Ionospheric measurements of relative coronal brightness during the total solar eclipses of 11 August, 1999 and 9 July, 1945

Swept-frequency (1/10 MHz) ionosonde measurements were made at Helston, Cornwall (50°06N, 5°18W) during the total solar eclipse on August 11, 1999. Soundings were made every three minutes. We present a method for estimating the percentage of the ionising solar radiation which remains unobscured at any time during the eclipse by comparing the variation of the ionospheric E-layer with the behaviour of the layer during a control day. Application to the ionosonde date for 11 August, 1999, shows that the flux of solar ionising radiation fell to a minimum of 25±2% of the value before and after the eclipse. For comparison, the same technique was also applied to measurements made during the total solar eclipse of 9 July, 1945, at Sörmjöle (63°68N, 20°20E) and yielded a corresponding minimum of 16 ± 2%. Therefore the method can detect variations in the fraction of solar emissions that originate from the unobscured corona and chromosphere. We discuss the differences between these two eclipses in terms of the nature of the eclipse, short-term fluctuations, the sunspot cycle and the recently-discovered long-term change in the coronal magnetic field.     

多波束测量中换能器瞬时精密高程的确定

分析了GPS高程信号和Heave信号的频段特征，利用数字信号处理技术，提取了GPS高程和Heave中的有效频段信号，合成了一个全新的信号。该合成信号能够全面反映多波束换能器的实际垂直运动，并能够克服传统多波束测量和数据处理方法的缺陷，大大提高了多波束在垂直方向的成果精度。实验证明了该方法的正确性和可行性。     

Mathematical expressions used in amino acid racemisation geochronology—A review

A variety of mathematical expressions that describe changes over time (t) in the extent of amino acid racemisation (AAR, expressed as the ratio of d- to l-amino acid isomers or epimers) have been used in Quaternary geochronology. The integrated rate equation was first used to estimate fossil age from D/L but its geochronological utility is disadvantaged by uncertainties regarding the conformity of AAR in fossil protein to apparent reversible first-order kinetics for the entire reaction history. ‘Non-linear’ models have subsequently been used to relate D/L to t. The logarithmic equation successfully applied to Atlantic Coastal Plain research has not achieved widespread application, perhaps due to the regional calibration required if sensitivity to temperature is to be modelled, or the difficulties encountered when extending the model to include fossils with D/L<0.1. Success producing a linear correlation between D/L transformed with a power function and t has seen this approach emerge as one of the most commonly applied in AAR geochronology in recent years. Like parabola curve fitting, which has been applied to trends in D/L versus t in a variety of fossils and geographic settings, power transformations may not be suitable for geochronological modelling during the latter stages of amino acid diagenesis. Several studies have demonstrated the utility of simple and contingent linear equations for relating D/L to t. Future research should aim to reduce reliance on independent calibration and explore the geochronological benefits of AAR in pools other than the total hydrolysable amino acids.     

Feature Extraction in Remote Sensing High-Dimensional Image Data

High-dimensional image data open new possibilities in remote sensing digital image classification, particularly when dealing with classes that are spectrally very similar. The main problem refers to the estimation of a large number of classifier's parameters. One possible solution to this problem consists in reducing the dimensionality of the original data without a significant loss of information. In this letter, a new approach to reduce data dimensionality is proposed. In the proposed methodology, each pixel's curve of spectral response is initially segmented, and the digital numbers (DNs) at each segment are replaced by a smaller number of statistics. In this letter, the proposed statistics are the mean and variance of the segment's DNs, which are supposed to carry information about the segment's position and shape, respectively. Tests were performed by using Airborne Visible/Infrared Imaging Spectrometer hyperspectral image data. The experiments have shown that this methodology is capable of providing very acceptable results, in addition of being computationally efficient     

GPS sidereal filtering: coordinate- and carrier-phase-level strategies

Multipath error is considered one of the major errors affecting GPS observations. One can benefit from the repetition of satellite geometry approximately every sidereal day, and apply filtering to help minimize this error. For GPS data at 1 s interval processed using a double-difference strategy, using the day-to-day coordinate or carrier-phase residual autocorrelation determined with a 10-h window leads to the steadiest estimates of the error-repeat lag, although a window as short as 2 h can produce an acceptable value with > 97% of the optimal lag’s correlation. We conclude that although the lag may vary with time, such variation is marginal and there is little advantage in using a satellite-specific or other time-varying lag in double-difference processing. We filter the GPS data either by stacking a number of days of processed coordinate residuals using the optimum “sidereal” lag (23 h 55 m 54 s), and removing these stacked residuals from the day in question (coordinate space), or by a similar method using double-difference carrier-phase residuals (observational space). Either method results in more consistent and homogeneous set of coordinates throughout the dataset compared with unfiltered processing. Coordinate stacking reduces geometry-related repeating errors (mainly multipath) better than carrier-phase residual stacking, although the latter takes less processing time to achieve final filtered coordinates. Thus, the optimal stacking method will depend on whether coordinate precision or computational time is the over-riding criterion.     

Aliphatic and aromatic hydrocarbons in benthic invertebrates from two sites in Antarctica

Samples of marine benthic invertebrates collected from two sites in the Antarctic have been analysed for both aliphatic and aromatic hydrocarbons in order to establish baseline concentrations for some classes of hydrocarbons.Samples from Signy Island, a pristine site, contained low concentrations of the hydrocarbons determined, whereas those from King Edward Cove, South Georgia, contained significantly higher concentrations. King Edward Cove has a known history of pollution from whaling operations.Platt & Mackie (1979) have suggested that the hydrocarbons in sediments from King Edward Cove are a result of the world-wide dissemination of the pyrolysis products of fossil fuels. Our work suggests, in contrast, that the hydrocarbons in the benthos are derived from local sources.     

Magmatic andalusite from the South Mountain batholith,Nova Scotia

Accessory andalusite has been found in some late-stage granitic differentiates of the South Mountain batholith. The andalusite is petrographically distinct from the andalusite of the thermal aureole, and it occurs in regions of the batholith which show little evidence of contamination by the country rocks. Analyses of biotites from andalusite-bearing and andalusite-free phases suggest that those coexisting with andalusite actually grew in equilibrium with the andalusite. It is concluded that magmatic andalusite must be confined mainly to water-saturated, peraluminous, epizonal granites, and some possible P-T paths for the crystallization of magmatic andalusite are considered.     

Green garnets from the Newlands kimberlite,Cape Province,South Africa

Six crystals of green, uvarovite-rich garnet from the Newlands kimberlite have been analysed. The range of Cr₂O₃ is 10.04–14.04% and CaO is 19.18–25.94% (wt.), and thus they are similar to garnets found in only one other kimberlite province, namely Yakutia. By combining data from both the Russian and South African occurrences, four models are considered for the formation of such garnets. The model which best accounts for the available chemical data, and mode of occurrence, involves formation of the uvarovitic garnets during subsolidus recrystallization of spinel wehrlitic cumulates, which themselves had been produced by a fractionating magma at a depth of about 200–250 km.