A new mixed-integer programming model for harvest scheduling subject to maximum area restrictions

Forest ecosystem management often requires spatially explicit planning because the spatial arrangement of harvests has become a critical economic and environmental concern. Recent research on exact methods has addressed both the design and the solution of forest management problems with constraints on the clearcut size, but where simultaneously harvesting two adjacent stands in the same period does not necessarily exceed the maximum opening size. Two main integer programming approaches have been proposed for this area restriction model. However, both encompass an exponential number of variables or constraints. In this work, we present a new integer programming model with a polynomial number of variables and constraints. Branch and bound is used to solve it. The model was tested with both real and hypothetical forests ranging from 45 to 1,363 polygons. Results show that the proposed model’s solutions were within or slightly above 1% of the optimal solution and were obtained in a short computation time

Formulations of the 3+1 evolution equations in curvilinear coordinates

Following Brown, in this paper we give an overview of how to modify standard hyperbolic formulations of the 3+1 evolution equations of General Relativity in such a way that all auxiliary quantities are true tensors, thus allowing for these formulations to be used with curvilinear sets of coordinates such as spherical or cylindrical coordinates. After considering the general case for both the Nagy-Ortiz-Reula (NOR) and the Baumgarte-Shapiro-Shibata-Nakamura (BSSN) formulations, we specialize to the case of spherical symmetry and also discuss the issue of regularity at the origin. Finally, we show some numerical examples of the modified BSSN formulation at work in spherical symmetry.Comment: 19 pages, 12 figure

On the importance of relative permeability data for estimating CO2 injectivity in brine aquifers

Performance assessment of possible CO2 storage schemes is often investigated through numerical simulation of the CO2 injection process. An important criterion of interest is the maximum sustainable injection rate. Relevant numerical models generally employ a multi-phase extension to Darcy's law, requiring data concerning the evolution of relative permeability for CO2 and brine mixtures with increasing CO2 saturation. Relative permeability data is acutely scarce for many geographical regions of concern and often cited as a major source of uncertainty. However, such data is expensive and time consuming to acquire. With a view to improving our understanding concerning the significance of relative permeability uncertainty on injectivity, this article presents a sensitivity analysis of sustainable CO2 injection rate with respect to permeability, porosity and relative permeability. Based on available relative permeability data obtained from 25 sandstone and carbonate cores discussed in the literature, injectivity uncertainty associated with relative permeability is found to be as high as ±57% for open aquifers and low permeability closed aquifers (100 mD), aquifer compressibility plays a more important role and the uncertainty due to relative permeability is found to reduce to ±6%

Interaction potentials for soft and hard ellipsoids

Using results from colloid science we derive interaction potentials for computer simulations of mixtures of soft or hard ellipsoids of arbitrary shape and size. Our results are in many respects reminicent of potentials of the Gay-Berne type but have a well-defined microscopic interpretation and no adjustable parameters. Since our potentials require the calculation of similar variables, the modification of existing simulation codes for Gay-Berne potentials is straightforward. The computational performance should remain unaffected.Comment: 8 pages, 4 figure

The Network of Scientific Collaborations within the European Framework Programme

We use the emergent field of Complex Networks to analyze the network of scientific collaborations between entities (universities, research organizations, industry related companies,...) which collaborate in the context of the so-called Framework Programme. We demonstrate here that it is a scale--free network with an accelerated growth, which implies that the creation of new collaborations is encouraged. Moreover, these collaborations possess hierarchical modularity. Likewise, we find that the information flow depends on the size of the participants but not on geographical constraints.Comment: 13 pages, 6 figure

Lameness in cattle: recent research to inform clinical practice

Lameness in cattle has significant consequences for welfare, health and productivity. More research is now being done on lameness and this article, the first in a two-part series, provides an update on research-based advances in the field published from around the world over the past five years. These developments have improved our understanding of lameness in cattle and can inform clinical practice and the control of lameness on-farm. The second article, to be published in a subsequent issue of In Practice, will cover the understanding and management of claw health and claw horn lesions

A New Cosmological Scenario in String Theory

We consider new cosmological solutions with a collapsing, an intermediate and an expanding phase. The boundary between the expanding (collapsing) phase and the intermediate phase is seen by comoving observers as a cosmological past (future) horizon. The solutions are naturally embedded in string and M-theory. In the particular case of a two-dimensional cosmology, space-time is flat with an identification under boost and translation transformations. We consider the corresponding string theory orbifold and calculate the modular invariant one-loop partition function. In this case there is a strong parallel with the BTZ black hole. The higher dimensional cosmologies have a time-like curvature singularity in the intermediate region. In some cases the string coupling can be made small throughout all of space-time but string corrections become important at the singularity. This happens where string winding modes become light which could resolve the singularity. The new proposed space-time casual structure could have implications for cosmology, independently of string theory.Comment: 28 pages, 3 figures; v2: Added new subsection relating two-dimensional model to BTZ black hole, typos corrected and references added; v3: minor corrections, PRD versio

Scalar Loops in Little Higgs Models

Loops of the scalar particles present in Little Higgs models generate radiatively scalar operators that have been overlooked before in Little Higgs analyses. We compute them using a technique, recently proposed to deal with scalar fluctuations in non-linear sigma models, that greatly simplifies the calculation. In particular models some of these operators are not induced by loops of gauge bosons or fermions, are consistent with the Little Higgs symmetries that protect the Higgs boson mass, and must also be included in the Lagrangian. In general, scalar loops multiplicatively renormalize the tree-level scalar operators, O_S -> O_S [1- N \Lambda^2/(4\pi f)^2] with large N (e.g. N ~ 20 for the Littlest Higgs), suggesting a true UV cutoff \Lambda < 4 \pi f/\sqrt{N} significantly below the estimate 4\pi f of naive dimensional analysis. This can have important implications for the phenomenology and viability of Little Higgs models.Comment: 28 pages, LaTe