A mark-recapture experiment showed Australian bass to be sparsely distributed through sheltered parts of their habitat, but no significant differences in population density among major habitat categories were detected by catch-per-effort analyses. Total mortality, estimated from the catch curve, was low (Z = 0.28). Tabular and graphical calculations of annual production in a lagoon resulted in similar low estimates (0.84 g m-2 year-1), and a strikingly low P/B (annual production/biomass) ratio (0.19) results from the bass' catadromous life history. Populations of bass in the Sydney Basin showed declining recruitment, distribution restricted by impoundments, and increasing mortality attributable to exploitation and habitat damage during the period 1977-82. Estimates of initial cohort abundance indicated that recruitment and subsequent year-class strength are positively related to the level of flooding in the spawning months, but flooding is suppressed by dams. Population declines and continuing environmental degradation give cause for concern over the status of bass populations.

The age of M. novemaculeata from the Hawkesbury River and other streams in the Sydney Basin, New South Wales, was determined by using otoliths. Annuli were counted after simple sectioning of otoliths and intensification of the growth-check pattern by a two-stage burning technique. Age determinations were validated by the use of fish of known age; an error of + 1 year occurred in 17% of determinations. Ages of older fish (14+ to 18+ years) were not overestimated by more than 2-4 years, if at all. Progression of year-classes, and the annual nature of growth-check formation, further validated age determinations. Scale-reading seriously underestimated the age of bass. M. novemaculeata is a long-lived species. The oldest fish was 22+ years, and the mean age of the sample (n = 607) was 4.9 years. There are significant differences in longevity between the sexes; fewer males reach the older age-groups. About 10% of juvenlle fish deposited a growth-check in their otoliths during their upstream recruitment migration. The frequency of this 'migration check' was increased to 20% by capture and relocation of juveniles to isolated waters. A procedure was designed to identify migration checks in wild fish.

It is generally accepted that the presence of thoracic skeletal injuries has a predictive value for acute traumatic aortic tear (ATAT). The purpose of this study is to objectively assess the validity of that premise. The initial chest radiographs of 548 patients who underwent aortic angiography for suspected ATAT were reviewed for thoracic skeletal injuries. The incidence of thoracic skeletal injuries was compared between patients with and without angiographically confirmed ATAT. Rib fracture is the only thoracic skeletal injury whose incidence is statistically significantly higher in patients with ATAT (36 of 62, 58.1%) than in those without (207 of 486, 42.6%) (p = 0.0209). The positive predictive value of rib fractures in evaluating ATAT, however, is 14.8%, a rate similar to the incidence of ATAT at most trauma centers, and the specificity is 57.4%. The second most common finding in patients with ATAT, the absence of thoracic skeletal injury, is not statistically significantly different between patients with ATAT (24 of 62, 38.7%) and those without (220 of 486, 45.3%) (p = 0.3279). We conclude that (1) there is no clinically relevant correlation between thoracic skeletal injuries and ATAT, and (2) selection of patients requiring thoracic aortography must be based on appropriate mechanism of injury and radiographic evidence of mediastinal hematoma.

Access to the MHD second stability regime has been achieved in the ATF torsatron. Experimental p values (j3 0 < 3%, with fast ions contributing « j of the pressure at high p) are well above the theoretical transition value (p c « 1.3% for ideal modes) required to reach this regime. The relatively low p c results from operation with peaked pressure profiles. The measured magnetic fluctuations decrease with increasing /?, and the pressure profile broadens. This behavior is consistent with theoretical predictions for p self-stabilization of resistive interchange modes. PACS numbers: 52.55.Hc, 52.30.Jb, 52.35.PyThe ideal magnetohydrodynamic (MHD) second stability regime has attracted increasing attention in toroidal confinement fusion research 1 ' 2 because it offers the hope of operation at high p=2fiop/B 2 (the ratio of the plasma kinetic pressure to the magnetic pressure) with favorable confinement, which would improve the prospects for a viable D-T fusion reactor. This theory predicts that the changes in the internal magnetic surfaces (plasma axis shift and shape) caused by an increase in plasma pressure act to stabilize instabilities driven by unfavorable field-line curvature. l As a result, the plasma can become more stable as p increases ("/? self-stabilization"), with an accompanying reduction in the anomalous transport induced by the curvature-driven instabilities. In this Letter we describe experiments in which operation in the second stability regime has been achieved at relatively low p in a torsatron (a type of stellarator).Because of their external control of magnetic configuration and the absence of plasma current, stellarators are well suited for exploring the second stability regime and studying p self-stabilization. In stellarators with significant shear (dx/dr > 0, where % is the rotational transform and r is the plasma minor radius) the dominant instabilities are interchange modes. 3,4 These modes can be stabilized by the magnetic well produced by the outward magnetic axis shift at finite p (Shafranov shift), and this p self-stabilization effect can open a stable path to the second stability regime. 5 ' 6 The ATF torsatron design was optimized to explore this possibili- ty. 7ATF is an / -2, twelve-field-period torsatron with major radius /?o™2.10 m, average minor radius a *=0.27 m, magnetic field on axis 5o<2T, central rotational transform £o«0.3, and edge transform ^f l «l. For the profile assumed in the ATF design studies 6 the p selfstabilization effect should dominate at /?o«5%. Electron-beam field mapping in early 1988 revealed substantial magnetic islands (6 cm wide at the x ™ T surface and smaller at other rational surfaces). 8 These islands, now corrected, acted as a magnetic limiter and effectively reduced the plasma radius to r p *=*0.6d (increasing the effective aspect ratio A from 8 to 10) and the effective edge transform Xa » 0.5. This led to a large increase in the Shafranov shift id/accp^A/xl) that enhanced the self-stabilization effect and afforded the results reported here, which ...

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