A 1 × 2 optical switch using one multimode interference region

A 1 × 2 optical switch using only one multimode interference (MMI) region is designed and demonstrated in GaAs/AlGaAs. This design makes a single MMI region works as MMI coupler using paired interference at “off” state and symmetric interference at “on” state. By injecting a current of 110 mA, the measured on/off ratio and crosstalk are 23 dB and 33 dB, respectively in the demonstrated device with GaAs/GaAlAs.     

Electron emission studies of CNTs grown on Ti and Ni containing amorphous carbon nanocomposite films

Carbon nanotubes (CNTs) were grown successfully on the as-deposited dual metal (Ti and Ni) embedded films using a radio frequency plasma-enhanced chemical vapor deposition system. The microstructure of CNTs grown on the dual metal films proved to be heavily dependent on the percentages of metals included, varying both in size and in density. Electron emission tests carried out on the films with CNTs grown showed that the threshold field was dependent on the surface morphology of the CNTs, with the lowest threshold field at 3.5 V/μm from 2.5% Ti/Ni film with CNTs. The field enhancement factor, β, of the emitting tips was also calculated from the Fowler–Nordheim plots, where CNTs from the 2.5% Ti/Ni film gave the highest field enhancement factor. However, it was observed that films with a single metal of either Ti or Ni did not manage to grow CNTs, possibly due to a lack of catalyst centres at the surface of the films. It was believed that the Ni nanoclusters acted as catalysts centres giving a rather uniform but randomly orientated type of CNTs. Results obtained pointed that the fabricated nanocomposite material could be a possible choice for cold cathode emitters and the Ti/Ni mixture could be an effective composite for controlling the CNT density.     

Halogen‐Bonding‐Induced Conjugate Addition of Thiophenes to Enones and Enals

Herein, we report the conjugate addition of α,β‐unsaturated carbonyl compounds to thiophene derivatives. We used a 2‐iodoimidazolinium triflate salt as a halogen‐bonding donor, which afforded moderate‐to‐excellent yields of the corresponding alkylated thiophenes. Insight into the catalytic process was obtained from ¹H NMR spectroscopy studies and DFT calculations, which indicated a halogen‐bonding‐supported mechanism with limited Brønsted acid catalysis.     

Analytic Center Cutting-Plane Method with Deep Cuts for Semidefinite Feasibility Problems

An analytic center cutting-plane method with deep cuts for semidefinite feasibility problems is presented. Our objective in these problems is to find a point in a nonempty bounded convex set in the cone of symmetric positive-semidefinite matrices. The cutting plane method achieves this by the following iterative scheme. At each iteration, a query point that is an approximate analytic center of the current working set is chosen. We assume that there exists an oracle which either confirms that or returns a cut A S ^m {YS ^m : AY AY - } , where 0. If , an approximate analytic center of the new working set, defined by adding the new cut to the preceding working set, is then computed via a primal Newton procedure. Assuming that contains a ball with radius > 0, the algorithm obtains eventually a point in , with a worst-case complexity of O ^*(m ³/²) on the total number of cuts generated.     

Electroluminescence model of bipolar resonant tunnelling diode

An electroluminescence model of a bipolar resonant tunnelling diode is carried out. The current is the sum of the electron and hole current. The electron and hole density at the resonant level of a quantum well are related to the electron and hole current, respectively. A radiative recombination rate formula is derived from the matrix element, electron and hole distribution. The results show that a large on-off ratio of light output can be achieved by the bipolar resonant tunnelling diode.     

A classification scheme for the light-current (L/I) characteristics of a two photon mode semiconductor laser

The behaviour of a semiconductor laser in which two photon modes exist above threshold is analysed using the rate equations. This paper classifies the different qualitative behaviour of mode competition by using a single parameterγ. The simplified analysis, neglecting electronic diffusion is sufficient to explain the experimentalL/I characteristics of weak and strong polarization in semiconductor lasers which were previously treated theoretically using a power distribution model.     

Anti-tack action of polyvinylpyrrolidone on hydroxypropylmethylcellulose solution

The anti-tack action of polyvinylpyrrolidone (PVP) on hydroxypropylmethylcellulose (HPMC) solution was elucidated using a probe test method. The influence of PVP of varying molecular weights at various PVP concentrations and solution temperatures on the tackiness of HPMC solution was studied. The viscosity, surface tension, cloud point and solution spectroscopy of HPMC solutions and glass transition temperature of HPMC films, with and without PVP, were investigated. The tackiness of HPMC solutions in response to the addition of PVP, at different concentrations of HPMC and using HPMC with varying contents of hydroxypropyl/methoxyl substitution, was also evaluated. PVP is a commonly used binder and adhesive. However, it reduced the tack of the HPMC solution when used at low concentrations, without affecting the state of hydration of HPMC. Lower molecular weight PVP was more effective as an anti-tack agent owing to suitable hydrodynamic size to intersperse among the HPMC chains. The degree of reduction in tack values was more pronounced for HPMC that showed a greater extent of interaction between polymer chains such as when high concentration of HPMC or low solution temperature was employed. This indicated that the tack reduction property of PVP relied on its ability to interact with the HPMC chains. The profile of reduction in tack values was affected by the contents of HPMC substitution and was a result of net reduction in the extent of hydrogen bonding between HPMC chains. It was significantly correlated to the changes of viscosity and surface tension of the HPMC solutions but not to the glass transition temperatures of the polymers prepared as solid films. The results suggested that the anti-tack action of PVP was attributed to its ability to interact with HPMC chains in the aqueous medium and consequently to reduce the extent of HPMC-HPMC bonding.     

Biosorption and desorption of copper (II) ions by Bacillus sp.

Batch biosorption experiments were conducted to investigate the removal of Cu²⁺ ions from aqueous solutions by a series of bacterial strains isolated from a local activated sludge process. The characteristics of 12 isolates were identified and examined for their ability to bind Cu²⁺ ions from aqueous solution. Among the isolates, two species exhibited biosorption capacity >40 mg of Cu/g of dry cell. Isotherms for the biosorption of copper on bacterial cells were developed and compared, and the equilibrium data fitted well to the Langmuir and Freundlich isotherm models. The biosorption of copper increased significantly with increasing pH from 2.0 to 6.0 regardless of the species. More than 90% of copper sorbed on the cells of Bacillus sp. could be recovered by washing with 0.1 M HNO₃ for 5 min. The performance of two different desorption processes was also tested and compared. The results show that five biosorption and desorption cycles are a better operation process than five successive biosorptions followed by one desorption to remove and recover copper from aqueous solution. The biosorbent could be used for at least five biosorptions and desorption cycles without loss of copper removal capacity. It can be concluded that the activated sludge or sludge-isolated bacteria could be a potential biosorbent for copper removal.