Corrosion susceptibility of potential rock bolts in aerated multi-ionic simulated concentrated water

Rock bolts used for the reinforcement of underground mines, tunnels and nuclear waste repositories are made up of low and medium carbon steels, and high strength low alloy steels. Typical rock bolt systems used for rock reinforcement are mechanically anchored bolts, grout anchored, frictional rock stabilizers and strand anchors. For nuclear waste repository sites such as Yucca Mountain (YM) as well as for mines and tunnels, in addition to mechanical properties, corrosion properties are also important due to potential seepage of water through the fractures or pores in the rock. During temporary rock support period of 50-100 years, the temperature of the tunnel at YM should be maintained at ambient conditions. For any reason if the rock bolts are exposed to YM waters and high temperatures in the tunnel then there is a chance of corrosion of steel rock bolts. In this study an attempt was made to study the corrosion properties of various potential rock bolts for YM tunnel support via the aid of electrochemical corrosion testing. At ambient temperature (25 °C) all the rock bolts that were studied showed good corrosion resistance in these waters. At higher temperatures, 60 °C and 90 °C, corrosion resistance of rock bolts decreased, but due to special stress relief heat treatment of one of the frictional rock stabilizers (Swellex Mn 24) the corrosion rates were lower than all other tested rock bolts. Note: Swellex, Split set and Williams are the proprietary names of Atlas Copco, International Roll Forms, Inc. and Williams Form Engineering Corp, respectively.     

Microwave dielectric properties of flexible butyl rubber–strontium cerium titanate composites

Butyl rubber–strontium cerium titanate (BS) composites have been prepared by hot pressing. The tensile tests show that the BS composites are flexible. The dielectric properties of the composites have been investigated at 1 MHz and 5 GHz as a function of ceramic contents. The composite with volume fraction 0.43 of ceramic filler has a dielectric constant (ε_r) of 11.9 and dielectric loss (tan δ) 1.8 × 10^?3 at 5 GHz. The measured values of ε_r are compared with the effective values calculated using different theoretical models. The thermal conductivity of the composites is found to increase with ceramic contents and reaches a value of 4.5 Wm^?1 K^?1 for maximum filler loading 0.43 volume fraction. The coefficient of thermal expansion of the composites decreases gradually with filler loading and reaches a minimum value of 30.2 ppm °C^?1 at a volume fraction 0.43. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

29Si MAS NMR study of the hydration of tricalcium silicate in the presence of finely divided silica

²⁹Si magic angle spinning nuclear magnetic resonance spectroscopy has been used to investigate the effect of finely divided silica on the hydration of tricalcium silicate (C₃S). In order to reduce the time needed to obtain quantitative results, low levels of paramagnetic iron oxide were added to materials to increase the nuclear relaxation rate. The reactions of the C₃S and the finely divided silica could then be monitored separately and without chemical modification. The results were correlated with data from microcalorimetry, thermogravimetric analysis and electron microscopy. Under the conditions used here the presence of the silica accelerates greatly the hydration process, and results in a markedly increased degree of polymerization in the resulting gel, without significantly affecting the induction period of the reaction. The significance of these results for understanding the hydration process of C₃S in the presence of silica is outlined.     

An unsupervised approach to learn the kernel functions: from global influence to local similarity

Recently there has been a steep growth in the development of kernel-based learning algorithms. The intrinsic problem in such algorithms is the selection of the optimal kernel for the learning task of interest. In this paper, we propose an unsupervised approach to learn a linear combination of kernel functions, such that the resulting kernel best serves the objectives of the learning task. This is achieved through measuring the influence of each point on the structure of the dataset. This measure is calculated by constructing a weighted graph on which a random walk is performed. The measure of influence in the feature space is probabilistically related to the input space that yields an optimization problem to be solved. The optimization problem is formulated in two different convex settings, namely linear and semidefinite programming, dependent on the type of kernel combination considered. The contributions of this paper are twofold: first, a novel unsupervised approach to learn the kernel function, and second, a method to infer the local similarity represented by the kernel function by measuring the global influence of each point toward the structure of the dataset. The proposed approach focuses on the kernel selection which is independent of the kernel-based learning algorithm. The empirical evaluation of the proposed approach with various datasets shows the effectiveness of the algorithm in practice.     

Effect of Zn2+ substitution on the microwave dielectric properties of LiMgPO4 and the development of a new temperature stable glass free LTCC

The LiMg_(1?x)Zn_xPO₄ ceramics have been prepared by the solid state ceramic route. The LiMg_(1?x)Zn_xPO₄ ceramic retains the orthorhombic structure up to x = 0.2. The compositions with 0.3 ≤ x ≤ 0.8 exist as a mixture of orthorhombic and monoclinic phases. When Mg²⁺ is fully replaced with Zn²⁺ (x = 1.0) complete transition to monoclinic phase occurs. The ceramic with x = 0.1 (LiMg_0.9Zn_0.1PO₄) sintered at 925 °C exhibits low relative permittivity (?_r) of 6.7, high quality factor (Q_u × f) of 99,700 GHz with a temperature coefficient of resonant frequency (τ_f) of ?62 ppm/°C. The slightly large τ_f is adjusted nearly to zero with the addition of TiO₂. LiMg_0.9Zn_0.1PO₄–TiO₂ composite with 0.12 volume fraction TiO₂ sintered at 950 °C shows good microwave dielectric properties: ?_r = 10.1, Q_u × f = 52,900 GHz and τ_f = ?5 ppm/°C. The ceramic is found to be chemically compatible with silver.     

A survey of the state of the art in learning the kernels

In recent years, the machine learning community has witnessed a tremendous growth in the development of kernel-based learning algorithms. However, the performance of this class of algorithms greatly depends on the choice of the kernel function. Kernel function implicitly represents the inner product between a pair of points of a dataset in a higher dimensional space. This inner product amounts to the similarity between points and provides a solid foundation for nonlinear analysis in kernel-based learning algorithms. The most important challenge in kernel-based learning is the selection of an appropriate kernel for a given dataset. To remedy this problem, algorithms to learn the kernel have recently been proposed. These methods formulate a learning algorithm that finds an optimal kernel for a given dataset. In this paper, we present an overview of these algorithms and provide a comparison of various approaches to find an optimal kernel. Furthermore, a list of pivotal issues that lead to efficient design of such algorithms will be presented.     

A study using Monte Carlo Simulation for failure probability calculation in Reliability-Based Optimization

In this study, a Reliability-Based Optimization (RBO) methodology that uses Monte Carlo Simulation techniques, is presented. Typically, the First Order Reliability Method (FORM) is used in RBO for failure probability calculation and this is accurate enough for most practical cases. However, for highly nonlinear problems it can provide extremely inaccurate results and may lead to unreliable designs. Monte Carlo Simulation (MCS) is usually more accurate than FORM but very computationally intensive. In the RBO methodology presented in this paper, limit state approximations are used in conjunction with MCS techniques in an approximate MCS-based RBO that facilitates the efficient calculation of the probabilities of failure. A FORM-based RBO is first performed to obtain the initial limit state approximations. A Symmetric Rank-1 (SR1) variable metric algorithm is used to construct and update the quadratic limit state approximations. The approximate MCS-based RBO uses a conditional-expectation-based MCS, that was chosen over indicator-based MCS because of the smoothness of the probability of failure estimates and the availability of analytic sensitivities. The RBO methodology was implemented for an analytic test problem and a higher-dimensional, control-augmented-structure test problem. The results indicate that the SR1 algorithm provides accurate limit state approximations (and therefore accurate estimates of the probabilities of failure) for these test problems. It was also observed that the RBO methodology required two orders of magnitude fewer analysis calls than an approach that used exact limit state evaluations for both test problems.     

氮钾施用量对生长在安大略邦北部轻壤土上CM-12(KA)烤烟产质量的影响

1993～1995年间,在安大略邦北部的轻壤土上,选用16/103和CM-12(KA)2个品种、2个施钾水平(80kg K2O/hm2和120kg K2O/hm2)和5个施氮水平(60kg N/hm2、70kg N/hm2、80kg N/hm2、90kg N/hm2和100kg N/hm2)进行了本项试验.试验的目的是为了找出适合于CM-12(KA)品种种植的施氮量和施钾量.除施氮量外,其它因素对烟叶产量和质量的影响均没有达到显著水平.施氮量从60kg N/hm2增加到80kgN/hm2,鲜烟叶的产量显著增加,施氮量为100kg N/hm2时,产量最高.施氮量80kg N/hm2、90kgN/hm2和100kg N/hm2处理的烟叶(烘烤的烟叶)明显高于其它处理.施氮量60kg N/hm2和70kg N/hm2的等级指数最高.施氮量从60kg N/hm2增加到100kgN/hm2,从下到上不同部位(P、X、L和T)烟叶的糖含量减少,氮和烟碱含量增加.不同施氮量之间,烟叶的物理性状差异不显著.结论是就烟叶的产量和质量综合评定而言,适宜于CM-12(KA)烤烟品种种植的施氮量和施钾量分别为80kg N/hm2和80kg K2O/hm2.     

Microwave dielectric properties of BaNb(2?x)TaxP2O11 (x?=?0, 0.5, 1, 1.5 and 2) ceramics

BaNb_(2−x)Ta_xP₂O₁₁ (x = 0, 0.5, 1, 1.5 and 2) ceramics were prepared by the conventional solid state ceramic route. The relative permittivity (ε_r) of the ceramics decreased from 25.3 for x = 0 to 12.9 for x = 2. BaTa₂P₂O₁₁ (x = 2) sintered at 1250°C showed good microwave dielectric properties with Q_u × f = 28,900 GHz and τ_f = − 29 ppm/°C. The addition of 5 wt% TiO₂ lowered the sintering temperature to 1225°C and improved τ_f to −6 ppm/°C with ε_r = 13.4 and Q_u × f = 17,200 GHz.     

Metal hydrides for vehicular applications: The state of the art

Recent developments in light metal complex hydrides show that there is a potential for hydrogen storage using these hydrides in fuel cells for on-board vehicular and other applications. The search for new alloys promises to have practical significance with the realization that hydrogen as a fuel holds the key to filling energy needs and solving environmental problems. This review presents the U.S. Department of Energy FreedomCAR goals for hydrogen storage, storage capacities of important hydrides, and current developments in light-metal complex hydrides.