Limit Dextrinase — Does Its Malt Activity Relate to Its Activity During Brewing?

Limit dextrinase (EC 3.2.1.142) hydrolyses α‐1,6 glucosidic bonds in amylopectin and branched dextrins. Measurement of limit dextrinase activity during fermentation of unboiled wort at the pH of the wort has shown that its activity increases almost 10 fold during the first 10–15 h of fermentation and this increase in activity is unaffected by the presence of leupeptin, a cysteine protease inhibitor. The increase in activity seen when assays were carried out at pH 5.5 was much smaller and was reduced by leupeptin. The activity of limit dextrinase declined slowly during the latter part of the fermentation. It was established that the optimum pH for rapid extraction and assay of malt limit dextrinase in the absence of a reducing agent is approximately 4.5, but in the presence of dithiothreitol, at pH 5.5, activities 2–3 times higher can be obtained after 5 h extraction (600–700 mU/g dry weight). Limit dextrinase activities after 1 h extraction at mashing temperatures were below 20 mU/g dry weight if the mash pH was below 5.0. It is concluded that at pHs below 5.0, where limit dextrinase activity is below its optimum for activity, limit dextrinase activity increases due to dissociation of the inhibitor/enzyme complex. The protection from mashing temperatures of 65°C afforded by the inhibitor is lost at these lower pHs.     

Amorphization of α-quartz and comparative study of defects in amorphized quartz and Si nanocrystals embedded in amorphous silica

Ion irradiation of α-quartz renders the crystal SiO₂ structure amorphous. The enormous amount of structural defects produced after ion irradiation give a chance for photoactive intrinsic defects to be formed. These may be responsible for the photoluminescence in irradiated α-quartz. On the other hand, the radiation defects are not stable, and thus, an alternative structure where the defects of interest can be stabilized is required. The stabilization of the defects can be achieved in the structures of amorphous silica with embedded Si nanocrystals (NC), thanks to the unique structure of the formed interface. By means of Molecular Dynamics (MD), we analyze defects in both amorphized α-quartz and Si-NC/a-SiO₂ interfaces formed by 1.1, 2.4 and 4 nm diameter NC’s. In the simulation, we employ a classical interatomic potential and a potential, which takes into consideration a charge transfer between Si and O atoms. We show that although the number of silanone bonds SiO in irradiated quartz is higher, they are also found in a Si-NC/a-SiO₂ interface without the necessity of preceding irradiation of the sample. We also compare the defects in irradiation-amorphized quartz and the three sizes of Si-NC/a-SiO₂ interfaces. Analysis of the charges showed that the charge state of coordination defects depends on the type of atoms in the near neighborhood.     

塑造地域性的城市特色——以贵港市城市风貌规划为例

贵港城市风貌规划以地域特色的规划表达为重点,以主题演绎的设计手法为载体,对贵港地域性城市特色要素进行了演绎,以塑造“南国荷城”为核心内容,从分区规划、分项规划、风貌演绎等方面提出贵港城市风貌的控制措施和实施意向,并结合局部片区进行意向性城市设计,以使贵港的城市风貌得到较大的转变和提升。     

Structure–Property Relationships in Lanthanide‐Doped Upconverting Nanocrystals: Recent Advances in Understanding Core–Shell Structures

The production of upconverting nanostructures with tailored optical properties is of major technological interest, and rapid progress toward the realization of such production has been made in recent years. Ultimately, accurate understanding of nanostructure organization will lead to design rules for accurately tailoring optical properties. Here, the context of open questions still of general importance to the upconversion and nanocrystal communities is presented, with a particular emphasis on the structure–property relationships of core–shell upconverting nanocrystals. Although the optical properties of the latter have been thoroughly investigated, little is known regarding their atomic‐scale organization. Indeed, solving the atomic‐scale structure of such nanomaterials is challenging because of their intrinsic nonperiodic nature. Familiar concepts of crystallography are no longer appropriate; chemical and structural modulation waves must be introduced. To reveal the exact core–shell structures, innovative characterization techniques need to be applied and developed, as discussed herein. The continued development and application of structural characterization techniques will be vital to consolidate the currently incomplete link between atomic‐scale structure and upconversion properties. This will ultimately provide a valuable contribution to the emerging detailed guidelines on how to better design upconverting nanostructures to achieve given optical properties in terms of efficiency, absorption, spectral emission, and dynamics.     

Evaluation of the Detonation Performance of Insensitive Explosive Formulations Based on 3,3ʹ Diamino-4,4ʹ-Azoxyfurazan (DAAF) and 3-Nitro-1,2,4-Triazol-5-One (NTO)

Two energetic materials identified for relatively high energy, but little to no response to impact, spark or friction stimuli are 3-nitro-1,2,4-triazole-5-one (NTO), and 3,3? diamino-4,4?-azoxyfurazan (DAAF). More of an outlier in performance versus sensitivity, DAAF illustrates insensitivity by small-scale sensitivity tests, yet has a failure diameter estimated to be 1.25 mm and a short run length to detonation. Because of this unusual behavior, DAAF is an ideal material to formulate with NTO to obtain tailored shock sensitivity and critical diameter, with detonation velocities and pressures higher than PBX 9502. Here, we present detonation properties of Kel-F^® bonded formulations with ratios of 20–70 wt.-% DAAF added to NTO. All formulations were evaluated for detonation velocity, aluminum flyer acceleration at jump-off, and via the cylinder expansion test.     

Tetrathiafulvalenes as π-Electron Donors for Intramolecular Charge-Transfer Materials

Although tetrathiafulvalene (TTF) and its derivatives have been extensively studied for more than 25 years as π-electron donors in intermolecular charge-transfer materials, the intriguing potential of TTF as a donor in an intramolecular sense has only recently been developed. Many versatile, functionalized TTF building blocks are now readily available, and this article will review a range of compounds in which TTF is covalently linked to an electron acceptor moiety by a variety of linking units, sometimes giving rise to an intramolecular charge-transfer (ICT) interaction, which is most frequently manifested in the optical and electrochemical properties. In this context, acceptor subunits include: tetracyano-p-quinodimethane, quinones, electron-deficient aryl groups, pyridinium and bipyridinium units, fullerenes, phthalocyanines, and mesomerically conjugated carbonyl, thiocarbonyl, ester, and related groups. This work paves the way for more systematic and detailed studies of TTF–spacer–A molecules (where A is an acceptor) in which there is increased control of the structural, electronic, optical, and magnetic properties arising from ICT interactions in the ground state, or in the excited state.     

Epitaxial,electro-optically active barium titanate thin films on silicon by chemical solution deposition

Recent progress in the integration of BaTiO₃ thin films with silicon has shown great promise for the development of on-chip photonic devices. However, the highest performing thin films in the literature are deposited by costly and/or complex vacuum techniques. In this study, epitaxial BaTiO₃ thin films are deposited on thin SrTiO₃ template layers on Si(001) from an alkoxide-based chemical solution under atmospheric conditions and yield an effective Pockels coefficient of 27 ± 4 pm/V for an ~85 nm film. Film crystallinity, microstructure, and defect nature are examined by X-ray diffraction and high-resolution transmission and scanning electron microscopy techniques and discussed within the context of the growth method as well as the observed electro-optical response.