A Unification of Models of Tethered Satellites

In this paper, different conservative models of tethered satellites are related mathematically, and it is established in what limit they may provide useful insight into the underlying dynamics. An infinite dimensional model is linked to a finite dimensional model, the slack-spring model, through a conjecture on the singular perturbation of tether thickness. The slack-spring model is then naturally related to a billiard model in the limit of an inextensible spring. Next, the motion of a dumbbell model, which is lowest in the hierarchy of models, is identified within the motion of the billiard model through a theorem on the existence of invariant curves by exploiting Moser's twist map theorem. Finally, numerical computations provide insight into the dynamics of the billiard model

Collapse of linefish stocks between cape hangklip and Walker bay, South Africa

The state of the linefishery between Cape Hangklip and Walker Bay on the Cape south coast, South Africa, is assessed. The coast was subdivided into 20 “beats” to provide high spatial resolution on catch and effort of theshore-based recreational fishery. An observer recorded the number of anglers in each fishery sector, and their catch, during shore patrols over a two-year period. Catch-and-effort data for the commercial boat-based fishery were obtained from an historical database at the turn of last century and from the extant National Marine Linefish System database. Catch per unit effort (cpue) of shore-anglers was low and many of the species caught earlier in the century have disappeared from catches. Compared to the early records, contemporary commercial linefish cpue had dropped by approximately 80%, despite a greater fishing capacity. It is argued that most targeted stocks have been overexploited (notwithstanding indications of environmental change) and many are severely depleted. Poor management of the fishery, including a lack of control of commercial effort and inadequate enforcement, contributed to overexploitation

Is there a role for a Carer Support Nurse?

Carers play a vital role in supporting family and friends with health conditions, particularly long-term health conditions. This impacts on their own health and well-being. The NHS is committed to supporting carers, and community nurses are well-placed to identify and support them, but changes in the workforce and the patient population mean that nurses’ time is limited: their focus is on meeting patients’ needs. We propose a solution: a Carer Support Nurse role, dedicated to the needs of carers. We would welcome your views on this proposal

Distinctive populations of basement membrane and cell membrane heparan sulfate proteoglycans are produced by cultured cell lines

Abstract. We have investigated the nature and distribution of different populations of heparan sulfate proteoglycans (HSPGs) in several cell lines in culture. Clone 9 hepatocytes and NRK and CHO cells were biosynthetically labeled with 35SO4, and proteoglycans were isolated by DEAE-Sephacel chromatography. Heterogeneous populations of HSPGs and chondroitin/dermatan proteoglycans (CSPGs) were found in the media and cell layer extracts of all cultures. HSPGs were further purified from the media and cell layers and separated from CSPGs by ion exchange chromatography after chondroitinase ABC digestion. In all cell types, HSPGs were found both in the cell layers (20-70 % of the total) as well as the medium. When the purified HSPG fractions were further separated b

Lead Isotope Data for Gold-Bearing Veins and Their Host Metasedimentary Rocks of the Goldenville Formation, Eastern Nova Scotia

Lead isotope analyses have been determined for galenas which occur in small quantities in quartz veins in the Goldenville Formation of the Meguma Terrane, and also for five whole rock samples from this formation- The ten least radiogenic galenas are homogeneous in isotopic composition, and they plot close to the average terrestrial growth curve of Stacey and Kramers and the "orogene" curve of Doe and Zartman. The mean model ages are 550 Ma (Stacey and Kramers) and 600 Ma (Doe and Zartman), which are in approximate agreement with the Cambro-Ordovician age of deposition of the sediments. The close position of the galena compositions to these average growth curves suggests that these compositions were established by mixing processes as envisaged in the Doe and Zartman "plumbotectonics" model. The isotopic analyses of the whole rocks indicate that small amounts of radiogenic lead are present in non-mineralized sections of the sedimentary sequence- Three galenas from veins in rocks metamorphosed to biotite and staurolite-andalusite grades, and from late veins (post-dating deformation, metamorphism and plutonism) are significantly more radiogenic than the majority of the samples. We interpret the isotopic characteristics of these galenas to be the result of extraction of lead from Meguma metasediments or of additions of radiogenic lead to less radiogenic lead during remobllization. Other interpretations consistent with the isotopic data are possible. RÉSUMÉ Des analyses aux isotopes de plomb ont été déterminé pour les galènes qui se trouvent en petite quantitié's dans les veines de quartz de la formation Goldenville du terrane Meguma, et aussi pour cinq échantillons de roches entieres de cette formation. Les dix galènes les moins radiogèniques sont homogènes en composition isotopique, et elles ont une trace proche de la courbe de croissauce terreste moyenne de Stacey et Kramers, et de la courbe "orogène" de Doe et Zartman. Le âges moyens des modules sont de 550 Ma (Stacey et Kramers) et de 600 Ma (Doe et Zartman), ce qui s'accorde approximativement avec l'âge Cambro-Ordovicien du dépôt des sédiments. La position proche des compositions de la galène avec ces courbes moyennes de croissance, indique que ces compositions ont été établies par un processus de mélanges, comme le propose le modèle "Piumbotectonique" de Doe et Zartman. Les analyses isotopiques de roche entiere indiquent que de petites quantitié's de plomb radiogenique sont présences dans les sections non-minéralisees de la séquence sédimentaire. Trois galènes, provenant de veines de roches métamorphosée au dégris de biotite et de staurolite-anda lusite, et de veines avancées (post-datant la déformation, le métamorphisine et le plutonisme) sont d'une maniere significative plus radiogèniques que la majoritié des échantillons. Nous interprètons les caractéristiques isotopiques de ces galènes comme le résultat de l'extraction de plomb des méta-sédiments Meguma, ou a L’addition de plomb radiogènique au plomb moins radiogènique durant la remobilisation. D'autres Interprètations en accord avec les donnés isotopiques sont possible. [Traduit par le journal

Liquid rocket engine axial-flow turbopumps

The axial pump is considered in terms of the total turbopump assembly. Stage hydrodynamic design, pump rotor assembly, pump materials for liquid hydrogen applications, and safety factors as utilized in state of the art pumps are among the topics discussed. Axial pump applications are included

Trajectory and stability of Lagrangian point L2L_2 in the Sun-Earth system

This paper describes design of the trajectory and analysis of the stability of collinear point $L_2$ in the Sun-Earth system. The modified restricted three body problem with additional gravitational potential from the belt is used as the model for the Sun-Earth system. The effect of radiation pressure of the Sun and oblate shape of the Earth are considered. The point $L_2$ is asymptotically stable upto a specific value of time $t$ correspond to each set of values of parameters and initial conditions. The results obtained from this study would be applicable to locate a satellite, a telescope or a space station around the point $L_2$.Comment: Accepted for publication in Astrophysics & Space Scienc

Asymptotic analysis of displaced lunar orbits

The design of spacecraft trajectories is a crucial task in space mission design. Solar sail technology appears as a promising form of advanced spacecraft propulsion which can enable exciting new space science mission concepts such as solar system exploration and deep space observation. Although solar sailing has been considered as a practical means of spacecraft propulsion only relatively recently, the fundamental ideas are by no means new (see McInnes1 for a detailed description). A solar sail is propelled by reflecting solar photons and therefore can transform the momentum of the photons into a propulsive force. Solar sails can also be utilised for highly non-Keplerian orbits, such as orbits displaced high above the ecliptic plane (see Waters and McInnes2). Solar sails are especially suited for such non-Keplerian orbits, since they can apply a propulsive force continuously. In such trajectories, a sail can be used as a communication satellite for high latitudes. For example, the orbital plane of the sail can be displaced above the orbital plane of the Earth, so that the sail can stay fixed above the Earth at some distance, if the orbital periods are equal (see Forward3). Orbits around the collinear points of the Earth-Moon system are also of great interest because their unique positions are advantageous for several important applications in space mission design (see e.g. Szebehely4, Roy,5 Vonbun,6 Thurman et al.,7 Gomez et al.8, 9). Several authors have tried to determine more accurate approximations (quasi-Halo orbits) of such equilibrium orbits10. These orbits were first studied by Farquhar11, Farquhar and Kamel10, Breakwell and Brown12, Richardson13, Howell14, 15.If an orbit maintains visibility from Earth, a spacecraft on it (near the L2 point) can be used to provide communications between the equatorial regions of the Earth and the lunar poles. The establishment of a bridge for radio communications is crucial for forthcoming space missions, which plan to use the lunar poles.McInnes16 investigated a new family of displaced solar sail orbits near the Earth-Moon libration points.Displaced orbits have more recently been developed by Ozimek et al.17 using collocation methods. In Baoyin and McInnes18, 19, 20 and McInnes16, 21, the authors describe new orbits which are associated with artificial Lagrange points in the Earth-Sun system. These artificial equilibria have potential applications for future space physics and Earth observation missions. In McInnes and Simmons22, the authors investigate large new families of solar sail orbits, such as Sun-centered halo-type trajectories, with the sail executing a circular orbit of a chosen period above the ecliptic plane. We have recently investigated displaced periodic orbits at linear order in the Earth-Moon restricted three-body system, where the third massless body is a solar sail (see Simo and McInnes23). These highly non-Keplerian orbits are achieved using an extremely small sail acceleration. It was found that for a given displacement distance above/below the Earth-Moon plane it is easier by a factor of order 3.19 to do so at L4=L5 compared to L1=L2 - ie. for a fixed sail acceleration the displacement distance at L4=L5 is greater than that at L1=L2. In addition, displaced L4=L5 orbits are passively stable, making them more forgiving to sail pointing errors than highly unstable orbits at L1=L2.The drawback of the new family of orbits is the increased telecommunications path-length, particularly the Moon-L4 distance compared to the Moon-L2 distance

Diverse CD81 proteins support hepatitis C virus infection.

Hepatitis C virus (HCV) entry is dependent on CD81. To investigate whether the CD81 sequence is a determinant of HCV host range, we expressed a panel of diverse CD81 proteins and tested their ability to interact with HCV. CD81 large extracellular loop (LEL) sequences were expressed as recombinant proteins; the human and, to a low level, the African green monkey sequences bound soluble HCV E2 (sE2) and inhibited infection by retrovirus pseudotype particles bearing HCV glycoproteins (HCVpp). In contrast, mouse or rat CD81 proteins failed to bind sE2 or to inhibit HCVpp infection. However, CD81 proteins from all species, when expressed in HepG2 cells, conferred susceptibility to infection by HCVpp and cell culture-grown HCV to various levels, with the rat sequence being the least efficient. Recombinant human CD81 LEL inhibited HCVpp infectivity only if present during the virus-cell incubation, consistent with a role for CD81 after virus attachment. Amino acid changes that abrogate sE2 binding (I182F, N184Y, and F186S, alone or in combination) were introduced into human CD81. All three amino acid changes in human CD81 resulted in a molecule that still supported HCVpp infection, albeit with reduced efficiency. In summary, there is a remarkable plasticity in the range of CD81 sequences that can support HCV entry, suggesting that CD81 polymorphism may contribute to, but alone does not define, the HCV susceptibility of a species. In addition, the capacity to support viral entry is only partially reflected by assays measuring sE2 interaction with recombinant or full-length CD81 proteins