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排序方式: 共有648条查询结果,搜索用时 15 毫秒
111.
Yann Sarazin Pierre de Frmont Liana Annunziata Michel Duc Jean‐Franois Carpentier 《Advanced Synthesis \u0026amp; Catalysis》2011,353(8):1367-1374
Combinations of the discrete neutral allyl ansa‐lanthanidocenes {Me2C(Cp)(Flu)}Nd[1,3‐ (SiMe3)2C3H3] and rac‐{Me2C(Ind)2}Y[1,3‐ (SiMe3)2C3H3] with di(n‐butyl)magnesium constitute efficient binary catalytic systems for the stereocontrolled coordinative chain transfer polymerization of styrene, yielding near‐perfect syndio‐ and isospecific polystyrenes, respectively, with high activities and productivities. By adjusting the amount of di(n‐butyl)magnesium, up to 200 polymer chains can be generated per lanthabide center, and good control of the molecular weight features enables the tailoring of low to medium molecular weight polymers. 相似文献
112.
The growth of carbon nanotubes from Ni catalysts is reversed and observed in real time in a transmission electron microscope, at room temperature. The Ni catalyst is found to be Ni3C and remains attached to the nanotube throughout the irradiation sequence, indicating that C most likely diffuses on the surface of the catalyst to form nanotubes. We calculate the energy barrier for saturating the Ni3C (2-13) surface with C to be 0.14 eV, thus providing a low-energy surface for the formation of graphene planes. 相似文献
113.
Influence of strontium for calcium substitution in bioactive glasses on degradation,ion release and apatite formation 总被引:1,自引:0,他引:1
Yann C. Fredholm Natalia Karpukhina Delia S. Brauer Julian R. Jones Robert V. Law Robert G. Hill 《Journal of the Royal Society Interface》2012,9(70):880-889
Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo. A melt-derived glass series (SiO2–P2O5–CaO–Na2O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions. 相似文献
114.
Matthieu DubarryCyril Truchot Mikaël CugnetBor Yann Liaw Kevin GeringSergiy Sazhin David JamisonChristopher Michelbacher 《Journal of power sources》2011,196(23):10328-10335
Evaluating commercial Li-ion batteries presents some unique benefits. One of them is to use cells made from established fabrication process and form factor, such as those offered by the 18650 cylindrical configuration, to provide a common platform to investigate and understand performance deficiency and aging mechanism of target chemistry. Such an approach shall afford us to derive relevant information without influence from processing or form factor variability that may skew our understanding on cell-level issues. A series of 1.9 Ah 18650 lithium ion cells developed by a commercial source using a composite positive electrode comprising {LiMn1/3Ni1/3Co1/3O2 + LiMn2O4} is being used as a platform for the investigation of certain key issues, particularly path-dependent aging and degradation in future plug-in hybrid electric vehicle (PHEV) applications, under the US Department of Energy's Applied Battery Research (ABR) program. Here we report in Part I the initial characterizations of the cell performance and Part II some aspects of cell degradation in 2C cycle aging. The initial characterizations, including cell-to-cell variability, are essential for life cycle performance characterization in the second part of the report when cell-aging phenomena are discussed. Due to the composite nature of the positive electrode, the features (or signature) derived from the incremental capacity (IC) of the cell appear rather complex. In this work, the method to index the observed IC peaks is discussed. Being able to index the IC signature in details is critical for analyzing and identifying degradation mechanism later in the cycle aging study. 相似文献
115.
Prestressed concrete is commonly used in a wide range of applications, yet on rare occasions spalling problems have been reported
for concrete structures prestressed in two directions. The tensile behaviour of concrete may be affected by prestressing;
consequently a number of experiments have been performed to reproduce this load combination on laboratory samples. Tests were
carried out in a compression-tension triaxial cell suitable for the independent application of a lateral confining pressure,
as well as a direct axial tension load. Results reveal a measurable but limited reduction in concrete tensile strength with
a confining pressure of a similar magnitude as the prestress (order of magnitude of 10 MPa). Further experiments were conducted
at higher confining pressures, in both confined tension and in triaxial extension, in order to generate an overview of limit
state behaviour for the studied high performance concrete. 相似文献
116.
To be practical in automotive traction applications, fuel cell systems must provide power output levels of performance that rival that of typical internal combustion engines. In so doing, transient behavior is one of the keys for success of fuel cell systems in vehicles. The focus of this paper is on the air/fuel supply subsystem in tracking an optimum variable pressurization and air flow for maximum system efficiency during load transients. The control-oriented model developed for this study considers electrochemistry, thermodynamics, and fluid flow principles for a 13-state, nonlinear model of a pressurized fuel cell system. For control purposes, a model reduction is performed, and several multi-variable control designs are examined. The first technique uses an observer-based linear optimum control which combines a feed-forward approach based on the steady-state plant inverse response, coupled to a multi-variable LQR feedback control. An extension of that approach, for control in the full nonlinear range of operation, leads to the second technique, nonlinear gain-scheduled control. Some enhancements were applied to overcome the fast variations in the scheduling variable. Finally, a rule-based, output feedback control, implemented with fuzzy logic, is coupled with a nonlinear feed-forward approach, and is examined under the same conditions applied to the first two techniques. The control designs developed are compared in simulation studies to investigate robustness to disturbance, time delay, and actuator limitations. 相似文献
117.
Wenhao Fang Yann Romani Yaqian Wei Mónica Jiménez-Ruiz Hervé Jobic Sébastien Paul Louise Jalowiecki-Duhamel 《International Journal of Hydrogen Energy》2018,43(37):17643-17655
Mg2AlNiXHZOY nano-oxyhydrides formation is evidenced during pre-treatment in H2 at 450 °C of Mg2AlNiXOY nano-compounds leading to highly performant catalysts in ethanol conversion and H2 formation, particularly at low temperature, through catalytic steam reforming (SRE) and oxidative steam reforming (OSRE). Total conversion of ethanol is obtained in SRE and OSRE with high stability. A higher production of H2 (60 L h?1 gcat?1) can be achieved at a reaction temperature of 300 °C in OSRE conditions compared to SRE (10 L h?1 gcat?1) mainly because of a beneficial use of a high concentration of ethanol (14 mol%) in presence of O2. Moreover, carbon formation is decreased and a much lower input of energy of 50 °C is used to get a temperature of 300 °C when O2 is added. Different physico-chemical characterizations and in particular in H2 (TPR, H2-XRD, INS) and after tests allow to conclude that the presence of Ni2+ cations in strong interaction with other cations, anionic vacancies and hydride species on and inside the solid play an important role in the catalytic performance (conversion and selectivity) and stability. 相似文献
118.
The structural build-up of rigid fiber reinforced cement-based materials is studied. It has recently been shown that the behaviour of fiber reinforced concrete depends on the orientation of the fibers that has to be optimized during casting. As a result, there is a great interest to study the rheology of fiber reinforced concrete. One of the most important characteristics of modern fresh concretes is the structural build-up which is involved in many recent issues of concrete casting. This characteristic depends on the cement pastes chemical activity. This present work shows that structural build-up modelling used for common concretes can be generalized to fiber reinforced concretes. It can be shown that, if the inclusions percolation threshold is not reached, the structural build-up rate A thix is amplified by the addition of fibers and aggregates. Finally, this amplification of the structuration is estimated using modelling initially developed for spherical inclusions and aggregates. 相似文献
119.
Benjamin Dierre Karine Costuas Noée Dumait Serge Paofai Maria Amela-Cortes Yann Molard 《Science and Technology of Advanced Materials》2013,14(1):458-466
AbstractWe report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [Mo6Xi8La6]2? (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo6 metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the AxMo6Xi8La6 series (A = Cs+, (n-C4H9)4N+, NH4+) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.). 相似文献
120.
Since their introduction in image denoising, the family of non-local methods, whose Non-Local Means (NL-Means) is the most famous member, has proved its ability to challenge other powerful methods such as wavelet based approaches or variational techniques. Though simple to implement and efficient in practice, the classical NL-Means algorithm suffers from several limitations: noise artifacts are created around edges and regions with few repetitions in the image are not treated at all. In this paper, we present an easy to implement and time efficient modification of the NL-Means based on a better reprojection from the patches space to the original pixel space, specially designed to reduce the artifacts due to the rare patch effect. We compare the performance of several reprojection schemes on a toy example and on some classical natural images. 相似文献