50,359 research outputs found
Daze fasteners
A daze fastener system for connecting two or more structural elements wherein the structural elements and fastener parts have substantially different coefficient of thermal expansion physical property characteristics is employed in this invention. By providing frusto-conical abutting surfaces between the structural elements and fastener parts any differences in thermal expansion/contraction between the parts is translated to sliding motion and avoids deleterious thermal stresses in the connection. An essential feature for isotropic homogeneous material connections is that at least two sets of mating surfaces are required wherein each set of mating surfaces have line element extensions that pass through a common point
Measuring gravitational lens time delays using low-resolution radio monitoring observations
Obtaining lensing time delay measurements requires long-term monitoring
campaigns with a high enough resolution (< 1 arcsec) to separate the multiple
images. In the radio, a limited number of high-resolution interferometer arrays
make these observations difficult to schedule. To overcome this problem, we
propose a technique for measuring gravitational time delays which relies on
monitoring the total flux density with low-resolution but high-sensitivity
radio telescopes to follow the variation of the brighter image. This is then
used to trigger high-resolution observations in optimal numbers which then
reveal the variation in the fainter image. We present simulations to assess the
efficiency of this method together with a pilot project observing radio lens
systems with the Westerbork Synthesis Radio Telescope (WSRT) to trigger Very
Large Array (VLA) observations. This new method is promising for measuring time
delays because it uses relatively small amounts of time on high-resolution
telescopes. This will be important because instruments that have high
sensitivity but limited resolution, together with an optimum usage of followup
high-resolution observations from appropriate radio telescopes may in the
future be useful for gravitational lensing time delay measurements by means of
this new method.Comment: 10 pages, 7 figures, accepted by MNRA
Robotic and automatic welding development at the Marshall Space Flight Center
Welding automation is the key to two major development programs to improve quality and reduce the cost of manufacturing space hardware currently undertaken by the Materials and Processes Laboratory of the NASA Marshall Space Flight Center. Variable polarity plasma arc welding has demonstrated its effectiveness on class 1 aluminum welding in external tank production. More than three miles of welds were completed without an internal defect. Much of this success can be credited to automation developments which stabilize the process. Robotic manipulation technology is under development for automation of welds on the Space Shuttle's main engines utilizing pathfinder systems in development of tooling and sensors for the production applications. The overall approach to welding automation development undertaken is outlined. Advanced sensors and control systems methodologies are described that combine to make aerospace quality welds with a minimum of dependence on operator skill
Legacy data and cosmological constraints from the angular-size/redshift relation for ultra-compact radio sources
We have re-examined an ancient VLBI survey of ultra-comact radio sources at
2.29 GHz, which gave fringe amplitudes for 917 such objects with total flux
density >0.5 Jy approximately. A number of cosmological investigations based
upon this survey have been published in recent years. We have updated the
sample with respect to both redshift and radio information, and now have full
data for 613 objects, significantly larger than the number (337) used in
earlier investigations. The corresponding angular-size/redshift diagram gives
Omega_m=0.25+0.04/-0.03, Omega_\Lambda=0.97+0.09/-0.13 and K=0.22+0.07/-0.10.
In combination with supernova data, and a simple-minded approach to CMB data
based upon the angular size of the acoustic horizon, our best figures are
Omega_m=0.298+0.025/-0.024, Omega_\Lambda=0.702+0.035/-0.036 and K=
0.000+0.021/-0.019. We have examined simple models of dynamical vacuum energy;
the first, based upon a scalar potential V(phi)=omega_C^2 phi^2/2, gives
w(0)=-1.00+0.06/-0.00, (dw/dz)_0=+0.00/-0.08; in this case conditions at z=0
require particular attention, to preclude behaviour in which phi becomes
singular as z -->infinity. For fixed w limits are w=-1.20+0.15/-0.14. The above
error bars are 68% confidence limits.Comment: 24 pages, 9 figure
Local Molecular Dynamics with Coulombic Interaction
We propose a local, O(N) molecular dynamics algorithm for the simulation of
charged systems. The long ranged Coulomb potential is generated by a
propagating electric field that obeys modified Maxwell equations. On coupling
the electrodynamic equations to an external thermostat we show that the
algorithm produces an effective Coulomb potential between particles. On
annealing the electrodynamic degrees of freedom the field configuration
converges to a solution of the Poisson equation much like the electronic
degrees of freedom approach the ground state in ab-initio molecular dynamics.Comment: 4 pages with 3 figure
NICMOS images of JVAS/CLASS gravitational lens systems
We present Hubble Space Telescope (HST) infrared images of four gravitational
lens systems from the JVAS/CLASS gravitational lens survey and compare the new
infrared HST pictures with previously published WFPC2 HST optical images and
radio maps. Apart from the wealth of information that we get from the flux
ratios and accurate positions and separations of the components of the lens
systems that we can use as inputs for better constraints on the lens models we
are able to discriminate between reddening and optical/radio microlensing as
the possible cause of differences observed in the flux ratios of the components
across the three wavelength bands. Substantial reddening has been known to be
present in the lens system B1600+434 and has been further confirmed by the
present infrared data. In the two systems B0712+472 and B1030+074 microlensing
has been pinpointed down as the main cause of the flux ratio discrepancy both
in the optical/infrared and in the radio, the radio possibly caused by the
substructure revealed in the lensing galaxies. In B0218+357 however the results
are still not conclusive. If we are actually seeing the two "true" components
of the lens system then the flux ratio differences are attributed to a
combination of microlensing and reddening or alternatively due to some
variability in at least one of the images. Otherwise the second "true"
component of B0218+357 maybe completely absorbed by a molecular cloud and the
anomalous flux density ratios and large difference in separation between the
optical/infrared and radio that we see can be explained by emission from either
a foreground object or from part of the lensing galaxy.Comment: 10 pages, 4 figures (original higher resolution figures can be
obtained at the e-mail above), to appear in MNRAS (accepted
Plasmon polaritons in photonic superlattices containing a left-handed material
We analyze one-dimensional photonic superlattices which alternate layers of
air and a left-handed material. We assume Drude-type dispersive responses for
the dielectric permittivity and magnetic permeability of the left-handed
material. Maxwell's equations and the transfer-matrix technique are used to
derive the dispersion relation for the propagation of obliquely incident
optical fields. The photonic dispersion indicates that the growth-direction
component of the electric (or magnetic) field leads to the propagation of
electric (or magnetic) plasmon polaritons, for either TE or TM configurations.
Furthermore, we show that if the plasma frequency is chosen within the photonic
zeroth-order bandgap, the coupling of light with plasmons
weakens considerably. As light propagation is forbidden in that particular
frequency region, the plasmon-polariton mode reduces to a pure plasmon mode.Comment: 4 pages, 4 figure
Antisite effect on ferromagnetism in (Ga,Mn)As
We study the Curie temperature and hole density of (Ga,Mn)As while
systematically varying the As-antisite density. Hole compensation by
As-antisites limits the Curie temperature and can completely quench long-range
ferromagnetic order in the low doping regime of 1-2% Mn. Samples are grown by
molecular beam epitaxy without substrate rotation in order to smoothly vary the
As to Ga flux ratio across a single wafer. This technique allows for a
systematic study of the effect of As stoichiometry on the structural,
electronic, and magnetic properties of (Ga,Mn)As. For concentrations less than
1.5% Mn, a strong deviation from Tc ~ p^0.33 is observed. Our results emphasize
that proper control of As-antisite compensation is critical for controlling the
Curie temperatures in (Ga,Mn)As at the low doping limit.Comment: 10 pages, 7 figure
SP mountain data analysis
An analysis of synthetic aperture radar data of SP Mountain was undertaken to demonstrate the use of digital image processing techniques to aid in geologic interpretation of SAR data. These data were collected with the ERIM X- and L-band airborne SAR using like- and cross-polarizations. The resulting signal films were used to produce computer compatible tapes, from which four-channel imagery was generated. Slant range-to-ground range and range-azimuth-scale corrections were made in order to facilitate image registration; intensity corrections were also made. Manual interpretation of the imagery showed that L-band represented the geology of the area better than X-band. Several differences between the various images were also noted. Further digital analysis of the corrected data was done for enhancement purposes. This analysis included application of an MSS differencing routine and development of a routine for removal of relief displacement. It was found that accurate registration of the SAR channels is critical to the effectiveness of the differencing routine. Use of the relief displacement algorithm on the SP Mountain data demonstrated the feasibility of the technique
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Review: Consumption-stage food waste reduction interventions - What works and how to design better interventions
Food waste prevention has become an issue of international concern, with Sustainable Development Goal 12.3 aiming to halve per capita global food waste at the retail and consumer levels by 2030. However there is no review that has considered the effectiveness of interventions aimed at preventing food waste in the consumption stages of the food system. This significant gap, if filled, could help support those working to reduce food waste in the developed world, providing knowledge of what interventions are specifically effective at preventing food waste.
This paper fills this gap, identifying and summarizing food-waste prevention interventions at the consumption/consumer stage of the supply chain via a rapid review of global academic literature from 2006 to 2017.
We identify 17 applied interventions that claim to have achieved food waste reductions. Of these, 13 quantified food waste reductions. Interventions that changed the size or type of plates were shown to be effective (up to 57% food waste reduction) in hospitality environments. Changing nutritional guidelines in schools were reported to reduce vegetable waste by up to 28%, indicating that healthy diets can be part of food waste reduction strategies. Information campaigns were also shown to be effective with up to 28% food waste reduction in a small sample size intervention.
Cooking classes, fridge cameras, food sharing apps, advertising and information sharing were all reported as being effective but with little or no robust evidence provided. This is worrying as all these methods are now being proposed as approaches to reduce food waste and, except for a few studies, there is no reproducible quantified evidence to assure credibility or success. To strengthen current results, a greater number of longitudinal and larger sample size intervention studies are required. To inform future intervention studies, this paper proposes a standardised guideline, which consists of: (1) intervention design; (2) monitoring and measurement; (3) moderation and mediation; (4) reporting; (5) systemic effects.
Given the importance of food-waste reduction, the findings of this review highlight a significant evidence gap, meaning that it is difficult to make evidence-based decisions to prevent or reduce consumption-stage food waste in a cost-effective manner
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