3,326 research outputs found
Wavelets, ridgelets and curvelets on the sphere
We present in this paper new multiscale transforms on the sphere, namely the
isotropic undecimated wavelet transform, the pyramidal wavelet transform, the
ridgelet transform and the curvelet transform. All of these transforms can be
inverted i.e. we can exactly reconstruct the original data from its
coefficients in either representation. Several applications are described. We
show how these transforms can be used in denoising and especially in a Combined
Filtering Method, which uses both the wavelet and the curvelet transforms, thus
benefiting from the advantages of both transforms. An application to component
separation from multichannel data mapped to the sphere is also described in
which we take advantage of moving to a wavelet representation.Comment: Accepted for publication in A&A. Manuscript with all figures can be
downloaded at http://jstarck.free.fr/aa_sphere05.pd
Optimum quantum dot size for highly efficient fluorescence bioimaging
Semiconductor quantum dots of few nanometers have demonstrated a great potential for bioimaging. The size determines the emitted color, but it is also expected to play an important role in the image brightness. In this work, the size dependence of the fluorescence quantum yield of the highly thermal sensitive CdTe quantum dots has been systematically investigated by thermal lens spectroscopy. It has been found that an optimum quantum yield is reached for 3.8-nm quantum dots. The presence of this optimum size has been corroborated in both one-photon excited fluorescence experiments and two-photon fluorescence microscopy of dot-incubated cancer cells. Combination of quantum yield and fluorescence decay time measurements supports that the existence of this optimum size emerges from the interplay between the frequency-dependent radiative emission rate and the size-dependent coupling strength between bulk excitons and surface trapping states
The AMS-02 RICH Imager Prototype - In-Beam Tests with 20 GeV/c per Nucleon Ions -
A prototype of the AMS Cherenkov imager (RICH) has been tested at CERN by
means of a low intensity 20 GeV/c per nucleon ion beam obtained by
fragmentation of a primary beam of Pb ions. Data have been collected with a
single beam setting, over the range of nuclear charges 2<Z<~45 in various beam
conditions and using different radiators. The charge Z and velocity beta
resolutions have been measured.Comment: 4 pages, contribution to the ICRC 200
The Ring Imaging Cherenkov detector (RICH) of the AMS experiment
The Alpha Magnetic Spectrometer (AMS) experiment to be installed on the
International Space Station (ISS) will be equipped with a proximity focusing
Ring Imaging Cherenkov (RICH) detector for measuring the electric charge and
velocity of the charged cosmic particles. A RICH prototype consisting of 96
photomultiplier units, including a piece of the conical reflector, was built
and its performance evaluated with ion beam data. Preliminary results of the
in-beam tests performed with ion fragments resulting from collisions of a 158
GeV/c/nuc primary beam of Indium ions (CERN SPS) on a Pb target are reported.
The collected data included tests to the final front-end electronics and to
different aerogel radiators. Cherenkov rings for a large range of charged
nuclei and with reflected photons were observed. The data analysis confirms the
design goals. Charge separation up to Fe and velocity resolution of the order
of 0.1% for singly charged particles are obtained.Comment: 29th International Conference on Cosmic Rays (Pune, India
The AMS-RICH velocity and charge reconstruction
The AMS detector, to be installed on the International Space Station,
includes a Ring Imaging Cerenkov detector with two different radiators, silica
aerogel (n=1.05) and sodium fluoride (n=1.334). This detector is designed to
provide very precise measurements of velocity and electric charge in a wide
range of cosmic nuclei energies and atomic numbers. The detector geometry, in
particular the presence of a reflector for acceptance purposes, leads to
complex Cerenkov patterns detected in a pixelized photomultiplier matrix. The
results of different reconstruction methods applied to test beam data as well
as to simulated samples are presented. To ensure nominal performances
throughout the flight, several detector parameters have to be carefully
monitored. The algorithms developed to fulfill these requirements are
presented. The velocity and charge measurements provided by the RICH detector
endow the AMS spectrometer with precise particle identification capabilities in
a wide energy range. The expected performances on light isotope separation are
discussed.Comment: Contribution to the ICRC07, Merida, Mexico (2007); Presenter: F.
Bara
Towards the critical behavior for the light nuclei by NIMROD detector
The critical behavior for the light nuclei with A has been
investigated experimentally by the NIMROD multi-detectors. The wide variety of
observables indicate the critical point has been reached in the disassembly of
hot nuclei at an excitation energy of 5.60.5 MeV/u.Comment: 4 pages, 2 figures; Proceeding of 18th Nuclear Physics Division
Conference of the Euro. Phys. Society (NPDC18) "Phase transitions in strongly
interacting matter", Prague, 23.8.-29.8. 2004. To be published in Nuclear
Physics
Evidence of Critical Behavior in the Disassembly of Nuclei with A ~ 36
A wide variety of observables indicate that maximal fluctuations in the
disassembly of hot nuclei with A ~ 36 occur at an excitation energy of 5.6 +-
0.5 MeV/u and temperature of 8.3 +- 0.5 MeV. Associated with this point of
maximal fluctuations are a number of quantitative indicators of apparent
critical behavior. The associated caloric curve does not appear to show a
flattening such as that seen for heavier systems. This suggests that, in
contrast to similar signals seen for liquid-gas transitions in heavier nuclei,
the observed behavior in these very light nuclei is associated with a
transition much closer to the critical point.Comment: v2: Major changes, new model calculations, new figure
Critical Behavior in Light Nuclear Systems: Experimental Aspects
An extensive experimental survey of the features of the disassembly of a
small quasi-projectile system with 36, produced in the reactions of 47
MeV/nucleon Ar + Al, Ti and Ni, has been carried
out. Nuclei in the excitation energy range of 1-9 MeV/u have been investigated
employing a new method to reconstruct the quasi-projectile source. At an
excitation energy 5.6 MeV/nucleon many observables indicate the presence
of maximal fluctuations in the de-excitation processes. The fragment
topological structure shows that the rank sorted fragments obey Zipf's law at
the point of largest fluctuations providing another indication of a liquid gas
phase transition. The caloric curve for this system shows a monotonic increase
of temperature with excitation energy and no apparent plateau. The temperature
at the point of maximal fluctuations is MeV. Taking this
temperature as the critical temperature and employing the caloric curve
information we have extracted the critical exponents , and
from the data. Their values are also consistent with the values of the
universality class of the liquid gas phase transition. Taken together, this
body of evidence strongly suggests a phase change in an equilibrated mesoscopic
system at, or extremely close to, the critical point.Comment: Physical Review C, in press; some discussions about the validity of
excitation energy in peripheral collisions have been added; 24 pages and 32
figures; longer abstract in the preprin
The RICH detector of the AMS-02 experiment: status and physics prospects
The Alpha Magnetic Spectrometer (AMS), whose final version AMS-02 is to be
installed on the International Space Station (ISS) for at least 3 years, is a
detector designed to measure charged cosmic ray spectra with energies up to the
TeV region and with high energy photon detection capability up to a few hundred
GeV. It is equipped with several subsystems, one of which is a proximity
focusing RICH detector with a dual radiator (aerogel+NaF) that provides
reliable measurements for particle velocity and charge. The assembly and
testing of the AMS RICH is currently being finished and the full AMS detector
is expected to be ready by the end of 2008. The RICH detector of AMS-02 is
presented. Physics prospects are briefly discussed.Comment: 5 pages. Contribution to the 10th ICATPP Conference on Astroparticle,
Particle, Space Physics, Detectors and Medical Physics Applications (Como
2007). Presenter: Rui Pereir
- …