Computer simulation of H and He effects in fusion reactor materials

Fusion power is an appealing source of clean and abundant energy. The radiation resistance of reactor materials is one of the greatest obstacles on the path towards commercial fusion power. These materials are subject to a harsh radiation environment, and cannot fail mechanically or contaminate the fusion plasma. Moreover, for a power plant to be economically viable, the reactor materials must withstand long operation times, with little maintenance. The fusion reactor materials will contain hydrogen and helium, due to deposition from the plasma and nuclear reactions because of energetic neutron irradiation. The first wall divertor materials, carbon and tungsten in existing and planned test reactors, will be subject to intense bombardment of low energy deuterium and helium, which erodes and modifies the surface. All reactor materials, including the structural steel, will suffer irradiation of high energy neutrons, causing displacement cascade damage. Molecular dynamics simulation is a valuable tool for studying irradiation phenomena, such as surface bombardment and the onset of primary damage due to displacement cascades. The governing mechanisms are on the atomic level, and hence not easily studied experimentally. In order to model materials, interatomic potentials are needed to describe the interaction between the atoms. In this thesis, new interatomic potentials were developed for the tungsten-carbon-hydrogen system and for iron-helium and chromium-helium. Thus, the study of previously inaccessible systems was made possible, in particular the effect of H and He on radiation damage. The potentials were based on experimental and ab initio data from the literature, as well as density-functional theory calculations performed in this work. As a model for ferritic steel, iron-chromium with 10% Cr was studied. The difference between Fe and FeCr was shown to be negligible for threshold displacement energies. The properties of small He and He-vacancy clusters in Fe and FeCr were also investigated. The clusters were found to be more mobile and dissociate more rapidly than previously assumed, and the effect of Cr was small. The primary damage formed by displacement cascades was found to be heavily influenced by the presence of He, both in FeCr and W. Many important issues with fusion reactor materials remain poorly understood, and will require a huge effort by the international community. The development of potential models for new materials and the simulations performed in this thesis reveal many interesting features, but also serve as a platform for further studies.

Modeling of Surface UV Radiation Using Satellite Data

Solar UV radiation is harmful for life on planet Earth, but fortunately the atmospheric oxygen and ozone absorb almost entirely the most energetic UVC radiation photons. However, part of the UVB radiation and much of the UVA radiation reaches the surface of the Earth, and affect human health, environment, materials and drive atmospheric and aquatic photochemical processes. In order to quantify these effects and processes there is a need for ground-based UV measurements and radiative transfer modeling to estimate the amounts of UV radiation reaching the biosphere. Satellite measurements with their near-global spatial coverage and long-term data conti-nuity offer an attractive option for estimation of the surface UV radiation. This work focuses on radiative transfer theory based methods used for estimation of the UV radiation reaching the surface of the Earth. The objectives of the thesis were to implement the surface UV algorithm originally developed at NASA Goddard Space Flight Center for estimation of the surface UV irradiance from the meas-urements of the Dutch-Finnish built Ozone Monitoring Instrument (OMI), to improve the original surface UV algorithm especially in relation with snow cover, to validate the OMI-derived daily surface UV doses against ground-based measurements, and to demonstrate how the satellite-derived surface UV data can be used to study the effects of the UV radiation. The thesis consists of seven original papers and a summary. The summary includes an introduction of the OMI instrument, a review of the methods used for modeling of the surface UV using satellite data as well as the con-clusions of the main results of the original papers. The first two papers describe the algorithm used for estimation of the surface UV amounts from the OMI measurements as well as the unique Very Fast Delivery processing system developed for processing of the OMI data received at the Sodankylä satellite data centre. The third and the fourth papers present algorithm improvements related to the surface UV albedo of the snow-covered land. Fifth paper presents the results of the comparison of the OMI-derived daily erythemal doses with those calculated from the ground-based measurement data. It gives an estimate of the expected accuracy of the OMI-derived sur-face UV doses for various atmospheric and other conditions, and discusses the causes of the differences between the satellite-derived and ground-based data. The last two papers demonstrate the use of the satellite-derived sur-face UV data. Sixth paper presents an assessment of the photochemical decomposition rates in aquatic environment. Seventh paper presents use of satellite-derived daily surface UV doses for planning of the outdoor material weathering tests.

Seismic passive earth pressures in soils

Seismic passive earth pressure coefficients were computed by the method of limit equilibrium using a pseudostatic approach for seismic forces. Composite curved rupture surfaces were considered in the analysis. While earlier studies using this type of analysis were mainly for sands, seismic passive earth pressure coefficients were obtained in the present study considering the effects of cohesion, surcharge, and own weight. The minimum seismic passive force was obtained by adding the individual minimum values of these components and the validity of the principle of superposition was examined. Other parameters considered in the analysis were wall batter angle, ground surface slope, soil friction angle, wall friction angle, wall adhesion to soil cohesion ratio, and horizontal and vertical seismic accelerations. The seismic earth pressure coefficients were found to be highly sensitive to the seismic acceleration coefficients both in the horizontal and vertical directions. Results of the study are presented in the form of figures and tables. Comparisons of the proposed method with available theories in the seismic case are also presented.

Antipyrine complexes of rare-earth nitrates

Antipyrine complexes of eight rare-earth nitrates of the composition M(C11H12N2O)3 (NO3)3 where M = La, Ce, Pr, Nd, Sm, Gd, Er, and Y, have been prepared by a new, simple method and characterised. The complexes undergo exothermic decomposition at ~3oo°C. Infrared and U.V. spectral studies of the complexes indicate that antipyrine coordinates to metal through oxygen. The nature of the nitrate bonding is discussed in the light of infrared evidence, and conductivity studies in nitromethane and dimethylformamide.

Rare-earth trichloroacetates

The rare-earth trichloroacetates having the formula Ln(Cl3CCOO)3. 3H2O, where Ln = La, Pr, Nd, Sm, Gd or Y, were investigated by conductimetric, cryoscopic and infrared methods. The results suggest a structure in which the acetate anion coordinates to the metal through both the oxygen and the water molecules remain outside the coordination sphere.

Antipyrine complexes of rare earth perchlorates

Rare earth perchlorate-antipyrine (ap) complexes of the formula Ln (ClO4)3.6 ap have been prepared and characterised. Infrared and electronic spectra showed the co-ordination through carbonyl oxygen. Conductivity and molecular weight data indicated a co-ordination number of six for these complexes.

Dimethyl sulphoxide complexes of rare-earth perchlorates

Dimethylsulphoxide (DMSO) complexes of rare-earth perchlorates of the formula M(ClO4)3·n DMSO (M = La, Ce, Pr and Nd, n = 8; M = Sm, Gd and Y, n = 7) have been prepared. I.r. studies indicate co-ordination through oxygen. Cryoscopic and conductivity data show co-ordination number of 7 and 8.

Dimethyl formamide complexes of rare-earth nitrates

Dimethyl formamide complexes of five rare-earth nitrates, M(DMF)4(NO3)3 where M = La, Pr, Nd, Sm or Y have been prepared and their infra-red spectra and conductivities in nitromethane and DMF studied. It is suggested that the co-ordination number of the metal ion in these complexes is nine.

Influence of External Light Waves on the Thermoelectric Power Under Strong Magnetic Field in Ultrathin Films, Quantum Wires and Quantum Dots of Optoelectronic Materials

In this paper, an attempt is made to study the influence of external light waves on the thermoelectric power under strong magnetic field (TPSM) in ultrathin films (UFs), quantum wires (QWs) and quantum dots (QDs) of optoelectronic materials whose unperturbed dispersion relation of the conduction electrons are defined by three and two band models of Kane together with parabolic energy bands on the basis of newly formulated electron dispersion laws in each case. We have plotted the TPSM as functions of film thickness, electron concentration, light intensity and wavelength for UFs, QWs and ODs of InSb, GaAs, Hg1-xCdxTe and In1-xGaxAsyP1-y respectively. It appears from the figures that for UFs, the TPSM increases with increasing thickness in quantum steps, decreases with increasing electron degeneracy exhibiting entirely different types of oscillations and changes with both light intensity and wavelength and these two latter types of plots are the direct signature of light waves on opto-TPSM. For QWs, the opto-TPSM exhibits rectangular oscillations with increasing thickness and shows enhanced spiky oscillations with electron concentration per unit length. For QDs, the opto-TPSM increases with increasing film thickness exhibiting trapezoidal variations which occurs during quantum jumps and the length and breadth of the trapezoids are totally dependent on energy band constants. Under the condition of non-degeneracy, the results of opto-TPSM gets simplified into the well-known form of classical TPSM equation which the function of three constants only and being invariant of the signature of band structure.

On the theory of the indentation test for the measurement of tensile strength of brittle materials

A theoretical solution has been obtained for the state of stress in a rectangular plate under a pair of symmetrically placed rigid indenters. The stress distributions along the two central axes have been calculated for a square plate assuming the pressure distribution under the indenters as uniform, parabolic and one resulting from 'constant displacement' on a semiinfinite boundary, for different ratios of indenter-width to side of square. The results are compared with those of photoelastic analysis of Berenbaum and Brodie and the validity of the solution is discussed. The solution has been extended to orthotropic materials and numerical results for one type of coal are given.

Investigation of activated transport in hole doped rare earth manganites in the high temperature paramagnetic regime

Electronic transport in the high temperature paramagnetic regime of the colossal magnetoresistive oxides, La(1-x)A(x)MnO(3), A=Ca, Sr, Ba, x similar or equal to 0.1-0.3, has been investigated using resistivity measurements. The main motivation for this work is to relook into the actual magnitude of the activation energy for transport in a number of manganites and study its variation as a function of hole doping (x), average A-site cation radius (< r(A)>), cationic disorder (sigma(2)) and strain (epsilon(zz)). We show that contrary to current practice, the description of a single activation energy in this phase is not entirely accurate. Our results clearly reveal a strong dependence of the activation energy on the hole doping as well as disorder. Comparing the results across different substituent species with different < r(A)> reveals the importance of sigma(2) as a metric to qualify any analysis based on (r(A)). (c) 2006 Elsevier Ltd. All rights reserved.

A Formalised Model of the Information and Materials Handling Activities in the Construction Process

A model of the information and material activities that comprise the overall construction process is presented, using the SADT activity modelling methodology. The basic model is further refined into a number of generic information handling activities such as creation of new information, information search and retrieval, information distribution and person-to-person communication. The viewpoint could be described as information logistics. This model is then combined with a more traditional building process model, consisting of phases such as design and construction. The resulting two-dimensional matrix can be used for positioning different types of generic IT-tools or construction specific applications. The model can thus provide a starting point for a discussion of the application of information and communication technology in construction and for measurements of the impacts of IT on the overall process and its related costs.

Reliability Analysis of Earth Dams

In the present study, results of reliability analyses of four selected rehabilitated earth dam sections, i.e., Chang, Tapar, Rudramata, and Kaswati, under pseudostatic loading conditions, are presented. Using the response surface methodology, in combination with first order reliability method and numerical analysis, the reliability index (beta) values are obtained and results are interpreted in conjunction with conventional factor of safety values. The influence of considering variability in the input soil shear strength parameters, horizontal seismic coefficient (alpha(h)), and location of reservoir full level on the stability assessment of the earth dam sections is discussed in the probabilistic framework. A comparison of results with those obtained from other method of reliability analysis, viz., Monte Carlo simulations combined with limit equilibrium approach, provided a basis for discussing the stability of earth dams in probabilistic terms, and the results of the analysis suggest that the considered earth dam sections are reliable and are expected to perform satisfactorily.

Piezoresistivity (with uniaxial strain) in nanocrystalline films of rare-earth manganites

We present a study of the piezoresistivity in nanostructured. polycrystalline films of La0.67Ca0.33MnO3 and La0.67Sr0.33MnO3 grown on oxidized Si (100) substrates. We have observed that the hole doped rare-earth manganites, which are well known for being colossal magnetoresistive (CMR) show change in its resistance under uniaxial strain even at room temperature. The piezoresistance was measured at room temperature by bending the Si cantilevers (on which the film is grown) in flexural mode both with compressive and tensile strain. The resistance of the film increases with tensile strain and decreases with compressive strain. A large gauge factor of 15-20 is seen in these films at room temperature.