Hyperbaric pressure – laser assisted chemical vapor deposition of ceramic Si-based fibers

A method of growing ceramic fibers for CMC’s directly from the gas phase, called hyperbaric pressure laser-assisted chemical vapor deposition (HP-LCVD), has been investigated using SiC as a case study. In this process, a laser is focused onto a substrate whereupon the gas precursor decomposes under the focal point into its constituent species. Those species are deposited as a solid onto a substrate, nucleating a fiber which continues to grow parallel to the beam as the laser focus is withdrawn from the surface. This unique processing technique can be used to grow many fibers simultaneously using an array of beams as well as three-dimensional shapes by changing the orientation of the laser beam with respect to the tip. Depending on system pressure, laser energy, and tip retraction speed from the laser’s focus, a range of fiber diameters, surface morphologies, stable or meta-stable phases, and micro/nano-structures can be achieved. These features have been assembled into a process-structure map for SiC fabrication by this method. To gain further insights into the variables that drive the thermodynamics of nucleation and growth, an in situ two-color pyrometry technique has been employed to measure the temperature in the reaction zone during the fiber’s growth. Please click Additional Files below to see the full abstract

Additive manufacturing of bulk refractory fiber within the Ta-Hf-C system for ultra high-temperature reinforced composite materials

This work discusses the production of ultra-high temperature material (UHTM) fibers that can be used to reinforce composite materials in extreme environments. Carbon-fiber-based, carbon-matrix composites are commonly used for many UHTM applications; however within an oxygen containing atmosphere, C-C composites are limited by oxidation well-below their ultimate sublimation temperatures. Hence, research is being carried out to create alternative materials, with very high melting points, but that have greater oxidation resistance. SiC-fiber reinforced composites offer one alternative, but are limited to temperatures below 1870K. Of the 12 binary compounds that have melting points above 3270K, Hafnium Carbide (4170K) and tantalum carbide (4150K) have the highest melting points. The ternary tantalum-hafnium-carbide system, which is derived from hot-isostatically-pressed HfC and TaC powders, has been shown to have a melting point in excess of 4260K. Obviously, these refractory materials are extremely hard to draw/extrude into wires or fibers. In this paper, we demonstrate the first-ever synthesis of Ta-Hf-C compounds in fiber form, where we have used hyperbaric laser chemical vapor deposition (HP-LCVD) to decompose gas-phase precursors. TaC, HfC, and TaxHfyCz fibers were grown from tantalum (V) chloride, hafnium (IV) bromide, and octadecane precursors within a heated glass chamber. Fine-grained and amorphous fibers were grown, depending on the precursor pressures and laser-induced temperatures. Several growth modes were observed, including kinetically-limited and mass-transport limited growth. This additive manufacturing approach holds promise for the bulk fabrication of fine-grained and glassy Ta-Hf-C chopped fiber for UHTM composites, and can be applied to many different material systems. An overview of the HP-LCVD process will be provided, as well as various implementations for producing bulk fiber and microstructures for metal-matrix and ceramic-matrix composites fabrication

A Comparison of Male and Female Teachers' Approval and Disapproval Interactions with Children

This study was designed to determine the relationships between three variables in fifth- and sixth-grade classroom verbal interactions. These variables include sex of teacher, sex of pupil, and approval/disapproval interactions between teacher and pupil

Usage of the Extension Agents' Handbook of Insects, Plant Diseases and Weed Control as Perceived by Oklahoma County Agents and Clientele

Agricultural Educatio

Modern contraceptive use among women in Uganda: An analysis of trend and patterns (1995-2011)

There is an extensive body of literature concerning modern contraceptive use among women in Uganda. A questionable aspect however is whether the impact of factors associated with modern contraceptive use has remained the same in the recent past. Demographic Health Survey (DHS) data of women in the period 1995-2011 was adopted to establish an understanding of this issue. The focus in the investigations was none pregnant sexually active women. Variations in patterns of modern contraceptive use were assessed by socioeconomic and demographic characteristics of women using a logistic regression based on a complex survey design. In the results, an upward trend in modern contraceptive use - from 11.6% in 1995 to 32.1% in 2011 - shows that progress has been made in this regard. Increased odds of modern contraceptive use across the study period were noted among women with primary and post-primary education, those in urban areas, women in the higher wealth quartiles and those with a higher number of surviving children (p < 0.01). Further, reduced odds of modern contraceptive use across the study period were noted among married women and those in cohabiting relationships (p < 0.05). The study however demonstrates variations in the impact of these factors across the study period. All the same, efforts towards enhancing modern contraceptive use in the near future should focus on enhancing: (i) literacy levels of woman particularly, (ii) access to and affordability of the services and (iii) awareness campaigns on family planning use targeting both men and women

Effects of Stride Rate Manipulation in Shoes with Different Drop Heights

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Kindred Practice: Experiences of a Research Group Working Towards Decolonization and Indigenization in the Everyday

This paper engages the question of kindred practice as contemplated by three members of a research group working toward decolonization and Indigenization. The focus on kindred practice is informed by the title and description of the wâhkôhtowin: Indigenizing practice, linking kindred spirits conference held in September 2014, at the University of Saskatchewan. Being each positioned uniquely in relation to social power hierarchies, for the authors, the notion of what it means to be kindred in advocacy carries nuanced dynamics and inflections. As the piece unfolds, each author elaborates key attributes of practice believed to both underlie our kindred relationship and align with the ends of decolonization and Indigenization ôma masinahikan ôta e-kî-nistokamâtocik e-nanitonâhkik tânisi cîhkâhtaw peyakwan e-kî-isi-wâpahtamihk ôma kâkwe-kweskipimâtisihk ekwa ka-kîwe-totamihk iyiniwewin. e-kî-mâmiskohtamihk esa wâhkôhtowin: iyiniwewin,  kâkî-mâmawi-api nôcihtowipîsim 2014, kihci-kiskinwamâtohwikamikohk U of S.  ôma mîna kîtapicik ekwa ka-isi-atoskâtahkik, wâpahtamok mitoni cîhkâhtaw peykwan e-isi-nayâhtakik ôma kâkwe-kweskipitâhkik kihci-kiskinwamâtohwikamikohk ekwa ka-mâmawi-kamâtocik

Radial Temperature Profiles of X-Ray--Emitting Gas Within Clusters of Galaxies

Previous analyses of ASCA data of clusters of galaxies have found conflicting results regarding the slope of the temperature profile of the hot X-ray gas within clusters, mainly because of the large, energy-dependent point spread function (PSF) of the ASCA mirrors. We present a summary of all ASCA-determined cluster temperature profiles found in the literature, and find a discrepancy in the radial temperature trend of clusters based on which PSF-correction routine is used. This uncertainty in the cluster temperature profile in turn can lead to large uncertainties in the amount of dark matter in clusters. In this study, we have used ROSAT PSPC data to obtain independent relative temperature profiles for 26 clusters, most of which have had their temperature profiles determined by ASCA. Our aim is not to measure the actual temperature values of the clusters, but to use X-ray color profiles to search for a hardening or softening of the spectra with radius for comparison to ASCA-derived profiles. The radial color profiles indicate that outside of the cooling flow region, the temperature profiles of clusters are in general constant. Within 35% of the virial radius, we find a temperature drop of 20% at 10 keV and 12% at 5 keV can be ruled out at the 99% confidence level. A subsample of non-cooling flow clusters shows that the condition of isothermality applies at very small radii too, although cooling gas complicates this determination in the cooling flow subsample. The colors predicted from the temperature profiles of a series of hydrodynamical cluster simulations match the data very well, although they cannot be used to discriminate among different cosmologies. An additional result is that the color profiles show evidence for a central peak in metallicity in low temperature clusters.Comment: 39 pages, 15 embedded Postscript figures, uses aaspp4.sty, accepted for publication in Astrophysical Journa