1,456 research outputs found
Upper-surface blowing nacelle design study for a swept wing airplane at cruise conditions
A study was made to design two types of overwing nacelles for an existing wing-body at a design condition of Mach = 0.8 and C sub L = 0.2. Internal and external surface contours were developed for nacelles having either a D-shaped nozzle or a high-aspect-ratio nozzle for upper-surface blowing in the powered-lift mode of operation. The goal of the design was the development of external nacelle lines that would minimize high-speed aerodynamic interference effects. Each nacelle type was designed for both two- and four-engine airplanes using an iterative process of aerodynamic potential flow analysis. Incremental nacelle drag estimates were made for flow-through wind tunnel models of each configuration
Magnetic properties of 3d-impurities substituted in GaAs
We have calculated the magnetic properties of substituted 3d-impurities
(Cr-Ni) in a GaAs host by means of first principles electronic structure
calculations. We provide a novel model explaining the ferromagnetic long rang
order of III-V dilute magnetic semiconductors. The origin of the ferromagnetism
is shown to be due to delocalized spin-uncompensated As dangling bond
electrons. Besides the quantitative prediction of the magnetic moments, our
model provides an understanding of the halfmetallicity, and the raise of the
critical temperature with the impurity concentration
The Effect of Flow at Maud Rise on the Sea Ice Cover - Numerical Experiments
The role of seamounts in the formation and evolution of sea ice isinvestigated in a series of numerical experiments with a coupled seaice-ocean model. Bottom topography, stratification and forcing areconfigured for the Maud Rise region in the Weddell Sea. The specificflow regime that develops at the seamount as the combined response tosteady and tidal forcing consists of free and trapped waves and aTaylor column, which is caused by mean flow and tidal flowrectification. The enhanced variability through tidal motion inparticular is capable of modifying the mixed layer above the seamountenough to delay and reduce sea ice formation throughout the winter.The induced sea ice anomaly spreads and moves westward and affects anarea of several 100~000 km. Process studies reveal the complexinteraction between wind, steady and periodic ocean currents: allthree are required in the process of generation of the sea ice andmixed layer anomalies (mainly through tidal flow), their detachmentfrom the topography (caused by steady oceanic flow), and the westwardtranslation of the sea ice anomaly (driven by the time-mean wind)
Skummingsproblemer i råtnetanker ved Rambekk renseanlegg, Gjøvik kommune
Årsliste 2002Gjøvik kommune har skummingsproblemer i råtnetankene ved Rambekk RA. Problemet har vært særlig alvorlig sen-vinter og vår 2002. Skummingen i råtnetankene mener vi skyldes et kjemisk stoff i slammet, og primært ikke tilstedeværelsen av spesielle organismer. Problemene kan forsterkes av rask og kraftig oppvarming av slammet i en varmeveksler på anlegget. Høy fettilførsel er en mulig hovedårsak til problemene. Selv om mye fett tilføres via Lillehammer-slammet (ca 250 kg/uke), er det sannsynligvis en stor uidentifisert fettkilde internt i Gjøvik kommune. en stor uidentifisert fettkilde internt i Gjøvik kommune. Det er flere slamtyper som har evne til å produsere mye skum, i særlig grad slam fra Skreia RA, Lena RA og Lillehammer RA. Skummet elimineres effektivt med ca 15 ppm Nalco skumdemper. Vi anbefaler en mer inngående kildekartlegging for fett. Videre bør man vurdere å montere en skumfelle på gassavdraget, og jobbe med tiltak for å øke spesifikk slamtilførsel. Varmeveksleren for slamoppvarming bør gjennomgås. Det er mulig et skum-radarsystem kan være nyttig for å få stabil drift, men dette eliminerer ikke årsaken til problemene. Øvrige årsaker til drifts-problemene kan være lav belastning på råtnetanker, høyt fettsyrenivå og høy alkalitet.Gjøvik kommun
Ecosystem engineering creates a direct nutritional link between 600-m deep cold-water coral mounds and surface productivity
Cold-water corals (CWCs) form large mounds on the seafloor that are hotspots of biodiversity in the deep sea, but it remains enigmatic how CWCs can thrive in this food-limited environment. Here, we infer from model simulations that the interaction between tidal currents and CWC-formed mounds induces downwelling events of surface water that brings organic matter to 600-m deep CWCs. This positive feedback between CWC growth on carbonate mounds and enhanced food supply is essential for their sustenance in the deep sea and represents an example of ecosystem engineering of unparalleled magnitude. This ’topographically-enhanced carbon pump’ leaks organic matter that settles at greater depths. The ubiquitous presence of biogenic and geological topographies along ocean margins suggests that carbon sequestration through this pump is of global importance. These results indicate that enhanced stratification and lower surface productivity, both expected consequences of climate change, may negatively impact the energy balance of CWCs
Spontaneous separation of two-component Fermi gases in a double-well trap
The two-component Fermi gas in a double-well trap is studied using the
density functional theory and the density profile of each component is
calculated within the Thomas-Fermi approximation. We show that the two
components are spatially separate in the two wells once the repulsive
interaction exceeds the Stoner point, signaling the occurrence of the
ferromagnetic transition. Therefore, the double-well trap helps to explore
itinerant ferromagnetism in atomic Fermi gases, since the spontaneous
separation can be examined by measuring component populations in one well.Comment: 6 pages, 6 figures, to appear in ep
Finite-temperature magnetism of FePd and CoPt alloys
The finite-temperature magnetic properties of FePd and
CoPt alloys have been investigated. It is shown that the
temperature-dependent magnetic behaviour of alloys, composed of originally
magnetic and non-magnetic elements, cannot be described properly unless the
coupling between magnetic moments at magnetic atoms (Fe,Co) mediated through
the interactions with induced magnetic moments of non-magnetic atoms (Pd,Pt) is
included. A scheme for the calculation of the Curie temperature () for
this type of systems is presented which is based on the extended Heisenberg
Hamiltonian with the appropriate exchange parameters obtained from
{\em ab-initio} electronic structure calculations. Within the present study the
KKR Green's function method has been used to calculate the parameters.
A comparison of the obtained Curie temperatures for FePd and
CoPt alloys with experimental data shows rather good agreement.Comment: 10 pages, 12 figure
Field-dependent AC susceptibility of itinerant ferromagnets
Whereas dc measurements of magnetic susceptibility, , fail to
distinguish between local and weak itinerant ferromagnets, radio-frequency (rf)
measurements of in the ferromagnetic state show dramatic differences
between the two. We present sensitive tunnel-diode resonator measurements of
in the weak itinerant ferromagnet ZrZn at a frequency of 23 MHz.
Below Curie temperature, K, the susceptibility is seen to
increase and pass through a broad maximum at approximately 15 K in zero applied
dc magnetic field. Application of a magnetic field reduces the amplitude of the
maximum and shifts it to lower temperatures. The existence and evolution this
maximum with applied field is not predicted by either the Stoner or
self-consistent renormalized (SCR) spin fluctuations theories. For temperatures
below both theories derive a zero-field limit expression for . We
propose a semi-phenomenological model that considers the effect of the internal
field from the polarized fraction of the conduction band on the remaining,
unpolarized conduction band electrons. The developed model accurate describes
the experimental data
Stable longitudinal associations of family income with children's hippocampal volume and memory persist after controlling for polygenic scores of educational attainment
Despite common notion that the correlation of socioeconomic status with child cognitive performance may be driven by both environmentally- and genetically-mediated transactional pathways, there is a lack of longitudinal and genetically informed research that examines these postulated associations. The present study addresses whether family income predicts associative memory growth and hippocampal development in middle childhood and tests whether these associations persist when controlling for DNA-based polygenic scores of educational attainment. Participants were 142 6-to-7-year-old children, of which 127 returned when they were 8-to-9 years old. Longitudinal analyses indicated that the association of family income with children's memory performance and hippocampal volume remained stable over this age range and did not predict change. On average, children from economically disadvantaged background showed lower memory performance and had a smaller hippocampal volume. There was no evidence to suggest that differences in memory performance were mediated by differences in hippocampal volume. Further exploratory results suggested that the relationship of income with hippocampal volume and memory in middle childhood is not primarily driven by genetic variance captured by polygenic scores of educational attainment, despite the fact that polygenic scores significantly predicted family income
Complex itinerant ferromagnetism in noncentrosymmetric Cr11Ge19
The noncentrosymmetric ferromagnet Cr11Ge19 has been investigated by
electrical transport, AC and DC magnetization, heat capacity, x-ray
diffraction, resonant ultrasound spectroscopy, and first principles electronic
structure calculations. Complex itinerant ferromagnetism in this material is
indicated by nonlinearity in conventional Arrott plots, unusual behavior of AC
susceptibility, and a weak heat capacity anomaly near the Curie temperature (88
K). The inclusion of spin wave excitations was found to be important in
modeling the low temperature heat capacity. The temperature dependence of the
elastic moduli and lattice constants, including negative thermal expansion
along the c axis at low temperatures, indicate strong magneto-elastic coupling
in this system. Calculations show strong evidence for itinerant ferromagnetism
and suggest a noncollinear ground state may be expected
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