Video tape manufacture by high vacuum evaporation—aspects of machine technology

The next generation of video tapes will use evaporated thin films with their superior properties such as recording density, output level, frequency characteristics and signal-to-noise ratio. This paper describes the metal layer formation by a simple model for the growth of microcolumns at oblique incidence deposition. The most relevant process parameters are discussed. The layout of a production coater is described.     

Understanding heterogeneous catalysis on an atomic scale: a combined surface science and reactivity investigation for the dehydrogenation of ethylbenzene over iron oxide catalysts

In order to study the dehydrogenation of ethylbenzene to styrene, epitaxial iron oxide model catalyst films with Fe₃O₄(111), -Fe₂O₃(0001) and KFe _x O _y (111) stoichiometry were prepared in single crystal quality on Pt(111). They were investigated using surface science techniques before and after atmospheric pressure reaction experiments in a newly designed single crystal flow reactor. As expected from low-pressure measurements, Fe₃O₄(111) is catalytically inactive. The catalytic activity of -Fe₂O₃(0001) starts after an activation period of about 45 min. After that, the surface is essentially clean but shows a high concentration of defects. On the potassium-promoted films, however, the activation period is much longer, the activity then is higher and the surface gets covered completely with carbon and oxygen during reaction. This indicates a different reaction pathway on the promoted films with a carbon–oxygen species as catalytically active species.     

The isothermal variation of the entropy (ΔST) may be miscalculated from magnetization isotherms in some cases: MnAs and Gd5Ge2Si2 compounds as examples

The determination of the isothermal variation of the entropy (ΔS_T) is discussed in the present work. We show that ΔS_T has very different profiles and magnitudes when calculated from M vs. H or M vs. T experimental data. For MnAs compound, ΔS_T obtained from M vs. T data does not present a colossal peak. This result and the agreement between theoretical and experimental non-colossal magnetocaloric effect indicate that the colossal peak may be miscalculated from M vs. H experimental data. For Gd₅Ge₂Si₂ compound, ΔS_T obtained from M vs. T data does not present the peak observed in ΔS_T from M vs. H data.     

Persistence of antifouling agents in the marine biosphere

Risk indicators provide an interesting way to compare chemical substances with respect to the risks of their large-scaled release. The present study implies that, for antifouling agents used in commercial shipping, residence times in the marine biosphere are especially suitable to represent their inherent potential to cause exposure of organisms. A simple box model is described providing the possibility to estimate residence times in the marine biosphere from water-particle equilibrium partitioning constants and half-lives in water and sediment. Resulting residence times in the marine biosphere range from about 5 d (4,5-dichloro-2-n-octyl-4-isothiazolin-3-one) up to about 40,000 yr (copper). For an evaluation of the validity of the model, calculated values are compared with measured environmental concentrations. Remaining uncertainties are also discussed. The main purpose of the presented residence times is to serve as a basis for decisions in antifouling paint development or environmentally conscious purchasing of antifouling paints.     

Reference values for height and weight in Prader-Willi syndrome based on 315 patients

The spontaneous growth of 315 patients (109 girls and 208 boys) with Prader-Willi syndrome (PWS) was analysed in a mixed longitudinal and cross-sectional manner. 33 patients were seen in the department between 1970 and 1994; height and weight of 76 patients from Germany were evaluated by means of a questionnaire with detailed measuring instructions, and 206 definite cases were added from the literature. Mean ( SD) length of newborn babies with PWS was 50.2+/-2.8 cm (145 boys) and 48.9 3.3 cm (79 girls). Mean weight at birth was 2945 570 g in boys and 2782+/-594 g in girls. During the 1st year, the children's growth was nearly normal, thereafter short stature was present in approximately 50% of PWS patients. Between 3 and 13 years of age, the 50th percentile for height in PWS is roughly identical with the 3rd percentile in healthy controls. Body weight was normal for all boys and girls during the first 2 years. Thereafter, a rapid weight gain occurred; after an age of 10 years weight-for-height index in nearly all patients exceeded the normal range. The extent of pubertal growth was reduced for the group. Mean adult height was 161.6+/-8.1 cm (23 males) and 150.2+/-5.5 cm (21 females). Head circumference for age was normal for boys and girls. CONCLUSION: Reference data on spontaneous development of growth and weight gain of children with Prader-Willi syndrome are described allowing a better counselling of patients and parents.     

Hydraulic Calculations for Cross‐channeled Packings in Distillation Unit Based on a Physical Model

A physically based calculation model has been developed in order to describe the liquid and the gas flow in column packings with any arbitrary cross‐channel structure. An equation system is presented which characterizes the film flow on the surface as influenced by the countercurrent flowing gas stream and the respective geometric parameters of the packing. The considered hydraulic operating parameters are the pressure drop, the film thickness, and the radial liquid distribution as a function of the column load up to the flooding point. Care was taken to introduce only constants that can be interpreted physically. Their number was reduced to a minimum of three in order to provide the possibility of easy extrapolation to other packing dimensions. Numerical simulations have been carried out for different liquids assuming a fully wetted packing surface. A distribution width is introduced as the parameter characterizing the radial liquid distribution. Its value together with the respective gas split factors are important variables for the inclusion of maldistribution in the calculation of a distillation column. The numerical simulations up to the flooding point correspond well to the experimental data obtained from a test column.