The inhomogeneity of plastic deformation

Considerable local strain differences occur in single crystals as a consequence of slip bands. A significant contribution to this phenomenon is the effect of the deformation rate on the inhomogeneity of its distribution. In polycrystalline materials the plastic deformation is affected by grain boundaries and their vicinity as well as by various orientations of single grains in onephase metals and alloys, and by various component properties in multiphase materials. In some cases it has been possible to describe these phenomena by means of micromechanics. Valuable information has also been acquired by means of three-dimensional stereology.     

Twin Paradox and the Logical Foundation of Relativity Theory

We study the foundation of space-time theory in the framework of first-order logic (FOL). Since the foundation of mathematics has been successfully carried through (via set theory) in FOL, it is not entirely impossible to do the same for space-time theory (or relativity). First we recall a simple and streamlined FOL-axiomatization Specrel of special relativity from the literature. Specrel is complete with respect to questions about inertial motion. Then we ask ourselves whether we can prove the usual relativistic properties of accelerated motion (e.g., clocks in acceleration) in Specrel. As it turns out, this is practically equivalent to asking whether Specrel is strong enough to “handle” (or treat) accelerated observers. We show that there is a mathematical principle called induction (IND) coming from real analysis which needs to be added to Specrel in order to handle situations involving relativistic acceleration. We present an extended version AccRel of Specrel which is strong enough to handle accelerated motion, in particular, accelerated observers. Among others, we show that~the Twin Paradox becomes provable in AccRel, but it is not provable without IND.     

Stealth scalar field overflying a 2+1 black hole

A nontrivial scalar field configuration of vanishing energy-momentum is reported. These matter configurations have no influence on the metric and therefore they are not be “detected" gravitationally. This phenomenon occurs for a time–dependent nonminimally coupled and self-interacting scalar field on the 2+1 (BTZ) black hole geometry. We conclude that such stealth configurations exist for the static 2+1 black hole for any value of the nonminimal coupling parameter ζ≠0 with a fixed self-interaction potential U _ζ(Φ). For the range 0 < ζ≤1/2 potentials are bounded from below and for the range 0 < ζ < 1/4 the stealth field falls into the black hole and is swallowed by it at an exponential rate, without any consequence for the black hole.     

A Note on the Lorentz Transformations for the Photon

We discuss transformation laws of electric and magnetic fields under Lorentz transformations, deduced from the classical field theory. It is found that we can connect the resulting expression for a bivector formed with those fields, with the expression deduced from the Wigner transformation rules for spin-1 functions of massive particles. This mass parameter should be interpreted because the constancy of speed of light forbids the existence of the photon mass.     

Stable isotope geochemistry of calcrete nodules and septarian concretions in a Quaternary 'red clay' paleovertisol from Hungary

Calcrete nodules and concretions in unusually large amounts are embedded in the Quaternary clay-rich (Vertisol-type) 'red clay' soil-sedimentary complex at the pediment of the Mátra Mountains (Hungary). Stable isotope signatures were studied in nodules and septarian concretions, uncommon due to their several millimeter sized calcite crystals filling voids and fractures, to reveal their origin. The isotope composition of calcrete covers a wide range: delta18O=-5.9 to-10.4 per thousand and delta13C=-8.9 to-12.3 per thousand (vs. V-PDB). Isotope compositions support pedogenic (sensu stricto) and/or shallow groundwater origin for the calcrete nodules and concretions, the role of 'evolved' (isotopically modified) groundwaters in the formation of secondary carbonate was possibly subordinate. Late-stage, large, Mn-rich euhedral calcite crystals in concretions have the lowest delta13C values, which are interpreted as a result of larger contribution of isotopically light organic carbon due to decomposition of organic matter under reducing conditions. Precipitation of late calcite crystals in concretions occurred in early diagenetic environment after shallow burial of the 'red clay' paleovertisol.     

Adhesion hysteresis in dynamic atomic force microscopy

The effects of adhesion hysteresis in the dynamic‐dissipation curves measured in amplitude‐modulation atomic force microscopy are discussed. Hysteresis in the interaction forces is shown to modify the dynamics of the cantilever leading to different power dissipation curves in the repulsive and attractive regimes. Experimental results together with numerical simulations show that power dissipation, as measured in force microscopy, is not always proportional to the energy dissipated in the tip–sample interaction process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Study of micro‐channel geometries for internally cooled Si monochromators

Rocking curves of micro‐channel (MC) water‐cooled monochromators are broadened by stresses introduced during fabrication and under X‐ray thermal load. This is a problem which will be even more serious with the rise of the fourth‐generation synchrotron sources, i.e. the free‐electron lasers. The X‐ray optics group at the Institute of Physics at the ASCR v.v.i. in Prague is designing, testing and, with company Polovodi?e a.s., fabricating novel internally water‐cooled Si monochromators. Here three new micro‐channel geometries are introduced which reduce rocking‐curve enlargement owing to the fabrication to less than 2.5 µrad (～0.5 arcsec). All three MC designs show less rocking‐curve enlargement and smoother topographic images. The designs also show better cooling efficiencies than the classical MC design in finite‐element analysis calculations.     

Reinstallation of the COMPASS-D tokamak in IPP ASCR

The COMPASS-D tokamak, originally operated by UKAEA at Culham, UK, will be reinstalled at the Institute of Plasma Physics (IPP) AS CR. The COMPASS device was designed as a flexible tokamak in the 1980s mainly to explore the MHD physics. Its operation (with D-shaped vessel) began at the Culham Laboratory of the Association EURATOM/ UKAEA in 1992.The COMPASS-D tokamak will have the following unique features after putting in operation on IPP Prague. It will be the smallest tokamak with a clear H-mode and ITER-relevant geometry. ITER-relevant plasma conditions will be achieved by installation of two neutral beam injection systems (2 × 300 kW), enabling co-and counter-injections. Redeployment of the existing LH system (400 kW) is also envisaged. A comprehensive set of diagnostics focused mainly on the edge plasma will be installed.The scientific programme proposed for the COMPASS-D tokamak installed in IPP Prague will benefit from these unique features of COMPASS-D and consist of two main scientific projects, both highly relevant to ITER-Edge plasma physics (H-mode studies) and Wave-plasma interaction studies.The COMPASS-D tokamak will offer an important research potential as a small, flexible and low-cost facility with ITER-relevant geometry.     

Experimental investigation of Risken–Nummedal–Graham–Haken laser instability in fiber ring lasers

It has been suggested (by Pessina et al. in 1997) that the observed spontaneous mode beating of erbium-doped-fiber ring lasers can be explained as the multimode instability described in 1968 by Risken and Nummedal and by Graham and Haken (the RNGH instability), which is based on Rabi-splitting-induced gain. If true, this would constitute the first ever example of this instability in an actual experiment. We test the hypothesis through a quantitative experimental investigation. We demonstrate that there is indeed a clear, marked onset of the instability, a fact that went unnoticed in all previous experiments because it is very close to the lasing threshold. We intentionally raise cavity loss to better separate onset of lasing and of instability. We obtain quantitative information on the instability onset. An interpretation as the predicted second threshold is reasonable provided inhomogeneous gain line broadening is taken into account. We also observe that instability above its onset exists only intermittently; this may hint at a subcritical bifurcation and noise-driven transitions. In any event, the RNGH mechanism is present, if not in a pure form. PACS 42.65.Sf; 42.60.Mi; 42.55.Wd     

Remote characterization of defects in plates with viscoelastic coatings using guided waves

The remote inspection for defects in large metallic elements such as pipes, tubes and plates is a field where guided waves are being applied with success. There are a number of situations where a surface coating is added for corrosion protection or insulation purposes. Since the coating materials are usually viscoelastic, the guided wave inspection range may be severely reduced unless a proper mode and an adequate frequency range is selected. Previous authors found the existence of low-attenuated modes at certain frequency ranges, which were used to detect and locate defects at reasonably large distances. This paper studies the potential of guided waves for not only locating but also sizing defects in plates with viscoelastic coatings. A hybrid finite element-boundary element method which explicitly includes the attenuating characteristics of the coating is used to determine Lamb and SH mode conversion factors at corrosion defects under the coating. Through parametric studies and analysis of the numerical results, some trends and features are highlighted that could be used for sizing purposes.