Exact stability of a platoon of vehicles by considering time delay and lag

The problem of controlling a string of vehicles moving in one dimension is considered so that they all follow a lead vehicle with constant time headway spacing between successive vehicles. Due to realistic design and execution, the negative effect of the tracking lag parameter and time delay is taken into account. By applying an acceleration feedforward, the distance error of each vehicle will be independent of the behavior of other vehicles. As a result, the vehicle is better able to track a desired trajectory, which improves the string stability. Cluster treatment of characteristic roots (CTCR) paradigm is utilized to reveal the stabilizing parametric regions in the domain of the time delay to render the stability of closed loop system. The string stability analysis is performed to evaluate the disturbance attenuation. Finally, an example of multiple vehicle platoon control is presented, which demonstrates the effectiveness of the proposed method.     

Neural network solution for a real-time no-reference video quality assessment of H.264/AVC video bitstreams

The ever-growing video streaming services require accurate quality assessment with often no reference to the original media. One primary challenge in developing no-reference (NR) video quality metrics is achieving real-timeliness while retaining the accuracy. A real-time no-reference video quality assessment (VQA) method is proposed for videos encoded by H.264/AVC codec. Temporal and spatial features are extracted from the encoded bit-stream and pixel values to train and validate a fully connected neural network. The hand-crafted features and network dynamics are designed in a manner to ensure a high correlation with human judgment of quality as well as minimizing the computational complexities. Proof-of-concept experiments are conducted via comparison with: 1) video sequences rated by a full-reference quality metric, and 2) H.264-encoded sequences from the LIVE video dataset which are subjectively evaluated through differential mean opinion scores (DMOS). The performance of the proposed method is verified by correlation measurements with the aforementioned objective and subjective scores. The framework achieves real-time execution while outperforming state-of-art full-reference and no-reference video quality assessment methods.

     

A Survey on Traffic Management in Software-Defined Networks: Challenges,Effective Approaches,and Potential Measures

Software-defined networks (SDNs), as an emerging paradigm by separating the control plane from the data plane, increases flexibility and network utilization and reduces redundancy and operational cost. Traffic management of software-defined networks can be defined as network traffic monitoring and analyzing measures to improve network performance and quality of service metrics. Traffic management as an effective instrument for optimizing network traffic can offer the appropriate services according to network situation. Due to the inherent characteristics of SDN, special techniques are required to analyze, predict, and adapt the network traffic in order to achieve an efficient traffic management mechanism. This paper surveys traffic management techniques of SDN in four distinct categories including, routing, load balancing, congestion control, and flow control to cover the impressible issues. Moreover, the differences between SDN and traditional networks are analyzed in terms of traffic management necessities across the various groups to further determine the dimensions affecting research in this area. Furthermore, the available algorithms in each group and their role in traffic management are reviewed as well as the research challenges and future trends.

     

A second-order blind source separation method for bilinear mixtures

In this paper, we are interested in the problem of Blind Source Separation using a Second-order Statistics (SOS) method in order to separate autocorrelated and mutually independent sources mixed according to a bilinear (BL) model. In this context, we propose a new approach called Bilinear Second-order Blind Source Separation, which is an extension of linear SOS methods, devoted to separate sources present in BL mixtures. These sources, called extended sources, include the actual sources and their products. We first study the statistical properties of the different extended sources, in order to verify the assumption of identifiability when the actual sources are zero-mean and when they are not. Then, we present the different steps performed in order to estimate these actual centred sources and to extract the actual mixing parameters. The obtained results using artificial mixtures of synthetic and real sources confirm the effectiveness of the new proposed approach.     

SDN-based wireless user management system

The degradation of end-to-end quality of service (QoS) on mobile users is becoming a common issue for IEEE 802.11 infrastructure-based networks in crowded areas. This research tackles the issue by employing an SDN framework on an integrated wireless/wired environment. Thereby, we present the development and implementation of a system that performs user management by analyzing the network load from the OpenFlow statistics, as well as the wireless information collected from the associated users. In order to analyse the behaviour of the proposed user migration algorithm, we evaluate the system under scenarios with different traffic load and user session duration. From the experiments, we observed that in several cases wireless users get a considerable QoS improvement at the application layer (up to 30% improvement in throughput and up to 20% in delay in our simulations) once the system is activated. Based on the results, we present an analysis on how and when user migration in multi-access point IEEE 802.11 networks can be most effective.     

New simple transistor realizations of second- generation voltage conveyor

In this paper, two new complementary metal oxide semiconductor (CMOS) realizations for second-generation voltage conveyor (VCII) are presented. The first proposed VCII has a very simple structure employing only six transistors. The second proposed VCII employs 11 transistors, and none of the transistors at both proposed circuits suffer from the body effect. Small-signal analysis, parasitic elements, and input-referred noise of the proposed VCIIs are given. Moreover, a new active element called voltage controlled second-generation voltage conveyor (VC-VCII) is proposed as dual element of current controlled second-generation current conveyor (CCCII) active element. Its parasitic resistance at the Y terminal can be controlled electronically. Two presented CMOS structures of VCII are worked as VC-VCII with slight modification. Proposed circuits are simulated in Cadence Analog environment using TSMC 0.18-μm process parameters with ±0.9-V supply voltages. Both CMOS structures occupy a small chip area of 276.8 and 271 μm², respectively. The bandwidth of the current follower stage of the proposed VCIIs is found as 794 MHz, whereas the bandwidth of the voltage follower stage for the first and second proposed VCIIs is found as 2.57 and 1.92 GHz, respectively. As an application example, voltage-mode first-order low-pass filter has been given with its tunable gain by using VC-VCII.     

A reappraisal of transition elements in linear elastic fracture mechanics

This article offers a detailed comparison of the transition elements described by P.P. Lynn and A.R. Ingraffea [International Journal for Numerical Methods in Engineering 12,1031–1036] and C. Manu[Engineering Fracture Mechanics 24,509–512]. The source of a numerical phenomenon in using Manu's transitionelement (TE) is explained. The effect of eight-noded TEs with differentquarter-point elements (QPE) on the calculated stress intensity factors (SIFs) isinvestigated. Strain at the crack tip is shown to be singular for any ray emanating from the crack tip within an eight-noded TE, but strain has bothr ^–1/2andr ^–1singularities, withr ^–1/2dominating for large TEs. Semi-transition elements (STEs) are defined and shown to have a marginal effect on the calculated SIFs. Nine-nodedtransition elements are formulated whose strain singularity is shown to be the same as that of eight-noded TEs. Then the effect of eight-noded and nine-noded TEs with collapsed triangular QPEs, and rectangular and nonrectangular quadrilateral eight-noded and nine-noded QPEs, is studied, and nine-noded TEs are shown to behave exactly like eight-noded TEs with rectangular eight-noded and nine-noded QPEs and to behave almost the same with other QPEs. The layered transition elements proposed by V. Murti and S.Valliapan [Engineering Fracture Mechanics 25, 237–258] areformulated correctly. The effect of layered transition elements is shown by two numerical examples.     

Synthesis and characterization of new soluble and thermostable polyimides via novel diisocyanates

A facile synthesis of two novel diisocyanates containing methylene groups and preformed imide structure is described. Furthermore, six thermally stable and soluble polyimides were synthesized by polycondensation of these two diisocyanates with pyromellitic dianhydride (PMDA), 3, 3 ′,4, 4 ′‐benzophenonetetracarboxylic dianhydride (BTDA) and hexafluoroisopropylidene‐2,2‐bis‐(phthalic anhydride) (6FDA) in N,N ‐dimethyl acetamide. All monomers and polymers were characterized by conventional methods and their physical properties such as solution viscosity, solubility properties, thermal stability and thermal behaviour were studied. © 1999 Society of Chemical Industry     

Effect of parameters on roll dynamic response of an articulated vehicle carrying liquids

Directional response and roll stability characteristics of a partly filled tractor semi-trailer vehicle, with cylindrical tank, under different parameters and conditions are investigated. The effective parameters and conditions in the stability of a tractor semi-trailer carrying liquid can be considered as filled volume, kinematic viscosity of liquid cargo and vehicle steering input. The dynamic interaction of liquid cargo with the tractor semi-trailer vehicle is evaluated by integrating a dynamic slosh model of the partly filled tank with five-degrees-offreedom of a tractor semi-trailer tank model. The dynamic fluid slosh within the tank is modeled using three-dimensional Navier-Stokes equations, coupled with the volume-of-fluid equations and analyzed using FLUENT software. The coupled tank-vehicle model is subsequently analyzed to determine the roll stability characteristics for different conditions and maneuvers. The results show effects of parameter variations on roll stability of the vehicle carrying liquid and also fluid’s behavior in interaction with a vehicle’s dynamics.