Transport and Quantum Coherence in Graphene Rings: Aharonov–Bohm Oscillations,Klein Tunneling,and Particle Localization

Simulating quantum transport through mesoscopic, ring-shaped graphene structures, we address various quantum coherence and interference phenomena. First, a perpendicular magnetic field, penetrating the graphene ring, gives rise to Aharonov–Bohm oscillations in the conductance as a function of the magnetic flux, on top of the universal conductance fluctuations. At very high fluxes, the interference gets suppressed and quantum Hall edge channels develop. Second, applying an electrostatic potential to one of the ring arms, \(nn'n\)- or npn-junctions can be realized with particle transmission due to normal tunneling or Klein tunneling. In the latter case, the Aharonov–Bohm oscillations weaken for smooth barriers. Third, if potential disorder comes in to play, both Aharonov–Bohm and Klein tunneling effects rate down, up to the point where particle localization sets in.     

Macroscopic simulation and experimental measurement of melt pool characteristics in selective electron beam melting of Ti-6Al-4V

Selective electron beam melting of Ti-6Al-4V is a promising additive manufacturing process to produce complex parts layer-by-layer additively. The quality and dimensional accuracy of the produced parts depend on various process parameters and their interactions. In the present contribution, the lifetime, width and depth of the pools of molten powder material are analyzed for different beam powers, scan speeds and line energies in experiments and simulations. In the experiments, thin-walled structures are built with an ARCAM AB A2 selective electron beam melting machine and for the simulations a thermal finite element simulation tool is used, which is developed by the authors to simulate the temperature distribution in the selective electron beam melting process. The experimental and numerical results are compared and a good agreement is observed. The lifetime of the melt pool increases linearly with the line energy, whereby the melt pool dimensions show a nonlinear relation with the line energy.     

The association of plasma IL-6 levels with functional disability in community-dwelling elderly

BACKGROUND: IL-6 is a multifunctional cytokine that has been shown to increase with age. METHODS: Plasma IL-6 was measured by ELISA in 1,727 community-dwelling elderly subjects whose blood was drawn during the third in-person survey of the Duke Established Populations for Epidemiologic Studies of the Elderly (EPESE). Demographics, functional status (disability), and disease states were determined. Correlations of these factors with IL-6 were analyzed with Spearman's Rho while differences between groups were assessed by Wilcoxon test. RESULTS: IL-6 levels were higher with age (p = .0001) even in this older population (> 70 years). There was a positive correlation between IL-6 and functional disability for each of the functional status measures (p = .0001), as well as a correlation between self-rated health and IL-6. Significantly higher median levels of IL-6 were found in subjects reporting prevalent cancer, heart attack, and high blood pressure, but not diabetes or arthritis. The association between age and functional status with high IL-6 remained when all other variables were controlled, in multivariable analysis. CONCLUSIONS: This association between increased plasma IL-6 levels and functional status suggests that dysregulation of IL-6 may be related to the functional disability seen with aging, and that IL-6 may be useful as a component of an overall marker of health.     

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Mobility of nanosized cerium dioxide and polymeric capsules in quartz and loamy sands saturated with model and natural groundwaters

The environmental and health risks posed by emerging engineered nanoparticles (ENPs) released into aquatic environments are largely dependent on their aggregation, transport, and deposition behavior. Herein, laboratory-scale columns were used to examine the mobility of polyacrylic acid (PAA)-coated cerium dioxide nanoparticles (nCeO₂) and an analogous nanosized polymeric capsule (nCAP) in water saturated quartz sand or loamy sand. The influence of solution ionic strength (IS) and cation type (Na⁺, Ca²⁺, or Mg²⁺) on the transport potential of these ENPs was examined in both granular matrices and results were also compared to measurements obtained using a natural groundwater. ENP suspensions were characterized using dynamic light scattering and nanoparticle tracking analysis to establish aggregate size, and laser Doppler electrophoresis to determine ENP electrophoretic mobility. Regardless of IS, virtually all nCeO₂ particles suspended in NaNO₃ eluted from the quartz sand-packed columns. In contrast, heightened nCeO₂ and nCAP particle retention and dynamic (time-dependent) transport behavior was observed with increasing concentrations of the divalent salts and in the presence of natural groundwater. Enhanced particle retention was also observed in loamy sand in comparison to the quartz sand, emphasizing the need to consider the nature of the aqueous matrix and granular medium in evaluating contamination risks associated with the release of ENPs in natural and engineered aquatic environments.     

The insulting Internet: universal access and cyberbullying

Universal Access in the Information Society - With the growing popularity of online communication, a certain harassment can be observed to increasingly disavow the positive implications of an...     

Rheological properties and irreversible dispersion changes in carbon nanotube/epoxy systems

We report on the rheological properties of semidilute carbon nanotube (CNT)/epoxy suspensions with varying filler content prepared with different dispersion methods. We show that dispersion techniques can be distinguished by means of the rheological response. It was found that the suspensions undergo a lasting dispersion changes during the first shear sweep measurement. Shear‐induced changes within the suspension can also be visualized optically. Our results demonstrate that the rheological properties are strongly influenced by the measurement procedure, which has to be known in order to guarantee reproducible and comparable results. Finally, it does not seem possible to completely reset the sample history by shear treatment. POLYM. ENG. SCI., 2011. ©2011 Society of Plastics Engineers     

Furan in heat‐treated foods: Formation,exposure, toxicity,and aspects of risk assessment

Furan is formed in a variety of heat‐treated foods through thermal degradation of natural food constituents. Relatively high levels of furan contamination are found in ground roasted coffee, instant coffee, and processed baby foods. European exposure estimates suggest that mean dietary exposure to furan may be as high as 1.23 and 1.01 μg/kg bw/day for adults and 3‐ to 12‐month‐old infants, respectively. Furan is a potent hepatotoxin and hepatocarcinogen in rodents, causing hepatocellular adenomas and carcinomas in rats and mice, and high incidences of cholangiocarcinomas in rats at doses ≥2 mg/kg bw. There is therefore a relatively low margin of exposure between estimated human exposure and doses that cause a high tumor incidence in rodents. Since a genotoxic mode of action cannot be excluded for furan‐induced tumor formation, the present exposures may indicate a risk to human health and need for mitigation. This review summarizes the current knowledge on mechanisms of furan formation in food, human dietary exposure to furan, and furan toxicity, and highlights the need to establish the risk resulting from the genotoxic and carcinogenic properties of furan at doses lower than 2 mg/kg bw.     

Organization of knowledge about a relationship partner: Implications for liking and loving.

In close relationships, the association between negative beliefs about a partner and loving was found to be moderated by how that negative knowledge was organized. In general, evaluatively integrative organization (i.e., categorizing positive and negative beliefs together) was associated with more positive thoughts, feelings, and behaviors toward the partner when the negative content of beliefs was high and relationships were relatively long. Additional evidence suggests that compartmentalization (i.e., organizing positive and negative beliefs in separate categories) may be an effective strategy for handling negative beliefs about a partner in a new relationship. Findings for behavioral closeness raise the possibility that the nature of shared activities, as well as an individual's cognitive processes, may influence how knowledge about a relationship partner is organized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigating the prospects of bacterial biosurfactants for metal nanoparticle synthesis – a comprehensive review

Establishing biological synthesis of nanoparticles is increasing nowadays in the field of nanotechnology. The search for an optimal source with durability, stability, capacity to withstand higher environmental conditions with excellent characteristics is yet to meet. Consequently, there is need to create an eco‐friendly strategy for metal nanoparticle synthesis. One approach investigated in this review is the use of biosurfactants to enhance the synthesis biologically. In comparison with the other technologies, biosurfactants are less toxic and exhibit higher properties. This method is different from the conventional practice like physical and chemical methods. Several research studies represented that the biosurfactant influences the production of nanoparticles about 2–50 nm. In this manner, the research towards the biosurfactant has raised. This review also addressed the feasibility of biosurfactant and their benefits in the synthesis of metallic nanoparticles. The findings from this review can recommend a conceivable use of biosurfactant as a source for metal nanoparticle synthesis.Inspec keywords: nanoparticles, microorganisms, nanotechnology, biotechnology, nanofabrication, durability, surfactants, reviewsOther keywords: biological synthesis, bacterial biosurfactants, environmental conditions, metallic nanoparticles synthesis, nanotechnology, durability, review, stability, size 2.0 nm to 50.0 nm