An investigation of shock strengthening in a conical convergent channel

The behaviour of an initially plane, strong shock wave propagating into a conical convergence is investigated experimentally and theoretically. In the experiment a 10° half-angle cone is mounted on the end of a pressure-driven shock tube. Shock waves with initial Mach numbers varying from 6.0 to 10·2 are generated in argon a t a pressure of 1·5 Torr. During each run local shock velocities a t several positions along the cone axis are measured using a thin multi-crystal piezoelectric probe inserted from the vertex. This technique produces accurate velocity data for both the incident and reflected shock waves. In the corresponding analysis, a simplified characteristics method is used to obtain an approximate solution of the axisymmetric diffraction equations derived by Whitham (1959). Both the shock velocity measurements and the axisymmetric diffraction solution confirm that the incident shock behaviour is dominated by cyclic diffraction processes which originate at the entrance of the cone. Each diffraction cycle is characterized by Mach reflexion on the cone wall followed by Mach reflexion on the axis, These cycles evidently persist until the shock reaches the cone vertex, where the measured velocity has increased by as much as a factor of three. Real-gas effects, enhanced in the experiment by increasing the initial Mach number and decreasing the pressure, apparently alter the shock wave behaviour only in the region near the vertex. Velocity measurements for the reflected shock within the cone show that the shock velocity is nearly constant throughout most of the convergence length

Forecasting Pre-World War I Inflation: The Fisher Effect Revisited

We consider the puzzling behavior of interest rates and inflation in the United States and the United Kingdom between 1879 and 1913. A deflationary regime prior to 1896 was followed by an inflationary one from 1896 until the beginning of World War I; the average inflation rate was 3.8 percentage points higher in the second period than in the first. Yet nominal interest rates were no higher after 1896 than they had been before. This nonadjustment of nominal interest rates would be consistent with rational expectations if inflation were not forecastable, and indeed univariate tests show little sign of serial correlation in inflation. However, inflation was forecastable on the basis of lagged gold production. Investors' expectations of inflation should have risen by at least three percentage points in the United States between 1890 and 1910. We consider in an information processing context alternative ways of accounting for this failure of interest rates to adjust, for example the possible beliefs that increases in gold production might be transitory. We conclude that the failure of investors to exhibit foresight with regard to the shift in the trend inflation rate after 1896 is not persuasive evidence that investors were negligent or naive in processing information.

Cellular and extracellular siderophores of Aspergillus nidulans and Penicillium chrysogenum

Aspergillus nidulans and Penicillium chrysogenum produce specific cellular siderophores in addition to the well-known siderophores of the culture medium. Since this was found previously in Neurospora crassa, it is probably generally true for filamentous ascomycetes. The cellular siderophore of A. nidulans is ferricrocin; that of P. chrysogenum is ferrichrome. A. nidulans also contains triacetylfusigen, a siderophore without apparent biological activity. Conidia of both species lose siderophores at high salt concentrations and become siderophore dependent. This has also been found in N. crassa, where lowering of the water activity has been shown to be the causal factor. We used an assay procedure based on this dependency to reexamine the extracellular siderophores of these species. During rapid mycelial growth, both A. nidulans and P. chrysogenum produced two highly active, unidentified siderophores which were later replaced by a less active or inactive product--coprogen in the case of P. chrysogenum and triacetylfusigen in the case of A. nidulans. N. crassa secreted coprogen only. Fungal siderophore metabolism is varied and complex

Two source units in group guidance for the senior high school

Thesis (Ed.M.)--Boston University This item was digitized by the Internet Archive

A Hybrid Ragweed

During the summer of 1914 an unusual specimen of Ambrosia was noted which seems likely to have been a hybrid. The plant grew by the roadside on bottom land a few hundred yards from the Butler\u27s Landing Bridge a couple of miles north of Iowa City. It stood near the foot of the long hill beyond the bridge and near the margin of the lowland. The location in the edge of the grading was favorable in that its soil received the wash from the higher land. The plant was surrounded by various weeds and among them and nearby were several specimens of the supposed parent species, Ambrosia trifida L., and Ambrosia artemisiifobia L

Earth rotation and core topography

The NASA Geodynamics program has as one of its missions highly accurate monitoring of polar motion, including changes in length of day (LOD). These observations place fundamental constraints on processes occurring in the atmosphere, in the mantle, and in the core of the planet. Short-timescale (t less than or approx 1 yr) variations in LOD are mainly the result of interaction between the atmosphere and the solid earth, while variations in LOD on decade timescales result from the exchange of angular momentum between the mantle and the fluid core. One mechanism for this exchange of angular momentum is through topographic coupling between pressure variations associated with flow in the core interacting with topography at the core-mantel boundary (CMB). Work done under another NASA grant addressing the origin of long-wavelength geoid anomalies as well as evidence from seismology, resulted in several models of CMB topography. The purpose of work supported by NAG5-819 was to study further the problem of CMB topography, using geodesy, fluid mechanics, geomagnetics, and seismology. This is a final report