Development of Accurate Constitutive Models for Simulation of Superplastic Forming

Superplastic forming (SPF) has been considered a process for improving the formability of aluminum alloys for the production of automotive body panels. In order to accurately simulate the SPF process, elevated temperature, uniaxial tension tests are used to develop the material flow model. Due to the high temperature and large degree of deformation in these tests, strain is typically calculated using crosshead displacement rather than with an extensometer. This approach requires the assumption of a constant material volume in the gage section to calculate the uniform strain. It has been observed that a significant amount of material flows from the grips into the gage section during testing which results in inaccuracies in the material model. This article presents a numerical tool that accounts for material flow from the grips and produces a more accurate constitutive equation. Experimental and numerical validations of the results of the developed tool are presented. This article was presented at Materials Science & Technology 2006, Innovations in Metal Forming symposium held in Cincinnati, OH, October 15-19, 2006.     

Synthesis and characterization of Y3Al5O12 and ZrO2-Y2O3 thermal barrier coatings by combustion spray pyrolysis

Y₃Al₅O₁₂ and ZrO₂-Y₂O₃ (8 mol% YSZ) coatings for potential application as thermal barrier coatings were prepared by combustion spray pyrolysis. Thermal cycling of as deposited coatings on stainless steel and FeCrAlY bond coat substrates was carried out at 1000 °C and 1200 °C to determine the thermal fatigue response. Structural and morphological studies on Y₃Al₅O₁₂ and 8 mol% YSZ coatings before and after thermal cycling have been carried out. It has been noted that the coatings on FeCrAlY substrates remain intact after 50 cycles between room temperature and 1200 °C, whereas the coatings on stainless steel show some minor damage such as peeling off near the periphery after 50 cycles at 1000 °C. Thermal diffusivity values of Y₃Al₅O₁₂ and 8 mol% YSZ films were measured by using photo thermal deflection spectroscopy and the values are lower than those of coatings produced by conventional techniques such as EBPVD and APS.     

The urban context for adjustments to the planning process in post-soviet Russia: Responses from local planners in Siberia

This paper examines changes to planning practices in different types of Russian cities that inherited varying levels of administrative status and economic diversification during the Soviet period. Considered the hallmark of the previous regime, planning faces a tenuous fate because of its perceived incompatibility with a democratic, market-based society. For many cities, urban development plans created during the Soviet period do not represent or accommodate the needs of post-Soviet society. Local planners, whose main responsibility previously was to execute these now-defunct plans, are redefining their role within city administration in order to remain relevant. The responses to these fundamental issues at the local level vary by city-type because of post-Soviet realities distinctly impacting each type of city.     

New Channel Estimation Method Using Singular Spectrum Analysis for OFDM Systems

Wireless Personal Communications - This paper presents a new method for OFDM channel estimation (CE) using singular spectrum analysis (SSA). In this method, the conventional LMMSE procedure is used...     

A survey of multimedia content adaptation for mobile devices

With continued increase in the use of smartphones, user expectations of content access have also increased. Most of the content that exists today is not designed for mobile devices. Mobile devices cannot directly access most of the content due to the mismatch in device capability and content playback requirements. Content adaptation is an essential tool that bridges the gap between device capabilities and content formats. In this paper we present an overview of content adaptation and survey recent papers on content adaptation for mobile devices. We introduce the when, where, and what of content adaptation to help classify the content adaptation techniques and to select the appropriate techniques for a given content delivery environment.     

Estimating myocardial motion by 4D image warping

A method for spatio-temporally smooth and consistent estimation of cardiac motion from MR cine sequences is proposed. Myocardial motion is estimated within a four-dimensional (4D) registration framework, in which all three-dimensional (3D) images obtained at different cardiac phases are simultaneously registered. This facilitates spatio-temporally consistent estimation of motion as opposed to other registration-based algorithms which estimate the motion by sequentially registering one frame to another. To facilitate image matching, an attribute vector (AV) is constructed for each point in the image, and is intended to serve as a “morphological signature” of that point. The AV includes intensity, boundary, and geometric moment invariants (GMIs). Hierarchical registration of two image sequences is achieved by using the most distinctive points for initial registration of two sequences and gradually adding less-distinctive points to refine the registration. Experimental results on real data demonstrate good performance of the proposed method for cardiac image registration and motion estimation. The motion estimation is validated via comparisons with motion estimates obtained from MR images with myocardial tagging.     

Optomechanics for a four-stage hybrid-self-electro-optic-device-based free-space optical backplane

We present the design, fabrication, and testing of optomechanics for a free-space optical backplane mounted in a standard 6U VME backplane chassis. The optomechanics implement an optical interconnect consisting of lenslet-to-lenslet, as well as conventional lens-to-lens, links. Mechanical, optical, electrical, thermal, material, and fabrication constraints are studied. Design trade-offs that affect system scalability and ease of assembly are put forward and analyzed. Novel mounting techniques such as a thermal-loaded interference-fitted lens-mounting technique are presented and discussed. Diagnostic tools are developed to quantify the performance of the optomechanics, and experimental results are given and analyzed.     

Study of Porous Silicon Prepared Using Metal-Induced Etching (MIE): a Comparison with Laser-Induced Etching (LIE)

Porous silicon (p-Si), prepared by two routes (metal induced etching (MIE) and laser induced etching (LIE)) have been studied by comparing the observed surface morphologies using SEM. A uniformly distributed smaller (submicron sized) pores are formed when MIE technique is used because the pore formation is driven by uniformly distributed metal (silver in present case) nanoparticles, deposited prior to the porosification step. Whereas in p-Si, prepared by LIE technique, wider pores with some variation in pore size as compared to MIE technique is observed because a laser having gaussian profile of intensity is used for porosification. Uniformly distribute well-aligned Si nanowires are observed in samples prepared by MIE method as seen using cross-sectional SEM imaging. A single photoluminescence (PL) peak at 1.96 eV corresponding to red emission at room temperature is observed which reveals that the Si nanowires, present in p-Si prepared by MIE, show quantum confinement effect. The single PL peak confirms the presence of uniform sized nanowires in MIE samples. These vertically aligned Si nanowires can be used for field emission application.