Comparison of vegetation phenology in the western USA determined from reflected GPS microwave signals and NDVI

The normalized microwave reflection index (NMRI) is a measure of multipath scattering calculated daily from continuously operating GPS sites. GPS satellites transmit L-band microwave signals, and thus NMRI is sensitive to the amount of water in vegetation, not plant greenness or dry biomass. The sensing footprint is approximately 1000 m², although reflections from a distance of hundreds of metres are important at some sites. NMRI exhibits clear seasonal variations that are linked to the changes in vegetation water content that accompany plant growth and senescence. In this paper, NMRI and the normalized difference vegetation index (NDVI) are compared for the period 2008–2012. NMRI data are derived from 184 GPS sites in the western USA. NDVI data are from the 250 m, 16-day pixel containing each GPS station. Amplitude of the annual growth cycle and correlation between NMRI and NDVI are estimated, with and without lags. Phenology metrics are calculated from both indices (i.e. the start of the growing season, timing of peak growth, and season length).

NMRI and NDVI are correlated at most sites, but the degree of correlation varies regionally. Correlation is lowest in California and coastal regions (R = 0.25), where NDVI increases earlier in the spring than NMRI. It is highest for mountain and prairie sites (R = 0.66 and 0.73, respectively). Allowing for a lag between NMRI and NDVI greatly increases the correlation. The lag that yields the greatest correlation is nearly 30 days for the California sites (R = 0.71 with lag), but only 10 days for mountain and prairie sites (R = 0.78 and 0.85 with lag). There are clear differences in phenology metrics extracted from NMRI and NDVI that are consistent with the correlation-lag analysis. Using NMRI, there is a later start to the season, later peak day of the year, and shorter season length. The greatest differences are in California where NDVI start of the season is nearly 60 days earlier than that calculated from NMRI. These data suggest that green-up precedes increases in vegetation water content, with the duration of offset varying regionally. This study is the first to compare GPS-derived microwave reflectance data with NDVI at multiple sites, and highlights both opportunities and limitations offered by NMRI data.     

Atresia of the right atrioventricular orifice

The results are reported of a study of 83 necropsied hearts with atresia of the right atrioventricular orifice. It is emphasised that right atrial or atrioventricular orificial atresia is a better term to describe this anomaly than "tricuspid atresia". Use of the latter term can be confusing when the morphologically tricuspid valve is located beneath the left atrium. It is accepted that the definition employed may include cases in which the mitral valve may be atretic, blocking normal exit from the right atrium, but it is argued that such cases would present clinically as "tricuspid atresia" and therefore are correctly designated as right atrial orificial atresia. The results show that the majority of hearts with right atrial orificial atresia have the ventricular morphology of primitive ventricle, most with, but a few without an outlet chamber. However, in a minority of hearts an imperforate membrane interposes between the right atrium and a formed but hypoplastic right ventricle. In two of the hearts, the imperforate membrane showed features of Ebstein's malformation. The hearts could be further subdivided according to the ventriculoarterial connection. Most had normally connected arteries (66 of 83), and all but 2 also had normal relations between the arteries; in these 2 hearts there was "anatomically corrected malposition". Twelve hearts showed transposition, one had double-outlet outlet chamber, and another persistent truncus arteriosus. The remaining 3 hearts, all without outlet chamber, had by definition a double outlet connection. A segmental approach provides the best way of classifying this anomaly, and an embryological explanation is offered for the variations in anatomy observed.     

Moving target tracking using symbolic registration

This correspondence describes a moving target tracking (MTT) algorithm that performs image registration and motion analysis between pairs of images from a passive sensor. Unlike previously reported moving target indicators that operate at the signal level, the registration and motion analysis in the MTT is totally performed at a symbolic level. The operation of the MTT is demonstrated by simulation results obtained from applications of the algorithm to infrared images.     

Investigation of the anisotropic confinement-dependent brittleness of a Utah coal

Changes of failure mechanism with increasing confinement,from extensional to shear-dominated failure,are widely observed in the rupture of intact specimens at t...     

Similarity queries: their conceptual evaluation, transformations, and processing

Many application scenarios can significantly benefit from the identification and processing of similarities in the data. Even though some work has been done to extend the semantics of some operators, for example join and selection, to be aware of data similarities, there has not been much study on the role and implementation of similarity-aware operations as first-class database operators. Furthermore, very little work has addressed the problem of evaluating and optimizing queries that combine several similarity operations. The focus of this paper is the study of similarity queries that contain one or multiple first-class similarity database operators such as Similarity Selection, Similarity Join, and Similarity Group-by. Particularly, we analyze the implementation techniques of several similarity operators, introduce a consistent and comprehensive conceptual evaluation model for similarity queries, and present a rich set of transformation rules to extend cost-based query optimization to the case of similarity queries.     

从正反馈级获得迟滞的非稳态多谐振荡器

很多设计都采用基于逻辑元件的非稳态多谐振荡器,最简单的办法是围绕一个单反相施密特触发转换器的RC反馈回路(图1)。输出端将电容充电至较高的开关阈值,在该点上输出切换至其相反状态,阈值转换为一个不同值,而电容的充电电流反向。当电容的     

Aeration of large-scale municipal wastewater treatment plants: state of the art.

Aeration is the most energy-intensive operation in wastewater treatment, amounting to 45-75% of plant energy costs. Fine-pore diffusers are today almost ubiquitous in municipal wastewater aeration, due to their advantageous aeration efficiency (mass of oxygen transferred per unit energy required). Nevertheless, older municipal treatment facilities and many industrial treatment plants are still equipped with coarse-bubble or surface aerators. Fine-pore diffusers are subject to two major disadvantages: a) fouling, if not cleaned periodically; b) decrease in oxygen transfer efficiency caused by dissolved surfactants. Coarse-bubble and surface aerators are typically not subject to the traditional problems affecting fine-pore diffusers. Nonetheless, they achieve oxygen transfer at the expense of increased energy intensity. The increased biomass concentration associated with high mean cell retention time (MCRT) operations has a beneficial effect on aeration. Nutrient-removing selectors are able to further increase aeration efficiency, as they sorb and utilize the readily available substrate which otherwise would accumulate at bubble surfaces and dramatically decrease aeration efficiency. We summarise here our 30-year long experience in aeration research, and results obtained with clean- and process-water tests are used to show the beneficial effects of high MCRT operations, the beneficial effect of selectors, and the decline of aeration efficiency due to dissolved surfactants.