An extended Kalman filter for spinning spacecraft attitude estimation

An extended Kalman filter for real-time ground attitude estimation of a gyro-less spinning spacecraft was developed and tested. The filter state vector includes the angular momentum direction, phase angle, inertial nutation angle, and inertial and body nutation rates. The filter solves for the nutating three-axis attitude and accounts for effects due to principle axes offset from the body axes. The attitude is propagated using the kinematics of a rigid body symmetric about the principle spin axis; disturbance torques are assumed to be small. Filter updates consist only of the measured angles between celestial objects (Sun, Earth, etc.) and the nominal spin axis, and the times these angles were measured. Both simulated data and real data from the Dynamics Explorer -A (DE-A) spacecraft were used to test the filter; the results are presented. Convergence was achieved rapidly from a wide range of a priori state estimates, and sub-degree accuracy was attained. Systematic errors affecting the solution accuracy are discussed, as are the results of an attempt to solve for sensor measurement angle biases in the state vector

Quarterly Economic Commentary, December 1997

For the fourth successive year, the Irish economy has performed extremely well in 1997. Real GDP is estimated to have increased by about 10½ per cent and real GNP by 9 per cent, above even the average growth rate of the previous three years. The growth has remained well balanced between exports and domestic demand, with the result that the current account of the balance of payments is estimated to have risen to 2¾ per cent of GNP while annual average employment is estimated to have increased by about 57,000 or over 4¼ per cent. Unemployment, including long term unemployment, has declined significantly, and the standardised unemployment rate for 1997 is likely to have been less than 10 per cent when final revisions are made. The public finances have been exceptionally strong, with a general government surplus having been achieved, and consumer price inflation has averaged 1½ per cent. Economic growth will continue to be rapid by historical or international standards in 1998, but considerable uncertainty surrounds the actual rate of growth that can be expected. The impact of the Asian financial crisis, and of countervailing measures by major western economies, on world output and trade cannot yet be assessed with accuracy. While currency volatility on a world basis appears set to continue, its precise evolution cannot be foreseen, and, more specifically, it is still too early for a final decision to be made on the bilateral exchange rates of the Irish pound within EMU. Making what we hope are balanced assumptions regarding such uncertainties, we forecast that real GNP will grow by about 6 per cent in 1988, implying a significant slowing of expansion in the course of the year. Total employment is projected to increase by 42,000 on an annual average basis, and the unemployment rate to decline to an average of 9¼ per cent. The public finances should remain strong, with a further general government surplus, but a major improvement over the Budget targets seems unlikely in 1998. With export growth projected to slacken and a deterioration likely in the terms of trade, the current account is forecast to fall quite sharply, although remaining in comfortable surplus. Price inflation will almost certainly accelerate, and on our assumptions the annual increase in the consumer price index seems likely to be in the region of 2¼ per cent. If the depreciation in the trade-weighted value of the Irish pound is larger and comes sooner than we have assumed, the annual average increase in prices will be greater, and could well exceed 3 per cent. This would have relatively little effect on the forecast rate of growth of real GNP in 1998, although it could alter its composition. Given the unavoidable uncertainties concerning economic prospects in 1998 and beyond, it would be most unfortunate if euphoria generated by the economic performance of the past four years were to undermine the self-discipline which was an essential contributing factor in that success. To realise the potential for sustained high growth in the coming years it is necessary that prudence and realism continue to be exercised by government, interest groups, institutions and individuals. Favourable long-term factors could be negated by short-term impatience and unrealistic expectations

Evaluation of uterine ultrasound imaging in cervical radiotherapy; a comparison of autoscan and conventional probe

OBJECTIVE: In cervical radiotherapy, it is essential that the uterine position is correctly determined prior to treatment delivery. The aim of this study was to evaluate an autoscan ultrasound (A-US) probe, a motorized transducer creating three-dimensional (3D) images by sweeping, by comparing it with a conventional ultrasound (C-US) probe, where manual scanning is required to acquire 3D images. METHODS: Nine healthy volunteers were scanned by seven operators, using the Clarity(®) system (Elekta, Stockholm, Sweden). In total, 72 scans, 36 scans from the C-US and 36 scans from the A-US probes, were acquired. Two observers delineated the uterine structure, using the software-assisted segmentation in the Clarity workstation. The data of uterine volume, uterine centre of mass (COM) and maximum uterine lengths, in three orthogonal directions, were analyzed. RESULTS: In 53% of the C-US scans, the whole uterus was captured, compared with 89% using the A-US. F-test on 36 scans demonstrated statistically significant differences in interobserver COM standard deviation (SD) when comparing the C-US with the A-US probe for the inferior–superior (p < 0.006), left–right (p < 0.012) and anteroposterior directions (p < 0.001). The median of the interobserver COM distance (Euclidean distance for 36 scans) was reduced from 8.5 (C-US) to 6.0 mm (A-US). An F-test on the 36 scans showed strong significant differences (p < 0.001) in the SD of the Euclidean interobserver distance when comparing the C-US with the A-US scans. The average Dice coefficient when comparing the two observers was 0.67 (C-US) and 0.75 (A-US). The predictive interval demonstrated better interobserver delineation concordance using the A-US probe. CONCLUSION: The A-US probe imaging might be a better choice of image-guided radiotherapy system for correcting for daily uterine positional changes in cervical radiotherapy. ADVANCES IN KNOWLEDGE: Using a novel A-US probe might reduce the uncertainty in interoperator variability during ultrasound scanning

A modified Oster-Murray-Harris mechanical model of morphogenesis

There are two main modeling paradigms for biological pattern formation in developmental biology: chemical prepattern models and cell aggregation models. This paper focuses on an example of a cell aggregation model, the mechanical model developed by Oster, Murray, and Harris [Development, 78 (1983), pp. 83--125]. We revisit the Oster--Murray--Harris model and find that, due to the infinitesimal displacement assumption made in the original version of this model, there is a restriction on the types of boundary conditions that can be prescribed. We derive a modified form of the model which relaxes the infinitesimal displacement assumption. We analyze the dynamics of this model using linear and multiscale nonlinear analysis and show that it has the same linear behavior as the original Oster--Murray--Harris model. Nonlinear analysis, however, predicts that the modified model will allow for a wider range of parameters where the solution evolves to a bounded steady state. The results from both analyses are verified through numerical simulations of the full nonlinear model in one and two dimensions. The increased range of boundary conditions that are well-posed, as well as a wider range of parameters that yield bounded steady states, renders the modified model more applicable to, and more robust for, comparisons with experiments

Carbon source/sink information provided by column CO2 measurements from the Orbiting Carbon Observatory

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Atmospheric Chemistry and Physics 10 (2010): 4145-4165, doi:10.5194/acp-10-4145-2010.We quantify how well column-integrated CO2 measurements from the Orbiting Carbon Observatory (OCO) should be able to constrain surface CO2 fluxes, given the presence of various error sources. We use variational data assimilation to optimize weekly fluxes at a 2°×5° resolution (lat/lon) using simulated data averaged across each model grid box overflight (typically every ~33 s). Grid-scale simulations of this sort have been carried out before for OCO using simplified assumptions for the measurement error. Here, we more accurately describe the OCO measurements in two ways. First, we use new estimates of the single-sounding retrieval uncertainty and averaging kernel, both computed as a function of surface type, solar zenith angle, aerosol optical depth, and pointing mode (nadir vs. glint). Second, we collapse the information content of all valid retrievals from each grid box crossing into an equivalent multi-sounding measurement uncertainty, factoring in both time/space error correlations and data rejection due to clouds and thick aerosols. Finally, we examine the impact of three types of systematic errors: measurement biases due to aerosols, transport errors, and mistuning errors caused by assuming incorrect statistics. When only random measurement errors are considered, both nadir- and glint-mode data give error reductions over the land of ~45% for the weekly fluxes, and ~65% for seasonal fluxes. Systematic errors reduce both the magnitude and spatial extent of these improvements by about a factor of two, however. Improvements nearly as large are achieved over the ocean using glint-mode data, but are degraded even more by the systematic errors. Our ability to identify and remove systematic errors in both the column retrievals and atmospheric assimilations will thus be critical for maximizing the usefulness of the OCO data.SD and DB acknowledge support from NASA grant NNG06G127G. DB also acknowledges initial support from NOAA Grant NA16GP2935

Uptake of tritiated thymidine by primordial germinal cells in the ovaries of the adult slender loris

Six adult lorises (Loris tardigradus lydekkerianus) in anoestrus were selected for study. Four of the animals were pretreated with an injection of 0&#183;5 mg oestradiol-17&#946;, two were given FSH (2 &#215; 50 i.u. with a 12-hr interval), while the remaining two were not treated with hormones. All of the animals were subsequently given a subcutaneous injection of 0&#183;5 mCi [3H]thymidine and their ovaries were recovered for autoradiography 24 hr later.It was found that the non-follicular germinal cells within 'nests' in the ovarian cortex actively incorporated the radioisotope. Some of the labelled germinal cells appeared to reach the pachytene-diplotene stages of meiotic prophase, although this would not be expected to occur in such a short time after treatment. None of the labelled germinal cells appeared to enter upon the phase of follicular growth, although a few (especially in ovaries treated with oestrogen and FSH) seemed to be in primordial follicles consisting of an incomplete layer of flattened cells

Representation in Westminster in the 1990s : The ghost of Edmund Burke

Why are 'trustee' notions of representation still invoked in the UK House of Commons in the 1990s? In answering this question this article analyses the premises of Burkean theory and the arguments that these premises are of little relevance in the late twentieth century. Despite these dismissals of trusteeship, Burkean ideas are still articulated in the Commons some 200 years after they were first voiced. The idea of trusteeship can prove extremely useful to justify the actions of representatives when those actions conflict with constituency 'opinion', party policy or the wishes of interest groups. Examples of the occasions when Burkean notions have been invoked in the 1990s are provided

Subclinical infection of macaques and baboons with a baboon simarterivirus

Simarteriviruses (Arteriviridae: Simarterivirinae) are commonly found at high titers in the blood of African monkeys but do not cause overt disease in these hosts. In contrast, simarteriviruses cause severe disease in Asian macaques upon accidental or experimental transmission. Here, we sought to better understand the host-dependent drivers of simarterivirus pathogenesis by infecting olive baboons (n = 4) and rhesus monkeys (n = 4) with the simarterivirus Southwest baboon virus 1 (SWBV-1). Surprisingly, none of the animals in our study showed signs of disease following SWBV-1 inoculation. Three animals (two rhesus monkeys and one olive baboon) became infected and sustained high levels of SWBV-1 viremia for the duration of the study. The course of SWBV-1 infection was highly predictable: plasma viremia peaked between 1 × 107 and 1 × 108 vRNA copies/mL at 3–10 days post-inoculation, which was followed by a relative nadir and then establishment of a stable set-point between 1 × 106 and 1 × 107 vRNA copies/mL for the remainder of the study (56 days). We characterized cellular and antibody responses to SWBV-1 infection in these animals, demonstrating that macaques and baboons mount similar responses to SWBV-1 infection, yet these responses are ineffective at clearing SWBV-1 infection. SWBV-1 sequencing revealed the accumulation of non-synonymous mutations in a region of the genome that corresponds to an immunodominant epitope in the simarterivirus major envelope glycoprotein GP5, which likely contribute to viral persistence by enabling escape from host antibodies

Diasporic Literary Archives Network and the Commonwealth: Namibia, Nigeria, Trinidad & Tobago, and other examples

This article brings together three themes: primary sources for the study of literature; the diasporic nature of literary manuscripts; and the impact of the diaspora on the English-speaking world, in general, and the Commonwealth, in particular. The article begins by describing some general characteristics of literary manuscripts, focusing in particular on their diasporic nature. It then outlines the work of the project known as the Diasporic Literary Archives Network in the years 2012-15. It concludes with an assessment of the archival diaspora as it affects cultural and literary heritage work in Commonwealth countries