Divergence and non-determinism play a fundamental role in the theory of computation, and their combined effect on computational equality deserves further study. By looking at the issue from the point of view of both c...
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Divergence and non-determinism play a fundamental role in the theory of computation, and their combined effect on computational equality deserves further study. By looking at the issue from the point of view of both computation and interaction, we are led to a canonical equality for non-deterministic computation, revealing its rich algebraic structure. We study this structure in three ways. First, we construct a complete equational system for finite-state non-deterministic computation. The challenge with such a system is to find an equational alternative to fixpoint induction a la Milner. We establish a negative result in the form of the non-existence of a finite equational system for the canonical equality of non-deterministic computation to support our approach. We then investigate infinite-state non-deterministic computation in the light of definability and show that every recursively enumerable set is generated by an unobservable process. Finally, we prove that, as far as computation is concerned, the effect produced jointly by divergence and non-determinism is model independent for a large class of process models. We use C-graphs, which are interesting in their own right, as abstract representations of the computational objects throughout the paper.
In this paper we investigate the computational power of particular tree transducers, viz., macro tree transducers and attributed tree transducers. The former tree transducers formalize the idea of syntax-directed tran...
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In this paper we investigate the computational power of particular tree transducers, viz., macro tree transducers and attributed tree transducers. The former tree transducers formalize the idea of syntax-directed translation, with the possibility of handling context;the latter tree transducers can serve as a formal model for the reduction semantics of attribute grammars. Here we generalize these tree transducers by allowing the invocation of external functions during the usual rewriting process. The main result of this paper is the characterization of macro tree transducers with external function calls in terms of attributed tree transducers with external function calls. Furthermore, such tree transducers with external function calls induce, in an obvious way, two operators on the set of all classes of tree functions. According to this point of view, we define two classes of tree functions inductively in the same way as the class PREC of primitive recursive tree functions, except that the closure under the scheme of primitive recursion is replaced by the closure under macro tree transducers with external function calls and attributed tree transducers with external function calls, respectively. As a second result of this paper we prove that these two classes are equal to PREC.
Non-covalent interactions between sulfur centers and aromatic rings play important roles in biological chemistry. We examined here the sulfur-arene interactions between the fused aromatic heterocycle benzofuran and tw...
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Non-covalent interactions between sulfur centers and aromatic rings play important roles in biological chemistry. We examined here the sulfur-arene interactions between the fused aromatic heterocycle benzofuran and two prototype sulfur divalent triatomics (sulfur dioxide and hydrogen sulfide). The weakly-bound adducts were generated in a supersonic jet expansion and characterized with broadband (chirped-pulsed) time-domain microwave spectroscopy. The rotational spectrum confirmed the detection of a single isomer for both heterodimers, consistent with the computational predictions for the global minima. The benzofuran center dot center dot center dot sulfur dioxide dimer exhibits a stacked structure with sulfur closer to benzofuran, while in benzofuran center dot center dot center dot hydrogen sulfide the two S-H bonds are oriented towards the bicycle. These binding topologies are similar to the corresponding benzene adducts, but offer increased interaction energies. The stabilizing interactions are described as S center dot center dot center dot pi or S-H center dot center dot center dot p, respectively, using a combination of density-functional theory calculations (dispersion corrected B3LYP and B2PLYP), natural bond orbital theory, energy decomposition and electronic density analysis methods. The two heterodimers present a larger dispersion component, but nearly balanced by electrostatic contributions.
This paper intends to give a theoretical foundation of machine discovery from facts. We point out that the essence of a computational logic of scientific discovery or a logic of machine discovery is the refutability o...
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This paper intends to give a theoretical foundation of machine discovery from facts. We point out that the essence of a computational logic of scientific discovery or a logic of machine discovery is the refutability of the entire spaces of hypotheses. We discuss this issue in the framework of inductive inference of length-bounded elementary formal systems (EFSs), which are a kind of logic programs over strings of characters and correspond to context-sensitive grammars in Chomsky hierarchy. First we present some characterization theorems on inductive inference machines that can refute hypothesis spaces. Then we show differences between our inductive inference and some other related inferences such as in the criteria of reliable identification, finite identification and identification in the limit. Finally we show that for any n, the class, i.e. hypothesis space, of length-bounded EFSs with at most n axioms is inferable in our sense, that is, the class is refutable by a consistently working inductive inference machine. This means that sufficiently large hypothesis spaces are identifiable and refutable.
This paper defines the notion of hybrid atomicity for nested transaction systems, and presents and verifies an algorithm providing this property. Hybrid atomicity is a modular property;it allows the correctness of a s...
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This paper defines the notion of hybrid atomicity for nested transaction systems, and presents and verifies an algorithm providing this property. Hybrid atomicity is a modular property;it allows the correctness of a system to be deduced from the fact that each object is implemented to have the property. It allows more concurrency than dynamic atomicity, by assigning timestamps to transactions at commit. The Avalon system provides exactly this facility. The results in this paper extend earlier work using the same model for locking and timestamp-based algorithms, providing further evidence for the generality of the approach. However, there are some subtle differences with the definitions used in earlier work, showing the difficulties of developing precise general models for nested transaction systems.
Traditionally, dependency theory has been developed for uninterpreted data. Specifically, the only assumption that is made about the data domains is that data values can be compared for equality. However, data is ofte...
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Traditionally, dependency theory has been developed for uninterpreted data. Specifically, the only assumption that is made about the data domains is that data values can be compared for equality. However, data is often interpreted and there can be advantages in considering data as such, for instance, obtaining more compact representations as is done in constraint databases. This paper considers dependency theory in the context of interpreted data. Specifically, it studies constraint-generating dependencies. These are a generalization of equality-generating dependencies where equality requirements are replaced by constraints on an interpreted domain. The main technical results in the paper are a general decision procedure for the implication and consistency problems for constraint-generating dependencies and complexity results for specific classes of such dependencies over given domains. The decision procedure proceeds by reducing the dependency problem to a decision problem for the constraint theory of interest and is applicable as soon as the underlying constraint theory is decidable. The complexity results are, in some cases, directly lifted from the constraint theory;in other cases, optimal complexity bounds are obtained by taking into account the specific form of the constraint decision problem obtained by reducing the dependency implication problem. (C) 1999 Academic Press.
Recent work, both theoretical and computational, in the modelling of time-dependent phenomena (Edge Localized Modes (ELMs)) in the plasma edge is reviewed.
Recent work, both theoretical and computational, in the modelling of time-dependent phenomena (Edge Localized Modes (ELMs)) in the plasma edge is reviewed.
We investigate the problem of learning disjunctions of counting functions, which are general cases of parity and module functions, with equivalence and membership queries. We prove that, for any prime number p, the cl...
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We investigate the problem of learning disjunctions of counting functions, which are general cases of parity and module functions, with equivalence and membership queries. We prove that, for any prime number p, the class of disjunctions of integer-weighted counting functions with modulus p over the domain Z(q)(n) (or Z(n)) for any given integer q greater than or equal to 2 is polynomial time learnable using at most n + 1 equivalence queries, where the hypotheses issued by the learner are disjunctions of at most n counting functions with weights from Z(p). In general, a counting function may have a composite modulus. We prove that, for any given integer q greater than or equal to 2, over the domain Z(2)(n), the class of read-once disjunctions of Boolean-weighted counting functions with modulus q is polynomial-time learnable with only one equivalence query and O(n(q)) membership queries.
Double pushout (algebraic) graph rewriting, which works by first removing the part of the graph to be regarded as garbage, and then gluing in the new part of the graph, is contrasted with term graph rewriting, which w...
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Double pushout (algebraic) graph rewriting, which works by first removing the part of the graph to be regarded as garbage, and then gluing in the new part of the graph, is contrasted with term graph rewriting, which works by first gluing in the new part of the graph (the contractum) and performing redirections, and then removing garbage. It is shown that in the algebraic framework these two strategies can be reconciled. This is done by finding a natural analogue of the contractum in the algebraic framework, which requires the reformulation of the customary double pushout construction. The new and old algebraic constructions coexist within a pushout cube. In this, the usual ''outward'' form of the double pushout appears as the two rear squares, and the alternative ''inward'' formulation as the two front squares. The two formulations are entirely equivalent in the world of double pushout graph rewriting.
Quantum chemistry simulations offer a cost-effective way to computationally design BODIPY photosensitizers. However, accurate predictions of excitation energies pose a challenge for time-dependent density functional t...
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Quantum chemistry simulations offer a cost-effective way to computationally design BODIPY photosensitizers. However, accurate predictions of excitation energies pose a challenge for time-dependent density functional theory and equation-of-motion coupled-cluster singles and doubles methods. By contrast, reliable predictions can be achieved by multireference quantum chemistry methods;unfortunately, their computational cost increases exponentially with the number of electrons. Alternatively, quantum computing holds potential for an exact simulation of the photophysical properties in a computationally more efficient way. Herein, we introduce the state-specific Delta UCCSD-VQE (unitary coupled-cluster singles and doubles-variational quantum eigensolver) and Delta ADAPT-VQE methods in which the electronically excited state is calculated via a non-Aufbau configuration. We show for six BODIPY derivatives that the proposed methods predict accurate excitation energies that are in good agreement with those from experiments. Due to its performance and simplicity, we believe that Delta ADAPT will become a useful approach for the simulation of BODIPY photosensitizers on near-term quantum devices.
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