584 research outputs found
Tubular initial conditions and ridge formation
The 2D azimuth & rapidity structure of the two-particle correlations in
relativistic A+A collisions is altered significantly by the presence of sharp
inhomogeneities in superdense matter formed in such processes. The causality
constraints enforce one to associate the long-range longitudinal correlations
observed in a narrow angular interval, the so-called (soft) ridge, with
peculiarities of the initial conditions of collision process. This study's
objective is to analyze whether multiform initial tubular structures,
undergoing the subsequent hydrodynamic evolution and gradual decoupling, can
form the soft ridges. Motivated by the flux-tube scenarios, the initial energy
density distribution contains the different numbers of high density tube-like
boost-invariant inclusions that form a bumpy structure in the transverse plane.
The influence of various structures of such initial conditions in the most
central A+A events on the collective evolution of matter, resulting spectra,
angular particle correlations and v_n-coefficients is studied in the framework
of the HydroKinetic Model (HKM).Comment: 18 pages, 6 figures, the paper to be published in Advances of High
Energy Physics (2013, in press
Surface roughening during low temperature Si(100) epitaxy
Reflection high energy electron diffraction (RHEED) was used to investigate surface roughening during low temperature Si(100) homoepitaxy. The use of RHEED allowed in situ real-time collection of structural information from the growth surface. RHEED patterns were analyzed using a simple kinematic diffraction model which related average surface roughness and average in-plane coherence lengths to the lengths and widths of individual RHEED diffraction features, respectively. These RHEED analyses were quantified by calibrating against cross-section transmission electron microscopy (TEM) analyses of surface roughening. Both the RHEED and TEM analyses revealed similar scaling of surface roughness with deposited thickness, with RHEED analyses resulting in roughness values a factor of ∼2 times lower than those obtained from TEM analyses. RHEED was then used to analyze surface roughening during Si(100) homoepitaxial growth in a range of temperatures, 200–275 °C. Initially, surface roughness increased linearly with deposited thickness at a roughening rate that decreased with increasing growth temperature. At each growth temperature, near the crystalline/amorphous Si phase transition, the rate of surface roughening decreased. This decrease coincided with the formation of facets and twins along Si{111} planes. Surface roughness eventually saturated at a value which followed an Arrhenius relation with temperature Eact ∼ 0.31±0.1Eact∼0.31±0.1 eV. This activation energy agrees well with the activation energy for the crystalline/amorphous Si phase transition, Eact ∼ 0.35Eact∼0.35 eV, and suggests that limited thickness epitaxy is characterized by this saturation roughness. Once the saturation roughness was reached, no significant changes in surface roughness were detected. In addition, the decay of average in-plane coherence lengths was also temperature dependent. Values of average coherence lengths, at the crystalline/amorphous Si phase transition, also increased with growth temperature. All of these data are consistent with a model that links surface roughening to the formation of critically sized Si{100} facets and the eventual breakdown in crystalline growth. © 1997 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70948/2/JAPIAU-82-3-1157-1.pd
Hydrokinetic predictions for femtoscopy scales in A+A collisions in the light of recent ALICE LHC results
A study of energy behavior of the pion spectra and interferometry scales is
carried out for the top SPS, RHIC and for LHC energies within the hydrokinetic
approach. The main mechanisms that lead to the paradoxical, at first sight,
dependence of the interferometry scales with an energy growth, in particular, a
decrease ratio, are exposed. The hydrokinetic predictions
for the HBT radii at LHC energies are compared with the recent results of the
ALICE experiment.Comment: Based on the talks given at the Sixth Workshop on Particle
Correlations and Femtoscopy, BITP, Kiev, September 14 - 18, 2010 and GSI/EMMI
Seminar, January 14, 201
New solutions of relativistic wave equations in magnetic fields and longitudinal fields
We demonstrate how one can describe explicitly the present arbitrariness in
solutions of relativistic wave equations in external electromagnetic fields of
special form. This arbitrariness is connected to the existence of a
transformation, which reduces effectively the number of variables in the
initial equations. Then we use the corresponding representations to construct
new sets of exact solutions, which may have a physical interest. Namely, we
present new sets of stationary and nonstationary solutions in magnetic field
and in some superpositions of electric and magnetic fields.Comment: 25 pages, LaTex fil
GUIDELINES FOR AN INDIVIDUAL WORK FOR THE DISCIPLINE "1C-ACCOUNTING (in english)" (for 4th year full-time students and 5th year distance learning students - field of study 6.030509 - "Accounting and Auditing")
(for 4th year full-time students and 5th year distance learning students - field of study 6.030509 - "Accounting and Auditing"
Evidence for Hydrodynamic Evolution in Proton-Proton Scattering at LHC Energies
In scattering at LHC energies, large numbers of elementary scatterings
will contribute significantly, and the corresponding high multiplicity events
will be of particular interest. Elementary scatterings are parton ladders,
identified with color flux-tubes. In high multiplicity events, many of these
flux tubes are produced in the same space region, creating high energy
densities. We argue that there are good reasons to employ the successful
procedure used for heavy ion collisions: matter is assumed to thermalizes
quickly, such that the energy from the flux-tubes can be taken as initial
condition for a hydrodynamic expansion. This scenario gets spectacular support
from very recent results on Bose-Einstein correlations in scattering at
900 GeV at LHC.Comment: 11 pages, 20 figure
Equivariant pretheories and invariants of torsors
In the present paper we introduce and study the notion of an equivariant
pretheory: basic examples include equivariant Chow groups, equivariant K-theory
and equivariant algebraic cobordism. To extend this set of examples we define
an equivariant (co)homology theory with coefficients in a Rost cycle module and
provide a version of Merkurjev's (equivariant K-theory) spectral sequence for
such a theory. As an application we generalize the theorem of
Karpenko-Merkurjev on G-torsors and rational cycles; to every G-torsor E and a
G-equivariant pretheory we associate a graded ring which serves as an invariant
of E. In the case of Chow groups this ring encodes the information concerning
the motivic J-invariant of E and in the case of Grothendieck's K_0 -- indexes
of the respective Tits algebras.Comment: 23 pages; this is an essentially extended version of the previous
preprint: the construction of an equivariant cycle (co)homology and the
spectral sequence (generalizing the long exact localization sequence) are
adde
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