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831 results on '"Thomas, Peter J."'

102. Tables

Author

Reed, Duncan, Thomas, Peter J., Cowell, John, editor, Reed, Duncan, and Thomas, Peter J.

Published
1998
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117. Control in triphasic rhythmic neural systems: a comparative mechanistic analysis via infinitesimal local timing response curves

Author

Yu, Zhuojun, Rubin, Jonathan E., and Thomas, Peter J.

Subjects
FOS: Biological sciences, FOS: Mathematics, Neurons and Cognition (q-bio.NC), Dynamical Systems (math.DS)
Abstract

Similar activity patterns may arise from model neural networks with distinct coupling properties and individual unit dynamics. These similar patterns may, however, respond differently to parameter variations and, specifically, to tuning of inputs that represent control signals. In this work, we analyze the responses resulting from modulation of a localized input in each of three classes of model neural networks that have been recognized in the literature for their capacity to produce robust three-phase rhythms: coupled fast-slow oscillators, near-heteroclinic oscillators, and threshold-linear networks. Triphasic rhythms, in which each phase consists of a prolonged activation of a corresponding subgroup of neurons followed by a fast transition to another phase, represent a fundamental activity pattern observed across a range of central pattern generators underlying behaviors critical to survival, including respiration, locomotion, and feeding. To perform our analysis, we extend the recently developed local timing response curve (lTRC), which allows us to characterize the timing effects due to perturbations, and we complement our lTRC approach with model-specific dynamical systems analysis. Interestingly, we observe disparate effects of similar perturbations across distinct model classes. Thus, this work provides an analytical framework for studying control of oscillations in nonlinear dynamical systems, and may help guide model selection in future efforts to study systems exhibiting triphasic rhythmic activity., 47 pages, 21 figures, 8 tables

Published
2022
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123. A Longitudinal Analysis of Age of Onset Effects on Delinquency.

Author

Tolan, Patrick H. and Thomas, Peter J.

Abstract

This study is a re-analysis of four waves of data from the National Youth Survey (NYS) begun in 1976 on 1,725 adolescents and comprising a representative national sample. A subset of 423 subjects were selected for this study. Subjects were categorized into three delinquency onset groups: early onset (onset at age 12 years or younger); late onset (onset after age 12 years), and no-onset. The NYS data contained data on delinquency involvement, psychosocial conditions, and demographic characteristics. Analyses were undertaken to determine the impact of age on onset of delinquency on subsequent level, type, and persistence of participation in delinquency. With the exception of damaged property and minor assault, no significant differences between early and late onset groups were found as to type of crime. Early onset subjects, however, were more likely to engage in serious patterned delinquency and to do so chronically. No significant demographic differences were found, except that males were more likely than females to be in the early onset group. The early and late onset subjects scored poorly on all psychosocial scales and scored significantly poorer than did no-onset subjects. These results suggest age of onset may be an important risk determinant in delinquency research. (Author/NB)

Published
1988

125. A Metallic Additively Manufactured Metamaterial for Enhanced Monitoring of Acoustic Cavitation‐Based Therapeutic Ultrasound

Author

Nie, Luzhen, primary, Hutchins, David A., additional, Astolfi, Lorenzo, additional, Cooper, Timothy P., additional, Clare, Adam T., additional, Adams, Chris, additional, Watson, Richard L., additional, Thomas, Peter J., additional, Cowell, David M. J., additional, McLaughlan, James R., additional, Laureti, Stefano, additional, Ricci, Marco, additional, and Freear, Steven, additional

Published
2021
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135. Measurement of photon indistinguishability to a quantifiable uncertainty using a Hong--Ou--Mandel interferometer

Author

Thomas, Peter J., Cheung, Jessica Y., Chunnilall, Christopher J., and Dunn, Malcolm H.

Subjects
Optical instruments -- Usage, Optical instruments -- Properties, Optics -- Research, Optics -- Methods, Astronomy, Physics
Abstract

We present a method for using the Hong--Ou--Mandel (HOM) interference technique to quantify photon indistinguishability within an associated uncertainty. The method allows the relative importance of various experimental factors affecting the HOM visibility to be identified, and enables the actual indistinguishability, with an associated uncertainty, to be estimated from experimentally measured quantities. A measurement equation has been derived that accounts for the non-ideal performance of the interferometer. The origin of each term of the equation is explained, along with procedures for their experimental evaluation and uncertainty estimation. These uncertainties are combined to give an overall uncertainty for the derived photon indistinguishability. The analysis was applied to measurements from an interferometer sourced with photon pairs from a parametric downconversion process. The measured photon indistinguishably was found to be 0.954 [+ or -] 0.036 by using the prescribed method. [c] 2010 Optical Society of America OCIS codes: 120.3940, 270.5585, 190.4410.

Published
2010

144. A Metallic Additively Manufactured Metamaterial for Enhanced Monitoring of Acoustic Cavitation‐Based Therapeutic Ultrasound.

Author

Nie, Luzhen, Hutchins, David A., Astolfi, Lorenzo, Cooper, Timothy P., Clare, Adam T., Adams, Chris, Watson, Richard L., Thomas, Peter J., Cowell, David M. J., McLaughlan, James R., Laureti, Stefano, Ricci, Marco, and Freear, Steven

Subjects
MICROBUBBLE diagnosis, MICROBUBBLES, ULTRASONIC therapy, CAVITATION, METAMATERIALS, SHEAR waves, INTRAOPERATIVE monitoring, LONGITUDINAL waves
Abstract

The combination of ultrasound and microbubbles allows treatment of indications that would be impossible or too risk adverse with conventional surgery. During treatment, subharmonic and ultraharmonic components that can only be generated from microbubbles are of great interest for intraoperative monitoring. However, the microbubble emissions are several orders of magnitude lower in power compared to that of the fundamental frequency component from the ultrasound applicator, resulting in a low signal‐to‐noise ratio (SNR) for monitoring. A 3D acoustic metamaterial (AMM) immersed in water is proposed for suppressing unwanted ultrasound waves, which allows the improved sensitivity for detecting weak microbubble emissions. Numerically, the importance of shear waves on the AMM transfer properties is highlighted, though only longitudinal ultrasound waves are transmitted through water. Experimentally, the design is implemented in titanium using additive manufacturing, with an attenuation level of 40 dB at the fundamental frequency. Consequently, the application of the AMM efficiently improves the SNR for subharmonic and ultraharmonic microbubble emissions by 11.8 and 11.9 dB, respectively. The subharmonic components originally overwhelmed by noise are recovered. This is the first time that AMMs have been applied to passive acoustic monitoring and this work stands to improve treatment outcomes from cavitation‐mediated focused ultrasound therapy. [ABSTRACT FROM AUTHOR]

Published
2022
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