直接键连原子间的NMR偶合常数的自然杂化轨道研究V.13C-13C和13C-31P核自旋偶合常数1JCC和1JCP

在前文工作的基础上,结合MNDO/EHMO分子轨道方法和自然杂化轨道方法,具体计算了C-C键和C-P键的核自旋偶合常数.计算结果表明,¹J_CC和¹J_CP主要由成键原子的轨道杂化作用和键极性这两种结构因素所决定.为从简单价键理论角度解释和计算¹J_CC和¹J_CP值提供了简便直观的方法.     

叠加态下3色场波形优化增大谐波辐射截止能量及强度

在He~+离子1s态和2s态的叠加态作为初始态时,提出一种优化3束激光场来增大谐波截止能量和强度的方法.结果表明:在叠加初始态下,谐波强度要比基态初始态下增强3个数量级以上.随后,在3色场波形优化下,谐波截止能量又得到增大,进而获得一个高强度、高光子能量的谐波光谱连续区.通过叠加光谱连续区上最后100次的谐波可以获得一个27 as的孤立阿秒脉冲.     

Projective synchronization of two coupled excitable spiral waves

Interaction of two identical excitable spiral waves in a bilayer system is studied. We find that the two spiral waves can be completely synchronized if the coupling strength is sufficiently large. Prior to the complete synchronization, we find a new type of weak synchronization between the two coupled systems, i.e., the spiral wave of the driven system has the same geometric shape as the spiral wave of the driving system but with a much lower amplitude. This general behavior, called projective synchronization of two spiral waves, is similar to projective synchronization of two coupled nonlinear oscillators, which has been extensively studied before. The underlying mechanism is uncovered by the study of pulse collision in one-dimensional systems.     

Learning alters theta amplitude, theta-gamma coupling and neuronal synchronization in inferotemporal cortex

Background

How oscillatory brain rhythms alone, or in combination, influence cortical information processing to support learning has yet to be fully established. Local field potential and multi-unit neuronal activity recordings were made from 64-electrode arrays in the inferotemporal cortex of conscious sheep during and after visual discrimination learning of face or object pairs. A neural network model has been developed to simulate and aid functional interpretation of learning-evoked changes.

Results

Following learning the amplitude of theta (4-8 Hz), but not gamma (30-70 Hz) oscillations was increased, as was the ratio of theta to gamma. Over 75% of electrodes showed significant coupling between theta phase and gamma amplitude (theta-nested gamma). The strength of this coupling was also increased following learning and this was not simply a consequence of increased theta amplitude. Actual discrimination performance was significantly correlated with theta and theta-gamma coupling changes. Neuronal activity was phase-locked with theta but learning had no effect on firing rates or the magnitude or latencies of visual evoked potentials during stimuli. The neural network model developed showed that a combination of fast and slow inhibitory interneurons could generate theta-nested gamma. By increasing N-methyl-D-aspartate receptor sensitivity in the model similar changes were produced as in inferotemporal cortex after learning. The model showed that these changes could potentiate the firing of downstream neurons by a temporal desynchronization of excitatory neuron output without increasing the firing frequencies of the latter. This desynchronization effect was confirmed in IT neuronal activity following learning and its magnitude was correlated with discrimination performance.

Conclusions

Face discrimination learning produces significant increases in both theta amplitude and the strength of theta-gamma coupling in the inferotemporal cortex which are correlated with behavioral performance. A network model which can reproduce these changes suggests that a key function of such learning-evoked alterations in theta and theta-nested gamma activity may be increased temporal desynchronization in neuronal firing leading to optimal timing of inputs to downstream neural networks potentiating their responses. In this way learning can produce potentiation in neural networks simply through altering the temporal pattern of their inputs.     

Bichromatic laser frequency stabilization with Doppler effect and polarization spectroscopy

The interaction between polychromatic fields and atoms is an important subject in quantum optics.Frequency locking for small frequency interval multi-field is usually required in some experiments.In this letter,we experimentally demonstrate a holistic scheme for bichromatic laser frequency stabilization.Compared with traditional saturation absorption methods and complicated frequency shift schemes,offset locking for bichromatic fields is simply achieved using polarization spectroscopy and Doppler effect.Frequency locking with a wide-range asymmetry of the detuning is also shown.Our scheme makes laser spectroscopy experiments with polychromatic fields more convenient.     

Bohmian mechanics to high-order harmonic generation

This paper introduces Bohmian mechanics (BM) into the intense laser-atom physics to study high-order harmonic generation. In BM, the trajectories of atomic electron in an intense laser field can be obtained with the Bohm--Newton equation. The power spectrum with the trajectory of an atomic electron is calculated, which is found to be irregular. Next, the power spectrum associated with an atom ensemble from BM is considered, where the power spectrum becomes regular and consistent with that from quantum mechanics. Finally, the reason of the generation of the irregular spectrum is discussed.     

Tripartite states Bell-nonlocality sudden death in a quantum-critical environment

We demonstrate that multipartite Bell-inequalities violations can be fully destroyed in finite time in three-qubit states under a quantum-critical environment, which is an Ising model in a transverse field. We use the Mermin--Ardehali--Belinksii--Klyshko (MABK) inequality to detect the degree of nonlocality as measured by the extent of their violations. The effects of system-environment couplings, the size of degrees of freedom of environment and the strength of transverse field on the Bell-inequality violations are given for two different initial states, namely, the W class and GHZ class states. The results indicate that the Bell-inequality violations of the tripartite states will be completely destroyed by the decoherence under certain conditions.     

Simple schemes for generation of W-type multipartite entangled states and realization of quantum- information concentration

We propose simple schemes for generating W-type multipartite entangled states in cavity quantum electrodynamics (CQED). Our schemes involve a largely detuned interaction of Λ-type three-level atoms with a single-mode cavity field and a classical laser, and both the symmetric and asymmetric W states can be created in a single step. Our schemes are insensitive to both the cavity decay and atomic spontaneous emission. With the above system, we also propose a scheme for realizing quantum-information concentration which is the reverse process of quantum cloning. In this scheme, quantum-information originally coming from a single qubit, but now distributed into many qubits, is concentrated back to a single qubit in only one step.     

应用NiZn铁氧体的宽带传输线变压器性能分析

研究了变换比为4∶1的宽频带传输线变压器,给出了考虑线圈互耦的等效电路模型,分析了其阻抗变换特性。针对在以往传输线变压器分析中忽略频率变化对磁导率的影响这一问题,以应用NiZn铁氧体的宽带传输线变压器为例,将频率变化对磁导率的影响应用到分析传输线变压器特性中。对测试结果的分析和比较表明:在传输线变压器输入阻抗的分析中,频率对其的影响是存在的,在等效电路模型分析中加以考虑,可以更好地与实际值吻合。     

全光纤高效超连续谱光源实验研究

 报道了一个全光纤的高效率超连续谱产生系统,系统采用增加一段匹配光纤的办法解决增益光纤和光子晶体光纤直接熔接损耗较大的问题,并且对匹配光纤和光子晶体光纤熔接对准过程进行实时监控,使熔接损耗降到最低,从而实现了较高的全系统转换效率(76%)和较好的光束质量。实验研究了超连续光谱展宽的过程,结果显示：超连续谱展宽的初始阶段,拉曼效应和自相位调制效应起主要作用,光谱呈现长波方向展宽较多的非对称性,并出现明显的拉曼斯托克斯峰;光谱继续展宽时,满足相位匹配条件的四波混频开始起作用,拉曼效应产生的加宽光谱成分作为四波混频参量过程的泵浦,使光谱开始向长波和短波两个方向扩展。