4,407 research outputs found
Calculation of isotope shifts and relativistic shifts in CI, CII, CIII and CIV
We present an accurate ab initio method of calculating isotope shifts and
relativistic shifts in atomic spectra. We test the method on neutral carbon and
three carbon ions. The relativistic shift of carbon lines may allow them to be
included in analyses of quasar absorption spectra that seek to measure possible
variations in the fine structure constant, alpha, over the lifetime of the
Universe. Carbon isotope shifts can be used to measure isotope abundances in
gas clouds: isotope abundances are potentially an important source of
systematic error in the alpha-variation studies. These abundances are also
needed to study nuclear reactions in stars and supernovae, and test models of
chemical evolution of the Universe
Strength of inserts in titanium alloy machining
In this paper, a stressed state of a non-worn cutting wedge in a machined titanium alloy (Ti[6]Al[2]Mo[2]Cr) is analyzed. The distribution of contact loads on the face of a cutting tool was obtained experimentally with the use of a 'split cutting tool'. Calculation of internal stresses in the indexable insert made from cemented carbide (WC8Co) was carried out with the help of ANSYS 14.0 software. Investigations showed that a small thickness of the cutting insert leads to extremely high compressive stresses near the cutting edge, stresses that exceed the ultimate compressive strength of cemented carbide. The face and the base of the insert experience high tensile stresses, which approach the ultimate tensile strength of cemented carbide and increase a probability of cutting insert destruction. If the thickness of the cutting insert is bigger than 5 mm, compressive stresses near the cutting edge decrease, and tensile stresses on the face and base decrease to zero. The dependences of the greatest normal and tangential stresses on thickness of the cutting insert were found
Moths and butterflies (Lepidoptera) of the continental part of the Nenets Autonomous Okrug, Russia
Until very recently, Nenets Autonomous Okrug (NAO), located in the northeastern
part of European Russia, was the least studied region of Russia in terms of
itsmoth fauna. Intensive sampling in the surroundings of Naryan-Mar, combined
with critical revision of earlier publications and evaluation of museum collections,
resulted in the discovery of a relatively rich fauna of Lepidoptera. The first
regional checklist of moths and butterflies of the continental part of NAO includes
324 species (169 species of microlepidoptera and 155 species of
macrolepidoptera), 178 of which are reported fromNAOfor the first time.We estimate
that 40 to 180 species remain to be found in the study region. The recorded
speciesmostly belong to residents of northern boreal forests and bogs. The fauna
of moths and butterflies of NAO clearly differs from the fauna of Fennoscandia,
due to the relatively higher proportion ofEast Palaearctic andBeringian species
Theory of lossless polarization attraction in telecommunication fibers
In this work, polarization attraction is meant to be the conservative nonlinear effect that transforms any arbitrary input state of polarization (SOP) of an intense optical signal beam fed to a nonlinear medium into approximately one and the same SOP at the output, provided that the medium is driven by a relatively stronger counterpropagating pump beam. Essentially, the combination of the nonlinear medium and the pump beam serves as a lossless polarizer for the signal beam. The degree of polarization of the outcoming signal beam can be close to 100% (90% in our present simulations). With an eye toward the development of such lossless polarizers for fiber optics applications, we theoretically study the polarization attraction effect in the optical fibers that are used in telecommunication links; i.e., randomly birefringent fibers. A generic model for the fiber-based lossless polarizers is derived, and a statistical scheme for the quantification of their performance is proposed
A Necessary Condition for existence of Lie Symmetries in Quasihomogeneous Systems of Ordinary Differential Equations
Lie symmetries for ordinary differential equations are studied. In systems of
ordinary differential equations, there do not always exist non-trivial Lie
symmetries around equilibrium points. We present a necessary condition for
existence of Lie symmetries analytic in the neighbourhood of an equilibrium
point. In addition, this result can be applied to a necessary condition for
existence of a Lie symmetry in quasihomogeneous systems of ordinary
differential equations. With the help of our main theorem, it is proved that
several systems do not possess any analytic Lie symmetries.Comment: 15 pages, no figures, AMSLaTe
Theory of lossless polarization attraction in telecommunication fibers: erratum
An erroneous procedure of averaging the components of the Stokes vector of a polarization scrambled beam over the Poincare sphere introduced in our earlier paper [J. Opt. Soc. Am. B 28, 100-108 (2011)] has been corrected
Classification of symmetric periodic trajectories in ellipsoidal billiards
We classify nonsingular symmetric periodic trajectories (SPTs) of billiards
inside ellipsoids of R^{n+1} without any symmetry of revolution. SPTs are
defined as periodic trajectories passing through some symmetry set. We prove
that there are exactly 2^{2n}(2^{n+1}-1) classes of such trajectories. We have
implemented an algorithm to find minimal SPTs of each of the 12 classes in the
2D case (R^2) and each of the 112 classes in the 3D case (R^3). They have
periods 3, 4 or 6 in the 2D case; and 4, 5, 6, 8 or 10 in the 3D case. We
display a selection of 3D minimal SPTs. Some of them have properties that
cannot take place in the 2D case.Comment: 26 pages, 77 figures, 17 table
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