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1.
Modelling of effects of ultrastructural morphology on the hygroelastic properties of wood fibres 总被引:1,自引:0,他引:1
Wood fibres constitute the structural framework of e.g. wood, paper, board and composites, where stiffness and dimensional
stability are of importance. An analytical modelling approach has been used for prediction of hygroelastic response, and assessment
of the stresses in thick-walled cylinder models of wood fibres. A wood fibre was idealised as a multilayered hollow cylinder
made of orthotropic material with helical orientation. The hygroelastic response of the layered assembly due to axisymmetric
loading and moisture content changes was obtained by solving the corresponding boundary value problem of elasticity. A simple
solution scheme based on the state space approach and the transfer matrix method was employed. This was combined with an analytical
ultrastructural homogenisation method, used to link hygroelastic properties of constituent wood polymers to properties of
each layer. Predicted hygroelastic response captured experimentally measured behaviour. Fibres that were constrained not to
twist showed a stiffer response than fibres allowed twisting under uniaxial loading. It was also shown that the ultrastructure,
i.e. the microfibril angle, will control the hygroexpansion in the same way as it controls the compliance of the cell wall.
Qualitative failure trends comparable with experimental observations could be established with stress analysis and a simple
plane-stress failure criterion. 相似文献
2.
Using the batch method, the retention of Ga(III) from HCl solutions by two gel‐type pyridine strong‐base anion exchangers containing 1‐methyl‐ or 1‐butyl‐4‐vinylpyridinium chloride structural units, called S1 and S2 resins, respectively, was studied. The influence of the HCl and Ga(III) concentrations as well as of the contact time between the resin and the liquid phase was investigated. The parameters, which characterize the retention process, were estimated using Langmuir and Freundlich isotherms. Both resins exhibited a higher affinity for gallium ions from a 6M HCl solution. According to Langmuir isotherms, maximum retention capacities of 44.44 and 60 mg Ga(III)/g dry resin for the S1 and S2 resins, respectively, were obtained. Freundlich isotherms provide additional proof for a higher affinity of the S2 resin for Ga(III) from HCl solutions. It is clear that the substituent length increase on N+ atoms led to an increasing affinity of the pyridine strong base anion exchangers toward Ga(III). © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3440–3444, 2002 相似文献
3.
Fuzzy grey relational analysis for software effort estimation 总被引:1,自引:1,他引:0
Accurate and credible software effort estimation is a challenge for academic research and software industry. From many software
effort estimation models in existence, Estimation by Analogy (EA) is still one of the preferred techniques by software engineering
practitioners because it mimics the human problem solving approach. Accuracy of such a model depends on the characteristics
of the dataset, which is subject to considerable uncertainty. The inherent uncertainty in software attribute measurement has
significant impact on estimation accuracy because these attributes are measured based on human judgment and are often vague
and imprecise. To overcome this challenge we propose a new formal EA model based on the integration of Fuzzy set theory with
Grey Relational Analysis (GRA). Fuzzy set theory is employed to reduce uncertainty in distance measure between two tuples
at the k
th
continuous feature ( | ( xo(k) - xi(k) | ) \left( {\left| {\left( {{x_o}(k) - {x_i}(k)} \right.} \right|} \right) .GRA is a problem solving method that is used to assess the similarity between two tuples with M features. Since some of these features are not necessary to be continuous and may have nominal and ordinal scale type, aggregating
different forms of similarity measures will increase uncertainty in the similarity degree. Thus the GRA is mainly used to
reduce uncertainty in the distance measure between two software projects for both continuous and categorical features. Both
techniques are suitable when relationship between effort and other effort drivers is complex. Experimental results showed
that using integration of GRA with FL produced credible estimates when compared with the results obtained using Case-Based
Reasoning, Multiple Linear Regression and Artificial Neural Networks methods. 相似文献
4.
5.
Neagu E.R. Marat-Mendes J.N. 《Dielectrics and Electrical Insulation, IEEE Transactions on》2004,11(2):249-254
By sequential use of the isothermal charging, the isothermal discharging, the final thermally stimulated discharge current and the final isothermal discharging current techniques, the charge dynamics in highly insulating materials may be investigated. The method is demonstrated for polyethylene terephthalate. The injected charge for a field of 20 MV m/sup -/1 and polarization temperatures up to 110/spl deg/C is almost totally trapped in the material and is released during the heating of the sample at 180/spl deg/C for a sufficiently long time. A significant current at high temperatures, about 90/spl deg/C above the poling temperature, was observed proving that it originates from charge detrapping. The final thermally stimulated discharge current peaks shift to higher temperature when the polarization temperature increases, and are characterized by activation energies in the range from 1.03 to 1.56 eV. They allowed the identification of the glass transition around 114/spl deg/C. The relaxation time of the trapped charge, at 180/spl deg/C, was determined to be about 3780 s, explaining the very good stability of trapped charge. 相似文献
6.
C. Tsonos A. KanapitsasD. Triantis C. AnastasiadisI. Stavrakas P. PissisE. Neagu 《Ceramics International》2011,37(1):207-214
The main purpose of this work is to study the dielectric response of commercial low voltage ZnO varistors by means of dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC) in a wide temperature range. Four relaxation processes have been studied here and all of them demonstrate Cole-Davidson behaviour. The first two faster relaxation mechanisms are known processes in ZnO varistors and those are related to the ZnO bulk traps. The next one faster relaxation mechanism attributed to the MWS polarization which should be related to the intergranular Bi-rich microregions. The remaining slower relaxation mechanism is associated to the grain boundaries interfaces. Based on the block model for the ZnO varistor a gradual reduction in the total depletion width is observed at a temperature about 330 K, which can be considered that is due to the gradual decrease of the interface states density at this temperature region. 相似文献
7.
Paul-Mihai Boarescu Ioana Boarescu Raluca Maria Pop tefan Horia Roian Ioana Corina Bocan Vasile Rus Rzvan Olimpiu Mada Iulia Diana Popa Nicholas Neagu Adriana Elena Bulboac Anca Dana Buzoianu Sorana D. Bolboac 《International journal of molecular sciences》2022,23(3)
The present study aims to compare the oxidative stress biomarkers, pro-inflammatory cytokines, and histological changes induced by three cardiovascular risk factors, namely, hypertension, dyslipidemia, and type 1 diabetes mellitus. Hypertension was induced with 40 mg/kg body weight (b.w.) of N omega-nitro-L-arginine-methyl (L-NAME) administered orally. Dyslipidemia was induced by the administration of a diet with a high cholesterol (2%) content. Diabetes mellitus was induced by intraperitoneal administration of a single dose of streptozocin (65 mg/kg). Malondialdehyde (MDA) and total oxidative status (TOS) are increased by all three cardiovascular risk factors (up to 207%). The indirect assessment of NO synthesis (NOx) is observed to be reduced after L-NAME administration (43%), and dyslipidemia induction (16%), while type 1 diabetes mellitus is associated with the highest levels of NOx (increased 112%). Hypertension, dyslipidemia, and type 1 diabetes reduced the total antioxidative capacity (TAC) and total thiol (SH) levels (up to 57%). The values of evaluated pro-inflammatory cytokines, tumour necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), assessed from the ascending aorta were elevated by all three cardiovascular risk factors, with the highest levels induced by type 1 diabetes mellitus (up to 259%). The histopathological examination of the ascending and descending aorta revealed reversible pro-atherogenic changes consisting of the accumulation of lipid droplets in the subendothelial connective tissue on rats with hypertension and dyslipidemia. Irreversible pro-atherogenic changes consisting of a reduction of the specific elasticity of the arteries were observed in rats with type 1 diabetes mellitus. Type 1 diabetes mellitus demonstrates an alteration of the oxidative stress parameters, the elevation of tissue levels of the pro-inflammatory cytokines and causing irreversible pro-atherogenic changes on the aortic wall. 相似文献
8.
Adriana Barsanescu Rodica Buhaceanu Viorica Dulman I. Bunia Violeta Neagu 《应用聚合物科学杂志》2004,93(2):803-808
Adsorption of Zn(II) ions from diluted aqueous solutions by the acrylic copolymer based on ethylacrylate : acrylonitrile : divinylbenzene matrix with different crosslinking degrees and ethylenediamine and triethylenetetramine functional groups was investigated. Adsorption experiments were carried out by batch method. The effects of the pH, initial concentration of zinc, time of contact, and the crosslinking degree of the copolymers were studied. On the basis of Langmuir and Freundlich isotherms, the parameters that characterize the adsorption were determined. The maximum Zn(II) retention capacity value (500 mg g?1) was obtained for the acrylic copolymer with 2% crosslinking degree and ethylenediamine, as functional groups. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 803–808, 2004 相似文献
9.
Marcus Vinícius Tavares da Costa Cristian Neagu Pierre Fayet Urban Wiklund Hu Li Klaus Leifer E. Kristofer Gamstedt 《Journal of Coatings Technology and Research》2018,15(4):743-752
A key engineering parameter of thin coatings is their stiffness. Stiffness characterization of ultrathin coatings with a nanometer scale thickness is experimentally challenging. In this work, three feasible methods have been used to estimate the Young’s modulus of metal coatings on polymer films. The methods are: (1) nanoindentation, (2) strain-induced elastic buckling and (3) peak-force measurements integrated in atomic force microscopy. The samples were prepared by atomic layer deposition of TiO2 (6 and 20 nm thick) and mixed oxides of TiO2 and Al2O3 (4 and 20 nm thick). The differences in estimated Young’s modulus are interpreted in terms of the underlying assumptions and test conditions. Their specific advantages and drawbacks are also compared and discussed. In particular, the nanoindentation necessitates a sufficiently sharp indenter tip to make localized measurements dominated by the coating. The strain-induced elastic buckling method is simple in practice, but showed a large scatter due to variation in local coating thickness and irregular deformation patterns. The stiffness characterization using atomic force microscopy gave the most consistent results, due to a sharp tip with a radius comparable to the thinnest coating thickness. All methods gave a higher Young’s modulus for the TiO2 coating than for the mixed oxide coating, with a variation within one order of magnitude between the methods. 相似文献
10.
Synthesis and characterization of quaternary PtRuIrSn/C electrocatalysts for direct ethanol fuel cells 总被引:1,自引:0,他引:1
K. Fatih V. Neburchilov V. Alzate R. Neagu H. Wang 《Journal of power sources》2010,195(21):7168-10631
To find a more durable anode with high performance for direct ethanol fuel cells (DEFCs), the present study investigates a series of quaternary electrocatalysts, Pt30Ru30Ir40−xSnx/C (wt.%), for the ethanol electro-oxidation reaction (EOR). The carbon-supported Pt30Ru30Ir40−xSnx/C electrocatalysts were prepared by a known impregnation-reduction (borohydride) method. The microstructure and chemical composition were determined by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX) and transmission electron microscopy (TEM). The activity of the electrocatalysts for EOR was compared to commercial Pt67Ru33/C (HISPEC5000) using linear sweep voltammetry (LSV) based on similar Pt loading. The results of this study show that electrocatalyst composition with 10 and 20% Ir (wt.%) exhibit higher electrocatalytic activity than the commercial PtRu electrocatalyst. The single fuel cell testing at 90 °C comparing Pt30Ru30Ir40−xSnx/C to commercial Pt67Ru33/C and Pt83Sn17/C anodes showed an enhancement of Pt activity (normalized to Pt loading) in the following order: Pt30Ru30Ir10Sn30 > Pt30Ru30Sn40 ≥ Pt30Ru30Ir40 ≥ Pt83Sn17 > Pt67Ru33. After a long-term performance test, the activity changed to the following order: Pt30Ru30Ir10Sn30 > Pt30Ru30Ir40 > Pt30Ru30Sn40 > Pt83Sn17 > Pt67Ru33. Pt30Ru30Ir10Sn30/C exhibited both a higher performance with a specific power density of 29 mW mgPt−1 without O2 backpressure at the cathode and an excellent long-term stability in a DEFC operating at 90 °C. 相似文献