206 research outputs found
Cross-Phase Modulation and Population Redistribution in a Periodic Tripod Medium
The cross-Kerr effect is studied for two pulses propagating in an atomic
medium in a tripod configuration, dressed by a strong standing wave coupling
beam. Nonlinear phase shifts for both transmitted and reflected beams are
calculated taking into account the redistribution of the population among the
atomic levels which allows one to study the phase shifts in a wide range of
pulse detunings. The influence of other parameters, e.g., the intensity of the
control field and the relaxation rates, on the cross-Kerr effect is also
examined in detail.Comment: 6 figure
Policy and Environmental Indicators for Heart Disease and Stroke Prevention: Data Sources in Two States
INTRODUCTION: Investigators in South Carolina and Alabama assessed the availability of data for measuring 31 policy and environmental indicators for heart disease and stroke prevention. The indicators were intended to determine policy and environmental support for adopting heart disease and stroke prevention guidelines and selected risk factors in 4 settings: community, school, work site, and health care. METHODS: Research teams used literature searches and key informant interviews to explore the availability of data sources for each indicator. Investigators documented the following 5 qualities for each data source identified: 1) the degree to which the data fit the indicator; 2) the frequency and regularity with which data were collected; 3) the consistency of data collected across time; 4) the costs (time, money, personnel) associated with data collection or access; and 5) the accessibility of data. RESULTS: Among the 31 indicators, 11 (35%) have readily available data sources and 4 (13%) have sources that could provide partial measurement. Data sources are available for most indicators in the school setting and for tobacco control policies in all settings. CONCLUSION: Data sources for measuring policy and environmental indicators for heart disease and stroke prevention are limited in availability. Effort and resources are required to develop and implement mechanisms for collecting state and local data on policy and environmental indicators in different settings. The level of work needed to expand data sources is comparable to the extensive work already completed in the school setting and for tobacco control
Enhancement of electron magnetic susceptibility due to many-body interactions in monolayer MoSe
Employing the original, all-optical method, we quantify the magnetic
susceptibility of a two-dimensional electron gas (2DEG) confined in the
MoSe monolayer in the range of low and moderate carrier densities. The
impact of electron-electron interactions on the 2DEG magnetic susceptibility is
found to be particularly strong in the limit of, studied in detail, low carrier
densities. Following the existing models, we derive for the
bare (single particle) g-factor of the ground state electronic band in the
MoSe monolayer. The derived value of this parameter is discussed in the
context of estimations from other experimental approaches. Surprisingly, the
conclusions drawn differ from theoretical ab-initio studies
Compressive Sensing of Signals Generated in Plastic Scintillators in a Novel J-PET Instrument
The J-PET scanner, which allows for single bed imaging of the whole human
body, is currently under development at the Jagiellonian University. The dis-
cussed detector offers improvement of the Time of Flight (TOF) resolution due
to the use of fast plastic scintillators and dedicated electronics allowing for
sam- pling in the voltage domain of signals with durations of few nanoseconds.
In this paper we show that recovery of the whole signal, based on only a few
samples, is possible. In order to do that, we incorporate the training signals
into the Tikhonov regularization framework and we perform the Principal
Component Analysis decomposition, which is well known for its compaction
properties. The method yields a simple closed form analytical solution that
does not require iter- ative processing. Moreover, from the Bayes theory the
properties of regularized solution, especially its covariance matrix, may be
easily derived. This is the key to introduce and prove the formula for
calculations of the signal recovery error. In this paper we show that an
average recovery error is approximately inversely proportional to the number of
acquired samples
Application of the Compress Sensing Theory for Improvement of the TOF Resolution in a Novel J-PET Instrument
Nowadays, in Positron Emission Tomography (PET) systems, a Time of Flight
information is used to improve the image reconstruction process. In Time of
Flight PET (TOF-PET), fast detectors are able to measure the difference in the
arrival time of the two gamma rays, with the precision enabling to shorten
significantly a range along the line-of-response (LOR) where the annihilation
occurred. In the new concept, called J-PET scanner, gamma rays are detected in
plastic scintillators. In a single strip of J-PET system, time values are
obtained by probing signals in the amplitude domain. Owing to Compress Sensing
theory, information about the shape and amplitude of the signals is recovered.
In this paper we demonstrate that based on the acquired signals parameters, a
better signal normalization may be provided in order to improve the TOF
resolution. The procedure was tested using large sample of data registered by a
dedicated detection setup enabling sampling of signals with 50 ps intervals.
Experimental setup provided irradiation of a chosen position in the plastic
scintillator strip with annihilation gamma quanta
Novel method for hit-position reconstruction using voltage signals in plastic scintillators and its application to Positron Emission Tomography
Currently inorganic scintillator detectors are used in all commercial Time of
Flight Positron Emission Tomograph (TOF-PET) devices. The J-PET collaboration
investigates a possibility of construction of a PET scanner from plastic
scintillators which would allow for single bed imaging of the whole human body.
This paper describes a novel method of hit-position reconstruction based on
sampled signals and an example of an application of the method for a single
module with a 30 cm long plastic strip, read out on both ends by Hamamatsu
R4998 photomultipliers. The sampling scheme to generate a vector with samples
of a PET event waveform with respect to four user-defined amplitudes is
introduced. The experimental setup provides irradiation of a chosen position in
the plastic scintillator strip with an annihilation gamma quanta of energy
511~keV. The statistical test for a multivariate normal (MVN) distribution of
measured vectors at a given position is developed, and it is shown that signals
sampled at four thresholds in a voltage domain are approximately normally
distributed variables. With the presented method of a vector analysis made out
of waveform samples acquired with four thresholds, we obtain a spatial
resolution of about 1 cm and a timing resolution of about 80 p
Superconception in mammalian pregnancy can be detected and increases reproductive output per breeding season
The concept of superfetation, a second conception during pregnancy, has been controversial for a long time. In this paper we use an experimental approach to demonstrate that female European brown hares (Lepus europaeus) frequently develop a second pregnancy while already pregnant and thereby increase their reproductive success. After a new, successful copulation, we confirmed additional ovulations before parturition in living, late-pregnant females by detecting a second set of fresh corpora lutea using high-resolution ultrasonography. The presence of early embryonic stages in the oviduct, demonstrated by oviduct flushing, next to fully developed fetuses in the uterus is best explained by passage of semen through the late-pregnant uterus; this was confirmed by paternity analysis using microsatellite profiling. Subsequent implantation occurred after parturition. This superfetation, categorized as superconception, significantly increased litter size and permitted females to produce up to 35.4% more offspring per breeding season. It is therefore most likely an evolutionary adaptation
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