Study on the microstructure in a friction stir welded 2519-T87 Al alloy

The microhardness, grain size and distribution of the precipitates in various zones of a 2519-T87 aluminum alloy welded joint welded by friction stir welded were investigated. The dynamic recrystallization occurred in the weld nugget zone and the size of recrystallized grains was smaller than that in the thermo-mechanically affected zone, besides, θ′ and θ phase precipitated. The thermo-mechanically affected zone was divided into three ones: the zone close to the thermo-mechanically affected zone, where coarse θ′ precipitates were observed; the middle zone, where the mainly θ precipitates appeared; and the zone close to the heat-affected zone, where both thin θ′ and θ precipitates were observed. In the heat-affected zone, the size of θ′ precipitates was less than those in the base metal zone. On the transverse cross-section of welded joint the microhardness curve shows a W-shape.     

Ground surface integrity of granite by using dry electro-contact discharge dressing of #600 diamond grinding wheel

Dry electro-contact discharge (ECD) dressing of metal-bonded #600 diamond grinding wheel is proposed for grinding of various granites. As compared to mechanical GC dressing, Dry ECD dressing can not only protrude fine diamond grains from wheel metal-bond without any damage, but also eliminate bond-tail behind the protruded grain. The objective is to understand how the synthetic factors including granite structure, grinding parameters and dressing method influence the ground surface integrity of multi-crystal granite such as surface roughness and surface crack appearance in contrast to homogeneous optic glass. First a micron-scale indentation experiment was carried out to display the growth mechanism of micro-cracks on polished surface, then Dry ECD dressing and mechanical GC dressing were carried out in grinding experiment, respectively, finally surface roughness and micro-surface crack were investigated in connection with granite crystal size, work speed and dressing method. It is found that in almost all cases the multi-crystal granite has always worse ground surface than homogeneous optic glass even if grinding parameter is changed. Moreover, the improvement of ground surface for granite is more sensitive to grain protrusion feature than that for optic glass. Although it is very difficult to find out obvious relationship between surface roughness and grinding parameter such as work speed, it has a good correlation with granite structure such as granite crystal size: it decreases with the increase of the granite crystal size. It is concluded that Dry ECD dressing may more greatly improve the ground surface integrity of various granites than mechanical GC dressing.     

An iterative multi-scale tensor voting scheme for perceptual grouping of natural shapes in cluttered backgrounds

Grouping processes, which “organize” a given data by eliminating the irrelevant items and sorting the rest into groups, each corresponding to a particular object, can provide reliable pre-processed information to higher level computer vision functions, such as object detection and recognition. In this paper, we consider the problem of grouping oriented segments in highly cluttered images. In this context, we have developed a general and powerful method based on an iterative, multiscale tensor voting approach. Segments are represented as second-order tensors and communicate with each other through a voting scheme that incorporates the Gestalt principles of visual perception. The key idea of our approach is removing background segments conservatively on an iterative fashion, using multi-scale analysis, and re-voting on the retained segments. We have performed extensive experiments to evaluate the strengths and weaknesses of our approach using both synthetic and real images from publicly available datasets including the Williams and Thornber’s fruit-texture dataset [L. Williams, Fruit and texture images. Available from: <http://www.cs.unm.edu/~williams/saliency.html>, 2008 (last viewed in July 2008)] and the Berkeley segmentation dataset [C.F.P. Arbelaez, D. Martin, The berkeley segmentation dataset and benchmark. Available from: <http://www.eecs.berkeley.edu/Research/Projects/CS/vision/grouping/segbench/>, 2008 (last viewed in July 2008)]. Our results and comparisons indicate that the proposed method improves segmentation results considerably, especially under severe background clutter. In particular, we show that using the iterative multiscale tensor voting approach to post-process the posterior probability map, produced by segmentation methods, improves boundary detection results in 84% of the grayscale test images in the Berkeley segmentation benchmark.     

A probabilistic analysis of two university parking issues

The uncertain nature of the demand for university parking has now created a major problem for university planners. From a facilities planning perspective, it is important to comprehend the probabilistic nature of the demand for parking and parking rules violations. Given this background, in our note, we shed light on two insufficiently studied issues concerning university parking. First, we focus on short-term and long-term parkers. We determine the mean parking time of an arriving car and then we compute the probability distribution function of the number of occupied parking spots at any particular time. Second, we concentrate on parking rules violators and we calculate the probability distribution function of the number of violators who are fined at an inspection.     

An Investigation of the Relationship Between the Gaussian Process Model Parameters and Surface Area in Three Dimensions

In this paper, we study the relationship between the fitted parameters in a Gaussian process (kriging) model and the complexity of the resulting response surface. This study is done for models with one response and two input variables. An analytical calculation of surface roughness is used as a measure of the complexity of the response surface fit by the Gaussian process model. Our findings indicate that the size of the fitted model parameters as measured across different fits and data sets do not give indication as to the complexity of the surface. We do, however, show that the magnitude of each of the parameters in a single fitted model gives indication about the amount of variability in the direction of that fitted parameter. Copyright © 2015 John Wiley & Sons, Ltd.     

MAC-layer rate control for 802.11 networks: a survey

Rate control at the MAC-layer is one of the fundamental building blocks in many wireless networks. Over the past two decades, around thirty mechanisms have been proposed in the literature. Among them, there are mechanisms that make rate selection decisions based on sophisticated measurements of wireless link quality, and others that are based on straight-forward heuristics. Minstrel, for example, is an elegant mechanism that has been adopted by hundreds of millions of computers, yet, not much was known about its performance until recently. The purpose of this paper is to provide a comprehensive survey and analysis of the existing solutions from the two fundamental aspects of rate control—metrics and algorithms. We also review how these solutions were evaluated and compared against each other. Based on our detailed studies and observations, we share important insights on future development of rate control mechanisms at the MAC-layer. This discussion also takes into account the recent developments in wireless technologies and emerging applications, such as Internet-of-Things, and shows issues that need to be addressed in the design of new rate control mechanisms suitable for these technologies and applications.

     

Quantum dot light emitting devices for photomedical applications

While OLEDs have struggled to find a niche lighting application that can fully take advantage of their unique form factors as thin, flexible, lightweight and uniformly large‐area luminaire, photomedical researchers have been in search of low‐cost, effective illumination devices with such form factors that could facilitate widespread clinical applications of photodynamic therapy (PDT) or photobiomodulation (PBM). Although existing OLEDs with either fluorescent or phosphorescent emitters cannot achieve the required high power density at the right wavelength windows for photomedicine, the recently developed ultrabright and efficient deep red quantum dot light emitting devices (QLEDs) can nicely fit into this niche. Here, we report for the first time the in‐vitro study to demonstrate that this QLED‐based photomedical approach could increase cell metabolism over control systems for PBM and kill cancerous cells efficiently for PDT. The perspective of developing wavelength‐specific, flexible QLEDs for two critical photomedical fields (wound repair and cancer treatment) will be presented with their potential impacts summarized. The work promises to generate flexible QLED‐based light sources that could enable the widespread use and clinical acceptance of photomedical strategies including PDT and PBM.     

Learning Automata from Ordered Examples

Connectionist learning models have had considerable empirical success, but it is hard to characterize exactly what they learn. The learning of finite-state languages (FSL) from example strings is a domain which has been extensively studied and might provide an opportunity to help understand connectionist learning. A major problem is that traditional FSL learning assumes the storage of all examples and thus violates connectionist principles. This paper presents a provably correct algorithm for inferring any minimum-state deterministic finite-state automata (FSA) from a complete ordered sample using limited total storage and without storing example strings. The algorithm is an iterative strategy that uses at each stage a current encoding of the data considered so far, and one single sample string. One of the crucial advantages of our algorithm is that the total amount of space used in the course of learning for encoding any finite prefix of the sample is polynomial in the size of the inferred minimum state deterministic FSA. The algorithm is also relatively efficient in time and has been implemented. More importantly, there is a connectionist version of the algorithm that preserves these properties. The connectionist version requires much more structure than the usual models and has been implemented using the Rochester Connectionist Simulator. We also show that no machine with finite working storage can iteratively identify the FSL from arbitrary presentations.     

A new comprehensive model for nucleate pool boiling heat transfer of pure liquid at low to high heat fluxes including CHF

Based on the fractal distribution of nucleation sites present on heating surfaces, a new comprehensive model is developed for the nucleate pool boiling of pure liquid at low to high heat fluxes including the critical heat flux (CHF). The proposed model is expressed as a function of total number, minimum and maximum sizes of active nucleation sites, fractal dimension, superheat temperature, and properties of fluids. No additional empirical constant is introduced in the proposed model. This fractal model contains less empirical constants than the conventional models. The model predictions are in good agreement with the available experimental data.