Long-wavelength optical phonon behavior in uniaxial strained graphene: Role of electron-phonon interaction

We derive the frequency shifts and the broadening of $\Gamma$ point longitudinal optical (LO) and transverse optical (TO) phonon modes, due to electron-phonon interaction, in graphene under uniaxial strain as a function of the electron density and the disorder amount. We show that, in the absence of a shear strain component, such interaction gives rise to a lifting of the degeneracy of the LO and TO modes which contributes to the splitting of the G Raman band. The anisotropy of the electronic spectrum, induced by the strain, results in a polarization dependence of the LO and TO modes. This dependence is in agreement with the experimental results showing a periodic modulation of the Raman intensity of the splitted G peak. Moreover, the anomalous behavior of the frequency shift reported in undeformed graphene is found to be robust under strain

Determinants of the extent of voluntary disclosure in the annual reports of the Moroccan banks

Many studies have been conducted on the voluntary disclosure practices. Researchers still continue to come up with various conclusions with regard to the determinants of voluntary disclosure. The main objective of this study is to investigate the determinants of the level of voluntary disclosure of banking companies listed on the Casablanca Stock Exchange. In particular, we examine associations between the internal and external mechanisms of governance and the extent of voluntary disclosure. Analysis of annual reports of the Moroccan listed banks during the period 2005-2015, shows that the foreign ownership has the most significant positive impact on the extent of voluntary disclosure. The results also show that larger banks provide greater level of voluntary disclosure. However, contrary to Agency theory predictions, the CEO duality has a significant positive impact on the extent of voluntary disclosure of Moroccan listed banks. Other mechanisms of governance like board size, board independence, block ownership and government ownership are not significantly associated with voluntary disclosure. Keywords: Voluntary disclosure, banking companies, internal and external mechanisms of governance, annual reports, Agency theory predictions

Topological Superfluid Responses of Graphene-Superconductor Platforms

We provide a rigorous and transparent explanation for the puzzling theoretical findings of a quantized superfluid stiffness of superconducting graphene in the Dirac regime. We prove that the contribution of a single Dirac cone to the superfluid stiffness is proportional to its topological charge, and can be controlled in experiments using a Zeeman field. Further, we show that the quantization persists upon effecting strain and is resilient against weak disorder. By employing an adiabatic approach for superfluid responses, we unify the superfluid stiffness and quantum capacitance in Dirac superconductors. Based on this unified picture we predict a topological quantum capacitance for a Josephson junction consisting of a strained graphene hybrid and a conventional superconductor.Comment: 13 pages: 6 pages main text with 2 figures and 7 pages supplemental material with 3 figures. V3 has a modified title and a substantially improved manuscript with a rigorous proof. Part of the contents in V2 now appear in a new manuscript with title "Superfluid Stiffness and Josephson Quantum Capacitance: Adiabatic Approach and Topological Effects", which appears on the same day on arXi

Superfluid Stiffness and Josephson Quantum Capacitance: Adiabatic Approach and Topological Effects

We bring forward a unified framework for the study of the superfluid stiffness and the quantum capacitance of superconducting platforms exhibiting conventional spin-singlet pairing. We focus on systems which in their normal phase contain topological band touching points or crossings, while in their superconducting regime feature a fully gapped energy spectrum. Our unified description relies on viewing these two types of physical quantities as the charge current and density response coefficients obtained for ``slow" spatiotemporal variations of the superconducting phase. Within our adiabatic formalism, the two coefficients are given in terms of Berry curvatures defined in synthetic spaces. Our work lays the foundations for the systematic description of topological diagonal superfluid responses induced by singularities dictating the synthetic Berry curvatures. We exemplify our approach for concrete one- and two-dimensional models of superconducting topological (semi)metals. We discuss topological phenomena which arise in the superfluid stiffness of bulk systems and the quantum capacitance of Josephson junctions. We show that both coefficients become proportional to a topological invariant which counts the number of topological touchings/crossings of the normal phase band structure. These topological effects can be equivalently viewed as manifestations of chiral anomaly. Our predictions are experimentally testable in graphene-superconductor hybrids.Comment: 21 pages, 4 figures, and 4 appendices. This work accompanies preprint arXiv:2211.07676v3 which appears on the same day. Some parts of this work have been transferred from arXiv:2211.07676v

Optimal Design of a Wide Area Measurement System Using Hybrid Wireless Sensors and Phasor Measurement Units

Real-time monitoring of the power system by phasor measurement units (PMUs) leads to the development of such devices in a wide area measurement system (WAMS). However, the power system observability cannot be obtained by employing only PMUs. The communication infrastructure (CI) is a significant part of the WAMS that has to be optimally designed and implemented to collect data from PMUs and deliver them to control centers. In this paper, a novel hybrid wireless sensor network is proposed for the connection of PMUs throughout the system to enable convenient and low-cost communication media. The problem of observability in the communication system is checked along with the optimal placement of PMUs in the power system to reach full observability. A hybrid wireless sensor network including plug-in powered sensor nodes (PPSNs) and energy harvesting sensor nodes (EHSNs) is utilized for increasing the reliability of the communication system. In the proposed co-optimal PMU-sensor placement problem, the main objective is to minimize the total cost of PMU placement and the related communication system, considering full observability of the power system and CI. To achieve better results, the zero-injection bus (ZIB) effect and system observability redundancy index (SORI) are considered as a constraint in the objective function. A binary-coded genetic algorithm is used for solving the proposed mixed-objective optimization problem subject to different technical operating constraints. The proposed method is examined on IEEE 13-bus and IEEE 37-bus test feeder systems. The results show the applicability and effectiveness of the proposed method compared with the conventional methods in this subject area

L’EFFET DE LA RELATION D’AGENCE SUR LA POLITIQUE DE DIVIDENDE : CAS DES ENTREPRISES MAROCAINES COTEES

La théorie de l’agence s’attache à étudier les différentes relations qui existent entre les parties prenantes de l’entreprise : actionnaires, dirigeants et obligataires. Cette théorie a fait ressortir les conflits d’intérêt naissant entre ces trois acteurs tout en mettant en avant leur impact sur les décisions financières de l’entreprise en particulier sur la distribution des dividendes. De nombreuses études ont été menées pour tester la relation entre la distribution des dividendes et les coûts d’agence dans les marchés développés mais les évidences empiriques se font rares sur les marchés émergents. Cet article vise à étudier l’impact de la structure de  propriété et de la performance de l’entreprise sur la politique de dividende dans le cadre du marché marocain. Nous proposons un modèle de régressions multiples sur un échantillon de 133 observations. Sur la base des résultats obtenus, nous avons démontré le rôle positif de la concentration du capital et de la performance de l’entreprise dans la détermination du niveau du dividende distribué. Nous avons démontré également que la distribution des dividendes est négativement corrélée avec la propriété familiale et managériale