851 research outputs found
On the Algebraic Structure of Petri Nets
No full textThis paper retraces, collects, and summarises the contributions of the author --- both individually and in collaboration with others --- on the theme of algebraic, compositional approaches to the semantics of Petri nets
The Algebraic Structure of Petri Nets
No full textThis survey retraces, collects, and summarises the contributions of the author --- both individually and in collaboration with others --- on the theme of algebraic, compositional approaches to the semantics of Petri nets
Oxidative activation of wood fibers for the manufacture of medium-density fiberboard (MDF)
Full text linkThe aim of this thesis work was to study the possibilities of radical formation in wood fiber surfaces to enable direct fiber-to-fiber adhesion by radical-based reactions in the manufacture of fibreboard, particularly medium-density fiberboard (MDF). The fibers were produced by defibration at high temperatures. Radical formation was achieved by treatment with laccase, treatment with Fenton's reagent, or gamma-irradiation.
High-temperature defibration was found to cause cleavage of interunit beta-aryl ether linkages of lignin, resulting in formation of mechanoradicals and phenolic hydroxyl groups. The proportion of water-extractable low-molecular weight lignin and hemicelluloses present in the fibers increased with an increase in defibration temperature.
In the laccase treatment of fibers in water suspension, much more radicals were formed in hardwood than in softwood fibers for fibers produced at equal temperature. Radical formation increased with increasing defibration temperature. The treatment of fibers with Fenton's reagent in water suspension resulted in the formation of similar numbers of radicals in hardwood and softwood fibers. Radical formation increased with increasing defibration temperature but not so drastically as with laccase treatments. Also the gamma-irradiated fibers contained large numbers of radicals. Their content increased as a function of increasing defibration temperature and was higher for hardwood than for softwood fibers.
The internal bond strength (IB) of fiberboards made from fibers treated with laccase or Fenton's reagent in the defibrator blowline improved with increasing defibration temperature. The IB of boards made from laccase-treated fibers correlated with the number of radicals formed in the fibers on laccase treatment in water suspension, indicating that adhesion in the boards was largely due to reactions of radicals on the fiber surfaces. The IB of boards made from fibers treated with Fenton's reagent also correlated with the radical content of the fibers, but this relationship was not as strong as with the laccase treatments. This suggests that bonding mechanisms other than radical coupling may have contributed significantly to adhesion. Gamma-irradiation of fibers before their fabrication into boards resulted in a marked increase in board IB, indicating that radicals play a significant role in the adhesion of boards made from gamma-irradiated fibers.reviewe
Lignin-Based Sunscreens:State-of-the-Art, Prospects and Challenges
Full text linkThis review covers the latest developments and challenges in the field of broad-spectrum sunscreens and how sunscreens based on lignin address their requirements in terms of sunlight protection, antioxidants, and preservative
Petri Inheritance: The Foundation of Nondeterministic, Concurrent Systems
Full text linkThe personal contacts of the first author with Carl Adam Petri and Petri nets are initially described and the role of Petri nets as a connector algebra is then examined
A group learning management method for intelligent tutoring systems
Full text linkIn this paper we propose a group management specification and execution method that seeks a compromise between simple course design and complex adaptive group interaction. This is achieved through an authoring method that proposes predefined scenarios to the author. These scenarios already include complex learning interaction protocols in which student and group models use and update are automatically included. The method adopts ontologies to represent domain and student models, and object Petri nets to specify the group interaction protocols. During execution, the method is supported by a multi-agent architecture
Improved Fire Retardancy of Cellulose Fibres via Deposition of Nitrogen-Modified Biopolyphenols
Full text linkDriven by concerns over the health and environmental impacts of currently used fire retardants (FRs), recent years have seen strong demand for alternative safer and sustainable bio-based FRs. In this paper, we evaluated the potential of nitrogen-modified biopolyphenols as FRs for cellulosic natural fibres that could be used in low-density cellulose insulations. We describe the preparation and characterisation of nitrogen-modified lignin and tannin containing over 10% nitrogen as well as the treatment of cellulose pulp fibres with combinations of lignin or tannin and adsorption-enhancing retention aids. Combining lignin or tannin with a mixture of commercial bio-based flocculant (cationised tannin) and anionic retention chemical allowed for a nearly fourfold increase in lignin adsorption onto cellulosic pulp. The nitrogen-modified biopolyphenols showed significant improvement in heat release parameters in micro-scale combustion calorimetry (MCC) testing compared with their unmodified counterparts. Moreover, the adsorption of nitrogen-modified lignin or tannin onto cellulose fibres decreased the maximum heat release rate and total heat release compared with cellulose reference by 15–23%. A further positive finding was that the temperature at the peak heat release rate did not change. These results show the potential of nitrogen-modified biopolyphenols to improve fire-retarding properties of cellulosic products
The Mediterranean Metaphor in Early Geopolitical Writings
Full text linkThe article focuses on the view of the Mediterranean in early geopolitical writings. Through this lens, it looks at the space metaphors and imaginative geographies that defined the core meanings of the Middle Sea over the last 200 years. The author discusses the role that the Enlightenment philosophy of history had in the shaping of classical geography. Moving on similar grounds, early geopolitical writers believed in the ‘force of history’ as a
generator of spatial order. They used episodes of the Mediterranean past as a parable for
the spatial articulation of contact, conflict and power in the overall ‘process of cvivilization’, and transformed the Middle Sea into a metaphor for the universal mission of Europe
Essentials of Petri nets
Full text linkThis contribution highlights some concepts and aspects of Petri nets that are frequently neglected, but that the authors consider important or interesting, or that Carl Adam Petri emphasized.19 pages, 26 figures, author prepared version of the talk given at the Sixth Advanced Course on Petri Nets, September 3-8, 2023, Toruń, Polan
State Estimation and Fault Detection Using Petri Nets
No full textThis extended abstract serves as a support for the plenary address given by the author at the 32nd International Conference on Application and Theory of Petri Nets and Concurrency
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