Xinlu Cheng

Enhanced near-infrared absorption in graphene with multilayer metal-dielectric-metal nanostructure

A multilayer metal-dielectric-metal nanostructure is proposed to enhance the absorption in graphene in a near-infrared region. The main feature of the structure is the generation of strong magnetic response within the dielectric spacer, which is directly related to absorption enhancement in graphene to over 22 times higher than that of free-standing monolayer graphene. We also show that absorption enhancement in graphene can be easily controlled by adjusting the geometry of the propose structure. The simple structural configuration and the flexible tunability in absorption enhancement are beneficial for practical fabrication and future applications in graphene-based active optoelectronic devices.

Influence of New Interaction Potential on MD Simulation of MgSiO3 Perovskite Thermodynamic Properties

The interaction potential plays an important role in molecular dynamics (MD) simulations. Pair potential has been used to simulate the melting temperature of MgSiO3 perovskite in previous studies, but considerable discrepancy of melting temperature exists between these simulations. Comparisons of potential energy curves are performed to explain the discrepancy. To further investigate the influence of the interaction potential parameters on the MD simulation result, a new set of potential parameters is developed based on two fitting potential parameters of previous studies, and is applied in the present study. The simulated molar volume MgSiO3 perovskite agrees well with the study by Belonoshko and Dubrovinsky at ambient condition. The equations of state, constant-pressure heating capacity and the constant-pressure thermal expansivity of MgSiO3 perovskite are close to the experimental data. Calculated melting temperatures are also comparable with those derived from previous studies.

Reaction of H2 and N+ Ion under Titan's Atmosphere

Abstract The thermochemical properties of reaction N + +H 2 →NH + +H have been computed under Titans atmosphere conditions. It is observed that this reaction is an endothermic reaction and cannot proceed forward spontaneously under low temperature. The rate for this reaction at 300 K has been calculated as k =4.16×10 −10 cm 3 ·mol −1 ·s −1 . The reaction barrier is 109.847 kJ·mol −1 at 298.15 K, which is probably too high to allow this reaction to occur in the atmosphere of Titan. The kinetic properties of the reaction are calculated at a pressure of 90 Pa and a temperature ranging from 1 to 5000 K. It is found that this reaction has a very low reaction rate under low temperature in Titans atmosphere and that the rate decreases drastically with decreasing temperature. This result should be applicable to interstellar place with low temperature values. The results are compared with those obtained from experiments.

Quantitative structure-pharmacokinetic/pharmacodynamic relationship for fluoroquinolones

Quantitative structure-pharmacokinetic/pharmacodynamic (PK/PD) relationship (QSPR) techniques and chemometric methods were employed to classify fluoroquinolones with respect to their activity against Streptococcus pneumoniae. Density functional theory (DFT) was used to calculate a set of molecular descriptors (properties) for 13 synthetic fluoroquinolones. The descriptors were further analyzed using chemometric methods including principal component analysis (PCA), hierarchical cluster analysis (HCA), and stepwise discriminant analysis (SDA). The PCA and SDA methods were employed in order to reduce the dimensionality and select a subset of variables that would be more effective for classifying the fluoroquinolones according to their degree of antipneumococcal activity. The methods of PCA, SDA and HCA were quite efficient to classify 13 compounds in two groups (active and inactive), and the net charge on ring B (QB), molecular volume (VOL), and partition coefficient (log P ) were found to be descriptors important for the classification. These methodologies of PCA, SDA and HCA provide a reliable rule for classifying new fluoroquinolones with respect to antipneumococcal activity. The application of the SPP relationship is of considerable value for clinicians, drug developers, and regulators because PK/PD principles form the basis of modern antimicrobial chemotherapy.

Calculation of wavelengths and oscillator strengths in high-Z Mg-like ions

Wavelengths and oscillator strengths for transitions among the levels of the terms belonging to the 3s2, 3s3p, 3s3d, 3s4s, 3s4p, 3s4d, 3p2, 3p3d, 3p4s, 3p4p, 3p4d, 3d4s, 3d4p, 3d4d and 3d2 configurations of Mg-like Nd48+, Pm49+ and Sm50+ are systematically calculated using multiconfiguration-Dirac–Fock method. The predicted spectra of these three ions are, for the first time, extensively reported for n = 3–4 transitions in the 5–8 A range and the variant trends of wavelengths and oscillator strengths along the isoelectronic sequence are discussed.

A comment on “Ab initio study: the potential energy curves and ro-vibrational spectrum of low-lying excited states of HCl+ cation”

ABSTRACT Since the 2Π state in HCl+ is an inverted doublet, the energy of the 2Π1/2 state is higher than the 2Π3/2. Therefore, the larger value of intensity correspond to the transition of 2Π3/2. We calculated the Einstein A coefficients and radiation lifetimes for the A2Σ+-X2Π transition. Our results are in good agreement with the experimental data and theoretical values. Then the ro-vibrational line intensities of the 1-0 band were calculated for the 2Π3/2 and 2Π1/2 states of HCl+. Employing the RKR potential, the predicted band origins for Δν=1-0 are 2569.3 and 2568.55 cm-1 for 2Π3/2 and 2Π1/2, respectively.

Theoretical study of spectral parameters for the γ and β band systems of NO for atmosphere and high temperature

ABSTRACT Highly correlated ab initio calculations were performed for accurate determination of γ (A2Σ+-X2П) and β (B2П-X2П) band systems of NO molecule. Highly accurate multi-reference configuration interaction approach was used to investigate the potential energy curves (PECs) and transition dipole moment curves. We correctly and fully described their diffuse wave functions by the obvious balance between the valence and Rydberg character of the X2П, A2Σ+, B2П, C2П and D2Σ+ states. The PECs of the three states (X2П, A2Σ+ and B2П) by using the aug-cc-pV5Z (aV5Z) basis set for N and O atoms agreed well with the Rydberg–Klein–Rees potential. Moreover, the Einstein A coefficients were calculated to predict the lifetimes, where the vibrational bands included v′ = 0–8, v″ = 0–29 for γ system and v′ = 0–11, v″ = 0–31 for β system. The spectral line intensities of the γ and β systems for atmosphere and high temperature were provided.