156 research outputs found

    Thermal effects on electron-phonon interaction in silicon nanostructures

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    Raman spectra from silicon nanostructures, recorded using excitation laser power density of 1.0 kW/cm^2, is employed here to reveal the dominance of thermal effects at temperatures higher than the room temperature. Room temperature Raman spectrum shows only phonon confinement and Fano effects. Raman spectra recorded at higher temperatures show increase in FWHM and decrease in asymmetry ratio with respect to its room temperature counterpart. Experimental Raman scattering data are analyzed successfully using theoretical Raman line-shape generated by incorporating the temperature dependence of phonon dispersion relation. Experimental and theoretical temperature dependent Raman spectra are in good agreement. Although quantum confinement and Fano effects persists, heating effects start dominating at higher temperatures than room tempaerature.Comment: 9 Pages, 3 Figures and 1 Tabl

    Spectroscopic investigation of quantum confinement effects in ion implanted silicon-on-sapphire films

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    Crystalline Silicon-on-Sapphire (SOS) films were implanted with boron (B+^+) and phosphorous (P+^+) ions. Different samples, prepared by varying the ion dose in the range 101410^{14} to 5 x 101510^{15} and ion energy in the range 150-350 keV, were investigated by the Raman spectroscopy, photoluminescence (PL) spectroscopy and glancing angle x-ray diffraction (GAXRD). The Raman results from dose dependent B+^+ implanted samples show red-shifted and asymmetrically broadened Raman line-shape for B+^+ dose greater than 101410^{14} ions cm2^{-2}. The asymmetry and red shift in the Raman line-shape is explained in terms of quantum confinement of phonons in silicon nanostructures formed as a result of ion implantation. PL spectra shows size dependent visible luminescence at \sim 1.9 eV at room temperature, which confirms the presence of silicon nanostructures. Raman studies on P+^+ implanted samples were also done as a function of ion energy. The Raman results show an amorphous top SOS surface for sample implanted with 150 keV P+^+ ions of dose 5 x 101510^{15} ions cm2^{-2}. The nanostructures are formed when the P+^+ energy is increased to 350 keV by keeping the ion dose fixed. The GAXRD results show consistency with the Raman results.Comment: 9 Pages, 6 Figures and 1 Table, \LaTex format To appear in SILICON(SPRINGER

    Assessment and comparison of four lab made tris-base extenders for preservation of Labrador retriever dog semen at 4ºC

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    131-139The present study was aimed to develop a most effective extender for long term storage of Labrador dog semen at 4oC. Tris-citric acid-fructose was supplemented with egg yolk (TEY), egg yolk plasma (TEYP), low density lipoproteins (TLDL) and coconut water (TCW) @10, 15 and 20; 10, 15 and 20; 11-15; and 25, 50 and 75 percent, respectively. Extended semen was stored at 4oC and analyzed for sperm attributes and lipid peroxidation. Values for motility, viability and plasma membrane integrity remained significantly (p < 0.05) higher in 15% TEY, 15% TEYP, 13% TLDL and 25%/50% TCW from 0 hr to 72 hrs of storage. It indicated superiority of 15% TEY, 15% TEYP, 13% TLDL and 25% /50% TCW over other concentrations for storage of Labrador dog semen at 4oC. A significant (p < 0.05) decline in motility, viability and membrane integrity was observed from 0-72 hrs of preservation in all extenders, but sperm attributes were still >50% at 72 hrs of preservation. Decline was comparatively less in 15% TEY, 15% TEYP, 25%/50% TCW and 13% TLDL compared to other concentrations. Values for acrosome integrity also differ significantly (p > 0.05) among different concentrations of extenders except TEY. Lipid peroxidation did not vary among different extenders except TEY. In conclusion, both 15% TEY and 15% TEYP were better than 13% TLDL and 25% TCW. TEY extender may be substituted with TEYP for preservation of dog semen at 4°C and further interventions may improve TLDL and TCW extenders

    Continuity of the measure of the spectrum for quasiperiodic Schrodinger operators with rough potentials

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    We study discrete quasiperiodic Schr\"odinger operators on \ell^2(\zee) with potentials defined by γ\gamma-H\"older functions. We prove a general statement that for γ>1/2\gamma >1/2 and under the condition of positive Lyapunov exponents, measure of the spectrum at irrational frequencies is the limit of measures of spectra of periodic approximants. An important ingredient in our analysis is a general result on uniformity of the upper Lyapunov exponent of strictly ergodic cocycles.Comment: 15 page

    Depression, anxiety, stress symptoms and their determinants among secondary students with vision impairment in rural Northwestern China during the COVID-19 pandemic

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    ObjectiveThe measures implemented to control the spread of Coronavirus disease 2019 (COVID-19) could affect children’s mental and vision health. Youth particularly from minority and socioeconomically disadvantaged backgrounds were more likely to be impacted by these measures. This study aimed to examine the mental health of children with vision impairment and associated factors in North-western China during the COVID-19 pandemic.MethodsA cross-sectional study was conducted among 2,036 secondary school children living in Ningxia Hui Autonomous Region. Participants completed a survey on sociodemographic and lifestyle information and answered the Chinese version of the 21-item Depression Anxiety Stress Scales (DASS-21) questionnaire. Presenting visual acuity was measured by a trained enumerator. Multivariate logistic regression analysis was used to identify potential risk factors for mental health problems.ResultsResponses from 1,992 (97.8%) children were included in the analysis after excluding those with incomplete mental health outcome data. The prevalence of depression, anxiety and stress symptoms within the dataset were 28.9, 46.4, and 22.3%, respectively. The distribution of children with different stress levels differed significantly between those with and without vision impairment (p = 0.03). Multivariable logistic regression analyses revealed that depression symptoms decreased with higher parental education (OR, 0.76, 95% confidence intervals (CI):0.63–0.96), longer sleep duration (OR, 0.90, 95% CI: 0.81–0.97) and longer study time (OR, 0.82, 95% CI: 0.74–0.91), whereas they increased with higher recreational screen time (OR, 1.19, 95% CI: 1.08–1.32). Anxiety symptoms decreased with higher parental education (OR, 0.80, 95% CI: 0.66–0.96) and increased with higher recreational screen time (OR, 1.15, 95% CI: 1.04–1.27) and being a left-behind child (OR, 1.26, 95% CI: 1.04–1.54). In addition, stress symptoms decreased with longer sleep duration (OR, 0.92, 95%CI: 0.85–0.99) and increased with higher number of siblings (OR, 1.10, 95% CI: 1.01–1.19), higher recreational screen time (OR, 1.15, 95% CI: 1.04–1.28) and older age (OR,1.12, 95% CI: 1.004–1.24).ConclusionA considerable proportion of our sample experienced mental health problems during the pandemic. Healthcare planners in China should consider interventions such as reducing recreational screen time, ensuring sufficient sleep, and timely detection of mental health symptoms among socioeconomically disadvantaged groups

    Strategic crossing of biomass and harvest index—source and sink—achieves genetic gains in wheat

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    To accelerate genetic gains in breeding, physiological trait (PT) characterization of candidate parents can help make more strategic crosses, increasing the probability of accumulating favorable alleles compared to crossing relatively uncharacterized lines. In this study, crosses were designed to complement “source” with “sink” traits, where at least one parent was selected for favorable expression of biomass and/or radiation use efficiency—source—and the other for sink-related traits like harvest-index, kernel weight and grains per spike. Female parents were selected from among genetic resources—including landraces and products of wide-crossing (i.e. synthetic wheat)—that had been evaluated in Mexico at high yield potential or under heat stress, while elite lines were used as males. Progeny of crosses were advanced to the F4 generation within Mexico, and F4-derived F5 and F6 generations were yield tested to populate four international nurseries, targeted to high yield environments (2nd and 3rd WYCYT) for yield potential, and heat stressed environments (2nd and 4th SATYN) for climate resilience, respectively. Each nursery was grown as multi-location yield trials. Genetic gains were achieved in both temperate and hot environments, with most new PT-derived lines expressing superior yield and biomass compared to local checks at almost all international sites. Furthermore, the tendency across all four nurseries indicated either the superiority of the best new PT lines compared with the CIMMYT elite checks, or the superiority of all new PT lines as a group compared with all checks, and in some cases, both. Results support—in a realistic breeding context—the hypothesis that yield and radiation use efficiency can be increased by improving source:sink balance, and validate the feasibility of incorporating exotic germplasm into mainstream breeding efforts to accelerate genetic gains for yield potential and climate resilience

    Radionuclide imaging of bone marrow disorders

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    Noninvasive imaging techniques have been used in the past for visualization the functional activity of the bone marrow compartment. Imaging with radiolabelled compounds may allow different bone marrow disorders to be distinguished. These imaging techniques, almost all of which use radionuclide-labelled tracers, such as 99mTc-nanocolloid, 99mTc-sulphur colloid, 111In-chloride, and radiolabelled white blood cells, have been used in nuclear medicine for several decades. With these techniques three separate compartments can be recognized including the reticuloendothelial system, the erythroid compartment and the myeloid compartment. Recent developments in research and the clinical use of PET tracers have made possible the analysis of additional properties such as cellular metabolism and proliferative activity, using 18F-FDG and 18F-FLT. These tracers may lead to better quantification and targeting of different cell systems in the bone marrow. In this review the imaging of different bone marrow targets with radionuclides including PET tracers in various bone marrow diseases are discussed

    Antioxidant activity of twenty five plants from Colombian biodiversity

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    The antioxidant activity of the crude n-hexane, dichloromethane, and methanol extracts from 25 species belonging to the Asteraceae, Euphorbiaceae, Rubiaceae, and Solanaceae families collected at natural reserves from the Eje Cafetero Ecorregión Colombia, were evaluated by using the spectrophotometric 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical-scavenging method. The strongest antioxidant activities were showed by the methanol and dichloromethane extracts from the Euphorbiaceae, Alchornea coelophylla (IC50 41.14 mg/l) and Acalypha platyphilla (IC50 111.99 mg/l), respectively. These two species had stronger DPPH radical scavenging activities than hydroquinone (IC50 151.19 mg/l), the positive control. The potential use of Colombian flora for their antioxidant activities is discussed
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