Atlantic mackerel (Scomber scombrus L.) adenosine deaminase, esterase-D, and otolith L1     

Jamieson  Alan; Turner  Robert J.; Dawson  Wendy A.; Birley  Andrew J. 《ICES Journal of Marine Science》1987,44(1):59-65

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The threshold feeding response of microzooplankton within Pacific high-nitrate low-chlorophyll ecosystem models under steady and variable iron input     

Andrew W. Leising  Wendy C. Gentleman  Bruce W. Frost 《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):2877

The equatorial Pacific is an HNLC (High-Nitrate Low-Chlorophyll) region. Modeling and in-situ process studies have confirmed the importance of microzooplankton grazing in this ecosystem. Unfortunately, both the parameters and functions representing microzooplankton grazing within current ecosystem models are poorly constrained. We used a simple 4-component food web model to test the assumption that a lower grazing threshold, which is common in many models, is necessary to achieve the HNLC condition. Without the grazing threshold, the model did not reproduce the HNLC condition. However, by raising the half-saturation constant within the microzooplankton functional response with no threshold, it was possible to reproduce the critical dynamics of the HNLC condition under both steady and moderate seasonal variability in nutrient input. It was also possible to reproduce the HNLC system using a sigmoidal functional response for the microzooplankton, with results somewhere between the other two forms of the model, although this version had the highest sensitivity to changes in its parameters. The three models predicted similar phytoplankton biomass and primary productivity under steady nutrient input, but diverge in these metrics as the amplitude of nutrient input variability increases. These three functional responses also imply certain important differences in the microzooplankton community. Whereas the threshold model had the least sensitivity to parameter choice, the high half-saturation constant, no-threshold model may actually be a better approximation when modeling a community of grazers. Ecosystem models that predict carbon production and export in HNLC regions can be very sensitive to assumptions concerning microzooplankton grazing; future studies need to concentrate on the functional responses of microzooplankton before these models can be used for predicting fluxes in times or regions where forcing is beyond that used to constrain the original model.  相似文献   

The Risk Atlas of Mexico City,Mexico: a tool for decision-making and disaster prevention     

Novelo-Casanova  David A.  Suárez  Gerardo  Cabral-Cano  Enrique  Fernández-Torres  Enrique A.  Fuentes-Mariles  Oscar A.  Havazli  Emre  Jaimes  Miguel Á.  López-Espinoza  Erika D.  Martin-Del Pozzo  Ana Lillian  Morales-Barrera  Wendy V.  Morales-Rodríguez  Hipólito L.  Nieto-Torres  Amiel  Rodríguez-Elizarrarás  Sergio R.  Solano-Rojas  Darío  Velasco-Herrera  Victor M. 《Natural Hazards》2022,111(1):411-437

Natural Hazards - We present a Risk Atlas of Mexico City based on a Geographical Information System (RA-GIS). We identified the prevalent social risk to the more relevant hazards in Mexico City...  相似文献   

Reconstruction of catastrophic outburst floods of the Diexi ancient landslide-dammed lake in the Upper Minjiang River,Eastern Tibetan Plateau     

Ma  Junxue  Chen  Jian  Cui  Zhijiu  Zhou  Wendy  Chen  Ruichen  Wang  Chengbiao 《Natural Hazards》2022,112(2):1191-1221

Natural Hazards - Landslide-dammed lake outburst floods (LLOFs) may pose serious safety threats to nearby residents and their livelihoods, as well as cause major damages to the downstream areas in...  相似文献   

Understanding Today's Online GIS User Through the Lens of a WorldMap Survey          下载免费PDF全文

Weihe Wendy Guan  Alenka Poplin  Benjamin G. Lewis 《Transactions in GIS》2015,19(3):417-438

WorldMap is an open source online mapping application which aims to lower barriers for scholars who wish to visualize, analyze, organize, present, and publish mapped information. In late 2013, 290 respondents among the 8,000 registered users participated in an online survey in which they described their activities, purposes, experiences, and preferences regarding the system. Participants also described their professional background, GIS skill level, age, gender, and country of work. This study analyzes the results of the survey, by summarizing the responses to each question independently and by examining the relationships and dependencies of these answers across the different questions to try to better understand why users responded the way they did. The study is based on the user‐centered design (UCD) approach. We aim to use the survey results to improve our understanding of user demographics and needs. Findings from this study will be used to guide WorldMap improvements, and we hope the findings will also shed light on the broader requirements of online GIS users.  相似文献   

Formation of H₂ on an olivine surface: a computational study     

T. P. M. Goumans  C. Richard  A. Catlow  Wendy A. Brown 《Monthly notices of the Royal Astronomical Society》2009,393(4):1403-1407

The formation of H₂ on a pristine olivine surface [forsterite (010)] is investigated computationally. Calculations show that the forsterite surface catalyzes H₂ formation by providing chemisorption sites for H atoms. The chemisorption route allows for stepwise release of the reaction exothermicity and stronger coupling to the surface, which increases the efficiency of energy dissipation. This suggests that H₂ formed on a pristine olivine surface should be much less rovibrationally excited than H₂ formed on a graphite surface. Gas-phase H atoms impinging on the surface will first physisorb relatively strongly  ( E _phys= 1240 K)  . The H atom can then migrate via desorption and re-adsorption, with a barrier equal to the adsorption energy. The barrier for a physisorbed H atom to become chemisorbed is equal to the physisorption energy, therefore there is almost no gas-phase barrier to chemisorption. An impinging gas-phase H atom can easily chemisorb  ( E _chem= 12 200 K)  , creating a defect where a silicate O atom is protonated and a single electron resides on the surface above the adjacent magnesium ion. This defect directs any subsequent impinging H atoms to chemisorb strongly (39 800 K) on the surface electron site. The two adjacent chemisorbed atoms can subsequently recombine to form H₂ via a barrier (5610 K) that is lower than the chemisorption energy of the second H atom. Alternatively, the adsorbed surface species can react with another incoming H atom to yield H₂ and regenerate the surface electron site. This double chemisorption 'relay mechanism' catalyzes H₂ formation on the olivine surface and is expected to attenuate the rovibrational excitation of H₂ thus formed.  相似文献   

Hydrogeological investigation of mud-mound springs developed over a weathered basalt aquifer on the Liverpool Plains,New South Wales,Australia   总被引：1，自引：0，他引：1  

R.?Ian?AcworthEmail author  Wendy?A.?Timms 《Hydrogeology Journal》2003,11(6):659-672

The growth and collapse of mud mounds at a site on the Liverpool Plains in northern New South Wales, Australia has been observed over a 12-year period. The mud mounds appeared in a flat field for the first time in living memory in 1989, but their prior existence in the early Holocene is indicated by archaeological data. The piezometric head in bores drilled through a 7-m bed of clayey silt and screened in weathered basalt at a depth of 8 m was more than 2 m above ground level. Clay has been carried in suspension by water seeping to the ground surface where it has accumulated and formed a mound. Approximately eight years after their initial appearance, the growth of the mounds stopped and within a further three years they had almost completely disappeared.Mechanisms for the growth and decay of the mounds are reviewed. The chemistry of the shallow bore water and the water seeping from the surface of the mounds was dominated by sodium bicarbonate with a 4 mEq/l increase between the weathered basalt and the surface of the mound. Inverse modelling (PHREEQC) is used to determine possible chemical reactions that can account for this increase.

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Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10040-003-0278-0.

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Resumen Se ha observado durante 12 años el crecimiento y el colapso de montículos de lodo en un emplazamiento ubicado en las Llanuras de Liverpool, en el estado australiano de Nueva Gales del Sur. Según la memoria existente, los montículos de lodo aparecieron en un campo llano por vez primera en 1989, pero, por datos arqueológicos, se conoce de su existencia a comienzos del Holoceno. Los niveles piezométricos en sondeos perforados a través de 7 m de limos arcillosos y ranurados en el basalto meteorizado a 8 m son superiores en más de 2 m a la superficie del terreno. La arcilla es portada en suspensión por el agua que descarga hacia la superficie del terreno, donde se acumula y forma el montículo. Unos 8 años después de su aparición, el crecimiento de los montículos se detiene y éstos acaban prácticamente desapareciendo en otros 3 años.Se revisa los mecanismos que originan el crecimiento y desaparición de los montículos. La química de las aguas someras de los sondeos y del agua que se filtra desde la superficie de los montículos está dominada por bicarbonato sódico, con un incremento de 4 meq/L entre el basalto meteorizado y la superficie del montículo. Se utiliza la modelación inversa (PHREEQC) para determinar las reacciones químicas que pueden explicar dicho aumento.

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Résumé La croissance et l'effondrement de monticules de vase situés dans les plaines de Liverpool, dans le nord des Nouvelles Galles du Sud, ont été observés pendant 12 ans. Les monticules de vase sont apparus en terrain plat pour la première fois de mémoire d'homme en 1989; mais leur existence antérieure dès le début de l'Holocène est attesté par des données archéologiques. Le niveau piézométrique dans des forages traversant 7 m de silt argileux et recouvrant un basalte altéré à 8 m était de plus de 2 m au-dessus de la surface du sol. L'argile a été apportée en suspension par l'eau suintant à la surface du sol où elle s'est accumulée pour former un monticule. Environ 8 ans après leur première apparition, la croissance des monticules s'est arrêtée et ils ont presque complètement disparu dans les 3 ans qui ont suivi.Les mécanismes de croissance et de régression de ces monticules sont passés en revue. La chimie de l'eau des forages à proximité de la surface et de l'eau filtrant à la surface des monticules était dominée par le bicarbonate de sodium, avec une augmentation de 4 meq/l entre le basalte altéré et la surface du monticule. Une modélisation inverse (PHREEQC) a été mise en uvre pour déterminer les réactions possibles pouvant rendre compte de cet accroissement.

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The Role of a PhD Field Exam in Preparing Graduate Students for Academic Careers*     

Alex P. Oberle  Wendy Bigler  Timothy W. Hawkins 《The Professional geographer》2005,57(3):452-461

The Department of Geography at Arizona State University implemented a field exam as part of its PhD program requirements. This field exam requires students to develop an independent field‐based research project based on a general question in the student's specialty area. A survey of current and former PhD students and faculty members document how the field exam assists students in developing skills necessary for continuing graduate research and for preparing them for the rigors of academic employment. The outcomes of the exam include both long‐term, process‐related benefits and more immediate tangible rewards. For some students, the preliminary fieldwork and results redirect student interests and form the basis for their eventual dissertation. The field exam is adaptable to a diversity of geography research methods, subject areas, and graduate degree programs, while remaining grounded in the discipline's vibrant, widely respected fieldwork tradition.  相似文献   

The 322 ka Tiribí Tuff: stratigraphy, geochronology and mechanisms of deposition of the largest and most recent ignimbrite in the Valle Central, Costa Rica     

Wendy Pérez  Guillermo E. Alvarado  Phillip B. Gans 《Bulletin of Volcanology》2006,69(1):25-40

The Tiribí Tuff covered much of the Valle Central of Costa Rica, currently the most densely populated area in the country (∼2.4 million inhabitants). Underlying the tuff, there is a related well-sorted pumice deposit, the Tibás Pumice Layer. Based on macroscopic characteristics of the rocks, we distinguish two main facies in the Tiribí Tuff in correlation to the differences in welding, devitrification, grain size, and abundance of pumice and lithic fragments. The Valle Central facies consists of an ignimbritic plateau of non-welded to welded deposits within the Valle Central basin and the Orotina facies is a gray to light-bluish gray, densely to partially welded rock, with yellowish and black pumice fragments cropping out mainly at the Grande de Tárcoles River Gorge and Orotina plain. This high-aspect ratio ignimbrite (1:920 or 1.1×10⁻³) covered an area of at least 820 km² with a long runout of 80 km and a minimum volume outflow of 25 km³ (15 km³ DRE). Geochemically, the tuff shows a wide range of compositions from basaltic-andesites to rhyolites, but trachyandesites are predominant. Replicate new ⁴⁰Ar/³⁹Ar age determinations indicate that widespread exposures of this tuff represent a single ignimbrite that was erupted 322±2 ka. The inferred source is the Barva Caldera, as interpreted from isopach and isopleth maps, contours of the ignimbrite top and geochemical correlation (∼10 km in diameter). The Tiribí Tuff caldera-forming eruption is interpreted as having evolved from a plinian eruption, during which the widespread basal pumice fall was deposited, followed by fountaining pyroclastic flows. In the SW part of the Valle Central, the ignimbrite flowed into a narrow canyon, which might have acted as a pseudo-barrier, reflecting the flow back towards the source and thus thickening the deposits that were filling the Valle Central depression. The variable welding patterns are interpreted to be a result of the lithostatic load and the influence of the content and size of lithic fragments.  相似文献   

Cd, Cr, Cu, Ni and Pb in the water column and sediments of the Ob-Irtysh Rivers, Russia     

S. BradleyMoran  Wendy L. Woods 《Marine pollution bulletin》1997,35(7-12):270-279

Concentrations of Cd, Cr, Cu, Ni and Pb were determined in filtered water, suspended particulate matter, and bottom sediments from a 2000 km section of the Ob and Irtysh Rivers. Dissolved Cd, Cr, Cu and Ni concentrations are similar to, or higher than, results from other Russian Arctic and large world river-estuaries. Concentrations of Cd, Cr, Cu, Ni and Pb in suspended particulate matter are generally comparable to results from other Russian Arctic and large world rivers and estuaries. Comparison of trace metal ratios in crustal material and suspended particulate matter and bottom sediment suggests that the source of Cr, Cu and Ni is continental weathering. Particulate Cd and Pb are elevated relative to their crustal abundance, suggesting a source of these metals to the Ob-Irtysh in addition to continental weathering.  相似文献