Offshore Turbine Arrays: Numerical Modeling and Experimental Validation

The interaction between wind turbines in a large wind farm needs to be better understood to reduce array losses and improve energy production. A numerical test bed for an array of offshore wind turbines was developed in the open-source computational fluid dynamics (CFD) framework OpenFOAM. It provides a computational tool which can be used in combination with physical model turbine array studies in the Flow Physics Facility (FPF) at UNH as well as other test facilities. Turbines were modeled as actuator disks with turbulence sources to reduce computational cost. Both k-ϵ and k-ω SST turbulence models were utilized to capture the flow in the near-wall, wake, and free stream regions. Experimental studies were performed in the FPF to validate the numerical results and to provide realistic initial and boundary conditions, for example turbulent boundary layer inlet velocity profiles. Mesh refinement and boundary condition studies were performed. Numerical simulations were executed on a custom-built server, designed to be the head node of a future CFD cluster. The entire project was built on open-source software to facilitate replication and expansion. The numerical model provides building blocks for simulations of large wind turbine arrays, computational resources permitting. The numerical model currently replicates a three by one array of wind turbines in the FPF, and provides detailed insight into the array fluid dynamics

On the electronic structure of layered sodium cobalt oxides

The discovery of an unexpectedly large thermopower accompanied by low resistivity and low thermal conductivity in NaxCoO2 raised significant research interest in these materials and let to a number of experimental and theoretical investigations. This interest has strongly been reinforced by the discovery of superconductivity in the hydrated compound Na0.35CoO2 •1.3H2O in 2003, and thus, NaxCoO2 experiences an again increasing attention. The similarity of the Na cobaltates to the high temperature superconductors (HTSC) - both are transition metal oxides and adopt a layered crystal structure with quasi-two-dimensional (Cu,Co)O2 layers - is an important aspect of the research activities. In contrast to the HTSC cuprates however, the CoO2 layers consist of edge sharing CoO6 octahedra which are distorted in such a way that the resulting local symmetry is trigonal. The trigonal coordination of the Co sites results in geometric frustration which favours unconventional electronic ground states. The geometrically frustrated CoO2 sublattice also exists in the nonhydrated parent compound NaxCoO2, which has been investigated in this work. The intercalation of water into the parent compound is expected to have little effect on the Fermi surface beside the increase in two dimensionality due to the effect of expansion. Upon lowering the symmetry from cubic to trigonal, the t2g states split into states with eg_and a1g symmetry. Measurements of polarisation and temperature dependent soft X-ray absorption have been performed on a wide doping range of NaxCoO2 single crystals. Beside the Co L_2,3-edges, the O K-edge and the Na K-edge have been measured. These measurements show strong polarisation dependencies especially for the excitations into the lower lying a1g energy level. In addition to that, also an unexpected polarisation dependence for higher energies has been observed, which should be absent in trigonal symmetry. These results point towards a deviation of the local trigonal symmetry of the CoO6 octahedra, which is temperature independent in a temperature range between 25 K and 372 K. This deviation was found to be different for Co3+ and Co4+ sites, which leads to a polaronic electron transport. Furthermore, a strong hybridisation between the Co and O ions has been found. In order to shed further light on the electronic structure of NaxCoO2, the electronic spectrum of a CoO6 cluster has been calculated including all interactions between 3d orbitals as well as hopping processes between Co and O and O and O ions. The ground state for two electronic occupations in the cluster (i.e. Co3+ and Co4+) that correspond nominally to all O in the O−2 oxidation state, and Co+3 or Co+4 has been obtained. Then, all excited states obtained by promotion of a Co 2p electron to a 3d electron, and the corresponding matrix elements are calculated. A fit of the observed experimental spectra is good and points out a large Co-O covalence and cubic crystal field effects, that result in low spin Co 3d configurations. The results indicate that the effective hopping between different Co atoms plays a major role in determining the symmetry of the ground state in the lattice. Remaining quantitative discrepancies with the XAS experiments are expected to come from composition effects of itineracy in the ground and excited states. Beside these points, results of photoemission spectroscopy, magnetisation measurements as well as resonant and non-resonant X-ray diffraction using high energy X-rays are shown and discussed.Die Entdeckung unerwartet großer Thermokraft bei gleichzeitigem niedrigem Widerstand und niedriger thermischen Leitfähigkeit in NaxCoO2 führte zu einem großen wissenschaftlichem Interesse an diesen Materialien und zu einer großen Anzahl an experimentellen und theoretischen Arbeiten. Dieses Interesse steigerte sich noch einmal nach der Entdeckung von Supraleitung in der hydrierten Verbindung Na0.35CoO2 •1.3H2O im Jahre 2003. Die Ähnlichkeit der Na Kobaltate zu den Hochtemperatur-Supraleitern (HTSL) – beides sind Übergangsmetalloxide mit einer geschichteten Kristallstruktur in der quasi zwei dimensionale (Cu,Co)O2 Ebenen enthalten sind – ist ein wichtiger Aspekt moderner wissenschaftlicher Arbeiten. Im Gegensatz zu den HTSL Kupraten bestehen die CoO2 Ebenen aus CoO6 Oktaedern die über ihre Kanten verbunden sind und in der Art verzerrt sind, dass die resultierende Symmetrie trigonal ist. Die trigonale Anordnung der Co Plätze führt zu einer geometrischen Frustration und unkonventionellen elektronischen Grundzuständen. Diese geometrisch frustrierten CoO2 Untergitter existieren ebenfalls in den nicht hydrierten Mutterverbindungen NaxCoO2, welche in dieser Arbeit untersucht wurden. Interkalierung von Wasser in die Mutterverbindung hat nur einen kleinen Einfluss auf die Fermi Oberfläche und führt zu einem Anstieg des zwei dimensionalen Charakters durch den Effekt der Ausdehnung. Durch Verminderung der Symmetrie von kubisch zu trigonal splitten die vormals entarteten t2g Zustände auf in Zustände mit eg und a1g Symmetrie. Zur Bestimmung der elektronischen Struktur von NaxCoO2 wurden polarisations- und temperaturabhängige Messungen der Röntgenabsorption im weichen Röntgenbereich für einen großen Dotierungsbereich durchgeführt. Neben den Co L_2,3-Kanten wurden auch die O K-Kante und die Na K-Kante gemessen. Sie zeigen eine starke Polarisationsabhängigkeit speziell für Anregungen in die niederenergetischen a1g Level. Zusätzlich wurde eine unerwartete Polarisationsabhängigkeit bei höheren Energien gefunden, die für trigonalen Symmetrie so nicht auftauchen dürfte. Diese Ergebnisse weisen auf eine Abweichung von der lokalen trigonalen Symmetrie der CoO6 Oktaeder hin, welche Temperatur unabhängig ist in einem Temperaturbereich zwischen 25 und 372 Kelvin. Diese Abweichung ist unterschiedlich für Co3+ und Co4+ Ionen was wiederum auf einen polaronischen Transport hinweist. Zusätzlich wird deutlich, dass eine starke Co-O Hybridisierung existieren muss. Um weiteres Informationen über die elektronische Struktur von NaxCoO2 zu erhalten, wurde das elektronische Spektrum eines CoO6 Oktaeders berechnet in dem alle Wechselwirkungen zwischen 3d Orbitalen sowie Hüpfprozesse zwischen Co und O sowie O und O Ionen enthalten sind. Der Grundzustand für zwei elektronische Besetzungen in einem Cluster (d.h. Co3+ und Co4+) wurde bestimmt für O Ionen mit einer nominellen O-2 Oxidation sowie Co3+ und Co4+ Ionen. Im angeregten Zustand werden die entsprechenden Anregungen eines Co 2p Elektrons in einen unbesetzten 3d Zustand berücksichtigt und die entsprechenden Matrixelemente berechnet. Ein Fit an den experimentellen Daten ist gut und weist auf eine starke Co-O Kovalenz und auf einen starken Einfluss des kubischen Kristallfeldes hin, der zu einer Low-Spin Co 3d Konfiguration führt. Die Ergebnisse zeigen, dass ein effektives Hüpfen zwischen benachbarter Co Ionen eine große Rolle für die Symmetrie des Grundzustandes im Gitter spielt. Quantitative Unterschiede zwischen den experimentellen und theoretischen Daten kommen anscheinend von itineranten Effekten im Grund- und angeregten Zustand. Zusätzlich zu den oben kurz beschriebenen Ergebnissen werden in dieser Arbeit weitere Ergebnisse der Photoemissionsspektroskopie, der Magnetisierung sowie aus resonanter und nicht resonanter Röntgenbeugung mit harter Röntgenstrahlung gezeigt und diskutiert

The Science and Psychology of Survival

Our brains and bodies are wired to survive-whether you are lost in the mountains, lost in a foreign city, or just feeling lost in a crowd. It\u27s not about how many matches, maps, or knives you have, but how adaptable you are and how persistent you are about wanting to live

Justifying Rehabilitation Intensity Through Functional Performance Measures in Postacute Care

The Centers for Medicare and Medicaid Services (CMS) has scrutinized the provision of rehabilitation services in skilled nursing facilities (SNFs) for some time. Little research guidance exists on appropriate dosage or rehabilitation intensity (RI) among SNF patients or patients in other postacute care (PAC) settings. CMS developed a PAC assessment, the Continuity Assessment Record and Evaluation (CARE) Tool, in response to questions about what issues drive placement in various PAC settings under Medicare. The ability to adequately assess functional outcomes and correlate them to the RI provided by using the CARE Tool is promising. However, further research, policy advocacy, and practice analysis must be undertaken to promote and protect adequate access to occupational therapy and physical therapy in SNFs and other PAC settings. Individual practitioners must participate in data gathering to ensure that the data for analysis are fully informed by the occupational therapy perspective

Einfluss der Einkommensposition auf die Gesundheit und Lebenserwartung

Income is an important determinant of individual standards of living and participation in social life. Data from the German Socio-Economic Panel shows that the level of income also affects a person's health and life expectancy. People's self-assessment of their health and health-related quality of life follow a distribution pattern which can be described as gradient: the lower the income, the more frequent the impairments to subjective health. Life expectancy statistics also reflect income differences, primarily due to premature deaths among lower-income groups. Clues for explaining income-related differences in health and life expectancy can be found in the results on health-related behaviour and use of the medical system.Income; Poverty; Social inequality; Health; German Socio-Economic Panel

Probing the nucleon at large momentum tramsfer

The central role of soft nucleon matrix elements in reactions of high energy electrons or real photons with nucleons is emphasized. These soft matrix elements are described in terms of skewed parton distributions. Their connections to ordinary parton distributions, form factors, Compton scattering and hard meson electroproduction is discussed.Comment: 11 pages, 12 Postscript figures, fleqn, espcrc1, epsfi

Could job insecurity (also) be a motivator?

"This study tested the idea that there is not only a negative effect of job insecurity on performance but also a positive one. The positive effect can be expected because job insecurity might also motivate people to work hard because good performance might be believed to lessen the chance of being made redundant. We assume that both effects work simultaneously but that the negative effect is stronger than the positive one. Furthermore, we assume that the negative effect is mediated by work attitudes. Job insecurity, performance (in-role behavior and organizational citizenship behaviour), and work attitudes (job satisfaction, commitment, and justice perceptions) data were collected from 132 German nonmanagerial employees. Structural equation modeling provided some evidence for the hypothesized relationships. In addition, our data replicate the finding of Borg & Elizur (1992) that there are two separate dimensions of job insecurity with different correlational patterns: cognitive job insecurity (i.e., the probability estimate of loosing one's job) and affective job insecurity (i.e., being worried about loosing one's job)." (author's abstract

The endemic gastropod fauna of Lake Titicaca : correlation between molecular evolution and hydrographic history

Lake Titicaca, situated in the Altiplano high plateau, is the only ancient lake in South America. This 2- to 3-My-old (where My is million years) water body has had a complex history that included at least five major hydrological phases during the Pleistocene. It is generally assumed that these physical events helped shape the evolutionary history of the lake´s biota. Herein, we study an endemic species assemblage in Lake Titicaca, composed of members of the microgastropod genus Heleobia, to determine whether the lake has functioned as a reservoir of relic species or the site of local diversification, to evaluate congruence of the regional paleohydrology and the evolutionary history of this assemblage, and to assess whether the geographic distributions of endemic lineages are hierarchical. Our phylogenetic analyses indicate that the Titicaca/Altiplano Heleobia fauna (together with few extralimital taxa) forms a species flock. A molecular clock analysis suggests that the most recent common ancestor (MRCAs) of the Altiplano taxa evolved 0.53 (0.28–0.80) My ago and the MRCAs of the Altiplano taxa and their extralimital sister group 0.92 (0.46–1.52) My ago. The endemic species of Lake Titicaca are younger than the lake itself, implying primarily intralacustrine speciation. Moreover, the timing of evolutionary branching events and the ages of two precursors of Lake Titicaca, lakes Cabana and Ballivián, is congruent. Although Lake Titicaca appears to have been the principal site of speciation for the regional Heleobia fauna, the contemporary spatial patterns of endemism have been masked by immigration and/or emigration events of local riverine taxa, which we attribute to the unstable hydrographic history of the Altiplano. Thus, a hierarchical distribution of endemism is not evident, but instead there is a single genetic break between two regional clades. We also discuss our findings in relation to studies of other regional biota and suggest that salinity tolerance was the most likely limiting factor in the evolution of Altiplano species flocks