An X-ray ptycho-tomography model of ‘Seeing order in “amorphous” materials’

The nature of the atomic structure of many non-crystalline materials remains a long-standing open question. We use X-ray scattering to model electron images of amorphous materials, where the analogue ‘atoms’ consist of 1μm diameter glass beads. The beads form a substantially random close-packed structure, but are partially ordered in places. X-ray ptycho-tomography reveals the exact position of the beads in 3D and so can be used to compare the modelled electron image with full knowledge of the underlying real structure. Using this, we repeat an experiment reported by Archie Howie and colleagues in 1978 that sought to test for real structure in bright-field electron images of amorphous materials; we demonstrate the validity of the technique, at least in the case of the resolution of the microscopes available at that time and the first Born approximation. We also illustrate how extremely demanding it would have been to infer 3D structure of amorphous material from pairs of stereoscopic images obtained with the same experimental kit: an approach that Archie proposed in the 1970s. We briefly discuss the possibility of using electron ptycho-tomography to solve the amorphous structure problem

Preparation of Isotopically Labeled Ribonucleotides for Multidimensional NMR Spectroscopy of RNA

A general method for large scale preparation of uniformly isotopically labeled ribonucleotides and RNAs is described. Bacteria are grown on isotopic growth medium, and their nucleic acids are harvested and degraded to mononucleotides. These are enzymatically converted into ribonucleoside triphosphates, which are used in transcription reactions in vitro to prepare RNAs for NMR studies. For 15N-labeling, E.coli is grown on15N-ammonium sulfate, whereas for 13C-labeling, Methylophilus methylotrophus is grown on 13C-methanol, which is more economical than 13C-glucose. To demonstrate the feasibility and utility of this method, uniformly 13C-labeled ribonucleotides were used to synthesize a 31 nucleotide HIV TAR RNA that was analyzed by 3D-NMR. This method should find widespread use in the structural analysis of RNA by NMR

Biliary sludge and recurrent ketoacidosis: a case report

A five year old boy, weighing 14 kg with no family history of diabetes, presented in frank diabetic ketoacidosis. He recovered, but continued to have episodes of ketoacidosis. He was diagnosed to have biliary sludge, which recovered with insulin treatment

High Affinity Binding of N2-Modified Guanine Derivatives Significantly Disrupts the Ligand Binding Pocket of the Guanine Riboswitch

Riboswitches are important model systems for the development of approaches to search for RNA-targeting therapeutics. A principal challenge in finding compounds that target riboswitches is that the effector ligand is typically almost completely encapsulated by the RNA, which severely limits the chemical space that can be explored. Efforts to find compounds that bind the guanine/adenine class of riboswitches with a high affinity have in part focused on purines modified at the C6 and C2 positions. These studies have revealed compounds that have low to sub-micromolar affinity and, in a few cases, have antimicrobial activity. To further understand how these compounds interact with the guanine riboswitch, we have performed an integrated structural and functional analysis of representative guanine derivatives with modifications at the C8, C6 and C2 positions. Our data indicate that while modifications of guanine at the C6 position are generally unfavorable, modifications at the C8 and C2 positions yield compounds that rival guanine with respect to binding affinity. Surprisingly, C2-modified guanines such as N2-acetylguanine completely disrupt a key Watson&ndash;Crick pairing interaction between the ligand and RNA. These compounds, which also modulate transcriptional termination as efficiently as guanine, open up a significant new chemical space of guanine modifications in the search for antimicrobial agents that target purine riboswitches.</p

Walking the Walk: Gender-bland Sexism, the Fan Experience and Perceptions of Value in Professional Women's Cricket

Australian cricket has traditionally been an exemplar of hyper-masculine sporting conservatism. However, cricket, as with a number of Australian sports, has recently introduced an elite women's league. Despite growth in participation and funding of women's cricket, it remains poorly understood at the elite level and particularly its fans. Drawing on the concept of gender-bland sexism (Musto et al., 2017), we investigate differences in fan engagement and perceptions of men's and women's cricket matches. Through a case study of Australian Women's Big Bash cricket team the ‘Sydney Sixers’, this chapter explores how women's cricket was experienced on match-day by fans, as well as perceptions of the value and quality of attending women's professional cricket. We first undertook participant observation at matches to understand how women's cricket was delivered, experienced and engaged with by fans. These observations informed a survey which was distributed to club members. Our findings suggest that there continue to be noticeable differences in the presentation of women's matches when compared to their male equivalents, providing evidence for the presence of gender-bland sexism in areas other than sports media

Near-field multi-slice ptychography: quantitative phase imaging of optically thick samples with visible light and X-rays

Ptychography is a form of lens-free coherent diffractive imaging now used extensively in electron and synchrotron-based X-ray microscopy. In its near-field implementation, it offers a route to quantitative phase imaging at an accuracy and resolution competitive with holography, with the added advantages of extended field of view and blind deconvolution of the illumination beam profile from the sample image. In this paper we show how near-field ptychography can be combined with a multi-slice model, adding to this list of advantages the unique ability to recover high-resolution phase images of larger samples, whose thickness places them beyond the depth of field of alternative methods

Evolution of ferroelastic domain walls during phase transitions in barium titanate nanoparticles

In this work, ferroelastic domain walls inside BaTiO3 (BTO) tetragonal nanocrystals are distinguished by Bragg peak position and studied with Bragg coherent x-ray diffraction imaging (BCDI). Convergence-related features of the BCDI method for strongly phased objects are reported. A ferroelastic domain wall inside a BTO crystal has been tracked and imaged across the tetragonal-cubic phase transition and proves to be reversible. The linear relationship of relative displacement between two twin domains with temperature is measured and shows a different slope for heating and cooling, while the tetragonality reproduces well over temperature changes in both directions. An edge dislocation is also observed and found to annihilate when heating the crystal close to the phase transition temperature

Porosity and Structure of Hierarchically Porous Ni/Al2O3 Catalysts for CO2 Methanation

CO2 methanation is often performed on Ni/Al2O3 catalysts, which can suffer from mass transport limitations and, therefore, decreased efficiency. Here we show the application of a hierarchically porous Ni/Al2O3 catalyst for methanation of CO2. The material has a well-defined and connected meso- and macropore structure with a total porosity of 78%. The pore structure was thoroughly studied with conventional methods, i.e., N2 sorption, Hg porosimetry, and He pycnometry, and advanced imaging techniques, i.e., electron tomography and ptychographic X-ray computed tomography. Tomography can quantify the pore system in a manner that is not possible using conventional porosimetry. Macrokinetic simulations were performed based on the measures obtained by porosity analysis. These show the potential benefit of enhanced mass-transfer properties of the hierarchical pore system compared to a pure mesoporous catalyst at industrially relevant conditions. Besides the investigation of the pore system, the catalyst was studied by Rietveld refinement, diffuse reflectance ultraviolet-visible (DRUV/vis) spectroscopy, and H2-temperature programmed reduction (TPR), showing a high reduction temperature required for activation due to structural incorporation of Ni into the transition alumina. The reduced hierarchically porous Ni/Al2O3 catalyst is highly active in CO2 methanation, showing comparable conversion and selectivity for CH4 to an industrial reference catalyst