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Initial Stages of Metal Films Growth on a SiO2-Cristobalite Surface
Get PDFUsing the density functional theory approach and pseudopotentials we studied energetics and electron structures of metal layers (Al, Cu, Ni, and Cr) deposited on a cristobalite surface. We have found that the properties of the first adsorbed layers decide by interaction of metal atoms with oxygen atoms of a substrate surface. Aluminum as an easily oxidized metal, is characterized by the high adhesion, it is followed by nickel and chromium, and copper closes the studied group of metals. Further plating is characterized by significant reduction of binding energy; the properties of films tend to properties of bulk metal
Single-Fiber Based Endoscopic Imaging: Methods and Characteristics
Get PDFDifferent from imaging an object through a multimode optical fiber (MMF) directly, it is much more challenging to use a single MMF for practical endoscopic imaging in which the light wave has been distorted twice: on the way in for the illumination and on the way out for the detection. In this paper, based on obtaining the optical transmission matrix (TM) of the MMF working in the reflective mode, we demonstrate that, via the measured optical TM, the object can be reconstructed directly from its round-trip distorted output speckle fields. Compared with other single-fiber based endoscopic imaging methods, our method doesn’t involve any scanning operation during the imaging process. Such an efficient method might have potential applications for wide-field and ultrathin fiber endoscopic imaging
A METHOD FOR THERMAL HISTORY PREDICTION DURING ADDITIVE MANUFACTURING USING FAR-FIELD TEMPERATURE MEASUREMENTS
Get PDFDirected Energy Deposition is a near net-shape, additive manufacturing process that uses high-energy lasers for powder melting and consolidation. While a detailed knowledge of the thermal histories of the process can help understand and ultimately predict the resulting microstructure, residual-stresses, and/or material properties of the component, experimental limitations usually restrict all temperature measurements to far-field locations. When fixed, these measurements become increasingly removed from the laser/material interactions as the build process unfolds. To help offset this limitation, a relatively straightforward method using finite-elements and a fixed far-field measurement was developed that considers experimental processing conditions such as a moving heat source and relevant (and evolving) boundary conditions to generate more complete thermal histories. In essence, an inverse problem was iteratively solved using a direct computational approach. Once validated, the model was then used over multiple depositions with the outcome discussed relative to the agreement and disparities in peak temperatures, heating, and cooling rates. The increasing importance of the growing surface area and evolving radiative and convective boundary conditions with each layer was clearly demonstrate
Drilling of CFRP/Ti Stacks in Wet and Cryogenic Condition
Get PDFThis paper studies the effects of cryogenic liquid nitrogen compared with conventional wet coolant in drilling of CFRP/Ti using diamond-like carbon coated solid carbide tools. The experimental investigation was carried out taking into account the influence of main process parameters and adopting different strategies in the two different materials. The influence of the two different cooling conditions on tool wear was investigated through the comparison of the thrust force and torque; the effect on the hole quality was analysed through the measurements of burr height and diameters. The use of a cryogenic coolant results in both lower thrust force and torque but in a slightly poorer quality of the holes
Solar Energy in Cuba: Current Situation and Future Development
Get PDFCuba, a small island in the Caribbean Sea with a total land area of 109.884 km2 and a population of around 11.423 million, has no significant proved oil, gas and coal reserves. Also use, in a very limited manner, some of the four main renewable energy sources available in the country for electricity production, generating just 50,1 GW/h or 4,04% of the total electricity consumed in 2015 (20.288 GW/h). In 2016, electricity consumption fell to 15.182 GW/h; this means a reduction of 25% in comparison to 2015. In 2016, the participation of renewable energy sources in the energy mix of the country reached 4,65%.
The different renewable energy sources available in the country are hydropower, wind power, solar photovoltaic, and bioenergy. In 2015, out of Cuba’s total 566 MW of renewable energy capacity installed, 83% of the total was in the bioenergy sector. In 2016, the renewable energy capacity installed in the country reached 642 MW.
According to the decision adopted by the Cuban government, the participation of renewable energy sources in the energy mix of the country should reach 24% in 2030, an increase of almost 20% compared to the level reported in 2016. Among the different renewable energy sources available in the country, solar energy is one of the main contributors to the national energy system, and also one of the leading supplier of energy to independent users all over the country
Graphene for Flexible Photovoltaic Devices
Get PDFFlexible photovoltaic devices (FPD’s) are emerging as next-generation technology in photovoltaic research. FPD’s have attracted great research attention because of their broad potential applications especially in wearable devices, portable electronics, integrated textiles, unmanned aerial vehicles, transportation, and military etc. The existing technologies have evolved over the years, improving efficiency and performance of photovoltaic devices. However, these technologies mostly rely on rigid electrodes that are brittle, costly and chemically unstable. For FPD’s to become practical, new materials that offer inherent flexibility without compromising on mechanical and optical properties must be the focus. Researchers have made significant advances over the past decade towards developing various aspects of FPD’s to improve its optical transmittance, mechanical stability, chemical stability etc. Graphene is increasingly been recognized as an excellent material for flexible photovoltaic devices because of its unique optical, electrical and mechanical properties. The prospects of introducing an inexpensive and abundant carbon-based material such as graphene in making flexible, low-cost, transparent PV cells cannot be over emphasized. However, the method to synthesize graphene to achieve the best performance is still complicated. This paper presents a brief overview of recent developments made in flexible photovoltaic devices using graphene
Fine Precipitates in Nickel Base Superalloys
Get PDFPresence of fine, secondary/tertiary precipitates in superalloys improves especially the creep-fatigue properties of these alloys. It is conveniently accepted that the fine precipitates form non-isothermally, for example, during cooling from an aging temperature or isothermally during a secondary, lower temperature aging. In the current study, several single-aging treatments were conducted to assess the formation of the fine precipitates in the polycrystalline, nickel-base superalloy IN738LC. The agings were carried out stress-free at 950oC, 1050oC, 1120oC, and 1140oC for various times. Stressed agings at 950oC and 1050oC were also conducted. A time-dependent isothermal formation of the fine precipitates was observed. The formation time decreased as the aging temperature increased. It is suggested that dissolution of some coarse precipitates, evolution of the precipitate-matrix interface toward a fully faceted one, and increased matrix channel width saturate the channels and control the formation of the fine precipitates
Influence of the Base Element on the Thermal Properties of Non- Ferrous Chromium-Rich TaC-Containing Alloys Elaborated by Conventional Casting: Part 3: Surface and Cross-Sectional Metallographic Characterization of the Oxidized Alloys
Get PDFThe six alloys the thermal properties of which and the tendency to oxide spallation of which were studied in the first two parts of this work, were here characterized after oxidation for 70 hours at 1250°C. The external chromia scale, and also the CrTaO4 subsurface oxide, formed for all the alloys, almost independently of the Co and Ni proportions in the base element content. But, because of the formation of more CrTaO4 for the nickel-richest alloys probably due to the higher availability of Ta in the matrix and its easier diffusion towards the neighbourhood of the oxidation front, the adherence of chromia was weakened and spallation, suggested by the thermogravimetric curves in the second part of this work, is here really observed and the denuded part of alloys clearly seen. The degradation of the subsurface, which can be in a first time summarized by the development of a carbide-free zone and a {Cr, Ta}-depleted zone, depends on the Co and Ni proportions. The microstructure of the bulk is differently affected by long exposure at elevated temperature. The changes in carbide population characteristics are stronger for the nickel-based alloys than for the cobalt-based ones. Finally, the isothermal oxidation behaviour is best for the nickel-richest alloys but the oxide spallation behaviour and the potential mechanical properties are the best for the cobalt-richest alloys
The Design, Fabrication and Preliminary Testing of a Variable Configuration Mobile Robot
Get PDFIn this paper a novel low cost mobile robot that can adjust the balance between the energy efficiency and the running performance according to the environment by changing the number of wheels is introduced. The developed robot, which can be constructed by combining the modules and is driven by Robot Operating System (ROS) tools, has a 3D light detection and distance measurement (LiDAR) for generation of 3D digital map and travels through several environment with saving the energy by adaptively changing the number and arrangement of the wheels according to the environment. The robot can easily change the three types of mechanisms by changing the number of modularized driving wheels and their combination. Furthermore, the developed robot can construct a 3D map in a rough outdoor environment and the running performance of three kinds of robots was investigated by an extensive characterization. Finally, the limits of this prototype have been meticulously analyzed, highlighting new improvements in the future perspective development for permitting an autonomous environment perception with a simple, modular and low-cost device
Design and Development of an Educational 5-DoF Robotic Arm
Get PDFThe effective training of engineering students require hands-on experience in what they would later work with in the industry. The trend in manufacturing nowadays is towards robotics and automation. Relevant to this technology is the robotic hand. This paper outlines the design and the development of a 5-DoF (Degree of Freedom) robotic arm. The robotic arm is intended for educational purposes. The design proposed the use of servos to power the joints and to implement the inverse kinematics of the robotic arm. A simulation of the robotic arm was achieved by using the Matlab Robotics Toolbox, to visualise the joint movements. A suitable servo controller was selected for the implementation and a control software for the robotic arm was developed using Microsoft\u27s C# programming language. The software allows the robotic arm gripper to be postioned in space, by specifying the coordinates of its centre position. Polymethyl methacrylate was selected to fabricate the components of the robotic arm. The robotic arm was tested by specifying various coordinates for the gripper with reference to the robot\u27s base and measuring the corresponding coordinates of the centre position of the gripper, which gave satisfactory results