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排序方式: 共有162条查询结果,搜索用时 9 毫秒
21.
Amir Esmaeili Abharian Hamid Khaloozadeh Roya Amjadifard 《Neural computing & applications》2013,23(7-8):2351-2365
In this paper, the problems of stochastic robust approximate covariance assignment and robust covariance feedback stabilization, which are applied to variable parameters of additive increase/multiplicative decrease (AIMD) networks, are considered. The main idea of the developed algorithm is to use the parameter settings of an AIMD network congestion control scheme, where parameters may assign the desired network’s window covariance, with respect to the current network conditions. The aim is to search for the optimal AIMD parameters of a feedback gain matrix such that the objective functions defined via appropriate robustness measures and covariance assignment constraints can be optimized using an adaptive genetic algorithm (AGA). It is shown that the results can be used to develop tools for analyzing the behavior of AIMD communication networks. Quality of service (QoS) and other performance measures of the network have been improved by using the proposed congestion control. The accuracy of the controller is demonstrated by using MATLAB and NS software programs. 相似文献
22.
Dendritic macromolecules containing several types of functional groups were successfully synthesized through divergent method. Poly(ethylene glycol) was functionalized using cyanuric chloride and it was reacted with p‐toluidine at room temperature and a macromolecule containing chloride and methyl functional groups (PEG‐Cl2‐Me2) was obtained. Substitution of chloride functional groups of PEG‐Cl2‐Me2 by hydroxyl functional groups led to a macromolecule containing methyl and hydroxyl functional groups (PEG‐Me2‐OH4). Hydroxyl functional groups of PEG‐Me2‐OH4 were reacted with cyanuric chloride and PEG‐Me2‐Cl8 was obtained. Finally, PEG‐Me2‐Cl8 was reacted with p‐aminophenol at room temperature and a macromolecule containing methyl, hydroxyl, and chloride functional groups (PEG‐Me2‐(PhOH)4‐Cl4) was obtained. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
23.
Shabnam Asghari Niari Reza Rahbarghazi Roya Salehi Leila Kazemi Sonia Fathi Karkan Mohammad Karimipour 《Microscopy research and technique》2022,85(4):1433-1443
In recent years with regard to the development of nanotechnology and neural stem cell discovery, the combinatorial therapeutic strategies of neural progenitor cells and appropriate biomaterials have raised the hope for brain regeneration following neurological disorders. This study aimed to explore the proliferation and neurogenic effect of PLGA and PLGA–PEG nanofibers on human SH-SY5Y cells in in vitro condition. Nanofibers of PLGA and PLGA–PEG biomaterials were synthesized and fabricated using electrospinning method. Physicochemical features were examined using HNMR, FT-IR, and water contact angle assays. Ultrastructural morphology, the orientation of nanofibers, cell distribution and attachment were visualized by SEM imaging. Cell survival and proliferation rate were measured. Differentiation capacity was monitored by immunofluorescence staining of Map-2. HNMR, FT-IR assays confirmed the integration of PEG to PLGA backbone. Water contact angel assay showed increasing surface hydrophilicity in PLGA–PEG biomaterial compared to the PLGA substrate. SEM analysis revealed the reduction of PLGA–PEG nanofibers' diameter compared to the PLGA group. Cell attachment was observed in both groups while PLGA–PEG had a superior effect in the promotion of survival rate compared to other groups (p < .05). Compared to the PLGA group, PLGA–PEG increased the number of Ki67+ cells (p < .01). PLGA–PEG biomaterial induced neural maturation by increasing protein Map-2 compared to the PLGA scaffold in a three-dimensional culture system. According to our data, structural modification of PLGA with PEG could enhance orientated differentiation and the dynamic growth of neural cells. 相似文献
24.
Ian Laboriante Maxwell Fisch Amir Payamipour Fang Liu Carlo Carraro Roya Maboudian 《Tribology Letters》2011,44(1):13-17
The evolution of morphology, electrical properties, and chemical composition has been studied in cyclically contacting polycrystalline silicon (polysilicon) surfaces coated with perfluoroalkylsilane self-assembled monolayer (SAM). The microinstrument used is a MEMS cantilever that is repeatedly actuated out-of-plane to impact a landing pad and is then moved in-plane to enable nondestructive in situ inspection of the impacted area. Analyses show that a device with a monolayer coating exhibits signs of surface degradation after a much higher number of cycles than its uncoated counterpart. A sharp increase in contact resistance between the cantilever and landing pad is observed at ~10 billion cycles for a coated device, versus ~25 million cycles for an uncoated device. Likewise, the onset of grain fracture in the landing pad occurs at ~25 billion cycles for the SAM-coated device, versus ~3 billion cycles for its uncoated counterpart. The effectiveness of the monolayer coating diminishes after more than 100 billion contact cycles as the SAM layer is removed, and the polysilicon substrate becomes susceptible to adhesive wear. 相似文献
25.
A galvanic displacement technique is used to coat silicon scanning force microscopy cantilevers with copper. The copper coating is characterized using X-ray photoelectron spectroscopy, scanning force microscopy, contact angle measurements, scanning electron microscopy and energy-dispersive X-ray spectroscopy. This coating technique results in uniform, reflective and conformal films and hence, no stress-induced bending of the cantilever is observed. To demonstrate the effectiveness of this approach for tribological studies, the coated cantilevers are chemically modified with alkanethiol monolayers in order to functionalize the cantilevers. The effect of changed surface energy are detected with adhesion measurements in water and ethanol. 相似文献
26.
A series of Ni-Mo/Al2O3-Y hybrid nanocatalysts were synthesized for hydrocracking of heavy oil. The well crystallized Y zeolite was synthesized from mineral bentonite and rice husk ash by a two-step synthesis method. The solution combustion method was applied to develop a fast and simple technique for preparing of alumina-supported NiMo catalyst with high hydrodesulfurization activity. Such activity may be due to the morphological and textural modification as a consequence of the release of a high amount of exhaust gases during the combustion process. The XRD analysis revealed that the P zeolite was a competitive phase presented in the obtained product that could be eliminated using a two-step synthesis method. Compared to a one-step method, the pore volume and external surface area of the synthesized zeolite by the two-step method increased by 74 and 62%, respectively. The hydrocracking results illustrated that the synthesized zeolite was able to convert 66% of heavy oil to lighter products and reduce the viscosity up to 60%. Furthermore, the amount of sulfur removal was found to be 58%. The spent catalyst characterization suggested that the type of deposited coke was hard coke with the unsaturated aromatic ring which could be responsible for the pores blockage after the cracking reaction. 相似文献
27.
Adhesion plays an important role in the final properties of nanocomposites. This study explored the surface interaction of cellulose nanocrystals (CNCs) and the effect of CNC sources on adhesion between individual CNCs and the Si tip of an AFM cantilever using a force mapping technique called FMap. The adhesion between CNCs and a Si tip from five different sources has been studied: cotton, Whatman filter paper, hemp, softwood chemical kraft pulp, and softwood-dissolving pulp (alistaple). Mica was used as the background substrate to act as an internal standard. This study’s findings suggest that adhesion is not the same for all CNCs. Transmission electron microscopy and atomic force microscopy were used to determine the size and shape of each CNC. The experimental quantitative data showed that adhesion between CNCs and the Si tip has a close correlation with the diameter of the CNCs. X-ray photoelectron spectroscopy confirmed the presence of sulfate groups on the surface of the CNCs and a correlation between adhesion and surface chemistry of the CNCs was observed. 相似文献
28.
Arrays of precisely positioned single crystal silicon nanopillars, nanoneedles, and nanoblades with minimum feature sizes as small as 30 nm are fabricated using entirely scalable top-down fabrication techniques. Using the same scalable technologies, devices consisting of electrically connected silicon nanopillars with multiple addressable electrodes for each nanostructure are realized. The arrays of nanopillars, nanoneedles, and nanoblades are shown to exhibit Raman signal enhancement on 1,2-benzenedithiol monolayers, opening a path to nanodevices that manipulate, position, detect and analyze molecules. 相似文献
29.
K. Fatehi F. Moztarzadeh M. Solati-Hashjin M. Tahriri M. Rezvannia R. Ravarian 《Bulletin of Materials Science》2008,31(2):101-108
Titanium alloy (Ti6A14V) substrates, having the ability of biomimetic calcium phosphate-based materials, especially hydroxyapatite
deposition in a simulated body fluid (SBF) means of chemical treatment (alkaline treatment) and subsequent heat treatment,
was studied. The effects of alkaline treatment time, concentration and heat treatment temperature on the formation of calcium
phosphate (carbonate-hydroxyapatite) on Ti6A14V surface were examined. For this purpose, the metallic substrates were treated
in 0, 5 and 10 M NaOH solutions at a temperature of 60 or 80°C for 1 and 3 days. Subsequently the substrate was heat-treated
at 500, 600 and 700°C for 1 h for consolidation of the sodium titanate hydrogel layer. Finally, they were soaked in SBF for
1 and 3 days. The substrate surfaces were characterized by the techniques commonly used for bulk material such as scanning
electron microscopy (SEM) and thin film X-ray diffraction (TF-XRD). With regard to the SEM and TF-XRD results, the optimum
process consists of 3 days soaking in 5 M NaOH in 80°C and subsequent heat treatment at 600°C for 1h. It is worth mentioning
that the results showed that the apatite formed within 3 days on the specimen surfaces, however, there was no sign of apatite
formation in the control samples (without alkaline and heat treatment) which was treated for up to 3 days immersion in SBF. 相似文献
30.
Paola Fabbri Francesco Pilati Roya Aghababazadeh Ghasem Kavei 《Materials Letters》2010,64(20):2265-2268
In this work a new approach has been developed for the synthesis of SiO2@Y2O3 particles with core-shell structure. The method is based on the synthesis of a covalently bonded sacrificial polymer shell grown onto silica particles. It is suitable to promote and stabilize the adsorption of different ions, namely Yttrium from its nitrate solution. After calcination and consequent elimination of the sacrificial polymer shell, the SiO2@Y2O3 core-shell particles are obtained. Results reveal that the shell thickness of these core-shell particles is higher and more uniform than that of particles prepared without sacrificial polymer shell. 相似文献