Taking the alpine cold meadow grassland in the southeastern part of the Qinghai-Tibetan Plateau as an ex-ample, this research deals with the characteristics of alpine meadow soil property changes, including soil nutri...Taking the alpine cold meadow grassland in the southeastern part of the Qinghai-Tibetan Plateau as an ex-ample, this research deals with the characteristics of alpine meadow soil property changes, including soil nutrients, soil physical properties and soil moisture content under different land coverage conditions. With the degradation of grassland vegetation and the decline of vegetation coverage, soil com-pactness reduces, gravel content increases and bulk density increases. The originally dense root-system layer is gradually denuded, making the soil coarse and gravel. The change of the organic matter contents with the vegetation coverage change in the surface soil layer (0—20 cm) has shown an obvious cubic polynomial curve process. The organic matter contents increase rapidly when land coverage is above 60%, contrarily decreases on a large scale when land coverage is below 30%. Between 30%—60% of land coverage the or-ganic matter contents remain stable. The total N and organic matter contents in soil have shown quite similar change regularity. Following this the mathematic equations are de-rived to describe such change processes. Moisture content in soil changes sharply with the vegetation coverage change. Soil moisture content change with the vegetation coverage change has shown a quadratic parabola process. Results have shown that organic matter content and the total N con-tent of the alpine meadow soil decrease by 14890 kg/hm2 and 5505 kg/hm2 respectively as the vegetation coverage reduces from 90% to less than 30%. The heavy changes of soil physical and chemical properties with grassland degradation have made the recovery of alpine meadow ecological system impossible. The protection of alpine meadow vegetation is of vital importance to the maintenance of the regional soil en-vironment and the regional ecological system.展开更多
AIM: To probe into the genetic susceptibility of HLA-DRB1 alleles to esophageal carcinoma in Han Chinese in Hubei Province.METHODS: HLA-DRB1 allele polymorphisms were typed by polymerase chain reaction with sequence-s...AIM: To probe into the genetic susceptibility of HLA-DRB1 alleles to esophageal carcinoma in Han Chinese in Hubei Province.METHODS: HLA-DRB1 allele polymorphisms were typed by polymerase chain reaction with sequence-specific primers (PCR-SSP) in 42 unrelated patients with esophageal cancer and 136 unrelated normal control subjects and the associated HLA-DRB1 allele was measured by nucleotide sequence analysis with PCR.SAS software was used in statistics.RESULTS: Allele frequency (AF) of HLA-DRB1·0901 was significantly higher in esophageal carcinoma patients than that in the normal controls (0.2500 vs0.1397, P=0.028, the odds ratio 2.053, etiologic fraction 0.1282). After analyzed the allele nucleotide sequence of HLA-DRB1·0901 which approachs to the corresponded exon 2 sequence of the allele in genebank. There was no association between patients and controls in the rested HLA-DRB1 alleles.CONCLUSION: HLA-DRB1·0901 allele is more common in the patients with esophageal carcinoma than in the healthy controls, which is positively associated with the patients of Hubei Han Chinese. Individuals carrying HLA-DRB1·0901may be susceptible to esophageal carcinoma.展开更多
The heat convection in ballast mass and ripped-stone mass in railway embankments is the problem of heat convection in porous media. In order to calculate the temperature distribution of Qing-Tibet railway embankment, ...The heat convection in ballast mass and ripped-stone mass in railway embankments is the problem of heat convection in porous media. In order to calculate the temperature distribution of Qing-Tibet railway embankment, from the governing equations used to study forced convec-tion for incompressible fluids porous media, the finite ele-ment formulae for heat convection in porous media are de-rived by using Galerkin抯 method. The temperature fields of the traditional ballast embankment and the ripped-stone mass embankment, constructed on July 15, have been ana-lyzed and compared under the case that the air temperature in Qinghai-Tibetan Plateau will be warmed up by 2.0℃ in the future 50 years. The calculated results indicate that, the permafrost 5 m below the traditional ballast embankment will be thawed in the regions in which the air yearly-average temperature is larger than -3.5℃ or the yearly-average temperature at the native surface is larger than -1℃. The embankment will cause large thawing settlement. The rail-way embankment will be damaged by permafrost degrada-tion. The ripped-stone mass embankment can not only resist the effect of climatic warm up on it but also provide cool energy for the permafrost under it. It can assure permafrost stability and not subjected to thawing. Therefore, it is highly recommended that the ripped-stone mass embankment be taken as the Qing-Tibet railway embankment structure in high-temperature permafrost regions so that permafrost embankment can be protected as possible as we could.展开更多
A field experiment was conducted from 1999 to 2002 to compare and evaluate the effects of nutrient and water regimes on paddy soil quality by investigating soil chemical and microbiological parameters. Four nutrient r...A field experiment was conducted from 1999 to 2002 to compare and evaluate the effects of nutrient and water regimes on paddy soil quality by investigating soil chemical and microbiological parameters. Four nutrient regimes, a control, chemical fertilizers only (CF), chemical fertilizers with swine manure (SM), and chemical fertilizers with wheat straw (WS), and two soil moisture regimes, continuous waterlogging (CWL) and alternate wetting and drying (AWD), were investigated. With SM and WS total organic carbon and total nitrogen in the paddy soil were significantly higher (P < 0.05) than those with CF. A similar effect for organic amendments was observed in the soil light fraction organic C (LFOC), water-soluble carbohydrates (WSC), and water-soluble organic C (WSOC). CWL, in particular when swine manure was incorporated into the paddy soil, markedly decreased soil redox potential (Eh) and increased total active reducing substances (ARS). Meanwhile, as compared to CF, SM and WS significantly (P < 0.05) increased soil microbial biomass C (MBC) and mineralizable carbon, with differences in AWD being higher than CWL. In addition, SM and WS treatments significantly (P < 0.05) improved rice above-ground biomass and grain yield, with AWD being greater than CWL. Thus, for ecologically sustainable agricultural management of paddy soils, long-term waterlogging should be avoided when organic manure was incorporated into paddy soil.展开更多
Actual evapotranspiration is a key process of hydrological cycle and a sole term that links land surface water balance and land surface energy balance. Evapotranspiration plays a key role in simulating hydrological ef...Actual evapotranspiration is a key process of hydrological cycle and a sole term that links land surface water balance and land surface energy balance. Evapotranspiration plays a key role in simulating hydrological effect of climate change, and a review of evapotranspiration estimation methods in hydrological models is of vital importance. This paper firstly summarizes the evapotranspiration estimation methods applied in hydrological models and then classifies them into the integrated converting methods and the classification gathering methods by their mechanism. Integrated converting methods are usually used in hydrological models and two differences exist among them： one is in the potential evaporation estimation methods, while the other in the function for defining relationship between potential evapora tion and actual evapotranspiration. Due to the higher information requirements of the Pen- man-Monteith method and the existing data uncertainty, simplified empirical methods for calculating potential and actual evapotranspiration are widely used in hydrological models. Different evapotranspiration calculation methods are used depending on the complexity of the hydrological model, and importance and difficulty in the selection of the most suitable evapotranspiration methods is discussed. Finally, this paper points out the prospective de velopment trends of the evapotranspiration estimating methods in hydrological modeling.展开更多
A novel scheme of M-ary multi-carrier spread spectrum based on wavelet packet is proposed. Its performance is investigated for a multipath, slow Rayteigh fading channel. The performance advantages of the system over t...A novel scheme of M-ary multi-carrier spread spectrum based on wavelet packet is proposed. Its performance is investigated for a multipath, slow Rayteigh fading channel. The performance advantages of the system over that based on DFT are demonstrated by both analytical and simulation methods.展开更多
Surface modification of magnesium alloy AZ91HP (9wt%Al, 0.5wt%Zn, 0.5wt%Mn, Mg remaining percentage) by high current pulsed electron beam (HCPEB) treatment was studied in this paper. The secondary phase MgnAln is near...Surface modification of magnesium alloy AZ91HP (9wt%Al, 0.5wt%Zn, 0.5wt%Mn, Mg remaining percentage) by high current pulsed electron beam (HCPEB) treatment was studied in this paper. The secondary phase MgnAln is nearly completely dissolved and as a result, a super-saturated solid solution forms on the re-melted surface. The microhardness is increased both in and far beyond the heat-affected zone (HAZ), reaching about 250um. Measurements on sliding wear have shown that the wear resistance of the treated samples was improved by a factor of about 2.4 as compared to the as-received sample. It is also found that the sliding wear resistance can be further improved by surface alloying with TiN.展开更多
An experimental way to analyze the thermal characterization of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed. By using this way the thermal characteristics of stra...An experimental way to analyze the thermal characterization of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed. By using this way the thermal characteristics of strain compensated 1.3 μm InAsP/InGaAsP ridge waveguide MQW laser diodes have been investigated. Results show that by measuring and analyzing the lasing spectra under appropriate driving parameters and temperature ranges, the thermal resistance of the laser diodes could be deduced easily. A higher thermal resistance of 640 K/W has been measured on a narrow ridge laser chip without soldering. Other thermal and spectral properties of the lasers have also been measured and discussed.展开更多
Solder bridge is a serious defect of solder joints in ultrafine pitch electronic device assemblies. Generation of the solder bridge is closely related to forming process of the solder joints. A three-dimensional model...Solder bridge is a serious defect of solder joints in ultrafine pitch electronic device assemblies. Generation of the solder bridge is closely related to forming process of the solder joints. A three-dimensional model to simulate the formation of the solder bridge of QFP256 (quad flat packaging with 256 leads) is established and numerically calculated to predict the formation shape of the solder joints using surface evolver program. Based on the model, influence of structure of pads printed on circuit board on solder bridging is investigated. The results show that there is a critical solder volume Vc for solder joints to avoid solder bridging, and parameters of the pad size influence the critical solder volume.展开更多
Synthesis of the third-order nonlinear materials: bis (1,4-dihydroxynaphthalene) tetrathiafulvalene and bis (1,4-dialkoxylnaphthalene) tetrathiafulvalene has been achieved in four steps, starting from 2,3-dichloro-1,4...Synthesis of the third-order nonlinear materials: bis (1,4-dihydroxynaphthalene) tetrathiafulvalene and bis (1,4-dialkoxylnaphthalene) tetrathiafulvalene has been achieved in four steps, starting from 2,3-dichloro-1,4-naphthaquinone. The materials exhibit larger third-order nonlinear optical susceptibilities c(3) .展开更多
Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magn...Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.展开更多
The mobilities of holes in thin,spin-casting films of poly( N -vinylcarbazole)(PVK) based on silicium are measured using a time-of-flight (TOF) technique.The drift of hole mobility is strongly dependent on the elect...The mobilities of holes in thin,spin-casting films of poly( N -vinylcarbazole)(PVK) based on silicium are measured using a time-of-flight (TOF) technique.The drift of hole mobility is strongly dependent on the electric field and temperature.At room temperature and an electric field of 2×10 5 V·cm -1 ,the effective mobility of hole is 7.14×10 -6 cm 2·V -1 ·s -1 ,in a 200 nm thick sample.展开更多
The characteristics of low frequency electrical noise, voltage current ( V I ) and electrical derivation for 980 nm InGaAsP/InGaAs/GaAs high power double quantum well lasers(DQWLs) are measured under different conditi...The characteristics of low frequency electrical noise, voltage current ( V I ) and electrical derivation for 980 nm InGaAsP/InGaAs/GaAs high power double quantum well lasers(DQWLs) are measured under different conditions. The correlation of the low frequency electrical noise with surface non radiative current of devices is discussed. The results indicate the low frequency electrical noise of 980 nm DQWLs with high power is mainly 1/ f noise and has good relation with the device surface current at low injection.展开更多
A sedimentation method is proposed to fabricate functionally graded materials (FGMs) with the continuous andsmooth variations of composition. The relations between the compositional distribution of deposited body and ...A sedimentation method is proposed to fabricate functionally graded materials (FGMs) with the continuous andsmooth variations of composition. The relations between the compositional distribution of deposited body and thepowder characteristics of raw materials as well as settling parameters are derived. Subsequently, the mathematicalmodel of forming FGM based on the co-sedimentation has been established. At last, numerical simulations areconducted to explore the effects of the particle sizes of raw materials and suspension height on the compositionaldistribution of final products.展开更多
Organic multiple quantum wells(OMQWs) consisting of alternating layers of organic materials have been fabricated from tris(8-hydroxyquinoline) aluminum(Alq)and 2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,3,3-oxadiazole(P...Organic multiple quantum wells(OMQWs) consisting of alternating layers of organic materials have been fabricated from tris(8-hydroxyquinoline) aluminum(Alq)and 2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,3,3-oxadiazole(PBD) by a multisource-type high-vacuum organic molecular deposition.From the small-angle X-ray diffraction patterns of Alq/PBD OMQWs,a periodically layered structure is confirmed through the entire stack.The Alq layer thickness in the OMQWs was varied from 1 nm to 4 nm.From the optical absorption,photoluminescence and electroluminescence measurements,it is found that the exciton energy shifts to higher energy with decreasing Alq layer thickness,The changes of the exciton energy could be interpreted as the confinement effects of exciton in the Alq thin layers.Narrowing of the emission spectrum has also been observed for the electroluminescent devices (ELDs) with the OMQWs structure at room temperature.展开更多
An electro-optic sampling system utilizing proton-bombarded GaP crystal as probe material has been built. Microwave signals propagating on the indium -tin oxide coplanar waveguide were measured by the system. Measurem...An electro-optic sampling system utilizing proton-bombarded GaP crystal as probe material has been built. Microwave signals propagating on the indium -tin oxide coplanar waveguide were measured by the system. Measurements of bombarded sample gave the resistance value of four orders greater than that of un- bombarded. The electric field shield effect induced by doped GaP was effectively decreased to approximate semi-insulator material. The system has the voltage sensitivity of about 40 mV/21/Hz with the microwave frequency of 1.15 GHz.展开更多
Nineteen kinds of spiro enol ether analogues were screened with larvae of Pieris rapae for antifeedant activity. The results showed that the antifeedant activity of compounds No.20 and No.12 was higher than others. In...Nineteen kinds of spiro enol ether analogues were screened with larvae of Pieris rapae for antifeedant activity. The results showed that the antifeedant activity of compounds No.20 and No.12 was higher than others. In non-choice test, AFC50 values within 24 h of compounds No.20 and No.12 against 3rd instar larvae of P. rapae were 226.93ug/mL and 370.00ug/mL, and that in choice test against 4th larvae were 280.54 ug/mL and 398.88 ug/mL, respectively. Compd. No.20 could prolong the eggs hatch time and reduce the haemolymph content and the protein content in haemolymph of 4th instar larvae obviously. Compd. No.20 could protect tested leaves and control larvae of P. rapae effectively.展开更多
Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia...Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The crystalline quality of GaN films revealed by high resolution X-ray diffraction were strongly dependent on the nitridation time, which determined substrate surface topography. The different nitridation schemes strongly affected the morphology of GaN overlayers resulting in the blue shift of the main excitonic peak in photoluminescence spectra at room temperature.展开更多
A new geometric constraint model is described, which is hierarchical and suitable for parametric feature based modeling. In this model, different levels of geometric information are represented to support various stag...A new geometric constraint model is described, which is hierarchical and suitable for parametric feature based modeling. In this model, different levels of geometric information are represented to support various stages of a design process. An efficient approach to parametric featu-re based modeling is also presented, adopting the high level geometric constraint model. The low level geometric model such as B-reps can be derived automatically from the high level geometric constraint model, enabling designers to perform their task of detailed design.展开更多
The application of irradiation in silicon crystal is introduced.The defects caused by irradiation are reviewed and some major ways of studying defects in irradiated silicon are summarized.Furthermore the problems in t...The application of irradiation in silicon crystal is introduced.The defects caused by irradiation are reviewed and some major ways of studying defects in irradiated silicon are summarized.Furthermore the problems in the investigation of irradiated silicon are discussed as well as its properties.展开更多
基金This work was supported by the Knowledge Innovation Programs of the Chinese Academy of Sciences (Grant Nos. KXCX1-10-06 and KZCX1-SW-04) and the National Natural Science Foundation of China (Grant Nos. 90102006 and 40171002).
文摘Taking the alpine cold meadow grassland in the southeastern part of the Qinghai-Tibetan Plateau as an ex-ample, this research deals with the characteristics of alpine meadow soil property changes, including soil nutrients, soil physical properties and soil moisture content under different land coverage conditions. With the degradation of grassland vegetation and the decline of vegetation coverage, soil com-pactness reduces, gravel content increases and bulk density increases. The originally dense root-system layer is gradually denuded, making the soil coarse and gravel. The change of the organic matter contents with the vegetation coverage change in the surface soil layer (0—20 cm) has shown an obvious cubic polynomial curve process. The organic matter contents increase rapidly when land coverage is above 60%, contrarily decreases on a large scale when land coverage is below 30%. Between 30%—60% of land coverage the or-ganic matter contents remain stable. The total N and organic matter contents in soil have shown quite similar change regularity. Following this the mathematic equations are de-rived to describe such change processes. Moisture content in soil changes sharply with the vegetation coverage change. Soil moisture content change with the vegetation coverage change has shown a quadratic parabola process. Results have shown that organic matter content and the total N con-tent of the alpine meadow soil decrease by 14890 kg/hm2 and 5505 kg/hm2 respectively as the vegetation coverage reduces from 90% to less than 30%. The heavy changes of soil physical and chemical properties with grassland degradation have made the recovery of alpine meadow ecological system impossible. The protection of alpine meadow vegetation is of vital importance to the maintenance of the regional soil en-vironment and the regional ecological system.
文摘AIM: To probe into the genetic susceptibility of HLA-DRB1 alleles to esophageal carcinoma in Han Chinese in Hubei Province.METHODS: HLA-DRB1 allele polymorphisms were typed by polymerase chain reaction with sequence-specific primers (PCR-SSP) in 42 unrelated patients with esophageal cancer and 136 unrelated normal control subjects and the associated HLA-DRB1 allele was measured by nucleotide sequence analysis with PCR.SAS software was used in statistics.RESULTS: Allele frequency (AF) of HLA-DRB1·0901 was significantly higher in esophageal carcinoma patients than that in the normal controls (0.2500 vs0.1397, P=0.028, the odds ratio 2.053, etiologic fraction 0.1282). After analyzed the allele nucleotide sequence of HLA-DRB1·0901 which approachs to the corresponded exon 2 sequence of the allele in genebank. There was no association between patients and controls in the rested HLA-DRB1 alleles.CONCLUSION: HLA-DRB1·0901 allele is more common in the patients with esophageal carcinoma than in the healthy controls, which is positively associated with the patients of Hubei Han Chinese. Individuals carrying HLA-DRB1·0901may be susceptible to esophageal carcinoma.
基金supported in part by the National Science Fund for Distinguished Young Scholars of China(Grant No.40225001)the Foundation of"Hundred People Plan"of the Chinese Academy of Sciences and the Knowled ge Innovation Program of the Chinese Academy of Sciences(Grant No.KZCX1-SW-04).
文摘The heat convection in ballast mass and ripped-stone mass in railway embankments is the problem of heat convection in porous media. In order to calculate the temperature distribution of Qing-Tibet railway embankment, from the governing equations used to study forced convec-tion for incompressible fluids porous media, the finite ele-ment formulae for heat convection in porous media are de-rived by using Galerkin抯 method. The temperature fields of the traditional ballast embankment and the ripped-stone mass embankment, constructed on July 15, have been ana-lyzed and compared under the case that the air temperature in Qinghai-Tibetan Plateau will be warmed up by 2.0℃ in the future 50 years. The calculated results indicate that, the permafrost 5 m below the traditional ballast embankment will be thawed in the regions in which the air yearly-average temperature is larger than -3.5℃ or the yearly-average temperature at the native surface is larger than -1℃. The embankment will cause large thawing settlement. The rail-way embankment will be damaged by permafrost degrada-tion. The ripped-stone mass embankment can not only resist the effect of climatic warm up on it but also provide cool energy for the permafrost under it. It can assure permafrost stability and not subjected to thawing. Therefore, it is highly recommended that the ripped-stone mass embankment be taken as the Qing-Tibet railway embankment structure in high-temperature permafrost regions so that permafrost embankment can be protected as possible as we could.
基金1Project supported by the Knowledge Innovative Program of the Chinese Academy of Sciences (No. KZCX2-413) andthe National High Technology Research and Development Program of China (863 Program) (No. 2002AA601012).
文摘A field experiment was conducted from 1999 to 2002 to compare and evaluate the effects of nutrient and water regimes on paddy soil quality by investigating soil chemical and microbiological parameters. Four nutrient regimes, a control, chemical fertilizers only (CF), chemical fertilizers with swine manure (SM), and chemical fertilizers with wheat straw (WS), and two soil moisture regimes, continuous waterlogging (CWL) and alternate wetting and drying (AWD), were investigated. With SM and WS total organic carbon and total nitrogen in the paddy soil were significantly higher (P < 0.05) than those with CF. A similar effect for organic amendments was observed in the soil light fraction organic C (LFOC), water-soluble carbohydrates (WSC), and water-soluble organic C (WSOC). CWL, in particular when swine manure was incorporated into the paddy soil, markedly decreased soil redox potential (Eh) and increased total active reducing substances (ARS). Meanwhile, as compared to CF, SM and WS significantly (P < 0.05) increased soil microbial biomass C (MBC) and mineralizable carbon, with differences in AWD being higher than CWL. In addition, SM and WS treatments significantly (P < 0.05) improved rice above-ground biomass and grain yield, with AWD being greater than CWL. Thus, for ecologically sustainable agricultural management of paddy soils, long-term waterlogging should be avoided when organic manure was incorporated into paddy soil.
基金CAS-CSIRO Cooperative Research Program,No.CJHZ1223National Basic Research Program of China, No.2010CB428406
文摘Actual evapotranspiration is a key process of hydrological cycle and a sole term that links land surface water balance and land surface energy balance. Evapotranspiration plays a key role in simulating hydrological effect of climate change, and a review of evapotranspiration estimation methods in hydrological models is of vital importance. This paper firstly summarizes the evapotranspiration estimation methods applied in hydrological models and then classifies them into the integrated converting methods and the classification gathering methods by their mechanism. Integrated converting methods are usually used in hydrological models and two differences exist among them： one is in the potential evaporation estimation methods, while the other in the function for defining relationship between potential evapora tion and actual evapotranspiration. Due to the higher information requirements of the Pen- man-Monteith method and the existing data uncertainty, simplified empirical methods for calculating potential and actual evapotranspiration are widely used in hydrological models. Different evapotranspiration calculation methods are used depending on the complexity of the hydrological model, and importance and difficulty in the selection of the most suitable evapotranspiration methods is discussed. Finally, this paper points out the prospective de velopment trends of the evapotranspiration estimating methods in hydrological modeling.
基金Supported by the National Natural Science Foundation of China(No.60172029)
文摘A novel scheme of M-ary multi-carrier spread spectrum based on wavelet packet is proposed. Its performance is investigated for a multipath, slow Rayteigh fading channel. The performance advantages of the system over that based on DFT are demonstrated by both analytical and simulation methods.
文摘Surface modification of magnesium alloy AZ91HP (9wt%Al, 0.5wt%Zn, 0.5wt%Mn, Mg remaining percentage) by high current pulsed electron beam (HCPEB) treatment was studied in this paper. The secondary phase MgnAln is nearly completely dissolved and as a result, a super-saturated solid solution forms on the re-melted surface. The microhardness is increased both in and far beyond the heat-affected zone (HAZ), reaching about 250um. Measurements on sliding wear have shown that the wear resistance of the treated samples was improved by a factor of about 2.4 as compared to the as-received sample. It is also found that the sliding wear resistance can be further improved by surface alloying with TiN.
文摘An experimental way to analyze the thermal characterization of semiconductor lasers based on spectroscopy method under pulse driving conditions has been developed. By using this way the thermal characteristics of strain compensated 1.3 μm InAsP/InGaAsP ridge waveguide MQW laser diodes have been investigated. Results show that by measuring and analyzing the lasing spectra under appropriate driving parameters and temperature ranges, the thermal resistance of the laser diodes could be deduced easily. A higher thermal resistance of 640 K/W has been measured on a narrow ridge laser chip without soldering. Other thermal and spectral properties of the lasers have also been measured and discussed.
文摘Solder bridge is a serious defect of solder joints in ultrafine pitch electronic device assemblies. Generation of the solder bridge is closely related to forming process of the solder joints. A three-dimensional model to simulate the formation of the solder bridge of QFP256 (quad flat packaging with 256 leads) is established and numerically calculated to predict the formation shape of the solder joints using surface evolver program. Based on the model, influence of structure of pads printed on circuit board on solder bridging is investigated. The results show that there is a critical solder volume Vc for solder joints to avoid solder bridging, and parameters of the pad size influence the critical solder volume.
基金This research was supported by the National Natural Science Foundation (29476227) the Natural Science Foundation of Zhejiang Province (1999-299003).
文摘Synthesis of the third-order nonlinear materials: bis (1,4-dihydroxynaphthalene) tetrathiafulvalene and bis (1,4-dialkoxylnaphthalene) tetrathiafulvalene has been achieved in four steps, starting from 2,3-dichloro-1,4-naphthaquinone. The materials exhibit larger third-order nonlinear optical susceptibilities c(3) .
基金supported by the National High Technique Development Foundation of China(No.2002AA331160).
文摘Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.
文摘The mobilities of holes in thin,spin-casting films of poly( N -vinylcarbazole)(PVK) based on silicium are measured using a time-of-flight (TOF) technique.The drift of hole mobility is strongly dependent on the electric field and temperature.At room temperature and an electric field of 2×10 5 V·cm -1 ,the effective mobility of hole is 7.14×10 -6 cm 2·V -1 ·s -1 ,in a 200 nm thick sample.
文摘The characteristics of low frequency electrical noise, voltage current ( V I ) and electrical derivation for 980 nm InGaAsP/InGaAs/GaAs high power double quantum well lasers(DQWLs) are measured under different conditions. The correlation of the low frequency electrical noise with surface non radiative current of devices is discussed. The results indicate the low frequency electrical noise of 980 nm DQWLs with high power is mainly 1/ f noise and has good relation with the device surface current at low injection.
基金This research is sponsored by the National Natural Science Foundation of China under grant No,50171049the Doctoral Science Foundation of Ministty of Education of China under the grant 1999049702.
文摘A sedimentation method is proposed to fabricate functionally graded materials (FGMs) with the continuous andsmooth variations of composition. The relations between the compositional distribution of deposited body and thepowder characteristics of raw materials as well as settling parameters are derived. Subsequently, the mathematicalmodel of forming FGM based on the co-sedimentation has been established. At last, numerical simulations areconducted to explore the effects of the particle sizes of raw materials and suspension height on the compositionaldistribution of final products.
文摘Organic multiple quantum wells(OMQWs) consisting of alternating layers of organic materials have been fabricated from tris(8-hydroxyquinoline) aluminum(Alq)and 2-(4-biphenylyl)-5-(4-tertbutylphenyl)-1,3,3-oxadiazole(PBD) by a multisource-type high-vacuum organic molecular deposition.From the small-angle X-ray diffraction patterns of Alq/PBD OMQWs,a periodically layered structure is confirmed through the entire stack.The Alq layer thickness in the OMQWs was varied from 1 nm to 4 nm.From the optical absorption,photoluminescence and electroluminescence measurements,it is found that the exciton energy shifts to higher energy with decreasing Alq layer thickness,The changes of the exciton energy could be interpreted as the confinement effects of exciton in the Alq thin layers.Narrowing of the emission spectrum has also been observed for the electroluminescent devices (ELDs) with the OMQWs structure at room temperature.
基金National Natural Science Foundation of China!(No. 69876014 )Research Fund for the Doctoral Program of Higher Education!(RFDP
文摘An electro-optic sampling system utilizing proton-bombarded GaP crystal as probe material has been built. Microwave signals propagating on the indium -tin oxide coplanar waveguide were measured by the system. Measurements of bombarded sample gave the resistance value of four orders greater than that of un- bombarded. The electric field shield effect induced by doped GaP was effectively decreased to approximate semi-insulator material. The system has the voltage sensitivity of about 40 mV/21/Hz with the microwave frequency of 1.15 GHz.
文摘Nineteen kinds of spiro enol ether analogues were screened with larvae of Pieris rapae for antifeedant activity. The results showed that the antifeedant activity of compounds No.20 and No.12 was higher than others. In non-choice test, AFC50 values within 24 h of compounds No.20 and No.12 against 3rd instar larvae of P. rapae were 226.93ug/mL and 370.00ug/mL, and that in choice test against 4th larvae were 280.54 ug/mL and 398.88 ug/mL, respectively. Compd. No.20 could prolong the eggs hatch time and reduce the haemolymph content and the protein content in haemolymph of 4th instar larvae obviously. Compd. No.20 could protect tested leaves and control larvae of P. rapae effectively.
基金National"863"Project of China (2001AA311100 and 2002AA305304) Sino French Cooperation Project:CNRS/ASC Chine 2003 Project(14915)
文摘Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The crystalline quality of GaN films revealed by high resolution X-ray diffraction were strongly dependent on the nitridation time, which determined substrate surface topography. The different nitridation schemes strongly affected the morphology of GaN overlayers resulting in the blue shift of the main excitonic peak in photoluminescence spectra at room temperature.
文摘A new geometric constraint model is described, which is hierarchical and suitable for parametric feature based modeling. In this model, different levels of geometric information are represented to support various stages of a design process. An efficient approach to parametric featu-re based modeling is also presented, adopting the high level geometric constraint model. The low level geometric model such as B-reps can be derived automatically from the high level geometric constraint model, enabling designers to perform their task of detailed design.
文摘The application of irradiation in silicon crystal is introduced.The defects caused by irradiation are reviewed and some major ways of studying defects in irradiated silicon are summarized.Furthermore the problems in the investigation of irradiated silicon are discussed as well as its properties.
