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61.
62.
Multiphysics simulation of a novel concept of MEMS-based solid propellant thruster for space propulsion 总被引:1,自引:0,他引:1
This work analyzes a novel MEMS-based architecture of submillimeter size thruster for the propulsion of small spacecrafts,
addressing its preliminary characterization of performance. The architecture of microthruster comprises a setup of miniaturized
channels surrounding the solid-propellant reservoir filled up with a high-energetic polymer. These channels guide the hot
gases from the combustion region towards the nozzle entrance located at the opposite side of the thruster. Numerical simulations
of the transient response of the combustion gases and wafer heating in thruster firings have been conducted with FLUENT under
a multiphysics modelling that fully couples the gas and solid parts involved. The approach includes the gas-wafer and gas-polymer
thermal exchange, burnback of the polymer with a simplified non-reacting gas pyrolysis model at its front, and a slip-model
inside the nozzle portion to incorporate the effect of gas-surface and rarefaction onto the gas expansion. Besides, accurate
characterization of thruster operation requires the inclusion of the receding front of the polymer and heat transfer in the
moving gas-solid interfaces. The study stresses the improvement attained in thermal management by the inclusion of lateral
micro-channels in the device. In particular, the temperature maps reveal the significant dependence of the thermal loss on
the instantaneous surface of the reservoir wall exposed to the heat flux of hot gases. Specifically, the simulations stress
the benefit of implementing such a pattern of micro-channels connecting the exit of the combustion reservoir with the nozzle.
The results prove that hot gases flowing along the micro-channels exert a sealing action upon the heat flux at the reservoir
wall and partly mitigate the overall thermal loss at the inner-wall vicinity during the burnback. The analysis shows that
propellant decomposition rate is accelerated due to surface preheating and it suggests that a delay of the flame extinction
into the reservoir is possible. The simulated operation of the thruster concept shows encouraging performance. 相似文献
63.
J. Mera C. Córdoba J. Benavidez O. Paredes J. Doria A. Gómez C. Sanchez C. Paucar O. Morán 《Journal of Materials Science》2010,45(19):5398-5405
Polymeric precursor method (Pechini) was employed to fabricate single- and multilayers of Zn1−x
Mn
x
O (x = 0–0.3) on glass substrates. X-ray diffraction measurements revealed that crystal structure of Zn1−x
Mn
x
O multilayers is the typical hexagonal würzite structure of pristine ZnO. A reduced peak intensity and widened full width
half maximum (FWHM) value of prominent peaks suggested that the Mn2+ ions have substituted the Zn2+ ion without changing the würzite structure of pristine ZnO up to Mn concentrations x ≤ 0.2. A distinct redshift of the absorption edge was observed as the Mn concentration x was increased. Additionally, the absorption edge was less sharp due, probably, to s–d and p–d interactions, which give rise to band gap bowing. Nevertheless, amorphous states appearing in the band gap as a consequence
of reduced crystallinity may also be responsible for the shrinking of the band gap in this material. Interestingly, the field
dependence of the magnetization showed typical paramagnetic behavior for all the chosen Mn concentrations with no evidence
of ferromagnetic ordering. Probably, the absence of ferromagnetism in the studied Zn1−x
Mn
x
O films is strongly related to defects (say Mn impurities at the interface between nano-crystallites) in ZnO due to partial
substitution of host Zn ions by Mn ions. 相似文献
64.
F. Perez E. Baca W. Saldarriaga O. Morán H. Shi D. Lederman 《Journal of Superconductivity and Novel Magnetism》2013,26(6):2289-2293
In this work, we study the magnetoelectrical properties of La2/3Ca1/3MnO3/YBa2Cu3O7?δ /La2/3Ca1/3MnO3 heterostructures grown by means of high oxygen-pressure dc sputtering onto (001)-oriented SrTiO3 substrates. The test heterostructures are composed of ferromagnetic layers of constant thicknesses (~280 unit cells, ~110 nm) and superconducting interlayers with thicknesses ranging between 5 (~6 nm) and 15 unit cells (~17 nm). Transport measurements show a strong suppression of the superconducting properties when the thickness of the YBa2Cu3O7?δ interlayer is reduced to a value below 10 unit cells. Magnetic measurements show superconducting transition in junctions with YBa2Cu3O7?δ interlayers with thicknesses larger than ~15 unit cells. The observed difference in the values of the superconductivity onset when determined by electrical and magnetic measurements might be related with the presence of a spontaneous vortex phase in the temperature range around the superconducting transition. 相似文献
65.
Prof. Silvia Rivara Dr. Daniele Pala Dr. Alessio Lodola Prof. Marco Mor Dr. Valeria Lucini Dr. Silvana Dugnani Prof. Francesco Scaglione Dr. Annalida Bedini Dr. Simone Lucarini Prof. Giorgio Tarzia Prof. Gilberto Spadoni 《ChemMedChem》2012,7(11):1954-1964
The design of compounds selective for the MT1 melatonin receptor is still a challenging task owing to the limited knowledge of the structural features conferring selectivity for the MT1 subtype, and only few selective compounds have been reported so far. N‐(Anilinoalkyl)amides are a versatile class of melatonin receptor ligands that include nonselective MT1/MT2 agonists and MT2‐selective antagonists. We synthesized a new series of N‐(anilinoalkyl)amides bearing 3‐arylalkyloxy or 3‐alkyloxy substituents at the aniline ring, looking for new potent and MT1‐selective ligands. To evaluate the effect of substituent size and shape on binding affinity and intrinsic activity, both flexible and conformationally constrained derivatives were prepared. The phenylbutyloxy substituent gave the best result, providing the partial agonist 4 a , which was endowed with high MT1 binding affinity (pKi=8.93) and 78‐fold selectivity for the MT1 receptor. To investigate the molecular basis for agonist recognition, and to explain the role of the 3‐arylalkyloxy substituent, we built a homology model of the MT1 receptor based on the β2 adrenergic receptor crystal structure in its activated state. A binding mode for MT1 agonists is proposed, as well as a hypothesis regarding the receptor structural features responsible for MT1 selectivity of compounds with lipophilic arylalkyloxy substituents. 相似文献
66.
Thirty-two Merino lambs fed barley straw and a concentrate alone (CONTROL group) or enriched with carnosic acid [0.6 g kg(-1) dry matter (DM), CARN006 group; 1.2 g kg(-1) DM, CARN012 group] or vitamin E (0.6 g kg(-1) DM, VITE006 group) were used to assess the effect of these antioxidant compounds on meat quality. After being fed the experimental diets for at least 5 weeks, the animals were slaughtered with the 25 kg intended body weight and the different muscles (longissimus lumborum; LL, gluteus medius; GM) were sliced and kept refrigerated under modified atmosphere packaging during 0, 7 and 14 days. The results indicate that carnosic acid seemed to be useful to delay lipid peroxidation in a medium colour-stable muscle such as GM, but this effect was lower than that observed when vitamin E was supplemented to fattening lambs. On the contrary, meat texture and protection against cholesterol oxidation were equally improved with both compounds. 相似文献
67.
Márquez-Ríos E Morán-Palacio EF Lugo-Sánchez ME Ocano-Higuera VM Pacheco-Aguilar R 《Journal of food science》2007,72(7):C356-C362
ABSTRACT: Several freshness and spoilage indicators were monitored to characterize the postmortem biochemistry of giant squid ( Dosidicus gigas ) mantle muscle. Squid samples were obtained directly from the sea and kept at 0 °C during a 15-d storage period. Data at zero time were obtained from cryogenically frozen samples at time of capture. The adenosine 5'-triphosphate (ATP) degradation followed a different pattern as compared with that from fish species. ATP was almost completely depleted at 24-h postcatch from 6.54 to <1 μmol/g, while at the same time Hx was the predominant catabolite with a concentration of 4 μmol/g, reaching 6.85 μmol/g at day 15. K -value data followed a logarithmic pattern with time instead of a linear one, with no change after day 3, thus reducing its suitability as a freshness index. The coefficient Hx/AMP seems to be an adequate alternative for this purpose due to its constant increment with time. The high NH4 Cl content in mantle muscle (461.3 ± 24.5 mg of NH4 + /100 g) derived from its physiological importance for the species compromises the use of the distillation step of the TVB-N analysis commonly used as a spoilage index. This fact explains why the initially high value of TVB-N detected in mantle muscle (243.7 mg N/100 g) did not correlate with the initial low TMA-N content (1.5 ± 0.1 mg/100 g of muscle). The results suggested that under the experimental conditions the shelf life of squid exceeds 15 d. 相似文献
68.
The potential of colour measurement for strength prediction of thermally treated wood 总被引:2,自引:2,他引:2
This paper investigates the effects of thermal treatment of birch with respect to colour and strength. Birch wood was treated at 175 °C and 200 °C for 0 h, 1 h, 3 h and 10 h. In bending-strength experiments, treatment was also performed at 185 °C for 2 h. Both static bending strength and impact bending strength were investigated using multivariate statistics (PLS) for correlation to process parameters, density, EMC, position in board, modulus of elasticity (only in static bending), colour and dimensions of samples. In static bending, two PLS models were designed, one based on process parameters and the other based on colour and EMC. From these models it was concluded that colour is not a useful parameter for prediction of strength. In impacted bending, the correlation was too small to give useful results. One test of static bending strength with matched samples was performed, and it showed a strength reduction of 43% when treatment was conducted at 200 °C for 3 h. Measurement of colour homogeneity of the treated boards showed that the colour is not homogeneous. 相似文献
69.
International Regulations of Propolis Quality: Required Assays do not Necessarily Reflect their Polyphenolic‐Related In Vitro Activities 下载免费PDF全文
Raquel Bridi Gloria Montenegro Gabriel Nuñez‐Quijada Ady Giordano Maria Fernanda Morán‐Romero Isaac Jara‐Pezoa Hernán Speisky Elias Atala Camilo López‐Alarcón 《Journal of food science》2015,80(6):C1188-C1195
Propolis has been proposed as a polyphenolic‐rich natural product potentially able to be used for human consumption or even for medicinal proposes. To guarantee a minimum phenolic and flavonoid content and as consequence of their related‐biological activities, international requirements of propolis quality are commonly applied. In this work we assessed phenolic and flavonoid contents of propolis; the antioxidant capacity (toward peroxyl radicals and hypochlorous acid); the ability to generate nitric oxide (NO); and, finally the antimicrobial activity of 6 propolis samples from the VI region of Chile. Our results show that the total phenolic and flavonoid content of propolis samples are not always in agreement with their polyphenolic‐associated in vitro activities. For example, P03 and P06 samples showed the lowest (25 ± 4 GAE/g propolis) and the highest (105 ± 3 GAE/g propolis) total phenolic content, respectively. This was in agreement with flavonoid content and their Oxygen Radical Absorbance Capacity (ORAC) activity. However, this dependence was not observed toward HOCl, NO release and antimicrobial activity. Based on our results, we consider that, in order to guarantee the antioxidant or antimicrobial in vitro effects, the international regulations of propolis quality should contemplate the convenience of incorporating other simple analytical test such as ORAC or antimicrobial tests. 相似文献
70.
Abstract We test the hypothesis that the combination of kiln drying of double-stacked boards and contact heat treatment will reduce the susceptibility of treated boards to colonization by mold fungi. Winter-felled Scots pine (Pinus sylvestris L.) sapwood boards were double-stacked in an industrial kiln in ‘‘sapwood out’’ and ‘‘sapwood in’’ positions. Dried samples were then contact heat-treated using a hot press at three different temperatures (140°C, 170°C, and 200°C) for three different periods (1, 3, and 10 min). An accelerated mold test was performed in a climate chamber where naturally mold-infected samples were used as a source of mold inocula. Contact heat treatment degraded the saccharides that accumulated at dried surfaces, and reduced the mold growth. The threshold temperature and time for inhibiting mold growth were 170°C for 10 min. However, for industrial application, the most feasible combination of temperature and time would be 200°C for 3 min. We concluded that double stacking/contact heat treatment used is an environmentally friendly alternative to chemicals for reducing mold on Scots pine sapwood boards. 相似文献