High temperature stability of natural maghemite: a magnetic and spectroscopic study

A combined magneto-mineralogical approach is used to diagnose maghemitization in magnetic grains of basaltic rock fragments from sand dunes in the Namibian desert in SW Africa. Data were obtained from static magnetic analysis, ferromagnetic resonance (FMR) spectroscopy, micro-Raman spectroscopy and electron microscopy. Micro-Raman spectroscopy showed that the magnetic grains in the lithic fragments form oxidative solid solution series with magnetite and maghemite as end-members. The five active Raman modes at 712, 665, 507, 380 and 344 cm−1 indicate that maghemite in the magnetic grains has well-defined structural properties. The FMR spectral analysis provides evidence for long-range dipolar coupling, which suggests intergrowth of the magnetic phases of the oxidative solid solution series. Thermomagnetic experiments and hysteresis measurements reveal a Curie temperature of about 890 K for this maghemite. Upon heating to 970 K part of the maghemite is altered to thermodynamically more stable hematite. After selective thermal decomposition of the maghemite in a protected atmosphere, the remaining magnetic phase has a Curie temperature of 850 K, characteristic for magnetite. The unique thermal stability of this natural maghemite above its Curie temperature is explained by the well-defined mineral structure, which formed during slow oxidative alteration of magnetite under arid climate condition

Agreement between prospective diary data and retrospective questionnaire report of abdominal pain and stooling symptoms in children with irritable bowel syndrome

BACKGROUND: In functional gastrointestinal disorders, patient recall of symptoms drives diagnostic decisions and evaluation of treatment response, and research conclusions about potential treatments. In pediatrics, parent report also impacts assessment and care. Hence, identifying methods for accurately capturing patient and parent report of irritable bowel syndrome (IBS) symptoms is important. This study evaluated correspondence between retrospective questionnaire (parent and child report) and prospective diary data for children and adolescents with IBS. METHODS: Participants included 50 children/adolescents with IBS per Rome III criteria. Children completed a 2-week pain and stool diary. Children and parents subsequently completed a 2-week recall questionnaire, reporting number of pain days, maximum pain, days without bowel movement, and days with diarrhea during the diary interval. Intraclass correlation coefficients and Bland-Altman plots assessed agreement. KEY RESULTS: For pain and days without bowel movement, overall agreement between child recall questionnaire and child diary was strong, although under conditions likely to facilitate agreement and with individual variation observed. Parent recall and child diary were less concordant, and agreement about diarrhea was poor for parent and child. Age did not significantly correlate with agreement. CONCLUSIONS & INFERENCES: Child questionnaire with short recall interval may be a reasonable approximation for diary data, although this varies by individual and replication/investigation of lengthier recall are needed. Relying on parent questionnaire does not appear a suitable proxy, and recall of stool form by both parent and child appears more problematic. These results combined with existing literature support use of diary data whenever possible

Liquid-Phase Quasi-Epitaxial Growth of Highly Stable, Monolithic UiO-66-NH₂ MOF thin Films on Solid Substrates

High quality, monolithic UiO‐66‐NH2 thin films on diverse solid substrates have been prepared via a low temperature liquid phase epitaxy method. The achievement of continuous films with low defect densities and great stability against high temperatures and hot water is proven, clearly outperforming other reported types of MOF thin films

Electrospun carbon nanofibre-assisted patterning of metal oxide nanostructures

This work establishes carbon nanofibre-mediated patterning of metal oxide nanostructures, through the combination of electrospinning and vapor-phase transport growth. Electrospinning of a suitable precursor with subsequent carbonization results in the patterning of catalyst gold nanoparticles embedded within carbon nanofibres. During vapor-phase transport growth, these nanofibres allow preferential growth of one-dimensional metal oxide nanostructures, which grow radially outward from the nanofibril axis, yielding a hairy caterpillar-like morphology. The synthesis of metal oxide caterpillars is demonstrated using zinc oxide, indium oxide, and tin oxide. Source and substrate temperatures play the most crucial role in determining the morphology of the metal oxide caterpillars, whereas the distribution of the nanofibres also has a significant impact on the overall morphology. Introducing the current methodology with near-field electrospinning further facilitates user-defined custom patterning of metal oxide caterpillar-like structures

Polycrystalline texture causes magnetic instability in greigite

Magnetic stability of iron mineral phases is a key for their use as paleomagnetic information carrier and their applications in nanotechnology, and it critically depends on the size of the particles and their texture. Ferrimagnetic greigite (Fe$_{3}$S$_{4}$) in nature and synthesized in the laboratory forms almost exclusively polycrystalline particles. Textural effects of inter-grown, nano-sized crystallites on the macroscopic magnetization remain unresolved because their experimental detection is challenging. Here, we use ferromagnetic resonance (FMR) spectroscopy and static magnetization measurements in concert with micromagnetic simulations to detect and explain textural effects on the magnetic stability in synthetic, polycrystalline greigite flakes. We demonstrate that these effects stem from inter-grown crystallites with mean coherence length (MCL) of about 20 nm in single-domain magnetic state, which generate modifiable coherent magnetization volume (CMV) configurations in the flakes. At room temperature, the instability of the CVM configuration is exhibited by the angular dependence of the FMR spectra in fields of less than 100 mT and its reset by stronger fields. This finding highlights the magnetic manipulation of polycrystalline greigite, which is a novel trait to detect this mineral phase in Earth systems and to assess its fidelity as paleomagnetic information carrier. Additionally, our magneto-spectroscopic approach to analyse instable CMV opens the door for a new more rigorous magnetic assessment and interpretation of polycrystalline nano-materials

Multiple Factors Converge to Influence Women’s Persistence in Computing: A Qualitative Analysis of Persisters and Nonpersisters

Previous research has suggested that access and exposure to computing, social supports, preparatory privilege, a sense of belonging in computing and/or a computing identity all contribute to women pursuing computing as a field of study or intended career. What we know less about is what keeps young women persisting in computing despite the obstacles they encounter. This paper describes findings from analysis of 64 in-depth interviews with young women who in high school expressed interest in computing by looking into NCWIT’s Aspirations in Computing Award. The dataset includes Award winners and nonwinners, some of whom have persisted in computing and some who have not. Our findings suggest that multiple, redundant supports, including community reinforcement, as well as a bolstered sense of identity/belonging, may make the difference in who persists and who does not