Determinants of oxygen uptake. Implications for exercise testing

For exercise modalities such as cycling which recruit a substantial muscle mass, muscle oxygen uptake (VO2) is the primary determinant of pulmonary VO2. Indeed, the kinetic complexities of pulmonary VO2 associated with exercise onset and the non-steady state of heavy (> lactate threshold) and severe [> asymptote of power-time relationship for high intensity exercise (W)] exercise reproduce with close temporal and quantitative fidelity those occurring across the exercising muscles. For moderate (< lactate threshold) exercise and also rapidly incremental work tests, pulmonary (and muscle) VO2 increases as a linear function of work rate (approximately equal to 9 to 11 ml O2/W/min) in accordance with theoretical determinations of muscle efficiency (approximately equal to 30%). In contrast, for constant load exercise performed in the heavy and severe domains, a slow component of the VO2 response is manifest and pulmonary and muscle VO2 increase as a function of time as well as work rate beyond the initial transient associated with exercise onset. In these instances, muscle efficiency is reduced as the VO2 cost per unit of work becomes elevated, and in the severe domain, this VO2 slow component drives VO2 to its maximum and fatigue ensues rapidly. At pulmonary maximum oxygen uptake (VO2max) during cycling, the maximal cardiac output places a low limiting ceiling on peak muscle blood flow, O2 delivery and thus muscle VO2. However, when the exercise is designed to recruit a smaller muscle mass (e.g. leg extensors, 2 to 3kg), mass-specific muscle blood flow and VO2 at maximal exercise are 2 to 3 times higher than during conventional cycling. consequently, for any exercise which recruits more than approximately equal to 5 to 6kg of muscle at pulmonary VO2max, there exists a mitochondrial or VO2 reserve capacity within the exercising muscles which cannot be accessed due to oxygen delivery limitations. The implications of these latter findings relate to the design of exercise tests. Specifically, if the purpose of exercise testing is to evaluate the oxidative capacity of a small muscle mass (< 5 to 6kg), the testing procedure should be designed to restrict the exercise to those muscles so that a central (cardiac output, muscle O2 delivery) limitation is not invoked. It must be appreciated that exercise which recruits a greater muscle mass will not stress the maximum mass-specific muscle blood flow and VO2 but rather the integration of central (cardiorespiratory) and peripheral (muscle O2 diffusing capacity) limitations.     

Observations of the columnar-to-equiaxed transition in stainless steels

Observations are reported for the columnar-to-equiaxed transition (CET) in stainless steel bars which have been solidified slowly and progressively in a horizontal configuration. For ferritic, austenitic, and ferritic/austenitic stainless steels containing more than 0.085 wt pct carbon, CETs occur at about the same distance from the start of solidification at a given growth rate. With increasing growth rates, the transition occurs closer to the start of solidification. At low carbon levels, near 0.02 wt pct carbon, the ferritic/austenitic steel is entirely columnar, in most cases. Adding nickel to the ferritic/austenitic steel, which makes the leading phase austenitic, produces a CET with small equiaxed grains. This suggests that different particles which are effective with austenitic growth become operative as nucleants. The transition from a columnar to an equiaxed structure occurs abruptly across the diameter of the sample. There is extensive fluid flow in the bulk melt, which produces shallow temperature gradients in the melt prior to the onset of solidification. The bulk melt flow does not appear to interact significantly with the melt in the interdendritic region or the melt immediately ahead of this region. The width of the solid/liquid region in the present experiments is observed to be between 10 and 20 mm, depending on the growth velocity and the distance from the start of solidification.     

Influence of the MexAB-OprM multidrug efflux system on quorum sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa nalB mutants which hyperexpress the MexAB-OprM multidrug efflux system produce reduced levels of several extracellular virulence factors known to be regulated by quorum sensing. Such mutants also produce less acylated homoserine lactone autoinducer PAI-1, consistent with an observed reduction in lasI expression. These data suggest that PAI-1 is a substrate for MexAB-OprM, and its resulting exclusion from cells hyperexpressing MexAB-OprM limits PAI-1-dependent activation of lasI and the virulence genes.     

Development of an instrument to assess stress levels and quality of life in children with asthma

The purpose of this study was to develop and evaluate a new instrument, About My Asthma (AMA), to assess stressors affecting quality of life in children with asthma. The AMA is a 55-item, 4-point Likert-type scale. Concurrent validity was established by comparing the AMA with the Pediatric Asthma Quality of Life Questionnaire (PAQLQ). Increased levels of stress measured by the AMA correlated with a decreased quality of life measured by the PAQLQ. We conclude that the AMA is a valid and reliable instrument to measure the quantity and type of stressors experienced by children who have asthma.     

On the precipitation-hardening behavior of the Al-Mg-Si-Cu alloy AA6111

The precipitation-hardening behavior of aluminum alloy AA6111 during artificial aging and the influence of prior natural aging on the aging behavior were investigated. The evolution of microstructure was studied using quantitative transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The evolution of the relative volume fraction of precipitates for the solution-treated alloy was determined using isothermal calorimetry and a new analysis based on the DSC technique. Quantitative TEM was also used to obtain the rate of precipitation of microscopically resolvable phases during aging at 180 °C. Three types of precipitates, i.e., unresolved Guinier-Preston (GP) zones, β″, and Q′, were found to form during aging at 180 °C. The evolution of yield strength was related to the evolution of microstructure. It was found that the high hardening rate during artificial aging for the solution-treated alloy is due to the rapid precipitation of the β″ phase. Natural aging prior to artificial aging was found to decrease the rate of precipitation of β″. The slow hardening rate for the naturally aged alloy was attributed to the slower nucleation and growth of β″ phase.     

The application of simulators in teaching digital electronics

Digital simulators offer many potential benefits in the teaching of introductory courses in digital electronics. This paper sets the scene for their application in contemporary higher education and suggests possible areas where they can be applied. The requirements of the particular educational simulator software package employed are discussed and examples of practical exercises used with students are presented. The advantages and disadvantages of the simulator approach are compared with conventional courses. Conclusions are drawn based upon observations from practical implementation experience and progression to professional level digital design tools is considered     

PCB glass-fibre laminates: Thermal conductivity measurements and their effect on simulation

Accurate values of thermal conductivity are required for the simulation of temperature phenomena in electronic circuits. This paper presents the results of measurements carried out to determine the thermal conductivity along and normal to the plane of fibre glass laminates used in the manufacture of printed circuit boards. It has been found that the reinforced fibre-glass substrates used in PCBs are strongly anisotropic with the conductivity normal to the boards being much smaller than tangential to it. The test samples were type FR4 epoxy/glass laminates. An experiment has been designed which determines the thermal conductivity in-the-plane of the laminates by matching the measured temperature distribution along a heated specimen with a finite difference solution. An electrically heated Lees’ disc apparatus is also used to measure the thermal conductivity of these boards in a direction normal to their plane. The samples tested yielded values of 0.343 W/mK and 1.059 W/mK for thermal conductivity through and along the plane of the boards, respectively.     

Convection heat transfer from a hybrid circuit

Accurate values of heat transfer coefficient are needed for simulation of the thermal characteristics of a thick film resistor. In this paper, the results of an investigation are presented where an optical technique is used to study the convection plumes from a horizontally positioned hybrid resistor package. The observations have shown that simplifying approximations to the convection coefficients may be made in thermal analysis of such devices. Using these approximations and an optimization technique, values have been estimated for the coefficients.     

Aggressive management of HELLP syndrome and eclampsia

The nursing care of women critically ill during pregnancy is an ever-changing specialty that presents unique clinical problems and issues. The woman and the fetus can be profoundly affected by the hypertensive disorders of pregnancy. The underlying pathology must be identified in relation to its effects on the pregnancy, the effects of the pregnancy on the disease, and the implications for the woman and the fetus. Severe preeclampsia, the HELLP syndrome (hemolysis, elevated liver enzymes, and low platelets), and eclampsia present such challenges and management problems. This article discusses the pathophysiology and management implications of severe preeclampsia, the HELLP syndrome, and eclampsia.     

Fragmentation in thermal explosionsFragmentation dans les explosions thermiquesZerfallserscheinungen bei thermischen explosionenПpoцecc диcпepгиpoвaния пpи тeплoвыч взpывaч

A series of experiments involving explosions between molten tin and water is described. The results, together with information from other work, indicate that thermal explosions usually involve several distinct interactions in the same mass of material, and that each interaction forms a bubble containing some vapour whose collapse initiates the next interaction. It is thus shown that a small disturbance can escalate by successive growth and collapse cycles into a large explosion.It is postulated that vapour collapse is the main cause of dispersion in many thermal explosions. A possible mechanism for this is that during collapse a high-speed liquid jet is formed (as observed in cavitation damage studies), which penetrates and disperses in the molten material. It is shown that the jet penetration hypothesis can account for both the timescales and energy transfer rates characteristic of thermal explosions, including those in shock tube geometry.