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991.
992.
It was found that the manganese perovskite oxides Ln0.5Ca0.5MnO3 (Ln=Ho, Er, Tm, Yb and Lu) have an orthorhombic structure (space group Pnma). The Mn-O-Mn angles were calculated to be ∼148-150°, revealing an existence of a large crystallographic distortion in these oxides. Electrical resistivity measurements indicated both an insulating nature and a small magnetoresistance effect, both of which are owing to narrow bandwidths of the Mn-3d electrons arising from the crystallographic distortion. DC magnetization measurements showed the three characteristic temperatures, which could be assigned to charge-order, antiferromagnetism of Mn moments, and possible glassy states. All of these temperatures were decreased for the heavier Ln ions, which is explained in connection with both a difference of ionic radii of Ln3+ and Ca2+, and a lowering of electron transfer. The charge-ordering transition was not clearly observed only for Lu0.5Ca0.5MnO3 containing the smallest lanthanide ion, plausibly due to a large randomness of magnetic interactions arising from the ionic radii difference of Lu3+ and Ca2+. In addition, preliminary measurements of AC dielectric response suggested that these manganites belong to a so-called multiferroic system. 相似文献
993.
A microscopic photothermal lensing measurement under two-color continuous-wave laser excitation was performed to investigate a signal enhancement owing to the transient absorption by photoexcited solute molecules in liquid solutions. An intensity-modulated 409 nm laser beam and an un-modulated 532 nm laser beam were used for excitation, and a 670 nm probe beam was used for detecting the modulation amplitude of thermal lensing signals generated with a microscopic objective lens focusing laser beams into a capillary flow cell of 0.1 mm optical path length. The amplitude of the modulated signal increased as the power of the un-modulated laser beam increased, and a 143-times magnification was observed for an iso-propanol solution of naphthacene having 4.6 x 10(-4) absorbance at 409 nm and a negligible absorbance at 532 nm. A four-level model explaining the signal enhancement is proposed, and an important role of the transient absorption by photoexcited molecules is discussed. 相似文献
994.
Multimetal‐Substituted Epsilon‐Iron Oxide ϵ‐Ga0.31Ti0.05Co0.05Fe1.59O3 for Next‐Generation Magnetic Recording Tape in the Big‐Data Era 下载免费PDF全文
Prof. Shin‐ichi Ohkoshi Dr. Asuka Namai Marie Yoshikiyo Dr. Kenta Imoto Kazunori Tamazaki Koji Matsuno Osamu Inoue Tsutomu Ide Kenji Masada Masahiro Goto Takashi Goto Takayuki Yoshida Tatsuro Miyazaki 《Angewandte Chemie (International ed. in English)》2016,55(38):11403-11406
From the viewpoints of large capacity, long‐term guarantee, and low cost, interest in magnetic recording tapes has undergone a revival as an archive storage media for big data. Herein, we prepared a new series of metal‐substituted ?‐Fe2O3, ?‐GaIII0.31TiIV0.05CoII0.05FeIII1.59O3, nanoparticles with an average size of 18 nm. Ga, Ti, and Co cations tune the magnetic properties of ?‐Fe2O3 to the specifications demanded for a magnetic recording tape. The coercive field was tuned to 2.7 kOe by introduction of single‐ion anisotropy on CoII (S=3/2) along the c‐axis. The saturation magnetization was increased by 44 % with GaIII (S=0) and TiIV (S=0) substitution through the enhancement of positive sublattice magnetizations. The magnetic tape media was fabricated using an actual production line and showed a very sharp signal response and a remarkably high signal‐to‐noise ratio compared to the currently used magnetic tape. 相似文献
995.
Zameer Shervani Yutaka Ikushima Masahiro Sato Hajime Kawanami Yukiya Hakuta Toshirou Yokoyama Takako Nagase Hironobu Kuneida Kenji Aramaki 《Colloid and polymer science》2008,286(4):403-410
We have employed a number of reducing and capping agents to obtain Ag(0) metallic nanoparticles of various sizes and morphologies.
The size and morphology were tuned by selecting reducing and capping agents. Spherical particles of 15 and 43 nm diameter
were obtained when 1 wt% aqueous starch solution of AgNO3 precursor salt was reduced by d(+)-glucose and NaOH, respectively, on heating at 70 °C for 30 min. Smaller size particles obtained in the case of d(+)-glucose reduction has been attributed to the slow reduction rate by mild reducing agent d(+)-glucose compared to strong NaOH. Conducting the reduction at ambient temperature of silver salt in liquid crystalline
pluronic P123 and L64 also gave spherical particles of 8 and 24 nm, respectively, without the addition of any separate reducing
agent. NaOH reduction of salt in ethylene glycol (11 g)/polyvinyl pyrolidone (PVP; 0.053 g) mixture produced large self-assembled
cubes of 520 nm when smaller (26–53 nm) star-shaped sharp-edged structures formed initially aggregated on heating the preparation
at 190 °C for 1 h. Increasing the amount of PVP (0.5 g) in ethylene glycol (11 g) and heating at 70 °C for 30 min yielded
a mixture of spherical and non-spherical (cubes, hexagons, pentagons, and triangle) particles without the addition of an extra
reducing agent. Addition of 5 wt% PVP to 1 wt% aqueous starched solution resulted in the formation of a mixture of spherical
and anisotropic structures when solution heated at 70 °C for 1 h. Homogeneous smaller sized (29 nm) cubes were synthesized
by NaOH reduction of AgNO3 in 12.5 wt% of water-soluble polymer poly(methyl vinyl ether) at ambient temperature in 30 min reaction time. 相似文献
996.
Kenji Morokuma 《Tetrahedron letters》2008,49(42):6043-6045
Aldol reaction of di-tert-butyl 4-(4-methoxybenzyloxy)-2-oxobutanoate with pent-4-enal using (S)-1-(3,5-bis(trifluoromethyl)phenyl)-3-(pyrrolidin-2-ylmethyl)thiourea hydrochloride as a catalyst, followed by Pinnick oxidation and tert-butyl esterification, gave (2S,3S)-di-tert-butyl 2-(2-(4-methoxybenzyloxy)ethyl)-3-allyl-2-hydroxysuccinate in high optical purity (85% ee), from which the total synthesis of (+)-trachyspic acid, a tumor cell heparanase inhibitor, was accomplished. 相似文献
997.
We study self-assembly and polymorphic transitions of surfactant molecules in water within a nanotube and the effect of water-nanotube interactions on the self-assembly morphologies. We present a simulation evidence of a cornucopia of polymorphic structures of surfactant assemblies--many of which have not been observed in bulk solutions--through adjusting the water-nanotube chemical interactions which range from hydrophilic to hydroneutral and to hydrophobic. The ability to control the morphologies of surfactant assemblies within nanoscale confinement can be used for patterning the interior surface of nanochannels for application in nanofluidics and nanomedical devices. 相似文献
998.
Higuchi M Nagata K Abiko S Tanaka M Kinoshita T 《Langmuir : the ACS journal of surfaces and colloids》2008,24(23):13359-13363
Gold nanoparticles having sequential alternating amphiphilic peptide chains, Phe-(Leu-Glu)8, on the surface have been prepared. We describe structural control of the amphiphilic peptide coated gold nanoparticle assembly by a conformational transition of the surface peptides. Under the acidic condition, the conformation of the surface amphiphilic peptide was converted to a beta-sheet structure from an aggregated alpha-helix by incubation. Under this condition, the amphiphilic peptide coated gold nanoparticles formed a nanosheet assembly. The plasmon absorption maximum of the gold nanoparticles shifted to a shorter wavelength with the formation of the beta-sheet assembly of the surface peptide. This suggests that the structure of the peptide coated gold nanoparticle assembly could be controlled by the conformational transition of the surface peptide. Furthermore, the core gold nanoparticle could be fixed in the beta-sheet assembly in the state that stood alone. This system may be useful for novel molecular devices that exhibit quantized properties. 相似文献
999.
The extraordinary stability of the photoinduced red form of a cationic spiropyran ( k approximately 10 (-6) s (-1) in water and approximately 10 (-6) to less than 10 (-8) s (-1) in the solid state) was employed to obtain in situ X-ray diffraction evidence of its molecular structure. By UV excitation under selected experimental conditions, on average, approximately one third of the cations in a single crystal of spiropyran iodide salt was converted and retained as the red form during the experiment. According to the structure of the mixed crystal, the ring opening, which is due to increased distance between the spiro oxygen and carbon atoms, is associated with slight molecular flattening caused by concurrent out-of-plane shift (11.2(5) degrees ) of the pyranopyridinium half and in-plane shift (4.8(7) degrees ) of the indoline half. The overall geometry change of the cation fits the steric requirements imposed by the ion packing in the crystal and can be viewed as molecular flattening caused by breaking of the spiroconjugation. The structure of the cation confirms that (at least in the case of cationic spiropyrans) the product is confined in the crystal mainly as a zwitterionic resonance structure in cis configuration similar to the (early) transition state. Although the positive charge of the closed form facilitates the ring-opening reaction by moving the reactant closer to the transition state, neither the weakening of the spiropyran C-O bond nor the space provided by the iodide alone can account for the stability of the product. Instead, the density functional theory calculations indicate that the stabilization of the red form of the cationic relative to the neutral spiropyran is thermodynamically controlled, probably through compensation of the charge within the zwitterion by the methylpyridinium group. 相似文献
1000.
Yamada M Wakahara T Tsuchiya T Maeda Y Kako M Akasaka T Yoza K Horn E Mizorogi N Nagase S 《Chemical communications (Cambridge, England)》2008,(5):558-560
Dimetallofullerene Ce(2)@C(78) and its bis-silylated derivative (1) were successfully prepared and fully characterized. 相似文献