Femtosecond time-resolved transient grating(TG) technique is used to study the intermolecular dynamics in liquid phase. Non-resonant excitation of the sample by two crossing laser pulses results in a transient Kerr gr...Femtosecond time-resolved transient grating(TG) technique is used to study the intermolecular dynamics in liquid phase. Non-resonant excitation of the sample by two crossing laser pulses results in a transient Kerr grating, and the molecular motion of liquid can be detected by monitoring the diffraction of a third time-delayed probe pulse. In liquid nitrobenzene(NB), three intermolecular processes are observed with lifetimes of 37.9±1.4 ps, 3.28±0.11 ps, and 0.44±0.03 ps, respectively. These relaxations are assigned to molecular orientational diffusion, dipole/induced dipole interaction, and libration in liquid cage, respectively. Such a result is slightly different from that obtained from OKE experiment in which the lifetime of the intermediate process is measured to be 1.9 ps. The effects of electric field on matter are different in TG and optical Kerr effect(OKE) experiments, which should be responsible for the difference between the results of these two types of experiments. The present work demonstrates that TG technique is a useful alternative in the study of intermolecular dynamics.展开更多
Currently, we are under the perception of a <em>visible universe</em> which has an <em>accelerated expansion</em>, because repeated evidences obtained by several technics since the well known o...Currently, we are under the perception of a <em>visible universe</em> which has an <em>accelerated expansion</em>, because repeated evidences obtained by several technics since the well known observations performed by Edwin Powell Hubble. The world scientific community was astonished by these observations, and since then until today, countless calculations have been made that only leave the hypothesis of the existence of an unknown <em>cosmic entity</em> that has the particularity of repelling matter from each other when it is sufficiently separated by huge amounts of that entity, which was called as “<em>dark energy</em>”. This “<em>dark energy</em>” is a completely unknown thing, and it is understood by some researchers as the convenient hypothesis, because it is which emerges from deep calculations and observations. Bearing in mind that we already know about all cosmic objects and systems are in rotation, both locally and not so locally, and that everything is full and endowed with intrinsic and extrinsic angular momentum, it seems logical to think that <em>rotational dynamics</em> must also apply to the more extensive, and that if locally (and not so locally) we perceive and infer rotating objects everywhere, then they must also exist globally. So, starting from the idea that rotation is omnipresent, at every level of sizes;from the invisibly small to the invisibly large, I thought that it is really wise to cover it through <em>rotation dynamics</em>, or that in the worst case, we cannot ignore the fact of the omnipresent rotation in any entity to infer. And this is the main reason for the resolution and the motivation of the birth of the publication of this study. Based on this seemingly simple idea, these results and conclusions of this study was reached: following a formal logic and evidence of the accelerated unfolding of the cosmic fabric, another hypothesis is proposed as an alternative to the existence of the “<em>dark energy</em>”: The <em>intensities of centrifugal acceleration fluxes</em展开更多
In this work,metal oxide nanoparticle ZnO was employed for the reinforcement of TNT.Scanning electronic microscopy(SEM)was used to study the microstructure on the fractured surface of TNT/nano-ZnO,and ultraviolet-visi...In this work,metal oxide nanoparticle ZnO was employed for the reinforcement of TNT.Scanning electronic microscopy(SEM)was used to study the microstructure on the fractured surface of TNT/nano-ZnO,and ultraviolet-visible(UV-Vis)spectroscopy was utilized for structure characterization.Moreover,to understand the reinforcing mechanism between ZnO and TNT,quantum chemistry and molecular dynamics simulation were undertaken to investigate the intermolecular interaction and mechanical properties.It is concluded that with 2.85 wt%ZnO nanoparticle addition,the amount of voids and defects decreases with the increase in bulk and shear modulus.The modified TNT/ZnO composite has high heat of formation,negative oxygen balance,and good detonation properties,which is expected to be a candidate for high-energy blended explosives.展开更多
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
Nanostructures self-assembled by cross-β peptides with ordered structures and advantageous mechanical properties have many potential applications in biomaterials and nanotechnologies. Quantifying the intra-and inter-...Nanostructures self-assembled by cross-β peptides with ordered structures and advantageous mechanical properties have many potential applications in biomaterials and nanotechnologies. Quantifying the intra-and inter-molecular driving forces for peptide self-assembly at the atomistic level is essential for understanding the formation mechanism and nanomechanics of various morphologies of self-assembled peptides. We investigate the thermodynamics of the intra-and inter-sheet structure formations in the self-assembly process of cross-β peptide KⅢIK by means of steered molecular dynamics simulation combined with umbrella sampling. It is found that the mechanical properties of the intra-and inter-sheet structures are highly anisotropic with their intermolecular bond stiffness at the temperature of 300 K being 5.58 N/m and 0.32 N/m, respectively. This mechanical anisotropy comes from the fact that the intra-sheet structure is stabilized by enthalpy but the inter-sheet structure is stabilized by entropy. Moreover, the formation process of KⅢIK intra-sheet structure is cooperatively driven by the van der Waals （VDW） interaction between the hydrophobic side chains and the electrostatic interaction between the hydrophilic backbones, but that of the inter-sheet structure is primarily driven by the VDW interaction between the hydrophobic side chains. Although only peptide KⅢIK is studied, the qualitative conclusions on the formation mechanism should also apply to other cross-β peptides.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.11304058 and 11404307)NSAF(Grant No.U1330106)
文摘Femtosecond time-resolved transient grating(TG) technique is used to study the intermolecular dynamics in liquid phase. Non-resonant excitation of the sample by two crossing laser pulses results in a transient Kerr grating, and the molecular motion of liquid can be detected by monitoring the diffraction of a third time-delayed probe pulse. In liquid nitrobenzene(NB), three intermolecular processes are observed with lifetimes of 37.9±1.4 ps, 3.28±0.11 ps, and 0.44±0.03 ps, respectively. These relaxations are assigned to molecular orientational diffusion, dipole/induced dipole interaction, and libration in liquid cage, respectively. Such a result is slightly different from that obtained from OKE experiment in which the lifetime of the intermediate process is measured to be 1.9 ps. The effects of electric field on matter are different in TG and optical Kerr effect(OKE) experiments, which should be responsible for the difference between the results of these two types of experiments. The present work demonstrates that TG technique is a useful alternative in the study of intermolecular dynamics.
文摘Currently, we are under the perception of a <em>visible universe</em> which has an <em>accelerated expansion</em>, because repeated evidences obtained by several technics since the well known observations performed by Edwin Powell Hubble. The world scientific community was astonished by these observations, and since then until today, countless calculations have been made that only leave the hypothesis of the existence of an unknown <em>cosmic entity</em> that has the particularity of repelling matter from each other when it is sufficiently separated by huge amounts of that entity, which was called as “<em>dark energy</em>”. This “<em>dark energy</em>” is a completely unknown thing, and it is understood by some researchers as the convenient hypothesis, because it is which emerges from deep calculations and observations. Bearing in mind that we already know about all cosmic objects and systems are in rotation, both locally and not so locally, and that everything is full and endowed with intrinsic and extrinsic angular momentum, it seems logical to think that <em>rotational dynamics</em> must also apply to the more extensive, and that if locally (and not so locally) we perceive and infer rotating objects everywhere, then they must also exist globally. So, starting from the idea that rotation is omnipresent, at every level of sizes;from the invisibly small to the invisibly large, I thought that it is really wise to cover it through <em>rotation dynamics</em>, or that in the worst case, we cannot ignore the fact of the omnipresent rotation in any entity to infer. And this is the main reason for the resolution and the motivation of the birth of the publication of this study. Based on this seemingly simple idea, these results and conclusions of this study was reached: following a formal logic and evidence of the accelerated unfolding of the cosmic fabric, another hypothesis is proposed as an alternative to the existence of the “<em>dark energy</em>”: The <em>intensities of centrifugal acceleration fluxes</em
基金financially supported by Joint Fund of the National Natural Science Foundation of China and China Academy of Engineering Physics(No.11076002)the National Natural Science Foundation of China(Nos.51373159 and 11402237)the Science and Technology Fund of China Academy of Engineering Physics(No.2015B0302055)。
文摘In this work,metal oxide nanoparticle ZnO was employed for the reinforcement of TNT.Scanning electronic microscopy(SEM)was used to study the microstructure on the fractured surface of TNT/nano-ZnO,and ultraviolet-visible(UV-Vis)spectroscopy was utilized for structure characterization.Moreover,to understand the reinforcing mechanism between ZnO and TNT,quantum chemistry and molecular dynamics simulation were undertaken to investigate the intermolecular interaction and mechanical properties.It is concluded that with 2.85 wt%ZnO nanoparticle addition,the amount of voids and defects decreases with the increase in bulk and shear modulus.The modified TNT/ZnO composite has high heat of formation,negative oxygen balance,and good detonation properties,which is expected to be a candidate for high-energy blended explosives.
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Project supported by the National Basic Research Program of China(Grant No.2013CB932804)the National Natural Science Foundation of China(Grant Nos.11421063,11647601,11504431,and 21503275)+1 种基金the Scientific Research Foundation of China University of Petroleum(East China)for Young Scholar(Grant Y1304073)financial support through the CAS Biophysics Interdisciplinary Innovation Team Project(Grant No.2060299)
文摘Nanostructures self-assembled by cross-β peptides with ordered structures and advantageous mechanical properties have many potential applications in biomaterials and nanotechnologies. Quantifying the intra-and inter-molecular driving forces for peptide self-assembly at the atomistic level is essential for understanding the formation mechanism and nanomechanics of various morphologies of self-assembled peptides. We investigate the thermodynamics of the intra-and inter-sheet structure formations in the self-assembly process of cross-β peptide KⅢIK by means of steered molecular dynamics simulation combined with umbrella sampling. It is found that the mechanical properties of the intra-and inter-sheet structures are highly anisotropic with their intermolecular bond stiffness at the temperature of 300 K being 5.58 N/m and 0.32 N/m, respectively. This mechanical anisotropy comes from the fact that the intra-sheet structure is stabilized by enthalpy but the inter-sheet structure is stabilized by entropy. Moreover, the formation process of KⅢIK intra-sheet structure is cooperatively driven by the van der Waals （VDW） interaction between the hydrophobic side chains and the electrostatic interaction between the hydrophilic backbones, but that of the inter-sheet structure is primarily driven by the VDW interaction between the hydrophobic side chains. Although only peptide KⅢIK is studied, the qualitative conclusions on the formation mechanism should also apply to other cross-β peptides.
