Design of a Rotary Vane Compressor by Genetic Algorithms

The genetic optimization algorithm method is used to design rotary compressors with sliding vanes. After the air properties, volume segment, compression power, loadings and stresses of vanes, friction forces and power loss are calculated, the objective function of the maximum efficiency and the constrained conditions can be derived and integrated. Using the ambient air conditions and the properties of Vespel, the effects of the mutation rate, crossover rate and population size of the genetic algorithm on the design parameters are studied. These design parameters include the major axis length, minor axis length, angular locations of inlet and outlet ports and rotational speed of the compressor, the thickness, depth and height of vanes, and the polytropic exponent. The efficiency of the compressor increases to 0.55 compared with the value of 0.4 obtained from the existing data.

Effect of lung volume on forced expiratory flows during rapid thoracoabdominal compression in infants

The rapid thoracoabdominal compression (RTC) technique is commonly used in pulmonary function laboratories to assess flow-volume relationships in infants unable to produce a voluntary forced expiration maneuver. This technique produces forced expiratory flows over only a small lung volume segment (i.e., tidal volume). It has been argued that the RTC technique should be modified to measure flow-volume relationships over a larger portion of the vital capacity range to imitate the voluntary maximal forced expiratory maneuver obtained in older children and adults. We examined the effect of volume history on forced expiratory flows by generating forced expiratory flow-volume curves by RTC from well-defined inspiratory volumes delineated by inspiratory pressures of 10, 20, 30, and 40 cmH2O down to residual volume (i.e., the reference volume) in seven intubated and anesthetized infants with normal lungs [age 8.0 +/- 2.0 (SE) mo, weight 6.7 +/- 0.6 kg]. We compared maximal expiratory flows at isovolume points (25 and 10% of forced vital capacity) and found no significant differences in maximal isovolume flow rates measured from the different lung volumes. We conclude that there is no obvious need to initiate RTC from higher lung volumes if the technique is used for flow comparisons. However, compared with measurements of maximal flows at functional residual capacity by RTC from end-tidal inspiration, the initiation of RTC from a defined and reproducible inspiratory level appears to decrease the intrasubject variability of the maximal expiratory flows at low lung volumes.

A Spectroscopic Search for Duplicity Among a Complete Sample of Northern Galactic Wolf-Rayet Stars

We have analysed new spectroscopic observations of 22 population I WR stars in a sample defined by b<12.5 mag, 18h<α<6h, δ > −30°. This completes the search for orbital duplicity among all of the 30 pop I WR stars contained within these limits. We thus have an unbiased data base in a volume segment bounded by a distance of 3–4 kpc for WNE and WC stars , and 4–5 kpc for WNL stars Although more observations are still needed in some cases, we have found several new binary systems. Some of these are low-amplitude, single-line binaries, often with runaway velocities and/or large separations from the galactic plane. We consider them to be candidates for a WR + collapsar stage, as originally predicted by Tutukov and Yungelson (1973) and de Loore and De Grève (1975).

Edema affects intra-alveolar fluid pressures and interdependence in dog lungs

The pressures in occluded, fluid-filled segments of lung were measured in closed-chest supine dogs ventilated with positive pressure at a constant tidal volume. Segment fluid pressures decreased in response to lung inflation and were used with esophageal and airway pressures to calculate an index of bronchiolar-parenchymal interdependence. Animals were subjected to three sequential 5% body wt infusions of Tyrode's solution followed by a 20- to 30 min-recovery period after each infusion. The interdependence index decreased significantly following each infusion, with infusions as small as 1% body wt producing a detectable decrease. The mean pressures in the Tyrode's solution-filled segments generally increased in response to the infusions, but the time course of the response was variable. The base-line pressure in Tyrode's solution-filled segments was -4.8 +/- 2.4 cmH2O. This increased to -1.1 +/- 2.7 cmH2O after a total of 15% body wt had been infused. At the same time, extravascular lung water increased by approximately 17%. Thus negative collapse pressures in the occluded segments were opposed by mechanical stresses transmitted through alveolar wall attachments. This counterbalancing stress was consistently reduced by both increased tissue hydration and increased pulmonary vascular pressure.