10,297 research outputs found
Proton imaging of stochastic magnetic fields
Recent laser-plasma experiments report the existence of dynamically
significant magnetic fields, whose statistical characterisation is essential
for understanding the physical processes these experiments are attempting to
investigate. In this paper, we show how a proton imaging diagnostic can be used
to determine a range of relevant magnetic field statistics, including the
magnetic-energy spectrum. To achieve this goal, we explore the properties of an
analytic relation between a stochastic magnetic field and the image-flux
distribution created upon imaging that field. We conclude that features of the
beam's final image-flux distribution often display a universal character
determined by a single, field-scale dependent parameter - the contrast
parameter - which quantifies the relative size of the correlation length of the
stochastic field, proton displacements due to magnetic deflections, and the
image magnification. For stochastic magnetic fields, we establish the existence
of four contrast regimes - linear, nonlinear injective, caustic and diffusive -
under which proton-flux images relate to their parent fields in a qualitatively
distinct manner. As a consequence, it is demonstrated that in the linear or
nonlinear injective regimes, the path-integrated magnetic field experienced by
the beam can be extracted uniquely, as can the magnetic-energy spectrum under a
further statistical assumption of isotropy. This is no longer the case in the
caustic or diffusive regimes. We also discuss complications to the
contrast-regime characterisation arising for inhomogeneous, multi-scale
stochastic fields, as well as limitations currently placed by experimental
capabilities on extracting magnetic field statistics. The results presented in
this paper provide a comprehensive description of proton images of stochastic
magnetic fields, with applications for improved analysis of given proton-flux
images.Comment: Main paper pp. 1-29; appendices pp. 30-84. 24 figures, 2 table
Coronal hole boundaries at small scales: IV. SOT view Magnetic field properties of small-scale transient brightenings in coronal holes
We study the magnetic properties of small-scale transients in coronal hole.
We found all brightening events are associated with bipolar regions and caused
by magnetic flux emergence followed by cancellation with the pre-existing and
newly emerging magnetic flux. In the coronal hole, 19 of 22 events have a
single stable polarity which does not change its position in time. In eleven
cases this is the dominant polarity. The dominant flux of the coronal hole form
the largest concentration of magnetic flux in terms of size while the opposite
polarity is distributed in small concentrations. In the coronal hole the number
of magnetic elements of the dominant polarity is four times higher than the
non-dominant one. The supergranulation configuration appears to preserve its
general shape during approximately nine hours of observations although the
large concentrations in the network did evolve and were slightly displaced, and
their strength either increased or decreased. The emission fluctuations seen in
the X-ray bright points are associated with reoccurring magnetic cancellation
in the footpoints. Unique observations of an X-ray jet reveal similar magnetic
behaviour in the footpoints, i.e. cancellation of the opposite polarity
magnetic flux. We found that the magnetic flux cancellation rate during the jet
is much higher than in bright points. Not all magnetic cancellations result in
an X-ray enhancement, suggesting that there is a threshold of the amount of
magnetic flux involved in a cancellation above which brightening would occur at
X-ray temperatures. Our study demonstrates that the magnetic flux in coronal
holes is continuously recycled through magnetic reconnection which is
responsible for the formation of numerous small-scale transient events. The
open magnetic flux forming the coronal-hole phenomenon is largely involved in
these transient features.Comment: 19 pages, 18 figures, A&A in pres
Coherent vibrations of submicron spherical gold shells in a photonic crystal
Coherent acoustic radial oscillations of thin spherical gold shells of
submicron diameter excited by an ultrashort optical pulse are observed in the
form of pronounced modulations of the transient reflectivity on a subnanosecond
time scale. Strong acousto-optical coupling in a photonic crystal enhances the
modulation of the transient reflectivity up to 4%. The frequency of these
oscillations is demonstrated to be in good agreement with Lamb theory of free
gold shells.Comment: Error in Eqs.2 and 3 corrected; Tabl. I corrected; Fig.1 revised; a
model that explains the dependence of the oscillation amplitude of the
transient reflectivity with wavelength adde
Lowest Landau-level description of a Bose-Einstein condensate in a rapidly rotating anisotropic trap
A rapidly rotating Bose-Einstein condensate in a symmetric two-dimensional
trap can be described with the lowest Landau-level set of states. In this case,
the condensate wave function psi(x,y) is a Gaussian function of r^2 = x^2 +
y^2, multiplied by an analytic function P(z) of the single complex variable z=
x+ i y; the zeros of P(z) denote the positions of the vortices. Here, a similar
description is used for a rapidly rotating anisotropic two-dimensional trap
with arbitrary anisotropy (omega_x/omega_y le 1). The corresponding condensate
wave function psi(x,y) has the form of a complex anisotropic Gaussian with a
phase proportional to xy, multiplied by an analytic function P(zeta), where
zeta is proportional to x + i beta_- y and 0 le beta_- le 1 is a real parameter
that depends on the trap anisotropy and the rotation frequency. The zeros of
P(zeta) again fix the locations of the vortices. Within the set of lowest
Landau-level states at zero temperature, an anisotropic parabolic density
profile provides an absolute minimum for the energy, with the vortex density
decreasing slowly and anisotropically away from the trap center.Comment: 13 pages, 1 figur
Artificial intelligence and augmented intelligence collaboration: Regaining trust and confidence in the financial sector
Robots and chatbots are sophisticated. Artificial intelligence (AI) is increasingly popular in the financial industry due to its ability to provide customers with cheap, efficient and personalised services. This article uses doctrinal sources and a case study to show that many banks and FinTech start-ups are investing in AI. Yet, there are a number of challenges arising from the use of AI which could undermine trust and confidence amongst consumers. This article features the issue of bias and discrimination in banking. There is evidence that algorithms discriminate against certain races and gender. Legislative gaps in the Equality Act 2010 and the General Data Protection Regime will be analysed. Ultimately, human beings are still needed to input, train and help machines to learn. Fortunately, the FCA are leading in regulating technology, from the launch of regulatory sandboxes to their co-operative collaboration with FinTech start-ups on regulatory matters. Augmented intelligence collaboration is needed to enable industry players and regulators to provide seamless regulation and financial stability. The future of AI regulation is inter-disciplinary in approach
Analysis of parainfluenza virus-5 hemagglutinin-neuraminidase protein mutants that are blocked in internalization and degradation
AbstractThe PIV-5 hemagglutinin-neuraminidase (HN) protein is a multifunctional protein with sialic acid binding, neuraminidase and fusion promotion activity. HN is internalized by clathrin-mediated endocytosis and degraded. HN lacks internalization signals in its cytoplasmic tail but a single glutamic acid present at residue 37 at the putative transmembrane/ectodomain boundary is critical. We rescued rPIV-5 with mutations E37D or E37K, which have been shown to impair or abolish HN internalization, respectively. These viruses exhibited growth properties similar to wild-type (wt) virus but are impaired for fitness in tissue culture. Biochemical analysis of HN activities showed differences between HN E37D and HN E37K in fusion promotion and incorporation of HN and F into virions. Furthermore, oligomeric analyses indicate that HN E37 mutants perturb the tetrameric organization of HN, probably by destabilizing the dimer-of-dimers interface
The Role of Education in AIDS Prevention
The severity of the current AIDS epidemic, combined with the lack of successful biological interventions, necessitates an active educational program as the primary intervention strategy. Health education theories abound, but relatively little definitive application of these theories has been made to the issues involved with HIV transmission: sexual behavior and the sharing of intravenous drug apparatus. Significant behavior changes have occurred in some people, but the consistency of the behavior change may be difficult to sustain. Thus, the authors suggest that health education should be delivered repeatedly in culturally acceptable language and format, by community leaders, and through many different approaches (churches, schools, media, and so on). Finally, because of the limited definitive evidence regarding these approaches with respect to AIDS, considerable resources should be provided to evaluate these strategies and to revise programs on the basis of the evaluations
Gamma-Ray Bursts as a Probe of the Very High Redshift Universe
We show that, if many GRBs are indeed produced by the collapse of massive
stars, GRBs and their afterglows provide a powerful probe of the very high
redshift (z > 5) universe.Comment: To appear in Proc. of the 5th Huntsville Gamma-Ray Burst Symposium, 5
pages, LaTe
Treatment compliance and effectiveness of a cognitive behavioural intervention for low back pain : a complier average causal effect approach to the BeST data set
Background:
Group cognitive behavioural intervention (CBI) is effective in reducing low-back pain and disability in comparison to advice in primary care. The aim of this analysis was to investigate the impact of compliance on estimates of treatment effect and to identify factors associated with compliance.
Methods:
In this multicentre trial, 701 adults with troublesome sub-acute or chronic low-back pain were recruited from 56 general practices. Participants were randomised to advice (control n = 233) or advice plus CBI (n = 468). Compliance was specified a priori as attending a minimum of three group sessions and the individual assessment. We estimated the complier average causal effect (CACE) of treatment.
Results:
Comparison of the CACE estimate of the mean treatment difference to the intention-to-treat (ITT) estimate at 12 months showed a greater benefit of CBI amongst participants compliant with treatment on the Roland Morris Questionnaire (CACE: 1.6 points, 95% CI 0.51 to 2.74; ITT: 1.3 points, 95% CI 0.55 to 2.07), the Modified Von Korff disability score (CACE: 12.1 points, 95% CI 6.07 to 18.17; ITT: 8.6 points, 95% CI 4.58 to 12.64) and the Modified von Korff pain score (CACE: 10.4 points, 95% CI 4.64 to 16.10; ITT: 7.0 points, 95% CI 3.26 to 10.74). People who were non-compliant were younger and had higher pain scores at randomisation.
Conclusions:
Treatment compliance is important in the effectiveness of group CBI. Younger people and those with more pain are at greater risk of non-compliance
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