21,986 research outputs found
Quadrupole moment of a magnetically confined mountain on an accreting neutron star: effect of the equation of state
Magnetically confined mountains on accreting neutron stars are promising
sources of continuous-wave gravitational radiation and are currently the
targets of directed searches with long-baseline detectors like the Laser
Interferometer Gravitational Wave Observatory (LIGO). In this paper, previous
ideal-magnetohydrodynamic models of isothermal mountains are generalized to a
range of physically motivated, adiabatic equations of state. It is found that
the mass ellipticity drops substantially, from \epsilon ~ 3e-4 (isothermal) to
\epsilon ~ 9e-7 (non-relativistic degenerate neutrons), 6e-8 (relativistic
degenerate electrons) and 1e-8 (non-relativistic degenerate electrons)
(assuming a magnetic field of 3e12 G at birth). The characteristic mass M_{c}
at which the magnetic dipole moment halves from its initial value is also
modified, from M_{c}/M_{\sun} ~ 5e-4 (isothermal) to M_{c}/M_{\sun} ~ 2e-6,
1e-7, and 3e-8 for the above three equations of state, respectively. Similar
results are obtained for a realistic, piecewise-polytropic nuclear equation of
state. The adiabatic models are consistent with current LIGO upper limits,
unlike the isothermal models. Updated estimates of gravitational-wave
detectability are made. Monte Carlo simulations of the spin distribution of
accreting millisecond pulsars including gravitational-wave stalling agree
better with observations for certain adiabatic equations of state, implying
that X-ray spin measurements can probe the equation of state when coupled with
magnetic mountain models.Comment: 20 pages, 15 figures, to be published in MNRA
Comparative (computational) analysis of the DNA methylation status of trinucleotide repeat expansion diseases
Copyright © 2013 Mohammadmersad Ghorbani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.This article has been made available through the Brunel Open Access Publishing Fund.Previous studies have examined DNA methylation in different trinucleotide repeat diseases. We have combined this data and used a pattern searching algorithm to identify motifs in the DNA surrounding aberrantly methylated CpGs found in the DNA of patients with one of the three trinucleotide repeat (TNR) expansion diseases: fragile X syndrome (FRAXA), myotonic dystrophy type I (DM1), or Friedreich’s ataxia (FRDA). We examined sequences surrounding both the variably methylated (VM) CpGs, which are hypermethylated in patients compared with unaffected controls, and the nonvariably methylated CpGs which remain either always methylated (AM) or never methylated (NM) in both patients and controls. Using the J48 algorithm of WEKA analysis, we identified that two patterns are all that is necessary to classify our three regions CCGG* which is found in VM and not in AM regions and AATT* which distinguished between NM and VM + AM using proportional frequency. Furthermore, comparing our software with MEME software, we have demonstrated that our software identifies more patterns than MEME in these short DNA sequences. Thus, we present evidence that the DNA sequence surrounding CpG can influence its susceptibility to be de novo methylated in a disease state associated with a trinucleotide repeat.European Union Seventh Framework Programme and The Brunel University Graduate Program
Identifiability of generalised Randles circuit models
The Randles circuit (including a parallel resistor and capacitor in series
with another resistor) and its generalised topology have widely been employed
in electrochemical energy storage systems such as batteries, fuel cells and
supercapacitors, also in biomedical engineering, for example, to model the
electrode-tissue interface in electroencephalography and baroreceptor dynamics.
This paper studies identifiability of generalised Randles circuit models, that
is, whether the model parameters can be estimated uniquely from the
input-output data. It is shown that generalised Randles circuit models are
structurally locally identifiable. The condition that makes the model structure
globally identifiable is then discussed. Finally, the estimation accuracy is
evaluated through extensive simulations
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Use of creative tools, technologies, processes and practices in the sectors of Art, Media, and Architecture: State-of the-Art and desired future scenarios
The aim of the paper is to analyse and present the preliminary findings of the EU FP7 funded CRe-AM project for the Art, Media, and Architecture sectors. This project bridges communities of technology providers and innovators with the creative industries, with the aim to build sector-specific dynamic roadmaps for the future of the European creative industries by examining the current state-of-the-art tools, technologies, processes, and practices supporting the creative process against the future scenarios envisioned by stakeholders in these sectors.This work was carried out as part of CRe-AM project, which is supported by European Commission (grant agreement n°612451)
New Consequences of Induced Transparency in a Double-Lambda scheme: Destructive Interference In Four-wave Mixing
We investigate a four-state system interacting with long and short laser
pulses in a weak probe beam approximation. We show that when all lasers are
tuned to the exact unperturbed resonances, part of the four-wave mixing (FWM)
field is strongly absorbed. The part which is not absorbed has the exact
intensity required to destructively interfere with the excitation pathway
involved in producing the FWM state. We show that with this three-photon
destructive interference, the conversion efficiency can still be as high as
25%. Contrary to common belief,our calculation shows that this process, where
an ideal one-photon electromagnetically induced transparency is established, is
not most suitable for high efficiency conversion. With appropriate
phase-matching and propagation distance, and when the three-photon destructive
interference does not occur, we show that the photon flux conversion efficiency
is independent of probe intensity and can be close to 100%. In addition, we
show clearly that the conversion efficiency is not determined by the maximum
atomic coherence between two lower excited states, as commonly believed. It is
the combination of phase-matching and constructive interference involving the
two terms arising in producing the mixing wave that is the key element for the
optimized FWM generation. Indeed, in this scheme no appreciable excited state
is produced, so that the atomic coherence between states |0> and |2> is always
very small.Comment: Submitted to Phys. Rev. A, 7 pages, 4 figure
Spectroscopy of drums and quantum billiards: perturbative and non-perturbative results
We develop powerful numerical and analytical techniques for the solution of
the Helmholtz equation on general domains. We prove two theorems: the first
theorem provides an exact formula for the ground state of an arbirtrary
membrane, while the second theorem generalizes this result to any excited state
of the membrane. We also develop a systematic perturbative scheme which can be
used to study the small deformations of a membrane of circular or square
shapes. We discuss several applications, obtaining numerical and analytical
results.Comment: 29 pages, 12 figures, 7 tabl
Heterodyne range imaging as an alternative to photogrammetry
Solid-state full-field range imaging technology, capable of determining the distance to objects in a scene simultaneously for every pixel in an image, has recently achieved sub-millimeter distance measurement precision. With this level of precision, it is becoming practical to use this technology for high precision three-dimensional metrology applications. Compared to photogrammetry, range imaging has the advantages of requiring only one viewing angle, a relatively short measurement time, and simplistic fast data processing. In this paper we fist review the range imaging technology, then describe an experiment comparing both photogrammetric and range imaging measurements of a calibration block with attached retro-reflective targets. The results show that the range imaging approach exhibits errors of approximately 0.5 mm in-plane and almost 5 mm out-of-plane; however, these errors appear to be mostly systematic. We then proceed to examine the physical nature and characteristics of the image ranging technology and discuss the possible causes of these systematic errors. Also discussed is the potential for further system characterization and calibration to compensate for the range determination and other errors, which could possibly lead to three-dimensional measurement precision approaching that of photogrammetry
The Waikato range imager
We are developing a high precision simultaneous full-field acquisition range imager. This device measures range with sub millimetre precision in range simultaneously over a full-field view of the scene. Laser diodes are used to illuminate the scene with amplitude modulation with a frequency of 10MHz up to 100 MHz. The received light is interrupted by a high speed shutter operating in a heterodyne configuration thus producing a low-frequency signal which is sampled with a digital camera. By detecting the phase of the signal at each pixel the range to the scene is determined. We show 3D reconstructions of some viewed objects to demonstrate the capabilities of the ranger
Projector self-consistent DFT+U using non-orthogonal generalized Wannier functions
We present a formulation of the density-functional theory + Hubbard model
(DFT+U) method that is self-consistent over the choice of Hubbard projectors
used to define the correlated subspaces. In order to overcome the arbitrariness
in this choice, we propose the use of non-orthogonal generalized Wannier
functions (NGWFs) as projectors for the DFT+U correction. We iteratively refine
these NGWF projectors and, hence, the DFT+U functional, such that the
correlated subspaces are fully self-consistent with the DFT+U ground-state. We
discuss the convergence characteristics of this algorithm and compare
ground-state properties thus computed with those calculated using hydrogenic
projectors. Our approach is implemented within, but not restricted to, a
linear-scaling DFT framework, opening the path to DFT+U calculations on systems
of unprecedented size.Comment: 4 pages, 3 figures. This version (v2) matches that accepted for
Physical Review B Rapid Communications on 26th July 201
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