Wednesday, August 20, 2014

 

 



Soy un nuevo usuario

Olvidé mi contraseña

Entrada usuarios

Lógica Matemáticas Astronomía y Astrofísica Física Química Ciencias de la Vida
Ciencias de la Tierra y Espacio Ciencias Agrarias Ciencias Médicas Ciencias Tecnológicas Antropología Demografía
Ciencias Económicas Geografía Historia Ciencias Jurídicas y Derecho Lingüística Pedagogía
Ciencia Política Psicología Artes y Letras Sociología Ética Filosofía
 

rss_1.0 Clasificación por Disciplina

Nomenclatura Unesco > (22) Física > (2213) Termodinámica
(2213.01) Cambios de estado (2213.02) Física de la transmisión del calor
(2213.03) Altas presiones (2213.04) Altas temperaturas
(2213.05) Teoría cinética (2213.06) Bajas temperaturas
(2213.07) Cambio de fase (2213.08) Técnicas de medida del calor
(2213.09) Equilibrios termodinámicos (2213.10) Relaciones termodinámicas
(2213.11) Fenómenos de transporte (2213.99) Otras (especificar)

Mostrando recursos 1 - 20 de 2,262

1. Método dos modelos termodinâmicos simplificados (MMTS) : uma abordagem eficiente para descrever o equilíbrio líquido-vapor - Paranhos, Juliana Feldens
O estudo e a compreensão da termodinâmica é extremamente importante para todos os processos que envolvam equilíbrio de fases. A determinação das propriedades termodinâmicas de uma mistura pode ser obtida por diferentes formas de cálculo, que podem consumir um grande tempo computacional e apresentar difícil solução. Para casos que envolvam controle e simulações online, otimizações em tempo real e até simuladores de treinamento de operadores (OTS) isso pode ser um fator decisivo no emprego da aplicação. Esta dissertação propõe uma nova formulação denominada de Método dos Modelos Termodinâmico Simplificado (MTS) em lugar da utilização dos modelos termodinâmicos locais (MTL), os...

2. Thermodynamics of stress-induced ferroelastic transitions: Influence of anisotropy and disorder - Lloveras Muntané, Pol Marcel; Castán, Teresa; Porta, Marcel; Planes, Antoni; Saxena, Avadh
Stress-induced stress-strain constitutive behavior has been studied in detail in ferroelastic martensites. It has been found that the weights of the long-range anisotropic interactions and of the disorder are important to determine the fine structure of the stress-strain curves. As experiments show, a wide variety of behaviors has been observed. A decrease of anisotropy and/or increase in the disorder results in changes in the temperature range where pseudoplastic and superelastic regimes are observed. Also, a smoothing of the stress-induced ferroelastic transition, accompanied with a decrease in the transition stress and the hysteresis area, is found. However, Clausius-Clapeyron slope has been observed not to depend on the...

3. Bose e Einstein : do nascimento da estatística quântica à condensação sem interação I - Dahmen, Silvio Renato
Em 1924, motivado por um trabalho de S. Bose sobre a radia,c˜ao do corpo negro, A. Einstein escreveu uma série de três artigos acerca das propriedades termodinâmicas de um gás ideal quântico. No segundo destes artigos, publicado em janeiro de 1925, ele previu o fenômeno da “condensação” dos átomos não interagentes no estado fundamental a partir de uma certa densidade crítica do gás, fenômeno este que veio a ser posteriormente conhecido como Condensação de Bose-Einstein (CBE). Neste primeiro artigo discuto detalhadamente o trabalho de Bose e as implicações do método por ele desenvolvido sobre o trabalho de Einstein. Em um...

4. Estudio estructural de proteínas implicadas en el metabolismo del genoma mitocondrial: Helicasa y Factor de Transcripción A Mitocondrial, TFAM - Fernández Millán, Pablo
La mitocondria es un orgánulo de las células eucariotas en el cual se desarrollan multitud de procesos esenciales para la célula de los cuales se destacan la cadena de transporte de electrones, la síntesis de ATP, el ciclo de Krebs, regulación de la osmosis del calcio, apoptosis, etc. La mitocondria posee su propio genoma (mtADN) y su conservación es esencial para la viabilidad de la mitocondria y por tanto de la célula. El mtADN se transcribe y replica de modo independiente a la división celular y posee su propia maquinaria de replicación y transcripción. En este trabajo se expone el...

5. Preparation and characterization of PVDF-HFP copolymer hollow fiber membranes for membrane distillation - Khayet Souhaimi, Mohamed; García Payo, María del Carmen; Essalhi, M.
Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were prepared by the dry/wet spinning technique at different copolymer concentrations from 17 to 24 wt%. All the spinning parameters were kept constant except the copolymer concentration. The temperature of both the internal and external coagulants was maintained at 40 degrees C. The effects of the copolymer concentration on the morphological properties of the hollow fibers were studied in terms of external and internal diameter and scanning electron microscopy (SEM). It was found that the thickness of all tested hollow fibers did not change significantly. An evolution of the cross-section structure with the increase...

6. Novel porous composite hydrophobic/hydrophilic polysulfone membranes for desalination by direct contact membrane distillation - Khayet Souhaimi, Mohamed; Qtaishat, M.; Matsuura, T.
Novel composite membrane distillation membranes were prepared by blending the hydrophilic polysulfone with hydrophobic surface modifying macromolecules (SMMs). Three different types of SMMs were tested. These SMMs were synthesized and characterized for fluorine content, molecular weights and glass transition temperature. Phase inversion method in a single casting step was used to prepare the composite membranes. The membranes were characterized by means of different techniques such as contact angle measurement, gas permeation test, liquid entry pressure of water and scanning electron microscopy. Finally, these membranes were tested for desalination by direct contact membrane distillation (DCMD). Different membrane preparation conditions affecting membrane...

7. Effect of surface modifying macromolecules stoichiometric ratio on composite hydrophobic/hydrophilic membranes characteristics and performance in direct contact membrane distillation - Khayet Souhaimi, Mohamed; Qtaishat, M.; Rana, D.; Matsuura, T.
The stoichiometric ratio for the synthesis components of hydrophobic new surface modifying macromolecules (nSMM) was altered systematically to produce three different types of nSMMs, which are called hereafter nSMM1, nSMM2, and nSMM3. The newly synthesized SMMs were characterized for fluorine content, average molecular weight, and glass transition temperature. The results showed that fluorine content decreased with increasing the ratio of alpha,omega-aminopropyl poly(dimethyl siloxane) to 4,4'-methylene bis(phenyl isocyanate). The synthesized nSMMs were blended into hydrophilic polyetherimide (PEI) host polymer to form porous hydrophobic/hydrophilic composite membranes by the phase inversion method. The prepared membranes were characterized by the contact angle measurement, X-ray...

8. Effects of PVDF-HFP concentration on membrane distillation performance and structural morphology of hollow fiber membranes - Khayet Souhaimi, Mohamed; García Payo, María del Carmen; Essalhi, M.
Poly(vinylidene fluoride-hexafluoropropylene), PVDF-HFP, hollow fiber membranes were prepared by the dry/wet spinning technique using different copolymer concentrations in the dope solutions ranging from 17 to 24 wt.%. All the spinning parameters were maintained constant except the copolymer concentration. The morphological properties of the hollow fiber membranes were studied in terms of scanning electron microscopy (SEM), atomic force microscopy (AFM) and void volume fraction. The effects of PVDF-HFP content in the spinning solutions were also studied by measuring the water entry pressure and direct contact membrane distillation (DCMD) permeate flux of the hollow fiber membranes. An increase in the copolymer concentration...

9. Response surface modeling and optimization of composite nanofiltration modified membranes - Khayet Souhaimi, Mohamed; Abu Seman, M. N.; Hilal, N.
The experimental design and response surface methodology (RSM) have been used to develop predictive models for simulation and optimization of nanofiltration modified membranes by UV-initiated graft polymerization technique. The objective is to prepare optimum membrane with high nanofiltration performance and low fouling. The factors considered for experimental design were the UV-irradiation time, UV-intensity and the concentration of the monomer N-vinyl-2-pyrrolidone (NVP) in aqueous grafting solution. The dip method has been followed for membrane grafting employing 365 nm wavelength UV-lamp. The significant factors were optimized using a central composite design of orthogonal type. The nanofiltration membrane performance has been studied using...

10. Self-sustained webs of polyvinylidene fluoride electrospun nanofibers at different electrospinning times: 1. Desalination by direct contact membrane distillation - Khayet Souhaimi, Mohamed; Essalhi, M.
Self-sustained electrospun nanofibrous membranes (ENMs) were prepared using the polymer polyvinylidene fluoride (PVDF) and applied for desalination by direct contact membrane distillation (DCMD). Different electrospinning times were considered to prepare the PVDF ENMs of different thicknesses ranging from 144.4 to 1529.3 mu m. A systematic experimental study on the effects of membrane thickness on the DCMD performance is carried out for the first time. The surface and cross-section of the ENMs were studied by scanning electron microscopy and the mean size of the fibers together with its distribution was determined. The water contact angle, the inter-fiber space, the void volume...

11. Evaluación del empleo de biocombustibles en motores de encedido por comprensión - Lópz Díaz, Iosvani
La presente tesis doctoral es el resultado del trabajo conjunto realizado en el Área de Máquinas y Motores Térmicos, perteneciente al departamento de Química Física y Termodinámica Aplicada de la Universidad de Córdoba (España) y en el Centro de Estudios Energéticos y Tecnologías Ambientales de la Universidad Central “Marta Abreu ” de Las Villas (Cuba), orientado a la obtención de biodiésel (procedente de materias prima de interés para las instituciones implicadas) y su posterior evaluación en el motor de biodiésel. Esta tesis constituye un modesto aporte a la solución de la problemática ambiental que hoy presenta la humanidad como resultado de la limitación de reservas petrolíferas y su...

12. Nanofiltration thin-film composite polyester polyethersulfone-based membranes prepared by interfacial polymerization - Khayet Souhaimi, Mohamed; Abu Seman, M. N.; Hilal, N.
Nanofiltration polyester thin-film composite membranes have been prepared by interfacial polymerization using commercial polyethersulfone membrane support. Different monomer bisphenol A (BPA) concentrations in the aqueous solution and various interfacial polymerization times in the organic solution containing trimesoyl chloride (TMC) were studied. The success of the conducted interfacial polymerization procedure was corroborated by FTIR-ATR. Irreversible fouling of both the unmodified polyethersulfone and the modified polyester thin-film composite polyethersulfone membranes have been studied using humic acid model solutions at different pH values. It was observed that polyester thin-film composite membranes exhibited practically no tendency to be irreversibly fouled by humic acid molecules...

13. Monte Carlo simulation and experimental heat and mass transfer in direct contact membrane distillation - Khayet Souhaimi, Mohamed; Imdakm, A. O.; Matsuura, T.
A Monte Carlo (MC) simulation model is developed to study heat and mass transfer through hydrophobic membranes applying direct contact membrane distillation (DCMD) process. In this study, the membrane pore space is described by a three-dimensional network model of inter-connected cylindrical pores with distributive pore size. Vapor flux through membrane pores is described by gas transport mechanism(s) based on the kinetic theory of gases. The present MC model can take into consideration the influence of temperature polarization phenomenon, membrane physical properties including pores interconnectivity and the DCMD fluid dynamic conditions. The developed model can simultaneously predict the DCMD process vapor...

14. Experimental design and optimization of asymmetric flat-sheet membranes prepared for direct contact membrane distillation - Khayet Souhaimi, Mohamed; Cojocaru, C.; García Payo, María del Carmen
Flat-sheet poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, membranes have been prepared using the phase inversion technique based on fractional factorial design. Combined effects of polymer and additive (polyethylene glycol, PEG) concentrations in the casting solutions, solvent evaporation time and coagulation bath temperature on the structural characteristics of the prepared membranes as well as on their direct contact membrane distillation (DCMD) performance have been investigated using statistical approach. The morphological properties of the membranes have been studied in terms of scanning electron microscopy, atomic force microscopy and void volume fraction. The factorial linear models have been developed to describe the main effects of factors...

15. Reduction of nanofiltration membrane fouling by UV-initiated graft polymerization technique - Khayet Souhaimi, Mohamed; Abu Seman, M. N.; Bin Ali, Z. I.; Hilal, N.
Nanofiltration polyethersulfone membrane has been modified by means of UV-initiated graft polymerization technique using the weakly acidic monomer acrylic acid and the immersion method. Different UV-irradiation times and acrylic acid concentrations in water were studied. Both the unmodified and the modified polyethersulfone nanofiltration membranes were characterized by attenuated total reflection-Fourier transform infrared spectra (FTIR-ATR) and atomic force microscopy (AFM). Irreversible membrane fouling has been studied by using humic acid model solutions at two different pH values (7 and 3). It was observed that some modified membranes exhibited higher permeance than the unmodified polyethersulfone nanofiltration membrane. The humic acid rejection factor...

16. Water desalination by membrane distillation using PVDF-HFP hollow fiber membranes - Khayet Souhaimi, Mohamed; García Payo, María del Carmen; Essalhi, M.; García Fernández, L.; Charfi, K.; Arafat, H.
Poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, hollow fiber membranes were prepared by the dry/wet spinning technique using different polyethylene glycol (PEG) concentrations as non-solvent additive in the dope solution. Two different PEG concentrations (3 and 5 wt.%). The morphology and structural characteristics of the hollow fiber membranes were studied by means of optical microscopy, scanning electron microscopy, atomic force microscopy (AFM) and void volume fraction. The experimental permeate flux and the salt (NaCl) rejection factor were determined using direct contact membrane distillation (DCMD) process. An increase of the PEG content in the spinning solution resulted in a faster coagulation of the PVDF-HFP copolymer...

17. Estudio termodinámico y estructural del motivo de unión a ADN de HESX-1: relación estabilidad-función en homeodominios - Torrado del Rey, Mario
Homeodomain proteins are transcription factors present in all eukaryotes and play key roles in cellular differentiation during development. In fact, mutations in homeodomain-encoding genes give rise to several inherited diseases in humans. The homeodomain consists of a 60-residue DNA binding domain composed of disordered N- and C-terminal regions and three helical segments. These structural features, together with the highly charged nature of the polypeptide, determine a typically low stability, property also shared by other DNA-binding proteins. Conversely, homeodomains usually present a large DNA-binding affinity. From a molecular recognition perspective, the association process is sequence-specific and represents an example of the “induced fit” mechanism. Thus, it has been shown that disordered...

18. Numerical simulation and experimental studies on heat and mass transfer using sweeping gas membrane distillation - Khayet Souhaimi, Mohamed; Charfi, K.; Safi, M. J.
A plate-and-frame membrane module has been used in sweeping gas membrane distillation process. Both numerical simulation and experimental studies have been carried out. The numerical simulation focuses on modelling heat, mass and momentum transport through the three parts of the sweeping gas membrane distillation system, namely: feed, membrane and permeate side. The model is based on Navier-Stokes equations coupled with the Darcy-Brinkman-Forcheimer formulation in transient regime in two-dimensions. A strong solver based on a compact Hermitian method has been used for solving partial derivative equations. The whole parts of the system are represented by only one domain of resolution instead...

19. Optimization of solar-powered reverse osmosis desalination pilot plant using response surface methodology - Khayet Souhaimi, Mohamed; Essalhi, M.; Armenta Déu, Carlos; Cojocaru, C.; Hilal, N.
A solar thermal and photovoltaic-powered reverse osmosis (RO) desalination plant has been constructed and optimized for brackish water desalination. The central composite experimental design of orthogonal type and response surface methodology (RSM) have been used to develop predictive models for simulation and optimization of different responses such as the salt rejection coefficient, the specific permeate flux and the RO specific performance index that takes into consideration the salt rejection coefficient, the permeate flux, the energy consumption and the conversion factor. The considered input variables were the feed temperature, the feed flow-rate and the feed pressure. Analysis of variance (ANOVA) has...

20. Measurement of the thermal conductivity of clays used in pelotherapy by the multi-current hot-wire technique - Khayet Souhaimi, Mohamed; Ortiz de Zárate Leira, José María; Luis Hita, Jorge; Legido, José Luis
We measured using the multi-current hot-wire method the thermal conductivity (lambda) of two different clay pastes suitable to be used as peloids The same wire and system was used to measure the lambda of water and the results were compared with literature data Special attention was paid to statistical data analysis The obtained lambda values for the clay pastes are higher than the lambda of water at the same temperature.

Página de resultados:
 

Busque un recurso