Primary productivity of the Palmer Long Term Ecological Research Area and the Southern Ocean

A major objective of the Palmer Long Term Ecological Research (Palmer LTER) project is to obtain a comprehensive understanding of the various components of the Antarctic marine ecosystem. Phytoplankton production plays a key role in this so-called high nutrient, low chlorophyll environment, and factors that regulate production include those that control cell growth (light, temperature, and nutrients) and those that control cell accumulation rate and hence population growth (water column stability, grazing, and sinking). Sea ice mediates several of these factors and frequently conditions the water column for a spring bloom which is characterized by a pulse of production restricted in both time and space. This study models the spatial and temporal variability of primary production within the Palmer LTER area west of the Antarctic Peninsula and discusses this production in the context of historical data for the Southern Ocean. Primary production for the Southern Ocean and the Palmer LTER area have been computed using both light-pigment production models [Smith, R.C., Bidigare, R.R., Prézelin, B.B., Baker, K.S., Brooks, J.M., 1987. Optical characterization of primary productivity across a coastal front. Mar. Biol. (96), 575–591; Bidigare, R.R., Smith, R.C., Baker, K.S., Marra, J., 1987. Oceanic primary production estimates from measurements of spectral irradiance and pigment concentrations. Global Biogeochem. Cycles (1), 171–186; Morel, A., Berthon, J.F., 1989. Surface pigments, algal biomass profiles and potential production of the euphotic layer—relationships reinvestigated in view of remote-sensing applications. Limnol. Oceanogr. (34), 1545–1562] and an ice edge production model [Nelson, D.M., Smith, W.O., 1986. Phytoplankton bloom dynamics of the western Ross Sea ice edge: II. Mesoscale cycling of nitrogen and silicon. Deep-Sea Res. (33), 1389–1412; Wilson, D.L., Smith, W.O., Nelson, D.M., 1986. Phytoplankton bloom dynamics of the Western Ross Sea ice edge: I. primary productivity and species-specific production. Deep-Sea Res., 33, 1375–1387; Smith, W.O., Nelson, D.M., 1986. Importance of ice edge phytoplankton production in the Southern Ocean. BioScience (36), 251–257]. Chlorophyll concentrations, total photosynthetically available radiation (PAR) and sea ice concentrations were derived from satellite data. These same parameters, in addition to hydrodynamic conditions, have also been determined from shipboard and Palmer Station observations during the LTER program. Model results are compared, sensitivity studies evaluated, and productivity of the Palmer LTER region is discussed in terms of its space time distribution, seasonal and interannual variability, and overall contribution to the marine ecology of the Southern Ocean.     

Changes in multi-mode bus transit efficiency, 1988–1992

This paper examines the claim that US bus transit productivity has declined in recent years. It does so with reference to a piecewise-linear best-practice (DEA) production frontier, computed for multi-modal bus transit between 1988 and 1992. Efficiency is measured both by a Russell (static) and Malmquist (dynamic) measure of productivity change. The principal finding is that, overall, bus transit efficiency has improved slightly over the period.     

Late-Quaternary changes in productivity of the Southern Ocean

Paleoceanographic records based on new proxies of export production have been constructed for the South Atlantic sector of the Southern Ocean. A radionuclide-ratio proxy of particle flux (¹⁰Be/²³⁰Th) and the accumulation rate of authigenic uranium, which responds to the flux of organic carbon to the sea bed, both indicate a dramatic increase, compared to the present, in the export production of the Subantarctic zone (approximately the region between the present-day positions of the Subtropical Convergence and the Antarctic Polar Front) during glacial periods. If the South Atlantic is representative of the entire Southern Ocean, then export production in the Southern Ocean during the Last Glacial Maximum was substantially greater than at present. Previous studies, focusing on the burial of biogenic opal, failed to recognize the glacial increase in export production of the Southern Ocean because of a strong non-linearity between accumulation rates of opal and of organic carbon.     

A simulation model proposal to improve the productivity of container terminal operations through investment alternatives

Development of a container terminal (CT) closely deals with the efficiency of operating systems. This paper proposed a model to decide optimum investment alternatives to improve CT productivity. The proposed approach incorporates the parameters such as number of quay cranes, total length of a quay, yard trucks and yard cranes. The objectives of the model are minimizing the average ship turnaround time while maximizing the container throughput generated by the terminal. The methodology behind the model includes Discrete Event Simulation Model, data envelopment analysis (DEA) and cost-efficiency analysis. Considering container ship visits to Container Terminal Alpha (CT-A), the proposed model is demonstrated with 16 different investment scenario along with 10-months recorded operational data. The results addressed the Scenario LENG-2 (extent current total length of quays from 1.560 meters to 2.000 meters) as the optimal feasible solution for an investment in existing conditions. The model is also considered to besides contributions to investment decisions in CT, the developed framework might be extended to other transportation infrastructures.     

Productivity assessment of African seaports with biased technological change

Abstract

This paper analyses the productivity of a representative sample of African seaports from 2002 to 2008. Productivity scores are decomposed, based on the Luenberger productivity indicator, and the nature of technological change is analysed. The paper finds that Nigerian seaports are the most efficient, followed by Angola and Mozambique. Discussions of the results as well as related policy implications are provided.     

砂性土粒径与水力式疏浚施工输送产量的关系

砂性土输送生产率计算需要较为复杂的过程,其涉及泥泵特性、管路布设信息、驱动功率、天然土密度、沉降流速等数据,且往往其中部分量难以准确获取。为此,专门针对砂性土粒径对输送的影响进行研究,依据浆体管路输送原理,对疏浚施工水力式挖泥船砂性土输送生产率限制条件进行分析,得到简化的砂性土生产率计算方法,在已知某种砂性土粒径的情况下,可直接求出输送生产率,而不必经过泥泵特性曲线、管路曲线求取等复杂过程,该方法可为疏浚工程生产预测提供参考。     

Impacts of Transport Infrastructure on Productivity and Economic Growth: Recent Advances and Research Challenges

ABSTRACT

The paper provides an update of the survey focusing on estimating the contribution of transport infrastructure to productivity and economic growth. The central questions addressed are possible reasons behind the conflicting results reported in the literature on the elasticity of economic output with respect to transport infrastructure investment. After providing a systematic review of recent empirical studies on the effects of transport infrastructure on productivity and economic growth, the paper notes that controversial results can be attributed to ten causes (grouped into three categories for distinguishing): (1) related to different contexts: research period, geographical scales, and country's capability in enabling economic development; (2) related to different phenomena that are being measured: different economic sectors, different types of transport infrastructure, and different quality levels of transport infrastructure; and (3) related to distinct ways of measuring a similar phenomenon: measures used to describe the dependent variable and explanatory variable, functional specification, and estimation method of the econometric model. Strong network externalities of transport infrastructure may result in nonlinearity of the relationship between transport infrastructure and economic growth. Moreover, the absence of spatial concerns in infrastructure's impacts is another important source of inconclusive results. Finally, building on recent literature, the paper has discussed policy implications and identified several research avenues for further research.     

Non-parametric analyses of efficiency of airports

This paper estimates the efficiencies and productivity changes of 12 international airports in the Asia-Pacific region based on data from 1998 to 2006. We apply stochastic frontier analysis (SFA) to compute efficiency estimates and use the Malmquist productivity index (MPI) to analyze productivity changes. We use the SFA model with a translog-type production function after testing the statistical hypotheses. According to the results of the SFA hypothesis tests, airports have experienced a technological regression; the deviations from the efficiency frontier are caused more by technical inefficiency than random noise. However, the inefficiency was found to decrease. The MPI reveals a declining trend resulting more from technological change than from efficiency change, with a decrease in inefficiency. Taken together, both the hypothesis tests and the MPI not only provide consistent conclusions, but also suggest that airports should concentrate on technological progress.     

Productive efficiency and ownership of urban bus services

The established ownership mix of urban bus operations in Australia provides a unique opportunity to investigate the productivity differences between public and private bus service supply. Using duality theory in economics which links economic indices of factor productivity to the cost structure of a firm, we develop empirical measures of total and partial productivity of inputs, and adjust the differences for the effects of ownership status and operating environment. The evidence supports the notion that private supply of public passenger transport in general has performed more efficiently in the past than public supply, although the differences in productivity need not continue in the future.     

基于智能疏浚模式的滨州港产能与控制模型

高效疏浚是疏浚施工一直追求的目标,也是研究的热点。基于智能疏浚模式的控制原理,对智能疏浚模式下"航浚6008"轮的滨州港工程施工数据进行分析,建立产能与控制模型,并对该耙吸挖泥船在滨州港工程的产能做进一步优化计算。结果表明,生产率受流量、浆体相对密度与泥泵特性等因素的影响和制约;疏浚过程中,智能疏浚模式主要依靠活动罩控制器与泥泵控制器的相互配合,当实际泥浆流速高于(最佳)设定值时,在其他边界条件不变时,活动罩自动控制器将活动罩下压,使耙头生产率与泥泵汽蚀控制相匹配;检测到泥泵汽蚀时,泥泵控制器通过降低泥泵转速而降低泥浆流速,以达到最佳混合物流速。