The Demand for Forest Sector Products

In this paper the issue of demand analysis for the forest sector product is analyzed from a theoretical and an econometric points of view. An intermediary demand approach is advocated and applied. For the econometric estimates presented a database for Canada is used. The results indicate that the dual (cost) procedure to intermediate demand function estimation is preferable to the use of production functions to generate demand equations

One component of the curvature tensor of a Lorentzian manifold

The holonomy algebra \g of an $n+2$-dimensional Lorentzian manifold $(M,g)$ admitting a parallel distribution of isotropic lines is contained in the subalgebra \simil(n)=(\Real\oplus\so(n))\zr\Real^n\subset\so(1,n+1). An important invariant of \g is its \so(n)-projection \h\subset\so(n), which is a Riemannian holonomy algebra. One component of the curvature tensor of the manifold belongs to the space \P(\h) consisting of linear maps from \Real^n to \h satisfying an identity similar to the Bianchi one. In the present paper the spaces \P(\h) are computed for each possible \h. This gives the complete description of the values of the curvature tensor of the manifold $(M,g)$. These results can be applied e.g. to the holonomy classification of the Einstein Lorentzian manifolds.Comment: An extended version of a part from arXiv:0906.132

Unimodular Gravity and Averaging

The question of the averaging of inhomogeneous spacetimes in cosmology is important for the correct interpretation of cosmological data. In this paper we suggest a conceptually simpler approach to averaging in cosmology based on the averaging of scalars within unimodular gravity. As an illustration, we consider the example of an exact spherically symmetric dust model, and show that within this approach averaging introduces correlations (corrections) to the effective dynamical evolution equation in the form of a spatial curvature term.Comment: 10 page

The Evolution of Λ\Lambda Black Holes in the Mini-Superspace Approximation of Loop Quantum Gravity

Using the improved quantization technique to the mini-superspace approximation of loop quantum gravity, we study the evolution of black holes supported by a cosmological constant. The addition of a cosmological constant allows for classical solutions with planar, cylindrical, toroidal and higher genus black holes. Here we study the quantum analog of these space-times. In all scenarios studied, the singularity present in the classical counter-part is avoided in the quantized version and is replaced by a bounce, and in the late evolution, a series of less severe bounces. Interestingly, although there are differences during the evolution between the various symmetries and topologies, the evolution on the other side of the bounce asymptotes to space-times of Nariai-type, with the exception of the planar black hole analyzed here, whose $T$-$R$=constant subspaces seem to continue expanding in the long term evolution. For the other cases, Nariai-type universes are attractors in the quantum evolution, albeit with different parameters. We study here the quantum evolution of each symmetry in detail.Comment: 26 pages, 7 figures.V2 has typos corrected, references added, and a more careful analysis of the planar case. Accepted for publication in Physical Review

Derived Demand and Substitution for Forest Products Based on Cobb-Douglas and CES Production Functions

Standard production theory with Cobb-Douglas and CES production functions is applied to derive demand functions for forest products. Time-series data for 1961-1978 from Canadian construction sector is employed for estimation, and sensitivity of the demand forecast is tested with respect to the choice of the production function

On supersymmetric Einstein-Weyl spaces

We consider weighted parallel spinors in Lorentzian Weyl geometry in arbitrary dimensions, choosing the weight such that the integrability condition for the existence of such a spinor, implies the geometry to be Einstein-Weyl. We then use techniques developed for the classification of supersymmetric solutions to supergravity theories to characterise those Lorentzian EW geometries that allow for a weighted parallel spinor, calling the resulting geometries supersymmetric. The overall result is that they are either conformally related to ordinary geometries admitting parallel spinors (w.r.t. the Levi-Civita connection) or are conformally related to certain Kundt spacetimes. A full characterisation is obtained for the 4 and 6 dimensional cases.Comment: 17 pages, version to be published in JG

General Kundt spacetimes in higher dimensions

We investigate a general metric of the Kundt class of spacetimes in higher dimensions. Geometrically, it admits a non-twisting, non-shearing and non-expanding geodesic null congruence. We calculate all components of the curvature and Ricci tensors, without assuming any specific matter content, and discuss algebraic types and main geometric constraints imposed by general Einstein's field equations. We explicitly derive Einstein-Maxwell equations, including an arbitrary cosmological constant, in the case of vacuum or possibly an aligned electromagnetic field. Finally, we introduce canonical subclasses of the Kundt family and we identify the most important special cases, namely generalised pp-waves, VSI or CSI spacetimes, and gyratons.Comment: 15 page