229 research outputs found
Pressure-induced phase transition of Bi2Te3 into the bcc structure
The pressure-induced phase transition of bismuth telluride, Bi2Te3, has been
studied by synchrotron x-ray diffraction measurements at room temperature using
a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a
high-pressure body-centered cubic (bcc) phase in Bi2Te3 at 25.2 GPa, which is
denoted as phase IV, and this phase apperars above 14.5 GPa. Upon releasing the
pressure from 29.8 GPa, the diffraction pattern changes with pressure
hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc
structure can explain the phase IV peaks. We assumed that the structural model
of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms
are distributed in the bcc-lattice sites with space group Im-3m. The results of
Rietveld analysis based on this model agree well with both the experimental
data and calculated results. Therefore, the structure of phase IV in Bi2Te3 can
be explained by a solid solution with a bcc lattice in the Bi-Te (60 atomic%
tellurium) binary system.Comment: 12 pages, 5 figure
Understanding Novel Superconductors with Ab Initio Calculations
This chapter gives an overview of the progress in the field of computational
superconductivity.
Following the MgB2 discovery (2001), there has been an impressive
acceleration in the development of methods based on Density Functional Theory
to compute the critical temperature and other physical properties of actual
superconductors from first-principles. State-of-the-art ab-initio methods have
reached predictive accuracy for conventional (phonon-mediated) superconductors,
and substantial progress is being made also for unconventional superconductors.
The aim of this chapter is to give an overview of the existing computational
methods for superconductivity, and present selected examples of material
discoveries that exemplify the main advancements.Comment: 38 pages, 10 figures, Contribution to Springer Handbook of Materials
Modellin
Successful application of ancient DNA extraction and library construction protocols to museum wet collection specimens
Millions of scientific specimens are housed in museum collections, a large part of which are fluid preserved. The use of formaldehyde as fixative and subsequent storage in ethanol is especially common in ichthyology and herpetology. This type of preservation damages DNA and reduces the chance of successful retrieval of genetic data. We applied ancient DNA extraction and single stranded library construction protocols to a variety of vertebrate samples obtained from wet collections and of different ages. Our results show that almost all samples tested yielded endogenous DNA. Archival DNA extraction was successful across different tissue types as well as using small amounts of tissue. Conversion of archival DNA fragments into single-stranded libraries resulted in usable data even for samples with initially undetectable DNA amounts. Subsequent target capture approaches for mitochondrial DNA using homemade baits on a subset of 30 samples resulted in almost complete mitochondrial genome sequences in several instances. Thus, application of ancient DNA methodology makes wet collection specimens, including type material as well as rare, old or extinct species, accessible for genetic and genomic analyses. Our results, accompanied by detailed step-by-step protocols, are a large step forward to open the DNA archive of museum wet collections for scientific studies
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