Experimental investigations of artificial low-frequency amplitude modulation of radiowaves reflected from the ionosphere

1991 ◽  
Vol 34 (1) ◽  
pp. 18-22 ◽  
Author(s):  
G. N. Boiko ◽  
L. M. Erukhimov ◽  
V. L. Frolov
Keyword(s):  
Amplitude Modulation ◽  
Low Frequency ◽  
Experimental Investigations

Multiple-S-Shaped Critical Manifold and Jump Phenomena in Low Frequency Forced Vibration with Amplitude Modulation

2019 ◽  
Vol 29 (05) ◽  
pp. 1930012 ◽  
Author(s):  
Yue Yu ◽  
Qianqian Wang ◽  
Qinsheng Bi ◽  
C. W. Lim
Keyword(s):  
Amplitude Modulation ◽  
Large Amplitude ◽  
Low Frequency ◽  
Slow Variable ◽  
Critical Manifold ◽  
Singular Orbit ◽  
Modulation Control ◽  
Cycle Oscillation ◽  
Tuning Frequency ◽  
Complex Mechanical Systems

Motivated by the forced harmonic vibration of complex mechanical systems, we analyze the dynamics involving different waves in a double-well potential oscillator coupling amplitude modulation control of low frequency. The combination of amplitude modulation factor significantly enriches the dynamical behaviors on the formation of multiple-S-shaped manifold and multiple jumping phenomena that alternate between epochs of slow and fast motion. We can conduct bifurcation analysis to identify two harmonic vibrations. One is that the singular orbit makes multiple jumps to a fast trajectory segment from one attracting equilibrium to another as the expression of slow variable by using the DeMoivre formula. With the increase of tuning frequency, the system exhibits relaxation-type oscillations whose small amplitude oscillations are produced by nonlinear local cycles together with a distinct large amplitude cycle oscillation accounting for the Melnikov threshold values. The tuning frequency may not only affect the asymptotic expressions for the solution curves near fold singularities but also allow for the large amplitude orbit vibrations near fold-cycle singularities. Numerical analysis for computing critical manifolds and their intersections is used to detect the dynamical features in this paper.

scholarly journals Notched-noise precursors improve detection of low-frequency amplitude modulation

2017 ◽  
Vol 141 (1) ◽  
pp. 324-333 ◽  
Author(s):  
Ali Almishaal ◽  
Gavin M. Bidelman ◽  
Skyler G. Jennings
Keyword(s):  
Amplitude Modulation ◽  
Low Frequency

Experimental investigations on instability evolution in a transonic compressor at different rotor speeds

2015 ◽  
Vol 229 (18) ◽  
pp. 3378-3391 ◽  
Author(s):  
Qiushi Li ◽  
Tianyu Pan ◽  
Tailu Sun ◽  
Zhiping Li ◽  
Yifang Gong
Keyword(s):  
Low Frequency ◽  
Axial Flow ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Experimental Investigations ◽  
Rotor Speed ◽  
Axial Flow Compressor ◽  
Transonic Compressor ◽  
New Type ◽  
Flow Compressor

Experimental investigations are conducted to study the instability evolution in a transonic axial flow compressor at four specific rotor speeds covering both subsonic and transonic operating conditions. Two routes of evolution to final instability are observed in the test compressor: at low rotor speeds, a disturbance in the rotor tip region occurs and then leads to rotating stall, while at high rotor speeds, a low-frequency disturbance in the hub region leads the compressor into instability. Different from stall and surge, this new type of compressor instability at high rotor speed is initiated through the development of a low-frequency axisymmetric disturbance at the hub, and we name it “partial surge”. The frequency of this low-frequency disturbance is approximately the Helmholtz frequency of the system and remains constant during instability inception. Finally, a possible mechanism for the occurrence of different instability evolutions and the formation of partial surge are also discussed.

"Smooth" Rhythms as Probes of Entrainment

1993 ◽  
Vol 10 (4) ◽  
pp. 503-508 ◽  
Author(s):  
Robert O. Gjerdingen
Keyword(s):  
Frequency Domain ◽  
Amplitude Modulation ◽  
Acoustic Signal ◽  
Low Frequency ◽  
Digital Filtering ◽  
Acoustic Signals ◽  
Frequency Range ◽  
Carrier Wave ◽  
The Brain

If one hypothesizes rhythmic perception as a process employing oscillatory circuits in the brain that entrain to low-frequency periodicities in the neural firings evoked by an acoustic signal, then among the conceptually purest probes of those oscillatory circuits would be acoustic signals with only simple sinusoidal periodicities in the appropriate frequency range (perhaps from 0.3 Hz to 20 Hz). Such signals can be produced by the low- frequency amplitude modulation of an audible carrier wave by one or more sinusoids. The resulting rhythms are "smooth" in that their amplitude envelopes are smoothly varying with no obvious points of onset or offset. Because preliminary experiments with smooth rhythms have produced some unexpected results, and because smooth rhythms can be precisely controlled and varied (including, for example, the digital filtering of their Fourier components in the frequency domain), they are proposed as versatile stimuli for studies in rhythmic perception.

Experimental Investigations of the Onset of Rotating Stall

2008 ◽  
Author(s):  
P. B. V. Johansson ◽  
M. Henriksson
Keyword(s):  
Time Domain ◽  
Pressure Sensors ◽  
Low Frequency ◽  
Pressure Profile ◽  
Rotational Frequency ◽  
Rotating Stall ◽  
Test Facility ◽  
Experimental Investigations ◽  
Measurement Signal ◽  
Low Pass

This work focuses on analysis of data obtained in experimental investigations of a military fan in a whole-engine test facility. The data was simultaneously obtained by using multiple pressure sensors located at different axial and angular positions in the fan. In particular, the origin of rotating stall was investigated by analyzing the experimental data both in the frequency-time domain as well as the correlation in time between the typical pressure profile and the pressure profile for each revolution of the rotor. First, the measurement signal was high-pass filtered with a cut-off frequency slightly lower than the spool rotational frequency. These high frequency data were subjected to a typical pressure distribution test. Second, the measurement signal was low-pass filtered slightly lower than the spool rotational frequency. The low frequency part was investigated in the frequency-time domain. A quantitative measurement of an indicator of rotating stall is presented and its limitation for practical use is discussed.

scholarly journals Аномалии частотной отсечки полупроводниковых диодов на сверхвысоких частотах

2021 ◽  
Vol 47 (1) ◽  
pp. 9
Author(s):  
Г. Абдурахманов ◽  
А. Есбергенова ◽  
С. Рейимбаева
Keyword(s):  
Frequency Dependence ◽  
Low Frequency ◽  
Experimental Investigations ◽  
Parametric Amplifiers

Results of the experimental investigations of frequency dependence of detected voltage of various types of semiconductor diodes (detectors, parametric amplifiers, low-frequency rectifiers) are presented. It is found that diodes having low frequency cut-off (less then 100 MHz) can display detector properties at 10 GHz.

scholarly journals Improvement of Pressing Technology of Products from Polytetrafluoroethylene

2001 ◽  
Vol 14 (5) ◽  
pp. 564-571
Author(s):  
Dmitriy A. Negrov ◽  
Keyword(s):  
Amplitude Modulation ◽  
New Technology ◽  
Low Frequency ◽  
Modern Material ◽  
Simultaneous Application ◽  
New Methods ◽  
Friction Units ◽  
The Coefficient Of Friction ◽  
Modern Material Science ◽  
Pressing Technology

The development of new methods for obtaining materials with predetermined operational properties that ensure the durability and the wear resistance of friction units is an urgent problem in modern material science. The article considers the effect of ultrasonic pressing modes with simultaneously superimposed low-frequency amplitude modulation on the mechanical and tribotechnical properties of polytetrafluoroethylene. The comparison of the obtained research results of the new technology is carried out with the traditional pressing technology. The results of studies indicated that the technology of ultrasonic pressing with the simultaneous application of low-frequency amplitude modulation makes it possible to increase the mechanical properties of PTFE: the tensile strength by 15 %, elongation by 13 %, the elastic modulus by 8 %, the hardness by 12 %, while the intensity of the mass wear rate is reduced by 40 %, and the coefficient of friction by 27 %

Combustor Configuration Influence on Combusion Instabilities Performance

2010 ◽  
Author(s):  
Georgy K. Vedeshkin ◽  
Evgeniy D. Sverdlov ◽  
Alexey N. Doubovitsky
Keyword(s):  
Gas Flow ◽  
Flow Instability ◽  
Combustion Instability ◽  
Low Frequency ◽  
Experimental Investigations ◽  
Flow Recirculation ◽  
Instability Modes ◽  
Conical Diffuser ◽  
Recirculation Zones ◽  
The Given

The paper describes the results of calculations and experimental investigations of combustor configurations. It is shown that combustor configuration effects high frequency and low frequency combustor instabilities, gas dynamics of the flow, recirculation zones dimensions and lean flame out limits. Combustion instability modes had been investigated in two versions of combustor configurations: with the abrupt divergence of the channel and with an inlet conical diffuser. Gas flow instabilities had been investigated in the central recirculation zone without any chemical reactions. As a result the combustion instability model in which a role of a feed back mechanism is performed by hydrodynamic gas flow instability in the combustor is suggested. Modification of the combustor with a conical diffuser with the suggested model of the hydrodynamic combustion instability taken into account made it possible to settle the instability problem for the given combustor.

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