Dendritic to globular morphology transition in ternary alloy solidification

The evolution of solidification microstructures in ternary metallic alloys is investigated by adaptive finite element simulations of a general multicomponent phase-field model. A morphological transition from dendritic to globular growth is found by varying the alloy composition at a fixed undercooling. The dependence of the growth velocity and of the impurity segregation in the solid phase on the composition is analyzed and indicates a smooth type of transition between the dendritic and globular growth structures.Comment: 4 pages, 2 figure

A phase‐field based model for coupling two‐phase flow with the motion of immersed rigid bodies

The interaction of immersed rigid bodies with two-phase flow is of high interest in many applications. A model for the coupling of a Hohenberg–Halperin type model for two-phase flow and a fictitious domain method for consideration of rigid bodies is introduced leading to a full multiphase-field method to address the overall problem. A normalized phase variable is used alongside a method for application of wetting boundary conditions over a diffuse fluid-solid interface. This enables the representation of capillary effects and different wetting behavior based on Young\u27s law. A number of simulations is conducted in order to validate the model and highlight its ability to handle a variety of setups for two-phase particulate flow. This includes dynamic wetting situations, the motion of multiple particles within the two-phase flow and the interaction with arbitrarily shaped solid structures inside the domain

Modeling Anisotropic Transport in Polycrystalline Battery Materials

Hierarchical structures of many agglomerated primary crystals are often employed as cathode materials, especially for layered-oxide compounds. The anisotropic nature of these materials results in a strong correlation between particle morphology and ion transport. In this work, we present a multiphase-field framework that is able to account for strongly anisotropic diffusion in polycrystalline materials. Various secondary particle structures with random grain orientation as well as strongly textured samples are investigated. The observed ion distributions match well with the experimental observations. Furthermore, we show how these simulations can be used to mimic potentiostatic intermittent titration technique (PITT) measurements and compute effective diffusion coefficients for secondary particles. The results unravel the intrinsic relation between particle microstructure and the apparent diffusivity. Consequently, the modeling framework can be employed to guide the microstructure design of secondary battery particles. Furthermore, the phase-field method closes the gap between computation of diffusivities on the atomistic scale and the effective properties of secondary particles, which are a necessary input for Newman-type cell models

Distinct sites of opiate reward and aversion within the midbrain identified using a herpes simplex virus vector expressing GluR1

Repeated administration of morphine increases expression of GluR1 (an AMPA glutamate receptor subunit) in the ventral tegmental area (VTA) of the midbrain, an important neural substrate for the rewarding actions of morphine. Microinjections of a herpes simplex virus (HSV) vector that causes local overexpression of GluR1 (HSV-GluR1) into the VTA can enhance the ability of morphine to establish conditioned place preferences, suggesting that altered GluR1 expression in this region is directly associated with changes in the rewarding efficacy of morphine. We now report that in rats given HSV-GluR1 directly into the VTA, morphine is most rewarding when maximal transgene expression is in the rostral VTA, whereas morphine is aversive when maximal transgene expression is in the caudal VTA. Dual-labeling immunohistochemistry shows that this difference cannot be explained by a different fraction of dopaminergic neurons infected in the rostral versus caudal VTA. No such anatomical specificity is seen in rats given VTA microinjections of HSV-LacZ, a vector expressing a control protein (beta-galactosidase). These results suggest that distinct substrates within the VTA itself differentially contribute to the rewarding and aversive properties of opiates

Epigenetic suppression of hippocampal calbindin-D28k by ΔFosB drives seizure-related cognitive deficits.

The calcium-binding protein calbindin-D28k is critical for hippocampal function and cognition, but its expression is markedly decreased in various neurological disorders associated with epileptiform activity and seizures. In Alzheimer\u27s disease (AD) and epilepsy, both of which are accompanied by recurrent seizures, the severity of cognitive deficits reflects the degree of calbindin reduction in the hippocampal dentate gyrus (DG). However, despite the importance of calbindin in both neuronal physiology and pathology, the regulatory mechanisms that control its expression in the hippocampus are poorly understood. Here we report an epigenetic mechanism through which seizures chronically suppress hippocampal calbindin expression and impair cognition. We demonstrate that ΔFosB, a highly stable transcription factor, is induced in the hippocampus in mouse models of AD and seizures, in which it binds and triggers histone deacetylation at the promoter of the calbindin gene (Calb1) and downregulates Calb1 transcription. Notably, increasing DG calbindin levels, either by direct virus-mediated expression or inhibition of ΔFosB signaling, improves spatial memory in a mouse model of AD. Moreover, levels of ΔFosB and calbindin expression are inversely related in the DG of individuals with temporal lobe epilepsy (TLE) or AD and correlate with performance on the Mini-Mental State Examination (MMSE). We propose that chronic suppression of calbindin by ΔFosB is one mechanism through which intermittent seizures drive persistent cognitive deficits in conditions accompanied by recurrent seizures

Crystal structures and isometricity comparison of methylated bisphenol F derivatives

The syntheses and X-ray structures of three methylated bisphenol F derivatives and one respective analogue are reported. A special emphasis lies on the influence of methyl groups on the conformation of the common diphenylmethane scaffold. The introduction of four methyl groups to bisphenol F was found not to disturb its typical strong hydrogen bond network, and yet, to change the pattern of the aromatic interactions in the overall packing. According to the isometricity comparison, the addition of methyl groups to the diphenylmethane core has a greater influence on the conformation of the individual molecules, than the presence or absence of hydrogen bonding donors or acceptors. © 2013 Elsevier B.V. All rights reserved

Quasi-fission reactions as a probe of nuclear viscosity

Fission fragment mass and angular distributions were measured from the ^{64}Ni+^{197}Au reaction at 418 MeV and 383 MeV incident energy. A detailed data analysis was performed, using the one-body dissipation theory implemented in the code HICOL. The effect of the window and the wall friction on the experimental observables was investigated. Friction stronger than one-body was also considered. The mass and angular distributions were consistent with one-body dissipation. An evaporation code DIFHEAT coupled to HICOL was developed in order to predict reaction time scales required to describe available data on pre-scission neutron multiplicities. The multiplicity data were again consistent with one-body dissipation. The cross-sections for touch, capture and quasi-fission were also obtained.Comment: 25 pages REVTeX, 3 tables, 13 figures, submitted to Phys. Rev

Phase-field approach to heterogeneous nucleation

We consider the problem of heterogeneous nucleation and growth. The system is described by a phase field model in which the temperature is included through thermal noise. We show that this phase field approach is suitable to describe homogeneous as well as heterogeneous nucleation starting from several general hypotheses. Thus we can investigate the influence of grain boundaries, localized impurities, or any general kind of imperfections in a systematic way. We also put forward the applicability of our model to study other physical situations such as island formation, amorphous crystallization, or recrystallization.Comment: 8 pages including 7 figures. Accepted for publication in Physical Review