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Search Results: 1 - 10 of 554762 matches for " K. A. Yates "
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Coral Reefs and Ocean Acidification
Joan A. Kleypas,Kimberly K. Yates
Oceanography , 2009,
Abstract: Coral reefs were one of the first ecosystems to be recognized as vulnerable to ocean acidification. To date, most scientific investigations into the effects of ocean acidification on coral reefs have been related to the reefs’ unique ability to produce voluminous amounts of calcium carbonate. It has been estimated that the main reef-building organisms, corals and calcifying macroalgae, will calcify 10–50% less relative to pre-industrial rates by the middle of this century. This decreased calcification is likely to affect their ability to function within the ecosystem and will almost certainly affect the workings of the ecosystem itself. However, ocean acidification affects not only the organisms, but also the reefs they build. The decline in calcium carbonate production, coupled with an increase in calcium carbonate dissolution, will also diminish reef building and the benefits that reefs provide, such as high structural complexity that supports biodiversity on reefs, and breakwater effects that protect shorelines and create quiet habitats for other ecosystems, such as mangroves and seagrass beds. The focus on calcification in reefs is warranted, but the responses of many other organisms, such as fish, noncalcifying algae, and seagrasses, to name a few, deserve a close look as well.
Scanning Raman spectroscopy for characterizing compositionally spread films
A. Venimadhav,K. A. Yates,M. G. Blamire
Physics , 2004,
Abstract: Composition-spread La1-xSrxMnO3 thin films were prepared by pulsed laser deposition technique from LaMnO3 and SrMnO3 targets. The films were epitaxial with a continuous variation of the out of plane lattice parameter along the direction of composition gradient. Scanning Raman spectroscopy has been employed as a non-destructive tool to characterize the composition-spread films. Raman spectra showed the variation of the structural, Jahn Teller distortions and the presence of coexisting phases at particular compositions that are in agreement with the previous observation on the single crystal samples. Raman spectra on the continuous composition-spread film also reveal the effect of disorder and strain on the compositions.
Strong influence of boron precursor powder on the critical current density of MgB2
S. K. Chen,K. A. Yates,M. G. Blamire,J. L. MacManus-Driscoll
Physics , 2005, DOI: 10.1088/0953-2048/18/11/011
Abstract: The influence of the nature of the boron precursor on the superconducting properties of polycrystalline MgB2 was studied. Critical current densities for the MgB2 made from high purity amorphous boron are at least a factor of three higher than typical values measured for standard MgB2 samples made from amorphous precursors. Two possible mechanisms are proposed to account for this difference. Samples made from crystalline boron powders have around an order of magnitude lower Jc compared to those made from amorphous precursors. X-ray, Tc and resistivity studies indicate that this is as a result of reduced current cross section due to the formation of Mg-B-O phases. The samples made from amorphous B contain far fewer Mg-B-O phases than crystalline B despite the fact that the amorphous B contains more B2O3. The different reactivity rates of the precursor powders accounts for this anomaly.
A Study Identifying Biological Evolution-Related Misconceptions Held by Prebiology High School Students  [PDF]
Tony B. Yates, Edmund A. Marek
Creative Education (CE) , 2015, DOI: 10.4236/ce.2015.68085
Abstract: Students bring a diverse array of ideas about natural events to their science classes, and many of these ideas are often at variance with the scientifically accepted views. Numerous studies have identified multiple biological evolution-related misconceptions held by select groups of students. Collectively, these studies repeatedly indicate that students with varying educational backgrounds have difficulties accurately understanding the concepts of evolution. Because scientific literacy in the field of biology necessitates a basic understanding of evolution concepts and theory, students’ possession of biological evolution-related misconceptions is problematic. The focus of this study was to identify the types and prevalence of such misconceptions within a state’s public high schools’ prebiology students and to correlate those findings with demographic variables. Some 993 students enrolled in their initial high school biology course during the 2010-2011 academic years in one of 42 Oklahoma public high schools served as this study’s unit of analysis. The Biological Evolution Literacy Survey which presents 23 biological misconception statements grouped into five categories, served as the research tool for identifying students’ misconceptions, calculating conception index scores, and collecting demographic data. Multiple statistical analyses were performed to identify statistically significant (p < 0.05) relationships between variables related to students’ number and types of misconceptions. Analysis revealed that participants possess a mean 43.9% rate of understanding of those biological evolution concepts presented in the BEL Survey combined with a 39.1% mean misconception rate. A statistically significant difference in participants’ BEL Survey mean index scores when related to biological evolution knowledge self-rating was also disclosed. Strategies for identifying and eliminating students’ misconceptions are offered. Misconceptions of biological evolution were prevalent within this student population and the findings corroborate the literature that reports a strikingly high prevalence of biological evolution-related misconceptions in students at all levels, from elementary pupils to university science majors.
Disorder induced collapse of the electron phonon coupling in MgB$_{2}$ observed by Raman Spectroscopy
K. A. Yates,G. Burnell,N. A. Stelmashenko,D. -J. Kang,H. N. Lee,B. Oh,M. G. Blamire
Physics , 2003, DOI: 10.1103/PhysRevB.68.220512
Abstract: The Raman spectrum of the superconductor MgB$_{2}$ has been measured as a function of the Tc of the film. A striking correlation is observed between the $T_{c}$ onset and the frequency of the $E_{2g}$ mode. Analysis of the data with the McMillan formula provides clear experimental evidence for the collapse of the electron phonon coupling at the temperature predicted for the convergence of two superconducting gaps into one observable gap. This gives indirect evidence of the convergence of the two gaps and direct evidence of a transition to an isotropic state at 19 K. The value of the electron phonon coupling constant is found to be 1.22 for films with T$_{c}$ 39K and 0.80 for films with T$_{c}\leq$19K.
Anomalous scaling behavior of the dynamical spin susceptibility of Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$
W. Knafo,S. Raymond,J. Flouquet,B. F?k,M. A. Adams,P. Haen,F. Lapierre,S. Yates,P. Lejay
Physics , 2004, DOI: 10.1103/PhysRevB.70.174401
Abstract: Inelastic neutron scattering measurements have been performed on single crystals of the heavy fermion compound Ce$_{0.925}$La$_{0.075}$Ru$_{2}$Si$_{2}$ in broad energy [0.1, 9.5 meV] and temperature [40 mK, 294 K] ranges in order to address the question of scaling behavior of the dynamical spin susceptibility at the quantum critical point of an itinerant magnetic system. For two wavevectors $\mathbf{Q}$ corresponding to uncorrelated and antiferromagnetically correlated spin fluctuations, it is found that the dynamical spin susceptibility $\chi''(\mathbf{Q},E,T)$ is independent of temperature below a cut-off temperature $T_{\mathbf{Q}}$: the spin fluctuation amplitude saturates at low temperatures contrarily to its expected divergence at a quantum critical point. Above $T_{\mathbf{Q}}$, a $\mathbf{Q}$-dependent scaling behavior of the form $T\chi''(\mathbf{Q},E,T) = C_{\mathbf{Q}}f[E/(a_{\mathbf{Q}}T^{\beta_{\mathbf{Q}}})]$ with $\beta_{\mathbf{Q}}<1$ is obtained. This scaling does not enter the general framework of quantum phase transition theories, since it is obtained in a high temperature range, where Kondo spin fluctuations depend strongly on temperature.
Ergodic directional switching in mobile insect groups
Carlos Escudero,Christian A. Yates,Jerome Buhl,Iain D. Couzin,Radek Erban,Ioannis G. Kevrekidis,Philip K. Maini
Quantitative Biology , 2010, DOI: 10.1103/PhysRevE.82.011926
Abstract: We obtain a Fokker-Planck equation describing experimental data on the collective motion of locusts. The noise is of internal origin and due to the discrete character and finite number of constituents of the swarm. The stationary probability distribution shows a rich phenomenology including non-monotonic behavior of several order/disorder transition indicators in noise intensity. This complex behavior arises naturally as a result of the randomness in the system. Its counterintuitive character challenges standard interpretations of noise induced transitions and calls for an extension of this theory in order to capture the behavior of certain classes of biologically motivated models. Our results suggest that the collective switches of the group's direction of motion might be due to a random ergodic effect and, as such, they are inherent to group formation.
Cerebral Microbleeds: A Review of Clinical, Genetic, and Neuroimaging Associations
Paul A. Yates
Frontiers in Neurology , 2014, DOI: 10.3389/fneur.2013.00205
Abstract: Cerebral microbleeds (microbleeds) are small, punctuate hypointense lesions seen in T2* Gradient-Recall Echo (GRE) and Susceptibility-Weighted (SWI) Magnetic Resonance Imaging (MRI) sequences, corresponding to areas of hemosiderin breakdown products from prior microscopic hemorrhages. They occur in the setting of impaired small vessel integrity, commonly due to either hypertensive vasculopathy or cerebral amyloid angiopathy. Microbleeds are more prevalent in individuals with Alzheimer’s disease (AD) dementia and in those with both ischemic and hemorrhagic stroke. However they are also found in asymptomatic individuals, with increasing prevalence with age, particularly in carriers of the Apolipoprotein (APOE) ε4 allele. Other neuroimaging findings that have been linked with microbleeds include lacunar infarcts and white matter hyperintensities on MRI, and increased cerebral β-amyloid burden using 11C-PiB Positron Emission Tomography. The presence of microbleeds has been suggested to confer increased risk of incident intracerebral hemorrhage – particularly in the setting of anticoagulation – and of complications of immunotherapy for AD. Prospective data regarding the natural history and sequelae of microbleeds are currently limited, however there is a growing evidence base that will serve to inform clinical decision-making in the future.
Microwave Surface Resistance in MgB2
A. A. Zhukov,K. Yates,G. K Perkins,Y. Bugoslavsky,M. Polichetti,A. Berenov,J. Driscoll,A. D. Caplin,L. F. Cohen,Ling Hao,J. Gallop
Physics , 2001,
Abstract: Measurements of the temperature dependence of the surface resistance at 3 GHz of 100 micron size grains of MgB_2 separated powder are presented and discussed. The microwave surface resistance data is compared to experimental results of Nb, Bi_2Sr_2CaCu_2O_{8+\delta} (BSCCO) and theoretical predictions of s-wave weak coupling electron-phonon theory (BCS).
Evidence for Nodal superconductivity in Sr$_{2}$ScFePO$_{3}$
K. A. Yates,I. T. M. Usman,K. Morrison,J. D. Moore,A. M. Gilbertson,A. D. Caplin,L. F. Cohen,H. Ogino,J. Shimoyama
Physics , 2009, DOI: 10.1088/0953-2048/23/2/022001
Abstract: Point contact Andreev reflection spectra have been taken as a function of temperature and magnetic field on the polycrystalline form of the newly discovered iron-based superconductor Sr2ScFePO3. A zero bias conductance peak which disappears at the superconducting transition temperature, dominates all of the spectra. Data taken in high magnetic fields show that this feature survives until 7T at 2K and a flattening of the feature is observed in some contacts. Here we inspect whether these observations can be interpreted within a d-wave, or nodal order parameter framework which would be consistent with the recent theoretical model where the height of the P in the Fe-P-Fe plane is key to the symmetry of the superconductivity. However, in polycrystalline samples care must be taken when examining Andreev spectra to eliminate or take into account artefacts associated with the possible effects of Josephson junctions and random alignment of grains.
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