2,755 research outputs found
The bend stiffness of S-DNA
We formulate and solve a two-state model for the elasticity of nicked,
double-stranded DNA that borrows features from both the Worm Like Chain and the
Bragg--Zimm model. Our model is computationally simple, and gives an excellent
fit to recent experimental data through the entire overstretching transition.
The fit gives the first value for the bending stiffness of the overstretched
state as about 10 nm*kbt, a value quite different from either B-form or
single-stranded DNA.Comment: 7 pages, 1 figur
Automated myocardial perfusion from coronary X-ray angiography
The purpose of our study is the evaluation of an algorithm to determine the physiological relevance of a coronary\ud
lesion as seen in a coronary angiogram. The aim is to extract as much as possible information from a standard\ud
coronary angiogram to decide if an abnormality, percentage of stenosis, as seen in the angiogram, results in\ud
physiological impairment of the blood supply of the region nourished by the coronary artery. Coronary angiography,\ud
still the golden standard, is used to determine the cause of angina pectoris based on the demonstration\ud
of an important stenose in a coronary artery. Dimensions of a lesion such as length and percentage of narrowing\ud
can at present easily be calculated by using an automatic computer algorithm such as Quantitative Coronary\ud
Angiography (QCA) techniques resulting in just anatomical information ignoring the physiological relevance of\ud
the lesion. In our study we analyze myocardial perfusion images in standard coronary angiograms in rest and\ud
in artificial hyperemic phases, using a drug e.g. papaverine intracoronary. Setting a Region of Interest (ROI) in\ud
the angiogram without overlying major vessels makes it possible to calculate contrast differences as a function of\ud
time, so called time-density curves, in the basal and hyperemic phases. In minimizing motion artifacts, end diastolic\ud
images are selected ECG based in basal and hyperemic phase in an identical ROI in the same angiographic\ud
projection. The development of new algorithms for calculating differences in blood supply in the region as set\ud
are presented together with the results of a small clinical case study using the standard angiographic procedur
CAD of myocardial perfusion
Our purpose is in the automated evaluation of the physiological relevance of lesions in coronary angiograms. We aim to extract as much as possible quantitative information about the physiological condition of the heart from standard angiographic image sequences. Coronary angiography is still the gold standard for evaluating and diagnosing coronary abnormalities as it is able to locate precisely the coronary artery lesions. The dimensions of the stenosis can be assessed nowadays successfully with image processing based Quantitative Coronary Angiography (QCA) techniques. Our purpose is to assess the clinical relevance of the pertinent stenosis. We therefore analyze the myocardial perfusion as revealed in standard angiographic image sequences. In a Region-of-Interest (ROI) on the angiogram (without an overlaying major blood vessel) the contrast is measured as a function of time (the so-called time-density curve). The required hyperemic state of exercise is induced artificially by the injection of a vasodilator drug e.g. papaverine. In order to minimize motion artifacts we select based on the recorded ECG signal end-diastolic images in both a basal and a hyperemic run in the same projection to position the ROI. We present the development of the algorithms together with results of a small study of 20 patients which have been catheterized following the standard protocol
Critical behaviour in the nonlinear elastic response of hydrogels
In this paper we study the elastic response of synthetic hydrogels to an
applied shear stress. The hydrogels studied here have previously been shown to
mimic the behaviour of biopolymer networks when they are sufficiently far above
the gel point. We show that near the gel point they exhibit an elastic response
that is consistent with the predicted critical behaviour of networks near or
below the isostatic point of marginal stability. This point separates rigid and
floppy states, distinguished by the presence or absence of finite linear
elastic moduli. Recent theoretical work has also focused on the response of
such networks to finite or large deformations, both near and below the
isostatic point. Despite this interest, experimental evidence for the existence
of criticality in such networks has been lacking. Using computer simulations,
we identify critical signatures in the mechanical response of sub-isostatic
networks as a function of applied shear stress. We also present experimental
evidence consistent with these predictions. Furthermore, our results show the
existence of two distinct critical regimes, one of which arises from the
nonlinear stretch response of semi-flexible polymers.
InAs nanowire transistors with multiple, independent wrap-gate segments
We report a method for making horizontal wrap-gate nanowire transistors with
up to four independently controllable wrap-gated segments. While the step up to
two independent wrap-gates requires a major change in fabrication methodology,
a key advantage to this new approach, and the horizontal orientation more
generally, is that achieving more than two wrap-gate segments then requires no
extra fabrication steps. This is in contrast to the vertical orientation, where
a significant subset of the fabrication steps needs to be repeated for each
additional gate. We show that cross-talk between adjacent wrap-gate segments is
negligible despite separations less than 200 nm. We also demonstrate the
ability to make multiple wrap-gate transistors on a single nanowire using the
exact same process. The excellent scalability potential of horizontal wrap-gate
nanowire transistors makes them highly favourable for the development of
advanced nanowire devices and possible integration with vertical wrap-gate
nanowire transistors in 3D nanowire network architectures.Comment: 18 pages, 5 figures, In press for Nano Letters (DOI below
Search for the second forbidden beta decay of 8B to the ground state of 8Be
A significant decay branch of 8B to the ground state of 8Be would extend the
solar neutrino spectrum to higher energies than anticipated in the standard
solar models. These high-energy neutrinos would affect current neutrino
oscillation results and also would be a background to measurements of the hep
process. We have measured the delayed alpha particles from the decay of 8B,
with the goal of observing the two 46-keV alpha particles arising from the
ground-state decay. The 8B was produced using an in-flight radioactive beam
technique. It was implanted in a silicon PIN-diode detector that was capable of
identifying the alpha-particles from the 8Be ground state. From this
measurement we find an upper limit (at 90% confidence level) of 7.3 x 10^{-5}
for the branching ratio to the ground state. In addition to describing this
measurement, we present a theoretical calculation for this branching ratio.Comment: One reference corrected. Minor edits in tex
Finite-time Lyapunov exponents of deep neural networks
We compute how small input perturbations affect the output of deep neural
networks, exploring an analogy between deep networks and dynamical systems,
where the growth or decay of local perturbations is characterised by
finite-time Lyapunov exponents. We show that the maximal exponent forms
geometrical structures in input space, akin to coherent structures in dynamical
systems. Ridges of large positive exponents divide input space into different
regions that the network associates with different classes. These ridges
visualise the geometry that deep networks construct in input space, shedding
light on the fundamental mechanisms underlying their learning capabilities.Comment: 6 pages, 4 figure
Electron elastic scattering cross sections from 1 keV to 100 MeV for elements Z = 1 to 100
Tables of electron elastic scattering differential cross sections of elements (Z = 1 to 100) are given for electron energies in the range of 1 keV to 100 MeV and scattering angles in the range of 1 to 179. The function describing the asymmetry of a polarized electron beam after the scattering process is also included in the tables. (auth
CARMA Large Area Star Formation Survey: Observational Analysis of Filaments in the Serpens South Molecular Cloud
We present the N2H+(J=1-0) map of the Serpens South molecular cloud obtained
as part of the CARMA Large Area Star Formation Survey (CLASSy). The
observations cover 250 square arcminutes and fully sample structures from 3000
AU to 3 pc with a velocity resolution of 0.16 km/s, and they can be used to
constrain the origin and evolution of molecular cloud filaments. The spatial
distribution of the N2H+ emission is characterized by long filaments that
resemble those observed in the dust continuum emission by Herschel. However,
the gas filaments are typically narrower such that, in some cases, two or three
quasi-parallel N2H+ filaments comprise a single observed dust continuum
filament. The difference between the dust and gas filament widths casts doubt
on Herschel ability to resolve the Serpens South filaments. Some molecular
filaments show velocity gradients along their major axis, and two are
characterized by a steep velocity gradient in the direction perpendicular to
the filament axis. The observed velocity gradient along one of these filaments
was previously postulated as evidence for mass infall toward the central
cluster, but these kind of gradients can be interpreted as projection of
large-scale turbulence.Comment: 12 pages, 4 figures, published in ApJL (July 2014
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