35,359 research outputs found
Diagrammatic Coupled Cluster Monte Carlo
We propose a modified coupled cluster Monte Carlo algorithm that
stochastically samples connected terms within the truncated
Baker--Campbell--Hausdorff expansion of the similarity transformed Hamiltonian
by construction of coupled cluster diagrams on the fly. Our new approach --
diagCCMC -- allows propagation to be performed using only the connected
components of the similarity-transformed Hamiltonian, greatly reducing the
memory cost associated with the stochastic solution of the coupled cluster
equations. We show that for perfectly local, noninteracting systems, diagCCMC
is able to represent the coupled cluster wavefunction with a memory cost that
scales linearly with system size. The favorable memory cost is observed with
the only assumption of fixed stochastic granularity and is valid for arbitrary
levels of coupled cluster theory. Significant reduction in memory cost is also
shown to smoothly appear with dissociation of a finite chain of helium atoms.
This approach is also shown not to break down in the presence of strong
correlation through the example of a stretched nitrogen molecule. Our novel
methodology moves the theoretical basis of coupled cluster Monte Carlo closer
to deterministic approaches.Comment: 31 pages, 6 figure
A Formalism for Scattering of Complex Composite Structures. 1 Applications to Branched Structures of Asymmetric Sub-Units
We present a formalism for the scattering of an arbitrary linear or acyclic
branched structure build by joining mutually non-interacting arbitrary
functional sub-units. The formalism consists of three equations expressing the
structural scattering in terms of three equations expressing the sub-unit
scattering. The structural scattering expressions allows a composite structures
to be used as sub-units within the formalism itself. This allows the scattering
expressions for complex hierarchical structures to be derived with great ease.
The formalism is furthermore generic in the sense that the scattering due to
structural connectivity is completely decoupled from internal structure of the
sub-units. This allows sub-units to be replaced by more complex structures. We
illustrate the physical interpretation of the formalism diagrammatically. By
applying a self-consistency requirement we derive the pair distributions of an
ideal flexible polymer sub-unit. We illustrate the formalism by deriving
generic scattering expressions for branched structures such as stars, pom-poms,
bottle-brushes, and dendrimers build out of asymmetric two-functional
sub-units.Comment: Complete rewrite generalizing the formalism to arbitrary functional
sub-units and including a new Feynmann like diagrammatic interpretatio
A review of information flow diagrammatic models for product-service systems
A product-service system (PSS) is a combination of products and services to
create value for both customers and manufacturers. Modelling a PSS based on
function orientation offers a useful way to distinguish system inputs and
outputs with regards to how data are consumed and information is used, i.e.
information flow. This article presents a review of diagrammatic information
flow tools, which are designed to describe a system through its functions. The
origin, concept and applications of these tools are investigated, followed by an
analysis of information flow modelling with regards to key PSS properties. A
case study of selection laser melting technology implemented as PSS will then be
used to show the application of information flow modelling for PSS design. A
discussion based on the usefulness of the tools in modelling the key elements of
PSS and possible future research directions are also presented
Inverse spin galvanic effect in the presence of impurity spin-orbit scattering: a diagrammatic approach
Spin-charge interconversion is currently the focus of intensive experimental
and theoretical research both for its intrinsic interest and for its potential
exploitation in the realization of new spintronic functionalities. Spin-orbit
coupling is one of the key microscopic mechanisms to couple charge currents and
spin polarizations. The Rashba spin-orbit coupling in a two-dimensional
electron gas has been shown to give rise to the inverse spin galvanic effect,
i.e. the generation of a non-equilibrium spin polarization by a charge current.
Whereas the Rashba model may be applied to the interpretation of experimental
results in many cases, in general in a given real physical system spin-orbit
coupling also occurs due other mechanisms such as Dresselhaus bulk inversion
asymmetry and scattering from impurities. In this work we consider the inverse
spin galvanic effect in the presence of Rashba, Dresselhaus and impurity
spin-orbit scattering. We find that the size and form of the inverse spin
galvanic effect is greatly modified by the presence of the various sources of
spin-orbit coupling. Indeed, spin-orbit coupling affects the spin relaxation
time by adding the Elliott-Yafet mechanism to the Dyakonov-Perel and,
furthermore, it changes the non-equilibrium value of the current-induced spin
polarization by introducing a new spin generation torque. We use a diagrammatic
Kubo formula approach to evaluate the spin polarization-charge current response
function. We finally comment about the relevance of our results for the
interpretation of experimental results.Comment: 14 pages, 1 figure, invited paper for a special issue of Condensed
Matter (MDPI) on "Control and Enhancement of Quantum Coherence in
Nanostructured Materials
Active templates: Manipulating pointers with pictures
Active templates are a semi-automatic visual mechanism for generating algorithms for manipulating pointer-based data structures. The programmer creates a picture showing the affected part of a data structure before and after a general-case manipulation. Code for the operation is compiled directly from the picture, which also provides the development environment with enough information to generate, automatically, a series of templates for other similar pictures, each describing a different configuration which the data structure may possess. The programmer completes the algorithm by creating matching after-pictures for each of these cases.
At every stage, most of the picture-generation is automatic. Much of the tedious detail of conventional pointer-based data-structure manipulation, such as maintenance of current pointers, is unnecessary in a system based on active templates
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