Characterizing forest fragmentation : Distinguishing change in composition from configuration

This project was funded by the Government of Canada through the Mountain Pine Beetle Program, a three-year, $100 million program administered by Natural Resources Canada, Canadian Forest Service. Additional information on the Mountain Pine Beetle Program may be found at: http://mpb.cfs.nrcan.gc.ca.Forest fragmentation can generally be considered as two components: 1) compositional change representing forest loss, and 2) configurational change or change in the arrangement of forest land cover. Forest loss and configurational change occur simultaneously, resulting in difficulties isolating the impacts of each component. Measures of forest fragmentation typically consider forest loss and configurational change together. The ecological responses to forest loss and configurational change are different, thus motivating the creation of measures capable of isolating these separate components. In this research, we develop and demonstrate a measure, the proportion of landscape displacement from configuration (P), to quantify the relative contributions of forest loss and configurational change to forest fragmentation. Landscapes with statistically significant forest loss or configurational change are identified using neutral landscape simulations to generate underlying distributions for P. The new measure, P, is applied to a forest landscape where substantial forest loss has occurred from mountain pine beetle mitigation and salvage harvesting. The percent of forest cover and six LPIs (edge density, number of forest patches, area of largest forest patch, mean perimeter area ratio, corrected mean perimeter area ratio, and aggregation index) are used to quantify forest fragmentation and change. In our study area, significant forest loss occurs more frequently than significant configurational change. The P method we demonstrate is effective at identifying landscapes undergoing significant forest loss, significant configurational change, or experiencing a combination of both loss and configurational change.PostprintPeer reviewe

Casimir-Polder forces in the presence of the cosmic photon heat bath

We study the effect of a photon background at finite temperature $T$ on the Van der Waals interactions among neutral bodies. It turns out that the long-range Casimir-Polder force is unaffected for distances much less than $T^{-1}$ and strongly enhanced for distances much above $T^{-1}$.Comment: 8 pages, 2 figure

A Bayesian space-time model for discrete spread processes on a lattice

Funding for this work was provided by GEOIDE through the Government of Canada’s Networks for Centres of Excellence program.In this article we present a Bayesian Markov model for investigating environmental spread processes. We formulate a model where the spread of a disease over a heterogeneous landscape through time is represented as a probabilistic function of two processes: local diffusion and random-jump dispersal. This formulation represents two mechanisms of spread which result in highly peaked and long-tailed distributions of dispersal distances (i.e., local and long-distance spread), commonly observed in the spread of infectious diseases and biological invasions. We demonstrate the properties of this model using a simulation experiment and an empirical case study - the spread of mountain pine beetle in western Canada. Posterior predictive checking was used to validate the number of newly inhabited regions in each time period. The model performed well in the simulation study in which a goodness-of-fit statistic measuring the number of newly inhabited regions in each time interval fell within the 95% posterior predictive credible interval in over 97% of simulations. The case study of a mountain pine beetle infestation in western Canada (1999-2009) extended the base model in two ways. First, spatial covariates thought to impact the local diffusion parameters, elevation and forest cover, were included in the model. Second, a refined definition for translocation or jump-dispersal based on mountain pine beetle ecology was incorporated improving the fit of the model. Posterior predictive checks on the mountain pine beetle model found that the observed goodness-of-fit test statistic fell within the 95% posterior predictive credible interval for 8 out of 10. years. The simulation study and case study provide evidence that the model presented here is both robust and flexible; and is therefore appropriate for a wide range of spread processes in epidemiology and ecology.PostprintPeer reviewe

Gallium oxide and gadolinium gallium oxide insulators on Si δ-doped GaAs/AlGaAs heterostructures

Test devices have been fabricated on two specially grown GaAs/AlGaAs wafers with 10 nm thick gate dielectrics composed of either Ga<sub>2</sub>O<sub>3</sub> or a stack of Ga<sub>2</sub>O<sub>3</sub> and Gd<sub>0.25</sub>Ga<sub>0.15</sub>O<sub>0.6</sub>. The wafers have two GaAs transport channels either side of an AlGaAs barrier containing a Si delta-doping layer. Temperature dependent capacitance-voltage (C-V) and current-voltage (I-V) studies have been performed at temperatures between 10 and 300 K. Bias cooling experiments reveal the presence of DX centers in both wafers. Both wafers show a forward bias gate leakage that is by a single activated channel at higher temperatures and by tunneling at lower temperatures. When Gd<sub>0.25</sub>Ga<sub>0.15</sub>O<sub>0.6</sub> is included in a stack with 1 nm of Ga<sub>2</sub>O<sub>3</sub> at the interface, the gate leakage is greatly reduced due to the larger band gap of the Gd<sub>0.25</sub>Ga<sub>0.15</sub>O<sub>0.6</sub> layer. The different band gaps of the two oxides result in a difference in the gate voltage at the onset of leakage of ~3 V. However, the inclusion of Gd<sub>0.25</sub>Ga<sub>0.15</sub>O<sub>0.6</sub> in the gate insulator introduces many oxide states (≤4.70Ã�Â�10<sup>12</sup> cm<sup>âÂ�Â�2</sup>). Transmission electron microscope images of the interface region show that the growth of a Gd<sub>0.25</sub>Ga<sub>0.15</sub>O<sub>0.6</sub> layer on Ga<sub>2</sub>O<sub>3</sub> disturbs the well ordered Ga<sub>2</sub>O<sub>3</sub>/GaAs interface. We therefore conclude that while including Gd<sub>0.25</sub>Ga<sub>0.15</sub>O<sub>0.6</sub> in a dielectric stack with Ga<sub>2</sub>O<sub>3</sub> is necessary for use in device applications, the inclusion of Gd decreases the quality of the Ga<sub>2</sub>O<sub>3</sub>/GaAs interface and near interface region by introducing roughness and a large number of defect states

Monte Carlo simulations of high-performance implant free In_0.3Ga_0.7 nano-MOSFETs for low-power CMOS applications

No abstract available

Hole-hole correlations in the U=∞U=\infty limit of the Hubbard model and the stability of the Nagaoka state

We use exact diagonalisation in order to study the infinite - $U$ limit of the two dimensional Hubbard model. As well as looking at single-particle correlations, such as $n_{{\bf k}\sigma }=\langle c^\dagger _{{\bf k}\sigma }c_{{\bf k}\sigma } \rangle$, we also study {\it N-particle correlation functions} which compare the relative positions of {\it all} the particles in different models. In particular we study 16 and 18-site clusters and compare the charge correlations in the Hubbard model with those of spinless fermions and hard-core bosons. We find that although low densities of holes favour a `locally-ferromagnetic' fermionic description, the correlations at larger densities resemble those of pure hard-core bosons surprisingly well .Comment: 15 pages, REVTE

Studying Kaon-pion S-wave scattering in K-matrix formalism

We generalize our previous work on \pi\pi scattering to K\pi scattering, and re-analyze the experiment data of K\pi scattering below 1.6 GeV. Without any free parameter, we explain K\pi I=3/2 S-wave phase shift very well by using t-channel rho and u-channel K^* meson exchange. With the t-channel and u-channel meson exchange fixed as the background term, we fit the K\pi I=1/2 S-wave data of the LASS experiment quite well by introducing one or two s-channel resonances. It is found that there is only one s-channel resonance between K\pi threshold and 1.6 GeV, i.e., K_0^*(1430) with a mass around 1438~1486 MeV and a width about 346 MeV, while the t-channel rho exchange gives a pole at (450-480i) MeV for the amplitude.Comment: REVTeX4 file, 11 pages and 3 figure

3D Printing of a Polymer Bioactive Glass Composite for Bone Repair

A major limitation of synthetic bone repair is insufficient vascularization of the interior region of the scaffold. In this study, we investigated the 3D printing of adipose derived mesenchymal stem cells (AD-MSCs) with polycaprolactone (PCL)/bioactive glass composite in a single process. This offered a three-dimensional environment for complex and dynamic interactions that govern the cell’s behavior in vivo. Borate based bioactive (13-93B3) glass of different concentrations (10 to 50 weight %) was added to a mixture of PCL and organic solvent to make an extrudable paste. AD-MSCs suspended in Matrigel was extruded as droplets using a second syringe. Scaffolds measuring 10x10x1 mm3 in overall dimensions with a filament width of ~500 μm and pore sizes ranging from 100 to 200 μm were fabricated. Strut formability dependence on paste viscosity, scaffold integrity, and printing parameters for droplets of ADMSCs suspended in Matrigel were investigated

Analysis of Generalized Grover's Quantum Search Algorithms Using Recursion Equations

The recursion equation analysis of Grover's quantum search algorithm presented by Biham et al. [PRA 60, 2742 (1999)] is generalized. It is applied to the large class of Grover's type algorithms in which the Hadamard transform is replaced by any other unitary transformation and the phase inversion is replaced by a rotation by an arbitrary angle. The time evolution of the amplitudes of the marked and unmarked states, for any initial complex amplitude distribution is expressed using first order linear difference equations. These equations are solved exactly. The solution provides the number of iterations T after which the probability of finding a marked state upon measurement is the highest, as well as the value of this probability, P_max. Both T and P_max are found to depend on the averages and variances of the initial amplitude distributions of the marked and unmarked states, but not on higher moments.Comment: 8 pages, no figures. To appear in Phys. Rev.

Vanishing of cosmological constant in nonfactorizable geometry

We generalize the results of Randall and Sundrum to a wider class of four-dimensional space-times including the four-dimensional Schwarzschild background and de Sitter universe. We solve the equation for graviton propagation in a general four dimensional background and find an explicit solution for a zero mass bound state of the graviton. We find that this zero mass bound state is normalizable only if the cosmological constant is strictly zero, thereby providing a dynamical reason for the vanishing of cosmological constant within the context of this model. We also show that the results of Randall and Sundrum can be generalized without any modification to the Schwarzschild background.Comment: 8 Pages(expanded version), Accepted in Phys. Rev.