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Time And Frequency Domain (time + and_frequency_domain)

Distribution by Scientific Domains
Engineering66%
Medical Sciences33%

Terms modified by Time And Frequency Domain

  • time and frequency domain measure
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    Selected Abstracts

    BEM-analysis of interaction of elastic waves with unilateral interface crack

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 3 2001
    Gai Bing-Zheng
    Abstract In this paper, to solve the problems of the interaction between the unilateral interface cracks and elastic wave, a new numerical method based on boundary element method (BEM) has been proposed. In this method, an iterating,correcting process of the solution in frequency domain and the correction in time domain has been designed to eliminate the mutual interference between the time and frequency domain. As an illustration to the algorithm, an interface crack between two half-planes under the attack of harmonic plane elastic wave has been analysed in detail. The contact configurations and stress field at the crack surface, and dynamic stress intensity factor (DSIF) at the crack tip have been given. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Heart Rate Variability and Sympathetic Skin Response in Male Patients Suffering From Acute Alcohol Withdrawal Syndrome

    ALCOHOLISM, Issue 9 2006
    Karl-Jürgen Bär
    Background: Many symptoms of alcohol withdrawal (AW) such as tachycardia or elevated blood pressure might be explained by increased peripheral and central adrenergic activity. In contrast to many neurochemical studies of sympathetic activation during AW, only very few studies investigated autonomic balance using neurophysiological methods. Methods: We investigated heart rate variability (HRV) and sympathetic skin response (SSR) in male patients suffering from mild AW syndrome (n=20, no treatment required) and in patients with moderate to severe AW syndrome (n=20, clomethiazole treatment) in the acute stage. Sympathovagal influence was quantified using measures of time and frequency domain of HRV as well as modern nonlinear parameters (compression entropy). Furthermore, we obtained latencies and amplitudes of SSR to quantify isolated sympathetic influence. Measures were obtained during the climax of withdrawal symptomatology before treatment, 1 day after climax, and shortly before discharge from hospital. Alcohol withdrawal scores were obtained and correlated to autonomic measures. Results: Ambulatory blood pressure and AW scores revealed characteristic withdrawal symptoms in both patient groups. Apart from the nonlinear parameter compression entropy, Hc, measures of HRV revealed no sign of autonomic dysfunction in contrast to the significantly increased heart rates at the time of admission. Latencies and amplitudes of SSR did not indicate any increase of sympathetic activity. A negative correlation was found between Hc and mental withdrawal symptoms. Conclusions: We show here that classical measures for autonomic nervous system activity such as HRV and SSR are not suitable for describing the autonomic changes seen in acute AW, although a major role for the sympathetic nervous system has been proposed. This might be due to multiple dysregulation of metabolites in AWS or to subtle alcohol-induced damage to neuronal structures, issues that should be addressed in future studies. [source]

    Performance evaluation of Gunn oscillators for active mode-locking of erbium doped fiber ring lasers

    MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2008
    Deepa Venkitesh
    Abstract A cost-effective and rugged actively mode-locked erbium-doped fiber laser operated at GHz repetition rate is demonstrated with the use of a Gunn oscillator as the RF source for driving the optical modulator. The high power from the Gunn oscillator eliminates the need of an RF driver. The output of the laser in the time domain is processed numerically to predict its modal characteristics in the spectral domain. Experimental results regarding the evaluation of the Gunn oscillator for its suitability in active mode-locking, tunable operation of the laser in the C -band using a band pass filter as well as the results on the stability of the laser output in the time and frequency domain are presented. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2684,2688, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23778 [source]

    Exploiting statistical properties of wavelet coefficient for face detection and recognition

    PROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2007
    Naseer Al-Jawad
    Wavelet transforms (WT) are widely accepted as an essential tool for image processing and analysis. Image and video compression, image watermarking, content-base image retrieval, face recognition, texture analysis, and image feature extraction are all but few examples. It provides an alternative tool for short time analysis of quasi-stationary signals, such as speech and image signals, in contrast to the traditional short-time Fourier transform. The Discrete Wavelet Transform (DWT) is a special case of the WT, which provides a compact representation of a signal in the time and frequency domain. In particular, wavelet transforms are capable of representing smooth patterns as well anomalies (e.g. edges and sharp corners) in images. We are focusing here on using wavelet transforms statistical properties for facial feature detection, which allows us to extract the image facial feature/edges easily. Wavelet sub-bands segmentation method been developed and used to clean up the non-significant wavelet coefficients in wavelet sub-band (k) based on the (k-1) sub-band. Moreover, erosion which is considered as one of the fundamental operation in morphological image processing, been used to reduce the unwanted edges in certain directions. For face detection, face template profiles been built for both the face and the eyes for different wavelet sub-band levels to achieve better computational performance, these profiles used to match the extracted profiles from the wavelet domain of the input image using the Dynamic Time Warping technique DTW. The DTW smallest distance allows identifying the face and the eyes location. The performance of face features distances and ratio has been also tested for face verification purposes. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Broadband wireless access based on VSF-OFCDM and VSCRF-CDMA and its experiments

    EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 3 2004
    Hiroyuki Atarashi
    This paper presents broadband packet wireless access schemes based on variable spreading factor (VSF)-orthogonal frequency and code division multiplexing (OFCDM) in the downlink and variable spreading and chip repetition factors (VSCRF)-CDMA in the uplink for the systems beyond IMT-2000. In our design concept for wireless access in both links, radio parameters such as the spreading factor (SF) are optimally controlled so that the system capacity is maximized according to the cell configuration, channel load and radio channel conditions, based on the tradeoff between efficient suppression of other-cell interference and the capacity increase in the target cell by exploiting orthogonality in the time and frequency domains. We demonstrate that the peak throughput of greater than 100,Mbps and 20,Mbps is achieved by the implemented base station and mobile station transceivers using the 100-MHz and 40-MHz bandwidths in the downlink and uplink respectively. Moreover, the simulation results show the possibility of the peak throughput of approximately 1,Gbps for short-range area applications using the 100-MHz bandwidth OFCDM downlink by applying four-branch multiple input multiple output (MIMO) multiplexing with 16,QAM data modulation and punctured turbo coding. Copyright © 2004 AEI [source]

    Electrocardiographic Evaluation in Patients with Systemic Scleroderma and without Clinically Evident Heart Disease

    ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2009
    Anna Bie, Ph.D., ous-Wilk M.D.
    Background: In patients with systemic scleroderma (SSc), clinically evident cardiac involvement is recognized to be a poor prognostic factor. The aim of the study was to evaluate electrocardiographic changes, parameters of heart rate variability (HRV), and heart rate turbulence (HRT) in patients with SSc without evident symptoms of heart disease. Methods: A group of 27 patients with SSc were subjected to standard electrocardiography (ECG) examination and 24-hour Holter monitoring. Analysis of HRV in time and frequency domains, HRT, and echocardiography were also performed. Results: Holter monitoring revealed a larger number of premature supraventricular contractions (PSVCs), as well as premature ventricular contractions (PVCs) in the patients with systemic scleroderma, as compared with the control group. Moreover, the SSc patients showed decreased parameters of time and frequency domains, as referred to the controls, especially during night hours. In four patients, abnormal HRT values were present. On echocardiography, only slight changes were found, however in five patients left ventricle diastolic dysfunction was diagnosed. Conclusions: The noninvasive electrocardiographic methods seems to be useful for detecting early heart involvement in course of SSc and could be recommended for routine used in clinical practice. Significance of HRT analysis in patients with SSc needs further elucidation. [source]