2,366 research outputs found
Strong Correlations Produce the Curie-Weiss Phase of NaCoO
Within the t-J model we study several experimentally accessible properties of
the 2D-triangular lattice system NaCoO, using a numerically exact
canonical ensemble study of 12 to 18 site triangular toroidal clusters as well
as the icosahedron. Focusing on the doping regime of , we study the
temperature dependent chemical potential, specific heat, magnetic
susceptibility and the dynamic Hall coefficient as well as the
magnetic field dependent thermopower. We find a crossover between two phases
near in susceptibility and field suppression of the thermopower
arising from strong correlations. An interesting connection is found between
the temperature dependence of the diamagnetic susceptibility and the
Hall-coefficient. We predict a large thermopower enhancement, arising from {\em
transport corrections} to the Heikes-Mott formula, in a model situation where
the sign of hopping is reversed from that applicable to NaCoO.Comment: 5 pages, 4 figure
Enhanced aging properties of HKUST-1 in hydrophobic mixed-matrix membranes for ammonia adsorption.
Metal-organic frameworks (MOFs) in their free powder form have exhibited superior capacities for many gases when compared to other materials, due to their tailorable functionality and high surface areas. Specifically, the MOF HKUST-1 binds small Lewis bases, such as ammonia, with its coordinatively unsaturated copper sites. We describe here the use of HKUST-1 in mixed-matrix membranes (MMMs) prepared from polyvinylidene difluoride (PVDF) for the removal of ammonia gas. These MMMs exhibit ammonia capacities similar to their hypothetical capacities based on the weight percent of HKUST-1 in each MMM. HKUST-1 in its powder form is unstable toward humid conditions; however, upon exposure to humid environments for prolonged periods of time, the HKUST-1 MMMs exhibit outstanding structural stability, and maintain their ammonia capacity. Overall, this study has achieved all of the critical and combined elements for real-world applications of MOFs: high MOF loadings, fully accessible MOF surfaces, enhanced MOF stabilization, recyclability, mechanical stability, and processability. This study is a critical step in advancing MOFs to a stable, usable, and enabling technology
Quantum Hall Phase Diagram of Second Landau-level Half-filled Bilayers: Abelian versus Non-Abelian States
The quantum Hall phase diagram of the half-filled bilayer system in the
second Landau level is studied as a function of tunneling and layer separation
using exact diagonalization. We make the striking prediction that bilayer
structures would manifest two distinct branches of incompressible fractional
quantum Hall effect (FQHE) corresponding to the Abelian 331 state (at moderate
to low tunneling and large layer separation) and the non-Abelian Pfaffian state
(at large tunneling and small layer separation). The observation of these two
FQHE branches and the quantum phase transition between them will be compelling
evidence supporting the existence of the non-Abelian Pfaffian state in the
second Landau level.Comment: 4 pages, 3 figure
Orbital Landau level dependence of the fractional quantum Hall effect in quasi-two dimensional electron layers: finite-thickness effects
The fractional quantum Hall effect (FQHE) in the second orbital Landau level
at filling factor 5/2 remains enigmatic and motivates our work. We consider the
effect of the quasi-2D nature of the experimental FQH system on a number of FQH
states (fillings 1/3, 1/5, 1/2) in the lowest, second, and third Landau levels
(LLL, SLL, TLL,) by calculating the overlap, as a function of quasi-2D layer
thickness, between the exact ground state of a model Hamiltonian and the
consensus variational wavefunctions (Laughlin wavefunction for 1/3 and 1/5 and
the Moore-Read Pfaffian wavefunction for 1/2). Using large overlap as a
stability, or FQHE robustness, criterion we find the FQHE does not occur in the
TLL (for any thickness), is the most robust for zero thickness in the LLL for
1/3 and 1/5 and for 11/5 in the SLL, and is most robust at finite-thickness
(4-5 magnetic lengths) in the SLL for the mysterious 5/2 state and the 7/3
state. No FQHE is found at 1/2 in the LLL for any thickness. We examine the
orbital effects of an in-plane (parallel) magnetic field finding its
application effectively reduces the thickness and could destroy the FQHE at 5/2
and 7/3, while enhancing it at 11/5 as well as for LLL FQHE states. The
in-plane field effects could thus be qualitatively different in the LLL and the
SLL by virtue of magneto-orbital coupling through the finite thickness effect.
In the torus geometry, we show the appearance of the threefold topological
degeneracy expected for the Pfaffian state which is enhanced by thickness
corroborating our findings from overlap calculations. Our results have
ramifications for wavefunction engineering--the possibility of creating an
optimal experimental system where the 5/2 FQHE state is more likely described
by the Pfaffian state with applications to topological quantum computing.Comment: 27 pages, 20 figures, revised version (with additional author) as
accepted for publication in Physical Review
Rescuing Economics From The Discipline: The Green Learning Community
Undergraduate economics is poised for reform because of readily available data and multimedia content. However, we argue that deep reform is needed to teach complex contemporary problems. This requires including institutional and historical content and restructuring the classroom to facilitate interdisciplinary pedagogy. Using Colander’s (2006) analysis of reform as a starting point, we review the economics literature to identify alternative approaches and interdisciplinary pedagogy. The Green Learning Community is introduced as an intentional approach that links economics, humanities and environmental studies and provides first-year students adequate time to study, reflect upon, and internalize economic assumptions, models, values, and interdisciplinary insights
Laser Tag - An Application of Infrared Communication
The purpose of this project is to design, build, and test laser tag system from the ground up. Much of the laser tag equipment that is available on the market right now use infrared technology to track and register “hits” between players. Our goal is to take this system and redesign it to shoot farther, be more energy efficient, and make it cheaper to produce
Fractional quantum Hall effects in bilayers in the presence of inter-layer tunneling and charge imbalance
Two-component fractional quantum Hall systems are providing a major
motivation for a large section of the physics community. Here we study
two-component fractional quantum Hall systems in the spin-polarized half-filled
lowest Landau level (filling factor 1/2) and second Landau level (filling
factor 5/2) with exact diagonalization utilizing both the spherical and torus
geometries. The two distinct two-component systems we consider are the true
bilayer and effective bilayers (wide-quantum-well). In each model (bilayer and
wide-quantum-well) we completely take into account inter-layer tunneling and
charge imbalancing terms. We find that in the half-filled lowest Landau level,
the FQHE is described by the two-component Abelian Halperin 331 state which is
remarkably robust to charge imbalancing. In the half-filled second Landau, we
find that the FQHE is likely described by the non-Abelian Moore-Read Pfaffian
state which is also quite robust to charge imbalancing. Furthermore, we suggest
the possibility of experimentally tuning from an Abelian to non-Abelian FQHE
state in the second Landau level, and comment on recent experimental studies of
FQHE in wide quantum well structures.Comment: 25 pages, 27 figure
DEMAND AND SUPPLY ASSESSMENT FOR THE MICHIGAN FROZEN POTATO INDUSTRY
This report presents a general assessment of the demand and supply conditions affecting the Michigan frozen potato industry. The information has been drawn from various secondary sources and interviews with key industry informants. The report is one of the major outputs of an ongoing study being prepared for the Michigan Potato Industry Commission and funded by the Michigan Agricultural Experiment Station. This analysis was necessitated by the 80% reduction in Michigan frozen processing potato acreage by Simplot in 1997. This reduction of 5,000 acres for the Grand Rapids processing facility has created both short-term and long-term concerns for the Michigan potato industry. This assessment provides broad background information relevant to determining why this cutback occurred and its likely impact if continued in the future. The report begins with a consideration of demand conditions, including both domestic and international demand trends for consumption and consumer preferences. The report then discusses supply issues, including current North American production capacity, international sourcing trends, competition from Canadian imports, cost considerations, processing innovation, and industry consolidation. The report concludes with a section addressing key strategic issues suggested by the demand and supply trends. NOTE: This staff paper contains text only. For charts and graphs (exhibits 1-17b) which have been omitted, contact Christopher Peterson at ([email protected]).Crop Production/Industries,
Characterization of the denaturation and renaturation of human plasma vitronectin I. Biophysical characterization of protein unfolding and multimerization
Upon treatment with denaturing agents, vitronectin has been observed to exhibit conformational alterations which are similar to the structural changes detected when vitronectin binds the thrombin-antithrombin complex or associates with the terminal attack complex of complement. Denaturation and renaturation of vitronectin isolated from human plasma were characterized by changes in intrinsic fluorescence. Unfolding by chemical denaturants was irreversible and accompanied by self-association of the protein to form vitronectin multimers. Self-association was evaluated by equilibrium analytical ultracentrifugation which demonstrated that multimers form only during the refolding process after removal of denaturant, that multimeric vitronectin dissociates to constituent subunits readily upon treatment with chemical denaturant, and that intermolecular disulfide cross-linking occurs primarily at the dimer level among a subset of constituent vitronectin subunits within the multimer. The monomeric form of vitronectin isolated from human plasma partially unfolds at intermediate concentrations of denaturant to an altered conformation with a high propensity to associate into multimers. Folding of vitronectin in vivo appears to be regulated by partitioning of folding intermediates toward either of two conformations, one that exists as a stable monomer and another that associates into a multimeric form
The Kelvin Formula for Thermopower
Thermoelectrics are important in physics, engineering, and material science
due to their useful applications and inherent theoretical difficulty,
especially in strongly correlated materials. Here we reexamine the framework
for calculating the thermopower, inspired by ideas of Lord Kelvin from 1854. We
find an approximate but concise expression, which we term as the Kelvin formula
for the the Seebeck coefficient. According to this formula, the Seebeck
coefficient is given as the particle number derivative of the entropy
, at constant volume and temperature ,
. This formula is shown to be competitive compared to other
approximations in various contexts including strongly correlated systems. We
finally connect to a recent thermopower calculation for non-Abelian fractional
quantum Hall states, where we point out that the Kelvin formula is exact.Comment: 6 pages, 2 figure
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