High Flux Femtosecond X-ray Emission from the Electron-Hose Instability in Laser Wakefield Accelerators

Bright and ultrashort duration X-ray pulses can be produced by through betatron oscillations of electrons during Laser Wakefield Acceleration (LWFA). Our experimental measurements using the \textsc{Hercules} laser system demonstrate a dramatic increase in X-ray flux for interaction distances beyond the depletion/dephasing lengths, where the initial electron bunch injected into the first wake bucket catches up with the laser pulse front and the laser pulse depletes. A transition from an LWFA regime to a beam-driven plasma wakefield acceleration (PWFA) regime consequently occurs. The drive electron bunch is susceptible to the electron-hose instability and rapidly develops large amplitude oscillations in its tail, which leads to greatly enhanced X-ray radiation emission. We measure the X-ray flux as a function of acceleration length using a variable length gas cell. 3D particle-in-cell (PIC) simulations using a Monte Carlo synchrotron X-ray emission algorithm elucidate the time-dependent variations in the radiation emission processes.Comment: 6 pages, 4 figures, accepted for publication in Phys. Rev. Accel. Beam

Dynamic changes of Au/ZnO catalysts during methanol synthesis: A model study by temporal analysis of products (TAP) and Zn L_III near Edge X-Ray absorption spectroscopy

Small gold nanoparticles supported on ZnO have been identified as highly active and selective catalysts for the green synthesis of methanol from CO2 and H2. Furthermore, they can serve also a model system for the mechanistic understanding of methanol synthesis on the industrial Cu/ZnO catalyst. The dynamic changes in the structure of Au/ZnO upon exposure to methanol synthesis gas mixtures were studied using a combination of TAP reactor and near edge X-ray absorption spectroscopy (XANES) measurements at the Zn LIII edge, both in CO2/H2 and CO/H2 gas mixtures. TAP measurements indicated that CO can create significant amounts of O-vacancy defects in ZnO at 240°C, while CO2 can re-oxidize a pre-reduced catalyst or maintain this state in the presence of s trongly reducing gases (CO and H2). Furthermore, CO2 present as reactant or resulting from the reactive removal of surface lattice oxygen by interaction with CO can be deposited on the pre-reduced Au/ZnO surface as stable adsorbed carbon containing species, e.g., as surface carbonates, which decompose at T≥250°C. In situ XANES measurements at the Zn LIII edge revealed that ZnO is significantly reduced during reaction, both in CO2/H2 and CO/H2 gas mixtures, but with the extent of the reduction being more pronounced in CO/H2 than in CO2/H2. These results will be critically discussed in the light of previous findings on the role of ZnO reduction in the activity of methanol synthesis catalysts

As interseções do self e as políticas: Uma pesquisa poética sobre a complexidade da formação de professores

This article explores the intersection of selves and policies for teacher educators in an era of teacher education reform. Borne out of a promise to one another to write about our experiences navigating increasingly complex market-driven, neoliberal attacks on our work and world, we collected data across several years that documented our attempt to break our silence (Lorde, 1977) and explore how we, as teacher educators, make sense of neoliberal reforms and policies in teacher preparation. We draw specifically on Dunn’s theory of the Hydra of Teacher Education (2016), alongside literature on reforms and policies in teacher preparation and teacher educators’ forms of resistance to frame our work, and utilize arts-based poetic inquiry methodology (Prendergast, 2009; Rath, 2001) to explore the real, everyday implications of educational policy in our lives and in our careers. The poems we created as a “performative act” (Prendergast, 2009, p. xxiii) revealed that our experiences seemed to follow a cycle from hopelessness, to silence, to acquiescence, to collective resistance. We look carefully at this last portion of the cycle in our work, wondering how, if at all, teacher educators can resist the neoliberalization of teacher preparation. We conclude with implications for research, policy, and the practice of teacher education as we write to understand, write to resist, and write to survive.Este artículo explora la intersección del yo y las políticas para la educación del profesorado en una era de reforma de la formación docente. Nacidos de una promesa mutua de escribir sobre nuestras experiencias navegando cada vez más complejos ataques neoliberales impulsados por el mercado en nuestro trabajo y en el mundo, recopilamos datos durante varios años que documentaban nuestro intento de romper nuestro silencio (Lorde, 1977) y exploramos cómo nosotros damos sentido a las reformas y políticas neoliberales en la preparación de los docentes, como formadores de docentes. Nos referimos específicamente a la teoría de Dunn en Hydra of Teacher Education (2016), junto con la literatura sobre reformas y políticas de preparación docente y las formas de resistencia de los formadores de docentes para enmarcar nuestro trabajo, y utilizar una metodología de investigación poética basada en las artes (Prendergast, 2009; Rath, 2001) para explorar las implicaciones reales y cotidianas de la política educativa en nuestras vidas y en nuestras carreras. Los poemas que creamos como un “acto performativo” (Prendergast, 2009, p. Xxiii) revelaron que nuestras experiencias parecían seguir un ciclo desde la desesperanza, al silencio, a la aquiescencia, a la resistencia colectiva. Miramos detenidamente esta última parte del ciclo en nuestro trabajo, preguntándonos cómo, si es que lo hacen, los formadores de docentes pueden resistir la neoliberalización de la preparación del maestro. Concluimos con implicaciones para la investigación, las políticas y la práctica de la formación docente mientras escribimos para comprender, escribimos para resistir y escribimos para sobrevivir.Este artigo explora a interseção do eu e das políticas para a formação de professores em uma era de reforma da formação docente. Nascido de uma promessa mútua de escrever sobre nossas experiências explorando ataques neoliberais cada vez mais complexos, impulsionados pelo mercado em nosso trabalho e no mundo, recolhemos dados por vários anos documentando nossa tentativa de romper nosso silêncio (Lorde, 1977) e nós exploramos nós damos sentido às reformas e políticas neoliberais na preparação de professores como como educadores de professores. Referimo-nos especificamente à teoria de Dunn na Hydra of Teacher Education (2016), juntamente com a literatura sobre reformas e políticas de preparação de professores e as formas de resistência dos educadores de professores para enquadrar nosso trabalho e usar uma metodologia de pesquisa poética com base nas artes (Prendergast, 2009; Rath, 2001) para explorar as implicações reais e diárias da política educacional em nossas vidas e carreiras. Os poemas que criamos como um “ato performativo” (Prendergast, 2009, p. xxiii) revelaram que nossas experiências pareciam acompanhar o ciclo do desespero, do silêncio, da aquiescência, da resistência coletiva. Observamos atentamente esta última parte do ciclo em nosso trabalho, perguntando-nos como, se o fizerem, educadores de professores podem resistir à neoliberalização da preparação de professores. Concluímos com implicações para a pesquisa, políticas e práticas de formação de professores à medida que escrevemos para compreender, escrever para resistir e escrever para sobreviver

The Role of Professional Development in Bridging High-Quality Social-Emotional Learning in Laboratory and Community Preschools

The current study presents an exploratory model of comprehensive professional development that provides early childhood education and care teachers with opportunities to enhance their skills in social-emotional learning (SEL). Skills development strategies include a combination of workshops, observations of high-quality university laboratory preschool classrooms, consultation with master educators, on-site coaching, and communities of practice. The study found statistically significant improvements in content knowledge, knowledge of evidence-based strategies, and self-efficacy to implement new strategies in the classroom for participants of the Promoting Prosocial Behavior workshop. Teachers and administrators who participated in observations, coaching, and/or communities of practice reported value in each component of professional development. Results of this project suggest that a multipronged approach of supporting SEL in the classroom has a positive impact on teachers’ self-regulation and modeling skills

A Combined XPS and Computational Study of the Chemical Reduction of BMP‐TFSI by Lithium

Employing density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS), we identify products of the reaction of the ionic liquid N,N-butylmethylpyrrolidinum bis(trifluoromethylsulfonyl)imide (BMP-TFSI) with lithium in order to model the initial chemical processes contributing to the formation of the solid electrolyte interphase in batteries. Besides lithium oxide, sulfide, carbide and fluoride, we find lithium cyanide or cyanamide as possible, thermodynamically stable product in the Li-poor regime, whilst Li$_{3}$N is the stable product in the Li-rich regime. The thermodynamically controlled reaction products as well as larger fragments of TFSI persisting due to kinetic barriers could be identified by a comparison of experimentally and computationally determined core level binding energies

Atomistic modeling of the directed-assembly of bimetallic Pt-Ru nanoclusters on Ru(0001)-supported monolayer graphene

The formation of Pt-Ru nanoclusters (NCs) by sequential deposition of Pt and Ru on a periodically rumpled graphene sheet supported on Ru(0001) is analyzed by atomistic-level modeling and kinetic Monte Carlo simulations. The “coarse-scale” periodic variation of the adsorption energy of metal adatoms across the graphene sheet directs the assembly of NCs to a periodic array of thermodynamically preferred locations. The modeling describes not only just the NC densities and size distributions, but also the composition distribution for mixed NCs. A strong dependence of these quantities on the deposition order is primarily related to different effective mobilities of Pt and Ru on the supported graphene

Navegando no terreno disputado da política e prática da formação de professores: Os autores respondem a SCALE

Stanford Center for Assessment, Learning, and Equity (SCALE) provided a commentary on the manuscripts in the first part of this special issue, which highlighted the benefits of edTPA and the necessity for such assessment programs to improve teacher education and strengthen teaching practices. In turn, the authors responded to the SCALE commentary. The authors’ responses raise concerns about equity, fairness, and unintended consequences of teacher performance assessments. These responses highlight the need for continued dialogue on ways to improve teacher education and strengthen the teaching profession.Stanford Center for Assessment, Learning and Equity (SCALE) ofreció un comentario sobre los manuscritos en la primera parte de esta edicion especial, que destacó los beneficios de edTPA y la necesidad de dichos programas de evaluación para mejorar la formación docente y para fortalecer las prácticas docentes. A la vez, los autores respondieron al comentario SCALE. Las respuestas de los autores plantean inquietudes sobre la equidad, la rectitud y las consecuencias involuntarias de las evaluaciones del desempeño docente. Estas respuestas revelan la necesidad de un diálogo continuo sobre las formas de mejorar la formación docente y fortalecer la profesión docente.Stanford Center for Assessment, Learning and Equity Stanford (SCALE) ofereceu um comentário sobre os manuscritos na primeira parte desta edição especial, que destacou os benefícios do edTPA e a necessidade de tais programas de avaliação para melhorar a formação de professores e fortalecer práticas de ensino. Ao mesmo tempo, os autores responderam ao comentário SCALE. As respostas dos autores levantam preocupações sobre equidade, retidão e as conseqüências involuntárias das avaliações de desempenho dos professores. Essas respostas revelam a necessidade de um diálogo contínuo sobre formas de melhorar a formação de professores e fortalecer a profissão docente

Approaching the low-temperature limit in nucleation and two-dimensional growth of fcc (100) metal films Ag/Ag(100)

We analyze the formation of two-dimensional Ag islands following deposition of about 0.1 ML of Ag on Ag(100) over a temperature regime ranging from classical nucleation and growth behavior to almost immobile adatoms, from 300 to 125 K. Particular emphasis is placed on the post-deposition dynamics at the lower end of the temperature range, where the saturation island density is not reached at the end of the deposition, and nucleation and aggregation processes continue with adatoms from the remaining adatom gas. Our analysis combines VT scanning tunneling microscopy experiments with kinetic Monte Carlo simulation of appropriate atomistic models. The only adjustable parameters in the model are the terrace diffusion barrier and prefactor, which can be determined from island density behavior near room temperature. Other processes such as rapid edge diffusion, and “easy” nucleation and aggregation of diagonally adjacent adatoms, are treated as instantaneous. The model excellently reproduces all aspects of behavior at low temperatures, demonstrating that nucleation and growth processes can be described in one consistent scheme, down to the regime of almost immobile adatoms

Safe Design Suggestions for Vegetated Roofs

Rooftop vegetation is becoming increasingly popular because of its environmental benefits and its ability to earn green-building certification credits. With the exception of one international guideline, there is little mention of worker safety and health in vegetated-roof codes and literature. Observations and field investigations of 19 vegetated roofs in the United States revealed unsafe access for workers and equipment, a lack of fall-protection measures, and other site-specific hazards. Design for safety strategies and the integration of life-cycle safety thinking with green-building credits systems are the preferred methods to reduce risk to workers on vegetated roofs. Design suggestions have been developed to add to the body of knowledge. The findings complement several National Institute for Occupational Safety and Health (NIOSH) construction and prevention through design (PtD) goals and are congruent with NIOSH’s Safe Green Jobs initiative. Organizations that install and maintain vegetated roofs can utilize the findings to understand hazards, take precautions, and incorporate safety into their bids The published version of this article is available here: 10.1061/(ASCE)CO.1943-7862.0000500Support from the the Virginia Tech Occupational Safety and Health Research Center through the Kevin P. Granata Pilot Program funded by the Institute for Critical Technology and Applied Sciences