Practical Limits on Nanosatellite Telescope Pointing: The Impact of Disturbances and Photon Noise

Accurate and stable spacecraft pointing is a requirement of many astronomical observations. Pointing particularly challenges nanosatellites because of an unfavorable surface area–to-mass ratio and a proportionally large volume required for even the smallest attitude control systems. This work explores the limitations on astrophysical attitude knowledge and control in a regime unrestricted by actuator precision or actuator-induced disturbances such as jitter. The external disturbances on an archetypal 6U CubeSat are modeled, and the limiting sensing knowledge is calculated from the available stellar flux and grasp of a telescope within the available volume. These inputs are integrated using a model-predictive control scheme. For a simple test case at 1 Hz, with an 85-mm telescope and a single 11th magnitude star, the achievable body pointing is predicted to be 0.39 arcseconds. For a more general limit, integrating available star light, the achievable attitude sensing is approximately 1 milliarcsecond, which leads to a predicted body pointing accuracy of 20 milliarcseconds after application of the control model. These results show significant room for attitude sensing and control systems to improve before astrophysical and environmental limits are reached.

A Note on Two Fundamental Recursive Sequences

In this note, we establish some general results for two fundamental recursive sequences that are the basis of many well-known recursive sequences, as the Fibonacci sequence, Lucas sequence, Pell sequence, Pell-Lucas sequence, etc. We establish some general limit formulas, where the product of the first n terms of these sequences appears. Furthermore, we prove some general limits that connect these sequences to the number e(≈ 2.71828...).

Single-clause when-defining models in English monolingual pedagogical dictionaries

The paper is concerned with the single-clause when-definition, which is a common folk-defining style that has been established by lexicographers in English monolingual learners’ dictionaries (the Big Five), especially the Longman Dictionary of Contemporary English and Cambridge Advanced Learner’s Dictionary. In brief, the single-clause when-definition format can be applied to explain the meaning of abstract nouns and it closely resembles the double-clause (full-sentence) definition, which can also begin with a subordinating conjunction such as when or if. However, the when-definition does not include the word which is being defined (definiendum) and it is formed out of a single, subordinate clause. This definition-type has received metalexicographers’ attention as it appears to, in general, limit the effectiveness of correct extraction of word class information from abstract noun entries in contrast to the traditional defining model – the analytical definition. In this paper, an attempt is made to investigate two types of single-clause when-defining models: (1) when + personal pronoun; and (2) when + indefinite pronoun (someone/something).1 The collected evidence from the Linear Mixed-effects Modelling analysis indicates that the effect of when-definition type on syntactic class identification accuracy is statistically significant at the 8% level of significance, with the when + personal pronoun defining style being the superior defining model.

ANÁLISE 2D E 3D DA ESTABILIDADE DA BARRAGEM DE FUNDÃO

RESUMO: A falha da Barragem de Fundão, o maior desastre de seu tipo no mundo, foi estudada por Morgenstern et al. (2016) através de abordagens bidimensionais. A investigação realizada não apontou mecanismos de instabilidade de taludes como sendo as causas do desastre. No entanto, o formato complexo da face da barragem, com regiões côncavas e convexas, não foi considerado devido às limitações das ferramentas empregadas. Este trabalho apresenta análises bidimensionais (2D) e tridimensionais (3D), teoricamente mais rigorosas e adequadas para a geometria da barragem. As análises de estabilidade do maciço foram realizadas utilizando o Método Geral das Fatias e das Colunas (GLE), por meio do software SVSLOPE. Foram realizadas buscas por superfícies críticas 2D e 3D, ao longo de todas as zonas da estrutura. Considerando-se parâmetros de resistência drenada, observou-se que Fundão se encontraria em condições de elevada segurança, sendo o menor Fator de Segurança igual a 1,744. Valores próximos de 1,0 foram obtidos considerando rejeitos na condição não drenada, supostamente menos representativa das condições reais de campo. Os Fatores de Segurança 3D se mostraram muito próximos dos 2D, porém com variações significativas nas regiões côncava e convexa. Desta forma, conclui-se que o formato próximo à região do recuo exige maior atenção e análises 3D podem identificar as regiões críticas. ABSTRACT: The failure of the Fundão Dam, the largest disaster of its kind in the world, was studied by Morgenstern et al. (2016) using two-dimensional approaches. The carried out investigation did not point to mechanisms of slope instability as the causes of the disaster. However, the complex shape of the dam and its concave and convex regions were not originally considered due to limitations of the analysis tools employed. This paper presents two-dimensional (2D) and three-dimensional (3D) analyses that are more rigorous and well suited for the Fundão dam geometry. Slope stability analyses were accomplished using the General Limit Equilibrium Method of Slices and Columns (GLE) using the SVSLOPE software. Critical slip surfaces were searched in 2D and 3D, across the entire dam face. Drained shear strength parameters led to Factors of Safety that would indicate fairly stable conditions, with a lowest Factor of Safety of 1.744. Values close to 1.0 were obtained considering undrained conditions of the tailings, which are supposedly less representative of field conditions. The 3D factors of safety were very close to the 2D values, but with noticeably higher variations near the concave and convex regions. This leads to the conclusion that the dam shape near the setback region requires closer examination by means of 3D analyses that enable the identification of critical zones.

A practical method for estimating coupling functions in complex dynamical systems

A foremost challenge in modern network science is the inverse problem of reconstruction (inference) of coupling equations and network topology from the measurements of the network dynamics. Of particular interest are the methods that can operate on real (empirical) data without interfering with the system. One such earlier attempt (Tokuda et al. 2007 Phys. Rev. Lett. 99 , 064101. ( doi:10.1103/PhysRevLett.99.064101 )) was a method suited for general limit-cycle oscillators, yielding both oscillators' natural frequencies and coupling functions between them (phase equations) from empirically measured time series. The present paper reviews the above method in a way comprehensive to domain-scientists other than physics. It also presents applications of the method to (i) detection of the network connectivity, (ii) inference of the phase sensitivity function, (iii) approximation of the interaction among phase-coherent chaotic oscillators, and (iv) experimental data from a forced Van der Pol electric circuit. This reaffirms the range of applicability of the method for reconstructing coupling functions and makes it accessible to a much wider scientific community. This article is part of the theme issue ‘Coupling functions: dynamical interaction mechanisms in the physical, biological and social sciences’.

Sources of Electromagnetic Field in Transportation System and Their Possible Health Impacts

Exposure to electromagnetic field caused by transportation systems is a cause of concern for many people. In public and personal transport there are many sources of electromagnetic field. Plenty of dosimetric analyses of electromagnetic field carried out by various research groups found out very high exposure values in the transport. Although the measured fields in transport remain well below the general limit for public exposure as defined by ICNIRP (1998) standards, they are relatively high compared to other micro-environments in daily life, especially for children seated in the rear seat, as field strengths are comparatively high there and children are a sensitive part of the population. How long-term effects of these fields affect the human organism and what is the mechanism of action, are questions without known answers. Several studies point to the potential association of various diseases with exposure to electromagnetic field. The key to understanding the effect of the electromagnetic field on the human organism is to reveal the mechanism of action of the field.

JSJ DECOMPOSITIONS OF DOUBLES OF FREE GROUPS

We classify all possible JSJ decompositions of doubles of free groups of rank two, and we also compute the Makanin–Razborov diagram of a particular double of a free group and deduce that in general limit groups are not freely subgroup separable.

Comparative Study with 89Y-foil and 89Y-pressed Targets for the Production of 89Zr †

Zirconium-89 (89Zr, t1/2 = 3.27 days) owns great potential in nuclear medicine, being extensively used in the labelling of antibodies and nanoparticules. 89Zr can be produced by cyclotron via an 89Y(p,n)89Zr reaction while using an 89Y-foil target. In this study, we investigated for the first time the use of 89Y-pressed target for the preparation of 89Zr-oxalate via a (p,n) reaction. We performed comparative studies with an 89Y-foil target mounted on custom-made target supports. A new automated cassette-based purification module was used to facilitate the purification and the fractionation of 89Zr-oxalate. The effective molar activity (EMA) was calculated for both approaches via titration with deferoxamine (DFO). The radionuclidic purity was determined by gamma-ray spectroscopy and the metal impurities were quantified by ICP-MS on the resulting 89Zr-oxalate solution. The cassette-based purification process leading to fractionation is simple, efficient, and provides very high EMA of 89Zr-oxalate. The total recovered activity was 81 ± 4% for both approaches. The highest EMA was found at 13.3 MeV and 25 μA for 0.25-mm thick 89Y-foil. Similar and optimal production yields were obtained at 15 MeV and 40 μA while using 0.50-mm thick 89Y-foil and pressed targets. Metallic impurities concentration was below the general limit of 10 ppm for heavy metals in the US and Ph.Eur for both 89Y-foil and pressed targets. Overall, these results show that the irradiation of 89Y-pressed targets is a very effective process, offering an alternative method for 89Zr production.