Dynamics of a single ion in a perturbed Penning trap. Sextupolar perturbation

In the frame work of classical mechanics, we study the nonlinear dynamics of a single ion trapped in a Penning trap perturbed by an electrostatic sextupolar perturbation. The perturbation is caused by a deformation in the configuration of the electrodes. By using a Hamiltonian formulation, we obtain that the system is governed by three parameters: the z-component of the canonical angular momentum P _φ - which is a constant of the motion because the perturbation we assume is axial-symmetric -, the parameter δ that determines the ratio between the axial and the cyclotron frequencies, and the parameter a which indicates how far from the ideal design the electrodes are. We study the case P _φ = 0. By means of surfaces of section, we show that the phase space structure is made of three fundamental families of orbits: arch, loop and box orbits. The coexistence of these kinds of orbits depends on the parameter δ. The escape is also explained on the basis of the shape of the potential energy surface as well as of the phase space structure. Received 6 September 2001 / Received in final form 19 March 2002 Published online 28 June 2002     

φ-meson photoproduction from nuclei

We study coherent and incoherent φ-meson photoproduction from nuclei. The available data are analyzed in terms of single- and coupled-channel photoproduction. It is found that the data on coherent photoproduction can be well reproduced within a single-channel optical model and show only little room for ω-φ mixing. These data indicate a normal distortion of the φ-meson in nuclei, which is compatible with the results obtained through the vector meson dominance model. The data on incoherent φ-meson photoproduction show an anomalous A-dependence resulting in a very strong φ-meson distortion. These data can be explained by a coupled-channel effect through the dominant contribution from the ω↦φ or the π↦φ transition or, more speculative, through the excitation of a cryptoexotic B _φ-baryon.     

Duality between different mechanisms of QCD factorization in <Emphasis Type="Italic">γ</Emphasis><Superscript>*</Superscript><Emphasis Type="Italic">γ</Emphasis> collisions

We study the phenomenon of duality in hard exclusive reactions to which QCD factorization applies. Considering “two-photon”-like processes in the scalar φ _E ³ model and also two-hadron (pion) production from the collisions of a real (transversely polarized) and a highly-virtual, longitudinally polarized photon in QCD, we identify two regimes of factorization, each of them associated with a distinct nonperturbative mechanism. One mechanism involves twist-3 Generalized Distribution Amplitudes, whereas the other one employs leading-twist Transition Distribution Amplitudes. In the case of the scalar φ _E ³ model, we find duality in that kinematical region where the two mechanisms overlap. In the QCD case, the appearance of duality is sensitive to the particular nonperturbative model applied and can, therefore, be used as an additional adjudicator.     

Pinning-depinning of the contact line on nanorough surfaces

We study the pinning-depinning phenomenon of a contact line on a solid surface decorated by a random array of nanometric structures. For this purpose, we have investigated the contact angle hysteresis behaviour of six different wetting and non-wetting fluids with surface tensions varying from 25 to 72mN m^-1. For low values of the areal density of defects φ_d, the hysteresis H increases linearly with φ_d indicating that “individual” defects pin the contact line. Then, from a given value of φ_d, the hysteresis H becomes to decrease with increasing φ_d, indicating a new kind of collective depinning. These two regimes were observed for all fluids used. In both cases, our experimental results are compared with the theoretical predictions for contact angle hysteresis induced by single or multiple topographical defects. We ascribe the decrease of H to the formation of cavities along the wetting front.     

3d Monte Carlo simulation of site-bond continuum percolation of spheres

We present off-lattice Monte Carlo simulations of site-bond percolation of semi-penetrable spheres or, equivalently, of hard spheres with a finite bond range. We will show that the crucial parameter is the effective volume fraction ( φ_e), i.e. the volume that is occupied or within the bond range of at least one particle. For the equivalent system of semi-penetrable spheres 1 - φ_e is the porosity. The bond percolation threshold (p _b) can be described in terms of φ_e by a simple analytical expression: log(φ_e)/log(φ_ec) + log(p _b)/log(p _bc) = 1, with p _bc = 0.12 independent of the bond range and φ_ec a constant that decreases with increasing bond range. Received: 10 March 2003 / Accepted: 23 April 2003 / Published online: 21 May 2003 RID="a" ID="a"e-mail: jean-christophe.gimel@univ-lemans.fr     

Strange-quark collectivity of the φ-meson at RHIC

Based on A Multi-Phase Transport (AMPT) model, the elliptic flow v₂ of φ-mesons which is reconstructed from K ⁺ K ^- at the Relativistic Heavy-Ion Collider (RHIC) energy has been studied. The results show that the reconstructed v₂ of the φ-meson can keep the earlier information before φ decays and it seems to obey the number of constituent-quark scaling as other mesons and baryons. This result indicates that the φ v₂ mostly reflects the parton level collectivity developed during the early stage of the collisions and the strange and light up/down quarks have similar collectivity properties before the hadronization.     

The underdamped Josephson junction subjected to colored noises

The properties of the underdamped Josephson junction subjected to colored noises were investigated with large and small phase difference (φ). For the case of the large φ, we found numerically that: (i) the probability distribution function of φ exhibits monostability → bistability → monostability transitions as the autocorrelation rate (λ) of a colored noise increases; (ii) in the bistability region the multiplicative noise drives the phase difference to turn over periodically; (iii) the slope K of the linear response of the junction potential difference (〈V 〉) can be somewhat reduced by means of tuning an optimal λ; (iv) the amplitude of φ in response to external sinusoidal signals changes with λ. For the case of small φ, after deriving the analytical expressions of the potential difference amplitude (〈V 〉_max) and the K in the presence of a dichotomous noise, we found nonmonotonic behavior of 〈V 〉_max and the slope K as a function of λ.     

Monte-Carlo simulation of transient gel formation and break-up during reversible aggregation

Monte-Carlo simulations of reversible aggregation on a cubic lattice were done by introducing a finite probability (P) of nearest neighbours to form a bond. Depending on the volume fraction of occupied sites (φ) and P we observed different phenomena by monitoring as a function of time the space filling and the distribution of the aggregates and the gel fraction. At smaller values of P the system develops into an equilibrium distribution of aggregates of which the average size increases with increasing φ until above a critical value the system percolates. At larger values of P the system phase separates into two phases with different densities. Above a critical value of φ the system percolates during a finite time. The life time of the gel and the maximum gel fraction were studied as a function of P. Received 1st March 2001 and Received in final form 24 April 2001     

Model for laser-induced thermal degradation and ablation of polymers

Ablation of organic polymers is described on the basis of photothermal bond breaking within the bulk material. Here, we assume a first-order chemical reaction, which can be described by an Arrhenius law. Ablation starts when the density of broken bonds at the surface reaches a certain critical value. In order to understand the ablation behavior near the threshold fluence, φ_th, non-stationary regimes must be considered. The present treatment reveals several qualitative differences with respect to models that treat ablation as a surface process: (i) Ablation starts sharply with a front velocity that has its maximum value just after the onset. (ii) The transition to the quasi-stationary ablation regime is faster. (iii) Near threshold, the ablated depth h has a square-root dependence on laser fluence, i.e., h∝(φ-φ_th)^1/2. The ablation velocity is very high even near φ_th. (iv) With φ≈φ_th ablation starts well after the laser pulse. (v) The depletion of species is responsible for the Arrhenius tail observed with fluences φ≤φ_th. (vi) Residual modification of material has maximum near the threshold. (vii) Stationary regimes of ablation demonstrate change of effective activation energy with laser intensity. The model calculations are applied to Polyimide (Kapton^TM H). Here, differences in single-pulse ablated depth determined from mass loss and profilometry should be about 10 nm. Received: 16 February 1999 / Accepted: 18 February 1999 / Published online: 28 April 1999     

A micro Z-pinch as a spark of an axial detonation

Summary In order that a Z-pinch in a DT plasma could spark off an axial nuclear detonation wave severe conditions on space and time concentration of electromagnetic energy must be satisfied. Such energy compression could be achieved by a magnetic-field compressor (MFC) in which a fast liner compresses an azimuthal field (B _φ) of a micro Z-pinch. The driver of the MFC could be either a heavy-ion beam or an explosive magnetic-field generator (EMG) destroyed at each shot. In conclusion, some of the major problems associated with this approach to ICF are outlined.     

The Variational Principle for a Class of Asymptotically Abelian C*-Algebras

Let (A,α) be a C^*-dynamical system. We introduce the notion of pressure P _α(H) of the automorphism α at a self-adjoint operator H∈A. Then we consider the class of AF-systems satisfying the following condition: there exists a dense α-invariant *-subalgebra ? of A such that for all pairs a,b∈? the C^*-algebra they generate is finite dimensional, and there is p=p(a,b)∈ℕ such that [α ^j (a),b]= 0 for |j|≥p. For systems in this class we prove the variational principle, i.e. show that P _α(H) is the supremum of the quantities h _φ(α) −φ(H), where h _φ(α) is the Connes–Narnhofer–Thirring dynamical entropy of α with respect to the α-invariant state φ. If H∈A, and P _α(H) is finite, we show that any state on which the supremum is attained is a KMS-state with respect to a one-parameter automorphism group naturally associated with H. In particular, Voiculescu's topological entropy is equal to the supremum of h _φ(α), and any state of finite maximal entropy is a trace. Received: 19 April 2000 / Accepted: 14 June 2000     

Unraveling the f<Subscript>0</Subscript> nature by connecting KLOE and BABAR data through analyticity

We define a general procedure, based on analyticity and dispersion relations, to estimate low-energy amplitudes for processes like: φ→e ⁺ e ^- M and φ→γM, starting from cross-section data on e ⁺ e ^-→φM, where M is a generic light scalar or pseudoscalar meson. In particular this procedure is constructed to obtain predictions on the radiative decay rate which are crucially linked on the assumed quark structure for the meson M under consideration. Three cases are analyzed: M = η, M = f ₀(qˉ) and M = f ₀(qqˉ). While in the η case the estimate of the branching fraction for the radiative decay φ→ηγ is in agreement with the data, in the case of f ₀, such agreement is obtained only under the hypothesis of a tetraquark scalar meson.     

Quantum efficiency of Nd-doped lasers measured by pump-induced crystal heating: application to the Nd3+:Gd2(MoO4)3 crystal

In this paper we show how the quantum efficiency of Nd³⁺-doped laser crystals can be measured by means of a very simple method. This method is based on a multiwavelength study of pump-induced crystal heating, and its major advantage is the simplicity of the required experimental set-up. It has been used to determine the quantum efficiency of the main infrared laser channel (⁴ F _3/2?⁴ I _11/2) of the Nd³⁺:Gd₂(MoO₄)₃ non-linear laser crystal. The value obtained for the quantum efficiency (φ=0.97) is in good agreement with that obtained from the Judd–Ofelt formalism (φ=0.95). Received: 25 October 2000 / Revised version: 2 January 2001 / Published online: 27 April 2001     

Bulk singularities at critical end points: a field-theory analysis

A class of continuum models with a critical end point is considered whose Hamiltonian [φ,ψ] involves two densities: a primary order-parameter field, φ, and a secondary (noncritical) one, ψ. Field-theoretic methods (renormalization group results in conjunction with functional methods) are used to give a systematic derivation of singularities occurring at critical end points. Specifically, the thermal singularity ∼ | t|^{2 - α} of the first-order line on which the disordered or ordered phase coexists with the noncritical spectator phase, and the coexistence singularity ∼ | t|^{1 - α} or ∼ | t|^β of the secondary density <ψ> are derived. It is clarified how the renormalization group (RG) scenario found in position-space RG calculations, in which the critical end point and the critical line are mapped onto two separate fixed points _CEP ^* and _λ ^*, translates into field theory. The critical RG eigenexponents of _CEP ^* and _λ ^* are shown to match. _CEP ^* is demonstrated to have a discontinuity eigenperturbation (with eigenvalue y = d), tangent to the unstable trajectory that emanates from _CEP ^* and leads to _λ ^*. The nature and origin of this eigenperturbation as well as the role redundant operators play are elucidated. The results validate that the critical behavior at the end point is the same as on the critical line. Received 18 January 2001     

Spectrum and losses of surface magnetostatic waves in a 1D magnon crystal

The spectrum and propagation losses of a surface magnetostatic wave in a 1D ferrite magnon crystal are experimentally studied as a function of angle φ between the wavevectors of the surface magnetostatic wave and periodic crystal lattice. Variation in the positions of Bragg forbidden bands with angle φ is described. A wide transmission band is discovered near long-wave frequency boundary f ₀ of the surface magnetostatic wave in a narrow interval of angles around φ ≈ 57°. In the interval 70° < φ < 90° and at frequencies below f ₀, there exists a magnetostatic wave with a wavevector that is normal to the bias field.     

Numerical study of the oscillatory convergence to the attractor at the edge of chaos

This paper compares three different types of “onset of chaos” in the logistic and generalized logistic map: the Feigenbaum attractor at the end of the period doubling bifurcations; the tangent bifurcation at the border of the period three window; the transition to chaos in the generalized logistic with inflection 1/2 (x_n+1 = 1-μx_n^1/2), in which the main bifurcation cascade, as well as the bifurcations generated by the periodic windows in the chaotic region, collapse in a single point. The occupation number and the Tsallis entropy are studied. The different regimes of convergence to the attractor, starting from two kinds of far-from-equilibrium initial conditions, are distinguished by the presence or absence of log-log oscillations, by different power-law scalings and by a gap in the saturation levels. We show that the escort distribution implicit in the Tsallis entropy may tune the log-log oscillations or the crossover times.     

How to make sense of the jet correlations results at RHIC?

We review the di-hadron correlation results from RHIC. A consistent physical picture was constructed based on the correlation landscape in p _T , Δφ, Δη and particle species. We show that the data are consistent with competition between fragmentation of survived jets and response of the medium to quenched jets. At intermediate p _T where the medium response are important, a large fraction of trigger hadrons do not come from jet fragmentation. We argue that these hadrons can strongly influence the interpretation of the low p _T correlation data. We demonstrate this point through a simple geometrical jet absorption model simulation. The model shows that the correlation between medium response hadrons dominates the pair yield and mimics the double hump structure of the away-side Δφ distribution at low p _T . This correlation was also shown to lead to complications in interpreting the results on reaction plane dependence and three particle correlations. Finally, we briefly discuss several related experimental issues which are important for proper interpretations of the experimental data.     

A model of strain relaxation in hetero-epitaxial films on compliant substrates

0 these maximum relieved strains are φ₀/2, φ₀, 3φ₀/2 and 2φ₀ respectively, at the end of each of stages I–IV. Films relaxed in each stage are characterized by a specific set of macroscopic crystallographic features that can be observed experimentally, including lattice rotation, lattice tilt, and the presence of more than one variant in some cases. For example, complete untwisting is predicted for stage IV relaxation, resulting in the disappearance of the initial twist angle between the two lattices. To relax the elastic misfit strain, extensive plastic deformation of the substrate film is involved, thus making it compliant to the hetero-epitaxial film. This thin film substrate may be called the plastically compliant substrate (PCS). Received: 18 June 1997/Accepted: 27 June 1997     

Influence of storage time on laser cleaning of SiO<Subscript>2</Subscript> on Si

The influence of the ‘storage time’ τ_s on the threshold fluence φ_cl and the efficiency in dry laser cleaning is investigated. τ_s denotes the time between the deposition of particles and the cleaning. As a model system we employed silica spheres with diameters of 500 nm and 1500 nm on commercial silicon wafers and single-pulse KrF excimer laser radiation (τ_FWHM=28 ns). For the 1500-nm silica spheres, φ_cl was found to increase from about 65 mJ/cm² to 125 mJ/cm² for storage times of 4 h and 362 h, respectively. For 500-nm silica spheres the increase in the threshold fluence was less than 20% for storage times up to 386 h. Received: 12 July 2002 / Accepted: 12 July 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. E-mail:dieter.baeurle@jku.at     

Final-state polarization in <Emphasis Type="Italic">B</Emphasis><Stack><Subscript><Emphasis Type="Italic">s</Emphasis></Subscript><Superscript>0</Superscript></Stack> decays

Certain B _s ⁰→V ₁ V ₂ decays (V _i is a vector meson) can be related by flavor SU(3) symmetry to corresponding B _d ⁰→V ₃ V ₄ decays. In this paper, we show that the final-state polarization can be predicted in the B _s ⁰ decay, assuming polarization measurements of the B _d ⁰ decay. This can be done within the scenario of penguin annihilation (PA), which has been suggested as an explanation of the unexpectedly large transverse polarization in B→φ K ^*. PA is used to estimate the breaking of flavor SU(3) symmetry in pairs of decays. Two of these for which PA makes a reasonably precise prediction of the size of SU(3) breaking are (B _s ⁰→φ φ,B _d ⁰→φ K ^0*) and ( ). The polarization measurement in the B _d ⁰ decay can be used to predict the transverse polarization in the B _s ⁰ decay and will allow for testing of PA as well as the other assumptions in the analysis.