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31 results on '"Stevenson, M. G."'

2. Indirect evidence for elemental hydrogen in laser-compressed hydrocarbons

Author

Kraus, D., primary, Vorberger, J., additional, Hartley, N. J., additional, Lütgert, J., additional, Rödel, M., additional, Chekrygina, D., additional, Döppner, T., additional, van Driel, T., additional, Falcone, R. W., additional, Fletcher, L. B., additional, Frydrych, S., additional, Galtier, E., additional, Gericke, D. O., additional, Glenzer, S. H., additional, Granados, E., additional, Inubushi, Y., additional, Kamimura, N., additional, Katagiri, K., additional, MacDonald, M. J., additional, MacKinnon, A. J., additional, Matsuoka, T., additional, Miyanishi, K., additional, McBride, E. E., additional, Nam, I., additional, Neumayer, P., additional, Ozaki, N., additional, Pak, A., additional, Ravasio, A., additional, Saunders, A. M., additional, Schuster, A. K., additional, Stevenson, M. G., additional, Sueda, K., additional, Sun, P., additional, Togashi, T., additional, Voigt, K., additional, Yabashi, M., additional, and Yabuuchi, T., additional

Published
2023
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3. Toward using collective x-ray Thomson scattering to study C–H demixing and hydrogen metallization in warm dense matter conditions

Author

Ranjan, D., primary, Ramakrishna, K., additional, Voigt, K., additional, Humphries, O. S., additional, Heuser, B., additional, Stevenson, M. G., additional, Lütgert, J., additional, He, Z., additional, Qu, C., additional, Schumacher, S., additional, May, P. T., additional, Amouretti, A., additional, Appel, K., additional, Brambrink, E., additional, Cerantola, V., additional, Chekrygina, D., additional, Fletcher, L. B., additional, Göde, S., additional, Harmand, M., additional, Hartley, N. J., additional, Hau-Riege, S. P., additional, Makita, M., additional, Pelka, A., additional, Schuster, A. K., additional, Šmíd, M., additional, Toncian, T., additional, Zhang, M., additional, Preston, T. R., additional, Zastrau, U., additional, Vorberger, J., additional, and Kraus, D., additional

Published
2023
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4. Indirect evidence for elemental hydrogen in laser-compressed hydrocarbons

Author

(0000-0002-6350-4180) Kraus, D., (0000-0001-5926-9192) Vorberger, J., Hartley, N. J., Lütgert, J., Rödel, M., Chekrygina, D., Döppner, T., Driel, T., Falcone, R. W., Fletcher, L. B., Frydrych, S., Galtier, E., Gericke, D. O., Glenzer, S. H., Granados, E., Inubushi, Y., Kamimura, N., Katagiri, K., Macdonald, M. J., Mackinnon, A. J., Matsuoka, T., Miyanishi, K., McBride, E. E., Nam, I., Neumayer, P., Ozaki, N., Pak, A., Ravasio, A., Saunders, A. M., Schuster, A. K., Stevenson, M. G., Sueda, K., Sun, P., Togashi, T., Voigt, K., Yabashi, M., Yabuuchi, T., (0000-0002-6350-4180) Kraus, D., (0000-0001-5926-9192) Vorberger, J., Hartley, N. J., Lütgert, J., Rödel, M., Chekrygina, D., Döppner, T., Driel, T., Falcone, R. W., Fletcher, L. B., Frydrych, S., Galtier, E., Gericke, D. O., Glenzer, S. H., Granados, E., Inubushi, Y., Kamimura, N., Katagiri, K., Macdonald, M. J., Mackinnon, A. J., Matsuoka, T., Miyanishi, K., McBride, E. E., Nam, I., Neumayer, P., Ozaki, N., Pak, A., Ravasio, A., Saunders, A. M., Schuster, A. K., Stevenson, M. G., Sueda, K., Sun, P., Togashi, T., Voigt, K., Yabashi, M., and Yabuuchi, T.

Abstract

We demonstrate a significantly simplified experimental approach for investigating liquid metallic hydrogen, which is crucial to understand the internal structure and evolution of giant planets. Plastic samples were shockcompressed and then probed by short pulses of X-rays generated by free electron lasers. By comparison with ab initio simulations, we provide indirect evidence for the creation of elemental hydrogen in shock-compressed plastics at ∼150GPa and ∼5,000K and thus in a regime where hydrogen is predicted to be metallic. Being the most common form of condensed matter in our solar system, and ostensibly the simplest of all elements, hydrogen is the model case for many theoretical studies and we provide a new possibility to benchmark models for conditions with extreme pressures and temperatures. Moreover, this approach will also allow to probe the chemical behavior of metallic hydrogen in mixture with other elements, which, besides its importance for planetary physics, may open up promising pathways for the synthesis of new materials.

Published
2023

5. Toward using collective x-ray Thomson scattering to study C–H demixing and hydrogen metallization in warm dense matter conditions

Author

(0000-0002-8641-4794) Ranjan, D., (0000-0003-4211-2484) Ramakrishna, K., (0000-0001-8090-2626) Voigt, K., (0000-0001-6748-0422) Humphries, O. S., (0000-0001-6363-1780) Heuser, B., (0009-0006-9039-5756) Stevenson, M. G., (0000-0002-2593-573X) Lütgert, B. J., (0000-0001-5416-456X) He, Z., (0000-0002-4890-7440) Qu, C., (0000-0002-1846-0000) Schumacher, S., (0009-0003-4989-8704) May, P. T., Amouretti, A., (0000-0002-2902-2102) Appel, K., Brambrink, E., (0000-0002-2808-2963) Cerantola, V., (0000-0002-7337-2337) Chekrygina, D., (0000-0002-7120-7194) Fletcher, L. B., Göde, S., (0000-0003-0713-5824) Harmand, M., (0000-0002-6268-2436) Hartley, N., (0000-0001-7331-6485) Hau-Riege, S. P., (0000-0003-1513-9198) Makita, M., Pelka, A., (0000-0001-5489-5952) Schuster, A., (0000-0002-7162-7500) Smid, M., (0000-0001-7986-3631) Toncian, T., Zhang, M., (0000-0003-1228-2263) Preston, T. R., (0000-0002-3575-4449) Zastrau, U., (0000-0001-5926-9192) Vorberger, J., (0000-0002-6350-4180) Kraus, D., (0000-0002-8641-4794) Ranjan, D., (0000-0003-4211-2484) Ramakrishna, K., (0000-0001-8090-2626) Voigt, K., (0000-0001-6748-0422) Humphries, O. S., (0000-0001-6363-1780) Heuser, B., (0009-0006-9039-5756) Stevenson, M. G., (0000-0002-2593-573X) Lütgert, B. J., (0000-0001-5416-456X) He, Z., (0000-0002-4890-7440) Qu, C., (0000-0002-1846-0000) Schumacher, S., (0009-0003-4989-8704) May, P. T., Amouretti, A., (0000-0002-2902-2102) Appel, K., Brambrink, E., (0000-0002-2808-2963) Cerantola, V., (0000-0002-7337-2337) Chekrygina, D., (0000-0002-7120-7194) Fletcher, L. B., Göde, S., (0000-0003-0713-5824) Harmand, M., (0000-0002-6268-2436) Hartley, N., (0000-0001-7331-6485) Hau-Riege, S. P., (0000-0003-1513-9198) Makita, M., Pelka, A., (0000-0001-5489-5952) Schuster, A., (0000-0002-7162-7500) Smid, M., (0000-0001-7986-3631) Toncian, T., Zhang, M., (0000-0003-1228-2263) Preston, T. R., (0000-0002-3575-4449) Zastrau, U., (0000-0001-5926-9192) Vorberger, J., and (0000-0002-6350-4180) Kraus, D.

Abstract

The insulator–metal transition in liquid hydrogen is an important phenomenon to understand the interiors of gas giants, such as Jupiter and Saturn, as well as the physical and chemical behavior of materials at high pressures and temperatures. Here, the path toward an experimental approach is detailed based on spectrally resolved x-ray scattering, tailored to observe and characterize hydrogen metallization in dynamically compressed hydrocarbons in the regime of carbon–hydrogen phase separation. With the help of time-dependent density functional theory calculations and scattering spectra from undriven carbon samples collected at the European x-ray Free-Electron Laser Facility (EuXFEL), we demonstrate sufficient data quality for observing C–H demixing and investigating the presence of liquid metallic hydrogen in future experiments using the reprated drive laser systems at EuXFEL.

Published
2023

6. Toward using collective x-ray Thomson scattering to study C-H demixing and hydrogen metallization in warm dense matter conditions

Author

Ranjan, D, Ramakrishna, K, Voigt, K, Humphries, O, Heuser, B, Stevenson, M, Lütgert, J, He, Z, Qu, C, Schumacher, S, May, P, Amouretti, A, Appel, K, Brambrink, E, Cerantola, V, Chekrygina, D, Fletcher, L, Göde, S, Harmand, M, Hartley, N, Hau-Riege, S, Makita, M, Pelka, A, Schuster, A, Šmíd, M, Toncian, T, Zhang, M, Preston, T, Zastrau, U, Vorberger, J, Kraus, D, Ranjan D., Ramakrishna K., Voigt K., Humphries O. S., Heuser B., Stevenson M. G., Lütgert J., He Z., Qu C., Schumacher S., May P. T., Amouretti A., Appel K., Brambrink E., Cerantola V., Chekrygina D., Fletcher L. B., Göde S., Harmand M., Hartley N. J., Hau-Riege S. P., Makita M., Pelka A., Schuster A. K., Šmíd M., Toncian T., Zhang M., Preston T. R., Zastrau U., Vorberger J., Kraus D., Ranjan, D, Ramakrishna, K, Voigt, K, Humphries, O, Heuser, B, Stevenson, M, Lütgert, J, He, Z, Qu, C, Schumacher, S, May, P, Amouretti, A, Appel, K, Brambrink, E, Cerantola, V, Chekrygina, D, Fletcher, L, Göde, S, Harmand, M, Hartley, N, Hau-Riege, S, Makita, M, Pelka, A, Schuster, A, Šmíd, M, Toncian, T, Zhang, M, Preston, T, Zastrau, U, Vorberger, J, Kraus, D, Ranjan D., Ramakrishna K., Voigt K., Humphries O. S., Heuser B., Stevenson M. G., Lütgert J., He Z., Qu C., Schumacher S., May P. T., Amouretti A., Appel K., Brambrink E., Cerantola V., Chekrygina D., Fletcher L. B., Göde S., Harmand M., Hartley N. J., Hau-Riege S. P., Makita M., Pelka A., Schuster A. K., Šmíd M., Toncian T., Zhang M., Preston T. R., Zastrau U., Vorberger J., and Kraus D.

Abstract

The insulator-metal transition in liquid hydrogen is an important phenomenon to understand the interiors of gas giants, such as Jupiter and Saturn, as well as the physical and chemical behavior of materials at high pressures and temperatures. Here, the path toward an experimental approach is detailed based on spectrally resolved x-ray scattering, tailored to observe and characterize hydrogen metallization in dynamically compressed hydrocarbons in the regime of carbon-hydrogen phase separation. With the help of time-dependent density functional theory calculations and scattering spectra from undriven carbon samples collected at the European x-ray Free-Electron Laser Facility (EuXFEL), we demonstrate sufficient data quality for observing C-H demixing and investigating the presence of liquid metallic hydrogen in future experiments using the reprated drive laser systems at EuXFEL.

Published
2023

8. Diamond formation kinetics in shock-compressed C-H-O samples recorded by small-angle X-ray scattering and X-ray diffraction

Author

He, Z., Rödel, M., Lütgert, J., Bergermann, A., Bethkenhagen, M., Chekrygina, D., (0000-0002-5845-000X) Cowan, T., Descamps, A., French, M., Galtier, E., Gleason, A. E., Glenn, G. D., Glenzer, S. H., Inubushi, Y., (0000-0002-6268-2436) Hartley, N., Hernandez, J.-A., Heuser, B., (0000-0001-6748-0422) Humphries, O. S., Kamimura, N., Katagiri, K., Khaghani, D., Ja Lee, H., McBride, E. E., Miyanishi, K., Nagler, B., Ofori-Okai, B., Ozaki, N., Pandolfi, S., Qu, C., Ranjan, D., Redmer, R., Schoenwaelder, C., (0000-0001-5489-5952) Schuster, A., Stevenson, M. G., Sueda, K., Togashi, T., Vinci, T., Voigt, K., (0000-0001-5926-9192) Vorberger, J., Yabashi, M., Yabuuchi, T., Zinta, L. M. V., Ravasio, A., (0000-0002-6350-4180) Kraus, D., He, Z., Rödel, M., Lütgert, J., Bergermann, A., Bethkenhagen, M., Chekrygina, D., (0000-0002-5845-000X) Cowan, T., Descamps, A., French, M., Galtier, E., Gleason, A. E., Glenn, G. D., Glenzer, S. H., Inubushi, Y., (0000-0002-6268-2436) Hartley, N., Hernandez, J.-A., Heuser, B., (0000-0001-6748-0422) Humphries, O. S., Kamimura, N., Katagiri, K., Khaghani, D., Ja Lee, H., McBride, E. E., Miyanishi, K., Nagler, B., Ofori-Okai, B., Ozaki, N., Pandolfi, S., Qu, C., Ranjan, D., Redmer, R., Schoenwaelder, C., (0000-0001-5489-5952) Schuster, A., Stevenson, M. G., Sueda, K., Togashi, T., Vinci, T., Voigt, K., (0000-0001-5926-9192) Vorberger, J., Yabashi, M., Yabuuchi, T., Zinta, L. M. V., Ravasio, A., and (0000-0002-6350-4180) Kraus, D.

Abstract

Extreme conditions inside ice giants like Uranus and Neptune can result in peculiar chemistry and structural transitions, e.g., the precipitation of diamonds or superionic water, as so far experimentally observed only for pure C-H and H2O systems, respectively. Here we investigate a stoichiometric mixture of C and H2O by shock-compressing PET plastics and performing in situ X-ray probing. We observe diamond formation at pressures between 72±7 GPa and 125±13 GPa at temperatures ranging from ~3500 K to ~6000 K. Combining X-ray diffraction and small angle X-ray scattering, we access the kinetics of this exotic reaction. The observed demixing of C and H2O suggests that diamond precipitation inside the ice giants is enhanced by oxygen, which can lead to isolated water and thus the formation of superionic structures relevant to the planets’ magnetic fields. Moreover, our measurements indicate a way of producing nanodiamonds by simple laser-driven shock-compression of cheap PET plastics.

Published
2022

11. Reconstruction of nanoparticle size distribution in laser-shocked matter from small-angle X-ray scattering via neural networks

Author

He, Z., Lütgert, J., Stevenson, M. G., Heuser, B., Ranjan, D., Qu, C., and Kraus, D.

Abstract

AbstractSmall-angle X-ray scattering (SAXS) has been widely used as a microstructure characterization technology. In this work, a fully connected dense forward network is applied to inversely retrieve the mean particle size and particle distribution from SAXS data of samples dynamically compressed with high-power lasers and probed with X-ray free electron lasers. The trained network allows automatic acquisition of microstructure information, performing well in predictions on single-species nanoparticles on the theoretical model and in situexperimental data. We evaluate our network by comparing it with other methods, revealing its reliability and efficiency in dynamic experiments, which is of great value for in situcharacterization of materials under high-power laser-driven dynamic compression.

Published
2024
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18. Assessment, re-design and evaluation of changes to the driver's cab in a suburban electric train.

Author

Stevenson, M G, Coleman, N, Long, A F, and Williamson, A M

Abstract

A new type of electric train, called the Tangara, began replacing older trains on the Sydney city and suburban network in 1990. Shortly afterwards, some of the train drivers began reporting pain in the arms while driving the new train. The Ergonomics Unit of Worksafe Australia was then engaged to identify and assess ergonomic problems in the driver's cab. This process included direct observation of drivers at work, distribution of a self-administered questionnaire to all drivers, and analysis of anthropometric problems using a computer-aided design package. The analysis of 193 completed questionnaires and the problems shown by the design study were used in developing an improved design. A mock-up of the modified cab was made and tried out by 134 drivers whose comments led to further changes. The modified design was applied to new production, and existing cabs were modified during major maintenance. By 1996, 96% of the driver's cabs were to the new design. An evaluation of the new design was undertaken using written questionnaires, which were completed by 227 drivers. The results were strongly in favour of the new design, showing the effectiveness of the ergonomic modifications. [ABSTRACT FROM AUTHOR]

Published
2000
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19. Local muscle fatigue in repetitive work.

Author

BAIDYA, K. N. and STEVENSON, M. G.

Abstract

Severe local muscle fatigue may be a precursor of repetition strain injuries (RSI). In any event it produces discomfort and limits production. This fatigue is evaluated by analysing the amplitude and frequency of the electromyographic signals of the extensor and flexor muscles during repetitive wrist extension against a constant torque. The absolute integral of the signal increased with extension angle but did not change with the exercise time period. This suggests that amplitude analysis is better for the evaluation of load, and frequency analysis is better in evaluating fatigue. The rate of decrease of the centre frequency with exercise time was also higher for the higher extension angle, and it was higher for female than for male subjects. Ulnar deviation did not affect the rate of fatigue in these experiments. The methodology used here shows promise for the evaluation of tool, job and layout design to prevent RSI. [ABSTRACT FROM PUBLISHER]

Published
1988
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20. An optical method for direct measurements of strain in a torsional Hopkinson-bar apparatus

Author

Stevenson, M G and Campbell, J D

Abstract

A method has been developed to measure the related rotation of the flanges of a thin-walled tubular specimen during a torsion test. The method, which is based on the Moiré-fringe technique, is capable of use at the high rates of strain encountered during a Hopkinson-bar test, as well as at low rates of strain. In the application described, the specimen gauge length is very short, but the method could be used for specimens of considerably longer gauge length.Direct calibration of the system is easily carried out at low angular velocities. The method can then be used to measure directly the specimen strain during a Hopkinson-bar test, and thus to check the value derived from measuremets of torsional waves in the elastic bars. Results of such comparisons are given, and it is found that the values given by the two method agree well, the differnce being attributable largely to inaccuracies in the torque measurement. The new method permits the determination of specimen deformation during the later stages of the test when multiple wave reflections render the wave analysis iaccurate. In particular, it has been found that the specimen may be subjected to reversed plastic straining, so that the total plastic strain connot be determined from the permenent deformation at the end of the test.

Published
1975
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21. Further Developments in Applying the Finite Element Method to the Calculation of Temperature Distributions in Machining and Comparisons With Experiment

Author

Stevenson, M. G., Wright, P. K., and Chow, J. G.

Abstract

The finite element program developed in previous work [1] for calculating the temperature distributions in the chip and tool in metal machining has been extended in its range of application. Specifically, the program no longer needs a flow field as input and it can accommodate a wide range of shear angle and contact lengths. An important feature of this paper is that temperature fields from the finite element method have been compared with temperatures obtained with a previously described metallographic method [7]. This is the first time these two techniques have been used for the same machining conditions and the comparisons are very good.

Published
1983
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22. High Strain Rate Testing of a Low Carbon Steel to High Strains over a Range of Temperatures, Using a Torsional Hopkinson-bar Apparatus

Author

OXFORD UNIV (UNITED KINGDOM) DEPT OF ENGINEERING SCIENCE, Stevenson, M. G., Campbell, J. D., OXFORD UNIV (UNITED KINGDOM) DEPT OF ENGINEERING SCIENCE, Stevenson, M. G., and Campbell, J. D.

Abstract

A recent version of a torsional Hopkinson-bar apparatus, capable of high strains such as found in metal working, is briefly described. The magnitude of axial forces and bending waves in the system during a test is determined and their effects on measured flow stress shown to be negligible. Test results for a low carbon free-machining steel are given, for shear strain rates up to 4330/s and temperatures up to 500C. In all but one case this material fractured in the dynamic tests before the potential strain was realized, but shear strains of about 1.3 were usually obtained. Because of the large strains, adiabatic heating during the dynamic tests had a substantial effect on the stress-strain curves. The dynamic strain ageing effect was clearly evident from the tests at 400C and 500C.

Published
1974

25. Phase Changes in Dynamically Compressed Water

Author

Stevenson, M. G., Zinta, L. M. V., Heuser, B., He, Z., Ranjan, D., Bethkenhagen, M., French, M., Bergermann, A., Redmer, R., Cowan, T. E., Humphries, O., Lutgert, J., Voigt, K., Schuster, A. K., Lefevre, F., Vinci, T., Mcbride, E. E., Hartley, N. J., Gleason-Holbrook, A. E., Glenzer, S. H., Pandolfi, S., Descamps, A., Ofori-Okai, B., Schoenwaelder, C., Glenn, G., Fletcher, L. B., Nagler, B., Lee, H. J., Dimitri Khaghani, Galtier, E., Hernandez, J., Ravasio, A., and Kraus, D.

Subjects
Inorganic Chemistry, Structural Biology, General Materials Science, Physical and Theoretical Chemistry, Condensed Matter Physics, Biochemistry

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