Analytical and experimental investigation on vibrating rectangular plates with two opposite free edges and internal supports while the remaining are elastically restrained against rotation

This paper deals with the determination of an approximate fundamental frequency equation for a rectangular plate with two edges (y = 0, b) elastically restrained against rotation while the edges x=0, a are free but internal supports parallel to the free edges are present in the structural system. The algorithmic procedure can be easily implemented on a micro computer or even a hand, programmable calculator.Good engineering agreement with experimental results is shown to exist in the case of a plate with edges y=0,b rigidly clamped.     

A Pull-Up Shallow Water Seismometer

An inexpensive Pull-Up Shallow Water Seismometer (PUSS) has been designed and built to conduct long range seismic refraction experiments in the North Sea and the continental shelf around Britain, with the particular goal of studying the crustal and lithospheric structure under the epeirogenic basin of the North Sea. Signals from a gimbal-mounted 3-component geophone and a hydrophone are frequency modulated and mixed with clock and flutter correction signals before being recorded on a standard speed cassette tape recorder, with one hour of recording time. A 100 hour programmable timer allows the interval between the time of reset of the clock and each shot window of optional 5 or 10 min duration, to be preselected. The PUSS is launched and recovered using a pull-up technique originally developed for current meters. The replay system is also described.In May 1976 sea trials of 5 PUSSes were conducted along a 200 km refraction line in the North Sea. The encouraging performance of the equipment resulted in the decision to build a further 10 units and to proceed with a 400 km refraction line planned for the summer of 1977.     

An experimental facility for testing loaded structures in a high hydrostatic pressure environment and an application to axially loaded columns

An experimental facility is described for the testing of structures under a combined axial load and hydrostatic pressure load. This facility was used to determine the effects of hydrostatic pressure (up to 6000 psi) on the load-carrying capacity of slender metal columns. There appeared to be no significant effect in this case.     

Maternal transfer of bioactive polychlorinated aromatic hydrocarbons in spawning chinook salmon (Oncorhynchus tschawytscha)

The biological potency (relative to 2,3,7,8-tetrachlorodibenzo-p-dioxin. TCDD) of planar polychlorinated aromatic hydrocarbons (PCHs) in extracts of eggs and flesh from spawning female chinook salmon (Oncorhynchus tschawytscha) from Lake Michigan was determined by measuring the induction of 7-ethoxyresorufin O-deethylase activity in H-4-II-E rat hepatoma cells. TCDD-equivalents in flesh and egg samples ranged from 0 to 115·8 pg/g, and were approximately 5-fold greater in eggs than in flesh. These results suggest that the maternal transfer of PCHs may play a role in determining the reproductive success of Lake Michigan chinook salmon.     

Thickening of the oceanic layer in the Pacific Ocean

A statistical analysis of published seismic refraction results in the Pacific Ocean confirms the existence of a progressive thickening of the oceanic layer with age, following an inverse exponential law. There is no strong indication in the Pacific data of an increase in the thickness of layer 2 with decreasing spreading rate.Contribution No. 93 of the Département Scientifique of the Centre Océanologique de Bretagne, B.P. 337, 29200, Brest, France.     

The method of calculating the current velocity's verticla component in problems of fluid dynamics in reservoirs

A new algorithm for calculating the vertical velocity is suggested. Horizontal current velocity components are expressed through level inclination and wind/temperature forcing. The acquired relations are given in the difference form, with the accuracy being sufficiently high. The algorithm is tested using cases where a numerical solution is matched up with an exact one. The derived data are subsequently analysed. Translated by Vladimir A. Puchkin.     

Effects of organic pollutants on methanogenesis,sulfate reduction and carbon dioxide evolution in salt marsh sediments

Anaerobic salt marsh sediments were amended with a variety of organic pollutants and the effects on methanogenesis, sulfate reduction and carbon dioxide evolution were examined. Addition of 1000 μg g^?1 (dry weight sediment) Arochlor 1221, lindane, endrin, benzene and phenanthrene resulted in no significant effects on the activities studied. Methanogenesis was inhibited by 1000 μg g^?1toxaphene, PCP, chlordane, naphthalene, DDT, Kepone and heptachlor and by 100 μg g^?1 PCP and toxaphene. At 1000 μg g^?1 naphthalene and toxaphene and 100 μg g^?1 PCP, a period of initial inhibition of methanogenesis was followed by stimulation relative to controls. Arochlor 1254 (1000 μg g^?1) and Temik (500 and 10 μg g^?1) stimulated methanogenesis from the outset. Temik at 500 μg g^?1 gave the greatest stimulation of methanogenesis (900% of controls) of any of the compounds studied. Sulfate reduction was inhibited by 1000 μg g^?1 PCP, toxaphene, naphthalene and chlordane and by 500 μg g^?1 atrazine and 100 μg g^?1 heptachlor. Sustained inhibition of sulfate reduction by naphthalene, toxaphene and PCP may have contributed to the stimulation of methanogenesis. Carbon dioxide evolution was not significantly affected by most of the compounds studied except for 100 μg g^?1 PCP and 1000 μg g^?1 aphthalene, each of which gave significant inhibition in only one of three experiments.Concentrations of individual organic pollutants required to cause observable effects were high. It is concluded that, except for highly polluted sediments, methanogenesis, sulfate reduction and CO₂ evolution would not be affected by the compounds studied here at concentrations typically found in the environment.     

Evidence for slope instability and current-induced sediment transport,the RMSTitanic wreck search area,Newfoundland rise

The first map of the sea bed morphology and sedimentary features within the RMSTitanic search area is proposed from the interpretation of SAR side-scan sonar images. Downslope sedimentary features such as erosional furrows and crown scarps constitute a 7 km wide instability corridor. A large field (15 km²) of asymmetrical sediment waves indicating a downslope transport is identified. Current-induced features corresponding to associated sand ribbons and barchan dunes resulting from the Western Boundary Undercurrent action are mapped. The morphology of theTitanic Canyon is also precised from the SAR images. Finally, the origin of the sea bed features is discussed in an attempt to link each bed form to a sedimentary process.     

Waveform Shaping of Sonar Transducers for Improving the Vertical Resolution in Sub-bottom Sediments Profiling

Vertical resolution is of fundamental importance in sonar exploration and is directly related to the duration of the acoustic pulse generated by the transducer. The shorter the radiated pulse, the higher the vertical resolution. Many sub-bottom profiling sonar systems use piezoelectric transducers because they are reversible and well understood. Piezoelectric projectors are normally resonant transducers, which are intrinsically narrowband. A piezoelectric transducer is usually driven by a tone-burst. However, it is possible to use Fourier techniques to find a pre-compensated electrical driving function so that the transducer radiates a prescribed wider band acoustic waveform. This technique can be applied to synthesize zero-phase cosine-magnitude, Gaussian, and bionic pulses, with a conventional sandwich transducer. Zero-phase cosine-magnitude waveforms provide minimum length pulses (and therefore maximum resolution) within a prescribed frequency band.The aim of this paper is to illustrate the synthesis of wideband acoustic pulses using an underwater piezoelectric projector. The conventional acoustic waveform radiated when a Tonpiltz transducer is transiently excited using a “click” and allows its frequency response function to be measured. This function is used to design the electrical signal which then drives the transducer so that it radiates the shortest pulse compatible with its mechanical response. The significant resolution enhancement of the waveform shaping process is illustrated by its application to a sediment wedge model.