粘度法测定植物纤维素的聚合度

介绍了以饱和氢氧化铜的乙二胺溶液(CED)为溶剂,通过测定CED溶液和一定浓度的植物纤维素-CED溶液在粘度计毛细管中的流出时间,利用Martin公式计算出试样特性粘数后,由Mark方程计算植物纤维素的聚合度的方法。利用该方法测得的纤维素棉浆粕的平均聚合度为546-556;该法使用的仪器简单,且准确度较高,相对误差小于1．5％。     

Determination of C22:5 and C22:6 marine fatty acids in pork fat with Fourier transform mid-infrared spectroscopy

Fatty acids in samples (n=74) of pork adipose tissue were measured with a Fourier transform mid-infrared (FT-MIR) spectrometer and by gas chromatography. The measured absorption spectra provided information to estimate partial least squares regression models for fatty acid groups, the iodine value and several fatty acids. The iodine values were predicted with correlation coefficient R=0.996 and root mean square error of cross-validation RMSECV=0.658. The sum of the two marine fatty acids of main interest, C22:5n3+C22:6n3, were predicted with R=0.982 and RMSECV=0.062. The K nearest neighbours procedure successfully classified the samples in three classes, depending on their proportions of marine fatty acids. Application of fat and absorption measurements were rapid, requiring less than 5 min of labour per sample. The results reported in this paper demonstrate that FT-MIR measurements can serve as a rapid method to determine marine fatty acids in pork fat.     

Real-time game-theoretic model predictive control for differential game of target defense

This paper evaluates experimentally a novel strategy for solving a variant of the differential game of target defense in presence of obstacles. The game is widely applied in the areas of military defense for protecting important equipment such as a ship, an aircraft, a moving vehicle, or a sensitive installation from a malicious attacker. The state-of-the-art approaches mostly employ an offline optimization strategy that is only applicable to holonomic robots. Moreover, most of the approaches could not autonomously avoid obstacles or take into account uncertainties. As a consequence, this paper presents an online optimization technique, by designing a trade-off parameter that integrates game theory with the model predictive control, which allows a nonholonomic defender to intercept the attacker while simultaneously defending the target. Simulations under different conditions as well as several indoor laboratory experiments validate the proposed approach. Moreover, performance is compared with a standard model predictive control approach.     

The concentrated emulsion approach to toughened polymer composites: A review

A series of tough polymers were prepared by combining flexible with rigid chains, using the method of concentrated emulsion polymerization. The tough materials obtained can be classified into four types: [a] those prepared via the polymerization of a monomer containing a dissolved elastomer, starting from its concentrated emulsion in water; [b] those prepared via heterogeneous (interfacial) crosslinking of two partially polymerized concentrated emulsion in water containing incipient latexes; [c] those prepared as semi-interpenetrating or AB network latexes, starting from a concentrated emulsion in water and [d] those prepared by mixing two partially polymerized concentrated emulsions and completing the polymerization. A concentrated emulsion differs from the conventional emulsion in that the volume fraction of the dispersed phase is higher than that of the most compact arrangement of monosize spheres (0.74) and can be as high as 0.99. The cells of a highly concentrated emulsion are no longer spherical, but polyhedral in shape, compactly packed and separated by thin films of continuous phase. As a result of such structure, a high polymerization rate and a high molecular weight can be achieved, the size (in the colloidal range) of the flexible phase can be controlled and the latter phase can be uniformly dispersed in the rigid one. Consequently, the concentrated emulsion method constitutes a suitable pathway to toughened composites. Owing to the compact packing of cells, the concentrated emulsion polymerization method is particularly suitable for cases in which reactions occur at the cell interface. For the materials of type [d], these reactions generate quasi-block copolymers, which compatibilize (via “auto-compatibilization”) the components of blends.     

Degradation kinetics of monacolin K in red yeast rice powder using multiresponse modeling approach

The effects of storage temperature (4, 20, 30, 40, 50 °C) and atmospheric conditions in packages (vacuum, atmospheric) on degradation kinetics of monacolin K, an antihypercholesterolemic agent, in red yeast rice powder were investigated using multiresponse modeling approach. Storage of red yeast rice powder at 4 °C under vacuum package was found to enhance retention of monacolin K. Multiresponse modeling revealed degradation path of monacolin K acid form into their dehydromonacolin K and unknown product under vacuum package, while oxidized product was also formed under atmospheric package. Monacolin K lactone form and precursor were degraded into dehydromonacolin K lactone form, while degradation of dehydromonacolin K lactone form to unknown was more pronounced at temperature higher than 30 °C. Oxidized product was also generated from monacolin K lactone form in atmospheric package. High activation energy of monacolin K degradation in acid form indicated that degradation of monacolin K to their dehydromonacolin K was more susceptible to temperature change as compared to lactone form.     

Self-Assembly of Mixed-Dimensional GeS1−xSex (1D Nanowire)–(2D Plate) Van der Waals Heterostructures

The integration of dissimilar materials into heterostructures is a mainstay of modern materials science and technology. An alternative strategy of joining components with different electronic structure involves mixed-dimensional heterostructures, that is, architectures consisting of elements with different dimensionality, for example, 1D nanowires and 2D plates. Combining the two approaches can result in hybrid architectures in which both the dimensionality and composition vary between the components, potentially offering even larger contrast between their electronic structures. To date, realizing such heteromaterials mixed-dimensional heterostructures has required sequential multi-step growth processes. Here, it is shown that differences in precursor incorporation rates between vapor–liquid–solid growth of 1D nanowires and direct vapor–solid growth of 2D plates attached to the wires can be harnessed to synthesize heteromaterials mixed-dimensional heterostructures in a single-step growth process. Exposure to mixed GeS and GeSe vapors produces GeS_1−xSe_x van der Waals nanowires whose S:Se ratio is considerably larger than that of attached layered plates. Cathodoluminescence spectroscopy on single heterostructures confirms that the bandgap contrast between the components is determined by both composition and carrier confinement. These results demonstrate an avenue toward complex heteroarchitectures using single-step synthesis processes.     

Electronic Properties of SiB Nanoribbons in Density Functional Theory

Silicon - The present study investigates the electronic and magnetic properties of hydrogenated armchair/zigzag SiB nanoribbons with different widths. The calculations are carried out within the...     

Solution-processed high-performance organic light-emitting diodes containing a green-emitting multiresonant thermally activated delayed fluorescent dendrimer

A multi-resonance thermally activated delayed fluorescence (MR-TADF) dendrimer emitter and a related reference MR-TADF compound were designed, synthesized, and characterized for use as narrowband emitters in solution-processed OLEDs. The 1 wt% doped films in PMMA film revealed that the compounds MR-D1 and MR-D2 showed narrowband green emission at λ_PL of 490 and 495 nm and with FWHM of 23 and 29 nm, respectively. The 50 wt% doped films in mCP still show narrowband green emission at λ_PL of 495 and 499 nm and with FWHM of 28 nm for MR-D1 and MR-D2 , respectively, while conserving the small ΔE_ST of 0.14 and 0.13 eV, respectively. OLEDs containing an emissive layer consisting of 50 wt% MR-D1 and MR-D2 in mCP showed high EQE_max of 27.7% and 21.0%, respectively, and low efficiency roll-off of 19% and 30% at a luminance of 2000 cd/m⁻².     

“Magic Numbers” in Self-Faceting of Alcohol-Doped Emulsion Droplets

Oil-in-water emulsion droplets spontaneously adopt, below some temperature T_d, counterintuitive faceted and complex non-spherical shapes while remaining liquid. This transition is driven by a crystalline monolayer formed at the droplets' surface. Here, we show that ppm-level doping of the droplet's bulk by long-chain alcohols allows tuning T_d by >50 °C, implying formation of drastically different interfacial structures. Furthermore, “magic” alcohol chain lengths maximize T_d. This we show to arise from self-assembly of mixed alcohol:alkane interfacial structures of stacked alkane layers, co-crystallized with hydrogen-bonded alcohol dimers. These structures are accounted for theoretically and resolved by direct cryogenic transmission electron microscopy (cryoTEM), confirming the proposed structures. The discovered tunability of key properties of commonly-used emulsions by minute concentrations of specific bulk additives should benefit these emulsions' technological applicability.