2,011 research outputs found
Possible effects of charge frustration in NaCoO: bandwidth suppression, charge orders and resurrected RVB superconductivity
Charge frustration due to further neighbor Coulomb repulsion can have
dramatic effects on the electronic properties of NaCoO in the full
doping range. It can significantly reduce the effective mobility of the charge
carriers, leading to a low degeneracy temperature . Such
strongly renormalized Fermi liquid has rather unusual properties--from the
point of view of the ordinary metals with --but similar to
the properties that are actually observed in the NaCoO system. For
example, we show that the anomalous thermopower and Hall effect observed in
NaCoO may be interpreted along these lines. If the repulsion is
strong, it can also lead to charge order; nevertheless, away from the
commensurate dopings, the configurational constraints allow some mobility for
the charge carriers, i.e., there remains some ``metallic'' component. Finally,
the particularly strong bandwidth suppression around the commensurate
can help resurrect the RVB superconductivity, which would otherwise not be
expected near this high doping. These suggestions are demonstrated specifically
for a -like model with an additional nearest neighbor repulsion.Comment: 15 pages, 17 figure
Pyridine is an organocatalyst for the reductive ozonolysis of alkenes
Whereas the cleavage of alkenes by ozone typically generates peroxide intermediates that must be decomposed in an accompanying step, ozonolysis in the presence of pyridine directly generates ketones or aldehydes through a process that neither consumes pyridine nor generates any detectable peroxides. The reaction is hypothesized to involve nucleophile-promoted fragmentation of carbonyl oxides via formation of zwitterionic peroxyacetals
Municipal Solid Waste Management Performance
Sustainable municipal solid waste management (MSWM) is a major challenge in urban areas throughout the world, with the situation getting worse in most developing countries. This paper evaluates MSWM performance in Ghana, using the Wa Municipality as a case study. The policy and legal, institutional, and financial frameworks, as well as the technical capacity for waste management, were examined. The methodology and research design for the study was an exploratory and interpretive case study that was analysed through both qualitative and quantitative research methods. The study findings indicate that Ghana has a good institutional framework, sufficient and robust legislation, existing bylaws, policies and programmes regarding MSWM. However, the challenge is the non-enforcement of and non-compliance with the laws and regulations governing MSWM. Also, the emphasis on stakeholders’ involvement in MSWM in the country is focused mainly on waste collection, and no attention paid to waste reduction, treatment and final disposal. Additionally, waste management financing and the technical capacity for waste management are woefully inadequate. Thus, improving the enabling environment for sustainable MSWM with a focus on the examined indicators could scale up MSWM performance in Ghana for the attainment waste management goals
Method for defect free keyhole plasma arc welding
A plasma arc welding process for welding metal of increased thickness with one pass includes operating the plasma arc welding apparatus at a selected plasma gas flow rate, travel speed and arc current, to form a weld having a penetration ratio to weld height to weld width, and maintaining the penetration ratio at less than 0.74. Parameters for the plasma gas flow rate, travel speed and arc current are adjusted to a steady state condition during a start up period and maintained during the steady state condition to complete a weld. During a terminal stopping period, the travel speed is stopped and instantaneously replaced by filler wire which adds material to fill the keyhole that had been formed by the welding process. Parameters are subsequently adjusted during the stopping period to terminate the weld in a sound manner
Modeling postglacial vegetation dynamics of temperate forests on the Olympic Peninsula (WA, USA) with special regard to snowpack
Past and future forest composition and distribution in temperate mountain ranges is strongly influenced by temperature and snowpack. We used LANDCLIM, a spatially explicit, dynamic vegetation model, to simulate forest dynamics for the last 16,000 years and compared the simulation results to pollen and macrofossil records at five sites on the Olympic Peninsula (Washington, USA). To address the hydrological effects of climate-driven variations in snowpack on simulated forest dynamics, we added a simple snow accumulation-and-melt module to the vegetation model and compared simulations with and without the module. LANDCLIM produced realistic present-day species composition with respect to elevation and precipitation gradients. Over the last 16,000 years, simulations driven by transient climate data from an atmosphere-ocean general circulation model (AOGCM) and by a chironomid-based temperature reconstruction captured Late-glacial to Late Holocene transitions in forest communities. Overall, the reconstruction-driven vegetation simulations matched observed vegetation changes better than the AOGCM-driven simulations. This study also indicates that forest composition is very sensitive to snowpack-mediated changes in soil moisture. Simulations without the snow module showed a strong effect of snowpack on key bioclimatic variables and species composition at higher elevations. A projected upward shift of the snow line and a decrease in snowpack might lead to drastic changes in mountain forests composition and even a shift to dry meadows due to insufficient moisture availability in shallow alpine soils
Numerical continuation methods: a perspective
AbstractIn this historical perspective the principal numerical approaches to continuation methods are outlined in the framework of the mathematical sources that contributed to their development, notably homotopy and degree theory, simplicial complexes and mappings, submanifolds defined by submersions, and singularity and foldpoint theory
Modular Invariance of Finite Size Corrections and a Vortex Critical Phase
We analyze a continuous spin Gaussian model on a toroidal triangular lattice
with periods and where the spins carry a representation of the
fundamental group of the torus labeled by phases and . We find the
{\it exact finite size and lattice corrections}, to the partition function ,
for arbitrary mass and phases . Summing over phases gives
the corresponding result for the Ising model. The limits and
do not commute. With the model exhibits a {\it vortex
critical phase} when at least one of the is non-zero. In the continuum or
scaling limit, for arbitrary , the finite size corrections to are
{\it modular invariant} and for the critical phase are given by elliptic theta
functions. In the cylinder limit the ``cylinder charge''
is a non-monotonic function of that ranges from
for to zero for .Comment: 12 pages of Plain TeX with two postscript figure insertions called
torusfg1.ps and torusfg2.ps which can be obtained upon request from
[email protected]
Association of Demographic Factors and Comorbid Diagnoses with Crime Typein an Arrest Cohort with Schizophrenia and/or Related Psychosis
The implications of the interface between the criminal justice system and individuals with schizophrenia persist despite decades of research on criminalization and risk of arrest. Research exploring the broader construct of criminality has predominantly focused on individuals with severe mental illness as a collective. This study diverges from others by examining diagnoses comorbid with schizophrenia and related psychoses and their relationships with risk of arrest across a spectrum of criminal categories ranging in severity
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