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Search Results: 1 - 10 of 462605 matches for " A. Watson "
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Lithography and Fabrication of Frictional Tiers on Poly(Dimethylsiloxane) Using Atomic Force Microscopy  [PDF]
Gregory S. Watson, Jolanta A. Watson
Journal of Surface Engineered Materials and Advanced Technology (JSEMAT) , 2012, DOI: 10.4236/jsemat.2012.223036
Abstract: This study investigates controlled micro/nano manipulation of polydimethylsiloxane (PDMS) using Atomic Force Microscopy (AFM). Lithographic results revealed stick-slip phenomena along the slow scan direction. Varying the normal loading force, scan size, scan number and contact conditions allowed the control of certain lithographic outcomes e.g., channel spacing. The PDMS surface experienced significant in-plane deformation in response to the tip-induced lateral force. This displacement increased with increasing loading force, creating greater spacing between channels in the slow scan direction. Simultaneous generation of a lateral displacement in the fast scan direction caused a decrease in channel length with increasing loading force due to an increase in static friction with normal force, resulting in a greater surface relaxation, and shorter track length of dynamic friction. By controlling both the loading force and the number of scans over an area, frictional tiers were produced.
High-Energy Cosmic Rays and the Greisen-Zatsepin-Kuzmin Effect
A A Watson
Physics , 2013, DOI: 10.1088/0034-4885/77/3/036901
Abstract: Although cosmic rays were discovered over 100 years ago their origin remains uncertain. They have an energy spectrum that extends from 1 GeV to beyond 1020 eV, where the rate is less than 1 particle per km2 per century. Shortly after the discovery of the cosmic microwave background in 1965, it was pointed out that the spectrum of cosmic rays should steepen fairly abruptly above about 4 x 1019 eV, provided the sources are distributed uniformly throughout the Universe. This prediction, by Greisen and by Zatsepin and Kuzmin, has become known as the GZK-effect and in this article I discuss the current position with regard to experimental data on the energy spectrum of the highest cosmic-ray energies that have been accumulated in a search that has lasted nearly 50 years. Although there is now little doubt that a suppression of the spectrum exists near the energy predicted, it is by no means certain that this is a manifestation of the GZK-effect as it might be that this energy is also close to the maximum to which sources can accelerate particles, with the highest-energy beam containing a large fraction of nuclei heavier than protons. The way forward is briefly mentioned.
Ultra High Energy Cosmic Rays: present status and future prospects
A. A. Watson
Physics , 2001,
Abstract: Reasons for the current interest in cosmic rays above 10^19 eV are described. The latest results on the energy spectrum, arrival direction distribution and mass composition of cosmic rays are reviewed, including data that were reported after the meeting in Blois in June 2001. The enigma set by the existence of ultra high-energy cosmic rays remains. Ideas proposed to explain it are discussed and progress with the construction of the Pierre Auger Observatory is outlined.
The Discovery of Cherenkov Radiation and its use in the detection of extensive air showers
A A Watson
Physics , 2011, DOI: 10.1016/j.nuclphysbps.2011.03.003
Abstract: Cascades of charged particles are created when high-energy cosmic rays enter the earth's atmosphere: these 'extensive air-showers' are studied to gain information on the energy spectrum, arrival direction distribution and mass composition of the particles above 1014 eV where direct observations using instruments carried by balloons or satellites become impractical. Detection of light in the visible and ultra-violet ranges of the electromagnetic spectrum plays a key role in this work, the two processes involved being the emission of Cherenkov light and the production of fluorescence radiation. In this paper I will outline some of the history of the discovery of the Cherenkov process and describe the use to which it has been put in the study of extensive air-showers at ground level.
Intron Phase Patterns in Genes: Preservation and Evolutionary Changes
A. Ruvinsky and C. Watson
The Open Evolution Journal , 2007, DOI: 10.2174/1874404400701010001]
Abstract: Introns are located either between codons (phase 0) or within codons (phase 1 and 2) and their phases as well as location usually stay unchanged for a long time. A string of intron phases represents a structure which may carry useful additional information about internal rearrangements of a gene. Combined search for intron phase patterns and exon lengths serves as a helpful approach for finding conserved intragenic duplications and other rearrangements. In vertebrate genes intragenic duplications usually are more numerous than in orthologs from other animal taxons. Intron phase patterns and exon lengths are highly conservative in some genes and can be traced back to a common ancestor of mammals and nematodes. Despite this, there are orthologs which show drastic losses of intron-exon structures as found in insects and urochordata. Driving forces behind such changes in exon-intron structures remain unknown and need further investigation.
Economic dependency and geopolitics: recurring ideological themes in Caribbean intellectual culture
Hilbourne A. Watson
Nieuwe West-Indische Gids , 1986,
Erich Regener and the maximum in ionisation of the atmosphere
P. Carlson,A. A. Watson
Physics , 2014,
Abstract: In the 1930s the German physicist Erich Regener (1881-1955) did important work on the measurement of the rate of production of ionisation deep under-water and in the atmosphere. He discovered, along with one of his students, Georg Pfotzer, the altitude at which the production of ionisation in the atmosphere reaches a maximum, often, but misleadingly, called the Pfotzer maximum. Regener was one of the first to estimate the energy density of cosmic rays, an estimate that was used by Baade and Zwicky to bolster their postulate that supernovae might be their source. Yet Regener's name is less recognised by present-day cosmic ray physicists than it should be largely because in 1937 he was forced to take early retirement by the National Socialists as his wife had Jewish ancestors. In this paper we briefly review his work on cosmic rays and recommend an alternative naming of the ionisation maximum. The influence that Regener had on the field through his son, his son-in-law, his grandsons and his students and through his links with Rutherford's group in Cambridge is discussed in an appendix. Regener was nominated for the Nobel Prize in Physics by Schroedinger in 1938. He died in 1955 at the age of 73.
A. M. Watson,R. Costero
Revista mexicana de astronomía y astrofísica , 2011,
Abstract: We review the papers The Law of Interstellar Extinction in Orion by H. Johnson and E. E. Mendoza, 1964, BOTT, 3, 25, 331 and The Extinction Law in the Orion Nebula by R. Costero and M. Peimbert, 1970, BOTT, 5, 34, 229. Each review is preceded by a brief account of the professional relationship between the authors.
Dirichlet-Neumann bracketing for boundary-value problems on graphs
Sonja Currie,Bruce A. Watson
Electronic Journal of Differential Equations , 2005,
Abstract: We consider the spectral structure of second order boundary-value problems on graphs. A variational formulation for boundary-value problems on graphs is given. As a consequence we can formulate an analogue of Dirichlet-Neumann bracketing for boundary-value problems on graphs. This in turn gives rise to eigenvalue and eigenfunction asymptotic approximations.
The quantum state vector in phase space and Gabor's windowed Fourier transform
A. J. Bracken,P. Watson
Physics , 2010, DOI: 10.1088/1751-8113/43/39/395304
Abstract: Representations of quantum state vectors by complex phase space amplitudes, complementing the description of the density operator by the Wigner function, have been defined by applying the Weyl-Wigner transform to dyadic operators, linear in the state vector and anti-linear in a fixed `window state vector'. Here aspects of this construction are explored, with emphasis on the connection with Gabor's `windowed Fourier transform'. The amplitudes that arise for simple quantum states from various choices of window are presented as illustrations. Generalized Bargmann representations of the state vector appear as special cases, associated with Gaussian windows. For every choice of window, amplitudes lie in a corresponding linear subspace of square-integrable functions on phase space. A generalized Born interpretation of amplitudes is described, with both the Wigner function and a generalized Husimi function appearing as quantities linear in an amplitude and anti-linear in its complex conjugate. Schr\"odinger's time-dependent and time-independent equations are represented on phase space amplitudes, and their solutions described in simple cases.
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