Experimental Investigation of Stability Enhancement in Semiconductor Lasers with Optical Feedback

The stability enhancement of laser output power for the change of external cavity position in semiconductor lasers with optical feedback is observed by experiment. The relaxation oscillation frequency which plays an important role in the dynamics of the nonlinear system is also investigated as a function of the external cavity length. The period of the stability enhancement along the position of the external cavity is exactly coincident with the length corresponding to the relaxation oscillation frequency of the solitary laser. The experimental results are compared with theoretical and excellent coincidence between the two is found.     

Static and Dynamic Electron Holography of Electrically Active Grain Boundaries in SrTiO3

The dynamics of electrostatic potential barriers at grain boundaries (GBs) in Nb-doped SrTiO₃ bicrystals is investigated using a unique combination of bulk and in-situ TEM electrical measurements across isolated GBs, coupled with electron holography under in-situ applied bias. The Nb bulk-doped bicrystals exhibit a positive GB potential that suppresses reversibly under applied bias greater than the nonlinearity threshold in the current-voltage curve. This suppression is interpreted as break-down of the potential barrier to current transport.The results on Nb bulk-doped bicrystals have been compared to those in which Mn has been added as a grain boundary specific dopant. This acceptor doping of the grain boundary causes an appreciable increase in the grain boundary resistance and extension of the nonlinear regime. A preliminary account of static electron holography shows a relatively flat potential profile across the GB, indicating probable compensation of donor states at the GB core with Mn-acceptors. Interestingly, the phase profile under applied bias in this case exhibits a reversible dip at the GB which is interpreted as an activation of GB trap states due to Mn-acceptor dopants trapping extra electrons (the majority charge carriers) at the GB core, inducing a negative GB potential, and diminishing current transport until the threshold bias is exceeded.The synergistic combination of nanoscale TEM measurements coupled with traditional macroscopic electrical measurements is emphasized.     

重复脉冲注入下半导体光放大器皮秒增益和折射率非线性的数值模拟

对重复周期小于载流子寿命的重复脉冲注入的情况，从速率方程出发，用分段模型对半导体光放大器的皮秒增益和折射率非线性进行了数值模拟，给出了重复脉冲注入下输出光脉冲时域波形的畸变、注入光脉冲引起的增益和相位变化，输出光脉冲上的频率啁啾随注入脉冲数增加的变化，以及归零光信号码流引起的增益和相位变化。     

复合外场中磁光材料(BiTm)3(FeGa)5O12薄膜畴壁运动特性的研究

通过对BiTm)₃(FeGa)₅O₁₂膜施工加低频交变磁场,匀速率增加的直流磁场和同时对该膜施加这两种磁场(复合外场),用照相划线读数方法和通过电荷耦合器件(CCD)-计算机作数字化处理获得磁畴壁(DW)的相对百分数。结果表明:(1)复合外场下DW运动规律中存在交互作用项;(2)低频交变磁场幅值(140A/m)远低于等效阻力场(10³A/m)时,DW可以运动,但不同步,频率大于1Hz时明显滞后,(3)利用图像转换有利于提高实验结果的分辨率。     

复合外场中磁光材料(BiTm)_3(FeGa)_5O_(12)薄膜畴壁运动特性的研究

通过对 (BiTm) 3 (FeGa) 5O12 膜施工加低频交变磁场 ,匀速率增加的直流磁场和同时对该膜施加这两种磁场 (复合外场 ) ,用照相划线读数方法和通过电荷耦合器件 (CCD) 计算机作数字化处理获得磁畴壁 (DW)的相对百分数。结果表明 :( 1 )复合外场下DW运动规律中存在交互作用项 ;( 2 )低频交变磁场幅值 ( 1 4 0A/m)远低于等效阻力场 ( 1 0 3 A/m)时 ,DW可以运动 ,但不同步 ,频率大于 1Hz时明显滞后 ,( 3 )利用图像转换有利于提高实验结果的分辨率。     

Modeling and Simulation of Ionic Currents in Three-Dimensional Microfluidic Devices with Nanofluidic Interconnects

Electrokinetic fluid flow in nanocapillary array (NCA) membranes between vertically separated microfluidic channels offers an attractive alternative to using mechanical action to achieve fluidic communication between different regions of lab-on-a-chip devices. By adjusting the channel diameter, a, and the inverse Debye length, к, and applying the appropriate external potential, the nanochannel arrays, can be made to behave like digital fluidic switches, and the movement of molecules from one side of the array to the other side can be controlled. However, inherent differences in ionic mobility lead to non-equilibrium ion populations on the downstream side, which, in turn, shows up through transient changes in the microchannel conductance. Here we describe coupled calculations and experiments in which the electrical properties of a microfluidic–nanofluidic hybrid architecture are simulated by a combination of a compact model for the bulk electrical properties and iterative self-consistent solutions of the coupled Poisson, Nernst–Planck, and Navier–Stokes equations to recover the detailed ion motion in the nanopores. The transient electrical conductivity in the microchannel, after application of a forward bias pulse to the NCA membrane, is recovered in quantitative detail. The surface charge density of the nanopores and the capacitance of the membrane, which are critical determinants of electrokinetic flow through NCA, fall out of the analysis in a natural way, providing a clear mechanism to determine these critically important parameters.     

离子缔合物光度法测定微量BrO3-

在 0 .1 6 mol/ L H2 SO4介质中 ,2 - (5 -氯 - 2 -吡啶偶氮 ) - 5 -二乙氨基苯酚 (5 - Cl- PADAP)与 Br O-3 和 SCN-形成紫红色三元离子缔合物 ,最大吸收波长为 5 6 0 nm,表观摩尔吸光系数为 1 .9× 1 0 4L· mol-1 · cm-1 ,Br O-3 含量在 0— 2× 1 0 -5mol/ L范围内符合比耳定律。方法可用于化学试剂中微量 Br O-3 的测定。     

Interpretation of the Experimental Electron Momentum Spectra of 5e1/2 and 5e3/2 Orbitals of CF3I with Relativistic Calculations

With our newly developed method, we calculate the spin-orbit splitting states 5e1/2 and 5e3/2 of the CF3I molecule incorporating the relativistic effects. Our theoretical results agree excellently with the recent experimental observations. The present study shows that relativistic effects can evidently change the electron momentum distributions of molecular orbitals when a medium Z element is included, such as iodine.     

Dynamics of the superconducting mixed state in YBa2Cu3O7-δ/PrBa2Cu3O7-δ superlattices in radio frequency regime

Epitaxial multilayers of YBa₂Cu₃O_7-δ and P₁Ba₂Cu₃O_7-δ have been deposited on (100) cut SrTiO₃ substrates using the technique of pulsed laser deposition. Standard ϑ-2ϑ X-ray diffraction measurements on the films showed excellent superlattice reflections. The mixed state of these superlattices has been probed through measurements of radio frequency penetration depth (λ) as a function of temperature (T), magnetic field (H) and it’s orientation (ϑ) with respect to the planes of the superlattices. These data reflect the two-dimensional nature of the mixed state in these systems.     

新试剂2-(3-羧基-2,4,5-三氮唑偶氮)-5-二甲氨基苯磺酸与钯显色反应的研究及应用

本文合成了水溶性新型显色剂 2 - (3-羧基 - 2 ,4 ,5 -三氮唑偶氮 ) - 5 -二甲氨基苯磺酸 (CTZAMBS) ,并研究了其与钯的显色反应。结果表明 ,在 p H=1.5 8邻苯二甲酸氢钾缓冲液中 ,试剂与钯形成 2∶ 1蓝色络合物 ,λmax为 5 78.6nm,钯含量在 0— 2 .0 μg·m L-1范围内符合比耳定律 ,表观摩尔吸光系数为 3.19× 10 4 L·mol-1· cm-1,选择性好。本方法可直接测定钯催化剂中的微量钯 ,操作简便 ,结果令人满意     

Active inflammation increases the heterogeneity of MRI texture in mice with relapsing experimental allergic encephalomyelitis

Inflammation modulates tissue damage in relapsing-remitting multiple sclerosis (MS) both acutely and chronically, but its severity is difficult to evaluate with conventional MRI analysis. In mice with experimental allergic encephalomyelitis (EAE, a model of MS), we administered ultra small particles of iron oxide to track macrophage-mediated inflammation during the onset (relapse) and recovery (remission) of disease activity using high field MRI. We performed MRI texture analysis, a sensitive measure of tissue regularity, and T2 assessment both in EAE lesions and the control tissue, and measured spinal cord volume. We found that inflammation was 3 times more remarkable at onset than at recovery of EAE in histology yet demyelination appeared similar across animals and disease course. In MRI, lesion texture was more heterogeneous; T2 was lower; and spinal cord volume was greater in EAE than in controls, but only MRI texture was worse at relapse than at remission of EAE. Moreover, MRI texture correlated with spinal cord volume and tended to correlate with the extent of disability in EAE. While subject to further confirmation, our findings may suggest the sensitivity of MRI texture analysis for accessing inflammation.     

Generation of Submillimeter-Wave Radiation with GaAs Tunnett Diodes and InP Gunn Devices in a Second or Higher Harmonic Mode

Efficient second-harmonic power extraction was demonstrated recently with GaAs tunnel injection transit-time (TUNNETT) diodes up to 235 GHz and with InP Gunn devices up to 325 GHz. This paper discusses the latest theoretical and experimental results from second-harmonic power extraction at submillimeter-wave frequencies and explores the potential of using power extraction at higher harmonic frequencies to generate continuous-wave radiation with significant power levels at frequencies above 325 GHz. Initial experimental results include output power levels of more than 50 W at 356 GHz from a GaAs TUNNETT diode in a third-harmonic mode and at least 0.2–5 W in the frequency range 400–560 GHz from InP Gunn devices in a third or higher harmonic mode. The spectral output of these submillimeter-wave sources was analyzed with a simple Fourier-transform terahertz spectrometer and, up to 426 GHz, with a spectrum analyzer and appropriate harmonic mixers. Initial experimental results from a GaAs/AlAs superlattice electronic device at D-band (110–170 GHz) and J-band (170–325 GHz) frequencies are also included.     

Electron paramagnetic resonance study of exchange coupled Ce3+ ions in Lu2SiO5 single crystal scintillator

The Ce³⁺ ions incorporation inside lutetium oxyorthosilicate (Lu₂SiO₅) single crystals was studied by electron paramagnetic resonance. Already known Ce1 and Ce2 centers originating from the lattice peculiarity allowing two lutetium sites coordinated by different number of the oxygen ions were detected. Remarkably, for the Ce2 center, the determined g² tensor is asymmetric and could not be diagonalized as compared to the Ce1 center, for which the three principal values and corresponding axes orientation have been determined and reported previously. Besides, the much weaker resonance lines found in spectra close to those coming from the Ce1 and Ce2, and following them under crystal rotation with respect to the direction of an external magnetic field, have been revealed as well. They were classified as doublets produced by the exchange coupled Ce³⁺ ions, creating the Ce1–Ce1, Ce2–Ce2 and Ce1–Ce2-like dimers. The corresponding spin–spin coupling constants were estimated. They are in the range 0.04–0.4 cm⁻¹. The Ce1, Ce2 and total dimer centers populations were calculated as 89%, 4.5% and 6.5%, comparing integral intensities of corresponding resonance lines.     

Spectral-Structural Correlations in the Complexes of Transitional Elements with an Incompletely Filled 5f Electron Shell and XO3 n−-Type Trigonal Oxoligands

The specifics of the kinematic and dynamic parameters of the XO₃ ^n– groups attached in a different way to a central atom have been determined by the methods of experimental and computational vibrational spectroscopy. The characteristic nature of individual vibrations has been revealed and recommendations for their use in a spectral-structural analysis have been given. Spectral criteria to estimate the degree of the dentate character of ligands in insular-type and polymeric structures are suggested.     

Spectra of 2, 5- and 3, 4-Dichlorobromobenzene Molecules in Ultraviolet

Vibrational analyses have been presented for the absorption bands of 2, 5- and 3, 4-dichlorobromobenzene molecules photographed in the regions 2925 - 2690 A and 2900 - 2580 A respectively. The following constants have been determined:

The 0.0 band shifts have been explaine on the basis of simple additivity rule.     

复合外场中磁光薄膜(BiTm)3(FeGa)5O12缺陷周围磁畴壁的形貌特征

用自组装系记录了外场分别为均速率增加的直流磁场，低频交变磁场和它们同时存在时，磁光薄膜（BiTm)3(FeGa)5O12一种缺陷周围磁畴壁的形貌特征。分析表明：三种不同取向磁畴壁的交界处往往是磁光薄膜的缺陷所在处；在低频交变场下，该缺陷区域出现无畴条块或区域，在直流场中无此现象。在低频交变场以及复合外场下该缺陷周围磁畴壁形成椭圆形图案。     

特定频率响应FIR滤波器的设计及其在水声中的应用

在水声信号处理中，有时普通滤波器不能够满足应用要求，需要利用具有任意的给定频率响应的滤波器，本文利用自适应方法设计具有给定频率响应的FIR滤波器，将将该方法设计的滤波器用于产生宽带信号的精确时延信号和进行时域宽带波速形成，使用效果较好。该类滤波器使用非常有效。而且计算量小，易于工程实现。     

2-(2''-喹啉偶氮)-5-二甲氨基苯甲酸光度法测定钢铁中的钴

合成了新试剂 2 - (2’-喹啉偶氮 ) - 5 - N,N-二甲氨基苯甲酸 (QADMAB) ,并研究了其与钴的显色反应 ,在 p H=4 .0的 KH2 PO4- K2 HPO4缓冲介质中 ,CTMAB存在下 ,QADMAB与钴反应生成 2∶ 1稳定配合物 ,λmax=6 2 0 nm,ε=1.2 5× 10 5L·mol-1· cm-1。钴含量在 0— 0 .4 mg/ L范围内符合比耳定律 ,方法用于钢铁样品中钴含量的测定 ,结果令人满意     

1-偶氮苯-3-(3-硝基-5-氯-2-吡啶)-三氮烯的合成及其与铜的显色反应

合成了新显色剂1-偶氮苯-3-(3-硝基-5-氯-2-吡啶)-三氮烯(ABNCPDT)。研究了它与铜的显色反应。在pH10.5的Na2B4O7-NaOH缓冲溶液中,Triton X-100表面活性剂存在下,试剂与铜生成4∶1型红色配合物。配合物的最大吸收峰位于540nm,表观摩尔吸光系数为1.48×105L·mol-1·cm-1。Cu2 浓度在0—480μg/L范围内符合比耳定律,用于测定铝合金中微量铜,结果满意。