Absolute measurement of F2-laser power at 157 nm

We report a comparison of laser power measurements at the F2-laser wavelength of 157 nm made at two facilities of the Physikalisch-Technische Bundesanstalt (PTB), the German national metrology institute. At the PTB laboratory at the electron storage ring BESSY II in Berlin, the scale for laser power was directly traced to a cryogenic radiometer operating at 157 nm, whereas at the PTB laser radiometry facility in Braunschweig the calibration of transfer detectors was performed with a newly developed standard for laser power at 157 nm, which is traceable in several steps to a cryogenic radiometer operating at 633 nm. The comparison was performed under vacuum conditions with laser pulse energies of approximately 10 microJ, however with different average powers because different primary standard radiometers were used. The relative deviation for the responsivity of the transfer detector was 4.8% and thus within the combined standard uncertainty.     

Gold-coated copper cone detector as a new standard detector for F2 laser radiation at 157 nm

A new standard detector for high-accuracy measurements of F2 laser radiation at 157 nm is presented. This gold-coated copper cone detector permits the measurement of average powers up to 2 W with an uncertainty of approximately 1%. To the best of our knowledge, this is the first highly accurate standard detector for F2 laser radiation for this power level. It is fully characterized according to Guide to the Expression of Uncertainty in Measurement of the International Organization for Standardization and is connected to the calibration chain for laser radiation established by the German National Metrology Institute.     

Radicals,radical pairs and triplet states in photosynthesis

The investigation of radical ions, radical pairs, and triplet states that occur in the primary processes of photosynthesis by various EPR techniques is described. The determination of the valence electron spin density distribution by ENDOR/TRIPLE spectroscopy is demonstrated for the primary electron donor. In combination with site-directed mutagenesis, these studies show that the spin distribution in the chlorophyll donor is strongly affected by the protein environment, and a link is established with the donor's oxidation potential and function in the electron transfer process. Similarities and differences between electron donors in anoxygenic (bacterial) and oxygenic photosynthesis are briefly discussed. Application of transient and pulse EPR techniques give information also on short-lived intermediates, such as radical pairs and triplet states, and allow the determination of distances and relative orientations of these species. The extension to time-resolved pulse ENDOR spectroscopy opens the possibility to resolve the electron-nuclear hyperfine structure of these reaction intermediates, even on a very short time scale.     

Intermembrane cholesterol transfer: Role of sterol carrier proteins and phosphatidylserine

The effect of phosphatidylserine and sterol carrier proteins on cholesterol exchange was determined using an assay not requiring separation of donor and acceptor membrane vesicles. Sterol carrier protein-2 (SCP₂, also called nonspecific lipid transfer protein), but not fatty acid binding protein (FABP, also called sterol carrier protein), enhanced the initial rate of sterol exchange between neutral zwitterionic phosphatidylcholine small unilamellar vesicles (SUV) 2.3-fold. Phosphatidylserine at 10 mol% increased the initial rate of spontaneous and of SCP₂-mediated (but not FABP-mediated) sterol exchange by 22% and 44-fold, respectively. The SCP₂ potentiation of sterol transfer was dependent on SCP₂ concentration and on phosphatidylserine concentration. The SCP₂-mediated sterol transfer was inhibited by a variety of cations including KCl, divalent metal ions, and neomycin. The data suggest that SCP₂ increase in activity for sterol transfer may be partly ascribed to charge on the phospholipid. A portion of this work was presented as an abstract: Nemecz, G., Butko, P., and Schroeder, f. (1989)Biophysical Journal 55, 137a.     

Pestizide Polymere, 1. Herstellung und Untersuchung endosulfanhaltiger LDPE- und EVA-Folien

Endosulfan was mixed with granules of LDPE and EVA and drawn into sheets under different conditions in an extruder. It was observed that endosulfan incurred no change up to a temperature of 190°C in the extrusion process. The additives like derivatives of benzophenone and amide of oleic acid had no effect. The LDPE sheets saturated with endosulfan contained about 0.8% α- and 0.2% β-isomer. This phenomenon was attributed to the different solubilities of the two isomers. Sheets drawn from EVA containing ≥ 10% VAC could dissolve ≥ 8% of the two isomers homogeneously.     

An automatic counter for autoradiographed cells in Petri dishes

A simple automatic counting device for cells on Petri dishes is described. The device is tested up to 1 × 10⁴ cells (0·01 m)^?2 and counts linearly without coincidence error. The counting time for each dish is c. 3– 4 min including the time required to place the dish in the apparatus.     

Synapses on the mauthner cell of the goldfish: Thin section,freeze-fracture,and immunocytochemical studies

Large myelinated club ending and small-vesicle bouton synapses on the distal part of the lateral dendrite of the goldfish Mauthner cell were investigated with thin section, freeze-fracture, and immunocytochemical electron microscopic methods. Large myelinated club endings form mixed synapses, having both gap junctions and chemical synaptic junctions. The correlation of the number of gap junction particles (connexons) and the data from electrophysiological studies of single large myelinated club ending synapses suggest that only a small fraction of gap junction channels are open at any given time during electrical synaptic transmission. The chemical synaptic junctions at the large myelinated club ending synapse have large, round synaptic vesicles, indicating that they are excitatory. This result is in agreement with electrophysiological data demonstrating the excitatory nature of this chemical synapse. Freeze-fracture of these excitatory chemical synaptic junctions reveals the presence of the intramembrane particle aggregates in the postsynaptic E face. Small-vesicle boutons form chemical synaptic junctions with small, flat or oval synaptic vesicles. These structural data, in combination with previous electrophysiological studies, suggest that the small-vesicle bouton synapses are inhibitory. In support of this theory, the cytoplasmic side of the postsynaptic membrane of some of these synapses show positive immunocytochemical reaction to monoclonal antibodies against the rat glycine receptor. Freeze-fracture data reveal intramembrane particle aggregates in the postsynaptic P face of some small-vesicle bouton synapses which could possibly represent glycine receptor aggregates.