The paper deals with the potential sanitary risk of the human presence on the seaside. The levels of microbial contamination of beach sands are generally higher than those observed in the waters due to bioaccumulation phenomena. The diseases, which could be contracted through skin contact, are related to the potential infecting dose and the most widespread illnesses are a consequence of several species of fungi and bacteria inhabiting the coastline. Despite few studies have been performed to determine Guideline Values, preventive measures and health risk assessments should be considered.

A mixed bacterial population was isolated from a garden soil inoculum after enrichment in a defined medium containing increasing amounts of 4-chlorobiphenyl (4-CB) as sole carbon source. The established population was composed of five bacteria from different genera, but only one, identified as belonging to the genus Bacillus and named MCS, had the ability to utilize 4-CB. In pure culture, the Bacillus isolate caused a reduction of 60% in the initial 4-CB concentration (200 mg litre−1) after 48 h of incubation and achieved total removal of the compound from the medium after seven days. Catabolite analysis provided evidence that Bacillus sp. MCS metabolizes 4-CB through a chain of reactions that ultimately generates 4-chlorobenzoic acid.

The tricyclic structure of known natural photochemotherapeutic drugs such as 8-methoxypsoralen and 5-methoxypsoralen is often taken as a model in the search of new photosensitizer agents with less phototoxic and mutagenic effects. This paper describes the synthesis, characterization, photobinding to DNA, photobiological properties and computational chemistry of some 8-methoxypsoralen derivatives bearing two or three methyl groups at the key positions of the two photoactive double bonds. Results showed that photoreactivity and photobiological behaviour depend on the pattern of methyl substitutions. Antiproliferative activity in cell lines shows good correlation with DNA interaction data.

Structural defects in MLEK grown InP single crystals have been studied using synchrotron white beam X-ray topography. Results here are presented for both a S-doped boule which was wafered longitudinally (i.e., parallel to the growth axis) and an Fe-doped boule which was wafered laterally (i.e., perpendicular to the growth axis). For longitudinal wafers from the S-doped boule, slip bands were observed to have nucleated from high-stress concentration located at the peripheral regions of the boule and to have propagated into the interior of the samples. In the same crystals, the growth interface morphology at different stages of crystal growth was determined. The interface is revealed as contours of equal lattice parameter, visible via strain contrast, as the concentration of the dopant changed periodically during growth. The interface shape was observed to be slightly convex to the melt, once the growth conditions were stabilized. For the laterally sliced wafers from the Fe-doped boule, systematic studies revealed that the density of dislocations changed during growth. A high density of uniformly distributed dislocations were observed in wafers taken from the early and later stages of growth. On the other hand, dislocations in well-defined four-fold symmetric distributions were observed in wafers sliced from the intermediate growth stages. The origins of this four-fold distribution were investigated using a thermal stress model which consisted of imposing a compressive radial stress, uniformly distributed around the boule circumference. The calculated stress distributions also showed four-fold symmetry in agreement with the observed dislocation distributions.

Alloy crystals of silicon-germanium have been grown by the liquid-encapsulated zone-melting (LEZM) method. This method combines zone melting in a quartz container with liquid encapsulation by the molten salt CaCl2 to prevent nucleation at the container-melt interface. The thermal gradient from seed through the molten zone to the feed material was investigated to determine the alloy composition and molten zone length. Electron beam and X-ray analysis were used to characterize the crystal structure and composition of bulk crystals. Crystals of constant alloy composition at 4.5 at% are grown by this technique and reveal single-crystal structure and a high degree of compositional uniformity.

We have developed a comprehensive model that accounts for oscillatory, laminar and turbulent flows caused by buoyancy and surface tension forces; forced convection due to crucible and crystal rotations; and complex thermal boundary conditions. The model also accounts for magnetohydrodynamics and sophisticated radiation heat exchange. Thermal elastic stress in the InP crystal is simultaneously calculated using the temperature distribution and crystal/melt interface shape obtained from the thermal transport simulation. A sophisticated adaptive grid generation technique together with the curvilinear finite volume discretization and several other high resolution numerical schemes have made it possible to simulate the growth of a compound crystal in a high pressure system

Two long-term solid-pellets feed continuous Czochralski growth experiments were performed in an industrial Czochralski crystal puller as an extension to our previous work [7]. The goals of these experiments were to examine how polysilicon pellets would melt in a standard Cz system, to discover the thermal effects the pellets would have on the overall melt, and to find if pellet addition could be an effective melt replenishment technique. These experiments demonstrate that the quality of the melt for the CCz growth is based heavily on the surface temperature of the melt. A novel characterization method (''impact severity'') is developed to characterize the quality of the CCz melt. Stable feed rate and melt conditions were achieved for three different pull rates. These experiments demonstrate that the process is technically feasible, and can be retrofitted to the existing industrial systems. Several critical issues that need to be addressed to develop a successful CCz process are also discussed.

A polysilicon pellets (≅1 mm diameter) feed continuous Czochralski (CCZ) growth process for silicon single crystals is proposed and investigated. Experiments in an industrial puller (14–18 inch diameter crucible) successfully demonstrate the feasibility of this process. The advantages of the proposed scheme are: a steady state growth process, a low aspect ratio melt, uniformity of heat addition and a growth apparatus with single crucible and no baffle(s). The addition of dopant with the solid charge will allow a better control of oxygen concentration leading to crystals of uniform properties and better quality. This paper presents theoretical results on melting of fully and partially immersed silicon spheres and numerical solutions on temperature and flow fields in low aspect ration melts with and without the addition of solid pellets. The theoretical and experimental results obtained thus far show a great promise for the proposed scheme.

Modeling of the crucible in bulk crystal growth simulations as a right circular cylinder may be adequate for high aspect ratio melts but this may be unrealistic when the melt height is low. Low melt height is a unique feature of a solid feed continuous Czochralski growth process for silicon single crystals currently under investigation. At low melt heights, the crucible bottom curvature has a dampening effect on the buoyancy-induced oscillations, a source of inhomogeneities in the grown crystal. The numerical results demonstrate how the mode of convection changes from vertical wall-dominated recirculating flows to Benard convection as the aspect ratio is lowered. This phenomenon is strongly dependent on the boundary condition at the free surface of the melt, which has been generally considered to be either adiabatic or radiatively cooled. A comparison of the flow oscillations in crucibles with and without curved bottoms at aspect ratios in the range of 0.25 to 0.50, and at realistic Grashof numbers (107 < Gr < 108) illustrate that changing the shape of the crucible may be an effective means of suppressing oscillations and controlling the melt flow.

An investigation is reported on the use of parametric scattering from an electrostatic wiggler for the growth of space charge waves. This investigation extends previous work on slow space charge wave generation and propagation in inhomogeneous waveguides. Observations show that the scattering technique may be used for the growth of large amplitude waves and that this technique permits wave growth at all values of interest for the ratio of beam to limiting current.

Summary

In this paper we discuss the potential role of pulse power technology for future high gradient accelerators. Compared to present day pulse power sources the requirements are quite modest and, with the exception of a detailed testing of high repetition rate systems, all components have been tested over several years. We review pulse power technology and its use in collective acceleration of ions and electrons. An account is presented of a new concept for collective electron acceleration through the parametric excitation of fast waves on beams. A summary is given also of achievements in the generation of high power microwave signals, and a discussion presented of structure requirements to take full advantage of the newly evolving ultra high power sources.

In this paper, an account is presented of an investigation into the propagation of large amplitude space-charge waves in an inhomogeneous waveguide. The study is motivated by the possibility of using these waves for the collective acceleration of ions. Measurements are reported that show an increase in the wave phase velocity as the guide diameter, and hence the effective plasma frequency is decreased. Results are also presented which show that the wave phase velocity is a function of its amplitude, and that large amplitude, nonlinear waves propagate more slowly than those described by linear theory. The results demonstrate that it is possible to control the wave propagation characteristics, and therefore indicate the electron-beam-supported slow space-charge waves provide a suitable medium for collective ion acceleration. Finally, a summary is given of possible advantages of an electron beam-wave accelerator over those using externally generated rf fields.

A 400 kV, 2kA, electron beam has been used to grow space charge waves in a 5.0 cm diameter drift tube. The waves are excited by propagating the pencil beam through a series of annular metallic rings with alternate rings grounded and the others capacitively coupled to the beam. Measurements have been made and will be presented of the wave characteristics downstream of the exciting structure. The wave excitation may result from a parametric excitation of eigenmodes of the beam in the guide.

An account will be presented describing the present status of electron beam supported wave accelerator research. We shall review the various approaches to collective acceleration using waves on an electron beam, and then focus attention on ion acceleration in space charge waves. We shall describe the results of experiments on nonlinear wave propagation in inhomogeneous guides. Results will also be presented reviewing work on the use of beat waves on electron beams for collective acceleration. In both cases we shall summarize the status of theoretical studies of these acceleration techniques and will indicate direction for future research.