The influence of D-branes' backreaction upon gravitational interactions between open strings

We argue that gravitational interactions between open strings ending on D3-branes are largely shaped by the D3-branes' backreaction. To this end we consider classical open strings coupled to general relativity in Poincare AdS5 backgrounds. We compute the linear gravitational backreaction of a static string extending up to the Poincare horizon, and deduce the potential energy between two such strings. If spacetime is non-compact, we find that the gravitational potential energy between parallel open strings is independent of the strings' inertial masses and goes like 1/r at large distance r. If the space transverse to the D3-branes is suitably compactified, a collective mode of the graviton propagates usual four-dimensional gravity. In that case the backreaction of the D3-branes induces a correction to the Newtonian potential energy that violates the equivalence principle. The observed enhancement of the gravitational attraction is specific to string theory; there is no similar effect for point-particles.Comment: 28 pages, 7 figures. Typos corrected, minor addition

The momentum analyticity of two-point correlators from perturbation theory and AdS/CFT

The momentum plane analyticity of two point function of a relativistic thermal field theory at zero chemical potential is explored. A general principle regarding the location of the singularities is extracted. In the case of the N=4 supersymmetric Yang-Mills theory at large $N_c$, a qualitative change in the nature of the singularity (branch points versus simple poles) from the weak coupling regime to the strong coupling regime is observed with the aid of the AdS/CFT correspondence.Comment: 18 pages, 3 figures, typos fixed, 1 figure update

EFTEM assistant: A tool to understand the limitations of EFTEM

The first version of a free tool for Gatan's Digital Micrograph™ is presented which aims to aid the energy-filtered TEM (EFTEM) community by predicting and correcting the most common sources of degradation. The software allows selection of either Krivanek's or Egerton's approach to account for the spatial resolution degradation caused by the electron optical aberrations. The effects of aberrations and signal 'delocalization' are combined to simulate the blurring caused in EFTEM elemental maps. Two microstructural features with ideal geometry are used to illustrate use of the software: spherical particles and parallel sided interfaces. The software also allows the simulation of the effects of the noise and drift in the final elemental map, independently or in combination. It can be easily demonstrated that when the dimensions of the feature of interest are comparable in scale to the image degradation factors, the effects of the latter should not be neglected. More importantly, the software can deconvolute the effects of the degradation factors, revealing the true dimensions and signal intensity of the feature of interest. © 2006 Elsevier B.V. All rights reserved

TEM investigations of intergranular stress corrosion cracking in austenitic alloys in PWR environmental conditions

Analytical transmission microscopy has been used to investigate the initiation of stress corrosion cracking in Inconel 600 subjected to constant load testing under simulated pressured water reactor primary water conditions. The observations revealed that intergranular attack proceeded by the development of a zone of polycrystalline chromia along the boundary plane intersecting either the free surface or a blunted, open crack in contact with the free surface. Ni-rich metal particles were interspersed within the chromia. Conversely, open cracks were filled with nanocrystalline NiO and large compound particles of spinel and NiO, indicating a difference in potential between closed, attacked boundaries and open cracks. Open cracks appeared to have initiated by fracture of the chromia zones, such fracture being strongly dependent on boundary geometry with respect to loading direction. The observations suggest that stress corrosion crack initiation and propagation is dependent on diffusion of oxygen through the porous oxides. Dislocations and stress could enhance diffusion as chromia was observed along slip planes at the arrested tips of blunt cracks

The effect of radiation damage on anomalous absorption in the TEM

In-situ electron irradiation of Si at 400keV was performed to determine the variation of two-beam absorption parameters by the method of Hashimoto. Corresponding theoretical sensitivity studies were performed to assess limitations of experimental errors. No significant variations in parameters were revealed. Possible reasons for this are discussed

Quantification of plastic strain of stainless steel and nickel alloy by electron backscatter diffraction

Electron backscatter diffraction (EBSD) in conjunction with scanning electron microscopy is applied to assess the plastic strain present in stainless steel and nickel alloys following tensile loading. A parameter, which quantifies the spread of the crystal orientation within individual grains arising due to dislocation accumulation during plastic deformation, is correlated with imposed plastic strain. The parameter is called the 'modified crystal deformation' and is determined from the spread in misorientation from the central grain orientation. It was confirmed that the parameter has a good correlation to the degree of the plastic strain and is independent of the measurement conditions such as the EBSD system used for the measurement, number of data and step size in the crystal orientation map, electron beam condition, grain size and material. © 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Measurement of plastic strain of polycrystalline material by electron backscatter diffraction

It is important to know the degree of plastic strain in order to evaluate the susceptibility and crack growth rate of stress corrosion cracking (SCC) in stainless steel and nickel based alloy, because SCC is enhanced by the cold work and causes many problems in nuclear power plant components. In this study, electron backscatter diffraction in conjunction with scanning electron microscopy is applied to measure the plastic strain imposed to stainless steel by tensile load. A new parameter, which quantifies the spread of the crystal orientation within individual grains arising due to dislocation accumulation during plastic deformation, is correlated with imposed plastic strain. The new parameter is called 'crystal deformation' and is determined from the spread in misorientation from the central grain orientation. It is confirmed that this parameter has a good correlation with plastic strain and is not affected by the data density of the crystal orientation map. The dislocation density distribution is also evaluated from the misorientation from the central orientation. Relatively high dislocation density was observed near grain boundaries and grain boundary triple points, which was consistent with the observed deterioration of EBSD pattern quality in those locations. © 2004 Elsevier B.V. All rights reserved

The use of EELS elemental mapping to study precipitation reactions in a stainless maraging steel

The precipitation processes in an age-hardenable maraging steel, Sandvik 1RK91, have been investigated using energy-filtered transmission electron microscopy and conventional highresolution imaging and diffraction techniques. It proved possible to use EELS elemental mapping to identify and obtain information on the composition of precipitates as small as 1.5 nm. A number of different precipitate types were identified, including Cu-rich precipitates with the bcc and 9R structures, omega-Fe7Mo2 and eta-Ni-3(Ti, Mo), and the formation sequences of these precipitates during ageing were clarified. Ni-rich precipitates tended to form adjacent to existing Cu-rich precipitates, consistent with an earlier suggestion from atom-probe studies of the same material that Cu-rich precipitates act as nucleation sites for Ni-3(Ti, Mo) precipitates

On the importance of fifth-order spherical aberration for a fully corrected electron microscope.

Next generation aberration correctors will not only eliminate the third-order spherical aberration, but also improve the information limit by correction of chromatic aberration. As a result of these improvements, higher order aberrations, which have largely been neglected in image analysis, will become important. In this paper, we concern ourselves with situations where sub-A resolution can be achieved, and where the third-order spherical aberration is corrected and the fifth-order spherical aberration is measurable. We derive formulae to explore the maximum value of the fifth-order spherical aberration for directly interpretable imaging and discuss the optimum imaging conditions and their applicable range

Electron microscopy study of the nanocrystalline precipitates in a 12Cr-9Ni-4Mo-2Cu maraging steel

The precipitation processes in a new type of age-hardenable maraging steel, Sandvik 1RK91, have been investigated using energy filtered transmission electron microscopy, high resolution electron microscopy and selected area electron diffraction techniques. EELS elemental mapping has allowed the sizes, spatial distributions, number densities and the formation sequences of different types of precipitates, including Cu-rich precipitates with the 9R structure, omega-Fe7Mo2 and eta-Ni-3(Ti, Mo), to be revealed with high spatial resolution. Elemental maps reveal that Ni-rich particles tend to form adjacent to existing copper-rich precipitates. These observations provide insight into the hardening mechanism of the steel during ageing