6,156 research outputs found
Multiscale Turbulence Models Based on Convected Fluid Microstructure
The Euler-Poincar\'e approach to complex fluids is used to derive multiscale
equations for computationally modelling Euler flows as a basis for modelling
turbulence. The model is based on a \emph{kinematic sweeping ansatz} (KSA)
which assumes that the mean fluid flow serves as a Lagrangian frame of motion
for the fluctuation dynamics. Thus, we regard the motion of a fluid parcel on
the computationally resolvable length scales as a moving Lagrange coordinate
for the fluctuating (zero-mean) motion of fluid parcels at the unresolved
scales. Even in the simplest 2-scale version on which we concentrate here, the
contributions of the fluctuating motion under the KSA to the mean motion yields
a system of equations that extends known results and appears to be suitable for
modelling nonlinear backscatter (energy transfer from smaller to larger scales)
in turbulence using multiscale methods.Comment: 1st version, comments welcome! 23 pages, no figures. In honor of
Peter Constantin's 60th birthda
Equivalent variational approaches to biaxial liquid crystal dynamics
Within the framework of liquid crystal flows, the Qian & Sheng (QS) model for
Q-tensor dynamics is compared to the Volovik & Kats (VK) theory of biaxial
nematics by using Hamilton's variational principle. Under the assumption of
rotational dynamics for the Q-tensor, the variational principles underling the
two theories are equivalent and the conservative VK theory emerges as a
specialization of the QS model. Also, after presenting a micropolar variant of
the VK model, Rayleigh dissipation is included in the treatment. Finally, the
treatment is extended to account for nontrivial eigenvalue dynamics in the VK
model and this is done by considering the effect of scaling factors in the
evolution of the Q-tensor.Comment: 8 pages. Third versio
Toward the automation of business process ontology generation
Semantic Business Process Management (SBPM) utilises semantic technologies (e.g., ontology) to model and query process representations. There are times in which such models must be reconstructed from existing textual documentation. In this scenario the automated generation of ontological models would be preferable, however current methods and technology are still not capable of automatically generating accurate semantic process models from textual descriptions. This research attempts to automate the process as much as possible by proposing a method that drives the transformation through the joint use of a foundational ontology and lexico-semantic analysis. The method is presented, demonstrated and evaluated. The original dataset represents 150 business activities related to the procurement processes of a case study company. As the evaluation shows, the proposed method can accurately map the linguistic patterns of the process descriptions to semantic patterns of the foundational ontology to a high level of accuracy, however further research is required in order to reduce the level of human intervention, expand the method so as to recognise further patterns of the foundational ontology and develop a tool to assist the business process modeller in the semi-automated generation of process models
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Business Grid Services
Grid services have come to represent the synthesis of web services and grid computing paradigms. Web services provide the means to modularize software, enabling loosely coupled and novel synthesis. Grid computing removes the binding between functional software components and specific hosting hardware, enabling software to be deployed dynamically over a network (e.g. intra-, extra- or inter-net). Applying the constructs of grid computing to the service orientation of enterprise software will allow business service networks to utilize more specialized services. An upper service ontology that enables business grid services to be described and then related to the grid hosting platform is presented. Explicit knowledge is required for enterprise software, hosting servers and the domain that can then be utilized by both SLA and reservation systems. The ontology presented is derived from and validated using a collection of web services taken from leading investment banks
Room temperature dynamic correlation between methylammonium molecules in lead-iodine based perovskites: An ab-initio molecular dynamics perspective
The high efficiency of lead organo-metal-halide perovskite solar cells has
raised many questions about the role of the methylammonium (MA) molecules in
the Pb-I framework. Experiments indicate that the MA molecules are able to
'freely' spin around at room temperature even though they carry an intrinsic
dipole moment. We have performed large supercell (2592 atoms) finite
temperature ab-initio molecular dynamics calculations to study the correlation
between the molecules in the framework. An underlying long range
anti-ferroelectric ordering of the molecular dipoles is observed. The dynamical
correlation between neighboring molecules shows a maximum around room
temperature in the mid-temperature phase. In this phase, the rotations are slow
enough to (partially) couple to neighbors via the Pb-I cage. This results in a
collective motion of neighboring molecules in which the cage acts as the
mediator. At lower and higher temperatures the motions are less correlated
Efficient evaluation of accuracy of molecular quantum dynamics using dephasing representation
Ab initio methods for electronic structure of molecules have reached a
satisfactory accuracy for calculation of static properties, but remain too
expensive for quantum dynamical calculations. We propose an efficient
semiclassical method for evaluating the accuracy of a lower level quantum
dynamics, as compared to a higher level quantum dynamics, without having to
perform any quantum dynamics. The method is based on dephasing representation
of quantum fidelity and its feasibility is demonstrated on the
photodissociation dynamics of CO2. We suggest how to implement the method in
existing molecular dynamics codes and describe a simple test of its
applicability.Comment: 5 pages, 2 figure
Relativistic +BSE study of the optical properties of Ruddlesden-Popper iridates
We study the optical properties of the Ruddlesden-Popper series of iridates
SrIrO (=1, 2 and ) by solving the
Bethe-Salpeter equation (BSE), where the quasiparticle (QP) energies and
screened interactions are obtained by the approximation including
spin-orbit coupling. The computed optical conductivity spectra show strong
excitonic effects and reproduce very well the experimentally observed
double-peak structure, in particular for the spin-orbital Mott insulators
SrIrO and SrIrO. However, does not account well for
the correlated metallic state of SrIrO owing to a much too small band
renormalization, and this affects the overall quality of the optical
conductivity. Our analysis describes well the progressive redshift of the main
optical peaks as a function of dimensionality (), which is correlated with
the gradual decrease of the electronic correlation (quantified by the
constrained random phase approximation) towards the metallic limit.
We have also assessed the quality of a computationally cheaper BSE approach
that is based on a model dielectric function and conducted on top of DFT+
one-electron energies. Unfortunately, this model BSE approach does not
accurately reproduce the outcome of the full +BSE method and leads to
larger deviations to the measured spectra.Comment: 13 pages, 8 figure
Noncommutative families of instantons
We construct -deformations of the classical groups SL(2,H) and Sp(2).
Coacting on the basic instanton on a noncommutative four-sphere ,
we construct a noncommutative family of instantons of charge 1. The family is
parametrized by the quantum quotient of by .Comment: v2: Minor changes; computation of the pairing at the end of Sect. 5.1
improve
A Lagrangian kinetic model for collisionless magnetic reconnection
A new fully kinetic system is proposed for modeling collisionless magnetic
reconnection. The formulation relies on fundamental principles in Lagrangian
dynamics, in which the inertia of the electron mean flow is neglected in the
expression of the Lagrangian, rather then enforcing a zero electron mass in the
equations of motion. This is done upon splitting the electron velocity into its
mean and fluctuating parts, so that the latter naturally produce the
corresponding pressure tensor. The model exhibits a new Coriolis force term,
which emerges from a change of frame in the electron dynamics. Then, if the
electron heat flux is neglected, the strong electron magnetization limit yields
a hybrid model, in which the electron pressure tensor is frozen into the
electron mean velocity.Comment: 15 pages, no figures. To Appear in Plasma Phys. Control. Fusio
Efficiency of Xist-mediated silencing on autosomes is linked to chromosomal domain organisation
BACKGROUND: X chromosome inactivation, the mechanism used by mammals to equalise dosage of X-linked genes in XX females relative to XY males, is triggered by chromosome-wide localisation of a cis-acting non-coding RNA, Xist. The mechanism of Xist RNA spreading and Xist-dependent silencing is poorly understood. A large body of evidence indicates that silencing is more efficient on the X chromosome than on autosomes, leading to the idea that the X chromosome has acquired sequences that facilitate propagation of silencing. LINE-1 (L1) repeats are relatively enriched on the X chromosome and have been proposed as candidates for these sequences. To determine the requirements for efficient silencing we have analysed the relationship of chromosome features, including L1 repeats, and the extent of silencing in cell lines carrying inducible Xist transgenes located on one of three different autosomes. RESULTS: Our results show that the organisation of the chromosome into large gene-rich and L1-rich domains is a key determinant of silencing efficiency. Specifically genes located in large gene-rich domains with low L1 density are relatively resistant to Xist-mediated silencing whereas genes located in gene-poor domains with high L1 density are silenced more efficiently. These effects are observed shortly after induction of Xist RNA expression, suggesting that chromosomal domain organisation influences establishment rather than long-term maintenance of silencing. The X chromosome and some autosomes have only small gene-rich L1-depleted domains and we suggest that this could confer the capacity for relatively efficient chromosome-wide silencing. CONCLUSIONS: This study provides insight into the requirements for efficient Xist mediated silencing and specifically identifies organisation of the chromosome into gene-rich L1-depleted and gene-poor L1-dense domains as a major influence on the ability of Xist-mediated silencing to be propagated in a continuous manner in cis
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