Single-Sided Ultrasonic Technique to Characterize Thick FRP Composites

This paper reports on the development of a single-sided, laser ultrasonic technique that is capable of measuring all of the engineering constants of a pultruded FRP composite structural member. The complex nature of these members (which are used in civil infrastructure applications) precludes the determination of all of the engineering constants using mechanical tests, while immersion ultrasonic techniques have certain drawbacks. The proposed technique, which uses a combination of contact piezoelectric and optical methodologies, does not call for cutting the specimen or placing it in an immersion tank. Optical generation and detection of ultrasound enble the direct measurement of the longitudinal and surface acoustic wave speeds in the pultrusion direction, without requiring access to the ends of the specimen, or relying on reflected quasilongitudinal waves. The measured engineering constants are compared to immersion technique results, and the advantages of the proposed technique are clearly demonstrated.     

Short-Term Behavior and Design of Fiber-Reinforced Polymeric Slender Members under Axial Compression

Presented in this paper are results of an experimental investigation pertaining to the short-term behavior of concentrically loaded fiber-reinforced polymeric composite slender members. Tested members had box and I-shape cross sections and were pultruded using a vinylester matrix containing flame retardant additives reinforced with E-glass roving and nonwoven mats. Material properties for each tested member are used in a limit state predictor equation to correlate the experimental and the predicted results. Design guidelines and a step-by-step example are also presented.     

The elderly homeless men in Bloomsbury hostels: their needs for services

OBJECTIVES: The objectives of this study are: (1) to assess the feasibility and usefulness of using the Needs Schedule on older homeless individuals; (2) to measure the needs of the elderly homeless individual for mental health services and whether these needs could be met by the same services that cater for younger individuals. DESIGN AND SETTING: This article analyses the needs of a subsample of 37 elderly residents in four inner London hostels for homeless people. Their needs were compared with those of 64 younger residents within the same hostels. RESULTS: The data related to demographic characteristics and health problems showed that the elderly homeless were physically frail and socially isolated. This group demonstrated more need for physical health services than the younger sample. However, the needs assessment method used in this study failed to show significant differences between the needs of these elderly and those of the younger residents. CONCLUSIONS: The article discusses ways of improving the assessment of needs for services in the elderly homeless and the way forward in meeting the needs of this disadvantaged group.     

Effects of roasting on phenolics composition and antioxidant activity of peanut (<Emphasis Type="Italic">Arachis hypogaea</Emphasis> L.) kernel flour

The effects of roasting on the phenolics composition and antioxidant activity of peanut (Arachis hypogaea L.) kernel flour were appraised. Peanut kernel flour, with and without skin, were roasted at 160 °C for 10, 20, 30, 40 and 50 min. The resultant changes in the antioxidant activity of roasted peanut kernel flour were assessed by the determinations of total phenolics, 1,1-diphenyl-2-picrylhydrazyl free radical-scavenging capacity, percent inhibition of linoleic acid oxidation and thiobarbituric acid test and compared with those of unroasted kernel flour. It was observed that roasting significantly (p < 0.05) increased the antioxidant activity of the peanut kernel flour. HPLC analysis revealed the detection of three phenolic acids (p-hydroxybenzoic, chlorogenic, p-coumaric), two flavonols (quercetin, kaempferol), and a stilbene (resveratrol) both in the roasted and unroasted samples. In peanut kernel flour without skin, the contents of the phenolics increased in the initial roasting phase, however, decreased gradually in the later phase (>20 min of roasting time). In contrast, over the course of heating, the amounts of phenolics were noted to be slightly increased in the peanut kernel flour with skin; the most significant (p < 0.05) increase occurred in the concentration of p-coumaric acid and quercetin at 30, 40, and 50 min of roasting. The results of this study reveal that optimum roasting time should be sought to enhancing the antioxidant capacity and phenolics concentration in peanut kernel flour.     

The rotation of a rigid spheroidal inclusion embedded in a transversely isotropic medium

The exact three-dimensional elasticity solutions are given for two problems related to a rigid spheroidal inclusion embedded in bonded contact with an infinite transversely isotropic elastic medium. The first is of axisymmetric nature in which the inclusion is given a constant rotation about its axis of revolution which coincides with the axis of symmetry of the material. The second problem is asymmetric where the spheroidal inclusion is given a constant rotation about a direction that is perpendicular to the axis of elastic symmetry of the material. The displacement potential representation for the equilibrium of three-dimensional transversely isotropic bodies is used to solve the problem. In both cases, the moment-rotation relationship for the spheroidal inclusion and its limiting configurations are obtained in closed form. Numerical results are presented to show the effect of the aspect ratio of the spheroid on the rotational stiffness.     

Direct Pyrolysis of Supermolecules: An Ultrahigh Edge-Nitrogen Doping Strategy of Carbon Anodes for Potassium-Ion Batteries

Most reported carbonaceous anodes of potassium-ion batteries (PIBs) have limited capacities. One approach to improve the performance of carbon anodes is edge-nitrogen doping, which effectively enhances the K-ion adsorption energy. It remains challenging to achieve high edge-nitrogen doping due to the difficulty in controlling the nitrogen dopant configuration. Herein, a new synthesis strategy is proposed to prepare carbon anodes with ultrahigh edge-nitrogen doping for high-performance PIBs. Specifically, self-assembled supermolecule precursors derived from pyromellitic acid and melamine are directly pyrolyzed. During the pyrolysis process, the amidation and imidization reactions between pyromellitic acid and melamine before carbonization enable the successful carbonization of pyromellitic acid–melamine supermolecule. The obtained 3D nitrogen-doped turbostratic carbon (3D-NTC) possesses a 3D framework composed of carbon nanosheets, turbostratic crystalline structure, and an ultrahigh edge-nitrogen-doping level up to 16.8 at% (73.7% of total 22.8 at% nitrogen doping). These features endow 3D-NTCs with remarkable performances as PIB anodes. The 3D-NTC anode displays a high capacity of 473 mAh g⁻¹, robust rate capability, and a long cycle life of 500 cycles with a high capacity retention of 93.1%. This new strategy will boost the development of carbon anodes for rechargeable alkali-metal-ion batteries.     

Si MAS-NMR Study of Hydrated Cement Paste and Mortar Made with and without Silica Fume

This paper presents ²⁹Si MAS-NMR measurements that trace the hydration process in both cement paste and mortar specimens made from ordinary portland cement, Type I, when the cement content is replaced by 0, 10, 15, and 20 wt% of silica fume. The specimens were moist-cured for 3, 7, 14, 28, 90, and 180 days at a laboratory temperature of 21°C (69.8°F). Compressive strength for all tested specimens was also determined. The results show that the degree of hydration (Q¹+ Q²)/(Q°+ Q¹+ Q²) increased with increasing content of silica fume, especially at the early ages of 3 to 28 days. In the same manner, compressive strength results were markedly increased up to 14 days and were lowered at later ages, compared to the control mix (0 wt% silica fume).     

Probabilistic Analysis of Circular Tunnels in Homogeneous Soil Using Response Surface Methodology

A probabilistic analysis of a shallow circular tunnel driven by a pressurized shield in a frictional and/or cohesive soil is presented. Both the ultimate limit state (ULS) and serviceability limit state (SLS) are considered in the analysis. Two deterministic models based on numerical simulations are used. The first one computes the tunnel collapse pressure and the second one calculates the maximal settlement due to the applied face pressure. The response surface methodology is utilized for the assessment of the Hasofer-Lind reliability index for both limit states. Only the soil shear strength parameters are considered as random variables while studying the ULS. However, for the SLS, both the shear strength parameters and Young’s modulus of the soil are considered as random variables. For ULS, the assumption of uncorrelated variables was found conservative in comparison to the one of negatively correlated parameters. For both ULS and SLS, the assumption of nonnormal distribution for the random variables has almost no effect on the reliability index for the practical range of values of the applied pressure. Finally, it was found that the system reliability depends on both limit states. Notice however that the contribution of ULS to the system reliability was not significant. Thus, SLS can be used alone for the assessment of the tunnel reliability.     

Three-Dimensional Passive Earth Pressures by Kinematical Approach

The 3D passive earth pressure problem is investigated by the upper-bound method in limit analysis. Three kinematically admissible failure mechanisms referred to as M1, Mn, and Mnt are considered for the calculation schemes. The M1 mechanism is an extension into three dimensions of the classical 2D Coulomb mechanism. The Mn mechanism is a generalization of the M1 mechanism and is composed of a sequence of rigid blocks. Finally, the Mnt mechanism is a more elaborate mechanism in which the final block of the Mn mechanism is truncated by two portions of right circular cones. The lowest upper-bound solutions given by the present analysis are compared with other authors' results and presented in a form of design tables relating the geometrical parameters, soil properties, and the 3D passive earth pressure coefficients.