An MDP decomposition approach for traffic control at isolated signalized intersections

This article presents a novel approach for the dynamic control of a signalized intersection. At the intersection, there is a number of arrival flows of cars, each having a single queue (lane). The set of all flows is partitioned into disjoint combinations of nonconflicting flows that will receive green together. The dynamic control of the traffic lights is based on the numbers of cars waiting in the queues. The problem concerning when to switch (and which combination to serve next) is modeled as a Markovian decision process in discrete time. For large intersections (i.e., intersections with a large number of flows), the number of states becomes tremendously large, prohibiting straightforward optimization using value iteration or policy iteration. Starting from an optimal (or nearly optimal) fixed-cycle strategy, a one-step policy improvement is proposed that is easy to compute and is shown to give a close to optimal strategy for the dynamic proble

Transient handover blocking probabilities in road covering cellular mobile networks

This paper investigates handover and fresh call blocking probabilities for subscribers moving along a road in a traffic jam passing through consecutive cells of a wireless network. It is observed and theoretically motivated that the handover blocking probabilities show a sharp peak in the initial part of a traffic jam roughly at the moment when the traffic jam starts covering a new cell. The theoretical motivation relates handover blocking probabilities to blocking probabilities in the M/D/C/C queue with time-varying arrival rates. We provide a numerically efficient recursion for these blocking probabilities. \u

Spin-Dependent Electron Transmission Model for Chiral Molecules in Mesoscopic Devices

Various device-based experiments have indicated that electron transfer in certain chiral molecules may be spin-dependent, a phenomenon known as the Chiral Induced Spin Selectivity (CISS) effect. However, due to the complexity of these devices and a lack of theoretical understanding, it is not always clear to what extent the chiral character of the molecules actually contributes to the magnetic-field-dependent signals in these experiments. To address this issue, we report here an electron transmission model that evaluates the role of the CISS effect in two-terminal and multi-terminal linear-regime electron transport experiments. Our model reveals that for the CISS effect, the chirality-dependent spin transmission is accompanied by a spin-flip electron reflection process. Furthermore, we show that more than two terminals are required in order to probe the CISS effect in the linear regime. In addition, we propose two types of multi-terminal nonlocal transport measurements that can distinguish the CISS effect from other magnetic-field-dependent signals. Our model provides an effective tool to review and design CISS-related transport experiments, and to enlighten the mechanism of the CISS effect itself

Unified description of bulk and interface-enhanced spin pumping

The dynamics of non-equilibrium spin accumulation generated in metals or semiconductors by rf magnetic field pumping is treated within a diffusive picture. The dc spin accumulation produced in a uniform system by a rotating applied magnetic field or by a precessing magnetization of a weak ferromagnet is in general given by a (small) fraction of hbar omega, where omega is the rotation or precession frequency. With the addition of a neighboring, field-free region and allowing for the diffusion of spins, the spin accumulation is dramatically enhanced at the interface, saturating at the universal value hbar omega in the limit of long spin relaxation time. This effect can be maximized when the system dimensions are of the order of sqrt(2pi D omega), where D is the diffusion constant. We compare our results to the interface spin pumping theory of A. Brataas et al. [Phys. Rev. B 66, 060404(R) (2002)]

Appropriate Accuracy of Models for Decision-Support Systems: Case Example for the Elbe River Basin

Given the growing complexity of water-resources management there will be an increasing need\ud for integrated tools to support policy analysis, communication, and research. A key aspect of the design is the\ud combination of process models from different scientific disciplines in an integrated system. In general these\ud models differ in sensitivity and accuracy, while non-linear and qualitative models can be present. The current\ud practice is that the preferences of the designers of a decision-support system, and practical considerations\ud such as data availability guide the selection of models and data. Due to a lack of clear scientific guidelines the\ud design becomes an ad-hoc process, depending on the case study at hand, while selected models can be overly\ud complex or too coarse for their purpose. Ideally, the design should allow for the ranking of selected\ud management measures according to the objectives set by end users, without being more complex than\ud necessary. De Kok and Wind [2003] refer to this approach as appropriate modeling. A good case example is\ud the ongoing pilot project aiming at the design of a decision-support system for the Elbe river basin. Four\ud functions are accounted for: navigability, floodplain ecology, flooding safety, and water quality. This paper\ud concerns the response of floodplain biotope types to river engineering works and changes in the flooding\ud frequency of the floodplains. The HBV-D conceptual rainfall-runoff model is used to simulate the impact of\ud climate and land use change on the discharge statistics. The question was raised how well this rainfall-runoff\ud model should be calibrated as compared to the observed discharge data. Sensitivity analyses indicate that a\ud value of R2 = 0.87 should be sufficient

Circuit-Model Analysis for Spintronic Devices with Chiral Molecules as Spin Injectors

Recent research discovered that charge transfer processes in chiral molecules can be spin selective and named the effect chiral-induced spin selectivity (CISS). Follow-up work studied hybrid spintronic devices with conventional electronic materials and chiral (bio)molecules. However, a theoretical foundation for the CISS effect is still in development and the spintronic signals were not evaluated quantitatively. We present a circuit-model approach that can provide quantitative evaluations. Our analysis assumes the scheme of a recent experiment that used photosystem~I (PSI) as spin injectors, for which we find that the experimentally observed signals are, under any reasonable assumptions on relevant PSI time scales, too high to be fully due to the CISS effect. We also show that the CISS effect can in principle be detected using the same type of solid-state device, and by replacing silver with graphene, the signals due to spin generation can be enlarged four orders of magnitude. Our approach thus provides a generic framework for analyzing this type of experiments and advancing the understanding of the CISS effect

The method of successive approximations for the discounted Markov game

This paper presents a number of successive approximation algorithms for the repeated two-person zero-sum game called Markov game using the criterion of total expected discounted rewards. As Wessels [12] did for Markov decision processes stopping times are introduced in order to simplify the proofs. It is shown that each algorithm provides upper and lower bounds for the value of the game and nearly optimal stationary strategies for both players