993 research outputs found
Manifestation of pseudogap in ab-plane optical characteristics
A model in which a gap forms in the renormalized electronic density of state
(DOS) with missing states recovered just above the pseudogap , is
able to give a robust description of the striking, triangular like, peak seen
in the real part of the optical self-energy of underdoped cuprates. We use this
model to explore the effect of the pseudogap on the real part of the optical
conductivity and on the partial sum rule associated with it. An important
result is that the optical spectral weight redistributes over a much larger
frequency window than it does in the DOS.Comment: 12 pages, 3 figures. Submitted to Journal of Physics: Condensed
Matte
Study of single-phase convection and condensation in thermoplate heat exchanger (part I)
Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The heat transfer and pressure drop in a thermoplate heat
exchanger operated as condenser have been investigated
experimentally. In order to separate the heat transfer resistances
in the condensation process, first the single phase forced
convection in the thermoplate using distilled water and
Marlotherm oil has been studied and correlation for the Nusselt
number and friction factor developed. For the condensation
experiments an apparatus has been conceived comprising two
identical condensers made of the same thermoplate type as
employed in the single phase experiments. Isopropanol was used
as test fluid at pressures below the atmospheric pressure. With
the aid of the results obtained in the single phase studies the heat
transfer resistances in the condensation experiments were
separated and expressions for the condensation heat transfer and
pressure drop developed.cs201
Numerical simulation of fluid flow, heat transfer and pressure drop in thermoplates
Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The objective of our investigations is to numerically investigate
the optimal geometry of the thermoplate with respect to
heat transfer of the inside fluid that passes through the channel
as a single phase. In order to achieve this, the geometrical and
process parameters such as the pattern of welding spots, the
distance between the sheets, and the Reynolds number have
been varied. For the simulation, the commercial software
StarCD was used. The numerical experiments show that the
heat transfer potential of the thermoplate having a staggered arrangement
of welding spots is markedly higher than the one of
a common flat channel, particularly at larger Reynolds numbers.
The variations of the geometrical parameters indicate the
welding spot pitch in a streamwise direction to be a pivotal
quantity regarding the heat transfer optimisation.cs201
How much support is necessary for self-regulated learning?
Self-regulated learning is crucial for learning success, and is even of greater
importance for online learning as there is less support and feedback available to students. We
describe a simple intervention designed to support self-regulated learning in the context of
SQL-Tutor, a mature intelligent tutoring system. SQL-Tutor logged data about all interactions
students performed, including interactions with the SRL support. Frequency-based analyses did
not identify any differences in behaviors of low or high scoring students. However, epistemic
network analysis identified significant differences in how students use help available from
SQL-Tutor. Students who scored low on the SQL test asked for high-level help (in the form of
partial or full solution), copied the provided solutions and submitted them as their own. We
conclude that additional support is necessary for students with weak self-regulation skills
Study of single-phase convection and condensation in thermoplate heat exchanger (part II)
Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.The heat transfer and pressure drop in a thermoplate heat
exchanger operated as condenser have been investigated
experimentally. In order to separate the heat transfer resistances
in the condensation process, first the single phase forced
convection in the thermoplate using distilled water and
Marlotherm oil has been studied and correlation for the Nusselt
number and friction factor developed. For the condensation
experiments an apparatus has been conceived comprising two
identical condensers made of the same thermoplate type as
employed in the single phase experiments. Isopropanol was used
as test fluid at pressures below the atmospheric pressure. With
the aid of the results obtained in the single phase studies the heat
transfer resistances in the condensation experiments were
separated and expressions for the condensation heat transfer and
pressure drop developed.cs201
NMR Studies of Field Induced Magnetism in CeCoIn
Recent Nuclear Magnetic Resonance and elastic neutron scattering experiments
have revealed conclusively the presence of static incommensurate magnetism in
the field-induced B phase of CeCoIn5. We analyze the NMR data assuming the
hyperfine coupling to the In(2) nuclei is anisotropic and simulate the spectra
for several different magnetic structures. The NMR data are consistent with
ordered Ce moments along the [001] direction, but are relatively insensitive to
the direction of the incommensurate wavevector.Comment: 4 pages, 3 figure
Combined Catalysis and Optical Screening for High Throughput Discovery of Solar Fuels Catalysts
Considerable research and development efforts are being devoted to the efficient generation of solar fuels. A solar fuels device
couples a solar photoabsorber with catalysts to convert solar energy to chemical energy via reactions such as oxygen evolution
(water splitting). Widespread deployment of this technology hinges upon discovery of new materials through efforts such as the high
throughput screening of oxygen evolution catalysts, as discussed in this manuscript. We derive an expression for the efficiency of
the oxygen evolution catalyst that combines catalytic and optical properties. Using this hybrid efficiency, we screen 5456 samples in
a (Fe-Co-Ni-Ti)O_x pseudo-quaternary catalyst library using automated, high throughput electrochemical and optical experiments.
The observed compositional trends in this catalyst efficiency lead to the discovery of a new high performance composition region
Leaf litter breakdown along an elevational gradient in Australian alpine streams
The breakdown of allochthonous organic matter, is a central step in nutrient cycling in stream ecosystems. There is concern that increased temperatures from climate change will alter the breakdown rate of organic matter, with important consequences for the ecosystem functioning of alpine streams. This study investigated the rate of leaf litter breakdown and how temperature and other factors such as microbial and invertebrate activities influenced this over elevational and temporal gradients. Dried leaves of Snow Gum (Eucalyptus pauciflora) and cotton strips were deployed in coarse (6 mm), and fine (50 mu m) mesh size bags along an 820 m elevation gradient. Loss of mass in leaf litter and cotton tensile strength per day (k per day), fungal biomass measured as ergosterol concentration, invertebrate colonization of leaf litter, and benthic organic matter (mass and composition) were determined. Both microbial and macroinvertebrate activities were equally important in leaf litter breakdown with the abundance of shredder invertebrate taxa. The overall leaf litter breakdown rate and loss of tensile strength in cotton strips (both k per day) were greater during warmer deployment periods and at lower elevations, with significant positive relationships between mean water temperature and leaf breakdown and loss of tensile strength rate, but no differences between sites, after accounting for the effects of temperature. Despite considerably lower amounts of benthic organic matter in streams above the tree line relative to those below, shredders were present in coarse mesh bags at all sites. Ergosterol concentration was greater on leaves in coarse mesh bags than in fine mesh bags, implying differences in the microbial communities. The importance of water temperatures on the rate of leaf litter breakdown suggests the potential effects of climate change-induced temperature increases on ecological processes in such streams
Composition and field tuned magnetism and superconductivity in Nd1-xCexCoIn5
The Nd1-xCexCoIn5 alloys evolve from local moment magnetism (x = 0) to heavy
fermion superconductivity (x =1). Magnetic order is observed over a broad range
of x. For a substantial range of x (0.83 <= x <= 0.95) in the temperature -
composition phase diagram we find that superconductivity may coexist with spin
- density wave magnetic order at the Fermi surface. We show that a delicate
balance betwen superconducting and magnetic instabilities can be reversibly
tuned by both the Ce/Nd ratio and magnetic field, offering a new and unique
model electronic system.Comment: 7 pages, 7 figures. Physical Review B in pres
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