基于准相位匹配晶体的宽带可调谐光参量放大过程研究

系统分析了基于准相位匹配晶体的光参量放大过程中极化周期和非共线结构对信号光调谐带宽的影响.提出了最大极化周期的概念,用于描述非共线相位匹配和群速度匹配同时满足时晶体的极化周期所能达到的最大值,给出了用于计算不同温度下周期极化铌酸锂晶体的最大极化周期的数学公式,并确定了宽带可调谐光参量放大过程应使用的最佳非共线结构.当采用此非共线结构时,通过将晶体的极化周期设定为最大极化周期可以在相对最大的波长范围内实现信号光的调谐放大输出.在此基础上提出了一个用于最大化光参量放大过程的信号光调谐带宽、确定工作温度等最佳工作参数以及简化实验操作方法的可行性方案.最后对最大极化周期和非共线结构对光参量放大的参量带宽的影响进行了研究. 关键词： 光参量放大 极化周期 非共线结构 带宽     

Ni75Cr25-xAlx合金中L12相和D022相形核孕育期的微观相场模拟

基于微观相场动力学模型,运用原子图像、平均长程序参数和平均成分偏离序参数,研究了Al浓度对Ni₇₅Cr_25-xAl_x合金中L1₂相和D0₂₂相形核孕育期的影响以及孕育期与沉淀相析出顺序之间的关系.结果表明,L1₂相和D0₂₂相的形核孕育期不仅与Al浓度有关,而且与两相析出的先后顺序密切相关.当Al浓度小于7.5%时,先析出相为D0₂₂相,随着Al浓度的增大,D0₂₂相形核孕育期延长,后析出的L1₂相的形核孕育期也延长,L1₂相的原子簇?聚?速度加快;当Al浓度大于7.5%时,先析出相为L1₂相,随着Al浓度的增大,L1₂相的形核孕育期缩短,后析出的D0₂₂相形核孕育期也缩短.当Al浓度为7.5%时,L1₂相和D0₂₂相几乎同时析出,两者的孕育期没有明显的差别. 关键词： 形核孕育期 序参数 沉淀 微观相场模拟     

慢波结构参数对同轴相对论返波管线性增长率的影响

 根据线性理论推导同轴相对论返波管色散方程和线性增长率,分别给出了波纹深度和波纹周期改变对于同轴相对论返波管线性增长率的影响规律,发现在一定范围内,减小波纹周期或者增大波纹深度能够降低结构波相速度,获得较大的线性增长率。     

线性啁啾长周期光纤光栅用作EDFA增益平坦滤波器的理论研究

提出用具有特定折射率调制包络的线性啁啾长周期光纤光栅作为掺铒光纤放大器(EDFA)的增益平坦滤波器.采用龙格库塔迭代法数值求解该类型光栅耦合模方程,就特定的掺铒光纤放大器增益谱,用Nelder-Mead优化算法对光栅结构参量(光栅长度、周期、线性啁啾系数、折射率调制包络的形状等)进行优化,设计出能在C波段35 nm带宽范围内对掺铒光纤放大器进行平坦化(增益起伏在±0.5 dB之内)的平坦滤波器.     

Surface Modified Long Period Fiber Grating Sensor for Rapid Detection of Aspergillus Niger Fungal Spores

We present development of a compact and label-free sensor based on the surface modification of copper vapor laser fabricated long period fiber gratings for detection of airborne Aspergillus niger (A. niger) fungal spores. Surface of sensors were functionalized with monoclonal glucose oxidases IgG1 for target-specific covalent binding. In process of functionalization and binding of 10³ cfu/ml of pathogenic A. niger fungal spores, notable shorter wave transition in resonance wavelength from 1562.93 nm to 1555.97 nm, and significant reduction in peak loss from 61.72 dB to 57.48 dB were recorded. The implementation was cost effective and yielded instantaneous results.     

An extended stable isotope‐labeled signature peptide internal standard for tracking immunocapture of human plasma osteopontin for LC‐MS/MS quantification

A stable isotope‐labeled signature peptide, whose sequence corresponds to the human osteopontin (hOPN) specific antibody epitope, was evaluated as an internal standard to compensate for immunocapture variability during quantification of hOPN by immunoaffinity‐coupled LC‐MS/MS. Immunocapture variability was induced by varying the antibody amount per well from 150 to 4500 ng and analysis was carried out with internal standards added before and after the immunocapture step. The immunocapture variability ranged from ?80.9 to 77.0% when the IS was added after immunocapture and from ?37.5 to 20.3% when the internal standard was added before immunocapture. The lower variability demonstrates the ability of stable labeled isotope internal standard peptide to compensate for variation during immunocapture. Copyright © 2015 John Wiley & Sons, Ltd.     

Maintenance optimization for second‐hand products following periodic imperfect preventive maintenance warranty period

The maintenance policy for a product's life cycle differs for second‐hand and new products. Although several maintenance policies for second‐hand products exist in the literature, they are rarely investigated with reference to periodic inspection and preventive maintenance action during the warranty period. In this research, we study an optimal post‐warranty maintenance policy for a second‐hand product, which was purchased at age x with a fixed‐length warranty period. During the warranty period, the product is periodically inspected and maintained preventively at a prorated cost borne by the user, while any product failure is only minimally repaired by the dealer. After the warranty expires, the product is self‐maintained by the user for a fixed‐length maintenance period and the costs incurred during this time are fully borne by the user. At the end of the maintenance period, the product is replaced with a product of the user's choice. This study is focused on the determination of an optimal length for the maintenance period after the warranty expiration. As a criterion for the optimality, we adopt the long‐run mean cost during the second‐hand product's life cycle from the user's perspective. Finally, our results are analyzed numerically for sensitive analysis of several relevant factors, assuming that the failure distribution follows a Weibull distribution.     

Transient Heat Transfer for Forced Convection Flow of Helium Gas Over a Horizontal Plate

Transient heat transfer coefficients for helium gas flowing over a horizontal plate (ribbon) were measured under wide experimental conditions. The platinum plate with a thickness of 0.1 mm was used as the test heater and heated by electric current. The heat generation rate was exponentially increased with a function of Q₀ exp(t/τ). The gas flow velocities ranged from 4 to 10 m/s, the gas temperatures ranged from 290 to 353 K, and the periods of heat generation rate, τ, ranged from 50 ms to 17 s. The surface superheat and heat flux increase exponentially as the heat generation rate increases with the exponential function. It was clarified that the heat transfer coefficient approaches the quasi-steady-state one for the period τ longer than about 1 s, and it becomes higher for the period shorter than around 1 s. Empirical correlation for transient heat transfer was also obtained based on the experimental data.     

Chain folding and the structure of nylon 6.6 spherulites

Following the assignment of the 1329 and 1224 cm^?1 infrared bands to chain-folded conformations in nylon 6.6 by Koenig et al. examination of the infrared spectra of positively birefringent and negatively birefringent spherulitic films has been made. The spectra indicate extensive regular folding in negative spherulites but fewer folds or less regular folding in the positive spherulite structure.

The assignment of the infrared fold bands to modes of vibration of the repeat unit is discussed with reference to the spectra of films with varying extents of N deuteration (normal 6.6, disordered regions deuterated, N deutero 6.6, disordered regions hydrogenated).

Electron micrographs of negative spherulites are analyzed with the infrared and previous evidence. We suggest they are built up of single-crystal lamellae of 0.2 to 0.3 μ lateral dimensions packed with a preferential orientation of the lamellae planes parallel to the radial direction but otherwise randomly oriented.     

Impact of scene changes during data acquisition in Fourier spectroscopy

The impact of changes of the spectral radiance in a Fourier transform spectrometer's field of view (FOV) during recording time of an interferogram is examined. Particularly systematic changes, with a time constant which is in the order of the time required to record one interferogram, are of interest here. Both an analytic and a simulative approach is made to examine the impact on the measured spectrum. Airborne measurements of fire scenes are a typical example where changes of spectral radiance during data acquisition time are inevitable. In such cases, flight velocity causes the scene in the spectrometer's FOV to change continuously, and the scene elements (fire, for example) might be expected to be dynamical even by themselves.