scholarly journals D’Yakov–Kontorovich instability in planar reactive shocks

2019 ◽  
Vol 879 ◽  
pp. 54-84 ◽  
Author(s):  
César Huete ◽  
Marcos Vera
Keyword(s):  
Detonation Front ◽  
Direct Result ◽  
Linear Perturbation ◽  
Shock Strength ◽  
Sound Waves ◽  
Constant Amplitude ◽  
Hugoniot Curve ◽  
Thermoacoustic Instability ◽  
Long Time ◽  
Heat Released

The standard D’Yakov and Kontorovich (DK) instability occurs when a planar shock wave is perturbed and then oscillates with constant amplitude in the long-time regime. As a direct result, pressure perturbations generated directly behind the shock propagate downstream as non-evanescent sound waves, an effect known as spontaneous acoustic emission (SAE). To reach the DK regime, the slope of the Rankine–Hugoniot curve in the post-shock state must satisfy certain conditions, which have usually been related to non-ideal equations of state. This study reports that the DK instability and SAE can also occur in shocks moving in perfect gases when exothermic effects occur. In particular, a planar detonation, initially perturbed with a wavelength much larger than the detonation thickness, may exhibit constant-amplitude oscillations when the amount of heat released is positively correlated with the shock strength, a phenomenon that resembles the Rayleigh thermoacoustic instability. The opposite strongly damped oscillation regime is reached when the shock strength and the change in the heat released are negatively correlated. This study employs a linear perturbation model to describe the long-time and transient evolution of the detonation front, which is assumed to be infinitely thin, and the sound and entropy–vorticity fields generated downstream.

On the collision of impulsive gravitational waves when coupled with fluid motions

1985 ◽  
Vol 402 (1822) ◽  
pp. 37-65 ◽  
Keyword(s):  
Exact Solution ◽  
Gravitational Waves ◽  
Massive Particle ◽  
Natural Generalization ◽  
Space Time ◽  
Direct Result ◽  
Sound Waves ◽  
Time Singularity ◽  
Consistent Extension ◽  
Ultimate Result

An exact solution of Einstein’s equations, with a source derived from a perfect fluid in which the energy density, ε , is equal to the pressure, p , is obtained. The solution describes the space–time following the collision of plane impulsive gravitational waves and is the natural generalization of the Nutku─Halil solution of the vacuum equations, in the region of interaction under similar basic conditions. A consistent extension of the solution, prior to the instant of collision, requires that the fluid in the region of interaction is the direct result of a transformation of incident null-dust (i. e. of massless particles describing null trajectories). The ultimate result of the collision is the development of a space─time singularity, the nature of which is strongly dependent on the amplitude and the character of the sound waves that are present. The distribution of ε that follows the collision has many intriguing features. The solution obtained in this paper provides the first example of an induced transformation of a massless into a massive particle.

A SPH Implementation with Ignition and Growth and Afterburning Models for Aluminized Explosives

2017 ◽  
Vol 14 (04) ◽  
pp. 1750046 ◽  
Author(s):  
Guangyu Wang ◽  
Guirong Liu ◽  
Qing Peng ◽  
Suvranu De
Keyword(s):  
Growth Model ◽  
Detonation Front ◽  
High Explosives ◽  
Combustion Chemistry ◽  
Metal Combustion ◽  
Military Industry ◽  
Particle Hydrodynamics ◽  
Long Time ◽  
History Of ◽  
Multi Phase

Aluminized explosives have been applied in military industry since decades ago. Compared with ideal explosives such as TNT, HMX, RDX, aluminized explosives feature both fast detonation and slow metal combustion chemistry, generating a complex multi-phase reactive flow. Though aluminized explosives have been employed for a long time, the mechanism underneath the chemical process is still not thoroughly understood. In this paper, a smooth particle hydrodynamics (SPH) method incorporated ignition and growth model, and afterburning model has been proposed for the simulation of aluminized explosive. Ignition and growth model is currently the most popular model for the simulation of high explosives, which is capable of accurately reproducing arrival time of detonation front and pressure history of high explosives. It has been integrated in commercial software such as ANSYS-LS DYNA. In addition, an afterburning model has been integrated in the SPH code to simulate the combustion of aluminum particles. Simulation is compared with experiment and good agreement is observed. The proposed mathematical model can be used to study the detonation of aluminized explosives.

Longitudinal sound waves in a collisionless, quasineutral plasma

2017 ◽  
Vol 83 (6) ◽  
Author(s):  
J. J. Ramos
Keyword(s):  
Electric Field ◽  
Time Evolution ◽  
Initial Conditions ◽  
Normal Modes ◽  
Adjoint Problem ◽  
Plasma Phys ◽  
Landau Damping ◽  
Linear Perturbation ◽  
Sound Waves ◽  
Quasineutral Plasma

The time evolution of slow sound waves in a homogeneous, collisionless and quasineutral plasma, in particular their Landau damping, is investigated using the kinetic-magnetohydrodynamics formulation of Ramos (J. Plasma Phys. vol. 81, 2015 p. 905810325; vol. 82, 2016 p. 905820607). In this approach, the electric field is eliminated from a closed, hybrid fluid-kinetic system that ensures automatically the fulfilment of the charge neutrality condition. Considering the time dependence of a spatial-Fourier-mode linear perturbation with wavevector parallel to the equilibrium magnetic field, this can be cast as a second-order self-adjoint problem with a continuum spectrum of real and positive squared frequencies. Therefore, a conventional resolution of the identity with a continuum basis of singular normal modes is guaranteed, which simplifies significantly a Van Kampen-like treatment of the Landau damping. The explicit form of such singular normal modes is obtained, along with their orthogonality relations. These are used to derive the damped time evolution of the fluid moments of solutions of initial-value problems, for the most general kinds of initial conditions. The non-zero parallel electric field is not used explicitly in this analysis, but it is calculated from any given solution after the later has been obtained.

scholarly journals Noise-Canceling Office Chair with Multiple Reference Microphones

2018 ◽  
Vol 8 (9) ◽  
pp. 1702
Author(s):  
László Sujbert ◽  
Attila Szarvas
Keyword(s):  
Noise Source ◽  
Feedforward Control ◽  
Acoustic Noise ◽  
Sound Waves ◽  
Efficient Suppression ◽  
Reference Signals ◽  
Long Time ◽  
Office Employees ◽  
Multiple Reference ◽  
Noise Canceling

Office employees are exposed to acoustic noise, especially in an open office environment. Passive or active headsets sufficiently reduce the level of noise, but their long-time wear is uncomfortable. The paper presents an active headrest system built into a chair. Feedforward control is utilized with multiple reference microphones, and flexible gooseneck microphones serve as error sensors. The reference sensors surround the chair, allowing the suppression of sound waves arriving from any direction. The concept of multiple reference control has been tested by extensive experiments showing that multiple reference signals help to increase the suppression in normal rooms where reverberation occurs, even if only one noise source is present. The preliminary experiments are completed by a series of simulations aiming to explore the zones of quiet at the user’s ears. The paper introduces the construction details of the noise-canceling chair: The two loudspeakers are controlled by the signals of two error microphones and four reference signals. The controller is based on the normalized filtered error least mean squared algorithm, implemented on an Analog Devices ADSP-21262 signal processor-based hardware. Experimental results are reported that show the efficient suppression of tonal, as well as broadband disturbances.

Constant amplitude sound waves in non-Hermitian metamaterials

2017 ◽  
Vol 142 (4) ◽  
pp. 2684-2684 ◽  
Author(s):  
Etienne Rivet ◽  
Andre Brandstötter ◽  
Konstantinos Makris ◽  
Stefan Rotter ◽  
Herve Lissek ◽  
...  
Keyword(s):  
Sound Waves ◽  
Constant Amplitude

The long time asymptotics of solutions to the generalized Burgers equation

1981 ◽  
Vol 373 (1755) ◽  
pp. 443-456 ◽  
Keyword(s):  
Burgers Equation ◽  
Analytic Form ◽  
Variable Cross Section ◽  
Variable Cross ◽  
Sound Waves ◽  
Limiting Profile ◽  
Generalized Burgers Equation ◽  
Long Time ◽  
Constant State ◽  
Long Time Asymptotics

The long time (i.e. range following a wavefront) behaviour of finiteamplitude sound waves in ducts (‘horns’) of variable cross section is considered, the wave evolution being governed by a generalized form of Burgers equation. The type of initial data far behind and far ahead of the wavefront is restricted to a transition from one constant state to another. It is proved that the form of the wave for large range is dependent on the limiting value of a certain function of the duct parameters. We have termed the various cases that arise ‘supercylindrical’, ‘cylindrical’ and ‘subcylindrical’, for reasons that should be clear from the details to follow. The analytic form of the limiting profile is determined in all but one case. In particular, it is shown that the similarity solution for cylindrical waves possesses very strong global stability properties.

scholarly journals The right to death. Fiction or reality?

2016 ◽  
Vol 17 (31) ◽  
pp. 37-45
Author(s):  
Maria Casandra Lucan
Keyword(s):  
Social Action ◽  
Assisted Suicide ◽  
Direct Result ◽  
Right To Life ◽  
The World ◽  
Long Time ◽  
Protection Of Human Rights ◽  
The Right ◽  
Literature Result ◽  
Protection Of Life

Abstract The present article is part of a dense literature – result of a perennial debate – that has polarized societies for a long time and has evident reverberations in the present. It deals with “the right to death”, trying to offer some answers referring to its existence in fact and the way in which it is perceived by different states and diverse entities with juridical nature. In the first part of the paper, it is insisted upon the right to life, so that subsequently, to speak in detail about a “right to death” and the moral and juridical implications of using such phrases. There are analyzed different states of the world found on one part or the other of the barricade in what concerns the legality of euthanasia and assisted suicide – considered the two hypostasis of the right in question. It is offered, as well, an analysis of the Convention for the Protection of Human Rights and Fundamental Freedoms, mentioning that, paradoxically, while it cannot be modified so that it allows the appearance of some new rights, it can tacitly accept the creation by some states that have adhered to it of some rights antagonistic with those presented in its text. The conclusion, is that not any liberalization movement of a social action – quantified through the request of a right – has as a direct result a progress of the respective society, especially when the action creates something diametrically opposed to some fundamental functioning norms, such as, by excellence, the granting of the protection of life of all individuals.

Computer Operator Cervical Disease Prevention and Physical Exercise

2014 ◽  
Vol 1030-1032 ◽  
pp. 2344-2347
Author(s):  
Seng Lin Lu ◽  
Li Hua Wu
Keyword(s):  
Physical Exercise ◽  
Rapid Development ◽  
Universal Coverage ◽  
Development Trend ◽  
Direct Result ◽  
Computer Operating System ◽  
Younger Age ◽  
Cervical Disease ◽  
Long Time ◽  
Computer Operator

With the rapid development of computer technology, computer use has been universal coverage and promotion, the promotion of social development and the progress of civilization, but also a direct result of the incidence of cervical disease growing computer operations personnel toward younger age and development trend. In order to effectively prevent the occurrence of cervical disease, a computer operator for the work and life of special investigations carried out pathological studies of patients with cervical disease mechanisms, and found the risk factors which affect computer operations personnel, such as the presence of cervical disease: Continuing operations a long time, incorrect body posture, habits unscientific. Must take effective measures to deal with the timely evacuation exercises to do some exercise, posture alignment operation, pay attention to the computer operating system and placed in the correct position to strengthen targeted physical exercise, can effectively prevent the occurrence of cervical spondylosis, computer operator jobs and improve the quality of life.

Temperature Dependence of the Critical Electron Dose for Fatty Acid Monolayers

1982 ◽  
Vol 40 ◽  
pp. 78-79
Author(s):  
Kenneth H. Downing ◽  
Robert M. Glaeser
Keyword(s):  
Electron Beam ◽  
Fatty Acid ◽  
Inelastic Scattering ◽  
Temperature Dependence ◽  
Structural Damage ◽  
Direct Result ◽  
Second Step ◽  
Strong Temperature Dependence ◽  
Electron Dose ◽  
Covalent Bonds

The structural damage of molecules irradiated by electrons is generally considered to occur in two steps. The direct result of inelastic scattering events is the disruption of covalent bonds. Following changes in bond structure, movement of the constituent atoms produces permanent distortions of the molecules. Since at least the second step should show a strong temperature dependence, it was to be expected that cooling a specimen should extend its lifetime in the electron beam. This result has been found in a large number of experiments, but the degree to which cooling the specimen enhances its resistance to radiation damage has been found to vary widely with specimen types.

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