10,281 research outputs found
A Complete Characterization of Irreducible Cyclic Orbit Codes and their Pl\"ucker Embedding
Constant dimension codes are subsets of the finite Grassmann variety. The
study of these codes is a central topic in random linear network coding theory.
Orbit codes represent a subclass of constant dimension codes. They are defined
as orbits of a subgroup of the general linear group on the Grassmannian. This
paper gives a complete characterization of orbit codes that are generated by an
irreducible cyclic group, i.e. a group having one generator that has no
non-trivial invariant subspace. We show how some of the basic properties of
these codes, the cardinality and the minimum distance, can be derived using the
isomorphism of the vector space and the extension field. Furthermore, we
investigate the Pl\"ucker embedding of these codes and show how the orbit
structure is preserved in the embedding.Comment: submitted to Designs, Codes and Cryptograph
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Use and cost of disease-modifying therapies by Sonya Slifka Study participants: has anything really changed since 2000 and 2009?
Background:Disease-modifying therapies benefit individuals with relapsing forms of multiple sclerosis, but their utility remains unclear for those without relapses. Objective:To determine disease-modifying therapy use and costs in 2009, compare use in 2009 and 2000, and examine compliance with evidence-based guidelines. Methods:We determined the extent and characteristics of disease-modifying therapy use by participants in the Sonya Slifka Longitudinal Multiple Sclerosis Study (Slifka) in 2000 (n=2156) and 2009 (n=2361) and estimated out-of-pocket and total (payer) costs for 2009. Two multivariable logistic regressions predicted disease-modifying therapy use. Results:Disease-modifying therapy use increased from 55.3% in 2000 to 61.5% in 2009. In 2009, disease-modifying therapy use was reported by 76.5% of participants with relapsing-remitting multiple sclerosis, 73.2% with progressive-relapsing multiple sclerosis, 62.5% with secondary progressive multiple sclerosis, and 41.8% with primary progressive multiple sclerosis. Use was significantly associated with relapsing-remitting multiple sclerosis, shorter duration of illness, one to two relapses per year, non-ambulatory symptoms, using a cane, younger age, higher family income, and having health insurance. Average annual costs in 2009 were US16,302-18,928 for payers. Conclusion:Use rates were highest for individuals with relapsing-remitting multiple sclerosis, but substantial for those with progressive courses although clinical trials have not demonstrated significant benefits for them
Resource Competition on Integral Polymatroids
We study competitive resource allocation problems in which players distribute
their demands integrally on a set of resources subject to player-specific
submodular capacity constraints. Each player has to pay for each unit of demand
a cost that is a nondecreasing and convex function of the total allocation of
that resource. This general model of resource allocation generalizes both
singleton congestion games with integer-splittable demands and matroid
congestion games with player-specific costs. As our main result, we show that
in such general resource allocation problems a pure Nash equilibrium is
guaranteed to exist by giving a pseudo-polynomial algorithm computing a pure
Nash equilibrium.Comment: 17 page
NEAR-SURFACE EFFECTS IN MODELLING OSCILLATIONS OF ETA BOO
Following the report of solar-like oscillations in the G0 V star eta Boo
(Kjeldsen et al. 1995, AJ 109, 1313), a first attempt to model the observed
frequencies was made by Christensen-Dalsgaard et al. (1995, ApJ Letters, in
press). This attempt succeeded in reproducing the observed frequency
separations, although there remained a difference of about 10 microHz between
observed and computed frequencies. In those models, the near-surface region of
the star was treated rather crudely. Here we consider more sophisticated models
that include non-local mixing-length theory, turbulent pressure and
nonadiabatic oscillations.Comment: uuencoded and compressed Postscript (2 pages, including figure); To
appear in Proceedings of IAU Colloquium 155, "Astrophysical Applications of
Stellar Pulsation", Cape Town, South Afric
Excitonic effects on coherent phonon dynamics in single wall carbon nanotubes
We discuss how excitons can affect the generation of coherent radial
breathing modes in ultrafast spectroscopy of single wall carbon nanotubes.
Photoexcited excitons can be localized spatially and give rise to a spatially
distributed driving force in real space which involves many phonon wavevectors
of the exciton-phonon interaction. The equation of motion for the coherent
phonons is modeled phenomenologically by the Klein-Gordon equation, which we
solve for the oscillation amplitudes as a function of space and time. By
averaging the calculated amplitudes per nanotube length, we obtain
time-dependent coherent phonon amplitudes that resemble the homogeneous
oscillations that are observed in some pump-probe experiments. We interpret
this result to mean that the experiments are only able to see a spatial average
of coherent phonon oscillations over the wavelength of light in carbon
nanotubes and the microscopic details are averaged out. Our interpretation is
justified by calculating the time-dependent absorption spectra resulting from
the macroscopic atomic displacements induced by the coherent phonon
oscillations. The calculated coherent phonon spectra including excitonic
effects show the experimentally observed symmetric peaks at the nanotube
transition energies in contrast to the asymmetric peaks that would be obtained
if excitonic effects were not included.Comment: submitted to Phys. Rev. B on 7 May 2013, revised on 17 July and 13
August 2013, published 30 August 201
Investigating mechanisms of social support effectiveness: The case of locomotion motivation
Although social support can entail costs, individuals with a higher locomotion orientation, who are motivated to move and take action, benefit from support. In two dyadic studies, we tested whether perceived movement towards important goals would mediate the effect of recipients’ locomotion motivation on positive outcomes in support contexts. In Study 1, couples completed a 10-day diary and then recalled support interactions with their partner after the diary period. In Study 2, couples engaged in laboratory support interactions for important goals. Perceived goal movement mediated the effect of higher (vs. lower) locomotion on self-reported ratings and coder ratings of support outcomes. Higher locomotion recipients may benefit in support contexts because they perceive they can move smoothly towards their goals
Immorality and Irrationality
Does immorality necessarily involve irrationality? The question is often taken to be among the deepest in moral philosophy. But apparently deep questions sometimes admit of deflationary answers. In this case we can make way for a deflationary answer by appealing to dualism about rationality, according to which there are two fundamentally distinct notions of rationality: structural rationality and substantive rationality. I have defended dualism elsewhere. Here, I’ll argue that it allows us to embrace a sensible – I will not say boring – moderate view about the relationship between immorality and irrationality: roughly, that immorality involves substantive irrationality, but not structural irrationality. I defend this moderate view, and argue that many of the arguments for less moderate views turn either on missing the distinction between substantive and structural rationality, or on misconstruing it
In-depth analysis of the Naming Game dynamics: the homogeneous mixing case
Language emergence and evolution has recently gained growing attention
through multi-agent models and mathematical frameworks to study their behavior.
Here we investigate further the Naming Game, a model able to account for the
emergence of a shared vocabulary of form-meaning associations through
social/cultural learning. Due to the simplicity of both the structure of the
agents and their interaction rules, the dynamics of this model can be analyzed
in great detail using numerical simulations and analytical arguments. This
paper first reviews some existing results and then presents a new overall
understanding.Comment: 30 pages, 19 figures (few in reduced definition). In press in IJMP
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