28,480 research outputs found
Conceptual approach study of a 200 watt per kilogram solar array
Solar array candidate configurations (flexible rollup, flexible flat-pact, semi-rigid panel, semi-rigid flat-pack) were analyzed with particular attention to the specific power (W/kg) requirement. Two of these configurations (flexible rollup and flexible flat-pack) are capable of delivering specific powers equal to or exceeding the baseline requirement of 200 W/kg. Only the flexible rollup is capable of in-flight retraction and subsequent redeployment. The wrap-around contact photovoltaic cell configuration has been chosen over the conventional cell. The demand for ultra high specific power forces the selection of ultra-thin cells and cover material. Based on density and mass range considerations, it was concluded that 13 micrometers of FEP Teflon is sufficient to protect the cell from a total proton fluency of 2(10 to the 12th power) particles/sq cm over a three-year interplanetary mission. The V-stiffened, lattice boom deployed, flexible substrate rollup array holds the greatest promise of meeting the baseline requirements set for this study
Magnetic reconnection in plasma under inertial confinement fusion conditions driven by heat flux effects in Ohm's law
In the interaction of high-power laser beams with solid density plasma there
are a number of mechanisms that generate strong magnetic fields. Such fields
subsequently inhibit or redirect electron flows, but can themselves be advected
by heat fluxes, resulting in complex interplay between thermal transport and
magnetic fields.We show that for heating by multiple laser spots reconnection
of magnetic field lines can occur, mediated by these heat fluxes, using a fully
implicit 2D Vlasov-Fokker-Planck code. Under such conditions, the reconnection
rate is dictated by heat flows rather than Alfv\`enic flows. We find that this
mechanism is only relevant in a high plasma. However, the Hall
parameter can be large so that thermal transport is
strongly modified by these magnetic fields, which can impact longer time scale
temperature homogeneity and ion dynamics in the system
Simulation of organismic morphology and behavior by synthetic poly-alpha-amino acids
Simulation of organismic morphology and behavior by synthetic poly-amino acid
Study of application of practical performance criteria for the implementation of efficient error-reduction coding Final report
Criteria for implementation of efficient error reduction codin
High-severity wildfire leads to multi-decadal impacts on soil biogeochemistry in mixed-conifer forests.
During the past century, systematic wildfire suppression has decreased fire frequency and increased fire severity in the western United States of America. While this has resulted in large ecological changes aboveground such as altered tree species composition and increased forest density, little is known about the long-term, belowground implications of altered, ecologically novel, fire regimes, especially on soil biological processes. To better understand the long-term implications of ecologically novel, high-severity fire, we used a 44-yr high-severity fire chronosequence in the Sierra Nevada where forests were historically adapted to frequent, low-severity fire, but were fire suppressed for at least 70Â yr. High-severity fire in the Sierra Nevada resulted in a long-term (44Â +yr) decrease (>50%, PÂ <Â 0.05) in soil extracellular enzyme activities, basal microbial respiration (56-72%, PÂ <Â 0.05), and organic carbon (>50%, PÂ <Â 0.05) in the upper 5Â cm compared to sites that had not been burned for at least 115Â yr. However, nitrogen (N) processes were only affected in the most recent fire site (4Â yr post-fire). Net nitrification increased by over 600% in the most recent fire site (PÂ <Â 0.001), but returned to similar levels as the unburned control in the 13-yr site. Contrary to previous studies, we did not find a consistent effect of plant cover type on soil biogeochemical processes in mid-successional (10-50Â yr) forest soils. Rather, the 44-yr reduction in soil organic carbon (C) quantity correlated positively with dampened C cycling processes. Our results show the drastic and long-term implication of ecologically novel, high-severity fire on soil biogeochemistry and underscore the need for long-term fire ecological experiments
Laser-induced currents along molecular wire junctions
The treatment of the previous paper is extended to molecular wires.
Specifically, the effect of electron-vibrational interactions on the electronic
transport induced by femtosecond laser fields along unbiased
molecular nanojunctions is investigated. For this, the photoinduced vibronic
dynamics of trans-polyacetylene oligomers coupled to macroscopic metallic leads
is followed in a mean-field mixed quantum-classical approximation. A reduced
description of the dynamics is obtained by introducing projective lead-molecule
couplings and deriving an effective Schr\"odinger equation satisfied by the
orbitals in the molecular region. Two possible rectification mechanisms are
identified and investigated. The first one relies on near-resonance
photon-absorption and is shown to be fragile to the ultrafast electronic
decoherence processes introduced by the wire's vibrations. The second one
employs the dynamic Stark effect and is demonstrated to be highly efficient and
robust to electron-vibrational interactions.Comment: 14 pages, 10 figures. Accepted in J. Chem. Phy
The Integrated Basic Education and Skills Training (I-BEST) Program: Equiping All Adults for the Global Economy
Abstract
In 2004, educational leaders in Washington State, recognizing the necessity of rapidly equipping adults with career skills, developed the Integrated Basic Education and Skills Training (I-BEST) program to meet workforce needs. I-BEST is now operational in all 34 of the State’s community colleges. I-BEST is an instructional method which provides basic skills support to ABE and ESL students while they receive career training. I-BEST uniquely pairs a basic skills instructor with a vocational instructor in the classroom at the same time. Previous research on the I-BEST program has been positive, but it has ignored the pivotal role instructors and administrators play in the program’s success. This study explores the perceptions of the instructors and administrators regarding the I-BEST program.
The study investigates whether there were differences in the perceptions of the instructors, program managers, and the managers’ immediate supervisors. The group differences were compared using t tests. Statistical differences were observed in areas such as the adequacy of instructor release time, adequacy of student support services, and using employment outcomes to modify instruction. Recommendations include limiting the number of data collection items being tracked, and increasing the number of minority instructors involved in the I-BEST program. Implications of the findings may assist the Washington State Board of Community and Technical Colleges and community college presidents in enhancing the program
High accuracy measure of atomic polarizability in an optical lattice clock
Despite being a canonical example of quantum mechanical perturbation theory,
as well as one of the earliest observed spectroscopic shifts, the Stark effect
contributes the largest source of uncertainty in a modern optical atomic clock
through blackbody radiation. By employing an ultracold, trapped atomic ensemble
and high stability optical clock, we characterize the quadratic Stark effect
with unprecedented precision. We report the ytterbium optical clock's
sensitivity to electric fields (such as blackbody radiation) as the
differential static polarizability of the ground and excited clock levels:
36.2612(7) kHz (kV/cm)^{-2}. The clock's fractional uncertainty due to room
temperature blackbody radiation is reduced an order of magnitude to 3 \times
10^{-17}.Comment: 5 pages, 3 figures, 2 table
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