技术柔性、柔性生产与柔性技术的价值

在产品市场和要素市场存在不确定性的条件下,将企业的生产行为和技术柔性水平的选择纳入一个统一框架进行分析,给出了柔性技术的价值函数及其特征.结果表明,给定技术柔性水平,柔性生产行为价值不会低于非柔性生产行为的价值;给定生产行为,柔性技术的价值不会随着其柔性增加而降低.进一步,在一定条件下,柔性生产行为比非柔性生产行为更具价值,柔性技术的价值随着其柔性水平的增加而增加.     

Thermoelectric characteristics of flexible reduced graphene oxide/silver selenide nanowire composites prepared by a facile vacuum filtration process

The reduced graphene oxide/silver selenide nanowire (rGO/Ag₂Se NW) composite powders were fabricated via a wet chemical approach, and then flexible rGO/Ag₂Se NW composite film was prepared by a facile vacuum filtration method combined with cold-pressing treatment. A highest power factor of 228.88 μW·m^-1·K^-2 was obtained at 331 K for the cold-pressed rGO/Ag₂Se NW composite film with 0.01 wt% rGO. The rGO/Ag₂Se NW composite film revealed superior flexibility as the power factor retained 94.62% after bending for 500 times with a bending radius of 4 mm, which might be due to the interwoven network structures of Ag₂Se NWs and pliability of rGO as well as nylon membrane. These results demonstrated that the GO/Ag₂Se NW composite film has a potential for preparation of flexible thermoelectric devices.     

Use of a modified Drude's equation to investigate the optical rotation property of sugars

Sugar compounds (glucose, xylose, arabinose, and galactose) and their mixed solutions were examined using the optical rotatory dispersion (ORD) measurement technique with a modified Drude's equation. Commonly, spectroscopic methods utilize the observation of absorption bands which are, in the case of sugars, located in the UV-spectral range. However, the polarization method used in this study allows us to investigate sugar samples in a convenient visible spectral range where sugar solutions are relatively transparent. The ORD set-up can be simple and robust as we will demonstrate: the self-constructed apparatus consists of only two linear polarizers, placed one after the other, with the angle between their transmission axes adjusted to 45°. The sugar solution sample in a cuvette was put between the polarizers. The set-up was connected to a sample compartment of a commercial UV–vis spectrophotometer. The method provided us the specific optical rotation and concentration of sugar solutions with a reasonable accuracy. In addition, the optical rotation value for mixed sugars has been found to be the average optical rotation value of individual sugar content. Beside use in the laboratory environment, the method could also have industrial on-site monitoring applications, for example in bio fuel production.     

Including ligand‐induced protein flexibility into protein tunnel prediction

In proteins with buried active sites, understanding how ligands migrate through the tunnels that connect the exterior of the protein to the active site can shed light on substrate specificity and enzyme function. A growing body of evidence highlights the importance of protein flexibility in the binding site on ligand binding; however, the influence of protein flexibility throughout the body of the protein during ligand entry and egress is much less characterized. We have developed a novel tunnel prediction and evaluation method named IterTunnel, which includes the influence of ligand‐induced protein flexibility, guarantees ligand egress, and provides detailed free energy information as the ligand proceeds along the egress route. IterTunnel combines geometric tunnel prediction with steered molecular dynamics in an iterative process to identify tunnels that open as a result of ligand migration and calculates the potential of mean force of ligand egress through a given tunnel. Applying this new method to cytochrome P450 2B6, we demonstrate the influence of protein flexibility on the shape and accessibility of tunnels. More importantly, we demonstrate that the ligand itself, while traversing through a tunnel, can reshape tunnels due to its interaction with the protein. This process results in the exposure of new tunnels and the closure of preexisting tunnels as the ligand migrates from the active site. © 2014 Wiley Periodicals, Inc.     

Synthesis of 2,3-unsaturated glycosides via metal-free Ferrier reaction

Hexafluoroisopropanol (HFIP) is explored as an effective medium for the synthesis of 2,3-unsaturated glycosides through allylic rearrangement of 3,4,6-tri-O-acetyl glucal. This metal-free, exclusively solvent-promoted Ferrier glycosylation, affords products in good to excellent yields and with good α-selectivity.     

pH shifting effect on anionic dye removal by surfactant-modified sugar beet pulp: Modeling of column studies

pH shifting effect on the adsorption of anionic RBB dye was tested by using untreated and CTAB-treated SBP as adsorbent in both batch and continuous systems. Characterization of the sorbents revealed the effects of surface modification. Enhanced binding sites and more porous surface structure resulted in improved adsorption capability. Flow rate and initial RBB concentration effects were tested in packed bed column. Optimum pH value of the adsorption, which was determined as 2.0 in the batch studies with untreated SBP, shifted to 8.0 with 20 g/L CTAB treated SBP. Experimental data in column studies showed the decreasing capacity with increasing flow rate and enhanced performance with increasing inlet RBB concentration for both sorbents. Maximum capacities of the columns were found as 36.9 and 2.6 mg/g with dried SBP at pH 2.0 and 8.0, respectively, at a maximum inlet RBB concentration of 500 mg/L and a minimum flow rate of 0.8 mL/min. The highest capacity value at pH 8.0 was found as 140.0 mg/g under the same operating conditions, which reveals positive effect of the treatment on adsorptive performance. Langmuir isotherm was found to be most convenient model for the all equilibrium cases in the column. Moreover, Thomas model accurately predicted the breakthrough curves of each system. This is the first study reporting the modeling data of an anionic dye adsorption in a packed bed column by using modified SBP.     

Interactionist perspective on negotiation processes of students’ different understandings during small group work on linear algebra

Student group work represents a central learning setting within mathematics programs at the university level. In this study, a theoretical perspective on collaboration is adopted in which the differences between students’ interpretations of a mathematical concept are seen as an opportunity for individual restructuring processes. This so-called interactionist perspective is applied to student group work on linear algebra. The concepts of linear algebra at the university level are characterized by a versatility of different modes of expression and interpretation. For students of linear algebra, the flexible transitions between the different interpretations of linear algebra concepts usually pose a challenge. This study focuses on how students negotiate their different interpretations during group work on linear algebra and how transitions between interpretations might be stimulated or hindered. Video recordings of eight student groups working on a task that required flexible transition between interpretations of homomorphisms were sampled. The recordings were analyzed from an interactionist perspective, focusing on interaction situations in which the participating students expressed and negotiated different interpretations of homomorphisms. The analyses of students’ interactions highlight a phenomenon whereby differences in students’ interpretations remain implicit in group discussions, which constitutes an obstacle to the negotiation process.     

HPLC Separation of Sugar Anomers in a Very Low Temperature Region

Abstract

High-performance liquid chromatographic (HPLC) separation of sugar anomers was carried out on -NH₂ columns in acidic eluents in a very low temperature region. Chromatogram patterns were found to show remarkable changes with decreasing column temperatures. This was attributed to the fact that interconversion between sugar anomers (mutarotation) occurred during the chromatographic process. Since mutarotation was suppressed in a very low temperature region, pyranose anomers of each mono- and di-saccharide were separated completely. Furanose anomers were also separated from an equilibrium mixture, and the necessary conditions for complete separation of furanose anomers were discussed.     

Preparation and characterization of four polymeric metal complexes based on the flexible ligand 1H-1,2,4-triazole-1-propionic acid in different conformations

Three 2-D layered coordination polymers with (4,4) topology, {[Cu(trzp)₂(H₂O)]·1.18H₂O} _n (1), {[Co(trzp)₂(H₂O)₂]·2H₂O} _n (2), and {[Cd(trzp)₂(H₂O)]·2H₂O} _n (3), have been synthesized with the flexible, bifunctional ligand 1H-1,2,4-triazole-1-propionate (trzp^?) as a two-connected bridge. In addition, a complicated 3-D MOF [Ag₃(trzp)₂(NO₃)] _n (4) has been obtained with the help of Ag?Ag interactions and trzp^? as a four-connected linker. Htrzp and 1–4 have been characterized by single-crystal X-ray diffraction, elemental analysis, and infrared spectroscopy. The structural analysis showed that Htrzp has a gauche conformation in the solid state. However, both gauche and trans conformers of trzp^? are observed in the crystals of 1; only one conformer of trzp^? exists in the other three compounds (trans conformation in 2 and 3, and gauche conformation in 4). The thermal behaviors of 1–4 have been examined by thermal gravimetric analysis under nitrogen, which revealed that metal cyanide salts M(CN) _n (M?=?Cu(II), Co(II), Cd(II), and Ag(I), n?=?1 or 2) may be an intermediate pyrolytic decomposition product of the corresponding compounds.