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排序方式: 共有655条查询结果,搜索用时 31 毫秒
121.
M. Kersemans I. De Baere J. Degrieck K. Van Den Abeele L. Pyl F. Zastavnik H. Sol W. Van Paepegem 《Experimental Mechanics》2014,54(8):1467-1477
This study investigates the use of both the amplitude and time-of-flight based pulsed ultrasonic polar scan (P-UPS) for the nondestructive detection and evaluation of fatigue damage in fabric reinforced composites. Several thermoplastic carbon fabric reinforced PPS specimens (CETEX), loaded under various fatigue conditions, have been scanned at multiple material spots according to the P-UPS technique in order to extract material degradation in a quantitative way. The P-UPS results indicate that shear dominated fatigued carbon/PPS goes with a reduction of shear properties combined with large fiber distortions. The P-UPS results of the tension-tension fatigued carbon/PPS samples on the other hand reveal a directional degradation of the stiffness properties, reaching a maximum reduction of ?12.8 % along the loading direction. The P-UPS extracted damage characteristics are fully supported by simulations, conventional destructive tests as well as visual inspection. The results demonstrate the excellent capability of the P-UPS method for nondestructively assessing and quantifying both shear-dominated and tension-tension fatigue damage in fabric reinforced plastics. 相似文献
122.
Osuna S Valencia R Rodríguez-Fortea A Swart M Solà M Poblet JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(29):8944-8956
In this work a detailed investigation of the exohedral reactivity of the most important and abundant endohedral metallofullerene (EMF) is provided, that is, Sc(3)N@I(h)-C(80) and its D(5h) counterpart Sc(3)N@D(5h)-C(80) , and the (bio)chemically relevant lutetium- and gadolinium-based M(3)N@I(h)/D(5h)-C(80) EMFs (M = Sc, Lu, Gd). In particular, we analyze the thermodynamics and kinetics of the Diels-Alder cycloaddition of s-cis-1,3-butadiene on all the different bonds of the I(h)-C(80) and D(5h)-C(80) cages and their endohedral derivatives. First, we discuss the thermodynamic and kinetic aspects of the cycloaddition reaction on the hollow fullerenes and the two isomers of Sc(3)N@C(80). Afterwards, the effect of the nature of the metal nitride is analyzed in detail. In general, our BP86/TZP//BP86/DZP calculations indicate that [5,6] bonds are more reactive than [6,6] bonds for the two isomers. The [5,6] bond D(5h)-b, which is the most similar to the unique [5,6] bond type in the icosahedral cage, I(h)-a, is the most reactive bond in M(3)N@D(5h)-C(80) regardless of M. Sc(3)N@C(80) and Lu(3)N@C(80) give similar results; the regioselectivity is, however, significantly reduced for the larger and more electropositive M = Gd, as previously found in similar metallofullerenes. Calculations also show that the D(5h) isomer is more reactive from the kinetic point of view than the I(h) one in all cases which is in good agreement with experiments. 相似文献
123.
Mentink JH Hellsvik J Afanasiev DV Ivanov BA Kirilyuk A Kimel AV Eriksson O Katsnelson MI Rasing T 《Physical review letters》2012,108(5):057202
We propose a general theoretical framework for ultrafast laser-induced spin dynamics in multisublattice magnets. We distinguish relaxation of relativistic and exchange origin and show that when the former dominates, nonequivalent sublattices have distinct dynamics despite their strong exchange coupling. Even more interesting, in the exchange dominated regime sublattices can show highly counterintuitive transitions between parallel and antiparallel alignment. This allows us to explain recent experiments with antiferromagnetically coupled sublattices, and predict that such transitions are possible with ferromagnetic coupling as well. In addition, we predict that exchange relaxation enhances the demagnetization speed of both sublattices only when they are antiferromagnetically coupled. 相似文献
124.
Park SJ Shin S Koo OJ Moon JH Jang G Ahn C Lee BC Yoo YJ 《Experimental & molecular medicine》2012,44(1):20-25
Transplantation of islet cells into diabetic patients is a promising therapy, provided that the islet cells are able to evade host immune rejection. With improved islet viability, this strategy may effectively reverse diabetes. We applied 2% calcium alginate to generate small and large capsules to encapsulate porcine neonatal pancreatic cell clusters (NPCCs) using an air-driven encapsulator. After encapsulation, the viability was assessed at 1, 4, 7, 14 and 28 days and secretion of functional insulin in response to glucose stimulation were tested at days 14 and 28. Selective permeability of the small alginate capsules was confirmed using various sizes of isothiocyanate-labeled dextran (FITC-dextran). Encapsulation of NPCCs was performed without islet protrusion in the small and large capsules. The viability of NPCCs in all experimental groups was greater than 90% at day 1 and then gradually decreased after day 7. The NPCCs encapsulated in large capsules showed significantly lower viability (79.50 ± 2.88%) than that of naïve NPCCs and NPCCs in small capsule (86.83 ± 2.32%, 87.67 ± 2.07%, respectively) at day 7. The viability of naïve NPCCs decreased rapidly at day 14 (75.67 ± 1.75%), whereas the NPCCs encapsulated in small capsules maintained (82.0 ± 2.19%). After 14 and 28 days NPCCs' function in small capsules (2.67 ± 0.09 and 2.13 ± 0.09) was conserved better compared to that of naïve NPCCs (2.04 ± 0.25 and 1.53 ± 0.32, respectively) and NPCCs in large capsules (2.04 ± 0.34 and 1.13 ± 0.10, respectively), as assessed by a stimulation index. The small capsules also demonstrated selective permeability. With this encapsulation technique, small capsules improved the viability and insulin secretion of NPCCs without islet protrusion. 相似文献
125.
AK Peacock SI Cauët A Taylor P Murray SR Williams JV Weaver DJ Adams MJ Rosseinsky 《Chemical communications (Cambridge, England)》2012,48(75):9373-9375
Poly[2-(methacryloyloxy)ethylphosphorylcholine]-coated SPIONs were prepared through ATRP and amidation coupling reactions. The coated SPIONs exhibited high stability and re-dispersability in phosphate buffered saline and uptake in a stem cell line, with high T(2) relaxivity. 相似文献
126.
Lievano R Pérez HI Manjarrez N Solís A Solís-Oba M 《Molecules (Basel, Switzerland)》2012,17(3):3148-3154
A novel application of whole cells of Nocardia corallina B-276 for the deracemisation of ibuprofen is reported. This microorganism successfully hydrolysed ibuprofen nitrile to ibuprofen amide, and ibuprofen amide to ibuprofen, using a suspension of cells in a potassium phosphate buffer solution (0.1 M, pH = 7.0). These results can be explained by the presence of NHase and amidase enzymes, but the reactions are not enantioselective and low ee values were obtained. However, (R)-ibuprofen was isolated with > 99% ee by a deracemisation process catalysed by N. corallina B-276. This is the first report of this kind of catalysis with this microorganism. 相似文献
127.
Using maps due to Ozeki and Broué-Enguehard between graded spaces of invariants for certain finite groups and the algebra of modular forms of even weight we equip these invariants spaces with a differential operator which gives them the structure of a Rankin-Cohen algebra. A direct interpretation of the Rankin-Cohen bracket in terms of transvectant for the group SL(2, C) is given. 相似文献
128.
Anton J. Stasyuk Olga A. Stasyuk Miquel Solà Alexander A. Voityuk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(47):10896-10902
A triquinoline cationic moiety (TQ⋅H+) has recently been designed as a novel molecular unit for supramolecular chemistry. In addition to some useful features, TQ⋅H+ has strong electron-acceptor properties, which renders the molecular cation a unique element in nanochemistry. TQ⋅H+ is found to form complexes with coronene (COR) and cycloparaphenylene (CPP). In this work, we report a computational study of photoinduced electron transfer in supramolecular complexes TQ⋅H+-COR, TQ⋅H+⊂[12]CPP and (TQ⋅H+-COR)⊂[12]CPP. The electron-transfer rates are estimated by using the semi-classical approach. The results are compared with the data previously obtained for a structurally similar inclusion complex Li+@C60⊂[10]CPP. In particular, we found a red solvatochromic shift for charge-shift bands in the TQ⋅H+-complexes unlike a blueshift showed by Li+@C60⊂[10]CPP. This distinction is explored in terms of electronic and structural features of the systems. 相似文献
129.
Dr. Solène Gentil Dr. Pierre Rousselot-Pailley Ferran Sancho Dr. Viviane Robert Dr. Yasmina Mekmouche Prof. Victor Guallar Dr. Thierry Tron Dr. Alan Le Goff 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(21):4798-4804
A maximization of a direct electron transfer (DET) between redox enzymes and electrodes can be obtained through the oriented immobilization of enzymes onto an electroactive surface. Here, a strategy for obtaining carbon nanotube (CNTs) based electrodes covalently modified with perfectly control-oriented fungal laccases is presented. Modelizations of the laccase-CNT interaction and of electron conduction pathways serve as a guide in choosing grafting positions. Homogeneous populations of alkyne-modified laccases are obtained through the reductive amination of a unique surface-accessible lysine residue selectively engineered near either one or the other of the two copper centers in enzyme variants. Immobilization of the site-specific alkynated enzymes is achieved by copper-catalyzed click reaction on azido-modified CNTs. A highly efficient reduction of O2 at low overpotential and catalytic current densities over −3 mA cm−2 are obtained by minimizing the distance from the electrode surface to the trinuclear cluster. 相似文献
130.
Dr. Juan Pablo Martínez Prof. Dr. Miquel Solà Dr. Albert Poater 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(72):18074-18083
Predictive catalysis must be the tool that does not replace experiments, but acts as a selective agent, so that synthetic strategies of maximum profitability are used in the laboratory in a surgical way. Here, nanotechnology has been used in olefin metathesis from homogeneous Ru-NHC catalysts, specifically annulating a C60 fullerene to the NHC ligand. Based on results with the C60 in the backbone, a sterile change with respect to the catalysis of the metal center, an attempt has been made to bring C60 closer to the metal, by attaching it to one of the two C−N bonds of the imidazole group of the SIMes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) ligand (reference NHC ligand of the 2nd generation Grubbs catalysts) to increase the steric pressure of C60 in the first sphere of reactivity of the metal. The DFT calculated thermodynamics and the kinetics of SIMes-derived systems show that they are efficient catalysts for olefin metathesis. 相似文献