62,406 research outputs found
Terahertz magneto-spectroscopy of transient plasmas in semiconductors
Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have
performed picosecond time-resolved THz spectroscopy of transient carriers in
semiconductors. Specifically, we measured the temporal evolution of THz
transmission and reflectivity after NIR excitation. We systematically
investigated transient carrier relaxation in GaAs and InSb with varying NIR
intensities and magnetic fields. Using this information, we were able to
determine the evolution of the THz absorption to study the dynamics of
photocreated carriers. We developed a theory based on a Drude conductivity with
time-dependent density and density-dependent scattering lifetime, which
successfully reproduced the observed plasma dynamics. Detailed comparison
between experimental and theoretical results revealed a linear dependence of
the scattering frequency on density, which suggests that electron-electron
scattering is the dominant scattering mechanism for determining the scattering
time. In InSb, plasma dynamics was dramatically modified by the application of
a magnetic field, showing rich magneto-reflection spectra, while GaAs did not
show any significant magnetic field dependence. We attribute this to the small
effective masses of the carriers in InSb compared to GaAs, which made the
plasma, cyclotron, and photon energies all comparable in the density, magnetic
field, and wavelength ranges of the current study.Comment: 8 pages, 9 figures, submitted to Phys. Rev.
Transmission Efficiency Measurements and Correlations with Physical Characteristics of the Lubricant
Data from helicopter transmission efficiency tests were compared to physical properties of the eleven lubricants used in those tests. The tests were conducted with the OH-58 helicopter main rotor transmission. Efficiencies ranged from 98.3 to 98.8 percent. The data was examined for correlation of physical properties with efficiency. There was a reasonable correlation of efficiency with absolute viscosity if the viscosity was first corrected for temperature and pressure in the lubricated contact. Between lubricants, efficiency did not correlate well with viscosity at atmospheric pressure. Between lubricants, efficiency did not correlate well with calculated lubricant film forming capacity. Bench type sliding friction and wear measurements could not be correlated to transmission efficiency and component wear
Rubidium resonant squeezed light from a diode-pumped optical-parametric oscillator
We demonstrate a diode-laser-pumped system for generation of quadrature
squeezing and polarization squeezing. Due to their excess phase noise, diode
lasers are challenging to use in phase-sensitive quantum optics experiments
such as quadrature squeezing. The system we present overcomes the phase noise
of the diode laser through a combination of active stabilization and
appropriate delays in the local oscillator beam. The generated light is
resonant to the rubidium D1 transition at 795nm and thus can be readily used
for quantum memory experiments.Comment: 6 pages 4 figure
A Content Analysis of Youth Internet Safety Programs: Are Effective Prevention Strategies Being Used?
ABSTRACT: Almost half of youth in the U.S. report receiving internet safety education (ISE) in their schools. Unfortunately, we know little about what educational messages make a difference in problems such as cyberbullying, sexting, or online predators. To consider directions for improving effectiveness, a content analysis was conducted on materials from four ISE programs. Results indicate that ISE programs are mostly not incorporating proven educational strategies. Common ISE messages have proliferated without a clear rationale for why they would be effective. It is recommended that program developers and other stakeholders reconsider ISE messages, improve educational strategies, and participate in evaluation. The field must also consider whether ISE messages would be better delivered through broader youth safety prevention programs versus stand-alone lessons
Nutritional and cultural aspects of plant species selection for a controlled ecological life support system
The feasibility of using higher plants in a controlled ecological life support system is discussed. Aspects of this system considered important in the use of higher plants include: limited energy, space, and mass, and problems relating to cultivation and management of plants, food processing, the psychological impact of vegetarian diets, and plant propagation. A total of 115 higher plant species are compared based on 21 selection criteria
A Systematic Review of Effective Youth Prevention Education: Implications for Internet Safety Education.
ABSTRACT: Over the past two decades, a wide array of internet safety education materials and programs have developed to increase positive youth behavior and safety online. Although it is a new area of prevention, programs should incorporate practices that prior prevention evaluation studies tell us work best. To inform internet safety education, 31 youth prevention education meta-analyses across a wide range of youth prevention (substance abuse, risky sex behavior, delinquency, etc.) were coded to identify prevention program characteristics shown by research to be most effective. The review identified that active, skill-based lessons, focused on research based causal and risk factors, and provided with adequate dosage were key. Such strategies must be included as a starting place when developing prevention in new areas of youth risk concerns. Implications of the finding suggest some need for reevaluating how internet safety education is delivered in the future
Nonlinear metrology with a quantum interface
We describe nonlinear quantum atom-light interfaces and nonlinear quantum
metrology in the collective continuous variable formalism. We develop a
nonlinear effective Hamiltonian in terms of spin and polarization collective
variables and show that model Hamiltonians of interest for nonlinear quantum
metrology can be produced in Rb ensembles. With these Hamiltonians,
metrologically relevant atomic properties, e.g. the collective spin, can be
measured better than the "Heisenberg limit" . In contrast to other
proposed nonlinear metrology systems, the atom-light interface allows both
linear and non-linear estimation of the same atomic quantities.Comment: 8 pages, 1 figure
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