177 research outputs found
Ternary numbers and algebras. Reflexive numbers and Berger graphs
The Calabi-Yau spaces with SU(m) holonomy can be studied by the algebraic way
through the integer lattice where one can construct the Newton reflexive
polyhedra or the Berger graphs. Our conjecture is that the Berger graphs can be
directly related with the -ary algebras. To find such algebras we study the
n-ary generalization of the well-known binary norm division algebras, , , , , which helped to discover the
most important "minimal" binary simple Lie groups, U(1), SU(2) and G(2). As the
most important example, we consider the case , which gives the ternary
generalization of quaternions and octonions, , , respectively. The
ternary generalization of quaternions is directly related to the new ternary
algebra and group which are related to the natural extensions of the binary
algebra and SU(3) group. Using this ternary algebra we found the
solution for the Berger graph: a tetrahedron.Comment: Revised version with minor correction
A note on the breathing mode of an elastic sphere in Newtonian and complex fluids
Experiments on the acoustic vibrations of elastic nanostructures in fluid
media have been used to study the mechanical properties of materials, as well
as for mechanical and biological sensing. The medium surrounding the
nanostructure is typically modeled as a Newtonian fluid. A recent experiment
however suggested that high-frequency longitudinal vibration of bipyramidal
nanoparticles could trigger a viscoelastic response in water-glycerol mixtures
[M. Pelton et al., "Viscoelastic flows in simple liquids generated by vibrating
nanostructures," Phys. Rev. Lett. 111, 244502 (2013)]. Motivated by these
experimental studies, we first revisit a classical continuum mechanics problem
of the purely radial vibration of an elastic sphere, also called the breathing
mode, in a compressible viscous fluid, and then extend our analysis to a
viscoelastic medium using the Maxwell fluid model. The effects of fluid
compressibility and viscoelasticity are discussed. Although in the case of
longitudinal vibration of bipyramidal nanoparticles, the effects of fluid
compressibility were shown to be negligible, we demonstrate that it plays a
significant role in the breathing mode of an elastic sphere. On the other hand,
despite the different vibration modes, the breathing mode of a sphere triggers
a viscoelastic response in water-glycerol mixtures similar to that triggered by
the longitudinal vibration of bipyramidal nanoparticles. We also comment on the
effect of fluid viscoelasticity on the idea of destroying virus particles by
acoustic resonance
An Automatic Control System for Conditioning 30 GHz Accelerating Structures
A software application programme has been developed to allow fast and automatic high-gradient conditioning of accelerating structures at 30 GHz in CTF3. The specificity of the application is the ability to control the high-power electron beam which produces the 30 GHz RF power used to condition the accelerating structures. The programme permits operation round the clock with minimum manpower requirements. In this paper the fast control system, machine control system, logging system, graphical user control interface and logging data visualization are described. An outline of the conditioning control system itself and of the feedback controlling peak power and pulse length is given. The software allows different types of conditioning strategies to be programme
Vibrational modes of metal nanoshells and bimetallic core-shell nanoparticles
We study theoretically spectrum of radial vibrational modes in composite
metal nanostructures such as bimetallic core-shell particles and metal
nanoshells with dielectric core in an environment. We calculate frequencies and
damping rates of fundamental (breathing) modes for these nanostructures along
with those of two higher-order modes. For metal nanoshells, we find that the
breathing mode frequency is always lower than the one for solid particles of
the same size, while the damping is higher and increases with reduction of the
shell thickness. We identify two regimes that can be characterized as weakly
damped and overdamped vibrations in the presence of external medium. For
bimetalllic particles, we find periodic dependence of frequency and damping
rate on the shell thickness with period determined by mode number. For both
types of nanostructures, the frequency of higher modes is nearly independent of
the environment, while the damping rate shows strong sensitivity to outside
medium.Comment: 7 pages, 8 figure
Simple model for the vibrations of embedded elastically cubic nanocrystals
The purpose of this work is to calculate the vibrational modes of an
elastically anisotropic sphere embedded in an isotropic matrix. This has
important application to understanding the spectra of low-frequency Raman
scattering from nanoparticles embedded in a glass matrix. First some low
frequency vibrational modes of a free cubically elastic sphere are found to be
nearly independent of one combination of elastic constants. This is then
exploited to obtain an isotropic approximation for these modes which enables to
take into account the surrounding isotropic matrix. This method is then used to
quantatively explain recent spectra of gold and copper nanocrystals in glasses.Comment: 6 pages, 5 figure
Comment on "Estimate of the vibrational frequencies of spherical virus particles"
This comment corrects some errors which appeared in the calculation of an
elastic sphere eigenenergies. As a result, the symmetry of the mode having the
lowest frequency is changed. Also a direction for calculating the damping of
these modes for embedded elastic spheres is given.Comment: comment L. H. Ford Phys. Rev. E 67 (2003) 05192
Pinning Enhancement by Heterovalent Substitution in YREBaCuO
The intragrain pinning in high- superconductor compounds
YREBaCuO with low concentration of RE
(La, Ce, Pr) was investigated. Magnetic and transport measurements reveal that
the pinning is maximal for the concentration of heterovalent RE such that the
average distance between the impurity ions in the plane of rare-earth elements
close to the diameter of Abrikosov vortices in YBCO.Comment: 11 pages, 6 figures, will be published in SUS
Policy Challenges Faced by Low-Income CIS Economies
In the 1990s, the CIS region experienced a painful transformation following the collapse of the USSR and the command economy. For the less developed republics of the former USSR, this process was even more dramatic as they lost subsidies from the Union's budget and some of them suffered devastating conflicts. In the 2000s, after overcoming the adaptation output decline and the consequences of the 1998-1999 financial crises, these economies started to grow rapidly, reducing poverty and macroeconomic imbalances. However, their future growth prospects are increasingly vulnerable due to their strong dependence on commodity exports, a poor business and investment climate, endemic corruption and weak governance. Quite recently, fighting high inflation has returned to the policy agenda. The modernization and diversification of the low-income CIS economies requires further market and institutional reforms aimed at overcoming the Soviet legacy of a repressive and inefficient state. The international community can help by resolving regional conflicts, assisting with trade and economic integration, and offering well-targeted development assistance
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