Structure Analysis and Classification of Precipitation Cells by Fractal Geometry

This paper analyzes the possibility to discriminate between convective precipitation and stratiform precipitation.This study aims to improve the measurement of rainfall from teledetection data obtained both on the ground and in space.For this,two parameters,fractal dimension and fractal lacunarity,are considered.To calculate the fractal dimension,we use the approach of box-counting and show that the fractal dimension differs between convectives cells and stratiforms ones.And then the fractal lacunarity parameter is calculated by using the sliding boxes algorithm.The study for all the regions shows that precipitation cells can be described by different lacunarities whatever the scale of analysis.We deduce that the two parameters,fractal dimension and fractal lacunarity,can be used to classify precipitations in convective regime and stratiform regime.     

Small Angle Neutron Scattering at the National Institute of Standards and Technology

The small angle neutron scattering technique is a valuable method for the characterization of morphology of various materials. It can probe inhomogeneities in the sample (whether occurring naturally or introduced through isotopic substitution) at a length scale from the atomic size (nanometers) to the macroscopic (micrometers) size. This work provides an overview of the small angle neutron scattering facilities at the National Institute of Standards and Technology and a review of the technique as it has been applied to polymer systems, biological macromolecules, ceramic, and metallic materials. Specific examples have been included.     

Mode II stress intensity factors for central slant cracks with frictional surfaces in uniaxially compressed plates

The effect of crack surface friction on mode II stress intensity factor (SIF) of a central slant crack in a plate uniformly loaded in uniaxial compression is quantified. A previously developed two-dimensional finite element analysis was utilised after its modification to accommodate the friction between the crack surfaces. The plane strain state was assumed. A new numerical technique was devised to avoid the iteration procedures, which had to be employed due to the existence of frictional forces.

The crack inclination angle varied between zero and 75° measured from the horizontal direction. The coefficient of friction of the crack surfaces changed from zero to 1. In case of relatively sliding crack surfaces, mode II SIF existed. As is well known, the resulting mode II SIF decreased with increasing the coefficient of friction of the crack surfaces. Further, mode II SIF increased with increasing crack line inclination angle and then decreased after reaching a maximum value. The angle corresponding to that maximum SIF increased as the coefficient of friction of the crack surfaces increased.     

On the correlation between radiation-induced oxide- and border-trap effects in the gate-oxide nMOSFET’s

In this study, combined voltage- and frequency-charge pumping techniques were used to investigate the generation and evolution of border-traps in degraded NMOS transistors by using 1.25 MeV ⁶⁰Co γ-rays. In addition, gate length effects on border-trap charge density were discussed. First result, both border- and oxide-trap reveal two behaviors as function of total dose at low dose rate. Primarily, there is an increase of both trapped charges, followed later by a decrease of their net charge. Second result, border-trap presents a strong dependence on designed transistor channel length. Transistors with longer gate lengths exhibit less important border-trap during irradiation than transistors with smaller gate lengths. This is due to differences in the near-interfacial stress. However, the same effects were observed for oxide-traps. These results show a great correlation between radiation-induced border- and oxide-trap behaviors at low dose rate. Therefore, this similarity strengthens the idea that both border- and oxide-trap could have the same defect (E^′).     

CORRELATION OF FATIGUE CRACK GROWTH BY CRACK TIP DEFORMATION BEHAVIOUR

Growth of a long mode I crack under variable fatigue loading was experimentally investigated on mild steel specimens. A dynamic elastic-plastic two-dimensional finite element program, purposely developed for the simulation of cyclic crack tip deformation, was utilised to model the transient effects on crack tip advance. The model accommodated crack tip opening displacement and both crack tip and crack edge closure. Fifty one different cycle patterns were analysed to include the application of a single overload, a single underload, a single cycle having a combined overload and underload and finally loading blocks of different sequences. Correlations of experimental fatigue crack growth rates were made from knowledge of crack tip deformation behaviour, including the use of data found in the literature. Specimens of eight materials and different geometries were analysed to determine the validity of the present approach.     

Two-phase turbulent mixing and buoyancy drift in rod bundles

This paper describes the development of generalized relationships for single- and two-phase intersubchannel turbulent mixing in vertical and horizontal flows, and lateral buoyancy drift in horizontal flows.The relationships for turbulent mixing, together with a recommended one for void drift, have been implemented in a subchannel thermalhydraulics code, and assessed using a range of data on enthalpy migration in vertical steam–water flows under BWR and PWR diabatic conditions. The intent of this assessment was to optimize these relationships to give the best agreement with the enthalpy migration data for vertical flows. The optimized turbulent mixing relationships were then used as a basis to benchmark a proposed buoyancy drift model to give the best predictions of void and enthalpy migration data in horizontal flows typical of PHWR CANDU¹ reactor operation under normal and off-normal conditions.Overall, the optimized turbulent mixing and buoyancy drift relationships have been found to predict the available data quite well, and generally better and more consistently than currently used models. This is expected to result in more accurate calculations of subchannel distributions of phasic flows, and hence, in improved predictions of critical heat flux (CHF).     

Use of the polar method to predict the hygroscopic transient stresses for balanced [θ/−θ] nS laminates under asymmetrical environmental loadings

This paper presents an analytical method to assess the transient hygroscopic stresses in laminated composite plates due to asymmetrical constant environmental conditions. The developed method permits us to determine directly the values of such stresses without the calculation of the moisture concentration through laminated plates. The present method is the extension of the method developed by Tounsi and Adda-Bedia [Tounsi, A., Adda-Bedia, E.A.: Appl Compos Mater 10, 1–18 (2003)] which is limited only to the problems with symmetrical environmental conditions. Thus by the present method, we can study the effect of symmetrical and asymmetrical environmental conditions. A validation was made with the results of the same authors [Tounsi, A., Adda-Bedia, E.A.: Appl Compos Mater 10, 1–18 (2003); Sereir, Z., et al.: J. Thermal Stres. 28(9), 889–910 (2005)] for symmetrical environmental conditions and the results of benkeddad [Benkeddad, A., et al.: Compos. Struct. 30(2), 201–215 (1995)] for asymmetrical environmental conditions. In order to evaluate the performances of each balanced [θ/?θ] _S laminate proposed for this applications, we use the polar method introduced by Verchery [Vannucci, P., Verchery, G.: Int. J. Solids Struct. 38, 9281–9294 (2001), Vincenti, A., et al.: Composites: Part A, 1525–1532 (2001), Valot, E., et al.: Compos. Struct. 60, 413–429 (2003), Vannucci, P., Verchery, G.: Compos. Sci. Technol. 61, 1465–1473 (2001)]. This method enables us to locate the favourite directions of the mechanical characteristics and to estimate the degree of anisotropy of all stacking sequences. Therefore, we can reduce the transient hygroscopic stresses, particularly at the edges of laminated plates. Through this theoretical study presented here, we hope to contribute to the understanding of hygrothermal behaviour of composite laminated plates.