1,407 research outputs found
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
supersymmetric gauge theory with bifundamental chiral
superfields and a quartic tree level superpotential in four dimensions is dual
to type IIB string theory on 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 () and mineral accretion
normal to the surface (). These processes are sufficient to account
for the growth and form of many ancient stromatolities. Domical stromatolites
form when is less than or comparable to . Coniform structures with
thickened apical zones, typical of Conophyton, form when . More
angular coniform structures, similar to the stromatolites claimed as the oldest
macroscopic evidence of life, form when .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 -NaVO
Anomalous x-ray diffraction studies show that the charge ordering in
-NaVO 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
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