239 research outputs found
Templates for Convex Cone Problems with Applications to Sparse Signal Recovery
This paper develops a general framework for solving a variety of convex cone
problems that frequently arise in signal processing, machine learning,
statistics, and other fields. The approach works as follows: first, determine a
conic formulation of the problem; second, determine its dual; third, apply
smoothing; and fourth, solve using an optimal first-order method. A merit of
this approach is its flexibility: for example, all compressed sensing problems
can be solved via this approach. These include models with objective
functionals such as the total-variation norm, ||Wx||_1 where W is arbitrary, or
a combination thereof. In addition, the paper also introduces a number of
technical contributions such as a novel continuation scheme, a novel approach
for controlling the step size, and some new results showing that the smooth and
unsmoothed problems are sometimes formally equivalent. Combined with our
framework, these lead to novel, stable and computationally efficient
algorithms. For instance, our general implementation is competitive with
state-of-the-art methods for solving intensively studied problems such as the
LASSO. Further, numerical experiments show that one can solve the Dantzig
selector problem, for which no efficient large-scale solvers exist, in a few
hundred iterations. Finally, the paper is accompanied with a software release.
This software is not a single, monolithic solver; rather, it is a suite of
programs and routines designed to serve as building blocks for constructing
complete algorithms.Comment: The TFOCS software is available at http://tfocs.stanford.edu This
version has updated reference
Nonlinear Dynamical Stability of Newtonian Rotating White Dwarfs and Supermassive Stars
We prove general nonlinear stability and existence theorems for rotating star
solutions which are axi-symmetric steady-state solutions of the compressible
isentropic Euler-Poisson equations in 3 spatial dimensions. We apply our
results to rotating and non-rotating white dwarf, and rotating high density
supermassive (extreme relativistic) stars, stars which are in convective
equilibrium and have uniform chemical composition. This paper is a continuation
of our earlier work ([28])
Existence and Nonlinear Stability of Rotating Star Solutions of the Compressible Euler-Poisson Equations
We prove existence of rotating star solutions which are steady-state
solutions of the compressible isentropic Euler-Poisson (EP) equations in 3
spatial dimensions, with prescribed angular momentum and total mass. This
problem can be formulated as a variational problem of finding a minimizer of an
energy functional in a broader class of functions having less symmetry than
those functions considered in the classical Auchmuty-Beals paper. We prove the
nonlinear dynamical stability of these solutions with perturbations having the
same total mass and symmetry as the rotating star solution. We also prove local
in time stability of W^{1, \infty}(\RR^3) solutions where the perturbations
are entropy-weak solutions of the EP equations. Finally, we give a uniform (in
time) a-priori estimate for entropy-weak solutions of the EP equations
Slow relaxation in weakly open vertex-splitting rational polygons
The problem of splitting effects by vertex angles is discussed for
nonintegrable rational polygonal billiards. A statistical analysis of the decay
dynamics in weakly open polygons is given through the orbit survival
probability. Two distinct channels for the late-time relaxation of type
1/t^delta are established. The primary channel, associated with the universal
relaxation of ''regular'' orbits, with delta = 1, is common for both the closed
and open, chaotic and nonchaotic billiards. The secondary relaxation channel,
with delta > 1, is originated from ''irregular'' orbits and is due to the
rationality of vertices.Comment: Key words: Dynamics of systems of particles, control of chaos,
channels of relaxation. 21 pages, 4 figure
The metabolic syndrome and risk of sudden cardiac death: The atherosclerosis risk in communities study
Background--Prior studies have demonstrated a link between the metabolic syndrome and increased risk of cardiovascular mortality. Whether the metabolic syndrome is associated with sudden cardiac death is uncertain. Methods and Results--We characterized the relationship between sudden cardiac death and metabolic syndrome status among participants of the ARIC (Atherosclerosis Risk in Communities) Study (1987-2012) free of prevalent coronary heart disease or heart failure. Among 13 168 participants, 357 (2.7%) sudden cardiac deaths occurred during a median follow-up of 23.6 years. Participants with the metabolic syndrome (n=4444) had a higher cumulative incidence of sudden cardiac death than those without it (n=8724) (4.1% versus 2.3%, P < 0.001). After adjustment for participant demographics and clinical factors other than components of the metabolic syndrome, the metabolic syndrome was independently associated with sudden cardiac death (hazard ratio, 1.70, 95% confidence interval, 1.37-2.12, P < 0.001). This relationship was not modified by sex (interaction P=0.10) or race (interaction P=0.62) and was mediated by the metabolic syndrome criteria components. The risk of sudden cardiac death varied according to the number of metabolic syndrome components (hazard ratio 1.31 per additional component of the metabolic syndrome, 95% confidence interval, 1.19-1.44, P < 0.001). Of the 5 components, elevated blood pressure, impaired fasting glucose, and low high-density lipoprotein were independently associated with sudden cardiac death. Conclusions--We observed that the metabolic syndrome was associated with a significantly increased risk of sudden cardiac death irrespective of sex or race. The risk of sudden cardiac death was proportional to the number of metabolic syndrome components
Stellar structure and compact objects before 1940: Towards relativistic astrophysics
Since the mid-1920s, different strands of research used stars as "physics
laboratories" for investigating the nature of matter under extreme densities
and pressures, impossible to realize on Earth. To trace this process this paper
is following the evolution of the concept of a dense core in stars, which was
important both for an understanding of stellar evolution and as a testing
ground for the fast-evolving field of nuclear physics. In spite of the divide
between physicists and astrophysicists, some key actors working in the
cross-fertilized soil of overlapping but different scientific cultures
formulated models and tentative theories that gradually evolved into more
realistic and structured astrophysical objects. These investigations culminated
in the first contact with general relativity in 1939, when J. Robert
Oppenheimer and his students George Volkoff and Hartland Snyder systematically
applied the theory to the dense core of a collapsing neutron star. This
pioneering application of Einstein's theory to an astrophysical compact object
can be regarded as a milestone in the path eventually leading to the emergence
of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal
Mastocytosis: a Rare Case of Anaphylaxis in Paediatric Age and Literature Review
The term “mastocytosis” denotes a heterogeneous group of disorders characterised by abnormal growth and accumulation of mast cells (MC) in one
or more organ systems. Symptoms result from MC chemical mediator’s release, pathologic infiltration of neoplastic MC in tissues or both. Multiple molecular, genetic and chromosomal defects seem to contribute
to an autonomous growth, but somatic c-kit
D816V mutation is more frequently encountered, especially in systemic disease.
We present a literature review of mastocytosis and a rare case report of an 18 month-old-girl with a bullous dermatosis, respiratory distress and anaphylaxis,
as clinical manifestations of mastocytosis.
The developments of accepted classification systems and novel useful markers allowed a re-evaluation and updating of the classification of mastocytosis.
In paediatric age cutaneous forms of disease
prevail and may regress spontaneously. SM is more frequently diagnosed in adults and is a persistent(clonal) disease of bone marrow. The clinical course in these patients is variable.Today diagnostic criteria for each disease variant are reasonably well defined. There are, however, peculiarities,
namely in paediatric age, that makes the diagnostic approach difficult. Systemic disease may pose differential diagnostic problems resulting from multiple organ systems involvement. Coversly, the “unexplained” appearance of those symptoms with no skin lesions should raise the suspicion of MC disease. This case is reported in order to stress the clinical
severity and difficult diagnostic approach that paediatric mastocytosis may assume
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