Coexistence diameter in two-dimensional colloid-polymer mixtures

We demonstrate that the law of the rectilinear coexistence diameter in two-dimensional (2D) mixtures of non-spherical colloids and non-adsorbing polymers is violated. Upon approach of the critical point, the diameter shows logarithmic singular behavior governed by a term t ln(t), with t the relative distance from the critical point. No sign of a term t^2b could be detected, with b the critical exponent of the order parameter, indicating a very weak or absent Yang-Yang anomaly. Our analysis thus reveals that non-spherical particle shape alone is not sufficient for the formation of a pronounced Yang-Yang anomaly in the critical behavior of fluids.Comment: 4 pages, 4 figures, to appear in Phys. Rev. E (R

Combining Insertion and Deletion in RNA-editing Preserves Regularity

Inspired by RNA-editing as occurs in transcriptional processes in the living cell, we introduce an abstract notion of string adjustment, called guided rewriting. This formalism allows simultaneously inserting and deleting elements. We prove that guided rewriting preserves regularity: for every regular language its closure under guided rewriting is regular too. This contrasts an earlier abstraction of RNA-editing separating insertion and deletion for which it was proved that regularity is not preserved. The particular automaton construction here relies on an auxiliary notion of slice sequence which enables to sweep from left to right through a completed rewrite sequence.Comment: In Proceedings MeCBIC 2012, arXiv:1211.347

Probing the evolving massive star population in Orion with kinematic and radioactive tracers

We assemble a census of the most massive stars in Orion, then use stellar isochrones to estimate their masses and ages, and use these results to establish the stellar content of Orion's individual OB associations. From this, our new population synthesis code is utilized to derive the history of the emission of UV radiation and kinetic energy of the material ejected by the massive stars, and also follow the ejection of the long-lived radioactive isotopes 26Al and 60Fe. In order to estimate the precision of our method, we compare and contrast three distinct representations of the massive stars. We compare the expected outputs with observations of 26Al gamma-ray signal and the extent of the Eridanus cavity. We find an integrated kinetic energy emitted by the massive stars of 1.8(+1.5-0.4)times 10^52 erg. This number is consistent with the energy thought to be required to create the Eridanus superbubble. We also find good agreement between our model and the observed 26Al signal, estimating a mass of 5.8(+2.7-2.5) times 10^-4 Msol of 26Al in the Orion region. Our population synthesis approach is demonstrated for the Orion region to reproduce three different kinds of observable outputs from massive stars in a consistent manner: Kinetic energy as manifested in ISM excavation, ionization as manifested in free-free emission, and nucleosynthesis ejecta as manifested in radioactivity gamma-rays. The good match between our model and the observables does not argue for considerable modifications of mass loss. If clumping effects turn out to be strong, other processes would need to be identified to compensate for their impact on massive-star outputs. Our population synthesis analysis jointly treats kinematic output and the return of radioactive isotopes, which proves a powerful extension of the methodology that constrains feedback from massive stars.Comment: Accepted for publication in A&A, 10 page

MODELLING LONG-TERM COMMODITIES: THE DEVELOPMENT OF A SIMULATION MODEL FOR THE SOUTH AFRICAN WINE INDUSTRY WITHIN A PARTIAL EQUILIBRIUM FRAMEWORK

Econometric demand and supply models of agricultural commodities and crops have been around for a long time with extensive research and adaptations being made in the grain and livestock sectors. This much attention has, however, not been afforded to long term commodities. This paper presents a partial equilibrium framework for modelling long term commodities using the South African wine industry as an example. The model structure and important assumptions are presented, after which the usefulness of the model is tested in the form of baseline projections and the analysis of a typical “what if” question. The wine model presented in this paper is housed and maintained in the Bureau for Food and Agricultural Policy (BFAP) at the Department of Agriculture, Western Cape and the Universities of Pretoria and Stellenbosch.wine market, South Africa, partial equilibrium model, Crop Production/Industries, Demand and Price Analysis,

An explanation for the curious mass loss history of massive stars: from OB stars, through Luminous Blue Variables to Wolf-Rayet stars

The stellar winds of massive stars show large changes in mass-loss rates and terminal velocities during their evolution from O-star through the Luminous Blue Variable phase to the Wolf-Rayet phase. The luminosity remains approximately unchanged during these phases. These large changes in wind properties are explained in the context of the radiation driven wind theory, of which we consider four different models. They are due to the evolutionary changes in radius, gravity and surface composition and to the change from optically thin (in continuum) line driven winds to optically thick radiation driven winds.Comment: Accepted for publication in Astronomy and Astrophysics (Letter to the Editor

A companion to coalgebraic weak bisimulation for action-type systems

We propose a coalgebraic definition of weak bisimulation for classes of coalgebras obtained from bifunctors in the category Set. Weak bisim-ilarity for a system is obtained as strong bisimilarity of a transformed system. The particular transformation consists of two steps: First, the behavior on actions is lifted to behavior on finite words. Second, the behavior on finite words is taken modulo the hiding of internal or in-visible actions, yielding behavior on equivalence classes of words closed under silent steps. The coalgebraic definition is validated by two cor-respondence results: one for the classical notion of weak bisimulation of Milner, another for the notion of weak bisimulation for generative probabilistic transition systems as advocated by Baier and Hermanns.

RACIAL DISCRIMINATION IN HIRE/PURCHASE LENDING IN APARTHEID SOUTH AFRICA

A partial-observability model finds evidence of racial discrimination by retailers of consumer durables in apartheid South Africa. In particular, black households are 13 percentage points more likely to demand a hire/purchase loan but not to have one supplied than are other households, all else equal.Consumer finance, disequilibrium models, racial discrimination, truncated and censored models, South Africa, Financial Economics,