465 research outputs found

    Tunnelling Characteristics of Stone-Wales Defects in Monolayers of Sn and Group-V Elements

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    Topological defects in ultrathin layers are often formed during synthesis and processing, thereby, strongly influencing their electronic properties . In this paper, we investigate the role of Stone-Wales (SW) defects in modifying the electronic properties of the monolayers of Sn and group-V elements. The calculated results find the electronic properties of stanene (monolayer of Sn atoms) to be strongly dependent on the concentration of SW-defects e.g., defective stanene has nearly zero band gap (~ 0.03 eV) for the defect concentration of 2.2 x 10^13 cm^-2 which opens up to 0.2 eV for the defect concentration of 3.7 x 10^13 cm^-2. In contrast, SW-defects appear to induce conduction states in the semiconducting monolayers of group-V elements. These conduction states act as channels for electron tunnelling, and the calculated tunnelling characteristics show the highest differential conductance for the negative bias with the asymmetric current-voltage characteristics. On the other hand, the highest differential conductance was found for the positive bias in stanene. Simulated STM topographical images of stanene and group-V monolayers show distinctly different features in terms of their cross-sectional views and distance-height profiles which can serve as fingerprints to identify the topological defects in the monolayers of group-IV and group-V elements in experiments.Comment: 18 pages, 5 figures, 1 tabl

    Reactivity of neutral and charged B13 clusters with O2: A theoretical study

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    The chemical reactivity of neutral, cationic, and anionic species of the gas phase B13 cluster with molecular oxygen, O2, was investigated using density functional theory. All three species of B 13 interact with an oxygen molecule to generate a variety of stable isomers, with those representing a dissociative chemisorption process forming the most stable configurations. Our results also show site-specific bonding of oxygen to the B13(+/0/-) cluster. The effect of sequential ionization on the formation of products is pronounced. In ionic B13 clusters, in addition to energetics, the spin of the reactants and products plays a vital role in determining the most favorable product channel. In addition, this study reveals a richness of phenomena requiring a unified consideration of energy, geometry, spin conversion, and details of the electronic structure not previously illustrated for the reactivity of boron clusters. © 2010 American Institute of Physics

    Sperm penetration assay and its correlation with semen analysis parameters

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    Background: Aim of current study was to determine whether the Sperm Penetration Assay (SPA) can be used as a test to discriminate the infertile male from fertile one. We have also correlated the SPA with semen analysis.Methods: Sperm characteristics namely Semen analysis and the sperm penetration assay were tested in 44 infertile and 10 fertile men. Sperm penetration assay was determined by using zona free hamster eggs.Results: With decreasing spermatozoa concentration in the semen there was significant decrease in percentage penetration of zona free Hamster eggs (p0.05).  Conclusions: The Sperm penetration assay could discriminate the infertile group from fertile group significantly (p<0.001). The test appeared to be highly reproducible and probably identifies a truly infertile male.

    Possible microlensing event in the direction of M31

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    The Cousin R and I band photometric observations of ~ 13' × 13' field in the direction of M31 galaxy have been carried out during 1999-2001 to search for microlensing events using pixel technique. Here we report a microlensing-like event, of which preliminary analysis indicates that it is a long duration (t1/2 ~ 66 days) event

    Adaptation and human migration, and evidence of agriculture coincident with changes in the Indian summer monsoon during the Holocene

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    Human societies have evolved through a complex system of climate and ecological interactions. Known records suggest intimate relationship of adaptations, mitigations and migrations to climate extremes leaving their impacts on human societies. The northwestern part of India provides such an example, where human civilizations flourished in the early Holocene along the major fluvial systems when the Indian summer (southwest) monsoon was much stronger and rainfall was higher over the Indian land mass. Summers were thus wetter, conducive to agriculture and ecodiversity. Changes in the early civilizations in the Indian subcontinent had a close relation to changes in the monsoon climate over the past 10,000 years. The summer monsoon has weakened over the last 7000 years since its peak intensification in the early Holocene (10,000-7000 cal yrs BP). Discrete intervals of dry phases in the summer monsoon are visible in the proxy record of the monsoon winds from the marine sediments of the Arabian Sea, which had significant impact on human settlements in South Asia. The strongest aridity in the Indian subcontinent and extended periods of droughts at ca 5000- 4000 cal yrs BP seems to have triggered eastward human migrations towards the Ganga plain. Other times of monsoon weakening during the Holocene are coincident with the initial development of ponds, reservoirs and other rainwater harvesting structures that may have served as an adaptation to climate change

    Two Dimensional Allotropes of Arsenene with Wide Range of High and Anisotropic Carrier Mobility

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    Considering the rapid development of experimental techniques for fabricating 2D materials in recent years, various monolayers are expected to be experimentally realized in the near future. Motivated by the recent research activities focused on the honeycomb arsenene monolayers, stability and carrier mobility of non-honeycomb and porous allotropic arsenene are determined using first principles calculations. In addition to five honeycomb structures of arsenene, a total of eight other structures are considered in this study. An extensive analysis comprising energetics, phonon spectra and mechanical properties confirms that these structures are energetically and dynamically stable. All these structures are semiconductors with a broad range of band gap varying from ~1 eV to ~2.5 eV. Significantly, these monolayer allotropes possess anisotropic carrier mobilities as high as several hundred cm^{2}V^{-1}s^{-1} which is comparable with the well-known 2D materials such as black phosphorene and monolayer MoS_{2}. Combining such broad band gaps and superior carrier mobilities, these monolayer allotropes can be promising candidates for the superior performance of the next generation nanoscale devices. We further explore these monolayer allotropes for photocatalytic water splitting and find that arsenene monolayers have potential for usage as visible light driven photocatalytic water splitting.Comment: 31 pages, 8 figures, 3 table

    Age Sequence in Small Clusters Associated with Bright-Rimmed Clouds

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    Bright-rimmed clouds (BRCs) found in H II regions are probable sites of triggered star formation due to compression by ionization/shock fronts, and it is hypothesized that star formation proceeds from the exciting star(s) side outward of the HII region ("small-scale sequential star formation"). In order to quantitatively testify this hypothesis we undertook BVIc photometry of four BRC aggregates. The amounts of interstellar extinction and reddening for each star have been estimated by using the JHKs photometry. Then we constructed reddening-corrected V/V-Ic color-magnitude diagrams, where the age of each star has been derived. All the stars turned out to be a few tenths to a few Myr old. Although the scatters are large and the numbers of the sample stars are small, we found a clear trend that the stars inside or in the immediate vicinity of the bright rim are younger than those outside it in all the four aggregates, confirming the hypothesis in question.Comment: 10 pages, 2 figures; accepted for publication in PAS

    RNAi-Mediated Downregulation of Inositol Pentakisphosphate Kinase (IPK1) in Wheat Grains Decreases Phytic Acid Levels and Increases Fe and Zn Accumulation

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    Enhancement of micronutrient bioavailability is crucial to address the malnutrition in the developing countries. Various approaches employed to address the micronutrient bioavailability are showing promising signs, especially in cereal crops. Phytic acid (PA) is considered as a major antinutrient due to its ability to chelate important micronutrients and thereby restricting their bioavailability. Therefore, manipulating PA biosynthesis pathway has largely been explored to overcome the pleiotropic effect in different crop species. Recently, we reported that functional wheat inositol pentakisphosphate kinase (TaIPK1) is involved in PA biosynthesis, however, the functional roles of the IPK1 gene in wheat remains elusive. In this study, RNAi-mediated gene silencing was performed for IPK1 transcripts in hexaploid wheat. Four non-segregating RNAi lines of wheat were selected for detailed study (S3-D-6-1; S6-K-3-3; S6-K-6-10 and S16-D-9-5). Homozygous transgenic RNAi lines at T4 seeds with a decreased transcript of TaIPK1 showed 28–56% reduction of the PA. Silencing of IPK1 also resulted in increased free phosphate in mature grains. Although, no phenotypic changes in the spike was observed but, lowering of grain PA resulted in the reduced number of seeds per spikelet. The lowering of grain PA was also accompanied by a significant increase in iron (Fe) and zinc (Zn) content, thereby enhancing their molar ratios (Zn:PA and Fe:PA). Overall, this work suggests that IPK1 is a promising candidate for employing genome editing tools to address the mineral accumulation in wheat grains
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