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 …

Effect Of Uranium Doping And Thermal Neutron Irradiation On The Flux-Pinning Of Silver-Clad Bi-Sr-Ca-Cu-O Tapes, D. Marinaro, S X. Dou, J. Horvat, J. Boldeman, R. Weinstein, R. Sawh

Faculty of Engineering - Papers (Archive)

Ag/Bi-2223 tapes doped with small quantities of 235UO 4 powder were prepared by the powder-in-tube process and irradiated in a thermal neutron environment. Substantial improvements in critical current density (Jc)-applied field (H) performance and anisotropy have been previously reported. However, the radioactivity of the silver sheath is a limiting factor for commercial and industrial applications of this technique. Here we report the performance of the technique using various doping levels (from 0.15 to 2 percent by weight (wt.%) UO4) and thermal neutron fluences (Φn), in order to further reduce the silver radioactivity. Optimum fluence levels are identified and an optimum …

Spectral Characterization Of A Blue-Enhanced Silicon Photodetector, M. L. Lerch, Anatoly B. Rosenfeld, Philip E. Simmonds, G. N. Taylor, S. R. Meikle, V. L. Perevertailo

Faculty of Engineering - Papers (Archive)

In this paper, we report on spectral response data and gamma ray spectroscopy measurements using two newly developed silicon photodetectors that are designed to have enhanced sensitivity in the blue spectral region. The enhanced sensitivity is a result of our newly developed ion implantation profile used to create the active area of the photodetector. The quantum efficiency of the new photodetectors (without any optimized antireflective coating) has been measured to be ~40% at a wavelength of 420 nm. Gamma ray spectroscopy experiments have been performed using a thallium doped cesium iodide, [CsI(Tl)], and a cerium doped lutetium oxy-orthosilicate, (LSO) crystal …

Comparative Studies On “Sandwich” Rolling And Flat Rolling In Processing Ag/Bi-2223 Tapes, W. M. Chen, Y. C. Guo, X. K. Fu, Hua-Kun Liu, S. X. Dou, M. Apperley

Faculty of Engineering - Papers (Archive)

The normal rolling method is commonly used for intermediate mechanical deformation in the powder-in-tube process to make Ag-clad Bi-based superconducting tapes. To compare the effects of different reduction processing on the superconducting properties of Ag/Bi-2223 tapes, the reduction rate dependence of the critical current densities J c of tapes processed by three methods, including normal rolling, pressing and “sandwich” rolling, has been systematically studied. Experimental results show that Jc dependence on the reduction rate for the three processes follows the same law. There is an optimal reduction rate in each case, which gives the highest physical density and the highest …

Improved In-Field Behaviour Of Uranium Doped Biscco Tapes By Enhanced Flux Pinning, S. Tonies, H. W. Weber, Y. C. Guo, S. X. Dou, R. Sawh, R. Weinstein

Faculty of Engineering - Papers (Archive)

Uranium doped BiSCCO 2223 tapes were irradiated by thermal neutrons. The resulting fission-induced defects improve flux pinning and shift the irreversibility line to higher fields. Significant enhancements of the transport critical current density as well as a reduction of the Jc-anisotropy are found for the irradiated samples. Furthermore, inter- and intragranular critical current densities were determined from the remanent magnetic moments by SQUID magnetometry.

Superconductivity And Flux Pinning In Y And Heavily Pb Codoped Bi-2212 Single Crystals, Xiaolin Wang, Hua-Kun Liu, S X. Dou, J. Horvat, D. Millikon, G. Heine, W. Lang, H. M. Luo, Shichao Ding

Faculty of Engineering - Papers (Archive)

Studies of superconductivity and flux pinning were carried out on (Bi1.64Pb0.36)Sr2Ca1–xYxCu2O8 + y (x = 0, 0.05, 0.11, 0.33) single crystals grown by the self-flux method. X-ray diffraction, transport, and magnetic measurements were performed for purposes of characterization. X-ray analysis revealed that the c lattice parameter systemically decreases as the Y doping level increases. The superconducting transition temperature Tc decreases from 80 to 30 K as x increases. A strong annealing effect on Tc and superconducting volume has been observed. Resistance measurements show that x = 0.33 samples are semiconductive over a wide temperature range between 4.2 and 300 K …

On The Current Transport Limitations In Bi-Based High Temperature Superconducting Tapes, S. Tonies, H. W. Weber, Y. C. Guo, S. X. Dou, R. Sawh, R. Weinstein

Faculty of Engineering - Papers (Archive)

The transport critical current densities, Jc, of superconducting (Bi, Pb)2Sr2Ca2Cu3Ox/Ag tapes were measured before and after employing a special radiation technique, which leaves the grain boundary properties largely unaffected. We identify two regions separated by a temperature dependent crossover field Hgb–p. In the low field region, Jc is limited by the transport currents across the grain boundaries, which remain unchanged after irradiation. Above Hgb–p, Jc is limited by flux pinning. In this field region, the artificial defects optimize flux pinning and enhance Jc.

Observation Of Heat Flow At Transition Temperature In La1–Xcaxmno3 + Delta Oxides, Y. B. Zhang, S. Li, C. Q. Sun, W. Gao, S. X. Dou, P. Hing

Faculty of Engineering - Papers (Archive)

Heat-flow changes of La1–xCaxMnO3 + delta (x=0.25, 0.33, and 0.375) magnetoresistive oxides at their Curie temperatures have been detected using differential scanning calorimetry in the temperature range from 173 to 293 K. However, the transition does not occur in the samples of x=0.125 and 0.5. It was found that the heat flow reflected the transition behavior and the enthalpy change of the transition decreased as the transition temperature increased. These results indicate that the La1–xCaxMnO3 + delta oxides (x=0.25, 0.33, and 0.375) undergo an endothermic phase transition from a low-temperature ferromagnetic metal to a high-temperature paramagnetic insulator. It is assumed …

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 …

The Impact Of Floodgate Modifications On Water Quality In Acid Sulphate Soil Terrains, William Glamore, Buddhima Indraratna

Faculty of Engineering - Papers (Archive)

The installation of one-way tidal restricting floodgates in regions containing acid sulphate soils has increased the problems associated with acid drainage in many areas of coastal Australia. In southeastern NSW, one-way flap gates installed in deep flood mitigation drains maintain a low groundwater table and increase acid production and transport. Moreover, by restricting the intrusion of brackish water into the drainage system, the floodgates create a reservoir of acidic water. Recent studies suggest that by allowing a controlled amount of brackish water into the drains, via modified floodgates, buffering agents can neutralize the acidic water. A fifteen-month study was undertaken …

Thermal Diffusivity Of Iron At High Temperature In Both The Liquid And Solid States, Brian J. Monaghan, P N Quested

Faculty of Engineering - Papers (Archive)

Process models that simulate industrial processes are increasingly being used to reduce costs and improve productivity. 1–8) The success of such models is highly dependent on the thermophysical property data used in the simulation calculations. Unfortunately high temperature thermophysical data for liquid metals and slags are scarce. Also what data that are available often have a high uncertainty associated with them.1,2,9–11) Therefore regardless of how well a process model may be physically based it is likely, given the current state of high temperature thermophysical property data, in particular heat capacity, viscosity and thermal conductivity/ diffusivity, that the models predictions will …

Mechanism For Unstable Pneumatic Conveying Of Granular Materials Through Horizontal Pipe, J Yi, Peter W. Wypych, David B. Hastie

Faculty of Engineering - Papers (Archive)

Since the pneumatic conveying performance of granular materials in the transition zone between dilute- phase and dense-phase still lacks full understanding and assessment, especially the mechanism for the formation of unstable flow, tests have been carried out on poly pellets (particle diameter = 4.7 mm, particle density = 897 kg/m3) and two different stainless steel pipelines (60.3 and 98.4 mm ID, each 21 m long). By careful observation and analysis of flow behaviours (covering dilute-phase, unstable zone and low-velocity slug-flow), five different flow modes (as the air velocity is decreased): fully suspended flow; strand flow; stable or unstable strand flow …

A Versatile Experimental Test Rig For Gma Welding Research, Gary Dean, Dominic Cuiuri, John Norrish, Christopher David Cook

Faculty of Engineering - Papers (Archive)

Welding process research is severely hampered when adequate experimental equipment is not available. With the development of numerous welding processes and the control techniques associated with them, the need now exists for experimental equipment that offers the flexibility to control these processes and to set up parameters associated with the research.

At the University of Wollongong an experimental research rig has been developed based on a digital signal processor control system that offers the researcher the facilities to study the various processes associated with GMA welding.

Feasibility Study Of Online High-Spatial-Resolution Mosfet Dosimetry In Static And Pulsed X-Ray Radiation Fields, Anatoly B. Rosenfeld, M. L. Lerch, T. Kron, E. Brauer-Krisch, A. Bravin, A. Holmes-Siedle, B. J. Allen

Faculty of Engineering - Papers (Archive)

Improvements have been made in the measurement of dose profiles in several types of X-ray beams. These include 120-kVp X-ray beams from an orthovoltage X-ray machine, 6-MV Bremsstrahlung from a medical LINAC in conformal mode and the 50-200 keV energy spectrum of microbeams produced at the medical beamline station of the European Synchrotron Radiation Facility. Using a quadruple metal-oxide-semiconductor field-effect transistor (MOSFET) sensor chip in "edge on" mode together with a newly developed sensor readout system, the feasibility of online scanning of the profiles of quasi-static and pulsed radiation beams was demonstrated. Measurements of synchrotron pulsed microbeams showed that a …