Quantum transport in graphene nanonetworks

The quantum transport properties of graphene nanoribbon networks are investigated using first-principles calculations based on density functional theory. Focusing on systems that can be experimentally realized with existing techniques, both in-plane conductance in interconnected graphene nanoribbons and tunneling conductance in out-of-plane nanoribbon intersections were studied. The characteristics of the ab initio electronic transport through in-plane nanoribbon cross-points is found to be in agreement with results obtained with semiempirical approaches. Both simulations confirm the possibility of designing graphene nanoribbon-based networks capable of guiding electrons along desired and predetermined paths. In addition, some of these intersections exhibit different transmission probability for spin up and spin down electrons, suggesting the possible applications of such networks as spin filters. Furthermore, the electron transport properties of out-of-plane nanoribbon cross-points of realistic sizes are described using a combination of first-principles and tight-binding approaches. The stacking angle between individual sheets is found to play a central role in dictating the electronic transmission probability within the networks.     

Fluorescence from nano-particle doped optical fibres

The fabrication of microstructured polymer optical fibre with embedded organo-silica nano-particles and quantum dots is reported. Measurements of their in-fibre fluorescence spectra are presented.     

Lifetime RC time delay of on-chip copper interconnect

Increasing resistance and RC time delay induced by an oxidation in a copper line during its lifetime may limit copper-based metallization for technologies with critical dimension. Based on the mechanisms of resistance, constriction resistance and material diffusion, two dynamic models to access lifetime behavior of resistance and RC time delay were developed and discussed. These models also provide a means to gain insight into the correlation between the resistance and RC time delay of copper interconnect and such key variables as feature dimension, operating condition, and oxidation     

Gaussian approximations of fluorescence microscope point-spread function models

We comprehensively study the least-squares Gaussian approximations of the diffraction-limited 2D-3D paraxial-nonparaxial point-spread functions (PSFs) of the wide field fluorescence microscope (WFFM), the laser scanning confocal microscope (LSCM), and the disk scanning confocal microscope (DSCM). The PSFs are expressed using the Debye integral. Under an L(infinity) constraint imposing peak matching, optimal and near-optimal Gaussian parameters are derived for the PSFs. With an L1 constraint imposing energy conservation, an optimal Gaussian parameter is derived for the 2D paraxial WFFM PSF. We found that (1) the 2D approximations are all very accurate; (2) no accurate Gaussian approximation exists for 3D WFFM PSFs; and (3) with typical pinhole sizes, the 3D approximations are accurate for the DSCM and nearly perfect for the LSCM. All the Gaussian parameters derived in this study are in explicit analytical form, allowing their direct use in practical applications.     

Generalized higher-order nonlinear energy operators

We extend and generalize the Teager-Kaiser [in Proceedings of IEEE International Conference on Acoustics, Speech, and Signal Processing (1993), Vol. 3, p. 149] and the higher-order differential energy operators [IEEE Signal Process. Lett.2, 152 (1995)] to a large class of operators called higher-order energy operators. We show that for AM-FM signal demodulation, the introduced partial derivative orders have to satisfy certain conditions. These operators are parameterized for local processing of AM-FM signals. The operators are illustrated using synthetic signals and a real signal from light scanning interferometry.     

Photoinduced Fluidity and Viscoelasticity in Chalcogenide Glasses

This work is an attempt to apply conventional mechanical testing to characterize the photoinduced viscoelastic behavior of chalcogenide glasses. Creep or relaxation-recovery experiments are usually performed to characterize the delayed elastic contribution to deformation, during thermally activated flow. In this article, relaxation-recovery is used to characterize delayed elasticity under irradiation condition and to investigate the influence of the photon irradiation on the viscoelastic behavior. It is showed that thermally activated processes and photoinduced ones are decoupled. The viscoplastic deformation under irradiation is the sum of thermally activated and photoinduced processes. As soon as the irradiation ceases, chalcogenide glasses behave exactly as if they had never been irradiated. The photoinduced viscoelastic behavior seems to be solely due to transient photoinduced structural defects.     

Cold-set whey protein microgels for the stable immobilization of lipids

Novel sub-millimeter cold-set whey protein isolate (WPI) microgels for the stable immobilization of lipids were prepared by an emulsification/internal gelation technique. Microgels were prepared by the addition of a denatured WPI/lipid primary emulsion (containing a micronized calcium source) into an oil bath with gentle stirring, into which an oil soluble acid was added to liberate calcium and initiate gelling of the whey-based matrices. The efficiency of these matrices to entrap lipids was assessed by comparing to extrusion/externally gelled matrices, where the production process is potentially less destructive, but microgels under 1 mm in diameter are difficult to achieve. The micron-sized (below 100 μm in diameter) internally gelled matrices produced by an optimized process, successfully immobilized incorporated lipids, with greater than 93% retention of lipids, regardless of the investigated manufacturing conditions. Migration of exterior oil, during the O/W/O production process, into the microgels was also avoided. Examination of the micro-structure by scanning electron microscopy revealed voids uniformly distributed throughout the matrix, representative in size (under 0.4 μm) of the original primary emulsion lipid droplets. The study shows relevant feasibility for the stable inclusion of a wide range of sensitive lipophilic bioactive ingredients into these matrices, where the sub-millimeter size of the microgels represents potential for incorporation into a variety of food systems.     

Compression dewatering of municipal activated sludge: effects of salt and pH

Even after mechanical dewatering, activated sludge contains a large amount of water. Due to its composition and biological nature this material is usually highly compressible and known to be difficult to dewater. In the present work, two treatments (salt addition and pH modification) are proposed to highlight some aspects which could explain the poor dewaterability of activated sludge. Dewatering tests are carried out in a pressure-driven device in order to well examine both, filtration and compression stages. Physico-chemical parameters, such as surface charge, hydrophobicity, extracellular polymeric substances (EPS) content and filtrate turbidity are measured on the tested sludge, for a better analysis of dewatering results.The dewatering ability of the sludge is widely linked to the cohesion of the flocculated matrix and the presence of fine particles. Both treatments alter the flocculated matrix and release fine particles. The release of fine particles tends to clog both, the filter cake and the filter medium. Consequently, the filtration rate decreases due to higher resistances to the flow. On another hand, the polymeric matrix breakdown enables to release some water trapped within the floc to the bulk liquid phase and thus facilitates its removal, which tends to decrease the moisture content of the filter-cake. It also impacts the compression dewatering step. The more destroyed structures lead to less elastic cakes and thus a slower primary consolidation stage. At the opposite, the mobility of the broken aggregates within the filter-cake does not seem to be improved by size reduction (the kinetics of the secondary consolidation stage are not significantly modified).     

Highly defective graphene: A key prototype of two-dimensional Anderson insulators

Electronic structure and transport properties of highly defective two-dimensional (2D) sp² graphene are investigated theoretically. Classical molecular dynamics are used to generate large graphene planes containing a considerable amount of defects. Then, a tight-binding Hamiltonian validated by ab initio calculations is constructed in order to compute quantum transport within a real-space order-N Kubo-Greenwood approach. In contrast to pristine graphene, the highly defective sp² carbon sheets exhibit a high density of states at the charge neutrality point raising challenging questions concerning the electronic transport of associated charge carriers. The analysis of the electronic wavepacket dynamics actually reveals extremely strong multiple scattering effects giving rise to mean free paths as low as 1 nm and localization phenomena. Consequently, highly defective graphene is envisioned as a remarkable prototype of 2D Anderson insulating materials.