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Search Results: 1 - 10 of 378531 matches for " T. J. Sumner "
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Earth Flyby and Pioneer Anomalies
M. B. Gerrard,T. J. Sumner
Physics , 2008,
Abstract: Applying Newtonian dynamics in five dimensions rather than four, to a universe that is closed, isotropic and expanding,suggests that under certain circumstances an additional and previously unidentified acceleration, a_A, can arise affecting the four dimensional motion of spacecraft. The two cases of this acceleration being either real or virtual are considered. In the real case, simple estimates of a_A are shown to be in partial agreement with reported acceleration anomalies from several Earth flybys and from the Pioneer spacecraft. However, these estimates do not fully reconcile with radio Doppler tracking data. The virtual case, by contrast, appears to overcome these and other difficulties with the real case, and is discussed in an addendum. Furthermore, the virtual case has an altitude dependence which makes detection of any anomaly unlikely above ~2000 km. Equations governing this additional acceleration have been derived from first principles, without the introduction of free parameters or new constants and without amendment to the law of gravity.
The effect of a fifth large-scale space-time dimension on the conservation of energy in a four dimensional Universe
M. B. Gerrard,T. J. Sumner
Physics , 2007,
Abstract: The effect of introducing a fifth large-scale space-time dimension to the equations of orbital dynamics was analysed in an earlier paper by the authors. The results showed good agreement with the observed flat rotation curves of galaxies and the Pioneer Anomaly. This analysis did not require the modification of Newtonian dynamics, but rather only their restatement in a five dimensional framework. The same analysis derived a acceleration parameter ar, which plays an important role in the restated equations of orbital dynamics, and suggested a value for ar. In this companion paper, the principle of conservation of energy is restated within the same five-dimensional framework. The resulting analysis provides an alternative route to estimating the value of ar, without reference to the equations of orbital dynamics, and based solely on key cosmological constants and parameters, including the gravitational constant, G. The same analysis suggests that: (i) the inverse square law of gravity may itself be due to the conservation of energy at the boundary between a four-dimensional universe and a fifth large-scale space-time dimension; and (ii) there is a limiting case for the Tulley-Fisher relationship linking the speed of light to the mass of the Universe.
The effect of a fifth large-scale space-time dimension on orbital dynamics
M. B. Gerrard,T. J. Sumner
Physics , 2006,
Abstract: A model based on simple assumptions about 4-dimensional space-time being closed and isotropic, and embedded in a 5th large-scale dimension, r, representing the radius of curvature of space-time, has been used in an application of Newton's Second Law to describe a system with angular momentum. It has been found that the equations of MOND used to explain the rotation curves of galaxies appear as a limit within this derivation and that there is a universal acceleration constant, ao, with a value, again consistent with that used by MOND. This approach does not require modification of Newtonian dynamics, only its extension into a fifth large-scale dimension. The transition from the classical Newtonian dynamics to the MOND regime emerges naturally and without the introduction of arbitrary fitting functions, if this 5-dimensional model is adopted. The paper also includes the derivation of an effect in 5-dimensional orbital dynamics which is in reasonable agreement with the observed Pioneer Anomaly.
Characterising and Testing Deep UV LEDs for Use in Space Applications
D. Hollington,J. T. Baird,T. J. Sumner,P. J. Wass
Physics , 2015, DOI: 10.1088/0264-9381/32/23/235020
Abstract: Deep ultraviolet (DUV) light sources are used to neutralise isolated test masses in highly sensitive space-based gravitational experiments. An example is the LISA Pathfinder charge management system, which uses low-pressure mercury lamps. A future gravitational-wave observatory such as eLISA will use UV light-emitting diodes (UV LEDs), which offer numerous advantages over traditional discharge lamps. Such devices have limited space heritage but are are now available from a number of commercial suppliers. Here we report on a test campaign that was carried out to quantify the general properties of three types of commercially available UV LEDs and demonstrate their suitability for use in space. Testing included general electrical and UV output measurements, spectral stability, pulsed performance, temperature dependence as well as thermal vacuum, radiation and vibration survivability.
Muon-induced neutron production and detection with GEANT4 and FLUKA
H. M. Araujo,V. A. Kudryavtsev,N. J. C. Spooner,T. J. Sumner
Physics , 2004, DOI: 10.1016/j.nima.2005.02.004
Abstract: We report on a comparison study of the Monte Carlo packages GEANT4 and FLUKA for simulating neutron production by muons penetrating deep underground. GEANT4 is found to generate fewer neutrons at muon energies above ~100 GeV, by at most a factor of 2 in some materials, which we attribute mainly to lower neutron production in hadronic cascades. As a practical case study, the muon-induced neutron background expected in a 250 kg liquid-xenon WIMP dark matter detector was calculated and good agreement was found for the recoil event rates. The detailed model of neutron elastic scattering in GEANT4 was also shown to influence the nuclear recoil spectrum observed in the target, which is presently a shortcoming of FLUKA. We conclude that both packages are suited for this type of simulation, although further improvements are desirable in both cases.
Timescales of Growth Response of Microbial Mats to Environmental Change in an Ice-Covered Antarctic Lake
Ian Hawes,Dawn Y. Sumner,Dale T. Andersen,Anne D. Jungblut,Tyler J. Mackey
Biology , 2013, DOI: 10.3390/biology2010151
Abstract: Lake Vanda is a perennially ice-covered, closed-basin lake in the McMurdo Dry Valleys, Antarctica. Laminated photosynthetic microbial mats cover the floor of the lake from below the ice cover to >40 m depth. In recent decades, the water level of Lake Vanda has been rising, creating a “natural experiment” on development of mat communities on newly flooded substrates and the response of deeper mats to declining irradiance. Mats in recently flooded depths accumulate one lamina (~0.3 mm) per year and accrue ~0.18 μg chlorophyll-a cm ?2 y ?1. As they increase in thickness, vertical zonation becomes evident, with the upper 2-4 laminae forming an orange-brown zone, rich in myxoxanthophyll and dominated by intertwined Leptolyngbya trichomes. Below this, up to six phycobilin-rich green/pink-pigmented laminae form a subsurface zone, inhabited by Leptolyngbya, Oscillatoria and Phormidium morphotypes. Laminae continued to increase in thickness for several years after burial, and PAM fluorometry indicated photosynthetic potential in all pigmented laminae. At depths that have been submerged for >40 years, mats showed similar internal zonation and formed complex pinnacle structures that were only beginning to appear in shallower mats. Chlorophyll-a did not change over time and these mats appear to represent resource-limited “climax” communities. Acclimation of microbial mats to changing environmental conditions is a slow process, and our data show how legacy effects of past change persist into the modern community structure.
Experimental Searches for Dark Matter
Sumner Timothy J.
Living Reviews in Relativity , 2002,
Abstract: There is now an enormously rich variety of experimental techniques being brought to bear on experimental searches for dark matter, covering a wide range of suggested forms for it. The existence of 'dark matter', in some form or other, is inferred from a number of relatively simple observations and the problem has been known for over half a century. To explain 'dark matter' is one of the foremost challenges today -- the answer will be of fundamental importance to cosmologists, astrophysicists, particle physicists, and general relativists. In this article, I will give a brief review of the observational evidence (concentrating on areas of current significant activity), followed by an equally brief summary of candidate solutions for the 'dark matter'. I will then discuss experimental searches, both direct and indirect. Finally, I will offer prospects for the future.
Entanglement, Invariants, and Phylogenetics
J G Sumner
Quantitative Biology , 2007,
Abstract: This thesis develops and expands upon known techniques of mathematical physics relevant to the analysis of the popular Markov model of phylogenetic trees required in biology to reconstruct the evolutionary relationships of taxonomic units from biomolecular sequence data. The techniques of mathematical physics are plethora and have been developed for some time. The Markov model of phylogenetics and its analysis is a relatively new technique where most progress to date has been achieved by using discrete mathematics. This thesis takes a group theoretical approach to the problem by beginning with a remarkable mathematical parallel to the process of scattering in particle physics. This is shown to equate to branching events in the evolutionary history of molecular units. The major technical result of this thesis is the derivation of existence proofs and computational techniques for calculating polynomial group invariant functions on a multi-linear space where the group action is that relevant to a Markovian time evolution. The practical results of this thesis are an extended analysis of the use of invariant functions in distance based methods and the presentation of a new reconstruction technique for quartet trees which is consistent with the most general Markov model of sequence evolution.
Electrochemical Characterization of Riboflavin-Enhanced Reduction of Trinitrotoluene
James J. Sumner,Kevin Chu
Sensors , 2011, DOI: 10.3390/s111110840
Abstract: There is great interest in understanding trinitrotoluene (TNT) and dinitrotoluene (DNT) contamination, detection and remediation in the environment due to TNT’s negative health effects and security implications. Numerous publications have focused on detecting TNT in groundwater using multiple techniques, including electrochemistry. The main degradation pathway of nitrotoluenes in the environment is reduction, frequently with biological and/or photolytic assistance. Riboflavin has also been noted to aid in TNT remediation in soils and groundwater when exposed to light. This report indicates that adding riboflavin to a TNT or DNT solution enhances redox currents in electrochemical experiments. Here AC voltammetry was performed and peak currents compared with and without riboflavin present. Results indicated that TNT, DNT and riboflavin could be detected using AC voltammetry on modified gold electrodes and the addition of riboflavin affected redox peaks of TNT and DNT. Poised potential experiments indicated that it is possible to enhance reduction of TNT in the presence of riboflavin and light. These results were dramatic enough to explain long term enhancement of bioremediation in environments containing high levels of riboflavin and enhance the limit of detection in electrochemically-based nitrotoluene sensing.
Removing the trend of drift induced from acceleration noise for LISA
Alf Tang,Timothy J. Sumner
Physics , 2012,
Abstract: In this paper we demonstrate a methodology to remove the power of the drift induced from random acceleration on LISA proof mass in the frequency domain. The drift must be cleaned from LISA time series data in advance of any further analysis. The cleaning is usually performed in the time domain by using a quadratic function to fit the time series data, and then removing the fitted part from the data. Having Fourier transformed the residuals, and then convolved with LISA transfer function, LISA sensitivity curve can be obtained. However, cosmic gravitational-wave background cannot be retrieved with this approach due to its random nature. Here we provide a new representation of power spectrum given by discrete Fourier transform, which is applied to find the function of the drift power for the cleaning in the frequency domain. We also give the probability distribution used to analyze the data in the frequency domain. We combine several techniques, including Markov Chain Monte Carlo method, simulated annealing, and Gelman & Rubin's method, with Baye's theorem to build the algorithm. The algorithm is utilized to analyze 24 simulations of LISA instrumental noise. We prove that the LISA sensitivity can be recovered through this approach. It can help us to build algorithms for some tasks which are must accomplished in the frequency domain for LISA data analysis. This method can be applied to other space-borne interferometers if charges on their proof masses cannot be perfectly cancelled.
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