增强型AlGaN/GaN高电子迁移率晶体管高温退火研究     

王冲  全思  马晓华  郝跃  张进城  毛维 《海洋学报》2010,32(10):7333-7337

深入研究了两种增强型AlGaN/GaN高电子迁移率晶体管(HEMT)高温退火前后的直流特性变化.槽栅增强型AlGaN/GaN HEMT在500 ℃ N₂中退火5 min后,阈值电压由0.12 V正向移动到0.57 V,器件Schottky反向栅漏电流减小一个数量级.F注入增强型AlGaN/GaN HEMT在 400 ℃ N₂中退火2 min后,器件阈值电压由0.23 V负向移动到-0.69 V,栅泄漏电流明显增大.槽栅增强型器件退火过程中Schottky有效势垒  相似文献   

Improving performances of ITO/GaP contact on AlGaInP light-emitting diodes     

李春伟  朱彦旭  沈光地  张勇辉  秦园  高伟  蒋文静  邹德恕 《海洋学报(英文版)》2010,29(9)

In this paper AlGaInP light emitting diodes with different types of electrodes: Au/Zn/Au-ITO Au/Ti-ITO Au/Ge/Ni-ITO and Au-ITO are fabricated. The photoelectricity properties of those LEDs are studied. The results show that the Au/Zn/Au electrode greatly improves the performance of LEDs compared with the other electrodes. Because the Au/Zn/Au electrode not only forms a good Ohmic contact with indium tin oxide (ITO), but also reduces the specific contact resistances between ITO and GaP, which are 1.273×10^-6 Ω · cm² and 1.743×10^-3 Ω ·cm² between Au/Zn/Au-ITO and ITO-GaP respectively. Furthermore, the textured Zn/Au-ITO/Zn electrode is designed to improve the performances of LEDs, reduce the forward-voltage of the LED from 1.93 to 1.88 V, and increase the luminous intensity of the LEDs from 126 to 134 mcd when driven at 20 mA.  相似文献   

日本海西南陆坡全新世对马暖流演化的沉积学和地球化学记录     

徐兆凯  崔镇勇  林东日  李铁刚  李安春 《海洋地质与第四纪地质》2010,(1)

对日本海西南陆坡对马暖流主流轴下方高沉积速率沉积物柱状样,进行了沉积学和地球化学系统研究,以探讨全新世以来对马暖流在研究区的形成与演化,并得出了与附近地区古海洋学方法非常相近的结果,从而为今后研究区的对马暖流演化研究提供了沉积学和地球化学指标。据此,该柱状样中所记录的对马暖流演化可划分为5个主要阶段。全新世初期(9.6kaBP),对马暖流开始进入日本海,其强度较弱,同时,伴随着富营养东海沿岸水的影响,海底环境由还原性向氧化性转变;6.5kaBP时,对马暖流控制下的日本海南部现代对流模式最终建立起来,东海沿岸水的影响基本消失,随后,对马暖流明显减弱;3.0kaBP时,对马暖流再次增强并基本达到现在水平,且在随后的3ka里保持总体稳定,期间在2.0～0.7kaBP存在一次较弱的减弱过程。  相似文献   

The effects of wastewater discharges on the functioning of a small temporarily open/closed estuary     

Robynne A. Lawrie  Derek D. Stretch  Renzo Perissinotto 《Estuarine, Coastal and Shelf Science》2010

Wastewater discharges affect the functioning of small temporarily open/closed estuaries (TOCEs) through two main mechanisms: (1) they can significantly change the water balance by altering the quantity of water inflows, and (2) they can significantly change the nutrient balance and hence the water quality. This study investigated the bio-physical responses of a typical, small TOCE on the east coast of South Africa, the Mhlanga Estuary. This estuary receives significant inflows of treated effluent from upstream wastewater treatment works. Water and nutrient budgets were used together with biological sampling to investigate changes in the functioning of the system. The increase in inflows due to the effluent discharges has significantly increased the mouth breaching frequency. Furthermore, when the mouth closes, the accumulation of nutrients leads to eutrophication and algal blooms. A grey water index, namely the proportion of effluent in the estuary and an indicator of the additional nutrient inputs into the estuary, reached high values (?50%) during low flow regimes and when the mouth was closed. In these hyper-eutrophic conditions (DIN and DIP concentrations up to 457 μM and 100 μM respectively), field measurements showed that algal blooms occurred within about 14 days following closure of the mouth (chlorophyll-a concentrations up to 375 mg chl-a m⁻³). Water and nutrient balance simulations for alternative scenarios suggest that further increases in wastewater discharges would result in more frequent breaching events and longer open mouth conditions, but the occurrence of hyper-eutrophic conditions would initially intensify despite more frequent openings. The study indicates how water and nutrient balance simulations can be used in the planning and impact assessment of wastewater treatment facilities.  相似文献   

聚合物驱组合段塞分注实验研究     

李宜强  林丽华  梁双庆 《海洋地质译丛》2010,(1):85-89

萨尔图油田南二区东部140号断层以东地区葡11—4油层，以多段多韵律和正韵律沉积为主，平均孔隙度30．0％，平均空气渗透率1980×10^-3μm2。水驱结束时该油层平均含水92％，采出程度39．5％。计划对该区块实施聚合物驱开采。以往经验认为，组合段塞调整注聚技术能够有效改善流度控制作用。然而对组合注入情况下如何进一步提高驱油效果、注入井分注时机、层段注入强度对开发效果有何影响却很少探讨。通过室内驱油实验，在聚驱的组合段塞注入不同时机（水驱空白阶段、含水下降阶段、含水稳定阶段、含水回升阶段）下调整注入强度实施分注以及在含水回升分注基础上进一步调整注入强度，同时对比不分注实验，评价各方案驱油效果。实验表明：不实施分注时聚驱采收率在水驱基础上提高了19．07个百分点，而组合段塞注入时实施分注均能够在不分注基础上进一步提高驱油效果；空白水驱时实施分注采收率提高幅度最大，为26．55个百分点；随着分注时机的滞后采收率提高幅度增加值依次递减，分注时机越早越好。  相似文献   

Changes in survivorship,behavior, and morphology in native soft‐shell clams induced by invasive green crab predators     

W. Lindsay Whitlow 《Marine Ecology》2010,31(3):418-430

Many studies on invasive species show reduced native densities, but few studies measure trait‐mediated effects as mechanisms for changes in native growth rates and population dynamics. Where native prey face invasive predators, mechanisms for phenotypic change include selective predation, or induced behavioral or morphological plasticity. Invasive green crabs, Carcinus maenas, have contributed to declines in native soft‐shell clams, Mya arenaria, in coastal New England, USA. We tested the hypothesis that clam ability to detect chemical cues from predators or damaged conspecifics would induce greater burrowing depth as a refuge from invasive crabs, and greater burrowing would require increased siphon growth. To determine how crab predation affected clam survivorship and phenotypic traits in the field, clams in exclosure, open, and crab enclosure plots were compared. Crab predation reduced clam density, and surviving clams were deeper and larger, with longer siphons. To determine whether the mechanism for these results was selective predation or induced plasticity, phenotypes were compared between clams exposed to chemical cues from crab predation and clams exposed to seawater in laboratory and field experiments. In response to crab predation cues, clams burrowed deeper, with longer siphons and greater siphon mass. Overall, crab predation removed clams with shorter siphons at shallow depths, and crab predation cues induced greater burrowing depths and longer siphons. Longer siphons and greater siphon mass of deeper clams suggests clams may allocate energy to siphon growth in response to crabs. By determining native behavior and morphological changes in response to an invasive predator, this study adds to our understanding of mechanisms for invasive impacts and illustrates the utility of measuring trait‐mediated effects to investigate predator–prey dynamics.  相似文献   

Application of a Bayesian model to infer the contribution of coalbed natural gas produced water to the Powder River,Wyoming and Montana          下载免费PDF全文

Jason M. Mailloux  Kiona Ogle  Carol D. Frost 《水文研究》2014,28(4):2361-2381

The Powder River Basin (PRB) of Wyoming and Montana contains significant coal and coal bed natural gas (CBNG) resources. CBNG extraction requires the production of large volumes of water, much of which is discharged into existing drainages. Compared to surface waters, the CBNG produced water is high in sodium relative to calcium and magnesium, elevating the sodium adsorption ratio (SAR). To mitigate the possible impact this produced water may have on the quality of surface water used for irrigation, the State of Montana passed water anti‐degradation legislation, which could affect CBNG production in Wyoming. In this study, we sought to determine the proportion of CBNG produced water discharged to tributaries that reaches the Powder River by implementing a four end‐member mixing model within a Bayesian statistical framework. The model accounts for the ⁸⁷Sr/⁸⁶Sr, δ¹³C_DIC, [Sr] and [DIC] of CBNG produced water and surface water interacting with the three primary lithologies exposed in the PRB. The model estimates the relative contribution of the end members to the river water, while incorporating uncertainty associated with measurement and process error. Model results confirm that both of the tributaries associated with high CBNG activity are mostly composed of CBNG produced water (70–100%). The model indicates that up to 50% of the Powder River is composed of CBNG produced water downstream from the CBNG tributaries, decreasing with distance by dilution from non‐CBNG impacted tributaries from the point sources to ~10–20% at the Montana border. This amount of CBNG produced water does not significantly affect the SAR or electrical conductivity of the Powder River in Montana. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Temporal patterns and controls on runoff magnitude and solution chemistry of urban catchments in the semiarid southwestern United States     

Erika L. Gallo  Paul D. Brooks  Kathleen A. Lohse  Jean E. T. McLain 《水文研究》2013,27(7):995-1010

Urban expansion and the scarcity of water supplies in arid and semiarid regions have increased the importance of urban runoff to localized water resources. However, urban catchment responses to precipitation are poorly understood in semiarid regions where intense rainfall often results in large runoff events during the short summer monsoon season. To evaluate how urban runoff quantity and quality respond to rainfall magnitude and timing, we collected stream stage data and runoff samples throughout the 2007 and 2008 summer monsoons from four ephemeral drainages in Tucson, Arizona. Antecedent rainfall explained 20% to 30% of discharge (mm) and runoff ratio in the least impervious (22%) catchment but was not statistically related to hydrologic responses at more impervious sites. Regression models indicated that rainfall depth, imperviousness and their combined effect control discharge and runoff ratios (p < 0.01, r² = 0.91 and 0.75, respectively). In contrast, runoff quality did not vary with imperviousness or catchment size. Rainfall depth and duration, time since antecedent rainfall and event and cumulative discharge controlled runoff hydrochemistry and resulted in five specific solute response patterns: (i) strong event and seasonal solute mobilization (solute flush), (ii) event chemostasis and strong seasonal flush, (iii) event chemostasis and weak seasonal flush, (iv) event and seasonal chemostasis and (v) late seasonal flush. Our results indicate that hydrologic responses of semiarid catchments are controlled by rainfall partitioning at the event scale, whereas wetting magnitude, frequency and timing alter solute stores readily available for transport and control temporal runoff quality. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

A mixing-length model for predicting vertical velocity distribution in flows through emergent vegetation     

PAWEŁ M. ROWIŃSKI  JANUSZ KUBRAK 《水文科学杂志》2013,58(6):893-904

Abstract

The vertical profiles of streamwise velocities are computed on flood plains vegetated with trees. The calculations were made based on a newly developed one-dimensional model, taking into account the relevant forces acting on the volumetric element surrounding the considered vegetation elements. A modified mixing length concept was used in the model. An important by-product of the model is the method for evaluating the friction velocities, and consequently bed shear stresses, in a vegetated channel. The model results were compared with the relevant experimental results obtained in a laboratory flume in which flood plains were covered by simulated vegetation.  相似文献   

Energy balance and evaporation loss of an agricultural reservoir in a semi‐arid climate (south‐eastern Spain)     

B. Gallego‐Elvira  A. Baille  B. Martín‐Górriz  V. Martínez‐Álvarez 《水文研究》2010,24(6):758-766

A typical agricultural water reservoir (AWR) of 2400 m² area and 5 m depth, located in a semi‐arid area (southern Spain), was surveyed on a daily basis for 1 year. The annual evaporation flux was 102·7 W m^?2, equivalent to an evaporated water depth of 1310 mm year^?1. The heat storage rate G exhibited a clear annual cycle with a peak gain in April (G ～ 45 W m^?2) and a peak loss in November (G ～ 40 W m^?2), leading to a marked annual hysteretic trend when evaporation (λE) was related to net radiation (R_n). λE was strongly correlated with the available energy A, representing 91% of the annual AWR energy loss. The sensible heat flux H accounted for the remaining 9%, leading to an annual Bowen ratio in the order of 0·10. The equilibrium and advective evaporation terms of the Penman formula represented 76 and 24%, respectively, of the total evaporation, corresponding to a annual value of the Priestley–Taylor (P–T) coefficient (α) of 1·32. The P–T coefficient presented a clear seasonal pattern, with a minimum of 1·23 (July) and a maximum of 1·65 (December), indicating that, during periods of limited available energy, AWR evaporation increased above the potential evaporation as a result of the advection process. Overall, the results stressed that accurate prediction of monthly evaporation by means of the P–T formula requires accounting for both the annual cycle of storage and the advective component. Some alternative approaches to estimating R_n, G and α are proposed and discussed. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献