Neutron Resonances in Few-Body Systems and the EOS of Neutron Star Crust

The effective interactions formed by neutron rescattering between the nuclei fixed in nodes of the crystalline lattice of neutron star crusts have been considered. In the case of two-body resonances in neutron–nucleus subsystems new neutron resonances of few-body nature come into existence in the overdense crystal under certain conditions. The energies and widths of new resonances get additional dependence on the lattice parameters. The effective interactions result in nonlinear correction to the equation of state determined by the balance of gravitational, Coulomb and nuclear resonance forces. This leads to resonant oscillations of density in the accordant layers of crusts that are accompanied by oscillations of gamma radiation. The phenomena may clarify some processes connected with few-body neutron resonances in neutron star crusts, that have influence on the microstructure of pulsar impulses.     

Chaotic oscillations in a coupled system of bistable oscillators

The influence of the asymmetry of the nonlinear element characteristic on the chaotic oscillations of Chua’s bistable oscillator is studied. It is shown that such asymmetry causes asymmetry of a chaotic attractor that maps the switching of motions between two basins of attraction up to the concentration of oscillations in one basin. Oscillation control in a bistable chaotic self-oscillating system (two coupled Chua’s oscillators) is considered. It is demonstrated that oscillations excited in two basins of attraction may pass to one of them and that oscillations may build up in two basins when they are autonomously excited in different basins. It is also found that chaotic oscillations in a coupled system may be excited at parameter values for which the autonomous chaotic oscillations of partial oscillators are absent. The influence of external noiselike oscillations is investigated.     

Quantum electrodynamics resonances in a pulsed laser field

This review contains theoretical study of resonant quantum electrodynamics processes in a pulsed laser field. The approximation is examined when the pulse width is considerably greater than the characteristic time of wave oscillations. The lepton??s interaction with the Coulomb potential of a nucleus and each other is considered in the Born approximation. It is demonstrated that the resonant differential cross section of a process in a pulsed light fields may considerably exceed the corresponding cross section in an absence of a laser field. Results obtained may be experimentally verified by the scientific facilities at the SLAC National Accelerator Laboratory and FAIR (Facility for Antiproton and Ion Research, Darmstadt, Germany) project.     

Estimates of radioactive decay by the emission of nuclei heavier than α-particles

We estimate the lifetimes for radioactive decay of a nucleus by the emission of α-particles or heavier fragments like ¹⁴C, by treating these processes as extreme cases of spontaneous fission. The lifetime is accordingly written as a frequency factor of the order of collective nuclear oscillations (10^?21?10^?22 sec) times a Gamow penetrability factor for the appropriate deformation-energy barrier. For the very asymmetric decays, an approximation to the barrier is obtained by combining the Coulomb repulsion between the fragments with the nuclear proximity potential (up to contact) and interpolating smoothly between the contact configuration and the configuration of the parent nucleus. We give a closed formula for the penetrability factor and find that, to within about one power of ten, we can account for the recently observed branching ratios between α-particle and ¹⁴C emissions from ^222,223,224Ra. We apply our method to calculate branching ratios for other exotic decays (involving isotopes of O and Ne among others) and estimate that there may be a number of such decays that will be accessible to observation.     

Hadron–nucleus scattering in the local reggeon model with pomeron loops for realistic nuclei

The contribution of the simplest loops for hadron–nucleus scattering cross-sections is studied in Local Reggeon Field Theory with a supercritical pomeron. It is shown that inside the nucleus the supercritical pomeron transforms into a subcritical one, so that perturbative treatment becomes possible. The pomeron intercept becomes complex, which leads to oscillations in the cross-sections.     

Theorem relating spatial and temporal harmonics for nuclear interlevel transfer driven by collective electronic oscillation

A crucial step in the development of gamma-ray lasers will be the discovery of an efficient mechanism for nuclear interlevel transfer. One promising mechanism uses the near-field interaction between the nucleus and laser-driven collective electronic oscillations. I prove an important theorem relating spatial and temporal harmonics: 2²ⁿ-poles are driven only at even multiples of the laser frequency, while 2²ⁿ⁺¹-poles are driven only at odd multiples of the laser frequency. I comment on the theorem's relevance to a proposed interlevel-transfer experiment.     

Slow Oscillations of the Perpendicular Magnetization of the Pt/Co/Ir/Co/Pt Spin Valve

The time dependences of the transfer of the magnetic moment between stable magnetic states of heterostructures with two Pt/Co/Ir/Co/Pt ferromagnetic layers with the perpendicular magnetization have been studied. Spontaneous oscillations of the macroscopic magnetization with a period of several hours are observed after switching the magnetic field to a new value. The phase portrait of the magnetic relaxation corresponds to damped oscillations. The macrospin oscillation may be due to the high nucleation rate of the reverse magnetization phase induced by the exchange and magnetic dipole interaction between the phase nucleation centers, which arise in different layers. The changes in the Zeeman energy of the system under magnetic oscillations are considered.     

Transverse oscillations of a long-pulse electron beam on alaser-formed channel

An intense relativistic electron beam may be transported in low-pressure gas using an ion channel which focuses and guides the beam. The beam can be unstable to the growth of transverse oscillations caused by the electric force between the beam and channel-the ion hose instability. Beam propagation on channels created by photoionization of gas with an excimer laser is discussed. Ion hose oscillations have been recorded which have a betatron wavelength of approximately 1.5 m. The growth rate of the ion hose instability in the linear regime was measured as 1.67±0.45. At this level of growth, the amplitude of beam oscillations equals the channel radius after a period of one-third of an ion oscillation time     

Coherent interaction of ion and electron beams in systems with electron cooling

A hydrodynamic approximation is used to study the behavior of dipole modes of the transverse oscillations of an ion beam in a storage ring with an electron cooling section. It is shown that in addition to the finite interaction time of the beams, instability may be caused by a specific interaction effect between the ion and electron beams in the magnetic field which leads to redistribution of energy between the various modes of the ion beam oscillations. In this case, the condition that the determinant of the transfer matrix for the cooling section does not exceed unity no longer guarantees the stability of the transverse coherent oscillations of the ion beam and all the eigenvalues of the complete matrix of the ion motion including the storage ring must be analyzed. Calculations of the stability of ion beam dipole oscillations are presented for the parameters of CELSIUS.     

Unexpected behavior in a two-path electron interferometer

We report the observation of an unpredictable behavior of a simple, two-path, electron interferometer. Utilizing an electronic analog of the well-known optical Mach-Zehnder interferometer, with current carrying edge channels in the quantum Hall effect regime, we measured high contrast Aharonov-Bohm (AB) oscillations. Surprisingly, the amplitude of the oscillations varied with energy in a lobe fashion, namely, with distinct maxima and zeros (namely, no AB oscillations) in between. Moreover, the phase of the AB oscillations was constant throughout each lobe period but slipped abruptly by pi at each zero. The periodicity of the lobes defines a new energy scale, which may be a general characteristic of quantum coherence of interfering electrons.     

Deformation of a fresh-water ice cover due to the capillary oscillations of underlying water

Full-scale measurements indicate that the frequencies of ice bending oscillations fall mostly into the range of 1–5 Hz. However, rarely bending oscillations may take place at about 13 Hz. Such oscillations are viewed as an intermediate between the ice bending oscillations and capillary wave oscillations on water. It is found theoretically that frequency f of the ice bending oscillations and interfacial tension coefficient α at the water-ice interface obey the relationship f ～ α^?1/4. The proportionality factor omitted here depends on the physical properties of water and ice. Putting f = 13 Hz, we, substituting the respective known quantities into this relationship, find that interfacial tension coefficient α equals α = 3.3 N/m. Thus, the interfacial tension coefficient at the water-ice interface can be estimated in this way.     

Circadian rhythms and molecular noise

Circadian rhythms, characterized by a period of about 24 h, are the most widespread biological rhythms generated autonomously at the molecular level. The core molecular mechanism responsible for circadian oscillations relies on the negative regulation exerted by a protein on the expression of its own gene. Deterministic models account for the occurrence of autonomous circadian oscillations, for their entrainment by light-dark cycles, and for their phase shifting by light pulses. Stochastic versions of these models take into consideration the molecular fluctuations that arise when the number of molecules involved in the regulatory mechanism is low. Numerical simulations of the stochastic models show that robust circadian oscillations can already occur with a limited number of mRNA and protein molecules, in the range of a few tens and hundreds, respectively. Various factors affect the robustness of circadian oscillations with respect to molecular noise. Besides an increase in the number of molecules, entrainment by light-dark cycles, and cooperativity in repression enhance robustness, whereas the proximity of a bifurcation point leads to less robust oscillations. Another parameter that appears to be crucial for the coherence of circadian rhythms is the binding/unbinding rate of the inhibitory protein to the promoter of the clock gene. Intercellular coupling further increases the robustness of circadian oscillations.     

On the interaction between a charged drop and an external acoustic field

An interaction between capillary oscillations of a charged drop and an external acoustic field is investigated under conditions in which nonlinear components of the acoustic pressure on the drop surface may be neglected. It is shown that equations describing the temporal evolution of modes of the capillary waves in this case may be either the Mathieu-Hill equations or ordinary inhomogeneous equations of the second order describing forced oscillations. In both cases, the drop instability (of a parametric or resonance type) may result in its disintegration due to deformation caused by the acoustic field at its own drop charge, subcritical in the sense of the Rayleigh criterion.     

Coupled catalytic oscillators: Beyond the mass-action law

We present Monte Carlo simulations of the reaction kinetics corresponding to two coupled catalytic oscillators in the case when oscillations result from the interplay between the reaction steps and adsorbate-induced surface restructuring. The model used is aimed to mimic oscillations on a single nm catalyst particle with two kinds of facets or on two catalyst particles on a support. Specifically, we treat the NO reduction by H(2) on a composite catalyst containing two catalytically active Pt(100) parts connected by an inactive link. The catalyst is represented by a rectangular fragment of a square lattice. The left- and right-hand parts of the lattice mimic Pt(100). With an appropriate choice of the model parameters, these sublattices play a role of catalytic oscillators. The central catalytically inactive sublattice is considered to be able only to adsorb NO reversibly and can be viewed as a Pt(111) facet or a support. The interplay of the reactions running on the catalytically active areas occurs via NO diffusion over the boundaries between the sublattices. Using this model, we show that the coupling of the catalytically active sublattices may synchronize nearly harmonic oscillations observed on these sublattices and also may result in the appearance of aperiodic partly synchronized oscillations. The spatio-temporal patterns corresponding to these regimes are nontrivial. In particular, the model predicts that, due to phase separation, the reaction may be accompanied by the formation of narrow NO-covered zones on the left and right sublattices near the boundaries between these sublattices and the central sublattice. Such patterns cannot be obtained by using the conventional mean-field reaction-diffusion equations based on the mass-action law. The experimental opportunities to observe the predicted phenomena are briefly discussed. (c) 2001 American Institute of Physics.     

Resonant electron-positron pair photoproduction on a nucleus in a pulsed light field

The resonant photoproduction of an electron-positron pair on a nucleus in the field of a pulsed light wave is studied theoretically. The approximation where the electromagnetic pulse duration is much longer than the characteristic time of wave oscillations is considered. The interaction of the electron and positron with the Coulomb potential of the nucleus is considered in the Born approximation. An analytical expression for the resonant differential cross section is derived for the range of moderately strong external fields. This cross section contains a resonant peak whose height and width are determined by the external pulsed wave characteristics. The resonant cross section for pair photoproduction on a nucleus in a pulsed laser field can exceed the corresponding cross section for pair photoproduction on a nucleus in the absence of an external field by an order of magnitude.     

Mixing of neutral atoms and lepton number oscillations

We discuss oscillations of two neutral atoms which proceed with the violation of lepton number. One of the neutral atoms is stable, the other one represents a quasistationary state subjected to electromagnetic deexcitation. The system of neutral atoms exhibits oscillations similar to those of the system of neutral kaons and neutron-antineutron oscillations in the nuclear medium. The underlying mechanism is a transition of two protons and two bound electrons to two neutrons p + p + e _b ⁻ + e _b ⁻ ↔ n + n. A signature of the oscillations might be an electromagnetic deexcitation of the involved unstable nucleus and atomic shell with the electron holes. A resonant enhancement of the neutrinoless double electron capture takes place when the atomic masses tend to be degenerate. Qualitative estimates show that in searches for lepton number violation oscillations of atoms might be a possible alternative to the conventional mechanism of the neutrinoless double β decay process with emission of two electrons. The article is published in the original.     

Limiting nonideal metastable supercooled plasma

Direct modeling of the dynamics of a system of many Coulomb particles is applied to analyze the formation stage of a metastable plasma state from an initial, highly nonideal state, and also to consider some properties of this metastable supercooled state. It is shown that relaxation of the average particle kinetic energy may be characterized by a universal dimensionless function and in particular, there is a limiting degree of plasma nonideality which may be achieved in the metastable state, in the absence of any external influence. The calculated pair correlation functions agree with the results of the Debye model, even outside its limits of validity. The time dependence of the total dipole moment of the particle system is investigated. It is shown that oscillations of the total dipole moment are observed. These collective oscillations take place at a frequency slightly below the Langmuir frequency and the oscillations of free and bound electrons are in antiphase. The hypothesis is put forward that recombination relaxation is frozen as a result of interaction between quasibound electrons and Langmuir oscillations of free electrons. Zh. Tekh. Fiz. 67, 42–52 (August 1997)