Atomistic Studies of Defect Nucleation during Nanoindentation of Au (001)

Atomistic studies are carried out to investigate the formation and evolution of defects during nanoindentation of a gold crystal. The results in this theoretical study complement the experimental investigations [J. D. Kiely and J. E. Houston, Phys. Rev. B, v57, 12588 (1998)] extremely well. The defects are produced by a three step mechanism involving nucleation, glide and reaction of Shockley partials on the {111} slip planes noncoplanar with the indented surface. We have observed that slip is in the directions along which the resolved shear stress has reached the critical value of approximately 2 GPa. The first yield occurs when the shear stresses reach this critical value on all the {111} planes involved in the formation of the defect. The phenomenon of strain hardening is observed due to the sessile stair-rods produced by the zipping of the partials. The dislocation locks produced during the second yield give rise to permanent deformation after retraction.Comment: 11 pages, 13 figures, submitted to Physical Review

The impact of ‘exile’ on thought: Plotinus, Derrida and Gnosticism

This article examines the impact of ‘exile’ – as an individual or collective experience – on how human experience is theorized. The relationship between ‘exile’ and thought is initially approached historically by looking at the period that Eric Dodds famously called the ‘age of anxiety’ in late antiquity, i.e. the period between the emperors Aurelius and Constantine. A particular interest is in the dynamics of ‘empire’ and the concomitant religious ferment as a context in which ‘exile’, both experientially and symbolically, appears to assume an overbearing significance. Plotinus’ narrative of emanation and epistrophe as well as a group of narratives often classified as ‘Gnosticism’ are juxtaposed as two radical examples of a wider spiritual trend at the time according to which ‘exile’ could be considered constitutive of human experience. By way of an historical analogy, the insights gained from this study of late antiquity are then used to guide an analysis of the current, ‘restless’ epoch, in which experiences of displacement and exile on a mass scale undermine traditional notions of belonging, thus reviving the gnostic vision of cosmic reality as an alien, exilic environment. The article concludes with a discussion of Jacques Derrida’s work as an example of contemporary gnosticism, in which a ‘metaphysics of exile’ is presented in the disguise of an ‘exile from metaphysics’

Loss-of-function ABCC8 mutations in pulmonary arterial hypertension

Background: In pulmonary arterial hypertension (PAH), pathological changes in pulmonary arterioles progressively raise pulmonary artery pressure and increase pulmonary vascular resistance, leading to right heart failure and high mortality rates. Recently, the first potassium channelopathy in PAH, because of mutations in KCNK3, was identified as a genetic cause and pharmacological target. Methods: Exome sequencing was performed to identify novel genes in a cohort of 99 pediatric and 134 adult-onset group I PAH patients. Novel rare variants in the gene identified were independently identified in a cohort of 680 adult-onset patients. Variants were expressed in COS cells and function assessed by patch-clamp and rubidium flux analysis. Results: We identified a de novo novel heterozygous predicted deleterious missense variant c.G2873A (p.R958H) in ABCC8 in a child with idiopathic PAH. We then evaluated all individuals in the original and a second cohort for rare or novel variants in ABCC8 and identified 11 additional heterozygous predicted damaging ABCC8 variants. ABCC8 encodes SUR1 (sulfonylurea receptor 1)—a regulatory subunit of the ATP-sensitive potassium channel. We observed loss of ATP-sensitive potassium channel function for all ABCC8 variants evaluated and pharmacological rescue of all channel currents in vitro by the SUR1 activator, diazoxide. Conclusions: Novel and rare missense variants in ABCC8 are associated with PAH. Identified ABCC8 mutations decreased ATP-sensitive potassium channel function, which was pharmacologically recovered

Contact Hysteresis and Friction of Alkanethiol SAMs on Au

Nanoindentation has been combhed with nanometer-scale friction measurements to identi~ dissipative mechanisms responsible for friction in hexadecanethiol self-assembled monolayer on Au. We have demonstrated that friction is primarily due to viscoelastic relaxations within the films, which give rise to contact hysteresis when deformation rates are within the ranges of 5 and 200 k. We observe that this contact hysteresis increases with exposure to air such that the friction coefficient increases from 0.004 to 0.075 when films are exposed to air for 40 days. Both hysteresis and friction increase with probe speed, and we present a model of friction that characterizes this speed dependence and which also predicts a linear dependence of friction on normal force in thin organic films. Finally, we identify several short-term wear regimes and identify that wear changes dramatically when fdms age

Indentation modulus and yield point of Au(111), (001), and (110)

Nanoscale indentation experiments were performed on Au using the Interfacial Force Microscope (IFM) in an indentation mode. The indentation modulus and yield point were measured for three orientations of the Au surface: (111), (110), and (001). The indentation modulus for the (111) surface was found to be 36% greater than for the (001) surface and only 3% higher than the (110) surface. Additionally, the yield point was found to vary between orientations, but the shear stress resolved on {l_brace}111{r_brace} slip planes beneath the indenter on the axis of symmetry was found to be approximately 1.8 GPa for yield points of all three orientations

Attitudes and barriers to pulmonary arterial hypertension screening in systemic sclerosis patients: A survey of UK-based rheumatologists

Objectives: The objectives were to explore rheumatologists’ current clinical screening practices of pulmonary arterial hypertension in patients with systemic sclerosis in the United Kingdom and to identify barriers to screening and consider potential solutions. Methods: A survey of 31 questions was developed and included six sections: clinician demographics, the importance of screening, screening practices, barriers to screening, treatment and patient education. The survey was disseminated among rheumatologists working in the United Kingdom. Results: Forty-four rheumatologists working in the United Kingdom participated in the study, and the majority completed all the questions. Around one-third (37.0%) worked in specialised systemic sclerosis units (university or general hospitals (54.5% and 45.4%, respectively)). The majority recognised that systemic sclerosis-pulmonary arterial hypertension is a major cause of morbidity and mortality. Over half (60.0%) reported using the DETECT algorithm to screen for systemic sclerosis-pulmonary arterial hypertension, although other algorithms were also sometimes used. All of the respondents utilised transthoracic echocardiogram, and almost all (95.0%) performed pulmonary function tests for screening purposes. Various challenges and barriers were identified relating to systemic sclerosis-pulmonary arterial hypertension screening, with the difficulty in interpreting results from other hospitals and extended wait times for diagnostic tests being the most reported (76.0% and 74.0%, respectively). Most respondents agreed that access to key investigations (87.0%), ongoing clinician education (82.0%), multidisciplinary meetings (79.5%) and a better understanding of proposed screening algorithms (79.5%) could be potential solutions. Conclusion: Screening patients with systemic sclerosis for pulmonary arterial hypertension is crucial to improve survival, but variable practices exist among UK rheumatologists. Solutions include educating healthcare professionals on guidelines, sharing information between centres and integrating care services

Mechanical properties of zinc and calcium phosphates

Recent studies on a variety of metal phosphates (MP) have revealed that MPs tend to be soft at ambient pressure if the coordination on the metal cation is low and the degree of hydration or hydrogenation is high, while they are stiff otherwise. In addition, the softer MPs were found to stiffen dramatically more quickly with increasing pressure than the stiffer MPs. Here we review these findings and support their relevance with new results on the mechanical properties of tribofilms aged in air of relative humidity, which were produced from commercial, zinc phosphate-containing lubricant packages via heating and rubbing. We find that the films can soften quite substantially after having been exposed to humidity, as to be expected from the studies of bulk MPs. Moreover, when the hydrated films are exposed to high loads, the force-distance withdrawal curve becomes identical to that of unaged, non-hydrated films. A straightforward explanation of this observation is that large pressure reverses the hydration of the tribofilms. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2010