Improving the sign problem in QCD at finite density

If the fermion mass is large enough, the phase of the fermion determinant of QCD at finite density is strongly correlated with the imaginary part of the Polyakov loop. This fact can be exploited to reduce the fluctuations of the phase significantly, making numerical simulations feasible in regions of parameters where the naive brute force method does not work.Comment: LATTICE99 (Finite Temperature and Density II

The role of the Polyakov loop in finite density QCD

We study the behavior of the fermion determinant at finite temperature and chemical potential, as a function of the Polyakov loop. The phase of the determinant is correlated with the imaginary part of the Polyakov loop. This correlation and its consequences are considered in static QCD, in a toy model of free quarks in a constant $A_0$ background, and in simulations constraining the imaginary part of the Polyakov loop to zero.Comment: 11 pages, 8 Postscript figures, Minor changes, quality of figures improve

Nucleon axial charge and structure functions with domain wall fermions

We report the current status of RBCK calculations on nucleon structure with both quenched and unquenched lattice QCD. The combination of domain wall fermions and DBW2 gauge action works well for isovector vector and axial charges, and moments of structure functions _q, d_1, and _{\delta q}.Comment: 3 pages, 4 figures, Lattice2003(matrix

The Physics of Protoplanetesimal Dust Agglomerates. Vi. Erosion of Large Aggregates as a Source of Micrometer-Sized Particles

Observed protoplanetary disks consist of a large amount of micrometer-sized particles. Dullemond and Dominik (2005) pointed out for the first time the difficulty in explaining the strong mid-IR excess of classical T-Tauri stars without any dust-retention mechanisms. Because high relative velocities in between micrometer-sized and macroscopic particles exist in protoplanetary disks, we present experimental results on the erosion of macroscopic agglomerates consisting of micrometer-sized spherical particles via the impact of micrometer-sized particles. We find that after an initial phase, in which an impacting particle erodes up to 10 particles of an agglomerate, the impacting particles compress the agglomerate's surface, which partly passivates the agglomerates against erosion. Due to this effect the erosion halts within our error bars for impact velocities up to ~30 m/s. For larger velocities, the erosion is reduced by an order of magnitude. This outcome is explained and confirmed by a numerical model. In a next step we build an analytical disk model and implement the experimentally found erosive effect. The model shows that erosion is a strong source of micrometer-sized particles in a protoplanetary disk. Finally we use the stationary solution of this model to explain the amount of micrometer-sized particles in observational infrared data of Furlan et al. (2006)

A hidden population of Wolf-Rayet stars in the massive galactic cluster Westerlund 1

We report the discovery of a hitherto undetected population of Wolf-Rayet stars in the young galactic open cluster Westerlund 1. Optical spectroscopy of the cluster identified 11 such objects; provisional classification suggests that 6 are nitrogen rich (WN) and 5 carbon rich (WC). Including the previously identified Blue, Yellow and Red Super- & Hypergiants, Westerlund 1 clearly has a very rich population of massive post-Main Sequence objects. To date, the post-MS population of Westerlund 1 is significantly larger than that of any other galactic young open cluster - with the possible exception of the Arches - implying that it is potentially amongst the most massive young clusters yet identified in the Local Group.Comment: 3 figures; uses new A&A style (included) Letter accepted for publication in Astronomy & Astrophysic

HIV with contact-tracing: a case study in Approximate Bayesian Computation

Missing data is a recurrent issue in epidemiology where the infection process may be partially observed. Approximate Bayesian Computation, an alternative to data imputation methods such as Markov Chain Monte Carlo integration, is proposed for making inference in epidemiological models. It is a likelihood-free method that relies exclusively on numerical simulations. ABC consists in computing a distance between simulated and observed summary statistics and weighting the simulations according to this distance. We propose an original extension of ABC to path-valued summary statistics, corresponding to the cumulated number of detections as a function of time. For a standard compartmental model with Suceptible, Infectious and Recovered individuals (SIR), we show that the posterior distributions obtained with ABC and MCMC are similar. In a refined SIR model well-suited to the HIV contact-tracing data in Cuba, we perform a comparison between ABC with full and binned detection times. For the Cuban data, we evaluate the efficiency of the detection system and predict the evolution of the HIV-AIDS disease. In particular, the percentage of undetected infectious individuals is found to be of the order of 40%

Concentrated Differential Privacy: Simplifications, Extensions, and Lower Bounds

"Concentrated differential privacy" was recently introduced by Dwork and Rothblum as a relaxation of differential privacy, which permits sharper analyses of many privacy-preserving computations. We present an alternative formulation of the concept of concentrated differential privacy in terms of the Renyi divergence between the distributions obtained by running an algorithm on neighboring inputs. With this reformulation in hand, we prove sharper quantitative results, establish lower bounds, and raise a few new questions. We also unify this approach with approximate differential privacy by giving an appropriate definition of "approximate concentrated differential privacy.

Brane Box Realization of Chiral Gauge Theories in Two Dimensions

We study type IIA configurations of D4 branes and three kinds of NS fivebranes. The D4 brane world-volume has finite extent in three directions, giving rise to a two-dimensional low-energy field theory. The models have generically $(0,2)$ supersymmetry. We determine the rules to read off the spectrum and interactions of the field theory from the brane box configuration data. We discuss the construction of theories with enhanced $(0,4)$, $(0,6)$ and $(0,8)$ supersymmetry. Using T-duality along the directions in which the D4 branes are finite, the configuration can be mapped to D1 branes at \IC^4/\Gamma singularities, with $\Gamma$ an abelian subgroup of SU(4). This provides a rederivation of the rules in the brane box model. The enhancement of supersymmetry has a nice geometrical interpretation in the singularity picture in terms of the holonomy group of the four-fold singularity.Comment: 48 pages, 10 eps figures, uses harvmac. Minor corrections, footnote on conventions adde

Spin relaxation and anticrossing in quantum dots: Rashba versus Dresselhaus spin-orbit coupling

The spin-orbit splitting of the electron levels in a two-dimensional quantum dot in a perpendicular magnetic field is studied. It is shown that at the point of an accidental degeneracy of the two lowest levels above the ground state the Rashba spin-orbit coupling leads to a level anticrossing and to mixing of spin-up and spin-down states, whereas there is no mixing of these levels due to the Dresselhaus term. We calculate the relaxation and decoherence times of the three lowest levels due to phonons. We find that the spin relaxation rate as a function of a magnetic field exhibits a cusp-like structure for Rashba but not for Dresselhaus spin-orbit interaction.Comment: 6 pages, 1 figur

Patterns of management of patients with dual disorder (psychosis) in Italy: a survey of psychiatrists and other physicians focusing on clinical practice

© 2018 Clerici, de Bartolomeis, De Filippis, Ducci, Maremmani, Martinotti and Schifano. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).Patients with severe psychotic disorders such as schizophrenia, schizoaffective and bipolar disorders frequently suffer from concomitant substance use disorders (SUDs) – Dual Disorder (DD) patients. In order to better understand current practices for management of patients with psychotic episodes and concomitant SUD in Italy, we carried out a survey of psychiatrists on current routine practice among prescribers. These aspects can help to identify at-risk patients, improve current prescribing practices, and favor early intervention. An ad hoc survey of 17 questions was administered to psychiatrists via electronic polling and on-line distribution; 448 completed questionnaires were collected. Comorbid substance abuse was most frequently diagnosed within the context of anxiety disorder (46%), followed by bipolar disorder (25%), and schizophrenia/schizoaffective disorder (12%). The vast majority of respondents felt that patient management was becoming more complex due to substance abuse. The areas reported to be most affected in patients with SUD were functioning, interpersonal relations, and impulsivity, while sensory perception disorders, ideation, agitation, and impulsivity were the most frequently reported symptoms. In the acute setting, haloperidol was used as the first-line agent of choice followed by aripiprazole and olanzapine. In the maintenance phase, aripiprazole was the dominantly used first-line agent, followed by olanzapine. Almost half of respondents used long-acting agents, while about one-third did not. Among those prescribing long-acting agents, efficacy, control of impulsivity, and control of specific symptoms were cited as motivators, while in the maintenance phase, better adherence and tolerability were mainly cited. From the responses to the present survey, it is clear that the respondents are aware of the problem of SUD in psychotic patients. While treatment be optimized in terms of the choice and formulation of antipsychotics, greater emphasis should be placed on efficacy, tolerability and the negative metabolic consequences of some antipsychotics. When considering the ideal antipsychotic, long-acting agents were considered to be superior in reducing relapse, even if current treatment guidelines often give preference to oral formulations.Peer reviewe