两级R744超市中央制冷系统节能特性

比较了以二氧化碳（R744）为工质的超市中央制冷系统制冷技术方案,包括普通两级制冷（CB）、旁通压缩两级制冷（PC）和多引射器-旁通压缩耦合两级制冷（EJ）,讨论了配置空调系统（AC）之后的功耗变化。根据计算得到,在环境温度20℃以上,相较于CB系统,PC系统的功耗减少了6.8%～12.3%;EJ系统功耗降低了6.3%～17.5%。在耦合了AC系统之后,相较于PC-AC系统,EJ-AC系统的功耗降低了4.9%～6.5%。与R404a系统相比,超市两级R744系统都有明显的节能效果。     

Multifunctional Nanocomposites with High Strength and Capacitance Using 2D MXene and 1D Nanocellulose

The family of two‐dimensional (2D) metal carbides and nitrides, known as MXenes, are among the most promising electrode materials for supercapacitors thanks to their high metal‐like electrical conductivity and surface‐functional‐group‐enabled pseudocapacitance. A major drawback of these materials is, however, the low mechanical strength, which prevents their applications in lightweight, flexible electronics. A strategy of assembling freestanding and mechanically robust MXene (Ti₃C₂T_x ) nanocomposites with one‐dimensional (1D) cellulose nanofibrils (CNFs) from their stable colloidal dispersions is reported. The high aspect ratio of CNF (width of ≈3.5 nm and length reaching tens of micrometers) and their special interactions with MXene enable nanocomposites with high mechanical strength without sacrificing electrochemical performance. CNF loading up to 20%, for example, shows a remarkably high mechanical strength of 341 MPa (an order of magnitude higher than pristine MXene films of 29 MPa) while still maintaining a high capacitance of 298 F g^?1 and a high conductivity of 295 S cm^?1. It is also demonstrated that MXene/CNF hybrid dispersions can be used as inks to print flexible micro‐supercapacitors with precise dimensions. This work paves the way for fabrication of robust multifunctional MXene nanocomposites for printed and lightweight structural devices.     

A hybrid semismooth quasi-Newton method for nonsmooth optimal control with PDEs

Optimization and Engineering - We propose a semismooth Newton-type method for nonsmooth optimal control problems. Its particular feature is the combination of a quasi-Newton method with a...     

On the extraordinary low quench sensitivity of an AlZnMg alloy

The scope of this work was to investigate the quench sensitivity of a high-purity wrought aluminum alloy Al6Zn0.75 Mg (in this work called 7003_pure). This is compared to a similar alloy with the additions of Fe, Si, and Zr at a sum less than 0.3 at.% (in this work called 7003_Fe,Si,Zr). Differential scanning calorimetry (DSC) was used for an in situ analysis of quench induced precipitation in a wide range of cooling rates varying between 0.0003 and 3 K/s. In 7003_pure, three main precipitation reactions were observed during cooling, a medium temperature reaction with a distinct double peak between 325 and 175 °C and a very low temperature reaction starting at about 100 °C. An additional high temperature reaction related to the precipitation of Mg₂Si starting at 425 °C has been observed for 7003_Fe,Si,Zr. In terms of hardness after natural as well as artificial aging, alloy 7003_pure shows a very low quench sensitivity. Hardness values on the saturation level of about 120 HV1 are seen down to cooling rates of 0.003 K/s. The as-quenched hardness (5 min of natural aging) shows a maximum at a cooling rate of 0.003 K/s, while slower and faster cooling results in a lower hardness. In terms of hardness after aging, 0.003 K/s could be defined as the technological critical cooling rate, which is much higher for 7003_Fe,Si,Zr (0.3–1 K/s). The physical critical cooling rates for the suppression of any precipitation during cooling were found to be about 10 K/s for both variants.

     

Superparamagnetic magnetite nanoparticles for cancer cells treatment via magnetic hyperthermia: effect of natural capping agent,particle size and concentration

Journal of Materials Science: Materials in Electronics - Superparamagnetic iron oxide nanoparticles (SPMNPs) continue to emerge as one of the most potential candidates in biomedical applications....     

Crystallization of indium tin oxide nanoparticles: from cooperative behavior to individuality

The crystallization pathway of indium tin oxide nanoparticles during solvothermal synthesis in benzyl alcohol was investigated. The synthesis was stopped after different reaction times in the range of 1-24 h, and the structural and morphological characteristics of the products were analyzed by powder X-ray diffraction, electron microscopy, and UV/Vis spectroscopy. Interestingly, the crystallization mechanism does not proceed along a simple nucleation and growth pathway, but involves a two-step process. In the first 12 h an intermediate phase is formed, which consists of nanocrystallites 3-6 nm in size stabilized by an organic matrix. In this organic-inorganic network the nanoparticles are aligned into superstructures, but without any crystallographic orientation. After 12 h the intermediate phase is abruptly transformed into indium tin oxide nanoparticles with the bixbyite structure and with crystallite sizes of about 10-12 nm. This step is accompanied by the disappearance of the organic phase and the loss of the superstructure.     

Stereoisomere Aromastoffe

Zusammenfassung 5-Alkyl-substituierte-Lactone finden sich als aromarelevante Substanzen in tierischen Fetten, aber auch in einigen Früchten. Vor kurzem gelang die erste direkte gaschromatographische Stereodifferenzierung einiger-Lactone an der chiralen Phase Oktakis(3-O-butyryl-2,6-di-O-pentyl)--cyclodextrin [4]. Es wird nun die Enantiomerentrennung der-Lactone bis zu den langkettigen Verbindungen-Trideca-(-C₁₃-)- und-Tetradeca-(-C₁₄-)-lacton aufgezeigt. Über optisch reine Referenzsubstanzen konnte die Elutionsfolge S(I), R(II) der drei wichtigsten aromarelevanten Vertreter dieser-Lactonklasse bestimmt werden. Die Enantiomerenverteilung der C₈-, C₁₀-, C₁₂--Lactone im Wasserdampfdestillat verschiedener Milchprodukte (Milch, Sahne, Butter), in Margarine sowie im Kokosnußfleisch wurde exemplarisch mit Hilfe der HRGC, auch unter Einsatz der multidimensionalen Gaschromatographie (MDGC), untersucht. Es zeigten sich charakteristische, substratspezifische Enantiomerenverteilungen. Die Verteilungsmuster der untersuchten Spiegelbildisomeren aus Kokosnüssen unterschieden sich wesentlich von denen der Milchprodukte.

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Stereoisomeric flavour compoundsXLVII. Direct chirospecific HRGC-analysis of natural -lactones

Summary 5-Alkylated-lactones are well known flavour compounds in animal fats and also some special kinds of fruit. Recently, the first direct stereo-differentiation of chiral-lactones was reported using Oktakis(3-O-butyryl-2,6-di-O-pentyl)--cyclodextrin as the chiral stationary phase [4]. The enantiomeric separation of-lactones up to the long-chain compounds-trideca-(-C_13–) and-tetradeca-(-C_14–)-lactone is demonstrated. By means of optically pure references, the order of elution S(I), R(II) was determined for the important flavour compounds-octa-,-deca-, and-dodecalactone. Analysis of the steam distillate of some dairy products (milk, cream, butter), of margarine and of coconut has been carried out, in order to yield the enantiomeric distribution of C₈-, C₁₀- and C₁₂--lactones by HRGC and multidimensional gas chromatography. Characteristic and product-specific ratios of-lactone enantiomers are detected. The pattern of enantiomeric composition of-octa-,-deca-,-dodecalactone in coconuts differs completely from that found in the dairy products.

     

Genetic transformation of auxotrophic mutants of the filamentous yeast Trichosporon cutaneum using homologous and heterologous marker genes

A transformation system for the filamentous yeast Trichosporon cutaneum based on auxotrophic markers is presented and techniques for the induction, isolation and characterization of mutants are described. A number of auxotrophic mutants were isolated and characterized by using biosynthetic precursors and/or inhibitors. A mutant unable to grow in the presence of ornithine could be complemented successfully by spheroplast transformation experiments using the cloned Aspergillus nidulans ornithine transcarbamoylase gene (argB gene) as selection marker with an efficiency of 5-100 transformants per microgram of DNA. In these transformants the heterologous argB gene was present in multiple tandem copies and the transforming DNA was found to remain stable after more than 50 generations in non-selective media. The same mutant could be complemented by a T. cutaneum cosmid gene library and a complementary cosmid was subsequently isolated from this library by a sib-selection strategy. This cosmid transformed T. cutaneum spheroblasts with an efficiency of 50-200 colonies per microgram of DNA. Southern blot analyses were consistent with the view that the transforming sequences became stably integrated into the host genome at the homologous site.     

PTR-MS assessment of photocatalytic and sorption-based purification of recirculated cabin air during simulated 7-h flights with high passenger density

Four different air purification conditions were established in a simulated 3-row 21-seat section of an aircraft cabin: no air purifier; a photocatalytic oxidation unit with an adsorptive prefilter; a second photocatalytic unit with an adsorptive prefilter; and a two-stage sorption-based air filter (gas-phase absorption and adsorption). The air purifiers placed in the cabin air recirculation system were commercial prototypes developed for use in aircraft cabin systems. The four conditions were established in balanced order on 4 successive days of each of 4 successive weeks during simulated 7-h flights with 17 occupants. Proton-transfer reaction mass spectrometry was used to assess organic gas-phase pollutants and the performance of each air purifier. The concentration of most organic pollutants present in aircraft cabin air was efficiently reduced by all three units. The photocatalytic units were found to incompletely oxidize ethanol released by the wet wipes commonly supplied with airline mealsto produce unacceptably high levels of acetaldehyde and formaldehyde.     

Colloidal-quantum-dot photovoltaics using atomic-ligand passivation

Colloidal-quantum-dot (CQD) optoelectronics offer a compelling combination of solution processing and spectral tunability through quantum size effects. So far, CQD solar cells have relied on the use of organic ligands to passivate the surface of the semiconductor nanoparticles. Although inorganic metal chalcogenide ligands have led to record electronic transport parameters in CQD films, no photovoltaic device has been reported based on such compounds. Here we establish an atomic ligand strategy that makes use of monovalent halide anions to enhance electronic transport and successfully passivate surface defects in PbS CQD films. Both time-resolved infrared spectroscopy and transient device characterization indicate that the scheme leads to a shallower trap state distribution than the best organic ligands. Solar cells fabricated following this strategy show up to 6% solar AM1.5G power-conversion efficiency. The CQD films are deposited at room temperature and under ambient atmosphere, rendering the process amenable to low-cost, roll-by-roll fabrication.