Stevens Institute of Technology

About: Stevens Institute of Technology is a education organization based out in Hoboken, New Jersey, United States. It is known for research contribution in the topics: Cognitive radio & Wireless network. The organization has 5440 authors who have published 12684 publications receiving 296875 citations. The organization is also known as: Stevens & Stevens Tech.

Constitutive equations for polymer solutions derived from the bead/spring model of Rouse and Zimm

Abstract: The theory of dilute polymer solutions based on the bead/spring model in the form given by Zimm is reformulated for arbitrary homogeneous flow histories. It is shown that the center of resistance of a polymer molecule moves with the solvent. By a preliminary transformation [3.4], the equations for the center-of- resistance motion are separated from those for the motion of the N spring vectors. The spring-vector equations involve a symmetric non-singular matrix B [3.14] whose characteristic values equal the non-zero characteristic values of Zimms singular matrix HA. A further transformation [4.2] which diagonalizes B yields separate differential eq. [5.4] for pq*, the polymer contribution to the stress tensor associated with the q normal mode. Transformation to an embedded basis enables one to integrate these equations so as to obtain pq* in terms of the flow history ([5.6], [5.9]), and summation over q then gives the required constitutive eq. [5.17] for the polymer solution. These are of the same form as the “rubber-like liquid” constitutive equations (with addition of a solvent-contribution term) derived from the network theory of Lodge, but the memory function is determined to within three constants (e. g. N, h*, τ1). Peterlina solution for the normal-coordinate distribution function in steady shear flow is generalized for an arbitrary homogeneous (time-dependent or steady) flow and expressed in terms of pq* which can be evaluated when the flow history is given.

Optimal decorrelating receivers for DS-CDMA systems: a signal processing framework

Abstract: Code division multiple access (CDMA) schemes allow a number of asynchronous users to share a transmission medium with minimum cooperation among them. However, sophisticated signal processing algorithms are needed at the receiver to combat interference from other users and multipath effects. A discrete-time multirate formulation is introduced for asynchronous CDMA systems, which can incorporate multipath effects. This formulation reveals interesting links between CDMA receivers and array processing problems. In this framework, linear receivers are derived that can completely suppress multiuser interference (decorrelating receivers). A criterion is introduced, which guarantees the decorrelating property, while providing optimal solutions in the presence of noise. Parametric FIR designs as well as nonparametric solutions are delineated, and their performance is analyzed. The proposed receivers are resistant to near-far effects and do not require the estimation of the users' and noise powers.

Mechanisms of mixing in single and co-rotating twin screw extruders

Abstract: Previous experimental studies have revealed that the mixing efficiencies of widely used continuous processors such as the single and twin screw extruders depend on the types of screw elements, which are utilized. It is generally recognized that the basic single screw extruder and the fully-fighted sections of the fully-intermeshing co-rotating twin screw extruders are not efficient mixers, in contrast to the specialized mixing elements such as the kneading discs used in co-rotating twin screw extruders. However, no simulation techniques were available to characterize quantitatively and rigorously the mixing efficiencies of continuous processors. In this study, we have solved the three-dimensional equations of conservation of mass and momentum, and utilized various tools of dynamics to analyze the mixing occurring in single and co-rotating twin screw extruders. It is shown that simulation methods can indeed capture the relative differences in the mixing mechanisms of continuous processors like the single and twin screw extruders. The ability to distinguish quantitatively between the distributive mixing capabilities of various continuous processors should facilitate numerical testing of new continuous mixer designs, optimization of operating conditions and geometries of existing mixers and the material-specific design of new mixers.

Outage Probability Analysis of Cognitive Transmissions: Impact of Spectrum Sensing Overhead

Abstract: In cognitive radio networks, a cognitive source node requires two essential phases to complete a cognitive transmission process: the phase of spectrum sensing with a certain time duration (also referred to as spectrum sensing overhead) to detect a spectrum hole and the phase of data transmission through the detected spectrum hole. In this paper, we focus on the outage probability analysis of cognitive transmissions by considering the two phases jointly to examine the impact of spectrum sensing overhead on system performance. A closed-form expression of an overall outage probability that accounts for both the probability of no spectrum hole detected and the probability of a channel outage is derived for cognitive transmissions over Rayleigh fading channels. We further conduct an asymptotic outage analysis in high signal-to-noise ratio regions and obtain an optimal spectrum sensing overhead solution to minimize the asymptotic outage probability. Besides, numerical results show that a minimized overall outage probability can be achieved through a tradeoff in determining the time durations for the spectrum hole detection and data transmission phases. In this paper, we also investigate the use of cognitive relay to improve the outage performance of cognitive transmissions. We show that a significant improvement is achieved by the proposed cognitive relay scheme in terms of the overall outage probability.