19,608 research outputs found
Thermionic reactor power system: Effects of radiation on integration with Manned Space Station
The application of a thermionic reactor power system to the modular space station is described. The nominal net power is 40 kWe, with the power system designed to be applicable over the power range from 25 to 60 kWe. The power system is designed to be launched by the space shuttle. Radiation protection is provided by LiH neutron shielding and W gamma shielding in a shaped 4 pion configuration, i.e., the reactor is shielded on all sides but not to equal extent. Isodose contours are presented for the region around the modular space station. Levels and spectral distribution of radiation are given for later evaluation of effects on space station experiments. Parametric data on the effects of separation distance on power system mass are presented
The capacity to maintain ion and water homeostasis underlies interspecific variation in Drosophila cold tolerance
Many insects, including Drosophila, succumb to the physiological effects of chilling at temperatures well above those causing freezing. Low temperature causes a loss of extracellular ion and water homeostasis in such insects, and chill injuries accumulate. Using an integrative and comparative approach, we examined the role of ion and water balance in insect chilling susceptibility/ tolerance. The Malpighian tubules (MT), of chill susceptible Drosophila species lost [Na+] and [K+] selectivity at low temperatures, which contributed to a loss of Na+ and water balance and a deleterious increase in extracellular [K+]. By contrast, the tubules of chill tolerant Drosophila species maintained their MT ion selectivity, maintained stable extracellular ion concentrations, and thereby avoided injury. The most tolerant species were able to modulate ion balance while in a cold-induced coma and this ongoing physiological acclimation process allowed some individuals of the tolerant species to recover from chill coma during low temperature exposure. Accordingly, differences in the ability to maintain homeostatic control of water and ion balance at low temperature may explain large parts of the wide intra- and interspecific variation in insect chilling tolerance
Receiver-Based Auralization of Broadband Aircraft Flyover Noise Using the NASA Auralization Framework
The NASA Auralization Framework (NAF) consists of a set of dynamic link libraries (DLLs) to facilitate auralization of aircraft noise. Advanced capabilities for synthesis, propagation, and external interfaces are provided by the NAF Advanced Plugin Libraries (APL); a separate set of DLLs that are made accessible through the NAFs plugin architecture. In the typical time domain use case, the sound is first synthesized at the source location based on a source noise definition, and is then propagated in the time domain to a receiver on or near the ground. Alternatively, it may be desirable to synthesize the sound at the receiver, after it has been propagated in the frequency domain, e.g., when the source definition is inaccessible or when alternative propagation methods are needed. Receiver-based auralization requires three new developments in the NAF APL: a component plugin to interpolate the propagated noise spectra as a function of time for input to sound synthesis, and a path finder and path traversal plugin to calculate the effects of the differential propagation path length between the direct and ground reflected rays. This paper describes those developments and demonstrates their use in the auralization of broadband flyover noise
Universities’ engagement with vocationalism: historical perspective
The aim of this article is to explore the historical context of vocationalism in universities. It is based on an analysis of the history of the university from a vocational perspective. It looks for evidence of vocational engagement in the activities of universities over time, taking a long view from the birth of the Western University in the Middle Ages to the 1980s with the emergence of current issues of vocationalism in university education. It adopts a chronological perspective initially and then a thematic one. The main findings are: (1) vocationalism in university education is as old as the Western University itself, (2) there is evidence from the start of the Western University of vocational engagement in terms of the provision of vocationally relevant subjects, vocationally relevant skills and the development of vocationally relevant attitudes, (3) whereas most graduate employers used to be concerned with the vocationally relevant knowledge, skills and attitudes students acquired on their degree courses, most are now more concerned with graduate capacity and disposition to learn within their employment after graduation and (4) subject-centred education is compatible with university education that supports the vocational aspirations of students
Variations in the stratospheric ozone field inferred from Nimbus satellite observations
The ultraviolet earth radiance data from the Backscatter Ultraviolet Experiment on Nimbus 4 have been inverted to infer ozone profiles using a single Rayleigh scattering model. Two methods of solution give essentially the same results. Comparisons of these profiles with simultaneous rocket sounding data shows satisfactory agreement at low and middle latitudes. Vertical cross sections of ozone mixing ratio along the orbital tracks indicate that while the gross characteristics of the ozone field above 10 mb are under photochemical control, the influence of atmospheric motions can be found up to the 4 mb level
Electron Transport through a Molecular Conductor with Center-of-Mass Motion
The linear conductance of a molecular conductor oscillating between two
metallic leads is investigated numerically both for Hubbard interacting and
noninteracting electrons. The molecule-leads tunneling barriers depend on the
molecule displacement from its equilibrium position. The results present an
interesting interference which leads to a conductance dip at the electron-hole
symmetry point, that could be experimentally observable. It is shown that this
dip is caused by the destructive interference between the purely electronic and
phonon-assisted tunneling channels, which are found to carry opposite phases.
When an internal vibrational mode is also active, the electron-hole symmetry is
broken but a Fano-like interference is still observed
Foraging Strategies are Related to Skull Morphology and Life History Traits of \u3cem\u3eMelanerpes\u3c/em\u3e Woodpeckers
Links between morphology and foraging strategies have been well established for many vertebrate groups. Foraging strategies of Melanerpes woodpeckers are especially variable, with at least six species being proficient flycatchers; the remainder of the better known species do not flycatch. Our objective was to examine variation in foraging tactics as it relates to skull morphology and other life history traits among these species to better understand the biology of these diverse woodpeckers. We measured eight skull characters from 241 individuals representing 19 species, but focused on eight species for which we had the most data. We used the log-geometric mean and a principal components analysis (PCA) to calculate size-scaled shape variables. Cluster analysis based on PCA scores clearly separated birds by foraging behavior. Species with similar foraging behaviors (i.e., flycatchers vs. non-flycatchers) also share a number of other life history characteristics including similar plumage, diets, and migratory behavior. Diversity within Melanerpes may imply a high degree of plasticity or that species have been incorrectly placed in a polyphyletic group. Woodpeckers currently in the genus Melanerpes share few uniting characters and historically have been placed in as many as eight different genera. Additional life history, morphological, and genetic studies of the group, especially of Caribbean and Neotropical species, is warranted
The Dynamical Mean Field Theory phase space extension and critical properties of the finite temperature Mott transition
We consider the finite temperature metal-insulator transition in the half
filled paramagnetic Hubbard model on the infinite dimensional Bethe lattice. A
new method for calculating the Dynamical Mean Field Theory fixpoint surface in
the phase diagram is presented and shown to be free from the convergence
problems of standard forward recursion. The fixpoint equation is then analyzed
using dynamical systems methods. On the fixpoint surface the eigenspectra of
its Jacobian is used to characterize the hysteresis boundaries of the first
order transition line and its second order critical end point. The critical
point is shown to be a cusp catastrophe in the parameter space, opening a
pitchfork bifurcation along the first order transition line, while the
hysteresis boundaries are shown to be saddle-node bifurcations of two merging
fixpoints. Using Landau theory the properties of the critical end point is
determined and related to the critical eigenmode of the Jacobian. Our findings
provide new insights into basic properties of this intensively studied
transition.Comment: 11 pages, 12 figures, 1 tabl
Practical food-based dietary guidelines developed for 12-24 month old New Zealand toddlers
The Role of Attention-deficit Hyperactivity Disorder in the Self-perceptions of Children with Emotional and Behavioural Difficulties
The present study compared the teacher ratings and self-perceptions of two groups of children with emotional and/or behavioural difficulties: a) Those with attention-deficit hyperactivity disorder (ADHD) and b) those with average or below average levels of hyperactivity and attention. Results showed that the ADHD group was rated more poorly by teachers in academic, social, and behavioural domains. This group also inflated their competency ratings in these domains relative to teacher report more than the comparison group.La présente étude compare les différences entre la manière dont les enseignants perçoivent deux groupes d’enfants ayant des difficultés affectives et (ou) comportementales et celle dont les enfants se perçoivent eux-mêmes : a) Un groupe souffrant du trouble d’hyperactivité avec déficit de l’attention (TDAH) et b) Un groupe ayant des niveaux d’hyperactivité et d’attention moyens ou inférieurs à la moyenne. Les résultats ont mis en évidence que le groupe était moins bien noté par les enseignements dans les domaines scolaire, social et comportemental. En comparaison des enseignants, ce groupe a davantage surestimé ses compétences dans ces domaines que le groupe témoin
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