3,856 research outputs found
Searching for hexagonal analogues of the half-metallic half-Heusler XYZ compounds
The XYZ half-Heusler crystal structure can conveniently be described as a
tetrahedral zinc blende YZ structure which is stuffed by a slightly ionic X
species. This description is well suited to understand the electronic structure
of semiconducting 8-electron compounds such as LiAlSi (formulated
Li[AlSi]) or semiconducting 18-electron compounds such as TiCoSb
(formulated Ti[CoSb]). The basis for this is that [AlSi]
(with the same electron count as Si) and [CoSb] (the same electron
count as GaSb), are both structurally and electronically, zinc-blende
semiconductors. The electronic structure of half-metallic ferromagnets in this
structure type can then be described as semiconductors with stuffing magnetic
ions which have a local moment: For example, 22 electron MnNiSb can be written
Mn[NiSb]. The tendency in the 18 electron compound for a
semiconducting gap -- believed to arise from strong covalency -- is carried
over in MnNiSb to a tendency for a gap in one spin direction. Here we similarly
propose the systematic examination of 18-electron hexagonal compounds for
semiconducting gaps; these would be the "stuffed wurtzite" analogues of the
"stuffed zinc blende" half-Heusler compounds. These semiconductors could then
serve as the basis for possibly new families of half-metallic compounds,
attained through appropriate replacement of non-magnetic ions by magnetic ones.
These semiconductors and semimetals with tunable charge carrier concentrations
could also be interesting in the context of magnetoresistive and thermoelectric
materials.Comment: 11 pages, 6 figures, of which 4 are colou
Systematical, experimental investigations on LiMgZ (Z= P, As, Sb) wide band gap semiconductors
This work reports on the experimental investigation of the wide band gap
compounds LiMgZ (Z = P, As, Sb), which are promising candidates for
opto-electronics and anode materials for Lithium batteries. The compounds
crystallize in the cubic (C1_b) MgAgAs structure (space group F-43m). The
polycrystalline samples were synthesized by solid state reaction methods. X-ray
and neutron diffraction measurements show a homogeneous, single-phased samples.
The electronic properties were studied using the direct current (DC) method.
Additionally UV-VIS diffuse reflectance spectra were recorded in order to
investigate the band gap nature. The measurements show that all compounds
exhibit semiconducting behavior with direct band gaps of 1.0 eV to 2.3 eV
depending on the Z element. A decrease of the peak widths in the static 7Li
nuclear magnetic resonance (NMR) spectra with increasing temperature was
observed, which can directly be related to an increase of Li ion mobility.Comment: 8 page
A study of atmospheric neutrinos with the IMB detector
A sample of 401 contained neutrino interactions collected in the 3300 metric ton fiducial mass IMB detector was used to study neutrino oscillations, geomagnetic modulation of the flux and to search for point sources. The majority of these events are attributed to neutrino interactions. For the most part, these neutrinos are believed to originate as tertiary products of cosmic ray interactions in the atmosphere. The neutrinos are a mixture of v sub e and v sub micron
Measuring the to Ratio in a High Statistics Atmospheric Neutrino Experiment
By exploiting differences in muon lifetimes it is possible to distinguish
from charged current interactions in underground
neutrino detectors. Such observations would be a useful tool in understanding
the source of the atmospheric neutrino anomaly.Comment: 6 pages no figure
Проблемы процесса управления в техносферной безопасности
В статье будет рассмотрены проблемы техносферной безопасности через интеграционный подход, как самый эффективный в сфере управления природопользования. Самые важные проблемы будут обобщены в вопросах государственного регулирования, также будут выявлены факторы влияния на эффективность управления данного процесса
Off-diagonal structure of neutrino mass matrix in see-saw mechanism and electron-muon-tau lepton universality
By a simple extension of the standard model in which ()
universality is not conserved, we present a scenario within the framework of
see-saw mechanism in which the neutrino mass matrix is strictly off-diagonal in
the flavor basis. We show that a version of this scenario can accomodate the
atmospheric neutrino oscillations and
oscillations claimed by the LSND collaboration.
PACS: 14.60.Pq; 14.60.St;13.15.+gComment: 5 pages, Revtex, 1 figure: The model accomodate another version which
explains atmospheric neutrino data and the observed solar neutrino
oscillations (large angle solution). In the previous version the value of
\lambda parameter is changed to the expected one. This version now
accomodates LSND result and solar neutrino oscillations (small angle MSW
solution
Testing maximal electron and muon neutrino oscillations with sub-GeV SuperKamiokande atmospheric neutrino data
Motivated by the Exact Parity Model and other theories, the hypothesis that
each of the known neutrinos oscillates maximally with a sterile partner has
been put forward as an explanation of the atmospheric and solar neutrino
anomalies. We provide detailed predictions for muon and electron flux ratios
induced in the Kamiokande and SuperKamiokande detectors by sub-GeV atmospheric
neutrinos. Several different, carefully chosen cuts on momentum and zenith
angle are proposed, emphasizing the role of up-down flux asymmetries.Comment: LaTeX, 8 figures, 17 pages, version to appear in Phys. Rev. D Rapid
Communication
Measurements and Computations of Second-Mode Instability Waves in Three Hypersonic Wind Tunnels
High-frequency pressure-fluctuation measurements were made in AEDC Tunnel 9 at Mach 10 and the NASA Langley 15-Inch Mach 6 and 31-Inch Mach 10 tunnels. Measurements were made on a 7deg-half-angle cone model. Pitot measurements of freestream pressure fluctuations were also made in Tunnel 9 and the Langley Mach-6 tunnel. For the first time, second-mode waves were measured in all of these tunnels, using 1-MHz-response pressure sensors. In Tunnel 9, second-mode waves could be seen in power spectra computed from records as short as 80 micro-s. The second-mode wave amplitudes were observed to saturate and then begin to decrease in the Langley tunnels, indicating wave breakdown. Breakdown was estimated to occur near N approx. equals 5 in the Langley Mach-10 tunnel. The unit-Reynolds-number variations in the data from Tunnel 9 were too large to see the same processes. In Tunnel 9, the measured transition locations were found to be at N = 4.5 using thermocouples, and N = 5.3 using 50-kHz-response pressure sensors. What appears to be a very long transitional region was observed at a unit Reynolds number of 13.5 million per meter in Tunnel 9. These results were consistent with the high-frequency pressure fluctuation measurements. High-frequency pressure fluctuation measurements indicated that transition did occur in the Langley Mach-6 tunnel, but the location of transition was not precisely determined. Unit Reynolds numbers in the Langley Mach-10 tunnel were too low to observe transition. More analysis of this data set is expected in the future
The global field of multi-family offices: An institutionalist perspective
We apply the notion of the organisational field to internationally operating multi-family offices. These organisations specialise on the preservation of enterprising and geographically dispersed families’ fortunes. They provide their services across generations and countries. Based on secondary data of Bloomberg’s Top 50 Family Offices, we show that they constitute a global organisational field that comprises two clusters of homogeneity. Clients may decide between two different configurations of activities, depending on their preferences regarding asset management, resource management, family management, and service architecture. The findings also reveal that multi-family offices make relatively similar value propositions all over the world. The distinctiveness of the clusters within the field is not driven by the embeddedness of the multi-family offices in different national environments or their various degrees of international experience. Rather, it is weakly affected by two out of four possible value propositions, namely the exclusiveness and the transparency of services
A Closed-Form Expression for the Gravitational Radiation Rate from Cosmic Strings
We present a new formula for the rate at which cosmic strings lose energy
into gravitational radiation, valid for all piecewise-linear cosmic string
loops. At any time, such a loop is composed of straight segments, each of
which has constant velocity. Any cosmic string loop can be arbitrarily-well
approximated by a piecewise-linear loop with sufficiently large. The
formula is a sum of polynomial and log terms, and is exact when the
effects of gravitational back-reaction are neglected. For a given loop, the
large number of terms makes evaluation ``by hand" impractical, but a computer
or symbolic manipulator yields accurate results. The formula is more accurate
and convenient than previous methods for finding the gravitational radiation
rate, which require numerical evaluation of a four-dimensional integral for
each term in an infinite sum. It also avoids the need to estimate the
contribution from the tail of the infinite sum. The formula has been tested
against all previously published radiation rates for different loop
configurations. In the cases where discrepancies were found, they were due to
errors in the published work. We have isolated and corrected both the analytic
and numerical errors in these cases. To assist future work in this area, a
small catalog of results for some simple loop shapes is provided.Comment: 29 pages TeX, 16 figures and computer C-code available via anonymous
ftp from directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-10,
(section 7 has been expanded, two figures added, and minor grammatical
changes made.
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