528 research outputs found
Emission of Scission Neutrons in the Sudden Approximation
At a certain finite neck radius during the descent of a fissioning nucleus
from the saddle to the scission point, the attractive nuclear forces can no
more withstand the repulsive Coulomb forces producing the neck rupture and the
sudden absorption of the neck stubs by the fragments. At that moment, the
neutrons, although still characterized by their pre-scission wave functions,
find themselves in the newly created potential of their interaction with the
separated fragments. Their wave functions become wave packets with components
in the continuum. The probability to populate such states gives evidently the
emission probability of neutrons at scission. In this way, we have studied
scission neutrons for the fissioning nucleus U, using two-dimensional
realistic nuclear shapes. Both the emission probability and the distribution of
the emission points relative to the fission fragments strongly depend on the
quantum numbers of the pre-scission state from which the neutron is emitted. In
particular it was found that states with = 1/2+ dominate the
emission. Depending on the assumed pre- and post-scission configurations and on
the emission-barrier height, 30 to 50% of the total scission neutrons are
emitted from 1/2+ states. Their emission points are concentrated in the region
between the newly separated fragments. The upper limit for the total number of
neutrons per scission event is predicted to lie between 0.16 and 1.73
(depending on the computational assumptions).Comment: 31 pages, 16 figures, 2 table
Digital pulse-shape discrimination of fast neutrons and gamma rays
Discrimination of the detection of fast neutrons and gamma rays in a liquid
scintillator detector has been investigated using digital pulse-processing
techniques. An experimental setup with a 252Cf source, a BC-501 liquid
scintillator detector, and a BaF2 detector was used to collect waveforms with a
100 Ms/s, 14 bit sampling ADC. Three identical ADC's were combined to increase
the sampling frequency to 300 Ms/s. Four different digital pulse-shape analysis
algorithms were developed and compared to each other and to data obtained with
an analogue neutron-gamma discrimination unit. Two of the digital algorithms
were based on the charge comparison method, while the analogue unit and the
other two digital algorithms were based on the zero-crossover method. Two
different figure-of-merit parameters, which quantify the neutron-gamma
discrimination properties, were evaluated for all four digital algorithms and
for the analogue data set. All of the digital algorithms gave similar or better
figure-of-merit values than what was obtained with the analogue setup. A
detailed study of the discrimination properties as a function of sampling
frequency and bit resolution of the ADC was performed. It was shown that a
sampling ADC with a bit resolution of 12 bits and a sampling frequency of 100
Ms/s is adequate for achieving an optimal neutron-gamma discrimination for
pulses having a dynamic range for deposited neutron energies of 0.3-12 MeV. An
investigation of the influence of the sampling frequency on the time resolution
was made. A FWHM of 1.7 ns was obtained at 100 Ms/s.Comment: 26 pages, 14 figures, submitted to Nuclear Instruments and Methods in
Physics Research
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Retrieval of attosecond pulse ensembles from streaking experiments using mixed state time-domain ptychography
The electric field of attosecond laser pulses can be retrieved from laser-dressed photoionisation measurements, where electron wavepackets that result from single-photon ionisation by the attosecond pulse in the presence of a dressing field are produced. In case of fluctuating dressing laser and/or attosecond pulses, e.g. due to pulse-to-pulse fluctuations of the carrier envelope phase of the infrared laser pulse, commonly applied retrieval algorithms result in the erroneous extraction of the pulse fields. We present a mixed state time-domain ptychography algorithm for the retrieval of pulse ensembles from attosecond streaking experiments. © 2020 The Author(s). Published by IOP Publishing Ltd
On neoclassical impurity transport in stellarator geometry
The impurity dynamics in stellarators has become an issue of moderate concern
due to the inherent tendency of the impurities to accumulate in the core when
the neoclassical ambipolar radial electric field points radially inwards (ion
root regime). This accumulation can lead to collapse of the plasma due to
radiative losses, and thus limit high performance plasma discharges in
non-axisymmetric devices.\\ A quantitative description of the neoclassical
impurity transport is complicated by the breakdown of the assumption of small
drift and trapping due to the electrostatic
potential variation on a flux surface compared to those due to
the magnetic field gradient. The present work examines the impact of this
potential variation on neoclassical impurity transport in the Large Helical
Device (LHD) stellarator. It shows that the neoclassical impurity transport can
be strongly affected by . The central numerical tool used is the
particle in cell (PIC) Monte Carlo code EUTERPE. The
used in the calculations is provided by the neoclassical code GSRAKE. The
possibility of obtaining a more general self-consistently with
EUTERPE is also addressed and a preliminary calculation is presented.Comment: 11 pages, 15 figures, presented at Joint Varenna-Lausanne
International Workshop on Theory of Fusion Plasmas, 2012. Accepted for
publication to Plasma Phys. and Control. Fusio
Retrieval of attosecond pulse ensembles from streaking experiments using mixed state time-domain ptychography
The electric field of attosecond laser pulses can be retrieved from laser-dressed photoionisation measurements, where electron wavepackets that result from single-photon ionisation by the attosecond pulse in the presence of a dressing field are produced. In case of fluctuating dressing laser and/or attosecond pulses, e.g. due to pulse-to-pulse fluctuations of the carrier envelope phase of the infrared laser pulse, commonly applied retrieval algorithms result in the erroneous extraction of the pulse fields. We present a mixed state time-domain ptychography algorithm for the retrieval of pulse ensembles from attosecond streaking experiments
Transformation of social and environmental views during the sporting events (on an example of the Kazan Universiade 2013)
The article considers the issues of transformation of social and environmental systems from the standpoint of social constructivist approach during carrying out Kazan Universiade 2013. Designing an image of sport achievements fosters a positive range in assessing of big city environmental issues. Publication based on the study of sociological questionnaire of citizens and guests of Kazan in the area of the Universiade venues during its implementation
Photometric observations of the supernova 2009nr
We present the results of our UBVRI CCD photometry for the second brightest
supernova of 2009, SN 2009nr, discovered during a sky survey with the
telescopes of the MASTER robotic network. Its light and color curves and
bolometric light curves have been constructed. The light-curve parameters and
the maximum luminosity have been determined. SN 2009nr is shown to be similar
in light-curve shape and maximum luminosity to SN 1991T, which is the prototype
of the class of supernovae Ia with an enhanced luminosity. SN 2009nr exploded
far from the center of the spiral galaxy UGC 8255 and most likely belongs to
its old halo population. We hypothesize that this explosion is a consequence of
the merger of white dwarfs
THE INFLUENCE OF COMPUTER-ASSISTED SURGERY ON CLINICAL AND RADIOGRAPHIC OUTCOMES OF PERIАRTICULAR FEMUR AND TIBIA OSTEOTOMIES IN OSTEOARTHRITIC PATIENTS (REVIEW)
Nowadays the clinical application of digital technologies became a growing trend at every stage of orthopedic patient treatment: from diagnostic procedures and pre-operative planning to intra-operative control of surgical manipulations and evaluation of final results later. The aim of thi sresearch was to analyze the studies dedicated to application of computer-assisted surgery (CAS) for femur and tibial osteotomies in patients with gonarthrosis. The hypothesis was that CAS improves the precision of leg alignment correction in frontal and sagittal planes that positively influencing both functional result of treatment and longevity of clinical effect. The PubMed, PubMedCentral, GoogleScholar and eLIBRARY searched for relevant studies using following key words: knee, osteoarthritis, gonarthrosis, osteotomy, CAS, navigation and its russian analogs. The majority of publications favored CAS in comparison to traditional osteotomy techniques both for leg alignment and tibial slope control. Despite generally researchers paid less attention to functional results after CASosteotomies than to precision of surgical manipulations it is possible of confirm that there is strong tendency to better knee scores after navigation while the difference is not always statistically significant. Rare publications dedicated to long term results favor CAS: 10 years survival rate is 97% that correspond to outcomes of modern total knee arthroplasty. Hence, the current literature confirms the hypothesis of our study and don’t reveal increase of complications rate associated with CAS
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