Study on the temperature characteristic and high temperature risk of asphalt layer of Beijing-Xinjiang ExpresswayWutong Daquan to Yiwu Section

High temperature rutting is a typical highway damage in Xinjiang, China, and its trigger process usually has a close relationship with characteristics of road temperature distribution. A numerical model of earth-atmosphere coupling heat transfer on a typical section of the Beijing-Xinjiang Expressway(G7) from Wutong Daquan to Yiwu was established in this work. Spatiotemporal characteristics of pavement structure layer temperature distribution, frequency and duration times of road surface high temperature from May 1 to September 30 are statistically studied. The effects of wind speed, weather and air temperature on asphalt layer and pavement temperature are analyzed. The results show that:(1) Spatial and temporal temperature distribution characteristics of pavement structural layers are greatly affected by the coupled earth-atmosphere heat transfer process. Surface temperature increases along the airflow direction and daily temperature variation of the pavement structure layer decreases with an increase of depth.(2) G7 expressway will face the challenge of high rutting damage. The proportion of temperature higher than 50 ℃ for pavement surface and asphalt upper layer both exceeds 50%and high temperature of road lasts for more than six hours in numerous days.(3) High temperatures of asphalt pavement are usually associated with low ambient wind speeds, while the wind flow has little cooling effect when the road surface temperature is relative high. Weather conditions have a significant impact on temperature of the road surface. The probability of high temperature in sunny days is obviously higher than other weather conditions.(4) Pavement temperature rises as air temperature rises. When air temperature is higher than 30 °C, the proportion of pavement daily maximum temperature over softening point reaches up to 78%.

High temperature characteristics of AlGaN/GaN high electron mobility transistors

Direct current （DC） and pulsed measurements are performed to determine the degradation mechanisms of A1GaN/GaN high electron mobility transistors （HEMTs） under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas （2DEG）. The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.

An Experimental Study on the Temperature Characteristic of a 940 nm Semiconductor Laser Diode

This paper is focused on a 940 nm edge type of semiconductor laser, which is made from 940 nm InGaAs double-quantum-well epitaxial wafer, produced by Metal Organic Chemical Vapor Deposition (MOCVD). In the absence of coating, the efficiency at the room temperature is 0.89 W/A, and the averaged threshold current is 0.307 A. The present study investigates the impact of temperature on the P-I curve, V-I curve and the centre wavelength, the temperature ranging from 286.15 - 333.15 K. It shows that the threshold current increases from 0.28 A to 0.41 A with the increasing temperature. The increase rate is 0.0027 A/K. With the temperature ranging from 286.15 - 333.15 K, the characteristic temperature is calculated to be 120 K. At driven current of 2 A, the output power decreases from 1.47 W to 1.27 W at a rate of 0.00425 W/K. At a constant voltage, the output current initially increases with the temperature within a certain range, beyond which the impact of the temperature is minimum. The ideal factor obtained from V-I curve by curve fitting is 1.076. The series resistance is 0.609 Ω. The centre wavelength shifts to a longer wavelength with the increasing temperature at a rate of 0.275288 nm/K.

High temperature characteristics of bilayer epitaxial graphene field-effect transistors on SiC Substrate

In this paper,high temperature direct current（DC） performance of bilayer epitaxial graphene device on SiC substrate is studied in a temperature range from 25℃ to 200℃.At a gate voltage of-8 V（far from Dirac point）,the drainsource current decreases obviously with increasing temperature,but it has little change at a gate bias of ＋8 V（near Dirac point）.The competing interactions between scattering and thermal activation are responsible for the different reduction tendencies.Four different kinds of scatterings are taken into account to qualitatively analyze the carrier mobility under different temperatures.The devices exhibit almost unchanged DC performances after high temperature measurements at 200℃ for 5 hours in air ambience,demonstrating the high thermal stabilities of the bilayer epitaxial graphene devices.

GaSb p-channel metal-oxide-semiconductor field-effect transistor and its temperature dependent characteristics

GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） with an atomic layer deposited Al2O3 gate dielectric and a self-aligned Si-implanted source/drain are experimentally demonstrated. Temperature dependent electrical characteristics are investigated. Different electrical behaviors are observed in two temperature regions, and the un- derlying mechanisms are discussed. It is found that the reverse-bias pn junction leakage of the drain/substrate is the main component of the off-state drain leakage current, which is generation-current dominated in the low temperature regions and is diffusion-current dominated in the high temperature regions. Methods to further reduce the off-state drain leakage current are given.

Temperature Dependence of Electrical Characteristics in Indium-Zinc-Oxide Thin Film Transistors from 10 K to 400 K

The transfer characteristics of amorphous indium-zinc-oxide thin film transistors are measured in the temperature range of 10-400K. The variation of electrical parameters （threshold voltage, field effect mobility, sub-threshold swing, and leafage current） with decreasing temperature are then extracted and analyzed. Moreover, the dom- inated carrier transport mechanisms at different temperature regions are investigated. The experimental data show that the carrier transport mechanism may change from trap-limited conduction to variable range hopping conduction at lower temperature. Moreover, the field effect mobilities are also extracted and simulated at various temperatures.

Analysis on Change Characteristics of Diurnal Temperature Range in Benxi County from 1958 to 2010

Based on annual mean maximum and minimum temperatures,diurnal temperature range,precipitation,sunshine,total cloud cover and water barometric pressure data in Benxi County from 1958 to 2010,using statistical analysis,the results show that the annual and seasonal diurnal temperature ranges present significant decreasing tendencies,and the reducing tendency is the most remarkable in winter. Autumn reducing tendency is stronger than that in spring,and it is the weakest in summer. Annual and seasonal average temperatures,average maximum and minimum temperatures all present the remarkable rising trends. Rising trend of the minimum temperature is more significant than that of the maximum temperature. The monthly mean diurnal temperature range also presents reducing tendency,and the most reducing scope appear in January and February. Annual and season diurnal temperature range changes are related to sunshine,mean minimum temperature,mean maximum temperature,precipitation,total cloud cover and water barometric pressure,but various essential factors are different in each season. Annual mean temperature,annual mean minimum temperature,annual mean maximum temperature and annual diurnal temperature range all have sudden changes,but the age is inconsistent.

1.3μm AlInGaAs Strained Single Quantum Well Laser Diodes with High Characteristic Temperature of 200K

A high characteristic temperature （T0） of 200K from a 1.3μm AlInGaAs/AlInAs single-quantum-well laser diode with the asymmetric waveguide layer structure under CW operation at 20 to 80℃ was obtained,which is the best result reported in the laser diodes （LDs） of the same active materials structure and emitting wave- length. AllnGaAs as an active layer,therefore,is very promising for the fabrication of long-wavelength LDs with excellent high-temperature performance. It is found that the asymmetric waveguide layer structure can decrease optical absorption and improve the high-temperature performance and catastrophic optical damage threshold of LDs.

The Evolutionary Characteristics of the Temperature in Typical Counties in Southwest China——Taking Meitan County in Guizhou Province as an Example

Based on the method of linear trending,analysis was made upon the daily temperature statistics of Meitan County from 1951 to 2009,and the results showed that the temperature in general was on the rise.With 1980 as the turning point,it was on the decline before while later the temperature increased quickly.Among these figures,the variation rates of annual average temperature,annual maximum temperature,and annual minimum temperature are 0.11 ℃/10 a,0.08 ℃/10 a,and 0.36 ℃/10 a.The variation rates of average temperature in spring,summer,fall and winter are respectively 0.12 ℃/10 a,0.07 ℃/10 a,0.12 ℃/10 a,and 0.13 ℃/10 a.Morlet wavelet was adopted to analyze the periodicity of temperature change which has periods of different scales.But since 2000,during different time scales most of the areas have been in the period of temperature rises.Besides,certain rule exists in the periodicity of maximum temperature and minimum temperature.Before 1970s,they had opposite changing rules,and the alteration of the peak value occurred.However,in the late 1980s,they had similar changing rules,and their peak values appeared at the same time.It means that against the background of global warming,the reaction of temperature evolution in Meitan County is quite remarkable.

Dielectric properties and temperature increase characteristics of zinc oxide dust from fuming furnace

Cavity perturbation method was used to determine the dielectric properties （ε′,ε″, and tanδ） of zinc oxide dust in different apparent densities. The process was conducted to study the microwave-absorption properties of zinc oxide dust and the feasibility of microwave roasting zinc oxide dust to remove fluorine and chlorine. The dielectric constant, dielectric loss, and loss tangent were proportional to the apparent density of zinc oxide dust. The effects of sample mass and microwave power on the temperature increase characteristics under the microwave field were also studied. The results show that the apparent heating rate of the zinc oxide dust increases with the increase in microwave roasting power and decreases with the increase in the sample mass. The temperature of the samples reaches approximately 800 ＆#176;C after microwave treatment for 8 min, which indicates that the zinc oxide dust has strong microwave-absorption ability.

Temperature Characteristics of Bilayer Thin-Film Devices Under Organic Interface Limited Current Conduction

Temperature characteristics are important for the performance of organic thin film devices. On the basis of the hopping theory of Miller-Abrahams,an analytical model of charge transport for bilayer organic devices under the organicorganic interface limited current conduction is developed. The dependence of current, field,and carrier distribution in bilayer organic devices with the structure of ＂injection electrode/Layer Ⅰ/Layer Ⅱ/collection electrode＂ on temperature are numerically analyzed. We conclude that, for a given applied voltage, when temperature is raised, the voltage of LayerⅠ will increase,and the field will be higher. Meanwhile, the voltage of Layer Ⅲ will decrease, the field will become weaker accordingly,and the current of the device will increase.

High Temperature Characteristics of 3C-SiC/SiHeterojunctionDiodes Grown by LPCVD

The high temperature (300 ～480K) characteristics of the n-3C-SiC/p-Si heterojunction diodes (HJD) fabr icated by low-pressure chemical vapor deposition on Si (100) substrates are inv estigated.The obtained diode with best rectifying properties has 1.8×104 of ratio at room temperature,and slightly rectifying characteristics with 3.1 of rectification ratio is measured at 480K of an ambient temperature .220V of reverse breakdown voltage is acquired at 300K.Capacitance-voltage char acteristics show that the abrupt junction model is applicable to the SiC/Si HJD structure and the built-in voltage is 0.75V.An ingenious equation is employed to perfectly simulate and explain the forward current density-voltage data meas ured at various temperatures.The 3C-SiC/Si HJD represents a promising approach for the fabrication of high quality heterojunction devices such as SiC-emitter heterojunction bipolar transistors.

Characteristic Temperatures of Waxy Crude Oils

Gel point or pour point is widely used to evaluate the low temperature flowability of crude oil. However, it is not adequate to describe the gelling properties of waxy crude oils under flow conditions with gel point or pour point, since the theological behavior of crude oils is dependent on shear history. Waxy crude oils tend to gel at a low temperature. Based on gelation theory, the characteristic temperature of waxy crude oil was determined by analyzing viscosity-temperature data. Two mathematical models were developed for calculating characteristic temperatures of virgin crude oils and pour point depressants （PPD） beneficiated crude oils, respectively. By using these two models, the characteristic temperatures of crude oils that have experienced shearing and thermal histories can be predicted. The model for predicting the characteristic temperature of virgin crude oils has an average relative deviation of 4.5%, and all predicted values have a deviation within 2 ℃. Tested by 42 sets of data, the prediction model for crude oil treated with PPD has a high accuracy, with an average relative deviation of 4.2%, and 95.2 percent of predicted values have a deviation within 2 ℃. These two models provide useful ways for predicting the flowability of crude oils in pipelines when only wax content, wax appearance point and gel point are available.

Characteristics of High Temperature Rupture of a Cast Ni-Based Superalloy M963

The rupture behavior of a cast Ni-base superalloy M963 at high temperature has been investi- gated. The microstructure examination shows that there exists a large amount of the carbide and γ-γ' eutectic, which is very harmful to the mechanical properties of M963 superalloy. The tensile strength of M963 superalloy both at room temperature and at high temperatures is higher than that of K17G alloy, but the tensile ductility of the former is much lower than that of the latter. In tensile fracture process with the high strain rate, the open carbides are the initiation site and the carbide/matrix interface is the propagation path of cracks. But in fracture process with the low strain rate, the carbide/matrix interface and cast microvoids are the initiation sites, and the carbide/matrix interface is the propagation path of cracks. The effective ways to improve ductility of M963 superalloy are also suggested.

Analysis of the Temperature Characteristics of High-speed Train Bearings Based on a Dynamics Model and Thermal Network Method

High-speed trains often use temperature sensors to monitor the motion state of bearings.However,the temperature of bearings can be affected by factors such as weather and faults.Therefore,it is necessary to analyze in detail the relationship between the bearing temperature and influencing factors.In this study,a dynamics model of the axle box bearing of high-speed trains is established.The model can obtain the contact force between the rollers and raceway and its change law when the bearing contains outer-ring,inner-ring,and rolling-element faults.Based on the model,a thermal network method is introduced to study the temperature field distribution of the axle box bearings of high-speed trains.In this model,the heat generation,conduction,and dispersion of the isothermal nodes can be solved.The results show that the temperature of the contact point between the outer-ring raceway and rolling-elements is the highest.The relationships between the node temperature and the speed,fault type,and fault size are analyzed,finding that the higher the speed,the higher the node temperature.Under different fault types,the node temperature first increases and then decreases as the fault size increases.The effectiveness of the model is demonstrated using the actual temperature data of a high-speed train.This study proposes a thermal network model that can predict the temperature of each component of the bearings on a high-speed train under various speed and fault conditions.

Temperature Characteristics of Surface Acoustic Waves Propagating on La_3Ga_5SiO_4 Substrates

Langasite (LGS) is a novel piezoelectric crystal. The authors numerically analyses the temperature stability of surface acoustic waves (SAW) and the relation of SAW propagation with temperature on certain optimal cuts on LGS in this paper. The results show that LGS has better temperature stability than traditional piezo crystals. The results also demonstrate that the velocity of SAW decrease with temperature, the electro-mechanical coupling constant (k2) and temperature coefficient of frequency increases parabolically and the power flow angle increases linearly on certain optimal cuts of LGS. The calculation result compared with the experimental and show good agreement.

Physical and mechanical properties of sandstone containing a single fissure after exposure to high temperatures

In order to investigate the physical and mechanical properties of sandstone containing fissures after exposure to high temperatures,fissures with different angles α were prefabricated in the plate sandstone samples,and the processed samples were then heated at 5 different temperatures.Indoor uniaxial compression was conducted to analyze the change rules of physical properties of sandstone after exposure to high temperature,and the deformation,strength and failure characteristics of sandstone containing fissures.The results show that,with increasing temperature,the volume of sandstone increases gradually while the quality and density decrease gradually,and the color of sandstone remains basically unchanged while the brightness increases markedly when the temperature is higher than 585 ℃;the peak strength of sandstone containing fissures first decreases then increases when the temperature is between 25℃and 400℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature,and the mechanical properties of sandstone show obvious deterioration after 400 ℃.The peak strain of sandstone containing fissures increases gradually while the average modulus decreases gradually with increasing temperature;with increasing angle αof the fissure,the evolution characteristics of the macro-mechanical parameters of sandstone are closely related to the their own mechanical properties.When the temperature is 800 ℃,the correlation between the peak strength and average modulus of sandstone and the angle α of the fissure is obviously weakened.The failure modes of sandstone containing fissures after high temperature exposure are of three different kinds including:tensile crack failure,tensile and shear cracks mixed failure,and shear crack failure.Tensile and shear crack mixed failure occur mainly at low temperatures and small angles;tensile crack failure occurs at high temperatures and large angles.

ANALYSIS OF LONG TERM CHARACTERISTICS OF INTERANNUAL CHANGE OF TEMPERATURE IN DONGGUAN OVER THE RECENT 50 YEARS

With the series of annual and seasonal temperature during 1957 – 2001 in Dongguan, Guangdong, the statistical characteristic and power spectrum and secular trend and sudden change phenomena are computed in this paper. From the results it is known that (1) the temperatures have obvious characteristics of monsoon climate but do not have normal distribution, showing biased distribution of high or low kurtosis; (2) over the recent half- century, the temperatures tend to rise, specially in the last 10 years, in which mean temperature have quickly ascended by about 1.5°C, and except for the spring, there were sudden change of seasonal temperature rising from the 1980’s to 1990’s, which really reflected the influence of developing and opening and urbanization on Dongguan temperature; (3) except for the spring, the temperature of other seasons show some oscillatory periods in Dongguan and some of them also include long-term variation trends.

Martensite Aging Effect and Thermal Cyclic Characteristics in Ti-Pd and Ti-Pd-Ni High Temperature Shape Memory Alloys

The effect of thermal cycling and aging in martensitic state in Ti-Pd-Ni alloys were investigated by DSC and TEM observations. It is shown that the thermal cycling causes the decreases in M, and Af temperatures in Ti50Pd50-xNix (x=10, 20, 30) alloys, but no obvious thermal cycling effect was observed in Ti50Pd50Pd40Ni10 alloys and the aging effect shows a curious feature, i.e., the Af temperature does not saturate even after relatively long time aging, which is considered to be due to the occurrence of recovery recrystallization during aging.

CFD-Based Evaluation of Flowand Temperature Characteristics of Airflow in an Aircraft Cockpit

The rational design of airflow distribution is of great importance for comfort and energy conservation.Several numerical investigations of flow and temperature characteristics in cockpits have been performed to study the distinct airflow distribution.This study developed the coupled heat transfer model of radiation,convection,and heat conduction for the cockpit flight environment.A three-dimensional physical model was created and a shear stress transfer(SST)k-w turbulence model was well verified with a high prediction accuracy of 91%for the experimental data.The strong inhomogeneous flow and temperature distribution were captured for various initial operating conditions(inlet temperature,inlet pressure,and gravitational acceleration).The results indicated that the common feature of the flow field was stable in the middle part of the cockpit,while the temperature field showed a large temperature gradient near the cockpit’s top region.It was also found that there was remarkable consistency in the distributed features,regardless of the applied initial operating conditions.Additionally,the mass flux and the top heat source greatly affected the flow and temperature characteristics.This study suggests that an optimized operating condition does exist and that this condition makes the flow and temperature field more stable in the cockpit.The corresponding results can provide necessary theoretical guidance for the further design of the cockpit structure.