Voltammetric and Scanning Electrochemical Microscopic Studies of the Adsorption Kinetics and Self-Assembly of n-Alkanethiol Monolayers on Gold

The adsorption kinetics and self-assembly of hexadecyl mercaptan on gold have been investigated by scanning electrochemical microscopy (SECM), chronoamperometry, and cyclic voltammetry. The developed methodology allows one to evaluate the surface coverage and the average size of the defects in the monolayer film from the effective rate constant of electron transfer. Two kinetic regimes of self-assembly were identified: a rapid initial adsorption of hexadecyl mercaptan onto a clean gold surface from 5 mM solution (more than 90% coverage obtained in 1 to 5 min), and a slower subsequent annealing of a thiol monolayer resulting in a more compact film. Typically, a long-chain-length thiol-treated gold surface acts as an electronically insulating surface after about 1 h. The SECM images of partially covered gold surfaces were always featureless, suggesting that the defects in the film were smaller than 0.5 μm for any exposure time ≥ 1 min.     

Sol-gel multimode interference power splitters

We report on the design and fabrication of 1×32 MMI power splitters through the sol-gel process. The MMI splitter is designed for 1.55-μm wavelength and characterized in terms of tolerance, wavelength response, and polarization sensitivity. The splitter is then UV-imprinted in aluminosilicate material coated on SiO₂. It is found that the responses of fabricated and designed splitter are in good agreement, with an excess loss of ~0.75 dB and power uniformity of ~0.95 dB     

Biodegradation of Medicinal Plants Waste in an Anaerobic Digestion Reactor for Biogas Production

Glycyrrhiza glabra, Mint, Cuminum cyminum, Lavender and Arctium medicinal are considered as edible plants with therapeutic properties and as medicinal plants in Iran. After extraction process of medicinal plants, residual wastes are not suitable for animal feed and are considered as waste and as an environmental threat. At present there is no proper management of waste of these plants and they are burned or buried. The present study discusses the possibility of biogas production from Glycyrrhiza Glabra Waste (GGW), Mentha Waste (MW), Cuminum Cyminum Waste (CCW), Lavender Waste (LW) and Arctium Waste (AW). 250 g of these plants with TS of 10% were digested in the batch type reactors at the temperature of 35°C. The highest biogas production rate were observed to be 13611 mL and 13471 mL for CCW and GGW (10% TS), respectively. While the maximum methane was related to GGW with a value of 9041 mL (10% TS). The highest specific biogas and methane production were related to CCW with value of 247.4 mL.(g.VS)-1 and 65.1 mL.(g.VS)-1, respectively. As an important result, it was obvious that in lignocellulose materials, it cannot be concluded that the materials with similar ratio of C/N has the similar digestion and biogas production ability.     

Microstructural evolution during fabrication of alumina via laser stereolithography technique

Application of additive manufacturing (AM) technology in production of ceramic parts is considered as a state-of-the-art technique which has been recently introduced to industry. In the current study the imperative microstructural characteristics of the alumina manufactured via laser stereolithography (SLA) has been investigated. The microstructural characteristics of the developed ceramic parts and components are still unknown and require detailed investigation. A combination of optical microscopy and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), image analysis, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM) and micro-computed tomography (micro-CT) scans was used to evaluate the microstructural features of the alumina samples after each step of the manufacturing process (i.e. printing, debinding and sintering). In addition, the apparent density of each sample was measured using water displacement method. Results indicated that the porosity of printed alumina samples was significantly reduced after sintering process. EDS analysis confirmed elimination of binder material after debinding and sintering processes. XRD analysis detected existence of α-Al₂O₃ in initial printed samples which was not changed during debinding and sintering processes. Due to detection of identical peaks for all samples, only one set of lattice parameters ($\mathrm{a}$ and $\mathrm{c}$) was calculated from XRD patterns of all samples which was close to the ones reported in literature for alumina. TEM micrographs and corresponding diffraction patterns confirmed polycrystalline structure from different layers of the samples. High resolution transmission electron microscopy (HRTEM) and diffraction patterns from single layers were used to calculate lattice parameters for each sample. A slight increase was noticed in unit cell and grain size after sintering process. The obtained results help for better understanding of the properties through microstructural characteristics of the 3D printed ceramic parts.     

Implementation of IEEE 802.16e Standard on Xilinx ZC706: A C-RAN Prototype

Wireless Personal Communications - In this paper, we propose an architecture to implement IEEE 802.16e transmitter and receiver physical (PHY) layer on field programmable gate arrays. Several...     

Numerical simulation of planar shear flow passing a rotating cylinder at low Reynolds numbers

Two-dimensional shear flow over a rotating circular cylinder is investigated using lattice Boltzmann method. Simulations are performed at a fixed blockage ratio (B = 0.1) while the Reynolds number, nondimensional shear rate (K) and absolute rotational speed range as 80 ≤ Re ≤ 180, 0 ≤ K ≤ 0.2 and −2 ≤ β ≤ 2, respectively. To verify the simulation, the results are compared to previous experimental and numerical data. Quantitative information about the flow variables such as drag and lift coefficients, pressure coefficient and vorticity distributions on the cylinders is highlighted. It is found that, generally, with the increment in |β|, the absolute value of time average lift coefficient increases and time average drag coefficient decreases, and beyond a certain magnitude of β, the vortex shedding vanishes. It is also revealed that the drag coefficient decreases as the Reynolds number increases while the effect of the Reynolds number on lift is almost negligible. At the end, correlations for drag and lift coefficients ([`(C<sub>D</sub> )] ,[`(C_L )]){(\overline {C_D } ,\overline {C_L })} are extracted from the numerical data.     

Hybrid sol-gel materials for integration of optoelectroniccomponents

We report on the integration of the Bragg filters with 1×8 multimode interference (MMI) power splitters on silicon substrate, and the demonstration of 1×8 external cavity distributed Bragg reflector (DBR) lasers. Hybrid organic-inorganic material is developed based on the sol-gel synthesis of an organically modified silicon alkoxide. The sol-gel material is spin coated on grating SiO₂-Si wafers, and the designed components (splitters and filters) are UV imprinted and developed using solvent assisted photolithography. The Bragg reflectors show filtering up to 98% with a bandwidth of about 0.8 nm consistent with their theoretical prediction. Integrated reflectors and MMI splitters are then used as feedback resonators for DBR lasers. Single-mode lasing with sidemode suppressions of up to 40 dB and a linewidth of about 400 kHz is observed. At 1550- nm wavelength, the loss and power uniformity in the MMI splitters, designed on the basis of lowest loss, are, respectively, 0.13 dB and 0.03 dB poorer than their theoretical calculations     

Microstructural Properties of Air Plasma Sprayed Coating Consisting of Tungsten Carbide and Yttria‐Stabilized Zirconia

Thermal Spraying technologies are proven to be capable of producing composite materials and structures. In the present work, an innovative composite coating was produced to achieve high wear and thermal resistant properties in a single‐step process using air plasma spraying (APS) technique. Tungsten carbide has shown high wear resistance and zirconia coatings exhibited excellent tribological and insulation properties. It is speculated that a composite material consisting of zirconia and tungsten carbide exhibits excellent thermomechanical properties. A powder mixture of 50wt% WC‐10wt% Ni (WC‐Ni) and 50wt% ZrO₂‐8wt% Y₂O₃ (YPSZ) was deposited on a low carbon steel substrate using APS technique. Important microstructural properties of WC‐Ni/YPSZ coating such as splat boundaries, pore and grain morphology, microcracks, phase composition, elemental distribution of coatings, and lattice parameters of the crystals were investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X‐ray (EDS), and X‐ray diffractometry (XRD). A good adhesion was observed between different phases in tungsten carbide mixed with zirconia coatings. Decarburization process which occurred during APS process resulted in formation of tungsten hemi‐carbide (W₂C) phase in plasma sprayed samples. The calculated crystal size for APS‐deposited coating was smaller than those of feedstock powder.     

Fabrication of ridge waveguides: a new solgel route

Passive ridge waveguides can be deposited on silicon by a solvent-assisted lithographic process incorporating simple mask technology and photosensitive solgel-derived glasses. Thick films (~4 mum) are dip coated in one step, and channel waveguides and power splitters are imprinted in them by UV light through appropriate masks. Unexposed regions of the glass are removed by soaking of the films in n-propanol. The remaining ridges are then treated at 200 degrees C and planarized with a solgel cladding layer. Circular mode profiles are observed from ridge guides covered with the cladding. The waveguides are characterized with scanning electron microscopy, atomic force microscopy, surface profilometry, ellipsometry, and fiber end coupling. Overall, the procedure is simple and reproducible and leads to waveguides with low loss, of the order of 0.13 dB/cm.