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[en] In this paper we have proposed a wavelet-based approach to study peak components fitting to the Raman 2D band of few layer graphene. As a result of the Continuous Wavelet Transform application peak components of the Raman 2D band are visualized and their number and peak frequencies are determined. It is found that there are four and five peak components of the 2D band for bilayer and trilayer graphene stacked in the Bernal (ABA) configuration respectively. In the case of tetralayer graphene with the rhombohedral (ABC) stacking there are also five peak components of the Raman 2D band. The peak frequencies of detected components are in good agreement with the experimental data.
[en] The preference for icosahedral B12 amongst polyhedral boranes and elemental boron is explained based on an optimization of overlap model. The ingenious ways in which elemental boron and boron-rich solids achieve icosahedron-related structures are explained by a fragment approach. The Jemmis mno rules are used to get the electron requirements. The extra occupancies and vacancies in β-rhombohedral structures are shown to be inevitable results of electron requirements. The detailed understanding of the structure suggests ways of doping β-rhombohedral boron with metals for desired properties. Theoretical studies of model β-rhombohedral solids with metal dopings provide support for the analysis. - Graphical abstract: A short legend: Principal building blocks B12, B57, and B84 of elemental boron and boron-rich solids
[en] A powder neutron diffraction structure analysis of a dehydrated Na-A zeolite with Si/Al ratio of unity confirmed that the space group is R3 and verified the Si:Al ordering scheme proposed by Bursill, Lodge, Thomas and Cheetham (J. Phys. Chem., (1981)). Each cuboctahedral cage of the aluminosilicate framework contains one 3-fold axis and each Si(Al) is connected via oxygen bridges to 3Al (Si) and one other Si(Al). Total profile analysis by the Rietveld method gave cell parameters a=17.392 A, α = 59.62 deg. and final profile reliability index as 9.78%
[en] The structure of the HIV-1 reverse transcriptase Q151M mutant was determined at a resolution of 2.6 Å in space group P321. Hepatitis B virus polymerase (HBV Pol) is an important target for anti-HBV drug development; however, its low solubility and stability in vitro has hindered detailed structural studies. Certain nucleotide reverse transcriptase (RT) inhibitors (NRTIs) such as tenofovir and lamivudine can inhibit both HBV Pol and Human immunodeficiency virus 1 (HIV-1) RT, leading to speculation on structural and mechanistic analogies between the deoxynucleotide triphosphate (dNTP)-binding sites of these enzymes. The Q151M mutation in HIV-1 RT, located at the dNTP-binding site, confers resistance to various NRTIs, while maintaining sensitivity to tenofovir and lamivudine. The residue corresponding to Gln151 is strictly conserved as a methionine in HBV Pol. Therefore, the structure of the dNTP-binding pocket of the HIV-1 RT Q151M mutant may reflect that of HBV Pol. Here, the crystal structure of HIV-1 RT Q151M, determined at 2.6 Å resolution, in a new crystal form with space group P321 is presented. Although the structure of HIV-1 RT Q151M superimposes well onto that of HIV-1 RT in a closed conformation, a slight movement of the β-strands (β2–β3) that partially create the dNTP-binding pocket was observed. This movement might be caused by the introduction of the bulky thioether group of Met151. The structure also highlighted the possibility that the hydrogen-bonding network among amino acids and NRTIs is rearranged by the Q151M mutation, leading to a difference in the affinity of NRTIs for HIV-1 RT and HBV Pol
[en] In this paper, the relation between the dielectric properties and the lattice distortion in the phase coexistence region is discussed using a phase statistical distribution model, and in the rhombohedral phase region the two connection equations on the dielectric properties and the lattice distortion are established. Particularly, the relation between the dielectric properties and the lattice distortion is investigated in the phase coexistence region of PZT ceramics, and the fitting value of the volume fraction of the tetragonal phase VT to composition x in the equation is determined. Further, the fitting results are well consistent with the related experimental data. It involves more profound physical process than relation between the dielectric properties and composition x.
[en] The electronic and mechanical properties of AlGaN and InGaN were analyzed in the pressure range of 0 GPa to 50 GPa by the first-principles study. Moreover, the energy band structure gets modified upon increasing pressure. The density of states (DOS) spectrum of AlGaN and InGaN shows the shift in the peaks upon increase in the pressure. The elastic constants for rhombohedral AlGaN and InGaN were established. By estimating the Young’s, bulk and shear moduli, an upsurge in the magnitude was observed with the intensifying pressure. The ductility of AlGaN and InGaN were demonstrated by examining the Poisson’s ratio, Cauchy’s pressure and Pugh’s criterion under increasing the pressure. We observed increase in the ductility of AlGaN and InGaN upon applied pressure. Thus, the findings suggest that the band gap of AlGaN and InGaN can be fine-tuned on applying the pressure, which is suitable to fabricate new optoelectronic devices. (paper)