17 research outputs found
A Mathematical Model of Package Management Systems -- from General Event Structures to Antimatroids
This paper brings mathematical tools to bear on the study of package
dependencies in software systems. We introduce structures known as Dependency
Structures with Choice (DSC) that provide a mathematical account of such
dependencies, inspired by the definition of general event structures in the
study of concurrency. We equip DSCs with a particular notion of morphism and
show that the category of DSCs is isomorphic to the category of antimatroids.
We study the exactness properties of these equivalent categories, and show that
they are finitely complete, have finite coproducts but not all coequalizers.
Further, we construct a functor from a category of DSCs equipped with a certain
subclass of morphisms to the opposite of the category of finite distributive
lattices, making use of a simple finite characterization of the Bruns-Lakser
completion, and finally, we introduce a formal account of versions of packages
and introduce a mathematical account of package version-bound policies.Comment: Version 2: grammatical improvement
Expansion-induced contribution to the precession of binary orbits
We point out the existence of new effects of global spacetime expansion on
local binary systems. In addition to a possible change of orbital size, there
is a contribution to the precession of elliptic orbits, to be added to the
well-known general relativistic effect in static spacetimes, and the
eccentricity can change. Our model calculations are done using geodesics in a
McVittie metric, representing a localized system in an asymptotically
Robertson-Walker spacetime; we give a few numerical estimates for that case,
and indicate ways in which the model should be improved.Comment: revtex, 7 pages, no figures; revised for publication in Classical and
Quantum Gravity, with minor changes in response to referees' comment
The fog of copyleft
In this paper we question the notion of using copyleft, in its current form, as the principle contractual framework of free culture. We argue that there are many flaws in the copyleft concept and its execution which are beginning to immerse free culture activity in a “fog” of risk and uncertainty. The main feature of copyleft which is causing problems is its “license lock” aspect, while the main problem with the execution of copyleft is the exercise of too much control by license authors. We give examples from our own experiences with PlanetMath, as well as the free culture community in general, to illustrate. Finally, we provide a wide array of solutions to the problem, ranging from immediately usable legalistic ones to long–term societal transformations
The evolutionary dynamics of metabolic protocells.
Protocell multilevel selection models have been proposed to study the evolutionary dynamics of vesicles encapsulating a set of replicating, competing and mutating sequences. The frequency of the different sequence types determines protocell survival through a fitness function. One of the defining features of these models is the genetic load generated when the protocell divides and its sequences are assorted between the offspring vesicles. However, these stochastic assortment effects disappear when the redundancy of each sequence type is sufficiently high. The fitness dependence of the vesicle with its sequence content is usually defined without considering a realistic account on how the lower level dynamics would specify the protocell fitness. Here, we present a protocell model with a fitness function determined by the output flux of a simple metabolic network with the aim of understanding how the evolution of both kinetic and topological features of metabolism would have been constrained by the particularities of the protocell evolutionary dynamics. In our model, the sequences inside the vesicle are both the carriers of information and Michaelis-Menten catalysts exhibiting saturation. We found that the saturation of the catalysts controlling the metabolic fluxes, achievable by modifying the kinetic or stoichiometric parameters, provides a mechanism to ameliorate the assortment load by increasing the redundancy of the catalytic sequences required to achieve the maximum flux. Regarding the network architecture, we conclude that combinations of parallel network motifs and bimolecular catalysts are a robust way to increase the complexity of the metabolism enclosed by the protocell