Experimental and computational analysis of toughness anisotropy in an AA2139 Al-alloy for aerospace applications

International audienceFracture toughness anisotropy of AA2139 (Al-Cu-Mg) in T351 and T8 conditions has been investigated via mechanical testing of smooth and notched specimens of different geometries, loaded in the rolling direction (L) or in the transverse direction (T). Fracture mechanisms were investigated via SEM and synchrotron radiation computed tomography (SRCT). Contributions to failure anisotropy are identified with: (i) anisotropic initial void shape and growth, (ii) plastic behaviour including isotropic/kinematic hardening and plastic anisotropy, and (iii) nucleation at a 2nd population of 2nd phase particles leading to coalescence via narrow crack regions. A model based in part on the Gurson-Tvergaard-Needleman approach is constructed to describe and predict deformation behaviour, crack propagation and, in particular, toughness anisotropy. Model parameters are fitted using microstructural data and data on deformation and crack propagation for a range of small test samples. Its transferability has been shown by simulating tests of large M(T) samples

Structures in the Gauge/Gravity Duality Cascade

We study corrections to the anomalous mass dimension and their effects in the Seiberg duality cascade in the Klebanov-Strassler throat, where $\mathcal{N}=1$ supersymmetric $SU(N+M)\times SU(N)$ gauge theory with bifundamental chiral superfields and a quartic tree level superpotential in four dimensions is dual to type IIB string theory on $AdS_5 \times T^{1,1}$ background. Analyzing the renormalization group flow of the couplings on the gauge theory side, we propose specific corrections to the anomalous mass dimension. Applying gauge/gravity duality, we then show that the corrections reveal structures on the supergravity side with steps appearing in the running of the fluxes and the metric. The "charges" at the steps provide a gravitational source for Seiberg duality transformations. The finiteness of these corrections suggests that the theory flows to a baryonic branch rather than to a confining branch. The cosmological implication of the duality cascade and the gauge/gravity duality on the brane inflationary scenario and the cosmic microwave background radiation is pointed out.Comment: v3: 40 pages, minor changes and typos fixe

A case for biotic morphogenesis of coniform stromatolites

Mathematical models have recently been used to cast doubt on the biotic origin of stromatolites. Here by contrast we propose a biotic model for stromatolite morphogenesis which considers the relationship between upward growth of a phototropic or phototactic biofilm ($v$) and mineral accretion normal to the surface ($\lambda$). These processes are sufficient to account for the growth and form of many ancient stromatolities. Domical stromatolites form when $v$ is less than or comparable to $\lambda$. Coniform structures with thickened apical zones, typical of Conophyton, form when $v >> \lambda$. More angular coniform structures, similar to the stromatolites claimed as the oldest macroscopic evidence of life, form when $v >>> \lambda$.Comment: 10 pages, 3 figures, to appear in Physica

Schwarz Waveform Relaxation Methods for Systems of Semi-Linear Reaction-Diffusion Equations

Domain decomposition methods in science and engineering XIX, LNCSE, Springer Verlag, 2010.Schwarz waveform relaxation methods have been studied for a wide range of scalar linear partial differential equations (PDEs) of parabolic and hyperbolic type. They are based on a space-time decomposition of the computational domain and the subdomain iteration uses an overlapping decomposition in space. There are only few convergence studies for non-linear PDEs. We analyze in this paper the convergence of Schwarz waveform relaxation applied to systems of semi-linear reaction-diffusion equations. We show that the algorithm converges linearly under certain conditions over long time intervals. We illustrate our results, and further possible convergence behavior, with numerical experiments

On the practicality of time-optimal two-qubit Hamiltonian simulation

What is the time-optimal way of using a set of control Hamiltonians to obtain a desired interaction? Vidal, Hammerer and Cirac [Phys. Rev. Lett. 88 (2002) 237902] have obtained a set of powerful results characterizing the time-optimal simulation of a two-qubit quantum gate using a fixed interaction Hamiltonian and fast local control over the individual qubits. How practically useful are these results? We prove that there are two-qubit Hamiltonians such that time-optimal simulation requires infinitely many steps of evolution, each infinitesimally small, and thus is physically impractical. A procedure is given to determine which two-qubit Hamiltonians have this property, and we show that almost all Hamiltonians do. Finally, we determine some bounds on the penalty that must be paid in the simulation time if the number of steps is fixed at a finite number, and show that the cost in simulation time is not too great.Comment: 9 pages, 2 figure

Introducing LandScaleR : A novel method for spatial downscaling of land use projections

Funding Information: TW was funded by an EASTBIO UKRI BBSRC grant number BB/T00875X/1 . Downscaling simulations and calculation of landscape pattern metrics were performed on the University of Aberdeen HPC, Maxwell.Peer reviewedPublisher PD

X-ray anomalous scattering investigations on the charge order in α′\alpha^\prime-NaV2_2O5_5

Anomalous x-ray diffraction studies show that the charge ordering in $\alpha^\prime$-NaV$_2$O$_5$ is of zig-zag type in all vanadium ladders. We have found that there are two models of the stacking of layers along \emph{c-}direction, each of them consisting of 2 degenerated patterns, and that the experimental data is well reproduced if the 2 patterns appears simultaneously. We believe that the low temperature structure contains stacking faults separating regions corresponding to the four possible patterns.Comment: Submitted to Phys. Rev. Lett., 4 pages, 4 eps figures inserted in the tex

The Centurion 18 telescope of the Wise Observatory

We describe the second telescope of the Wise Observatory, a 0.46-m Centurion 18 (C18) installed in 2005, which enhances significantly the observing possibilities. The telescope operates from a small dome and is equipped with a large-format CCD camera. In the last two years this telescope was intensively used in a variety of monitoring projects. The operation of the C18 is now automatic, requiring only start-up at the beginning of a night and close-down at dawn. The observations are mostly performed remotely from the Tel Aviv campus or even from the observer's home. The entire facility was erected for a component cost of about 70k$ and a labor investment of a total of one man-year. We describe three types of projects undertaken with this new facility: the measurement of asteroid light variability with the purpose of determining physical parameters and binarity, the following-up of transiting extrasolar planets, and the study of AGN variability. The successful implementation of the C18 demonstrates the viability of small telescopes in an age of huge light-collectors, provided the operation of such facilities is very efficient.Comment: 16 pages, 13 figures, some figures quality was degraded, accepted for publication in Astrophysics and Space Scienc

Constraining warm dark matter with cosmic shear power spectra

We investigate potential constraints from cosmic shear on the dark matter particle mass, assuming all dark matter is made up of light thermal relic particles. Given the theoretical uncertainties involved in making cosmological predictions in such warm dark matter scenarios we use analytical fits to linear warm dark matter power spectra and compare (i) the halo model using a mass function evaluated from these linear power spectra and (ii) an analytical fit to the non-linear evolution of the linear power spectra. We optimistically ignore the competing effect of baryons for this work. We find approach (ii) to be conservative compared to approach (i). We evaluate cosmological constraints using these methods, marginalising over four other cosmological parameters. Using the more conservative method we find that a Euclid-like weak lensing survey together with constraints from the Planck cosmic microwave background mission primary anisotropies could achieve a lower limit on the particle mass of 2.5 keV.Comment: 26 pages, 9 figures, minor changes to match the version accepted for publication in JCA