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排序方式： 共有821条查询结果，搜索用时 15 毫秒
811.
Mathematical models are developed to describe the polymerization of ethylene and 1‐hexene with a constrained geometry catalyst (CGC‐Ti) and with bis(cyclopentadienyl)‐zirconium (IV) dichloride (Cp2ZrCl2). Particle swarm optimization is used to fit these models to homo‐ and copolymerization data. The models are also used to describe copolymerizations with mixtures of CGC‐Ti and Cp2ZrCl2 to make copolymers with inverse short chain branching distribution. Copolymer molecular weight and short chain branch distributions, as well as polymerization rates with the dual metallocene system, are measured to test whether they agreed with model predictions. The results show that the two metallocenes do not interact strongly when used as a mixture to make ethylene/1‐hexene copolymers. 相似文献
812.
The essential amino acid lysine is of great importance in the nutrition and pharmaceutical industries and is mainly produced in biorefineries by the fermentation of glucose. In biorefineries, downstream processing is often the most energy-consuming step. Adsorption on hydrophobic adsorbents represents an energy, resource, and cost-saving alternative. The results reported herein provide insights into the selective separation of l -lysine from aqueous solution by liquid-phase adsorption using tailored activated carbons. A variety of commercial activated carbons with different textural properties and surface functionalities is investigated. Comprehensive adsorbent characterization establishes structure–adsorption relationships that define the major roles of the specific surface area and oxygen functionalities. A 13-fold increase of the separation of lysine and glucose is achieved through systematic modification of a selected activated carbon by oxidation, and lysine adsorption is enhanced by 30 %. 相似文献
813.
Jin He Jeff Armstrong Peixi Cong Barak Menagen Lior Igaher Andrew M. Beale Lioz Etgar David Avnir 《Angewandte Chemie (International ed. in English)》2020,59(12):4698-4704
An ultra‐high increase in the WF of silver, from 4.26 to 7.42 eV, that is, an increase of up to circa 3.1 eV is reported. This is the highest WF increase on record for metals and is supported by recent computational studies which predict the potential ability to affect an increase of the WF of metals by more than 4 eV. We achieved the ultra‐high increase by a new approach: Rather than using the common method of 2D adsorption of polar molecules layers on the metal surface, WF modifying components, l ‐cysteine and Zn(OH)2, were incorporated within the metal, resulting in a 3D architecture. Detailed material characterization by a large array of analytical methods was carried out, the combination of which points to a WF enhancement mechanism which is based on directly affecting the charge transfer ability of the metal separately by cysteine and hydrolyzed zinc(II), and synergistically by the combination of the two through the known Zn‐cysteine finger redox trap effect. 相似文献
814.
Dr. Jeff M. Van Raden Dr. Nanette N. Jarenwattananon Dr. Lev N. Zakharov Prof. Ramesh Jasti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(45):10205-10209
Molecules and materials that demonstrate large amplitude responses to minor changes in their local environment play an important role in the development of new forms of nanotechnology. Molecular daisy chains are a type of a mechanically interlocked molecule that are particularly sensitive to such changes in which, in the presence of certain stimuli, the molecular linkage enables muscle-like movement between a reduced-length contracted form and an increased-length expanded form. To date, all reported syntheses of molecular daisy chains are accomplished via passive-template methods, resulting in a majority of structures being switchable only through the addition of an exogenous stimuli such as metal ions or changes in pH. Here, we describe a new approach to these structural motifs that exploits a multi-component active-metal template synthesis to mechanically interlock two pi-rich nanohoop macrocycles into a molecular daisy chain that undergoes large conformational changes using thermal energy. 相似文献
815.
Kritsadi Thetpraphi Minh Quyen Le Afef Houachtia Pierre‐Jean Cottinet Lionel Petit David Audigier Jeff Kuhn Gil Moretto Jean‐Fabien Capsal 《Advanced Optical Materials》2019,7(13)
The interdisciplinary approach presented here creates next‐generation large mirrors using electroactive polymer (EAP) actuators without classical glass abrasive polishing (“live mirrors”). The outstanding electromechanical coupling properties of terpolymer are taken advantage of, particularly when doped with plasticizer, e.g., diisononyl phthalate (DINP). This doped terpolymer creates a large strain response as well as excellent mechanical energy density under relatively low electric fields. Classical EAPs (e.g., polyurethane, silicone) require extremely high input voltages to reach sufficient mechanical strain. Using the high‐permittivity doped terpolymer and the concept of stacking multilayers, high displacements and large forces are generated. The actuation performance of multilayered terpolymer filled with DINP has been proven to shape mirror glass with a preliminary prototype of an 8‐layer actuator stack. The experimental results demonstrate surface deformations under load conditions of several microns. This is large enough to usefully control large optical telescope mirrors. This technology may enable much larger high‐quality optical mirror systems for ground‐ and space‐based astronomy and communications telescopes. 相似文献
816.
Danny Bottenus Shirmir Branch Hope Lackey Cornelius Ivory Jeff Katalenich Sue Clark Amanda Lines 《Electrophoresis》2019,40(18-19):2531-2540
Elemental analysis of rare earth elements is essential in a variety of fields including environmental monitoring and nuclear safeguards; however, current techniques are often labor intensive, time consuming, and/or costly to perform. The difficulty arises in preparing samples, which requires separating the chemically and physically similar lanthanides. However, by transitioning these separations to the microscale, the speed, cost, and simplicity of sample preparation can be drastically improved. Here, all fourteen non‐radioactive lanthanides (lanthanum through lutetium minus promethium) are separated by ITP for the first time in a serpentine fused‐silica microchannel (70 µm wide × 70 µm tall × 33 cm long) in <10 min at voltages ≤8 kV with limits of detection on the order of picomoles. This time includes the 2 min electrokinetic injection time at 2 kV to load sample into the microchannel. The final leading electrolyte consisted of 10 mM ammonium acetate, 7 mM α‐hydroxyisobutyric acid, 1% polyvinylpyrrolidone, and the final terminating electrolyte consisted of 10 mM acetic acid, 7 mM α‐hydroxyisobutyric acid, and 1% polyvinylpyrrolidone. Electrophoretic electrodes are embedded in the microchip reservoirs so that voltages can be quickly applied and switched during operation. The limits of detection are quantified using a commercial capacitively coupled contactless conductivity detector (C4D) to calculate ITP zone lengths in combination with ITP theory. Optimization of experimental procedures and reproducibility based on statistical analysis of subsequent experimental results are addressed. Percent error values in band length and conductivity are ≤8.1 and 0.37%, respectively. 相似文献
817.
Peter Rowlett Edward Smith Alexander S. Corner David O’Sullivan Jeff Waldock 《International Journal of Mathematical Education in Science & Technology》2019,50(7):972-986
ABSTRACTA literature review establishes a working definition of recreational mathematics: a type of play which is enjoyable and requires mathematical thinking or skills to engage with. Typically, it is accessible to a wide range of people and can be effectively used to motivate engagement with and develop understanding of mathematical ideas or concepts. Recreational mathematics can be used in education for engagement and to develop mathematical skills, to maintain interest during procedural practice and to challenge and stretch students. It can also make cross-curricular links, including to history of mathematics. In undergraduate study, it can be used for engagement within standard curricula and for extra-curricular interest. Beyond this, there are opportunities to develop important graduate-level skills in problem-solving and communication. The development of a module ‘Game Theory and Recreational Mathematics’ is discussed. This provides an opportunity for fun and play, while developing graduate skills. It teaches some combinatorics, graph theory, game theory and algorithms/complexity, as well as scaffolding a Pólya-style problem-solving process. Assessment of problem-solving as a process via examination is outlined. Student feedback gives some indication that students appreciate the aims of the module, benefit from the explicit focus on problem-solving and understand the active nature of the learning. 相似文献
818.
Jeff Steinhauer 《Annalen der Physik》2018,530(5)
The observation of quantum Hawking radiation and its entanglement in an analogue black hole was recently reported. A subsequent article presented critical comments of the study. The article suffers from technical difficulties which invalidate its claims. These include the misunderstanding of a simple Fourier transform, the unnecessary modification of experimental data, and the assertion that the experiment measured a strictly‐zero population. 相似文献
819.
Jeff Waldock Peter Rowlett Claire Cornock Mike Robinson Hannah Bartholomew 《International Journal of Mathematical Education in Science & Technology》2017,48(4):587-602
By helping create a shared, supportive, learning community, the creative use of custom-designed spaces outside the classroom has a major impact on student engagement. The intention is to create spaces that promote peer interaction within and across year groups, encourage closer working relationships between staff and students and support specific coursework activities – particularly group work. Such spaces make better use of time since students are motivated to stay and work during long gaps in their timetable, can provide a sense of ‘home’ within the institution and can lead to a cohesive community of practice. In this paper, we describe how this has been achieved and currently delivered in Mathematics at Sheffield Hallam University and provide some detailed analysis of the student usage of the space. 相似文献
820.
Shu‐Wei Chang Huw Waters Jeff Kettle Zi‐Rui Kuo Chun‐Han Li Chin‐Yang Yu Masaki Horie 《Macromolecular rapid communications》2012,33(22):1927-1932
Low‐bandgap conjugated copolymers based on a donor–acceptor structure have been synthesised via palladium‐complex catalysed direct arylation polymerisation. Initially, we report the optimisation of the synthesis of poly(cyclopentadithiophene‐alt‐benzothiadiazole) (PCPDTBT) formed between cyclopentadithiophene and dibromobenzothiadiazole units. The polymerisation condition has been optimised, which affords high‐molecular‐weight polymers of up to M n = 70 k using N‐methylpyrrolidone as a solvent. The polymers are used to fabricate organic photovoltaic devices and the best performing PCPDTBT device exhibits a moderate improvement over devices fabricated using the related polymer via Suzuki coupling. Similar polymerisation conditions have also been applied for other monomer units. 相似文献