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61.
S.-S. Bae D.K. Lim J.-I. Park J. Cheon I.C. Jeon S. Kim 《Applied Physics A: Materials Science & Processing》2005,80(6):1305-1310
We present a new strategy to fabricate a monolayer assembly of Br-terminated Co nanoparticles on functionalized Si surfaces by using chemical covalent bonding and microcontact printing method. Self-assembled monolayers (SAMs) of the Co nanoparticles formed on the hydroxyl-terminated Si surface exhibit two-dimensional island networks with locally ordered arrays via covalent linkage between nanoparticles and surface. On the other hand, SAMs of the nanoparticles on the aminopropyl-terminated Si surface show an individual and random distribution over an entire surface. Furthermore, we have fabricated striped architectures of Co nanoparticles using a combination of microcontact printing and covalent linkage. Microcontact printing of octadecyltrichlorosilane and selective covalent linkage between nanoparticles and functionalized Si surfaces lead to a hybrid nanostructure with selectively assembled nanoparticles stripes on the patterned functionalized Si surfaces. PACS 81.07.Ta; 61.46.+w; 81.16.Dn; 81.16.Be; 68.37.Hk; 82.80.Pv 相似文献
62.
The burning and extinction characteristics of isolated small nonane droplets are examined in a buoyant convective environment and in an environment with no external axial convection (as created by doing experiments at low gravity) to promote spherical droplet flames. The ambience is air and a mixture of 30%O2/70%He to assess the influence of soot formation. The initial droplet diameter (Do) ranges from 0.4 to 0.95 mm. Measurements are reported of the extinction diameter and time to extinction, and of the evolution of droplet diameter, flame diameter, soot shell diameter, burning rate, and broadband radiative emissions.In a buoyancy-free environment for air larger droplets burn slower than smaller droplets for the range of Do examined, which is attributed to the influence of soot. In the presence of a buoyant flow in air, no influence of Do is observed on the burning rate while the buoyant flames are still heavily sooting. The effect of Do is believed to be due to a combination of dominance of the nonluminous, nonsooting, portion of the buoyant flame around the forward half of the droplet on heat transport and the secondary role of the luminous wake portion of the flame. In a non-sooting helium inert at low gravity, no effect of Do is found on the evolution of droplet diameter.Flame extinction is observed only in the 30%O2/70%He ambience. For all of the observations, extinction appears to occur before the disappearance of the droplet which is then followed by a period of evaporation. The extinction diameter and time to extinction increases with Do and an empirical correlation is presented for these two variables. 相似文献
63.
Hee-Kap Ahn Sang Won Bae Otfried Cheong Joachim Gudmundsson 《Discrete and Computational Geometry》2008,40(3):414-429
The aperture angle
α(x,Q) of a point x
∉
Q in the plane with respect to a convex polygon Q is the angle of the smallest cone with apex x that contains Q. The aperture angle approximation error of a compact convex set C in the plane with respect to an inscribed convex polygon Q⊂C is the minimum aperture angle of any x∈C∖Q with respect to Q. We show that for any compact convex set C in the plane and any k>2, there is an inscribed convex k-gon Q⊂C with aperture angle approximation error
. This bound is optimal, and settles a conjecture by Fekete from the early 1990s.
The same proof technique can be used to prove a conjecture by Brass: If a polygon P admits no approximation by a sub-k-gon (the convex hull of k vertices of P) with Hausdorff distance σ, but all subpolygons of P (the convex hull of some vertices of P) admit such an approximation, then P is a (k+1)-gon. This implies the following result: For any k>2 and any convex polygon P of perimeter at most 1 there is a sub-k-gon Q of P such that the Hausdorff-distance of P and Q is at most
.
This research was supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (KRF-2006-311-D00763).
NICTA is funded through the Australian Government’s Backing Australia’s Ability initiative, in part through the Australian
Research Council. 相似文献
64.
Sodium magnetic resonance (MR) imaging is a promising technique for detecting changes of proteoglycan (PG) content in cartilage associated with knee osteoarthritis. Despite its potential clinical benefit, sodium MR imaging in vivo is challenging because of intrinsically low sodium concentration and low MR signal sensitivity. Some of the challenges in sodium MR imaging may be eliminated by the use of a high-sensitivity radiofrequency (RF) coil, specifically, a dual-tuned (DT) proton/sodium RF coil which facilitates the co-registration of sodium and proton MR images and the evaluation of both physiochemical and structural properties of knee cartilage. Nevertheless, implementation of a DT proton/sodium RF coil is technically difficult because of the coupling effect between the coil elements (particularly at high field) and the required compact design with improved coil sensitivity. In this study, we applied a multitransceiver RF coil design to develop a DT proton/sodium coil for knee cartilage imaging at 3 T. With the new design, the size of the coil was minimized, and a high signal-to-noise ratio (SNR) was achieved. DT coil exhibited high levels of reflection S11 (~-21 dB) and transmission coefficient S12 (~-19 dB) for both the proton and sodium coils. High SNR (range 27-38) and contrast-to-noise ratio (CNR) (range 15-21) were achieved in sodium MR imaging of knee cartilage in vivo at 3-mm(3) isotropic resolution. This DT coil performance was comparable to that measured using a sodium-only birdcage coil (SNR of 28 and CNR of 20). Clinical evaluation of the DT coil on four normal subjects demonstrated a consistent acquisition of high-resolution proton images and measurement of relative sodium concentrations of knee cartilages without repositioning of the subjects during the same MR scanning session. 相似文献
65.
A new C‐glycosyl flavone containing a 3‐keto sugar, isocassiaoccidentalin B ( 1 ), was isolated from whole Cassia nomame (Sieber ) Honda plants, along with eleven known compounds, including two flavonoids ( 2 and 3 ), five flavonoid glycosides ( 4 – 8 ), two chalcones ( 9 and 10 ), and two phenylpropanoids ( 11 and 12 ). The chemical structures of all compounds were determined via 1D‐ and 2D‐NMR, and ESI‐MS. Among these, compounds 2 , 3 , 7 , and 8 were found to be the most potent in inhibiting nitric oxide release. Compounds 1 , 2 , 4 , 8 , 9 , and 10 showed significant free‐radical scavenging activity. 相似文献
66.
The Ag nanoprisms with controlled arrangements show distinct optical, crystallographic, and surface-enhanced Raman scattering properties depending on their orientation in the assemblies, demonstrating that the controlled assembly of anisotropic nanostructures can be utilized as a powerful tool for studying their physicochemical properties and for the creation of new classes of functional materials. 相似文献
67.
Seonghwa Jeong Eunji Park Jiyeon Kim Seok Bae Park Dr. Sung Hoon Kim Prof. Wonyoung Choe Prof. Joonghan Kim Prof. Young S. Park 《Angewandte Chemie (International ed. in English)》2023,62(50):e202314148
Increasing the chemical diversity of organic semiconductors is essential to develop efficient electronic devices. In particular, the replacement of carbon-carbon (C−C) bonds with isoelectronic boron-nitrogen (B−N) bonds allows precise modulation of the electronic properties of semiconductors without significant structural changes. Although some researchers have reported the preparation of B2N2 anthracene derivatives with two B−N bonds, no compounds with continuous multiple BN units have been prepared yet. Herein, we report the synthesis and characterization of a B2N2 anthracene derivative with a BNBN unit formed by converting the BOBN unit at the zigzag edge. Compared to the all-carbon analogue 2-phenylanthracene, BNBN anthracene exhibits significant variations in the C−C bond length and a larger highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap. The experimentally determined bond lengths and electronic properties of BNBN anthracene are confirmed through theoretical calculations. The BOBN anthracene organic light-emitting diode, used as a blue host, exhibits a low driving voltage. The findings of this study may facilitate the development of larger acenes with multiple BN units and potential applications in organic electronics. 相似文献
68.
Jinsu Bae Yeo-Ok Kim Xuehao Han Myung-Ha Yoon Woong-Mo Kim Yong-Chul Kim 《Molecules (Basel, Switzerland)》2022,27(4)
P2X3 receptors (P2X3R) are ATP-gated ion channels predominantly expressed in C- and Aδ-fiber primary afferent neurons and have been introduced as a novel therapeutic target for neurological disorders, including neuropathic pain and chronic cough. Because of its localized distribution, antagonism of P2X3R has been thoroughly considered, and the avoidance of issues related to CNS side effects has been proven in clinical trials. In this article, benzimidazole-4,7-dione-based derivatives were introduced as a new chemical entity for the development of P2X3R antagonists. Starting from the discovery of a hit compound from the screening of 8364 random library compounds in the Korea Chemical Bank, which had an IC50 value of 1030 nM, studies of structure–activity and structure–property relationships enabled further optimization toward improving the antagonistic activities as well as the drug’s physicochemical properties, including metabolic stability. As for the results, the final optimized compound 14h was developed with an IC50 value of 375 nM at P2X3R with more than 23-fold selectivity versus P2X2/3R, along with properties of metabolic stability and improved solubility. In neuropathic pain animal models evoked by either nerve ligation or chemotherapeutics in male Sprague-Dawley rats, compound 14h showed anti-nociceptive effects through an increase in the mechanical withdrawal threshold as measured by von Frey filament following intravenous administration. 相似文献
69.
Jack C. Kim Sang-Duk Bae Ji-A Kim Soon-Kyu Choi 《Journal of heterocyclic chemistry》1998,35(3):531-533
A Regioselective synthesis of (R)-11-hydroxyaporphine 2 directly from (R)-10,11-dihydroxyaporphine ((R)-apomorphine, 1 ) is described for the first time. The isopropylidene ketal ring of 10,11-(isopropyl-idenyldioxy)aporphine 5 obtained by the isopropylidenation of apomorphine was regioselectively opened by ten equivalents of trimethylaluminum to give (R)-10-hydroxy-11-tert-butyloxyaporphine 6 . The free 10-hydioxyl position of 6 was triflated with N-pbenyltrifluoromethanesulfonimide and potassium carbonate under reflux to give (R)-10-[(trifluoromethyl)sulfonyloxy]-11-tert-butyloxyaporphine 7 . The reduced product, 11-tert-butyloxyaporphine 8 was prepared from 7 by a palladium-catalyzed hydrogenolysis. The ether cleavage of (R)-11-tert-butyloxyaporphine with 48% hydrobromic acid afforded the desired (R)-11-hydroxyaporphine 2 in good yield. 相似文献
70.
Adhesion and migration of vascular smooth muscle cells (VSMCs) play an important role in the pathogenesis of atherosclerosis. These processes involve the interaction of VSMCs with extracellular matrix proteins. Here, we investigated integrin isoforms and signaling pathways mediating the adhesion and migration of VSMCs on betaig-h3, a transforming growth factor (TGF)-beta-inducible extracellular matrix protein that is elevated in atherosclerotic plaques. Adhesion assays showed that the alphavbeta5 integrin is a functional receptor for the adhesion of aortic VSMCs to betaig-h3. An YH18 motif containing amino acids between 563 and 580 of betaig-h3 was an essential motif for the adhesion and growth of VSMCs. Interaction between the YH18 motif and the alphavbeta5 integrin was responsible for the migration of VSMCs on betaig-h3. Inhibitors of phosphatidylinositide 3-kinase, extracellular signal-regulated kinase (ERK), and Src kinase reduced the adhesion and migration of VSMCs on betaig-h3. betaig-h3 triggered phosphorylation and activation of AKT, ERK, focal adhesion kinase, and paxillin mediating the adhesion and migration of VSMCs. Taken together, these results suggest that betaig-h3 and alphavbeta5 integrin play a role in the adhesion and migration of VSMCs during the pathogenesis of atherosclerosis. 相似文献