1,283 research outputs found
Forecast B-modes detection at large scales in presence of noise and foregrounds
We investigate the detectability of the primordial CMB polarization B-mode
power spectrum on large scales in the presence of instrumental noise and
realistic foreground contamination. We have worked out a method to estimate the
errors on component separation and to propagate them up to the power spectrum
estimation. The performances of our method are illustrated by applying it to
the instrumental specifications of the Planck satellite and to the proposed
configuration for the next generation CMB polarization experiment COrE. We
demonstrate that a proper component separation step is required in order
achieve the detection of B-modes on large scales and that the final sensitivity
to B-modes of a given experiment is determined by a delicate balance between
noise level and residual foregrounds, which depend on the set of frequencies
exploited in the CMB reconstruction, on the signal-to-noise of each frequency
map, and on our ability to correctly model the spectral behavior of the
foreground components. We have produced a flexible software tool that allows
the comparison of performances on B-mode detection of different instrumental
specifications (choice of frequencies, noise level at each frequency, etc.) as
well as of different proposed approaches to component separation.Comment: 7 pages, 2 tables, 1 figure, accepted by MNRA
Observations of the Sunyaev-Zel'dovich effect at high angular resolution towards the galaxy clusters A665, A2163 and CL0016+16
We report on the first observation of the Sunyaev-Zel'dovich effect with the
Diabolo experiment at the IRAM 30 metre telescope. A significant brightness
decrement is detected in the direction of three clusters (Abell 665, Abell 2163
and CL0016+16). With a 30 arcsecond beam and 3 arcminute beamthrow, this is the
highest angular resolution observation to date of the SZ effect.Comment: 23 pages, 8 figures, 6 tables, accepted to New Astronom
Estimates of metabolic rate and major constituents of metabolic demand in fishes under field conditions: Methods, proxies, and new perspectives
Metabolic costs are central to individual energy budgets, making estimates of metabolic rate vital to understanding how an organism interacts with its environment as well as the role of species in their ecosystem. Despite the ecological and commercial importance of fishes, there are currently no widely adopted means of measuring field metabolic rate in fishes. The lack of recognized methods is in part due to the logistical difficulties of measuring metabolic rates in free swimming fishes. However, further development and refinement of techniques applicable for field-based studies on free swimming animals would greatly enhance the capacity to study fish under environmentally relevant conditions. In an effort to foster discussion in this area, from field ecologists to biochemists alike, we review aspects of energy metabolism and give details on approaches that have been used to estimate energetic parameters in fishes. In some cases, the techniques have been applied to field conditions; while in others, the methods have been primarily used on laboratory held fishes but should be applicable, with validation, to fishes in their natural environment. Limitations, experimental considerations and caveats of these measurements and the study of metabolism in wild fishes in general are also discussed. Potential novel approaches to FMR estimates are also presented for consideration. The innovation of methods for measuring field metabolic rate in free-ranging wild fish would revolutionize the study of physiological ecology
Optical properties of Au colloids self-organized into rings via copolymer templates
The investigation of the Localized Surface Plasmon Resonance for plasmonic
nanoparticles has opened new perspectives for optical nanosensors. Today, an
issue in plasmonics is the development of large scale and low cost devices. We
focus here on the Langmuir-Blodgett technique to self-organize gold
nanoparticles (~ 7 nm) into rings (~ 60 nm) via
polystyrene-b-polymethylmethacrylate templates. In particular, we investigated
the optical properties of organized gold nanoparticle rings over large areas
and report experimental evidence for plasmon resonances of both individual
nanoparticles and collective modes. This paves the way for designing devices
with multiple resonances in the visible-Infra-red spectrum and developing
optical sensors
A cryogenic waveplate rotator for polarimetry at mm and sub-mm wavelengths
Mm and sub-mm waves polarimetry is the new frontier of research in Cosmic
Microwave Background and Interstellar Dust studies. Polarimeters working in the
IR to MM range need to be operated at cryogenic temperatures, to limit the
systematic effects related to the emission of the polarization analyzer. In
this paper we study the effect of the temperature of the different components
of a waveplate polarimeter, and describe a system able to rotate, in a
completely automated way, a birefringent crystal at 4K. We simulate the main
systematic effects related to the temperature and non-ideality of the optical
components in a Stokes polarimeter. To limit these effects, a cryogenic
implementation of the polarimeter is mandatory. In our system, the rotation
produced by a step motor, running at room temperature, is transmitted down to
cryogenic temperatures by means of a long shaft and gears running on custom
cryogenic bearings. Our system is able to rotate, in a completely automated
way, a birefringent crystal at 4K, dissipating only a few mW in the cold
environment. A readout system based on optical fibers allows to control the
rotation of the crystal to better than 0.1{\deg}. This device fulfills the
stringent requirements for operation in cryogenic space experiments, like the
forthcoming PILOT, BOOMERanG and LSPE.Comment: Submitted to Astronomy and Astrophysics. v1: 10 pages, 8 figures. v2:
corrected labels for the bibliographic references (no changes in the
bibliography). v3: revised version. 9 pages, 7 figures. Added a new figure.
Updated with a more realistic simulation for the interstellar dust and with
the latest cryogenic test
The Sunyaev-Zeldovich Effect and Its Cosmological Significance
Comptonization of the cosmic microwave background (CMB) radiation by hot gas
in clusters of galaxies - the Sunyaev-Zeldovich (S-Z) effect - is of great
astrophysical and cosmological significance. In recent years observations of
the effect have improved tremendously; high signal-to-noise images of the
effect (at low microwave frequencies) can now be obtained by ground-based
interferometric arrays. In the near future, high frequency measurements of the
effect will be made with bolomateric arrays during long duration balloon
flights. Towards the end of the decade the PLANCK satellite will extensive S-Z
surveys over a wide frequency range. Along with the improved observational
capabilities, the theoretical description of the effect and its more precise
use as a probe have been considerably advanced. I review the current status of
theoretical and observational work on the effect, and the main results from its
use as a cosmological probe.Comment: Invited review; in proceedings of the Erice NATO/ASI `Astrophysical
Sources of High Energy Particles and Radiation'; 11 pages, 3 figure
Photoionization spectroscopy of CH3C3N in the vacuum-ultraviolet range
International audienceUsing vacuum-ultraviolet (VUV) synchrotron radiation, threshold and dissociative photoionization of cyanopropyne (CH3C3N) in the gas phase have been studied from 86 000 cmâ1 up to 180 000 cmâ1 by recording Threshold-PhotoElectron Spectrum (TPES) and PhotoIon Yield (PIY). Ionization energies of the four lowest electronic states XÌ+2E,AÌ+2A1,BÌ+2E and CÌ+ of CH3C3N+ are derived from the TPES with a better accuracy than previously reported. The adiabatic ionization potential of CH3C3N is measured as 86872±20 cmâ1. A description of the vibrational structure of these states is proposed leading to the first determination of the vibrational frequencies for most modes. The vibrational assignments of the XÌ+ state are supported by density functional theory calculations. In addition, dissociative photoionization spectra have been recorded for several cationic fragments in the range 12â15.5 eV (96 790â125 000 cmâ1) and they bring new information on the photophysics of CH3C3N+. Threshold energies for the cationic dissociative channels leading to CH2C3N+, CHC3N+, HC3H+, HCNH+ and CH3+ have been measured for the first time and are compared with quantum chemical calculations
Dynamic validation of the Planck/LFI thermal model
The Low Frequency Instrument (LFI) is an array of cryogenically cooled
radiometers on board the Planck satellite, designed to measure the temperature
and polarization anisotropies of the cosmic microwave backgrond (CMB) at 30, 44
and 70 GHz. The thermal requirements of the LFI, and in particular the
stringent limits to acceptable thermal fluctuations in the 20 K focal plane,
are a critical element to achieve the instrument scientific performance.
Thermal tests were carried out as part of the on-ground calibration campaign at
various stages of instrument integration. In this paper we describe the results
and analysis of the tests on the LFI flight model (FM) performed at Thales
Laboratories in Milan (Italy) during 2006, with the purpose of experimentally
sampling the thermal transfer functions and consequently validating the
numerical thermal model describing the dynamic response of the LFI focal plane.
This model has been used extensively to assess the ability of LFI to achieve
its scientific goals: its validation is therefore extremely important in the
context of the Planck mission. Our analysis shows that the measured thermal
properties of the instrument show a thermal damping level better than
predicted, therefore further reducing the expected systematic effect induced in
the LFI maps. We then propose an explanation of the increased damping in terms
of non-ideal thermal contacts.Comment: Planck LFI technical papers published by JINST:
http://www.iop.org/EJ/journal/-page=extra.proc5/1748-022
LEVERAGING PLASMA-DERIVED EXOSOMES FOR BIOMARKER DISCOVERY IN SICKLE CELL DISEASE: PREPARATION FOR A LARGE PROSPECTIVE STUDY
Diverse clinical variability among sickle cell disease (SCD) patients opposes crises prediction, health monitor- ing and streamlined management. Thus, an unmet need for objective biomarkers prevails. Exosomes are extra-cellular nano-vesicles (50-150nm), enriched in bioactive lipids, proteins, mRNAs and miRNAs, released by cells. They transport molecular cargo to nearby/distant cells to affect-regulate biological processes. Recent studies by Khalyfa et al. assessed the plasma exosome content, their sources and transcriptomics signature as predictive marker in SCD children with acute chest syndrome. However, the small sample sizes (32 and 33 individuals, respectively) may not capture the clinical variability
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