分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Cluster structures in light unstable nuclei are discussed. The structures of neutron-rich Be isotopes are theoretically investigated and the molecular orbital bond structure and its role in the vanishing of the neutron magic number N=8 are discussed. The two-body cluster resonances in highly excited states of neutron-rich Li, Be and B isotopes are predicted theoretically.
分类: 核科学技术 >> 粒子加速器 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Terahertz vibrational spectroscopy has recently been demonstrated as a novel noninvasive technique for the characterization of biological molecules. But the interpretation of the experimentally measured terahertz absorption bands requires robust computational method. In this paper, we present a statistical method for predicting the absorption peak positions of a macromolecule in the terahertz region. The essence of this method is to calculate the absorption spectra of a biological molecule based on multiple short scale molecular dynamics trajectories instead of using a long time scale trajectory. The method was employed to calculate the absorption peak positions of the protein, thioredoxin from Escherichia coli (E.coli), in the range of 1025 cm1 to verify the reliability of this statistical method. The predicted absorption peak positions of thioredoxin show good correlation with measured results demonstrating that the proposed method is effective in terahertz absorption spectra modeling. Such approach can be applied to predict characteristic spectral features of biomolecules in the terahertz region.
分类: 物理学 >> 凝聚态:结构、力学和热性能 提交时间: 2016-06-14
摘要: Heat conduction through one-dimensional (1D) coupled rotator lattices is investigated in the presence of mass gradient. It is found that thermal current in the direction of mass increasing is not asymmetric with heat flux though mass decreasing system, which is called thermal rectification. Moreover, we find that the larger is the mass gradient, the more evident is the thermal rectification effect, which is consistent with FPU lattice with mass gradient. Based on the influences of the thermal rectification on shape parameters K and A of nearest-neighbor interactions, the average temperature of atomic chain and the system size, a optimum thermal rectifier is designed, which thermal rectification efficiency has reached 70. These investigations would contribute to controlling and manipulating thermal current.
分类: 核科学技术 >> 裂变堆工程技术 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: Molecular dynamics method is used to investigate the displacement cascades in Ni-Mo binary alloy. Effects of the irradiation temperature, energy of the primary knock-on atoms and concentration of solute Mo atoms are taken into consideration on radiation damage to the Ni-Mo alloy. It is found that Mo atoms reduce production of the Frenkel pairs at 100 K, while they enhance defect production at 300 K and 600 K. Size of the largest defect clusters decreases with increasing concentrations of Mo atoms (CMo) at 100 K, but it increases with CMo at 300 K and 600 K. Most of the point defects get clustered in cascades leaving only a few vacancies and interstitials isolated.
分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: The molecular behaviors of interfacial water molecules at the solid/liquid interface are of a fundamental significance in a diverse set of technical and scientific contexts, thus have drawn extensive attentions. On certain surfaces, the water monolayer may exhibit an ordered feature, which may result in the novel wetting phenomenon. In this article, based on the molecular dynamics simulations, we make a detailed structure analysis of the ordered water monolayer on ionic model surface with graphene-like hexagonal lattices under various charges and unit cell sizes. We carefully analyze the water density profiles and potential of mean force, which are the origin of the special hexagonal ordered water structures near the solid surface. The number of hydrogen bonds of the ordered water monolayer near the solid surface is carefully investigated.
分类: 物理学 >> 核物理学 提交时间: 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要: We studied the role that electron gas has on the formation of nuclear structures at subsaturation densities and low temperatures (T < 1 MeV). Using a classical molecular dynamics model we studied isospin symmetric and asymmetric matter at subsaturation densities and low temperatures varying the Coulomb interaction strength. The effect of such variation was quantified on the fragment size multiplicity, the inter-particle distance, the isospin content of the clusters, the nucleon mobility and cluster persistence, and on the nuclear structure shapes. We found that the presence of an electron gas distributes matter more evenly, disrupts the formation of larger objects, reduces the isospin content, and modifies the nucleon average displacement, but does not affect the inter-nucleon distance in clusters. The nuclear structures are also found to change shapes by different degrees depending on their isospin content, temperature and density.
分类: 机械工程 >> 机械工程其他学科 提交时间: 2024-03-28
摘要: Increasing the transfer (HT) coefficient used in thermal industries is very important. Various methods are used to improve the efficiency of thermal heat HT so that maximum HT takes place in a smaller space. Ethylene glycol (EG) is generally used as an agent for convective HT. EG obtains energy from a hot source and discharges it to the required location. At present, the most consumption of EG is to produce engine cooling fluid. In the upcoming research, the TB of EG fluid in two-dimensional microchannels (MCs) has been investigated using molecular dynamics (MD) simulations, and the effect of variables such as MC dimensions and MC wall temperature (Temp) on the TB of the simulated fluid has been investigated. The results revealed that by increasing the Temp difference of the MC wall from 10 to 50 K, the maximum temperature (Max-Temp) and velocity (Max-Vel) of the target sample increased to 640.94 K and 0.024 Å/ps. It can be concluded that the increase in the cross-sectional area and the wall Temp difference leads to an increase in the HT rate in the MC.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-05-02
摘要: Molecular dynamics simulation was performed to investigate the effect of thickness on the properties and struc- ture of ultrathin tetrahedral amorphous carbon films (ta-C). The present simulation showed that both the density and residual compressive stress decreased with increasing the thickness of ultrathin ta-C films, which was in agreement with the experimental results. The gradient of properties with the thickness was dependent on the incident kinetic energy of deposited atoms; when the incident kinetic energy was 10 eV/atom, the slower gradient was observed. Further structural analysis indicated that the critical relaxation of highly distorted bond angles was responsible for the reduction of residual compressive stress in the films deposited at 10 eV/atom, while the joint relaxation of both the distorted bond angles and C\C bond length led to the fast release of residual compressive stress in the films deposited at 70 eV/atom.
分类: 核科学技术 >> 核材料与工艺技术 提交时间: 2023-08-14
摘要: Alloys of uranium and molybdenum are considered as the future of nuclear fuel and defense materials. However, surface corrosion is a fundamental problem in practical applications and storage. In this study, the static and dynamic evolution of carbon monoxide (CO) adsorption and dissociation on -U (1 0 0) surface with different Mo doping levels was investigated based on density functional theory and ab initio molecular dynamics. During the static calculation phase, parameters, such as adsorption energy, configuration, and Bader charge, were evaluated at all adsorption sites. Furthermore, the time-dependent behavior of CO molecule adsorption were investigated at the most favorable sites. The minimum energy paths for CO molecular dissociation and atom migration were investigated using the transition state search method. The results demonstrated that the CO on the uranium surface mainly manifests as chemical adsorption before dissociation of the CO molecule. The CO molecule exhibited a tendency to rotate and tilt upright adsorption. However, it is difficult for CO adsorption on the surface in one of the configurations with CO molecule in vertical direction but oxygen (O) is closer to the surface. Bader charge illustrates that the charge transfers from slab atoms to the 2* antibonding orbital of CO molecule and particularly occurs in carbon (C) atoms. The time is less than 100 fs for the adsorptions that forms embryos with tilt upright in dynamics evolution. The density of states elucidates that the overlapping hybridization of C and O 2p orbitals is mainly formed via the d orbitals of uranium and molybdenum (Mo) atoms in the dissociation and re-adsorption of CO molecule. In conclusion, Mo-doping of the surface can decelerate the adsorption and dissociation of CO molecules. A Mo-doped surface, created through ion injection, enhanced the resistance to uranium-induced surface corrosion.
分类: 物理学 >> 核物理学 分类: 核科学技术 >> 核聚变工程技术 提交时间: 2024-02-27
摘要: The helium bubbles induced by 14 MeV neutron irradiation can cause intergranular fractures in reduced activation ferritic martensitic (RAFM) steel, which is a candidate structural material for fusion reactors. In order to elucidate the susceptibility of different grain boundaries (GBs) to helium-induced embrittlement, the tensile fracture processes of 10 types of GBs with and without helium bubbles in body-centered cubic (bcc) iron at the relevant service temperature of 600 K were investigated via molecular dynamics methods. The results indicate that in the absence of helium bubbles, the GBs studied here can be classified into two distinct categories: brittle GBs and ductile GBs. The atomic scale analysis shows that the plastic deformation of ductile GB at high temperatures originates from complex plastic deformation mechanisms, including the Bain/Burgers path phase transition and deformation twinning, in which the Bain path phase transition is the most dominant plastic deformation mechanism. However, the presence of helium bubbles severely inhibits the plastic deformation channels of the GBs, resulting in a significant decrease in elongation at fractures. For bubble-decorated GBs, the ultimate tensile strength increases with the increase of the misorientation angle. Interestingly, the coherent twin boundary Ʃ3{112} was found to maintain relatively high fracture strength and maximum failure strain under the influence of helium bubbles.
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2016-05-03
摘要: An efficient novel algorithm was developed to estimate the Density of States (DOS) for large systems by calculating the ensemble means of an extensive physical variable, such as the potential energy, U, in generalized canonical ensembles to interpolate the interior reverse temperature curve beta S(U) partial derivative S(U)/partial derivative U, where S(U) is the logarithm of the DOS. This curve is computed with different accuracies in different energy regions to capture the dependence of the reverse temperature on U without setting prior grid in the U space. By combining with a U-compression transformation, we decrease the computational complexity from O(N-3/2) in the normal Wang Landau type method to O(N-1/2) in the current algorithm, as the degrees of freedom of system N. The efficiency of the algorithm is demonstrated by applying to Lennard Jones fluids with various N, along with its ability to find different macroscopic states, including metastable states.
分类: 核科学技术 >> 辐射物理与技术 提交时间: 2024-04-08
摘要: In the framework of the Lanzhou Quantum Molecular Dynamics (LQMD) model, a possible probe to the neutron-skin thickness (δnp) of neutron-rich 48Ca is studied in 140A MeV 48Ca + 9Be projectile fragmentation reaction based on parallel momentum distribution (p//) of residual fragments.The Fermi-type density distribution is employed to initiate the neutron density distributions in the LQMD simulation. A combined Gaussian function with different width parameters for the left side (ΓL) and the right side (ΓR) in distribution are used to describe the p// of residual fragments. The value of ΓL, taking neutron-rich sulfur isotopes as examples, shows a sensitive correlation to δnp of 48Ca, which is suggested to be a probe to determine the neutron-skin thickness of the projectile nucleus.
分类: 物理学 >> 核物理学 提交时间: 2023-06-20
摘要: Two-nucleon momentum correlation functions are investigated for different single thermal sourcesat given initial temperature (T ) and density (). To this end, the evolutions of various singleexcited nuclei at T = 1 20 MeV and = 0.2 - 1.2 0 are simulated using the thermal isospindependent quantum molecular dynamics (T hIQMD) model. Momentum correlation functions ofidentical proton-pairs (Cpp(q)) or neutron-pairs (Cnn(q)) at small relative momenta are calculatedby Lednick y and Lyuboshitz analytical method. The results illustrate that Cpp(q) and Cnn(q) keepsensitivities to the source size (A) at lower T or higher , but almost not at higher T or lower . Andthe sensitivities become stronger for smaller source. Moreover, the T , and A dependencies of theGaussian source radii are also extracted by fitting the two-proton momentum correlation functions,and the results are consistent with the above conclusions.
分类: 生物学 >> 生物物理学 >> 生物力学与生物流变学 提交时间: 2016-05-12
摘要: Talin is an integrin-binding protein located at focal adhesion site and serves as both an adapter and a force transmitter. Its integrin binding activity is regulated by the intramolecular autoinhibition interaction between its F3 and RS domains. Here, we used atomic force microscopy to measure the strength of talin autoinhibition complex. Our results suggest that the lifetime of talin autoinhibition complex shows weak catch bond behavior and does not change significantly at smaller forces, while it drops rapidly at larger forces (>10 pN). Moreover, besides the complex conformation revealed by crystal structure, our molecular dynamics (MD) simulations indicate the possible existence of another stable conformation. Further analysis indicates that forces may regulate the equilibrium of the two stable binding states and result in the non-exponential force dependence of the binding lifetime. Our findings reveal a negative regulation mechanism on talin activation and provide a new point of view on the function of talin in focal adhesion.
分类: 物理学 >> 核物理学 提交时间: 2023-06-20
摘要: The proton-proton momentum correlation function (Cpp) from di#11;erent rapidity regions are systematically investigated for the Au + Au collisions at di#11;erent impact parameters and di#11;erentenergies from 400A MeV to 1500A MeV in the framework of the isospin-dependent quantum molecular dynamics model (IQMD) complemented by the Lednick #19; y and Lyuboshitz analytical method.In particular, in-medium nucleon-nucleon cross section (NNCS) dependence of the correlation function is brought into focus, while the impact parameter and energy dependence of the momentumcorrelation function are also explored. The sizes of the emission source are extracted by #12;tting themomentum correlation functions using the Gaussian source method. We #12;nd that the in-mediumnucleon-nucleon cross section obviously in uence the proton-proton momentum correlation functionwhich is from the whole rapidity or projectile/target rapidity region at smaller impact parameters,but there is no e#11;ect on the mid-rapidity proton-proton momentum correlation function, whichindicates that the emission mechanism di#11;ers between projectile/target rapidity and mid-rapidityprotons.
分类: 物理学 >> 核物理学 提交时间: 2023-06-20
摘要: The number of nucleon (NN) scaling of the directed ow v1 and elliptic ow (v2) as well as thenuclear modi#12;cation factor (Rcp) are tested for light nuclei which are produced in 0.4A GeVAu +Au collisions at di#11;erent impact parameters with two di#11;erent in-medium nucleon-nucleon cross sections in aframework of an isospin-dependent quantum molecular dynamics (IQMD) model. In that energy domain,the emission of light nuclei can be well described by the squeeze-out phenonomenon. The results show anice NN scaling behavior for ow parameters v1, v2 and Rcp. These results demonstrate that the nucleoncoalescence mechanism is responsible for nucleon-number scaling of above physical observables in squeezeout region in heavy-ion collisions at intermediate energy.
分类: 生物学 >> 生物物理学 提交时间: 2016-05-11
摘要: Enterovirus 71 (EV71), a primary pathogen of hand, foot, and mouth disease (HFMD), affects primarily infants and children. Currently, there are no effective drugs against HFMD. EV71 3C protease performs multiple tasks in the viral replication, which makes it an ideal antiviral target. We synthesized a small set of fluorogenic model peptides derived from cleavage sites of EV71 polyprotein and examined their efficiencies of cleavage by EV71 3C protease. The novel peptide P08 [(2-(N-methylamino)benzoyl) (NMA)-IEALFQGPPK(DNP)FR] was determined to be the most efficiently cleaved by EV71 3C protease, with a kinetic constant k(cat)/K-m of 11.8 +/- 0.82mM(-1) min(-1). Compared with literature reports, P08 gave significant improvement in the signal/background ratio, which makes it an attractive substrate for assay development. A Molecular dynamics simulation study elaborated the interactions between substrate P08 and EV71 3C protease. Arg39, which is located at the bottom of the S2 pocket of EV71 3C protease, may participate in the proteolysis process of substrates. With an aim to evaluate EV71 3C protease inhibitors, a reliable and robust biochemical assay with a Z' factor of 0.87 +/- 0.05 was developed. A novel compound (compound 3) (50% inhibitory concentration [IC50] = 1.89 +/- 0.25 mu M) was discovered using this assay, which effectively suppressed the proliferation of EV 71 (strain Fuyang) in rhabdomyosarcoma (RD) cells with a highly selective index (50% effective concentration [EC50] = 4.54 +/- 0.51 mu M; 50% cytotoxic concentration [CC50] > 100 mu M). This fast and efficient assay for lead discovery and optimization provides an ideal platform for anti-EV71 drug development targeting 3C protease.
分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间: 2017-04-06
摘要: A new direct summation method, named as polyhedron method, is proposed to calculate Madelung energy. This method calculates sums of electrostatic interactions over sets of neutral polyhedron unit pairs rather than conventional ion pairs; this gives Madelu
分类: 生物学 >> 生物物理学 提交时间: 2016-05-12
摘要: Tandem duplications and fusions of single genes have led to magnificent expansions in the divergence of protein structures and functions over evolutionary timescales. One of the possible results is polydomain enzymes with interdomain cooperativities, few examples of which have been structurally characterized at the full-length level to explore their innate synergistic mechanisms. This work reports the crystal structures of a double-domain phosphagen kinase in both apo and ligand-bound states, revealing a novel asymmetric L-shaped arrangement of the two domains. Unexpectedly, the interdomain connections are not based on a flexible hinge linker but on a rigid secondary-structure element: a long alpha-helix that tethers the tandem domains in relatively fixed positions. Besides the connective helix, the two domains also contact each other directly and form an interdomain interface in which hydrogen bonds and hydrophobic interactions further stabilize the L-shaped domain arrangement. Molecular-dynamics simulations show that the interface is generally stable, suggesting that the asymmetric domain arrangement crystallographically observed in the present study is not a conformational state simply restrained by crystal-packing forces. It is possible that the asymmetrically arranged tandem domains could provide a structural basis for further studies of the interdomain synergy.
分类: 物理学 >> 交叉学科物理及相关领域的科学与技术 提交时间: 2016-05-03
摘要: Inherited the advantages of inorganic salts and organic solvents, ionic liquids (ILs) exhibit many superior properties allowing them promising green solvents for the future. Although it has been widely acknowledged that the unique features of ILs originate from their dual ionic and organic nature, its microscopic physical origin still remains blurry. In this work, by comparing the ion/molecule cage structures obtained from molecular dynamics simulations for seven prototypic liquids-a molten inorganic salt, four ILs, a strongly polar organic solvent, and a weakly polar organic solvent, we have revealed that the depth of the cage energy landscape characterizes the ionic nature of ILs, whereas the slope and curvature of its mimimum determine the organic nature of ILs. This finding advances our understanding of ILs and thus will help their efficient utilization as well as the systematic design of novel functionalized ILs.