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81.
Coral reefs are threatened by impacts such as from scuba diving, and ongoing research is required to assess diving impacts, diver behavior and environmental knowledge. This study investigated perceived diving impacts, reef condition and norms among scuba divers at Sodwana Bay (South Africa). Divers viewed contact with coral as damaging, and perceived environmental degradation at dive sites. However, most divers saw activities such as photography as causing little or no damage to reefs. One meter or less was believed to be a safe distance from the reef or the wildlife to avoid contact or disturbance, and encounter norms were high. Age and experience influenced most perceptions, although cannot be accepted as reliable indicators of divers' perceptions or behavior, due to the heterogeneous conduct of divers of various experience and age as described in literature. The importance of human perceptions to understand what strategies need implementation in diving management is discussed. 相似文献
82.
Van Cauwenberg Jelle De Bourdeaudhuij Ilse Clarys Peter de Geus Bas Deforche Benedicte 《Transportation》2019,46(6):2151-2172
Transportation - The promotion of sustainable and healthy mobility among older adults (≥?65 years) is an important challenge. E-bikes may be part of the solution, but research... 相似文献
83.
84.
James G. Mitchell Hidekatsu Yamazaki Laurent Seuront Fabian Wolk Hua Li 《Journal of Marine Systems》2008,69(3-4):247
Marine phytoplankton experience competition, predation, infection and aggregation occurring across distances of micrometres to centimetres. However, the consequences of these interactions influence global processes, such as climate and fisheries productivity. There is a long-standing default assumption that these global processes cannot be traced to plankton distributions and interactions below a few metres because of the homogenising effect of turbulence [Hutchinson, G.E., 1961. The paradox of the plankton. Am. Nat. 95, 137–146.; Siegel, D.A., 1998. Resource competition in a discrete environment: Why are plankton distributions paradoxical? Limnol. Oceanogr. 43, 1133–1146.]. We show that, in active turbulence, phytoplankton patches, on the order of 10 cm, have repeatable asymmetry and regular spacing over distances of centimetres to tens of metres. The regularity and hierarchical nature of the patches in mixed ocean water means that phytoplankton are distributed in a dynamic, but definite seascape topography, where groups of patches coalesce between intermittent turbulent eddies. These patches may link large scale processes and microscale interactions, acting as fundamental components of marine ecosystems that influence grazing efficiency, taxonomic diversity, and the initiation of aggregation and subsequent carbon flux. 相似文献
85.
We investigated perceived travel possibilities (or subjective choice-sets, consideration-sets) of car and train travellers on the main corridors to the city of Amsterdam, The Netherlands, and associations with traveller and trip characteristics. We conducted secondary analysis on a survey sample consisting of 7950 train and 19,232 car travellers. Forty-five percent of train travellers had a car in their objective choice-set, 27% of them would however never use it for this trip. Trip destination city centre, trip purpose, paying for the trip, public transport commitment, traffic congestion and parking problems were associated with consideration of car as alternative. Forty-two percent of car travellers had public transport in their subjective choice-set. The ratio between perceived public transport and objective car travel time stood out as determinant of consideration-sets, next to destination city centre, trip purpose, travel time and private versus company car ownership. On average, car travellers’ perceptions of public transport travel time exceeded objective values by 46%. We estimated that if perceptions would be more accurate, two out of three car travellers that currently do not see public transport as an alternative would include it in their choice-set, and use it from time to time. This effect has strong theoretical and policy implications. 相似文献
86.
M. A. H. Van Der J. H. E. A. Muijderman F. E. Veldpaus 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1997,28(4):307-323
Controllers for semi-active suspensions have to account for constraints on damper range, tire force and suspension travel. Two approaches to incorporate these constraints in the design of controllers to minimize peak values in the chassis acceleration are considered. It is assumed that information on the oncoming road elevations (preview) is available. In the soft constraint approach, the constraints on tire force and suspension travel are included in a quadratic performance index. Two clipped optimal control laws, which deal with preview in a different way, are presented. Simulation results with a 2-DOF vehicle model on some rounded pulses show that these laws do not work satisfactorily with respect to the constraints. Therefore, the control problem is reformulated as a constrained optimization problem with hard constraints on tire force and suspension travel. Simulations with the same model on the same rounded pulses show that the hard constraint approach handles the constraints more properly. 相似文献
87.
Preview Estimation and Control for (Semi-) Active Suspensions 总被引:3,自引:0,他引:3
R.G.M. Huisman F.E. Veldpaus J.G.A.M. Van Heck J.J. Kok 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1993,22(5):335-346
An active suspension with preview is tested for rounded pulses and a stochastic road surface, and is compared to a passive suspension. The spectacular performance improvement obtained for a step function as road surface is not achieved but the improvement is still significant. The frequency response of the active suspension is determined for comparison with some suspension systems found in literature
An observer to reconstruct the preview information is presented. No model of the road surface is needed. From simulations, it appears that the observer reconstructs both deterministic and stochastic road surfaces satisfactory. However, the influence of measurement noise is not reduced sufficiently. 相似文献
An observer to reconstruct the preview information is presented. No model of the road surface is needed. From simulations, it appears that the observer reconstructs both deterministic and stochastic road surfaces satisfactory. However, the influence of measurement noise is not reduced sufficiently. 相似文献
88.
R. Van Der Valk H.B. Pacejka 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》1993,22(2):97-121
A dynamical model is presented to analyse the stability of motion of the two-wheeled 'Fokker F.28-like' landing gear including tyres. The model is equally applicable to similar landing gears. The influence of the introduction of a specially designed torsional damper on the dynamical behaviour of the landing gear-tyre combination is investigated. Results of the stability calculations are supported by test results. 相似文献
89.
In Europe, ports are confronted with a closer integration in the maritime and shipping industries. The co-operation agreements can take several forms such as alliances and mergers among shipping lines, conferences, involvement of shipping companies in terminal management, and extending interests in inland transport of shipping companies. In this paper we give a brief overview of these different types of agreement and we examine the consequences of this evolution of the market structures in which ports and shipping companies have to operate. More specifically, attention goes to the competitive position of the port in this new environment. It is clear that the role of the port and the port authorities has to be redefined to guarantee that it remains a fully fledged player in this fast evolving integrated market. 相似文献
90.
Despite the emphasis placed on the contextual nature of integrated coastal management (ICM) implementation in the literature, many uniformities are encountered in ICM implementation worldwide. In this article the tangled threads of ICM practice are unravelled and a theoretically founded set of criteria for evaluating the design of ICM implementation models is provided. First, paradigms in integrated environmental management (IEM) implementation, the broader domain within which ICM practice is nested, are characterized in terms of their key concepts. Next, the paradigms are used as a mechanism to distill uniformities in ICM practice as reported in review articles. Finally a set of fourteen building blocks against which the scientific credibility of contextual, country-specific ICM implementation models can be validated, is generated by translating the theory-based characterization into evaluation criteria readily accessible to practitioners. 相似文献