An improved damage diagnostic technique based on Singular Spectrum Analysis and time series models

An approach to enhance the sensitivity of the damage index using the prediction errors of autoregressive – autoregressive exogenous models by augmenting Singular Spectrum Analysis (SSA) to detect and locate minor damage is presented. Numerical simulation studies are carried out by considering a simply supported beam with single and multiple cracks. An experimental study on a reinforced cement concrete beam has been carried out to validate the technique using different levels of damage. The studies emphasise that the SSA improves the sensitivity of the damage index for detection and also localisation, handling environmental/operational variability and measurement noise.     

Finite-horizon scheduling of radar dwells with online template construction

Timing constraints for radar tasks are usually specified in terms of the minimum and maximum temporal distance between successive radar dwells. We utilize the idea of feasible intervals for dealing with the temporal distance constraints. In order to increase the freedom that the scheduler can offer a high-level resource manager, we introduce a technique for nesting and interleaving dwells online while accounting for the energy constraint that radar systems need to satisfy. Further, in radar systems, the task set changes frequently and we advocate the use of finite horizon scheduling in order to avoid the pessimism inherent in schedulers that assume a task will execute forever. The combination of feasible intervals and online dwell packing allows modular schedule updates whereby portions of a schedule can be altered without affecting the entire schedule, hence reducing the complexity of the scheduler. Through extensive simulations we validate our claims of providing greater scheduling flexibility without compromising on performance when compared with earlier work based on templates constructed offline. We also evaluate the impact of two parameters in our scheduling approach: the template length (or the extent of dwell nesting and interleaving) and the length of the finite horizon. Sathish Gopalakrishnan is a visting scholar in the Department of Computer Science, University of Illinois at Urbana-Champaign, where he defended his Ph.D. thesis in December 2005. He received an M.S. in Applied Mathematics from the University of Illinois in 2004 and a B.E. in Computer Science and Engineering from the University of Madras in 1999. Sathish’s research interests concern real-time and embedded systems, and the design of large-scale reliable systems. He received the best student paper award for his work on radar dwell scheduling at the Real-Time Systems Symposium 2004. Marco Caccamo graduated in computer engineering from the University of Pisa in 1997 and received the Ph.D. degree in computer engineering from the Scuola Superiore S. Anna in 2002. He is an Assistant Professor of the Department of Computer Science at the University of Illinois. His research interests include real-time operating systems, real-time scheduling and resource management, wireless sensor networks, and quality of service control in next generation digital infrastructures. He is recipient of the NSF CAREER Award (2003). He is a member of ACM and IEEE. Chi-Sheng Shih is currently an assistant professor at the Graduate Institute of Networking and Multimedia and Department of Computer Science and Information Engineering at National Taiwan University since February 2004. He received the B.S. in Engineering Science and M.S. in Computer Science from National Cheng Kung University in 1993 and 1995, respectively. In 2003, he received his Ph.D. in Computer Science from the University of Illinois at Urbana-Champaign. His main research interests are embedded systems, hardware/software codesign, real-time systems, and database systems. Specifically, his main research interests focus on real-time operating systems, real-time scheduling theory, embedded software, and software/hardware co-design for system-on-a-chip. Chang-Gun Lee received the B.S., M.S. and Ph.D. degrees in computer engineering from Seoul National University, Korea, in 1991, 1993 and 1998, respectively. He is currently an Assistant Professor in the Department of Electrical Engineering, Ohio State University, Columbus. Previously, he was a Research Scientist in the Department of Computer Science, University of Illinois at Urbana-Champaign from March 2000 to July 2002 and a Research Engineer in the Advanced Telecomm. Research Lab., LG Information & Communications, Ltd. from March 1998 to February 2000. His current research interests include real-time systems, complex embedded systems, QoS management, and wireless ad-hoc networks. Chang-Gun Lee is a member of the IEEE Computer Society. Lui Sha graduated with the Ph.D. degree from Carnegie-Mellon University in 1985. He was a Member and then a Senior Member of Technical Staff at Software Engineering Institute (SEI) from 1986 to 1998. Since Fall 1998, he has been a Professor of Computer Science at the University of Illinois at Urbana Champaign, and a Visiting Scientist of the SEI. He was the Chair of IEEE Real Time Systems Technical Committee from 1999 to 2000, and has served on its Executive Committee since 2001. He was a member of National Academy of Science’s study group on Software Dependability and Certification from 2004 to 2005, and is an IEEE Distinguished Visitor (2005 to 2007). Lui Sha is a Fellow of the IEEE and the ACM.     

Transition metal chalcogenides exhibiting quasi-one-dimensional behaviour

This paper presents a survey of transition metal chalcogenides (mainly sulphides and selenides) that exhibit unidimensional structural features and electronic properties arising therefrom. The survey indicates that linear, single-atom, chains of transition metals are formed in chalcogenides by sharing faces of MX₆ (X=chalcogen) trigonal prisms or octahedra as well as corners or edges of MX₄ tetrahedra. Besides these single-atom chain compounds, chalcogenides possessing multiple-atom chains are known among the early members of the transition series when the transition metal is in a low formal oxidation state. Typical examples of this class are Ti₅Te₄ and TlMo₃Se₃. Contribution No. 223 from the Solid State and Structural Chemistry Unit.     

Ternary bismuth oxides Bi26−xMxO40−y (M = Mg,Al, Co and Ni) related to α - Bi2O3

Reaction of Bi₂O₃ with MgO, NiO, Co₃O₄ and Al₂O₃ gives rise to the corresponding ternary bismuth oxides, Bi₁₈Mg₈O₃₆, Bi₁₈Ni₈O₃₆, Bi₂₀Co₆O₃₉ and Bi₂₄Al₂O₃₉. These oxides have the general formula Bi_26?xM_xO_40?y and exhibit BCC structures related to α - Bi₂O₃. In the first three solids, the metal ions, M, replace bismuth randomly at the octahedral 24r sites (space group 123); in the last case, aluminium ions occupy the tetrahedral 2a sites, the phase being isostructural with Bi₂₄Ge₂O₄₀. Starting from Bi₂O₃ and NiO, orthorhombic Bi₂Ni₂O₅ has also been obtained.     

A higher-order spectral element for wave propagation analysis in functionally graded materials

Summary. A new higher-order spectral element (SE) is developed for wave propagation analysis of a functionally graded material (FGM) beam in the presence of thermal and mechanical loading. The element is based on first order shear deformation theory (FSDT) and takes into account the depthwise contraction due to Poissons ratio. A new method of element formulation is employed, which is the most general one and devoid of all previous cumbersome wavenumber and wave amplitude computation. The beam can be subjected to temperature variation in depth direction. This variation is found by solving the one-dimensional heat conduction equation uncoupled from the elasticity equation. The effect of the computed temperature field is subsequently superimposed on the mechanical loading in the form of an equivalent nodal load. Numerical examples are directed towards highlighting the effect of the Poissons contraction on the structural response and stress wave. The spectrum and the dispersion relation are studied in detail. The stress field generated by the element and its difference from the FSDT stress field is outlined. The response of an FGM beam to thermo-mechanical loading is analysed and the effect of thermal loading on the overall response is elicited.     

A new composite of crystalline silicotitanate for sequestration of 137Cs and 90Sr from low-level aqueous waste solution

ABSTRACT

A new composite of crystalline silicotitanate (CST) has been synthesized for the sequestration of Cs and Sr from low-level liquid waste generated in the nuclear industry. The product characterization using X-RAY DEFRACTION (XRD) and Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of CST crystals in the composite. Sorption studies carried out under various test conditions showed that the composite has high affinity for both Cs and Sr. Results of structural characterization of Cs and Sr-loaded CST indicated that the overall structural integrity remained intact after substitution of Na⁺ by Cs⁺ or Sr²⁺. The exceedingly good Cs and Sr sorption performance displayed by the CST composite will find applications in the treatment of nuclear waste.     

Sediment Oxygen Demand and Nutrient Fluxes for a Tropical Reservoir in Singapore

Sediment oxygen demand (SOD) and nutrient flux studies were conducted for a tropical reservoir in Singapore in order to determine the approximate SOD and nutrient release rates from the sediments. SOD values obtained from laboratory experiments ranged from 1.4 to 3.3?g?O2/m2-day. Similar results were also obtained by calculating SOD values from in situ DO measurements taken in the field. The nutrient flux study was performed in the laboratory at a constant temperature of 25°C in oxic and anoxic columns. Except for nitrate+nitrite, higher nutrient release rates were generally observed under anoxic conditions. The ammonium release rate was 0.06?g?O2/m2-day under oxic conditions and 0.117?g?O2/m2-day under anoxic conditions. The nitrate flux rate was 0.17?g?O2/m2-day under oxic conditions but was negligible under anoxic conditions. Orthophosphate flux results were negative throughout the oxic incubation implying that sediments acted as a sink. The release rate of orthophosphate was 0.007?6?g?O2/m2-day under anoxic conditions.     

Health and wellness monitoring through wearable and ambient sensors: exemplars from home-based care of elderly with mild dementia

Monitoring and timely intervention are extremely important in the continuous management of health and wellness among all segments of the population, but particularly among those with mild dementia. In relation to this, we prescribe three design principles for the construction of services and applications. These are ambient intelligence, service continuity, and micro-context. In this paper, we provide three exemplars from our research and development activities that illustrate the use of these design principles in the construction of services and applications. All the applications are drawn from the field of care for mild dementia patients in their living quarters.     

Pressure-induced band cross-over in Pb1−x Sn x Te

Resistivity and thermoelectric power studies have been carried out on two semiconductor alloy systems viz Pb_0·8Sn_0·2Te and Pb_0·6Sn_0·4Te up to 35 kbar pressure. Thermoelectric power and resistivity data on Pb_0·8Sn_0·2Te indicate that the energy gapE _g=E _{L −} ⁶ −E _{L 6} ⁺ decreases with pressure resulting in a zero gap state near 35 kbar pressure. TEP studies on the alloy system Pb_0·6Sn_0·4Te provide direct evidence for a pressure induced L ₆ ⁻ →L ₆ ⁺ cross over transition.