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Search Results: 1 - 10 of 9696 matches for " Scott Franklin "
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Heterotrophic and Autotrophic Soil Respiration under Simulated Dormancy Conditions  [PDF]
Daniel Beverly, Scott Franklin
Open Journal of Forestry (OJF) , 2015, DOI: 10.4236/ojf.2015.53024
Abstract: Carbon cycling research has increased over the past 20 years, but less is known about the primary contributors to soil respiration (i.e. heterotrophic and autotrophic) under dormant conditions. It is understood that soil CO2 effluxes are significantly lower during the winter of temperate ecosystems and assumed microorganisms dominate efflux origination. We hypothesized that heterotrophic contributions would be greater than autotrophic under simulated dormancy conditions. To test this hypothesis, we designed an experiment with the following treatments: combined autotrophic heterotrophic respiration, heterotrophic respiration, autotrophic respiration, no respiration, autotrophic respiration in vermiculite, and no respiration in vermiculite. Engelmann spruce seedlings and soil substrates were placed in specially designed respiration chambers and soil CO2 efflux measurements were taken four times over the course of a month. Soil microbial densities and root volumes were measured for each chamber after day thirty-three. Seedling presence resulted in significantly higher soil CO2 efflux rates for all soil substrates. Autotrophic respiration treatments were not representative of solely autotrophic soil CO2 efflux due to soil microbial contamination of autoclaved soil substrates; however, the mean autotrophic contributions averaged less than 25% of the total soil CO2 efflux. Soil microorganism communities were likely the primary contributor to soil CO2 efflux in simulated dormant conditions, as treatments with the greatest proportions of microbial densities had the highest soil CO2 efflux rates. Although this study is not directly comparable to field dormant season soil CO2 effluxes of Engelmann spruce forest, as snowpack is not maintained throughout this experiment, relationships, and metrics from such small-scale ecosystem component processes may yield more accurate carbon budget models.
Column collapse of granular rods
M. Trepanier,Scott V. Franklin
Physics , 2010, DOI: 10.1103/PhysRevE.82.011308
Abstract: We find the collapse of columns of granular rods to show range of behaviors that depends on particle aspect ratio (length $L$ to diameter $d$) and initial pile geometry (height/radius). For all aspect ratios $L/d$ below 24 there exists a critical height at $L/4$ below which the pile acts as a solid, maintaining its initial shape, and a second critical height at $3L/4$ above which the pile always collapses like an ordinary granular material. Separating the critical heights is a transition region in which the probability of collapse increases linearly from 0 to 1. This behavior is independent of particle length, width, or aspect ratio. When the pile does collapse, the runoff radius $r_f$ scales as a power-law with dimensionless height $\tilde H$, agreeing with previous experiments on ordinary sand. For low piles the scaling is linear, with $r_f\sim \tilde H^{1.2\pm 0.1}$. Above a critical pile aspect ratio (pile height/radius) this switches to a square-root scaling, with $H^{0.6\pm0.1}$.
Jamming of 3D Prolate Granular Materials
K. Desmond,Scott V. Franklin
Physics , 2006, DOI: 10.1103/PhysRevE.73.031306
Abstract: We have found that the ability of long thin rods to jam into a solid-like state in response to a local perturbation depends upon both the particle aspect ratio and the container size. The dynamic phase diagram in this parameter space reveals a broad transition region separating granular stick-slip and solid-like behavior. In this transition region the pile displays both solid and stick-slip behavior. We measure the force on a small object pulled through the pile, and find the fluctuation spectra to have power law tails with an exponent characteristic of the region. The exponent varies from $\beta=-2$ in the stick-slip region to $\beta=-1$ in the solid region. These values reflect the different origins -- granular rearrangements vs. dry friction -- of the fluctuations. Finally, the packing fraction shows only a slight dependence on container size, but depends on aspect ratio in a manner predicted by a mean field theory and implies an aspect-ratio independent contact number of $ = 5.25 \pm 0.03$.
Two-dimensional Packing in Prolate Granular Materials
Kevin Stokely,Ari Diacou,Scott V. Franklin
Physics , 2002, DOI: 10.1103/PhysRevE.67.051302
Abstract: We investigate the two-dimensional packing of extremely prolate (aspect ratio $\alpha=L/D>10$) granular materials, comparing experiments with Monte-Carlo simulations. The average packing fraction of particles with aspect ratio $\alpha=12$ is $0.68\pm0.03$. We quantify the orientational correlation of particles and find a correlation length of two particle lengths. The functional form of the decay of orientational correlation is the same in both experiments and simulations spanning three orders of magnitude in aspect ratio. This function decays over a distance of two particle lengths. It is possible to identify voids in the pile with sizes ranging over two orders of magnitude. The experimental void distribution function is a power law with exponent $-\beta=-2.43\pm0.08$. Void distributions in simulated piles do not decay as a power law, but do show a broad tail. We extend the simulation to investigate the scaling at very large aspect ratios. A geometric argument predicts the pile number density to scale as $\alpha^{-2}$. Simulations do indeed scale this way, but particle alignment complicates the picture, and the actual number densities are quite a bit larger than predicted.
Compression- and Shear-Driven Jamming of U-Shaped Particles in Two Dimensions
Theodore Marschall,Scott V. Franklin,S. Teitel
Physics , 2014, DOI: 10.1007/s10035-014-0540-2
Abstract: We carry out numerical simulations of soft, U-shaped, frictionless particles in $d=2$ dimensions in order to explore the effects of complex particle shape on the jamming transition. We consider both cases of uniform compression-driven and shear-driven jamming as packing fraction $\phi$ and compression or shear rate is varied. Upon slow compression, jamming is found to occur when the isostatic condition is satisfied. Under driven steady state shearing, jamming occurs at a higher packing fraction $\phi_J$ than observed in compression. A growing relaxation time and translational correlation length is found as $\phi$ increases towards $\phi_J$. We consider the orientational ordering and rotation of particles induced by the shear flow. Both nematic and tetratic ordering are found, but these decrease as $\phi$ increases to $\phi_J$. At the jamming transition, the nematic ordering further decreases, while the tetratic ordering increases, but the orientational correlation lengths remain small throughout. The average angular velocity of the particles is found to increase as $\phi$ increases, saturating to a plateau just below $\phi_J$, but then increasing again as $\phi$ increases above $\phi_J$.
Realizing a New Research Agenda for Writing-to-Learn: Embedding Process in Context
Lisa M. Hermsen,Scott V. Franklin
Physics , 2006,
Abstract: Writing-to-learn initiatives such as Writing Across the Curriculum or Writing in the Disciplines occupy the center of writing programs nationwide. Nevertheless, research to support the core of the writing-to-learn philosophy--that the writing process can facilitate content learning--is, at best, inconclusive. Calls for additional research have noted the importance of either additional cognitive analyses or new contextual research methods. This paper argues for a unique research agenda that would embed cognitive processes into disciplinary contexts and thus provide a layered, multi-modal research approach into writing and learning.
Dynamic facilitation observed near the colloidal glass transition
Scott V. Franklin,Eric R. Weeks
Physics , 2014,
Abstract: We present experimental confirmation of dynamic facilitation in monodisperse and bidisperse colloidal suspensions near the glass transition volume fraction. Correlations in particle dynamics are seen to exist not only in space (clusters and strings) but also as bubbles in space-time. Quantitatively, highly mobile particles are more likely (than immobile particles) to have nearest neighbors that were highly mobile in immediately preceding times. The interpretation is that a particle's mobility enables or facilitates the subsequent motion of its neighbors. Facilitation is most pronounced at the relaxation time that corresponds with cage-breaking, when dynamic heterogeneity is also maximized.
Assessing the Impact of Student Learning Style Preferences
Stacey M. Davis,Scott V. Franklin
Physics , 2006,
Abstract: Students express a wide range of preferences for learning environments. We are trying to measure the manifestation of learning styles in various learning environments. In particular, we are interested in performance in an environment that disagrees with the expressed learning style preference, paying close attention to social (group vs. individual) and auditory (those who prefer to learn by listening) environments. These are particularly relevant to activity-based curricula which typically emphasize group-work and de-emphasize lectures. Our methods include multiple-choice assessments, individual student interviews, and a study in which we attempt to isolate the learning environment.
Appraising and applying evidence about a diagnostic test during a performance-based assessment
George Bergus, Scott Vogelgesang, Janeta Tansey, Ellen Franklin, Ronald Feld
BMC Medical Education , 2004, DOI: 10.1186/1472-6920-4-20
Abstract: 4th year medical students who previously had demonstrated competency at probability revision and just starting first-year Internal Medicine residents were used for this research. Following an encounter with a simulated patient, subjects critically appraised a paper about an applicable diagnostic test and revised the patient's pretest probability given the test result.The medical students and residents demonstrated similar skills at critical appraisal, correctly answering 4.7 and 4.9, respectively, of 6 questions (p = 0.67). Only one out of 28 (3%) medical students and none of the 15 residents were able to correctly complete the probability revision task (p = 1.00).This study found that most students completing medical school are able to appraise an article about a diagnostic test but few are able to apply the information from the article to a patient. These findings raise questions about the clinical usefulness of the EBM skills possessed by graduating medical students within the area of diagnostic testing.Evidence-based medicine (EBM) has been described as the "conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients" [1]. Thus, to practice EBM clinicians need to critically appraise articles in the medical literature and then apply the evidence to specific patients. In the area of diagnostic testing, EBM requires the use of Bayesian inference so that appraised evidence can be used in the evaluation of a specific patient [2].Nearly all medical schools now provide their students with instruction on EBM [3]. Students at the University of Iowa Carver College of Medicine receive instruction on EBM during required course work during their two preclinical years. Medical students are introduced to EBM in a series of lectures in the first year, including one on the evaluation of diagnostic tests that introduces students to the concept of test characteristics and probability revision. Other lectures focus o
Learning, retention, and forgetting of Newton’s third law throughout university physics
Eleanor C. Sayre,Scott V. Franklin,Stephanie Dymek,Jessica Clark
Physical Review Special Topics. Physics Education Research , 2012,
Abstract: We present data from a between-student study on student response to questions on Newton’s third law given in two introductory calculus-based physics classes (Mechanics and Electromagnetism) at a large northeastern university. Construction of a response curve reveals subtle dynamics in student learning not capturable by pretesting and post-testing. We find a significant positive effect of instruction that diminishes by the end of the quarter. Two quarters later, a significant dip in correct response occurs when instruction changes from the vector quantities of electric forces and fields to the scalar quantity of electric potential. When instruction returns to vector topics, performance rebounds to initial values.
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