Observation of a (2X8) surface reconstruction on Si_(1-x)Ge_x alloys grown on (100) Si by molecular beam epitaxy

We present evidence supporting the formation of a new, (2×8) surface reconstruction on Si_(1−x)Ge_x alloys grown on (100) Si substrates by molecular‐beam epitaxy. Surfaces of Si_(1−x)Ge_x alloys were studied using reflection high‐energy electron diffraction (RHEED) and low‐energy electron diffraction (LEED) techniques. RHEED patterns from samples with Ge concentrations, x, falling within the range 0.10–0.30 and grown at temperatures between 350 and 550 °C, exhibit n/8 fractional‐order diffraction streaks in addition to the normal (2×1) pattern seen on (100) Si. The presence of fractional‐order diffracted beams is indicative of an eight‐fold‐periodic modulation in electron scattering factor across the alloy surface. LEED patterns from surfaces of samples grown under similar conditions are entirely consistent with these results. In addition, the LEED patterns support the conclusion that the modulation is occurring in the direction of the dimer chains of a (2×1) reconstruction. We have examined the thermal stability of the (2×8) reconstruction and have found that it reverts to (2×1) after annealing to 700 °C and reappears after the sample temperature is allowed to cool below 600 °C. Such behavior suggests that the reconstruction is a stable, ordered phase for which the pair‐correlation function of surface Ge atoms exhibits an eightfold periodicity in the "1" direction of a Si‐like (2×1) reconstruction. We also present a simulation in the kinematic approximation, confirming the validity of our interpretation of these finding

Extracting the depolarization coefficient D_NN from data measured with a full acceptance detector

The spin transfer from vertically polarized beam protons to Lambda or Sigma hyperons of the associated strangeness production pp -> pK Lambda (Sigma) is described with the depolarization coefficient D_NN. As the polarization of the hyperons is determined by their weak decays, detectors, which have a large acceptance for the decay particles, are needed. In this paper a formula is derived, which describes the depolarization coefficient D_NN by count rates of a 4 pi detector. It is shown, that formulas, which are given in publications for detectors with restricted acceptance, are specific cases of this formula for a 4 pi detector.Comment: Accepted for publication by Nuclear Instruments and Methods in Physics Research Section

Mental Health Treatment Seeking Patterns and Preferences of Appalachian Women with Depression

This qualitative study explored social-cultural factors that shape treatment seeking behaviors among depressed rural, low-income women in Appalachia—a region with high rates of depression and a shortage of mental health services. Recent research shows that increasingly rural women are receiving some form of treatment and identifying their symptoms as depression. Using purposive sampling, investigators recruited 28 depressed low-income women living in Appalachian Kentucky and conducted semistructured interviews on participants’ perceptions of depression and treatment seeking. Even in this sample of women with diverse treatment behaviors (half reported current treatment), participants expressed ambivalence about treatment and its potential to promote recovery. Participants stressed that poor treatment quality—not merely access—limited their engagement in treatment and at times reinforced their depression. While women acknowledged the stigma of depression, they indicated that their resistance to seek help for their depression was influenced by the expectation of women’s self-reliance in the rural setting and the gendered taboo against negative thinking. Ambivalence and stigma led women to try to cope independently, resulting in further isolation. This study’s findings reiterate the need for improved quality and increased availability of depression treatment in rural areas. In addition, culturally appropriate depression interventions must acknowledge rural cultural values of self-reliance and barriers to obtaining social support that lead many women to endure depression in isolation

Center of Mass Motion of Short-Range Correlated Nucleon Pairs Studied Via the A(e, e\u27pp) Reaction

Short-range correlated (SRC) nucleon pairs are a vital part of the nucleus, accounting for almost all nucleons with momentum greater than the Fermi momentum (kF). A fundamental characteristic of SRC pairs is having large relative momenta as compared to kF, and smaller center of mass (c.m.) which indicates a small separation distance between the nucleons in the pair. Determining the c.m. momentum distribution of SRC pairs is essential for understanding their formation process. We report here on the extraction of the c.m. motion of proton-proton (pp) SRC pairs in carbon and, for the first time in heavier and ansymetric nuclei: aluminum, iron, and lead, from measurements of the A(e,e′pp) reaction. We find that the pair c.m. motion for these nuclei can be described by a three-dimensional Gaussian with a narrow width ranging from 140 to 170  MeV/c , approximately consistent with the sum of two mean-field nucleon momenta. Comparison with calculations appears to show that the SRC pairs are formed from mean-field nucleons in specific quantum states

LINFA: a Python library for variational inference with normalizing flow and annealing

Variational inference is an increasingly popular method in statistics and machine learning for approximating probability distributions. We developed LINFA (Library for Inference with Normalizing Flow and Annealing), a Python library for variational inference to accommodate computationally expensive models and difficult-to-sample distributions with dependent parameters. We discuss the theoretical background, capabilities, and performance of LINFA in various benchmarks. LINFA is publicly available on GitHub at https://github.com/desResLab/LINFA

Ensamble de macroinvertebrados bentónicos como indicadores de calidad de agua a través de la aplicación de un índice biótico modificado en un contexto espacio-estacional en una cuenca costera del sur de Chile

Tapia, J (Tapia, Jaime).Univ Talca, Inst Chem & Nat Resources, Talca, Chile.The water quality in a Southern Chile river was characterized using the Biotic Index in a spatio-seasonal context, to analyze the composition and distribution of benthic macroinvertebrates and their correlation with 14 physico-chemical parameters. Sampling was done over a year at 5 sampling stations in the basin of the Boroa River. A total of 77 taxa were recorded, with the most represented orders being the Ephemeroptera (43.30%), Diptera (24.16%) and Plecoptera (18.03%). The most abundant species were Meridialaris diguillina, Nousia maculata (Ephemeroptera) and Limnoperla jaffueli (Plecoptera). According to the modified FBI (Family Biotic Index), the findings indicated excellent, very good and good water quality, the latter quality being registered principally in winter. Likewise, the physico-chemical parameters indicated exceptional water quality. These results suggested a low level of anthropogenic impact in the basin. Applying the modified Hilsenhoff Biotic Index based on macroinvertebrates, the influence of seasonality on water quality was evident

Laser Calibration System for Time of Flight Scintillator Arrays

A laser calibration system was developed for monitoring and calibrating time of flight (TOF) scintillating detector arrays. The system includes setups for both small- and large-scale scintillator arrays. Following test-bench characterization, the laser system was recently commissioned in experimental Hall B at the Thomas Jefferson National Accelerator Facility for use on the new Backward Angle Neutron Detector (BAND) scintillator array. The system successfully provided time walk corrections, absolute time calibration, and TOF drift correction for the scintillators in BAND. This showcases the general applicability of the system for use on high-precision TOF detectors.Comment: 11 pages, 11 figure