1,722,201 research outputs found
P-Delta effect of slender RC columns under seismic load
No full textThis study investigates the seismic P-Delta effect in slender reinforced concrete (RC) columns on the basis of the layered section method. For an effective analysis of the cyclic behavior of RC columns, which show changes in the load-displacement relationship according to the magnitude of the applied axial force, the layered section approach is adopted, and a procedure for the indirect implementation of the bond-slip effect into the stress-strain relationship of the reinforcing steel is used [Kwak HG, Kim JK. Implementation of bond-slip effect in analyses of RC frames under cyclic loads using layered section method. Engineering Structures 2006;28(12):1715-27]. To verify the validity of the method and to identify the significance of various effects in terms of the global response of the slender RC columns, nonlinear dynamic analyses are conducted for 60 sets of horizontal and vertical earthquakes with practical ranges of slenderness and stability coefficients. On the basis of the obtained numerical results, the influences of axial force, the P-Delta effect and the effect of a vertical earthquake on the structural response are reviewed. Their relative contribution is also assessed. In addition, the applicability of the capacity-demand diagram method in the seismic design of RC structures is reviewed by comparing the results obtained from the introduced method with those from rigorous nonlinear dynamic analyses. (c) 2007 Elsevier Ltd. All rights reserved.The research reported in this paper was made possible by
the financial support from the Smart Infrastructure Technology Centre funded by the Korea Science and Engineering
Foundation and 05CCTRD09-High Performance Construction
Material Research Centre funded by Ministry of Construction
& Transportation of Korean government. The authors would
like to express their gratitude to this organization for the
financial support
COMPATIBILIZATION EFFECT OF A BLOCK-COPOLYMER IN 2 RANDOM COPOLYMER BLENDS
No full textThe stability limit and spinodal points of a multicomponent polymer system have been studied with the structure factors, S-ij(q), which were obtained using the random phase approximation and incompressibility constraint. Emphasis was placed on the effect of the volume fraction of component A,f(I), in a block copolymer, A-block-B, on the spinodal points for macrophase separation of an (A-block-B)(B-ran-C)/(A-ran-D) mixture. The behaviour of the spinodal point for macrophase separation, and thus the compatibilization effect, depends very much on f(I) for given weight fractions of the two homopolymers (or a homopolymer and a random copolymer). The spinodal points of microphase transitions in addition to those of macrophase separation are also discussed.X1114sciescopu
Modulation of hole-injection in GaInN-light emitting triodes and its effect on carrier recombination behavior
Full text linkThe effects of the hole injection modulated by using a three-terminal GaInN-based light emitter, light-emitting triode (LET), on carrier recombination behavior and efficiency droop are investigated. It was found that the lateral electric field created by applying voltage bias between the two anodes effectively reduces efficiency droop as well as dynamic conductance of LETs. Detailed analyses of LETs under various operation conditions by APSYS simulations reveal that the asymmetry in carrier transport between electrons and holes is alleviated by promoted injection of hot holes over the potential barrier, increasing the hole concentration as well as the radiative recombination rate in the multiple quantum well active region. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.110Ysciescopu
NORMATIVE STUDY OF THE KOREAN-CALIFORNIA VERBAL LEARNING TEST (K-CVLT)
No full textAs a normative study of the Korean version of the California Verbal Learning Test (K-CVLT), the present study examined the K-CVLT performances of 357 neurologically intact Koreans (181 males and 176 females) who were selected by stratified sampling reflecting the recent Korean census data. The factor analysis of the K-CVLT showed that the K-CVLT was a valid and useful tool for qualitatively assessing a number of theoretically meaningful processes and strategies underlying verbal memory. Norms were developed on the 22 memory indices separately for gender and age groups. Implications for the K-CVLT's factor analytic results are discussed, and the K-CVLT's normative data is compared with that of the CVLT.X1116sciescopu
RHEOLOGICAL BEHAVIOR OF HOMOGENEOUS POLY(ALPHA-METHYLSTYRENE)-BLOCK-POLYSTYRENE COPOLYMERS
No full textA series of poly(alpha-methylstyrene)-block-polystyrene (P-alpha-MS-PS) copolymers having molecular weights ranging from 120 000 to 250 000 and different block length ratios were synthesized via anionic polymerization. Oscillatory shear flow properties of these block copolymers were measured using a Rheometrics mechanical spectrometer at temperatures ranging from 116 to 251-degrees-C, depending on the block copolymer composition. We have concluded that these block copolymers are homogeneous as determined by differential scanning calorimetry and, also, by logarithmic plots of dynamic storage modulus versus dynamic loss modulus. This conclusion is further supported by the fact that temperature-frequency superposition gives rise to temperature-independent master curves for the block copolymers. In view of the fact that the block copolymers synthesized must be regarded as entangled homogeneous block copolymers, using the concept of the tube model we have modified on an ad hoc basis the Stockmayer-Kennedy molecular viscoelasticity theory which was developed on the basis of the Rouse theory. The predicted zero-shear viscosities of the P-alpha-MS-PS diblock copolymers are compared with experimental results.X1114sciescopu
MEDIATIONAL EFFECT OF SLEEP QUALITY IN THE RELATIONSHIP BETWEEN CIRCADIAN SLEEP PHASE PREFERENCE AND DEPRESSIVE MOOD
No full textX11sciescopu
Interfacial tension measurement with the Neumann triangle method
No full textThe interfacial tensions between polystyrene (PS) and poly(butylene terephthalate)(a) (PBT), PS/poly(methyl methacrylate) (PMMA), and PBT/PMMA pairs have been obtained by employing the Neumann Triangle method (NT). The results are in good agreement with those obtained by the breaking thread method. For the first time, the NT method was applied to a reactive polymer pair with an in-situ compatibilizer to measure the interfacial tension. We found that the interfacial tension of the PS/PBT system with a small amount of poly(styrene-co-glycidyl methacrylate)(b) (PS-GMA) is significantly reduced compared to that without PS-GMA.X1117sciescopu
Fiber orientation and rheological properties of short fiber-reinforced plastics at higher shear rates
No full textFiber orientation and rheological properties of short fiber-reinforced polystyrene at high shear rates were investigated by scanning electron microscopy (SEM) and rheometry. This is the first attempt to observe fiber orientations in samples taken from inside the capillary as well as taken from the extrudate by employing SEM. The fiber orientations near the center of the capillary are similar to those near the wall. Also, the fiber orientations inside the capillary changed very little, even if the shear rate was varied from 25.4 to 3110 s(-1). This is because most fibers near the center as well as near the wall of the barrel are already aligned toward the flow direction before entering the capillary. The possible sources to induce surface roughness of the extrudate or fiber protrusion are discussed. It appears that the surface roughness depends mainly upon the velocity rearrangement at the capillary exit. Interestingly, fiber flexing was seen in the filament taken from the extrudate as well as from inside the capillary, which suggests that this is not likely a dominant source for inducing surface roughness. (C) 2000 Kluwer Academic Publishers.X116sciescopu
The effect of PS-GMA as an in situ compatibilizer on the morphology and rheological properties of the immiscible PBT/PS blend
No full textPoly(styrene-co-glycidyl methacrylate) (PS-GMA) is used as an in situ compatibilizer for incompatible (or immiscible) blends of poly(butylene terephthalate) (PET) and polystyrene (PS). The epoxy group in PS-GMA reacts with the carboxylic acid group in PET, thus PS-graft-PBT copolymer is formed and acts as a compatibilizer between PS and PET during the melt blending. The degree of the reaction is investigated by the observation of the torque change with time at various temperatures, since the torque is directly related to the amount of graft copolymer formed in the mixer. But, the actual temperature in the mixer is higher than the specific setting temperature due to the viscous heating and exothermic reaction with time. Thus, the torque, as obtained from a torque rheometer, must be appropriately compensated based on the reference temperature, which becomes more useful in finding a relationship between the degree of the reaction and the amount of graft copolymer formed. Rheological behaviour of blends having in situ compatibilizer was investigated by dynamic oscillatory shearing measurement. It is shown that as the amount of graft copolymer formed during blending increases, the viscosity at low shear rates increases but the degree of shear thinning is not pronounced. For polymer alloys prepared at the setting temperature of 230 degrees C, the finer morphology was obtained when more than 5 phr PS-GMA was added to PBT/PS blend, but this amount of PS-GMA decreased to 3 phr when the setting temperature in the mixer was increased to 240 degrees C since at higher temperature more graft copolymer can be formed.X1183sciescopu
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