共查询到20条相似文献，搜索用时 31 毫秒
1.
This paper deduces the expression of the Schottky contact capacitance of AlGaN/AlN/GaN high electron mobility transistors (HEMTs), which will help to understand the electron depleting process. Some material parameters related with capacitance--voltage profiling are given in the expression. Detailed analysis of the forward-biased capacitance has been carried on. The gate capacitance of undoped AlGaN/AlN/GaN HEMT will fall under forward bias. If a rising profile is obviously observed, the donor-like impurity or trap is possibly introduced in the barrier. 相似文献
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From the theoretical analysis of the thermionic emission model of current--voltage characteristics, this paper extracts the parameters for the gate Schottky contact of two ion-implanted 4H-SiC metal--semiconductor field-effect transistors (sample A and sample B for three and four times multiple ion-implantation channel region respectively) fabricated in the experiment, including the ideality factor, the series resistance, the zero-field barrier height, the interface oxide capacitance, the interface state density distribution, the neutral level of interface states and the fixed space charge density. The methods to improve the interface of the ion-implanted Schottky contact are given at last. 相似文献
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将黄渤海海域概化为矩形海湾,山东半岛概化为垂直于海岸的巨型丁坝,形成一个带丁坝型半封闭矩形海湾。利用DELFT3D-FLOW计算模块在上述海湾中进行了M2分潮数值模拟,对其无潮点和辐射状潮流场的特性进行了分析。研究发现:考虑科氏力影响和巨型丁坝反射作用,坝前形成了明显的无潮点,但在等水深条件下并未形成辐射状潮流场,而叠加上倾斜海底地形后其得以形成;无潮点和辐射状潮流场顶端位置受水深影响明显,随着平均水深的增大,无潮点将向湾口和湾中轴线方向偏移,而辐射状潮流场顶端则向湾口方向偏移。研究结果有助于加深对带丁坝型半封闭矩形海湾中驻潮波系统形成机制和动力特性的理解和认识。 相似文献
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海上油气田开发由于所处地理环境恶劣、地质条件复杂、投资巨大,是一个风险较大的行业。海上油气田开发在地质、开发技术、工程技术、政治及经济等方面较陆上油气田有更大的风险,特别是开发建设投资占比大,因此分析其开发风险因素,提出相应对策,对后续海上油气田开发项目管理有着极为重要的意义。此文结合我国海域已投入开发的油气田案例,探讨海上油气田开发项目的风险因素,并由此提出关注的一些技术问题,以期在开发管理过程中降低风险、提高项目经济效益提供一定帮助。 相似文献
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This paper investigates the high frequency behaviours and magnetic anisotropy of rapidly solidified FINEMET (Fe73.5Si13.5B9Nb3Cu1) alloy ribbons annealed in an applied magnetic field. It finds that the ribbons annealed with the applied magnetic field show much higher resonance frequencies and have even higher permeability at higher frequencies than the samples annealed without the magnetic field and the non-annealed ribbons. M?ssbauer spectroscopy had been employed to study the spatial distribution of the magnetic moments of five selected FINEMET alloy ribbons in different heat-treated conditions. The results show that an easy plane has been established after annealling in the magnetic field, while for the other ribbons this effect is not significant. Hence, the relationship between magnetic field annealing and high frequency property has been bridged by the bianisotropic theory. 相似文献
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以成矿作用反应场中的成矿物质和成矿环境为切入点,指出洋底水-沉积物界面附近形成了金属垒、碱性垒和氧化垒的垒群带以及矿物的沉析带;溶解态成矿金属的存在形式除Fe主要呈高价态外,Mn、Cu、Ni、Co均呈低价态;洋底沉析的矿物有赤铁矿、针铁矿、石英、硅酸盐类和碳酸盐类矿物。成矿溶液中存在富含Mn、Fe的胶体和微粒,其Mn、Fe含量比溶解态的高出百倍至千倍,Cu、Ni、Co含量也以增高为主。南极底层流的供氧使表层沉积物均呈浅黄、黄褐、褐色系列色调,并且成矿溶液呈低温、弱碱性、强氧化环境。在构筑成矿金属运聚和分异的动态模型基础上,提出了氧化、胶体化学和生物化学是结核生成的作用链,归纳为以洋底垒群带和矿物沉析带的复合带为背景、胶体化学作用为主导、物理化学作用和生物化学作用叠加的外生成因水下沉析的结核成矿模式。 相似文献
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Shili Liao Chuanwei Zhu Jianping Zhou Weiyong Liu Junyu Yu Jin Liang Weifang Yang Wei Li Jia Liu Chunhui Tao 《海洋学报(英文版)》2021,40(5):105-113
The newly discovered East Longjing-2 hydrothermal field (ELHF-2) is located on the Dragon Horn oceanic core complex of the ultraslow-spreading Southwest Indian Ridge, approximately 12 km from the ridge axis. This study measured the chemical compositions of pyrite from ELHF-2 using a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to investigate the genesis of the field. Three generations of pyrite were classified, and found that: Py1 and Py2, rich in V, Mn, U, and Se, occur in altered basalt debris and the silica alteration matrix, respectively. Py3 was mainly intergrown with chalcopyrite in quartz veins and had higher Cu, In, Ag, Sb, and Au contents than Py1 and Py2. Some elements, such as Au, Se, and Pb, are likely presented as direct substitution with Fe2+ in pyrite, while Cu, Zn, Co, Ni, and Ag probably occur both as direct substitution with Fe and as distributed micro- to nanoparticle-sized sulfides. Meanwhile, the occurrence of V, Mn, and U is likely presented as oxide inclusions. Trace element geochemistry suggested that the pyrite was formed under high-temperature conditions, and the ore forming elements were likely derived from ultramafic rocks. In addition, Py1 and Py2 were formed under higher water/rock ratio and higher temperature conditions, with more seawater involvement compared with Py3. The formation of ELHF-2 was probably driven by exothermic serpentinization reactions with an additional magmatic heat. This study shows that high-temperature hydrothermal circulation driven by magmatic activity can be developed on distal rift flank areas of magma-starved ultraslow-spreading ridges. 相似文献
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High-frequency propagation close to an active surf line is explored with 12and 100-kHz propagation paths together with measurements of bubble clouds, bubble size distributions, and waves. Breaking waves inject massive bubble plumes that are mixed downwards from the roller region by intense turbulence. If these injections follow one another at intervals less than the time taken for the bubbles to rise to the surface, acoustic signals will be continuously blocked, forming an acoustical barrier that effectively inhibits any propagation. Occasionally, waves break seaward of this barrier. In this case, dense bubble clouds are mixed down beneath the air entrainment zone, but there is sufficient time for them to disappear before succeeding breakers, allowing intermittent high-frequency propagation recharge the bubble field. The duration and shape of signal dropouts are then determined by the selective removal of bubbles by buoyancy and dissolution. In addition to turbulence created by the air entrainment process, a lower level of continuous background turbulence may be generated by interaction of residual currents with the wave boundary layer. Our observations illustrate the variable character of acoustic blocking by bubble clouds and serve as a basis for quantitative analysis of these effects with a 2D propagation model coupled to 2D models of bubble cloud evolution and background turbulence 相似文献
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文章介绍最新的第12代国际地磁参考场(IGRF-12)模型,选取5个具有代表性的日期,应用该模型提取和计算1997—2017年全球地磁正常场值并绘制平面分布图,研究结果表明:全球地磁正常场的总体结构较稳定,IGRF模型具有可靠性。以南海及其周边区域为例,应用IGFR-12模型,采用数据统计、图形展示和时间域对比的综合分析方式,分析其在不同时间段内地磁正常场的分布特征和变化规律,研究结果表明:研究区地磁正常场值总体较低,变化较缓慢,呈增长趋势;地磁正常场总体北高南低且变化较大,同一纬度西高东低且变化较小;地磁正常场变化量由大到小的时间段依次为2012—2017年、2007—2012年、1997—2002年、2002—2007年,与IGRF-12中不同模型的差异相对应;IGRF模型中确定场模型数据的稳定性较优,预测场模型的可靠性较高但需进一步校正。 相似文献
11.
Thermal property is one of the most important properties of light-emitting diode (LED). Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly having an influence on the light-emitting efficiency and the life-span of the device. In this paper, photoacoustic piezoelectric (PAPE) technique has been employed to investigate the thermal properties of polyvinyl alcohol (PVA) and silicon dioxide, which are the new and the traditional packaging materials in white LED, respectively. Firstly, the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials; secondly, the experimental system has been set up and adjusted by measuring the reference sample; thirdly, the thermal diffusivities of PVA and silicon dioxide are measured and analysed. The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED. 相似文献
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The impact of rain and spray on the ocean disturbs the sea surface and generates underwater ambient noise. The short scale roughness is influenced by impacting drops due to the momentum transfer. Radar and sonar signals are scattered by the short elements of the sea surface. Spray and rain impact change their characteristics, and consequently affect radar and sonar backscatter. In situ measurements of rain and spray impact are necessary to study their effects on the sea surface. Accurate sea measurements of rain momentum fluxes and drop size distributions are a complex problem, especially on buoys. A new measuring technique has been developed using hydrophones. Exposed to precipitation, these instruments are affected directly by the impact of rain. A drop falling on the hydrophone deforms its surface and is sensed by a piezoelectric transducer. The voltage output of the sensor is a rapidly decaying oscillation. The integral value of this signal is a measure of the drop momentum, and the drop size can be deduced. Laboratory studies of defined drops as well as field measurements of natural rain have shown that hydrophones can be used to determine drop momentums and drop size distributions. Based on simultaneous rain measurements by a Joss-Waldvogel Disdrometer and a hydrophone, an analytical function has been derived which relates drop size and hydrophone voltage output 相似文献
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水下加筋圆柱壳结构声散射特性研究 总被引：1，自引：0，他引：1
采用有限元/边界元(FEM/BEM)方法对水下加筋圆柱壳结构的声散射特性进行分析。考虑入射声场激发弹性结构振动产生二次辐射声场,总声场为入射场与散射场之和。基于Mindlin理论建立结构受迫振动的有限元模型,考虑入射声场为简谐激励,采用模态叠加法求出结构振动表面速度。根据声学边界元相关理论,利用有限元方法计算得出的弹性结构表面动力相应,可求出弹性结构的散射声场。研究结果表明,在同一波数下,不加筋结构后向散射强于加筋结构;加筋结构的散射指向性图案分叉较为明显;同种结构在波数增加的时候后向散射强度逐渐增大,前向散射强度逐渐减弱。 相似文献
16.
Li Yucheng Zhang Ningchuan
Professor Dalian University of Technology Dalian . Lecturere Delian University of Technology Dalian 《中国海洋工程》1994,(1)
- A composite pipeline is defined as a main big pipe composed of one or several small pipes. The flow behaviour around a submarine composite pipeline is more complicated than that around a single submarine pipeline. A series model test of composite pipelines in a wave-current coexisting field was conducted by the authors. Both in-line and lift forces were measured, and the resultant forces were also analyzed. The results of lift forces and resultant forces are reported in this paper. It is found that the lift force coefficients for composite pipelines are well related to the KC number. The lift force coefficients for an irregular wave-current coexisting field are smaller than those for a regular wave-current coexisting field. The frequency of lift force is usually twice the wave frequency or higher. The authors test indicates that the resultant forces are about 10 to 20 percent larger than in-line forces (horizontal forces). The effect of water depth is analyzed. Finally, the relationship between lift f 相似文献
17.
We discuss the results of analysis of published data and field and laboratory investigations aimed at the solution of the
problem of comparabilityof the results of detection of hydrogen sulfide in the Black Sea by spectrophotometric and iodometric
methods. We show that the reproducibility of the results of spectrophotometric analysis is higher than hat of the iodometric
method only in the case where the content of sulfide in a sample is less than 10–30 μMl−1. When larger concentrations are involved, the traditional iodometric analysis proves to be the most precise and reliable
method for the detection of hydrogen sulfide in the Black-Sea waters.
Translated by Peter V. Malyshev and Dmitry V. Malyshev 相似文献
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目前关于青弹涂鱼（Scartelaos virids）的研究多数集中在胚胎和仔鱼发育等个体生物学研究上。本文研究广东省湛江海域中青弹涂鱼在性周期内卵母细胞的发育时相及卵巢结构的周年变化，揭示卵巢发育和卵母细胞的组织学发育规律。结果表明：湛江海域的青弹涂鱼卵母细胞在3月进入大生长期发育阶段，4—6月为繁殖盛期，7—8月为繁殖末期，10月卵巢基本修整完毕，进入Ⅱ恢复期。青弹涂鱼属于一次性产卵类型。在小生长期，卵核的体积较核质的体积增大快，核质比大；大生长期，随着卵黄物质的积累，卵母细胞体积快速增加，核质比下降。最后讨论青弹涂鱼卵膜结构及其生理机能，围核透明层，繁殖习性等问题。 相似文献
19.
南沙暖水形成的动力和热动力过程的初步数值研究 总被引：1，自引：0，他引：1
利用一个简化的上混合层垂直积分模式,对南海南部“南沙暖水”形成的动力和热动力过程进行数值研究。结果表明：(1)在春季,南沙暖水的形成主要来自海面净热通量的贡献,而通过热平流、苏禄海或巽它陆架以南的暖水进入的贡献甚小;(2)在冬季,南沙群岛海区流场强度增大,热平流项的贡献大于或等于海面净热通量的贡献,海温的降低幅度也较其他深海区的要大。但由于该海区在此前的季节中初始温度场较高,因而使得该海区的海温仍保持较高的水平;(3)南沙暖水的形成和维持高温的机制是随着季节的变化而变化的。 相似文献
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Louisiana barrier islands, such as the chain surrounding the southeast region of the state, are experiencing rapid loss of
land area, shoreline erosion, and landward migration due to transgression and in-place drowning, and the landfall of several
major hurricanes in the last decade. Observations of migration rates and overall impacts to these barrier islands are poorly
understood since they do not respond in a traditional way, such as barrier rollover. This paper aims to verify how wave energy
and potential longshore sediment transport trends have influenced the recent evolution of the Chandeleur Islands, by direct
comparison with recent observations of migration and erosion trends. The Chandeleur Islands are characterized by a bidirectional
transport system, with material moving from the central arc to the flanks. The longshore sediment transport along the barrier
islands was calculated after propagation and transformation of waves to breaking (generated using observed winds), and through
the use of a common longshore sediment transport formula. Seasonal variations in wind climate produced changes in the transport
trends and gradients that agree with migration and rotation patterns observed for this barrier island system. Results suggest
that wind dominance produces seasonal oscillations that cause an imbalance in the resulting transport gradients that over
time are responsible for higher rates of transport in the northward direction. These results and data from other works verify
the evolutionary model previously suggested, and qualitatively confirm the recent observations in asymmetric shoreline erosion. 相似文献