Forward and inverse cascades in decaying two-dimensional electron magnetohydrodynamic turbulence

Electron magnetohydrodynamic (EMHD) turbulence in two dimensions is studied via high-resolution numerical simulations with a normal diffusivity. The resulting energy spectra asymptotically approach a $k^{-5/2}$ law with increasing $R_B$, the ratio of the nonlinear to linear timescales in the governing equation. No evidence is found of a dissipative cutoff, consistent with non-local spectral energy transfer. Dissipative cutoffs found in previous studies are explained as artificial effects of hyperdiffusivity. Relatively stationary structures are found to develop in time, rather than the variability found in ordinary or MHD turbulence. Further, EMHD turbulence displays scale-dependent anisotropy with reduced energy transfer in the direction parallel to the uniform background field, consistent with previous studies. Finally, the governing equation is found to yield an inverse cascade, at least partially transferring magnetic energy from small to large scales.Comment: 16 pages, 6 figures, accepted by Physics of Plasmas. For high resolution figures, please visit the PoP website or contact C.Warein

On the necessary conditions for bursts of convection within the rapidly rotating cylindrical annulus

Zonal flows are often found in rotating convective systems. Not only are these jet-flows driven by the convection, they can also have a profound effect on the nature of the convection. In this work the cylindrical annulus geometry is exploited in order to perform nonlinear simulations seeking to produce strong zonal flows and multiple jets. The parameter regime is extended to Prandtl numbers that are not unity. Multiple jets are found to be spaced according to a Rhines scaling based on the zonal flow speed, not the convective velocity speed. Under certain conditions the nonlinear convection appears in quasi-periodic bursts. A mean field stability analysis is performed around a basic state containing both the zonal flow and the mean temperature gradient found from the nonlinear simulations. The convective growth rates are found to fluctuate with both of these mean quantities suggesting that both are necessary in order for the bursting phenomenon to occur

From Planning to Passing: The Amherst, Massachusetts Plastic Bag Ban

This case study will detail the background and influences for a plastic bag ban in the town of Amherst, outline the steps taken from planning to passage, and address roadblocks and missteps that may be avoided with the implementation of future bans. It is my hope that this document will not only serve as a guide, but also an inspiration for additional local action in Massachusetts and across the country. No matter what the national political climate or attitude towards environmental issues, local action is always possible, and change is usually easier than you think. Think globally, act locally

Magnetized Ekman Layer and Stewartson Layer in a Magnetized Taylor-Couette Flow

In this paper we present axisymmetric nonlinear simulations of magnetized Ekman and Stewartson layers in a magnetized Taylor-Couette flow with a centrifugally stable angular-momemtum profile and with a magnetic Reynolds number below the threshold of magnetorotational instability. The magnetic field is found to inhibit the Ekman suction. The width of the Ekman layer is reduced with increased magnetic field normal to the end plate. A uniformly-rotating region forms near the outer cylinder. A strong magnetic field leads to a steady Stewartson layer emanating from the junction between differentially rotating rings at the endcaps. The Stewartson layer becomes thinner with larger Reynolds number and penetrates deeper into the bulk flow with stronger magnetic field and larger Reynolds number. However, at Reynolds number larger than a critical value $\sim 600$, axisymmetric, and perhaps also nonaxisymmetric, instabilities occur and result in a less prominent Stewartson layer that extends less far from the boundary.Comment: 24 pages, 12 figures, accepted by PRE, revision according to referee

Experimental study of super-rotation in a magnetostrophic spherical Couette flow

We report measurements of electric potentials at the surface of a spherical container of liquid sodium in which a magnetized inner core is differentially rotating. The azimuthal angular velocities inferred from these potentials reveal a strong super-rotation of the liquid sodium in the equatorial region, for small differential rotation. Super-rotation was observed in numerical simulations by Dormy et al. [1]. We find that the latitudinal variation of the electric potentials in our experiments differs markedly from the predictions of a similar numerical model, suggesting that some of the assumptions used in the model - steadiness, equatorial symmetry, and linear treatment for the evolution of both the magnetic and velocity fields - are violated in the experiments. In addition, radial velocity measurements, using ultrasonic Doppler velocimetry, provide evidence of oscillatory motion near the outer sphere at low latitude: it is viewed as the signature of an instability of the super-rotating region

Kinematically redundant robot manipulators

Research on control, design and programming of kinematically redundant robot manipulators (KRRM) is discussed. These are devices in which there are more joint space degrees of freedom than are required to achieve every position and orientation of the end-effector necessary for a given task in a given workspace. The technological developments described here deal with: kinematic programming techniques for automatically generating joint-space trajectories to execute prescribed tasks; control of redundant manipulators to optimize dynamic criteria (e.g., applications of forces and moments at the end-effector that optimally distribute the loading of actuators); and design of KRRMs to optimize functionality in congested work environments or to achieve other goals unattainable with non-redundant manipulators. Kinematic programming techniques are discussed, which show that some pseudo-inverse techniques that have been proposed for redundant manipulator control fail to achieve the goals of avoiding kinematic singularities and also generating closed joint-space paths corresponding to close paths of the end effector in the workspace. The extended Jacobian is proposed as an alternative to pseudo-inverse techniques

Cascades in decaying three-dimensional electron magnetohydrodynamic turbulence

Decaying electron magnetohydrodynamic (EMHD) turbulence in three dimensions is studied via high-resolution numerical simulations. The resulting energy spectra asymptotically approach a k^{-2} law with increasing R_B, the ratio of the nonlinear to linear timescales in the governing equation, consistent with theoretical predictions. No evidence is found of a dissipative cutoff, consistent with non-local spectral energy transfer and recent studies of 2D EMHD turbulence. Dissipative cutoffs found in previous studies are explained as artificial effects of hyperdiffusivity. In another similarity to 2D EMHD turbulence, relatively stationary structures are found to develop in time, rather than the variability found in ordinary or MHD turbulence. Further, cascades of energy in 3D EMHD turbulence are found to be suppressed in all directions under the influence of a uniform background field. Energy transfer is further reduced in the direction parallel to the field, displaying scale dependent anisotropy. Finally, the governing equation is found to yield a weak inverse cascade, at least partially transferring magnetic energy from small to large scales.Comment: 16 pages, 7 figures, accepted to Journal of Plasma Physics. High resolution figures available from the autho

North D Compost Pilot Semester Report

Following the completion of a 14-week-long residential compost pilot program in North Apartment D at the University of Massachusetts Amherst, this review summarizes the proposition, implementation, and operation of the project. The success of this pilot provides the framework for the expansion of residential composting at UMass Amherst, resulting in higher trash diversion rates from residence halls, and encouraging students to reduce their environmental footprint both on and off campus. The demonstrated success for this pilot program and upcoming expanded pilot provides further justification for expansion across residential life, other University departments, or other institutions to participate in waste-reduction initiatives. The program also highlights the continued commitment by students, faculty, and staff to create a more sustainable UMass

Compensation of compliance errors in parallel manipulators composed of non-perfect kinematic chains

The paper is devoted to the compliance errors compensation for parallel manipulators under external loading. Proposed approach is based on the non-linear stiffness modeling and reduces to a proper adjusting of a target trajectory. In contrast to previous works, in addition to compliance errors caused by machining forces, the problem of assembling errors caused by inaccuracy in the kinematic chains is considered. The advantages and practical significance of the proposed approach are illustrated by examples that deal with groove milling with Orthoglide manipulator.Comment: Advances in Robot Kinematics, France (2012

UMass Amherst Guide to Zero-Waste Events

As the University of Massachusetts Amherst continues to grow, and as programming for the campus community becomes an ever-rising priority, events organizers will need to consider the waste implications of every event to comply with state and University standards, goals, and policies. This Guide to Zero-Waste Events aims to streamline the planning process as well as provide tips and examples for follow-through to implementing a successful zero-waste event. The guide also presents actionable policy recommendations for the University to reduce waste and increase diversion from large-scale outdoor events on the UMass Amherst campus