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Frequency Modulation (frequency + modulation)

Distribution by Scientific Domains
Medical Sciences33%
Life Sciences22%

Selected Abstracts

Effect of auditory cortex lesions on the discrimination of frequency-modulated tones in rats

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2006
Natalia Rybalko
Abstract The lateralization of functions to individual hemispheres of the mammalian brain remains, with the exception of the human brain, unresolved. The aim of this work was to investigate the ability to discriminate between falling and rising frequency-modulated (FM) stimuli in rats with unilateral or bilateral lesions of the auditory cortex (AC). Using an avoidance conditioning procedure, thirsty rats were trained to drink in the presence of a rising FM tone and to stop drinking when a falling FM tone was presented. Rats with a lesion of the AC were able to learn to discriminate between rising and falling FM tones; however, they performed significantly worse than did control rats. A greater deficit in the ability to discriminate the direction of frequency modulation was observed in rats with a right or bilateral AC lesion. The discrimination performance (DP) in these rats was significantly worse than the DP in rats with a left AC lesion. Animals with a right or bilateral AC lesion improved their DP mainly by recognizing the pitch at the beginning of the stimuli. The lesioning of the AC in trained animals caused a significant decrease in DP, down to chance levels. Retraining resulted in a significant increase in DP in rats with a left AC lesion; animals with a right lesion improved only slightly. The results demonstrate a hemispheric asymmetry of the rat AC in the recognition of FM stimuli and indicate the dominance of the right AC in the discrimination of the direction of frequency modulation. [source]

High K Capacitors and OFET Gate Dielectrics from Self-Assembled BaTiO3 and (Ba,Sr)TiO3 Nanocrystals in the Superparaelectric Limit

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010
Limin Huang
Abstract Nanodielectrics is an emerging field with applications in capacitors, gate dielectrics, energy storage, alternatives to Li-ion batteries, and frequency modulation in communications devices. Self-assembly of high k dielectric nanoparticles is a highly attractive means to produce nanostructured films with improved performance,namely dielectric tunability, low leakage, and low loss,as a function of size, composition, and structure. One of the major challenges is conversion of the nanoparticle building block into a reliable thin film device at conditions consistent with integrated device manufacturing or plastic electronics. Here, the development of BaTiO3 and (Ba,Sr)TiO3 superparaelectric uniform nanocrystal (8,12,nm) films prepared at room temperature by evaporative driven assembly with no annealing step is reported. Thin film inorganic and polymer composite capacitors show dielectric constants in the tunable range of 10,30, dependent on composition, and are confirmed to be superparaelectric. Organic thin film transistor (TFT) devices on flexible substrates demonstrate the readiness of nanoparticle-assembled films as gate dielectrics in device fabrication. [source]

High efficiency DC,DC converter for wide-ranging loads with gradual reverse current stopping technique

IEEJ TRANSACTIONS ON ELECTRICAL AND ELECTRONIC ENGINEERING, Issue 6 2008
Kouhei Yamada Member
Abstract A novel reverse current stopping technique for synchronous rectifiers in DC,DC converters is proposed. It is based on gradual adjustment of the ON-time of the synchronous rectifier to finally stop the reverse current. Therefore, delay to detect and stop reverse current does not cause extra reverse current, so almost perfect reverse current stopping can be achieved with small DC power consumption. An example circuit of the proposed technique was designed and included in a fixed ON-time pulse frequency modulation (PFM) control DC,DC converter. The designed converter was fabricated in the 0.35 µm CMOS process, and then its operation was verified. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. [source]

AM,FM techniques in the analysis of optical coherence tomography signals

JOURNAL OF BIOPHOTONICS, Issue 6-7 2009
Costas Pitris
Abstract The subtle tissue changes associated with the early stages of malignancies, such as cancer, are not clearly discernible even at the current, improved, resolution of optical coherence tomography (OCT) systems. However, these changes directly affect the spectral content of the OCT image that contains information regarding these unresolvable features. Spectral analysis of OCT signals has recently been shown to provide additional information, resulting in improved contrast, directly related to scatterer size changes. Amplitude modulation,frequency modulation (AM,FM) analysis, a fast and accurate technique for the estimation of the instantaneous frequency, phase, and amplitude of a signal, can also be applied to OCT images to extract scatterer-size information. The proposed technique could make available an extremely valuable tool for the investigation of disease characteristics that now remain below the resolution of OCT and could significantly improve the technology's diagnostic capabilities. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Double stimulation of the inner ear organs of an anuran species (Alytes cisternasii) with simple tonal advertisement calls

JOURNAL OF ZOOLOGY, Issue 4 2003
J. Bosch
Midwife toads present one of the simplest calls in anurans, with the whole energy concentrated in a single band without frequency modulation. The tuning curves of the Iberian midwife toads Alytes cisternasii show the typical bimodal pattern in anurans, with two best excitatory frequencies at 0.412 kHz (corresponding to the amphibian papilla) and at 1.358 kHz (corresponding to the basilar papilla and matching the male call frequency). In this study, the hypothesis that complex calls arose in anurans because they were inherently more attractive to females, since they provided greater acoustic stimulation, was tested. However, our results indicate that splitting the call energy to stimulate both inner ear organs simultaneously, the male call is not more attractive to female midwife toads, but sometimes renders it unattractive. The biological role of the amphibian papilla is discussed in ecological and evolutionary terms. [source]

Laser frequency stabilization using selective reflection from a vapor cell with a half-wavelength thickness

LASER PHYSICS LETTERS, Issue 11 2007
E.A. Gazazyan
Abstract We have experimentally studied the selective reflection spectra of a circularly-polarized laser beam from a sub-micrometric Rb vapor cell with a thickness L around , /2 (, = 780 nm being the laser wavelength tuned to the D2 line) in the presence of a longitudinal magnetic field. Based on the results of these studies, we propose a new method for the tunable locking of the diode laser frequency, which does not require frequency modulation nor complex electronics. The experimental realization of the technique has demonstrated its effectiveness and its competitiveness with the known DAVVL-type methods. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Computer modeling of frequency-modulation spectra of coherent dark resonances

LASER PHYSICS LETTERS, Issue 9 2006
J. Vladimirova
Abstract Dynamics of a three-level quantum system in , -configuration driven by a resonant laser field with and without frequency modulation (FM) is studied for the first time in detail using two simulation techniques , the density matrix and quantum trajectories analysis. This analysis was applied to the Fmspectroscopy of coherent dark resonances in Cs atoms and computer simulation results for the absorption spectra are in qualitative agreement with those taken in an experiment. (© 2006 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

Length Dependent Potentiation in Electrically Stimulated Human Ankle Dorsiflexor Muscles

NEUROMODULATION, Issue 2 2002
Petra Mela PhD
Abstract The purpose of this study was to investigate the short-term history effect of a decreasing frequency train on force and the influence of joint angle on such effect in human dorsiflexor muscles. Six able-bodied and three spinal cord injured (SCI) subjects took part in the study. Their isometric left dorsiflexor muscles were stimulated with two-second bursts at three ankle joint positions and movements at the ankle were measured. Trains with constant stimulation frequencies (CSF: 50, 25, 20, 16, 12, 8 Hz) and with decreasing stimulation frequencies (DSF1,2) were used. Each DSF tetanus consisted of four 0.5 second bursts of different frequencies (DSF1: 50, 25, 16, 8 Hz; DSF2: 50, 20, 12, 8 Hz). To evaluate the effect of preceding higher stimulation frequencies (DSF), the average moment at corresponding time intervals in the DSF and CSF trials were compared for 25, 20, 16, 12, 8 Hz. Preceding higher stimulation frequencies caused increase of the moment elicited by a given frequency. This was true for all the subjects at dorsiflexed positions, but the effect is highly dependent on joint ankle. At plantar flexed positions moment enhancement was seen only in SCI subjects. We conclude that effects of joint angle as well as individual muscle properties should be taken into account when optimizing muscle force by means of frequency modulation. [source]

Devices for Noninvasive Transcranial Electrostimulation of the Brain Endorphinergic System: Application for Improvement of Human Psycho-Physiological Status

ARTIFICIAL ORGANS, Issue 3 2002
Valery P. Lebedev
Abstract: It is well known that deficit of endorphins plays an important role in disturbances of human psycho-physiological status. Previously, we revealed that brain endorphinergic structures have quasiresonance characteristics. On the basis of these data, a method of activation of the brain endorphinergic structures by means of noninvasive and rather selective transcranial electrostimulation (TES) as a kind of functional electrical stimulation (FES) was elaborated. New models of TES devices (TRANSAIR) were developed for indoor and outdoor usage. To increase the efficacy of TES, the frequency modulation according to normal distribution in the limits of the quasiresonance characteristics was put into operation. The blind and placebo-controlled (passive and active placebo) study was produced to estimate the TES effects on stress events and accompanied psycho-physiological and autonomic disturbances of different intensities on volunteers and patients in the following groups: everyday stress and fatigue; stress in regular military service and in field conditions; stress in the relatives of those lost in mass disaster; posttraumatic stress (thermal burns); and affective disorders in a postabstinence period. Some subjective verbal and nonverbal tests and objective tests (including heart rate variability) were used for estimation of the initial level of psycho-physiological status, which changes after TES sessions. It was demonstrated that fatigue, stress, and other accompanied psycho-physiological disturbances were significantly improved or abolished after 2,5 TES sessions. The TES effects were more pronounced in cases of heavier disturbances. In conclusion, activation of the brain endorphinergic structures by TES is an effective homeostatic method of FES that sufficiently improves quality of life. [source]