Denoising of arterial spin labeling data: wavelet-domain filtering compared with Gaussian smoothing

Purpose  

To investigate a wavelet-based filtering scheme for denoising of arterial spin labeling (ASL) data, potentially enabling reduction of the required number of averages and the acquisition time.     

Technical note an evaluation of water corrosivity of the river tigris at Baghdad

A series of experiments was carried out on different samples of tap water abstracted from the Baghdad water supply network in order to observe the effect of water on supply pipes, either scale forming or corrosive. This experimental investigation on the corrosive effect of the city of Baghdad tap water showed that the water can be classified as corrosive according to the Ryznar index, while the Langelier index showed that the water has the ability to form scale on the pipes. However, personal field observation indicated that the water is corrosive to the pipes and to the network appurtenance. Other findings are reported herein.     

FPGA Based Implementation and Comparison of Beamformers for CDMA2000

For the integration of smart antennas into third generation code division multiple access (CDMA) base stations, it still remains as a challenging task to implement smart antenna algorithms on programmable processors. In this paper, we study implementations of some CDMA compatible beamforming algorithms, namely least mean square (LMS), constant modulus (CM), and space code correlator (SCC) algorithms, using Xilinx??s Virtex family FPGAs. This study exhibits feasibility of implementing even simple, practical, and computationally small algorithms based on today??s most powerful FPGA technologies. 16 and 32 bits floating point implementations of the algorithms are investigated using both Virtex II and Virtex IV FPGAs. CDMA2000 reverse link baseband signal format is used in the signal modeling. Randomly changing fading and Direction-of-arrivals (DOAs) of multipaths are considered as a channel condition. The implementation results in terms of beamforming accuracy, FPGA resource utilization, weight vector computation time, and DOA estimation error are presented. Beamformer weight vectors using LMS and CM can be computed within less than 20 ??s on Virtex II FPGA and 10 ??s on Virtex IV FPGA, and using SCC it can be achieved within less than 22 ??s on Virtex IV FPGA. These results show that FPGAs provide approximately 500 times faster speed in implementations than our previous work with DSPs.     

Construction safety issues in Gaza Strip

Safety is considered a critical problem in developed and developing countries. The author examines the causes of accidents on building sites and the safety procedures used by local contractors in Gaza Strip. A wide range of recommendations are necessary if hazards are to be eliminated and accidents reduced. Recommendations include a suitable training programme, supervisory methods for product quality and working conditions on site, improved working conditions, a safety regulatory framework including a safety institution, standards, and penalties. La securite est consideree comme un probleme critique dans les pays industrialises et dans les pays en developpement. L'auteur examine les causes des accidents sur les chantiers de construction dans la Bande de Gaza ainsi que les procedures de securite appliquees par les entreprises locales. Pour eliminer les dangers et reduire le nombre d'accidents, il conviendrait de formuler de nombreuses recommandations portant, notamment, sur un programme de formation approprie, des methodes de suivi de la "qualito produits" et de supervision des conditions de travail sur les chantiers. Il faudrait d'ailleurs ameliorer ces conditions et definir un cadre de reglementation en matiere de securite comprenant, entre autres, la creation d'un institut de la securite, l'elaboration de normes et la mise en place d'un mecanisme de penalites.     

Sliding mode control of a bioreactor

In this paper, sliding mode control (SMC) of a bioreactor is considered and is compared with PID control. The magnitude of the error in SMC is found to be lower than that in PID control. Moreover, the magnitudes of cells and nutrients were very close to the selected reference values in SMC, whereas they were quite different in PID control. Overall, SMC was more robust against disturbances and had better performance than PID control.     

Micromechanical modeling of load transfer in fibrous composites

A unified analytical treatment is presented for the study of micromechanical stress distribution in unidirectional fibrous composites loaded with various thermal and mechanical loads. Two models are considered to represent the composite. Both use a concentric cylindrical system with the difference that one requires laterally free while the other requires laterally constrained outer boundaries, broadly describing situations of plane stress and plane strain, respectively. The present work has been motivated by the recent work of McCartney (McCartney, Proc. Roy. Soc. London, Ser. A 425 (1989) 215–244) who analyzed the laterally free system, and by our previous work (Nayfeh, Fibre Sci. Technol. 10 (1977)) in which we analyzed the laterally constrained one. For axisymmetric loading, and upon adopting some appropriate restrictions on the radial behavior of some field quantities, an elasticity-based procedure reduces the two-dimensional field equations, which hold in both the fiber and matrix components, together with the appropriate interface and boundary conditions, to a quasi-one-dimensional system. The resulting system is capable of identifying the stress distribution in each component as influenced by the other component via the readily identifiable interaction (transfer) terms. The model is general and applicable to a large variety of situations. These include situations of matrix cracking, fiber break and even regions of slip at the fiber–matrix interface. As a by-product, the model was capable of obtaining the classical Lamé solutions (the iso-strain case) as a degenerate case. Confidence in the modeling was gained when it identically reproduced all of the numerical examples presented by McCartney. Numerical results that parallel some of the ones presented by McCartney are included in the form of comparisons between results obtained based upon the laterally constrained and the laterally free systems.     

On the role of material property gradients in noncontacting thermoelectric NDE

Inclusions and other types of imperfections in nonmagnetic metals can be nondestructively detected by noncontacting magnetic measurements that sense the thermoelectric currents produced by directional heating and cooling of the specimen. The detectability of small and/or weak imperfections is ultimately limited by the intrinsic anisotropy and inhomogeneity of the material to be inspected. This paper investigates the spurious magnetic signature produced by the simplest type of macroscopic inhomogeneity when the material properties exhibit a linear spatial variation in the cross section of a slender bar. An analytical method has been developed for calculating the normal and tangential magnetic fields produced by the resulting thermoelectric currents. Experimental results from a highly inhomogeneous artificial copper/brass sintered specimen were found to be in very good quantitative agreement with our theoretical predictions and fully verified our analytical model. Similar measurements on a weakly inhomogeneous Ti–6Al–4V titanium-alloy bar were also shown to be in very good qualitative agreement with the predictions of the analytical model although the unexpectedly high magnitude of the observed signatures could not be verified by conventional contact measurements, therefore further efforts are needed to better understand the underlying physical phenomenon and clarifying the relationship between the strength of the signature and the very complex microstructural features of this popular high-strength alloy.     

Microwave preheating of anisotropic conductive adhesive films for high-speed flip chip on flex bonding

Anisotropic conductive adhesive film (ACF) can be preheated by microwave (MW) radiation in order to reduce the bonding time for flip-chip technology. Due to sluggish and nonuniform curing kinetics at the beginning of the curing reaction, thermal curing of epoxy is more time consuming. Therefore, MW radiation may be more effective, due to its uniform heating rate during the cycle. In this paper, MW preheating (for 1–4 sec) of ACF prior to final bonding has been applied to determine the electrical and mechanical performance of the bond. Powers of 80 and 240 W MW were used to study the effect of the MW preheating. A final bonding time of 6–7 sec can be used for flip chip on flex bonding instead of 10–15 sec (standard time for flip chip bonding) for MW preheating time and power used in this study. The contact resistance (as low as 0.01) is low in these samples, whereas the standard resistance is 0.017 ohm (bonded at 180°C for 10 sec without prior MW preheating). The shear forces at breakage were satisfactory (0.167–0.183 KN) for the samples bonded for 6–7 sec with MW preheating. This is very close and even higher than the standard sample (0.173 KN). For MW preheating power of 80 W and sweeping time of 2 sec, final bonding at 6 sec can also be used because of its low contact resistance (0.019 ohm). Scanning electron microscope (SEM) investigation of microjoints and fracture surface shows uneven distribution of conductive particles and thick bond lines in samples bonded for 5 sec (with MW preheating). Samples treated with MW radiation (80 W and 2–3 sec time) serve as evidence that well-distributed particles along with thin bond lines cause low contact resistance and high joint strength.     

Microbial-Catalyzed Biotransformation of Multifunctional Triterpenoids Derived from Phytonutrients

Microbial-catalyzed biotransformations have considerable potential for the generation of an enormous variety of structurally diversified organic compounds, especially natural products with complex structures like triterpenoids. They offer efficient and economical ways to produce semi-synthetic analogues and novel lead molecules. Microorganisms such as bacteria and fungi could catalyze chemo-, regio- and stereospecific hydroxylations of diverse triterpenoid substrates that are extremely difficult to produce by chemical routes. During recent years, considerable research has been performed on the microbial transformation of bioactive triterpenoids, in order to obtain biologically active molecules with diverse structures features. This article reviews the microbial modifications of tetranortriterpenoids, tetracyclic triterpenoids and pentacyclic triterpenoids.