54 research outputs found
Scattering length of the helium atom - helium dimer collision
We present our recent results on the scattering length of ^4He-^4He_2
collisions. These investigations are based on the hard-core version of the
Faddeev differential equations. As compared to our previous calculations of the
same quantity, a much more refined grid is employed, providing an improvement
of about 10%. Our results are compared with other ab initio, and with model
calculations
The ^4He trimer as an Efimov system
We review the results obtained in the last four decades which demonstrate the
Efimov nature of the He three-atomic system.Comment: Review article for a special issue of the Few-Body Systems journal
devoted to Efimov physic
Probing the dynamics of quasicrystal growth using synchrotron live imaging
The dynamics of quasicrystal growth remains an unsolved problem in condensed
matter. By means of synchrotron live imaging, facetted growth proceeding by the
tangential motion of ledges at the solid-melt interface is clearly evidenced
all along the solidification of icosahedral AlPdMn quasicrystals. The effect of
interface kinetics is significant so that nucleation and free growth of new
facetted grains occur in the melt when the solidification rate is increased.
The evolution of these grains is explained in details, which reveals the
crucial role of aluminum rejection, both in the poisoning of grain growth and
driving fluid flow
Borromean Binding of Three or Four Bosons
We estimate the ratio of the critical coupling constants
and which are required to achieve binding of 2 or 3 bosons,
respectively, with a short-range interaction, and examine how this ratio
depends on the shape of the potential. Simple monotonous potentials give
. A wide repulsive core pushes this ratio close to R=1. On the
other hand, for an attractive well protected by an external repulsive barrier,
the ratio approaches the rigorous lower bound . We also present results
for N=4 bosons, sketch the extension to , and discuss various
consequences.Comment: 12 pages, RevTeX, 5 Figures in tex include
Jost Function for Singular Potentials
An exact method for direct calculation of the Jost function and Jost
solutions for a repulsive singular potential is presented. Within this method
the Schrodinger equation is replaced by an equivalent system of linear
first-order differential equations, which after complex rotation, can easily be
solved numerically. The Jost function can be obtained to any desired accuracy
for all complex momenta of physical interest, including the spectral points
corresponding to bound and resonant states. The method can also be used in the
complex angular-momentum plane to calculate the Regge trajectories. The
effectiveness of the method is demonstrated using the Lennard-Jones (12,6)
potential. The spectral properties of the realistic inter-atomic He4-He4
potentials HFDHE2 and HFD-B of Aziz and collaborators are also investigated.Comment: 12 pages, latex, 2 eps-figures, submitted to Phys.Rev.
The Three-Boson System at Next-To-Next-To-Leading Order
We discuss effective field theory treatments of the problem of three
particles interacting via short-range forces (range R >> a_2, with a_2 the
two-body scattering length). We show that forming a once-subtracted scattering
equation yields a scattering amplitude whose low-momentum part is
renormalization-group invariant up to corrections of O(R^3/a_2^3). Since
corrections of O(R/a_2) and O(R^2/a_2^2) can be straightforwardly included in
the integral equation's kernel, a unique solution for 1+2 scattering phase
shifts and three-body bound-state energies can be obtained up to this accuracy.
We use our equation to calculate the correlation between the binding energies
of Helium-4 trimers and the atom-dimer scattering length. Our results are in
excellent agreement with the recent three-dimensional Faddeev calculations of
Roudnev and collaborators that used phenomenological inter-atomic potentials.Comment: 20 pages, 3 eps figure
Актуальные вопросы оценки качества препаратов в лекарственной форме «таблетки»
The article reviews major ways of streamlining approaches to testing the following quality parameters of drugs presented in the dosage form oftablets: “Identification”, “Dissolution”, “Disintegration”, “Related impurities”, “Residual organic solvents”, “Assay”. The article describes results of a comparative analysis of requirements laid down in the leading world pharmacopoeias, WHO documents and national requirements for tablets standardization. The analysis covers such issues as classification of drugs, terms used to describe various tablet groups, differences in the choice of test methods, as well as in approaches to assessment of parameters and use of reference standards. The analysis makes it possible to define national requirements for tablets quality, which is particularly important in view of the future work on the development of pharmacopoeial monographs on drugs for the State Pharmacopoeia of the Russian Federation.Рассмотрены основные направления совершенствования подходов к оценке качества препаратов в лекарственной форме «таблетки» по показателям «Подлинность», «Растворение», «Распадаемость», «Родственные примеси», «Остаточные органические растворители», «Количественное определение». Проведен сравнительный анализ требований ведущих зарубежных фармакопей, материалов ВОЗ и национальных требований по стандартизации таблеток. Обсуждены вопросы, связанные с классификацией препаратов, используемой терминологией в наименованиях выделяемых групп таблеток, различием в выборе методов анализа, подходах к оценке показателей, использовании стандартных образцов. Проведенный анализ позволяет определить национальные требования к качеству таблеток, что особенно важно в связи с предстоящей работой по подготовке фармакопейных статей на лекарственные препараты для Государственной фармакопеи РФ
High-Multiplicity Lead-Lead Interactions at 158 GeV/c per nucleon
The Krakow-Louisiana-Minnesota-Moscow Collaboration (KLMM) has exposed a set of emulsion chambers with lead targets to a 158 GeV/c per nucleon beam of Pb-208 nuclei, and we report the initial analysis of 40 high-multiplicity Pb-Pb collisions. To test the validity of the superposition model of nucleus-nucleus interactions in this new regime, we compare the shapes of the pseudorapidity distributions with FRITIOF Monte Carlo model calculations, and find close agreement for even the most central events. We characterize head-on collisions as having a mean multiplicity of 1550 +/- 120 and a peak pseudorapidity density of 390 +/- 30. These estimates are significantly lower than our FRITIOF calculations
Automated Track Recognition and Event Reconstruction in Nuclear Emulsion
The major advantages of nuclear emulsion for detecting charged particles are its submicron position resolution and sensitivity to minimum ionizing particles. These must be balanced, however, against the difficult manual microscope measurement by skilled observers required for the analysis. We have developed an automated system to acquire and analyze the microscope images from emulsion chambers. Each emulsion plate is analyzed independently, allowing coincidence techniques to be used in order to reject back- ground and estimate error rates. The system has been used to analyze a sample of high-multiplicity Pb-Pb interactions (charged particle multiplicities approx. 1100) produced by the 158 GeV/c per nucleon Pb-208 beam at CERN. Automatically reconstructed track lists agree with our best manual measurements to 3%. We describe the image analysis and track reconstruction techniques, and discuss the measurement and reconstruction uncertainties
- …