Results 11 to 20 of about 81,623 (245)

Quasar Clustering and the Lifetime of Quasars [PDF]

The Astrophysical Journal, 2000
Although the population of luminous quasars rises and falls over a period of 10^9 years, the typical lifetime of individual quasars is uncertain by several orders of magnitude.
Baugh C. M., Boyle B. J., Croom S. M., Efstathiou G., Eke V. R., Haehnelt M. G., Heath D. J., Katz N., Lacey C., Mo H. J., Peacock J. A., Richstone D., Shanks T., Shanks T., Shaver P. A., Webster A., White S. D. M., Zeldovich Ya. B.   +17 more
core   +6 more sources

A Main Sequence for Quasars [PDF]

Frontiers in Astronomy and Space Sciences, 2018
The last 25 years saw a major step forward in the analysis of optical and UV spectroscopic data of large quasar samples. Multivariate statistical approaches have led to the definition of systematic trends in observational properties that are the basis of
Paola Marziani, Deborah Dultzin, Jack W. Sulentic, Ascensión Del Olmo, C. A. Negrete, Mary L. Martínez-Aldama, Mauro D'Onofrio, Edi Bon, Natasa Bon, Giovanna M. Stirpe   +9 more
doaj   +7 more sources

Quasars and their host galaxies [PDF]

, 2006
This review attempts to describe developments in the fields of quasar and quasar host galaxies in the past five. In this time period, the Sloan and 2dF quasar surveys have added several tens of thousands of quasars, with Sloan quasars being found to z>6.
A. Laor, A. Laor, A. Mesinger, A. Soltan, A. Stockton, A. Stockton, A. Wandel, A.J. Barth, A.R. Marble, B.M. Peterson, C. Leipski, C. Norman, C.A. Onken, C.H. Nelson, C.H. Nelson, C.N. Tadhunter, D. Stern, D.E. Vanden Berk, D.E. Vanden Berk, D.J.E. Floyd, D.P. Schneider, E. Glikman, G. Canalizo, G. Kauffmann, G. Kauffmann, G.A. Shields, G.L. Granato, G.T. Richards, G.T. Richards, J. Everett, J. Silk, J.-H. Woo, J.B. Hutchings, J.H. Krolik, J.N. Bahcall, J.S. Dunlop, J.S. Dunlop, L. Ho, L.A. Nolan, M. Cirasuolo, M. Elvis, M. estergaard, M. Kool de, M. Lacy, M. Lacy, M. Lacy, M. Lacy, M. Lacy, M.D. Gregg, M.J. Disney, M.J. Kukula, M.S. Brotherton, N. Arav, N. Zakamska, P. Padovani, P.B. Hall, Q. Yu, R. Falomo, R. Falomo, R.D. Blandford, R.D. Blandford, R.H. Becker, R.H. Becker, R.J. McLure, R.L. White, R.L. White, R.M. Cutri, R.P. Fender, R.P. Marel van der, S. Vaughan, S.E. Ridgway, S.M. Croom, S.M. Croom, T. Boroson, T.A. Boroson, T.A. Boroson, W. Freudling, W. Vries de, X. Fan, X. Fan, X. Fan, Z. Ivezic   +81 more
core   +5 more sources

Impact of extended source-to-surface distances and respiratory motion on the precision of electron beam therapy. [PDF]

J Appl Clin Med Phys
Abstract Purpose In electron beam therapy targeting superficial thoracic and abdominal lesions, the source‐to‐surface distance (SSD) varies due to patient respiration. This study aimed to investigate the percentage depth dose (PDD) and off‐center ratio (OCR) of 6, 9, and 12 MeV electron beams at extended SSDs; and to assess the variations in dose ...
Ito T, Kosaka H, Yanagi Y, Sakai Y, Monzen H.   +4 more
europepmc   +2 more sources

Clinical comparison of four commercial MRI phantoms on a 0.35T MR-linac using a standard clinical TRUFI sequence at a single institution. [PDF]

J Appl Clin Med Phys
Abstract Purpose Real‑time magnetic resonance–guided radiation therapy (MRgRT) integrates MRI with a linear accelerator (Linac) for gating and adaptive radiotherapy, which requires robust image‑quality assurance over a large field of view (FOV). Specialized phantoms capable of accommodating this extensive FOV are therefore essential.
Khalifa MA, Ma T, Aljuaid H, Kim S, Song WY.   +4 more
europepmc   +2 more sources

A streamlined workflow for comprehensive 4DCT imaging QA with automated analysis of spatial integrity and image quality. [PDF]

J Appl Clin Med Phys
Abstract Purpose A comprehensive 4DCT QA program that includes the assessment of spatial integrity and image quality of 4D phantom scans can be resource‐intensive, especially because the analysis burden scales with the number of motion traces used for QA.
Yang Y, Lee D, Whitaker M, Harris W, Jeong J, Lin SC, Yorke E, Santanam L, Tang G.   +8 more
europepmc   +2 more sources

Guselkumab in East Asians With Moderate-to-Severe Ulcerative Colitis: Subgroup Analysis of the QUASAR Induction and Maintenance Studies. [PDF]

J Gastroenterol Hepatol
ABSTRACT Background and Aim The global QUASAR (NCT04033445) clinical program demonstrated the efficacy and safety of guselkumab, a dual‐acting interleukin‐23 p19 subunit inhibitor, as induction and maintenance therapy in participants with moderate to severely active ulcerative colitis (UC).
Chen B, Ye BD, Cao Q, Hirai F, Saruta M, Chen M, Pelak S, Shipitofsky N, Miao Y, Herr K, Wahking B, Zhuo J, Hisamatsu T.   +12 more
europepmc   +2 more sources

Quantitative susceptibility mapping in magnetically inhomogeneous tissues. [PDF]

Magn Reson Med
Abstract Purpose Conventional quantitative susceptibility mapping (QSM) methods rely on simplified physical models that assume isotropic and homogeneous tissue properties, leading to artifacts and inaccuracies in biological tissues. This study aims to develop and evaluate DEEPOLE, a deep learning–based method that incorporates macroscopically ...
Jochmann T, Salman F, Dwyer MG, Bergsland N, Zivadinov R, Haueisen J, Schweser F.   +6 more
europepmc   +2 more sources

Quasars Probing Quasars. X. The Quasar Pair Spectral Database [PDF]

The Astrophysical Journal Supplement Series, 2018
Abstract The rare close projection of two quasars on the sky provides the opportunity to study the host galaxy environment of a foreground quasar in absorption against the continuum emission of a background quasar. For over a decade the “Quasars probing quasars” series has utilized this technique to further the understanding of galaxy ...
J. Xavier Prochaska, B. Chehade, Stephanie Bartle, M. A. DiPompeo, Joseph R. Findlay, Tom Shanks, Michele Fumagalli, Joseph F. Hennawi, Joseph F. Hennawi, Adam D. Myers, Marie Wingyee Lau, Kate H. R. Rubin   +11 more
openaire   +8 more sources

Some constraints on quasar progenitors and quasar evolution [PDF]

Symposium - International Astronomical Union, 1986
There is strong evidence that quasars are powered by the gravitational energy released by in fall of matter into a compact supermassive object which is most likely a black hole with mass M>106 to 109MO. The question then arises as to how such massive black holes came to be formed. What sort of objects were the progenitors?
C. Sivaram
openalex   +3 more sources