University of Patras

About: University of Patras is a education organization based out in Pátrai, Greece. It is known for research contribution in the topics: Population & Catalysis. The organization has 13372 authors who have published 31263 publications receiving 677159 citations. The organization is also known as: Panepistímio Patrón.

Accelerated environmental ageing study of polyester/glass fiber reinforced composites (GFRPCs)

Abstract: The failure of polymer matrix composites upon exposure to the environment has been assessed in the present study. In order to investigate the combined action of temperature, humidity and UV radiation on polymers and composites, an environmental ageing chamber has been constructed and tested. The accelerated environmental ageing was based on two kinds of alternating cycles, which provided humidity, temperature and ultraviolet radiation. The materials examined were isophthalic polyester and isophthalic polyester reinforced with a glass fiber random mat onto which glass fibers were knitted at 0°/90° (GFRPC) at a total volume fraction of approximately 20%. Dynamic mechanical analysis, for a range of temperatures and frequencies under tensile and three-point bending loadings, revealed that the aged materials gained in stiffness, whereas a small deterioration in strength was found. Scanning electron microscopy studies performed before and after environmental chamber conditioning revealed that some microcracks had occurred on the surface of the specimens. Nevertheless, the length of these microcracks was less than the critical value of 0.1 mm, required for crack propagation.

On thermal modeling of Additive Manufacturing processes

Abstract: A two-dimensional Finite Difference (FD) model of the thermal history of parts manufactured in powder bed fusion Additive Manufacturing (AM) processes is presented. The temperature of the part is calculated in each time-step taking into account the moving laser heat source, the melting phase change and functions of both temperature and porosity are used for the material thermal properties. Also, an algorithm for node birth and distance adaptation over time is utilized, minimizing computational time and memory. A validation of the results of the model is included.

Benzothiazoles with Tunable Electron-Withdrawing Strength and Reverse Polarity: A Route to Triphenylamine-Based Chromophores with Enhanced Two-Photon Absorption

Abstract: A series of dipolar and octupolar triphenylamine-derived dyes containing a benzothiazole positioned in the matched or mismatched fashion have been designed and synthesized via palladium-catalyzed Sonogashira cross-coupling reactions. Linear and nonlinear optical properties of the designed molecules were tuned by an additional electron-withdrawing group (EWG) and by changing the relative positions of the donor and acceptor substituents on the heterocyclic ring. This allowed us to examine the effect of positional isomerism and extend the structure–property relationships useful in the engineering of novel heteroaromatic-based systems with enhanced two-photon absorption (TPA). The TPA cross-sections (δTPA) in the target compounds dramatically increased with the branching of the triphenylamine core and with the strength of the auxiliary acceptor. In addition, a change from the commonly used polarity in push–pull benzothiazoles to a reverse one has been revealed as a particularly useful strategy (regioisomeric ...

A comparative study of three methods for robot kinematics

Abstract: Three methods for the formulation of the kinematic equations of robots with rigid links are presented in this paper. The first and most common method in the robotics community is based on 4/spl times/4 homogeneous matrix transformation, the second one is based on Lie algebra, and the third one on screw theory expressed via dual quaternions algebra. These three methods are compared in this paper for their use in the kinematic analysis of robot arms. The basic theory and the transformation operators, upon which every method is based, are referenced. Three analytic algorithms are presented for the solution of the direct kinematic problem corresponding to each method, and the geometric significance of the transformation operators and parameters is explained. Finally, a comparative study on the computation and storage requirements for the three methods is worked out.