Efficient generation of a photon pair in a bulk periodically poled potassium titanyl phosphate

In this report, we demonstrate the efficient generation of collinearly propagating photon pairs in a bulk periodically poled potassium titanyl phosphate pumped by a cw laser. The detected coincidence counts are more than 7400/s with 3.58 mW pump power in a Hanbury-Brown-Twiss-type experiment. The estimated photon pair production rate is about 0.73 MHz/mW. This is very promising for some applications, such as quantum key distribution, proof of the Bell-inequality, preparation of single photon states in broadband wave packets, Franson-type interference and so on.     

A 100 kHz Narrow-Pulse-Width Mid-Infrared Optical Parametric Oscillator Based on PPMgLN Crystal

We report a narrow pulse width optical parametric oscillator based on periodically poled MgO:LiNbO₃ (PPMgLN) with a high repetition rate under quasi-phase matched conditions. When the maximum pumping power of the 1,064-nm laser was 14.57 W, the acousto-optical (A-O) Q-switch repetition rate was 100 kHz, and the PPMgLN crystal grating period was 29.5 μm. A 1,474-nm signal light output power of 4.21 W and a 3,828 nm idler light output power of 1.547 W were obtained, corresponding to a pulse width of 9.52 ns and 9.65 ns, respectively. The overall optical–optical conversion efficiency was 39.5%. Additionally, by changing the temperature from 25°C to 150°C, a tunable signal wavelength of 1,474–1,499 nm and idler wavelength at 3,676–3,828 nm of the output laser were achieved.     

Opportunistic spectrum access for TDMA-based cognitive radio networks

In this paper, opportunistic spectrum access is proposed for TDMA-based cognitive radio networks. In TDMA-based networks, the time is divided into slots with fixed length one by one. If a primary user (PU) needs to transmit data, one or several slots will be used. Otherwise, the slots are idle and can be utilized by secondary users (SUs). When SUs want to use the licensed channel, they should sense the channel at the beginning period of each slot. Then SUs exchange their sensing results and make the same decision about the channel state (idle or used by PUs), which could reduce the probability of false sensing. The aforementioned duration is called spectrum sensing phase. When SUs decide there is an idle channel, they contend to use the channel at the rest time of the slot. The duration is called access phase. In this period, SUs contend the channel with backoff counters. When the remaining time is less than one data transmission duration, SUs cannot transmit data packets. Therefore, the remaining time is wasted. To solve this problem, SUs transmit control packets with small length in the remaining time instead. The SU who exchange control packets successfully reserves the channel and sends a data packet prior to other SUs in access phase of the next idle slot. Obviously, this reserved transmission is without collision. The independent spectrum sensing, channel state decision and control packets reservation influence the performance of SUs. The proposed scheme is formulated with all above factors. Simulations which consist with the numerical results show the proposed access scheme achieve higher throughput than the existed scheme without channel reservation.     

连续变量量子离物传态的实验研究

利用单个Ⅱ类相位匹配OPA产生的双模压缩态实现连续变量压缩纠缠态，完成了连续变量量 子离物传态. Ⅱ类相位匹配OPA参量反放大过程可以实现正交振幅反关联、正交位相关联的 压缩纠缠态，这不同于一般运转于阈值以下的OPO产生的正交振幅关联、正交位相反关联的 压缩纠缠态，可以采用直接平衡测量的方法完成Bell态测量. 利用双KTP补偿非线性过程的 离散效应，获得了最大压缩大于2dB的双模压缩纠缠态，实现保真度06，考虑到探测效率 实际保真度为057. 这种方案简化了测量方法与纠缠光源产生装置，有利于进行量子通信 的实验研究与应用. 同时，讨论了探测过程中的一些非理想因素. 关键词： 量子离物传态 压缩纠缠态 Bell态测量     

Dynamics of vibrational chaos and entanglement in triatomic molecules： Lie algebraic model

In this paper, the dynamics of chaos and the entanglement in triatomic molecular vibrations are investigated. On the classical aspect, we study the chaotic trajectories in the phase space. We employ the linear entropy to examine the dynamical entanglement of the two bonds on the quantum aspect. The correspondence between the classical chaos and the quantum dynamical entanglement is also investigated. As an example, we apply our algebraic model to molecule H2O.     

Evaluation of an oral carrier system in rats: bioavailability and gastrointestinal absorption properties of curcumin encapsulated PBCA nanoparticles

A new oral delivery system, polybutylcyanoacrylate nanoparticles (PBCNs), was introduced to improve the oral bioavailability of curcumin (CUR), a poorly soluble drug. The formulation was optimized by orthogonal design and the optimal PBCNs loading CUR exhibited a spherical shape under transmission electron microscopy with a range of 40?C400?nm. Physicochemical state of CUR in PBCN was investigated by X-ray diffraction and the possible structure changes occurring in CUR after conjugating with polybutylcyanoacrylate were studied with FTIR. The results indicated that CUR in PBCN was in a non-crystalline state and CUR was encapsulated in PBCN without chemical reaction. The oral pharmacokinetic study was conducted in rats and the relative bioavailability of CUR encapsulated PBCNs to the crude CUR was more than 800%. The in situ absorption experiment in rat intestine indicated the absorption was first order with passive diffusion mechanism. The absorption results in various segments of intestine showed that the main absorption sites were ileum and colon. It can be concluded that PBCNs as an oral carrier can significantly improve the oral absorption of a poorly soluble drug.     

制冷系统的广义预测控制方法研究

制冷系统的蒸发器过热度的控制对于制冷系统稳定、高效运行具有重要作用。文中通过实验辨识了基于过热度和蒸发温度的制冷系统多输入多输出模型,并采用广义模型预测控制方法,针对制冷系统的变负荷运行工况下进行了实验研究。结果表明,该方法很好的适应了制冷系统变过热度、变蒸发温度的控制要求,相比常规的单输入单输出PID控制,跟踪性能良好、动态控制精度高,可以适应制冷系统负荷大范围变动的控制需求。     

带有高压储液器的制冷系统建模研究

通过对制冷系统循环特性、变工况特性和参数间耦合特性的分析,遵循热力学基本定律和能量、动量、质量守恒定律,采用稳态和动态建模相结合的方法建立压缩式制冷系统的数学模型。针对换热器建模难点采用分相区和移动边界相结合的方法建立其集总参数动态模型,并且冷凝器与高压储液器相结合,构成冷凝器加储液器的整体部件,文中建立的制冷系统的整体模型,反映了制冷系统工况变化时制冷剂质量的重新分配及其对状态变量的影响,提高了系统建模的精度,最后通过实验对所建模型的准确性进行了验证。     

快速凝固Cu-Pb过偏晶合金的性能表征

研究了Cu-Pb过偏晶合金的急冷快速凝固组织特征,定量表征了快速凝固Cu-Pb过偏晶合金的电阻率和力学性能,理论分析了冷却速率和组织形态对合金性能的影响规律. 研究结果表明,在急冷快速凝固条件下,Cu-Pb过偏晶合金中的(Cu)相和(Pb)相均以枝晶方式生长,晶体形态以均匀细小的等轴晶为特征. 随着冷却速率增大,一方面,凝固组织显著细化,晶界增多,对自由电子的散射作用增强,合金电阻率显著增大;另一方面,细晶强化作用增强,合金的抗拉强度呈线性升高,同时,伴随着晶体缺陷数量的增多,合金的伸长率降低. 关键词： Cu-Pb过偏晶合金 快速凝固 电阻率 力学性能     

Enhanced mechanism of catalytic ozonation by ultrasound with orthogonal dual frequencies for the degradation of nitrobenzene in aqueous solution

The experiments have been performed with a semi-continuous batch reactor to investigate the degradation efficiency of nitrobenzene in aqueous solution by ultrasound with the different orthogonal dual frequencies catalytic ozonation. The introduction of ultrasound can enhance the degradation efficiency of nitrobenzene compared to the results obtained from the processes of ozonation alone and ultrasound alone. The degradation of nitrobenzene is found to be zero-order in the two systems of ultrasound alone, and the reactions follow the pseudo-first-order kinetic model in the processes of ozone alone and ozone/ultrasound. The investigation confirms that the degradation of nitrobenzene follows the mechanism of hydroxyl radical (^•OH) oxidation, and the enhancement function is even more pronounced in the presence of ultrasound with the greater difference between the orthogonal dual frequencies due to the obvious synergetic effect between ozone and ultrasound, which increases the utilization efficiency of ozone, and accelerates the initiation of ^•OH and the formation of H₂O₂, resulting in the rapid formation of an increasing diversity of byproducts and the advancement degree of mineralization of total organic carbon (TOC). The oxidative byproducts have been, respectively identified in the different processes selected, including o, p, m-nitrophenols, phenol, malonic acid, 4-nitrocatechol, nitrate ion, maleic acid, oxalic acid, hydroquinone, p-quinone, 1,2,3-trihydroxy-5-nitrobenzene and acetic acid.