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排序方式: 共有261条查询结果,搜索用时 15 毫秒
91.
Chang X Duncan LK Jinschek J Vikesland PJ 《Langmuir : the ACS journal of surfaces and colloids》2012,28(20):7622-7630
C(60) forms colloidally stable nanoscale particles (nC(60)) when mixed with water for extended periods. Past studies have shown that macromolecules such as natural organic matter (NOM) and proteins accelerate nC(60) formation and stabilize the resulting nanoparticles. To better elucidate the mechanisms underlying this behavior, nC(60) was produced via extended mixing in the presence of sodium citrate and other carboxylates. Carboxyl groups are a predominant functional group in many environmentally relevant macromolecules, thus studies examining carboxyl-C(60) interactions are merited. nC(60) produced in the presence of citrate (cit/nC(60)) and other carboxylates differs from nC(60) produced in water alone (aq/nC(60)), exhibiting enhanced negative surface charge, smaller particle size, and different spectroscopic characteristics. Importantly, the simultaneous detection of irregular nC(60) nanoparticles and small, regularly shaped nC(60) suggests that mixing-mediated "top-down" and carboxyl group-mediated "bottom-up" processes occur concurrently when nC(60) is produced in the presence of carboxylates and, by extension, in the presence of carboxylate-containing macromolecules. The "bottom-up" process is expected to involve molecular C(60) or small clusters of C(60) molecules as an important intermediate. 相似文献
92.
Siebert JM Baier G Musyanovych A Landfester K 《Chemical communications (Cambridge, England)》2012,48(44):5470-5472
A facile method to produce nanocapsules by copper-free interfacial "click"-polymerization as orthogonal reaction for the encapsulation of functional molecules is successfully performed using stable miniemulsion droplets. Difunctional azides and alkynes have been used for polymerization around the miniemulsion droplets, leading to the formation of nanocapsules. The results were compared with copper-catalyzed systems. 相似文献
93.
Jacquot de Rouville HP Garbage R Ample F Nickel A Meyer J Moresco F Joachim C Rapenne G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(29):8925-8928
The future's wheel: A new class of wheels, based on subphthalocyanine fragments, for future incorporation in functional nanovehicles is reported (see figure). The syntheses of a symmetric wheel, a nitrogen-tagged wheel, and their ethynyl-bridged homodimers are presented. Theoretical calculations and STM imaging demonstrate the advantage of a bowl-shaped structure and the efficiency of the tag for STM imaging. 相似文献
94.
Michael Markl Stefanie M. Brendecke Jan Simon Alex J. Barker Cornelius Weiller Andreas Harloff 《Magnetic resonance imaging》2013
Previous studies provide evidence that atherosclerosis develops in vascular regions exposed to low wall shear stress (WSS) and high oscillatory shear index (OSI). 4D flow MRI was analyzed in 70 stroke patients with complex plaques (≥ 4 mm thickness, ulcerated or superimposed thrombi) and in 12 young healthy volunteers. The segmental distribution of peak systolic WSSsystole and OSI was quantified in analysis planes positioned directly at the location of 140 complex plaques found in the 70 patients. In addition, WSSsystole and OSI were evaluated in 8 standard analysis planes distributed along the aorta. Complex plaques were predominantly found at the inner curvature of the aortic arch and of the descending aorta. High OSI was co-located with the segments mostly affected by complex plaque while WSSsystole demonstrated a homogenous distribution. In standard analysis planes, patients demonstrated significantly (p < 0.01) altered distribution of wall parameters compared to volunteers (reduced WSSsystole in 91% of aortic wall segments, increased OSI in 48% of segments). OSI distribution was asymmetric with higher values at the inner curvature of the aorta. While WSS and OSI showed expected changes in patients compared to healthy controls, their distribution pattern at complex plaques indicated a more complex and heterogeneous relationship than previously anticipated. 相似文献
95.
Jrg Harloff Dirk Michalik Simon Nier Axel Schulz Philip Stoer Alexander Villinger 《Angewandte Chemie (International ed. in English)》2019,58(16):5452-5456
Starting from fluoridosilicate precursors in neat cyanotrimethylsilane, Me3Si?CN, a series of different ammonium salts [R3NMe]+ (R=Et, nPr, nBu) with the novel [SiF(CN)5]2? and [Si(CN)6]2? dianions was synthesized in facile, temperature controlled F?/CN? exchange reactions. Utilizing decomposable, non‐innocent cations, such as [R3NH]+, it was possible to generate metal salts of the type M2[Si(CN)6] (M+=Li+, K+) via neutralization reactions with the corresponding metal hydroxides. The ionic liquid [BMIm]2[Si(CN)6] (m.p.=72 °C, BMIm=1‐butyl‐3‐methylimidazolium) was obtained by a salt metathesis reaction. All the synthesized salts could be isolated in good yields and were fully characterized. 相似文献
96.
Hoffmann K Mix R Friedrich JF Buschmann HJ Resch-Genger U 《Journal of fluorescence》2009,19(2):229-237
Polypropylene supports were functionalized by plasma-deposition of polymeric allylamine layers. The surface amino groups generated
were wet-chemically reacted with xanthene dyes resulting in fluorescent polymer films. The effect of polymer-attachment of
the dyes on their emission features was studied fluorometrically and different methods were tested to improve the fluorescence
properties of the films. Modification with cucurbit[6]uril (CB6) yields a moderately enhanced fluorescence as well as an improved
photostability. The observed effect is most likely due to CB6-induced rigidization of the linker molecules which seems to
reduce fluorescence quenching dye–dye and fluorophore–surface interactions. 相似文献
97.
With the development of high power ultrafast laser passively mode-locked by a semiconductor saturable absorber mirror (SESAM), the damage threshold and degeneration mechanism of the SESAM become more and more important. One way to reduce the maximum electric field inside the active part of the SESAM is the use of a dielectric coating on the top of the semiconductor structure. With Presnel formula, optical transfer matrix, and optical thin film theory, the electric field distribution and reflectance spectrum can be simulated. We introduce the design principles of SESAM including the dependence of reflectance spectrum on dielectric function of absorber, and investigate the dependences of the electric field distribution, modulation depth, reflectance spectrum, and the relative value of incident light power at the top quantum well of SESAM on the number of SiO2/Ta2O5 layers. 相似文献
98.
Markl M Dudler P Fydrychowicz A Strecker C Weiller C Hennig J Harloff A 《Magnetic resonance imaging》2008,26(3):330-336
PURPOSE: To evaluate the feasibility of an optimized bright blood MRI protocol at 3 T in combination with contrast agent administration for the detection and characterization of aortic high-risk plaques for the improved workup of acute stroke patients. MATERIALS AND METHODS: ECG synchronized T1-weighted 3D gradient echo MRI was performed in 45 acute stroke patients. Data were acquired with high near isotropic spatial resolution (approximately 1 mm(3)) covering the entire thoracic aorta. To compensate for breathing and vessel motion artifacts, images were collected using respiratory navigator gating in combination with short diastolic data acquisition windows adjusted on a patient-by-patient basis. In patients with aortic plaques > or =3 mm in thickness, gadolinium contrast agent was administered and both pre- and post-contrast T1-weighted 3D measurements with identical vessel coverage were performed. RESULTS: Bright blood 3D MRI detected 33 high-risk plaques with an average maximum plaque thickness of 4.2+/-1.0 mm in 23 of 45 acute stroke patients. The availability of pre- and post-contrast images acquired within the same session enhanced the identification of calcified plaque components in 77% of all analyzed plaques: post-contrast MRI clearly improved the delineation of hypointense plaque cores in 23 of 30 cases and assisted in the classification of core shape and of core fraction. CONCLUSION: 3D bright blood MRI at 3 T was feasible for the detection of aortic high-risk sources and may help to improve the detection of causes of cerebral embolism in acute stroke patients. 相似文献
99.
Transitory starch plays a central role in the life cycle of plants. Many aspects of this important metabolism remain unknown; however, starch granules provide insight into this persistent metabolic process. Therefore, monitoring alterations in starch granules with high temporal resolution provides one significant avenue to improve understanding. Here, a previously established method that combines LCSM and safranin-O staining for in vivo imaging of transitory starch granules in leaves of Arabidopsis thaliana was employed to demonstrate, for the first time, the alterations in starch granule size and morphology that occur both throughout the day and during leaf aging. Several starch-related mutants were included, which revealed differences among the generated granules. In ptst2 and sex1-8, the starch granules in old leaves were much larger than those in young leaves; however, the typical flattened discoid morphology was maintained. In ss4 and dpe2/phs1/ss4, the morphology of starch granules in young leaves was altered, with a more rounded shape observed. With leaf development, the starch granules became spherical exclusively in dpe2/phs1/ss4. Thus, the presented data provide new insights to contribute to the understanding of starch granule morphogenesis. 相似文献
100.
Frank Katzenberg Joerg C. Tiller 《Journal of polymer science. Part A, Polymer chemistry》2016,54(14):1381-1388
Charles Goodyear discovered the vulcanization of natural rubber (NR) 170 years ago and transferred the gooey natural compound into the first representative of an entirely new class of materials; the elastomers. Thenceforth, NR was intensively explored and was used for countless products to date. All the more surprising, it was found recently that NR exhibits superior and unexpected properties whenever it is cross-linked to a degree smaller than 0.4% which is fairly below the commonly used 1%–2%. This article gives a brief overview on the exceptional properties of lightly cross-linked NR, named shape memory natural rubber (SMNR), including the cold programmable shape memory effect, storing of extremely large strain, energy and cold, and its capability to sense and memorize environmental parameters. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1381–1388 相似文献