402 research outputs found
Implications of latency data for threshold and nonthreshold models of signal detection
Two detection cum latency models are constructed by combining sets of plausible assumptions about latency with, in the first instance, the model of the. Theory of Signal Detection and, in the second instance, a general threshold model. The aim of this paper is to show that latency statistics can be used to provide sharp tests for distinguishing between the two models. The two statistics studied are the reaction time operating characteristic (RT-ROC) and the plot of average reaction time against response probability (RT-probability curve). It is shown that, under the first detection model, the RT-ROC lies below the ROC derived from detection rates except at the "yes-no" point, and the RT-probability curve is decreasing whereas, under the second model, the RT-ROC coincides with portions of the latter ROC, and decreasing RT-probability curves do not arise naturally.The effect of criterion variability on the ROC is discussed in detail and conditions are given under which the RT-ROC is equivalent to a ROC generated by variable criteria.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34057/1/0000335.pd
Supersymmetric AdS_3, AdS_2 and Bubble Solutions
We present new supersymmetric AdS_3 solutions of type IIB supergravity and
AdS_2 solutions of D=11 supergravity. The former are dual to conformal field
theories in two dimensions with N=(0,2) supersymmetry while the latter are dual
to conformal quantum mechanics with two supercharges. Our construction also
includes AdS_2 solutions of D=11 supergravity that have non-compact internal
spaces which are dual to three-dimensional N=2 superconformal field theories
coupled to point-like defects. We also present some new bubble-type solutions,
corresponding to BPS states in conformal theories, that preserve four
supersymmetries.Comment: v2: 33 pages, published version in JHE
The Decay of Magnetic Fields in Kaluza-Klein Theory
Magnetic fields in five-dimensional Kaluza-Klein theory compactified on a
circle correspond to ``twisted'' identifications of five dimensional Minkowski
space. We show that a five dimensional generalisation of the Kerr solution can
be analytically continued to construct an instanton that gives rise to two
possible decay modes of a magnetic field. One decay mode is the generalisation
of the ``bubble decay" of the Kaluza-Klein vacuum described by Witten. The
other decay mode, rarer for weak fields, corresponds in four dimensions to the
creation of monopole-anti-monopole pairs. An instanton for the latter process
is already known and is given by the analytic continuation of the \KK\ Ernst
metric, which we show is identical to the five dimensional Kerr solution. We
use this fact to illuminate further properties of the decay process. It appears
that fundamental fermions can eliminate the bubble decay of the magnetic field,
while allowing the pair production of Kaluza-Klein monopoles.Comment: 25 pages, one figure. The discussion of fermions has been revised: We
show how fundamental fermions can eliminate the bubble-type instability but
still allow pair creation of monopole
The Role of Demography and Markets in Determining Deforestation Rates Near Ranomafana National Park, Madagascar
The highland forests of Madagascar are home to some of the world's most unique and diverse flora and fauna and to some of its poorest people. This juxtaposition of poverty and biodiversity is continually reinforced by rapid population growth, which results in increasing pressure on the remaining forest habitat in the highland region, and the biodiversity therein. Here we derive a mathematical expression for the subsistence of households to assess the role of markets and household demography on deforestation near Ranomafana National Park. In villages closest to urban rice markets, households were likely to clear less land than our model predicted, presumably because they were purchasing food at market. This effect was offset by the large number of migrant households who cleared significantly more land between 1989–2003 than did residents throughout the region. Deforestation by migrant households typically occurred after a mean time lag of 9 years. Analyses suggest that while local conservation efforts in Madagascar have been successful at reducing the footprint of individual households, large-scale conservation must rely on policies that can reduce the establishment of new households in remaining forested areas
On the universal outcome of star-formation: Is there a link between stars and brown-dwarfs?
(abridged) The recent evidence obtained by Briceno et al. that star-formation
in Taurus-Auriga (TA) may be producing significantly fewer brown dwarfs (BDs)
per star than the ONC is investigated by setting up a realistic model stellar
plus BD population and explicitly taking into account a high binary proportion
and dynamical evolution in the TA groups and the ONC. The Briceno result is
reproduced almost exactly despite an identical IMF in both systems because many
BD-BD and star-BD binaries are disrupted in the ONC thus freeing BDs, while the
TA groups remain unevolved dynamically. However, the resulting populations do
not have the correct star-star, star-BD and expecially BD-BD binary properties,
even if a variable BD IMF is allowed for. The conclusion is therefore that BDs
need to be added as a separate population which has its own binary properties.
Such an extra population can have various origins which are briefly discussed
in this contribution but more fully in an associated paper.Comment: MNRAS, accepted, 23 pages, 14 figures, LaTeX, two references adde
Nucleation of -Branes and Fundamental Strings
We construct a solution to the low-energy string equations of motion in five
dimensions that describes a circular loop of fundamental string exponentially
expanding in a background electric -field. Euclideanising this gives an
instanton for the creation of a loop of fundamental string in a background
-field, and we calculate the rate of nucleation. Solutions describing
magnetically charged strings and -branes, where the gauge field comes from
Kaluza-Klein reduction on a circle, are also constructed. It is known that a
magnetic flux tube in four (reduced) spacetime dimensions is unstable to the
pair creation of Kaluza-Klein monopoles. We show that in dimensions,
magnetic ``fluxbranes" are unstable to the nucleation of a magnetically
charged spherical -brane. In ten dimensions the instanton describes the
nucleation of a Ramond-Ramond magnetically charged six-brane in type IIA string
theory. We also find static solutions describing spherical charged -branes
or fundamental strings held in unstable equilibrium in appropriate background
fields. Instabilities of intersecting magnetic fluxbranes are also discussed.Comment: 28 pages, harvmac (b), reference added, typos correcte
Quantum state preparation and macroscopic entanglement in gravitational-wave detectors
Long-baseline laser-interferometer gravitational-wave detectors are operating
at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within
a broad frequency band. Such a low classical noise budget has already allowed
the creation of a controlled 2.7 kg macroscopic oscillator with an effective
eigenfrequency of 150 Hz and an occupation number of 200. This result, along
with the prospect for further improvements, heralds the new possibility of
experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical
behavior of objects in the realm of everyday experience - using
gravitational-wave detectors. In this paper, we provide the mathematical
foundation for the first step of a MQM experiment: the preparation of a
macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum
state, which is possible if the interferometer's classical noise beats the SQL
in a broad frequency band. Our formalism, based on Wiener filtering, allows a
straightforward conversion from the classical noise budget of a laser
interferometer, in terms of noise spectra, into the strategy for quantum state
preparation, and the quality of the prepared state. Using this formalism, we
consider how Gaussian entanglement can be built among two macroscopic test
masses, and the performance of the planned Advanced LIGO interferometers in
quantum-state preparation
- …