199 research outputs found
Algebraic Theories over Nominal Sets
We investigate the foundations of a theory of algebraic data types with
variable binding inside classical universal algebra. In the first part, a
category-theoretic study of monads over the nominal sets of Gabbay and Pitts
leads us to introduce new notions of finitary based monads and uniform monads.
In a second part we spell out these notions in the language of universal
algebra, show how to recover the logics of Gabbay-Mathijssen and
Clouston-Pitts, and apply classical results from universal algebra.Comment: 16 page
Relation Liftings on Preorders and Posets
The category Rel(Set) of sets and relations can be described as a category of
spans and as the Kleisli category for the powerset monad. A set-functor can be
lifted to a functor on Rel(Set) iff it preserves weak pullbacks. We show that
these results extend to the enriched setting, if we replace sets by posets or
preorders. Preservation of weak pullbacks becomes preservation of exact lax
squares. As an application we present Moss's coalgebraic over posets
Semantics of Higher-Order Recursion Schemes
Higher-order recursion schemes are recursive equations defining new
operations from given ones called "terminals". Every such recursion scheme is
proved to have a least interpreted semantics in every Scott's model of
\lambda-calculus in which the terminals are interpreted as continuous
operations. For the uninterpreted semantics based on infinite \lambda-terms we
follow the idea of Fiore, Plotkin and Turi and work in the category of sets in
context, which are presheaves on the category of finite sets. Fiore et al
showed how to capture the type of variable binding in \lambda-calculus by an
endofunctor H\lambda and they explained simultaneous substitution of
\lambda-terms by proving that the presheaf of \lambda-terms is an initial
H\lambda-monoid. Here we work with the presheaf of rational infinite
\lambda-terms and prove that this is an initial iterative H\lambda-monoid. We
conclude that every guarded higher-order recursion scheme has a unique
uninterpreted solution in this monoid
Relation lifting, with an application to the many-valued cover modality
We introduce basic notions and results about relation liftings on categories
enriched in a commutative quantale. We derive two necessary and sufficient
conditions for a 2-functor T to admit a functorial relation lifting: one is the
existence of a distributive law of T over the "powerset monad" on categories,
one is the preservation by T of "exactness" of certain squares. Both
characterisations are generalisations of the "classical" results known for set
functors: the first characterisation generalises the existence of a
distributive law over the genuine powerset monad, the second generalises
preservation of weak pullbacks. The results presented in this paper enable us
to compute predicate liftings of endofunctors of, for example, generalised
(ultra)metric spaces. We illustrate this by studying the coalgebraic cover
modality in this setting.Comment: 48 pages, accepted for publication in LMC
Hydrothermal carbonization and torrefaction of cabbage waste
ArticleIn recent years, waste biomass has been increasingly becoming an energy source. The
utilization of biomass includes a number of potential treatments: thermochemical,
physicochemical and biochemical. In the food industry, significant amounts of biodegradable
wastes are produced which have to be quickly treated to not pose an environmental problem. In
this work cabbage waste (Brassica oleracea var. capitata) was treated by hydrothermal
carbonization and torrefaction.
Hydrothermal carbonization experiments were carried out in a pressure reactor vessel
Berghof BR-300 (inner volume 400 mL, temperature regulation by Berghof BTC 3000). The
carbonization took place at target temperatures 180 °C and 225 °C. Torrefaction tests were
carried out in a thermogravimetric programmable oven LECO TGA701 under nitrogen
atmosphere at temperatures 225 °C, 250 °C and 275 °C. The residence time was 30 min for both
processes. Proximate and elemental composition, as well as calorific value was analysed in all
samples. To express the influence of the treatments on combustion behaviour, stoichiometric
combustion calculations were performed.
The analyses show a positive effect of both torrefaction and hydrothermal carbonization on fuel
properties in the samples. Most obvious is the reduction in oxygen content which depends on the
process temperature. After hydrothermal carbonization at 225 °C the oxygen content was lowered
by 46.7%. The net calorific value increased proportionally with temperature in both processes.
After hydrothermal carbonization at 225 °C the net calorific value increased on average by
3 MJ kg-1
to 20.89 MJ kg-1
. Both tested processes significantly increased the fuel value of this
biodegradable waste
Specialty types of waste paper as an energetic commodity
ArticleThe collection and recycling rate of paper and paper packaging material has been on a
rise. From 2010 to 2016 in Czech Republic, the recycled amount of all paper went up by 32%,
while the share of energy use in waste paper utilization decreased f
rom 5.5% to 3.8%. However,
not every paper and cardboard product can be recycled, and some are rejected from the recycling
stream. Recycling specialty types of paper with other grades of recyclable paper is often not
possible and their production is not hi
gh enough for their separate recycling to be feasible. If
material utilization is not feasible then within the waste hierarchy the next best treatment is their
energy utilization. Therefore, this article evaluates selected types of specialty paper for thei
r
energy content. They were silicone coated papers, polymer coated papers, and paper cores. For
all samples proximate, elemental and calorimetric analyses were determined and based on them
stoichiometric combustion calculations were performed. Silicon coat
ed papers fared generally
well having small to reasonable ash content 1
–
10% and net calorific value from 15.10 to 17.10
MJ
kg
-
1
on dry basis. Polymer coated papers had ash content around 6% and net calorific value
from value from 16.29 to 22.98
MJ
kg
-
1
on
dry basis. With the exception of paper cores and self
-
copying paper, all evaluated paper types could be recommended as a component in refuse derived
fuels. The least suitable samples were paper cores with nearly 20% wt. of ash and net calorific
value 12.45
MJ
kg
-
1
on dry basis
How Iterative are Iterative Algebras?
AbstractIterative algebras are defined by the property that every guarded system of recursive equations has a unique solution. We prove that they have a much stronger property: every system of recursive equations has a unique strict solution. And we characterize those systems that have a unique solution in every iterative algebra
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