Neural simulation of a system that learns representations of sensory experience

The pyriform cortex forms stable representations of smells to allow their subsequent recognition. Clustering systems are shown to perform a similar function, so they provide a guide to understanding the operation of the pyriform. A neural model of a sample of pyriform cortex was built that adheres to most known biological constraints, including learning by long-term potentiation. Results of early simulations suggest some interesting properties. The effort has implications for the knowledge representations used in artificial intelligence work

Mathematicians take a stand

We survey the reasons for the ongoing boycott of the publisher Elsevier. We examine Elsevier's pricing and bundling policies, restrictions on dissemination by authors, and lapses in ethics and peer review, and we conclude with thoughts about the future of mathematical publishing.Comment: 5 page

Ceric and ferrous dosimeters show precision for 50-5000 rad range

Ammonium thiocyanate, added to the usual ferrous sulfate dosimeter solution, yielded a very stable, precise and temperature-independent system eight times as sensitive as the classical Fricke system in the 50 to 5000 rad range. The ceric dosimeters, promising for use in mixed radiation fields, respond nearly independently of LET

A stochastic control approach to no-arbitrage bounds given marginals, with an application to lookback options

We consider the problem of superhedging under volatility uncertainty for an investor allowed to dynamically trade the underlying asset, and statically trade European call options for all possible strikes with some given maturity. This problem is classically approached by means of the Skorohod Embedding Problem (SEP). Instead, we provide a dual formulation which converts the superhedging problem into a continuous martingale optimal transportation problem. We then show that this formulation allows us to recover previously known results about lookback options. In particular, our methodology induces a new proof of the optimality of Az\'{e}ma-Yor solution of the SEP for a certain class of lookback options. Unlike the SEP technique, our approach applies to a large class of exotics and is suitable for numerical approximation techniques.Comment: Published in at http://dx.doi.org/10.1214/13-AAP925 the Annals of Applied Probability (http://www.imstat.org/aap/) by the Institute of Mathematical Statistics (http://www.imstat.org

Cyclic nucleotide-gated channels: structural basis of ligand efficacy and allosteric modulation

Most working proteins, including metabolic enzymes, transcription regulators, and membrane receptors, transporters, and ion channels, share the property of allosteric coupling. The term 'allosteric' means that these proteins mediate indirect interactions between sites that are physically separated on the protein. In the example of ligand-gated ion channels, the binding of a suitable ligand elicits local conformational changes at the binding site, which are coupled to further conformational changes in regions distant from the binding site. The physical motions finally arrive at the site of biological activity: the ion-permeating pore. The conformational changes that lead from the ligand binding to the actual opening of the pore comprise 'gating'. In 1956, del Castillo and Katz suggested that the competition between different ligands at nicotinic acetylcholine receptors (nAChRs) could be explained by formation of an intermediate, ligand-bound, yet inactive state of the receptor, which separates the active state of the receptor from the initial binding of the ligand (del Castillo & Katz, 1957). This 'binding-then-gating', two-step model went beyond the then-prevailing drug-receptor model that assumes a single bimolecular binding reaction, and paralleled Stephenson's conceptual dichotomy of 'affinity' and 'efficacy' (Stephenson, 1956). In 1965 Monod, Wyman and Changeux presented a simple allosteric model (the MWC model) (Monod et al. 1965) that explained the cooperative binding of oxygen to haemoglobin; it was adopted as an important paradigm for ligand-gated channels soon after its initial formulation (Changeux et al. 1967; Karlin, 1967; Colquhoun, 1973)

The Effects of Uncertainty on Macroeconomic Performance: The Importance of the Conditional Covariance Model.

We study the effects of growth volatility and inflation volatility on average rates of output growth and inflation for postwar U.S. data in a multivariate asymmetric GARCH-M model. Our statistical model differs from other work in that we allow the conditional covariance of inflation and growth to be both nondiagonal and asymmetric. We show that the data reject diagonality and symmetry restrictions frequently imposed in the literature. Our results on the macroeconomic effects of uncertainty also differ from those in other recent studies using a more restrictive covariance model. Specifically, we find that increased growth uncertainty is associated with significantly higher average growth, and that higher inflation uncertainty is significantly negatively correlated with lower output growth and lower average inflation.Asymmetry; Multivariate GARCH-M; Inflation; Uncertainty; Growth

Rational Habit Modification: the Role of Credit.

This paper proposes an asymmetric model within which consumer credit facilitates both consumption smoothing and rational habit modification. The model provides a better description of aggregate time series consumption data than competeting models. In particular, the model can account for the various aggregate consumption anomalies that have led to repeated rejections of Hall's (1978) random walk model of consumption. The model is applied to US data using a GMM approach. The evidence suggests that new credit can predict short-run changes in consumption and has assisted consumers to become more forward-looking since 1975.CONSUMPTION ; CREDIT ; ESTIMATOR