Greedy kernel methods for accelerating implicit integrators for parametric ODEs

We present a novel acceleration method for the solution of parametric ODEs by single-step implicit solvers by means of greedy kernel-based surrogate models. In an offline phase, a set of trajectories is precomputed with a high-accuracy ODE solver for a selected set of parameter samples, and used to train a kernel model which predicts the next point in the trajectory as a function of the last one. This model is cheap to evaluate, and it is used in an online phase for new parameter samples to provide a good initialization point for the nonlinear solver of the implicit integrator. The accuracy of the surrogate reflects into a reduction of the number of iterations until convergence of the solver, thus providing an overall speedup of the full simulation. Interestingly, in addition to providing an acceleration, the accuracy of the solution is maintained, since the ODE solver is still used to guarantee the required precision. Although the method can be applied to a large variety of solvers and different ODEs, we will present in details its use with the Implicit Euler method for the solution of the Burgers equation, which results to be a meaningful test case to demonstrate the method's features

Collisions of Slow Highly Charged Ions with Surfaces

Progress in the study of collisions of multiply charged ions with surfaces is reviewed with the help of a few recent examples. They range from fundamental quasi-one electron processes to highly complex ablation and material modification processes. Open questions and possible future directions will be discussed.Comment: 13 pages, 16 figures, review pape

A Framework For Discussing Ethics In Principles Of Accounting

The main focus of the discussion in this paper is on the principles or introductory level of accounting and is applicable for all students in the class, but much of its content is equally applicable to upper level accounting classes and our accounting majors. Early and Kelly (2004) and Clikeman (2003) support the value of ethics education in heightening a student’s moral reasoning skills. “The goals of ethics education are creating an awareness of ethical dilemmas and providing methods of resolution.” (Haas 2005

Cold Induction of EARLI1, a Putative Arabidopsis Lipid Transfer Protein, Is Light and Calcium Dependent

As sessile organisms, plants must adapt to their environment. One approach toward understanding this adaptation is to investigate environmental regulation of gene expression. Our focus is on the environmental regulation of EARLI1, which is activated by cold and long-day photoperiods. Cold activation of EARLI1 in short-day photoperiods is slow, requiring several hours at 4ºC to detect an increase in mRNA abundance. EARLI1 is not efficiently cold-activated in etiolated seedlings, suggesting that photomorphogenesis is necessary for its cold activation. Cold activation of EARLI1 is inhibited in the presence of the calcium channel blocker lanthanum chloride or the calcium chelator EGTA. Addition of the calcium ionophore Bay K8644 results in cold-independent activation of EARLI1. These data suggest that EARLI1 is not an immediate target of the cold response, and that calcium flux affects its expression. EARLI1 is a putative secreted protein and has motifs found in lipid transfer proteins. Over-expression of EARLI1 in transgenic plants results in reduced electrolyte leakage during freezing damage, suggesting that EARLI1 may affect membrane or cell wall stability in response to low temperature stress

Mouse model for acute Epstein-Barr virus infection

Epstein-Barr Virus (EBV) infects human B cells and drives them into continuous proliferation. Two key viral factors in this process are the latent membrane proteins LMP1 and LMP2A, which mimic constitutively activated CD40 receptor and B-cell receptor signaling, respectively. EBV-infected B cells elicit a powerful T-cell response that clears the infected B cells and leads to life-long immunity. Insufficient immune surveillance of EBV-infected B cells causes life-threatening lymphoproliferative disorders, including mostly germinal center (GC)-derived B-cell lymphomas. We have modeled acute EBV infection of naive and GC B cells in mice through timed expression of LMP1 and LMP2A. Although lethal when induced in all B cells, induction of LMP1 and LMP2A in just a small fraction of naive B cells initiated a phase of rapid B-cell expansion followed by a proliferative T-cell response, clearing the LMP-expressing B cells. Interfering with T-cell activity prevented clearance of LMP-expressing B cells. This was also true for perforin deficiency, which in the human causes a life-threatening EBV-related immunoproliferative syndrome. LMP expression in GC B cells impeded the GC reaction but, upon loss of T-cell surveillance, led to fatal B-cell expansion. Thus, timed expression of LMP1 together with LMP2A in subsets of mouse B cells allows one to study major clinically relevant features of human EBV infection in vivo, opening the way to new therapeutic approaches

Recrystallization and composition dependent thermal fatigue response of different tungsten grades

Industrial pure tungsten grades, manufactured by using a variety of manufactured techniques, are available worldwide in many different types of semifinished products, i.e. rods, wires, ribbons, and sheets. Thereby, the recrystallization temperature varies depending on the applied degree of deformation but also depending on the materials composition, i.e. the materials purity and in particular the level of certain impurities. In order to compare different available industrial tungsten grades and a newly developed PIM-W grade, on the one hand recrystallization studies at three different temperatures from 1300 to 1800 °C for 1 h were performed using Vickers hardness testing. On the other hand, the thermal shock induced low cycle thermal fatigue response of the material in its different recrystallization stages was done using high heat flux tests at 1000 °C base temperature, applying 1000 shots with 1 ms and 0.38 GW/m2 and post mortem characterization, i.e. profilometry and metallography. The obtained results are related to the chemical composition of the individual tungsten grades obtained from Auger electron spectroscopy analyses on cold fracture surfaces

Anisotropic excitonic effects in the energy loss function of hexagonal boron nitride

We demonstrate that the valence energy-loss function of hexagonal boron nitride (hBN) displays a strong anisotropy in shape, excitation energy and dispersion for momentum transfer q parallel or perpendicular to the hBN layers. This is manifested by e.g. an energy shift of 0.7 eV that cannot be captured by single-particle approaches and is a demonstration of a strong anisotropy in the two-body electron-hole interaction. Furthermore, for in-plane directions of q we observe a splitting of the -plasmon in the M direction that is absent in the K direction and this can be traced back to band-structure effects.Comment: 10 pages, 4 figure

Ion-matter interactions by MD simulations making use of reactive force fields

In the field of SIMS, ion-matter interactions have been largely investigated by numerical simulations like TRIM (or other programs using the binary-collision approximation) or molecular dynamics (MD) simulations. For MD simulations related to inorganic samples, mostly classical force fields assuming stable bonding structure have been used. In materials science, level-three force fields capable of simulating the breaking and formation of chemical bonds have recently been conceived. One such force field has been developed by Kieffer et al. 1–4 This potential includes directional covalent bonds, Coulomb and dipolar interaction terms, dispersion terms, etc. Important features of this force field for simulating systems that undergo significant structural reorganization are: (i) the ability to account for the redistribution of electron density upon ionization, formation, or breaking of bonds, through a charge transfer term; and (ii) the fact that the angular constraints dynamically adjust when a change in the coordination number of an atom occurs. In this work, we will present preliminary results of this potential, parameterized for silicon, for the simulation of atomic trajectories in samples subject to ion bombardment. Compared to normal force fields, ion-matter interactions as well as the sputtering of matter are expected to be described more accurately, especially when using reactive primary ions (oxygen or cesium) at low-impact energies. Copyright © 2010 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79412/1/3427_ftp.pd