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Search Results: 1 - 10 of 189972 matches for " G Eracleous "
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Character strengths of adolescent survivors of childhood cancer
T Guse, G Eracleous
Health SA Gesondheid , 2011,
Abstract: There is increased interest in possible positive outcomes for survivors of childhood cancer. This study investigated the manifestation of character strengths in adolescents who have survived cancer compared to that seen in healthy adolescents. The aim was to establish whether specific character strengths may be more prominent in adolescents who have survived cancer than in healthy adolescents. Two groups of participants, consisting of adolescents who have survived childhood cancer (n = 21) and a group of healthy adolescents (n = 21), were obtained through convenience sampling. They completed the Values in Action Inventory for Youth (VIAYouth) (Park & Peterson 2006) as a measure of character strengths. No significant differences were found between the character strengths of adolescents who have survived cancer and their healthy peers, unlike the findings of a similar earlier study with adults (Peterson, Park & Seligman 2006). It is concluded that the experience of serious illness such as cancer neither hindered nor enhanced the development of character strengths in this group of adolescent survivors. More research is needed to understand positive psychological functioning in the aftermath of childhood cancer. Daar is toenemende belangstelling in moontlike positiewe uitkomste vir kinders wat kanker oorleef het. Hierdie studie het ondersoek hoe karaktersterktes na vore kom in adolessente wat as kinders met kanker gediagnoseer is in vergelyking met dié in ‘n groep gesonde adolessente. Die studie het ten doel gehad om vas te stel of spesifieke karaktersterktes meer opvallend na vore kom in adolessente wat kanker oorleef het. Die deelnemers is deur middel van gerieflikheidsteekproefneming gekies. Die twee groepe het bestaan uit adolessente wat as kinders met kanker gediagnoseer is (n = 21) en ‘n groep gesonde adolessente (n = 21). Deelnemers het die Values in Action Inventory for Youth (VIA-Youth) (Park & Peterson 2006) voltooi ten einde karaktersterktes te bepaal. Daar was geen beduidende verskil tussen die karaktersterktes van die adolessente wat kanker oorleef het en die gesonde groep nie, anders as met ‘n soortgelyke vroe re studie onder volwassenes (Peterson, Park & Seligman 2006). Dit blyk dat die ervaring wat met ernstige siekte soos kanker gepaardgaan, ontwikkeling van karaktersterktes nóg bevorder nóg belemmer het in hierdie groep adolessente kankeroorwinnaars. Verdere navorsing is nodig om aspekte van positiewe sielkundige funksionering in adolessente kankeroorwinnaars te verstaan.
Double- (and Single-) Peaked Emission Lines as Probes of the Structure of the Outer Accretion Disks in AGN
H. M. L. G. Flohic,M. Eracleous
Revista mexicana de astronomía y astrofísica , 2008,
Abstract:
Spectral Energy Distributions of Weak Active Galactic Nuclei Associated With Low-Ionization Nuclear Emission Regions
Michael Eracleous,Jason A. Hwang,Helene M. L. G. Flohic
Physics , 2010, DOI: 10.1088/0067-0049/187/1/135
Abstract: We present a compilation of spectral energy distributions of 35 weak AGNs in LINERs using recent data from the published literature. We make use of previously published compilations of data, after complementing and extending them with more recent data. The main improvement in the recent data is afforded by high-spatial resolution observations with the Chandra X-Ray Observatory and high-spatial resolution radio observations utilizing a number of facilities. In addition, a considerable number of objects have been observed with the HST in the near-IR through near-UV bands since the earlier compilations were published. The data include upper limits resulting from either non-detections or observations at low spatial resolution that do not isolate the AGN. For the sake of completeness, we also compute and present a number of quantities from the data, such as alpha-ox, bolometric corrections, bolometric luminosities, Eddington ratios, and the average SED. We anticipate that these data will be useful for a number of applications. In a companion paper, we use a subset of these data ourselves to assess the energy budgets of LINERs.
An Assessment of the Energy Budgets of Low-Ionization Nuclear Emission Regions
Michael Eracleous,Jason A. Hwang,Helene M. L. G. Flohic
Physics , 2010, DOI: 10.1088/0004-637X/711/2/796
Abstract: Using the SEDs of the weak AGNs 35 LINERs presented in a companion paper, we assess whether photoionization by the weak AGN can power the emission-line luminosities measured through the large (few-arcsecond) apertures used in ground-based spectroscopic surveys. Spectra taken through such apertures are used to define LINERs as a class and constrain non-stellar photoionization models for LINERs. Therefore, our energy budget test is a self-consistency check of the idea that the observed emission lines are powered by an AGN. We determine the ionizing luminosities and photon rates by integrating the observed SEDs and by scaling a template SED. Even if all ionizing photons are absorbed by the line-emitting gas, more than half of our LINERs suffer from a deficit of ionizing photons. In 1/3 of LINERs the deficit is severe. If only 10% of the ionizing photons are absorbed by the gas, there is an ionizing photon deficit in 85% of LINERs. We disfavor the possibility that additional electromagnetic power, either obscured or emitted in the unobservable far-UV band, is available from the AGN. We consider other power sources such as mechanical heating by compact jets and photoionization by young or old stars. Photoionization by young stars may be important in a small fraction of cases. Mechanical heating provides enough power in most cases but it is not clear how this power is transferred to the emission-line gas. Photoionization by post-AGB stars is an important power source; it provides more ionizing photons that the AGN in more than half of the LINERs and enough ionizing photons to power the emission lines in 1/3 of the LINERs. It appears likely that the emission-line spectra of LINERs obtained from the ground include the sum of emission from different regions where different power sources dominate.
Three LINERs Under the Chandra X-Ray Microscope
M. Eracleous,J. C. Shields,G. Chartas,E. C. Moran
Physics , 2001, DOI: 10.1086/324394
Abstract: We use X-ray observations of three galaxies hosting LINERs (NGC 404, NGC 4736, NGC 4579) with Chandra to study their power sources. We find very diverse properties within this small group: NGC 404 has an X-ray-faint nucleus with a soft, thermal spectrum, NGC 4736 harbors a plethora of discrete X-ray sources in and around its nucleus, and NGC 4579 has a dominant nuclear point source embedded in a very extended, diffuse nebulosity. From their multi- wavelength properties we conclude the following: the nucleus of NGC 404 is the site of a weak, compact starburst, whose X-ray emission is due to gas heated by stellar winds and supernovae, NGC 4736 is in a recent or aging starburst phase, where the X-ray emission is dominated by a dense cluster of X-ray binaries, and NGC 4579 is powered by accretion onto a supermassive black hole. We detect 39 discrete sources in NGC 4736 and 21 in NGC 4579, most with L_X > 10^37 erg/s. One source in the disk of NGC 4579 could be an ultraluminous X-ray binary with L_X (2-10 keV) = 9x10^39 erg/s, but it could also be a background quasar. The most luminous discrete sources have simple power-law spectra, which along with their luminosities suggest that these are X-ray binaries accreting near or above the Eddington rate for a neutron star. By comparing the luminosity functions of discrete X-ray sources in these and other galaxies we find a potential connection between the age of the stellar population and the slope of the cumulative X-ray source luminosity function: galaxies with primarily old stellar populations have steeper luminosity functions than starburst galaxies. We suggest that this difference results from the contribution of high-mass X-ray binaries from the young stellar population to the upper end of the luminosity function.
Variable X-ray Absorption in mini-BAL QSOs
M. Giustini,M. Cappi,G. Chartas,M. Eracleous,G. G. C. Palumbo,C. Vignali
Physics , 2009,
Abstract: We present the results of X-ray spectral analysis of two mini-BAL QSOs, PG 1126-041 and PG 1351+640, aimed at getting insights into the physics of quasar outflows. We find strong X-ray spectral variability on timescales of years. These variations can be well reproduced by variations of physical properties as the covering factor and column density of ionized gas along the line of sight, compatible with radiatively-driven accretion disk wind models.
A deep look at the inner regions of the mini-BAL QSO PG 1126-041 with XMM-Newton
M. Giustini,M. Cappi,G. Chartas,M. Eracleous,G. G. C. Palumbo,C. Vignali
Physics , 2009, DOI: 10.1063/1.3475287
Abstract: A long XMM-Newton observation of the mini-BAL QSO PG 1126-041 allowed us to detect a highly ionized phase of X-ray absorbing gas outflowing at v~15000 km/s. Physical implications are briefly discussed.
Caught in the Act; Chandra Observations of Microlensing of the Radio-Loud Quasar MG J0414+0534
G. Chartas,E. Agol,M. Eracleous,G. Garmire,M. W. Bautz,N. D. Morgan
Physics , 2001, DOI: 10.1086/339162
Abstract: We present results from monitoring of the distant (z = 2.64), gravitationally lensed quasar MG J0414+0534 with the Chandra X-ray Observatory. An Fe Ka line at 6.49 +/- 0.09 keV (rest-frame) with an equivalent width of ~ 190eV consistent with fluorescence from a cold medium is detected at the 99 percent confidence level in the spectrum of the brightest image A. During the last two observations of our monitoring program we detected a five-fold increase of the equivalent width of a narrow Fe Ka line in the spectrum of image B but not in the brighter image A whereas image C is too faint to resolve the line. The continuum emission component of image B did not follow the sudden enhancement of the iron line in the last two observations. We propose that the sudden increase in the iron line strength from ~ 190eV to 900eV only in image B can be explained with a caustic crossing due to microlensing that selectively enhances a strip of the line emission region of the accretion disk. The non-enhancement of the continuum emission in the spectrum of image B suggests that the continuum emission region is concentrated closer to the center of the accretion disk than the iron line emission region and the magnification caustic has not reached close enough to the former region to amplify it. A model of a caustic crossing event predicts discontinuities in the light-curve of the magnification and provides an upper limit of ~ 5 x 10^(-4) pc on the outer radius of the Fe Ka emission region. The non-detection of any relativistic or Doppler shifts of the iron line in the spectrum of image B implies that the magnification caustic for the last two observations was located at a radius greater than ~ 100 gravitational radii.
Chandra uncovers a hidden Low-Luminosity AGN in the radio galaxy Hydra~A (3C~218)
R. M. Sambruna,G. Chartas,M. Eracleous,R. Mushotzky,J. Nousek
Physics , 2000, DOI: 10.1086/312569
Abstract: We report the detection with Chandra of a Low-Luminosity AGN (LLAGN) in the Low Ionization Emission Line Region (LINER) hosted by Hydra A, a nearby (z=0.0537) powerful FRI radio galaxy with complex radio and optical morphology. In a 20 ks ACIS-S exposure during the calibration phase of the instrument, a point source is detected at energies $\grtsim$ 2 keV at the position of the compact radio core, embedded in diffuse thermal X-ray emission ($kT \sim 1$ keV) at softer energies. The spectrum of the point source is well fitted by a heavily absorbed power law with intrinsic column density N$_H^{int} \sim 3 \times 10^{22}$ \nh and photon index $\Gamma \sim 1.7$. The intrinsic (absorption-corrected) luminosity is $L_{2-10 keV} \sim 1.3 \times 10^{42}$ \lum. These results provide strong evidence that an obscured AGN is present in the nuclear region of Hydra~A. We infer that the optical/UV emission of the AGN is mostly hidden by the heavy intrinsic reddening. In order to balance the photon budget of the nebula, we must either postulate that the ionizing spectrum includes a UV bump or invoke and additional power source (shocks in the cooling flow or interaction with the radio jets). Using an indirect estimate of the black hole mass and the X-ray luminosity, we infer that the accretion rate is low, suggesting that the accretion flow is advection dominated. Finally, our results support current unification schemes for radio-loud sources, in particular the presence of the putative molecular torus in FR~Is. These observations underscore the power of the X-rays and of \chandra in the quest for black holes.
Character strengths of adolescent survivors of childhood cancer
Tharina Guse,Gloria Eracleous
Health SA Gesondheid , 2011, DOI: 10.4102/hsag.v16i1.544
Abstract: There is increased interest in possible positive outcomes for survivors of childhood cancer. This study investigated the manifestation of character strengths in adolescents who have survived cancer compared to that seen in healthy adolescents. The aim was to establish whether specific character strengths may be more prominent in adolescents who have survived cancer than in healthy adolescents. Two groups of participants, consisting of adolescents who have survived childhood cancer (n = 21) and a group of healthy adolescents (n = 21), were obtained through convenience sampling. They completed the Values in Action Inventory for Youth (VIAYouth)(Park & Peterson 2006) as a measure of character strengths. No significant differences were found between the character strengths of adolescents who have survived cancer and their healthy peers, unlike the findings of a similar earlier study with adults (Peterson, Park & Seligman 2006). It is concluded that the experience of serious illness such as cancer neither hindered nor enhanced the development of character strengths in this group of adolescent survivors. More research is needed to understand positive psychological functioning in the aftermath of childhood cancer. Opsomming Daar is toenemende belangstelling in moontlike positiewe uitkomste vir kinders wat kanker oorleef het. Hierdie studie het ondersoek hoe karaktersterktes na vore kom in adolessente wat as kinders met kanker gediagnoseer is in vergelyking met dié in ‘n groep gesonde adolessente. Die studie het ten doel gehad om vas te stel of spesifieke karaktersterktes meer opvallend na vore kom in adolessente wat kanker oorleef het. Die deelnemers is deur middel van gerieflikheidsteekproefneming gekies. Die twee groepe het bestaan uit adolessente wat as kinders met kanker gediagnoseer is (n = 21) en ‘n groep gesonde adolessente (n = 21).Deelnemers het die Values in Action Inventory for Youth (VIA-Youth) (Park & Peterson 2006)voltooi ten einde karaktersterktes te bepaal. Daar was geen beduidende verskil tussen die karaktersterktes van die adolessente wat kanker oorleef het en die gesonde groep nie, anders as met ‘n soortgelyke vroe re studie onder volwassenes (Peterson, Park & Seligman 2006).Dit blyk dat die ervaring wat met ernstige siekte soos kanker gepaardgaan, ontwikkeling van karaktersterktes nóg bevorder nóg belemmer het in hierdie groep adolessente kankeroorwinnaars. Verdere navorsing is nodig om aspekte van positiewe sielkundige funksionering in adolessente kankeroorwinnaars te verstaan. How to cite this article: Guse,T. & Eracleous,G.,2011, ‘Charac
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