10,118 research outputs found
X-ray reflection in the nearby Seyfert 2 galaxy NGC 1068
We use the full broad-band XMM-Newton EPIC data to examine the X-ray spectrum
of the nearby Seyfert 2 galaxy NGC 1068, previously shown to be complex with
the X-ray continuum being a sum of components reflected/scattered from cold
(neutral) and warm (ionised) matter, together with associated emission line
spectra. We quantify the neutral and ionised reflectors in terms of the
luminosity of the hidden nucleus. Both are relatively weak, a result we
interpret on the Unified Seyfert Model by a near side-on view to the putative
torus, reducing the visibility of the illuminated inner surface of the torus
(the cold reflector), and part of the ionised outflow. A high inclination in
NGC 1068 also provides a natural explanation for the large (Compton-thick)
absorbing column in the line-of-sight to the nucleus. The emission line fluxes
are consistent with the strength of the neutral and ionised continuum
components, supporting the robustness of the spectral model.Comment: 8 pages. 7 figures. Accepted for publication in MNRA
An extended XMM-Newton observation of the Seyfert galaxy NGC 4051. I. Evidence for a shocked outflow
An extended XMM-Newton observation of the Seyfert 1 galaxy NGC 4051 has
revealed a rich absorption line spectrum indicating the presence of a
photoionized outflow with a wide range of velocities and ionization parameter.
At low continuum fluxes an emission line spectrum is well defined with both
narrow and broad components of several abundant metal ions. The absorption line
velocity structure and a broad correlation of velocity and ionization parameter
are consistent with an outflow scenario where a highly ionized, high velocity
wind, perhaps launched during intermittent super-Eddington accretion, runs into
the interstellar medium or previous ejecta, losing much of its kinetic energy
in the resultant strong shock. We explore the possibility that a quasi-constant
soft X-ray emission component may be evidence of this post-shock cooling. This
revised view of AGN outflows is consistent with multiple minor Eddington
accretion episodes creating a momentum-driven feedback linking black hole and
host galaxy growth.Comment: accepted for publication in Monthly Notices of the Royal Astronomical
Societ
Evidence for a high accretion rate as the defining parameter of Narrow-Line Seyfert 1 galaxies
X-ray spectral features which are unusually strong in many Narrow-Line
Seyfert galaxies are found to be consistent with reflection from strongly
ionized matter, providing further evidence of a high accretion rate in these
objects and offering a unique signature of that key parameter in future
observations.Comment: Contributed talk presented at the Joint MPE,AIP,ESO workshop on
NLS1s, Bad Honnef, Dec. 1999, to appear in New Astronomy Reviews; also
available at http://wave.xray.mpe.mpg.de/conferences/nls1-worksho
Dielectric Breakdown Strength of Polyethylene Nanocomposites
The term ânanometric dielectricsâ or simply ânanodielectricsâ was introduced in 1994 when Lewis [1] anticipated the potential property changes that would benefit electrical insulation due to nano-sized inclusion. Such materials, containing homogenous dispersion of small amount (normally less than 10wt%) of nanoparticles (with at least one dimension in nanometre range) in host matrix, are of specific dielectric interest. Although much effort has been put forth to investigate the potential dielectric benefit of such newly emerging materials, many uncertainties remain unanswered, and much remains to be explored [2]. Current experimental work is to investigate the preparation of nanodielectrics via solution blending approach. Polyethylene blend composed of 20wt% of high density polyethylene (HDPE) in low density polyethylene (LDPE) is proposed as the base polymer, with varying content of nanosilica (between 0wt% and 10wt%) as the fillers. Although expensive, solution blending method, when compared with melt compounding method, is expected to provide better dispersion of nanoparticles in polymers, thus providing qualitative data in understanding the behaviour of nanodielectrics [3]. Upon successful preparation of polyethylene nanocomposites, breakdown strength based on ASTM Standard D149-87 is to be conducted to determine the feasibility of such dielectric materials in engineering point of view. Figure 1 illustrates the schematic diagram of the breakdown test configuration. The samples are placed between two 6.3mm diameter steel ball bearings immersed in silicone fluid. AC voltage at a preset ramp rate will be applied until the samples fail and the values of breakdown voltages will be recorded and analysed using two-parameter Weibull distribution. Based upon top-down research approach, the underlying physics and chemistry associated with dielectric property changes will then be explored
The pattern-matching approach and its application in tourism development
Tourism development cannot be fully understood and validated from a positivist perspective without the testing of theory against empirical evidence. Thus the pattern-matching approach studies phenomena on the basis of facts and observations relevant to the testing of theories and models. This paper compares two selected tourism development theories, diffusion and dependency, against empirical evidence from Crete. In doing this it has three main objectives: to set out the nature of the pattern matching approach; to illustrate the application of the pattern matching approach, in an exploratory way; and to evaluate the approach based on the evidence of the exploratory application
Urban residents' attitudes toward tourism development: the case of Crete
This paper focuses on the identification and explanation of the attitudes of a sample of urban residents towards tourism development on Crete and their grouping with respect to these attitudes. Urban residents of Crete are quite strong in their support for tourism. However, the residents are not homogenous in their perceptions of tourism development. Education and employment in tourism were found to be the major single factors affecting the attitudes of residents of the island. A segmentation procedure based on attitude statements produced three clusters: the âAdvocatesâ (identified by their high appreciation of tourism benefits); the âSocially and Environmentally Concernedâ (characterised by a consensus towards the environmental and social costs from tourism expansion); and the âEconomic Scepticsâ (who showed lower appreciation of tourismâs economic benefits). The findings of the study are discussed with reference to the social exchange and the social representations theories and the conclusions of the study are provided
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