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991.
Adjusting the properties of the photon generated via an optical parametric oscillator by using a pulse pumped laser 下载免费PDF全文
The cavity-enhanced spontaneous parametric down-conversion far below threshold can be used to generate a narrow-band photon pair efficiently. Previous experiments on the cavity-enhanced spontaneous parametric down-conversion almost always utilize continuous wave pump light, but the pulse pumped case is rarely reported. One disadvantage of the continuous wave case is that the photon pair is produced randomly within the coherence time of the pump, which limits its application in the quantum information realm. However, a pulse pump can help to solve this problem. In this paper, we theoretically analyze pulse pumped cavity-enhanced spontaneous parametric down-conversion in detail and show how the pump pulse affects the multi-photon interference visibility, two-photon waveform, joint spectrum and spectral brightness. 相似文献
992.
Room-temperature anomalous Hall effect and magnetroresistance in (Ga, Co)-codoped ZnO diluted magnetic semiconductor films 下载免费PDF全文
This paper reports that the(Ga,Co)-codoped ZnO thin films have been grown by inductively coupled plasma enhanced physical vapour deposition.Room-temperature ferromagnetism is observed for the as-grown thin films.The x-ray absorption fine structure characterization reveals that Co 2+ and Ga 3+ ions substitute for Zn 2+ ions in the ZnO lattice and exclude the possibility of extrinsic ferromagnetism origin.The ferromagnetic(Ga,Co)-codoped ZnO thin films exhibit carrier concentration dependent anomalous Hall effect and positive magnetoresistance at room temperature.The mechanism of anomalous Hall effect and magneto-transport in ferromagnetic ZnO-based diluted magnetic semiconductors is discussed. 相似文献
993.
994.
In this paper, we study the weighted norm inequalities for commutators formed by a class of one-sided oscillatory integral
operators and functions in one-sided BMO spaces. 相似文献
995.
在室温条件下, 采用超声辅助电化学方法合成了几种三维铂纳米电催化剂. 利用透射电子显微镜(TEM)、X射线粉末衍射(XRD)以及电化学测试对该三维铂纳米电催化剂进行了表征. 结果表明, 这些铂纳米电催化剂的形貌、结构可以通过添加不同的形貌控制剂来调控, 在水溶液、聚乙烯吡咯烷酮(PVP)溶液和十六烷基三甲基氯化铵(CTAC)溶液中分别得到了立方海绵状铂、分枝状铂和球形多孔状铂. 其中, 球形多孔状铂纳米电催化剂由于其多孔的结构, 因此具有更高的电化学活性面积, 对氧气还原和甲醇氧化反应具有更好的催化作用. 相似文献
996.
Pd催化的配体导向C-H键官能化反应已经成为有机化学中一种重要的合成手段. 我们用B3PW91密度泛函方法研究了Pd催化的配体导向C-H键乙酰化反应中催化剂和底物配合步骤以及C-H键活化步骤中的热力学性质. 研究发现, 具有不同导向基团的反应物之间竞争反应的选择性取决于导向基团与Pd(OAc)2的配合步骤, 配合反应稳定常数大的较容易生成乙酰化的产物. 另一方面, 反应的选择性与C-H键的活化步骤无关, 并且与导向基团的配位原子的气相碱性、原子上的电荷密度以及最高占据轨道能量都没有相关性. 相似文献
997.
998.
In this paper, a wavelet multiresolution technique is proposed to identify time-varying properties of hysteretic structures. It is well known that arbitrary transient functions can be effectively and accurately approximated using wavelet multiresolution expansions due to wavelet's good time-frequency localization property. By decomposing the time-varying parameters with wavelet multiresolution expansion, a time-varying parametric identification problem can be transformed into a time-invariant non-parametric one. The identification in the time-invariant wavelet multiresolution domain can be achieved by choosing a wavelet basis function and performing a suitable parameter estimation technique. Since wavelet representation of arbitrary signal uses only a small number of terms, the orthogonal forward regression algorithm can be adopted for significant term selection and parameter estimation. Single and multiple degrees of freedom Bouc-Wen hysteretic structures with gradual and abrupt varying properties are used to illustrate the proposed approach. Results show that the wavelet multiresolution technique can identify and track the time-varying hysteretic parameters quite accurately. The effect of measurement noise is also studied. It is found that the presence of noise would affect more on the damping ratios and the Bouc-Wen parameters but less on the equivalent stiffness coefficients. 相似文献
999.
We demonstrated two experimental methods of producing and
guiding pulsed atomic beams on chip. One is to trap atoms first in a
U-type magneto-optical trap on the chip, then transfer them to the
magnetic guide field and push them simultaneously by a continuous
force from the power imbalance of the magneto-optical trap laser
beams hence the pulsed cold atom beams are produced and move along
the magnetic guide to the destination. The other is to trap atoms
directly by a H-type magneto-optical trap, then push them to make
them move along the magnetic guide field, thus high rate cold atom
beams can be produced and guided on the chip. 相似文献
1000.
Advanced high-pressure plasma diagnostics with hairpin resonator probe surrounded by film and sheath 下载免费PDF全文
The hairpin probe using microwave resonance in plasma is applicable to high pressure 1.33×10 3-1.01×10 5 Pa)) as developed recently.In this work,an analytic model of the hairpin resonator probe surrounded by a thin dielectric layer and a sheath layer is proposed.The correction factor due to these surroundings is analytically found and confirmed by electromagnetic field finite difference time domain simulation,thus enabling the accurate measurement of electron density in a high-pressure non-equilibrium uniform discharge. 相似文献