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21.
Sheet G Mehta M Dikin DA Lee S Bark CW Jiang J Weiss JD Hellstrom EE Rzchowski MS Eom CB Chandrasekhar V 《Physical review letters》2010,105(16):167003
The normal state properties of the recently discovered ferropnictide superconductors might hold the key to understanding their exotic superconductivity. Using point-contact spectroscopy we show that Andreev reflection between an epitaxial thin film of Ba(Fe(0.92)Co(0.08))?As? and a silver tip can be seen in the normal state of the film up to temperature T~1.3T(c), where T(c) is the critical temperature of the superconductor. Andreev reflection far above T(c) can be understood only when superconducting pairs arising from strong fluctuation of the phase of the complex superconducting order parameter exist in the normal state. Our results provide spectroscopic evidence of phase-incoherent superconducting pairs in the normal state of the ferropnictide superconductors. 相似文献
22.
Jang HW Baek SH Ortiz D Folkman CM Das RR Chu YH Shafer P Zhang JX Choudhury S Vaithyanathan V Chen YB Felker DA Biegalski MD Rzchowski MS Pan XQ Schlom DG Chen LQ Ramesh R Eom CB 《Physical review letters》2008,101(10):107602
Direct measurement of the remanent polarization of high quality (001)-oriented epitaxial BiFeO3 thin films shows a strong strain dependence, even larger than conventional (001)-oriented PbTiO3 films. Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization of (001) BiFeO3 with biaxial strain while the spontaneous polarization itself remains almost constant. 相似文献
23.
Hyun Cheol Koo Jae Hyun Kwon Jonghwa Eom Joonyeon Chang Suk-Hee Han 《Journal of magnetism and magnetic materials》2008
The spin transport signals from NiFe and Co into two-dimensional electron gas layers are measured for various thicknesses of transmission barriers. A stable and reproducible electrical detection of spin transport was obtained only when the barrier thickness is less than 10 nm. The typical interface resistance to observe spin signals in this experiment is about 0.5–250 Ω, which is a neither transparent nor a severe tunneling limit. The optimal interface resistance depends on the ferromagnetic materials, but severe tunneling barrier is not proper for fully electrical spin transport. Device size is also a critical factor to decide the proper range of interface resistance. 相似文献
24.
Youngho Eom Hyejin Ju Byoung C. Kim Han G. Chae 《Journal of Polymer Science.Polymer Physics》2019,57(16):1080-1089
The effect of dipole–dipole interaction by nitrile groups of PAN on the bound state of solvent molecules and the concentrated solution properties in DMSO was investigated. Variation of a solution viscosity exhibited three overlap concentrations, C1*, C2*, and C3*, at 2.7, 8.6, and 16.3 wt%, respectively, representing the transition of concentration regions in the order of dilute, unentangled‐semi dilute, entangled‐semi dilute, and concentrated regions. The two‐dimensional mapping of FT‐IR analysis and dielectric measurement confirmed that the intermolecular interaction of PAN was suddenly enhanced at the C*s, inducing polarization to DMSO. In the ice‐melting process of PAN solutions, two different melting peaks (Tm2 and Tm3) of DMSO newly appeared at each C2* and C3*, suggesting the different types of bound solvents. In the concentrated solutions, the saturated dielectric constant and the strongly delayed evaporation of the solvent even at the boiling point of DMSO along with strong thixotropic behavior were indicative of the stronger confinement state of bound DMSO than in the semidilute solutions. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1080–1089 相似文献
25.
In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed. 相似文献
26.
A single-mode fiber (SMF) acousto-optic tunable filter (AOTF) with a tuning range of more than 300 nm is demonstrated. The SMF used in the experiment has a ring of symmetric holes within the cladding, which causes a larger mode-index difference between the first and the second higher-order antisymmetric modes than those of a conventional SMF. As a result, the difference in beatlengths between the core mode and the higher-order modes is highly increased, which makes it possible for the SMF AOTF to exhibit a single resonance peak in the transmission spectrum over the wavelength range of 1.3-1.6 μm for given acoustic frequencies of 3.1-3.8 MHz. 相似文献
27.
We propose a novel fiber attenuator based on photonic crystal fibers. The difference in the modal field diameters of a conventional single mode fiber and a photonic crystal fiber was used. A variable optical attenuator was also achieved by applying macro-bending on the PCF part of the proposed attenuator 相似文献
28.
Lee PH Mo J Kang D Eom D Park C Lee CH Jung YM Hwang H 《The Journal of organic chemistry》2011,76(1):312-315
Pd-catalyzed cross-coupling reactions of aryl iodides containing not only an electron-donating group but also an electron-withdrawing group on the aryl ring with organoindium reagents generated in situ from indium and ethyl 4-bromo-2-alkynoates produced selectively ethyl 2-aryl-2,3-alkadienoates in good yield. 相似文献
29.
An efficient method compatible with Fmoc synthesis for preparing peptide thioesters via an acid-catalyzed tandem "thiol switch" of esters is described first by an intramolecular O-S acyl shift and then by an intermolecular S-S exchange, with concurrent deblocking of side chain protection groups. 相似文献
30.
Minseok Song Eunji Eom Dr. Jae Won Shin Prof. Hae Sung Cho Dr. Jeong-Chul Kim Prof. Changbum Jo 《Angewandte Chemie (International ed. in English)》2023,62(27):e202303503
We report a general synthetic strategy for post-encapsulation of metal nanoparticles within preformed zeolites using post-synthetic modification. Both anionic and cationic precursors to metal nanoparticle are supported on 8- and 10-membered ring zeolites and analogues during wet impregnation using 2-aminoethanethiol (AET) as a bi-grafting agent. Thiol groups are coordinated to metal centers, whereas amine moieties are dynamically attached to micropore walls via acid-base interactions. The dynamic acid-base interactions cause the even distribution of the metal-AET complex throughout the zeolite matrix. These processes encapsulate Au, Rh, and Ni precursors within the CHA, *MRE, MFI zeolite, and SAPO-34 zeolite analogues, for which small channel apertures preclude the post-synthesis impregnation of metal precursors. Sequential activation forms small and uniform nanoparticles (1–2.5 nm in diameter), as confirmed through electron microscopy and X-ray absorption spectroscopy. Containment within the small micropores protected the nanoparticles against harsh thermal sintering conditions and prevented the fouling of the metal surface by coke, thus resulting in a high catalytic performance in n-dodecane hydroisomerization and methane decomposition. The remarkable specificity of the thiol to metal precursors and the dynamic acid-base interaction make these protocols extendable to various metal-zeolite systems, suitable for shape-selective catalysts in challenging chemical environments. 相似文献