4-aperture differential image motion monitor as a new approach for estimating atmospheric turbulence parameters

The present study aims to evaluate the possibility of simultaneous measurements of Fried parameter and atmospheric Zernike defocus by measuring defocus aberration with 4-aperture differential image motion monitor (DIMM) for a portable telescope. Based on the results, a relation was observed between the variances of the defocus aberration (4-aperture defocus) and Fried parameter for G-tilt and Z-tilt methods. In addition, the variance of the 4-aperture defocus was compared with those of the Zernike defocus and the conventional DIMM and the results indicated a linear relationship. Based on the telescope and 4-aperture specifications, the variance of the 4-aperture defocus was converted into the Zernike defocus or the DIMM variances. Finally, the ability of estimating atmospheric coherence time by measuring the variance of the Zernike defocus velocity or the sum of the variances of two astigmatisms velocities with 4-aperture DIMM was investigated.     

Multivariable autopilot design for sounding rockets using intelligent Eigenstructure Assignment technique

When a sounding rocket rolls about its longitudinal axis, the role of angle of attack and sideslip angle exchange regularly. This interchange causes the aerodynamic moments to alternate between pitching and yawing moments, which, coupled with the moment of inertia effects, further aggravates the inertial cross-coupling. In this paper, first we analyze the cross-coupling phenomena and derive a Linear, Time-Invariant (LTI), multi input — multi output model of a spinning sounding rocket and then we design an autopilot for this system. An application of multivariable control technique is presented to the design of the autopilot. The involved controller is advanced by combining Eigenstructure Assignment (EA) approach with the Particle Swarm Optimization (PSO) algorithm. Results of linear and nonlinear simulations are reported to demonstrate the performance and stability margin of the considered autopilot.     

Nature‐inspired meta‐heuristic algorithms for solving the load balancing problem in the software‐defined network

The growth of the networks has difficult network management. Recently, a concept called software‐defined network (SDN) has been proposed to address this issue, which makes network management more adaptable. Control and forwarding planes are separated in SDN. The control plane is a centralized logical controller that controls the network. The forwarding plane that consists of transfer devices is responsible for transmitting packets. Because the network resources are limited, optimizing the use of resources in the networks is an important issue. Load balancing improves the balanced distribution of loads across multiple resources in order to maximize the reliability and network resources efficiency. SDN controllers can create an optimal load balancing compared to traditional networks because they have a network global view. The load‐balancing problem can be solved using many different nature‐inspired meta‐heuristic techniques because it has the NP‐complete nature. Hence, for solving load balancing problem in SDN, nature‐inspired meta‐heuristic techniques are important methods. However, to the best of our knowledge, there is not a survey or systematic review on studying these matters. Accordingly, in the area of the load balancing in the SDN, this paper reviews systematically the nature‐inspired meta‐heuristic techniques. Also, this study demonstrates advantages and disadvantages regarded of the chosen nature‐inspired meta‐heuristic techniques and considers their algorithms metrics. Moreover, to apply better load balancing techniques in the future, the important challenges of these techniques have been investigated.     

Real-Time Operation of Pumping Systems for Urban Flood Mitigation: Single-Period vs. Multi-Period Optimization

To reduce flood risk in urban regions, it is important to optimize the performance of operational elements such as gates and pumps. This paper compares the performances of two approaches of multi-period and single-period simulation-optimization that are used to derive real-time control policies for operating urban drainage systems. The EPA storm water management model (SWMM), converting real-time rainfall data to surface runoff at network control points, i.e. pump stations, is linked to the particle swarm optimization (PSO) algorithm, evaluating the system operation performance measure (objective function) for different sets of control policies. A prototype network in a portion of the Seoul urban drainage system is used to investigate the efficiency of the proposed approaches. Results justify the high efficiency of multi-period optimization, leading to 32 and 29% average reductions in peak water level violations from a pre-defined permissible threshold at target points and the number of pump switches, respectively, in comparison with the online single-period optimization. The myopic policies derived by single-period optimization are not reliable, and in some cases, they even perform worse than ad-hoc policies applied by system operators based on their past experiences.     

Deformation Tracking in 3D Point Clouds Via Statistical Sampling of Direct Cloud-to-Cloud Distances

Dense three-dimensional (3D) point clouds of infrastructure systems, generated from laser scanners or through multi-view photogrammetry, have significant potential as a source of nondestructive evaluation information. The growing maturity of these techniques make them capable of reconstructing photorealistic 3D models with accuracy on the millimeter scale, adequate for inspection and evaluation practices. Manual analysis of these point clouds is often time consuming and labor intensive and does not provide explicit information on structural performance and health conditions, highlighting the need for new techniques to efficiently analyze these models. This paper presents a new 3D point cloud change analysis approach for tracking small movements over time through localized spatial analytics. This technique uses a combination of a direct point-wise distance metric in conjunction with statistical sampling to extract structural deformations. By identifying and tracking these changes, mechanical deformations can be quantified along with the associated strains and stresses. These measurements can then be used to assess both service conditions and remaining system capacity. The results of a series of laboratory experiments designed to test the proposed approach are presented as well. The findings indicate measurement accuracy on the order of +/? 0.2 mm (95% confidence interval), making it suitable for accurate and automatic geometrical analyses and change detection in a variety of infrastructure inspection scenarios. Ongoing work seeks to connect this technique to automated finite element model updating, and to field test the measurement technique.     

Intrinsic optical bistability in doped polymer

One of the most interesting and applicable effects of nonlinear optics is optical bistability. This phenomenon is exhibited by certain resonant optical structures where it is possible to have two stable steady transmission states for the device, depending on the history of the input. Such a bistable device may be useful for optical computing elements as a result of its memory characteristics. Optical bistability behaviour is usually observed by inserting a nonlinear matter inside a Fabry–Perot interferometer. But in this study, it was shown that this can be achieved without the application of any optical resonator. Two laser beams were used to interact with the photorefractive media (doped PMMA polymer) which resulted in the bistability of the intensity of transmitted wave. Feedback was provided by a periodic grating created in the photorefractive polymer PMMA.     

Numerical solution of multi-variable order fractional integro-differential equations using the Bernstein polynomials

In practice, computer simulations cannot be perfectly controlled because of the inherent uncertainty caused by variability in the environment (e.g., demand rate in the inventory management). Ignoring this source of variability may result in sub-optimality or infeasibility of optimal solutions. This paper aims at proposing a new method for simulation–optimization when limited knowledge on the probability distribution of uncertain variables is available and also limited budget for computation is allowed. The proposed method uses the Taguchi robust terminology and the crossed array design when its statistical techniques are replaced by design and analysis of computer experiments and Kriging. This method offers a new approach for weighting uncertainty scenarios for such a case when probability distributions of uncertain variables are unknown without available historical data. We apply a particular bootstrapping technique when the number of simulation runs is much less compared to the common bootstrapping techniques. In this case, bootstrapping is undertaken by employing original (i.e., non-bootstrapped) data, and thus, it does not result in a computationally expensive task. The applicability of the proposed method is illustrated through the Economic Order Quantity (EOQ) inventory problem, according to uncertainty in the demand rate and holding cost.

     

Rheology, Morphology and Estimation of Interfacial Tension of LDPE/EVA and HDPE/EVA Blends

Summary Rheological characteristics and morphology of low-density polyethylene (LDPE) /ethylene vinyl acetate copolymer (EVA) and high-density polyethylene (HDPE)/EVA blends were compared. Morphological examinations clearly reveal a two-phase morphology in which the LDPE/EVA blends have smaller dispersed domain size than HDPE/EVA Furthermore, LDPE/EVA shows a finely interconnected morphology at 50wt% of EVA while HDPE/EVA exhibits a coarse co-continuous morphology at the same composition. The morphological observations can be attributed to the lower viscosity ratio and lower interfacial tension in the LDPE/EVA system. The Palierne model also successfully fits to the experimental data giving higher values for interfacial tension of HDPE/EVA system as compared to LDPE/EVA.