2,301 research outputs found
Maximally-fast coarsening algorithms
We present maximally-fast numerical algorithms for conserved coarsening
systems that are stable and accurate with a growing natural time-step . For non-conserved systems, only effectively finite timesteps
are accessible for similar unconditionally stable algorithms. We compare the
scaling structure obtained from our maximally-fast conserved systems directly
against the standard fixed-timestep Euler algorithm, and find that the error
scales as -- so arbitrary accuracy can be achieved.Comment: 5 pages, 3 postscript figures, Late
Controlling the accuracy of unconditionally stable algorithms in Cahn-Hilliard Equation
Given an unconditionally stable algorithm for solving the Cahn-Hilliard
equation, we present a general calculation for an analytic time step \d \tau
in terms of an algorithmic time step \dt. By studying the accumulative
multi-step error in Fourier space and controlling the error with arbitrary
accuracy, we determine an improved driving scheme \dt=At^{2/3} and confirm
the numerical results observed in a previous study \cite{Cheng1}.Comment: 4 pages, late
Evidence of widespread degradation of gene control regions in hominid genomes
Although sequences containing regulatory elements located close to protein-coding genes are often only weakly conserved during evolution, comparisons of rodent genomes have implied that these sequences are subject to some selective constraints. Evolutionary conservation is particularly apparent upstream of coding sequences and in first introns, regions that are enriched for regulatory elements. By comparing the human and chimpanzee genomes, we show here that there is almost no evidence for conservation in these regions in hominids. Furthermore, we show that gene expression is diverging more rapidly in hominids than in murids per unit of neutral sequence divergence. By combining data on polymorphism levels in human noncoding DNA and the corresponding human¿chimpanzee divergence, we show that the proportion of adaptive substitutions in these regions in hominids is very low. It therefore seems likely that the lack of conservation and increased rate of gene expression divergence are caused by a reduction in the effectiveness of natural selection against deleterious mutations because of the low effective population sizes of hominids. This has resulted in the accumulation of a large number of deleterious mutations in sequences containing gene control elements and hence a widespread degradation of the genome during the evolution of humans and chimpanzees
Transformation and fate of microphytobenthos carbon in subtropical, intertidal sediments: potential for long-term carbon retention revealed by <sup>13</sup>C-labeling
Microphytobenthos (MPB) are ubiquitous in coastal sediments, but the fate of
their production (carbon biomass) is poorly defined. The processing and fate
of MPB-derived carbon in subtropical intertidal sediments was investigated
through in situ labeling with <sup>13</sup>C-bicarbonate. Of the added <sup>13</sup>C,
100% was fixed within ~ 4 h, suggesting that MPB
productivity was limited by inorganic carbon availability. Although there
was rapid transfer of <sup>13</sup>C to bacteria (within 12 h), a relatively small
fraction of <sup>13</sup>C was transferred to heterotrophs (up to 12.5% of
total fixed <sup>13</sup>C into bacteria and 0.01% into foraminifera). MPB was
the major reservoir for <sup>13</sup>C throughout the study, suggesting that
production of extracellular polymeric substances was limited and/or MPB
recycled <sup>13</sup>C. This retention of <sup>13</sup>C was reflected in remarkably
slow estimated turnover times for the MPB community (66–100 d). Over 31 d,
~ 70% of the <sup>13</sup>C was lost from sediments. This was
primarily via resuspension (~ 55%), enhanced by elevated
freshwater flow following rainfall. A further ~ 13% was
lost via fluxes of dissolved inorganic carbon during inundation. However,
<sup>13</sup>C losses via dissolved organic carbon fluxes from inundated sediments
(0.5%) and carbon dioxide fluxes from exposed sediments (<0.1%) were minimal. The retention of ~ 30% of the carbon
fixed by MPB within one tidal exposure after > 30 d, despite high
resuspension, demonstrates the potentially substantial longer term retention
of MPB-derived carbon in unvegetated sediments and suggests that MPB may
contribute to carbon burial ("blue carbon")
Articular cartilage collagen: an irreplaceable framework?
Adult articular cartilage by dry weight is two-thirds collagen. The collagen has a unique molecular phenotype. The nascent type II collagen fibril is a heteropolymer, with collagen IX molecules covalently linked to the surface and collagen XI forming the filamentous template of the fibril as a whole. The functions of collagens IX and XI in the heteropolymer are far from clear but, evidently, they are critically important since mutations in COLIX and COLXI genes can result in chondrodysplasia syndromes. Here we review what is known of the collagen assembly and present new evidence that collagen type III becomes covalently added to the polymeric fabric of adult human articular cartilage, perhaps as part of a matrix repair or remodelling process
A combined field/remote sensing approach for characterizing landslide risk in coastal areas
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Understanding the key factors controlling slope failure mechanisms in coastal areas is the
first and most important step for analyzing, reconstructing and predicting the scale, location
and extent of future instability in rocky coastlines. Different failure mechanisms may be
possible depending on the influence of the engineering properties of the rock mass (including the fracture network), the persistence and type of discontinuity and the relative aspect or orientation of the coastline. Using a section of the North Coast of Cornwall, UK, as an example we present a multi-disciplinary approach for characterizing landslide risk associated with coastal instabilities in a blocky rock mass. Remotely captured terrestrial and aerial LiDAR and photogrammetric data was interrogated using Geographic Information System (GIS) techniques to provide a framework for subsequent analysis, interpretation and validation. The remote sensing mapping data was used to define the rock mass discontinuity network of the area and to differentiate between major and minor geological structures controlling the evolution of the North Coast of Cornwall. Kinematic instability maps generated from aerial LiDAR data using GIS techniques and results from structural and engineering geological surveys are presented. With this method, it was possible to highlight the types of kinematic failure mechanism that may generate coastal landslides and highlight areas that are more susceptible to instability or increased risk of future instability. Multi-temporal aerial LiDAR data and orthophotos were also studied using GIS techniques to locate recent landslide failures, validate the results obtained from the kinematic instability maps through site observations and provide improved understanding of the factors controlling the coastal geomorphology. The approach adopted is not only useful for academic research, but also for local authorities and consultancy's when assessing the likely risks of coastal instability
Assessment of the ergogenic effect of caffeine supplementation on mood, anticipation timing, and muscular strength in older adults
The effect of caffeine to promote improvements in mood, cognition, and exercise performance has been well established in young and athletic adults. However, little is known about whether such nutritional ergogenic aids are effective in enhancing psychological well-being, physiological or cognitive performance in older adults. This study assesses the ergogenic effect of caffeine on mood, perceptual-motor coupling, and muscular strength in an older human population. Following a familiarization session, 12 apparently healthy volunteers (nine females and three males; 69 ± 6 years) completed two laboratory visits. "Pre ingestion" trials of mood state Brunel Mood State Inventory (BRUMS) and coincidence anticipation performance (Bassin anticipation timer) at slow (3 mph) and fast (8 mph) stimulus speeds were completed on both visits. Using a randomized, double-blind, cross-over design, participants consumed either caffeine (3 mg/kg body mass) or a placebo. Sixty minutes postingestion participants repeated the trials before completing a set of 10 consecutive repetitions of maximal knee extension using isokinetic dynamometry. Rating of perceived exertion (RPE) was assessed following the fifth and final repetition. Caffeine ingestion significantly improved mood state scores for vigor by 17% (P = 0.009) and reduced absolute error by 35% (P = 0.045) during coincidence anticipation assessment at 8 mph compared to placebo. There were no other significant effects. Caffeine ingestion failed to augment maximal voluntary contraction of the knee extensors and RPE did not prove to be significantly different to from placebo (P > 0.33 in each case). Acute caffeine ingestion may not be an effective ergogenic aid for improving muscular strength in older adults but could possibly be used as a nutrition supplement for enhancing mood and improving cognitive performance in daily living tasks where interceptive timing skills are required
Covert Quantum Communication Over Optical Channels
We explore the problem of covertly communicating qubits over the lossy
thermal-noise bosonic channel, which is a quantum-mechanical model of many
practical channels, including optical. Covert communication ensures that an
adversary is unable to detect the presence of transmissions, which are
concealed in channel noise. We investigate an achievable lower bound on quantum
covert communication using photonic dual-rail qubits. This encoding has
practical significance, as it has been proposed for long-range repeater-based
quantum communication over optical channels
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