The isospin effects of projectile fragmentation at intermediate energies are investigated using an isospin-dependent Boltzmann-Langevin model.The collisions of mass-symmetric reactions including 58Fe,58Ni+58Fe,and Ni at intermediate energies,in the 30 to 100 MeV/A range,are studied for different symmetry energies.Yield ratios of the isotopic,isobaric,and isotonic pairs of fragments from the intermediate-mass region using three symmetry energies are extracted as functions of the N/Z ratio of the composite systems in the entrance channel and the incident energies.It is found that the yield ratios are sensitive to symmetry energies,especially for neutron-rich systems,and the calculations using soft symmetry energy are closer to the experimental data.The isospin effect is stronger for the soft symmetry energy,owing to the competition of the repulsive Coulomb force and the symmetry energy attractive force on the proton.For the first time,the splits are presented,revealing a transition from the isospin equilibrium at lower energies to translucency at intermediate energies.The results show a degree of transparency in that intermediate mass fragments undergo a transition from dependence on the composite systems in the entrance channel to reliance on the projectile and target nuclei.
Molecular dynamics simulations are performed to investigate the polymorphism and flexibility of DNA in water,ethylene glycol(EG)and ethanol(EA)solutions.DNA in EG resembles the structure of DNA in water exhibiting B-DNA.In contrast,the DNA is an A-DNA state in the EA.We demonstrate that one important cause of these A$\leftrightarrow$B state changes is the competition between hydration and direct cation coupling to the phosphate groups on DNA backbones.To DNA structural polymorphism,it is caused by competition between hydration and cation coupling to the base pairs on grooves.Unlike flexible DNA in water and EA,DNA is immobilized around the canonical structure in EG solution,eliminating the potential biological effects of less common non-canonical DNA sub-states.
We study the properties of the ethylene glycol solutions and the conformational transitions of DNA segment in the ethylene glycol solutions by molecular dynamics simulations based on GROMACS. The hydrogen network structures of water–water and ethylene glycol–water are reinforced by ethylene glycol molecules when the concentrations of the solutions increase from 0% to 80%. As illustrated by the results, conformation of the double-stranded DNA in ethylene glycol solutions, although more compact, is similar to the structure of DNA in the aqueous solutions. In contrast, the DNA structure is an A–B hybrid state in the ethanol/water mixed solution. A fraying of terminal base-pairs is observed for the terminal cytosine. The ethylene glycol molecules preferentially form a ring structure around the phosphate groups to influence DNA conformation by hydrogen interactions, while water molecules tend to reside in the grooves. The repulsion between the negatively charged phosphate groups is screened by ethylene glycol molecules, preventing the repulsion from unwinding and extending the helix and thus making the conformation of DNA more compact.
Effect of linear chirp frequency on the process of electron–positron pairs production from vacuum is investigated by the computational quantum field theory.With appropriate chirp parameters,the number of electrons created under combined potential wells can be increased by two or three times.In the low frequency region,frequency modulation excites interference effect and multiphoton processes,which promotes the generation of electron–positron pairs.In the high frequency region,high frequency suppression inhibits the generation of electron–positron pairs.In addition,for a single potential well,the number of created electron–positron pairs can be enhanced by several orders of magnitude in the low frequency region.
The multinucleon transfer reaction in the collisions of 40 Ca+^124 Sn at Ec.m.= 128.5 MeV is investigated using the improved quantum molecular dynamics model. The measured angular distributions and isotopic distributions of the products are reproduced reasonably well by the calculations. The multinucleon transfer reactions of 40 Ca+^112 Sn, 58 Ni+^112 Sn, 106 Cd+^112 Sn, and 48 Ca+^112 Sn are also studied. This demonstrates that the combinations of neutron-deficient projectile and target are advantageous for the production of exotic neutron-deficient nuclei near N,Z =50. The charged particles’ emission plays an important role at small impact parameters in the de-excitation processes of the system. The production cross sections of the exotic neutron-deficient nuclei in multinucleon transfer reactions are much larger than those measured in the fragmentation and fusion-evaporation reactions. Several new neutron-deficient nuclei can be produced in the 106 Cd+^112 Sn reaction. The corresponding production cross sections for the new neutron-deficient nuclei,101,112 Sb,103 Te,and 106,107) I,are 2.0 nb,4.1 nb,6.5 nb,0.4 μb and 1.0 μb,respectively.
Theα-decay properties of even-Z nuclei with Z=120,122,124,126 are predicted.We employ the generalized liquid drop model(GLDM),Royer's formula,and universal decay law(UDL)to calculate theα-decay half-lives.By comparing the theoretical calculations with the experimental data of known nuclei from Fl to Og,we confirm that all the employed methods can reproduce theα-decay half-lives well.The preformation factor Pαandα-decay energy Qαshow that ^298,304,314,316,324,326,338,348120,^304,306,318,324,328,338122,and ^328,332,340,344124 might be stable.Theα-decay half-lives show a peak at Z=120,N=184,and the peak vanishes when Z=122,124,126.Based on detailed analysis of the competition betweenα-decay and spontaneous fission,we predict that nuclei nearby N=184 undergoα-decay.The decay modes of ^287−339120,^294−339122,^300−339124,and ^306−339126 are also presented.
Zhishuai GeGen ZhangShihui ChengYu.S.TsyganovFeng-Shou Zhang
