Dendrite to symmetry-broken dendrite transition in directional solidification of non-axially oriented crystals

In this paper, the morphological transition from dendrite to symmetry-broken dendrite is investigated in the directional ;olidification of non-axially-oriented crystals using a quantitative phase-field model. The effects of pulling velocity and zrystal orientation on the morphological transition are investigated. The results indicate the orientation dependence of the ;ymmetry-broken double dendrites. A dendrite to symmetry-broken dendrite transition is found by varying the pulling telocity at different crystal orientations and the symmetry-broken multiple dendrites emerge as a transition state for the ;ymmetry-broken double dendrites. The state region during the transition can be well characterized through the variations ff the characteristic angle and the average primary dendritic spacing.

Phase Equilibria of Hydrogen Bonding Fluid in a Slit Pore with Broken Symmetry

Phase equilibria of hydrogen bonding （HB） fluid confined in a slit pore with broken symmetry were investigated by the density functional theory incorporated with modified fundamental measure theory, where the symmetry breaking originated from the distinct interactions between fluid molecules and two walls of the slit pore. In terms of adsorption-desorption isotherms and the corresponding grand potentials, phase diagrams of HB fluid under various conditions are presented. Furthermore, through phase coexistences of laying transition and capillary condensation, the effects of HB interaction, pore width, fluid-pore interaction and the broken symmetry on the phase equilibrium properties are addressed. It is shown that these factors can give rise to apparent influences on the phase equilibria of confined HB fluid because of the competition between intermolecular interaction and fluid-pore interaction. Interestingly, a significant influence of broken symmetry of the slit pore is found, and thus the symmetry breaking can provide a new way to regulate the phase behavior of various confined fluids.

Recent advances of defect-induced spin and valley polarized states in graphene

Electrons in graphene have fourfold spin and valley degeneracies owing to the unique bipartite honeycomb lattice and an extremely weak spin-orbit coupling,which can support a series of broken symmetry states.Atomic-scale defects in graphene are expected to lift these degenerate degrees of freedom at the nanoscale,and hence,lead to rich quantum states,highlighting promising directions for spintronics and valleytronics.In this article,we mainly review the recent scanning tunneling microscopy(STM)advances on the spin and/or valley polarized states induced by an individual atomicscale defect in graphene,including a single-carbon vacancy,a nitrogen-atom dopant,and a hydrogen-atom chemisorption.Lastly,we give a perspective in this field.

Polarization and structure dependent optical characteristics of the three-arm nanoantenna with C_(3v) symmetry and broken symmetry

The optical properties of a three-arm plasmonic nanoantenna with and without broken symmetry were analyzed in detail. For the symmetrical structure, the local electric field can be significantly enhanced and well confined within the feed gap, whilst the extinction spectrum illustrates polarization independence. With broken symmetry, multi-wavelength resonances are observed due to the single dipole resonance and dipole–dipole coupling effect, and wide tunability is also available through minor structural adjustment. Especially when illuminated by a circularly polarized light beam, the extinction and the electric field distribution can be effectively modulated by just varying the incident wavelength.

3-硝基-1,2,4-三唑-5-酮(NTO)热分解机理的对称破缺密度泛函理论研究

共价键均裂在含能分子的热分解过程中普遍存在,因此极为重要.然而,以往的理论研究通常用键能(ΔH,BDE)估算均裂能垒,因忽略了熵效应,必然造成较大误差.采用对称破缺密度泛函方法(BS-UB3LYP/6-311+G**),对含能分子3-硝基-1,2,4-三唑-5-酮(NTO)的热分解机理进行了系统研究和梳理,计算了共价键均裂的过渡态及能垒.结果表明,C—NO_(2)键均裂和随后的自由基复合是最优途径,能垒为216.9 k J·mol^(-1)(523 K).随后产生的NO自由基通过多次“复合-均裂”过程促进三唑中间体开环,分解为HNCO,N_(2)O和CO等小分子,它们相互反应又生成NO_(2),N_(2)和CO_(2).这些分解产物与诸多实验观测结果一致.