Rain erosion damage in brittle materials

In order to understand the processes involved in the high-velocity rain erosion of brittle materials the impact damage produced in soda-lime-silica glass by single and multiple jet impact was studied. The damage was quantified by measuring the post-impact strength of specimens. It is shown that the impact damage depends on the impact velocity, the number of impacts and the specimen dimensions. A new analysis for calculating the velocity dependence of jet/drop impact damage in brittle materials is presented. The model is based on Hertzian contact analysis and dynamic fracture mechanics and takes into account the statistical nature of the flaws in the specimen. A good qualitative agreement with experimental results is obtained.     

Selected area channelling patterns in the scanning electron microscope

A technique is presented and illustrated for generating orientation dependent electron channelling patterns in the scanning electron microscope from small selected areas on the surface of bulk specimens. Methods of reducing the pattern area to 1 to 2 m in diameter are discussed. Numerous applications not previously possible are listed.     

Direct interpretation of high resolution electron images of substitutional alloy systems with a column structure

It is shown that in substitutional alloy systems with a column structure, high resolution electron micrographs viewed along the columns may still show a one-to-one correspondence with the atomic configurations even for crystal thicknesses beyond the thin phase grating limit. For such cases the atomic positions can be determined unambiguously from the images, without any need for image simulation. The required experimental conditions and the nature of the contrast are discussed.     

The influence of preparation and doping on the reducibility of hematite by hydrogen

Samples of hematite and of hematite doped with 1 at% lithium and 1 at% vanadium are prepared by the hot kerosene drying technique. The doped samples are also prepared by an impregnation method. The various samples are used to study the reduction with hydrogen to form iron. The results indicate that the rates of reduction are strongly influenced by the particle size of the initial samples and by the repartition of the additive in the bulk and surface layer of the hematite particles. It has been shown that both additives can retard the rate of reduction. The lithium exerts its maximum influence when present in solid solution and vanadium when concentrated in the surface layer. The importance of a careful preparation of samples to be used for reduction studies, is stressed.     

Study of electron traps in the thin interfacial oxide layer of Al-, Au- and Sn-n GaAs Schottky barriers by detrapping experiments

Electron traps in MIS-type Schottky barriers on n-GaAs were investigated by measuring the change of the flat-band voltage, due to detrapping, as a function of time. The trap depth and the capture cross section for a particular trap were obtained from the temperature dependence of the time constant for detrapping. It was found that the detrapping process in some cases is a two-state thermionic emission and tunneling process. For other trapping levels the results indicated clearly that the mechanism was different from the thermionic emission and tunneling process.     

Characterization of Al-Si-alloys rapidly quenched from the melt

Aluminium-silicon alloys with compositions in the range 0 at% to 33.9 at % Si were rapidly quenched from the melt at cooling rates between 10⁶ and 10⁷ K sec^–1 using the melt-spinning technique. The resulting ribbons were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and X-ray diffraction methods. Metastable solid solubilities of silicon in aluminium were determined from lattice parameter and DSC data. The values found were strongly dependent on specimen thickness and a maximum of about 5 at % Si was reached for an alloy composition of 15 at % Sl (maximal equilibrium solid solubility of silicon in aluminium is 1.58 at % Si). Discrepancies between published values of metastable silicon solid solubities were related to the interpretation of the lattice parameter data. Alloy composition was shown to determine the lattice parameter of the silicon-rich phase. The crystallite sizes and the lattice distortions in the aluminium-rich and silicon-rich phases were determined by X-ray diffraction line profile analysis. From the aluminiumrich phase only strain broadening was observed whereas the silicon-rich phase gave rise to both size and strain broadening. The origin of the lattice strains was discussed. Changes in solidification behaviour are reflected in the structure parameters measured.     

A surgical technique for resecting malignancies invading the facial nerve and petrous pyramid

Certain head and neck malignancies tend to invade branches of the cranial nerves and progress centripetally. The maxillary and mandibular divisions of the V (trigeminal) nerve are the most commonly invaded, but the VII (facial) nerve may harbor extensions of primary parotid malignancies and/or skin cancers originating in or near the ear. Paresis of the VII nerve signifies a serious but not entirely hopeless situation if countered with an appropriate surgical procedure. The optimal treatment of malignancies invading cranial nerves is surgical excision, which may necessitate removal of substantial portions of the cranium. Surgical pursuit of a malignancy in the facial nerve leads to a direct confrontation with the petrous pyramid of the temporal bone. Resection of the petrous pyramide is surgically feasible, but, if performed en bloc, extracts a high morbidity and mortality. An alternate technique in which the soft tissue and bones are removed disjunct is advocated. In this technique, the soft tissues are excised flush with the surface of the temporal bone. After making perforator and burr openings in the squamous temporal bone, a subtotal temporal craniectomy is completed with rongeurs. A prerequisite for success with this technique is the rotation of a large scalp flap and other local flaps to cover the exposed meninges and carotid arteries. A resume of four cases using this technique is presented. The age of the patients, the type, stage, and duration of the malignancies, and other factors which might influence the end stage results are given.     

Basics of process modeling

Modeling in Chemical Engineering should as a major objective possess the capability to predict. But, what does one know about the reliability of prediction?This article reviews earlier and recent studies and thinking on this matter: the relation to fundamentals, the role of mathematics and computing, the place of dimensional analysis and the connection between micro- and macro-scale events.     

A comparison of in vivo and in vitro methods for determining availability of iron from meals

A comparison is made between in vitro and human and rat in vivo methods for estimating food iron availability. Complex meals formulated to replicate meals used by Cook and Monsen (Am J Clin Nutr 1976;29:859) in human iron availability trials were used in the comparison. The meals were prepared by substituting pork, fish, cheese, egg, liver, or chicken for beef in two basic test meals and were evaluated for iron availability using in vitro and rat in vivo methods. When the criterion for comparison was the ability to show statistically significant differences between iron availability in the various meals, there was substantial agreement between the in vitro and human in vivo methods. There was less agreement between the human in vivo and the rat in vivo and between the in vivo and the rat in vivo and between the in vitro and the rat in vivo methods. Correlation analysis indicated significant agreement between in vitro and human in vivo methods. Correlation between the rat in vivo and human in vivo methods were also significant but correlations between the in vitro and rat in vivo methods were less significant and, in some cases, not significant. The comparison supports the contention that the in vitro method allows a rapid, inexpensive, and accurate estimation of nonheme iron availability in complex meals.     

Superconductivity and Mössbauer effect of Nb3Sn produced by Sn implantation

We have implanted Sn, Ge, and Si into Nb films. The resulting Nb-Sn compounds and their annealing behavior have been analyzed by the Mössbauer effect and compared to samples obtained by diffusion of Sn into Nb foils. Mössbauer spectra show that Nb₃Sn is obtained just by implantation, but with a T _cof only 5 K. The 925°C annealing temperature necessary to form the A15 structure with long-range order of Nb chains and T _cvalues up to 17.8 K is at least 100 °C higher in implanted samples than in samples prepared by diffusion of Sn into Nb. This is explained in terms of implantation-induced lattice defects. The metastable A15 phases of Nb₃Ge and Nb₃Si could not be formed by Ge or Si implantation, regardless of target or annealing temperature. It is suggested that the high-energy ions only form phases stable at high temperatures and with low T _cvalues.On leave from North Dakota State University, Fargo, North Dakota.