Enhanced photoemission from laser-excited plasmonic nano-objects in periodic arrays.

The process of photoelectron emission from gold surfaces covered with nano-objects that are organized in the form of a periodic array is addressed in the short laser pulse regime ([Formula: see text] fs) at moderate intensities [Formula: see text] W cm(-2) and for various laser wavelengths. The emission spectrum from a gold single crystal measured under the same conditions is used for reference. The comparison of the photo-emission yield and the energy of the ejected electrons with their counterparts from the (more simple) reference system shows that the periodic conditions imposed on the target surface drastically enhance both quantities. In addition to the standard mechanism of Coulomb explosion, a second mechanism comes into play, driven by surface plasmon excitation. This can be clearly demonstrated by varying the laser wavelength. This interpretation of the experimental data is supported by predictions from model calculations that account both for the primary quantum electron emission and for the subsequent surface-plasmon-driven acceleration in the vacuum. Despite the fact that the incident laser intensity is as low as [Formula: see text] W cm(-2), such a structured target permits generating electrons with energies as high as 300 eV. Experiments with two incident laser beams of different wavelengths with an adjustable delay, have also been carried out. The results show that there exist various channels for the decay of the photo-emission signal, depending on the target type. These observations are shedding light on the various relaxation mechanisms that take place on different timescales.

Cell density-dependent stimulation of PAI-1 and hyaluronan synthesis by TGF-ß in orbital fibroblasts.

During the course of Graves' orbitopathy (GO), orbital fibroblasts are exposed to factors that lead to proliferation and extracellular matrix (ECM) overproduction. Increased levels of tissue plasminogen activator inhibitor type 1 (PAI-1 (SERPINE1)) might promote the accumulation of ECM components. PAI-1 expression is regulated by cell density and various cytokines and growth factors including transforming growth factorß(TGF-ß). We examined the effects of increasing cell densities and TGF-ß on orbital fibroblasts obtained from GO patients and controls. Responses were evaluated by the measurement of proliferation, PAI-1 expression, and ECM production. There was an inverse correlation between cell density and the per cell production of PAI-1. GO orbital, normal orbital, and dermal fibroblasts behaved similarly in this respect. Proliferation rate also declined with increasing cell densities. Hyaluronan (HA) production was constant throughout the cell densities tested in all cell lines. In both GO and normal orbital fibroblasts, but not in dermal fibroblasts, TGF-ß stimulated PAI-1 production in a cell density-dependent manner, reaching up to a five-fold increase above baseline. This has been accompanied by increased HA secretion and pericellular HA levels at high cell densities. Increasing cell density is a negative regulator of proliferation and PAI-1 secretion both in normal and GO orbital fibroblasts; these negative regulatory effects are partially reversed in the presence of TGF-ß. Cell density-dependent regulation of PAI-1 expression in the orbit, together with the local cytokine environment, may have a regulatory role in the turnover of the orbital ECM and may contribute to the expansion of orbital soft tissue in GO.

Analysis of folded pulse forming line operation.

A compact pulse forming line (CPFL) concept based on a folded transmission line and high-breakdown strength dielectric was explored through an effort combining proof-of-principle experiments with electromagnetic modeling. A small-scale folded CPFL was fabricated using surface-mount ceramic multilayer capacitors. The line consisted of 150 capacitors close-packed in parallel and delivered a 300 ns flat-top pulse. The concept was carried to a 10 kV class device using a polymer-ceramic nanocomposite dielectric with a permittivity of 37.6. The line was designed for a 161 ns FWHM length pulse into a matched load. The line delivered a 110 ns FWHM pulse, and the pulse peak amplitude exceeded the matched load ideal. Transient electromagnetic analysis using the particle-in-cell code ICEPIC was conducted to examine the nature of the unexpected pulse shortening and distortion. Two-dimensional analysis failed to capture the anomalous behavior. Three-dimensional analysis replicated the pulse shape and revealed that the bends were largely responsible for the pulse shortening. The bends not only create the expected reflection of the incident TEM wave but also produce a non-zero component of the Poynting vector perpendicular to the propagation direction of the dominant electromagnetic wave, resulting in power flow largely external to the PFL. This analysis explains both the pulse shortening and the amplitude of the pulse.

Applied magnetic field design for the field reversed configuration compression heating experiment.

Detailed calculations of the formation, guide, and mirror applied magnetic fields in the FRC compression-heating experiment (FRCHX) were conducted using a commercially available generalized finite element solver, COMSOL Multiphysics(®). In FRCHX, an applied magnetic field forms, translates, and finally captures the FRC in the liner region sufficiently long to enable compression. Large single turn coils generate the fast magnetic fields necessary for FRC formation. Solenoidal coils produce the magnetic field for translation and capture of the FRC prior to liner implosion. Due to the limited FRC lifetime, liner implosion is initiated before the FRC is injected, and the magnetic flux that diffuses into the liner is compressed. Two-dimensional axisymmetric magnetohydrodynamic simulations using MACH2 were used to specify optimal magnetic field characteristics, and this paper describes the simulations conducted to design magnetic field coils and compression hardware for FRCHX. This paper presents the vacuum solution for the magnetic field.