Self similar Barkhausen noise in magnetic domain wall motion

A model for domain wall motion in ferromagnets is analyzed. Long-range magnetic dipolar interactions are shown to give rise to self-similar dynamics when the external magnetic field is increased adiabatically. The power spectrum of the resultant Barkhausen noise is of the form $1/\omega^\alpha$, where $\alpha\approx 1.5$ can be estimated from the critical exponents for interface depinning in random media.Comment: 7 pages, RevTex. To appear in Phys. Rev. Let

Phase cascade bridge rectifier array in a 2-D lattice

We report on a novel rectification phenomenon in a 2-D lattice network consisting of N×N sites with diode and AC source elements with controllable phases. A phase cascade configuration is described in which the current ripple in a load resistor goes to zero in the large N limit, enhancing the rectification efficiency without requiring any external capacitor or inductor based filters. The integrated modular configuration is qualitatively different from conventional rectenna arrays in which the source, rectifier and filter systems are physically disjoint. Exact analytical results derived using idealized diodes are compared to a realistic simulation of commercially available diodes. Our results on nonlinear networks of source-rectifier arrays are potentially of interest to a fast evolving field of distributed power networks

Analytic Model for Advection-Dominated Accretion Flows in a Global Magnetic Field

A model for advection-dominated accretion flows (ADAFs) in a global magnetic field is proposed. In contrast to the well known ADAF models in which the viscosity of a fluid determines both angular momentum transfer and energy dissipation in the flow, the magnetic field and the electric resistivity, respectively, control them in this model. A manageable set of analytic solutions for the flow and the magnetic field is obtained to vertically non-integrated basic equations. This set describes mathematically a fully advective accretion flow and, in physically plausible situations for most AGNs, it is also confirmed that the radiation cooling estimated on this solution is really negligible compared with the internal energy of the flow.Comment: 27pages, 1 figure, to appear in ApJ vol 529, Feb.1, 200

Where are all the gravastars? Limits upon the gravastar model from accreting black holes

The gravastar model, which postulates a strongly correlated thin shell of anisotropic matter surrounding a region of anti-de Sitter space, has been proposed as an alternative to black holes. We discuss constraints that present-day observations of well-known black hole candidates place on this model. We focus upon two black hole candidates known to have extraordinarily low luminosities: the supermassive black hole in the Galactic Center, Sagittarius A*, and the stellar-mass black hole, XTE J1118+480. We find that the length scale for modifications of the type discussed in Chapline et al. (2003) must be sub-Planckian.Comment: 11 pages, 4 figure

Phase cascade lattice rectifier array: an exactly solvable nonlinear network circuit

An exact analysis of a 2-D lattice network consisting of N × N sites with rectifier and AC source elements with controllable phases reveals a method for generating ripple-free DC power without the use of any filtering circuit elements. A phase cascade configuration is described in which the current ripple in a load resistor goes to zero in the large N limit, enhancing the rectification efficiency without requiring any additional capacitor or inductor based filters. The integrated modular configuration is qualitatively different from conventional rectenna arrays in which the source, rectifier and filter systems are physically disjoint. Nonlinear networks in the large N limit of source-rectifier arrays are potentially of interest to a fast evolving field of distributed power networks.MNacknowledges support from a Graduate Fellowship in the ECE department at Boston University. We thank CMaedler, R Averitt, and members of the Photonics Center staff for assistance. JC acknowledges support from the Boston University RISE summer program. (Graduate Fellowship in the ECE department at Boston University; Boston University RISE summer program)Published versio

Green-Kubo formula for heat conduction in open systems

We obtain an exact Green-Kubo type linear response result for the heat current in an open system. The result is derived for classical Hamiltonian systems coupled to heat baths. Both lattice models and fluid systems are studied and several commonly used implementations of heat baths, stochastic as well as deterministic, are considered. The results are valid in arbitrary dimensions and for any system sizes. Our results are useful for obtaining the linear response transport properties of mesoscopic systems. Also we point out that for systems with anomalous heat transport, as is the case in low-dimensional systems, the use of the standard Green-Kubo formula is problematic and the open system formula should be used.Comment: 4 page

“Life Expectancy Analysis and Optimization of Electric Vehicle Traction Motors”

The development of electric vehicles (EVs) is a technological advancement that builds upon the momentous milestones achieved in the personal transportation industry throughout the last century. The vehicles of this era have been driven through the power of internal combustion engines (ICE). In the most recent decades the drawbacks of running fossil fuel based vehicles has become quite apparent. The effect of emissions on both the environment and public health has become a major cause of concern for policy makers and the general population. Additionally, fossil fuel commodities have been utilized as a political and economic weapon, giving producers extreme amounts of power and hurting consumers who have been at the mercy of large market fluctuations [1]. These challenges have provided the perfect conditions for the rise of electrical vehicles as an alternative method of transportation. Although electric vehicles have many benefits including being quieter, requiring less maintenance, and providing better handling than traditional vehicles, several engineering challenges remain before mass adoption will occur. A significant area of concern where further optimizations can be made is in the life expectancy of the electric motors that propel electric vehicles. At the University of Windsor’s Centre for Hybrid Automotive Research and Green Energy (CHARGE) laboratory methods of improving electric traction motors are already under investigation. Industrial collaborations including a venture with Ford Motor Company have provided significant opportunities for testing electric motors and their life expectancy. The approach undertaken involves data acquisition from electric motor tests. Several key factors identified as having significant impact on motor life expectancy will be studied. Preliminary results show that factors such as extreme temperatures, high humidity, voltage disturbances, insulation weakness, and large vibrations all have very negative effects on motor life expectancy. By displaying work done to minimize the effects of these factors, conference attendees will learn how electric motor testing done by local researchers in collaboration with industry partners is improving upon electric motor life expectancy, overall electric vehicle performance, and thus in turn society, which receives the environmental and health benefits that come with electric vehicle adoption