Activation process of air stable nanoscale zero-valent iron particles

Nanoscale Zero Valent Iron (nZVI) represents a promising material for subsurface water remediation technology. However, dry, bare nZVI particles are highly reactive, being pyrophoric when they are in contact with air. The current trends of nZVI manufacturing lead to the surface passivation of dry nZVI particles with a thin oxide layer, which entails a decrease in their reactivity. In this work an activation procedure to recover the reactivity of air-stable nZVI particles is presented. The method consists of exposing nZVI to water for 36 h just before the reaction with the pollutants. To assess the increase in nZVI reactivity based on the activation procedure, three types of nZVI particles with different oxide shell thicknesses have been tested for Cr(VI) removal. The two types of air-stable nZVI particles with an oxide shell thickness of around 3.4 and 6.5 nm increased their reactivity by a factor of 4.7 and 3.4 after activation, respectively. However, the pyrophoric nZVI particles displayed no significant improvement in reactivity. The improvement in reactivity is related mainly to the degradation of the oxide shell, which enhances electron transfer and leads secondarily to an increase in the specific surface area of the nZVI after the activation process. In order to validate the activation process, additional tests with selected chlorinated compounds demonstrated an increase in the degradation rate by activated nZVI particles.Postprint (author's final draft

Removing multiple outliers and single-crystal artefacts from X-ray diffraction computed tomography data

This paper reports a simple but effective filtering approach to deal with single-crystal artefacts in X-ray diffraction computed tomography (XRD-CT). In XRD-CT, large crystallites can produce spots on top of the powder diffraction rings, which, after azimuthal integration and tomographic reconstruction, lead to line/streak artefacts in the tomograms. In the simple approach presented here, the polar transform is taken of collected two-dimensional diffraction patterns followed by directional median/mean filtering prior to integration. Reconstruction of one-dimensional diffraction projection data sets treated in such a way leads to a very significant improvement in reconstructed image quality for systems that exhibit powder spottiness arising from large crystallites. This approach is not computationally heavy which is an important consideration with big data sets such as is the case with XRD-CT. The method should have application to two-dimensional X-ray diffraction data in general where such spottiness arises

Interlaced X-ray diffraction computed tomography

An X-ray diffraction computed tomography data-collection strategy that allows, post experiment, a choice between temporal and spatial resolution is reported. This strategy enables time-resolved studies on comparatively short timescales, or alternatively allows for improved spatial resolution if the system under study, or components within it, appear to be unchanging. The application of the method for studying an Mn–Na–W/SiO2 fixed-bed reactor in situ is demonstrated. Additionally, the opportunities to improve the data-collection strategy further, enabling post-collection tuning between statistical, temporal and spatial resolutions, are discussed. In principle, the interlaced scanning approach can also be applied to other pencil-beam tomographic techniques, like X-ray fluorescence computed tomography, X-ray absorption fine structure computed tomography, pair distribution function computed tomography and tomographic scanning transmission X-ray microscopy

Volumetric high dynamic range windowing for better data representation

Volume data is usually generated by measuring devices (eg. CT scanners, MRI scanners), mathematical functions (eg., Marschner/Lobb function), or by simulations. While all these sources typically generate 12bit integer or floating point representations, commonly used displays are only capable of handling 8bit gray or color levels. In a typical medical scenario, a 3D scanner will generate a 12bit dataset, which will be downsampled to an 8bit per-voxel accuracy. This downsampling is usually achieved by a linear windowing operation, which maps the active full accuracy data range of 0 up to 4095 into the interval between 0 and 255. In this paper, we propose a novel windowing operation that is based on methods from high dynamic range image mapping. With this method, the contrast of mapped 8bit volume datasets is significantly enhanced, in particular if the imaging modality allows for a high tissue differentiation (eg., MRI). Henceforth, it also allows better and easier segmentation and classification. We demonstrate the improved contrast with different error metrics and a perception-driven image difference to indicate differences between three different high dynamic range operators

Contrasting crystal packing arrangements in triiodide salts of radical cations of chiral bis(pyrrolo[3,4-d])tetrathiafulvalenes

Crystal structures of six 1 : 1 triiodide salts of a series of enantiopure bis(pyrrolo[3,4-d])TTF derivatives, the first structures of radical cation salts reported for this bis(pyrrolo) donor system, show three different arrangements of triiodide ions, organised either in head-to-tail pairs, in infinite lines, or in a castellated arrangement. The complex crystal structures, obtained by electrocrystallisation, are influenced by the presence of solvent, for example changing an ABCABC packing arrangement to ABAB with inclusion of THF, as well as by the size of the chiral side chain

All Employment Is Local: Examining the Impact of the American Recovery and Revitalization (ARRA) Act on Two Missouri Counties (as Well as an Analysis of Missouri Tax Credit Programs)

Employment is explored in the aftermath of the most recent “Great Recession”—the lingering effects are still being felt. Employment growth largely depends on what happens locally. This article examines the American Recovery and Revitalization Act (ARRA) often thought of as the Economic Stimulus Plan of the Obama Administration and its impact on two adjacent Missouri counties (Ste. Genevieve and Perry). County particulars are examined which impact how to understand employment in both counties. Furthermore, the issue of jobs created versus jobs retained is examined, as well as the difficulties of measuring the multiplier effect. Finally, Missouri tax credit programs are explored, again demonstrating the difficulties of measuring the multiplier effect as well as the cost effectiveness of these state government programs. Census data from the “County Business Patterns” are used to analyze local employment situations. Small Business issues related to local situations are addressed since they are essential to “jump starting” local economies

Guns, Campus and the Courts

The Newtown shooting opened up (again) the issue of guns on school grounds, both at the K-12 level and university level, and whether teachers and administrators should be armed. The Newtown shooting also focused attention again on the shootings at the Virginia Polytechnic Institute and State University in Blacksburg. In that incident, 32 people were killed and 17 wounded on April 2007. The shooter, Seung-Hui Cho, a senior, ended his killing spree by committing suicide. Following Cho’s shooting spree, the National Rifle Association (NRA) created NRA-U, or National Rifle Association University, an organization that reaches out to college students interested in having guns on campus or learning about having guns on campus. In addition to NRA-U, an organization called Students for Concealed Carry was established to promote the cause of students, or more specifically students 21 and over, who want to have a concealed gun on campus. This organization has chapters on various campuses in a number of states. Since 2007, they have held Open Holster protests on campuses, which is as it sounds—students wearing open holsters to demonstrate their desire to carry guns on campus. The push to allow students 21 and over to have guns inevitably involves court cases. The point is that school administrators and teachers are not the only focus of who should be allowed to have guns on campus: There is a broad-based push to allow many to have concealed guns on campus, even people who are not students, administrators, or faculty members, as will be noted in a case from Virginia. This article looks at federal court cases (two United States Supreme Court cases and one Court of Appeals case) and briefly examines how they open ways to examine the issue of guns and schools

A two-circle powder diffractometer for synchrotron radiation on Station 2.3 at the SRS

The two-circle powder diffractometer on Station 8.3 at the SRS has recently been relocated to station 2.3, some half the distance from a dipole radiation source with the same nominal 1.2T field. The purpose of this paper is to detail the changes and modifications to the diffractometer operation