Cracks in rubber under tension exceed the shear wave speed

The shear wave speed is an upper limit for the speed of cracks loaded in tension in linear elastic solids. We have discovered that in a non-linear material, cracks in tension (Mode I) exceed this sound speed, and travel in an intersonic range between shear and longitudinal wave speeds. The experiments are conducted in highly stretched sheets of rubber; intersonic cracks can be produced simply by popping a balloon.Comment: 4 pages, 5 eps figure

Direct Numerical Simulation of Acoustic Disturbances in the Rectangular Test Section of a Hypersonic Wind Tunnel

Direct numerical simulations (DNS) of the full-scale rectangular nozzle of a hypersonic wind tunnel are conducted to study the acoustic freestream fluctuations radiating from turbulent boundary layers (TBLs) along the nozzle walls. The nozzle geometry and the flow conditions of the DNS match those of the NASA 20-Inch Mach 6 Tunnel, and the DNS has been completed for a domain without spanwise sidewall boundary conditions. The turbulent boundary layer parameters based on the DNS compare well with those derived from Reynolds Averaged Navier-Stokes (RANS) calculations as well as with the predictions based on Pates correlation. A similarly good comparison is observed for both the Mach number distribution and the Reynolds stresses obtained from the DNS and RANS calculations, respectively. Various characteristics of the acoustic pressure fluctuations within the inviscid core of the nozzle flow are compared with those associated with a single flat plate at a similar freestream Mach number. The frequency spectrum and bulk propagation speeds match well between the nozzle and the flat plate, but the rms pressure fluctuation is higher for the nozzle configuration, likely due to the combined effect of acoustic radiation from the top and bottom walls. Spatial contours of the two-point correlation coefficient display elliptical tails with approximately equal but opposite angles corresponding to the preferred directionality of acoustic structures radiated from both walls. Future work will focus on DNS of the full nozzle configuration, including the effects of the nozzle side walls

CO Reduction to CH_3OSiMe_3: Electrophile-Promoted Hydride Migration at a Single Fe Site

One of the major challenges associated with developing molecular Fischer–Tropsch catalysts is the design of systems that promote the formation of C–H bonds from H_2 and CO while also facilitating the release of the resulting CO-derived organic products. To this end, we describe the synthesis of reduced iron-hydride/carbonyl complexes that enable an electrophile-promoted hydride migration process, resulting in the reduction of coordinated CO to a siloxymethyl (LnFe-CH_2OSiMe_3) group. Intramolecular hydride-to-CO migrations are extremely rare, and to our knowledge the system described herein is the first example where such a process can be accessed from a thermally stable M(CO)(H) complex. Further addition of H_2 to LnFe-CH_2OSiMe_3 releases CH_3OSiMe_3, demonstrating net four-electron reduction of CO to CH_3OSiMe_3 at a single Fe site

Electrophile-promoted Fe-to-N_2 hydride migration in highly reduced Fe(N_2)(H) complexes

One of the emerging challenges associated with developing robust synthetic nitrogen fixation catalysts is the competitive formation of hydride species that can play a role in catalyst deactivation or lead to undesired hydrogen evolution reactivity (HER). It is hence desirable to devise synthetic systems where metal hydrides can migrate directly to coordinated N2 in reductive N–H bond-forming steps, thereby enabling productive incorporation into desired reduced N_2-products. Relevant examples of this type of reactivity in synthetic model systems are limited. In this manuscript we describe the migration of an iron hydride (Fe-H) to N_α of a disilylhydrazido(2-) ligand (Fe=NNR_2) derived from N_2 via double-silylation in a preceding step. This is an uncommon reactivity pattern in general; well-characterized examples of hydride/alkyl migrations to metal heteroatom bonds (e.g., (R)M=NR′ → M–N(R)R′) are very rare. Mechanistic data establish the Fe-to-N_α hydride migration to be intramolecular. The resulting disilylhydrazido(1-) intermediate can be isolated by trapping with CN^tBu, and the disilylhydrazine product can then be liberated upon treatment with an additional acid equivalent, demonstrating the net incorporation of an Fe-H equivalent into an N-fixed product

Imiglucerase in the treatment of Gaucher disease: a history and perspective

The scientific and therapeutic development of imiglucerase (Cerezyme®) by the Genzyme Corporation is a paradigm case for a critical examination of current trends in biotechnology. In this article the authors argue that contemporary interest in treatments for rare diseases by major pharmaceutical companies stems in large part from an exception among rarities: the astonishing commercial success of Cerezyme. The fortunes of the Genzyme Corporation, latterly acquired by global giant Sanofi SA, were founded on the evolution of a blockbuster therapy for a single but, as it turns out, propitious ultra-orphan disorder: Gaucher disease

Learn And Work: A Hybrid Educational Model For Engineering Education

Traditional models of education are undergoing significant change in recent times due to evolving graduate attributes, shaped in no small part by the changing demands of modern industrial practices. Technology is one of the key elements of the factory of the future. Advances in manufacturing and digital technologies facilitate automation and offer significant benefits in a variety of areas. Academic programmes that feature industrial work placement have long been a feature of engineering education in TU Dublin. The BSc in Process Instrumentation and Automation is a three-year programme that goes further in that it evenly balances on-campus instruction with work placement. The programme was specifically devised in response to industry feedback that had identified significant skills shortages in the areas of industrial instrumentation and automation. It is a hybrid between the apprenticeship model of education (www.apprenticeship.ie) and the traditional engineering degree model and directly addresses industry\u27s immediate need for experienced graduates. Participation in the programme is sponsored by Irish Medtech Skillnet, a learning network for companies in the medical technology and engineering sector that responds to the training needs of that sector. This is one step in the lifelong learning path of a modern graduate. This paper will provide a detailed critical review of the ‘learn and work’ model; strengths, challenges and opportunities offered by this mode of engineering education

Dihydrogen Adduct (Co-H₂) Complexes Displaying H-atom and Hydride Transfer

The prototypical reactivity profiles of transition metal dihydrogen complexes (M‐H₂) are well‐characterized with respect to oxidative addition (to afford dihydrides, M(H)₂) and as acids, heterolytically delivering H⁺ to a base and H⁻ to the metal. In the course of this study we explored plausible alternative pathways for H₂ activation, namely direct activation through H‐atom or hydride transfer from the σ‐H₂ adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutral S = ½ and an anionic S = 0 Co‐H₂ adduct, both supported by a trisphosphine borane ligand (P₃^B). The thermally stable metalloradical, (P₃^B)Co(H₂), serves as a competent precursor for hydrogen atom transfer to ᵗBu₃ArO·. What is more, its anionic derivative, the dihydrogen complex [(P₃^B)Co(H₂)]¹⁻, is a competent precursor for hydride transfer to BEt₃, establishing its remarkable hydricity. The latter finding is essentially without precedent among the vast number of M‐H₂ complexes known

Dihydrogen Adduct (Co-H₂) Complexes Displaying H-atom and Hydride Transfer

The prototypical reactivity profiles of transition metal dihydrogen complexes (M‐H₂) are well‐characterized with respect to oxidative addition (to afford dihydrides, M(H)₂) and as acids, heterolytically delivering H⁺ to a base and H⁻ to the metal. In the course of this study we explored plausible alternative pathways for H₂ activation, namely direct activation through H‐atom or hydride transfer from the σ‐H₂ adducts. To this end, we describe herein the reactivity of an isostructural pair of a neutral S = ½ and an anionic S = 0 Co‐H₂ adduct, both supported by a trisphosphine borane ligand (P₃^B). The thermally stable metalloradical, (P₃^B)Co(H₂), serves as a competent precursor for hydrogen atom transfer to ᵗBu₃ArO·. What is more, its anionic derivative, the dihydrogen complex [(P₃^B)Co(H₂)]¹⁻, is a competent precursor for hydride transfer to BEt₃, establishing its remarkable hydricity. The latter finding is essentially without precedent among the vast number of M‐H₂ complexes known

Disgustingly Queer: George Kuchar's Video Diaries

In the realm of underground film and video, George Kuchar is primarily discussed in connection with his twin brother, Mike, and their trash-spectacular narratives that injected the queer underground movement in the 1960s with a taste of the bizarre. Since their amicable split, George not only left their Bronx homestead to teach at the San Francisco Art Institute until his death in 2011, but also made a significant switch from 16mm film to video in 1985. By switching to this more affordable and accessible format, George embarked on what would become a vast body of diaristic videos. Kuchar kept some of the thematic foundations from his collaborative films with Mike, but instead focused on his cross-country travels, mainly his summer-long excursions in Oklahoma, on the lookout for tornadoes. In creating these personal videos, Kuchar presents himself as an affable, unserious person whose life is steeped in lowbrow culture or kitsch aesthetic. Kuchar focuses on the culturally and socially undervalued, and he is not interested in elevating its value status. Instead, he desires to join the muck. This thesis examines Kuchar's video diaries for their specifically queer investment in the debased and devalued. I consider them in relation to the affect of disgust, and I argue that these videos show disgust to be a complex response to "low" forms, whether aesthetic, cultural, or social. Disgust is conventionally understood as a gesture of refusal or aversion, a rejection of the object or value deemed disgusting. Kuchar's queer form of disgust, by contrast, savors impropriety and excess, and revels in the violation of boundaries.Englis