On stress propagation and fracture in compacted graphite iron

In this work, initiation and propagation of fracture in compacted graphite iron (CGI) has been investigated and modeled under the dynamic loading scenario. Fracture initiation was found to originate at the graphite particles and at graphite/matrix interface at no particular preference of order and propagated into the metal matrix in the form of a network of microcracks which eventually coalesced leading to complete failure of the material. Metallurgical investigations of fracture in CGI under both quasi-static and quasi-dynamic tests were comprehensively implemented. Investigation of stress concentration propagation at specific fracture propensity regions have been modeled and simulated on a real CGI sample RVE using commercial finite element package, ABAQUS?/CAE? v6.9. The CGI sample consisted of >90% pearlite matrix. Furthermore, FE modeling allowed the observation of stress concentration initiation and propagation at the CGI graphite particles and graphite–matrix interfaces until fracture. Crack bluntness was observed in the model and a change in the potential crack path was visual. Several findings were documented in an effort to better understand the behavior of CGI under quasi-static and dynamic conditions. This work is a milestone among a series of successive tasks all aiming to better understand, validate, and build a yet unavailable comprehensive model of CGI behavior under diverse loading schemes.     

On the interplay of network structure and routing strategies in scale-free networks

In this paper, we examine how the structural characteristics of network topologies affect the network performance, and we examine the interplay between structural characteristics of network topologies and routing strategies. We consider routing strategies subject to practical constraints (router technology) and economic considerations (link costs) at layer 3. We propose two new routing methods suitable for implementation in large networks and examine various routing strategies (local, global, and hybrid) with tunable parameters and explore how they can enhance the network performance. We find that there exists an optimal range of values for the tunable parameters to achieve high network performance which depends on the structural properties of the network topology. We also show that our proposed routing scheme, which requires minimum local information, achieves high network performance.     

On the appropriate monitoring period for voltage flicker measurement in the presence of distributed generation

Voltage flicker or voltage fluctuations are considered a major power quality problem causing temperature rise, generators and motors overloading and affecting humans through the irritating light flicker. It is expected that the level of voltage flicker will increase due to the increased penetration of distributed generation (DG) in the distribution system. Site monitoring is required to make sure that the level of voltage flicker is within the allowed limit. In order to determine the appropriate monitoring period for voltage flicker measurement while considering DGs, two case studies were considered in the paper; 1 week and 1 day monitoring periods. The results reveal that a monitoring period of 1 week may be very long especially in the presence of DG and it may hide valuable information. On the other hand a 1-day monitoring period is more appropriate in these situations. Therefore it is recommended to use 1-day monitoring period instead of 1 week especially in the presence of DG.     

A household’s power load response to a change in the electricity pricing scheme: An expanded microeconomic-physical approach

Energy economists are interested in how changes in electricity prices prompt a response in end-user electricity demand. If historical prices are low or seldom change, it becomes difficult to estimate price elasticities statistically, especially in the short-run. Thus, a framework that merges the physical equations that govern how electricity is consumed, and a utility-maximizing household the responds to varying expenditures on electricity, is used.We have parameterized the physical component to a house in Saudi Arabia. Three electricity pricing schemes are analyzed: progressive tariffs, time-of-use prices, and real-time prices. We show that for a household with a low preference for electricity, slight price increases do warrant adjustment in indoor temperature in the hot summer months and lower consumer electronics use. Since we adopt a dwelling in Saudi Arabia, the response measure that is most exercised is the thermostat set-point adjustment. A subdued response is found for households that have adopted higher energy efficiency, or have high preference for electricity.     

Nested saturation based control of an actuated knee joint orthosis

Wearable robots have opened a new horizon for assistance and rehabilitation of dependent/elderly persons. The present study deals with the control of an actuated lower limb orthosis at the knee joint level. The dynamics of the shank–foot–orthosis system are expressed through a nonlinear second order model taking into account viscous, inertial and gravitational properties. Shank–foot–orthosis system parameters are identified experimentally. Since the underlying dynamic model is nonlinear, a robust control strategy is needed to guarantee an accurate and precise movement generation. The proposed control strategy ensures, at the same time, the stability of the closed-loop system. A bounded control torque is applied to guarantee the asymptotic stability of the shank–foot–orthosis. The generated control respects the physical constraints imposed by the system. The effectiveness of the proposed control strategy is shown in real-time in terms of stability, position tracking performances and robustness with respect to identification errors and external disturbances.     

A novel hardware/software embedded system based on automatic censored target detection for radar systems

This paper presents a practical design exploration for a new application related to real-time, high-resolution target detection for radar systems. In this paper, an embedded architecture that combines the hardware and software components in a single platform is experienced using a field programmable gate array FPGA-based PC-board. The detection process utilises three techniques: namely, automatic censored ordered statistics detection (ACOSD), cell averaging (CA) and ordered statistics (OS) CFAR techniques, all of which operate in parallel to increase the accuracy of the detection and to reduce the false-alarm rate for both homogeneous and non-homogeneous environments. A prototype of the embedded system detector has been implemented for homogeneous and non-homogeneous environments on Stratix IV FPGA Board. The prototype operates at 200 MHz and performs real-time target detection with an execution delay of 0.27 μs, which is less than the critical time (0.5 μs) for high-resolution detection.     

Diffusion analysis and modeling of kinetic behavior for treatment of brine water using electrodialysis process

In this study, the removal of monovalent and divalent cations, Na⁺, K⁺, Mg²⁺, and Ca²⁺, in a diluted solution from Chott-El Jerid Lake, Tunisia, was investigated with the electrodialysis technique. The process was tested using two cation-exchange membranes: sulfonated polyether sulfone cross-linked with 10% hexamethylenediamine (HEXCl) and sulfonated polyether sulfone grafted with octylamine (S-PESOS). The commercially available membrane Nafion® was used for comparison. The results showed that Nafion® and S-PESOS membranes had similar removal behaviors, and the investigated cations were ranked in the following descending order in terms of their demineralization rates: Na⁺ > Ca²⁺ > Mg²⁺ > K⁺. Divalent cations were more effectively removed by HEXCl than by monovalent cations. The plots based on the Weber–Morris model showed a strong linearity. This reveals that intra-particle diffusion was not the removal rate-determining step, and the removal process was controlled by two or more concurrent mechanisms. The Boyd plots did not pass through their origin, and the sole controlling step was determined by film-diffusion resistance, especially after a long period of electrodialysis. Additionally, a semi-empirical model was established to simulate the temporal variation of the treatment process, and the physical significance and values of model parameters were compared for the three membranes. The findings of this study indicate that HEXCl and S-PESOS membranes can be efficiently utilized for water softening, especially when effluents are highly loaded with calcium and magnesium ions.     

Distributed Coalition Formation Games for Secure Wireless Transmission

Cooperation among wireless nodes has been recently proposed for improving the physical layer (PHY) security of wireless transmission in the presence of multiple eavesdroppers. While existing PHY security literature answered the question “what are the link-level secrecy rate gains from cooperation?”, this paper attempts to answer the question of “how to achieve those gains in a practical decentralized wireless network and in the presence of a cost for information exchange?”. For this purpose, we model the PHY security cooperation problem as a coalitional game with non-transferable utility and propose a distributed algorithm for coalition formation. Using the proposed algorithm, the wireless users can cooperate and self-organize into disjoint independent coalitions, while maximizing their secrecy rate taking into account the costs during information exchange. We analyze the resulting coalitional structures for both decode-and-forward and amplify-and-forward cooperation and study how the users can adapt the network topology to environmental changes such as mobility. Through simulations, we assess the performance of the proposed algorithm and show that, by coalition formation using decode-and-forward, the average secrecy rate per user is increased of up to 25.3 and 24.4% (for a network with 45 users) relative to the non-cooperative and amplify-and-forward cases, respectively.     

Estimation of shale volume using a combination of the three porosity logs

An equation was developed for evaluating the volume of shale using standard porosity logs such as neutron, density and acoustic logs. The equation is written in terms of several parameters that are readily available from well-log measurements. This equation, which takes into consideration the effect of matrix, fluid and shale parameters, applies reasonably well for many shaly formations independent of the distribution of shales. The results demonstrate the applicability of the equation to well-log interpretation as a procedure for computing shale volume in shaly sand sedimentary sections.Three key advantages of the proposed equation are: (1) it incorporates several parameters that directly or indirectly affect the determination of shale in one equation, (2) it integrates the three porosity tools for a more accurate determination, and (3) it works well in hydrocarbon-bearing formations and where radioactive material other than shale is present.Successful application of the equation to shaly sand reservoirs is illustrated by analyses of samples from the Gulf of Suez.     

Implicitly Heterogeneous Multi-Stage Programming

Previous work on semantics-based multi-stage programming (MSP) language design focused on homogeneous designs, where the generating and the generated languages are the same. Homogeneous designs simply add a hygienic quasi-quotation and evaluation mechanism to a base language. An apparent disadvantage of this approach is that the programmer is bound to both the expressivity and performance characteristics of the base language. This paper proposes a practical means to avoid this by providing specialized translations from subsets of the base language to different target languages. This approach preserves the homogeneous “look” of multi-stage programs, and, more importantly, the static guarantees about the generated code. In addition, compared to an explicitly heterogeneous approach, it promotes reuse of generator source code and systematic exploration of the performance characteristics of the target languages. To illustrate the proposed approach, we design and implement a translation to a subset of C suitable for numerical computation, and show that it preserves static typing. The translation is implemented, and evaluated with several benchmarks. The implementation is available in the online distribution of MetaOCaml.