Non-destructive testing of concrete strength: statistical control

Some problems of statistical control of concrete strength in non-destructive testing are considered. The procedures for rejection of gross errors and accounting for the actual law of concrete strength distribution are given. In the non-destructive control, the reliability and accuracy of a test result, f_i, as well as the probability of a specified concrete strength, f′ _c , should be the same as in testing with the use of a standard method (specimen testing). Proceeding from this concept, known acceptance criteria are analysed and those recommended by the author are described. The use of the latter permits a considerable reduction of the consumer's risk. Procedures for specifying a required average strength, f _cr , are also analysed. In the use of the proposed acceptance criteria, the value of f _cr may be reduced in many cases, and hence the cement content may be decreased.     

洁净煤技术项目融资的可能性综述

在不久的将来煤仍然是世界能源生产的主要燃料,煤消耗量的预期增长和对环境保护的日益关注使得洁净煤技术拥有巨大的市场潜力。这一巨大的市场将提供重大的投资机会,吸引众多大型融资机构,同时也将激励公共部门投资示范工程和洁净煤技术的发展。洁净煤技术的主要融资机构包括世界银行、欧洲投资银行、欧洲改革和发展银行、出口信用代理机构和商业银行。能源服务公司、当地的融资机构、完整的资源规划和需求侧管理将有助于克服融资障碍。     

Analyzing Dynamic Behavior of Geosynthetic-Reinforced Soil Retaining Walls

An advanced generalized plasticity soil model and bounding surface geosynthetic model, in conjunction with a dynamic finite element procedure, are used to analyze the behavior of geosynthetic-reinforced soil retaining walls. The construction behavior of a full-scale wall is first analyzed followed by a series of five shaking table tests conducted in a centrifuge. The parameters for the sandy backfill soils are calibrated through the results of monotonic and cyclic triaxial tests. The wall facing deformations, strains in the geogrid reinforcement layers, lateral earth pressures acting at the facing blocks, and vertical stresses at the foundation are presented. In the centrifugal shaking table tests, the response of the walls subject to 20 cycles of sinusoidal wave having a frequency of 2 Hz and of acceleration amplitude of 0.2g are compared with the results of analysis. The acceleration in the backfill, strain in the geogrid layers, and facing deformation are computed and compared to the test results. The results of analysis for both static and dynamic tests compared reasonably well with the experimental results.     

Immunological evaluation of a 26-kDa antigen from Taenia solium larvae for specific immunodiagnosis of human neurocysticercosis

Human neurocysticercosis, due to infection of the central nervous system by cysticerci of Taenia solium, is a severe form of neurologic disease occurring in Central and South America. Specific proteins from scolex antigen from cysticerci were purified by polyacrylamide gel electrophoresis and electroelution and recognized in Western blots by antibodies present in sera from patients with neurocysticercosis. The proteins appeared as 13-, 17-, and 26-kDa bands on Coomassie blue-stained gels and proved to be specific to cysticerci of T. solium. No cross-reactivity with sera from patients with taeniasis or hydatidosis was observed. Enzyme-linked immunosorbent assay using the purified proteins of 13, 17, and 26 kDa demonstrated rates of 53%, 88%, and 100% specificity, respectively, at the cutoff serum dilution of 1:32 for the specific immunodiagnosis of human neurocysticercosis.     

General Analytical Framework for Design of Flexible Reinforced Earth Structures

Current design methods divide reinforced earth structures into walls and slopes by using an arbitrary face inclination of 70° as the boundary. The required maximum strength of reinforcement computed for reinforced walls are significantly higher than that computed for reinforced slopes even if the inclination is practically the same. Presented is a general analytical framework for design of flexible reinforced earth structures regardless of the slope face inclination. In fact, the framework is consistent for any structural geometry and any applicable slope stability analysis although, for demonstration purposes, the simple Culmann formulation is utilized for simple geometry with zero batter. Using an adequate slope stability formulation, the required tensile resistance of reinforcement for a given layout is calculated so as to produce the same prescribed factor of safety anywhere within the reinforced zone. That is, using the design shear strength of the soil, the required reinforcement resistance along each layer is computed to fully mobilize this shear strength for all possible slip surfaces. That is, a baseline solution is produced for an ideal long-term strength of reinforcement at any location. Consequently, the required strength of the connection between each reinforcement layer and the facing unit can also be determined. This connection strength, however, assumes small facing units with negligibly small shear and moment resistance. Parametric study is conducted to demonstrate the reasonableness of the presented framework. It is shown that the required tensile resistance and connection strength depend on factors such as: reinforcement length; intermediate reinforcement; percent coverage; and quality of fill. When compared with the current AASHTO design for walls, the required maximum long-term strength of the reinforcement as well as the required connection strength in the proposed approach are substantially smaller.     

Required Unfactored Strength of Geosynthetic in Reinforced Earth Structures

Current reinforced earth structure designs arbitrarily distinguish between reinforced walls and slopes, that is, the batter of walls is 20° or less while in slopes it is larger than 20°. This has led to disjointed design methodologies where walls employ a lateral earth pressure approach and slopes utilize limit equilibrium analyses. The earth pressure approach used is either simplified (e.g., ignoring facing effects), approximated (e.g., considering facing effects only partially), or purely empirical. It results in selection of a geosynthetic with a long-term strength that is potentially overly conservative or, by virtue of ignoring statics, potentially unconservative. The limit equilibrium approach used in slopes deals explicitly with global equilibrium only; it is ambiguous about the load in individual layers. Presented is a simple limit equilibrium methodology to determine the unfactored global geosynthetic strength required to ensure sufficient internal stability in reinforced earth structures. This approach allows for seamless integration of the design methodologies for reinforced earth walls and slopes. The methodology that is developed accounts for the sliding resistance of the facing. The results are displayed in the form of dimensionless stability charts. Given the slope angle, the design frictional strength of the soil, and the toe resistance, the required global unfactored strength of the reinforcement can be determined using these charts. The global strength is then distributed among individual layers using three different assumed distribution functions. It is observed that, generally, the assumed distribution functions have secondary effects on the trace of the critical slip surface. The impact of the distribution function on the required global strength of reinforcement is minor and exists only when there is no toe resistance, when the slope tends to be vertical, or when the soil has low strength. Conversely, the impact of the distribution function on the maximum unfactored load in individual layers, a value which is typically used to select the geosynthetics, can result in doubling its required long-term strength.     

Entrance radiation doses during paediatric cardiac catheterisations performed for diagnosis or the treatment of congenital heart disease

The purpose of this study was to estimate the radiation exposure of children, during cardiac catheterisations for the diagnosis or treatment of congenital heart disease. Radiation doses were estimated for 45 children aged from 1 d to 13 y old. Thermoluminescent dosemeters (TLDs) were used to estimate the posterior entrance dose (DP), the lateral entrance dose (DLAT), the thyroid dose and the gonads dose. A dose-area product (DAP) meter was also attached externally to the tube of the angiographic system and gave a direct value in mGy cm2 for each procedure. Posterior and lateral entrance dose values during cardiac catheterisations ranged from 1 to 197 mGy and from 1.1 to 250.3 mGy, respectively. Radiation exposure to the thyroid and the gonads ranged from 0.3 to 8.4 mGy to 0.1 and 0.7 mGy, respectively. Finally, the DAP meter values ranged between 360 and 33,200 mGy cm2. Radiation doses measured in this study are comparable with those reported to previous studies. Moreover, strong correlation was found between the DAP values and the entrance radiation dose measured with TLDs.     

Microwave pulses compressed in a quasi-optical resonator with corrugated mirror

A microwave pulse compressor, representing a three-mirror resonator supplied with a radiation beam reflected from a corrugated mirror, was constructed and experimentally tested. A fivefold compression of microwave pulses with a 70% efficiency was obtained in a 9-mm wavelength range.     

A simple drug anchoring microfiber scaffold for chondrocyte seeding and proliferation

The structural properties of microfiber meshes made from poly(2-hydroxyethyl methacrylate) (PHEMA) were found to significantly depend on the chemical composition and subsequent cross-linking and nebulization processes. PHEMA microfibres showed promise as scaffolds for chondrocyte seeding and proliferation. Moreover, the peak liposome adhesion to PHEMA microfiber scaffolds observed in our study resulted in the development of a simple drug anchoring system. Attached foetal bovine serum-loaded liposomes significantly improved both chondrocyte adhesion and proliferation. In conclusion, fibrous scaffolds from PHEMA are promising materials for tissue engineering and, in combination with liposomes, can serve as a simple drug delivery tool.