5,467 research outputs found
Study of strange particle production in pp collisions with the ALICE detector
ALICE is well suited for strange particles production studies since it has
very good reconstruction capabilities in the low transverse momentum ()
region and it also allows to extend the identification up to quite high
. Charged strange mesons (\kp, \km,) are reconstructed via energy
loss measurements whereas neutral strange mesons (\ks) and strange hyperons
(\lam, , ) are identified via vertex reconstruction. All these
particles carry important information: first, the measurement of production
yields and the particle ratio within the statistical models can help to
understand the medium created and secondly the dynamics at intermediate
investigated via the baryon over meson ratio (\lam / \ks) allows a better
understanding of the hadronization mechanisms and of the underlying event
processes. We present these two aspects of the strange particles analysis in pp
collisions using simulated data.Comment: Proceeding SQM (2009), 5 figures, 6 page
First light of the VLT planet finder SPHERE II. The physical properties and the architecture of the young systems PZ Telescopii and HD 1160 revisited
Context. The young systemsPZ Tel and HD 1160, hosting known low-mass companions, were observed during the commissioning of the new planet finder of the Very Large Telescope (VLT) SPHERE with several imaging and spectroscopic modes.
Aims. We aim to refine the physical properties and architecture of both systems.
Methods. We use SPHERE commissioning data and dedicated Rapid Eye Mount (REM) observations, as well as literature and unpublished data from VLT/SINFONI, VLT/NaCo, Gemini/NICI, and Keck/NIRC2.
Results. We derive new photometry and confirm the short-term (P = 0.94 d) photometric variability of the star PZ Tel A with values of 0.14 and 0.06 mag at optical and near-infrared wavelengths, respectively. We note from the comparison to literature data spanning 38 yr that the star also exhibits a long-term variability trend with a brightening of ~0.25 mag. The 0.63−3.8 μm spectral energy distribution of PZ Tel B (separation ~25 AU) allows us to revise its physical characteristics: spectral type M7 ± 1, T_(eff) = 2700 ± 100 K, log(g) 0.66). For eccentricities below 0.9, the inclination, longitude of the ascending node, and time of periastron passage are well constrained. In particular, both star and companion inclinations are compatible with a system seen edge-on. Based on “hot-start” evolutionary models, we reject other brown dwarf candidates outside 0.25" for both systems, and giant planet companions outside 0.5" that are more massive than 3 MJ for the PZ Tel system. We also show that K1−K2 color can be used along with YJH low-resolution spectra to identify young L-type companions, provided high photometric accuracy (≤0.05 mag) is achieved.
Conclusions. SPHERE opens new horizons in the study of young brown dwarfs and giant exoplanets using direct imaging thanks to high-contrast imaging capabilities at optical (0.5−0.9 μm) and near-infrared (0.95−2.3 μm) wavelengths, as well as high signal-to-noise spectroscopy in the near-infrared domain (0.95−2.3 μm) from low resolutions (R ~ 30−50) to medium resolutions (R ~ 350)
Fermi Edge Singularities in Transport through Quantum Dots
We study the Fermi-edge singularity appearing in the current-voltage
characteristics for resonant tunneling through a localized level at finite
temperature. An explicit expression for the current at low temperature and near
the threshold for the tunneling process is presented which allows to coalesce
data taken at different temperatures to a single curve. Based on this scaling
function for the current we analyze experimental data from a GaAs-AlAs-GaAs
tunneling device with embedded InAs quantum dots obtained at low temperatures
in high magnetic fields.Comment: 12 pages, 5 figure
Design of trials for interrupting the transmission of endemic pathogens
Many interventions against infectious diseases have geographically diffuse effects. This leads to contamination between arms in cluster-randomized trials (CRTs). Pathogen elimination is the goal of many intervention programs against infectious agents, but contamination means that standard CRT designs and analyses do not provide inferences about the potential of interventions to interrupt pathogen transmission at maximum scale-up.; A generic model of disease transmission was used to simulate infections in stepped wedge cluster-randomized trials (SWCRTs) of a transmission-reducing intervention, where the intervention has spatially diffuse effects. Simulations of such trials were then used to examine the potential of such designs for providing generalizable causal inferences about the impact of such interventions, including measurements of the contamination effects. The simulations were applied to the geography of Rusinga Island, Lake Victoria, Kenya, the site of the SolarMal trial on the use of odor-baited mosquito traps to eliminate Plasmodium falciparum malaria. These were used to compare variants in the proposed SWCRT designs for the SolarMal trial.; Measures of contamination effects were found that could be assessed in the simulated trials. Inspired by analyses of trials of insecticide-treated nets against malaria when applied to the geography of the SolarMal trial, these measures were found to be robust to different variants of SWCRT design. Analyses of the likely extent of contamination effects supported the choice of cluster size for the trial.; The SWCRT is an appropriate design for trials that assess the feasibility of local elimination of a pathogen. The effects of incomplete coverage can be estimated by analyzing the extent of contamination between arms in such trials, and the estimates also support inferences about causality. The SolarMal example illustrates how generic transmission models incorporating spatial smoothing can be used to simulate such trials for a power calculation and optimization of cluster size and randomization strategies. The approach is applicable to a range of infectious diseases transmitted via environmental reservoirs or via arthropod vectors
The new servo-spill power converter of the CERN SPS machine
The so-called servo-spill system of the SPS machine requires a very specific power converter to be used as the power actuator of the system. Due to this particular function, the main performance required, for this power converter, is an unusual large signal current bandwidth of up to 1.5 kHz. The procurement is based on a similar industrial product using switch mode technology. This paper describes the main power part as well as the control approach chosen to fulfil the specific requirements of this power converter. Final operational results are also presented
Search for cool giant exoplanets around young and nearby stars - VLT/NaCo near-infrared phase-coronagraphic and differential imaging
[Abridged] Context. Spectral differential imaging (SDI) is part of the
observing strategy of current and future high-contrast imaging instruments. It
aims to reduce the stellar speckles that prevent the detection of cool planets
by using in/out methane-band images. It attenuates the signature of off-axis
companions to the star, such as angular differential imaging (ADI). However,
this attenuation depends on the spectral properties of the low-mass companions
we are searching for. The implications of this particularity on estimating the
detection limits have been poorly explored so far. Aims. We perform an imaging
survey to search for cool (Teff<1000-1300 K) giant planets at separations as
close as 5-10 AU. We also aim to assess the sensitivity limits in SDI data
taking the photometric bias into account. This will lead to a better view of
the SDI performance. Methods. We observed a selected sample of 16 stars (age <
200 Myr, d < 25 pc) with the phase-mask coronagraph, SDI, and ADI modes of
VLT/NaCo. Results. We do not detect any companions. As for the sensitivity
limits, we argue that the SDI residual noise cannot be converted into mass
limits because it represents a differential flux, unlike the case of
single-band images. This results in degeneracies for the mass limits, which may
be removed with the use of single-band constraints. We instead employ a method
of directly determining the mass limits. The survey is sensitive to cool giant
planets beyond 10 AU for 65% and 30 AU for 100% of the sample. Conclusions. For
close-in separations, the optimal regime for SDI corresponds to SDI flux ratios
>2. According to the BT-Settl model, this translates into Teff<800 K. The
methods described here can be applied to the data interpretation of SPHERE. We
expect better performance with the dual-band imager IRDIS, thanks to more
suitable filter characteristics and better image quality.Comment: 19 pages, 16 figures, accepted for publication in A&A, version
including language editin
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