ALBERT

Notes: Abstract New-production (nitrate uptake) rates in the equatorial Pacific were estimated by parallel measurements of nitrate disappearance from sea water using a colorimetric method and of 15N-labelled nitrate (15NO3 −) incorporation into particulate organic nitrogen (PON) collected on GF/F filters (net nitrate uptake, conventional 15N-tracer method) and Anopore (0.2 μm) membranes. Regression analyses of 74 sample pairs gathered during 12 and 24 h productivity experiments revealed a significant positive relationship between decreasing nitrate level and 15NO3 − accumulation into PON retained on GF/F filters, but the slopes of Model I and Model II regression lines were 1.18 and 1.29, respectively, suggesting that 15 to 22% of 15NO3 − removed from the dissolved fraction were lost to another N-pool. Two possible avenues for the missing 15NO3 − have been examined: uptake by submicron particles passed through the GF/F filters, and loss as dissolved organic nitrogen (DON). Nitrate uptake by small cells not recovered on GF/F filters, could be safely eliminated as a cause of loss, since 15NO3 − uptake rates obtained from 15N entering PON collected on GF/F filters agreed well with those obtained from 15N entering PON collected on Anopore membranes (32 sample pairs). Inspection of the DON pool of 0.2 μm filtrates for excess-15N enrichment (20 samples) revealed that in nitrate-rich waters (equatorial upwelling between 1°N and 10°S), loss of 15NO3 − as DO15N accounted for 〈5% of net nitrate uptake. In samples from subtropical oligotrophic waters (from 11°S southward), however, 15NO3 loss as DO15N represented up to 20% of net NO3 − uptake. These results, as well as experimental considerations concerning the use of colorimetric and isotopic methods to measure new production show that: (1) earlier reported high discrepancies between nitrate decreases (ΔNO3 −) and 15NO3 − incorporation into filterable particles (ΔNO3 −/15NO3 − incorporation 〉2) were probably erroneous; (2) the use of GF/F filters does not result in an underestimation of new production, although it was found to underestimate PON concentrations by up to 60%; (3) in the equatorial upwelling area (1°N to 10°S), which has high ambient nitrate levels (〉2000 nmol l−1) but only slight changes in concentration (0 to 80 nmol l−1 d−1), new production is more accurately estimated by the isotopic method than by the chemical method; (4) in subtropical oligotrophic waters (from 11°S southward) with low ambient nitrate levels (0 to 100 nmol l−1), both procedures are appropriate as long as nitrate removal per incubation period is 〉3 nmol l−1 (lower rates are only detectable with the isotopic method); (5) the traditional 15N-tracer technique does not substantially underestimate net new-production in the equatorial Pacific, and failure to account for the loss of 15NO3 − as DON, i.e. to estimate gross nitrate uptake (gross uptake = net uptake + 15N loss) tends to underestimate new production on an average by only 10%. Overall, the apparent low level of new production in the nitrate-rich area of the central equatorial Pacific seems to be a fact, and may be ascribable to other nutrient (macro and micro) deficiencies and/or to intense in situ recycling of ammonium and nitrate (regenerated production) rather than to inaccurate nitrate uptake rates measured with the classical 15N-tracer technique.

Notes: Abstract An equation of motion for a cavitating gas bubble immersed in a liquid is introduced which includes a flexoelectric energy term. This energy is deduced from the electric field produced by the bubble wall acceleration (pressure gradient) in the fluid (the flexoelectric effect). We show that under conditions of sonoluminescence, this electric field reaches values typical of the electric breakdown field in water. Our theoretical results are consistent with the duration of light emission, minimum bubble radius, and energy release as measured in sonoluminescence experiments in water.

Notes: Abstract We discuss an hypothesis wherein single-bubble sonoluminescence is attributed to electrical breakdown due to large pressure gradients existing for small bubble radii. These large gradients produce large electric fields (the flexoelectric effect) that lead to electrical breakdown, releasing energies up to 10−10 J, which is much larger than the light energy released in each cycle. This hypothesis appears to be consistent with several observations made in studies of the sonoluminescence process.

Notes: Abstract In a preceding paper we put forward the hypothesis that the single-bubble sonoluminescence (SBSL) is caused by strong electric fields arising near the surface of a collapsing gas bubble on account of the flexoelectric effect in water. Here we argue that these fields can indeed provoke a multiple electric breakdown in water, in a micron-size region near the surface of the collapsing gas bubble, and show that the main numerical characteristics of the SBSL can be naturally explained within this mechanism. The SBSL spectra are determined by radiative transitions between high-energy levels of noble-gas atoms excited by hot electrons produced by the strong flexoelectric field in “cold” water.

Notes: Abstract We have studied the physical properties of Y−Ba−Cu−Oxide superconducting materials by using Levitation, AC-susceptibility, macroscopic conductivity, Scanning Tunneling Microscopy (STM) local conductivity, Scanning Electron Microscope (SEM), X-rays, and Hall effect experimental techniques. Our results tend to indicate systematically that the grains formed in the synthesis do not show bulk superconductivity but rather are superconductors at the domain boundaries of the orthorhombic phase. It seems that a coexistence of semiconductor and metallic regions are formed at the twinned domain boundaries. The pellets become superconductors when the grains form clusters and are in intimate contact. This seems to suggest that the bulk of the grains is semiconducting and that a conducting percolative network of grain and domain boundaries may be responsible for the superconductivity. To understand the observed constant high transition temperature we propose a model of semiconductor-metal-semiconductor boundaries that give rise to superconductivity in a model like that of Little, Ginzburg, and Allender-Bray-Bardeen (1).

Notes: Abstract. We use scanning tunneling microscopy to measure magnetic field induced strains in highly oriented pyrolytic graphite. This is done by using a scanning tunneling microscope with some magnetic components, which however do not produce an observable response within our resolution in the case of pure (99.999%) paramagnetic or diamagnetic metals (at the low field strengths applied). We study also ferromagnetic metals with this method for comparison. We find a relatively large (similar to that of permalloy) magnetostrictive response of graphite for the low applied field. The data shows saturation of the strain and also that the strain observed is localized and is not the cumulative strain from the mounted edge of the sample to the position of measurement, implying that volume is not conserved with the strains. We believe that the observed strains correspond to a signal of a ferromagnetic material and in this case may be due to the defects observed on the graphite planes.

Notes: Abstract The groove structure in polycarbonate substrates, commonly used in the fabrication of optical discs, has been studied with the scanning tunnelling microscope. Comparative studies of the same structures were also performed using more conventional scanning electron microscopy and transmission electron microscopy techniques. These studies illustrate the ability to characterize the shape of man-made structures that are commonly recorded in these polymer-based materials. The scanning tunnelling microscope images show the superiority of this technique for detailed cross-sectional studies of the profiles of structures with typical dimensions ∼ 500 nm in width by ∼ 50 nm in depth.

Notes: Abstract After 20 years of research, the Atapuerca sites have provided a large amount of archaeological and palaeontological remains. Human fossils have been found in three sites: Gran Dolina, galería and Sima de los Huesos. The Early Pleistocene human fossils from Gran Dolina have been ascribed to a new species,Homo antecessor, that represent the last common ancestor of Neandertals and modern humans. The Sima de los Huesos fossils and all the European Middle Pleistocene human fossils are the ancestors exclusively of the Neandertals, which evolved in Europe in conditions of geographic and genetic isolation.