Multiple pulses in dE/dt and the fine-structure of E during the onset of first return strokes in cloud-to-ocean lightning     

Natalie D. Murray  E. Philip Krider  John C. Willett 《Atmospheric Research》2005,76(1-4):455

We have analyzed the fine-structure of 131 electric field (E) waveforms that were radiated during the onset of first return strokes in cloud-to-ocean lightning. The dE/dt waveforms were recorded using an 8-bit waveform digitizer sampling at 100 MHz, and the E waveforms were sampled at 10 MHz using a 10-bit digitizer. 49 (or 37%) of the dE/dt waveforms contain one or more large pulses within ± 1 μs of the largest (or dominant) peak in dE/dt, i.e. within an interval from − 1 μs to + 1 μs, where t = 0 μs is the time of the dominant peak, and 37 (or 28%) have one or more large pulses in the interval from 4 μs before to 1 μs before the dominant peak, i.e. − 4 μs to − 1 μs, and only the dominant peak within ± 1 μs . We give statistics on the amplitude and timing of dE/dt pulses that are near the dominant peak, and we show how the presence of these pulses adds considerable fine-structure to the shape of E_int, the integrated dE/dt waveform, on a time-scale of tens to hundreds of nanoseconds. This fine-structure includes fast pulses near the beginning of the slow front, large pulses and shoulders within the slow front and during the fast-transition, and very narrow peaks in E_int. Our overall conclusion is that the electromagnetic environment near the point(s) where lightning leaders attach to the surface is often more complicated than what would be produced by a single current pulse propagating up a single channel at the time of onset.  相似文献   

Geological applications of multi-response permutation procedures     

L. A. Orlowski  W. D. Grundy  P. W. Mielke  S. A. Schumm 《Mathematical Geology》1993,25(4):483-500

The multi-purpose permutation procedures (MRPP) test statistic is designed to analyze multivariate data at the ordinal or higher levels. It is based on the weighted averages of symmetric distance functions over all paired objects withina priori disjoint groups of objects from a finite population of objects where each object's response is a point in anr-dimensional space. Thus, the arguments of eachr-dimensional point correspond to ther measured responses of each object in the finite population of objects. The null hypothesis underlying MRPP is that the observed sample of objects within groups of a specified size structure is randomly obtained from the pooled collection of objects comprising the finite population. The procedure is used to test the presumed geomorphic differences among three reaches of the Lower Mississippi River. A combination of the proposed reaches is favored and several variable-based reach configurations are proposed.  相似文献   

Chemical characterization of DOM in channels of a seasonal wetland   总被引：3，自引：0，他引：3  

Natalie Mladenov  Diane M. McKnight  Stephan A. Macko  Marnie Norris  Rose M. Cory  Lars Ramberg 《Aquatic Sciences - Research Across Boundaries》2007,69(4):456-471

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Direct and Indirect Interactions Between Lower Estuarine Mangrove and Saltmarsh Habitats and a Commercially Important Penaeid Shrimp     

Matthew D. Taylor  Alistair Becker  Natalie A. Moltschaniwskyj  Troy F. Gaston 《Estuaries and Coasts》2018,41(3):815-826

Vegetated habitats in estuaries may provide a structural refuge and food supply in the same place, but benefits are also derived where a productive food source and suitable habitat are adjacent to each other. Quantifying these relationships is fundamental to understanding the structural and functional characteristics of estuarine ecosystems and for informing management actions. Effective juvenile habitat (habitat that contributes greater-than-average numbers of recruits to the adult population), recruitment patterns and trophic relationships were studied for Eastern King Prawn (Penaeus plebejus) in the lower Clarence River estuary, New South Wales, between 2014 and 2016. Effective juvenile habitat was identified in both the north arm and main river channel of the estuary, and these areas also supported a higher abundance of juvenile prawns. There was minimal recruitment to the southern channels of the estuary, possibly due to reduced connectivity with the incoming tide arising from a rock wall. Trophic relationships in parts of the lower estuary were evaluated using stable isotopes, and saltmarsh grass (Sporobolus virginicus) was the dominant primary producer supporting juvenile Eastern King Prawn productivity across the area. Mangroves were of minimal importance, and seagrass cover was minimal in the area studied. The patterns observed indicate that nursery function of different areas within the lower estuary is a product of connectivity, recruitment and nutrition derived from primary productivity of vascular plants. Habitats within the lower Clarence River estuary have seen substantial degradation over decadal time scales, and the implications of our findings for targeting future habitat repair are discussed.  相似文献   

Responding to flood risk in Louisiana: the roles of place attachment,emotions, and location     

Holley  Jason R.  McComas  Katherine A.  Lambert  Catherine E.  Snider  Natalie P.  Tucker  Grace K. 《Natural Hazards》2022,113(1):615-640

Natural Hazards - Drawing from protection motivation theory (PMT), we examined how place attachment and negative emotions, alongside threat and coping appraisals, personal experiences, and...  相似文献   

An examination of midwestern US cities’ preparedness for climate change and extreme hazards     

Qiao Hu  Zhenghong Tang  Martha Shulski  Natalie Umphlett  Tarik Abdel-Monem  Frank E. Uhlarik 《Natural Hazards》2018,90(2):777-801

Disasters continue to have a dramatic impact on lives, livelihoods and environments communities depend on. In response to these losses, the global community has developed various theories, assessment methodologies and policies aimed at reducing global losses. A contemporary outcome of these interventions is to build the disaster resilience. However, despite the disaster resilience-building endeavours espoused by policies, theories and methodologies, very little progress is being made in reducing disaster losses. This paper argues that a possible reason behind the limitations of current resilience-building policies and methodologies could be that most of these policies are based a mechanistic scientific paradigm that places an emphasis on system components that are perceived to build resilience and not the function of systems as a whole. This often leads to resilience-building initiatives that are based on a ‘one-size-fits-all’ approach. This paper argues for the use of a complex adaptive systems approach to building resilience. This approach argues that contextual factors within different social systems will have a nonlinear affect on disaster resilience-building efforts. Therefore, it is crucial to move away from ‘one-size-fits-all’ approaches to more flexible approaches to building resilience. These hypotheses are tested by means of a correlation statistical analysis of agricultural communities in Southern Africa. Results of this analysis indicate that unique resilience profiles are evident in almost all of the communities studied. This indicates that resilience is not the same for everybody, and that resilience-building endeavours should be flexible enough to be adapted for different contexts.  相似文献   

A Meta‐Analysis on the Return on Investment of Geospatial Data and Systems: A Multi‐Country Perspective          下载免费PDF全文

Natalie Trapp  Uwe A. Schneider  Ian McCallum  Steffen Fritz  Christian Schill  Maria Teresa Borzacchiello  Christine Heumesser  Max Craglia 《Transactions in GIS》2015,19(2):169-187

The availability, quality and accessibility of Geographic Information (GI) have significant socio‐economic and environmental benefits, but the collection and maintenance of GI require substantial investments. Cost‐benefit assessments (CBAs) attempt to justify the costs of geospatial data investments, applying different methodologies and focusing on diverse areas. Therefore, the Returns on Investment (ROI) vary considerably across studies, regions and sectors. The objective of this study is to explain some of the variation in the average ROI of GI by conducting a meta‐analysis of 82 cost‐benefit assessments between 1994 and 2013. In a first step, CBAs are systematically reviewed and relevant information is extracted. Particular emphasis is given to investment conditions and study characteristics. In a second step, multivariate regression methods are used to assess the size, significance and direction of individual effects. The results suggest that regional factors have the largest impact on the profitability of GI. Returns in Australia and New Zealand, for example, are four times larger than in Europe. In addition, small‐scale regional investments have a 2.5 times lower return than large‐scale international investments. Overall, the expected benefits of GI investments are approximately 3.2 times larger than the costs.  相似文献   

Green Laboratories: University Campuses as Sustainability “Exemplars” in the Arabian Peninsula     

Natalie Koch 《社会与自然资源》2018,31(5):525-540

ABSTRACT

Like many universities in the West, universities across the Arabian Peninsula are increasingly home to various conspicuous sustainability initiatives. This article examines this trend at three of the region’s most prominent projects: NYU-Abu Dhabi in the Emirates, Qatar Foundation’s Education City, and Saudi Arabia’s King Abdullah University of Science and Technology. Based on the textual analysis and informed by fieldwork in these countries since 2012, this article joins interdisciplinary research in political geography, sustainability experimentation, and laboratory studies to understand their iconic campuses not as enclaves, but as “exemplars” of sustainability and renewable energy futures in the region. Tracing their effects beyond their walls, I argue that they have mostly been limited to symbolically injecting sustainability into public discourse. While more substantial shifts toward sustainable development in the region are underway, these have largely stemmed from market forces rather than a new environmental consciousness promoted by these three iconic universities.  相似文献   

Alternative measures of dispersion applied to flow in a convoluted channel     

Monica Moroni  Natalie Kleinfelter-Domelle  John H. Cushman 《Advances in water resources》2009

Steady flow in a convoluted channel is studied via Particle Tracking Velocimetry. The channel is constructed from a sequence of closed parallel cylindrical tubes welded together in plane which are then sliced down the lateral mid-plane and the lower complex is laterally shifted relative to the upper complex. Flow is induced in the lateral direction normal to the axis of the tubes. The a-time, T_a, finite-size Lyapunov exponent, λ_a, and the real-space self- and distinct-part of the intermediate scattering functions, G_s and G_d, and the pair density function, G_p, are computed from the data. Particle trajectories, velocity maps and streamlines show the channel has two prominent recirculation zones and a main flow region. The first passage time probability density function of tagged particles past a plane transverse to the mean flow illustrates how particles are delayed by recirculation zones. The delay caused by fluid element folding is manifested in single particle statistics such as the first passage time and the slowing increase in horizontal evolution of G_s. G_p describes initial particle distribution and allows areas in the flow domain trapping particles to be identified and visualized. G_d shows the evolution of the average separation of pairs of particles and when examined in a recirculation zone, it evolves little because of fluid element rotation. λ_a gives information on what transpires at a fixed scale and provides an estimate of the rate at which particles initially separated by a distance x separate to a distance ax as opposed to G_d which allows one to view changes over time. At small separations, λ_1.3 approaches a constant and for intermediate separations it scales as x^−0.8.  相似文献   

Porosity problems: Comparing and reviewing methods for estimating porosity and volume of wood jams in the field     

Bridget Livers  Katherine B. Lininger  Natalie Kramer  Alicia Sendrowski 《地球表面变化过程与地形》2020,45(13):3336-3353

Porosity, or void space, of large wood jams in stream systems has implications for estimating wood volumes and carbon storage, the impacts of jams on geomorphic and ecological processes, and instream habitat. Estimating porosity and jam dimensions (i.e. jam volume) in the field is a common method of measuring wood volume in jams. However, very few studies explicitly address the porosity values in jams, how porosity is calculated and assessed for accuracy, and the effect such estimates have on carbon and wood budgets in river corridors. We compare methods to estimate jam porosity and wood volume using field data from four different depositional environments in North America (jam types include small in-channel jams, large channel-margin jams, a large island apex jam, and a large coastal jam), and compare the results with previous studies. We find that visual estimates remain the most time-efficient method for porosity estimation in the field, although they appear to underpredict back-calculated porosity values; the accuracy of jam porosity, and thus wood volume, estimates are difficult to definitively measure. We also find that porosity appears to be scale invariant, dictated mostly by jam type, (which is influenced by depositional processes), rather than the size of the jam. Wood piece sorting and structural organization are likely the most influential properties on jam porosity, and these factors vary according to depositional environment. We provide a framework and conceptual model that uses these factors to demonstrate how modeled jam porosity values differ and give recommendations as a catalyst for future work on porosity of wood jams. We conclude that jam type and size and/or the study goals may dictate which porosity method is the most appropriate, and we call for greater transparency and reporting of porosity methods in future studies. © 2020 John Wiley & Sons, Ltd.  相似文献