Random Access Transport Capacity

We develop a new metric for quantifying end-to-end throughput in multihop wireless networks, which we term random access transport capacity, since the interference model presumes uncoordinated transmissions. The metric quantifies the average maximum rate of successful end-to-end transmissions, multiplied by the communication distance, and normalized by the network area. We show that a simple upper bound on this quantity is computable in closed-form in terms of key network parameters when the number of retransmissions is not restricted and the hops are assumed to be equally spaced on a line between the source and destination. We also derive the optimum number of hops and optimal per hop success probability and show that our result follows the well-known square root scaling law while providing exact expressions for the preconstants as well. Numerical results demonstrate that the upper bound is accurate for the purpose of determining the optimal hop count and success (or outage) probability.Comment: Submitted to IEEE Trans. on Wireless Communications, Sept. 200

The generation of latent-ion-transport capacity

Of the various hypotheses designed to explain the movement of ions from the environment into the plant cell, the most attractive suggests that ions traverse cell membranes in combination with an endogenously produced carrier substance.(1,2) The hypothesis stems from the recognition that absorption kinetics are not first-order, but are, rather, best represented by a formulation analogous to that which describes the reversible combination of substrate and enzyme.(3) The carrier hypothesis is at least consistent with the known characteristics of the absorption process. Thus the remarkable specificity of the absorption process may be imputed to specificity on the part of the carriers; the requirement for respiratory energy may be related either to the production of carrier or to the degradation of ion-carrier complex; and the ability of ions to penetrate ion-impermeable cellular membranes may be ascribed to the formation of a permeating ion-carrier complex

The impact of freight transport capacity limitations on supply chain dynamics

We investigate how capacity limitations in the transportation system affect the dynamic behaviour of supply chains. We are interested in the more recently defined, 'backlash' effect. Using a system dynamics simulation approach, we replicate the well-known Beer Game supply chain for different transport capacity management scenarios. The results indicate that transport capacity limitations negatively impact on inventory and backlog costs, although there is a positive impact on the 'backlash' effect. We show that it is possible for both backlog and inventory to simultaneous occur, a situation which does not arise with the uncapacitated scenario. A vertical collaborative approach to transport provision is able to overcome such a trade-off. © 2013 Taylor & Francis

High-performance heat pipes for heat recovery applications

Methods to improve the performance of reflux heat pipes for heat recovery applications were examined both analytically and experimentally. Various models for the estimation of reflux heat pipe transport capacity were surveyed in the literature and compared with experimental data. A high transport capacity reflux heat pipe was developed that provides up to a factor of 10 capacity improvement over conventional open tube designs; analytical models were developed for this device and incorporated into a computer program HPIPE. Good agreement of the model predictions with data for R-11 and benzene reflux heat pipes was obtained

Optimal transport on supply-demand networks

Previously, transport networks are usually treated as homogeneous networks, that is, every node has the same function, simultaneously providing and requiring resources. However, some real networks, such as power grid and supply chain networks, show a far different scenario in which the nodes are classified into two categories: the supply nodes provide some kinds of services, while the demand nodes require them. In this paper, we propose a general transport model for those supply-demand networks, associated with a criterion to quantify their transport capacities. In a supply-demand network with heterogenous degree distribution, its transport capacity strongly depends on the locations of supply nodes. We therefore design a simulated annealing algorithm to find the optimal configuration of supply nodes, which remarkably enhances the transport capacity, and outperforms the degree target algorithm, the betweenness target algorithm, and the greedy method. This work provides a start point for systematically analyzing and optimizing transport dynamics on supply-demand networks.Comment: 5 pages, 1 table and 4 figure

Gas Release and Transport Capacity Investment as Instruments to Foster Competition in Gas Markets

Motivated by recent policy events experienced by the European natural gas industry, this paper develops a simple model for analyzing the interaction between gas release and capacity investment programs as tools to improve the performance of imperfectly competitive markets. We consider a regional market in which a measure that has an incumbent release part of its gas to a marketer complements a program of investment in transport capacity dedicated to imports by the marketer, at a regulated transport charge, of competitively-priced gas. First, we examine the case where transport capacity is regulated while gas release is not, i.e., the volume of gas released is determined by the incumbent. We then analyze the effect of the "artifcial" duopoly created by the regulator when the latter regulates both gas release and transport capacity. Finally, using information on the French industry, we calibrate the basic demand and cost elements of the model and perform some simulations of these two scenarios. Besides allowing us to analyze the economic properties of these scenarios, a policy implication that comes out of the empirical analysis is that, when combined with network expansion investments, gas-release measures applied under regulatory control are indeed effective short-term policies for promoting gas-to-gas competition.Natural gas, Gas release, Regulation, Competition

Effect of hydraulic parameters on sediment transport capacity in overland flow over erodible beds

Sediment transport is an important component of the soil erosion process, which depends on several hydraulic parameters like unit discharge, mean flow velocity, and slope gradient. In most of the previous studies, the impact of these hydraulic parameters on transport capacity was studied for non-erodible bed conditions. Hence, this study aimed to examine the influence of unit discharge, mean flow velocity and slope gradient on sediment transport capacity for erodible beds and also to investigate the relationship between transport capacity and composite force predictors, i.e. shear stress, stream power, unit stream power and effective stream power. In order to accomplish the objectives, experiments were carried out in a 3.0 m long and 0.5 m wide flume using four well sorted sands (0.230, 0.536, 0.719, 1.022 mm). Unit discharges ranging from 0.07 to 2.07 × 10<sup>−3</sup> m<sup>2</sup> s<sup>−1</sup> were simulated inside the flume at four slopes (5.2, 8.7, 13.2 and 17.6%) to analyze their impact on sediment transport rate. The sediment transport rate measured at the bottom end of the flume by taking water and sediment samples was considered equal to sediment transport capacity, because the selected flume length of 3.0 m was found sufficient to reach the transport capacity. The experimental result reveals that the slope gradient has a stronger impact on transport capacity than unit discharge and mean flow velocity due to the fact that the tangential component of gravity force increases with slope gradient. Our results show that unit stream power is an optimal composite force predictor for estimating transport capacity. Stream power and effective stream power can also be successfully related to the transport capacity, however the relations are strongly dependent on grain size. Shear stress showed poor performance, because part of shear stress is dissipated by bed irregularities, bed form evolution and sediment detachment. An empirical transport capacity equation was derived, which illustrates that transport capacity can be predicted from median grain size, total discharge and slope gradient

Nodal prices, capacity valuation and investments in natural gas markets - Overview and Analytical Framework

Especially in the short-term, prices in natural gas markets are not exclusively determined by overall supply and demand, but also by the availability of the transport infrastructure. If transportation capacity is scarce, prices may form in (local) residual markets and can differ regionally. If available, storages provide intertemporal arbitrage possibilities which also impact prices. Temporal and regional price differences, in turn, determine the value of storage and transport capacity if either one is scarce. This paper applies an analytical framework for a simple pipeline grid with a storage over two periods to illustrate the interdependencies between prices, scarce capacity and capacity value. The theoretically optimal transportation and storage tariffs are described analytically. The optimal pipeline investment size is shown to be related to marginal storage investment and a function of the discounted and aggregated cost of congestion over the lifetime's asset.Natural gas; Prices; Transport capacity; Storage; Investment

Design of a robust railway line system for severe winter conditions in The Netherlands

Winter weather has a major impact on railway operations in The Netherlands. To stay in control, the number of trains is reduced by half in a special “winter timetable”. This results in a more robust network, but an insufficient amount of transport capacity. Adapting the line system can result in more transport capacity without losing robustness. This paper therefore focuses on the performance of a line system under extreme weather conditions. We define several criteria to assess the performance of the line system in terms of robustness and transport capacity. A case study has been conducted on the railway network in The Netherlands, which indicates that all alternatives are more robust and yield more transport capacity than the current winter timetable