Channel flow past bluff-body: outlet boundary condition,vortex shedding and effects of buoyancy

 Structure of laminar flow and heat transfer, in a two-dimensional horizontal plane channel differentially heated, with a built-in triangular prism is investigated from the numerical solutions of complete Navier–Stokes and energy equations. Results are obtained for Reynolds and Grashof numbers ranging respectively from 30 to 200 and from 0 to 1.5 × 10⁴ at Pr=0.71. In forced convection, results are specially presented to show how the vortex shedding at downstream affects the upstream. Also, two correlations giving the Strouhal and the averaged Nusselt numbers as functions of the Reynolds number are proposed. In mixed convection, the superposition of Von Karman street and convective cells is discussed. Received 15 May 2001     

Supporting design of primary shaped micro parts and systems through provision of experience

Nowadays, miniaturization is one observable trend in the development of new technical systems. Based on the miniaturization of existing macroscopic production technologies e.g. powder injection molding, a new process chain for the development of primary shaped microparts and systems is being developed in the collaborative research center 499 “design, production and quality assurance of molded micro components made of metallic and ceramic materials”. Because of the constantly evolving miniaturization and growing complexity of the developed microparts and systems, new development processes and methods are needed. Because of the mostly restrictive influence of the downstream phases (production and quality assurance) over the design phase, micro-specific design processes require well-founded knowledge about micro-specific manufacturing techniques (e.g. restrictions) which may be stored in form of design rules. However, many micro-specific aspects cannot be represented in design rules. In this paper the authors propose a new approach to ensure this other kind of knowledge.     

Optimizing NFV placement for distributing micro-data centers in cellular networks

With the popularity of mobile devices, the next generation of mobile networks has faced several challenges. Different applications have been emerged, with different requirements. Offering an infrastructure that meets different types of applications with specific requirements is one of these issues. In addition, due to user mobility, the traffic generated by the mobile devices in a specific location is not constant, making it difficult to reach the optimal resource allocation. In this context, network function virtualization (NFV) can be used to deploy the telecommunication stacks as virtual functions running on commodity hardware to meet users’ requirements such as performance and availability. However, the deployment of virtual functions can be a complex task. To select the best placement strategy that reduces the resource usage, at the same time keeps the performance and availability of network functions is a complex task, already proven to be an NP-hard problem. Therefore, in this paper, we formulate the NFV placement as a multi-objective problem, where the risk associated with the placement and energy consumption are taken into consideration. We propose the usage of two optimization algorithms, NSGA-II and GDE3, to solve this problem. These algorithms were taken into consideration because both work with multi-objective problems and present good performance. We consider a triathlon circuit scenario based on real data from the Ironman route as an use case to evaluate and compare the algorithms. The results show that GDE3 is able to attend both objectives (minimize failure and minimize energy consumption), while the NSGA-II prioritizes energy consumption.

     

Continuous elliptic and multi-dimensional hyperbolic Darcy-flux finite-volume methods

Elliptic and hyperbolic Darcy-flux approximations are presented. Families of flux-continuous finite-volume methods are investigated for the elliptic full-tensor pressure equation with general discontinuous coefficients. Full pressure continuity across control-volume interfaces is built into the methods leading to an important distinction from the earlier pointwise continuous methods. The families of quasi-positive methods significantly reduce spurious oscillations (induced by earlier schemes) in discrete pressure solutions for strongly anisotropic full-tensor fields. Anisotropy favoring triangulation and non-linear flux splitting are also shown to be effective for computing solutions free of spurious oscillations.Multi-dimensional upwind schemes that reduce cross-wind numerical diffusion induced by the standard upwind scheme are also presented for hyperbolic Darcy-flux approximation.     

Cornea and its adaptation to environment and accommodation function in veiled chameleon (Chamaeleo calyptratus): ultrastructure and 3D transmission electron tomography

We investigate the ultrastructural features and 3D electron tomography of chameleon (Chamaeleon calyptratus) which is a native of desert environments of Saudi Arabia. The corneas of the chameleon were fixed in 2.5% glutaraldehyde containing cuprolinic blue in sodium acetate buffer for electron microscopy and tomography, and observed under a JEOL 1400 transmission electron microscope. The thin cornea (21.92 μm) contained 28–30 collagen fibril lamellae. The middle stromal lamellae (from 13 to 19) contained keratocytes with a long cell process and filled with granular material. The CF diameter increased from lamella 1 (30.44 ± 1.03) to Lamella 5 (52.83 ± 2.00) then decreased towards the posterior stoma. The percentage of large CF diameters (55–65 nm) was very high in the lamellae L14 (38.8%) and L15 (85.7%). The mean PGs area of the posterior stroma (448.21 ± 24.84 nm²) was significantly larger than the mean PGs area of the anterior, (309.86 ± 8.2 nm²) and middle stroma 245.94 ± 8.28 nm²). 3D electron tomography showed the distribution of PGs around and over the CF. Variable diameters of CFs in the anterior stroma may provide compact lamellae which may restrict the low wavelength of light. Variable diameters of CFs in the anterior stroma may provide compact lamellae which may restrict the low wavelength of light. This accommodation function is achieved by bending of the cornea. During bending the anterior stroma was stretched and the posterior stroma was compressed due to the presence of small CFs. The middle stroma remained stiff due to the presence of large CFs. Large proteoglycans not only maintain hydration for a longer period of time, but also act as a lubricant to neutralise the shear forces in the anterior and posterior stroma during bending.     

Nonaveraged control‐oriented modeling and relative stability analysis of DC‐DC switching converters

This paper presents a unified and exact nonaveraged approach to derive a frequency‐domain control‐oriented model for accurate prediction of the fast timescale dynamics and performances of switching converters with fixed frequency naturally sampled pulse width modulation and integrating feedback loop. Because the approach avoids averaging and approximations related to this process, a very good accuracy of the derived model is obtained. The main difference between the presented approach and the existing methodology for accurately predicting the behavior of switching converters is that, here, we break the feedback loop and we focus on analyzing the open‐loop gain and the effect of the system parameters on relative stability. This results in an approach much similar to control systems techniques rather than nonlinear dynamical system approaches. Consequently, the relative stability is tackled easily in the frequency domain. In particular, by treating the modulator as a gain depending on the operating point, the new model is formulated in such a way that standard control‐oriented tools such as Bode diagrams and root‐loci can be easily used. Therefore, the proposed approach gives some important issues like gain and phase margins that are highly useful in controller design. It is noticed that the crossover frequency, gain, and phase margins predicted by using the averaged model may deviate significantly from the actual values given by the proposed approach. The paper points out the sources of discrepancies and the theoretical results are validated by simulations using a circuit‐level switched model.     

A complete multi-robot path-planning algorithm

In the domain of multi-robot path-planning problems, robots must move from their start locations to their goal locations while avoiding collisions with each other. The research problem that we addressed is to find a complete solution for the multi-robot path-planning problem. Our first contribution is to recognize the solvable instances of the problem with our solvability test; the theoretical analysis has already been provided to show the validity of this test. Our second contribution is to solve this problem completely, in polynomial time, with the Push and Spin (PASp) algorithm. Once the problem was solved, we found decisions within the complete solution that may improve the performance of the complete algorithm. Hence, our third contribution is to improve the performance by selecting the best path from the set of complete paths. We refer to the improved version of our algorithm as the improved PASp algorithm. In terms of the completeness evaluation, the mathematical proofs demonstrate that the PASp is a complete algorithm for a wider class of problem instances than the classes solved by the Push and Swap (PAS), Push and Rotate (PAR), Bibox or the tractable multi-robot path-planning (MAPP) algorithms. Moreover, PASp solves any graph recognized to be solvable without any assumptions. In addition, the theoretical proof of the PASp algorithm showed completive polynomial performance in terms of total-path-lengths and execution time. In our performance evaluation, the experimental results showed that the PASp performs competitively, in reasonable execution time, in terms of number of moves compared to the PAS, PAR, Bibox and MAPP algorithms on a set of benchmark problems from the video-game industry. In addition, the results showed the scalability and robustness of PASp in problems that can be solved only by PASp. Such problems require high levels of coordination with an efficient number of moves and short execution time. In grid and bi-connected graphs with too many cycles, PASp required more moves and more time than the PAS, PAR and Bibox algorithms. However, PASp is the only algorithm capable of solving such instances with only one unoccupied vertex. Furthermore, adding heuristic search and smooth operation to the improved PASp showed significant further improvement by reducing the number of moves for all problem instances. PASp produced the best plans in a bit higher time. Finally, the PASp algorithm solves a wider class of problems and performs more completely in very complex/crowded environments than other state-of-art algorithms. Additionally, the Spin operation introduces a novel swapping technique to exchange two items and restore others in a graph for industrial applications.     

Energy optimization with authentication and cost effective storage in the wireless sensor IoTs using blockchain

In this paper, a hybrid blockchain-based authentication scheme is proposed that provides the mechanism to authenticate the randomly distributed sensor IoTs. These nodes are divided into three types: ordinary nodes, cluster heads and sink nodes. For authentication of these nodes in a Wireless Sensor IoTs (WSIoTs), a hybrid blockchain model is introduced. It consists of both private and public blockchains, which are used to authenticate ordinary nodes and cluster heads, respectively. Moreover, to handle the issue of cluster head failure due to inefficient energy consumption, Improved Heterogeneous Gateway-based Energy-Aware Multi-hop Routing (I-HMGEAR) protocol is proposed in combination with blockchain. It provides a mechanism to efficiently use the overall energy of the network. Besides, the processed data of subnetworks is stored on blockchain that causes the issue of increased monetary cost. To solve this issue, an external platform known as InterPlanetary File System (IPFS) is used, which distributively stores the data on different devices. The simulation results show that our proposed model outperforms existing clustering scheme in terms of network lifetime and data storage cost of the WSIoTs. Our proposed scheme increases the lifetime of the network as compared to existing trust management model, intrusion prevention and multi WSN authentication schemes by 17.5%, 24.2% and 19.6%, respectively.     

Application of a Screen-Printed Sensor Modified with Carbon Nanofibers for the Voltammetric Analysis of an Anticancer Disubstituted Fused Triazinone

In this paper, we propose the first analytical procedure—using a screen-printed carbon electrode modified with carbon nanofibers (SPCE/CNFs)—for the detection and quantitative determination of an electroactive disubstituted fused triazinone, namely 4-Cl-PIMT, which is a promising anticancer drug candidate. The electrochemical performances of the sensor were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and square-wave adsorptive stripping voltammetry (SWAdSV). The presence of carbon nanofibers on the sensor surface caused a decrease in charge-transfer resistance and an increase in the active surface compared to the bare SPCE. Under the optimised experimental conditions, the proposed voltammetric procedure possesses a good linear response for the determination of 4-Cl-PIMT in the two linear ranges of 0.5–10 nM and 10–100 nM. The low limits of detection and quantification were calculated at 0.099 and 0.33 nM, respectively. In addition, the sensor displays high reproducibility and repeatability, as well as good selectivity. The selectivity was improved through the use of a flow system and a short accumulation time. The SWAdSV procedure with SPCE/CNFs was applied to determine 4-Cl-PIMT in human serum samples. The SWAdSV results were compared to those obtained by the ultra-high-performance liquid chromatography coupled with electrospray ionization/single-quadrupole mass spectrometry (UHPLC-ESI-MS) method.     

Modeling and assessing an intelligent system for safety in human-robot collaboration using deep and machine learning techniques

Multimedia Tools and Applications - The introduction of technological innovations is essential for accident mitigation in work environments. In a human-robot collaboration scenario, the current...