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.

Work Function Tuning of Reduced Graphene Oxide Thin Films

Abstract: Graphene oxide (GO) has shown great potential as a component in various devices due to its excellent solution processability and two-dimensional structure. However, the oxygenated form of graphene has a moderate charge-transport capability. The latter parameter may be enhanced through controlled deoxygenation of GO with subsequent tuning of its work function (WF). Various reduction approaches were employed to investigate the effect of the oxygen content on the work function of GO derivatives as thin films on an indium tin oxide substrate. Such films were reduced by stepwise thermal annealing in ultrahigh vacuum up to 650 °C, by chemical reduction with hydrazine, or by a combination of chemical and thermal reduction processes. The effect of the GO film thickness and the flake size on the WF was also investigated. UV photoelectron spectroscopy and X-ray photoelectron spectroscopy were used to correlate the WF of GO derivatives with their oxygen content. The results showed that the WF is strongly dependent o...

Steady bubble rise and deformation in Newtonian and viscoplastic fluids and conditions for bubble entrapment

Abstract: We examine the buoyancy-driven rise of a bubble in a Newtonian or a viscoplastic fluid assuming axial symmetry and steady flow. Bubble pressure and rise velocity are determined, respectively, by requiring that its volume remains constant and its centre of mass remains fixed at the centre of the coordinate system. The continuous constitutive model suggested by Papanastasiou is used to describe the viscoplastic behaviour of the material. The flow equations are solved numerically using the mixed finite-element/Galerkin method. The nodal points of the computational mesh are determined by solving a set of elliptic differential equations to follow the often large deformations of the bubble surface. The accuracy of solutions is ascertained by mesh refinement and predictions are in very good agreement with previous experimental and theoretical results for Newtonian fluids. We determine the bubble shape and velocity and the shape of the yield surfaces for a wide range of material properties, expressed in terms of the Bingham Bn=τy*ρ*g*R b Bond B o = ρ*g*R* 2 b /γ* and Archimedes A r =ρ *2 g*R *3 b /μ * o 2 numbers, where ρ* is the density, μ * o the viscosity, γ* the surface tension and τ * y the yield stress of the material, g* the gravitational acceleration and R * b the radius of a spherical bubble of the same volume. If the fluid is viscoplastic, the material will not be deforming outside a finite region around the bubble and, under certain conditions, it will not be deforming either behind it or around its equatorial plane in contact with the bubble. As Bn increases, the yield surfaces at the bubble equatorial plane and away from the bubble merge and the bubble becomes entrapped. When Bo is small and the bubble cannot deform from the spherical shape the critical Bn is 0.143, i.e. it is a factor of 3/2 higher than the critical Bn for the entrapment of a solid sphere in a Bingham fluid, in direct correspondence with the 3/2 higher terminal velocity of a bubble over that of a sphere under the same buoyancy force in Stokes flow. As Bo increases allowing the bubble to squeeze through the material more easily, the critical Bingham number increases as well, but eventually it reaches an asymptotic value. Ar affects the critical Bn value much less.

A three‐dimensional progressive damage model for bolted joints in composite laminates subjected to tensile loading

Abstract: A three-dimensional progressive damage model was developed to simulate the damage accumulation and predict the residual strength and final failure mode of bolted composite joints under in-plane tensile loading. The parametric study included stress analysis, failure analysis and material property degradation. Stress analysis of the three-dimensional geometry was performed numerically using the finite element code ANSYS with special attention given to the detailed modelling of the area around the bolt in order to account for all damage modes. Failure analysis and degradation of material properties were implemented using a set of stress-based Hashin-type failure criteria and a set of appropriate degradation rules, respectively. In order to validate the finite element model, a comparison of stress distributions with results from analytical models found in the literature was carried out and good agreement was obtained. A parametric study was performed to examine the effect of bolt position and friction upon damage accumulation and residual strength.

In vivo small animal imaging: current status and future prospects.

Abstract: The use of small animal models in basic and preclinical sciences constitutes an integral part of testing new pharmaceutical agents prior to commercial translation to clinical practice. Whole-body small animal imaging is a particularly elegant and cost-effective experimental platform for the timely validation and commercialization of novel agents from the bench to the bedside. Biomedical imaging is now listed along with genomics, proteomics, and metabolomics as an integral part of biological and medical sciences. Miniaturized versions of clinical diagnostic modalities, including but not limited to microcomputed tomography, micromagnetic resonance tomography, microsingle-photon-emission tomography, micropositron-emission tomography, optical imaging, digital angiography, and ultrasound, have all greatly improved our investigative abilities to longitudinally study various experimental models of human disease in mice and rodents. After an exhaustive literature search, the authors present a concise and critical review of in vivo small animal imaging, focusing on currently available modalities as well as emerging imaging technologies on one side and molecularly targeted contrast agents on the other. Aforementioned scientific topics are analyzed in the context of cancer angiogenesis and innovative antiangiogenic strategies under-the-way to the clinic. Proposed hybrid approaches for diagnosis and targeted site-specific therapy are highlighted to offer an intriguing glimpse of the future.