Application of Monte‐Carlo simulation to estimate the kinetic parameters for pyrolysis—Part I

A mathematical model was developed to represent pyrolysis. The components of primary and secondary pyrolysis reactions were simply lump into different groups and were represented through a set of pseudo‐first‐order reactions. This study presents an algorithm to estimate the kinetic parameters using Monte‐Carlo (MC) simulation. The combination of an analytical reaction model and the MC simulation technique rapidly generates a large number of numerical values. Results show that MC‐simulated data and experimental data are in fair agreement. Though the technique developed in this study proved to have potential, more experimental data are needed to check the robustness of the model. © 2011 Canadian Society for Chemical Engineering     

High-performance optical wavelength-selective switches based on double ring resonators

In order to improve the performance of optical wavelength-selective switches based on double micro-ring resonators, an asymmetric intra-step-barrier coupled double strained quantum wells (AICD-SQWs) structure is utilized as the active light guiding medium. The AICD-SQW active layer has advantages, such as large change range in absorption coefficient, high extinction ratio, large Stark shift and very low insertion. For predicting the switching characteristics of double ring resonators structure, the absorption coefficient and real refractive index changes of the AICD-SQW active layer are calculated for different applied electric fields for TE input light polarization. Simulation results show that switching characteristics strongly depend on changes in absorption coefficient and real refractive index of active layer. In addition, isolations of 37.44 dB and 26.84 dB are realized between drop and through ports, when drop and through ports are ON and OFF, respectively, and vice versa.     

An adaptive spacetime discontinuous Galerkin method for cohesive models of elastodynamic fracture

This paper describes an adaptive numerical framework for cohesive fracture models based on a spacetime discontinuous Galerkin (SDG) method for elastodynamics with elementwise momentum balance. Discontinuous basis functions and jump conditions written with respect to target traction values simplify the implementation of cohesive traction–separation laws in the SDG framework; no special cohesive elements or other algorithmic devices are required. We use unstructured spacetime grids in a h‐adaptive implementation to adjust simultaneously the spatial and temporal resolutions. Two independent error indicators drive the adaptive refinement. One is a dissipation‐based indicator that controls the accuracy of the solution in the bulk material; the second ensures the accuracy of the discrete rendering of the cohesive law. Applications of the SDG cohesive model to elastodynamic fracture demonstrate the effectiveness of the proposed method and reveal a new solution feature: an unexpected quasi‐singular structure in the velocity response. Numerical examples demonstrate the use of adaptive analysis methods in resolving this structure, as well as its importance in reliable predictions of fracture kinetics. Copyright © 2009 John Wiley & Sons, Ltd.     

Novel plasma nitriding-oxidizing duplex treatment of AISI 316 austenitic stainless steel

In this work, plasma nitriding and plasma nitriding-oxidizing treatment have been performed on AISI 316 austenitic stainless steel. In order to evaluate its response to this treatment, their microstructures and wear resistance have been compared with conventional plasma nitrided. The treatment of plasma nitriding was performed at temperature of 450 °C for 5 h with gas mixture of N₂/H₂:1/3 whereas plasma nitriding-oxidizing was performed with the same parameters of plasma nitriding and temperature of 450 °C with gas mixture of O₂/H₂:1/5 for 15, 30 and 60 min. The structural, mechanical and tribological properties were analyzed using XRD, SEM, microhardness testing and pin-on-disk tribotesting. The results showed that oxidation treatment reduces wear resistance of plasma nitrided sample under high loads. Furthermore the tribological evaluation indicates that by increasing the oxidation time further reduction of wear resistance can be occurred. In addition, it was found that oxidation treatment after plasma nitriding provides an important improvement in the friction coefficient against a AISI 52100 steel pin and reduces surface roughness.     

A critical review on spark plasma sintering of copper and its alloys

Journal of Materials Science - Copper and its alloys have been in the service of humankind earlier than any other metal throughout history. In the present review, all aspects of the SPS of copper...     

The episodal associative memory: Managing manufacturing information on the basis of similarity and associativity

In this paper we report on continuing research on the organization and functionalities of a certain type of computer-implemented associative memory. The associative memory in question is being created to serve as part of a feature-based design system, at present to be used primarily in support of the design, fabrication planning, or inspection planning of discrete mechanical machine parts. This present effort is consonant with prior related work in the realm of case-based reasoning, especially as related to the role of memory in design. Our associative memory innovations are in the use of fuzzy sets and neural net computing in the representation, storage and retrieval of design, fabrication, inspection and materials knowledge. We have designed and implemented a considerable portion of the associative memory and have demonstrated retrieval of previous designs on the basis of qualitative geometry. We have also demonstrated ability to explore materials composition with the objective of meeting critical materials properties constraints.     

Genetically modified multiuser detection for code division multipleaccess systems

The problem of multiple access interference (MAI) and intersymbol interference (ISI) suppression in code division multiple access (CDMA) systems is considered. By combining the theory of multiuser detection (MUD) and evolutionary computation, a hybrid genetic engine is proposed, suitable for the detection of CDMA signals in the presence of MAI and ISI. The proposed hybrid detector structure can be extended to most multiuser detectors and used as the base detector within the structure. Using random selection, mutation and crossover operators and a unique chromosome structure, the genetic algorithm evolves the base detector to a group of more efficient detectors in terms of bit-error rate performance. First, a new packet-level genetic MUD technique, using a conventional single user detector as the base detector, is proposed for asynchronous CDMA (ACDMA) with negligible ISI. Then the signal-subspace-based minimum mean square error detector is chosen as a base detector and wrapped inside the hybrid genetic engine to evolve to a better structure nearly to eliminate both ISI and MAI. The novelty of the proposed structure is the way the deterministic closed-form solution of the base detector is mapped to a genetic engine resulting in a group of more efficient and adaptive detectors     

An energy-efficient power allocation scheme for millimeter-wave MIMO-NOMA systems

There are many challenges in fifth generation (5G) telecommunication systems, due to the increasing demands and applications. The most important of which are need to have higher energy efficiency (EE) and spectral efficiency (SE). They are critical in the practical multiple-input multiple-output (MIMO) telecommunication systems. Non-orthogonal multiple access (NOMA) methods and millimeter-waves can be used in conjunction with MIMO systems to improve their EE and SE performance. In this paper, we investigate the application of NOMA and mm-Wave transmission in the downlink of MIMO systems. Then, we formulate the optimization problem for users in MIMO-NOMA systems to maximize the EE that is subject to minimum data rate to satisfy required quality of service (QoS) and maximum transmission power. To achieve the optimal power allocation for users, we reach a problem for the EE maximization that is non-convex and solution of the optimization problem is not trivial. We exploit a lower bound of the data rate and the Lagrange dual function to convert it to a convex and unconstrained problem, which is easy to solve. In the next step, we derive a relation for determining the optimal power allocation of users. In addition, a numerical algorithm is presented that can be used to solve the problem. According to the simulation results of the proposed algorithm, our method performs better and provides higher EE than both orthogonal multiple access and equal power allocation schemes.