Tunneling of Massive Dirac Fermions in Graphene through Time-periodic Potential

The energy spectrum of graphene sheet with a single barrier structure having a time periodic oscillating height and subjected to magnetic field is analyzed. The corresponding transmission is studied as function of the obtained energy and the potential parameters. Quantum interference within the oscillating barrier has an important effect on quasiparticles tunneling. In particular the time-periodic electromagnetic field generates additional sidebands at energies \epsilon + l\hbar \omega (l=0,\pm 1, \cdots) in the transmission probability originating from the photon absorption or emission within the oscillating barrier. Due to numerical difficulties in truncating the resulting coupled channel equations we limited ourselves to low quantum channels, i.e. l=0,\pm 1.Comment: 20 pages, 13 figures, references added. Version to appear in EPJ

Survivorship Pensions in the Middle East and North Africa Region : Current Situation, Costs and Options for Reforms.

The purpose of the survivor's pension is to create rights for young and old age dependants. In the case of developed countries, the system deals essentially with the spouse survival. In the case of MENA countries, the survivor’s pensions scheme provides a wider perspective of coverage and is extended to protect children, brothers, sisters, dependant parents and grand-parents according to specific criteria. Two objectives of survivor's pensions can be distinguished. On the one hand, the survivor's pensions aim at providing a minimum of resources when the widow(er) could not acquire any other sources of income. In this case, the widow survivor's pension is provided to the most modest households in order to help them from plunging in extreme poverty. This context prevails widely in MENA countries, where poverty is high and the level of dependancy is also prominent. On the other hand, a second perspective considers the survivor's pensions as a pension right to the widow (er) with the aim of maintaining her/his former standard of living. Developed countries are particularly concerned by this environment. This paper propose an analysis of the impact of pension reforms, particurlarly, of the survirvorship pensions reforms on the individual situations of retirees. The analysis focuses on Moroccan pension system and will consider a representative sample of members of the main schemes in Morocco.Survivorship Pensions; Reforms; MENA countries; Morocco;

Les cours de soutien scolaire privé : Quels effets sur la dynamique de l’enseignement apprentissage ?

Nécessité ou effet de mode, les cours de soutien scolaire privé ont beaucoup évolué au point d’être entrepris au sein d’instituts bien structurés et au point d’être une activité lucrative. Une activité à « la marge » (Glasman & Besson, 2004) qui n’est plus saisonnière comme à ses débuts, mais quasi permanente, tout au long de l’année scolaire. Elle couvre le spectre de différentes disciplines et s’étend à tous les niveaux du système éducatif. Bien qu’elle soit à « l’ombre », elle demeure un phénomène complexe. L’objectif de cet article est de mettre en évidence les causes qui seraient derrière le recours des apprenants aux cours de soutien scolaire privé. Il vise également à expliciter l’impact sociale de cette pratique ainsi que ses répercussions sur les éléments suivants : le savoir, la dynamique de l’enseignement apprentissage, le rapport apprenant savoir, et le rapport apprenant enseignant. Les guides des entretiens qui sont administrés aux différents acteurs, apprenants, enseignants et acteurs assurant ces cours de soutien scolaire privé), seront également présentés.   &nbsp

Rule-Extraction Methods From Feedforward Neural Networks: A Systematic Literature Review

Motivated by the interpretability question in ML models as a crucial element for the successful deployment of AI systems, this paper focuses on rule extraction as a means for neural networks interpretability. Through a systematic literature review, different approaches for extracting rules from feedforward neural networks, an important block in deep learning models, are identified and explored. The findings reveal a range of methods developed for over two decades, mostly suitable for shallow neural networks, with recent developments to meet deep learning models' challenges. Rules offer a transparent and intuitive means of explaining neural networks, making this study a comprehensive introduction for researchers interested in the field. While the study specifically addresses feedforward networks with supervised learning and crisp rules, future work can extend to other network types, machine learning methods, and fuzzy rule extraction

Intra-daily put call parity in the PHLX currency options market

This study examines the Put-Call Parity efficiency of the PHLX currency options market for the Deutsche Mark for the period between 30 September 1992 to 1 October 1993. Using a large database of currency option data, a sample of 7968 American and European put and call options are tested for the presence of reversal and conversion profit opportunities. Data from two data providers and eleven different exchange rate measures are used. Exchange rates recorded in the PHLX market surveillance tape and originally reported by Telerate are used in conjunction with more frequently observed exchange rate data collected by Olsen & Associates and reported by Reuters. The presence of positive PCP deviations is examined with transactions costs and specifically taking into account simultaneity of the data. Censored regressions are used to determine the causes of these positive PCP deviations. The results from all exchange rate measures indicate that less than 3.571% of the sample result in profitable opportunities. This is true for all strategies except for the European conversion. Upon further examination, this result is shown to be sample specific. A degree of intra-daily and intra-weekly seasonality was found in the number of positive deviations from Put-Call Parity. This is explained by thin markets and high spreads. The conclusion is drawn that the prices of PHLX Deutsche Mark currency options for this period are consistent with Put-Call Parity Theorem

Transmission in graphene through tilted barrier in laser field

We study the transmission of Dirac fermions in graphene through a tilted barrier potential in the presence of a laser field of frequency $\omega$. By using Floquet theory, we solve the Dirac equation and then obtain the energy spectrum. The boundary conditions together with the transfer matrix method allow us to determine the transmission probabilities corresponding to all energy bands $E+l\hbar\omega$ $(l=0,\pm1, \cdots)$. By limiting to the central band $l=0$ and the two first side bands $l=\pm 1$, we show that the transmissions are strongly affected by the laser field and barrier. Indeed, it is found that the Klein effect is still present, a variety of oscillations are inside the barrier, and there is essentially no transmission across all bands.Comment: 10 pages, 6 figures. Clarifications and references added. Version to appear in Ann. Phys. (Berlin

Transmission in graphene through a double laser barrier

In this work, we will study the transmission probability of Dirac fermions through a double laser barrier. As part of the Floquet approximation, we will determine the spinors in the five regions. Due to the continuity of the wave function at the barrier edges, we find eight equations, each with infinity modes. To simplify, we use the matrix formalism and limit our study to the first three bands, the central band, and the first two side bands. From the continuity equation and the spinors in the five regions, we will determine the current density in each region, which makes it possible to determine the expression of the transmission probability corresponding to each energy band. The time-dependent laser fields generate several transmission modes, which give two transmission processes: transmission with zero photon exchange corresponds to the central band $\varepsilon$, and transmission with emission or absorption of photons corresponds to the first two sidebands $\varepsilon\pm\varpi$. One of the two modes can be suppressed by varying the distance between the two barriers or the barrier width. The transmission is not permitted if the incoming energy is below an energy threshold $\varepsilon>k_y+2\varpi$. Increasing the intensity of the laser fields makes it possible to modify the sharpness and amplitude of the transmission.Comment: 11 pages, 6 figure

A microeconometric analysis of households saving determinants in Morocco.

Economic fluctuations, climate risk and a number of individual specific shocks leave households vulnerable to severe hardship in developing countries. Moreover, the credit and insurance markets are limited and the social coverage is weak. In this context, households saving is crucial to provide an insurance against the economic and social shocks. Additionally, a better knowledge of households saving behaviour could develop the potential to finance investments. This article provides an analysis of microeconomic factors which explain the household savings behaviour in Morocco by using a new survey. Household saving functions are estimated in order to test households' responses to income, monetary or non-monetary wealth and socio-demographic variables in urban and rural areas. Our results confirm that current income strongly affects the saving level whatever the home place. Surprisingly, the household’s size is significant only in the urban case : an additional person reduces the household saving. For the life cycle hypothesis, the results are not significant. Finally, we find that Moroccan women save more than men when we take into account the interaction between gender and income. Nevertheless, for highest income levels, we observe the opposite results. In the case of rural households, there is no statistically significant effect on saving behaviour from the ownership indicators of household’s lands or other real estate. The results suggest that the self financing of rural household activities may be due to the lack of access to formal financial intermediaries.Saving; Morocco; individual data; microeconometrics;

Transmission in Graphene through Time-oscillating Linear Barrier

Transmission probabilities of Dirac fermions in graphene under linear barrier potential oscillating in time are investigated. Solving Dirac equation we end up with the solutions of the energy spectrum depending on several modes coming from the oscillations. These will be used to obtain a transfer matrix that allows to determine transmission amplitudes of all modes. Due to numerical difficulties in truncating the resulting coupled channel equations, we limit ourselves to low quantum channels, i.e. $l = 0, \pm1$, and study the three corresponding transmission probabilities.Comment: 14 pages, 6 figures, clarifications added, misprints corrected. Version to appear in EPJB (2019