Approximation Algorithms for Time-Constrained Scheduling on Line Networks

We consider the problem of time-constrained scheduling of packets in a communication network. Each packet has, in addition to its source and its destination, a release time and a deadline. The goal of an algorithm is to maximize the number of packets that arrive to their destinations by their respective deadlines, given the network constraints.     

Pretreatment of wastewater: optimal coagulant selection using Partial Order Scaling Analysis (POSA)

Jar-test is a well-known tool for chemical selection for physical-chemical wastewater treatment. Jar test results show the treatment efficiency in terms of suspended matter and organic matter removal. However, in spite of having all these results, coagulant selection is not an easy task because one coagulant can remove efficiently the suspended solids but at the same time increase the conductivity. This makes the final selection of coagulants very dependent on the relative importance assigned to each measured parameter. In this paper, the use of Partial Order Scaling Analysis (POSA) and multi-criteria decision analysis is proposed to help the selection of the coagulant and its concentration in a sequencing batch reactor (SBR). Therefore, starting from the parameters fixed by the jar-test results, these techniques will allow to weight these parameters, according to the judgments of wastewater experts, and to establish priorities among coagulants. An evaluation of two commonly used coagulation/flocculation aids (Alum and Ferric Chloride) was conducted and based on jar tests and POSA model, Ferric Chloride (100 ppm) was the best choice. The results obtained show that POSA and multi-criteria techniques are useful tools to select the optimal chemicals for the physical-technical treatment.     

Morphology and mechanical properties of styrene homoblends of methacrylate and sulfonate ionomers

Summary Dynamic mechanical properties and morphology of homoblends of sulfonated polystyrene and poly(styrene-co-methacrylate) ionomers were investigated. While two tan δ peaks were found in the unblended ionomer samples, three tan δ peaks were observed for the homoblend. The peak at 152 °C is thought to be due to the matrix T _g, and those at 194 and 261 °C probably represent the glass transitions of cluster regions, containing methacrylate-rich multiplets and sulfonate-rich multiplets, respectively. In SAXS profile, only a very broad plateau-type feature was seen for the homoblend. This result implies either that the number density of the scattering centers at prevalent distances is low or that each scattering center has a different electron density. Thus we suggest that in the present study the multiplets of the homoblend consist of random mixtures of sulfonate and carboxylate groups. Received: 27 July 1998/Revised version: 21 September 1998/Accepted: 19 October 1998     

Active vision for controlling an electric wheelchair

Most of the electric wheelchairs available in the market are joystick-driven and therefore assume that the user is able to use his hand motion to steer the wheelchair. This does not apply to many users that are only capable of moving the head like quadriplegia patients. This paper presents a vision-based head motion tracking system to enable such patients of controlling the wheelchair. The novel approach that we suggest is to use active vision rather than passive to achieve head motion tracking. In active vision-based tracking, the camera is placed on the user’s head rather than in front of it. This makes tracking easier, more accurate and enhances the resolution. This is demonstrated theoretically and experimentally. The proposed tracking scheme is then used successfully to control our electric wheelchair to navigate in a real world environment.     

Virtual marionettes: a system and paradigm for real-time 3D animation

This paper describes a computer graphics system that enables users to define virtual marionette puppets, operate them using relatively simple hardware input devices, and display the scene from a given viewpoint on the computer screen. This computerized marionette theater has the potential to become a computer game for children, an interaction tool over the Internet, enabling the creation of simultaneously viewed and operated marionette show by users on the World Wide Web, and, most importantly, a versatile and efficient professional animation system.     

Analytic expressions for rate and CV of a type I neuron driven by white gaussian noise

We study the one-dimensional normal form of a saddle-node system under the influence of additive gaussian white noise and a static "bias current" input parameter, a model that can be looked upon as the simplest version of a type I neuron with stochastic input. This is in contrast with the numerous studies devoted to the noise-driven leaky integrate-and-fire neuron. We focus on the firing rate and coefficient of variation (CV) of the interspike interval density, for which scaling relations with respect to the input parameter and noise intensity are derived. Quadrature formulas for rate and CV are numerically evaluated and compared to numerical simulations of the system and to various approximation formulas obtained in different limiting cases of the model. We also show that caution must be used to extend these results to the Theta neuron model with multiplicative gaussian white noise. The correspondence between the first passage time statistics for the saddle-node model and the Theta neuron model is obtained only in the Stratonovich interpretation of the stochastic Theta neuron model, while previous results have focused only on the Ito interpretation. The correct Stratonovich interpretation yields CVs that are still relatively high, although smaller than in the Ito interpretation; it also produces certain qualitative differences, especially at larger noise intensities. Our analysis provides useful relations for assessing the distance to threshold and the level of synaptic noise in real type I neurons from their firing statistics. We also briefly discuss the effect of finite boundaries (finite values of threshold and reset) on the firing statistics.     

RFID Authentication Efficient Proactive Information Security within Computational Security

We consider repeated communication sessions between a RFID Tag (e.g., Radio Frequency Identification, RFID Tag) and a RFID Verifier. A proactive information theoretic security scheme is proposed. The scheme is based on the assumption that the information exchanged during at least one of every n successive communication sessions is not exposed to an adversary. The Tag and the Verifier maintain a vector of n entries that is repeatedly refreshed by pairwise xoring entries, with a new vector of n entries that is randomly chosen by the Tag and sent to the Verifier as a part of each communication session. The general case in which the adversary does not listen in k≥1 sessions among any n successive communication sessions is also considered. A lower bound of n⋅(k+1) for the number of random numbers used during any n successive communication sessions is proven. In other words, we prove that an algorithm must use at least n⋅(k+1) new random numbers during any n successive communication sessions. Then a randomized scheme that uses only O(nlog n) new random numbers is presented. A computational secure scheme which is based on the information theoretic secure scheme is used to ensure that even in the case that the adversary listens in all the information exchanges, the communication between the Tag and the Verifier is secure.     

On the additive constant of the k-server Work Function Algorithm

We consider the Work Function Algorithm for the k-server problem (Chrobak and Larmore, 1991; Koutsoupias and Papadimitriou, 1995) [2] and [4]. We show that if the Work Function Algorithm is c-competitive, then it is also strictly(2c)-competitive. As a consequence of (Koutsoupias and Papadimitriou, 1995) [4] this also shows that the Work Function Algorithm is strictly (4k−2)-competitive.