The pressure-amorphized state in zirconium tungstate: a precursor to decomposition

In contrast to widely accepted view that pressure-induced amorphization arises due to kinetic hindrance of equilibrium phase transitions, here we provide evidence that the metastable pressure-amorphized state in zirconium tungstate is a precursor to decomposition of the compound into a mixture of simple oxides. This is from the volume collapse ΔV across amorphization, which is obtained for the first time by measuring linear dimensions of irreversibly amorphized samples during their recovery to the original cubic phase upon isochronal annealing up to 1000 K. The anomalously large ΔV of 25.7 ± 1.2% being the same as that expected for the decomposition indicates that this amorphous state is probably a precursor to kinetically hindered decomposition. A P–T diagram of the compound is also proposed

Reentrant phase transition in charged colloidal suspensions

We report the observation of a novel phase transition in dilute aqueous suspensions of polystyrene particles as a function of ionic impurity concentration C. The suspension phase separates into dense and rare phases only for a restricted range of C which depends on particle concentration n. The dense phase has liquidlike or crystalline order depending on n and C. Free energies of the homogeneous and the phase-separated states are calculated with an effective interparticle potential. The calculated phase diagram is in qualitative agreement with the present experimental results

Genome-wide identification, organization and phylogenetic analysis of Dicer-like, Argonaute and RNA-dependent RNA Polymerase gene families and their expression analysis during reproductive development and stress in rice

<p>Abstract</p> <p>Background</p> <p>Important developmental processes in both plants and animals are partly regulated by genes whose expression is modulated at the post-transcriptional level by processes such as RNA interference (RNAi). Dicers, Argonautes and RNA-dependent RNA polymerases (RDR) form the core components that facilitate gene silencing and have been implicated in the initiation and maintenance of the trigger RNA molecules, central to process of RNAi. Investigations in eukaryotes have revealed that these proteins are encoded by variable number of genes with plants showing relatively higher number in each gene family. To date, no systematic expression profiling of these genes in any of the organisms has been reported.</p> <p>Results</p> <p>In this study, we provide a complete analysis of rice Dicer-like, Argonaute and RDR gene families including gene structure, genomic localization and phylogenetic relatedness among gene family members. We also present microarray-based expression profiling of these genes during 14 stages of reproductive and 5 stages of vegetative development and in response to cold, salt and dehydration stress. We have identified 8 Dicer-like (<it>OsDCLs</it>), 19 Argonaute (<it>OsAGOs</it>) and 5 RNA-dependent RNA polymerase (<it>OsRDRs</it>) genes in rice. Based on phylogeny, each of these genes families have been categorized into four subgroups. Although most of the genes express both in vegetative and reproductive organs, 2 <it>OsDCLs</it>, 14 <it>OsAGOs </it>and 3 <it>OsRDRs </it>were found to express specifically/preferentially during stages of reproductive development. Of these, 2 <it>OsAGOs </it>exhibited preferential up-regulation in seeds. One of the Argonautes (<it>OsAGO2</it>) also showed specific up-regulation in response to cold, salt and dehydration stress.</p> <p>Conclusion</p> <p>This investigation has identified 23 rice genes belonging to DCL, Argonaute and RDR gene families that could potentially be involved in reproductive development-specific gene regulatory mechanisms. These data provide an insight into probable domains of activity of these genes and a basis for further, more detailed investigations aimed at understanding the contribution of individual components of RNA silencing machinery during reproductive phase of plant development.</p

Amorphization and decomposition of scandium molybdate at high pressure

The behavior of negative thermal-expansion material scandium molybdate Sc2(MoO4)3 is investigated at high pressure (HP) and high temperature (HT) using x-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The compound exhibits unusually high compressibility (bulk modulus ~6 GPa) and undergoes amorphization at 12 GPa. On the other hand, in situ laser heating of amorphous samples inside the diamond-anvil cell is found to result in crystalline diffraction pattern and Raman spectrum different from those of the original compound. Upon release of the pressure subsequent to laser heating, the Raman spectrum and the diffraction pattern remain unchanged. Matching of several of the diffraction lines and Raman peaks in the laser-heated samples with those of MoO3 suggests a solid-state decomposition of the parent compound under HP-HT conditions into MoO3 and other compounds. Other diffraction lines are found to correspond to Sc2Mo2O9, Sc2O3, and the parent compound. Quantitative analysis of the characteristic x-ray emission from different regions of the sample during scanning electron microscopic observations is used for obtaining the compositions of the daughter compounds. The stoichiometries of two main phases are found to be close to those of MoO3 and Sc2Mo2O9. These results support the model that the pressure-induced amorphization occurred in this system because a pressure-induced decomposition was kinetically constrained

MADS-box gene family in rice: genome-wide identification, organization and expression profiling during reproductive development and stress

<p>Abstract</p> <p>Background</p> <p>MADS-box transcription factors, besides being involved in floral organ specification, have also been implicated in several aspects of plant growth and development. In recent years, there have been reports on genomic localization, protein motif structure, phylogenetic relationships, gene structure and expression of the entire MADS-box family in the model plant system, <it>Arabidopsis</it>. Though there have been some studies in rice as well, an analysis of the complete MADS-box family along with a comprehensive expression profiling was still awaited after the completion of rice genome sequencing. Furthermore, owing to the role of MADS-box family in flower development, an analysis involving structure, expression and functional aspects of MADS-box genes in rice and <it>Arabidopsis </it>was required to understand the role of this gene family in reproductive development.</p> <p>Results</p> <p>A genome-wide molecular characterization and microarray-based expression profiling of the genes encoding MADS-box transcription factor family in rice is presented. Using a thorough annotation exercise, 75 MADS-box genes have been identified in rice and categorized into MIKC^c, MIKC*, Mα, Mβ and Mγ groups based on phylogeny. Chromosomal localization of these genes reveals that 16 MADS-box genes, mostly MIKC^c-type, are located within the duplicated segments of the rice genome, whereas most of the M-type genes, 20 in all, seem to have resulted from tandem duplications. Nine members belonging to the Mβ group, which was considered absent in monocots, have also been identified. The expression profiles of all the MADS-box genes have been analyzed under 11 temporal stages of panicle and seed development, three abiotic stress conditions, along with three stages of vegetative development. Transcripts for 31 genes accumulate preferentially in the reproductive phase, of which, 12 genes are specifically expressed in seeds, and six genes show expression specific to panicle development. Differential expression of seven genes under stress conditions is also evident. An attempt has been made to gain insight into plausible functions of rice MADS-box genes by collating the expression data of functionally validated genes in rice and <it>Arabidopsis</it>.</p> <p>Conclusion</p> <p>Only a limited number of MADS genes have been functionally validated in rice. A comprehensive annotation and transcriptome profiling undertaken in this investigation adds to our understanding of the involvement of MADS-box family genes during reproductive development and stress in rice and also provides the basis for selection of candidate genes for functional validation studies.</p

Laser-Raman spectroscopic studies on graphite from East Antarctica

We report here the Laser-Raman spectroscopic data on the carbonaceous matter (CM) from Schirmacher Oasis (70°45\u27S, 11°40\u27E), East Antarctica for the first time. The sample was collected from the Precambrian rock, which consists of garnet-biotite gneiss. The first order Laser-Raman spectra of the sample shows a strong well-ordered Raman peak (0) at 1581 cm^ and a weak broad peak due to disorder (D) at 1354 cm^. The intensity ratio disordered-to-ordered Raman peak (D/O)_ has been used to estimate the in-plan crystallite size (L_a) of the graphite. The experimental values of D/0=0.143 and D/D+O=0.125 indicate that the CM is well crystallized graphite, thereby indicating the high metamorphic grade of the host rocks. Powder X-ray diffraction studies on the same sample of CM also indicate that the CM is well-crystalline hexagonal graphite with d_=0.3354 nm. The structural parameters obtained by Raman spectroscopic method and the estimated in-plane crystallite size (L_a=298A) indicate that the metamorphic grade of the host rock of the studied sample falls in the upper sillimanite zone. The present study suggests that the peak metamorphic temperature of the host rock could be in the temperature range of about 700℃

Aggregation and precipitation stages in NaCl:Pb<SUP>2+</SUP> studied by UV absorption

UV absorption measurements during isochronal annealing of homogenised and as-grown single crystals show two distinct stages in NaCl:Pb2+ where number density of free impurities reduce. With the help of our earlier light scattering results the low temperature stage has been attributed to aggregation of impurity-vacancy dipoles whereas the stage appearing at the higher temperature is assigned to the precipitation process

Reentrant Phase Transition in Charged Colloidal Suspensions

We report the observation of a novel phase transition in dilute aqueous suspensions of polystyrene particles as a function of ionic impurity concentration C. The suspension phase separates into dense and rare phases only for a restricted range of C which depends on particle concentration. The dense phase has liquidlike or crystalline order depending on n and C. Free energies of the homogeneous and the phase-separated states are calculated with an effective interparticle potential. The calculated phase diagram is in qualitative agreement with the present experimental results