Crystal Symmetry Breaking in Few-Quintuple Bismuth Telluride Films: Applications in Nanometrology of Topological Insulators

We report results of micro-Raman spectroscopy investigation of the "graphene-like" mechanically exfoliated single-crystal bismuth telluride films with the thickness ranging from a few-nm-range to bulk limit. It is found that the optical phonon mode A1u, which is not-Raman active in bulk bismuth telluride crystals, appears in the atomically-thin films due to crystal-symmetry breaking. The intensity ratios of the out-of-plane A1u and A1g modes to the in-plane Eg mode grow with decreasing film thickness. The evolution of Raman signatures with the film thickness can be used for identification of bismuth telluride crystals with the thickness of few-quintuple layers, which are important for topological insulator and thermoelectric applications.Comment: 13 pages, 2 tables, 3 figures; to be presented at MRS Spring Meeting, 201

Micro-Raman Spectroscopy of Mechanically Exfoliated Few-Quintuple Layers of Bi(2)Te(3), Bi(2)Se(3) and Sb(2)Te(3) Materials

Bismuth telluride - Bi(2)Te(3)- and related compounds have recently attracted strong interest owing to the discovery of the topological insulator properties in many members of this family of materials. The few-quintuple films of these materials are particularly interesting from the physics point of view. We report results of the micro-Raman spectroscopy study of the "graphene-like" exfoliated few-quintuple layers of Bi(2)Te(3), Bi(2)Se(3) and Sb(2)Te(3). It is found that crystal symmetry breaking in few-quintuple films results in appearance of A1u-symmetry Raman peaks, which are not active in the bulk crystals. The scattering spectra measured under the 633-nm wavelength excitation reveals a number of resonant features, which could be used for analysis of the electronic and phonon processes in these materials. In order to elucidate the influence of substrates on the few-quintuple-thick topological insulators we examined the Raman spectra of these films placed on mica, sapphire and hafnium-oxide substrates. The obtained results help to understand the physical mechanisms of Raman scattering in the few-quintuple-thick films and can be used for nanometrology of topological insulator films on various substrates.Comment: 19 pages; 7 figure

Fatigue degradation and electric recovery in Silicon solar cells embedded in photovoltaic modules

Cracking in Silicon solar cells is an important factor for the electrical power-loss of photovoltaic modules. Simple geometrical criteria identifying the amount of inactive cell areas depending on the position of cracks with respect to the main electric conductors have been proposed in the literature to predict worst case scenarios. Here we present an experimental study based on the electroluminescence (EL) technique showing that crack propagation in monocrystalline Silicon cells embedded in photovoltaic (PV) modules is a much more complex phenomenon. In spite of the very brittle nature of Silicon, due to the action of the encapsulating polymer and residual thermo-elastic stresses, cracked regions can recover the electric conductivity during mechanical unloading due to crack closure. During cyclic bending, fatigue degradation is reported. This pinpoints the importance of reducing cyclic stresses caused by vibrations due to transportation and use, in order to limit the effect of cracking in Silicon cells

Perceptions of women, their husbands and healthcare providers about anemia in rural Pakistan: Findings from a qualitative exploratory study

Background: In Pakistan, there is a dearth of literature on the perceptions of anemia among women of reproductive age (WRA). This study was undertaken to explore the perceptions of women, their husbands, and healthcare providers about anemia, its possible causes, and how anemia impacts maternal and child health in Thatta, Pakistan.Methods: A qualitative study was conducted in Thatta, Pakistan from September to December 2018. Using a pre-tested semi-structured interview (SSI), we collected data to understand their definitions of anemia through ten focus group discussions (FGDs) with women and their partners and ten primary informant interviews (KIIs) with healthcare providers. We identified six major themes: (I) Knowledge and awareness of anemia, (II) Causes and consequences of Anemia, (III) Dietary practices, (IV) Knowledge and practices regarding the use of iron-folic acid supplements, (V) Factors influencing prevention and control of anemia and (VI) Women\u27s health behavior. We analyzed the data through thematic analysis using NVivo 10 software.Results: Most community members were not aware of the term anemia but described anemia as a condition characterized by \u27blood deficiency\u27 in the body. All study participants perceived anemia as an important health problem tending to cause adverse outcomes among WRA and their children. Study participants perceived gutka (chewable tobacco) consumption as an important cause of anemia. Healthcare providers identified short inter-pregnancy intervals, lack of family planning, poor health-seeking behavior, and consumption of unhealthy food as causes of anemia in the district. Consumption of unhealthy food might not be related to related to a poorer knowledge of iron-deficient foods, but economic constraints. This was further endorsed by the healthcare providers who mentioned that most women were too poor to afford iron-rich foods. All men and women were generally well versed with the sources of good nutrition to be consumed by WRA to prevent anemia.Conclusion: The findings suggest that the government should plan to develop strategies for poverty-stricken and vulnerable rural women and plan health awareness programs to improve dietary practices, compliance with supplements, and health-seeking behavior among women of reproductive age. There is a need to develop effective counseling strategies and context-specific health education sessions to improve the health-seeking behavior of women and men in the Thatta district of Pakistan. Besides, there is need to address social determinants of health such as poverty that pushes women of poorer socioeconomic strata to eat less nutritious foods and have more anaemia. Therefore, a comprehensive and robust strategic plan need to be adopted by government that focuses not only on the awareness programs, but also aim to reduce inequities that lead to pregnant women eat iron-poor foods, which, in turn, forces them to become anemic

Standard operating procedure for curation and clinical interpretation of variants in cancer

Manually curated variant knowledgebases and their associated knowledge models are serving an increasingly important role in distributing and interpreting variants in cancer. These knowledgebases vary in their level of public accessibility, and the complexity of the models used to capture clinical knowledge. CIViC (Clinical Interpretation of Variants in Cancer - www.civicdb.org) is a fully open, free-to-use cancer variant interpretation knowledgebase that incorporates highly detailed curation of evidence obtained from peer-reviewed publications and meeting abstracts, and currently holds over 6300 Evidence Items for over 2300 variants derived from over 400 genes. CIViC has seen increased adoption by, and also undertaken collaboration with, a wide range of users and organizations involved in research. To enhance CIViC\u27s clinical value, regular submission to the ClinVar database and pursuit of other regulatory approvals is necessary. For this reason, a formal peer reviewed curation guideline and discussion of the underlying principles of curation is needed. We present here the CIViC knowledge model, standard operating procedures (SOP) for variant curation, and detailed examples to support community-driven curation of cancer variants

Phonon Transport in Graphene

Properties of phonons - quanta of the crystal lattice vibrations - in graphene have attracted strong attention of the physics and engineering communities. Acoustic phonons are the main heat carriers in graphene near room temperature while optical phonons are used for counting the number of atomic planes in Raman experiments with few-layer graphene. It was shown both theoretically and experimentally that transport properties of phonons, i.e. energy dispersion and scattering rates, are substantially different in the quasi two-dimensional system such as graphene compared to basal planes in graphite or three-dimensional bulk crystals. The unique nature of two-dimensional phonon transport translates to unusual heat conduction in graphene and related materials. In this review we outline different theoretical approaches developed for phonon transport in graphene, discuss contributions of the in-plane and cross-plane phonon modes and provide comparison with available experimental thermal conductivity data. Particular attention is given to analysis of recent theoretical results for the phonon thermal conductivity of graphene and few-layer graphene, and the effects of the strain, defects and isotopes on the phonon transport in these systems.Comment: invited review; 41 pages; 9 figures; 3 table

Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials

Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range - of over five orders of magnitude - from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. A special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe prospects of applications of graphene and carbon materials for thermal management of electronics.Comment: Review Paper; 37 manuscript pages; 4 figures and 2 boxe

CIViCdb 2022: Evolution of an open-access cancer variant interpretation knowledgebase

CIViC (Clinical Interpretation of Variants in Cancer; civicdb.org) is a crowd-sourced, public domain knowledgebase composed of literature-derived evidence characterizing the clinical utility of cancer variants. As clinical sequencing becomes more prevalent in cancer management, the need for cancer variant interpretation has grown beyond the capability of any single institution. CIViC contains peer-reviewed, published literature curated and expertly-moderated into structured data units (Evidence Items) that can be accessed globally and in real time, reducing barriers to clinical variant knowledge sharing. We have extended CIViC\u27s functionality to support emergent variant interpretation guidelines, increase interoperability with other variant resources, and promote widespread dissemination of structured curated data. To support the full breadth of variant interpretation from basic to translational, including integration of somatic and germline variant knowledge and inference of drug response, we have enabled curation of three new Evidence Types (Predisposing, Oncogenic and Functional). The growing CIViC knowledgebase has over 300 contributors and distributes clinically-relevant cancer variant data currently representing \u3e3200 variants in \u3e470 genes from \u3e3100 publications