Acoustic measurements of stress fields and microstructure

A very precise system for measuring two-dimensional velocity fields in solid samples has been used for nondestructive measurements of both externally applied and residual inhomogeneous stresses in solids,J integrals, stress intensity factors of cracks, and hardness of quenched steel. The longitudinal velocity measurement is based on precise determination of the propagation transit time through the stressed solid specimen using a small diameter, water-coupled acoutic transducer, which is scanned mechanically over the sample. Changes in velocity are then related to changes of stress in the sample by the theory of acoustoelasticity. Similar measurements show a high degree of correlation between longitudinal velocity changes and changes in microstructure in steel samples. Applications to problems of solid mechanics and material science illustrate the utility of this nondestructive measuring technique.     

Structure and Optical Characteristics of DLC Films

Using a RF-Plasma Enhanced Chemical Vapor (RF-PECVD) Depositions method, employing hydrogen and methane gas, Diamond like carbon (DLC) films were fabricated on glass and silicon substrates. The impact of varying CH₄ to H₂ ratios on the resulting film's structure, optical characteristics, and mechanical properties was investigated. The deposition process occurred at methane flow rates spanning 5 to 40 sccm. The films' surface morphology, and roughness were analyzed through Atomic Force Microscopy. Moreover, the Vickers hardness tests was employed to determine the hardness of produced films. The optical behavior of the DLC thin films was explored utilizing UV-visible spectrometry and ellipsometry. A thorough investigation was conducted to understand how the CH₄ flow rate influences layer growth, morphology, topography, and how these factors relate to the films' transmittance, reflectance, refractive index, and optical band gap.     

Dynamic output feedback stabilization of deterministic finite automata via the semi‑tensor product of matrices approach

This paper deals with the dynamic output feedback stabilization problem of deterministic finite automata (DFA). The static form of this problem is defined and solved in previous studies via a set of equivalent conditions. In this paper, the dynamic output feedback (DOF) stabilization of DFAs is defined in which the controller is supposed to be another DFA. The DFA controller will be designed to stabilize the equilibrium point of the main DFA through a set of proposed equivalent conditions. It has been proven that the design problem of DOF stabilization is more feasible than the static output feedback (SOF) stabilization. Three simulation examples are provided to illustrate the results of this paper in more details. The first example considers an instance DFA and develops SOF and DOF controllers for it. The example explains the concepts of the DOF controller and how it will be implemented in the closed-loop DFA. In the second example, a special DFA is provided in which the DOF stabilization is feasible, whereas the SOF stabilization is not. The final example compares the feasibility performance of the SOF and DOF stabilizations through applying them to one hundred random-generated DFAs. The results reveal the superiority of the DOF stabilization.     

A framework for multi-robot motion planning from temporal logic specifications

We propose a framework for the coordination of a network of robots with respect to formal requirement specifications expressed in temporal logics.A regular tessellation is used to partition the space of interest into a union of disjoint regular and equal cells with finite facets,and each cell can only be occupied by a robot or an obstacle.Each robot is assumed to be equipped with a finite collection of continuous-time nonlinear closed-loop dynamics to be operated in.The robot is then modeled as a hybrid automaton for capturing the finitely many modes of operation for either staying within the current cell or reaching an adjacent cell through the corresponding facet.By taking the motion capabilities into account,a bisimilar discrete abstraction of the hybrid automaton can be constructed.Having the two systems bisimilar,all properties that are expressible in temporal logics such as Linear-time Temporal Logic,Computation Tree Logic,and μ -calculus can be preserved.Motion planning can then be performed at a discrete level by considering the parallel composition of discrete abstractions of the robots with a requirement specification given in a suitable temporal logic.The bisimilarity ensures that the discrete planning solutions are executable by the robots.For demonstration purpose,a finite automaton is used as the abstraction and the requirement specification is expressed in Computation Tree Logic.The model checker Cadence SMV is used to generate coordinated verified motion planning solutions.Two autonomous aerial robots are used to demonstrate how the proposed framework may be applied to solve coordinated motion planning problems.     

Catalytic Metal Foam by Chemical Melting and Sintering of Liquid Metal Nanoparticles

Metal foams are highly sought‐after porous structures for heterogeneous catalysis, which are fabricated by templating, injecting gas, or admixing blowing agents into a metallic melt at high temperatures. They also require additional catalytic material coating. Here, a low‐melting‐point liquid metal is devised for the single‐step formation of catalytic foams in mild aqueous environments. A hybrid catalytic foam fabrication process is presented via simultaneous chemical foaming, melting, and sintering reaction of liquid metal nanoparticles. As a model, nanoparticles of tertiary low‐melting‐point eutectic alloy of indium, bismuth, and tin (Field's metal) are processed with sodium hydrogen carbonate, an environmentally benign blowing agent. The competing endothermic foaming and exothermic sintering reactions are triggered by an aqueous acidic bath. The overall foaming process occurs at a localized temperature above 200 °C, producing submicron‐ to micron‐sized open‐cell pore foams with conductive cores and semiconducting surface decorations. The catalytic properties of the metal foams are explored for a range of applications including photo‐electrocatalysis, bacteria electrofiltration, and CO₂ electroconversion. In particular, the Field's metal‐based foams show exceptional CO₂ electrochemical conversion performance at low applied voltages. The facile process presented here can be extended to other low‐temperature post transition and transition metal alloys.     

Investigation of rheology and morphology to follow physical fibrillar network evolution through fiber spinning of PP/PA6 blend fiber

This work is aimed at investigating the influence of fibrillar morphology of deformed Polyamide 6 (PA6) droplets dispersed in Polypropylene (PP) matrix on the melt viscoelastic behavior of their blends. The blends of PP with various amounts of PA6 (1%, 6%, 10%, and 20%) were prepared by melt mixing in a co‐rotating twin screw extruder and fibrillated by fiber spinning process. Scanning Electron Microscopy revealed that the PA6 spherical droplets form fibrillar inclusions after fiber spinning. The steady and transient shear rheological responses of samples were evaluated in both linear and nonlinear ranges of deformation. Non‐terminal behavior of storage modulus at low frequency appeared as a typical characteristic of fibrillar morphology whose width and value depend on fibril growth. Storage modulus and complex viscosity of the blends containing PA6 fibrillated structure were remarkably enhanced compared to as‐extruded samples. The fibrillar‐induced elasticity of the fibers is a distinguishable behavior which was revealed by conducting transient stress and creep‐recovery measurements and upon appearing mature fibrils, elasticity of the polymer blend fibers increased significantly. POLYM. ENG. SCI., 58:1251–1260, 2018. © 2017 Society of Plastics Engineers     

Solving unit commitment problem using a novel version of harmony search algorithm

In this context, a novel structure was proposed for improving harmony search (HS) algorithm to solve the unit comment (UC) problem. The HS algorithm obtained optimal solution for defined objective function by improvising, updating and checking operators. In the proposed improved self-adaptive HS (SGHS) algorithm, two important control parameters were adjusted to reach better solution from the simple HS algorithm. The objective function of this study consisted of operation, start-up and shut-down costs. To confirm the effectiveness, the SGHS algorithm was tested on systems with 10, 20, 40 and 60 generating units, and the obtained results were compared with those of the simple HS algorithm and other related works.     

Linear and nonlinear melt viscoelastic properties of fibrillated blend fiber based on polypropylene/polytrimethylene terephthalate

Polymer Bulletin - This work was aimed at understanding the influence of fibrillar morphology on melt viscoelastic properties of polymer blends containing various blend ratios...     

An Insight into Phenomenology of Polytrimethylene Terephthalate Fibrillation

The objective of this work is to analyze the effect of the processing temperature on fibrillation of the dispersed phase and to correlate melt viscoelastic responses to formed morphologies. A blend system of polypropylene (PP)/polytrimethylene terephthalate (PTT) with varying ratios (PP/PTT: 99/1, 94/6, 90/10, and 80/20) is prepared on a co‐rotating twin screw extruder, and then pelletized blend samples are fed into a laboratory mixing extruder to spin monofilaments at three different orifice temperatures of 180, 195, and 240 °C. As revealed by scanning electron microscopy, a nano‐fibrillar morphology forms after employing spinning. Rheological approach performed in the linear region shows a transition from terminal trend into non‐terminal trend in the low‐frequency region when the fibrillar morphology forms, the magnitude and width of which are reflective of the fibril growth. Transient stress measurements prove its capability to enable the blend system to show potentials of morphology development during dynamic tests. Startup of steady shear flow shows that after reaching the percolation concentration of dispersed phase, fibril–fibril coalescence leads to the formation of long fibrils whose contribution to the blend system increases the elasticity of the blend fibers.     

Dynamic output feedback stabilization of deterministic finite automata via the semi-tensor product of matrices approach

This paper deals with the dynamic output feedback stabilization problem of deterministic finite automata (DFA).The static form of this problem is defined and so...