An analytical solution to electromagnetically coupled duct flow in MHD

The flow of an electrically conducting fluid in an array of square ducts, separated by arbitrary thickness conducting walls, subject to an applied magnetic field is studied. The analytical solution presented here is valid for thick walls and is based on the homogeneous solution obtained by Shercliff (Math. Proc. Camb. Phil. Soc., vol. 49 (01), 1953, pp. 136-144). Arrangements of ducts arise in a number of applications, most notably in fusion blankets, where liquid metal is used both as coolant and for tritium generation purposes. Analytical solutions, such as those presented here, provide insight into the physics and important benchmarking and validation data for computational magnetohydrodynamics (MHD), as well as providing approximate flow parameters for 1D systems codes. It is well known that arrays of such ducts with conducting walls exhibit varying degrees of coupling, significantly affecting the flow. An important practical example is the so-called Madarame problem (Madarame et al., Fusion Technol., vol. 8, 1985, pp. 264-269). In this work analytical results are derived for the relevant hydrodynamic and magnetic parameters for a single duct with thick walls analogous to the Hunt II case. These results are then extended to an array of such ducts stacked in the direction of the applied magnetic field. It is seen that there is a significant coupling affect, resulting in modifications to pressure drop and velocity profile. In certain circumstances, counter-current flow can occur as a result of the MHD effects, even to the point where the mean flow is reversed. Such phenomena are likely to have significant detrimental effects on both heat and mass transfer in fusion applications. The dependence of this coupling on parameters such as conductivities, wall thickness and Hartmann number is studied

Fabrication of slender struts for deployable antennas

A procedure for manufacturing long slender graphite tubing is desired. Such tubing has considerable application in truss supported spacecraft applications. The motivation for the selection of the tubing size developed in this program is for use as struts in a NASA, Langley Research Center truss supported antenna concept. The manufacturing procedure uses the LMSC vertical winding machine. A procedure for fabricating graphite epoxy tubing with an aluminum foil inner and outer wrap was also developed. The aluminum foil provides a vapor barrier, significantly improves the thermal conductivity, and provides an excellent thermal control surface

Seamless metal-clad fiber-reinforced organic matrix composite structures and process for their manufacture

A metallic outer sleeve is provided which is capable of enveloping a hollow metallic inner member having continuous reinforcing fibers attached to the distal end thereof. The inner member is then introduced into outer sleeve until inner member is completely enveloped by outer sleeve. A liquid matrix member is then injected into space between inner member and outer sleeve. A pressurized heat transfer medium is flowed through the inside of inner member, thereby forming a fiber reinforced matrix composite material. The wall thicknesses of both inner member and outer sleeve are then reduced to the appropriate size by chemical etching, to adjust the thermal expansion coefficient of the metal-clad composite structure to the desired value. thereby forming a fiber reinforced matrix composite material. The wall thicknesses of both inner member and outer sleeve are then reduced to the appropriate size by chemical etching, to adjust the thermal expansion coefficient of the metal-clad composite structure to the desired value. The novelty of this invention resides in the development of a efficient method of producing seamless metal clad fiber reinforced organic matrix composite structures

Stellar mass functions of galaxies, disks and spheroids at z~0.1

We present the stellar mass functions (SMF) and mass densities of galaxies, and their spheroid and disk components in the local (z~0.1) universe over the range 8.9 <= log(M/M_solar) <= 12 from spheroid+disk decompositions and corresponding stellar masses of a sample of over 600,000 galaxies in the SDSS-DR7 spectroscopic sample. The galaxy SMF is well represented by a single Schechter function (M* = 11.116+/-0.011, alpha = -1.145+/-0.008), though with a hint of a steeper faint end slope. The corresponding stellar mass densities are (2.670+/-0.110), (1.687+/-0.063) and (0.910+/-0.029)x10^8 M_solar Mpc^-3 for galaxies, spheroids and disks respectively. We identify a crossover stellar mass of log(M/M_solar) = 10.3+/-0.030 at which the spheroid and disk SMFs are equal. Relative contributions of four distinct spheroid/disk dominated sub-populations to the overall galaxy SMF are also presented. The mean disk-to-spheroid stellar mass ratio shows a five fold disk dominance at the low mass end, decreasing monotonically with a corresponding increase in the spheroidal fraction till the two are equal at a galaxy stellar mass, log(M/M_solar)=10.479+/-0.013, the dominance of spheroids then grows with increasing stellar mass. The relative numbers of composite disk and spheroid dominated galaxies show peaks in their distributions, perhaps indicative of a preferred galaxy mass. Our characterization of the low redshift galaxy population provides stringent constraints for numerical simulations to reproduce.Comment: 30 pages, 18 figures, 5 tables (2 online), Accepted for publication in MNRA

Mapping Community Mindscapes: Visualizing Social Autobiography as Political Transformation and Mobilization

Historically, autobiography has been used to perpetuate neo-liberal ideologies. Yet, when autobiography becomes social and is used to engage political communities of color, political transformation is possible. This project, through the collaborative visualization of Asian American social biography using pedagogical and relational methods as a means for engagement, seeks to destabilize dominant notions of time and space, and provide a mechanism for the retention of and documentation of institutional, and social histories using the Asian American Student Union at Scripps College as the site for political praxis

Optical and magnetic resonance studies of doped magnesium oxide

Magnesium Oxide crystals doped with chromium and cobalt have been investigated by optical spectroscopy and electron spin resonance spectroscopy. The optical work has provided information about the oxidation state and lattice site of the dopant ions, whilst the magnetic resonance results have given insight into the experience interactions between them. The Optical work on MgO:Cr has confirmed that the majority of dopant enters the lattice substitutionally as Cr3-*'up to I5IOO p.p.m., although at the higher concentration samples show evidence for a small amount of a second phase being formed. This has tentatively been ascribed as the spinel structure MgCr(_2)o(_4). A linewidth analysis of the electron spin resonance signal due to the even isotopes of Cr(^3+) in substitutional sites has been made at room temperature. The value of linewidth is found to be considerably less than predicted by Van Vleck's second moment theory, and furthermore is independent of concentration as opposed to the (concentration)(^½) dependance expected from this theory. The discrepancy has been explained on the grounds of a strong exchange field between the chromic ions which gives rise to exchange narrowing. This idea is supported by the coefficients of 1-nirtosis for the absorption lines which indicate a substantial trend to the Lorentsian lineshape. The strength of the exchange field has been measured as 4.45 X 10(^12) Hz from the e.s.r, data at both 9.3155 GHz and 35.5 GHz. A similar course of study was adopted for MgO:Co, Optical spectroscopy at both room and liquid nitrogen temperatures has shown that when discussing the 24-optical energy levels of Co substitutional in MgO considerable attention must be payed to spin-orbit coupling. The linewidth of the e.s.r. spectrum of this Co(^2+) taken at 9.5155 GHz between 4.2 and 65 K showed the linewidth to be a function of both temperature and concentration. The temperature dependance is attributed to a change in relaxation mechanism, and it is postulated that the Orbach process dominates above about utilising the first excited state of the spin orbit coupling levels, An attempt to factor off the temperature dependence of the linewidth has been made and again strong evidence for exchange narrowing, both from linewidth and lineshape arguments is seen. The strength of the exchange field has been calculated as 4.53 x 10(^12) Hz. Finally some previously published results for iron have been examined. From these the corresponding exchange field for Fe(^3+) in MgO has been evaluated as 1.14 x l0(^13) Hz

Current controversies in the Caledonides

No abstract available

Multiuser collaborative practical learning using packet tracer

To support the delivery of group-based remote collaborative work in the practice based learning domain of computer networking. Historically this has presented challenges in scale, management, security and technological resource to support delivery, assessment and learning. In partnership with the packet tracer development team at Cisco Systems, this paper explores the pedagogical and technological potential for a worldwide ‘simulated’ Internet and reports on initial researc

Development of assembly and joint concepts for erectable space structures

The technology associated with the on-orbit assembly of tetrahedral truss platforms erected of graphite epoxy tapered columns is examined. Associated with the assembly process is the design and fabrication of nine member node joints. Two such joints demonstrating somewhat different technology were designed and fabricated. Two methods of automatic assembly using the node designs were investigated, and the time of assembly of tetrahedral truss structures up to 1 square km in size was estimated. The effect of column and node joint packaging on the Space Shuttle cargo bay is examined. A brief discussion is included of operating cost considerations and the selection of energy sources. Consideration was given to the design assembly machines from 5 m to 20 m. The smaller machines, mounted on the Space Shuttle, are deployable and restowable. They provide a means of demonstrating the capabilities of the concept and of erecting small specialized platforms on relatively short notice