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611.
P. W. de Langen 《Maritime Policy and Management》2002,29(3):209-221
Over the last years, the concept of clustering has become a central concept for analysing the competitiveness of nations, industries and firms. The cluster concept can be usefully applied to study clustering of maritime activities. Maritime activities, such as shipping, shipbuilding and port and maritime services, are clearly geographically concentrated in a number of maritime clusters. Due to ongoing internationalization in these industries, the concentration of maritime activities in clusters is likely to increase. This observation leads to two important research questions: what are the advantages for firms to locate in clusters and what factors influence the development of maritime clusters? This study identifies four agglomeration economies that attract firms to cluster: a joint labour pool, a broad supplier and customer base, knowledge spillovers, and low transaction costs. Furthermore, it discusses the effects of aspects of the cluster structure, being the presence of internal competition, the heterogeneity of the cluster population, the entry and exit barriers, and the presence of (above mentioned) agglomeration effects. It also briefly discusses the important issue of cluster governance. This overview allows one to develop a theoretical framework to analyse clusters. In the empirical part, this framework is applied to the maritime cluster in The Netherlands. Based on empirical data, from surveys amongst firms in the maritime cluster, studies commissioned by the Dutch maritime Network and regional statistics, the presence of agglomeration economies in the cluster is shown. Secondly, it is shown that the cluster structure is beneficial for the performance. This paper finishes with conclusions and suggestions for further research. 相似文献
613.
P.G. Gipps 《Transportation Research Part B: Methodological》1981,15(2):105-111
The ability to predict the response of a vehicle in a stream of traffic to the behaviour of its predecessor is important in estimating what effect changes to the driving environment will have on traffic flow. Various proposed to explain this behaviour have different strengths and weaknesses. The paper constructs a new model for the response of the following vehicle based on the assumption that each driver sets limits to his desired braking and acceleration rates. The parameters in the model correspond directly to obvious characteristics of driver behaviour and the paper goes on to show that when realistic values are assigned to the parameters in a simulation, the model reproduces the characteristics of real traffic flow. 相似文献
614.
S. P. Jung K. J. Jun T. W. Park J. H. Yoon 《International Journal of Automotive Technology》2008,9(1):45-51
It is quite challenging to estimate the braking performance of a vehicle because the brake system is comprised of many parts, including a booster, master cylinder, and caliper. Calculation of characteristics such as braking force through vehicle tests requires much time and money. Therefore, the development of a method to estimate the braking performance of a vehicle using qualitative methods is beneficial. In this study, a program that can analyze the braking capabilities of a vehicle such as pressure, efficiency, and pedal travel is presented. The increase in disc temperature during braking as well as the properties of various boosters can be calculated using the proposed program. Dynamic characteristics of a vehicle equipped with a Load Sensing Proportional Valve (LSPV) were computed more precisely by obtaining the change in valve pressure according to the displacement of a suspension system. Since all input and output files are composed in the Microsoft Excel format, both design data management and database construction can easily completed. 相似文献
615.
N.P. Holliday J.J. Waniek R. Davidson D. Wilson L. Brown R. Sanders R.T. Pollard J.T. Allen 《Journal of Marine Systems》2006,59(3-4):201-218
Hydrographic surveys in three consecutive seasons in the Irminger Sea in 2001/2002 have revealed six physical regimes (zones) in which different surface mixing and spring re-stratification processes dominate. They are the South Irminger Current, the North Irminger Current, the Central Irminger Sea, the Polar-origin East Greenland Current, the Atlantic-origin East Greenland Current and the Reykjanes Ridge. The variations in restratification processes in particular have significant implications for the timing of shallow spring mixed layer development and therefore the timing and strength of the spring bloom. The relative roles of heat and freshwater in controlling re-stratification are examined for each hydrographic zone, and it is shown that the simplest concept of solar warming generating spring stratification is appropriate for the Irminger Current and the central Irminger Sea. However in the East Greenland Current and the Reykjanes Ridge zones, the springtime arrival of fresh or saline water at the surface dominates re-stratification and generates the earliest and strongest spring blooms of the region. In the cool fresh centre of the Irminger Sea the relatively low chlorophyll-a throughout the year cannot be wholly explained by stratification or nutrient concentrations. Details of the annual cycle in temperature, salinity, chlorophyll-a and nutrients are presented for each hydrographic zone. 相似文献
616.
This paper addresses a highly researched area, the reshuffling problem in ports, using a new paradigm-modified containership service order in light of credit risk assessment. Container stacking and reshuffling operations can cause ship delays and additional risk. In deep-sea terminals, outbound containers are tightly stacked according to the retrieval sequence. Due to lack of space, terminals stack containers in multiple tiers. This means any delay in the arrival of a ship can impose extra handlings and reshuffling of containers delaying future cargo handling. This paper addresses the reshuffling problem with a concept similar to the credit scoring and rating of creditworthiness used in the banking industry. By utilizing this comparison to the banking credit risk concept, a heuristic estimation model is proposed that illustrates the side effects of unscheduled modifications in containership service order. Further, the mega-ship trend amplifies the reshuffling debate. Probability of delay, reshuffles given delay, and call size at delay are introduced as the three-point risk metrics of the model. Numerical simulations illustrate the functionality to develop terminal stacking strategies as well as emphasize the mega-ship phenomenon and its side effects on terminals (i.e. yard operation deadlock). 相似文献
617.
Most global trade statistics in the public domain refer to official customs data, which are not generally available on a micro (individual cargo) level. With the increasing availability and completeness of ship positioning data from the global Automated Identification System (AIS), it is possible to derive more timely and detailed trade statistics for homogeneous commodity groups. The objective of this article is twofold: (1) to compare the accuracy of AIS-derived trade statistics to official customs data in the crude oil market and (2) to add a breakdown of trade by vessel size over time. We find that while AIS-derived data for seaborne crude exports show good alignment with official export numbers in aggregate, there are substantial temporal and geographical differences across countries and time due to the use of pipelines and transshipment in parts of the supply chain. We highlight the challenges in properly structuring and aggregating micro-level cargo data. Our findings are important for the proper derivation of shipping demand from trade data. 相似文献
618.
Haiying Jia Ove Daae Lampe Veronika Solteszova Siri P. Strandenes 《Maritime Policy and Management》2017,44(8):956-966
The importance of a seaport depends on how well it is connected in a transportation network. A port’s connectivity is therefore one of the key issues in determining its competitiveness and developments in regions and countries. We construct a port connectivity index for major Norwegian ports based on a unique dataset derived from the automated identification system (AIS) for multiple vessel types over a 7-year period. Port connectivity is evaluated empirically by the number of unique vessel visits, vessel sizes, and cargo sizes. The research has implications for port authorities and policy makers in the areas of port planning, infrastructure investment, short sea shipping promotion, and environmental policies. The contributions of this research are twofold. First, the methodology linking the AIS vessel-tracking system with port connectivity is a pioneering empirical application of maritime big data. Second, the port connectivity index is constructed for multiple vessel types and regional port groups, which is an improvement from the current literature where conceptual measures are constructed based on hypothetical and usually too simple optimization rules. The methodology can be easily expanded to other regions in the world. 相似文献
619.
David Cimba John Wagner Abhijit Baviskar 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2006,44(9):719-736
The increasing popularity of sport utility/light-duty vehicles has prompted the investigation of active roll management systems to reduce vehicle body roll. To minimize vehicle body roll and improve passenger comfort, one emerging solution is an active torsion bar control system. The validation of automotive safety systems requires analytical evaluation and laboratory testing prior to implementation on an actual vehicle. In this article, a computer simulation tool and accompanying hardware-in-the-loop test environment are presented for active torsion bar systems to study component configurations and performance limits. The numerical simulation illustrates that the hydraulic cylinder extension limits the active torsion system's ability to provide body roll angle reduction under various driving conditions. To compare the control system's time constant and body roll minimization capabilities for different hydraulic valve assemblies and equivalent hose lengths, an experimental test stand was created. For a typical hydraulic pressure and hose diameter, the equivalent hose length was not a key design variable that impacted the system response time. However, the servo-valve offered a quicker transient response and smoother steady-state behavior than the solenoid poppet actuators that may increase occupant safety and comfort. 相似文献
620.
W. E. Misselhorn N. J. Theron P. S. Els 《Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility》2006,44(1):65-81
Hardware-in-the-loop (HiL) is a testing method in which real-time measurements on physical hardware replace the mathematical model of the particular hardware during simulation. The development of a semi-active suspension prompted the need for such capability. HiL, implemented on a PC with a dSpaceTM board in conjunction with a hydrodynamic actuator, was compared to software simulations of single degree of freedom (DOF) and two DOF systems. HiL was also compared to a physical (ballast-based) two DOF system, comprising the rear suspension of a motorcycle. Comparisons between the HiL and software responses showed its suitability for testing suspension systems, thus providing a viable alternative to ballast-based suspension tests, using available hardware. The research also showed that actuator dynamics, filter types and amounts, and signal reference levels required special consideration. 相似文献