Study of impulse model in reaction Kd → pΛπ+ neutrals

In an analysis of 1114 events of the type K⁻d → pΛ⁰π⁻+ neutrals with ‘spectator’ proton momentum in excess of 0.11 GeV/c we have found that the number of protons having a momentum in the range 0.25–1.2 GeV/c exceeds that predicted on the basis of the impulse model using the Hulthén distribution by 3 : 1. Final-state interactions in which the proton does not form resonances with the other final-state particles are mainly held responsible for this effect.     

On the importance of zero-point effects in molecular level classical simulations of water

We discuss the fundamental difficulties involved in comparing energetic results obtained via classical simulations of bulk water with the observed values. Emphasis is placed on the difference between quantum and classical dynamics, and correction techniques, which can be used to emulate quantum effects in a classical system, are investigated. We present molecular dynamics simulation results for liquid water using the ‘Thole-type’ all atom polarizable water model, which has previously been shown to give reasonable results for both ice Ih and small water clusters. We employ expressions for the density of states power spectrum in the liquid in either atomic or rigid-body coordinates that are appropriate for rigid molecule simulations. It is demonstrated that the atomic power spectra can be written as a linear combination of the center of mass and rotational power spectra via the use of the ‘coupling matrix’ of linear coefficients. This approach allows us to introduce the concept of ‘fractional degrees of freedom’ (DOF) for nuclei in rigid molecule simulation. Within this framework, it is illustrated that in a rigid water molecule the oxygen and hydrogen atoms have 2.82 and 1.59 DOF, respectively (for the TIP4P geometry). Within our suggested approach, we finally demonstrate that Debye–Waller factors can be obtained from the coupling matrix and show that quantum corrections to the structure can be accounted for by raising the temperature of the system in a classical simulation by approximately 50°, a result consistent with previous suggestions.     

Erratum to “Master equation for structured reservoirs” [Photonics Nanostruct.: Fundam. Appl. 2/3 (2004) 167]

In this work we generalize the formalism developed in our previous work [D. Mogilevtsev, S. Kilin, S.B. Cavalcanti, PNFA (2–3) (2004) 161]. We derive a master equation suitable to describe atom-field interaction in structured reservoirs, particulary those that exhibit ‘freezing’ of spontaneous decay as well as atom-field bound states. For a wide range of reservoir densities-of-states, this equation can be reduced to the Markovian form. In this work we extend the range of applicability of the method to times comparable to those of the atom-field bound state formation. We discuss novel features that such an extension brings forth and confirm predictions made in our previous work, namely, the stationary positive atomic inversion, a possibility of in-reservoir coherent control of the atom-field bound state and bipartite character of such a state in the absence of external perturbations.     

Exciton–dopant and exciton–charge interactions in electronically doped OLEDs

The electronic dopants, like tetrafluorocyanoquinodimethane (F₄–TCNQ) molecules, used for p-doping of hole transport layers in organic light-emitting diodes (OLEDs) are found to quench the electroluminescence (EL) if they diffuse into the emissive layer. We observed EL quenching in OLED with F₄-TCNQ doped N,N′-diphenyl-N′N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine hole transport layer at large dopant concentrations, >5%. To separate the effects of exciton–dopant quenching, from exciton–polaron quenching we have intentionally doped the emissive layer of (8-tris-hydroxyquinoline) with three acceptors (A) of different electron affinities: F₄-TCNQ, TCNQ, and C₆₀, and found that C₆₀ is the strongest EL-quencher, while F₄-TCNQ is the weakest, contrary to intuitive expectations. The new effects of charge transfer and usually considered energy transfer from exciton to neutral (A) and charged acceptors (A⁻) are compared as channels for non-radiative Ex–A decay. At high current loads the EL quenching is observed, which is due to decay of Ex on free charge carriers, hole polarons P⁺. We consider contributions to Ex–P⁺ interaction by short-range charge transfer and describe the structure of microscopic charge transfer (CT)-processes responsible for it. The formation of metastable states of ‘charged excitons’ (predicted and studied by Agranovich et al. Chem. Phys. 272 (2001) 159) by electron transfer from a P to an Ex is pointed out, and ways to suppress non-radiative Ex–P decay are suggested.     

η,η′→ππγ with coupled channels

The decays η,η′→π⁺π⁻γ are investigated within an approach that combines one-loop chiral perturbation theory with a coupled channel Bethe–Salpeter equation which satisfies unitarity constraints and generates vector mesons dynamically from composite states of two pseudoscalar mesons. It is furthermore shown that the inclusion of the η′ as a dynamical degree of freedom does not renormalize the Wess–Zumino–Witten term.     

On the control of complex dynamic systems

A method is described for the limited control of the dynamics of systems which generally have several dynamic attractors. associated either with maps or first order ordinary differential equations (ODE) in ⁿ. The control is based on the existence of ‘convergent’ regions, C_C(k = 1,2,…), in the phase space of such systems, where there is ‘local convergence’ of all nearby orbits. The character of the control involves the ‘entrainment’ and subsequent possible ‘migration’ of the experimental system from one attractor to another. Entrainment means that lim_{t > → ∞} |x(t) − g(t)| = 0, where is the system's controlled dynamics, and the goal-dynamics, g(t) ε G_k, has any topological form but is limited dynamically and to regions of phase space, G_k, contained in some C_k, G_k C_k. The control process is initiated only when the system enters a ‘basin of entrainment’, BE_k G_k, associated with the goal-region G_k. Aside from this ‘macroscopic’ initial-state information about the system, no further feedback of dynamic information concerning the response of the system is required. The experimental reliability of the control requires that the regions, BE_k, be convex regions in the phase space, which can apparently be assured if G_k C_k. Simple illustrations of these concepts are given, using a general linear and a piecewise-linear ODE in . In addition to these entrainment-goals, ‘migration-goal’ dynamics is introduced, which intersects two convergent regions G ∩ C_j ≠ , G ∩ C_j ≠ (i ≠ j), and permits transferring the dynamics of a system from one attractor to another, or from one convergent region to another. In the present study these concepts are illustrated with various one-dimensional maps involving one or more attractors and convergent regions. Several theorems concerning entrainment are derived for very general, continuous one-dimensional maps. Sufficient conditions are also established which ensure ‘near-entrainment’ for a system, when the dynamic model of the system is not exactly known. The applications of these concepts to higher dimensional maps and flows will be presented in subsequent studies.     

The dissolution kinetics of free iron in Nd-Fe-B permanent magnet alloys

Three kinds of NdFeB alloys, near the Nd₂Fe₁₄B ( φ phase ) composition of the Fe-(Nd₂B) pseudobinary phase diagram, were used to study the kinetics of free iron dissolution in the matrix, which is extremely important for the attainment of high coercivity. The dissolution equations together with the time exponent, n( , ) and activation energies of rate constants, Q(34–40.9 kcal/mol) were derived. These indicate that the quantity of Nd-rich liquid phase plays an important role in the dissolution kinetics. For the ‘hypo-φ’ composition (Fe-rich), grain boundary diffusion dominates. For φ and ‘hyper-φ’ (Nd-rich) composition, interface reaction dominates. The low activation energies of this system are attributed to the activated effect of φ phase formation and liquid phase assisted grain boundary diffusion, it is found that there will be no free iron left after powder pulverizing and sintering of the commercial Nd₁₅Fe₇₇B₈ alloy.     

Momentum-carrying waves on D1–D5 microstate geometries

If one attempts to add momentum-carrying waves to a black string then the solution develops a singularity at the horizon; this is a manifestation of the ‘no hair theorem’ for black objects. However individual microstates of a black string do not have a horizon, and so the above theorem does not apply. We construct a perturbation that adds momentum to a family of microstates of the extremal D1–D5 string. This perturbation is analogous to the ‘singleton’ mode localized at the boundary of AdS; to leading order it is pure gauge in the AdS interior of the geometry.     

Critical manifolds and stability in Hamiltonian systems with non-holonomic constraints

We explore a particular approach to the analysis of dynamical and geometrical properties of autonomous, Pfaffian non-holonomic systems in classical mechanics. The method is based on the construction of a certain auxiliary constrained Hamiltonian system, which comprises the non-holonomic mechanical system as a dynamical subsystem on an invariant manifold. The embedding system possesses a completely natural structure in the context of symplectic geometry, and using it in order to understand properties of the subsystem has compelling advantages. We discuss generic geometric and topological properties of the critical sets of both embedding and physical system, using Conley–Zehnder theory, and by relating the Morse–Witten complexes of the ‘free’ and constrained system to one another. Furthermore, we give a qualitative discussion of the stability of motion in the vicinity of the critical set. We point out key relations to sub-Riemannian geometry, and a potential computational application.     

Randomly chosen chaotic maps can give rise to nearly ordered behavior

Parrondo’s paradox [J.M.R. Parrondo, G.P. Harmer, D. Abbott, New paradoxical games based on Brownian ratchets, Phys. Rev. Lett. 85 (2000), 5226–5229] (see also [O.E. Percus, J.K. Percus, Can two wrongs make a right? Coin-tossing games and Parrondo’s paradox, Math. Intelligencer 24 (3) (2002) 68–72]) states that two losing gambling games when combined one after the other (either deterministically or randomly) can result in a winning game: that is, a losing game followed by a losing game = a winning game. Inspired by this paradox, a recent study [J. Almeida, D. Peralta-Salas, M. Romera, Can two chaotic systems give rise to order? Physica D 200 (2005) 124–132] asked an analogous question in discrete time dynamical system: can two chaotic systems give rise to order, namely can they be combined into another dynamical system which does not behave chaotically? Numerical evidence is provided in [J. Almeida, D. Peralta-Salas, M. Romera, Can two chaotic systems give rise to order? Physica D 200 (2005) 124–132] that two chaotic quadratic maps, when composed with each other, create a new dynamical system which has a stable period orbit. The question of what happens in the case of random composition of maps is posed in [J. Almeida, D. Peralta-Salas, M. Romera, Can two chaotic systems give rise to order? Physica D 200 (2005) 124–132] but left unanswered. In this note we present an example of a dynamical system where, at each iteration, a map is chosen in a probabilistic manner from a collection of chaotic maps. The resulting random map is proved to have an infinite absolutely continuous invariant measure (acim) with spikes at two points. From this we show that the dynamics behaves in a nearly ordered manner. When the foregoing maps are applied one after the other, deterministically as in [O.E. Percus, J.K. Percus, Can two wrongs make a right? Coin-tossing games and Parrondo’s paradox, Math. Intelligencer 24 (3) (2002) 68–72], the resulting composed map has a periodic orbit which is stable.     

An STM study of the localized atomic reaction of 1,2- and 1,4-dibromoxylene with Si(1 1 1)-7 × 7

Thermal reactions of 1,2- and 1,4-dibromoxylene (1,2- and 1,4-diBrXy) with Si(1 1 1)-7 × 7 were investigated by STM at room temperature under UHV conditions. Reaction led to the formation of single adsorbed Br-atoms or pairs of Br-atoms, in a ratio approx. 3:1 for both reagents. Experimental results were interpreted in terms of ‘parent-mediated’ (halogen atom accompanied by organic residue), and ‘daughter-mediated’ (no accompanying organic residue) reaction dynamics. Both mechanisms contributed to the bromination of the silicon surface in comparable amounts. For pairs of bromine atoms the Br–Br separation had a most probable value of 7.6 Å for 1,2-diBrXy, and 11.5 Å for 1,4-diBrXy. This separation was in each case greater than that in the diBrXy parent molecule by a few angstroms. For parent-mediated reaction the dynamics were revealed in detail by the STM images which gave the vectorial location of the halogen-atom products (distance and angle of the daughter atoms) relative to the prior location and alignment of the adsorbed parent molecule. Both reagents, 1,2- and 1,4-diBrXy, were found to be less reactive than the corresponding dibromobenzenes studied earlier in this laboratory [S. Dobrin et al., Surf. Sci. 561 (2004) 11], in both parent- and daughter-mediated modes.     

Measurement of apex angle of the prism using total internal reflection

Total internal reflection technique is examined critically for the measurement of apex angle of the prism. Recognition of the critical boundary completely specifies the apex angle ‘A’ of the prism by keeping constant the ratio of refractive index of sample fluid (n₁=1.4) to that of glass (n₂=1.7). Recording of observations in the laboratory is dependent upon whether the apex angle ‘A’ of prism is greater than or less than or equal to critical angle ‘r_c’. The minimum value of error function ‘χ’ in the proximity of Abbe angle explain the choice of Abbe type instruments and shown invariant by relating positive ‘₊’ and the negative angle of emergence ‘₋’. Using ray-tracing technique, an expression for the length of the critical boundary ‘l’ is derived and is shown as a measure of the apex angle ‘A’ of the prism.

The choice of the realistic grazing condition leads us to two turning points for which error function ‘χ’ is minimal and yields appropriate option of the measurement of apex angle ‘A’ of the prism. It is further shown that the small error ‘ζ’ crept in the apex angle ‘A’ of the prism can lead to a significant error in the design of Pulfrich type instruments.

Experimental measurements are in-line with the predictions made.     

Development of a 4–15 μm infrared GaAs hyperspectral QWIP imager

In the on-going evolution of GaAs quantum well infrared photodetectors (QWIPs) we have developed a four band, 640 × 512, 23 μm × 23 μm pixel array which we have subsequently integrated with a linear variable etalon (LVE) filter providing over 200 spectral bands across the 4–15.4 μm wavelength region. This effort was a collaboration between NASA’s Goddard Space Flight Center (GSFC), the Jet Propulsion Laboratory (JPL) and the Army Research Laboratory (ARL) sponsored by the Earth Science Technology Office of NASA. The QWIP array was fabricated by graded molecular beam epitaxial (MBE) growth that was specifically tailored to yield four distinct bands (FWHM): Band 1; 4.5–5.7 μm, Band 2; 8.5–10 μm, Band 3; 10–12 μm and Band 4; 13.3–14.8 μm. Each band occupies a swath that comprises 128 × 640 elements. The addition of the LVE (which is placed directly over the array) further divides the four “broad” bands into 209 separate spectral bands ranging in width from 0.02 μm at 5 μm to 0.05 μm at 15 μm. The detector is cooled by a mechanical cryocooler to 46 K. The camera system is a fully reflective, f/4.2, 3-mirror system with a 21° × 25° field of view. The project goals were: (1) develop the 4 band GaAs QWIP array; (2) develop the LVE and; (3) implement a mechanical cryocooler. This paper will describe the efforts and results of this undertaking with emphasis on the overall system characteristics.     

Polymorphism in supramolecular chiral structures of R- and S-alanine on Cu(1 1 0)

A comprehensive study of the local and supramolecular adsorption structures created by the chiral R- and S-enantiomers of alanine on the Cu(1 1 0) surface has been conducted using a multi-technique approach, including reflection absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). Over the entire 300–470 K temperature range studied, the amino acid is found to adsorb as an alaninate species with a local chiral adsorption motif. However, this singular preference of local chemical form contrasts sharply with the supramolecular organisation at the surface where polymorphism is exhibited. This polymorphic behaviour arises from subtle and dynamic changes in the bonding, orientation and adsorption footprints of individual molecules, leading to alterations in the molecule–metal, intermolecular and metal–metal interactions that dictate self-assembly. Thus, at low coverage, a single disordered phase is observed but at higher coverage, three other temperature dependent phases occur. At room temperature, a two-dimensional equivalent of a ‘nematic’ phase is constructed from short single- and double-chain chiral assemblies that possess a preferred chiral orientation but no long range periodicity. This ‘nematic’ phase acts as a precursor to a highly ordered chiral supramolecular assembly, created at 430 K, that consists of regular arrays of size- and shape-defined chiral clusters. This phase possesses global organisational chirality with only one chiral domain observed for each enantiomer. For both the ‘nematic’ and the highly ordered chiral phase, the organisation for the R-enantiomer is the mirror image of that seen for the S-enantiomer, i.e., there is chirality transfer from the nanoscale to the macroscale. By 470 K, both R- and S-alanine form an achirally organised (3 × 2) structure that appears to be the thermodynamically favoured phase for the alanine/Cu(1 1 0) system. The supramolecular organisation and chirality of the various structures are discussed in terms of the molecular chirality and footprint chirality of the alaninate, together with possible intermolecular interactions and reconstructions of the underlying metal surface atoms. A number of candidate models for the system are suggested, but it is clear that a full understanding of this complex adsorption system will only emerge from further careful, high level experimental and computational efforts that currently remain a challenge.     

New Developments in the Eight Vertex Model II. Chains of Odd Length

We study the transfer matrix of the 8 vertex model with an odd number of lattice sites N. For systems at the root of unity pointsη=mK/L with m odd the transfer matrix is known to satisfy the famous ‘‘TQ’’ equation where Q(υ) is a specifically known matrix. We demonstrate that the location of the zeroes of this Q(υ) matrix is qualitatively different from the case of evenN and in particular they satisfy a previously unknown equation which is more general than what is often called ‘‘Bethe’s equation.’’ For the case of even m where no Q(υ) matrix is known we demonstrate that there are many states which are not obtained from the formalism of the SOS model but which do satisfy the TQ equation. The ground state for the particular case of η=2K/3 and N odd is investigated in detail.     

Comparison of ‘blue’ and ‘infrared’ emission bands in thermoluminescence of alkali feldspars

Dating quaternary sediments by thermoluminescence (TL) or optically stimulated luminescence (OSL) calls for a detailed knowledge of the luminescence of feldspars. TL of the various alkali feldspars ((K, Na) Si₃AlO₈) display many common features, and some of these cause great difficulties for dating. After long storage following ionizing irradiation, the TL of most alkali feldspars is known to fade away by “anomalous fading”, which is incompatible with dating. This effect had been attributed to tunnel recombination. Following irradiation, a very intense tunnelling afterglow is observed at temperatures down to liquid nitrogen, in accordance with the observed rate of fading. This emission has a Gaussian spectrum entirely in the infrared (IR) with a maximum at 1.7 eV. It displays an important thermal quenching from 77 to 300 K. Its intensity is related with the ‘disorder’ of the crystal lattice. At higher temperatures, in TL proper, two emission bands can be separated. One is the well-studied complex visible emission, distributed over the spectral region from UV to orange, but mostly ‘blue’. The other is the ‘infrared’ band already observed at lower temperatures, which is attributed to Fe³⁺ ions. These two bands are clearly separated, with the spectral maxima, respectively, below and above 600 nm. They have also different kinetics, the glow peaks temperatures are different. But these two different bands are also coupled in many ways, they have parallel growth and fading. With ‘disordered’ feldspars, the ‘blue’ emission displays anomalous fading, which is stronger than that of the ‘infrared’. The infrared emission is more stable, which may be interesting for the purpose of dating.     

Radiation-induced processes and defects in alkali and alkaline-earth borate crystals

The paper presents the results of a study of the radiation-induced processes and defects in nonlinear optical crystals Li₂B₄O₇ (LTB), LiB₃O₅ (LBO), CsLiB₆O₁₀, KB₅O₈·4H₂O, β-BaB₂O₄. It was revealed that a pulsed electron beam irradiation at 290 K forms the radiation-induced pairs of the ‘vacancy—interstitial atom’ defects in the cation sublattice of these crystals. This gives rise to a creation of metastable electronic (interstitial atom) and hole (small-radius polaron near the cation vacancy) centers in high concentrations. Optical hole-transitions from the local level of the trapped hole centers to the valence band states are responsible for the transient optical absorptions (TOA) of borates in the visible and UV spectral ranges. A sublattice of the weakly bound mobile lithium cations in LTB and LBO favors a spatial separation of the radiation-induced pair defects ‘hole polaron near Li-vacancy—mobile interstitial Li⁰ atom’. Their decay rated by the electron–hole nonradiative tunnel recombination determines a peculiar feature of the TOA decay kinetics in LTB and LBO.     

Possible vortex production by a vibrating wire in superfluid He–B

We observe spectacular features on the force–velocity characteristic of a vibrating wire resonator in superfluid ³He–B at ultralow temperatures. There are both plateaux and discontinuities in the characteristic. The plateaux seem to have two separate critical velocities where firstly some ‘event’ occurs, which causes the wire to lose energy and slow down, followed by a second critical velocity where the ‘event’ decouples. The shape of the pulses so created depends on the precise position on the particular plateau. At the low-velocity end of the plateau, the pulses show a sudden decrease in velocity followed by a gradual growth, whereas at the high-velocity end the pulses consist of a sudden increase in velocity followed by a gradual decrease. Eventually, the pulsing ceases indicating a saturation effect. We speculate that these events are due to vortex creation and annihilation/separation.     

How does Europe Make Its Mind Up? Connections,cliques, and compatibility between countries in the Eurovision Song Contest

We investigate the complex relationships between countries in the Eurovision Song Contest, by recasting past voting data from 1992–2003 in terms of a dynamical network. Our analysis shows that the UK is remarkably compatible, or ‘in tune’, with other European countries during the period of study. Equally surprising is our finding that some other core countries, most notably France, are significantly ‘out of tune’ with the rest of Europe during the same period. In addition, our analysis enables us to confirm a widely-held belief that there are unofficial cliques of countries; however, these cliques are not always the expected ones, nor can their existence be explained solely on the grounds of geographical proximity. The complexity in this system emerges via the group ‘self-assessment’ process, and in the absence of any central controller. One might therefore speculate that such complexity is representative of many real-world situations in which groups of ‘agents’ establish their own inter-relationships and hence ultimately decide their own fate. Possible examples include groups of individuals, societies, political groups or even governments.     

Arc arrays: studies of high resolution techniques for multibeam bathymetric applications

In this paper a theoretical study is initiated to observe the utility of directional spectral estimation techniques for ‘arc array’ geometries. We examine the suitability of a 15 ° arc transducer geometry for multibeam bathymetric applications. This geometry is tested using the Bartlett method for varying arc and linear arrays of 30-elements. We also examine ‘high resolution techniques’ such as the Maximum Likelihood (ML) method and the Maximum Entropy (ME) methods (different orders), for 16-element arrays of 15 ° arc. The superiority of the high resolution methods is seen by examining the beam patterns of the 15 ° arc array under multiple source/interference conditions, i.e. the situation for rough terrain or artefactcreating conditions. Furthermore, the 15 ° arc array geometry is found to be useful for multifrequency applications at different operating wavelengths, which is useful for underwater bathymetric applications.