International Journal of Engineering
Volume:24 Issue: 4, Nov 2011

Marvelous bending/straightening effects of two-way shape memory alloy (TWSMA) help their employment in design and manufacturing of new medical appliances. Constrained ageing with bending load scheme can induce two-way shape memory effect (TWSME). Scanning electron microscope (SEM) analysis, electrical resistivity measurement (ERM) and differential scanning calorimetry (DSC) are employed to determine the property change due to flat strip constrained aging. Results show that flat-annealing prior to the aging shifts NiTi transformations temperatures higher. Superelastic behavior of the as-received/flat-annealed/aged samples with more adequate transition temperatures due to biological tissue replacement is studied by three-point flexural tests. Results show that curing changes the transition points of the NiTi strips. These changes affect the shape memory behavior of the NiTi strips embedded within the biocompatible flexible composite segments.

Development of technology has made possible the invention of innovative and modern methods to solve partially the problems caused by traffic congestion, through decreasing the need for physical transportation; one such method being telecommuting. Few predictions have been reported regarding its aggregate demand at the level of a city, generally because of the complexity and multi-dimensionality of the subject. In this paper, an approach for the estimation of potential telecommuting demand is proposed and applied for the city of Tehran, using a 3-level generalization process to compensate for the incompleteness of the unattainable vast and expensive data. In the first level of the proposed approach, the matrix of average potential telecommuting demand for 36 job categories is derived. In the second level, the data of 14 percent of the government employees are collected, in the third level, the geographic distribution of all governmental employees with telecommuting potential is determined. Results show that 53,898 out of 148,551 government employees are able to participate in telecommuting programs on a daily basis, removing 53,898 peak hour work trips on a daily basis. Although based on rather strong assumptions, forced by the limitation of data, the approach is implemented for Tehran.

The present work demonstrates the successful application of a simple active vibration control procedure based on structural dynamics. Based on mathematical and structural dynamics’ theories, the appropriate locations of sensor and actuator locations of the smart structure are predicted. Also, the optimum value of actuator force which controls the structural vibrations as quickly as it is possible is formulated so that the first damping coordinates becomes critical. The validity and efficiency of the proposed method have been examined by investigating the active vibration suppression of some classic structural models. The results presented here, show the ability of suggested active control processes in suppression of the unwanted structural vibrations.

In this paper, the region in which the structural system is situated is divided into four subregions, namely upper, lower, left and right subregions. The stiffness matrix of the entire system is then formed and using the existing direct symmetry and reverse symmetry, the relationships between the entries of the matrix are established. Examples are included to illustrate the steps of the method.

Supply chain excellence has a real huge impact on business strategy. Building supply chains (SCs) as flexible system represents one of the most exciting opportunities to create value. This requires integrated decision making amongst autonomous chain partners with effective decision knowledge sharing among them. The key to success lies in knowing which decision has more impact on the supply chains performance. Here, we propose a supply chain which considers multiple depots, multiple vehicles, multiple products, multiple customers, and different time periods. This paper presents a mathematical model for selecting the appropriate depots among candidate depots, the allocation of orders to depots and vehicles, also the allocation of the returning vehicles to depots, to minimize the total costs.

In this paper static and dynamic response of nanotweezers composed of two carbon nanotube (CNT) arms are investigated. Taking into account a continuum model and considering the electrostatic actuation as well as the presence of the van der Waals forces, the static nonlinear equations are solved by a step by step linearization and Galerkin projection method. Simulating the closing dynamics of a specific nanotweezer, the effective diameters of its nanotube cantilevers are specified and compared with existing experimental data. Then by imposing a step DC voltage and taking into account the inertia effects, dynamic responses and pull-in conditions of nanotweezers are studied. In the analyses, the effects of various parameters such as initial gap, nanotube length and diameter on the pull-in conditions are investigated. Effects of damping and asymmetric stiffness''s of the arms on the pull-in voltages of a nanotweezer are also reported. Comparing the results with the published experimental data shows that the use of continuum model and employing the Galerkin based step by step linearization method (SSLM) could effectively simulate the response of nanotweezers.

This paper deals with finite capacity single server queuing system with vacations. Vacation starts at rate nu if the system is empty. Also the server takes another vacation if upon his arrival to the system, finds the system empty. Customers arrive in the system in Poisson fashion at rate lamda0 during vacation, faster rate lamdaf during active service and slower rate lamdas during the breakdown. Customers are served exponentially with the rate mu. Server breakdowns at rate b and it immediately repaired exponentially with the rate r. We derive the explicit formulas for queue length distribution, average queue length, average number of customers in the system and average waiting time for a customer in queue and in the system. Numerical illustrations have been cited to show the model proposed is practically sound.

In this paper authors have considered a system having three units A, B1 and B2. A is controlled by a controller and B1 and B2 are independent. Two repairmen are involved in repair of the system. One of the repairmen (the first) is the foreman (boss) and the other an assistant (apprentice). Whenever any unit fails, repair is undertaken by boss. If the boss is busy in repairing and at the same time other unit fails then the repair is undertaken by apprentice. The mathematical model obtained has been analyzed with the application of Copula. The Laplace transforms of the transition state probabilities being in various complex systems have been obtained. Using Abel’s lemma steady state behavior of the system has also been examined. MTTF and important characteristic of reliability measures have also been evaluated.

Aerodynamic drag is an important factor in vehicles fuel consumption. Pressure drag which is the main component of total drag is a result of boundary layer separation from vehicle surface. Flow control methods are applied to avoid or at least delay separation. Depending upon whether these methods consume energy to control the flow or not, they are called active or passive control methods. In this paper, we investigate experimentally, the effect of suction and base bleeding as two active flow control methods on aerodynamic drag reduction of Ahmed body with 35 degree rear slant angle. Suction in boundary layer is applied in order to delay flow separation by extracting flow particles with low kinetic energy near the model surface and the sucked air is blown into the wake of the model to increase the static pressure of the wake region. The location of suction is at the beginning of rear slant surface and the location of blowing is at the middle part of rear vertical part of the model. Moreover, the effect of change in control flow rate and suction and base bleeding area is investigated.