410 research outputs found
An Alternative Method to Deduce Bubble Dynamics in Single Bubble Sonoluminescence Experiments
In this paper we present an experimental approach that allows to deduce the
important dynamical parameters of single sonoluminescing bubbles (pressure
amplitude, ambient radius, radius-time curve) The technique is based on a few
previously confirmed theoretical assumptions and requires the knowledge of
quantities such as the amplitude of the electric excitation and the phase of
the flashes in the acoustic period. These quantities are easily measurable by a
digital oscilloscope, avoiding the cost of expensive lasers, or ultrafast
cameras of previous methods. We show the technique on a particular example and
compare the results with conventional Mie scattering. We find that within the
experimental uncertainties these two techniques provide similar results.Comment: 8 pages, 5 figures, submitted to Phys. Rev.
Approximating Mexican highways with slime mould
Plasmodium of Physarum polycephalum is a single cell visible by unaided eye.
During its foraging behavior the cell spans spatially distributed sources of
nutrients with a protoplasmic network. Geometrical structure of the
protoplasmic networks allows the plasmodium to optimize transport of nutrients
between remote parts of its body. Assuming major Mexican cities are sources of
nutrients how much structure of Physarum protoplasmic network correspond to
structure of Mexican Federal highway network? To find an answer undertook a
series of laboratory experiments with living Physarum polycephalum. We
represent geographical locations of major cities by oat flakes, place a piece
of plasmodium in Mexico city area, record the plasmodium's foraging behavior
and extract topology of nutrient transport networks. Results of our experiments
show that the protoplasmic network formed by Physarum is isomorphic, subject to
limitations imposed, to a network of principle highways. Ideas and results of
the paper may contribute towards future developments in bio-inspired road
planning
Phenotyping vs. genotyping for prediction of clopidogrel efficacy and safety: the PEGASUS-PCI study
Background: Prognostic values of genotyping and
phenotyping for assessment of clopidogrel responsiveness have
been shown in independent studies. Objectives: To compare
different assays for prediction of events during long-term
follow-up. Methods: In this prospective cohort study polymorphisms
of CYP2C19*2 and CYP2C19*17 alleles, vasodilator-
stimulated phosphoprotein phosphorylation (VASP)
assay, multiple electrode aggregometry (MEA), cone and
platelet analyser (CPA) and platelet function analyser (PFA-
100) were performed in 416 patients undergoing percutaneous
coronary intervention. The rates of events were recorded during
a 12-month follow-up. Results: Platelet aggregation by MEA
predicted stent thrombosis (2.4%) better (c-index = 0.90;
P < 0.001; sensitivity = 90%; specificity = 83%) than the
VASP assay, CPA or PFA-100 (c-index 0.05;
sensitivity < 70%; specificity < 70% for all) or even the
CYP2C19*2 polymorphism (c-index 0.05; sensitivity
= 30%; specificity = 71%). Survival analysis indicated
that patients classified as poor responders by MEA had a
substantially higher risk of developing stent thrombosis or
MACE than clopidogrel responders (12.5% vs. 0.3%,
P < 0.001, and 18.5% vs. 11.3%, P = 0.022, respectively),
whereas poor metabolizers (CYP2C19*1/*2 or *2/*2 carriers)
were not at increased risks (stent thrombosis, 2.7% vs. 2.5%,
P > 0.05; MACE, 13.5% vs. 12.1%, P = 0.556). The incidence
of major bleedings (2.6%) was numerically higher in
patients with an enhanced vs. poor response to clopidogrel
assessed by MEA (4% vs. 0%) or in ultra-metabolizers vs.
regular metabolizers (CYP2C19*17/*17 vs. CYP2C19*1/*1;
9.5% vs. 2%). The classification tree analysis demonstrated that
acute coronary syndrome at hospitalization and diabetes
mellitus were the best discriminators for clopidogrel responder
status. Conclusions: Phenotyping of platelet response to clopidogrel
was a better predictor of stent thrombosis than
genotyping
miR-17-5p regulates endocytic trafficking through targeting TBC1D2/ Armus
miRNA cluster miR-17-92 is known as oncomir-1 due to its potent oncogenic function. miR-17-92 is a polycistronic cluster that encodes 6 miRNAs, and can both facilitate and inhibit cell proliferation. Known targets of miRNAs encoded by this cluster are largely regulators of cell cycle progression and apoptosis. Here, we show that miRNAs encoded by this cluster and sharing the seed sequence of miR-17 exert their influence on one of the most essential cellular processes – endocytic trafficking. By mRNA expression analysis we identified that regulation of endocytic trafficking by miR-17 can potentially be achieved by targeting of a number of trafficking regulators. We have thoroughly validated TBC1D2/Armus, a GAP of Rab7 GTPase, as a novel target of miR-17. Our study reveals regulation of endocytic trafficking as a novel function of miR-17, which might act cooperatively with other functions of miR-17 and related miRNAs in health and disease
Investigation of transition frequencies of two acoustically coupled bubbles using a direct numerical simulation technique
The theoretical results regarding the ``transition frequencies'' of two
acoustically interacting bubbles have been verified numerically. The theory
provided by Ida [Phys. Lett. A 297 (2002) 210] predicted the existence of three
transition frequencies per bubble, each of which has the phase difference of
between a bubble's pulsation and the external sound field, while
previous theories predicted only two natural frequencies which cause such phase
shifts. Namely, two of the three transition frequencies correspond to the
natural frequencies, while the remaining does not. In a subsequent paper [M.
Ida, Phys. Rev. E 67 (2003) 056617], it was shown theoretically that transition
frequencies other than the natural frequencies may cause the sign reversal of
the secondary Bjerknes force acting between pulsating bubbles. In the present
study, we employ a direct numerical simulation technique that uses the
compressible Navier-Stokes equations with a surface-tension term as the
governing equations to investigate the transition frequencies of two coupled
bubbles by observing their pulsation amplitudes and directions of translational
motion, both of which change as the driving frequency changes. The numerical
results reproduce the recent theoretical predictions, validating the existence
of the transition frequencies not corresponding to the natural frequency.Comment: 18 pages, 8 figures, in pres
Efficient Enumeration of Bipartite Subgraphs in Graphs
Subgraph enumeration problems ask to output all subgraphs of an input graph
that belongs to the specified graph class or satisfy the given constraint.
These problems have been widely studied in theoretical computer science. As
far, many efficient enumeration algorithms for the fundamental substructures
such as spanning trees, cycles, and paths, have been developed. This paper
addresses the enumeration problem of bipartite subgraphs. Even though bipartite
graphs are quite fundamental and have numerous applications in both theory and
application, its enumeration algorithms have not been intensively studied, to
the best of our knowledge. We propose the first non-trivial algorithms for
enumerating all bipartite subgraphs in a given graph. As the main results, we
develop two efficient algorithms: the one enumerates all bipartite induced
subgraphs of a graph with degeneracy in time per solution. The other
enumerates all bipartite subgraphs in time per solution
Isoperimetric Inequalities in Simplicial Complexes
In graph theory there are intimate connections between the expansion
properties of a graph and the spectrum of its Laplacian. In this paper we
define a notion of combinatorial expansion for simplicial complexes of general
dimension, and prove that similar connections exist between the combinatorial
expansion of a complex, and the spectrum of the high dimensional Laplacian
defined by Eckmann. In particular, we present a Cheeger-type inequality, and a
high-dimensional Expander Mixing Lemma. As a corollary, using the work of Pach,
we obtain a connection between spectral properties of complexes and Gromov's
notion of geometric overlap. Using the work of Gunder and Wagner, we give an
estimate for the combinatorial expansion and geometric overlap of random
Linial-Meshulam complexes
Sonoluminescence as a QED vacuum effect. I: The Physical Scenario
Several years ago Schwinger proposed a physical mechanism for
sonoluminescence in terms of changes in the properties of the
quantum-electrodynamic (QED) vacuum state. This mechanism is most often phrased
in terms of changes in the Casimir Energy: changes in the distribution of
zero-point energies and has recently been the subject of considerable
controversy. The present paper further develops this quantum-vacuum approach to
sonoluminescence: We calculate Bogolubov coefficients relating the QED vacuum
states in the presence of a homogeneous medium of changing dielectric constant.
In this way we derive an estimate for the spectrum, number of photons, and
total energy emitted. We emphasize the importance of rapid spatio-temporal
changes in refractive indices, and the delicate sensitivity of the emitted
radiation to the precise dependence of the refractive index as a function of
wavenumber, pressure, temperature, and noble gas admixture. Although the
physics of the dynamical Casimir effect is a universal phenomenon of QED,
specific experimental features are encoded in the condensed matter physics
controlling the details of the refractive index. This calculation places rather
tight constraints on the possibility of using the dynamical Casimir effect as
an explanation for sonoluminescence, and we are hopeful that this scenario will
soon be amenable to direct experimental probes. In a companion paper we discuss
the technical complications due to finite-size effects, but for reasons of
clarity in this paper we confine attention to bulk effects.Comment: 25 pages, LaTeX 209, ReV-TeX 3.2, eight figures. Minor revisions:
Typos fixed, references updated, minor changes in numerical estimates, minor
changes in some figure
Comparing the Cost-Effectiveness of Short Orthopedic Missions in Elective and Relief Situations in Developing Countries
Ó The Author(s) 2011. This article is published with open access at Springerlink.com Background The earthquake that occurred in Haiti on 12 January 2010 elicited an unprecedented response from the American orthopedic community. Many small organizations, such as Operation Rainbow, were thrust into the unfamiliar environment of relief surgery, whereas they normally provide short elective reconstruction missions in developing countries. Materials Because of the chaotic nature of relief work, it was assumed that the organization’s efforts would be less cost-effective than their usual elective work. To evaluate this conclusion, the present study was designed to compare the cost-effectiveness of the organization’s usual elective missions with the emergency relief provided in the wake of the Haiti earthquake. Results and conclusions The assumption that emergency costs would be higher was proven wrong, with estimates of 343 per DALY averted in the relief group
An objective comparison of cell-tracking algorithms
We present a combined report on the results of three editions of the Cell Tracking Challenge, an ongoing initiative aimed at promoting the development and objective evaluation of cell segmentation and tracking algorithms. With 21 participating algorithms and a data repository consisting of 13 data sets from various microscopy modalities, the challenge displays today's state-of-the-art methodology in the field. We analyzed the challenge results using performance measures for segmentation and tracking that rank all participating methods. We also analyzed the performance of all of the algorithms in terms of biological measures and practical usability. Although some methods scored high in all technical aspects, none obtained fully correct solutions. We found that methods that either take prior information into account using learning strategies or analyze cells in a global spatiotemporal video context performed better than other methods under the segmentation and tracking scenarios included in the challenge
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