Tunable band gaps in bilayer graphene-BN heterostructures

We investigate band gap tuning of bilayer graphene between hexagonal boron nitride sheets, by external electric fields. Using density functional theory, we show that the gap is continuously tunable from 0 to 0.2 eV and is robust to stacking disorder. Moreover, boron nitride sheets do not alter the fundamental response from that of free-standing bilayer graphene, apart from additional screening. The calculations suggest that graphene-boron nitride heterostructures could provide a viable route to graphene-based electronic devices.     

Spatially resolved, single-ended two-dimensional visualization of gas flow phenomena using structured illumination

A method for 3D mapping of scattering particle concentration in a gaseous medium based on the backscattered light in a single direction has been demonstrated. The technique is originally developed for microscopy but now implemented on larger-scale samples. The technique used is known as structured illumination, where a sinusoidal grid pattern is projected onto the medium, thus marking the in-focus plane. This makes it possible to discriminate against light originating from the out-of-focus parts of the sample, which usually makes it difficult to detect inner structures of the medium. In this study a flow of nitrogen was introduced into a flow of water droplets, with the aim to optically select only the plane where nitrogen was present. The results indicate that the technique could be used to study, e.g., combustion devices with limited optical access.     

Glycogen storage disease type II: identification of four novel missense mutations (D645N, G648S, R672W, R672Q) and two insertions/deletions in the acid alpha-glucosidase locus of patients of differing phenotype

Glycogen storage disease type II (GSDII), an autosomal recessive myopathic disorder, results from deficiency of lysosomal acid alpha-glucosidase. We searched for mutations in an evolutionarily conserved region in 54 patients of differing phenotype. Four novel mutations (D645N, G448S, R672W, and R672Q) and a previously described mutation (C647W) were identified in five patients and their deleterious effect on enzyme expression demonstrated in vitro. Two novel frame-shifting insertions/deletions (delta nt766-785/insC and +insG@nt2243) were identified in two patients with exon 14 mutations. The remaining three patients were either homozygous for their mutations (D645N/D645 and C647W/C647W) or carried a previously described leaky splice site mutation (IVS1-13T-->G). For all patients "in vivo" enzyme activity was consistent with clinical phenotype. Agreement of genotype with phenotype and in vitro versus in vivo enzyme was seen in three patients (two infantile patients carrying C647W/C647W and D645N/+insG@nt2243 and an adult patient heteroallelic for G648S/IVS1-13T-->G). Relative discordance was found in a juvenile patient homozygous for the non-expressing R672Q and an adult patient heterozygous for the minimally expressing R672W and delta nt766-785/+insC. Possible explanations include differences in in vitro assays vs in vivo enzyme activity, tissue specific expression with diminished enzyme expression/stability in fibroblasts vs muscle, somatic mosaicism, and modifying genes.     

On the formation and stability of dislocation patterns—III: Three-dimensional considerations

A model is proposed to describe the occurrence of the vein structures and the nucleation of persistent slip bands in fatigued metals as a cooperative phenomenon of motion and interaction of dislocation populations. It is based on the competition between diffusive-like mobilities for random or stress induced dislocation motion and cubic-like non-linearities for the pinning of stress driven dislocations by immobile dipoles. It describes the coexistence of rod-like vein structures and ladder-like persistent slip bands in three dimensions, integrating the qualitative picture of pattern formation in one and two dimensions given earlier in Parts I and II.     

Study of the action of alpha-hederin on the ultrastructure of Candida albicans

alpha-Hederin, a saponin isolated from Hedera helix (L.) (Araliaceae), was tested on Candida albicans ultrastructure. The concentrations used were 6.25, 12.5, and 25 micrograms ml-1 for an exposure time of 24 h. Transmission electron microscopy observations indicated that compared with untreated control yeasts, alpha-hederin induced modifications of cellular contents and alterations of cell envelope with degradation and death of the yeasts. The impact of alpha-hederin on the biomembranes and in particular on the plasmalemma is discussed. The antifungal activity of alpha-hederin was confirmed, as was the minimal inhibitory concentration (25 micrograms ml-1).     

Multiple Experiment Environments for Testing

Concurrent simulation (CS) has been used successfully as areplacement for serial simulation. Based on storing differences fromexperiments, CS saves storage, speeds up simulation time and allowsexcellent internal observation of events. In this paper, we introduceMultiple Domain Concurrent Simulation (MDCS) which like concurrentsimulation, maintains efficiency by only simulating differences. MDCS alsoallows experiments to interact with one another and create new experimentsthrough the use of domains. These experiments can be traced and observed atany point, providing insight into the origin and causes of new experiments.While many experiment scenarios can be created, MDCS uses dynamic spawningand experiment compression rather than explicit enumeration to ensure thatthe number of experiment scenarios does not become exhaustive. MDCS does notrequire any pre-analysis or additions to the circuit under test. Providingthis capability in digital logic simulators allows more test cases to be runin less time. MDCS gives the exact location and causes of every experimentbehavior and can be used to track the signature paths of test patterns forcoverage analysis.We will describe the algorithms for MDCS, discuss the rules forpropagating experiments and describe the concepts of domains for makingdynamic interactions possible. We will report on the effectiveness of MDCSfor attacking an exhaustive simulation problem such as Multiple Stuck-atFault simulations for digital logic. Finally, the applicability of MDCS formore general experimentation of digital logic systems will be discussed.     

ZnO Nanowires,Nanotubes, and Complex Hierarchical Structures Obtained by Electrochemical Deposition

Increasing the aspect ratio of ZnO nanostructures is one possible strategy to improve their thermoelectric properties. ZnO nanostructures with one-dimensional (1D) and three-dimensional (3D) morphologies were obtained using electrochemical deposition. Adjusting various deposition parameters made it possible to obtain arrays of vertically aligned ZnO nanowires (NWs) with controlled dimensions, density, and electrical properties. The concentrations of zinc or chloride ions in the solution were found to be key parameters. ZnO NWs were transformed into ZnO nanotubes (NTs), with an increased aspect ratio compared with the NWs, by selectively dissolving the core of the ZnO NWs in a concentrated KCl solution. The aspect ratio was strongly increased when the ZnO NWs were hierarchically organized in a 3D morphology. The synthesis of thin films composed of ordered hollow urchin-like ZnO NW structures was performed by combining the electrochemical deposition and polystyrene sphere templating methods. The electronic properties of the urchin-like ZnO structures were investigated by means of photoluminescence and transmission measurements.     

Quasi-solid-state dye-sensitized solar cells employing nanocrystalline TiO2 films made at low temperature

Quasi-solid-state dye-sensitized solar cells with enhanced performance were made by using nanocrystalline TiO₂ films without any template deposited on plastic or glass substrates at low temperature. A simple and benign procedure was developed to synthesize the low-temperature TiO₂ nanostructured films. According to this method, a small quantity of titanium isopropoxide (TTIP) was added in an ethanolic dispersion of TiO₂ powder consisting of nanoparticles at room temperature, which after alkoxide's hydrolysis helps to the connection between TiO₂ particles and to the formation of mechanically stable thick films on plastic or glass substrates. Pure TiO₂ films without any organic residuals consisting of nanoparticles were formed with surface area of 56 m²/g and pore volume of 0.383 cm³/g similar to that obtained for Degussa-P25 powder. The structural properties of the films were characterized by microscopy techniques, X-ray diffractometry, and porosimetry. Overall solar to electric energy conversion efficiencies of 5.3% and 3.2% (under 1sun) were achieved for quasi-solid-state dye-sensitized solar cells employing such TiO₂ films on F:SnO₂ glass and ITO plastic substrates, respectively. Thus, the quasi-solid-state device based on low-temperature TiO₂ attains a conversion efficiency which is very close to that obtained for cells consisting of TiO₂ nanoparticles sintered at high temperature.     

A multi-criteria decision support for optimal instrumentation in scoliosis spine surgery

In adolescent idiopathic scoliosis, the selection of an optimal instrumentation configuration for correcting a specific spinal deformity is a challenging combinatorial problem. Current methods mostly rely on surgeons’ expertise, which has been shown to lead to different treatment strategies for the same patients. In this work, a mathematical model of the human spine derived from in-vitro experimentally-obtained data was used to simulate the biomechanical behavior of the spine under the application of corrective forces and torques. The corrective forces and torques were optimized based on the particle swarm optimization algorithm for each combinatorially possible instrumentation strategy. Finally, a multi-criteria decision support for optimal instrumentation in scoliosis spine surgery has been proposed and applied to five patient data sets exhibiting similar spinal deformities according to two commonly used classification systems. Results indicated that the classification of the spinal deformities based on the current standardized clinical classifications systems is not a sufficient condition for recommending selective fusion of spinal motion segments. In addition, the particle swarm optimization algorithm was successfully applied to solve a realistic interdisciplinary clinical problem in a patient-specific fashion. The proposed method enables a better understanding of the biomechanical behavior of spinal structures and has the potential to become a standard tool in preoperative planning.