102 research outputs found
Horizon fluxes of binary black holes in eccentric orbits
I compute the rate of change of mass and angular momentum of a black hole,
namely tidal heating, in an eccentric orbit. The change is caused due to the
tidal field of the orbiting companion. I compute the result for both the
spinning and non-spinning black holes in the leading order of the mean motion,
namely . I demonstrate that the rates get enhanced significantly for
nonzero eccentricity. Since eccentricity in a binary evolves with time I also
express the results in terms of an initial eccentricity and azimuthal frequency
. In the process, I developed a prescription that can be used to
compute all physical quantities in a series expansion of initial eccentricity,
. This result was only known in the leading order while ignoring the
contribution of the spin on the eccentricity evolution. Although the
eccentricity evolution result still ignores the spin effect in the current
work, the prescription can be used to compute higher-order corrections of
initial eccentricity post-leading order. Using this result I computed the rate
of change of mass and angular momentum of a black hole in terms of initial
eccentricity and azimuthal frequency up to .Comment: arXiv admin note: text overlap with arXiv:1605.00304 by other author
On the Consistency of Maximum Likelihood Estimation of Probabilistic Principal Component Analysis
Probabilistic principal component analysis (PPCA) is currently one of the
most used statistical tools to reduce the ambient dimension of the data. From
multidimensional scaling to the imputation of missing data, PPCA has a broad
spectrum of applications ranging from science and engineering to quantitative
finance.
Despite this wide applicability in various fields, hardly any theoretical
guarantees exist to justify the soundness of the maximal likelihood (ML)
solution for this model. In fact, it is well known that the maximum likelihood
estimation (MLE) can only recover the true model parameters up to a rotation.
The main obstruction is posed by the inherent identifiability nature of the
PPCA model resulting from the rotational symmetry of the parameterization. To
resolve this ambiguity, we propose a novel approach using quotient topological
spaces and in particular, we show that the maximum likelihood solution is
consistent in an appropriate quotient Euclidean space. Furthermore, our
consistency results encompass a more general class of estimators beyond the
MLE. Strong consistency of the ML estimate and consequently strong covariance
estimation of the PPCA model have also been established under a compactness
assumption.Comment: 15 pages, 1 figure, to appear in NeurIPS 2023. Update: included minor
typographical correction
Relativistic tidal properties of superfluid neutron stars
We investigate the tidal deformability of a superfluid neutron star. We
calculate the equilibrium structure in the general relativistic two-fluid
formalism with entrainment effect where we take neutron superfluid as one fluid
and the other fluid is comprised of protons and electrons, making it a charge
neutral fluid. We use a relativistic mean field model for the equation of state
of matter where the interaction between baryons is mediated by the exchange
, and mesons. Then, we study the linear, static
perturbation on the star to compute the electric-type Love number following
Hinderer's prescription.Comment: Accepted for publication in Physical Review
Imprint of black hole area quantization and Hawking radiation on inspiraling binary
We study the potential of gravitational wave astronomy to observe the quantum
aspects of black holes. According to Bekenstein's quantization, we find that
black hole area discretization can have observable imprints on the
gravitational wave signal from an inspiraling binary black hole. We study the
impact of quantization on tidal heating. We model the absorption lines and
compute gravitational wave flux due to tidal heating in such a case. By
including the quantization we find the dephasing of the gravitational wave, to
our knowledge it has never been done before. We discuss the observability of
the phenomena in different parameter ranges of the binary. We show that in the
inspiral, it leads to vanishing tidal heating for the high spin values.
Therefore measuring non-zero tidal heating can rule out area quantization. We
also argue that if area quantization is present in nature then our current
modeling with reflectivity can possibly probe the Hawking radiation which may
bring important information regarding the quantum nature of gravity
Synthesis of gold nano-particles in a microfluidic platform for water quality monitoring applications
A microfluidic lab-on-a-chip (LOC) device for in-situ synthesis of gold nano-particles
was developed. The long term goal is to develop a portable hand-held diagnostic
platform for monitoring water quality (e.g., detecting metal ion pollutants).
The LOC consists of micro-chambers housing different reagents and samples that feed to
a common reaction chamber. The reaction products are delivered to several waste
chambers in a pre-defined sequence to enable reagents/ samples to flow into and out of
the reaction chamber. Passive flow actuation is obtained by capillary driven flow
(wicking) and dissolvable microstructures called ‘salt pillars’. The LOC does not require
any external power source for actuation and the passive microvalves enable flow
actuation at predefined intervals. The LOC and the dissolvable microstructures are
fabricated using a combination of photolithography and soft lithography techniques.
Experiments were conducted to demonstrate the variation in the valve actuation time
with respect to valve position and geometric parameters. Subsequently, analytical models were developed using one dimensional linear diffusion theory. The analytical
models were in good agreement with the experimental data. The microvalves were
developed using various salts: polyethylene glycol, sodium chloride and sodium acetate.
Synthesized in-situ in our experiments, gold nano-particles exhibit specific colorimetric
and optical properties due to the surface plasmon resonance effect. These stabilized
mono-disperse gold nano-particles can be coated with bio-molecular recognition motifs
on their surfaces. A colorimetric peptide assay was thus developed using the intrinsic
property of noble metal nano-particles. The LOC device was further developed on a
paper microfluidics platform. This platform was tested successfully for synthesis of gold
nano-particles using a peptide assay and using passive salt-bridge microvalves.
This study proves the feasibility of a LOC device that utilizes peptide assay for
synthesis of gold nano-particles in-situ. It could be highly significant in a simple
portable water quality monitoring platform
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