8,119 research outputs found
Dynamic Kerr effect responses in the Terahertz-range
Dynamic Kerr effect measurements provide a simple realization of a nonlinear
experiment. We propose a field-off experiment where an electric field of one or
several sinusoidal cycles is applied to a sample in thermal equilibrium.
Afterwards, the evolution of the polarizability is measured. If such an
experiment is performed in the Terahertz-range it might provide valuable
information about the low-frequency dynamics in disordered systems. We treat
these dynamics in terms of a Brownian oscillator model and calculate the Kerr
effect response. It is shown that frequency-selective behaviour can be
expected. In the interesting case of underdamped vibrational motion we find
that the frequency-dependence of the phonon-damping can be determined from the
experiment. Also the behaviour of overdamped relaxational modes is discussed.
For typical glassy materials we estimate the magnitude of all relevant
quantities, which we believe to be helpful in experimental realizations.Comment: 26 pages incl. 5 figure
General practice and the New Zealand health reforms – lessons for Australia?
New Zealand's health sector has undergone three significant restructures within 10 years. The most recent has involved a Primary Health Care Strategy, launched in 2001. Primary Health Organisations (PHOs), administered by 21 District Health Boards, are the local structures for implementing the Primary Health Care Strategy. Ninety-three percent of the New Zealand population is now enrolled within 79 PHOs, which pose a challenge to the well-established Independent Practitioner Associations (IPAs). Although there was initial widespread support for the philosophy underlying the Primary Health Care Strategy, there are concerns amongst general practitioners (GPs) and their professional organisations relating to its implementation. These centre around 6 main issues: 1. Loss of autonomy 2. Inadequate management funding and support 3. Inconsistency and variations in contracting processes 4. Lack of publicity and advice around enrolment issues 5. Workforce and workload issues 6. Financial risks On the other hand, many GPs are feeling positive regarding the opportunities for PHOs, particularly for being involved in the provision of a wider range of community health services. Australia has much to learn from New Zealand's latest health sector and primary health care reforms. The key lessons concern: • the need for a national primary health care strategy • active engagement of general practitioners and their professional organisations • recognition of implementation costs • the need for infrastructural support, including information technology and quality systems • robust management and governance arrangements • issues related to critical mass and population/distance trade offs in service delivery model
Gunrock: A High-Performance Graph Processing Library on the GPU
For large-scale graph analytics on the GPU, the irregularity of data access
and control flow, and the complexity of programming GPUs have been two
significant challenges for developing a programmable high-performance graph
library. "Gunrock", our graph-processing system designed specifically for the
GPU, uses a high-level, bulk-synchronous, data-centric abstraction focused on
operations on a vertex or edge frontier. Gunrock achieves a balance between
performance and expressiveness by coupling high performance GPU computing
primitives and optimization strategies with a high-level programming model that
allows programmers to quickly develop new graph primitives with small code size
and minimal GPU programming knowledge. We evaluate Gunrock on five key graph
primitives and show that Gunrock has on average at least an order of magnitude
speedup over Boost and PowerGraph, comparable performance to the fastest GPU
hardwired primitives, and better performance than any other GPU high-level
graph library.Comment: 14 pages, accepted by PPoPP'16 (removed the text repetition in the
previous version v5
Targeting determinants of dosage compensation in Drosophila
The dosage compensation complex (DCC) in Drosophila melanogaster is responsible for up-regulating transcription from the single male X chromosome to equal the transcription from the two X chromosomes in females. Visualization of the DCC, a large ribonucleoprotein complex, on male larval polytene chromosomes reveals that the complex binds selectively to many interbands on the X chromosome. The targeting of the DCC is thought to be in part determined by DNA sequences that are enriched on the X. So far, lack of knowledge about DCC binding sites has prevented the identification of sequence determinants. Only three binding sites have been identified to date, but analysis of their DNA sequence did not allow the prediction of further binding sites. We have used chromatin immunoprecipitation to identify a number of new DCC binding fragments and characterized them in vivo by visualizing DCC binding to autosomal insertions of these fragments, and we have demonstrated that they possess a wide range of potential to recruit the DCC. By varying the in vivo concentration of the DCC, we provide evidence that this range of recruitment potential is due to differences in affinity of the complex to these sites. We were also able to establish that DCC binding to ectopic high-affinity sites can allow nearby low-affinity sites to recruit the complex. Using the sequences of the newly identified and previously characterized binding fragments, we have uncovered a number of short sequence motifs, which in combination may contribute to DCC recruitment. Our findings suggest that the DCC is recruited to the X via a number of binding sites of decreasing affinities, and that the presence of high-and moderate-affinity sites on the X may ensure that lower-affinity sites are occupied in a context-dependent manner. Our bioinformatics analysis suggests that DCC binding sites may be composed of variable combinations of degenerate motifs
On the iterated Crank-Nicolson for hyperbolic and parabolic equations in numerical relativity
The iterated Crank-Nicolson is a predictor-corrector algorithm commonly used
in numerical relativity for the solution of both hyperbolic and parabolic
partial differential equations. We here extend the recent work on the stability
of this scheme for hyperbolic equations by investigating the properties when
the average between the predicted and corrected values is made with unequal
weights and when the scheme is applied to a parabolic equation. We also propose
a variant of the scheme in which the coefficients in the averages are swapped
between two corrections leading to systematically larger amplification factors
and to a smaller numerical dispersion.Comment: 7 pages, 3 figure
On discriminating temporal relations: Is it relational?
Pigeons were presented on each trial with a pair of keylight stimuli that varied in duration. One of two subsequent choices was reinforced, depending on which of the two stimuli was longer. For some pairs, the duration of one stimulus was predictive of relative duration, but for other pairs, absolute duration was unpredictive. Choice responses depended on relative differences between the stimuli, but were also controlled to some degree by absolute duration of the second member of the pair. Individual differences in control by absolute and relative duration were evident. Those pigeons whose behavior was most influenced by absolute duration showed poorer transfer to a different set of duration pairs
Designing an information system for updating land records in Bangladesh: action design ethnographic research (ADER)
Open Access. This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.This article has been made available through the Brunel Open Access Publishing Fund.Information Systems (IS) has developed through adapting, generating and applying diverse methodologies, methods, and techniques from reference disciplines. Further, Action Design Research (ADR) has recently developed as a broad research method that focuses on designing and redesigning IT and IS in organizational contexts. This paper reflects on applying ADR in a complex organizational context in a developing country. It shows that ADR requires additional lens for designing IS in such a complex organizational context. Through conducting ADR, it is seen that an ethnographic framework has potential complementarities for understanding complex contexts thereby enhancing the ADR processes. This paper argues that conducting ADR with an ethnographic approach enhances design of IS and organizational contexts. Finally, this paper aims presents a broader methodological framework, Action Design Ethnographic Research (ADER), for designing artefacts as well as IS. This is illustrated through the case of a land records updating service in Bangladesh
A Period and a Prediction for the Of?p Spectrum Alternator HD 191612
The observational picture of the enigmatic O-type spectrum variable HD191612
has been sharpened substantially. A symmetrical, low-amplitude light curve with
a period near 540 d has recently been reported from Hipparcos photometry. This
period satisfies all of the spectroscopy since at least 1982, including
extensive new observations during 2003 and 2004, and it has predicted the next
transition during September--October 2004. Measurements of the H alpha
equivalent width reveal a sharp emission peak in the phase diagram, in contrast
to the apparently sinusoidal light curve. The He II absorption-line strength is
essentially constant, while He I varies strongly, possibly filled in by
emission in the O6 state, thus producing the apparent spectral-type variations.
The O8 state appears to be the "normal" one. Two intermediate O7 observations
have been obtained, which fall at the expected phases, but these are the only
modern observations of the transitions so far. The period is too long for
rotation or pulsation; although there is no direct evidence as yet for a
companion, a model in which tidally induced oscillations drive an enhanced wind
near periastron of an eccentric orbit appears promising. Further observations
during the now predictable transitions may provide a critical test. Ultraviolet
and X-ray observations during both states will likely also prove illuminating.Comment: 7 pages, 3 figures, 1 table; scheduled for the 2004 December 10 issue
of ApJL, Vol. 617, No. 1. ApJ
Performance of the EUDET-type beam telescopes
Test beam measurements at the test beam facilities of DESY have been
conducted to characterise the performance of the EUDET-type beam telescopes
originally developed within the EUDET project. The beam telescopes are equipped
with six sensor planes using MIMOSA26 monolithic active pixel devices. A
programmable Trigger Logic Unit provides trigger logic and time stamp
information on particle passage. Both data acquisition framework and offline
reconstruction software packages are available. User devices are easily
integrable into the data acquisition framework via predefined interfaces.
The biased residual distribution is studied as a function of the beam energy,
plane spacing and sensor threshold. Its standard deviation at the two centre
pixel planes using all six planes for tracking in a 6\,GeV
electron/positron-beam is measured to be
(2.88\,\pm\,0.08)\,\upmu\meter.Iterative track fits using the formalism of
General Broken Lines are performed to estimate the intrinsic resolution of the
individual pixel planes. The mean intrinsic resolution over the six sensors
used is found to be (3.24\,\pm\,0.09)\,\upmu\meter.With a 5\,GeV
electron/positron beam, the track resolution halfway between the two inner
pixel planes using an equidistant plane spacing of 20\,mm is estimated to
(1.83\,\pm\,0.03)\,\upmu\meter assuming the measured intrinsic resolution.
Towards lower beam energies the track resolution deteriorates due to increasing
multiple scattering. Threshold studies show an optimal working point of the
MIMOSA26 sensors at a sensor threshold of between five and six times their RMS
noise. Measurements at different plane spacings are used to calibrate the
amount of multiple scattering in the material traversed and allow for
corrections to the predicted angular scattering for electron beams
Crystallization and preliminary diffraction analysis of Wzi, a member of the capsule export and assembly pathway in Escherichia coli
Wzi is a membrane protein from E. coli thought to be involved in the attachment of capsular polysaccharides to the bacterial surface. This reports describes recombinant Wzi’s purification, crystallization and the results of initial diffraction studies
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