1,137 research outputs found
From soft harmonic phonons to fast relaxational dynamics in CHNHPbBr
The lead-halide perovskites, including CHNHPbBr, are
components in cost effective, highly efficient photovoltaics, where the
interactions of the molecular cations with the inorganic framework are
suggested to influence the electronic and ferroelectric properties.
CHNHPbBr undergoes a series of structural transitions
associated with orientational order of the CHNH (MA) molecular
cation and tilting of the PbBr host framework. We apply high-resolution
neutron scattering to study the soft harmonic phonons associated with these
transitions, and find a strong coupling between the PbBr framework and
the quasistatic CHNH dynamics at low energy transfers. At higher
energy transfers, we observe a PbBr octahedra soft mode driving a
transition at 150 K from bound molecular excitations at low temperatures to
relatively fast relaxational excitations that extend up to 50-100 meV.
We suggest that these temporally overdamped dynamics enables possible indirect
band gap processes in these materials that are related to the enhanced
photovoltaic properties.Comment: (main text - 5 pages, 4 figures; supplementary information - 3 pages,
3 figures
Action Emulation
The effects of public announcements, private
communications, deceptive messages to groups, and so on, can all be
captured by a general mechanism of updating multi-agent models with
update action models, now in widespread use. There is a natural
extension of the definition of a bisimulation to action models.
Surely enough, updating with bisimilar action models gives the same
result (modulo bisimulation). But the converse turns out to be
false: update models may have the same update effects without being
bisimilar. We propose action emulation as a notion of equivalence
more appropriate for action models, and generalizing standard
bisimulation. It is proved that action emulation provides a full
characterization of update effect. We first concentrate on the
general case, and next focus on the important case of action models
with propositional preconditions. Our notion of action emulation
yields a simplification procedure for action models, and it gives
designers of multi-agent systems a useful tool for comparing
different ways of representing a particular communicative action
Epistemic Logic with Partial Dependency Operator
In this paper, we introduce dependency modality
into epistemic logic so as to reason about
dependency relationship in Kripke models. The resulted dependence epistemic
logic possesses decent expressivity and beautiful properties. Several
interesting examples are provided, which highlight this logic's practical
usage. The logic's bisimulation is then discussed, and we give a sound and
strongly complete axiomatization for a sub-language of the logic
Action Emulation
The effects of public announcements, private
communications, deceptive messages to groups, and so on, can all be
captured by a general mechanism of updating multi-agent models with
update action models, now in widespread use. There is a natural
extension of the definition of a bisimulation to action models.
Surely enough, updating with bisimilar action models gives the same
result (modulo bisimulation). But the converse turns out to be
false: update models may have the same update effects without being
bisimilar. We propose action emulation as a notion of equivalence
more appropriate for action models, and generalizing standard
bisimulation. It is proved that action emulation provides a full
characterization of update effect. We first concentrate on the
general case, and next focus on the important case of action models
with propositional preconditions. Our notion of action emulation
yields a simplification procedure for action models, and it gives
designers of multi-agent systems a useful tool for comparing
different ways of representing a particular communicative action
Introducing a Calculus of Effects and Handlers for Natural Language Semantics
In compositional model-theoretic semantics, researchers assemble
truth-conditions or other kinds of denotations using the lambda calculus. It
was previously observed that the lambda terms and/or the denotations studied
tend to follow the same pattern: they are instances of a monad. In this paper,
we present an extension of the simply-typed lambda calculus that exploits this
uniformity using the recently discovered technique of effect handlers. We prove
that our calculus exhibits some of the key formal properties of the lambda
calculus and we use it to construct a modular semantics for a small fragment
that involves multiple distinct semantic phenomena
A Denotational Semantics for First-Order Logic
In Apt and Bezem [AB99] (see cs.LO/9811017) we provided a computational
interpretation of first-order formulas over arbitrary interpretations. Here we
complement this work by introducing a denotational semantics for first-order
logic. Additionally, by allowing an assignment of a non-ground term to a
variable we introduce in this framework logical variables.
The semantics combines a number of well-known ideas from the areas of
semantics of imperative programming languages and logic programming. In the
resulting computational view conjunction corresponds to sequential composition,
disjunction to ``don't know'' nondeterminism, existential quantification to
declaration of a local variable, and negation to the ``negation as finite
failure'' rule. The soundness result shows correctness of the semantics with
respect to the notion of truth. The proof resembles in some aspects the proof
of the soundness of the SLDNF-resolution.Comment: 17 pages. Invited talk at the Computational Logic Conference (CL
2000). To appear in Springer-Verlag Lecture Notes in Computer Scienc
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