Parametric amplification of laser-driven electron acceleration in underdense plasma

A new mechanism is reported that increases electron energy gain from a laser beam of ultrarelativistic intensity in underdense plasma. The increase occurs when the laser produces an ion channel that confines accelerated electrons. The frequency of electron oscillations across the channel is strongly modulated by the laser beam, which causes parametric amplification of the oscillations and enhances the electron energy gain. This mechanism has a threshold determined by a product of beam intensity and ion density.     

低密等离子体通道中的非共振激光直接加速

在低密等离子体通道中, 横向有质动力可以有效调制电子的横向振荡过程. 一方面, 横向有质动力可以向外推动电子, 增大电子横向振荡振幅, 减小失相率, 使电子获得能量增益; 另一方面, 横向有质动力也可以通过对失相率的非线性调制来降低失相率, 在电子横向振荡振幅很小的情况下导致激光直接加速. 横向有质动力调制的大小由等离子体密度、激光强度和束宽共同决定. 三维模型结果也证实可以通过参数放大实现激光直接加速, 弥补了准二维模型的局限性.     

Exponential DNA replication by laminar convection

It is shown that laminar thermal convection can drive a chain reaction of DNA replication. The convection is triggered by a constant horizontal temperature gradient, moving molecules along stationary paths between hot and cold regions. This implements the temperature cycling for the classical polymerase chain reaction (PCR). The amplification is shown to be exponential and reaches 100,000-fold gains within 25 min. Besides direct applications, the mechanism might have implications for the molecular evolution of life.     

Comparison of Rate Oscillations in Reactions of CO and Methane Oxidation on a Nickel Catalyst

Self-oscillations of the rate of oxidation reactions of CO and CH₄ on nickel foil are compared. It has been shown that, despite significant differences in the stepwise mechanism of the two reactions, the properties of oscillation regimes are very close. In both reactions, oscillation regimes result from oxidation and reduction of nickel and are accompanied by wave processes on the catalyst surface. The similarity in the properties of rate oscillations in the reactions of CO and CH₄ oxidation shows that a change in the selectivity and the formation of carbon on the nickel surface are not key factors in the mechanism of the rate oscillations in CH₄ oxidation. An observed periodic change in the concentrations of reactants and reaction products when the reaction mixture is supplied in a pulse mode proves that, in both cases, the self-oscillations of the reaction rate are due only to the reaction mechanism and are not caused by a change in the catalyst temperature.     

Premixed flame response to equivalence ratio perturbations

This paper studies the heat-release oscillation response of premixed flames to oscillations in reactant stream fuel/air ratio. Prior analyses have studied this problem in the linear regime and have shown that heat release dynamics are controlled by the superposition of three processes: flame speed, heat of reaction, and flame surface area oscillations. Each contribution has somewhat different dynamics, leading to complex frequency and mean fuel/air ratio dependencies. The present work extends these analyses to include stretch and non quasi-steady effects on the linear flame dynamics, as well as analysis of nonlinearities in flame response characteristics. Because the flame response is controlled by a superposition of multiple processes, each with a highly nonlinear dependence upon fuel/air ratio, the results are quite rich and the key nonlinearity mechanism varies with mean fuel/air ratio, frequency, and amplitude of excitation. In the quasi-steady framework, two key mechanisms leading to heat-release saturation have been identified. The first of these is the flame-kinematic mechanism, previously studied in the context of premixed flame response to flow oscillations and recently highlighted by Birbaud et al. (Combustion and Flame 154 (2008), 356–367). This mechanism arises due to fluctuations in flame position associated with the oscillations in flame speed. The second mechanism is due to the intrinsically nonlinear dependence of flame speed and mixture heat of reaction upon fuel/air ratio oscillations. This second mechanism is particularly dominant at perturbation amplitudes that cause the instantaneous stoichiometry to oscillate between lean and rich values, thereby causing non-monotonic variation of local flame speed and heat of reaction with equivalence ratio.     

Local flattening of the Fermi surface and quantum oscillations in the magnetoacoustic response of a metal

In the present work, we theoretically analyze the effect of the Fermi surface local geometry on quantum oscillations in the velocity of an acoustic wave travelling in metal across a strong magnetic field. We show that local flattenings of the Fermi surface could cause significant amplification of quantum oscillations. This occurs due to enhancement of commensurability oscillations modulating the quantum oscillations in the electron density of states on the Fermi surface. The amplification in the quantum oscillations could be revealed at fitting directions of the magnetic field.     

One-particle theory of Ion-Channel Laser

Following the work of Chen and Dawson (1991) on Ion-Channel Laser (ICL), we study the amplification mechanism of the ICL by using the one-particle model proposed by them, and methods of secular perturbation theory. We calculate the conditions for resonance in the wave-particle interaction, and estimate the gain expected. The resonant Electro-Magnetic wave frequency appears to depend strongly on the amplitudes of oscillations of the beam particles. This may significantly reduce the amplification, and limit the use of ICL to relatively low frequencies, up to Infra-Red, where high output power (~GW) is achievable. Analytical results are confirmed by numerical simulations     

Synthetic gene network for entraining and amplifying cellular oscillations

We present a model for a synthetic gene oscillator and consider the coupling of the oscillator to a periodic process that is intrinsic to the cell. We investigate the synchronization properties of the coupled system, and show how the oscillator can be constructed to yield a significant amplification of cellular oscillations. We reduce the driven oscillator equations to a normal form, and analytically determine the amplification as a function of the strength of the cellular oscillations. The ability to couple naturally occurring genetic oscillations to a synthetically designed network could lead to possible strategies for entraining and/or amplifying oscillations in cellular protein levels.     

Are the Peaks in the Cosmic Microwave Background Really Acoustic?

It is shown that the widely accepted interpretation of the peaks in the CMB as acoustic oscillations seems to be not correct. It is further shown that the peaks correspond to the extension of galaxies in a non-standard scenario of galaxy formation forwarded by the author in a previous paper. Hence this result and the generating mechanism of the peaks by amplification of zero-point quantum oscillations in the very early universe as proposed by Bose and Grishchuk might complement one another to an overall picture of galaxy formation.     

Kinetic oscillations in the rate of CO oxidation on Pd(110)

The oxidation of carbon monoxide on a Pd(110) single crystal plane has been studied using work function changes (Δφ) and mass spectrometric measurements. The rate of reaction showed oscillatory behaviour for oxygen pressures greater than 10⁻³ Torr. The existence region for oscillations was determined for pressures ranging from 10⁻³ to 1.0 Torr and depended on the pressures of oxygen and carbon monoxide and the sample temperature (P_co, PO₂ T). Transitions from regular oscillation to chaos via period doubling have been observed in certain areas of the existence region. A comparison between Pd(110) and platinum single crystal surfaces that exhibit oscillations showed that similar but not identical oscillatory behaviour and existence regions exist in each case. Our results indicate that oscillations can occur on other metal single crystal surface that are less likely than platinum to reconstruct under reaction conditions. The extension of oscillations from UHV conditions to the 1.0 Torr pressure region indicates that the mechanism responsible for isothermal oscillations is basically independent of the reactant pressure up to several Torr.     

Isothermal sustained oscillations in a very simple surface reaction

A simple model is used to illustrate that a bimolecular Langmuir—Hinshelwood surface reaction with two empty sites in its reaction step, non-equilibrium in the adsorption steps, and coverage independent parameters may lead to sustained oscillatory reaction rates. The two empty sites in the reaction step play an essential role in the establishment of these oscillations. Numerical simulation is used to demonstrate the periodic behavior predicted by the model. Several similar surface reaction models with coverage independent parameters can also yield oscillations. A mechanism with one vacant site in the adsorption steps, two vacant sites in the reaction step and only two dimensionless non-zero parameters may lead to sustained oscillations.     

Mechanical oscillations at the cellular scale

Active phenomena which involve force generation and motion play a key role in a number of phenomena in living cells such as cell motility, muscle contraction and the active transport of material and organelles. Here we discuss mechanical oscillations generated by active systems in cells. Examples are oscillatory regimes in muscles, the periodic beating of axonemal cilia and flagella and spontaneous oscillations of auditory hair cells which play a role in active amplification of weak sounds in hearing. As a prototype system for oscillation generation by proteins, we discuss a general mechanism by which many coupled active elements such as motor molecules can generate oscillations.     

Coherent wake emission of high-order harmonics from overdense plasmas

We present a new mechanism for high-order harmonic generation by reflection of a laser beam from an overdense plasma, efficient even at moderate laser intensities (down to Igamma2 approximately 4x10(15) W cm-2 microm2). In this mechanism, a transient phase matching between the electromagnetic field and plasma oscillations within a density gradient leads to the emission of harmonics up to the plasma frequency. These plasma oscillations are periodically excited in the wake of attosecond electron bunches which sweep across the density gradient. This process leads to a train of unevenly spaced chirped attosecond pulses and, hence, to broadened and chirped harmonics. This last effect is confirmed experimentally.     

Kinetic description of vacuum particle production in collisions of ultrarelativistic nuclei

The dynamics of partons that emerge as the result of quantum tunneling in a spatially uniform time-dependent field is studied under conditions prevalent in ultrarelativistic heavy-ion collisions. A self-consistent set of coupled equations that consists of the renormalized Maxwell equation and the Vlasov kinetic equation that involves a source and which is derived on a dynamical basis is solved numerically. The time dependence of the distributions of internal fields and currents for bosons and fermions is investigated within this back-reaction mechanism, and their momentum spectra are constructed. Clear evidence that oscillations in the time dependence of parton distributions in phase-space cells are of a stochastic character is obtained, and a significant irregularity in the momentum distribution on large time scales is found. If the influence of the back reaction is disregarded, these effects disappear completely, the oscillations becoming regular. A possible thermalization scenario for such a quasiparticle plasma is considered in the relaxation-time approximation. A locally equilibrium state is described within the two-component thermodynamics of particles and antiparticles. The possibility of introducing temperature under conditions of a strong vacuum polarization is discussed.     

Origin of the spatiotemporal oscillations observed during the NO + H2 reaction on a Rh field emitter

The main purpose of the study described in the present paper was to obtain more detailed information on the mechanism of the spatiotemporal oscillations found recently by field emission microscopy for the NO + H₂ reaction on a Rh tip. These oscillations are related to the kinetics of the reaction over a Rh wire. There are two kinetic regions of the steady-state reaction. The oscillations are attributed to the reversible transition between these kinetic regions. The observed sharp moving wave can be ascribed to the hydrogenation of a nitrogen layer, followed by fast combination and/or decomposition of the adsorbed intermediate NH and restoring of its surface coverage by the NO + H₂ interaction. Surface defects and, probably, grain boundaries are responsible for the initiation of the chemical waves in the course of the sustained oscillations.     

Neutrino oscillations in the field of a linearly polarized electromagnetic wave

Neutrino oscillations ν _iL ? ν _jR in the field of a linearly polarized electromagnetic wave are studied on the basis of a recently proposed effective Hamiltonian that describes the evolution of a spin in an arbitrary electromagnetic field. The condition of resonance amplification of the oscillations is analyzed in detail. A method is developed for qualitatively studying solutions to the equation of neutrino evolution in the resonance region. This method can be used to explore neutrino oscillations in fields of various configurations.     

Radion-induced brane preheating

When the interbrane separation in the compact Randall-Sundrum model is stabilized using the Goldberger-Wise mechanism, a potential is generated for the four-dimensional field, the radion, that encodes this separation. Coherent oscillations of the radion in the early universe will produce an exponential growth in the number of brane particles due to parametric amplification. We describe the conditions necessary for this process, which resembles the preheating phase in inflation, and show the exponential growth in the case of a scalar field confined to a brane.     

Amplifying discharge instabilities in the emission channel of a plasma electron emitter

We consider the amplification of oscillations of the plasma parameters in the emission channel of an electron source with a plasma emitter. The relationship between the modulation level of the emission current and the oscillations of the concentration and potential of the emitting plasma is determined. The amplification of the discharge instabilities is seen to be a function of the ratio of the size of the boundary layer in the channel to the channel radius. The amplification factor is calculated as a function of the emission current and the accelerating voltage. The change in the plasma parameters at the emission boundary for a plasma shift in the channel is taken into account.Tomsk Academy of Control Systems and Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 73–76, Feburary, 1994.     

Amplitude-detuning characteristic of a CO2 laser with biharmonic loss modulation

The nonlinear response of a CO₂ laser to biharmonic loss modulation was theoretically investigated for tuning of the radiation frequency within the limits of the amplification band. It is shown that the value and form of the amplitude-detuning characteristic (and, consequently, the temporal and energy parameters of the laser radiation) can be controlled within sufficiently wide limits by changing the modulation frequency and the phase shift of oscillations. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 43–47, January–February, 1999.