Accurate Ab-initio Predictions of III-V Direct-Indirect Band Gap Crossovers

We report the compositional dependence of the electronic band structure for a range of III-V alloys. Density functional theory with the PBE functional is insufficient to mimic the electronic gap energies at different symmetry points of the Brillouin zone. The HSE hybrid functional with screened exchange accurately reproduces the experimental band gaps and, more importantly, the alloy concentration of the direct-indirect gap crossovers for the III-V alloys studied here: AlGaAs, InAlAs, AlInP, InGaP, and GaAsP.Comment: 3 pages, 2 figure

Analysis of a Multimedia Stream using Stochastic Process Algebra

It is now well recognised that the next generation of distributed systems will be distributed multimedia systems. Central to multimedia systems is quality of service, which defines the non-functional requirements on the system. In this paper we investigate how stochastic process algebra can be used in order to determine the quality of service properties of distributed multimedia systems. We use a simple multimedia stream as our basic example. We describe it in the Stochastic Process Algebra PEPA and then we analyse whether the stream satisfies a set of quality of service parameters: throughput, end-to-end latency, jitter and error rates

Thermodynamic bounds on ultrasensitivity in covalent switching

Switch-like motifs are among the basic building blocks of biochemical networks. A common motif that can serve as an ultrasensitive switch consists of two enzymes acting antagonistically on a substrate, one making and the other removing a covalent modification. To work as a switch, such covalent modification cycles must be held out of thermodynamic equilibrium by continuous expenditure of energy. Here, we exploit the linear framework for timescale separation to establish tight bounds on the performance of any covalent-modification switch, in terms of the chemical potential difference driving the cycle. The bounds apply to arbitrary enzyme mechanisms, not just Michaelis-Menten, with arbitrary rate constants, and thereby reflect fundamental physical constraints on covalent switching.Comment: 29 pages, 6 figure

A Parallel Solver for Graph Laplacians

Problems from graph drawing, spectral clustering, network flow and graph partitioning can all be expressed in terms of graph Laplacian matrices. There are a variety of practical approaches to solving these problems in serial. However, as problem sizes increase and single core speeds stagnate, parallelism is essential to solve such problems quickly. We present an unsmoothed aggregation multigrid method for solving graph Laplacians in a distributed memory setting. We introduce new parallel aggregation and low degree elimination algorithms targeted specifically at irregular degree graphs. These algorithms are expressed in terms of sparse matrix-vector products using generalized sum and product operations. This formulation is amenable to linear algebra using arbitrary distributions and allows us to operate on a 2D sparse matrix distribution, which is necessary for parallel scalability. Our solver outperforms the natural parallel extension of the current state of the art in an algorithmic comparison. We demonstrate scalability to 576 processes and graphs with up to 1.7 billion edges.Comment: PASC '18, Code: https://github.com/ligmg/ligm

Can Deliberative Democracy Favor a Flourishing Relationship Between Humans and Carnivores?

There is considerable interest in improving participatory governance in decision-making processes for the conservation of biodiversity and management of conflicts between humans and wildlife. Among the various modes of participatory governance, deliberative democracy has received virtually no attention for decisions focused on conserving biodiversity. This is surprising given that deliberative democracy is an important branch of democratic theory and is associated with decision-making processes that have been successfully applied to a wide range of complicated decisions across diverse cultural settings. Moreover, deliberative democracy has several distinctive properties that would seem to make it well-suited for many conservation decisions. First, deliberative democracy is better-designed than other processes to handle cases where the object of conservation appears to be insufficiently valued by those who have the most detrimental impacts on its conservation. Second, deliberative democracy engenders a rich kind of representation and impartiality that is nearly impossible to achieve with participatory governance focused on managing conflicts among hyper-engaged stakeholders. Here, we review the principles of deliberative democracy, outline procedures for its application to carnivore conservation, and consider its likelihood to favor carnivore conservation