Quantum quenches in the Dicke model: statistics of the work done and of other observables

We study the statistics of the work done in a zero temperature quench of the coupling constant in the Dicke model describing the interaction between a gas of two level atoms and a single electromagnetic cavity mode. When either the final or the initial coupling constants approach the critical coupling $\lambda_c$ that separates the normal and superradiant phases of the system, the probability distribution of the work done displays singular behavior. The average work tends to diverge as the initial coupling parameter is brought closer to the critical value $\lambda_c$. In contrast, for quenches ending close to criticality, the distribution of work has finite moments but displays a sequence of edge singularities. This contrasting behavior is related to the difference between the processes of compression and expansion of a particle subject to a sudden change of its confining potential. We confirm this by studying in detail the time dependent statistics of other observables, such as the quadratures of the photons and the total occupation of the bosonic modes.Comment: 8 pages, 2 figure

Solid-State Quantum Communication With Josephson Arrays

Josephson junction arrays can be used as quantum channels to transfer quantum information between distant sites. In this work we discuss simple protocols to realize state transfer with high fidelity. The channels do not require complicate gating but use the natural dynamics of a properly designed array. We investigate the influence of static disorder both in the Josephson energies and in the coupling to the background gate charges, as well as the effect of dynamical noise. We also analyze the readout process, and its backaction on the state transfer

Upper Bounds to the Performance of Cooperative Traffic Relaying in Wireless Linear Networks

Wireless networks with linear topology, where nodes generate their own traffic and relay other nodes' traffic, have attracted increasing attention. Indeed, they well represent sensor networks monitoring paths or streets, as well as multihop networks for videosurveillance of roads or vehicular traffic. We study the performance limits of such network systems when (i) the nodes' transmissions can reach receivers farther than one-hop distance from the sender, (ii) the transmitters cooperate in the data delivery, and (iii) interference due to concurrent transmissions is taken into account. By adopting an information-theoretic approach, we derive analytical bounds to the achievable data rate in both the cases where the nodes have full-duplex and half-duplex radios. The expressions we provide are mathematically tractable and allow the analysis of multihop networks with a large number of nodes. Our analysis highlights that increasing the number of coop- erating transmitters beyond two leads to a very limited gain in the achievable data rate. Also, for half-duplex radios, it indicates the existence of dominant network states, which have a major influence on the bound. It follows that efficient, yet simple, communication strategies can be designed by considering at most two cooperating transmitters and by letting half-duplex nodes operate according to the aforementioned dominant state

Evidence of radius inflation in stars approaching the slow-rotator sequence

Average stellar radii in open clusters can be estimated from rotation periods and projected rotational velocities under the assumption of random orientation of the spin axis. Such estimates are independent of distance, interstellar absorption, and models, but their validity can be limited by missing data (truncation) or data that only represent upper/lower limits (censoring). We present a new statistical analysis method to estimate average stellar radii in the presence of censoring and truncation. We use theoretical distribution functions of the projected stellar radius $R \sin i$ to define a likelihood function in the presence of censoring and truncation. Average stellar radii in magnitude bins are then obtained by a maximum likelihood parametric estimation procedure. This method is capable of recovering the average stellar radius within a few percent with as few as $\approx$ 10 measurements. Here it is applied for the first time to the dataset available for the Pleiades. We find an agreement better than $\approx$ 10 percent between the observed $R$ vs $M_K$ relationship and current standard stellar models for 1.2 $\ge M/M_{\odot} \ge$ 0.85 with no evident bias. Evidence of a systematic deviation at $2\sigma$ level are found for stars with 0.8 $\ge M/M_{\odot} \ge$ 0.6 approaching the slow-rotator sequence. Fast-rotators ($P$ < 2 d) agree with standard models within 15 percent with no systematic deviations in the whole 1.2 $\ge M/M_{\odot} \ge$ 0.5 range. The evidence found of a possible radius inflation just below the lower mass limit of the slow-rotator sequence indicates a possible connection with the transition from the fast to the slow-rotator sequence.Comment: Accepted by Astronomy and Astrophysics, 11 pages, 6 figure

A systematic review of the cost and cost effectiveness of using standard oral nutritional supplements in the hospital setting

Background & aims: There is limited information about the economic impact of nutritional support despite its known clinical benefits. This systematic review examined the cost and cost effectiveness of using standard (non-disease specific) oral nutritional supplements (ONS) administered in the hospital setting only. Methods: A systematic literature search of multiple databases, data synthesis and analysis were undertaken according to recommended procedures. Results: Nine publications comprising four full text papers, two abstracts and three reports, one of which contained 11 cost analyses of controlled cohort studies, were identified. Most of these were based on retrospective analyses of randomised controlled trials designed to assess clinically relevant outcomes. The sample sizes of patients with surgical, orthopaedic and medical problems and combinations of these varied from 40 to 1.16 million. Of 14 cost analyses comparing ONS with no ONS (or routine care), 12 favoured the ONS group, and among those with quantitative data (12 studies) the mean cost saving was 12.2%. In a meta-analysis of five abdominal surgical studies in the UK, the mean net cost saving was $746 per patient (se$338; P = 0.027). Cost savings were typically associated with significantly improved outcomes, demonstrated through the following meta-analyses: reduced mortality (Risk ratio 0.650, P < 0.05; N = 5 studies), reduced complications (by 35% of the total; P < 0.001, N = 7 studies) and reduced length of hospital stay (by ~2 days, P < 0.05; N = 5 surgical studies) corresponding to ~13.0% reduction in hospital stay. Two studies also found ONS to be cost effective, one by avoiding development of pressure ulcers and releasing hospital beds, and the other by gaining quality adjusted life years. Conclusion: This review suggests that standard ONS in the hospital setting produce a cost saving and are cost effective. The evidence base could be further strengthened by prospective studies in which the primary outcome measures are economic

A systematic review of the cost and cost effectiveness of using standard oral nutritional supplements in community and care home settings

Background & aims: Despite the clinical benefits of using standard (non-disease specific) oral nutritional supplements (ONS) in the community and care homes, there is uncertainty about their economic consequences. Methods: A systematic review was undertaken according to recommended procedures to assess whether ONS can produce cost savings and cost-effective outcomes. Results: 19 publications with and without a hospital component were identified: 9 full text papers, 9 abstracts, and 1 report with retrospective analyses of 6 randomised controlled trials. From these publications a total of 31 cost and 4 cost-effectiveness analyses were identified. Most were retrospective analyses based on clinical data from randomised controlled trials (RCTs). In 9 studies/economic models involving ONS use for 0.05; 5 studies). In RCTs, ONS accounted for less than 5% of the total costs and the investment in the community produced a cost saving in hospital. Meta-analysis indicated that ONS reduced hospitalisation significantly (16.5%; P < 0.001; 9 comparisons) and mortality non-significantly (Relative risk 0.86 (95% CI, 0.61, 1.22); 8 comparisons). Many clinically relevant outcomes favouring ONS were reported: improved quality of life, reduced infections, reduced minor post-operative complications, reduced falls, and functional limitations. Of the cost-effectiveness analyses involving quality adjusted life years or functional limitations, most favoured the ONS group. The care home studies (4 cost analyses; 2 cost-effectiveness analyses) had differing aims, designs and conclusions. Conclusions: Overall, the reviewed studies, mostly based on retrospective cost analyses, indicate that ONS use in the community produce an overall cost advantage or near neutral balance, often in association with clinically relevant outcomes, suggesting cost effectiveness. There is a need for prospective studies designed to examine primary economic outcomes

CORRECTING FOR SPATIAL EFFECTS IN LIMITED DEPENDENT VARIABLE REGRESSION: ASSESSING THE VALUE OF "AD-HOC" TECHNIQUES

A common test for spatial dependence in regression analysis with continuous dependent variables is the Moran's I. For limited dependent variable models, the standard definition of a residual breaks down because yi is qualitative. Efforts to correct for potential spatial effects in limited dependent variable models have relied on ad-hoc methods such as including a spatial lag variable or using a regular sample that omits neighboring observations. Kelejian and Prucha have recently developed a version of Moran's I for limited dependent variable models. We present the statistic in a more accessible way and use it to test the value of previously-used ad-hoc techniques with a specific data set. Keywords: Morans I, Spatial Autocorrelation, Limited Dependent Variable Models, Land-Use Change, Geographical Information Systems (GIS),Moran's I, Spatial Autocorrelation, Limited Dependent Variable Models, Land-Use Change, Geographical Information Systems (GIS), Research Methods/ Statistical Methods,

Modeling Deforestation and Land Use Change: Sparse Data Environments

Land use change in developing countries is of great interest to policymakers and researchers from many backgrounds. Concerns about consequences of deforestation for global climate change and biodiversity have received the most publicity, but loss of wetlands, declining land productivity, and watershed management are also problems facing developing countries. In developing countries, analysis is especially constrained by lack of data. This paper reviews modeling approaches for data-constrained environments that involve methods such as neural nets and dynamic programming and research results that link individual household survey data with satellite images using geographic positioning systems.Land Economics/Use, Q15, Q23, R14,