3,641 research outputs found
Galactic Plane H Surveys: IPHAS & VPHAS+
The optical Galactic Plane H surveys IPHAS and VPHAS+ are
dramatically improving our understanding of Galactic stellar populations and
stellar evolution by providing large samples of stars in short lived, but
important, evolutionary phases, and high quality homogeneous photometry and
images over the entire Galactic Plane. Here I summarise some of the
contributions these surveys have already made to our understanding of a number
of key areas of stellar and Galactic astronomy.Comment: 5 pages, 2 figures, refereed proceeding of the "The Universe of
Digital Sky Surveys" conference, November 2014, to be published in the
Astrophysics and Space Science Proceeding
Square vortex lattice at anomalously low magnetic fields in electron-doped NdCeCuO
We report here on the first direct observations of the vortex lattice in the
bulk of electron-doped NdCeCuO single crystals. Using
small angle neutron scattering, we have observed a square vortex lattice with
the nearest-neighbors oriented at 45 from the Cu-O bond direction,
which is consistent with theories based on the d-wave superconducting gap.
However, the square symmetry persists down to unusually low magnetic fields.
Moreover, the diffracted intensity from the vortex lattice is found to decrease
rapidly with increasing magnetic field.Comment: 4 pages, 4 Figures, accepted for publication in Phys. Rev. Let
IPHAS and the symbiotic stars. I. Selection method and first discoveries
The study of symbiotic stars is essential to understand important aspects of
stellar evolution in interacting binaries. Their observed population in the
Galaxy is however poorly known, and is one to three orders of magnitudes
smaller than the predicted population size. IPHAS, the INT Photometric Halpha
survey of the Northern Galactic plane, gives us the opportunity to make a
systematic, complete search for symbiotic stars in a magnitude-limited volume,
and discover a significant number of new systems.
A method of selecting candidate symbiotic stars by combining IPHAS and
near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic
binaries from normal stars and most of the other types of Halpha emission line
stars in the Galaxy. The only exception are T Tauri stars, which can however be
recognized because of their concentration in star forming regions. Using these
selection criteria, we discuss the classification of a list of 4338 IPHAS stars
with Halpha in emission. 1500 to 2000 of them are likely to be Be stars. Among
the remaining objects, 1183 fulfill our photometric constraints to be
considered candidate symbiotic stars. The spectroscopic confirmation of three
of these objects, which are the first new symbiotic stars discovered by IPHAS,
proves the potential of the survey and selection method.Comment: Accepted for publication on Astronomy and Astrophysics. 12 pages, 8
figure
Likelihood-ratio ranking of gravitational-wave candidates in a non-Gaussian background
We describe a general approach to detection of transient gravitational-wave
signals in the presence of non-Gaussian background noise. We prove that under
quite general conditions, the ratio of the likelihood of observed data to
contain a signal to the likelihood of it being a noise fluctuation provides
optimal ranking for the candidate events found in an experiment. The
likelihood-ratio ranking allows us to combine different kinds of data into a
single analysis. We apply the general framework to the problem of unifying the
results of independent experiments and the problem of accounting for
non-Gaussian artifacts in the searches for gravitational waves from compact
binary coalescence in LIGO data. We show analytically and confirm through
simulations that in both cases the likelihood ratio statistic results in an
improved analysis.Comment: 10 pages, 6 figure
Mid-infrared Hall effect in thin-film metals: Probing the Fermi surface anisotropy in Au and Cu
A sensitive mid-infrared (MIR, 900-1100 cm-1, 112-136 meV) photo-elastic
polarization modulation technique is used to measure simultaneously Faraday
rotation and circular dichroism in thin metal films. These two quantities
determine the complex AC Hall conductivity. This novel technique is applied to
study Au and Cu thin films at temperatures down to 20 K and magnetic fields up
to 8 T. The Hall frequency is consistent with band theory predictions. We
report the first measurement of the MIR Hall scattering rate, which is
significantly lower than that derived from Drude analysis of zero magnetic
field MIR transmission measurements. This difference is qualitatively explained
in terms of the anisotropy of the Fermi surface in Au and Cu.Comment: 14 pages of text, 5 figure
Prevalence and Distribution of Ranavirus in Amphibians From
Several infectious diseases are threatening amphibian species worldwide and have resulted in massmortality events across the globe. An emerging group of viral pathogens (ranaviruses) are documented to cause die-offs in amphibian populations worldwide, including in several regions of the U.S. Unfortunately, large gaps remain in our understanding of the distribution of this systemic pathogen in the U.S., including within the state of Oklahoma. To address this gap in our understanding, we carried out surveys of this infectious pathogen across 14 sites in seven southeastern Oklahoma counties in spring 2015, screening 17 amphibian species from this region. Using liver and tail tissue samples collected from individual amphibians, we screened for the presence and infection load of ranavirus. Of the 390 samples, 84 (21.5%) tested positive for ranavirus, with infection prevalence varying among species surveyed. Notably, the family Bufonidae had no samples that tested positive for ranavirus, whereas the remaining families had an infection prevalence ranging from 14–50%. Despite an overall infection prevalence of 21.5%, we detected no clinical signs of ranavirosis and all sampled individuals appeared outwardly healthy. These results provide data on the geographic and host distribution of ranavirus in southeastern Oklahoma, as well as the first documented cases of the pathogen in three species of anurans: Gastrophryne carolinensis (Eastern Narrow-mouthed Toad), G. olivacea (Western Narrow-mouthed Toad), and Pseudacris fouquettei (Cajun Chorus Frog). With widespread ranavirus infection, there is potential for transmission from abundant, widespread species to more vulnerable, state-threatened amphibians
Small Unmanned Aircraft System Off Nominal Operations Reporting System Unmanned Aircraft System: Traffic Management Technical Capability Level 4 Implementation, Data Collection and Analysis
NASA performed research and development of technologies and requirements for traffic management of small Unmanned Aircraft Systems (UAS). In this effort, a small UAS off-nominal situation reporting system was developed to capture information from off-nominal situations to understand their nature and reduce occurrences. This Technical Memorandum (TM) describes the reporting system and analysis of 116 off-nominal situation reports from 352 small UAS operations, which were conducted at two flight test ranges in Summer 2019
Infrared Hall effect in high Tc superconductors: Evidence for non-Fermi liquid Hall scattering
Infrared (20-120 cm-1 and 900-1100 cm-1) Faraday rotation and circular
dichroism are measured in high Tc superconductors using sensitive polarization
modulation techniques. Optimally doped YBCO thin films are studied at
temperatures down to 15 K and magnetic fields up to 8 T. At 1000 cm-1 the Hall
conductivity varies strongly with temperature in contrast to the longitudinal
conductivity which is nearly independent of temperature. The Hall scattering
rate has a T^2 temperature dependence but, unlike a Fermi liquid, depends only
weakly on frequency. The experiment puts severe constraints on theories of
transport in the normal state of high Tc superconductors.Comment: 8 pages, 3 figure
Magnetoresistance of YBa2Cu3O7 in the "cold spots" model
We calculate the in-plane magnetoresistance of
YBaCuO in a magnetic field applied perpendicular to the
planes for the ``cold spots'' model. In this model, the electron relaxation
time at small regions on the Fermi surface near the
Brillouin zone diagonals is much longer than the relaxation time
at the rest of the Fermi surface ( is temperature). In
qualitative agreement with the experiment, we find that Kohler's rule is
strongly violated, but the ratio ,
where is the Hall angle, is approximately
temperature-independent. We find the ratio is about 5.5, which is of the same
order of magnitude as in the experiment.Comment: RevTeX, 4 pages, 6 figures. V.2: 2 references adde
- …