38,585 research outputs found
Portable reflectance spectrometer
A portable reflectance spectrometer is disclosed. The spectrometer essentially includes an optical unit and an electronic recording unit. The optical unit includes a pair of thermoelectrically-cooled detectors, for detecting total radiance and selected radiance projected through a circular variable filter wheel, and is capable of operating to provide spectral data in the range 0.4 to 2.5 micrometers without requiring coventional substitution of filter elements. The electronic recording unit includes power supplies, amplifiers, and digital recording electronics designed to permit recordation of data on tape casettes. Both the optical unit and electronic recording unit are packaged to be manually portable
A Surprising Lack of LGRB Metallicity Evolution with Redshift
Recent additions to the population of Long-duration Gamma Ray Burst (LGRB)
host galaxies with measured metallicities and host masses allow us to
investigate how the distributions of both these properties change with
redshift. We form a sample out to z of 2.5 which we show does not have strong
redshift dependent populations biases in mass and metallicity measurements.
Using this sample, we find a surprising lack of evolution in the LGRB
metallicity distribution across different redshifts and in particular the
fraction of LGRB hosts with relatively high-metallicity, that is those with
12+log(O/H) > 8.4, remains essentially constant out to z = 2.5. This result is
at odds with the evolution in the mass metallicity relation of typical
galaxies, which become progressively more metal poor with increasing redshift.
By converting the measured LGRB host masses and redshifts to expected
metallicities using redshift appropriate mass-metallicity relations, we further
find that the increase in LGRB host galaxy mass distribution with redshift seen
in the Perley et al. (2016) SHOALS sample is consistent with that needed to
preserve a non-evolving LGRB metallicity distribution. However, the estimated
LGRB host metallicity distribution is at least a quarter dex higher at all
redshifts than the measured metallicity distribution. This corresponds to about
a factor of two in raw metallicity and resolves much of the difference between
the LGRB host metallicity cutoffs determined by Graham & Fruchter (2017) and
Perley et al. (2016). As LGRB hosts do not follow the general mass metallicity
relations, there is no substitute for actually measuring their metallicities.Comment: 20 pages, 7 figures, 10 table
Indirect Signals from Dark Matter in Split Supersymmetry
We study the possibilities for the indirect detection of dark matter in Split
Supersymmetry from gamma-rays, positrons, and antiprotons. The most promising
signal is the gamma-ray line, which may be observable at the next generation of
detectors. For certain halo profiles and a high mass neutralino, the line can
even be visible in current experiments. The continuous gamma-ray signal may be
observable, if there is a central spike in the galactic halo density. The
signals are found to be similar to those in MSSM models. These indirect signals
complement other experiments, being most easily observable for regions of
parameter space, such as heavy wino and higgsino dominated neutralinos, which
are least accessible for direct detection and accelerator searches.Comment: 10 pages, 5 figures; experimental sensitivities added to figure 2,
revised version to appear in Phys. Rev.
The search for novel analgesics: re-examining spinal cord circuits with new tools
In this perspective, we propose the absence of detailed information regarding spinal cord
circuits that process sensory information remains a major barrier to advancing analgesia.
We highlight recent advances showing that functionally discrete populations of neurons in
the spinal cord dorsal horn play distinct roles in processing sensory information. We then
discuss new molecular, electrophysiological, and optogenetic techniques that can be
employed to understand how dorsal horn circuits process tactile and nociceptive
information. We believe this information can drive the development of entirely new classes
of pharmacotherapies that target key elements in spinal circuits to selectively modify
sensory function and blunt pain
Application of the coherent state formalism to multiply excited states
A general expression is obtained for the matrix element of an m-body operator
between coherent states constructed from multiple orthogonal coherent boson
species. This allows the coherent state formalism to be applied to states
possessing an arbitrarily large number of intrinsic excitation quanta. For
illustration, the formalism is applied to the two-dimensional vibron model
[U(3) model], to calculate the energies of all excited states in the large-N
limit.Comment: LaTeX (iopart); 10 pages; to be published in J. Phys.
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