84 research outputs found
Enhanced mesoscopic fluctuations in the crossover between random matrix ensembles
In random-matrix ensembles that interpolate between the three basic ensembles
(orthogonal, unitary, and symplectic), there exist correlations between
elements of the same eigenvector and between different eigenvectors. We study
such correlations, using a remarkable correspondence between the interpolating
ensembles late in the crossover and a basic ensemble of finite size. In small
metal grains or semiconductor quantum dots, the correlations between different
eigenvectors lead to enhanced fluctuations of the electron-electron interaction
matrix elements which become parametrically larger than the non-universal
fluctuations.Comment: 4 pages, RevTeX; 3 figure
Observation of discrete time-crystalline order in a disordered dipolar many-body system
Understanding quantum dynamics away from equilibrium is an outstanding
challenge in the modern physical sciences. It is well known that
out-of-equilibrium systems can display a rich array of phenomena, ranging from
self-organized synchronization to dynamical phase transitions. More recently,
advances in the controlled manipulation of isolated many-body systems have
enabled detailed studies of non-equilibrium phases in strongly interacting
quantum matter. As a particularly striking example, the interplay of periodic
driving, disorder, and strong interactions has recently been predicted to
result in exotic "time-crystalline" phases, which spontaneously break the
discrete time-translation symmetry of the underlying drive. Here, we report the
experimental observation of such discrete time-crystalline order in a driven,
disordered ensemble of dipolar spin impurities in diamond at
room-temperature. We observe long-lived temporal correlations at integer
multiples of the fundamental driving period, experimentally identify the phase
boundary and find that the temporal order is protected by strong interactions;
this order is remarkably stable against perturbations, even in the presence of
slow thermalization. Our work opens the door to exploring dynamical phases of
matter and controlling interacting, disordered many-body systems.Comment: 6 + 3 pages, 4 figure
Quantum Quench in the Transverse Field Ising chain I: Time evolution of order parameter correlators
We consider the time evolution of order parameter correlation functions after
a sudden quantum quench of the magnetic field in the transverse field Ising
chain. Using two novel methods based on determinants and form factor sums
respectively, we derive analytic expressions for the asymptotic behaviour of
one and two point correlators. We discuss quenches within the ordered and
disordered phases as well as quenches between the phases and to the quantum
critical point. We give detailed account of both methods.Comment: 65 pages, 21 figures, some typos correcte
Pathways of Superoxide (O2-) decay in the Eastern Tropical North Atlantic
Superoxide (O2-: IUPAC name dioxide (âą1â)) is an important transient reactive oxygen species (ROS) in the ocean formed as an intermediate in the redox transformation of oxygen (O2) into hydrogen peroxide (H2O2) and vice versa. This highly reactive and very short-lived radical anion can be produced both via photochemical and biological processes in the ocean. In this paper we examine the decomposition rate of O2- throughout the water column, using new data collected in the Eastern Tropical North Atlantic (ETNA) Ocean. For this approach we applied a semi factorial experimental design, to identify and quantify the pathways of the major identified sinks in the ocean. In this work we occupied 6 stations, 2 on the West African continental shelf and 4 open ocean stations, including the CVOO time series site adjacent to Cape Verde. Our results indicate that in the surface ocean, impacted by Saharan aerosols and sediment resuspension, the main decay pathways for superoxide is via reactions with Mn(II) and organic matter
Predicting climate change using response theory: global averages and spatial patterns
The provision of accurate methods for predicting the climate response to anthropogenic and natural forcings is a key contemporary scientific challenge. Using a simplified and efficient open-source general circulation model of the atmosphere featuring O(105105) degrees of freedom, we show how it is possible to approach such a problem using nonequilibrium statistical mechanics. Response theory allows one to practically compute the time-dependent measure supported on the pullback attractor of the climate system, whose dynamics is non-autonomous as a result of time-dependent forcings. We propose a simple yet efficient method for predictingâat any lead time and in an ensemble senseâthe change in climate properties resulting from increase in the concentration of CO22 using test perturbation model runs. We assess strengths and limitations of the response theory in predicting the changes in the globally averaged values of surface temperature and of the yearly total precipitation, as well as in their spatial patterns. The quality of the predictions obtained for the surface temperature fields is rather good, while in the case of precipitation a good skill is observed only for the global average. We also show how it is possible to define accurately concepts like the inertia of the climate system or to predict when climate change is detectable given a scenario of forcing. Our analysis can be extended for dealing with more complex portfolios of forcings and can be adapted to treat, in principle, any climate observable. Our conclusion is that climate change is indeed a problem that can be effectively seen through a statistical mechanical lens, and that there is great potential for optimizing the current coordinated modelling exercises run for the preparation of the subsequent reports of the Intergovernmental Panel for Climate Change
Iron Behaving Badly: Inappropriate Iron Chelation as a Major Contributor to the Aetiology of Vascular and Other Progressive Inflammatory and Degenerative Diseases
The production of peroxide and superoxide is an inevitable consequence of
aerobic metabolism, and while these particular "reactive oxygen species" (ROSs)
can exhibit a number of biological effects, they are not of themselves
excessively reactive and thus they are not especially damaging at physiological
concentrations. However, their reactions with poorly liganded iron species can
lead to the catalytic production of the very reactive and dangerous hydroxyl
radical, which is exceptionally damaging, and a major cause of chronic
inflammation. We review the considerable and wide-ranging evidence for the
involvement of this combination of (su)peroxide and poorly liganded iron in a
large number of physiological and indeed pathological processes and
inflammatory disorders, especially those involving the progressive degradation
of cellular and organismal performance. These diseases share a great many
similarities and thus might be considered to have a common cause (i.e.
iron-catalysed free radical and especially hydroxyl radical generation). The
studies reviewed include those focused on a series of cardiovascular, metabolic
and neurological diseases, where iron can be found at the sites of plaques and
lesions, as well as studies showing the significance of iron to aging and
longevity. The effective chelation of iron by natural or synthetic ligands is
thus of major physiological (and potentially therapeutic) importance. As
systems properties, we need to recognise that physiological observables have
multiple molecular causes, and studying them in isolation leads to inconsistent
patterns of apparent causality when it is the simultaneous combination of
multiple factors that is responsible. This explains, for instance, the
decidedly mixed effects of antioxidants that have been observed, etc...Comment: 159 pages, including 9 Figs and 2184 reference
Prevalence of Age-Related Macular Degeneration in Europe: The Past and the Future
Purpose Age-related macular degeneration (AMD) is a frequent, complex disorder in elderly of European ancestry. Risk profiles and treatment options have changed considerably over the years, which may have affected disease prevalence and outcome. We determined the prevalence of early and late AMD in Europe from 1990 to 2013 using the European Eye Epidemiology (E3) consortium, and made projections for the future. Design Meta-analysis of prevalence data. Participants A total of 42 080 individuals 40 years of age and older participating in 14 population-based cohorts from 10 countries in Europe. Methods AMD was diagnosed based on fundus photographs using the Rotterdam Classification. Prevalence of early and late AMD was calculated using random-effects meta-analysis stratified for age, birth cohort, gender, geographic region, and time period of the study. Best-corrected visual acuity (BCVA) was compared between late AMD subtypes; geographic atrophy (GA) and choroidal neovascularization (CNV). Main Outcome Measures Prevalence of early and late AMD, BCVA, and number of AMD cases. Results Prevalence of early AMD increased from 3.5% (95% confidence interval [CI] 2.1%â5.0%) in those aged 55â59 years to 17.6% (95%
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