18,593 research outputs found
Fast-acting calorimeter measures heat output of plasma gun accelerator
Calorimeter measures the exhaust energy from a shot of a pulsed plasma gun accelerator. It has a fast response time and requires only one measurement to determine the total energy. It uses a long ribbon of copper foil wound around a glass frame to form a reentrant cavity
Experimental and evaluation studies of a coaxial plasma gun accelerator Final report
Pulsed coaxial plasma gun accelerators in space thrustor developmen
Unequal arm space-borne gravitational wave detectors
Unlike ground-based interferometric gravitational wave detectors, large
space-based systems will not be rigid structures. When the end-stations of the
laser interferometer are freely flying spacecraft, the armlengths will change
due to variations in the spacecraft positions along their orbital trajectories,
so the precise equality of the arms that is required in a laboratory
interferometer to cancel laser phase noise is not possible. However, using a
method discovered by Tinto and Armstrong, a signal can be constructed in which
laser phase noise exactly cancels out, even in an unequal arm interferometer.
We examine the case where the ratio of the armlengths is a variable parameter,
and compute the averaged gravitational wave transfer function as a function of
that parameter. Example sensitivity curve calculations are presented for the
expected design parameters of the proposed LISA interferometer, comparing it to
a similar instrument with one arm shortened by a factor of 100, showing how the
ratio of the armlengths will affect the overall sensitivity of the instrument.Comment: 14 pages, 7 figures, REVTeX
Negative thermal expansion in the Prussian Blue analog Zn3[Fe(CN)6]2: X-ray diffraction and neutron vibrational studies
The cubic Prussian Blue (PB) analog, Zn3 [Fe(CN)6]2, has been studied by
X-ray powder diffraction and inelastic neutron scattering (INS). X-ray data
collected at 300 and 84 K revealed negative thermal expansion (NTE) behaviour
for this material. The NTE coefficient was found to be -31.1 x 10-6 K-1. The
neutron vibrational spectrum for Zn3[Fe(CN)6]2.xH2O, was studied in detail. The
INS spectrum showed well-defined, well-separated bands corresponding to the
stretching of and deformation modes of the Fe and Zn octahedra, all below 800
cm-1.Comment: 4 pages, 3 figure
Pionic Color Transparency
We use a semi-classical approximation to investigate the effects of color
transparency on pion electroproduction reactions. The resulting reduced nuclear
interactions produce significant, but not dominating, differences with the
results of conventional distorted-wave, Glauber-type treatments at kinematics
accessible to Jefferson Laboratory. Nuclear effects that could mimic the
influence of color transparency are also discussed.Comment: 10 pages, 6 figure
Conserving All the Pollinators: Variation in Probability of Pollen Transport among Insect Taxa
As concern about declining pollinator populations mounts, it is important to understand the range of insect taxa that provide pollination services. We use pollen transport information acquired over three years in two habitats at Badlands National Park, South Dakota, USA, to compare probabilities of pollen transport among insect taxa and between sexes of bees. Sampling was conducted on 1-ha plots, eight in sparse vegetation (May–October samples; N = 74 surveys) and 12 in wheatgrass prairie vegetation (June–July samples; N = 87 surveys). Insects contacting reproductive parts of flowers were netted, placed individually into tubes charged with ethyl acetate, then transferred to individual labeled glassine envelopes for transport to the lab. Pollen was removed from insect bodies with fuchsin jelly cubes which were then mounted on microscope slides for identification. The probability of taxa transporting only conspecific pollen (with respect to the plant species upon which it was collected), mixed pollen, only non-conspecific, or no pollen was estimated with multinomial logistic regression. Bees were the most commonly captured flower visitor and carried by far the most pollen (females \u3e10× as much as males), but they were most likely to carry mixed pollen loads. Flies, beetles, and wasps were also common flower visitors and beetles were most likely to carry only conspecific pollen. Ants and diurnal lepidopterans were unlikely to carry any pollen. Bees, beetles, flies, and wasps varied in the timing and habitat in which they were most likely to transport pollen, suggesting that all played a role in providing robust pollination services
Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys
A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations
TEMPORAL PAYMENT ISSUES IN CONTINGENT VALUATION ANALYSIS
We analyze agent response to disparate payment schedules for protection of critical habitat units for the Seller sea lion in Alaska. The model allows for identification of implicit and explicit discount rates using information from a system of maximum likelihood equations. Testing is done using data for one, five, and fifteen year payment treatments.Research Methods/ Statistical Methods,
Air data position-error calibration using state reconstruction techniques
During the highly maneuverable aircraft technology (HiMAT) flight test program recently completed at NASA Ames Research Center's Dryden Flight Research Facility, numerous problems were experienced in airspeed calibration. This necessitated the use of state reconstruction techniques to arrive at a position-error calibration. For the HiMAT aircraft, most of the calibration effort was expended on flights in which the air data pressure transducers were not performing accurately. Following discovery of this problem, the air data transducers of both aircraft were wrapped in heater blankets to correct the problem. Additional calibration flights were performed, and from the resulting data a satisfactory position-error calibration was obtained. This calibration and data obtained before installation of the heater blankets were used to develop an alternate calibration method. The alternate approach took advantage of high-quality inertial data that was readily available. A linearized Kalman filter (LKF) was used to reconstruct the aircraft's wind-relative trajectory; the trajectory was then used to separate transducer measurement errors from the aircraft position error. This calibration method is accurate and inexpensive. The LKF technique has an inherent advantage of requiring that no flight maneuvers be specially designed for airspeed calibrations. It is of particular use when the measurements of the wind-relative quantities are suspected to have transducer-related errors
Statistics of Velocity from Spectral Data: Modified Velocity Centroids
We address the problem of studying interstellar turbulence using spectral
line data. We find a criterion when the velocity centroids may provide
trustworthy velocity statistics. To enhance the scope of centroids
applications, we construct a measure that we term ``modified velocity
centroids'' (MVCs) and derive an analytical solution that relates the 2D
spectra of the modified centroids with the underlying 3D velocity spectrum. We
test our results using synthetic maps constructed with data obtained through
simulations of compressible magnetohydrodynamical (MHD) turbulence. We show
that the modified velocity centroids (MVCs) are complementary to the the
Velocity Channel Analysis (VCA) technique. Employed together, they make
determining of the velocity spectral index more reliable and for wider variety
of astrophysical situations.Comment: 4 pages, 1 figure, Accepted for publication in ApJ Letters. minor
change
- …