4,059 research outputs found
Justifying Social Discounting: The Rank-Discounted Utilitarian Approach
The discounted utilitarian criterion for infinite horizon social choice has been criticized for treating generations unequally. We propose an extended rank-discounted utilitarian (ERDU) criterion instead. The criterion amounts to discounted utilitarianism on non-decreasing streams, but it treats all generations impartially: discounting becomes the mere expression of intergenerational inequality aversion. We show that more inequality averse ERDU societies have higher social discount rates when future generations are better-off. We apply the ERDU approach in two benchmark economic growth models and prove that it promotes sustainable policies that maximize discounted utilitarian welfare.intergenerational equity, social discounting, discounted utilitarianism, sustainability
Haldane's Fractional Statistics and the Riemann-Roch Theorem
The new definition of fractional statistics given by Haldane can be
understood in some special cases in terms of the Riemann-Roch theorem.Comment: 38050 Povo, Trento and Division de Physique Th\'eorique, IPN, 91406
Orsay Cedex, 19 pages, IPNO/TH 94-11, SISSA/27/94/EP,UFT/32
The Dark Matter equation of state through cosmic history
Cold Dark Matter (CDM) is a crucial constituent of the current concordance
cosmological model. Having a vanishing equation of state (EoS), its energy
density scales with the inverse cosmic volume and is thus uniquely described by
a single number, its present abundance. We test the inverse cosmic volume law
for Dark Matter (DM) by allowing its EoS to vary independently in eight
redshift bins in the range and . We use the latest measurements
of the Cosmic Microwave Background radiation from the Planck satellite and
supplement them with Baryon Acoustic Oscillation (BAO) data from the 6dF and
SDSS-III BOSS surveys, and with the Hubble Space Telescope (HST) key project
data. We find no evidence for nonzero EoS in any of the eight redshift bins.
With Planck data alone, the DM abundance is most strongly constrained around
matter-radiation equality (95%
c.l.), whereas its present day value is more weakly constrained (95% c.l.). Adding BAO or HST data does not
significantly change the constraint, while
tightens to (95% c.l.) and
(95% c.l.) respectively. Our results constrain for the first time the level of
"coldness" required of the DM across various cosmological epochs and show that
the DM abundance is strictly positive at all times.Comment: 6 pages, 4 figures, changed color scheme for figure
An extremal model for amorphous media plasticity
An extremal model for the plasticity of amorphous materials is studied in a
simple two-dimensional anti-plane geometry. The steady-state is analyzed
through numerical simulations. Long-range spatial and temporal correlations in
local slip events are shown to develop, leading to non-trivial and highly
anisotropic scaling laws. In particular, the plastic strain is shown to
statistically concentrate over a region which tends to align perpendicular to
the displacement gradient. By construction, the model can be seen as giving
rise to a depinning transition, the threshold of which (i.e. the macroscopic
yield stress) also reveal scaling properties reflecting the localization of the
activity.Comment: 4 pages, 5 figure
The Bulge-Halo Connection in Galaxies: A Physical Interpretation of the Vcirc-sigma_0 Relation
We explore the dependence of the ratio of a galaxy's circular velocity,
Vcirc, to its central velocity dispersion, sigma_0, on morphology, or
equivalently total light concentration. Such a dependence is expected if light
traces the mass. Over the full range of galaxy types, masses and brightnesses,
and assuming that the gas velocity traces the circular velocity, we find that
galaxies obey the relation log(Vcirc/sigma_0)= 0.63-0.11*C28 where
C28=5log(r80/r20) and the radii are measured at 80 percent and 20 percent of
the total light. Massive galaxies scatter about the Vcirc = sqrt(2)*sigma_0
line for isothermal stellar systems. Disk galaxies follow the simple relation
Vcirc/sigma_0=2(1-B/T), where B/T is the bulge-to-total light ratio. For pure
disks, C28~2.8, B/T -> 0, and Vcirc~=2*sigma_0. Self-consistent equilibrium
galaxy models from Widrow & Dubinski (2005) constrained to match the
size-luminosity and velocity-luminosity relations of disk galaxies fail to
match the observed Vcirc/sigma_0 distribution. Furthermore, the matching of
dynamical models for Vcirc(r)/sigma(r) with observations of dwarf and
elliptical galaxies suffers from limited radial coverage and relatively large
error bars; for dwarf systems, however, kinematical measurements at the galaxy
center and optical edge suggest Vcirc(Rmax) > 2*sigma_0 (in contrast with past
assumptions that Vcirc = sqrt(2)*sigma_0 for dwarfs.) The Vcirc-sigma_0-C28
relation has direct implications for galaxy formation and dynamical models,
galaxy scaling relations, the mass function of galaxies, and the links between
respective formation and evolution processes for a galaxy's central massive
object, bulge, and dark matter halo.Comment: Accepted for publication in ApJL. Current version matches ApJL page
requiremen
Soll man in der klinischen Praxis Frailty abschÀtzen?
Frailty, ein geriatrisches Syndrom mit altersbedingter Gebrechlichkeit assoziiert, heisst Verlust physiologischer Reserven verschiedener Organe. Die Folge ist eine erhöhte Verletzlichkeit durch Stress. Eine allseits anerkannte Definition fehlt, und die AbschÀtzung erfolgt hauptsÀchlich aufgrund zweier Modelle: des PhÀnotyps nach Fried und des Index nach Rockwood.
Frailty bringt ein deutlich erhöhtes Risiko fĂŒr funktionelle HilfebedĂŒrftigkeit, Hospitalisation oder Einweisung in eine Institution fĂŒr Langzeitpflege sowie Tod mit sich.
Der Spontanverlauf ist progressiv, kann aber auch reversibel sein, und daher könnte PrĂ€vention grundsĂ€tzlich in Frage kommen. Unsere Kenntnisse sind derzeit aber immer noch zu lĂŒckenhaft, als dass wir gezielt gegen Frailty angehen könnten.
Klinische Forschung ĂŒber Frailty wird erst seit kurzem betrieben. Die Empfehlung, den Frailtygrad durch Leistungsmessung (wie Ganggeschwindigkeit, Griffkraft etc.) zu evaluieren, stĂŒtzt sich auf die Beobachtung eines Zusammenhangs mit einer spĂ€teren ungĂŒnstigen Entwicklung, und nicht darauf, dass wir wirksam eingreifen könnten.
Klinische und epidemiologische Studien ĂŒber Frailty sind wichtig. Da die Babyboomer nun Ă€lter werden, ist die Gefahr einer Epidemie funktioneller HilfebedĂŒrftigkeit Mitte des Jahrhunderts absehbar, und somit stellt das Problem der Frailty eine grosse Herausforderung dar
Energy loss of a heavy quark produced in a finite-size quark-gluon plasma
We study the energy loss of an energetic heavy quark produced in a high
temperature quark-gluon plasma and travelling a finite distance before emerging
in the vacuum. While the retardation time of purely collisional energy loss is
found to be of the order of the Debye screening length, we find that the
contributions from transition radiation and the Ter-Mikayelian effect do not
compensate, leading to a reduction of the zeroth order (in an opacity
expansion) energy loss.Comment: QM2006 Proceedings; caption of fig 1 and ref [7] modified in v
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