7,078 research outputs found
RF transparent, energy absorbing, structural elements, phase II Final report, 5 Jun. 1963 - 16 Mar. 1964
Energy absorbing, structural elements having high specific energy absorption and low dielectric constant and loss tangent - space vehicle applicatio
Wavelength Dependent PSFs and their impact on Weak Lensing Measurements
We measure and model the wavelength dependence of the PSF in the Hyper
Suprime-Cam (HSC) Subaru Strategic Program (SSP) survey. We find that PSF
chromaticity is present in that redder stars appear smaller than bluer stars in
the and -bands at the 1-2 per cent level and in the and
-bands at the 0.1-0.2 per cent level. From the color dependence of the PSF,
we fit a model between the monochromatic PSF trace radius, , and wavelength
of the form . We find values of between -0.2
and -0.5, depending on the epoch and filter. This is consistent with the
expectations of a turbulent atmosphere with an outer scale length of m, indicating that the atmosphere is dominating the chromaticity. We
find evidence in the best seeing data that the optical system and detector also
contribute some wavelength dependence. Meyers and Burchat (2015) showed that
must be measured to an accuracy of not to dominate the
systematic error budget of the Large Synoptic Survey Telescope (LSST) weak
lensing (WL) survey. Using simple image simulations, we find that can be
inferred with this accuracy in the and -bands for all positions in the
LSST field of view, assuming a stellar density of 1 star arcmin and that
the optical PSF can be accurately modeled. Therefore, it is possible to correct
for most, if not all, of the bias that the wavelength-dependent PSF will
introduce into an LSST-like WL survey.Comment: 14 pages, 10 figures. Submitted to MNRAS. Comments welcom
Impact of the U.S. Export Enhancement Program on the World Wheat Market,The
The U.S. Export Enhancement Program (EEP) was built into the 1985 U.S. Food Security Act with a major objective being to increase sales of U.S. agricultural commodities. Through the EEP, the U.S. government subsidizes exports of agricultural commodities to targeted countries. The EEP was applied to the majority of U.S. wheat sales n 1987/88 and 1988/89. Coincident with the 1985 act and EEP legislation, U.S. wheat exports have increased significantly.
This study uses a nonspatial, partial equilibrium model of world wheat trade to analyze the impact of the EEP on U.S. wheat exports and share of world wheat trade. The study indicates that the effect of the EEP on the wheat market over the period 1986/87 to 1988/89 has been a large displacement of commercial wheat sales (87-92%), with export additionally due to the EEP being only 8-13%. The impact of the EEP on other exporters\u27 wheat trade and importer demand has been small relative to the magnitude of total EEP sales
Significance of low energy impact damage on modal parameters of composite beams by design of experiments
This paper presents an experimental study on the effects of multi-site damage on the vibration response of composite beams damaged by low energy impacts around the barely visible impact damage limit (BVID). The variation of the modal parameters with different levels of impact energy and density of damage is studied. Vibration tests have been carried out with both burst random and classical sine dwell excitations in order to compare that which of the methods among Polymax and Half Bandwidth Method is more suitable for damping estimation in the presence of damage. Design of experiments (DOE) performed on the experimental data show that natural frequency is a more sensitive parameter for damage detection than the damping ratio. It also highlighted energy of impact as the factor having a more significant effect on the modal parameters. Half Bandwidth Method is found to be unsuitable for damping estimation in the presence of damage
Incommensurate phonon anomaly and the nature of charge density waves in cuprates
While charge density wave (CDW) instabilities are ubiquitous to
superconducting cuprates, the different ordering wavevectors in various cuprate
families have hampered a unified description of the CDW formation mechanism.
Here we investigate the temperature dependence of the low energy phonons in the
canonical CDW ordered cuprate LaBaCuO. We discover
that the phonon softening wavevector associated with CDW correlations becomes
temperature dependent in the high-temperature precursor phase and changes from
a wavevector of 0.238 reciprocal space units (r.l.u.) below the ordering
transition temperature up to 0.3~r.l.u. at 300~K. This high-temperature
behavior shows that "214"-type cuprates can host CDW correlations at a similar
wavevector to previously reported CDW correlations in non-"214"-type cuprates
such as YBaCuO. This indicates that cuprate CDWs may
arise from the same underlying instability despite their apparently different
low temperature ordering wavevectors.Comment: Accepted in Phys. Rev. X; 9 pages; 5 figures; 3 pages of
supplementary materia
Predicting the size and probability of epidemics in a population with heterogeneous infectiousness and susceptibility
We analytically address disease outbreaks in large, random networks with
heterogeneous infectivity and susceptibility. The transmissibility
(the probability that infection of causes infection of ) depends on the
infectivity of and the susceptibility of . Initially a single node is
infected, following which a large-scale epidemic may or may not occur. We use a
generating function approach to study how heterogeneity affects the probability
that an epidemic occurs and, if one occurs, its attack rate (the fraction
infected). For fixed average transmissibility, we find upper and lower bounds
on these. An epidemic is most likely if infectivity is homogeneous and least
likely if the variance of infectivity is maximized. Similarly, the attack rate
is largest if susceptibility is homogeneous and smallest if the variance is
maximized. We further show that heterogeneity in infectious period is
important, contrary to assumptions of previous studies. We confirm our
theoretical predictions by simulation. Our results have implications for
control strategy design and identification of populations at higher risk from
an epidemic.Comment: 5 pages, 3 figures. Submitted to Physical Review Letter
Anisotropic softening of magnetic excitations in lightly electron doped SrIrO
The magnetic excitations in electron doped (SrLa)IrO with
were measured using resonant inelastic X-ray scattering at the Ir
-edge. Although much broadened, well defined dispersive magnetic
excitations were observed. Comparing with the magnetic dispersion from the
parent compound, the evolution of the magnetic excitations upon doping is
highly anisotropic. Along the anti-nodal direction, the dispersion is almost
intact. On the other hand, the magnetic excitations along the nodal direction
show significant softening. These results establish the presence of strong
magnetic correlations in electron doped SrLa)IrO with close
analogies to the hole doped cuprates, further motivating the search for high
temperature superconductivity in this system
Properties of HxTaS2
The preparation of Hx TaS2 (0 \u3c x \u3c 0.87) is described. The compounds are only marginally stable at room temperature, slowly evolving H2S and H2 (and possibly Hp in air). Magnetic susceptibility data show that a low temperature transformation in 2H ... TaS2 (at so•K) is suppressed with the addition of hydrogen, and· at the same time the superconducting transition temperature T c rises from 0.8 to ~4.2•K at x = 0.11. Heat capacity measurements near this concentration show the superconductivity to be a bulk effect. Finally, by correlation of this data with susceptibility and T c measurements in other intercalation compounds, we suggest that the rise of T c (at low electron transfer) is due to suppression of the low temperature transformation and not due to an excitonic mechanism of superconductivity
Plastic Deformation in Laser-Induced Shock Compression of Monocrystalline Copper
Copper monocrystals were subjected to shock compression at pressures of 10–60 GPa by a short (3 ns initial) duration laser pulse. Transmission electron microscopy revealed features consistent with previous observations of shock-compressed copper, albeit at pulse durations in the µs regime. The results suggest that the defect structure is generated at the shock front. A mechanism for dislocation generation is presented, providing a realistic prediction of dislocation density as a function of pressure. The threshold stress for deformation twinning in shock compression is calculated from the constitutive equations for slip, twinning, and the Swegle-Grady relationship
Transient x-ray diffraction used to diagnose shock compressed Si crystals on the Nova laser
Transient x-ray diffraction is used to record time-resolved information about the shock compression of materials. This technique has been applied on Nova shock experiments driven using a hohlraum x-ray drive. Data were recorded from the shock release at the free surface of a Si crystal, as well as from Si at an embedded ablator/Si interface. Modeling has been done to simulate the diffraction data incorporating the strained crystal rocking curves and Bragg diffraction efficiencies. Examples of the data and post-processed simulations are presented
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