3,057 research outputs found
Price Formation under Small Numbers Competition: Evidence from Land Auctions in Singapore
This paper examines the price formation process under small numbers competition using data from Singapore land auctions. The theory predicts that bid prices are less than the zero-profit asset value in these first-price sealed-bid auctions. The model also shows that expected sales price increases with the number of bidders both because each bidder has an incentive to offer a higher price and because of a greater likelihood that a high-value bidder is present. The empirical estimates are consistent with auction theory and show that the standard land attributes are reflected in auction prices as expected. Working Paper No. 04-0
Vortex matching effect in engineered thin films of NbN
We report robust vortex matching effects in antidot arrays fabricated on thin
films of NbN. The near absence of hysteresis between field sweep directions
indicates a negligible residual pinning in the host thin film. Owing to the
very small coherence length of NbN thin films (), the observations
suggests the possibility of probing physics of vortices at true nanometer
length scales in suitably fabricated structures.Comment: Submitted to Appl. Phys. Let
Regular or random: a discussion on SPH initial particle distribution
Smoothed Particle Hydrodynamics (SPH) has been used to model a variety of objects and for a number of applications in engineering and science. These have ranged from astrophysicstofluidandsolidmechanicsproblems. Muchresearchhasbeendedicatedtoforming a better understanding of the SPH method. As a consequence, new numerical techniques have been developed in order to overcome some of its difficulties and limitations. Nonetheless, there is still a gap in information concerning the impact of the initial particle distribution on the effectiveness of the SPH method. With this in mind, a review of existing recommendations for SPH initial configurations has been conducted in this paper. In addition to this, a numerical exampleispresentedwhichisbasedontheclassical2-Dliddrivencavityproblem,whereinthe upperboundaryexertsahorizontalshearforceonthefluidinsidethecavity. Thevelocityofthe lid is v = 10−3 m/s and the cavity is square with length l = 1x10−3 m. The fluid was modelled with a density ρ = 1000 kg/m3, a viscosity µ = 10−3 kg/ms) (Re = 1). These parameters were held constant for all consequent comparisons. The number of particles is varied from (20 × 20) to (80 × 80). The initial distribution is modelled in three different ways: (i) regular, (ii) pseudo-random (with a 30% random deviation from the regular grid) and (iii) fully random. Theeffectivenessofeachinitialparticledistributionisassessedaccordingtothefieldvelocities and horizontal and vertical centreline velocity profiles. The impact of the initial particle distribution is highlighted and compared against a reference CFD result, and recommendations and conclusions are drawn for the SPH method
XAX: a multi-ton, multi-target detection system for dark matter, double beta decay and pp solar neutrinos
A multi-target detection system XAX, comprising concentric 10 ton targets of
136Xe and 129/131Xe, together with a geometrically similar or larger target of
liquid Ar, is described. Each is configured as a two-phase
scintillation/ionization TPC detector, enhanced by a full 4pi array of
ultra-low radioactivity Quartz Photon Intensifying Detectors (QUPIDs) replacing
the conventional photomultipliers for detection of scintillation light. It is
shown that background levels in XAX can be reduced to the level required for
dark matter particle (WIMP) mass measurement at a 10^-10 pb WIMP-nucleon cross
section, with single-event sensitivity below 10^-11 pb. The use of multiple
target elements allows for confirmation of the A^2 dependence of a coherent
cross section, and the different Xe isotopes provide information on the
spin-dependence of the dark matter interaction. The event rates observed by Xe
and Ar would modulate annually with opposite phases from each other for WIMP
mass >~100 GeV/c^2. The large target mass of 136Xe and high degree of
background reduction allow neutrinoless double beta decay to be observed with
lifetimes of 10^27-10^28 years, corresponding to the Majorana neutrino mass
range 0.01-0.1 eV, the most likely range from observed neutrino mass
differences. The use of a 136Xe-depleted 129/131Xe target will also allow
measurement of the pp solar neutrino spectrum to a precision of 1-2%.Comment: 16 pages with 17 figure
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Do you think I should be scared? The effect of peer discussion on children's fears
This study investigated whether close friends affect each other’s fear responses (fear beliefs and avoidance) when they discuss fear-related issues together. Children (N = 242) aged 7 to 10 years were first presented with ambiguous and threatening information about two novel animals respectively, after which their fear responses towards each animal were assessed (T1). Next, dyads of close friends had a discussion about their feelings regarding the animals, and their fear responses were measured again (T2). Results showed that children influenced each other’s cognitions following the discussion; from T1 to T2 their fear responses became more similar and close friends’ fear responses at T1 significantly predicted children’s fear responses at T2. Gender pair type predicted change in children’s fear responses over time. Children in boy-boy pairs showed a significant increase in fear responses following the discussion; their fear level became more in line with that of other gender pairs at T2, while those in girl-girl pairs showed a significant decrease in their fear beliefs, at least when threatening information was given. Differences in anxiety level between close friends did not affect change in fear responses over time. Altogether, the results indicate that children may affect each other’s fears
Global three-dimensional flow of a neutron superfluid in a spherical shell in a neutron star
We integrate for the first time the hydrodynamic
Hall-Vinen-Bekarevich-Khalatnikov equations of motion of a -paired
neutron superfluid in a rotating spherical shell, using a pseudospectral
collocation algorithm coupled with a time-split fractional scheme. Numerical
instabilities are smoothed by spectral filtering. Three numerical experiments
are conducted, with the following results. (i) When the inner and outer spheres
are put into steady differential rotation, the viscous torque exerted on the
spheres oscillates quasiperiodically and persistently (after an initial
transient). The fractional oscillation amplitude () increases
with the angular shear and decreases with the gap width. (ii) When the outer
sphere is accelerated impulsively after an interval of steady differential
rotation, the torque increases suddenly, relaxes exponentially, then oscillates
persistently as in (i). The relaxation time-scale is determined principally by
the angular velocity jump, whereas the oscillation amplitude is determined
principally by the gap width. (iii) When the mutual friction force changes
suddenly from Hall-Vinen to Gorter-Mellink form, as happens when a rectilinear
array of quantized Feynman-Onsager vortices is destabilized by a counterflow to
form a reconnecting vortex tangle, the relaxation time-scale is reduced by a
factor of compared to (ii), and the system reaches a stationary state
where the torque oscillates with fractional amplitude about a
constant mean value. Preliminary scalings are computed for observable
quantities like angular velocity and acceleration as functions of Reynolds
number, angular shear, and gap width. The results are applied to the timing
irregularities (e.g., glitches and timing noise) observed in radio pulsars.Comment: 6 figures, 23 pages. Accepted for publication in Astrophysical
Journa
Avoiding the dry season: dispersal time and syndrome mediate seed dormancy in grasses in Neotropical savanna and wet grasslands.
Question: In seasonal rainfall systems, seed dormancy is a strategy to avoid germination and seedling emergence in the dry season. Grass species in Brazilian savannas (Cerrado) show variation in seed dispersal timing and mechanisms, and occur in different habitat types (distinguished by soil moisture) within a seasonal rainfall environment. However, it is unknown whether dormancy has evolved in these systems as a dominant way in which germination is deferred, or how it correlates with other key traits such as dispersal, where known trade-offs exist for avoiding competition. We asked whether seed germination and dormancy vary with dispersal and abiotic factors in savanna systems. Specifically, we assessed dormancy by comparing seeds: (1) from species living in habitats with contrasting soil moisture during the dry season (open savannas vs wet grasslands); (2) dispersed at different times (early in the wet season, late in the wet season and in the dry season); and (3) showing alternate dispersal syndromes (barochoric vs anemochoric).
Location: Open savannas and wet grasslands in central Brazil.
Methods: We collected seeds of 29 grass species and tested viability and dormancy using germination trials with fresh seeds, which was then repeated after dry storage for 3, 6, 9 and 12 mo. GLMM were used to test whether the degree of dormancy was dependent on habitat type, seed dispersal time and seed dispersal syndrome.
Results: Seeds from wet grasslands lived longer and had consistently higher germination rates than seeds from open savannas. Additionally, fresh seeds dispersed late in the wet season had higher levels of seed dormancy compared to seeds dispersed early in the wet season. Finally, we found that anemochoric seeds had lower levels of dormancy than barochoric seeds.
Conclusions: Seed dormancy among Neotropical grasses was higher for seeds of species from dry habitats, dispersed late in the wet season, and with short distance dispersal (barochory). These results suggest that seed dormancy is a key mechanism by which seeds avoid seedling emergence in the dry season, an effect offset by habitat-specific soil moisture availability. The trade-off between dormancy and seed dispersal suggests that both strategies are costly and had non-additive benefits
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