3,867 research outputs found
UNDERSTANDING THE GLOBAL COMMONS
We want to clarify the way in which we think about the global commons, particularly the problem of global warming caused by greenhouse gas emissions and tropical deforestation. We develop a policy framework in which the policy goal is the sustainability of the earth's ability to absorb greenhouse gases. The framework considers the unequal incidence of benefits and costs of particular policies. We identify several resource management regimes and suggest that management under a common property regime is most appropriate. We conclude by identifying and briefly discussing types of policies that can achieve sustainability.Environmental Economics and Policy,
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Discharge-generated electrical fields and electrical tree structures
The discharge-avalanche (D-A) model for electrical tree propagation in polymers is founded entirely upon basic physical concepts. Electrical discharges in an existing tree structure are taken to raise the electrical field in the polymer both along the discharge path and particularly at the tree tips. As a result of the field increase, electron multiplication avalanches occur within the polymer causing damage, possibly through ionisation of polymer molecules, which is accumulated over a period of thousands (or more) cycles and eventually leads to a tree extension of limited size. The assumption that the damage produced in an avalanche is proportional to the number of ionisations allows the model to be expressed quantitatively in terms of material properties: such as the ionisation potential, I; the impact-ionisation length parameter λ; the critical number of ionisations for tree extension Nc; discharge features such as the number of 1-electron initiated avalanches per half cycle, Nb ; and the potential difference ÎV between the start and end of the avalanche over a distance Lb
Milton's Utopian Millennium: Ideal Society and Eschatology in Seventeenth-Century England
This thesis presents the argument that in John Miltonâs theology, political philosophy and poetry there is an underexplored relationship between utopianism and millenarianism. The study defines this relationship as the utopian millennium, through which the utopian values of control and regulation secure a chiliastic future. In a series of comparative chapters, the thesis traces how Miltonâs utopian millenarianism can be situated within and how it develops through the intellectual, political and radical landscape of mid-seventeenth-century England. The study analyses Miltonâs theology and political philosophy alongside contemporary intellectuals and radical figures, such as, amongst others, Samuel Hartlib, James Harrington, Thomas Hobbes, Marchamont Nedham, and Gerrard Winstanley. It also considers how the utopian and millenarian ideas of Miltonâs prose works are reflected in his epic poetry. In doing so, the study observes how Miltonâs gradual loss of faith in the English people encourages utopian formulations in the hope of ensuring the realisation of his eschatology. Miltonâs growing disillusionment with the people coincides with his growing elitism: from the early 1640s to the end of his life, he placed his faith of those who he believed were capable of realising the millennium in fewer and fewer people. In contrast to the studious community of London in Areopagitica in 1644, by 1671, Milton idealises perfect, elect individuals, to whom he can aspire, if not with whom he self-identifies. Miltonâs utopian millennium, tolerant and yet elitist, unorthodox and yet conservative, encodes the dynamic changes of the political and intellectual landscape of the mid-seventeenth-century
Is the cosmic microwave background really non-Gaussian?
Two recent papers have claimed detection of non-Gaussian features in the COBE
DMR sky maps of the cosmic microwave background. We confirm these results, but
argue that Gaussianity is still not convincingly ruled out. Since a score of
non-Gaussianity tests have now been published, one might expect some mildly
significant results even by chance. Moreover, in the case of one measure which
yields a detection, a bispectrum statistic, we find that if the non-Gaussian
feature is real, it may well be due to detector noise rather than a
non-Gaussian sky signal, since a signal-to-noise analysis localizes it to
angular scales smaller than the beam. We study its spatial origin in case it is
nonetheless due to a sky signal (eg, a cosmic string wake or flat-spectrum
foreground contaminant). It appears highly localized in the direction b=39.5,
l=257, since removing a mere 5 pixels inside a single COBE beam area centered
there makes the effect statistically insignificant. We also test Guassianity
with an eigenmode analysis which allows a sky map to be treated as a random
number generator. A battery of tests of this generator all yield results
consistent with Gaussianity.Comment: Revised to match accepted ApJL version. 4 pages with 2 figs included.
Links and color fig at http://www.sns.ias.edu/~max/gaussianity_frames.html or
from [email protected]
Terrestrial Planet Formation I. The Transition from Oligarchic Growth to Chaotic Growth
We use a hybrid, multiannulus, n-body-coagulation code to investigate the
growth of km-sized planetesimals at 0.4-2 AU around a solar-type star. After a
short runaway growth phase, protoplanets with masses of roughly 10^26 g and
larger form throughout the grid. When (i) the mass in these `oligarchs' is
roughly comparable to the mass in planetesimals and (ii) the surface density in
oligarchs exceeds 2-3 g/sq cm at 1 AU, strong dynamical interactions among
oligarchs produce a high merger rate which leads to the formation of several
terrestrial planets. In disks with lower surface density, milder interactions
produce several lower mass planets. In all disks, the planet formation
timescale is roughly 10-100 Myr, similar to estimates derived from the
cratering record and radiometric data.Comment: Astronomical Journal, accepted; 22 pages + 15 figures in ps format;
eps figures at http://cfa-www.harvard.edu/~kenyon/dl/ revised version
clarifies evolution and justifies choice of promotion masse
Detecting the Dusty Debris of Terrestrial Planet Formation
We use a multiannulus accretion code to investigate debris disks in the
terrestrial zone, at 0.7-1.3 AU around a 1 solar mass star. Terrestrial planet
formation produces a bright dusty ring of debris with a lifetime of at least 1
Myr. The early phases of terrestrial planet formation are observable with
current facilities; the late stages require more advanced instruments with
adaptive optics.Comment: 11 pages of text, 3 figures, accepted for ApJ Letters, additional
info at http://cfa-www.harvard.edu/~kenyon/pf/terra/td
Polarimetric Imaging of the Massive Black Hole at the Galactic Center
The radio source Sgr A* in the Galactic center emits a polarized spectrum at
millimeter and sub-millimeter wavelengths that is strongly suggestive of
relativistic disk accretion onto a massive black hole. We use the
well-constrained mass of Sgr A* and a magnetohydrodynamic model of the
accretion flow to match both the total flux and polarization from this object.
Our results demonstrate explicitly that the shift in the position angle of the
polarization vector, seen at wavelengths near the peak of the mm to sub-mm
emission from this source, is a signal of relativistic accretion flow in a
strong gravitational field. We provide maps of the polarized emission to
illustrate how the images of polarized intensity from the vicinity of the black
hole would appear in upcoming observations with very long baseline radio
interferometers (VLBI). Our results suggest that near-term VLBI observations
will be able to directly image the polarized Keplerian portion of the flow near
the horizon of the black hole.Comment: 12 pages, 2 figures, Accepted for publciation in ApJ Letter
A study of cerium extraction by TBP and TODGA using a rotating diffusion cell
For the study of the coupled interfacial-mass transfer kinetics of, inter alia, TBP, TODGA, CyMe4-BTBP and CyMe4-BTPhen based solvent extraction processes, a new rotating diffusion cell (RDC) apparatus has been established at Lancaster University. RDC studies of Ce(IV)/TBP and Ce(III)/TODGA extraction systems have been undertaken in order to improve the understanding of the chemical and kinetic processes involved. In each case, an interesting dependency on local hydrodynamics at the solution phase boundary with results suggesting that the organic extractant molecules migrate into the aqueous phase in order to capture Ce
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