ORCID Profile
0000-0001-5895-7575
Current Organisation
Retired
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Publisher: IOP Publishing
Date: 03-1997
Publisher: American Physical Society (APS)
Date: 15-04-1997
Publisher: Springer Science and Business Media LLC
Date: 23-03-2017
Publisher: MDPI AG
Date: 28-12-2020
Abstract: Ever since Eddington’s analysis of the gravitational redshift a century ago, and the arguments in the relativity community that it produced, fine details of the roles of proper time and coordinate time in the redshift remain somewhat obscure. We shed light on these roles by appealing to the physics of the uniformly accelerated frame, in which coordinate time and proper time are well defined and easy to understand and because that frame exists in flat spacetime, special relativity is sufficient to analyse it. We conclude that Eddington’s analysis was indeed correct—as was the 1980 analysis of his detractors, Earman and Glymour, who (it turns out) were following a different route. We also use the uniformly accelerated frame to pronounce invalid Schild’s old argument for spacetime curvature, which has been reproduced by many authors as a pedagogical introduction to curved spacetime. More generally, because the uniformly accelerated frame simulates a gravitational field, it can play a strong role in discussions of proper and coordinate times in advanced relativity.
Publisher: World Scientific Pub Co Pte Ltd
Date: 06-2022
DOI: 10.1142/S2661339522500093
Abstract: Derivations of the rocket equation that use a momentum-conservation argument are notorious for often encountering a problem that would produce an incorrect sign in their result, if it were not “fixed” in various ad hoc ways that can always be shown to be mathematically invalid. Here, we show that the problem of the unwanted minus sign typically (perhaps always) results from a misunderstanding of the language of calculus. When one adheres to a simple and fundamental rule of calculus notation, the derivation of the rocket equation becomes straightforward, and no unwanted minus sign appears.
Publisher: Cambridge University Press (CUP)
Date: 09-2022
DOI: 10.1017/S0373463322000480
Abstract: The Earth Gravity Model 2008 (EGM2008) is now some years old, and yet information on how to use it to calculate Earth's gravity remains obscure outside the field of geodesy. We describe the mathematics necessary to implement EGM2008, and use this to discuss several points of the model: its sensitivity to the number of spherical harmonics being summed, nuances and a trap for physicists and mathematicians in the normalisation it uses, and a comparison with other work. We conclude that one must not overestimate the precision shown by a global-fit model such as EGM2008.
Publisher: Institution of Engineering and Technology (IET)
Date: 18-09-2022
DOI: 10.1049/TJE2.12190
Publisher: American Physical Society (APS)
Date: 19-03-2021
Publisher: American Association of Physics Teachers (AAPT)
Date: 11-1996
DOI: 10.1119/1.18362
Abstract: The electromotive force (emf) in a loop outside an infinite solenoid with changing current is usually calculated using the vector potential because the magnetic field outside an infinite solenoid is supposed to be zero. However, the magnetic field will only be zero for steady currents. A change in the applied voltage will give rise to a change in the current, which will propagate along the solenoid in the same way as a wave on a transmission line. This gives rise to a transient magnetic field outside the solenoid. It is quite possible to calculate this transient magnetic field and use it in Faraday’s law to calculate the emf directly without using the vector potential. In practice, it is usually simpler to use the vector potential. However, care should be taken to ensure that students are not given the impression that there is no magnetic field and that it is the vector potential that acts on charges in the loop. We give ex les of the magnetic field configuration outside an infinite solenoid for a steplike change in driving voltage and for an ac driving voltage.
Publisher: MDPI AG
Date: 16-12-2019
Abstract: I analyse the role of simultaneity in relativistic rotation by building incrementally on its role in simpler scenarios. Historically, rotation has been analysed in 1 + 1 dimensions but my stance is that a 2 + 1 -dimensional treatment is necessary. This treatment requires a discussion of what constitutes a frame, how coordinate choices differ from frame choices, and how poor coordinates can be misleading. I determine how precisely we are able to define a meaningful time coordinate on a gravity-free rotating Earth, and discuss complications due to gravity on our real Earth. I end with a critique of several statements made in relativistic precision-timing literature, that I maintain contradict the tenets of relativity. Those statements tend to be made in the context of satellite-based navigation but they are independent of that technology, and hence are not validated by its success. I suggest that if relativistic precision-timing adheres to such analyses, our civilian timing is likely to suffer in the near future as clocks become ever more precise.
Publisher: American Physical Society (APS)
Date: 15-05-1997
Publisher: Wiley
Date: 04-2018
DOI: 10.1111/TID.12866
Abstract: Conjugated pneumococcal vaccine is recommended for kidney transplant recipients, however, their immunogenicity and potential to trigger allograft rejection though generation of de novo anti-human leukocyte antigen antibodies has not been well studied. Clinically stable kidney transplant recipients participated in a prospective cohort study and received a single dose of 13-valent conjugate pneumococcal vaccine. Anti-pneumococcal IgG was measured for the 13 vaccine serotypes pre and post vaccination and functional anti-pneumococcal IgG for 4 serotypes post vaccination. Anti-human leukocyte antigen antibodies antibodies were measured before and after vaccination. Kidney transplant recipients were followed clinically for 12 months for episodes of allograft rejection or invasive pneumococcal disease. Forty-five kidney transplant recipients participated. Median days between pre and post vaccination serology was 27 (range 21-59). Post vaccination, there was a median 1.1 to 1.7-fold increase in anti-pneumococcal IgG antibody concentrations for all 13 serotypes. Kidney transplant recipients displayed a functional antibody titer ≥1:8 for a median of 3 of the 4 serotypes. Post vaccination, there were no de novo anti-human leukocyte antigen antibodies, no episodes of biopsy proven rejection or invasive pneumococcal disease. A single dose of 13-valent conjugate pneumococcal vaccine elicits increased titers and breadth of functional anti-pneumococcal antibodies in kidney transplant recipients without stimulating rejection or donor-specific antibodies.
Publisher: Springer New York
Date: 2006
Publisher: American Physical Society (APS)
Date: 15-10-1997
Publisher: Springer International Publishing
Date: 2018
No related grants have been discovered for Don Koks.