Pulse-Frequency Characteristics in Bifurcation Problems

Generation of self-oscillations under unstable stationary states of nonlinear control systems, which may contain delay of complicated nature (the Andronov–Hopf bifurcation), and approximate design of self-oscillating states and their asymptotes are studied with the help of pulse-frequency characteristics of the linear component of a system.     

Formation and elimination of surface ion milling defects in cadmium telluride,zinc sulphide and zinc selenide

The nature of damage produced by low energy Ar⁺ ion and Ar atom milling in the II–VI semiconductors CdTe, ZnS and ZnSe is studied in detail by conventional and high resolution transmission electron microscopy. It is demonstrated that the damage consists of dense arrays of small dislocation loops near to each milled surface. When ion or atom milling of this type is used for thin specimen preparation prior to microscopy the loop arrays can seriously obscure images and so complicate their interpretation. This problem concerning the presence of artifactual defects can be greatly reduced by the use of reactive I⁺ ion milling for specimen thinning and, in the case of CdTe, spurious dislocation loop formation can be completely suppressed.     

Phosphorus Inputs to Lake Simcoe from 1990 to 2003: Declines in Tributary Loads and Observations on Lake Water Quality

Total phosphorus (TP) inputs to Lake Simcoe have led to hypolimnetic dissolved oxygen (DO) depletion and loss of cold water fish habitat. Since 1990, efforts have been made to reduce the total TP input to the lake below a defined target of 75 t/year, which was predicted to lead to reductions in spring TP concentration and improvements in end-of-summer hypolimnetic DO concentrations. The total TP load to the lake during the most recent period of record (1998/99-2003/04) ranged from 53 to 76 t/yr and averaged 67 t/yr, compared to an average of 114 t/yr estimated between 1990/91 and 1997/98 (range 85-157 t/yr). Reductions in TP loads from the catchment via tributary discharge (∼26 t) accounted for the majority of the decrease in total load between the two time periods. Total P concentrations decreased significantly in four out of six long-term monitored tributaries; however, concentrations in all six tributaries remain above the level recommended to avoid nuisance plant growth (30 μg/L). Although TP loads to the lake are currently below the target 75 t/yr, excessive growths of filamentous algae and macrophytes continue to be a problem in the nearshore zone. End-of-summer minimum hypolimnetic DO concentrations (average 4.3 mg/L, 1998/99-2003/04) remain substantially below the level (7 mg/L) that is considered protective of lake trout. Efforts to reduce TP loads to the lake therefore need to continue.     

A limit analysis of nonlinear elastic lateral displacements of thin-walled reinforced and prestressed beams

An incremental iterative process based on direct energy minimization is presented for a limit analysis of nonlinear elastic lateral displacements and twists of reinforced and prestressed beams. Problems encountered with the constitutive relations are discussed and two possible material models are presented.