A novel fiber Bragg grating high-temperature sensor

A novel fiber Bragg grating (FBG) sensor for the measurement of high temperature is proposed and experimentally demonstrated. The interrogation system of the sensor system is simple, low cost but effective. The sensor head is comprised of one FBG and two metal rods. The lengths of the rods are different from each other. The coefficients of thermal expansion of the rods are also different from each other. The FBG will be strained by the sensor head when the temperature to be measured changes. The temperature is measured basis of the wavelength shifts of the FBG induced by strain. A dynamic range of 0-800 degrees C and a resolution of 1 degrees C have been obtained by the sensor system. The experiment results agree with theoretical analyses. (c) 2007 Elsevier GmbH. All rights reserved.

Temperature dependence of the 1.03 mu m stimulated emission cross section of Cr : Yb : YAG crystal

The fluorescence emission spectra of Cr:Yb:YAG crystal are measured and the effective stimulated emission cross section of the crystal are obtained from -80 degrees C to +80 degrees C. A linear temperature dependence between -80 degrees C and +80 degrees C is reported for the 1.03 mu m peak stimulated emission cross section of Cr:Yb:YAG crystal. (c) 2004 Elsevier B.V. All rights reserved.

Temperature dependence of the 1.064-mu m stimulated emission cross-section of Cr : Nd : YAG crystal

The fluorescence emission spectra of Cr:Nd:YAG crystal are measured and the effective stimulated emission cross-section of the crystal is obtained from -80 to +80 degrees C. A linear temperature dependence between -80 and +80 degrees C is reported for the 1.064-mu m peak stimulated emission cross-section of Cr:Nd:YAG crystal. (C) 2005 Elsevier Ltd. All rights reserved.

On the selection of effective impulse frequencies for specific movements of fish in an electrical field

In order to determine effective pulse limits for Salmo irideus, Cyprinus carpio, Gasterosteus aculeatus, Tinca tinca, Salmo fario and ldus melanotus in impulse D. C. for galvanotaxis and galvanonarcosis, studies were carried out with rectangular and square impulses. The narcotizing pulse limits remained constant for each variety in an impulse D. C. of specific wave form. The anodic effect of fishes was better in square wave form and varied with the variation of temperature of surrounding medium. S. fario reacted better when placed parallel to the lines of electrical force. Transversal escape movement occured when the axis of fish body was at right angles to the direction of current.

Optimised two-temperature growth of GaAs nanowire s by metalorganic chemical vapour deposition

We report a two-temperature procedure for the growth of GaAs nanowires by metalorganic chemical vapour deposition. An initial high temperature step affords effective nucleation and promotes epitaxial growth of straight (111)B-oriented nanowires. Lower temperatures are employed subsequently, to minimise nanowire tapering during growth. © 2006 IEEE.

Temperature-Dependent Growth and Life Cycle of Nemoura sichuanensis (Plecoptera: Nemouridae) in a Chinese Mountain Stream

Plecoptera constitute a numerically and ecologically significant component in mountain streams all over the world, but little is known of their life cycles in Asia. The life cycle of Nemoura sichuanensis and its relationship to water temperature was investigated during a 4-year study in a headwater stream (known as the Jiuchong torrent) of the Xiangxi River in Central China. Size structure histograms suggest that the life cycle was univoltine, and the relationships between the growth of Nemoura sichuanensis, physiological time, and effective accumulated water temperature were described using logistic regressions. The growth pattern was generally similar within year classes but growth rates did vary between year-classes. Our field data suggest a critical thermal threshold for emergence in Nemoura sichuanensis, that was close to 9 degrees C. The total number of physiological days required for completing larval development was 250 days. The effective accumulated water temperature was 2500 degree-days in the field. Development during the life cycle increased somewhat linearly with the physiological time and the effective accumulated water temperature, but some non-linear relationships were best developed by logistic equations.

Low temperature annealing effects on the structure and optical properties of ZnO films grown by pulsed laser deposition

ZnO thin films were deposited on glass substrates at room temperature (RT) similar to 500 degrees C by pulsed laser deposition (PLD) technique and then were annealed at 150-450 degrees C in air. The effects of annealing temperature on the microstructure and optical properties of the thin films deposited at each substrate temperature were investigated by XRD, SEM, transmittance spectra, and photoluminescence (PL). The results showed that the c-axis orientation of ZnO thin films was not destroyed by annealing treatments: the grain size increased and stress relaxed for the films deposited at 200-500 degrees C, and thin films densified for the films deposited at RT with increasing annealing temperature. The transmittance spectra indicated that E-g of thin films showed a decreased trend with annealing temperature. From the PL measurements, there was a general trend, that is UV emission enhanced with lower annealing temperature and disappeared at higher annealing temperature for the films deposited at 200-500 degrees C; no UV emission was observed for the films deposited at RT regardless of annealing treatment. Improvement of grain size and stoichiometric ratio with annealing temperature can be attributed to the enhancement of UV emission, but the adsorbed oxygen species on the surface and grain boundary of films are thought to contribute the annihilation of UV emission. It seems that annealing at lower temperature in air is an effective method to improve the UV emission for thin films deposited on glass substrate at substrate temperature above RT.

Temperature-dependent transport and spin accumulation in a quantum wire with Rashba spin-orbit interaction

We study the theory of temperature-dependent electron transport, spin polarization, and spin accumulation in a Rashba spin-orbit interaction (RSOI) quantum wire connected nonadiabatically to two normal conductor electrode leads. The influence of both the wire-lead connection and the RSOI on the electron transport is treated analytically by means of a scattering matrix technique and by using an effective free-electron approximation. Through analytical analysis and numerical examples, we demonstrate a simple way to design a sensitive spin-transfer switch that operates without applying any external magnetic fields or attaching ferromagnetic contacts. We also demonstrate that the antisymmetry of the spin accumulation can be destroyed slightly by the coupling between the leads and the wire. Moreover, temperature can weaken the polarization and smear out the oscillations in the spin accumulation.

Room-temperature highly anisotropic ferromagnetism and uniaxial spin amplification in (In,Mn)As quantum dots

The hole-mediated ferromagnetism in (In,Mn)As quantum dots is investigated using the k center dot p method and the mean field model. It is found that the (In,Mn)As quantum dot can be ferromagnetic at room temperature when there is one hole in the dot. For the spherical quantum dots, the Curie temperature decreases as the diameter increases, and increases as the effective composition of magnetic ions increases. It is interesting to find that the (In,Mn)As oblate quantum dot has highly anisotropic Zeeman splitting and ferromagnetism due to the spin-orbit coupling effect, which can be used as an uniaxial spin amplifier. (c) 2008 American Institute of Physics.

Temperature Insensitivity of Optical Properties of InAs/GaAs Quantum Dots due to a Pregrown InGaAs Quantum Well

Both the peak position and linewidth in the photoluminescence spectrum of the InAs/GaAs quantum dots usually vary in an anomalous way with increasing temperature. Such anomalous optical behaviour is eliminated by inserting an In0.2Ga0.8As quantum well below the quantum dot layer in molecular beam epitaxy. The insensitivity of the photoluminescence spectra to temperature is explained in terms of the effective carrier redistribution between quantum dots through the In0.2Ga0.8As quantum well.

Effects of lattice vibration on the effective mass of quasi-two-dimensional strong-coupling polaron

The effects of lattice vibration on the system in which the electron is weakly coupled with bulk longitudinal optical phonons and strongly coupled with interface optical phonons in an infinite quantum well were studied by using Tokuda' linear-combination operator and a modified LLP variational method. The expressions for the effective mass of the polaron in a quantum well QW as functions of the well's width and temperature were derived. In particular, the law of the change of the vibration frequency of the polaron changing with well' s width and temperature are obtained. Numerical results of the effective mass and the vibration frequency of the polaron for KI/AgCl/Kl QW show that the vibration frequency and the effective mass of the polaron decrease with increasing well's width and temperature, but the contribution of the interaction between the electron and the different branches of phonons to the effective mass and the vibration frequency and the change of their variation with the well's width and temperature are greatly different.

Temperature-independent fiber Bragg grating strain sensor using bimetal cantilever

A new packaged fiber Bragg grating using bimetal cantilever beam as the strain agent is presented. The grating is two-point attached on one specific surface of the bimetal beam which consists of two metallic material with different thermal-expansion coefficient. Thereby the grating can be compressed or stretched along with the cantilever beam while temperature varies and temperature compensation can be realized. At the same time, grating chirping can be avoided for the particular attaching method. Experiment results demonstrated that the device is able to automatically compensate temperature induced wavelength shift. The temperature dependence of Bragg wavelength reduced to -0.4 pm/degrees C over the temperature range from -20 to 60 degrees C. This fiber grating package technique is cost effective and can be used in strain sensing. (c) 2005 Elsevier Inc. All rights reserved.

Design of the low-temperature AlN interlayer for GaN grown on Si(111) substrate

We have investigated the effect of the thickness and layer number of the low-temperature A1N interlayer (LT-A1N IL) on the stress relaxation and the crystal quality of GaN epilayers grown on Si (111) substrate by metalorganic chemical vapor deposition. It is found that the stress decreases with the increase of the LT-AIN IL thickness, but the crystal quality of the GaN epilayer goes worse quickly when the LT-AIN IL thickness is larger than 16 nm. This is because the increase of the LT-AIN IL thickness will increase the coalescence thickness of its upper GaN layer, which sensitively affects the crystal quality of the epilayer. Using multiple LT-AIN ILs is an effective method not only to reduce the stress, but also to improve the crystal quality of the GaN epilayer. With the increase of the interlayer number, the probability that dislocations are blocked increases and the probability that dislocations are produced at interfaces decreases. Thus, dislocations in the most upper part of GaN are reduced, resulting in the improvement of the crystal quality. Finally, it is suggested that when the total thickness of the epilayer is fixed, both the thickness and the number of the LT-AIN IL should be carefully designed to reduce the stress and improve the crystal quality of the epilayer simultaneously. (c) 2004 Elsevier B.V.. All rights reserved.

Realization of quantum cascade laser operating at room temperature

X-ray diffraction, as an effective probe and simple method, is used to ascertain the precise control of the epilayer thickness and composition. Intersubband absorption from the whole structure of the QC laser is used to monitor the wavelength of the QC laser and the material quality. Path for growth of high-quality InP-based InGaAs/InAlAs quantum cascade laser material is realized. The absorption between two quantized energy levels is achieved at similar to4.7 mum. Room temperature laser action is achieved at lambda approximate to 5.1 - 5.2 mum. For some devices, if the peak output power is kept at 2 mW, quasi-continuous wave operation at room temperature can persist for more than I It. (C) 2002 Elsevier Science B.V. All rights reserved.

Conduction band offset and electron effective mass in GaInNAs/GaAs quantum-well structures with low nitrogen concentration

We have investigated the optical transitions in Ga1-yInyNxAs1-x/GaAs single and multiple quantum wells using photovoltaic measurements at room temperature. From a theoretical fit to the experimental data, the conduction band offset Q(c), electron effective mass m(e)*, and band gap energy E-g were estimated. It was found that the Q(c) is dependent on the indium concentration, but independent on the nitrogen concentration over the range x=(0-1)%. The m(e)* of GaInNAs is much greater than that of InGaAs with the same concentration of indium, and increases as the nitrogen concentration increases up to 1%. Our experimental results for the m(e)* and E-g of GaInNAs are quantitatively explained by the two-band model based on the strong interaction of the conduction band minimum with the localized N states. (C) 2001 American Institute of Physics.