Impact failure of poly(methyl methacrylate)

Damage development during instrumented falling weight impact (IFWIM) testing of poly(methyl methacrylate) (PMMA) is recorded using short pulse photography. The first visible damage is cracking on application of the peak force. Finite element analysis predicts the deformation and state of stress throughout the specimen until the first point of failure is reached. A variation in the specimen geometry produces a significant change in initial failure energy, while the maximum tensile stress is approximately constant. The proposed failure criterion is the attainment of a critical time-dependent value of tensile stress. © 1992 John Wiley & Sons, Inc.     

First principles modeling of disorder scattering in graphene

It is important to investigate impurity scattering phenomena when modeling graphene nanoscale devices, as impurities are invariably present in any realistic system and can significantly influence graphene carrier transport. We present a short review of quantum transport where density functional theory (DFT) is carried out within the nonequilibrium Green’s function formalism (NEGF), focusing on a recent extension of this framework in the form of nonequilibrium vertex correction (NVC) that captures random graphene impurity scattering in a systematic fashion. Our results show that disorder effects significantly alters the electronic and transport properties of graphene devices. We argue that disorder effects should not be ignored if one were to model graphene nanoscale devices in realistic situations, including arriving at fundamental electronic properties such as Ohm’s law.     

Oxygen content of the fixative is important in the interpretation of the ultrastructure of ischaemic myocardium

Isolated rat hearts were subjected to 15, 45, or 60 minutes of global ischaemia and then fixed by perfusion at 37°C with glutaraldehyde containing various amounts of oxygen. This either had been bubbled with 100% oxygen (PO₂ 620 mm Hg) or with 100% nitrogen (PO₂ 40 mm Hg) immediately before use, or it had been routinely prepared and stored exposed to atmospheric oxygen (PO₂ 245 mm Hg). The ultrastructure of myocytes and endothelial cells subjected to 15 minutes of ischaemia was not affected by the treatment of the fixative. However, when the tissue subjected to longer periods of ischaemia was fixed with routinely prepared or oxygen-bubbled glutaraldehyde, ultrastructural changes characteristic of reoxygenation damage were uniformly evident in both the microvasculature and myocytes. These qualitatively distinct changes included mitochondrial swelling, cell swelling, endothelial bleb formation, and narrowing of capillary lumina. These abnormalities were not observed in tissue fixed with nitrogen-bubbled glutaraldehyde. These findings indicate that deliberate steps should be taken to reduce or eliminate dissolved oxygen from the fixatives used to study ischaemic tissues. Otherwise artefactual reoxygenation damage in vitro may occur and make valid ultrastructural interpretation difficult or impossible.     

Stress analysis of crazes at moving crack tips

Summary The finite element method is applied to contours of craze zones in front of moving crack tips in polymethylmethacrylate (PMMA), measured by interferometry, in order to compute the stress distribution. In contrast to the constant stress assumed in the Dugdale model, a stress distribution is found with a maximum at the crack tip then a sharp decrease and a more gradual decline over the larger part of the craze length. Computed stresses as well as the Dugdale stress increase with increasing crack speed and, hence, decreasing loading time. Generally the results obtained are in good agreement with those already found for growing crazes at stationary crack tips.     

Negative emotional and cognitive responses to being unfriended on Facebook: An exploratory study

We consider Facebook unfriending as a form of relationship termination with negative emotional and cognitive consequences. Specifically, ruminative and negative emotional responses are examined via an online survey of adult Facebook users who were unfriended. These responses were positively related to each other and to Facebook intensity. Rumination was positively predicted by using Facebook to connect with existing contacts and was more likely when the unfriender was a close partner. Participants also responded with greater rumination and negative emotion when they knew who unfriended them, when they thought they were unfriended for Facebook-related reasons, and when participants initiated the Facebook friend request. The contribution of these exploratory findings to our growing understanding of negative relational behaviors on Facebook are discussed.     

Sound-precipitated convulsions: 1947-1954.

Approximately 129 papers on audiogenic seizure are examined. Among the variables influencing seizure susceptibility are audition, intense light, pain, temperature, regulation of free movement, opportunity for escape; genetic, age and sex, and physiological status differences; and psychological status. "Perhaps the most promising developments are concerned with the inheritance of susceptibility in mice, stimulus priming, and learned control of the seizure." 145 references. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Preparation and characterisation of high surface area semiconducting oxides

The conventional method of preparing doped semiconducting oxides involves solid state sintering at elevated temperatures and the resultant products have a very low surface area (< 1 m² g^–1). This severely limits the activity of semiconducting oxide catalysts, such as lithiated NiO. A cryochemical method based on the freeze drying of mixed salt solutions, followed by low temperature calcining has yielded lithiated NiO of over 60 m² g^–1. DTA, conductivity measurements and chemical analyses confirmed that under these conditions, very uniform mixing between Li₂O and NiO is achieved and that Li₂O can diffuse into the NiO lattice at about 400° C, as compared to 950 to 1000° C for products prepared by conventional means.     

Sigmund Koch (1917–1996): Obituary.

Memorializes Sigmund Koch. Although dismissive of grand systems, on both principled and empirical grounds, Koch indicated ways in which psychologists can realize the kind of sensibility-based, context-dependent, finely textured insights that can result from authentic probing of human experience. His own inquiries into a perceptual theory of definition, the nature of objective value-properties, and the processes of creative activity in the arts illustrate the sort of qualitative, philosophically informed, and empirically grounded investigations that should be central to what he christened "the psychological studies." (PsycINFO Database Record (c) 2010 APA, all rights reserved)