Toward computational design of efficient plasticizers for nylon

Polyamides are semi‐crystalline polymers useful in a wide range of applications in the plastics industry. Some applications require higher flexibility and workability of the polyamides. Therefore, plasticizers are added to ease compounding and processing procedures and produce the desired product properties. The goal of the present study was to use computational tools to estimate plasticizer efficiency in plasticizing nylon 66/6. It is known that plasticizer efficiency is greatly influenced by structural effects of the plasticizer and the nature of the polymer, and therefore in this research, a systematic study is reported to explore these factors. A homology series of esters of 4‐hydroxybenzoate with various chain lengths of the alcohol moiety was examined. Also, the efficiency of linear plasticizers was compared to branched ones and stereoisomers were considered. Plasticizer efficiency was determined by calculating cohesive energy density (CED), solubility parameters, free volume and interaction intensities of pristine nylon and the nylon–plasticizer blends. It was found that plasticizer efficiency of esters with linear alcohol moiety is higher than branched chains. Whereas plasticizer efficiency increases when the branched side chain is more bulky, no coherent trend was observed for the linear side chain of the alcohol moiety. Surprisingly, a significant difference was observed between the pair of enantiomers. The most efficient plasticizer of the eight examined was the chiral molecule (R)‐2‐Methylbutyl‐4‐Hydroxybenzoate (R‐MB4HB), increasing the free volume of the nylon by 60‐fold (3‐fold greater than the original Methyl 4‐Hydroxybenzoate (M4HB)). Copyright © 2013 John Wiley & Sons, Ltd.     

Allostatic load as a complex clinical construct: A case‐based computational modeling approach

Allostatic load (AL) is a complex clinical construct, providing a unique window into the cumulative impact of stress. However, due to its inherent complexity, AL presents two major measurement challenges to conventional statistical modeling (the field's dominant methodology): it is comprised of a complex causal network of bioallostatic systems, represented by an even larger set of dynamic biomarkers; and, it is situated within a web of antecedent socioecological systems, linking AL to differences in health outcomes and disparities. To address these challenges, we employed case‐based computational modeling (CBM), which allowed us to make four advances: (1) we developed a multisystem, 7‐factor (20 biomarker) model of AL's network of allostatic systems; (2) used it to create a catalog of nine different clinical AL profiles (causal pathways); (3) linked each clinical profile to a typology of 23 health outcomes; and (4) explored our results (post hoc) as a function of gender, a key socioecological factor. In terms of highlights, (a) the Healthy clinical profile had few health risks; (b) the pro‐inflammatory profile linked to high blood pressure and diabetes; (c) Low Stress Hormones linked to heart disease, TIA/Stroke, diabetes, and circulation problems; and (d) high stress hormones linked to heart disease and high blood pressure. Post hoc analyses also found that males were overrepresented on the High Blood Pressure (61.2%), Metabolic Syndrome (63.2%), High Stress Hormones (66.4%), and High Blood Sugar (57.1%); while females were overrepresented on the Healthy (81.9%), Low Stress Hormones (66.3%), and Low Stress Antagonists (stress buffers) (95.4%) profiles. © 2015 Wiley Periodicals, Inc. Complexity 21: 291–306, 2016     

On modifying properties of polymeric melts by nanoscopic particles

We study geometric and energetic factors that partake in modifying properties of polymeric melts via inserting well‐dispersed nanoscopic particles (NP). Model systems are cis‐1,4‐polybutadiene melts including a single atomic clusters of size varied in the range 10–150 atoms (3–7 Å in radius; 0.1–1.5% v/v). We modify the interactions between the chains and the particle by tuning attractive van der Waals interactions. Using molecular dynamics, we study equilibrium fluctuations and dynamical properties at the interface. The NPs move in the polymer matrix in two different regimes corresponding to trapped and free diffusion, depending on the NP size. Furthermore, degree of crowding around the NP by the polymer chains is quantified. Effect of NP size and interaction strength both on volume and volumetric fluctuations is manifested in mechanical properties, quantified here by bulk modulus, K. Tuning NP size and nonbonded interactions results in ～15% enhancement in K by addition of a maximum of 1.5% v/v NP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Sonocatalytic degradation of Acid Blue 92 using sonochemically prepared samarium doped zinc oxide nanostructures

Pure and Sm-doped ZnO nanoparticles were synthesized applying a simple sonochemical method. The nanocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) techniques which confirmed the successful synthesis of the doped sonocatalyst. The sonocatalytic degradation of Acid Blue 92 (AB92), a model azo dye, was more than that with sonolysis alone. The 6% Sm-doped ZnO nanoparticles had a band gap of 2.8 eV and demonstrated the highest activity. The degradation efficiency (DE%) of sonolysis and sonocatalysis with undoped ZnO and 6% Sm-doped ZnO was 45.73%, 63.9%, and 90.10%, after 150 min of treatment, respectively. Sonocatalytic degradation of AB92 is enhanced with increasing the dopant amount and catalyst dosage and with decreasing the initial AB29 concentration. DE% declines with the addition of radical scavengers such as chloride, carbonate, sulfate, and tert-butanol. However, the addition of enhancers including potassium periodates, peroxydisulfate, and hydrogen peroxide improves DE% by producing more free radicals. The results show adequate reusability of the doped sonocatalyst. Degradation intermediates were recognized by gas chromatography–mass spectrometry (GC–MS). Using nonlinear regression analysis, an empirical kinetic model was developed to estimate the pseudo-first-order constants (k_app) as a function of the main operational parameters, including the initial dye concentration, sonocatalyst dosage, and ultrasonic power.     

Quantitative modeling and mapping of blistering zone of the Magoksa Temple stone pagoda (13th century,Republic of Korea) by graduated heating thermography

Blistering occurring at the stone’s subsurface layer is easily overlooked compared to different deterioration types, so conservation treatments are not applied often. Therefore, non-destructive detection and mapping of blistering zones with the infrared thermography are very important for preservation of the original forms of stone monuments. In this study, the critical temperature and transitional zone of the blistering zone were established by drawing the temperature distribution curve and the mapping for blistering zone was completed by monochrome process and extraction of vector lines. Analysis of the blistering deterioration degree of the Magoksa Temple stone pagoda with the quantitative modeling yielded a total area and average rate of blistering zones of approximately 2.6 m² and 7.4%, respectively. Thus, there is a high probability of scaling on the stone pagoda (area of approximately 2.6 m²) if conservation treatment is not applied to the blistering zones as early as possible. Therefore, the blistering zones require joining and filling, and state changes of the blistering zones should be continuously monitored after completion of the intensive conservation treatments. Modeling will improve the reliability of deterioration maps by mapping for blistering zone; most deterioration maps to date have overlooked blistering zones.     

Study of electron-vibrational interaction and concentration quenching effect of Cu+ ions in lithium based sulphate phosphors

The objective of this work is to study electron-vibrational interaction (EVI) and concentration quenching and their manifestation in experimental photoluminescence spectra of Cu⁺ ion in various lithium based phosphors namely, Li₂SO₄, LiNaSO₄ and LiKSO₄. The main parameters of EVI, such as the Stokes shift, Huang-Rhys factor and zero-phonon line positions, were estimated. The studied systems shows strong electron lattice coupling. The validity of results was established by modeling the shape of the emission spectra, which was found to be in good agreement with experimental photoluminescence spectra. The concentration quenching study is also carried out for these compounds. The studied systems correspond to the nearest neighbor energy transfer mechanism.     

鲍曼不动杆菌LpxC的同源模建及分子对接

鲍曼不动杆菌已成为最普遍的医院致病菌,且耐药情况严峻.LpxC作为新抗菌药物靶点被大量研究,但鲍曼不动杆菌LpxC晶体尚未解析得到,基于其结构的药物设计等工作无法开展.以铜绿假单胞菌LpxC晶体结构为模板,通过同源模建方法获得鲍曼不动杆菌LpxC结构模型.较好的Ramachandran plot分布和Profile-3D结果验证了模型的合理性.用分子动力学模拟优化鲍曼不动杆菌LpxC模型,修补部分不合理构象.后续分子对接结果显示S构型的苄氧乙酰基羟肟酸类抑制剂比R构型分子能更有效地结合在F191,H237和K238组成的较浅口袋中,这可能是S构型抑制剂活性更高的主要因素,模拟结果与实验数据吻合较好.     

数学建模思想渗入大学数学课堂教学的试验研究

以高等数学课堂教学为例,通过科学试验的方法分析数学建模思想渗入大学数学课堂教学对学生学习的影响力。通过精心设计教学试验,采集大量试验数据进行建模分析,结果表明,数学建模思想渗入高等数学课堂教学会对学生的学习产生积极影响,值得推广并长期坚持。