Sea surface shape derivation above the seismic streamer

The rough sea surface causes perturbations in the seismic data that can be significant for time‐lapse studies. The perturbations arise because the reflection response of the non‐flat sea perturbs the seismic wavelet. In order to remove these perturbations from the received seismic data, special deconvolution methods can be used, but these methods require, as input, the time varying wave elevation above each hydrophone in the streamer. In addition, the vertical displacement of the streamer itself must also be known at the position of each hydrophone and at all times. This information is not available in conventional seismic acquisition. However, it can be obtained from the hydrophone measurements provided that the hydrophones are recorded individually (not grouped), that the recording bandwidth is extended down to 0.05 Hz and that data are recorded without gaps between the shot records. The sea surface elevation, and also the wave‐induced vertical displacement of the streamer, can be determined from the time‐varying pressure that the sea waves cause in the hydrophone measurements. When this was done experimentally, using a single sensor seismic streamer without a conventional low cut filter, the wave induced pressure variations were easily detected. The inversion of these experimental data gives results for the sea surface elevation that are consistent with the weather and sea state at the time of acquisition. A high tension approximation allows a simplified solution of the equations that does not demand a knowledge of the streamer tension. However, best results at the tail end of the streamer are obtained using the general equation.     

The Parkes Southern Pulsar Survey — II. Final results and population analysis

A survey of the entire southern sky for millisecond and low-luminosity pulsars using the ATNF Parkes radio telescope has now been completed. The survey detected 298 pulsars, of which 101 were previously unknown. The new pulsars include 17 millisecond pulsars. This is the largest sample of both normal and millisecond pulsars detected in any survey. Combining our sample with other recent surveys in the Northern Hemisphere, we present a statistical study of the populations of both normal and millisecond pulsars. We find that the improved statistics allow us to estimate the number and birth-rate of both types of pulsar down to a 400-MHz luminosity limit of 1 mJy kpc². The local surface densities of potentially observable normal pulsars and millisecond pulsars are both about 30 kpc⁻², corresponding to ∼ 30000 potentially observable pulsars of each type in the Galaxy. Once beaming effects are taken into consideration we estimate that the active population of normal pulsars is ∼ 160000. Although there is evidence for flattening of the luminosity function of normal pulsars, this is not evident for millisecond pulsars which probably have a substantial population with luminosities below 1 mJy kpc². After correcting for beaming effects, we estimate that a normal pulsar is born with a luminosity greater than 1 mJy kpc² between once every 60 and 330 yr in the Galaxy. The birth-rate of millisecond pulsars is at least 3 × 10⁻⁶ yr⁻¹ above the same luminosity limit. Modelling the observed transverse speeds of millisecond pulsars using a dynamical simulation, we find their mean birth velocity to be 130 ± 30 km s⁻¹, significantly lower than that of the normal pulsars.     

Timing models for the long orbital period binary pulsar PSR B1259–63

The pulsar PSR B1259–63 is in a highly eccentric 3.4-yr orbit with the Be star SS 2883. Timing observations of this pulsar, made over a 7-yr period using the Parkes 64-m radio telescope, cover two periastron passages, in 1990 August and 1994 January. The timing data cannot be fitted by the normal pulsar and Keplerian binary parameters. A timing solution including a (non-precessing) Keplerian orbit and timing noise (represented as a polynomial of fifth order in time) provides a satisfactory fit to the data. However, because the Be star probably has a significant quadrupole moment, we prefer to interpret the data by a combination of timing noise, dominated by a cubic phase term, and ω^. and x ^. terms. We show that the ω^. and x ^. terms are likely to be a result of a precessing orbit caused by the quadrupole moment of the tilted companion star. We further rule out a number of possible physical effects which could contribute to the timing data of PSR B1259–63 on a measurable level.     

Changes in Soybean Yields in the Midwestern United States as a Result of Future Changes in Climate, Climate Variability, and CO2 Fertilization

This modeling study addresses the potential impacts of climate change and changing climate variability due to increased atmospheric CO₂ concentration on soybean (Glycine max (L.) Merrill) yields in theMidwestern Great Lakes Region. Nine representative farm locations and six future climate scenarios were analyzed using the crop growth model SOYGRO. Under the future climate scenarios earlierplanting dates produced soybean yield increases of up to 120% above current levels in the central and northern areas of the study region. In the southern areas, comparatively small increases (0.1 to 20%) and small decreases (–0.1 to–25%) in yield are found. The decreases in yield occurred under the Hadley Center greenhouse gas run (HadCM2-GHG), representing a greater warming, and the doubled climate variability scenario – a more extreme and variableclimate. Optimum planting dates become later in the southern regions. CO₂fertilization effects (555 ppmv) are found to be significant for soybean, increasing yields around 20% under future climate scenarios.For the study region as a whole the climate changes modeled in this research would have an overall beneficial effect, with mean soybean yield increases of 40% over current levels.     

Fatty acids in fossil fruits

Fatty acids extracted from six fruit of Nyssa fissilis from the Early Tertiary Brandon Lignite, Vermont, include mainly palmitic, palmitoleic, stearic, and oleic acids and a number of probable branched chain acids. Four unidentified ‘round fruit’ from the lignite contained the same acids in predominance. The two taxa were chemically indistinguishable because of wide intraspecific variation in percentage of each n-fatty acid present. ‘Fingerprint’ chromatograms of non-aromatic hydrocarbon extracts from two distinct taxa of fruit from an Eocene clay of Tennessee also showed no consistent interspecific differences. We conclude that degradation and removal of the seed food reserves and introduction of extraneous lipids limits the utility of fatty acids and hydrocarbons in chemosystematic study of fossil fruits at the species and genus levels.     

Ecological regionalization in Canada and the United States

Present interest in environmental problems which are international, interstate or interprovincial in scope is drawing attention to the necessity for ecological regionalizations that will serve as a basis for intraregional transfer of experience. The major efforts at ecological regionalization by the national governmental agencies are described and compared. Although similar concepts have evolved in both countries, different systems of units have been developed for defining and mapping ecosystems at the regional scale. Before any regionalization is used it should be thoroughly tested, and modified if necessary.     

Experimental ‘syntectonic’ hydration of basalt

This paper outlines in general terms the role of metamorphic transformations during rock deformation. Long duration, triaxial stress relaxation tests at 600°C. 160 MPa confining pressure on wet crushed basalt, sheared in sawcuts made in intact basalt cylinders are reported. Mechanical data are interpreted in terms of a material which shows a small strain-rate sensitivity to large variations in applied stress, but which work hardens dramatically as a result of marked microstructural changes which occur during straining. Permanent distortions of c. 20% were produced in the samples.Tests at 100 MPa pore-water pressure resulted in the formation of oriented overgrowths of amphibole, preferentially developed on less stressed interfaces between original grains and in pore spaces. Substantial redistribution of feldspar also occurred. At low pore pressures no amphibole formed and only feldspar was recrystallized. Much of the original porosity of the rock was eliminated in all cases.The mechanical and microstructural data are interpreted in terms of flow by some combination of grain sliding and diffusional accommodation, with the reprecipitated, diffused material being the product of a chemical reaction involving all original solid phases plus water. From a consideration of the effects of the reaction on the chemical potential gradients driving diffusion, it is concluded that although the syntectonic hydration exerts a profound effect on the microstructural and mineralogical development of the rock during deformation, there is no substantial enhancement of the rate of strain.Similar microstructural developments also occur in natural rocks deformed during retrogressive metamorphic events, and examples are described for comparison.     

A magnetic method for determining the geometry of hydraulic fractures

Summary We propose a method that may be used to determine the spatial orientation of the fracture plane developed during hydraulic fracture. In the method, magnetic particles are injected into the crack with the fracturing fluid so as to generate a sheet of magnetized material. Since the magnetization of a body with extreme dimension ratios, such as a crack, exceeds that of an equidimensional body and since this magnetization is sensitive both to orientation and geometry, this could be used to obtain information about the crack. By measuring the vertical and horizontal components of the magnetic field and field gradients at the earth's surface surrounding the injection well with superconducting magnetometers having 10^–4 gamma sensitivity and also by measuring field direction within the well itself, it should be possible to calculate the orientation and perhaps infer the approximate geometry of the fracture surface. Experiments on electric field potential operated in conjunction with this experiment could further constrain estimates of shape and orientation.