@article{10_4064_sm198_3_7,
     author = {Jan Swoboda and Harald K. Wimmer},
     title = {Spectraloid operator polynomials, the
 approximate numerical range and an
 {Enestr\"om{\textendash}Kakeya} theorem in {Hilbert} space},
     journal = {Studia Mathematica},
     pages = {279--300},
     publisher = {mathdoc},
     volume = {198},
     number = {3},
     year = {2010},
     doi = {10.4064/sm198-3-7},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm198-3-7/}
}