9,724 research outputs found
A parallel multistate framework for atomistic non-equilibrium reaction dynamics of solutes in strongly interacting organic solvents
We describe a parallel linear-scaling computational framework developed to
implement arbitrarily large multi-state empirical valence bond (MS-EVB)
calculations within CHARMM. Forces are obtained using the Hellman-Feynmann
relationship, giving continuous gradients, and excellent energy conservation.
Utilizing multi-dimensional Gaussian coupling elements fit to CCSD(T)-F12
electronic structure theory, we built a 64-state MS-EVB model designed to study
the F + CD3CN -> DF + CD2CN reaction in CD3CN solvent. This approach allows us
to build a reactive potential energy surface (PES) whose balanced accuracy and
efficiency considerably surpass what we could achieve otherwise. We use our PES
to run MD simulations, and examine a range of transient observables which
follow in the wake of reaction, including transient spectra of the DF
vibrational band, time dependent profiles of vibrationally excited DF in CD3CN
solvent, and relaxation rates for energy flow from DF into the solvent, all of
which agree well with experimental observations. Immediately following
deuterium abstraction, the nascent DF is in a non-equilibrium regime in two
different respects: (1) it is highly excited, with ~23 kcal mol-1 localized in
the stretch; and (2) not yet Hydrogen bonded to the CD3CN solvent, its
microsolvation environment is intermediate between the non-interacting
gas-phase limit and the solution-phase equilibrium limit. Vibrational
relaxation of the nascent DF results in a spectral blue shift, while relaxation
of its microsolvation environment results in a red shift. These two competing
effects result in a post-reaction relaxation profile distinct from that
observed when DF vibration excitation occurs within an equilibrium
microsolvation environment. The parallel software framework presented in this
paper should be more broadly applicable to a range of complex reactive systems.Comment: 58 pages and 29 Figure
Does responsibility affect the public valuation of health care interventions? A relative valuation approach to health care safety
This article is available open access through the publisherâs website at the link below. Copyright © 2012, International Society for Pharmacoeconomics and
Outcomes Research (ISPOR).Objective - Health services often spend more on safety interventions than seems cost-effective. This study investigates whether the public value safety-related health care improvements more highly than the same improvements in contexts where the health care system is not responsible.
Method - An online survey was conducted to elicit the relative importance placed on preventing harms caused by 1) health care (hospital-acquired infections, drug administration errors, injuries to health care staff), 2) individuals (personal lifestyle choices, sports-related injuries), and 3) nature (genetic disorders). Direct valuations were obtained from members of the public by using a person trade-off or âmatchingâ method. Participants were asked to choose between two preventative interventions of equal cost and equal health benefit per person for the same number of people, but differing in causation. If participants indicated a preference, their strength of preference was measured by using person trade-off.
Results - Responses were obtained from 1030 people, reflecting the sociodemographic mix of the UK population. Participants valued interventions preventing hospital-acquired infections (1.31) more highly than genetic disorders (1.0), although drug errors were valued similarly to genetic disorders (1.07), and interventions to prevent injury to health care staff were given less weight than genetic disorders (0.71). Less weight was also given to interventions related to lifestyle (0.65) and sports injuries (0.41).
Conclusion - Our results suggest that people do not attach a simple fixed premium to âsafety-relatedâ interventions but that preferences depend more subtly on context. The use of the results of such public preference surveys to directly inform policy would therefore be premature.Brunel University
Remote functionalisation via sodium alkylamidozincate intermediates : access to unusual fluorenone and pyridyl ketone reactivity patterns
Treating fluorenone or 2-benzoylpyridine with the sodium zincate [(TMEDA)center dot Na(mu-Bu-t)(mu-TMP)Zn(Bu-t)] in hexane solution, gives efficient Bu-t addition across the respective organic substrate in a highly unusual 1,6-fashion, producing isolable organometallic intermediates which can be quenched and aerobically oxidised to give 3-tert-butyl-9H-fluoren-9-one and 2-benzoyl-5-tert-butylpyridine respectively
Performance of LPG Storage Tanks on Ground Improved by Stone Columns
This paper describes the construction of four large tanks on poor soil conditions consisting of hydraulic fill placed over estuarine silt in Dublin port. The limited differential settlement that could be tolerated by the tanks required that they could not be placed on the existing ground. The optimum solution was found to be ground treatment using vibro-replacement with the formation of stone columns and compaction of the fill. The paper describes the design method used and the control tests. The predicted settlements are compared with settlement readings of the tanks following construction. These show that the chosen solution has performed well and satisfied the design requirements
Benefits of using liquid sources of potassium fertilizer in northern highbush blueberry
Fertigation with N increases growth and production relative to granular N applications in northern highbush blueberry (Vaccinium corymbosum L.), but little information is available on whether there is any benefit to fertigating with other nutrients. The objective of this study was to evaluate the use of K for fertigation. An initial study was done in a greenhouse to identify appropriate combinations of liquid N and K sources for fertigation using potted plants of âDukeâ blueberry. The results indicated that the concentration of K in the soil solution increased by 25% with potassium sulfate (K2SO4) and by 39% with potassium thiosulfate (KTS) and, depending on the soil type, was highest when KTS was applied with urea or ammonium sulfate. Leaf K was affected by K as well as N fertilizers and, on average, was greater with than without K in both an optimum and high pH soil and with KTS than with K2SO4 in the latter soil. A second study was conducted to compare fertigation to granular application of K fertilizer using a mature planting of âDukeâ blueberry. Treatments included fertigation (once a week from April to August) with water-soluble K2SO4 or KTS, a single application (April) of granular K2SO4, and no K fertilizer. Each K fertilizer was applied at a total rate of 84 kg/ha K2O per year. After 2 years, the treatments have had no effect on yield or fruit quality. However, fertigation with K2SO4 or KTS resulted in lower pH and higher concentrations of K, Ca, Mg, and S in soil solution under the drip emitters than either no K or granular K2SO4, while granular K2SO4 resulted in higher concentration of K than any other treatment at 15 cm from the drip emitter (edge of the wetting front). The fertigated treatments also had greener leaves (based on SPAD meter readings), greater whole-plant leaf K concentrations, and nearly twice as much extractable K in the soil as the non-fertigated treatments. Additional measurements are underway to determine whether K fertigation will have any effect on yield or fruit quality over the long term
The relationship between Hippocampal asymmetry and working memory processing in combat-related PTSD: a monozygotic twin study
BACKGROUND: PTSD is associated with reduction in hippocampal volume and abnormalities in hippocampal function. Hippocampal asymmetry has received less attention, but potentially could indicate lateralised differences in vulnerability to trauma. The P300 event-related potential component reflects the immediate processing of significant environmental stimuli and has generators in several brain regions including the hippocampus. P300 amplitude is generally reduced in people with PTSD. METHODS: Our study examined hippocampal volume asymmetry and the relationship between hippocampal asymmetry and P300 amplitude in male monozygotic twins discordant for Vietnam combat exposure. Lateralised hippocampal volume and P300 data were obtained from 70 male participants, of whom 12 had PTSD. We were able to compare (1) combat veterans with current PTSD; (2) their non-combat-exposed co-twins; (3) combat veterans without current PTSD and (4) their non-combat-exposed co-twins. RESULTS: There were no significant differences between groups in hippocampal asymmetry. There were no group differences in performance of an auditory oddball target detection task or in P300 amplitude. There was a significant positive correlation between P300 amplitude and the magnitude of hippocampal asymmetry in participants with PTSD. CONCLUSIONS: These findings suggest that greater hippocampal asymmetry in PTSD is associated with a need to allocate more attentional resources when processing significant environmental stimuli.Timothy Hall, Cherrie Galletly, C.R. Clark, Melinda Veltmeyer, Linda J. Metzger, Mark W. Gilbertson, Scott P. Orr, Roger K. Pitman and Alexander McFarlan
Analysis of ultrasonic transducers with fractal architecture
Ultrasonic transducers composed of a periodic piezoelectric composite are generally accepted as the design of choice in many applications. Their architecture is normally very regular and this is due to manufacturing constraints rather than performance optimisation. Many of these manufacturing restrictions no longer hold due to new production methods such as computer controlled, laser cutting, and so there is now freedom to investigate new types of geometry. In this paper, the plane wave expansion model is utilised to investigate the behaviour of a transducer with a self-similar architecture. The Cantor set is utilised to design a 2-2 conguration, and a 1-3 conguration is investigated with a Sierpinski Carpet geometry
Monotonicity of Fitness Landscapes and Mutation Rate Control
A common view in evolutionary biology is that mutation rates are minimised.
However, studies in combinatorial optimisation and search have shown a clear
advantage of using variable mutation rates as a control parameter to optimise
the performance of evolutionary algorithms. Much biological theory in this area
is based on Ronald Fisher's work, who used Euclidean geometry to study the
relation between mutation size and expected fitness of the offspring in
infinite phenotypic spaces. Here we reconsider this theory based on the
alternative geometry of discrete and finite spaces of DNA sequences. First, we
consider the geometric case of fitness being isomorphic to distance from an
optimum, and show how problems of optimal mutation rate control can be solved
exactly or approximately depending on additional constraints of the problem.
Then we consider the general case of fitness communicating only partial
information about the distance. We define weak monotonicity of fitness
landscapes and prove that this property holds in all landscapes that are
continuous and open at the optimum. This theoretical result motivates our
hypothesis that optimal mutation rate functions in such landscapes will
increase when fitness decreases in some neighbourhood of an optimum, resembling
the control functions derived in the geometric case. We test this hypothesis
experimentally by analysing approximately optimal mutation rate control
functions in 115 complete landscapes of binding scores between DNA sequences
and transcription factors. Our findings support the hypothesis and find that
the increase of mutation rate is more rapid in landscapes that are less
monotonic (more rugged). We discuss the relevance of these findings to living
organisms
Continuous gravity measurementsr evealal ow-density lava lake at Kılauea Volcano, Hawaiâi
On 5 March 2011, the lava lake within the summit eruptive vent at KÄ«lauea Volcano, Hawaiâi, began to drain as magma withdrew to feed a dike intrusion and fissure eruption on the volcanoâs east rift zone. The draining was monitored by a variety of continuous geological and geophysical measurements, including deformation, thermal and visual imagery, and gravity. Over the first ~14 hours of the draining, the ground near the eruptive vent subsided by about 0.15 m, gravity dropped by more than 100 ÎŒGal, and the lava lake retreated by over 120 m. We used GPS data to correct the gravity signal for the effects of subsurface mass loss and vertical deformation in order to isolate the change in gravity due to draining of the lava lake alone. Using a model of the eruptive vent geometry based on visual observations and the lava level over time determined from thermal camera data, we calculated the best fit lava density to the observed gravity decreaseâto our knowledge, the first geophysical determination of the density of a lava lake anywhere in the world. Our result, 950 ± 300 kg m-3, suggests a lava density less than that of water and indicates that KÄ«laueaâs lava lake is gas-rich, which can explain why rockfalls that impact the lake trigger small explosions. Knowledge of such a fundamental material property as density is also critical to investigations of lava-lake convection and degassing and can inform calculations of pressure change in the subsurface magma plumbing system
Minimal seeds for shear flow turbulence: using nonlinear transient growth to touch the edge of chaos
We propose a general strategy for determining the minimal finite amplitude
isturbance to trigger transition to turbulence in shear flows. This involves
constructing a variational problem that searches over all disturbances of fixed
initial amplitude, which respect the boundary conditions, incompressibility and
the Navier--Stokes equations, to maximise a chosen functional over an
asymptotically long time period. The functional must be selected such that it
identifies turbulent velocity fields by taking significantly enhanced values
compared to those for laminar fields. We illustrate this approach using the
ratio of the final to initial perturbation kinetic energies (energy growth) as
the functional and the energy norm to measure amplitudes in the context of pipe
flow. Our results indicate that the variational problem yields a smooth
converged solution providing the amplitude is below the threshold amplitude for
transition. This optimal is the nonlinear analogue of the well-studied (linear)
transient growth optimal. At and above this threshold, the optimising search
naturally seeks out disturbances that trigger turbulence by the end of the
period, and convergence is then practically impossible. The first disturbance
found to trigger turbulence as the amplitude is increased identifies the
`minimal seed' for the given geometry and forcing (Reynolds number). We
conjecture that it may be possible to select a functional such that the
converged optimal below threshold smoothly converges to the minimal seed at
threshold. This seems at least approximately true for our choice of energy
growth functional and the pipe flow geometry chosen here.Comment: 27 pages, 19 figures, submitted to JF
- âŠ