2,514 research outputs found
Time-frequency detection algorithm for gravitational wave bursts
An efficient algorithm is presented for the identification of short bursts of
gravitational radiation in the data from broad-band interferometric detectors.
The algorithm consists of three steps: pixels of the time-frequency
representation of the data that have power above a fixed threshold are first
identified. Clusters of such pixels that conform to a set of rules on their
size and their proximity to other clusters are formed, and a final threshold is
applied on the power integrated over all pixels in such clusters. Formal
arguments are given to support the conjecture that this algorithm is very
efficient for a wide class of signals. A precise model for the false alarm rate
of this algorithm is presented, and it is shown using a number of
representative numerical simulations to be accurate at the 1% level for most
values of the parameters, with maximal error around 10%.Comment: 26 pages, 15 figures, to appear in PR
The Electron Spectral Function in Two-Dimensional Fractionalized Phases
We study the electron spectral function of various zero-temperature
spin-charge separated phases in two dimensions. In these phases, the electron
is not a fundamental excitation of the system, but rather ``decays'' into a
spin-1/2 chargeless fermion (the spinon) and a spinless charge e boson (the
chargon). Using low-energy effective theories for the spinons (d-wave pairing
plus possible N\'{e}el order), and the chargons (condensed or quantum
disordered bosons), we explore three phases of possible relevance to the
cuprate superconductors: 1) AF*, a fractionalized antiferromagnet where the
spinons are paired into a state with long-ranged N\'{e}el order and the
chargons are 1/2-filled and (Mott) insulating, 2) the nodal liquid, a
fractionalized insulator where the spinons are d-wave paired and the chargons
are uncondensed, and 3) the d-wave superconductor, where the chargons are
condensed and the spinons retain a d-wave gap. Working within the gauge
theory of such fractionalized phases, our results should be valid at scales
below the vison gap. However, on a phenomenological level, our results should
apply to any spin-charge separated system where the excitations have these
low-energy effective forms. Comparison with ARPES data in the undoped,
pseudogapped, and superconducting regions is made.Comment: 10 page
Parity (and time-reversal) anomaly in a semiconductor
The physics of a parity anomaly, potentially observable in a narrow-gap
semiconductor, is revisited. Fradkin, Dagotto, and Boyanovsky have suggested
that a Hall current of anomalous parity can be induced by a Peierls distortion
on a domain wall. I argue that a perturbation inducing the parity anomaly must
break the time reversal symmetry, which rules out the Peierls distortion as a
potential cause. I list all possible perturbations that can generate the
anomaly.Comment: 11 pages, 1 figure. Sign errors fixe
The spectrum of gastric cancer as seen in a large quaternary hospital in KwaZulu-Natal, South Africa
Background. Gastric cancer (GC) is the fifth most commonly diagnosed cancer in the world, with the third-highest associated mortality. It has a varying geographical, ethnic and socioeconomic distribution.Objective. To assess the presentation and management of GC in the Durban metropolitan area, South Africa.Methods. A retrospective review of 131 patients treated at the quaternary Inkosi Albert Luthuli Central Hospital in Durban from 2009 to 2014 was performed.Results. The 131 patients were predominantly black African (n=59, 45.0%) and Indian (n=63, 48.1%). Gender was evenly distributed, with 72 males (55.0%) and 59 females (45.0%). The average age of the patients was 60 years (standard deviation 13.3). More than 70% were in advanced stages of cancer and were treated conservatively. There was no significant relationship between body mass index (BMI) and the position of the tumour (p=0.175). Creatinine and albumin levels differed significantly between the genders (p<0.001 and p=0.01, respectively).Conclusions. GC appears to have a disproportionately high prevalence among Indians in Durban, and the prevalence of GC appears to be slightly higher among males. Both these observations may simply reflect referral patterns and warrant further investigation. More than 70% of patients presented with advanced-stage disease, and anaemia was common. No relationship was found between BMI and the location of the tumour, although most of the cancers were in the body and distal part of the stomach
Operator-Algebraic Approach to the Yrast Spectrum of Weakly Interacting Trapped Bosons
We present an operator-algebraic approach to deriving the low-lying
quasi-degenerate spectrum of weakly interacting trapped N bosons with total
angular momentum \hbar L for the case of small L/N, demonstrating that the
lowest-lying excitation spectrum is given by 27 g n_3(n_3-1)/34, where g is the
strength of the repulsive contact interaction and n_3 the number of excited
octupole quanta. Our method provides constraints for these quasi-degenerate
many-body states and gives higher excitation energies that depend linearly on
N.Comment: 7 pages, one figur
Kolmogorov turbulence, Anderson localization and KAM integrability
The conditions for emergence of Kolmogorov turbulence, and related weak wave
turbulence, in finite size systems are analyzed by analytical methods and
numerical simulations of simple models. The analogy between Kolmogorov energy
flow from large to small spacial scales and conductivity in disordered solid
state systems is proposed. It is argued that the Anderson localization can stop
such an energy flow. The effects of nonlinear wave interactions on such a
localization are analyzed. The results obtained for finite size system models
show the existence of an effective chaos border between the
Kolmogorov-Arnold-Moser (KAM) integrability at weak nonlinearity, when energy
does not flow to small scales, and developed chaos regime emerging above this
border with the Kolmogorov turbulent energy flow from large to small scales.Comment: 8 pages, 6 figs, EPJB style
Doping Dependence of the Magnetic Resonance Peak in YBa_2 Cu_3 O_{6+x}
We report inelastic neutron scattering experiments on the doping dependence
of the energy and spectral weight of the sharp magnetic resonance peak in YBa_2
Cu_3 O_{6+x}. These measurements also shed light on the relationship between
the magnetic excitations in the normal and superconducting states.Comment: (mostly corrections to figures and minor change to caption in Fig.5)
5 figures. It will be published in the proceedings of M2S-HTSC-V. It needs
the elsevier style file (not included) to convert to postscrip
Re-localization due to finite response times in a nonlinear Anderson chain
We study a disordered nonlinear Schr\"odinger equation with an additional
relaxation process having a finite response time . Without the relaxation
term, , this model has been widely studied in the past and numerical
simulations showed subdiffusive spreading of initially localized excitations.
However, recently Caetano et al.\ (EPJ. B \textbf{80}, 2011) found that by
introducing a response time , spreading is suppressed and any
initially localized excitation will remain localized. Here, we explain the lack
of subdiffusive spreading for by numerically analyzing the energy
evolution. We find that in the presence of a relaxation process the energy
drifts towards the band edge, which enforces the population of fewer and fewer
localized modes and hence leads to re-localization. The explanation presented
here is based on previous findings by the authors et al.\ (PRE \textbf{80},
2009) on the energy dependence of thermalized states.Comment: 3 pages, 4 figure
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