Fitness distributions in exponentially growing asexual populations

We explore a mean-field model for the evolution of exponentially growing populations of mutating replicators. Motivated by recent in vitro experiments devised to analyze phenotypic properties of bacterial and viral populations subjected to serial population transfers, we allow our in silico individuals to undergo unrestricted growth before applying bottleneck events. Different dynamical regimes of our model can be mapped to different experimental situations. Numerical and analytical results for fitness distributions calculated at the statistically stationary states of the dynamics compare favorably with available experimental data. Our model and results provide a common framework to better understand populations evolving under different selection pressures.     

Principal component analysis and cluster analysis for the characterization of dental composites

Various experimental dental materials were characterized using chemometric methods. The main aim of the study was to ascertain which composite materials present the best properties for use in restorative dentistry. Bisphenol-alpha-glycidyl methacrylate-based composites containing hydroxyapatite as a filler and a coupling agent were prepared using a photocuring polymerization procedure. Several chemical and mechanical properties of experimental composites were measured and the corresponding data were further studied using principal component analysis and cluster analysis. Results from the characterization allowed the most appropriate materials to be selected. Various composites presented acceptable general properties suggesting their suitability as substitutes for commercial materials in dentistry.     

Elastic pion-deuteron scattering near the 3-3 resonance

The elastic scattering of positive pions by deuterium has been studied at seven energies between 82 MeV and 292 MeV laboratory kinetic energy in the angular range between 30° and 130° (lab). The results are compared to recent relativistic three-body calculations.     

Synthesis of Cycloprop[b]anthracenes via Trapping of o-Naphthoquinodimethane

Cycloprop[b]anthracenes 1, 1a, 1b are prepared in a 3-step synthesis starting from o-di(iodomethyl)benzene. The key step consists of trapping of o-naphthoquinodimethane (9) with 1,2-di- and tetrahalogenocyclopropenes (3, 3a, 4b) .     

Calibration factor for estimating personal dose equivalent with imaging plates

A personal imaging plate (IP) dosimeter is in the process of being developed for neutron fields using the BaFBr:Eu²⁺ phosphor. A configuration incorporating a polyethylene radiator placed before the IP detector is used to produce protons via (n,p) elastic scattering. For a dosimeter sensitive to thermal neutrons, a Nylon plate ( thick) is placed between the polyethylene (1.2 mm thick) radiator and the IP ( thick sensitive layer) detector to produce protons via the ¹⁴N(n,p)¹⁴C reaction. Dosimeters having these configurations have been exposed to neutrons from ²⁴¹Am–Be and ²⁵²Cf sources at the Institute for Radioprotection and Nuclear Safety of Cadarache at angles of 0 (normal incidence), 30 and 60 and several dose equivalents. The personal dose equivalent response in terms of H_p(10) is evaluated from the net measured photostimulated luminescence densities (). The calibration factor obtained for estimating the personal dose equivalent with this dosimeter is for ²⁴¹Am–Be and for ²⁵²Cf.     

The Volterra operator is a compact universal quasinilpotent

Every compact quasinilpotent Hilbert space operator can be uniformly approximated by operators that are similar to the Volterra operator in L²([0,1],dx).     

Synthesis and Bergman cyclization of a beta-extended porphyrenediyne

Condensation of a porphyrin-2,3-dione with a 1,2-diaminoarenediyne affords a [small beta]-extended porphyrinic-enediyne: upon thermal Bergman cyclization the quinoxaline spacer positioned between the macrocycle and the enediyne prevents tandem radical cyclization to a picenoporphyrin.     

A robust nanocontainer based on a pure organic free radical

A new pure organic paramagnetic porous molecular material, which combines hydrophilic windows with large hydrophobic nanocontainers, is shown to be stable even in absence of solvent guest molecules.     

Gross alpha and gross beta radioactivity in drinking water from Zacatecas and Guadalupe cities, Mexico

The conditions to measure the gross alpha and gross beta radioactivity in water samples from Zacatecas and Guadalupe cities in the State of Zacatecas, Mexico were established. The gross alpha and beta radioactivity of water samples were measured using a liquid scintillation detector. The results show that the gross beta radioactivity in all cases is lower than the maximum contaminant level and the gross alpha radioactivity is higher in the samples collected from Guadalupe City and in the samples collected from the Southwest of Zacatecas City.     

Using theozymes for designing transition‐state analogs for the intramolecular aldol reaction of δ‐diketones

Two theozymes for the intramolecular aldol reaction of δ‐diketones have been studied using ab initio methods. The presence of both acid/base residues favors several steps of the aldol reaction. The appropriate positioning of these residues can accelerate one of two diastereromeric reaction pathways, the catalyzed aldol reaction being highly stereoselective. Analysis of the geometrical parameters, charge distribution, and the shape of molecular electrostatic potential for the corresponding acid/base catalyzed transition structure allows us to design adequate transition‐state analogs to favor a reactive channel of this intramolecular aldol reaction. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 338–347, 2001