Quantitative feedback theory with applications in welding

Two different control systems were developed using quantitative feedback theory for weld quality improvement. The first application to be discussed was designed for the resistance pinch welding process and uses electrode displacement and force as feedback parameters. A correlation between weld quality and electrode displacement is established for constant electrode force. The system is capable of producing repeatable welds of consistent quality, with wide variations in weld parameters. This is the first time feedback control has been successfully applied to pinch welding. The second example presented in this paper was developed for penetration control of the gas-tungsten-arc welding process. The feedback signal is obtained by measuring the amount of light emitted from the back side of the weld. Welds of constant penetration have been demonstrated in tests with travel speeds varying from 1.5 to 6 inches per minute and with 200 per cent changes in part thickness.     

Generic Representation of Solid-Object Geometry for Genetic Search

Abstract: This paper examines the first stage of using genetic algorithms in design—how to encode designs as chromosomes. Generic representations capable of describing the geometry of any solid object to eliminate the unnecessary duplication of work at this stage are explored. A suitable low-parameter, spatial-partitioning representation is then proposed, using partitions consisting of six-sided polyhedra intersected by planes. Finally, the coding of the representation is examined, with the conclusion that allelic coding with control genes and user-definable, fixed-value alleles would provide the most flexible system.     

Characterization of the repair tissue in articular cartilage defects using silver-enhanced colloidal gold immunostaining

The newly developed silver-enhanced colloidal gold staining method was used in a rabbit model to characterize the repair tissue in large articular cartilage defects filled with a heterocyclic methacrylate polymer. By 6 weeks the resurfacing tissue consisted of highly organized hyaline-like articular cartilage, fully integrated with the adjacent normal cartilage. Immuno-histochemistry detected collagen type ll, keratan sulphate, chondroitin 4-sulphate and chondroitin 6-sulphate in the matrix of the neocartilage. The level to which the polymer plug was recessed apeared to be critical to the overall quality of the repair tissue. Optimum results were obtained when the top surface of the biomaterial was at the level of the subchondral bone, below the level of the surrounding articular cartilage. Other technical aspects of implantation, that also affect the repair, are also discussed.     

Unexpected relations between matrix elements of the three-body scalar operators ti in the f shell

It has been known for some time that crystal-field matrix elements (i.e., matrix elements of sums over spherical harmonics involving the coordinates of the individual electrons) are often unexpectedly proportional to one another in the f shell. To see whether similar relations hold for more complicated operators than those provided by the crystal field, we examined the matrix elements of the three-electron scalar operators t_i for all configurations f^N, as calculated by W. T. Carnall on the basis of the computer program of Hannah Crosswhite. These operators are widely used to take configuration interaction into account, and we found a surprising number of proportionalities that go beyond what would be expected on a straightforward application of the Wigner-Eckart theorem, as applied to the irreducible representations of the classic groups SO(7), G₂ and SO(3) used by Racah in defining the f-electron states. A listing of such relations is provided.     

Distal femoral osteotomy for lateral compartment osteoarthritis of the knee

Arachidonic acid (AA) in the diet can be efficiently absorbed and incorporated into tissue membranes, resulting in an increased production of thromboxane A2 by platelets and increased ex vivo platelet aggregability. Results from previous studies have shown that AA is concentrated in the membrane phospholipids of lean meats. However, the concentration of AA in the visible fat portion of meats also may be significant despite being ignored in most studies. The aim of this study was to accurately quantitate the AA content of visible fat and the lean portion of beef, lamb, pork, chicken, duck, and turkey. The visible fat of meat contained a significant quantity of AA, ranging from 20 to 180 mg/100 g fat, whereas the AA content of the lean portion of meat was lower, ranging from 30 to 99 mg/100 g lean meat. Beef and lamb meats contained lower levels of AA in both the visible fat and lean portion than that from the other species. The highest level of AA in lean meat was in duck (99 mg/100 g), whereas pork fat had the highest concentration for the visible fats (180 mg/100 g). The lean portions of beef and lamb contained the higher levels of n-3 polyunsaturated fatty acids (PUFA) compared with white meats which were high in AA and low in n-3 PUFA. The present data indicate that the visible meat fat can make a contribution to dietary intake of AA, particularly for consumers with high intakes of fat from pork or poultry meat.     

Changes in seebeck coefficient of Pt and Pt 10% Rh after use to 1700°C in High-purity polycrystalline alumina

A technique is presented that enables the effects of temperature on the Seebeck coefficient to be assessed for individual wires. The technique, involving a high-resolution thermoelectric scanning rig and a nonuniform conditioning furnace of known temperature profile, was applied to 0.5-mm-diameter wires of Pt and Pt 10% Rh. Changes were observed in Seebeck coefficient when these wires were used in high-purity twin-bore insulation for up to 200 h at temperatures over the range 500 to 1700°C. Contamination from the insulation was found to be transmitted by a vaporization process, having an activation energy of 3 eV. This caused changes of up to 0.14 V · °C^–1 in Pt and 0.01 V · °C^–1 in Pt 10% Rh. Rhodium transfer to the pure Pt wire changed its Seebeck coefficient by up to 5 V · °C^–1. The consequences of both processes for thermocouple pyrometry are presented.     

The role of latent and active failures in workplace slips, trips and falls: an information processing approach

The vast majority of the published workplace slips, trips and falls (STF) literature is exceedingly narrow in its focus and often ignores wider systems issues in workplace STF aetiology. There is little recognition within the published literature of the importance of latent failures or the upstream organisational and cultural contexts within which workplace STF occur. This is unfortunate, as a systems approach to workplace STF analysis, that is inclusive of latent design and work organisation factors that often shape worker behaviour patterns related to STF risk (e.g. rushing, risk taking), is fundamental to the development of effective prevention measures. The aims of this paper are to provide an understanding of workplace STF causation that is cognisant of the potential role of both active and latent failures in STF causation. The paper presents an ergonomics model for workplace STF analysis that highlights information processing in STF aetiology, the STF incident process and the interaction between latent and active failures in STF causation. The paper draws upon ergonomics research conducted in a range of occupational contexts to illustrate the key features of the model as it applies to workplace STF. Implications of the model for analysis and prevention of STF are discussed.     

Adventure tourism and adventure sports injury: the New Zealand experience

The primary aims of this study were to establish a client injury baseline for the New Zealand adventure tourism and adventure sport sector, and to examine patterns and trends in claims for injury during participation in adventure activities. Content analysis of narrative text data for compensated injuries occurring in a place for recreation and sport over a 12-month period produced over 15,000 cases involving adventure tourism and adventure sport. As found in previous studies in New Zealand, highest claim counts were observed for activities that are often undertaken independently, rather than commercially. Horse riding, tramping, surfing and mountain biking were found to have highest claim counts, while hang gliding/paragliding/parasailing and jet boating injuries had highest claim costs, suggesting greatest injury severity. Highest claim incidence was observed for horse riding, with female claimants over-represented for this activity. Younger male claimants comprised the largest proportion of adventure injuries, and falls were the most common injury mechanism.