6,813 research outputs found
Equilibrium Existence and Approximation for Incomplete Market Models with Substantial Heterogeneity
This paper contains an analysis of incomplete market models with finitely
but arbitrarily many heterogeneous agents. We discuss the mathematical
foundation for equilibrium conditions which leads to two findings. First,
we establish existence of equilibria for small and large risks. Second,
we develop a simple but general solution technique which handles many
state and choice variables for each agent and thus an extremely
high-dimensional state space. The method is based on perturbations
around a point at which the solution is known. The novel idea is to
exploit the symmetry of the problem to overcome the curse of
dimensionality. We use the analysis to demonstrate the impact of
heterogeneity on macroeconomic quantities and the pricing of risk.
Furthermore, we set our technique apart from the standard method used in
the literature
Scattering and absorption of ultracold atoms by nanotubes
We investigate theoretically how cold atoms, including Bose-Einstein
condensates, are scattered from, or absorbed by nanotubes with a view to
analysing recent experiments. In particular we consider the role of potential
strength, quantum reflection, atomic interactions and tube vibrations on atom
loss rates. Lifshitz theory calculations deliver a significantly stronger
scattering potential than that found in experiment and we discuss possible
reasons for this. We find that the scattering potential for dielectric tubes
can be calculated to a good approximation using a modified pairwise summation
approach, which is efficient and easily extendable to arbitrary geometries.
Quantum reflection of atoms from a nanotube may become a significant factor at
low temperatures, especially for non-metallic tubes. Interatomic interactions
are shown to increase the rate at which atoms are lost to the nanotube and lead
to non-trivial dynamics. Thermal nanotube vibrations do not significantly
increase loss rates or reduce condensate fractions, but lower frequency
oscillations can dramatically heat the cloud.Comment: 7 pages, 4 figure
Detecting periodicity in experimental data using linear modeling techniques
Fourier spectral estimates and, to a lesser extent, the autocorrelation
function are the primary tools to detect periodicities in experimental data in
the physical and biological sciences. We propose a new method which is more
reliable than traditional techniques, and is able to make clear identification
of periodic behavior when traditional techniques do not. This technique is
based on an information theoretic reduction of linear (autoregressive) models
so that only the essential features of an autoregressive model are retained.
These models we call reduced autoregressive models (RARM). The essential
features of reduced autoregressive models include any periodicity present in
the data. We provide theoretical and numerical evidence from both experimental
and artificial data, to demonstrate that this technique will reliably detect
periodicities if and only if they are present in the data. There are strong
information theoretic arguments to support the statement that RARM detects
periodicities if they are present. Surrogate data techniques are used to ensure
the converse. Furthermore, our calculations demonstrate that RARM is more
robust, more accurate, and more sensitive, than traditional spectral
techniques.Comment: 10 pages (revtex) and 6 figures. To appear in Phys Rev E. Modified
styl
Difference score correlations in relationship research: A conceptual primer
The practice of computing correlations between “difference” or “discrepancy” scores and an outcome variable is common in many areas of social science. Relationship researchers most commonly use difference scores to index the (dis)similarity of members of two-person relationships. Using an intuitive, graphical approach—and avoiding formulas and pointing fingers—we illustrate problems with using difference score correlations in relationship research, suggest ways to ensure that difference score correlations are maximally informative, and briefly review alternatives to difference score correlations in studying similarity, accuracy, and related constructs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73008/1/j.1475-6811.1999.tb00206.x.pd
Group Formation Among Peer-to-Peer Agents: Learning Group Characteristics
This paper examines the decentralized formation of groups within a peer-to-peer multi-agent system. More specifically, it frames group formation as a clustering problem, and examines how to determine cluster characteristics such as area and density in the absence of information about the entire data set, such as the number of points, the number of clusters, or the maximum distance between points, that are available to centralized clustering algorithms. We develop a method in which agents individually search for other agents with similar characteristics in a peer-to-peer manner. These agents group into small centrally controlled clusters which learn cluster parameters by examining and improving their internal composition over time. We show through simulation that this method allows us to find clusters of a wide variety of sizes without adjusting agent parameters
Analytic Treatment of Positronium Spin Splittings in Light-Front QED
We study the QED bound-state problem in a light-front hamiltonian approach.
Starting with a bare cutoff QED Hamiltonian, , with matrix elements
between free states of drastically different energies removed, we perform a
similarity transformation that removes the matrix elements between free states
with energy differences between the bare cutoff, , and effective
cutoff, \lam (\lam < \Lam). This generates effective interactions in the
renormalized Hamiltonian, . These effective interactions are derived
to order in this work, with . is renormalized
by requiring it to satisfy coupling coherence. A nonrelativistic limit of the
theory is taken, and the resulting Hamiltonian is studied using bound-state
perturbation theory (BSPT). The effective cutoff, \lam^2, is fixed, and the
limit, 0 \longleftarrow m^2 \alpha^2\ll \lam^2 \ll m^2 \alpha \longrightarrow
\infty, is taken. This upper bound on \lam^2 places the effects of
low-energy (energy transfer below \lam) emission in the effective
interactions in the sector. This lower bound on \lam^2
insures that the nonperturbative scale of interest is not removed by the
similarity transformation. As an explicit example of the general formalism
introduced, we show that the Hamiltonian renormalized to reproduces
the exact spectrum of spin splittings, with degeneracies dictated by rotational
symmetry, for the ground state through . The entire calculation is
performed analytically, and gives the well known singlet-triplet ground state
spin splitting of positronium, . We discuss remaining
corrections other than the spin splittings and how they can be treated in
calculating the spectrum with higher precision.Comment: 46 pages, latex, 3 Postscript figures included, section on remaining
corrections added, title changed, error in older version corrected, cutoff
placed in a windo
The Effects Of Students Predispositions Toward Communication, Learning Styles, And Sex On Academic Achievement
Females are more apprehensive when talking in class, but more nonverbally immediate, and prefer a collaborative learning style. Males prefer independent and avoidant learning styles, and report learning less than females
Influence of composite particle formation on the performance and economics of grit removal
Grit is routinely removed at the headworks of municipal wastewater treatment works to limit its onerous impact on downstream processes. Grit separation technologies are normally based on sedimentation of a homogeneous material (usually sand). However, in practice inorganic grit particles are likely to be combined with organic matter, such as fats oils and grease (FOG), producing a composite particle whose settling properties vary with the inorganic/organic content.
A study of the impact of particle composition on its sedimentation has been conducted encompassing theoretical description (for particle settling in transitional flow), practical measurement and economic analysis. Practical measurement included sedimentation tests of homogeneous and composite particles along with characterisation of accumulated granular material sampled from actual municipal wastewater treatment works. The economic assessment was based on data from full-scale installations in the UK and US pertaining to remedial measures undertaken as a result of grit impacts, primarily accumulation in vessels and channels and damage of mechanical equipment through abrasion.
Practical tests revealed coating of the sand grains with a FOG analogue (candlewax) to generate composite particles containing 45% wax by weight. The coated particles were then 30% less dense, 22% larger and 14% less settleable, on average, than the uncoated particles. Samples of accumulated grit taken from anaerobic digesters and aeration lanes from a full-scale plant indicated a FOG content (43%) similar to that of the waxed particles in the bench-scale tests, thus leading to a similar grain retardation of 14% assuming the FOG to be entirely associated with the grit. An assessment of the impact of the consequential breakthrough of grit particles due to buoyancy generated by composite particle formation indicated a $1.1 increase in operating costs per megalitre (ML) wastewater
Sum Rules for Multi-Photon Spectroscopy of Ions in Finite Symmetry
Models describing one- and two-photon transitions for ions in crystalline
environments are unified and extended to the case of parity-allowed and parity-
forbidden p-photon transitions. The number of independent parameters for
characterizing the polarization dependence is shown to depend on an ensemble of
properties and rules which combine symmetry considerations and physical models.Comment: 16 pages, Tex fil
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