Dynamic mechanical response and microstructural effects in commercially hot-pressed boron carbide under different loading rates and stress states

Boron carbide, with its high hardness and superior compressive strength, has become an attractive engineering material. Certain applications, notably ballistic protection, have drawn attention to its dynamic behavior. Like other brittle materials, the mechanical behavior of boron carbide is strongly related to the intrinsic microstructural flaws, e.g., non-metallic inclusions that form separate phases (graphite, BN, AlN) or voids. The critically sized and/or critically spaced flaws play important roles in dynamic failure processes as potential nucleation sites, and their relative importance depends on a combination of several mechanical properties. This study investigated the failure of a commercially hot-pressed boron carbide subjected to dynamic uniaxial and biaxial compression. The process was studied by loading small-size cubic specimens in a compression Kolsky Bar at strain-rates of ~103 s‑1. A high-speed camera was used to capture the failure process. SEM/EDS analysis was used to determine the chemical composition of the material matrix and flaws, and to identify critical actors in the failure process from the postmortem fragments. To study the strain-rate sensitivity, the mechanical behavior was also evaluated in the quasi-static regime (~10‑3 s–1) by using a servo-hydraulic testing machine in compression. The strain rate sensitivity for this material is typical of other advanced ceramics; the strength under dynamic compression was higher compared with the quasi-static strength. SEM/EDS examination showed that boron carbide has a microstructure with a complex superposition of inclusions of different composition and properties. It appears that the larger graphite-based inclusions are key factors contributing to the dynamic failure of this material

Signatures of Primordial Non-Gaussianity in the Large-Scale Structure of the Universe

We discuss how primordial (e.g. inflationary) non-Gaussianity in the cosmological perturbations is left imprinted in the Large-Scale Structure of the universe. Our findings show that the information on the primordial non-Gaussianity set on super-Hubble scales flows into Post-Newtonian terms, leaving an observable imprint in the Large-Scale Structure. Future high-precision measurements of the statistics of the dark matter density and peculiar velocity fields will allow to pin down the primordial non-Gaussianity, thus representing a tool complementary to studies of the Cosmic Microwave Background anisotropies.Comment: 8 pages, LaTeX file; Revised to match the final version accepted for publication on JCAP (some comments and one figure added

Defects of Tensioned Membrane Structures (TMS) In Tropics

The wide use of tensioned membrane structures (TMS) becomes prominent in many designs because of its aesthetic, ergonomic, and economical nature. Recently, TMS has been applied in the tropics with success, yet defects specific to this region have received little attention. Through a questionnaire survey of 890 uses and technicians of TMS in three different areas in Malaysia, this study identified the most frequently occurring TMS defects in the tropics, such as "deterioration of roof coatings", "corrosion or fatigue in fixings", "fungal decay, mould growth, and dirt in membrane", "corrosion in anchor cables", and "degradation of fabrics". These defects are quite different from those in other climatic zones. The top five causes of TMS defects in the tropics are weather, aging, design, construction/installation, and material selection. However, only "corrosion or fatigue in fixings" is a significant predictor for "deterioration of roof coatings". While this is not a causal effect, a practical implication is that TMS maintenance workers do not have to climb up to the roof to check the deterioration in coating but only need to predict the deterioration through the corrosion levels of the fixings. Further, seven countermeasures for TMS in tropic are recommended. This study is the first comprehensive study examining tensioned membrane structure defects in the tropics

ACC/AHA/ESC Guidelines for the Management of Patients With Supraventricular Arrhythmias—Executive Summary

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Early childhood pedagogies: spaces for young children to flourish

This paper introduces the Special Issue of Early Child Development and Care focused on Early Childhood Pedagogy. It opens by considering past and present discourses concerning early childhood pedagogy, and focus is given to established philosophical underpinnings in the field and their translation to contemporary guidance, alongside research and policy. It is argued that early childhood pedagogy is a contested, complex and diverse space, yet these factors are entirely appropriate for supporting young children to flourish as valued individuals in different contexts. Building on this argument, it is posited that it may be more appropriate to discuss early childhood pedagogies rather than early childhood pedagogy. The paper goes on to critique a range of established early childhood pedagogies, before introducing 18 papers from across the world that make exciting new contributions to the discourse. It is intended that this collection will inspire new debates and fresh endeavours concerning early childhood pedagogies

Applying an extended theoretical framework for data collection mode to health services research

<p>Abstract</p> <p>Background</p> <p>Over the last 30 years options for collecting self-reported data in health surveys and questionnaires have increased with technological advances. However, mode of data collection such as face-to-face interview or telephone interview can affect how individuals respond to questionnaires. This paper adapts a framework for understanding mode effects on response quality and applies it to a health research context.</p> <p>Discussion</p> <p>Data collection modes are distinguished by key features (whether the survey is self- or interviewer-administered, whether or not it is conducted by telephone, whether or not it is computerised, whether it is presented visually or aurally). Psychological appraisal of the survey request will initially entail factors such as the cognitive burden upon the respondent as well as more general considerations about participation. Subsequent psychological response processes will further determine how features of the data collection mode impact upon the quality of response provided. Additional antecedent factors which may further interact with the response generation process are also discussed. These include features of the construct being measured such as sensitivity, and of the respondent themselves (e.g. their socio-demographic characteristics). How features of this framework relate to health research is illustrated by example.</p> <p>Summary</p> <p>Mode features can affect response quality. Much existing evidence has a broad social sciences research base but is of importance to health research. Approaches to managing mode feature effects are discussed. Greater consideration must be given to how features of different data collection approaches affect response from participants in studies. Study reports should better clarify such features rather than rely upon global descriptions of data collection mode.</p