693 research outputs found
Innovation, the diesel engine and vehicle markets: Evidence from OECD engine patents
This paper uses a patent data set to identify factors fostering innovation of diesel engines between 1974 and 2010 in the OECD region. The propensity of engine producers to innovate grew by 1.9 standard deviations after the expansion of the car market, by 0.7 standard deviations following a shift in the EU fuel economy standard, and by 0.23 standard deviations. The propensity to develop emissions control techniques was positively influenced by pollution control laws introduced in Japan, in the US, and in the EU, but not with the expansion of the car market. Furthermore, a decline in loan rates stimulated the propensity to develop emissions control techniques, which were simultaneously crowded out by increases in publicly-funded transport research and development. Innovation activities in engine efficiency are explained by market size, loan rates and by (Organisation for Economic Cooperation and Development) diesel prices, inclusive of taxes. Price effects on innovation, outweigh that of the US corporate average fuel economy standards. Innovation is also positively influenced by past transport research and development. © 2014 Elsevier Ltd
Nuclear bars and blue nuclei within barred spiral galaxies
Multicolour near IR photometry for a sample of 32 large barred spiral
galaxies is presented. By applying ellipse fitting techniques, we identify
significant isophote twists with respect to the primary bar axis in the nuclear
regions of 70 \%\ of the sample. These twists are identified in galaxies
as late as SBbc and are clearly distinguishable from spiral arm morphology. At
most seven of the galaxies with isophote twists are inferred to possess
secondary (nuclear) bars, the axis ratios of which appear to correlate with
morphological type. The remainder may result from triaxial bulges, or from
oblate bulges misaligned with the primary bar. The near IR colour distributions
in these data show evidence for (red) circumnuclear star forming rings in 4
galaxies. The majority of the sample (19) also possess striking blue nuclear
regions, bluer than typical old stellar populations by 0.3 mag. in (J--H)
and 0.23 mag. in (H--K). Such blue colours do not appear to correlate
with the presence of nuclear rings or pseudo--rings, nor with the activity of
the host galaxy (as determined from emission--line spectroscopic
characteristics). Several mechanisms to explain this blue colour are
considered.Comment: 24 pages plain LaTex( including table captions), 5 tables and 18
figures. Accepted for publication in MNRAS. Paper and tables available via
anonymous ftp://143.167.4.101/pub/papers as sqiid-paper.tex and
table1,2,3.tex, table4.ps, table5.ps. Figures available as postcript upon
request to first Autho
The evidence for jet-cloud interactions in a sample of high/intermediate-redshift radio galaxies
We present the result obtained from a study, based on long-slit spectroscopy,
of the kinematics and ionization mechanisms of the line-emitting gas for a
sample of four high/intermediate-redshift radio galaxies. In two of the
galaxies (3C352 and 3C435A) the radio sources are of the same scale as the
emission-line regions, whereas in the other two (3C34 and 3C330) the radio
sources are extended on a larger scale than the emission-line structures. We
see evidence for shock-acceleration of the emission-line gas in the extended
regions of all the galaxies, even in the largest radio sources of our sample,
in which the radio hot spots have passed the extended gas of the galaxies. The
extended regions present highly disturbed kinematics (line-splitting and/or
underlying broad components), which are difficult to explain if we do not
consider a strong interaction between the radio-emitting components and the
ambient gas. However, the dominant ionization mechanism of the line-emitting
gas remains uncertain. We have compared the optical diagnostic line ratios of
the galaxies in our sample with both AGN-photoionization and shock-ionization
models. We find a lack of consistency in explaining the main ionization
mechanism of the emission-line gas. This suggest that, if the extended regions
are shock-ionized, some of the assumptions implicit in the shock models may
need to be reconsidered. In addition, we have investigated the nebular
continuum cointribution to the UV excess in the galaxies of our sample. We find
a substantial nebular emission contribution to the UV continuum in all the
cases. However, after the subtraction iof the nebular component, a significant
UV excess remains in the extended nebulae of most of the objects.Comment: 33 pages, 24 figures, accepted for publication in MNRAS. (Abstract
shortened for astro-ph
The optical polarization of M82 and the local spiral arm
This thesis comprises two separate but related topics in the study of optical polarization of galaxies. In part I we investigate interstellar polarization within 2 kpc of the sun and attempt to quantify the local structure of the galactic magnetic field. In part II we report the results of polarization measurements of the peculiar galaxy M82, obtained using a new polarimeter and digital reduction techniques, and discuss models of the origin of the polarization. Measurements of the linear polarization of starlight have been collated into a catalogue containing the Stokes' parameters in galactic coordinates for those stars for which reliable distances could be determined. The catalogue is presented in the form of vector maps on the sky in several distance intervals. Assuming a magnetic alignment hypothesis we have investigated the direction and form of the galactic magnetic field through e-vector plots and from the periodicity of the Stokes' parameters Q(É) and U(É) with galactic longitude. The results show the existence of a longitudinal field directed towards É = 45º ± 10º within 500 pc, and beyond this there is much confusion with a possible change in direction, associated with the bifurcation of the spiral arm, to É = 74º ± 10º, There is no evidence for a field directed towards É = 90º, It is clear however that a simple longitudinal model of the field is rather naive. The U(É) plots show strong evidence for an inclination of the field by 15º to the plane and this is not associated with a helical structure. The possible significance of this conclusion to the origin of the field is discussed. Incremental polarization maps have been produced but show little correlation with the spiral structure of the galaxy. There is strong evidence for irregularities in the field. The polarization appears to saturate in all directions at about 1 kpc from the sun. We interpret this as an observational selection effect. The major part of this work is directed towards studying the importance of irregularities in the field structure. Autocorrelation techniques have been used and unlike previous authors we can find no coherence in this component on scales greater than 50 pc. In the second part of the thesis we describe an imaging polarimeter constructed for use with a McMullan electronographic camera and designed to operate at an f/15 focus. This is the first polarimeter to use electronographic detection and the principles, construction and method of operation are described. The instrument is intended for observations of galaxies and other nebulae to diameters of up to 8 minutes of arc and has been successfully used to observe the irregular galaxy M82 in the B-band. The results of these observations are reported in this thesis. The polarimeter enables the simultaneous measurement of the linear polarization at more than 1500 locations in a 40 mm field of view to be made. This information is obtained in a series of eight exposures, which enables the effect of cathode sensitivity variations to be removed. The method is independent of variations in background sky brightness and polarization, and in atmospheric transparency. A review of the existing designs of polarimeter, their advantages and disadvantages and the possible sources of systematic errors are discussed. The optical system is also suitable for use with two-dimensional digital detectors but so far none have been used with the instrument. In order to take full advantage of the vast amount of information contained on each electronograph an entirely new digital analysis technique has been developed. Attempts have been made to locate features such as stars, grid overlaps, scratches and dirt blobs automatically using a random search technique. This proved unsatisfactory, and possible explanations and refinement in the approach outlined. A simple contour method is shown to be a satisfactory means of carrying out the feature extraction with manual assistance. A Highly accurate image registration method capable of producing a picture to picture registration better than 2µ is developed and the method takes into account small scale flaws, saturation effects, cathode sensitivity variations and differing exposure times. The technique is vastly superior to conventional methods of plate analysis and future refinements are discussed. The performance of the instrument in the laboratory and at the telescope is reported, the existence of severe instrumental effects established, and corrections derived and applied to the polarization data. Their eradication from the instrument is described and results of calibration measurements of standard stars with the improved optics presented, showing the instrument is capable of reaching a precision of ±0.5% in p and ± 3º in ɵ. The results of polarization measurements of M82 are presented and compared with previous observations. These results have a spatial resolution of between 5 and 8 times that of previous observations, are 20 times as numerous and have comparable accuracy (± 2.5% in p and ± 4º in ɵ). These results represent the first complete mapping of the linear polarization in an extragalactic system at optical wavelengths. A review of the existing observational material on M82 is presented and the relevance of the current observations established. The predictions of simple scattering models for producing the observed polarization are compared with the observations and show moderate agreement. The active region of the galaxy is located and the evolutionary status and energetics of M82 are discussed. The current problems in our understanding of the galaxy and suggestions for future work are detailed
Polarization Profiles of Scattered Emission Lines. II. Upstream Dust Scattering in the HH 1 Jet
Detailed comparisons are made between observations of scattered light
upstream of the head of the HH~1 jet and predictions of simple scattering
models. It is shown that, in order to unambiguously determine the velocity of
the head of the jet (bow shock) with respect to the upstream dust, existing
spectroscopic observations are insufficient and that spectropolarimetric
observations of the scattered light are necessary. Such an independent measure
of the bow shock velocity is important in order to test ``multiple outflow''
theories of Herbig-Haro jets. It is also shown 2that the scattering dust must
have a very forward-throwing scattering phase function
(\langle\cos\theta\rangle\msim 0.7) and slight evidence is found for a
dust-gas ratio that is higher than average.Comment: 11 pages, uuencoded compressed postscript (including 9 figures),
accepted for publication in Ap.J., IAUNAM_contrib.#34
Spectroastrometry of rotating gas disks for the detection of supermassive black holes in galactic nuclei. III. CRIRES observations of the Circinus galaxy
We present new CRIRES spectroscopic observations of BrGamma in the nuclear
region of the Circinus galaxy, obtained with the aim of measuring the black
hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an
ideal benchmark for the spectroastrometric technique given its proximity and
secure BH measurement obtained with the observation of its nuclear H2O maser
disk. The kinematical data have been analyzed both with the classical method
based on the analysis of the rotation curves and with the new method developed
by us and based on spectroastrometry. The classical method indicates that the
gas disk rotates in the gravitational potential of an extended stellar mass
distribution and a spatially unresolved mass of (1.7 +- 0.2) 10^7 Msun,
concentrated within r < 7 pc. The new method is capable of probing gas rotation
at scales which are a factor ~3.5 smaller than those probed by the rotation
curve analysis. The dynamical mass spatially unresolved with the
spectroastrometric method is a factor ~2 smaller, 7.9 (+1.4 -1.1) 10^6 Msun
indicating that spectroastrometry has been able to spatially resolve the
nuclear mass distribution down to 2 pc scales. This unresolved mass is still a
factor ~4.5 larger than the BH mass measurement obtained with the H2O maser
emission indicating that it has not been possible to resolve the sphere of
influence of the BH. Based on literature data, this spatially unresolved
dynamical mass distribution is likely dominated by molecular gas and it has
been tentatively identified with the circum-nuclear torus which prevents a
direct view of the central BH in Circinus. This mass distribution, with a size
of ~2pc, is similar in shape to that of the star cluster of the Milky Way
suggesting that a molecular torus, forming stars at a high rate, might be the
earlier evolutionary stage of the nuclear star clusters which are common in
late type spirals.Comment: A&A in press. We wish to honor the memory of our great friend and
colleague David Axon. He will be greatly missed by all of us. arXiv admin
note: text overlap with arXiv:1110.093
HST and Spitzer point source detection and optical extinction in powerful narrow-line radio galaxies
We present the analysis of infrared HST and Spitzer data for a sample of 13
FRII radio galaxies at 0.03<z<0.11 that are classified as narrow-line radio
galaxies (NLRG). In the context of the unified schemes for active galactic
nuclei (AGN), our direct view of the AGN in NLRG is impeded by a parsec-scale
dusty torus structure. Our high resolution infrared observations provide new
information about the degree of extinction induced by the torus, and the
incidence of obscured AGN in NLRG.
We find that the point-like nucleus detection rate increases from 25 per cent
at 1.025m, to 80 per cent at 2.05m, and to 100 per cent at 8.0m.
This supports the idea that most NLRG host an obscured AGN in their centre. We
estimate the extinction from the obscuring structures using X-ray, near-IR and
mid-IR data. We find that the optical extinction derived from the 9.7m
silicate absorption feature is consistently lower than the extinction derived
using other techniques. This discrepancy challenges the assumption that all the
mid-infrared emission of NLRG is extinguished by a simple screen of dust at
larger radii. This disagreement can be explained in terms of either weakening
of the silicate absorption feature by (i) thermal mid-IR emission from the
narrow-line region, (ii) non-thermal emission from the base of the radio jets,
or (iii) by direct warm dust emission that leaks through a clumpy torus without
suffering major attenuation.Comment: 18 pages, 7 figures, 8 tables, accepted for publication in MNRA
High Accuracy Near-infrared Imaging Polarimetry with NICMOS
The findings of a nine orbit calibration plan carried out during HST Cycle
15, to fully determine the NICMOS camera 2 (2.0 micron) polarization
calibration to high accuracy, are reported. Recently Ueta et al. and Batcheldor
et al. have suggested that NICMOS possesses a residual instrumental
polarization at a level of 1.2-1.5%. This would completely inhibit the data
reduction in a number of GO programs, and hamper the ability of the instrument
to perform high accuracy polarimetry. We obtained polarimetric calibration
observations of three polarimetric standards at three spacecraft roll angles
separated by ~60deg. Combined with archival data, these observations were used
to characterize the residual instrumental polarization in order for NICMOS to
reach its full potential of accurate imaging polarimetry at p~1%. Using these
data, we place an 0.6% upper limit on the instrumental polarization and
calculate values of the parallel transmission coefficients that reproduce the
ground-based results for the polarimetric standards. The uncertainties
associated with the parallel transmission coefficients, a result of the
photometric repeatability of the observations, are seen to dominate the
accuracy of p and theta. However, the updated coefficients do allow imaging
polarimetry of targets with p~1.0% at an accuracy of +/-0.6% and +/-15deg. This
work enables a new caliber of science with HST.Comment: 13 pages, 9 figures, PASP accepte
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