A Physical Interpretation for Broken Reciprocity in Spatiotemporal Modulated Periodic Rods

2017 ◽  
Author(s):  
Jacopo Marconi ◽  
Gabriele Cazzulani ◽  
Massimo Ruzzene ◽  
Francesco Braghin
Keyword(s):  
Wave Propagation ◽  
Vibration Suppression ◽  
Periodic Structures ◽  
Previous Analysis ◽  
Travelling Waves ◽  
Periodic Systems ◽  
Mathematical Methods ◽  
Elastic Structures ◽  
The Mean ◽  
And Control

Periodic systems have long been known for their peculiar characteristics in wave propagation and have been studied in many fields over the last century, going from electro-magnetics and optics to elastic structures, which drew an increasing interest in structural and mechanical engineering for vibration suppression and control spanning over broadband frequency ranges. Recently, on the stream of other studies conducted in different fields, spatiotemporal modulated elastic structures have been studied, showing promising results for wave control in that one-way propagation in the so called directional-bands can be achieved, constituting what may be called a mechanical diode. Despite of the fact that mathematical methods for the analysis of such structures have already been developed, often physics behind them is difficult to grasp. In this work, a simplified interpretation of the undergoing phenomena is thus given relating wave propagation in the mean to its physical characteristics as well as to modulation parameters. Exploiting Doppler effect and passive equivalent structures, it is shown that the broken reciprocity is due to the fact that opposite travelling waves effectively see two different periodic structures. To this aim the rod case is analysed for low modulation speeds and low modulation amplitudes; finally, in the light of the previous analysis, an explanation for First Brillouin Zone’s asymmetry is given.

Structural Intensity Analysis of Periodic Elastic Structures With Frequency Stop Bands

2016 ◽  
Author(s):  
M. Nouh
Keyword(s):  
Wave Propagation ◽  
Vibration Suppression ◽  
Periodic Structures ◽  
External Disturbance ◽  
Stop Band ◽  
Bloch Wave ◽  
Periodic Medium ◽  
Elastic Structures ◽  
Structural Intensity ◽  
Wide Range

Periodic elastic structures consisting of self-repeating geometric or material arrangements exhibit unique wave propagation characteristics culminating in frequency stop bands, i.e. ranges of frequency where elastic waves can propagate the periodic medium. Such features make periodic structures appealing for a wide range of vibration suppression and noise control applications. Stop bands in periodic media are achieved via Bragg scattering of elastic which is attributed to impedance mismatches between the different constituents of the self-repeating cells. Stop band frequencies can be numerically predicted using mathematical models which generally utilize the Bloch wave theorem and a transfer matrix method to track the spatial and temporal parameters of the propagating waves from one cell to the next. Such analysis generates what is referred to as the band structure (or the dispersion curves) of the periodic medium which can be used to predict the location of the pass and stop bands. Although capable, these models become significantly more involved when analyzing structures with dissipative constituents and/or material damping and need further adjustments to account for complex elastic moduli and frequency dependent loss factors. A new approach is presented which relies on evaluating structural intensity parameters, such as the active vibrational power and energy transmission paths. It is shown that the steady-state spatial propagation of vibrational power caused by an external disturbance accurately reflects the wave propagation pattern in the periodic medium, and can thus be reverse engineered to numerically predict the stop band frequencies for different degrees of damping via a stop band index (SBI). The developed framework is mathematically applied to a one-dimensional periodic rod to validate the proposed method.

Hydrodynamic Analysis of Waveforms Induced by Vibrational Stimuli at Meridian and Non-meridian Points

2004 ◽  
Vol 32 (06) ◽  
pp. 977-984 ◽  
Author(s):  
Myeong Soo Lee ◽  
Yong-Chin Kim ◽  
Sun-Rock Moon ◽  
Byung-Chul Shin ◽  
Dong-Myong Jeong
Keyword(s):  
Wave Propagation ◽  
Chinese Medicine ◽  
Control Points ◽  
Mechanical Vibrations ◽  
Hydrodynamic Analysis ◽  
Pericardium Meridian ◽  
Attenuation Rate ◽  
The Mean ◽  
And Control ◽  
Control Regions

Meridian theory is an important part of traditional Chinese medicine (TCM). Although acupuncture has been accepted in many countries, the nature of the meridian theory and the principles of acupuncture are still unclear in the modern scientific view. The purpose of this study was to determine the differences in wave propagation of mechanical vibrations (optimal stimulator frequency of 40 Hz) through the pericardium meridian [EH-4 (Chieh-Men) and EH-5 (Chien-Shih)] and adjacent control regions in 20 subjects using hydrodynamic analysis. The mean transfer speed was significantly lower in the meridian (4 m/s) than in the adjacent control region (8.5 m/s, P<0.001). There were also significant differences between the meridian and control points in the attenuation rate (P<0.001) and peak amplitude (P<0.001). In conclusion, these results imply that the substance of the meridian differs from that of the adjacent control regions.

Random Mobility Variation of Disordered Periodic Structures

1991 ◽  
Author(s):  
G. Q. Cai
Keyword(s):  
Wave Propagation ◽  
Periodic Structures ◽  
Excitation Frequency ◽  
Normal Modes ◽  
Computational Procedure ◽  
Energy Concentration ◽  
Periodic Cell ◽  
Structure Response ◽  
Spatially Periodic ◽  
The Mean

Abstract Due to material, geometric and manufacturing irregularities, a structure designed to be spatially periodic cannot be exactly periodic. The departure from perfect periodicity is referred to as disorder, and it is known to cause spatial localization of normal modes and attenuation of wave propagation even if the structure is undamped. In this paper, another effect of disorder is investigated; namely, possible energy concentration near where a excitation is applied, thus, inducing higher level of structure response, A computational procedure is developed for calculating the mobility, or mechanical admittance, of deterministically disordered periodic structures based on wave propagation theory, and then extended to the case of randomly disordered periodic structures. It is shown that, given the probability distribution of the disordered parameters of a periodic structure, the mean and standard deviation of the mobility magnitude can be obtained. The results are exact if the number of the periodic cell units is not large, and approximate if the number is large. Depending on the excitation frequency, the mean mobility magnitude of a disordered system may be either greater or smaller than that of the perfectly periodic counterpart.

Substructuring and Wave Propagation: An Efficient Technique for Impeller Dynamic Analysis

1984 ◽  
Vol 106 (1) ◽  
pp. 2-10 ◽  
Author(s):  
R. Henry ◽  
G. Ferraris
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wave Propagation ◽  
Dynamic Analysis ◽  
Periodic Structures ◽  
Mode Shapes ◽  
Periodic Systems ◽  
The Finite Element Method ◽  
Compressor Impeller ◽  
Detailed Application

This paper is of particular interest of gas turbine designers because it proposes an efficient method for dynamic analysis of rotationally periodic structures encountered in turbomachines. It combines the advantages of a substructure technique and that of wave propagation in periodic systems. The mode shapes and frequencies are obtained from the analysis of a single repetitive sector of the whole structure. The finite element method is the numerical method used. A detailed application of the method to a centrifugal compressor impeller is reported along with experimental verification of the computed results.

Design of Disordered Periodic Structures for Mode Localization

2017 ◽  
Author(s):  
Gabriele Cazzulani ◽  
Emanuele Riva ◽  
Edoardo Belloni ◽  
Francesco Braghin
Keyword(s):  
Wave Propagation ◽  
Periodic Structures ◽  
Unit Cell ◽  
Band Gaps ◽  
Mode Shapes ◽  
Mode Localization ◽  
Geometrical Properties ◽  
Unit Cells ◽  
The Mean ◽  
Propagation Properties

Periodic structures are the repetition of unit cells in space, that provide a filtering behavior for wave propagation. In particular, it is possible to tailor the geometrical, physical and elastic properties of the unit cells, in order to attenuate certain frequency bands, called band-gaps or stop-bands. Having each element characterized with the same parameters, the filtering behavior of the system can be described through the wave propagation properties of the unit cell. This is technologically impossible to obtain, therefore the Lyapunov factor is used, in order to define the mean attenuation of a quasi-periodic structure. Tailoring Gaussian unit cell properties potentially allows to extend the stop-bands width in the frequency domain. A drawback is that some unexpected resonance peaks may lie in the neighborhood of the extended regions. However, the correspondent mode-shapes are localized in a particular region of the structure, and they partially decrease the global attenuating behavior. In this paper, the aperiodicity introduced in the otherwise perfect repetition is investigated, providing an explanation for the mode-localization problem and for the stop-bands extension. Then, the proposed approach is applied to a passive quasi-periodic beam, characterized from a localized peak within a designed band-gap. The geometrical properties of its aperiodic parts are changed in order to deterministically move the localization peak in the frequency response. Numerical and experimental results are compared.

Response of Periodic Systems to a Moving Load

1981 ◽  
Vol 48 (3) ◽  
pp. 613-618 ◽  
Author(s):  
L. Jezequel
Keyword(s):  
Wave Propagation ◽  
Periodic Structures ◽  
Moving Load ◽  
Continuous Model ◽  
Periodic Systems ◽  
Free Wave ◽  
Moving Force ◽  
Definition Of ◽  
Free Wave Propagation ◽  
Support Reactions

The motion of a beam or a plate resting on an elastic foundation and subjected to a moving load has been studied by numerous authors. But the extension of these studies to the case of periodic structures is difficult. In this paper, a method allowing the calculation at low numerical cost of periodically supported beams subjected to a moving force, is proposed. The interpretation of this method on the basis of the free-wave propagation equations in periodic structures has led to the definition of the predominant, so-called “primary,” critical speeds. Individual examples were used to test the method. It was also possible to define the limits of a Winkler continuous model in representing the support reactions.

Prothrombin Time Standardization: Report of the Expert Panel on Oral Anticoagulant Control

1979 ◽  
Vol 42 (04) ◽  
pp. 1073-1114 ◽  
Keyword(s):  
Prothrombin Time ◽  
Expert Panel ◽  
The Other ◽  
Rabbit Brain ◽  
Calibration Constant ◽  
Freeze Dried ◽  
The Mean ◽  
Point Of Intersection ◽  
And Control ◽  
Standardization Report

SummaryIn collaborative experiments in 199 laboratories, nine commercial thromboplastins, four thromboplastins held by the National Institute for Biological Standards and Control (NIBS & C), London and the British Comparative Thromboplastin were tested on fresh normal and coumarin plasmas, and on three series of freeze-dried plasmas. One of these was made from coumarin plasmas and the other two were prepared from normal plasmas; in each series, one plasma was normal and the other two represented different degrees of coumarin defect.Each thromboplastin was calibrated against NIBS&C rabbit brain 70/178, from the slope of the line joining the origin to the point of intersection of the mean ratios of coumarin/normal prothrombin times when the ratios obtained with the two thromboplastins on the same fresh plasmas were plotted against each other. From previous evidence, the slopes were calculated which would have been obtained against the NIBS&C “research standard” thromboplastin 67/40, and termed the “calibration constant” of each thromboplastin. Values obtained from the freeze-dried coumarin plasmas gave generally similar results to those from fresh plasmas for all thromboplastins, whereas values from the artificial plasmas agreed with those from fresh plasmas only when similar thromboplastins were being compared.Taking into account the slopes of the calibration lines and the variation between laboratories, precision in obtaining a patient’s prothrombin time was similar for all thromboplastins.

CHROMATOGRAPHY OF THE 17-KETOGENIC STEROIDS IN THE DIAGNOSIS AND CONTROL OF CONGENITAL ADRENAL HYPERPLASIA

1960 ◽  
Vol XXXIII (II) ◽  
pp. 230-250 ◽  
Author(s):  
Eileen E. Hill
Keyword(s):  
Congenital Adrenal Hyperplasia ◽  
List Type ◽  
Adrenal Hyperplasia ◽  
Normal Children ◽  
Paediatric Practice ◽  
The Mean ◽  
Cortisone Therapy ◽  
And Control ◽  
Clinical Problems ◽  
Stimulation Of

ABSTRACT A method for the fractionation of the urinary 17-ketogenic steroids with no oxygen grouping at C11 and those oxygenated at C11, is applied to the clinical problems of congenital adrenal hyperplasia. In normal children the mean ratio of the non-oxygenated to oxygenated steroids is 0.24. In childrern with congenital adrenal hyperplasia the ratio is 2.3. The reason for this difference in ratio is discussed. The changes in ratio found under stimulation of the adrenal gland with exogenous or endogenous corticotrophin and the suppression with cortisone therapy are studied. This test can be applied to isolated samples of urine, a major advantage in paediatric practice, and can be carried out in routine laboratories. It is found to be reliable in the diagnosis and sensitive in the control of congenital adrenal hyperplasia.

IOP Lowering Effects of Ocimum basilicum Seed Extract in Two Rabbit Models of Ocular Hypertension

2019 ◽  
Vol 4 (1) ◽  
pp. 39
Author(s):  
Renu Agarwal ◽  
SK Gupta ◽  
Sushma Srivastava ◽  
Rohit Saxena
Keyword(s):  
Ocular Hypertension ◽  
Antioxidant Properties ◽  
Ocimum Basilicum ◽  
Seed Extract ◽  
Water Loading ◽  
Antiglaucoma Medication ◽  
Lowering Effect ◽  
Significant Difference ◽  
The Mean ◽  
And Control

Introduction: Ocimum basilicum (OB), a herb known for its antihypertensive, anticholinesterase and antioxidant properties was investigated for possible intraocular pressure (IOP) lowering effects in rabbits with ocular hypertension (OHT). Methods: The IOP lowering effect of a single drop of OB extract (OBE) was evaluated in oculonormotensive rabbits using three concentrations (0.25, 0.5 and 1% w/v). The concentration showing maximum IOP reduction was further evaluated in rabbits with water-loading and steroid-induced OHT. Results: IOP lowering effect of OBE 0.5% in oculonormotensive rabbit eyes was significantly greater compared to OBE 0.25% (p<0.05) but was comparable (p>0.05) to OBE 1%. Therefore, 0.5% concentration was selected for further evaluation. Pretreatment with OBE (0.5%) caused significantly lower increase in IOP after water loading amounting to 23.39% above baseline as compared to 54.00% in control eye, 15 minutes post water loading. At 60 minutes, post water loading, mean IOP rise was 95.12% and 63.58% in control and test eyes, respectively. Significant difference between the mean IOP of two eyes persisted during the 2nd hr. In rabbits with steroid induced OHT, OBE 0.5% produced a mean IOP reduction of 24.73% at the end of first hr and the mean peak IOP reduction of 31.63% was observed at the end of 2 hr. A significant difference between the IOP of test and control eyes persisted from 1 to 6 hr. Conclusions: Ocimum basilicum seed extract showed significant IOP lowering effect in rabbits with water loading and steroid induced OHT, however, its utility as an effective antiglaucoma medication needs further investigations.

Mantle Of The Expert Strategy Effectiveness In The Development Of Creative Thinking

2019 ◽  
Author(s):  
Ibrahim Arman
Keyword(s):  
Creative Thinking ◽  
Role Playing ◽  
Thinking Skills ◽  
Measurement Unit ◽  
Quasi Experimental ◽  
Males And Females ◽  
The Mean ◽  
Girls School ◽  
And Control ◽  
Experimental Group

<p>This study aimed at investigating the Effectiveness of Mantle of the Expert in creative thinking Skills among the 7<sup>th</sup> Graders. The study conducted on a sample of 7<sup>th</sup> Graders at Kober Secondary Boys School and Upper Kober Elementary Girls School. The study sample consisted of (100) students split into two groups (experimental and control). The researcher adopting the Torrance test for creative thinking the verbal image "A" by examining the tests used in the Ristow study (1988), Edwards and Baldov (1987) study, and designing a teacher book for the (engineering and measurement) unit according to the integration between the strategies of the mantle of the expert and role playing.</p> <p>This study adopted quasi-experimental design. It included two groups (experimental and controlled) in two branches (males and females) for each group. The controlled group was taught by using the traditional method whereas the experimental group by the mantle of the expert. The data analyzed using (ANCOVA) test to measure the differences in the development of creative thinking between the control and experimental groups.</p> <p>The Conclusions showed that there are statistically significant differences in the mean scores of the creative thinking test due to the way, gender and interaction between them.</p> <p>Based on the Conclusions of the study, the researcher recommends the need to use the mantles of the expert in the teaching of mathematics.</p>

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