No description available.

Abstract In this study, a static electric contact tester with a vacuum system and gas supply system is used to investigate the effects of experimental parameters, such as inert gas kind, supply voltage, and the gap between the contacts, on the electric-arc characteristics and the erosion type for the electric contacts of silver. The experimental results show that chargeable threshold voltage in helium is higher than that in argon or air. In addition, the erosion surface of anode is observed, and the erosion area and volume are calculated and analyzed. Results show that the erosion area and volume in helium are smaller than that in argon or air. According to the observation of SEM photomicrographs, metal sputtering of the erosion hole in helium is smaller than that in argon or air. It is expected to provide the domestic electrical contact manufacturer in improving the research and development technique of the electrical contacts, and the design reference related to ultra-precision machining using a clean room.

Pool oscillations in tungsten inert gas welding pools have been used in a closed-loop control system for orbital welding of ultra high purity tubing, determining a target level of penetration by altering the welding current in real-time. The technique is ideally suited to this application since it is does not contravene the cleanliness requirements for the inner bore and can be implemented outside the small orbital heads that are commonly used. The results presented in this thesis show how clear pool oscillation signals in extremely small molten pools can be monitored by optimising the welding conditions and signal processing of the arc voltage signal. As an indicator of the likely variation in cast behaviour present particularly in austenitic stainless steels, a 'time-to-penetrate' characterisation was made of the materials, using the time of the transition from the Mode 1 to the Mode 3 oscillation behaviour as the measured variable. By applying the test across a range of welding currents, significant insight was obtained into the cast and associated penetration behaviour. Late transitions indicated casts that exhibited significantly different responses to the more usually applied welding procedures, especially at the lower levels of welding current (highlighting their potentially more problematic penetration behaviour). It was shown that the established theoretical models were difficult to apply with certainty to moving weld pools, and consequently a fuzzy logic model was used in the control strategy. The closed-loop system comprised a user-interface PC, a control rack and commercial welding power source - control signals were applied every 2 to 3 Hz. Mode 3 pool oscillations were found to offer a more than satisfactory sensitivity to the inner bead width created for the various casts of 1.65 mm wall thickness materials studied.

No description available.

Flammability limit is a most significant property of substances to ensure safety of chemical processes and fuel application. Although there are numerous flammability literature data available for pure substances, for fuel mixtures these are not always available. Especially, for fuel mixture storage, operation, and transportation, inert gas inerting and blanketing have been widely applied in chemical process industries while the related date are even more scarce. Lower and upper flammability limits of hydrocarbon mixtures in air with and without additional nitrogen were measured in this research. Typically, the fuel mixture lower flammability limit almost keeps constant at different contents of added nitrogen. The fuel mixture upper flammability limit approximately linearly varies with the added nitrogen except mixtures containing ethylene. The minimum added nitrogen concentration at which lower flammability limit and upper flammability limit merge together is the minimum inerting concentration for nitrogen, roughly falling into the range of 45 plus/minus 10 vol % for all the tested hydrocarbon mixtures. Numerical analysis of inert gas dilution effect on lower flammability limit and upper flammability limit was conducted by introducing the parameter of inert gas dilution coefficient. Fuel mixture flammability limit can be quantitatively characterized using inert gas dilution coefficient plus the original Le Chatelier's law or modified Le Chatelier's law. An extended application of calculated adiabatic flame temperature modeling was proposed to predict fuel mixture flammability limits at different inert gas loading. The modeling lower flammability limit results can represent experimental data well except the flammability nose zone close to minimum inerting concentration. Le Chatelier's law is a well-recognized mixing rule for fuel mixture flammability limit estimation. Its application, unfortunately, is limited to lower flammability limit for accurate purpose. Here, firstly a detailed derivation was conducted on lower flammability limit to shed a light on the inherent principle residing in this rule, and then its application was evaluated at non-ambient conditions, as well as fuel mixture diluted with inert gases and varied oxygen concentrations. Results showed that this law can be extended to all these conditions.

Akademisk avhandling--Gothenburg. / Bibliography: p. 69-74.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2005. / Includes bibliographical references.

Thesis (MScMedSc)-- Stellenbosch University, 2014. / ENGLISH ABSTRACT: The commercial and military deep diving environment is typically a low visibility environment, where dependence on the visual senses often needs to be replaced by a reliance on tactile senses. This thesis reviewed the current knowledge regarding neuropsychological manifestations of nitrogen narcosis and exposed a number of shortcomings in the current body of knowledge. In particular, the human performance effects of hyperbaric exposure on tactile perception and memory have not been systematically studied. It is further not clear, how exactly psychological factors (e.g. anxiety, mood states) and biographical factors (e.g. age, education, technical exposure, experience) might influence tactile perception and memory performance under conditions of hyperbaric exposure. The correlation between subjective experiences of narcosis, tactile performance, and psychological and biographical variables is also unknown. This study thus set out to investigate certain neuropsychological aspects of nitrogen narcosis, with special reference to tactile perception and memory, and to examine the relationships of tactile performance with other psychological and biographical factors. The effects of experimental hyperbaric exposure (EHE) on tactile (form) perception and tactile shape memory were examined by testing these functions at 6 ATA and 1 ATA, using a cross-over design where two groups completed the same tasks, in opposite sequence. The psychological variables included trait anxiety, transient mood states, and subjective ratings of narcosis, while the biographical variables included age, education, and previous technical exposure. The results demonstrated the detrimental effect of nitrogen narcosis on tactile form perception and manipulation, irrespective of the sequence of testing. It also demonstrated this effect on tactile form memory, although the sequence of testing also played a role here. Higher trait anxiety was associated with poorer recall, and tension was associated with a larger decrement in recall performance, while fatigue was associated with poorer task completion. Subjective experiences also played a role, where feelings of physical anxiety (i.e. increased arousal) were associated with better recall, and feelings of cognitive suppression (decreased arousal) were associated with a larger decrement in recall performance. Lower academic attainment was associated with poorer recall, while higher diving qualification was associated with better recall. Performance on the surface was a good predictor of performance at depth. Qualitative analysis rendered three themes, namely focus vs. distraction, following instructions, and shape memory. Psychometric properties of the subjective narcosis measure were also reported. Theoretical implications include support for the slowed information processing model when completing complex neuropsychological tasks, as well as support for the memory model, thus suggesting that this particular pattern of memory impairment occurs because encoding under narcosis produces a weaker memory trace than normal. Lastly, the study has a number of implications for industry. For example, divers need to compensate for slowed task completion by, firstly, planning more time to complete complex tasks, and secondly, by practicing those tasks prior to the actual deep dive (either on the surface or in shallow water). The need for using additional forms of recording of events or objects at depth, to aid memory encoding and subsequent recall at surface was also emphasised. / AFRIKAANSE OPSOMMING: Kommersieële en militêre duik vind dikwels plaas in ‘n omgewing met swak sig, waar duikers moet staatmaak op taktiele sintuie, eerder as op visuele sintuie. Die tesis begin met ‘n oorsig oor die huidige kennis rakende neurosielkundige verskynsels van stikstof narkose, en het ‘n aantal tekortkominge gevind. Meer spesifiek, die menslike faktor in die effek van hiperbariese druk op taktiese persepsie en geheue is nog nie sistematies bestudeer nie. Dit is verder nie duidelik presies hoe sielkundige faktore (angs, gemoedstoestande) en demografiese faktore (ouderdom, opvoeding, tegniese blootstelling, ondervinding) taktiele persepsie en geheue onder toestande van hiperbariese druk sou beïnvloed nie. The korrelasie tussen die subjektiewe ervaring van narkose, taktiele taakverigting, en sielkundige en biografiese veranderlikes is ook nie bekend nie. Die studie het verskeie neurosielkundige aspekte van stikstof narkose, met spesifieke verwysing na taktiele persepsie en geheue, sowel as die verhouding tussen taktiele prestasie en sielkundige en biografiese faktore ondersoek. Die effek van hiperbariese druk op taktiele persepsie en geheue is ondersoek deur hierdie funksies te toets by 6 en 1 ATA, deur middel van ‘n oorkruis studie ontwerp, waar twee groepe die take voltooi het, in teenoorgestelde volgorde. Die sielkundige veranderlikes het bestaan uit trek-angs, tydelike gemoedstoestande, en die subjektiewe evaluering van narkose, terwyl die biografiese veranderlikes ouderdom, opvoeding, en vorige tegniese blootstelling ingesluit het. Die resultate het die nadelige effek van stikstof narkose op taktiele vorm persepsie en manipulasie gedemonstreer, ongeag die rigting van toetsing. Dit het ook hierdie effek op taktiele vorm geheue gedemonstreer, hoewel die rigting van toetsing wel hier ‘n rol gespeel het. Hoër trek-angs was geassosieër met swakker herroeping, en spanning met ‘n groter agteruitgang in herroeping, terwyl matheid geassosieer was met swakker taakvoltooiing. Subjektiewe ervarings het ook ‘n rol gespeel, met ervarings van fisiese spanning (verhoogde opwekking) geassosieer met beter herroeping, en ervarings van kognitiewe onderdrukking (verlaagde opwekking) met groter agteruitgang in herroeping. Laer akademiese kwalifikasie was geassosieer met swakker herroeping, terwyl hoër duik kwalifikasie geassosieer was met beter herroeping. Taakverrigting op die oppervlak was ‘n goeie voorspeller van prestasie op diepte. Kwalitatiewe analiese het drie temas geidentifiseer, naamlik fokus vs. afleibaarheid, die volg van instruksies, en vorm geheue. Die psigometriese eienskappe van die subjektiewe narkose meetinstrument is ook gerapporteer. Teoretiese implikasies van die studie sluit in ondersteuning vir die vertraagde prosesseringsmodel, wanneer komplekse neurosielkundige take voltooi word, sowel as ondersteuning vir die model vir hierdie spesifieke herroepingspatroon wat ‘n swakker geheuespoor laat wanneer enkodering plaasvind onder toestande van narkose. Die studie het ook praktiese implikasies vir industrie. Dit is byvoorbeeld nodig om te kompenseer vir vertraagde taakvoltooïng deur, eerstens, die beplanning vir meer tyd om komplekse take te voltooi, en tweedens, deur daardie take te oefen voor die diep duik plaasvind. Die noodsaaklikheid vir additionele maniere om gebeure of voorwerpe op diepte vas te lê is ook beklemtoon.

A técnica de soldagem apresenta vantagem de união de partes metálicas que permite melhora na adaptação e uniformidade na distribuição das forças mastigatórias, minimizando falhas no tratamento reabilitador. O objetivo foi avaliar a resistência flexural entre três métodos de soldagem diferentes: Chama Direta a maçarico, método TIG - Tungstênio gás inerte (Soldadora NTY - Kernit, Brasil) e o método de solda a Laser (Soldadora Desktop - Dentaurum, Alemanha) comparando a um grupo controle (Monobloco). Os espécimes cilíndricos foram obtidos a partir de canais de cera pré-fabricados com 3mm de diâmetro e 30mm de comprimento, fundidos em liga de Ni-Cr e seccionados transversalmente, formando os grupos T1 e L1. Depois da secção, dez espécimes dos grupos L e T receberam chanfros em 45° para preenchimento, formando os grupos (L2 e T2). As extremidades foram unidas com resina acrílica obedecendo a uma distância pré-determinada, de 0,3mm para o grupo chama direta, 0,1mm para o grupo TIG e juntas do tipo topo a topo para o grupo laser. Os corpos foram incluídos e soldados de acordo com a proposição. Após a soldagem os corpos de prova foram torneados e levados ao teste de flexão. Os dados foram submetidos aos testes estatísticos (ANOVA e Student-Newman-Keuls - p <0,05) para comparações múltiplas. De acordo com os resultados (MPa) o grupo M (1796,55) obteve o maior valor, seguindo pelo grupo C(1370,56), ficando o grupo T1(990,84) com o valor menor. Não houve diferença estatística entre os grupos soldados, existindo somente diferença entre os grupos de teste para o grupo controle em monobloco. No entanto podemos afirmar que o preenchimento parece influenciar discretamente os resultados da resistência flexural no grupo TIG. Conclui-se que o método TIG produz resultado semelhante ao laser e a chama direta, o que é clínica e operacionalmente importante. / The welding technique presents advantage of union of metallic parts that improves the adaptation and appropriate distribution of the bite forces, minimizing flaws in the dental prostheses. The objective was to evaluate the flexural strength in different welding methods: Brazing; Laser (Welder Desktop - Dentaurum, Germany) and Tungsten inert gas - TIG (Welder NTY - Kernit, Brazil), comparing to a control group (non-welded). The cylindrical specimens were obtained from prefabricated wax conduits with 3mm of diameter and 30mm of length, melted in Ni-Cr alloys and split up transversally, forming the groups T1 and L1. After of the section the groups L and T received slices in 45° for fulfill, forming the groups (L2 and T2). The extremities were united with acrylic resin obeying a predetermined distance, from 0,3 mm to the brazing group, 0,1 mm to the TIG group, and in the laser group there wasn\' t any space between the extremities of jointing. The specimes were included and welding in agreement with the proposition, turned and conducted to the flexion test. The data were submitted to the statistical test (ANOVA and Student-Newman-Keuls - p<0,05) for multiple comparisons. According to the results (MPa) the control group (1796,55) obtained the largest average value, followed by the brazing group (1370,56), being the group T1(990,84) with the smallest value. In terms of statistics there was no difference between the groups with welding, existing only difference among the tested groups for the control group. However, we can affirm that the completion seems to influence the results of the resistance flexural discreetly in the TIG group. It can be concluded that the TIG method produces similar result to the laser and the brazing, what is clinical and important operationally.

A técnica de soldagem apresenta vantagem de união de partes metálicas que permite melhora na adaptação e uniformidade na distribuição das forças mastigatórias, minimizando falhas no tratamento reabilitador. O objetivo foi avaliar a resistência flexural entre três métodos de soldagem diferentes: Chama Direta a maçarico, método TIG - Tungstênio gás inerte (Soldadora NTY - Kernit, Brasil) e o método de solda a Laser (Soldadora Desktop - Dentaurum, Alemanha) comparando a um grupo controle (Monobloco). Os espécimes cilíndricos foram obtidos a partir de canais de cera pré-fabricados com 3mm de diâmetro e 30mm de comprimento, fundidos em liga de Ni-Cr e seccionados transversalmente, formando os grupos T1 e L1. Depois da secção, dez espécimes dos grupos L e T receberam chanfros em 45° para preenchimento, formando os grupos (L2 e T2). As extremidades foram unidas com resina acrílica obedecendo a uma distância pré-determinada, de 0,3mm para o grupo chama direta, 0,1mm para o grupo TIG e juntas do tipo topo a topo para o grupo laser. Os corpos foram incluídos e soldados de acordo com a proposição. Após a soldagem os corpos de prova foram torneados e levados ao teste de flexão. Os dados foram submetidos aos testes estatísticos (ANOVA e Student-Newman-Keuls - p <0,05) para comparações múltiplas. De acordo com os resultados (MPa) o grupo M (1796,55) obteve o maior valor, seguindo pelo grupo C(1370,56), ficando o grupo T1(990,84) com o valor menor. Não houve diferença estatística entre os grupos soldados, existindo somente diferença entre os grupos de teste para o grupo controle em monobloco. No entanto podemos afirmar que o preenchimento parece influenciar discretamente os resultados da resistência flexural no grupo TIG. Conclui-se que o método TIG produz resultado semelhante ao laser e a chama direta, o que é clínica e operacionalmente importante. / The welding technique presents advantage of union of metallic parts that improves the adaptation and appropriate distribution of the bite forces, minimizing flaws in the dental prostheses. The objective was to evaluate the flexural strength in different welding methods: Brazing; Laser (Welder Desktop - Dentaurum, Germany) and Tungsten inert gas - TIG (Welder NTY - Kernit, Brazil), comparing to a control group (non-welded). The cylindrical specimens were obtained from prefabricated wax conduits with 3mm of diameter and 30mm of length, melted in Ni-Cr alloys and split up transversally, forming the groups T1 and L1. After of the section the groups L and T received slices in 45° for fulfill, forming the groups (L2 and T2). The extremities were united with acrylic resin obeying a predetermined distance, from 0,3 mm to the brazing group, 0,1 mm to the TIG group, and in the laser group there wasn\' t any space between the extremities of jointing. The specimes were included and welding in agreement with the proposition, turned and conducted to the flexion test. The data were submitted to the statistical test (ANOVA and Student-Newman-Keuls - p<0,05) for multiple comparisons. According to the results (MPa) the control group (1796,55) obtained the largest average value, followed by the brazing group (1370,56), being the group T1(990,84) with the smallest value. In terms of statistics there was no difference between the groups with welding, existing only difference among the tested groups for the control group. However, we can affirm that the completion seems to influence the results of the resistance flexural discreetly in the TIG group. It can be concluded that the TIG method produces similar result to the laser and the brazing, what is clinical and important operationally.