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Search Results: 1 - 10 of 128399 matches for " George T. Gillies "
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Momentum of electromagnetic fields, speed of light in moving media, and the photon mass
Gianfranco Spavieri,George T. Gillies
Physics , 2010, DOI: 10.1134/S0202289310040018
Abstract: In both the equations for matter and light wave propagation, the momentum of the electromagnetic fields Pe reflects the relevant em interaction. As a review of some applications of wave propagation properties, an optical experiment which tests the speed of light in moving rarefied gases is described. Moreover, Pe is also the link to the unitary vision of the quantum effects of the Aharonov-Bohm (AB) type, which provide a useful quantum approach for the limit of the photon mass mph. A bench-top experiment based on effects of the AB type that exploit new interferometric techniques, is foreseen to yield the limit mph = 10^-54 g, a value that improves upon the results achieved with other approaches.
Precise Gravitational Tests via the SEE Mission: A Proposal for Space-Based Measurements
Alvin J. Sanders,George T. Gillies
Physics , 2010,
Abstract: The objective of a SEE mission is to support development of unification theory by carrying out sensitive gravitational tests capable of determining whether various alternative theories are compatible with nature. Gravitation is a key "missing link" in unification theory. Nearly all unification theories incorporate gravity at a fundamental level, and therefore precise measurements of gravitational forces will place important constraints on unification theories. Ground-based gravitational measurements to the accuracy required are impossible due to the many sources of noise present in the terrestrial environment. The proposed space-based Satellite Energy Exchange (SEE) mission will measure several important parameters to an accuracy between 100 and 10,000 times better than current or planned measurement capabilities. It will test for time variation of the gravitational "constant" G and for violations of the weak equivalence principle (WEP) and the inverse-square-law (ISL), and it will determine G. It is well-known that the discovery of breakdowns in WEP or ISL and the possible determination of a time-varying G would have significant consequences on virtually all aspects of unification theory.
Universality in the Gravitational Stretching of Clocks, Waves and Quantum States
C. S. Unnikrishnan,George T. Gillies
Physics , 2011, DOI: 10.1142/S0218271811020615
Abstract: There are discernible and fundamental differences between clocks, waves and physical states in classical physics. These fundamental concepts find a common expression in the context of quantum physics in gravitational fields; matter and light waves, quantum states and oscillator clocks become quantum synonymous through the Planck-Einstein-de Broglie relations and the equivalence principle. With this insight, gravitational effects on quantum systems can be simply and accurately analyzed. Apart from providing a transparent framework for conceptual and quantitative thinking on matter waves and quantum states in a gravitational field, we address and resolve with clarity the recent controversial discussions on the important issue of the relation and the crucial difference between gravimetery using atom interferometers and the measurement of gravitational time dilation.
Rigorous Comparison of Gravimetry Employing Atom Interferometers and the Measurement of Gravitational Time Dilation
C. S. Unnikrishnan,George T. Gillies
Physics , 2011,
Abstract: We present a gravitationally rigorous and clear answer, in the negative, to the question whether gravimetry with atom interferometers is equivalent to the the measurement of the relative gravitational time dilation of two clocks separated in space. Though matter and light waves, quantum states and oscillator clocks are quantum synonymous through the Planck-Einstein-de Broglie relations and the equivalence principle, there are crucial differences in the context of tests of gravitation theories.
Implications upon theory discrimination of an accurate measurement of the time rate of change of the gravitational parameter and other cosmological parameters
Alvin J. Sanders,George T. Gillies,Ernst Schmutzer
Physics , 2010, DOI: 10.1002/andp.201010460
Abstract: A substantial improvement in the accuracy of G-dot tests (The dot denotes the time derivative.) would make it realistic to speak in terms of a measurement of G-dot, rather than merely a smaller upper bound on |G-dot|. We show that the accuracy delta|G-dot/G| \approx 10^-14 yr^-1 may be sufficient, given the accuracy of other cosmological parameters, to observe effects predicted by higher dimensions theories and, hence, to discriminate among different models. The \.G design goal for the SEE (Satellite Energy Exchange) mission is delta(G-dot/G) \approx 10^-14 yr^-1.
Standard and derived Planck quantities: selected analysis and derivations
Jason R. Buzcyna,C. S. Unnikrishnan,George T. Gillies
Physics , 2010, DOI: 10.1134/S0202289311040037
Abstract: We provide an overview of the fundamental units of physical quantities determined naturally by the values of fundamental constants of nature. We discuss a comparison between the 'Planck units', now widely used in theoretical physics and the pre-quantum 'Stoney units' in which, instead of the Planck constant, the charge of the electron is used with very similar quantitative results. We discuss some of the physical motivation for these special units, attributed much after they were introduced, and also put forth a summary of the arguments supporting various cases for making specific physical interpretations of the meanings of some of these units. The new aspects we discuss are a possible physical basis for the Stoney units, their link to the Planck units, and also the importance of Planck units for thermodynamical quantities in the context of quantum gravity.
Some observations on the mechanics and dynamics of tumor heterogeneity
G. T. Gillies
AIP Advances , 2012, DOI: 10.1063/1.3697847
Abstract: The genetic, proteomic and cytostructural complexities of malignant neoplasms have received much attention in cancer research for many years. However, studies of the mechanics of neoplastic phenomena at the meso- and macroscales are also now providing opportunities for understanding some aspects of tumor growth and developing new therapeutic possibilities. We provide a brief overview of some of the recent work in these areas, with emphasis on physical considerations of certain aspects of the mechanics and fluid dynamics of tumor cell invasion and dispersion.
Intracranial Somatosensory Responses with Direct Spinal Cord Stimulation in Anesthetized Sheep
Oliver E. Flouty, Hiroyuki Oya, Hiroto Kawasaki, Chandan G. Reddy, Douglas C. Fredericks, Katherine N. Gibson-Corley, Nicholas D. Jeffery, George T. Gillies, Matthew A. Howard
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0056266
Abstract: The efficacy of spinal cord stimulators is dependent on the ability of the device to functionally activate targeted structures within the spinal cord, while avoiding activation of near-by non-targeted structures. In theory, these objectives can best be achieved by delivering electrical stimuli directly to the surface of the spinal cord. The current experiments were performed to study the influence of different stimulating electrode positions on patterns of spinal cord electrophysiological activation. A custom-designed spinal cord neurostimulator was used to investigate the effects of lead position and stimulus amplitude on cortical electrophysiological responses to spinal cord stimulation. Brain recordings were obtained from subdural grids placed in four adult sheep. We systematically varied the position of the stimulating lead relative to the spinal cord and the voltage delivered by the device at each position, and then examined how these variables influenced cortical responses. A clear relationship was observed between voltage and electrode position, and the magnitude of high gamma-band oscillations. Direct stimulation of the dorsal column contralateral to the grid required the lowest voltage to evoke brain responses to spinal cord stimulation. Given the lower voltage thresholds associated with direct stimulation of the dorsal column, and its possible impact on the therapeutic window, this intradural modality may have particular clinical advantages over standard epidural techniques now in routine use.
Satellite E?tv?s Test of the Weak Equivalence Principle for Zero-Point Vacuum Energy
J. W. Moffat,G. T. Gillies
Physics , 2002, DOI: 10.1088/1367-2630/4/1/392
Abstract: An E\"otv\"os experiment to test the weak equivalence principle (WEP) for zero-point vacuum energy is proposed using a satellite. Following the suggestion of Ross for a terrestrial experiment of this type, the acceleration of a spherical test mass of aluminum would be compared with that of a similar test mass made from another material. The estimated ratio of the zero-point vacuum energy density inside the aluminum sphere to the rest mass energy density is ~ 1.6 X 10^{-14}, which would allow a 1% resolution of a potential WEP violation observed in a satellite mission test that had a baseline sensitivity to WEP violations of ~ 10^{-16}. An observed violation of the WEP for vacuum energy density would constitute a significant clue as to the origin of the cosmological constant and the source of dark energy, and test a recently proposed resolution of the cosmological constant problem, based on a model of nonlocal quantum gravity and quantum field theory.
Nano-constraints on the spatial anisotropy of the Gravitational Constant
C. S. Unnikrishnan,G. T. Gillies
Physics , 2002, DOI: 10.1016/S0375-9601(02)01390-7
Abstract: We present constraints from various experimental data that limit any spatial anisotropy of the Gravitational constant to less than a part per billion or even smaller. This rules out with a wide margin the recently reported claim of a spatial anisotropy of G with a diurnal temporal signature.
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