A preliminary investigation on the distribution of heavy metals in surface sediments of the Cona tidal marsh (Venice Lagoon)

Summary Data are from the two series of surface sediment samplings in an interface area between the Venice Lagoon and the mainland. The distribution of heavy metals gives a correlation with polluted source-sites—identified in the channel systems with a highly polluted input—and allows us to identify the localities of accumulation. Restricted to the estuary of the river tributary transporting a high concentration of pollutants into a tidal marsh area of the lagoon, the study shows the effect of the fresh water forcing to distribute heavy metals on surface sediments. Within the scope of this preliminary investigation, indications from sampling identify a sector of the ?Palude di Cona? in this estuary, which is highly suitable for detailed studies on processes affecting heavy-metal distributions in bottom surface sediments of shallow-water areas. Paper presented at the IV Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 22–24, 1987, Rome.     

The modelling of short waves in shallow waters and in the surf zone

Summary Two different flow models of the surf zone wave current dynamics based on Boussinesq and Serre equations have been implemented and tested. Good results were obtained while testing the models against many different wave and current data sets. Highly satisfactory reproduction of the experimental current patterns have been obtained by the model based on the Serre equations. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Characterization of ?ngstr?m''s turbidity parameters in the Po Valley area for summer conditions of the atmosphere

Summary Measurements of direct solar irradiance were taken at the San Pietro Capofiume station in the centre of the Po Valley using two examples of the multispectral sun photometer, model UVISIR, on several clear-sky days of late spring and early summer in the years 1989 and 1990. Realistic evaluations of aerosol optical thickness at several sun-photometric wavelengths were obtained from these measurements by i) using values of the calibration constants carefully found by following both the Langley plot method and the spectral-correction procedure, which had previously been applied with satisfactory results to the sun-photometric measurements carried out in Antarctica and ii) taking into account the extinction effects produced by Rayleigh scattering and absorption due to ozone, water vapour and nitrogen dioxide on the solar radiation passing through the atmosphere. By examining a wide set of spectral series of the aerosol optical thickness in terms of the well-known Ångstr?m formula, a large number of pairs of atmospheric-turbidity parameters α and β was obtained, presenting a range of the mean daily values of α from 1.0 to 1.7 (with the median of 1.48) and a range of the mean daily values of β from 0.10 to 0.30 (with the median of 0.15). Using the particulate extinction models CR (for continental particles) and TR (for small tropospheric particles and large rural particles), the aerosol mass loading of the atmosphere calculated for these values of α and β was estimated to vary between 0.09 and 0.31 g m⁻² (with the median of 0.21 g m⁻²) during the measurement period of 1989 and between 0.09 and 0.41 g m⁻² (with the median of 0.13 g m⁻² for model CR and of 0.21 g m⁻² for model TR) during June and July 1990. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Study of local scaling in the stable atmospheric boundary layer for the evaluation of turbulence parameters

Summary A renewed interest in the dynamic and thermal structure of the atmospheric boundary layer (ABL) has recently revived, due to the contribution that this layer can provide to the improvement of skill of weather prediction and climate simulation in the most advanced general circulation models. The attention is particularly focused on non-stationary and non-homogeneous turbulent structures of this transition layer, for which many parametrization schemes, based on local-and non-local-closure assumptions, have been proposed. However, also stationary, non-homogeneous, continous-turbulence conditions can give rise to some complication in the ABL parametrization when air stability becomes stronger and stronger. In this situation, the governing scales of the classical non-local Monin-Obukhov similarity theory are no more representative, and new local scales must be derived from local forcings of the flux. This paper summarizes a few relevant points of the local-similarity theory and shows the results of a local-scaling analysis obtained by observation data of wind and temperature profiles in the ABL in the northern Po Valley Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

Micrometeorological data collection via meteosat in the MICMET project of Friuli-Venezia Giulia

Summary As part of the MICMET regional project in Friuli-Venezia Giulia, an automatic system for the collection of micrometeorological data from a network of remote and impervious stations has been set up by adopting the Meteosat Data Retransmission System (DRS) for communications. To this end, a programmable data controller has been implemented over an RS-232 data link between the collecting station and the DCP (Data Collection Platform). In this paper, some details of both the electronic apparatus and the software program have been reported. An appropriate coding and decoding algorithm was used to recover the messages returned from satellite containing certain errors. The rate of success for the interpretation of satellite messages at the test station of Udine-Rizzi was greater than 90%. Paper presented at the IX Congresso del Gruppo Nazionale per la Fisica dell'Atmosfera e dell'Oceano, June 8–10, 1992, Rome.     

A simple model for the pore size distribution in random fibre networks

A heuristic approach based upon excluded volume arguments is developed for modelling the distribution of pore sizes in isotropic networks of randomly distributed cylindrical fibres. Our formalism accounts for the finite hard core diameters of the fibres, and leads to compact, analytically tractable expressions that span the complete range of volume fractions. Results are presented for the mean and mean-squared pore radii as functions of the fibre volume fraction, and for the partition coefficient of a spherical tracer particle into such a network under conditions such that steric effects are dominant.     

Dependence of surface coverage on pore geometry in dispenser cathodes

This paper shows that the surface coverage of Ba/BaO on tungsten is more complete when the activator is supplied via slotted pores rather than circular pores. Both theoretical and experimental evidence is given to support this contention. The effect is primarily a geometrical one, since the surface diffusion in the case of circular pores is two-dimensional, whereas the surface diffusion for slotted pores is linear. The contrast becomes less pronounced as the circular pore size decreases. For dimensions of the order of those found on cathode surfaces (e.g., 10 μ m diameter pores), a hexagonal array of circular pores can be optimized to produce an emitting area of 88% of the total, with a pore open area of about 11%. For slotted pores, the slot widths can be made arbitrarily narrow, consequently, the emitting area approaches 100% while pore evaporation losses are minimized. A slotted-pore cathode should, therefore, be capable of higher and more uniform current density with less barium dispensation. When the pore geometry is controlled, either for round holes or slots, the cathode should be less prone to space-charge-limited slump than those based on random sintered pores     

A preliminary study of the distribution of plankton using hologrammetry

The distribution and dynamics of particles in the aquatic environment play an important role in the modelling of bio-geochemical processes. Previous work on the measurement of such particles, which vary in size from tens of micrometres (individual cells) to several centimetres (aggregates such as ‘marine snow’), has mainly used electronic counting or conventional photography coupled with image analysis. Here we report on an initial study of the use of holographic mensuration, otherwise known as hologrammetry, for the enumeration, sizing and spatial distribution determination of plankton. We present results on imaging plankton in water tanks using both in-line and off-axis pulsed-laser holography. In this work, we have recorded in-line holograms in a volume of 2400 cm³ of water with a resolution of better than 20 μm and off-axis holograms in a volume of 36000 cm³ with a resolution of 140 μm. In both cases, identifiable images of plankton were obtained and precise spatial coordinates determined from the in-line holograms.     

Towards a reference ultrasonic cavitation vessel. Part 1: preliminary investigation of the acoustic field distribution in a 25 kHz cylindrical cell

The acoustic field produced by a 25 kHz, 25 l cylindrical sonochemical processing cell has been characterised systematically using a sonar hydrophone, with the aim of establishing it as a reference test bed on which future investigations into acoustic cavitation activity may be based. Data acquired at sonication levels up to 500 W have shown that though significant cavitation activity is generated throughout the vessel, the acoustic field generated is reproducible, typically to +/- 12%. The increases in acoustic pressure are shown to be nonlinear with applied power, suggesting an intermediate optimum level for future study.     

A computer simulation investigation of surface disordering in adsorbed multilayers

Multilayers of methane on a magnesium oxide substrate have been simulated using a model potential. Layer-by-layer disordering was found below the bulk melting point. This disordering is the result of the formation of vacancies by promotion of molecules to overlayers. Both static and dynamic properties show that there is a continuous change in the nature of the disordered layer from solid-like through a lattice liquid to a random liquid as the temperature is raised rather than successive roughening and pre-melting transitions. There is a marked difference in the sharpness of the disordering in the outer layers of multilayers with different exposed faces. In the close packed (111) face the outermost layer disorders over a temperature range of less than 10 K, while the corresponding layers of a (100) or (110) face disorders gradually over a range of 50 K.     

Effect of surface modification on the pore condensation of fluids: experimental results and density functional theory

The physisorption and pore condensation of a polar fluid (CHF₃) in a series of MCM-41 type mesoporous silica materials with native and chemically modified pore walls has been studied over the temperature range 168–293 K, corresponding to reduced temperatures T/T_c in the range 0.56-0.98, where T_c is the critical temperature of the fluid. Chemical modification of the pore walls by attachment of Si(CH₃)₃ groups causes a shift in pore condensation to higher relative pressures p/p0. This effect is most pronounced for materials with narrow pores (2.9 nm) at low temperatures. In the theoretical part of the work density functional theory based on a simple cubic lattice model of the confined fluid has been used to analyse the combined effect of a reduced pore width and weaker fluid-wall interaction caused by the surface coating. For realistic values of the model parameters it is found that the effect of the lower pore width is outweighed by the opposing effect of the lower fluid-wall interactions. The weaker temperature dependence of the pore existence curve observed experimentally for the surface modified materials can be traced back to a crossover from a two-step to a single-step process of pore filling predicted by the model.     

Analysis of fluid permeability in tortuous fibrous bed based on pore radius distribution

Journal of Visualization - The effect of fiber tortuosity on fluid permeability in fibrous beds has been investigated. A particle model is employed in which a fiber is replaced by spherical...     

SANS investigation on evolution of pore morphology for varying sintering time in porous ceria

Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine at 80°C. The precipitates were ground to fine particles of average size ∼0.7 μm. Circular disks with 10 mm diameter, 2 and 3 mm thickness were prepared from the green compacts by sintering at 1300° C for three different sintering times. Evolution of the pore structures in these specimens with sintering time was investigated by small-angle neutron scattering (SANS). The results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones.     

Alteration on the surface of the pore walls of the porous silicon under high temperature ageing: Computer simulation

Alterations in the atomic arrangement on the surface of the pore walls of porous silicon with oxygen adsorbent were studied by a statistical Monte-Carlo method for temperatures from 300 to 1200 K. Substantial atomic reconstructions were shown to occur above 500 K. It was demonstrated that atomic rearrangements corresponding to melting start at 1100 K.     

Origin and distribution of sulphate in surface waters of the Mansfeld mining district (Central Germany)--a sulphur isotope study.

In the Mansfeld region (Central Germany) copper mining contributed to an enormous pollution of the environment. Metal- and sulphate-bearing sediments and leachates emerge from the former copper smelters and mining waste heaps, spread along local rivers and finally reach the Saale river. A sulphur isotope study on water and stream sediments was performed along the River "B?se Sieben" and from its tributaries to determine the different sulphur sources. Four major sulphur sources exist in the area: metal sulphide mineralisations (Kupferschiefer), met alliferous sulphidic flue dust, slag, and anhydrite and gypsum of Permian and Triassic age. We obtained delta34S(SO4)-values in water samples varying from +4 per thousand to -18 per thousand CDT, clearly reflecting the input of sulphate from different sources. Sulphate from the oxidation of sulphidic mining residues is restricted to the mining area and cannot be traced for more than 5 km downstream. The major source for sulphate is the dissolution of gypsum and anhydrite. The sulphur isotope composition in dissolved and sedimentary adsorbed sulphate differs only slightly from each other. Microbial dissimilatory sulphate reduction can not be excluded in the shallow sediment layers.     

An array of scarlet and grey booklets: 65 years of the Symposium on Molecular Spectroscopy

A history of the OSU International Symposium on Molecular Spectroscopy is presented with a broad brush, inspired by looking at the evolution of the program booklets of the meeting, and drawing upon a selection of abstracts, all of which are now accessible on-line, and on reminiscences. The important and enduring aspects of the meeting from the perspective of the author are identified, and a few of the changes traced. The essential contributions of the founders and successive official hosts of the meeting, Harald H. Nielsen, David Dennison, K. Narahari Rao, and Terry A. Miller are acknowledged.     

The acoustic method of the surface potential investigation in GaP:Te (110) real surface

The acoustic method of the surface potential investigation in semiconductors has been described. The method is based on the transverse acoustoelectric effect TAV in layered structure: piezoelectric waveguide – semiconductor. The paper presents experimental results of the surface potential investigations obtained after various surface treatments in the GaP:Te (110) single crystals. Strong impact of mechanical and chemical surface treatments upon the surface potential values are observed. It follows from the measurements that the acoustic method may give interesting information about the surface potential of the semiconductor monocrystals in the high frequency range.     

A LEED study of the InP(110) surface: I. Experiment and preliminary analysis

A preliminary LEED theory experiment comparison for the InP(110) surface has been performed using experimental I(V) data recorded in the authors' laboratory from a clean, UHV-cleaved, single crystal specimen. A range of model surface geometries including both lateral and vertical displacements of the top layer In and P atoms have been examined. The results clearly demonstrate that the structure of this surface is substantially different from a simple termination of the bulk lattice and that the disturbance extends more than one layer into the real crystal. The possibility of extending the analysis to include second layer distortions is considered.     

A LEED investigation of the chemisorption of nitrous oxide on a tungsten (100) surface

Nitrous oxide has been adsorbed on the tungsten (100) surface at 295 and 500°K. Flash desorption experiments show two binding states of nitrogen which desorb at 1005 and 1275°K. When both nitrogen states and the oxygen state from the dissociated nitrous oxide molecule are on the surface, there are no new LEED features. When the 1005°K nitrogen state is desorbed, a (4 × 1) LEED pattern occurs. When all the nitrogen is desorbed, a (2 × 1) oxide pattern remains. The oxygen is desorbed as a volatile tungsten oxide. A model of the sorbate surface which is consistent with the facts currently available on the nitrous oxide-tungsten system is described.