Cellular responses to gravity: extracellular, intracellular and in-between.

Our understanding of gravitational effects (inertial effects in the vicinity of 1 x g) on cells has matured to a stage at which it is possible to define, on the basis of experimental evidence, extracellular effects on small cells and intracellular effects on eukaryotic gravisensing cells. Yet undetermined is the nature of response, if any, of those classes of cells that are not governed solely by extracellular physical events (as are prokaryotes) and are devoid of obvious mechanical devices for sensing inertial forces (such as those possessed by certain plant cells and sensory cells of animals). This "in-between" class of cells needs to be understood on the basis of the combination of intracellular and extracellular gravity-dependent processes that govern experimentally-measurable variables that are relevant to the cell's responses to modified inertial forces. The forces that certain cell types generate or respond to are therefore compared to those imposed by approximately 1 x g in the context of cytoskeletal action and symmetry-breaking pathways.     

Variations in statistical parameters of the NmF2 equinoctial asymmetry with latitude and solar activity near noon

Hourly values of the F2-layer peak density, NmF2, measured by 95 ionosondes near noon from 1957 to 2011 at low and middle geomagnetic latitudes of the northern and southern geographic hemispheres are used in a statistical study of the NmF2 equinoctial asymmetry. The ratios, R, of NmF2 measured during 61 days around the March equinox to NmF2 measured during 61 days around the September equinox at the same UT near noon during geomagnetically quiet daytime conditions for approximately the same solar activity conditions over the same ionosonde are analyzed. The conditional probability of the occurrence of R in an interval of R, the most probable value of R, and the mean expected value of R are calculated for the first time for the low, moderate, and high solar activity levels to study variations in these statistical parameters with latitude and solar activity. These statistical parameters are averaged over 5° geomagnetic latitude interval in the northern and southern geographic hemispheres to calculate and to study for the first time trends in latitude and solar activity of these averaged NmF2 equinoctial asymmetry statistical characteristics.     

Local-time variations of geomagnetic disturbances during intense geomagnetic storms and possible association with their interplanetary causes

In the present paper the local-time variations in the disturbance of the geomagnetic-field horizontal component (H) for eight intense geomagnetic storms that occurred during the descending phase of solar cycle 23 have been analyzed. The study was based on the plot of contour lines of the H-depletion intensity in the plane local time versus universal time (LT–UT maps) with the objective of observing how the morphology and evolution of the ring current is mapped into the surface of the Earth in presence of intense geomagnetic storms.     

Vertical motions in Thailand after the 2004 Sumatra–Andaman Earthquake from GPS observations and its geophysical modelling

Following previous findings from ongoing GPS research in Thailand since 2004 we continue to exploit the GPS technique to monitor and model land motions induced by the Sumatra–Andaman Earthquake. Our latest results show that up to the end of 2010, Thailand has been co-seismically displaced and is subsequently undergoing a post-seismic horizontal deformation with total displacements (co-seismic plus post-seismic) ranging from 10.5 to 74.7 cm. We observed the largest horizontal displacements in the southern part of Thailand and moderate and small displacements in the central and northern parts. In addition to horizontal displacements throughout Thailand, continuous GPS measurements show that large parts of Thailand are subsiding at rates up to 1 cm/yr. It is the first time that such vertical post-seismic deformations at large distances (650–1500 km away from the Earthquake’s epicentre) have been recorded. We have investigated the physical processes leading to the observed subsidence. While after-slip on the subduction interface induces negligible or even slightly positive vertical motions, relaxation in the asthenosphere is associated with a sizable subsidence. Predictions from a 3D finite element model feature an asthenosphere with an effective viscosity of the order of 3 * 10¹⁸ Pas, fit the horizontal post-seismic data and the observed subsidence well. This model is then used to predict the subsidence over the whole seismic cycle. The subsidence should go on with a diminishing rate through the next two decades and its final magnitude should not exceed 10 cm in the Bangkok area.     

The concept of selecting the main parameters of a lightweight airplane with regard to the requirements of the contemporary Russian market

The basic principles of selecting some design parameters of a lightweight airplane for the contemporary Russian market are presented. Recommendations for selecting these parameters with the service requirements specified are given based on the study performed.     

Spectres auroraux

Summary The paper presents a review of the main spectroscopic studies of polar aurora accomplished during the past eight years.In a first part, the few new results concerning knowledge of the spectrum itself are examined. They concern detailed spectrum analysis, a few spectral features (sodium doublet, helium lines) and the extension of spectral observations to very low wavelengths (3000 to 1000 Å). The main features discovered in this region are the Vegard-Kaplan and Lyman-Birge-Hopfield systems as well as the 1304 oxygen line. A comparison of observed and theoretical intensities shows serious discrepancies, not all of which may be attributed to difficulties of observation. Next is given classification, from a spectral point of view, of the various kinds of auroral phenomena, with respect to altitude and latitude. Particular attention is given to high altitude and sunlit aurorae, and to low intensity, non discrete aurorae observed around the 70th degree (geomagnetic) and around the polar cap.A second part underlines the influence of two important parameters, time and location, mainly as a possible means of detection of different mechanisms.As far as the time parameter is concerned, a few pages are devoted to statistical analysis of the great wealth of observational data accumulated over twenty or thirty years.It is shown that important conclusions emerge from such studies. Very small scale time variations are mainly concerned with the study of metastable states, their lifetimes and de-excitation due to shocks between particles. Differences of spectra with the location of the observed emitting volume is a much more recent subject, which has, however, produced important results. These concern mainly observations made from rockets, although a few results have been obtained from the ground. All these indicate significant differences that may shed some light on the difficult problem of mechanisms. The latter has not been developed, since a recent review has been written on the subject. The same is true for the very important problem of hydrogen emissions.The last pages are concerned with the latest developments of experimental methods, with some stress on image tubes, which will probably be one of the main detecting devices for observing auroral spectra in the near future.     

Controlling spacecraft by means of solar radiation

The possibility of using solar sails in Earth orbit is investigated. The characteristic parameters of a solar sail consisting of six spheres attached by mutually orthogonal long rods are estimated.     

Toward Accurate On-Ground Attitude Determination for the Gaia Spacecraft

The work presented in this paper concerns the accurate On-Ground Attitude (OGA) reconstruction for the astrometry spacecraft Gaia in the presence of disturbance and of control torques acting on the spacecraft. The reconstruction of the expected environmental torques which influence the spacecraft dynamics will be also investigated. The telemetry data from the spacecraft will include the on-board real-time attitude, which is of order of several arcsec. This raw attitude is the starting point for the further attitude reconstruction. The OGA will use the inputs from the field coordinates of known stars (attitude stars) and also the field coordinate differences of objects on the Sky Mapper (SM) and Astrometric Field (AF) payload instruments to improve this raw attitude. The on-board attitude determination uses a Kalman Filter (KF) to minimize the attitude errors and produce a more accurate attitude estimation than the pure star tracker measurement. Therefore the first approach for the OGA will be an adapted version of KF. Furthermore, we will design a batch least squares algorithm to investigate how to obtain a more accurate OGA estimation. Finally, a comparison between these different attitude determination techniques in terms of accuracy, robustness, speed and memory required will be evaluated in order to choose the best attitude algorithm for the OGA. The expected resulting accuracy for the OGA determination will be on the order of milli-arcsec.     

Estimation of Correlation Functions by Stochastic Approximation

Two techniques for estimating the correlation function of a stationary random process using the method of stochastic approximation are developed. Both provide updated estimates as successive T-second observations are processed. Both assume a functional form for the correlation function that depends on a number of parameters that are estimated. One technique is based on the mean-square error; the other maximizes a likelihood function. Examples are included.