Active mode-locking in semiconductor lasers

This paper presents the results of experimental studies of active mode-locking in an external-cavity semiconductor laser. Two methods of obtaining active mode-locking regimes have been studied: by modulation from an external generator with a frequency close to the intermode frequency of the external laser cavity and by laser current modulation at the frequency of intermode beats of the external laser cavity through an amplification feedback loop. In the first case, a stability of intermode beats of 10^-14 is experimentally achieved, and in the second case, it is shown that semiconductor laser current modulation by an amplified intermode beat signal from the output of a photodetector provides a stable mode-locking regime also with mode frequency tuning, i.e., a mode-locking regime involving intermode frequency tuning with optical cavity tuning. The effects that accompany mode locking, in particular, the pulling effect and the stability of the mode-locking regime, and possibility of obtaining highly stable intermode beats by suppressing the amplitude noise component in the modulating signal have been studied. A phenomenological study of the pulling and phase locking of the intermode frequency is attempted.     

纳米半导体复合薄膜的非线性光学性质及其在激光器中的应用

采用射频磁控溅射技术制备了Ge掺二氧化硅（Ge-SiO₂）和Ge,Al共掺二氧化硅（Ge/Al-SiO₂）两种复合薄膜,并进行了热退火处理形成了纳米Ge镶嵌结构。通过紫外-可见吸收谱测量,确定了两种薄膜中纳米Ge的光学带隙,并采用皮秒激光Z-扫描技术研究了薄膜的非线性光学性质。测试结果显示,在1 064 nm激发下得到的Ge-SiO₂和Ge/Al-SiO₂薄膜的非线性吸收系数分别为-1.23×10^-7 m/V和4.35×10^-8 m/W,前者为饱和吸收,而后者为双光子吸收。把两种薄膜作为可饱和吸收体均可实现1.06 μm激光的被动调Q和被动锁模运转。与Ge-SiO₂薄膜比较,采用Ge/Al-SiO2薄膜可以获得较窄的调Q脉冲和锁模脉冲。最后,理论分析和实验比较了两种薄膜实现被动调Q和锁模的机理。     

Generation of dissipative solitons in femtosecond fiber lasers

The results of the design and study of femtosecond fiber lasers are reviewed. Various methods of mode-locking and generation regimes are considered. Special attention is paid to the regime of dissipative solitons in an all-fiber resonator with normal dispersion. The main results and analysis of the possibilities of energy scaling of femtosecond pulses are given.     

CO激光在非线性晶体ZnGeP2和GaSe中的混频效应（英文）

为了获得2.15～1 500μm的相干光源,研究了CO激光在高质量非线性晶体ZnGeP2和GaSe中的混频效应。为了提高转换效率,在激光锁模方式下对CO激光器的二次谐波、和频和差频的产生进行了研究。结果显示,利用GaSe晶体和ZnGeP2晶体,调Q多谱线CO激光辐射的谱线内倍频效率分别大于0.3%和1.1%。采用ZnGeP2晶体进行倍频时,可调谐锁膜CO激光器的转换效率为12.5%。模拟结果显示,二次谐波与和频产生的输出光谱相同。相邻谱线下,和频和差频的产生过程中,基波和一次谐波可以分别在4.0～5.0μm和100～≥1 200μm(太赫兹范围)形成振荡。利用锁模CO激光器在ZnGeP2晶体中的混频效应,可以得到2.15～≥1 500μm的相干光源,同时转换效率可达到甚至高于12.5%。     

Mode-locking optimization with a real-time feedback system in a Nd:yttrium lithium fluoride laser cavity

We present a control system, which allows an automatic optimization of the pulse train stability in a mode-locked laser cavity. In order to obtain real-time corrections, we chose a closed loop approach. The control variable is the cavity length, mechanically adjusted by gear system acting on the rear cavity mirror, and the controlled variable is the envelope modulation of the mode-locked pulse train. Such automatic control system maintains the amplitude of the mode-locking pulse train stable within a few percent rms during the working time of the laser. Full implementation of the system on an Nd:yttrium lithium fluoride actively mode-locked laser is presented.     

A technique for preparing samples of metal nanowires for electron and atomic-force microscopy

Methods for preparing nanowire samples for experiments with transmission electron and atomic-force microscopes are described. In the method used for transmission electron microscopy investigations, metal is electrochemically deposited into etched channels of a track membrane kept close against the end surface of a thin metal foil. A method for forming nanowires in a slit of a thin epoxy film is proposed for atomic-force microscopy examinations. Original Russian Text ￠ V.F. Reutov, M.F. Miklyaev, B.V. Mchedlishvili, 2007, published in Pribory i Tekhnika Eksperimenta, 2007, No. 3, pp. 144–147.     

Improvement of earliness and lateness by postponement on an automotive production line

This article takes an interest in improving the performance of a subproblem of car sequencing: the resequencing problem. It extends a model of assembly line with the simulation of buffer stocks with drawers. Presequencing and resequencing are modeled with different types of stock management policy. Furthermore, postponement is introduced by two points of differentiation within the line. After choosing relevant variables and performance indicators a large-scale design of experiments finally enables to estimate average improvement brought by postponement to more than 39.7%, compared to the situation without postponement.

“Supermarket warehouses”: stocking policies optimization in an assembly-to-order environment

In modern assembly-to-order systems, sub-assemblies warehouse locations, dimensions, and supply are critical decisional variables. Persona et al. (Int J Prod Econ 110(1–2):147–159, 2007) affirm the structural diversity between assembly parts can largely influence the stocking policies. On the other hand, Zhang et al. (2007) and Hsu et al. (Nav Res Logist 54(5):510–523, 2007) substantiate that the problem gets more complex when it comes to choosing the correct physical locations for common assembly parts. The study at hand concentrates on components warehouse centralization/decentralization choices in an assembly-to-order (ATO) environment, which typically supplies the assembly systems with components’ kits through decentralized warehouses called “Supermarkets”. Specifically, this paper applies an innovative step-by-step procedure to support materials management decision-making policies in order to define when, how, and where it is convenient to install a supermarket warehouse, considering the typical aspect of an ATO environment: number, type, position of the assembly systems, demand rate and commonality degree of components used, internal transportation equipment and transportation costs, load unit capacity, space cost for stocking, space availability in the plant, inventory costs, and safety stock dimension.     

A Study on Central Moments of the Histograms from Scanning Electron Microscope Charging Images

This paper presents a study on using the statistical parameter, central moment, to describe the properties of the histograms of scanning electron microscope (SEM) images. Various charging effects of SEM images and the corresponding histogram profiles are analyzed. The central moment distributions are used to describe the overview of the histograms of an image. The results show that central moments can be used to quantify and characterize the charging images. In particular, the second moment (variance) and third moment (skewness) can be used to distinguish the differences between charging and noncharging images. SCANNING 29: 211‐218, 2007. © 2007 Wiley Periodicals, Inc.     

A note on “Selection of cutting parameters in side milling operation using graph theory and matrix approach”

Determination of optimal cutting parameters is one of the vital modules in process planning of parts since economy of machining operations plays an important role in increasing productivity and competitiveness. Recently, Gadakh and Shinde (Int J Adv Manuf Technol 2011) presented a graph theory and matrix approach (GTMA) and few other multiple attribute decision making (MADM) methods for selection of cutting parameters in side milling operation in their paper “Selection of cutting parameters in side milling operation using graph theory and matrix approach” Gadakh and Shinde (Int J Adv Manuf Technol DOI 10.1007/S00170-011-3256-Z, 2011). The authors had presented the experimental results of Chiang-Kao and Lu (Int J Adv Manuf Technol 34:440–447, 2007) to demonstrate the proposed methods. However, the systematic procedures of GTMA and the other MADM methods were already reported exhaustively by Rao (2007), and Gadakh and Shinde (Int J Adv Manuf Technol 2011) had reproduced the related contents. Many computational and fundamental mistakes were also present in their work. Furthermore, the authors had presented the incorrect values of metal removal rate (MRR) and these values were different from the values presented by Chiang-Kao and Lu (Int J Adv Manuf Technol 34:440–447, 2007). This note discusses these mistakes and presents the correct approaches and the results.     

Analysis of reactive deadlock-free scheduling in flexible job shops

Reactive scheduling is a procedure followed in production systems to react to unforeseen events that disturb the normal operation of the system. In this paper, a novel operations insertion heuristic is proposed to solve the deadlock-free reactive scheduling problem in flexible job shops, upon the arrival of new jobs. The heuristic utilizes rank matrices (Latin rectangles) to insert new jobs in schedules, while preventing the occurrence of deadlocks or resolving them using the available buffer space (if any). Jobs with alternative processing routes through the system are also considered. The heuristic can be employed to execute two reactive scheduling approaches in a timely efficient manner; to insert the new jobs in the already existing schedule (job insertion) or to reschedule all the jobs in the system (total rescheduling). Using experimental design and analysis of variance (ANOVA), the relative performance of the two approaches is studied and analyzed to provide some measures and guidelines for selecting the appropriate reactive scheduling approach for different problem settings. Three measures of performance are considered in the analysis; efficiency of the revised schedules in terms of the mean flow time, resulting system nervousness, and the required solution time. The results show that, on average, job insertion obtains revised schedules featuring significantly lower system nervousness and slightly higher mean flow time than total rescheduling. However, depending on the system size, number and processing times of the new jobs, and the available flexibility in the system, a trade-off between the two approaches should sometimes be considered.

World valve market to exceed US$44BN by 2007

The world market for industrial valves will grow from US$38 billion in 2003 to more than US$44 billion in 2007, according to Valves: World Markets, an on-line report published by the McIlvaine Co.This is a short news story only. Visit www.worldpumps.com for the latest pump industry news.     

Experimental validation of steering torque feedback simulator through vehicle running test

This paper describes a force feedback system based on real-time multibody dynamic analysis. This system can provide the analyzed reactive force to the operator through the operational device. In this study, this system is used as a steering torque feedback simulator of an automobile. This simulator can provide the haptic sensation of the steering wheel to the operator. For the purpose of evaluating the validity of the developed simulator, we conducted some vehicle running tests with an experimental electric vehicle. The results of these tests were compared with the results simulated on the steering torque feedback simulator. It was shown that the developed simulator can provide a suitable steering torque to the operator. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Dr. Taichi Shiiba received a Doctor of Engineering from The University of Tokyo in 2001. He became an Associate Professor at Meiji University in 2007. A Member of JSME and JSAE, his major areas are multibody dynamics, vehicle dynamics, and driving simulators. Wataru Murata received a B.S. degree in mechanical engineering from Meiji University in 2007. His research interests are vehicle dynamics, real-time analysis, and multibody dynamics.     

CTOD试验方法与转子材料的延性断裂性能

对国标GB/T 21143—2007和美标ASTM E1820-08a中的CTOD(crack tip opening displacement)计算公式和阻力曲线评定方法进行对比研究,采用柔度法完成汽轮机转子材料Cr2Ni2MoV钢的CTOD试验,并分别根据两个标准对试验结果进行分析。结果表明,GB/T 21143—2007中的CTOD计算公式和钝化线方程存在不合理的表达,对其进行相应修正;根据ASTM E1820-08a得到的CTOD值通常稍低于由GB/T 21143—2007得到的结果;钝化线方程的选取对启裂CTOD临界值的确定影响显著。     

Chromatographic and non‐chromatographic characterization of poly‐α‐olefins

Both chromatographic and non‐chromatographic techniques were used in the characterization and identification of poly‐α‐olefins. Synthetic base oils, although produced from the same raw material, exhibit different physico‐chemical properties. Their mutual miscibility and behaviour in final engine oils may be predicted from data collected through classical physico‐chemical analysis, simulated distillation chromatography as well as inverse gas chromatography. Copyright © 2007 John Wiley & Sons, Ltd.     

Charge Contrast Imaging of Nonconductive Samples in the High‐Vacuum Field Emission Scanning Electron Microscope

The charge contrast images (CCI) on insulating or poorly conducting samples were observed under steady‐state charging conditions with a thermal field emission scanning electron microscope under high vacuum by using an Everhart‐Thornley detector. The charge contrast on plumbous titanate‐nickel composite particles and patterned sapphires could be the indicators of near‐surface features, compositional variations and conductivity distributions. Optimum imaging conditions for observing the CCI include the electron energy, the electron flux density and the electron dose. Contrast characteristics associated with surface and near‐surface secondary electron emission yield enhanced above the trapped charge‐up regions, as charge trapping selectively enhanced the poorly conductive phase and lattice distorted area. SCANNING 29: 230‐237, 2007. © 2007 Wiley Periodicals, Inc.     

Idaho Explosives Detection System: Development and Enhancements

The Idaho Explosives Detection System (IEDS) was developed at the Idaho National Laboratory (INL) to respond to threats imposed by delivery trucks carrying bulk explosives into military bases. The system consists of two platforms, one on each side of a subject vehicle. Each platform includes a neutron generator and an array of sodium iodide (NaI) detectors. The two neutron generators are pulsed and synchronized. A computer connects to the system via Ethernet and is able to control the system remotely. The system was developed to detect bulk explosives in a medium size truck within a 5-min measurement time. In 2004, a full-scale prototype IEDS was built for testing and continued development. System performance was successfully tested at the INL from November 2005 to February 2006 using different types of real explosives with a variety of cargo. Recently, the first deployable prototype system was installed at Wright–Patterson Air Force Base in Ohio and has been in operation since May 2007. The capability of passively detecting radiological material within a delivery truck has also been added. This article is to be published in 2007 in Sensing and Imaging: An International Journal.     

Experimental study on two-way flow passages in pumping system

Based on the model test of pumping system with two-way flow passages, the flow characteristic and flow pattern in two-way outflow passage are specially observed and analyzed. The various schemes are compared by means of test and the measures for improving flow pattern in outflow passage are come up with by the authors. This research possesses reference value for pump selection and flow passages design of analogous pumping station. This paper was presented at the 9^th Asian International Conference on Fluid Machinery (AICFM9), Jeju, Korea, October 16–19, 2007.     

Friction-induced ignition modeling of energetic materials

The heat released during the external frictional motion is a factor responsible for initiating energetic materials under all types of mechanical stimuli including impact, drop, or penetration. We model the friction-induced ignition of cyclotrimethylenetrinitramine (RDX), cyclotetramethylene-tetranitramine (HMX), and ammonium-perchlorate/ hydroxylterminated-polybutadiene (AP/HTPB) propellant using the BAM friction apparatus and one-dimensional time to explosion (ODTX) apparatus whose results are used to validate the friction ignition mechanism and the deflagration kinetics of energetic materials, respectively. A procedure to obtain the time-to-ignition for each energetic sample due to friction is outlined. This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. Min-cheol Gwak received his B.S. degree in Mechanical Engineering from Korea Aerospace University, Korea, in 2007. Now he is a graduate student of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests are ignition of high energy material and combustion phenomena. Tae-yong Jung received his B.S. degree in Mechanical and Aerospace Engineering from Seoul National University, Korea, in 2007. Now he is a graduate student of Mechanical and Aerospace Engineering at Seoul National University in Seoul, Korea. His research interests are solid propellant combustion and phase transformation. Professor J. Yoh received his BSME from UC Berkeley in 1992 and MSME from UCLA in 1995. His doctoral degree is in Theoretical & Applied Mechanics from the University of Illinois at Urbana-Champaign, 2001. His research interest is in high energy system design using high power lasers and condensed energetic materials.     

Elastic stresses for 90° elbows under in-plane bending

Using finite element analysis, this paper extends elastic stress solutions for 90° pipe elbows under in-plane bending, given in Marie et al. (2007) [1], to cases of mean pipe radius-to-thickness ratio up to 50. It is found that for 90° elbows an in-plane bending moment produces not only an axial membrane stress component but also axial and hoop bending stress components. Furthermore, the magnitudes of these stress components depend strongly on the mean radius-to-thickness ratio, the circumferential location and the longitudinal location. Maximum stresses tend to occur in the centre of the elbow at or near the crown.