410 research outputs found
Purely electronic transport and localization in the Bose glass
We discuss transport and localization properties on the insulating side of
the disorder dominated superconductor-insulator transition, described in terms
of the dirty boson model. Analyzing the spectral properties of the interacting
bosons in the absence of phonons, we argue that the Bose glass phase admits
three distinct regimes. For strongest disorder the boson system is a fully
localized, perfect insulator at any temperature. At smaller disorder, only the
low temperature phase exhibits perfect insulation while delocalization takes
place above a finite temperature. We argue that a third phase must intervene
between these perfect insulators and the superconductor. This conducting Bose
glass phase is characterized by a mobility edge in the many body spectrum,
located at finite energy above the ground state. In this insulating regime
purely electronically activated transport occurs, with a conductivity following
an Arrhenius law at asymptotically low temperatures, while a tendency to
superactivation is predicted at higher T. These predictions are in good
agreement with recent transport experiments in highly disordered films of
superconducting materials.Comment: Discussion about 2d case added. Proceddings of TIDS 13, to be
published in Annals of Physic
On the Necessary Memory to Compute the Plurality in Multi-Agent Systems
We consider the Relative-Majority Problem (also known as Plurality), in
which, given a multi-agent system where each agent is initially provided an
input value out of a set of possible ones, each agent is required to
eventually compute the input value with the highest frequency in the initial
configuration. We consider the problem in the general Population Protocols
model in which, given an underlying undirected connected graph whose nodes
represent the agents, edges are selected by a globally fair scheduler.
The state complexity that is required for solving the Plurality Problem
(i.e., the minimum number of memory states that each agent needs to have in
order to solve the problem), has been a long-standing open problem. The best
protocol so far for the general multi-valued case requires polynomial memory:
Salehkaleybar et al. (2015) devised a protocol that solves the problem by
employing states per agent, and they conjectured their upper bound
to be optimal. On the other hand, under the strong assumption that agents
initially agree on a total ordering of the initial input values, Gasieniec et
al. (2017), provided an elegant logarithmic-memory plurality protocol.
In this work, we refute Salehkaleybar et al.'s conjecture, by providing a
plurality protocol which employs states per agent. Central to our
result is an ordering protocol which allows to leverage on the plurality
protocol by Gasieniec et al., of independent interest. We also provide a
-state lower bound on the necessary memory to solve the problem,
proving that the Plurality Problem cannot be solved within the mere memory
necessary to encode the output.Comment: 14 pages, accepted at CIAC 201
Single and two-particle energy gaps across the disorder-driven superconductor-insulator transition
The competition between superconductivity and localization raises profound
questions in condensed matter physics. In spite of decades of research, the
mechanism of the superconductor-insulator transition (SIT) and the nature of
the insulator are not understood. We use quantum Monte Carlo simulations that
treat, on an equal footing, inhomogeneous amplitude variations and phase
fluctuations, a major advance over previous theories. We gain new microscopic
insights and make testable predictions for local spectroscopic probes. The
energy gap in the density of states survives across the transition, but
coherence peaks exist only in the superconductor. A characteristic pseudogap
persists above the critical disorder and critical temperature, in contrast to
conventional theories. Surprisingly, the insulator has a two-particle gap scale
that vanishes at the SIT, despite a robust single-particle gap.Comment: 7 pages, 5 figures (plus supplement with 4 pages, 5 figures
Sleep quality in middle-aged and elderly Chinese: distribution, associated factors and associations with cardio-metabolic risk factors
Background
Poor sleep quality has been associated with increased risk of heart disease, diabetes and mortality. However, limited information exists on the distribution and determinants of sleep quality and its associations with cardio-metabolic risk factors in Chinese populations. We aimed to evaluate this in the current study.
Methods
A cross-sectional survey conducted in 2005 of 1,458 men and 1,831 women aged 50–70 years from urban and rural areas of Beijing and Shanghai. Using a questionnaire, sleep quality was measured in levels of well, common and poor. Comprehensive measures of socio-demographical and health factors and biomarkers of cardio-metabolic disease were recorded. These were evaluated in association with sleep quality using logistic regression models.
Results
Half of the population reported good sleep quality. After adjusting for potential confounders, women and Beijing residents had almost half the probability to report good sleep quality. Good physical and mental health (good levels of self-rated health (OR 2.48; 95%CI 2.08 to 2.96) and no depression (OR 4.05; 95%CI 3.12 to 5.26)) related to an increased chance of reporting good sleep quality, whereas short sleep duration (<7 hrs OR 0.10; 95%CI 0.07 to 0.14)) decreased it substantially. There were significant associations between levels of sleep quality and concentrations of plasma insulin, total and LDL cholesterol, and index of insulin resistance.
Conclusion
Levels of good sleep quality in middle-age and elderly Chinese were low. Gender, geographical location, self-rated health, depression and sleep quantity were major factors associated with sleep quality. Prospective studies are required to distil the factors that determine sleep quality and the effects that sleep patterns exert on cardio-metabolic health
A system for the management of clinical tasks throughout the clinical process with notification features
Computer-Interpretable Guidelines have been associated with a higher integration of standard practices in the daily context of health care institutions. The Clinical Decision Support Systems that deliver these machine-interpretable recommendations usually follow a Q & A style of communication, retrieving information from the user or a clinical repository and performing reasoning upon it, based on the rules from Clinical Practice Guidelines. However, these systems are limited in the reach they are capable of achieving as they were initially conceived for use in very specific moments of the clinical process, namely in physician appointments. The purpose of this work is thus to present a system that, in addition to Q & A reasoning, is equipped with other functionalities such as the scheduling and temporal management of clinical tasks, the mapping of these tasks onto an agenda of activities to allow an easy consultation by health care professionals, and notifications that let health care professionals know of task enactment times and information collection times. In this way, the system ensures the delivery of procedures. The main components of the system, which reflect a different perspective on the delivery of CIG advice that we call guideline as a service, are disclosed, and they include a health care Personal Assistant Web Application, a health care assistant mobile application, and the integration with the private calendar services of the user.(POCI-01-0145-)info:eu-repo/semantics/publishedVersio
Fractal superconductivity near localization threshold
We develop a semi-quantitative theory of electron pairing and resulting
superconductivity in bulk "poor conductors" in which Fermi energy is
located in the region of localized states not so far from the Anderson mobility
edge . We review the existing theories and experimental data and argue
that a large class of disordered films is described by this model.
Our theoretical analysis is based on the analytical treatment of pairing
correlations, described in the basis of the exact single-particle eigenstates
of the 3D Anderson model, which we combine with numerical data on eigenfunction
correlations. Fractal nature of critical wavefunction's correlations is shown
to be crucial for the physics of these systems.
We identify three distinct phases: 'critical' superconductive state formed at
, superconducting state with a strong pseudogap, realized due to
pairing of weakly localized electrons and insulating state realized at
still deeper inside localized band. The 'critical' superconducting phase is
characterized by the enhancement of the transition temperature with respect to
BCS result, by the inhomogeneous spatial distribution of superconductive order
parameter and local density of states. The major new feature of the
pseudo-gaped state is the presence of two independent energy scales:
superconducting gap , that is due to many-body correlations and a new
"pseudogap" energy scale which characterizes typical binding energy
of localized electron pairs and leads to the insulating behavior of the
resistivity as a function of temperature above superconductive . Two gap
nature of the "pseudo-gaped superconductor" is shown to lead to a number of
unusual physical properties.Comment: 110 pages, 39 figures. The revised version corrects a number of
typos, adds references and discussion of recent result
Localization of preformed Cooper pairs in disordered superconductors
International audienceThe most profound effect of disorder on electronic systems is the localization of the electrons transforming an otherwise metallic system into an insulator. If the metal is also a superconductor then, at low temperatures, disorder can induce a pronounced transition from a superconducting into an insulating state. An outstanding question is whether the route to insulating behaviour proceeds through the direct localization of Cooper pairs or, alternatively, by a two-step process in which the Cooper pairing is first destroyed followed by the standard localization of single electrons. Here we address this question by studying the local superconducting gap of a highly disordered amorphous superconductor by means of scanning tunnelling spectroscopy. Our measurements reveal that, in the vicinity of the superconductor-insulator transition, the coherence peaks in the one-particle density of states disappear whereas the superconducting gap remains intact, indicating the presence of localized Cooper pairs. Our results provide the first direct evidence that the superconductor-insulator transition in some homogeneously disordered materials is driven by Cooper-pair localization
A Scalable Architecture for Incremental Specification and Maintenance of Procedural and Declarative Clinical Decision-Support Knowledge
Clinical guidelines have been shown to improve the quality of medical care and to reduce its costs. However, most guidelines exist in a free-text representation and, without automation, are not sufficiently accessible to clinicians at the point of care. A prerequisite for automated guideline application is a machine-comprehensible representation of the guidelines. In this study, we designed and implemented a scalable architecture to support medical experts and knowledge engineers in specifying and maintaining the procedural and declarative aspects of clinical guideline knowledge, resulting in a machine comprehensible representation. The new framework significantly extends our previous work on the Digital electronic Guidelines Library (DeGeL) The current study designed and implemented a graphical framework for specification of declarative and procedural clinical knowledge, Gesher. We performed three different experiments to evaluate the functionality and usability of the major aspects of the new framework: Specification of procedural clinical knowledge, specification of declarative clinical knowledge, and exploration of a given clinical guideline. The subjects included clinicians and knowledge engineers (overall, 27 participants). The evaluations indicated high levels of completeness and correctness of the guideline specification process by both the clinicians and the knowledge engineers, although the best results, in the case of declarative-knowledge specification, were achieved by teams including a clinician and a knowledge engineer. The usability scores were high as well, although the clinicians’ assessment was significantly lower than the assessment of the knowledge engineers
Measurement error adjustment in essential fatty acid intake from a food frequency questionnaire: alternative approaches and methods
<p>Abstract</p> <p>Background</p> <p>We aimed at assessing the degree of measurement error in essential fatty acid intakes from a food frequency questionnaire and the impact of correcting for such an error on precision and bias of odds ratios in logistic models. To assess these impacts, and for illustrative purposes, alternative approaches and methods were used with the binary outcome of cognitive decline in verbal fluency.</p> <p>Methods</p> <p>Using the Atherosclerosis Risk in Communities (ARIC) study, we conducted a sensitivity analysis. The error-prone exposure – visit 1 fatty acid intake (1987–89) – was available for 7,814 subjects 50 years or older at baseline with complete data on cognitive decline between visits 2 (1990–92) and 4 (1996–98). Our binary outcome of interest was clinically significant decline in verbal fluency. Point estimates and 95% confidence intervals were compared between naïve and measurement-error adjusted odds ratios of decline with every SD increase in fatty acid intake as % of energy. Two approaches were explored for adjustment: (A) External validation against biomarkers (plasma fatty acids in cholesteryl esters and phospholipids) and (B) Internal repeat measurements at visits 2 and 3. The main difference between the two is that Approach B makes a stronger assumption regarding lack of error correlations in the structural model. Additionally, we compared results from regression calibration (RCAL) to those from simulation extrapolation (SIMEX). Finally, using structural equations modeling, we estimated attenuation factors associated with each dietary exposure to assess degree of measurement error in a bivariate scenario for regression calibration of logistic regression model.</p> <p>Results and conclusion</p> <p>Attenuation factors for Approach A were smaller than B, suggesting a larger amount of measurement error in the dietary exposure. Replicate measures (Approach B) unlike concentration biomarkers (Approach A) may lead to imprecise odds ratios due to larger standard errors. Using SIMEX rather than RCAL models tends to preserve precision of odds ratios. We found in many cases that bias in naïve odds ratios was towards the null. RCAL tended to correct for a larger amount of effect bias than SIMEX, particularly for Approach A.</p
Achieving Safety and Affordability in the UK Payday Loans Market
In the aftermath of the global financial crisis, financial regulation and supervision has been significantly reformed in the UK. As an important part of this reform, consumer credit, including payday loans, has been transferred to the new conduct of business regulator and supervisor, the Financial Conduct Authority. This paper considers the key rules on responsible lending and product regulation, introduced to protect the payday loans consumers. It shows that the responsible lending regime now reduces the risk that payday loans will be given to those who cannot afford the high costs involved, although responsible lending will only be fully effective if credit reference agencies hold up-to-date and correct information. Product regulation, in the form of a rollover restriction and a price cap, should make payday loans cheaper and safer for those who do use them, although, for the price cap to be most effective, steps must be taken to enhance price competition in the space below the cap. Finally, it is shown that firms are now subject to interventionist, rigorous, and consumer-centric supervision, which seems to stand a good chance of securing compliance with the new rules
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