Gravity field information from Gravity Probe-B

The Gravity Probe-B Mission will carry the Stanford Gyroscope relativity experiment into orbit in the mid 1990's, as well as a Global Positioning System (GPS) receiver whose tracking data will be used to study the earth gravity field. Estimates of the likely quality of a gravity field model to be derived from the GPS data are presented, and the significance of this experiment to geodesy and geophysics are discussed

Geopotential research mission, science, engineering and program summary

This report is based upon the accumulated scientific and engineering studies pertaining to the Geopotential Research Mission (GRM). The scientific need and justification for the measurement of the Earth's gravity and magnetic fields are discussed. Emphasis is placed upon the studies and conclusions of scientific organizations and NASA advisory groups. The engineering design and investigations performed over the last 4 years are described, and a spacecraft design capable of fulfilling all scientific objectives is presented. In addition, critical features of the scientific requirements and state-of-the-art limitations of spacecraft design, mission flight performance, and data processing are discussed

Dynamic sea surface topography, gravity and improved orbit accuracies from the direct evaluation of SEASAT altimeter data

A method for the simultaneous solution of dynamic ocean topography, gravity and orbits using satellite altimeter data is described. A GEM-T1 based gravitational model called PGS-3337 that incorporates Seasat altimetry, surface gravimetry and satellite tracking data has been determined complete to degree and order 50. The altimeter data is utilized as a dynamic observation of the satellite's height above the sea surface with a degree 10 model of dynamic topography being recovered simultaneously with the orbit parameters, gravity and tidal terms in this model. PGS-3337 has a geoid uncertainty of 60 cm root-mean-square (RMS) globally, with the uncertainty over the altimeter tracked ocean being in the 25 cm range. Doppler determined orbits for Seasat, show large improvements, with the sub-30 cm radial accuracies being achieved. When altimeter data is used in orbit determination, radial orbital accuracies of 20 cm are achieved. The RMS of fit to the altimeter data directly gives 30 cm fits for Seasat when using PGS-3337 and its geoid and dynamic topography model. This performance level is two to three times better than that achieved with earlier Goddard earth models (GEM) using the dynamic topography from long-term oceanographic averages. The recovered dynamic topography reveals the global long wavelength circulation of the oceans with a resolution of 1500 km. The power in the dynamic topography recovery is now found to be closer to that of oceanographic studies than for previous satellite solutions. This is attributed primarily to the improved modeling of the geoid which has occurred. Study of the altimeter residuals reveals regions where tidal models are poor and sea state effects are major limitations

Hierarchy of the Selberg zeta functions

We introduce a Selberg type zeta function of two variables which interpolates several higher Selberg zeta functions. The analytic continuation, the functional equation and the determinant expression of this function via the Laplacian on a Riemann surface are obtained.Comment: 14 page

An investigation of the failure mechanisms in high temperature materials subjected to isothermal and anisothermal fatigue and creep conditions

Many engineering components are subjected to conditions which have a detrimental effect on the materials from which they are made. Such components are used, for example, within high temperature regions of aeroengines (e.g. turbine discs) and power plant (e.g. steam pipes) and such conditions can include periods of isothermal and/or thermo-mechanical cyclic loading which may cause fatigue, excessive plasticity and creep. The combination of conditions to which the materials are subjected can have a strong influence on the failure mechanisms induced within the material. This study is concerned with the identification of the failure mechanisms which occur in RR1000 (a Nickel-based superalloy used in aeroengine turbine discs) tested under both isothermal and anisothermal cyclic conditions. The various types of test conditions applied to the specimens (e.g. waveforms which contain high temperature tensile conditions or alternatively low temperature tensile conditions) and the related failure mechanisms (e.g. intergranular, transgranular or mixed cracking), have been identified. Comparisons of the predictions of failure lives with experimental data from tested specimens, subjected to various test conditions, are also presented

Effect of altered loading conditions during haemodialysis on left ventricular filling pattern

Changes in the circulating volume associated with haemodialysis result in modification of left ventricular loading conditions. To determine the influence of haemodialysis on Doppler indices of left ventricular filling, 12 patients (mean age 40.8 ±2.7 (SEM) years) with renal insufficiency but without overt heart disease were studied by Doppler-echocardiography immediately before and after haemodialysis. Haemodialysis resulted in a decrease in body weight from 68.0±3.8 kg to 65.0 ±3.7 kg (P< 0.01). Heart rate and blood pressure did not change significantly during haemodialysis. Left ventricular diastolic dimension (M-mode) decreased from 53.5±1.1 mm to 49.5±1.9 mm (P < 0.05), whereas the shortening fraction did not change. Haemodialysis elicited marked changes in the early diastolic rapid filling wave (E wave) recorded by pulsed Doppler at the level of the mitral annulus. Peak velocity of the early rapid filling phase (peak E) decreased significantly from 95.3 ± 8.2 cm .s−1 to 63.0 ±5.7cm .s−1 (P< 0.001) and mid-diastolic deceleration of transmitral velocity decreased from 437.3 ±54.2 cm . s−2 to 239.7 ±54.4 cm . s−2 (P<0.01). The peak filling velocity during atrial contraction (peak A) did not change (79.7 ±6.3 cm .s−1 vs 74.1±4.7 cm.s−1;P=NS). The ratio peak E/peak A decreasedfrom 1.19±0.06 to 0.85 ± 0.04 (P < 0.01) during haemodialysis. The results provide further evidence for the pronounced preload-dependence of Doppler indices of left ventricular diastolic functio

Effects of nicotine on the digestive performance of nectar-feeding birds reflect their relative tolerance to this alkaloid

The paradox of secondary metabolites, toxic defence compounds produced by plants, in nectar and fruits is well known. Deterrence of feeding by nectarivorous and frugivorous birds is better understood than the effect of these chemicals on the digestive performance of birds. Digestive parameters such as transit time and sugar assimilation are important in assessing nutrient utilization and deterrence may be related to post-ingestive effects involving these parameters. Nectar andmany fruits contain mainly sugars andwater, and avian consumers compensate for lowsugar content in their diet by increasing food intake: thismay also increase their intake of secondary metabolites. We investigated howthe alkaloid nicotine, naturally present in nectar of Nicotiana species, influences compensatory feeding and digestive performance of nectar-feeding birds. High nicotine concentration negatively affected compensatory feeding and apparent assimilation efficiency of white-bellied sunbirds Cinnyris talatala and Cape white-eyes Zosterops virens; but nicotine slowed gut transit time only in the latter species. In contrast, food intake and digestive performance of dark-capped bulbuls Pycnonotus tricolor was unaffected by nicotine up to a concentration of 50 μM. Bulbuls are primarily frugivorous; hence, they are more exposed to secondary metabolites than sunbirds and possibly white-eyes. Because their diet is richer in toxins, frugivorous birds may have evolved more efficient detoxification strategies than those of specialist nectar-feeding birds.South African National Research Foundation (73671) and the University of Pretoria.http://www.elsevier.com/locate/cbpa2016-12-31hb201

Bird pollinators differ in their tolerance of a nectar alkaloid

Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as anti-herbivore defences are frequently present in floral nectars. Greater understanding is needed of the effects of secondary metabolites in nectar on the foraging behaviour and performance of pollinators, and on plant–pollinator interactions. We investigated how nectar-feeding birds, both specialist (white-bellied sunbirds Cinnyris talatala) and generalist (dark-capped bulbuls Pycnonotus tricolor and Cape white-eyes Zosterops virens), respond to artificial nectar containing the alkaloid nicotine, present in nectar of Nicotiana species. Preference tests were carried out with a range of nicotine concentrations (0.1–300 μM) in two sucrose concentrations (0.25 and 1 M), and for bulbuls also in two sugars (sucrose and hexose). In addition, we measured short-term feeding patterns in white-bellied sunbirds that were offered nicotine (0–50 μM) in 0.63 M sucrose. Both nicotine and sugar concentrations influenced the response of bird pollinators to nicotine. The birds showed dose-dependent responses to nicotine; and their tolerance of high nicotine concentrations was reduced on the dilute 0.25 M sucrose diet, on which they increased consumption to maintain energy intake. White-bellied sunbirds decreased both feeding frequency and feeding duration as the nicotine concentration in artificial nectar increased. Of the three species, bulbuls showed the highest tolerance for nicotine, and sugar type (sucrose or hexose) had no effect. The indifference of bulbuls to nicotine may be related to their primarily frugivorous diet. However, the response of white-eyes to nicotine in the dilute sucrose solution was very similar to that of sunbirds, even though white-eyes are generalist nectar-feeders. Additional testing of other avian nectarivores and different secondary metabolites is required to further elucidate whether generalist bird pollinators, which utilise dilute nectars in which secondary metabolites have stronger deterrent effects, are more tolerant of ‘toxic’ nectar.The University of Pretoria and the South African National Research Foundation (NRF).http://www.wiley.com/10.1111/(ISSN)1600-048Xhb2013ab201