Absorption of intense electromagnetic beams in a magnetoplasma

The multiphoton inverse bremsstrahlung absorption of two intense electromagnetic beams passing through a magnetized plasma is studied. The rate of absorption of electromagnetic energy by the electrons is calculated by deriving a kinetic equation for the electrons. It is found that the absorption enhances when the frequency of one electromagnetic beam is more, and that of the other electromagnetic beam is less, than the electron-cyclotron frequency. A possible application to extragalactic radio sources is discussed.

Surface waves in the presence of external high frequency fields

The system equations of a collisionless, unmagnetized plasma, contained in a box where a high frequency (HF) electric field is incident, are solved in the electrostatic approximation. The surface modes of the plasma in the semi-infinite and box geometry are investigated. In thi high frequency limit, the mode frequencies are not significantly changed by the HF field but their group velocities can be quite different. Two long wavelength low frequency modes, which are not excited in the absence of HF field, are found. These modes are true surface modes (decaying on one wavelength from the surface) unlike the only low frequency ion acoustic mode in the zero field case. In the short wavelength limit the low frequency mode occurs at omega i/ square root 2, omega i being the ion plasma frequency, as a result similar to the case of no HF field.

Helmholtz Instability In Stratified Shear Flows With Magnetic-Fields

The stability characteristics of a Helmholtz velocity profile in a stratified Boussinesq fluid in the presence of a rigid boundary is studied, A jump in the magnetic field is introduced at a level different from the velocity discontinuity. New unstable modes in addition to the Kelvin-Helmhottz mode are found. The wavelengths of these unstable modes are close to the wavelengths of internal Alfv6n gravity waves in the atmospher.

Formative time lags in nitrogen, oxygen and dry air In crossed electric and magnetic fields

Formative time lags in nitrogen, oxygen, and dry air are measured with and without a magnetic field over a range of gas pressures (0.05 ' p ' 20.2 torr 5 kPa to 2 MPa, electric field strengths (1.8xO14 EEs 60xlO V m l) and magnetic field strengths (85xl0-4 < B ' 16x10-2 Tesla). For experiments below the Paschen minimum, the electrodes are designed to ensure that breakdown occurs over longer gaps and for experiments above the Paschen minimum, a coaxial cylindrical system is employed. The experimental technique consists of applying pulse voltages to the gap at various constant values of E/p and B/p and measuring the time lags from which the formative time lags are separated. In the gases studed, formative time lags decrease on application of a magnetic field at a given pressure for conditions below the Paschen minimum. The voltages at which the formative time lags remain the same without and with magnetic fields are determined, and electron molecule collision frequencies (v/p) are determined using the Effective Reduced Electric Field [EREF] concept. With increasing ratio of E/p in crossed fields, v/p decreases in all the three gases. Measurements above the Paschen minimum yield formative time lags which increase on application of a magnetic field. Formative time lags in nitrogen in ExB fields are calculated assuming an average collision frequency of 8.5x109 sec-1 torr 1. It is concluded that the EREF concept can be applied to explain formative time lags in ExB fields.

Bond graph toolbox for handling complex variable

Bond graph is an apt modelling tool for any system working across multiple energy domains. Power electronics system modelling is usually the study of the interplay of energy in the domains of electrical, mechanical, magnetic and thermal. The usefulness of bond graph modelling in power electronic field has been realised by researchers. Consequently in the last couple of decades, there has been a steadily increasing effort in developing simulation tools for bond graph modelling that are specially suited for power electronic study. For modelling rotating magnetic fields in electromagnetic machine models, a support for vector variables is essential. Unfortunately, all bond graph simulation tools presently provide support only for scalar variables. We propose an approach to provide complex variable and vector support to bond graph such that it will enable modelling of polyphase electromagnetic and spatial vector systems. We also introduced a rotary gyrator element and use it along with the switched junction for developing the complex/vector variable's toolbox. This approach is implemented by developing a complex S-function tool box in Simulink inside a MATLAB environment This choice has been made so as to synthesise the speed of S-function, the user friendliness of Simulink and the popularity of MATLAB.

Gluon-field contribution in QCD sum rules for the magnetic moments of the nucleons

The Wilson coefficient corresponding to the gluon-field strength GμνGμν is evaluated for the nucleon current correlation function in the presence of a static external electromagnetic field, using a regulator mass Λ to separate the high-momentum part of the Feynman diagrams. The magnetic-moment sum rules are analyzed by two different methods and the sensitivity of the results to variations in Λ are discussed.

Absorption of electromagnetic radiation by superconducting YBa2Cu3O7: an oxygen-induced phenomenon

In the superconducting state, YBa2Cu3O7 absorbs electromagnetic radiation over a wide range of frequencies (8 MHz-9 GHz). The absorption is extremely sensitive to temperature, particle size and the magnetic field and depends crucially on the presence of oxygen. A possible explanation for the phenomenon based on the formation of Josephson junctions is suggested.

Technicolor

The need for reexamination of the standard model of strong, weak, and electromagnetic interactions is discussed, especially with regard to 't Hooft's criterion of naturalness. It has been argued that theories with fundamental scalar fields tend to be unnatural at relatively low energies. There are two solutions to this problem: (i) a global supersymmetry, which ensures the absence of all the naturalness-violating effects associated with scalar fields, and (ii) composite structure of the scalar fields, which starts showing up at energy scales where unnatural effects would otherwise have appeared. With reference to the second solution, this article reviews the case for dynamical breaking of the gauge symmetry and the technicolor scheme for the composite Higgs boson. This new interaction, of the scaled-up quantum chromodynamic type, keeps the new set of fermions, the technifermions, together in the Higgs particles. It also provides masses for the electroweak gauge bosons W± and Z0 through technifermion condensate formation. In order to give masses to the ordinary fermions, a new interaction, the extended technicolor interaction, which would connect the ordinary fermions to the technifermions, is required. The extended technicolor group breaks down spontaneously to the technicolor group, possibly as a result of the "tumbling" mechanism, which is discussed here. In addition, the author presents schemes for the isospin breaking of mass matrices of ordinary quarks in the technicolor models. In generalized technicolor models with more than one doublet of technifermions or with more than one technicolor sector, we have additional low-lying degrees of freedom, the pseudo-Goldstone bosons. The pseudo-Goldstone bosons in the technicolor model of Dimopoulos are reviewed and their masses computed. In this context the vacuum alignment problem is also discussed. An effective Lagrangian is derived describing colorless low-lying degrees of freedom for models with two technicolor sectors in the combined limits of chiral symmetry and large number of colors and technicolors. Finally, the author discusses suppression of flavor-changing neutral currents in the extended technicolor models.

The three faces of Maxwell�s equations

In dealing with electromagnetic phenomena and in particular the phenomena of optics, despite the recognition of the quanta of light people tend to talk of the amplitudes and field strengths, as if the electromagnetic field were a classical field. For example we measure the wavelength of light by studying interference fringes. In this paper we study the inter-relationship of three ways of looking at the problem: in terms of classical wave fields, wave function of the photon; and the quantized wave field. The comparison and contrasts of these three modes of description are carefully analyzed in this paper. The ways in which these different modes complement our intuition and insight are also discussed.

The Networks of Learning in Technological Innovation : The Emergence of Collaboration Across Fields of Expertise

This study addresses four issues concerning technological product innovations. First, the nature of the very early phases or "embryonic stages" of technological innovation is addressed. Second, this study analyzes why and by what means people initiate innovation processes outside the technological community and the field of expertise of the established industry. In other words, this study addresses the initiation of innovation that occurs without the expertise of established organizations, such as technology firms, professional societies and research institutes operating in the technological field under consideration. Third, the significance of interorganizational learning processes for technological innovation is dealt with. Fourth, this consideration is supplemented by considering how network collaboration and learning change when formalized product development work and the commercialization of innovation advance. These issues are addressed through the empirical analysis of the following three product innovations: Benecol margarine, the Nordic Mobile Telephone system (NMT) and the ProWellness Diabetes Management System (PDMS). This study utilizes the theoretical insights of cultural-historical activity theory on the development of human activities and learning. Activity-theoretical conceptualizations are used in the critical assessment and advancement of the concept of networks of learning. This concept was originally proposed by the research group of organizational scientist Walter Powell. A network of learning refers to the interorganizational collaboration that pools resources, ideas and know-how without market-based or hierarchical relations. The concept of an activity system is used in defining the nodes of the networks of learning. Network collaboration and learning are analyzed with regard to the shared object of development work. According to this study, enduring dilemmas and tensions in activity explain the participants' motives for carrying out actions that lead to novel product concepts in the early phases of technological innovation. These actions comprise the initiation of development work outside the relevant fields of expertise and collaboration and learning across fields of expertise in the absence of market-based or hierarchical relations. These networks of learning are fragile and impermanent. This study suggests that the significance of networks of learning across fields of expertise becomes more and more crucial for innovation activities.

Note On The Stability Of Parallel Magnetic-Fields - Comment

It is shown that the conclusions arrived at regarding the instability of an incompressible fluid cylinder in the presence of the magnetic field and the streaming velocity in a recent communication easily follow from the study of propagation characteristics of Alfvén surface waves along cylindrical plasma columns made earlier.

Do elasmobranch reactions to magnetic fields in water show promise for bycatch mitigation?

Elasmobranchs are under increasing pressure from targeted fisheries worldwide, but unregulated bycatch is perhaps their greatest threat. This study tested five elasmobranch bycatch species (Sphyrna lewini, Carcharhinus tilstoni, Carcharhinus amblyrhynchos, Rhizoprionodon acutus, Glyphis glyphis) and one targeted teleost species (Lates calcarifer) to determine whether magnetic fields caused a reaction response and/or change in spatial use of an experimental arena. All elasmobranch species reacted to magnets at distances between 0.26 and 0.58 m at magnetic strengths between 25 and 234 gauss and avoided the area around the magnets. Contrastingly, the teleosts showed no reaction response and congregated around the magnets. The different reactions of the teleosts and elasmobranchs are presumably driven by the presence of ampullae of Lorenzini in the elasmobranchs; different reaction distances between elasmobranch species appeared to correlate with their feeding ecology. Elasmobranchs with a higher reliance on the electroreceptive sense to locate prey reacted to the magnets at the greatest distance, except G. glyphis. Notably, this is the only elasmobranch species tested with a fresh- and saltwater phase in their ecology, which may account for the decreased magnetic sensitivity. The application of magnets worldwide to mitigate the bycatch of elasmobranchs appears promising based on these results.