Phase Error Characteristics of a Second-Order Phase-Lock Loop

An analytical expression for the phase error characteristics of a second-order phase-lock loop (PLL) is determined using the results of a previous nonlinear analysis. The characteristics determined are for sinusoidal FM in the absence of noise. Theoretical and experimental results are compared and are in close agreement. The theoretical results are useful as a design aid and in determining the proper parameters for the operation of a second-order PLL.     

Diazepam's impact on self-stimulation but not stimulation-escape suggests hedonic modulation.

In rats that self-administered lateral hypothalamic (LH) stimulation through chronically implanted electrodes, ip diazepam (DZ) increased rates and decreased thresholds of self-stimulation (SS) in a dose-related manner. Stimulation-escape (SE), however, was refractory to the drug. There was a complete dichotomy in electrode placements along the anterior/posterior plane. Every pure-reward electrode location was posterior to every reward-escape electrode. DZ-sensitive SS appears to be mediated by a reward substrate common to both pure-reward and reward-escape rats, whereas SE is supported by an aversive system unaffected by DZ and stimulated only in those rats with anterior placements. The lack of control over SE suggests that the drug's effect on stimulation-induced conduct is to increase reward rather than to decrease aversion. This hypothesis is discussed in the context of DZ's interactions with drugs of abuse. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fuzzy Clustering of Stability Diagrams for Vibration-Based Structural Health Monitoring

Abstract:   A primary challenge to implementing structural health monitoring techniques on civil infrastructure is the identification of structural changes in the presence of natural changes in structural response due to environmental variables such as temperature. Data from the Z24 Bridge recorded over the course of nearly a year are analyzed in this article. Covariance-driven Stochastic Subspace Identification is applied to the data to identify the modal parameters of the structure. A large number of numerical poles are identified with the real physical poles. A Fuzzy Clustering Algorithm is then used to extract parameters indicative of the bridge's state from the mixture of real and numerical poles. The main benefit of this approach is the lack of need for mode shape information and thus its applicability to structures monitored with spatially sparse sensor grids. The method is shown to provide very encouraging results in separating the response data from the Z24 Bridge in healthy and damaged states in varying environmental conditions. The method does not explicitly identify the changes due to environmental variables but it is found that the changes in the parameters identified due to damage are greater than those due to environmental variability and therefore may be flagged. The procedure is also applied successfully to a second data set obtained from monitoring a tall building over several years of its early life to identify gradual or sudden structural changes.     

Noninvasive method for the assessment of dermal uptake of pesticides using attenuated total reflectance infrared spectroscopy

Dermal absorption of pesticides is a primary exposure route for agricultural workers, but is not well characterized. Current measurement techniques are either invasive, such as tape-stripping, or require extensive sample preparation or analysis time, such as urinary metabolite monitoring or wipe sampling followed by gas chromatography analysis. We present the application of a noninvasive, spectroscopic approach for the measurement of pesticide absorption into skin. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to monitor directly the absorption of two pesticides--captan and azinphos-methyl--in ten volunteers over 20 min under occlusive conditions. We found substantial variability in absorption across subjects. Our results were comparable to those measured by the more traditional method of wipe-sampling followed by extraction and gas chromatography analysis. Multivariate data analysis, in the form of multivariate curve resolution (MCR), is a novel addition to this type of experiment, yielding time-resolved information unachievable by standard methods. These data are potentially more informative than the monitoring of blood or urinary metabolites because they can be acquired in essentially real-time, allowing observations of pesticide absorption on a rapid timescale rather than over hours or days.     

Experimentally Validated Added Mass Identification Algorithm Based on Frequency Response Functions

A methodology is presented for detecting added mass in structural systems maintaining a linear response. A single frequency response function measured at several frequencies along with a correlated analytical model of the structure in its original state are used to detect and quantify the added mass. A computationally efficient method of recalculating a single frequency response function is utilized in the identification algorithm. Experimental results from a frame structure are presented to validate and assess the proposed approach.     

Ecological applications using a novel expert system shell

Much of the information used by ecologists in modelling and decision making is imprecise. The imprecision arises both from data that are inexact or incomplete and from the use of ecological principles that are sometimes less than fully reliable and may be conflicting. Nevertheless, expert ecologists are able to construct usable models and make decisions that are used to manage and control ecological resources. This paper describes a unique expert system shell, developed in conjunction with user ecologists, which incorporates features enabling ecologists to represent knowledge and uncertainty in their expert systems in a way that is natural and appropriate. The reasoning mechanism was similarly developed in conjunction with user ecologists. It produces solutions to a class of expert level problems along with explanatory mechanisms and an appropriate analysis of the reasoning process. Three expert systems have been constructed by ecologists using this expert system shell. This enabled the shell designers to evaluate features for inclusion in the shell. The successful use of the shell by the ecologists has shown that significant economies arise when expert system shell design is tailored to use by a specific class of experts, in this case ecologists.     

Context effects in two-month-old infants' perception of labiodental/interdental fricative contrasts.

We investigated 2-month-old infants' perception of a subset of highly confusable English fricatives. In Experiment 1, infants discriminated modified natural tokens of the voiceless fricative pair [fa]/[οa] but only when the syllables included their frication noises. They also discriminated the voiced pair [va]/[δa] both with and without fricative noises. These results parallel those found with adults by Carden, Levitt, Jusczyk, and Walley (1981). In Experiment 2 [f] and [ο] noises were appended to [a], and the same [f] noise was appended to the previously indiscriminable fricationless versions of [fa] and [οa]. Infants discriminated both pairs of stimuli, indicating that (a) the frication is a sufficient cue for [fa]/[οa] discrimination and that (b) it provides a context for discriminating the [f] and [ο] formant transitions. We conclude that infants' perception of labiodental/interdental fricative contrasts show evidence of context effects similar to those observed with adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Further Investigations into Rigidity-Activity Relationships in BisQAC Amphiphilic Antiseptics

Thirty-six biscationic quaternary ammonium compounds were efficiently synthesized in one step to examine the effect of molecular geometry of two-carbon linkers on antimicrobial activity. The synthesized compounds showed strong antimicrobial activity against a panel of both Gram-positive and Gram-negative bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). While the linker geometry showed only a modest correlation with antimicrobial activity, several of the synthesized bisQACs are promising potential antiseptics due to good antimicrobial activity (MIC≤2 μM) and their higher therapeutic indices compared to previously reported QACs.