Dislocation-Stacking Fault Tetrahedron Interactions in Cu

In copper and other face centered cubic metals, high-energy particle irradiation produces hardening and shear localization. Post-irradiatio

Computer simulation of the effect of copper on defect production and damage evolution in ferritic steels

It has long been noticed that the effect of Cu solute atoms is important for the microstructural evolution of ferritic pressure vessel steels under neutron irradiation conditions. Despite the low concentration of Cu in steel, Cu precipitates form inside the a-Fe surrounding matrix and by impeding free dislocation motion considerably contribute to the hardening of the material. It has been suggested that Cu-rich clusters and combined Cu solute atoms-defect clusters that may act as initiating structures of further precipitates nucleate during annealing of displacement cascades. In order to assess the importance of the different mechanisms taking place during collision events in the formation and later evolution of these structures, a detailed Molecular Dynamics (MD) analysis of displacement cascades in a Fe-1.3% at. Cu binary alloy has been carried out. Cascade energies ranging from 1 to 20 keV have been simulated at temperatures of 100 and 600 K using the MDCASK code, in which the Ackland-Finnis-Sinclair many-body interatomic potential has been implemented. The behavior of metastable Cu self-interstitial atoms (SIAs) in the form of mixed Fe-Cu features is studied as well as their impact on the resulting defect structures. It is observed that above 300 K generated Cu SIAs undergo recombination with no substantial effect on the after-cascade microstructure while at 100 K Cu SIAs remain sessile and exhibit a considerable binding to interstitial and vacancy clusters, Finally, the effect that the production of vacancies via collision cascades may have on the self-diffusion of Cu solute atoms is quantitatively addressed by means of determining diffusion coefficients for Cu atoms under different microstructural conditions

Dynamical properties of the Landau-Ginzburg model with long-range correlated quenched impurities

We investigate the critical dynamics of the time-dependent Landau-Ginzburg model with non conserved n-component order parameter (Model A) in the presence of long-range correlated quenched impurities. We use a special kind of long-range correlations, previously introduced by Weinrib and Halperin. Using a double expansion in \epsilon and \delta we calculate the critical exponent z up to second order on the small parameters. We show that the quenched impurities of this kind affect the critical dynamics already in first order of \epsilon and \delta, leading to a relevant correction for the mean field value of the exponent zComment: 7 pages, REVTEX, to be published in Phys. Rev.

CMS Annual Report 2004

Glance at the articles in this report, and you will sense the transformation that is reshaping the landscape of materials science and chemistry. This transformation is bridging the gaps among chemistry, materials science, and biology--ushering in a wealth of innovative technologies with broad scientific impact. The emergence of this intersection is reinvigorating our strategic investment into areas that build on our strength of interdisciplinary science. It is at the intersection that we position our strategic vision into a future where we will provide radical materials innovations and solutions to our national-security programs and other sponsors. Our 2004 Annual Report describes how our successes and breakthroughs follow a path set forward by our strategic plan and four organizing research themes, each with key scientific accomplishments by our staff and collaborators. We have organized this report into two major sections: research themes and our dynamic teams. The research-theme sections focus on achievements arising from earlier investments while addressing future challenges. The dynamic teams section illustrates the directorate's organizational structure of divisions, centers, and institutes that support a team environment across disciplinary and institutional boundaries. The research presented in this annual report gives substantive examples of how we are proceeding in each of these four theme areas and how they are aligned with our national-security mission. By maintaining an organizational structure that offers an environment of collaborative problem-solving opportunities, we are able to nurture the discoveries and breakthroughs required for future successes

Atomic scale models of Ion implantation and dopant diffusion in silicon

We review our recent work on an atomistic approach to the development of predictive process simulation tools. First principles methods, molecular dynamics simulations, and experimental results are used to construct a database of defect and dopant energetics in Si. This is used as input for kinetic Monte Carlo simulations. C and B trapping of the Si self- interstitial is shown to help explain the enormous disparity in its measured diffusivity. Excellent agreement is found between experiments and simulations of transient enhanced diffusion following 20-80 keV B implants into Si, and with those of 50 keV Si implants into complex B-doped structures. Our simulations predict novel behavior of the time evolution of the electrically active B fraction during annealing

Estudio de validación del Cuestionario de Afrontamiento del Estrés en personas trans de México

Abstract: Validation study of the Stress Coping Questionnaire with trans people from Mexico. The Coping Strategies Questionnaire (CAE) is one of the most used instruments to evaluate coping strategies and styles in diverse populations; however, there is no evidence of its application in trans people, although this population is often discriminated, stigmatized, and presents social, occupational and health vulnerabilities. Therefor, the present study aimed to test factor structure of the CAE, prove internal consistency and convergent and discriminant validity of its factors, and describe the average profile of coping among trans people from Mexico. The sample consisted of 100 trans men and trans women, with ages ranging from 16 to 52 years, from different states of Mexico. The results showed that the CAE presents a factor structure different from that reported in other populations, with six first-order factors that show internal consistency and convergent and discriminant validity. The positive reappraisal factor was not defined, but was partially associated with the negative self-focusing factor. It is concluded that the CAE among trans people presents six first-order factors, with three higher-order underlying factors: negative emotional coping, social support and avoidant coping/religiosity.Resumen: El Cuestionario de Afrontamiento del Estrés (CAE) es uno de los instrumentos más usados para evaluar estrategias y estilos de afrontamiento; sin embargo, no se cuenta con evidencia sobre su aplicación en población trans, cuando ésta es objeto frecuente de discriminación, estigmatización y presenta diversas vulnerabilidades sociales, laborales y sanitarias. Así, este estudio tuvo como objetivos contrastar la estructura factorial del CAE, probar la consistencia interna y validez convergente y discriminante de sus factores, y describir el perfil promedio del afrontamiento en personas trans de México. La muestra se conformó por 100 hombres trans y mujeres trans con un rango de edad de 16 a 52 años de distintos estados de México. Los resultados mostraron que el CAE presenta una estructura factorial distinta a la reportada en otras poblaciones, con seis factores de primer orden que muestran consistencia interna y validez convergente y discriminante. El factor de reevaluación positiva no se definió, sino que parcialmente se asoció al de autofocalización negativa. Se concluye que el CAE en las personas trans presenta seis factores de primer orden a los que subyacen tres factores de orden superior: afrontamiento emocional negativo, apoyo social y afrontamiento evitativo/religiosidad.

First-principles calculation of intrinsic defect formation volumes in silicon

We present an extensive first-principles study of the pressure dependence of the formation enthalpies of all the know vacancy and self-interstitial configurations in silicon, in each charge state from -2 through +2. The neutral vacancy is found to have a formation volume that varies markedly with pressure, leading to a remarkably large negative value (-0.68 atomic volumes) for the zero-pressure formation volume of a Frenkel pair (V + I). The interaction of volume and charge was examined, leading to pressure--Fermi level stability diagrams of the defects. Finally, we quantify the anisotropic nature of the lattice relaxation around the neutral defects.Comment: 9 pages, 9 figure

LLNL's program on multiscale modeling of polycrystal plasticity

At LLNL a multiscale modeling program based on information-passing has been established for modeling the strength properties of a body-centered-cubic metal (tantalum) ,. under conditions of extreme plastic deformation. The plastic deformation experienced by an explosively-formed shaped-charge jet is an example of �extreme deformation�. The shaped charge liner material undergoes high strain rate deformation at high hydrostatic pressure. The constitutive model for flow stress, which describes the deformation, is highly dependent on pressure, temperature, and strain-rate. Current material models can not be extrapolated to these extreme conditions because the underlying mechanisms of plastic deformation are poorly reflected in the models and laboratory experiments are limited to pressures orders of magnitude less than actual pressures. This disparity between actual deformation conditions and those that can be attained in laboratory experiments is the principle motivation behind the multiscale modeling program. The fundamental elements of LLNL� s multiscale modeling program are distinct models at the atomistic, microscale and mesoscale/continuum length scales. The information that needs to be passed from the lower to higher length scales has been carefully defined to bound the levels of effort required to ''bridge'' length scales. Information that needs to be generated by the different simulations has been specified by a multidisciplinary steering group comprised of physicists, materials scientists and engineers. The ultimate goal of the program is to provide critical information on strength properties to be used in continuum computer code simulations. The technical work-plan involves three principle areas which are highly coupled: 1) simulation development, 2) deformation experiments and 3) characterizations of deformed crystals. The three work areas are presented which provide examples of the progress of LLNL's program

Atomic scale modeling of boron transient diffusion in silicon

We presents results from a predictive atomic level simulation of Boron diffusion in Silicon under a wide variety of implant and annealing conditions. The parameters for this simulation have been extracted from first principle approximation models and molecular dynamics simulations. The results are compared with experiments showing good agreement in all cases. The parameters and reactions used have been implemented into a continuum-level model simulator

Pulse Frequency Effect on Neutron Damage in -Iron: A KMC Analysis

The pulsed nature of the irradiation and the high neutron dose are the critical factors in an Inertial Fusion Energy reactor (IFE). The damage that structural materials suffer under these extremes conditions require a careful study and assessment. The goal of our work is to simulate, trough the multiscale modeling approach, the damage accumulation in {alpha}-Fe under conditions relevant to a IFE Reactor. We discuss how the pulse frequency, 1 Hz, 10 Hz, and the dose rate of 10{_} and 10{_}dpa/s affect the damage production and accumulation. Results of the damage that this demanding environment can produce on a protected first structural exposed to 150 keV average recoil ion will be presented. A further comparison it has been made with the damage produced by a continuous irradiation at similar average dose