Packaging technology for improving shelf‐life of fruits based on a nanoporous–crystalline polymer

The ability of films with an active layer of nanoporous–crystalline syndiotactic polystyrene (s‐PS) to prolong shelf‐life, not only of climacteric but also of non‐climacteric fruits, is discussed. Studies on oxygen and carbon dioxide concentrations in the environment of packaged fruits as well as in s‐PS active layers have been combined. Reported results indicate that prolonged shelf‐life can be associated with large increases and decreases of carbon dioxide and oxygen concentrations inside the package, respectively. These data are consistent with a higher barrier offered to both gases by nanoporous–crystalline s‐PS layers. This barrier phenomenon is due to reduction of gas diffusivity typical of nanoporous–crystalline polymer films, which is further enhanced by orientation, parallel to the film plane, of crystalline planes of closely packed s‐PS helices. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46256.     

Solution structure of human corticotropin releasing factor by 1H NMR and distance geometry with restrained molecular dynamics

The structure of human corticotropin releasing factor (hCRF)has been determined by proton nuclear magnetic resonance (¹HNMR) in a mixed-solvent system of 66% trifluoroethanol/34% H₂Oat pH 3.8 and 37°C. Nearly complete resonance assignmentwas achieved by using standard two-dimensional methods. Distancerestraints for structure calculations were obtained by qualitativeanalysis of intra- and interresidue nuclear Overhauser effects.Structures were obtained from the distance restraints by distancegeometry, followed by refinement using molecular dynamics andwere completed with amide hydrogen exchange data. The structureof hCRF in this solvent comprises an extended N-terminal tetrapeptideconnected to a well-defined -helix between residues 6 and 36.The first half of the -helix (residues 6–20) is clearlyamphipathic. The five carboxy-terminal residues are predominantlydisordered.     

The Effects of Electronic Impurities and Electron–Hole Recombination Dynamics on Large‐Grain Organic–Inorganic Perovskite Photovoltaic Efficiencies

Hybrid organic‐inorganic perovskites have attracted considerable attention after promising developments in energy harvesting and other optoelectronic applications. However, further optimization will require a deeper understanding of the intrinsic photophysics of materials with relevant structural characteristics. Here, the dynamics of photoexcited charge carriers in large‐area grain organic‐inorganic perovskite thin films is investigated via confocal time‐resolved photoluminescence spectroscopy. It is found that the bimolecular recombination of free charges is the dominant decay mechanism at excitation densities relevant for photovoltaic applications. Bimolecular coefficients are found to be on the order of 10^?9 cm³ s^?1, comparable to typical direct‐gap semiconductors, yet significantly smaller than theoretically expected. It is also demonstrated that there is no degradation in carrier transport in these thin films due to electronic impurities. Suppressed electron–hole recombination and transport that is not limited by deep level defects provide a microscopic model for the superior performance of large‐area grain hybrid perovskites for photovoltaic applications.     

驱动LED串的DCM升压转换器简化分析(1)——理论分析

固定频率升压转换器采用不连续导电模式(DCM)工作,能够有效地用于快速调光操作,提供比采用连续导电模式(CCM工作的竞争器件更优异的瞬态响应,这种转换器非常适合于以恒流模式驱动LED串。但驱动LED的升压转换器的交流分析,与使用标准电阻型负载的升压转换器的交流分析不同,在推导最终的传递函数时必须非常审慎。本文分为两个单元:⑴理论分析,介绍如何推导驱动LED串的升压转换器的小信号响应;⑵实际考虑,深入研究实施方案,并验证经验结果及与理论推导比较。     

Nanodiamond synthesis by pulsed laser ablation in liquids

Pulsed laser ablation in liquids (PLAL) has become an attractive method for the synthesis of nanodiamond. This work deals with the growth kinetics study of structures of nano-diamonds embedded in sp² carbon synthetized by this method. The plasma created by the laser pulse has been monitored by time resolved spectroscopy to analyze the evolution of the plume and therefore the transient species created. Typical C₂ vibrational bands appear, as well as a continuous spectrum due to various phenomena. The study of both the background and the vibrational features gives information on the reaction kinetics and on the plasma density. The presence of nanodiamonds has been confirmed by Raman spectroscopy as well as TEM analysis.     

Optimisation of the aqueous extraction conditions of phenols from meadowsweet (Filipendula ulmaria L.) for incorporation into beverages

Meadowsweet was extracted in water at a range of temperatures (60–100 °C), and the total phenols, tannins, quercetin, salicylic acid content and colour were analysed. The extraction of total phenols followed pseudo first-order kinetics, the rate constant (k) increased from 0.09 ± 0.02 min⁻¹ to 0.44 ± 0.09 min⁻¹, as the temperature increased from 60 to 100 °C. An increase in temperature from 60 to 100 °C increased the concentration of total phenols extracted from 39 ± 2 to 63 ± 3 mg g⁻¹ gallic acid equivalents, although it did not significantly affect the proportion of tannin and non-tannin fractions. The extraction of quercetin and salicyclic acid from meadowsweet also followed pseudo first-order kinetics, the rate constant of both compounds increasing with an increase in temperature up until 90 °C. Therefore, the aqueous extraction of meadowsweet at temperatures at or above 90 °C for 15 min yields extracts high in phenols, which may be added to beverages.     

An Automated Liquid-Liquid Extraction System Supervised by an Industrial Programmable Logic Controller

In the case of development of new products in organic synthesis, the final step of the process must offer the best purity. In this way, the final step is a unit operation of isolation like distillation, crystallisation or liquid-liquid extraction. Therefore, it is necessary to integrate a module of purification on an automated platform for achieving the whole process.In our case, an automated platform was based on Zymark architecture allowing us to automate sample preparation and the reaction steps. For the purification module, we opted to develop our own home module: a liquid-liquid extraction module. This unit operation permits us to separate the final product in the case of peptide synthesis in liquid phase, but equally, in the case of isolation of vegetable molecules.The module capacities had to permit the multistage extraction and the determination of the binodal curve for optimising the process, and to possess in our own system for liberating the Zymark robot for other tasks. The operator interface is developed by using a SCADA (supervisory control).     

Probabilistic modeling of a nonlinear dynamical system used for producing voice

This paper is devoted to the construction of a stochastic nonlinear dynamical system for signal generation such as the production of voiced sounds. The dynamical system is highly nonlinear, and the output signal generated is very sensitive to a few parameters of the system. In the context of the production of voiced sounds the measurements have a significant variability. We then propose a statistical treatment of the experiments and we developed a probability model of the sensitive parameters in order that the stochastic dynamical system has the capability to predict the experiments in the probability distribution sense. The computational nonlinear dynamical system is presented, the Maximum Entropy Principle is used to construct the probability model and an experimental validation is shown.     

开关电源环路中的TL43I

虽然上一期文章介绍了如何以TL431实现2类补偿器。然而在补偿电路方面，TL431并非万能药。由于原极点和零点之间以固定系数相关联，采用运放构建的补偿器时，运放的灵活性会降低，而这个运放中可以创建自选的中频带增益。为解决LED串联电阻对可能的增益变化进行钳位的问题，1类补偿器将提供稳定所选转换器时的灵活性，符合期望。然而，这种1类补偿器也有局限，即它不提供任何相位提升。     

Comparative study of 2-group and diffusion theories for the calculation of the neutron noise in 1D 2-region systems

In this paper, the neutron noise, i.e. the stationary fluctuations of the neutron flux around its mean value, is calculated in 2-group P₁ and diffusion theories for a 2-region slab reactor using Green’s function technique. The applicability of diffusion theory for different types and locations of the perturbation, as well as different frequencies, is assessed. Material data, i.e. nuclear cross-sections and kinetic parameters, representative of a Light Water Reactor (LWR) and of a Heavy Water Reactor (HWR), respectively, are used in this work. It is demonstrated that for practical situations in LWRs and HWRs, there is no significant advantage to use P₁ theory since diffusion theory gives acceptable results. The largest deviations between the two formalisms are observed in regions of large gradients of the static neutron flux, such as close to the reflector interface and close to the perturbation. Such observations are in agreement with theoretical expectations. This study also indicates that neglecting the effect of cross-section perturbation on the diffusion coefficient gives a rather small impact on the solution. This allows drastically simplifying the determination of the neutron noise. When using numerical techniques for such a determination the memory requirements and computational effort can be significantly reduced.