134,273 research outputs found
Control of laser wake field acceleration by plasma density profile
We show that both the maximum energy gain and the accelerated beam quality
can be efficiently controlled by the plasma density profile. Choosing a proper
density gradient one can uplift the dephasing limitation. When a periodic wake
field is exploited, the phase synchronism between the bunch of relativistic
particles and the plasma wave can be maintained over extended distances due to
the plasma density gradient. Putting electrons into the th wake period
behind the driving laser pulse, the maximum energy gain is increased by the
factor over that in the case of uniform plasma. The acceleration is
limited then by laser depletion rather than by dephasing. Further, we show that
the natural energy spread of the particle bunch acquired at the acceleration
stage can be effectively removed by a matched deceleration stage, where a
larger plasma density is used
Gravitational Laser Back-Scattering
A possible way of producing gravitons in the laboratory is investigated. We
evaluate the cross section electron + photon electron + graviton
in the framework of linearized gravitation, and analyse this reaction
considering the photon coming either from a laser beam or from a Compton
back-scattering process.Comment: 11 pages, 2 figures (available upon request), RevTeX, IFT-P.03/9
On reduced density matrices for disjoint subsystems
We show that spin and fermion representations for solvable quantum chains
lead in general to different reduced density matrices if the subsystem is not
singly connected. We study the effect for two sites in XX and XY chains as well
as for sublattices in XX and transverse Ising chains.Comment: 10 pages, 4 figure
A robust method for measurement of fluctuation parallel wavenumber in laboratory plasmas
Measuring the parallel wavenumber is fundamental for the experimental characterization of electrostatic instabilities. It becomes particularly important in toroidal geometry, where spatial inhomogeneities and curvature can excite both drift instabilities, whose wavenumber parallel to the magnetic field is finite, and interchange instabilities, which typically have vanishing parallel wavenumber. We demonstrate that multipoint measurements can provide a robust method for the discrimination between the two cases
Strongly nonlinear waves in capillary electrophoresis
In capillary electrophoresis, sample ions migrate along a micro-capillary
filled with a background electrolyte under the influence of an applied electric
field. If the sample concentration is sufficiently high, the electrical
conductivity in the sample zone could differ significantly from the
background.Under such conditions, the local migration velocity of sample ions
becomes concentration dependent resulting in a nonlinear wave that exhibits
shock like features. If the nonlinearity is weak, the sample concentration
profile, under certain simplifying assumptions, can be shown to obey Burgers'
equation (S. Ghosal and Z. Chen Bull. Math. Biol. 2010, 72(8), pg. 2047) which
has an exact analytical solution for arbitrary initial condition.In this paper,
we use a numerical method to study the problem in the more general case where
the sample concentration is not small in comparison to the concentration of
background ions. In the case of low concentrations, the numerical results agree
with the weakly nonlinear theory presented earlier, but at high concentrations,
the wave evolves in a way that is qualitatively different.Comment: 7 pages, 5 figures, 1 Appendix, 2 videos (supplementary material
A Comprehensive Four-Quark Interpretation of D_s(2317), D_s(2457) and D_s(2632)
The recently observed new member of the charm-strange family D_s(2632) which
has a surprisingly narrow width is challenging our theory. D_s(2317) and
D_s(2457) which were observed earlier have similar behaviors and receive
various theoretical explanations. Some authors use the heavy hadron chiral
effective theory to evaluate heavy-light quark systems and obtain a reasonable
evaluation on the masses of D_s(2317) and D_s(2457). An alternative picture is
to interpret them as four-quark or molecular states. In this work, we are
following the later and propose a unitive description for all the three new
members D_s(2632), D_s(2317) and D_s(2457) and at least, so far our picture is
consistent with the data.Comment: 6 page
Further analysis of field effects on liquids and solidification
Numerical calculations of the magnitude of external field effects on liquids are presented to describe how external fields can influence the substructure of the field. Quantitative estimates of magnetic and gravitational effects are reported on melts of metals and semiconductors. The results are condensed in tables which contain the input data for calculation of the field effects on diffusion coefficient, solidification rate and for calculation of field forces on individual molecules in the melt
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