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Elastomeric proteins are characterized by their large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Motivated by their unique mechanical properties, there has been tremendous research in understanding and manipulating elastomeric polypeptides, with most work conducted on the elastins but more recent work on an expanded set of polypeptide elastomers. Facilitated by biosynthetic strategies, it has been possible to manipulate the physical properties, conformation, and mechanical properties of these materials. Detailed understanding of the roles and organization of the natural structural proteins has permitted the design of elastomeric materials with engineered properties, and has thus expanded the scope of applications from elucidation of the mechanisms of elasticity to the development of advanced drug delivery systems and tissue engineering substrates. 相似文献
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本文根据对钢磨陨表面系统的扫描电子显微镜与俄歇电子能谱仪分析提出了摩擦磨损的概率统计模型,其要点在于将真实接触面积内的接触形式区分为3种,即氧化膜-氧化膜、金属-金属和金属-氧化膜,并且指出每一种接触形式的比率都是随机的,因而都服从概率分布。本文应用概率统计方法推导出了摩擦系数与磨损率的数学表达式。在推导过程中使用了一个“新鲜暴露金属发面”的新概念。理论计算结果与实测值相吻合。 相似文献
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Inside Back Cover: Intermolecular Enantioselective Dearomatization Reaction of β‐Naphthol Using meso‐Aziridine: A Bifunctional In Situ Generated Magnesium Catalyst (Angew. Chem. Int. Ed. 7/2015)
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Catalytic Asymmetric Michael Reaction of 5H‐Oxazol‐4‐Ones with α,β‐Unsaturated Acyl Imidazoles
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Bangzhi Zhang Fengxia Han Linqing Wang Dan Li Dongxu Yang Xiaoli Yang Junxian Yang Xiaofang Li Dr. Depeng Zhao Prof. Dr. Rui Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(48):17234-17238
The asymmetric Michael reaction between 5H‐oxazol‐4‐ones and α,β‐unsaturated acyl imidazoles is reported. A novel 2‐benzo[b]thiophenyl‐modified chiral ProPhenol species is synthesized and used as a ligand, leading to good enantioselectivities in this asymmetric conjugate addition reaction. Furthermore, the introduction of phenol additives as achiral co‐ligands is found to improve the reaction’s chemical yields, diastereoselectivities, and enantioselectivities. 相似文献
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Linqing Li Hui Han Bruce J. Balcom 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,198(2):252-260
Fluid density imaging is highly desirable in a wide variety of porous media measurements. The SPRITE class of MRI methods has proven to be robust and general in their ability to generate density images in porous media, however the short encoding times required, with correspondingly high magnetic field gradient strengths and filter widths, and low flip angle RF pulses, yield sub-optimal S/N images, especially at low static field strength. This paper explores two implementations of pure phase encode spin echo 1D imaging, with application to a proposed new petroleum reservoir core analysis measurement.In the first implementation of the pulse sequence, we modify the spin echo single point imaging (SE-SPI) technique to acquire the k-space origin data point, with a near zero evolution time, from the free induction decay (FID) following a 90° excitation pulse. Subsequent k-space data points are acquired by separately phase encoding individual echoes in a multi-echo acquisition. T2 attenuation of the echo train yields an image convolution which causes blurring. The T2 blur effect is moderate for porous media with T2 lifetime distributions longer than 5 ms. As a robust, high S/N, and fast 1D imaging method, this method will be highly complementary to SPRITE techniques for the quantitative analysis of fluid content in porous media.In the second implementation of the SE-SPI pulse sequence, modification of the basic measurement permits fast determination of spatially resolved T2 distributions in porous media through separately phase encoding each echo in a multi-echo CPMG pulse train. An individual T2 weighted image may be acquired from each echo. The echo time (TE) of each T2 weighted image may be reduced to 500 μs or less. These profiles can be fit to extract a T2 distribution from each pixel employing a variety of standard inverse Laplace transform methods. Fluid content 1D images are produced as an essential by product of determining the spatially resolved T2 distribution. These 1D images do not suffer from a T2 related blurring.The above SE-SPI measurements are combined to generate 1D images of the local saturation and T2 distribution as a function of saturation, upon centrifugation of petroleum reservoir core samples. The logarithm mean T2 is observed to shift linearly with water saturation. This new reservoir core analysis measurement may provide a valuable calibration of the Coates equation for irreducible water saturation, which has been widely implemented in NMR well logging measurements. 相似文献
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Palladium nanoparticles/wool keratin-assisted carbon composite-modified flexible and disposable electrochemical solid-state pH sensor
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张文立 刘笑天 林友辉 马利芸 孔令庆 闵光宗 吴荣辉 Sharwari K.Mengane 杨丽坤 Aniruddha B.Patil 刘向阳 《中国物理 B》2022,31(2):28201-028201
Several p H-dependent processes and reactions take place in the human body;hence,the p H of body fluids is the best indicator of disturbed health conditions.However,accurate and real-time diagnosis of the p H of body fluids is complicated because of limited commercially available p H sensors.Hence,we aimed to prepare a flexible,transparent,disposable,userfriendly,and economic strip-based solid-state p H sensor using palladium nanoparticles(Pd NPs)/N-doped carbon(NC)composite material.The Pd NPs/NC composite material was synthesized using wool keratin(WK)as a precursor.The insitu prepared Pd NPs played a key role in the controlled switching of protein structure to the N-doped carbon skeleton withπ–πarrangement at the mesoscale level,which mimics the A–B type polymeric structure,and hence,is highly susceptible to H+ions.The optimized carbonization condition in the presence of Pd NPs showed that the material obtained using a modified Ag/Ag Cl reference electrode had the highest p H sensitivity with excellent stability and durability.The optimized p H sensor showed high specificity and selectivity with a sensitivity of 55 m V/p H unit and a relative standard deviation of 0.79%.This study is the first to synthesize Pd NPs using WK as a stabilizing and reducing agent.The applicability of the sensor was investigated for biological samples,namely,saliva and gastric juices.The proposed protocol and material have implications in solid-state chemistry,where biological material will be the best choice for the synthesis of materials with anticipated performance. 相似文献
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Asymmetric anti‐Selective Michael Reaction of Imidazole‐Modified Ketones with trans‐β‐Nitroalkenes
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Dongxu Yang Linqing Wang Dan Li Fengxia Han Dr. Depeng Zhao Prof. Dr. Rui Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(4):1458-1462
The successful application of imidazole‐modified ketones in asymmetric anti‐selective Michael reactions with trans‐β‐nitroalkenes is presented by employing a newly developed 3‐bromothiophene‐modified chiral diamine ligand. The corresponding conjugate adduct was submitted to further transformations with Grignard reagents to solve the problem of α‐site selectivity of simple linear ketones. Additionally, the syn‐selective product was obtained by treating the anti‐selective adduct with a simple base. In this way, the site‐specific products for both diastereomers in the asymmetric conjugate addition of simple ketones to nitroalkenes can be obtained. 相似文献