Diagnostic probes for particle and molecule distributions in laser-generated plumes

Laser microprobe analysis (LMA) offers good spatial and depth resolution for solid sampling of virtually any material. Coupled with numerous optical spectroscopic and mass spectrometric detection methods, LMA is a powerful analytical tool. Yet, fundamental understanding of the interaction between the laser and the sample surface leading to the formation of the high temperature plasma (plume) is far from complete;To better understand the process of plume formation, an imaging method based on acousto-optic laser beam deflection has been coupled with light scattering methods and absorption methods to record temporal and spatial maps of the particle and molecule distributions in the plume with good resolution;Because particles can make up a major fraction of the vaporized material under certain operating conditions, they can reflect a large loss of atomic signal for elemental analysis, even when using auxiliary excitation to further vaporize the particles. Characterization of the particle size distributions in plumes should provide insight into the vaporization process and information necessary for studies of efficient particle transfer. Light scattering methods for particle size analysis based on the Mie Theory are used to determine the size of particles in single laser-generated plumes. The methods used, polarization ratio method and dissymmetry ratio method, provide good estimates of particle size with good spatial and temporal resolution for this highly transient system. Large particles, on the order of 0.02-0.2 [mu]m in radius, were observed arising directly from the sample surface and from condensation;Due to its ability to induce a rapid temperature increase at surfaces, LMA is used to promote desorption over decomposition for large thermally labile bio-organic compounds. Extremely large molecules can then be studied in the gas phase and detected with sensitive mass spectrometric methods. The desorption process is poorly understood. Molecular absorption is used to record the desorption of organic dyes from thin films. Classical absorption at the vaporization wavelength by the sample and power density of the vaporization laser is found to affect the extent of chromophore destruction. The major fraction of fragmentation appears to occur early (\u3c100 [mu]s) in the desorption process

Young Latino students\u27 learning in problem-based reform Mathematics classrooms: Developing mathematical thinking and communication

This study explores how Latino first grade students develop mathematical problem solving and communication in their native language. Problem types came from Cognitively Guided Instruction (Carpenter et al. 1999) and were embedded in students’ cultural and linguisticexperiences. Findings show students solved a wide range of CGI problems and developed confidence, flexibility, and sophistication in their strategies and explanations

Attention Allocation Aid for Visual Search

This paper outlines the development and testing of a novel, feedback-enabled attention allocation aid (AAAD), which uses real-time physiological data to improve human performance in a realistic sequential visual search task. Indeed, by optimizing over search duration, the aid improves efficiency, while preserving decision accuracy, as the operator identifies and classifies targets within simulated aerial imagery. Specifically, using experimental eye-tracking data and measurements about target detectability across the human visual field, we develop functional models of detection accuracy as a function of search time, number of eye movements, scan path, and image clutter. These models are then used by the AAAD in conjunction with real time eye position data to make probabilistic estimations of attained search accuracy and to recommend that the observer either move on to the next image or continue exploring the present image. An experimental evaluation in a scenario motivated from human supervisory control in surveillance missions confirms the benefits of the AAAD.Comment: To be presented at the ACM CHI conference in Denver, Colorado in May 201

Introduction: On Connection, Diversity, and Resilience in Writing Across the Curriculum

Developed from presentations at the 2018 International Writing Across the Curriculum conference, this collection documents a key moment in the history of WAC, foregrounding connection and diversity as keys to the sustainability of the WAC movement in the face of new and long-standing challenges. Contributors reflect on the history and ongoing evolution of WAC, honoring grassroots efforts while establishing a more unified structure of collaborative leadership and mentorship. The chapters in this collection offer a rich variety of practices, pedagogies, mindsets, and methodologies for readers who are invested in using writing in a wide range of institutional and disciplinary contexts. Boldly engaging such pressing topics as translingualism, anti-racism, emotional labor, and learning analytics, the 18 chapters collected here testify to WAC\u27s durability, persistence, and resilience in an ever-changing educational landscape

An Untriggered Search for Optical Bursts

We present an untriggered search for optical bursts with the ROTSE-I telephoto array. Observations were taken which monitor an effective 256 square degree field continuously over 125 hours to m_{ROTSE}=15.7. The uniquely large field, moderate limiting magnitude and fast cadence of $\sim$10 minutes permits transient searches in a new region of sensitivity. Our search reveals no candidate events. To quantify this result, we simulate potential optical bursts with peak magnitude, m_{p}, at t=10 s, which fade as f=(\frac{t}{t_{0}}) ^{\alpha_{t}}, where \alpha_t < 0. Simple estimates based on observational evidence indicate that a search of this sensitivity begins to probe the possible region occupied by GRB orphan afterglows. Our observing protocol and image sensitivity result in a broad region of high detection efficiency for light curves to the bright and slowly varying side of a boundary running from [\alpha_{t},m_{p}]=[-2.0,6.0] to [-0.3,13.2]. Within this region, the integrated rate of brief optical bursts is less than 1.1\times 10^{-8} {\rm s}^{-1} {\rm deg}^{-2}. At $\sim$22 times the observed GRB rate from BATSE, this suggests a limit on \frac{\theta_{opt}}{\theta_{\gamma}}\lesssim 5 where \theta_{opt} and \theta_{\gamma} are the optical and gamma-ray collimation angles, respectively. Several effects might explain the absence of optical bursts, and a search of the kind described here but more sensitive by about 4 magnitudes should offer a more definitive probe.Comment: 8 pages, 6 figures, 1 tabl

Extended comprehension training reconsidered

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Reducing Sentence Production Time in Chronic Broca's Aphasia

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Using microdialysis with a deuterium oxide tracer to estimate water exchange, water content and active surface area of the probe

Microdialysis is a useful tool for measuring in situ fluxes of soil compounds with minimal disturbance of soil structure and function. Fluxes of sampled compounds are commonly calculated per unit of membrane surface area, assuming that the entire membrane surface is capable of exchange - which is unlikely given varying soil moisture and the occlusion of membrane pores by the soil solid phase. We present a method to quantify the degree of connectivity of the microdialysis probe membrane to the surrounding soil by means of water exchange between a microdialysis perfusate and soil solution using deuterium (2H2O; equilibrated to DHO) as an internal standard. We applied the method to a range of probe membrane surface areas and soil moisture conditions to generate empirical models that estimate membrane surface area active in exchange. Our results suggest that even in a saturated sandy soil, active membrane surface areas reach only 40.3% of the probe surface area, perhaps due to occlusion by soil particles. However, when accounting for volumetric water content of the soil, active surface areas approached 80-90% of the area likely in contact with water, indicating that sampling efficiency of waterfilled pores may still be high, particularly at slow flow rates. Furthermore, our method enables assessment of local soil water content around the probe. Models estimating soil water content were applied to field measurements of DHO exchange in three soil horizons (Organic, B1, B2) at two boreal sites, and in situ estimates were similar to those from conventional soil moisture methods when models were calibrated with the same soil type. We present DHO exchange as a powerful method for improving microdialysis flux interpretations in future studies, and for exploring small-scale water variability in relatively undisturbed soils