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1. X-ray reverberation modelling of the continuum, optical/UV time-lags in quasars

Author

Langis, D. A., Papadakis, I. E., Kammoun, E., Panagiotou, C., and Dovčiak, M.

Subjects
Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract

Context: Extensive, multi-wavelength monitoring campaigns of nearby and higher redshift active galactic nuclei (AGN) have shown that the UV/optical variations are well correlated with time delays which increase with increasing wavelength. Such behaviour is expected in the context of the X-ray thermal reverberation of the accretion disc in AGN. Aims: Our main objective is to use time-lag measurements of luminous AGN and fit them with sophisticated X-ray reverberation time-lags models. In this way we can investigate whether X-ray reverberation can indeed explain the observed continuum time lags, and whether time-lag measurements can be used to measure physical parameters such as the X-ray corona height and the spin of the black hole (BH) in these systems. Methods: We use archival time-lag measurements for quasars from different surveys, and we compute their rest frame, mean time-lags spectrum. We fit the data with analytical X-ray reverberation models, using $\chi^2$ statistics, and fitting for both maximal and non spinning BHs, for various colour correction values and X-ray corona heights. Results: We found that X-ray reverberation can explain very well the observed time lags, assuming the measured BH mass, accretion rate and X-ray luminosity of the quasars in the sample. The model agrees well with the data both for non-rotating and maximally rotating BHs, as long as the corona height is larger than $\sim 40$ gravitational radii. This is in agreement with previous results which showed that X-ray reverberation can also explain the disc radius in micro-lensed quasars, for the same corona heights. The corona height we measure depends on the model assumption of a perfectly flat disc. More realistic disc models may result in lower heights for the X-ray corona., Comment: 10 pages, 7 figures

Published
2024
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2. X-ray reverberation as an explanation for UV/optical variability in nearby Seyferts

Author

Papoutsis, M., Papadakis, I. E., Panagiotou, C., Dovčiak, M., and Kammoun, E.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

Active galactic nuclei (AGNs) are known to be variable across all wavelengths. Significant observational efforts have been invested in the last decade in studying their ultraviolet (UV) and optical variability. Long and densely sampled, multi-wavelength monitoring campaigns of numerous Seyfert galaxies have been conducted with the aim of determining the X-ray/UV/optical continuum time lags. Time-lag studies can be used to constrain theoretical models. The observed time lags can be explained by thermal reprocessing of the X-rays illuminating the accretion disc (known as the X-ray reverberation model). However, the observed light curves contain more information that can be used to further constrain physical models. Our primary objective is to investigate whether, in addition to time lags, the X-ray reverberation model can also explain the UV/optical variability amplitude of nearby Seyferts. To do this, we measured the excess variance of four sources (namely Mrk 509, NGC 4151, NGC 2617, and Mrk 142) as a function of wavelength using data from archival long, multi-wavelength campaigns with Swift, and ground-based telescopes. We also computed the model excess variance in the case of the X-ray reverberation model by determining the disc's transfer function and assuming a bending power law for the X-ray power spectrum. We tested the validity of the model by comparing the measured and model variances for a range of accretion rates and X-ray source heights. We conclude that the X-ray thermal reverberation model can fit both the continuum, UV/optical time lags, as well as the variance in these AGNs, for the same physical parameters. Our results suggest that the accretion disc is constant and that all the observed UV/optical variations, on timescales of days and up to a few weeks, can be fully explained by the variable X-rays as they illuminate the accretion disc., Comment: 16 pages, 10 figures, accepted for publication in Astronomy & Astrophysics

Published
2024

3. Broadband X-ray/UV/optical time-resolved spectroscopy of NGC 5548: The origin of the UV/optical variability in active galactic nuclei

Author

Kammoun, E., Papadakis, I. E., Dovčiak, M., and Panagiotou, C.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies
Abstract

Recently, nearby active galactic nuclei (AGN) have been subject to long X-rays/UV/optical monitoring campaigns. These campaigns reveal a strong correlation between the various UV and optical bands, with time lags increasing with wavelength. In a series of papers, we demonstrated that a scenario in which a central X-ray source illuminates the accretion disc explains the observed correlations. However, some of the monitored AGN show low/moderate X-rays-UV correlations, which could challenge this scenario. In this paper, we study the broadband X-ray/UV/optical spectral energy distributions (SEDs) of NGC 5548, one of the most intensively monitored AGN. We aim to test if the X-ray illumination model explains the broadband spectral behaviour of the source, despite the moderate X-ray-UV/optical correlation. We model the broadband time-averaged SED, from the STORM monitoring campaign of the source, using the KYNSED model which assumes an X-ray illuminated disc. We assume that the accretion process powers the X-ray corona. We also model 15 time-resolved SEDs from the same campaign to check whether this scenario can account for the observed spectral variability. The proposed model describes well the time-averaged and the time-resolved SEDs of NGC 5548. In this scenario, the corona height, the X-ray photon index, and the power transferred to the corona all vary. This explains the variability behaviour at different wavelengths. The best-fit model is obtained for a non-rotating black hole accreting at a constant rate of 5% its Eddington limit. Since each of the variable parameters affects the observed flux in a particular way, the combined variability of all parameters explains the moderate X-ray-UV/optical correlation. The X-ray illuminated disc model provides a complete description of the behaviour of NGC 5548, explaining its broadband SEDs, time-lag spectrum, and its power spectral distribution., Comment: Accepted for publication in A&A

Published
2024
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4. X-ray polarization measurement of the gold standard of radio-quiet active galactic nuclei : NGC 1068

Author

Marin, F., Marinucci, A., Laurenti, M., Kim, D. E., Barnouin, T., Di Marco, A., Ursini, F., Bianchi, S., Ravi, S., Marshall, H. L., Matt, G., Chen, C. -T., Gianolli, V. E., Ingram, A., Maksym, W. P., Panagiotou, C., Podgorny, J., Puccetti, S., Ratheesh, A., Tombesi, F., Agudo, I., Antonelli, L. A., Bachetti, M., Baldini, L., Baumgartner, W., Bellazzini, R., Bongiorno, S., Bonino, R., Brez, A., Bucciantini, N., Capitanio, F., Castellano, S., Cavazzuti, E., Ciprini, S., Costa, E., De Rosa, A., Del Monte, E., Di Gesu, L., Di Lalla, N., Donnarumma, I., Doroshenko, V., Dovciak, M., Ehlert, S., Enoto, T., Evangelista, Y., Fabiani, S., Ferrazzoli, R., Garcia, J., Gunji, S., Heyl, J., Iwakiri, W., Jorstad, S., Kaaret, P., Karas, V., Kislat, F., Kitaguchi, T., Kolodziejczak, J., Krawczynski, H., La Monaca, F., Latronico, L., Liodakis, I., Madejski, G., Maldera, S., Manfreda, A., Marscher, A., Massaro, F., Mitsuishi, I., Mizuno, T., Muleri, F., Negro, M., Ng, S., O'Dell, S., Omodei, N., Oppedisano, C., Papitto, A., Pavlov, G., Perri, M., Pesce-Rollins, M., Petrucci, P. -O., Pilia, M., Possenti, A., Poutanen, J., Ramsey, B., Rankin, J., Roberts, O., Romani, R., Sgro, C., Slane, P., Soffitta, P., Spandre, G., Swartz, D., Tamagawa, T., Tavecchio, F., Taverna, R., Tawara, Y., Tennant, A., Thomas, N., Trois, A., Tsygankov, S., Turolla, R., Vink, J., Weisskopf, M., Wu, K., Xie, F., and Zane, S.

Subjects
Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies, J.2.3, J.2.9
Abstract

We used the Imaging X-ray Polarimetry Explorer (IXPE) satellite to measure, for the first time, the 2-8 keV polarization of NGC 1068. We pointed IXPE for a net exposure time of 1.15 Ms on the target, in addition to two ~ 10 ks each Chandra snapshots in order to account for the potential impact of several ultraluminous X-ray source (ULXs) within IXPE's field-of-view. We measured a 2 - 8 keV polarization degree of 12.4% +/- 3.6% and an electric vector polarization angle of 101{\deg} +/- 8{\deg} at 68% confidence level. If we exclude the spectral region containing the bright Fe K lines and other soft X-ray lines where depolarization occurs, the polarization fraction rises up to 21.3% +/- 6.7% in the 3.5 - 6.0 keV band, with a similar polarization angle. The observed polarization angle is found to be perpendicular to the parsec scale radio jet. Using a combined Chandra and IXPE analysis plus multi-wavelength constraints, we estimated that the circumnuclear "torus" may sustain a half-opening angle of 50{\deg} - 55{\deg} (from the vertical axis of the system). Thanks to IXPE, we have measured the X-ray polarization of NGC 1068 and found comparable results, both in terms of polarization angle orientation with respect to the radio-jet and torus half-opening angle, to the X-ray polarimetric measurement achieved for the other archetypal Compton-thick AGN : the Circinus galaxy. Probing the geometric arrangement of parsec-scale matter in extragalactic object is now feasible thanks to X-ray polarimetry., Comment: 9 pages, 5 figures, 2 tables, submited to A&A

Published
2024
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5. Revisiting UV/optical continuum time lags in AGN

Author

Kammoun, E. S., Robin, L., Papadakis, I. E., Dovčiak, M., and Panagiotou, C.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

In this paper, we present an updated version of our model (KYNXiltr) which considers thermal reverberation of a standard Novikov-Thorne accretion disc illuminated by an X-ray point-like source. Previously, the model considered only two cases of black hole spins, and assumed a colour correction factor $f_{\rm col} = 2.4$. Now, we extend the model to any spin value and colour correction. In addition, we consider two scenarios of powering the X-ray corona, either via accretion, or external to the accretion disc. We use KYNXiltr to fit the observed time lags obtained from intense monitoring of four local Seyfert galaxies (NGC 5548, NGC 4395, Mrk 817, and Fairall 9). We consider various combinations of black hole spin, colour correction, corona height, and fraction of accretion power transferred to the corona. The model fits well the overall time-lags spectrum in these sources (for a large parameter space). For NGC 4593 only, we detect a significant excess of delays in the U-band. The contribution of the diffuse BLR emission in the time-lags spectrum of this source is significant. It is possible to reduce the large best-fitting parameter space by combining the results with additional information, such as the observed Eddington ratio and average X-ray luminosity. We also provide an update to the analytic expression provided by Kammoun et al., for an X-ray source that is not powered by the accretion process, which can be used for any value of colour correction, and for two values of the black hole spin (0 and 0.998)., Comment: Accepted for publication in MNRAS

Published
2023
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6. The geometry of the hot corona in MCG-05-23-16 constrained by X-ray polarimetry

Author

Tagliacozzo, D., Marinucci, A., Ursini, F., Matt, G., Bianchi, S., Baldini, L., Barnouin, T., Rodriguez, N. Cavero, De Rosa, A., Di Gesu, L., Dovciak, M., Harper, D., Ingram, A., Karas, V., Kim, D. E., Krawczynski, H., Madejski, G., Marin, F., Middei, R., Marshall, H. L., Muleri, F., Panagiotou, C., Petrucci, P. O., Podgorny, J., Poutanen, J., Puccetti, S., Soffitta, P., Tombesi, F., Veledina, A., Zhang, W., Agudo, I., Antonelli, L. A., Bachetti, M., Baumgartner, W. H., Bellazzini, R., Bongiorno, S. D., Bonino, R., Brez, A., Bucciantini, N., Capitanio, F., Castellano, S., Cavazzuti, E., Chen, C. T., Ciprini, S., Costa, E., Del Monte, E., Di Lalla, N., Di Marco, A., Donnarumma, I., Doroshenko, V., Ehlert, S. R., Enoto, T., Evangelista, Y., Fabiani, S., Ferrazzoli, R., Garcia, J. A., Gunji, S., Heyl, J., Iwakiri, W., Jorstad, S. G., Kaaret, P., Kislat, F., Kitaguchi, T., Kolodziejczak, J. J., La Monaca, F., Latronico, L., Liodakis, I., Maldera, S., Manfreda, A., Marscher, A. P., Massaro, F., Mitsuishi, I., Mizuno, T., Negro, M., Ng, C. Y., O'Dell, S. L., Omodei, N., Oppedisano, C., Papitto, A., Pavlov, G. G., Peirson, A. L., Perri, M., Rollins, M. Pesce, Pilia, M., Possenti, A., Ramsey, B. D., Rankin, J., Ratheesh, A., Roberts, O. J., Romani, R. W., Sgrò, C., Slane, P., Spandre, G., Swartz, D. A., Tamagawa, T., Tavecchio, F., Taverna, R., Tawara, Y., Tennant, A. F., Thomas, N. E., Trois, A., Tsygankov, S. S., Turolla, R., Vink, J., Weisskopf, M. C., Wu, K., Xie, F., and Zane, S.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We report on the second observation of the radio-quiet active galactic nucleus (AGN) MCG-05-23-16 performed with the Imaging X-ray Polarimetry Explorer (IXPE). The observation started on 2022 November 6 for a net observing time of 640 ks, and was partly simultaneous with NuSTAR (86 ks). After combining these data with those obtained in the first IXPE pointing on May 2022 (simultaneous with XMM-Newton and NuSTAR) we find a 2-8 keV polarization degree $\Pi$ = 1.6 $\pm$ 0.7 (at 68 per cent confidence level), which corresponds to an upper limit $\Pi$ = 3.2 per cent (at 99 per cent confidence level). We then compare the polarization results with Monte Carlo simulations obtained with the MONK code, with which different coronal geometries have been explored (spherical lamppost, conical, slab and wedge). Furthermore, the allowed range of inclination angles is found for each geometry. If the best fit inclination value from a spectroscopic analysis is considered, a cone-shaped corona along the disc axis is disfavoured., Comment: 9 pages, 8 figures, 3 table. Submitted to MNRAS

Published
2023

7. Uncovering the geometry of the hot X-ray corona in the Seyfert galaxy NGC4151 with IXPE

Author

Gianolli, V. E., Kim, D. E., Bianchi, S., Agís-González, B., Madejski, G., Marin, F., Marinucci, A., Matt, G., Middei, R., Petrucci, P-O., Soffitta, P., Tagliacozzo, D., Tombesi, F., Ursini, F., Barnouin, T., De Rosa, A., Di Gesu, L., Ingram, A., Loktev, V., Panagiotou, C., Podgorny, J., Poutanen, J., Puccetti, S., Ratheesh, A., Veledina, A., Zhang, W., Agudo, I., Antonelli, L. A., Bachetti, M., Baldini, L., Baumgartner, W. H., Bellazzini, R., Bongiorno, S. D., Bonino, R., Brez, A., Bucciantini, N., Capitanio, F., Castellano, S., Cavazzuti, E., Chen, C. -T., Ciprini, S., Costa, E., Del Monte, E., Di Lalla, N., Di Marco, A., Donnarumma, I., Doroshenko, V., Dovčiak, M., Ehlert, S. R., Enoto, T., Evangelista, Y., Fabiani, S., Ferrazzoli, R., García, J. A., Gunji, S., Heyl, J., Iwakiri, W., Jorstad, S. G., Kaaret, P., Karas, V., Kislat, F., Kitaguchi, T., Kolodziejczak, J. J., Krawczynski, H., La Monaca, F., Latronico, L., Liodakis, I., Maldera, S., Manfreda, A., Marscher, A. P., Marshall, H. L., Massaro, F., Mitsuishi, I., Mizuno, T., Muleri, F., Negro, M., Ng, C. -Y., ODell, S. L., Omodei, N., Oppedisano, C., Papitto, A., Pavlov, G. G., Peirson, A. L., Perri, M., Pesce-Rollins, M., Pilia, M., Possenti, A., Ramsey, B. D., Rankin, J., Roberts, O. J., Romani, R. W., Sgrò, C., Slane, P., Spandre, G., Swartz, D. A., Tamagawa, T., Tavecchio, F., Taverna, R., Tawara, Y., Tennant, A. F., Thomas, N. E., Trois, A., Tsygankov, S. S., Turolla, R., Vink, J., Weisskopf, M. C., Wu, K., Xie, F., and Zane, S.

Subjects
Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract

We present an X-ray spectro-polarimetric analysis of the bright Seyfert galaxy NGC4151. The source has been observed with the Imaging X-ray Polarimetry Explorer (IXPE) for 700 ks, complemented with simultaneous XMM-Newton (50 ks) and NuSTAR (100 ks) pointings. A polarization degree ${\Pi} = 4.9 {\pm} 1.1 \%$ and angle ${\Psi}= 86{\deg} {\pm} 7{\deg}$ east of north ($68\%$ confidence level) are measured in the 2-8 keV energy range. The spectro-polarimetric analysis shows that the polarization could be entirely due to reflection. Given the low reflection flux in the IXPE band, this requires however a reflection with a very large ($> 38 \%$) polarization degree. Assuming more reasonable values, a polarization degree of the hot corona ranging from ${\sim}4$ to ${\sim}8\%$ is found. The observed polarization degree excludes a spherical lamppost geometry for the corona, suggesting instead a slab-like geometry, possibly a wedge, as determined via Monte Carlo simulations. This is further confirmed by the X-ray polarization angle, which coincides with the direction of the extended radio emission in this source, supposed to match the disc axis. NGC4151 is the first AGN with an X-ray polarization measure for the corona, illustrating the capabilities of X-ray polarimetry and IXPE in unveiling its geometry., Comment: 9 pages, 4 figures

Published
2023
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8. Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16

Author

Marinucci, A., Muleri, F., Dovčiak, M., Bianchi, S., Marin, F., Matt, G., Ursini, F., Middei, R., Marshall, H. L., Baldini, L., Barnouin, T., Rodriguez, N. Cavero, De Rosa, A., Di Gesu, L., Harper, D., Ingram, A., Karas, V., Krawczynski, H., Madejski, G., Panagiotou, C., Petrucci, P. O., Podgorny, J., Puccetti, S., Tombesi, F., Veledina, A., Zhang, W., Agudo, I., Antonelli, L. A., Bachetti, M., Baumgartner, W. H., Bellazzini, R., Bongiorno, S. D., Bonino, R., Brez, A., Bucciantini, N., Capitanio, F., Castellano, S., Cavazzuti, E., Ciprini, S., Costa, E., Del Monte, E., Di Lalla, N., Di Marco, A., Donnarumma, I., Doroshenko, V., Ehlert, S. R., Enoto, T., Evangelista, Y., Fabiani, S., Ferrazzoli, R., Garcia, J. A., Gunji, S., Hayashida, K., Heyl, J., Iwakiri, W., Jorstad, S. G., Kitaguchi, T., Kolodziejczak, J. J., La Monaca, F., Latronico, L., Liodakis, I., Maldera, S., Manfreda, A., Marscher, A. P., Mitsuishi, I., Mizuno, T., Ng, C. -Y., O'Dell, S. L., Omodei, N., Oppedisano, C., Papitto, A., Pavlov, G. G., Peirson, A. L., Perri, M., Pesce-Rollins, M., Pilia, M., Possenti, A., Poutanen, J., Ramsey, B. D., Rankin, J., Ratheesh, A., Romani, R. W., Sgrò, C., Slane, P., Soffitta, P., Spandre, G., Tamagawa, T., Tavecchio, F., Taverna, R., Tawara, Y., Tennant, A. F., Thomas, N. E., Trois, A., Tsygankov, S. S., Turolla, R., Vink, J., Weisskopf, M. C., Wu, K., Xie, F., and Zane, S.

Subjects
Astrophysics - High Energy Astrophysical Phenomena
Abstract

We report on the first observation of a radio-quiet Active Galactic Nucleus (AGN) using polarized X-rays: the Seyfert 1.9 galaxy MCG-05-23-16. This source was pointed with the Imaging X-ray Polarimetry Explorer (IXPE) starting on May 14, 2022 for a net observing time of 486 ks, simultaneously with XMM-Newton (58 ks) and NuSTAR (83 ks). A polarization degree smaller than $\Pi<4.7\%$ (at the 99% c.l.) is derived in the 2-8 keV energy range, where emission is dominated by the primary component ascribed to the hot corona. The broad-band spectrum, inferred from a simultaneous fit to the IXPE, NuSTAR, and XMM-Newton data, is well reproduced by a power law with photon index $\Gamma=1.85\pm0.01$ and a high-energy cutoff $E_{\rm C}=120\pm15$ keV. A comparison with Monte Carlo simulations shows that a lamp-post and a conical geometry of the corona are consistent with the observed upper limit, a slab geometry is allowed only if the inclination angle of the system is less than 50$^{\circ}$., Comment: 7 pages, 3 figures, 1 table. Submitted to MNRAS Letters

Published
2022
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9. X-ray polarization measurement of the gold standard of radio-quiet active galactic nuclei: NGC 1068

Author

Marin, F., primary, Marinucci, A., additional, Laurenti, M., additional, Kim, D.E., additional, Barnouin, T., additional, Di Marco, A., additional, Ursini, F., additional, Bianchi, S., additional, Ravi, S., additional, Marshall, H.L., additional, Matt, G., additional, Chen, C.-T., additional, Gianolli, V.E., additional, Ingram, A., additional, Middei, R., additional, Maksym, W.P., additional, Panagiotou, C., additional, Podgorny, J., additional, Puccetti, S., additional, Ratheesh, A., additional, Tombesi, F., additional, Agudo, I., additional, Antonelli, L.A., additional, Bachetti, M., additional, Baldini, L., additional, Baumgartner, W., additional, Bellazzini, R., additional, Bongiorno, S., additional, Bonino, R., additional, Brez, A., additional, Bucciantini, N., additional, Capitanio, F., additional, Castellano, S., additional, Cavazzuti, E., additional, Ciprini, S., additional, Costa, E., additional, De Rosa, A., additional, Del Monte, E., additional, Di Gesu, L., additional, Di Lalla, N., additional, Donnarumma, I., additional, Doroshenko, V., additional, Dovčiak, M., additional, Ehlert, S., additional, Enoto, T., additional, Evangelista, Y., additional, Fabiani, S., additional, Ferrazzoli, R., additional, Garcia, J., additional, Gunji, S., additional, Heyl, J., additional, Iwakiri, W., additional, Jorstad, S., additional, Kaaret, P., additional, Karas, V., additional, Kislat, F., additional, Kitaguchi, T., additional, Kolodziejczak, J., additional, Krawczynski, H., additional, La Monaca, F., additional, Latronico, L., additional, Liodakis, I., additional, Madejski, G., additional, Maldera, S., additional, Manfreda, A., additional, Marscher, A., additional, Massaro, F., additional, Mitsuishi, I., additional, Mizuno, T., additional, Muleri, F., additional, Negro, M., additional, Ng, S., additional, O'Dell, S., additional, Omodei, N., additional, Oppedisano, C., additional, Papitto, A., additional, Pavlov, G., additional, Perri, M., additional, Pesce-Rollins, M., additional, Petrucci, P.-O., additional, Pilia, M., additional, Possenti, A., additional, Poutanen, J., additional, Ramsey, B., additional, Rankin, J., additional, Roberts, O., additional, Romani, R., additional, Sgrò, C., additional, Slane, P., additional, Soffitta, P., additional, Spandre, G., additional, Swartz, D., additional, Tamagawa, T., additional, Tavecchio, F., additional, Taverna, R., additional, Tawara, Y., additional, Tennant, A., additional, Thomas, N., additional, Trois, A., additional, Tsygankov, S., additional, Turolla, R., additional, Vink, J., additional, Weisskopf, M., additional, Wu, K., additional, Xie, F., additional, and Zane, S., additional

Published
2024
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11. Modelling the variable broad-band optical/UV/X-ray spectrum of PG1211+143: Implications for the ionized outflow

Author

Papadakis, I. E., Nicastro, F., and Panagiotou, C.

Subjects
Astrophysics - Astrophysics of Galaxies, Astrophysics - High Energy Astrophysical Phenomena
Abstract

We present the results from a detailed analysis of the 2007 Swift monitoring campaign of the quasar PG1211+143. We constructed broad-band, optical/UV/X-ray spectral energy distributions over three X-ray flux intervals. We fitted them with a model which accounts for the disc and the X-ray coronal emission and the warm absorber (well established in this source). The three flux spectra are well fitted by the model we considered. The disc inner temperature remains constant at ~2 eV, while X-rays are variable both in spectral slope and normalization. The absorber covers almost 90% of the central source. It is outflowing with a velocity less than 2.3*10^4 km/s (3sigma upper limit), and has a column density of ~10^23.2. Its ionization parameter varies by a factor of 1.6, and it is in photo-ionizing equilibrium with the ionizing flux. It is located at a distance of less than 0.35 pc from the central source and its relative thickness, DR/R is less than 0.1. The absorber' s ionization parameter variations can explain the larger than average amplitude of the X-ray variations. The absence of optical/UV variations (consistent with the high black hole mass estimate) argues against the presence of inward propagating disc fluctuations and strong X-ray illumination of the disc (in agreement with the low ratio of X-ray over the bolometric luminosity of ~20-35). We estimate an upper limit for the mass outflow of ~5 solar masses per year (~2.3 times the Eddington mass accretion rate). If the outflow rate is indeed that high, then it must be a short-lived episode in the quasar's life time. Finally, we estimate an upper limit for the kinetic power of the outflow of ~1.4*10^43 ergs/s. This outflow cannot deploy significant mechanical energy to the surrounding ISM of the quasar's host galaxy, but is sufficient to heat the ISM to 10^7 K and to produce a fast decline to the star formation rate of the galaxy., Comment: Accepted for publication by A&A

Published
2016
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16. The geometry of the hot corona in MCG-05-23-16 constrained by X-ray polarimetry

Author

Tagliacozzo, D, primary, Marinucci, A, additional, Ursini, F, additional, Matt, G, additional, Bianchi, S, additional, Baldini, L, additional, Barnouin, T, additional, Cavero Rodriguez, N, additional, De Rosa, A, additional, Di Gesu, L, additional, Dovčiak, M, additional, Harper, D, additional, Ingram, A, additional, Karas, V, additional, Kim, D E, additional, Krawczynski, H, additional, Madejski, G, additional, Marin, F, additional, Middei, R, additional, Marshall, H L, additional, Muleri, F, additional, Panagiotou, C, additional, Petrucci, P-O, additional, Podgorny, J, additional, Poutanen, J, additional, Puccetti, S, additional, Soffitta, P, additional, Tombesi, F, additional, Veledina, A, additional, Zhang, W, additional, Agudo, I, additional, Antonelli, L A, additional, Bachetti, M, additional, Baumgartner, W H, additional, Bellazzini, R, additional, Bongiorno, S D, additional, Bonino, R, additional, Brez, A, additional, Bucciantini, N, additional, Capitanio, F, additional, Castellano, S, additional, Cavazzuti, E, additional, Chen, C-T, additional, Ciprini, S, additional, Costa, E, additional, Del Monte, E, additional, Di Lalla, N, additional, Di Marco, A, additional, Donnarumma, I, additional, Doroshenko, V, additional, Ehlert, S R, additional, Enoto, T, additional, Evangelista, Y, additional, Fabiani, S, additional, Ferrazzoli, R, additional, Garcia, J A, additional, Gunji, S, additional, Heyl, J, additional, Iwakiri, W, additional, Jorstad, S G, additional, Kaaret, P, additional, Kislat, F, additional, Kitaguchi, T, additional, Kolodziejczak, J J, additional, La Monaca, F, additional, Latronico, L, additional, Liodakis, I, additional, Maldera, S, additional, Manfreda, A, additional, Marscher, A P, additional, Massaro, F, additional, Mitsuishi, I, additional, Mizuno, T, additional, Negro, M, additional, Ng, C-Y, additional, O’Dell, S L, additional, Omodei, N, additional, Oppedisano, C, additional, Papitto, A, additional, Pavlov, G G, additional, Peirson, A L, additional, Perri, M, additional, Pesce-Rollins, M, additional, Pilia, M, additional, Possenti, A, additional, Ramsey, B D, additional, Rankin, J, additional, Ratheesh, A, additional, Roberts, O J, additional, Romani, R W, additional, Sgrò, C, additional, Slane, P, additional, Spandre, G, additional, Swartz, D A, additional, Tamagawa, T, additional, Tavecchio, F, additional, Taverna, R, additional, Tawara, Y, additional, Tennant, A F, additional, Thomas, N E, additional, Trois, A, additional, Tsygankov, S S, additional, Turolla, R, additional, Vink, J, additional, Weisskopf, M C, additional, Wu, K, additional, Xie, F, additional, and Zane, S, additional

Published
2023
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17. Information theoretic regularization in diffuse optical tomography

Author

Panagiotou, C.

Subjects
610
Abstract

Diffuse optical tomography (DOT) retrieves the spatially distributed optical characteristics of a medium from external measurements. Recovering these parameters of interest involves solving a non-linear and severely ill-posed inverse problem. In this thesis we propose methods towards the regularization of DOT via the introduction of spatially unregistered, a priori information from alternative high resolution anatomical modalities, using the information theory concepts of joint entropy (JE) and mutual information (MI). Such functionals evaluate the similarity between the reconstructed optical image and the prior image, while bypassing the multi-modality barrier manifested as the incommensurate relation between the gray value representations of corresponding anatomical features in the modalities involved. By introducing structural a priori information in the image reconstruction process, we aim to improve the spatial resolution and quantitative accuracy of the solution. A further condition for the accurate incorporation of a priori information is the establishment of correct alignment between the prior image and the probed anatomy in a common coordinate system. However, limited information regarding the probed anatomy is known prior to the reconstruction process. In this work we explore the potentiality of spatially registering the prior image simultaneously with the solution of the reconstruction process. We provide a thorough explanation of the theory from an imaging perspective, accompanied by preliminary results obtained by numerical simulations as well as experimental data. In addition we compare the performance of MI and JE. Finally, we propose a method for fast joint entropy evaluation and optimization, which we later employ for the information theoretic regularization of DOT. The main areas involved in this thesis are: inverse problems, image reconstruction & regularization, diffuse optical tomography and medical image registration.

Published
2011

18. Uncovering the geometry of the hot X-ray corona in the Seyfert galaxy NGC 4151 with IXPE

Author

Gianolli, V E, primary, Kim, D E, additional, Bianchi, S, additional, Agís-González, B, additional, Madejski, G, additional, Marin, F, additional, Marinucci, A, additional, Matt, G, additional, Middei, R, additional, Petrucci, P-O, additional, Soffitta, P, additional, Tagliacozzo, D, additional, Tombesi, F, additional, Ursini, F, additional, Barnouin, T, additional, De Rosa, A, additional, Di Gesu, L, additional, Ingram, A, additional, Loktev, V, additional, Panagiotou, C, additional, Podgorny, J, additional, Poutanen, J, additional, Puccetti, S, additional, Ratheesh, A, additional, Veledina, A, additional, Zhang, W, additional, Agudo, I, additional, Antonelli, L A, additional, Bachetti, M, additional, Baldini, L, additional, Baumgartner, W H, additional, Bellazzini, R, additional, Bongiorno, S D, additional, Bonino, R, additional, Brez, A, additional, Bucciantini, N, additional, Capitanio, F, additional, Castellano, S, additional, Cavazzuti, E, additional, Chen, C-T, additional, Ciprini, S, additional, Costa, E, additional, Del Monte, E, additional, Di Lalla, N, additional, Di Marco, A, additional, Donnarumma, I, additional, Doroshenko, V, additional, Dovčiak, M, additional, Ehlert, S R, additional, Enoto, T, additional, Evangelista, Y, additional, Fabiani, S, additional, Ferrazzoli, R, additional, García, J A, additional, Gunji, S, additional, Heyl, J, additional, Iwakiri, W, additional, Jorstad, S G, additional, Kaaret, P, additional, Karas, V, additional, Kislat, F, additional, Kitaguchi, T, additional, Kolodziejczak, J J, additional, Krawczynski, H, additional, La Monaca, F, additional, Latronico, L, additional, Liodakis, I, additional, Maldera, S, additional, Manfreda, A, additional, Marscher, A P, additional, Marshall, H L, additional, Massaro, F, additional, Mitsuishi, I, additional, Mizuno, T, additional, Muleri, F, additional, Negro, M, additional, Ng, C-Y, additional, O’Dell, S L, additional, Omodei, N, additional, Oppedisano, C, additional, Papitto, A, additional, Pavlov, G G, additional, Peirson, A L, additional, Perri, M, additional, Pesce-Rollins, M, additional, Pilia, M, additional, Possenti, A, additional, Ramsey, B D, additional, Rankin, J, additional, Roberts, O J, additional, Romani, R W, additional, Sgrò, C, additional, Slane, P, additional, Spandre, G, additional, Swartz, D A, additional, Tamagawa, T, additional, Tavecchio, F, additional, Taverna, R, additional, Tawara, Y, additional, Tennant, A F, additional, Thomas, N E, additional, Trois, A, additional, Tsygankov, S S, additional, Turolla, R, additional, Vink, J, additional, Weisskopf, M C, additional, Wu, K, additional, Xie, F, additional, and Zane, S, additional

Published
2023
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20. Uncovering the geometry of the hot X-ray corona in the seyfert galaxy NGC 4151 with IXPE

Author

E Gianolli, V, E Kim, D, Bianchi, S, Ag??s-Gonz??lez, B, Madejski, G, Marin, F, Marinucci, A, Matt, G, Middei, R, P-O, Petrucci, Soffitta, P, Tagliacozzo, D, Tombesi, F, Ursini, F, Barnouin, T, A De Rosa, L Di Gesu, Ingram, A, Loktev, V, Panagiotou, C, Podgorny, J, Poutanen, J, Puccetti, S, Ratheesh, A, Veledina, A, Zhang, W, Agudo, I, A Antonelli, L, Bachetti, M, Baldini, L, H Baumgartner, W, Bellazzini, R, D Bongiorno, S, Bonino, R, Brez, A, Bucciantini, N, Capitanio, F, Castellano, S, Cavazzuti, E, C-T, Chen, Ciprini, S, Costa, E, E Del Monte, N Di Lalla, A Di Marco, Donnarumma, I, Doroshenko, V, Dov??iak, M, R Ehlert, S, Enoto, T, Evangelista, Y, Fabiani, S, Ferrazzoli, R, A Garc??a, J, Gunji, S, Heyl, J, Iwakiri, W, G Jorstad, S, Kaaret, P, Karas, V, Kislat, F, Kitaguchi, T, J Kolodziejczak, J, Krawczynski, H, F La Monaca, Latronico, L, Liodakis, I, Maldera, S, Manfreda, A, P Marscher, A, L Marshall, H, Massaro, F, Mitsuishi, I, Mizuno, T, Muleri, F, Negro, M, C-Y, Ng, L O???Dell, S, Omodei, N, Oppedisano, C, Papitto, A, G Pavlov, G, L Peirson, A, Perri, M, Pesce-Rollins, M, Pilia, M, Possenti, A, D Ramsey, B, Rankin, J, J Roberts, O, W Romani, R, Sgr??, C, Slane, P, Spandre, G, A Swartz, D, Tamagawa, T, Tavecchio, F, Taverna, R, Tawara, Y, F Tennant, A, E Thomas, N, Trois, A, S Tsygankov, S, Turolla, R, Vink, J, C Weisskopf, M, K, Wu, Xie, F, Zane, S, E Gianolli, V, E Kim, D, Bianchi, S, Ag??s-Gonz??lez, B, Madejski, G, Marin, F, Marinucci, A, Matt, G, Middei, R, Petrucci, P-O, Soffitta, P, Tagliacozzo, D, Tombesi, F, Ursini, F, Barnouin, T, De Rosa, A, Di Gesu, L, Ingram, A, Loktev, V, Panagiotou, C, Podgorny, J, Poutanen, J, Puccetti, S, Ratheesh, A, Veledina, A, Zhang, W, Agudo, I, A Antonelli, L, Bachetti, M, Baldini, L, H Baumgartner, W, Bellazzini, R, D Bongiorno, S, Bonino, R, Brez, A, Bucciantini, N, Capitanio, F, Castellano, S, Cavazzuti, E, Chen, C-T, Ciprini, S, Costa, E, Del Monte, E, Di Lalla, N, Di Marco, A, Donnarumma, I, Doroshenko, V, Dov??iak, M, R Ehlert, S, Enoto, T, Evangelista, Y, Fabiani, S, Ferrazzoli, R, A Garc??a, J, Gunji, S, Heyl, J, Iwakiri, W, G Jorstad, S, Kaaret, P, Karas, V, Kislat, F, Kitaguchi, T, J Kolodziejczak, J, Krawczynski, H, La Monaca, F, Latronico, L, Liodakis, I, Maldera, S, Manfreda, A, P Marscher, A, L Marshall, H, Massaro, F, Mitsuishi, I, Mizuno, T, Muleri, F, Negro, M, Ng, C-Y, L O???Dell, S, Omodei, N, Oppedisano, C, Papitto, A, G Pavlov, G, L Peirson, A, Perri, M, Pesce-Rollins, M, Pilia, M, Possenti, A, D Ramsey, B, Rankin, J, J Roberts, O, W Romani, R, Sgr??, C, Slane, P, Spandre, G, A Swartz, D, Tamagawa, T, Tavecchio, F, Taverna, R, Tawara, Y, F Tennant, A, E Thomas, N, Trois, A, S Tsygankov, S, Turolla, R, Vink, J, C Weisskopf, M, Wu, K, Xie, F, and Zane, S

Published
2023

21. Polarization constraints on the X-ray corona in Seyfert Galaxies: MCG-05-23-16

Author

Marinucci, A, primary, Muleri, F, additional, Dovciak, M, additional, Bianchi, S, additional, Marin, F, additional, Matt, G, additional, Ursini, F, additional, Middei, R, additional, Marshall, H L, additional, Baldini, L, additional, Barnouin, T, additional, Rodriguez, N Cavero, additional, De Rosa, A, additional, Di Gesu, L, additional, Harper, D, additional, Ingram, A, additional, Karas, V, additional, Krawczynski, H, additional, Madejski, G, additional, Panagiotou, C, additional, Petrucci, P O, additional, Podgorny, J, additional, Puccetti, S, additional, Tombesi, F, additional, Veledina, A, additional, Zhang, W, additional, Agudo, I, additional, Antonelli, L A, additional, Bachetti, M, additional, Baumgartner, W H, additional, Bellazzini, R, additional, Bongiorno, S D, additional, Bonino, R, additional, Brez, A, additional, Bucciantini, N, additional, Capitanio, F, additional, Castellano, S, additional, Cavazzuti, E, additional, Ciprini, S, additional, Costa, E, additional, Del Monte, E, additional, Di Lalla, N, additional, Di Marco, A, additional, Donnarumma, I, additional, Doroshenko, V, additional, Ehlert, S R, additional, Enoto, T, additional, Evangelista, Y, additional, Fabiani, S, additional, Ferrazzoli, R, additional, Garcia, J A, additional, Gunji, S, additional, Hayashida, K, additional, Heyl, J, additional, Iwakiri, W, additional, Jorstad, S G, additional, Kitaguchi, T, additional, Kolodziejczak, J J, additional, La Monaca, F, additional, Latronico, L, additional, Liodakis, I, additional, Maldera, S, additional, Manfreda, A, additional, Marscher, A P, additional, Mitsuishi, I, additional, Mizuno, T, additional, Ng, C-Y, additional, O’Dell, S L, additional, Omodei, N, additional, Oppedisano, C, additional, Papitto, A, additional, Pavlov, G G, additional, Peirson, A L, additional, Perri, M, additional, Pesce-Rollins, M, additional, Pilia, M, additional, Possenti, A, additional, Poutanen, J, additional, Ramsey, B D, additional, Rankin, J, additional, Ratheesh, A, additional, Romani, R W, additional, Sgrš, C, additional, Slane, P, additional, Soffitta, P, additional, Spandre, G, additional, Tamagawa, T, additional, Tavecchio, F, additional, Taverna, R, additional, Tawara, Y, additional, Tennant, A F, additional, Thomas, N E, additional, Trois, A, additional, Tsygankov, S S, additional, Turolla, R, additional, Vink, J, additional, Weisskopf, M C, additional, Wu, K, additional, Xie, F, additional, and Zane, S, additional

Published
2022
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25. Insufficient glucocorticoid receptor signaling and flattened salivary cortisol profile are associated with metabolic and inflammatory indices in type 2 diabetes

Author

Panagiotou, C. Lambadiari, V. Maratou, E. Geromeriati, C. Artemiadis, A. Dimitriadis, G. Moutsatsou, P.

Subjects
endocrine system, hormones, hormone substitutes, and hormone antagonists
Abstract

Purpose: Impaired negative feedback and hyperactivation of the hypothalamic–pituitary–adrenal (HPA) axis characterizes type 2 diabetes mellitus (T2DM). The glucocorticoid receptor (GR) is a key mediator of HPA axis negative feedback; however, its role in linking hypercortisolemia and T2DM-associated hyperglycemia, hyperlipidemia and inflammation is not yet known. Methods: In peripheral mononuclear cells (PBMC) from 31 T2DM patients and 24 healthy controls, we measured various GR-signaling parameters such as phosphorylated GR (pGR-S211), GRα/GRβ gene expression and GC-sensitivity [using the basal and dexamethasone (DEX)-induced leucine zipper (GILZ) and FK506 binding-protein (FKBP5) mRNA levels as well as the basal interleukin (IL)-1β protein levels]. Diurnal salivary cortisol curve parameters such as the cortisol awaking response (CAR) and area under the curve (AUCtotal and AUCi) as well as inflammatory and metabolic indices were also determined. Results: T2DM patients exhibited diminished pGR-S211 protein content, increased GRβ, decreased basal GILZ and FKBP5 mRNA levels and increased IL-1β levels. Flattened DEX-induced GILZ and FKBP5 response curves and a flattened salivary cortisol profile characterized T2DM patients. Significant associations of GR measures and saliva cortisol curve parameters with biochemical and clinical characteristics were found. Conclusion: Our novel data implicate an insufficient GR signaling in PBMCs in T2DM patients and HPA axis dysfunction. The significant associations of GR-signaling parameters with inflammatory and metabolic indices implicate that GR may be the critical link between HPA axis dysfunction, hypercortisolemia and diabetes-associated metabolic disturbances. Our findings provide significant insights into the contribution of GR-mediated mechanisms in T2DM aetiopathology and therapy. © 2020, Italian Society of Endocrinology (SIE).

Published
2021

31. Effect of steviol, steviol glycosides and stevia extract on glucocorticoid receptor signaling in normal and cancer blood cells

Author

Panagiotou, C. Mihailidou, C. Brauhli, G. Katsarou, O. Moutsatsou, P.

Abstract

The use of steviol glycosides as non-caloric sweeteners has proven to be beneficial for patients with type 2 diabetes mellitus (T2D), obesity, and metabolic syndrome. However, recent data demonstrate that steviol and stevioside might act as glucocorticoid receptor (GR) agonists and thus correlate with adverse effects on metabolism. Herein, we evaluated the impact of steviol, steviol glycosides, and a Greek-derived stevia extract on a number of key steps of GR signaling cascade in peripheral blood mononuclear cells (PBMCs) and in Jurkat leukemia cells. Our results revealed that none of the tested compounds altered the expression of primary GR-target genes (GILZ, FKPB5), GR protein levels or GR subcellular localization in PBMCs; those compounds increased GILZ and FKPB5 mRNA levels as well as GRE-mediated luciferase activity, inducing in parallel GR nuclear translocation in Jurkat cells. The GR-modulatory activity demonstrated by stevia-compounds in Jurkat cells but not in PBMCs may be due to a cell-type specific effect. © 2017 Elsevier B.V.

Published
2018

34. A structure-based model for transport in stably stratified homogeneous turbulent flows

Author

Panagiotou, C. F., Kassinos, Stavros C., and Kassinos, Stavros C. [0000-0002-3501-3851]

Subjects
Buoyancy, Additional buoyancy, K-epsilon turbulence model, Prandtl number, Scalar (mathematics), Stratified flows, Inverse, Tensors, engineering.material, 01 natural sciences, 010305 fluids & plasmas, Physics::Fluid Dynamics, Image processing, Representation model, Transport modeling, 0103 physical sciences, 010306 general physics, Turbulent structures, Physics, Fluid Flow and Transfer Processes, Turbulence, Velocity gradient, Mechanical Engineering, Turbulent Prandtl number, Mathematical analysis, Interactive particles, Decaying turbulence, Condensed Matter Physics, Classical mechanics, engineering, Inclination angles
Abstract

We present an extension that allows a recently proposed structure-based model for turbulent scalar transport to account for buoyancy effects. The proposed model is based on a generalization of the Interactive Particle Representation Model (IPRM) and is accompanied by a four-equation transport model that provides the turbulence scales needed for the closure of the complete structure-based model (SBM). The structure tensors and their invariants are used to model the additional buoyancy terms that emerge in the four-equation transport equations. Model parameters are set by matching the asymptotic decay exponents in decaying turbulence. The validity of the model is considered for a large number of different types of stably stratified flows at different Richardson numbers (Ri), showing encouraging results. The complete structure-based model achieves fair agreement with LES and DNS predictions for vertical shear in the presence of vertical mean stratification, while the structure tensors are shown to be suitable for use as diagnostic tools for the morphology of highly anisotropic turbulent structures. Additionally, the proposed model is shown to be sensitive to the variation of the inclination angle θ between the direction of the mean velocity gradient and the orientation of the mean scalar gradient. Furthermore, the model correctly predicts that the evolution of the inverse shear parameter is insensitive to the choice of inclination angle, yielding a turbulent Prandtl number close to unity, in accordance with DNS results. © 2016 The Authors 65 309 322 309-322

Published
2016
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36. Crosstalk between C/EBP homologous protein (CHOP) and glucocorticoid receptor in lung cancer

Author

Mihailidou, C. Panagiotou, C. Kiaris, H. Kassi, E. Moutsatsou, P.

Abstract

Loss of homeostasis triggers the endoplasmic reticulum (ER) stress response and activates the unfolded protein response (UPR) resulting in the induction of the CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP). Glucocorticoids (GCs), via the glucocorticoid receptor (GR), regulate numerous physiological processes in an effort to maintain homeostasis. Previous studies demonstrated that glucocorticoids suppress ER stress by enhancing correct folding of secreted proteins and degradation of misfolded proteins. Here, we describe a novel crosstalk between ER-stress and the glucocorticoid receptor signaling. We showed that treatment of wild type mice with Tunicamycin (inducer of ER-stress) increased GR protein levels in the lungs. Treatment of A549 cells (human lung cancer cells) with ER stress inducers modulated the Dexamethasone-induced subcellular localization of GR and the phosphorylated forms of GR (pGRSer211 and pGRSer203) with concomitant changes in the expression of primary GR-target genes. We demonstrated a significant protein-protein interaction between GR and CHOP, (GR-CHOP heterocomplex formation) under ER stress conditions. The functional consequences of ER stress- GR signaling crosstalk were assessed and demonstrated that long time exposure (24–48 h) of A549 cells to dexamethasone (10−6 M) reversed the Tunicamycin-induced cell death, a phenomenon associated with parallel increases in GR protein content, increases in cell survival parameters and decreases in cell apoptosis-related parameters. Our study provides evidence that there is a cross talk between ER-stress and GR signaling, this being associated with mutual functional antagonism between CHOP and GR-mediated pathways in lung cells with important implications in lung cell function. © 2016

Published
2016

37. A structure-based model for the transport of passive scalars in homogeneous turbulent flows

Author

Panagiotou, C. F., Kassinos, Stavros C., and Kassinos, Stavros C. [0000-0002-3501-3851]

Subjects
Structure-based, K-epsilon turbulence model, Scalar (mathematics), Velocity, 02 engineering and technology, K-omega turbulence model, Enstrophy, 01 natural sciences, 010305 fluids & plasmas, Turbulent flow, Physics::Fluid Dynamics, Shear flow, 0203 mechanical engineering, Representation model, 0103 physical sciences, Passive scalar, Scale equations, Homogeneous turbulence, Fluid Flow and Transfer Processes, Physics, Scalar dissipation rate, Passive scalars, Turbulence, Mechanical Engineering, Mechanics, Condensed Matter Physics, Vector Laplacian, 020303 mechanical engineering & transports, Classical mechanics, Structure-based modeling, Isotropic turbulence, Vector field, Interacting particles, Scalar field
Abstract

A structure-based model has been constructed, for the first time, for the study of passive scalar transport in turbulent flows. The scalar variance and the large-scale scalar gradient variance are proposed as the two turbulence scales needed for closure of the scalar equations in the framework of the Interacting Particle Representation Model (IPRM). The scalar dissipation rate is modeled in terms of the scalar variance and the large-scale enstrophy of the velocity field. Model parameters are defined by matching the decay rates in freely isotropic turbulence. The model is validated for a large number of cases of deformation in both fixed and rotating frames, showing encouraging results. The model shows good agreement with DNS results for the case of pure shear flow in the presence of either transverse or streamwise mean scalar gradient, while it correctly predicts the presence of direct cascade for the passive scalar variance in two dimensional isotropic turbulence. © 2015 Elsevier Inc. 57 109 129 109-129

Published
2016

39. The ASBM-SA turbulence closure: Taking advantage of structure-based modeling in current engineering CFD codes

Author

Panagiotou, C. F., Kassinos, Stavros C., Aupoix, B., University of Cyprus [Nicosia], ONERA - The French Aerospace Lab [Toulouse], ONERA, and Kassinos, Stavros C. [0000-0002-3501-3851]

Subjects
Algebraic Structure-Based Model (ASBM), Structure-based, Computer science, K-epsilon turbulence model, 02 engineering and technology, K-omega turbulence model, Computational fluid dynamics, Reynolds-averaged Navier-Stokes, 01 natural sciences, Turbulence closures, ALGEBRAIC STRUCTURE-BASED MODEL (ASBM), Reynolds number, Turbulent flow, 010305 fluids & plasmas, 0203 mechanical engineering, 0103 physical sciences, Algebraic structures, Applied mathematics, Explicit Algebraic Reynolds stress models, Wall flow, Fluid Flow and Transfer Processes, STRUCTURE-BASED MODELING, business.industry, Mechanical Engineering, Turbulence modeling, Reynolds stress equation model, Reynolds - Averaged Navier-Stokes, Condensed Matter Physics, EXPLICIT ALGEBRAIC REYNOLDS STRESS MODEL, [INFO.INFO-MO]Computer Science [cs]/Modeling and Simulation, Navier Stokes equations, Kinetics, TURBULENCE CLOSURE, Algebra, 020303 mechanical engineering & transports, Test case, Structure-based modeling, Turbulence kinetic energy, business, Reynolds-averaged Navier–Stokes equations, Kinetic energy, REYNOLDS-AVERAGED NAVIER–STOKES, Turbulence models
Abstract

Structure-based turbulence models (SBM) carry information about the turbulence structure that is needed for the prediction of complex non-equilibrium flows. SBM have been successfully used to predict a number of canonical flows, yet their adoption rate in engineering practice has been relatively low, mainly because of their departure from standard closure formulations, which hinders easy implementation in existing codes. Here, we demonstrate the coupling between the Algebraic Structure-Based Model (ASBM) and the one-equation Spalart-Allmaras (SA) model, which provides an easy route to bringing structure information in engineering turbulence closures. As the ASBM requires correct predictions of two turbulence scales, which are not taken into account in the SA model, Bradshaw relations and numerical optimizations are used to provide the turbulent kinetic energy and dissipation rate. Attention is paid to the robustness and accuracy of the hybrid model, showing encouraging results for a number of simple test cases. An ASBM module in Fortran-90 is provided along with the present paper in order to facilitate the testing of the model by interested readers. © 2014 Elsevier Inc. 52 111 128 111-128

Published
2015

41. Posters 159Misdiagnosed, misbelieved and misdirected; largest uk study casts doubt on some long held but poorly validated assumptions about the pots population and suggests improvements in care pathways and service provision60An acute comparison of different strategies for targeting the left ventricular lead for cardiac resynchronisation therapy61Relationship of phase singularities and high dominant frequency regions during persistent atrial fibrillation in humans62Restoration of sinus rhythm results in early and late improvements in the functional reserve of the heart following direct current cardioversion of persistent af: fresh-af63Non-concomitant hybrid ablation using the estech cobra device for the treatment of longstanding persistent atrial fibrillation: an initial single-centre experience64Artificial intelligence outperforms manual ecg scoring in the detection of arrhythmia substrate65Single centre experience and outcome of persistent af ablation using nmarq catheter: 2 year follow up66The growing burden of atrial fibrillation and management at a typical district general hospital67Haemodynamic effects of single-vein, simultaneous, multipoint pacing compared with bipolar pacing in patients undergoing cardiac resynchronisation therapy68Is multisite pacing of interest in cardiac resynchronization therapy? teachings from a long-term follow-up of a cohort of patients implanted with triventricular pacing systems69Differences in fractionated electrogram detection: a direct quantitative comparison between navx and carto: Table 1

Author

Kavi, L.A., primary, Gamble, J.H.P., primary, Dastagir, N., primary, Gilbert, K.A., primary, Furniss, G.O., primary, Rosengarten, J.A., primary, Shunmugam, S.R., primary, Signy, J.S.G., primary, Umar, F., primary, Providência, R., primary, Almeida, T.P, primary, Newton, J.L., additional, Nuttall, M., additional, Opie-Moran, M., additional, Low, D A, additional, Nicholson, L.M., additional, Toora, D., additional, Caldow, E., additional, Gregory, K., additional, Khiani, R., additional, Herring, N., additional, Foley, P.W.X., additional, Ginks, M.R., additional, Rajappan, K., additional, Bashir, Y., additional, Betts, T.R., additional, Salinet, J.L., additional, Li, X., additional, Vanheusden, F.J., additional, Almeida, T.P., additional, Chu, G.S., additional, Stafford, P.J., additional, Schlindwein, F.S., additional, Ng, G.A., additional, Hogarth, A.J., additional, MacDonald, W., additional, Lewis, N.T., additional, Tan, L.B., additional, Tayebjee, M.H., additional, Villaquiran, J., additional, Newcombe, D., additional, Lines, I., additional, Dalrymple-Hay, M., additional, Haywood, G.A., additional, Chui, K.H.O., additional, Dima, S.M., additional, Panagiotou, C., additional, Maharatna, K., additional, Curzen, N.P., additional, Morgan, J.M., additional, Veasey, R.A., additional, Sugihara, C., additional, Anderson, S., additional, Furniss, S., additional, Sulke, N., additional, Puri, N., additional, Steele, J., additional, Furniss, S.S., additional, Sulke, A.N., additional, Patel, N.R., additional, Taylor, R.J., additional, Stegemann, B., additional, Marshall, H., additional, Flannigan, S., additional, Leyva, F., additional, Rogers, D., additional, Cobb, V., additional, Babu, G., additional, Mann, I., additional, Bronis, K., additional, Posdziech, V., additional, Lambiase, P., additional, Ahsan, S., additional, Segal, O., additional, Lowe, M., additional, Rowland, E., additional, Khan, F., additional, Chow, A., additional, Tuan, J.H., additional, and Ng, G. André, additional

Published
2015
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43. Oral Abstract Session: Novel non-invasive risk marker

Author

Park, S. J., primary, Lee, S. H., additional, Byeon, K. M., additional, On, Y. K., additional, Huh, J., additional, Kim, J. S., additional, Berezin, A., additional, Kremzer, A., additional, Kouraki, K., additional, Strauss, M., additional, Skarlos, A., additional, Zeymer, U., additional, Zahn, R., additional, Kleemann, T., additional, Rosengarten, J. A., additional, Dima, S. M., additional, Panagiotou, C., additional, Scott, P. A., additional, Chui, K. H. O., additional, Mazomenos, E. B., additional, Maharatna, K., additional, Curzen, N. P., additional, and Morgan, J., additional

Published
2013
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