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114 results on '"Pistorius, C"'

3. Effect of Na2O on Crystallisation Behaviour and Heat Transfer of Fluorine-free Mould Fluxes

Author

Reddy, R, Chaubal, P, Pistorius, C, Pal, U, Yang, J, Zhang, J, Sasaki, Y, Ostrovski, O, Zhang, C, Cai, D, Kashiwaya, Y, Reddy, R, Chaubal, P, Pistorius, C, Pal, U, Yang, J, Zhang, J, Sasaki, Y, Ostrovski, O, Zhang, C, Cai, D, and Kashiwaya, Y

Abstract

Most of the commercial mould fluxes contain fluorides which bring about serious environmental problems. The major challenge in the application of fluorine-free mould fluxes is to control the heat transfer from the strand to copper mould which is closely related to crystallisation behaviour. In this study, the effects of Na2O on the crystallisation behaviour and heat transfer of CaO-SiO2-Na2O-B2O3-TiO2-Al2O3-MgO-Li2O mould fluxes were investigated using single hot thermocouple technique (SHTT) and infrared emitter technique (IET), respectively. Continuous cooling transformation (CCT) and time-temperature transformation (TTT) diagrams constructed using SHTT showed that the increase of Na2O concentration led to higher critical cooling rate and shorter incubation time. The heat flux measured by IET showed that the increase of Na2O concentration decreased the heat flux when Na2O was lower than 9 mass% but the further increase of Na2O raised the heat flux. The relationship between flux crystallisation and heat transfer was also discussed.

Published
2016

4. Stability of Fluorine-free Mould Fluxes SiO2-CaO-Al2O3-B2O3-Na2O for Steel Continuous Casting

Author

Reddy, R, Chaubal, P, Pistorius, C, Pal, U, Wang, L, Zhang, J, Sasaki, Y, Ostrovski, O, Zhang, C, Cai, D, Reddy, R, Chaubal, P, Pistorius, C, Pal, U, Wang, L, Zhang, J, Sasaki, Y, Ostrovski, O, Zhang, C, and Cai, D

Abstract

B2O3 and Na2O are key components of fluorine-free mould fluxes for continuous casting, but both are highly volatile what affects the flux stability. This paper investigates evaporation of the SiO2-CaO-Al2O3-B2O3-Na2O fluxes (Na2O: 6-10 wt%, CaO/SiO2 ratio: 0.8-1.5) in the temperature range 1573 to 1673K using a thermogravimetric analysis method. The weight loss as a result of the flux evaporation increased with increasing temperature. The rate of evaporation increased significantly with the increase in the Na2O content. The effect of the CaO/SiO2 ratio in the range 0.8-1.3 on the evaporation rate was marginal, however, the increase of this ratio to 1.5 slowed down evaporation after approximately 1000 s. When 6.2 wt% Na2O was added to the SiO2-CaO-Al2O3-B2O3 flux, the apparent activation energy Ea for the evaporation reaction decreased from 365 to 193 kJ/mol, and while a further increase in the Na2O content to 9.1 wt% had a minor effect on Ea. The high evaporation rate of boracic fluxes in the presence of B2O3 and Na2O was attributed to the formation of highly volatile NaBO2 and Na2O.

Published
2016

5. Diffusion Coefficients and Structural Parameters of Molten Slags

Author

Reddy, R, Chaubal, P, Pistorius, C, Pal, U, Maroufi, S, Amini, S, Jahanshahi, S, Ostrovski, O, Reddy, R, Chaubal, P, Pistorius, C, Pal, U, Maroufi, S, Amini, S, Jahanshahi, S, and Ostrovski, O

Abstract

This paper presents the results of two experimental studies on diffusion of SiO2 in “silicomanganese” (SiO2-MnO-CaO-Al2O3- MgO) slag and CaO in calcium aluminosilicate slag. The diffusivity of SiO2 was measured in the temperature range of 1400-1550 °C; while the diffusivity of CaO was determined at 1430-1600°C. The effects of additives on the chemical diffusivities of SiO2 and CaO were also examined. Addition of CaO and MnO to the silicomanganese slag increased silica diffusivity, while addition of SiO2 and Al2O3 slowed it down. Addition of TiO2 and MnOx to the aluminosilicate slag increased the diffusivity of CaO, while the addition of SiO2 had a negative effect on the diffusivity of CaO. Analysis of diffusivity in relation to the structure of silicate melts demonstrated a good correlation between diffusion coefficients of SiO2 and CaO and NBO/T (non-bridging oxygen per tetrahedrally coordinated atom).

Published
2016

12. A growth related, multi-mode framework for interaction among technologies

Author

James M. Utterback., Sloan School of Management, Pistorius, C. W. I. (Carl W. I.), 1958, James M. Utterback., Sloan School of Management, and Pistorius, C. W. I. (Carl W. I.), 1958

Abstract

Thesis (M.S.)--Massachusetts Institute of Technology, Sloan School of Management, 1994., Includes bibliographical references (leaves 242-248)., by Carl W.I. Pistorius., M.S.

Published
2005

14. Multi-mode interaction among technologies

Author

Pistorius, C. W. I. (Carl W. I.), 1958, Utterback, James M., 1941, Pistorius, C. W. I. (Carl W. I.), 1958, and Utterback, James M., 1941

Abstract

Cover title. "November 1995.", Includes bibliographical references (p. 28-30)., Carl W.I. Pistorius, James M. Utterback.

Published
2003

15. A Lotka-Volterra model for multi-mode technological interaction : modeling competition, symbiosis and predator prey modes

Author

Pistorius, C. W. I. (Carl W. I.), 1958, Utterback, James M., 1941, Pistorius, C. W. I. (Carl W. I.), 1958, and Utterback, James M., 1941

Abstract

Cover title. "March 1996." "Technology Management in a Changing World, Proceedings of the Fifth International Conference on Management of Technology, Miami, Florida, February 27-March 1, 1996"--Added t.p., Includes bibliographical references (leaves [7-8])., Carl W.I. Pistorius, James M. Utterback.

Published
2003

16. New main reflector, subreflector and dual chamber concepts for compact range applications

Author

Pistorius, C. W. I and Burnside, W. D

Subjects
Research And Support Facilities (Air)
Abstract

A compact range is a facility used for the measurement of antenna radiation and target scattering problems. Most presently available parabolic reflectors do not produce ideal uniform plane waves in the target zone. Design improvements are suggested to reduce the amplitude taper, ripple and cross polarization errors. The ripple caused by diffractions from the reflector edges can be reduced by adding blended rolled edges and shaping the edge contour. Since the reflected edge continues smoothly from the parabola onto the rolled surface, rather than being abruptly terminated, the discontinuity in the reflected field is reduced which results in weaker diffracted fields. This is done by blending the rolled edges from the parabola into an ellipse. An algorithm which enables one to design optimum blended rolled edges was developed that is based on an analysis of the continuity of the surface radius of curvature and its derivatives across the junction. Futhermore, a concave edge contour results in a divergent diffracted ray pattern and hence less stray energy in the target zone. Design equations for three-dimensional reflectors are given. Various examples were analyzed using a new physical optics method which eliminates the effects of the false scattering centers on the incident shadow boundaries. A Gregorian subreflector system, in which both the subreflector and feed axes are tilted, results in a substantial reduction in the amplitude taper and cross polarization errors. A dual chamber configuration is proposed to eliminate the effects of diffraction from the subreflector and spillover from the feed. A computationally efficient technique, based on ray tracing and aperture integration, was developed to analyze the scattering from a lossy dielectric slab with a wedge termination.

Published
1987

17. The design of blended rolled edges for compact range main reflectors

Author

Pistorius, C. W. I and Burnside, W. D

Subjects
Communications And Radar
Abstract

In a compact range (which employs a parabolic main reflector to convert the spherical wave originating from a point source to a reflected plane wave) the edge-generated diffractive fields degrade the uniformity of the plane wave. To reduce the energy diffracted from the edge surfaces, terminations can be added to the parabola, such that the slope of the surface is continuous at the junctions. This paper discusses the problem of designing an optimized rolled edge. Two examples of reflectors with rolled edges are presented, one with elliptic rolled edges and the other with blended rolled edges, both adhering to the same constraints on minimum operating frequency and size. It was found that the reflector with the cosine-squared blended rolled edges has a much larger usable target zone than the one with the elliptic rolled edges.

Published
1987

19. On the future of technological forecasting

Author

Coates, V, Farooque, M, Klavans, R, Lapid, K, Linstone, H, Pistorius, C, and Porter, A

Subjects
Technological forecasting -- Analysis, Food services, High technology industry, Social sciences
Abstract

Research is presented describing the changing demands on technological forecasting organizations and the need for integrated assessment tools which utilize experiences from other forms of science forecasting.

Published
2001

32. Has South Africa fallen into a competitiveness trap?

Author

Pistorius, C. W. I.

Subjects
*INTERNATIONAL competition, SOUTH African economy
Abstract

South Africa is in an extremely precarious position with regard to international competitiveness, according to various authorities. Moreover, the country's sustained poor performance in the competitiveness domain is a national threat. Even though strategic intent is there, the desired outcomes are not reflected in the results. One may debate the accuracy of published ratings, but ultimately a concerted national competitiveness initiative must be deployed. This will not detract from current initiatives that are aimed at, for example, relieving poverty, creating jobs, providing adequate housing, health care and education or fostering innovation and entrepreneurship, but rather provide a meta coordinating and benchmarking policy vehicle. If the country's competitiveness can be improved, many of its other problems will be addressed as well. [ABSTRACT FROM AUTHOR]

Published
2001

33. FIELD APPROXIMATIONS AT THIN-WIRE JUNCTIONS FOR THE FINITE-DIFFERENCE TIME-DOMAIN METHOD.

Author

Boonzaaier, J. J. and Pistorius, C. W. I.

Subjects
*ANTENNAS (Electronics), *RADIATION, *MAGNETIC fields, *FINITE differences, *NUMERICAL analysis, *TIME-domain analysis, *MOMENTS method (Statistics)
Abstract

Approximations for the circumferential magnetic fields at right-angled functions are derived and validated by computing the radiation patterns of a square-loop antenna by means of the finite-difference time-domain (FD-TD) method. The radiated time-domain fields are transformed to the frequency domain and then compared to the frequency, domain results obtained from the method of moments. [ABSTRACT FROM AUTHOR]

Published
1991

40. A normal coordinate treatment of the plane symmetrical XY4 molecule

Author

Pistorius, C. W. F. T.

Abstract

The secular equations for the various irreducible representations of the plane XY4 molecule (symmetry point group D4h) are deduced by means of Wilson's F-G matrix method, using the most general harmonic force field. The equations for the case of the SVFF are also given.

Published
1958
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41. REDUCTION OF THE RCS OF LEADING EDGE OF A CONDUCTING WING-SHAPED STRUCTURE BY MEANS OF LOSSLESS DIELECTRIC MATERIAL.

Author

Booysen, A. J., Pistorius, C. W. I., and Malherbe, J. A. G.

Subjects
*DIELECTRICS, *ELECTRICAL engineering materials, *AERODYNAMICS, *RADAR, *ELECTRONIC systems
Abstract

The radar cross section of the leading edge of a conducting wing-shaped structure is reduced by replacing part of the structure with a lossless dielectric material. The structure retains its original external shape, thereby ensuring that the aerodynamic properties are not altered by the structural changes needed to reduce the radar cross section. [ABSTRACT FROM AUTHOR]

Published
1991
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42. AN ENVELOPE DESCRIPTION OF THE RCS OF COMPLEX SCATTERING BODIES.

Author

Pistorius, C. W. I.

Subjects
*SCATTERING (Physics), *COLLISIONS (Nuclear physics), *MICROWAVES, *ELECTRIC waves, *OPTICS, *TECHNOLOGY
Abstract

A new method whereby the radar cross section (RCS) of complex scattering bodies can easily and rapidly be estimated is described. The RCS envelope of a scatterer is found by extracting and adding the envelopes of the component canonical shapes acting as the scattering centers of the body. [ABSTRACT FROM AUTHOR]

Published
1989
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44. Predicted effect of ore composition on slag formation in manganese ore reduction.

Author

Coetsee T., Pistorius C., Zietsman J., Coetsee T., Pistorius C., and Zietsman J.

Abstract

Previous work showed that manganese ore reduction rates are strongly influenced by the extent of slag phase formation. In this work, the effect of ore composition on slag formation during manganese oxide reduction was predicted using thermochemical calculations; FactSage 6.4 was used to calculate the equilibrium phase relations in the oxide system MnO-SiO2-CaO-MgO-Al2O3. Practically observed differences in ore composition, even within the same orebody, are predicted to cause significant differences in slag formation during reduction, with large differences in ore reducibility expected. (Authors.), Previous work showed that manganese ore reduction rates are strongly influenced by the extent of slag phase formation. In this work, the effect of ore composition on slag formation during manganese oxide reduction was predicted using thermochemical calculations; FactSage 6.4 was used to calculate the equilibrium phase relations in the oxide system MnO-SiO2-CaO-MgO-Al2O3. Practically observed differences in ore composition, even within the same orebody, are predicted to cause significant differences in slag formation during reduction, with large differences in ore reducibility expected. (Authors.)

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