Do 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline data support the conclusion of threshold carcinogenic effects?     

Chao Chen  Kate Z. Guyton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):487-494

The objectives of this paper are to (1) reexamine the data that were used to support the conclusion of a threshold effect for 2-amino-3,8-dimethylimidazo[4,5-f] quinoxaline (MeIQx)-induced initiation and carcinogenicity at low doses in the rat liver, and (2) discuss issues and uncertainties about assessing cancer risk at low doses. Our analysis is part of an effort to understand proper interpretation and modeling of data related to cancer mechanisms and is not an effort to develop a risk assessment for this compound. The data reanalysis presented herein shows that the low-dose initiation activity of MeIQx, which can be found in cooked meat, cannot be dismissed. It is argued that the threshold effect for carcinogenic agents cannot be determined by statistical non-significance alone; more relevant biological information is required. A biologically motivated procedure is proposed for data analyses. The concept and procedure that are appropriate for analyzing MeIQx data are equally applicable to other compounds with comparable data. The ideas and approaches in this presentation are those of the authors and do not necessarily represent the positions or policies of the USEPA.  相似文献   

Water use strategies of two co‐occurring tree species in a semi‐arid karst environment          下载免费PDF全文

Brooke A. Swaffer  Kate L. Holland  Tanya M. Doody  Chris Li  John Hutson 《水文研究》2014,28(4):2003-2017

The flow of precipitation from the surface through to groundwater in karst systems is a complex process involving storage in the unsaturated zone and diffuse and preferential recharge pathways. The processes associated with this behaviour are not well understood, despite the prevalence of karst aquifers being used as freshwater supplies. As a result, uncertainty regarding the ecohydrological processes in this geological setting remains large. In response to the need to better understand the impact of woody vegetation on groundwater recharge, annual evapotranspiration (ET) rates and tree water sources were measured for two years above a shallow, fresh karst aquifer. Water use strategies of the co‐occurring Eucalyptus diversifolia subsp. diversifolia Bonpl. and Allocasuarina verticillata (Lam.) L. Johnson were investigated using a monthly water balance approach, in conjunction with measurement of the stable isotopes of water, leaf water potentials and soil matric potentials. The results suggest that it is unlikely groundwater resources are required to sustain tree transpiration, despite its shallow proximity to the soil surface, and that similarities exist between ET losses and the estimated long‐term average rainfall for this area. Irrespective of stand and morphological differences, E. diversifolia and A. verticillata ET rates showed remarkable convergence, demonstrating the ability of these co‐occurring species to maximise their use of the available precipitation, which avoids the requirement to differentiate between these species when estimating ET at a landscape scale. We conclude that the water holding capacity of porous geological substrates, such as those associated with karst systems, will play an important role in equilibrating annual rainfall variability and should be considered when assessing ecohydrological links associated with karst systems. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

The multipole vectors of the Wilkinson Microwave Anisotropy Probe, and their frames and invariants     

Kate Land  João Magueijo 《Monthly notices of the Royal Astronomical Society》2005,362(3):838-846

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The effects of Martian near surface conditions on the photochemistry of amino acids     

Inge Loes ten Kate  James R.C. Garry  Bernard Foing 《Planetary and Space Science》2006,54(3):296-302

In order to understand the complex multi-parameter system of destruction of organic material on the surface of Mars, step-by-step laboratory simulations of processes occurring on the surface of Mars are necessary. This paper describes the measured effects of two parameters, a CO₂ atmosphere and low temperature, on the destruction rate of amino acids when irradiated with Mars-like ultraviolet light (UV). The results show that the presence of a 7 mbar CO₂ atmosphere does not affect the destruction rate of glycine, and that cooling the sample to 210 K (average Mars temperature) lowers the destruction rate by a factor of 7. The decrease in the destruction rate of glycine by cooling the sample is thought to be predominantly caused by the slower reaction kinetics. When these results are scaled to Martian lighting conditions, cold thin films of glycine are assumed to have half-lives of 250 h under noontime peak illumination. It has been hypothesised that the absence of detectable native organic material in the Martian regolith points to the presence of oxidising agents. Some of these agents might form via the interaction of UV with compounds in the atmosphere. Water, although a trace component of Mars’ atmosphere, is suggested to be a significant source of oxidising species. However, gaseous CO₂ or adsorbed H₂O layers do not influence the photodestruction of amino acids significantly in the absence of reactive soil. Other mechanisms such as chemical processes in the Martian regolith need to be effective for rapid organic destruction.  相似文献   

Improving the assessment and valuation of climate change impacts for policy and regulatory analysis     

Alex L. Marten  Robert E. Kopp  Kate C. Shouse  Charles W. Griffiths  Elke L. Hodson  Elizabeth Kopits  Bryan K. Mignone  Chris Moore  Steve C. Newbold  Stephanie Waldhoff  Ann Wolverton 《Climatic change》2013,117(3):433-438

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The phase 0/A study of the ESA M3 mission candidate EChO     

Ludovic Puig  Kate Isaak  Martin Linder  Isabel Escudero  Pierre-Elie Crouzet  Roger Walker  Matthias Ehle  Jutta Hübner  Rainer Timm  Bram de Vogeleer  Pierre Drossart  Paul Hartogh  Christophe Lovis  Giusi Micela  Marc Ollivier  Ignasi Ribas  Ignas Snellen  Bruce Swinyard  Giovanna Tinetti  Paul Eccleston 《Experimental Astronomy》2015,40(2-3):393-425

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The three-dimensional clustering of radio galaxies in the Texas–Oxford NVSS structure survey     

Kate Brand  Steve Rawlings  Gary J. Hill  Joseph R. Tufts 《Monthly notices of the Royal Astronomical Society》2005,357(4):1231-1254

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Resistance of salt marsh substrates to near-instantaneous hydrodynamic forcing     

Helen Brooks  Iris Möller  Simon Carr  Clementine Chirol  Elizabeth Christie  Ben Evans  Kate L. Spencer  Tom Spencer  Katherine Royse 《地球表面变化过程与地形》2021,46(1):67-88

Salt marshes deliver vital ecosystem services by providing habitats, storing pollutants and atmospheric carbon, and reducing flood and erosion risk in the coastal hinterland. Net losses in salt marsh areas, both modelled globally and measured regionally, are therefore of concern. Amongst other controls, the persistence of salt marshes in any one location depends on the ability of their substrates to resist hydrodynamic forcing at the marsh front, along creek margins and on the vegetated surface. Where relative sea level is rising, marsh elevation must keep pace with sea-level rise and landward expansion may be required to compensate for areal loss at exposed margins. This paper reviews current understanding of marsh substrate resistance to the near-instantaneous (seconds to hours) forcing induced by hydrodynamic processes. It outlines how variability in substrate properties may affect marsh substrate stability, explores current understanding of the interactions between substrate properties and erosion processes, and how the cumulative impact of these interactions may affect marsh stability over annual to decadal timescales. Whilst important advances have been made in understanding how specific soil properties affect near-instantaneous marsh substrate stability, less is known about how these properties interact and alter bulk substrate resistance to hydrodynamic forcing. Future research requires a more systematic approach to quantifying biological and sedimentological marsh substrate properties. These properties must then be linked to specific observable erosion processes, particularly at the marsh front and along creek banks. A better understanding of the intrinsic dynamics and processes acting on, and within, salt marsh substrates will facilitate improved prediction of marsh evolution under future hydrodynamic forcing scenarios. Notwithstanding the additional complications that arise from morphodynamic feedbacks, this would allow us to more accurately model the future potential protection from flooding and erosion afforded by marshes, while also increasing the effectiveness of salt marsh restoration and recreation schemes. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Effect of different transport observations on inverse modeling results: case study of a long-term groundwater tracer test monitored at high resolution     

Ehsan Rasa  Laura Foglia  Douglas M. Mackay  Kate M. Scow 《Hydrogeology Journal》2013,21(7):1539-1554

Conservative tracer experiments can provide information useful for characterizing various subsurface transport properties. This study examines the effectiveness of three different types of transport observations for sensitivity analysis and parameter estimation of a three-dimensional site-specific groundwater flow and transport model: conservative tracer breakthrough curves (BTCs), first temporal moments of BTCs (m ₁), and tracer cumulative mass discharge (M _d) through control planes combined with hydraulic head observations (h). High-resolution data obtained from a 410-day controlled field experiment at Vandenberg Air Force Base, California (USA), have been used. In this experiment, bromide was injected to create two adjacent plumes monitored at six different transects (perpendicular to groundwater flow) with a total of 162 monitoring wells. A total of 133 different observations of transient hydraulic head, 1,158 of BTC concentration, 23 of first moment, and 36 of mass discharge were used for sensitivity analysis and parameter estimation of nine flow and transport parameters. The importance of each group of transport observations in estimating these parameters was evaluated using sensitivity analysis, and five out of nine parameters were calibrated against these data. Results showed the advantages of using temporal moment of conservative tracer BTCs and mass discharge as observations for inverse modeling.  相似文献   

Zero Tolerance in Latin America: Punitive Paradox in Urban Policy Mobilities     

Kate Swanson 《Urban geography》2013,34(7):972-988

In Latin America, high levels of crime have prompted many politicians to embrace zero tolerance policing in order to quell public fears. While the overall impacts on urban crime are debatable, zero tolerance in the region has morphed into a powerful policy narrative that symbolizes strong leaders who crack down crime and disorder. Its impacts have been far-reaching; to date, it has been implemented in various guises in Mexico, Brazil, Ecuador, Venezuela, Chile, Argentina, Honduras, El Salvador, Guatemala and the Dominican Republic. Yet, the policy transfer of zero tolerance to Latin America has mutated into a much more punitive approach. In this paper, I develop a critical analysis of the punitive inequalities of zero tolerance policing in Latin American cities, and the consequences for marginalized and racialized youth. I also explore the emergence of a new, unexpected consequence of zero tolerance: the South-North migration of undocumented people.  相似文献