Effects of material thickness and processing method on poly(lactic-co-glycolic acid) degradation and mechanical performance

In this study, the effects of material thickness and processing method on the degradation rate and the changes in the mechanical properties of poly(lactic-co-glycolic acid) material during simulated physiological degradation were investigated. Two types of poly(lactic-co-glycolic acid) materials were considered: 0.12?mm solvent-cast films and 1?mm compression-moulded plates. The experimental results presented in this study were compared to the experimental results of Shirazi et al. (Acta Biomaterialia 10(11):4695–703, 2014) for 0.25?mm solvent-cast films. These experimental observations were used to validate the computational modelling predictions of Shirazi et al. (J Mech Behav Biomed Mater 54: 48–59, 2016) on critical diffusion length scale and also to refine the model parameters. The specific material processing methods considered here did not have a significant effect on the degradation rate and the changes in mechanical properties during degradation; however, they influenced the initial molecular weight and they determined the stiffness and hardness of the poly(lactic-co-glycolic acid) material. The experimental observations strongly supported the computational modelling predictions that showed no significant difference in the degradation rate and the changes in the elastic modulus of poly(lactic-co-glycolic acid) films for thicknesses larger than 100?μm.     

Trust establishment in cooperative wireless relaying networks

In cooperative wireless networks, relay nodes are employed to improve the performance of the network in terms of throughput and reliability. However, the presence of malicious relay nodes in the network may severely degrade the performance of the system. When a relay node behaves maliciously, there exists a possibility that such a node refuses to cooperate when it is selected for cooperation or deliberately drops the received packets. Trust establishment is a mechanism to detect misbehaving nodes in a network. In this paper, we propose a trust establishment method for cooperative wireless networks by using Bayesian framework. In contrast with the previous schemes proposed in wireless networks, this approach takes the channel state information and the relay selection decisions into account to derive a pure trust value for each relay node. The proposed method can be applied to any cooperative system with a general relay selection policy whose decisions in each cooperative transmission are independent of the previous ones. Moreover, it does not impose additional communication overhead on the system as it uses the available information in relay selection procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

Prediction of fabric handle value using ordinal regression model

Bed sheet fabric as a kind of home textile has been used since many years ago. Bed sheet is very significant because of being in direct contact with body consecutively for a long period of time. Bed sheet surplus qualitative parameters such as fiber substance, method of printing, finishing, etc., have a significant parameter called handle. In this paper, we proceeded to consider the relationship between fabric handle as a qualitative parameter and physical parameters which influenced the fabric handle using statistical modeling. The statistical model used was ordinal regression model. The modeling was done by SPSS V.19 software. We used 15 bed sheet fabrics. For subjective evaluation of 15 bed sheet fabrics, we selected 55 persons randomly as sample members according to Cochran’s formula. Population was selected from senior BS students and MS students at Isfahan University of Technology (IUT). We asked persons to classify bed sheet fabrics based on their preference of fabric handle from 1 (lowest) to 5 (highest). Physical parameters values were obtained through standard experiments. Finally, we analyzed obtained data through SPSS V.19 using ordinal regression model. Results showed a satisfying match between extracted data from the software and the real data from person’s evaluation.     

Cooperative effect of 2-(dibutylcarbamoyl)benzoic acid and 2-thenoyltrifluoroacetone for the synergistic extraction of lanthanide ions

2-(Dibutylcarbamoyl)benzoic acid (HL) has been examined for the extraction-separation of La³⁺, Eu³⁺ and Er³⁺ from aqueous chloride solutions into organic diluents; dichloromethane, ethylacetate and carbon tetrachloride. The efficiency and the selectivity of the extraction process were significantly affected by the organic diluent. The application of a mixture of HL and 2-thenoyltrifluoroacetone (HTTA) showed a synergistic effect on the extraction of the studied lanthanides. The extracted species was found to be as ML₃(HTTA) complexes (M is La³⁺, Eu³⁺ and Er³⁺). The proposed method was applied for the extraction of lanthanides from simulated leach solution of spent Ni-MH batteries.     

Seismic response of mega buckling‐restrained braces subjected to fling‐step and forward‐directivity near‐fault ground motions

Special characteristics of earthquakes in the near‐fault regions caused failures for many modern‐engineered structures. Fling‐step and forward‐directivity are the main consequences of these earthquakes. High‐amplitude pulses at the beginning of the seismograph have been obviously presented in forward‐directivity sites. These pulses have high amount of seismic energy released in a very short time and caused higher demands for engineering structures. Fling‐step is generally characterized by a unidirectional large‐amplitude velocity pulse and a monotonic step in the displacement time history. These monotonic steps cause residual ground displacements that are associated with rupture mechanism. In this paper, the seismic performance of steel buckling‐restrained braced frames with mega configuration under near‐source excitation was investigated. Fourteen near‐fault records with forward‐directivity and fling‐step characteristics and seven far‐faults have been selected. Nonlinear time‐history analyses of 4‐story, 8‐story, 12‐story and 15‐story frames have been performed using OpenSees software. After comparing the results, it is shown that, for all frames subjected to the selected records, the maximum demand occurred in lower floors, and higher modes were not triggered. Near‐fault records imposed higher demands on the structures. The results for near‐fault records with fling‐step were very dispersed, and in some cases, these records were more damaging than others. Copyright © 2014 John Wiley & Sons, Ltd.     

The MPAW of Ti-3Al-2.5V Thin Sheets and Its Effects on Mechanical and Microstructural Properties

This research work deals with joining of Ti-3Al-2.5V titanium alloy thin sheets by means of microplasma arc welding (MPAW). An experimental set-up was developed to produce specimens welded in butt joint under controlled welding parameters, such as voltage, current, travel speed, and shielding gas flow rate. The performance of MPAW process was examined by mechanical properties tests and microstructural characterization. Results show that tensile strength and elongation of the welded specimens for a range of specific input heat are comparable to those of the base material (BM). Scanning electron microscopy (SEM) images of the fracture surface presented characteristics of ductile rupture. Studies on microstructure morphology of the specimens at the fusion zone (FZ) and heat-affected zone (HAZ) reveal occurrence of phase transformation from high temperature β phase to acicular $ \alpha^{\prime} $ phase, while the BM is of equiaxed α with intergranular β. An increasing variation in hardness was measured at the HAZ and FZ, which can be attributed to the presence of acicular $ \alpha^{\prime} $ phase and decreasing the amount of β phase at these regions. Based on the experimental results, it can be stated that MPAW process is an effective method for joining Ti-3Al-2.5V thin sheets provided appropriate welding parameters are used.     

Optimal reliable relay selection in multiuser cooperative relaying networks

In this paper, we investigate the problem of optimal reliable relay selection in multiuser cooperative wireless networks in the presence of malicious relay nodes. A general discrete time queueing model for such networks is introduced which takes into account the dynamic variations of the channel state, the dynamic malicious behaviour of relay nodes as well as stochastic arrival of data packets into the system. The model consists of a set of mobile users, one destination node and a set of relay nodes which may be either mobile or fixed. The system uses the benefit of cooperative diversity by relaying in the decode and forward mode. We assume that each user either transmits its packets directly to the destination (direct mode) or transmits them with the cooperation of a selected relay node (cooperative mode). It is assumed that a centralized network controller manages the relay selection process in the system. At each time slot, a malicious relay node in the system may behave spitefully and refuse to cooperate with a user deliberately when it is selected to cooperate with that user. A malicious relay node usually acts stochastically to hide its malicious behaviour for longer time. In such a system, at each time slot the network controller should decide whether a user has to cooperate with any relay node or not and if so, which relay node must be selected for cooperation. First, we show that the malicious behaviour of relay nodes makes the stable throughput region shrink. Then, we propose a throughput optimal secure relay selection policy that can stabilize the system for all the arrival rate vectors strictly inside the network stability region. We show that the optimal policy is equivalent to finding the maximum weighted matching in a weighted bipartite graph at each time slot. Finally, we use simulations to compare the performance of the proposed policy with that of four other sub-optimal policies in terms of average queue occupancy (or queueing delay).     

Cellular Goore Game and its application to quality-of-service control in wireless sensor networks

The Journal of Supercomputing - The Goore Game (GG) is a model for collective decision-making under uncertainty, which can be used as a tool for stochastic optimization of a discrete variable...