Characterizing and Modeling Arctic Shrub Expansion on the North Slope of Alaska, USA

Shrub expansion is one of the most recognized components of terrestrial Arctic change and has been documented in studies involving fine-scale experimental manipulations or broad-scale satellite remote sensing. The characteristics and drivers of this phenomenon at the landscape scale, however, are understudied. The motivation of this dissertation was to develop an improved understanding of the historic spatial characteristics of shrub expansion on the North Slope of Alaska and its environmental drivers at this landscape scale. This work has three objectives, which include: 1) mapping and quantifying historic shrub expansion patterns; 2) examining a relationship between shrub expansion and its hydrological controls; and 3) designing and implementing a spatially-explicit simulation model to develop hypotheses regarding the landscape-scale drivers of shrub expansion (i.e., modes of reproduction, hydrological constraints, and their interactions). Shrubs maps were generated from semi-automated classification of historic vertical aerial photographs and contemporary high-resolution satellite imagery within a GIS. The spatial patterns of historic shrub expansion were quantified using FRAGSTATS and the multi-scale information fractal dimension. Relationships between shrub expansion and local hydrology was determined statistically through associations between areas that gained shrub cover and topographic wetness index values derived from a digital elevation model. The contribution of shrub reproductive characteristics was determined by developing a C#-based spatially-explicit simulation model that simulates clonal and sexual reproduction of shrubs. The reproductive mode(s) producing spatial patterns most similar to the observed patterns was determined through principal components analyses. Results from this work suggest that: 1) the shrub-tundra ecotone within river valleys on the North Slope is has either initiated or completed a phase transition from tundra to shrubland; 2) shrub development is promoted in areas where the potential for water accumulation or throughflow is higher; and 3) vegetative reproduction appears to have been dominant mode of reproduction . Considering our current understanding of the fine-scale relationships between shrub expansion and hydrology, surface energy balances, and C and nutrient cycling, continued expansion may have considerable implications for circumpolar tundra ecosystems. These findings will facilitate the development of improved projections of the structure and function of these ecosystems and their feedbacks to climate change

ILC Reference Design Report Volume 1 - Executive Summary

The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^34 cm^-2s^-1. This report is the Executive Summary (Volume I) of the four volume Reference Design Report. It gives an overview of the physics at the ILC, the accelerator design and value estimate, the detector concepts, and the next steps towards project realization.The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^34 cm^-2s^-1. This report is the Executive Summary (Volume I) of the four volume Reference Design Report. It gives an overview of the physics at the ILC, the accelerator design and value estimate, the detector concepts, and the next steps towards project realization

ILC Reference Design Report Volume 4 - Detectors

This report, Volume IV of the International Linear Collider Reference Design Report, describes the detectors which will record and measure the charged and neutral particles produced in the ILC's high energy e+e- collisions. The physics of the ILC, and the environment of the machine-detector interface, pose new challenges for detector design. Several conceptual designs for the detector promise the needed performance, and ongoing detector R&D is addressing the outstanding technological issues. Two such detectors, operating in push-pull mode, perfectly instrument the ILC interaction region, and access the full potential of ILC physics.This report, Volume IV of the International Linear Collider Reference Design Report, describes the detectors which will record and measure the charged and neutral particles produced in the ILC's high energy e+e- collisions. The physics of the ILC, and the environment of the machine-detector interface, pose new challenges for detector design. Several conceptual designs for the detector promise the needed performance, and ongoing detector R&D is addressing the outstanding technological issues. Two such detectors, operating in push-pull mode, perfectly instrument the ILC interaction region, and access the full potential of ILC physics

ILC Reference Design Report Volume 3 - Accelerator

The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^34 cm^-2 s^-1. The complex includes a polarized electron source, an undulator-based positron source, two 6.7 km circumference damping rings, two-stage bunch compressors, two 11 km long main linacs and a 4.5 km long beam delivery system. This report is Volume III (Accelerator) of the four volume Reference Design Report, which describes the design and cost of the ILC.The International Linear Collider (ILC) is a 200-500 GeV center-of-mass high-luminosity linear electron-positron collider, based on 1.3 GHz superconducting radio-frequency (SCRF) accelerating cavities. The ILC has a total footprint of about 31 km and is designed for a peak luminosity of 2x10^34 cm^-2 s^-1. The complex includes a polarized electron source, an undulator-based positron source, two 6.7 km circumference damping rings, two-stage bunch compressors, two 11 km long main linacs and a 4.5 km long beam delivery system. This report is Volume III (Accelerator) of the four volume Reference Design Report, which describes the design and cost of the ILC

International Linear Collider Reference Design Report Volume 2: PHYSICS AT THE ILC

This article reviews the physics case for the ILC. Baseline running at 500 GeV as well as possible upgrades and options are discussed. The opportunities on Standard Model physics, Higgs physics, Supersymmetry and alternative theories beyond the Standard Model are described.This article reviews the physics case for the ILC. Baseline running at 500 GeV as well as possible upgrades and options are discussed. The opportunities on Standard Model physics, Higgs physics, Supersymmetry and alternative theories beyond the Standard Model are described