Biphasic responses in multi-site phosphorylation systems

Multi-site phosphorylation systems are repeatedly encountered in cellular biology and multi-site modification is a basic building block of post-translational modification. In this paper, we demonstrate how distributive multi-site modification mechanisms by a single kinase/phosphatase pair can lead to biphasic/partial biphasic dose–response characteristics for the maximally phosphorylated substrate at steady state. We use simulations and analysis to uncover a hidden competing effect which is responsible for this and analyse how it may be accentuated. We build on this to analyse different variants of multi-site phosphorylation mechanisms showing that some mechanisms are intrinsically not capable of displaying this behaviour. This provides both a consolidated understanding of how and under what conditions biphasic responses are obtained in multi-site phosphorylation and a basis for discriminating between different mechanisms based on this. We also demonstrate how this behaviour may be combined with other behaviour such as threshold and bistable responses, demonstrating the capacity of multi-site phosphorylation systems to act as complex molecular signal processors.     

A biomimetic mesoporous silica–polymer composite scaffold for bone tissue engineering

A biomimetic organic–inorganic composite system comprising of microspheres fabricated from combination of a biodegradable polymer poly(lactide-co-glycolide) (PLGA) and bioactive mesoporous silica (SBA-15) has been developed through sintering technique for bone regeneration applications. The morphological and structural properties of the SBA-15/PLGA composite scaffold were evaluated using electron microscopy and fourier transform infrared spectroscopy and the results showed spherical morphology and composite nature. The presence of mesopores in the silica was confirmed through nitrogen adsorption–desorption isotherms. The surface area and pore size of mesoporous silica were found to be 792 m² g^?1 and 3.7 nm, respectively. The thermal characteristics of the SBA-15/PLGA composites studied using thermogravimetry analysis shows a weight loss of around 80% with the degradation occurring at 324?°C. The prepared scaffold is also found to support the adhesion and proliferation of osteoblast cells. The expression of specific bone markers is significantly enhanced in the SBA-15/PLGA composite scaffold when compared with the pristine polymeric scaffold indicating the positive effect of mesoporous silica. Hence, these SBA-15/PLGA composite scaffolds can be explored further for bone regeneration applications.     

Lift force in bubbly suspensions

Closure relations are presented for the lift coefficient for ordered arrays of 2-D and 3-D bubbles at various bubble volume fractions. These were determined via lattice Boltzmann simulations of bubble rise in periodic boxes, where the bubbles were also subjected to shear. The single-bubble lift coefficient, determined by low-shear computational experiments, varies in a systematic manner with the aspect ratio of the bubbles. At high shear rates the lift coefficient manifested a noticeable shear rate-dependence and it could even become negative. Through a linear stability analysis of the uniformly bubbling state, it is demonstrated that the lift force can destabilize a uniformly rising array of highly distorted bubbles and give way to columnar structures.     

ATH浓度对PP/ATH复合材料力学性能的影响(英文)

ATH被广泛添加到聚丙烯(PP)中用于制成阻燃复合材料。PP/ATH复合材料比纯PP材料更具防火性。材料中成分的比例最终取决于应用要求。已有文献对这种复合材料的阻燃性能的提高进行了研究,但对机械强度的影响还没有涉及。本文研究了ATH浓度对PP/ATH复合材料的影响,利用实验测试、ASTM分析公式和有限元方法研究了材料的拉伸、弯曲和断裂特性。研究结果表明:增加ATH对材料的机械强度有不利的影响。     

Effect of concentration of ATH on mechanical properties of polypropylene/aluminium trihydrate (PP/ATH) composite

Aluminium trihydrate (ATH) is being extensively added to polypropylene (PP) to make a fire retardant composite. Blends of PP/ATH composite are more fire resistant as compared to pure PP. Percentage proportion of both the constituents in the final composite depends upon the application. Improvement in the fire retardant properties of such composites have been studied and published in literature but effects on mechanical strength have not been addressed. The effect of concentration of ATH on the strength of PP/ATH composite was presented. The tensile, flexural and fracture properties were studied and discussed. Experimental tests, ASTM analytical formulae and finite element approach were used. It has been found that increase in ATH has an inverse effect on the mechanical strength.     

A Local Damage Approach to Predict Crack Initiation in Type AISI 316L(N) Stainless Steel

A local damage approach based on plastic strain equivalent to uniform strain and grain diameter of the material is proposed for prediction of crack initiation. Plane strain, plane stress, and 3D FEM simulations are carried out for compact tension (CT) geometry with blunt notch of different a/W ratios under mode-I loading. Elastic-plastic fracture parameters have been estimated based on certain assumptions on blunting at notch tip and micromechanisms of events leading to onset of crack. The various crack initiation parameters evaluated based on proposed local damage approach and initial assumptions have been verified by conducting experiments on CT specimens and subsequent scanning electron microscopy study on fracture surface. The laboratory scale experimental results of AISI 316L(N) stainless steel material are in good agreement with FEM-predicted fracture parameters for notch type of stress raisers. The local damage approach and FEM procedure established in the present study would be easily extendable to the analysis of stress raisers in components for the prediction of crack initiation under elastic-plastic condition.     

A Study on Thermal Conductivity and Stability of Nanofluids Containing Chemically Synthesized Nanoparticles for Advanced Thermal Applications

This study presents easy methods of synthesizing silver (Ag) and copper (Cu) nanoparticles through chemical route in an aqueous medium under atmospheric condition at ambient temperature. The synthesized nanoparticles have been characterized with different techniques, such as x-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive x-ray spectroscopy, high-resolution transmission electron microscopy, UV–visible spectroscopy and dynamic light scattering measurements. Experimental observations have revealed the absence of any metal oxide layer around the nanoparticles which are found to remain stable under ambient conditions. The featured properties, such as narrow size distribution, stability, make these nanoparticles potential candidates for the synthesis of effective nanofluids. The nanofluids have been prepared by dispersing the nanoparticles synthesized through chemical route in a suitable base fluid. The thermal conductivity of nanofluids with different nanoparticles loading has been measured by transient hot-wire method, and the results have shown that the increasing trend of enhancement in thermal conductivity with respect to nanoparticles concentration is attainable only when the nanoparticles concentration is below some limiting value depending on the type of nanofluid. Beyond this limiting value of loading, the thermal conductivity of the nanofluid decreases due to pronounced agglomeration effect. The measurements of thermal conductivity of nanofluids over varying temperatures for a given volume fraction loading of nanoparticles have shown that the thermal conductivity increases markedly with the increase in temperature. Hence, nanofluids are likely to be much more promising at high-temperature applications.     

Oxidative Heck Coupling Using Pd(II) Supported on Organosilane-Functionalized Silica Mesocellular Foam

Oxidative Heck couplings of arylboronic acids and olefins are carried out under air to facilitate reoxidation of palladium without the need for an added co-oxidant using Pd(II) supported on silica surface-tethered bipyridyl, iminopyridine, or 3-aminopropyl ligands. Use of silica-supported iminopyridine or bipyridine ligands gives active catalysts, with the bipyridine-based catalyst being most efficient. The Heck products are formed with high yields and selectivities over the 1,4-addition product, and the silica supported bipyridine-based catalyst is easily recovered via simple filtration. Unlike similar supported catalysts in traditional Heck reactions involving aryl halides and olefins, the catalysts presented here can be used for multiple catalytic cycles without activity or selectivity loss.     

Performance of higher poly(alkyl lactate acrylate)s as viscosity modifiers in vegetable oils

Recently, bio-derived materials such as vegetable oils are significantly employed in lubricating oil formulations due to its high flash point, high lubricity, low evaporation loss, renewability, biodegradability, and eco-friendliness when compared to mineral oil. We investigated the performance of seven poly(alkyl lactate acrylate)s as viscosity modifiers in two vegetable oils, namely, coconut oil and sunflower oil, which differ in the percentage of polar compounds and degree of unsaturation. Poly(alkyl lactate acrylate)s having alkyl as hexyl to dodecyl group in different concentrations between 1 and 2 wt% were added to coconut and sunflower oil and parameters such as thickening power or Q factor, kinematic viscosity (μ), and viscosity index (VI) were calculated. The μ values at 40°C and 100°C of vegetable oils studied were lower than commercially available SAE20W40 engine oil, but the VI of coconut and sunflower oil was higher by about 22%. Value of Q factor higher than 1, indicated that these poly(alkyl lactate acrylate)s were VI improvers. VI increased with increase in the polymer concentration in both the vegetable oils. The length of the alkyl side chain of these polymers and the polarity of vegetable oil had predominant effect in determining the values of VI of vegetable oils. By using these polymer additives, VI was improved by 85.5% in coconut oil and by 61.7% in sunflower oil. Varying the concentration and alkyl group of these additives, one can largely modify the viscosity ranges enabling them to be used in different lubricating applications.