792 research outputs found
Friends or Foes? Emerging Impacts of Biological Toxins
Toxins are substances produced from biological sources (e.g., animal, plants, microorganisms) that have deleterious effects on a living organism. Despite the obvious health concerns of being exposed to toxins, they are having substantial positive impacts in a number of industrial sectors. Several toxin-derived products are approved for clinical, veterinary, or agrochemical uses. This review sets out the case for toxins as ‘friends’ that are providing the basis of novel medicines, insecticides, and even nucleic acid sequencing technologies. We also discuss emerging toxins (‘foes’) that are becoming increasingly prevalent in a range of contexts through climate change and the globalisation of food supply chains and that ultimately pose a risk to health
Transient domain walls and lepton asymmetry in the Left-Right symmetric model
It is shown that the dynamics of domain walls in Left-Right symmetric models,
separating respective regions of unbroken SU(2)_L and SU(2)_R in the early
universe, can give rise to baryogenesis via leptogenesis. Neutrinos have a
spatially varying complex mass matrix due to CP-violating scalar condensates in
the domain wall. The motion of the wall through the plasma generates a flux of
lepton number across the wall which is converted to a lepton asymmetry by
helicity-flipping scatterings. Subsequent processing of the lepton excess by
sphalerons results in the observed baryon asymmetry, for a range of parameters
in Left-Right symmetric models.Comment: v2 version accepted for publication in Phys. Rev. D. Discussion in
Introduction and Conclusion sharpened. Equation (12) corrected. 16 pages, 3
figure files, RevTeX4 styl
Asymptotically cylindrical 7-manifolds of holonomy G_2 with applications to compact irreducible G_2-manifolds
We construct examples of exponentially asymptotically cylindrical Riemannian
7-manifolds with holonomy group equal to G_2. To our knowledge, these are the
first such examples. We also obtain exponentially asymptotically cylindrical
coassociative calibrated submanifolds. Finally, we apply our results to show
that one of the compact G_2-manifolds constructed by Joyce by desingularisation
of a flat orbifold T^7/\Gamma can be deformed to one of the compact
G_2-manifolds obtainable as a generalized connected sum of two exponentially
asymptotically cylindrical SU(3)-manifolds via the method given by the first
author (math.DG/0012189).Comment: 36 pages; v2: corrected trivial typos; v3: some arguments corrected
and improved; v4: a number of improvements on presentation, paritularly in
sections 4 and 6, including an added picture
A parallel implementation of an off-lattice individual-based model of multicellular populations
As computational models of multicellular populations include ever more detailed descriptions of biophysical and biochemical processes, the computational cost of simulating such models limits their ability to generate novel scientific hypotheses and testable predictions. While developments in microchip technology continue to increase the power of individual processors, parallel computing offers an immediate increase in available processing power. To make full use of parallel computing technology, it is necessary to develop specialised algorithms. To this end, we present a parallel algorithm for a class of off-lattice individual-based models of multicellular populations. The algorithm divides the spatial domain between computing processes and comprises communication routines that ensure the model is correctly simulated on multiple processors. The parallel algorithm is shown to accurately reproduce the results of a deterministic simulation performed using a pre-existing serial implementation. We test the scaling of computation time, memory use and load balancing as more processes are used to simulate a cell population of fixed size. We find approximate linear scaling of both speed-up and memory consumption on up to 32 processor cores. Dynamic load balancing is shown to provide speed-up for non-regular spatial distributions of cells in the case of a growing population
Transient Magnetic and Doppler Features Related to the White-light Flares in NOAA 10486
Rapidly moving transient features have been detected in magnetic and Doppler
images of super-active region NOAA 10486 during the X17/4B flare of 28 October
2003 and the X10/2B flare of 29 October 2003. Both these flares were extremely
energetic white-light events. The transient features appeared during impulsive
phases of the flares and moved with speeds ranging from 30 to 50 km s.
These features were located near the previously reported compact acoustic
\cite{Donea05} and seismic sources \cite{Zharkova07}. We examine the origin of
these features and their relationship with various aspects of the flares, {\it
viz.}, hard X-ray emission sources and flare kernels observed at different
layers - (i) photosphere (white-light continuum), (ii) chromosphere (H
6563\AA), (iii) temperature minimum region (UV 1600\AA), and (iv) transition
region (UV 284\AA).Comment: 26 pages, 13 figures, 2 tables, accepted for publication in Solar
Physic
The General Solution of Bianchi Type Vacuum Cosmology
The theory of symmetries of systems of coupled, ordinary differential
equations (ODE) is used to develop a concise algorithm in order to obtain the
entire space of solutions to vacuum Bianchi Einstein Field Equations (EFEs).
The symmetries used are the well known automorphisms of the Lie algebra for the
corresponding isometry group of each Bianchi Type, as well as the scaling and
the time re-parametrization symmetry. The application of the method to Type
VII_h results in (a) obtaining the general solution of Type VII_0 with the aid
of the third Painlev\'{e} transcendental (b) obtaining the general solution of
Type with the aid of the sixth Painlev\'{e} transcendental (c) the
recovery of all known solutions (six in total) without a prior assumption of
any extra symmetry (d) The discovery of a new solution (the line element given
in closed form) with a G_3 isometry group acting on T_3, i.e. on time-like
hyper-surfaces, along with the emergence of the line element describing the
flat vacuum Type VII_0 Bianchi Cosmology.Comment: latex2e source file, 27 pages, 2 tables, no fiure
A viewpoint on material and design considerations for oesophageal stents with extended lifetime
Oesophageal stents are meshed tubular implants designed to maintain patency of the oesophageal lumen and attenuate the symptoms of oesophageal cancer. Oesophageal cancers account for one in twenty cancer diagnoses and can lead to dysphasia, malnutrition and the diminishment of patient quality of life (QOL). Self-expanding oesophageal stents are the most common approach to attenuate these symptoms. Recent advances in oncological therapy have enabled patient survival beyond the lifetime of current devices. This introduces new complications for palliation, driving the need for innovation in stent design. This review identifies the factors responsible for stent failure. It explores the challenges of enhancing the longevity of stent therapies and outlines solutions to improving clinical outcomes. Discussions focus on the role of stent materials, construction methods, and coatings upon device performance. We found three key stent enhancement strategies currently used; material surface treatments, anti-migratory modifications, and biodegradable skeletons. Furthermore, radioactive and drug eluting stent designs were identified as emerging novel treatments. In conclusion, the review offers an overview of remaining key challenges in oesophageal stent design and potential solutions. It is clear that further research is needed to improve the clinical outcome of stents and patient QOL
Atomic and molecular suite of R-matrix codes for ultrafast dynamics in strong laser fields and electron/positron scattering
Synopsis: We describe and illustrate a number of recent developments of the atomic and molecular ab initio R-matrix suites for both time-dependent calculations of ultrafast laser-induced dynamics and time-independent calculations of photoionization and electron scattering
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