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921.
Trimethyl(trichloromethyl)silane and trimethyl(tribromomethyl)silane react with anhydrous potassium fluoride in diglyme to give good yields of CX2 transfer products (dihalocyclopropanes) with olefins. Catalysis by 18-crown-6 ether is observed. 相似文献
922.
923.
Single photons are generated from an ensemble of cold Cs atoms via the protocol of Duan et al. [Nature (London), ()]]. Conditioned upon an initial detection from field 1 at 852 nm, a photon in field 2 at 894 nm is produced in a controlled fashion from excitation stored within the atomic ensemble. The single-quantum character of field 2 is demonstrated by the violation of a Cauchy-Schwarz inequality, namely w(1(2),1(2)|1(1))=0.24+/-0.05 not > or = 1, where w(1(2),1(2)|1(1)) describes the detection of two events (1(2),1(2)) conditioned upon an initial detection 1(1), with w-->0 for single photons. 相似文献
924.
The synthesis of syn-sesterbicyclo[2.2.2]octene (7) bilaterally grafted by an exocyclic s-cis-butadiene moiety is achieved from 1,8,9,10-tetrachloro-11,11-dimethoxy-endo-tricyclo[6.2.1.02,7]undeca-3,5,9-triene (8) employing repetitive Diels-Alder cycloadditions between 1,3-cyclohexadiene, generated from p-benzoquinone, and diethyl fumarate or maleic anhydride as the exocyclic butadienyl equivalent, followed by subsequent transformation to the conjugated diene moieties. In comparison with the corresponding sesquibicyclo[2.2.2]octene 6, the 1H NMR demonstrates the anisotropic shielding effect operating within the three parallel laticyclic double bonds. However, the UV absorption of 7 shows less effect by the increase of laticyclic conjugated ethylene units. 相似文献
925.
Cheng CC Yu WS Chou PT Peng SM Lee GH Wu PC Song YH Chi Y 《Chemical communications (Cambridge, England)》2003,(20):2628-2629
A new series of pyridyl pyrazolate boron complexes 2a-e have been synthesized, in which 2a-c exhibit remarkable dual fluorescence properties due to the photoinduced electron transfer reaction. 相似文献
926.
A method that uses a Zeeman laser in conjunction with a Glan-Thompson analyzer to image an object in a turbid medium is proposed. A heterodyne signal is generated only when the scattering photons are partially polarized, and the spatial coherence is not seriously degraded after the signal propagates in the turbid medium. A system combining polarization discrimination with optical coherence detection to image the object in a scattering medium is successfully demonstrated. The medium is a solution of polystyrene microspheres measuring 1.072 mum in diameter suspended in distilled water contained in a 10-mm-thick quartz cuvette. The advantages of this optical system, including better selectivity of the weak partially polarized scattering photons and better imaging ability in higher-scattering media, are discussed. 相似文献
927.
Reconfigurable time-domain spectral shaping of an optical pulse stretched by a fiber Bragg grating 总被引:2,自引:0,他引:2
We demonstrate a method for spectrally shaping optical pulses that is readily reconfigurable and can produce variable filter functions. This practical technique relies on a compact and robust 3.86-m-long linearly chirped fiber Bragg grating that chromatically disperses the pulse to ~30 ns. We then shape the pulse envelope, and thus the pulse spectrum, with a programmable arbitrary waveform generator and an amplitude modulator to obtain several filter functions. 相似文献
928.
In this paper we consider covolume or finite volume element methods for variable coefficient elliptic and parabolic problems on convex smooth domains in the plane. We introduce a general approach for connecting these methods with finite element method analysis. This unified approach is used to prove known convergence results in the norms and new results in the max-norm. For the elliptic problems we demonstrate that the error between the exact solution and the approximate solution in the maximum norm is in the linear element case. Furthermore, the maximum norm error in the gradient is shown to be of first order. Similar results hold for the parabolic problems.
929.
Tung-Yuan Yu Kun-Lin Lin Pin-Guang Chen Tung-Huan Chou 《Surface and interface analysis : SIA》2022,54(8):864-872
The thermal stability and material properties of HfO2 thin films on Si substrates with and without H2O2 wet chemical oxidation were investigated. The HfO2 samples were deposited through plasma-enhanced atomic layer deposition and subjected to thermal annealing. They were then examined using X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, and conductive atomic force microscopy. For the Si substrate without H2O2 wet chemical oxidation, a native oxide (~1.8 nm) was formed on the substrate before HfO2 deposition. After the annealing process at 600°C, the band gap (Eg) of the HfO2 films increased from 6.0 to 6.2 eV due to the diffusion of Si into HfO2. Furthermore, the conduction and valence band offsets (ΔEc and ΔEv, respectively) between HfO2 and Si changed from 1.02 to 1.42 and 3.86 to 3.66 eV, respectively. After the H2O2 wet oxidation of the Si substrate, a 1.5-nm chemical oxide was formed instead of a native oxide. The band offset and Eg values of HfO2 were similar before and after 600°C annealing (ΔEv = 3.86 eV, ΔEc = 1.02 eV, and Eg = 6.0 eV), implying the high thermal stability of the HfO2 films. Accordingly, wet oxidation not only prevents diffusion from chemical oxide but also markedly improves the oxide leakage current, which is useful for developing highly efficient and thermally stable HfO2 gate oxides in Si-based integrated circuit devices. 相似文献
930.
控制致裂岩体应力量测的模型试验研究 总被引:1,自引:0,他引:1
本文阐明了控制致裂岩体应力量测的基本原理、试验方法。介绍了几种控制致裂的模型试验结果及其分析,证明了控制致裂理论的正确性。 相似文献