102 research outputs found
Reality property of discrete Wronski map with imaginary step
For a set of quasi-exponentials with real exponents, we consider the discrete
Wronskian (also known as Casorati determinant) with pure imaginary step 2h. We
prove that if the coefficients of the discrete Wronskian are real and for every
its roots the imaginary part is at most |h|, then the complex span of this set
of quasi-exponentials has a basis consisting of quasi-exponentials with real
coefficients. This result is a generalization of the statement of the B. and M.
Shapiro conjecture on spaces of polynomials. The proof is based on the Bethe
ansatz for the XXX model.Comment: Latex, 9 page
Adhesion at TiNi interfaces with Ta, Mo and Si
Atomic and electronic structure of (001) and (110) interfaces between TiNi and Ta, Mo, Si thin films are investigated by ab-initio method within density functional theory. It is shown that high adhesion properties can be attained at the Mo/TiNi(001)Ti interface, whereas the work of separation of Ta and Si films from alloy is substantial less. We found that the work of separation in case of (110) interface is lower than that at (001). Structural and electronic properties of considered interfaces are analysed. Our calculations of metal-oxide interfaces demonstrate that formation of intermediate titanium oxides layers can result in decrease of adhesion at Me/TiNi(110) interfaces
Psychological and Pedagogical Foundations of the Formation of Students' Own Educational Strategies in the Process of Independent Learning
The scientific problem to which this article is devoted is determined by the tasks facing modern education. One of these tasks is to build a continuous education system, covering all stages of a person’s life. To ensure the movement of the individual in the educational space, it is necessary to form a culture of lifelong learning, which implies the development of technologies of self-education and self-learning. The latter become a fundamental factor in the system of continuous learning. The analysis of pedagogical, psychological and methodical literature showed that the independent work of students in its theoretical justification has always been interpreted as the most important component of the educational process. However, in recent years the problem of improving its effectiveness began to attract increasing attention of researchers. One of the ways, according to scientists, psychologists and methodologists, is to teach students the ability to learn. But in order to "learn how to learn", it is necessary to master various methods of organization and implementation of educational activities. This is facilitated, according to foreign scientists, by the use of various learning strategies. The purpose of this article is to consider different types of educational strategies formed within the framework of independent foreign language training of students. According to the authors of the article, educational process should be organized in such a way that the consistent and purposeful work on formation of teaching strategies is conducted, mastery of which promotes students’ ability to learn. The formation of this skill becomes a support for personal readiness to continuously learn throughout life
Radiative Decay Width of Neutral non-Strange Baryons from PWA
An overview of the GW SAID and ITEP groups effort to analyze pion
photoproduction on the neutron-target will be given. The disentanglement the
isoscalar and isovector EM couplings of N* and Delta* resonances does require
compatible data on both proton and neutron targets. The final-state interaction
plays a critical role in the state-of-the-art analysis in extraction of the
gamma n --> pi N data from the deuteron target experiments. It is important
component of the current JLab, MAMI-C, SPring-8, ELSA, and ELPH programsComment: 7 pages, 7 figures, 1 table; Proceedings of International Conference
Dark Matter, Hadron Physics and Fusion Physics, Messina, Italy, Sept. 2014;
will be published in EPJ Web of Conference
Algebraic Bethe ansatz for the gl(12) generalized model II: the three gradings
The algebraic Bethe ansatz can be performed rather abstractly for whole
classes of models sharing the same -matrix, the only prerequisite being the
existence of an appropriate pseudo vacuum state. Here we perform the algebraic
Bethe ansatz for all models with , rational, gl(12)-invariant
-matrix and all three possibilities of choosing the grading. Our Bethe
ansatz solution applies, for instance, to the supersymmetric t-J model, the
supersymmetric model and a number of interesting impurity models. It may be
extended to obtain the quantum transfer matrix spectrum for this class of
models. The properties of a specific model enter the Bethe ansatz solution
(i.e. the expression for the transfer matrix eigenvalue and the Bethe ansatz
equations) through the three pseudo vacuum eigenvalues of the diagonal elements
of the monodromy matrix which in this context are called the parameters of the
model.Comment: paragraph added in section 3, reference added, version to appear in
J.Phys.
Holocene vegetation and climate history in Baikal Siberia reconstructed from pollen records and its implications for archaeology
Past research has greatly improved our understanding of palaeoenvironmental changes in the Lake Baikal Region, but at the same time has indicated intra-regional variations in this vast study area. Here we present a new AMS-dated late glacial-middle Holocene (ca. 13,500-4000 cal. yr BP) pollen record from Lake Ochaul (54 degrees 14'N, 106 degrees 28'E; altitude 641 m a.s.l.) situated in the less-studied area of Cis-Baikal and compare reconstructed vegetation and climate dynamics with the published environmental history of Trans-Baikal based on the pollen record from Lake Kotokel (52 degrees 47'N, 108 degrees 07'E; altitude 458 m a.s.l.). Although both records show comparable major long-term trends in vegetation, there are considerable differences. Around Ochaul the landscape was relatively open during the Younger Dryas stadial, but forest vegetation started to spread at the late glacial/Holocene transition (ca. 11,650 cal. yr BP), thus ca. 1000 years earlier than around Kotokel. While in both regions taiga forests spread during the early and middle Holocene, the marked increase in Scots pine pollen in the Kotokel record after ca. 6800 cal. yr BP is not seen in that from Ochaul, where birch and coniferous taxa, such as Siberian pine, larch, spruce and fir, dominate, indicating different environmental conditions and driving forces in both study regions. However, the pollen data from Ochaul emphasizes that the Cis-Baikal area also saw a continuous increase in forest cover and in the proportion of conifers over birch trees and shrubs during the early-middle Holocene, which may have contributed to a decrease in the number of large herbivores, the main food resource of the Early Neolithic hunter-gatherer groups. This and rather abrupt reorganization of atmospheric circulation, which affected atmospheric precipitation distribution resulting in thicker and longer-lasting snow cover, may have led to a collapse of Early Neolithic Kitoi populations ca. 6660 cal. yr BP followed by a cultural "hiatus" in the archaeological records during the Middle Neolithic phase (ca. 6660-6060 cal. yr BP). The results stress the importance of sub-regional palaeoenvironmental studies and the need for a representative network of well-dated, high-resolution sediment archives for a better understanding of environmental changes and their potential impacts on the hunter-gatherer populations in the archaeologically-defined micro-regions
Magnetic Dirac semimetal state of (Mn,Ge)BiTe
For quantum electronics, the possibility to finely tune the properties of
magnetic topological insulators (TIs) is a key issue. We studied solid
solutions between two isostructural Z TIs, magnetic MnBiTe and
nonmagnetic GeBiTe, with Z invariants of 1;000 and 1;001,
respectively. For high-quality, large mixed crystals of
GeMnBiTe, we observed linear x-dependent magnetic
properties, composition-independent pairwise exchange interactions along with
an easy magnetization axis. The bulk band gap gradually decreases to zero for
from 0 to 0.4, before reopening for , evidencing topological phase
transitions (TPTs) between topologically nontrivial phases and the semimetal
state. The TPTs are driven purely by the variation of orbital contributions. By
tracing the x-dependent contribution to the states near the fundamental
gap, the effective spin-orbit coupling variation is extracted. As varies,
the maximum of this contribution switches from the valence to the conduction
band, thereby driving two TPTs. The gapless state observed at closely
resembles a Dirac semimetal above the Neel temperature and shows a magnetic gap
below, which is clearly visible in raw photoemission data. The observed
behavior of the GeMnBiTe system thereby demonstrates an
ability to precisely control topological and magnetic properties of TIs
Bremsstrahlung of a Quark Propagating through a Nucleus
The density of gluons produced in the central rapidity region of a heavy ion
collision is poorly known. We investigate the influence of the effects of
quantum coherence on the transverse momentum distribution of photons and gluons
radiated by a quark propagating through nuclear matter. We describe the case
that the radiation time substantially exceeds the nuclear radius (the relevant
case for RHIC and LHC energies), which is different from what is known as
Landau-Pomeranchuk-Migdal effect corresponding to an infinite medium. We find
suppression of the radiation spectrum at small transverse photon/gluon momentum
k_T, but enhancement for k_T>1GeV. Any nuclear effects vanish for k_T > 10GeV.
Our results allow also to calculate the k_T dependent nuclear effects in prompt
photon, light and heavy (Drell-Yan) dilepton and hadron production.Comment: Appendix A is extended compared to the version to be published in
Phys.Rev.
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