44,307 research outputs found
Endowment Effects in Contests
We design an experiment to test if the manner in which subjects receive the endowment has any bearing on the amount of overbidding in contests. We find that overbidding is significantly higher when subjects are given a large per-experiment endowment rather than when the endowment is given per-period. Risk-aversion and non-monetary utility of winning play important roles in explaining our findings.rent-seeking, contest, experiments, overbidding, endowment
Mapping the Berry Curvature from Semiclassical Dynamics in Optical Lattices
We propose a general method by which experiments on ultracold gases can be
used to determine the topological properties of the energy bands of optical
lattices, as represented by the map of the Berry curvature across the Brillouin
zone. The Berry curvature modifies the semiclassical dynamics and hence the
trajectory of a wave packet undergoing Bloch oscillations. However, in two
dimensions these trajectories may be complicated Lissajous-like figures, making
it difficult to extract the effects of Berry curvature in general. We propose
how this can be done using a "time-reversal" protocol. This compares the
velocity of a wave packet under positive and negative external force, and
allows a clean measurement of the Berry curvature over the Brillouin zone. We
discuss how this protocol may be implemented and explore the semiclassical
dynamics for three specific systems: the asymmetric hexagonal lattice, and two
"optical flux" lattices in which the Chern number is nonzero. Finally, we
discuss general experimental considerations for observing Berry curvature
effects in ultracold gases.Comment: 12 page
Track and capture of the orbiter with the space station remote manipulator system
Results of the first study using the real-time, man-in-the-loop Systems Engineering Simulator (SES) for track and capture of the Space Shuttle Orbiter with the space station manipulator are presented. The objectives include evaluation of the operational coordination required between the orbiter pilot and the space station manipulator operator, evaluation of the locations and required number of closed-circuit television cameras, and evaluation of the orbiter grapple fixture clearance geometry. The SES is a premium quality real-time facility with full fidelity orbiter and space station crew workstations and cockpits
A smoothing algorithm using cubic spline functions
Two algorithms are presented for smoothing arbitrary sets of data. They are the explicit variable algorithm and the parametric variable algorithm. The former would be used where large gradients are not encountered because of the smaller amount of calculation required. The latter would be used if the data being smoothed were double valued or experienced large gradients. Both algorithms use a least-squares technique to obtain a cubic spline fit to the data. The advantage of the spline fit is that the first and second derivatives are continuous. This method is best used in an interactive graphics environment so that the junction values for the spline curve can be manipulated to improve the fit
Continuous-flow laboratory simulation of stream water quality changes downstream of an untreated wastewater discharge.
In regions of the world with poor provision of wastewater treatment, raw sewage
is often discharged directly into surface waters. This paper describes an
experimental evaluation of the fate of two organic chemicals under these
conditions using an artificial channel cascade fed with a mix of settled sewage
and river water at its upstream end and operated under continuous steady-state
conditions. The experiments underpin an environmental risk assessment
methodology based on the idea of an âimpact zoneâ (IZ) â the zone downstream of
wastewater emission in which water quality is severely impaired by high
concentrations of unionised ammonia, nitrite and biochemical oxygen demand
(BOD). Radiolabelled dodecane-6-benzene sulphonate (DOBS) and aniline
hydrochloride were used as the model chemical and reference compound
respectively. Rapid changes in 14C counts were observed with flow-time for both
these materials. These changes were most likely to be due to complete
mineralisation. A dissipation half-life of approximately 7.1 h was observed for
the 14C label with DOBS. The end of the IZ was defined as the point at which the
concentration of both unionised ammonia and nitrite fell below their respective
predicted no-effect concentrations for salmonids. At these points in the
cascade, approximately 83 and 90% of the initial concentration of 14C had been
removed from the water column, respectively. A simple model of mineral nitrogen
transformations based on MichaelisâMenten kinetics was fitted to observed
concentrations of NH4, NO2 and NO3. The cascade is intended to provide a
confirmatory methodology for assessing the ecological risks of chemicals under
direct discharge co
The effect of magnetic fields on star cluster formation
We examine the effect of magnetic fields on star cluster formation by
performing simulations following the self-gravitating collapse of a turbulent
molecular cloud to form stars in ideal MHD. The collapse of the cloud is
computed for global mass-to-flux ratios of infinity, 20, 10, 5 and 3, that is
using both weak and strong magnetic fields. Whilst even at very low strengths
the magnetic field is able to significantly influence the star formation
process, for magnetic fields with plasma beta < 1 the results are substantially
different to the hydrodynamic case. In these cases we find large-scale
magnetically-supported voids imprinted in the cloud structure; anisotropic
turbulent motions and column density structure aligned with the magnetic field
lines, both of which have recently been observed in the Taurus molecular cloud.
We also find strongly suppressed accretion in the magnetised runs, leading to
up to a 75% reduction in the amount of mass converted into stars over the
course of the calculations and a more quiescent mode of star formation. There
is also some indication that the relative formation efficiency of brown dwarfs
is lower in the strongly magnetised runs due to the reduction in the importance
of protostellar ejections.Comment: 16 pages, 9 figures, 8 very pretty movies, MNRAS, accepted. Version
with high-res figures + movies available from
http://www.astro.ex.ac.uk/people/dprice/pubs/mcluster/index.htm
The resurrection of group selection as a theory of human cooperation
Two books edited by members of the MacArthur Norms and Preferences Network (an interdisciplinary group, mainly anthropologists and economists) are reviewed here. These books in large part reflect a renewed interest in group selection
that has occurred among these researchers: they promote the theory that human cooperative behavior evolved via selective processes which favored biological and/or cultural group-level adaptations as opposed to individual-level adaptations. In support of this theory, an impressive collection of cross-cultural data are presented which suggest that participants in experimental economic games often do not behave as self-interested income maximizers; this lack of self-interest is regarded as evidence of group selection. In this review, problems with these data and with the theory are discussed. On the data side, it is argued that even if a behavior seems individually-maladaptive in a game context, there is no reason to believe that it would have been that way in ancestral contexts, since the environments of experimental games do not at all resemble those in which ancestral humans would have interacted cooperatively. And on the theory side, it is argued that it is premature to invoke group selection in order to explain human cooperation, because more parsimonious individual-level theories have not yet been exhausted. In summary, these books represent ambitious interdisciplinary contributions on an important topic, and they include unique and useful data; however, they do not make a convincing case that the evolution of human cooperation required group selection
Does Inflation Provide Natural Initial Conditions for the Universe?
If our universe underwent inflation, its entropy during the inflationary
phase was substantially lower than it is today. Because a low-entropy state is
less likely to be chosen randomly than a high-entropy one, inflation is
unlikely to arise through randomly-chosen initial conditions. To resolve this
puzzle, we examine the notion of a natural state for the universe, and argue
that it is a nearly-empty spacetime. If empty space has a small vacuum energy,
however, inflation can begin spontaneously in this background. This scenario
explains why a universe like ours is likely to have begun via a period of
inflation, and also provides an origin for the cosmological arrow of time.Comment: Submitted to Gravity Research Foundation Essay Competition; based on
hep-th/041027
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