Lookback time as a test for f(R) gravity in the Palatini approach     

Zhong-Xu Zhai  Wen-Biao Liu 《中国天文和天体物理学报》2011,(11)

We use the recently released data of lookback time (LT)-redshift relation, the cosmic microwave background shift parameter and the baryon acoustic oscillation measurements to constrain cosmological parameters of f (R) gravity in the Palatini formalism by considering the f (R) form of type (a) f (R) = R β/Rn and (b) f (R) = R + α ln R β. Under the assumption of a Friedmann-Robertson-Walker universe, we achieved the best fitting results of the free parameters (Ωm0, n) for (a) and (Ωm0, α) for (b). We find tha...  相似文献   

中尺度模式和新一代天气雷达产品识别云降水方法     

胡雯  黄勇  翟菁 《气象科技》2007,35(4):470-473

介绍一种结合中尺度模式产品和新一代天气雷达产品的云降水识别方法。首先利用中尺度模式(MM5)产品计算得到降水潜力区识别因子,分析降水潜力区。进一步结合新一代天气雷达产品,分析潜力区内云团的降水参数,确定有利于降水的云团。分析结果表明,潜力综合指标对未来可能出现的具有大量水资源的对流性系统具有指示意义,可以用于分析对流性系统的降水潜力;另一方面雷达降水等级是对实际对流云团水资源等级的划分。综合这两者进行降水潜力的分析判别,可以增强降水云的识别能力。  相似文献   

Observations of the dynamical response of a coastal embayment to wind, tide and buoyancy forcing     

Li Zhai  Jinyu Sheng  Richard J. Greatbatch 《Continental Shelf Research》2007,27(20):2534-2555

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Cracking mechanisms during galena mineralization in a sandstone-hosted lead–zinc ore deposit: case study of the Jinding giant sulfide deposit, Yunnan, SW China     

Junlai Liu  Anjian Wang  Haoran Xia  Yunfeng Zhai  Lan Gao  Qunye Xiu  Zhaochong Zhang  Zhidan Zhao  Dianhua Cao 《Mineralium Deposita》2010,45(6):567-582

There are two types of lead–zinc ore bodies, i.e., sandstone-hosted ores (SHO) and limestone-hosted ores (LHO), in the Jinding giant sulfide deposit, Yunnan, SW China. Structural analysis suggests that thrust faults and dome structures are the major structural elements controlling lead–zinc mineralization. The two types of ore bodies are preserved in two thrust sheets in a three-layered structural profile in the framework of the Jinding dome structure. The SHO forms the cap of the dome and LHO bodies are concentrated beneath the SHO cap in the central part of the dome. Quartz, feldspar and calcite, and sphalerite, pyrite, and galena are the dominant mineral components in the sandstone-hosted lead–zinc ores. Quartz and feldspar occur as detrital clasts and are cemented by diagenetic calcite and epigenetic sulfides. The sulfide paragenetic sequence during SHO mineralization is from early pyrite to galena and late sphalerite. Galena occurs mostly in two types of cracks, i.e., crescent-style grain boundary cracks along quartz–pyrite, or rarely along pyrite–pyrite boundaries, and intragranular radial cracks in early pyrite grains surrounding quartz clasts. The radial cracks are more or less perpendicular to the quartz–pyrite grain boundaries and do not show any overall (whole rock) orientation pattern. Their distribution, morphological characteristics, and geometrical relationships with quartz and pyrite grains suggest the predominant role of grain-scale cracking. Thermal expansion cracking is one of the most important mechanisms for the generation of open spaces during galena mineralization. Cracking due to heating or cooling by infiltrating fluids resulted from upwelling fluid phases through fluid passes connecting the SHO and LHO bodies, provided significant spaces for crystallization of galena. The differences in coefficients of thermal expansion between pyrite and quartz led to a difference in volume changes between quartz grains and pyrite grains surrounding them and contributed to cracking of the pyrite grains when temperature changed. Combined thermal expansion and elastic mismatch due to heating and subsequent cooling resulted in the radial and crescent cracking in the pyrite grains and along the quartz–pyrite grain boundaries.  相似文献   

Unveiling controls of the latitudinal gradient of surface pCO₂ in the Kuroshio Extension and its recirculation regions（northwestern North Pacific） in late spring     

Chenglong Li  Weidong Zhai  Di Qi 《海洋学报(英文版)》2022,41(5):110-123

In the northwestern North Pacific, annual net air-sea CO₂ flux is greatest in the Kuroshio Extension（KE） zone,owing to its low annual mean partial pressure of CO₂（pCO₂）, and it decreases southward across the basin. To quantify the influences of factors controlling the latitudinal gradient in CO₂ uptake, sea surface pCO₂ and related parameters were investigated in late spring of 2018 in a study spanning the KE, Kuroshio Recirculation（KR）, and...  相似文献   

Radiative forcing over China due to albedo change caused by land cover change during 1990–2010     

Jun Zhai  Ronggao Liu  Jiyuan Liu  Guosong Zhao  Lin Huang 《地理学报(英文版)》2014,24(5):789-801

Land cover change affects surface radiation budget and energy balance by chang- ing surface albedo and further impacts the regional and global climate. In this article, high spatial and temporal resolution satellite products were used to analyze the driving mechanism for surface albedo change caused by land cover change during 1990-2010. In addition, the annual-scale radiative forcing caused by surface albedo changes in China＇s 50 ecological regions were calculated to reveal the biophysical mechanisms of land cover change affecting climate change at regional scale. Our results showed that the national land cover changes were mainly caused by land reclamation, grassland desertification and urbanization in past 20 years, which were almost induced by anthropogenic activities. Grassland and forest area decreased by 0.60% and 0.11%, respectively. The area of urban and farmland increased by 0.60% and 0.19%, respectively. The mean radiative forcing caused by land cover changes during 1990-2010 was 0.062 W/m2 in China, indicating a warming climate effect. However, spatial heterogeneity of radiative forcing was huge among different ecological regions. Farmland conversing to urban construction land, the main type of land cover change for the urban and suburban agricultural ecological region in Beijing-Tianjin-Tangshan region, caused an albedo reduction by 0.00456 and a maximum positive radiative forcing of 0.863 WIm2, which was presented as warming climate effects. Grassland and forest conversing to farmland, the main type of land cover change for the temperate humid agricultural and wetland ecological region in Sanjiang Plain, caused an albedo increase by 0.00152 and a maximum negative radiative forcing of 0.184 W/m2, implying cooling climate effects.  相似文献   

Cold–wet spells in mainland China during 1951–2011     

Xi Qian  Qilong Miao  Panmao Zhai  Yang Chen 《Natural Hazards》2014,74(2):931-946

Two types of persistent extreme weather events, the cold–wet spell (CWS) and the persistent wet-freezing event (PWFE), are defined by considering the persistence of both extreme low temperature (ELT) and precipitation. Regional CWS and PWFE are identified based on temporal persistence and spatial contiguity of single-station-based CWS event and PWFE, respectively. Relevant factors are further discussed to reveal the features of spatial distribution and temporal variability of such events. The results indicate that: (1) station-based CWSs are mostly observed in southern China, especially in eastern part of southwest China and south China. PWFEs are relatively frequently observed immediate south of middle reach of the Yangtze River. Both CWS and PWFE of longer duration are frequently observed in the northern part of the Yunnan–Guizhou Plateau. Further analyses indicate that the occurrence of these events in southern China is positively related to elevation. (2) A total of 48 regional CWSs and 21 regional PWFEs are identified during cold season over 1951–2011 in China. The long-lasting ELT and rainy (snowy)/freezing condition render the event in southern China in 2008, the most severe one in the last five decades. (3) Precipitation is the limitation condition for the occurrence of CWS and PWFE in northern China, while ELT is the dominant factor for CWS and PWFE in southern China.  相似文献   

短期增温和降水减少对沙质草地土壤微生物量碳氮和酶活性的影响     

王怀海  黄文达  何远政  牛亚毅  朱远忠 《中国沙漠》2022,42(3):274-281

通过模拟气候变化,探究短期增温和降水减少对沙质草地土壤微生物量碳氮及酶活性的影响,揭示沙质草地土壤微生物量碳氮和酶活性对短期气候变化的响应规律。结果表明：（1）短期增温和降水减少对土壤微生物量碳氮和酶活性均产生显著影响。（2）在自然温度下,与自然降水相比,降水减少40%时土壤微生物量碳（MBC）和微生物氮（MBN）含量最高,增幅分别为87.9%和98.8%;降水减少60%时土壤碱性蛋白酶（S-ALPT）活性最低,降幅达32.8%。（3）在增温条件下,与自然降水相比,降水减少40%时土壤MBC和MBN含量最低,降幅分别为25.67%和48.16%,土壤脲酶（S-UE）活性最高,增幅20.42%。（4）土壤pH与3种土壤酶活性正相关,与土壤微生物量碳氮负相关。土壤微生物量碳氮与土壤纤维素酶（S-CL）活性负相关,与S-UE、S-ALPT活性正相关。  相似文献   

塔中1井储层段岩石学特征及成岩作用     

翟永红  王泽中  王正允  王方平 《地球科学与环境学报》1994,(3)

本文对塔中１井储层段进行了岩芯、薄片、阴极发光等观察和分析，划分出了角砾白云岩、残余颗粒白云岩和晶粒白云岩３种岩石类型，识别出了白云石化、硅化、方解石化、重晶石化、萤石化、黄铁矿化、自生粘土矿物化以及溶解、压溶等成岩作用类型；归纳出塔中１井储层段经历了３个成岩阶段、４种成岩环境的改造和叠加，并在物性测定的基础上给出３个岩性段的储集条件．  相似文献   

Interactions of aquaculture and waste disposal in the coastal zone     

Zhai Xuemei  S. J. Hawkins 《中国海洋大学学报(英文版)》2002,1(1):8-12

Throughout the world, the coastal zones of many countries are used increasingly for aquaculture in addition to other activities such as waste disposal. These activities can cause environmental problems and health problems where they overlap. The interaction between aquaculture and waste disposal, and their relationship with eutrophication are the subjects of this paper. Sewage discharge without adequate dispersion can lead to nutrient elevation and hence eutrophication which has clearly negative effects on aquaculture with the potential for toxic blooms. Blooms may be either toxic or anoxia-causing through the decay process or simply clog the gills of filter-feeding animals in some cases. With the development of aquaculture, especially intensive aquaculture, many environmental problems appeared, and have resulted in eutrophication in some areas. Eutrophication may destroy the health of whole ecosystem which is important for sustainable aquaculture. Sewage discharge may also cause serious public health problems. Filter-feeding shellfish growing in sewage-polluted waters accumulate micro-organims, including human pathogenic bacteria and viruses, and heavy metal ion, presenting a significant health risk. Some farmed animals may also accumulate heavy metals from sewage. Bivalves growing in areas affected by toxic algae blooms may accumulate toxins (such as PSP, DSP) which can be harmful to human beings.  相似文献