Room-temperature ferromagnetism and in-plane magnetic anisotropy characteristics of nonpolar GaN:Mn films

Diluted magnetic nonpolar GaN Mn films have been fabricated by implanting Mn ions into nonpolar aplane (1 1 (2) over bar 0) p-type GaN films and a subsequent rapid thermal annealing process. The ferromagnetism properties of the films were studied by means of superconducting quantum interference device (SQUID). Clearly in-plane magnetic anisotropy characteristics of the sample at 10 K were revealed with the direction of the applied magnetic field rotating along the in-plane [0 0 0 1]-axis. Moreover, obvious ferromagnetic properties of the sample up to 350 K were detected by means of the temperature-dependent SQUID. (C) 2009 Elsevier B.V. All rights reserved.

Structure characteristics of InGaN quantum dots fabricated by passivation and low temperature method

Passivation and low temperature method was carried out to grow InGaN/GaN quantum dots (QDs). Atomic force microscope observations were performed to investigate the evolution of the surface morphology of the InGaN QDs superlattices with increasing the superlattices layer number. The result shows that the size of the QDs increases with increasing superlattices layer number. The QDs height and diameter increase from 18 and 50 run for the monolayer InGaN QDs to 37 and 80 urn for the four-stacked InGaN QDs layers, respectively. This result is considered to be due to the stress field from the sub-layer dots. (C) 2003 Elsevier Science B.V. All rights reserved.

Temperature-dependent modulation characteristics for 1.3 mu m InAs/GaAs quantum dot lasers

Temperature-dependent modulation characteristics of 1.3 mu m InAs/GaAs quantum dot (QD) lasers under small signals have been carefully studied at various bias currents. Based on experimental observations, it is found that the modulation bandwidth significantly increases when excited state (ES) lasing emerges at high temperature. This is attributed to additional photons emitted by ES lasing which contribute to the modulation response. A rate equation model including two discrete electron energy levels and the level of wetting layer has been used to investigate the temperature-dependent dynamic behavior of the QD lasers. Numerical investigations confirm that the significant jump for the small signal modulation response is indeed caused by ES photons. Furthermore, we identify how the electron occupation probabilities of the two discrete energy levels can influence the photon density of different states and finally the modulation rate. Both experiments and numerical analysis show that the modulation bandwidth of QD lasers at high temperature can be increased by injecting more carriers into the ES that has larger electron state degeneracy and faster carrier's relaxation time than the ground state.

Effect of temperature on implant isolation characteristics of AlGaAs/GaAs multilayer heterojunction structure

Thermally stable high-resistivity regions have been formed using hydrogen ion implantation at three energies (50, 100, and 180 keV) with three corresponding doses (6 X 10(14) 1.2 X 10(15), and 3 X 10(15) cm(-2)), oxygen implantation at 280keV with 2 X 10(14) cm(-2) as well as subsequent annealing at about 600 degrees C for 10-20s, in AlGaAs/GaAs multiple epitaxial heterojunction structure. After anncaling at 600 degrees C, the sheet resistivity increases by six orders more of magnitude from the as-grown values. This creation of high resistivity is different from that of the conventional damage induced isolation by H or O single implantation which becomes ineffective when anneal is carried out at 400-600 degrees C and the mechanism there of is discussed.

Temperature Distribution in Ridge Structure InGaN Laser Diodes and Its Influence on Device Characteristics

Time-dependent thermal simulation of ridge-geometry InGaN laser diodes is carried out with a two-dimensional model. A high temperature in the waveguide layer and a large temperature step between the regions under and outside the ridge are generated due to the poor thermal conductivity of the sapphire substrate and the large threshold current and voltage. The temperature step is thought to have a strong influence on the characteristics of the laser diodes. Time-resolved measurements of light-current curves,spectra, and the far-field pattern of the InGaN laser diodes under pulsed operation are performed. The results show that the thermal lensing effect improves the confinement of the higher order modes and leads to a lower threshold current and a higher slope efficiency of the device while the high temperature in the active layer results in a drastic decrease in the slope efficiency.

Temperature Dependence of Characteristics for Multimode Interference Based 3-dB Coupler in SOI

The temperature dependence of characteristics for multimode interference (MMI) based 3-dB coupler in silicon-on-insulator is analyzed, which originates from the relatively high thermo-optic coefficient of silicon. For restricted interference 3-dB MMI coupler, the output power uniformity is ideally 0 at room temperature and becomes 0. 32 dB when temperature rises up to 550 K. For symmetric interference 3-dB MMI coupler, the power uniformity keeps ideally 0 due to its intrinsic symmetric interference mechanism. With the temperature rising, the excess loss of the both devices increases. The performance deterioration due to temperature variety is more obvious to restricted interference MMI 3-dB coupler, comparing with that of symmetric interference MMI 3-dB coupler.

Volt-ampere characteristics, nozzle temperature and thruster performances in a low power argon arcjet

Argon gas with simple atomic structure and favorite arcing stability at low input power was used as the propellant. The thruster with a regeneratively cooled nozzle were tested in a vacuum system capable of keeping the chamber pressure at about 10 Pa at a propellant feeding rate of 5 slm. Arc current, arc voltage, thrust, nozzle temperature and propellant feeding rate were measured in situ simultaneously. Effects of the working parameters such as the propellant feeding rate and arc current on the thruster performances, mainly the produced thrust, specific impulse and thrust efficiency, were examined. The variation of arc volt-ampere characteristics with running time and the effect of nozzle temperature on thruster property are discussed.

Structure characteristics and valence state study for La1-xNaxTiO3 synthesized under high-pressure and high-temperature conditions

By using a novel high-pressure, high-temperature method, perovskite oxides of La1-xNaxTiO3 (x = 0.05, 0.1-0.8) with mixed valence state were synthesized. XRD analysis shows a cubic cell for the samples. Cell volumes of the samples with 0.1 less than or equal to x less than or equal to 0.5 decreases as x increases, and the cell Volume for x = 0.05 is smaller than that for x = 0.1. XPS of surface and EPR measurements indicate that Ti ions are of mixed valence of +3 and +4 and that A-cations vacancies exist in the samples. As x increases, the amount of Ti3+ ions decreases and the amount of A-cations vacancies increases. The valence state of Ti ions can be altered by changing both pressure and temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

Effects of Inlet Temperature Uniformity and Nonuniformity on the Tip Leakage Flow and Rotor Blade Tip and Casing Heat Transfer Characteristics

High thermal load appears at the blade tip and casing of a gas turbine engine. It becomes a significant design challenge to protect the turbine materials from this severe situation. As a result of geometric complexity and experimental limitations, computational fluid dynamics tools have been used to predict blade tip leakage flow aerodynamics and heat transfer at typical engine operating conditions. In this paper, the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer has been studied numerically. Uniform low (444 K) and high (800 K) inlet temperatures and nonuniform (parabolic) temperature profiles have been considered at a fixed rotor rotation speed (9500 rpm). The results showed that the change of flow properties at a higher inlet temperature yields significant variations in the leakage flow aerodynamics and heat transfer relative to the lower inlet temperature condition. Aerodynamic behavior of the tip leakage flow varies significantly with the distortion of turbine inlet temperature. For more realistic inlet condition, the velocity range is insignificant at all the time instants. At a high inlet temperature, reverse secondary flow is strongly opposed by the tip leakage flow and the heat transfer fluctuations are reduced greatly.

Effects of sintering temperature on morphology and mechanical characteristics of 3D printed porous titanium used as dental implant

Porous titanium samples were manufactured using the 3D printing and sintering method in order to determine the effects of final sintering temperature on morphology and mechanical properties. Cylindrical samples were printed and split into groups according to a final sintering temperature (FST). Irregular geometry samples were also printed and split into groups according to their FST. The cylindrical samples were used to determine part shrinkage, in compressive tests to provide stress-strain data, in microCT scans to provide internal morphology data and for optical microscopy to determine surface morphology. All of the samples were used in microhardness testing to establish the hardness. Below 1100 C FST, shrinkage was in the region of 20% but increased to approximately 30% by a FST of 1300 C. Porosity varied from a maximum of approximately 65% at the surface to the region of 30% internally. Between 97 and 99% of the internal porosity is interconnected. Average pore size varied between 24 µm at the surface and 19 µm internally. Sample hardness increased to in excess of 300 HV0.05 with increasing FST while samples with an FST of below 1250 C produced an elastic-brittle stress/strain curve and samples above this displayed elastic-plastic behaviour. Yield strength increased significantly through the range of sintering temperatures while the Young's modulus remained fairly consistent. © 2013 Elsevier B.V.

Effect of high-pressure processing on the shelf life, safety and organoleptic characteristics of lasagne ready meals during storage at refrigeration and abuse temperature

The effect of different pressure levels (500 and 600. MPa for 1. min at ambient temperature) on lasagne ready meal as a means of increasing the safety and shelf life during storage at refrigeration (4. °C) and abuse temperature (8. °C) was investigated. High-pressure processing (500 and 600. MPa for 1. min) was able to significantly reduce the total aerobic and lactic acid bacteria counts and prolong the microbiological shelf life of lasagne at both refrigeration and abuse temperatures. Pressure at 600. MPa was a useful tool to reduce the safety risks associated with Staphylococcus aureus and Listeria monocytogenes. However, abuse storage temperature facilitated the recovery of L. monocytogenes towards the end of storage. Organoleptic evaluation revealed that HPP did not negatively influence the quality attributes of lasagne and prolonged its organoleptic shelf life. HPP treatment can serve as a useful additional step to enhance safety and increase the shelf life of multicomponent ready meals, such as lasagne. Industrial relevance: The ready meals sector of the food industry has been experiencing increasing growth in the past years. This comprehensive study explored the effects of HPP on a very popular multicomponent ready meal i.e., lasagne after treatment and during storage. The results showed that HPP can be successfully applied to lasagne ready meals to decrease the risk from S. aureus and L. monocytogenes and also significantly prolong its shelf life without affecting its organoleptic properties. The utilisation of HPP by the industry can significantly increase safety and also provide the opportunity for this product to reach markets further away.

Effect of Substrate Temperature on the Structural and Luminescent Characteristics of RF-Magnetron-Sputtered ZnGa2O4:Dy3+ Thin Films

ZnGa2O4:Dy3+ phosphor thin films were deposited on quartz substrates by radio frequency rf magnetron sputtering and the effect of substrate temperature on its structural and luminescent properties was investigated. Polycrystalline film could be deposited even at room temperature. The crystalline behavior, Zn/Ga ratio, and surface morphology of the films were found to be highly sensitive to substrate temperature. Under UV illumination, the as-deposited films at and above 300°C gave white luminescence even without any postdeposition treatments. The photoluminescent PL emission can be attributed to the combined effect of multicolor emissions from the single luminescence center Dy3+ via host-sensitization. Maximum PL emission intensity was observed for the film deposited at 600°C, and the CIE chromaticity coordinates of the emission were determined to be x,y = 0.34, 0.31 .

An investigation into observational characteristics of rainfall and temperature in Central Northeast India—a historical perspective 1889–2008

Mann–Kendall non-parametric test was employed for observational trend detection of monthly, seasonal and annual precipitation of five meteorological subdivisions of Central Northeast India (CNE India) for different 30-year normal periods (NP) viz. 1889–1918 (NP1), 1919–1948 (NP2), 1949–1978 (NP3) and 1979–2008 (NP4). The trends of maximum and minimum temperatures were also investigated. The slopes of the trend lines were determined using the method of least square linear fitting. An application of Morelet wavelet analysis was done with monthly rainfall during June– September, total rainfall during monsoon season and annual rainfall to know the periodicity and to test the significance of periodicity using the power spectrum method. The inferences figure out from the analyses will be helpful to the policy managers, planners and agricultural scientists to work out irrigation and water management options under various possible climatic eventualities for the region. The long-term (1889–2008) mean annual rainfall of CNE India is 1,195.1 mm with a standard deviation of 134.1 mm and coefficient of variation of 11%. There is a significant decreasing trend of 4.6 mm/year for Jharkhand and 3.2 mm/day for CNE India. Since rice crop is the important kharif crop (May– October) in this region, the decreasing trend of rainfall during themonth of July may delay/affect the transplanting/vegetative phase of the crop, and assured irrigation is very much needed to tackle the drought situation. During themonth of December, all the meteorological subdivisions except Jharkhand show a significant decreasing trend of rainfall during recent normal period NP4. The decrease of rainfall during December may hamper sowing of wheat, which is the important rabi crop (November–March) in most parts of this region. Maximum temperature shows significant rising trend of 0.008°C/year (at 0.01 level) during monsoon season and 0.014°C/year (at 0.01 level) during post-monsoon season during the period 1914– 2003. The annual maximum temperature also shows significant increasing trend of 0.008°C/year (at 0.01 level) during the same period. Minimum temperature shows significant rising trend of 0.012°C/year (at 0.01 level) during postmonsoon season and significant falling trend of 0.002°C/year (at 0.05 level) during monsoon season. A significant 4– 8 years peak periodicity band has been noticed during September over Western UP, and 30–34 years periodicity has been observed during July over Bihar subdivision. However, as far as CNE India is concerned, no significant periodicity has been noticed in any of the time series.