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.

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.

Temperature characteristics of wood during microwave treatments

In order to investigate the temperature characteristics of wood during microwave(MW) treatments,optical fiber sensors were used to measure wood(Pinus sylvestris L. var. mongolica Litv.) temperatures. The results show that the development of internal temperatures in wood basically includes two patterns during the process of MW treatment. The first may be divided into three phases: warming, constant temperature, and a sharply rising phase. The second pattern may be divided into two phases: warming, and constant temperature. The maximum temperature(MT) and rate of temperature increase(RTI)rose as the microwave power increased. The initial wood moisture content decreased while the period of constant temperature fell. Temperatures varied in different positions in the wood. The order of MT and RTI levels were the upper surface, center, bottom surface and the end point.Along the direction of wood thickness, the closer the monitoring point was to the generator, the faster the temperature increased. The MT and RTI of the end point was a minimum value because of the rapid removal of steam.

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.

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.

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.

On the temperature characteristics of phase measurement in homodyne fiber interferometer

Different from the traditional way of using piezoelectric （PZT）phase shifter to measure phase difference, a new method is designed to calculate it between signals in the two arms of a homodyne fiber interferometer. A simple homodyne fiber interferometer system is then established to measure the interference photoeurrent and the photocurrents from the two fiber arms generated by the signal power on a temperature control plat. The homodyne fiber interferometer system is composed of fiber and sensitive to the variation of temperature. Thus, is necessary to study the temperature characteristics in the phase measurement of homodyne fiber interferometer. The experimental results show that the variation of the phase difference of signals in the two fiber arms is proportional to the variation of temperature.

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.

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 M8 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.

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.

ON SWELLING CHARACTERISTICS AND MECHANISM OF TEMPERATURE SENSITIVE HYDROGELS

A series of N-substituted acrylamide monomers and the temperature sensitive hydrogels of their copolymer with N, N'-methylene-bis -acrylamide (Bis) have been synthesized. The effects of monomer structures, composition of the initial monomer mixture, polymerization temperature, the extent of ionization of the network and the presence of acid, base, salt or organic compound on the formation and the swelling characteristics of the temperature sensitive hydrogels have been systematically studied. The mechanism of the temperature sensitive phase transformation of the hydrogels was also investigated.

Deterioration Characteristics of Cement-Fly Ash Paste under Strong Ultraviolet Radiation and Low Temperature Conditions

The pastes containing different dosages of fly ash were taken into ultraviolet radiation and low temperature freeze condition simultaneously（URL）for 30 days and only ultraviolet radiation condition（UR）for 30 days after standard curing,so as to investigate the influences of the conditions on the deterioration characteristics of the pastes.Microscopic test methods,such as XRD,TG-DTA and SEM,were used to study the UR effect on the deterioration process of hardened paste.The results show that the deterioration tests,such as URL and UR,inhibit the common development of paste strength,especially after the standard curing age of 360days.With the increase of fly ash dosage,from 0 to 50%,the reference value decreases,especially at early age.While at the later age,i e,180 and 360 days,the paste strength cured for 30 days under URL and UR conditions all increase to different extent and the strength is slightly affected very low,especially for the paste containing25%fly ash.From XRD results,URL and UR dispositions do not influence the hydration product kinds but the amount,especially Ca（OH）2 and CaCO3.Deterioration experiments can decrease the diffraction peak of Ca（OH）2 sharply,and increase that of CaCO3 rapidly,especially under only ultraviolet radiation.From TG-DTA and SEM results,with the increase of curing age,the content of Ca（OH）2 decreases and that of CaCO3 increases.The Ca（OH）2 content of paste under continuous UR curing for 30 days is less than that under URL curing for 30days,which indicates that UR has more negative effects on the pastes than URL.

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.

Characteristics Analysis of the Temperature inside and outside the Themometer Shelter in Changsha during Summer

A statistical analysis on the simultaneous observation data of the temperature inside and outside the themometer shelter in Changsha during summer of 2011 and 2012 was carried out. The results show that the temperature outside the themometer shelter is higher（ lower） than that inside the themometer shelter in the daytime（ nighttime）. However,there exists a similar variation trend for the average temperature and the extremely maximum temperature inside and outside the themometer shelter in summer. The average temperature and the extremely maximum temperature outside the themometer shelter are higher than that inside the themometer shelter. Furthermore,there exists a difference between the temperatures inside and outside the themometer shelter during different weather conditions. The difference of average temperature reaches 1. 2 ℃ in rainy day,2. 8 ℃ in cloudy day and 3. 1 ℃ in sunny day,and the extremely maximum temperature difference reaches 6. 4 ℃. Especially for the days of high temperature ≥35 ℃,there is 61 high temperature days inside the themometer shelter,while there is 125 high temperature days inside the themometer shelter during 2011- 2012. Furthermore,the extremely maximum temperatures inside and outside the themometer shelter are 38. 9 and42. 0 ℃ respectively. Rainfall and showery rain are the most effective ways to relieve the high temperature in summer. Therefore,the difference between the temperatures inside and outside the themometer shelter should be taken into account in the high temperature forecast and public meteorological service.

Design of Uncooled Thermal Imaging Systems Operating at Multiple Temperatures

The reasons why thermal imaging systems consume power are analyzed,and a low power consumption design scheme is presented for the thermal imaging systems operating at multiple temperatures. The relation between the response performance of α-Si microbolometer detector and its operating temperature is studied by means of formulas of microbolometer detector's noise equivalent temperature difference(NETD) and detectivity. Numerical analysis based on true parameters demonstrates that the detectivity decreases slightly and NETD increases slightly when operating temperature rises,which indicates that α-Si microbolometer detector has approximately uniform response in a wide operating temperature range. According to these analyses,a thermal imaging system operating at multiple temperatures is designed. The power of thermoelectric stabilizer(TEC) is less than 350 mW and NETD is less than 120 mK in the ambient temperature range of-40 ℃-60 ℃,which shows that this system not only outputs high-quality images but consumes low power.

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.

Phase Transformation Strengthening of Hot Extruded Inconel 625 under High-temperature Load Environment

Microstructure evolution and properties of hot-extruded Inconel 625 alloy were investigated at different creep temperatures, aging time and strain rates. The experimental results indicate that the Inconel 625 alloy exhibits an excellent creep resistance at 700 ℃ and below. When the creep temperature rises to 750 ℃, the creep resistance falls drastically due to the failure of phase transformation strengthening and the precipitation of a large amount of δ phase and σ phase at the grain boundary. The special temperature-sensitive characteristics of Inconel 625 alloy play a very important role in its fracture. When the strain rate is 8.33×10^-3s^-1, the strength of the specimen is higher than that of other parameters attributed to the effect of phase transformation strengthening. With the increase of Ni3(Al, Ti), the phase transformation strengthening inhibits thickening of the stacking faults into twins and improves the overall mechanical properties of the alloy. With the increase of the aging time, the granular Cr-rich M23C6 carbides continue to precipitate at the grain boundary, which hinders the movement of the dislocations and obviously increases the strength of the samples. Especially, the yield strength increases several times.

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%.

Effects of Root Zone Temperature on Growth and Photosynthetic Parameters of Grafted Cucumber

Taking Cucurbita maxima and Cucurbita moschata as root stocks,and‘Jinyou No 3＇cucumber as scion,the effects of different root zone temperature conditions optimal temperature（ CK）（ 18-20 ℃）,suboptimal temperature（ 13-15 ℃） and low temperature（ 8-10 ℃） on the growth and photosynthesis indexes were studied. The results showed that,compared with optimal temperature（ CK）,suboptimal temperature and low temperature produced a significant inhibition of growth on cucumbers. The plant height,stem diameter,leaf area,number of leaves and dry weight of aboveground part were all reduced,dry weight of underground part and root shoot ratio all increased,while the inhibition was more significant at low temperature. Low and suboptimal temperature conditions also reduced SPAD value,net photosynthetic rate,transpiration rate,intercellular CO2 concentration and stomatal conductance of the grafted cucumber. And there were differences between different grafted seedlings,and seedlings with‘black seeds＇ as stock performed better than those with‘white seeds＇ as stock at low temperature.