Results 11 to 20 of about 5,584 (162)

Commissioning and clinical implementation of an MLC tracking system: An evaluation of AAPM TG-264 guidelines. [PDF]

J Appl Clin Med Phys
Abstract Background Precise radiotherapy relies on accurately targeting tumours while minimising exposure to healthy tissue, yet patient and organ motion complicate treatment delivery. To address intra‐fractional motion, multi‐leaf collimator (MLC) tracking systems have recently been adopted, adapting beam shapes in real‐time.
Haraldsson A, Pommer T, Persson E, Enocsson H, Kadhim M, Gunnlaugsson A, Munck Af Rosenschöld P.   +6 more
europepmc   +2 more sources

Evaluation of QUASAR Insight Phantom for daily imaging QA of MRgRT linacs. [PDF]

J Appl Clin Med Phys
Abstract Purpose Magnetic resonance imaging (MRI) and its importance in modern radiation therapy requires a standardized daily quality assurance (QA) procedure that is both comprehensive and efficient. Current imaging QA guidelines require a more inclusive analysis of imaging characteristics, as well as a simplification of setup procedures.
Grant E, Liu J, Etemadpour R, Shi C, Ai H, Lee P, Williams T, Liu A, Maraghechi B.   +8 more
europepmc   +2 more sources

Characterization of a deformable beating cardiac phantom with real-time dosimetric capabilities for validation of MRI-guided heart radiotherapy. [PDF]

Med Phys
Abstract Background Stereotactic arrhythmia radioablation (STAR) has emerged as a salvage treatment for patients with ventricular tachycardia, and the MR‐linacs offer MRI‐guidance during such treatment. However, available workflows on MR‐linacs are not yet optimized and characterized dedicatedly to perform heart radiotherapy due to a lack of realistic ...
Aubert MMN, Uijtewaal P, Penev KI, LeChasseur Y, Hartman N, de Vries LJM, Tzitzimpasis P, Borman PTS, Mandija S, Fast MF, van Lier ALHMW.   +10 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 ...
Joseph R. Findlay, J. Xavier Prochaska, Joseph F. Hennawi, Michele Fumagalli, Adam D. Myers, Stephanie Bartle, Ben Chehade, Michael A. DiPompeo, Tom Shanks, Marie Wingyee Lau, Kate H. R. Rubin   +10 more
openaire   +6 more sources

Quasars Probing Quasars. I. Optically Thick Absorbers near Luminous Quasars [PDF]

The Astrophysical Journal, 2006
With close pairs of quasars at different redshifts, a background quasar sightline can be used to study a foreground quasar's environment in absorption. We search 149 moderate resolution background quasar spectra, from Gemini, Keck, the MMT, and the SDSS to survey Lyman Limit Systems (LLSs) and Damped Ly-alpha systems (DLAs) in the vicinity of 1.8 < ...
Hennawi, Joseph F., Prochaska, Jason X., Burles, Scott, Strauss, Michael A., Richards, Gordon T., Schlegel, David J., Fan, Xiaohui, Schneider, Donald P., Zakamska, Nadia L., Oguri, Masamune, Gunn, James E., Lupton, Robert H., Brinkmann, Jon, Brunner, Robert J.   +13 more
openaire   +2 more sources

Do Quasars Lens Quasars? [PDF]

The Astrophysical Journal, 1997
If the unexpectedly high frequency of quasar pairs with very different component redshifts is due to the lensing of a population of background quasars by the foreground quasar, typical lens masses must be $\sim10^{12}M_{\sun}$ and the sum of all such quasar lenses would have to contain $\sim0.005$ times the closure density of the Universe.
openaire   +2 more sources

Two Close Separation Quasar-Quasar Pairs in the Large Bright Quasar Survey [PDF]

The Astronomical Journal, 1998
Accepted for publication in the Astronomical Journal, Paper, 4 Figures + 1 ...
Hewett, Paul C., Foltz, Craig B., Harding, Margaret E., Lewis, Geraint F.   +3 more
openaire   +2 more sources

Construction Tender Subcontract Selection using Case-based Reasoning

Construction Economics and Building, 2012
Obtaining competitive quotations from suitably qualified subcontractors at tender tim n significantly increase the chance of w1nmng a construction project.
Due Luu, Wily Sher
doaj   +3 more sources

Circum-Galactic Medium in the Halo of Quasars

Frontiers in Astronomy and Space Sciences, 2017
The properties of circum-galactic gas in the halo of quasar host galaxies are investigated analyzing Mg II 2800 and C IV 1540 absorption-line systems along the line of sight close to quasars.
Riccardo Ottolina, Renato Falomo, Aldo Treves, Michela Uslenghi, Jari K. Kotilainen, Riccardo Scarpa, Emanuele Paolo Farina   +6 more
doaj   +1 more source

Quasars [PDF]

Symposium - International Astronomical Union, 1994
I review recent results for quasars and discuss how they are related to activity in galaxies. Topics included are studies of quasar host galaxies with HST; searches for quasars in the Hubble Deep Field; evolution of the quasar luminosity function; news highlights from astro-ph; and current observational research problems and their relation to ...
openaire   +2 more sources