3,974 research outputs found
Work relations for a system governed by Tsallis statistics
We derive analogues of the Jarzynski equality and Crooks relation to
characterise the nonequilibrium work associated with changes in the spring
constant of an overdamped oscillator in a quadratically varying spatial
temperature profile. The stationary state of such an oscillator is described by
Tsallis statistics, and the work relations for certain processes may be
expressed in terms of q-exponentials. We suggest that these identities might be
a feature of nonequilibrium processes in circumstances where Tsallis
distributions are 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
Steel Melting in a Pilot Plant Shaft Furnace
One of the present authors, in a paper to the Iron
and Steel Institute in 1954 entitled "The Future of Steel Melting", re-introduced the idea of continuous counterflow steel melting.
In this paper it was stated that a suitable counterflow
furnace, in which the heat of the waste gases from a melt-ing chamber is used to preheat the charge in a counter current system, could attain thermal efficiencies of the order of 70%, compared with the maximum possible effic-iency of 50% for the existing open hearth furnace
Development and application of a catchment scale pesticide fate and transport model for use in drinking water risk assessment
This paper describes the development and application of IMPT (Integrated Model for Pesticide Transport), a parameter-efficient tool for predicting diffuse-source pesticide concentrations in surface waters used for drinking water supply. The model was applied to a small UK headwater catchment with high frequency (8 h) pesticide monitoring data and to five larger catchments (479–1653 km2) with sampling approximately every 14 days. Model performance was good for predictions of both flow (Nash Sutcliffe Efficiency generally > 0.59 and PBIAS < 10%) and pesticide concentrations, although low sampling frequency in the larger catchments is likely to mask the true episodic nature of exposure. The computational efficiency of the model, along with the fact that most of its parameters can be derived from existing national soil property data mean that it can be used to rapidly predict pesticide exposure in multiple surface water resources to support operational and strategic risk assessments
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")
A non-linear optimal estimation inverse method for radio occultation measurements of temperature, humidity and surface pressure
An optimal estimation inverse method is presented which can be used to
retrieve simultaneously vertical profiles of temperature and specific humidity,
in addition to surface pressure, from satellite-to-satellite radio occultation
observations of the Earth's atmosphere. The method is a non-linear, maximum
{\it a posteriori} technique which can accommodate most aspects of the real
radio occultation problem and is found to be stable and to converge rapidly in
most cases. The optimal estimation inverse method has two distinct advantages
over the analytic inverse method in that it accounts for some of the effects of
horizontal gradients and is able to retrieve optimally temperature and humidity
simultaneously from the observations. It is also able to account for
observation noise and other sources of error. Combined, these advantages ensure
a realistic retrieval of atmospheric quantities.
A complete error analysis emerges naturally from the optimal estimation
theory, allowing a full characterisation of the solution. Using this analysis a
quality control scheme is implemented which allows anomalous retrieval
conditions to be recognised and removed, thus preventing gross retrieval
errors.
The inverse method presented in this paper has been implemented for bending
angle measurements derived from GPS/MET radio occultation observations of the
Earth. Preliminary results from simulated data suggest that these observations
have the potential to improve NWP model analyses significantly throughout their
vertical range.Comment: 18 (jgr journal) pages, 7 figure
Bringing Lunar LiDAR Back Down to Earth: Mapping Our Industrial Heritage through Deep Transfer Learning
This is the final version. Available on open access from MDPI via the DOI in this recordThis article presents a novel deep learning method for semi-automated detection of historic mining pits using aerial LiDAR data. The recent emergence of national scale remotely sensed datasets has created the potential to greatly increase the rate of analysis and recording of cultural heritage sites. However, the time and resources required to process these datasets in traditional desktop surveys presents a near insurmountable challenge. The use of artificial intelligence to carry out preliminary processing of vast areas could enable experts to prioritize their prospection focus; however, success so far has been hindered by the lack of large training datasets in this field. This study develops an innovative transfer learning approach, utilizing a deep convolutional neural network initially trained on Lunar LiDAR datasets and reapplied here in an archaeological context. Recall rates of 80% and 83% were obtained on the 0.5 m and 0.25 m resolution datasets respectively, with false positive rates maintained below 20%. These results are state of the art and demonstrate that this model is an efficient, effective tool for semi-automated object detection for this type of archaeological objects. Further tests indicated strong potential for detection of other types of archaeological objects when trained accordingly
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