51,531 research outputs found
Non-equilibrium thermodynamics in sheared hard-sphere materials
We combine the shear-transformation-zone (STZ) theory of amorphous plasticity
with Edwards' statistical theory of granular materials to describe shear flow
in a disordered system of thermalized hard spheres. The equations of motion for
this system are developed within a statistical thermodynamic framework
analogous to that which has been used in the analysis of molecular glasses. For
hard spheres, the system volume replaces the internal energy as a
function of entropy in conventional statistical mechanics. In place of the
effective temperature, the compactivity
characterizes the internal state of disorder. We derive the STZ equations of
motion for a granular material accordingly, and predict the strain rate as a
function of the ratio of the shear stress to the pressure for different values
of a dimensionless, temperature-like variable near a jamming transition. We use
a simplified version of our theory to interpret numerical simulations by
Haxton, Schmiedeberg and Liu, and in this way are able to obtain useful
insights about internal rate factors and relations between jamming and glass
transitions.Comment: 9 pages, 6 figure
Analysis of a closed-kinematic chain robot manipulator
Presented are the research results from the research grant entitled: Active Control of Robot Manipulators, sponsored by the Goddard Space Flight Center (NASA) under grant number NAG-780. This report considers a class of robot manipulators based on the closed-kinematic chain mechanism (CKCM). This type of robot manipulators mainly consists of two platforms, one is stationary and the other moving, and they are coupled together through a number of in-parallel actuators. Using spatial geometry and homogeneous transformation, a closed-form solution is derived for the inverse kinematic problem of the six-degree-of-freedom manipulator, built to study robotic assembly in space. Iterative Newton Raphson method is employed to solve the forward kinematic problem. Finally, the equations of motion of the above manipulators are obtained by employing the Lagrangian method. Study of the manipulator dynamics is performed using computer simulation whose results show that the robot actuating forces are strongly dependent on the mass and centroid locations of the robot links
Development of kinematic equations and determination of workspace of a 6 DOF end-effector with closed-kinematic chain mechanism
This report presents results from the research grant entitled Active Control of Robot Manipulators, funded by the Goddard Space Flight Center, under Grant NAG5-780, for the period July 1, 1988 to January 1, 1989. An analysis is presented of a 6 degree-of-freedom robot end-effector built to study telerobotic assembly of NASA hardware in space. Since the end-effector is required to perform high precision motion in a limited workspace, closed-kinematic mechanisms are chosen for its design. A closed-form solution is obtained for the inverse kinematic problem and an iterative procedure employing Newton-Raphson method is proposed to solve the forward kinematic problem. A study of the end-effector workspace results in a general procedure for the workspace determination based on link constraints. Computer simulation results are presented
Cartesian path control of a two-degree-of-freedom robot manipulator
The problem of cartesian trajectory control of a closed-kinematic chain mechanism robot manipulator with possible space station applications is considered. The study was performed by both computer simulation and experimentation for tracking of three different paths: a straight line, a sinusoid and a circle. Linearization and pole placement methods are employed to design controller gains. Results show that the controllers are robust and there are good agreements between simulation and experimentation. Excellent tracking quality and small overshoots are also evident
Spatial Autocorrelation in a Retail Context
This paper describes and applies the weighted least squares (WLS) technique that corrects for spatial autocorrelation in the residuals of hedonic regressions. Most empirical studies to date have focused on spatial autocorrelation in the housing market, i.e., single family home valuation. This study focuses on mall stores within shopping centers, with an emphasis on retail site selection within the mall.Spatial autocorrelation, hedonic modeling, bid rent, retail rents
Early production of the passive in two Eastern Bantu languages
The passive construction is acquired relatively late by children learning to speak many languages, with verbal passives not fully acquired till age 6 in English. In other languages it appears earlier, around age 3 or before. Use of passive construction in young children was examined in two Eastern Bantu languages spoken in Kenya (Kiswahili and Kigiriama), both with frequent use of passive. The passive was used productively very early (2;1) in these languages, regardless of the method used to measure productivity. In addition non-actional passives, particularly rare in English and some other European languages, were seen at these early ages. The proportion of verbs that were passive varied between individuals, both in children's speech and in the input to children. Pragmatic and grammatical features of the passive in some languages have previously been suggested to drive early passive acquisition, but these features are not found consistently in the two languages studied here. Findings suggest that the relatively high frequency of input found in these languages is the most plausible reason for early productive use of the passive
Authentic Corporate Social Responsibility Based on Authentic Empowerment: An Exemplary Business Leadership Case
Authors Dillon, Back, and Manz examine the underpinnings of genuine or authentic Corporate Social Responsibility (CSR), noting the direct nexus between stakeholder empowerment and the socially-responsible actions of authentic leaders. Such an empowering leadership approach– involving structural, psychological, developmental, and financial components – is particularly exemplified by a family-owned (Back) wine and cheese company (Fairview Trust), situate in South Africa
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