Speed control of electrical machines: unknown load torque case

The problem of specifying a desired torque trajectory to achieve speed tracking in passivity-based control of induction motors is addressed. This paper presents a solution to the problem that does not require an acceleration measurement nor knowledge of the load torque. To prove the main result a variant of Sontag's input to state stability is used     

Efficient deployment of wireless sensor networks targeting environment monitoring applications

Maximizing network connectivity while maintaining a useful lifetime period without exceeding cost constraints is a challenging design objective for wireless sensor networks. Satisfying such objective becomes even a more intricate task with 3-D setups and harsh operational conditions found in typical large scale environment monitoring applications. While much work has been performed in environment monitoring, only few have addressed the unique characteristics of such applications. In this paper, we introduce a novel 3-D deployment strategy, called Optimized 3-D deployment with Lifetime Constraint (O3DwLC), for relay nodes in environmental applications. The strategy optimizes network connectivity, while guarantying specific network lifetime and limited cost. Key to our contribution is a very limited search space for the optimization problem, in addition to a revised definition for network lifetime that is more appropriate in environment monitoring. The effectiveness of our strategy is validated through extensive simulations and comparisons, assuming practical considerations of signal propagation and connectivity.     

Synthesis and Antimicrobial Evaluation of Some Novel Thiazole,Pyridone, Pyrazole,Chromene, Hydrazone Derivatives Bearing a Biologically Active Sulfonamide Moiety

This study aimed for the synthesis of new heterocyclic compounds incorporating sulfamoyl moiety suitable for use as antimicrobial agents via a versatile, readily accessible N-[4-(aminosulfonyl)phenyl]-2-cyanoacetamide (3). The 2-pyridone derivatives were obtained via reaction of cyanoacetamide with acetylacetone or arylidenes malononitrile. Cycloaddition reaction of cyanoacetamide with salicyaldehyde furnished chromene derivatives. Diazotization of 3 with the desired diazonium chloride gave the hydrazone derivatives 13a–e. Also, the reactivity of the hydrazone towards hydrazine hydrate to give Pyrazole derivatives was studied. In addition, treatment of 3 with elemental sulfur and phenyl isothiocyanate or malononitrile furnished thiazole and thiophene derivatives respectively. Reaction of 3 with phenyl isothiocyanate and KOH in DMF afforded the intermediate salt 17 which reacted in situ with 3-(2-bromoacetyl)-2H-chromen-2-one and methyl iodide afforded the thiazole and ketene N,S-acetal derivatives respectively. Finally, reaction of 3 with carbon disulfide and 1,3-dibromopropane afforded the N-[4-(aminosulfonyl) phenyl]-2-cyano-2-(1,3-dithian-2-ylidene)acetamide product 22. All newly synthesized compounds were elucidated by considering the data of both elemental and spectral analysis. The compounds were evaluated for both their in vitro antibacterial and antifungal activities and showed promising results.     

Nonlinear observers for spacecraft attitude estimation in case of yaw angle measurement absence

This paper provides a brief presentation and a useful comparison between two nonlinear observers Extended Kalman Filter (EKF) and sliding mode observer (SMO). Both can be used for moderate-accuracy attitude determination systems for Low Earth Orbit (LEO) Earth-pointing spacecraft (s/c), which is typically achieved using Gyroscopes, Earth, and Sun sensors for attitude sensing. The use of these observers provides a substitute for the yaw data in case of the s/c eclipse periods or limited field of views. The nonlinear observability for this system is analytically investigated via the calculation of Lie derivatives to check the possibility of the system states estimation. The performances of both observers are presented, the SMO stability is proved and the SMO enhanced estimates are shown by simulation.     

Pile-clayey soil interaction analysis by boundary element method

This paper is an attempt to solve the soil-pile interaction problems using the boundary element method(BEM).A computer package called PGroupN,which deals mainly with the analysis of the pile group problem,is employed in this study.Parametric studies are carried out to assess the impacts of the pile diameter,pile length,ratio of spacing to diameter and the thickness of soil stratum.The external load is applied incrementally and,at each increment,a check is made that the stress state at the pile-soil interfaces does not violate the yield criteria.This is achieved by specifying the limited stresses of the soil for the axial pile shaft capacity and end-bearing resistance.The elements of the pile-soil interface yielded can take no additional load,and any increase in load is therefore redistributed between the remaining elements until all elements have failed.Thus,by successive application of loading increments,the entire load-displacement relationship for the pile group is determined.It is found that as the applied load reaches the ultimate bearing capacity of the pile group,all the piles will share the same amount of load.An exception to this case is for the center pile in a group of 9 piles embedded in clay,which is not consistent with the behaviors of the other piles in the group even if the load reaches the ultimate state.For the 4 piles group embedded in clay,the maximum load carried by the base does not exceed 8% of the load carried by each pile with different diameters.This low percentage ascertains that the piles embedded in cohesive soils carry most of the load throughout their shafts.     

Effect of humidity on nanoparticle-based chemiresistors: a comparison between synthetic and real-world samples

Chemiresistors based on metal monolayer-capped nanoparticles (MCNPs) are promising candidates for fast, inexpensive, and portable tracing of (bio)chemical species in the gas phase. However, the sensitivity of such sensors to humidity is problematic, limiting their reliable and reproducible application in real-world environmental conditions. In this work, we employed a compensation method to explore the effect of humidity on a single MCNP chemiresistor as well as on an array of MCNP sensors used to analyze either synthetic or real-world samples. We show that an array of MCNP chemiresistors is able to precisely detect and estimate subtle concentrations of (mixtures of) volatile organic compounds (VOCs) under variable backgrounds of 2-83% relative humidity (RH) only after humidity compensation. Humidity effects were also tested in two clinical trials aimed at detecting prostate cancer and breast cancer through exhaled breath analysis. Analysis of the results showed improved cancer detection capabilities as a result of RH compensation, though less substantial than the impact of RH compensation on synthetic samples. This outcome is attributed to one - or a combination - of the following effects: (i) the RH variance was smaller in the breath samples than that in the synthetic samples; (ii) the VOC composition in the breath samples is less controlled than the synthetic samples; and (iii) the responses to small polar VOCs and water are not necessarily additive in breath samples. Ultimately, the results presented here could assist the development of a cost-effective, low-power method for widespread detection of VOCs in real-world applications, such as breath analysis, as well as for environmental, security, and food applications.     

Managing connection costs in heterogeneous wireless networks

Common Radio Resource Management techniques have shown great promise in both enhancing network operation and user satisfication. Such gains are achieved through the joint management of the individual access technologies in a Heterogeneous Wireless Network. The objective of this work is to expand on the existing body of work to accommodate heterogeneity not just at the traditional access‐network level but to other connectivity modes such as dynamic spectrum access. Such modes affect operator profitability in both the long and short terms. Specifically, we explore the design of a cost‐management model that adapts to the short‐term variability in connectivity costs. We also display the operational aspects and effectiveness of this functionality through both simulation and an analytical model. Copyright © 2012 John Wiley & Sons, Ltd.     

IEEE 802.11 medium access control enhancements based on simultaneous multiple‐input multiple‐output bandwidth sharing

The demand for higher data rate has spurred the adoption of multiple‐input multiple‐output (MIMO) transmission techniques in IEEE 802.11 products. MIMO techniques provide an additional spatial dimension that can significantly increase the channel capacity. A number of multiuser MIMO system have been proposed, where the multiple antenna at the physical layer are employed for multiuser access, allowing multiple users to share the same bandwidth. As these MIMO physical layer technologies further evolve, the usable bandwidth per application increases; hence, the average service time per application decreases. However, in the IEEE 802.11 distributed coordination function‐based systems, a considerable amount of bandwidth is wasted during the medium access and coordination process. Therefore, as the usable bandwidth is enhanced using MIMO technology, the bandwidth wastage of medium access and coordination becomes a significant performance bottleneck. Hence, there is a fundamental need for bandwidth sharing schemes at the medium access control (MAC) layer where multiple connections can concurrently use the increased bandwidth provided by the physical layer MIMO technologies. In this paper, we propose the MIMO‐aware rate splitting (MRS) MAC protocol and examine its behavior under different scenarios. MRS is a distributed MAC protocol where nodes locally cooperate with one another to share bandwidth via splitting the spatial channels of MIMO systems. Simulation results of MRS protocol are obtained and compared with those of IEEE 802.11n protocol. We show that our proposed MRS scheme can significantly outperform the IEEE 802.11n in medium access delay and throughput. Copyright © 2012 John Wiley & Sons, Ltd.     

Characterization of Electroslag Remelted Super Hard High Speed Tool Steel Containing Niobium

In this work, thermodynamical equilibria have been calculated for super hard high speed tool steel (HSS), AISI M41 composition belonging to the multicomponent system Fe–C–Cr–W–Mo–V–Co as well as for its three different variant containing niobium. Some temperature‐concentration diagram for both class of alloys are presented and calculated quantities (melting and transformations, amount and composition of phases) are compared with experimental data. Effect of niobium and high cooling rate during electroslag remelting on the precipitated carbides were discussed. In this work, the effect of niobium on morphology of carbides secondary hardening temperature and wear rate of investigated HSSs were studied. This work aims to study the effect of niobium as alloying element on precipitated carbides type and shape, in addition to study the effect of precipitated carbides after full heat treatment on secondary hardening and wear resistance for investigated steels.     

A Parametrics Architecture for Design, Management, and Coordination in a Collaborative AEC Environment

This article describes a unified system architecture for representation and reasoning in a concurrent, collaborative architectural/engineering/construction (AEC) environment. The architecture is built on a formal unified modeling methodology for products and processes based on parametrics techniques. The architecture forms the core of a domain‐independent shell that could be used for incremental knowledge integration. The integrated knowledge base could be used at any point of inference to propagate changes in data values or knowledge items using parameter‐dependency networks. The article concentrates on the representation standards of the core elements of the collaborative architecture. It starts by describing the needs set by the nature of project organization in the AEC industry as well as the research philosophy. The article briefly illustrates the generic parametric representation and inference foundation, including the role of exogenous variables in domain knowledge control. The article concentrates on the standards of object‐oriented representation that form the core of domain modeling and knowledge integration. The representation covers various tasks such as context knowledge control for version management, knowledge integration with other systems, and efficient propagation control. The article shows that the careful use of domain knowledge in modeling the problem and controlling inference through exogenous variables provides guidelines toward creating sound standards for representation.