Comparison of the Acquisition Performance of the Matched Filter and Integrate-and-Dump Receivers in a Multipath Delay and Fading Environment

The Matched Filter and the Integrate-and-Dump circuit techniques are both attractive acquisition methods for CDMA systems. Acquisition using the matched filter technique has attracted considerable interest in recent years since it shows a better performance in the presence of Gaussian noise. On the other hand acquisition using an integrate-and-dump circuit is attractive because it is less complex to implement. However, the acquisition performance can be affected significantly by the channel characteristics. In this paper, a numerical method and a computer simulation have been developed in order to compare the two acquisition systems in different propagation environments. Results show that the acquisition using a matched filter is much faster than that using the integrate-and-dump circuit for the reception of spread-spectrum signals in the presence of Gaussian noise. However, in a multipath delay and fading environment, the results show that the mean acquisition time using the matched filter is not always faster than that using the integrate-and-dump circuit. The results show that it depends on the fading, the delay, the number of users and the signal-to-noise ratio.     

Why do implicit and explicit attitude tests diverge? The role of structural fit.

Implicit and explicit attitude tests are often weakly correlated, leading some theorists to conclude that implicit and explicit cognition are independent. Popular implicit and explicit tests, however, differ in many ways beyond implicit and explicit cognition. The authors examined in 4 studies whether correlations between implicit and explicit tests were influenced by the similarity in task demands (i.e., structural fit) and, hence, the processes engaged by each test. Using an affect misattribution procedure, they systematically varied the structural fit of implicit and explicit tests of racial attitudes. As test formats became more similar, the implicit-explicit correlation increased until it became higher than in most previous research. When tests differ in structure, they may underestimate the relationship between implicit and explicit cognition. The authors propose a solution that uses procedures to maximize structural fit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fading rate and multipath delay effects on signal acquisition using sliding correlation in a multi-user environment

The ability of spread spectrum systems to combat interference can only be realised if the receiver is precisely synchronised with the incoming signal. The use of the sliding correlator for the acquisition of direct sequence spread spectrum signals is a popular method. Previous work considered either the single user in the fading and delay mobile environment or multi-users in the additive white Gaussian noise environment. In this paper the acquisition performance of the sliding correlator for direct sequence spread spectrum signals is investigated for the uplink case and in an environment where interference is caused both by multiple users and by multipath delays with different fading rates. The results show that a longer correlator length is required for optimum mean acquisition time in a slow fading environment. However in the multi-user, multipath environment when larger delays are present, the use of a longer correlation length is necessary in order to optimise the mean acquisition time.     

Adaptive error analysis in seepage problems

Numerical experiments in adapting variations of a computationally simple error estimator (the Zienkiewicz-Zhu estimator) to an existing finite element code are shown. The error estimator used allows both overall and local errors to be estimated. From the local estimates of error, refinements of the mesh are calculated to reach a prescribed error tolerance. These calculated refinements are used by a mesh refiner to produce a modified mesh which lowers the overall error to the prescribed value while keeping the mesh as crude as possible. The physical example on which these numerical experiments are performed is that of free surface flow through an earth dam with a toe drain. It is also shown how the problem formulation affects the error analysis and how the choice of computational scheme affects the mesh adaptation.     

Conserving self-control strength.

Individuals may be motivated to limit their use of self-control resources, especially when they have depleted some of that resource. Expecting to need self-control strength in the future should heighten the motivation to conserve strength. In 4 experiments, it was found that depleted participants who anticipated exerting self-control in the future performed more poorly in an intervening test of self-control than participants who were not depleted, and more poorly than those who did not expect to exert self-control in the future. Conversely, those who conserved strength performed better on tasks that they conserved the strength for as compared with those who did not conserve. The underlying economic or conservation of resource model sheds some light on the operation of self-control strength. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Computational analysis of a double-shell solar house

A simplified, one-dimensional formulation is used to study the role of natural circulation in the double-shell solar house. We consider the house as a complex thermosiphon, in which air warmed in a greenhouse travels through a loop formed by double walls around the house. The air carries heat to be stored in the ground for later use and also acts as a buffer between the inner living space and the outdoors. The Boussinesq approximation is considered to be valid for the air between the double walls, and the transient governing equations are integrated until steady state conditions are reached. The shape of the house is achieved in the context of a one-dimensional formulation by changing the direction in which gravity acts relative to the flow direction. The model includes radiation in the form of a source term on the south side of the house, heat loss through all surfaces using appropriate U-values and heat storage in and recovery from the ground and living space itself. The model clearly indicates trends in the way airflow and temperature distributions around the loop are affected by varying each parameter.