Conception et optimisation d’un synthétiseur de fréquence pour les communications mobiles sur GSM

Cet article décrit la simulation et la conception d'un synthétiseur de fréquence destiné pour les applications des communications mobiles sur GSM. Dans ce travail, nous discutons les effets du bruit de phase dans chaque composant dans le circuit et les raies de référence sur les performances du système. Une évaluation précise du filtre de boucle est nécessaire afin d’optimiser les performances du circuit en trouvant un compromis entre le temps du changement de la fréquence (PLL lockup time) et les raies de référence.Mots-clés : PLL, GSM, synthétiseur de fréquence, bruit de phase

Simulating and Designing RF Transmitter for Small Satellites

This paper discusses the simulation and the design of an RF transmitter for small satellites operating in the commercial S- band (2.2 - 2.29 GHz) with a data rate of 8Mbps. In such systems, modelling frequency-dependent nonlinear characteristics of complex analog blocks and subsystems is critical for enabling efficient verification of mixed-signal system designs. In order to provide efficient and accurate simulation for the transmitter circuits, simple macromodels for weakly nonlinear mixer and power amplifier are used in the system simulation. Also, we introduce the noise in several circuits (frequency synthesizer, crystal oscillator, power amplifier, mixer,…) and we demonstrate their effect on the noise performance system. In the simulation we consider features of components and technologies commercially available

Removal of Tannic Acid From Aqueous Solution by Cloud Point Extraction and Investigation of Surfactant Regeneration by Microemulsion Extraction

The aim of this work is the extraction of tannic acid (TA) with two commercial nonionic surfactants, separately: Lutensol ON 30 and Triton X-114 (TX-114).The experimental cloud point extraction results are expressed by four responses to surfactant concentration and temperature variations: extent of TA extraction (E), remaining solute (X s,w) and surfactant (X t,w) concentrations in dilute phase and volume fraction of coacervate (Φc) at equilibrium. An empirical smoothing method was used and the results are represented on three dimensional plots. In optimal conditions, the extraction extent of TA reaches 95 and 87 % using TX-114 and Lutensol ON 30, respectively. Sodium sulfate, cetyltrimethylammonium bromide (CTAB) addition and pH effect are also studied. Finally, the possibility of recycling of the surfactant is proved

Electrochemical and spectroscopic characterisations of cation exchange membrane equilibrated in acid and salt solutions: application as separator in microbial fuel cell

<div><p>The polymer cation exchange membrane (Nafion117) was equilibrated garden soil leachate. It was then characterised using the stationary voltamperometry method and the mass transfer electrochemical Hittorf-based method. The results obtained with these two techniques were compared to those obtained with the membrane conditioned only with conventional acid and/or salt electrolytes solutions. These two conditions highlighted the good proton conduction of the membrane, against metal ions. This finding was supported and complemented by impedance spectroscopic studies at both transient and stationary regimes. The parameters studied were electrical impedance and specific conductivity. It was found that at higher frequencies, the conductivity of the membrane conditioned with protons was five times higher than that stored in distilled water. As an application, the membrane was tested successfully in a garden soil microbial fuel cell under study, thereby evidencing its good proton conduction. Nafion exhibits, therefore, a high protonic conductivity when hydrated, because protons can be transported via Grotthus and hopping mechanisms via its functional sites.</p></div

Розробка наночастинок фериту цинку міді: застосування в каталітичному вологому окисленні H2O2 фенолу

Ця робота стосується синтезу і характеристики змішаних оксидів металів та їх застосування як каталізаторів. Синтезований твердий розчин фериту Fe2Zn1 – xCuxO4. Чистота зразків була підтверджена рентгенівською дифракцією (XRD). Характеристики зразків отримували за допомогою інфрачервоної спектроскопії з використанням перетворення Фур'є (FTIR) та скануючої електронної мікроскопії (SEM). Уточнення параметрів решітки твердого розчину було розроблено з індексації основної сполуки NiFe2O4 у кубічній елементарній комірці просторової групи Fd3m. Тенденція ліній дифракції показує, що структура була добре кристалізована, і справді утворився повноцінний твердий розчин кубічної симетрії. Мікрофотографія SEM виявляє, що зразки представлені у вигляді кристалітів нанометрового розміру; зразки представлені у вигляді фрагментів різної величини в суміші Cu-Zn. Результати показують нанометровий розмір зерен, що змінюється між 90 і 130 нм. Ці нещодавно розроблені матеріали застосовуються як каталізатори для неоднорідної реакції окислення фенольних сполук; предмет дослідження за наявності перекису водню. Продукти деструкції аналізували високоефективною рідинною хроматографією. Отримані результати показали потужний каталітичний характер цих оксидів до повного розкладання фенолу.This work deals with the synthesis, characterization of mixed oxides of metals and their applications as catalysts. The synthesized ferrite solid solution of formula Fe2Zn1 – xCuxO4 has been prepared from ground frost. The purity of the samples has been verified by X-Ray Diffraction (XRD). The characterizations of samples have been carried out using Fourier Transform InfraRed Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM). Refinement of lattice parameters of the solid solution has been elaborated from the basic compound NiFe2O4 indexing in a cubic unit cell of space group Fd3m. The trend of the diffraction lines shows that the structure was well crystallized, and there indeed a complete solid solution of cubic symmetry was formed. The SEM micrograph reveals that the samples are presented in the form of nanometer sized crystallites; the samples are in the form of fragments of different sizes in the Cu-Zn mixture. The results show the nanometric size of the grains varying between 90 and 130 nm. These newly elaborated materials have been applied as catalysts for heterogeneous reaction of oxidation of phenolic compounds; subject of investigations in the presence of hydrogen peroxide. The degradation products were analyzed by High Performance Liquid Phase Chromatography (HPLC). The obtained results showed powerful catalytic character of these oxides to completely degrade phenol

Electro-remediation of lead contaminated kaolinite: An electro-kinetic treatment

International audienceElectroextraction is an innovating separation process which removes in situ heavy metal contained in soil, under the application of an electric field. The paper reports the remediation of kaolinite contaminated with lead by electro-kinetic treatment using a three compartment cell. As a consequence of intensive water dissociation, the high concentration of hydroxyl ions led to precipitation of lead from the soil and formed non-conducting species such as Pb(OH)(2). The two chelating agents Citric acid and EDTA are used as anode reservoir to produce protons which exchanged lead cation. Meanwhile, they were also used as cathode reservoir to neutralize hydroxyl anionsgenerated at the electrode, to avoid the formation of the solid species. After seven days, EDTA allowed complete lead removal twice than citric acid, with low energy consumption. The ion migration and the concentration gradient were described by Nernst Planck equations. In contrast to long period experiments, the ion migration inside the soil progressed from cathode toward anode for short periods. This finding was well supported by pH values. (C) 2015 Elsevier B.V. All rights reserved

Study of Fouling of a Cation Exchange Membrane with a Surfactant Using Voltamperometry

International audienc