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1.
Overview of finite elements simulation of temperature profile to estimate properties of materials 3D-printed by laser powder-bed fusion 下载免费PDF全文
Habimana Jean Willy 李辛未 Yong Hao Tan 陈哲 Mehmet Cagirici Ramadan Borayek Tun Seng Herng Chun Yee Aaron Ong 李朝将 丁军 《中国物理 B》2020,(4):98-109
Laser powder bed fusion(LPBF),like many other additive manufacturing techniques,offers flexibility in design expected to become a disruption to the manufacturing industry.The current cost of LPBF process does not favor a try-anderror way of research,which makes modelling and simulation a field of superior importance in that area of engineering.In this work,various methods used to overcome challenges in modeling at different levels of approximation of LPBF process are reviewed.Recent efforts made towards a reliable and computationally effective model to simulate LPBF process using finite element(FE)codes are presented.A combination of ray-tracing technique,the solution of the radiation transfer equation and absorption measurements has been used to establish an analytical equation,which gives a more accurate approximation of laser energy deposition in powder-substrate configuration.When this new analytical energy deposition model is used in in FE simulation,with other physics carefully set,it enables us to get reliable cooling curves and melt track morphology that agree well with experimental observations.The use of more computationally effective approximation,without explicit topological changes,allows to simulate wider geometries and longer scanning time leading to many applications in real engineering world.Different applications are herein presented including:prediction of printing quality through the simulated overlapping of consecutive melt tracks,simulation of LPBF of a mixture of materials and estimation of martensite inclusion in printed steel. 相似文献
2.
Discovery,Characterization, and Analogue Synthesis of Bohemamine Dimers Generated by Non‐enzymatic Biosynthesis 下载免费PDF全文
Dr. Peng Fu Aaron Legako Scott La Prof. Dr. John B. MacMillan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(10):3491-3495
Dibohemamines A–C ( 5 – 7 ), three new dimeric bohemamine analogues dimerized through a methylene group, were isolated from a marine‐derived Streptomyces spinoverrucosus. The structures determined by spectroscopic analysis were confirmed through the semi‐synthetic derivatization of monomeric bohemamines and formaldehyde. These reactions, which could occur under mild conditions, together with the detection of formaldehyde in the culture, revealed that this dimerization is a non‐enzymatic process. In addition to the unique dimerization of the dibohemamines, dibohemamines B and C were found to have nm cytotoxicity against the non‐small cell‐lung cancer cell line A549. In view of the potent cytotoxicity of compounds 6 and 7 , a small library of bohemamine analogues was generated for biological evaluation by utilizing a series of aryl and alkyl aldehydes. 相似文献
3.
Bob Boyd Gareth Brenton Eddie Clayton Jonathan Curtis R. M. Elliott G. A. Errock B. N. Green R. H. Bateman Simon J. Gaskell Iwan Griffiths Zdenek Herman Philip Jonathan Rich Kondrat Mila Laušević Chris Lock Deepak Mathur John F. J. Todd Károly Vékey 《Rapid communications in mass spectrometry : RCM》2016,30(11):1253-1264
4.
Synthesis and physical properties of highly branched perfluorinated polymers from AB and AB2 monomers 下载免费PDF全文
Matthew J. Quast Aaron D. Argall Cassandra J. Hager Anja Mueller 《Journal of polymer science. Part A, Polymer chemistry》2015,53(16):1880-1894
Highly branched perfluorinated aromatic polyether copolymers were prepared from the polycondensation of the AB2 monomer, 3,5‐bis[(pentafluorobenzyl)oxy]benzyl alcohol with a variety of fluoroaryl and alkyl bromide AB comonomers. The structures and comonomer distribution of the resulting polymers were characterized in detail. 1H NMR data from kinetic trials illustrated that perfluoroaryl AB comonomer distribution correlated to AB comonomer sterics. 19F NMR data revealed that fluorinated AB monomers and 3‐bromo‐1‐propanol AB monomers were distributed within the AB2 polymer backbone, while longer alkyl bromide AB monomers, 6‐bromo‐1‐hexanol, were mostly distributed along hyperbranched polymer chain ends. In general, as AB comonomer incorporation increased for nonsterically hindered copolymers, thermal decomposition onset increased and glass transition temperatures decreased. The combined data demonstrated the effect of comonomer distribution and sterics on physical properties of AB2‐based polymer systems. The resulting materials were used to cast thin polymer films for measurement of contact angle, which were shown to be directly related to comonomer content. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1880–1894 相似文献
5.
Smita Patnaik Aaron D. Sadow 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2527-2531
The high catalytic reactivity of homoleptic tris(alkyl) lanthanum La{C(SiHMe2)3}3 is highlighted by C?O bond cleavage in the hydroboration of esters and epoxides at room temperature. The catalytic hydroboration tolerates functionality typically susceptible to insertion, reduction, or cleavage reactions. Turnover numbers (TON) up to 10 000 are observed for aliphatic esters. Lanthanum hydrides, generated by reactions with pinacolborane, are competent for reduction of ketones but are inert toward esters. Instead, catalytic reduction of esters requires activation of the lanthanum hydride by pinacolborane. 相似文献
6.
Dr. Sampa Maiti Dr. Saikat Manna Nicholas Banahene Lucynda Pham Zhijie Liang Jun Wang Yi Xu Reuben Bettinger John Zientko Prof. Dr. Aaron P. Esser-Kahn Prof. Dr. Wenjun Du 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(43):19105-19109
Efforts to synthesize degradable polymers from renewable resources are deterred by technical and economic challenges; especially, the conversion of natural building blocks into polymerizable monomers is inefficient, requiring multistep synthesis and chromatographic purification. Herein we report a chemoenzymatic process to address these challenges. An enzymatic reaction system was designed that allows for regioselective functional group transformation, efficiently converting glucose into a polymerizable monomer in quantitative yield, thus removing the need for chromatographic purification. With this key success, we further designed a continuous, three-step process, which enabled the synthesis of a sugar polymer, sugar poly(orthoester), directly from glucose in high yield (73 % from glucose). This work may provide a proof-of-concept in developing technically and economically viable approaches to address the many issues associated with current petroleum-based polymers. 相似文献
7.
Gabrielle A. Leith Allison M. Rice Brandon J. Yarbrough Anna A. Berseneva Richard T. Ly Charles N. Buck III Dr. Denis Chusov Amy J. Brandt Prof. Dr. Donna A. Chen Benjamin W. Lamm Prof. Dr. Morgan Stefik Kenneth S. Stephenson Dr. Mark D. Smith Prof. Dr. Aaron K. Vannucci Dr. Perry J. Pellechia Prof. Dr. Sophya Garashchuk Prof. Dr. Natalia B. Shustova 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(15):6056-6062
The effect of donor (D)–acceptor (A) alignment on the materials electronic structure was probed for the first time using novel purely organic porous crystalline materials with covalently bound two- and three-dimensional acceptors. The first studies towards estimation of charge transfer rates as a function of acceptor stacking are in line with the experimentally observed drastic, eight-fold conductivity enhancement. The first evaluation of redox behavior of buckyball- or tetracyanoquinodimethane-integrated crystalline was conducted. In parallel with tailoring the D-A alignment responsible for “static” changes in materials properties, an external stimulus was applied for “dynamic” control of the electronic profiles. Overall, the presented D–A strategic design, with stimuli-controlled electronic behavior, redox activity, and modularity could be used as a blueprint for the development of electroactive and conductive multidimensional and multifunctional crystalline porous materials. 相似文献
8.
Aaron D. W. Kennedy Isolde Sandler Prof. Joakim Andréasson Dr. Junming Ho Dr. Jonathon E. Beves 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(5):1103-1110
Three visible-light responsive photoswitches are reported, azobis(1-methyl-benzimidazole) ( 1 ), azobis(benzoxazole) ( 2 ) and azobis(benzothiazole) ( 3 ). Photostationary distributions are obtained upon irradiation with visible light comprising approximately 80 % of the thermally unstable isomer, with thermal half-lives up to 8 min and are mostly invariant to solvent. On protonation, compound 1 H+ has absorption extending beyond 600 nm, allowing switching with yellow light, and a thermal half-life just under 5 minutes. The two isomers have significantly different pKa values, offering potential as a pH switch. The absorption spectra of 2 and 3 are insensitive to acid, although changes in the thermal half-life of 3 indicate more basic intermediates that significantly influence the thermal barrier to isomerization. These findings are supported by high-level ab initio calculations, which validate that protonation occurs on the ring nitrogen and that the Z isomer is more basic in all cases. 相似文献
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