辐射交联聚合物的结晶动力学(英文)

电离辐射在工业上应用的基础是聚合物的辐射交联,它们是绝缘电线和电缆的交联,热收缩性材料的生产,泡沫塑料等等。辐射引发交联已经被广泛地研究,特别是凝胶的形成和聚合物结构、辐照条件对交联度的影响。对于一般法和辐射法交联的聚合物却很少有人研究它的结晶过程。例如,已经证明除了在非常高的吸收剂量外,辐照的聚乙烯中总的结晶度不受影响,但对于聚丙烯和聚丁烯在凝胶点剂量时,它们的结晶度大大减少。辐照聚合物的重新熔融,进一步减少了总结晶度。 本工作表明不仅总的结晶度而且结晶动力学也受辐射引发交联的影响。结晶速率指出结晶划分成二种不同增长机理的过程。冷却速率是一个重要的因素,它决定结晶过程并影响与交联的半晶聚合物的结晶度和形态有关的其它性质。     

Prodrug-Based Targeting Approach for Inflammatory Bowel Diseases Therapy: Mechanistic Study of Phospholipid-Linker-Cyclosporine PLA2-Mediated Activation

Therapeutics with activity specifically at the inflamed sites throughout the gastrointestinal tract (GIT) would be a major advance in our therapeutic approach to inflammatory bowel disease (IBD). We aimed to develop the prodrug approach that can allow such site-specific drug delivery. Currently, using cyclosporine as a drug of choice in IBD is limited to the most severe cases due to substantial systemic toxicities and narrow therapeutic index of this drug. Previously, we synthesized a series of a phospholipid-linker-cyclosporine (PLC) prodrugs designed to exploit the overexpression of phospholipase A₂ (PLA₂) in the inflamed intestinal tissues, as the prodrug-activating enzyme. Nevertheless, the extent and rate of prodrug activation differed significantly. In this study we applied in-vitro and modern in-silico tools based on molecular dynamics (MD) simulation, to gain insight into the dynamics and mechanisms of the PLC prodrug activation. We aimed to elucidate the reason for the significant activation change between different linker lengths in our prodrug design. Our work reveals that the PLC conjugate with the 12-carbon linker length yields the optimal prodrug activation by PLA₂ in comparison to shorter linker length (6-carbons). This optimized length efficiently allows cyclosporine to be released from the prodrug to the active pocket of PLA₂. This newly developed mechanistic approach, presented in this study, can be applied for future prodrug optimization to accomplish optimal prodrug activation and drug targeting in various conditions that include overexpression of PLA₂.     

Comparative study of hydraulic structures alternatives using promethee II complete ranking method

Hydraulic structures have a direct, strong and long-lasting impact on the economy and society in general. Providing the proper structural solution implies finding a balance between economic, environmental and social requirements while decisions taken are associated with serious and irreversible consequences. Optimization techniques play a key role in finding the right solution. In this paper, for a selected stretch of a river, PROMETHEE complete ranking method was employed for selecting the appropriate solution for river training works. This study goal is to determine the level of agreement and to test the sensitivity of the results obtained by two techniques ELECTRE simplified and PROMETHEE method - subjective and objective approach to determining the criterion weight. Findings confirm the justification of implementing both optimization techniques, particularly in the pre-feasibility studies. These techniques still have important implementation and development possibilities, although they have not yet been largely accepted by the engineering community.     

Synthesis of Strictly Alternating Siloxane Copolymers and Cyclics

Herein we report a “One-Pot” synthetic route for preparing 1,1,5,5-tetramethyl-3,3,7,7-tetraphenyl cyclo-tetrasiloxane and strictly alternating poly(dimethylsiloxane-alt-diphenylsiloxane) copolymers by heterofunctional poly-condenzation of diphenylsilanediol with dichlorodimethylsilane in the presence of two different amines, triethylamine and diethylamine, respectively. The products have been characterized by single-crystal X-ray diffraction, ¹H, ¹³C and ²⁹Si nuclear magnetic resonance spectroscopy, thermogravimetric analysis and differential scanning calorimeter.     

Popliteal artery aneurysms

Altogether 59 patients with 76 popliteal artery aneurysms were treated during the last 36 years. There were 50 (85%) male and 9 (15%) female patients with an average age of 61 years. Nineteen (32%) patients had bilateral aneurysms. The clinical manifestations of the aneurysms included ruptures 4 (5.3%); deep venous thrombosis 4 (5.3%); sciatic nerve compression 1 (1.3%); leg ischemia 52 (68.4%), and asymptomatic pulsatile masses 15 (19.7%). Seventy (92%) aneurysms were atherosclerotic, one (1.3%) mycotic, and four (5.3%) traumatic; one (1.3%) developed owing to fibromuscular displasia. Seven (9.2%) small, asymptomatic aneurysms were not operated on. Reconstructive procedures end-to-end anastomosis, graft interposition, bypass) after aneurysmal resection or exclusion using a medial or posterior approach were done in 59 cases. An autologous saphenous vein graft was used in 49 cases, polytetrafluoroethylene (PTFE) in 5, and heterograft in 2 cases. The in-hospital mortality rate was 2.9%, the early patency rate 93.3%, and limb salvage 95%. The long-term patency rate after a mean follow-up of 4 years was 78% and long-term limb salvage 89%. The total limb salvage was 73%, and the total amputation rate was 27%. The dangerous complications associated with popliteal artery aneurysms and the good results after elective procedures suggest that operative treatment is appropriate.     

Studies of the structure of the N-terminal domain from the Y4 receptor - a G protein-coupled receptor - and its interaction with hormones from the NPY family

Binding of peptide hormones to G protein-coupled receptors is believed to be mediated through formation of contacts of the ligands with residues of the extracellular loops of family 1 GPCRs. Here we have investigated whether additional binding sites exist within the N-terminal domain, as studied in the form of binding of peptides from the neuropeptide Y (NPY) family to the N terminus of the Y4 receptor (N-Y4). The N-terminal domain of the Y4 receptor has been expressed in isotopically enriched form and studied by solution NMR spectroscopy. The peptide is unstructured in solution, whereas a micelle-associated helical segment is formed in the presence of dodecylphosphocholine (DPC) or sodium dodecylsulfate (SDS). As measured by surface plasmon resonance (SPR) spectroscopy, N-Y4 binds with approximately 50 microM affinity to the pancreatic polypeptide (PP), a high-affinity ligand to the Y4 receptor, whereas binding to neuropeptide Y (NPY) and peptide YY (PYY) is much weaker. Residues critical for binding in PP and in N-Y4 have been identified by site-directed mutagenesis. The data indicate that electrostatic interactions dominate and that this interaction is mediated by acidic ligand and basic receptor residues. Residues of N-Y4 are likely to contribute to the binding of PP, and in addition might possibly also help to transfer the hormone from the membrane-bound state into the receptor binding pocket.     

Impact of nanotechnology advances in ICT on sustainability and energy efficiency

Urbanization, sustainability, energy efficiency, information and communication technology (ICT) and nanotechnology are emerging at the beginning of the 21st century. They are seeking to improve environmental effectiveness in the context of connected communities, global competitiveness, economic development, climate change, and demographic shifts. Virtually all proposed solutions to energy consumption and climate change acknowledge the role ICT plays as a key enabler of environmental effectiveness. One of the major challenges that the ICT sector faces today is that hardware is being pushed to its physical limits. The traditional means to reduce product size, increase functionality and enhance computing capabilities are becoming difficult and expensive every passing day. On the other hand, the industry is benefiting from nanotechnology advances with numerous applications including those in smarter sensors, logic elements, computer chips, memory storage devices, optoelectronics, quantum computing, etc. This paper presents an overview of the ICT benefiting from development in nanotechnology with respect to sustainability and energy efficiency.     

Multi criteria Analysis of Hydraulic Structures for River Training Works

Traditional selection of structural solutions in river training works are mainly focused on basic requirements as flood protection, coastal protection, protection of the river bed, providing the space for economic development. These solutions may lead to environmental degradation, i.e. alteration of physical-chemical and structural characteristics of the natural components of the environment, decrease of diversity and biological productivity of natural and anthropogenic ecosystems, impacts on the ecological balance and quality of life. These negative effects are also caused by the poor management and use of water, as well as inappropriate planning of the territory in general and river channels in particular. The main goal of this study was to present the approach for selection of hydraulic structures using multi criteria analysis, which would in addition to the basic requirements provide the ecological development of rivers and coastal rivers in accordance with the objective of ??sustainable development??. For comparative review of alternative engineering solutions simplified ELECTRA method is applied.     

Rheological behavior of highly filled ethylene propylene diene rubber compounds

The rheological behavior of highly filled ethylene propylene diene rubber (EPDM) compounds was studied with respect to the effect of curative system, grafted rubber, shear rate, temperature and die swell using a Monsanto Processability Tester (MPT) to gain an understanding of the molecular parameters that control the surface finish. All systems show pseudoplastic behavior. At a particular shear rate, shear viscosity increases with blend ratio. The dependence of flow behavior on extrusion velocity indicates a surface effect. The extrudate die swell and maximum recoverable deformation are related by a linear relationship, which is independent of sulfur/accelerator ratio, extrusion temperature and shear rates and blend ratio. The principal normal stress difference increases nonlinearly with shear stress. Activation energy decreases with shear rate in most cases. The faster relaxing system produces extrudate of better surface quality.