3,210 research outputs found
The "analysis of competing hypotheses" in intelligence analysis
The intelligence community uses ‘structured analytic techniques’ to help analysts think critically and avoid cognitive bias. However, little evidence exists of how techniques are applied and whether they are effective. We examined the use of the Analysis of Competing Hypotheses (ACH) – a technique designed to reduce ‘confirmation bias’. Fifty intelligence analysts were randomly assigned to use ACH or not when completing a hypothesis testing task that had probabilistic ground truth. Data on analysts’ judgment processes and conclusions was collected using written protocols that were then coded for statistical analyses. We found that ACH-trained analysts did not follow all of the steps of ACH. There was mixed evidence for ACH’s ability to reduce confirmation bias, and we observed that ACH may increase judgment inconsistency and error. It may be prudent for the intelligence community to consider the conditions under which ACH would prove useful, and to explore alternatives
Towards Rapid Parameter Estimation on Gravitational Waves from Compact Binaries using Interpolated Waveforms
Accurate parameter estimation of gravitational waves from coalescing compact
binary sources is a key requirement for gravitational-wave astronomy.
Evaluating the posterior probability density function of the binary's
parameters (component masses, sky location, distance, etc.) requires computing
millions of waveforms. The computational expense of parameter estimation is
dominated by waveform generation and scales linearly with the waveform
computational cost. Previous work showed that gravitational waveforms from
non-spinning compact binary sources are amenable to a truncated singular value
decomposition, which allows them to be reconstructed via interpolation at fixed
computational cost. However, the accuracy requirement for parameter estimation
is typically higher than for searches, so it is crucial to ascertain that
interpolation does not lead to significant errors. Here we provide a proof of
principle to show that interpolated waveforms can be used to recover posterior
probability density functions with negligible loss in accuracy with respect to
non-interpolated waveforms. This technique has the potential to significantly
increase the efficiency of parameter estimation.Comment: 7 pages, 2 figure
Report on the first round of the Mock LISA Data Challenges
The Mock LISA Data Challenges (MLDCs) have the dual purpose of fostering the development of LISA data analysis tools and capabilities, and demonstrating the technical readiness already achieved by the gravitational-wave community in distilling a rich science payoff from the LISA data output. The first round of MLDCs has just been completed: nine challenges consisting of data sets containing simulated gravitational-wave signals produced either by galactic binaries or massive black hole binaries embedded in simulated LISA instrumental noise were released in June 2006 with deadline for submission of results at the beginning of December 2006. Ten groups have participated in this first round of challenges. All of the challenges had at least one entry which successfully characterized the signal to better than 95% when assessed via a correlation with phasing ambiguities accounted for. Here, we describe the challenges, summarize the results and provide a first critical assessment of the entries
Gaussian-State Theory of Two-Photon Imaging
Biphoton states of signal and idler fields--obtained from spontaneous
parametric downconversion (SPDC) in the low-brightness, low-flux regime--have
been utilized in several quantum imaging configurations to exceed the
resolution performance of conventional imagers that employ coherent-state or
thermal light. Recent work--using the full Gaussian-state description of
SPDC--has shown that the same resolution performance seen in quantum optical
coherence tomography and the same imaging characteristics found in quantum
ghost imaging can be realized by classical-state imagers that make use of
phase-sensitive cross correlations. This paper extends the Gaussian-state
analysis to two additional biphoton-state quantum imaging scenarios: far field
diffraction-pattern imaging; and broadband thin-lens imaging. It is shown that
the spatial resolution behavior in both cases is controlled by the nonzero
phase-sensitive cross correlation between the signal and idler fields. Thus,
the same resolution can be achieved in these two configurations with
classical-state signal and idler fields possessing a nonzero phase-sensitive
cross correlation.Comment: 14 pages, 5 figure
BDDC and FETI-DP under Minimalist Assumptions
The FETI-DP, BDDC and P-FETI-DP preconditioners are derived in a particulary
simple abstract form. It is shown that their properties can be obtained from
only on a very small set of algebraic assumptions. The presentation is purely
algebraic and it does not use any particular definition of method components,
such as substructures and coarse degrees of freedom. It is then shown that
P-FETI-DP and BDDC are in fact the same. The FETI-DP and the BDDC
preconditioned operators are of the same algebraic form, and the standard
condition number bound carries over to arbitrary abstract operators of this
form. The equality of eigenvalues of BDDC and FETI-DP also holds in the
minimalist abstract setting. The abstract framework is explained on a standard
substructuring example.Comment: 11 pages, 1 figure, also available at
http://www-math.cudenver.edu/ccm/reports
Quantum Monte Carlo study of ring-shaped polariton parametric luminescence in a semiconductor microcavity
We present a quantum Monte Carlo study of the quantum correlations in the
parametric luminescence from semiconductor microcavities in the strong
exciton-photon coupling regime. As already demonstrated in recent experiments,
a ring-shaped emission is obtained by applying two identical pump beams with
opposite in-plane wavevectors, providing symmetrical signal and idler beams
with opposite in-plane wavevectors on the ring. We study the squeezing of the
signal-idler difference noise across the parametric instability threshold,
accounting for the radiative and non-radiative losses, multiple scattering and
static disorder. We compare the results of the complete multimode Monte Carlo
simulations with a simplified linearized quantum Langevin analytical model
Double Compact Objects III: Gravitational Wave Detection Rates
The unprecedented range of second-generation gravitational-wave (GW)
observatories calls for refining the predictions of potential sources and
detection rates. The coalescence of double compact objects (DCOs)---i.e.,
neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black
hole-black hole (BH-BH) binary systems---is the most promising source of GWs
for these detectors. We compute detection rates of coalescing DCOs in
second-generation GW detectors using the latest models for their cosmological
evolution, and implementing inspiral-merger-ringdown (IMR) gravitational
waveform models in our signal-to-noise ratio calculations. We find that: (1)
the inclusion of the merger/ringdown portion of the signal does not
significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by
a factor for BH-BH systems; (2) in almost all of our models BH-BH
systems yield by far the largest rates, followed by NS-NS and BH-NS systems,
respectively, and (3) a majority of the detectable BH-BH systems were formed in
the early Universe in low-metallicity environments. We make predictions for the
distributions of detected binaries and discuss what the first GW detections
will teach us about the astrophysics underlying binary formation and evolution.Comment: published in ApJ, 19 pages, 11 figure
Photon-added coherent states as nonlinear coherent states
The states , defined as up to a
normalization constant and is a nonnegative integer, are shown to be the
eigenstates of where is a nonlinear
function of the number operator . The explicit form of
is constructed. The eigenstates of this operator for negative values of are
introduced. The properties of these states are discussed and compared with
those of the state .Comment: Rev Tex file with two figures as postscript files attached. Email:
[email protected]
Quantum bistability and spin current shot noise of a single quantum dot coupled to an optical microcavity
Here we explore spin dependent quantum transport through a single quantum dot
coupled to an optical microcavity. The spin current is generated by electron
tunneling between a single doped reservoir and the dot combined with intradot
spin flip transitions induced by a quantized cavity mode. In the limit of
strong Coulomb blockade, this model is analogous to the Jaynes-Cummings model
in quantum optics and generates a pure spin current in the absence of any
charge current. Earlier research has shown that in the classical limit where a
large number of such dots interact with the cavity field, the spin current
exhibits bistability as a function of the laser amplitude that drives the
cavity. We show that in the limit of a single quantum dot this bistability
continues to be present in the intracavity photon statistics. Signatures of the
bistable photon statistics manifest themselves in the frequency dependent shot
noise of the spin current despite the fact that the quantum mechanical average
spin current no longer exhibits bistability. Besides having significance for
future quantum dot based optoelectronic devices, our results shed light on the
relation between bistability, which is traditionally viewed as a classical
effect, and quantum mechanics
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