6,599 research outputs found
Classification of General Sequences by Frame-Related Operators
This note is a survey and collection of results, as well as presenting some
original research. For Bessel sequences and frames, the analysis, synthesis and
frame operators as well as the Gram matrix are well-known, bounded operators.
We investigate these operators for arbitrary sequences, which in general lead
to possibly unbounded operators. We characterize various classes of sequences
in terms of these operators and vice-versa. Finally, we classify these
sequences by operators applied on orthonormal bases
Rediscounting Under Aggregate Risk with Moral Hazard
Freeman (1999) proposes a model in which discount window lending and open market operations have different effects. This is important because in most of the literature, these policies are indistinguishable. However, Freeman's argument that the central bank should absorb losses associated with default to provide risk-sharing stands in stark contrast to the concern that central banks should limit their exposure to credit risk. We extend Freeman's model by introducing moral hazard. With moral hazard, the central bank should avoid absorbing losses and Freeman's argument breaks down. However, we show that policies resembling discount window lending and open market operations can still be distinguished in this new framework. The optimal policy is for the central bank to make a restricted number of creditors compete for funds. By restricting the number of agents, the central bank can limit the moral hazard problem. By making them compete with each other, the central bank can exploit market information that reveals the state of the economy.Payment, clearing, and settlement systems; Financial markets; Central bank research
Fuels characterization studies
Current analytical techniques used in the characterization of broadened properties fuels are briefly described. Included are liquid chromatography, gas chromatography, and nuclear magnetic resonance spectroscopy. High performance liquid chromatographic ground-type methods development is being approached from several directions, including aromatic fraction standards development and the elimination of standards through removal or partial removal of the alkene and aromatic fractions or through the use of whole fuel refractive index values. More sensitive methods for alkene determinations using an ultraviolet-visible detector are also being pursued. Some of the more successful gas chromatographic physical property determinations for petroleum derived fuels are the distillation curve (simulated distillation), heat of combustion, hydrogen content, API gravity, viscosity, flash point, and (to a lesser extent) freezing point
Electronic correlations, magnetism and Hund's rule coupling in the ruthenium perovskites SrRuO and CaRuO
A comparative density functional plus dynamical mean field theory study of
the pseudocubic ruthenate materials CaRuO and SrRuO is presented. Phase
diagrams are determined for both materials as a function of Hubbard repulsion
and Hund's rule coupling . Metallic and insulating phases are found, as
are ferromagnetic and paramagnetic states. The locations of the relevant phase
boundaries are determined. Based on the computed phase diagrams, Mott-dominated
and Hund's dominated regimes of strong correlation are distinguished.
Comparison of calculated properties to experiments indicates that the actual
materials are in the Hund's coupling dominated region of the phase diagram so
can be characterized as Hund's metals, in common with other members of the
ruthenate family. Comparison of the phase diagrams for the two materials
reveals the role played by rotational and tilt (GdFeO-type) distortions of
the ideal perovskite structure. The presence of magnetism in SrRuO and its
absence in CaRuO despite the larger mass and larger tilt/rotational
distortion amplitude of CaRuO can be understood in terms of density of
states effects in the presence of strong Hund's coupling. Comparison of the
calculated low- properties of CaRuO to those of SrRuO provides
insight into the effects of magnetic order on the properties of a Hund's metal.
The study provides a simultaneous description of magnetism and correlations and
explicates the roles played by band theory and Hubbard and Hund's interactions
Spin wave contribution to the nuclear spin-lattice relaxation in triplet superconductors
We discuss collective spin wave excitations in triplet superconductors with
an easy axis anisotropy for the order parameter. Using a microscopic model for
interacting electrons we estimate the frequency of such excitations in
Bechgaard salts and ruthenate superconductors to be one and twenty GHz
respectively. We introduce an effective bosonic model to describe spin-wave
excitations and calculate their contribution to the nuclear spin lattice
relaxation rate. We find that in the experimentally relevant regime of
temperatures, this mechanism leads to the power law scaling of 1/T_1 with
temperature. For two and three dimensional systems the scaling exponents are
three and five respectively. We discuss experimental manifestations of the spin
wave mechanism of the nuclear spin lattice relaxation.Comment: 4 pages, 2 figure
Importance of electronic correlations for structural and magnetic properties of the iron pnictide superconductor LaFeAsO
We present calculations of structural and magnetic properties of the
iron-pnictide superconductor LaFeAsO including electron-electron correlations.
For this purpose we apply a fully charge self-consistent combination of
Density-Functional Theory with the Dynamical Mean-Field theory, allowing for
the calculation of total energies. We find that the inclusion of correlation
effects gives a good agreement of the Arsenic z position with experimental data
even in the paramagnetic (high-temperature) phase. Going to low temperatures,
we study the formation of the ordered moment in the striped spin-density-wave
phase, yielding an ordered moment of about 0.60, again in good agreement with
experiments. This shows that the inclusion of correlation effects improves both
structural and magnetic properties of LaFeAsO at the same time.Comment: 7 pages, 5 figures, published versio
Remedial Reading: Evaluation of a Reading-and-Study Course With Implications for a College Reading Center
The main purpose of the study was to evaluate the effectiveness of the method of teaching a How to Study class in helping students more adequately meet their reading needs.
Research was conducted to test the reading gains made by students in the program with respect to ability and group size. The results indicate that group size had the greatest effect as to changes in reading behavior.
Instruction was based on diagnosing student needs. It was shown that a significant number of students who decreased in rate of reading, increased in comprehension. The same diagnostic principle was observed for those who were judged able to increase rate, since a significant number in this category also increased in comprehension. It was concluded that the training was effective in helping students to adjust their rate of reading in order to facilitate an increase in comprehension. There was a wide range of individual differences in the actual amount of comprehension increase. The average increase of 14.5 percent was not significant. However, of the 163 students in the program 82 made a 10 percent increase or better.
The principle problem of students making no progress was motivation. While 13.8 percent rated the course as one of the best, 30.2 percent rated the course as above average, and 34.5 percent rated the course average, 14.5 percent rated the course below average, and 6.2 percent were very critical of the course
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