The spectrum of the Hilbert space valued second derivative with general self-adjoint boundary conditions

We consider a large class of self-adjoint elliptic problem associated with the second derivative acting on a space of vector-valued functions. We present two different approaches to the study of the associated eigenvalues problems. The first, more general one allows to replace a secular equation (which is well-known in some special cases) by an abstract rank condition. The latter seems to apply particularly well to a specific boundary condition, sometimes dubbed "anti-Kirchhoff" in the literature, that arise in the theory of differential operators on graphs; it also permits to discuss interesting and more direct connections between the spectrum of the differential operator and some graph theoretical quantities. In either case our results yield, among other, some results on the symmetry of the spectrum

Last in, first out? Estimating the effect of seniority rules in Sweden

In this paper we investigate whether a relaxation in seniority rules (the ‘last-in-first-out’ principle) had any effect on firms’ employment behaviour. Seniority rules exist in several countries and, like Sweden, most European countries have a more lenient employment protection for firms below a certain size. Despite the fact that small firms represent a large share of all firms and stand for a substantial share of total employment, there is limited knowledge of how such exemption rules affect firms’ employment behaviour — the consequences of seniority rules on firms’ employment behaviour have not been examined at all. Using data including the population of firms matched with the population of workers for the period 1999–2002, we do not find any general effects on worker flows or on hires and separations. The only exception is a tendency of an increase in the share of separations for older workers and workers with longer seniority. The result points to the importance of considering in detail how legislation is formulated and how it works in practice.Employment protection; employment change; hires; separations; regression discontinuity

Uncertainty, Climate Change and the Global Economy

The paper illustrates how one may assess our comprehensive uncertainty about the various relations in the entire chain from human activity to climate change. Using a modified version of the RICE model of the global economy and climate, we perform Monte Carlo simulations, where full sets of parameters in the model’s most important equations are drawn randomly from pre-specified distributions, and present results in the forms of fan charts and histograms. Our results suggest that under a Business-As-Usual scenario, the median increase of global mean temperature in 2105 relative to 1900 will be around 4.5 C. The 99 percent confidence interval ranges from 3.0 C to 6.9 C. Uncertainty about socio-economic drivers of climate change lie behind a non-trivial part of this uncertainty about global warming.Climate-economy models; Global warming; Monte Carlo study

Harmonic functions on metric graphs under the anti-Kirchhoff law

When does an infinite metric graph allow nonconstant bounded harmonic functions under the anti-Kirchhoff transition law? We give a complete answer to this question in the cases where Liouville’s theorem holds, for trees, for graphs with finitely many essential ramification nodes and for generalized lattices. It turns out that the occurrence of nonconstant bounded harmonic functions under the anti-Kirchhoff law differs strongly from the one under the classical continuity condition combined with the Kirchhoff incident flow law.Peer ReviewedPostprint (author's final draft

The Complexity of Finding Small Triangulations of Convex 3-Polytopes

The problem of finding a triangulation of a convex three-dimensional polytope with few tetrahedra is proved to be NP-hard. We discuss other related complexity results.Comment: 37 pages. An earlier version containing the sketch of the proof appeared at the proceedings of SODA 200

REIT Pricing Efficiency; Should Investors Still Be Concerned?

This study examines the impact of the REIT boom on the market microstructure of REIT common stocks. We analyze NYSE-traded REITs during the pre-boom period (1992) and the post-boom period (1994), and find significant reductions in bid/ask spreads over the period. We also find that the bid/ask spread differential between REITs and non-REITs has been roughly halved between 1991 and 1994. These reductions provide a direct benefit to REIT investors in terms of reduction in transaction costs and improved liquidity, and suggest that the level of uncertainty on the part of the REIT specialist has been reduced.

An Examination of Informed Traders and the Market Microstructure of Real Estate Investment Trusts

A significant body of research exists documenting that REITs perform differently from other types of equity securities, although the reasons for these differences are unclear. This study examines the intraday trading behavior of Real Estate Investment Trusts (REITs). Specifically, intraday REIT returns, volume, trading activity, and bid/ask spread are examined in an attempt to better understand the patterns of intraday information flow for a sample of REITs trading on the NYSE. After controlling for differences in market capitalization, share price, and institutional holdings, this paper analyzes differences between REITs and non-REITs, and between REITs that are widely held by institutions and those that are not. The results suggest that, as a group, REITs exhibit lower average volumes and number of trades than do similar non-REITs. In addition, the findings suggest that mortgage REITs trade at spreads that are wider. Surprisingly, the analysis of institutional ownership suggests that equity REITs that are widely held by institutions exhibit the largest divergence from non-REITs in terms of both intraday trading activity and volume, but at the same time trade closer to non-REITs in terms of bid/ask spread. Overall, the results of this study confirm that REITs are treated differently by investors than similar non-REITs, and the institutional ownership findings suggest that trading activity is less important as a determinant of REIT performance than is the level of institutional ownership.