Dual-wavelength cascaded Raman fibre laser

Dual-wavelength lasing at 1480 and 1500 nm has been demonstrated from a cascaded Raman fibre laser with a WDM coupler and two pairs of Bragg gratings. Intensity-adjustable, wavelength-tunable laser operation was achieved by tensile stress wavelength tuning of the gratings     

Studies on the heating capacity control of a multi-type heat pump system applying a multi-input multi-output (MIMO) method

This paper describes a method to control capacity of a multi-type heat pump system. Because indoor units are interconnected, alteration of the heating or cooling setting of one indoor unit can influence the performance of the other indoor units. Proportional-integral (PI) controllers were used to assess system performance, and the PI controllers’ gain values were optimized by using a genetic algorithm. A system model was established following a system identification optimization process, and a pseudo random binary sequence was selected as the system identification input signal. A multi-input multi-output (MIMO) controller was more effective in reducing such cross-coupling effects than a single-input single-output (SISO) controller. The temperature at the secondary fluid outlet in the condenser and the saturation pressure at the evaporator were selected as the control variables in the MIMO controller. The experimental results showed that an optimized MIMO controller could reduce overshoot by up to 40% compared with the results using a SISO controller.     

X-ray photoelectron study of the MoCl2C30H30 composite

The surface of a MoCl₂C₃₀H₃₀ composite in the form of molybdenum nanoclusters in a polyacetylene matrix, produced by reacting MoCl₅ with C₂H₂ in benzene and toluene, has been studied by X-ray photoelectron spectroscopy before and after Ar⁺ ion milling. The composite actively reacts with atmospheric oxygen and moisture. As a result, the molybdenum clusters on its surface oxidize to molybdenum(V) or molybdenum(VI) oxides or oxychlorides (E _b(Mo 3d _5/2) = 232.3–232.5 eV) during the sample preparation process. The electron binding energy of molybdenum affter surface etching (E _b(Mo 3d _5/2) = 228.5 eV) suggests that the oxidation state of the molybdenum in the composite is 2⁺ or 3⁺. Analysis of the structure of the spectrum of the C 2s electrons of the inner valence molecular orbitals using the energy level diagram of the C₂ molecule suggests that the hydrocarbon matrix of the composite contains, in addition to-CH=CH-CH=CH- conjugate bonds, linear carbyne fragments: -HC=C=CH- or -C≡C-. After etching, the surface layer of the composite contained argon, which might be due to adsorption because of the small particle size of the composite or chemisorption on the surface of the polyacetylene matrix. The composite is stable in a high vacuum of 1.3 × 10⁻⁵ Pa up to 350°C and does not experience charging when exposed to X-rays, which indicates that it has weak dielectric properties.     

Molecular dynamics study on nanotube-resonators with mass migration applicable to both frequency-tuner and data-storage-media

We investigated the cantilevered carbon-nanotube-resonator including electromigratively movable nanoparticle via classical molecular dynamics simulations and continuum model. The change of the effective mass value, which was closely correlated with the position change of the encapsulated nanoparticle, could be regressed by a power function, the resonance frequency of the carbon-nanotube-resonator could be tuned by controlling the nanoparticle’s position, and the possible frequency-shift-ranges then reached 18–85%. The suggested device could be served as a data-storage-media for electromechanical nonvolatile-memory as well as a frequency-tuner.     

Optimisation of location and dimension of SMC precharge in compression moulding process

The main goal of the present study is to optimise the precharge conditions such as the precharge location and dimensions that give significant effects on the mechanical performance of composite structures manufactured by the compression moulding process. As preliminary step of optimisation, we developed a manufacturing simulation program to predict the fibre volume fraction and fibre orientation. And coupled with this simulation program and a structural analysis program, a genetic algorithm (GA) is implemented to optimise the precharge conditions. The penalty function method and the repair algorithm are modified for handling constraints. The repair algorithm is applied to a symmetric structure and an arbitrary shape structure to find optimal precharge conditions.     

Kink effect upon the electromagnetic generation of ultrasound in isotropic ferromagnets

The influence of the shape anisotropy on the field dependences of double electromagnetic-acoustic conversion in samples of an Invar alloy 29NK in the high-temperature range below the Curie point is experementally studied. It is shown that at a constant temperature the value of the polarizing field in which a jumplike generation of ultrasound occurs is determined by the demagnetizing factor of the sample, and the observed anomaly of the electromagnetic-acoustic conversion is caused by the kink effect.     

A risk management approach to safety assessment of trenchless technologies for culvert rehabilitation

Proper functioning of culverts is not only critical to protecting the transportation system from flooding but also critical to maintaining the expected service life of the overall transportation system. During the service life of culverts, they deteriorate due to many reasons such as corrosion caused by road salt, blockage by debris and sediment, poor construction techniques, etc. Trenchless technologies have been used by several State Departments of Transportation (DOTs) to rehabilitate deteriorated drainage structures without disrupting the traffic and within a relatively short span of time. These technologies provide many benefits in terms of cost, time, quality, and expected service life. However, the safety aspects of these techniques have not been discussed and documented in detail probably due to the complexity and the lack of safety standards and specifications directly associated with the techniques. This paper discusses the application of a risk assessment framework to assess potential safety issues of currently available trenchless technologies for culvert rehabilitation. The findings of the study will provide additional information to improve the decision making process in selecting and planning culvert rehabilitation projects.     

Delay-Dependent Robust Stability of Stochastic Uncertain Systems with Time Delay and Markovian Jump Parameters

This paper is concerned with the delay-dependent stability for a class of stochastic uncertain systems with time delay and Markovian jump parameters. The uncertainties considered in this paper are norm-bounded and governed by the Markov process. Un like the topics in the existing literature, the stability criterion is expressed in terms of linear matrix inequalities, which can be efficiently solved by using a convex-optimization algorithm. Finally, a numerical example is given to illustrate the effectiveness of the proposed method.     

Highly stable optical add/drop multiplexer using polarization beam splitters and fiber Bragg gratings

We demonstrate a novel wavelength-division add/drop multiplexer employing fiber Bragg gratings and polarization beam splitters. The multiplexer is easy to fabricate without any special technique such as UV trimming, and yet shows very stable performance with less than 0.3-dB crosstalk power penalty in a 0.8-nm-spaced, 2.5-Gb/s-per-channel wavelength-division multiplexing (WDM) transmission system.     

Fixed Point Implementation of the QCELP Speech Coder

The Qualcomm code excited linear prediction (QCELP) speech coder was adopted to increase the capacity of the CDMA Mobile System (CMS). In this paper, we implemented the QCELP speech coding algorithm by using TMS320C50 fixed point DSP chip. Also the fixed point simulation was done with C language. The computation complexity of QCELP on TMS320C50 was about 33 MIPS and program size was 10k words and data memory was 4k words. In the normal call test on the CMS, where mobile to mobile call test was done in the bypass mode without double vocoding, mean opinion score for the speech quality was 3.11.