10,369 research outputs found
Simulation of valveless micropump and mode analysis
In this work, a 3-D simulation is performed to study for the solid-fluid
coupling effect driven by piezoelectric materials and utilizes asymmetric
obstacles to control the flow direction. The result of simulation is also
verified. For a micropump, it is crucial to find the optimal working frequency
which produce maximum net flow rate. The PZT plate vibrates under the first
mode, which is symmetric. Adjusting the working frequency, the maximum flow
rate can be obtained. For the micrpump we studied, the optimal working
frequency is 3.2K Hz. At higher working frequency, say 20K Hz, the fluid-solid
membrane may come out a intermediate mode, which is different from the first
mode and the second mode. It is observed that the center of the mode drifts.
Meanwhile, the result shows that a phase shift lagging when the excitation
force exists in the vibration response. Finally, at even higher working
frequency, say 30K Hz, a second vibration mode is observed.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/EDA-Publishing
Quantum super-cavity with atomic mirrors
We study single-photon transport in an array of coupled microcavities where
two two-level atomic systems are embedded in two separate cavities of the
array. We find that a single-photon can be totally reflected by a single
two-level system. However, two separate two-level systems can also create,
between them, single-photon quasi-bound states. Therefore, a single two-level
system in the cavity array can act as a mirror while a different type of cavity
can be formed by using two two-level systems, acting as tunable "mirrors",
inside two separate cavities in the array. In analogy with superlattices in
solid state, we call this new "cavity inside a coupled-cavity array" a
super-cavity. This supercavity is the quantum analog of Fabry-Perot
interferometers. Moreover, we show that the physical properties of this quantum
super-cavity can be adjusted by changing the frequencies of these two-level
systems.Comment: 13 pages, 9 figure
Efficient generation of an isolated single-cycle attosecond pulse
A new method for efficiently generating an isolated single-cycle attosecond
pulse is proposed. It is shown that the ultraviolet (UV) attosecond pulse can
be utilized as a robust tool to control the dynamics of electron wave packets
(EWPs). By adding a UV attosecond pulse to an infrared (IR) few-cycle pulse at
a proper time, only one return of the EWP to the parent ion is selected to
effectively contribute to the harmonics, then an isolated two-cycle 130-as
pulse with a bandwidth of 45 eV is obtained. After complementing the chirp, an
isolated single-cycle attosecond pulse with a duration less than 100 as seems
achievable. In addition, the contribution of the quantum trajectories can be
selected by adjusting the delay between the IR and UV fields. Using this
method, the harmonic and attosecond pulse yields are efficiently enhanced in
contrast to the scheme [G. Sansone {\it et al.}, Science {\bf314}, 443 (2006)]
using a few-cycle IR pulse in combination with the polarization gating
technique.Comment: 5 pages, 4 figure
Magneto-Optical Stern-Gerlach Effect in Atomic Ensemble
We study the birefringence of the quantized polarized light in a
magneto-optically manipulated atomic ensemble as a generalized Stern-Gerlach
Effect of light. To explain this engineered birefringence microscopically, we
derive an effective Shr\"odinger equation for the spatial motion of two
orthogonally polarized components, which behave as a spin with an effective
magnetic moment leading to a Stern-Gerlach split in an nonuniform magnetic
field. We show that electromagnetic induced transparency (EIT) mechanism can
enhance the magneto-optical Stern-Gerlach effect of light in the presence of a
control field with a transverse spatial profile and a inhomogeneous magnetic
field.Comment: 7 pages, 5 figure
Evolutionary tracks for Betelgeuse
We have constructed a series of non-rotating quasi-hydrostatic evolutionary
models for the M2 Iab supergiant Betelgeuse (). Our models are
constrained by multiple observed values for the temperature, luminosity,
surface composition and mass loss for this star, along with the parallax
distance and high resolution imagery that determines its radius. We have then
applied our best-fit models to analyze the observed variations in surface
luminosity and the size of detected surface bright spots as the result of
up-flowing convective material from regions of high temperature in the surface
convective zone. We also attempt to explain the intermittently observed
periodic variability in a simple radial linear adiabatic pulsation model. Based
upon the best fit to all observed data, we suggest a best progenitor mass
estimate of and a current age from the start of the
zero-age main sequence of Myr based upon the observed ejected mass
while on the giant branch.Comment: 27 pages, 11 figures, Revised per referee suggestions, Accepted for
publication in the Astrophysical Journa
Coherent control of photon transmission : slowing light in coupled resonator waveguide doped with Atoms
In this paper, we propose and study a hybrid mechanism for coherent
transmission of photons in the coupled resonator optical waveguide (CROW) by
incorporating the electromagnetically induced transparency (EIT) effect into
the controllable band gap structure of the CROW. Here, the configuration setup
of system consists of a CROW with homogeneous couplings and the artificial
atoms with -type three levels doped in each cavity. The roles of three
levels are completely considered based on a mean field approach where the
collection of three-level atoms collectively behave as two-mode spin waves. We
show that the dynamics of low excitations of atomic ensemble can be effectively
described by an coupling boson model. The exactly solutions show that the light
pulses can be stopped and stored coherently by adiabatically controlling the
classical field.Comment: 10 pages, 6 figure
Inherent Mach-Zehnder interference with "which-way" detection for single particle scattering in one dimension
We study the coherent transport of single photon in a one-dimensional
coupled-resonator-array, "non-locally" coupled to a two-level system. Since its
inherent structure is a Mach-Zehnder interferometer, we explain the destructive
interference phenomenon of the transmission spectrums according to the effect
of which-way detection. The quantum realization of the present model is a
nano-electromechanical resonator arrays with two nearest resonators coupled to
a single spin via their attached magnetic tips. Its classical simulation is a
waveguide of coupled defected cavity array with double couplings to a side
defected cavity.Comment: 5 papges, 4 figure
Family Names, City Size Distributions and Residential Differentiation in Great Britain, 1881-1901
Cities have specialised in particular urban functions throughout history, with consequential implications for urban and regional patterns of economic and social change. This specialisation takes place within overall national city size distributions and is manifest in different but often similarly variegated residential structures. Here we develop a novel and consistent methodological approach for measuring macro-scale city size and micro-scale residential differentiation using individual digital census records for the period 1881–1901. The use of family names and neighbourhood classification of dominant economic and social roles makes it possible to relate the changing city size distribution in Great Britain to patterns of urban growth and residential differentiation within urban areas. Together, we provide an integrated and consistent methodology that links the classification of all major urban area growth in Great Britain to attendant intra-urban geodemographic changes in urban residential structures. We suggest ways in which this manifests social and economic change across the settlement system for both new and long-established residents
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