Influence Of Surface Geometry Research Articles

Ab initio study of the adsorption of O, O2, H2O and H2O2 on UO2 surfaces using DFT+U and non-collinear magnetism

In order to model correctly the corrosion of spent nuclear fuel under disposal conditions, it is important to understand its behavior in the presence of oxidants. To advance in this direction, we consider the oxidation of UO2. We investigate computationally the adsorption of various species on its three most stable surfaces: (111), (110), and (100), with emphasis on incorporating a full non-collinear PBE+U approach. Various species, namely O, O2, H2O and H2O2 are considered due to their relevance for the oxidation of UO2. The dissociation energy and an estimate for the dissociation barrier for O2 were obtained, using the preferred adsorption configurations of O and O2. The adsorption configurations for H2O in our study compare well with previous studies that used collinear approximations, both in terms of relative stability of configurations and bond lengths. Differences in adsorption energies were found, which may be important for reaction kinetics. Dissociative reactions in which the water molecule splits in hydrogen and hydroxyl occur only on one of the three surfaces. The hydrogen further reacts with a surface oxygen to also form a hydroxyl group. Not surprisingly, we find that H2O2 binds more strongly to the three surfaces than water (lower formation energy), and similar to H2O adsorption, dissociative reactions may occur. The dissociated hydrogen reacts with a surface oxygen to form a hydroxyl group and the hydroperoxyl molecule binds with a surface uranium. Our study, which includes a detailed study of electron transfer, magnetic structure and the preferred adsorption configurations, gives insight into the uranium oxidation states and the influence of surface geometry on adsorption. The findings contribute to a more comprehensive understanding of the early stages of UO2 oxidation.

Controlled Release of Felodipine from 3D-Printed Tablets with Constant Surface Area: Influence of Surface Geometry.

In this study, 3D-printed tablets with a constant surface area were designed and fabricated using polylactic acid (PLA) in the outer compartment and polyvinyl alcohol and felodipine (FDP) in the inner compartment. The influences of different surface geometries of the inner compartment, namely, round, hexagon, square, and triangle, on drug release from 3D-printed tablets were also studied. The morphology and porosity of the inner compartment were determined using scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy, respectively. Additionally, drug content and drug release were also evaluated. The results revealed that the round-shaped geometry seemed to have the greatest total surface area of the inner compartment, followed by square-shaped, hexagon-shaped, and triangle-shaped geometries. FDP-loaded 3D-printed tablets with triangle and hexagon surface geometries had the slowest drug release (about 80% within 24 h). In the round-shaped and square-shaped 3D-printed tablets, complete drug release was observed within 12 h. Furthermore, the drug release from triangle-shaped 3D-printed tablets with double the volume of the inner compartment was faster than that of a smaller volume. This was due to the fact that a larger tablet volume increased the surface area contacting the medium, resulting in a faster drug release. The findings indicated that the surface geometry of 3D-printed tablets with a constant surface area affected drug release. This study suggests that 3D printing technology may be used to develop oral solid dosage forms suitable for customized therapeutic treatments.

Pentacene growth on the (111) surface of the 1/1 Au-Al-Tb approximant: Influence of surface geometry on adsorption

Molecular adsorption on both quasicrystalline and approximant substrates has produced a number of pseudomorphic films, and has led to a deeper understanding of the chemistry of the surfaces of these materials. Here, the recently reported reconstructed (111) surface of the 1/1 Au-Al-Tb Tsai-type approximant has been used as a template for pentacene (Pn) adsorption, which is investigated using scanning tunneling microscopy. This surface provides unique varieties of adsorption sites compared to a normal metal surface. After room-temperature deposition, the Pn molecules are mobile yet exhibit a structure which indicates a bond with the Tb atoms of the surface, while reflecting the twofold symmetrical nature of the reported Au/Al row reconstruction. Postdeposition annealing shows a linear arrangement of molecules in a specific adsorption geometry, likely corresponding to the most favorable energetic configuration.

Establishment of a Rolling-Sliding Test Bench to Analyze Abrasive Wear Propagation of Different Bearing Materials for Knee Implants

Currently, new materials for knee implants need to be extensively tested but such tests are expensive in a knee wear simulator in a realized design. However, using a rolling-sliding test bench, these materials can be examined under the same test conditions, but with simplified geometries. In the present study, the test bench was optimized, and forces were adapted to the physiological contact pressure in the knee joint using the available geometric parameters. Various polymers made of polyethylene and polyurethane, articulating against test wheels made of cobalt-chromium and aluminum titanate, were tested in the test bench using adapted forces based on ISO 14243–1. Polyurethane materials showed distinctly higher wear rates than polyethylene materials and showed inadequate wear resistance for use as knee implant material. Thus, the rolling-sliding test bench is an adaptable test setup to evaluate newly developed bearing materials for knee implants. It combines the advantages of screening and simulator tests and allows for the testing of various bearing materials under physiological load and tribological conditions of the human knee joint. The wear behavior of different material compositions and the influence of surface geometry and quality can be initially investigated without the need to produce complex implant prototypes of total knee endoprosthesis or interpositional spacers.

Influence of Surface Geometry on the Hydrodynamic Performances of Parallel Bearings in Transient Flow Conditions

Because a perfectly smooth surface does not actually exist, the classical principles of fluid mechanics dictate that the flow between two surfaces that are in relative motion is fundamentally unsteady. Therefore, the fluid film profile can be submitted to rapid oscillations in both space and time. This article shows how these oscillations become dependent on the surface geometry. By employing a transient mass-conserving cavitation model, we study several cases in which surface roughness and surface texturing are considered on both surfaces of a parallel bearing. For an applied load, the model shows the impact of surface geometry on the hydrodynamic performance of the bearing in terms of nominal film thickness, friction force, and volumetric flow rate. In addition, the results illustrate how different operating parameters such as the applied load and the speed of the moving surface affect the presence of cavitation within the bearing.

Influence of surface geometry and structure after non-conventional methods of parting on the following milling operations

This investigates influence of non-conventional methods of parting of steel 11 373.0 on structure transformations and associated geometry. Wire electro discharge machining (WEDM), plasma and laser cutting methods were used and compared as competitive methods from the point of view of structure transformations, associated geometry of a part and associated cutting forced produced during the following milling process. Results of this study indicate that significant differences can be found among the mentioned technology since the different thermal load of machined surface. Furthermore, structure and geometry alteration occurring after parting strongly affect cutting forces during the following milling operations.

Using Nanoscale Substrate Curvature to Control the Dimerization of a Surface-Bound Protein

The influence of surface geometry on adsorbed proteins offers new possibilities for controlling quaternary structure by manipulating protein-protein interactions at a surface, with applications that are relevant to protein aggregation, fibrillation, ligand binding, and surface catalysis. To understand the effect of surface curvature on the structure of the surface-bound protein β-lactoglobulin (β-LG), we have used a combination of polystyrene (PS) nanoparticles (NPs) and ultrathin PS films to fabricate chemically pure, hydrophobic surfaces that have nanoscale curvature and are stable in aqueous buffer. We have used single molecule force spectroscopy to measure the detachment contour lengths L(c) for β-LG adsorbed on the highly curved PS surfaces, and we compare these values in situ to those measured for β-LG adsorbed on flat PS surfaces on the same samples. The L(c) distributions measured on all flat PS surfaces show a large monomer peak near 60 nm and a smaller dimer peak at 120 nm. For 190 and 100 nm diameter NPs, which are effectively flat on the scale of the β-LG molecules, there is no measurable difference between the L(c) distributions obtained for the flat and curved surfaces. However, for 60 nm diameter NPs the dimer peak is smaller, and for 25 nm diameter NPs the dimer peak is absent, indicating that the number of surface-bound dimers is significantly reduced by an increase in the curvature of the underlying surface. These results indicate that surface curvature provides a new method of manipulating protein-protein interactions and controlling the quaternary structure of adsorbed proteins.

Influence of Surface Geometry of Paper on Colour Rendering of Impression

Quality standards of polygraphic production are raising at the market. Hereupon a role of the surface of paper quality becomes more important and its ability of image reproduction. Particularly color reproduction quality is highly required. Samples of paper with different surface texture and structure were taken to investigation. Techniques of an estimation of properties of a surface of materials are presented. By results of work it is possible to track character of dependence between indicators of quality of a surface and a material color rendition. In this work presents investigation of microgeometry of paper and influence of this factor on color coverage area of printing system.

Overview and discussion on pool boiling heat transfer data and correlations of ammonia

An overview on the heat transfer behaviour of boiling ammonia (R 717) under pool boiling conditions will be given. The influence of surface geometry (smooth, microfin, coated) and oil will be discussed. Experimental results and prediction methods will be presented. In addition to the open English literature, experimental data on pool boiling heat transfer of ammonia published in former German and Russian papers will be analyzed. The experimental pool boiling data investigated cover the following range: ϑ s = −40 to +38.7 °C, p s = 0.72 to 15 bar ( p r = 0.006–0.13), q = 0.44–2500 kW/m 2. Different heater materials have been used: carbon steel, stainless steel, platinum, silver, copper. The experimental data are compared with correlations e.g. by Stephan/Abdelsalam, Stephan/Preuβer, Mostinski, Cooper and Gorenflo. Porous structures and spray evaporation yield enhancement in pool boiling heat transfer. The oil diminishes the heat transfer coefficient strongly.

The influence of surface geometry and topography on the fatigue cracking behaviour of laser hybrid welded eccentric fillet joints

Laser hybrid welding of an eccentric fillet joint causes a complex geometry for fatigue load by 4-point bending. The weld surface geometry and topography were measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. It can be explained why the root and the upper weld toe are uncritical for cracking. The cracks that initiate from the weld bead show higher fatigue strength than the samples failing at the lower weld toe, as can be explained by a critical radius for the toe below which surface ripples instead determine the main stress raiser location for cracking. The location of maximum surface stress is related to a combination of throat depth, toe radius and sharp surface ripples along which the cracks preferably propagate.

Influence of surface geometry and the cam-post mechanism on the kinematics of total knee replacement

Abnormal sagittal kinematics after total knee replacement (TKR) can adversely affect functional outcome. Two important determinants of knee kinematics are component geometry and the presence or absence of a posterior-stabilising mechanism (cam-post). We investigated the influence of these variables by comparing the kinematics of a TKR with a polyradial femur with a single radius design, both with and without a cam-post mechanism. We assessed 55 patients, subdivided into four groups, who had undergone a TKR one year earlier by using an established fluoroscopy protocol in order to examine their kinematics in vivo. The kinematic profile was obtained by measuring the patellar tendon angle through the functional knee flexion range (0 degrees to 90 degrees ) and the results compared with 14 normal knees. All designs of TKR had abnormal sagittal kinematics compared with the normal knee. There was a significant (p < 0.05) difference between those of the two TKRs near to full extension. The presence of the cam-post mechanism did not influence the kinematics for either TKR design. These differences suggest that surface geometry is a stronger determinant of kinematics than the presence or absence of a cam-post mechanism for these two designs. This may be because the cam-post mechanism is ineffective.

Wear behavior of carbide coated Co-Cr-Mo implant alloy.

The wear behavior of a new type of metal carbide surface coating on Co-Cr-Mo implant alloy was studied. The coating was created using a microwave plasma-assisted reaction. Codeposition of impurity diamond film, diamond particles, and soot was prevented by controlling process conditions. Wear tests were carried out using a sapphire ball-on-Co-Cr-Mo disc unidirectional sliding configuration with harsh conditions of high contact stress and slow sliding speed in both no-lubrication, and deionized water lubrication environments. In the case of uncoated Co-Cr-Mo discs, the effect of deionized water lubrication was remarkable and reduced the wear factor by one order of magnitude compared to the no-lubrication tests. The wear factor of carbide coated Co-Cr-Mo discs was slightly smaller than that of uncoated Co-Cr-Mo discs with deionized water lubrication (2.7 x 10(-6) mm3 N(-1) m(-1) vs. 4.2 x 10(-6) mm3 N(-1) m(-1)). The addition of deionized water lubrication did not greatly affect the wear factor of carbide coated Co-Cr-Mo discs. The influence of surface geometry resulting from the "brain coral-like" surface morphology of carbide layers on wear behavior was analyzed considering stress concentrations and effective contact area.

Thermodynamics of gas adsorption on fractal surfaces of heterogeneous microporous solids

Thermodynamic equations are derived for physical adsorption of gases and vapors on fractal surfaces of heterogeneous microporous solids. The influence of surface geometry on gas adsorption on a microporous solid is studied by analyzing the dependence of the differential molar enthalpy ΔH, the immersion enthalpy ΔHim, and the differential molar entropy ΔS on the fractal dimension D, which is used to characterize the surface irregularity. It is shown that −ΔH, −ΔHim, −ΔS, and the average adsorption potential Ā increase as the fractal dimension of the surface accessible for adsorption increases. The dependence of these thermodynamic quantities on the fractal dimension D is attributed to the fact that the fraction of small micropores in microporous solids increases as the fractal dimension D increases.