Optical Communication

Optical communication is very much useful in telecommunication systems, data processing and networking. It consists of a transmitter that encodes a message into an optical signal, a channel that carries the signal to its desired destination, and a receiver that reproduces the message from the received optical signal. It presents up to date results on communication systems, along with the explanations of their relevance, from leading researchers in this field. The chapters cover general concepts of optical communication, components, systems, networks, signal processing and MIMO systems. In recent years, optical components and other enhanced signal processing functions are also considered in depth for optical communications systems. The researcher has also concentrated on optical devices, networking, signal processing, and MIMO systems and other enhanced functions for optical communication. This book is targeted at research, development and design engineers from the teams in manufacturing industry, academia and telecommunication industries

Active thermography for the investigation of corrosion in steel surfaces

The present work aims at developing an experimental methodology for the analysis of corrosion phenomena of steel surfaces by means of Active Thermography (AT), in reflexion configuration (RC). The peculiarity of this AT approach consists in exciting by means of a laser source the sound surface of the specimens and acquiring the thermal signal on the same surface, instead of the corroded one: the thermal signal is then composed by the reflection of the thermal wave reflected by the corroded surface. This procedure aims at investigating internal corroded surfaces like in vessels, piping, carters etc. Thermal tests were performed in Step Heating and Lock-In conditions, by varying excitation parameters (power, time, number of pulse, ….) to improve the experimental set up. Surface thermal profiles were acquired by an IR thermocamera and means of salt spray testing; at set time intervals the specimens were investigated by means of AT. Each duration corresponded to a surface damage entity and to a variation in the thermal response. Thermal responses of corroded specimens were related to the corresponding corrosion level, referring to a reference specimen without corrosion. The entity of corrosion was also verified by a metallographic optical microscope to measure the thickness variation of the specimens

Laser Scanner Technology

Laser scanning technology plays an important role in the science and engineering arena. The aim of the scanning is usually to create a digital version of the object surface. Multiple scanning is sometimes performed via multiple cameras to obtain all slides of the scene under study. Usually, optical tests are used to elucidate the power of laser scanning technology in the modern industry and in the research laboratories. This book describes the recent contributions reported by laser scanning technology in different areas around the world. The main topics of laser scanning described in this volume include full body scanning, traffic management, 3D survey process, bridge monitoring, tracking of scanning, human sensing, three-dimensional modelling, glacier monitoring and digitizing heritage monuments

NASA SBIR abstracts of 1991 phase 1 projects

The objectives of 301 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1991 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 301, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1991 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Micro/Nano Structures and Systems

Micro/Nano Structures and Systems: Analysis, Design, Manufacturing, and Reliability is a comprehensive guide that explores the various aspects of micro- and nanostructures and systems. From analysis and design to manufacturing and reliability, this reprint provides a thorough understanding of the latest methods and techniques used in the field. With an emphasis on modern computational and analytical methods and their integration with experimental techniques, this reprint is an invaluable resource for researchers and engineers working in the field of micro- and nanosystems, including micromachines, additive manufacturing at the microscale, micro/nano-electromechanical systems, and more. Written by leading experts in the field, this reprint offers a complete understanding of the physical and mechanical behavior of micro- and nanostructures, making it an essential reference for professionals in this field

NASA thesaurus. Volume 1: Hierarchical Listing

There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions

In Silico Analysis of Advanced Processing Methods for Light-weight Alloys Powders

Light-weight Al and Mg-based metal-matrix nanocomposites (MMNCs) are lauded as one of the most promising structural materials for vehicle, military, and construction applications. These MMNCs are often synthesized using the powder metallurgy (PM) process under liquid nitrogen cryogenic environments to control the grain sizes. It is believed that proper incorporation of the nitrogen species into the bulk lattice during processing could strongly enhance the mechanical properties of MMNCs by forming N-rich dispersoids. In this work, using the density-functional theory (DFT), the adsorption, absorption and diffusion behavior of nitrogen molecule/atoms have been studied and related to t Al and Mg MMNC PM processing. The study includes the impacts of binding sites, alloying elements (Al, Zn, and Y in Mg and Mg, Mn and Fe for Al), and surface crystallographic planes on the nitrogen molecule adsorption energies. The transition state (TS) behaviors for the bond breaking and lattice diffusion of nitrogen were examined. The results show that in presence of Mg (0001) or Al (111) surfaces, dissociation of $N_2$ to N atoms requires 1/9 to 1/5 of the isolated state energy , respectively. As a critical issue limiting the application of Mg-based MMNCs, the degradation (corrosion) of Mg alloys in aqueous media was modeled in this work. It is known that both the internal crystal structures and the impurity compositions/contents in the Mg alloys can affect the degradation rates. Density-functional theory (DFT) computation was utilized to understand the surface degradation behaviors with different crystallographic orientations and impurity elements from an atomistic standpoint. The adsorption response of the Mg alloy surface to the water molecule and the dissolution of surface atoms were studied to describe the degradation behavior of Mg and Mg alloys. The tendency for water molecule adsorption was quantified for Mg-based slab systems with low-index surface planes and various alloying elements including Al, Zn, Ca, and Y. The trends for surface degradation from these systems were examined using surface energy analysis and electrode potential shift analysis. The results showed that adding Ca and/or Y increases the propensity to attract a water molecule to the alloy surface. Also, it was generally found that the relative electrode potential shift of Mg-Y alloys is positive while those of all other alloys are negative. After having a comprehensive understanding about the atomistic behavior of metal powder in contact with the cryomilling media, the consolidation process was analyzed, including the melting and resolidification of powder through selective laser melting. At this stage of the work the concerns were to achieve the maximum connectivity between the powder layers after resolidification and to avoid extreme superheat. Since the efficiency of the MMNCs strongly relies on homogeneous distribution of reinforcement particles the SLM process was optimized to avoid any clustering of the reinforcement particles. Focusing on consolidation of MMNCS, Al10SiMg/AlN with weight ratio of 99:1 was chosen. AlSi10Mg with $10\%$ Si and $0.5\%$ Mg is one the most convenient compositions among the light weight alloys for laser melting processes, due to its narrow solidification range, that provides sufficient fluidity to produce sound products. Also, as the powder had been prepared via cryomilling process, the presence of AlN particles was proven based on the DFT calculations and experimental evidence described earlier. The laser power, scanning velocity and initial temperature of the powder were selected as the most important factors affecting the melting and solidification of the alloy powder. Finite volume analysis and experimental design were applied to optimize the SLM processing condition. Finite volume method was used to estimate the melt pool geometry, temperature profile of the part and velocity of solidification front. This information is necessary to produce strong parts with homogeneous properties all over the specimen, minimize energy consumption and avoid formation of defects in the sample. It was confirmed that even in the most extreme conditions the maximum temperature during the process would not exceed 1710K, which is roughly 460K below the melting temperature of the AlN reinforcement particles. The laser speed and power have significant effect on the melt pool geometry and maximum temperature of melt pool while the effect of initial powder temperature was insignificant for both of the response values. The AlN reinforcement particles are expected to have a homogeneous distribution since the velocity of the solidification front is higher than the critical calculated value of 5900 $\mu$ m/s. Results also showed that the solidification front velocity depends on the laser speed and the effects of laser power and initial temperature are insignificant. This work provides a comprehensive multiscale computational model tracking the Al and Mg based light-weight alloys from powder preparation stage to shaping the final product that considers potential gaps with focus on solidification process. These findings are particularly important to eliminate the extra processing steps to save time, energy and material maintaining the high quality of the final product

NASA Thesaurus. Volume 1: Hierarchical listing

There are 16,713 postable terms and 3,716 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary

Acoustic Waves

The concept of acoustic wave is a pervasive one, which emerges in any type of medium, from solids to plasmas, at length and time scales ranging from sub-micrometric layers in microdevices to seismic waves in the Sun's interior. This book presents several aspects of the active research ongoing in this field. Theoretical efforts are leading to a deeper understanding of phenomena, also in complicated environments like the solar surface boundary. Acoustic waves are a flexible probe to investigate the properties of very different systems, from thin inorganic layers to ripening cheese to biological systems. Acoustic waves are also a tool to manipulate matter, from the delicate evaporation of biomolecules to be analysed, to the phase transitions induced by intense shock waves. And a whole class of widespread microdevices, including filters and sensors, is based on the behaviour of acoustic waves propagating in thin layers. The search for better performances is driving to new materials for these devices, and to more refined tools for their analysis

Technology for large space systems: A bibliography with indexes (supplement 17)

This bibliography lists 512 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1987 and June 30, 1987. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems