1,725 research outputs found
Beyond the Small-Angle Approximation For MBR Anisotropy from Seeds
In this paper we give a general expression for the energy shift of massless
particles travelling through the gravitational field of an arbitrary matter
distribution as calculated in the weak field limit in an asymptotically flat
space-time. It is {\it not} assumed that matter is non-relativistic. We
demonstrate the surprising result that if the matter is illuminated by a
uniform brightness background that the brightness pattern observed at a given
point in space-time (modulo a term dependent on the oberver's velocity) depends
only on the matter distribution on the observer's past light-cone. These
results apply directly to the cosmological MBR anisotropy pattern generated in
the immediate vicinity of of an object like a cosmic string or global texture.
We apply these results to cosmic strings, finding a correction to previously
published results for in the small-angle approximation. We also derive the
full-sky anisotropy pattern of a collapsing texture knot.Comment: 23 pages, FERMILAB-Pub-94/047-
A Causal Source which Mimics Inflation
How unique are the inflationary predictions for the cosmic microwave
anisotropy pattern? In this paper, it is asked whether an arbitrary causal
source for perturbations in the standard hot big bang could effectively mimic
the predictions of the simplest inflationary models. A surprisingly simple
example of a `scaling' causal source is found to closely reproduce the
inflationary predictions. This letter extends the work of a previous paper
(ref. 6) to a full computation of the anisotropy pattern, including the Sachs
Wolfe integral. I speculate on the possible physics behind such a source.Comment: 4 pages, RevTex, 3 figure
Shape Dynamical Models for Activity Recognition and Coded Aperture Imaging for Light-Field Capture
Classical applications of Pattern recognition in image processing and computer vision have typically dealt with modeling, learning and recognizing static patterns in images and videos.
There are, of course, in nature, a whole class of patterns that dynamically evolve over time.
Human activities, behaviors of insects and animals, facial expression changes, lip reading, genetic expression profiles are some examples of patterns that are dynamic.
Models and algorithms to study these patterns must take into account the dynamics of these patterns while exploiting the classical pattern recognition techniques.
The first part of this dissertation is an attempt to model and recognize such dynamically evolving patterns.
We will look at specific instances of such dynamic patterns like human activities, and behaviors of insects and develop algorithms to learn models of such patterns and classify such patterns.
The models and algorithms proposed are validated by extensive experiments on gait-based person identification, activity recognition and simultaneous tracking and behavior analysis of insects.
The problem of comparing dynamically deforming shape sequences arises repeatedly in problems like activity recognition and lip reading.
We describe and evaluate parametric and non-parametric models for shape sequences.
In particular, we emphasize the need to model activity execution rate variations and propose a non-parametric model that is insensitive to such variations.
These models and the resulting algorithms are shown to be extremely effective for a wide range of applications from gait-based person identification to human action recognition.
We further show that the shape dynamical models are not only effective for the problem of recognition, but also can be used as effective priors for the problem of simultaneous tracking and behavior analysis.
We validate the proposed algorithm for performing simultaneous behavior analysis and tracking on videos of bees dancing in a hive.
In the last part of this dissertaion, we investigate computational imaging, an emerging field where the process of image formation involves the use of a computer.
The current trend in computational imaging is to capture as much information about the scene as possible during capture time so that appropriate images with varying focus, aperture, blur and colorimetric settings may be rendered as required.
In this regard, capturing the 4D light-field as opposed to a 2D image allows us to freely vary viewpoint and focus at the time of rendering an image.
In this dissertation, we describe a theoretical framework for reversibly modulating {4D} light fields using an attenuating mask in the optical path of a lens based camera.
Based on this framework, we present a novel design to reconstruct the {4D} light field from a {2D} camera image without
any additional refractive elements as required by previous light field cameras.
The patterned mask attenuates light rays inside the camera instead
of bending them, and the attenuation recoverably encodes the rays on
the {2D} sensor. Our mask-equipped camera focuses just as a traditional camera to capture conventional {2D} photos at full
sensor resolution, but the raw pixel values also hold a modulated
{4D} light field. The light field can be recovered by rearranging
the tiles of the {2D} Fourier transform of sensor values into {4D}
planes, and computing the inverse Fourier transform.
In addition, one can also recover the full resolution image information for the in-focus parts
of the scene
The Doppler Peaks from Cosmic Texture
We compute the angular power spectrum of temperature anisotropies on the
microwave sky in the cosmic texture theory, with standard recombination
assumed. The spectrum shows `Doppler' peaks analogous to those in scenarios
based on primordial adiabatic fluctuations such as `standard CDM', but at quite
different angular scales. There appear to be excellent prospects for using this
as a discriminant between inflationary and cosmic defect theories.Comment: 14 pages, latex, 3 figures, compressed and uuencoded, replaced
version has minor typographical correction
Cardiac Arrhythmias as Manifestations of Nanopathies: An Emerging View
A nanodomain is a collection of proteins localized within a specialized, nanoscale structural environment, which can serve as the functional unit of macroscopic physiologic processes. We are beginning to recognize the key roles of cardiomyocyte nanodomains in essential processes of cardiac physiology such as electrical impulse propagation and excitationâcontraction coupling (ECC). There is growing appreciation of nanodomain dysfunction, i.e., nanopathy, as a mechanistic driver of life-threatening arrhythmias in a variety of pathologies. Here, we offer an overview of current research on the role of nanodomains in cardiac physiology with particular emphasis on: (1) sodium channel-rich nanodomains within the intercalated disk that participate in cell-to-cell electrical coupling and (2) dyadic nanodomains located along transverse tubules that participate in ECC. The beat to beat function of cardiomyocytes involves three phases: the action potential, the calcium transient, and mechanical contraction/relaxation. In all these phases, cell-wide function results from the aggregation of the stochastic function of individual proteins. While it has long been known that proteins that exist in close proximity influence each otherâs function, it is increasingly appreciated that there exist nanoscale structures that act as functional units of cardiac biophysical phenomena. Termed nanodomains, these structures are collections of proteins, localized within specialized nanoscale structural environments. The nano-environments enable the generation of localized electrical and/or chemical gradients, thereby conferring unique functional properties to these units. Thus, the function of a nanodomain is determined by its protein constituents as well as their local structural environment, adding an additional layer of complexity to cardiac biology and biophysics. However, with the emergence of experimental techniques that allow direct investigation of structure and function at the nanoscale, our understanding of cardiac physiology and pathophysiology at these scales is rapidly advancing. Here, we will discuss the structure and functions of multiple cardiomyocyte nanodomains, and novel strategies that target them for the treatment of cardiac arrhythmias
Conservation Laws and Cosmological Perturbations in Curved Universes
When working in synchronous gauges, pseudo-tensor conservation laws are often
used to set the initial conditions for cosmological scalar perturbations, when
those are generated by topological defects which suddenly appear in an up to
then perfectly homogeneous and isotropic universe. However those conservation
laws are restricted to spatially flat (K=0) Friedmann-Lema\^\i tre spacetimes.
In this paper, we first show that in fact they implement a matching condition
between the pre- and post- transition eras and, in doing so, we are able to
generalize them and set the initial conditions for all . Finally, in the
long wavelength limit, we encode them into a vector conservation law having a
well-defined geometrical meaning.Comment: 15 pages, no figure, to appear in Phys. Rev.
Cosmic Strings in an Open Universe with Baryonic and Non-Baryonic Dark Matter
We study the effects of cosmic strings on structure formation in open
universes. We calculate the power spectrum of density perturbations for two
class of models: one in which all the dark matter is non baryonic (CDM) and one
in which it is all baryonic (BDM). Our results are compared to the 1 in 6 IRAS
QDOT power spectrum. The best candidates are then used to estimate , the
energy per unit length of the string network. Some comments are made on
mechanisms by which structures are formed in the two theories.Comment: uu-encoded compressed tar of postscript files, Imperial/TP/94-95/0
Spatiotemporal patterns of cholera hospitalization in Vellore, India
Systematically collected hospitalization records provide valuable insight into disease patterns and support comprehensive national infectious disease surveillance networks. Hospitalization records detailing patientâs place of residence (PoR) can be utilized to better understand a hospitalâs case load and strengthen surveillance among mobile populations. This study examined geographic patterns of patients treated for cholera at a major hospital in south India. We abstracted 1401 laboratory-confirmed cases of cholera between 2000â2014 from logbooks and electronic health records (EHRs) maintained by the Christian Medical College (CMC) in Vellore, Tamil Nadu, India. We constructed spatial trend models and identified two distinct clusters of patient residenceâone around Vellore (836 records (61.2%)) and one in Bengal (294 records (21.5%)). We further characterized differences in peak timing and disease trend among these clusters to identify differences in cholera exposure among local and visiting populations. We found that the two clusters differ by their patient profiles, with patients in the Bengal cluster being most likely older males traveling to Vellore. Both clusters show well-aligned seasonal peaks in mid-July, only one week apart, with similar downward trend and proportion of predominant O1 serotype. Large hospitals can thus harness EHRs for surveillance by utilizing patientsâ PoRs to study disease patterns among resident and visitor populations
CMB polarization as a direct test of Inflation
We study the auto-correlation function of CMB polarization anisotropies and
their cross correlation with temperature fluctuations as probe of the causal
structure of the universe. Because polarization is generated at the last
scattering surface, models in which fluctuations are causally produced on
sub-horizon scales cannot generate correlations on scales larger then . Inflationary models, on the other hand, predict a peak in the correlation
functions at these scales: its detection would be definitive evidence in favor
of a period of inflation. This signal could be detected with the next
generation of satellites.Comment: 4 pages, 1 figure. Minor changes to match the Phys. Rev. Lett.
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