837 research outputs found
Diversion as a Work-Oriented Welfare Reform Strategy and its Effect on Access to Medicaid: An Examination of the Experiences of Five Local Communities
The Personal Responsibility and Work Opportunity Reconciliation Act of 1996 (PRWORA) ended the individual entitlement to welfare benefits and gave states new flexibility to emphasize work instead welfare. PRWORA also severed the traditional eligibility link between Medicaid and welfare. This research examined the emergence of diversion programs as a particular aspect of state welfare reform efforts and the potential for diversion programs to reduce access to Medicaid. In this second of two reports, we present the results of case studies in five states
Grain size threshold for enhanced irradiation resistance in nanocrystalline and ultrafine tungsten
Nanocrystalline metals are considered highly radiation-resistant materials due to their large grain boundary areas. Here, the existence of a grain size threshold for enhanced irradiation resistance in high-temperature helium-irradiated nanocrystalline and ultrafine tungsten is demonstrated. Average bubble density, projected bubble area and the corresponding change in volume were measured via transmission electron microscopy and plotted as a function of grain size for two ion fluences. Nanocrystalline grains of less than 35 nm size possess ∼10–20 times lower change in volume than ultrafine grains and this is discussed in terms of the grain boundaries defect sink efficienc
The equation of state of solid nickel aluminide
The pressure-volume-temperature equation of state of the intermetallic
compound NiAl was calculated theoretically, and compared with experimental
measurements. Electron ground states were calculated for NiAl in the CsCl
structure, using density functional theory, and were used to predict the cold
compression curve and the density of phonon states. The Rose form of
compression curve was found to reproduce the ab initio calculations well in
compression but exhibited significant deviations in expansion. A
thermodynamically-complete equation of state was constructed for NiAl. Shock
waves were induced in crystals of NiAl by the impact of laser-launched Cu
flyers and by launching NiAl flyers into transparent windows of known
properties. The TRIDENT laser was used to accelerate the flyers to speeds
between 100 and 600m/s. Point and line-imaging laser Doppler velocimetry was
used to measure the acceleration of the flyer and the surface velocity history
of the target. The velocity histories were used to deduce the stress state, and
hence states on the principal Hugoniot and the flow stress. Flyers and targets
were recovered from most experiments. The effect of elasticity and plastic flow
in the sample and window was assessed. The ambient isotherm reproduced static
compression data very well, and the predicted Hugoniot was consistent with
shock compression data
Transcending the MAX phases concept of nanolaminated early transition metal carbides/nitrides -- the ZIA phases
A new potential class of nanolaminated and structurally complex materials,
herein conceived as the Zigzag IntermetAllic (ZIA) phases, is proposed. A study
of the constituent phases of a specific Nb--Si--Ni intermetallic alloy revealed
that its ternary H-phase, \textit{i.e.}, the NbSiNi intermetallic
compound (IMC), is a crystalline solid with the close-packed \textit{fcc}
Bravais lattice, the 312 MAX phase stoichiometry and a layered atomic
arrangement that may define an entire class of nanolaminated IMCs analogous to
the nanolaminated ceramic compounds known today as the MAX phases. The electron
microscopy investigation of the NbSiNi compound -- the first
candidate ZIA phase -- revealed a remarkable structural complexity, as its
ordered unit cell is made of 96 atoms. The ZIA phases extend the concept of
nanolaminated crystalline solids well beyond the MAX phases family of early
transition metal carbides/nitrides, most likely broadening the spectrum of
achievable material properties into domains typically not covered by the MAX
phases. Furthermore, this work uncovers that both families of nanolaminated
crystalline solids, \textit{i.e.}, the herein introduced \textit{fcc} ZIA
phases and all known variants of the \textit{hcp} MAX phases, obey the same
overarching stoichiometric rule , where and are integers
ranging from 1 to 6
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Progress report on the accelerator production of tritium materials irradiation program
The Accelerator Production of Tritium (APT) project is developing an accelerator and a spoliation neutron source capable of producing tritium through neutron capture on He-3. A high atomic weight target is used to produce neutrons that are then multiplied and moderated in a blanket prior to capture. Materials used in the target and blanket region of an APT facility will be subjected to several different and mixed particle radiation environments; high energy protons (1-2 GeV), protons in the 20 MeV range, high energy neutrons, and low energy neutrons, depending on position in the target and blanket. Flux levels exceed 10{sup 14}/cm{sup 2}s in some areas. The APT project is sponsoring an irradiation damage effects program that will generate the first data-base for materials exposed to high energy particles typical of spallation neutron sources. The program includes a number of candidate materials in small specimen and model component form and uses the Los Alamos Spallation Radiation Effects Facility (LASREF) at the 800 MeV, Los Alamos Neutron Science Center (LANSCE) accelerator
Three dimensional hysdrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic flow through porous media
We report the results of a study of multiphase flow in porous media. A
Darcy's law for steady multiphase flow was investigated for both binary and
ternary amphiphilic flow. Linear flux-forcing relationships satisfying Onsager
reciprocity were shown to be a good approximation of the simulation data. The
dependence of the relative permeability coefficients on water saturation was
investigated and showed good qualitative agreement with experimental data.
Non-steady state invasion flows were investigated, with particular interest in
the asymptotic residual oil saturation. The addition of surfactant to the
invasive fluid was shown to significantly reduce the residual oil saturation.Comment: To appear in Phys. Rev.
Crack Front Waves and the dynamics of a rapidly moving crack
Crack front waves are localized waves that propagate along the leading edge
of a crack. They are generated by the interaction of a crack with a localized
material inhomogeneity. We show that front waves are nonlinear entities that
transport energy, generate surface structure and lead to localized velocity
fluctuations. Their existence locally imparts inertia, which is not
incorporated in current theories of fracture, to initially "massless" cracks.
This, coupled to crack instabilities, yields both inhomogeneity and scaling
behavior within fracture surface structure.Comment: Embedded Latex file including 4 figure
Pinning/depinning of crack fronts in heterogeneous materials
The fatigue fracture surfaces of a metallic alloy, and the stress corrosion
fracture surfaces of glass are investigated as a function of crack velocity. It
is shown that in both cases, there are two fracture regimes, which have a well
defined self-affine signature. At high enough length scales, the universal
roughness index 0.78 is recovered. At smaller length scales, the roughness
exponent is close to 0.50. The crossover length separating these two
regimes strongly depends on the material, and exhibits a power-law decrease
with the measured crack velocity , with . The exponents and characterising the dependence of
and upon the pulling force are shown to be close to and
.Comment: 4 pages, latex, and 4 encapsulated postscript figure
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