6,941 research outputs found
85% efficiency for cw frequency doubling from 1.08 to 0.54 μm
Conversion efficiency of 85% has been achieved in cw second-harmonic generation from 1.08 to 0.54 μm with a potassium titanyl phosphate crystal inside an external ring cavity. An absolute comparison between the experimental data and a simple theory is made and shows good agreement
Comparisons and Applications of Four Independent Numerical Approaches for Linear Gyrokinetic Drift Modes
To help reveal the complete picture of linear kinetic drift modes, four
independent numerical approaches, based on integral equation, Euler initial
value simulation, Euler matrix eigenvalue solution and Lagrangian particle
simulation, respectively, are used to solve the linear gyrokinetic
electrostatic drift modes equation in Z-pinch with slab simplification and in
tokamak with ballooning space coordinate. We identify that these approaches can
yield the same solution with the difference smaller than 1\%, and the
discrepancies mainly come from the numerical convergence, which is the first
detailed benchmark of four independent numerical approaches for gyrokinetic
linear drift modes. Using these approaches, we find that the entropy mode and
interchange mode are on the same branch in Z-pinch, and the entropy mode can
have both electron and ion branches. And, at strong gradient, more than one
eigenstate of the ion temperature gradient mode (ITG) can be unstable and the
most unstable one can be on non-ground eigenstates. The propagation of ITGs
from ion to electron diamagnetic direction at strong gradient is also observed,
which implies that the propagation direction is not a decisive criterion for
the experimental diagnosis of turbulent mode at the edge plasmas.Comment: 12 pages, 10 figures, accept by Physics of Plasma
Instability and Periodic Deformation in Bilayer Membranes Induced by Freezing
The instability and periodic deformation of bilayer membranes during freezing
processes are studied as a function of the difference of the shape energy
between the high and the low temperature membrane states. It is shown that
there exists a threshold stability condition, bellow which a planar
configuration will be deformed. Among the deformed shapes, the periodic curved
square textures are shown being one kind of the solutions of the associated
shape equation. In consistency with recent expe rimental observations, the
optimal ratio of period and amplitude for such a texture is found to be
approximately equal to (2)^{1/2}\pi.Comment: 8 pages in Latex form, 1 Postscript figure. To be appear in Mod.
Phys. Lett. B. 199
Quantum Communication with Correlated Nonclassical States
Nonclassical correlations between the quadrature-phase amplitudes of two
spatially separated optical beams are exploited to realize a two-channel
quantum communication experiment with a high degree of immunity to
interception. For this scheme, either channel alone can have an arbitrarily
small signal-to-noise ratio (SNR) for transmission of a coherent ``message''.
However, when the transmitted beams are combined properly upon authorized
detection, the encoded message can in principle be recovered with the original
SNR of the source. An experimental demonstration has achieved a 3.2 dB
improvement in SNR over that possible with correlated classical sources.
Extensions of the protocol to improve its security against eavesdropping are
discussed.Comment: 8 pages and 4 figures (Figure 1; Figures 2a, 2b; Figure 2
Deformation and fracture of AMC under different heat treatment conditions and its suitability for incremental sheet forming
By evaluating the deformation and fracture mechanisms of a 6092Al alloy metal matrix composite reinforced with 17.5p vol. % SiC particles (6092Al/SiCp), this paper investigates the applicability of using incremental sheet forming (ISF) process to form the 6092Al/SiCp aluminium matrix composite (AMC) under different heat treatment conditions. Tensile tests were carried out at different strain rates to study the microstructure and topography of the 6092Al/SiCp sheet by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The tensile test results and the morphology of the fracture showed that the 6092Al/SiCp to T6 condition has low elongation to fracture (0.08), whilst much improved elongation can be achieved after annealing to O-condition. A series of ISF tests were carried out to form 6092Al/SiCp sheet into a truncated hyperbolic shape with different ISF process parameters. At T6 condition, ISF testing showed unsatisfactory results for the 6092Al/SiCp with a low wall angle (31.2ο) to fracture and a significant amount of springback. After annealing to O-condition, a much increased wall angle was achieved with reduced springback due to the enhanced ductility of the 6092Al/SiCp material. Microstructural and topographic evaluation of the 6092Al/SiCp parts formed by ISF allowed a detailed characterisation of brittle and ductile fractures for different heat treatments. The obtained ISF results and evaluation enabled the recommendation of optimum ISF operational windows for 6092Al/SiCp materials
Can Electric Field Induced Energy Gaps In Metallic Carbon Nanotubes?
The low-energy electronic structure of metallic single-walled carbon nanotube
(SWNT) in an external electric field perpendicular to the tube axis is
investigated. Based on tight-binding approximation, a field-induced energy gap
is found in all (n, n) SWNTs, and the gap shows strong dependence on the
electric field and the size of the tubes. We numerically find a universal
scaling that the gap is a function of the electric field and the radius of
SWNTs, and the results are testified by the second-order perturbation theory in
weak field limit. Our calculation shows the field required to induce a 0.1
gap in metallic SWNTs can be easily reached under the current
experimental conditions. It indicates a kind of possibility to apply nanotubes
to electric signal-controlled nanoscale switching devices
Entanglement and interference between different degrees of freedom of photons states
In this paper, photonic entanglement and interference are described and
analyzed with the language of quantum information process. Correspondingly, a
photon state involving several degrees of freedom is represented in a new
expression based on the permutation symmetry of bosons. In this expression,
each degree of freedom of a single photon is regarded as a qubit and operations
on photons as qubit gates. The two-photon Hong-Ou-Mandel interference is well
interpreted with it. Moreover, the analysis reveals the entanglement between
different degrees of freedom in a four-photon state from parametric down
conversion, even if there is no entanglement between them in the two-photon
state. The entanglement will decrease the state purity and photon interference
visibility in the experiments on a four-photon polarization state.Comment: 11 pages and 2 figure
Finite resolution measurement of the non-classical polarization statistics of entangled photon pairs
By limiting the resolution of quantum measurements, the measurement induced
changes of the quantum state can be reduced, permitting subsequent measurements
of variables that do not commute with the initially measured property. It is
then possible to experimentally determine correlations between non-commuting
variables. The application of this method to the polarization statistics of
entangled photon pairs reveals that negative conditional probabilities between
non-orthogonal polarization components are responsible for the violation of
Bell's inequalities. Such negative probabilities can also be observed in finite
resolution measurements of the polarization of a single photon. The violation
of Bell's inequalities therefore originates from local properties of the
quantum statistics of single photon polarization.Comment: 15 pages, 5 figures and 1 table, new figure to illustrate results,
improved explanation of statistical analysi
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