1,985 research outputs found
Water resources management in a homogenizing world: Averting the Growth and Underinvestment trajectory
Biotic homogenization, a de facto symptom of a global biodiversity crisis, underscores the urgency of reforming water resources management to focus on the health and viability of ecosystems. Global population and economic growth, coupled with inadequate investment in maintenance of ecological systems, threaten to degrade environmental integrity and ecosystem services that support the global socioeconomic system, indicative of a system governed by the Growth and Underinvestment (G&U) archetype. Water resources management is linked to biotic homogenization and degradation of system integrity through alteration of water systems, ecosystem dynamics, and composition of the biota. Consistent with the G&U archetype, water resources planning primarily treats ecological considerations as exogenous constraints rather than integral, dynamic, and responsive parts of the system. It is essential that the ecological considerations be made objectives of water resources development plans to facilitate the analysis of feedbacks and potential trade-offs between socioeconomic gains and ecological losses. We call for expediting a shift to ecosystem-based management of water resources, which requires a better understanding of the dynamics and links between water resources management actions, ecological side-effects, and associated long-term ramifications for sustainability. To address existing knowledge gaps, models that include dynamics and estimated thresholds for regime shifts or ecosystem degradation need to be developed. Policy levers for implementation of ecosystem-based water resources management include shifting away from growth-oriented supply management, better demand management, increased public awareness, and institutional reform that promotes adaptive and transdisciplinary management approaches
Simulated Dark-Matter Halos as a Test of Nonextensive Statistical Mechanics
In the framework of nonextensive statistical mechanics, the equilibrium
structures of astrophysical self-gravitating systems are stellar polytropes,
parameterized by the polytropic index n. By careful comparison to the
structures of simulated dark-matter halos we find that the density profiles, as
well as other fundamental properties, of stellar polytropes are inconsistent
with simulations for any value of n. This result suggests the need to
reconsider the applicability of nonextensive statistical mechanics (in its
simplest form) to equilibrium self-gravitating systems.Comment: Accepted for publication in Physical Review
Delayed soft X-ray emission lines in the afterglow of GRB 030227
Strong, delayed X-ray line emission is detected in the afterglow of GRB
030227, appearing near the end of the XMM-Newton observation, nearly twenty
hours after the burst. The observed flux in the lines, not simply the
equivalent width, sharply increases from an undetectable level (<1.7e-14
erg/cm^2/s, 3 sigma) to 4.1e-14 erg/cm^2/s in the final 9.7 ks. The line
emission alone has nearly twice as many detected photons as any previous
detection of X-ray lines. The lines correspond well to hydrogen and/or
helium-like emission from Mg, Si, S, Ar and Ca at a redshift z=1.39. There is
no evidence for Fe, Co or Ni--the ultimate iron abundance must be less than a
tenth that of the lighter metals. If the supernova and GRB events are nearly
simultaneous there must be continuing, sporadic power output after the GRB of a
luminosity >~5e46 erg/s, exceeding all but the most powerful quasars.Comment: Submitted to ApJL. 14 pages, 3 figures with AASLaTe
Arrays of Josephson junctions in an environment with vanishing impedance
The Hamiltonian operator for an unbiased array of Josephson junctions with
gate voltages is constructed when only Cooper pair tunnelling and charging
effects are taken into account. The supercurrent through the system and the
pumped current induced by changing the gate voltages periodically are discussed
with an emphasis on the inaccuracies in the Cooper pair pumping.
Renormalisation of the Hamiltonian operator is used in order to reliably
parametrise the effects due to inhomogeneity in the array and non-ideal gating
sequences. The relatively simple model yields an explicit, testable prediction
based on three experimentally motivated and determinable parameters.Comment: 13 pages, 9 figures, uses RevTeX and epsfig, Revised version, Better
readability and some new result
Spectroscopic confirmation of a cluster of galaxies at z=1 in the field of the gravitational lens MG2016+112
We present new optical data on the cluster AX J2019+1127 identified by the
X-ray satellite ASCA at z\sim 1 (Hattori et al. 1997). The data suggest the
presence of a high-redshift cluster of galaxies responsible for the large
separation triple quasar MG2016+112. Our deep photometry reveals an excess of
z\sim 1 galaxy candidates, as already suspected by Benitez et al. (1999). Our
spectroscopic survey of 44 objects in the field shows an excess of 6 red
galaxies securely identified at z \sim 1, with a mean redshift of z =1.005 +/-
0.002. We estimate a velocity dispersion of \sigma = 771 (+430/-160) km s(-1)
based on these 6 galaxies and a V-band mass-to-light ratio of 215 (+308/-77)
h_50 M/L_sol. Our observations thus confirm the existence of a massive
structure acting as the lens, which explains the unusual configuration of the
triple quasar. Hence, there is no more need to invoke the existence of a ``dark
cluster'' to understand this lens system.Comment: 8 pages, 4 figures, uses aa.cls, accepted to Astronomy and
Astrophysics with minor change
The Optically Unbiased GRB Host (TOUGH) survey. IV. Lyman-alpha emitters
We report the results of a spectroscopic search for Lyman-alpha emission from
gamma-ray burst host galaxies. Based on the well-defined TOUGH sample of 69
X-ray selected Swift GRBs, we have targeted the hosts of a subsample of 20 GRBs
known from afterglow spectroscopy to be in the redshift range 1.8-4.5. We
detect Lya emission from 7 out of the 20 hosts, with the typical limiting
3sigma line flux being 8E-18 erg/cm2/s, corresponding to a Lya luminosity of
6E41 erg/s at z=3. The Lya luminosities for the 7 hosts in which we detect Lya
emission are in the range (0.6-2.3)E42 erg/s corresponding to star-formation
rates of 0.6-2.1 Msun/yr (not corrected for extinction). The rest-frame Lya
equivalent widths (EWs) for the 7 hosts are in the range 9-40A. For 6 of the 13
hosts for which Lya is not detected we place fairly strong 3sigma upper limits
on the EW (<20A), while for others the EW is either unconstrained or has a less
constraining upper limit. We find that the distribution of Lya EWs is
inconsistent with being drawn from the Lya EW distribution of bright Lyman
break galaxies at the 98.3% level, in the sense that the TOUGH hosts on average
have larger EWs than bright LBGs. We can exclude an early indication, based on
a smaller, heterogeneous sample of pre-Swift GRB hosts, that all GRB hosts are
Lya emitters. We find that the TOUGH hosts on average have lower EWs than the
pre-Swift GRB hosts, but the two samples are only inconsistent at the 92%
level. The velocity centroid of the Lya line is redshifted by 200-700 km/s with
respect to the systemic velocity, similar to what is seen for LBGs, possibly
indicating star-formation driven outflows from the host galaxies. There seems
to be a trend between the Lya EW and the optical to X-ray spectral index of the
afterglow (beta_OX), hinting that dust plays a role in the observed strength
and even presence of Lya emission. [ABRIDGED]Comment: ApJ accepted (v2: minor changes in the Subject headings and reference
list
The galaxies in the field of the nearby GRB980425/SN1998bw
We present spectroscopic observations of ESO 184-G82, the host galaxy of
GRB980425/SN1998bw, and six galaxies in its field. A host redshift of
z=0.0087+/-0.0006 is derived, consistent with that measured by Tinney et al.
(1998). Redshifts are obtained for the six surrounding galaxies observed. Three
of these galaxies lie within 11 Mpc of each other, confirming the suggestion
that some of these galaxies form a group. However, all of the field galaxies
observed lie at significantly greater distances than ESO 184-G82 and are
therefore not associated with it. The host galaxy of GRB980425/SN1998bw thus
appears to be an isolated dwarf galaxy and interactions with other galaxies do
not seem to be responsible for its star formation.Comment: 5 pages, 2 figures, accepted for publication in A&
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