Amplification and Attenuation of Acoustic Phonons in Graphenelike Silicene

Because of unique physical properties, graphene, a 2D honeycomb arrangement of carbon atoms, has attracted tremendous attention. Silicene, the graphene equivalent for silicon, could follow this trend, opening new perspectives for applications, especially due to its compatibility with Si-based electronics. Silicene has been theoretically predicted as a buckled honeycomb arrangement of Si atoms and having an electronic dispersion resembling that of relativistic Dirac fermions. We calculate theoretically in this article, the amplification and attenuation of acoustic phonons due to an external temperature gradient in Silicene at temperature ࢀ= 77K in the hypersound regime. The dependence of normalized amplification or attenuation on the frequency wasnumerically evaluated. It is observed from our calculations that when the temperature gradient is zero, absorption of acoustic phonons occurs and when temperature gradient is greater than zero, absorption switches to amplification of acoustic phonons. Keywords: Silicene, Amplification, Attenuation, Acoustic phonons, Temperature gradient.

Analysis and Compensation of Chromatic Dispersion in Long-hauls Optical Coherent System

In this paper, we demonstrate the efficiency of Electronic Dispersion Compensation (EDC) for coherent optical systems based on Polarization Division Multiplexed Quadrature Phase Shift Keying (PDM-QPSK). The performance of the proposed system is tested using a pulse that has been recently used in the presence of nonlinear effects.The proposed system is compared to the 0.3RZ-PDM-QPSK system at the optimum launched power under different symbol-rates and lengths of transmission. The simulation results confirm that the proposed method enhances the system performance. In addition, it secures a low penalty that is below 0.6 dB. As a result, the feasible transmission distance is improved by 29 %, 20.15 %, and 26.7 %, at 14 GBaud, 28 Gbaud, and 56 Gbaud, respectively.

Electronic properties of bilayer sheets forming moiré patterns

In this article, we report the electronic band structures of hexagonal bilayer systems, specifically, rotated graphene-graphene and boron nitride-boron nitride bilayers, by introducing an angle between the layers and forming new periodic structures, known as moiré patterns. Using a semi-empirical tight-binding approach with a parametrized hopping parameter between the layers, using one orbital per-site approximation, and taking into account nearest-neighbor interactions only, we found he electronic dispersion relations to be around K points in a low energy approximation. Our results show that graphene bilayers exhibit zero band gap for all angles tested in this work. In boron nitride bilayers, the results reveal a tunable bandgap that satisfies the prediction of the bandgap found in one-dimensional diatomic systems presented in the literature.

A A new matrix of MALDI-TOF MS derivative of 9-aminoacridine for lipid identification in positive ions mode

Matrix-assisted laser desorption/ionization (MALDI) has evolved to become a well- established technique during the last decades. Because of matrix peak interference in the low molecular-weight region, however, new matrices are often studied with the purpose of improving the spectral quality under m/z 500. Herein, we present the substance 2,4,5,7-tetranitro-9-aminoacridine (TNA) as a suitable alternative matrix for lipid detection in the positive-ion mode. TNA is obtained from 9-aminoacridine, a matrix commonly used to analyze lipids in negative-ion mode, with the addition of 4 nitro groups through a synthetic path. The procedure results in a highly conjugated system that presents a bigger electronic dispersion and therefore higher UV absorption. First, we demonstrated the high sensitivity of TNA for retinol. Second, TNA was applied to detect lipids in the liver of the water rat Nectomys squamipes. By using this natural model of hepatic steatosis (fat liver), a condition in which there is excessive accumulation of lipids, TNA provided a clearer identification of three species of polyunsaturated fatty acids (PUFAs) compared to other matrices. TNA presents better sensitivity and spectral resolution, little or no interference from matrix ions, high intensity of signal and low cost with high yield of matrix production.