2,920 research outputs found
Study of nonequilibrium two-phase flow of a gas-particle mixture Technical note no. 2
Two-phase nonequilibrium flow of particle suspensions in gaseous mediu
Summed Parallel Infinite Impulse Response (SPIIR) Filters For Low-Latency Gravitational Wave Detection
With the upgrade of current gravitational wave detectors, the first detection
of gravitational wave signals is expected to occur in the next decade.
Low-latency gravitational wave triggers will be necessary to make fast
follow-up electromagnetic observations of events related to their source, e.g.,
prompt optical emission associated with short gamma-ray bursts. In this paper
we present a new time-domain low-latency algorithm for identifying the presence
of gravitational waves produced by compact binary coalescence events in noisy
detector data. Our method calculates the signal to noise ratio from the
summation of a bank of parallel infinite impulse response (IIR) filters. We
show that our summed parallel infinite impulse response (SPIIR) method can
retrieve the signal to noise ratio to greater than 99% of that produced from
the optimal matched filter. We emphasise the benefits of the SPIIR method for
advanced detectors, which will require larger template banks.Comment: 9 pages, 6 figures, for PR
The quantum one-time pad in the presence of an eavesdropper
A classical one-time pad allows two parties to send private messages over a
public classical channel -- an eavesdropper who intercepts the communication
learns nothing about the message. A quantum one-time pad is a shared quantum
state which allows two parties to send private messages or private quantum
states over a public quantum channel. If the eavesdropper intercepts the
quantum communication she learns nothing about the message. In the classical
case, a one-time pad can be created using shared and partially private
correlations. Here we consider the quantum case in the presence of an
eavesdropper, and find the single letter formula for the rate at which the two
parties can send messages using a quantum one-time pad
Model-based Cognitive Neuroscience: Multifield Mechanistic Integration in Practice
Autonomist accounts of cognitive science suggest that cognitive model building and theory construction (can or should) proceed independently of findings in neuroscience. Common functionalist justifications of autonomy rely on there being relatively few constraints between neural structure and cognitive function (e.g., Weiskopf, 2011). In contrast, an integrative mechanistic perspective stresses the mutual constraining of structure and function (e.g., Piccinini & Craver, 2011; Povich, 2015). In this paper, I show how model-based cognitive neuroscience (MBCN) epitomizes the integrative mechanistic perspective and concentrates the most revolutionary elements of the cognitive neuroscience revolution (Boone & Piccinini, 2016). I also show how the prominent subset account of functional realization supports the integrative mechanistic perspective I take on MBCN and use it to clarify the intralevel and interlevel components of integration
Towards low-latency real-time detection of gravitational waves from compact binary coalescences in the era of advanced detectors
Electromagnetic (EM) follow-up observations of gravitational wave (GW) events
will help shed light on the nature of the sources, and more can be learned if
the EM follow-ups can start as soon as the GW event becomes observable. In this
paper, we propose a computationally efficient time-domain algorithm capable of
detecting gravitational waves (GWs) from coalescing binaries of compact objects
with nearly zero time delay. In case when the signal is strong enough, our
algorithm also has the flexibility to trigger EM observation before the merger.
The key to the efficiency of our algorithm arises from the use of chains of
so-called Infinite Impulse Response (IIR) filters, which filter time-series
data recursively. Computational cost is further reduced by a template
interpolation technique that requires filtering to be done only for a much
coarser template bank than otherwise required to sufficiently recover optimal
signal-to-noise ratio. Towards future detectors with sensitivity extending to
lower frequencies, our algorithm's computational cost is shown to increase
rather insignificantly compared to the conventional time-domain correlation
method. Moreover, at latencies of less than hundreds to thousands of seconds,
this method is expected to be computationally more efficient than the
straightforward frequency-domain method.Comment: 19 pages, 6 figures, for PR
Semantic Decomposition Improves Learning of Large Language Models on EHR Data
Electronic health records (EHR) are widely believed to hold a profusion of
actionable insights, encrypted in an irregular, semi-structured format, amidst
a loud noise background. To simplify learning patterns of health and disease,
medical codes in EHR can be decomposed into semantic units connected by
hierarchical graphs. Building on earlier synergy between Bidirectional Encoder
Representations from Transformers (BERT) and Graph Attention Networks (GAT), we
present H-BERT, which ingests complete graph tree expansions of hierarchical
medical codes as opposed to only ingesting the leaves and pushes patient-level
labels down to each visit. This methodology significantly improves prediction
of patient membership in over 500 medical diagnosis classes as measured by
aggregated AUC and APS, and creates distinct representations of patients in
closely related but clinically distinct phenotypes.Comment: Extended Abstract presented at Machine Learning for Health (ML4H)
symposium 2022, November 28th, 2022, New Orleans, United States & Virtual,
http://www.ml4h.cc, 9 page
Use and Abuse of the Fisher Information Matrix in the Assessment of Gravitational-Wave Parameter-Estimation Prospects
The Fisher-matrix formalism is used routinely in the literature on
gravitational-wave detection to characterize the parameter-estimation
performance of gravitational-wave measurements, given parametrized models of
the waveforms, and assuming detector noise of known colored Gaussian
distribution. Unfortunately, the Fisher matrix can be a poor predictor of the
amount of information obtained from typical observations, especially for
waveforms with several parameters and relatively low expected signal-to-noise
ratios (SNR), or for waveforms depending weakly on one or more parameters, when
their priors are not taken into proper consideration. In this paper I discuss
these pitfalls; show how they occur, even for relatively strong signals, with a
commonly used template family for binary-inspiral waveforms; and describe
practical recipes to recognize them and cope with them.
Specifically, I answer the following questions: (i) What is the significance
of (quasi-)singular Fisher matrices, and how must we deal with them? (ii) When
is it necessary to take into account prior probability distributions for the
source parameters? (iii) When is the signal-to-noise ratio high enough to
believe the Fisher-matrix result? In addition, I provide general expressions
for the higher-order, beyond--Fisher-matrix terms in the 1/SNR expansions for
the expected parameter accuracies.Comment: 24 pages, 3 figures, previously known as "A User Manual for the
Fisher Information Matrix"; final, corrected PRD versio
Structure functions and intermittency in ionospheric plasma turbulence
Low frequency electrostatic turbulence in the ionospheric E-region is studied by means of numerical and experimental methods. We use the structure functions of the electrostatic potential as a diagnostics of the fluctuations. We demonstrate the inherently intermittent nature of the low level turbulence in the collisional ionospheric plasma by using results for the space-time varying electrostatic potential from two dimensional numerical simulations. An instrumented rocket can not directly detect the one-point potential variation, and most measurements rely on records of potential differences between two probes. With reference to the space observations we demonstrate that the results obtained by potential difference measurements can differ significantly from the one-point results. It was found, in particular, that the intermittency signatures become much weaker, when the proper rocket-probe configuration is implemented. We analyze also signals from an actual ionospheric rocket experiment, and find a reasonably good agreement with the appropriate simulation results, demonstrating again that rocket data, obtained as those analyzed here, are unlikely to give an adequate representation of intermittent features of the low frequency ionospheric plasma turbulence for the given conditions
Human Time-Frequency Acuity Beats the Fourier Uncertainty Principle
The time-frequency uncertainty principle states that the product of the
temporal and frequency extents of a signal cannot be smaller than .
We study human ability to simultaneously judge the frequency and the timing of
a sound. Our subjects often exceeded the uncertainty limit, sometimes by more
than tenfold, mostly through remarkable timing acuity. Our results establish a
lower bound for the nonlinearity and complexity of the algorithms employed by
our brains in parsing transient sounds, rule out simple "linear filter" models
of early auditory processing, and highlight timing acuity as a central feature
in auditory object processing.Comment: 4 pages, 2 figures; Accepted at PR
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