47,156 research outputs found
A Simple Approach to Maximum Intractable Likelihood Estimation
Approximate Bayesian Computation (ABC) can be viewed as an analytic
approximation of an intractable likelihood coupled with an elementary
simulation step. Such a view, combined with a suitable instrumental prior
distribution permits maximum-likelihood (or maximum-a-posteriori) inference to
be conducted, approximately, using essentially the same techniques. An
elementary approach to this problem which simply obtains a nonparametric
approximation of the likelihood surface which is then used as a smooth proxy
for the likelihood in a subsequent maximisation step is developed here and the
convergence of this class of algorithms is characterised theoretically. The use
of non-sufficient summary statistics in this context is considered. Applying
the proposed method to four problems demonstrates good performance. The
proposed approach provides an alternative for approximating the maximum
likelihood estimator (MLE) in complex scenarios
About the holographic pseudo-Goldstone boson
Pseudo-Goldstone bosons in 4D strongly coupled theories have a dual
description in terms of 5D gauge theories in warped backgrounds. We introduce
systematic methods of computing the pseudo-Goldstone potential for an arbitrary
warp factor in 5D. When applied to electroweak symmetry breaking, our approach
clarifies the relation of physical observables to geometrical quantities in
five dimensions.Comment: 16 page
Millisecond single-molecule localization microscopy combined with convolution analysis and automated image segmentation to determine protein concentrations in complexly structured, functional cells, one cell at a time
We present a single-molecule tool called the CoPro (Concentration of
Proteins) method that uses millisecond imaging with convolution analysis,
automated image segmentation and super-resolution localization microscopy to
generate robust estimates for protein concentration in different compartments
of single living cells, validated using realistic simulations of complex
multiple compartment cell types. We demonstrates its utility experimentally on
model Escherichia coli bacteria and Saccharomyces cerevisiae budding yeast
cells, and use it to address the biological question of how signals are
transduced in cells. Cells in all domains of life dynamically sense their
environment through signal transduction mechanisms, many involving gene
regulation. The glucose sensing mechanism of S. cerevisiae is a model system
for studying gene regulatory signal transduction. It uses the multi-copy
expression inhibitor of the GAL gene family, Mig1, to repress unwanted genes in
the presence of elevated extracellular glucose concentrations. We fluorescently
labelled Mig1 molecules with green fluorescent protein (GFP) via chromosomal
integration at physiological expression levels in living S. cerevisiae cells,
in addition to the RNA polymerase protein Nrd1 with the fluorescent protein
reporter mCherry. Using CoPro we make quantitative estimates of Mig1 and Nrd1
protein concentrations in the cytoplasm and nucleus compartments on a
cell-by-cell basis under physiological conditions. These estimates indicate a
4-fold shift towards higher values in concentration of diffusive Mig1 in the
nucleus if the external glucose concentration is raised, whereas equivalent
levels in the cytoplasm shift to smaller values with a relative change an order
of magnitude smaller. This compares with Nrd1 which is not involved directly in
glucose sensing, which is almost exclusively localized in the nucleus under
high and..
Determinantal equations for secant varieties and the Eisenbud-Koh-Stillman conjecture
We address special cases of a question of Eisenbud on the ideals of secant
varieties of Veronese re-embeddings of arbitrary varieties. Eisenbud's question
generalizes a conjecture of Eisenbud, Koh and Stillman (EKS) for curves. We
prove that set-theoretic equations of small secant varieties to a high degree
Veronese re-embedding of a smooth variety are determined by equations of the
ambient Veronese variety and linear equations. However this is false for
singular varieties, and we give explicit counter-examples to the EKS conjecture
for singular curves. The techniques we use also allow us to prove a gap and
uniqueness theorem for symmetric tensor rank. We put Eisenbud's question in a
more general context about the behaviour of border rank under specialisation to
a linear subspace, and provide an overview of conjectures coming from signal
processing and complexity theory in this context.Comment: 21 pages; presentation improved as suggested by the referees; To
appear in Journal of London Mathematical Societ
Calculating Non-adiabatic Pressure Perturbations during Multi-field Inflation
Isocurvature perturbations naturally occur in models of inflation consisting
of more than one scalar field. In this paper we calculate the spectrum of
isocurvature perturbations generated at the end of inflation for three
different inflationary models consisting of two canonical scalar fields. The
amount of non-adiabatic pressure present at the end of inflation can have
observational consequences through the generation of vorticity and subsequently
the sourcing of B-mode polarisation. We compare two different definitions of
isocurvature perturbations and show how these quantities evolve in different
ways during inflation. Our results are calculated using the open source
Pyflation numerical package which is available to download.Comment: v2: Typos fixed, references and comments added; v1: 8 pages, 10
figures, software available to download at http://pyflation.ianhuston.ne
Supersymmetric extensions of K field theories
We review the recently developed supersymmetric extensions of field theories
with non-standard kinetic terms (so-called K field theories) in two an three
dimensions. Further, we study the issue of topological defect formation in
these supersymmetric theories. Specifically, we find supersymmetric K field
theories which support topological kinks in 1+1 dimensions as well as
supersymmetric extensions of the baby Skyrme model for arbitrary nonnegative
potentials in 2+1 dimensions.Comment: Contribution to the Proceedings of QTS7, Prague, August 201
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