2,701 research outputs found
Space shuttle elevon seal panel mechanism
The orbiter elevon seal panel mechanism controls the position of fairing panels between the orbiter wing and elevon. Early mechanism designs used linkages which approximately matched the panel motion to elevon position, depending on panel deflections to maintain sealing. These linkages were refined during orbiter development to match panel motion to elevon motion more exactly, thus reducing panel deflections, loads, and weight. Changes to the adjacent cove seal resulted in the use of curved tension compression links. Mechanism temperatures up to 750 F (locally) posed difficulties in bearing lubrication. Despite the adverse effect of the many fabrication tolerances, the system successfully prevented the entry of 1200 F hot gases into the wing/elevon joint
NEC violation in mimetic cosmology revisited
In the context of Einstein gravity, if the null energy condition (NEC) is
satisfied, the energy density in expanding space-times always decreases while
in contracting space-times the energy density grows and the universe eventually
collapses into a singularity. In particular, no non-singular bounce is
possible. It is, though, an open question if this energy condition can be
violated in a controlled way, i.e., without introducing pathologies, such as
unstable negative-energy states or an imaginary speed of sound. In this paper,
we will re-examine the claim that the recently proposed mimetic scenario can
violate the NEC without pathologies. We show that mimetic cosmology is prone to
gradient instabilities even in cases when the NEC is satisfied (except for
trivial examples). Most interestingly, the source of the instability is always
the Einstein-Hilbert term in the action. The matter stress-energy component
does not contribute spatial gradient terms but instead makes the problematic
curvature modes dynamical. We also show that mimetic cosmology can be
understood as a singular limit of known, well-behaved theories involving
higher-derivative kinetic terms and discuss ways of removing the instability.Comment: 7 page
The Rural Reconstruction Scheme
In 1971 the Commonwealth Government passed the State Grants (Rural Reconstruction) Act to provide $100m to assist rural industry to adjust itself to the severe downturn in income. The money was to be divided amongst the States to enable State Governments to make loans to farmers and pastoralists.
In Western Australia the Government passed the Rural Reconstruction Scheme Act, 1971 , to implement the Scheme
Last resort loans for farmers
Several sources of finance are available to help fsrmers survive through a crisis.
One source of last resort is Rural Adjustment Authority
Probate another farm cost
Death duties are too big a cost to be ignored on most farms, because most farms have substantial assets in land, stock, buildings and machinery. The saying a wise man does not lay up treasures, the more he gives to others the more he keeps for his own seems true of the types of estate planning outlined in the following article
Within The City Gates : Theme Varie
https://digitalcommons.library.umaine.edu/mmb-ps/1721/thumbnail.jp
Life history traits and population processes in marine bivalve molluscs
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 1998In this thesis, I investigated the how the life history characteristics of the clam Mya
arenaria determine the population response to chronic contaminant exposure. To
predict the potential responses of a broadcast-spawning life history such as that of
M. arenaria, I surveyed the literature on a variety of bivalve species. By incorporating
information on growth, survival, and reproduction into matrix population models I
could evaluate the relative contributions of these factors to fitness. For broadcast-spawners,
long life is an important factor enabling them to gamble on rare, large
recruitment events. Another important aspect of the broadcast spawning strategy is
the possibility of high variation in larval settlement from year to year. I evaluated
the role that this variability plays using a stochastic matrix model, and showed that
it tends to increase population growth because of the larger size of rarer, successful
recruitment events.
With an understanding of how the life history traits of M. arenaria might control
its responses to change in the environment, I analyzed the vital rates of clams at
clean and contaminated sites. The effects of contaminants measured in the lab do
not necessarily predict population condition in the field. Since surviving with a long
life span contributes the most to fitness in broadcast-spawning bivalves, effects on
reproductive output and juvenile survival, which are strong in many lab studies, may
not necessarily playa large role in field populations. The life history of this clam, with
natural variation in recruitment from year to year, further reduces the population dependence on high reproductive output and larval survival. The combination of
little population-level relevance of the strongest contaminant effects, and potential
contaminant effects on very important clam predators, could explain why populations
at contaminated sites are observed to be growing the fastest. The interaction of
contaminant exposure and normal ecological processes determines the overall impact
on the population.This research was supported by a Massachusetts Bay Programs grant to Judith
McDowell and Damian Shea, NSF grant # DEB-9211945 to Hal Caswell, a National
Defense Science and Engineering Graduate Fellowship to Bonnie Ripley, a Pew Fellowship
in Conservation and the Environment to Judith McDowell, Sea Grant grant
# NA46RG0470 (project # RIP-54), and by the M.I.T./W.H.O.I. Joint Program
Education Office
Differential parental nutrient allocation in two congeneric pipefish species (Syngnathidae: Syngnathus spp.)
Creation and characterization of vortex clusters in atomic Bose-Einstein condensates
We show that a moving obstacle, in the form of an elongated paddle, can
create vortices that are dispersed, or induce clusters of like-signed vortices
in 2D Bose-Einstein condensates. We propose new statistical measures of
clustering based on Ripley's K-function which are suitable to the small size
and small number of vortices in atomic condensates, which lack the huge number
of length scales excited in larger classical and quantum turbulent fluid
systems. The evolution and decay of clustering is analyzed using these
measures. Experimentally it should prove possible to create such an obstacle by
a laser beam and a moving optical mask. The theoretical techniques we present
are accessible to experimentalists and extend the current methods available to
induce 2D quantum turbulence in Bose-Einstein condensates.Comment: 9 pages, 9 figure
VALIDATION OF A COMMERCIALLY AVAILABLE STRAIN GAUGE AGAINST A SERIES OF KNOWN LOADS USING A SHORT TIME APPROACH
The purpose of this study was to identify the content validity and accuracy of a commercially available strain gauge (GSTRENGTH (Exsurgo Technologies, Virginia, USA), aimed at use within athletic populations. Six standardised IWF (International Weightlifting Federation) calibrated weights (5-, 25-, 50-, 100-, 200-, 250-kg) were hung from the strain gauge and raw data was collected over a five-second period and exported to a computer. A perfect relationship between the known loads and the strain gauge (r = 1.00, p\u3c0.001) was identified, although the strain gauge was found to have a small overestimation error with no fixed or proportional bias. During data collection there were non-significant, trivial-small differences between the first and last second, demonstrating minimal drift. The commercially available strain gauge was found to be valid when compared to the known loads. Further investigation of the strain gauge is required to assess the concurrent validity when compared to gold standard methods of assessment, such as force plates, in a range of test designs
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