Exploring Replica-Exchange Wang-Landau sampling in higher-dimensional parameter space

We considered a higher-dimensional extension for the replica-exchange Wang-Landau algorithm to perform a random walk in the energy and magnetization space of the two-dimensional Ising model. This hybrid scheme combines the advantages of Wang-Landau and Replica-Exchange algorithms, and the one-dimensional version of this approach has been shown to be very efficient and to scale well, up to several thousands of computing cores. This approach allows us to split the parameter space of the system to be simulated into several pieces and still perform a random walk over the entire parameter range, ensuring the ergodicity of the simulation. Previous work, in which a similar scheme of parallel simulation was implemented without using replica exchange and with a different way to combine the result from the pieces, led to discontinuities in the final density of states over the entire range of parameters. From our simulations, it appears that the replica-exchange Wang-Landau algorithm is able to overcome this difficulty, allowing exploration of higher parameter phase space by keeping track of the joint density of states.Comment: Proceedings of CCP2014 will appear in Journal of Physics: Conference Series (JPCS), published by the IO

Example of two different potentials which have practically the same fixed-energy phase shifts

It is shown that the Newton-Sabatier procedure for inverting the fixed-energy phase shifts for a potential is not an inversion method but a parameter-fitting procedure. Theoretically there is no guarantee that this procedure is applicable to the given set of the phase shifts, if it is applicable, there is no guaran- tee that the potential it produces generates the phase shifts from which it was reconstructed. Moreover, no generic potential, specifically, no potential which is not analytic in a neighborhood of the positive real semiaxis can be reconstructed by the Newton-Sabatier procedure. A numerical method is given for finding spherically symmetric compactly supported potentials which produce practically the same set of fixed-energy phase shifts for all values of angular momentum. Concrete example of such potentials is given

Ballistic transport in random magnetic fields with anisotropic long-ranged correlations

We present exact theoretical results about energetic and dynamic properties of a spinless charged quantum particle on the Euclidean plane subjected to a perpendicular random magnetic field of Gaussian type with non-zero mean. Our results refer to the simplifying but remarkably illuminating limiting case of an infinite correlation length along one direction and a finite but strictly positive correlation length along the perpendicular direction in the plane. They are therefore ``random analogs'' of results first obtained by A. Iwatsuka in 1985 and by J. E. M\"uller in 1992, which are greatly esteemed, in particular for providing a basic understanding of transport properties in certain quasi-two-dimensional semiconductor heterostructures subjected to non-random inhomogeneous magnetic fields

Disease extinction in the presence of non-Gaussian noise

We investigate stochastic extinction in an epidemic model and the impact of random vaccinations in large populations. We show that, in the absence of vaccinations, the effective entropic barrier for extinction displays scaling with the distance to the bifurcation point, with an unusual critical exponent. Even a comparatively weak Poisson-distributed vaccination leads to an exponential increase in the extinction rate, with the exponent that strongly depends on the vaccination parameters.Comment: Accepted for publication to PR

Shifting attention in viewer- and object-based reference frames after unilateral brain injury

The aims of the present study were to investigate the respective roles that object- and viewer-based reference frames play in reorienting visual attention, and to assess their influence after unilateral brain injury. To do so, we studied 16 right hemisphere injured (RHI) and 13 left hemisphere injured (LHI) patients. We used a cueing design that manipulates the location of cues and targets relative to a display comprised of two rectangles (i.e., objects). Unlike previous studies with patients, we presented all cues at midline rather than in the left or right visual fields. Thus, in the critical conditions in which targets were presented laterally, reorienting of attention was always from a midline cue. Performance was measured for lateralized target detection as a function of viewer-based (contra- and ipsilesional sides) and object-based (requiring reorienting within or between objects) reference frames. As expected, contralesional detection was slower than ipsilesional detection for the patients. More importantly, objects influenced target detection differently in the contralesional and ipsilesional fields. Contralesionally, reorienting to a target within the cued object took longer than reorienting to a target in the same location but in the uncued object. This finding is consistent with object-based neglect. Ipsilesionally, the means were in the opposite direction. Furthermore, no significant difference was found in object-based influences between the patient groups (RHI vs. LHI). These findings are discussed in the context of reference frames used in reorienting attention for target detection

Tunneling Time and Weak Measurement in Strong Field Ionization

Tunneling delays represent a hotly debated topic, with many conflicting definitions and little consensus on when and if such definitions accurately describe the physical observables. Here, we relate these different definitions to distinct experimental observables in strong field ionization, finding that two definitions, Larmor time and Bohmian time, are compatible with the attoclock observable and the resonance lifetime of a bound state, respectively. Both of these definitions are closely connected to the theory of weak measurement, with Larmor time being the weak measurement value of tunneling time and Bohmian trajectory corresponding to the average particle trajectory, which has been recently reconstructed using weak measurement in a two-slit experiment [S. Kocsis, B. Braverman, S. Ravets, M. J. Stevens, R. P. Mirin, L. K. Shalm, and A. M. Steinberg, Science 332, 1170 (2011)]. We demonstrate a big discrepancy in strong field ionization between the Bohmian and weak measurement values of tunneling time, and we suggest this arises because the tunneling time is calculated for a small probability postselected ensemble of electrons. Our results have important implications for the interpretation of experiments in attosecond science, suggesting that tunneling is unlikely to be an instantaneous process

Intact Grammar in HFA? Evidence from Control and Binding

This study contributes original results to the topical issue of the degree to which grammar is intact in high-functioning children with autism (HFA). We examine the comprehension of binding and obligatory control in 26 HFA children, mean age=12;02, compared with two groups of younger typically developing (TD) children: one matched on non-verbal mental age (MA), mean age=9;09, and the other on verbal MA, mean age=8;09. On the binding task, our HFA group showed a good performance on reflexives on a par with TD matched children, in line with recent reports of intact knowledge of reflexive binding in higher but not lower-functioning children with autism. Their comprehension of personal pronouns was somewhat poorer, with no difference observed between the groups, again supporting the existing literature. Results on the control task, which probed mastery of syntactic relations never previously examined in autism, revealed that both HFA children and the two matched TD groups were at ceiling on single-complement subject control (try) and object control (persuade). However, a considerably poorer attainment on double-complement subject control (promise) was present equally in the HFA group and the verbal MA-matched TD group but not in the non-verbal MA-matched group. Performance on promise correlated with age only in the verbal MA-matched group, whilst in HFA it correlated with general cognitive and language abilities. These novel findings demonstrate that regular obligatory control and reflexive binding are preserved in HFA. We contrast these results with previous literature that has demonstrated deficiencies with passives and raising in HFA populations. The emerging bifurcation suggests different analyses for the principles underlying these constructions: whereas the latter incorporate movement, control and binding do not. The poor performance on promise supports all previous literature on this lexically and syntactically idiosyncratic construction. Its breaking of locality, which in turn results in a conflict between lexical and syntactic requirements, is exceptional and introduces an extra step of learning. This step appears to be related to maturation in TD children, and to stronger language and cognitive skills in HFA children

Pandemic-related emergency psychiatric presentations for self-harm of children and adolescents in 10 countries (PREP-kids): a retrospective international cohort study

To examine the differences in hospital emergency psychiatric presentations for self-harm of children and adolescents during the covid-19 lockdown in March and April 2020 compared with the same period in 2019. Retrospective cohort study. We used electronic patient records from 23 hospital emergency departments in ten countries grouped into 14 areas. We examined data on 2073 acute hospital presentations by 1795 unique children and adolescents through age 18. We examined the total number of emergency psychiatric hospital presentations and the proportion of children and adolescents presenting with severe self-harm as our two main outcome measures. In addition, we examined sociodemographic and clinical characteristics and clinical management variables for those presenting with self-harm. To compare the number of hospital presentations between 2020 and 2019 a negative binomial model was used. For other variables, individual participant data (IPD) meta-analyses were carried out. Emergency psychiatric hospital presentations decreased from 1239 in 2019 to 834 in 2020, incident rate ratio 0.67, 95% CI 0.62-0.73; p < 0.001. The proportion of children and adolescents presenting with self-harm increased from 50% in 2019 to 57% in 2020, odds ratio 1.33, 1.07-1.64; p = 0.009 but there was no difference in the proportion presenting with severe self-harm. Within the subpopulation presenting with self-harm the proportion of children and adolescents presenting with emotional disorders increased from 58 to 66%, odds ratio 1.58, 1.06-2.36; p = 0.025. The proportion of children and adolescents admitted to an observation ward also decreased from 13 to 9% in 2020, odds ratio 0.52, 0.28-0.96; p = 0.036. Service planners should consider that, during a lockdown, there are likely to be fewer emergency psychiatric presentations. Many children and adolescents with psychiatric emergencies might not receive any service. A focus on developing intensive community care services with outreach capabilities should be prioritised

Impact on mental health care and on mental health service users of the COVID-19 pandemic: a mixed methods survey of UK mental health care staff

PURPOSE: The COVID-19 pandemic has potential to disrupt and burden the mental health care system, and to magnify inequalities experienced by mental health service users. METHODS: We investigated staff reports regarding the impact of the COVID-19 pandemic in its early weeks on mental health care and mental health service users in the UK using a mixed methods online survey. Recruitment channels included professional associations and networks, charities, and social media. Quantitative findings were reported with descriptive statistics, and content analysis conducted for qualitative data. RESULTS: 2,180 staff from a range of sectors, professions, and specialties participated. Immediate infection control concerns were highly salient for inpatient staff, new ways of working for community staff. Multiple rapid adaptations and innovations in response to the crisis were described, especially remote working. This was cautiously welcomed but found successful in only some clinical situations. Staff had specific concerns about many groups of service users, including people whose conditions are exacerbated by pandemic anxieties and social disruptions; people experiencing loneliness, domestic abuse and family conflict; those unable to understand and follow social distancing requirements; and those who cannot engage with remote care. CONCLUSION: This overview of staff concerns and experiences in the early COVID-19 pandemic suggests directions for further research and service development: we suggest that how to combine infection control and a therapeutic environment in hospital, and how to achieve effective and targeted tele-health implementation in the community, should be priorities. The limitations of our convenience sample must be noted