Three Dimensional Gravity From SU(2) Yang-Mills Theory in Two Dimensions

We argue that two dimensional classical SU(2) Yang-Mills theory describes the embedding of Riemann surfaces in three dimensional curved manifolds. Specifically, the Yang-Mills field strength tensor computes the Riemannian curvature tensor of the ambient space in a thin neighborhood of the surface. In this sense the two dimensional gauge theory then serves as a source of three dimensional gravity. In particular, if the three dimensional manifold is flat it corresponds to the vacuum of the Yang-Mills theory. This implies that all solutions to the original Gauss-Codazzi surface equations determine two dimensional integrable models with a SU(2) Lax pair. Furthermore, the three dimensional SU(2) Chern-Simons theory describes the Hamiltonian dynamics of two dimensional Riemann surfaces in a four dimensional flat space-time

A bibliography of Lake Kariba 1987-1994

The bibliography contains some 116 citations, including unpublished reports and manuscripts, regarding Lake Kariba. Most of the reports are from the Zambia/Zimbabwe SADC Fisheries and Lake Kariba Fisheries Research Institute. The citations are listed in alphabetical order according to author

An Economic Analysis of Agricultural Sustainability in Orissa

The development of a method for generating Sustainable Livelihood Security Index (SLSI) for agricultural sustainability and evaluating the existing status has been reported. Some measures have been suggested to promote sustainable agriculture of Orissa. This state has been selected since it faces wide inequality, improper management and over-exploitation of natural resources and explosion of population. These have created a threat to ecological balance and economic as well as social status of households in different districts of the state. The study of Ecological Security Index (ESI), Economic Efficiency Index (EEI) and Social Equity Index (SEI) has revealed that the agricultural systems of all districts display wide variations in their ecological and social equity aspects relative to their economic aspects. The districts with better SLSI ranks are often described as advanced districts and vice versa. Hence, SLSI has been found to reflect the picture of overall performance of a district in three dimensions of sustainability. On the basis of the overall performance of districts in terms of their SLSI, only eight districts in the state have an index value of more than 0.5, while thirteen districts have SLSI less than 0.4. Also, many districts of coastal Orissa have depicted better performance in agricultural sustainability in comparison to the districts of western Orissa as a whole. Some policy implications of SLSI approach have also been reported.Environmental Economics and Policy, Farm Management,

Seedless electroplating on patterned silicon

Nickel thin films have been electrodeposited without the use of an additional\ud seed layer, on highly doped silicon wafers. These substrates conduct\ud sufficiently well to allow deposition using a peripherical electrical contact on\ud the wafer. Films 2 μm thick have been deposited using a nickel sulfamate\ud bath on both n+- and p+-type silicon wafers, where a series of trenches with\ud different widths had been previously etched by plasma etching. A new,\ud reliable and simple procedure based on the removal of the native oxide layer\ud is presented which allows uniform plating of patterned substrates

Instabilities of Twisted Strings

A linear stability analysis of twisted flux-tubes (strings) in an SU(2) semilocal theory -- an Abelian-Higgs model with two charged scalar fields with a global SU(2) symmetry -- is carried out. Here the twist refers to a relative phase between the two complex scalars (with linear dependence on, say, the $z$ coordinate), and importantly it leads to a global current flowing along the the string. Such twisted strings bifurcate with the Abrikosov-Nielsen-Olesen (ANO) solution embedded in the semilocal theory. Our numerical investigations of the small fluctuation spectrum confirm previous results that twisted strings exhibit instabilities whose amplitudes grow exponentially in time. More precisely twisted strings with a single magnetic flux quantum admit a continuous family of unstable eigenmodes with harmonic $z$ dependence, indexed by a wavenumber $k\in[-k_{\rm m},k_{\rm m}]$. Carrying out a perturbative semi-analytic analysis of the bifurcation, it is found that the purely numerical results are very well reproduced. This way one obtains not only a good qualitative description of the twisted solutions themselves as well as of their instabilities, but also a quantitative description of the numerical results. Our semi-analytic results indicate that in close analogy to the known instability of the embedded ANO vortex a twisted string is also likely to expand in size caused by the spreading out of its magnetic flux.Comment: 27 pages, 18 figures. Typos corrected, references adde

Electron density stratification in two-dimensional structures tuned by electric field

A new kinetic instability which results in formation of charge density waves is proposed. The instability is of a purely classical nature. A spatial period of arising space-charge and field configuration is inversely proportional to electric field and can be tuned by applied voltage. The instability has no interpretation in the framework of traditional hydrodynamic approach, since it arises from modulation of an electron distribution function both in coordinate and energy spaces. The phenomenon can be observed in thin 2D nanostructures at relatively low electron density.Comment: 4 pages, 2 figure

SU3SU_3 coherent state operators and invariant correlation functions and their quantum group counterparts

Coherent state operators (CSO) are defined as operator valued functions on G=SL(n,C), homogeneous with respect to right multiplication by lower triangular matrices. They act on a model space containing all holomorphic finite dimensional representations of G with multiplicity 1. CSO provide an analytic tool for studying G invariant 2- and 3-point functions, which are written down in the case of $SU_3$. The quantum group deformation of the construction gives rise to a non-commutative coset space. We introduce a "standard" polynomial basis in this space (related to but not identical with the Lusztig canonical basis) which is appropriate for writing down $U_q(sl_3)$ invariant 2-point functions for representaions of the type $(\lambda,0)$ and $(0,\lambda)$. General invariant 2-point functions are written down in a mixed Poincar\'e-Birkhoff-Witt type basis.Comment: 33 pages, LATEX, preprint IPNO/TH 94-0

Rotors on Active Magnetic Bearings: Modeling and Control Techniques

In the last decades the deeper and more detailed understanding of rotating machinery dynamic behavior facilitated the study and the design of several devices aiming at friction reduction, vibration damping and control, rotational speed increase and mechanical design optimization. Among these devices a promising technology is represented by active magnetic actuators which found a great spread in rotordynamics and in high precision applications due to (a) the absence of all fatigue and tribology issues motivated by the absence of contact, (b) the small sensitivity to the operating conditions, (c) the wide possibility of tuning even during operation, (d) the predictability of the behavior. This technology can be classified as a typical mechatronic product due to its nature which involves mechanical, electrical and control aspects, merging them in a single system. The attractive potential of active magnetic suspensions motivated a considerable research effort for the past decade focused mostly on electrical actuation subsystem and control strategies. Examples of application areas are: (a) Turbomachinery, (b) Vibration isolation, (c) Machine tools and electric drives, (d) Energy storing flywheels, (e) Instruments in space and physics, (f) Non-contacting suspensions for micro-techniques, (g) Identification and test equipment in rotordynamics. This chapter illustrates the design, the modeling, the experimental tests and validation of all the subsystems of a rotors on a five-axes active magnetic suspension. The mechanical, electrical, electronic and control strategies aspects are explained with a mechatronic approach evaluating all the interactions between them. The main goals of the manuscript are: • Illustrate the design and the modeling phases of a five-axes active magnetic suspension; • Discuss the design steps and the practical implementation of a standard suspension control strategy; • Introduce an off-line technique of electrical centering of the actuators; • Illustrate the design steps and the practical implementation of an online rotor selfcentering control technique. The experimental test rig is a shaft (Weight: 5.3 kg. Length: 0.5 m) supported by two radial and one axial cylindrical active magnetic bearings and powered by an asynchronous high frequency electric motor. The chapter starts on an overview of the most common technologies used to support rotors with a deep analysis of their advantages and drawbacks with respect to active magnetic bearings. Furthermore a discussion on magnetic suspensions state of the art is carried out highlighting the research efforts directions and the goals reached in the last years. In the central sections, a detailed description of each subsystem is performed along with the modeling steps. In particular the rotor is modeled with a FE code while the actuators are considered in a linearized model. The last sections of the chapter are focused on the control strategies design and the experimental tests. An off-line technique of actuators electrical centering is explained and its advantages are described in the control design context. This strategy can be summarized as follows. Knowing that: a) each actuation axis is composed by two electromagnets; b) each electromagnet needs a current closed-loop control; c) the bandwidth of this control is depending on the mechanical airgap, then the technique allows to obtain the same value of the closed-loop bandwidth of the current control of both the electromagnets of the same actuation axis. This approach improves performance and gives more steadiness to the control behavior. The decentralized approach of the control strategy allowing the full suspensions on five axes is illustrated from the design steps to the practical implementation on the control unit. Furthermore a selfcentering technique is described and implemented on the experimental test rig: this technique uses a mobile notch filter synchronous with the rotational speed and allows the rotor to spin around its mass center. The actuators are not forced to counteract the unbalance excitation avoiding saturations. Finally, the experimental tests are carried out on the rotor to validate the suspension control, the off-line electrical centering and the selfcentering technique. The numerical and experimental results are superimposed and compared to prove the effectiveness of the modeling approach

Interaction of a surface acoustic wave with a two-dimensional electron gas

When a surface acoustic wave propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coefficient is calculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is largely dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.Comment: 3 figure

When feeling attractive matters too much to women: a process underpinning the relation between psychological need satisfaction and unhealthy weight control behaviors

This study examined a process model linking psychological need satisfaction to unhealthy weight control behaviors. Female University students (N = 220; M age = 20.47; SD = 5.07) completed questionnaires measuring need satisfaction, appearance-contingent self-worth, weight-related appearance anxiety and unhealthy weight control behaviors. Structural equation modeling revealed that need satisfaction indirectly related to engagement in unhealthy weight control behaviors through appearance-contingent self-worth and weight-related appearance anxiety. The results indicate that appearance-contingent self-worth might help to explain how low levels of psychological need satisfaction are related to maladaptive weight-related outcomes in young women