# Physics Letters A

Online ISSN: 0375-9601
Publications
Article
So far fluid mechanical Nambu brackets have mainly been given on an intuitive basis. Alternatively an algorithmic construction of such a bracket for the two-dimensional vorticity equation is presented here. Starting from the Lie--Poisson form and its algebraic properties it is shown how the Nambu representation can be explicitly constructed as the continuum limit from the structure preserving Zeitlin discretization.

Article
A resonant transition amplitude, valid to arbitrary order, is derived through the use of a complex energy T-matrix. A feature of this amplitude is its generality and simplicity making it useful for widespread applications in resonance theory.

Article
We begin by giving correct expressions for the short-time action following the work Makri-Miller. We use these estimates to derive an accurate expression modulo [Formula: see text] for the quantum propagator and we show that the quantum potential is negligible modulo [Formula: see text] for a point source, thus justifying an unfortunately largely ignored observation of Holland made twenty years ago. We finally prove that this implies that the quantum motion is classical for very short times.

Article
We consider the influence of a terahertz field on the breathing dynamics of double-stranded DNA. We model the spontaneous formation of spatially localized openings of a damped and driven DNA chain, and find that linear instabilities lead to dynamic dimerization, while true local strand separations require a threshold amplitude mechanism. Based on our results we argue that a specific terahertz radiation exposure may significantly affect the natural dynamics of DNA, and thereby influence intricate molecular processes involved in gene expression and DNA replication.

Article
The upper limit of momentum transfer by a proton to K-shell electrons is calculated in a restricted three-body classical model. The model shows that the infinite upper limit used in practice, is generally good except for low energy protons passing through an extremely rarefied gas.

Article
Statistical physics and information theory is applied to the clinical chemistry measurements present in a patient database containing 2.5 million patients' data over a 20-year period. Despite the seemingly naive approach of aggregating all patients over all times (with respect to particular clinical chemistry measurements), both a diurnal signal in the decay of the time-delayed mutual information and the presence of two sub-populations with differing health are detected. This provides a proof in principle that the highly fragmented data in electronic health records has potential for being useful in defining disease and human phenotypes.

Article
We study the weak values of a quantum observable from the point of view of the Wigner formalism. The main actor is here the cross-Wigner transform of two functions, which is in disguise the cross-ambiguity function familiar from radar theory and time-frequency analysis. It allows us to express weak values using a complex probability distribution. We suggest that our approach seems to confirm that the weak value of an observable is, as conjectured by several authors, due to the interference of two wavefunctions, one coming from the past, and the other from the future.

Conference Paper
The characteristics of pulse compression during the laser pulse amplification using a counter-propagating pump and plasmas have been investigated using a one-dimensional fluid model of stimulated Raman backscattering. The pulse widths of the amplified laser at the front and rear half are examined in terms of the initial amplitudes of the pump and the seed, and the ratio of the electron plasma frequency to the laser frequency. The pulse widths have a common scaling behaviour in time over the considered parameter regime. The scaling exponents of the pulse widths during broadening and compression are all the same as 1.0. The pulse compression scaling shows a reciprocal behaviour to the peak energy growth.

Conference Paper
In this work, a method for storing and retrieving spatio-temporal patterns in large systems of coupled delay differential equations is presented. Spatio-temporal patterns are sets of sequences of binary variables of fixed period that are embedded in the network dynamics as stable limit cycles. As a consequence, an input signal converges to the limit cycle that best represents it. A given set of limit cycles is constructed using a generalization of the correlation learning rule in the definition of the couplings

Conference Paper
In this Letter, the domain of attraction of memory patterns and exponential convergence rate of the network trajectories to memory patterns for Hopfield continuous associative memory are estimated by means of matrix measure and comparison principle. A new estimation is given for the domain of attraction of memory patterns and exponential convergence rate. These results can be used for the evaluation of fault-tolerance capability and the synthesis procedures for Hopfield continuous feedback associative memory neural networks.

Conference Paper
Robust control problem of nonlinear time delay chaotic systems is investigated. For such uncertain systems, we propose adaptive feedback controller and novel nonlinear feedback controller. They are both independent of the time delay and can render the corresponding closed-loop systems globally uniformly ultimately bounded stable. The simulations on controlling logistic system are made and the results show the controllers are feasible.

Conference Paper
We consider the delayed feedback control (DFC) scheme for one dimensional discrete time systems. To analyze the stability, we construct a map whose fixed points correspond to the periodic orbits of the system to be controlled. Then the stability of the DFC is equivalent to the stability of the corresponding equilibrium point of the constructed map.

Conference Paper
The electronic contribution to the attenuation of sound waves is dependent on the product a = qℓ, q being the phonon wave number and ℓ the electron mean free path.1 For qℓ » 1, the attenuation parameter $$\frac{\alpha }{\nu }$$ ν being the phonon frequency, is independent of qℓ. In general, the attenuation at arbitrary qℓ can be expressed in the form $$\frac{\alpha }{\nu } = \mathop {\lim }\limits_{q\ell \to \infty } \left( {\frac{\alpha }{\nu }} \right){\text{ }}P\left( {q\ell } \right)$$ (1) where P(qℓ) tends to unity for large qℓ.

Article
Information is inevitably tied to a physical representation and therefore to restrictions and possibilities related to the laws of physics and the parts available in the universe. Quantum mechanical superpositions of information bearing states can be used, and the real utility of that needs to be understood. Quantum parallelism in computation is one possibility and will be assessed pessimistically. The energy dissipation requirements of computation, of measurement and of the communications link are discussed. The insights gained from the analysis of computation has caused a reappraisal of the perceived wisdom in the other two fields. A concluding section speculates about the nature of the laws of physics, which are algorithms for the handling of information, and must be executable in our real physical universe.

Article
A newly derived generalized moments expansion (GMX), based on the “t-expansion” of Horn and Weinstein, is used to calculate the correlation energy of a model Hamiltonian representing N coupled one-dimensional harmonic oscillators. Comparisons are made with a related calculational scheme the canonical sequence method (CSM).

Article
We introduce a new observable for reading out a which-way detector in a Young-type interferometer whose eigenstates either contain full which-way information or none at all. We calculate the which-way knowledge K that can be retrieved from this observable and find that K depends on the phase difference \delta that the interfering object accumulates on its way from either slit to the detector. In particular, it turns out that K(\delta) has an upper bound of 1, almost independent of the visibility V of the interference pattern generated by the interfering object on a screen, which is in marked contrast to the well-known inequality K^2 + V^2 <= 1 (cf. B.-G. Englert, Phys. Rev. Lett. 77, 2154 (1996)).

Article
Dilute solution of He 3 in He 4 near absolute zero measured for viscosity, showing temperature effect

Article
The effective charges extracted from measured stopping powers of heavy ions depend clearly on the stopping medium. Effective charges in gases differ systematically from the measured mean charge states after the medium.

Article
We investigate the transmission of electrons through a quantum point contact by using a quasi-one-dimensional model with a local bound state below the band bottom. While the complete transmission in lower channels gives rise to plateaus of conductance at multiples of $2e^{2}/h$, the electrons in the lowest channel are scattered by the local bound state when it is singly occupied. This scattering produces a wide zero-transmittance (anti-resonance) for a singlet formed by tunneling and local electrons, and has no effect on triplets, leading to an exact $0.75(2e^{2}/h)$ shoulder prior to the first $2e^{2}/h$ plateau. Formation of a Kondo singlet from electrons in the Fermi sea screens the local moment and reduces the effects of anti-resonance, complementing the shoulder from 0.75 to 1 at low temperatures.

Article
We provide a security analysis of the Y-00 protocol under heterodyne measurement and correlation attack. We show that the secrecy of the data encryption scheme is extremely sensitive to the running-key generation process. In many situations our simple attack succeeds in recovering the initial shared secret key. Our simulation results suggest that a truly secure implementation of the protocol should take into account the effective key generation method. (c) 2006 Elsevier B.V. All rights reserved.

Article
It is claimed by T. Nishioka et al. in [T. Nishioka, T. Hasegawa, H. Ishiziuka, K. Imafuku, H. Imai, Phys. Lett. A 327 (2004) 28-321 that the security of Y-00 is equivalent to that of a classical stream cipher. In this Letter it is shown that the claim is false in either the use of Y-00 for direct encryption or key generation, in all the parameter ranges it is supposed to operate including those of the experiments reported thus far. The security of Y-00 type protocols is clarified. (c) 2005 Elsevier B.V. All rights reserved.

Article
The potential weakness of the Y-00 direct encryption protocol when the encryption box ENC in Y-00 is not chosen properly is demonstrated in a fast correlation attack by S. Donnet et al in Phys. Lett. A 35, 6 (2006) 406-410. In this paper, we show how this weakness can be eliminated with a proper design of ENC. In particular, we present a Y-00 configuration that is more secure than AES under known-plaintext attack. It is also shown that under any ciphertext-only attack, full information-theoretic security on the Y-00 seed key is obtained for any ENC when proper deliberate signal randomization is employed.

Article
New quantum cryptography, often called Y-00 protocol, has much higher performance than the conventional quantum cryptographies. It seems that the conventional quantum cryptographic attacks are inefficient at Y-00 protocol as its security is based on the different grounds from that of the conventional ones. We have, then, tried to cryptoanalyze Y-00 protocol in the view of cryptographic communication system. As a result, it turns out that the security of Y-00 protocol is equivalent to that of classical stream cipher.

Article
Using first-principles calculations, we systematically study the potential energy surfaces and dissociation processes for hydrogen molecules on the clean and hydrogen-preadsorbed Be(0001) surfaces. It is found that the most energetically favored dissociation channel for H2 molecules on the clean Be surface is at the surface top site, with the minimum energy barrier of 0.75 eV. It is further found that after dissociation, hydrogen atoms do not like to cluster with each other, as well as to penetrate into subsurface sites. For the hydrogen-preadsorbed Be(0001) surface, the smallest dissociation energy barrier for H2 molecules is found to be 0.50 eV, which is smaller than the dissociation energy barrier on a clean Be(0001) surface. The critical dependence of the dissociation energy barriers for H2 molecules on their horizontal distances from the preadsorbed hydrogen atom is revealed. Our studies well describe the adsorption behaviors of hydrogen on the Be(0001) surface.

Article
By using the density functional theory method, we systematically study the influences of the doping of an Al atom on the electronic structures of the Mg(0001) surface and dissociation behaviors of H2 molecules. We find that for the Al-doped surfaces, the surface relaxation around the doping layer changes from expansion of a clean Mg(0001) surface to contraction, due to the redistribution of electrons. After doping, the work function is enlarged, and the electronic states around the Fermi energy have a major distribution around the doping layer. For the dissociation of H2 molecules, we find that the energy barrier is enlarged for the doped surfaces. Especially, when the Al atom is doped at the first layer, the energy barrier is enlarged by 0.30 eV. For different doping lengths, however, the dissociation energy barrier decreases slowly to the value on a clean Mg(0001) surface when the doping layer is far away from the top surface. Our results well describe the electronic changes after Al-doping for the Mg(0001) surface, and reveal some possible mechanisms for improving the resistance to corrosion of the Mg(0001) surface by doping of Al atoms.

Article
In an attempt to find generic features on the fractal growth of Au films deposited on Ru(001), a simple simulation model based on irreversible diffusion-limited aggregation (DLA) is discussed. Highly irregular two-dimensional dentritic islands of Au particles that gradually grow on a larger host lattice of Ru particles and have fractal dimension d_{f}~ 1.70 each, are generated via a multiple had-hoc version of the DLA algorithm for single aggregates. Annealing effects on the islands morphology are reproduced assuming different sticking probabilities at nearest-neighbour lattice sites of Au films on Ru(001). Using simulation data, islands growth are described in analogy to diffusion-limited, precipitate growth with soft impingement of precipities. This leads to analyse thin film island growth kinetics in such fractal systems and to predict a main peak in scattering intensity patterns due to interisland interference. ---------------- Copies upon request to: canessae@itsictp.bitnet Comment: CM-ICTP/92/123

Article
We have measured the binding energy shift of the Au-4f core levels at the (001) surface of equi-atomic CuAuI. We show that this result enables us to make a definitive determination of the termination at the surface.

Article
Iridium adsorption on γ-Al2O3 (001) surface has been studied using the ab initio calculation method and the electronic structures of the bare and the Ir adsorbed γ-Al2O3 (001) surfaces have been analyzed. By modeling different adsorption sites, one can conclude that the energetically most favorable sites for the Ir are the top sites of the O atoms at the γ-Al2O3 (001) surface terminated with octahedral Al. Charge redistribution around the Ir atom adsorbed on the surface improves the activity of the Ir atom as a catalyst.

Article
We find eigenmodes of an integral equation describing N 2-level atoms interacting with a scalar field, one atom being initially excited. Neglect of virtual field quanta would replace the correct kernel by its real part. This has serious consequences both for small and large samples.

Article
All the hermitian representations of the symmetric" $q$-oscillator are obtained by means of expansions. The same technique is applied to characterize in a systematic way the $k$-order boson realizations of the $q$-oscillator and $su(1,1)_q$. The special role played by the quadratic realizations of $su(1,1)_q$ in terms of boson and $q$-boson operators is analysed and clarified. Comment: 13 pages, AMS-TEX file, UVA/93-92

Article
In this Letter, an entropy operator for the general unitary SU(1,1) TFD formulation is proposed and used to lead a bosonic system from zero to finite temperature. Namely, considering the closed bosonic string as the target system, the entropy operator is used to construct the thermal vacuum. The behaviour of such a state under the breve conjugation rules is analyzed and it was shown that the breve conjugation does not affect the thermal effects. From this thermal vacuum the thermal energy, the entropy and the free energy of the closed bosonic string are calculated and the appropriated thermal distribution for the system is found after the free energy minimization.

Article
We decouple the Dirac's radial equations in $D+1$ dimensions with Coulomb-type scalar and vector potentials through appropriate transformations. We study each of these uncoupled second-order equations in an algebraic way by using an $su(1,1)$ algebra realization. Based on the theory of irreducible representations, we find the energy spectrum and the radial eigenfunctions. We construct the Perelomov coherent states for the Sturmian basis, which is the basis for the unitary irreducible representation of the $su(1,1)$ Lie algebra. The physical radial coherent states for our problem are obtained by applying the inverse original transformations to the Sturmian coherent states.

Article
We have applied laser calorimetry to the measurement of optical absorption in mono-crystalline sapphire at cryogenic temperatures. Sapphire is a promising candidate for the mirror substrates of the large-scale cryogenic gravitational wave telescope. The optical absorption coefficients of different sapphire samples at a wavelength of 1.064 μm at 5 K were found to average 90 ppm/cm.

Article
The resistivity of rapidly quenched quasicrystalline ribbons Ti41.5Zr41.5Ni17, Ti53Zr27Ni20 and Ti45Zr38Ni17 are investigated in the interval 1.3–300 K. The “metallic” behaviour of the resistance is found at T>20 K. Such behaviour is connected with electron–phonon s–d scattering. The beginning of superconducting transition in Ti41.5Zr41.5Ni17 is found out at T<1.6 K. There is shallow minimum of ρ(T) close by 20 K.

Article
A 1.5 um synchronous heralded single photon source (HSPS) is experimentally demonstrated based on dispersion shifted fiber and commercial fiber components in the paper. Experimental results show that both the preparation efficiency and the conditional second order correlation function g2(0) increase with the pump light level. Between the two important parameters, tradeoff should be taken in order to obtain a high quality fiber-based synchronous HSPS. A synchronous HSPS with a prepare efficiency of >60% and g2(0)<0.06 is achieved, the multi-photon probability of which is reduced by a factor of more than 16 compared with the Poissonian light sources. The experimental results show a great potential of the fiber-based synchronous HSPS for quantum information applications. Comment: 5 pages, 3 figures

Article
We present an easy analytical method for designing dispersion-managed fiber systems with map strength of 1.65, where the transmission lines have minimal pulse–pulse interactions.

Article
Light mixing techniques were used to scatter at small forward angles with a hybrid CO2-laser from a thermal plasma. The ion temperature and the enhancement of ion-acoustic resonances by ion-ion collisions were obtained from the scattered spectrum recorded in one shot.

Article
Spin-based quantum computation (QC) in the solid state is considered to be one of the most promising approaches to scalable quantum computers. However, it faces problems such as initializing the spins, selectively addressing and manipulating single spins, and reading out the state of the individual spins. We have recently sketched a scheme that potentially solves all of these problems5. This is achieved by making use of a unique phosphorus-doped 28Si sample (28Si:P), and applying powerful new electron spin resonance (ESR) techniques for parallel excitation, detection, and imaging in order to implement QCs and efficiently obtain their results. The beauty of our proposed scheme is that, contrary to other approaches, single-spin detection sensitivity is not required and a capability to measure signals of ~100-1000 spins is sufficient to implement it. Here we take the first experimental step towards the actual implementation of such scheme. We show that, by making use of the smallest ESR resonator constructed to date (~5 microns), together with a unique cryogenic amplification scheme and sub-micron imaging capabilities, a sensitivity of less than 1000 electron spin is obtained with spatial resolution of ~500 nm. This is the most sensitive induction-detection experiment carried out to date, and such capabilities put this approach on the fast track to the demonstration of a scalable QC capability.

Article
Theoretical results are given for the electrical conductivity of a hot dense plasma. The gradient formulation of density functional theory is applied to calculate the ionization states and electron-ion potentials. Elastic scattering cross sections are obtained by partial wave calculations. These are then combined with ionic static structure factors to compute electrical resistivity according to the extended Ziman formula. Calculation results are compared with qualitatively novel experimental data.

Article
The non-empirical model proposed by Staszewska et al. in 1983 for the imaginary part of electron scattering optical potential is revised. Electron indistinguishability in Pauli blocking conditions and an screening correction are proposed. Results for He, Ne and Ar favourably compare with previous model and experimental values, for inelastic processes.

Article
The similarity of distinctive skeletal structures (namely, cartwheels and tubules) in the range 10−5–1023 cm is found. The former analysis of dust deposits in tokamak (10−6–10−3 cm) and of electric discharges in tokamaks, Z-pinches, plasma focus and vacuum spark (10−2–10 cm) is extended here to hail particles (1–10 cm), tornado (103–105 cm), and various objects in space (1011–1023 cm). The similarity and the observed trend toward self-similarity within above skeletal structures suggest all of them, similarly to skeletons in the particles of dust and hail, to be basically a fractal condensed matter which, similarly to submicron dust skeletons, is assembled from nanotubular blocks.

Article
We demonstrate that the description of the optical reflectance anisotropy of GaAs(110) requires a complete microscopic treatment of both surface and bulk, which is feasible in the discrete cellular method. This method is an extension of standard discrete dipole calculations and accounts for non-locality in the electro-dynamical and quantum-mechanical interactions through the use of both real space local fields and ab-initio nonlocal polarizabilities. The results of our calculations are in excellent agreement with experiment and we show that the anisotropy is surface induced.

Article
The spin polarization of electrons captured into excited atomic levels of atoms during the scattering of fast ions from a magnetized Ni(110) surface under a grazing angle of incidence is deduced from the polarization of the fluorescence light. In our studies we have investigated the dependence of the spin polarization on projectile velocity and angle of incidence and observed generally small polarizations for captured electrons.

Article
The transient behavior of the one-dimensional two-state three-input cellular automaton rule 110, one of the simplest “edge of chaos” cellular automata, is investigated numerically. The simulations show that the average transient time Tave increases algebraically with system size N, Tave∼Nα, with α≈1.08, and that the density of propagating objects (gliders) decays with time as ngl∼-γ with γ≈0.64.

Article
The authors of the paper indicated in the title derived an erroneous effective free energy of superconducting slabs (films) and this error led them to entirely wrong conclusions. Here we shall make clear the genesis of this mistake. Comment: 4 pages, Miktex; submitted to Phys. Lett. A

Article
The highly energetic and high fluence argon ions emitted in a dense plasma focus device have been used for the first time to get fullerene films by ablating the graphite target such that the ablated material is deposited on a Si(111) substrate. These films have been studied using XRD, high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, FTIR spectroscopy and SEM microscopy. The XRD, Raman and FTIR spectra show peaks corresponding to fullerenes, mainly C60 and C70. Moreover, prominent peaks of C60 have been observed in XRD spectra. The TEM micrograph shows crystalline fullerene structures and the selected area diffraction (SAD) pattern shows single crystalline spot patterns exhibiting the (110) and (006) planes of the hcp C60 clusters. The SEM micrographs also show spherical clusters of fullerenes.

Article
A surfactant-mediated homoepitaxial metal system, Cu/In/Cu(111), is studied by using first-principles calculations and the kinetic Monte Carlo method. A new repulsion model is proposed for the Cu/In/Cu(111) system where surface-substitutional In atoms repel diffusing Cu adatoms and build a repulsion network. This repulsion network results in an average increase of terrace barriers for adatoms Cu and enhanced island density. The layer-by-layer growth for the Cu/In/Cu(111) system is achieved with a repulsion model in a kinetic Monte Carlo simulation. The importance of the additional barrier ΔE is confirmed in determining film morphology.

Article
Perturbed angular correlation measurements were performed after 111In implantation into CuO and Cu2O powder samples and 1 μm thick Cu2O surface layers. The quadrupole hyperfine interaction of 111Cd was studied in isochronal annealing cycles at 370–1170 K covering the CuO→Cu2O phase transition. The electric field gradients obtained for 111Cd on substitutional Cu lattice sites were associated with the repective oxygen coordinations. Annealing of Cu2O surface layers on copper foils resulted in a texture with the efg pointing preferentially out of the surface plane.

Article
Using a surface ionization ion microscope the desorption kinetics and the directional dependence of the diffusion of potassium were measured on an oxygen covered W(112) surface at extremely low K-coverages. The mean adsorption lifetime τ can be expressed as τ = 4.8×10−14 s×exp(2.24 eV/kT); compared to the clean surface the activation energy of ionic desorption is reduced by 0.3 eV. The oxygen coverage does not change the anisotropy of diffusion observed on the clean surface fundamentally, but slows down the diffusion process. The diffusion constants along the [1̄1̄1] direction (direction of the “channels” on W(112)) and at an angle of 60° relative to it are given by D∥,ox = 0.9 cm2 s−1 × exp(−0.60 eV/kT) and D60°,ox = 0.2 cm2 s−1 × exp(−0.72 eV/kT), respectively.

Article
We report on the IR spectroscopic studies in both reflection (50-900 cm^{-1}) and transmission (900-3000 cm^{-1}) mode of the vibration spectrum of the cuprous oxide. A detailed analysis based on a comparison of the temperature dependences of the absorption band at 1125 cm^{-1} and of IR and Raman active fundamental vibrations results in assignment of the former to a biphonon. Comment: 5 pages, 5 figures (to appear in Phys.Lett. A)

Top-cited authors
• University of Gdansk
• University of Tuebingen
• Center for Physical Sciences and Technology
• Fudan University
• Fudan University