621 research outputs found
Spatial distributions in static heavy-light mesons: a comparison of quark models with lattice QCD
Lattice measurements of spatial distributions of the light quark bilinear
densities in static mesons allow to test directly and in detail the wave
functions of quark models. These distributions are gauge invariant quantities
directly related to the spatial distribution of wave functions. We make a
detailed comparison of the recent lattice QCD results with our own quark
models, formulated previously for quite different purposes. We find a striking
agreement not only between our two quark models, but also with the lattice QCD
data for the ground state in an important range of distances up to about 4/GeV.
Moreover the agreement extends to the L=1 states [j^P=(1/2)^+]. An explanation
of several particular features completely at odds with the non-relativistic
approximation is provided. A rather direct, somewhat unexpected and of course
approximate relation between wave functions of certain quark models and QCD has
been established.Comment: 40 pages, 5 figures (version published in PRD
Magnetic properties of the non-stoichiometric TbCo2Nix alloys
The magnetic and magnetothermal properties of the non-stoichiometric TbCo2Nix (0 ≤ x ≤0.2) alloys were studied. It was found that the concentration dependence of the Curie temperature and magnetic moment of the 3d-sublattice have a maximum at x = 0.025. The obtained experimental magnetic properties of the TbCo2Nix alloys were discussed under assumption that the Co magnetic moment in the compounds changes with increasing x. The magnetic entropy change was determined using the temperature dependences of the magnetization and Maxwell's thermodynamic relation. The obtained results for TbCo2Nix were compared with those for the ErCo2Mnx alloys. © 2018 The Authors, published by EDP Sciences.The research was carried out within the state assignment of )$62 of 5Xssia (thePe ³0aJnet´ 1o ȺȺȺȺ-Ⱥ - 118020290129 -5) and supported by project of UB RAS (No. 18-10-2-5)
Constraints on B--->pi,K transition form factors from exclusive semileptonic D-meson decays
According to the heavy-quark flavour symmetry, the transition
form factors could be related to the corresponding ones of D-meson decays near
the zero recoil point. With the recent precisely measured exclusive
semileptonic decays and , we perform a
phenomenological study of transition form factors based on this
symmetry. Using BK, BZ and Series Expansion parameterizations of the form
factor slope, we extrapolate transition form factors from
to . It is found that, although being consistent with
each other within error bars, the central values of our results for form factors at , , are much smaller than
predictions of the QCD light-cone sum rules, but are in good agreements with
the ones extracted from hadronic B-meson decays within the SCET framework.
Moreover, smaller form factors are also favored by the QCD factorization
approach for hadronic B-meson decays.Comment: 19 pages, no figure, 5 table
Restoration of rotational invariance of bound states on the light front
We study bound states in a model with scalar nucleons interacting via an
exchanged scalar meson using the Hamiltonian formalism on the light front. In
this approach manifest rotational invariance is broken when the Fock space is
truncated. By considering an effective Hamiltonian that takes into account two
meson exchanges, we find that this breaking of rotational invariance is
decreased from that which occurs when only one meson exchange is included. The
best improvement occurs when the states are weakly bound.Comment: 20 pages, 6 figures, uses feynMF; changed typos, clarified use of
angular momentu
Doctoral Students’ Academic Supervision: A Systematic Review of Approaches to Conceptualization and Empirical Analysis
В статье представлен систематический обзор теоретико-методологических подходов российских и зарубежных исследователей к концептуализации и эмпирическому изучению научного руководства аспирантами. В зависимости от того, кому приписывается основная ответственность за итоговый результат, выделяются три подхода: наставнический, аспирантоцентрированный и средовой. В рамках наставнического подхода ответственность за результат приписывается научному руководителю. Этот подход укоренен в так называемой модели наставничества, когда аспирант рассматривается в качестве «неофита», которого научный руководитель вводит в академический мир. Для аспирантоцентрированного подхода характерно возложение значительной части ответственности на аспиранта, и в фокусе изучения оказываются его характеристики (мотивационные, коммуникационные, психологическое благополучие и др.), а также ожидания от научного руководства и его результаты. Этот подход предполагает активную роль аспиранта и восходит к моделям студентоцентрированной педагогики. Средовой подход фокусируется на изучении роли среды, помещая в центр изучения вопросы, связанные с академической и социальной интеграцией аспирантов. Отмечается, что все эти подходы обладают рядом ограничений, связанных с фокусировкой на отдельных факторах образовательного процесса и с недостаточным вниманием к динамическому и относительному характеру различных аспектов научного руководства и их связи с результативностью аспирантской подготовки. Обосновывается важность развития реляционного подхода к изучению научного руководства, который синтезирует ключевые положения рассмотренных подходов, предполагая распределенную модель ответственности в процессе научного руководства и обращение к изучению «образовательных альянсов», понимаемых шире пар или команд научных руководителей и аспирантов. В фокусе такого подхода – не только активность отдельных акторов, но и система взаимоотношений между ними.The article presents a systematic review of theoretical and methodological approaches to the conceptualization and empirical study of doctoral students’ supervision. Three approaches (mentoring, doctoral student-centered, and environmental) are distinguished depending on the main responsibility for the result. The mentoring approach attributes the responsibility for the result to the supervisor. This approach is generally associated with the so-called «apprentice model», which understands the doctoral student as a «neophyte» introduced to the academic world by the supervisor. The doctoral student-centered approach is characterized by imposing the responsibility mainly on the doctoral student. This approach assumes a more active role of the doctoral student and goes back to the models of student-centered pedagogy. The environmental approach focuses on studying the role of the environment and on the issues related to the academic and social integration of doctoral students. All these approaches notably have a number of limitations due to their concentration on certain factors of the educational process and less attention to the dynamic and relative nature of various aspects of academic supervision and its relationship with the effectiveness of doctoral training. There is substantiated the importance of developing a relational approach, which would synthesize the key points of the three approaches considered, and assume a distributed model of responsibility within the academic supervision. As it understands «learning alliances» more broadly than pairs or teams of scientific supervisors and graduate students, this approach focuses not only on the activity of individual actors, but also on the system of relationships between them
Martensitic transformation and magnetotransport properties of Ni47Mn42In11 alloy
The structure, electrical and magnetic properties of the Ni47Mn42In11 alloy, in which the temperature of the martensitic transformation is close to room temperature and practically coincides with the Curie temperature of austenite, have been investigated. The martensitic transformation in the Ni47Mn42In11 alloy proceeds with the formation of modulated martensite type 14M. It has been established that the spontaneous transformation from martensite to austenite is accompanied by a decrease in the specific resistance of 45%. In the martensitic transformation induced by a magnetic field of 18 kOe, a negative magnetoresistance is observed, reaching ∼ 15%. © Published under licence by IOP Publishing Ltd.Ural Branch, Russian Academy of Sciences, UB RAS: 18-10-2-39Federal Agency for Scientific Organizations: AAAA-A18-118020190116-6This work was supported by the Federal Agency for Scientific Organizations (themes “Structure”, project no. AAAA-A18-118020190116-6) and partly supported by the Comprehensive Program of the Ural Branch of the Russian Academy of Sciences (project No. 18-10-2-39)
Magnetic properties of the non-stoichiometric TbCo2Mn x and TbCo2Nix alloys
The crystal structure, magnetic and magnetothermal properties of non-stoichiometric TbCo2Mnx and TbCo2Nix alloys were studied. It was shown that single-phase compounds with the MgCu2-type structure exist up to a certain content of x (x < 0.4 for compounds with Mn and x ≤ 0.1 for compounds with Ni). The concentration changes of the lattice parameter, Curie temperature, magnetic moment of the 3d sublattice in TbCo2Mn x and TbCo2Nix alloys were compared. The magnetocaloric effect in alloys were estimated using data of magnetic and heat capacity measurements. © Published under licence by IOP Publishing Ltd.Russian Foundation for Basic Research, RFBR: 18-02-00294The research was carried out within the state assignment of Minobrnauki of Russia (theme “Magnet” No. АААА-А18-118020290129-5), supported in part by RFBR (project No. 18-02-00294)
Professional Doctorates: International Experience and Russian Context
The diversification of forms and types of doctoral programs is currently a global trend. Universities across the globe offer programs that differ in the modes of training, characteristics of the target audience, and possible labor markets after graduation. In Russia, doctoral education exists in a unified format, focusing primarily on the academic labor market. Recently, there have been discussions about the need to expand the range of programs and the types of academic degrees in Russia. In this article, we present the analysis of professional doctoral programs: in response to what challenges and needs they appeared, how they are implemented, in what forms they exist. In addition, we consider the Russian experience of implementing professional doctoral programs; analyze the existing opportunities and barriers for their development. Based on the analysis, we came to a conclusion about the relevance of the professional doctoral programs’ development in Russia, the expediency of simplifying the conditions for their implementation and legitimizing special requirements for the design of dissertations with an applied orientation
The omega rho pi coupling in the VMD model revisited
We determine the value of the \omega -\rho- \pi mesons coupling
(g_{\omega\rho\pi}), in the context of the vector meson dominance model, from
radiative decays, the \omega \rightarrow 3\pi decay width and the e^+e^-
\rightarrow 3\pi cross section. For the last two observables we consider the
effect of either a heavier resonance (\rho'(1450)) or a contact term. A
weighted average of the results from the set of observables yields
g_{\omega\rho\pi} =14.7 \pm 0.1 GeV^{-1} in absence of those contributions, and
g_{\omega\rho\pi} =11.9 \pm 0.2 GeV^{-1} or g_{\omega\rho\pi} =11.7 \pm 0.1
GeV^{-1} when including the \rho' or contact term respectively. The inclusion
of these additional terms makes the estimates from the different observables to
lay in a more reduced range. Improved measurements of these observables and the
\rho'(1450) meson parameters are needed to give a definite answer on the
pertinence of the inclusion of this last one in the considered processes.Comment: 14 pages, 5 figures. Extended analysis including SND and CMD2 data.
References added. Matches published versio
Planet Hunters X: Searching for Nearby Neighbors of 75 Planet and Eclipsing Binary Candidates from the K2 Kepler Extended Mission
We present high-resolution observations of a sample of 75 K2 targets from
Campaigns 1-3 using speckle interferometry on the Southern Astrophysical
Research (SOAR) telescope and adaptive optics (AO) imaging at the Keck II
telescope. The median SOAR -band and Keck -band detection limits at 1"
were ~mag and ~mag, respectively. This
sample includes 37 stars likely to host planets, 32 targets likely to be
eclipsing binaries (EBs), and 6 other targets previously labeled as likely
planetary false positives. We find nine likely physically bound companion stars
within 3" of three candidate transiting exoplanet host stars and six likely
EBs. Six of the nine detected companions are new discoveries; one of the six,
EPIC 206061524, is associated with a planet candidate. Among the EB candidates,
companions were only found near the shortest period ones ( days), which is
in line with previous results showing high multiplicity near short-period
binary stars. This high-resolution data, including both the detected companions
and the limits on potential unseen companions, will be useful in future planet
vetting and stellar multiplicity rate studies for planets and binaries.Comment: Accepted in A
- …