44,132 research outputs found
Time Dependent Effects and Transport Evidence for Phase Separation in La_{0.5}Ca_{0.5}MnO_{3}
The ground state of La_{1-x}Ca_{x}MnO_{3} changes from a ferromagnetic
metallic to an antiferromagnetic charge-ordered state as a function of Ca
concentration at x ~ 0.50. We present evidence from transport measurements on a
sample with x = 0.50 that the two phases can coexist, in agreement with other
observations of phase separation in these materials. We also observe that, by
applying and then removing a magnetic field to the mainly charge-ordered state
at some temperatures, we can "magnetically anneal" the charge order, resulting
in a higher zero-field resistivity. We also observe logarithmic time dependence
in both resistivity and magnetization after a field sweep at low temperatures.Comment: 9 pages, LATEX, 3 postscript figure
Archetypal analysis of galaxy spectra
Archetypal analysis represents each individual member of a set of data
vectors as a mixture (a constrained linear combination) of the pure types or
archetypes of the data set. The archetypes are themselves required to be
mixtures of the data vectors. Archetypal analysis may be particularly useful in
analysing data sets comprising galaxy spectra, since each spectrum is,
presumably, a superposition of the emission from the various stellar
populations, nebular emissions and nuclear activity making up that galaxy, and
each of these emission sources corresponds to a potential archetype of the
entire data set. We demonstrate archetypal analysis using sets of composite
synthetic galaxy spectra, showing that the method promises to be an effective
and efficient way to classify spectra. We show that archetypal analysis is
robust in the presence of various types of noise.Comment: 6 pages, 5 figures, 1 style-file. Accepted for publication by MNRA
Potential for measuring the longitudinal and lateral profile of muons in TeV air showers with IACTs
Muons are copiously produced within hadronic extensive air showers (EAS)
occurring in the Earth's atmosphere, and are used by particle air shower
detectors as a means of identifying the primary cosmic ray which initiated the
EAS. Imaging Atmospheric Cherenkov Telescopes (IACTs), designed for the
detection of gamma-ray initiated EAS for the purposes of Very High Energy (VHE)
gamma-ray astronomy, are subject to a considerable background signal due to
hadronic EAS. Although hadronic EAS are typically rejected for gamma-ray
analysis purposes, single muons produced within such showers generate clearly
identifiable signals in IACTs and muon images are routinely retained and used
for calibration purposes. For IACT arrays operating with a stereoscopic
trigger, when a muon triggers one telescope, other telescopes in IACT arrays
usually detect the associated hadronic EAS. We demonstrate for the first time
the potential of IACT arrays for competitive measurements of the muon content
of air showers, their lateral distribution and longitudinal profile of
production slant heights in the TeV energy range. Such information can provide
useful input to hadronic interaction models.Comment: 15 pages, 11 figures, 2 tables, accepted for publication in
Astroparticle Physic
Terahertz magneto-spectroscopy of transient plasmas in semiconductors
Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have
performed picosecond time-resolved THz spectroscopy of transient carriers in
semiconductors. Specifically, we measured the temporal evolution of THz
transmission and reflectivity after NIR excitation. We systematically
investigated transient carrier relaxation in GaAs and InSb with varying NIR
intensities and magnetic fields. Using this information, we were able to
determine the evolution of the THz absorption to study the dynamics of
photocreated carriers. We developed a theory based on a Drude conductivity with
time-dependent density and density-dependent scattering lifetime, which
successfully reproduced the observed plasma dynamics. Detailed comparison
between experimental and theoretical results revealed a linear dependence of
the scattering frequency on density, which suggests that electron-electron
scattering is the dominant scattering mechanism for determining the scattering
time. In InSb, plasma dynamics was dramatically modified by the application of
a magnetic field, showing rich magneto-reflection spectra, while GaAs did not
show any significant magnetic field dependence. We attribute this to the small
effective masses of the carriers in InSb compared to GaAs, which made the
plasma, cyclotron, and photon energies all comparable in the density, magnetic
field, and wavelength ranges of the current study.Comment: 8 pages, 9 figures, submitted to Phys. Rev.
Search for Stable Magnetohydrodynamic Equilibria in Barotropic Stars
It is now believed that magnetohydrodynamic equilibria can exist in stably
stratified stars due to the seminal works of Braithwaite & Spruit (2004) and
Braithwaite & Nordlund (2006). What is still not known is whether
magnetohydrodynamic equilibria can exist in a barotropic star, in which stable
stratification is not present. It has been conjectured by Reisenegger (2009)
that there will likely not exist any magnetohydrodynamical equilibria in
barotropic stars. We aim to test this claim by presenting preliminary MHD
simulations of barotropic stars using the three dimensional stagger code of
Nordlund & Galsgaard (1995).Comment: 4 pages, 2 figures, to appear in the proceedings of IAUS 302:
"Magnetic Fields Throughout Stellar Evolution
Thirteen-color narrow-band photometry of one thousand bright stars
Thirteen-color narrow-band photometry of one thousand bright star
Circular 78
Historically, sales of exotic meats have been limited only by supply. As supply has increased in recent years, national
and international exotic game markets have grown rapidly. In the United States, growth
has occurred primarily in the restaurant section, although over-the-counter sales
have also increased.
The Alaskan reindeer industry is exploring the potential of expanding its meat sales as well as antler sales. Meat production increased from 320,000 pounds in 1987 to 432,000 pounds in 1988. This production increase is reflected in a 27
percent increase in dollar value (Alaska Crop and Livestock Reporting Service, 1989). Under current management procedures, potential meat production has been estimated at 500,000 pounds (Pearson and Lewis, 1988). Any future market expansion
is likely to occur in urban Alaska and in areas outside the state (Jones, 1988)
- …