13,917 research outputs found
All-Optical Switching with Transverse Optical Patterns
We demonstrate an all-optical switch that operates at ultra-low-light levels
and exhibits several features necessary for use in optical switching networks.
An input switching beam, wavelength , with an energy density of
photons per optical cross section [] changes
the orientation of a two-spot pattern generated via parametric instability in
warm rubidium vapor. The instability is induced with less than 1 mW of total
pump power and generates several Ws of output light. The switch is
cascadable: the device output is capable of driving multiple inputs, and
exhibits transistor-like signal-level restoration with both saturated and
intermediate response regimes. Additionally, the system requires an input power
proportional to the inverse of the response time, which suggests thermal
dissipation does not necessarily limit the practicality of optical logic
devices
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Approach Tolerance in the Assemblies of Evolutionary Hybrid Prototypes
A new answer is proposed to replace the traditional âone shotâ prototype (manufactured in
one piece with one process): the hybrid rapid prototype. It is used to highly reduce time,
cost and increase reactivity during the development times of new products.
The part is decomposed in several components which can quickly be changed and can be
manufactured with a process the most adapted.
The main objective of the presented method is to propose an available technological
assembly between the different components of the part in the respect of technological and
topological function, and initial tolerance.
Using a graph of representation, fuzzy logic and a tolerance point of view, some entities are
associated with a CIA (Assembly Identity Card) in accordance with evolutionary and
manufacturing analysis. This work will be illustrated by an industrial tooling for plastic
injection.Mechanical Engineerin
Study of a navigation and traffic control technique employing satellites. Volume 3 - User hardware Interim report
User hardware configurations and requirements for navigation and air traffic control technique using satellite
Band engineering in graphene with superlattices of substitutional defects
We investigate graphene superlattices of nitrogen and boron substitutional
defects and by using symmetry arguments and electronic structure calculations
we show how such superlattices can be used to modify graphene band structure.
Specifically, depending on the superlattice symmetry, the structures considered
here can either preserve the Dirac cones (D_{6h} superlattices) or open a band
gap (D_{3h}). Relevant band parameters (carriers effective masses, group
velocities and gaps, when present) are found to depend on the superlattice
constant n as 1/n^{p} where p is in the range 1-2, depending on the case
considered. Overall, the results presented here show how one can tune the
graphene band structure to a great extent by modifying few superlattice
parameters.Comment: accepted, J. Phys. Chem.
Data types with symmetries and polynomial functors over groupoids
Polynomial functors are useful in the theory of data types, where they are
often called containers. They are also useful in algebra, combinatorics,
topology, and higher category theory, and in this broader perspective the
polynomial aspect is often prominent and justifies the terminology. For
example, Tambara's theorem states that the category of finite polynomial
functors is the Lawvere theory for commutative semirings. In this talk I will
explain how an upgrade of the theory from sets to groupoids is useful to deal
with data types with symmetries, and provides a common generalisation of and a
clean unifying framework for quotient containers (cf. Abbott et al.), species
and analytic functors (Joyal 1985), as well as the stuff types of Baez-Dolan.
The multi-variate setting also includes relations and spans, multispans, and
stuff operators. An attractive feature of this theory is that with the correct
homotopical approach - homotopy slices, homotopy pullbacks, homotopy colimits,
etc. - the groupoid case looks exactly like the set case. After some standard
examples, I will illustrate the notion of data-types-with-symmetries with
examples from quantum field theory, where the symmetries of complicated tree
structures of graphs play a crucial role, and can be handled elegantly using
polynomial functors over groupoids. (These examples, although beyond species,
are purely combinatorial and can be appreciated without background in quantum
field theory.) Locally cartesian closed 2-categories provide semantics for
2-truncated intensional type theory. For a fullfledged type theory, locally
cartesian closed \infty-categories seem to be needed. The theory of these is
being developed by D.Gepner and the author as a setting for homotopical
species, and several of the results exposed in this talk are just truncations
of \infty-results obtained in joint work with Gepner. Details will appear
elsewhere.Comment: This is the final version of my conference paper presented at the
28th Conference on the Mathematical Foundations of Programming Semantics
(Bath, June 2012); to appear in the Electronic Notes in Theoretical Computer
Science. 16p
The effect of atomic-scale defects and dopants on graphene electronic structure
Graphene, being one-atom thick, is extremely sensitive to the presence of
adsorbed atoms and molecules and, more generally, to defects such as vacancies,
holes and/or substitutional dopants. This property, apart from being directly
usable in molecular sensor devices, can also be employed to tune graphene
electronic properties. Here we briefly review the basic features of
atomic-scale defects that can be useful for material design. After a brief
introduction on isolated defects, we analyse the electronic structure of
multiple defective graphene substrates, and show how to predict the presence of
microscopically ordered magnetic structures. Subsequently, we analyse the more
complicated situation where the electronic structure, as modified by the
presence of some defects, affects chemical reactivity of the substrate towards
adsorption (chemisorption) of atomic/molecular species, leading to preferential
sticking on specific lattice positions. Then, we consider the reverse problem,
that is how to use defects to engineer graphene electronic properties. In this
context, we show that arranging defects to form honeycomb-shaped superlattices
(what we may call "supergraphenes") a sizeable gap opens in the band structure
and new Dirac cones are created right close to the gapped region. Similarly, we
show that substitutional dopants such as group IIIA/VA elements may have gapped
quasi-conical structures corresponding to massive Dirac carriers. All these
possible structures might find important technological applications in the
development of graphene-based logic transistors.Comment: 16 pages, 14 figures, "Physics and Applications of Graphene - Theory"
- Chapter 3,
http://www.intechweb.org/books/show/title/physics-and-applications-of-graphene-theor
Lessons learned: structuring knowledge codification and abstraction to provide meaningful information for learning
Purpose â To increase the spread and reuse of lessons learned (LLs), the purpose of this paper is to develop
a standardised information structure to facilitate concise capture of the critical elements needed to engage
secondary learners and help them apply lessons to their contexts.
Design/methodology/approach â Three workshops with industry practitioners, an analysis of over 60
actual lessons from private and public sector organisations and seven practitioner interviews provided
evidence of actual practice. Design science was used to develop a repeatable/consistent information model of
LL content/structure. Workshop analysis and theory provided the coding template. Situation theory and
normative analysis were used to define the knowledge and rule logic to standardise fields.
Findings â Comparing evidence from practice against theoretical prescriptions in the literature highlighted
important enhancements to the standard LL model. These were a consistent/concise rule and context
structure, appropriate emotional language, reuse and control criteria to ensure lessons were transferrable and
reusable in new situations.
Research limitations/implications â Findings are based on a limited sample. Long-term benefits of
standardisation and use need further research. A larger sample/longitudinal usage study is planned.
Practical implications â The implementation of the LL structure was well-received in one government
user site and other industry user sites are pending. Practitioners validated the design logic for improving
capture and reuse of lessons to render themeasily translatable to a new learnerâs context.
Originality/value â The new LL structure is uniquely grounded in user needs, developed from existing
best practice and is an original application of normative and situation theory to provide consistent rule logic
for context/content structure
The Los Alamos Trapped Ion Quantum Computer Experiment
The development and theory of an experiment to investigate quantum
computation with trapped calcium ions is described. The ion trap, laser and ion
requirements are determined, and the parameters required for quantum logic
operations as well as simple quantum factoring are described.Comment: 41 pages, 16 figures, submitted to Fortschritte der Physi
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