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This paper presents a mathematical characterization of the main features of the molecular communication between platelets and endothelial cells via CD40 signaling during the initial phases of atherosclerosis, known also as atherogenesis. We demonstrate through laboratory experimentation that the release of soluble CD40L molecules from platelets in a fluid medium is enough to trigger expression of adhesion molecules on endothelial cell's surface; that is, physical contact between the platelets and the endothelial cells is not necessary. We also propose the mathematical model of this communication, and we quantify the model parameters by matching the experiment results to the model. In addition, this mathematical model of platelet-endothelium interaction, along with propagation models typical of blood vessels, is incorporated into a simulation platform. Analysis of the simulation results indicates that these enhancements render the simulator a useful tool upon which to base discussion for planning research, and has the potential to be an important step in the understanding, diagnosis, and treatment of cardiovascular diseases.

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In a hierarchical network, groups of nodes are represented by logical nodes for the purposes of simpllfying routing. Each group has a set of ingress-egress nodes, and routing information is conveyed to the outside world in the form of a transition matrix that gives the cost of traversing the network between each ingress-egress node pair. In this paper, we present a minimal logical node representation that has suMicient descriptive power to enable path selection in su port of connection admission control for services that have both path &estrictive) and link (additive) constraints. For example, the representation can be used to find a path that maximizes bandwidth subject to a delay constraint or minimizes delay subject to a bandwidth constraint. We present our solution in the form of a matrix whose elements are vectors, each of which specifies the @-cient Jrontrer of the solution space, and we specify an efficient procedure for constructing the efficient frontier. We present the least upper bound on the number of elements that must be present in the efficient frontier. We provide numerical examples that illustrate construction of the efficient frontier.

A wide variety of acoustic systems has multiple sources and receivers. This paper proposes a technique for making acoustic measurements simultaneously for multiple sources. The proposed technique features a collection of excitation signals of the maximum-length sequence (MLS) and MLS-related classes. Each signal in the set has a pulse-like autocorrelation function, and the cross-correlation functions between arbitrary pairs of signals drawn from the set have peak values that are significantly lower than the peak magnitude of the autocorrelation functions. The proposed method is particularly valuable when characterization of multisource, multireceiver system must be accomplished in a limited time period. Both simulation and experimental results are presented that demonstrate the feasibility and fidelity of the proposed techniques in characterizing acoustic systems.

Abstract-We examine the traffic-handling capabilities of General Packet Radio Service (GPRS) with respect to supporting IP-based Internet services. We begin with an overview of GPRS in which we discuss its general characteristics, connection set-up procedures, and data transfer procedures, both for the reverse link and the forward link. We then present an analytical model to assess throughput of the reverse link as a function of the number of users connected and the distribution of user message lengths. Next, we investigate the capability of GPRS to support World Wide Web access using the analytical model. Specifically, we present a realistic scenario for user sessions operating under the Hypertext Transfer Protocol (HTTP) and we assess the transaction-handling capabilities as a function of the number of user sessions, taking into account network delays, forward link transmission, random access delay, and other factors. The results obtained by using the analytical model in both cases are verified by simulation. We also consider, via simulation, a scenario where both continuously backlogged users and users operating HTTP sessions are present. We find that, in the case of continuously backlogged users, an increase in the number of contention slots does not always translate to an increase in throughput, while, in the case of users operating HTTP sessions, the downlink serves as the main bottleneck in the system. We conclude with a discussion of some open issues in the design of GPRS-based Internet access.