814 research outputs found
Approximate Boltzmann Distributions for Nonreversible Markov Chains
While powerful theories for the analysis of reversible Markov chains have
enabled significant mathematical advances, nonequilibrium phenomena dominate
the sciences and nonequilibrium chains do not enjoy the same formal
foundations. For instance, the stationary distributions of reversible chains
are fundamentally simpler than those of nonreversible chains because they are
Boltzmann distributions -- they can be expressed in terms of a purely local
"free energy" landscape, in analogy with equilibrium statistical physics. In
general, it is impossible to similarly represent the steady states of
nonequilibrium physical systems in a purely local way. However, a series of
recent works on rattling theory (e.g., Chvykov et al., Science (2021)) provides
strong evidence that a broad class of such systems nevertheless exhibit
"approximate Boltzmann distributions," which allow some aspects of the global
distributions to be inferred, at least approximately, from local information.
We formalize the main claims of this physical theory to identify its hidden
assumptions and demonstrate its basis in the theory of continuous-time Markov
chains. To do so, we decompose an arbitrary stationary distribution into
its "local" part -- the exit rates out of each state -- and its "global"
part -- the stationary distribution of the embedded "jump" chain. We
explain a variety of experimental results by showing that, for a random state,
and are correlated to the extent that and
are correlated or the ratio of their variances is small. In
particular, the predictions of rattling theory apply when the global part of
varies over fewer scales than its local part. We use this fact to
demonstrate classes of nonreversible chains with stationary distributions that
are exactly of Boltzmann type.Comment: 14 pages, 1 figur
Segmentation-by-Detection: A Cascade Network for Volumetric Medical Image Segmentation
We propose an attention mechanism for 3D medical image segmentation. The
method, named segmentation-by-detection, is a cascade of a detection module
followed by a segmentation module. The detection module enables a region of
interest to come to attention and produces a set of object region candidates
which are further used as an attention model. Rather than dealing with the
entire volume, the segmentation module distills the information from the
potential region. This scheme is an efficient solution for volumetric data as
it reduces the influence of the surrounding noise which is especially important
for medical data with low signal-to-noise ratio. Experimental results on 3D
ultrasound data of the femoral head shows superiority of the proposed method
when compared with a standard fully convolutional network like the U-Net
End-to-end detection-segmentation network with ROI convolution
We propose an end-to-end neural network that improves the segmentation
accuracy of fully convolutional networks by incorporating a localization unit.
This network performs object localization first, which is then used as a cue to
guide the training of the segmentation network. We test the proposed method on
a segmentation task of small objects on a clinical dataset of ultrasound
images. We show that by jointly learning for detection and segmentation, the
proposed network is able to improve the segmentation accuracy compared to only
learning for segmentation. Code is publicly available at
https://github.com/vincentzhang/roi-fcn.Comment: ISBI 201
Connecting Youth Through Multiple Pathways
Presents findings from a field scan of efforts to help vulnerable youth graduate from high school, what is working, what should be done, and what opportunities exist for Casey's involvement. Explores risk factors and alternative programs. Lists resources
Youth at High Risk of Disconnection
Updates the 2003 report "Connected by 25: Improving the Life Chances of the Country's Most Vulnerable 14-24 Year Olds" with demographic changes in disconnected and at-risk youth -- teens who are dropouts, mothers, in foster care, and/or incarcerated
The clinical pharmacology of intranasal l-methamphetamine.
BackgroundWe studied the pharmacology of l-methamphetamine, the less abused isomer, when used as a nasal decongestant.Methods12 subjects self-administered l-methamphetamine from a nonprescription inhaler at the recommended dose (16 inhalations over 6 hours) then at 2 and 4 (32 and 64 inhalations) times this dose. In a separate session intravenous phenylephrine (200 microg) and l-methamphetamine (5 mg) were given to define alpha agonist pharmacology and bioavailability. Physiological, cardiovascular, pharmacokinetic, and subjective effects were measured.ResultsPlasma l-methamphetamine levels were often below the level of quantification so bioavailability was estimated by comparing urinary excretion of the intravenous and inhaled doses, yielding delivered dose estimates of 74.0 +/- 56.1, 124.7 +/- 106.6, and 268.1 +/- 220.5 microg for ascending exposures (mean 4.2 +/- 3.3 microg/inhalation). Physiological changes were minimal and not dose-dependent. Small decreases in stroke volume and cardiac output suggesting mild cardiodepression were seen.ConclusionInhaled l-methamphetamine delivered from a non-prescription product produced minimal effects but may be a cardiodepressant
On game chromatic number analogues of Mycielsians and Brooks' Theorem
The vertex coloring game is a two-player game on a graph with given color set in which the first player attempts to properly color the graph and the second attempts to prevent a proper coloring from being achieved. The smallest number of colors for which the first player can win no matter how the second player plays is called the game chromatic number of the graph. In this paper we initiate the study of game chromatic number for Mycielskians and a game chromatic number analogue of Brooks' Theorem (which characterizes graphs for which chromatic number is at most the maximum degree of the graph). In particular, we determine the game chromatic number of Mycielskians of complete graphs, complete bipartite graphs, and cycles. In the direction of Brooks' Theorem, we show that if there are few vertices of maximum degree or if all vertices of maximum degree are at least three edges apart, then the game chromatic number is at most the maximum degree of the grap
Punicalagin Induces Serum Low-Density Lipoprotein Influx to Macrophages
High levels of circulating low-density lipoprotein (LDL) are a primary initiating event in the development of atherosclerosis. Recently, the antiatherogenic effect of polyphenols has been shown to be exerted via a mechanism unrelated to their antioxidant capacity and to stem from their interaction with specific intracellular or plasma proteins. In this study, we investigated the interaction of the main polyphenol in pomegranate, punicalagin, with apolipoprotein B-100 (ApoB100) that surrounds LDL. Punicalagin bound to ApoB100 at low concentrations (0.25–4 μM). Upon binding, it induced LDL influx to macrophages in a concentration-dependent manner, up to 2.5-fold. In contrast, another polyphenol which binds to ApoB100, glabridin, did not affect LDL influx. We further showed that LDL influx occurs specifically through the LDL receptor, with LDL then accumulating in the cell cytoplasm. Taken together with the findings of Aviram et al., 2000, that pomegranate juice and punicalagin induce plasma LDL removal and inhibit macrophage cholesterol synthesis and accumulation, our results suggest that, upon binding, punicalagin stimulates LDL influx to macrophages, thus reducing circulating cholesterol levels
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