Simple batch processing for forming high-reflective mirrors ofshort-cavity AlGaAs/GaAs lasers

A simple technology for fabricating a short-cavity AlGaAs/GaAs laser with a high-reflective mirror that is compatible with batch processing is described. Chlorine-assisted ion beam etching was used for providing one of the facet reflectors. For increased reflectivity, the etched facet was anodized and then metallized simultaneously with the p-contact metallization step. A threshold current of 8 mA for a six-quantum-well separate confinement structure was achieved with a cavity length of 50 μm     

On Sequencing Retrievals In An Automated Storage/Retrieval System

This paper addresses throughput improvement by retrieval sequencing in conventional unit load automated storage/retrieval systems when several retrieval requests are available and dual command cycles are performed. Taking first-come-first-served as the reference sequencing rule, the potential for improvement is identified. A “nearest-neighbor” sequencing rule is proposed as an alternative, an analytic model for its expected performance is developed, and Monte Carlo simulation is used for evaluation. In addition, a lower bound on dual command cycle times is developed, and the dynamic behavior of two heuristic sequencing rules is discussed.     

Bit and Power Loading for Coherent Optical OFDM

We show the first experiment of bit and power loading for coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) systems. The data rate of CO-OFDM systems can be dynamically adjusted according to the channel condition. The system performance can be further improved through optimal power loading into each modulation band.     

Specific interactions in miscible polymer blends of poly(2‐hydroxypropyl methacrylate) with polyvinylpyrrolidone

The miscibility behaviour and hydrogen‐bonding interaction in blends of poly(2‐hydroxypropyl methacrylate) (PHPMA) with polyvinylpyrrolidone (PVP) were characterized using differential scanning calorimetry and Fourier‐transform infrared spectra. This polymer blend was miscible over the whole composition range and an unusually large positive deviation of T_g from the linearity rule was observed, indicating strong hydrogen bonding between the hydroxyl group of PHPMA and the carbonyl group of PVP. Infrared spectroscopic analysis provided positive evidence for the intra‐molecular hydrogen bonding of PHPMA and inter‐molecular hydrogen bonding between PHPMA and PVP at various compositions and temperatures. Furthermore, equilibrium constants and enthalpies of self‐association and inter‐association between functional groups in the blend of PHPMA and PVP were calculated to explain the results. Copyright © 2004 Society of Chemical Industry     

Secure encrypted-data aggregation for wireless sensor networks

This paper proposes a secure encrypted-data aggregation scheme for wireless sensor networks. Our design for data aggregation eliminates redundant sensor readings without using encryption and maintains data secrecy and privacy during transmission. Conventional aggregation functions operate when readings are received in plaintext. If readings are encrypted, aggregation requires decryption creating extra overhead and key management issues. In contrast to conventional schemes, our proposed scheme provides security and privacy, and duplicate instances of original readings will be aggregated into a single packet. Our scheme is resilient to known-plaintext attacks, chosen-plaintext attacks, ciphertext-only attacks and man-in-the-middle attacks. Our experiments show that our proposed aggregation method significantly reduces communication overhead and can be practically implemented in on-the-shelf sensor platforms.     

Evaluation of the antioxidant activity of Ruellia tuberosa

The antioxidant activity of Ruellia tuberosa L. (Acanthaceae) was investigated by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical-scavenging assay and the hydrogen peroxide-induced luminol chemiluminescence assay. The methanolic extract (ME) and its four fractions of water (WtF), ethyl acetate (EaF), chloroform (CfF), and n-hexane (HxF) were prepared and then subjected to antioxidant evaluation. The results of both methods revealed that R. tuberosa possesses potent antioxidant activity. The antioxidant activities of the different fractions tested decreased in the order of EaF > CfF > ME > WtF > HxF according to the hydrogen peroxide-induced luminol chemiluminescence assay, and results were the same with the exception of the rank order of HxF and WtF according to the DPPH free radical-scavenging assay. The results provide useful information on the pharmacological activities associated with free radicals of this traditional folk remedy.     

Stress paths and mechanical behavior of a sandstone in hollow cylinder tests

A series of hollow cylindrical triaxial tests was performed to investigate the potential effect of stress paths on the mechanical behavior of the Pei-Tou sandstone. The tests were carried out with a computer-controlled loading system. The axial loading, outer and inner confining pressures, and torque applied to the specimen were controlled according to a preselected stress path. The stress path moved from the hydrostatic stress axis in principal-stress space and elongated on an octahedral plane, while maintaining a constant angle θ against the projection of the major principal stress axis on the octahedral plane. The proposed hollow cylinder test is shown to be able to follow any designed stress paths in the principal stress space. Thus, it may be used to investigate the effect of stress paths on the mechanical behavior of rock and to construct its failure surface.     

The dual-edge alignment technique with improved spur reduction effects in ring oscillators

In this paper, the technique of dual-edge phase-alignment and its effects on ring oscillators are presented. This technique provides resetting of the built-up jitter at both rising and falling edges of a clean aligning signal named as the reference. Using signals and systems theory, the effect of the technique on the spurs due to the aligning reference signal is completely analyzed. We show that adding properly the dual-edge aligning feature to phase-aligned ring oscillators cause the spurs in the neighborhood of the carrier to disappear. First, the validity of the results obtained from the derived analytical equations is verified through simulations using MATLAB. Then a complete circuit considering realistic models for its components is simulated in TSMC RF CMOS 0.18um process using ADS for further validation.     

Study of aerodynamical interference for a wind turbine

A two-dimensional interference model of upwind wind turbine, based on NREL Phase VI, was simulated by an available Navier–Stokes solver under parallel process. The simulation domain was divided into a stationary tower domain and a sliding blade domain with varying geometric factors, including blade chord to tower diameter ratio and tower-blade gap to tower diameter ratio, to figure out the unsteady problem. The turbulence model was treated with SST k–ω turbulence model and the boundary layers around the solid walls were refined by the y⁺ value. The simulated results of velocity field were compared with the potential cylinder flow, and some phenomena were exhibited, including the movement of stagnation point of tower, the skewed wake of tower and the excess of velocity in the field. The lift force coefficient of blade was different from the ideal angle of attack for the blade passing in front of the potential cylinder flow.     

An application of the Beckmann-Ingene argument to a monopsonist's spatial pricing problem

The purpose of this note is to show that an analogue of the Beckmann-Ingene proposition on price policies of a spatial monopolist applies to a properly formulated profit maximization problem for a spatial monopsonist. The proof of this fact uses the same linear transformation employed in the Beckmann-Ingene argument. Received: 15 October 1998 / Accepted: 9 January 1999