Hodograph transformations can be used to linearize a nonlinear partial differential equation by judicious use of physical quantities (e.g. velocities or displacement gradients) as coordinate variables in the hodograph plane. This approach has been found useful for obtaining the leading order terms of eigenproblems that govern asymptotic singular crack fields in nonlinear materials. There is little work on the use of the hodograph transformation for obtaining higher order terms in the asymptotic expansion of the crack tip fields. In this paper, we develop a framework to obtain such higher order terms using the hodograph transformation. The method relies heavily on the representation of physical quantities of interest in terms of hodograph plane variables. We demonstrate the method via application to a generalized neo-Hookean material. In addition, asymptotic path-independent J-integrals are expressed in terms of either physical or hodograph variables and are used to compute the leading-order amplitude coefficients. A relationship between the asymptotic J-integrals and the energy release rate is established for a mixed crack mode. The asymptotic results are compared with numerical results from finite element computation and excellent agreement is obtained.
High proton conductivity is reported for unhumidified ammonium borosulfate, NH4[B(SO4)2], a solid acid coordination polymer that contains 1D, hydrogen-bonded NH4+···1∞[B(SO4)4/2]− chains. NH4[B(SO4)2] is thermally stable to 320 °C and is amenable to sintering into monolithic, polycrystalline discs at 200 °C and about 300 MPa of uniaxial pressure. Impedance spectroscopy measurements reveal ionic conductivities for sintered ammonium borosulfate of 0.1 mS cm−1 at 25 °C and up to 10 mS cm−1 at 180 °C in ambient air. No superprotonic transition is observed in the temperature range of 25–180 °C. Ab initio molecular dynamics simulations show these high conductivities are aided by free rotation of the NH4+ units and significant gyrational mobility of the SO4 tetrahedra, which, in turn, provide facile pathways for proton locomotion. High conductivities, a wide operational temperature window, and tolerance to both ambient and anhydrous conditions make NH4[B(SO4)]2 an attractive candidate electrolyte for intermediate-temperature hydrogen fuel cells that may enable operation at temperatures as high as 300 °C without active humidification. 相似文献
ABSTRACTParticipatory design’s (PD) shift from the workplace to civic settings has led to a reorientation of the field’s political bearings. Informed by science and technology studies, practice is now often framed in terms of design things, infrastructuring, and John Dewey’s concept of ‘publics’. Taking the publics concept as a starting point, the present article seeks to contribute by providing a broader outline of Dewey’s democratic vision. It is proposed that Dewey’s vision may be seen to offer a potentially useful perspective that directly relates the ‘publics’ concept to the areas of freedom, experientialism, and the institutions of government. Linking to contemporary developments in PD and beyond, the vision is seen to carry conceptual and practical implications, which, if borne out, would connect the discipline’s capacity to ‘spark’ publics into being to the processes of policy formation and institutional reform. 相似文献
An untapped source of amorphous SiO2, industrially generated Indian biomass ash (SA)—90% amorphous, with composition of ~60% SiO2 and ~20% unburnt carbon—can be used to produce cementitious and alkali-activated binders. This study reports dissolution of amorphous Si from SA in 0.5 mol/L and 1 mol/L aqueous NaOH, with and without added Ca(OH)2, at SA:Ca(OH)2 wt% ratios of 100:0, 87.5:12.5, and 82.5:17.5. Monitoring of elemental dissolution and subsequent/simultaneous product uptake by ICP-OES offers an effective process for evaluating utility of industrial wastes in binder-based systems. After 28 days in solution, up to 68% of total Si is dissolved from SA in 1 mol/L NaOH, with values as much as 38% lower in the presence of Ca(OH)2, due to the formation of tobermorite-like C-S-H. FTIR, 29Si MAS-NMR, and XRD are used to characterize solid reaction products and observe reaction progress. Product chemistries calculated from ICP-OES results and verified by selective dissolution in EDTA/NaOH—namely, Ca/Si of 0.6-1 and Na adsorption of 1-2 mmol/g—are found to be consistent with those indicated by aforementioned techniques. This indicates the efficacy of ICP-OES in estimating product chemistry via such a methodology. 相似文献
Hydroxyapatite (HA) is a bioceramic material that shares similar crystal and chemical structures with inorganic components of the bone. However, HA lacks osteoinductive activity and has a brittle nature, making it challenging to apply for direct load-bearing bone applications. In this study, we used a wet chemical method to synthesize zinc-doped hydroxyapatite powders with different Zn/(Zn+Ca) molar ratios of 0, 0.025, 0.05, and 0.1. The corresponding Zn-HA was designated as HA, Zn2.5-HA, Zn5-HA, and Zn10-HA. The Zn-HA powders at 30 wt% were used to fabricate poly(propylene fumarate) (PPF)-based nanocomposite scaffolds (HA/PPF, Zn2.5-HA/PPF, Zn5-HA/PPF, and Zn10-HA/PPF). The physical properties of obtained scaffolds were examined by scanning electron microscopy, energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). Live/dead cell viability assay showed that these scaffolds were biocompatible and supported excellent adhesion of MC3T3-E1 preosteoblast cells. Additionally, the proliferation of cells was detected at 1, 4, and 7 days on these scaffolds. Alkaline phosphatase (ALP) activity measurement and alizarin red staining showed good osteogenic differentiation and matrix mineralization for MC3T3-E1 cells growing on these scaffolds. Taken together, the results here indicate that Zn5-HA/PPF nanocomposite scaffolds are promising scaffold material for bone tissue engineering.
Autonomous Robots - This paper presents fast non-sampling based methods to assess the risk for trajectories of autonomous vehicles when probabilistic predictions of other agents’ futures are... 相似文献
The implementation of periodic boundary conditions (PBCs) is one of the most important and difficult steps in the computational analysis of structures and materials. This is especially true in cases such as mechanical metamaterials which typically possess intricate geometries and designs which makes finding and implementing the correct PBCs a difficult challenge. In this work, we analyze one of the most common PBCs implementation technique, as well as implement and validate an alternative generic method which is suitable to simulate any possible 2D microstructural geometry with a quadrilateral unit cell regardless of symmetry and mode of deformation. A detailed schematic of how both these methods can be employed to study 3D systems is also presented.
The burgeoning interest in archaic, traditional, and novel beer styles has coincided with a growing appreciation of the role of yeasts in determining beer character as well as a better understanding of the ecology and biogeography of yeasts. Multiple studies in recent years have highlighted the potential of wild Saccharomyces and non-Saccharomyces yeasts for production of beers with novel flavour profiles and other desirable properties. Yeasts isolated from spontaneously fermented beers as well as from other food systems (wine, bread, and kombucha) have shown promise for brewing application, and there is evidence that such cross-system transfers have occurred naturally in the past. We review here the available literature pertaining to the use of nonconventional yeasts in brewing, with a focus on the origins of these yeasts, including methods of isolation. Practical aspects of utilizing nondomesticated yeasts are discussed, and modern methods to facilitate discovery of yeasts with brewing potential are highlighted. 相似文献
The incorporation of microwave and pulsed electric field (PEF) technologies in optimising the extraction of polyphenols from defatted canola seed cake was determined by Box‐Behnken response surface methodology, using three parameters of microwave treatment (power, time and liquid: solid (L:S) ratio) and four parameters of PEF (ethanol concentration, time, frequency and voltage). After microwave and PEF pretreatments, the polyphenols of defatted canola seed cake were extracted by ultrasound treatment under fixed variables (200 W of ultrasonic power, 70 °C of water bath and 20 min of extraction time). The measured responses were total phenolics, total flavonoids, the DPPH˙ scavenging activity and ferric reducing antioxidant power (FRAP). The maximum yields of all responses were achieved under optimum conditions of microwave processing (5 min, L:S ratio of 6.0 and 633.3 W) and PEF‐assisted extraction (30 V, 30 Hz, 10% ethanol concentration and 10 s). 相似文献