75,084 research outputs found
Topological invariants of time-reversal-invariant band structures
The topological invariants of a time-reversal-invariant band structure in two
dimensions are multiple copies of the invariant found by Kane
and Mele. Such invariants protect the topological insulator and give rise to a
spin Hall effect carried by edge states. Each pair of bands related by time
reversal is described by a single invariant, up to one less than
half the dimension of the Bloch Hamiltonians. In three dimensions, there are
four such invariants per band. The invariants of a crystal
determine the transitions between ordinary and topological insulators as its
bands are occupied by electrons. We derive these invariants using maps from the
Brillouin zone to the space of Bloch Hamiltonians and clarify the connections
between invariants, the integer invariants that underlie the
integer quantum Hall effect, and previous invariants of -invariant
Fermi systems.Comment: 4 page
Investigation of the development of cracks in solder joints
Study consisted of an analytical approach, in which a mathematical model of existing printed circuit board component mounting techniques was analyzed, and an empirical investigation was performed to determine the extent of damage caused by temperature cycling of the printed circuit boards
HCMM energy budget data as a model input for assessing regions of high potential groundwater pollution
The author has identified the following significant results. Significant relationships were found between surface soil temperatures estimated from HCMM radiometric temperatures and depth to ground water and near surface soil moisture
The use of ion beam cleaning to obtain high quality cold welds with minimal deformation
A variation of cold welding is described which utilizes an ion beam to clean mating surfaces prior to joining in a vacuum environment. High quality solid state welds were produced with minimal deformation
HCMM energy budget data as a model input for assessing regions of high potential groundwater pollution
There are no author-identified significant results in this report
Stimulation of hepatic regeneration after partial hepatectomy by infusion of a cytosol extract from regenerating dog liver
A cytosol liver extract was prepared from adult dog livers and from liver remnants that had been regenerating for one, two and three days after 72 per cent partial hepatectomy. Given intraportally, the most active of these cytosols did not stimulate proliferation in the livers of normal dogs. However, infused during a six hour period into the portal vein of test group dogs, the cytosol from 48 and, especially, 72 hour regenerating livers augmented the regeneration response ordinarily produced by 44 per cent partial hepatectomy. The effect was delayed. It became identifiable 48 hours after infusion and reached a peak at 72 hours. Neither augmentation nor significant inhibition of the normal regeneration response was produced by cytosol from normal liver and 24 hour regenerating liver or by a six hour infusion of insulin. The amplification effect of active cytosol was equivocal when the infusions were given intraperitoneally and was not demonstrable at all by the intravenous route. In these investigations, it is confirmed that there are growth control factors in regenerating liver but the nature or physiologic significance of the factor or factors has not been clarified
Impact of Dark Matter Microhalos on Signatures for Direct and Indirect Detection
Detecting dark matter as it streams through detectors on Earth relies on
knowledge of its phase space density on a scale comparable to the size of our
solar system. Numerical simulations predict that our Galactic halo contains an
enormous hierarchy of substructures, streams and caustics, the remnants of the
merging hierarchy that began with tiny Earth mass microhalos. If these bound or
coherent structures persist until the present time, they could dramatically
alter signatures for the detection of weakly interacting elementary particle
dark matter (WIMP). Using numerical simulations that follow the coarse grained
tidal disruption within the Galactic potential and fine grained heating from
stellar encounters, we find that microhalos, streams and caustics have a
negligible likelihood of impacting direct detection signatures implying that
dark matter constraints derived using simple smooth halo models are relatively
robust. We also find that many dense central cusps survive, yielding a small
enhancement in the signal for indirect detection experiments.Comment: 6 pages, revision in response to referees report. Now accepted by
Phys. Rev D., in pres
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