Quantitative resonant soft x-ray reflectivity from an organic semiconductor single crystal.

Resonant soft X-ray reflectivity at the carbon K-edge was applied to a trigonal tetracene single crystal. The angular resolved reflectivity was quantitatively simulated describing the tetracene crystal in terms of its dielectric tensor, which was derived from the anisotropic absorption cross section of the single molecule, as calculated by density functional theory. A good agreement was found between the experimental and theoretically predicted reflectivity. This allows us to assess the anisotropic optical constants of the organic material, probed at the carbon K-edge, in relation to the bulk/surface structural and electronic properties of the crystal, through empty energy levels.

Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au.

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.

Integration of silk protein in organic and light-emitting transistors.

We present the integration of a natural protein into electronic and optoelectronic devices by using silk fibroin as a thin film dielectric in an organic thin film field-effect transistor (OFET) ad an organic light emitting transistor device (OLET) structures. Both n- (perylene) and p-type (thiophene) silk-based OFETs are demonstrated. The measured electrical characteristics are in agreement with high-efficiency standard organic transistors, namely charge mobility of the order of 10(-2) cm(2)/Vs and on/off ratio of 10(4). The silk-based optolectronic element is an advanced unipolar n-type OLET that yields a light emission of 100nW.

Distribution of trace elements in organs of six species of cetaceans from the Ligurian Sea (Mediterranean), and the relationship with stable carbon and nitrogen ratios.

Mercury (total and organic), cadmium, lead, copper, iron, manganese, selenium and zinc concentrations were measured in different organs of 6 different cetacean species stranded in an area of extraordinary ecological interest (Cetaceans' Sanctuary of the Mediterranean Sea) along the coast of the Ligurian Sea (North-West Mediterranean). Stable-isotopes ratios of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) were also measured in the muscle. A significant relationship exists between (15)N/(14)N, mercury concentration and the trophic level. The distribution of essential and non-essential trace elements was studied on several organs, and a significant relationship between selenium and mercury, with a molar ratio close to 1, was found in the cetaceans' kidney, liver and spleen, regardless of their species. High selenium concentrations are generally associated with a low organic to total mercury ratio. While narrow ranges of concentrations were observed for essential elements in most organs, mercury and selenium concentrations are characterised by a wide range of variation. Bio-accumulation and bio-amplification processes in cetaceans can be better understood by comparing trace element concentrations with the stable-isotopes data.

Solubilization and methylation of HgS, PbS, and SnS by iodomethane, a model experiment for the aquatic environment.

Iodomethane is produced in the marine environment by algae and plankton. Model experiments have shown that iodomethane can dissolve a series of metal sulphides, in agreement with some of the results mentioned in the relative literature. While no dissolution of SnS was observed, PbS and HgS were dissolved proportionally with the iodomethane concentration. The two forms of HgS (cinnabar and metacinnabar) behaved differently, with metacinnabar being more soluble than cinnabar. Moreover, iodomethane can methylate lead and tin and mercury can be methylated when methyllead and methyltin compounds are present in the model system. The methylated species were identified using gas chromatography, and there is evidence that lead and tin undergo the same methylation mechanism. Preliminary experiments with natural sediments were performed, but no dissolution of Pb, Sn or Hg was observed. CAPSULE: Iodomethane can solubilize Pb and Hg sulphides, and methylate Pb and Sn, and (indirectly) Hg.

The Fixion expansion nail in the surgical treatment of diaphyseal fractures of the humerus and tibia. Our experience.

The authors present their experience in the application of a Fixion expansion intramedullary nail for the treatment of diaphyseal fractures of the humerus and tibia, in a total of 40 surgeries. The features of the nail are: stability and flexibility of the instrumentation, speed of surgery, minimal exposure to radiation. The results obtained up to now are encouraging; there are no significant problems either during or after surgery, and mean consolidation time is 3 months for fractures of the humerus, and 4 months for those of the tibia. The Fixion nail is a versatile type of instrumentation that is easy to use.

Inorganic mercury in the rock pool environment (Ligurian Sea).

In the present study the mercury concentration has been investigated in three components of a rock pool environment of Genoa Nervi (Ligurian Sea): water, particulate matter and Tigriopus fulvus (Harpacticoid copepod). The influence of some parameters (pH, temperature, salinity, rainfall) on mercury concentration has been evaluated. These data show that the mercury concentration is greater in Tigriopus males than in females and that the concentration also depends on temperature variations.

Bioaccumulation of vanadium in the epiphytic lichen Parmelia caperata from Liguria (north-west Italy).

The concentration of vanadium was measured in 35 samples of the epiphytic lichen Parmelia caperata collected along the coast of the Ligurian Sea (Italy), in order to detect the possible bioaccumulation of vanadium due to a huge crude oil burning occurred in that area in 1991. The cartographic elaboration of data shows a pattern of distribution of vanadium concentrations according to different degrees of deviation from background condition, showing that 8 years later memory of the accident is still detectable in foliose lichen thalli.

Patellar realignment in recurrent subluxations and dislocations: long-term results.

A total of 41 patients affected with recurrent subluxations or dislocations of the patella treated with different surgical methods between 1972 and 1981 were examined. Radiographic and clinical monitoring according to Crosby-Insall in 35 patients ranges from 10 to 20 years, with the following results: excellent: 17%; good: 69%; fair: 14%; poor: 0; recurrent dislocations or subluxations: 0.

The presence of inorganic and organic mercury and selenium in Nephrops norvegicus from the Ligurian Sea.

Samples of Nephrops norvegicus from the Ligurian Sea were analysed for contents of organic mercury, total mercury and selenium. Results for 37 specimens are reported. Total mercury concentrations increase with size of the specimens. Percentage of organic mercury ranges from 31 to 88% with an average of 58%. Selenium does not correlate with size and the average content is 0.88 micrograms g-1 fresh weight (range 0.30-1.74 micrograms g-1 fresh weight).

Total mercury, organic mercury, copper, manganese, selenium, and zinc in Sarda sarda from the Gulf of Genoa.

The total mercury content of the Atlantic bonito (Sarda sarda) increases with increasing size of the specimen, as shown by other authors for other marine organisms (Renzoni et al., 1973; Buffoni et al., 1982; Bernhard and Andreae, 1984; Thibaud, 1986). Organic mercury content also increases with the size of the specimen, whereas inorganic mercury remains constant, which is in agreement with the prediction made on another species of Sgombridae (Bernhard, 1985). This kind of mercury partitioning has not, to our knowledge, been reported for other species of fish. It is interesting to note that the mercury concentration in the gonads also increases with the size of the specimen. A very small difference between the total mercury content of white and dark muscle was observed, while for selenium, zinc, copper, and manganese the concentrations are lower in white muscle than in dark muscle.

The presence of mercury (total and organic) and selenium in human placentae.

The concentrations of mercury (total and organic) and selenium in samples of human placentae obtained after normal births from 22 women living in Genova (Italy), were determined by atomic absorption spectrometry. The concentration of total mercury was between less than 0.005 and 0.230 microgram Hg/g dry weight, and the average value was 0.076 microgram Hg/g dry weight. For the same samples, the average percentage of organic mercury as mercury was 65%, with a maximum of 95%. Smaller variations were observed for selenium, i.e. concentrations ranging between 0.38 and 1.03 microgram Se/g dry weight, with an average value of 0.77 microgram Se/g dry weight. The ratio between wet weight and dry weight was determined for each sample and the average value found was 6.32. The placental selenium concentration did not correlate with total and organic mercury content, which is in accordance with the results of other researchers.