High-performance 850 nm vertical-cavity surface-emitting laser in Gigabit Ethernet network

High-performance oxide vertical-cavity surface-emitting (VCSEL) laser is fabricated, and its usefulness is demonstrated as a suitable transmitting light source at 850 nm operating wavelength for Gigabit Ethernet application. Utilization of barrier reduction layers reveals low-threshold current requirement for operation at high modulation bandwidth. The electrical and optical characteristics, measured from the fabricated VCSEL, are simulated for Gigabit Ethernet transmission. Data rates of 1.25 Gbps with a bit error rate of 10⁻¹¹ are achieved by the use of a specific multimode network simulator.     

Effect of mordenite dealumination on the structure of encapsulated molybdenum catalysts

A series of dealuminated mordenites treated under various conditions of acid leaching was impregnated in an aqueous solution of ammonium heptamolybdate to achieve a loading of 12 wt% Mo. These samples were characterized by XRD, UV-DRS, N(2) adsorption, TGA, and FTIR techniques. Special attention was given to the far-IR measurements and IR study of surface hydroxyl groups before and after dealumination. A polymolybdate species was recognized by the appearance of bands at 344, 319, and 236 (229) cm(-1) due to the vibrational modes of delta(Mo-O) and delta(Mo-O-Mo), respectively. The disappearance of the 236 cm(-1) band as well as that at 344 cm(-1) in favor of the 319 cm(-1) band, with the dealumination, was related to the high dispersion of Mo species in the produced mesopore surface assessed by the N(2) adsorption at 77 K. No bands due to bulk MoO(3) were detected from the IR and XRD results. A strong interaction between Mo species and dealuminated mordenite surfaces (OH groups) was recognized by a decrease in intensity and a marked shift of the band at 3745 to 3727 cm(-1) as well as the appearance of a new band at 3668 cm(-1). The latter band was produced by the interaction of the framework Al-OH with Mo species. The BET surface areas of Mo-dealuminated mordenite samples were higher than the corresponding Mo-free ones. The diffuse reflectance measurements suggested that Mo cations are predominantly present as an octahedrally coordinated Mo(6+), along with some tetrahedral Mo(6+). New spectral features as a consequence of dealumination events in the far-IR range were evaluated and discussed.     

On the convergence of a class of algorithms using linearly independent search directions

Powell has shown that the cyclic coordinate method with exact searches may not converge to a stationary point. In this note we consider a more general class of algorithms for unconstrained minimization, and establish their convergence under the assumption that the objective function has a unique minimum along any line.     

An algorithm for linearly constrained nonlinear programming problems

In this paper an algorithm for solving a linearly constrained nonlinear programming problem is developed. Given a feasible point, a correction vector is computed by solving a least distance programming problem over a polyhedral cone defined in terms of the gradients of the “almost” binding constraints. Mukai's approximate scheme for computing the step size is generalized to handle the constraints. This scheme provides an estimate for the step size based on a quadratic approximation of the function. This estimate is used in conjunction with Armijo line search to calculate a new point. It is shown that each accumulation point is a Kuhn-Tucker point to a slight perturbation of the original problem. Furthermore, under suitable second order optimality conditions, it is shown that eventually only one trial is needed to compute the step size.     

Electrical and chemical characteristics of nano-meter gold encapsulated in mesoporous and microporous channels and cages of FSM-16 and Y zeolites

The dc and ac conductivities as well as the dielectric constant () were measured for different zeolites encapsulated gold (AuCl₃) samples at different temperatures (300-500 K) and various frequencies (5 kHz-1 MHz). The conductivity was found to change in the order Au/FSM-27>Au/NaY>Au/FSM-47. Sorbed water contained inside zeolites assists greatly the proton mobility (zeolite protons) and the ion mobility (Na⁺ and Au⁺) and hence enhance the electric conduction in the temperature range 300-373 K. Raising the temperature over 373 K induces dehydration effect that assists the metallic gold formation and thus a dramatic loss in conductivity was revealed. The conduction mechanism was expected to be partially ionic and partially electronic. The IR study showed that the exposure of Au zeolites to CO gas produced a characteristic band of Au⁺-CO at 2180 cm⁻¹ that tends to decrease with temperatures and even vanishes at 376 K in favor of Au⁰-CO at 2128 cm⁻¹. Similarly, a phase transition at 338 K, that occurs in the range 300-376 K, was confirmed by DTA to further emphasize the temperature regions of either Au⁺ cations (338 K) or Au⁰ (376 K) formation.     

Synthesis of a cyclic peptide containing norlanthionine: effect of the thioether bridge on peptide conformation

Two diastereomeric analogues of ring C of nisin incorporating a novel norlanthionine residue have been synthesized via a triply orthogonal protecting group strategy. A full structural study was carried out by NMR, which elucidated the conformational properties of the two peptides and enabled the identity of each diastereoisomer to be proposed.     

Effect of Li2O and CoO-doping of CuO/Fe2O3 system on its surface and catalytic properties

Physicochemical, surface and catalytic properties of pure and doped CuO/Fe₂O₃ system were investigated using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), nitrogen adsorption at −196 °C and CO-oxidation by O₂ at 80-220 °C using a static method. The dopants were Li₂O (2.5 mol%) and CoO (2.5 and 5 mol%). The results revealed that the increase in precalcination temperature from 400 to 600 °C and Li₂O-doping of CuO/Fe₂O₃ system enhanced CuFe₂O₄ formation. However, heating both pure and doped solids at 600 °C did not lead to complete conversion of reacting oxides into CuFe₂O₄. The promotion effect of Li₂O dopant was attributed to dissolution of some of dopant ions in the lattices of CuO and Fe₂O₃ with subsequent increase in the mobility of reacting cations. CoO-doping led also to the formation of mixed ferrite Co_xCu_1−xFe₂O₄. The doping process of the system investigated decreased to a large extent the crystallite size of unreacted portion of Fe₂O₃ in mixed solids calcined at 600 °C. This process led to a significant increase in the S_BET of the treated solids. Doping CuO/Fe₂O₃ system with either Li₂O or CoO, followed by calcination at 400 and 600 °C decreased its catalytic activity in CO-oxidation by O₂. However, the activation energy of the catalyzed reaction was not much affected by doping.     

Neural networks for Nyquist plots prediction in a nanocomposite polymer electrolyte (PEO–LiPF<Subscript>6</Subscript>–EC–CNT)

In this study, the Nyquist plots for nanocomposite polymer electrolyte system (polyethylene oxide (PEO)–lithium hexafluorophosphate (LiPF₆)–ethylene carbonate (EC)–carbon nanotube (CNT)), which was produced by using solution cast technique, were obtained using Bayesian neural network. First, to prepare the training and test set of the network, some results were experimental obtained and recorded. In the experiment, PEO, LiPF₆, EC, and CNT were mixed at various ratios. The effects of the chemical composition on the impedance spectra of polymer electrolyte system were investigated. In neural network training, different chemical composition and real impedance were used as inputs and imaginary impedance in the produced polymer electrolytes was used as outputs. After the training process, the test data were used to check system accuracy. As a result, the neural network was found successful for the prediction of imaginary impedance of nanocomposite polymer electrolyte system.     

Silver nanoparticles supported on ionic‐tagged magnetic hydroxyapatite as a highly efficient and reusable nanocatalyst for hydrogenation of nitroarenes in water

A novel chemically modified magnetic hydroxyapatite (MHAp) was prepared and used as support and stabilizer for the synthesis of silver nanoparticles. First, 1,4‐diazabicyclo[2.2.2]octane (DABCO) was successfully grafted onto the surface of MHAp, and then silver nanoparticles were homogeneously loaded on mesoporous MHAp‐DABCO (ionic‐tagged MHAp) nanocomposite by in situ chemical reduction of silver nitrate using sodium borohydride. The structure and properties of the resulting MHAp‐DABCO‐Ag nanocomposite were confirmed using various techniques. The catalytic activity of ionic‐tagged MHAp‐Ag nanocatalyst was investigated for the hydrogenation reaction of nitroarenes in aqueous media. The results reveal that the Ag‐containing inorganic–organic nanocomposite is highly efficient for the reduction of a wide range of aromatic nitro compounds under green conditions. The superparamagnetic nature of the nanocatalyst leads to its being readily removed from solution via application of a magnetic field, and it can be easily stored and reused.