Engineering Commons^™

Discovery Of Ghost Cavities In The X-Ray Atmosphere Of Abell 2597, B. R. Mcnamara, M. W. Wise, P. Nulsen, L. P. David, C. L. Carilli, C. L. Sarazin, C. P. O'Dea, J. Houck, M. Donahue, S. Baum, M. Voit, R. W. O'Connell, A. Koekemoer

Faculty of Engineering - Papers (Archive)

A Chandra image of the central 100 kpc of the Abell 2597 cluster of galaxies shows bright irregular X-ray emission within the central dominant cluster galaxy (CDG) and two low surface brightness cavities located 30 kpc from the nucleus of the CDG. Unlike the cavities commonly seen in other clusters, the "ghost" cavities in Abell 2597 are not coincident with the bright central radio source. Instead, they appear to be associated with faint extended radio emission seen in a deep Very Large Array radio map. We interpret the ghost cavities as buoyantly rising relics of a radio outburst that occurred …

Bulk Stress Due To Surface Damage Of Crystalline Silicon And Germanium, P. Fisher, R. Vickers

Faculty of Engineering - Papers (Archive)

It is found that abrading two opposing surfaces of either crystalline Si or Ge samples results in homogeneous, uniaxial stress throughout the bulk perpendicular to the damaged surfaces. The latter are chosen to coincide with simple crystallographic planes. This conclusion is reached by analyzing the splittings, intensities, and polarizations of the absorption lines of the Lyman series of bulk shallow impurities in the abraded semiconductors. This effect has been observed for samples which range in thickness, t, from 1 to 3 mm, the internal stress being proportional to t–1.

Magneto-Optical Franz-Keldysh Effect Of An Electron Gas Subjected To Quantizing Magnetic Fields And Intense Terahertz Laser Fields, W. Xu

Faculty of Engineering - Papers (Archive)

When a three-dimensional electron gas is subjected to quantizing magnetic fields and intense laser fields in the Faraday geometry, the maximum electron density of states will be shifted by an energy Eem (eF0)2/4m*(2c 2), where and F0 are, respectively, the frequency and the electric-field strength of the laser field and c is the cyclotron frequency. This will result in a shift in the fundamental absorption edge by Eem , known as the magneto-optical Franz-Keldysh effect MOFKE. In this paper, the MOFKE is studied theoretically for a semiconductor-based electron gas system where terahertz free-electron lasers are employed as intense laser radiation …

A High-Resolution Study Of The Hydra A Cluster With Chandra: Comparison Of The Core Mass Distribution With Theoretical Predictions And Evidence For Feedback In The Cooling Flow, L. P. David, P. Nulsen, B. R. Mcnamara, W. Forman, C. Jones, T. Ponman, B. Robertson, M. Wise

Faculty of Engineering - Papers (Archive)

The cooling flow cluster Hydra A was observed during the orbital activation and calibration phase of the Chandra Observatory. While the X-ray image of the cluster exhibits complex structure in the central region as reported in McNamara et al., the large-scale X-ray morphology of the cluster is fairly smooth. A spectroscopic analysis of the ACIS data shows that the gas temperature in Hydra A increases outward, reaches a maximum temperature of 4 keV at 200 kpc, and then decreases slightly at larger radii. The distribution of heavy elements is nonuniform, with a factor of 2 increase in the Fe and …

Terahertz-Photon-Modified Magnetotransport In A Semiconductor In Voigt Geometry, W. Xu, I. Khmyrova, V. Ryzhii

Faculty of Engineering - Papers (Archive)

We present a theoretical study of transport and optical properties of a semiconductor-based electron gas subjected simultaneously to quantizing magnetic fields and intense terahertz THz laser fields in Voigt geometry. It is found that the presence of the THz radiation can result in an enhanced magnetophonon resonance effect and a resonant-absorption peak can be observed at about f1 THz for GaAs in high magnetic fields. The results are pertinent to experiments where THz free-electron lasers are employed as intense radiation sources.

Postgraduate And Undergraduate Mechatronics' Courses At The University Of Wollongong, C. Cook, Fazel Naghdy, F. De Boer

Faculty of Engineering - Papers (Archive)

This paper outlines the University's involvement with industry based manufacturing projects, and how this has lead to the recent establishment of postgraduate and undergraduate mechatronics degrees. The nature of the industrial projects is described with examples of specific problems, test equipment and experimental rigs given. This work can be used to explain the reasons for the design of the mechatronics courses at Wollongong. A new teaching methodology particularly suitable for mechatronic's education is also discussed.

Resonant Tunneling And Bistability In A Double Barrier Structure Under An Intense Terahertz Laser, C. Zhang

Faculty of Engineering - Papers (Archive)

By using exact wave functions of an electron in a terahertz laser field, we calculated the electron resonant tunneling through a double barrier structure. It is found that the laser field has two effects on the current voltage characteristics. First, it introduces additional tunneling states through the structure due to multiple photon processes (emission, absorption, scattering). Second, it reduces the width of the bistable region. At high field strength and low frequencies, the bistability can be completely removed. This can provide a method by which to tune the bistable region in a double barrier structure.

Laboratory Measurement Of Two-Phase Flow Parameters In Rock Joints Based On High Pressure Triaxial Testing, Buddhima Indraratna, P. G. Ranjith

Faculty of Engineering - Papers (Archive)

The accurate flow measurement of each individual phase is important in unsaturated flow through rock joints, where both air and water phases flow together. An increase in the quantity of one fluid phase decreases the relative permeability of the other phase. The relative permeability is important in numerical models to analyze the risk of ground-water inundation and uncontrollable gas flows in underground excavations in jointed rock. A new apparatus, the High Pressure Two-Phase Triaxial Apparatus (HPTPTA), has been designed for examining the strength and coefficient of permeability characteristics of fractured and intact rocks under two-phase flows. In single-phase triaxial equipment, …

Time-Dependent Particle Transport Through Granular Filters , M. Locke, Buddhima Indraratna, G. Adikari

Faculty of Engineering - Papers (Archive)

This paper describes an analytical model of filtration for granular media, based on the mechanics of particle migration under hydraulic loads. A new equation to predict the probability of particle movement through a 3D network model of the filter voids has been developed. Void constriction sizes are determined based on the particle-size distribution and relative density of the filter. An important new development is the differentiation between particles that form part of the filter structure and fine particles that are loose within the filter voids, or coarse particles that are enmeshed in a matrix of fines. The rate of particle …

Results Of Ac Loss Tests On Twisted And Untwisted Htsc Tape Exposed To An External Field, T. Hardono, C. Cook, F. Darmann

Faculty of Engineering - Papers (Archive)

This paper presents the results of magnetic losstests on twisted and untwisted 37 multifilaments tapes exposed to an alternating field at power frequencies. The losses are measured using calorimetric methods, which are capable of measuring losses in short tapes with the accuracy of several microwatts per centimeter of tape. The losses of the tape due to the longitudinal field of the untwisted tape agree well with theoretical calculations. The measurement results on the twisted filament tape, with 50-mm twist pitch, show that the losses are slightly lower than that in the untwisted tape. This is due to the reduction of …

A New Model For The Behaviour Of Granular Filters, M. Locke, Buddhima Indraratna

Faculty of Engineering - Papers (Archive)

Filters are used in geotechnical engineering to control seepage and to prevent erosion of soil due to the drag forces of seeping water. Filters act as barriers to retain the base soil while allowing seepage flows to exit without causing high hydraulic gradients or pore pressures which may damage the structure. This paper describes a new anyalytical model of filtration. The model is based on a three dimensional network model of filter pores, and the equations of conservatioln of mass and momentum which govern the rate of particle transport. The model has application in the design of granular filters for …

Pyrite Oxidation Model For Assessing Ground-Water Management Strategies In Acid Sulfate Soils , B. Blunden, Buddhima Indraratna

Faculty of Engineering - Papers (Archive)

A theoretical approach for calculating pyrite oxidation in acid sulfate soil with a macropore/matrix structure is described. This approach accounts for vertical oxygen transport through soil macropores and the subsequent lateral diffusion of oxygen into the soil matrix. As oxygen is supplied into the matrix, it is consumed by pyrite and other oxygen-consuming processes. A numerical solution to the theoretical model was developed and used in the computer simulation model ACID3D. The numerical approach is based on a linear relationship between oxygen consumption and dissolved oxygen concentration. The numerical scheme is shown to be in good agreement with the analytical …

Microstructural Variations With Uranium Compound Doping Of Bi-Sr-Ca-Cu-O/Ag Superconducting Tapes, D. A. Milliken, J. H. Ahn, S X. Dou

Faculty of Engineering - Papers (Archive)

Doping of Bi-Sr-Ca-Cu-O based silver sheathed superconducting tapes (BSCCO/Ag) with various uranium compounds was carried out. This work was aimed at minimising the detrimental effects of doping to allow for later irradiation and fission to create columnar defects for strong flux pinning. The effects on the transport current density of BSCCO/Ag of doping with a variety of uranium compounds up to 2 at% was determined. Microstructural changes due to the doping were investigated. Removal of elements from the BSCCO matrix by uranium compound dopants was studied by energy dispersive spectroscopy. It was found that UCa1.5Sr1.5O6 least degraded electrical performance and …

Design And Simulation Of Continuous Scintillator With Pixellated Photodetector, G. J. Takacs, Anatoly B. Rosenfeld, M. L. Lerch

Faculty of Engineering - Papers (Archive)

Presents results of simulations performed as part of the development of a gamma-ray detector module comprising a nonpixellated scintillator and pixellated photodiode detector. The simulations have been carried out to determine the effect of surface treatment and dimensions of the scintillator on the ability to determine the two-dimensional position of interaction. A set of 32 different combinations of surface treatments have been considered for each crystal size. Scintillator dimensions considered have been 25×25×(3-6 mm3). For scintillator thicknesses at the low end of this range, an average accuracy of 0.5-0.6 mm is achievable for many different surface treatments. At the higher …

Magneto-Optical Images Of Ag/Bi-2223 Tapes Processed By Flat Rolling, “Sandwich” Rolling And Pressing, Hua-Kun Liu, A. Polyanskii, W. M. Chen, Y. C. Guo, S. X. Dou, M. Apperley

Faculty of Engineering - Papers (Archive)

Magneto-optical imaging (MOI) has been used for study Ag/Bi-2223 tapes processed using flat rolling, “sandwich” rolling, and pressing methods for the intermediate mechanical deformation in powder-in-tube process. The results show that not only the density of the microcracks but also their distribution affect Jc. Rolled tapes have a higher density of microcracks than pressed tapes. Although the flat rolled tape and “sandwich” rolled tape have the same level density of microcracks at the same reduction, the cracks in the former are more in the transverse direction than in the latter. In all three cases, Jc reaches a maximum value at …

Effect Of The Sinter-Forging Deformation Rate On Properties Of Bi-2223 Current Leads, X. K. Fu, Y. C. Guo, W. M. Chen, Hua-Kun Liu, S. X. Dou

Faculty of Engineering - Papers (Archive)

The influence of the sinter-forging rate on the critical current density (Jc) behaviour in an external field and on the contact resistance Rc for Bi-2223 current leads has been investigated. The current leads were fabricated by a combination of cold isostatic pressing (CIP) and sinter-forging methods with the thickness reduction rate ranging from 0% to 90%. The two silver contact terminals of each sample were also prepared during the sinter-forging. The results revealed that Jc was strongly affected by the deformation rate of sinter-forging and reached a maximum of 725 A/cm2 at a deformation rate of 80%. From the measurements …

Cubic Beam Elements In Practical Analysis And Design Of Steel Frames, Lip H. Teh

Faculty of Engineering - Papers (Archive)

This paper discusses various issues in the use of cubic beam elements for computer structural analysis/design of steel frames. It is pointed out that the concern expressed in recent literature regarding the number of cubic elements required to model a steel member is not justified, and that the inaccuracy of one cubic element in Euler buckling analysis of a simply supported column is largely irrelevant to the second-order elastic analysis/design or advanced analysis of steel frames. The sources of inaccuracy of the cubic element are elucidated. It is also explained that the plastic-zone analysis method is not so inefficient as …

Second-Order Moments In Torsion Members, Nicholas S. Trahair, Lip H. Teh

Faculty of Engineering - Papers (Archive)

This paper is concerned with the elastic flexural buckling of structural members under torsion, and with second-order moments in torsion members. Previous research is reviewed, and the energy method of predicting elastic buckling is presented. This is used to develop the differential equilibrium equations for a buckled member. Approximate solutions based on the energy method are obtained for a range of conservative applied torque distributions and flexural boundary conditions. A comparison with the limited range of independent solutions available and with independent finite element solutions suggests that the errors in the approximate solutions may be as small as 1%. The …

Vortex Matter In Superconductors, V M Pan, Alexey Pan

Australian Institute for Innovative Materials - Papers

The behavior of the ensemble of vortices in the Shubnikov phase in biaxially oriented films of the high-temperature superconductor YBa₂Cu₃O_7−δ(YBCO) in an applied magnetic field is investigated for different orientations of the field. The techniques used are the recording of the current–voltage characteristics in the transport current and of resonance curves and damping of a mechanical oscillator during the passage of a transport current. It is shown that the behavior of the vortex ensemble in YBCOfilms, unlike the case of single crystals, is determined by the interaction of the vortices with linear defects—edge dislocations, …

Pilot-Scale Testing Of Diatomaceous Earth Filtration For Removal Of Cryptosporidium Oocysts, Jerry E. Ongerth, Primrose E. Hutton

Faculty of Engineering and Information Sciences - Papers: Part A

No abstract provided.

Numerical Investigation Of The Angle Of Repose Of Monosized Spheres, Y C. Zhou, B H. Xu, Aibing Yu, Paul Zulli

Faculty of Engineering and Information Sciences - Papers: Part A

This paper presents a numerical study of the angle of repose, a most important macroscopic parameter in characterizing granular materials, by means of a modified distinct element method. Emphasis is given to the effect of variables related to factors such as particle characteristics, material properties, and geometrical constraints. The results show that sliding and rolling frictions are the primary reasons for the formation of a sandpile; particle size and container thickness significantly influence the angle of repose; and the angle of repose is not so sensitive to density, Poisson's ratio, damping coefficient, and Young's modulus. Increasing rolling friction coefficient or …

Pure Type Systems With More Liberal Rules, Martin W. Bunder, Wil Dekkers

Faculty of Engineering and Information Sciences - Papers: Part A

Pure Type Systems. PTSs, introduced as a generalisation of the type systems of Barendregt's lambda-cube, provide a foundation for actual proof assistants, aiming at the mechanic verification of formal proofs. In this paper we consider simplifications of some of the rules of PTSs. This is of independent interest for PTSs as this produces more flexible PTS-like systems, but it will also help, in a later paper, to bridge the gap between PTSs and systems of Illative Combinatory Logic.

First we consider a simplification of the start and weakening rules of PTSs. which allows contexts to be sets of statements, and …

A General Projection Framwork For Constrained Smoothing, E Mammen, J S. Marron, B A. Turlach, M P. Wand

Faculty of Engineering and Information Sciences - Papers: Part A

There are a wide array of smoothing methods available for finding structure in data. A general framework is developed which shows that many of these can be viewed as a projection of the data, with respect to appropriate norms. The underlying vector space is an unusually large product space, which allows inclusion of a wide range of smoothers in our setup (including many methods not typically considered to be projections). We give several applications of this simple geometric interpretation of smoothing. A major payoff is the natural and computationally frugal incorporation of constraints. Our point of view also motivates new …

Filamentary Shell Structures From The Aao/Ukst Ha Survey, Andrew Walker, William Zealey, Q A. Parker

Faculty of Engineering and Information Sciences - Papers: Part A

Here we present the first results of a search for new optical supernova remnant candidates and other filamentary objects on films produced by the Anglo-Australian Observatory/UK Schmidt Telescope Há Survey. Sixty-one fields, or 26% of the Galactic plane survey fields, have been visually examined. This has resulted in the detection of four newlarge diameter filamentary structures, and the discovery of extensive new optical emission in two previously known optical supernova remnant candidates.

Longwalling And Its Impact In The Southern Coalfield - Recent Bhp Experiences, P. Eade, J. Wood

Resource Operators Conference

Illawarra Coal BHP Minerals currently operate five underground coal mines in the Southern Coalfield of New South Wales in Australia. Each mine operates a retreating longwall extraction system as the primary production process. Economic reserves at several of the mines are nearing exhaustion and a feasibility study is under way to maintain production levels by development of a new mine. The level of maturity of the current operations and the nature of the remaining coal reserves in the Southern Coalfield present significant challenges for continued viable longwall mining. A general overview of the challenges and recent BHP experiences in relation …

On The Soft X-Ray Spectrum Of Cooling Flows, A C. Fabian, R F. Mushotzky, Paul E. J Nulsen, J R. Peterson

Faculty of Engineering and Information Sciences - Papers: Part A

Strong evidence for cooling flows has been found in low-resolution X-ray imaging and spectra of many clusters of galaxies. However, high-resolution X-ray spectra of several clusters from the Reflection Grating Spectrometer on XMM-Newton now show a soft X-ray spectrum inconsistent with a simple cooling flow. The main problem is a lack of the emission lines expected from gas cooling below 1–2 keV. Lines from gas at about 2–3 keV are observed, even in a high-temperature cluster such as A1835, indicating that gas is cooling down to about 2–3 keV, but is not found at lower temperatures. Here we discuss several …

Asca And Rosat Observations Of Nearby Cluster Cooling Flows, S W. Allen, A C. Fabian, R M. Johnstone, K A. Arnaud, Paul E J Nulsen

Faculty of Engineering and Information Sciences - Papers: Part A

We present a detailed analysis of the X-ray properties of the cooling flows in a sample of nearby, X-ray-bright clusters of galaxies using high-quality ASCA spectra and ROSAT X-ray images. We demonstrate the need for multiphase models to consistently explain the spectral and imaging X-ray data for the clusters. The mass deposition rates of the cooling flows, independently determined from the ASCA spectra and ROSAT images, exhibit reasonable agreement. We confirm the presence of intrinsic X-ray absorption in the clusters using a variety of spectral models. We also report detections of 100-μm infrared emission, spatially coincident with the cooling flows, …

Outbursts - Management And Control, J. Hanes

Resource Operators Conference

This paper summarises some of the development of the understanding and management of outbursts in Australia, reviews the current situation and provides some thoughts on necessary research and development. It cannot be and is not comprehensive. Outbursts are better understood, prevented or controlled than they were 20 years ago. This is partly a result of the considerable amount of research into and documentation of outbursts and gas by a relatively small group of outburst pioneers supported by the coal industry. The result has been fewer outbursts in general, and the safe mining through a few potential outburst zones without risk …

Dependence Of The Flux-Creep Activation Energy On Current Density And Magnetic Field For The Mgb2 Superconductor, M. J. Qin, Xiaolin Wang, Saeid Soltanian, Aihua Li, Hua-Kun Liu, S. X. Dou

Faculty of Engineering - Papers (Archive)

Systematic ac susceptibility measurements have been performed on a MgB₂ bulk sample. We demonstrate that the flux creep activation energy is a nonlinear function of the current density U(j)∝j^-0.2, indicating a nonlogarithmic relaxation of the current density in this material. The dependence of the activation energy on the magnetic field is determined to be a power law U(B)∝B^-1.33, showing a steep decline in the activation energy with the magnetic field, which accounts for the steep drop in the critical current density with magnetic field that is observed in MgB₂. The irreversibility field is …

Measurement Of Air Leakage Through Rotary Valves, David B. Hastie, Ian Frew, David M. Cook, Peter W. Wypych

Faculty of Engineering - Papers (Archive)

This paper explains the procedure used to determine the amount of air leakage expelled from two different sized drop-through rotary valves. When designing a pneumatic conveying system, rotary valve air leakage may be overlooked, believed to be only a minor factor. This is somewhat true when conveying in dilute-phase where low pressures are generated, however in dense-phase pneumatic conveying where higher pressures can be produced, rotary valve air leakage can be a high proportion of the supplied air. Knowing the air leakage present for any given situation, the total supplied air mass flowrate can be adjusted to represent the actual …