On mossbauer dynamics in Nb3Sn

We compare the anharmonic Lamb Mossbauer factor and the q-Lamb Mossbauer factor by studying the anharmonicity observed in the f-factor data of Nb₃Sn. We also show that this anharmonicity does not arise due to the presence of potential.     

Mössbauer dynamics in YBaCuO systems

Mössbauer dynamics at very high temperature in YBaCuO system reveals anomalous behaviour in the recoil‐free fraction which may be due to the presence of anharmonic potential in the vicinity of Cu(1) sites. In this paper, we use q‐Lamb–Mössbauer factor and anharmonic Lamb–Mössbauer factor to study this anharmonicity.     

Classical and quantum oscillators of quartic anharmonicities: second-order solution

An analytical solution up to the second order in the coupling constant λ is obtained for a classical quartic anharmonic oscillator by using Taylor series method. Our solution yields, as a special instance, the corresponding results obtained by using Laplace transform. With the help of correspondence principle, the classical solution is used to obtain the solution corresponding to a quantum quartic anharmonic oscillator. In the weak coupling regime (i.e., anharmonic constant λ⪡1), the so-called secular terms in classical and quantum solutions are tucked in (summed up) to avoid the nonconvergence. Both the classical and quantum solutions are used to obtain the frequency shifts of the quartic oscillators. It is found that these frequency shifts coincide exactly with those of the earlier results obtained by other methods. From the quantum field theoretic point of view, our solution exhibits the so-called Lamb shift. As an application of the solution for the quantum oscillator, we examine the possibility of getting squeezed states out of the input coherent light interacting with a nonlinear medium of inversion symmetry.     

A combined finite element and modal decomposition method to study the interaction of Lamb modes with micro-defects

This paper presents a combined finite element and modal decomposition method to study the interaction of Lamb waves with damaged area. The finite element mesh is used to describe the region around the defects. On the contrary to other hybrid models already developed, the interaction between Lamb waves and defects is computed in the temporal domain. Then, the modal decomposition method permits to determine the wave reflected and transmitted by the damaged area. Modal analysis allows also identifying the mode conversions induced by the defects. These numerical results agree with previous finite element results concerning the interaction of Lamb modes with a notch. Experiments, carried out with gauged defects on an aluminum plate, are also compared to numerical predictions to validate the simulation. Compared to classical techniques of simulation, this new method allows us to investigate the interaction of Lamb modes generated at high frequency-thickness product with micro-defects as corrosion pitting.     

Numerical predictions and experiments for optimizing hidden corrosion detection in aircraft structures using Lamb modes

To increase the sensitivity of Lamb waves to hidden corrosion in aircraft structures, a preliminary step is to understand the phenomena governing this interaction. A hybrid model combining a finite element approach and a modal decomposition method is used to investigate the interaction of Lamb modes with corrosion pits. The finite element mesh is used to describe the region surrounding the corrosion pits while the modal decomposition method permits to determine the waves reflected and transmitted by the damaged area. Simulations make easier the interpretation of some parts of the measured waveform corresponding to superposition of waves diffracted by the corroded area. Numerical results permit to extract significant information from the transmitted waveform and thus to optimize the signal processing for the detection of corrosion at an early stage. Now, we are able to detect corrosion pits down to 80-μm depth distributed randomly on a square centimeter of an aluminum plate. Moreover, thickness variations present on aircraft structures can be discriminated from a slightly corroded area. Finally, using this experimental setup, aircraft structures have been tested.     

Dynamics of a three level atom interacting with a detuned SU (1,1) quantum system

We study the stability of attractive atomic Bose-Einstein condensate and the macroscopic quantum many-body tunneling (MQT) in the anharmonic trap. We utilize correlated two-body basis function which keeps all possible two-body correlations. The anharmonic parameter (λ) is slowly tuned from harmonic to anharmonic. For each choice of λ the many-body equation is solved adiabatically. The use of the van der Waals interaction gives realistic picture which substantially differs from the mean-field results. For weak anharmonicity, we observe that the attractive condensate gains stability with larger number of bosons compared to that in the pure harmonic trap. The transition from resonances to bound states with weak anharmonicity also differs significantly from the earlier study of [N. Moiseyev, L.D. Carr, B.A. Malomed, Y.B. Band, J. Phys. B 37, L193 (2004)]. We also study the tunneling of the metastable condensate very close to the critical number N _cr of collapse and observe that near collapse the MQT is the dominant decay mechanism compared to the two-body and three-body loss rate. We also observe the power law behavior in MQT near the critical point. The results for pure harmonic trap are in agreement with mean-field results. However, we fail to retrieve the power law behavior in anharmonic trap although MQT is still the dominant decay mechanism.     

Synthesis and properties of Mn1−XFeXS single-crystals at room temperature

Results of the first synthesis of Mn_1−XFe_XS single-crystals and its structural, electrical and magnetic properties at room temperature are presented. The Mn²⁺→Fe²⁺ substitution in Mn_1−XFe_XS solid solutions is accompanied by a compression of the NaCl lattice and a small deformation of the octahedral environments, and the concentration transition from dielectric to semimetal. Single-line Mossbauer spectra indicate the paramagnetic state Mn_1−XFe_XS sulfides at room temperature.     

Role of interparticle coupling on the tunneling magnetoresistance of granular films in interacting superparamagnetic system

A phenomenological model is employed to explain the departure of H/T scaling of tunneling magnetoresistance (TMR) in Co_0.43(ZrO₂)_0.57 granular films (see [B.J. Hattink, M. García del Muro, Z. Konstantinovi?, X. Batlle, A. Labarta, Phys. Rev. B 73 (2006) 045418]). The model bases on the modification of Langevin function by taking into account the field-dependent correlation length, in the framework of Inoue–Maekawa model. Both TMR–H and TMR–H/T curves can be reproduced very well by this model, indicating that the interparticle coupling plays an important role on TMR in the interacting superparamagnetic systems. The influence of anisotropy and spin polarization of the magnetic particles on TMR–H/T curves is also discussed.     

Fabrication and Mossbauer Study of FeCo Alloy Nanotube Array

Arrays of FeCo nanotubes are fabricated in the pores of porous anodic aluminium oxide templates. Transmission electron microscopic result shows that the nanotubes are regular and uniform. Magnetic hysteresis loops measured at room temperature are different from those of nanowires with the same composition, which are caused by the unique shape of nanotubes. The M6ssbauer spectra show that the hyperfine field is smaller than that of the bulk＇s and increases with decrease of measuring temperature. However, the areas of the doublets appeared in M6ssbauer spectra decrease with decrease of measuring temperature.     

Critical evaluation of anharmonic corrections to the equilibrium isotope effect for methyl cation transfer from vacuum to dielectric continuum

Harmonic and anharmonic vibrational frequencies are computed for isotopologues of methyl cation in vacuum and in a polarised continuum model (PCM) dielectric continuum (? = 80) within Gaussian09. Comparison of results in vacuum for two methods (B3LYP and second-order Møller–Plesset perturbation theory) and three basis sets (6-31+G(d), cc-aug-PVDZ, cc-aug-PVQZ) with published anharmonic frequencies obtained from an accurate vibrational configuration interaction (VCI) method shows the smallest root mean square error in the frequencies from B3LYP/6-31+G(d) with anharmonic corrections. Using this method to calculate isotopic partition function ratios (IPFRs) for all six pairs of CH₃⁺, CH₂D⁺, CHD₂⁺ and CD₃⁺ gives better results for anharmonic frequencies than for unscaled harmonic frequencies, but scaled harmonic frequencies give even better results for less cost. The scaling factor is simply the ratio of the sum of the anharmonic VCI frequencies to the sum of the harmonic B3LYP/6-31+G(d) frequencies, which corresponds to the dominance of zero-point energy changes in determining the IPFRs. Both the scaled and unscaled harmonic frequencies provide reasonable estimates for the equilibrium isotope effects (EIEs) upon transfer of methyl cation from vacuum to PCM ‘water’, but the anharmonic PCM calculations give erratic results. The use of scaled B3LYP/6-31+G(d) harmonic frequencies is recommended for the estimations of EIEs rather than expensive anharmonic corrections.     

Mossbauer f factor for 35.5 keV-Te125 transition in zinc-blende type crystals

The phonon frequency distribution for Zn, Cd and Hg tellurides calculated on the basis of the rigid ion model are used to calculate the Mossbauer f factor for these compounds. The available experimental result for ZnTe is compared with the theoretically calculated value.     

The effects of the N atom collective Lamb shift on single photon superradiance

The problem of single photon collective spontaneous emission, a.k.a. superradiance, from N atoms prepared by a single photon pulse of wave vector k₀ has been the subject of recent interest. It has been shown that a single photon absorbed uniformly by the N atoms will be followed by spontaneous emission in the same direction [M. Scully, E. Fry, C.H.R. Ooi, K. Wodkiewicz, Phys. Rev. Lett. 96 (2006) 010501; M. Scully, Laser Phys. 17 (2007) 635]; and in extensions of this work we have found a new kind of cavity QED in which the atomic cloud acts as a cavity containing the photon [A.A. Svidzinsky, J.T. Chang, M.O. Scully, Phys. Rev. Lett. 100 (2008) 160504]. In most of our studies, we have neglected virtual photon (“Lamb shift”) contributions. However, in a recent interesting paper, Friedberg and Mannassah [R. Friedberg, J.T. Manassah, Phys. Lett. A 372 (2008) 2514] study the effect of virtual photons investigating ways in which such effects can modify the time dependence and angular distributions of collective single photon emission. In the present Letter, we show that such virtual transitions play no essential role in our problem. The conclusions of [M. Scully, E. Fry, C.H.R. Ooi, K. Wodkiewicz, Phys. Rev. Lett. 96 (2006) 010501; M. Scully, Laser Phys. 17 (2007) 635; A.A. Svidzinsky, J.T. Chang, M.O. Scully, Phys. Rev. Lett. 100 (2008) 160504] stand as published. However, the N atom Lamb shift is an interesting problem in its own right and we here extend previous work both analytically and numerically.     

Vibrational anharmonicity and the inversion potential function of NH3

The nonrigid bender formulation of the vibration-inversion-rotation Hamiltonian for an XY₃ pyramidal molecule (V. ?pirko, J. M. R. Stone, and D. Papou?ek, J. Mol. Spectrosc.60, 159 (1976)) is improved by allowing for anharmonicity in all the vibrations. To model the anharmonic potential function of an XY₃ molecule with a low barrier to inversion a Plíva-type empirical potential (J. Plíva, Collect. Czech. Chem. Commun.23, 777 (1958)) is used. A fitting procedure that involves the numerical integration of the effective inversion Schrödinger equation (the nonrigid bender equation) and diagonalization of some resonance matrices is used to determine the equilibrium structure and the anharmonic potential function of the ammonia molecule.     

Application of the algebraic approach to molecular thermodynamics and quantum deformations

An algebraic model based on Lie-algebraic techniques is applied to vibrational molecular thermodynamics. The model uses the isomorphism between the SU(2) algebra and the one-dimensional Morse oscillator. A vibrational high-temperature partition function and the related thermodynamic properties are derived in terms of the parameters of the model. The anharmonic vibrations are described as anharmonic q-bosons using a first-order expansion of a quantum deformation. It is shown, that this quantum deformation is related to the shape of the Morse potential.     

The collective Lamb shift in nuclear γ-ray superradiance

The electromagnetic transitions of M?ssbauer nuclei provide almost ideal two-level systems to transfer quantum optical concepts into the regime of hard x-rays. If many identical atoms collectively interact with a resonant radiation field, one observes (quantum) optical properties that are strongly different from those of a single atom. The most prominent effect is the broadening of the resonance line known as collective enhancement, resulting from multiple scattering of real photons within the atomic ensemble. On the other hand, the exchange of virtual photons within the ensemble leads to a tiny energy shift of the resonance line, the collective Lamb shift, that remained experimentally elusive for a long time after its prediction. Here we illustrate how highly brilliant synchrotron radiation allows one to prepare superradiant states of excited M?ssbauer nuclei, an important condition for observation of the collective Lamb shift.     

Quartic oscillator potential in the γ-rigid regime of the collective geometrical model

A prolate γ-rigid version of the Bohr-Mottelson Hamiltonian with a quartic anharmonic oscillator potential in β collective shape variable is used to describe the spectra for a variety of vibrational-like nuclei. Speculating the exact separation between the two Euler angles and the β variable, one arrives at a differential Schrödinger equation with a quartic anharmonic oscillator potential and a centrifugal-like barrier. The corresponding eigenvalue is approximated by an analytical formula depending only on a single parameter up to an overall scaling factor. The applicability of the model is discussed in connection to the existence interval of the free parameter, which is limited by the accuracy of the approximation, and by comparison with the predictions of the related X(3) and X(3)-β ² models. The model is applied to qualitatively describe the spectra for nine nuclei which exhibit near-vibrational features.     

Symmetric and Anti-Symmetric Lamb Waves in a Two-Dimensional Phononic Crystal Plate

It is weft known that Lamb waves in a plate with a mirror plane can be separated into two uncoupled sets： symmetric and anti-symmetric modes. Based on this property, we present a revised plane wave expansion method （PWE） to calculate the band structure of a phononie crystal （PC） plate with a mirror plane. The developed PWE method can be used to calculate the band structure of symmetric and anti-symmetric modes separately, by which the depending relationship between the partial acoustic band gap （PABG）, which belongs to the symmetric and anti-symmetric modes alternatively, and the position of the scatterers can be determined. As an example of its application, the band structure of the Lamb modes in a two-dimensional PC plate with two layers of void circular inclusions is investigated. The results show that the band structure for the symmetric and anti-symmetric modes can be changed by the position of the scatterers drastically, and larger PABGs will be opened when the scatterers are inserted into the area of the plate, where the elastic potential energy is concentrated.     

Periodic orbits of the hydrogen molecular ion

Based on our previous work [Yiwu Duan, J.M. Yuan, C.G. Bao, Phys. Rev. A 52, 3497 (1995)], we study deeply the periodic orbits of the hydrogen molecular ion within the Born-Oppenheimer approximation (BOA). The Thiele-Burrau's transformation is introduced to regularize the singularities associated with the Coulomb potential terms and to transform the problem into a direct product of a pendulum and an anharmonic oscillator. This facilitates the analysis of the bifurcation properties of the periodic orbits. Some more details are also given about the calculation of the semiclassical density-of-state distribution using the Berry-Tabor formula. Received: 5 February 1999     

Simulation of pedestrian counter-flow with right-moving preference

People prefer to walk on the right-hand side of the road for physical and social reasons. In this paper, pedestrian counter-flow in a channel is simulated with the Cellular Automata (CA) Model, with focus on right-preference. Two types of pedestrians are taken into account, walking leftward and rightward along the channel. Circular and open boundaries are adopted respectively. The right-preference intensity, k, is introduced, defined as the ratio of the right-moving probability to left-moving probability. In simulations, the dynamical transition between fluid and jammed phase is presented. With a fixed k, the critical density is independent of the channel size. According to research results on physiology and sociology [O. Guentuerkuen, Nature 421 (2003) 711; M. Reiss, G. Reiss, Percept. Mot. Skill 85 (1997) 569; M.C. Corballis, Psychol. Rev. 104 (1997) 714], k=1,2,8 have been discussed, and k=8 is satisfied in this work. Furthermore, simulation results are compared with the ideal calculation, and other researchers’ experiments [M. Isobe, T. Adachi, T. Nagatani, Physica A 336 (2004) 638]. It is found that right-preference is effective when the density is below critical. The model is shown to be useful to simulate and analyze this situation numerically.     

Mössbauer emission spectroscopy of doped 57Co1−xO—I. Acceptor impurities: 57Co1−xO:Li

Mossbauer emission studies on Li-doped ⁵⁷Co_1?xO have been carried out It is shown that the number of Co vacancies as well as the number of L1⁺ impurities entering the lattice determine the Fe³⁺ fraction in the emission spectra A recombination model based on the acceptor character of the defects existing in the lattice is proposed This model reproduces well all the Mossbauer data.