3,307 research outputs found
Improved silicon carbide for advanced heat engines
Work performed to develop silicon carbide materials of high strength and to form components of complex shape and high reliability is described. A beta-SiC powder and binder system was adapted to the injection molding process and procedures and process parameters developed capable of providing a sintered silicon carbide material with improved properties. The initial effort has been to characterize the baseline precursor materials (beta silicon carbide powder and boron and carbon sintering aids), develop mixing and injection molding procedures for fabricating test bars, and characterize the properties of the sintered materials. Parallel studies of various mixing, dewaxing, and sintering procedures have been carried out in order to distinguish process routes for improving material properties. A total of 276 MOR bars of the baseline material have been molded, and 122 bars have been fully processed to a sinter density of approximately 95 percent. The material has a mean MOR room temperature strength of 43.31 ksi (299 MPa), a Weibull characteristic strength of 45.8 ksi (315 MPa), and a Weibull modulus of 8.0. Mean values of the MOR strengths at 1000, 1200, and 14000 C are 41.4, 43.2, and 47.2 ksi, respectively. Strength controlling flaws in this material were found to consist of regions of high porosity and were attributed to agglomerates originating in the initial mixing procedures. The mean stress rupture lift at 1400 C of five samples tested at 172 MPa (25 ksi) stress was 62 hours and at 207 MPa (30 ksi) stress was 14 hours. New fluid mixing techniques have been developed which significantly reduce flaw size and improve the strength of the material. Initial MOR tests indicate the strength of the fluid-mixed material exceeds the baseline property by more than 33 percent
A lattice model for the line tension of a sessile drop
Within a semi--infinite thre--dimensional lattice gas model describing the
coexistence of two phases on a substrate, we study, by cluster expansion
techniques, the free energy (line tension) associated with the contact line
between the two phases and the substrate. We show that this line tension, is
given at low temperature by a convergent series whose leading term is negative,
and equals 0 at zero temperature
Au/TiO2(110) interfacial reconstruction stability from ab initio
We determine the stability and properties of interfaces of low-index Au
surfaces adhered to TiO2(110), using density functional theory energy density
calculations. We consider Au(100) and Au(111) epitaxies on rutile TiO2(110)
surface, as observed in experiments. For each epitaxy, we consider several
different interfaces: Au(111)//TiO2(110) and Au(100)//TiO2(110), with and
without bridging oxygen, Au(111) on 1x2 added-row TiO2(110) reconstruction, and
Au(111) on a proposed 1x2 TiO reconstruction. The density functional theory
energy density method computes the energy changes on each of the atoms while
forming the interface, and evaluates the work of adhesion to determine the
equilibrium interfacial structure.Comment: 20 pages, 11 figure
Enhancing Agricultural Productivity of CLMV Countries: Challenges and Agenda for Reforms
Rigorous Probabilistic Analysis of Equilibrium Crystal Shapes
The rigorous microscopic theory of equilibrium crystal shapes has made
enormous progress during the last decade. We review here the main results which
have been obtained, both in two and higher dimensions. In particular, we
describe how the phenomenological Wulff and Winterbottom constructions can be
derived from the microscopic description provided by the equilibrium
statistical mechanics of lattice gases. We focus on the main conceptual issues
and describe the central ideas of the existing approaches.Comment: To appear in the March 2000 special issue of Journal of Mathematical
Physics on Probabilistic Methods in Statistical Physic
Long-term clinical outcome of oestrogen receptor-positive operable primary breast cancer in older women: a large series from a single centre
Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV
The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8 TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum
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