32 research outputs found
Moving Margins: Using Marginalia as a Tool for Critical Reflection
Marginalia is the practice of writing notes in the margins of texts as a way to capture ones\u27 thoughts and feelings about the text during reading. It is giving in to the impulse, based on what was read, to stop and record a comment. In this manuscript, we make the connection between marginalia and the visceral responses to text felt by one doctoral student (the second author) taking a course examining language as a place of struggle (hooks, 2004, p. 153). We also demonstrate how marginalia can be used as a qualitative method to document and investigate the way textual interaction facilitates learning. A found poem developed from the marginalia compiled throughout the semester is shared exemplifying the way a critical analysis of personal marginalia can facilitate awareness of transformative processes and highlighting the margins as a transformative space
Shear-driven size segregation of granular materials: modeling and experiment
Granular materials segregate by size under shear, and the ability to
quantitatively predict the time required to achieve complete segregation is a
key test of our understanding of the segregation process. In this paper, we
apply the Gray-Thornton model of segregation (developed for linear shear
profiles) to a granular flow with an exponential profile, and evaluate its
ability to describe the observed segregation dynamics. Our experiment is
conducted in an annular Couette cell with a moving lower boundary. The granular
material is initially prepared in an unstable configuration with a layer of
small particles above a layer of large particles. Under shear, the sample mixes
and then re-segregates so that the large particles are located in the top half
of the system in the final state. During this segregation process, we measure
the velocity profile and use the resulting exponential fit as input parameters
to the model. To make a direct comparison between the continuum model and the
observed segregation dynamics, we locally map the measured height of the
experimental sample (which indicates the degree of segregation) to the local
packing density. We observe that the model successfully captures the presence
of a fast mixing process and relatively slower re-segregation process, but the
model predicts a finite re-segregation time, while in the experiment
re-segregation occurs only exponentially in time
Segregation by thermal diffusion in granular shear flows
Segregation by thermal diffusion of an intruder immersed in a sheared
granular gas is analyzed from the (inelastic) Boltzmann equation. Segregation
is induced by the presence of a temperature gradient orthogonal to the shear
flow plane and parallel to gravity. We show that, like in analogous systems
without shear, the segregation criterion yields a transition between upwards
segregation and downwards segregation. The form of the phase diagrams is
illustrated in detail showing that they depend sensitively on the value of
gravity relative to the thermal gradient. Two specific situations are
considered: i) absence of gravity, and ii) homogeneous temperature. We find
that both mechanisms (upwards and downwards segregation) are stronger and more
clearly separated when compared with segregation criteria in systems without
shear.Comment: 8 figures. To appear in J. Stat. Mec
Scalar conservation laws with nonconstant coefficients with application to particle size segregation in granular flow
Granular materials will segregate by particle size when subjected to shear,
as occurs, for example, in avalanches. The evolution of a bidisperse mixture of
particles can be modeled by a nonlinear first order partial differential
equation, provided the shear (or velocity) is a known function of position.
While avalanche-driven shear is approximately uniform in depth, boundary-driven
shear typically creates a shear band with a nonlinear velocity profile. In this
paper, we measure a velocity profile from experimental data and solve initial
value problems that mimic the segregation observed in the experiment, thereby
verifying the value of the continuum model. To simplify the analysis, we
consider only one-dimensional configurations, in which a layer of small
particles is placed above a layer of large particles within an annular shear
cell and is sheared for arbitrarily long times. We fit the measured velocity
profile to both an exponential function of depth and a piecewise linear
function which separates the shear band from the rest of the material. Each
solution of the initial value problem is non-standard, involving curved
characteristics in the exponential case, and a material interface with a jump
in characteristic speed in the piecewise linear case
A compact UV timing fiducial system for use with x-ray streak cameras at NIF
Abstract not provide
Lawson criterion for ignition exceeded in an inertial fusion experiment
For more than half a century, researchers around the world have been engaged in attempts to achieve fusion ignition as a proof of principle of various fusion concepts. Following the Lawson criterion, an ignited plasma is one where the fusion heating power is high enough to overcome all the physical processes that cool the fusion plasma, creating a positive thermodynamic feedback loop with rapidly increasing temperature. In inertially confined fusion, ignition is a state where the fusion plasma can begin "burn propagation" into surrounding cold fuel, enabling the possibility of high energy gain. While "scientific breakeven" (i.e., unity target gain) has not yet been achieved (here target gain is 0.72, 1.37聽MJ of fusion for 1.92聽MJ of laser energy), this Letter reports the first controlled fusion experiment, using laser indirect drive, on the National Ignition Facility to produce capsule gain (here 5.8) and reach ignition by nine different formulations of the Lawson criterion