## 7 Conclusions  
In this work, we have investigated the Coulomb focused bremsstrahlung spectrum due to the electron-atom bremsstrahlung process in nonthermal plasmas. We derived the universal expression of the electron-atom bremsstrahlung cross section by using the Thomas-Fermi model with the effective charge method. We also derived the effective Coulomb focusing factor for the electron-atom bremsstrahlung process by using the modified Elwert-Sommerfeld factor with the mean effective charge for the binary-encounter. The Coulomb focused electron-atom bremsstrahlung cross section and the Coulomb focused bremsstrahlung emission rates in Lorentzian plasmas with Fe and W atoms were also obtained. The Coulomb focusing is found to increase the bremsstrahlung cross section. The effect of the Coulomb focusing on the electron-atom bremsstrahlung cross section becomes bigger with an increase of the radiation photon energy. Moreover, the bremsstrahlung emission rates for the electron-atom bremsstrahlung process in thermal Maxwellian plasmas are always greater than those in nonthermal Lorentzian plasmas. The nonthermal effect on the bremsstrahlung emission rate for the soft photon case is more significant than those for the hard photon case. Hence, it is expected that the hard-photon X-ray spectroscopy of the electron-atom bremsstrahlung process would be useful to explore the physical properties of nonthermal plasmas. In addition, we have found that the Coulomb focusing effect on the bremsstrahlung emission rate is important in thermal plasmas and in hard spectral ranges. It was shown that the synchrotron radiation image would be important for the investigation of the degree of anisotropy in fusion plasmas [28]. It was also shown that the screening effect plays a significant role in the photoionization process in weakly coupled plasmas [29; 30]. Hence, the Coulomb focusing effects on the bremsstrahlung process in magnetized plasmas and on the photoionization process will also be investigated elsewhere by using the modified effective charge method [31; 32]. Recently, the physical significance of dusty plasmas has received a considerable attention since the dusty plasmas can be found in various astrophysical complex plasmas as well as in laboratory plasma devices [33; 34; 35; 36; 37; 38]. The investigation of the influence of Coulomb focusing on the bremsstrahlung process in dusty plasmas will also be treated elsewhere since the charging of the dust grains takes a crucial role in the bremsstrahlungspectrum. It is quite obvious that the simple universal theoretical model such as the Thomas-Fermi model [39] provides a necessary intellectual framework for the collision and radiation processes as well as the geometrical configurations of the physical system. In addition, the simple analytical model can be used to understand simulations and experiments [40; 41], and to extract more physical information from them. Hence, our results for the analytic expressions of the Coulomb focused electron-atom bremsstrahlung cross section and the Coulomb focused bremsstrahlung emission rates in Lorentzian plasmas would provide the useful information on the astrophysical and laboratory nonthermal X-ray radiations. In this work, we have found that the nonthermal character of the plasma as well as the Coulomb focusing effect plays a very important role in the electron-atom bremsstrahlung process in Lorentzian plasma. These results should be useful for the investigation of radiation processes in nonthermal plasmas. Conceptualization, N.A. ; Formal analysis, M.-J.L., Y.-D.J. ; Funding acquisition, M.-J.L. ; Investigation, Y.-D.J. ; Methodology, Y.-D.J. ; Project administration, M.-J.L. ; Resources, N.A. ; Validation, N.A. ; Writing-original draft, M.-J.L., Y.-D.J. ; Writing-review & editing, M.-J.L., N.A., Y.-D.J. All authors have read and agreed to the published version of the manuscript.