Confluence versus Ample Sets in Probabilistic Branching Time

To improve the efficiency of model checking in general, and probabilistic model checking in particular, several reduction techniques have been introduced. Two of these, confluence reduction and partial-order reduction by means of ample sets, are based on similar principles, and both preserve branching-time properties for probabilistic models. Confluence reduction has been introduced for probabilistic automata, whereas ample set reduction has been introduced for Markov decision processes. In this presentation we will explore the relationship between confluence and ample sets. To this end, we redefine confluence reduction to handle MDPs. We show that all non-trivial ample sets consist of confluent transitions, but that the converse is not true. We also show that the two notions coincide if the definition of confluence is restricted, and point out the relevant parts where the two theories differ. The results we present also hold for non-probabilistic models, as our theorems can just as well be applied in a context where all transitions are non-probabilistic. To show a practical application of our results, we adapt a state space generation technique based on representative states, already known in combination with confluence reduction, so that it can also be applied with partial-order reduction

Reversible gelation and dynamical arrest of dipolar colloids

We use molecular dynamics simulations of a simple model to show that dispersions of slightly elongated colloidal particles with long-range dipolar interactions, like ferrofluids, can form a physical (reversible) gel at low volume fractions. On cooling, the particles first self-assemble into a transient percolating network of cross-linked chains, which, at much lower temperatures, then undergoes a kinetic transition to a dynamically arrested state with broken ergodicity. This transition from a transient to a frozen gel is characterised by dynamical signatures reminiscent of jamming in much denser dispersions.Comment: 6 pages, 7 figure

Trust and the Decision to Outsource: Affective Responses and Cognitive Processes

Many of the various forms of cooperative strategy that firms are pursuing in today's economy entail the placing of important business functions in the hands of a partner. This paper examines the role of trust in the decision by a producer to place the marketing function in the hands of another entity, namely a cooperative. Although others have studied the effect of what may be termed general trust on inter-organizational relationships, few have examined the antecedents of that trust. We propose a model in which affective responses and cognitive processes are precursors to a sense of general trust, which, in turn, influences the outsourcing decision. These affective responses and cognitive processes have both direct and indirect (mediated) effects on the decision to place an important function in the hands of another entity. Perceptions of partner expertise in the business function at hand and the perceived need for the focal firm to maintain control over that function are also considered in the model. The model is tested in a somewhat novel context: the decision of cotton producers to outsource the marketing of their cotton fiber. Using survey data gathered from the actual decision-maker, and structural equations modeling, we find that the inclusion of affective responses and cognitive processes in our model produces a richer explanation of the outsourcing decision. The differences between the effects of affective responses and cognitive processes have potentially important implications for managers engaged in cooperative strategies and for the scholars who study them.Agribusiness,

A spectroscopic binary in the Hercules dwarf spheroidal galaxy

We present the radial velocity curve of a single-lined spectroscopic binary in the faint Hercules dwarf spheroidal (dSph) galaxy, based on 34 individual spectra covering more than two years of observations. This is the first time that orbital elements could be derived for a binary in a dSph. The system consists of a metal-poor red giant and a low-mass companion, possibly a white dwarf, with a 135-days period in a moderately eccentric ($e=0.18$) orbit. Its period and eccentricity are fully consistent with metal-poor binaries in the Galactic halo, while the projected semimajor axis is small, at $a_p$ sin$i$ = 38 R$_{sun}$. In fact, a very close orbit could inhibit the production of heavier elements through $s$-process nucleosynthesis, leading to the very low abundances of neutron-capture elements that are found in this star. We discuss the further implications for the chemical enrichment history of the Hercules dSph, but find no compelling binary scenario that could reasonably explain the full, peculiar abundance pattern of the Hercules dSph galaxy.Comment: 7 pages, 3 figures, accepted for publication in the Astrophysical Journa

The structure and assembly history of cluster-size haloes in Self-Interacting Dark Matter

We perform dark-matter-only simulations of 28 relaxed massive cluster-sized haloes for Cold Dark Matter (CDM) and Self-Interacting Dark Matter (SIDM) models, to study structural differences between the models at large radii, where the impact of baryonic physics is expected to be very limited. We find that the distributions for the radial profiles of the density, ellipsoidal axis ratios, and velocity anisotropies ($\beta$) of the haloes differ considerably between the models (at the $\sim1\sigma$ level), even at $\gtrsim10\%$ of the virial radius, if the self-scattering cross section is $\sigma/m_\chi=1$ cm$^2$ gr$^{-1}$. Direct comparison with observationally inferred density profiles disfavours SIDM for $\sigma/m_\chi=1$ cm$^2$ gr$^{-1}$, but in an intermediate radial range ($\sim3\%$ of the virial radius), where the impact of baryonic physics is uncertain. At this level of the cross section, we find a narrower $\beta$ distribution in SIDM, clearly skewed towards isotropic orbits, with no SIDM (90\% of CDM) haloes having $\beta>0.12$ at $7\%$ of the virial radius. We estimate that with an observational sample of $\sim30$ ($\sim10^{15}$ M$_\odot$) relaxed clusters, $\beta$ can potentially be used to put competitive constraints on SIDM, once observational uncertainties improve by a factor of a few. We study the suppression of the memory of halo assembly history in SIDM clusters. For $\sigma/m_\chi=1$ cm$^2$ gr$^{-1}$, we find that this happens only in the central halo regions ($\sim1/4$ of the scale radius of the halo), and only for haloes that assembled their mass within this region earlier than a formation redshift $z_f\sim2$. Otherwise, the memory of assembly remains and is reflected in ways similar to CDM, albeit with weaker trends.Comment: 15 pages, 15 figures. Submitted to MNRAS. Revisions: added new figure with an observational comparison of density profiles, improvements and corrections to the section on velocity anisotropie

Equal Voice by Half Measures

In democratic theory, the ballot is the most perfect expression of the democratic commitment to the moral equality of persons. Every citizen, whether old or young, rich or poor, sophisticated or simple, enjoys the same endowment in an election: a single vote. The ballot not only gives citizens their voice in government, it also makes their voices equal. In practice, however, democracies have erected all sorts of impediments to the ideal of equal voice, such as restrictions on suffrage, legislative malapportionments, and discriminatory gerrymanders. Among the most egregious impediments, however, are surely the systems of indirect election purported to filter and to refine the voice of the people. The Electoral College is one such system. This Commentary examines the effects of that system and the proposed reforms to it on the prospect of equal voice in elections

Modeling and Optimization of Rare Earth Element Chromatography

The Rare Earth Elements are a group of metals, that are of growing technical and economical importance. Current separation techniques can be detrimental to the environment, and a clean technology for separation has been devised, based on analytical chromatography of the REEs. The thesis presents column preparation and impregnation to give desired properties of the separation system, experimental and model based optimization for operating points and design of a chromatography step for separating REEs

Equal Voice by Half Measures

In democratic theory, the ballot is the most perfect expression of the democratic commitment to the moral equality of persons. Every citizen, whether old or young, rich or poor, sophisticated or simple, enjoys the same endowment in an election: a single vote. The ballot not only gives citizens their voice in government, it also makes their voices equal. In practice, however, democracies have erected all sorts of impediments to the ideal of equal voice, such as restrictions on suffrage, legislative malapportionments, and discriminatory gerrymanders. Among the most egregious impediments, however, are surely the systems of indirect election purported to filter and to refine the voice of the people. The Electoral College is one such system. This Commentary examines the effects of that system and the proposed reforms to it on the prospect of equal voice in elections