1,308 research outputs found
Linearly continuous maps discontinuous on the graphs of twice differentiable functions
A function g : R n → R is linearly continuous provided its restriction g ` to every straight line ` ⊂ R n is continuous. It is known that the set D(g) of points of discontinuity of any linearly continuous g : R n → R is a countable union of isometric copies of (the graphs of) f P, where f : R n−1 → R is Lipschitz and P ⊂ R n−1 is compact nowhere dense. On the other hand, for every twice continuously differentiable function f : R → R and every nowhere dense perfect P ⊂ R there is a linearly continuous g : R 2 → R with D(g) = f P. The goal of this paper is to show that this last statement fails, if we do not assume that f 00 is continuous. More specifically, we show that this failure occurs for every continuously differentiable function f : R → R with nowhere monotone derivative, which includes twice differentiable functions f with such property. This generalizes a recent result of professor Ludek Zajicek and fully solves a problem from a 2013 paper of the first author and Timothy Glatzer.Depto. de Análisis Matemático y Matemática AplicadaFac. de Ciencias MatemáticasFALSEMinisterio de Ciencia e Innovación (MICINN)/FEDERunpu
George Santayana, The Genteel Tradition in American Philosophy and Character and Opinion in the United States: Edited and with an Introduction by James Seaton. New Haven and London: Yale University Press, 2009. 200pp. $16.00. ISBN-10: 0300116659; ISBN-13: 978-0300116656
A framework for adaptive MCMC targeting multimodal distributions
We propose a new Monte Carlo method for sampling from multimodal distributions. The idea of this technique is based on splitting the task into two: finding the modes of a target distribution π and sampling, given the knowledge of the locations of the modes. The sampling algorithm relies on steps of two types: local ones, preserving the mode; and jumps to regions associated with different modes. Besides, the method learns the optimal parameters of the algorithm while it runs, without requiring user intervention. Our technique should be considered as a flexible framework, in which the design of moves can follow various strategies known from the broad MCMC literature.
In order to design an adaptive scheme that facilitates both local and jump moves, we introduce an auxiliary variable representing each mode and we define a new target distribution π~ on an augmented state space X × I, where X is the original state space of π and I is the set of the modes. As the algorithm runs and updates its parameters, the target distribution π~ also keeps being modified. This motivates a new class of algorithms, Auxiliary Variable Adaptive MCMC. We prove general ergodic results for the whole class before specialising to the case of our algorithm
The Formation and Gravitational-Wave Detection of Massive Stellar Black-Hole Binaries
If binaries consisting of two 100 Msun black holes exist they would serve as
extraordinarily powerful gravitational-wave sources, detectable to redshifts of
z=2 with the advanced LIGO/Virgo ground-based detectors. Large uncertainties
about the evolution of massive stars preclude definitive rate predictions for
mergers of these massive black holes. We show that rates as high as hundreds of
detections per year, or as low as no detections whatsoever, are both possible.
It was thought that the only way to produce these massive binaries was via
dynamical interactions in dense stellar systems. This view has been challenged
by the recent discovery of several stars with mass above 150 Msun in the R136
region of the Large Magellanic Cloud. Current models predict that when stars of
this mass leave the main sequence, their expansion is insufficient to allow
common envelope evolution to efficiently reduce the orbital separation. The
resulting black-hole--black-hole binary remains too wide to be able to coalesce
within a Hubble time. If this assessment is correct, isolated very massive
binaries do not evolve to be gravitational-wave sources. However, other
formation channels exist. For example, the high multiplicity of massive stars,
and their common formation in relatively dense stellar associations, opens up
dynamical channels for massive black hole mergers (e.g., via Kozai cycles or
repeated binary-single interactions). We identify key physical factors that
shape the population of very massive black-hole--black-hole binaries. Advanced
gravitational-wave detectors will provide important constraints on the
formation and evolution of very massive stars.Comment: ApJ accepted, extended description of modelin
The role of supernova convection for the lower mass gap and the isolated binary formation of gravitational wave sources
Understanding astrophysical phenomena involving compact objects requires an
insight about the engine behind core-collapse supernovae (SNe) and the fate of
the stellar collapse of massive stars. In particular, this insight is crucial
in developing an understanding of the origin and formation channels of detected
population of BH-BH, BH-NS and NS-NS mergers. To gain this understanding, we
must tie our current knowledge of pre-SN stars properties and their potential
explosions to the final NS or BH mass distribution. The timescale of convection
growth may have a large effect on the strength of SN explosion and therefore
also on the mass distribution of stellar remnants. In this study we adopt the
new formulas for the relation between the pre-SN star properties and its
remnant from Fryer et al. 2022 in prep. into StarTrack population synthesis
code and check how they impact double compact object (DCO) mergers formed via
isolated binary evolution. The new formulas give one ability to test a wide
spectrum of assumptions on the convection growth time. In particular, different
variants allow for a smooth transition between having a deep lower mass gap and
a remnant mass distribution filled by massive NSs and low mass BHs. In this
paper we present distribution of masses, mass ratios and the local merger rate
densities of DCO mergers for different variants of new remnant mass formulas.
We test them together with different approaches to other highly uncertain
processes. We find that mass distribution of DCO mergers up to m_1+m_2 < 35
Msun is sensitive to adopted assumption on SN convection growth timescale.
Between the two extreme tested variants the probability of compact object
formation within the lower mass gap may differ up to 2 orders of magnitude. The
mass ratio distribution of DCO mergers is significantly influenced by SN model
only for our standard mass transfer stability criteria.Comment: 20 pages, submitted to MNRAS, comments welcom
Captions in 360 Video : Rapid Prototyping for User Testing
Extended reality is reinventing our approach to work, learning, culture, and social interaction. Nevertheless, the integration of accessible services within immersive environments is still in progress. This presentation will introduce new prototyping for immersive captioning and discuss how to achieve an optimal and fully inclusive viewing experience
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