A study of radiation resistance of silica optical fibers under conditions of reactor irradiation

A measuring system has been developed to investigate the characteristics of radiation-induced optical absorption and radioluminescence in the spectral range of 400–1000 nm for a set of optical fibers being irradiated by fast neutrons and γ rays. This system has been used on the IR-8 research nuclear reactor to perform comparative tests of eight types of silica optical fibers from Heraeus (Germany), Fujikura (Japan), Mitsubishi (Japan), and the Fiber Optics Research Center of the Russian Academy of Sciences’ Prokhorov General Physics Institute. The measured dependences of the induced absorption and radioluminescence intensity versus the nuclear radiation wavelength, flux, and fluence, as well as the temperature, are analyzed. The microscopic mechanisms of induced absorption and radioluminescence are discussed. The values of induced optical absorption and radioluminescence in glass fibers containing H₂ gas and having a hermetic coating (the technology for producing such fibers has been developed by the Fiber Optics Research Center) is found to be many times smaller than in other fibers.     

Temperature dependence of friction under cryogenic conditions in vacuum

We have constructed a sliding block cryotribometer designed to measure friction at cryogenic temperatures and UHV conditions. An optical cryostat and high speed video was used to monitor the motion of the block. The temperature range of the measurements was 4–460 K. Both the static and dynamic friction coefficients were determined for a steel ball on stainless steel, sapphire, and PTFE (Teflon) plates, and for a sapphire ball on a sapphire plate. For all material combinations, no systematic variation of friction with temperature was observed in the temperature range 4–200 K.     

Morphologic variations in bacteria under stress conditions: near-field optical studies

The morphologic and structural variations suffered by cells of a population of Pseudomonas aeruginosa ATCC 27853 under stress conditions were investigated by using scanning near-field optical microscopy. The analysis of the images, supported by microbiological data, showed that the bacteria evolved from the initial distribution of rod-shaped cells of standard size to a population with structural and morphologic modifications. The detection of variations in the optical reflectivity over a subwavelength scale (< or = 100 nm), combined with the concurrently acquired topographical signal, allowed the visualisation of rod-shaped bacteria going towards a lytic process and entire "U"-shaped cells. In the latter cells, which derived from a morphology refolding of rod bacteria, cellular matter seemed to rearrange itself to attain a coccoid stress resistant form, responsible for the residual viability of the population.     

The impact of processing conditions on the structural and optical properties of the as‐spun polyamides fibers

The development of crystallinity and orientation during the melt spinning of polyamides (nylon 66) was investigated. This study reports the question of the orientation and crystallinity determination of nylon 66 by means of differential scanning calorimetry, optical polarized microscope, and X‐ray diffraction techniques during the cold drawing process. The different structural properties such as crystallinity, crystal size, birefringence, and different orientation functions were measured as a function of the draw ratio. From the obtained thermogram, it is clear that the melting temperature of the drawn nylon 66 fibers did not show a significant change due to the cold drawing process. As the draw ratio increase, the crystallinity and crystal size increase. The drawing process improves the chain orientations along the fiber axis of nylon 66 fibers. The orientations of the chain segments enhanced due to the cold drawing process of nylon 66 fibers.     

Temperature measurement from the intensity ratio of the Raman-scattering lines in carbon tetrachloride constituting the liquid core of an optical fiber

A liquid-core optical fiber is used to measure the temperature from the intensity ratio of Ramanscattering lines. CCl₄ doped with benzene, which ensures conditions for the total internal reflection, serves as the fiber core. Measurements were performed at three Raman-scattering lines in CCl₄: 218, 314, and 459 cm^?1. The results obtained at 459 cm^?1 best correspond to the actual temperature. The advantages of using a liquidcore optical fiber and factors affecting the measurement results are discussed.     

Fatigue-induced surface failure of rolling-pair members under conditions of active lubricating medium

The work presents the results of experimental investigation of pitting in rolling pairs. The role of the microgeometry of friction surfaces and active components of the lubricating medium containing wear debris is shown in the formation of microcracks leading to fatigue failure of materials. A criterion for estimating resistance to pitting depending on the working surface quality of the parts is proposed.     

Interference of selective higher-order modes in optical fibers

1IntroductionIn recent years,multimode interference(MMI)effectsin integrated optics have attracted enormous research atten-tion and MMI-based devices with various functionalities,in-cluding directional couplers,powersplitters,sensors,modu-lators,bistable lasers,and optical switches,have been dem-onstrated[1-4].The obvious advantages of the MMI-based de-vices are their compact size,large fabrication tolerance,andlow-cost.MMI is becoming a promising technique in opticalcommutations,optical s…     

Temperature distribution in the lubricant film of sliding bearings under intensive lubricant-wall heat transfer conditions

It is assumed that the existence of some discontinuities in the experimentally determined circumferential temperature distribution of journal bearings is determined by the lubricant-wall heat transfer and the local hydrodynamic flow conditions. From this hypothesis a simplified theoretical model is proposed which uses adequate boundary conditions and reveals the existence of these discontinuities.The theory is developed by assuming both constant viscosity and a mean viscosity, constant across the film thickness, but varying with its length.     

An optical profilometer for characterizing complex surfaces under high vacuum conditions

The requirements for high precision metrology devices have increased rapidly in recent years. Furthermore, the applications are spreading to many new branches of science and technology. Hence new demands are appearing which are related not only to classical parameters such as precision and speed but also to other factors including the environment in which the measurements must be performed. In this paper we present a new device for measuring complex surface profiles of samples held under high vacuum conditions. The surface profile is obtained by scanning an optical sensor, held in air, across a standard view-port. The sensor has a lateral resolution of 25 m and a perpendicular distance resolution of 0.12 m over a range of 3 mm. The maximum scanning area is a circle, 30 mm in diameter. The device was developed to characterize silicon wafers for use as mirrors for atom optical applications. The mirrors are formed by bending the silicon under an applied electric field, which requires high vacuum conditions to prevent arc discharge. In the last part of the paper we discuss how simulations can be used to determine the required sampling grid spacing for obtaining the surface profile shape with a given accuracy.     

Electromechanical measurements of electric field-induced displacements of fibers

In this paper we report on a development of a new method for measurements of electric field-induced displacements in a cylindrical geometry (optical fiber with the deposited piezoelectric film). The measurement setup is based on a commercially available Fotonic Sensor MTI 2000 (MTI Inc.). Major disadvantages of measurement by standard techniques (e.g., interferometry) such as low reflectivity, high roughness of the coating resulting in poor fringe quality, and big displacement range are successfully avoided using a special configuration of an optical probe and a sample. The method allows performing investigations of electromechanically induced vibrations in a broad frequency range (from 0 up to 150 kHz) and various combinations of ac and dc voltages. The capabilities of the proposed method are validated by strain measurements of an optical fiber cantilever beam covered by Pb(Zr,Ti)O(3) thick film.     

Analysis of optical linear encoders’ errors under vibration at different mounting conditions

The optical linear encoders are the preferred choice sensors for positioning machine tools’ moveable parts. Machine tools’ errors have been traditionally focused on the analysis and performance of the machine tool structure until recent works have treated the encoder itself as a source of error. Encoder error quantification has been done for several mounting conditions in static situations, but there is a lack of information regarding the performance of the encoder under dynamic solicitations. The aim of this work is to analyze the loss of accuracy of the sensor because of vibration for different mounting conditions. A finite element model of encoder has been developed and experimental results have been analyzed using this model.     

Monitoring of the concrete curing process using plastic optical fibers

In this paper we propose the application of plastic optical fiber to monitor the concrete curing process.The proposed method is based in the scattering of the propagated optical signal in grooves imposed to the fiber. By monitoring the intensity of the transmitted light signal, along time, we can determine the cement setting rate along all the curing period. The obtained results show that the system has enough sensitivity to analyze a curing period of 28 days, where the received optical power is 5% of the initial value.     

An inverse problem of estimating the heat source in tapered optical fibers for scanning near-field optical microscopy

A conjugate gradient method based on inverse algorithm is applied in this study to estimate the unknown space- and time-dependent heat source in aluminum-coated tapered optical fibers for scanning near-field optical microscopy, by reading the transient temperature data at the measurement positions. No prior information is available on the functional form of the unknown heat source in the present study; thus, it is classified as the function estimation in inverse calculation. The accuracy of the inverse analysis is examined by using the simulated exact and inexact temperature measurements. Results show that an excellent estimation on the heat source and temperature distributions in the tapered optical fiber can be obtained for all the test cases considered in this study.     

High density Langmuir probe array for NSTX scrape-off layer measurements under lithiated divertor conditions

A high density Langmuir probe array has been developed for measurements of scrape-off layer parameters in NSTX. Relevant scale lengths for heat and particle fluxes are 1-5 cm. Transient edge plasma events can occur on a time scale of several milliseconds, and the duration of a typical plasma discharge is ～1?s. The array consists of 99 individual electrodes arranged in three parallel radial rows to allow both swept and triple-probe operation and is mounted in a carbon tile located in the lower outer divertor of NSTX between two segments of the newly installed liquid lithium divertor. Initial swept probe results tracking the outer strike point through probe flux measurements are presented.     

Standard reference fibers for calibration of the optical time domain reflectometer

Calibration of optical time domain reflectometers by military and industrial users can be achieved by a number of published test procedures. For some performance parameters, a particularly convenient method for establishing measurement verification and traceability to national standards is through the use of a standard reference fiber. NIST has begun a program to evaluate such test lightguides. Prototype standard reference fibers have been characterized for spectral attenuation, group delay, group index, and length. This paper describes measurement methods and tolerances for these devices.     

Implementation of multifilter based twin-prototypes for core electron temperature measurements in the TJ-II stellarator

The design and preliminary results from a prototype of a multifilter based electron temperature diagnostic for the TJ-II stellarator are presented. The diagnostic consists of four photodiodes with filters of different thicknesses to determine the electron temperature in a wide variety of plasma compositions, thanks to the set of six different signal-pairs ratios available. The impurity transport code IONEQ, the TJ-II soft x-ray tomography, and the VUV survey diagnostics give the necessary information to assess the proposed diagnostic reliability. In parallel, a vacuum-compatible multichannel electronic board has been designed for a future linear array to determine electron temperature profiles in high-density plasmas.     

Energy absorption characteristics of composite tubes with different fibers and matrix under axial quasi-static and impact crushing conditions

The collapse characteristics and energy absorption capability of composite tubes with different fibers and matrix were studied in present article under axial quasi-static and impact crushing conditions. The sensitivity to fibers, matrix and loading conditions were thoroughly discussed for the crushing modes and energy absorption capability. Experimental results showed specimens with different matrix and fibers exhibit three typical types of crushing modes. Specimens G803/3234 and G827/3234 had better energy absorption performance than the specimens with 5224 matrix. Impact loading condition led to lower energy absorption capability as compared to quasi-static loading condition. Moreover, impact loading condition also caused the crushing mode transition from splaying mode to fragmentation mode for G803/3234 and G827/3234.     

Experimental study on pullout performance of sensing optical fibers in compacted sand

The distributed optical fiber sensing systems have played an increasingly important role in monitoring civil infrastructures over the past few years. One of the main challenges of their applications to geotechnical monitoring is to increase the reliability of strain sensing optical fibers in measuring the deformation of surrounding soil masses. In this paper, a pullout test method is proposed to characterize the deformation compatibility between an optical fiber and soil. A series of pullout tests on three types of sand-embedded optical fibers are conducted to investigate the performance of the fiber–sand interface. Based on the test results, an explicit tri-linear pullout force–displacement relationship is proposed to describe the mechanical behavior of the fiber–sand interface. The performance of the three fibers regarding fiber–sand interaction mechanism is evaluated in terms of ratio of effective pullout displacement to diameter, ratio of residual pullout displacement to diameter, peak shear strength and residual shear strength. All four parameters of the three fibers are found to have approximately linear relationships with the applied confining pressure, which reveals that the deformation compatibility of the fiber–sand interface is utterly dependent on the confining pressure. For all the three fibers, the first shear stiffness coefficient is about 8 N/mm and the ratio of residual to peak shear strength is about 0.5. Furthermore, the Mohr–Coulomb failure criterion is used to get the cohesions and friction angles of the three fiber–sand interfaces. Through a comparison of the pullout performance, one out of three types of fibers tested is found to be more preferable for soil deformation measurement in laboratory-scale tests. The conclusions can provide valuable references for predicting the fiber–soil interface behavior and evaluating the reliability of strain monitoring data.     

一种新型四光束光纤浊度仪的研制

设计了一种新型四光束在线浊度仪.介绍了仪器的工作原理和探头的结构.采用光纤传输光信号,有效地避免了水样中气泡、背景颜色和杂散光的干扰.双光源双光电探测器的结构模式,消除了光电器件老化和水样中气泡对探测结果的影响,提高了测量精确度和稳定度,仪器可用于在线测量.