250 research outputs found
On the Strength of Spin-Isospin Transitions in A=28 Nuclei
The relations between the strengths of spin-isospin transition operators
extracted from direct nuclear reactions, magnetic scattering of electrons and
processes of semi-leptonic weak interactions are discussed.Comment: LaTeX, 8 pages, 1Postscript with figur
New constraints for non-Newtonian gravity in nanometer range from the improved precision measurement of the Casimir force
We obtain constraints on non-Newtonian gravity following from the improved
precision measurement of the Casimir force by means of atomic force microscope.
The hypothetical force is calculated in experimental configuration (a sphere
above a disk both covered by two metallic layers). The strengthenings of
constraints up to 4 times comparing the previous experiment and up to 560 times
comparing the Casimir force measurements between dielectrics are obtained in
the interaction range 5.9 nmnm. Recent speculations about
the presence of some unexplained attractive force in the considered experiment
are shown to be unjustified.Comment: 5 pages, 1 figur
Toward An Empirical Theory of Pulsar Emission. VII. On the Spectral Behavior of Conal Beam Radii and Emission Heights
In this paper we return to the old problem of conal component-pair widths and
profile dimensions. Observationally, we consider a set of 10 pulsars with
prominent conal component pairs, for which well measured profiles exist over
the largest frequency range now possible. Apart from some tendency to narrow at
high frequency, the conal components exhibit almost constant widths. We use all
three profile measures, the component separation as well as the outside
half-power and 10% widths, to determine conal beam radii, which are the focus
of our subsequent analysis. These radii at different frequencies are well
fitted by a relationship introduced by Thorsett (1991), but the resulting
parameters are highly correlated. Three different types of behavior are found:
one group of stars exhibits a continuous variation of beam radius which can be
extrapolated down to the stellar surface along the ``last open field lines''; a
second group exhibits beam radii which asymptotically approach a minimum high
frequency value that is 3--5 times larger; and a third set shows almost no
spectral change in beam radius at all. The first two behaviors are associated
with outer-cone component pairs; whereas the constant separation appears to
reflect inner-cone emission.Comment: 21 pages, 11 figures, accepted for publication in Astrophysical
Journal, uses aaste
Quality standards for distance learning in higher education: a comparative analysis of Canadian and Russian practices
The aim of the investigation is to perform comparative analysis of the quality assessment and policies of quality assurance in postsecondary education in Canada and Russian Federation. Methods. The theoretical methods involve comparative analysis and synthesis, induction and deduction, extrapolation and modelling. Results. Russia and Canada have different policies on quality assurance in the distance learning and are at different stages of implementation of distance learning into postsecondary curricula. The Canadian system of postsecondary education is regulated not by the State but by professional societies, licensing organisations, and experts. Canadian postsecondary institutions have efficient systems of quality assurance, quality standards and accreditation. Blended learning is widely used in Canadian medical schools and is mandatory for continuous professional development. In Russia, the system of quality assurance for distance learning is regulated by the State. At present, Russia has developed policies on distance learning but unified quality standards in this field are absent. Blended learning is used in the medical schools but its implementation has just begun as continuous professional development. Scientific novelty. For the first time, the results of comparative analysis of the policies on quality assurance in distance learning in Russia and Canada are described. Practical significance. This research has showed the needs of the development of the system of quality standards and the policy on quality assurance of distance learning in the Russia postsecondary educationЦель статьи – сравнительный анализ стандартов качества дистанционного образования в высшей школе в Канаде и России. Методы исследования – теоретические: компаративный, анализ и синтез, индукция и дедукция, экстраполяция и моделирование. Результаты. Установлено, что в России и Канаде существуют разные модели оценки качества и экспертизы дистанционного образования, которые находятся на разных этапах внедрения в образовательный процесс дистанционного образования (ДО). В канадской высшей школе нормативное регулирование ДО осуществляется с участием негосударственных структур (независимых экспертов, профессионального сообщества); эффективно функционирует система стандартизации качества в этой области; есть система аккредитации электронных ресурсов; разработаны руководства для пользователей. На территории Канады широкое распространение получила смешанная форма обучения (hybrid method, blended method). Примером тому служит подготовка специалистов в области медицины, где дополнительное профессиональное образование стало невозможным без дистанционных технологий. В отличие от канадской, российская система оценки качества строго иерархизирована и полностью осуществляется государством. Отечественная высшая школа прошла этап создания нормативной базы ДО, определения понятий «цифровой педагогики», но критерии качества дистанционного образования в правовых документах отсутствуют. Общей чертой использования ДО в обеих странах является наличие смешанного обучения, однако в наших вузах дистанционные технологии постдипломного образования только начинают внедряться, а для канадских коллег они уже стали нормой, а зачастую и обязательной составляющей продолжения образования и повышения квалификации (как, например, в медицинской сфере). Научная новизна. Впервые представлены результаты компаративного анализа нормативной базы и практики оценивания результатов обучения в высшей школе с использованием дистанционных технологий в РФ и Канаде. Практическая значимость данного материала заключается в выявлении актуальных потребностей отечественной системы образования по стандартизации качества дистанционного обучения: в российской высшей школе назрела необходимость создания процедуры аттестации качества электронных образовательных ресурсов, и это касается всей системы непрерывного профессионального образовани
Constraints for hypothetical interactions from a recent demonstration of the Casimir force and some possible improvements
The Casimir force is calculated in the configuration of a spherical lens and
a disc of finite radius covered by and thin layers which was used in
a recent experiment. The correction to the Casimir force due to finiteness of
the disc radius is shown to be negligible. Also the corrections are discussed
due to the finite conductivity, large-scale and short-scale deviations from the
perfect shape of the bounding surfaces and the temperature correction. They
were found to be essential when confronting the theoretical results with
experimental data. Both Yukawa-type and power-law hypothetical forces are
computed which may act in the configuration under consideration due to the
exchange of light and/or massless elementary particles between the atoms of the
lens and the disc. New constraints on the constants of these forces are
determined which follow from the fact that they were not observed within the
limits of experimental errors. For Yukawa-type forces the new constraints are
up to 30 times stronger than the best ones known up today. A possible
improvement of experimental parameters is proposed which gives the possibility
to strengthen constraints on Yukawa-type interactions up to times and on
power-law interactions up to several hundred times.Comment: 15 pages, 3 figures, subm. to Phys. Rev.
Towards the solution of the anomaly in shell-model calculations of muon capture
Recently many authors have performed shell-model calculations of nuclear
matrix elements determining the rates of the ordinary muon capture in light
nuclei. These calculations have employed well-tested effective interactions in
large scale shell-model studies. For one of the nuclei of interest, namely
Si, there exists recent experimental data which can be used to deduce
the value of the ratio by using the calculated matrix elements.
Surprisingly enough, all the abovementioned shell-model results suggest a very
small value () for , quite far from the PCAC prediction
and recent data on muon capture in hydrogen. We show that this rather
disturbing anomaly is solved by employing effective transition operators. This
finding is also very important in studies of the scalar coupling of the weak
charged current of leptons and hadrons.Comment: Revtex, 6 pages, 2 figs include
Single- and double-beta decay Fermi-transitions in an exactly solvable model
An exactly solvable model suitable for the description of single and
double-beta decay processes of the Fermi-type is introduced. The model is
equivalent to the exact shell-model treatment of protons and neutrons in a
single j-shell. Exact eigenvalues and eigenvectors are compared to those
corresponding to the hamiltonian in the quasiparticle basis (qp) and with the
results of both the standard quasiparticle random phase approximation (QRPA)
and the renormalized one (RQRPA). The role of the scattering term of the
quasiparticle hamiltonian is analyzed. The presence of an exact eigenstate with
zero energy is shown to be related to the collapse of the QRPA. The RQRPA and
the qp solutions do not include this zero-energy eigenvalue in their spectra,
probably due to spurious correlations. The meaning of this result in terms of
symmetries is presented.Comment: 29 pages, 9 figures included in a Postsript file. Submitted to
Physcal Review
Measurement of the Pion Form Factor in the Energy Range 1.04-1.38 GeV with the CMD-2 Detector
The cross section for the process is measured in the
c.m. energy range 1.04-1.38 GeV from 995 000 selected collinear events
including 860000 events, 82000 events, and 33000
events. The systematic and statistical errors of measuring the
pion form factor are equal to 1.2-4.2 and 5-13%, respectively.Comment: 5 pages, 2 figure
Disorder Induced Ferromagnetism in Restricted Geometries
We study the influence of on-site disorder on the magnetic properties of the
ground state of the infinite Hubbard model. We find that for one
dimensional systems disorder has no influence, while for two dimensional
systems disorder enhances the spin polarization of the system. The tendency of
disorder to enhance magnetism in the ground state may be relevant to recent
experimental observations of spin polarized ground states in quantum dots and
small metallic grains.Comment: 4 pages, 4 figure
Study of the Power Beam Pattern of RATAN-600 During the Deep RZF Survey (1998-2003)
This paper proposes a method for constructing an experimental power beam
pattern (PB) of RATAN-600 based on the sample of NVSS sources observed in the
process of a deep sky survey near local zenith. The data obtained from
observations of radio sources at wave 7.6 cm in nine bands of the survey (the
2002 and 2003 sets) are used to construct vertical PB of the telescope at
rather large offsets from the central horizontal section of the PB (+/-36').
The experimental PBs obtained using different methods are compared and the
root-mean-square deviations of the experimental PB from the corresponding
computed PB are determined. The stability of the power beam pattern in its
central part (+/-6') during the RATAN-600 Zenith Field (RZF) survey (1998-2003)
and the accuracies of the fluxes of the sources observed within the framework
of this survey and included into the RZF catalog are estimated.Comment: 15 pages, 17 figure
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