36,932 research outputs found
Intensity correlations and entanglement by frequency doubling in a dual ported resonator
We show that non-classical intensity correlations and quadrature entanglement
can be generated by frequency doubling in a resonator with two output ports. We
predict twin-beam intensity correlations 6 dB below the coherent state limit,
and that the product of the inference variances of the quadrature fluctuations
gives an Einstein-Podolsky-Rosen (EPR) correlation coefficient of V_EPR = 0.6 <
1. Comparison with an entanglement source based on combining two frequency
doublers with a beam splitter shows that the dual ported resonator provides
stronger entanglement at lower levels of individual beam squeezing.
Calculations are performed using a self-consistent propagation method that does
not invoke a mean field approximation. Results are given for physically
realistic parameters that account for the Gaussian shape of the intracavity
beams, as well as intracavity losses.Comment: 12 pages, 9 figures, normalization corrected, fig 3 and fig 7 update
Optical studies of carrier and phonon dynamics in Ga_{1-x}Mn_{x}As
We present a time-resolved optical study of the dynamics of carriers and
phonons in Ga_{1-x}Mn_{x}As layers for a series of Mn and hole concentrations.
While band filling is the dominant effect in transient optical absorption in
low-temperature-grown (LT) GaAs, band gap renormalization effects become
important with increasing Mn concentration in Ga_{1-x}Mn_{x}As, as inferred
from the sign of the absorption change. We also report direct observation on
lattice vibrations in Ga1-xMnxAs layers via reflective electro-optic sampling
technique. The data show increasingly fast dephasing of LO phonon oscillations
for samples with increasing Mn and hole concentration, which can be understood
in term of phonon scattering by the holes.Comment: 13 pages, 3 figures replaced Fig.1 after finding a mistake in
previous versio
Diversity and Adaptation in Large Population Games
We consider a version of large population games whose players compete for
resources using strategies with adaptable preferences. The system efficiency is
measured by the variance of the decisions. In the regime where the system can
be plagued by the maladaptive behavior of the players, we find that diversity
among the players improves the system efficiency, though it slows the
convergence to the steady state. Diversity causes a mild spread of resources at
the transient state, but reduces the uneven distribution of resources in the
steady state.Comment: 8 pages, 3 figure
Control Laws for a Dual-Spin Stabilized Platform
This paper describes two attitude control laws suitable for atmospheric flight vehicles with a steady angular momentum bias in the vehicle yaw axis. This bias is assumed to be provided by an internal flywheel, and is introduced to enhance roll and pitch stiffness. The first control law is based on Lyapunov stability theory, and stability proofs are given. The second control law, which assumes that the angular momentum bias is large, is based on a classical PID control. It is shown that the large yaw-axis bias requires that the PI feedback component on the roll and pitch angle errors be cross-fed. Both control laws are applied to a vehicle simulation in the presence of disturbances for several values of yaw-axis angular momentum bias. It is seen that both control laws provide a significant improvement in attitude performance when the bias is sufficiently large, but the nonlinear control law is also able to provide improved performance for a small value of bias. This is important because the smaller bias corresponds to a smaller requirement for mass to be dedicated to the flywheel
CMG-Augmented Control of a Hovering VTOL Platform
This paper describes how Control Moment Gyroscopes (CMGs) can be used for stability augmentation to a thrust vectoring system for a generic Vertical Take-Off and Landing platform. The response characteristics of the platform which uses only thrust vectoring and a second configuration which includes a single-gimbal CMG array are simulated and compared for hovering flight while subject to severe air turbulence. Simulation results demonstrate the effectiveness of a CMG array in its ability to significantly reduce the agility requirement on the thrust vectoring system. Albeit simplifying physical assumptions on a generic CMG configuration, the numerical results also suggest that reasonably sized CMGs will likely be sufficient for a small hovering vehicle
Psychologists Collaborating With Clergy
If a patient adheres to religious values and practices, should the treating psychologist get input from a clergyperson? How frequent is clergy-psychologist collaboration? What obstacles impede such collaboration? An exploratory survey questionnaire was sent to 200 clergy, 200 psychologists interested in religious issues, and 200 psychologists selected without regard to religious interests or values. Four themes were assessed: types of collaborative activities, frequency of collaboration, obstacles to collaboration, and ways to enhance collaboration. Strategies for promoting clergy-psychologist collaboration include challenging unidirectional referral assumptions, building trust through proximity and familiarity, and considering the importance of shared values and beliefs
Sensitivity of Ru(bpy)_2dppz^(2+) Luminescence to DNA Defects
The luminescent characteristics of Ru(bpy)_2dppz^(2+) (dppz = dipyrido[3,2-a:2ā²,3ā²-c]phenazine), a DNA light switch, were investigated in the presence of oligonucleotides containing single base mismatches or an abasic site. In water, the ruthenium luminescence is quenched, but, bound to well matched duplex DNA, the Ru complex luminesces. Here we show that with DNAs containing a defect, rac-, Ī-, and Ī-Ru(bpy)_2dppz^(2+) exhibit significant luminescent enhancements above that with well matched DNA. In the presence of a single base mismatch, large luminescent enhancements are evident for the Ī-Ru isomer; the Ī-isomer shows particularly high luminescence bound to an oligonucleotide containing an abasic site. Similar increases are not evident with two common DNA-binding organic fluorophores, ethidium bromide and TO-PRO-3. Titrations with hairpin oligonucleotides containing a variable mismatch site show correlation between the level of luminescent enhancement and the thermodynamic destabilization associated with the mismatch. This correlation is reminiscent of that found earlier for a bulky rhodium complex that binds mismatched DNA sites through metalloinsertion, where the complex binds the DNA from the minor groove side, ejecting the mismatched bases into the major groove. Differential quenching studies with minor and major groove quenchers and time-resolved emission studies support this metalloinsertion mode for the dppz complex at the defect site. Certainly these data underscore the utility of Ru(bpy)_2dppz^(2+) as a sensitive luminescent reporter of DNA and its defects
Enhancement of plasticity in Ti-based metallic glass matrix composites by controlling characteristic and volume fraction of primary phase
In this study, Ti-based metallic glass matrix composites with high plasticity have been developed by controlling characteristic and volume fraction of primary phase embedded in the glass matrix. By careful alloy design procedure, the compositions of Ć/glass phases, which are in metastable equilibrium have been properly selected, therefore the mechanical properties can be tailored by selecting the alloy compositions between the composition of Ć and glass phases. The relation between the compressive yield strength and volume fraction of Ć phase is well described using the rule of mixtures
Experimental realization of strange nonchaotic attractors in a quasiperiodically forced electronic circuit
We have identified the three prominent routes, namely Heagy-Hammel,
fractalization and intermittency routes, and their mechanisms for the birth of
strange nonchaotic attractors (SNAs) in a quasiperiodically forced electronic
system constructed using a negative conductance series LCR circuit with a diode
both numerically and experimentally. The birth of SNAs by these three routes is
verified from both experimental and their corresponding numerical data by
maximal Lyapunov exponents, and their variance, Poincar\'e maps, Fourier
amplitude spectrum, spectral distribution function and finite-time Lyapunov
exponents. Although these three routes have been identified numerically in
different dynamical systems, the experimental observation of all these
mechanisms is reported for the first time to our knowledge and that too in a
single second order electronic circuit.Comment: 21 figure
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