We present a systematic investigation of the impact of changing the geometry structure of the SPC/E water model by performing a series of molecular dynamic simulations at 1 bar （1 bar = 105 Pa） and 298.15 K. The geo...We present a systematic investigation of the impact of changing the geometry structure of the SPC/E water model by performing a series of molecular dynamic simulations at 1 bar （1 bar = 105 Pa） and 298.15 K. The geometric modification includes altering the H-O-H angle range from 90° to 115° and modifying the O-H length range from 0.90 A to 1.10 A in the SPC/E model. The former is achieved by keeping the dipole moment constant by modifying the O-H length, while in the latter only the O-H length is changed. With the larger bond length and angle, we find that the liquid shows a strong quadrupole interaction and high tetrahedral structure order parameter, resulting in the enhancement of the network structure of the liquid. When the bond length or angle is reduced, the hydrogen bond lifetime and self-diffusion constant decrease due to the weakening of the intermolecular interaction. We find that modifying the water molecular bond length leading to the variation of the intermolecular interaction strength is more intensive than changing the bond angle. Through calculating the average reduced density gradient and thermal fluctuation index, it is found that the scope of vdW interaction with neighbouring water molecules is inversely proportional to the change of the bond length and angle. The effect is mainly due to a significant change of the hydrogen bond network. To study the effect of water models as a solvent whose geometry has been modified, the solutions of ions in different solvent environments are examined by introducing NaCI. During the dissolving process, NaCI ions are ideally dissolved in SPC/E water and bond with natural water more easily than with other solvent models.展开更多
A new detection method has been applied to study the penetration depth of low-energy heavy ions in botanic samples. Highly oriented pyrolytic graphite (HOPG) pieces were placed behind the target samples with certain t...A new detection method has been applied to study the penetration depth of low-energy heavy ions in botanic samples. Highly oriented pyrolytic graphite (HOPG) pieces were placed behind the target samples with certain thickness to receive energetic penetrated ions during the irradiation. After irradiation, statistic number density of protrusion-like damage induced by energetic penetrated ions can be ob- tained through scanning tunneling microscope (STM) observation on the surfaces of HOPG. The results of test indicate that the detection limit can be as low as 1.0×109 protrusions/cm2. With the method, the penetration depth of at least 60μm can be detected in kidney bean slices irradiated by N+ ions with dose of 0.3-3×1017ions/cm2.展开更多
Hot nuclei produced in the reactions of 25 MeV/u<sup>40</sup>Ar with <sup>209</sup>Bi and<sup>Na1</sup>Ag are studied.Theinitial properties of these nuclei :excitation energies,line...Hot nuclei produced in the reactions of 25 MeV/u<sup>40</sup>Ar with <sup>209</sup>Bi and<sup>Na1</sup>Ag are studied.Theinitial properties of these nuclei :excitation energies,linear momentum transfer and temperatures are char-acterized through the measurements of folding angle of fission fragments,light charged particle energyspectra and intermediate mass fragments.Nuclei with excitation energies as high as～600 MeV and tem-peratures as high as～6 MeV are produced.The spectra of alpha particles detected in coincidence with fis-sion fragments in the case of different average linear momentum transfer are analyzed and the initial tem-peratures of the hot nuclei are determined.A saturation（or limiting）temperature near 6 MeV is foundfor alpha emission from medium mass nuclei having excitation energies higher than 3 MeV/u.This resultprovides evidence for a soft nuclear equation of state at thee high excitation energies and is consistentwith predictions of statistic multifragmentation model calculations.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11635003,11025524,and 11161130520)the National Basic Research Program of China(Grant No.2010CB832903)the European Commission’s 7th Framework Programme(Fp7-PEOPLE-2010-IRSES)(Grant Agreement Project No.269131)
文摘We present a systematic investigation of the impact of changing the geometry structure of the SPC/E water model by performing a series of molecular dynamic simulations at 1 bar （1 bar = 105 Pa） and 298.15 K. The geometric modification includes altering the H-O-H angle range from 90° to 115° and modifying the O-H length range from 0.90 A to 1.10 A in the SPC/E model. The former is achieved by keeping the dipole moment constant by modifying the O-H length, while in the latter only the O-H length is changed. With the larger bond length and angle, we find that the liquid shows a strong quadrupole interaction and high tetrahedral structure order parameter, resulting in the enhancement of the network structure of the liquid. When the bond length or angle is reduced, the hydrogen bond lifetime and self-diffusion constant decrease due to the weakening of the intermolecular interaction. We find that modifying the water molecular bond length leading to the variation of the intermolecular interaction strength is more intensive than changing the bond angle. Through calculating the average reduced density gradient and thermal fluctuation index, it is found that the scope of vdW interaction with neighbouring water molecules is inversely proportional to the change of the bond length and angle. The effect is mainly due to a significant change of the hydrogen bond network. To study the effect of water models as a solvent whose geometry has been modified, the solutions of ions in different solvent environments are examined by introducing NaCI. During the dissolving process, NaCI ions are ideally dissolved in SPC/E water and bond with natural water more easily than with other solvent models.
基金Supported by the National Natural Science Foundation of China under Grant No.19675004 and (No.19890300)
文摘A new detection method has been applied to study the penetration depth of low-energy heavy ions in botanic samples. Highly oriented pyrolytic graphite (HOPG) pieces were placed behind the target samples with certain thickness to receive energetic penetrated ions during the irradiation. After irradiation, statistic number density of protrusion-like damage induced by energetic penetrated ions can be ob- tained through scanning tunneling microscope (STM) observation on the surfaces of HOPG. The results of test indicate that the detection limit can be as low as 1.0×109 protrusions/cm2. With the method, the penetration depth of at least 60μm can be detected in kidney bean slices irradiated by N+ ions with dose of 0.3-3×1017ions/cm2.
基金The project supported by the National Natural Science Foundation of China
文摘Hot nuclei produced in the reactions of 25 MeV/u<sup>40</sup>Ar with <sup>209</sup>Bi and<sup>Na1</sup>Ag are studied.Theinitial properties of these nuclei :excitation energies,linear momentum transfer and temperatures are char-acterized through the measurements of folding angle of fission fragments,light charged particle energyspectra and intermediate mass fragments.Nuclei with excitation energies as high as～600 MeV and tem-peratures as high as～6 MeV are produced.The spectra of alpha particles detected in coincidence with fis-sion fragments in the case of different average linear momentum transfer are analyzed and the initial tem-peratures of the hot nuclei are determined.A saturation（or limiting）temperature near 6 MeV is foundfor alpha emission from medium mass nuclei having excitation energies higher than 3 MeV/u.This resultprovides evidence for a soft nuclear equation of state at thee high excitation energies and is consistentwith predictions of statistic multifragmentation model calculations.
