117 research outputs found
Effects of interatomic interaction on cooperative relaxation of two-level atoms
We study effects of direct interatomic interaction on cooperative processes
in atom-photon dynamics. Using a model of two-level atoms with Ising-type
interaction as an example, it is demonstrated that interparticle interaction
combined with atom-field coupling can introduce additional interatomic
correlations acting as a phase synchronizing factor. For the case of weakly
interacting atoms with , where is the interparticle
coupling constant and is the atomic frequency, dynamical regimes of
cooperative relaxation of atoms are analyzed in Born-Markov approximation both
numerically and using the mean field approximation. We show that interparticle
correlations induced by the direct interaction result in inhibition of
incoherent spontaneous decay leading to the regime of collective pulse
relaxation which differs from superradiance in nature. For superradiant
transition, the synchronizing effect of interatomic interaction is found to
manifest itself in enhancement of superradiance. When the interaction is strong
and , one-partice one-photon transitions are excluded and
transition to the regime of multiphoton relaxation occurs. Using a simple model
of two atoms in a high-Q single mode cavity we show that such transition is
accompanied by Rabi oscillations involving many-atom multiphoton states.
Dephasing effect of dipole-dipole interaction and solitonic mechanism of
relaxation are discussed.Comment: 34 pages, 8 figure
Crystal Undulator As A Novel Compact Source Of Radiation
A crystalline undulator (CU) with periodically deformed crystallographic
planes is capable of deflecting charged particles with the same strength as an
equivalent magnetic field of 1000 T and could provide quite a short period L in
the sub-millimeter range. We present an idea for creation of a CU and report
its first realization. One face of a silicon crystal was given periodic
micro-scratches (grooves), with a period of 1 mm, by means of a diamond blade.
The X-ray tests of the crystal deformation have shown that a sinusoidal-like
shape of crystalline planes goes through the bulk of the crystal. This opens up
the possibility for experiments with high-energy particles channeled in CU, a
novel compact source of radiation. The first experiment on photon emission in
CU has been started at LNF with 800 MeV positrons aiming to produce 50 keV
undulator photons.Comment: Presented at PAC 2003 (Portland, May 12-16
Security challenges of small cell as a service in virtualized mobile edge computing environments
Research on next-generation 5G wireless networks is currently attracting a lot of attention in both academia and industry. While 5G development and standardization activities are still at their early stage, it is widely acknowledged that 5G systems are going to extensively rely on dense small cell deployments, which would exploit infrastructure and network functions virtualization (NFV), and push the network intelligence towards network edges by embracing the concept of mobile edge computing (MEC). As security will be a fundamental enabling factor of small cell as a service (SCaaS) in 5G networks, we present the most prominent threats and vulnerabilities against a broad range of targets. As far as the related work is concerned, to the best of our knowledge, this paper is the first to investigate security challenges at the intersection of SCaaS, NFV, and MEC. It is also the first paper that proposes a set of criteria to facilitate a clear and effective taxonomy of security challenges of main elements of 5G networks. Our analysis can serve as a staring point towards the development of appropriate 5G security solutions. These will have crucial effect on legal and regulatory frameworks as well as on decisions of businesses, governments, and end-users
BEAM POSITION MONITOR SYSTEM FOR 2 MEV ELECTRON COOLER FOR COSY
Abstract The 2 MEV electron cooler for COSY storage ring FZJ is assembling in BINP. Beam position monitor (BPM) system for orbit measurements has been developed and fabricated at BINP. The system contains 2 BPMs inside the cooling section and 10 BPMs in transport channels. Continuous electron beam is modulated with a 3 MHz signal for capability to get signals from pickup electrodes. The beam current modulation can be varied in the range of 0.3-1.5 mA. The BPMs inside the cooling section can measure both electron and proton beams. It is achieved by means of switching the reference signals inside the BPM electronics. The BPM electronics provides highly precise beam position measurements. Position measurement error doesn't exceed 1 micron. Design features of the BPM system, its parameters and testing results are presented in this paper
Ranks of twists of elliptic curves and Hilbert's Tenth Problem
In this paper we investigate the 2-Selmer rank in families of quadratic
twists of elliptic curves over arbitrary number fields. We give sufficient
conditions on an elliptic curve so that it has twists of arbitrary 2-Selmer
rank, and we give lower bounds for the number of twists (with bounded
conductor) that have a given 2-Selmer rank. As a consequence, under appropriate
hypotheses we can find many twists with trivial Mordell-Weil group, and
(assuming the Shafarevich-Tate conjecture) many others with infinite cyclic
Mordell-Weil group. Using work of Poonen and Shlapentokh, it follows from our
results that if the Shafarevich-Tate conjecture holds, then Hilbert's Tenth
Problem has a negative answer over the ring of integers of every number field.Comment: Minor changes. To appear in Inventiones mathematica
Perturbations of Noise: The origins of Isothermal Flows
We make a detailed analysis of both phenomenological and analytic background
for the "Brownian recoil principle" hypothesis (Phys. Rev. A 46, (1992), 4634).
A corresponding theory of the isothermal Brownian motion of particle ensembles
(Smoluchowski diffusion process approximation), gives account of the
environmental recoil effects due to locally induced tiny heat flows. By means
of local expectation values we elevate the individually negligible phenomena to
a non-negligible (accumulated) recoil effect on the ensemble average. The main
technical input is a consequent exploitation of the Hamilton-Jacobi equation as
a natural substitute for the local momentum conservation law. Together with the
continuity equation (alternatively, Fokker-Planck), it forms a closed system of
partial differential equations which uniquely determines an associated
Markovian diffusion process. The third Newton law in the mean is utilised to
generate diffusion-type processes which are either anomalous (enhanced), or
generically non-dispersive.Comment: Latex fil
Galois sections for abelianized fundamental groups
Given a smooth projective curve of genus at least 2 over a number field
, Grothendieck's Section Conjecture predicts that the canonical projection
from the \'etale fundamental group of onto the absolute Galois group of
has a section if and only if the curve has a rational point. We show that there
exist curves where the above map has a section over each completion of but
not over . In the appendix Victor Flynn gives explicit examples in genus 2.
Our result is a consequence of a more general investigation of the existence
of sections for the projection of the \'etale fundamental group `with
abelianized geometric part' onto the Galois group. We give a criterion for the
existence of sections in arbitrary dimension and over arbitrary perfect fields,
and then study the case of curves over local and global fields more closely. We
also point out the relation to the elementary obstruction of
Colliot-Th\'el\`ene and Sansuc.Comment: This is the published version, except for a characteristic 0
assumption added in Section 5 which was unfortunately omitted there. Thanks
to O. Wittenberg for noticing i
Experimental Study For The Feasibility Of A Crystalline Undulator
We present an idea for creation of a crystalline undulator and report its
first realization. One face of a silicon crystal was given periodic
micro-scratches (trenches) by means of a diamond blade. The X-ray tests of the
crystal deformation due to given periodic pattern of surface scratches have
shown that a sinusoidal shape is observed on both the scratched surface and the
opposite (unscratched) face of the crystal, that is, a periodic sinusoidal
deformation goes through the bulk of the crystal. This opens up the possibility
for experiments with high-energy particles channeled in crystalline undulator,
a novel compact source of radiation.Comment: 12 pages, 4 figure
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