Heterogeneous photobleaching in confocal microscopy

Photobleaching was studied during recording of confocal scanning laser microscopy. Studies on fluorescent gels of FITC-labeled dextran were used to evaluate differential bleaching along thez-axis. Differential bleaching along the z-axis was observed and it was seen that this was related to the numerical aperture of the objective in use. This points to the conclusion that photon energy flux density is an important parameter in photobleaching. To check if photon energy flux density heterogeneity is affected by local variation in the refractive index of the sample, photobleaching rates were calculated for different fluorescent objects (sections of seeds, animal cells stained with nuclear stains, immunocytochemistry preparations) and a pronounced similarity was found between photobleaching rates and DIC images.     

Bond functions for AB initio calculations on polyatomic molecules hydrocarbons

Transferable gaussian CH and CC bond functions and a C lone-pair function were optimized and compared to conventional polarization functions. The exponents (α) and position (γ,β) of these functions are α = 0.9, γ = 0.27 for CH bonds; α = 1.2, γ = 0.50 for CC bonds; α = 0.3, β = 0.47 for C lone-pair.     

Ab initio study of hydrazoic acid

SCF and CI calculations were carried out on the ground^1A state of HN₃. The equilibrium geometry and vibration frequencies were computed. The results point to a planar structure (groupC _s) but to a non-linear (170 °) N-N-N conformation. The calculated vibration frequencies are in fair agreement with experimental assignments.The dissociation path of the molecule to NH and N₂ products was investigated and compared to the isoelectronic reaction of diazomethane. The dissociation energy of hydrazoic acid is estimated to be about –8 kcal/mole, with a potential barrier to dissociation of about 30 kcal/mole.Boursier IRSIA     

A method for molecular correlation energy calculations. Application to the determination of dissociation energies of diatomic and polyatomic molecules

A simple and economical method for molecular correlation energy calculations is developed. In this method, the internal part of the correlation energy is calculated by means of a CI in a minimal basis set and the non-internal part (semi-internal and all-external) is evaluated using an original atoms-in-molecule method. It is successfully applied to the determination of dissociation energies of some diatomic (H₂, NH, C₂, CN, N₂, CO, NO, O₂, F₂) and polyatomic (H₂O, N₂O, CO₂, N₃H, CH₂N₂, CH₂CO, C₂N₂) molecules. The results are compared to those obtained using very elaborate variational methods.Aspirant du Fonds National Belge de la Recherche Scientifique.     

NanoSIMS50 — a powerful tool to elucidate cellular localization of halogenated organic compounds

Persistent organic pollutants are widely distributed in the environment and lots of toxicological data are available. However, little is known on the intracellular fate of such compounds. Here a method applying secondary ion mass spectrometry is described that can be used to visualize cellular localization of halogenated compounds and to semi-quantitatively calculate concentrations of such compounds. Of the model compounds tested, TBBPA was homogenously distributed in the cell membrane of the H295R cells while PFOS accumulated in very distinct locations in the cell membrane. Relative intracellular concentrations of 4-OH-BDE69 and 4-OH-BDE121 in GH3.TRE were 61?% and 18?%, respectively, compared to the parent compounds. These differences may partly explain that observed effect concentrations for 4-OH-BDEs in in vitro experiments are usually lower than what would be expected based on receptor binding studies. NanoSIMS50 proved to be a powerful tool to describe the cellular distribution of halogenated compounds. The semi-quantitative data that can be obtained may help to further explain results from in vitro or in vivo experiments.     

Flow cytometric viability assessment and transmission electron microscopic morphological study of bacteria in glycerol.

Human cadaveric skin allografts are used in the treatment of burns and can be preserved in glycerol at high concentrations. Previously, glycerol has been attributed some antimicrobial effect. In an experimental set-up, we aimed at investigating this effect of prolonged incubation of bacteria in 85% glycerol. Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis were incubated in 85% glycerol. The influence of duration of incubation and temperature on ultrastructure and viability were investigated. Unstressed cultures served as controls. Survival was studied after 24-36 h and 10 days incubation in 85% glycerol at 4 degrees C and 36 degrees C with transmission electron microscopy (TEM) and flow cytometry using viability stains indicating membrane damage (SYTO9, propidium iodide) or esterase activity (carboxyfluorescein diacetate). TEM clearly demonstrated variability in morphological changes of bacteria suggesting different mechanisms of damage. Viability stains supported these findings with faster declining viable cell populations in 85% glycerol at 36 degrees C compared with 4 degrees C. Both methods demonstrated that Gram-negative species were more susceptible than Gram-positive species. In conclusion, 85% glycerol may have some additional antimicrobial effect. Temperature is an important factor herein and Gram-negatives are most susceptible. The latter finding probably reflects the difference in cell wall composition between Gram-positive and Gram-negative bacteria.     

Theoretical determination of the ionization potentials of the 1σ and 2σ electrons of CO(Σ)

Large-basis-set calculations of near Hartree-Fock accuracy were performed on CO⁺(1σ-hole ²Σ⁺) and CO⁺)2σ-hole, ²Σ⁺); correlation energies for these systems and for CO were calculated using an atoms-in-molecule approach, relativistic energies and vibrational structure corrections were also considered. The results are: IP(CO, 1σ) = 542.4 (542.57) eV, IP(CO,2σ) = 297.0 (296.24) cV, D_c(CO, ¹Σ⁺) = 10.8 (11.1) Ev, D₃(CO⁺, 1σ, ²Σ⁺) = 11.9 eV, D_e(CO⁺, 2σ, ²Σ⁺) = 9.1 eV, where IP and D_e stand respectively for ionization potential and dissociation energy, and where the numbers in parentheses refer to the most recent experimental values. The electron transfers resulting from the ionization of inner-shell electrons are discussed. Finally a quantitative correlation is developed correlating absolute chemical shifts to charge densities. Agreement between the calculated values and those derived from the correlation is quite satisfactory.     

Ab initio study of the O4 molecule

SCF-CI calculations were done on tetratomic oxygen complexes at various geometries. The results point to the existence of a metastable covalent molecule O₄ completely different from the van der Waals structure (O₂)₂ detected experimentally. At its equilibrium geometry, the O₄ molecule is a quasi-square (r(OO) ≈ 1.4 Å), slightly twisted out of plane, corresponding to the symmetry group D_2d. The activation energy of the reaction O₄(¹A_g) → 20₂(X ³Σ^?_g) is found to be ≈ 15 kcal/mole, that of the inverse reaction, ≈ 75 kcal/mole.     

A data model for algorithmic multiple criteria decision analysis

Various software tools implementing multiple criteria decision analysis (MCDA) methods have appeared over the last decades. Although MCDA methods share common features, most of the implementing software have been developed independently from scratch. Majority of the tools have a proprietary storage format and exchanging data among software is cumbersome. Common data exchange standard would be useful for an analyst wanting to apply different methods on the same problem. The Decision Deck project has proposed to build components implementing MCDA methods in a reusable and interchangeable manner. A key element in this scheme is the XMCDA standard, a proposal that aims to standardize an XML encoding of common structures appearing in MCDA models, such as criteria and performance evaluations. Although XMCDA allows to present most data structures for MCDA models, it almost completely lacks data integrity checks. In this paper we present a new comprehensive data model for MCDA problems, implemented as an XML schema. The data model includes types that are sufficient to represent multi-attribute value/utility models, ELECTRE III/TRI models, and their stochastic extensions, and AHP. We also discuss use of the data model in algorithmic MCDA.