39,534 research outputs found
Comparing compact binary parameter distributions I: Methods
Being able to measure each merger's sky location, distance, component masses,
and conceivably spins, ground-based gravitational-wave detectors will provide a
extensive and detailed sample of coalescing compact binaries (CCBs) in the
local and, with third-generation detectors, distant universe. These
measurements will distinguish between competing progenitor formation models. In
this paper we develop practical tools to characterize the amount of
experimentally accessible information available, to distinguish between two a
priori progenitor models. Using a simple time-independent model, we demonstrate
the information content scales strongly with the number of observations. The
exact scaling depends on how significantly mass distributions change between
similar models. We develop phenomenological diagnostics to estimate how many
models can be distinguished, using first-generation and future instruments.
Finally, we emphasize that multi-observable distributions can be fully
exploited only with very precisely calibrated detectors, search pipelines,
parameter estimation, and Bayesian model inference
Top Quark Physics at the Tevatron
We review the field of top-quark physics with an emphasis on experimental
techniques. The role of the top quark in the Standard Model of particle physics
is summarized and the basic phenomenology of top-quark production and decay is
introduced. We discuss how contributions from physics beyond the Standard Model
could affect top-quark properties or event samples. The many measurements made
at the Fermilab Tevatron, which test the Standard Model predictions or probe
for direct evidence of new physics using the top-quark event samples, are
reviewed here.Comment: 50 pages, 17 figures, 2 tables; version accepted by Review of Modern
Physic
A fully-coherent all-sky search for gravitational-waves from compact binary coalescences
We introduce a fully-coherent method for searching for gravitational wave
signals generated by the merger of black hole and/or neutron star binaries.
This extends the coherent analysis previously developed and used for targeted
gravitational wave searches to an all-sky, all-time search. We apply the search
to one month of data taken during the fifth science run of the LIGO detectors.
We demonstrate an increase in sensitivity of 25% over the coincidence search,
which is commensurate with expectations. Finally, we discuss prospects for
implementing and running a coherent search for gravitational wave signals from
binary coalescence in the advanced gravitational wave detector data.Comment: 17 pages, 12 figure
Dynamic Decomposition of Spatiotemporal Neural Signals
Neural signals are characterized by rich temporal and spatiotemporal dynamics
that reflect the organization of cortical networks. Theoretical research has
shown how neural networks can operate at different dynamic ranges that
correspond to specific types of information processing. Here we present a data
analysis framework that uses a linearized model of these dynamic states in
order to decompose the measured neural signal into a series of components that
capture both rhythmic and non-rhythmic neural activity. The method is based on
stochastic differential equations and Gaussian process regression. Through
computer simulations and analysis of magnetoencephalographic data, we
demonstrate the efficacy of the method in identifying meaningful modulations of
oscillatory signals corrupted by structured temporal and spatiotemporal noise.
These results suggest that the method is particularly suitable for the analysis
and interpretation of complex temporal and spatiotemporal neural signals
Event-based simulation of quantum physics experiments
We review an event-based simulation approach which reproduces the statistical
distributions of wave theory not by requiring the knowledge of the solution of
the wave equation of the whole system but by generating detection events
one-by-one according to an unknown distribution. We illustrate its
applicability to various single photon and single neutron interferometry
experiments and to two Bell test experiments, a single-photon
Einstein-Podolsky-Rosen experiment employing post-selection for photon pair
identification and a single-neutron Bell test interferometry experiment with
nearly detection efficiency.Comment: Lectures notes of the Advanced School on Quantum Foundations and Open
Quantum Systems, Jo\~ao Pessoa, Brazil, July 2012, edited by T. M.
Nieuwenhuizen et al, World Scientific, to appea
Distributed Control of Microscopic Robots in Biomedical Applications
Current developments in molecular electronics, motors and chemical sensors
could enable constructing large numbers of devices able to sense, compute and
act in micron-scale environments. Such microscopic machines, of sizes
comparable to bacteria, could simultaneously monitor entire populations of
cells individually in vivo. This paper reviews plausible capabilities for
microscopic robots and the physical constraints due to operation in fluids at
low Reynolds number, diffusion-limited sensing and thermal noise from Brownian
motion. Simple distributed controls are then presented in the context of
prototypical biomedical tasks, which require control decisions on millisecond
time scales. The resulting behaviors illustrate trade-offs among speed,
accuracy and resource use. A specific example is monitoring for patterns of
chemicals in a flowing fluid released at chemically distinctive sites.
Information collected from a large number of such devices allows estimating
properties of cell-sized chemical sources in a macroscopic volume. The
microscopic devices moving with the fluid flow in small blood vessels can
detect chemicals released by tissues in response to localized injury or
infection. We find the devices can readily discriminate a single cell-sized
chemical source from the background chemical concentration, providing
high-resolution sensing in both time and space. By contrast, such a source
would be difficult to distinguish from background when diluted throughout the
blood volume as obtained with a blood sample
The TAOS Project: Statistical Analysis of Multi-Telescope Time Series Data
The Taiwanese-American Occultation Survey (TAOS) monitors fields of up to
~1000 stars at 5 Hz simultaneously with four small telescopes to detect
occultation events from small (~1 km) Kuiper Belt Objects (KBOs). The survey
presents a number of challenges, in particular the fact that the occultation
events we are searching for are extremely rare and are typically manifested as
slight flux drops for only one or two consecutive time series measurements. We
have developed a statistical analysis technique to search the multi-telescope
data set for simultaneous flux drops which provides a robust false positive
rejection and calculation of event significance. In this paper, we describe in
detail this statistical technique and its application to the TAOS data set.Comment: 15 pages, 14 figures. Submitted to PAS
A unified view on weakly correlated recurrent networks
The diversity of neuron models used in contemporary theoretical neuroscience
to investigate specific properties of covariances raises the question how these
models relate to each other. In particular it is hard to distinguish between
generic properties and peculiarities due to the abstracted model. Here we
present a unified view on pairwise covariances in recurrent networks in the
irregular regime. We consider the binary neuron model, the leaky
integrate-and-fire model, and the Hawkes process. We show that linear
approximation maps each of these models to either of two classes of linear rate
models, including the Ornstein-Uhlenbeck process as a special case. The classes
differ in the location of additive noise in the rate dynamics, which is on the
output side for spiking models and on the input side for the binary model. Both
classes allow closed form solutions for the covariance. For output noise it
separates into an echo term and a term due to correlated input. The unified
framework enables us to transfer results between models. For example, we
generalize the binary model and the Hawkes process to the presence of
conduction delays and simplify derivations for established results. Our
approach is applicable to general network structures and suitable for
population averages. The derived averages are exact for fixed out-degree
network architectures and approximate for fixed in-degree. We demonstrate how
taking into account fluctuations in the linearization procedure increases the
accuracy of the effective theory and we explain the class dependent differences
between covariances in the time and the frequency domain. Finally we show that
the oscillatory instability emerging in networks of integrate-and-fire models
with delayed inhibitory feedback is a model-invariant feature: the same
structure of poles in the complex frequency plane determines the population
power spectra
Quantum Phase Imaging using Spatial Entanglement
Entangled photons have the remarkable ability to be more sensitive to signal
and less sensitive to noise than classical light. Joint photons can sample an
object collectively, resulting in faster phase accumulation and higher spatial
resolution, while common components of noise can be subtracted. Even more, they
can accomplish this while physically separate, due to the nonlocal properties
of quantum mechanics. Indeed, nearly all quantum optics experiments rely on
this separation, using individual point detectors that are scanned to measure
coincidence counts and correlations. Scanning, however, is tedious, time
consuming, and ill-suited for imaging. Moreover, the separation of beam paths
adds complexity to the system while reducing the number of photons available
for sampling, and the multiplicity of detectors does not scale well for greater
numbers of photons and higher orders of entanglement. We bypass all of these
problems here by directly imaging collinear photon pairs with an
electron-multiplying CCD camera. We show explicitly the benefits of quantum
nonlocality by engineering the spatial entanglement of the illuminating photons
and introduce a new method of correlation measurement by converting time-domain
coincidence counting into spatial-domain detection of selected pixels. We show
that classical transport-of-intensity methods are applicable in the quantum
domain and experimentally demonstrate nearly optimal (Heisenberg-limited) phase
measurement for the given quantum illumination. The methods show the power of
direct imaging and hold much potential for more general types of quantum
information processing and control
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