12,369 research outputs found
Electronic structure of GaAs1-xNx alloy by soft-X-ray absorption and emission: Origin of the reduced optical efficiency
The local electronic structure of N atoms in a diluted GaAs1-xNx (x=3%)
alloy, in view of applications in optoelectronics, is determined for the first
time using soft-X-ray absorption (SXA) and emission (SXE). Deviations from
crystalline GaN, in particular in the conduction band, are dramatic. Employing
the orbital character and elemental specificity of the SXE/SXA spectroscopies,
we identify a charge transfer from the N atoms at the valence band maximum,
reducing the overlap with the wavefunction in conduction band minimum, as the
main factor limiting the optical efficiency of GaAs1-xNx alloys. Moreover, a
k-conserving process of resonant inelastic x-ray scattering involving the L1
derived valence and conduction states is discovered.Comment: 3 pages, physica status solidi (Rapid Research Notes), in pres
Timelike self-similar spherically symmetric perfect-fluid models
Einstein's field equations for timelike self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
using the theory of dynamical systems.Comment: 23 pages, 6 eps-figure
Spatially self-similar spherically symmetric perfect-fluid models
Einstein's field equations for spatially self-similar spherically symmetric
perfect-fluid models are investigated. The field equations are rewritten as a
first-order system of autonomous differential equations. Dimensionless
variables are chosen in such a way that the number of equations in the coupled
system is reduced as far as possible and so that the reduced phase space
becomes compact and regular. The system is subsequently analysed qualitatively
with the theory of dynamical systems.Comment: 21 pages, 6 eps-figure
Methanol in W3(H2O) and Surrounding Regions
We present the results of an interferometric study of 38 millimeter-wave
lines of CH3OH in the region around the water maser source W3(H2O) and a region
extending about 30" to the south and west of the hydroxyl maser source W3(OH).
The methanol emitting region around W3(H2O) has an extent of 2.0" x 1.2"
(4400 x 2600 AU). The density is of order 1.e7 cm-3, sufficient to thermalize
most of the methanol lines. The kinetic temperature is approximately 140 K and
the methanol fractional abundance greater than 1.e-6, indicative of a high
degree of grain mantle evaporation. The W3(H2O) source contains sub-structure,
with peaks corresponding to the TW source and Wyrowski's B/C, separated by 2500
AU in projection. The kinematics are consistent with these being distinct
protostellar cores in a wide binary orbit and a dynamical mass for the region
of a few tens of Mo.
The extended methanol emission to the southwest of W3(OH) is seen strongly
only from the lowest excitation lines and from lines known elsewhere to be
class I methanol masers, namely the 84.5 GHz 5(-1)-4(0)E and 95.2 GHz
8(0)-7(1)A+ lines. Within this region there are two compact clumps, which we
denote as swA and swB, each about 15" (0.16 pc projected distance) away from
W3(OH). Excitation analysis of these clumps indicates the presence of lines
with inverted populations but only weak amplification. The sources swA and swB
appear to have kinetic temperatures of order 50-100 K and densities of order
1.e5 - 1.e6 cm-3. The methanol fractional abundance for the warmer clump is of
order 1.e-7, suggestive of partial grain mantle evaporation. The clumping
occurs on mass scales of order 1 Mo.Comment: 28 pages including 6 figures and 4 tables, accepted by Ap
Self-Consistent Velocity Dependent Effective Interactions
The theory of self-consistent effective interactions in nuclei is extended
for a system with a velocity dependent mean potential. By means of the field
coupling method, we present a general prescription to derive effective
interactions which are consistent with the mean potential. For a deformed
system with the conventional pairing field, the velocity dependent effective
interactions are derived as the multipole pairing interactions in
doubly-stretched coordinates. They are applied to the microscopic analysis of
the giant dipole resonances (GDR's) of , the first excited
states of Sn isotopes and the first excited states of Mo isotopes.
It is clarified that the interactions play crucial roles in describing the
splitting and structure of GDR peaks, in restoring the energy weighted sum
rule, and in reducing the values of .Comment: 35 pages, RevTeX, 7 figures (available upon request), to appear in
Phys.Rev.
Multifrequency Observations of the Gamma-Ray Blazar 3C 279 in Low-State during Integral AO-1
We report first results of a multifrequency campaign from radio to hard X-ray
energies of the prominent gamma-ray blazar 3C 279 during the first year of the
INTEGRAL mission. The variable blazar was found at a low activity level, but
was detected by all participating instruments. Subsequently a multifrequency
spectrum could be compiled. The individual measurements as well as the compiled
multifrequency spectrum are presented. In addition, this 2003 broadband
spectrum is compared to one measured in 1999 during a high activity period of
3C 279.Comment: 4 pages including 6 figures, to appear in: 'Proc. of the 5th INTEGRAL
Workshop', ESA SP-552, in pres
Hygroscopic growth and activation of HULIS particles: experimental data and a new iterative parameterization scheme for complex aerosol particles
International audienceThe hygroscopic growth and activation of two HULIS and one Aerosol-Water-Extract sample, prepared from urban-type aerosol, were investigated. All samples were extracted from filters, redissolved in water and atomized for the investigations presented here. The hygroscopic growth measurements were done using LACIS (Leipzig Aerosol Cloud Interaction Simulator) together with a HH-TDMA (High Humidity Tandem Differential Mobility Analyzer). Hygroscopic growth was determined for relative humidities up to 99.75%. The critical diameters for activation were measured using LACIS for supersaturations between 2 and 10 per mill. All three samples showed a similar hygroscopic growth behaviour, and the two HULIS samples also were similar in their activation behavior, while the Aerosol-Water-Extract turned out to be more CCN active than the HULIS samples. The experimental data was used to derive parameterizations for the hygroscopic growth and activation of HULIS particles. The concept of ?ion (Wex et al., 2007a) and the Szyszkowski-equation (Szyszkowski, 1908; Facchini et al., 1999) were used for parameterizing the Raoult and the Kelvin (surface tension) terms of the Köhler equation, respectively. This concept proved to be very successful for the HULIS samples in the saturation range from relative humidities larger than 98% up to activation. However it failed for the Aerosol-Water extract
Compton Scattering from the Deuteron and Extracted Neutron Polarizabilities
Differential cross sections for Compton scattering from the deuteron were
measured at MAX-lab for incident photon energies of 55 MeV and 66 MeV at
nominal laboratory angles of , , and . Tagged
photons were scattered from liquid deuterium and detected in three NaI
spectrometers. By comparing the data with theoretical calculations in the
framework of a one-boson-exchange potential model, the sum and difference of
the isospin-averaged nucleon polarizabilities, and (in units of fm),
have been determined. By combining the latter with the global-averaged value
for and using the predictions of the Baldin sum rule for
the sum of the nucleon polarizabilities, we have obtained values for the
neutron electric and magnetic polarizabilities of (total) (model) and (total) (model), respectively.Comment: 4 pages, 2 figures, revtex. The text is substantially revised. The
cross sections are slightly different due to improvements in the analysi
Recommended from our members
Hygroscopic growth and activation of HULIS particles: Experimental data and a new iterative parameterization scheme for complex aerosol particles
The hygroscopic growth and activation of two HULIS (HUmic LIke Substance) and one Aerosol-Water-Extract sample, prepared from urban-type aerosol, were investigated. All samples were extracted from filters, redissolved in water and atomized for the investigations presented here. The hygroscopic growth measurements were done using LACIS (Leipzig Aerosol Cloud Interaction Simulator) together with a HH-TDMA (High Humidity Tandem Differential Mobility Analyzer). Hygroscopic growth was determined for relative humidities (RHs) up to 99.75%. The critical diameters for activation were measured for supersaturations between 0.2 and 1%. All three samples showed a similar hygroscopic growth behavior, and the two HULIS samples also were similar in their activation behavior, while the Aerosol-Water-Extract turned out to be more CCN active than the HULIS samples. The experimental data was used to derive parameterizations for the hygroscopic growth and activation of HULIS particles. The concept of ρion (Wex et al., 2007a) and the Szyszkowski-equation (Szyszkowski, 1908; Facchini, 1999) were used for parameterizing the Raoult and the Kelvin (surface tension) terms of the Köhler equation, respectively. This concept proved to be very successful for the HULIS samples in the saturation range from RHs larger than 98% up to activation. It was also shown to work well with data on HULIS taken from literature. Here, different atmospheric life-times and/or different sources for the different samples showed up in different coefficients for the parameterization. However, the parameterization did not work out well for the Aerosol-Water-Extract
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