Powerscapes

Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 149-151).In 2050, global oil supply will decline to 1/8 of today's. Migrating to the Post-Oil Era, over 10000's km2 of Powerscapes - the solar-collecting infrastructure - will be gradually constructed across the arid desert, for the indispensable production of solar energy to sustain Middle East's economy and global energy supply. The contingency of introducing the Powerscapes is a spatial problem. Unlike a powerplant that burns coal or oil, the scale of the Powerscapes is dramatically extensive. The inserted Powerscapes will interiorize the desert landscape and shelter the ground from the harsh direct sunlight that will be captured for power supply. Transformation in biological development, meteorological activity and geological phenomena will be inevitable, but the change that reduces the heat and evaporation rate will make its climatatic dynamics more habitable for human, animals and plants - an invaluable opportunity for the synthesis of energy production and climate conditioning. This thesis investigates the strategic programming and spatial configuration of such constructed landscape, capitalized by its new temporal characteristics, and sensitively adapting to it. Layers of material will be organized to form "Strata" of temporal conditions to be stretched across the landscape. To forge a symbiotic relationship between Solar Collection, human habitation, agricultural production and wild nature, the layers of material will delineate, push, flip, intersect, puncuate, wrap and merge, responding to programmatic needs and geographical dynamics that the natural geology and the Powerscapes together create. Such adaptive organization also permits certain geometrical and configuration logic to reiterate themselves in multiple scales, formulating a fractalic field with recursive part to whole relationships.by Chun Lun Otto Ng.M.Arch

The spectral energy distribution of fermi bright blazars

We have conducted a detailed investigation of the broadband spectral properties of the γ-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi γ-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/γ-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these γ-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log ν-log ν Fν representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low- and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, αro, and optical to X-ray, αox, spectral slopes) and from the γ-ray spectral index. Our data show that the synchrotron peak frequency (νSpeak) is positioned between 1012.5 and 1014.5 Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10 13 and 1017 Hz in featureless BL Lacertae objects. We find that the γ-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked (HBL) BL Lacs are detected in the LBAS sample, only less than 13% of known bright FSRQs and LBL BL Lacs are included. This suggests that the latter sources, as a class, may be much fainter γ-ray emitters than LBAS blazars, and could in fact radiate close to the expectations of simple SSC models. We categorized all our sources according to a new physical classification scheme based on the generally accepted paradigm for Active Galactic Nuclei and on the results of this SED study. Since the LAT detector is more sensitive to flat spectrum γ-ray sources, the correlation between νSpeak and γ-ray spectral index strongly favors the detection of high energy peaked blazars, thus explaining the Fermi overabundance of this type of sources compared to radio and EGRET samples. This selection effect is similar to that experienced in the soft X-ray band where HBL BL Lacs are the dominant type of blazars. © 2010 The American Astronomical Society

Bracken fern (Pteridium aquilinum L. kuhn) promotes an open nitrogen cycle in heathland soils

Background and Aims In spite of the broad array of studies conducted on the ecology of bracken fern (Pteridium aquilinum (L.) kuhn), there is currently only a limited understanding of how P. aquilinum alters the soil environment in which it succeeds. P. aquilinum is one of the world�s most aggressive invasive species and is known to effectively invade conservation priority habitats such as Calluna vulgaris (L.) heathland. The aim of this study was to evaluate differences in soil properties between intact stands of C. vulgaris and neighboring P. aquilinum to assess how P. aquilinum alters soil N transformations in a manner that might promote its success. Methods Replicate plots in five independently paired stands of P. aquilinum and C. vulgaris were established on land in which P. aquilinum is actively invading. Soils under the two plant types were evaluated for total N, mineralisable N, net nitrification, nitrifier activity, denitrification enzyme activity, polyphenol N complexing capacity, and resin sorption of inorganic N. Results Soils under P. aquilinum were consistently higher in NO3 - and NH4 + concentrations compared to C. vulgaris. Extractable organic and inorganic N concentrations for soil under P. aquilinum were respectively 65 %, 77 % and 358 % greater in amino N NH4 +-N and NO3 --N compared to that under C. vulgaris. In-situ net nitrification (NO3 - sorption to ionic resins) was found to be nearly 300 times greater under P. aquilinum than under C. vulgaris. Conclusions P. aquilinum alters the soil environment as to create an inorganic N-rich environment that is favorable to its growth and development