880 research outputs found
Longitudinal Losses Due to Breathing Mode Excitation in Radiofrequency Linear Accelerators
Transverse breathing mode oscillations in a particle beam can couple energy
into longitudinal oscillations in a bunch of finite length and cause
significant losses. We develop a model that illustrates this effect and explore
the dependence on mismatch size, space-charge tune depression, longitudinal
focusing strength, bunch length, and RF bucket length
Two-loop self-dual Euler-Heisenberg Lagrangians (II): Imaginary part and Borel analysis
We analyze the structure of the imaginary part of the two-loop
Euler-Heisenberg QED effective Lagrangian for a constant self-dual background.
The novel feature of the two-loop result, compared to one-loop, is that the
prefactor of each exponential (instanton) term in the imaginary part has itself
an asymptotic expansion. We also perform a high-precision test of Borel
summation techniques applied to the weak-field expansion, and find that the
Borel dispersion relations reproduce the full prefactor of the leading
imaginary contribution.Comment: 28 pp, 6 eps figure
Nanoelectromechanics of Piezoresponse Force Microscopy
To achieve quantitative interpretation of Piezoresponse Force Microscopy
(PFM), including resolution limits, tip bias- and strain-induced phenomena and
spectroscopy, analytical representations for tip-induced electroelastic fields
inside the material are derived for the cases of weak and strong indentation.
In the weak indentation case, electrostatic field distribution is calculated
using image charge model. In the strong indentation case, the solution of the
coupled electroelastic problem for piezoelectric indentation is used to obtain
the electric field and strain distribution in the ferroelectric material. This
establishes a complete continuum mechanics description of the PFM contact
mechanics and imaging mechanism. The electroelastic field distribution allows
signal generation volume in PFM to be determined. These rigorous solutions are
compared with the electrostatic point charge and sphere-plane models, and the
applicability limits for asymptotic point charge and point force models are
established. The implications of these results for ferroelectric polarization
switching processes are analyzed.Comment: 81 pages, 19 figures, to be published in Phys. Rev.
Zero modes, beta functions and IR/UV interplay in higher-loop QED
We analyze the relation between the short-distance behavior of quantum field
theory and the strong-field limit of the background field formalism, for QED
effective Lagrangians in self-dual backgrounds, at both one and two loop. The
self-duality of the background leads to zero modes in the case of spinor QED,
and these zero modes must be taken into account before comparing the
perturbative beta function coefficients and the coefficients of the
strong-field limit of the effective Lagrangian. At one-loop this is familiar
from instanton physics, but we find that at two-loop the role of the zero
modes, and the interplay between IR and UV effects in the renormalization, is
quite different. Our analysis is motivated in part by the remarkable simplicity
of the two-loop QED effective Lagrangians for a self-dual constant background,
and we also present here a new independent derivation of these two-loop
results.Comment: 15 pages, revtex
Vibrations and fractional vibrations of rods, plates and Fresnel pseudo-processes
Different initial and boundary value problems for the equation of vibrations
of rods (also called Fresnel equation) are solved by exploiting the connection
with Brownian motion and the heat equation. The analysis of the fractional
version (of order ) of the Fresnel equation is also performed and, in
detail, some specific cases, like , 1/3, 2/3, are analyzed. By means
of the fundamental solution of the Fresnel equation, a pseudo-process ,
with real sign-varying density is constructed and some of its properties
examined. The equation of vibrations of plates is considered and the case of
circular vibrating disks is investigated by applying the methods of
planar orthogonally reflecting Brownian motion within . The composition of
F with reflecting Brownian motion yields the law of biquadratic heat
equation while the composition of with the first passage time of
produces a genuine probability law strictly connected with the Cauchy process.Comment: 33 pages,8 figure
Poisson-Lie group of pseudodifferential symbols
We introduce a Lie bialgebra structure on the central extension of the Lie
algebra of differential operators on the line and the circle (with scalar or
matrix coefficients). This defines a Poisson--Lie structure on the dual group
of pseudodifferential symbols of an arbitrary real (or complex) order. We show
that the usual (second) Benney, KdV (or GL_n--Adler--Gelfand--Dickey) and KP
Poisson structures are naturally realized as restrictions of this Poisson
structure to submanifolds of this ``universal'' Poisson--Lie group.
Moreover, the reduced (=SL_n) versions of these manifolds (W_n-algebras in
physical terminology) can be viewed as subspaces of the quotient (or Poisson
reduction) of this Poisson--Lie group by the dressing action of the group of
functions.
Finally, we define an infinite set of functions in involution on the
Poisson--Lie group that give the standard families of Hamiltonians when
restricted to the submanifolds mentioned above. The Poisson structure and
Hamiltonians on the whole group interpolate between the Poisson structures and
Hamiltonians of Benney, KP and KdV flows. We also discuss the geometrical
meaning of W_\infty as a limit of Poisson algebras W_\epsilon as \epsilon goes
to 0.Comment: 64 pages, no figure
On q-deformed gl(l+1)-Whittaker function II
A representation of a specialization of a q-deformed class one lattice
gl(\ell+1}-Whittaker function in terms of cohomology groups of line bundles on
the space QM_d(P^{\ell}) of quasi-maps P^1 to P^{\ell} of degree d is proposed.
For \ell=1, this provides an interpretation of non-specialized q-deformed
gl(2)-Whittaker function in terms of QM_d(\IP^1). In particular the (q-version
of) Mellin-Barnes representation of gl(2)-Whittaker function is realized as a
semi-infinite period map. The explicit form of the period map manifests an
important role of q-version of Gamma-function as a substitute of topological
genus in semi-infinite geometry. A relation with Givental-Lee universal
solution (J-function) of q-deformed gl(2)-Toda chain is also discussed.Comment: Extended version submitted in Comm. Math. Phys., 24 page
Extraction of Kaon Formfactors from K^- -> mu^- nu_mu gamma Decay at ISTRA+ Setup
The radiative decay K->mu nu gamma has been studied at ISTRA+ setup in a new
kinematical region. About 22K events of K^- -> mu^- nu_mu gamma have been
observed. The sign and value of Fv-Fa have been measured for the first time.
The result is Fv-Fa=0.21(4)(4).Comment: 11 pages, 21 figures, submitted to Phys. Lett.
Search for Heavy Neutrino in K->mu nu_h(nu_h-> nu gamma) Decay at ISTRA+ Setup
Heavy neutrino nu_h with m_h < 300MeV/c^2 can be effectively searched for in
kaon decays. We put upper limits on mixing matrix element |U_mu_h}|^2 for
radiatively decaying nu_h from K->mu nu_h (nu_h -> nu gamma) decay chain in the
following parameter region: 30MeV/c^2 < m_h < 80MeV/c^2; 10^{-11}sec < tau_h <
10^{-9}sec. For the whole region |U_{mu h}|^2 < 5 x 10^{-5} for Majorana type
of nu_h and | U_{\mu h}|^2 < 8 x 10^{-5} for the Dirac case.Comment: Published in Phys. Lett.
СОЧЕТАНИЕ ОТКРЫТОЙ И ВИДЕОХИРУРГИИ ПРИ ОПУХОЛЯХ ТОРАКОАБДОМИНАЛЬНОЙ ЛОКАЛИЗАЦИИ У ДЕТЕЙ
The autors report original date on the combined use of videosurgery and open surgical intervention in 3 patients. One (1 yr 10 mo) had neuroblastoma in the posterior mediastinum spreading to the retroperitoneal region, another (5 yr) presented with neuroblastoma in the thoracic aperture region spreading to the neck, the third one (14 yr) suffered limphoepithelioma-like cancer of the thymus. The combined treatment permits to optimize the surgical procedure and avoid additional use of thoraco- and laparotomy.Описаны собственные наблюдения по сочетанному использованию видеохирургии и открытого хирургического вмешательства у 3-х пациентов: с нейробластомой заднего средостения с распространениемв забрюшинное пространство (возраст 1 год 10 мес); с нейробластомой зоны апертуры грудной клетки сраспорстранением на шею (5 лет) и с лимфоэпителиомо-подобным раком тимуса (14 лет). Показано, что методика позволяет оптимизировать операцию и избежать дополнительного использования торако- или лапаротомии
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