4,102 research outputs found
Symmetric achromatic low-beta collider interaction region design concept
We present a new symmetry-based concept for an achromatic low-beta collider
interaction region design. A specially-designed symmetric Chromaticity
Compensation Block (CCB) induces an angle spread in the passing beam such that
it cancels the chromatic kick of the final focusing quadrupoles. Two such CCBs
placed symmetrically around an interaction point allow simultaneous
compensation of the 1st-order chromaticities and chromatic beam smear at the IP
without inducing significant 2nd-order aberrations to the particle trajectory.
We first develop an analytic description of this approach and explicitly
formulate 2nd-order aberration compensation conditions at the interaction
point. The concept is next applied to develop an interaction region design for
the ion collider ring of an electron-ion collider. We numerically evaluate
performance of the design in terms of momentum acceptance and dynamic aperture.
The advantages of the new concept are illustrated by comparing it to the
conventional distributed-sextupole chromaticity compensation scheme.Comment: 12 pages, 17 figures, to be submitted to Phys. Rev. ST Accel. Beam
SU(2) Gluodynamics and HP1 sigma-model embedding: Scaling, Topology and Confinement
We investigate recently proposed HP1 sigma-model embedding method aimed to
study the topology of SU(2) gauge fields. The HP1 based topological charge is
shown to be fairly compatible with various known definitions. We study the
corresponding topological susceptibility and estimate its value in the
continuum limit. The geometrical clarity of HP1 approach allows to investigate
non-perturbative aspects of SU(2) gauge theory on qualitatively new level. In
particular, we obtain numerically precise estimation of gluon condensate and
its leading quadratic correction. Furthermore, we present clear evidences that
the string tension is to be associated with global (percolating) regions of
sign-coherent topological charge. As a byproduct of our analysis we estimate
the continuum value of quenched chiral condensate and the dimensionality of
regions, which localize the lowest eigenmodes of overlap Dirac operator.Comment: 22 pages, 18 ps figures, revtex4. Replaced to match published version
(PRD, to appear
Faces of matrix models
Partition functions of eigenvalue matrix models possess a number of very
different descriptions: as matrix integrals, as solutions to linear and
non-linear equations, as tau-functions of integrable hierarchies and as
special-geometry prepotentials, as result of the action of W-operators and of
various recursions on elementary input data, as gluing of certain elementary
building blocks. All this explains the central role of such matrix models in
modern mathematical physics: they provide the basic "special functions" to
express the answers and relations between them, and they serve as a dream model
of what one should try to achieve in any other field.Comment: 10 page
Orientations of the lamellar phase of block copolymer melts under oscillatory shear flow
We develop a theory to describe the reorientation phenomena in the lamellar
phase of block copolymer melt under reciprocating shear flow. We show that
similar to the steady-shear, the oscillating flow anisotropically suppresses
fluctuations and gives rise to the parallel-perpendicular orientation
transition. The experimentally observed high-frequency reverse transition is
explained in terms of interaction between the melt and the shear-cell walls.Comment: RevTex, 3 pages, 1 figure, submitted to PR
Is Strong Gravitational Radiation predicted by TeV-Gravity?
In TeV-gravity models the gravitational coupling to particles with energies
E\sim m_{Pl} \sim 10 TeV is not suppressed by powers of ultra-small ratio
E/M_{Pl} with M_{Pl} \sim 10^{19} GeV. Therefore one could imagine strong
synchrotron radiation of gravitons by the accelerating particles to become the
most pronounced manifestation of TeV-gravity at LHC. However, this turns out to
be not true: considerable damping continues to exist, only the place of
E/M_{Pl} it taken by a power of a ratio \theta\omega/E, where the typical
frequency \omega of emitted radiation, while increased by a number of
\gamma-factors, can not reach E/\vartheta unless particles are accelerated by
nearly critical fields. Moreover, for currently available magnetic fields B
\sim 10 Tesla, multi-dimensionality does not enhance gravitational radiation at
all even if TeV-gravity is correct.Comment: 7 pages, LaTe
Method to solve integral equations of the first kind with an approximate input
Techniques are proposed for solving integral equations of the first kind with
an input known not precisely. The requirement that the solution sought for
includes a given number of maxima and minima is imposed. It is shown that when
the deviation of the approximate input from the true one is sufficiently small
and some additional conditions are fulfilled the method leads to an approximate
solution that is necessarily close to the true solution. No regularization is
required in the present approach. Requirements on features of the solution at
integration limits are also imposed. The problem is treated with the help of an
ansatz proposed for the derivative of the solution. The ansatz is the most
general one compatible with the above mentioned requirements. The techniques
are tested with exactly solvable examples. Inversions of the Lorentz, Stieltjes
and Laplace integral transforms are performed, and very satisfactory results
are obtained. The method is useful, in particular, for the calculation of
quantum-mechanical reaction amplitudes and inclusive spectra of
perturbation-induced reactions in the framework of the integral transform
approach.Comment: 28 pages, 1 figure; the presentation is somewhat improved; to be
published in Phys. Rev.
Reentrant Melting of RNA with Quenched Sequence Randomness
The effect of quenched sequence disorder on the thermodynamics of RNA
secondary structure formation is investigated for two- and four-letter
alphabet models using the constrained annealing approach, from which the
temperature behavior of the free energy, specific heat, and helicity is
analytically obtained. For competing base pairing energies, the calculations
reveal reentrant melting at low temperatures, in excellent agreement with
numerical results. Our results suggest an additional mechanism for the
experimental phenomenon of RNA cold denaturation
Sheath parameters for non-Debye plasmas: simulations and arc damage
This paper describes the surface environment of the dense plasma arcs that
damage rf accelerators, tokamaks and other high gradient structures. We
simulate the dense, non-ideal plasma sheath near a metallic surface using
Molecular Dynamics (MD) to evaluate sheaths in the non-Debye region for high
density, low temperature plasmas. We use direct two-component MD simulations
where the interactions between all electrons and ions are computed explicitly.
We find that the non-Debye sheath can be extrapolated from the Debye sheath
parameters with small corrections. We find that these parameters are roughly
consistent with previous PIC code estimates, pointing to densities in the range
. The high surface fields implied by these
results could produce field emission that would short the sheath and cause an
instability in the time evolution of the arc, and this mechanism could limit
the maximum density and surface field in the arc. These results also provide a
way of understanding how the "burn voltage" of an arc is generated, and the
relation between self sputtering and the burn voltage, while not well
understood, seems to be closely correlated. Using these results, and equating
surface tension and plasma pressure, it is possible to infer a range of plasma
densities and sheath potentials from SEM images of arc damage. We find that the
high density plasma these results imply and the level of plasma pressure they
would produce is consistent with arc damage on a scale 100 nm or less, in
examples where the liquid metal would cool before this structure would be lost.
We find that the sub-micron component of arc damage, the burn voltage, and
fluctuations in the visible light production of arcs may be the most direct
indicators of the parameters of the dense plasma arc, and the most useful
diagnostics of the mechanisms limiting gradients in accelerators.Comment: 8 pages, 16 figure
Symmetries of Differential Equations via Cartan's Method of Equivalence
We formulate a method of computing invariant 1-forms and structure equations
of symmetry pseudo-groups of differential equations based on Cartan's method of
equivalence and the moving coframe method introduced by Fels and Olver. Our
apparoach does not require a preliminary computation of infinitesimal defining
systems, their analysis and integration, and uses differentiation and linear
algebra operations only. Examples of its applications are given.Comment: 15 pages, LaTeX 2.0
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