Multivalent aptamer refers to a technique that joins two or more identical or different types of aptamer monomers together, with or without the presence of structural or other functional elements. As a rapid and easy method for fabricating the multivalent aptamer constructs, rolling circle amplification (RCA) has attracted great attention in recent decades. The incorporation of properly designed structural elements, such as intra-molecular spacers, have been shown to greatly enhance the efficiency of the multivalent aptamer system [1]. The objective of this current study is to systemically investigate the effect of different lengths of poly thymine spacer designs (polyT, from no spacer/NT, 5T, 10T, and 15T) on the capturing performance of RCA-generated multivalent system. To achieve this, we designed four circular probe templates by inserting zero, five, ten, and fifteen adenine bases (polyA). These polyA domains in the circular probe template are complementary to polyT with respective lengths in between the adjacent aptamers on the resultant RCA products (RCAPs). We found that the resultant RCAPs with length shorter than 10T showed a lack or low ability to capture target cells E.Coli O157:H7. When spacer lengths reach or exceed 10T, the capturing performance of the respective multivalent aptamer chain is significantly enhanced. This phenomenon can be explained by larger hydrodynamic sizes and less nonspecific secondary structures observed in RCAP with spacer length no less than 10T. Moreover, we found that there is also a trade-off that the number of polyA bases added into the circular probe template can significantly impair the efficiency of RCA reaction in respective to cyclization yield and amplification rate. The results of this research explain with details how the design of spacer affects RCA reaction efficiency and RCAPs’ capturing performance, which provides ideas in designing an efficient RCA-generated multivalent system.

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<p>There have been considerable requirements for improved products of sheet metal in automobile industry. A quick and economical route to new products is to design novel surface textures of varying scales for improved product enhancement in better optical appearance and formability. The critical deformation in the surface texturing is on the order of only a few microns, and can not be accurately predicted by the classical plasticity due to the size effect. The theory of strain gradient plasticity has been developed to capture the size effect based on the concept of geometrically necessary dislocations (GNDs). A selected strain gradient theory has been implemented into the finite element (FE) model to simulate the surface texturing process. A 3D FE model was developed to simulate the rolling process of sheet metal which has band-type feature on the original surface. The numerical results show that a textured roller can efficiently modify the band-type feature without changing the whole mechanical property of the sheet. Size effect has significant contribution to the magnitude of the rolling force. A FE model was developed to simulate the tensile test of the sheet with textured surface. A textured surface of the sheet is prepared through the indention on the sheet surface. The results show that the textured surface becomes harder due to the strain gradient effect, and finally improves the formability of the sheet.</p> / Master of Applied Science (MASc)

Spindle failure during fast steel rolling is one of the major equipment failures encountered at Onesteel Whyalla Steelworks (WS). Spindle failure whilst infrequent has been occurring over a long period of time and is a significant cost impost in terms of replacement parts, repair and lost production. Previous attempts at mechanical analysis and spindle redesign have not rectified the problem. This thesis presents an in-depth investigation of the problem and uses a completely new approach, modeling and control, to obtain a solution to the problem.

Please read the abstract in the section, 00front of this document / Dissertation (M Eng (Electronic Engineering))--University of Pretoria, 2002. / Electrical, Electronic and Computer Engineering / MEng / unrestricted

Thread rolling is a unique metal forming process which is commonly used to form screw threads on threaded fasteners and precision leadscrews at relatively high rates of speed. Threads are formed on a cylindrical blank by flat or cylindrical dies having the reverse form on them, which rotate and penetrate the blank simultaneously, to plastically deform it into a precise geometry. Thread rolling dies are exposed to a complex state of cyclical contact stresses that eventually cause the dies to fail by fatigue and wear. The stress state is not easily ascertained through standard analytical models due to complex geometry and process conditions. This research seeks to better understand the state of contact stresses present in cylindrical thread rolling dies as they form material, to aid in identifying and testing economical methods of improving thread rolling die fatigue life. Some work has been published on using FEA simulation software to model the thread rolling process, but no work has been published on using FEA software to analyze the stresses in thread rolling dies. DEFORM®-3D Forming Simulation Software by Scientific Forming Technologies Corporation in Columbus, Ohio was used to simulate the throughfeed thread rolling process and model the state of stresses in the dies. The results were compared to the Hertzian contact stress model and the Smith Liu equations for rolling and sliding friction. Fatigue life prediction methods involving S-N curves, surface fatigue strength, and Weibull probability distributions were tested using the simulation data against field results. An optimized die design was generated from a design of experiments simulating different die design geometry. Findings show that field failures correlate well to the DEFORM® simulation results. The Hertz model with Smith Liu equations improved correlation with the simulation. Fatigue life prediction models correlated reasonably well to field results using the simulation data for inputs. These findings can aid in selecting appropriate die materials, design parameters, and fatigue life treatments.

"A Java pre- and post-processing graphical user-oriented interface has been developed by the authors to aid a mill engineer with little or no finite element experience throughout the analysis process of the finishing rolling stands. A case study is presented that uses the commercial finite element code ABAQUS/Explicit to predict roundness and tolerance customer requirements. Other parameters that are determined include spread, crosssectional area, percentage reduction in area, incremental plastic strain, total plastic strain and roll force. All parameters are compared to theoretical models and some are compared to full-scale mill testing."

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Measuring the roll rate or roll position of a rolling airframe can be difficult. Some of the smaller missiles, which have roll rates in excess of 20 revolutions per second, have the least amount of room for a roll sensor such as a laser ring gyro or a quartz rate sensor. The large roll rates coupled with the rate sensor’s resolution can cause large errors in just a few seconds. The cost for these devices can be very high. The roll problem on rolling airframes has been solved by using two magnetic sensors that are 90 degrees out of phase from each other to measure the roll. The cost of the sensor is approximately $15 and is packaged in a 20-pin-surface-mount device. This paper addresses the design and the data processing algorithm to produce roll position. The sensor and algorithm were checked for accuracy on a CARCO table.

<p>Recrystallisation annealing, a repeated heat treatment between different stages of cold rolling of martensitic chromium steel strip, is successful when neither high rolling forces nor wear of the working rolls occur during the subsequent cold rolling. Mechanical properties as tensile strength, yield, elongation or hardness have been, by tradition, the criteria that described the quality of the annealing process. In recent years, the development of the measurement equipment in the rolling mills and of the instruments for material investigations has accentuated more and more the role played by the microstructural properties in the evaluation of the heat treatment. Two microstructural characteristics of the degree of annealing are, firstly and most important, the recrystallisation degree, and, secondly, the secondary carbide density.</p><p>The sample manufacturing and heat treatment, modelling and microstructure investigations by light optical- (LOM) and scanning electron microscopy (SEM) described in this article were carried out at Sandvik Materials Technology’s R&D Department and Bell Furnace Line in Sandviken, Sweden, while microstructure investigations and evaluation by scanning electron microscopy with field emission gun (FEG-SEM) and electron back scatter diffraction (EBSD) were done at the Corrosion and Metals Research Institute (KIMAB) in Stockholm, Sweden.</p><p>The first part of this work shows that, in contrast to the traditional methods LOM and SEM, that use chemical etching for the preparation of the samples, EBSD can successfully characterise recrystallised structures in annealed martensitic chromium steels. Unlike conventional microscopy with LOM and SEM, EBSD is able to reveal the grain geometry, as well as to separate and identify the different phases in this kind of steels (ferrite, M23-, M6-carbides). Important parameters such as grain size, particle size and recrystallised fraction can be measured with high accuracy. This information can be used to understand, evaluate, control and even predict the recrystallisation annealing of martensitic chromium steel.</p><p>The second part of this work presents how the results from microstructure description by EBSD can be directly used in relatively simple empirical models for determination of recrystallisation degree as function of the annealing parameters and the deformation history. EBSD was applied to evaluate the degree of recrystallisation in a series of annealing tests, with the purpose to model recrystallisation temperature in two types of martensitic chromium steel strip, a traditional one and one alloyed with molybdenum, cold rolled with different amounts of reduction and annealed with different temperatures, soaking times and heating rates. The empirical quadratic models were built with Umetrics’ software for experimental design, MODDEÒ 8.0 and they defined the recrystallisation degree (limits for LAGB and HAGB were set to 1.5° and 7.5° for the first grade and 2.5° and 10° for second one) and the secondary carbides density as functions of annealing temperature, soaking time and cold reduction (the factor heating rate was removed as nonsignificant). To be observed that these empirical models were fit much better for the recrystallisation degree than for the secondary carbides density.</p><p>The modelling work described above, together with the implementation of online physical temperature models in the bell annealers may lead to an increased productivity in the production plant by shortening the annealing cycle and minimising scrap and thus to an economical gain of ca 1,5 MSEK per year at Sandvik Materials Technology.</p><p> </p>

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