Incipient motion conditions for single rock fragments in simulated rill flow     

D. Torri  J. Poesen 《地球表面变化过程与地形》1988,13(3):225-237

Laboratory experiments using simulated tilting rill channels with different bed roughnesses have been conducted to determine hydraulic conditions for incipient motion of single rock fragments lying on rill beds. These threshold conditions can be described by a modified Shields' entrainment parameter (θ_m) and relative depth (Z), adjusted for rill conditions. The negative relation found between θ_m and Z also fits steep (stream) channel data collected by other investigators. Plots of the classical Shields' entrainment parameter (θ) versus both relative depth and relative particle size also showed clear negative trends. Special care has been taken to avoid false relations that can arise between compound parameters. This occurs when the latter are not independent from each other because of their definitions.  相似文献   

地域分工与区位优势   总被引：7，自引：0，他引：7  

杨吾扬  梁进社 《地理学报》1987,(3)

地域分工和区位优势之间存在着内在的关联,它形成了区域开发或城市规划工作必须遵循的依据。本文由三部分组成。首先,对从亚当·斯密和大卫·李嘉图到俄林和巴朗斯基的地域分工学说作了历史性回顾;然后,提出了区域和城镇区位优势表现的完整体系,包括以下四对即有形和无形优势、绝对和相对优势、局部和全局优势以及空间和时间优势;文章结尾探讨了地域分异的外在因素和内在机制问题。  相似文献   

应用特征参数GU、FU、B处理区域伽玛能谱资料的效果初探   总被引：2，自引：0，他引：2  

张云宜 《铀矿地质》1986,(4)

从U、Th元素的地球化学特性出发,探讨了利用“古铀丰度”(Gu)、“活化铀”(Fu)和“相对变迂系数”(B)等特征参数处理区域伽玛能谱测量资料的可能性和实际应用效果。文中阐述了选用的能谱特征参数的理论基础及地球化学意义。同时,利用这些特征参数对成矿带上所作的区域地面伽玛能谱测量资料进行了处理。结果表明,利用这些参数在确定区域铀源体、研究该区铀元素活化运移和沉积富集规律、探讨该区控制铀矿化形成的主要地质因素以及预测区内铀矿找矿远景地段等方面都取得了较满意的效果,是一种值得进一步探索和完善的伽玛能谱资料处理方法。  相似文献   

滇西和北京区域重力场演化及其与地震关系的探讨   总被引：28，自引：0，他引：28  

孙少安  项爱民  李辉 《地震》1999,19(1):97-106

在总结,借鉴已有成果的基础上,采用新的区域重力场相对基准和图示技术,对滇西和北京区域重力网近十年来的观测资料进行了重新计算和分析,通过研究区域重力场空间分布变化与中强地震的关系,提出了适于滇西和北京区域重力网研究重力场空间分布变化的前兆异常指标,并对滇西和北京重力网区及周边地区未来的地震趋势进行了估计,所得结论可供分析同类区域重力网观测资料参考使用。  相似文献   

YRD型高温高压程控岩石热导仪          下载免费PDF全文

赵永信  伍向阳 《地球物理学报》1996,39(Z1):276-282

基于环形热源与点热源传热方程具有相同解的原理，研制一种非稳态相对测量的高温高压岩石热导仪．论述了仪器的结构、测量原理和主要设计思想，介绍了技术指标、数据采集与处理程序．测试结果重复率优于±３％，准确度优于±５％，工作温度为室温至１８０℃．工作压力为常压至２２ＭＰａ．  相似文献   

南极冰盖部分消融对海平面的影响   总被引：1，自引：0，他引：1  

汪汉胜  张赤军 《测绘学报》1996,(4)

本文假设地球具球对称、完全弹性和各向同性，推导了冰融相对海平面变化方程，采用汪汉胜等（１９９６）根据ＰＲＥＭ（１９８１）模型计算的地表弹性负荷勒夫数，估算了在今后５０年内，当南极冰盖消融１０米时所产生的全球海平面变化  相似文献   

APS解析测图仪的开发与应用     

黄小波 《测绘学院学报》1995,(3)

本文介绍了新开发的在ＡＰＳ解析测图仪上进行的自动定向、ＤＴＭ采集、近景摄影测量相对控制条件下的绝对定向等成果。  相似文献   

Smoothing GPS carrier phase double differences using inertial measurements for high performance applications     

Jeff Dickman  Chris Bartone 《GPS Solutions》2008,12(2):119-133

This paper will describe an enhancement to the GPS double difference carrier phase measurements on a single airborne platform by smoothing them with inertial measurements while preserving the dynamic bandwidth. This enhancement will reduce the impact of carrier phase multipath and carrier phase noise on baseline determination between multiple antennas on an aircraft when in flight. This type of measurement system has numerous applications where platform pointing and relative body motion must be determined at the mm-level for applications such as sensor stabilization, Synthetic Aperture Radar, long range RADAR (i.e. angle-of-arrival measurements). Lower noise levels (mm-level and below) enable more performance to the stabilized system such as increased aperture for longer range, operation at higher frequencies, and more image resolution. The focus of this paper will be on a technique to provide this enhanced performance for these various applications using the available navigation systems. Additionally, this type of smoothing can effectively remove the additional noise induced by carrier phase measurement differencing. The noise level of a double or triple difference can be reduced below that of the raw measurement. A complimentary synthesized double difference quantity with ultra-low-noise characteristics will be used to smooth the GPS carrier phase double difference measurements without losing dynamic bandwidth since it follows the airborne dynamics. Flight test data will be presented to demonstrate the performance improvement in the midst of aircraft dynamics. Results will show that the noise reduction follows the theoretical prediction.  相似文献   

2013—2018年大连中心城区臭氧时空变化及其影响因子分析     

马瑞丰  许敬红  严良政 《气象与环境学报》2022,38(3):75-84

基于2013—2018年大连中心城区O_(3)监测数据和气象数据,分析了该区O_(3)污染时空变化特征及气象要素对O_(3)污染的影响。结果表明:2013—2018年大连中心城区O_(3)已经逐渐成为最主要的大气污染物之一。O_(3)年平均浓度由2013年的66.66μg·m^(-3)上升至2018年的101.62μg·m^(-3)。秋季和夏季是大连O_(3)浓度较高的季节,其次是冬季和春季。O_(3)最高浓度月份主要为5月、6月及9月。O_(3)浓度日变化呈明显的单峰状,从上午08时开始增加,在下午14—16时达到最高,白天浓度高于夜晚。O_(3)污染物在2013—2017年从大连中心城区的西南向东北扩散。大连中心城区O_(3)与其他5种大气污染物均存在不同程度的负相关,与气温呈显著正相关,与相对湿度、气压及风速相关性较差。有利于大连O_(3)污染天气的气象条件主要为高气温(>30℃)、低湿度(≤80%)、低风速(1.5—2.0 m·s^(-1))、北风风向和长日照时间。高污染日的出现可能是受高温天气与本地逐渐增加的排放物共同影响。  相似文献   

Sensitivity analysis of planetary boundary layer schemes using the WRF model in Northern Colombia during 2016 dry season     

《Dynamics of Atmospheres and Oceans》2021

This study conducted meteorological simulations in northern Colombia by analyzing different planetary boundary layer (PBL) schemes available in the numerical Weather Research and Forecasting (WRF) model. The study area included three nested domains with horizontal resolutions of 18 km, 6 km, and 2 km, with 38 vertical levels. The evolution and structure of the PBL were analyzed during the driest months (March, April, and May 2016) and in regions with the highest particulate matter concentrations. Sensitivity analysis of the WRF model was performed with two local and two non-local PBL schemes. The results were validated using observations of the surface air temperature, relative humidity, and surface wind speed collected from three meteorological stations in the area. The PBL heights were experimentally determined using radiosonde data provided by a station located in the center of the study area. Variations in PBL heights were estimated using linear regression methods and minimization of statistical errors for the bulk Richardson number, as well as analysis of vertical temperature and wind profiles. The WRF model reliably reproduced the daily values and diurnal cycles of temperature, relative humidity, and wind speed within the PBL and accounted for the influence of topography and sea breezes. Horizontal heat advection dominates the upwelling of air masses when sea breezes are active. The onshore wind direction starts to change from east to northwest, implying a decay in the land breeze regime. All schemes overestimate the mixing height and tend to underestimate surface air temperature values at night. All show wetter conditions and underestimate wind speed. Although the non-local Yonsei University (YSU) scheme shows the best performance, it also shows the largest sources of errors when determining the behavior of the surface layer during stable conditions. Relative humidity and wind speed estimates provided by the local Mellor‐Yamada‐Nakanishi‐Niino (MYNN) scheme were closer to those recorded at the meteorological stations.  相似文献