The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Ilpo Vattulainen - One of the best experts on this subject based on the ideXlab platform.
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role of sterol type on Lateral Pressure profiles of lipid membranes affecting membrane protein functionality comparison between cholesterol desmosterol 7 dehydrocholesterol and ketosterol
Journal of Structural Biology, 2007Co-Authors: O Samuli H Ollila, Ilpo Vattulainen, Tomasz Rog, Mikko KarttunenAbstract:Lateral Pressure profiles have been suggested to play a significant role in many cellular membrane processes by affecting, for example, the activation of membrane proteins through changes in their conformational state. This may be the case if the Lateral Pressure profile is altered due to changes in molecular composition surrounding the protein. In this work, we elucidate the effect of varying sterol type on the Lateral Pressure profile, an issue of topical interest due to lipid rafts and their putative role for membrane protein functionality. We find that the Lateral Pressure profile is altered when cholesterol is replaced by either desmosterol, 7-dehydrocholesterol, or ketosterol. The observed changes in the Lateral Pressure profile are notable and important since desmosterol and 7-dehydrocholesterol are the immediate precursors of cholesterol along its biosynthetic pathway. The results show that the Lateral Pressure profile and the resulting elastic behavior of lipid membranes are sensitive to the sterol type, and support a mechanism where changes in protein conformational state are facilitated by changes in the Lateral Pressure profile. From a structural point of view, the results provide compelling evidence that despite seemingly minor differences, sterols are characterized by structural specificity.
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Polyunsaturation in lipid membranes: dynamic properties and Lateral Pressure profiles.
The journal of physical chemistry. B, 2007Co-Authors: Samuli Ollila, Marja T. Hyvönen, Ilpo VattulainenAbstract:We elucidate the influence of unsaturation on single-component membrane properties, focusing on their dynamical aspects and Lateral Pressure profiles across the membrane. To this end, we employ atomistic molecular dynamics simulations to study five different membrane systems with varying degrees of unsaturation, starting from saturated membranes and systematically increasing the level of unsaturation, ending up with a bilayer of phospholipids containing the docosahexaenoic acid. For an increasing level of unsaturation, we find considerable effects on dynamical properties, such as accelerated dynamics of the phosphocholine head groups and glycerol backbones and speeded up rotational dynamics of the lipid molecules. The Lateral Pressure profile is found to be altered by the degree of unsaturation. For an increasing number of double bonds, the peak in the middle of the bilayer decreases. This is compensated for by changes in the membrane-water interface region in terms of increasing peak heights of the Lateral Pressure profile. Implications of the findings are briefly discussed.
Ahmed F. Omran - One of the best experts on this subject based on the ideXlab platform.
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Progress to understand influence of reinforcement density on SCC Lateral Pressure
Materials and Structures, 2017Co-Authors: Ahmed F. Omran, Kamal H. KhayatAbstract:In addition to material properties, casting conditions, and formwork characteristics, presence and density of reinforcing bars can play a role on the resulting Lateral Pressure exerted by self-consolidating concrete (SCC) on formwork system. The effect of density of vertical reinforcement and spacing between reinforcing steel and formwork surface (concrete cover) on SCC Lateral Pressure were investigated in this study using laboratory-scale columns measuring 1.4 m in height. The effect of casting rate and concrete structural build-up at rest were also considered. A model was proposed to estimate SCC Lateral Pressure taking into consideration reinforcement density and concrete cover. A 6-m high column cast as part of field experimental study was used to validate the laboratory results. The results showed that the increase in steel reinforcement density placed at relatively small cover of 25 mm can reduce the maximum Lateral Pressure. At casting depth of 3 m and a concrete cover of 25 mm, increasing the reinforcement density from 0.5 to 4%, can reduce Lateral Pressure from 4 to 22%. The Lateral Pressure reduction is less significant when concrete cover increases to 50 mm or at deeper casting depths. A 2–17% Pressure reductions for the 50-mm concrete cover, and 1–7% for the 5-m casting depth can be estimated. Based on the obtained results, a factor accounting for Lateral Pressure reduction due to the inclusion of vertical reinforcement was introduced in the Pressure prediction models proposed by Khayat and Omran (State-of-the-art review of form Pressure exerted by self-consolidating concrete, 2. http://www.concretesdc.org/projects/SCCreport.htm).
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Effect of placement characteristics on SCC Lateral Pressure variations
Construction and Building Materials, 2014Co-Authors: Ahmed F. Omran, Y. M. ElaguabAbstract:Abstract Lateral Pressure exerted by fresh concrete on vertical formwork systems controls significantly the design of the formwork systems. Several factors including, material properties, placement conditions, and formwork characteristics can affect formwork Lateral Pressure. This paper presents the results of an extensive experimental work aimed at studying the influence of concrete temperature (10–32 °C), casting depth (up to 13 m), placement rate (2–30 m/h), waiting period between successive lifts, as well as concrete thixotropy on Lateral Pressure characteristics. The increase of concrete temperature is shown to accelerate the stiffening rate of the concrete leading to reduction in initial Lateral Pressure. For highly thixotropic SCC mixture even at very high casting rate of 30 m/h, the initial Lateral Pressure is limited to 26% of the equivalent hydrostatic Pressure at casting depth of 10 m and to 70% at the shallow casting depth of 3 m. These Pressure values can drop further (about 25%) when the casting rate reduces from 30 to 2 m/h. Interruption of concrete casting with a waiting period of 30 min can reduce Lateral Pressure up to 15%, especially for highly thixotropic concrete.
Y. M. Elaguab - One of the best experts on this subject based on the ideXlab platform.
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Effect of placement characteristics on SCC Lateral Pressure variations
Construction and Building Materials, 2014Co-Authors: Ahmed F. Omran, Y. M. ElaguabAbstract:Abstract Lateral Pressure exerted by fresh concrete on vertical formwork systems controls significantly the design of the formwork systems. Several factors including, material properties, placement conditions, and formwork characteristics can affect formwork Lateral Pressure. This paper presents the results of an extensive experimental work aimed at studying the influence of concrete temperature (10–32 °C), casting depth (up to 13 m), placement rate (2–30 m/h), waiting period between successive lifts, as well as concrete thixotropy on Lateral Pressure characteristics. The increase of concrete temperature is shown to accelerate the stiffening rate of the concrete leading to reduction in initial Lateral Pressure. For highly thixotropic SCC mixture even at very high casting rate of 30 m/h, the initial Lateral Pressure is limited to 26% of the equivalent hydrostatic Pressure at casting depth of 10 m and to 70% at the shallow casting depth of 3 m. These Pressure values can drop further (about 25%) when the casting rate reduces from 30 to 2 m/h. Interruption of concrete casting with a waiting period of 30 min can reduce Lateral Pressure up to 15%, especially for highly thixotropic concrete.
Chang Bing Chen - One of the best experts on this subject based on the ideXlab platform.
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Study on Lateral Pressure of Bulk Materials in Silos
Advanced Materials Research, 2011Co-Authors: Chang Bing ChenAbstract:With the development of modern industry, silo diameters are bigger and bigger. Lateral Pressure of bulk materials in silos is one important parameter for designing silos, which is related to the economy and safety of the structure. However, present calculation methods of the Lateral Pressure are mostly based on small diameter silos. For now, in the Chinese code the wall Pressure computation methods are based on Rankine theory to be calculated. It is shown that the calculated results of Rankine theory may overestimate the Pressure. In this paper, the Lateral Pressure of large diameter silos is studied. A new formula for calculating Lateral static Pressure on shallow silo wall is derived by static equilibrium method. The formula of this paper is simple of calculation and can be used for large diameter silos with a circular con top pile. The results agree with that of the full-sized silo experiment better than the current code.
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Study on Effect of Silo Wall Elasticity on Lateral Pressure Ratio
Advanced Materials Research, 2011Co-Authors: Chang Bing ChenAbstract:Lateral Pressure is a key parameter to silos’ design. It has an important effect on the safety and efficiency of silos. The Lateral Pressure ratios that recommended by some overseas design codes and literatures have been analyzed. These ratios didn’t take into account the elasticity of silo wall, one of which is 28% smaller than the measure value, but another goes up to super Pressure ratio. A new Lateral Pressure ratio is derived by considering the elasticity of silo wall, which is relevant to Passion ratio of stored material and relative stiffness coefficient . The coefficient of usual metal silo varies from 0.01 to 0.2, so it has significance to consider the wall elasticity.
Metin Arslan - One of the best experts on this subject based on the ideXlab platform.
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EFFECTS OF FORMWORK SURFACE MATERIALS ON CONCRETE Lateral Pressure
Construction and Building Materials, 2005Co-Authors: Metin Arslan, Osman Şimşek, Serkan SubaşıAbstract:Abstract In this study, the effect of formwork surface materials on the concrete Lateral Pressure was investigated. Seven wall formworks were constructed. Populus nigra timber, pinus silvestris timber, plywood and steel sheet were used as surface materials for these formworks. One of two formwork, which had the same surface material, was watered except for the steel formwork before placing the concrete. Concrete was placed into the formworks and the Lateral Pressures of concrete on formworks surface were measured by a strain measurement system. As comparison the limiting value of concrete Lateral Pressure was calculated by ACI-347 equation. It was concluded that, watering the surface of wood formworks increased Lateral Pressure of concrete on the formworks. Lateral Pressure of steel formwork was equal to limiting value of ACI-347 and larger than Lateral Pressure of populus nigra, pinus silvestris, and plywood formworks. The Lateral Pressure of pinus silvestris formwork was some less than 3.3%, 7.2%, 21%, respectively, Lateral Pressure of populus nigra, plywood, and steel formwork”.
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Effects of drainer formworks on concrete Lateral Pressure
Construction and Building Materials, 2002Co-Authors: Metin ArslanAbstract:Abstract This study focused on how formwork surfaces affected concrete Lateral Pressure when surface drainage was provided and their surfaces were covered with liners. Seven forms were constructed using different surface materials. On the surfaces of three forms, drainage was provided and different types of geotextile liners were used. The other forms were used as references. For comparison, the Lateral Pressure of concrete was calculated by ACI 347. Concrete was placed into the forms and the Lateral force of concrete on the form surface was measured by a strain gauge measurement system. It was concluded that the concrete Lateral Pressure could be decreased by some 40% using a drainer system on the formwork surface and covering the surface with liner.
