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排序方式: 共有751条查询结果,搜索用时 15 毫秒
21.
Nizhenko Valentin I. Skorokhod Valerii V. 《Powder Metallurgy and Metal Ceramics》2004,43(7-8):364-370
A kinetic equation for compaction with liquid-phase sintering is found on the basis of rheological sintering theory. Kinetic coefficients of the equation are determined from physicochemical properties of a dispersed system and its components. Compaction kinetics are studied for the system W – Ni – Sn where the liquid phase is eutectic alloy Ni – Sn with the greatest nickel content. It is shown that experimental results are in good agreement with those obtained by the kinetic equation on the coordinates porosity – time. Diffusion coefficient is evaluated for tungsten in melt (67.5 mass% Ni + 32.5 mass% Sn): at 1200°C it is 0.113·10–5 cm2/sec for grain diameter L 0 = 3 μm. Time dependences are also obtained for the compaction rate and viscosity of the pseudoalloys studied. 相似文献
22.
Radu Nicolae Revnic Gabriela Fabiola tiufiuc Valentin Toma Anca Onaciu Alin Moldovan Adrian Bogdan
igu Eva Fischer-Fodor Romulus Tetean Emil Burzo Rare Ionu tiufiuc 《International journal of molecular sciences》2022,23(15)
We report a very simple, rapid and reproducible method for the fabrication of anisotropic silver nanostars (AgNS) that can be successfully used as highly efficient SERS substrates for different bioanalytes, even in the case of a near-infra-red (NIR) excitation laser. The nanostars have been synthesized using the chemical reduction of Ag+ ions by trisodium citrate. This is the first research reporting the synthesis of AgNS using only trisodium citrate as a reducing and stabilizing agent. The key elements of this original synthesis procedure are rapid hydrothermal synthesis of silver nanostars followed by a cooling down procedure by immersion in a water bath. The synthesis was performed in a sealed bottom flask homogenously heated and brought to a boil in a microwave oven. After 60 s, the colloidal solution was cooled down to room temperature by immersion in a water bath at 35 °C. The as-synthesized AgNS were washed by centrifugation and used for SERS analysis of test molecules (methylene blue) as well as biological analytes: pharmaceutical compounds with various Raman cross sections (doxorubicin, atenolol & metoprolol), cell lysates and amino acids (methionine & cysteine). UV-Vis absorption spectroscopy, (Scanning) Transmission Electron Microscopy ((S)TEM) and Atomic Force Microscopy (AFM) have been employed for investigating nanostars’ physical properties. 相似文献
23.
Oregano: chemical analysis and evaluation of its antimalarial, antioxidant, and cytotoxic activities
El Babili F Bouajila J Souchard JP Bertrand C Bellvert F Fouraste I Moulis C Valentin A 《Journal of food science》2011,76(3):C512-C518
Abstract: GC‐FID and GC‐MS analysis of essential oil from oregano leaves (Origanum compactum) resulted in the identification of 46 compounds, representing more than 98% of the total composition. Carvacrol was the predominant compound (36.46%), followed by thymol (29.74%) and p‐cymene (24.31%). Serial extractions with petroleum ether, ethyl acetate, ethanol, and water were performed on aerials parts of Origanum compactum. In these extracts, different chemical families were characterized: polyphenols (gallic acid equivalent 21.2 to 858.3 g/kg), tannins (catechin equivalent 12.4 to 510.3 g/kg), anthocyanins (cyanidin equivalent 0.38 to 5.63 mg/kg), and flavonoids (quercetin equivalent 14.5 to 54.7 g/kg). The samples (essential oil and extracts) were subjected to a screening for antioxidant (DPPH and ABTS assays) and antimalarial activities and against human breast cancer cells. The essential oil showed a higher antioxidant activity with an IC50= 2 ± 0.1 mg/L. Among the extracts, the aqueous extract had the highest antioxidant activity with an IC50= 4.8 ± 0.2 mg/L (DPPH assay). Concerning antimalarial activity, Origanum compactum essential oil and ethyl acetate extract showed the best results with an IC50 of 34 and 33 mg/mL, respectively. In addition, ethyl acetate extract (30 mg/L) and ethanol extract (56 mg/L) showed activity against human breast cancer cells (MCF7). The oregano essential oil was considered to be nontoxic. 相似文献
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Marco Albertini Francesca Vallese Marilena Di Valentin Paola Berto Giorgio M. Giacometti Paola Costantini Donatella Carbonera 《International Journal of Hydrogen Energy》2014
[FeFe]-hydrogenases contain a complex [4Fe–4S]-2Fe cluster (H-cluster) and are able to efficiently reduce protons to H2. Due to their potential exploitation for renewable energy production biotechnologies, significant efforts have been put into understanding the mechanisms driving the H-cluster assembly, which involves three conserved proteins. Among them, HydF works as scaffold upon which the H-cluster precursor is synthesized and carrier to deliver it to the hydrogenase, resulting in its activation. A FeS cluster binding sequence (CxHx46-53HCxxC) is conserved in all HydF proteins and should in principle provide four ligands to coordinate the Fe atom. However, we found that alternative metal coordination may exist in different HydF proteins and that only the three cysteines are strictly required, whereas the fourth ligand may vary and is, in any case, readily exchangeable. In this work we analyzed by EPR/HYSCORE the FeS cluster proton environment of HydF from Thermotoga neapolitana to determine the possible role of surrounding residues in the non-cysteinyl iron ligation of the protein. 相似文献
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Simonetta Caira Gabriella Pinto Valentin A. Balteanu Lina Chianese Francesco Addeo 《Food chemistry》2013
A novel genetic variant at the αs1-casein locus of water buffalo (WB), 8-residue shorter than its wild-type has been found and sequenced. The internal deletion of the peptide E35KVNELsT42 was confirmed by the isolation of the junction peptide. The 8-residue deletion mutant has a molecular weight that is 919 Da less than that of the wild-type. The novel isoform with a unique f35-42 deletion could be the result of the skipping of exon 6, generating an exon 6-deleted variant of αs1-casein. The wild-type and its shortened αs1-casein forms were found to co-exist in many individual milk samples. In contrast, the 8-residue, internally deleted αs1-casein variant did not occur in water buffaloes of the Mediterranean breed reared in Italy. Wild-type αs1-casein has 6 to 8 phosphate groups (P) while the internally deleted form 6 and 7P per molecule. 相似文献