How Molecules with Dipole Moments Enhance the Selectivity of Electrodes in Organic Solar Cells – A Combined Experimental and Theoretical Approach

Simple organic molecules with permanent dipole moments – amino acids and heterocycles – have been successfully employed in bulk‐heterojunction organic solar cells as interlayer between photoactive material and electron contact. A large increase of open‐circuit voltage and fill factor can be observed for four different polymers as donor material in the photoactive layer. A combination of current–voltage curves, scanning Kelvin‐probe atomic force microscopy, ultraviolet photoelectron spectroscopy, and electroluminescence measurements as well as numerical simulations are carried out to clarify in detail the underlying mechanisms. All results fully confirm the hypothesis that the main effect is an accumulation of electrons and a depletion of holes in the photoactive layer in the vicinity of the electron contact induced by a decrease of its effective work function. Further, density functional theory calculations and literature reports of the energy levels of the dipole molecules strongly suggest that the charge carriers tunnel through the thin dipole layer which does however not limit the current. This represents a versatile, simple, and cheap method to realize highly selective contacts which may also be beneficial for other types of solar cells and devices where contact selectivity is crucial.     

A Probabilistic Atlas of Diffuse WHO Grade II Glioma Locations in the Brain

Diffuse WHO grade II gliomas are diffusively infiltrative brain tumors characterized by an unavoidable anaplastic transformation. Their management is strongly dependent on their location in the brain due to interactions with functional regions and potential differences in molecular biology. In this paper, we present the construction of a probabilistic atlas mapping the preferential locations of diffuse WHO grade II gliomas in the brain. This is carried out through a sparse graph whose nodes correspond to clusters of tumors clustered together based on their spatial proximity. The interest of such an atlas is illustrated via two applications. The first one correlates tumor location with the patient’s age via a statistical analysis, highlighting the interest of the atlas for studying the origins and behavior of the tumors. The second exploits the fact that the tumors have preferential locations for automatic segmentation. Through a coupled decomposed Markov Random Field model, the atlas guides the segmentation process, and characterizes which preferential location the tumor belongs to and consequently which behavior it could be associated to. Leave-one-out cross validation experiments on a large database highlight the robustness of the graph, and yield promising segmentation results.     

An estimation of the heritability of phototaxis in Daphnia magna Straus

Summary The phototactic responses of four clones of Daphnia magna were experimentally analysed. Broad-sense heritability of this behavioural character was estimated through an analysis of variance, and it was very high under the standardised experimental conditions of this study.     

The effects ofTilapia introductions in Lake Luhondo,Rwanda

Synopsis Cyprinid fishes apparently constituted the major part of the original fish fauna in Lake Luhondo, Rwanda, at least until 1934. At that time only three species, all cyprinids, were known from the lake:Barbus neumayeri, a small barbel, very common in the lake (described from the lake asBarbus luhondo) and two larger cyprinid species:Barbus microbarbis andVaricorhinus ruandae. These two large species were probably not very common in the lake. Between 1935 and 1938 some youngTilapia were introduced into Lake Luhondo. Since then and certainly since 1952 the large cyprinids seem to have disappeared completely from the lake. The smallBarbus neumayeri has become extremely rare; at present it survives only in some small tributaries of the lake. In the lake itselfTilapia andHaplochromis species are now the dominant fauna. A survey of the available information is given.Africa-Museum, Steenweg op Leuven, B-1980 Tervuren, Belgium (mailing address)     

Nuclear polyhedrosis virus for control of Spodoptera exigua larvae on glasshouse crops

the efficacy of a nuclear polyhedrosis virus, SeNPV, for controlling larval populations of the beet armyworm, Spodoptera exigua (Noctuidae) was studied in chrysanthemum, gerbera, kalanchoë and tomato crops in glasshouses. Applications of 1×10⁸ PIBs/m² on the various crops resulted in 95–100% larval mortality. Virus applications caused comparable levels of mortality in populations of early and late instar larvae. Reduction in feeding damage to the crops, however, was more pronounced when the larvae were early instars at the time of virus application. Single applications with the virus resulted in higher levels of larval mortality as double applications with 0.1% methomyl and diflubenzuron.The virus appears to be a potential control agent for the beet armyworm in Dutch glasshouses.

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Résumé Les résultats d'applications d'un virus de la polyédrose nucléaire contre des populations de chenilles de Spodoptera exigua sont examinés dans des chrysanthèmes, gerberas, kalanchoës et tomates. Une dose de 1×10⁸ PIBs/m² résulte à 95–100% mortalité larvale dans tous les végétaux. L'effet sur chemilles de première et seconde stade larvale et sur chenilles de troisième et quatrième stade larvale était pareille. Malgré le niveau élevé du mortalité larvale les végéteaux étaient damagés sérieusement, particulièrement quand le virus était appliqué contre des chenilles de troisième et quatrième stade larvale.Comparée avec des pesticides chimiques, méthomyl et diflubenzuron, applications de virus résultent à un mortalité larvale plus haute. Le conclusion était que le virus est un candidat sérieus pour l'utilisation dans le lutte biologique contre les chenilles de S. exigua dans des serres en Pays Bas.

     

Microinjection of glycosaminoglycan-degrading enzymes in the chicken blastoderm

The relationship between the presence of glycosaminoglycans (GAGs) and the morphology of the middle layer or mesoblast was examined by performing transmission electron microscopy of chicken blastoderms microinjected with GAG-degrading enzymes. The controls included microinjections with saline or trypsin, as well as solid-phase assays for proteolytic activity in commercially available GAG-degrading preparations. The results indicate that, in normal as well as in saline-injected blastoderms, middle-layer cells are rounded or cuboidal in shape, and are linked to each other by small intercellular junctions in the primitive-streak region. As they migrate laterally along the basal lamina, they appear as typical mesenchymal cells, being separated by large intercellular spaces and covered by cell processes. The removal of hyaluronate (by the microinjection of hyaluronidases) led to compaction of the middle-layer cells in the area lateral to the primitive streak. These cells lost their mesenchymal aspect and retracted their processes, and intercellular junctions were observed. The presence of proteolytic activity in the enzyme preparations did not interfere with the results. On the basis of the results obtained using this microinjection technique, we were able to confirm at the ultrastructural level that hyaluronate, due to its space-creating properties, promotes the detachment of ingressed primitive-streak cells and preserves the mesenchymal aspect of the middle layer during the lateral migration of single cells along the basal lamina. Whether the presence of hyaluronate is necessary to allow positioning of the mesoblast could not be inferred using our experimental procedure. We present evidence that this molecule, as well as having physicochemical properties, is also involved in the modulation of tissue interactions during gastrulation.     

Evaluation of laser-Doppler flowmetry as a measure of tissue blood flow

In this study the technique of laser-Doppler flowmetry was evaluated for the measurement of tissue blood flow by comparing laser-Doppler flow (LDF) signal in the renal cortex, gracilis muscle, and cremaster muscle of anesthetized rats to whole-organ blood flow measured with an electromagnetic flowmeter or radioactive microspheres. In vitro, LDF signal was closely correlated (r = 0.99) to changes in erythrocyte velocity generated with a rotating wheel. Although individual LDF readings varied in situ, mean LDF signal calculated from multiple readings on the tissue surface were significantly correlated (r = 0.74-0.95) with tissue blood flows measured at various perfusion pressures. However, significant differences in the slope of the LDF signal vs. blood flow relationship were observed in different tissues and with different methods of measurement in the same tissue. This study indicates that mean laser-Doppler flow signal provides a good estimate of tissue blood flow, provided a sufficient number of points is scanned. However, there appears to be no universal calibration factor for the method.     

Sur un ergatandromorphe deLeptothorax nylanderi förster (Hymenoptera,formicoidea)

Résumé Nous avons obtenu en élevage un individu ergatandromorphe deLeptothorax nylanderi Förster. Cet Insecte est remarquable par son thorax moitié mâle, moitié ouvrière, à l'exclusion du segment médiaire (màle). Les zones de contact entre éléments mâles et éléments ouvrières présentent quelques figures de transition.

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Summary We obtained, in a laboratory culture ofLeptothorax nylanderi Förster, an ergatandromorphous individual. That Insect was remarkable by its half male and half worker thorax, excluding the epinotum (male).The zones of contact between male and worker parts showed some transition figures.