1,381 research outputs found
Minimal AdS-Lorentz supergravity in three-dimensions
The AdS-Lorentz superalgebra is studied and its relationship
to semigroup expansion developed. Using this mathematical tool, the invariant
tensors and Casimir operators are found. In terms of these invariants, a
three-dimensionnal Chern--Simons supergravity action with AdS-Lorentz symmetry
is constructed. The Killing spinors for a BTZ black-hole like solution of the
theory are discussed.Comment: 18 pages, matches published versio
Two spatially separated phases in semiconducting RbFeS
We report neutron scattering and transport measurements on semiconducting
RbFeS, a compound isostructural and isoelectronic to the
well-studied FeSe K, Rb, Cs, Tl/K) superconducting
systems. Both resistivity and DC susceptibility measurements reveal a magnetic
phase transition at K. Neutron diffraction studies show that the 275 K
transition originates from a phase with rhombic iron vacancy order which
exhibits an in-plane stripe antiferromagnetic ordering below 275 K. In
addition, interdigitated mesoscopically with the rhombic phase is an ubiquitous
phase with iron vacancy order. This phase has a
magnetic transition at K and an iron vacancy order-disorder
transition at K. These two different structural phases are closely
similar to those observed in the isomorphous Se materials. Based on the close
similarities of the in-plane antiferromagnetic structures, moments sizes, and
ordering temperatures in semiconducting RbFeS and
KFeSe, we argue that the in-plane antiferromagnetic order
arises from strong coupling between local moments. Superconductivity,
previously observed in the FeSeS system, is absent
in RbFeS, which has a semiconducting ground state. The
implied relationship between stripe/block antiferromagnetism and
superconductivity in these materials as well as a strategy for further
investigation is discussed in this paper.Comment: 7 pages, 5 figure
Universal magnetic and structural behaviors in the iron arsenides
Commonalities among the order parameters of the ubiquitous antiferromagnetism
present in the parent compounds of the iron arsenide high temperature
superconductors are explored. Additionally, comparison is made between the well
established two-dimensional Heisenberg-Ising magnet, KNiF and iron
arsenide systems residing at a critical point whose structural and magnetic
phase transitions coincide. In particular, analysis is presented regarding two
distinct classes of phase transition behavior reflected in the development of
antiferromagnetic and structural order in the three main classes of iron
arsenide superconductors. Two distinct universality classes are mirrored in
their magnetic phase transitions which empirically are determined by the
proximity of the coupled structural and magnetic phase transitions in these
materials.Comment: 6 pages, 4 figure
Factors that influence the price of cattle in livestock auctions: the case of the stockyard of Melipilla (Chile)
Troncoso, JL (reprint author), Univ Talca, Fac Ciencias Agr, Dept Agr Econ, Casilla 747, Talca, Chile.Factors that influence the price of cattle in livestock auctions: the case of the stockyard of Melipilla (Chile). Cien. Inv. Agr. 39(1): 37-45. This study aims to weigh the influence of observable traits on live cattle prices, i.e., the percent impact on the final price of various physical characteristics. These characteristics are those that commonly are published in auction catalogues, as is the case of average lot weight, lot size, age, breed and corporal condition. In addition, the influence of seasonality and business cycles were also explored. Using the data collected from the records of El Tattersall S.A., a hedonic price function was fitted. The results showed that the most influential variables with respect to the price of beef cattle, in decreasing order, are as follows: 'condition', 'breed', 'quarter of sale' and 'year', which are followed far behind by 'lot size' and 'average weight'. The market pays a premium for Red Friesians, Crossbreds and Herefords and punishes the price of Holstein Friesians. Additionally, higher prices are paid in the last two quarters of the year than in the first two, and the third quarter is preferable to the fourth. Finally, the average lot weight and lot size are variables that have a positive, but small, influence on the price of cattle
Tracking Energy Flow Using a Volumetric Acoustic Intensity Imager (VAIM)
A new measurement device has been invented at the Naval Research Laboratory which images instantaneously the intensity vector throughout a three-dimensional volume nearly a meter on a side. The measurement device consists of a nearly transparent spherical array of 50 inexpensive microphones optimally positioned on an imaginary spherical surface of radius 0.2m. Front-end signal processing uses coherence analysis to produce multiple, phase-coherent holograms in the frequency domain each related to references located on suspect sound sources in an aircraft cabin. The analysis uses either SVD or Cholesky decomposition methods using ensemble averages of the cross-spectral density with the fixed references. The holograms are mathematically processed using spherical NAH (nearfield acoustical holography) to convert the measured pressure field into a vector intensity field in the volume of maximum radius 0.4 m centered on the sphere origin. The utility of this probe is evaluated in a detailed analysis of a recent in-flight experiment in cooperation with Boeing and NASA on NASA s Aries 757 aircraft. In this experiment the trim panels and insulation were removed over a section of the aircraft and the bare panels and windows were instrumented with accelerometers to use as references for the VAIM. Results show excellent success at locating and identifying the sources of interior noise in-flight in the frequency range of 0 to 1400 Hz. This work was supported by NASA and the Office of Naval Research
Reconstruction of the Acoustic Field Using a Conformal Array
Near-field acoustical holography (NAH) requires the measurement of the near-field pressure field over a conformal and closed surface in order to recover the acoustic field on a nearby surface. We are interested in the reconstruction of the acoustic field over the fuselage of a Boeing 757 airplane when pressure data is available over an array of microphones that are conformal to the fuselage surface. In this case the strict NAH theory does not hold, but still there are techniques used to overcome this difficulty. The best known is patch NAH, which has been used for planar surfaces. In this work we will discuss two new techniques used for surfaces with an arbitrarily shape: patch inverse boundary element methods (IBEM) and patch equivalent sources method (ESM). We will discuss the theoretical justification of the method and show reconstructions for in-flight data taken inside a Boeing 757 airplane
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