On the period function of Newtonian systems

We study the existence of centers of planar autonomous system of the form $$(S) \quad \dot x=y,\qquad \dot y = -h(x) - g(x)y - f(x)y^2.$$ We are interested in the period function $T$ around a center 0. A sufficient condition for the isochronicity of (S) at 0 is given. Such a condition is also necessary when $f,g,h$ are analytic functions. In that case a characterization of isochronous centers of system (S) is given. Some applications will be derived. In particular, new families of isochronous centers will be describedComment: 16 page

Subharmonic solutions for nonautonomous sublinear first order Hamiltonian systems

In this paper, the existence of subharmonic solutions for a class of non-autonomous first-order Hamiltonian systems is investigated. We also study the minimality of periods for such solutions. Our results which extend and improve many previous results will be illustrated by specific examples. Our main tools are the minimax methods in critical point theory and the least action principle. {\bf Key words.} Hamiltonian systems. Critical point theory. Least action principle. Subharmonic solutions.Comment: 17 page

Modeling Ultrasonically Assisted Convective Drying of Eggplan

[EN] Modeling constitutes a fundamental tool with which to analyze the influence of ultrasound on mass transfer phenomena during drying. In this work, the study of the effect of power ultrasound application on the drying kinetics of eggplant was addressed by using different models based on theoretical (diffusion) or empirical approaches. Drying kinetics of eggplant cylinders (height 20mm and diameter 24 mm) were carried at 40°C and 1 m/s applying different ultrasonic powers: 0, 6, 12, 19, 25, 31, and 37 kW/m 3. The experiments were carried out at least three times at each different ultrasonic power. Shrinkage and sorption isotherms were also addressed in order to attain an optimal description of eggplant drying. Applying ultrasound sped up the drying kinetics. The ultrasonic power was identified as having a significant (p<0.05) influence on both the effective moisture diffusivity and the mass transfer coefficient, which was well explained by linear relationships. The most complex model, which considered both external resistance and shrinkage to be significant phenomena, provided the best agreement with experimental data, giving percentages of explained variance of over 99.9% and mean relative errors of under 1.2% in every case. According to these results, ultrasound technology could have the potential to improve the convective drying of eggplant at an industrial scale. © 2011 Taylor & Francis Group, LLC.García Pérez, JV.; Ozuna López, C.; Ortuño Cases, C.; Carcel Carrión, JA.; Mulet Pons, A. (2011). Modeling Ultrasonically Assisted Convective Drying of Eggplan. Drying Technology. 29(13):1499-1509. doi:10.1080/07373937.2011.576321S149915092913Mujumdar, A. S. (2006). An overview of innovation in industrial drying: current status and R&D needs. Transport in Porous Media, 66(1-2), 3-18. doi:10.1007/s11242-006-9018-yChou, S. K., & Chua, K. J. (2001). New hybrid drying technologies for heat sensitive foodstuffs. Trends in Food Science & Technology, 12(10), 359-369. doi:10.1016/s0924-2244(01)00102-9Lewicki, P. P. (2006). Design of hot air drying for better foods. Trends in Food Science & Technology, 17(4), 153-163. doi:10.1016/j.tifs.2005.10.012Santos, P. H. S., & Silva, M. A. (2009). Kinetics ofL-Ascorbic Acid Degradation in Pineapple Drying under Ethanolic Atmosphere. Drying Technology, 27(9), 947-954. doi:10.1080/07373930902901950Suvarnakuta, P., Devahastin, S., & Mujumdar, A. S. (2005). Drying Kinetics and β-Carotene Degradation in Carrot Undergoing Different Drying Processes. Journal of Food Science, 70(8), s520-s526. doi:10.1111/j.1365-2621.2005.tb11528.xMayor, L., & Sereno, A. M. (2004). Modelling shrinkage during convective drying of food materials: a review. Journal of Food Engineering, 61(3), 373-386. doi:10.1016/s0260-8774(03)00144-4Gallego-Juarez, J. A. (2010). High-power ultrasonic processing: Recent developments and prospective advances. Physics Procedia, 3(1), 35-47. doi:10.1016/j.phpro.2010.01.006De la Fuente-Blanco, S., Riera-Franco de Sarabia, E., Acosta-Aparicio, V. M., Blanco-Blanco, A., & Gallego-Juárez, J. A. (2006). Food drying process by power ultrasound. Ultrasonics, 44, e523-e527. doi:10.1016/j.ultras.2006.05.181García-Pérez, J. V., Cárcel, J. A., Riera, E., & Mulet, A. (2009). Influence of the Applied Acoustic Energy on the Drying of Carrots and Lemon Peel. Drying Technology, 27(2), 281-287. doi:10.1080/07373930802606428García-Pérez, J. V., Cárcel, J. A., Clemente, G., & Mulet, A. (2008). Water sorption isotherms for lemon peel at different temperatures and isosteric heats. LWT - Food Science and Technology, 41(1), 18-25. doi:10.1016/j.lwt.2007.02.010Mulet, A. (1994). Drying modelling and water diffusivity in carrots and potatoes. Journal of Food Engineering, 22(1-4), 329-348. doi:10.1016/0260-8774(94)90038-8Cunha, L. M., Oliveira, F. A. R., & Oliveira, J. C. (1998). Optimal experimental design for estimating the kinetic parameters of processes described by the Weibull probability distribution function. Journal of Food Engineering, 37(2), 175-191. doi:10.1016/s0260-8774(98)00085-5Azzouz, S., Guizani, A., Jomaa, W., & Belghith, A. (2002). Moisture diffusivity and drying kinetic equation of convective drying of grapes. Journal of Food Engineering, 55(4), 323-330. doi:10.1016/s0260-8774(02)00109-7Simal, S., Femenia, A., Garau, M. C., & Rosselló, C. (2005). Use of exponential, Page’s and diffusional models to simulate the drying kinetics of kiwi fruit. Journal of Food Engineering, 66(3), 323-328. doi:10.1016/j.jfoodeng.2004.03.025Maroulis, Z. B., Saravacos, G. D., Panagiotou, N. M., & Krokida, M. K. (2001). MOISTURE DIFFUSIVITY DATA COMPILATION FOR FOODSTUFFS: EFFECT OF MATERIAL MOISTURE CONTENT AND TEMPERATURE. International Journal of Food Properties, 4(2), 225-237. doi:10.1081/jfp-100105189Simal, S., Femenia, A., Garcia-Pascual, P., & Rosselló, C. (2003). Simulation of the drying curves of a meat-based product: effect of the external resistance to mass transfer. Journal of Food Engineering, 58(2), 193-199. doi:10.1016/s0260-8774(02)00369-2Queiroz, M. R., & Nebra, S. A. (2001). Theoretical and experimental analysis of the drying kinetics of bananas. Journal of Food Engineering, 47(2), 127-132. doi:10.1016/s0260-8774(00)00108-4Hassini, L., Azzouz, S., Peczalski, R., & Belghith, A. (2007). Estimation of potato moisture diffusivity from convective drying kinetics with correction for shrinkage. Journal of Food Engineering, 79(1), 47-56. doi:10.1016/j.jfoodeng.2006.01.025Hernández, J. A., Pavón, G., & Garcı́a, M. A. (2000). Analytical solution of mass transfer equation considering shrinkage for modeling food-drying kinetics. Journal of Food Engineering, 45(1), 1-10. doi:10.1016/s0260-8774(00)00033-9Souma, S., Tagawa, A., & Iimoto, M. (2004). Structural Properties for Fruits and Vegetables during Drying. NIPPON SHOKUHIN KAGAKU KOGAKU KAISHI, 51(11), 577-584. doi:10.3136/nskkk.51.577García-Pérez, J. V., Cárcel, J. A., de la Fuente-Blanco, S., & Riera-Franco de Sarabia, E. (2006). Ultrasonic drying of foodstuff in a fluidized bed: Parametric study. Ultrasonics, 44, e539-e543. doi:10.1016/j.ultras.2006.06.059Cárcel, J. A., García-Pérez, J. V., Riera, E., & Mulet, A. (2007). Influence of High-Intensity Ultrasound on Drying Kinetics of Persimmon. Drying Technology, 25(1), 185-193. doi:10.1080/07373930601161070Blasco, M., García-Pérez, J. V., Bon, J., Carreres, J. E., & Mulet, A. (2006). Effect of Blanching and Air Flow Rate on Turmeric Drying. Food Science and Technology International, 12(4), 315-323. doi:10.1177/1082013206067352Garau, M. C., Simal, S., Femenia, A., & Rosselló, C. (2006). Drying of orange skin: drying kinetics modelling and functional properties. Journal of Food Engineering, 75(2), 288-295. doi:10.1016/j.jfoodeng.2005.04.017Wu, L., Orikasa, T., Ogawa, Y., & Tagawa, A. (2007). Vacuum drying characteristics of eggplants. Journal of Food Engineering, 83(3), 422-429. doi:10.1016/j.jfoodeng.2007.03.030Chaves , M. ; Sgroppo , S.C. ; Avanza , J.R. Cinéticas de secado de berenjena (Solanum melongenaL.). Comunicaciones Científicas y Tecnológicas (Universidad Nacional del Nordeste Corrientes Argentina),2003,Resumen E-060 .Akpinar, E. K., & Bicer, Y. (2005). Modelling of the drying of eggplants in thin-layers. International Journal of Food Science and Technology, 40(3), 273-281. doi:10.1111/j.1365-2621.2004.00886.xDe Lima, A. (2002). Simultaneous moisture transport and shrinkage during drying of solids with ellipsoidal configuration. Chemical Engineering Journal, 86(1-2), 85-93. doi:10.1016/s1385-8947(01)00276-5RAHMAN, N., & KUMAR, S. (2007). INFLUENCE OF SAMPLE SIZE AND SHAPE ON TRANSPORT PARAMETERS DURING DRYING OF SHRINKING BODIES. Journal of Food Process Engineering, 30(2), 186-203. doi:10.1111/j.1745-4530.2007.00104.

Structural, Optical, and Renewable Energy-Assisted Photocatalytic Dye Degradation Studies of ZnO, CuZnO, and CoZnO Nanostructures for Wastewater Treatment

Renewable energy can be harnessed from wastewater, whether from municipalities or industries, but this potential is often ignored. The world generates over 900 km3 of wastewater annually, which is typically treated through energy-consuming processes, despite its potential for energy production. Environmental pollution is a most important and serious issue for all and their adulterations to the aquatic system are very toxic in very low concentrations. Photocatalysis is a prominent approach to eliminating risky elements from the environment. The present study developed Zinc oxide (ZnO), Copper-doped Zinc oxide (CuZnO), and Cobalt-doped Zinc oxide (CoZnO) nanostructures (NSs) by facile hydrothermal route. The crystalline and structural stability of the synthesized nanostructures were evident from XRD and FESEM analysis. Metal, and oxygen bond and their interaction on the surfaces and their valency were explored from XPS spectra. Optical orientations and electron movements were revealed from UV-Visible analysis. After 100 min exposure time with 1 g of catalyst concentration 60%, 70%, and 89% of dye degraded, for dye concentration (5 mg/L to 50 mg/L), the huge variation observed (70% to 22%), (80% to 16%), (94% to 10%). The highest photodegradation rate (55%, 75%, 90%) was observed on pH~12 using ZnO, CoZnO, and CuZnO respectively. Photodegradation of methylene blue confirmed the largest surface area, rate of recombination, photo-excited charge carriers, photo-sensitivity range, and radical generations of ZnO, CuZnO, and CoZnO. The present study, therefore, suggested that CuZnO would be preferred to produce nanomaterials for industrial wastewater treatment like methylene

Anodic Aluminum Oxide Membrane-Assisted Fabrication of β-In2S3Nanowires

In this study, β-In2S3nanowires were first synthesized by sulfurizing the pure Indium (In) nanowires in an AAO membrane. As FE-SEM results, β-In2S3nanowires are highly ordered, arranged tightly corresponding to the high porosity of the AAO membrane used. The diameter of the β-In2S3nanowires is about 60 nm with the length of about 6–8 μm. Moreover, the aspect ratio of β-In2S3nanowires is up to 117. An EDS analysis revealed the β-In2S3nanowires with an atomic ratio of nearly S/In = 1.5. X-ray diffraction and corresponding selected area electron diffraction patterns demonstrated that the β-In2S3nanowire is tetragonal polycrystalline. The direct band gap energy (Eg) is 2.40 eV from the optical measurement, and it is reasonable with literature

Periodic solutions of a non coercive hamiltonian system

In this paper,we study the existence of periodic solutions of hamiltonian systems: $$\dot x = J H'(t, x)$$ where the hamiltonian $H$ is non coercive of the type $$H(t, r, p) = f(\vert p - Ar\vert) + h(t) \cdot (r, p) .$

Intensive study of coating multilayer TiO2 nanoparticles thin films used for optoelectronics devices

High-performance of TiO2 nanoparticles (NPs) thin films were synthesized using spin coating technique deposited on a glass substrate. The effect of the several layers of films which have formed is studied on the structure, morphology, surface, optical and electrical characteristics. From the analysis using X-ray diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), raman spectroscopy, ultraviolet–visible spectrophotometer and impedance spectroscopy the obtained results show that anatase crystalline is obtained after annealing at 400 °C from TiO2 (NPs) in powder form. The surface of samples is uniform and the rms roughness is dependent on the number of layers and varied within the range 25.40–43.81 nm. The optical bandgap energy is obtained in the 2.9–3.2 eV range of multilayer TiO2 (NPs) thin films. The electrical characteristic analyzed as a function of temperature and frequency demonstrated a semiconducting behavior, and showed a decreased of resistance with the increase of temperature. The obtained activation energy based on impedance analysis is about 0.7 eV. It is showed that TiO2 deposited on the SnO2 glass substrate has anatase crystalline structure and their optical bandgap energy is about 3.0 eV. Electrical analysis shows semiconductor behavior over the explored temperature range from 400 °C

Synthesis and characterization of In

In2S3 thin films containing different quantities of sodium have been synthesized by co-evaporation of sodium and In2S3 powder from separate sources using vacuum thermal evaporation method. Films were deposited on ordinary glass at 240 °C. The process of incorporation of sodium was studied as function of at.% Na. Films have been characterised by means of X-ray diffraction, SEM, EDAX and spectrophotometry. X-ray diffraction analysis confirmed the initial amorphous nature of deposited layers and revealed the formation of In2S3 as function of annealing layers containing sodium in nitrogen at 300 °C for 2 h. Energy Dispersive X-ray Analysis (EDAX) revealed the composition of the films as a function of the sodium incorporation. Surface Electron Microscopy showed that these films were granular and homogenous. The films have an n-type electrical conductivity and their optical direct band gap can be managed between 2.20 and 2.45 eV by controlling their sodium content. The variation of parameters for as-deposited and annealed films has been studied within $x\le 4$ at.% solid solution composition. Thin layers with homogeneous surfaces, direct band gap energy $(E_g)$ of about 2.45 eV for 4 at.% Na and 0.9 μm-thick have been achieved

Sn Doped In2S3 Films Elaborated by Spray Technique

Tin doped In2S3 films were grown by the chemical spray pyrolysis (CSP) method using the pneumatic spray set-up and compressed air as a carrier gas. The spraying solution contained indium chloride (InCl3), thiourea [CS(NH2)2] and (SnCl4) at a molar ratio of S/In = 2.5. The deposition was carried out at 350 °C on glass substrates. The Sn doping level was changed with Sn/In = 0-8 % in solution. The effect of Sn concentration on electrical, optical and structural properties of In2S3:Sn thin films have been investigated