Selective and uniform laser-induced failure of antireflection-coated LiNbO3surfaces

LiNbO3surfaces with different antireflection coatings and from different vendors were damaged with 1.06 μm 9.5 ns full width at half maximum laser pulses. By probing with a laser spot smaller than the separation of isolated surface defects, it was possible to separate uniform damage, which was characteristic of the coating itself, from premature defect-driven localized failures. Uniform failure modes were identified and thresholds extracted for each by multithreshold analysis. Frequency of defect damage was determined at several fluences much lower than required for uniform failure. It is likely that defect-driven selective failures reduce the apparent damage threshold of flood-loaded samples. Tentative identification of a selective damage threshold was made and correlated with large-spot multimode test results. Incorporation of these results into a product-improvement program has resulted in LiNbO3Q-switches with increased resistance to selective damage.     

Survey of liquefaction structures induced by recent moderate earthquakes

In April–May 1989, the eastern coastlands of Falcon State (Northwestern Venezuela) were affected by a seismic swarm of over 2000 weak shallow events located on the continental platform. Nevertheless two moderate earthquakes (mb 5.7 and 5.0) occurred during this swarm, [anicking inhabitants and producing scarce structural damage but frequent fissures, fractures and wall falls of house masonry in the mesoseismal area. The most relevant geological features observed in the mesoseismal area, as a consequence of these main events, are related to liquefaction of saturated sand-layers and are concentrated in the flood plains and delta of the Tocuyo river, located less than 20 km away from the epicentral area. Both shocks triggered liquefaction with ground acceleration values ranging between 0.1 and 0.3 g. The FUNVISIS Earth Sciences Workgroup carried out a prospect-pit survey across these features (sand boils and vent-fractures) to have a better understanding of this phenomenon and to evaluate the liquefaction potential of sand layers in the mesoseismal area. The liquefied material came to the surface from subsurficial silty-sand layers deposited in fluvio-deltaic environments and located between 0.2 and 4.0 m in depth. The pathways used by liquefied sands correspond to pre-existing crab burrows and soil fractures.     

A Study of Human Reactions to Emissions from Building Materials in Climate Chambers. Part II: VOC Measurements,Mouse Bioassay,and Decipol Evaluation in the 1–2 mg/m3 TVOC Range

Monitoring of human reactions to the emission of formaldehyde and volatile organic compounds (VOC) from four commonly used building materials was carried out. The building materials were: a painted gypsum board, a rubber floor, a nylon carpet, and a particle board with an acid-curing paint. The exposures were performed in climate chambers. The air quality was quantified on the decipol scale by a trained panel, measurements of formaldehyde and VOC being performed simultaneously. The irritating potency of the materials was measured by a mouse bioassay. The VOC measurements showed several malodorants and irritants. Some abundant VOC identified in the head-space analyses were absent in the climate chamber air. The rubber floor and the nylon carpet exhibited a marked increase in decipols compatible with a number of odorous VOC identified in the air. A high formaldehyde concentration (minimum 743μg/m³) was measured for the particle board coated with an acid-curing paint. This was not reflected by a corresponding relatively high decipol value but a long-lasting irritating potency was observed in the mouse bioassay. TVOC sampled on Tenax and expressed in mass per volume as well as in molar concentration, and decipol evaluation both have limitations and should be used with caution as indicators of (perceived) indoor air quality. Eye irritation expressed by means of the eye index reflecting the tear film quality index (comprised of break-up time, foam formation, thickness of the precorneal lipid layer of the tear film, and epithelial damage) was found to be insensitive to formaldehyde and a VOC mixture but sensitive to TVOC concentrations of 1–2 mg/m³. Lipophilic VOC may be the cause of reduced tear film quality by destabilization of the lipid multilayer of the tear film.     

A quantitative treatment of oscillatory phenomena in coarse-grained ion-exchanger membranes

The treatment developed in this text concerns the ion flux, volume flux and electric current through the highly porous ion-exchanger membrane of the Teorell membrane oscillator. It is based on the concept that inside the membrane exists a concentration profile of defined shape depending mainly on the volume flux caused by the hydrostatic pressure and the electro-osmotic effect of the membrane potential within the reach of the electric charge of the ion-exchanger grains forming the membrane texture.In particular it is shown that under conditions of zero volume flux the effective fixed charge responsible for the electro-osmotic driving force can be determined directly by measuring the hydrostatic pressure and its compensating electric potential. Like the electro-osmotic effect, also the derived flux equations proved to be independent of the special feature of the grain texture.The simultaneous differential equations describing the temporal (oscillatory) behaviour of the Teorell membrane system are derived on the basis of these flux equations leading to analog computer solutions which agree well with the experimental data.     

Study of normal incidence of three-component multilayer mirrors in the range 20-40 nm

We study theoretically and experimentally the increase of normal incidence reflectivity generated by addition of a third material in the period of a standard periodic multilayer, for wavelengths in the range 20 to 40 nm. The nature and thickness of the three materials has been optimized to provide the best enhancement of reflectivity. Theoretical reflectivity of an optimized B4C/Mo/Si multilayer reaches 42% at 32 nm. B4C/Mo/Si multilayers have been deposited with a magnetron sputtering system and a reflectivity of 34% at 32 nm has been measured on a synchrotron radiation source.     

Some concepts for languages more powerful than context-free

Some new restrictive devices for grammars are introduced: standard control-sets, G-control-sets, checking state grammars, besides the wellknown ones: matrix-sets, regular control-sets, programs. All these concepts turn out to be equivalent with respect to their generative power. So we get further characterizations of the class of recursively enumerable sets. The generative power of context-freelabel-grammars and Chomsky-grammars both with these restrictive devices is found to be equal. New characterizations of the unconditional-transfer programmed-grammars are introduced, namely unconditional-transfer programs correspond to all the other devices mentioned above under so-called “full-checking possibility” — i.e. the whole set of labels is the checking-set.