83 research outputs found
Interface engineering of graphene for universal applications as both anode and cathode in organic photovoltaics
The high transparency of graphene, together with its good electrical conductivity and mechanical robustness, enable its use as transparent electrodes in optoelectronic devices such as solar cells. While initial demonstrations of graphene-based organic photovoltaics (OPV) have been promising, realization of scalable technologies remains challenging due to their performance and, critically, poor device reproducibility and yield. In this work, we demonstrate by engineering the interface between graphene and organic layers, device performance and yield become close to devices using indium tin oxide. Our study confirms that the key issue leading to the poor performance or irreproducibility in graphene-based OPV originates from the graphene interface, and can be addressed by a simple interface modification method introduced in this work. We also show similar approach allows graphene to be used as cathode in inverted OPV geometry, thereby demonstrating the universal application of graphene as transparent conductors for both the anode and cathode.open11
Metal-Free Carbocyclization of Homoallylic Silyl Ethers Leading to Cyclopropanes and Cyclobutanes
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, WeinheimWe have developed a Hosomi-Sakurai type carbocyclization of homoallylic silyl ethers in reaction with silyl nucleophiles, catalyzed by Lewis acidic silylium salt. It offers cyclopropane and cyclobutane products with high efficiency and selectivity. A range of silyl nucleophiles could be engaged in this transformation to give small-sized carbocycles incorporating allyl, allenyl, carbonyl, indole or thioether groups. Diastereoselectivity in the cyclobutane formation was observed to be dependent on the steric bulkiness of incoming nucleophiles.11sciescopu
X-ray computed tomography method for macroscopic structural property evaluation of active twist composite blades
This paper describes an evaluation of the structural properties of the next-generation active twist blade using X-ray computed tomography (CT) combined with digital image processing. This non-destructive testing technique avoids the costly demolition of the blade structure. The CT scan covers the whole blade region, including the root, transition, and tip regions as well as the airfoil blade regions, in which there are spanwise variations in the interior structural layout due to the existence of heavy instrumentation. The three-dimensional digital image data are processed at selected radial stations, and finite element beam cross-section analyses are conducted to evaluate the structural properties of the blade at the macroscopic level. The fidelity of the digital blade model is first assessed by correlating the estimated blade mass with the measured data. A separate me- chanical measurement is then carried out to determine the representative elastic properties of the blade and to verify the predicted results. The agreement is found to be good to excellent for the mass, elastic axis, flap bending, and torsional rigidity. Finally, a sensitivity analysis is conducted to clarify the impact of modeling the sensor and actuator cables, nose weight, and manufacturing im- perfections on the structural properties of the blade
X-ray computed tomography method for macroscopic structural property evaluation of active twist composite blades
This paper describes an evaluation of the structural properties of the next-generation active twist blade using X-ray computed tomography (CT) combined with digital image processing. This non-destructive testing technique avoids the costly demolition of the blade structure. The CT scan covers the whole blade region, including the root, transition, and tip regions as well as the airfoil blade regions, in which there are spanwise variations in the interior structural layout due to the existence of heavy instrumentation. The three-dimensional digital image data are processed at selected radial stations, and finite element beam cross-section analyses are conducted to evaluate the structural properties of the blade at the macroscopic level. The fidelity of the digital blade model is first assessed by correlating the estimated blade mass with the measured data. A separate me- chanical measurement is then carried out to determine the representative elastic properties of the blade and to verify the predicted results. The agreement is found to be good to excellent for the mass, elastic axis, flap bending, and torsional rigidity. Finally, a sensitivity analysis is conducted to clarify the impact of modeling the sensor and actuator cables, nose weight, and manufacturing im- perfections on the structural properties of the blade
Oncologic outcomes after immediate breast reconstruction following mastectomy: comparison of implant and flap using propensity score matching
Although immediate breast reconstruction has been reported to be oncologically safe, no affirmative study comparing the two reconstruction methods exists. We investigated breast cancer recurrence rates in two breast reconstruction types; implant reconstruction and autologous flap reconstruction.
A retrospective cohort study was performed on propensity score-matched (for age, stage, estrogen receptor status) patients who underwent IBR after mastectomy at Seoul National University Hospital between 2010 and 2014. The main outcomes determined were locoregional recurrence-free interval (LRRFI) and disease-free interval (DFI).
We analyzed 496 patients among 731 patients following propensity score matching (Median age 43, 247 implant reconstruction and 249 flap reconstruction). During median follow-up of 58.2 months, DFI was not different between the two groups at each tumor stage. However, flap reconstruction showed inferior DFI compared to implant reconstruction in patients with high histologic grade (p = 0.012), and with high Ki-67 (p = 0.028). Flap reconstruction was related to short DFI in multivariate analysis in aggressive tumor subsets. Short DFI after flap reconstruction in aggressive tumor cell phenotype was most evident in hormone positive/Her-2 negative cancer (p = 0.008). LRRFI, on the other hand, did not show difference according to reconstruction method regardless of tumor cell aggressiveness.
Although there is no difference in cancer recurrence according to reconstruction method in general, flap-based reconstruction showed higher systemic recurrence associated with histologically aggressive tumors
Organic/inorganic hybrid nanostructures for chemical plasmonic sensors
The work presented in this dissertation suggests novel design of chemical plasmonic sensors which have been developed based on Localized Surface Plasmon Resonance (LSPR), and Surface-enhanced Raman scattering (SERS) phenomena. The goal of the study is to understand the SERS phenomena for 3D hybrid (organic/inorganic) templates and to design of the templates for trace-level detection of selected chemical analytes relevant to liquid explosives and hazardous chemicals. The key design criteria for the development of the SERS templates are utilizing selective polymeric nanocoatings within cylindrical nanopores for promoting selective adsorption of chemical analyte molecules, maximizing specific surface area, and optimizing concentration of hot spots with efficient light interaction inside nanochannels. The organic/inorganic hybrid templates are optimized through a comprehensive understanding of the LSPR properties of the gold nanoparticles, gold nanorods, interaction of light with highly porous alumina template, and the choice of physical and chemical attributes of the selective coating.
Furthermore, novel method to assemble silver nanoparticles in 3D as the active SERS-active substrate has been demonstrated by uniform, in situ growth of silver nanoparticles from electroless deposited silver seeds excluding any adhesive polymer layer on template. This approach can be the optimal for SERS sensing applications because it is not necessary to separate the Raman bands of the polyelectrolyte binding layer from those of the desired analyte. The fabrication method is an efficient, simple and fast way to assemble nanoparticles into 3D nanostructures.
Addressable Raman markers from silver nanowire crossbars with silver nanoparticles are also introduced and studied. Assembly of silver nanowire crossbar structure is achieved by simple, double-step capillary transfer lithography. The on/off SERS properties can be observed on silver nanowire crossbars with silver nanoparticles depending on the exact location and orientation of decorated silver nanoparticles nearby silver nanowire crossbars.
As an alternative approach for the template-assisted nanostructure design, porous alumina membrane (PAM) can be utilized as a sacrificial template for the fabrication of the nanotube structure. The study seeks to investigate the design aspects of polymeric/inorganic hybrid nanotube structures with plasmonic properties, which can be dynamically tuned by external stimuli such as pH.
This research suggests several different organic/inorganic nanostructure assemblies by various template-assisted techniques. The polymeric/inorganic hybrid nanostructures including SERS property, pH responsive characteristics, and large surface area will enable us to understand and design the novel chemical plasmonic sensors.Ph.D.Committee Chair: Vladimir V Tsukruk; Committee Member: Mostafa A. El-Sayed; Committee Member: Satish Kumar; Committee Member: Valeria Milam; Committee Member: Yonathan Thi
Borane-Catalyzed Ring-Opening and Ring-Closing Cascades of Furans Leading to Silicon-Functionalized Synthetic Intermediates
The conversion of renewable biomass resources to synthetically valuable chemicals is highly
desirable, but remains a formidable challenge in regards to the substrate scope and reaction
conditions. Here we present the development of tris(pentafluorophenyl)borane–catalysed
conversion of furans via ring-opening and closing cascade processes to afford siliconfunctionalized
synthetic chemicals under transition metal-free conditions. The furan
ring-opening with hydrosilanes is highly efficient (TON up to 2,000) and atom-economical
without forming any byproduct to give rise to a-silyloxy-(Z)-alkenyl silanes. Additional
equivalents of silane smoothly induce a subsequent B(C6F5)3-catalysed cyclization of initially
formed olefinic silane compounds to produce anti-(2-alkyl)cyclopropyl silanes, another
versatile synthon being potentially applicable in the synthesis of natural products and
pharmacophores.
(c) The Author(s) 201611sciescopu
Dual role of carboxylic acid additive: Mechanistic studies and implication for the asymmetric C-H amidation Dedicated to Professor Yoshiaki Nakao on his receipt of the Tetrahedron Young Investigator Award
Acid additive effects in the Ir-catalyzed CeH amidation of arylphosphoryl compounds were examined.
Structure of catalytically active metal species was elucidated: mono-cationic iridium catalyst [Cp*Ir(-
III)(OAc)](NTf2) being mainly responsible for the CeH bond activation. Mechanistic studies revealed
a dual role of carboxylic acid additive operating both in the generation of an iridacyclic intermediate and
in the protodemetalation process to release amidated products. The fact that asymmetric CeH amidation
was achieved albeit in moderate enantioselectivity by using chiral carboxylic acid supports our proposal
especially with regard to the role of acid additive. © 2015 Elsevier Ltd. All rights reserved118201sciescopu
Silylative Reductive Amination of alpha,beta-Unsaturated Aldehydes: AConvenient Synthetic Route to beta-Silylated Secondary Amines
Described here is a reductive amination/hydrosilylation cascade of alpha,beta-unsaturated aldehydes mediated by a Lewis acidic borane catalyst. The present reaction system provides an one-pot synthetic route towards beta-silylated secondary amines that have not been accessible by other previous catalysis. Comparative (HNMR)-H-1 studies on the silylative reduction of enimines revealed that steric bulkiness of primary amine reactants strongly affects both catalytic efficiency and regioselectivity. This strategy was applicable to a broad range of substrates and amenable to one-pot gram-scale synthesis. Moreover, a diastereoselective introduction of the beta-silyl group was also found to be feasible (d.r. up to 71:29) ⓒ 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinhei
Piers' borane-mediated hydrosilylation of epoxides and cyclic ethers
We report the first diarylborane-catalysed hydrosilylation of epoxides and cyclic ethers. Mechanistic studies on the in situ generated Piers' borane (C6F5)2BH with hydrosilanes in the presence of an epoxide revealed that an alkyloxy(diaryl)borane (C6F5)2BOR is readily formed as a catalytically competent species for the outer-sphere hydrosilylation of epoxides and cyclic ethers.
© The Royal Society of Chemistry 201
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