1,412 research outputs found
Mechanics of extended masses in general relativity
The "external" or "bulk" motion of extended bodies is studied in general
relativity. Compact material objects of essentially arbitrary shape, spin,
internal composition, and velocity are allowed as long as there is no direct
(non-gravitational) contact with other sources of stress-energy. Physically
reasonable linear and angular momenta are proposed for such bodies and exact
equations describing their evolution are derived. Changes in the momenta depend
on a certain "effective metric" that is closely related to a non-perturbative
generalization of the Detweiler-Whiting R-field originally introduced in the
self-force literature. If the effective metric inside a self-gravitating body
can be adequately approximated by an appropriate power series, the
instantaneous gravitational force and torque exerted on it is shown to be
identical to the force and torque exerted on an appropriate test body moving in
the effective metric. This result holds to all multipole orders. The only
instantaneous effect of a body's self-field is to finitely renormalize the
"bare" multipole moments of its stress-energy tensor. The MiSaTaQuWa expression
for the gravitational self-force is recovered as a simple application. A
gravitational self-torque is obtained as well. Lastly, it is shown that the
effective metric in which objects appear to move is approximately a solution to
the vacuum Einstein equation if the physical metric is an approximate solution
to Einstein's equation linearized about a vacuum background.Comment: 39 pages, 2 figures; fixed equation satisfied by the Green function
used to construct the effective metri
The Strategic Development of Irish Livestock Marts.
End of Project ReportA study of co-operative livestock marts revealed that cumulative marts turnover
decreased by 26% from 1990 to 1999: Commission income as a percentage
of turnover increased from 2% in 1990 to 3.2% in 1999. However operating
expenses increased by 25% from 1990 to 1999. Operating expenses have
since 1997, surpassed commision income, thus putting co-op marts in a
collective loss making situation from their mart activities. However overall
profit from co-op mart societies (including profit generated from all business
activities) almost doubled between 1990 and 1999. While overall profitability
of livestock marts societies has increased, twelve of thirty nine marts were in
a loss making situation in 1999. Four of these marts have been in a
permanent loss - making situation since 1990. All loss making societies in
1999 have little or no involvement in non-mart activities and almost all operate
from just one site. In general, the large diversified societies are showing
profitability.
A number of strategic alternatives to deal with their situation were placed before
mart executives. A diversification strategy is by far the most likely strategy to
be adopted by marts for the future Most marts are unlikely to consider
merging with other societies. Most marts have no plans to downsize and exit
from the industry is not considered an option by any society. There is a
recognition that there is an urgent need to rationalise the industry, but this
strategy is likely to meet with a strong resistance from marts . A problem with
rationalisation is that there are no incentives to make this strategy a reality.
On the one hand, management would be reluctant to follow this approach, as
it may be perceived to reflect badly on their own performance or may result in them being forced to seek alternative employment. On the other hand, the
shareholders have little to gain and much to lose if the mart closes.
Projections of past trends and impact of new policies would suggest continuing
decline in turnover and profitability in the co-operative mart sector.
Rationalisation is therefore absolutely essential. The industry cannot sustain
the present number of marts. Diversification seems the most obvious option
for the future of the industry. In general marts that have diversified are
profitable and there is no reason why this trend cannot continue into the
future
How geckos stick in nature: ecology and biomechanics of gecko feet
Phenotype and performance play a fundamental role in evolution and ecology. Studies of form and function often use correlations between morphology, performance, and habitat use to examine patterns of ecomorphology and morphological adaptation. Geckos, of the taxonomic group Gekkota, are an understudied yet diverse clade of lizards in which studies of form and function would greatly improve our understanding of their evolution. Geckos have the rather unique trait of adhesive toe pads, enabling them to use arboreal and rocky environments in a way few other creatures can. Gecko toe pad morphology and adhesive abilities are highly variable across species, suggesting ecological adaptations may have driven their evolution, yet few studies has considered gecko adhesive morphology and performance in an ecological context. In this study, we quantified morphology, adhesive performance, and habitat use of 13 gecko species from Queensland, Australia including tropical, arid, arboreal, and rock-dwelling species. We found toe detachment angle to be correlated with residual limb length. We also found residual limb length to be correlated with the use of arboreal and rock microhabitats as well as negatively correlated with perch diameter. This study is one of the first examples investigating gecko adhesive performance and specific microhabitat parameters. We suggest additional comparative studies investigating gecko limb kinematics and setal mechanics to corroborate our observational results
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Prevalence and demographics of systemic lupus erythematosus and lupus nephritis among US children with Medicaid coverage, 2002-2004
Relating relational networks: An initial experimental analysis
Studying relating of relational networks is a complex and challenging task. The main objective of the present study was to demonstrate relating within and across relational networks based on same/opposite and bigger/smaller contextual cues and establish antecedent control. After nonarbitrary pretraining of the contextual cues, two nonsense stimulus classes were established based on comparative relations. Participants were trained to select stimuli from an array of options based on a symbolic rule that established a relation between two stimuli: one of Network 1 and one of Network 2. Training involved relating Network 1 to Network 2, and testing assessed relating Network 2 to Network 1. Seven of eight participants reached the mastery criterion in training and responded accordingly in test. In a final stage, reinforcing and punishing consequences were varied systematically in the presence of two novel stimuli and antecedent control was observed for all 7 participants. Experiment 2 replicated the results of Experiment 1 but using contextual cues taken from natural language, and Experiment 3 sought to understand the effects of pretraining relational responding using natural language. The mastery criteria were reached by four of seven participants in Experiment 2 and by all eight participants in Experiment 3. Future studies could develop and refine the methods employed here in analyzing the relating of relational networks, thus allowing for an increasingly sophisticated behavior-analytic account of human language and cognition
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Dietary intake of vitamin D during adolescence and risk of adult onset systemic lupus erythematosus and rheumatoid arthritis
Spatial Scaling in Model Plant Communities
We present an analytically tractable variant of the voter model that provides
a quantitatively accurate description of beta-diversity (two-point correlation
function) in two tropical forests. The model exhibits novel scaling behavior
that leads to links between ecological measures such as relative species
abundance and the species area relationship.Comment: 10 pages, 3 figure
Altered fMRI restingâ state connectivity in individuals with fibromyalgia on acute pain stimulation
BackgroundFibromyalgia is a chronic widespread pain condition, with patients commonly reporting other symptoms such as sleep difficulties, memory complaints and fatigue. The use of magnetic resonance imaging (MRI) in fibromyalgia has allowed for the detection of neural abnormalities, with alterations in brain activation elicited by experimental pain and alterations in resting state connectivity related to clinical pain.MethodsIn this study, we sought to monitor state changes in resting brain connectivity following experimental pressure pain in fibromyalgia patients and healthy controls. Twelve fibromyalgia patients and 15 healthy controls were studied by applying discrete pressure stimuli to the thumbnail bed during MRI. Restingâ state functional MRI scanning was performed before and immediately following experimental pressure pain. We investigated changes in functional connectivity to the thalamus and the insular cortex.ResultsAcute pressure pain increased insula connectivity to the anterior cingulate and the hippocampus. Additionally, we observed increased thalamic connectivity to the precuneus/posterior cingulate cortex, a known part of the default mode network, in patients but not in controls. This connectivity was correlated with changes in clinical pain.ConclusionsThese data reporting changes in restingâ state brain activity following a noxious stimulus suggest that the acute painful stimuli may contribute to the alteration of the neural signature of chronic pain.What does this study/add?In this study acute pain application shows an echo in functional connectivity and clinical pain changes in chronic pain.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/122449/1/ejp832_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/122449/2/ejp832.pd
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