308 research outputs found
Femtosecond Resolution Experiments at Third-Generation Light Sources: a Concept Based on the Statistical Properties of Synchrotron Radiation
The paper describes a new concept of visible pump/X-ray probe/slow detector
experiments that could be performed at third-generation synchrotron light
sources. We propose a technique that would allow time resolution up to
femtosecond capabilities to be recovered from a long (100 ps) X-ray probe
pulse. The visible pump pulse must be as short as the desired time resolution.
The principle of operation of the proposed pump-probe scheme is essentially
based on the statistical properties of the synchrotron radiation. These
properties are well known in statistical optics as properties of completely
chaotic polarized light. Our technique utilizes the fact that, for any
synchrotron light beam there exist some characteristic time (coherence time),
which determines the time-scale of the random fluctuations. The typical
coherence time of soft X-ray synchrotron light at the exit of monochromator is
in the femtosecond range. An excited state is prepared with a pump pulse and
then projected with a probe pulse onto a final ion state. The first statistical
quantity of interest is the variance of the number of photoelectrons detected
during synchrotron radiation pulse. The statistics of concern are defined over
an ensemble of synchrotron radiation pulses. From a set of variances measured
as a function of coherence time (inversely proportional to monochromator
bandwidth) it is possible to reconstruct the femtosecond dynamical process.Comment: 54 pages, 20 figure
Uncertainty constants and quasispline wavelets
In 1996 Chui and Wang proved that the uncertainty constants of scaling and
wavelet functions tend to infinity as smoothness of the wavelets grows for a
broad class of wavelets such as Daubechies wavelets and spline wavelets. We
construct a class of new families of wavelets (quasispline wavelets) whose
uncertainty constants tend to those of the Meyer wavelet function used in
construction.Comment: 27 page
Scheme for Attophysics Experiments at a X-ray SASE FEL
We propose a concept for production of high power coherent attosecond pulses
in X-ray range. An approach is based on generation of 8th harmonic of radiation
in a multistage HGHG FEL (high gain high harmonic free electron laser)
configuration starting from shot noise. Single-spike phenomena occurs when
electron bunch is passed through the sequence of four relatively short
undulators. The first stage is a conventional "long" wavelength (0.8 nm) SASE
FEL which operates in the high-gain linear regime. The 0.1 nm wavelength range
is reached by successive multiplication (0.8 nm 0.4 nm 0.2 nm
0.1 nm) in a stage sequence. Our study shows that the statistical properties of
the high-harmonic radiation from the SASE FEL, operating in linear regime, can
be used for selection of radiation pulses with a single spike in time domain.
The duration of the spikes is in attosecond range. Selection of single-spike
high-harmonic pulses is achieved by using a special trigger in data acquisition
system. The potential of X-ray SASE FEL at TESLA at DESY for generating
attosecond pulses is demonstrated. Since the design of XFEL laboratory at TESLA
is based on the use of long SASE undulators with tunable gap, no special place
nor additional FEL undulators are required for attophysics experiments. The use
of a 10 GW-level attosecond X-ray pulses at X-ray SASE FEL facility will enable
us to track processes inside atoms.Comment: 21 pages, 12 figures, submitted to Optics Communication
Search for the Proton Decay Mode proton to neutrino K+ in Soudan 2
We have searched for the proton decay mode proton to neutrino K+ using the
one-kiloton Soudan 2 high resolution calorimeter. Contained events obtained
from a 3.56 kiloton-year fiducial exposure through June 1997 are examined for
occurrence of a visible K+ track which decays at rest into mu+ nu or pi+ pi0.
We found one candidate event consistent with background, yielding a limit,
tau/B > 4.3 10^{31} years at 90% CL with no background subtraction.Comment: 13 pages, Latex, 3 tables and 3 figures, Accepted by Physics Letters
Interaction of N solitons in the massive Thirring model and optical gap system: the Complex Toda Chain Model
Using the Karpman-Solov''ev quasiparticle approach for soliton-soliton
interaction I show that the train propagation of N well separated solitons of
the massive Thirring model is described by the complex Toda chain with N nodes.
For the optical gap system a generalised (non-integrable) complex Toda chain is
derived for description of the train propagation of well separated gap
solitons. These results are in favor of the recently proposed conjecture of
universality of the complex Toda chain.Comment: RevTex, 23 pages, no figures. Submitted to Physical Review
Mixture of latent trait analyzers for model-based clustering of categorical data
Model-based clustering methods for continuous data are well established and commonly used in a wide range of applications. However, model-based clustering methods for categorical data are less standard. Latent class analysis is a commonly used method for model-based clustering of binary data and/or categorical data, but due to an assumed local independence structure there may not be a correspondence between the estimated latent classes and groups in the population of interest. The mixture of latent trait analyzers model extends latent class analysis by assuming a model for the categorical response variables that depends on both a categorical latent class and a continuous latent trait variable; the discrete latent class accommodates group structure and the continuous latent trait accommodates dependence within these groups. Fitting the mixture of latent trait analyzers model is potentially difficult because the likelihood function involves an integral that cannot be evaluated analytically. We develop a variational approach for fitting the mixture of latent trait models and this provides an efficient model fitting strategy. The mixture of latent trait analyzers model is demonstrated on the analysis of data from the National Long Term Care Survey (NLTCS) and voting in the U.S. Congress. The model is shown to yield intuitive clustering results and it gives a much better fit than either latent class analysis or latent trait analysis alone
Balloon Measurements of Cosmic Ray Muon Spectra in the Atmosphere along with those of Primary Protons and Helium Nuclei over Mid-Latitude
We report here the measurements of the energy spectra of atmospheric muons
and of the cosmic ray primary proton and helium nuclei in a single experiment.
These were carried out using the MASS superconducting spectrometer in a balloon
flight experiment in 1991. The relevance of these results to the atmospheric
neutrino anomaly is emphasized. In particular, this approach allows
uncertainties caused by the level of solar modulation, the geomagnetic cut-off
of the primaries and possible experimental systematics to be decoupled in the
comparison of calculated fluxes of muons to measured muon fluxes. The muon
observations cover the momentum and depth ranges of 0.3-40 GeV/c and 5-886
g/cmsquared, respectively. The proton and helium primary measurements cover the
rigidity range from 3 to 100 GV, in which both the solar modulation and the
geomagnetic cut-off affect the energy spectra at low energies.Comment: 31 pages, including 17 figures, simplified apparatus figure, to
appear in Phys. Rev.
Dark matter and Colliders searches in the MSSM
We study the complementarity between dark matter experiments (direct
detection and indirect detections) and accelerator facilities (the CERN LHC and
a TeV Linear Collider) in the framework of the
constrained Minimal Supersymmetric Standard Model (MSSM). We show how
non--universality in the scalar and gaugino sectors can affect the experimental
prospects to discover the supersymmetric particles. The future experiments will
cover a large part of the parameter space of the MSSM favored by WMAP
constraint on the relic density, but there still exist some regions beyond
reach for some extreme (fine tuned) values of the supersymmetric parameters.
Whereas the Focus Point region characterized by heavy scalars will be easily
probed by experiments searching for dark matter, the regions with heavy
gauginos and light sfermions will be accessible more easily by collider
experiments. More informations on both supersymmetry and astrophysics
parameters can be thus obtained by correlating the different signals.Comment: 25 pages, 10 figures, corrected typos and reference adde
Exclusion limits on the WIMP-nucleon cross-section from the Cryogenic Dark Matter Search
The Cryogenic Dark Matter Search (CDMS) employs low-temperature Ge and Si
detectors to search for Weakly Interacting Massive Particles (WIMPs) via their
elastic-scattering interactions with nuclei while discriminating against
interactions of background particles. For recoil energies above 10 keV, events
due to background photons are rejected with >99.9% efficiency, and surface
events are rejected with >95% efficiency. The estimate of the background due to
neutrons is based primarily on the observation of multiple-scatter events that
should all be neutrons. Data selection is determined primarily by examining
calibration data and vetoed events. Resulting efficiencies should be accurate
to about 10%. Results of CDMS data from 1998 and 1999 with a relaxed
fiducial-volume cut (resulting in 15.8 kg-days exposure on Ge) are consistent
with an earlier analysis with a more restrictive fiducial-volume cut.
Twenty-three WIMP candidate events are observed, but these events are
consistent with a background from neutrons in all ways tested. Resulting limits
on the spin-independent WIMP-nucleon elastic-scattering cross-section exclude
unexplored parameter space for WIMPs with masses between 10-70 GeV c^{-2}.
These limits border, but do not exclude, parameter space allowed by
supersymmetry models and accelerator constraints. Results are compatible with
some regions reported as allowed at 3-sigma by the annual-modulation
measurement of the DAMA collaboration. However, under the assumptions of
standard WIMP interactions and a standard halo, the results are incompatible
with the DAMA most likely value at >99.9% CL, and are incompatible with the
model-independent annual-modulation signal of DAMA at 99.99% CL in the
asymptotic limit.Comment: 40 pages, 49 figures (4 in color), submitted to Phys. Rev. D;
v.2:clarified conclusions, added content and references based on referee's
and readers' comments; v.3: clarified introductory sections, added figure
based on referee's comment
Spin effects in intramolecular electron transfer in naproxen-N-methylpyrrolidine dyad
[EN] The intramolecular electron transfer in the naproxen-N-methylpyrrolidine dyad has been investigated by spin chemistry methods. The existence of CIDNP in a high magnetic field points to electron transfer as a possible mechanism of the quenching of the excited state of a dyad. However, the failure to detect magnetic field effects on triplet yield makes us conclude that this quenching mechanism is not the only one. The observation of CIDNP effects in the dyad in the media of low polarity and the short risetime of triplet state formation indicate a potential role of exciplex in the quenching of the excited state of the dyad.This work was supported by the Grants 08-03-00372 and 11-03-01104 of Russian Foundation of Basic Research, and the grant of Priority Programs of RAS, No. 5.1.5.Magin, I.; Polyakov, N.; Khramtsova, E.; Kruppa, A.; Tsentalovich, Y.; Leshina, T.; Miranda Alonso, MĂ.... (2011). Spin effects in intramolecular electron transfer in naproxen-N-methylpyrrolidine dyad. Chemical Physics Letters. 516(1-3):51-55. https://doi.org/10.1016/j.cplett.2011.09.057S51555161-
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