Optimal traffic control at railway junctions

Conflict occurs when two or more trains approach the same junction within a specified time. Such conflicts result in delays. Current practices to assign the right of way at junctions achieve orderly and safe passage of the trains, but do not attempt to reduce the delays. A traffic controller developed in the paper assigns right of way to impose minimum total weighted delay on the trains. The traffic flow model and the optimisation technique used in this controller are described. Simulation studies of the performance of the controller are given.

The conflict resolution in connected railway junctions

Purpose of study: Traffic conflicts occur when trains on different routes approach a converging junction in a railway network at the same time. To prevent collisions, a right-of-way assignment is needed to control the order in which the trains should pass the junction. Such control action inevitably requires the braking and/or stopping of trains, which lengthens their travelling times and leads to delays. Train delays cause a loss of punctuality and hence directly affect the quality of service. It is therefore important to minimise the delays by devising a suitable right-of-way assignment. One of the major difficulties in attaining the optimal right-of-way assignment is that the number of feasible assignments increases dramatically with the number of trains. Connected-junctions further complicate the problem. Exhaustive search for the optimal solution is time-consuming and infeasible for area control (multi-junction). Even with the more intelligent deterministic optimisation method revealed in [1], the computation demand is still considerable, which hinders real-time control. In practice, as suggested in [2], the optimality may be traded off by shorter computation time, and heuristic searches provide alternatives for this optimisation problem.

An event-based traffic flow model for traffic control at railway junctions

This paper introduces an event-based traffic model for railway systems adopting fixed-block signalling schemes. In this model, the events of trains' arrival at and departure from signalling blocks constitute the states of the traffic flow. A state transition is equivalent to the progress of the trains by one signalling block and it is realised by referring to past and present states, as well as a number of pre-calculated look-up tables of run-times in the signalling block under various signalling conditions. Simulation results are compared with those from a time-based multi-train simulator to study the improvement of processing time and accuracy.

Train control to reduce delays upon service disturbances at railway junctions

Train delay is one of the most important indexes to evaluate the service quality of the railway. Because of the interactions of movement among trains, a delayed train may conflict with trains scheduled on other lines at junction area. Train that loses conflict may be forced to stop or slow down because of restrictive signals, which consequently leads to the loss of run-time and probably enlarges more delays. This paper proposes a time-saving train control method to recover delays as soon as possible. In the proposed method, golden section search is adopted to identify the optimal train speed at the expected time of restrictive signal aspect upgrades, which enables the train to depart from the conflicting area as soon as possible. A heuristic method is then developed to attain the advisory train speed profile assisting drivers in train control. Simulation study indicates that the proposed method enables the train to recover delays as soon as possible in case of disturbances at railway junctions, in comparison with the traditional maximum traction strategy and the green wave strategy.

Artificial grain boundary Josephson junctions : properties and applications

Engineered grain boundary Josephson junctions in YBaCuO were formed on bicrystal Y-ZrO2 substrates. Laser deposited films were patterned into micron size microbridges. The authors obsd. a pronounced correlation between superconducting transport properties of grain boundary junctions and the misorientation angle θ between the two halves of the bicrystal. The crit. Josephson current Ic decreased about four orders of magnitude as θ was increased from 0 to 45 degrees. Clear microwave and magnetic field responses were obsd. at 77 K. At this temp., crit. current times normal resistance products, IcRn, of up to 1 mV were measured for low angle grain boundaries, and Shapiro steps were obsd. up to that voltage. DC SQUIDs were fabricated, and best performance at 77 K was obtained for θ = 32° with a 4-μm strip width. To utilize the higher IcRn value of a lower θ, submicron junctions have to be developed. [on SciFinder(R)]

Mathematical models of calcium and tight junctions in normal and reconstructed epidermis

This project investigated the calcium distributions of the skin, and the growth patterns of skin substitutes grown in the laboratory, using mathematical models. The research found that the calcium distribution in the upper layer of the skin is controlled by three different mechanisms, not one as previously thought. The research also suggests that tight junctions, which are adhesions between neighbouring skin cells, cannot be solely responsible for the differences in the growth patterns of skin substitutes and normal skin.

Zero-bias conductance and energy gap measurements in LaNiO3-YBa2Cu3O7-x junctions

Conductance measurements of junctions between a high- superconductor and a metallic oxide have been carried out along the a-b plane to examine the tunnel-junction spectra. For these measurements, in situ films have been grown on c-axis oriented thin films using the pulsed laser deposition technique. Two distinctive energy gaps have been observed along with conductance peaks around zero bias. The analysis of zero-bias conductance and energy gap data suggests the presence of midgap states located at the centre of a finite energy gap. The results obtained are also in accordance with the d-wave nature of high- superconductors.

Mathematical models of calcium and tight junctions in normal and reconstructed epidermis

This project investigated the calcium distributions of the skin, and the growth patterns of skin substitutes grown in the laboratory, using mathematical models. The research found that the calcium distribution in the upper layer of the skin is controlled by three different mechanisms, not one as previously thought. The research also suggests that tight junctions, which are adhesions between neighbouring skin cells, cannot be solely responsible for the differences in the growth patterns of skin substitutes and normal skin.

Some investigations on secondary breakdown in p-n junctions considering the effect of thermally generated carriers

The V-I characteristic of a p-n junction under breakdown is calculated taking the thermally generated carriers into account. The current density distributions computed under different conditions have been given. The light emission and other characteristics reported by Chiang and Lauritzen and others have been explained.

Power dissipation for systems with junctions of multiple quantum wires

We study power dissipation for systems of multiple quantum wires meeting at a junction, in terms of a current splitting matrix (M) describing the junction. We present a unified framework for studying dissipation for wires with either interacting electrons (i.e., Tomonaga-Luttinger liquid wires with Fermi-liquid leads) or noninteracting electrons. We show that for a given matrix M, the eigenvalues of (MM)-M-T characterize the dissipation, and the eigenvectors identify the combinations of bias voltages which need to be applied to the different wires in order to maximize the dissipation associated with the junction. We use our analysis to propose and study some microscopic models of a dissipative junction which employ the edge states of a quantum Hall liquid. These models realize some specific forms of the M matrix whose entries depends on the tunneling amplitudes between the different edges.

Reactive characteristics of narrow germanium p-n junctions in the breakdown region

An inductive behaviour observed in germanium p-n junctions in the breakdown region is reported.

Reverse bias capacitance measurements on copper-doped germanium p-n junctions in the breakdown region

Results of measurements at a high frequency on reverse bias capacitance of copper-doped germanium junctions are reported. Phenomenal increase in capacitance is found in the breakdown region, particularly at low temperatures.

Improved synthesis of carbon nanotubes with junctions and of single-walled carbon nanotubes

Pyrolysis of thiophene over nickel nanoparticles dispersed on silica is shown to yield Y-junction carbon nanotubes with smaller diameters than those obtained by the pyrolysis of organometallic-thiophene mixtures. In the presence of water vapour, the pyrolysis of organometallic-hydrocarbon mixtures yields single-walled nanotubes, as well as relatively narrow-diameter carbon nanotubes with Y-junctions. Pyrolysis-of organometallic-hydrocarbon mixtures, in the absence of water vapour, only gives nanotubes with T- and Y-junctions.