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151.
Salvatore Abate Yun Gyong Ahn Tobias Kind Tommaso R. I. Cataldi Oliver Fiehn 《Rapid communications in mass spectrometry : RCM》2010,24(8):1172-1180
Many metabolomic applications use gas chromatography/mass spectrometry (GC/MS) under standard 70 eV electron ionization (EI) parameters. However, the abundance of molecular ions is often extremely low, impeding the calculation of elemental compositions for the identification of unknown compounds. On changing the beam‐steering voltage of the ion source, the relative abundances of molecular ions at 70 eV EI were increased up to ten‐fold for alkanes, fatty acid methyl esters and trimethylsilylated metabolites, concomitant with 2‐fold absolute increases in ion intensities. We have compared the abundance, mass accuracy and isotope ratio accuracy of molecular species in EI with those in chemical ionization (CI) with methane as reagent gas under high‐mass tuning. Thirty‐three peaks of a diverse set of trimethylsilylated metabolites were analyzed in triplicate, resulting in 342 ion species ([M+H]+, [M–CH3]+ for CI and [M]+ . , [M–CH3]+ . for EI). On average, CI yielded 8‐fold more intense molecular species than EI. Using internal recalibration, average mass errors of 1.8 ± 1.6 mm/z units and isotope ratio errors of 2.3 ± 2.0% (A+1/A ratio) and 1.7 ± 1.8% (A+2/A ratio) were obtained. When constraining lists of calculated elemental compositions by chemical and heuristic rules using the Seven Golden Rules algorithm and PubChem queries, the correct formula was retrieved as top hit in 60% of the cases and within the top‐3 hits in 80% of the cases. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
152.
Oxidation of ethylene was carried out over alumina-supported metal oxide catalysts and highly dispersed gold catalysts, respectively, under atmospheric pressure. The ethylene was completely oxidized to produce carbon dioxide and water with both metal oxide and gold catalysts. The activity of gold catalyst prepared by deposition method was much higher than that of supported metal oxide catalysts. Ultra-fine gold particles on Co3O4 were more active than on Al2O3. Fe2O3/Al2O3 and MnO2/Al2O3 catalysts were more active than MoO3/Al2O3 catalyst. The activity of the supported metal oxide catalysts was greatly enhanced by addition of gold particles. It was therefore considered that gold particles promote dissociative adsorption of oxygen and the adsorbed oxygen reacts with adsorbed ethylene on support adjacent to the active site. 相似文献
153.
Cr3+ diffusion in chrysoberyl (BeAl2O4) irradiated by H+ ions and electrons has been studied and compared with diffusion in non-irradiated samples. Chrysoberyl crystals were irradiated with 6 MeV H+ ions to fluencies of 1×1016 cm–2 for 25 min and with 10 MeV electrons to fluencies of 2×1017 cm–2 for 1 h. Three different types of samples, which were doped with Cr3+, were annealed in horizontal alumina tube furnaces by 50 K intervals in the temperature range from 1773 to 1923 K for 200 h. Scanning electron microscope–energy dispersive X-ray spectrometer (SEM–EDX) was used to measure the diffusion. Arrhenius equations for the diffusion coefficient for Cr3+ in the temperature range 1773–1923 K were developed: 相似文献
154.
In the paper, we present an interactive decision procedure for aggregating group members’ preferences which are specified in incomplete ways. A group consensus under incomplete information is not usually reached at a single step since less-specific preferences on attribute weights and performance scores make a clear selection of best alternative more difficult. To circumvent these difficulties, a measure, indicating the strength of preference between alternatives, is derived to help each of decision makers change his/her preference structure. To make preference changes based on the measure effective, we present a solution method to convert an intractable nonlinear programme into a linear one. 相似文献
155.
Kwangmin Park Eungjin Ahn Yu Jin Jeon Hyeonsik M. Cheong Jin Soak Kim Eun Kyu Kim Jungil Lee Young Ju Park Gun-Do Lee Euijoon Yoon 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):169
InAs quantum dots (QDs) were grown on InP substrates by metalorganic chemical vapor deposition. The width and height of the dots were 50 and 5.8 nm, respectively on the average and an areal density of 3.0×1010 cm−2 was observed by atomic force microscopy before the capping process. The influences of GaAs, In0.53Ga0.47As, and InP capping layers (5–10 ML thickness) on the InAs/InP QDs were studied. Insertion of a thin GaAs capping layer on the QDs led to a blue shift of up to 146 meV of the photoluminescence (PL) peak and an InGaAs capping layer on the QDs led to a red shift of 64 meV relative to the case when a conventional InP capping layer was used. We were able to tune the emission wavelength of the InAs QDs from 1.43 to 1.89 μm by using the GaAs and InGaAs capping layers. In addition, the full-width at half-maximum of the PL peak decreased from 79 to 26 meV by inserting a 7.5 ML GaAs layer. It is believed that this technique is useful in tailoring the optical properties of the InAs QDs at mid-infrared regime. 相似文献
156.
For small Hamiltonian perturbation of a Hamiltonian systemof arbitrary number of degrees of freedom with anormally non-degenerate submanifold of periodic orbits we construct a nearbysubmanifold and an `effective Hamiltonian' on it such that the differencebetween the two Hamiltonian vector fields is small. The effective Hamiltonianis independent of one coordinate, the `overall phase', and hence thecorresponding action is preserved. Unlike standard averaging approaches,critical points of our effective Hamiltonian subject to given actioncorrespond to exact periodic solutions. We prove there has to be at least acertain number of these critical points given by global topological principles.The linearisation of the effective Hamiltonian about critical points is provedto give the linearised dynamics for the full system to leading order in theperturbation. Hence in the case of distinct eigenvalues which move at non-zerospeed with ,the linear stability type of the periodic orbit can be read offfrom the effective Hamiltonian. Our principal application is to networks ofoscillators or rotors where many such submanifolds of periodic orbits occurat the uncoupled limit – simply excite a number N 2 of the units inrational frequency ratio and put the others on equilibria, subject to anon-resonance condition. The resulting exact periodic solutions for weakcoupling are known as multibreathers. We call the approximate solutions givenby the effective Hamiltonian dynamics, `generalised multibreathers'. Theycorrespond to solutions which look periodic on a short time scale but therelative phases of the excited units may evolve slowly. Extensions aresketched to travelling breathers and energy exchange between degrees offreedom. 相似文献
157.
Ki Byung Sunwoo Seung Joon Park Seong Jae Lee Kyung Hyun Ahn Seung Jong Lee 《Rheologica Acta》2002,41(1-2):144-153
Three-dimensional numerical simulation of viscoelastic coextrusion process has been performed and numerical results were
compared with the experimental data of Karagiannis et al. (1990). By varying the magnitude of the second normal stress difference
and its ratio of Fluid I and Fluid II, we were able to control the interface profile and the degree of encapsulation along
the downstream direction. By increasing the parameter α (αFluid I=αFluid II) from 0.1 to 0.4 in the Giesekus model and increasing the α ratio (αFluid IαFluid II) between Fluid I and Fluid II from 2.0 to 4.0 in the permissible range of realistic polymeric systems, the interface profile
and the degree of encapsulation along the downstream direction were fitted with the experimental results. There was little
difference between the numerical results and the experimental data in the interface profile and the degree of encapsulation
along the downstream direction when the α ratio was set to 3.0 (0.3:0.1). Fluid I with larger magnitude of the second normal
stress difference protrudes into Fluid II with smaller magnitude of the second normal stress difference around the symmetric
plane, while Fluid II wraps around Fluid I near the side walls. As the ξ
1
ratio (ξ
1
,Fluid Iξ
1
,Fluid II) increases from 1.0 to 3.0 for the two-mode Phan-Thien and Tanner model, it was found that the curvature of the interface
profile increased, and the difference between the numerical results and the experimental data in the interface profile and
the degree of encapsulation along the downstream direction was almost negligible when the ξ
1
ratio was set to 3.0 (0.54:0.18). Although the parameters of viscoelastic models were fitted by using the shear viscosity
data only, quantitative agreements between the numerical results and the experimental coextrusion data were quite satisfactory.
Received: 24 April 2001 Accepted: 5 June 2001 相似文献
158.
We investigate the rheological behavior of the polymer blends with fibril morphology, with special focus on the effect of fibril morphology on the extensional properties under uniaxial extension. We add a small amount of the dispersed phase to the matrix, and control the blend morphology by changing the viscosity ratio. When the fibril morphology is maintained, the blend shows not only a significant increase of the extensional viscosity but the strain hardening behavior. The extensional viscosity increases depending on the aspect ratio of the fibers, while the strain hardening behavior originates from the restricted stretching of deformable fibers, which has been confirmed theoretically by introducing the concept of rigidity of the fiber. It suggests a way to induce the strain hardening behavior by introducing deformable fibrils into the matrix, that is, by the design of polymer blends with a small amount of dispersed phase such that the fibril structure is maintained. 相似文献
159.
A Family of Molecular Sieves Containing Framework‐Bound Organic Structure‐Directing Agents 下载免费PDF全文
Jun Kyu Lee Dr. Jiho Shin Nak Ho Ahn Alessandro Turrina Dr. Min Bum Park Dr. Youngchul Byun Prof. Sung June Cho Prof. Paul A. Wright Prof. Suk Bong Hong 《Angewandte Chemie (International ed. in English)》2015,54(38):11097-11101
Organic structure‐directing agents (OSDAs), such as quaternary ammonium cations and amines, used in the synthesis of zeolites and related crystalline microporous oxides usually end up entrapped inside the void spaces of the crystallized inorganic host lattice. But none of them is known to form direct chemical bonds to the framework of these industrially important catalysts and adsorbents. We demonstrate that ECR‐40, currently regarded as a typical silicoaluminophosphate molecular sieve, constitutes instead a new family of inorganic‐organic hybrid networks in which the OSDAs are covalently bonded to the inorganic framework. ECR‐40 crystallization begins with the formation of an Al–OSDA complex in the liquid phase in which the Al is octahedrally coordinated. This unit is incorporated in the crystallizing ECR‐40. Subsequent removal of framework‐bound OSDAs generates Al‐O‐Al linkages in a fully tetrahedrally coordinated framework. 相似文献
160.
Interfacial Engineering of CdO–CdSe 3D Microarchitectures with in situ Photopolymerized PEDOT for an Enhanced Photovoltaic Performance 下载免费PDF全文
Iseul Lim Dipak V. Shinde Supriya A. Patil Do Young Ahn Wonjoo Lee Nabeen K. Shrestha Joong Kee Lee Sung‐Hwan Han 《Photochemistry and photobiology》2015,91(4):780-785
In the present work, porous 3D CdO‐microstructured electrode obtained by pyrolysis of 3D CdCO3 microstructures is self‐sensitized with CdSe using an ion exchange reaction. After sensitization, an interfacial treatment of the CdO–CdSe interface is performed by depositing a thin film of PEDOT using a photoinduce polymerization route. The microstructured electrode before and after interfacial treatment is characterized using field‐emission scanning microscope, energy dispersive X‐ray analyzer, contact angle measurement, UV–Visible absorption spectrophotometer and X‐ray photoelectron spectrometer. After constructing a liquid junction solar cell with a Pt counter electrode, the photovoltaic performance and interfacial charge transfer kinetics across the CdO–CdSe interface before and after PEDOT treatment are investigated. The results exhibit an improved interfacial charge‐transfer resistance after the PEDOT treatment, which leads to enhance the short‐circuit current by 15.81% and the power conversion efficiency by 19.82%. 相似文献