@article{10_4064_sm210_2_1,
     author = {Omar Hirzallah and Fuad Kittaneh and Khalid Shebrawi},
     title = {Numerical radius inequalities for $2\times  2$ operator matrices},
     journal = {Studia Mathematica},
     pages = {99--115},
     publisher = {mathdoc},
     volume = {210},
     number = {2},
     year = {2012},
     doi = {10.4064/sm210-2-1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm210-2-1/}
}