25,606 research outputs found
All-optical steering of light via spatial Bloch oscillations in a gas of three-level atoms
A standing-wave control field applied to a three-level atomic medium in a
planar hollow-core photonic crystal waveguide creates periodic variations of
linear and nonlinear refractive indexes of the medium. This property can be
used for efficient steering of light. In this work we study, both analytically
and numerically, the dynamics of probe optical beams in such structures. By
properly designing the spatial dependence of the nonlinearity it is possible to
induce long-living Bloch oscillations of spatial gap solitons, thus providing
desirable change in direction of the beam propagation without inducing
appreciable diffraction. Due to the significant enhancement of the
nonlinearity, such self-focusing of the probe beam can be reached at extremely
weak light intensities.Comment: 8 pages, 4 figure
Exact 1-D Model for Coherent Synchrotron Radiation with Shielding and Bunch Compression
Coherent Synchrotron Radiation has been studied effectively using a
1-dimensional model for the charge distribution in the realm of small angle
approximations and high energies. Here we use Jefimenko's form of Maxwell's
equations, without such approximations, to calculate the exact wake-fields due
to this effect in multiple bends and drifts. It has been shown before that the
influence of a drift can propagate well into a subsequent bend. We show, for
reasonable parameters, that the influence of a previous bend can also propagate
well into a subsequent bend, and that this is especially important at the
beginning of a bend. Shielding by conducting parallel plates is simulated using
the image charge method. We extend the formalism to situations with compressing
and decompressing distributions, and conclude that simpler approximations to
bunch compression usually overestimates the effect. Additionally, an exact
formula for the coherent power radiated by a Gaussian bunch is derived by
considering the coherent synchrotron radiation spectrum, and is used to check
the accuracy of wake-field calculations
Amine-terminated nanoparticle films: pattern deposition by a simple nanostencilling technique and stability studies under X-ray irradiation
Exploring the surface chemistry of nanopatterned amine-terminated nanoparticle films.</p
Preventing eternality in phantom inflation
We have investigated the necessary conditions that prevent phantom inflation
from being eternal. Allowing additionally for a nonminimal coupling between the
phantom field and gravity, we present the slow-climb requirements, perform an
analysis of the fluctuations, and finally we extract the overall conditions
that are necessary in order to prevent eternality. Furthermore, we verify our
results by solving explicitly the cosmological equations in a simple example of
an exponential potential, formulating the classical motion plus the stochastic
effect of the fluctuations through Langevin equations. Our analysis shows that
phantom inflation can be finite without the need of additional exotic
mechanisms.Comment: 8 pages, V2 references added. V3 version published in Phys. Rev.
First measurements of the flux integral with the NIST-4 watt balance
In early 2014, construction of a new watt balance, named NIST-4, has started
at the National Institute of Standards and Technology (NIST). In a watt
balance, the gravitational force of an unknown mass is compensated by an
electromagnetic force produced by a coil in a magnet system. The
electromagnetic force depends on the current in the coil and the magnetic flux
integral. Most watt balances feature an additional calibration mode, referred
to as velocity mode, which allows one to measure the magnetic flux integral to
high precision. In this article we describe first measurements of the flux
integral in the new watt balance. We introduce measurement and data analysis
techniques to assess the quality of the measurements and the adverse effects of
vibrations on the instrument.Comment: 7 pages, 8 figures, accepted for publication in IEEE Trans. Instrum.
Meas. This Journal can be found online at
http://ieeexplore.ieee.org/xpl/RecentIssue.jsp?punumber=1
Exclusive Lambda_b -> Lambda l^+ l^- decay in two Higgs doublet model
Rare Lambda_b -> Lambda l^+ l^- decay is investigated in framework of general
two Higgs doublet model, in which a new source of CP violation exists (model
III). The polarization parameter, CP asymmetry and decay width are calculated.
It is shown that CP asymmetry is a very sensitive tool for establishing model
III.Comment: 16 pages, 3 figures, LaTeX formatte
Exciton gas transport through nano-constrictions
An indirect exciton is a bound state of an electron and a hole in spatially
separated layers. Two-dimensional indirect excitons can be created optically in
heterostructures containing double quantum wells or atomically thin
semiconductors. We study theoretically transmission of such bosonic
quasiparticles through nano-constrictions. We show that quantum transport
phenomena, e.g., conductance quantization, single-slit diffraction, two-slit
interference, and the Talbot effect, are experimentally realizable in systems
of indirect excitons. We discuss similarities and differences between these
phenomena and their counterparts in electronic devices.Comment: (v2) Updated title, text, and references; 12 pages, 9 figure
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