单级大功率斯特林型脉管制冷机模拟与实验研究

为了研究大功率斯特林型脉管制冷机中存在的流动的不均匀性、回热器和脉管内的温度不均匀性、制冷机与压缩机的阻抗匹配等问题,本文基于模拟软件Sage设计制造了一台单级大功率斯特林型脉管制冷机并对其进行了初步试验研究。在60 Hz工作频率,充气压力为1.9 MPa时,800 W输入功率下达到最低无负荷制冷温度56.9 K;充气压力为2.0MPa,输入功率为4 kW时制冷量为41.2 W@77 K,与理论模拟结果存在较大差距。实验发现回热器存在严重的温度不均匀性,中部最大温差高达120 K。     

Automatic deduction in (dynamic) geometry: Loci computation

A symbolic tool based on open source software that provides robust algebraic methods to handle automatic deduction tasks for a dynamic geometry construction is presented. The prototype has been developed as two different worksheets for the open source computer algebra system Sage, corresponding to two different ways of coding a geometric construction, namely with the open source dynamic geometry system GeoGebra or using the common file format for dynamic geometry developed by the Intergeo project. Locus computation algorithms based on Automatic Deduction techniques are recalled and presented as basic for an efficient treatment of advanced methods in dynamic geometry. Moreover, an algorithm to eliminate extraneous parts in symbolically computed loci is discussed. The algorithm, based on a recent work on the Gröbner cover of parametric systems, identifies degenerate components and extraneous adherence points in loci, both natural byproducts of general polynomial algebraic methods. Several examples are shown in detail.     

气动分置式斯特林制冷机间隙密封优化

气体泄漏及间隙传热会导致制冷机性能恶化,因此间隙密封技术是气动分置式斯特林制冷机的一项关键技术。对三种不同间隙密封结构展开研究,搭建Sage模型分析结构参数对制冷机性能的影响,模拟结果显示:间隙高度H不仅影响泄漏率,还与穿梭损失及泵气损失相关;双段式间隙密封的密封1长度比例越大,制冷量越大。当长度比例及密封1、间隙1高度分别为0.7-0.3,10μm,500μm时,双段式间隙密封结构性能达到最优。与单段式间隙密封相比,双段式间隙密封结构的制冷量与COP提高9%和21%;与三段式间隙密封相比,双段式间隙密封结构简单,加工方便,因此在设计膨胀气缸与活塞间隙密封时,优选该结构作为斯特林制冷机密封结构。     

Comparison of different extraction methods for the determination of α‐ and β‐thujone in sage (Salvia officinalis L.) herbal tea

Salvia officinalis L. (sage) is an important industrial plant used both for food and pharmaceutical purposes. The terpene fraction of this plant is responsible for many of its therapeutic and culinary properties. We used different extraction methods Tenax TA® purge and trap, headspace (HS) solid‐phase microextraction, HS sorptive extraction, and stir bar sorptive extraction to analyze the terpene fraction extracted from sage tea by GC–MS. Twenty compounds were identified, including α‐, β‐thujone, and several other oxygenated monoterpenes (1,8‐cineole, linalool, camphor, boneol, and bornyl acetate) and oxygenated sesquiterpenes (caryophyllene oxide, viridiflorol, humulene epoxide I, II, and III). Tenax TA® and HS sorptive extraction extracted a lower number of identified compounds, whereas HS solid‐phase microextraction allowed the complete extraction of volatiles with particular reference to α‐ and β‐thujone. The importance of the determination of thujones content in sage herbal tea is also discussed.     

Comparison of classical and ultrasound-assisted extraction of polysaccharides from Salvia officinalis L

After preparation of medicine tinctures from the herbal plant Salvia officinalis by classical and ultrasound-assisted extraction with aqueous ethanol, the insoluble plant residues were subsequently treated with hot water and dilute alkali to isolate polysaccharide cell wall components. The yields of the hot water extract as well as total extracted polysaccharides were higher in the case of the ultrasound-treated plant in both laboratory and pilot plant experiments. The water-extractable polysaccharide fractions, in all cases, contained glucose, galactose and arabinose as main sugar components, whereas the alkali-extractable fractions were rich in xylans. The fractions also contained considerable amounts of proteins. The water-soluble polysaccharides may contribute to the biological activity of the plant decoction. The results indicate that the addition of a subsequent extraction step during the preparation of the herbal tincture might contribute to a better exploitation of the raw material.     

Laccase-Nafion Based Biosensor for the Determination of Polyphenolic Secondary Metabolites

A laccase-based biosensor was developed by specific enzyme adsorption on screen-printed working electrodes of DROPSENS cells, and stabilized with Nafion 0.1% membrane. The electrode was characterized with respect to response time, sensitivity, linear range, detection limit, pH dependence, interferences, and long-term stability. The tested substrates were catechol, rosmarinic acid, caffeic acid, chlorogenic acid, and gallic acid. The optimized biosensor proved the following characteristic performances: the apparent Michaelis Menten calculated considering rosmarinic acid substrate 8.3 × 10^?6 mol L^?1 (r = 0.995, n = 6); the dynamic range of biosensor response for rosmarinic acid 7 × 10^?7 ? 1.5 × 10^?6 mol L^?1; the detection limit for rosmarinic acid 1.19 × 10^?7 mol L^?1 (RSD = 1.08%, n = 3). It was noticed that the biosensor reaches systematically 90% to 94.3% from the response obtained by LC-DAD-ESI-MS for real samples.     

Separation and identification of some common isomeric plant triterpenoids by thin-layer chromatography and high-performance liquid chromatography

Chromatographic separation of 10 triterpenoids (α-amyrin, β-amyrin, δ-amyrin, lupeol, lupenon, lupeol acetate, cycloartenol, cycloartenol acetate, ursolic acid, oleanolic acid) and 2 sterols (stigmasterol and β-sitosterol) was studied. The chromatographic techniques included silica gel and reversed-phase (C₁₈ RP) thin-layer chromatography (TLC) and C₁₈ RP high-performance liquid chromatography (HPLC) using UV and mass spectrometric (MS) detection with atmospheric pressure chemical ionization (APCI). The TLC separation of the isomeric triterpenols lupeol, α-amyrin, β-amyrin and cycloartenol was achieved for the first time using C₁₈ RP-HPTLC plates. Cycloartenol could be separated from related compounds only on C₁₈ RP-TLC but not on the C₁₈ RP-HPLC. δ-Amyrin isolated from the tomato fruit surface extract could be separated from other amyrins only by HPLC. Tandem mass spectrometry allowed discrimination between the isomers lupeol, α-amyrin, β-amyrin, δ-amyrin, cycloartenol and between lupeol acetate and cycloartenol acetate. The combination of 3 TLC methods and 2 HPLC methods enables qualitative determination of all 12 compounds and proves to be useful for the analysis of plant extracts. It is recommended that TLC screening on silica gel and C₁₈ RP be performed before HPLC analysis.