@article{10_4064_sm178_1_5,
     author = {Takeaki Yamazaki},
     title = {On upper and lower bounds of the numerical radius
 and an equality condition},
     journal = {Studia Mathematica},
     pages = {83--89},
     publisher = {mathdoc},
     volume = {178},
     number = {1},
     year = {2007},
     doi = {10.4064/sm178-1-5},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm178-1-5/}
}