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Articles by K. Nishimura
Total Records ( 2 ) for K. Nishimura

Flow modulation effect on N incorporation into GaAs(1-x)Nx films during chemical beam epitaxy growth

  H. Suzuki , K. Nishimura , K. Saito , Y. Ohshita , N. Kojima and M. Yamaguchi

The change in the surface concentration of N ([N]s) on a GaAs surface under N and As source injections is investigated using the N atomic layer doping (N-ALD) technique, and the key factor determining [N]s is discussed. The As and N precursors source gases are trisdimethylaminoarsenic (TDMAAs, [N(CH3)2]3As) and monomethylhydrazine (MMHy, N2H3CH3), respectively. N-ALD layers are prepared by using two gas injection sequences (A: MMHy injection and B: MMHy and TDMAAs injections). [N]s increases with decreasing growth temperature in both sequences. [N]s in sequence A is higher than that of sequence B. In sequence B, Δ[N]st is proportional to exp(–tN), where t and τN are the gas injection time and the residence time of N, respectively. It is observed that the number of vacant sites, [V]s,N, remaining constant during gas injections. In sequence A, Δ[N]st cannot be fitted by a single exponential function, indicating that [V]s,N is not constant. From these results, we suggest that the vacant sites at the surface are created not only by N desorption but also by As desorption. It has been found that As desorption is enhanced by MMHy injection. As desorption reaction has been confirmed by in situ auger electron spectroscopy measurements. These results indicate that [N]s is determined by the competitive absorption between N and As, [V]s,N, and τN.

  H. Sugawara , K. Nishimura , S. Kobayashi , H. Ishida , K. Tanabe and J. Ishigooka
  Paradoxical depression occurs despite a completely successful transplantation without tissue rejection or other medical complications. In this study, the occurrence of paradoxical depression was retrospectively investigated among 1139 Japanese successful renal transplant recipients January 1997 through September 2006. Among the 1139 recipients, 103 visited the Department of Psychiatry after renal transplantation, including 40 with depressive symptoms and 15 with a physical problem considered to have nonparadoxical depression. The other 25 recipients were considered to have paradoxical depression; that is, more than half of the 40 recipients with depressive symptoms had paradoxical depression. There were no significant differences in the clinical characteristics, including average age at the time of renal transplantation, rate of living-donor transplantation, rate of ABO incompatibility, method of dialysis (hemodialysis or peritoneal dialysis), duration of dialysis, and time interval between the renal transplantation and the initial visit to the Department of Psychiatry among the 2 groups. These results suggested that there was another risk factor or interactions between factors. Of the 25 recipients, 6 had relationship problems, 6 had social-rehabilitation problems, and 13 had mentioned no clear psychological problems. These psychological factors might in fact be related to the loss of an imagined past. Additional consecutive prospective studies are needed—a challenging prospect for consultation liaison psychiatrists in the field of transplantation.
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