1,360,499 research outputs found
Peter Halley e il dio che ride /Peter Halley and the laughing God
No full textIl saggio esamina l'installazione di Peter Halley al Museo Nivola di Orani, in Sardegna, con al quale l'artista ha creato la sua personale Cappella degli Scrovegni del XXI secolo: concettuale e decorativa, criticamente riflessiva e spettacolare, immergeva il visitatore nel clima dionisiaco di un Mediterraneo filtrato attraverso il Modernismo novecentesco e bagnato di una luce artificiale e psichedelica.
The essay examines Peter Halley's installation at Museo Nivola, Orani, Sardinia, with which the artist created his own contemporary Scrovegni chapel: conceptual and decorative, critically reflective and spectacular, it immersed the visitor in the Dionysian atmosphere of a Mediterranean world filteredthrough twentieth-century Modernism and bathed in an artificial, psychedelic light
Singularities in mass-loaded MHD flow: The cometary bow shock
No full textWe present a one-dimensional model of the mass-loading of the solar wind by cometary ions which predicts a singularity in the mass-loaded flow at M = 2. Further, a subshock occurs when the flow speed reaches M almost-equal-to 1.15. The shape of the cometary bow shock in two dimensions is predicted, by requiring that the flow Mach number of the shock is 2 taking the velocity component normal to the shock surface. The Mach number results compare favourably with observations at comet Halley
A chart of Borneo, Java and the Philippine Islands [cartographic material].
No full textEngraved chart with rhumb lines and wind roses which also shows part of New Guinea and Northern Australia.; Plate 36 from: Atlas maritimus et commercialis /Edmund Halley. 1728.; NMM, v. 3, no. 341.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.map-t135
A new & correct sea chart of the whole world [cartographic material] shewing the variations of the compass as they were found Año 1700 with a view of the generall and coasting trade winds and monsoons or shifting trade-winds /
No full textWorld map showing wind directions and degrees of variations.; In upper left corner: Vol.1. Plate 2 pag. 61.; From: Miscellanea curiosa : being a collection of some of the principle phaenomena in nature accounted for by the greatest philosophers of this age / Edmond Halley. London : J. Wale, 1705-1707.; Prime meridian: London.; Also available in an electronic version via the internet at: http://nla.gov.au/nla.map-rm3830. Inset: A map of North Pole.New and correct sea chart of the whole worl
Properties of mass-loading shocks: 1. Hydrodynamic considerations
No full textThe one-dimensional hydrodynamics of flows subjected to mass loading are considered anew, with particular emphasis placed on determining the properties of mass-loading shocks. This work has been motivated by recent observations of the outbound Halley bow shock (Neubauer et al., 1990), which cannot be understood in terms of simple hydrodynamical or magnetohydrodynamical descriptions. By including mass injection at the shock, we have investigated the properties of the Rankine-Hugoniot conditions on the basis of a geometric formulation of the entropy condition. Such a condition, which is more powerful than the usual thermodynamical formulation, serves to determine those solutions to the Rankine-Hugoniot conditions which correspond to a physically realizable downstream state. On this basis a concise theoretical description of hydrodynamic mass-loading shocks is obtained. We show that mass-loading shocks have more in common with combustion shocks than with ordinary nonreacting gas dynamical shocks. It is shown that for decelerated solutions to the Rankine-Hugoniot conditions to exist, the upstream flow speed u0 must satisfy u0 > ucrit > cs, where cs is the sound speed. Besides the usual supersonic-subsonic transition, mass-loading fronts can also admit a decelerating supersonic-supersonic transition, the structure of which consists of a sharp decrease in the flow velocity preceding a recovery and an increase in the final downstream flow speed. We suggest the possibility that such structures may describe the inbound Halley bow shock (Coates et al., 1987a). Both parallel and oblique shocks are considered, the primary difference being that oblique shocks are subjected to a shearing stress due to mass loading. It is conjectured that such a shearing may destabilize the shock
Properties of mass-loading shocks, 2. Magnetohydrodynamics
No full textThe one-dimensional magnetohydrodynamics of shocked flows subjected to significant mass loading are considered. Recent observations at comets Giacobini-Zinner and Halley suggest that simple nonreacting MHD is an inappropriate description for active cometary bow shocks. The thickness of the observed cometary shock implies that mass loading represents an important dynamical process within the shock itself, thereby requiring that the Rankine-Hugoniot condition for the mass flux possess a source term. In a formal sense, this renders mass-loading shocks qualitatively similar to combustion shocks, except that mass loading induces the shocked flow to shear. Nevertheless, a large class of stable shocks exist, identified by means of the Lax conditions appropriate to MHD. Thus mass-loading shocks represent a new and interesting class of shocks, which, although found frequently in the solar system, both at the head of comets and, under suitable conditions, upsteam of weakly magnetized and nonmagnetized planets, has not been discussed in any detail. Owing to the shearing of the flow, mass-loading shocks can behave like switch-on shocks regardless of the magnitude of the plasma beta. Thus the behavior of the magnetic field in mass-loading shocks is significantly different from that occurring in nonreacting classical MHD shocks. It is demonstrated that there exist two types of mass-loading fronts for which no classical MHD analogue exists, these being the fast and slow compound mass-loading shocks. These shocks are characterized by an initial deceleration of the fluid flow to either the fast or the slow magnetosonic speed followed by an isentropic expansion to the final decelerated downstream state. Thus these transitions take the flow from a supersonic to a supersonic, although decelerated, downstream state, unlike shocks which occur in classical MHD or gasdynamics. It is possible that such structures have been observed during the Giotto-Halley encounter, and a brief discussion of the appropriate Halley parameters is therefore given, together with a short discussion of the determination of the shock normal from observations. A further interesting new form of mass-loading shock is the “slow-intermediate” shock, a stable shock which possesses many of the properties of intermediate MHD shocks yet which propagates like a slow mode MHD shock. An important property of mass-loading shocks is the large parameter regime (compared with classical MHD) which does not admit simple or stable transitions from a given upstream to a downstream state. This suggests that it is often necessary to construct compound structures consisting of shocks, slip waves, rarefactions, and fast and slow compound waves in order to connect given upstream and downstream states. Thus the Riemann problem is significantly different from that of classical MHD
Predictions of the solar wind interaction with Comet Grigg-Skjellerup
No full textThe planned encounter of the Giotto spacecraft with comet Grigg-Skjellerup on 10th July 1992 promises to extend our knowledge of the solar wind interaction with comets substantially. While there have been spacecraft missions to comets before now, this mission is exploratory in the sense that the target comet is much older and there-fore it has a much lower gas production rate than comets Halley (by a factor approximately 200) or Giacobini-Zinner (factor approximately 10). Here we present theoretical predictions for the location of the bow shock and contact surface features, and compare similar predictions with the observed features at the previous encounters. We discuss the applicability of fluid-type theory which these models employ, in the case of strong and weak comets in the solar wind
Hypervelocity dust particle impacts observed by the Giotto Magnetometer and Plasma Experiments
No full textWe report thirteen very short events in the magnetic field of the inner magnetic pile‐up region of comet Halley observed by the Giotto magnetometer experiment together with simultaneous plasma data obtained by the Johnstone plasma analyzer and the ion mass spectrometer experiments. The events are due to dust impacts in the milligram range on the spacecraft at the relative velocity between the cemetery dust and the spacecraft of 68 km/sec. They are generally consistent with dust impact events derived from spacecraft attitude perturbations by the Giotto camera [Curdt and Keller, private communication]. Their characteristic shape generally involves a sudden decrease in magnetic field magnitude, a subsequent overshoot beyond initial field values and an asymptotic approach to the initial field somewhat reminiscent of the magnetic field signature after the AMPTE releases in the solar wind. These observations give a new way of analyzing ultra‐fast dust particles incident on a spacecraft
Stellarum fixarum hemisphærium boreale [cartographic material] : the northern hemisphere projected on the plane of the æquator in which all the stars contain'd in the Britannick catalogue (as publish'd by D' Halley) are carefully laid down and adapted to the beginning of the year 1690 the afterismes being drawn to answer the description of the ancients.
No full textA first issue of the engraved astronomical northern hemisphere star maps by Senex. The product of an uneasy alliance between Halley and Flamsteed and the most widely used of all contemporary star maps. The map includes their most recent discoveries including showing novas and nebulas derived from Halley's work in Philosophical transactions as well as the seventh-magnitude telesopic stars that had been observed by Flamsteed.; Includes 9 small spheres and numbered notes with problems and solutions in the left and right panels.; Also available in an electronic version via the internet at: http://nla.gov.au/nla.map-rm4129
Effects of spatial diffusion on nonequilibrium steady states in a model for prebiotic evolution Figure Data
No full textThe txt files contain space separated values, headers, and some contain descriptions of data. The python script files (*.py) ingest the txt data files and some calculate statistical errors and export more txt data files while other python scripts generate figures/plots. The GNUPlot script files (*.gnuplot) ingest txt data files and generate figures seen in the referenced 2016 PRE publication.This dataset contains data used to create the figures in the publication Intoy, B. F., A. Wynveen, and J. W. Halley. "Effects of spatial diffusion on nonequilibrium steady states in a model for prebiotic evolution." Physical Review E 94.4 (2016): 042424. This data set also contains extra data not presented in the publication.NASA NNX14AQ05GIntoy, Ben Frederick M; Wynveen, Aaron; Halley, J Woods. (2022). Effects of spatial diffusion on nonequilibrium steady states in a model for prebiotic evolution Figure Data. Retrieved from the University Digital Conservancy, https://doi.org/10.13020/fjqs-vt12
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