Sequential testing policies for complex systems under precedence constraints

We study the problem of sequentially testing the components of a multi-component system to learn the state of the system, when the tests are subject to precedence constraints and with the objective of minimizing the expected cost of the inspections. Our focus is on k-out-of-n systems, which function if at least k of the n components are functional. A solution is a testing policy, which is a set of decision rules that describe in which order to perform the tests. We distinguish two different classes of policies and describe exact algorithms (one branch-and-bound algorithm and one dynamic program) to find an optimal member of each class. We report on extensive computational experiments with the algorithms for representative datasets.     

Per tone equalization for DMT-based systems

An alternative receiver structure is presented for discrete multitone-based systems. The usual structure consisting of a (real) time-domain equalizer in combination with a (complex) 1-tap frequency-domain equalizer (FEQ) per tone, is modified into a structure with a (complex) multitap FEQ per tone. By solving a minimum mean-square-error problem, the signal-to-noise ratio is maximized for each individual tone. The result is a larger bit rate while complexity during data transmission is kept at the same level. Moreover, the per tone equalization is shown to have a reduced sensitivity to the synchronization delay     

The effect of pretreatment on the reactivity of Fe-ZSM-5 catalysts for N2O decomposition: Dehydroxylation vs. steaming

The N₂O decomposition activity of the Fe-ZSM-5 catalysts, prepared by chemical vapor deposition (CVD) and aqueous ion exchange (IE), was studied after steaming and high temperature treatment at 1218 K (HT) and compared with the activity of the corresponding non-steamed catalysts after pretreatment at 873 K. FTIR spectra showed that dehydroxylation and/or dealumination took place during steaming and high temperature treatment of the catalysts, which leads to the formation of oxygen vacancies (i.e. lattice defect). These lattice defects leads to a change in electronic properties of the iron sites, which are associated with electron withdrawing Al Lewis centers. The iron sites in close proximity of defects are responsible for the initial higher N₂O decomposition (transient activity) of the steamed and HT catalysts. The increase in steady-state activity over steamed and HT catalysts can be mainly attributed to an increase in the number of active sites created by autoreduction of the iron centers during steaming and high temperature treatment. The above-mentioned trends are valid for both CVD and IE samples.     

Equivalent system model and equalization of differential impulse radio UWB systems

A discrete-time equivalent system model is derived for differential and transmitted reference (TR) ultra-wideband (UWB) impulse radio (IR) systems, operating under heavy intersymbol-interference (ISI) caused by multipath propagation. In the systems discussed, data is transmitted using differential modulation on a frame-level, i.e., among UWB pulses. Multiple pulses (frames) are used to convey a single bit. Time hopping and amplitude codes are applied for multi user communications, employing a receiver front-end that consists of a bank of pulse-pair correlators. It is shown that these UWB systems are accurately modeled by second-order discrete-time Volterra systems. This proposed nonlinear equivalent system model is the basis for developing optimal and suboptimal receivers for differential UWB communications systems under ISI. As an example, we describe a maximum likelihood sequence detector with decision feedback, to be applied at the output of the receiver front-end sampled at symbol rate, and an adaptive inverse modeling equalizer. Both methods significantly increase the robustness in presence of multipath interference at tractable complexity.     

Validation of multiparametric MRI by histopathology after nephrectomy: a case study

Magnetic Resonance Materials in Physics, Biology and Medicine - Renal multiparametric MRI (mpMRI) is a promising tool to monitor renal allograft health to enable timely treatment of chronic...     

Automated 3-D PDM construction from segmented images using deformable models

In recent years, several methods have been proposed for constructing statistical shape models to aid image analysis tasks by providing a priori knowledge. Examples include principal component analysis of manually or semiautomatically placed corresponding landmarks on the learning shapes [point distribution models (PDMs)], which is time consuming and subjective. However, automatically establishing surface correspondences continues to be a difficult problem. This paper presents a novel method for the automated construction of three-dimensional PDM from segmented images. Corresponding surface landmarks are established by adapting a triangulated learning shape to segmented volumetric images of the remaining shapes. The adaptation is based on a novel deformable model technique. We illustrate our approach using computed tomography data of the vertebra and the femur. We demonstrate that our method accurately represents and predicts shapes.     

Biosorption of Cu(II) onto agricultural materials from tropical regions

BACKGROUND: In Ghana, the discharge of untreated gold mine wastewater contaminates the aquatic systems with heavy metals such as copper (Cu), threatening ecosystem and human health. The undesirable effects of these pollutants can be avoided by treatment of the mining wastewater prior to discharge. In this work, the sorption properties of agricultural materials, namely coconut shell, coconut husk, sawdust and Moringa oleifera seeds for Cu(II) were investigated. RESULTS: The Freundlich isotherm model described the Cu(II) removal by coconut husk (R² = 0.999) and sawdust (R² = 0.993) very well and the Cu(II) removal by Moringa oleifera seeds (R² = 0.960) well. The model only reasonably described the Cu(II) removal by coconut shell (R² = 0.932). A maximum Cu(II) uptake of 53.9 mg g^?1 was achieved using the coconut shell. The sorption of Cu(II) onto coconut shell followed pseudo‐second‐order kinetics (R² = 0.997). FTIR spectroscopy indicated the presence of functional groups in the biosorbents, some of which were involved in the sorption process. SEM‐EDX analysis confirmed an exchange of Mg(II) and K(I) for Cu(II) on Moringa oleifera seeds and K(I) for Cu(II) on coconut shell. CONCLUSION: This study shows that coconut shell can be an important low‐cost biosorbent for Cu(II) removal. The results indicate that ion exchange, precipitation and electrostatic forces were involved in the Cu(II) removal by the biosorbents investigated. Copyright © 2011 Society of Chemical Industry