Comparing the Effectiveness of Coatings on Carbide andCermet Cutting Tool Inserts

A series of metal cutting experiments was performed on a CNC lathe to evaluate the performance of various coatings on different tool substrates. The workpiece material was plain medium carbon steel and the cutting tool materials were carbide and cermet inserts coated with various single as well as multilayer coatings. Machining was done under various cutting conditions of speed and feed-rate, and for various durations of Cutting. The output parameters studied were the cutting forces (axial, radial and tangential), the surface roughness of the workpiece, as well as the tool wear (crater and flank wear). From these results, the performances of the various cutting inserts are evaluated and compared. Results show that cutting forces are significantly lower when using coated cermets than when using coated carbides although different coatings on the same substrate also result in different cutting forces. However, there is less difference in the surface roughness of the finished workpiece for the various coatings and substrates.     

Oxidative regeneration of sulfided sorbent by H2S without emission of SO2

Much SO₂, another perilous air pollutant, was emitted during the oxidative regeneration of sulfided sorbent by H₂S. In order to prevent emission of SO₂, we carried out oxidative regeneration with the physical mixture of CaO and sulfided sorbent and investigated the effect of regeneration temperature and oxygen concentration on the reactivity of CaO with S0₂. The effluent gases were analyzed by G.C. and the properties of sorbent were characterized by XRD. SEM, TG/DTA and EPMA. Deterioration of reactivity of CaO with S0₂ resulted in increment of emission of SO₁₂ due to the structural changes of CaO above 750°C and that at 850°C was more severe. Furthermore EPMA and XRD analysis revealed that product layer diffusion through the solid product, CaSO₄, was the rate limiting step for CaO sulfidation. The reaction of CaO w:.th SO₂ was first order approximately and that was accelerated by high O₂ concentration.     

隧道挖掘中采用补偿灌浆的实例

在英国伦敦多克兰斯轻便铁路刘易舍姆延长线（DLR－LWE）双隧道掘进工程中，在敏感建筑物下进行了补偿灌浆，以防止隧道开挖引起的过度沉降。但是，过度灌浆也会对隧道下部施加超越。介绍了由隧道掘进承包商所编辑的关于地面和建筑物沉降以及由补偿灌浆引起的隧道衬砌变形的详细现场监测数据。     

Principle and applications of retroreflective vision sensing for discrete part-presentation

For flexible manufacturing of short production runs where a large variety of product sizes, component types, and surface reflectance characteristics are encountered, it is desirable to build flexible computer-controlled systems for feeding parts into machine tools or assembly processes that combine maximum flexibility and reliability with minimum cost and cycle-time. This is not a general bin-picking problem; the parts are assumed to be propositioned approximately in totes/pallets/kits with regularly spaced locations. This article presents a machine vision technique based on the principle of retroreflective vision sensing for part-presentation. Since retroreflective material has a distinctive surface reflectance that is not commonly found in natural or man-made objects, the use of retroreflective surfaces enables reliable high object-to-background contrast images to be obtained for a wide variety of objects. Unlike conventional machine vision techniques, which rely on the variance of the surface reflectance of the objects to generate detailed images, retroreflective vision sensing aims at generating a reliable two-dimensional digital object silhouettes so that the location and orientation of the part can be reliably determined. Two application examples, machine loading and assembly, are illustrated.     

Linewidth and FM characteristics of a distributed feedback laser monolithically integrated with a tunable external cavity

A narrow linewidth has been obtained in a new 1.5 ?m distributed feedback laser integrated monolithically with a tunable external cavity. The linewidth of 18 MHz has been achieved by tuning the current in the external cavity, and the FM response was flat from 100 kHz to 500 MHz.     

Piezoelectrically actuated tunable capacitor

This paper describes the design, fabrication, and characterization of the first MEMS piezoelectric tunable capacitors employing zinc oxide (ZnO) actuation. Relatively simple design rules for the device-structure optimization for largest deflection are shown from simulation results based on theoretical equations. The ZnO-actuated tunable capacitors are accordingly designed and fabricated with both surface and bulk micromachining techniques. Through the surface micromachining process, sacrificial silicon is removed with XeF/sub 2/, and parylene is successfully used as a supporting layer for a piezoelectric unimorph cantilever. For comparison, other two different structures using plasma-enhanced chemical-vapor deposition (PECVD) SiN and SU-8 as supporting layers are also fabricated. Deflection analyses are performed for three specific structures, among which the parylene-supported one is demonstrated to have the largest displacement and most suitable for tunable capacitor application. For bulk-micromachined tunable capacitor, we have implemented a novel design of a large structure driven by a ZnO unimorph, and obtained a tuning ratio of more than 21:1 (0.46 pF-10.02 pF). This is the highest tuning ratio reported to date for parallel-plate tunable capacitors while requiring an applied voltage of only 35 V.     

Performance engineering and topological design of metro WDM opticalnetworks using computer simulation

This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures     

Electrical and growth characteristics of Au/Al0.15Ga0.85N:Si structures with various Si incorporations

We have investigated the growth characteristics of n-Al_0.15Ga_0.85N:Si/GaN and the electronic properties of Au/n-Al_0.15Ga_0.85N:Si diode structures grown by metal-organic chemical vapor deposition (MOCVD) with various Si incorporations. The Al_0.15Ga_0.85N:Si layers were grown on undoped GaN/sapphire (0001) epitaxial layers in a horizontal MOCVD reactor at the reduced pressure of 300 torr. The mirrorlike surface, free of defects, such as cracks or hillocks, can be seen in the undoped Al_0.15Ga_0.85N epilayer, which was grown without any intentional flow of SiH₄. However, many cracks are observed in the n-Al_0.15Ga_0.85N:Si, which was grown with Si incorporation above 1.0 nmol/min. While Au/n-Al_0.15Ga_0.85N:Si diodes having low incorporation of Si showed retively good rectifying behavior, the samples having high Si incorporation exhibited leaky current-voltage (I-V) behavior. Particularly, the Au/n-Al_0.15Ga_0.85N:Si structure grown with Si incorporation above 1.0 nmol/min cannot be used for electrical rectification. Both added tunneling components and thermionic emission influence the current transport at the Au/n-Al_0.15Ga_0.85N:Si barrier when Si incorporation becomes higher.     

Numerical modeling of combustion processes and pollutant formations in direct-injection diesel engines

The Representative Interactive Flamelet (RIF) concept has been applied to numerically simulate the combustion processes and pollutant formation in the direct injection diesel engine. Due to the ability for interactively describing the transient behaviors of local flame structures with CFD solver, the RIF concept has the capabilities to predict the auto-ignition and subsequent flame propagation in the diesel engine combustion chamber as well as to effectively account for the detailed mechanisms of soot formation, NO_X formation including thermal NO path, prompt and nitrous NO_X formation, and reburning process. Special emphasis is given to the turbulent combustion model which properly accounts for vaporization effects on the mixture fraction fluctuations and the pdf model. The results of numerical modeling using the RIF concept are compared with experimental data and with numerical results of the commonly applied procedure which the low-temperature and high-temperature oxidation processes are represented by the Shell ignition model and the eddy dissipation model, respectively. Numerical results indicate that the RIF approach including the vaporization effect on turbulent spray combustion process successfully predicts the ignition delay time and location as well as the pollutant formation.     

A critical heat flux model based on mass, energy, and momentum balance for upflow boiling at low qualities

A mechanistic modeling of critical heat flux (CHF) in upflow boiling at low qualities is performed. The developed model is based on a physical criterion of CHF occurrence and a mechanism limiting the thermal transport between a stagnant bubbly layer and bulk stream. The mechanism can be mathematically formulated by coupling the equation of limiting mixing mass flux, which is derived from momentum balance equations in two regions, with local mass and energy balance equations on the bubbly layer. The resulting form of the model is represented by a general and straightforward CHF formula involving two empirical constants related to the void fraction and the thickness of the bubbly layer. The predictions agree well with the extensive CHF data of water in uniformly heated tubes.