15,084 research outputs found
On separable Fokker-Planck equations with a constant diagonal diffusion matrix
We classify (1+3)-dimensional Fokker-Planck equations with a constant
diagonal diffusion matrix that are solvable by the method of separation of
variables. As a result, we get possible forms of the drift coefficients
providing separability of the
corresponding Fokker-Planck equations and carry out variable separation in the
latter. It is established, in particular, that the necessary condition for the
Fokker-Planck equation to be separable is that the drift coefficients must be linear. We also find the necessary condition for
R-separability of the Fokker-Planck equation. Furthermore, exact solutions of
the Fokker-Planck equation with separated variables are constructedComment: 20 pages, LaTe
Maximal Abelian Subgroups of the Isometry and Conformal Groups of Euclidean and Minkowski Spaces
The maximal Abelian subalgebras of the Euclidean e(p,0) and pseudoeuclidean
e(p,1)Lie algebras are classified into conjugacy classes under the action of
the corresponding Lie groups E(p,0) and E(p,1), and also under the conformal
groups O(p+1,1) and O(p+1,2), respectively. The results are presented in terms
of decomposition theorems. For e(p,0) orthogonally indecomposable MASAs exist
only for p=1 and p=2. For e(p,1), on the other hand, orthogonally
indecomposable MASAs exist for all values of p. The results are used to
construct new coordinate systems in which wave equations and Hamilton-Jacobi
equations allow the separation of variables.Comment: 31 pages, Latex (+ latexsym
Quantum Pair Creation of Soliton Domain Walls
A large body of experimental evidence suggests that the decay of the false
vacuum, accompanied by quantum pair creation of soliton domain walls, can occur
in a variety of condensed matter systems. Examples include nucleation of charge
soliton pairs in density waves [eg. J. H. Miller, Jr. et al., Phys. Rev. Lett.
84, 1555 (2000)] and flux soliton pairs in long Josephon junctions. Recently,
Dias and Lemos [J. Math. Phys. 42, 3292 (2001)] have argued that the mass
of the soliton should be interpreted as a line density and a surface density,
respectively, for (2+1)-D and (3+1)-D systems in the expression for the pair
production rate. As the transverse dimensions are increased and the total mass
(energy) becomes large, thermal activation becomes suppressed, so quantum
processes can dominate even at relatively high temperatures. This paper will
discuss both experimental evidence and theoretical arguments for the existence
of high-temperature collective quantum phenomena
Quasi-equilibria in one-dimensional self-gravitating many body systems
The microscopic dynamics of one-dimensional self-gravitating many-body
systems is studied. We examine two courses of the evolution which has the
isothermal and stationary water-bag distribution as initial conditions. We
investigate the evolution of the systems toward thermal equilibrium. It is
found that when the number of degrees of freedom of the system is increased,
the water-bag distribution becomes a quasi-equilibrium, and also the
stochasticity of the system reduces. This results suggest that the phase space
of the system is effectively not ergodic and the system with large degreees of
freedom approaches to the near-integrable one.Comment: 21pages + 7 figures (available upon request), revtex, submitted to
Physical Review
A quark model analysis of the charge symmetry breaking in nuclear force
In order to investigate the charge symmetry breaking (CSB) in the short range
part of the nuclear force, we calculate the difference of the masses of the
neutron and the proton, , the difference of the scattering
lengths of the p-p and n-n scatterings, , and the difference of the
analyzing power of the proton and the neutron in the n-p scattering, , by a quark model. In the present model the sources of CSB are the
mass difference of the up and down quarks and the electromagnetic interaction.
We investigate how much each of them contributes to , and . It is found that the contribution of CSB of the
short range part in the nuclear force is large enough to explain the observed
, while is rather underestimated.Comment: 26 pages,6 figure
Taxus and taxol: a compilation of research findings
History of the development of taxol as a cancer-fighting drug -- Traditional uses of yews -- A history of yews in the United States / Kenneth D. Cochran -- Taxus populations and clippings yields at commercial nurseries / Robert C. Hansen, Kenneth D. Cochran, Harold M. Keener and Edward M. Croom Jr. -- Genetic resources for ornamental Taxus in the United States / Kenneth D. Cochran -- Root rot of Taxus spp. in Ohio caused by Phytophthora cinnamomi / Michael A. Ellis, Sally A. Miller, A. F. Schmitthenner and Kenneth D. Cochran -- Growth rate of container-grown Taxus x media 'Hicksii' and 'Densiformis' compared at two levels of nutrition and irrigation / Robert C. Hansen, Kenneth D. Cochran and R. Peter Fynn -- Taxus clipping harvester / Robert G. Holmes and Don Wertz -- Thin-layer drying of cultivated Taxus clippings / Robert C. Hansen, Harold M. Keener and Hala N. ElSohly -- Evaluation of bin drying of Taxus biomass / Robert C. Hansen, Ralph B. Shugert Jr., Hala N. ElSohly, Edward M. Croom Jr., Harld M. Keener -- Selecting bed depth for drying cultivated Taxus clippings / Robert C. Hansen and Harold M. Keener -- Progress report and summary: National Cancer Institute Workshop on Taxus, Taxol, and Taxotere / Robert C. Hansen, Robert G. Holmes, Ralph B. Shugert Jr., Edward M. Croom Jr., Hala N. ElSohly, Harold M. Keener and Kenneth D. Cochra
Seeing Tree Structure from Vibration
Humans recognize object structure from both their appearance and motion;
often, motion helps to resolve ambiguities in object structure that arise when
we observe object appearance only. There are particular scenarios, however,
where neither appearance nor spatial-temporal motion signals are informative:
occluding twigs may look connected and have almost identical movements, though
they belong to different, possibly disconnected branches. We propose to tackle
this problem through spectrum analysis of motion signals, because vibrations of
disconnected branches, though visually similar, often have distinctive natural
frequencies. We propose a novel formulation of tree structure based on a
physics-based link model, and validate its effectiveness by theoretical
analysis, numerical simulation, and empirical experiments. With this
formulation, we use nonparametric Bayesian inference to reconstruct tree
structure from both spectral vibration signals and appearance cues. Our model
performs well in recognizing hierarchical tree structure from real-world videos
of trees and vessels.Comment: ECCV 2018. The first two authors contributed equally to this work.
Project page: http://tree.csail.mit.edu
Changes in androstenedione, dehydroepiandrosterone, testosterone, estradiol, and estrone over the menopausal transition
A bifunctional exoglucanase-endoglucanase fusion protein
A fusion was constructed between the cex gene of Cellulomonas fimi, which encodes an exoglucanase, and the cenA gene of the same organism, which encodes an endoglucanase. The cex-cenA fusion was expressed in Escherichia coli to give a fusion protein with both exoglucanase and endoglucanase activities. The fusion protein, unlike the cex and the cenA gene products from E. coli, did not bind to microcrystalline cellulose, presumably because it lacked an intact substrate-binding region. The fusion protein was exported to the periplasm in E. coli
SentiBench - a benchmark comparison of state-of-the-practice sentiment analysis methods
In the last few years thousands of scientific papers have investigated
sentiment analysis, several startups that measure opinions on real data have
emerged and a number of innovative products related to this theme have been
developed. There are multiple methods for measuring sentiments, including
lexical-based and supervised machine learning methods. Despite the vast
interest on the theme and wide popularity of some methods, it is unclear which
one is better for identifying the polarity (i.e., positive or negative) of a
message. Accordingly, there is a strong need to conduct a thorough
apple-to-apple comparison of sentiment analysis methods, \textit{as they are
used in practice}, across multiple datasets originated from different data
sources. Such a comparison is key for understanding the potential limitations,
advantages, and disadvantages of popular methods. This article aims at filling
this gap by presenting a benchmark comparison of twenty-four popular sentiment
analysis methods (which we call the state-of-the-practice methods). Our
evaluation is based on a benchmark of eighteen labeled datasets, covering
messages posted on social networks, movie and product reviews, as well as
opinions and comments in news articles. Our results highlight the extent to
which the prediction performance of these methods varies considerably across
datasets. Aiming at boosting the development of this research area, we open the
methods' codes and datasets used in this article, deploying them in a benchmark
system, which provides an open API for accessing and comparing sentence-level
sentiment analysis methods
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