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3. Pan, G.Q., Chen, Z.Y., Qian, Y.T., Zhang, Q.R.: Phys. Scr.: (to be published)
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5. Zhang, Q.R., Zhao, Y., He, Z.H., Yu, D.Q., Sun, S.F., Pan, G.Q., Chen, Z.Y.: J. Phys. C (submitted for publication)