scholarly journals Combination Frequency Differencing

2021 ◽  
Author(s):  
D. R. Kuhn ◽  
M. S. Raunak ◽  
R. N. Kacker
Keyword(s):  
Combination Frequency

Suppressing Flutter Vibrations by Parametric Inertia Excitation

2009 ◽  
Vol 76 (3) ◽  
Author(s):  
Fadi Dohnal ◽  
Aleš Tondl
Keyword(s):  
Parametric Excitation ◽  
Theoretical Study ◽  
Open Loop ◽  
Elastic Instability ◽  
Excitation Mechanism ◽  
Combination Frequency ◽  
Concentrated Mass ◽  
Time Harmonic ◽  
Flow Induced Vibrations ◽  
First Time

A theoretical study of a slender engineering structure with lateral and angular deflections is investigated under the action of flow-induced vibrations. This aero-elastic instability excites and couples the system’s bending and torsion modes. Semiactive means due to open-loop parametric excitation are introduced to stabilize this self-excitation mechanism. The parametric excitation mechanism is modeled by time-harmonic variation in the concentrated mass and/or moment of inertia. The conditions for full suppression of the self-excited vibrations are determined analytically and compared with numerical results of an example system. For the first time, example systems are presented for which parametric antiresonance is established at the parametric combination frequency of the sum type.

Asymmetry of combination frequency spectra in a bounded plasma

1971 ◽  
Vol 11 (1) ◽  
pp. 51-56
Author(s):  
B.N. Rutkevich ◽  
V.D. Fedorchenko ◽  
V.I. Muratov
Keyword(s):  
Combination Frequency ◽  
Frequency Spectra ◽  
Bounded Plasma

Dynamic Characteristics Analysis of a Seal-Rotor System with Rub-Impact Fault

2021 ◽  
Author(s):  
Yuegang Luo ◽  
Pengfei Wang ◽  
Haifeng Jia ◽  
Fengchao Huang
Keyword(s):  
Dynamic Characteristics ◽  
Element Model ◽  
Rolling Bearing ◽  
Rotor System ◽  
Dynamic Responses ◽  
Force Model ◽  
Nonlinear Phenomena ◽  
Combination Frequency ◽  
Labyrinth Seals ◽  
Frequency Locking

Abstract Labyrinth seals are widely used to prevent fluid leakage in high-low pressure areas of the rotating machinery. However, the rub-impact fault easily occurs in labyrinth seals. Considering the influence of gyroscopic effect, a finite element model of seal-rubbing rotor system is established in this study based on the Muszynska seal force model, the rolling bearing force model and the nonlinear rubbing force model. The vibration characteristics under the coupling faults of airflow excitation and rub-impact are analyzed. Firstly, the response of the system without rub-impact fault is numerically simulated and verified by experiments. Subsequently, the dynamic characteristics of the rotor under the conditions of slight rub-impact and severe rub-impact faults are analyzed. Finally, the influence of the rub-impact parameters is further studied. The results indicate that when the rub-impact fault is absent, airflow excitation occurs at a certain speed, which exhibits the characteristics of frequency locking and combination frequency. The coupling dynamic responses of airflow-induced vibration and rub-impact fault show a rich spectrum of nonlinear phenomena, which is closely related to the degree of rub-impact. This study may provide a theoretical basis for the detection and diagnosis of fluid-induced rub-impact fault in labyrinth seal-rotor systems.

scholarly journals VIBRATION-INDUCED CONDUCTIVITY FLUCTUATION (VICOF) TESTING OF SOILS

2006 ◽  
Vol 06 (04) ◽  
pp. L359-L365 ◽  
Author(s):  
L. B. KISH ◽  
C. L. S. MORGAN ◽  
A. SZ. KISHNÉ
Keyword(s):  
Electrical Conductance ◽  
Current Response ◽  
Conductivity Measurements ◽  
Combination Frequency ◽  
Simple Method ◽  
Additional Information ◽  
Frequency Components ◽  
The Mean ◽  
The Difference ◽  
Conductivity Fluctuation

In this Letter, we propose and experimentally demonstrate a simple method to provide additional information on the electro-mechanical properties of soils by electrical conductivity measurements. The AC electrical conductance of the soil is measured while it is exposed to a periodic vibration. The vibration-induced density fluctuation implies a corresponding conductivity fluctuation that can be seen as combination frequency components, the sum and the difference of the mean AC frequency and the double of vibration frequency, in the current response. The method is demonstrated by measurements on clayey and sandy soils.

Comparison of the disturbance of the combination frequency in both the sum and difference frequency methods for the detection of Doppler-free optoacoustic signals

1988 ◽  
Vol 20 (5) ◽  
pp. 263-267
Author(s):  
Guan-Rong Tan ◽  
Wen-Xia Yang ◽  
Ming-Xia Guo ◽  
Yan Sui ◽  
Ru-Lian Fu ◽  
...  
Keyword(s):  
Difference Frequency ◽  
Combination Frequency

scholarly journals Water Structure in Proteins in Solid State Studied by Near Infrared Spectroscopy

2017 ◽  
Vol 735 ◽  
pp. 168-172
Author(s):  
Siraporn Soonthonhut ◽  
Alfred A. Christy
Keyword(s):  
Infrared Spectroscopy ◽  
Near Infrared Spectroscopy ◽  
Water Adsorption ◽  
Near Infrared ◽  
Free Water ◽  
Adsorbed Water ◽  
Water Molecules ◽  
Combination Frequency ◽  
Adsorption Of Water ◽  
Combination Frequencies

Water adsorption in proteins is the crucial process of protein folding and structure stabilizing. Adsorption of water on proteins can be evaluated by near-infrared spectroscopy, a useful technique for observing combination frequency of a water molecule. In this work, albumin, lysozyme, and silk, were used as models for α-helix and β-pleated sheet proteins. Their NIR spectra during water adsorption process were measured by using an NIR spectrometer equipped with a transflectance accessory. Moreover, the quantitative adsorption of water was determined by gravimetric technique. The results indicate that, there are five different NIR absorptions arise from the OH combination frequencies of water adsorbed by albumin in the 5300-5100 cm-1 region. But there are only four absorptions for lysozyme and silk. The OH combination frequencies arising from water molecules in albumin indicate that it acquires free water molecules (5280 cm-1) and adsorbed water molecules through carbonyl-water interactions (5248 and 5160 cm-1) and amino-water interactions (5200 and 5120 cm-1). Interestingly, there is no indication for the presence of free water molecules in lysozyme and silk. Furthermore, the gravimetric results indicate that the rate of water adsorbed follows the order RW.Alb<RW.Lys<RW.Sil and total mass of water adsorbed per gram solid follows the order WAlb<WLys=WSil.

scholarly journals The uncommon is common: Structural similarities of symptom heterogeneity across mental disorders

2021 ◽  
Author(s):  
Tobias Raphael Spiller ◽  
Or Duek ◽  
Markus Helmer ◽  
John D. Murray ◽  
Roland von Känel ◽  
...  
Keyword(s):  
Mental Health ◽  
Mental Disorders ◽  
Stress Disorder ◽  
Combination Frequency ◽  
Specific Symptom ◽  
Targeted Treatments ◽  
Log Normal ◽  
Log Normal Distribution ◽  
Rare Symptom ◽  
Symptom Heterogeneity

The heterogeneity of symptoms among individuals diagnosed with the same mental disorder complicates the identification of biomarkers and the development of targeted treatments. Yet, the characteristics of this heterogeneity remain largely unknown. We investigated the frequency of disorder-specific symptom combinations, a marker of symptom heterogeneity, in five samples, each assessed for symptoms of a specific disorder (posttraumatic stress disorder, depression, anxiety, schizophrenia and burnout). The frequency of symptom combinations was heavily skewed in all samples, with most symptom combinations being reported only by few individuals. Moreover, the distribution of the symptom combination frequency could be approximated by a power-law and a log-normal distribution. This demonstrates similarities in the structure of symptom heterogeneity among mental disorders. Furthermore, we show that studies with sample sizes typical for research in mental health preclude many rare symptom combinations, limiting the validity of the obtained evidence by such studies for individuals with rare symptom combinations.

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