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81.
Due to the miniaturization seen in the last decades, several macro models that neglect some parameters have to be revised
in order to evaluate the behavior of different types of microsystems precisely. In this paper we present the analysis of one
such parameter which affects the thermal functionality, namely, the conduction of natural gases. In macro scale this parameter
is usually neglected, because the conductivity of gases is several magnitudes smaller than that of the base materials. With
the advance of microfabrication really good thermal isolation can be achieved and so the values of the conductivity of the
air and of the base material can be evenly compared and as a consequence the former models have to be revised. This effect
can be easily modeled on microstructures whose thermal resistance can be compared to the thermal resistance of natural gases.
In order to observe its behavior appropriately, different types of cantilevers with embedded thermopiles and heating resistors
were used. The modeling and experimental results show that in microsystems that are sensitive to temperature change, the parallel
heat flow created by the surrounding gases may have significant impact on the operation. 相似文献
82.
Jan Pinc Vilém Bartůněk Jiří Kubásek Vladimír Plecháček Tomáš Hlásek 《Journal of Superconductivity and Novel Magnetism》2016,29(7):1773-1778
It is known that mechanical properties of a high-temperature superconductor (HTS) can affect the superconducting behaviour of the material. In this study, the mechanical and basic superconducting properties of single-domain YBaCuO and GdBaCuO were determined and compared. The bulk single-grain superconductor samples were prepared by top-seeded melt growth process. Distribution of trapped fields in the samples was mapped using the Hall probe technique. Levitation force was assessed using a dynamometer. Phase composition of the samples, was characterised by X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) measurements. Microstructure was studied using scanning electron microscopy (SEM) and optical microscopy. Microhardness and comprehensive strength of the prepared samples were measured at a room temperature. The GdBaCuO superconductor has shown higher average hardness than the YBCO sample; higher fragility was also observed by comprehensive strength measurement of both types. Maximum trapped magnetic field was 0.65 T at 77 K in the case of a Gd-based material. In comparison with YBaCuO, the values of the trapped magnetic field and levitation force of GdBaCuO were higher. The results obtained can be useful for rare earth element (RE) superconductor device engineering as well as for the research in the field of superconducting ceramics. 相似文献
83.
Fire Technology - Textile-reinforced concrete is currently most frequently used for non-load–bearing structures, but there is a vision for also using it in load–bearing construction... 相似文献
84.
85.
Jana Dvořáková Petr Šálek Lucie Korecká Ewa Pavlova Peter Černoch Olga Janoušková Barbora Koutníková Vladimír Proks 《应用聚合物科学杂志》2020,137(21):48725
The current work presents a pivotal study of the nanogelation of the linear poly(N5-2-hydroxypropyl-L-glutamine) polymer precursor containing tyramine (TYR) units in an inverse miniemulsion by horseradish peroxidase/H2O2-mediated crosslinking. The effects of various nH2O2/nTYR ratios on the kinetics of nanogelation in the inverse miniemulsion and on the reaction time are investigated by linear sweep voltammetry, while the formation of dityramine crosslinking is explored by fluorescence spectroscopy. The study is completed using dynamic light scattering measurements, nanoparticle tracking analysis, and cryogenic transmission electron microscopy to acquire comprehensive information about the formed nanoparticulate systems. With the optimal ratio nH2O2/nTYR = 2, the strategy yields in the high-quality ~ 130 nm poly(amino acid)-based nanogel, which is prepared in 2 h. The nanogel is colloidally stable under different temperature and pH conditions for over 168 h. Moreover, the demonstrated nanogel is noncytotoxic for HeLa cells and human primary fibroblasts and is quickly enzymatically hydrolyzed into small fragments during a biodegradation study in human blood plasma. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48725. 相似文献
86.
Jan Kyselka Klára Cihelková Daise Lopes-Lutz Josef Chudoba Tereza Váchalová Katsiaryna Alishevich Iveta Hrádková Markéta Berčíková Monika Mikolášková Vladimír Filip 《European Journal of Lipid Science and Technology》2021,123(3):2000228
The aim of the present study is to describe the mechanism controlling heat-induced formation of sunflower oil triacylglycerol and fatty acid methyl ester oligomers. The unique combination of high-performance size-exclusion chromatography with hyphenated electrospray ionization mass spectrometry (MS), atmospheric pressure chemical ionization-MS, and high-temperature gas chromatography-MS techniques allows differentiating between radical coupling species and Diels–Alder cycloadducts. Targeted analysis of thermally degraded sunflower oils confirms the exact structures of various acyclic oligomers accompanied by less-abundant products of pericyclic transformations. A series of model experiments simulate the impact of dienophile nature on the course of Diels–Alder reactions. Thus, α-tocopherylquinone, δ-tocopherylquinone, and methyl-(E)-11-oxoundec-9-enoate are synthesized as naturally occurring dienophiles bearing electron-withdrawing groups. The geometry of poor dienophiles does not affect concerted cyclization, while the structure of electron deficient dienophiles can overcome low reactivity. Practical Application: In the absence of oxygen, heat-induced degradation of polyunsaturated triacylglycerols proceed predominantly via a radical pathway, whereas concerted reactions represent minor mechanisms. Sunflower oil triacylglycerol molecules in the system without propagation stage can be effectively protected by natural and/or synthetic antioxidants. Application of chelates is also recommended. However, antioxidant-derived quinones, such as α-tocopherylquinone, can enter the Diels–Alder reaction even more easily than dienophiles without electron-withdrawing groups. Unsaturated core aldehydes possess the same reactivity. Examination of the mechanism controlling high-temperature degradation of triacylglycerols is especially important for processing engineers in edible oil refineries and food technologists. New perspective may help them to minimize undesirable changes in polyunsaturated species. 相似文献
87.
Giorgio Pettinari Francesco Filippone Antonio Polimeni Giuseppe Mattioli Amalia Patanè Vladim Lebedev Mario Capizzi Aldo Amore Bonapasta 《Advanced functional materials》2015,25(33):5353-5359
Substitution of constituent atoms and/or changes of crystal structure are routinely used to tailor the fundamental properties of a semiconductor. Here, it is shown that such a tailoring can also be realized thanks to a novel hydrogen effect. Four hydrogen atoms can screen the effect the crystal potential has on a constituent cation, thus generating a solitary cation: an effectively isolated impurity, so chemically different from the unscreened constituent cations that it strongly perturbs the electronic properties of the material by increasing its fundamental band‐gap energy. Such a hydrogen‐induced screening effect is removed by thermal treatments, thus permitting reversible modifications of both the “crystal chemistry” and material's properties. This phenomenon, observed in InN and other topical nitrides, should permit the development of a new class of materials as well as the fabrication of photonic devices and optical integrated circuits with distinct, tailor‐made regions emitting or absorbing light, all integrated onto a monolithic semiconductor structure. 相似文献
88.
Buňková L Buňka F Pollaková E Podešvová T Dráb V 《International journal of food microbiology》2011,147(2):112-119
The aim of this work was to study, under model conditions, combined effects of the concentration of lactose (0-1% w/v), NaCl (0-2% w/v) and aero/anaerobiosis on the growth and tyramine production in 3 strains of Lactococcus lactis subsp. lactis and 2 strains of L. lactis subsp. cremoris. The levels of the factors tested were chosen with respect to the conditions which can occur during the real process of natural cheese production, including the culture temperature (10 ± 1 °C). In all strains tested, tyrosine decarboxylation was most influenced by NaCl concentration; the highest production of tyramine was obtained within the culture with the highest (2% w/v) salt concentration applied. Two of the strains L. lactis subsp. lactis produced tyramine only in broth with the highest NaCl concentration tested. In the remaining 3 strains of L. lactis, tyramine was detected under all conditions applied. The tested concentration of lactose and aero/anaerobiosis had a less significant effect on tyramine decarboxylation. However, it was also found that at the same concentrations of NaCl and lactose, a higher amount of tyramine was detected under anaerobic conditions. In all strains tested, tyramine decarboxylation started during the active growth phase of the cells. 相似文献
89.
Martin Plesch Mário Ziman Vladimír Bužek Peter Štelmachovič 《Open Systems & Information Dynamics》2006,13(3):255-262
When standard methods of process (black-box) estimation are applied straightforwardly then it may happen that some sets of experimental data result in unphysical estimations of the corresponding channels (maps) describing the process. To prevent this problem, one can use the method of maximum likelihood (MML), which provides an efficient scheme for reconstruction of quantum channels. This scheme always results in estimations of channels that are fully physical, e.g. the corresponding maps are linear, positive and completely positive. To show this property, we use the MML for a derivation of physical approximations of truly unphysical operations. In particular, we analyze physical approximations of the universal-NOT gate, the quantum nonlinear polarization rotation and the map ρ → ρ2. Given the result of MML, we examine retrospectively the quality of the experiment. Depending on the resulting value of the MML functional we can determine (physical) consistency of the input data. 相似文献
90.
Vladimír Číhal Jiřina Hubáčková Jiři Kubelka Karel Mazanec 《Materials Chemistry and Physics》1984,11(3):279-293
The evaluation of the electrochemical and structural corrosion properties of martensite-austenite stainless steels by using a new procedure is described. The characteristic maximum current densities and the potentials corresponding to them, or the proper changes by the continuous change of potential in the region of the activity and reactivity have been determined. In the application of the reactivation procedure from the full passivity region the susceptibility of the investigated type of steel to intercrystalline corrosion can be evaluated. The measurement based on the reactivation from incomplete passivity region indicates the local changes in chemical composition (above all nickel content) in relation with the phase transformations that are taking place. The results of the evaluation contribute to the elucidation of the processes occurring during the tempering at intercritical temperatures. 相似文献