Prediction of the fatigue life of slender web plates using fracture mechanics concepts

The results of a series of fatigue tests, on slender plate girders subjected to repeated shear loading, are summarised and used to establish a lower bound fatigue strength curve for the welded web boundary, based on geometric or principal surface stress ranges. The propagation of a semi-elliptical surface crack, through the thickness of a plate, is studied using fracture mechanics concepts. An extensive parametric study indicates that the initial crack size and aspect ratio, the geometric stress concentration at the weld toe, and the plate thickness, all have a significant influence on fatigue strength. It is concluded that the fracture mechanics approach requires specification of a number of parameters which are difficult to determine in practice. However, having specified a realistic crack size and aspect ratio and an approximate stress concentration at the weld toe, the solution can be calibrated against available experimental fatigue strength curves.     

Application of some commercial nonionic surfactants in the field of corrosion inhibition

The adsorption of series of commercial nonionic ethoxylated fatty acid surfactants Co(EO)_n (where n = 20, 40, and 80) onto low carbon mild steel is investigated at 25°C in 0.25 M H₂SO₄. The adsorption isotherms of both Co(EO)₂₀ and Co(EO)₈₀ are L‐shaped representing the formation of a monolayer while Co(EO)₄₀ was beginning by an L‐shaped followed by the formation of a multilayer. The level of the plateau shown by these samples decreases in the order Co(EO)₈₀ > Co(EO)₂₀ > Co(EO)₄₀. The effect of this adsorption on the protection of steel against corrosion in sulfuric acid has been studied. Potentiodynamic polarization studies clearly reveal the fact that these surfactants act as mixed‐type inhibitors. The inhibition efficiency increases with increasing the concentration as well as the hydrophilic chain length of these compounds.     

Chemical Fingerprinting of Heat Stress Responses in the Leaves of Common Wheat by Fourier Transform Infrared Spectroscopy

Wheat (Triticum aestivum L.) is known to be negatively affected by heat stress, and its production is threatened by global warming, particularly in arid regions. Thus, efforts to better understand the molecular responses of wheat to heat stress are required. In the present study, Fourier transform infrared (FTIR) spectroscopy, coupled with chemometrics, was applied to develop a protocol that monitors chemical changes in common wheat under heat stress. Wheat plants at the three-leaf stage were subjected to heat stress at a 42 °C daily maximum temperature for 3 days, and this led to delayed growth in comparison to that of the control. Measurement of FTIR spectra and their principal component analysis showed partially overlapping features between heat-stressed and control leaves. In contrast, supervised machine learning through linear discriminant analysis (LDA) of the spectra demonstrated clear discrimination of heat-stressed leaves from the controls. Analysis of LDA loading suggested that several wavenumbers in the fingerprinting region (400–1800 cm⁻¹) contributed significantly to their discrimination. Novel spectrum-based biomarkers were developed using these discriminative wavenumbers that enabled the successful diagnosis of heat-stressed leaves. Overall, these observations demonstrate the versatility of FTIR-based chemical fingerprints for use in heat-stress profiling in wheat.     

Temperature distribution in nuclear fuel rod and variation of the neutronic performance parameters in (D–T) driven hybrid reactor system

Temperature distribution in nuclear fuel rod and variation of the neutronic performance parameters are investigated for different coolants under various first wall loads (P_w=2, 5, 7, 8, 9, and 10 MW m⁻²) in (D, T) (deuterium and tritium) driven and fueled with UO₂ hybrid reactors. Plasma chamber dimension, DR, with a line fusion neutron source is 300 cm. The fissile fuel zone is considered to be cooled with four different coolants with various volume fractions, the volumetric ratio of coolant-to-fuel [(Vm/V_f) = 1:2, 1:1, and 2:1], gas (He, CO₂), flibe (Li₂BeF₄), natural lithium (Li), and eutectic lithium (Li₁₇Pb₈₃). Calculation in the fuel rods and the behavior of the fissile fuel have been observed during 4 years for discrete time intervals of Δt=15 days and by a plant factor (PF) of 75%. As a result of the calculation, cumulative fissile fuel enrichment (CFFE) value indicating rejuvenation performance has increased by increasing P_w for all coolants and . Although CFFE and neutronic performance parameter values increase to the higher values by increasing P_w, the maximum temperature in the centerline of the fuel roads has exceeded the melting point (T_m>2830°C) of the fuel material during the operation periods. However, the best CFFE (11.154%) is obtained in gas coolant blanket for =1:2 (29.462% coolant, 58.924% fuel, 11.614% clad), under 10 MW m⁻² first wall load, followed by flibe with CFFE=11.081% for =2:1 (62.557% coolant, 31.278% fuel, 6.165% clad), under 7 MW m⁻², and flibe with CFFE=9.995% for =1:1 (45.515% coolant, 45.515% fuel, 8.971% clad), under 7 MW m⁻² during operation period without reaching the melting point of the fuel material. While maximum CFFE value has been obtained in fuel rod row#10 in gas, natural lithium, and eutectic lithium coolant blankets, it has been obtained in fuel rod row#1 in flibe coolant blanket for all and P_w. At the same condition, the best neutronic performance parameter values, tritium breeding ratio (TBR)= 1.4454, energy multiplication factor (M)= 9.2018, and neutron leakage (L)= 0.0872, have been obtained in eutectic lithium coolant blankets for the =1:2, followed by gas, natural lithium, and flibe coolant blankets. The isotopic percentage of ²⁴⁰Pu is higher than 5% in all blankets for P_w 7 MW m⁻², so that plutonium component in all blankets can be never reach a nuclear weapon grade quality during the operation period.     

Vehicular Overloads: Load Model, Bridge Safety, and Permit Checking

All states in the United States issue special permits for nondivisible and∕or divisible truck overloads exceeding the weight limit of the highway jurisdiction. This causes stress levels higher than those induced by normal truck traffic. The rationality of such overstress levels has not been documented. This paper addresses several aspects of this issue. It presents (1) a method to develop live load models including overload trucks; (2) associated reliability models for assessing structural safety of highway bridges; and (3) proposed permit-load factors for overload checking in the load and resistance factor format. It shows that the proposed overload checking procedure leads to relatively uniform reliability of bridge structures. A sensitivity analysis is also presented here to assure that possible variations of the input data used to prescribe the proposed load factors will not adversely affect bridge safety. The proposed procedure is intended to be used by engineers responsible for checking overload permits. It may be included in evaluation specifications for highway bridges.     

On-line estimation of time-variant thermal load applied to machine tool structures using a s-domain inverse solution

Thermal deformation of machine tools is of prime concern due to its significant effect on machining errors. To compensate for residual thermal errors, the control system has to incorporate an inverse heat conduction problem IHCP solver to estimate the transient heat input to the structure in real-time. The limitations of available IHCP solutions to applications involving real-time state estimation of complex, multi-dimensional structures are identified. A new s-domain IHCP solution has been developed to resolve these problems and to ensure stability of the solution without using future data. An accelerated inverse numerical Laplace transformation procedure is developed to improve the computational efficiency of the solver. Analysis of results showed the proposed method to be inherently stable and that the random fluctuation in the temperature measurements is considerably attenuated by the numerical nature of the solution. The results also show that the computational time has been improved by at least one order of magnitude over available methods, without compromising the accuracy and stability requirements. Due to the generalized nature of the formulation and the solution algorithm, this method can readily be applied to all classes of machine tools without any further developments by the end user.     

Diffraction of Obliquely Incident Plane Waves by Resistive and Conductive Planar Surfaces

The multiple diffraction of obliquely incident plane waves by the three-part resistive and conductive plane is evaluated via uniform asymptotic high frequency analysis. This analysis is based on a spectral iteration technique consisting of employing the Fourier Integral representation of the diffracted field through the solution of a pair of uncoupled Wiener-Hopf equations. By studying these equations iteratively, the double and triple diffracted fields are obtained through the saddle-point technique. Some numerical examples are also presented.     

A simple subcircuit extension of the BSIM3v3 model for CMOS RFdesign

An accurate and simple lumped-element extension of the BSIM3v3 MOSFET model for small-signal radio-frequency circuit simulation is proposed and investigated. Detailed comparisons of the small-signal y and s parameters with both two-dimensional device simulations and measurement data are presented. A procedure is developed to extract the values of two lumped resistors-the only added elements. The non-quasi-static and substrate effects can be modeled with these two resistors to significantly improve the model accuracy up to a frequency of 10 GHz, which is about 70% of the f_T of the 0.5 μm NMOS transistor     

A New Approach to Parallelization of Serial Nested Loops Using Genetic Algorithms

Loop parallelization is an important issue in the acceleration of the execution of scientific programs. To exploit parallelism in loops a system of equations representing the dependencies between the loop iterations and a system of non-equations indicating the loop boundary conditions has to be solved. This is a NP-Complete problem. Our major contribution in this paper has been to apply genetic algorithm to solve system of equation and non-equation resulted from loop dependency analysis techniques to find two dependent loop iterations. We use distance vector to find the rest of dependencies.