Darwinian Selection and Non-existence of Nash Equilibria

We study selection acting on phenotype in a collection of agents playing local games lacking Nash equilibria. After each cycle one of the agents losing most games is replaced by a new agent with new random strategy and game partner. The network generated can be considered critical in the sense that the lifetimes of the agents is power law distributed. The longest surviving agents are those with the lowest absolute score per time step. The emergent ecology is characterized by a broad range of behaviors. Nevertheless, the agents tend to be similar to their opponents in terms of performance.Comment: 4 pages, 5 figure

Composite Fermions in Quantum Dots

We demonstrate the formation of composite fermions in two-dimensional quantum dots under high magnetic fields. The composite fermion interpretation provides a simple way to understand several qualitative and quantitative features of the numerical results obtained earlier in exact diagonalization studies. In particular, the ground states are recognized as compactly filled quasi-Landau levels of composite fermions.Comment: Revtex. Postscript files of figures are appended the tex

Darwin Meets Einstein: LISA Data Analysis Using Genetic Algorithms

This work presents the first application of the method of Genetic Algorithms (GAs) to data analysis for the Laser Interferometer Space Antenna (LISA). In the low frequency regime of the LISA band there are expected to be tens of thousands galactic binary systems that will be emitting gravitational waves detectable by LISA. The challenge of parameter extraction of such a large number of sources in the LISA data stream requires a search method that can efficiently explore the large parameter spaces involved. As signals of many of these sources will overlap, a global search method is desired. GAs represent such a global search method for parameter extraction of multiple overlapping sources in the LISA data stream. We find that GAs are able to correctly extract source parameters for overlapping sources. Several optimizations of a basic GA are presented with results derived from applications of the GA searches to simulated LISA data.Comment: 8 pages, 12 figure

Heteranthery in Clarkia: pollen performance of dimorphic anthers contradicts expectations.

Premise of the studyWild plant species that require the services of pollen-feeding insects for reliable pollination may evolve features that attract and reward their mutualistic partners. Heterantherous species have been proposed to exhibit a "division of labor" whereby "feeding anthers" (which produce pollen that may be consumed by an insect) are distinguished from "reproductive anthers" (which produce pollen more likely to contribute to reproduction). In some heterantherous species, including Clarkia unguiculata (Onagraceae), these two anther types differ with respect to stamen length, anther size, pollen production, and pollen color.MethodsThe primary goal of this study was to test one component of the "division of labor" hypothesis by comparing the performance of the pollen produced by each type of anther in C. unguiculata. To achieve this goal, under greenhouse conditions, we hand pollinated and assessed pollen performance (using epifluorescence microscopy) within ~228 flowers.Key resultsThe pollen produced by the two anther types differed significantly with respect to both stigma and style penetration. The inner series of anthers produce pollen with higher performance than the outer series of longer, dark red anthers.ConclusionsThese findings contradict previous descriptions of the genus, reporting that the inner diminutive series of anthers in Clarkia produce "abortive and nonfunctional" pollen. We outline the future research required to demonstrate the ecological function of heteranthery in this iconic wildflower group

Langevin dynamics in crossed magnetic and electric fields: Hall and diamagnetic fluctuations

Based on the classical Langevin equation, we have re-visited the problem of orbital motion of a charged particle in two dimensions for a normal magnetic field crossed with or without an in-plane electric bias. We are led to two interesting fluctuation effects: First, we obtain not only a longitudinal "work-fluctuation" relation as expected for a barotropic type system, but also a transverse work-fluctuation relation perpendicular to the electric bias. This "Hall fluctuation" involves the product of the electric and the magnetic fields. And second, for the case of harmonic confinement without bias, the calculated probability density for the orbital magnetic moment gives non-zero even moments, not derivable as field derivatives of the classical free energy.Comment: 4 pages, 2 figures, revised versio

Behavioral Recognition: Computer Algorithms Alerting Law Enforcement to Suspicious Activity

Abstrac

Action Potential Gating of Calcium Channels and Transmitter Release

The regulation of transmitter release at the neuromuscular junction is tightly regulated by the influx of calcium in the presynaptic nerve terminal. Interestingly, the probability that release sites at the neuromuscular junction will liberate transmitter during each action potential is very low. The reasons for this low probability of release are not well understood. To test the hypothesis that individual N-type calcium channels open with a low probability, single channel recordings of N-type voltage-gated calcium channels were performed. Using this approach I determined the conductance of these channels, their probability of gating during an action potential waveform, and the magnitude of calcium flux during a single channel opening. I conclude from these studies that N-type voltage-gated calcium channels have a very low probability of opening (< 5%) during an action potential and the characteristics of calcium entry during single channel openings can help to explain the low probability of transmitter release at release sites in the neuromuscular junction. To understand how calcium current is activated physiologically, the activation and resulting current from N-type calcium channels elicited by different action potential waveforms were studied. This work was carried out at both room temperature and 37°C to provide a physiological context. Using the whole-cell patch clamp techniques, I studied the activation of current during various action potential shapes and conditions, and the kinetics of N- and L-type current activation. Using this approach I determined that N-type channels activate more slowly than L-type. Furthermore, depending on the action potential shape used and the temperature, action potentials can activate varying proportions (I/Imax) of N-type calcium current (ranging from 10-100%). Under physiological conditions using a frog motoneuron action potential waveform I determined that there was a very low proportion of calcium current activated by a natural action potential (~32%). Adenosine 5´-triphosphate (ATP) is co-released with acetylcholine (ACh) at the neuromuscular junction, and has been found to inhibit transmission. I used the cutaneous pectoris muscle of the Rana pipiens to study ATP-mediated modulation of ACh release. Intracellular postsynaptic recordings were used as a measure of ACh release, and agents that perturb the ATP signaling were examined

The maximum density droplet to lower density droplet transition in quantum dots

We show that, Landau level mixing in two-dimensional quantum dot wave functions can be taken into account very effectively by multiplying the exact lowest Landau level wave functions by a Jastrow factor which is optimized by variance minimization. The comparison between exact diagonalization and fixed phase diffusion Monte Carlo results suggests that the phase of the many-body wave functions are not affected much by Landau level mixing. We apply these wave functions to study the transition from the maximum density droplet state (incipient integer quantum Hall state with angular momentum L=N(N-1)/2) to lower density droplet states (L>N(N-1)/2).Comment: 8 pages, 5 figures, accepted for publication in Phys. Rev.