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For many years, the gravity field of the Earth was only seen by satellite geodesy as the main factor affecting the orbit and consequently it was retrieved together with a number of other orbital perturbations. Since the advent of a new generation of accelerometers, non-gravitational perturbations can be separated from the gravity effects and a new era of gravity field estimates from space has been born. During preparatory data analysis for new missions performed by the geodetic community, three approaches have been proposed and numerically tested: the brute force method (direct approach), the semi-analytical (time-wise) method and the space-wise method. In particular, the time-wise method takes advantage of the incoming time flow of data and, after performing a Fourier transform of the observation equations, exploits the prevailing block diagonal structure of the normal equations to estimate the spherical harmonic coefficients of the gravity field. Complementary to this is the space-wise approach, which goes back to the traditional computation of the harmonic coefficients by an integration technique or by least-squares collocation. Some advantages and disadvantages are peculiar to both methods, particularly the space-wise approach, which has for a long time ignored the marked signature of the noise spectrum due to the specific measuring conditions of space-borne accelerometers. The application of a proper Wiener filter, exploiting the correlation along the orbit, embedded into an iterative scheme, seems to be the answer. The solution to this major problem of the space-wise approach is illustrated and simulation results are discussed.

Abstract.:  In the framework of a boundary value problem (BVP), when areas on the boundary are void of data the solution of the problem becomes undetermined and clearly more difficult. Physically, this could be the situation in which a gradiometer on a satellite on a perfectly circular orbit covers a sphere with measured second radial derivatives: if the satellite orbit is not polar, there are caps at satellite altitude which are not covered by data. A solution is presented based on an iterative algorithm, under the hypothesis of using a finite-dimensional model as is usually done in the time-wise approach. The convergence of the iterative solution is proved and a numerical example is shown to confirm the theoretical result.

ABSTRACTThe apical hook that forms at the apex of most dicotyledonous seedlings during germination has in the past been variously described either as the consequence of positive gravitropism or as an autonomous process. Recently, however, emphasis has shifted more on the role of positive gravitropism as the inducer of this structure. To address the question on the nature and origin of the hook, experiments were performed on sunflower seedlings, not only under gravitational conditions but also by means of a clinostat, i.e. in the presence of multidirectionally compensated gravitational stimulation. The results of this work show that at least two processes are involved in the formation of a hook: positive gravitropism and an autonomous movement. Consequently, both Darwin, with his conviction that an innate process such as circumnutation was involved, and the supporters of positive gravitropism, were partly correct. Moreover, it was found that, in contrast to the hook formed under normal unidirectional gravitational conditions, the one formed on the clinostat showed a preferential plane for its development: the plane that passes parallel to the closed cotyledons. This characteristic also suggests that a form of circumnutation may be part of the basic mechanism for hook formation.

Abstract: The problem of judging on model deficiency in S.L.R. data treatment is considered. In particular the correlation analysis of residuals of adjusted orbits is used to show the presence of unmodelled signals. This analysis seems suitable at least for a proper preprocessing of S.L.R. data, in the sense of being an efficient procedure of outliers rejection.

The problem of judging on model deficiency in S.L.R. data treatment is considered. In particular the correlation analysis of residuals of adjusted orbits is used to show the presence of unmodelled signals. This analysis seems suitable at least for a proper preprocessing of S.L.R. data, in the sense of being an efficient procedure of outliers rejection.

Excised roots obtained from maize plants, previously treated for 24 h with different solutes (K2SO4, Na2SO4, or mannitol) at decreasing osmotic potential values, showed clearly the persistence of osmo-saline shock in their chloride transport and in some metabolic processes. In particular, vacuolar accumulation of chloride was much reduced when the osmotic potential in pretreatment had been low; this effect was greater with solutions of electrolytes. Protein synthesis and [14C]leucine uptake were also reduced; thus there appeared to be a correlation between chloride accumulation in the vacuole and protein synthesis. By contrast, accumulation of chloride in the cytoplasm was only slightly modified or even stimulated. Chloride influx was affected less by osmotic pretreatment than accumulation, except in the case of very low osmotic potentials where influx was depressed. Chloride efflux was slightly enhanced by osmo-saline shocks and the fluxes at the tonoplast were less affected in comparison with those at the plasmalemma. Malate accumulation was stimulated by shock, but this effect was not persistent, so that a correlation with the effects on accumulation and fluxes was not possible. Oxygen uptake was affected only slightly except that at osmotic potential values of −750 kPa, perhaps because of a lowered viability of the roots subjected to very low osmotic potential for 24 h.