Controlled surface charging as a depth-profiling probe for mesoscopic layers

Probing the structure of material layers just a few nanometres thick requires analytical techniques with high depth sensitivity. X-ray photoelectron spectroscopy (XPS) provides one such method, but obtaining vertically resolved structural information from the raw data is not straightforward. There are several XPS depth-profiling methods, including ion etching, angle-resolved XPS (ref. 2) and Tougaard's approach, but all suffer various limitations. Here we report a simple, non-destructive XPS depth-profiling method that yields accurate depth information with nanometre resolution. We demonstrate the technique using self-assembled multilayers on gold surfaces; the former contain 'marker' monolayers that have been inserted at predetermined depths. A controllable potential gradient is established vertically through the sample by charging the surface of the dielectric overlayer with an electron flood gun. The local potential is probed by measuring XPS line shifts, which correlate directly with the vertical position of atoms. We term the method 'controlled surface charging' and expect it to be generally applicable to a large variety of mesoscopic heterostructures.     

Phylogenetic position of sponges in early metazoan evolution and bionic applications of siliceous sponge spicules

Sponges are the oldest and the simplest but not primitive multicellular animals. They represent the earliest evolutionary metazoan phylum still extant. It was a long and painful scientific process to posi-tion the most enigmatic and mysterious metazoan,the Porifera,into their correct phylogenetic place among the eukaryotes in general and multicellular animals in particular. As living fossils,sponges provide the best evidence for the early evolution of Metazoa. More recently,interest has been focused on the bionic applications of sponges' siliceous spicules,after the discovery of their unique structure and high fiber performance. In this review,the emergence of sponges,evolutionary novelties found in sponges,and the phylogenetic position of sponges in early metazoan evolution are highlighted. In ad-dition,the present state of knowledge on silicatein-mediated "biosilica" formation in marine sponges,including the involvement of other molecules in silica metabolism and their potential application in nanobiotechnology and medicine,is given.     

Neurosecretion and hydroelectrolytic regulation in Artemia salina (author's transl)]

The activity of Artemia protocerebral median neurosecretory cells is stimulated when animals are grown in media whose tonicity is lower than that of sea weater. The substance liberated by these cells could regulate the tonicity of the internal medium.     

Lymphokine dependence of in vivo expression of MHC class II antigens by endothelium

Changes in the expression of class II antigens of the major histocompatibility complex (MHC) have an integral role in the regulation of immune responses, and are brought about in vitro by soluble mediators. However, the mechanism that underlies in vivo expression of MHC class II antigens in, for example, endothelial cells in the absence of immunological stimulation has not been studied. We demonstrate here that expression of MHC class II antigens is not a constitutive property of endothelial cells, for MHC class II antigen-positive endothelial cells do not express these antigens during treatment with the immunosuppressive agent cyclosporin A. In vivo MHC class II antigen expression by canine endothelial cells is therefore dependent on factors, probably the lymphokine gamma-interferon produced by the immune system, whose secretion is inhibited by cyclosporin A.     

Ein Briefwechsel zwischen P. Finsler und B. L. van der Waerden über die Grundlegung der algebraischen Geometrie

Ohne Zusammenfassung     

Die Postulate und Konstruktionen in der frühgriechischen Geometrie

Ohne Zusammenfassung     

Hemoglobin causes both endothelium-dependent and endothelium-independent contraction of the pig coronary arteries, independently of an inhibition of EDRF effects

Hemoglobin is widely used as an inhibitor of EDRF effects. Hemoglobin contracts pig coronary arteries in vitro. However, during this contraction, effects of substance P and bradykinin which act via the EDRF are not inhibited. This means that the hemoglobin contraction is not caused by inhibition of the EDRF. This contraction is caused by a substance released from the endothelium, and by eicosano?ds released from the smooth muscles.