311 research outputs found
The matter distribution in z ~ 0.5 redshift clusters of galaxies. II : The link between dark and visible matter
We present an optical analysis of a sample of 11 clusters built from the
EXCPRES sample of X-ray selected clusters at intermediate redshift (z ~ 0.5).
With a careful selection of the background galaxies we provide the mass maps
reconstructed from the weak lensing by the clusters. We compare them with the
light distribution traced by the early-type galaxies selected along the red
sequence for each cluster. The strong correlations between dark matter and
galaxy distributions are confirmed, although some discrepancies arise, mostly
for merging or perturbed clusters. The average M/L ratio of the clusters is
found to be: M/L_r = 160 +/- 60 in solar units (with no evolutionary
correction), in excellent agreement with similar previous studies. No strong
evolutionary effects are identified even if the small sample size reduces the
significance of the result. We also provide a individual analysis of each
cluster in the sample with a comparison between the dark matter, the galaxies
and the gas distributions. Some of the clusters are studied for the first time
in the optical.Comment: 25 pages, 9 figues + 11 figures in Annex, 4 tables. Accepted for
publication in A&A. 1 reference correcte
How to estimate the differential acceleration in a two-species atom interferometer to test the equivalence principle
We propose a scheme for testing the weak equivalence principle (Universality
of Free Fall) using an atom-interferometric measurement of the local
differential acceleration between two atomic species with a large mass ratio as
test masses. A apparatus in free fall can be used to track atomic free-fall
trajectories over large distances. We show how the differential acceleration
can be extracted from the interferometric signal using Bayesian statistical
estimation, even in the case of a large mass and laser wavelength difference.
We show that this statistical estimation method does not suffer from
acceleration noise of the platform and does not require repeatable experimental
conditions. We specialize our discussion to a dual potassium/rubidium
interferometer and extend our protocol with other atomic mixtures. Finally, we
discuss the performances of the UFF test developed for the free-fall (0-g)
airplane in the ICE project (\verb"http://www.ice-space.fr"
Chirped Pulse Spectrometer Operating at 200 GHz
The combination of electronic sources operating at high frequencies and
modern microwave instrumentation has enabled the recent development of
chirped-pulse spectrometers for the millimetre and THz bands. This type of
instrument can operate at high resolution which is particularly suited to gas
phase rotational spectroscopy. The construction of a chirped pulse spectrometer
operating at 200 GHz is described in detail while attention is paid to the
phase stability and the data accumulation over many cycles. Validation using
carbonyl sulphide has allowed the detection limit of the instrument to be
established as function of the accumulation. A large number of OCS transitions
were identified using a 10 GHz chirped pulse and include the 6 most abundant
isotopologues, the weakest line corresponding to the fundamental R(17)
transition of 16 O 13 C 33 S with a line strength of 4.3 x 10-26 cm-1
/(molec.cm-2). The linearity of the system response for different degrees of
data accumulation and transition line strength was confirmed over 4 orders of
magnitudes. A simple analysis of the time domain data was demonstrated to
provide the line broadening coefficient without the need for conversion by a
Fourier transform. Finally, the pulse duration is discussed and optimal values
are given for both Doppler limited and collisional regimes
Assessing the impacts of shoreline hardening on beach response to hurricanes: Saint-Barthélemy, Lesser Antilles
International audienc
Functional SOM for variable-length signal windows
Functional data, often sampled at high frequency, lead to high-dimensional vectors. The curse of dimensionality makes the latter difficult to handle with standard data analysis tools. Functional data analysis tools take profit of the functional nature of data by projecting them on a smooth basis. This paper shows how to extend functional Self-Organizing Maps (SOM) to signal windows having different lengths. This technique may be applied for example on signal sampled regularly, but for which the duration of each signal is varying; an example concerns electrocardiography (ECG), where the signal is usually cut according to the variable period between two heart beats
Functional SOM for variable-length signal windows
Functional data, often sampled at high frequency, lead to high-dimensional vectors. The curse of dimensionality makes the latter difficult to handle with standard data analysis tools. Functional data analysis tools take profit of the functional nature of data by projecting them on a smooth basis. This paper shows how to extend functional Self-Organizing Maps (SOM) to signal windows having different lengths. This technique may be applied for example on signal sampled regularly, but for which the duration of each signal is varying; an example concerns electrocardiography (ECG), where the signal is usually cut according to the variable period between two heart beats
I.C.E.: a Transportable Atomic Inertial Sensor for Test in Microgravity
We present our the construction of an atom interferometer for inertial
sensing in microgravity, as part of the I.C.E. (\textit{Interf\'{e}rom\'{e}trie
Coh\'{e}rente pour l'Espace}) collaboration. On-board laser systems have been
developed based on fibre-optic components, which are insensitive to mechanical
vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency
stabilised for weeks at a time. A compact, transportable vacuum system has been
built, and used for laser cooling and magneto-optical trapping. We will use a
mixture of quantum degenerate gases, bosonic Rb and fermionic K,
in order to find the optimal conditions for precision and sensitivity of
inertial measurements. Microgravity will be realised in parabolic flights
lasting up to 20s in an Airbus. We show that the factors limiting the
sensitivity of a long-interrogation-time atomic inertial sensor are the phase
noise in reference frequency generation for Raman-pulse atomic beam-splitters
and acceleration fluctuations during free fall
Analysis of self-broadened pure rotational and rovibrational lines of methyl chloride at room temperature
International audienceRovibrational absorption spectra of methyl chloride in the spectral region between 2800 and 3200 cm 1 were recorded with a high-resolution Fourier spectrometer. A multispectrum fitting procedure was used to analyze 527 transitions of the ν1 band and to retrieve the self-broadening coefficients for various J- and K-values with an estimated accuracy around 8%. Pure rotational transitions of CH3Cl in the submillimeter/terahertz region (0.2-1.4 THz) were also investigated using two complementary techniques of frequency-multiplication and continuous-wave photomixing. 43 pure rotational self-broadening coefficients were extracted with the accuracy between 3 and 5%. The whole set of measured values was used to model the J- and K-rotational dependences of the self-broadening coefficients by second-order polynomials. In addition, semi-classical calculations were performed, based on the real symmetric-top geometry of the active molecule, an intermolecular potential model including not only the dominant electrostatic but also the short-range forces, as well as on an exact classical treatment of the relative translational motion of the colliding partners. Comparison of all experimental and theoretical results shows similar rotational dependences and no significant vibrational dependence, so that extrapolations to other spectral regions should be straightforward
Light-pulse atom interferometry in microgravity
We describe the operation of a light pulse interferometer using cold 87Rb
atoms in reduced gravity. Using a series of two Raman transitions induced by
light pulses, we have obtained Ramsey fringes in the low gravity environment
achieved during parabolic flights. With our compact apparatus, we have operated
in a regime which is not accessible on ground. In the much lower gravity
environment and lower vibration level of a satellite, our cold atom
interferometer could measure accelerations with a sensitivity orders of
magnitude better than the best ground based accelerometers and close to proven
spaced-based ones
Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy
A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are determined and the insensitivity of this technique to aerosols is demonstrated by the analysis of cigarette smoke. A multiple pass sample cell has been used to obtain a sensitivity improvement allowing transitions of the volatile organic compounds to be observed. A solution to the frequency metrology is presented and promises to yield accurate molecular line center measurements
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