1,117 research outputs found
Wave Dynamical Chaos in a Superconducting Three-Dimensional Sinai Billiard
Based on very accurate measurements performed on a superconducting microwave
resonator shaped like a desymmetrized three-dimensional (3D) Sinai billiard, we
investigate for the first time spectral properties of the vectorial Helmholtz,
i.e. non-quantum wave equation for a classically totally chaotic and
theoretically precisely studied system. We are thereby able to generalize some
aspects of quantum chaos and present some results which are consequences of the
polarization features of the electromagnetic waves.Comment: 4 pages RevTex; 4 postscript figures; to be published in Phys. Rev.
Lett.; Info: [email protected]
Thin-disk laser pump schemes for large number of passes and moderate pump source quality
Novel thin-disk laser pump layouts are proposed yielding an increased number
of passes for a given pump module size and pump source quality. These novel
layouts result from a general scheme which bases on merging two simpler pump
optics arrangements. Some peculiar examples can be realized by adapting
standard commercially available pump optics simply by intro ducing an
additional mirror-pair. More pump passes yield better efficiency, opening the
way for usage of active materials with low absorption. In a standard multi-pass
pump design, scaling of the number of beam passes brings ab out an increase of
the overall size of the optical arrangement or an increase of the pump source
quality requirements. Such increases are minimized in our scheme, making them
eligible for industrial applicationsComment: 16 pages, 9 figure
Modeling of field singularities at dielectric edges using grid based methods
Electric field singularities at sharp metallic edges or at a dielectric
contact line can be described analytically by asymptotic expressions. The a
priori known form of the field distribution in the vicinity of these edges
can be used to construct numerical methods with improved accuracy. This
contribution focuses on a modified Finite Integration Technique and on a
Discontinuous Galerkin Method with singular approximation functions. Both
methods are able to handle field singularities at perfectly electric
conducting as well as at dielectric edges. The numerical accuracy of these
methods is investigated in a number of simulation examples including static
and dynamic field problems
Compact 20-pass thin-disk amplifier insensitive to thermal lensing
We present a multi-pass amplifier which passively compensates for distortions
of the spherical phase front occurring in the active medium. The design is
based on the Fourier transform propagation which makes the output beam
parameters insensitive to variation of thermal lens effects in the active
medium. The realized system allows for 20 reflections on the active medium and
delivers a small signal gain of 30 with M = 1.16. Its novel geometry
combining Fourier transform propagations with 4f-imaging stages as well as a
compact array of adjustable mirrors allows for a layout with a footprint of 400
mm x 1000 mm.Comment: 7 pages, 6 figure
Hydration and the true water content of swellable clay minerals
Water affects biological, chemical and transportation processes as well as mechanical properties of soils. Thereby, clay mineral content determines the moisture balance of soils. In-situ moisture measurements depend on reliable calibration based on the true water content. Drying the soil at 105 °C is the most common procedure to determine the water content although it is known, swellable clay minerals retain hydration water up to much higher temperatures.
The amplified water uptake and retention by swellable clay minerals results from hydration of interlayer cations. Thereby, the water binding mechanisms are complex due to structural heterogeneity and are determined by layer charge density and location of substitutions. While several experimental studies deal with the maximum water uptake of selected smectites and heating conditions for full dehydration a comprehensive understanding of the relation between the structure of smectites and water uptake/release is still missing.
The Na-saturated smectite / water interface for the montmorillonite-beidellite series is investigated in the present work within the density functional theory (DFT). Layer charge is varied between 0.125 and 0.5 per formula unit [O10(OH)2] by substitution of Al3+ by Mg2+ in the octahedral sheet (montmorillonites) and by substitution of Si4+ by Al3+ in the tetrahedral sheets (beidellites). Starting from the water free supercells (with integer molar ratios), the number of water molecules is increased discretely. Stable hydration states (1H to 3H) do not necessarily correspond to the formation of water layers (1W to 3W) in the interlayer, which is deduced from the development of the basal spaces during hydration. With the help of ab initio thermodynamics, the energy states are related to temperature, and partial pressure of H2O and the resulting phase diagrams revealed hydration state in dependence of relative humidity (RH) as well as necessary temperatures for full dehydration to determine the true water content. Thereby it was shown that 2:1 layer silicates with a layer charge of 0.125 are swellable but reach only the 1H state even at 100% RH, but the removal of water molecules from the interlayer requires temperatures >110 °C and partial pressures of water <100 Pa. In contrast water uptake of smectites with layer charge 0.375 requires RH of >11% at room temperature, but dehydration occurs at moderate heating
Investigation of Planar Pick-up and Kicker Electrodes for Stochastic Cooling
The success of stochastic cooling crucially depends on the interaction between the beam and high frequency devices for detection (pick-up electrodes) and deflection (kicker electrodes). This contribution shows the theoretical investigation of a planar electrode to be used for stochastic cooling of secondary particles with a beta of 0.83. The coupling to the beam is realised by a slot line. Transition networks are added to extract the signal. The detailed investigation is performed via a numerical electromagnetic field analysis. The longitudinal kick of the deflectors is calculated as a function of the beam position and scaled to the applied voltage. According to the Panofsky-Wenzel theorem the transverse kick is obtained simultaneously. The electromagnetic properties of the discussed electrode are compared to existing ones as currently in use in the ESR storage ring (GSI, Darmstadt)
Higher-order sensitivity analysis of periodic 3-D eigenvalue problems for electromagnetic field calculations
An algorithm to perform a higher-order sensitivity analysis for
electromagnetic eigenvalue problems is presented. By computing the eigenvalue
and eigenvector derivatives, the Brillouin Diagram for periodic structures
can be calculated. The discrete model is described using the Finite
Integration Technique (FIT) with periodic boundaries, and the sensitivity
analysis is performed with respect to the phase shift φ between the
periodic boundaries.
For validation, a reference solution is calculated by solving multiple
eigenvalue problems (EVP). Furthermore, the eigenvalue derivatives are
compared to reference values using finite difference (FD) formulas
Great Sumatra Earthquake Registers on Electrostatic Sensor
Strong electrical signals that correspond to
the Mw = 9.3 earthquake of 26 December 2004,
which occurred at 0058:50.7 UTC
off the west coast of northern Sumatra, Indonesia,
were recorded by an electrostatic sensor
(a device that detects short-term variations in
Earth’s electrostatic fi eld) at a seismic station
in Italy, which had been installed to study the
infl uence of local earthquakes on a new landslide
monitoring system.
Electrical signals arrived at the station practically
instantaneously and were detected up
to several hours before the onset of the Sumatra
earthquake (Figure 1) as well as before
local quakes. The corresponding seismic signals
(p-waves) arrived 740 seconds after the
start of the earthquake. Because the electrical
signals travel at the speed of light, electrical
monitoring for the global detection of very
strong earthquakes could be an important
tool in signifi cantly increasing the hazard
alert window
Solubility of precursors and carbonation of waterglass-free geopolymers
Geopolymers have the potential to function as an environmentally friendly substitute for ordinary Portland cement, with up to 80% less CO emission during production. The effect is best utilized for geopolymers prepared with amorphous silica instead of waterglass (NaSiO) to adjust the Si:Al ratio. The reactivity of the precursors with the alkaline activator affects the final mineralogical properties of the binder. The purpose of the present study was to investigate the amount of different phases formed during geopolymerization and to understand the quantitative evolution of carbonation during geopolymer synthesis by determining the solubility of metakaolinite and amorphous SiO in NaOH at various concentrations. The solubility was studied by ICP-OES measurements. X-ray diffraction was used for qualitative and quantitative phase analysis of the geopolymers. The solubility of the precursors increased with calcination temperature of metakaolinite, reaction time for amorphous SiO, and at higher NaOH concentrations. Partial dissolution resulted in free Na, which is a source for the formation of carbonates in the geopolymers. Thermonatrite occurred prior to trona formation in all samples
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First steps in the logic-based assessment of post-composed phenotypic descriptions
In this paper we present a preliminary logic-based evaluation of the integration of post-composed phenotypic descriptions with domain ontologies. The evaluation has been performed using a description logic reasoner together with scalable techniques: ontology modularization and approximations of the logical difference between ontologies
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