Empirical Earth Rotation Model: a Consistent Way to Evaluate Earth Orientation Parameters
It is customary to perform analysis of the Earth’s rotation in two steps: first, to present results of estimation of the Earth orientation parameters in the form of time series based on a simplified model of variations of the Earth’s rotation for a short period of time, and then to process this time series of adjustmentsby applying smoothing, re-sampling and other numerical algorithms. This approach suffers from self-inconsistency: the total set of Earth orientation parameters depends on a subjective choice of the apriori Earth orientation model, crosscorrelations between points of the time series are lost, and results of an operational analysis per se have a limited use for end users. Here, an alternative approach of direct estimation of the coefficients of expansion of Euler angle perturbations into basis functions is developed. These coefficients describe the Earth’s rotation over the entire period of observations and are evaluated simultaneously with stationpositions, source coordinates and other parameters in a single LSQ solution. In the framework of this approach considerably larger errors in apriori EOP model are tolerated. This approachgives a significant conceptual simplification of representation and estimation of the Earth’s rotation.
Erratum: Correction to ``Geodesy by Radio Interferometry: Studies of the forced nutations of the Earth, 1, Data Analysis''
The analysis of 235 very long baseline interferometry observing sessions carried out between July 1980 and December 1984 has yielded estimates of corrections to the seven largest nutation series coefficients (with periods ≤1 year) in the Wahr nutation series, the most complete such model available at this time. The largest correction is to the amplitude of the retrograde annual nutation: −1.80±0.18 - i(0.42±0.18) milliarc seconds (mas), where the estimated standard deviations contain contributions from the effects of systematic as well as random errors. We interpret this correction as being due to an incompleteness in the model of the core-mantle coupling used by Wahr. We have also examined our results for evidence of any “free core nutation” and can place an upper bound of 1.0 mas (99.5% confidence interval) on its amplitude.
Axonal sensorimotor neuropathy in patients with β-thalassaemia
Objective: The purpose of this study was to investigate the prevalence of peripheral neuropathy in patients with β-thalassaemia. Methods: Thirty six patients with a mean age of 29.2±8.2 years and 17 healthy controls with a mean age of 27.6±9.1 were included in this study. Measurements included the neuropathy symptoms score (NSS), the neuropathy disability score (NDS) as well as nerve conduction studies of two motor (ulnar and peroneal) and two sensory (ulnar and sural) nerves of the right limbs. Results: A mainly sensory axonal polyneuropathy was present in 19 out of 36 patients (52.7%). Eight out of these 19 patients also had abnormal NDS values. The neuropathy correlated significantly with the age of the patients and the hematocrit. However, it did not correlate with the presence of antibodies against HCV, the ferritin levels, or with a history of transfusions, desferrioxamine treatment, or splenectomy. Conclusions: This study showed a high prevalence of a predominantly sensory neuropathy in patients with β-thalassaemia. The electrophysiological data suggest that the underlying pathology is an axonopathy. Chronic hypoxia of the nerves resulting from severe anaemia may contribute to the pathogenesis of this neuropathy.