595 research outputs found
Using the statistic to test for missed levels in mixed sequence neutron resonance data
The statistic is studied as a tool to detect missing levels in
the neutron resonance data where 2 sequences are present. These systems are
problematic because there is no level repulsion, and the resonances can be too
close to resolve. is a measure of the fluctuations in the number
of levels in an interval of length on the energy axis. The method used is
tested on ensembles of mixed Gaussian Orthogonal Ensemble (GOE) spectra, with a
known fraction of levels () randomly depleted, and can accurately return
. The accuracy of the method as a function of spectrum size is established.
The method is used on neutron resonance data for 11 isotopes with either s-wave
neutrons on odd-A, or p-wave neutrons on even-A. The method compares favorably
with a maximum likelihood method applied to the level spacing distribution.
Nuclear Data Ensembles were made from 20 isotopes in total, and their
statistic are discussed in the context of Random Matrix Theory.Comment: 22 pages, 12 figures, 4 table
Stability of the shell structure in 2D quantum dots
We study the effects of external impurities on the shell structure in
semiconductor quantum dots by using a fast response-function method for solving
the Kohn-Sham equations. We perform statistics of the addition energies up to
20 interacting electrons. The results show that the shell structure is
generally preserved even if effects of high disorder are clear. The Coulomb
interaction and the variation in ground-state spins have a strong effect on the
addition-energy distributions, which in the noninteracting single-electron
picture correspond to level statistics showing mixtures of Poisson and Wigner
forms.Comment: 7 pages, 8 figures, submitted to Phys. Rev.
Thirty-fold: Extreme gravitational lensing of a quiescent galaxy at
We report the discovery of eMACSJ1341-QG-1, a quiescent galaxy at
located behind the massive galaxy cluster eMACSJ1341.92442 (). The
system was identified as a gravitationally lensed triple image in Hubble Space
Telescope images obtained as part of a snapshot survey of the most X-ray
luminous galaxy clusters at and spectroscopically confirmed in
ground-based follow-up observations with the ESO/X-Shooter spectrograph. From
the constraints provided by the triple image, we derive a first, crude model of
the mass distribution of the cluster lens, which predicts a gravitational
amplification of a factor of 30 for the primary image and a factor of
6 for the remaining two images of the source, making eMACSJ1341-QG-1 by
far the most strongly amplified quiescent galaxy discovered to date. Our
discovery underlines the power of SNAPshot observations of massive, X-ray
selected galaxy clusters for lensing-assisted studies of faint background
populations
Light emission patterns from stadium-shaped semiconductor microcavity lasers
We study light emission patterns from stadium-shaped semiconductor (GaAs)
microcavity lasers theoretically and experimentally. Performing systematic wave
calculations for passive cavity modes, we demonstrate that the averaging by
low-loss modes, such as those realized in multi-mode lasing, generates an
emission pattern in good agreement with the ray model's prediction. In
addition, we show that the dependence of experimental far-field emission
patterns on the aspect ratio of the stadium cavity is well reproduced by the
ray model.Comment: 5 pages, 4 figure
Ergodicity of the statistic and purity of neutron resonance data
The statistic characterizes the fluctuations of the number of
levels as a function of the length of the spectral interval. It is studied as a
possible tool to indicate the regular or chaotic nature of underlying dynamics,
detect missing levels and the mixing of sequences of levels of different
symmetry, particularly in neutron resonance data. The relation between the
ensemble average and the average over different fragments of a given
realization of spectra is considered. A useful expression for the variance of
which accounts for finite sample size is discussed. An analysis
of neutron resonance data presents the results consistent with a maximum
likelihood method applied to the level spacing distribution.Comment: 24 pages, 19 figures, 1 tabl
Geometric and impurity effects on quantum rings in magnetic fields
We investigate the effects of impurities and changing ring geometry on the
energetics of quantum rings under different magnetic field strengths. We show
that as the magnetic field and/or the electron number are/is increased, both
the quasiperiodic Aharonov-Bohm oscillations and various magnetic phases become
insensitive to whether the ring is circular or square in shape. This is in
qualitative agreement with experiments. However, we also find that the
Aharonov-Bohm oscillation can be greatly phase-shifted by only a few impurities
and can be completely obliterated by a high level of impurity density. In the
many-electron calculations we use a recently developed fourth-order imaginary
time projection algorithm that can exactly compute the density matrix of a
free-electron in a uniform magnetic field.Comment: 8 pages, 7 figures, to appear in PR
Chaotic scattering of atoms at a standing laser wave
Atoms, propagating across a detuned standing laser wave, can be scattered in
a chaotic way even in the absence of spontaneous emission and any modulation of
the laser field. Spontaneous emission masks the effect in some degree, but the
Monte Carlo simulation shows that it can be observed in real experiments by the
absorption imaging method or depositing atoms on a substrate. The effect of
chaotic scattering is explained by a specific behavior of the dipole moments of
atoms crossing the field nodes and is shown to depend strongly on the value of
the atom-laser detuning.Comment: arXiv admin note: substantial text overlap with arXiv:1201.032
Periodic Orbits in Polygonal Billiards
We review some properties of periodic orbit families in polygonal billiards
and discuss in particular a sum rule that they obey. In addition, we provide
algorithms to determine periodic orbit families and present numerical results
that shed new light on the proliferation law and its variation with the genus
of the invariant surface. Finally, we deal with correlations in the length
spectrum and find that long orbits display Poisson fluctuations.Comment: 30 pages (Latex) including 11 figure
A recoil detector for the measurement of antiproton-proton elastic scattering at angles close to 90
The design and construction of a recoil detector for the measurement of
recoil protons of antiproton-proton elastic scattering at scattering angles
close to 90 are described. The performance of the recoil detector has
been tested in the laboratory with radioactive sources and at COSY with proton
beams by measuring proton-proton elastic scattering. The results of laboratory
tests and commissioning with beam are presented. Excellent energy resolution
and proper working performance of the recoil detector validate the conceptual
design of the KOALA experiment at HESR to provide the cross section data needed
to achieve a precise luminosity determination at the PANDA experiment.Comment: 10 pages, 15 figure
Cooperation between SSTC NRS and the EU in the Area of Nuclear Safety
The paper first briefly outlines the main characteristics of the EU assistance programs aimed to enhance nuclear safety in the Beneficiary countries. Then EU assistance provided to the Ukrainian regulator (SNRIU) is detailed, with specific emphasis on projects enhancing the capabilities of SSTC NRS as technical support organisation (TSO) to SNRIU, including training and tutoring (T&T) activities. The changing role of SSTC NRS in the cooperation activities is described as well. The broad range of cooperation is then illustrated by some selected projects focusing on various technical areas (e.g. severe accident management and mitigation, radioactive waste and spent fuel management, NPP service time extension, plant performance monitoring and operating experience feedback). Finally, the paper briefly discusses the future perspectives of the nuclear safety cooperation between the EU and UkraineНа початку статті коротко викладені основні характеристики програм підтримки ЄС, спрямованих на підвищення ядерної безпеки в країнах-бенефіціарах. Далі детально описується підтримка ЄС, що надається українському регулюючому органу (ДІЯРУ) з акцентом на проекти, спрямовані на розширення можливостей ДНТЦ ЯРБ як організації технічної підтримки (ОТП) ДІЯРУ, охоплюючи навчання і наставництво. Описується зміна ролі ДНТЦ ЯРБ у заходах зі співробітництва, широкий спектр співпраці в рамках деяких вибраних проектів з акцентом на різні технічні області (наприклад, управління важкими аваріями і пом’якшення наслідків, поводження з радіоактивними відходами та відпрацьованим паливом, продовження терміну експлуатації АЕС, контроль робочих характеристик станції та обмін досвідом експлуатації). Стисло обговорюються майбутні перспективи співпраці ЄС та України у сфері ядерної безпеки.В начале статьи кратко изложены основные характеристики программ поддержки ЕС, направленных на повышение ядерной безопасности в странах-бенефициарах. Далее подробно описывается поддержка ЕС, предоставляется украинском регулирующему органу (ГИЯРУ) с акцентом на проекты, направленные на расширение возможностей ГНТЦ ЯРБ как организации технической поддержки (ОТП) ГИЯРУ, включая обучение и наставничество. Описывается изменение роли ГНТЦ ЯРБ в мероприятиях по сотрудничеству, широкий спектр сотрудничества в рамках некоторых выбранных проектов с акцентом на различные технические области (например, управление тяжелыми авариями и смягчения последствий, обращение с радиоактивными отходами и отработанным топливом, продление срока эксплуатации АЭС, контроль рабочих характеристик станции и обмен опытом эксплуатации). Кратко обсуждаются будущие перспективы сотрудничества ЕС и Украины в сфере ядерной безопасности
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