Thematic accuracy of the NLCD 2001 land cover for the conterminous United States

The land-cover thematic accuracy of NLCD 2001 was assessed from a probability-sample of 15,000 pixels. Nationwide, NLCD 2001 overall Anderson Level II and Level I accuracies were 78.7% and 85.3%, respectively. By comparison, overall accuracies at Level II and Level I for the NLCD 1992 were 58% and 80%. Forest and cropland were two classes showing substantial improvements in accuracy in NLCD 2001 relative to NLCD 1992. NLCD 2001 forest and cropland user's accuracies were 87% and 82%, respectively, compared to 80% and 43% for NLCD 1992. Accuracy results are reported for 10 geographic regions of the United States, with regional overall accuracies ranging from 68% to 86% for Level II and from 79% to 91% at Level I. Geographic variation in class-specific accuracy was strongly associated with the phenomenon that regionally more abundant land-cover classes had higher accuracy. Accuracy estimates based on several definitions of agreement are reported to provide an indication of the potential impact of reference data error on accuracy. Drawing on our experience from two NLCD national accuracy assessments, we discuss the use of designs incorporating auxiliary data to more seamlessly quantify reference data quality as a means to further advance thematic map accuracy assessment.     

风化程度不均匀核岛环廊爆破施工实践

对核电站建设中的重点和难点问题——风化程度不均匀核岛环廊的开挖进行了探索,难点为上部边口的完整保护和环廊壁面开挖偏差的控制。福建某核电站建设的工程实践表明,预留适当保护层、分层开挖、炮孔的起爆次序、改进预裂爆破方法以及钻孔的质量是环廊开挖质量的保证。     

ANALYTICAL SOLUTION FOR LAMINAR-LAMINAR TWO-PHASE STRATIFIED FLOW IN CIRCULAR CONDUITS

Many attempts made in modelling stratified two-phase flow for predicting the operational flow characteristics (pressure drop, holdup, etc.) assume mostly plane interface between the phases. Obviously, the interaction between the stratified layers and the resulting flow characteristics may be significantly affected by the configuration of the interface. Moreover, complete analytical solutions for stratified flows in circular conduits a re not yet available even for laminar flows with plane interface and most of previous studies resort to average two-fluid modelling.

The present study presents analytical solutions for laminar stratified two-phase flows in pipes with plane and curved interfaces.     

Improved landscape sampling method for landscape character assessment

Landscape character assessment (LCA) is an effective tool for understanding people’s perceptions and preferences of landscape characteristics. Other than the assessment indicators and subjects, the reliability of photos as assessment objects is equally important for the LCA result. However, the commonly used onsite photos are mainly obtained at randomly selected locations by the researchers. We can neither know whether those photos represent the researchers’ own preferences, nor, to our best knowledge, can their reliability be tested scientifically. This method is also difficult to apply in large-scale geographical areas. To address these issues, we (1) propose an improved method including the protocols of photography and the sampling of photography locations, in which the fractal principle and stratified random sampling method were combined to minimize the effects of the researchers’ preferences and other factors; (2) apply the method to the Guanzhong region as an example, and obtain sampling photos and their geographical coordinates, which can be used as a data package for LCA; (3) use Fractalyse to test the sampled result and receive good validity. In conclusion, this study extends the methodological chain of the LCA and supports the application of LCA in large-scale regions.     

Transition between stratified and non-stratified horizontal oil-water flows. Part I: Stability analysis

The characteristics of waves at the interface of oil-water stratified flow and at the onset of entrainment, where drops of one phase appear into the other, were studied. Theoretically a model was developed based on Kelvin-Helmholtz instability to predict the critical wave amplitude at which the waves become unstable for a specific wavelength. According to the model, waves become unstable in stratified flow when at a particular wavelength they exceed a critical amplitude, which decreases with increasing wavelength until it acquires an almost constant value. The model predictions showed that for low-viscosity oils the maximum critical amplitude appears at slip velocity close to zero, while for high-viscosity oils, the maximum amplitude appears for water velocity higher than that of the oil. Also the required entrainment wavelength over the pipe diameter, calculated using literature experimental onset conditions, was found to decrease as the viscosity of the oil increased. Experimentally, wave characteristics before and at the onset of entrainment were investigated by measuring the instantaneous fluctuations of the interface between oil (5.5 mPa s, ) and water in a 0.038 m ID stainless steel horizontal pipe using a conductivity probe. The formation of drops and the onset of entrainment were identified using a high-speed video camera. At the onset of entrainment, wave characteristics were above the stability lines predicted by the model. Using a semi-empirical characteristic amplitude and wavelength in the model, it was possible to predict the onset of entrainment and transition from stratified to other mixed flow patterns reported in a number of studies.     

Computational methods for case-cohort studies

Computational methods, which can be implemented using standard Cox regression software, are given for fitting “exact” pseudolikehood estimates and robust and asymptotic variance estimators from case-cohort data. These methods are based on the computational approach of Therneau and Li [1999. Computing the Cox model for case cohort designs. Lifetime Data Anal. 5, 99-112] but will be less subject to small sample bias. Further, it is shown how to accommodate time-dependent covariates and estimate absolute risk. Extensions to stratified case-cohort sampled data are also provided. The methods are illustrated in analyses of case-cohort samples from a study of radiation exposure from fluoroscopy and breast cancer using SAS software.     

“组态王”在基于CAN总线的分布式控制系统中的应用

简述了基于CAN总线分布式控制系统的结构，并介绍了组态软件在现场总线控制系统中的作用，给出了组态王6．51组态软件开发监控程序的一般方法，重点分析了组态软件在基于CAN总线的分布式控制系统中的详细设计和开发应用的过程。     

Liquid layer characteristics in gas-liquid flow in slightly inclined pipes: Effect of non-ionic surfactant additives

The influence of non-ionic surfactant additives on the interfacial structure during both co-current gas-liquid upflow and downflow in slightly inclined pipes is investigated. Experiments are conducted in a 24 mm i.d. pipe for various gas-liquid flow rates and pipe inclination angles (β=±1° and ±3° from the horizontal position). Dilute aqueous solutions of the non-ionic surfactant Triton X-100 are employed, in order to study the effect of the additive on the flow pattern and the liquid layer characteristics (i.e. mean layer thickness, amplitude and frequency of the interfacial waves). In particular, the new data of the liquid layer characteristics indicate how the interfacial structure and the transition between the various flow regimes, during co-current gas-liquid flow in slightly inclined pipes, are affected by the addition of small amounts of the non-ionic surfactant.     

Denoising and despiking ADV velocity and salinity concentration data in turbulent stratified flows

Due to the presence of noise and spikes in velocity measurements of turbulent flow fields, understanding the flow pattern may be seriously affected by the spurious values for zones where certain flow behaviour is not necessarily expected. In a series of laboratory experiments the velocity data recorded, using Acoustic Doppler Velocity meters (ADVs), and the salinity measurements were noticeably noisy. In despiking and denoising the velocity data a linear correlation algorithm was established, which successfully lowered the noise levels and removed the spikes. For the assessment of the method, an autoregressive model was used to generate a clean velocity signal. The spikes were generated with a uniformly random time index and a Gaussian distributed value, where White Gaussian noise was added to this simulated signal. Assessment was also undertaken on the signals generated using a three-dimensional numerical model. To enhance the comprehension of the flow field, an interpolation method for producing the missing data has also been developed, which may be deployed to increase the sampling frequency, or to produce data for the spatial domain at locations which are not included in the measurements. For salinity a different strategy was applied where a moving average procedure was carried out, as the data did not suffer from spikes and exhibited almost a constant band of noisy fluctuations.     

修正的几何光学近似方法在平面分层媒质中的运用

利用修正的几何光学近似方法，在电小以电离层最大接收频率斜入射情况下，首次计算得到了包括抛物线层，三角形层在内的一种电离层平面分层模型的反射系数和透射系统统一的，精确的解析表达式。并对得到的结果进行了讨论。