Whole-pattern profile fitting of powder diffraction data collected in parallel-beam flat-plate asymmetric reflection geometry

Abstract: A simple, physically based model that allows the whole-pattern profile fitting of diffraction data collected in parallel-beam flat-plate asymmetric reflection geometry is presented. In this arrangement, there is a fixed angle between the incident beam and the sample, resulting in a fixed-length beam footprint. The use of a wide-angle detector for the simultaneous detection of the data precludes the use of any diffracted beam optics. Therefore, the observed peak widths are a function of the length of the beam footprint on the sample. The model uses up to three refinable parameters, depending on the intensity profile of the beam, to calculate the effect of diffraction angle on the width of all diffracted peaks. The use of this model reduces the total number of parameters required to fit the observed peak widths and shapes, hence leading to increased stability in the profile analysis. Implementations of the model are provided for both fundamental parameters and empirical approaches

Defining graphenic crystallites in disordered carbon: moving beyond the platelet model

We develop a picture of graphenic crystallites within disordered carbons that goes beyond the traditional model of graphitic platelets at random orientation. Using large atomistic models containing one million atoms, we redefine the meaning of the quantity La extracted from X-ray diffraction (XRD) patterns. Two complementary approaches are used to measure the size of graphenic crystallites, which are defined as regions of regularly arranged hexagons. Firstly, we calculate the X-ray diffraction pattern directly from the atomistic coordinates of the structure and analyse them following a typical experimental process. Second, the graphenic crystallites are identified from a direct geometrical approach. By mapping the structure directly, we replace the idealised picture of the crystallite with a more realistic representation of the material and provide a well-defined interpretation for $L_a$ measurements of disordered carbon. A key insight is that the size distribution is skewed heavily towards small fragments, with more than 75% of crystallites smaller than half of $L_a$

Social Anxiety and Peer Helping in Adolescent Addiction Treatment

The developmental need to fit in may lead to higher alcohol and other drug use among socially anxious youths which exacerbates the drink/trouble cycle. In treatment, youths with social anxiety disorder (SAD) may avoid participating in therapeutic activities with risk of negative peer appraisal. Peer-helping is a low-intensity, social activity in the 12-step program associated with greater abstinence among treatment-seeking adults. This study examined the influence of SAD on clinical severity at intake, peer-helping during treatment, and outcomes in a large sample of adolescents court-referred to residential treatment

A capillary specimen aberration for describing X-ray powder diffraction line profiles for convergent, divergent and parallel beam geometries

X-ray powder diffraction patterns of cylindrical capillary specimens have substantially different peak positions, shapes and intensities relative to patterns from flat specimens. These aberrations vary in a complex manner with diffraction angle and instrument geometry. This paper describes a fast numerical procedure that accurately describes the capillary aberration in the equatorial plane for convergent focusing, divergent and parallel beam instrument geometries. Axial divergence effects are ignored and only a cross section of the capillary, a disc, is considered; it is assumed that axial divergence effects can be described using an additional correction that is independent of the disc correction. Significantly, the present implementation uses the TOPAS-Academic aberration approximation technique of averaging nearby aberrations in 2? space to approximate in-between aberrations, which results in no more than ~30 disc aberrations calculated over the entire 2? range, even when the diffraction pattern comprises thousands of peaks. Finally, the disc aberration is convoluted with the emission profile and other instrument and specimen aberrations in a Rietveld refinement sense, allowing for refinement on the specimen's absorption coefficient and capillary diameter, as well as the instrument focal length. Large differences between refined and expected values give insight into instrument alignment

Correction to: Effects of Moisture-Induced Crystallization on the Aerosol Performance of Spray Dried Amorphous Ciprofloxacin Powder Formulations

Page 4, right column, under section heading “In-Vitro Aerosol Performance”, line 11. “ < 4 kPa (approximately 3.2 kPa at 100 L/min)” should be changed to “approximately 4 kPa at 100 L/min”

Place attachment among retirees in Greensburg, Kansas

On May 4, 2007, an EF-5 tornado passed through Greensburg leveling 95 percent of the town. Because city leaders encouraged everyone to use “green” building techniques as they rebuilt their homes and businesses, not only has the return to normalcy been exceedingly slow, but some of the town’s older residents feel that officials overlooked their needs. These minor episodes of discord enabled us to learn what features are most important to people in their retirement-age. They include: identifiable landmarks, a space to socialize, and age-specific businesses. We assert that the lessons learned in Greensburg are applicable to other communities with a sizeable older-aged population. As baby boomers rapidly enter retirement they will seek places to live that are elderly-friendly and enable them to effectively bond with place. As previous research attests, people who have a strong attachment to place commonly lead a good quality-of-life

Activation-free supercapacitor electrode based on surface-modified Sr2CoMo1-xNixO6-δ perovskite

Oxygen anion intercalation-type supercapacitors are promising charge storage devices. In this study, by taking advantage of the capability of selective exsolution of elements from perovskite lattice, a nanoparticles-modified perovskite composite is developed as new perovskite-based electrode for supercapacitor with further improved performance that allow the energy storage via two different mechanisms, i.e., Faradaic surface redox pseudocapacitance and oxygen anion-intercalation pseudocapacitance. The derived supercapacitor shows high power density and energy density, and no surface activation process, and stable performance. Specifically, perovskite oxides with the nominal composition of Sr2CoMo1-xNixO6-δ are designed and the strategy of controlled in-situ exsolution and re-oxidation of B-sites Ni and Co element to create Co3O4 and NiO nanoparticles on the perovskite surface and extra oxygen vacancies in perovskite bulk is applied. The Co3O4 and NiO nanoparticles on surface of electrode are found to effectively improve the surface redox pseudocapacitance, while the creation of additional oxygen vacancies enhances the oxygen anion intercalation pseudocapacitance. Consequently, the electrode displays excellent charge storage capability with a stable capacity as high as ~930 F g−1 and superior rate performance. As a universal strategy, it may also be applicable for the design and synthesis of alternative high-performance electrodes with mixed energy storage mechanisms

Energy-dispersive diffraction studies of inert anodes.

A tomographic study of electrochemical cells to observe scales formed on inert anodes has been conducted using energy-dispersive synchrotron X-ray diffraction. This study is preparatory to an investigation that will observe this formation in situ during the cells' operation. The purpose of the current work was to determine whether this technique would be appropriate for such a study in terms of its sensitivity and whether the results could be quantified satisfactorily. A method has been developed for the quantitative phase analysis of energy-dispersive data using crystal-structure-based Rietveld refinement. This has been tested with standard materials and found to be comparable in accuracy to results obtained from traditional angular-dispersive diffraction. The lower limits of detection of the method have not been established quantitatively but qualitative differences can be seen between cells that have been cycled at different times. These differences indicate a linear relationship between scale formation and electrolysis time