916 research outputs found
Search for Thermoelectrics with High Figure of Merit in half-Heusler compounds with multinary substitution
In order to improve the thermoelectric performance of TiCoSb we have
substituted 50% of Ti equally with Zr and Hf at Ti site and Sb with Sn and Se
equally at Sb site. The electronic structure of Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5
is investigated using the full potential linearized augmented plane wave method
and the thermoelectric transport properties are calculated on the basis of
semi-classical Boltzmann transport theory. Our band structure calculations show
that Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 has semiconducting behavior with indirect
band gap value of 0.98 eV which follow the empirical rule of 18
valence-electron content to bring semiconductivity in half Heusler compounds,
indicating that one can have semiconducting behavior in multinary phase of half
Heusler compounds if they full fill the 18 VEC rule and this open-up the
possibility of designing thermoelectrics with high figure of merit in half
Heusler compounds. We show that at high temperature of around 700K
Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 has high thermoelectric figure of merit of ZT =
1.05 which is higher than that of TiCoSb (~ 0.95) suggesting that by going from
ternary to multinary phase system one can enhance the thermoelectric figure of
merit at higher temperatures
Theoretical Investigation on the Effect of multinary Isoelectronic Substitution on TiCoSb based half-Heusler alloys
To understand the effect of isoelectronic substitution on thermoelectric
properties of TiCoSb based half - Heusler (HH) alloys, we have systematically
studied the transport properties with substitution of Zr at Ti and Bi at Sb
sites. The electronic structure of TixZr1-xCoSbxBi1-x (x = 0.25, 0.5, 0.75) and
parent TiCoSb are investigated using the full potential linearized augmented
plane wave method and the thermoelectric transport properties are calculated on
the basis of semiclassical Boltzmann transport theory. The band analysis of the
calculated band structures reveal that TixZr1-xCoSbxBi1-x has semiconducting
behavior with indirect band gap at x = 0.25, 0.5 concentration and direct band
gap behavior at x = 0.75 concentration. The TixZr1-xCoSbxBi1-x (x = 0.25, 0.5,
0.75) compounds show smaller band gap values as compared to the pure TiCoSb.
The d electrons of Ti/Zr and Co dominate the electronic transport properties of
TixZr1-xCoSbxBi1-x system. All these systems follow the empirical rule of 18
valence-electron content to bring semiconductivity in HH alloys. The
isoelectronic substitution in TiCoSb can tune the band structure by shifting
the Fermi level. This provides us lot of possibilities to get the desired band
gap values for designing thermoelectrics with high efficiency. In this study we
have showed that the isoelectronic substitution at both Ti and Sb site of
TiCoSb has very small effect for increasing the ZT values and one should go for
isoelectronic substitution at any one sites of TiCoSb HH alloys alone to
improve ZT
Effect of multinary substitution on electronic and transport properties of TiCoSb based half-Heusler alloys
The electronic structures of TixZrx/2CoPbxTex, TixZrx/2Hfx/2CoPbxTex (x =
0.5), and the parent compound TiCoSb were investigated using the full potential
linearized augmented plane wave method. The thermoelectric transport properties
of these alloys are calculated on the basis of semi-classical Boltzmann
transport theory. From the band structure calculations we show that the
substitution of Zr,Hf in the Ti site and Pb and Te in the Sb site lower the
band gap value and also change the indirect band (IB) gap of TiCoSb to the
direct band (DB) gap. The calculated band gap of TiCoSb, TixZrx/2CoPbxTex, and
TixZrx/2Hfx/2CoPbxTex are 1.04 eV (IB), 0.92 eV (DB), and 0.93 eV (DB),
respectively. All these alloys follow the empirical rule of 18 valence-electron
content which is essential for bringing semiconductivity in half Heusler
alloys. It is shown that the substitution of Hf at the Ti site improve the ZT
value (~1.05) at room temperature, whereas there is no significant difference
in ZT is found at higher temperature. Based on the calculated thermoelectric
transport properties, we conclude that the appropriate concentration of Hf
substitution can further improve the thermoelectric performance of
TixZrx/2Hfx/2CoPbxTex
Diet of Bengal Tigers (Panthera tigris tigris) in Chitwan National Park, Nepal
We studied the diet of the Bengal tigers (Panthera tigris tigris) in Chitwan National Park, Nepal, by identifying 109 prey items from 85 tiger scats. Tigers in this region fed upon eight different mammal species. Chital (Axis axis) was the major prey with a frequency of 45% of the Tigers’ diet. The occurrence of other prey species included sambar (Cervus unicolor, 23%), wild pig (Sus scrofa, 15%), hog deer (Axis porcinus, 9%), barking deer (Muntiacus muntjak, 4%), and gaur (Bos gaurus, 2%). Tigers also hunted livestock, but this prey comprised a small component of the relative biomass (buffalo 5% and cow 2%). Our study suggests that the tiger depends mostly upon wild prey for its subsistence in the Chitwan National Park, but will also sporadically hunt livestock
Transcript profiling reveals diverse roles of auxin-responsive genes during reproductive development and abiotic stress in rice
Auxin influences growth and development in plants by altering gene expression. Many auxin-responsive genes have been characterized in Arabidopsis in detail, but not in crop plants. Earlier, we reported the identification and characterization of the members of the GH3, Aux/IAA and SAUR gene families in rice. In this study, whole genome microarray analysis of auxin-responsive genes in rice was performed, with the aim of gaining some insight into the mechanism of auxin action. A comparison of expression profiles of untreated and auxin-treated rice seedlings identified 315 probe sets representing 298 (225 upregulated and 73 downregulated) unique genes as auxin-responsive. Functional categorization revealed that genes involved in various biological processes, including metabolism, transcription, signal transduction, and transport, are regulated by auxin. The expression profiles of auxin-responsive genes identified in this study and those of the members of the GH3, Aux/IAA, SAUR and ARF gene families were analyzed during various stages of vegetative and reproductive (panicle and seed) development by employing microarray analysis. Many of these genes are, indeed, expressed in a tissue-specific or developmental stage-specific manner, and the expression profiles of some of the representative genes were confirmed by real-time PCR. The differential expression of auxin-responsive genes during various stages of panicle and seed development implies their involvement in diverse developmental processes. Moreover, several auxin-responsive genes were differentially expressed under various abiotic stress conditions, indicating crosstalk between auxin and abiotic stress signaling
E-waste Management-Suggested Solutions
Electronic waste has been identified as discarded computers, old television sets, electronic equipment, entertainment devices, mobile phones, and refrigerators. This definition mostly include used electronics. Because loads of surplus electronics are frequently not eliminated including goods, recyclable, and non-recyclable so several people apply the term "e-waste" broadly to all surplus electronics. Rapid changes in technology, changes in media, falling prices, and planned obsolescence have resulted in a fast-growing surplus of electronic waste around the globe. This paper has an objective to present an overview of the problem and tries to advocate some concrete solutions to tackle the issue
Molecular characterization and differential expression of cytokinin-responsive type-A response regulators in rice (Oryza sativa)
Background
The response regulators represent the elements of bacterial two-component system and have been characterized from dicot plants like Arabidopsis but little information is available on the monocots, including the cereal crops. The aim of this study was to characterize type-A response regulator genes from rice, and to investigate their expression in various organs as well as in response to different hormones, including cytokinin, and environmental stimuli.
Results
By analysis of the whole genome sequence of rice, we have identified ten genes encoding type-A response regulators based upon their high sequence identity within the receiver domain. The exon-intron organization, intron-phasing as well as chromosomal location of all the RT-PCR amplified rice (Oryza sativa) response regulator (OsRR) genes have been analyzed. The transcripts of OsRR genes could be detected by real-time PCR in all organs of the light- and dark-grown rice seedlings/plants, although there were quantitative differences. The steady-state transcript levels of most of the OsRR genes increased rapidly (within 15 min) on exogenous cytokinin application even in the presence of cycloheximide. Moreover, the expression of the OsRR6 gene was enhanced in rice seedlings exposed to salinity, dehydration and low temperature stress.
Conclusion
Ten type-A response regulator genes identified in rice, the model monocot plant, show overlapping/differential expression patterns in various organs and in response to light. The induction of OsRR genes by cytokinin even in the absence of de novo protein synthesis qualifies them to be primary cytokinin response genes. The induction of OsRR6 in response to different environmental stimuli indicates its role in cross-talk between abiotic stress and cytokinin signaling. These results provide a foundation for further investigations on specific as well as overlapping cellular functions of type-A response regulators in rice
Genome-wide identification, classification, evolutionary expansion and expression analyses of homeobox genes in rice
Homeobox genes play a critical role in regulating various aspects of plant growth and development. In the present study, we identified a total of 107 homeobox genes in the rice genome and grouped them into ten distinct subfamilies based upon their domain composition and phylogenetic analysis. A significantly large number of homeobox genes are located in the duplicated segments of the rice genome, which suggests that the expansion of homeobox gene family, in large part, might have occurred due to segmental duplications in rice. Furthermore, microarray analysis was performed to elucidate the expression profiles of these genes in different tissues and during various stages of vegetative and reproductive development. Several genes with predominant expression during various stages of panicle and seed development were identified. At least 37 homeobox genes were found to be differentially expressed significantly (more than two-fold; P <0.05) under various abiotic stress conditions. The results of the study suggest a critical role of homeobox genes in reproductive development and abiotic stress signaling in rice, and will facilitate the selection of candidate genes of agronomic importance for functional validation
Internet: A place for patent retrieval
Countries design patent laws according to their respective economic interest. Before one files intellectual property one should know the regimes under which his intellectual property is placed. Intellectual properties are always of intense debate. The basic reason for the controversies is due tolack of transdisciplinary approaches to address patent concepts. In this present mini-review, we are presenting some web links that will help any researcher to get acquainted with the rules and regulationof filling an intellectual property of some countries as internet is now viewed as the place form where retrieval of information is possible with in second
Overexpression of putative topoisomerase 6 genes from rice confers stress tolerance in transgenic Arabidopsis plants
DNA topoisomerase 6 (TOP6) belongs to a novel family of type II DNA topoisomerases present, other than in archaebacteria, only in plants. Here we report the isolation of full-length cDNAs encoding putative TOP6 subunits A and B from rice (Oryza sativa ssp. indica), preserving all the structural domains conserved among archaebacterial TOP6 homologs and eukaryotic meiotic recombination factor SPO11. OsTOP6A1 was predominantly expressed in prepollinated flowers. The transcript abundance of OsTOP6A2, OsTOP6A3 and OsTOP6B was also higher in prepollinated flowers and callus. The expression of OsTOP6A2, OsTOP6A3 and OsTOP6B was differentially regulated by the plant hormones, auxin, cytokinin, and abscisic acid. Yeast two-hybrid analysis revealed that the full-length OsTOP6B protein interacts with both OsTOP6A2 and OsTOP6A3, but not with OsTOP6A1. The nuclear localization of OsTOP6A3 and OsTOP6B was established by the transient expression of their β-glucuronidase fusion proteins in onion epidermal cells. Overexpression of OsTOP6A3 and OsTOP6B in transgenic Arabidopsis plants conferred reduced sensitivity to the stress hormone, abscisic acid, and tolerance to high salinity and dehydration. Moreover, the stress tolerance coincided with enhanced induction of many stress-responsive genes in transgenic Arabidopsis plants. In addition, microarray analysis revealed that a large number of genes are expressed differentially in transgenic plants. Taken together, our results demonstrate that TOP6 genes play a crucial role in stress adaptation of plants by altering gene expression
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