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排序方式: 共有1054条查询结果,搜索用时 62 毫秒
151.
152.
Mingfei Xiao Aditya Sadhanala Mojtaba Abdi-Jalebi Tudor H. Thomas Xinglong Ren Tao Zhang Hu Chen Remington L. Carey Qijing Wang Satyaprasad P. Senanayak Cameron Jellett Ada Onwubiko Maximilian Moser Hailiang Liao Wan Yue Iain McCulloch Mark Nikolka Henning Sirringhaus 《Advanced functional materials》2021,31(7):2007359
The measurement of the mechanical properties of conjugated polymers can reveal highly relevant information linking optoelectronic properties to underlying microstructures and the knowledge of the glass transition temperature (Tg) is paramount for informing the choice of processing conditions and for interpreting the thermal stability of devices. In this work, we use dynamical mechanical analysis to determine the Tg of a range of state-of-the-art conjugated polymers with different degrees of crystallinity that are widely studied for applications in organic field-effect transistors. We compare our measured values for Tg to the theoretical value predicted by a recent work based on the concept of effective mobility ζ. The comparison shows that for conjugated polymers with a modest length of the monomer units, the Tg values agree well with theoretically predictions. However, for the near-amorphous, indacenodithiophene–benzothiadiazole family of polymers with more extended backbone units, values for Tg appear to be significantly higher, predicted by theory. However, values for Tg are correlated with the sub-bandgap optical absorption suggesting the possible role of the interchain short contacts within materials’ amorphous domains. 相似文献
153.
Stennicke Henning R.; Mortensen Uffe H.; Christensen Ulla; Remington S.James; Breddam Klaus 《Protein engineering, design & selection : PEDS》1994,7(7):911-916
Carboxypeptidase Y is a serine carboxypeptidase isolated fromSaccharomyces cerevisiae with a preference for Cterminal hydrophobicamino acid residues. In order to alter the inherent substratespecificity of CPD-Y into one for basic amino acid residuesin P'1, we have introduced Asp and/or Glu residues at a numberof selected positions within the Si binding site. Hie effectsof these substitutions on the substrate specificity, pH dependenceand protein stability have been evaluated. The results presentedhere demonstrate that it is possible to obtain significant changesin the substrate preference by introducing charged amino acidsinto the framework provided by an enzyme with a quite differentspecificity. The introduced acidic amino acid residues providea marked pH dependence of the (kcat/Km)FA-A-R-OH/(kcatm)FA-A-R-OHratio. The change in stability upon introduction of Asp/Gluresidues can be correlated to the difference in the mean buriedsurfac surface area between the substituted and the substitutingamino acid. Thus, the effects of acidic amino acid residueson the protein stability depend upon whether the introducedamino acid protrudes from the solvent accessible surface asdefined by the surrounding residues in the wild type enzymeor is submerged below. 相似文献
154.
The expected amount of plant nitrogen (N) at harvest which originates from soil N supply is of high relevance for N fertilization planning. Due to mineralization–immobilisation turnover processes, soil N supply is influenced by N fertilization which complicates its assessment. The soil N supply consists of two components: the soil mineral N measured at early spring and the ‘effective’ N mineralization (Mineff) under winter wheat (Triticum aestivum L.). Mineff was defined as the difference between crop N uptake (Ncrop) at harvest and N supply. Our aim was the identification and quantification of climate and site-related factors in order to achieve an improved assessment of the site-specific (long term average) Mineff. We used N rate experiments from 411 collective seasons, carried out at 98 sites across Germany in order to analyze the impact of climate and site-related factors on Mineff. Quadratic curves were fitted in order to describe the grain N uptake as a function of N supply. A fixed marginal N efficiency was defined in order to analyze Mineff at a reasonable N supply. Starting with estimates for Mineff as function of preceding crop, we found that climate (average temperature during May, annual rainfall) and site-related factors have a significant influence on Mineff. In order to ensure that the regression model is transferable to unknown sites, a “leave one site out” cross validation was carried out. Compared to considering preceding crop only (reference), the regression model reduced the RMSE by 9.5 (calibration) or 8.3 (cross validation) kg N/ha. 相似文献
155.
Cover Feature: Directed Evolution of Hyaluronic Acid Synthase from Pasteurella multocida towards High‐Molecular‐Weight Hyaluronic Acid (ChemBioChem 13/2018)
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156.
Lipid‐like Peptides can Stabilize Integral Membrane Proteins for Biophysical and Structural Studies
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Katharina Veith Maria Martinez Molledo Yasser Almeida Hernandez Dr. Inokentijs Josts Julius Nitsche Dr. Christian Löw Prof. Dr. Henning Tidow 《Chembiochem : a European journal of chemical biology》2017,18(17):1735-1742
A crucial bottleneck in membrane protein structural biology is the difficulty in identifying a detergent that can maintain the stability and functionality of integral membrane proteins (IMPs). Detergents are poor membrane mimics, and their common use in membrane protein crystallography may be one reason for the challenges in obtaining high‐resolution crystal structures of many IMP families. Lipid‐like peptides (LLPs) have detergent‐like properties and have been proposed as alternatives for the solubilization of G protein‐coupled receptors and other membrane proteins. Here, we systematically analyzed the stabilizing effect of LLPs on integral membrane proteins of different families. We found that LLPs could significantly stabilize detergent‐solubilized IMPs in vitro. This stabilizing effect depended on the chemical nature of the LLP and the intrinsic stability of a particular IMP in the detergent. Our results suggest that screening a subset of LLPs is sufficient to stabilize a particular IMP, which can have a substantial impact on the crystallization and quality of the crystal. 相似文献
157.
158.
A Roadmap for Controlled and Efficient n‐Type Doping of Self‐Assisted GaAs Nanowires Grown by Molecular Beam Epitaxy
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Marta Orrù Eva Repiso Stefania Carapezzi Alex Henning Stefano Roddaro Alfonso Franciosi Yossi Rosenwaks Anna Cavallini Faustino Martelli Silvia Rubini 《Advanced functional materials》2016,26(17):2836-2845
N‐type doping of GaAs nanowires has proven to be difficult because the amphoteric character of silicon impurities is enhanced by the nanowire growth mechanism and growth conditions. The controllable growth of n‐type GaAs nanowires with carrier density as high as 1020 electron cm?3 by self‐assisted molecular beam epitaxy using Te donors is demonstrated here. Carrier density and electron mobility of highly doped nanowires are extracted through a combination of transport measurement and Kelvin probe force microscopy analysis in single‐wire field‐effect devices. Low‐temperature photoluminescence is used to characterize the Te‐doped nanowires over several orders of magnitude of the impurity concentration. The combined use of those techniques allows the precise definition of the growth conditions required for effective Te incorporation. 相似文献
159.
Effective medium theories for irregular fluffy structures: aggregation of small particles 总被引:1,自引:0,他引:1
The extinction efficiencies as well as the scattering properties of particles of different porosity are studied. Calculations are performed for porous pseudospheres with small size (Rayleigh) inclusions using the discrete dipole approximation. Five refractive indices of materials covering the range from 1.20+0.00i to 1.75+0.58i were selected. They correspond to biological particles, dirty ice, silicate, and amorphous carbon and soot in the visual part of the spectrum. We attempt to describe the optical properties of such particles using Lorenz-Mie theory and a refractive index found from some effective medium theory (EMT) assuming the particle is homogeneous. We refer to this as the effective model. It is found that the deviations are minimal when utilizing the EMT based on the Bruggeman mixing rule. Usually the deviations in the extinction factor do not exceed approximately 5% for particle porosity P = 0 - 0.9 and size parameters x(porous) = 2 pi r(s,porous)/lambda < or approximately = 25. The deviations are larger for scattering and absorption efficiencies and smaller for particle albedo and the asymmetry parameter. Our calculations made for spheroids confirm these conclusions. Preliminary consideration shows that the effective model represents the intensity and polarization of radiation scattered by fluffy aggregates quite well. Thus the effective models of spherical and nonspherical particles can be used to significantly simplify the computations of the optical properties of aggregates containing only Rayleigh inclusions. 相似文献
160.
Davis AC Patterson BM Grassi ME Robertson BS Prommer H McKinley AJ 《Environmental science & technology》2007,41(20):7131-7137
Large-scale column experiments were carried out over a period of 545 days to assess the effect of increasing acidity on bacterial denitrification, sulfate reduction, and metal(loid) bioprecipitation in groundwater affected by acid mine drainage. At a groundwater pH of 5.5, denitrification and Cu2+ removal, probably via malachite (Cu2(OH)2CO3) precipitation, were observed in the ethanol-amended column. Sulfate reduction, sulfide production, and Zn2+ removal were also observed, with Zn2+ removal observed in the zone of sulfate reduction, indicating likely precipitation as sphalerite (ZnS). Se6+ removal was also observed in the sulfate reducing zone, probably as direct bioreduction to elemental selenium via ethanol/acetate oxidation or sulfide oxidation precipitating elemental sulfur. A step decrease in groundwater pH from 5.5 to 4.25 resulted in increased denitrification and sulfate reduction half-lives, migration of both these redox zones along the ethanol-amended column, and the formation of an elevated Cu2+ plume. Additionally, an elevated Zn2+ plume formed in the previous sulfate reducing zone of the ethanol-amended column, suggesting dissolution of precipitated sphalerite as a result of the reduction in groundwater pH. As Cu2+ passed through the zone of sphalerite dissolution, SEM imaging and EDS detection suggested that Cu2+ removal had occurred via chalcocite (Cu2S) or covellite (CuS) precipitation. 相似文献