Comparison and validation of three versions of a forest wind risk model

Predicting the probability of wind damage in both natural and managed forests is important for understanding forest ecosystem functioning, the environmental impact of storms and for forest risk management. We undertook a thorough validation of three versions of the hybrid-mechanistic wind risk model, ForestGALES, and a statistical logistic regression model, against observed damage in a Scottish upland conifer forest following a major storm. Statistical analysis demonstrated that increasing tree height and local wind speed during the storm were the main factors associated with increased damage levels. All models provided acceptable discrimination between damaged and undamaged forest stands but there were trade-offs between the accuracy of the mechanistic models and model bias. The two versions of the mechanistic model with the lowest bias gave very comparable overall results at the forest scale and could form part of a decision support system for managing forest wind damage risk

Efficient Classical Simulation of Optical Quantum Circuits

We identify a broad class of physical processes in an optical quantum circuit that can be efficiently simulated on a classical computer: this class includes unitary transformations, amplification, noise, and measurements. This simulatability result places powerful constraints on the capability to realize exponential quantum speedups as well as on inducing an optical nonlinear transformation via linear optics, photodetection-based measurement and classical feedforward of measurement results, optimal cloning, and a wide range of other processes.Comment: 4 pages, published versio

Properties of UK-Grown Sitka Spruce: Extent and Sources of Variation.

Structural timber produced from Sitka spruce plantations in the UK typically achieves the requirements for the C16 strength class. However, very little is known about the variability of this plantation resource, or the factors that contribute to this variability. A study to benchmark the properties of the current resource found that there was a considerable amount of variation in wood properties between sites as well as between trees within a site. This benchmarking study has been complemented by studies which have investigated the impacts of genetics, precommercial thinning and rotation length on timber properties. In these studies, measurements of stress wave velocity have been made on standing trees, freshly-felled logs and sawn timber. Knowledge gained should assist in better utilisation of the current resource as well as identifyingmanagement practices that will lead to an improved future resource for structural applications

Properties of UK-Grown Sitka Spruce: Extent and Sources of Variation.

Structural timber produced from Sitka spruce plantations in the UK typically achieves the requirements for the C16 strength class. However, very little is known about the variability of this plantation resource, or the factors that contribute to this variability. A study to benchmark the properties of the current resource found that there was a considerable amount of variation in wood properties between sites as well as between trees within a site. This benchmarking study has been complemented by studies which have investigated the impacts of genetics, precommercial thinning and rotation length on timber properties. In these studies, measurements of stress wave velocity have been made on standing trees, freshly-felled logs and sawn timber. Knowledge gained should assist in better utilisation of the current resource as well as identifyingmanagement practices that will lead to an improved future resource for structural applications

Release of multiple bubbles from cohesive sediments

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L08606, doi:10.1029/2011GL046870.Methane is a strong greenhouse gas, and marine and wetland sediments constitute significant sources to the atmosphere. This flux is dominated by the release of bubbles, and quantitative prediction of this bubble flux has been elusive because of the lack of a mechanistic model. Our previous work has shown that sediments behave as elastic fracturing solids during bubble growth and rise. We now further argue that bubbles can open previously formed, partially annealed, rise tracts (fractures) and that this mechanism can account for the observed preferential release at low tides in marine settings. When this mechanical model is applied to data from Cape Lookout Bight, NC (USA), the results indicate that methanogenic bubbles released at this site do indeed follow previously formed rise tracts and that the calculated release rates are entirely consistent with the rise of multiple bubbles on tidal time scales. Our model forms a basis for making predictions of future bubble fluxes from warming sediments under the influence of climate change.This research was funded by the U.S. Office of Naval research through grants N00014‐08‐0818 and N00014‐05‐1‐0175 (project managers J. Eckman and T. Drake), the Natural Sciences and Engineering Council of Canada, and the Killam Trust (Dalhousie University)

Strategic Integrated Research in Timber: Getting the most out of the UK's timber resource.

Sitka spruce (Picea sitchensis) is the United Kingdom’s main commercial tree species accounting for nearly one-third of the UK's total woodland area and half of its conifer estate. Sawn timber from this species readily grades to the C16 strength class, but there are factors beyond the structural grade that can influence its acceptance as a construction material. This paper summarises the results from resource characterisation studies that have investigated the properties of Sitka spruce at the standing-tree scale down to the scale of a few microns. These studies have substantially improved the understanding of the impact on mechanical performance of structural timber of factors at the micro-structural level (e.g. cellulose structure and abundance) and at the forest-level (e.g. genetics, the environment and forest management). End-user requirements for timber are discussed in terms of what is, and is not, provided by current grading practice and some of the main misconceptions about UK-timber are challenged

The high-velocity clouds and the Magellanic Clouds

From an analysis of the sky and velocity distributions of the high-velocity clouds (HVCs) we show that the majority of the HVCs has a common origin. We conclude that the HVCs surround the Galaxy, forming a metacloud of 300 kpc in size and with a mass of 3 10^9 M_sun, and that they are the product of a powerful ``superwind'' (about 10^58 ergs), which occurred in the Magellanic Clouds about 570 Myr ago as a consequence of the interaction of the Large and Small Magellanic Clouds. The HVCs might be magnetic bubbles of semi-ionized gas, blown from the Magellanic Clouds around 570 Myr ago, that circulate largely through the halo of the Galaxy as a stream or flow of gas.Comment: 28 pages with 23 figure

Counterintuitive active directional swimming behaviour by Atlantic salmon during seaward migration in the coastal zone

Acknowledgements We thank the Cromarty Firth District Salmon Fishery Board for logistical support and three anonymous referees who improved an earlier draft of this paper. Funding for this work came from Scottish & Southern Energy Renewables. We are grateful for the skills and expertise of Bill Ruck at Moray First Marine along with the crews of Marine Scotland Science vessels who were integral to the successful deployment and recovery of equipment. Some receivers were also made available from the Ocean Tracking Network (OTN) The data underlying this article will be shared on reasonable request to the corresponding author.Peer reviewedPublisher PD

Antigenic diversity is generated by distinct evolutionary mechanisms in African trypanosome species

Antigenic variation enables pathogens to avoid the host immune response by continual switching of surface proteins. The protozoan blood parasite Trypanosoma brucei causes human African trypanosomiasis ("sleeping sickness") across sub-Saharan Africa and is a model system for antigenic variation, surviving by periodically replacing a monolayer of variant surface glycoproteins (VSG) that covers its cell surface. We compared the genome of Trypanosoma brucei with two closely related parasites Trypanosoma congolense and Trypanosoma vivax, to reveal how the variant antigen repertoire has evolved and how it might affect contemporary antigenic diversity. We reconstruct VSG diversification showing that Trypanosoma congolense uses variant antigens derived from multiple ancestral VSG lineages, whereas in Trypanosoma brucei VSG have recent origins, and ancestral gene lineages have been repeatedly co-opted to novel functions. These historical differences are reflected in fundamental differences between species in the scale and mechanism of recombination. Using phylogenetic incompatibility as a metric for genetic exchange, we show that the frequency of recombination is comparable between Trypanosoma congolense and Trypanosoma brucei but is much lower in Trypanosoma vivax. Furthermore, in showing that the C-terminal domain of Trypanosoma brucei VSG plays a crucial role in facilitating exchange, we reveal substantial species differences in the mechanism of VSG diversification. Our results demonstrate how past VSG evolution indirectly determines the ability of contemporary parasites to generate novel variant antigens through recombination and suggest that the current model for antigenic variation in Trypanosoma brucei is only one means by which these parasites maintain chronic infections

Generation of 3 spinocerebellar ataxia type 1 (SCA1) patient-derived induced pluripotent stem cell lines LUMCi002-A, B, and C and 2 unaffected sibling control induced pluripotent stem cell lines LUMCi003-A and B

Spinocerebellar ataxia type 1 (SCA1) is a hereditary neurodegenerative disease caused by a CAG repeat expansion in exon 8 of the ATXN1 gene. We generated induced pluripotent stem cells (hiPSCs) from a SCA1 patient and his non-affected sister by using non-integrating Sendai Viruses (SeV). The resulting hiPSCs are SeVfree, express pluripotency markers, display a normal karyotype, retain the mutation (length of the CAG repeat expansion in the ATXN1 gene) and are able to differentiate into the three germ layers in vitro