2,592 research outputs found
Binding between endohedral Na atoms in Si clathrate I; a first principles study
We investigate the binding nature of the endohedral sodium atoms with the
ensity functional theory methods, presuming that the clathrate I consists of a
sheaf of one-dimensional connections of Na@Si cages interleaved in three
perpendicular directions. Each sodium atom loses 30% of the 3s charge to
the frame, forming an ionic bond with the cage atoms; the rest of the electron
contributes to the covalent bond between the nearest Na atoms. The presumption
is proved to be valid; the configuration of the two Na atoms in the nearest
Si cages is more stable by 0.189 eV than that in the Si and
Si cages. The energy of the beads of the two distorted Na atoms is more
stable by 0.104 eV than that of the two infinitely separated Na atoms. The
covalent bond explains both the preferential occupancies in the Si cages
and the low anisotropic displacement parameters of the endohedral atoms in the
Si cages in the [100] directions of the clathrate I.Comment: First page: Affiliation added to PDF and PS versio
TARGET: A Digitizing And Trigger ASIC For The Cherenkov Telescope Array
The future ground-based gamma-ray observatory Cherenkov Telescope Array (CTA)
will feature multiple types of imaging atmospheric Cherenkov telescopes, each
with thousands of pixels. To be affordable, camera concepts for these
telescopes have to feature low cost per channel and at the same time meet the
requirements for CTA in order to achieve the desired scientific goals. We
present the concept of the TeV Array Readout Electronics with GSa/s sampling
and Event Trigger (TARGET) Application Specific Circuit (ASIC), envisaged to be
used in the cameras of various CTA telescopes, e.g. the Gamma-ray Cherenkov
Telescope (GCT), a proposed 2-Mirror Small-Sized Telescope, and the
Schwarzschild-Couder Telescope (SCT), a proposed Medium-Sized Telescope. In the
latest version of this readout concept the sampling and trigger parts are split
into dedicated ASICs, TARGET C and T5TEA, both providing 16 parallel input
channels. TARGET C features a tunable sampling rate (usually 1 GSa/s), a 16k
sample deep buffer for each channel and on-demand digitization and transmission
of waveforms with typical spans of ~100 ns. The trigger ASIC, T5TEA, provides 4
low voltage differential signal (LVDS) trigger outputs and can generate a
pedestal voltage independently for each channel. Trigger signals are generated
by T5TEA based on the analog sum of the input in four independent groups of
four adjacent channels and compared to a threshold set by the user. Thus, T5TEA
generates four LVDS trigger outputs, as well as 16 pedestal voltages fed to
TARGET C independently for each channel. We show preliminary results of the
characterization and testing of TARGET C and T5TEA.Comment: 6 pages, 8 figures, Proceedings of the 6th International Symposium on
High-Energy Gamma-Ray Astronomy (Gamma2016
The Slow X-Ray Expansion of the Northwestern Rim of the Supernova Remnant RX J0852.0-4622
The detection of radioactive decay line of 44Ti provides a unique evidence
that the gamma-ray source is a young (< 1,000 yr) supernova remnant because of
its short lifetime of about 90 yr. Only two Galactic remnants, Cassiopeia A and
RX J0852.0-4622, are hitherto reported to be the 44Ti line emitter, although
the detection from the latter has been debated. Here we report on an expansion
measurement of the northwestern rim of RX J0852.0-4622 obtained with X-ray
observations separated by 6.5 yr. The expansion rate is derived to be
0.023+/-0.006% that is about five times lower than those of young historical
remnants. Such a slow expansion suggests that RX J0852.0-4622 is not a young
remnant as has been expected. We estimate the age of 1,700-4,300 yr of this
remnant depending on its evolutionary stage. Assuming a high shock speed of
about 3000 km/sec, which is suggested by the detection of non-thermal X-ray
radiation, the distance of about 750 pc to this remnant is also derived.Comment: 12 pages, 3 figures, Accepted for publication in the Astrophysical
Journal Letter
Comparative study of excitonic structures and luminescence properties of Bi4Ge3O12 and Bi12GeO20
Published in physica status solidi (b), Vol. 245, No. 12, pp2733-2736, 2008.Bi12GeO20 crystals have been performed, in addition to relativistic molecular orbital calculations. Both materials consist of the same elements but form different crystal structures. Based on the obtained results, the excitonic reflection structures and luminescence properties of Bi4Ge3O12 and Bi12GeO20 are discussed in comparison with each other.Bookphysica status solidi (b). 245(12):2733-2736 (2008)journal articl
Suppression of geometrical barrier in crystals by Josephson vortex stacks
Differential magneto-optics are used to study the effect of dc in-plane
magnetic field on hysteretic behavior due to geometrical barriers in
crystals. In absence of in-plane field a vortex
dome is visualized in the sample center surrounded by barrier-dominated
flux-free regions. With in-plane field, stacks of Josephson vortices form
vortex chains which are surprisingly found to protrude out of the dome into the
vortex-free regions. The chains are imaged to extend up to the sample edges,
thus providing easy channels for vortex entry and for drain of the dome through
geometrical barrier, suppressing the magnetic hysteresis. Reduction of the
vortex energy due to crossing with Josephson vortices is evaluated to be about
two orders of magnitude too small to account for the formation of the
protruding chains. We present a model and numerical calculations that
qualitatively describe the observed phenomena by taking into account the
demagnetization effects in which flux expulsion from the pristine regions
results in vortex focusing and in the chain protrusion. Comparative
measurements on a sample with narrow etched grooves provide further support to
the proposed model.Comment: 12 figures (low res.) Higher resolution figures are available at the
Phys Rev B version. Typos correcte
Infrared/optical - X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506
We investigate the origin of short X-ray flares which are occasionally
observed in early stages of afterglows of gamma-ray bursts (GRBs). We observed
two events, GRB 071112C and GRB 080506, before the start of X-ray flares in the
optical and near-infrared (NIR) bands with the 1.5-m Kanata telescope. In
conjunction with published X-ray and optical data, we analyzed densely sampled
light curves of the early afterglows and spectral energy distributions (SEDs)
in the NIR-X-ray ranges. We found that the SEDs had a break between the optical
and X-ray bands in the normal decay phases of both GRBs regardless of the model
for the correction of the interstellar extinction in host galaxies of GRBs. In
the X-ray flares, X-ray flux increased by 3 and 15 times in the case of GRB
071112C and 080506, respectively, and the X-ray spectra became harder than
those in the normal decay phases. No significant variation in the optical-NIR
range was detected together with the X-ray flares. These results suggest that
the X-ray flares were associated with either late internal shocks or external
shocks from two-component jets.Comment: 10 pages, 5 figures, accepted to Astronomy and Astrophysic
Identification of differentially expressed genes between developing seeds of different soybean cultivars
AbstractSoybean is a major source of protein and oil and a primary feedstock for biodiesel production. Research on soybean seed composition and yield has revealed that protein, oil and yield are controlled quantitatively and quantitative trait loci (QTL) have been identified for each of these traits. However, very limited information is available regarding the genetic mechanisms controlling seed composition and yield. To help address this deficiency, we used Affymetrix Soybean GeneChips® to identify genes that are differentially expressed between developing seeds of the Minsoy and Archer soybean cultivars, which differ in seed weight, yield, protein content and oil content. A total of 700 probe sets were found to be expressed at significantly different (defined as having an adjusted p-value below or equal to 0.05 and an at least 2-fold difference) levels between the two cultivars at one or more of the three developmental stages and in at least one of the two years assayed. Comparison of data from soybeans collected in two different years revealed that 97 probe sets were expressed at significantly different levels in both years. Functional annotations were assigned to 78% of these 97 probe sets based on the SoyBase Affymetrix™ GeneChip® Soybean Genome Array Annotation. Genes involved in receptor binding/activity and protein binding are overrepresented among the group of 97 probe sets that were differentially expressed in both years assayed. Probe sets involved in growth/development, signal transduction, transcription, defense/stress response and protein and lipid metabolism were also identified among the 97 probe sets and their possible implications in the regulation of agronomic traits are discussed. As the Minsoy and Archer soybean cultivars differ with respect to seed size, yield, protein content and lipid content, some of the differentially expressed probe sets identified in this study may thus play important roles in controlling these traits. Others of these probe sets may be involved in regulation of general seed development or metabolism. All microarray data and expression values after GCRMA are available at the Gene Expression Omnibus (GEO) at NCBI (http://www.ncbi.nlm.nih.gov/geo), under accession number GSE21598
Grain Size and Texture of Cu2ZnSnS4 Thin Films Synthesized by Cosputtering Binary Sulfides and Annealing: Effects of Processing Conditions and Sodium
We investigate the synthesis of kesterite Cu2ZnSnS4 (CZTS) polycrystalline
thin films using cosputtering from binary sulfide targets followed by annealing
in sulfur vapor at 500 {\deg}C to 650 {\deg}C. The films are the kesterite CZTS
phase as indicated by x-ray diffraction, Raman scattering, and optical
absorption measurements. The films exhibit (112) fiber texture and preferred
low-angle and Sigma3 grain boundary populations which have been demonstrated to
reduce recombination in Cu(In,Ga)Se2 and CdTe films. The grain growth kinetics
are investigated as functions of temperature and the addition of Na.
Significantly, lateral grain sizes above 1 um are demonstrated for samples
grown on Na-free glass,demonstrating the feasibility for CZTS growth on
substrates other than soda lime glass
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