Systematic motions in the Galactic plane found in the Hipparcos Catalogue using Herschel's Method

Two motions in the galactic plane have been detected and characterized, based on the determination of a common systematic component in Hipparcos catalogue proper motions. The procedure is based only on positions, proper motions and parallaxes, plus a special algorithm which is able to reveal systematic trends. Our results come from two stellar samples. Sample 1 has 4566 stars and defines a motion of apex (l,b)=(177.8,3.7)+/-(1.5,1.0) and space velocity V=27+/-1 km/s. Sample 2 has 4083 stars and defines a motion of apex (l,b)=(5.4,-0.6)+/-(1.9,1.1) and space velocity V=32+/-2 km/s. Both groups are distributed all over the sky and cover a large variety of spectral types, which means that they do not belong to a specific stellar population. Herschel's method is used to define the initial samples of stars and later to compute the common space velocity. The intermediate process is based on the use of a special algorithm to determine systematic components in the proper motions. As an important contribution, this paper sets out a new way to study the kinematics of the solar neighborhood, in the search for streams, associations, clusters and any other space motion shared by a large number of stars, without being restricted by the availability of radial velocities.Comment: 12 pages and 12 eps figures. LaTe

On the effective velocity created by a point vortex in two-dimensional hydrodynamics

We complete previous investigations on the statistics of velocity fluctuations arising from a random distribution of point vortices in two-dimensional hydrodynamics. We show that, on a statistical sense, the velocity created by a point vortex is shielded by cooperative effects on a distance $\Lambda \sim n^{-1/2}$, the inter-vortex separation. For $R\gg \Lambda$, the ``effective'' velocity decays as $R^{-2}$ instead of the ordinary law $R^{-1}$ recovered for $R\ll \Lambda$. These results are similar to those obtained by Agekyan [Sov. Astron. 5 (1962) 809] in his investigations on the fluctuations of the gravitational field. They give further support to our previous observation that the statistics of velocity fluctuations are (marginally) dominated by the contribution of the nearest neighbor.Comment: Submitted to Phys. Rev.

Isotope dependence of band-gap energy

The results of the quantitative investigations of the renormalization of the absorption edge of different compounds by the isotope effect are described.Comment: 7 pages, 3 figure

On a biphononic origin of the 1125 cm^(-1) absorption band in cuprous oxide

We report on the IR spectroscopic studies in both reflection (50-900 cm^{-1}) and transmission (900-3000 cm^{-1}) mode of the vibration spectrum of the cuprous oxide. A detailed analysis based on a comparison of the temperature dependences of the absorption band at 1125 cm^{-1} and of IR and Raman active fundamental vibrations results in assignment of the former to a biphonon.Comment: 5 pages, 5 figures (to appear in Phys.Lett. A

Detection of a coherent excitonic state in the layered semiconductor BiI3_{3}

The measurement and manipulation of the coherent dynamics of excitonic states constitute a forefront research challenge in semiconductor optics and in quantum coherence-based protocols for optoelectronic technologies. Layered semiconductors have emerged as an ideal platform for the study of exciton dynamics with accessible and technologically relevant energy and time scales. Here, we investigate the sub-picosecond exciton dynamics in a van-der-Waals semiconductor upon quasi-resonant excitation, and achieve to single out an incipient coherent excitonic state. Combining broadband transient reflectance spectroscopy and simulations based on many-body perturbation theory, we reveal a transient enhancement of the excitonic line intensity that originates from the photoinduced coherent polarization that is phase-locked with the interacting electromagnetic field. This finding allows us to define the spectral signature of a coherent excitonic state and to experimentally track the dynamical crossover from coherent to incoherent exciton, unlocking the prospective optical control of an exciton population on the intrinsic quantum-coherence timescale

Experimental evidence of strong phonon scattering in isotopical disordered systems: The case of LiH_xD_{1-x} crystals

The observation of the local - mode vibration, the two - mode behavior of the LO phonons at large isotope concentration, as well as large line broadening in LIH - D mixed crystals directly evidence strong additional phonon scattering due to the isotope - induced disorder.Comment: 9 pages, 4 figure

ЭКОНОМЕТРИЧЕСКОЕ ИССЛЕДОВАНИЕ ФАКТОРОВ РАЗВИТИЯ МАЛОГО ПРЕДПРИНИМАТЕЛЬСТВА В РЕГИОНАХ РОССИИ1

The article presents the methodological and methodical approaches to the analysis of socioeconomic factors affecting the development of small entrepreneurship in the regions of Russia. Aconstructed multiple linear regression model allowed to evaluate the impact on the small enterprises development of generalized factors that characterize different aspects of socio-economic development of the regions. It was proposed an approach based on the use of logistic regressionto assess the probability of hitting the region in the leading group by the level of small businessdevelopment (on the basis of a set of values formed by socio-economic characteristics). The comparative analysis of the correctness for the classification of the regions in terms of small business development through the application of discriminant analysis and logistic regression modelwas carried out. Taking into account the studied factors of small entrepreneurship development it is necessary to realize regional-differentiated policy for small business support and promotion.Встатьепредставленыметодологическиеиметодическиеподходыканализусоциально-экономическихфакторов, оказывающихвоздействиенаразвитиемалогопредпринимательства врегионахРоссии. Построенамножественнаялинейнаярегрессионнаямодель, позволившая оценитьвлияниенауровеньразвитиямалыхпредприятийобобщенныхфакторов, характеризующихразличныеаспектысоциально-экономическогоразвитиярегионов. Предложенподход, опирающийсянаприменениеаппараталогистическойрегрессии, коценкевероятности попаданиярегионавлидирующуюгруппупоуровнюразвитиямалогопредпринимательства на основе значений сформированного набора социально-экономических характеристик. Проведенсравнительныйанализкорректностиклассификациирегионовпоуровнюразвития малого бизнеса на основе применения дискриминантного анализа и построенной модели логистическойрегрессии. Учетвыявленныхвходеисследованияфакторовразвитиямалого предпринимательства будет способствовать реализации обоснованной регионально дифференцированной политики по его поддержке и стимулированию

The nearest young moving groups

The latest results in the research of forming planetary systems have led several authors to compile a sample of candidates for searching for planets in the vicinity of the sun. Young stellar associations are indeed excellent laboratories for this study, but some of them are not close enough to allow the detection of planets through adaptive optics techniques. However, the existence of very close young moving groups can solve this problem. Here we have compiled the members of the nearest young moving groups, as well as a list of new candidates from our catalogue of late-type stars possible members of young stellar kinematic groups, studying their membership through spectroscopic and photometric criteria.Comment: Latex file with 16 pages, 4 figures. Available at http://www.ucm.es/info/Astrof/invest/actividad/skg/skg_sag.html Accepted for publication in: The Astrophysical Journal (ApJ

Sn1-xBixO2 and Sn1-xTaxO2 (0 \leq x \leq 0.75): A first-principles study

The structural, elastic, electronic and optical (x = 0) properties of doped Sn1-xBixO2 and Sn1-xTaxO2 (0 \leq x \leq 0.75) are studied by using the first-principles pseudopotential plane-wave method within the local density approximation. The independent elastic constants Cij and other elastic parameters of these compounds have been calculated for the first time. The mechanical stability of the compounds with different doping concentrations has also been studied. The electronic band structure and density of states are calculated and the effect of doping on these properties is also analyzed. It is seen that the band gap of the undoped compound narrowed with dopant concentration which disappeared for x = 0.26 for Bi doping and 0.36 for Ta doping. The materials thus become conductive oxides through the change in the electronic properties of the compound for x \leq 0.75 which may be useful for potential application. The calculated optical properties, e.g. dielectric function, refractive index, absorption spectrum, loss-function, reflectivity and conductivity of the undoped SnO2 in two polarization directions are compared with both previous calculations and measurements. Keywords: Doped SnO2; First-principles; Mechanical properties; Electronic band structure; Optical properties.Comment: 10 pages, 5 figures, added 10 more references, comparison with mearements mad

Statistics of the gravitational force in various dimensions of space: from Gaussian to Levy laws

We discuss the distribution of the gravitational force created by a Poissonian distribution of field sources (stars, galaxies,...) in different dimensions of space d. In d=3, it is given by a Levy law called the Holtsmark distribution. It presents an algebraic tail for large fluctuations due to the contribution of the nearest neighbor. In d=2, it is given by a marginal Gaussian distribution intermediate between Gaussian and Levy laws. In d=1, it is exactly given by the Bernouilli distribution (for any particle number N) which becomes Gaussian for N>>1. Therefore, the dimension d=2 is critical regarding the statistics of the gravitational force. We generalize these results for inhomogeneous systems with arbitrary power-law density profile and arbitrary power-law force in a d-dimensional universe