10,566 research outputs found
Gemini/GMOS Transmission Spectral Survey: Complete Optical Transmission Spectrum of the hot Jupiter WASP-4b
We present the complete optical transmission spectrum of the hot Jupiter
WASP-4b from 440-940 nm at R ~ 400-1500 obtained with the Gemini Multi-Object
Spectrometers (GMOS); this is the first result from a comparative
exoplanetology survey program of close-in gas giants conducted with GMOS.
WASP-4b has an equilibrium temperature of 1700 K and is favorable to study in
transmission due to a large scale height (370 km). We derive the transmission
spectrum of WASP-4b using 4 transits observed with the MOS technique. We
demonstrate repeatable results across multiple epochs with GMOS, and derive a
combined transmission spectrum at a precision about twice above photon noise,
which is roughly equal to to one atmospheric scale height. The transmission
spectrum is well fitted with a uniform opacity as a function of wavelength. The
uniform opacity and absence of a Rayleigh slope from molecular hydrogen suggest
that the atmosphere is dominated by clouds with condensate grain size of ~1 um.
This result is consistent with previous observations of hot Jupiters since
clouds have been seen in planets with similar equilibrium temperatures to
WASP-4b. We describe a custom pipeline that we have written to reduce GMOS
time-series data of exoplanet transits, and present a thorough analysis of the
dominant noise sources in GMOS, which primarily consist of wavelength- and
time- dependent displacements of the spectra on the detector, mainly due to a
lack of atmospheric dispersion correction.Comment: 23 pages, 12 figures, accepted for publication in AJ, 2017 July
Vector magnetic hysteresis of hard superconductors
Critical state problems which incorporate more than one component for the
magnetization vector of hard superconductors are investigated. The theory is
based on the minimization of a cost functional
which weighs the changes of the magnetic field vector within the sample. We
show that Bean's simplest prescription of choosing the correct sign for the
critical current density in one dimensional problems is just a particular
case of finding the components of the vector . is
determined by minimizing under the constraint , with a bounded set. Upon the selection of
different sets we discuss existing crossed field measurements and
predict new observable features. It is shown that a complex behavior in the
magnetization curves may be controlled by a single external parameter, i.e.:
the maximum value of the applied magnetic field .Comment: 10 pages, 9 figures, accepted in Phys. Rev.
The Adiabatic Instability on Cosmology's Dark Side
We consider theories with a nontrivial coupling between the matter and dark
energy sectors. We describe a small scale instability that can occur in such
models when the coupling is strong compared to gravity, generalizing and
correcting earlier treatments. The instability is characterized by a negative
sound speed squared of an effective coupled dark matter/dark energy fluid. Our
results are general, and applicable to a wide class of coupled models and
provide a powerful, redshift-dependent tool, complementary to other
constraints, with which to rule many of them out. A detailed analysis and
applications to a range of models are presented in a longer companion paper.Comment: 4 pages, 1 figur
Superconductivity in Dense Wires
becomes superconducting just below 40 K. Whereas porous
polycrystalline samples of can be synthesized from boron powders, in
this letter we demonstrate that dense wires of can be prepared by
exposing boron filaments to vapor. The resulting wires have a diameter of
160 , are better than 80% dense and manifest the full shielding in the superconducting state. Temperature-dependent
resistivity measurements indicate that is a highly conducting metal in
the normal state with = 0.38 -. Using this value, an
electronic mean free path, can be estimated, indicating
that wires are well within the clean limit. , , and
data indicate that manifests comparable or better superconducting
properties in dense wire form than it manifests as a sintered pellet.Comment: Figures' layout fixe
Cosmon dark matter?
We investigate if the fluctuations of the scalar field mediating quintessence
-- the cosmon -- can play an important role in cosmology. Small fluctuations
with short wavelength behave similar to a relativistic gas. In contrast, the
contribution to the energy density from horizon size fluctuations may decrease
less rapidly than radiation. We discuss the possibility that the cosmon
fluctuations grow nonlinearly, form lumps and constitute the clustering dark
matter of the universe. Cosmon dark matter would lead to interesting
consequences for the equation of state and the coupling between quintessence
and dark matter.Comment: Published version,correction in appendix A, 43 pages, LaTe
Metallicities of M Dwarf Planet Hosts from Spectral Synthesis
We present the first spectroscopic metallicities of three M dwarfs with known
or candidate planetary mass companions. We have analyzed high resolution, high
signal-to-noise spectra of these stars which we obtained at McDonald
Observatory. Our analysis technique is based on spectral synthesis of atomic
and molecular features using recently revised cool-star model atmospheres and
spectrum synthesis code. The technique has been shown to yield results
consistent with the analyses of solar-type stars and allows measurements of M
dwarf [M/H] values to 0.12 dex precision. From our analysis, we find [M/H] =
-0.12, -0.32, and -0.33 for GJ 876, GJ 436, and GJ 581 respectively. These
three M dwarf planet hosts have sub-solar metallicities, a surprising departure
from the trend observed in FGK-type stars. This study is the first part of our
ongoing work to determine the metallicities of the M dwarfs included in the
McDonald Observatory planet search program.Comment: 13 pages, 2 figures, accepted for publication in ApJ
Autonomous clustering using rough set theory
This paper proposes a clustering technique that minimises the need for subjective
human intervention and is based on elements of rough set theory. The proposed algorithm is
unified in its approach to clustering and makes use of both local and global data properties to
obtain clustering solutions. It handles single-type and mixed attribute data sets with ease and
results from three data sets of single and mixed attribute types are used to illustrate the
technique and establish its efficiency
Using laboratory-based surveillance data for prevention: an algorithm for detecting Salmonella outbreaks.
By applying cumulative sums (CUSUM), a quality control method commonly used in manufacturing, we constructed a process for detecting unusual clusters among reported laboratory isolates of disease-causing organisms. We developed a computer algorithm based on minimal adjustments to the CUSUM method, which cumulates sums of the differences between frequencies of isolates and their expected means; we used the algorithm to identify outbreaks of Salmonella Enteritidis isolates reported in 1993. By comparing these detected outbreaks with known reported outbreaks, we estimated the sensitivity, specificity, and false-positive rate of the method. Sensitivity by state in which the outbreak was reported was 0%(0/1) to 100%. Specificity was 64% to 100%, and the false-positive rate was 0 to 1
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