22,431 research outputs found
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Bistability through triadic closure
We propose and analyse a class of evolving network models suitable for describing a dynamic topological structure. Applications include telecommunication, on-line social behaviour and information processing in neuroscience. We model the evolving network as a discrete time Markov chain, and study a very general framework where, conditioned on the current state, edges appear or disappear independently at the next timestep. We show how to exploit symmetries in the microscopic, localized rules in order to obtain conjugate classes of random graphs that simplify analysis and calibration of a model. Further, we develop a mean ļ¬eld theory for describing network evolution. For a simple but realistic scenario incorporating the triadic closure eļ¬ect that has been empirically observed by social scientists (friends of friends tend to become friends), the mean ļ¬eld theory predicts bistable dynamics, and computational results conļ¬rm this prediction. We also discuss the calibration issue for a set of real cell phone data, and ļ¬nd support for a stratiļ¬ed model, where individuals are assigned to one of two distinct groups having diļ¬erent within-group and across-group dynamics
A Fourier transform spectrometer for visible and near ultra-violet measurements of atmospheric absorption
The development of a prototype, ground-based, Sun-pointed Michelson interferometric spectrometer is described. Its intended use is to measure the atmospheric amount of various gases which absorb in the near-infrared, visible, and near-ultraviolet portions of the electromagnetic spectrum. Preliminary spectra which contain the alpha, 0.8 micrometer, and rho sigma tau water vapor absorption bands in the near-infrared are presented to indicate the present capability of the system. Ultimately, the spectrometer can be used to explore the feasible applications of Fourier transform spectroscopy in the ultraviolet where grating spectrometers were used exclusively
Arkansas Small-Grain Cultivar Performance Tests 2004-2005
Small-grain cultivar performance tests are conducted each year in Arkansas by the Arkansas Agricultural Experiment Station, Department of Crop, Soil and Environmental Sciences. The tests provide information to companies developing cultivars and/or marketing seed within the state and aid the Arkansas Cooperative Extension Service in formulating cultivar recommendations for smallgrain producers
Application of pushbroom altimetry from space using large space antennas
The capabilities of multibeam altimetry are discussed and an interferometric multibeam technique for doing precision altimetry is described. The antenna feed horn arrangement and the resulting footprint lube pattern are illustrated. Plans for a shuttle multibeam altimetry mission are also discussed
Carbon Brainprint Case Study: optimising defouling schedules for oil- refinerypreheat trains
In an oil refinery, crude oil is heated to 360-370Ā°C before entering a
distillation columnoperating at atmospheric pressure where the gas fraction and
several liquid fractions withdifferent boiling points (e.g. gasoline, kerosene,
diesel, gas oil, heavy gas oil) are separated off.The crude oil is heated in two
stages. The preheat train - a series of heat exchangers - heats itfrom ambient
temperature to about 270Ā°C when it enters the furnace, known as the coil
inlettemperature. The furnace then heats the oil to the temperature required for
distillation.The purpose of the preheat train is to recover heat from the liquid
products extracted in thedistillation column. Without this, 2-3% of the crude
oil throughput would be used for heating thefurnace; with the preheat train up
to 70% of the required heat is recovered. It also serves tocool the refined
products: further cooling normally uses air or water.
Over time, fouling reduces the performance of the heat exchangers, increasing
the amount ofenergy that has to be supplied. It is possible to bypass units to
allow them to be cleaned, withan associated cost and temporary loss of
performance. The cleaning schedule thus has animpact on the overall efficiency,
cost of operation and emissions.
The group at the Department of Chemical Engineering and Biotechnology at
Cambridgedeveloped a scheduling algorithm for this non-linear optimisation
problem. It yields a good,though not-necessarily optimal, schedule and can
handle additional constraints, such as thepresence of desalters with specific
temperature requirements within the preheat train. This isnow being developed
into a commercial software product.
Data from two refineries - one operated by Repsol YPF in Argentina and the Esso
FawleyRefinery in the UK - were used to model the systems and test the
algorithm.
For the Repsol YPF refinery, when compared with current practice and including a
constrainton the desalter inlet temperature, the most conservative estimate of
the emissions reductionwas 773 t CO2/year. This assumed a furnace efficiency of
90%. The emissions reductionincreased to 927 t CO2/year at 75% efficiency and
1730 t CO2/year at 40%. These were basedon a stoichiometric estimate of the
emissions from the furnace. Using a standard emissionfactor increased them by
7.4%.
For Esso Fawley, the estimated emission reduction compared to no maintenance
was1435 t CO2/year at 90% furnace efficiency. This increased to 1725 t CO2/year
at 75% and3225 t CO2/year at 40% efficien
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Soil microbial communities in restored and unrestored coastal dune ecosystems in California
Most restoration projects involving invasive plant eradication tend to focus on plant removal with little consideration given to how these invasives change soil microbial communities. However, soil microorganisms can determine invasibility of habitats and, in turn, be altered by invasives once established, potentially inhibiting native plant establishment. We studied soil microbial communities in coastal dunes with varying invasion intensity and different restoration approaches (herbicide, mechanical excavation) at Point Reyes National Seashore. Overall, we found evidence of a strong link between bacterial and fungal soil communities and the presence of invasives and restoration approach. Heavily invaded sites were characterized by a lower abundance of putatively identified nitrifiers, fermentative bacteria, fungal parasites, and fungal dung saprotrophs and a higher abundance of cellulolytic bacteria and a class of arbuscular mycorrhizal fungi (Archaeosporomycetes). Changes in soil microbiota did not fully dissipate following removal of invasives using herbicide, with exception of reductions in cellulolytic bacteria and Archaeosporomycetes abundance. Mechanical restoration effectively removed both invasives and soil legacy effects by inverting or āflippingā rhizome-contaminated surface soils with soils from below and may have inadvertently induced other adverse effects on soils that impeded reestablishment of native dune plants. Land managers should consider additional measures to counteract lingering legacy effects and/or focus restoration efforts in areas where legacy effects are less pronounced
Self-reported pain severity is associated with a history of coronary heart disease
This study was funded by Arthritis Research UK (grant number: 17292).Peer reviewedPublisher PD
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