A search for the decay μ → e γ

We report on the final analysis of a search for the decay μ⁺→e⁺γ performed at SIN. No evidence for the existence of the process has been found. An upper limit for the branching ratio of 1.0 × 10^?9 (90% confidence) is presented. The measured positron-photon energy distributions are completely described by the decay $\text{μ}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{ν}{}_{\mathrm{<mtext>e</mtext>}}\text{ν}{}_{\mathrm{\mu }}\text{γ}$ and accidental coincidences.     

Energy spectra and asymmetries of neutrons emitted after muon capture

Inclusive energy spectra and the energy dependence of the asymmetry parameter have been measured for neutrons emitted after muon capture in O, Si, Ca and Pb. In addition a neutron-neutron coincidence measurement has been performed for Ca. The results of these measurements confirm the exponential shape of the energy spectra and the positive asymmetry observed by Sundelin and Edelstein. The observation of neutrons with energies above 50 MeV and the observation of simultaneous emission of two high-energy neutrons suggest the importance of short-range nucleonnucleon correlations in this process.     

Laser nitriding of iron: Nitrogen profiles and phases

Armco iron samples were surface nitrided by irradiating them with pulses of an excimer laser in a nitrogen atmosphere. The resulting nitrogen depth profiles measured by Resonant Nuclear Reaction Analysis (RNRA) and the phase formation determined by Conversion Electron Mössbauer Spectroscopy (CEMS) were investigated as functions of energy density and the number of pulses. The nitrogen content of the samples was found to be independent of the number of pulses in a layer of 50 nm from the surface and to increase in depths exceeding 150 nm. The phase composition did not change with the number of pulses. The nitrogen content can be related to an enhanced nitrogen solubility based on high temperatures and high pressures due to the laser-induced plasma above the sample. With increasing pulse energy density, the phase composition changes towards phases with higher nitrogen contents. Nitrogen diffusion seems to be the limiting factor for the nitriding process.     

Zur darstellung der l-(diazinyl)-2-(pyridyl)-äthene (triazastilbene)

In continuation of our investigations of the aza analogues of stilbene, the 18 isomeric l-diazinyl-2-pyridylethenes (triaza-stilbenes) were synthesized. The results of electron density calculations (CNDO/2) were used to discuss the activation of methyl and carbonyl groups of the starting compounds in their aldol condensations.     

Giant liposome microreactors for controlled production of calcium phosphate crystals

Calcium phosphates are among the most important biominerals in living organisms, where they play both a mechanical and a calcium storage role. Their growth in vivo is under strong biological control, and this process occurs in closed spaces. Our aim in this paper is to describe a microreactor system able to control the mineralization process within closed spaces. To this aim we produce giant liposomes containing calcium ions as active ions in the mineralization process, spermine as an activator of crystal growth, and alkaline phosphatase as a catalyst to convert phosphate esters into phosphates. These phosphate esters are provided in the form of p-nitrophenyl phosphate outside of the liposomes. It is demonstrated that these amphiphilic molecules are able to diffuse through the lipidic container and to be subsequently hydrolyzed under enzymatic catalysis into active phosphate species which interact with the already available calcium and spermine to produce calcium phosphates only in the interior of the liposomes. This opens the route to control the calcium phosphate particle size in biomimetic systems.     

Glassy state of polystyrene sulfonate/polyallylamine polyelectrolyte multilayers revealed by the surface force apparatus

The interactions between two poly(allylamine)/poly(styrene sulfonate) multilayers made of 4.5 and 5 bilayers are investigated by the surface force apparatus (SFA). As the two surfaces approach, one reaches a threshold point where a repulsion sets in, until they become barely compressible. Repetitive load/unload cycles show that, once compressed, the films remain almost in their compressed state. This indicates that the poly(allylamine)/poly(styrene sulfonate) films are in a glassy state, in marked difference with the SFA findings on poly-(L-lysine)/poly-L-glutamic acid) multilayers. These results are discussed in the light of linearly and exponentially growing films.     

A simple six-input multichannel system for Mössbauer spectroscopy

A multichannel system for Mössbauer spectroscopy was developed and is presented. The system, constructed as an NIM module, is connected to the DMA port of an ATARI ST computer and can be used for six detectors simultaneously, thus allowing the operation of simultaneous triple radiation Mössbauer spectroscopy (STRMS). The multichannel system is explained and its capabilities are demonstrated.     

Human serum albumin self-assembly on weak polyelectrolyte multilayer films structurally modified by pH changes

Adsorption of proteins onto film surfaces built up layer by layer from oppositely charged polyelectrolytes is a complex phenomenon, governed by electrostatic forces, hydrogen bonds, and hydrophobic interactions. The amounts of the interacting charges, however, both in polyelectrolytes and in proteins adsorbed on such films are a function of the pH of the solution. In addition, the number and the accessibility of free charges in proteins depend on the secondary structure of the protein. The subtle interplay of all these factors determines the adsorption of the proteins onto the polyelectrolyte film surfaces. We investigated the effect of these parameters for polyelectrolyte films built up from weak "protein-like" polyelectrolytes (i.e., polypeptides), poly(L-lysine) (PLL), and poly(glutamic acid) (PGA) and for the adsorption of human serum albumin (HSA) onto these films in the pH range 3.0-10.5. It was found that the buildup of the polyelectrolyte films is not a simple function of the pure charges of the individual polyelectrolytes, as estimated from their respective pKa values. The adsorption of HSA onto (PLL/PGA)n films depended strongly on the polyelectrolyte terminating the film. For PLL-terminated polyelectrolyte films, at low pH, repulsion, as expected, is limiting the adsorption of HSA (having net positive charge below pH 4.6) since PLL is also positively charged here. At high pH values, an unexpected HSA uptake was found on the PGA-ending films, even when both PGA and HSA were negatively charged. It is suggested that the higher surface rugosity and the decrease of the alpha-helix content at basic pH values (making accessible certain charged groups of the protein for interactions with the polyelectrolyte film) could explain this behavior.