804 research outputs found
First-principles study on the intermediate compounds of LiBH
We report the results of the first-principles calculation on the intermediate
compounds of LiBH. The stability of LiBH and LiBH has been examined with the ultrasoft pseudopotential method based on
the density functional theory. Theoretical prediction has suggested that
monoclinic LiBH is the most stable among the candidate
materials. We propose the following hydriding/dehydriding process of LiBH
via this intermediate compound : LiBHLiBH LiH HLiH B H. The hydrogen content and enthalpy of the first
reaction are estimated to be 10 mass% and 56 kJ/mol H, respectively, and
those of the second reaction are 4 mass% and 125 kJ/mol H. They are in good
agreement with experimental results of the thermal desorption spectra of
LiBH. Our calculation has predicted that the bending modes for the
-phonon frequencies of monoclinic LiBH are lower than
that of LiBH, while stretching modes are higher. These results are very
useful for the experimental search and identification of possible intermediate
compounds.Comment: 7 pages, 5 figures, submitted to PR
Thermodynamic and Transport Properties of CeMg2Cu9 under Pressure
We report the transport and thermodynamic properties under hydrostatic
pressure in the antiferromagnetic Kondo compound CeMg2Cu9 with a
two-dimensional arrangement of Ce atoms. Magnetic specific heat Cmag(T) shows a
Schottky-type anomaly around 30 K originating from the crystal electric field
(CEF) splitting of the 4f state with the first excited level at \Delta_{1}/kB =
58 K and the second excited level at \Delta_{2}/kB = 136 K from the ground
state.
Electric resistivity shows a two-peaks structure due to the Kondo effect on
each CEF level around T_{1}^{max} = 3 K and T_{2}^{max} = 40 K. These peaks
merge around 1.9 GPa with compression. With increasing pressure, Neel
temperature TN initially increases and then change to decrease. TN finally
disappears at the quantum critical point Pc = 2.4 GPa.Comment: 10 pages, 6 figure
Optimal Protocol for Contrast-enhanced Free-running 5D Whole-heart Coronary MR Angiography at 3T.
Free-running 5D whole-heart coronary MR angiography (MRA) is gaining in popularity because it reduces scanning complexity by removing the need for specific slice orientations, respiratory gating, or cardiac triggering. At 3T, a gradient echo (GRE) sequence is preferred in combination with contrast injection. However, neither the injection scheme of the gadolinium (Gd) contrast medium, the choice of the RF excitation angle, nor the dedicated image reconstruction parameters have been established for 3T GRE free-running 5D whole-heart coronary MRA. In this study, a Gd injection scheme, RF excitation angles of lipid-insensitive binominal off-resonance RF excitation (LIBRE) pulse for valid fat suppression and continuous data acquisition, and compressed-sensing reconstruction regularization parameters were optimized for contrast-enhanced free-running 5D whole-heart coronary MRA using a GRE sequence at 3T. Using this optimized protocol, contrast-enhanced free-running 5D whole-heart coronary MRA using a GRE sequence is feasible with good image quality at 3T
CANGAROO-III Observation of TeV Gamma Rays from the vicinity of PSR B1 706-44
Observation by the CANGAROO-III stereoscopic system of the Imaging Cherenkov
Telescope has detected extended emission of TeV gamma rays in the vicinity of
the pulsar PSR B170644. The strength of the signal observed as
gamma-ray-like events varies when we apply different ways of emulating
background events. The reason for such uncertainties is argued in relevance to
gamma-rays embedded in the "off-source data", that is, unknown sources and
diffuse emission in the Galactic plane, namely, the existence of a complex
structure of TeV gamma-ray emission around PSR B170644.Comment: 10 pages, 13 figures, to be published in Ap
CANGAROO-III Search for Gamma Rays from SN 1987A and the Surrounding Field
Optical images of SN 1987A show a triple ring structure. The inner (dust)
ring has recently increased in brightness and in the number of hot spots
suggesting that the supernova shock wave has collided with the dense
pre-existing circumstellar medium, a scenario supported by radio and X-ray
observations. Such a shocked environment is widely expected to result in the
acceleration of charged particles, and the accompanying emission of very high
energy gamma-rays. Here, we report the results of observations made in 2004 and
2006 which yield upper limits on the TeV gamma-ray flux, which are compared
with a theoretical prediction. In addition, we set upper limits on the TeV flux
for four high energy objects which are located within the same field of view of
the observation: the super-bubble 30 Dor C, the Crab-like pulsar PSR
B054069, the X-ray binary LMC X-1, and the supernova remnant N157B.Comment: 5 pages, 5 figures, Accepted for publication in Ap
CANGAROO-III observation of TeV gamma rays from the unidentified gamma-ray source HESS J1614-518
We report the detection, with the CANGAROO-III imaging atmospheric Cherenkov
telescope array, of a very high energy gamma-ray signal from the unidentified
gamma-ray source HESS J1614-518, which was discovered in the H.E.S.S. Galactic
plane survey. Diffuse gamma-ray emission was detected above 760 GeV at the 8.9
sigma level during an effective exposure of 54 hr from 2008 May to August. The
spectrum can be represented by a power-law:
8.2+-2.2_{stat}+-2.5_{sys}x10^{-12}x (E/1TeV)^{-Gamma} cm^{-2} s^{-1} TeV^{-1}
with a photon index Gamma of 2.4+-0.3_{stat}+-0.2_{sys}, which is compatible
with that of the H.E.S.S. observations. By combining our result with
multi-wavelength data, we discuss the possible counterparts for HESS J1614-518
and consider radiation mechanisms based on hadronic and leptonic processes for
a supernova remnant, stellar winds from massive stars, and a pulsar wind
nebula. Although a leptonic origin from a pulsar wind nebula driven by an
unknown pulsar remains possible, hadronic-origin emission from an unknown
supernova remnant is preferred.Comment: 9 pages, 7 figures, accepted for publication in Ap
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