9,763 research outputs found
A New Zealand Electricity Market Model: Assessment of the Effect of Climate Change on Electricity Production and Consumption.
In this paper, we introduce an electricity market model and use it to explore the effect of climate change on electricity output and prices. It is calibrated to the New Zealand Electricity Market, and includes multiple generation fuels, uncertain fuel availability, and storage options. The model is formulated in continuous time, which mimics the many short trading periods that are common to electricity spot markets, while properly incorporating forward-looking generation decision making. Specifically, it is used to estimate the effects of changes that may arise in characteristics of fuels -water and gas- as a consequence of climate change and climate change policies. The model does this under the polar cases of a competitive market structure and monopoly. There are three key findings from the results. First, the results illustrate the importance of allowing for volatility and including management of storage in electricity market models. Second, they suggest that reductions in average hydro fuel availability will reduce welfare significantly. Increases in the volatility of hydro fuel availability will also affect welfare, but to a very small extent. Third, the value of reservoir expansion is sensitive to the distribution of hydro fuel availability. Finally, the effects of a carbon tax are also reported.dynamic optimisation, electricity spot market performance, stochastic fuel availability, storage options, climate change
The orbital motion of the Arches cluster — clues on cluster formation near the galactic center
The Arches cluster is one of the most massive, young clusters in the Milky Way. Located inside the central molecular zone in the inner 200 pc of the Galactic center, it formed in one of the most extreme star-forming environments in the present-day Galaxy. Its young age of only 2.5 Myr allows us to observe the cluster despite the strong tidal shear forces in the inner Galaxy. The orbit of the cluster determines its dynamical evolution, tidal stripping, and hence its fate. We have measured the proper motion of the Arches cluster relative to the ambient field from Keck/NIRC2 LGS-AO and VLT/NAOS-CONICA NGS-AO observations taken 4.3 years earlier. When combined with the radial velocity, we derive a 3D space motion of 232 ± 30 km/s for the Arches. This motion is exceptionally large when compared to molecular cloud orbits in the GC, and places stringent constraints on the formation scenarios for starburst clusters in dense, nuclear environments
The orbital motion of the Quintuplet cluster - a common origin for the Arches and Quintuplet clusters?
We investigate the orbital motion of the Quintuplet cluster near the Galactic
center with the aim of constraining formation scenarios of young, massive star
clusters in nuclear environments. Three epochs of adaptive optics high-angular
resolution imaging with Keck/NIRC2 and VLT/NACO were obtained over a time
baseline of 5.8 years, delivering an astrometric accuracy of 0.5-1 mas/yr.
Proper motions were derived in the cluster reference frame and were used to
distinguish cluster members from the majority of field stars. Fitting the
cluster and field proper motion distributions with 2D gaussian models, we
derive the orbital motion of the cluster for the first time. The Quintuplet is
moving with a 2D velocity of 132 +/- 15 km/s with respect to the field along
the Galactic plane, which yields a 3D orbital velocity of 167 +/- 15 km/s when
combined with the previously known radial velocity. From a sample of 119 stars
measured in three epochs, we derive an upper limit to the velocity dispersion
in the core of the Quintuplet cluster of sigma_1D < 10 km/s. Knowledge of the
three velocity components of the Quintuplet allows us to model the cluster
orbit in the potential of the inner Galaxy. Comparing the Quintuplet's orbit
with the Arches orbit, we discuss the possibility that both clusters originated
in the same area of the central molecular zone. [abridged]Comment: 40 pages, 12 figures, accepted for publication in Ap
Cavitation and Bubble Bursting as Sources of Oceanic Ambient Noise
Cavitationlike bubble collapses and the bursting of floating bubbles have been proposed in the literature as sources of oceanic ambient noise at kilohertz frequencies. The first process is shown to be physically impossible in the oceanic environment. The noise produced by the second mechanism is estimated and shown to be too weak to be of any significance
Mapping the Outer Edge of the Young Stellar Cluster in the Galactic Center
We present new near-infrared spectroscopic observations of the outer edges of
the young stellar cluster around the supermassive black hole at the Galactic
center. The observations show a break in the surface-density profile of young
stars at approximately 13 arcsec (0.52 pc). These observations
spectroscopically confirm previous suggestions of a break based on photometry.
Using Gemini North's Near-Infrared Integral Field Spectrometer (NIFS) we are
able to detect and separate early- and late-type stars with a 75% completeness
at Ks = 15.5. We sample a region with radii between 7" to 23" (0.28 pc to 0.92
pc) from Sgr A*, and present new spectral classifications of 144 stars brighter
than Ks = 15.5, where 140 stars are late-type (> 1 Gyr) and only four stars are
early-type (young, 4-6 Myr). A broken power-law fit of the early-type
surface-density matches well with our data and previously published values. The
projected surface-density of late-type stars is also measured and found to be
consistent with previous results. We find that the observed early-type
surface-density profile is inconsistent with the theory of the young stars
originating from a tightly bound infalling cluster, as no significant trail of
young stars is found at radii above 13". We also note that either a simple disk
instability criterion or a cloud-cloud collision could explain the location of
the outer edge, though we lack information to make conclusive remarks on either
alternative. If this break in surface-density represents an edge to the young
stellar cluster it would set an important scale for the most recent episode of
star formation at the Galactic center.Comment: 17 pages, 11 figures, 3 tables, ApJ accepte
Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters
We investigate the circumstellar disc fraction as determined from L-band
excess observations of the young, massive Arches and Quintuplet clusters
residing in the central molecular zone of the Milky Way. The Quintuplet cluster
was searched for L-band excess sources for the first time. We find a total of
26 excess sources in the Quintuplet cluster and 21 in the Arches cluster, of
which 13 are new detections. With the aid of proper motion membership samples,
the disc fraction of the Quintuplet cluster was derived for the first time to
be 4.0 +/- 0.7%. There is no evidence for a radially varying disc fraction in
this cluster. In the case of the Arches cluster, a disc fraction of 9.2 +/-
1.2% approximately out to the cluster's predicted tidal radius, r < 1.5 pc, is
observed. This excess fraction is consistent with our previously found disc
fraction in the cluster in the radial range 0.3 < r < 0.8 pc. In both clusters,
the host star mass range covers late A- to early B-type stars, 2 < M < 15 Msun,
as derived from J-band photospheric magnitudes. We discuss the unexpected
finding of dusty circumstellar discs in these UV intense environments in the
context of primordial disc survival and formation scenarios of secondary discs.
We consider the possibility that the L-band excess sources in the Arches and
Quintuplet clusters could be the high-mass counterparts to T Tauri
pre-transitional discs. As such a scenario requires a long pre-transitional
disc lifetime in a UV intense environment, we suggest that mass transfer discs
in binary systems are a likely formation mechanism for the B-star discs
observed in these starburst clusters.Comment: 47 pages, 22 figures, accepted by A&
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