Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99


Any time

2020 ( 68 )

2019 ( 638 )

2018 ( 756 )

2017 ( 773 )

Custom range...

Search Results: 1 - 10 of 449382 matches for " Paulo H. S. Picciani "
All listed articles are free for downloading (OA Articles)
Page 1 /449382
Display every page Item
Morphology and Thermal Properties of Core-Shell PVA/PLA Ultrafine Fibers Produced by Coaxial Electrospinning  [PDF]
Raquel P. Gon?alves, Flavia F. F. da Silva, Paulo H. S. Picciani, Marcos L. Dias
Materials Sciences and Applications (MSA) , 2015, DOI: 10.4236/msa.2015.62022
Abstract: Coaxial electrospinning process was used to produce biodegradable membranes made of coreshell fibers of a poly(lactic acid) (PLA) shell and a poly(vinyl alcohol) (PVA) core. Scanning electron microscopy analyses of these structures showed that the PLA shell can present certain porosity depending on the process condition. FTIR-ATR and contact angle measurements also suggested imprisonment of the PVA core within the PLA shell. This type of structure was also confirmed by means of transmissions electron microscopy. The morphology of these fibers was dependent on the flow rate of both core and shell solutions, and homogeneous and smooth surface was only attained when the flow rate of the external PLA solution was 4 times the flow rate of the internal PVA solution. The increase in the PLA solution flow rate increases the diameter of the core-shell fiber which reaches up to 1.7 μm. Nevertheless, fibers with smaller average diameter could also be produced (200 nm). These core-shell fibers presented improved hydrophilicity as compared with monolithic PLA fibers.
Development of Biobased Poly(Lactic Acid)/Epoxidized Natural Rubber Blends Processed by Electrospinning: Morphological, Structural and Thermal Properties  [PDF]
Jaqueline G. L. Cosme, Vanessa M. Silva, Regina R. C. Nunes, Paulo H. S. Picciani
Materials Sciences and Applications (MSA) , 2016, DOI: 10.4236/msa.2016.74021
Abstract: This article reports the production of electrospun fibers from blends of poly(lactic acid) (PLA) and epoxidized natural rubber (ENR) solutions. The produced fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). SEM images showed the reduction in fiber size with ENR content of up to 25% in the mixture PLA/ENR. FTIR analysis revealed a possible interaction between carboxylic group of PLA and epoxi group of ENR. Thermal analysis showed the increase of the crystallinity fraction with ENR content and a decrease in thermal stability of eletrospun mats with the addition of ENR. The dynamic mechanical properties showed an enhancement of the stiffness of PLA/ENR blends with the increase of ENR content, which can support the production of interesting materials for tissue engineering based on renewable and biocompatible polymers. The reported properties indicate the possibility to use such fiber mats as potential materials in tissue engineering.
Estudo das propriedades mecanicas e elétricas de fibras de curauá modificada com polianilina
S. Junior, Fernando G. de;Picciani, Paulo H. S.;Rocha, Eli V. da;Oliveira, Geiza E. de;
Polímeros , 2010, DOI: 10.1590/S0104-14282010005000058
Abstract: natural fibers have been employed as reinforcement filler in composite materials for the automobile industry. among the natural fibers, the curauá fiber is promising due to its high mechanical resistance associated with low density values. in this work curauá fibers are chemically modified by a conducting polyaniline coating, with the aim of using this new conductive composite as pressure sensors. the composite material obtained was characterized using fourier transform infrared spectroscopy (ftir), thermogravimetric analysis (tg) and optical microscopy. the results demonstrated that the methodology adopted was efficient in forming a partial, but effective, coating of the fiber, thus leading to conducting paths along the whole fiber. the electro-mechanical properties of the fibers were also evaluated and the composites have potential for low cost pressure sensors. furthermore, the modified fibers had good thermal stability and the partial coating allows the composite to be naturally degraded as an environmentally-friendly material.
Caracteriza??o físico-mecanica de filmes de borracha natural epoxidada curáveis em temperatura ambiente
Jorge, Rosane M.;Ferreira, Marcos T.;Picciani, Paulo H. S.;Gomes, Ailton S.;Nunes, Regina C. R.;
Polímeros , 2009, DOI: 10.1590/S0104-14282009000400013
Abstract: this paper presents the crosslinking study at room temperature of epoxidised natural rubber (enr), of 25% of epoxidation level, with a curing agent containing thiol trimethylolpropane tris(2-mercaptoacetate) (tmp-sh). the compositions were made from solubilization of enr, and subsequent reaction with tmp-sh. compositions with 5, 10 and 20 phr of tmp-sh, nr and enr controls were prepared. it was also prepared a composition with nr and 10 phr of tmp-sh to demonstrate the effect of epoxide group. the crosslinking formation of the films was determined by physical-mechanical properties as equilibrium swelling index, tensile strength and dynamic-mechanical properties. the results showed the efficiency of the cure agent and the influence of tmp-sh content incorporated, in the studied properties, and the enr composition with 10 phr of curing agent presented the best physical-mechanical performance.
Eletrofia??o de polímeros em solu??o: parte II: aplica??es e perspectivas
Costa, Rodrigo G. F.;Oliveira, Juliano E. de;Paula, Gustavo F. de;Picciani, Paulo H. de S.;Medeiros, Eliton S. de;Ribeiro, Cauê;Mattoso, Luiz H.C.;
Polímeros , 2012, DOI: 10.1590/S0104-14282012005000018
Abstract: in our previous review[1], the process of electrospinning was discussed on the basis of theoretical and experimental aspects toward preparation of different polymeric nanofibers. in this second review, we focus on the aspects related to the application of electrospun materials in various fields such as medicine, agriculture, sensors, and processing of other materials. we discuss the most often characterization techniques used for these materials and their potential. this review complements the previous one and uses the same terminology.
Eletrofia??o de Polímeros em Solu??o: parte I: fundamenta??o Te?3rica
Costa, Rodrigo G. F.;Oliveira, Juliano E. de;Paula, Gustavo F. de;Picciani, Paulo H. de S.;Medeiros, Eliton S. de;Ribeiro, Cauê;Mattoso, Luiz H. C.;
Polímeros , 2012, DOI: 10.1590/S0104-14282012005000026
Abstract: the electrospinning technique has been known since the 1930s, but only with the advent of new nanotechnology applications this technique was re-discovered and became important for production of nanomaterials. the potential for obtaining different nanofibers with sizes ranging from 50 to 500 nm and micrometer length has been investigated for different materials, with promising results in different applications. the first part of this review is aimed at describing the fundamentals of the electrospinning process. we describe the influence of process variables such as applied field, working distance, speed of rotation of the collector and solution injecting flow rate. the variables associated to this system, such as type of solvent and polymer of interest, are also discussed.
Calculation of reaction constants using Transition Path Sampling with a local Lyapunov bias
Massimiliano Picciani
Physics , 2011,
Abstract: We propose an efficient method to compute reaction rate constants of thermally activated processes occurring in many-body systems at finite temperature. The method consists in two steps: first, paths are sampled using a transition path sampling (TPS) algorithm supplemented with a local Lyapunov bias favoring diverging trajectories. This enhances the probability of observing rare reactive trajectories between stable states during relatively short simulations. Secondly, reaction constants are eventually estimated from the unbiased fraction of reactive paths, yielded by an appropriate statistical data analysis tool, the multistate Bennett acceptance ratio (MBAR) package. In order to test our algorithm, we compute reaction constants for structural transitions in LJ38, a well studied Lennard-Jones cluster, comparing our results to values previously reported in the literature. Additionally, we apply our method to the calculation of reaction rates for vacancy migration in an {\alpha}-Iron crystal, for temperatures ranging from 300 K to 850 K. Vacancy diffusion rates associated with activation barriers at finite temperature are then evaluated, and compared to values obtained using the standard harmonic approximation.
Estudo histológico da regenera o esplênica de ratos submetidos a esplenectomia subtotal
Torres Orlando Jorge Martins,Macedo Eliane Lopes,Picciani érica Regina Gomes,Nunes Paulo Márcio Sousa
Acta Cirurgica Brasileira , 2000,
Abstract: Um aumento da susceptibilidade à infec o severa é uma complica o reconhecida da esplenectomia. Um grande número de alternativas tem sido propostas que poderiam impedir esta complica o do estado asplênico. O presente estudo analisa a regenera o histológica do tecido esplênico em ratos submetidos a esplenectomia subtotal. Foram utilizados trinta ratos machos da linhagem Wistar, adultos, pesando entre 160 e 210g. Os animais foram submetidos a esplenectomia subtotal e divididos em três grupos contendo dez ratos cada onde foram estudados após 15, 30 e 45 dias. Após este período de observa o o tecido esplênico foi recuperado e submetido a exame histológico. A estrutura tecidual esplênica no 15o dia se apresentava irregular, porém sem necrose. Após 30 dias , a cápsula se apresentava histologicamente espessada e com maior desenvolvimento. Em 45 dias foi observado semelhan a considerável entre o tecido esplênico remanescente e o ba o normal. O presente estudo mostra que o ba o submetido a esplenectomia subtotal se regenera completamente em um período de 45 dias.
Agonistic Interactions and Reproductive Dominance in Pachycondyla Obscuricornis (Hymenoptera: Formicidae)
Paulo S. Oliveira,Bert Hölldobler
Psyche , 1991, DOI: 10.1155/1991/64635
Camacho,Jesús H.; Magalh?es,Paulo S. G.;
Agricultura Técnica , 2004, DOI: 10.4067/S0365-28072004000100007
Abstract: one of the main restrictive aspects of no-tillage is the handling of crop residues during amendment and fertilizer application, since when it is not carried out simultaneously with sowing, it is necessary to distribute these products on the surface to maintain the soil cover. the objective of the present study was to evaluate the operational capacity of a prototype designed with double disks, chisel tine and subsoiler, which allows fertilization at a depth between 0 and 0.30 m. the experimental design was randomized blocks, with seven treatments and four replicates. behavior of the horizontal and vertical forces, soil area disturbed, work depth and specific resistance were analyzed. the results indicated that the use of double disks in front of the chisels reduces the horizontal force and the disturbed area, but these results do not differ statistically. the treatments with chisels had higher values of horizontal force, higher disturbed areas and similar specific resistance. the combination of double disks and chisels reduced the vertical force. the maximum working depth was observed for the treatments with double disks and subsoiler. the double disks had smallest horizontal force, shallowest working depth, smallest disturbed area and the highest specific resistance.
Page 1 /449382
Display every page Item

Copyright © 2008-2017 Open Access Library. All rights reserved.