1,322 research outputs found
Flux quench in a system of interacting spinless fermions in one dimension
We study a quantum quench in a one-dimensional spinless fermion model
(equivalent to the XXZ spin chain), where a magnetic flux is suddenly switched
off. This quench is equivalent to imposing a pulse of electric field and
therefore generates an initial particle current. This current is not a
conserved quantity in presence of a lattice and interactions and we investigate
numerically its time-evolution after the quench, using the infinite
time-evolving block decimation method. For repulsive interactions or large
initial flux, we find oscillations that are governed by excitations deep inside
the Fermi sea. At long times we observe that the current remains non-vanishing
in the gapless cases, whereas it decays to zero in the gapped cases. Although
the linear response theory (valid for a weak flux) predicts the same long-time
limit of the current for repulsive and attractive interactions (relation with
the zero-temperature Drude weight), larger nonlinearities are observed in the
case of repulsive interactions compared with that of the attractive case.Comment: 10 pages, 10 figures; v2: Added references. Figures are refined and
animations are added. Corrected typos. Published versio
Magnon bands of N-leg integer-spin antiferromagnetic systems in the weak interchain-coupling regime
Using the exact results of the O(3) nonlinear sigma model (NLSM) and a few
quantitative numerical data for integer-spin antiferromagnetic (AF) chains, we
systematically estimate all magnon excitation energies of N-leg integer-spin AF
ladders and tubes in the weak-interchain-coupling regime. Our method is based
on a first-order perturbation theory for the strength of the interchain
coupling. It can deal with any kind of interchain interactions, in principle.
We confirm that results of the perturbation theory are in good agreement with
those of a quantum Monte Carlo simulation and with our recent study based on a
saddle-point approximation of the NLSM [Phys. Rev. B 72, 104438 (2005)]. Our
theory further supports the existence of a Haldane (gapped) phase even in a
d-dimensional (d\geq 2) spatially anisotropic integer-spin AF model, if the
exchange coupling in one direction is sufficiently strong compared with those
in all the other directions. The strategy in this paper is applicable to other
N-leg systems consisting of gapped chains which low-energy physics is exactly
or quantitatively known.Comment: 11 pages, 4 figures, Revtex, published version, see also
cond-mat/0506049 (PRB72, 104438 (2005)
Quantum counter automata
The question of whether quantum real-time one-counter automata (rtQ1CAs) can
outperform their probabilistic counterparts has been open for more than a
decade. We provide an affirmative answer to this question, by demonstrating a
non-context-free language that can be recognized with perfect soundness by a
rtQ1CA. This is the first demonstration of the superiority of a quantum model
to the corresponding classical one in the real-time case with an error bound
less than 1. We also introduce a generalization of the rtQ1CA, the quantum
one-way one-counter automaton (1Q1CA), and show that they too are superior to
the corresponding family of probabilistic machines. For this purpose, we
provide general definitions of these models that reflect the modern approach to
the definition of quantum finite automata, and point out some problems with
previous results. We identify several remaining open problems.Comment: A revised version. 16 pages. A preliminary version of this paper
appeared as A. C. Cem Say, Abuzer Yakary{\i}lmaz, and \c{S}efika
Y\"{u}zsever. Quantum one-way one-counter automata. In R\={u}si\c{n}\v{s}
Freivalds, editor, Randomized and quantum computation, pages 25--34, 2010
(Satellite workshop of MFCS and CSL 2010
Ab-initio calculations of the Optical band-gap of TiO2 thin films
Titanium dioxide has been extensively studied in recent decades for its
important photocatalytic application in environmental purification. The search
for a method to narrow the optical band-gap of TiO2 plays a key role for
enhancing its photocatalytic application. The optical band gap of epitaxial
rutile and anatase TiO2 thin films deposited by helicon magnetron sputtering on
sapphire and on SrTiO3 substrates was correlated to the lattice constants
estimated from HRTEM images and SAED. The optical band-gap of 3.03 eV for
bulk-rutile increased for the thin films to 3.37 on sapphire. The band gap of
3.20 eV for bulk-anatase increases to 3.51 on SrTiO3. In order to interpret the
optical band gap expansion for both phases, ab-initio calculations were
performed using the Vienna ab-initio software. The calculations for rutile as
well anatase show an almost linear increase of the band gap width with
decreasing volume or increasing lattice constant a. The calculated band gap
fits well with the experimental values. The conclusion from these calculations
is, in order to achieve a smaller band-gap for both, rutile or anatase, the
lattice constants c has to be compressed, and a has to be expanded.Comment: 4 pages, 4 figures, 1 tabl
LNG fueled barge for cold ironing: feasibility study for the emission abatement in the Port of Genoa
The scientific analysis presented in this paper aims at studying some maritime technical solutions for the electric energy generation and delivery to ships moored in port by means of LNG fueled generators installed onboard a floating unit. Two different scenarios regarding the LNG supply chain are supposed and some options for producing cleaner electric energy are then investigated. The reference area considered in this study is the old port of Genoa where the traffic of both passenger and cargo ships takes place. The paper presents an analysis concerning the main technical features of the considered solutions for an actual port calls scenario. The results regard dimensions and weights of the proposed floating units and the most significant characteristics of the generation equipment, as far as average load factor, fuel consumption and cost are concerned
Anatomical features of renal artery in a black Kenyan population: Correlation with markers of atherosclerosis
Knowledge of anatomical features of the renal artery is important in prediction, management and control of atherosclerotic renal artery stenosis. These features show population variations but data from black African populations are scarce. The aim of this study was therefore to describe the anatomical features of the renal artery in a black Kenyan population. Six hundred and ten (610) single renal arteries from 305 adult black Kenyans [206 males, 99 females; age range 22 â 79 years] were studied by dissection at Department of Human Anatomy, University of Nairobi, Kenya. Specimens with macroscopic features of stenosis and dilatation were excluded. The implantation angle, length and branching pattern were studied. These features were correlated with intima-media thickness and luminal diameter. The latter were determined by micrometry on Eosin/hematoxylin stained 5 micron sections obtained from the proximal segment of the renal artery. Data was analysed by SPSS version 16.0. Studentâs t-test, was used to test for statistical significance at 95% confidence interval where P value of < 0.05 was taken as significant. The results are presented in a bar graph, tables and macrographs. The mean implantation angle was 940±150 (range 580-1250). In 26.7% cases, the angle was more than 1000. Mean length was 34±1.4 mm with 21.6 % of arteries measuring †20 mm. Variant branching pattern was present in 40.5 % of cases. It comprised trifurcation (33 %), quadrifurcation (6.6 %) and pentafurcation (0.8 %). Higher implantation angle, short arteries and variant branching were associated with statistically significant higher intima - media thickness and luminal diameter. These results suggest that higher implantation angle, shorter length and variant branching pattern constitute geometric risk factors for renal artery atherosclerosis. Ultrasound screening for individuals with suboptimal geometric features for renal artery atherosclerosis is recommended.Keywords: anatomical risk factors, atherosclerosis, renal arter
Gd-based protein cage nanoparticles provide enhanced r1 relaxivity and detect experimental atherosclerosis
- âŠ