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Search Results: 1 - 10 of 281200 matches for " Richard K. H. Wyse "
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The role of eosinophils in asthma  [PDF]
Faris Q. Alenzi, Fahad G. B. Alanazi, Abdulaziz D. Al-Faim, Mohamed W. Al-Rabea, Waleed Tamimi, Bassel Tarakji, Omar Kujan, Ali Al-Jabri, Richard K. H. Wyse
Health (Health) , 2013, DOI: 10.4236/health.2013.52A045
Abstract: Asthma is a chronic inflammatory disorder of the airways characterized by recurring episodes of reversible airway obstruction, hyper-responsiveness, wheezing, breathlessness and coughing. Clinical diagnosis of asthma is based on the pattern of clinical symptoms and pulmonary fuction tests. Asthma affectes 5% - 10% of the population and the number of worldwide cases is approximately 300 milliones. The incidence of this disease is increasing particulry in western countries [1]. It is the cause of a huge economic burden to national healthcare services. In a minority of cases, asthma is potentially fatal. After a period when fatalities appeared to be increasing [2], in recent years asthma-related mortality has progressively declined due to the develop- ment of specific asthma disease management programs, as well as the extensive use of in- haled corticosteroids [3]. Inflammation of the airways is a central component in asthma. In- flammation is associated with infliltration of the airway wall with eosinophiles and or neutron- philes mast cell degranulation and T cell active- tion. Other pathological features include, sub- basement membrane thickening, loss of epithet- lial cell integrity, goblet cells hyperplasia In- crease in airway smooth muscle mass. Eosino- phils are thought to be vital in the development of airway hyperreactivity, with the eosinophil cationic protein playing a crucial role [4]. The fact that treatment of asthma with corticos-teroids reduces eosinophils numbers and decreases airway reactivity further supports this hypothesis.
Global rates of convergence in log-concave density estimation
Arlene K. H. Kim,Richard J. Samworth
Statistics , 2014,
Abstract: The estimation of a log-concave density on $\mathbb{R}^d$ represents a central problem in the area of nonparametric inference under shape constraints. In this paper, we study the performance of log-concave density estimators with respect to global loss functions, and adopt a minimax approach. We first show that no statistical procedure based on a sample of size $n$ can estimate a log-concave density with respect to the squared Hellinger loss function with supremum risk smaller than order $n^{-4/5}$, when $d=1$, and order $n^{-2/(d+1)}$ when $d \geq 2$. In particular, this reveals a sense in which, when $d \geq 3$, log-concave density estimation is fundamentally more challenging than the estimation of a density with two bounded derivatives (a problem to which it has been compared). Second, we show that for $d \leq 3$, the Hellinger $\epsilon$-bracketing entropy of a class of log-concave densities with small mean and covariance matrix close to the identity grows like $\max\{\epsilon^{-d/2},\epsilon^{-(d-1)}\}$ (up to a logarithmic factor when $d=2$). This enables us to prove that when $d \leq 3$ the log-concave maximum likelihood estimator achieves the minimax optimal rate (up to logarithmic factors when $d = 2,3$) with respect to squared Hellinger loss.
Loon Nest Viability Model: A Performance Indicator for Improving Water-Level Regulation of Large Water Bodies  [PDF]
Marianne Bachand, Julien Hénault Richard, Sylvain Martin, Steve K. Windels, Jean Morin
Natural Resources (NR) , 2018, DOI: 10.4236/nr.2018.91001
Rule curves dictating target water levels for management have been implemented in several water bodies in North America over the last 70 years or more. Anthropogenic alterations of water levels are known to affect several components of wetland ecosystems. Evaluating the influence of rule curves on biological components with simple performance indicators could help harmonize water level management with wetland integrity. We assessed the potential of using the probability of common loon nest viability as a performance indicator of long-term impacts of rule curves on nesting wetland birds. We analyzed the outcome of rule curves on the probability of loon nest viability in Rainy Lake and Namakan Reservoir, 2 regulated water bodies located along the Ontario-Minnesota border. The analysis was focused on 4 hydrological time series between 1950 and 2013: 2 sets of time series simulating rule curves used to manage the water bodies in the past decades (referred to as the 1970RC and 2000RC), one of the historical measured water levels, and one of computed natural water levels. The probability of loon nest viability under the 1970RC was 2× higher than under natural conditions in both water bodies. The probability was also 2× higher under the 2000RC than under the 1970RC in the Namakan Reservoir but not in Rainy Lake. The rule curves generally improved conditions for nesting loons in both water bodies. The presented performance indicator can be used to evaluate future rule curves before they are implemented in the Rainy-Namakan or other similar systems.
Approximate simulation-free Bayesian inference for multiple changepoint models with dependence within segments
Jason Wyse,Nial Friel,H?vard Rue
Statistics , 2010,
Abstract: This paper proposes approaches for the analysis of multiple changepoint models when dependency in the data is modelled through a hierarchical Gaussian Markov random field. Integrated nested Laplace approximations are used to approximate data quantities, and an approximate filtering recursions approach is proposed for savings in compuational cost when detecting changepoints. All of these methods are simulation free. Analysis of real data demonstrates the usefulness of the approach in general. The new models which allow for data dependence are compared with conventional models where data within segments is assumed independent.
Synthesis of chiral cyclohexanes and carbasugars by 6-exo-dig radical cyclisation reactions
Rajeev K Shrivastava,Elise Maudru,Gurdial Singh,Richard H Wightman
Beilstein Journal of Organic Chemistry , 2008, DOI: 10.3762/bjoc.4.43
Abstract: Treatment of 5-(tert-butyldimethylsilyl)-2,3-O-isopropylidene-D-ribose with lithium acetylides gave mixtures of syn- and anti-alkynols 2a–2c which were separated following protection as methoxymethyl ethers. These were converted to the corresponding iodides which underwent 6-exo-dig radical cyclisation to afford chiral cyclohexanes and carbasugars. Oxidation of the primary alcohols 6a–b gave the corresponding aldehydes which on treatment with Grignard reagents afforded a mixture of alcohols. The corresponding iodides underwent similar 6-exo-dig cyclisation to give fully functionalised cyclohexanes.
Shallow Water Quasi-Geostrophic Theory on the Sphere
Wayne H. Schubert,Richard K. Taft,Levi G. Silvers
Journal of Advances in Modeling Earth Systems , 2009, DOI: 10.3894/james.2009.1.2
Abstract: Quasi-geostrophic theory forms the basis for much of our understanding of mid-latitude atmospheric dynamics. The theory is typically presented in either its -plane form or its β-plane form. However, for many applications, including diagnostic use in global climate modeling, a fully spherical version would be most useful. Such a global theory does in fact exist and has for many years, but few in the scientific community seem to have ever been aware of it. In the context of shallow water dynamics, it is shown that the spherical version of quasi-geostrophic theory is easily derived (re-derived) based on a partitioning of the flow between nondivergent and irrotational components, as opposed to a partitioning between geostrophic and ageostrophic components. In this way, the invertibility principle is expressed as a relation between the streamfunction and the potential vorticity, rather than between the geopotential and the potential vorticity. This global theory is then extended by showing that the invertibility principle can be solved analytically using spheroidal harmonic transforms, an advancement that greatly improves the usefulness of this “forgotten” theory. When the governing equation for the time evolution of the potential vorticity is linearized about a state of rest, a simple Rossby-Haurwitz wave dispersion relation is derived and examined. These waves have a horizontal structure described by spheroidal harmonics, and the Rossby-Haurwitz wave frequencies are given in terms of the eigenvalues of the spheroidal harmonic operator. Except for sectoral harmonics with low zonal wavenumber, the quasi-geostrophic Rossby-Haurwitz frequencies agree very well with those calculated from the primitive equations. One of the many possible applications of spherical quasi-geostrophic theory is to the study of quasi-geostrophic turbulence on the sphere. In this context, the theory is used to derive an anisotropic Rhines barrier in three-dimensional wavenumber space.
Spatial Frequency Information Modulates Response Inhibition and Decision-Making Processes
Sara Jahfari, K. Richard Ridderinkhof, H. Steven Scholte
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0076467
Abstract: We interact with the world through the assessment of available, but sometimes imperfect, sensory information. However, little is known about how variance in the quality of sensory information affects the regulation of controlled actions. In a series of three experiments, comprising a total of seven behavioral studies, we examined how different types of spatial frequency information affect underlying processes of response inhibition and selection. Participants underwent a stop-signal task, a two choice speed/accuracy balance experiment, and a variant of both these tasks where prior information was given about the nature of stimuli. In all experiments, stimuli were either intact, or contained only high-, or low- spatial frequencies. Overall, drift diffusion model analysis showed a decreased rate of information processing when spatial frequencies were removed, whereas the criterion for information accumulation was lowered. When spatial frequency information was intact, the cost of response inhibition increased (longer SSRT), while a correct response was produced faster (shorter reaction times) and with more certainty (decreased errors). When we manipulated the motivation to respond with a deadline (i.e., be fast or accurate), removal of spatial frequency information slowed response times only when instructions emphasized accuracy. However, the slowing of response times did not improve error rates, when compared to fast instruction trials. These behavioral studies suggest that the removal of spatial frequency information differentially affects the speed of response initiation, inhibition, and the efficiency to balance fast or accurate responses. More generally, the present results indicate a task-independent influence of basic sensory information on strategic adjustments in action control.
Crystal Nucleation in a Supercooled Liquid with Glassy Dynamics
Ivan Saika-Voivod,Richard K. Bowles,Peter H. Poole
Physics , 2009, DOI: 10.1103/PhysRevLett.103.225701
Abstract: In simulations of supercooled, high-density liquid silica we study a range of temperature T in which we find both crystal nucleation, as well as the characteristic dynamics of a glass forming liquid, including a breakdown of the Stokes-Einstein relation. We find that the liquid cannot be observed below a homogeneous nucleation limit (HNL) at which the liquid crystallizes faster than it can equilibrate. We show that the HNL would occur at lower T, and perhaps not at all, if the Stokes-Einstein relation were obeyed, and hence that glassy dynamics plays a central role in setting a crystallization limit on the liquid state in this case. We also explore the relation of the HNL to the Kauzmann temperature, and test for spinodal-like effects near the HNL.
Fe-based superconductors: an angle-resolved photoemission spectroscopy perspective
P. Richard,T. Sato,K. Nakayama,T. Takahashi,H. Ding
Physics , 2011, DOI: 10.1088/0034-4885/74/12/124512
Abstract: Angle-resolved photoemission spectroscopy allows direct visualization and experimental determination of the electronic structure of crystals in the momentum space, including the precise characterization of the Fermi surface and the superconducting order parameter. It is thus particularly suited for investigating multiband systems such as the Fe-based superconductors. In this review, we cover several aspects of these recently discovered materials that have been addressed by this technique, with a special emphasis on their superconducting gap and their Fermi surface topology. We provide sufficient experimental evidence to support the reliability and the consistency of the angle-resolved photoemission spectroscopy measurements over a wide range of material compositions.
Test of classical nucleation theory on deeply supercooled high-pressure simulated silica
Ivan Saika-Voivod,Peter H. Poole,Richard K. Bowles
Physics , 2006, DOI: 10.1063/1.2203631
Abstract: We test classical nucleation theory (CNT) in the case of simulations of deeply supercooled, high density liquid silica, as modelled by the BKS potential. We find that at density $\rho=4.38$~g/cm$^3$, spontaneous nucleation of crystalline stishovite occurs in conventional molecular dynamics simulations at temperature T=3000 K, and we evaluate the nucleation rate J directly at this T via "brute force" sampling of nucleation events. We then use parallel, constrained Monte Carlo simulations to evaluate $\Delta G(n)$, the free energy to form a crystalline embryo containing n silicon atoms, at T=3000, 3100, 3200 and 3300 K. We find that the prediction of CNT for the n-dependence of $\Delta G(n)$ fits reasonably well to the data at all T studied, and at 3300 K yields a chemical potential difference between liquid and stishovite that matches independent calculation. We find that $n^*$, the size of the critical nucleus, is approximately 10 silicon atoms at T=3300 K. At 3000 K, $n^*$ decreases to approximately 3, and at such small sizes methodological challenges arise in the evaluation of $\Delta G(n)$ when using standard techniques; indeed even the thermodynamic stability of the supercooled liquid comes into question under these conditions. We therefore present a modified approach that permits an estimation of $\Delta G(n)$ at 3000 K. Finally, we directly evaluate at T=3000 K the kinetic prefactors in the CNT expression for J, and find physically reasonable values; e.g. the diffusion length that Si atoms must travel in order to move from the liquid to the crystal embryo is approximately 0.2 nm. We are thereby able to compare the results for J at 3000 K obtained both directly and based on CNT, and find that they agree within an order of magnitude.
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