2,900 research outputs found
Electricity Intensities of the OECD and South Africa: A Comparison
Improving a country’s electricity efficiency is considered one of the important ways to reduce its greenhouse gas emissions and to meet its commitments concerning climate change mitigation. In this paper, we conduct a comparative analysis between South Africa and OECD members’ total and sectoral electricity intensities. This is done to establish a sense of South Africa’s relative performance in this regard, to ascertain the possible scope for improvement and, if such scope exists, to determine in which of the industrial sectors
South Africa’s Electricity Consumption: A Sectoral Decomposition Analysis
South Africa's electricity consumption has increased sharply since the early 1990s. Here we conduct a sectoral decomposition analysis of the electricity consumption for the period 1993 to 2006, to determine the main drivers of this increase. The results show that the increase was due mainly to output- or production-related factors, with structural changes playing a secondary role. While there is some evidence of efficiency improvements, indicated here as a slowdown in the rate of increase in electricity intensity, it was not nearly sufficient to offset the combined production and structural effects that propelled electricity consumption higher.
The attitude control of a satellite in an elliptic orbit
Attitude control system for satellite in elliptical orbit calculated by linear equations and computer simulatio
Neighboring optimal feedback control of multi- input nonlinear dynamical systems using discontinuous control
Neighboring optimal feedback control of multi-input nonlinear dynamic system
Basic studies in space vehicle attitude control Ninth semiannual status report
Space vehicle attitude control systems - manned space station, satellite in elliptic orbit, and solar perturbation of Mars Orbite
Basic studies in space vehicle attitude control Semiannual status report, Dec. 1966 - Dec. 1967
Nonlinear optimal attitude control of planet pointing space vehicles, and optimal control of satellite trajectorie
Basic Studies in Space Vehicle Attitude Control Tenth Semiannual Status Report, Period Ending Jun. 1966
Nonlinear optimal control of planet-pointing space vehicle, basic methods for attitude control, and satellite orbit theorie
The Effect of Mass Ratio on the Morphology and Time-scales of Disc Galaxy Mergers
The majority of galaxy mergers are expected to be minor mergers. The
observational signatures of minor mergers are not well understood, thus there
exist few constraints on the minor merger rate. This paper seeks to address
this gap in our understanding by determining if and when minor mergers exhibit
disturbed morphologies and how they differ from the morphology of major
mergers. We simulate a series of unequal-mass moderate gas-fraction disc galaxy
mergers. With the resulting g-band images, we determine how the time-scale for
identifying galaxy mergers via projected separation and quantitative morphology
(the Gini coefficient G, asymmetry A, and the second-order moment of the
brightest 20% of the light M20) depends on the merger mass ratio, relative
orientations and orbital parameters. We find that G-M20 is as sensitive to 9:1
baryonic mass ratio mergers as 1:1 mergers, with observability time-scales ~
0.2-0.4 Gyr. In contrast, asymmetry finds mergers with baryonic mass ratios
between 4:1 and 1:1 (assuming local disc galaxy gas-fractions). Asymmetry
time-scales for moderate gas-fraction major disc mergers are ~ 0.2-0.4 Gyr, and
less than 0.06 Gyr for moderate gas-fraction minor mergers. The relative
orientations and orbits have little effect on the time-scales for morphological
disturbances. Observational studies of close pairs often select major mergers
by choosing paired galaxies with similar luminosities and/or stellar masses.
Therefore, the various ways of finding galaxy mergers (G-M20, A, close pairs)
are sensitive to galaxy mergers of different mass ratios. By comparing the
frequency of mergers selected by different techniques, one may place empirical
constraints on the major and minor galaxy merger rates.Comment: 16 pages; resubmitted to MNRA
The Specific Globular Cluster Frequencies of Dwarf Elliptical Galaxies from the Hubble Space Telescope
The specific globular cluster frequencies (S_N) for 24 dwarf elliptical (dE)
galaxies in the Virgo and Fornax Clusters and the Leo Group imaged with the
Hubble Space Telescope are presented. Combining all available data, we find
that for nucleated dEs --- which are spatially distributed like giant
ellipticals in galaxy clusters --- S_N(dE,N)=6.5 +- 1.2 and S_N increases with
M_V, while for non-nucleated dEs --- which are distributed like late-type
galaxies --- S_N(dE,noN)=3.1 +- 0.5 and there is little or no trend with M_V.
The S_N values for dE galaxies are thus on average significantly higher than
those for late-type galaxies, which have S_N < 1. This suggests that dE
galaxies are more akin to giant Es than to late-type galaxies. If there are
dormant or stripped irregulars hiding among the dE population, they are likely
to be among the non-nucleated dEs. Furthermore, the similarities in the
properties of the globular clusters and in the spatial distributions of dE,Ns
and giant Es suggest that neither galaxy mass or galaxy metallicity is
responsible for high values of S_N. Instead, most metal-poor GCs may have
formed in dwarf-sized fragments that merged into larger galaxies.Comment: 12 pages (uses aaspp4.sty), 2 figures, 1 table, to appear in the
Astrophysical Journa
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