A.Y.T. Leung

INFLUENCE OF STEEL FIBRES ON STRENGTH AND DUCTILITY OF NORMAL AND LIGHTWEIGHT HIGH STRENGTH CONCRETE

Abstract This paper presents the results of a series of experiments conducted to investigate the effectiveness of fibre inclusion in the improvement of mechanical performance of concrete with regard to concrete type and specimen size. Lightweight aggregate concrete and limestone aggregate concrete with and without steel fibres were used in the study. The compressive strength of the concrete mixes varied between 90 and 115 MPa and the fibre content was 1% by volume. Splitting tests on prisms and three-point bending test on notched beams were carried out on specimens of varying sizes to examine the size effect on splitting strength, flexural strength and toughness. The experimental findings indicate that the low volume of fibre has little effect on compressive strength but improve remarkably splitting tensile strength, flexural strength and toughness. The increase in splitting tensile strength, flexural strength and toughness index for lightweight concrete seems much higher than that of normal aggregate concrete. The size effect on prism splitting tensile strength is not significant beyond a critical (transition) size. There are apparent size effects on flexural strength and toughness index. As the specimen size increases, splitting and flexural strengths appear to decrease, and fracture behaviour tends to be more brittle.

The spectral element method in structural dynamics

The authors present a brief review of the spectral element method (SEM) in structural dynamics. A background discussion is included that provides a reference to previous works. The dynamic shape function approach of spectral element formulation is reviewed, and the state-vector approach is introduced for one-dimensional structures. The SEM for the forced vibrations of one-dimensional structures is briefly introduced in a general form for both the point and the distributed dynamic loads and is applied to Levy-type plates and smart beam structures. The accuracy of the spectral element is verified by comparing the SEM solutions with the solutions obtained by other methods including the conventional finite element method.

Accuracy of calculated free testosterone formulae in men.

Background  As reference laboratory methods for measuring free testosterone (FT) by equilibrium dialysis (ED) are laborious, costly and nonautomatable, FT levels are often calculated (cFT) rather than measured. However, the predictive accuracy of such estimates in routine use relative to laboratory measurements is not well defined. We provide a large‐scale evaluation of the predictive accuracy for different FT formulae compared with laboratory ED measurement and an analysis of clinical factors that may influence accuracy.

Prediction of maximum daily ozone level using combined neural network and statistical characteristics

Analysis and forecasting of air quality parameters are important topics of atmospheric and environmental research today due to the health impact caused by air pollution. As one of major pollutants, ozone, especially ground level ozone, is responsible for various adverse effects on both human being and foliage. Therefore, prediction of ambient ozone levels in certain environment, especially the ground ozone level in densely urban areas, is of great importance to urban air quality and city image. To date, though several ozone prediction models have been established, there is still a need for more accurate models to develop effective warning strategies. The development of such models is difficult because the meteorological variables and the photochemical reactions involved in ozone formation are very complex. The present work aims to develop an improved neural network model, which combines the adaptive radial basis function (ARBF) network with statistical characteristics of ozone in selected specific areas, and is used to predict the daily maximum ozone concentration level. The improved method is trained and testified by hourly time series data collected at three air pollutant-monitoring stations in Hong Kong during 1999 and 2000. The simulation results demonstrate the effectiveness and the reliability of the proposed method.

Simultaneous Measurement of Serum Testosterone and Dihydrotestosterone by Liquid Chromatography–Tandem Mass Spectrometry

BACKGROUND Recent reports have described inherent problems with androgen immunoassays compared with mass spectrometry analyses. METHODS We developed a method for measuring serum testosterone (T) and 5alpha-dihydrotestosterone (DHT) simultaneously via liquid-liquid extraction followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with positive-mode electrospray ionization. RESULTS The DHT and T calibrators showed a linear response from 0.069 nmol/L to 34.4 nmol/L and 69.3 nmol/L, respectively. T interference in the DHT assay and vice versa were negligible. Within- and between-run imprecision values were <5% for both analytes. Percent recoveries of T and DHT spiked into samples at concentrations spanning the calibration curve were 100%-113% and 98%-107%, respectively. The lower limit of quantification was 0.069 nmol/L for both steroids. Serum T concentrations measured by LC-MS/MS were different from those obtained by RIA, especially at lower T concentrations. Serum DHT concentrations measured by LC-MS/MS were markedly lower than those generated by RIA because of the nonselectivity of the RIA without chromatography. The reference intervals (mean +/- 2 SDs) determined for T and DHT were 9.2-33.7 nmol/L and 0.47-2.65 nmol/L, respectively, for 113 healthy adult men and 0.33-2.02 nmol/L and 0.09-0.91 nmol/L, respectively, for 133 healthy premenopausal women. CONCLUSIONS We have developed and validated a selective and precise method for simultaneous measurements of serum T and DHT that can be adopted for routine measurements of these androgens in health and disease in men and women.

The transient responses of magneto-electro-elastic hollow cylinders

By virtue of the separation of variables and orthogonal expansion technique, the plane strain dynamic problem of a magneto-electro-elastic hollow cylinder is reduced to two integral equations of two time functions. Then, by means of the interpolation method, the integral equations are solved successfully. As a result, all the transient responses of displacements, stresses, electric potentials, electric displacements, magnetic potentials and magnetic inductions are completely obtained. The present method is suitable for the analysis of hollow cylinders with arbitrary thickness and subjected to arbitrary mechanical and electromagnetic loads. Numerical results are also presented.

ANALYSIS OF POLLUTANT LEVELS IN CENTRAL HONG KONG APPLYING NEURAL NETWORK METHOD WITH PARTICLE SWARM OPTIMIZATION

Air pollution has emerged as an imminent issue in modernsociety. Prediction of pollutant levels is an importantresearch topic in atmospheric environment today. For fulfillingsuch prediction, the use of neural network (NN), and inparticular the multi-layer perceptrons, has presented to be acost-effective technique superior to traditional statisticalmethods. But their training, usually with back-propagation (BP)algorithm or other gradient algorithms, is often with certaindrawbacks, such as: 1) very slow convergence, and 2) easilygetting stuck in a local minimum. In this paper, a newlydeveloped method, particle swarm optimization (PSO) model, isadopted to train perceptrons, to predict pollutant levels, andas a result, a PSO-based neural network approach is presented. The approach is demonstrated to be feasible and effective bypredicting some real air-quality problems.

Mode I crack problems by fractal two level finite element methods

Abstract A semi-analytical method is suggested to determine the stress intensity factor (SIF) of two-dimensional (2D) crack problems. In it, the singularity is eliminated from the computational domain by the fractal two level finite element method (F2LFEM). In the present method, the fractal geometry concept and two level finite element method (2LFEM) are employed to automatically generate an infinitesimal mesh and transform these large number of degrees of freedom around the crack tip to a small set of generalized coordinates. By taking advantage of the same stiffness of 2D elements with similar shape, one transformation of the stiffness for the first layer of mesh is enough for all. This simple method is very economical in terms of computational time and computer memory. Highly accurate results of SIF and stresses are obtained.

A preliminary study on potential of developing shower/laundry wastewater reclamation and reuse system

With the ever-increasing urban population and economic activities, water usage and demand are continuously increasing. Hence, finding/re-creating adequate water supply and fully utilizing wastewater become important issues in sustainable urban development and environmental benign aspect. Considering Hong Kongs situation, e.g., lack of natural fresh water, domination of municipal wastewater, etc., developing wastewater reclamation and reuse system is of specific significance to exploit new water resource and save natural fresh water supplied from Mainland China. We propose and have carried out some preliminary studies on the potential of categorizing municipal wastewater, developing grey and storm water recycling system in public housing estate, investigating the feasibility and potential of using reclaimed grey water, etc. Since there is very limited experience in grey water recycling, such initial studies can help to understand and increase knowledge in utilizing grey water, to foresee the feasibility of developing new water resource, to estimate the cost-effectiveness of reclaiming grey water in metropolitan city.

A float-encoded genetic algorithm technique for integrated optimization of piezoelectric actuator and sensor placement and feedback gains

This paper presents a novel float-encoded genetic algorithm and applies it to the optimal control of flexible smart structures bonded with piezoelectric actuators and sensors. A performance function is initially developed, based on the maximization of dissipation energy due to a control action. Then, according to this characteristic, a float-encoded genetic algorithm is presented which is capable of solving this optimization problem reliably and efficiently. The optimization algorithm that is developed for the control of flexible systems allows an integrated determination of actuator and sensor locations and feedback gains. The paper demonstrates the suitability of the proposed technique through its application to three standard benchmark test functions and a collocated cantilever beam.