Some contributions of touch, pressure and kinesthesis to human spatial orientation and oculomotor control.

Human spatial orientation and oculomotor control are under multimodal influence. It is not possible in the normal animal to stimulate differentially the vestibular receptors without activating other receptor systems whose activity may have a profound influence on postural control and experienced orientation. Many patterns of behavior and response that have been attributed solely to vestibular function are actually dependent wholly or in part on touch, kinesthetic, and proprioceptive stimulation.     

ERS-1 and ERS-2 operational and precise orbit determination

This paper presents the European Space Operations Centre's orbit determination and prediction systems for the ERS-1 mission. The routine operational orbit determination and prediction subsystem is discussed briefly, and statistics of the accuracy compared to the requirements are given. The precise orbit determination subsystem is then described, and the accuracy of its results are compared to those of the operational orbit system and to the D-PAF preliminary orbit solutions. Some geophysical results from the altimeter data, processed in these orbit determinations, are also presented. The ESOC/OAD ‘ERS-1 Orbit Report’ is introduced as a document providing this information on a monthly basis. Finally, this paper describes how the experience gained with the precise orbit determination will be exploited to further improve the accuracy of the routine system that will be used for ERS-2, and provides an estimate of this accuracy.     

Ballistic missile track initiation from satellite observations

An algorithm is presented to initiate tracks of a ballistic missile in the initial exoatmospheric phase, using line of sight (LOS) measurements from one or more moving platforms (typically satellites). The major feature of this problem is the poor target motion observability which results in a very ill-conditioned estimation problem. The Gauss-Newton iterative least squares minimization algorithm for estimating the state of a nonlinear deterministic system with nonlinear noisy measurements has been previously applied to the problem of angles-only orbit determination using more than three observations. A major shortcoming of this approach is that convergence of the algorithm depends strongly on the initial guess. By using the more sophisticated Levenberg-Marquardt method in place of the simpler Gauss-Newton algorithm and by developing robust new methods for obtaining the initial guess in both single and multiple satellite scenarios, the above mentioned difficulties have been overcome. In addition, an expression for the Cramer-Rao lower bound (CRLB) on the error covariance matrix of the estimate is derived. We also incorporate additional partial information as an extra pseudomeasurement and determine a modified maximum likelihood (ML) estimate of the target state and the associated bound on the covariance matrix. In most practical situations, probabilistic models of the target altitude and/or speed at the initial point constitute the most useful additional information. Monte Carlo simulation studies on some typical scenarios were performed, and the results indicate that the estimation errors are commensurate with the theoretical lower bounds, thus illustrating that the proposed estimators are efficient     

Atomic and molecular hydrogen in interstellar space

This paper reviews the present state of knowledge of the abundances and physical state of interstellar atomic and molecular hydrogen. Much new data in this area have been obtained in recent rocket observations. There have also been new developments as a result of ground-based infrared and 21-cm observations, and theoretical research.Rocket observations of the Lyman- interstellar absorption line of atomic hydrogen indicate that, in many directions in the sky, atomic hydrogen is up to a factor of 10 less abundant than previously indicated by 21-cm emission measurements. In the direction of the Orion Nebula, most of the absorbing gas appears to be concentrated in the near vicinity of the nebula and to have a temperature considerably lower than the average of 100 K obtained from 21-cm emission measurements. Molecular hydrogen appears essentially absent from the general interstellar medium, as confirmed by theoretical studies of photodissociation processes. However, ground-based infrared and 21-cm studies indicate that the hydrogen in dark dust clouds is mostly molecular.     

Solar and Solar-Wind Composition Results from the Genesis Mission

The Genesis mission returned samples of solar wind to Earth in September 2004 for ground-based analyses of solar-wind composition, particularly for isotope ratios. Substrates, consisting mostly of high-purity semiconductor materials, were exposed to the solar wind at L1 from December 2001 to April 2004. In addition to a bulk sample of the solar wind, separate samples of coronal hole (CH), interstream (IS), and coronal mass ejection material were obtained. Although many substrates were broken upon landing due to the failure to deploy the parachute, a number of results have been obtained, and most of the primary science objectives will likely be met. These objectives include He, Ne, Ar, Kr, and Xe isotope ratios in the bulk solar wind and in different solar-wind regimes, and ¹⁵N/¹⁴N and ¹⁸O/¹⁷O/¹⁶O to high precision. The greatest successes to date have been with the noble gases. Light noble gases from bulk solar wind and separate solar-wind regime samples have now been analyzed. Helium results show clear evidence of isotopic fractionation between CH and IS samples, consistent with simplistic Coulomb drag theory predictions of fractionation between the photosphere and different solar-wind regimes, though fractionation by wave heating is also a possible explanation. Neon results from closed system stepped etching of bulk metallic glass have revealed the nature of isotopic fractionation as a function of depth, which in lunar samples have for years deceptively suggested the presence of an additional, energetic component in solar wind trapped in lunar grains and meteorites. Isotope ratios of the heavy noble gases, nitrogen, and oxygen are in the process of being measured.     

Analysis of the dynamic behavior of structures using the high-rate GNSS-PPP method combined with a wavelet-neural model: Numerical simulation and experimental tests

Recently, the high rate global navigation satellite system-precise point positioning (GNSS-PPP) technique has been used to detect the dynamic behavior of structures. This study aimed to increase the accuracy of the extraction oscillation properties of structural movements based on the high-rate (10?Hz) GNSS-PPP monitoring technique. A developmental model based on the combination of wavelet package transformation (WPT) de-noising and neural network prediction (NN) was proposed to improve the dynamic behavior of structures for GNSS-PPP method. A complicated numerical simulation involving highly noisy data and 13 experimental cases with different loads were utilized to confirm the efficiency of the proposed model design and the monitoring technique in detecting the dynamic behavior of structures. The results revealed that, when combined with the proposed model, GNSS-PPP method can be used to accurately detect the dynamic behavior of engineering structures as an alternative to relative GNSS method.     

Development of x-ray mirrors for high-energy astrophysics in czechoslovakia

The grazing incidence X-ray mirrors with diameters between 20 and 240 mm were produced by two different replica techniques. Five mirrors were flown in space experiments. It has been confirmed that the galvanoplastic replica mirrors are well suited for applications in space telescopes and laboratory microscopes.     

Extragalactic radio sources

Some recent observational results on extended and compact extragalactic radio sources are described. Theoretical interpretations are critically examined.