Angle-resolved photoemission study of the role of nesting and orbital orderings in the antiferromagnetic phase of BaFe2As2

We present a detailed comparison of the electronic structure of BaFe2As2 in its paramagnetic and antiferromagnetic (AFM) phases, through angle-resolved photoemission studies. Using different experimental geometries, we resolve the full elliptic shape of the electron pockets, including parts of dxy symmetry along its major axis that are usually missing. This allows us to define precisely how the hole and electron pockets are nested and how the different orbitals evolve at the transition. We conclude that the imperfect nesting between hole and electron pockets explains rather well the formation of gaps and residual metallic droplets in the AFM phase, provided the relative parity of the different bands is taken into account. Beyond this nesting picture, we observe shifts and splittings of numerous bands at the transition. We show that the splittings are surface sensitive and probably not a reliable signature of the magnetic order. On the other hand, the shifts indicate a significant redistribution of the orbital occupations at the transition, especially within the dxz/dyz system, which we discuss

Coronavirus and Nutrition: Approach for Boosting Immune System in Morocco

The Covid-19 pandemic is a pandemic of an emerging infectious disease, the 2019 coronavirus disease Covid-19, caused by the SARS-CoV-2 coronavirus. The essential protective measures recommended by WHO (2020) to limit the spread of the Coronavirus (Covid-19) limited in the suppression of travel, quarantine and containment. In the first part of this review, we will examine the origin of the coronavirus, the modes of spread and their adverse effects on human health. We will include in our analysis the nutritional importance of the different approaches based on mechanisms to boost the immune system and therefore good viral defense. The immune system helps protect the host against environmental agents such as pathogenic microorganisms (bacteria, fungi and viruses), thus preserving the integrity of the organism. To preserve the defense mechanisms of the organisms, an adequate nutritional state must be maintained with adequate intakes of calories, vitamins, minerals and water which must be continuously provided by a healthy diet. In addition, it is necessary to have nutritional information that will help boost the immune system of people in the fight against Covid-19, nutritional diagnosis and early nutritional management of affected patients must be integrated into the overall therapeutic strategy. Several clinical data have shown that micronutrients like vitamins, including vitamins A, C, D, E, B12, B6 and folic acid; trace elements like iron, zinc, copper, magnesium, selenium, and omega-3 fatty acids like docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) play a major role in supporting the immune system

Symmetry breaking in commensurate graphene rotational stacking; a comparison of theory and experiment

Graphene stacked in a Bernal configuration (60 degrees relative rotations between sheets) differs electronically from isolated graphene due to the broken symmetry introduced by interlayer bonds forming between only one of the two graphene unit cell atoms. A variety of experiments have shown that non-Bernal rotations restore this broken symmetry; consequently, these stacking varieties have been the subject of intensive theoretical interest. Most theories predict substantial changes in the band structure ranging from the development of a Van Hove singularity and an angle dependent electron localization that causes the Fermi velocity to go to zero as the relative rotation angle between sheets goes to zero. In this work we show by direct measurement that non-Bernal rotations preserve the graphene symmetry with only a small perturbation due to weak effective interlayer coupling. We detect neither a Van Hove singularity nor any significant change in the Fermi velocity. These results suggest significant problems in our current theoretical understanding of the origins of the band structure of this material.Comment: 7 pages, 6 figures, submitted to PR

Significant reduction of electronic correlations upon isovalent Ru substitution of BaFe2As2

We present a detailed investigation of Ba(Fe0.65Ru0.35)2As2 by transport measurements and Angle Resolved photoemission spectroscopy. We observe that Fe and Ru orbitals hybridize to form a coherent electronic structure and that Ru does not induce doping. The number of holes and electrons, deduced from the area of the Fermi Surface pockets, are both about twice larger than in BaFe2As2. The contribution of both carriers to the transport is evidenced by a change of sign of the Hall coefficient with decreasing temperature. Fermi velocities increase significantly with respect to BaFe2As2, suggesting a significant reduction of correlation effects. This may be a key to understand the appearance of superconductivity at the expense of magnetism in undoped iron pnictides

Study of dependence between two types of most abundant natural clays in Bejaad province (Central Morocco) using a statistical approach

This work proposes the studying of characterization analysis of two natural Moroccan clays (RC and GC) in the same location from Bejaad (Province of Khouribga, Morocco) and to know the relationship dependence between them. The values obtained during the determination of a few parameters (density, pH, conductivity, dry matter - moisture content, organic matter-mineral matter) show that the two materials RC and GC studied have the same physical-chemical properties. The all characterization of the two clays was carried out by XRD, XRF, FTIR, SEM/EDX and TGA. The results obtained show that the two materials have very irregular and microporous structures, a heterogeneity of the pore forms and they are contain a mixture of Kaolinite, Illite, Quartz, Calcite, and Dolomite, with the presence of Hematite only in clay RC. On the other hand, The statistical approach applied to determine the dependence relationship between the two clays was based on two tests: Student's t-test (Comparison of two means for physical-chemical parameters) and Pearson's test (contingency table for XRF analysis) in order to prove that the two materials studied are the same chemical and physical-chemical characteristics

Silicon intercalation into the graphene-SiC interface

In this work we use LEEM, XPEEM and XPS to study how the excess Si at the graphene-vacuum interface reorders itself at high temperatures. We show that silicon deposited at room temperature onto multilayer graphene films grown on the SiC(000[`1]) rapidly diffuses to the graphene-SiC interface when heated to temperatures above 1020. In a sequence of depositions, we have been able to intercalate ~ 6 ML of Si into the graphene-SiC interface.Comment: 6 pages, 8 figures, submitted to PR

Design and experimental implementation of voltage control scheme using the coefficient diagram method based PID controller for two-level boost converter with photovoltaic system

Introduction. Currently, in the solar energy systems and a variety of electrical applications, the power converters are essential part. The main challenge for similar systems is controller design. In the literature, the PID controller has proved its effectiveness in many industrial applications, but determining its parameters remains one of the challenges in control theory field. The novelty of the work resides in the design and experimental implementation of a two-level boost DC-DC converter controlled by a PID controller for photovoltaic (PV) maximum power extraction. Purpose. Analysis and control of the two-level boost topology with renewable energy source and design of the PID controller parameters using simple and accurate method. Methods. PID coefficients are optimized using Coefficient Diagram Method (CDM) in the MATLAB environment. Results. A mathematical model of a two-level boost converter with PID controller and PV energy source was developed and analyzed. The model allows to design the controller parameters of the proposed system. Practical value. A prototype steered by the proposed CDM-PID controller was tested using an Arduino embedded board. A comparison between the simulation results and the experimental one is presented. The obtained results illustrate that the experimental results match the simulation closely, and the proposed CDM-PID controller provides a fast and precise results.Вступ. В даний час перетворювачі потужності є невід’ємною частиною сонячних енергетичних систем та різних електричних пристроїв. Основною проблемою для таких систем є проектування контролера. У літературі ПІД-регулятор довів свою ефективність у багатьох промислових застосуваннях, але визначення його параметрів залишається однією з проблем у галузі теорії управління. Новизна роботи полягає у розробці та експериментальній реалізації дворівневого підвищувального перетворювача постійного струму, керованого ПІД-регулятором, для отримання максимальної потужності фотоелектричних пристроїв. Мета. Аналіз та управління дворівневою топологією підвищення з використанням відновлюваного джерела енергії та розрахунок параметрів ПІД-регулятора простим та точним методом. Методи. Коефіцієнти ПІД оптимізуються за допомогою методу діаграми коефіцієнтів (CDM) у середовищі MATLAB. Отримані результати. Розроблено та проаналізовано математичну модель дворівневого підвищувального перетворювача з ПІД-регулятором та фотоелектричним джерелом енергії. Модель дозволяє спроєктувати параметри контролера пропонованої системи. Практична цінність. Прототип, керований пропонованим контролером CDM-PID, протестували з використанням вбудованої плати Arduino. Наведено порівняння результатів моделювання з експериментальними даними. Отримані результати показують, що експериментальні результати близько відповідають моделюванню, а пропонований CDM-ПІД-регулятор забезпечує швидкі та точні результати