Beginning with a description of the prime mechanisms of fracture, i.e., cleavage, quasi-cleavage, intergranular cracking and microvoid coalescence, and then the crack-tip stress and strain fields which provide the driving forces to promote such fracture modes, this chapter explores the use of micromechanics to model mechanisms of fracture, beginning with the Ritchie-Knott-Rice model for stress-controlled brittle fracture and the corresponding strain-controlled model for ductile fracture. We also present the critical crack-tip opening angle model for ductile crack growth. The mechanisms for resistance to such fractures are then described in terms of the concept of intrinsic vs. extrinsic toughening, with examples given for the salient toughening mechanisms in metallic materials, ceramics, polymeric materials, and composites.
No abstract is provided for this article.
The borylation of alkanes and arenes has become some of the most practical C-H bond functionalization chemistry. Most striking is the high regioselectivity of these reactions. Rhodium and ruthenium complexes catalyze with exquisite selectivity the borylation of methyl C-H bonds over methylene or methine C-H bonds. Iridium complexes catalyze, with high steric control, the borylation of one aromatic C-H bond over another. In contrast, iridium-catalyzed borylation of heteroaromatic C-H bonds is more controlled by electronic effects. Detailed information on these selectivities and mechanistic information on the origins of this regioselectivity will be described in this critical review (95 references).
The kinetics of the hydrogen electrode reaction on a platinized nickel electrode in alkaline solutions over a wide temperature range from ambient up to 220oC have been investigated employing a controlled hydrodynamic cell. Due to the reversible nature of this reaction, the generalized Butler-Volmer equation was used in optimization upon the polarization data, so as to account for kinetic, thermodynamic, and mass transfer effects. The extracted model parameters are compared with those for other forms of platinum electrode, and platinized nickel shows excellent electrocatalytic activity as demonstrated by the exchange current density. The extracted apparent transfer coefficients for hydrogen evolution and hydrogen oxidation are temperature-dependent, while the apparent Tafel slope of the hydrogen evolution reaction is temperature-independent (approximately 120mV/dec), which is most probably due to two parallel reactions occurring at the interface with different rates and activation energies. An Arrhenius analysis yields an activation energy of 17.3 kJ/mole for the hydrogen electrode reaction on platinized nickel in alkaline solution.
The importance of simple geometrical invariants, such as the Berry curvature and quantum metric, constructed from the Bloch states of a crystal has become well-established over four decades of research. More complex aspects of geometry emerge in properties linking multiple bands, such as optical responses. In the companion work [arXiv:2409.16358], we identified novel multi-state geometrical invariants using an explicitly gauge-invariant formalism based on projection operators, which we used to clarify the relation between the shift current and the theory of electronic polarization among other advancements for second-order non-linear optics. Here, we provide considerably more detail on the projector formalism and the geometrical invariants arising in the vicinity of a specific value of crystal momentum. We combine the introduction to multi-state quantum geometry with broadly relevant algebraic relationships and detailed example calculations, enabling extensions toward future applications to topological and geometrical properties of insulators and metals.
Understanding and facilitating real-life social interaction is a high-impact goal for Ubicomp research. Microphone arrays offer the unique capability to provide continuous, calm capture of verbal interaction in large physical spaces, such as homes and (especially open-plan) offices. Most microphone array work has focused on arrays of custom sensors in small spaces, and a few recent works have tested small arrays of commodity sensors in single rooms. This paper describes the first working scalable and cost-effective array that offers high-precision localization of conversational speech, and hence enables ongoing studies of verbal interactions in large semi-structured spaces. This work represents significant improvements over prior work in three dimensions -- cost, scale and accuracy. It also achieves high throughput for real-time updates of tens of active sources using off-the-shelf components. We describe the system design, key localization algorithms, and a systematic performance evaluation. We then show how source location data can be usefully aggregated to reveal interesting patterns in group conversations, such as dominance and engagement.
Abstract A novel strategy for the enantioselective synthesis of α‐arylamino hydrazones, which can be hydrolyzed to the corresponding ketones, is described.
We report the study of a novel class of resists designed to be coated from and developed in pure water, avoiding both the need for the traditional organic solvents and the developers containing organic bases in aqueous solution. We have previously reported on the design of several negative tone resists that operate on the basis of radiation-induced crosslinking. The performance of these negative tone systems meets our fundamental objective of coating from and development in pure water, but their design involving the crosslinking of a matrix polymer limits the resolution that may be achieved because of the swelling that occurs during development. We have now explored novel designs involving positive tone water developable resists that may help alleviate this limitation. For example, water-soluble polymers containing pendant oxazoline units may be insolubilized in situ through their heat-activated reaction with additives containing carboxylic acid groups. Exposure to UV radiation is then used to cleave these solubility modifiers hence restoring solubility to the exposed areas. Analogous materials that involve the addition of divinyl ethers to poly(acrylic acid), followed by photogenerated acid cleavage of the crosslinks have been used generate water-developed positive tone images.
