Leafless roughness of complex tree morphology using terrestrial LiDAR

Strategies for extracting roughness parameters from riparian forests need to address the issue that the trees are more than just stems and that in large rivers flow can rise into the canopy. Remote sensing information with 3-D capabilities such as lidar can be used to extract information on trees. However, first and last pulse airborne lidar data are insufficient to characterize the complex vertical structure of vegetation because by definition, there are few data at intermediate levels. Terrestrial laser scanning (TLS) is used in this study to define complex structures at a millimetric scanning resolution for the purpose of extracting canopy parameters relevant for the parameterization of the flow resistance equations. We will mainly be concerned with the projected area of leafless trees, estimating the total tree dimensions using several different methods. These include manipulating mass point cloud data obtained from TLS to create stage-dependent projected areas through complex meshing techniques and voxelization. Stage-dependent projected areas were defined for natural and planted poplar forests in the riparian zone of the Garonne and Allier rivers in southern and central France, respectively. Roughness values for planted poplar forests dominant in many western European river floodplains range from Manning's n = 0.037–0.094 and n = 0.140–0.330 for below-canopy flow (2 m) and extreme in-canopy flow (8 m), respectively. Roughness values for natural poplar forests ranged from n = 0.066–0.210 and n = 0.202–0.720 for below-canopy flow (2 m) and extreme in-canopy flow (8 m), respectively

Rivervis::a tool for visualising river ecosystems

There is a growing need to better understand and communicate multi-dimensional river ecosystem processes and properties at the catchment scale for both scientific research and integrated catchment management. Data visualisation is believed as a very useful approach to support this need. However, there is a lack of visualisation applications tailored for river ecosystems, especially for visualising both river environmental data and their spatial and topological relations. To fill up the gap, this paper introduces an R package rivervis, which has been developed as a free, easy-to-use and efficient visualisation solution for river ecosystems. This novel tool is able to visualise riverine data in a compact and comparable way, with retaining the river network topology and reflecting real distance between sites of interest. The rivervis package visualises variables according to their measurement types – either quantitative or qualitative/semi-quantitative data. This type-based principle makes the package applicable for a wide range of scenarios with data in forms of index values, condition gradings and categories. By producing topological river network diagrams, the package helps to understand the functioning and interconnections of riverine ecosystem at the catchment scale, especially the longitudinal upstream-downstream and tributary-mainstream connectivity and relationships. It can also be used to study the associations between biological communities, physical conditions and anthropogenic activities. The Ballinderry River Basin in the UK, as a data-rich river basin with a reasonable complex river network, is used to demonstrate the rationale, functions and capabilities of the R-package

A Precision Calculation of the Next-to-Leading Order Energy-Energy Correlation Function

The O(alpha_s^2) contribution to the Energy-Energy Correlation function (EEC) of e+e- -> hadrons is calculated to high precision and the results are shown to be larger than previously reported. The consistency with the leading logarithm approximation and the accurate cancellation of infrared singularities exhibited by the new calculation suggest that it is reliable. We offer evidence that the source of the disagreement with previous results lies in the regulation of double singularities.Comment: 6 pages, uuencoded LaTeX and one eps figure appended Complete paper as PostScript file (125 kB) available at: http://www.phys.washington.edu/~clay/eecpaper1/paper.htm

Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

On 15 June 2010, a M_w5.7 earthquake occurred near Ocotillo, California, in the Yuha Desert. This event was the largest aftershock of the 4 April 2010 M_w7.2 El Mayor-Cucapah (EMC) earthquake in this region. The EMC mainshock and subsequent Ocotillo aftershock provide an opportunity to test the Coulomb failure hypothesis (CFS). We explore the spatiotemporal correlation between seismicity rate changes and regions of positive and negative CFS change imparted by the Ocotillo event. Based on simple CFS calculations we divide the Yuha Desert into three subregions, one triggering zone and two stress shadow zones. We find the nominal triggering zone displays immediate triggering, one stress shadowed region experiences immediate quiescence, and the other nominal stress shadow undergoes an immediate rate increase followed by a delayed shutdown. We quantitatively model the spatiotemporal variation of earthquake rates by combining calculations of CFS change with the rate-state earthquake rate formulation of Dieterich (1994), assuming that each subregion contains a mixture of nucleation sources that experienced a CFS change of differing signs. Our modeling reproduces the observations, including the observed delay in the stress shadow effect in the third region following the Ocotillo aftershock. The delayed shadow effect occurs because of intrinsic differences in the amplitude of the rate response to positive and negative stress changes and the time constants for return to background rates for the two populations. We find that rate-state models of time-dependent earthquake rates are in good agreement with the observed rates and thus explain the complex spatiotemporal patterns of seismicity

Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

On 15 June 2010, a M_w5.7 earthquake occurred near Ocotillo, California, in the Yuha Desert. This event was the largest aftershock of the 4 April 2010 M_w7.2 El Mayor-Cucapah (EMC) earthquake in this region. The EMC mainshock and subsequent Ocotillo aftershock provide an opportunity to test the Coulomb failure hypothesis (CFS). We explore the spatiotemporal correlation between seismicity rate changes and regions of positive and negative CFS change imparted by the Ocotillo event. Based on simple CFS calculations we divide the Yuha Desert into three subregions, one triggering zone and two stress shadow zones. We find the nominal triggering zone displays immediate triggering, one stress shadowed region experiences immediate quiescence, and the other nominal stress shadow undergoes an immediate rate increase followed by a delayed shutdown. We quantitatively model the spatiotemporal variation of earthquake rates by combining calculations of CFS change with the rate-state earthquake rate formulation of Dieterich (1994), assuming that each subregion contains a mixture of nucleation sources that experienced a CFS change of differing signs. Our modeling reproduces the observations, including the observed delay in the stress shadow effect in the third region following the Ocotillo aftershock. The delayed shadow effect occurs because of intrinsic differences in the amplitude of the rate response to positive and negative stress changes and the time constants for return to background rates for the two populations. We find that rate-state models of time-dependent earthquake rates are in good agreement with the observed rates and thus explain the complex spatiotemporal patterns of seismicity

Using a deformable discrete-element technique to model the compaction behaviour of mixed ductile and brittle particulate systems

This paper illustrates the application of a combined discrete- and finite-element simulation to the compaction of assemblies comprising both ductile and brittle particles. Through case studies, the results demonstrate the importance of using a fine mesh on the particle boundary, the effect of fragmentation and its impact on the form of the compression curve, and the effect of inclusion of ductile particles at ca. 25% by volume suppressing brittle failure mechanisms. Although, the calculations can be extended to three dimensions, the computational cost is a current limitation on such calculations. The novelty of this approach is in its ability to predict material yield surfaces for the compaction of a mixture of particles. The initial results are optimistic, but there is a need for model improvement, principally through the ability to capture the random packing of irregular particles since this will eliminate a key problem in defining an initial density for the simulation. The main advantage of this technology is in its ability to minimize the need for expensive triaxial testing of samples to develop the yield-surface history

Blazars in the Fermi Era: The OVRO 40-m Telescope Monitoring Program

The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope provides an unprecedented opportunity to study gamma-ray blazars. To capitalize on this opportunity, beginning in late 2007, about a year before the start of LAT science operations, we began a large-scale, fast-cadence 15 GHz radio monitoring program with the 40-m telescope at the Owens Valley Radio Observatory (OVRO). This program began with the 1158 northern (declination>-20 deg) sources from the Candidate Gamma-ray Blazar Survey (CGRaBS) and now encompasses over 1500 sources, each observed twice per week with a ~4 mJy (minimum) and 3% (typical) uncertainty. Here, we describe this monitoring program and our methods, and present radio light curves from the first two years (2008 and 2009). As a first application, we combine these data with a novel measure of light curve variability amplitude, the intrinsic modulation index, through a likelihood analysis to examine the variability properties of subpopulations of our sample. We demonstrate that, with high significance (7-sigma), gamma-ray-loud blazars detected by the LAT during its first 11 months of operation vary with about a factor of two greater amplitude than do the gamma-ray-quiet blazars in our sample. We also find a significant (3-sigma) difference between variability amplitude in BL Lacertae objects and flat-spectrum radio quasars (FSRQs), with the former exhibiting larger variability amplitudes. Finally, low-redshift (z<1) FSRQs are found to vary more strongly than high-redshift FSRQs, with 3-sigma significance. These findings represent an important step toward understanding why some blazars emit gamma-rays while others, with apparently similar properties, remain silent.Comment: 23 pages, 24 figures. Submitted to ApJ