1,907 research outputs found
Irradiation effects studies of NERVA materials
Several materials used in the NERVA project were irradiated at cryogenic temperatures to neutron fluences between 10 to the 17th and 10 to the 19th power newtons per square centimeter. Tensile properties were determined over a temperature range to evaluate the effects of irradiation on the material properties. The expected radiation damage typical of other materials was observed. A general increase in strength and decrease in ductility occurred. The effects at liquid nitrogen temperatures are more pronounced since radiation induced defects are not annealed out
Immiscible phase incorporation during directional solidification of hypermonotectics
Solidification processes in immiscible samples were investigated by directly observing the events taking place at the solid-liquid interface during directional solidification. Visualization of these events was made possible through the use of a transparent metal analog system and a temperature gradient stage assembly fitted to an optical microscope. The immiscible transparent analog system utilized was the succinonitrile-glycerol system. This system has been shown to exhibit the same morphological transitions as observed in metallic alloys of monotectic composition. Both monotectic and hypermonotectic composition samples were directionally solidified in order to gain an improved understanding of the manner in which the excess hypermonotectic liquid is incorporated into the solidifying structure. The processing conditions utilized prevented sedimentation of the excess hypermonotectic liquid by directionally solidifying the samples in very thin (13 microns), horizontally oriented cells. High thermal gradient to growth rate ratios (G/R) were used in an effort to prevent constitutional supercooling and the subsequent formation of L(sub 2) droplets in advance of the solidification front during the growth of fibrous composite structures. Results demonstrated that hypermonotectic composites could be produced in samples up to two weight percent off of the monotectic composition by using a G/R ratio greater than or equal to 4.6 x 10(exp 4) C(s)/mm(sup 2) to avoid constitutional supercooling. For hypermonotectic samples processed with G/R ratios below 4.6 x 10(exp 4) C(s)/mm(sup 2), constitutional supercooling occurred and resulted in slight interfacial instability. For these samples, two methods of incorporation of the hypermonotectic liquid were observed and are reported. The correlation between the phase spacing, lambda, and the growth rate, R, was examined and was found to obey a relationship generally associated with a diffusion controlled coupled growth process. For samples with compositions ranging from the monotectic composition up to 2 percent off of the monotectic composition, data indicated that the square of the phase spacing (lambda) varied linearly with the inverse of the growth rate (R)
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Assessing the Utility of Restaurant Descriptors and Typologies for Advancing the Body of Knowledge in Restaurant Management
The study begins with a review of existing typologies in the restaurant management literature. Segment labels from three typologies are used as keywords to collect 251 empirical studies from nine relevant academic journals serving the restaurant management discipline. Content analysis of titles, abstracts, and methodology sections reveals inconsistent use of existing typologies and limited use of effective restaurant descriptors. Recommendations are offered to optimize the use of restaurant descriptors so that the content of empirical studies may be more effectively accessed, digested, and compared across, thereby enhancing the communication of advances in the restaurant management body of knowledge
Photoluminescence spectroscopy of bandgap reduction in dilute InNAs alloys
Photoluminescence (PL) has been observed from dilute InNxAs1–x epilayers grown by molecular-beam epitaxy. The PL spectra unambiguously show band gap reduction with increasing N content. The variation of the PL spectra with temperature is indicative of carrier detrapping from localized to extended states as the temperature is increased. The redshift of the free exciton PL peak with increasing N content and temperature is reproduced by the band anticrossing model, implemented via a (5×5) k·p Hamiltonian
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Office design and health: a systematic review
Aim: To carry out a systematic review of recent research into the effects of workplace design, comparing individual with shared workspaces, on the health of employees.
Methods: The research question was "Does workplace design (specifically individual offices compared with shared workspaces) affect the health of workers?" A literature search limited to articles published between 2000 and 2017 was undertaken. A systematic review was carried out, and the findings of the reviewed studies grouped into themes according to the primary outcomes measured in the studies.
Results: The literature search identified 15 relevant studies addressing health effects of shared or open-plan offices compared with individual offices. Our systematic review found that, compared with individual offices, shared or open-plan office space is not beneficial to employees' health, with consistent findings of deleterious effects on staff health, wellbeing and productivity. Our findings are also consistent with those of earlier reviews.
Conclusion: These findings have public health implications for the New Zealand workforce. Decisions about workplace design should include weighing the short-term financial benefits of open-plan or shared workspaces against the significant harms, including increased sickness absence, lower job satisfaction and productivity, and possible threats to recruitment and retention of staff
Three applications of path integrals: equilibrium and kinetic isotope effects, and the temperature dependence of the rate constant of the [1,5] sigmatropic hydrogen shift in (Z)-1,3-pentadiene
Recent experiments have confirmed the importance of nuclear quantum effects
even in large biomolecules at physiological temperature. Here we describe how
the path integral formalism can be used to describe rigorously the nuclear
quantum effects on equilibrium and kinetic properties of molecules.
Specifically, we explain how path integrals can be employed to evaluate the
equilibrium (EIE) and kinetic (KIE) isotope effects, and the temperature
dependence of the rate constant. The methodology is applied to the [1,5]
sigmatropic hydrogen shift in pentadiene. Both the KIE and the temperature
dependence of the rate constant confirm the importance of tunneling and other
nuclear quantum effects as well as of the anharmonicity of the potential energy
surface. Moreover, previous results on the KIE were improved by using a
combination of a high level electronic structure calculation within the
harmonic approximation with a path integral anharmonicity correction using a
lower level method.Comment: 9 pages, 4 figure
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