22,925 research outputs found
Consistency of Markov chain quasi-Monte Carlo on continuous state spaces
The random numbers driving Markov chain Monte Carlo (MCMC) simulation are
usually modeled as independent U(0,1) random variables. Tribble [Markov chain
Monte Carlo algorithms using completely uniformly distributed driving sequences
(2007) Stanford Univ.] reports substantial improvements when those random
numbers are replaced by carefully balanced inputs from completely uniformly
distributed sequences. The previous theoretical justification for using
anything other than i.i.d. U(0,1) points shows consistency for estimated means,
but only applies for discrete stationary distributions. We extend those results
to some MCMC algorithms for continuous stationary distributions. The main
motivation is the search for quasi-Monte Carlo versions of MCMC. As a side
benefit, the results also establish consistency for the usual method of using
pseudo-random numbers in place of random ones.Comment: Published in at http://dx.doi.org/10.1214/10-AOS831 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Generalized curve fit and plotting (GECAP) program
Program generates graphs on 8 1/2 by 11 inch paper and is designed to be used by engineers and scientists who are not necessarily professional programers. It provides fast and efficient method for display of plotted data without having to generate any additional FORTRAN instructions
A family of filters to search for frequency dependent gravitational wave stochastic backgrounds
We consider a three dimensional family of filters based on broken power law
spectra to search for gravitational wave stochastic backgrounds in the data
from Earth-based laser interferometers. We show that such templates produce the
necessary fitting factor for a wide class of cosmological backgrounds and
astrophysical foregrounds and that the total number of filters required to
search for those signals in the data from first generation laser
interferometers operating at the design sensitivity is fairly smallComment: 4 pages, 4 figures, uses iopart.cls, accepted for publications on
Classical and Quantum Gravity (Special Issue, Proceedings of Amaldi 2003
Optimal randomized multilevel algorithms for infinite-dimensional integration on function spaces with ANOVA-type decomposition
In this paper, we consider the infinite-dimensional integration problem on
weighted reproducing kernel Hilbert spaces with norms induced by an underlying
function space decomposition of ANOVA-type. The weights model the relative
importance of different groups of variables. We present new randomized
multilevel algorithms to tackle this integration problem and prove upper bounds
for their randomized error. Furthermore, we provide in this setting the first
non-trivial lower error bounds for general randomized algorithms, which, in
particular, may be adaptive or non-linear. These lower bounds show that our
multilevel algorithms are optimal. Our analysis refines and extends the
analysis provided in [F. J. Hickernell, T. M\"uller-Gronbach, B. Niu, K.
Ritter, J. Complexity 26 (2010), 229-254], and our error bounds improve
substantially on the error bounds presented there. As an illustrative example,
we discuss the unanchored Sobolev space and employ randomized quasi-Monte Carlo
multilevel algorithms based on scrambled polynomial lattice rules.Comment: 31 pages, 0 figure
c-Src drives intestinal regeneration and transformation
The nonâreceptor tyrosine kinase câSrc, hereafter referred to as Src, is overexpressed or activated in multiple human malignancies. There has been much speculation about the functional role of Src in colorectal cancer (CRC), with Src amplification and potential activating mutations in up to 20% of the human tumours, although this has never been addressed due to multiple redundant family members. Here, we have used the adult <i>Drosophila</i> and mouse intestinal epithelium as paradigms to define a role for Src during tissue homeostasis, damageâinduced regeneration and hyperplasia. Through genetic gain and loss of function experiments, we demonstrate that Src is necessary and sufficient to drive intestinal stem cell (ISC) proliferation during tissue selfârenewal, regeneration and tumourigenesis. Surprisingly, Src plays a nonâredundant role in the mouse intestine, which cannot be substituted by the other family kinases Fyn and Yes. Mechanistically, we show that Src drives ISC proliferation through upregulation of EGFR and activation of Ras/MAPK and Stat3 signalling. Therefore, we demonstrate a novel essential role for Src in intestinal stem/progenitor cell proliferation and tumourigenesis initiation <i>in vivo.</i>
The Motion of a Body in Newtonian Theories
A theorem due to Bob Geroch and Pong Soo Jang ["Motion of a Body in General
Relativity." Journal of Mathematical Physics 16(1), (1975)] provides the sense
in which the geodesic principle has the status of a theorem in General
Relativity (GR). Here we show that a similar theorem holds in the context of
geometrized Newtonian gravitation (often called Newton-Cartan theory). It
follows that in Newtonian gravitation, as in GR, inertial motion can be derived
from other central principles of the theory.Comment: 12 pages, 1 figure. This is the version that appeared in JMP; it is
only slightly changed from the previous version, to reflect small issue
caught in proo
Low voltage control of ferromagnetism in a semiconductor p-n junction
The concept of low-voltage depletion and accumulation of electron charge in
semiconductors, utilized in field-effect transistors (FETs), is one of the
cornerstones of current information processing technologies. Spintronics which
is based on manipulating the collective state of electron spins in a
ferromagnet provides complementary technologies for reading magnetic bits or
for the solid-state memories. The integration of these two distinct areas of
microelectronics in one physical element, with a potentially major impact on
the power consumption and scalability of future devices, requires to find
efficient means for controlling magnetization electrically. Current induced
magnetization switching phenomena represent a promising step towards this goal,
however, they relay on relatively large current densities. The direct approach
of controlling the magnetization by low-voltage charge depletion effects is
seemingly unfeasible as the two worlds of semiconductors and metal ferromagnets
are separated by many orders of magnitude in their typical carrier
concentrations. Here we demonstrate that this concept is viable by reporting
persistent magnetization switchings induced by short electrical pulses of a few
volts in an all-semiconductor, ferromagnetic p-n junction.Comment: 11 pages, 4 figure
A Comprehensive Radio and Optical Study of Abell 2256: Activity from an Infalling Group
Abell 2256 is a nearby (z~0.06), rich cluster of galaxies with fascinating
observed properties across a range of wavelengths. Long believed to represent a
cluster merger, recent X-ray and optical results have suggested that in
addition to the primary cluster and subcluster there is evidence for a third,
poorer system. We present wide-field, high sensitivity 1.4 GHz VLA radio
observations of Abell 2256 in conjunction with optical imaging and additional
spectroscopy. Over 40 cluster radio galaxies are identified, with optical
spectroscopy indicating the emission source (star formation or AGN) for most of
them. While the overall fraction of galaxies exhibiting radio emission is
consistent with a large sample of other nearby clusters, we find an increase in
the activity level of galaxies belonging to the third system (hereafter, the
``Group''). Specifically, the Group has relatively more star formation than
both the primary cluster and main subcluster. The position of the Group is also
coincident with the observed cluster radio relic. We suggest that the Group
recently (~0.3 Gyr) merged with the primary cluster and that this merger, not
the ongoing merger of the primary and the main subcluster, might be responsible
for many of the unusual radio properties of Abell 2256. Furthermore, the
greater star formation activity of the Group suggests that the infall of groups
is an important driver of galaxy evolution in clusters.Comment: 21 pages plus 13 JPEG figures; to appear in the Astronomical Journa
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