Entanglement dynamics in the Lipkin-Meshkov-Glick model

The dynamics of the one-tangle and the concurrence is analyzed in the Lipkin-Meshkov-Glick model which describes many physical systems such as the two-mode Bose-Einstein condensates. We consider two different initial states which are physically relevant and show that their entanglement dynamics are very different. A semiclassical analysis is used to compute the one-tangle which measures the entanglement of one spin with all the others, whereas the frozen-spin approximation allows us to compute the concurrence using its mapping onto the spin squeezing parameter.Comment: 11 pages, 11 EPS figures, published versio

Entanglement in a second order quantum phase transition

We consider a system of mutually interacting spin 1/2 embedded in a transverse magnetic field which undergo a second order quantum phase transition. We analyze the entanglement properties and the spin squeezing of the ground state and show that, contrarily to the one-dimensional case, a cusp-like singularity appears at the critical point $\lambda_c$, in the thermodynamic limit. We also show that there exists a value $\lambda_0 \geq \lambda_c$ above which the ground state is not spin squeezed despite a nonvanishing concurrence.Comment: 4 pages, 4 EPS figures, minor corrections added and title change

Nonlinear response of superparamagnets with finite damping: an analytical approach

The strongly damping-dependent nonlinear dynamical response of classical superparamagnets is investigated by means of an analytical approach. Using rigorous balance equations for the spin occupation numbers a simple approximate expression is derived for the nonlinear susceptibility. The results are in good agreement with those obtained from the exact (continued-fraction) solution of the Fokker-Planck equation. The formula obtained could be of assistance in the modelling of the experimental data and the determination of the damping coefficient in superparamagnets.Comment: 7 PR pages, 2 figure

New determination of abundances and stellar parameters for a set of weak G-band stars

Weak G-band (wGb) stars are very peculiar red giants almost devoided of carbon and often mildly enriched in lithium. Despite their very puzzling abundance patterns, very few detailed spectroscopic studies existed up to a few years ago, preventing any clear understanding of the wGb phenomenon. We recently proposed the first consistent analysis of published data for 28 wGb stars and identified them as descendants of early A-type to late B-type stars, without being able to conclude on their evolutionary status or the origin of their peculiar abundance pattern. We used newly obtained high-resolution and high SNR spectra for 19 wGb stars in the southern and northern hemisphere to homogeneously derive their fundamental parameters, metallicities, as well as the spectroscopic abundances for Li, C, N, O, Na, Sr, and Ba. We also computed dedicated stellar evolution models that we used to determine the masses and to investigate the evolutionary status and chemical history of the stars in our sample. We confirm that the wGb stars are stars in the mass range 3.2 to 4.2 M$_\odot$. We suggest that a large fraction could be mildly evolved stars on the SGB currently undergoing the 1st DUP, while a smaller number of stars are more probably in the core He burning phase at the clump. After analysing their abundance pattern, we confirm their strong N enrichment anti-correlated with large C depletion, characteristic of material fully processed through the CNO cycle to an extent not known in other evolved intermediate-mass stars. However, we demonstrate here that such a pattern is very unlikely due to self-enrichment. In the light of the current observational constraints, no solid self-consistent pollution scenario can be presented either, leaving the wGb puzzle largely unsolved.Comment: 19 pages , 14 figures, accepted for publication in Astronomy & Astrophysic

Electrostatic Design and Characterization of a 200 keV Photogun and Wien Spin Rotator

High-energy nuclear physics experiments at the Jefferson Lab Continuous Electron Beam Accelerator Facility (CEBAF) require high spin-polarization electron beams produced from strained super-lattice GaAs photocathodes activated to negative electron affinity in a high voltage photogun operating at 130 kV dc. A pair of Wien filter spin rotators in the injector provides precise control of the electron beam polarization at the end station target. An upgrade of the CEBAF injector to better support the upcoming Moller experiment requires increasing the electron beam energy to 200 keV, resulting in better transmission through injector apertures and improved photocathode lifetime. In addition, the energy increase is expected to reduce unwanted helicity correlated intensity and position systematics. These requirements led to the design of a shielding electrode described in this work, which minimizes the electric field at the triple-point junction and linearizes the potential along the insulator, thus reducing the risk of field emission induced insulator arcing. The Wien spin rotator design was modified for increasing the electric field from 1.6 to 2.7 MV/m and the magnetic field from 9.1 to 13 mT. The upgrades required detailed modeling in Solidworks, electrostatic simulations using CST, beam dynamics using GPT, device implementation, and in situ high voltage characterization of the world’s first 200 keV polarized photoelectron gun and compatible Wien filter spin rotator

Exploring the genetic resources of Lens and Rhizobium to improve the biological nitrogen fixation (BNF) ability in the lentil crop

Lentil plants (Lens culinaris) have the ability to obtain most of the N they need from N fixation by establishing an efficient symbiotic relationship with Rhizobium. Plant-based diets are gaining the recognition they deserve for sustainability and producing legumes without the use of synthetic N fertilizers is the most sustainable approach. The N fixing ability of representative lentil cultivars, as well as accessions from 6 wild Lens species, was evaluated to determine the potential for wild germplasm to contribute positively to breeding for improved BNF. The contributions of diverse Rhizobium strains from 5 species to lentil productivity under local field conditions was also investigated. Subsequently, the level of specificity of the interactions between Lens accessions and Rhizobium strains with desirable N fixing abilities was explored. How traits related to N fixation are inherited was determined in three interspecific RIL populations from parents displaying contrasting phenotypes. Differential N fixing ability was found among cultivars and wild accessions; no particular species stood out. Wild accessions exhibited indeterminate nodulation, root modifications that responded to different N sources, higher seed percentage protein content, and yields comparable to plants fertilized with synthetic N. CDC Greenstar was the only cultivar with similar yield when inoculated or fertilized. CDC Maxim inoculated with the strain NZLR-24 (Rhizobium leguminosarum bv. viciae) had 9% higher yield under field conditions compared to when inoculated the commercial strain BASF 1435 (Rlv) and 15% more compared to a non-inoculated treatment. Some wild accessions demonstrated a promiscuous ability to efficiently fix N with a broad set of strains, but no cultivar did. The higher effective capacity of the strain NZLR-24 (Rlv) was also evident when used to inoculate Lens from 6 species, making it a suitable option for improved inoculants in the Northern Great Plains, as well as showing its value for selection in future breeding efforts. The strain Oyali B (Rlv) was also noteworthy for its superior interaction with wild Lens, and it is an attractive wild-type resource. Sixteen QTL were identified for nodulation traits among the three interspecific populations; eight were meta-QTL found across two or more populations. Chromosomes 1 and 6 had Meta-QTL for number of nodules, nodule weight and specific nodule weight. Chromosome 7 had one for specific nodule weight. This study establishes the necessary groundwork for understanding the role that exotic germplasm can play for the breeding of better N fixation ability in the lentil crop

26Al yields from rotating Wolf--Rayet star models

We present new $^{26}$Al stellar yields from rotating Wolf--Rayet stellar models which, at solar metallicity, well reproduce the observed properties of the Wolf-Rayet populations. These new yields are enhanced with respect to non--rotating models, even with respect to non--rotating models computed with enhanced mass loss rates. We briefly discuss some implications of the use of these new yields for estimating the global contribution of Wolf-Rayet stars to the quantity of $^{26}$Al now present in the Milky Way.Comment: 6 pages, 2 figures, to appear in New Astronomy Review

Head-mounted display-based therapies for adults post-stroke: A systematic review and meta-analysis

Immersive virtual reality techniques have been applied to the rehabilitation of patients after stroke, but evidence of its clinical effectiveness is scarce. The present review aims to find studies that evaluate the effects of immersive virtual reality (VR) therapies intended for motor function rehabilitation compared to conventional rehabilitation in people after stroke and make recommendations for future studies. Data from different databases were searched from inception until October 2020. Studies that investigated the effects of immersive VR interventions on poststroke adult subjects via a head-mounted display (HMD) were included. These studies included a control group that received conventional therapy or another non-immersive VR intervention. The studies reported statistical data for the groups involved in at least the posttest as well as relevant outcomes measuring functional or motor recovery of either lower or upper limbs. Most of the studies found significant improvements in some outcomes after the intervention in favor of the virtual rehabilitation group. Although evidence is limited, immersive VR therapies constitute an interesting tool to improve motor learning when used in conjunction with traditional rehabilitation therapies, providing a non-pharmacological therapeutic pathway for people after stroke