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61.
The optical dense comb filters are indispensable components for dense wavelength multiplexing systems. In this paper, a novel and basic method is proposed to realize optical dense comb filters. The reflection spectrum of sampled fiber Bragg grating is analyzed after applying a phase shifting technique that varies the phase of the grating. The spectral densification and shifting effects of periodic phase shifts are investigated and it is shown that desired amount of channel multiplying can be provided by using appropriate value of densification factor. Moreover, a quantization technique is proposed in order to reduce the phase shifting series which complicated by the increase of densification factor. 相似文献
62.
Tara B. Richardson Mirna A. Mosiewicki Cihan Uzunpinar Norma E. Marcovich Mirta I. Aranguren Fatma Kilinc‐Balci Roy M. Broughton Maria L. Auad 《Polymer Composites》2011,32(3):455-463
Multi‐walled carbon nanotubes (CNTs) and cellulose nanofibers (CNFs) reinforced shape memory polyurethane (PU) composite fibers and films have been fabricated via extrusion and casting methods. Cellulose nanofibers were obtained through acid hydrolysis of microcrystalline cellulose. This treatment aided in achieving stable suspensions of cellulose crystals in dimethylformamide (DMF), for subsequent incorporation into the shape memory matrix. CNTs were covalent functionalized with carboxyl groups (CNT‐COOH) and 4,4′‐methylenebis (phenylisocyanate) (MDI) (CNT‐MDI) to improve the dispersion efficiency between the CNT and the polyurethane. Significant improvement in tensile modulus and strength were achieved by incorporating both fillers up to 1 wt% without sacrificing the elongation at break. Electron microscopy was used to investigate the degree of dispersion and fracture surfaces of the composite fibers and films. The effects of the filler (type and concentration) on the degree of crystallinity and thermal properties of the hard and soft segments that form the PU sample were studied by calorimetry. Overall, results indicated that the homogeneous dispersion of nanotubes and cellulose throughout the PU matrix and the strong interfacial adhesion between nanotubes and/or cellulose and the matrix are responsible for the enhancement of mechanical and shape memory properties of the composites. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers 相似文献
63.
2‐Hydroxyethyl methacrylate (HEMA)‐clay nanocomposites were prepared via in situ free radical polymerization using montmorillonite (MMT) as a crosslinker. The structure and surface morphology of the nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction, and scanning electron microscopy. It was found that exfoliated or highly expanded intercalated nanocomposite structure was obtained. The swelling degree was determined in distilled water and various pH buffered solutions. The highest swelling capacity in distilled water was observed for the nanocomposite sample prepared with the MMT amount of 10 % (w). It was seen that the diffusion mechanism was Fickian type in distilled water and also in various pH‐buffered solutions. It is interesting that the swelling degree of nanocomposites in alkaline pH values increased by the increasing of MMT in the polymer structure. This result supports the possibility of future applications of the novel nanocomposite in systems for the controlled released of drugs. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers 相似文献
64.
Biochemical and thermal properties of β-galactosidase enzymes produced by artisanal yoghurt cultures
β-Galactosidases, produced by pure and mixed cultures of Streptococcus thermophilus 95/2 (St 95/2) and Lactobacillus delbrueckii ssp bulgaricus 77 (Lb 77) isolated from the Toros mountain region of Turkey, were characterised with respect to their biochemical and thermal properties. Optimum pH and temperature for maximum activity were determined and these enzymes were stable in the pH range 7–9 and in the temperature range 20–37 °C, retaining 80–90% of their initial activities. The inactivation energies of β-galactosidase from Lb 77, St 95/2 and mixed culture (Lb 77 and St 95/2) were 51.3, 44.0 and 48.3 kcal mol−1, respectively. Moreover, thermodynamic (ΔG, ΔS, ΔH) and kinetic constants (Km and Vmax) were determined and effects of metal ions were investigated. As a result, these enzymes could be considered as potential candidates for lactose hydrolysis of milk and milk products. 相似文献
65.
Fatma H. Abd El-Salam 《Journal of surfactants and detergents》2009,12(4):363-370
New gemini anionic surfactants were prepared from sodium salts of monoalkyl sulfosuccinate esters of ethylene glycol having
variably long tails (C12, C16, C18) and dichloroethane. The chemical structures of the prepared surfactants were confirmed using different spectroscopic techniques.
The surfaces tension values of the synthesized surfactants were measured at 25 °C individually or mixing at different molar
fractions with ethoxylated alkylphenol. In all cases, mixed micellar aggregates were formed and critical micellar concentrations
of binary mixtures containing different mole fractions of the surfactants were measured. The micellization processes of the
individual and mixed surfactants were investigated. The effect of different alkyl chains of gemini anionic surfactants on
properties of binary systems and molar ratio in the mixed aggregates were deduced. The critical micelle concentration of mixed
surfactants shifted to lower values compared to those of the single surfactants. Effectiveness values increased with decreases
in the mole fraction of gemini anionic surfactants. The negative values of interaction parameter (β) increased with increases
in the chain length of anionic surfactants. The activity coefficient (f
1, f
2) and total minimum surface area of mixed solution were calculated. Also, the gemini anionic surfactants prepared have moderate
antimicrobial activity towards bacteria and not active towards fungi. 相似文献
66.
67.
Fatma Tosun Çiğdem Akyüz Kızılay Kevser Erol Fatma Sultan Kılıç Mine Kürkçüoğlu Kemal Hüsnü Can Başer 《Food chemistry》2008
The anticonvulsant activity of furanocoumarins, coumarin mixture and the essential oil obtained from the fruits of Heracleum crenatifolium was examined against maximal electroshock (MES)-induced seizures in mice. Bergapten showed significant anticonvulsant activity. The furanocoumarins isolated from the fruits of the plant were identified using thin-layer chromatography, melting points and spectroscopic methods (IR, MS, 1H NMR) as isobergapten (1), pimpinellin (2), bergapten (3), isopimpinellin (4), sphondin (5) and byak-angelicol (6). The essential oil content of the fruits were found as 5.5%. Twenty-two compounds representing 99.3% of the essential oil obtained from the fruits of H. crenatifolium were determined and the major components were identified as octanol and octyl acetate (3.1% and 88.4% respectively) by GC and GC–MS. 相似文献
68.
Blends based on various compositions of low‐density polyethylene (LDPE) and plasticized starch (PLST) were prepared by melt extrusion and molding in the form of sheets under hot press. The rheology properties during mixing were studied in terms of torque and temperature against mixing time. The structural properties of LDPE/PLST blends before and after electron beam irradiation was characterized by IR spectroscopy, tensile mechanical testing, and scanning electron microscopy (SEM). The torque‐time curves during the mixing process showed that the values of torque in the first region of mixing for pure LDPE or LDPE/PLST blends are higher in the presence of the compatibilizer PEMA than that in the presence of EVA. In addition, the stability of mixing was attained after a short time in the presence of PEMA. The IR spectroscopy suggests that the compatibilization by EVA and PEMA compounds proceeds through the formation of hydrogen bonding during mixing and this compatibility was improved after electron beam irradiation. The stress–strain curves of pure LDPE and its blends with PLST showed the behavior of tough polymers with yielding properties. The SEM micrographs of the fracture surfaces give supports to the effect of EVA and PEMA as compatibilizers and the effect of electron beam irradiation. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers 相似文献
69.
70.
Fatma Osman Ibnouf 《Food Security》2011,3(2):215-231
This paper investigates the role of women in achieving household food security in the Western Region of Sudan, an area much
affected by the impacts of drought and civil conflicts. The study is based on a quantitative survey and qualitative focus
group discussions, supported by personal observations made during fieldwork. Additionally, the study draws upon secondary
data that is publicly available. Results demonstrate that women play a major role in producing and providing food for their
households in this high-risk climate and conflict area, while men are more likely to migrate seasonally and even permanently.
In addition, women are responsible for food preparation, processing, and food preservation and are wholly responsible for
attending to household garden plots. They therefore contribute more to household food security than men, though this contribution
is not recognized in official statistics. The study findings indicate that the main problems women face as food producers
and providers are a lack of access to the full package of improved production methods (improved seeds, fertilizers, modern
farming methods, credit services, pesticides, appropriate technologies, and marketing facilities), in addition to gender disparities
and gender-biased traditions. The impacts of natural crises and civil conflicts are gendered and therefore the responses to
these crises must be gender responsive. Holistic and strategic policies and plans that take gender issues into account are
thus needed in order to achieve food security. 相似文献