Carrier density dependence of plasmon-enhanced nonradiative energy transfer in a hybrid quantum well-quantum dot structure.

An array of Ag nanoboxes fabricated by helium-ion lithography is used to demonstrate plasmon-enhanced nonradiative energy transfer in a hybrid quantum well-quantum dot structure. The nonradiative energy transfer, from an InGaN/GaN quantum well to CdSe/ZnS nanocrystal quantum dots embedded in an ~80 nm layer of PMMA, is investigated over a range of carrier densities within the quantum well. The plasmon-enhanced energy transfer efficiency is found to be independent of the carrier density, with an efficiency of 25% reported. The dependence on carrier density is observed to be the same as for conventional nonradiative energy transfer. The plasmon-coupled energy transfer enhances the QD emission by 58%. However, due to photoluminescence quenching effects an overall increase in the QD emission of 16% is observed.

The changing role of the superficial region in determining the dynamic compressive properties of articular cartilage during postnatal development.

OBJECTIVE: To explore how changes to the superficial region (SR) of articular cartilage during skeletal development impact its functional properties. It was hypothesised that a functional superficial region is not present in skeletally immature articular cartilage, and removal of this zone of the tissue would only negatively impact the dynamic modulus of the tissue with the attainment of skeletal maturity. METHODS: Porcine osteochondral cores were mechanically tested statically and dynamically with and without their respective superficial regions in confined and unconfined compression at different stages of postnatal development and maturation. A novel combination of histological, biochemical and imaging techniques were utilised to accurately describe changes to the superficial region during postnatal development. RESULTS: Articular cartilage was found to become stiffer and less permeable with age. The confined and unconfined dynamic modulus significantly decreased after removal of the superficial region in skeletally mature cartilage, whilst no significant change was observed in the 4 week old tissue. Biochemical analysis revealed a significant decrease in overall sGAG content with age (as % dry weight), whilst collagen content significantly increased with age, although the composition of the superficial region relative to the remainder of the tissue did not significantly change with age. Helium ion microscopy (HIM) revealed dramatic changes to the organization of the superficial region with age. CONCLUSIONS: The findings demonstrate that the superficial region of articular cartilage undergoes dramatic structural adaptation with age, which in turn plays a key role in determining the dynamic compressive properties of the tissue.

Postnatal changes to the mechanical properties of articular cartilage are driven by the evolution of its collagen network.

While it is well established that the composition and organisation of articular cartilage dramatically change during skeletal maturation, relatively little is known about how this impacts the mechanical properties of the tissue. In this study, digital image correlation was first used to quantify spatial deformation within mechanically compressed skeletally immature (4 and 8 week old) and mature (1 and 3 year old) porcine articular cartilage. The compressive modulus of the immature tissue was relatively homogeneous, while the stiffness of mature articular cartilage dramatically increased with depth from the articular surface. Other, well documented, biomechanical characteristics of the tissue also emerged with skeletal maturity, such as strain-softening and a depth-dependent Poisson's ratio. The most significant changes that occurred with age were in the deep zone of the tissue, where an order of magnitude increase in compressive modulus (from 0.97 MPa to 9.4 MPa for low applied strains) was observed from 4 weeks postnatal to skeletal maturity. These temporal increases in compressive stiffness occurred despite a decrease in tissue sulphated glycosaminoglycan content, but were accompanied by increases in tissue collagen content. Furthermore, helium ion microscopy revealed dramatic changes in collagen fibril alignment through the depth of the tissue with skeletal maturity, as well as a fivefold increase in fibril diameter with age. Finally, computational modelling was used to demonstrate how both collagen network reorganisation and collagen stiffening play a key role in determining the final compressive mechanical properties of the tissue. Together these findings provide a unique insight into evolving structure-function relations in articular cartilage.

Programmability of nanowire networks.

Electrical connectivity in networks of nanoscale junctions must be better understood if nanowire devices are to be scaled up from single wires to functional material systems. We show that the natural connectivity behaviour found in random nanowire networks presents a new paradigm for creating multi-functional, programmable materials. In devices made from networks of Ni/NiO core-shell nanowires at different length scales, we discover the emergence of distinct behavioural regimes when networks are electrically stressed. We show that a small network, with few nanowire-nanowire junctions, acts as a unipolar resistive switch, demonstrating very high ON/OFF current ratios (>10(5)). However, large networks of nanowires distribute an applied bias across a large number of junctions, and thus respond not by switching but instead by evolving connectivity. We demonstrate that these emergent properties lead to fault-tolerant materials whose resistance may be tuned, and which are capable of adaptively reconfiguring under stress. By combining these two behavioural regimes, we demonstrate that the same nanowire network may be programmed to act both as a metallic interconnect, and a resistive switch device with high ON/OFF ratio. These results enable the fabrication of programmable, multi-functional materials from random nanowire networks.

Screening for smokers in four Sydney teaching hospitals.

BACKGROUND: Cardiovascular disease is a major cause of death and a reason for hospital admissions. The hospital stay is a window of opportunity to assist smokers to quit. METHODS: Patients from selected wards in four teaching hospitals in Sydney, Australia were screened using a self-completed general health questionnaire. The questionnaire included questions on demographic variables, tobacco and alcohol consumption, attitudes towards tobacco and alcohol use, and a measure of readiness to charge high-risk lifestyle behaviors, based on that proposed by Prochaska and DiClemente [1]. RESULTS: The total number of screening questionnaires completed was 2,815: 78% men and 22% women. The average age of the sample was 44 years, 48% were married or living in a de facto relationship whilst 35% never married, with the rest widowed, separated or divorced. A total of 877 (31%) patients reported smoking: 33% of men and 24% of women screened. Predictors of smoking were sex, age, marital status, education level and socio-economic status. A significant association was found between excessive drinking and smoking. Among the smoking patients, 157 (18%) planned no change in smoking (precontemplation), 379 (43%) were ambivalent about smoking (contemplation), and 334 (38%) were serious about quitting. CONCLUSION: As about one third of patients in hospital are smokers, the hospital is an ideal setting for the delivery of brief interventions by a range of health personnel at the patients bedside. The use of a detection instrument measuring levels of intake and readiness to change tobacco use is described, as a practical method for targeting patients in hospital who are at risk or have already developed cigarette-related diseases, such as cardiovascular disease.

Familiality of female and male homosexuality.

We examined data from a large cohort of homosexual and heterosexual females and males concerning their siblings' sexual orientations. As in previous studies, both male and female homosexuality were familial. Homosexual females had an excess of homosexual brothers compared to heterosexual subjects, thus providing evidence that similar familial factors influence both male and female homosexuality. Furthermore, despite the large sample size, homosexual females and males did not differ significantly from each other in their proportions of either homosexual sisters or homosexual brothers. Thus, results were most consistent with the possibility that similar familial factors influence male and female sexual orientation. However, because results conflicted with those of some other studies, and because siblings' sexual orientations were obtained in a manner likely to yield more errors than in these other, smaller studies, further work is needed using large samples and more careful methods before the degree of cofamiliality of male and female homosexuality can be resolved definitively. We also examined whether some parental influences comprised shared environmental effects on sexual orientation. Scales attempting to measure such influences failed to distinguish subjects with homosexual siblings from subjects with only heterosexual siblings and, thus, did not appear to measure shared environmental determinants of sexual orientation.

Avian sarcoma virus gag precursor polypeptide is not processed in mammalian cells.

We studied intracellular avian gag proteins (internal structural proteins of virions) in several mammalian cell lines transformed by Rous sarcoma virus. All lines examined contain gag antigens as determined by radioimmune assay. We used the techniques of protein blotting from polyacrylamide gels, which detects nanogram quantities of viral protein, to investigate the size of intracellular viral polypeptides. All of the lines that contained enough viral protein to be amenable to this type of analysis synthesized Pr76, the avian sarcoma virus gag precursor polypeptide, but failed to process it into mature virion proteins. In some cell lines, the recovery of Pr76 was greatly enhanced by the addition of a mixture of protease inhibitors, including the sulfhydryl-blocking reagent N-ethylmaleimide, to the lysis buffer. At least several of the mammalian cells also synthesized a viral polypeptide the size of Pr180, the precursor to reverse transcriptase. Since Rous sarcoma virus does not replicate or replicates extremely poorly in mammalian cells, the lack of processing suggests that cleavage and virion assembly are invariably associated.