Recent improvements in propositional satisfiability techniques (SAT) made it possible to tackle successfully some hard real-world
problems (e.g., model-checking, circuit testing, propositional planning) by encoding into SAT. However, a purely Boolean representation
is not expressive enough for many other real-world applications, including the verification of timed and hybrid systems, of
proof obligations in software, and of circuit design at RTL level. These problems can be naturally modeled as satisfiability
in linear arithmetic logic (LAL), that is, the Boolean combination of propositional variables and linear constraints over
numerical variables. In this paper we present MathSAT, a new, SAT-based decision procedure for LAL, based on the (known approach) of integrating a state-of-the-art SAT solver
with a dedicated mathematical solver for LAL. We improve MathSAT in two different directions. First, the top‐level line procedure is enhanced and now features a tighter integration between
the Boolean search and the mathematical solver. In particular, we allow for theory-driven backjumping and learning, and theory-driven
deduction; we use static learning in order to reduce the number of Boolean models that are mathematically inconsistent; we
exploit problem clustering in order to partition mathematical reasoning; and we define a stack-based interface that allows
us to implement mathematical reasoning in an incremental and backtrackable way. Second, the mathematical solver is based on
layering; that is, the consistency of (partial) assignments is checked in theories of increasing strength (equality and uninterpreted
functions, linear arithmetic over the reals, linear arithmetic over the integers). For each of these layers, a dedicated (sub)solver
is used. Cheaper solvers are called first, and detection of inconsistency makes call of the subsequent solvers superfluous.
We provide a through experimental evaluation of our approach, by taking into account a large set of previously proposed benchmarks.
We first investigate the relative benefits and drawbacks of each proposed technique by comparison with respect to a reference
option setting. We then demonstrate the global effectiveness of our approach by a comparison with several state-of-the-art
decision procedures. We show that the behavior of MathSAT is often superior to its competitors, both on LAL and in the subclass of difference logic.
This work has been partly supported by ISAAC, a European-sponsored project, contract no. AST3-CT-2003-501848; by ORCHID, a
project sponsored by Provincia Autonoma di Trento; and by a grant from Intel Corporation. The work of T. Junttila has also
been supported by the Academy of Finland, project 53695. S. Schulz has also been supported by a grant of the Italian Ministero
dell'Istruzione, dell'Università e della Ricerca and the University of Verona. 相似文献
The ability of many bacteria to adapt to stressful conditions may later protect them against the same type of stress (specific adaptive response) or different types of stresses (multiple adaptive response, also termed cross-protection). Arcobacter butzleri and Campylobacter jejuni are close phylogenetic relatives that occur in many foods of animal origin and have been linked with human illness (mainly diarrhoea). In the present study, sublethal stress adaptation temperatures (48 °C and 10 °C) and mild and lethal acid conditions (pH 5.0 and pH 4.0) were determined for A. butzleri and C. jejuni. In addition, it was evaluated whether these sublethal stress adaptations cause specific adaptive responses or cross-protection against subsequent mild or lethal acid stresses in these bacteria. The studies were conducted in broth adjusted to the different conditions and the results were determined by the dilution series plating method. It was shown that heat stress adapted A. butzleri (incubated for 2 h at 48 °C) were significantly more resistant to subsequent lethal acid stress (pH 4.0) than non-adapted cells at the 1 h time-point (p < 0.01 in Wilcoxon rank sum test). No specific adaptive responses against the stresses in A. butzleri or C. jejuni and no cross-protection in C. jejuni were found. The ability of heat stressed A. butzleri to tolerate later lethal acid conditions should be taken into account when designing new food decontamination and processing strategies. 相似文献
Fish assemblages in large rivers are governed by spatio‐temporal changes in habitat conditions, which must be accounted for when designing effective monitoring programmes. Using boat electrofishing surveys, this study contrasts species richness, catch per unit effort (CPUE), total biomass, and spatial distribution of fish species in the Saint John River, New Brunswick, Canada, sampled during different diel periods (day and night) and macrohabitats (hydropower regulated river and its reservoir) in the vicinity of the Mactaquac (hydropower) Generating Station. Taxa richness, total CPUE, and total biomass were significantly higher during night surveys, resulting in marked differences in community composition between the two diel periods. Furthermore, the magnitude of diel differences in catch rate was more pronounced in lentic than in lotic macrohabitats. The required sampling effort (i.e., number of sites) to increase accuracy and precision of CPUE estimates varied widely between fish species, diel periods, and macrohabitats and ranged from 15 to 185 electrofishing sites. Determining a correction factor to contrast accuracy and precision of day‐ with night‐time surveys provide useful insights to improve the design of long‐term monitoring programmes for fish communities in large rivers. The study also shows the importance of multihabitat surveys to detect differences in the magnitude of diel changes in fish community metrics. 相似文献
An improvement of lithium‐ion batteries with regard to their reversible capacity, cycling stability, rate performance, and safety under repetitive charge and discharge still requires considerable research activity. However, graphite has remained the unexcelled material for the anode so far. Here, it is shown that two novel quaternary lithium‐chalcogenidometalate phases, Li4MnGe2S7 ( 1 ) and Li4MnSn2Se7 ( 2 ), represent very promising new anode materials for lithium‐ion cells in that they achieve specific lithium storage capacities higher than that of the commercially used graphite, and display an excellent stability during cycling. These properties are based on the structural peculiarities of the phases, which adopt Wurtzite‐related topologies and provide high structural flexibility of the metal sulfide or selenide bonds as advantageous pre‐requisitions for a large ion accessible volume. 相似文献
The third body in tungsten/tungsten-carbide sliding systems is studied using a combination of experiments and atomistic simulations. Ex situ X-ray photoelectron spectroscopy and focused ion beam analysis of the structural and chemical changes near the surfaces reveals that sliding of tungsten against tungsten-carbide results in plastic deformation of the W surface, leading to grain refinement, and the formation of a mechanically mixed amorphous layer on the WC counter body. Molecular dynamics simulations of W/WC sliding couples exhibit the formation of a nanoscale amorphous W/WC interface. The infrequent occurrence of atomic jamming events in the interface resulted in the emission of dislocations into the W bulk and the generation of amorphous shear bands in the WC counter body in agreement with the different third bodies observed in W and WC after the experiments. 相似文献
The objective of this study was to evaluate the feasibility of combined modular processes to selectively remove Sb from mine-impacted waters in an Arctic environment in order to fulfil local environmental criteria for discharged waters. Novel ion exchange, selective extraction and ultrafiltration, electrocoagulation, and dissolved air flotation technologies were investigated, individually or in combination, from the laboratory- to pilot-demonstration scale. Laboratory-scale testing using Fe2(SO4)3 precipitation, ion exchange resin, selective ion extraction and ultrafiltration, and electrocoagulation with or without subsequent dissolved air flotation indicated that any of the methods are potentially applicable to Sb removal from mine water. The observed differences between Sb and As removal efficiency by ion exchange resin illustrated the need for Sb-specific removal and recovery technologies. Techno-economic analyses showed that treatment of mine water using electrocoagulation-dissolved air flotation yields the lowest comparative life-cycle cost of examined technologies. Results demonstrated increased Sb attenuation efficiency using either electrocoagulation-dissolved air flotation or selective extraction and ultrafiltration, even when treating only 50% of the mine-impacted water, compared with conventional Fe2(SO4)3 precipitation from mine water. Additional investigation is necessary to characterize the long-term stability of the mineral phases in Sb-containing solid residues and to inform selection of Sb recovery methods and utilisation or final disposal options for the residual materials.
To recognise just the same human reaction (for example, a strong excitement) in different contexts, customary behaviours in these contexts have to be taken into account; e.g. a happy sport audience may be cheering for long time, while a happy theatrical audience may produce only short bursts of laughter in order to not interrupt the performance. Tailoring recognition algorithms to contexts can be achieved by building either a context-specific or a generic system. The former is individually trained for each context to recognise sets of characteristic responses, whereas the latter??in contrast to the context-specific one??adapts to the context via significantly more lightweight modification of parameters. This paper follows the latter way and proposes a simple modification of a hidden Markov model (HMM) classifier that enables end users to adapt the generic system to a context or a personal perception of an annotator by labelling a fairly small number of data samples of each context. For better adaptability to the limited number of the user??s annotations, the proposed semi-supervised HMM classifier employs the maximum posterior marginal, rather than the more conventional maximum a posteriori decision rule. The proposed user- and context-adaptable semi-supervised HMM classifier was tested on recognising excitement of a show audience in three contexts (a concert hall, a circus, and a sport event), differing in how the excitement is expressed. In our experiments the proposed classifier recognised reactions of a non-neutral audience with 10% higher accuracy than the conventional HMM and support vector machine based classifiers. 相似文献