Discrete moving breather collisions in a Klein-Gordon chain of oscillators

We study the collisions of moving breathers with the same frequency, traveling with opposite directions within a Klein-Gordon chain of oscillators. Two types of collisions have been analyzed: symmetric and non-symmetric, head-on collisions. For low enough frequency the outcome is strongly dependent of the dynamical states of the two colliding breathers just before the collision. For symmetric collisions, several results can be observed: breather generation, with the formation of a trapped breather and two new moving breathers; breather reflection; generation of two new moving breathers; and breather fusion bringing about a trapped breather. For non-symmetric collisions some possible results are: breather generation, with the formation of three new moving breathers; breather fusion, originating a new moving breather; breather trapping with breather reflection; generation of two new moving breathers; and two new moving breathers traveling as a bound state. Breather annihilation has never been observed.     

One-dimensional statistical mechanics models with application to peapods

Quasi one-dimensional systems of molecules of C₆₀ encapsulated in (10/10) nanotubes were studied by both lattice-gas and Takashi–Gursey configurational integral methods of statistical mechanics for both open and capped finite nanotubes as well as infinite nanotubes. From well-established potentials, the energy, heat capacity compressibility, equation of state and absorption isotherms were computed as a function of temperature and molecular density. The existing theories were extended to include the calculation of clustering, and the number of clusters as a function of size was computed for a variety of temperatures and densities. For both models, all molecules are frozen into a single cluster, and increasing the temperature results in a break-up into smaller clusters. The corresponding heat capacity has a broad maximum, which is lower for the T–G model than for the lattice-gas model. The equations of state have a similar form in both models and are identical at low temperatures. The absorption isotherms show that filling of the tubes can take place at all temperatures of practical interest. Peapods are nearly ideal realizations of one-dimensional systems whose thermodynamic and structural properties can be accurately obtained by statistical mechanics. Received: 15 November 2001 / Accepted: 25 October 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +1-215/573-2128, E-mail: lag@sol1.lrsm.upenn.edu RID="**" ID="**"Present address: Dept. of Physics, North Carolina State University, Raleigh, NC 27695, USA     

Electrokinetic ‘ratchet’ pumps for microfluidics

The symmetry argument underlying ‘ratchet’ schemes for the motion of molecular motors and for selective transport of particles is shown to yield new means for the pumping of liquids. A practical realization consists in using surfaces bearing polar periodic arrays of electrodes addressed by an ac voltage difference. The resulting surface-induced pumping remains efficient under miniaturization and may find application in microfluidics. Received: 19 October 2001 / Accepted: 14 January 2002 / Published online: 22 April 2002     

FMR fine structure – A tool to investigate the spatial magnetic phase separation phenomena in manganites

An original approach is proposed to study the magnetic phase separation phenomenon. It is based on the registration of the noise‐like FMR Fine Structure (FMR FS) caused by the magnetic interparticle dipole–dipole interaction between spatially separated ferromagnetic regions. Data obtained for a La_0.7Pb_0.3MnO₃ single crystal point to the existence of spatially separated ferromagnetic regions. It is shown that FMR FS of the La_0.7Pb_0.3MnO₃ single crystal is temperature reversible and disappears at the maximum of magnetoresistance.

     

Nanotomographic examinations of ion tracks in cellulose nitrate by ion energy loss spectrometry

Received: 13 October 1997/Accepted: 25 August 1998     

Bridging of lateral nanoelectrodes with a metal particle chain

Received: 4 September 1998/Accepted: 9 September 1998     

Time-resolved 2-photon photoionization on metallic nanoparticles

Received: 16 October 1998 / Revised version: 11 December 1998     

Anomalous ferromagnetic behavior of CuO nanorods synthesized via hydrothermal method

Copper monoxide (CuO) nanorods of 30-40 nm in diameter and 100-200 nm in length were successfully synthesized using a hydrothermal reaction method in the presence of sodium citrate. On the basis of the morphology observation and X-ray diffraction patterns of the samples, a possible growth mechanism of the CuO nanorods was proposed. The magnetic properties of CuO nanorods were studied using a SQUID magnetometer and a vibrating sample magnetometer. It was interesting to note that the as-synthesized CuO nanorods showed an anomalous ferromagnetic behavior. The coercive force (H_c) for the CuO nanorods at and were estimated to be 331.39 and 175.88 Oe, respectively. The anomalous ferromagnetic behavior of the as-synthesized CuO nanorods was discussed in terms of the effect of the peculiar morphology.     

A miniaturized detector for high-resolution SEMPA

The basics of the scanning electron microscope with polarization analysis are briefly reviewed, emphasizing the achievable magnetic resolution and image contrast. The design of an optimized spin-polarization detector based on the well-established LEED scattering principle is presented. Results of first tests are reported. Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-40/42838-6368, E-mail: RFroemte@PHYSnet.Uni-Hamburg.de     

Scribing and cutting a blue LED wafer using a Q-switched. Nd:YAG laser

Chemical doping of single-wall carbon nanohorns (SWNHs) with K and Br was examined by vapor-phase reaction and studied by Raman scattering. Electro-chemical Li-ion doping using an electrolyte of LiAsF₆ in a mixture (1:1 by volume) of ethylene carbonate and diethyl carbonate was also carried out. All these experiments indicate that an anomalously small charge transfer occurs in saturation-doped SWNHs using these reagents, in sharp contrast to the behavior observed for single-wall carbon nanotube bundles and graphite. This rather remarkable result is not understood at present. Received: 13 July 2000 / Accepted: 14 July 2000 / Published online: 5 October 2000     

Methane analyzer based on TDL’s for measurements in the lower stratosphere: design and laboratory tests

This paper describes a tunable diode laser spectrometer for the in situ measurement of methane by high-resolution absorption spectroscopy of roto-vibrational lines, using a distributed feedback laser emitting in the near infrared (1.65 μm) and a multi-pass cell, with a two-tone detection scheme. The instrument was designed to be installed on the high-altitude aircraft M55 Geophysica, for high-sensitivity and high-temporal-resolution measurement of CH₄, both as a greenhouse gas and as a tracer of air-mass motion. The instrument-design criteria to achieve the compactness, low weight, and ruggedness necessary for automatic operation on an unpressurized high-altitude aircraft are reported. Results of the laboratory testing are also shown and discussed. Received: 1 April 2002 / Revised version: 28 May 2002 / Published online: 12 September 2002 RID="*" ID="*"Corresponding author. Fax: +39-050/313-7597, E-mail: damato@scintec.it     

Picosecond X-ray diffraction studies of laser-excited acoustic phonons in InSb

We have employed time-resolved X-ray diffraction with picosecond temporal resolution to measure the time-dependent rocking curves of laser-irradiated asymmetrically cut single InSb crystals. Coherent acoustic phonons were excited in the crystals by irradiation with 800-nm, 100-fs laser pulses at irradiances between 0.25 and 12 mJ/cm². The induced time-dependent strain profiles (corresponding to the coherent phonons) were monitored by diffracting collimated, monochromatic pulses of X-rays from the irradiated crystals. Recording of the diffracted radiation with a fast low-jitter X-ray streak camera resulted in an overall temporal resolution of better than 2 ps. The strain associated with the coherent phonons modifies the rocking curve of the crystal in a time-dependent manner, and the rocking curve is recorded by keeping the angle of incidence of the X-rays upon the crystal fixed, but varying the energy of the incident X-rays around a central energy of 8.453 keV (corresponding to the peak of the rocking curve of the unperturbed crystal). The observed time-dependent diffraction from the irradiated crystals is in reasonable agreement with simulations over a wide range of energies from the unperturbed rocking-curve peak. Received: 22 March 2002 / Revised version: 25 March 2002 / Published online: 6 June 2002     

High-stability reference setup for photoacoustic spectroscopy

2 laser at 9.676 μm. Received: 2 December 1996/Revised version: 2 April 1997     

Temperature dependence of the Josephson plasma resonance between vortex phases in the organic superconductor κ-(BEDT-TTF)2Cu(NCS)2

Using a microwave cavity perturbation technique, we probe different regimes of vortex interactions within the mixed superconducting state of the title compound. A Josephson plasma resonance (JPR) is observed which is sensitive to correlations between pancake vortices in adjacent layers. Previous investigations have conclusively identified a transition between liquid-like and pinned solid or glassy vortex phases. Here, we study this behavior via field-cooled experiments, obtaining further evidence for the transition. These experiments also allow us to probe the JPR over a wider range in temperature and magnetic field within the liquid phase than was previously reported. Theoretical models predict a squared plasma frequency which follows a power law dependence on magnetic field (B) within both phases, i.e. Our data agree well with this model, allowing a determination of the zero-field interlayer critical current density (J₀) and the parameter μ. Indeed, this parameter (μ) is seen to follow a dependence on frequency which is indicative of a continuous transition between the two vortex phases.     

Particle-plasmon decay-time determination by measuring the optical near-field’s autocorrelation: influence of inhomogeneous line broadening

A detailed analysis of the influence of inhomogeneous plasmon absorption band broadening on particle-plasmon decay-time determination by an interferometric autocorrelation method is reported. We present model calculations based on the representation of plasmons in an array of non-uniformly shaped particles by an ensemble of harmonic oscillators. Considering carefully the extent of the inhomogeneous broadening our theoretical treatment yields an unambiguous correlation between the autocorrelation function and the plasmon decay time. As an experimental example we find a plasmon decay time of 6 fs for a gold nanoparticle sample. Received: 24 November 1998 / Revised version: 12 March 1999 / Published online: 7 July 1999     

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     

Measurement of gas jet flow velocities using laser-induced electrostrictive gratings

We used time-resolved light scattering of cw probe laser radiation from laser-induced electrostrictive gratings for the determination of flow velocities in air at room temperature. Some possibilities of the technique have been experimentally demonstrated with submerged planar air jets in atmosphere, both for accumulated and single-shot measurements. The range of investigated flow velocities was 5–200 m/s. The method of data treatment and of the estimate of the experimental parameters is described. Received: 8 Febuary 2000 / Revised version: 2 May 2000 / Published online: 2 August 2000