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A nonlinear chain with six-order polynomial on-site potential is used to analyze the evolution of the total to kinetic energy ratio during development of modulational instability of extended nonlinear vibrational modes. For the on-site potential of hard-type (soft-type) anharmonicity, the instability of $q=\pi$ mode ($q=0$ mode) results in the appearance of long-living discrete breathers (DBs) that gradually radiate their energy and eventually the system approaches thermal equilibrium with spatially uniform and temporally constant temperature. In the hard-type (soft-type) anharmonicity case, the total to kinetic energy ratio is minimal (maximal) in the regime of maximal energy localization by DBs. It is concluded that DBs affect specific heat of the nonlinear chain and for the case of hard-type (soft-type) anharmonicity they reduce (increase) the specific heat., Comment: 32 pages, 11 figures; v2: major revision; matches the published version

The interaction of discrete breathers with the primary lattice defects in transition metals such as vacancy, dislocation, and surface is analyzed on the example of bcc iron employing atomistic simulations. Scattering of discrete breathers on the lattice defects induces localized atomic excitations, with intensity and relaxation time depending on the defect structure and breather kinetic energy. The dissipation of the intrinsic breather energy due to the scattering is computed and analyzed. It is concluded that the breather-to-defect energy transfer may stipulate the activation of the lattice defects causing unexpected athermal effects such as enhanced mass transfer or electroplasticity, already experimentally reported but so far not fully understood at the atomic-scale level., Comment: Submitted to Modelling and Simulation in Materials Science and Engineering 2015

Defects formed under irradiation in the bulk act as additional pinning centers resulting in the well-known effect of radiation-induced hardening. On the other hand, there is a poorly understood but well-established effect of instant and reversible softening of metals subjected to various types of irradiation. This radiation-induced softening (RIS) effect should be taken into account both in the theory of radiation effects and in the engineering approach for technological applications. In the present paper, the RIS is investigated experimentally in polycrystalline technically pure iron (0.048%C) and in commercial ferritic steel. The effect of the electron beam on plastic deformation of bcc Fe is compared with that in fcc Al (99.5%). Electron energy ranged from 0.5 to 0.8 MeV. Reversible drop of the yield stress and radiation-induced reduction of the elongation to fracture are measured as functions of the electron current and specimen thickness. Rate theory of RIS is proposed, which takes into account the radiation-induced excitation of moving discrete breathers (DBs), recently proven to exist in bcc Fe, and their interaction with dislocations enhancing unpinning from structural defects. The behavior of the DBs is studied using classical MD simulations providing input for the modified rate theory, which eventually demonstrates a reasonable agreement with experimental data. The relevance of results to the in-reactor behavior of pressure vessel steels is discussed., Comment: 26 pages, 12 figures. arXiv admin note: text overlap with arXiv:1406.3941, arXiv:1406.7471

Quasicrystals (QCs) are a novel form of matter, which are neither crystalline nor amorphous. Among many surprising properties of QCs is their high catalytic activity. We propose a mechanism explaining this peculiarity based on unusual dynamics of atoms at special sites in QCs, namely, localized anharmonic vibrations (LAVs) and phasons. In the former case, one deals with a large amplitude (~ fractions of an angstrom) time-periodic oscillations of a small group of atoms around their stable positions in the lattice, known also as discrete breathers, which can be excited in regular crystals as well as in QCs. On the other hand, phasons are a specific property of QCs, which are represented by very large amplitude (~angstrom) oscillations of atoms be-tween two quasi-stable positions determined by the geometry of a QC. Large amplitude atomic motion in LAVs and phasons results in time-periodic driving of adjacent potential wells occupied by hydrogen ions (protons or deuterons) in case of hydrogenated QCs. This driving may result in the increase of amplitude and energy of zero-point vibrations (ZPV). Based on that, we demonstrate a drastic increase of the D-D or D-H fusion rate with increasing number of modulation periods evaluated in the framework of Schwinger model, which takes into account suppression of the Coulomb barrier due to lattice vibrations. In this context, we present numerical solution of Schrodinger equation for a particle in a non-stationary double well potential, which is driven time-periodically imitating the action of a LAV or phason. We show that the rate of tunneling of the particle through the potential barrier separating the wells is enhanced drastically by the driving, and it increases strongly with increasing amplitude of the driving. These results support the concept of nuclear catalysis in QCs that can take place at special sites provided by their inherent topology., Comment: 16 pages, 11 figures, Int. Conf. on Cold Fusion (ICCF20). arXiv admin note: text overlap with arXiv:1510.06081

At sufficiently low temperatures, the reaction rates in solids are controlled by quantum rather than by thermal fluctuations. We solve the Schr\"odinger equation for a Gaussian wave packet in a nonstation-ary harmonic oscillator and derive simple analytical expressions for the increase of its mean energy with time induced by the time-periodic modulation. Applying these expressions to the modified Kra-mers theory, we demonstrate a strong increase of the rate of escape out of a potential well under the time-periodic driving, when the driving frequency of the well position equals its eigenfrequency, or when the driving frequency of the well width exceeds its eigenfrequency by a factor of ~2. Such re-gimes can be realized near localized anharmonic vibrations (LAVs), in which the amplitude of atomic oscillations greatly exceeds that of harmonic oscillations (phonons) that determine the system tem-perature. LAVs can be excited either thermally or by external triggering, which can result in strong catalytic effects due to amplification of the Kramers rate, Comment: 14 pages, 5 figures

In many-body nonlinear systems with sufficient anharmonicity, a special kind of lattice vibrations, namely, Localized Anharmonic Vibrations (LAV) can be excited either thermally or by external triggering, in which the amplitude of atomic oscillations greatly exceeds that of harmonic oscillations (phonons) that determine the system temperature. Coherency and persistence of LAV may have drastic effect on chemical and nuclear reaction rates due to time-periodic modulation of reaction sites. One example is a strong acceleration of chemical reaction rates driven by thermally-activated "jumps" over the reaction barrier due to the time-periodic modulation of the barrier height in the LAV vicinity. At sufficiently low temperatures, the reaction rate is controlled by quantum tunneling through the barrier rather than by classical jumping over it. A giant increase of sub-barrier transparency was demonstrated for a parabolic potential well with the time-periodic eigenfrequency, when the modulation frequency exceeds the eigenfrequency by a factor of ~2 (parametric regime). Such regime can be realized for a hydrogen or deuterium atom in metal hydrides/deuterides, such as NiH or PdD, in the vicinity of LAV. We present an analytical solution of the Schrodinger equation for a nonstationary harmonic oscillator, analyze the parametric regime in details and discuss its applications to the tunnel effect and to D-D fusion in PdD lattice. We obtain simple analytical expressions for the increase of amplitude and energy of zero-point oscillations (ZPO) induced by the parametric modulation. Based on that, we demonstrate a drastic increase of the D-D fusion rate with in-creasing number of modulation periods evaluated in the framework of Schwinger model, which takes into account suppression of the Coulomb barrier due to lattice vibrations., Comment: 7 pages, 7 figures

In many-body nonlinear systems with sufficient anharmonicity, a special kind of lattice vibrations, namely, Localized Anharmonic Vibrations (LAVs) can be excited either thermally or by external triggering, in which the amplitude of atomic oscillations greatly exceeds that of harmonic oscillations (phonons) that determine the system temperature. Coherency and persistence of LAVs may have drastic effect on quantum tunneling due to correlation effects discovered by Schrodinger and Robertson in 1930. These effects have been applied to the tunneling problem by a number of authors, who demonstrated a giant increase of sub-barrier transparency during the increase of the correlation coefficient at a special high-frequency periodic action on quantum system. Recently, it has been proposed that discrete breathers (a sub-class of LAVs arising in periodic systems) present the most natural and efficient way to produce correlation effects in regular crystals due to time-periodic modulation of the potential well (or the Coulomb barrier) width and hence to act as breather nano-colliders catalyzing low energy nuclear reactions (LENR) in solids. It has been shown that the tunneling probability for the D-D fusion under electrolysis of heavy water increases enormously with increasing number of oscillations resulting in the fusion rates comparable with those observed experimentally. In the present paper, we discuss possible ways of engineering the nuclear-active environment (NAE) and catalyzing LENR in NAE based on the LAV concept. We propose some practical ways of catalyzing LENR that are based on a special electro-magnetic treatment or electron irradiation, which trigger LAVs in crystals and clusters., Comment: arXiv admin note: substantial text overlap with arXiv:1503.09119

In many crystals with sufficient anharmonicity, a special kind of lattice vibrations, namely, discrete breathers (DBs) can be excited either thermally or by external triggering, in which the amplitude of atomic oscillations greatly exceeds that of harmonic oscillations (phonons). Coherency and persistence of large atomic oscillations in DBs may have drastic effect on quantum tunneling due to correlation effects discovered by Schrodinger and Robertson in 1930. These effects have been applied recently to the tunneling problem by Vysotskii et al, who demonstrated a giant increase of sub-barrier transparency during the increase of correlation coefficient at special high-frequency periodic action on quantum system. In the present paper, it is argued that DBs present the most natural and efficient way to produce correlation effects due to time-periodic modulation of the potential well width and hence to act as breather nano-colliders (BNC) triggering low energy nuclear reactions (LENR) in solids. Tunneling probability for deuterium (D-D) fusion in gap DBs formed in metal deuterides is shown to increase drastically with increasing number of oscillations resulting in the observed LENR rate at extremely low concentrations of DBs. Possible ways of engineering the nuclear active environment based on the present concept are discussed., Comment: 12 pages, 16 figures. arXiv admin note: text overlap with arXiv:1406.3941

A relative contribution to irradiation hardening caused by dislocation loops and solute-rich precipitates is established for RPV steels of WWER-440 and WWER-1000 reactors, based on TEM measurements and mechanical testing at reactor operating temperature of 563 K. The pinning strength factors evaluated for loops and precipitates are shown to be much lower than those obtained for model alloys based on the room temperature testing as well as those evaluated by means of atomistic simulations in the temperature range of 300 to 600 K. This discrepancy is explained in the framework of a model of thermally activated dislocation motion, which takes into account the difference in temperature and strain rate employed in atomistic simulations and in mechanical testing., Comment: 23 pages, 9 figures

Novel mechanisms of defect annealing in solids are discussed, which are based on the large amplitude anharmonic lattice vibrations, a.k.a. intrinsic localized modes or discrete breathers (DBs). A model for amplification of defect annealing rate in Ge by low energy plasma-generated DBs is proposed, in which, based on recent atomistic modelling, it is assumed that DBs can excite atoms around defects rather strongly, giving them energy $\gg k_BT$ for $\sim$100 oscillation periods. This is shown to result in the amplification of the annealing rates proportional to the DB flux, i.e. to the flux of ions (or energetic atoms) impinging at the Ge surface from inductively coupled plasma (ICP), Comment: 18 pages, 11 figures. arXiv admin note: text overlap with arXiv:1406.3941

Rate theory of the radiation-induced precipitation in solids is modified with account of non-equilibrium fluctuations driven by the gas of lattice solitons (a.k.a. quodons) produced by irradiation. According to quantitative estimations, a steady-state density of the quodon gas under sufficiently intense irradiation can be as high as the density of phonon gas. The quodon gas may be a powerful driver of the chemical reaction rates under irradiation, the strength of which exponentially increases with irradiation flux and may be comparable with strength of the phonon gas that exponentially increases with temperature. The modified rate theory is applied to modelling of copper precipitation in FeCu binary alloys under electron irradiation. In contrast to the classical rate theory, which disagrees strongly with experimental data on all precipitation parameters, the modified rate theory describes quite well both the evolution of precipitates and the matrix concentration of copper measured by different methods, Comment: V. Dubinko, R. Shapovalov, Theory of a quodon gas. With application to precipitation kinetics in solids under irradiation. (Springer International Publishing, Switzerland, 2014)

A majority of radiation effects studies are connected with creation of radiation-induced defects in the crystal bulk, which causes the observed degradation of material properties. The main objective of this chapter is to describe the mechanisms of recovery from radiation damage, which operate during irradiation but are usually obscured by the concurrent process of defect creation. Accordingly, the conventional rate theory is modified with account of radiation-induced Schottky defect formation at extended defects, which often acts against the mechanisms based on the Frenkel pair production in the crystal bulk. The theory is applied for the description of technologically and fundamentally important phenomena such as irradiation creep, radiation-induced void annealing and the void ordering., Comment: Nuclear Materials, Editor: Michael P. Hemsworth, 2011 Nova Science Publishers, Inc

A new mechanism of LENR in solids is proposed, which is based on the large amplitude anharmonic lattice vibrations, a.k.a. intrinsic localized modes or discrete breathers (DBs). In particular, so called gap DBs, which can arise in diatomic crystals such as metal hydrides, are argued to be the LENR catalyzers. The large mass difference between H or D and the metal atoms provides a gap in phonon spectrum, in which DBs can be excited in the H/D sub-lattice resulting in extreme dynamic closing of adjacent H/D atoms (~ 0.01 {\AA}) required for the tunneling through nuclear Coulomb barrier. DBs have been shown to arise either via thermal activation at elevated temperatures or via knocking atoms out of equilibrium positions under non-equilibrium gas loading conditions, employed under radiolysis or plasma deposition methods. The DB statistics in both cases is analyzed, and an attempt is made to quantify part of the vibrational problem in terms of electrochemical current or ion flux, connecting them with external excitation of DBs that act as nano-colliders of deuterons triggering LENR. Resulting analytical expressions (under selected set of material parameters) describe quantitatively the observed exponential dependence on temperature and linear dependence on the electric (or ion) current. Possible ways of engineering the nuclear active environment based on the present concept are discussed., Comment: 22 pages, 13 figures

Deep level transient spectroscopy shows that defects created by alpha irradiation of germanium are annealed by low energy plasma ions up to a depth of several thousand lattice units. The plasma ions have energies of 2-8eV and therefore can deliver energies of the order of a few eV to the germanium atoms. The most abundant defect is identified as the E-center, a complex of the dopant antimony and a vacancy with and annealing energy of 1.3eV as determined by our measurements. The inductively coupled plasma has a very low density and a very low flux of ions. This implies that the ion impacts are almost isolated both in time and at the surface of the semiconductor. We conclude that energy of the order of an eV is able to travel a large distance in germanium in a localized way and is delivered to the defects effectively. The most likely candidates are vibrational nonlinear wave packets known as intrinsic localized modes, which exist for a limited range of energies. This property is coherent with the fact that more energetic ions are less efficient at producing the annealing effect., Comment: 20 pages, 10 figures

Reaction rate theory in solids is modified taking into account intrinsic localized modes or discrete breathers (DBs) that can appear in crystals with sufficient anharmonicity resulting in violation of Arrhenius law. Large amplitude oscillations of atoms about their equilibrium positions in the lattice cause local potentials of alternating sign, which are described in terms of time-periodic modulations of the potential barriers for chemical reactions taking place in the vicinity of DBs. The reaction rate averaged over large macroscopic volumes and times including a lot of DBs is increased by a factor that depends on the DB statistics. The breather statistics in thermal equilibrium and in thermal spikes in solids under irradiation with swift particles is considered, and the corresponding reaction rate amplification factors are derived., Comment: 17 pages, 12 figures

New concept of radiation-induced emission of Schottky defects from extended defects is proposed, which acts in the opposite direction compared with Frenkel pair production, and it results in the radiation-induced recovery processes. The vacancy emission from a void surface results in a shrinkage of the void which is analogous to the thermal void shrinkage at high temperatures, but it is expected to operate at low and medium temperatures and high sink densities, when the radiation-induced vacancy emission from sinks becomes comparable with the absorption of Frenkel defects produced in the bulk. As a result, the void growth becomes negative below a threshold temperature (or above a threshold flux), and saturates after a threshold irradiation dose, at a level, which depends on the type of material. These effects have been observed experimentally for a long time but could not be explained by the conventional theory. One of the technologically important consequences of the new concept is a mechanism of irradiation creep, based on the radiation and stress induced preference emission, which is essentially temperature independent in contrast to the well-known SIPA or elastodiffusion mechanisms that can yield a significant irradiation creep only when recombination is negligible. The efficiency of the radiation-induced Schottky defect emission is different for different types of materials, which is shown to be one of the major causes of their different responses to irradiation., Comment: 27 pages, 10 figures