On sorting triangles in a delaunay tessellation

In a two-dimensional Delaunay-triangulated domain, there exists a partial ordering of the triangles (with respect to a vertex) that is consistent with the two-dimensional visibility of the triangles from that vertex. An equivalent statement is that a polygon that is star-shaped with respect to a given vertex can be extended, one triangle at a time, until it includes the entire domain. Arbitrary planar triangulations do not possess this useful property which allows incremental processing of the triangles.This work was partially supported by the National Science Foundation's US-Italy Collaborative Research Program under Grant INT-8714578 and Information, Robotics, and Intelligent Research Grant IRI-8704781.     

Complete forward displacement solutions for a class of three-branch parallel manipulators

Forward displacement solutions are presented for a class of spatial parallel manipulators. In particular, considered are manipulators consisting of a platform supported through passive spherical joints by three branches, each branch having three-revolute joints forming its main arm. Solutions are described for arbitrary main-arm layouts and for all possible cases of redundant (nine, eight, and seven sensors) and non-redundant (six sensors) sensing of branch main-arm joint displacements. It is demonstrated that closed-form forward displacement solutions can be found for all cases of redundant sensing. Furthermore, it is shown that a closed-form solution can be obtained for one of the two possible cases of non-redundant sensing of the main-arm joint displacements. The only case of joint displacement sensing not allowing a closed-form forward displacement solution is two joints sensed per branch, a case that can be expressed as a 16th-order polynomial of a single variable. Due to the importance of having efficient and failure-safe solutions for the forward displacement problem, it is suggested that appropriate redundancy in displacement sensing should be an important consideration in the design of parallel manipulation devices. © 1994 John Wiley & Sons, Inc.     

Religion and spirituality: Linkages to physical health.

Evidence is presented that bears on 9 hypotheses about the link between religion or spirituality and mortality, morbidity, disability, or recovery from illness. In healthy participants, there is a strong, consistent, prospective, and often graded reduction in risk of mortality in church/service attenders. This reduction is approximately 25% after adjustment for confounders. Religion or spirituality protects against cardiovascular disease, largely mediated by the healthy lifestyle it encourages. Evidence fails to support a link between depth of religiousness and physical health. In patients, there are consistent failures to support the hypotheses that religion or spirituality slows the progression of cancer or improves recovery from acute illness but some evidence that religion or spirituality impedes recovery from acute illness. The authors conclude that church/service attendance protects healthy people against death. More methodologically sound studies are needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Iron pyrite films prepared by sulfur vapor transport

Iron films deposited via thermal evaporation, with a thickness between 100 and 250 nm, were converted into FeS₂ by open sulfur transport using nitrogen as a gas vector. The films thus obtained constituted a single pyrite phase and were optically highly absorbing. The sulfurization process was optimized. As a result, sample temperature and conversion time were found to be the major determining parameters. The films were characterized using several methods. The crystallinity and phase identification were determined by X-ray diffractometry. Scanning electron microscopy showed a homogeneous surface of both iron and pyrite layers. Optical transmission measurements confirmed the highly absorbing character of FeS₂ and allowed the determination of direct (1.35 eV) and indirect (0.82 eV) transitions.     

Analytic computation of the photocurrent density in a n-6H-SiC/p-Si/n-Si/p-Si0.8Ge0.2 multilayer solar cell

In this work we conceived a model of a multilayer solar cell composed by four layers of opposite conductivities: an n-type 6H-SiC used as a frontal layer to absorb high energy photons (energy gap equals 2.9 eV), a p-type Si layer, an n-type Si layer and a p-type SiGe back layer to absorb low energy photons (Si_0.8Ge_0.2 with an energy gap equal to 0.8 eV). The impurity concentration in every layer of the model is taken equal to 10¹⁷ cm⁻³ to ensure abrupt junctions inside the cell. The optical properties of the separate layers have been fitted and tabulated to be used for thin films devices numerical simulation. We developed the equations giving the minority carrier concentration and the photocurrent density in each abscissa of the model. We used Matlab software to simulate and optimize the layers thicknesses to achieve the maximum photocurrent generated under AM0 solar spectrum. The results of simulation showed that the optimized structure could deliver, assuming 10⁵ cm/s surface recombination velocity, a photocurrent density of more than 53 mA/cm², which represents 88.3% of the ideal photocurrent (59.99 mA/cm²) that can be generated under AM0 solar spectrum.     

Fabrication and characterization of Cu2ZnSnS4 thin films deposited by spray pyrolysis technique

We have investigated synthesis conditions and some properties of sprayed Cu₂ZnSnS₄ (CZTS) thin films in order to determine the best preparation conditions for the realization of CZTS based photovoltaic solar cells. The thin films are made by means of spraying of aqueous solutions containing copper chloride, zinc chloride, tin chloride and thiourea on heated glass substrates at various temperatures. In order to optimize the synthesis conditions of the CZTS films, two series of experiments are performed. In the first series the sprayed duration was fixed at 30 min and in the second it is fixed at 60 min. In each series, the substrate temperature was changed from 553°K to 633°K. The X-ray diffraction shows, on one hand, that the best crystallinity was obtained for 613°K as substrate temperature and 60 min as sprayed duration. On the other hand, these CZTS films exhibit the kesterite structure with preferential orientation along the [112] direction. Atomical Force Microscopy was used to determine the grain sizes and the roughness of these CZTS thin film. After the annealing treatment, we estimated the optical band-gap energy of the CZTS thin film exhibiting the best crystallinity as 1.5 eV which is quite close to the optimum value for a solar cell.     

Effect of dispersion states (electrostatic/electrosteric stabilization) on particles arrangement in the yttria-stabilized zirconia sediments

In the present work, particle arrangement and their packing in the sediment layer of zirconia suspension were studied. To evaluate the particle settling, aqueous suspensions of zirconia nanoparticles were prepared in different dispersion states. In one state, Dolapix CE64 was used as a dispersant to provide electrosteric mechanism. In another state, pH of the suspension was adjusted at 4 to provide electrostatic mechanism. The other state was the combination of dispersant and pH adjustment which resulted in the most stable suspension. First of all, the stability of all dispersion states was evaluated by zeta potential, sediment volume (SV) and height, viscosity, and packing density (PD). Then, the sediment layers of all suspensions were characterized. Incorporation of electrostatic mechanism was resulted in a main decrease in viscosity with high surface charges, while electrosteric mechanism caused lower sedimentation of particles. Fall velocities of particles/agglomerates were estimated, and the influences of dispersion states on the particles fall velocities were characterized. The microstructural observation revealed homogeneous packing of particles in the sediment layer of the stable suspension demonstrating the proper dispersion of particles. Dolapix CE64 and pH adjustment resulted in a uniform arrangement of particles without agglomeration and spherical and regular granules with a uniform shape.     

Modification of phenol–formaldehyde resol resins by lignin,starch, and urea

Lignin‐based chemicals, starch, and urea were used as modifiers for phenol–formaldehyde resol resins. The effects of the addition stage of the modifiers used in the synthesis of the resins and the type of modification reagent on the structures of the resins and their molar masses and reactivities were investigated. The modifications with corn starch and lignin promoted condensation; this was verified by increased molar masses and high ratios of methylene bridges to the sum of free ortho and para aromatic groups with respect to the corresponding reference resin without a modification reagent. The later the modifier was added to the resin condensation mixture, the more methylene bridges were formed with respect to the amounts of free ortho and para aromatic groups. In addition, when urea or wheat starch was added in the later condensation stage, the final condensation also reached high stages. The modifications with lignosulfonate and starch, as well as the early addition of urea, enhanced p–p′ bridge structures. The lowest condensation stage and, therefore, the highest reactivity were found when wheat starch was added with the starting reagents. The curing heat of the wheat‐starch‐modified resins decreased according to the deferred addition point of starch. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 582–588, 2003     

Microstructure and morphology of amine-cured epoxy coatings before and after outdoor exposures—An AFM study

Atomic force microscopy (AFM) has been used to study the morphology and microstructure of an amine-cured epoxy before and after outdoor exposure. Measurements were made from samples prepared in an essentially CO₂-free, H₂O-free glove box and from samples prepared in ambient conditions. For those prepared in a CO₂-free glove box, AFM imaging was conducted on (1) an unexposed air/coating surface, (2) an unexposed coating bulk, (3) an unexposed coating/substrate interface, and (4) a field exposed air/coating surface. For samples prepared in ambient conditions, only the unexposed air/coating surface was investigated. The same regions of the exposed samples were scanned periodically by the AFM to monitor changes in the surface morphology of the coating as UV exposure progressed. Small angle neutron scattering and Fourier transform infrared spectroscopy (FTIR) studies were performed to verify the microstructure and to follow chemical changes during outdoor exposure, respectively. The results have shown that amine blushing, which occurs only under ambient conditions, had a significant effect on the surface morphology and microstructure of the epoxy. The surface morphology of the samples prepared under CO₂-free, dry conditions was generally smooth and homogeneous. However, the interface and the bulk samples clearly revealed a two-phase structure consisting of bright nodular domains and dark interstitial regions, indicating an inhomogeneous microstructure. Such heterogeneous structure of the bulk was in good agreement with results obtained by small angle neutron scattering of unexposed samples and by AFM phase imaging of the degraded sample surface. The relationship between submicrometer physical changes and molecular chemical degradation is discussed. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago, IL.     

Design and analysis of single-factor experiments: Analysis of variance of the effect of rice husk ash and commercial fillers in NR compounds

Summary White rice husk ash (WRHA) and black rice husk ash (BRHA) were incorporated into natural rubber (NR) using a laboratory-sized two-roll mill. A conventional vulcanization system was used for curing and physical tests of the NR vulcanized involved determining of tensile and tear resistances. For comparison purposes, precipitated silica (Zeosil-175) and carbon black (N774) were used too. Using the analysis of variance of single-factor experiments, it can be concluded that: BRHA is non-reinforcing filler and its use is limited to 20 phr; WRHA is semi-reinforcing filler and the variation of filler loading (0 up to 50 phr) causes the maximum variation upon tensile strength of NR compounds; and, that although carbon black and silica are reinforcing fillers, a real reinforcement is reached up to 20 phr for tensile strength.