Numerical simulation of the charge balance in an EBIT

The electron beam ions traps (EBITs) are widely used to study highly charged ions (HCIs). In an EBIT, a high energy electron beam collides with atoms and ions to generate HCIs in the trap region. It is important to study the physics in the trap. The atomic processes, such as electron impact ionisation (EI), radiative recombination (RR), dielectronic recombination (DR) and charge exchange (CX), occur in the trap and numerical simulation can give some parameters for design, predict the composition and describe charge state evolution in an EBIT [Phys. Rev. A 43 (199 1) 4861]. We are presently developing a new code, which additionally includes a description of the overlaps between the ion clouds of the various charge-states. It has been written so that it can simulate experiments where various machine parameters (e.g. beam energy and current) can vary throughout the simulation and will be able to use cross- sections either based on scaling laws or derived from atomic structure calculations. An object-oriented method is used in developing the new software, which is an efficient way to organize and write code. (C) 2003 Elsevier Science B.V. All rights reserved.

Size Effects on Thin Film Ferroelectrics: Experiments on Isolated Single Crystal Sheets

Thin lamellae were cut from bulk single crystal BaTiO3 using a Focused Ion Beam Microscope. They were then removed and transferred onto single crystal MgO substrates, so that their functional properties could be measured independent of the original host bulk ferroelectric. The temperature dependence of the capacitance of these isolated single crystal films was found to be strongly bulk-like, demonstrating a sharp Curie anomaly, as well as Curie-Weiss behaviour. In addition, the sudden change in the remanent polarisation as a function of temperature at TC was characteristic of a first order phase change. The work represents a dramatic improvement on that previously published by M. M. Saad, P. Baxter, R. M. Bowman, J. M. Gregg, F. D. Morrison & J. F. Scott, J. Phys: Cond. Matt., 16 L451-L456 (2004), as critical shortcomings in the original specimen geometry, involving potential signal contributions from bulk BaTiO3, have now been obviated. That the functional properties of single crystal thin film lamellae are comparable to bulk, and not like those of conventionally deposited heteroegenous thin film systems, has therefore been confirmed.

Sheets of Large Superhydrophobic Metal Particles Self Assembled on Water by the Cheerios Effect

A copper-rich cereal: Superhydrophobic copper particles show a very large Cheerios effect and rapidly self-assemble into robust sheets on the surface of water. These sheets can support objects (including water drops, see photo) placed on them, even though the irregular geometry of the particles means that they contain macroscopic holes.

Coherent X-ray production via pulse reflection from laser-driven dense electron sheets

A scheme to obtain brilliant x-ray sources by coherent reflection of a counter-propagating pulse from laser-driven dense electron sheets is theoretically and numerically investigated in a self-consistent manner. A radiation pressure acceleration model for the dynamics of the electron sheets blown out from laser-irradiated ultrathin foils is developed and verified by PIC simulations. The first multidimensional and integral demonstration of the scheme by 2D PIC simulations is presented. It is found that the reflected pulse undergoes Doppler-upshift by a factor 4?z2, where ?z = (1- vz2/c2)-1/2 is the effective Lorentz factor of the electron sheet al ong its normal direction. Meanwhile the pulse electric field is intensified by a factor depending on the electron density of the sheet in its moving frame ne/?, where ? is the full Lorentz factor.

Numerical simulation of the charge balance and temperature evolution in an electron beam ion trap

A computer code has been developed to simulate and study the evolution of ion charge states inside the trap region of an electron beam ion trap. In addition to atomic physics phenomena previously included in similar codes such as electron impact ionization, radiative recombination, and charge exchange, several aspects of the relevant physics such as dielectronic recombination, ionization heating, and ion cloud expansion have been included for the first time in the model. The code was developed using object oriented concepts with database support, making it readable, accurate, and well organized. The simulation results show a good agreement with various experiments, and give useful information for selection of operating conditions and experiment design.

Docosahexaenoic Acid Improves the Nitroso-Redox Balance and Reduces VEGF-Mediated Angiogenic Signaling in Microvascular Endothelial Cells

Purpose. Disturbances to the cellular production of nitric oxide (NO) and superoxide (O2-) can have deleterious effects on retinal vascular integrity and angiogenic signaling. Dietary agents that could modulate the production of these signaling molecules from their likely enzymatic sources, endothelial nitric oxide synthase (eNOS) and NADPH oxidase, would therefore have a major beneficial effect on retinal vascular disease. The effect of ?-3 polyunsaturated fatty acids (PUFAs) on angiogenic signaling and NO/superoxide production in retinal microvascular endothelial cells (RMECs) was investigated.

Methods. Primary RMECs were treated with docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) for 48 hours. RMEC migration was determined by scratch-wound assay, proliferation by the incorporation of BrdU, and angiogenic sprouting using a three-dimensional model of in vitro angiogenesis. NO production was quantified by Griess assay, and phospho-eNOS accumulation and superoxide were measured using the fluorescent probe dihydroethidine. eNOS localization to caveolin-rich microdomains was determined by Western blot analysis after subfractionation on a linear sucrose gradient.

Results. DHA treatment increased nitrite and decreased superoxide production, which correlated with the displacement of eNOS from caveolar subdomains and colocalization with the negative regulator caveolin-1. In addition, both ?-3 PUFAs demonstrated reduced responsiveness to VEGF-stimulated superoxide and nitrite release and significantly impaired endothelial wound healing, proliferation, and angiogenic sprout formation.

Conclusions. DHA improves NO bioavailability, decreases O2- production, and blunts VEGF-mediated angiogenic signaling. These findings suggest a role for ?-3 PUFAs, particularly DHA, in maintaining vascular integrity while reducing pathologic retinal neovascularization.