On the Origin and Use of the Emissivity Approximations for Alumina Particles

The commonly used spectral dependences for the emissivity of aluminum oxide particles are investigated. Theoretical considerations from Mie theory and the optical properties of alumina give rise to inverse wavelength and λ⁻² dependences when particles fall within the Rayleigh scattering regime. Analysis of particles of an arbitrary size (i.e. outside the Rayleigh regime) demonstrates that no general relationship exists between the wavelength and the spectral emissivity of these particles contrary to what has been routinely applied in the literature. This result was attributed to the dependence of both the spectral dependence and magnitude of the complex refractive index on the spectral emissivity. The significance of these results to applications (e.g. aluminized propellants) is discussed.     

Fatigue yield

The paper starts with a brief review of fatigue damage progression under block loadings and then investigates in more details a fatigue yield model. The study identifies the fatigue yield as a cause–effect interaction of damage and endurance rather than as a physical process in the traditional fatigue engineering. The experimental data under variable and constant stress amplitude loadings reported up to date were used for the evaluation of the fatigue yield approach. Analytical, numerical and recursive procedures for fatigue yield assessments were carried out and illustrated by examples.     

Engineering Model of Friction of Gas‐Solids Flow in a Jet Mill Nozzle

In this study we develop a model for estimating particle friction against the wall of a jet mill nozzle. The computation is reduced to a definition of conventional force acting on particles in a polydispersed stream. It is assumed that energy losses due to friction are caused by multiple particle collisions against the nozzle walls. The proposed model is oriented to calculating jet mill nozzles and is much simpler than previously applied methods. A parametric study of the proposed model was carried out and the effect of particle friction on particle and gas velocities was derived.     

Topotactically Modified Stress in Coatings

The unexpected occurrence of compressive stresses in solgel-derived alumina coatings following a densification transformation was found to be related to the topotactic transformation of boehmite (γ-AlOOH) to γ-alumina (γ-Al₂O₃) on heating. The boehmite coating showed a pronounced fiber texture with the [001] crystallographic axis perpendicular to the substrate-coating interface plane. At about 500°C, the orthorhombic boehmite transformed into tetragonal γ-alumina with very little, if any, reorientation of the crystallites. Because of the topotactic nature of the transformation, the fiber texture persisted in the γ-alumina phase. This resulted in an anisotropic change that generated compressive strains in the coating.     

Regions outside of the CAAX motif influence the specificity of prenylation of G protein gamma subunits

A family of GTP-binding regulatory proteins (G proteins) transduces signals across the plasma membrane from a large number of receptors to a smaller number of effectors. Recent studies indicate that a series of post-translational modifications are required for their association with the plasma membrane and for their function. In the case of the G protein gamma subunits, the post-translational modifications include the prenylation of a cysteine residue within a carboxyl-terminal CAAX motif. Although prenylation has been shown to involve the addition of either a C15 farnesyl or a C20 geranylgeranyl group to proteins, the structural requirements and functional consequences of adding different types of prenyl groups to various members of the gamma subunit family have not been examined. In the present study, we have employed the baculovirus expression system to study the structural requirements for attaching different types of prenyl groups to various members of the gamma subunit family. We show that the gamma 2 subunit is modified by a C20 geranylgeranyl group, consistent with the presence of a geranylgeranylation target sequence in this protein. However, we found that the gamma 1 and mutant gamma 2(Ser-71) subunits are modified by both C15 farnesyl and C20 geranylgeranyl groups, despite the presence of an accepted farnesylation target sequence in both of these proteins. Using chimeras of the gamma 1 and gamma 2 subunits, we provide evidence indicating that structural elements upstream of the carboxyl-terminal CAAX motif play a role in the recognition of members of the gamma subunit family by the appropriate insect and mammalian prenyltransferases.     

Preferential but not exclusive T cell receptor V beta chain utilization of myelin basic protein and peptide-specific T cell clones in mice

The repertoire of T cell receptor (TCR) V beta chain utilization was investigated in PL/J, CXJ-1, SJL/J and B10.S-->SJL/J chimeric mice in response to either myelin basic protein (MBP) or the strain-specific encephalitogenic peptide. Our analysis showed that there was an overlapping predominance in the TCR V beta gene utilization in the MBP-specific responses, which were independent of the major histocompatibility complex (MHC) class II haplotype present, and the immunodominant peptide region recognized in these different strains. In those mice having the TCR V beta b haplotype (PL/J, CXJ-1, and the B10.S-->SJL chimera) either the TCR V beta 4, 8, and 13 or the TCR V beta 4, 6, and 13 predominated. In contrast, in mice with TCR V beta a haplotype (SJL/J) V beta 4, 6, and 17a were found. However, the quantitative distribution of these preferentially utilized TCR V beta chains in each strain was defined by the MHC class II haplotype and the immunodominant peptide recognized. The expression of the V beta 8 gene product in the peripheral TCR repertoire did not always correlate with predominant V beta 8 utilization in the MBP-specific response.     

Chlordiazepoxide microinjected into the region of the dorsal raphe nucleus eliminates the interference with escape responding produced by inescapable shock whether administered before inescapable shock or escape testing.

Systemic administration of benzodiazepines before exposure to inescapable shock (IS) blocks the enhanced fear conditioning and escape learning deficits that follow exposure to IS, whereas administration before the subsequent behavioral testing eliminates the enhanced fear but not the interference with escape (N?=?44 male rats). The failure of benzodiazepines to reduce the IS-produced escape learning deficit when given before testing is inconsistent with a recent proposal that interference with escape is mediated by an IS-induced sensitization of dorsal raphe nucleus (DRN) activity. The present experiments demonstrate that chlordiazepoxide will block both the enhancement of fear and interference with escape responding when given before either IS or testing if microinjected in the region of the DRN. This suggests that systemic benzodiazepines fail to block escape deficits when given before testing because action at a site distant from the DRN counters the effect of the drug at the DRN. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A new test method for determination of wax content in crude oils,residues and bitumens

A new method for determining wax content in petroleum materials is developed. It is based on thin layer chromatography with flame ionization detection (TLC-FID) and involves two-step development with two solvents. The principle of the test method is first to separate saturates from other more polar components based on good solubility of saturates in n-heptane and weak strength of interaction with an adsorbent (silica). Waxes are then separated from the saturate fraction using a poor solvent methyl-ethyl ketone (MEK) at such a low temperature (typically ?20 °C) that waxes are in solid state. The separated fractions are quantified with FID. The test method is verified using various model compounds including n-alkanes of different molecular weight, isoalkane, as well as commercial waxes. Results indicate that the TLC-FID method detects the waxes mainly composed of n-alkanes ranging from C20 to C40, and large isoalkanes and cycloalkanes which are soluble in n-heptane. The method has been satisfactorily applied to a variety of samples of crude oils, residues, and bitumens. It is simple, quick, and reliable. By changing MEK temperature in the development chamber, waxes may be further characterized.     

Wikibooks in higher education: Empowerment through online distributed collaboration

In this case study, wiki technology was applied to the development of an introductory academic textbook on information systems. While the development, production and distribution of traditional textbooks are influenced by commercial interests, the wikitextbook was developed collaboratively by faculty and by students, and was made available online free of charge. After about two years of activity, the wikitextbook accumulated 564 sub-chapters, co-authored by undergraduate and graduate students in more than 20 classes offered by seven academic departments across three Israeli universities. We discuss the potential of wikitextbooks as vehicles of empowerment to students, teachers, and the discipline. This type of collaborative online technology intimates an influence on the status-quo in academic education in favor of less empowered stakeholders. However, caution is advised in drawing premature conclusions from results reported here. The implementation of wikitextbook should be augmented by a careful study of cultural, societal, behavioral and pedagogic variables.     

Comparison of coconut water and a carbohydrate-electrolyte sport drink on measures of hydration and physical performance in exercise-trained men

Background  

Sport drinks are ubiquitous within the recreational and competitive fitness and sporting world. Most are manufactured and artificially flavored carbohydrate-electrolyte beverages. Recently, attention has been given to coconut water, a natural alternative to manufactured sport drinks, with initial evidence indicating efficacy with regard to maintaining hydration. We compared coconut water and a carbohydrate-electrolyte sport drink on measures of hydration and physical performance in exercise-trained men.