138 research outputs found
Giant Negative Thermal Expansion Induced by the Synergistic Effects of Ferroelectrostriction and Spin-Crossover in PbTiO3-Based Perovskites
The discovery of unusual negative thermal expansion (NTE) provides the
opportunity to control the common but much desired property of thermal
expansion, which is valuable not only in scientific interests but also in
practical applications. However, most of the available NTE materials are
limited to a narrow temperature range, and the NTE effect is generally weakened
by means of various modifications. Here, we report an enhanced NTE effect that
occurs over a wide temperature range (\alpha V = -5.24 * 10-5 {\deg}C^-1,
25-575 {\deg} C), and this NTE effect is accompanied by an abnormal enhanced
tetragonality, a large spontaneous polarization, and a G-type antiferromagnetic
ordering in the present perovskite-type ferroelectric of (1-x)PbTiO3-xBiCoO3.
Specifically, for the composition of 0.5PbTiO3-0.5BiCoO3, an extensive
volumetric contraction of ~4.8 % has been observed near the Curie temperature
of 700 {\deg}C, which represents the highest level in PbTiO3-based
ferroelectrics. According to our experimental and theoretical results, the
giant NTE originates from a synergistic effect of the ferroelectrostriction and
spin-crossover of cobalt on the crystal lattice. The actual NTE mechanism is
contrasted with previous functional NTE materials, in which the NTE is simply
coupled with one ordering such as electronic, magnetic, or ferroelectric
ordering. The present study sheds light on the understanding of NTE mechanisms
and it attests that NTE could be simultaneouslycoupled with different
orderings, which will pave a new way toward the design of large NTE materials.Comment: 30 page
Bulk charge density wave and electron-phonon coupling in superconducting copper oxychlorides
Bulk charge density waves (CDWs) are now reported in nearly all
high-temperature superconducting (HTS) cuprates, with the noticeable exception
of one particular family: the copper oxychlorides. Here, we used resonant
inelastic X-ray scattering (RIXS) to reveal a bulk CDW in these materials.
Combining RIXS with non-resonant IXS, we investigate the interplay between the
lattice excitations and the CDW, and evidence bond-stretching (BS) phonon
anomalies at the CDW wave-vector. We propose that such electron-phonon
anomalies occur in the presence of dispersive charge excitations emanating from
the CDW and interacting with the BS phonon. Our observations in a structurally
simple cuprate promises to better connect bulk and surface properties and
bridge the gap between theory and experiment
Superconductivity at 5.4 K in -BiPd
We investigate bulk superconductivity in a high-quality single crystal of
BiPd (-BiPd, space group; I4/mmm) at temperatures less than 5.4
K by exploring its electrical resistivity, magnetic susceptibility, and
specific heat. The temperature dependence of the electrical resistivity shows
convex-upward behaviors at temperatures greater than 40-50 K, which can be
explained by a parallel-resistor model. In addition, we demonstrate that this
material is a multiple-band/multiple-gap superconductor based on the
temperature dependences of the specific heat and the upper critical field.Comment: 4 pages, 3 figure
Deep Annotation of Populus trichocarpa microRNAs from Diverse Tissue Sets
Populus trichocarpa is an important woody model organism whose entire genome has been sequenced. This resource has facilitated the annotation of microRNAs (miRNAs), which are short non-coding RNAs with critical regulatory functions. However, despite their developmental importance, P. trichocarpa miRNAs have yet to be annotated from numerous important tissues. Here we significantly expand the breadth of tissue sampling and sequencing depth for miRNA annotation in P. trichocarpa using high-throughput smallRNA (sRNA) sequencing. miRNA annotation was performed using three individual next-generation sRNA sequencing runs from separate leaves, xylem, and mechanically treated xylem, as well as a fourth run using a pooled sample containing vegetative apices, male flowers, female flowers, female apical buds, and male apical and lateral buds. A total of 276 miRNAs were identified from these datasets, including 155 previously unannotated miRNAs, most of which are P. trichocarpa specific. Importantly, we identified several xylem-enriched miRNAs predicted to target genes known to be important in secondary growth, including the critical reaction wood enzyme xyloglucan endo-transglycosylase/hydrolase and vascular-related transcription factors. This study provides a thorough genome-wide annotation of miRNAs in P. trichocarpa through deep sRNA sequencing from diverse tissue sets. Our data significantly expands the P. trichocarpa miRNA repertoire, which will facilitate a broad range of research in this major model system
Characterization of transcriptome dynamics during watermelon fruit development: sequencing, assembly, annotation and gene expression profiles
<p>Abstract</p> <p>Background</p> <p>Cultivated watermelon [<it>Citrullus lanatus </it>(Thunb.) Matsum. & Nakai var. <it>lanatus</it>] is an important agriculture crop world-wide. The fruit of watermelon undergoes distinct stages of development with dramatic changes in its size, color, sweetness, texture and aroma. In order to better understand the genetic and molecular basis of these changes and significantly expand the watermelon transcript catalog, we have selected four critical stages of watermelon fruit development and used Roche/454 next-generation sequencing technology to generate a large expressed sequence tag (EST) dataset and a comprehensive transcriptome profile for watermelon fruit flesh tissues.</p> <p>Results</p> <p>We performed half Roche/454 GS-FLX run for each of the four watermelon fruit developmental stages (immature white, white-pink flesh, red flesh and over-ripe) and obtained 577,023 high quality ESTs with an average length of 302.8 bp. <it>De novo </it>assembly of these ESTs together with 11,786 watermelon ESTs collected from GenBank produced 75,068 unigenes with a total length of approximately 31.8 Mb. Overall 54.9% of the unigenes showed significant similarities to known sequences in GenBank non-redundant (nr) protein database and around two-thirds of them matched proteins of cucumber, the most closely-related species with a sequenced genome. The unigenes were further assigned with gene ontology (GO) terms and mapped to biochemical pathways. More than 5,000 SSRs were identified from the EST collection. Furthermore we carried out digital gene expression analysis of these ESTs and identified 3,023 genes that were differentially expressed during watermelon fruit development and ripening, which provided novel insights into watermelon fruit biology and a comprehensive resource of candidate genes for future functional analysis. We then generated profiles of several interesting metabolites that are important to fruit quality including pigmentation and sweetness. Integrative analysis of metabolite and digital gene expression profiles helped elucidating molecular mechanisms governing these important quality-related traits during watermelon fruit development.</p> <p>Conclusion</p> <p>We have generated a large collection of watermelon ESTs, which represents a significant expansion of the current transcript catalog of watermelon and a valuable resource for future studies on the genomics of watermelon and other closely-related species. Digital expression analysis of this EST collection allowed us to identify a large set of genes that were differentially expressed during watermelon fruit development and ripening, which provide a rich source of candidates for future functional analysis and represent a valuable increase in our knowledge base of watermelon fruit biology.</p
DYNAMICS OF THE SPIN FLOP IN ANTIFERROMAGNET
La dynamique du retournement de spin dans une substance antiferromagnétique orthorhombique a été étudiée analytiquement et puis, par une méthode numérique, ceci a été appliqué au cas de CuCl2.2 H2O (orthorhombique) et MnF2 (uniaxiale).The dynamics of the spin flop in an orthorhombic antiferromagnet is studied analytically, and then a computational method is used to study the spin flop in orthorhombic CuCl2. 2H2O and in uniaxial MnF2
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