756 research outputs found
A Look at Philosophical Analysis
The author of this article, Dr. Ralph L. Pounds, is the author of many books and a Professor of Education at the University of Cincinnati. This article was first given as the presidential address of the Ohio Valley Philosophy of Education Society
Inter- and Intra-sensory Modality Stimulus Scaling: A Method for the Determination of the Relative Salience of Stimuli in Poison-based Aversion Learning by Pigeons
One of the most rapidly expanding areas of research in psychology has been poison-based aversion learning (PBAL). The PBAL paradigm typically involves: exposing an animal to a novel substance; inducing illness following ingestion of that substance; and then providing access to the substance at a later time. The initial reaction to the novel substance is generally to reduce consumption, a finding labeled neophobia. The reduction of substance intake on test day is called learned aversion.
Following demonstrations of cue-to-consequence specificity (i.e., the differential associability of some stimuli with certain consequences) in PBAL research with rats, recent research has focused on PBAL by avians. Such research has been instigated by speculation that avians might be specially adapted to better associate visual rather than flavor stimuli with illness. Studies to determine the relative salience of visual or flavor cues in avian PBAL have reported contradictory findings. A number of methodological differences exist between these studies including differences in stimulus intensity and type, duration between conditioning and assessment, and method of assessment. The current series of experiments made several methodological improvements to clarify the issue of cue to consequence specificity in PBAL with avians. Three experiments with pigeons as subjects are reported.
The first experiment equated (scaled) stimulus intensity across different sense modalities by equating neophobic responses to various concentrations of salt, sour, and red water.
The second experiment determined the extended effects of the illness-inducing stimulus alone on fluid consumption by pigeons in a restricted access to water environment.
The third experiment was based upon results from the first two experiments and assessed aversion, at two different post-injection times, to one of two concentrations of either salt, sour, or red water CSs. In addition, a compound (flavor plus color) conditioning group was employed.
Aversion was a function of flavor or color stimulus intensity. No differences were observed in degree of aversion demonstrated by groups receiving stimuli equated for initial suppression. Evidence for overshadowing or potentiation was not found.
The results support the position that neither flavor or color stimuli are necessarily the most salient in avian PBAL
Resolving the large scale spectral variability of the luminous Seyfert 1 galaxy 1H 0419-577: Evidence for a new emission component and absorption by cold dense matter
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in
September 2002, when the source was in an extreme low-flux state, found a very
hard X-ray spectrum at 1-10 keV with a strong soft excess below ~1 keV.
Comparison with an earlier XMM-Newton observation when 1H 0419-577 was `X-ray
bright' indicated the dominant spectral variability was due to a steep power
law or cool Comptonised thermal emission. Four further XMM-Newton observations,
with 1H 0419-577 in intermediate flux states, now support that conclusion,
while we also find the variable emission component in intermediate state
difference spectra to be strongly modified by absorption in low ionisation
matter. The variable `soft excess' then appears to be an artefact of absorption
of the underlying continuum while the `core' soft emission can be attributed to
recombination in an extended region of more highly ionised gas. We note the
wider implications of finding substantial cold dense matter overlying (or
embedded in) the X-ray continuum source in a luminous Seyfert 1 galaxy.Comment: 34 pages, 15 figures, submitted to Ap
Evidence of a high velocity ionised outflow in a second narrow line quasar PG0844+349
Following the discovery of X-ray absorption in a high velocity outflow from
the bright quasar PG1211+143 we have searched for similar features in XMM
archival data of a second (high accretion rate) quasar PG0844+349. Evidence is
found for absorption lines in both the EPIC and RGS spectra, whose
identification with resonance transitions in H-like Fe, S, and Ne implies an
origin in highly ionised matter with an outflow velocity of order ~0.2c. The
line equivalent widths require a line-of-sight column density of N_H ~ 4 x
10^23 cm^-2, at an ionisation parameter of log(xi) ~ 3.7. Assuming a radial
outflow being driven by radiation pressure from the inner accretion disc, as
suggested previously for PG1211+143, the flow is again likely to be optically
thick, in this case within ~ 25 Schwarzschild radii. We suggest that a high
velocity, highly ionised outflow is likely to be a significant component in the
mass and energy budgets of many AGN accreting at or above the Eddington rate.Comment: 7 pages, 4 figures, accepted by MNRA
1WGA J2223.7-0206: a Narrow-Line Quasi-Stellar Object in the XMM-Newton field of view of 3C445
We report the discovery of a Narrow Line QSO located at about 1.3' from the
Broad Line Radio Galaxy 3C445. The source,1WGA J2223.7-0206, although already
revealed by ROSAT has never been optically identified previously. An XMM-Newton
observation of 3C445 has allowed, for the first time, an accurate X-ray
spectral study of 1WGA J2223.7-0206, revealing an ultra-soft spectrum and fast
flux variations typical of Narrow Line AGN. The 0.2-10 keV spectrum is well
represented by a power law (Gamma=2.5) plus a black body component (kT = 117
eV) absorbed by Galactic NH. About 80% of the X-ray flux is emitted below 2
keV. The 0.2-2 keV flux is observed to decrease by about a factor 1.6 in about
5000 s. The optical observations, triggered by the X-ray study, confirm the
Narrow Line AGN nature of this source. The continuum is blue with typical AGN
emission lines, pointing to a redshift z=0.46. The full width half maximum of
H_beta is 2000 km/secand the flux rat io [OIII}]/H_beta=0.21. The optical
luminosity (M_R=-23.2) and the point-like appearance in the optical images
identify 1WGA J2223.7-0206 as a Narrow Line QSO. From the optical-UV-X-ray
Spectral Energy Distribution we obtain a lower limit of the bolometric
luminosity of 1WGA J2223.7-0206 (L_bol > 3 10^{45} erg/sec) implying, for
accretion rates close to the Eddington limit, a black hole mass M_BH > 2.4 x
10^{7} M_{\odot}Comment: 6 pages, 5 figures, accepted by A&A, removed pag. 7 containing a
duplication of Fig.
An XMM-Newton observation of Mrk 3 - a Seyfert galaxy just over the edge
A 100ks XMM-Newton observation of the nearby Seyfert 2 galaxy Mrk 3 offers a
unique opportunity to explore the complexity of its X-ray spectrum. We find the
\~3-8 keV continuum to be dominated by reflection from cold matter, with
fluorescent K-shell lines detected from Ni, Fe, Ca, Ar, S, Si and Mg. At higher
energies an intrinsic power law continuum, with canonical Seyfert 1 photon
index, is seen through a near-Compton-thick cold absorber. A soft excess below
\~3 keV is found to be dominated by line emission from an outflow of `warm'
gas, photo-ionised and photo-excited by the intrinsically strong X-ray
continuum. Measured blue-shifts in the strong Fe K-alpha and OVII and VIII
emission lines are discussed in terms of the properties of the putative
molecular torus and ionised outflow.Comment: 16 figures; accepted for publication in MNRA
A high velocity ionised outflow and XUV photosphere in the narrow emission line quasar PG1211+143
We report on the analysis of a ~60 ksec XMM observation of the bright, narrow
emission line quasar PG 1211+143. Absorption lines are seen in both EPIC and
RGS spectra corresponding to H- and He-like ions of Fe, S, Mg, Ne, O, N and C.
The observed line energies indicate an ionised outflow velocity of ~24000 km
s^-1. The highest energy lines require a column density of N_H ~ 5 x 10^23
cm^-2, at an ionisation parameter of log(xi) ~ 3.4. If the origin of this high
velocity outflow lies in matter being driven from the inner disc, then the flow
is likely to be optically thick within a radius ~130 Schwarzschild radii,
providing a natural explanation for the Big Blue Bump (and strong soft X-ray)
emission in PG 1211+143.Comment: Accepted by MNRAS; Table 1 correcte
Fe K emission and absorption features in XMM-Newton spectra of Mkn 766 - evidence for reprocessing in flare ejecta
We report on the analysis of a long XMM-Newton EPIC observation in 2001 May
of the Narrow Line Seyfert 1 galaxy Mkn 766. The 3-11 keV spectrum exhibits a
moderately steep power law continuum, with a broad emission line at ~6.7 keV,
probably blended with a narrow line at ~6.4 keV, and a broad absorption trough
above ~8.7 keV. We identify both broad spectral features with reprocessing in
He-like Fe. An earlier XMM-Newton observation of Mkn 766 in 2000 May, when the
source was a factor ~2 fainter, shows a similar broad emission line, but with a
slightly flatter power law and absorption at a lower energy. In neither
observation do we find a requirement for the previously reported broad 'red
wing' to the line and hence of reflection from the innermost accretion disc.
More detailed examination of the longer XMM-Newton observation reveals evidence
for rapid spectral variability in the Fe K band, apparently linked with the
occurrence of X-ray 'flares'. A reduction in the emission line strength and
increased high energy absorption during the X-ray flaring suggests that these
transient effects are due to highly ionised ejecta associated with the flares.
Simple scaling from the flare avalanche model proposed for the luminous QSO PDS
456 (Reeves etal. 2002) confirms the feasibility of coherent flaring being the
cause of the strong peaks seen in the X-ray light curve of \mkn.Comment: 9 pages, 11 figures, submitted to MNRA
A simultaneous XMM-Newton and BeppoSAX observation of the archetypal Broad Line Seyfert 1 galaxy NGC 5548
We report the spectral analysis of a long XMM-Newton observation of the
well-studied, moderate luminosity Broad Line Seyfert 1 galaxy NGC 5548. The
source was at an historically average brightness and we find the hard (3-10
keV) spectrum can be well fitted by a power law of photon index gamma ~ 1.75,
together with reflection. The only feature in the hard X-ray spectrum is a
narrow emission line near 6.4 keV, with an equivalent width of ~ 60 eV. The
energy and strength of this line is consistent with fluorescence from `neutral'
iron distant from the central continuum source. We find no evidence for a broad
Fe K line, with an upper limit well below previous reports, suggesting the
inner accretion disc is now absent or highly ionised. The addition of
simultaneous BeppoSAX data allows the analysis to be extended to 200 keV,
yielding important constraints on the total reflection. Extrapolation of the
hard X-ray power law down to 0.3 keV shows a clear `soft excess' below ~ 0.7
keV. After due allowance for the effects of a complex warm absorber, measured
with the XMM-Newton RGS, we find the soft excess is better described as a
smooth upward curvature in the continuum flux below ~ 2 keV. The soft excess
can be modelled either by Comptonised thermal emission or by enhanced
reflection from the surface of a highly ionised disc.Comment: 9 pages, 11 figures, accepted by MNRAS; minor changes to text and
figure
XMM-Newton observations of seven soft X-ray excess QSOs
XMM-Newton observations of seven QSOs are presented and the EPIC spectra
analysed. Five of the AGN show evidence for Fe K-alpha emission, with three
being slightly better fitted by lines of finite width; at the 99 per cent level
they are consistent with being intrinsically narrow, though. The broad-band
spectra can be well modelled by a combination of different temperature
blackbodies with a power-law, with temperatures between kT ~ 100-300 eV. On the
whole, these temperatures are too high to be direct thermal emission from the
accretion disc, so a Comptonization model was used as a more physical
parametrization. The Comptonizing electron population forms the soft excess
emission, with an electron temperature of ~ 120-680 eV. Power-law, thermal
plasma and disc blackbody models were also fitted to the soft X-ray excess. Of
the sample, four of the AGN are radio-quiet and three radio-loud. The
radio-quiet QSOs may have slightly stronger soft excesses, although the
electron temperatures cover the same range for both groups.Comment: 13 pages, 7 figures, accepted for publication in MNRA
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