11,981 research outputs found
The role of slip transfer at grain boundaries in the propagation of microstructurally short fatigue cracks in Ni-based superalloys
Crack initiation and propagation under high-cycle fatigue conditions have
been investigated for a polycrystalline Ni-based superalloy by in-situ
synchrotron assisted diffraction and phase contrast tomography. The cracks
nucleated along the longest coherent twin boundaries pre-existing on the
specimen surface, that were well oriented for slip and that presented a large
elastic incompatibility across them. Moreover, the propagation of
microstructurally short cracks was found to be determined by the easy slip
transfer paths across the pre-existing grain boundaries. This information can
only be obtained by characterization techniques like the ones presented here
that provide the full set of 3D microstructural information
A three-dimensional hydrodynamical line profile analysis of iron lines and barium isotopes in HD140283
Heavy-elements, i.e. those beyond the iron peak, mostly form via two neutron
capture processes: the s- and r-process. Metal-poor stars should contain fewer
isotopes that form via the s-process, according to currently accepted theory.
It has been shown in several investigations that theory and observation do not
agree well, raising questions on the validity of either the methodology or the
theory. We analyse the metal-poor star HD140283, for which we have a high
quality spectrum. We test whether a 3D LTE stellar atmosphere and spectrum
synthesis code permits a more reliable analysis of the iron abundance and
barium isotope ratio than a 1D LTE analysis. Using 3D model atmospheres, we
examine 91 iron lines of varying strength and formation depth. This provides us
with the star's rotational speed. With this, we model the barium isotope ratio
by exploiting the hyperfine structure of the singly ionised 4554 resonance
line, and study the impact of the uncertainties in the stellar parameters.
HD140283's vsini = 1.65 +/- 0.05 km/s. Barium isotopes under the 3D paradigm
show a dominant r-process signature as 77 +/- 6 +/- 17% of barium isotopes form
via the r-process, where errors represent the assigned random and systematic
errors, respectively. We find that 3D LTE fits reproduce iron line profiles
better than those in 1D, but do not provide a unique abundance (within the
uncertainties). However, we demonstrate that the isotopic ratio is robust
against this shortcoming. Our barium isotope result agrees well with currently
accepted theory regarding the formation of the heavy-elements during the early
Galaxy. The improved fit to the asymmetric iron line profiles suggests that the
current state of 3D LTE modelling provides excellent simulations of fluid
flows. However, the abundances they provide are not yet self-consistent. This
may improve with NLTE considerations and higher resolution models.Comment: 16 pages, 10 figures, 5 tables. Accepted for publication in A&
Large-q asymptotics of the random bond Potts model
We numerically examine the large-q asymptotics of the q-state random bond
Potts model. Special attention is paid to the parametrisation of the critical
line, which is determined by combining the loop representation of the transfer
matrix with Zamolodchikov's c-theorem. Asymptotically the central charge seems
to behave like c(q) = 1/2 log_2(q) + O(1). Very accurate values of the bulk
magnetic exponent x_1 are then extracted by performing Monte Carlo simulations
directly at the critical point. As q -> infinity, these seem to tend to a
non-trivial limit, x_1 -> 0.192 +- 0.002.Comment: 9 pages, no figure
Assessing digital preservation frameworks: the approach of the SHAMAN project
How can we deliver infrastructure capable of supporting the
preservation of digital objects, as well as the services that can be applied to those digital objects, in ways that future unknown systems will understand? A critical problem in developing systems is the process of validating whether the delivered solution effectively reflects the validated requirements. This is a challenge also for the EU-funded SHAMAN project, which aims to develop an integrated preservation framework using grid-technologies for distributed networks of digital preservation systems, for managing the storage, access, presentation, and manipulation of digital objects over time. Recognising this, the project team ensured that alongside the user requirements an assessment framework was developed. This paper presents the assessment of the SHAMAN demonstrators for the memory institution, industrial design and engineering and eScience domains, from the point of view of
user’s needs and fitness for purpose. An innovative synergistic use of TRAC criteria, DRAMBORA risk registry and mitigation strategies, iRODS rules and information system models requirements has been designed, with the underlying goal to define associated policies, rules and state information, and make them wherever possible machine-encodable and enforceable. The described assessment framework can be valuable not only for the implementers of this project preservation framework, but for the wider digital preservation community, because it provides a
holistic approach to assessing and validating the preservation of digital libraries, digital repositories and data centres
On the Wake Structure in Streaming Complex Plasmas
The theoretical description of complex (dusty) plasmas requires multiscale
concepts that adequately incorporate the correlated interplay of streaming
electrons and ions, neutrals, and dust grains. Knowing the effective dust-dust
interaction, the multiscale problem can be effectively reduced to a
one-component plasma model of the dust subsystem. The goal of the present
publication is a systematic evaluation of the electrostatic potential
distribution around a dust grain in the presence of a streaming plasma
environment by means of two complementary approaches: (i) a high precision
computation of the dynamically screened Coulomb potential from the dynamic
dielectric function, and (ii) full 3D particle-in-cell simulations, which
self-consistently include dynamical grain charging and non-linear effects. The
applicability of these two approaches is addressed
A double-dot quantum ratchet driven by an independently biased quantum point contact
We study a double quantum dot (DQD) coupled to a strongly biased quantum
point contact (QPC), each embedded in independent electric circuits. For weak
interdot tunnelling we observe a finite current flowing through the unbiased
Coulomb blockaded DQD in response to a strong bias on the QPC. The direction of
the current through the DQD is determined by the relative detuning of the
energy levels of the two quantum dots. The results are interpreted in terms of
a quantum ratchet phenomenon in a DQD energized by a nearby QPC.Comment: revised versio
Generalized Gibbs Ensemble Description of Real Space Entanglement Spectra of (2+1)-dimensional Chiral Topological Systems with Symmetry
We provide a quantitative analysis of the splittings in low-lying numerical
entanglement spectra (ES) of a number of quantum states that can be identified,
based on "Li-Haldane state-counting", as ground states of (2+1)-dimensional
chiral topological phases with global SU(2) symmetry. The ability to account
for numerical ES splittings away from their "ideal" chiral conformal field
theory (CFT) spectra, solely within the context of CFT, is an additional
diagnostic of the underlying topological theory, of finer sensitivity than
"state-counting". We use the conformal boundary state description of the ES,
which can be formulated as a quantum quench. In this language, the ES
splittings arise from higher local conservation laws in the chiral CFT besides
the energy, which we view as a Generalized Gibbs Ensemble (GGE). Global SU(2)
symmetry imposes strong constraints on the number of such conservation laws, so
that only a small number of parameters can be responsible for the splittings.
We work out these conservation laws for chiral SU(2) Wess-Zumino-Witten CFTs at
levels one and two, and for the latter we notably find that some of the
conservation laws take the form of local integrals of operators of fractional
dimension, as proposed by Cardy for quantum quenches [J. Stat. Mech.: Theory
Exp. 2016, 023103 (2016)]. We analyze numerical ES from systems with SU(2)
symmetry including chiral spin-liquid ground states of local 2D Hamiltonians
and two chiral Projected Entangled Pair States (PEPS) tensor networks, which
exhibit the "state-counting" of the SU(2)-level-one and -level-two theories. We
find that the low-lying ES splittings can be well understood by the lowest of
our conservation laws, and we demonstrate the importance of accounting for the
fractional conservation laws at level two. Thus the states we consider,
including the PEPS, appear chiral also under our more sensitive diagnostic.Comment: 43 pages, 9 figures, 4 table
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