1,367 research outputs found
Parametric optimization for terabit perpendicular recording
The design of media for ultrahigh-density perpendicular recording is discussed in depth. Analytical and semianalytical models are developed to determine the constraints upon the media to fulfill requirements of writability and thermal stability, and the effect of intergranular exchange coupling is examined. The role of vector fields during the write process is examined, and it is shown that one-dimensional models of perpendicular recording have significant deficiencies. A micromagnetic model is described and the results of simulations of recording undertaken with the model are presented. The paper demonstrates that there is no physical reason why perpendicular recording should not be possible at or above 1 Tb/in(2)
NOTE On the Degree ofLpApproximation with Positive Linear Operators
AbstractThe degree of approximation inLp-spaces by positive linear operators is estimated in terms of the integral modulus of smoothness. It is shown that the conjectured optimal degree of approximation is not attained in the class of functions having a second derivative belonging toLp
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Laser Direct-Write of Nanoporous Optical Coatings: Preliminary Results
Mechanical Engineerin
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Modeling and Characterization of a Novel, Low-Cost, Direct-Write Waveguide
Both the current long-term telecommunication trends toward optical networking and the
recent growth in information bandwidth have pushed the necessity for improved optical
communications. Our fabrication approach, which leverages our expertise in solid
freeform fabrication in conjunction with sol-gel technology, has advantages over these
other methods because of the inherent benefits of using a direct-write philosophy, such as
design flexibility and minimal post-processing. However, fabrication of such novel
optical components requires extensive knowledge of their light guidance capabilities.
This paper will show the technical issues involved in both modeling and characterizing
small optical components fabricated by locally densifying sol-gels in a modified directwrite process.Mechanical Engineerin
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Surface Roughness Enhancement of Indirect-SLS Metal Parts by Laser Surface Polishing
Laser polishing by means of shallow surface melting of indirect-SLS metal parts
was achieved using high power CO2 and Nd:YAG lasers raster scanned at high speed.
This was an effective technique for reducing surface roughness. The fast moving laser
beam provides just enough heat energy to cause melting of the surface peaks. The molten
mass then flows into the surface valleys by surface tension, gravity and laser pressure,
thus diminishing the roughness. Surface roughness Ra data were obtained by
profilometry measurements of the polished samples. An analytical model was developed
based on the assumption that the surface of an SLS part consists of semi-spherical caps.
The model was used to predict the Ra values as a function of laser power, scan speed and
precursor powder particle size. The modeled results fit the empirical data within a 15%
error.The Laboratory of Freeform Fabrication gratefully acknowledges the support of
the Office of Naval Research for funding the project “Surface Engineering for SFF
Processes”, Grant Nº: N00014-00-1-0334Mechanical Engineerin
Canine mesenchymal stem cells are neurotrophic and angiogenic:an in vitro assessment of their paracrine activity
Mesenchymal stem cells (MSCs) have been used in cell replacement therapies for connective tissue damage, but also can stimulate wound healing through paracrine activity. In order to further understand the potential use of MSCs to treat dogs with neurological disorders, this study examined the paracrine action of adipose-derived canine MSCs on neuronal and endothelial cell models. The culture-expanded MSCs exhibited a MSC phenotype according to plastic adherence, cell morphology, CD profiling and differentiation potential along mesenchymal lineages. Treating the SH-SY5Y neuronal cell line with serum-free MSC culture-conditioned medium (MSC CM) significantly increased SH-SY5Y cell proliferation (P < 0.01), neurite outgrowth (P = 0.0055) and immunopositivity for the neuronal marker βIII-tubulin (P = 0.0002). Treatment of the EA.hy926 endothelial cell line with MSC CM significantly increased the rate of wound closure in endothelial cell scratch wound assays (P = 0.0409), which was associated with significantly increased endothelial cell proliferation (P < 0.05) and migration (P = 0.0001). Furthermore, canine MSC CM induced endothelial tubule formation in EA.hy926 cells in a soluble basement membrane matrix. Hence, this study has demonstrated that adipose-derived canine MSC CM stimulated neuronal and endothelial cells probably through the paracrine activity of MSC-secreted factors. This supports the use of canine MSC transplants or their secreted products in the clinical treatment of dogs with neurological disorders and provides some insight into possible mechanisms of action
Density functional study of Au (n=2-20) clusters: lowest-energy structures and electronic properties
We have investigated the lowest-energy structures and electronic properties
of the Au(n=2-20) clusters based on density functional theory (DFT) with
local density approximation. The small Au clusters adopt planar structures
up to n=6. Tabular cage structures are preferred in the range of n=10-14 and a
structural transition from tabular cage-like structure to compact
near-spherical structure is found around n=15. The most stable configurations
obtained for Au and Au clusters are amorphous instead of
icosahedral or fcc-like, while the electronic density of states sensitively
depend on the cluster geometry. Dramatic odd-even alternative behaviors are
obtained in the relative stability, HOMO-LUMO gaps and ionization potentials of
gold clusters. The size evolution of electronic properties is discussed and the
theoretical ionization potentials of Au clusters compare well with
experiments.Comment: 6 pages, 7 figure
Neuromuscular synaptic function in mice lacking major subsets of gangliosides
Gangliosides are a family of sialylated glycosphingolipids enriched in the outer leaflet of neuronal membranes, in particular at synapses. Therefore, they have been hypothesized to play a functional role in synaptic transmission. We have measured in detail the electrophysiological parameters of synaptic transmission at the neuromuscular junction (NMJ) ex vivo of a GD3-synthase knockout mouse, expressing only the O- and a-series gangliosides, as well as of a GM2/GD2-synthase*GD3-synthase double-knockout (dKO) mouse, lacking all gangliosides except GM3. No major synaptic deficits were found in either null-mutant. However, some extra degree of rundown of acetylcholine release at high intensity use was present at the dKO NMJ and a temperature-specific increase in acetylcholine release at 35 °C was observed in GD3-synthase knockout NMJs, compared with wild-type. These results indicate that synaptic transmission at the NMJ is not crucially dependent on the particular presence of most ganglioside family members and remains largely intact in the sole presence of GM3 ganglioside. Rather, presynaptic gangliosides appear to play a modulating role in temperature- and use-dependent fine-tuning of transmitter output
Evidence for Shape Co-existence at medium spin in 76Rb
Four previously known rotational bands in 76Rb have been extended to moderate
spins using the Gammasphere and Microball gamma ray and charged particle
detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV.
The properties of two of the negative-parity bands can only readily be
interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model
calculations if they have the same configuration in terms of the number of g9/2
particles, but they result from different nuclear shapes (one near-oblate and
the other near-prolate). These data appear to constitute a unique example of
shape co-existing structures at medium spins.Comment: Accepted for publication in Physics Letters
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