Collapse of a Molecular Cloud Core to Stellar Densities: The First Three-Dimensional Calculations

We present results from the first three-dimensional calculations ever to follow the collapse of a molecular cloud core (~ 10^{-18} g cm^{-3}) to stellar densities (> 0.01 g cm^{-3}). The calculations resolve structures over 7 orders of magnitude in spatial extent (~ 5000 AU - 0.1 R_\odot), and over 17 orders of magnitude in density contrast. With these calculations, we consider whether fragmentation to form a close binary stellar system can occur during the second collapse phase. We find that, if the quasistatic core that forms before the second collapse phase is dynamically unstable to the growth of non-axisymmetric perturbations, the angular momentum extracted from the central regions of the core, via gravitational torques, is sufficient to prevent fragmentation and the formation of a close binary during the subsequent second collapse.Comment: ApJ Letters, in press (will appear in Nov 20 issue; available from the ApJ Rapid Release web page). 7 pages, incl. 5 figures. Also available at http://www.mpia-hd.mpg.de/theory/bat

An experimental investigation of a fully cavitating two-dimensional flat plate hydrofoil near a free surface

An experimental program was conducted to investigate the characteristics of a fully cavitating two-dimensional flat plate hydrofoil in the presence of a free surface. The submergence of the hydrofoil was varied from the planing condition at the free surface to a depth corresponding to 2.16 model chords. Near the surface the cavities formed by venting to the atmosphere, but at the deeper submergences, they had to be artificially formed by supplying them with air. The normal force, the moment about the leading edge, the center of pressure location, the cavity length, and the volumetric air flow rate into the cavity are presented as functions of angle of attack, cavitation number, Froude number, and proximity to the free surface

Evaluation of delays in technical approval of UK Highways Act section 278 projects

This paper attempts to address the causes of delays to the legal and technical approval processes involved in the creation of agreements authorising works to public highways under s.278 Highways Act (1980) specific to Warwickshire County Council, UK, and whether the type of contract (JCT or NEC) or s.278 agreement (minor or major) has any tangible influence. A series of questionnaires and interviews were carried out on a sample group of individuals including designers, developers, construction lawyers, and council engineers with extensive industry experience in relation to s.278 legal, technical, construction and adoption processes. The results revealed the key causes of delays, and therefore the barriers to prompt and efficient approval processes, as the lack of communication between developer and local authority, inexperienced developers’ engineers, poor quality drawings, and insufficient information in the local authority’s design guide. These key factors are discussed and recommendations are provided to tackle these issues

Justifying music in the national curriculum: The habit concept and the question of social justice and academic rigour

In June 2015, the British government presented ‘the social justice case for an academic curriculum’ as the justification for recent radical changes to educational policy. However, this justification failed to account for both the key changes in the newly-revised National Curriculum for Music and the place of music in the National Curriculum as a whole. Through a critical evaluation of the National Curriculum for Music, this study will propose how the place of music could successfully be justified within an education system wholly committed to ‘social justice’. Using the ‘habit concept’ of classical philosophical pragmatism, it will assess how and why music's educational value should be understood not through its ‘academic rigour’ but through its distinctive, inherently destabilising nature

Measurements on fully wetted and ventilated ring wing hydrofoils

Force measurements and visual observations were made in a water tunnel on fully wetted and ventilated flows past a family of conical ring wings having a flat plate section geometry. The diameter-chord ratio was varied from one to three, and the total included cone angle was 12 degrees. The fully wetted flows all exhibited separation from the leading edge except for the largest diameter-chord ratio, a result which was in agreement with previous work. The effect of ventilation is to reduce markedly the lift curve slope. Pressure distribution measurements were also made under ventilating conditions for one member of this series. The effect of ventilation over only a portion of the circumference of the ring was also briefly investigated. Large cross forces were developed by such ventilation and some comparisons are made between this method of obtaining control forces and more conventional methods

Complete Reducibility and Commuting Subgroups

Let G be a reductive linear algebraic group over an algebraically closed field of characteristic p. We study J.-P. Serre's notion of G-complete reducibility for subgroups of G. In particular, for a subgroup H and a normal subgroup N of H, we look at the relationship between G-complete reducibility of N and of H, and show that these properties are equivalent if H/N is linearly reductive, generalizing a result of Serre. We also study the case when H = MN with M a G-completely reducible subgroup of G which normalizes N. We show that if G is connected, N and M are connected commuting G-completely reducible subgroups of G, and p is good for G, then H = MN is also G-completely reducible.Comment: 21 pages; to appear in J. Reine Angew. Math. final for

A Preliminary Study of the Effect of the Free Surface on a Three-dimensional Cavity Produced by a Circular Disk

The influence of the free surface on the cavitation associated with bodies operating at shallow submergences has long been of interest because of the practical use for such information. The performance of hydrofoil boats is very much dependent on the submergence below the water surface of the hydrofoils, for example. Because of the extreme complexity introduced by the consideration of boundaries of any sort, most theories relating the parameters associated with cavitation are developed for a fluid of "infinite" extent. The task of determining the effects of the boundaries for such a cavitating flow problem then becomes one of experimentation. Such an experiment was performed to determine the free surface effects on a supercavitating, flat plate hydrofoil in two-dimensional flow p:: However, most real flow situations are three dimensional, and the present experiment is a preliminary study to determine the effects of the free surface on the geometry of a ventilated cavity in such a flow. Specifically, the variation of the length of a cavity due to submergence is studied. The cavity is produced by a sharp- edged, circular disk normal to the flow. Figures la and lb show this cavity at two different ventilation numbers. This experiment was planned as a preliminary study to determine the general trend and order of magnitude of the free surface effects, For this reason, the results are presented with the preliminary data reduced to the pertinent dimensionless parameters, uncorrected for tunnel blockage and model scale effects, if any