Exchanged momentum between moving atoms and a surface wave: theory and experiment

1979 ◽  
Vol 57 (5) ◽  
pp. 612-618 ◽  
Author(s):  
Serge Huard
Keyword(s):  
Surface Wave ◽  
Optical Pumping ◽  
Classical Method ◽  
Atomic Clock ◽  
Wave Theory ◽  
Resonant Interaction ◽  
Small Frequency ◽  
Homogeneous Wave ◽  
The One ◽  
Theory And Experiment

Momentum transfer during the resonant interaction between moving atoms and surface waves is calculated using a semi-classical method. Results show a greater Doppler shift than the one obtained in similar analysis with a plane homogeneous wave interacting with moving atoms. In order to measure such a small frequency shift, an atomic clock technique is used (accuracy: 10−10). An appropriate choice of surface wave frequency is the centimetre wavelength. The ΔF = 1, Δm = 0 transition in 87Rb is used and detected by the well-known optical pumping method.Experimental results are obtained for two different Rb atom speeds and compared with theoretical values.

Investigation of the One-Dimensional Endochronic Constitutive Equation for Metals by the Rivlin Test

1984 ◽  
Vol 106 (3) ◽  
pp. 264-270 ◽  
Author(s):  
Han C. Wu ◽  
C. C. Yang
Keyword(s):  
Constitutive Equation ◽  
Strain Path ◽  
Small Strain ◽  
One Dimensional ◽  
Good For ◽  
The One ◽  
Cyclic Straining ◽  
Strain Cycling ◽  
Theory And Experiment

Two sets of experiments with and without strain cycling have been carried out to test the validity of an equation derived from the improved theory of endochronic plasticity. It has been found that for strain path not involving cyclic straining the agreement between theory and experiment is quite good. In the test with strain cycling, the agreement is not good for small strain amplitudes of cycling but the discrepancy diminishes with the increasing amplitude of the strain cycling.

Steady State Motion and Surface Waves

1996 ◽  
Author(s):  
T. T. C. Ting
Keyword(s):  
Steady State ◽  
Surface Wave ◽  
Surface Waves ◽  
Existence And Uniqueness ◽  
Wave Speed ◽  
Wave Theory ◽  
Two Dimensional ◽  
Elastic Materials ◽  
Steady State Motion ◽  
Anisotropic Elastic

The Stroh formalism for two-dimensional elastostatics can be extended to elastodynamics when the problem is a steady state motion. Most of the identities in Chapters 6 and 7 remain applicable. The Barnett-Lothe tensors S, H, L now depend on the speed υ of the steady state motion. However S(υ), H(υ), L(υ) are no longer tensors because they do not obey the laws of tensor transformation when υ≠0. Depending on the problems the speed υ may not be prescribed arbitrarily. This is particularly the case for surface waves in a half-space where υ is the surface wave speed. The problem of the existence and uniqueness of a surface wave speed in anisotropic materials is the crux of surface wave theory. It is a subject that has been extensively studied since the pioneer work of Stroh (1962). Excellent expositions on surface waves for anisotropic elastic materials have been given by Farnell (1970), Chadwick and Smith (1977), Barnett and Lothe (1985), and more recently, by Chadwick (1989d).

scholarly journals Deep Learning–Based Methods for Automatic Diagnosis of Skin Lesions

Sensors ◽  
2020 ◽  
Vol 20 (6) ◽  
pp. 1753 ◽  
Author(s):  
Hassan El-Khatib ◽  
Dan Popescu ◽  
Loretta Ichim
Keyword(s):  
Neural Networks ◽  
Deep Learning ◽  
Classical Method ◽  
Skin Lesions ◽  
Support Vector ◽  
Dice Similarity Coefficient ◽  
Final Decision ◽  
Decision System ◽  
The One ◽  
Sensitivity Specificity

The main purpose of the study was to develop a high accuracy system able to diagnose skin lesions using deep learning–based methods. We propose a new decision system based on multiple classifiers like neural networks and feature–based methods. Each classifier (method) gives the final decision system a certain weight, depending on the calculated accuracy, helping the system make a better decision. First, we created a neural network (NN) that can differentiate melanoma from benign nevus. The NN architecture is analyzed by evaluating it during the training process. Some biostatistic parameters, such as accuracy, specificity, sensitivity, and Dice coefficient are calculated. Then, we developed three other methods based on convolutional neural networks (CNNs). The CNNs were pre-trained using large ImageNet and Places365 databases. GoogleNet, ResNet-101, and NasNet-Large, were used in the enumeration order. CNN architectures were fine-tuned in order to distinguish the different types of skin lesions using transfer learning. The accuracies of the classifications were determined. The last proposed method uses the classical method of image object detection, more precisely, the one in which some features are extracted from the images, followed by the classification step. In this case, the classification was done by using a support vector machine. Just as in the first method, the sensitivity, specificity, Dice similarity coefficient and accuracy are determined. A comparison of the obtained results from all the methods is then done. As mentioned above, the novelty of this paper is the integration of these methods in a global fusion-based decision system that uses the results obtained by each individual method to establish the fusion weights. The results obtained by carrying out the experiments on two different free databases shows that the proposed system offers higher accuracy results.

scholarly journals A Theoretical Prediction of the Acoustic Pressure Generated by Turbulence-Flame Front Interactions

1986 ◽  
Vol 108 (3) ◽  
pp. 315-321 ◽  
Author(s):  
R. G. Huff
Keyword(s):  
Wave Equation ◽  
Acoustic Pressure ◽  
Pressure Fluctuations ◽  
Orbit Space ◽  
Space Propulsion ◽  
Forcing Function ◽  
Homogeneous Wave ◽  
Gas Generators ◽  
The One ◽  
Nonhomogeneous Equation

The equations of momentum and continuity are combined and linearized yielding the one-dimensional nonhomogeneous acoustic wave equation. Three terms in the nonhomogeneous equation act as acoustic sources and are taken to be forcing functions acting on the homogeneous wave equation. The three source terms are: fluctuating entropy, turbulence gradients, and turbulence-flame interactions. Each source term is discussed. The turbulence-flame interaction source is used as the basis for computing the source acoustic pressure from the Fourier transformed wave equation. Pressure fluctuations created in turbopump gas generators and turbines may act as a forcing function for turbine and propellant tube vibrations in earth-to-orbit space propulsion systems and could reduce their life expectancy. A preliminary assessment of the acoustic pressure fluctuations in such system is presented.

scholarly journals Shock Initiation of a Satellite Tank under Debris Hypervelocity Impact

2019 ◽  
Vol 9 (19) ◽  
pp. 3957
Author(s):  
Zhao ◽  
Zhao ◽  
Cui ◽  
Wang
Keyword(s):  
Shock Wave ◽  
Power Density ◽  
Wave Theory ◽  
Hypervelocity Impact ◽  
Shock Initiation ◽  
One Dimensional ◽  
Minimum Power ◽  
Shock Wave Pressure ◽  
The One ◽  
Debris Impact

For the risk assessment of a satellite to determine whether the satellite tank explodes under the hypervelocity impact, the Walker–Wasley criterion is selected to predict the shock initiation of the satellite tank. Then, the minimum power density of liquid hydrazine is determined based on the tests, the expressions of shock wave pressure and pressure duration are constructed based on the one-dimensional wave theory, and the initiation criterion for the liquid hydrazine tank is established. Finally, numerical simulation and the initiation criterion are adopted to calculate the power density in the satellite tank under the debris impact at the velocity of 10 km/s. The calculated power density agrees well with the simulated power density, they are both larger than the minimum power density, demonstrating that the shock wave generated by the hypervelocity impact is sufficient to trigger an explosion in the satellite tank.

VERIFICATION OF THE SHB TEST RESULTS BASED ON THE ONE-DIMENSIONAL STRESS WAVE THEORY

2008 ◽  
Vol 22 (09n11) ◽  
pp. 1068-1073
Author(s):  
TOMOKAZU MASUDA ◽  
KENJI SAITO ◽  
IZUMI MORITA ◽  
SHUSHI IKEDA ◽  
KOICHI MAKII ◽  
...  
Keyword(s):  
Strain Rate ◽  
Stress Wave ◽  
High Speed ◽  
Wave Theory ◽  
High Speed Photography ◽  
Strain Rates ◽  
One Dimensional ◽  
Strain And Strain Rate ◽  
Deformation Behaviors ◽  
The One

In order to evaluate dynamic deformation behaviors under high strain rates, Kobe Steel has developed and applied a Split-Hopkinson Bar (SHB) apparatus. This paper discusses the validity of the strain measurements and strain rates measured by this SHB apparatus. The strain waves that propagated in the incident and transmitted bars and the specimen are captured using a high-resolution type high-speed photography in detail. The strain wave propagated many times in the incident and transmitted bars and the specimen when the specimen was not broken. The amount of the deformation of the specimen decreases with the propagation frequency of the incident wave. On the other hand, to improve accuracy at the strain and strain rate calculated by the one-dimensional stress wave theory, Young's modulus, the longitudinal wave speed, and the density were accurately determined. It was understood that the calculation value showed the strain and strain rate captured with the high-speed photography are a good agreement. As a result, the validity of the measurement accuracy of this SHB could be shown.

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