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排序方式: 共有168条查询结果,搜索用时 859 毫秒
51.
C. Wessel A. Cisilino O. Santi J. Otegui M. Chapetti 《Theoretical and Applied Fracture Mechanics》2001,35(1)
This work is concerned with the assessment of propagation of multiple fatigue cracks in three-dimensions. Computational modelling of fatigue crack propagation is made together with detection and monitoring of the crack shape development. The boundary element method (BEM) is used for automating the modelling of crack propagation in linear elastic as well as elastic–plastic regimes. Strain at several positions on the specimen surface near the crack mouth is measured to monitor crack initiation, shape development and closure levels. Examples are provided to validate the model by comparing the experimental results with those obtained by numerical predictions. 相似文献
52.
Abstract Glycosidation of 2′ 3′ 6′-tri-O-benzyl-α-d-glucopyranosyl 2,3-di-O-benzyl-4,6-O-benzylidene-α-d- glucopyranoside (2) with α-aceto-bromosophorose (1) gave the α- and β-linked tetrasaccharides 3 and 4 in an approximately 2:1 ratio in dichloromethane or acetonitrile. The reaction is discussed, notably the predominant formation of α-glycosides. Both compounds were fully characterized by 1H and 13C NMR spectroscopy applying 1D TOCSY, 1D T-ROESY, 1H-detected one-bond and multiple bond 1H, 13C 2D COSY. Deprotection of 3 and 4 furnished the free sophorosyl trehaloses 7 and 8. 相似文献
53.
So-Ryong Chae Mathieu Therezien Jeffrey Farner Budarz Lauren Wessel Shihong Lin Yao Xiao Mark R. Wiesner 《Journal of nanoparticle research》2011,13(10):5121-5127
Nanomaterials such as fullerene C60, carbon nanotubes (CNTs), and other fullerenes show unique electrical, chemical, mechanical, and thermal properties that
are not well understood in the context of the environmental behavior of this class of carbon-based materials. In this study,
aqueous suspensions of three fullerenes nanoparticles, C60, single-wall (SW) and multi-wall (MW) CNTs were prepared by sonication and tested for reactive oxygen species (ROS) production
and inactivation of Vibrio fischeri, a gram-negative rod-shaped bacterium, under ultraviolet (UV)-A irradiation. We show that ROS production and microbial inactivation
increases as colloidal aggregates of C60, SWCNT, and MWCNT are fractionated to enrich with smaller aggregates by progressive membrane filtration. As the quantity
and influence of these more reactive fractions of the suspension may increase with time and/or as the result of fractionation
processes in the laboratory or the environment, experiments evaluating photo-reactivity and toxicity endpoints must take into
account the evolution and heterogeneity of nanoparticle aggregates in water. 相似文献
54.
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56.
Albrecht M Wessel C de Groot M Rissanen K Lüchow A 《Journal of the American Chemical Society》2008,130(14):4600-4601
A series of pentafluorophenyl substituted ammonium, iminium, amidinium, and phosphonium halides are presented which show extensive anion-pi interactions. Hereby, the well-known anion-donor-pi-acceptor as well as "eta6" anion-pi-complex type interactions are observed. The latter is supported by fixation of the anion on top of the aromatic system through hydrogen bonding. This arrangement was investigated by theoretical methods showing a highly attractive anion-pi interaction. In addition an eta2-type coordination of the anions to only two C-atoms of the electron-deficient ring system is described. 相似文献
57.
Dr. Wengao Zhao Dr. Kuan Wang Prof. Xinming Fan Fucheng Ren Xieyu Xu Dr. Yangyang Liu Dr. Shizhao Xiong Dr. Xiangsi Liu Zhengfeng Zhang Mayan Si Ruizhuo Zhang Dr. Wessel van den Bergh Prof. Pengfei Yan Dr. Corsin Battaglia Dr. Torsten Brezesinski Prof. Yong Yang 《Angewandte Chemie (International ed. in English)》2023,62(32):e202305281
Single-crystal LiNixCoyMnzO2 (SC-NCM, x+y+z=1) cathodes are renowned for their high structural stability and reduced accumulation of adverse side products during long-term cycling. While advances have been made using SC-NCM cathode materials, careful studies of cathode degradation mechanisms are scarce. Herein, we employed quasi single-crystalline LiNi0.65Co0.15Mn0.20O2 (SC-NCM65) to test the relationship between cycling performance and material degradation for different charge cutoff potentials. The Li/SC-NCM65 cells showed >77 % capacity retention below 4.6 V vs. Li+/Li after 400 cycles and revealed a significant decay to 56 % for 4.7 V cutoff. We demonstrate that the SC-NCM65 degradation is due to accumulation of rock-salt (NiO) species at the particle surface rather than intragranular cracking or side reactions with the electrolyte. The NiO-type layer formation is also responsible for the strongly increased impedance and transition-metal dissolution. Notably, the capacity loss is found to have a linear relationship with the thickness of the rock-salt surface layer. Density functional theory and COMSOL Multiphysics modeling analysis further indicate that the charge-transfer kinetics is decisive, as the lower lithium diffusivity of the NiO phase hinders charge transport from the surface to the bulk. 相似文献
58.
Malberg H Bauernschmitt R Voss A Walther T Faber R Stepan H Wessel N 《Chaos (Woodbury, N.Y.)》2007,17(1):015113
Pre-eclampsia (PE) is a serious disorder with high morbidity and mortality occurring during pregnancy; 3%-5% of all pregnant women are affected. Early prediction is still insufficient in clinical practice. Although most pre-eclamptic patients show pathological uterine perfusion in the second trimester, this parameter has a positive predictive accuracy of only 30%, which makes it unsuitable for early, reliable prediction. The study is based on the hypothesis that alterations in cardiovascular regulatory behavior can be used to predict PE. Ninety-six pregnant women in whom Doppler investigation detected perfusion disorders of the uterine arteries were included in the study. Twenty-four of these pregnant women developed PE after the 30th week of gestation. During pregnancy, additional several noninvasive continuous blood pressure recordings were made over 30 min under resting conditions by means of a finger cuff. The time series extracted of systolic as well as diastolic beat-to-beat pressures and the heart rate were studied by variability and coupling analysis to find predictive factors preceding genesis of the disease. In the period between the 18th and 26th weeks of pregnancy, three special variability and baroreflex parameters were able to predict PE several weeks before clinical manifestation. Discriminant function analysis of these parameters was able to predict PE with a sensitivity and specificity of 87.5% and a positive predictive value of 70%. The combined clinical assessment of uterine perfusion and cardiovascular variability demonstrates the best current prediction several weeks before clinical manifestation of PE. 相似文献
59.
C. Wessel C. Reimann A. Müller D. Weber M. Lerch T. Ressler T. Bredow R. Dronskowski 《Journal of computational chemistry》2012,33(26):2102-2107
A metastable bixbyite‐type polymorph of vanadium sesquioxide, V2O3, has recently been synthesized, and it transforms to the corundum‐type phase at temperatures around 550 °C. The possibility of a paramagnetic to canted antiferromagnetic or even spin‐glass‐like transition has been discussed. Quantum‐chemical calculations on the density‐functional theory level including explicit electronic correlation confirm the metastability as well as the semiconducting behavior of the material and predict that the bixbyite‐type structure is about 0.1 eV less stable than the well‐known corundum‐type phase. Nonetheless, quasiharmonic phonon calculations manifest that bixbyite‐type vanadium sesquioxide is a dynamically stable compound. Other possible V2O3 polymorphs are shown to be even less suitable candidates for the composition V2O3. © 2012 Wiley Periodicals, Inc. 相似文献
60.
Snieder R Douma H Vasconcelos I 《The Journal of the Acoustical Society of America》2012,131(4):EL309-EL315
Existing methods for Green's function extraction give the Green's function from the correlation of field fluctuations recorded at those points. In this work it is shown that the Green's function for acoustic waves can be retrieved from measurements of the integrated energy flux through a closed surface taken from three experiments where two time-harmonic sources first operate separately, and then simultaneously. This makes it possible to infer the Green's function in acoustics from measurements of the energy flux through an arbitrary closed surface surrounding both sources. The theory is also applicable to quantum mechanics where the Green's function can be retrieved from measurement of the flux of scattered particles through a closed surface. 相似文献