Exceptional planes of percolation

Consider the standard continuous percolation in ℝ⁴, and choose the parameters so that the induced percolation on a fixed two dimensional linear subspace is critical. Although two dimensional critical percolation dies, we show that there are exceptional two dimensional linear subspaces, in which percolation occurs. Received: 1 April 1997 / Revised version: 20 January 1998     

Preparation and analysis of heart and skeletal muscle specimens with LAMMA

Summary A technique is described to obtain shockfrozen tissue specimens from a beating heart in situ using liquid propane as cooling agent. The method allows to take up to 8 samples from the ischemic area of the left ventricle of a pig heart following acute coronary artery occlusion.A freeze-drying apparatus was developed in which, under a vacuum of 10^–6 mm Hg, the specimens remain for 10 days with the temperature slowly rising from initially –100 C to room temperature. Freezing damages in the tissues samples due to the formation of ice crystals either during shock-freezing or freeze-drying are usually below the spatial resolution of the microscope system employed in the LAMMA instrument. Already after a few minutes of ischemia, a considerable decrease of the intracellular K/Na relation was measured. LAMMA spectra from skeletal muscle were taken to check for possible ion redistribution which had eventually occurred during the various steps of the preparation procedure employed.Supported by Deutsche Forschungsgemeinschaft, SFB 68, A 10     

Determination of particle-bound trace metals in high purity hydrogen chloride

Summary Two analytical procedures for the determination of particle-bound trace metals in high purity hydrogen chloride are described. Polycarbonate membrane filters with a pore diameter of 0.05 m were used for sampling. Membrane filtration with subsequent instrumental neutron activation analysis (using irradiation with a thermal neutron flux of 10¹³ n cm^–2 s^–1 and irradiation and measurement times of either 20 min) has made it possible to determine the elements Br, Mg, Mn, Na, Sb, Sn, Te, Ti and Zn. For a gas sample volume of 500 l the detection limits determined are in the range of 0.86 ng l^–1 for Zn to 0.30 pg l^–1 for Mn.The elements Cr, Cu, Fe, Mn and Ni were determined by membrane filtration with subsequent graphite tube furnace atomic absorption spectrometry. In this case the detection limits achieved are (for a gas sample volume of 500 l and 4 ml digestion solution) between 8.4 pg l^–1 for Fe and 2.1 pg l^–1 for Cu. The analytical procedures were applied for the characterisation of high purity hydrogen chloride, which is used in the manufacture of highly integrated semiconductor components, by trace analysis, both directly on the gas cylinder and at the 'point of use after passing through the supply system. A review of the status of element determination in high purity process gases is given.

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Bestimmung von partikelgebundenen Metallspuren in hochreinem Chlorwasserstoff

     

Prompt atmospheric neutrino production of W-bosons

It is shown that the recent CERN beam dump experiment implying direct neutrino production provides a straightforward way to detect W-bosons via ultrahigh energy cosmic rays hitting the atmosphere. This occurs because (1) at high energies, direct neutrinos will dominate over the standard π, K produced flux due to time dilation effects and (2) direct π-production produces a large fraction of $\text{ν}\text{?}{}_{\mathrm{e}}$.     

Composition of the “GaAs” quantum dot,grown by droplet epitaxy

Self-assembled strain-free quantum dot (QD) structures were grown on AlGaAs surface by the droplet epitaxal method. The QDs were developed from pure Ga droplets under As pressure. The QDs were investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Both techniques show that the QDs are very uniform in size and their distribution on the surface is also homogeneous. The high resolution cross-sectional TEM investigation shows perfect lattice matching between the QD and the substrate, and also the faceting of the side walls of QD can be identified exactly by lattice planes. Analytical TEM (elemental mapping by EELS) unambiguously identifies the presence of Al in the QD.     

Traveling-wave Thomson scattering and optical undulators for high-yield EUV and X-ray sources

We present a novel high-yield Thomson scattering geometry that takes advantage of compact electron bunches, as available in advanced, low-emittance linear accelerators or laser wakefield accelerators. In order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit, we use ultrashort, pulse-front tilted laser pulses in a side-scattering geometry. Such a traveling-wave setup allows an overlap of electron and laser beams, even after propagating over distances much longer than the Rayleigh length. Experimental designs are discussed and optimized for different scattering angles. Specifically, to minimize group delay dispersion at large scattering angles >10°, we propose the use of varied-line spacing (VLS) gratings for spatio-temporal laser pulse shaping. Compared to head-on (180°) Thomson scattering, interaction lengths are in the centimeter to meter range and photon numbers for ultrashort X-ray pulses can increase by several orders of magnitudes.