A Video Tour through ViSta 6.4

This paper offers a visual tour throughout ViSta 6.4, a freeware statistical program based on Lisp-Stat and focused on techniques for statistical visualization (Young 2004). This travel around ViSta is based on screen recordings that illustrate the main features of the program in action. The following aspects of ViSta 6.4 are displayed: the program's interface (ViSta's desktop, menubar and pop-up menus, help system); its data management capabilities (data input and editing, data transformations); features associated to data analysis (data description, statistical modeling); and the options for Lisp-Stat development in ViSta. The video recordings associated to this tour (.wmv files) can be visualized at http://www.jstatsoft.org/v13/i08/ using the Internet Explorer navigator, or by clicking on the figures in the paper.

Evaluating and modeling biological sulfur production in the treatment of sulfide-laden streams containing ammonium

BACKGROUND: Biological treatment of effluents containing H2S and ammonium are of great interest as both can trigger serious environmental problems when disposed of. The aim of this study was to optimize the production of biosulfur from the partial oxidation of sulfide in sulfide- and ammonium-containing streams. Biological performance was evaluated under various aerating conditions and key kinetic parameters were adjusted based on an existing mathematical model adapted to this system. RESULTS: An optimal conversion of sulfide to S0 of 86% (w/w) was found at an oxidation-reduction potential (ORP) of −380 ± 10 mV and at an O2/S2− molar ratio of 0.44. Partial nitrification was observed at ORP higher than −200 mV and in excess of oxygen supply. Sulfide-oxidizing bacteria (SOB) outcompeted ammonium-oxidizing bacteria (AOB) in the competition for dissolved oxygen. In a modeling effort, the maximum specific growth rate for SOB, the sulfur shrinking kinetic constant, the maximum specific growth rate for AOB and the AOB oxygen half-saturation constant were adjusted to 10.1 day−1, 0.3 mg2/3 VSS mg−2/3 S, 1.75 day−1 and 1.5 mg L−1, respectively, during model calibration. CONCLUSIONS: Optimal S0 production was found under limiting O2 conditions in which AOB were not able to outcompete SOB. The mathematical model described satisfactorily the experimental profiles for ammonium, nitrite, sulfide and sulfate as a function of the aeration flow rate

A small-correlation expansion to quantify information in noisy sensory systems

Neural networks encode information through their collective spiking activity in response to external stimuli. This population response is noisy and strongly correlated, with complex interplay between correlations induced by the stimulus, and correlations caused by shared noise. Understanding how these correlations affect information transmission has so far been limited to pairs or small groups of neurons, because the curse of dimensionality impedes the evaluation of mutual information in larger populations. Here we develop a small-correlation expansion to compute the stimulus information carried by a large population of neurons, yielding interpretable analytical expressions in terms of the neurons' firing rates and pairwise correlations. We validate the approximation on synthetic data and demonstrate its applicability to electrophysiological recordings in the vertebrate retina, allowing us to quantify the effects of noise correlations between neurons and of memory in single neurons