The Characteristics and Structure of High Pressure (1-42 bars) Gas Tungsten Arcs

The last decade has seen a considerable growth in the exploitation of deep sea mineral reserves. Accompanying these developments has come the need for suitable underwater repair and uainten-nce techniques. one such technique involves the use of fusion welding processes in localised dry high pressure environments created around weldments. Pressure chambers at Cranfield have been employed to simulate this sitiu. ation. These have been used to investigate the influence of ambient pressure (1 to 45 bars) on gas-tungsten arcs. The study has been of a basic nature with emphasis on arc characteristics and arc structure. Special attention is given to the argon TIG arc although helium TIG arcs and constricted argon-tungsten arcs have also been examined. Arc characteristics are reported in terms of arc appearance and modes, electrical characteristics and weld bead studies. The investigation of arc structure is concerned with gaining an understanding of observed characteristics. This has involved experimental and theoretical developments. Experimental techniques used include, electrostatic probes, calorimetry and the measurement of total power radiated from an arc. Models developed here have successfully explained many of the experimental findings and special emphasis has been directed at understanding gas flow in the column and arc stability. Much of the work included in this thesis has implications for the development of underwater welding procedures. Results presented should also contribute to gaining a better understanding of arcs operating under normal ambient conditions. However, these aspects are not discussed in any detail as the main emphasis has been placed on documenting and explaining the influence of pressure on gas-tungsten arcs

The effect of voluntary arm abduction on balance recovery following multidirectional stance perturbations

The goal of this study was to investigate how voluntarily abducting one arm, 90° at onset of a rotational perturbation of the support surface, influences the recovery of upright stance. Young adults were tested under four stance conditions: abducting one arm to the horizontal only (AO); perturbation of stance using a support surface rotation only (PO); combined support surface rotation and abduction of the downhill arm, ipsilateral to tilt (IPS); and fourth abduction of the uphill, contralateral arm (CON). Simultaneous auditory and visual trigger cues were used for arm raising. Perturbations consisted of six directions of combined support surface roll and pitch rotation (7.5° and 60°/s). Outcome measures were whole body centre of mass (COM) movements and body segment angular displacements recorded with a motion analysis system, as well as leg, trunk, and arm EMG responses. Arm raises contralateral and ipsilateral to the direction of support surface roll were more rapid than in the AO condition and significantly reduced or increased, respectively, COM lateral displacements relative to the PO condition. The changes in COM displacements and velocities during combined CON arm raise and perturbation were greater than expected from the sum of displacements for AO and PO conditions alone, but less for the IPS condition. Arm raising increased trunk roll in a direction opposite arm raising was more than for the AO and PO conditions. Robust effects were also observed for hip abduction but not for leg flexion. Early balance correcting activity was enhanced on the side opposite arm raising and later stabilising activity reduced bilaterally in lower trunk muscles compared to summed activity for the AO and PO conditions. Similar effects were observed in gluteus medius muscles but effects were weak in ankle muscles. EMG onsets in muscles of the raised arm were earlier than in the AO conditions. We conclude that triggered arm abduction, contralateral to the direction of support surface rotation, had significant stabilization benefits for young adults and ipsilateral arm movements had destabilizing effects. The arm raises could be simultaneously executed with balance corrections. These results provide insights into the integration of balance corrections and voluntary commands into one automatic reaction that may be useful in training fall avoidanc

The influence of artificially increased hip and trunk stiffness on balance control in man

Lightweight corsets were used to produce mid-body stiffening, rendering the hip and trunk joints practically inflexible. To examine the effect of this artificially increased stiffness on balance control, we perturbed the upright stance of young subjects (20-34years of age) while they wore one of two types of corset or no corset at all. One type, the "half-corset”, only increased hip stiffness, and the other, the "full-corset”, increased stiffness of the hips and trunk. The perturbations consisted of combined roll and pitch rotations of the support surface (7.5deg, 60deg/s) in one of six different directions. Outcome measures were biomechanical responses of the legs, trunk, arms and head, and electromyographic (EMG) responses from leg, trunk, and upper arm muscles. With the full-corset, a decrease in forward stabilising trunk pitch rotation compared to the no-corset condition occurred for backward pitch tilts of the support surface. In contrast, the half-corset condition yielded increased forward trunk motion. Trunk backward pitch motion after forwards support-surface perturbations was the same for all corset conditions. Ankle torques and lower leg angle changes in the pitch direction were decreased for both corset conditions for forward pitch tilts of the support-surface but unaltered for backward tilts. Changes in trunk roll motion with increased stiffness were profound. After onset of a roll support-surface perturbation, the trunk rolled in the opposite direction to the support-surface tilt for the no-corset and half-corset conditions, but in the same direction as the tilt for the full-corset condition. Initial head roll angular accelerations (at 100ms) were larger for the full-corset condition but in the same direction (opposite platform tilt) for all conditions. Arm roll movements were initially in the same direction as trunk movements, and were followed by large compensatory arm movements only for the full-corset condition. Leg muscle (soleus, peroneus longus, but not tibialis anterior) balance-correcting responses were reduced for roll and pitch tilts under both corset conditions. Responses in paraspinals were also reduced. These results indicate that young healthy normals cannot rapidly modify movement strategies sufficiently to account for changes in link flexibility following increases in hip and trunk stiffness. The changes in leg and trunk muscle responses failed to achieve a normal roll or pitch trunk end position at 700ms (except for forward tilt rotations), even though head accelerations and trunk joint proprioception seemed to provide information on changed trunk movement profiles over the first 300ms following the perturbation. The major adaptation to stiffness involved increased use of arm movements to regain stability. The major differences in trunk motion for the no-corset, half-corset and full-corset conditions support the concept of a multi-link pendulum with different control dynamics in the pitch and roll planes as a model of human stance. Stiffening of the hip and trunk increases the likelihood of a loss of balance laterally and/or backwards. Thus, these results may have implications for the elderly and others, with and without disease states, who stiffen for a variety of reason

Control of roll and pitch motion during multi-directional balance perturbations

Does the central nervous system (CNS) independently control roll and pitch movements of the human body during balance corrections? To help provide an answer to this question, we perturbed the balance of 16 young healthy subjects using multi-directional rotations of the support surface. All rotations had pitch and roll components, for which either the roll (DR) or the pitch (DP) component were delayed by 150ms or not at all (ND). The outcome measures were the biomechanical responses of the body and surface EMG activity of several muscles. Across all perturbation directions, DR caused equally delayed shifts (150ms) in peak lateral centre of mass (COM) velocity. Across directions, DP did not cause equally delayed shifts in anterior-posterior COM velocity. After 300ms however, the vector direction of COM velocity was similar to the ND directions. Trunk, arm and knee joint rotations followed this roll compared to pitch pattern, but were different from ND rotation synergies after 300ms, suggesting an intersegmental compensation for the delay effects. Balance correcting responses of muscles demonstrated both roll and pitch directed components regardless of axial alignment. We categorised muscles into three groups: pitch oriented, roll oriented and mixed based on their responses to DR and DP. Lower leg muscles were pitch oriented, trunk muscles were roll oriented, and knee and arm muscles were mixed. The results of this study suggest that roll, but not pitch components, of balance correcting movement strategies and muscle synergies are separately programmed by the CNS. Reliance on differentially activated arm and knee muscles to correct roll perturbations reveals a dependence of the pitch response on that of roll, possibly due to biomechanical constraints, and accounts for the failure of DP to be transmitted equally in time across all limbs segments. Thus it appears the CNS preferentially programs the roll response of the body and then adjusts the pitch response accordingl

The effect of voluntary lateral trunk bending on balance recovery following multi-directional stance perturbations

Stabilising shifts of the centre of mass (COM) are observed during balance recovery when subjects simultaneously execute voluntary unilateral knee flexion or unilateral arm raising. Here, we examined whether voluntary lateral trunk bending provided more beneficial stabilising effects, and how motor programs of balance corrections are combined with those of the focal voluntary action. The upright balance of 24 healthy young subjects (19-33years of age) was perturbed using multi-directional rotations of the support-surface. The perturbations consisted of combined pitch and roll rotations (7.5° and 60°/s) presented randomly in six different directions. Three conditions were tested: perturbation of stance only (PO); combined balance perturbation and cued uphill bending of the trunk (CONT); and combined perturbation and cued downhill bending of the trunk (IPS). For comparison, subjects were required to perform trunk bending alone (TO). Outcome measures were biomechanical responses and surface EMG activity of several muscles. Calculated predicted outcomes (PO+TO) were compared with combined measures (CONT or IPS). CONT trunk bending uphill showed two phases of benefit in balance recovery for laterally but, in contrast to voluntary knee bending, not for posterior directed components of the perturbations. IPS trunk bending had negative effects on balance. Early balance correcting muscle responses were marginally greater than PO responses. Prominent secondary balance correcting responses, having a similar timing as voluntary responses observed under TO conditions, were seen under CONT only in trunk muscles. These, and later stabilising, responses had amplitudes as expected from PO+TO conditions being significantly greater than PO responses. The ability with which different muscle synergies for balance corrections and voluntary trunk bending were integrated into one indicates a flexible adjustment of the CNS programs to the demands of both task

The Global Research Agenda on Volunteering for Peace and Development

This brief discusses the global research agenda on volunteering in activities designed to advance peace and foster development, reviewing the agenda’s history, objectives, and priorities. It also revisits key areas of research progress made from 2015 through 2018 and discusses the resources needed to further advance this agenda through 2025

A study of the behaviour of emulsion explosives

This study investigated the formulation and characterisation of emulsion explosives. This included the manufacture of more than 120kg of emulsion explosive of which around 105kg was used on the explosive ordnance range in over 350 individual firings. For each emulsion composition, an average of eight firings was undertaken with which to substantiate the explosive performance data. The formulation was varied to determine the effects of water content upon the physical characteristics of the emulsion. These physical effects included thermal conductivity, particle size, viscosity and the explosive performance of the emulsion. In respect of explosive performance, microballoons were added to sensitise the emulsion and the proportions of microballoons added were altered to look at their effect on velocity of detonation, sensitivity and the brisance of the emulsions. Emulsion explosives are commonly referred, in literature, as Type 11 non-ideal explosives. This is due to their non-linear behaviour with respect to the variation of velocity of detonation with density. Traditionally, when an emulsion explosive was commercially manufactured, the water content has been kept at a minimum (12-17%). This was accepted as the way to achieve the best explosive performance, based upon the belief that an emulsion with the highest concentration of active ingredients, ammonium nitrate and oil, would give the best explosive performance. This study examined a wider range of emulsion explosive water contents than has been previously studied, from 12% to 35% water. It was found, during this study, that higher water content emulsions, specifically 25% water, had a marked increase in explosive performance. The highest velocity of detonation recorded was in a 39mm diameter tube, at 25% water content with 3% microballoons, was 5558ms-1. This was some 15% higher than any other VOD recorded in this study. The high velocity of detonation, at 25% water content, was one of a number of physical characteristics in which this water content varied from the other emulsion water contents. This study endeavored to show that emulsion explosives could exhibit two differing types of explosive reaction, thermal explosion and grain burning. This was based on the velocity of detonation and plate dent data, both of which indicated that there was a change in reaction with water content. Emulsion explosives, with a high water and high microballoon content, exhibited a thermal explosion type reaction. They exhibited Type I ideal explosive behaviour, with increasing velocity of detonation with density. Lower water content emulsion explosives, displayed the more commonly expected Type 11 non-ideal behaviour and reacted in a grain burning type detonation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The influence of knee rigidity on balance corrections: a comparison with responses of cerebellar ataxia patients

Knee rigidity due to aging or disease is associated with falls. A causal relationship between instability and knee rigidity has not been established. Here, we examined whether insufficient knee movement due to knee rigidity could underlie poor balance control in patients. We addressed this by examining the effect of artificially "locking” the knees on balance control in 18 healthy subjects, tested with and without individually fitted knee casts on both legs. Subjects were exposed to sudden rotations of a support surface in six different directions. The primary outcome measure was body centre of mass (COM) movement, and secondary outcome measures included biomechanical responses of the legs, pelvis and trunk. Knee casts caused increased backward COM movement for backward perturbations and decreased vertical COM movement for forward perturbations, and caused little change in lateral COM movement. At the ankles, dorsiflexion was reduced for backward perturbations. With knee casts, there was less uphill hip flexion and more downhill hip flexion. A major difference with knee casts was a reversed pelvis pitch movement and an increased forward trunk motion. These alterations in pitch movement strategies and COM displacements were similar to those we have observed previously in patients with knee rigidity, specifically those with spinocerebellar ataxia (SCA). Pelvis roll and uphill arm abduction were also increased with the casts. This roll movement strategy and minor changes in lateral COM movement were not similar to observations in patients. We conclude that artificial knee rigidity increases instability, as reflected by greater posterior COM displacement following support surface tilts. Healthy controls with knee casts used a pitch movement strategy similar to that of SCA patients to offset their lack of knee movement in regaining balance following multidirectional perturbations. This similarity suggests that reduced knee movements due to knee rigidity may contribute to sagittal plane postural instability in SCA patients and possibly in other patient groups. However in the roll plane, healthy controls rapidly compensate by adjusting arm movements and hip flexion to offset the effects of knee rigidit

Trunk Sway Measures of Postural Stability During Clinical Balance Tests: Effects of Age

Background. The major disadvantage of current clinical tests that screen for balance disorders is a reliance on an examiner's subjective assessment of equilibrium control. To overcome this disadvantage we investigated, using quantified measures of trunk sway, age-related differences of normal subjects for commonly used clinical balance tests. Methods. Three age groups were tested: young (15-25 years; n = 48), middle-aged (45-55 years; n = 50) and elderly (65-75 years; n = 49). Each subject performed a series of fourteen tasks similar to those included in the Tinetti and Clinical Test of Sensory Interaction in Balance protocols. The test battery comprised stance and gait tasks performed under normal, altered visual (eyes closed), and altered proprioceptive (foam support surface) conditions. Quantification of trunk sway was performed using a system that measured trunk angular velocity and position in the roll (lateral) and pitch (fore-aft) planes at the level of the lower back. Ranges of sway amplitude and velocity were examined for age-differences with ANOVA techniques. Results. A comparison between age groups showed several differences. Elderly subjects were distinguished from both middle-aged and young subjects by the range of trunk angular sway and angular velocity because both were greater in roll and pitch planes for stance and stance-related tasks (tandem walking). The most significant age group differences (F = 30, p < .0001) were found for standing on one leg on a normal floor or on a foam support surface with eyes open. Next in significance was walking eight tandem steps on a normal floor (F = 13, p < .0001). For gait tasks, such as walking five steps while rotating or pitching the head or with eyes closed, pitch and roll velocity ranges were influenced by age with middle-aged subjects showing the smallest ranges followed by elderly subjects and then young subjects (F = 12, p < .0001). Walking over a set of low barriers also yielded significant differences between age groups for duration and angular sway. In contrast, task duration was the only variable significantly influenced when walking up and down a set of stairs. An interesting finding for all tasks was the different spread of values for each population. Population distributions were skewed for all ages and broadened with age. Conclusions. Accurate measurement of trunk angular sway during stance and gait tasks provides a simple way of reliably measuring changes in balance stability with age and could prove useful when screening for balance disorders of those prone to fal