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排序方式: 共有193条查询结果,搜索用时 15 毫秒
101.
Alexandra A.P. Mansur Herman S. Mansur 《Materials science & engineering. C, Materials for biological applications》2010,30(2):288-294
The major goal of this research was to investigate and characterize the deposition of a biomimetic apatite-like coating onto the surface of 3D porous calcium-silicate-hydrate scaffolds with suitable bioactivity for potential application in bone tissue engineering. Basically, Portland cement, water, sand and lime were mixed for preparing the slurry which was poured into molds, and fine aluminum powder was added as foaming agent resulting on the formation of porous 3D structures. After aging for 28 days, these porous inorganic scaffolds were immersed in calcium chloride supersaturated solution in PBS for 7 days at 37 °C for the biomimetic layer deposition. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier Transformed Infrared Spectroscopy (FTIR) techniques were used in order to characterize the porous scaffolds and the apatite-like biomimetic coating. The results have showed that 3D constructs were successfully produced with interconnected porosity, compressive strength and cytocompatibility appropriate for potential use as an alternative in trabecular bone repair. 相似文献
102.
Hermes S. Costa Alexandra A. P. Mansur Edel F. Barbosa-Stancioli Marivalda M. Pereira Herman S. Mansur 《Journal of Materials Science》2008,43(2):510-524
In bone tissue engineering, a highly porous artificial extracellular matrix or scaffold is required to accommodate cells and
guide the tissue regeneration in three-dimension. Calcium phosphate (CaP) ceramics are widely used for bone substitution and
repair due to their biocompatibility, bioactivity, and osteoconduction. However, compared to alumina ceramics, either in the
dense or porous form, the mechanical strength achieved for calcium phosphates is generally lower. In the present work, the
major goal was to develop a tri-dimensional macroporous alumina scaffold with a biocompatible PVA/calcium phosphate coating
to be potentially used as bone tissue substitute. This approach aims to combine the high mechanical strength of the alumina
scaffold with the biocompatibility of calcium phosphate based materials. Hence, the porous alumina scaffolds were produced
by the polymer foam replication procedure. Then, these scaffolds were submitted to two different coating methods: the biomimetic
and the immersion in a calcium phosphate/polyvinyl alcohol (CaP/PVA) slurry. The microstructure, morphology and crystallinity
of the macroporous alumina scaffolds samples and coated with CaP/PVA were characterized by X-ray diffraction (XRD), Fourier
Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM/EDX) analysis. Also, specific surface area was
assessed by BET nitrogen adsorption method and mechanical behavior was evaluated by axial compression tests. Finally, biocompatibility
and cytotoxicity were evaluated by VERO cell spreading and attachment assays under SEM. The morphological analysis obtained
from SEM photomicrograph results has indicated that 3D macroporous alumina scaffolds were successfully produced, with estimated
porosity of over 65% in a highly interconnected network. In addition, the mechanical test results have indicated that porous
alumina scaffolds with ultimate compressive strength of over 3.0 MPa were produced. Concerning to the calcium phosphate coatings,
the results have showed that the biomimetic method was not efficient on producing a detectable layer onto the alumina scaffolds.
On the other hand, a uniform and adherent inorganic–organic coating was effectively formed onto alumina macroporous scaffold
by the immersion of the porous structure into the CaP/PVA suspension. Viable VERO cells were verified onto the surface of
alumina porous scaffold samples coated with PVA–calcium phosphate. In conclusion, a new method was developed to produce alumina
with tri-dimensional porous structure and uniformly covered with a biocompatible coating of calcium phosphate/PVA. Such system
has high potential to be used in bone tissue engineering. 相似文献
103.
Selective extraction of zinc(II) over iron(II) from spent hydrochloric acid pickling effluents by liquid-liquid extraction 总被引:1,自引:0,他引:1
Mansur MB Rocha SD Magalhães FS Benedetto Jdos S 《Journal of hazardous materials》2008,150(3):669-678
The selective removal of zinc(II) over iron(II) by liquid–liquid extraction from spent hydrochloric acid pickling effluents produced by the zinc hot-dip galvanizing industry was studied at room temperature. Two distinct effluents were investigated: effluent 1 containing 70.2 g/L of Zn, 92.2 g/L of Fe and pH 0.6, and effluent 2 containing 33.9 g/L of Zn, 203.9 g/L of Fe and 2 M HCl. The following extractants were compared: TBP (tri-n-butyl phosphate), Cyanex 272 [bis(2,4,4-trimethylpentyl)phosphinic acid], Cyanex 301 [bis(2,4,4-trimethylpentyl) dithiophosphinic acid] and Cyanex 302 [bis(2,4,4-trimethylpentyl) monothiophosphinic acid]. The best separation results were obtained for extractants TBP and Cyanex 301. Around 92.5% of zinc and 11.2% of iron were extracted from effluent 1 in one single contact using 100% (v/v) of TBP. With Cyanex 301, around 80–95% of zinc and less than 10% of iron were extracted from effluent 2 at pH 0.3–1.0. For Cyanex 272, the highest extraction yield for zinc (70% of zinc with 20% of iron extraction) was found at pH 2.4. Cyanex 302 presented low metal extraction levels (below 10%) and slow phase disengagement characteristics. Reactions for the extraction of zinc with TBP and Cyanex 301 from hydrochloric acid solution were proposed. 相似文献
104.
This paper carries out a discussion concerning kernels in two-dimensional BEM analysis of transient scalar wave propagation problems. Kernels obtained after performing analytical time integration are compared. An example of quadratic time variation is presented in order to illustrate some of the mathematical concepts discussed. 相似文献
105.
H. Tian P. K. Liaw D. E. Fielden J. P. Strizak L. K. Mansur 《Metallurgical and Materials Transactions A》2004,35(10):3334-3339
The Type 316 stainless steel is being considered as a candidate target-container material for the spallation neutron source
(SNS) being built at the Oak Ridge National Laboratory. Satisfactory behavior under fatigue loading is a requirement for the
target container. Stress-controlled fatigue experiments were performed on the 316 stainless steel at 0.2 and 10 Hz with an
R ratio of −1, where R=σ
min./σ
max.; σ
min. and σ
max. are the minimum and maximum applied stresses, respectively. At R=−1, a large specimen-temperature increase at 10 Hz was observed, which approached approximately 350 °C at a stress amplitude
of 263 MPa, and affected fatigue lives. The specimen temperature at 0.2 Hz was about room temperature. The fatigue lives at
10 Hz were found to be shorter than those at 0.2 Hz. Different specimen temperatures were achieved by varying test frequencies.
Significant differences in fatigue lives as a function of test frequency were observed with shorter fatigue lives at higher
frequencies. The higher specimen temperature at 10 than at 0.2 Hz reduced the fatigue life at 10 Hz. A model based on the
dissipation energy of the specimen during fatigue tests was developed to explain the fatigue-life result and predict the specimen-temperature
evolution.
The present research is sponsored by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences,
United States Department of Energy, under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC. 相似文献
106.
107.
A ‘methanol economy’ based mainly on natural gas as a feedstock has a lot of potential to cope with the current and ongoing concerns for energy security along with the reduction of CO-2 emissions. It is, therefore, important to examine the price dynamics of methanol in order to ascertain whether the price of methanol is mainly natural-gas-cost driven or demand driven in the context of different regions. This paper is the first attempt to investigate the following: (i) is the natural gas price significantly related to the regional methanol prices in the Far East, United States and Europe? (ii) who drives the regional methanol prices? The paper is motivated by the recent and growing debate on the lead-lag relationship between natural gas and methanol prices. Our findings, based on the most recently developed ‘long-run structural modelling’ and subject to the limitations of the study, tend to suggest: (i) natural gas price is cointegrated with the regional methanol prices, (ii) our within-sample error-correction model results tend to indicate that natural gas was driving the methanol prices in Europe and the United States but not in the Far East. These results are consistent, during most of the period under review (1998.5–2007.3), with the surge in demand for methanol throughout the Far East, particularly in China, Taiwan and South Korea, which appears to have played a relatively more dominant role in the Far East compared to that in Europe and the United States within the framework of the dynamic interactions of input and product prices. However, during the post-sample forecast period as evidenced in our variance decompositions analysis, the emergence of natural gas as the main driver of methanol prices in all three continents is consistent with the recent surge in natural gas price fueled mainly, among others, by the strong hedging activities in the natural gas futures/options as well as refining tightness (similar to those that were happening in the crude oil markets). 相似文献
108.
Speckle noise reduction of medical ultrasound images in complex wavelet domain using mixture priors 总被引:1,自引:0,他引:1
Rabbani H Vafadust M Abolmaesumi P Gazor S 《IEEE transactions on bio-medical engineering》2008,55(9):2152-2160
109.
Venâncio J. S. Neto Felipe G. L. Dores Priscila F. Oliveira Claudia R. E. Mansur 《应用聚合物科学杂志》2024,141(9):e55019
Polymeric hydrogels have been evaluated for their ability to block high-permeability regions of heterogeneous reservoirs, distributing the injected fluids to low-permeability regions, aiming to improve oil recovery. However, the stability of these hydrogels can be reduced under conditions of high temperature and salinity typical of reservoirs. Thus, the objective of this study was to assess the properties of hydrogels based on partially hydrolyzed polyacrylamide, with different molar masses, crosslinked with aluminum citrate, in the presence or absence of bentonite clay. We call these systems composite hydrogels or conventional hydrogels, respectively, and prepared them in synthetic brine containing 29,940 mg/L of total dissolved solids. The selected hydrogels were submitted to rheology tests and scanning electron microscopy for assignment of gel strength codes. The results showed it was possible to obtain composite hydrogels with enhanced thermal properties in comparison with conventional hydrogels, mainly at a temperature of 85°C. The rheological tests, by determining the viscous modulus (G"), elastic modulus (G'), and the ratio between the two (G"/G'), along with the tan δ factor, indicated competition in the interaction between the clay and crosslinker, due to the latter's positive charges in relation to the negative charges present in the polymer chains. The scanning electron microscopy micrographs showed the presence of clay particles adhered in the polymer chain, improving the thermal resistance of the system. 相似文献
110.