Analysis of limit cycle oscillations in a magnetic suspension system using the describing function method

This paper presents the analysis of limit cycle oscillations observed in a magnetic suspension system which utilizes an optical transducer. Stability conditions for certain non-linearities have been obtained using the Describing Function approach and these conditions are later verified by the stability criterion of Gelb and Van der Velde [1] in the case of saturation non-linearity.     

Antihypertensive properties of aqueous extracts of vegetable leaf‐fortified bread after oral administration to spontaneously hypertensive rats

This study investigated the potential cardiovascular health benefits of leavened bread produced from wheat flour that contained 1%, 2% and 3% additions of leafy vegetable powders obtained from Amaranthus viridis (AO), Solanum macrocarpon (SM) or Telfairia occidentalis (TO). Dried breads were extracted with water at 60 °C followed by analysis for total polyphenolic content (TPC), as well as in vitro inhibitions of angiotensin‐converting enzyme and renin activities. HPLC analysis of the bread extracts indicated the presence of mainly rutin, gallic acid, myricetin and caffeic acid. TPC of the vegetable‐fortified breads was significantly (P < 0.05) higher (5.8–7.6 mg gallic acid equivalent, GAE/g) than that of control bread (5.5 mg GAE/g). Oral administration of 100 mg dried extract/kg body weight to spontaneously hypertensive rats led to reductions (up to 42 mmHg) in systolic, diastolic and mean arterial blood pressure in comparison with 20 mmHg for the control bread.     

Fuzzy smart failure modes and effects analysis to improve safety performance of system: Case study of an aircraft landing system

Failure modes and effects analysis (FMEA) is a safety and reliability technique that is widely used to evaluate, design, and process a system against diverse possible ways through which the potential failure has a tendency to occur. In conventional FMEA, the risk evaluation is determined by risk priority number (RPN) obtained by multiplying of three risk factors—severity, occurrence, and detection. However, because of many shortages in conventional FMEA, the RPN scores have been widely criticized along issues bothering on ambiguity and vagueness, scoring, appraising, evaluating, and selecting corrective actions. In this paper, we propose a new integrated fuzzy smart FMEA framework where the combination of fuzzy set theory, analytical hierarchy process (AHP), and data envelopment analysis (DEA) is used, respectively, to handle uncertainty and to increase the reliability of the risk assessment. These are achieved by employing a heterogeneous group of experts and determining the efficiency of FMEA mode with adequate priority and corrective actions using RPN, time, and cost as indicators. A numerical example (aircraft landing system) is provided to exemplify the feasibility and effectiveness of the proposed model. The outputs of the proposed model compared with the conventional risk assessment technique results show its effectiveness, reliability, and propensity for real applications.     

Performance benchmarking of wireless Web servers

The advent of mobile computers and wireless networks enables the deployment of wireless Web servers and clients in short-lived ad hoc network environments, such as classroom area networks. The purpose of this paper is to benchmark the performance capabilities of wireless Web servers in such an environment. Network traffic measurements are conducted on an in-building IEEE 802.11b wireless ad hoc network, using a wireless-enabled Apache Web server, several wireless clients, and a wireless network traffic analyzer. The experiments focus on the HTTP transaction rate and end-to-end throughput achievable in such an ad hoc network environment, and the impacts of factors such as Web object size, number of clients, and persistent HTTP connections. The results show that the wireless network bottleneck manifests itself in several ways: inefficient HTTP performance, client-side packet losses, server-side packet losses, network thrashing, and unfairness among Web clients. Persistent HTTP connections offer up to 350% improvement in HTTP transaction rate and user-level throughput, while also improving fairness for mobile clients accessing content from a wireless Web server.     

A simple and rapid method to graft hydroxyapatite on carbon nanotubes

Herein a simple and effective approach is introduced to functionalize single walled carbon nanotubes (SWCNTs) by in-situ grafting of hydroxyapatite (HA). The pristine SWCNTs were chemically activated through introduction of carboxylic groups on their surfaces by refluxing in the mixture of H(2)SO(4) and HNO(3). The resulting carboxylated SWCNTs were further utilized for grafting of HA. The Fourier transform infrared and Raman spectroscopic studies demonstrated the formation of HA and its grafting over SWCNTs. The phase composition of HA and existence Ca(2+) and PO(4) (3-) ions were studied using X-ray diffraction and energy dispersive X-ray analyses, respectively. The surface morphology of functionalized SWCNTs was analyzed using scanning electron microscopy and transmission electron microscopy. Thermogravimetric analysis confirmed the existence of HA on SWCNTs by exhibiting different thermogram for pure HA and functionalized SWCNTs. Overall this method produced uniform grafting of low crystalline HA on carboxylated SWCNTs with strong interfacial bonding.     

A long-term record of aerosol index from TOMS observations and horizontal visibility in sub-Saharan West Africa

Aerosol index (AI) observations from the Total Ozone Mapping Spectrometers (TOMS) on board the Nimbus-7 (1979–1992) and Earth Probe (1997–2004) satellites are used to investigate the annual and seasonal variations of dust haze in Sahelian West Africa. Eight synoptic stations, namely Port Harcourt (PHA), Lagos, Ilorin, Makurdi, Minna, Yola, Maiduguri and Kano, representing the four major climatic zones (tropical rainforest and Guinea, Sudan and Sahel savannahs) of Nigeria were considered in this study. Twenty-nine years (1979–2007) of horizontal visibility data are also analysed in order to investigate the effect of dust haze on visibility in the stations under study. Results show that there are general decreasing trends in the visibility with corresponding increases in TOMS AI trends in all the climatic zones of Nigeria. This clearly suggests that there had been an increase in the integrated column dust aerosols over the years, especially during the harmattan dusty months. The average visibility was highest in Ilorin (11363.2 ± 1644.4 m) and the lowest in Maiduguri (9017.9 ± 1021.3 m) when the dust-prone months of November to March of the following year were considered. Logarithmic equations with inverse relationships are developed between TOMS AI and horizontal visibility for each station with correspondingly high coefficients of determination (R ²) in all the locations. It is concluded that TOMS AI can reasonably be used to reproduce visibility measurement in sub-Saharan West Africa where sparse visibility data are available for meteorological uses.     

Robust validation of pattern classification methods for laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is an emerging technology that is suitable for a variety of material identification applications. For LIBS to successfully transition from the laboratory into field applications, the sensor must be paired with the appropriate algorithms for accurate and robust processing of the LIBS spectra. In this study we will report on the results of testing classification methods on eight distinct classification tasks using LIBS datasets. Results suggest that standard cross-validation techniques may not accurately estimate generalization performance and a proposed "leave-one-sample-out" approach to experiment design for classifier validation may provide a more robust measure of performance.