5,305 research outputs found
Tricriticalities and Quantum Phases in Spin-Orbit-Coupled Spin- Bose Gases
We study the zero-temperature phase diagram of a spin-orbit-coupled
Bose-Einstein condensate of spin , with equally weighted Rashba and
Dresselhaus couplings. Depending on the antiferromagnetic or ferromagnetic
nature of the interactions, we find three kinds of striped phases with
qualitatively different behaviors in the modulations of the density profiles.
Phase transitions to the zero-momentum and the plane-wave phases can be induced
in experiments by independently varying the Raman coupling strength and the
quadratic Zeeman field. The properties of these transitions are investigated in
detail, and the emergence of tricritical points, which are the direct
consequence of the spin-dependent interactions, is explicitly discussed.Comment: 6 pages, 2 figures + Supplemental Material. Revised version,
published in PR
Consequences of spectrograph illumination for the accuracy of radial-velocimetry
For fiber-fed spectrographs with a stable external wavelength source,
scrambling properties of optical fibers and, homogeneity and stability of the
instrument illumination are important for the accuracy of radial-velocimetry.
Optical cylindric fibers are known to have good azimuthal scrambling. In
contrast, the radial one is not perfect. In order to improve the scrambling
ability of the fiber and to stabilize the illumination, optical double
scrambler are usually coupled to the fibers. Despite that, our experience on
SOPHIE and HARPS has lead to identified remaining radial-velocity limitations
due to the non-uniform illumination of the spectrograph. We conducted tests on
SOPHIE with telescope vignetting, seeing variation and centering errors on the
fiber entrance. We simulated the light path through the instrument in order to
explain the radial velocity variation obtained with our tests. We then
identified the illumination stability and uniformity has a critical point for
the extremely high-precision radial velocity instruments (ESPRESSO@VLT,
CODEX@E-ELT). Tests on square and octagonal section fibers are now under
development and SOPHIE will be used as a bench test to validate these new feed
optics.Comment: to appear in the Proceedings conference "New Technologies for Probing
the Diversity of Brown Dwarfs and Exoplanets", Shanghai, 200
Towards agent-based crowd simulation in airports using games technology
We adapt popular video games technology for an agent-based crowd simulation in an airport terminal. To achieve this, we investigate the unique traits of airports and implement a virtual crowd by exploiting a scalable layered intelligence technique in combination with physics middleware and a socialforces approach. Our experiments show that the framework runs at interactive frame-rate and evaluate the scalability with increasing number of agents demonstrating
navigation behaviour
Recommendation to Use Exact P-values in Biomarker Discovery Research
Background: In biomarker discovery studies, markers are ranked for validation using P-values. Standard P-value calculations use normal approximations that may not be valid for small P-values and small sample sizes common in discovery research.
Methods: We compared exact P-values, valid by definition, with normal and logit-normal approximations in a simulated study of 40 cases and 160 controls. The key measure of biomarker performance was sensitivity at 90% specificity. Data for 3000 uninformative markers and 30 true markers were generated randomly, with 10 replications of the simulation. We also analyzed real data on 2371 antibody array markers measured in plasma from 121 cases with ER/PR positive breast cancer and 121 controls.
Results: Using the same discovery criterion, the valid exact P-values lead to discovery of 24 true and 82 false biomarkers while approximate P-values yielded 15 true and 15 false biomarkers (normal approximation) and 20 true and 86 false biomarkers (logit-normal approximation). Moreover, the estimated numbers of true markers among those discovered were substantially incorrect for approximate P-values: normal estimated 0 true markers discovered but found 15; logit-normal estimated 42 but found 20. The exact method estimated 22, close to the actual number of 24 true discoveries. With real data, exact and approximate P-values ranked candidate breast cancer biomarkers very differently.
Conclusions: Exact P-values should be used because they are universally valid. Approximate P-values can lead to inappropriate biomarker selection rules and incorrect conclusions.
Impact: Rigorous data analysis methodology in discovery research may improve the yield of biomarkers that validate clinically
APPLICATION OF A ONE-STEP REAL TIME RT-PCR PROTOCOL FOR NOROVIRUS DETECTION IN SHELLFISH HARVERSTED AND COMMERCIALIZED IN CAMPANIA REGION
Shellfish are recognized as a potential vehicle of viral diseases. However, according to European Regulations, only bacteriological parameters (Salmonella and E. coli) are used to establish their microbiological quality. Because of the lack of a standard reference method for the detection of viruses, data on the incidence of enteric viruses in European production areas are still limited. Aim of the present study was the evaluation of the Norovirus (NoV) contamination in shellfish from different harvesting areas (both class A and B) and from registered and not- registered retails of the Campania region (Tyrrhenian Sea, Italy). Seventy shellfish (Mytilus galloprovincialis) were collected from 15 harvesting areas, one authorized and two not authorized retails and were examined for virus presence (NoV genogroups I and II) by Real Time PCR. Ten harvesting areas (66%) showed presence of viral contamination, with three of them belonging to A areas and seven to B areas. The shellfish collected from the registered retail tested positive for Norovirus presence, whereas the shellfish collected from not-authorized retails didn't show viral contamination. Twenty-nine samples were positive for genogroup II, ten of which tested positive also for NoV genogroup I
The ELODIE and SOPHIE Search for Northern Extrasolar Planets: Jupiter-Analogs around Sun-Like Stars
We present radial-velocity measurements (RV) obtained in one of the numbers of programs underway to search for extrasolar planets with the spectrograph SOPHIE at the 1.93-m telescope of the Observatoire de Haute-Provence. Targets were selected from catalogs observed with ELODIE, which had been mounted previously at the telescope, in order to detect long-period planets with an extended database close to 15 year
The HARPS search for southern extrasolar planets. XXIII. 8 planetary companions to low-activity solar-type stars
In this paper, we present our HARPS radial-velocity data for eight
low-activity solar-type stars belonging to the HARPS volume-limited sample:
HD6718, HD8535, HD28254, HD290327, HD43197, HD44219, HD148156, and HD156411.
Keplerian fits to these data reveal the presence of low-mass companions around
these targets. With minimum masses ranging from 0.58 to 2.54 MJup, these
companions are in the planetary mass domain. The orbital periods of these
planets range from slightly less than one to almost seven years. The eight
orbits presented in this paper exhibit a wide variety of eccentricities: from
0.08 to above 0.8.Comment: 8 pages, 2 figures, accepted for publication in A&
The SOPHIE search for northern extrasolar planets. II. A multi-planet system around HD9446
We report the discovery of a planetary system around HD9446, performed from
radial velocity measurements secured with the spectrograph SOPHIE at the 193-cm
telescope of the Haute-Provence Observatory during more than two years. At
least two planets orbit this G5V, active star: HD9446b has a minimum mass of
0.7 M_Jup and a slightly eccentric orbit with a period of 30 days, whereas
HD9446c has a minimum mass of 1.8 M_Jup and a circular orbit with a period of
193 days. As for most of the known multi-planet systems, the HD9446-system
presents a hierarchical disposition, with a massive outer planet and a lighter
inner planet.Comment: 7 pages, 6 figures, 3 tables, accepted for publication in A&
- …