The weak choice principle WISC may fail in the category of sets

The set-theoretic axiom WISC states that for every set there is a set of surjections to it cofinal in all such surjections. By constructing an unbounded topos over the category of sets and using an extension of the internal logic of a topos due to Shulman, we show that WISC is independent of the rest of the axioms of the set theory given by a well-pointed topos. This also gives an example of a topos that is not a predicative topos as defined by van den Berg.Comment: v2 Change of title and abstract; v3 Almost completely rewritten after referee pointed out critical mistake. v4 Final version. Will be published in Studia Logica. License is CC-B

On the existence of bibundles

We consider the existence of bibundles, in other words locally trivial principal $G$ spaces with commuting left and right $G$ actions. We show that their existence is closely related to the structure of the group \Out(G) of outer automorphisms of $G$. We also develop a classifying theory for bibundles. The theory is developed in full generality for $(H, G)$ bibundles for a crossed-module $(H, G)$ and we show with examples the close links with loop group bundles.Comment: This version accepted to appear in the Proceedings of the London Mathematical Society. Various changes made at referee's suggestio

Are Bond Covenants Priced?

In this paper we ask the empirical question are bond covenants priced? Consistent with the Costly Contracting Hypothesis (CCH) developed by Smith and Warner (1979), we find that they are. We document a negative relation between the promised yield on corporate debt issues and the presence of covenants. We also find that loans made to high-growth firms are more likely to include restrictive covenants than loans made to low-growth firms. We show that the inclusion of a covenant varies systematically with macroeconomic factors as well as with supply-side factors, especially the identity of the lending institution. Finally, we show that consistent with the CCH, firms that elect to issue private rather than public debt are smaller, have greater growth opportunities, less long term debt, fewer tangible assets, and include more covenants in their debt agreements. An important byproduct of our analysis is to demonstrate empirically that the decision to include a covenant and the corresponding promised yield are determined simultaneously. Consequently, statistical models that ignore this simultaneity in analyzing the effects of covenants, like single-equation probit models, are misspecified and generate unreliable statisticsAgency Costs, Costly Contracting, Debt Covenants

Extending Whitney's extension theorem: nonlinear function spaces

We consider a global, nonlinear version of the Whitney extension problem for manifold-valued smooth functions on closed domains $C$, with non-smooth boundary, in possibly non-compact manifolds. Assuming $C$ is a submanifold with corners, or is compact and locally convex with rough boundary, we prove that the restriction map from everywhere-defined functions is a submersion of locally convex manifolds and so admits local linear splittings on charts. This is achieved by considering the corresponding restriction map for locally convex spaces of compactly-supported sections of vector bundles, allowing the even more general case where $C$ only has mild restrictions on inward and outward cusps, and proving the existence of an extension operator.Comment: 37 pages, 1 colour figure. v2 small edits, correction to Definition A.3, which makes no impact on proofs or results. Version submitted for publication. v3 small changes in response to referee comments, title extended. v4 crucial gap filled, results not affected. v5 final version to appear in Annales de l'Institut Fourie

Regulation of Arabidopsis 14-3-3 gene expression by GABA.

The function in plants of the non-protein amino acid, gamma-aminobutyric acid (GABA) is poorly understood. In this study, we show that GABA down-regulates the expression of a large sub-set of 14-3-3 gene family members in Arabidopsis thaliana seedlings in a calcium, ethylene and abscisic acid-dependent manner. Gene expression is not affected when seedlings are supplied with glutamate, a precursor of GABA. The repression of 14-3-3 gene expression by GABA is dependent on functional ethylene and abscisic acid signalling pathways, since the response is lost in the etr1-1, abi1-1 and abi2-1 mutants. Calcium measurements show that in contrast to glutamate, GABA does not elicit a cytoplasmic calcium elevation, suggesting that the GABA response is unlikely to be mediated by glutamate receptors, as has been suggested previously. We suggest that in addition to its role as a stress-related metabolite, GABA may regulate gene expression in Arabidopsis, including members of the 14-3-3 gene family

International labour mobility and unemployment

We develop a two-country labour-market model characterised by union wage-bargaining, in which the unemployed incur individual-specific costs of seeking work abroad. We explore the effects on equilibrium unemployment in each country of changes in union bargaining strength, the ratio of unemployment benefits to wages, and employers' willingness to hire foreign workers. Unfavourable labour-market institutions increase unemployment abroad as well as at home. We find that no country has an incentive to internationalise its own labour market unilaterally, because all the employment gains spill over abroad, which gives countries a strong incentive to co-ordinate on internationalisation.international labour mobility, unions, wage bargaining, globalization, unemployment

Plant methods:putting the spotlight on technological innovation in the plant sciences.

Plant Methods is a new journal for plant biologists, specialising in the rapid publication of peer-reviewed articles with a focus on technological innovation in the plant sciences. The aim of Plant Methods is to stimulate the development and adoption of new and improved techniques and research tools in plant biology. We hope to promote more consistent standards in the plant sciences, and make readily accessible laboratory and computer-based research tools available to the whole community. This will be achieved by publishing Research articles, Methodology papers and Reviews using the BioMed Central Open Access publishing model. The journal is supported by a prestigious editorial board, whose members all recognise the importance of technological innovation as a driver for basic science