case that Luttinger liquids are characterized by a form of
hidden order which is similar, but distinct in some crucial regards, to the
hidden order characterizing spin-1 Heisenberg chains. We construct a string
correlator for the Luttinger liquid which is similar to the string correlator
constructed by den Nijs and Rommelse for the spin chain. From a geometric
prespective on the so-called `squeezed space' construction, we demonstrate that
the physics at long wavelength can be reformulated in terms of a gauge
theory. Peculiarly, the normal spin chain lives at infinite gauge coupling
where it is characterized by deconfinement. We identify the microscopic
conditions required for confinement thereby identifying a novel phase of the
spin-chain. We demonstrate that the Luttinger liquid can be approached in the
same general framework. The difference from the spin chain is that the gauge
sector is critical in the sense that the Luttinger liquid is at the phase
boundary where the local symmetry emerges. We evaluate the string
correlator analytically and show that the squeezed space structure is present
both for the strongly coupled Hubbard model and the non-interacting fermion
gas. These structures are hard-wired in the mathematical structure of
bosonization and this becomes obvious by considering string correlators.
Numerical results are presented for the string correlator using a non-abelian
version of the density matrix renormalization group algorithm, confirming in
detail the expectations following from the theory. We conclude with some
observations regarding the generalization of bosonization to higher dimensions.Comment: 24 pages, 14 eps figures, Revtex
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