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排序方式: 共有157条查询结果,搜索用时 234 毫秒
1.
Ö. Jonsson T. Larsson M. Rönnqvist 《Structural and Multidisciplinary Optimization》1994,7(1-2):103-111
An efficient and commonly used approach to structural optimization is to solve a sequence of approximate design problems that are constructed iteratively. As is well-known, a major part of the computational burden of this scheme lies in the sensitivity analysis needed to state the approximate problems. We propose a possibility for reducing this burden by streamlining the calculations in a combined approximation and duality scheme for structural optimization. The difference between this scheme and the traditional one is that, instead of calculating all the constraint gradients to state an approximate design problem explicitly, linear combinations of these gradients are generated as they are needed during the solution of the approximate problem by the dual method. We show, by analysing some typical scenarios of problem characteristics, that this rearrangement of the calculations may be a computationally viable alternative to the traditional scheme. An advantage of streamlining the calculations is that there is no need to incorporate an active set strategy in the scheme, as is usually done, since all the design constraints may be taken into consideration without any loss of computational efficiency. This may, clearly, enhance the practical rate of convergence of the overall approximation scheme. Moreover, the proposed rearrangement of the calculations may make it computationally viable to apply iterative equation solvers to the structural analysis problem. Numerical results with direct as well as iterative equation solvers show that the streamlined scheme is a feasible and promising approach to structural optimization. 相似文献
2.
H. Ö. Özbelge T. F. Al-Fariss A. M. Abdulrazik 《Nutrient Cycling in Agroecosystems》1993,34(3):217-222
There is an appreciable amount of carbonaceous sedimentary phosphate deposits in the northern Africa and the Middle East which are expected to gain importance in the near future because of the depletion of the deposits in Florida. In many of the regions where phosphate deposits are found there is a shortage of fresh water, and sea is not very far. The use of sea water instead of fresh water in flotation of carbonaceous phosphate rock is successfully demonstrated. Thus an appreciable reduction in the operating cost and an ample amount of saving in the fresh water resources of the region is expected. 相似文献
3.
A steady‐state fluorescence technique was employed to study the swelling of κ‐carrageenan gels at various temperatures. Pyranine was used as a fluorescence probe. The fluorescence intensity of pyranine was measured during the insitu swelling process of κ‐carrageenan gels. The fluorescence intensity increased exponentially as the swelling time increased. The increase in the fluorescence intensity was modeled with the Li–Tanaka equation, from which the swelling time constants and cooperative diffusion coefficients were determined. The swelling time constants decreased and the cooperative diffusion coefficients increased as the swelling temperature was increased. The swelling activation energies were measured to be 47.05 kJ/mol. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
4.
Saziye Ugur Ayse Alemdar Önder Pekcan 《Journal of Coatings Technology and Research》2005,2(7):565-575
This study reports a steady-state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene
(PS) latex and Na-montmorillonite (SNaM) composites. The composite films were prepared from pyrene (P)-labeled PS particles
and SNaM clay at room temperature and annealed at elevated temperatures in 10-min intervals above glass transition temperature
(t3) of polystyrene. During the annealing processes, the transparency of the film improved considerably. Scattered light (Is) and fluorescence intensity (Ip) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of composite
films was monitored by using photon transmission intensity, Itr. Scanning electron microscopy (SEM) was used to detect the variation in physical structure of annealed composite films. Minimum
film formation temperature, Tq, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It
was observed that both activation energies increased as the percent of SNaM was increased in composite films. 相似文献
5.
Sevan Platin Elif Ö. Özer Ugur Akman Öner Hortaçsu 《Journal of the American Oil Chemists' Society》1994,71(8):833-837
Effects of temperature (at 35, 45 or 55°C) and pressure (10–110 atm) on the relative distribution coefficients of the twelve
key components of spearmint oil (essential oil ofMentha cardiaca; Scotch spearmint) at equilibrium in dense CO2 were investigated under conditions ranging from subcritical to supercritical regions. Effects of vapor pressure, molecular
weight and polarity of the key components on their equilibrium distributions in sub/supercritical CO2 are discussed. At 35°C, all key components of spearmint oil are equally soluble in dense CO2 within the 12–102 atm pressure region. At 45 and 55°C, the key components are equally soluble for pressures greater than
about 60 atm. However, around either 45°C/27 atm or 55°C/35 atm conditions, the relative distribution coefficients of all
monoterpene hydrocarbons and of isomenthone (an oxygenated monoterpene) exhibit maxima, which are due to significantly higher
vapor pressures of these components and significantly lower solvating power of the dense-gas solvent at these particular temperatures
and pressures. Vapor-pressure effects, coupled with the decrease in solvating power, dominate the effects of polarity and
molecular mass of the key components. Deterpenation of spearmint oil with dense CO2 is possible around either 45°C/27 atm or 55°C/35 atm, where the monoterpene hydrocarbons tend to concentrate in the CO2-rich phase. 相似文献
6.
Chromium alloys present a potential for development of new high-temperature materials. Precipitation characteristics of a Cr–5Ni–5Al–0.5Ti (at.%) alloy were investigated utilizing a series of heat treatments. XRD, SEM, and analytical TEM were used to characterize the microstructure. This study has shown that the small spherical B2-NiAl precipitates forming below 1345 °C are highly coherent and have a well-defined orientation relationship with the Cr-matrix. Also, some evidence has been presented for the formation of L21-Ni2AlTi phase within the B2-NiAl phase. 相似文献
7.
Meltem Ö. Gürel 《The Journal of Architecture》2013,18(3):215-233
Mundane objects and their everyday practices contain clues to the prevalent ideas and ideals of a society at a certain time; thus holding the power to decipher collective ideologies, contemporary beliefs, social norms and shared values. Bathroom fixtures are such ordinary products of the built environment that seem to be simultaneously insignificant and indispensable parts of daily life. This study is an historical analysis of the bathroom as a social space and of its fixtures as material culture. It reflects ideas and identities around the convoluted notions of modernisation and Westernisation in the Turkish context. It suggests that the values of being modern contributed to the transformation of traditional bathroom practices through spatial mechanisms and equipment. To unpack these values, the study engages the examination of oral histories, literary works, journals and flat plans as well as extant bathrooms. The research shows that the bathroom is a product of global modernity. Mediated through flats, which proliferated as a sign of contemporary living, the Western-style bathroom became the norm while its traditional counterpart became its other. This shift in perception indicates a concern for belonging to the world civilisation in the form of an aspiration toward being Western. A universal idea of modernisation pervades the ordinary domestic space of the bathroom and its everyday practices. 相似文献
8.
UV-Visible (UVV) technique used to monitor powder coating and its dissolution processes from hard latex particles. Three sets
of latex coatings were prepared from poly(methyl methacrylate) (PMMA) particles. The first set of coatings was annealed at
elevated temperatures in various time intervals during which reflected photon intensity, Irf, was measured. The second set of coatings was annealed at various temperatures in 10 min time intervals during which transmitted
intensity, Itr, was measured. Irf first decreased and then increased as the annealing temperature was increased. Decrease in Irf was explained with the void closure mechanism due to viscous flow. Increase in Itr and Irf against time and temperature were attributed to an increase in crossing density at the junction surface. The activation energy
of viscous flow, ΔH, was measured and found to be around 8 kcal/mol and the back and forth activation energies (ΔErf and ΔEtr) were measured and found to be around 49 and 53 kcal/mol for a reptating polymer chain across the junction surface. Diffusion
of solvent molecules (chloroform) into the annealed latex coatings was followed by desorption of PMMA chains for the third
set of films. Desorption of pyrene, P, labeled PMMA chains was monitored in real-time by the absorbance change of pyrene in
the polymer-solvent mixture. A diffusion model with a moving boundary was employed to quantify real-time UVV data. Diffusion
coefficients of desorbed PMMA chains were measured and found to be between 2 and 0.6 × 10−11 cm2 s−1 in the 100 and 275°C temperature range.
Presented at the 2000 Spring Meeting of the PMSE Div. of the American Chemical Society, March 26–30, 2000, San Francisco,
CA.
Dept. of Physics, Maslak 80626 Istanbul, Turkey.
Dept. of Physics, 22030 Edirne, Turkey. 相似文献
9.
Zekeriya Doğruyol Gokhan Temel Sevnur K. Doğruyol Önder Pekcan Nergis Arsu 《Progress in Organic Coatings》2013
Photopolymerization kinetics and conductivity changes of epoxyacrylate composites for various loading modified PSt-MWCNT weight fractions changing from 0.0025 to 0.2 wt.% were evaluated by performing photo differential scanning calorimetry (photo-DSC) and four point conductivity measurements. 0.2% PSt-MWCNT additive polymeric films had their electrical conductivity boosted by 6% more than non-additive polymeric films. 相似文献
10.
In situ photon transmission experiments were performed using UV‐visible (UVV) spectrometer during the drying of polyacrylamide (PAAm) gels. These gels are formed from acrylamide (AAm) with various N,N′‐methylenebis(acrylamide) (Bis) contents by free radical crosslinking copolymerization (FCC) in water. The transmitted light intensity, Itr increased continuously as PAAm gels are dried. Increase in Itr was attributed to the decrease in the scattered light intensity, Isc, which might be originated from the contrast between “frozen blob clusters” and holes in the drying gel. Decrease in Isc was modeled using Rayleigh's equation, where drying times with various exponents were found to be proportional to the volume of frozen blob clusters. It was observed that the radius of frozen blob cluster (correlation length), ξc increased in various power of time, depending on Bis contents during drying of gels. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1898–1906, 2001 相似文献