We study the influence of an open cluster environment on the formation and current structure of the Oort cloud. To do this, we have run 19 different simulations of the formation of the Oort cloud for 4.5 Gyrs. In each simulation, the Solar System spends its first 100 Myrs in a different open cluster environment before transitioning to its current field environment. We find that, compared to forming in the field environment, the inner Oort cloud is preferentially loaded with comets while the Sun resides in the open cluster and that most of this material remains locked in the interior of the cloud for the next 4.4 Gyrs. In addition, the outer Oort cloud trapping efficiencies we observe in our simulations are lower than previous formation models by about a factor of 2, possibly implying an even more massive early planetesimal disk. Furthermore, some of our simulations reproduce the orbits of observed extended scattered disk objects, which may serve as an observational constraint on the Sun's early environment. Depending on the particular open cluster environment, the properties of the inner Oort cloud and extended scattered disk can vary widely. On the other hand, the outer portions of the Oort cloud in each of our simulations are all similar. 相似文献
Natural Hazards - Building resilient infrastructure is one of the major challenges faced by cities due to increasing urbanization rates and climate change. Furthermore, the application of... 相似文献
Sense of place, including an individual’s attitudes toward specific geographic settings, is generally predicted to influence willingness to engage in place-protective behaviors. Relatively little research, however, has empirically examined the influence of people’s attitudes toward a place on their willingness to pay for environmental protection. Using the example of a payment for ecosystem services (PES) initiative in the McKenzie River watershed, Oregon, USA, we found that place attitudes were a significant predictor of respondents’ willingness to pay for a program designed to benefit drinking water quality. These results suggest that connecting conservation actions to landscapes that are meaningful to people may increase their financial support for PES and other conservation programs. While program managers have little or no influence over stakeholders’ political ideology, gender, or income, managers may be able to influence prospective PES buyers’ awareness and attitudes through targeted communications, thereby potentially increasing support for place-based conservation efforts. 相似文献
Climate change disproportionately impacts the world’s poorest countries. A recent World Bank report highlighted that over 100 million people are at risk of falling into extreme poverty as a result of climate change. There is currently a lack of information about how to simultaneously address climate change and poverty. Climate change challenges provide an opportunity for those impacted most to come up with new and innovative technologies and solutions. This article uses an example from Mozambique where local and international partners are working side-by-side, to show how developing countries can simultaneously address climate change and poverty reduction using an ecosystem-based adaptation approach. Using ecosystem-based adaptation, a technique that uses the natural environment to help societies adapt to climate change, developing countries can lead the way to improve climate adaptation globally. This paradigm shift would help developing countries become leaders in ecosystem-based adaptation and green infrastructure techniques and has implications for climate policy worldwide.
POLICY RELEVANCE
The Paris Agreement resulting from the United Nations Framework Convention on Climate Change (UNFCCC) 21st Conference of Parties (COP 21) in December 2015 was rightly lauded for its global commitment to cut greenhouse gas emissions. However, COP 21 was also historic because of its call for non-party stakeholders to address climate change, inclusion of a global goal of ‘enhancing adaptive capacity, strengthening resilience and reducing vulnerability’, and the United States’ commitment of $800 million to adaptation funding. The combination of recognizing the need for new stakeholders to commit to climate change adaptation, the large impact climate change will have on the developing world, and providing access to funds for climate change adaptation creates a unique opportunity for developing countries to pave the way in adaptation policies in practices. Currently, developing countries are creating National Adaptation Plans (NAPs) for the UNFCCC. Through including a strong component of ecosystem-based adaptation in NAPs, developing countries can shape their countries’ policies, improve local institutions and governments, and facilitate a new generation of innovative leaders. Lessons learned in places like Mozambique can help lead the way in other regions facing similar climatic risks. 相似文献
Chirp frequency-modulated (FM) systems offer deterministic, repeatable source-signatures for high-resolution, normal incidence marine seismic reflection data acquisition. An optimal processing sequence for uncorrelated Chirp data is presented to demonstrate the applicability of some conventional seismic reflection algorithms to high-resolution data sets, and to emphasise the importance of a known source-signature. An improvement of greater than 60dB in the signal- to-noise ratio is realised from correlating the FM reflection data with the transmitted pulse. Interpretability of ringy deconvolved data is enhanced by the calculation of instantaneous amplitudes. The signal-to-noise ratio and lateral reflector continuity are both improved by the application of predictive filters whose effectiveness are aided by the repeatability of the Chirp source. 相似文献
Since the work of Postma and Backus, much has been learned about elastic constants in vertical transversely isotropic (VTI) media when the anisotropy is due to fine layering of isotropic elastic materials. Nevertheless, there has continued to be some uncertainty about the possible range of Thomsen's anisotropy parameters ε and δ for such media. We use both Monte Carlo studies and detailed analysis of Backus' equations for both two- and three-component layered media to establish the results presented. We show that ε lies in the range ?3/8 ε ½[〈v2p〉〈v?2p〉?1], for finely layered media; smaller positive and all negative values of ε occur for media with large fluctuations in the Lamé parameter λ in the component layers. We show that δ can also be either positive or negative, and that for constant density media, sign (δ) = sign (〈v?2p〉 ? 〈v?2s〉〈v2s/v2p〉). Monte Carlo simulations show that among all theoretically possible random media, positive and negative δ are equally likely in finely layered media. (Of course, the δs associated with real earth materials may span some smaller subset of those that are theoretically possible, but answering this important question is beyond our present scope.) Layered media having large fluctuations in λ are those most likely to have positive δ. This is somewhat surprising since ε is often negative or a small positive number for such media, and we have the general constraint that ε ? δ > 0 for layered VTI media. Since Gassmann's results for fluid-saturated porous media show that the mechanical effects of fluids influence only the Lamé parameter λ, not the shear modulus μ, these results suggest that small positive δ occurring together with small positive ε (but somewhat larger than δ) may be indicative of changing fluid content in a layered earth. 相似文献
Hurricane Sandy was an extraordinarily large storm that affected most of the eastern coast of the USA in October 2012. To assess this storm’s impact, the benthic invertebrate community structure and sediment properties were compared in samples collected 3.5 months prior to (July 2012) and 8 months after (July 2013) the hurricane at 97 locations in Barnegat Bay, New Jersey, USA. Barnegat Bay is a shallow back-barrier estuary just north of where Sandy made landfall. For all locations taken together, sediment total nitrogen concentration was lower afterwards, while total organic carbon and total phosphorus concentrations were similar. Sediment median particle size was the same before and after, but the sediment was better sorted after the storm. There were no differences in total abundance of invertebrates, species richness, species diversity, or the abundance of polychaetes, bivalves, or gastropods. Malacostracan crustaceans were more abundant after Sandy (average 82 (0.04 m2)?1) than they were before (average 64), due almost entirely to increased abundance of ampeliscid amphipods, which showed a shift toward smaller sizes in 2013. Annelids in the order Clitellata were on average less abundant after the hurricane (17) than before (53). The apparent minimal effect of Sandy on the benthic community in Barnegat Bay was probably because the passage of the hurricane had no detectable effects on salinity or dissolved oxygen concentrations throughout the bay. 相似文献