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7,047 Matching Results
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7,033 - 7,047 of
7,047
Mechanical properties and shear failure surfaces of two alumina powders in triaxial compression
In the manufacture of ceramic components, near-net-shape parts are commonly formed by uniaxially pressing granulated powders in rigid dies. Density gradients that are introduced into a powder compact during press-forming often increase the cost of manufacturing, and can degrade the performance and reliability of the finished part. Finite element method (FEM) modeling can be used to predict powder compaction response, and can provide insight into the causes of density gradients in green powder compacts; however, accurate numerical simulations require accurate material properties and realistic constitutive laws. To support an effort to implement an advanced cap plasticity model within the finite element framework to realistically simulate powder compaction, the authors have undertaken a project to directly measure as many of the requisite powder properties for modeling as possible. A soil mechanics approach has been refined and used to measure the pressure dependent properties of ceramic powders up to 68.9 MPa (10,000 psi). Due to the large strains associated with compacting low bulk density ceramic powders, a two-stage process was developed to accurately determine the pressure-density relationship of a ceramic powder in hydrostatic compression, and the properties of that same powder compact under deviatoric loading at the same specific pressures. Using this …
Date:
April 24, 2000
Creator:
Zeuch, David H.; Grazier, J. Mark; Arguello, Jose G., Jr. & Ewsuk, Kevin G.
System:
The UNT Digital Library
Experimental observations of thermal spikes in microwave processing of ceramic oxide fibers
Microwave heating of alumina/silica fiber tows in a single-mode microwave cavity at 2.45 GHz have produced a surprising thermal spike behavior on the fiber bundles. During a thermal spike, a ``hot spot`` on the tow brightens rapidly, persists for a few seconds, and rapidly extinguishs. A hot spot can encompass the entire tow in the cavity or just a localized portion of the tow. Some local hot spots propagate along the fiber. Thermal spikes are triggered by relatively small (<15%) increases in power, thus having obvious implications for the development of practical microwave fiber processing systems. A tow can be heated through several successive thermal spikes, after which the tow is left substantially cooler than it was originally, although the applied microwave electric field is much larger. X-ray diffraction studies show that after each temperature spike there is a partial phase transformation of the tow material into mullite. After several excursions the tow has been largely transformed to the new, less lossy phase and is more difficult to heat. Heating experiments with Nextel 550 tows are examined for a pausible explanation of this microwave heating behavior.
Date:
April 1, 1994
Creator:
Vogt, G. J.; Unruh, W. P. & Thomas, J. R., Jr.
System:
The UNT Digital Library
Low-Density Ionization Behavior
As part of a continuing study of the physics of matter under extreme conditions, I give some results on matter at extremely low density. In particular I compare a quantum mechanical calculation of the pressure for atomic hydrogen with the corresponding pressure given by Thomas-Fermi theory. (This calculation differs from the ``confined atom`` approximation in a physically significant way.) Since Thomas-Fermi theory in some sense, represents the case of infinite nuclear charge, these cases should represent extremes. Comparison is also made with Saha theory, which considers ionization from a chemical point of view, but is weak on excited-state effects. In this theory, the pressure undergoes rapid variation as electron ionization levels are passed. This effect is in contrast to the smooth behavior of the Thomas-Fermi fixed temperature, complete ionization occurs in the low density limit, I study the case where the temperature goes appropriately to zero with the density. Although considerable modification is required, Saha theory is closer to the actual results for this case than is Thomas-Fermi theory.
Date:
April 1, 1995
Creator:
Baker, G. A., Jr.
System:
The UNT Digital Library
Radiation damage effects in channeling applications
Use of a bent single crystal to split off a small fraction of an incident high energy (400 to 800 GeV) particle beam has been demonstrated. The question which remains to be answered is: Will radiation damage effects deteriorate crystal performance in too short a time for practical application. Single Si crystals exposed to 10/sup 17/ high energy protons per cm/sup 2/ have been examined previously using low energy (1.5 to 3.0 MeV) helium ion backscattering. The amount of radiation damage indicated by this low penetration technique was very small. This paper reports verification that such an exposed crystal still channels high energy particles. Furthermore, results using helium ion backscattering following an irradiation to 10/sup 18//cm/sup 2/ predict no deterioration in channeling performance.
Date:
April 1, 1986
Creator:
Baker, S. I.; Carrigan, R. A., Jr.; Crawford, C.; Gibson, W. M.; Jin, H.; Kim, I. J. et al.
System:
The UNT Digital Library
Performance results for Beamlet: A large aperture multipass Nd glass laser
The Beamlet laser is a large aperture, flashlamp pumped Nd: glass laser that is a scientific prototype of an advanced Inertial Fusion laser. Beamlet has achieved third harmonic, conversion efficiency of near 80% with its nominal 35cm {times} 35cm square beam at mean 3{omega} fluences in excess of 8 J/cm{sup 2}(3-ns). Beamlet uses an adaptive optics system to correct for aberrations and achieve less than 2 {times} diffraction limited far field spot size.
Date:
April 11, 1995
Creator:
Campbell, J. H.; Barker, C. E.; VanWonterghem, B. M.; Speck, D. R.; Behrendt, W. C.; Murray, J. R. et al.
System:
The UNT Digital Library
Deterrence, disarmament, and post-cold war stability: Enhancing security for both ``haves`` and ``have nots``
This paper examines possible developments in nuclear disarmament resulting from the end of the Cold War.
Date:
April 1, 1995
Creator:
Lehman, R. F., II
System:
The UNT Digital Library
MATE2 Mediates Vacuolar Sequestration of Flavonoid Glycosides and Glycoside Malonates in Medicago truncatula
Article on MATE2 mediating vacuolar sequestration of flavonoid glycosides and glycoside malonates in Medicago truncatula.
Date:
April 2011
Creator:
Zhao, Jian; Huhman, David; Shadle, Gail L.; He, Xian-Zhi; Sumner, Lloyd W.; Tang, Yuhong et al.
System:
The UNT Digital Library
Acetaldehyde oxidation at elevated pressure
A detailed chemical kinetic model for oxidation of CH3CHO at intermediate to high temperature and elevated pressure has been developed and evaluated by comparing predictions to novel high-pressure flow reactor experiments as well as shock tube ignition delay measurements and jet-stirred reactor data from literature. The flow reactor experiments were conducted with a slightly lean CH3CHO/O2 mixture highly diluted in N2 at 600–900 K and pressures of 25 and 100 bar. This is the accepted manuscript version of the published article.
Date:
April 10, 2021
Creator:
Hashemi, Hamid; Christensen, Jakob M.; Marshall, Paul & Glarborg, Peter
System:
The UNT Digital Library
Experimental and kinetic modeling study of oxidation of acetonitrile
Article asserts that oxidation of acetonitrile has been studied in a flow reactor in the absence and presence of nitric oxide. A detailed chemical kinetic model for oxidation of acetonitrile was developed, based on a critical evaluation of data from literature. This is the accepted manuscript version of the published article.
Date:
April 10, 2021
Creator:
Alzueta, María U.; Guerrero, Marta; Millera, Angela; Marshall, Paul & Glarborg, Peter
System:
The UNT Digital Library
Did Anything Good Come Out of the Pandemic? COVID-19-Stress Induced Self-Regulatory Sustainable Apparel Consumption among the Millennials in the U.S.
Authors of the article proposed and tested a conceptual model delineating the relationships between COVID-19 stress, commitment to the environment, and intentions for sustainable apparel consumption in terms of intentions for purchasing sustainable apparel and divesting apparel. The authors recommend the sustainable apparel brands and marketers promote how sustainable apparel consumption can protect the environment to make the environment and human beings less susceptible to the future outbreaks of pandemics.
Date:
April 28, 2023
Creator:
Chakraborty, Swagata & Sadachar, Amrut
System:
The UNT Digital Library
A multiscale approach reveals elaborate circulatory system and intermittent heartbeat in velvet worms (Onychophora)
Article describes how an antagonistic hemolymph-muscular system is essential for soft-bodied invertebrates. The authors analyzed the entire circulatory system of the peripatopsid Euperipatoides rowelli and claimed they discovered a surprisingly elaborate organization.
Date:
April 28, 2023
Creator:
Jahn, Henry; Hammel, Jörg U.; Göpel, Torben; Wirkner, Christian S. & Mayer, Georg
System:
The UNT Digital Library
Stochastic two-fluid model for relativistic heavy-ion collisions
A reduction of the relativistic Boltzmann-Langevin Equation (BLE), to a stochastic two-fluid model is presented, and transport coefficients associated with fluid dynamical variables are extracted. The approach is applied to investigate equilibration in a counter-streaming nuclear system.
Date:
April 1, 1993
Creator:
Ayik, S.; Ivanov, Y. B.; Russkikh, V. N. & Noerenberg, W.
System:
The UNT Digital Library
Small businesses and government assistance during COVID-19: Evidence from the paycheck protection program in the U.S.
Article describes how the COVID-19 pandemic has caused unprecedented losses for small businesses in cities across the globe. The authors' study examines the spatial distribution of PPP loans at the neighborhood level.
Date:
April 3, 2023
Creator:
Wang, Qingfang & Kang, Wei
System:
The UNT Digital Library
An experimental and modeling study on auto-ignition kinetics of ammonia/methanol mixtures at intermediate temperature and high pressure
Article describes how a rapid compression machine has been applied to measure the ignition delay times of NH3/CH3OH mixtures covering pressures of 20 and 40 bar, equivalence ratios of 0.5, 1.0 and 2.0, and temperatures between 845 and 1100 K. Analysis of the pressure profiles shows three distinct ignition modes for NH3/CH3OH mixtures, facilitated by the pre-ignition heat release from NH3 consumption. A detailed mechanism for ignition of NH3/CH3OH fuel blends has been developed, capable of reproducing the ignition behavior of mixtures with reasonable accuracy.
Date:
April 29, 2022
Creator:
Li, Mengdi; He, Xiaoyu; Hashemi, Hamid; Glarborg, Peter; Lowe, Vincent M.; Marshall, Paul et al.
System:
The UNT Digital Library
Imaging Detectors for 20-100 ke V X-ray Backlighters in HEDES Petawatt Experiments
We are developing a petawatt laser for use as a high energy backlighter source in the 20{approx} 100 keV range. High energy x-ray backlighters will be essential for radiographing High-Energy- Density Experimental Science (HEDES) targets for NIF projects especially to probe implosions and high areal density planar samples. For these experiments we are employing two types of detectors: a columnar grown CsI scintillator coupled to a 2K x 2K CCD camera and a CdTe crystal with a special ASIC readout electronics in a 508 x 512 format array. We have characterized these sensors using radioactive sources. In addition, we utilized them to measure the Sm K{alpha} source size generated by the short pulse laser, JanUSP, at LLNL. This paper will present the results of our characterizations of these detectors.
Date:
April 16, 2004
Creator:
Wickersham, J. E.; Park, H.; Bell, P. M.; Koch, J. A.; Landen, O. L. & Moody, J. D.
System:
The UNT Digital Library