Stability and fragmentation processes of highly charged sodium clusters

Highly charged sodium clusters produced in collisions between neutral clusters and multiply charged ions are formed within a large range of temperatures and fissilities, and identified by means of a high-resolution reflectron-type time-of-flight mass spectrometer ( m/ent/vtcuwwpljj59rk96/xxlarge948.gif" alt="delta" align="BASELINE" BORDER="0">m ent/vtcuwwpljj59rk96/xxlarge8776.gif" alt="ap" align="MIDDLE" BORDER="0"> 14000). The limit of stability of these charged clusters is experimentally investigated, and the time-of-flight spectra are compared with theoretical spectra based on Monte-Carlo simulations. The results indicate that the maximum fissility (X) of stable clusters is approaching the Rayleigh limit (X = 1) for larger clusters sizes. It is mainly limited by the initial neutral cluster temperature ( T ent/vtcuwwpljj59rk96/xxlarge8776.gif" alt="ap" align="MIDDLE" BORDER="0"> 100 K) and the energy transfer in the ionizing collision. In addition, the comparison between the measured and simulated spectra suggests for high cluster charges a multi-fragmentation process, in which most of charge is emitted, creating low charged residual cluster ions.     

Engineering entanglement of a general three-level system interacting with a correlated two-mode nonlinear coherent state

In this article a treatment of a three-level atom interacting with two modes of light in a cavity with arbitrary forms of nonlinearities of both the fields and the intensity-dependent atom-field coupling is presented. A factorization of the initial density operator is assumed, with the privileged field modes being in a pair-coherent state. We derive and illustrate an exact expression for the time evolution of the density operator, by means of which we identify and numerically demonstrate the region of parameters where significantly large entanglement can be obtained. We show that entanglement can be significantly influenced by different kinds of nonlinearities. The nonlinear medium yields the superstructure of atomic Rabi oscillation. We propose a generation of Bell-type states having a simple initial state preparation of the present system. Received 29 July 2002 / Received in final form 18 October 2002 Published online 21 January 2003 RID="a" ID="a"e-mail: abdelaty@uni-flensburg.dePresent address: Institut für Mathematik, Universit?t Flensburg, Germany.     

Dispersion and alignment of carbon nanotubes in polycarbonate

Dispersion and alignment of carbon nanotubes in thermoplastic polymers such as polycarbonate have been studied. Dispersion was accomplished by mixing in a conical twin-screw extruder and alignment was carried out using a fiber-spinning apparatus. The effects of mixing time and fiber draw rates on dispersion and alignment were investigated. Uniform dispersions were produced with relatively short residence times in the extruder. Excellent alignment of carbon nanotubes in nanocomposite filaments was obtained when the fiber draw rate was greater than 70 m/min. The ability to closely control the dispersion and alignment of carbon nanotubes in polymers is expected to lead to the development of nanocomposites with desirable electronic and structural properties. Received: 7 January 2002 / Accepted: 11 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-508/233-5521, E-mail: Michael.Sennett@natick.army.mil     

Polymers grafted to a fluid and flexible membrane: Extreme sensitivity to the grafting density

Equilibrium phase coexistence between two chemical species implies the equality of the chemical potentials and of the osmotic pressures. We study this problem on a deformable membrane when one type of the molecules serves as anchor for polymeric chains immersed in the surrounding medium (considered as a good solvent). We derive the general conditions for phase coexistence when both the curvature of the membrane and the density field of the anchor molecule are free to adjust themselves. We show that curvature favors phase segregation. Our model predicts that membranes decorated with polymeric chains exhibit new shape bifurcations without equivalent in fixed density systems. Received: 26 November 2002 / Accepted: 2 April 2003 / Published online: 12 May 2003 RID="a" ID="a"e-mail: nicolas@drfmc.ceng.cea.fr RID="b" ID="b"e-mail: bfourcade@cea.fr     

UCN production in superfluid helium

Ultra-cold neutrons (UCN) are produced in superfluid helium by single- and multi-phonon excitation. The UCN production rate density R _II via multiphonons can be larger than that by one-phonon excitation R _I being due to the dependence of the incident neutron spectral flux density dφ/dλ on the wavelength λ. Received: 28 March 2002 / Accepted: 19 December 2002 / Published online: 11 March 2003 RID="a" ID="a"e-mail: wschott@e18.physik.tu-muenchen.de RID="b" ID="b"On leave of absence from PNPI, Gatchina, Russia Communicated by T. Walcher     

Fine structure in the α-decay of radium isotopes with mass numbers 209-212

Radium isotopes with mass numbers from 209 to 212 have been produced by heavy-ion fusion reactions ²⁰⁴Pb( ¹²C, xn) ^216-Ra. Radioactive decay properties were investigated by means of α- and α-γ-spectroscopy after in-flight separation of the evaporation residues from the projectile beam by the velocity filter SHIP and implantation into a 16-strip position-sensitive Si detector. For the even-even nuclei ^210,212Ra we identified α transitions into the first-excited 2⁺-state of the daughter nuclei ^206,208Rn. Weak α transitions into excited levels of the odd-A daughter nuclei ^205,207Rn were also observed. Received: 19 August 2002 / Accepted: 6 November 2002 / Published online: 18 February 2003 RID="a" ID="a"e-mail: f.p.hessberger@gsi.de Communicated by D. Guerreau     

Identities between q-hypergeometric and hypergeometric integrals of different dimensions

Given complex numbers <em>mem>₁,<em>lem>₁ and nonnegative integers <em>mem>₂,<em>lem>₂, such that <em>mem>₁+<em>mem>₂=<em>lem>₁+<em>lem>₂, for any <em>aem>,<em>bem>=0,&hellip;,min(<em>mem>₂,<em>lem>₂) we define an <em>lem>₂-dimensional Barnes type <em>qem>-hypergeometric integral <em>Iem>_{<em>aem>,<em>bem>}(<em>zem>,<em>μem>;<em>mem>₁,<em>mem>₂,<em>lem>₁,<em>lem>₂) and an <em>lem>₂-dimensional hypergeometric integral <em>Jem>_{<em>aem>,<em>bem>}(<em>zem>,<em>μem>;<em>mem>₁,<em>mem>₂,<em>lem>₁,<em>lem>₂). The integrals depend on complex parameters <em>zem> and <em>μem>. We show that <em>Iem>_{<em>aem>,<em>bem>}(<em>zem>,<em>μem>;<em>mem>₁,<em>mem>₂,<em>lem>₁,<em>lem>₂) equals <em>Jem>_{<em>aem>,<em>bem>}(<em>eem>^<em>μem>,<em>zem>;<em>lem>₁,<em>lem>₂,<em>mem>₁,<em>mem>₂) up to an explicit factor, thus establishing an equality of <em>lem>₂-dimensional <em>qem>-hypergeometric and <em>mem>₂-dimensional hypergeometric integrals. The identity is based on the eight="17" border="0" style="vertical-align:bottom" width="60" alt="View the MathML source" title="View the MathML source" src="http://ars.els-cdn.com/content/image/1-s2.0-S0001870804000593-si1.gif"> duality for the <em>qKZem> and dynamical difference equations.     

Some applications of free Fisher information on frame theory

We introduce the notion of operator-valued free Fisher information with respect to a positive map of a random variable in an operator-valued noncommutative probability space and point out its close relations to the modular frames arising from conditional expectations. Then we can apply this notion on the study of frame theory, especially on the disjointness problem of modular frames arising from conditional expectations.     

On a conjecture of S.P. Robinson

In his thesis, S.P. Robinson made a conjecture concerning the polynomials

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Molecular dynamics of hyperbranched polyesters in the confinement of thin films

Broadband Dielectric Spectroscopy is employed to investigate the molecular dynamics in thin films of hyperbranched polyesters (type AB₁B₂, with -OH and -OCOCH₃ as terminal groups). Three relaxation processes are detected: alpha, beta and gamma. While the latter two are not influenced by the confinement, a pronounced effect is observed on the alpha relaxation: with decreasing film thickness the slower relaxation modes of the dynamic glass transition are gradually suppressed, resulting in an increase of the average relaxation rate and in a linear decrease of the dielectric strength. This is attributed to an immobilization in confinement of the polymeric segments located at the periphery of the hyperbranched macromolecular structures.