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31.
Nic Wilson 《Journal of Heuristics》2006,12(4-5):241-262
Representing and reasoning with an agent’s preferences is important in many applications of constraints formalisms. Such preferences
are often only partially ordered. One class of soft constraints formalisms, semiring-based CSPs, allows a partially ordered
set of preference degrees, but this set must form a distributive lattice; whilst this is convenient computationally, it considerably
restricts the representational power. This paper constructs a logic of soft constraints where it is only assumed that the
set of preference degrees is a partially ordered set, with a maximum element 1 and a minimum element 0. When the partially
ordered set is a distributive lattice, this reduces to the idempotent semiring-based CSP approach, and the lattice operations
can be used to define a sound and complete proof theory. A generalised possibilistic logic, based on partially ordered values
of possibility, is also constructed, and shown to be formally very strongly related to the logic of soft constraints. It is
shown how the machinery that exists for the distributive lattice case can be used to perform sound and complete deduction,
using a compact embedding of the partially ordered set in a distributive lattice. 相似文献
32.
33.
McGregor LA Gauchotte-Lindsay C Daéid NN Thomas R Daly P Kalin RM 《Journal of chromatography. A》2011,1218(29):4755-4763
Ultra resolution chemical fingerprinting of dense non-aqueous phase liquids (DNAPLs) from former manufactured gas plants (FMGPs) was investigated using comprehensive two-dimensional gas chromatography coupled with time of flight mass spectrometry (GC×GC TOFMS). Reversed phase GC×GC (i.e. a polar primary column coupled to a non-polar secondary column) was found to significantly improve the separation of polycyclic aromatic hydrocarbons (PAHs) and their alkylated homologues. Sample extraction and cleanup was performed simultaneously using accelerated solvent extraction (ASE), with recovery rates between 76% and 97%, allowing fast, efficient extraction with minimal solvent consumption. Principal component analysis (PCA) of the GC×GC data was performed in an attempt to differentiate between twelve DNAPLs based on their chemical composition. Correlations were discovered between DNAPL composition and historic manufacturing processes used at different FMGP sites. Traditional chemical fingerprinting methods generally follow a tiered approach with sample analysis on several different instruments. We propose ultra resolution chemical fingerprinting as a fast, accurate and precise method of obtaining more chemical information than traditional tiered approaches while using only a single analytical technique. 相似文献
34.
35.
We present a new scenario for the breakdown of ferromagnetic order in a two-dimensional quantum magnet with competing ferromagnetic and antiferromagnetic interactions. In this, dynamical effects lead to the formation of two-magnon bound states, which undergo Bose-Einstein condensation, giving rise to bond-centered nematic order. This scenario is explored in some detail for an extended Heisenberg model on a square lattice. In particular, we present numerical evidence confirming the existence of a state with d-wave nematic correlations but no long-range magnetic order, lying between the saturated ferromagnetic and collinear antiferromagnetic phases of the ferromagnetic model J1-J2. We argue by continuity of spectra that this phase is also present in a model with 4-spin cyclic exchange. 相似文献
36.
The antiferromagnetic Heisenberg model on a pyrochlore lattice under external magnetic field is studied by classical Monte Carlo simulation. The model includes bilinear and biquadratic interactions; the latter effectively describes the coupling to lattice distortions. The magnetization process shows a half-magnetization plateau at low temperatures, accompanied with strong suppression of the magnetic susceptibility. Temperature dependence of the plateau behavior is clarified. Finite-temperature phase diagram under the magnetic field is determined. The results are compared with recent experimental results in chromium spinel oxides. 相似文献
37.
Zusammenfassung Es wurde eine eigenartige Methode der Kolloidsynthese ausgearbeitet, welche auf der Elektrolyse sehr verdünnter Salzl?sungen
beruht, wobei das Anion des Salzes mit dem von der Anode abgesto?enen Kation eine unl?sliche Verbindung bildet.
Es wurde der Einflu? verschiedener Faktoren (Stromdichte, Stromst?rke, Temperatur, Rührung usw.) studiert und die günstigsten
Bedingungen für die Solsynthese gew?hlt. Es zeigte sich, da? diese Methode in vielen F?llen eine Anwendung finden kann. Es
wurde auch gefunden, da? bei ganz bestimmten Bedingungen die kolloide Phase in Form von sch?n gebildeten Liesegang'schen Ringen
sich abscheiden kann. 相似文献
38.
39.
Nic Teclu 《Fresenius' Journal of Analytical Chemistry》1900,39(2):103-105
Ohne Zusammenfassung 相似文献
40.