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264 results on '"Peach, G"'

1. Ultracold homonuclear and heteronuclear collisions in metastable helium

Author

Cocks, D. G., Whittingham, I. B., and Peach, G.

Subjects
Physics - Atomic Physics
Abstract

Scattering and ionizing cross sections and rates are calculated for ultracold collisions between metastable helium atoms using a fully quantum-mechanical close-coupled formalism. Homonuclear collisions of the bosonic ${}^{4}$He$^{*} +{}^{4}$He$^{*}$ and fermionic ${}^{3}$He$^{*} + {}^{3}$He$^{*}$ systems, and heteronuclear collisions of the mixed ${}^{3}$He$^{*} +{}^{4}$He$^{*}$ system, are investigated over a temperature range 1 $\mu$K to 1 K. Carefully constructed Born-Oppenheimer molecular potentials are used to describe the electrostatic interaction between the colliding atoms, and complex optical potentials used to represent loss through ionization from the ${}^{1,3}\Sigma $ states. Magnetic spin-dipole mediated transitions from the ${}^{5}\Sigma $ state are included and results reported for spin-polarized and unpolarized systems. Comparisons are made with experimental results, previous semi-classical models, and a perturbed single channel model., Comment: 14 pages, 9 figures

Published
2019
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5. Collisional broadening of alkali doublets by helium perturbers

Author

Mullamphy, D. F. T., Peach, G., Venturi, V., Whittingham, I. B., and Gibson, S. J.

Subjects
Physics - Atomic Physics
Abstract

We report results for the Lorentzian profiles of the Li I, Na I and K I doublets and the Na I subordinate doublet broadened by helium perturbers for temperatures up to 3000 K They have been obtained from a fully quantum-mechanical close-coupling description of the colliding atoms, the Baranger theory of line shapes and new ab initio potentials for the alkali-helium interaction. For all lines except the 769.9 nm K I line, the temperature dependence of the widths over the range 70 < T < 3000 K is accurately represented by the power law form w=aT^b with 0.37 < b < 0.43. The 769.9 K I line has this form for 500 < T < 3000 K with b = 0.49. Although the shifts have a more complex temperature dependence, they all have the general feature of increasing with temperature above T=500 K apart from the 769.9 K I line whose shift decreases with temperature., Comment: 12 pages, 6 figures

Published
2006
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6. Ultracold atomic collisions in tight harmonic traps: Perturbation theory, ionization losses and application to metastable helium atoms

Author

Beams, T J, Peach, G, and Whittingham, I B

Subjects
Physics - Atomic Physics
Abstract

Collisions between tightly confined atoms can lead to ionization and hence to loss of atoms from the trap. We develop second-order perturbation theory for a tensorial perturbation of a spherically symmetric system and the theory is then applied to processes mediated by the spin-dipole interaction. Redistribution and loss mechanisms are studied for the case of spin-polarized metastable helium atoms and results obtained for the five lowest s states in the trap and trapping frequencies ranging from 1 kHz to 10 MHz., Comment: 13 pages, LaTeX2e

Published
2004
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17. Recent Results for Widths of Lines Important in the Spectra of Cool Stars

Author

Peach G.

Subjects
atomic processes, line, profiles, sun, photosphere, stars, white dwarfs, brown dwarfs, Astronomy, QB1-991
Abstract

The broadening of spectral lines by neutral perturbers is an important factor in the interpretation of the observed spectra of cool stars and is often included in the analysis by using a simple van der Waals formula. Detailed calculations are carried out for selected lines and are used to examine the validity of this formula for a range of temperatures.

Published
2011
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33. Neelum Jehum recovery

Author

Peach G., Ashcroft B., Peach G., and Ashcroft B.

Abstract

A severe rock-burst event, which occurred on 31 May 2015 at Neelum Jhelum water-tunnel project, Muzaffarabad district, Azad Jammu and Kashmir, Himalayan foothill zone, north-eastern Pakistan, and the subsequent main beam gripper hard-rock tunnel-boring machine (TBM) recovery activities are described. The general geological conditions and those immediately prior to the rock burst, and the physical effects on the trailing TBM 696 in the right tunnel and the leading TBM 697 in the left tunnel are discussed. Ten unusual circumstances under which the event had occurred are summarised. A description of the damage caused, and the responses to the rock burst for the recovery of the TBM (debris removal, support installation, inspection of cutterhead and main bearing, support design for damaged area, and equipment repair and replacement) and for the re-commencement of excavation (rock-burst mitigation measures) are presented. The TBM 696 recovery operation commenced in June 2015 and took ca. 7.5 months with excavation re-commencing in Jan. 2016 (TBM 697 continued excavation during the recovery period)., A severe rock-burst event, which occurred on 31 May 2015 at Neelum Jhelum water-tunnel project, Muzaffarabad district, Azad Jammu and Kashmir, Himalayan foothill zone, north-eastern Pakistan, and the subsequent main beam gripper hard-rock tunnel-boring machine (TBM) recovery activities are described. The general geological conditions and those immediately prior to the rock burst, and the physical effects on the trailing TBM 696 in the right tunnel and the leading TBM 697 in the left tunnel are discussed. Ten unusual circumstances under which the event had occurred are summarised. A description of the damage caused, and the responses to the rock burst for the recovery of the TBM (debris removal, support installation, inspection of cutterhead and main bearing, support design for damaged area, and equipment repair and replacement) and for the re-commencement of excavation (rock-burst mitigation measures) are presented. The TBM 696 recovery operation commenced in June 2015 and took ca. 7.5 months with excavation re-commencing in Jan. 2016 (TBM 697 continued excavation during the recovery period).

Published
2018

43. Traumatic arterial spasm causing transient limb ischaemia: a genuine clinical entity

Author

George A. Antoniou, Peach G, El Sakka K, and Mohamad Hamady

Subjects
Adult, Male, Leg, business.industry, GUNSHOT INJURY, Ischemia, Angiography, Digital Subtraction, Arterial Occlusive Diseases, General Medicine, medicine.disease, Arterial spasm, Tibial Arteries, body regions, Online Case Report, Anesthesia, Humans, Limb ischaemia, Medicine, Wounds, Gunshot, Surgery, Tibial artery, cardiovascular diseases, business, Perfusion
Abstract

Traumatic arterial spasm is a phenomenon that has long been questioned by clinicians. Indeed, some would argue that surgical exploration is mandatory whenever there are signs of distal ischaemia following limb trauma. We present a case of angiographically demonstrated tibial artery spasm following gunshot injury. Exploration was unnecessary and distal perfusion was reestablished spontaneously. This case demonstrates the existence of traumatic arterial spasm as a genuine clinical entity and suggests that immediate surgical exploration may not be necessary in all cases.

Published
2010
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44. Large-diameter tunnelling collapses: recovery design and execution.

Author

Townsend B.F., North American Tunnelling 2008 San Francisco, California 8-11 June 2008, Peach G., Speers C.R., Townsend B.F., North American Tunnelling 2008 San Francisco, California 8-11 June 2008, Peach G., and Speers C.R.

Abstract

Six collapses were studied that occurred during large-diameter tunnelling through weak sedimentary rocks and soil using sequential excavation-and-support methods in three stages: top heading, bench and invert. Excavation was carried out using hydraulic excavators and breakers. Four of the collapses occurred during the top-heading stage. The collapsed lengths, between 20 and 277 m, were re-mined using essentially the same tunnelling method with larger excavation profiles to accommodate the designed remedial measures, which consisted of ground treatment, pre-support and stronger initial support/outer lining to carry the higher ground loads acting in the collapsed lengths. Placement of the inner lining has been completed in two of the tunnels, and final design of the inner linings in the other tunnels is being carried out. The process requires evaluation of the performance of all the geological, geotechnical and monitoring data measured during excavation of the top headings. The results to date shows that sequential excavation-and- support soft-ground tunnelling methods can be applied to the re- excavation of large span excavations through collapsed ground, provided that an extensive programme of excavation pre-support is undertaken followed by careful excavation and tunnel monitoring., Six collapses were studied that occurred during large-diameter tunnelling through weak sedimentary rocks and soil using sequential excavation-and-support methods in three stages: top heading, bench and invert. Excavation was carried out using hydraulic excavators and breakers. Four of the collapses occurred during the top-heading stage. The collapsed lengths, between 20 and 277 m, were re-mined using essentially the same tunnelling method with larger excavation profiles to accommodate the designed remedial measures, which consisted of ground treatment, pre-support and stronger initial support/outer lining to carry the higher ground loads acting in the collapsed lengths. Placement of the inner lining has been completed in two of the tunnels, and final design of the inner linings in the other tunnels is being carried out. The process requires evaluation of the performance of all the geological, geotechnical and monitoring data measured during excavation of the top headings. The results to date shows that sequential excavation-and- support soft-ground tunnelling methods can be applied to the re- excavation of large span excavations through collapsed ground, provided that an extensive programme of excavation pre-support is undertaken followed by careful excavation and tunnel monitoring.

Published
2008

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