23,097 research outputs found
Reputation in perturbed repeated games
The paper analyzes reputation effects in perturbed repeated games with discounting. If there is some positive prior probability that one of the players is committed to play the same (pure) action in every period, then this provides a lower bound for her equilibrium playoff in all Nash equilibria. This bound is tight and independent of what other types have positive probability. It is generally lower than Fudenberg and Levine's bound for games with a long-run player facing a sequence of short-run opponents. The bound cannot be improved by considering types playing finitely complicated history-dependent commitment strategies
Measuring edge importance: a quantitative analysis of the stochastic shielding approximation for random processes on graphs
Mathematical models of cellular physiological mechanisms often involve random
walks on graphs representing transitions within networks of functional states.
Schmandt and Gal\'{a}n recently introduced a novel stochastic shielding
approximation as a fast, accurate method for generating approximate sample
paths from a finite state Markov process in which only a subset of states are
observable. For example, in ion channel models, such as the Hodgkin-Huxley or
other conductance based neural models, a nerve cell has a population of ion
channels whose states comprise the nodes of a graph, only some of which allow a
transmembrane current to pass. The stochastic shielding approximation consists
of neglecting fluctuations in the dynamics associated with edges in the graph
not directly affecting the observable states. We consider the problem of
finding the optimal complexity reducing mapping from a stochastic process on a
graph to an approximate process on a smaller sample space, as determined by the
choice of a particular linear measurement functional on the graph. The
partitioning of ion channel states into conducting versus nonconducting states
provides a case in point. In addition to establishing that Schmandt and
Gal\'{a}n's approximation is in fact optimal in a specific sense, we use recent
results from random matrix theory to provide heuristic error estimates for the
accuracy of the stochastic shielding approximation for an ensemble of random
graphs. Moreover, we provide a novel quantitative measure of the contribution
of individual transitions within the reaction graph to the accuracy of the
approximate process.Comment: Added one reference, typos corrected in Equation 6 and Appendix C,
added the assumption that the graph is irreducible to the main theorem
(results unchanged
Missing Shapiro steps and the -periodic Josephson effect in interacting helical electron systems
Two-particle backscattering in time-reversal invariant interacting helical
electron systems can lead to the formation of quasiparticles with charge .
We propose a way to detect such states by means of the Josephson effect in the
presence of proximity-induced superconductivity. In this case, the existence of
charges leads to an -periodic component of the Josephson current
which can be identified through measurement of Shapiro steps in Josephson
junctions. In particular, we show that even when there is weak explicit
time-reversal symmetry breaking, which causes the two-particle backscattering
to be a sub-leading effect at low energies, its presence can still be detected
in driven, current-biased Shapiro step measurements. The disappearance of some
of these steps as a function of the drive frequency is directly related to the
existence of non-Abelian zero-energy states. We suggest that this effect can be
measured in current state-of-the-art Rashba wires.Comment: 9 pages, 5 figures. A new submission extending and expanding our
analysis in arXiv:1507.08881. (v2) References adde
Modeling and experimental investigations of the stress-softening behavior of soft collagenous tissues
This paper deals with the formulation of a micro-mechanically based dam-age model for soft collagenous tissues. The model is motivated by (i) a sliding filament model proposed in the literature [1] and (ii) by experimental observations from electron microscopy (EM) images of human abdominal aorta specimens, see [2]. Specifically, we derive a continuum damage model that takes into account statistically distributed pro- teoglycan (PG) bridges. The damage model is embedded into the constitutive framework proposed by Balzani et al. [3] and adjusted to cyclic uniaxial tension tests of a hu- man carotid artery. Furthermore, the resulting damage distribution of the model after a circumferential overstretch of a simplified
arterial section is analyzed in a finite element calculation
Effective models for strong electronic correlations at graphene edges
We describe a method for deriving effective low-energy theories of electronic
interactions at graphene edges. Our method is applicable to general edges of
honeycomb lattices (zigzag, chiral, and even disordered) as long as localized
low-energy states (edge states) are present. The central characteristic of the
effective theories is a dramatically reduced number of degrees of freedom. As a
consequence, the solution of the effective theory by exact diagonalization is
feasible for reasonably large ribbon sizes. The quality of the involved
approximations is critically assessed by comparing the correlation functions
obtained from the effective theory with numerically exact quantum Monte-Carlo
calculations. We discuss effective theories of two levels: a relatively
complicated fermionic edge state theory and a further reduced Heisenberg spin
model. The latter theory paves the way to an efficient description of the
magnetic features in long and structurally disordered graphene edges beyond the
mean-field approximation.Comment: 13 pages, 9 figure
Fern Community Reassembly in Secondary Forests of Puerto Rico: Predictors, Complexity, and Niche Model Assessment
Approximately 94% of Puerto Rico’s forests were converted into agricultural systems by 1950. Since then, extensive abandonment of agricultural land has resulted in a considerable amount of forest regeneration throughout the main island. Ferns are a major non-woody component of oceanic, tropical island forests comprising up to seventy percent of the flora. Consequently, the composition and community structure of ferns may be indicative of the relative richness of these secondary forests. I used Maximum Entropy (Maxent), a widely-used mathematical tool for distinguishing suitable versus unsuitable fern niche space, along with ENMTools, a tool that assists Maxent with proper model selection, for accurately predicting 29 common, rare, terrestrial, and epiphytic tropical fern species’ distributions. Model discrimination was assessed via area under the receiver operating characteristic curve values, a common metric for model evaluation. Akaike information criteria were utilized for assessing model complexity and in selecting the most parsimonious model for each species. I highlight the importance of modeling with proper model complexity and emphasize the use of information criteria to accurately infer AUC values. Field testing of model predictions also reinforced that these models are successful at identifying suitable habitat for ferns in Puerto Rico and conservation recommendations are explored
Computation of transonic viscous-inviscid interacting flow
Transonic viscous-inviscid interaction is considered using the Euler and inverse compressible turbulent boundary-layer equations. Certain improvements in the inverse boundary-layer method are mentioned, along with experiences in using various Runge-Kutta schemes to solve the Euler equations. Numerical conditions imposed on the Euler equations at a surface for viscous-inviscid interaction using the method of equivalent sources are developed, and numerical solutions are presented and compared with experimental data to illustrate essential points
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