1,321 research outputs found
Time-Lapse Acoustic Imaging of Mesoscale and Fine-Scale Variability within the Faroe-Shetland Channel
We describe and analyze the results of a threeâdimensional seismic (i.e. acoustic) reflection survey from the FaroeâShetland Channel that is calibrated with nearâcoincident hydrographic and satellite observations. 54 vertical seismic transects were acquired over a period of 25 days. On each transect, a 250ââ400 m band of reflections is observed within the water column. Hydrographic measurements demonstrate that this reflective band is caused by temperature variations within the pycnocline that separates warm, nearâsurface waters of Atlantic origin from cold, deep waters which flow southward from the Nordic Seas. Tilting of reflective surfaces records geostrophic shear between these nearâsurface and deep waters. Measurements of temporal changes of pycnoclinic depth and of reflection tilt are used to infer the existence of an anticyclonic vortex that advects northeastward. Comparison with satellite measurements of seaâsurface temperature and height suggests that this vortex is caused by meandering of the Continental Slope Current. A model of a Gaussian vortex is used to match seismic and satellite observations. This putative vortex has a core radius of 20â30 km and a maximum azimuthal velocity of 0.3ââ0.4 m sâ1. It translates at 0.01ââ0.1 m sâ1. Within the pycnocline, diapycnal diffusivity, K , is estimaed by analyzing the turbulent spectral subrange of tracked reflections. K varies between 10â5.7 and 10â5.0 m 2 sâ1 in a pattern that is broadly consistent with translation of the vortex. Our integrated study demonstrates the ability of timeâlapse seismic reflection surveying to dynamically resolve the effects that mesoscale activity has upon deep thermohaline structure on scales from meters to hundreds of kilometers.Natural Environment Research Council (NERC)
Engineering and Physical Science Research Council
794 Program Grant EP/K034529/
Impact of Reflective Roofing on Cooling Electrical Use and Peak Demand in a Florida Retail Mall
Architects in hot climates have long recognized
that reflective roof colors can reduce building cooling
load. Experimentation spanning nearly three decades
has shown that white roofing surfaces can
significantly reduce surface temperatures and cooling
loads (Givoni and Hoffmann, 1968; Reagan and
Acklam, 1979; Griggs and Shipp, 1988; Anderson,
1989; Anderson et al., 1991 and Bansal et al., 1992).
More importantly, measured cooling energy savings
of white surfaces have been significant in
California's climate (Akbari et al., 1991, 1992,
1997).
In Florida, field research by the Florida Solar
Energy Center (FSEC) since 1993 has quantified the
impact of reflective roof coatings on sub-metered air
conditioning (AC) consumption in tests in a dozen
occupied homes (Parker et al., 1993; 1994; 1995;
1997). The coatings were applied to the roofs of each
home in mid-summer after a month-long period of
monitoring during which meteorological conditions,
building temperatures and AC energy use were
recorded. Using weather periods with similar
temperatures and solar insolation, air conditioning
energy use was reduced by 10% - 43% in the homes.
The average drop in space cooling energy use was
about 7.4 kWh/day or 19% of the pre-application air
conditioning consumption.
Unfortunately, until this project there has been
little objective testing of the impact of roof whitening
on the AC load of commercial buildings in Florida.
Two demonstration sites have been monitored. The
first was an elementary school in Cocoa Beach,
Florida, which was monitored for a year before and
after a white roof coating was applied. A final report
on this project was published in the CADDET
Newsletter (Parker et al., 1996a, b). The project
demonstrated a 10% annual savings in chiller energy
with a 30% reduction in peak cooling electrical
demand. This paper summarizes the findings from
the second demonstration at a commercial strip mall
Evaluating the genetic consequences of population subdivision as it unfolds and how to best mitigate them: A rare story about koalas
The genetic consequences of the subdivision of populations are regarded as significant to long-term evolution, and research has shown that the scale and speed at which this is now occurring is critically reducing the adaptive potential of most species which inhabit human-impacted landscapes. Here, we provide a rare and, to our knowledge, the first analysis of this process while it is happening and demonstrate a method of evaluating the effect of mitigation measures such as fauna crossings. We did this by using an extensive genetic data set collected from a koala population which was intensely monitored during the construction of linear transport infrastructure which resulted in the subdivision of their population. First, we found that both allelic richness and effective population size decreased through the process of population subdivision. Second, we predicted the extent to which genetic drift could impact genetic diversity over time and showed that after only 10 generations the resulting two subdivided populations could experience between 12% and 69% loss in genetic diversity. Lastly, using forward simulations we estimated that a minimum of eight koalas would need to disperse from each side of the subdivision per generation to maintain genetic connectivity close to zero but that 16 koalas would ensure that both genetic connectivity and diversity remained unchanged. These results have important consequences for the genetic management of species in human-impacted landscapes by showing which genetic metrics are best to identify immediate loss in genetic diversity and how to evaluate the effectiveness of any mitigation measures
Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels
Mitochondrial respiration in the African trypanosome undergoes dramatic developmental stage regulation. This requires co-ordinated control of components encoded by both the nuclear genome and the kinetoplast, the unusual mitochondrial genome of these parasites. As a model for understanding the co-ordination of these genomes, we have examined the regulation and mitochondrial import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosomes expressing intact or mutant forms of this protein, we demonstrate that COXVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitochondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and protein expression in parasites undergoing developmental stage differentiation demonstrates a temporal order of control involving regulation in the abundance of, first, mRNA and then protein. This represents the first dissection of the regulation and import of a nuclear-encoded protein into the cytochrome oxidase complex in these organisms, which were among the earliest eukaryotes to possess a mitochondrion
Thin-Film Metamaterials called Sculptured Thin Films
Morphology and performance are conjointed attributes of metamaterials, of
which sculptured thin films (STFs) are examples. STFs are assemblies of
nanowires that can be fabricated from many different materials, typically via
physical vapor deposition onto rotating substrates. The curvilinear--nanowire
morphology of STFs is determined by the substrate motions during fabrication.
The optical properties, especially, can be tailored by varying the morphology
of STFs. In many cases prototype devices have been fabricated for various
optical, thermal, chemical, and biological applications.Comment: to be published in Proc. ICTP School on Metamaterials (Augsut 2009,
Sibiu, Romania
InGaAs/InP hot electron transistors grown by chemical beam epitaxy
In this letter, we report on the dc performance of chemical beam epitaxy grown InGaAs/InP hot electron transistors (HETs). The highest observed differential β (dIC/dIB) is over 100. The HETs have Pd/Ge/Ti/Al shallow ohmic base contacts with diffusion lengths less than 300 Ă
. Furthermore, we also demonstrated ballistic transport of electrons in an InGaAs/InP HET by obtaining an energy distribution of electrons with âź60 meV full width at half maximum. The measured conduction band discontinuity of InGaAs/InP is 250.3 meV, which is 39.8% of the band gap difference.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70748/2/APPLAB-61-2-189-1.pd
Microtubule polarity and dynamics in the control of organelle positioning, segregation, and cytokinesis in the trypanosome cell cycle.
Dissipative Chaos in Semiconductor Superlattices
We consider the motion of ballistic electrons in a miniband of a
semiconductor superlattice (SSL) under the influence of an external,
time-periodic electric field. We use the semi-classical balance-equation
approach which incorporates elastic and inelastic scattering (as dissipation)
and the self-consistent field generated by the electron motion. The coupling of
electrons in the miniband to the self-consistent field produces a cooperative
nonlinear oscillatory mode which, when interacting with the oscillatory
external field and the intrinsic Bloch-type oscillatory mode, can lead to
complicated dynamics, including dissipative chaos. For a range of values of the
dissipation parameters we determine the regions in the amplitude-frequency
plane of the external field in which chaos can occur. Our results suggest that
for terahertz external fields of the amplitudes achieved by present-day free
electron lasers, chaos may be observable in SSLs. We clarify the nature of this
novel nonlinear dynamics in the superlattice-external field system by exploring
analogies to the Dicke model of an ensemble of two-level atoms coupled with a
resonant cavity field and to Josephson junctions.Comment: 33 pages, 8 figure
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