Autotomy in porcelain crabs is an effective escape mechanism from rockfish predation     

Matthew L. Knope  Ralph J. Larson 《Marine Ecology》2014,35(4):471-477

Porcelain crabs possess a ‘hair‐trigger’ propensity to autotomize their chelipeds (claws), and laboratory studies have demonstrated that this ability is highly effective in avoiding predation from other crabs. However, porcelain crabs are also subject to predation from fishes, which use a very different means of capture. In this study, we investigated whether autotomy in porcelain crabs is also effective against predation by fishes. To do this, we examined stomach‐contents data from four common species of kelp‐forest rockfishes and determined the frequency of disassociated chelipeds (those with no associated bodies) in porcelain crabs and in brachyuran crabs, which do not readily autotomize their chelipeds. We found that disassociated chelipeds of porcelain crabs were six times as common as those of brachyuran crabs (35% of the remains of all porcelain crabs versus 6% of the remains of all brachyuran crabs). We interpret this difference to be evidence that, through autotomy, porcelain crabs escaped ingestion of their entire bodies, and thus certain mortality, at a higher rate than did brachyuran crabs. We conclude that autotomy constituted an effective escape strategy from rockfish predation. This evidence, in conjunction with previous studies, suggests that autotomy of chelipeds in porcelain crabs is an effective anti‐predatory strategy against phylogenetically disparate predatory groups.  相似文献   

The effect of health benefits on climate change mitigation policies     

Masako Ikefuji  Jan R. Magnus  Hiroaki Sakamoto 《Climatic change》2014,126(1-2):229-243

This paper studies the interplay between climate, health, and the economy in a stylized world with eleven heterogeneous regions, with special emphasis on USA, Europe, China, India, and Africa. We introduce health impacts into a simple economic integrated assessment model where both the local cooling effect of SO ₂ and the global warming effect of CO ₂ are endogenous, and investigate how these factors affect the equilibrium path. Regions do not respond in the same way to climate change. In particular, emission abatement rates and health costs depend on the economic and geographical characteristics of each region. Two policy scenarios are considered, Nash and Optimal, for which we present both global and regional results. Results for Africa and China are highlighted.  相似文献   

Forward modeling of GPS multipath for near-surface reflectometry and positioning applications   总被引：4，自引：2，他引：2  

Felipe G. Nievinski  Kristine M. Larson 《GPS Solutions》2014,18(2):309-322

Multipath is detrimental for both GPS positioning and timing applications. However, the benefits of GPS multipath for reflectometry have become increasingly clear for soil moisture, snow depth, and vegetation growth monitoring. Most multipath forward models focus on the code modulation, adopting arbitrary values for the reflection power, phase, and delay, or they calculate the reflection delay based on a given geometry and keep reflection power empirically defined. Here, a fully polarimetric forward model is presented, accounting for right- and left-handed circularly polarized components of the GPS broadcast signal and of the antenna and surface responses as well. Starting from the fundamental direct and reflected voltages, we have defined the interferometric and error voltages, which are of more interest in reflectometry and positioning applications. We examined the effect of varying coherence on signal-to-noise ratio, carrier phase, and code pseudorange observables. The main features of the forward model are subsequently illustrated as they relate to the broadcast signal, reflector height, random surface roughness, surface material, antenna pattern, and antenna orientation. We demonstrated how the antenna orientation—upright, tipped, or upside-down—involves a number of trade-offs regarding the neglect of the antenna gain pattern, the minimization of CDMA self-interference, and the maximization of the number of satellites visible. The forward model was also used to understand the multipath signature in GPS positioning applications. For example, we have shown how geodetic GPS antennas offer little impediment for the intake of near-grazing reflections off natural surfaces, in contrast to off metal, because of the lack of diversity with respect to the direct signal—small interferometric delay and Doppler, same sense of polarization, and similar direction of arrival.  相似文献   

An open source GPS multipath simulator in Matlab/Octave   总被引：2，自引：1，他引：1  

Felipe G. Nievinski  Kristine M. Larson 《GPS Solutions》2014,18(3):473-481

Multipath is detrimental for both GPS positioning and timing applications. However, the benefits of GPS multipath for reflectometry have become increasingly clear for monitoring soil moisture, snow depth, and vegetation growth. In positioning applications, a simulator can support multipath mitigation efforts in terms of, e.g., site selection, antenna design, receiver performance assessment, and in relating different observations to a common parameterization. For reflectometry, in order to convert observed multipath parameters into useable environmental products, it is important to be able to explicitly link the GPS observables to known characteristics of the GPS receiver/antenna and the reflecting environment. Existing GPS multipath software simulators are generally not readily available for the general scientific community to use and/or modify. Here, a simulator has been implemented in Matlab/Octave and is made available as open source code. It can produce signal-to-noise ratio, carrier phase, and code pseudorange observables, based on L1 and L2 carrier frequencies and C/A, P(Y), and L2C modulations. It couples different surface and antenna types with due consideration for polarization and coherence. In addition to offering predefined material types (water, concrete, soil, etc.), it allows certain dimensional properties to be varied, such as soil moisture and snow density.  相似文献   

GPS snow sensing: results from the EarthScope Plate Boundary Observatory   总被引：5，自引：2，他引：3  

Kristine M. Larson  Felipe G. Nievinski 《GPS Solutions》2013,17(1):41-52

Accurate measurements of snowpack are needed both by scientists to model climate and by water supply managers to predict/mitigate drought and flood conditions. Existing in situ snow sensors/networks lack the necessary spatial and temporal sensitivity. Satellite measurements currently assess snow cover rather than snow depth. Existing GPS networks are a potential source of new snow data for climate scientists and water managers which complements existing snow sensors. Geodetic-quality GPS networks often provide signal-to-noise ratio data that are sensitive to snow depth at scales of ~1,000 m², a much larger area than for other in situ sensors. However, snow depth can only be estimated at GPS sites when the modulation frequency of multipath signals can be resolved. We use data from the EarthScope Plate Boundary Observatory to examine the potential for snow sensing in GPS networks. Examples are shown for successful and unsuccessful snow retrieval sites. In particular, GPS sites in forested regions typically cannot be used for snow sensing. Multiple-year time series of snow depth are estimated from GPS sites in the Rocky Mountains. Peak snow depths ranged from 0.4 to 1.2 m. Comparisons with independent sensors show strong correlations between the GPS snow depth estimates and the timing of snowstorms in the region.  相似文献   

Design and Production of an Atlas for Diplomacy in Zimbabwe and The Southern African Development Community     

Thomas W. Crawford Jr.  Charles R. Larson  Brian J. Granneman  Gayla A. Evans  Carolyn K. Gacke  Dennis R. Pearson 《国际地球制图》2013,28(4):58-69

Abstract

An atlas of Zimbabwe and the Southern African Development Community was designed and produced for use by American diplomats in Zimbabwe. Two copies of the bound atlas are used by the Embassy of the United States of America (U.S. Embassy) and the Mission of the U.S. Agency for International Development (USAID) in Harare, Zimbabwe, to orient visitors and discuss matters of diplomacy and development in Zimbabwe and the Southern African Development Community. The atlas contains maps derived from satellite images showing features of the physical geography of Southern Africa and Zimbabwe and plastic overlays showing rivers and lakes and manmade features, such as major roads, railroads, and cities. The atlas is an important tool that American diplomats can use to orient participants in discussions of the environment and to develop agreements for management of the environment in Zimbabwe and Southern Africa.  相似文献   

Mesozoic to Cenozoic tectono‐metamorphic history of the South Pamir–Hindu Kush (Chitral,NW Pakistan): Insights from phase equilibria modelling,and garnet–monazite petrochronology     

Mathieu Soret  Kyle P. Larson  John M. Cottle  Matthijs Smit  Alex Johnson  Sudip Shrestha  Asghar Ali  Shah Faisal 《Journal of Metamorphic Geology》2019,37(5):633-666

The Karakoram–Hindu Kush–Pamir and adjacent Tibetan plateau belt comprise a series of Gondwana‐derived crustal fragments that successively accreted to the Eurasian margin in the Mesozoic as the result of the progressive Tethys ocean closure. These domains provide unique insights into the thermal and structural history of the Mesozoic to Cenozoic Eurasian plate margin, which are critical to inform the initial boundary conditions (e.g. crustal thickness, structure and thermo‐mechanical properties) for the subsequent development of the large and hot Tibetan–Himalaya orogen, and the associated crustal deformation processes. Using a combination of microstructural analyses, thermobarometry modelling and U–Th–Pb monazite and Lu–Hf garnet geochronology, the study reappraises the metamorphic history of exposed mid‐crustal metapelites in the Chitral region of the South Pamir–Hindu Kush (NW Pakistan). This study also demonstrates that trace elements in monazite (especially Y and Dy), combined with thermodynamical modelling and Lu–Hf garnet dating, provides a powerful integrated toolbox for constraining long‐lived and polyphased tectono‐metamorphic histories in all their spatial and temporal complexity. Rocks from the Chitral region were progressively deformed and metamorphosed at sub‐ and supra‐solidus conditions through at least four distinct episodes from the Mesozoic to the Cenozoic. Rocks were first metamorphosed at ~400–500°C and ~0.3 GPa in the Late Triassic–Early Jurassic (210–185 Ma), likely in response to the accretion of the Karakoram during the Cimmerian orogeny. Pressure and temperature subsequently increased by ~0.3 GPa and 100°C in the Early‐ to Mid Cretaceous (140–80 Ma), coinciding with the intrusion of calcalkaline granitic plutons across the Karakoram and Pamir regions. This event is interpreted as the record of crustal thickening and the development of a proto‐plateau within the Eurasian margin due to a long‐lived episode of slab flattening in an Andean‐type margin. Peak metamorphism was reached in the Late Eocene–Early Oligocene (40–30 Ma) at conditions of 580–600°C and ~0.6 GPa and 700–750°C and 0.7–0.8 GPa for the investigated staurolite schists and sillimanite migmatites respectively. This crustal heating up to moderate anatexis likely resulted in the underthrusting of the Indian plate after a NeoTethyan slab‐break off or to the Tethyan Himalaya–Lhasa microcontinent collision and subsequent oceanic slab flattening. Near‐isothermal decompression/exhumation followed in the Late Oligocene (28–23 Ma) as marked by a pressure decrease in excess of ~0.1 GPa. This event was coeval with the intrusion of the 24 Ma Garam Chasma leucogranite. This rapid exhumation is interpreted to be related to the reactivation of the South Pamir–Karakoram suture zone during the ongoing collision with India. The findings of this study confirm that significant crustal shortening and thickening of the south Eurasian margin occurred during the Mesozoic in an accretionary‐type tectonic setting through successive episodes of terrane accretions and probably slab flattening, transiently increasing the coupling at the plate interface. Moreover, they indicate that the south Eurasian margin was already hot and thickened prior to Cenozoic collision with India, which has important implications for orogen‐scale strain‐accommodation mechanisms.  相似文献   

Note on Coriolis-Stokes force and energy     

Göran Broström  Kai H. Christensen  Magnus Drivdal  Jan Erik H. Weber 《Ocean Dynamics》2014,64(7):1039-1045

In this study, we consider the origin of the Coriolis-Stokes (CS) force in the wave-averaged momentum and energy equations and make a short analysis of possible energy input to the ocean circulation (i.e., Eulerian mean velocity) from the CS force. Essentially, we find that the CS force appears naturally when considering vertically integrated quantities and that the CS force will not provide any energy input into the system for this case. However, by including the “Hasselmann force”, we show some inconsistencies regarding the vertical structure of the CS force in the Eulerian framework and find that there is a distinct vertical structure of the energy input and that the net input strongly depends on whether the wave zone is included in the analysis or not. We therefore question the introduction of the “Hasselmann force” into the system of equations, as the CS force appears naturally in the vertically integrated equations or when Lagrangian vertical coordinates are used.  相似文献   

The feasibility of low CO₂ concentration targets and the role of bio-energy with carbon capture and storage (BECCS)     

Christian Azar  Kristian Lindgren  Michael Obersteiner  Keywan Riahi  Detlef P. van Vuuren  K. Michel G. J. den Elzen  Kenneth M?llersten  Eric D. Larson 《Climatic change》2010,100(1):195-202

The United Nations Framework Convention on Climate Change (UNFCCC 1992) calls for stabilization of atmospheric greenhouse gas (GHG) concentrations at a level that would prevent dangerous anthropogenic interference with the climate system. We use three global energy system models to investigate the technological and economic attainability of meeting CO₂ concentration targets below current levels. Our scenario studies reveal that while energy portfolios from a broad range of energy technologies are needed to attain low concentrations, negative emission technologies—e.g., biomass energy with carbon capture and storage (BECCS)—significantly enhances the possibility to meet low concentration targets (at around 350 ppm CO₂).  相似文献   

Digital Terrain Model Resolution and its Influence on Estimating the Extent of Rockfall Areas     

Thomas Zieher  Tobias Formanek  Magnus Bremer  Gertraud Meissl  Martin Rutzinger 《Transactions in GIS》2012,16(5):691-699

As rockfall can cause a great deal of damage, it is essential to know its spatial propagation. Rockfall models are sensitive to the resolution of input data, i.e. the Digital Terrain Model (DTM) used. Nowadays, high resolution elevation data are available area‐wide from airborne laser scanning (ALS). However, rockfall models are designed for analysis on a certain scale, which means that high resolution input might not necessarily improve model results (e.g. for regional scale studies). Our aim is to estimate the reach of rockfall by analysing different input resolutions of an ALS DTM. The presented empirically–based model, implemented in Python 2.7, is a modified version of the zenital method including an iterative random walk trajectory model, which is designed for rockfall hazard assessment at the regional scale. Trajectories and rockfall probability maps are generated for selected DTM input resolutions. The comparison shows that high resolution DTMs do consider local topography better and thus lead to more realistic results than low resolution DTMs.  相似文献