Reverse Wave Research Articles

Formation of Forward and Reverse Shock Waves in a Magnetized Plasma: Two-Dimensional Particle Simulations

Interactions of exploding and surrounding plasmas are studied with two-dimensional (2D) electromagnetic particle simulations, for a case in which the initial velocity of the exploding plasma is perpendicular to an external magnetic field. It is confirmed that essentially the same phenomena (the penetration of exploding ions, the formation of a strong magnetic-field pulse, and the generation of forward and reverse shock waves) as in the previous one-dimensional (1D) simulations occurred in the 2D simulation. Further, modified two-stream instabilities excited by relative cross-field motion between ions and electrons are investigated with attention to their effects on the 2D structure of the strong magnetic-field pulse and on ion reflection by the pulse.

Statistical Properties of GRB Afterglow Parameters as Evidence of Cosmological Evolution of Host Galaxies

The results of investigation of 43 peaked R-band light curves of optical transients of gamma-ray bursts with known redshifts are presented. The parameters of optical transients were calculated in the comoving frame, and then a search for pair correlations between them was conducted. As a result of the statistical analysis, a strong correlation between the peak luminosity and redshift was found for pure afterglows and the events with residual gamma activity, which can’t be explained as an effect of observational selection. It suggests the cosmological evolution of the parameters of the local interstellar medium around the sources of gamma-ray burst. In the models of forward and reverse shock waves, a relation between the density of interstellar medium and redshift was built for gamma-ray burst afterglows. It was shown that for GRB host galaxies the star formation rate increases with redshift.

REVERSE RADIATIVE SHOCK LASER EXPERIMENTS RELEVANT TO ACCRETING STREAM-DISK IMPACT IN INTERACTING BINARIES

We present the first results from high-energy-density laboratory astrophysics experiments that explore the hydrodynamic and radiative properties of a reverse shock relevant to a cataclysmic variable system. A reverse shock is a shock wave that develops when a freely flowing, supersonic plasma is impeded. In our experiments, performed on the Omega Laser Facility, a laser pulse is used to accelerate plasma ejecta into a vacuum. This flow is directed into an Al plate in front of which a shock forms in the rebounding plasma. The plasma flow is moving fast enough that it is shocked to high enough temperatures that radiative cooling affects the shock structure. These are the first experiments to produce a radiative reverse shock wave.

Investigation on the Interactions of Gas Explosion Flame and Reflected Pressure Waves in Closed Pipes

In the present research work, the basic concepts of the coupling interaction mechanisms of gas explosion–reflected over pressure and flame were outlined by experiments and theory analysis. During the test processes, high speed cameras were employed for shooting the flame images, and pressure and flame sensors were set along the pipes for the signals detection. The research results show that the reflected reverse pressure wave has a significant influence on the transmission properties of gas explosion flame in the closed pipes. Under the effects of reversed pressure waves, gas explosion flames also present several discontinuous characteristics, such as flame ruptures or extinguishing. Generally, it can be inferred that the main effects of reflected explosion pressure on the flame propagations in the closed pipes are inhibitions. The present research results of these studies are shown to allow for a significant improvement in our ability to address practical problems of coal mine gas explosion mitigations.

GREEN'S FUNCTION OF THE CONVECTIVE WAVE EQUATION FOR THE RIGIDWALLED PIPE

Green’s function of the three-dimensional wave equation for an infinite straight rigid-walled pipe of circular cross-section with mean flow is found. This function is written in terms of the series of the pipe acoustic modes, and is periodic in the azimuthal coordinate and symmetric about the pipe axial section of the unit point impulse source location. Each term of the series is a sum of the direct and reverse waves propagating in the corresponding pipe mode downstream and upstream of the noted source. In the found Green’s function, the mean flow effects are reflected in the direct manner. The effects become more significant as the flow Mach number increases, causing, in particular, the appearance and further growth of the function asymmetry about the pipe cross-section of the source location. And vice versa, the decrease of the Mach number results in the decrease of the ef-fects and, in particular, the decrease of the indicated asymmetry of the function. In the case of mean flow absence the obtained Green’s function is symmetric about the indicated cross-section and coincides with the corresponding Green’s function for the investigated pipe, which is available in the scientific literature.

The rise of the ‘China Model’ and ‘Beijing Consensus’: evidence of authoritarian diffusion?

The rise of authoritarian great powers has raised questions about the dominance of the liberal democratic model and has led to a perception that the relative balance between democracy and authoritarianism is shifting. Consequently, there is increasing interest in and concerns about the diffusion of alternative ‘models’ of political and economic development. Given that China's impressive economic development has led to growing military strength and geopolitical prestige, evaluating perceptions of the legitimacy, effectiveness, and applicability of that country's model of ‘illiberal capitalism’ is a good place to start. This paper evaluates whether the ‘China Model’ or ‘Beijing Consensus' is gaining traction internationally through a content analysis of eight years of US and non-US media sources. It finds that concerns about the beginnings of an anti-democratic ‘reverse wave’ are exaggerated and that at the present time there does not appear to be a decisive shift in favour of a model of authoritarian-capitalism.

The dynamics of the velocity field beneath the North group of volcanoes, Kamchatka, and its relationship to the evolution of volcanic activity

P- and S-wave travel times from local volcanic earthquakes recorded in the North group of volcanoes area during the 2005–2009 period were treated by the “reverse wave” method to calculate the VP velocity field and the TAU parameter, which is an analogue of the P- to S-wave velocity ratio. We constructed 3D velocity distributions along the line traversing the volcanic group along the direction from Ploskii Tolbachik Volcano in the southwest toward Shiveluch Volcano in the northeast. Dynamic changes in the velocity field were identified, both over time and depth. We examine the relationships of these dynamic changes to the evolution of volcanic activity during the period indicated.

The linear stability of plane Poiseuille flow of Burgers fluid at very low Reynolds numbers

The linear stability of plane Poiseuille flow of Burgers fluid at very low Reynolds numbers is studied. In the previous works, it was shown that plane Poiseuille flows of UCM and Oldroyd-B fluids at very low Reynolds numbers are linearly stable. However, in the present work, unstable modes for Burges fluid are detected with some special value of parameters. In critical stable condition, there are two kinds of perturbation waves. One travels downstream with the name of forward wave, while the other travels upstream with the name of reverse wave. The mean value of the two wave speeds is independent of the characteristic velocity of flow, while the difference between the wave speeds reflects the equivalent velocity of flow. By comparing the perturbation modes for Newtonian fluid and Burgers fluid under critical stable conditions, it can be found that although the shapes of their amplitudes are basically the same, their phase diagrams are significantly different. The neutral curve of Burgers fluid is also different from that of Newtonian fluid. Unstable modes can still be found at high wave numbers. The flow instability is induced due to the phase difference between the perturbation strain and stress. The perturbation energy caused by the forward wave, which is dissipated by the effects of the component of perturbation normal stress in the streamwise direction, is transported by the effects of both the perturbation normal stress in the wall-normal direction and the perturbation shear stress. The converse is true for the reverse wave.

The Time History Analysis of the Frame Structure with Special-Shaped Columns Considering Torsional Component of the Earthquake

This paper is concerned with the study on internal forces of structure by building model in ANSYS under unidirectional seismic wave, bi-directional seismic waves and two-way and reverse seismic wave. The results revealed that the moment effect of frame structure under bi-directional seismic waves and two-way and reverse seismic wave is bigger around 30% than it under unidirectional seismic wave. And the torque accretion multiple of irregular structure is bigger around 1 than the corresponding regular structure. Therefore, we should take into account the effect of multi-dimensional seismic and the torsional effect of the irregular structure in structure design.

Marcus–Hush–Chidsey theory of electron transfer applied to voltammetry: A review

The application of the Marcus–Hush–Chidsey (MHC) formalism to heterogeneous electron transfer processes is reviewed and compared with the commonly employed Butler–Volmer (BV) approach.The MHC model is potentially more powerful than BV since it enables us to analyze the electrode kinetics in terms of the microscopic nature of the electroactive species, electrode and solvent. Despite having been studied fairly extensively in the case of surface-bound redox couples, its application to heterogeneous electron transfer reactions has been limited. Here, we review the use of the MHC approach for the analysis of both surface-bound and solution phase redox systems and its suitability as a model for the parameterisation of electrode kinetics.Results obtained for several slow electrode reactions using cyclic voltammetry and reverse scan square wave voltammetry are reviewed which reveal that the simple MHC model does not always give a satisfactory fit to experimental data in contrast to BV parameterisation. Possible physical reasons for the experimental deviations from simple MHC theory are examined.

Quantitative weaknesses of the Marcus-Hush theory of electrode kinetics revealed by Reverse Scan Square Wave Voltammetry: The reduction of 2-methyl-2-nitropropane at mercury microelectrodes

The Marcus-Hush and Butler–Volmer kinetic electrode models are compared experimentally by studying the reduction of 2-methyl-2-nitropropane in acetonitrile at mercury microelectrodes using Reverse Scan Square Wave Voltammetry. This technique is found to be very sensitive to the electrode kinetics and to permit critical comparison of the two models. The Butler–Volmer model satisfactorily fits the experimental data whereas Marcus-Hush does not quantitatively describe this redox system.

A Reverse Transcriptase-Dependent Mechanism Is Essential for Murine Preimplantation Development

LINE-1 (Long Interspersed Nuclear elements) and HERVs (Human Endogenous Retroviruses) are two families of retrotransposons which together account for about 28% of the human genome. Genes harbored within LINE-1 and HERV retrotransposons, particularly that encoding the reverse transcriptase (RT) enzyme, are generally expressed at low levels in differentiated cells, but their expression is up-regulated in embryonic tissues and transformed cells. Here we review evidence indicating that the LINE-1-encoded RT plays regulatory roles in early embryonic development. Indeed, antisense-mediated inhibition of expression of a highly expressed LINE-1 family in mouse zygotes caused developmental arrest at the two- or four-cell embryo stages. Development is also arrested when the embryo endogenous RT activity is pharmacologically inhibited by nevirapine, an RT inhibitor currently employed in AIDS treatment. The arrest of embryonic development is irreversible even after RT inhibition is removed and it is associated with subverted gene expression profiles. These data indicate an early requirement for LINE-1-encoded RT to support early developmental progression. Consistent with this, recent findings indicate that a reverse transcription wave is triggered in the zygote a few hours after fertilization and is propagated at least through the first two rounds of cell division. On the whole these findings suggest that reverse transcription is strictly required in early embryos as a key component of a novel RT-dependent mechanism that regulated the proper unfolding of the developmental program.

Localization of a nonlinear source in the bulk of a solid.

Time reversal (TR) has the potential to become a powerful tool in non‐destructive evaluation. Coupled with nonlinear properties of cracks in a group of techniques known as Time reverse nonlinear elastic wave spectroscopy, it provides the means to detect and image mechanical damage in complex solids. In this prototype experimental study, we show that we can excite a buried nonlinear feature applying TR. The feature scatters energy that is detected on the sample perimeter. The time signals are filtered about the nonlinear‐generated components and are broadcast back, focusing on their source, the buried nonlinear feature. The current challenge is introducing sufficient energy in order to excite the buried feature and produce nonlinear scattering that can be detected on the edges of the sample. This was achieved using a 30 channel system. Two features were localized: a part of the interface between two blocks submitted to a high amplitude signal, and a defect on the same interface (a cured drop of glue creating hard contact between the two solids). Results are visualized using the energy flux quantity.

Calibrating Broadband Highly Mismatched Noise Sources

Two methods are presented for calibrating broadband highly mismatched noise sources. The first is a reformulation and an extension of the procedure used for very accurately calibrating matched noise sources. It uses isolators and works whatever the source reflection factor. With the second method, the excess noise ratio of the noise source is numerically optimized until the measured reverse noise wave of an attenuator is equal to the theoretical value derived from its S-parameters. It can be applied to sources with reflection factors of about 0.45 to 0.90. Both methods appear to give very consistent results.

Specification of absorbed-sound power in the ear canal: Application to suppression of stimulus frequency otoacoustic emissions

An insert ear-canal probe including sound source and microphone can deliver a calibrated sound power level to the ear. The aural power absorbed is proportional to the product of mean-squared forward pressure, ear-canal area, and absorbance, in which the sound field is represented using forward (reverse) waves traveling toward (away from) the eardrum. Forward pressure is composed of incident pressure and its multiple internal reflections between eardrum and probe. Based on a database of measurements in normal-hearing adults from 0.22 to 8 kHz, the transfer-function level of forward relative to incident pressure is boosted below 0.7 kHz and within 4 dB above. The level of forward relative to total pressure is maximal close to 4 kHz with wide variability across ears. A spectrally flat incident-pressure level across frequency produces a nearly flat absorbed power level, in contrast to 19 dB changes in pressure level. Calibrating an ear-canal sound source based on absorbed power may be useful in audiological and research applications. Specifying the tip-to-tail level difference of the suppression tuning curve of stimulus frequency otoacoustic emissions in terms of absorbed power reveals increased cochlear gain at 8 kHz relative to the level difference measured using total pressure.

Tracing Distortion Product (DP) Waves in a Cochlear Model.

In many cases a cochlear model suffices to explain (by simulation) the properties of waves in the cochlea. This is not so in the case of a distortion product (DP) set up by presenting two primary tones to the cochlea. A three-dimensional model predicts, apart from a DP wave traveling in the apical direction, a DP wave that travels from the region of overlap of the two tone patterns towards the stapes-setting the stapes in motion so as to produce an otoacoustic emission at the DP frequency. Experimental research has shown, however, that the actual DP wave in the cochlea appears to travel in the opposite direction, from near the stapes to the overlap region. This feature has been termed "inverted direction of wave propagation" (IDWP). The forward wave could result from an unknown process such as a "hidden source" near the stapes. In the present study we have disproved this notion, by using a one-dimensional model of the cochlea. It is found that both reverse and forward waves are set up by the source of nonlinearity, in the same way as has been published in an earlier work. The present results reveal that IDWP in the data corresponds to the region where the DP wave, originally created as a reverse wave but reflected from the stapes, has received so much amplification that it starts to dominate over the reverse wave. Hence we conclude that IDWP in a one-dimensional model is a direct manifestation of cochlear amplification.

Constructing a Framework of Authoritarian Diffusion: Concepts, Dynamics, and Future Research

As the color revolutions have stalled and the challenge to democracy by authoritarianism has increased, it is essential to explore the potential of a new ``reverse wave'' which may create a greater balance between liberalism and autocracy. This article seeks to begin this process by outlining a framework of authoritarian diffusion. Two key diffusion dynamics are outlined: appropriateness, the impact of changes in the relative normative power of democracy/autocracy, and effectiveness, how the successes of authoritarian countries increase the chances that others will see them as role models. A number of contributing factors are also identified, which make these processes more or less likely. These include: geography, linkage, international organizations, great power prestige, and reference groups. If we are to understand the future strength of authoritarianism as a global or regional phenomenon, which affects, reinforces, and aggravates domestic conditions, then a new theoretical framework is necessary.

Synthesis, electrochemistry and metal binding properties of monosubstituted ferrocenoyl peptides with thioether-containing sidechains

Ferrocenoyl peptides incorporating thioether functionality respond more strongly to mercury(II) than to other heavy metal ions in solution. Compounds reported previously in this context are all 1,1′-disubstituted, and all include two or more sulfur-containing amino acids. To test whether two thioether groups are required for effective mercury binding by these systems, we have prepared a series of singly-substituted ferrocenoyl peptides from ferrocenecarboxylic acid and l-methionine, S-methyl- l-cysteine or S-trityl- l-cysteine, and tested them as electrochemical probes for mercury(II). Nine ferrocenoyl peptides have been synthesised using a Boc-protecting group strategy and HBTU-mediated peptide coupling. The electrochemical properties of these compounds have been determined using cyclic voltammetry, and all show fully reversible one electron oxidation steps. Forward sweep half wave peaks (E F), reverse sweep half wave peaks (E R), peak separations (ΔE P) and half wave potentials (E 1/2) are reported. Changes in the potential of the iron(II)/iron(III) redox couple of the ferrocene core have been used to quantify heavy metal–peptide interactions, revealing that these monotopic systems also respond more strongly to mercury(II) than to zinc(II), cadmium(II), silver(I) and lead(II). NMR experiments to characterise the peptide–mercury interaction implicate the thioether sulfur as the site of mercury binding and indicate 1:1 stoichiometry. The crystal structure of ferrocenoyl- S-methyl- l-cysteine methyl ester is also reported. The greater responsiveness of these systems to mercury(II) makes them interesting leads for the development of biologically inspired sensors for this toxic heavy metal.

Synthesis and electrochemical studies of disubstituted ferrocene/dipeptide conjugates with sulfur-containing side chains

A series of 1,1′-disubstituted ferrocenoyl peptides incorporating dipeptide sidearms has been synthesized and studied electrochemically. The target peptides include ferrocene as an electrochemical reporter, sulfur-containing amino acids ( l-methionine, S-methyl- l-cysteine, S-trityl- l-cysteine, S-benzhydryl- l-cysteine) as metal binding agents, and amino acids with non-polar side chains ( l-alanine, l-valine, l-phenylalanine) as spacers between reporter and metal binding groups. Ferrocene/dipeptide conjugates were prepared using solution phase peptide synthesis methods employing a BOC-protecting group strategy and HBTU- ( O-(benzotriazol-1-yl)- N, N, N′, N′-tetramethyluronium hexafluorophosphate) mediated peptide coupling. The electrochemical properties of these 1,1′-substituted ferrocenoyl peptides have been characterized using cyclic voltammetry. All exhibit fully reversible one electron oxidation steps; forward sweep half wave peaks ( E F), reverse sweep half wave peaks ( E R), peak separations (Δ E P) and half wave potentials ( E 1/2) are reported. Finally, towards the goal of utilizing ferrocenoyl peptides to detect heavy metals in solution, the response of these ferrocene/dipeptide conjugates to metal cations (zinc(II), mercury(II), cadmium(II), lead(II), silver(I)) has been examined. Monitoring changes in the potential of the Fe(II)/Fe(III) redox couple to follow peptide/metal interactions, we have probed the influence of the spacer unit between the redox reporter and the metal-binding amino acid, and shown that these systems respond to mercury(II) more strongly than to other heavy metal ions.

A review of interplanetary discontinuities and their geomagnetic effects

Interplanetary discontinuities and their geomagnetic effects are reviewed for magnetospheric/space weather researchers. Discontinuities are particularly useful as diagnostics since they are clearly identifiable in interplanetary data and their geomagnetic effects are unambiguous most of the time. Directional discontinuities (DDs) are abrupt changes in the interplanetary magnetic field direction and plasma parameters. DDs may be rotational discontinuities (RDs), tangential discontinuities (TDs) contact discontinuities (CDs) or shocks (fast (FS), intermediate (IS) and slow (SS). Shocks can propagate in the direction of the driver (forward shocks or FSs) or opposite to the driver (reverse shocks of RSs). Discontinuities interacting with other discontinuities may create new discontinuities. Fast forward shocks (FFSs) are shown to energize trapped particles by compressive effects, cause dayside aurora, lead to the creation of new radiation belts and to trigger nightside sector magnetospheric substorms. Fast reverse shocks (FRSs) or reverse waves (RWs) lead to magnetospheric expansions and the cessation of geomagnetic activity. TD-bow shock interactions create hot flow anomalies (HFAs) which then lead to outward expansions of the local magnetopause and dayside auroral enhancements. Some DD crossings may cause sudden southward IMF turnings. These cause magnetic reconnection and energy input into the magnetosphere–ionosphere–magnetotail system. Substorms sometimes occur thereafter. DDs that entail northward IMF turnings may lead to the triggering of substorms.