1,930 research outputs found
An optical fibre dynamic instrumented palpation sensor for the characterisation of biological tissue
AbstractThe diagnosis of prostate cancer using invasive techniques (such as biopsy and blood tests for prostate-specific antigen) and non-invasive techniques (such as digital rectal examination and trans-rectal ultrasonography) may be enhanced by using an additional dynamic instrumented palpation approach to prostate tissue classification. A dynamically actuated membrane sensor/actuator has been developed that incorporates an optical fibre Fabry–Pérot interferometer to record the displacement of the membrane when it is pressed on to different tissue samples. The membrane sensor was tested on a silicon elastomer prostate model with enlarged and stiffer material on one side to simulate early stage prostate cancer. The interferometer measurement was found to have high dynamic range and accuracy, with a minimum displacement resolution of ±0.4μm over a 721μm measurement range. The dynamic response of the membrane sensor when applied to different tissue types changed depending on the stiffness of the tissue being measured. This demonstrates the feasibility of an optically tracked dynamic palpation technique for classifying tissue type based on the dynamic response of the sensor/actuator
Exciting dark matter in the galactic center
We reconsider the proposal of excited dark matter (DM) as an explanation for
excess 511 keV gamma rays from positrons in the galactic center. We
quantitatively compute the cross section for DM annihilation to nearby excited
states, mediated by exchange of a new light gauge boson with off-diagonal
couplings to the DM states. In models where both excited states must be heavy
enough to decay into e^+ e^- and the ground state, the predicted rate of
positron production is never large enough to agree with observations, unless
one makes extreme assumptions about the local circular velocity in the Milky
Way, or alternatively if there exists a metastable population of DM states
which can be excited through a mass gap of less than 650 keV, before decaying
into electrons and positrons.Comment: Dedicated to the memory of Lev Kofman; 16 pages, 9 figures; v3 added
refs, minor changes, accepted to PR
Investigation of the Gravitational Potential Dependence of the Fine-Structure Constant Using Atomic Dysprosium
Radio-frequency E1 transitions between nearly degenerate, opposite parity
levels of atomic dysprosium were monitored over an eight month period to search
for a variation in the fine-structure constant. During this time period, data
were taken at different points in the gravitational potential of the Sun. The
data are fitted to the variation in the gravitational potential yielding a
value of for the fit parameter . This
value gives the current best laboratory limit. In addition, our value of
combined with other experimental constraints is used to extract
the first limits on k_e and k_q. These coefficients characterize the variation
of m_e/m_p and m_q/m_p in a changing gravitational potential, where m_e, m_p,
and m_q are electron, proton, and quark masses. The results are and .Comment: 6 pages, 3 figure
Identifying network communities with a high resolution
Community structure is an important property of complex networks. An
automatic discovery of such structure is a fundamental task in many
disciplines, including sociology, biology, engineering, and computer science.
Recently, several community discovery algorithms have been proposed based on
the optimization of a quantity called modularity (Q). However, the problem of
modularity optimization is NP-hard, and the existing approaches often suffer
from prohibitively long running time or poor quality. Furthermore, it has been
recently pointed out that algorithms based on optimizing Q will have a
resolution limit, i.e., communities below a certain scale may not be detected.
In this research, we first propose an efficient heuristic algorithm, Qcut,
which combines spectral graph partitioning and local search to optimize Q.
Using both synthetic and real networks, we show that Qcut can find higher
modularities and is more scalable than the existing algorithms. Furthermore,
using Qcut as an essential component, we propose a recursive algorithm, HQcut,
to solve the resolution limit problem. We show that HQcut can successfully
detect communities at a much finer scale and with a higher accuracy than the
existing algorithms. Finally, we apply Qcut and HQcut to study a
protein-protein interaction network, and show that the combination of the two
algorithms can reveal interesting biological results that may be otherwise
undetectable.Comment: 14 pages, 5 figures. 1 supplemental file at
http://cic.cs.wustl.edu/qcut/supplemental.pd
Detectability of GRB optical afterglows with Gaia satellite
With the launch of Gaia satellite, detection of many different types of
transient sources will be possible, one of them being optical afterglows of
gamma-ray bursts (GRBs). Using the knowledge of the satellites dynamics and
properties of GRB optical afterglows we performed a simulation in order to
estimate an average GRB detection rate with Gaia. Here we present the
simulation results for two types of GRB optical afterglows, differing in the
observer's line-of-sight compared to a GRB jet axis: regular (on-axis) and
orphan afterglows. Results show that for on-axis GRBs, less than 10 detections
in five years of foreseen Gaia operational time are expected. The orphan
afterglows simulation results are more promising, giving a more optimistic
number of several tens of detections in five years.Comment: 14 pages, 10 figures, accepted to PAS
Nonlinear dynamics of two coupled nano-electromechanical resonators
As a model of coupled nano-electromechanical resonantors we study two
nonlinear driven oscillators with an arbitrary coupling strength between them.
Analytical expressions are derived for the oscillation amplitudes as a function
of the driving frequency and for the energy transfer rate between the two
oscillators. The nonlinear restoring forces induce the expected nonlinear
resonance structures in the amplitude-frequency characteristics with asymmetric
resonance peaks. The corresponding multistable behavior is shown to be an
efficient tool to control the energy transfer arising from the sensitive
response to small changes in the driving frequency. Our results imply that the
nonlinear response can be exploited to design precise sensors for mass or force
detection experiments based on nano-electromechanical resonators.Comment: 19 pages, 2 figure
On the regularization scheme and gauge choice ambiguities in topologically massive gauge theories
It is demonstrated that in the (2+1)-dimensional topologically massive gauge
theories an agreement of the Pauli-Villars regularization scheme with the other
schemes can be achieved by employing pairs of auxiliary fermions with the
opposite sign masses. This approach does not introduce additional violation of
discrete (P and T) symmetries. Although it breaks the local gauge symmetry only
in the regulator fields' sector, its trace disappears completely after removing
the regularization as a result of superrenormalizability of the model. It is
shown also that analogous extension of the Pauli-Villars regularization in the
vector particle sector can be used to agree the arbitrary covariant gauge
results with the Landau ones. The source of ambiguities in the covariant gauges
is studied in detail. It is demonstrated that in gauges that are softer in the
infrared region (e.g. Coulomb or axial) nonphysical ambiguities inherent to the
covariant gauges do not arise.Comment: Latex, 13 pages. Replaced mainly to change preprint references to
journal one
Towards an interactive, process-based approach to understanding range shifts : developmental and environmental dependencies matter
Funding – Funding received from NERC DTP. Supplementary material (Appendix ECOG‐03975 at ). Appendix 1.Peer reviewedPostprin
Electromagnetic properties of non-Dirac particles with rest spin 1/2
We resolve a number of questions related to an analytic description of
electromagnetic form factors of non-Dirac particles with the rest spin 1/2. We
find the general structure of a matrix antisymmetric tensor operator. We obtain
two recurrence relations for matrix elements of finite transformations of the
proper Lorentz group and explicit formulas for a certain set of such elements.
Within the theory of fields with double symmetry, we discuss writing the
components of wave vectors of particles in the form of infinite continued
fractions. We show that for (GeV/c), where is
the transferred momentum squared, electromagnetic form factors that decrease as
increases and are close to those experimentally observed in the proton
can be obtained without explicitly introducing an internal particle structure.Comment: 18 pages, 2 figure
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