1,432 research outputs found
Describing many-body localized systems in thermal environments
In this work we formulate an efficient method for the description of fully many-body localized systems in weak contact with thermal environments at temperature T. The key idea is to exploit the representation of the system in terms of quasi-local integrals of motion (l-bits) to efficiently derive the generator for the quantum master equation in Born-Markov approximation. We, moreover, show how to compute the steady state of this equation efficiently by using quantum-jump Monte-Carlo techniques as well as by deriving approximate kinetic equations of motion. As an example, we consider a one-dimensional disordered extended Hubbard model for spinless fermions, for which we derive the l-bit representation approximately by employing a recently proposed method valid in the limit of strong disorder and weak interactions. Coupling the system to a global thermal bath, we study the transport between two leads with different chemical potentials at both of its ends. We find that the temperature-dependent current is captured by an interaction-dependent version of Mott's law for variable range hopping, where transport is enhanced/lowered depending on whether the interactions are attractive or repulsive, respectively. We interpret these results in terms of spatio-energetic correlations between the l-bits
Survival probability in Generalized Rosenzweig-Porter random matrix ensemble
We study analytically and numerically the dynamics of the generalized
Rosenzweig-Porter model, which is known to possess three distinct phases:
ergodic, multifractal and localized phases. Our focus is on the survival
probability , the probability of finding the initial state after time
. In particular, if the system is initially prepared in a highly-excited
non-stationary state (wave packet) confined in space and containing a fixed
fraction of all eigenstates, we show that can be used as a dynamical
indicator to distinguish these three phases. Three main aspects are identified
in different phases. The ergodic phase is characterized by the standard
power-law decay of with periodic oscillations in time, surviving in the
thermodynamic limit, with frequency equals to the energy bandwidth of the wave
packet. In multifractal extended phase the survival probability shows an
exponential decay but the decay rate vanishes in the thermodynamic limit in a
non-trivial manner determined by the fractal dimension of wave functions.
Localized phase is characterized by the saturation value of ,
finite in the thermodynamic limit , which approaches
in this limit.Comment: 21 pages, 12 figures, 61 reference
Vertically resolved aerosol properties by multi-wavelength lidar measurements
An approach based on the graphical method of Gobbi and co-authors (2007) is
introduced to estimate the dependence on altitude of the aerosol fine mode
radius (<i>R</i><sub>f</sub>) and of the fine mode contribution (η) to the
aerosol optical thickness (AOT) from three-wavelength lidar measurements. The
graphical method of Gobbi and co-authors (2007) was applied to AERONET
(AErosol RObotic NETwork) spectral extinction observations and relies on the
combined analysis of the Ă
ngstrom exponent (<i>Ă„</i>) and its
spectral curvature Î<i>Ă„</i>. Lidar measurements at 355, 532 and
1064 nm were used in this study to retrieve the vertical profiles of
<i>Ă„</i> and Î<i>Ă„</i> and to estimate the dependence on
altitude of <i>R</i><sub>f</sub> and η(532 nm) from the
<i>Ă„</i>âÎ<i>Ă„</i> combined analysis. Lidar measurements
were performed at the Department of Mathematics and Physics of the
Universita' del Salento, in south-eastern Italy. Aerosol from continental
Europe, the Atlantic, northern Africa, and the Mediterranean Sea are often
advected over south-eastern Italy and as a consequence, mixed advection
patterns leading to aerosol properties varying with altitude are dominant.
The proposed approach was applied to ten measurement days to demonstrate its
feasibility in different aerosol load conditions. The selected days were
characterized by AOTs spanning the 0.26â0.67, 0.15â0.39, and 0.04â0.27
range at 355, 532, and 1064 nm, respectively. Mean lidar ratios varied
within the 31â83, 32â84, and 11â47 sr range at 355, 532, and 1064 nm,
respectively, for the high variability of the aerosol optical and
microphysical properties. <i>Ă„</i> values calculated from lidar
extinction profiles at 355 and 1064 nm ranged between 0.1 and 2.5 with a
mean value ± 1 standard deviation equal to 1.3 ± 0.7.
Î<i>Ă„</i> varied within the â0.1â1 range with mean value
equal to 0.25 ± 0.43. <i>R</i><sub>f</sub> and η(532 nm) values
spanning the 0.05â0.3 ÎŒm and the 0.3â0.99 range,
respectively, were associated with the <i>Ă„</i>âΔ<i>Ă„</i> data points. <i>R</i><sub>f</sub> and η values showed no
dependence on the altitude. 60% of the data points were in the Δ<i>Ă„</i>â<i>Ă„</i> space delimited by the η and
<i>R</i><sub>f</sub> curves varying within 0.80â0.99 and 0.05â0.15 ÎŒm,
respectively, for the dominance of fine-mode particles in driving the AOT
over south-eastern Italy. Vertical profiles of the linear particle
depolarization ratio retrieved from lidar measurements, aerosol products from
AERONET sun photometer measurements collocated in space and time, analytical
back trajectories, satellite true colour images, and dust concentrations from
the BSCâDREAM (Barcelona Super Computing Center-Dust REgional Atmospheric
Model) model were used to demonstrate the robustness of the proposed method
Persistent organochlorine compounds in fetal and maternal tissues: evaluation of their potential influence on several indicators of fetal growth and health
Some organochlorine compounds, such as polychlorinated biphenyls (PCBs), have a tendency to bioaccumulate in humans and predators at the top of the food chain. We have recently confirmed the transplacental transfer of these compounds and the present study has been designed on the same material with the aim of investigating their potential health effects on newborns from 70 pregnant women, resident in a Northern Italy industrial town. Organochlorine compounds [namely, p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), p,p'-dichlorodiphenyldichloroethene (p,p'-DDE), hexachlorobenzene (HCB), and PCBs] have been analyzed both in cord and maternal serum, placenta, and maternal subcutaneous adipose tissue by GC-MSD. p,p'-DDT levels in the adipose tissue resulted significantly (p<0.05) related to birth length. Mothers of neonates born by preterm programmed caesarean delivery showed significantly (p<0.005 for both) higher serum p,p'-DDE serum concentrations and p,p'-DDT levels in the adipose tissue, as compared to mothers delivering at term
Pinch Grip per SE Is Not an Occupational Risk Factor for the Musculoskeletal System: An Experimental Study on Field
Introduction: Some ergonomic evaluation methods define pinch grip as a risk factor independent of the exerted force. The present experimental study was performed with the main aim of objectively measuring the muscle engagement during the execution of pinch grip. Methods: the participants of the study were healthy workers occupationally involved in a high-intensity repetitive job related to the sorting of letters and small packages. Surface electromyography (sEMG) was used to study the activity of the abductor pollicis brevis and first dorsal interosseous fibers related to the execution of the required working tasks, while the force exerted during voluntary muscle contraction for pinch grip was measured by a portable acquisition system. The subjects were specifically asked to exert the maximum voluntary isometric contraction (MVIC) and further voluntary isometric contractions with a spontaneous force (SF) equal to 10%,20% and 50% of the MVIC; finally, the workers were asked to hold in pinch grip two types of envelopes, weighing 100 g and 500 g, respectively. Results: The force required to pinch 100 and 500 g envelopes by the fifteen subjects of the study corresponded to 4 and 5% MVIC, respectively. The corresponding sEMG average rectified values (ARV) were approximately 6% of that at MVIC for first dorsal interosseus (FDI) fibers and approximately 20-25% of MVIC for abductor pollicis brevis (ABP) fibers. Bivariate correlation analysis showed significant relationships between force at MVIC and FDI ARV at MCV. Conclusions: The obtained results demonstrate that muscle recruitment during pinch grip varies as a function of the SF: not only the position but also the exerted force should be considered when assessing the pinch grip as risk factor for biomechanical overload of the upper limb
Theory of solvation in polar nematics
We develop a linear response theory of solvation of ionic and dipolar solutes
in anisotropic, axially symmetric polar solvents. The theory is applied to
solvation in polar nematic liquid crystals. The formal theory constructs the
solvation response function from projections of the solvent dipolar
susceptibility on rotational invariants. These projections are obtained from
Monte Carlo simulations of a fluid of dipolar spherocylinders which can exist
both in the isotropic and nematic phase. Based on the properties of the solvent
susceptibility from simulations and the formal solution, we have obtained a
formula for the solvation free energy which incorporates experimentally
available properties of nematics and the length of correlation between the
dipoles in the liquid crystal. Illustrative calculations are presented for the
Stokes shift and Stokes shift correlation function of coumarin-153 in
4-n-pentyl-4'-cyanobiphenyl (5CB) and 4,4-n-heptyl-cyanopiphenyl (7CB) solvents
as a function of temperature in both the nematic and isotropic phase.Comment: 19 pages, 9 figure
Effect of Fourier filters in removing periodic systematic effects from CMB data
We consider the application of high-pass Fourier filters to remove periodic
systematic fluctuations from full-sky survey CMB datasets. We compare the
filter performance with destriping codes commonly used to remove the effect of
residual 1/f noise from timelines. As a realistic working case, we use
simulations of the typical Planck scanning strategy and Planck Low Frequency
Instrument noise performance, with spurious periodic fluctuations that mimic a
typical thermal disturbance. We show that the application of Fourier high-pass
filters in chunks always requires subsequent normalisation of induced offsets
by means of destriping. For a complex signal containing all the astrophysical
and instrumental components, the result obtained by applying filter and
destriping in series is comparable to the result obtained by destriping only,
which makes the usefulness of Fourier filters questionable for removing this
kind of effects.Comment: 10 pages, 8 figures, published in Astronomy & Astrophysic
Copper accumulation in vineyard soils: Rhizosphere processes and agronomic practices to limit its toxicity.
Viticulture represents an important agricultural practice in many countries worldwide. Yet, the continuous use of fungicides has caused copper (Cu) accumulation in soils, which represent a major environmental and toxicological concern. Despite being an important micronutrient, Cu can be a potential toxicant at high concentrations since it may cause morphological, anatomical and physiological changes in plants, decreasing both food productivity and quality. Rhizosphere processes can, however, actively control the uptake and translocation of Cu in plants. In particular, root exudates affecting the chemical, physical and biological characteristics of the rhizosphere, might reduce the availability of Cu in the soil and hence its absorption. In addition, this review will aim at discussing the advantages and disadvantages of agronomic practices, such as liming, the use of pesticides, the application of organic matter, biochar and coal fly ashes, the inoculation with bacteria and/or mycorrhizal fungi and the intercropping, in alleviating Cu toxicity symptoms
- âŠ