Loss-free Transport Research Articles

Controlling fast electron transfer at the nano-scale by solitonic excitations along crystallographic axes

We present computational evidence of the possibility of fast, supersonic or subsonic, nearly loss-free transport of electrons bound to lattice solitons along crystallographic axes in two-dimensional anharmonic crystal lattices.

Multihop Field Trial of Optical Burst Switching Testbed With PLZT Optical Matrix Switch

We report 92-km 2-hop field trial of an optical burst-switching (OBS) network testbed, consisting of a (Pb, La)(Zr, Ti)O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (PLZT) space switching matrix and a contention-resolving wavelength converter. Owing to the low polarization-dependent loss of the PLZT switch, we achieve stable forwarding of 40/10-Gb/s mixed-bit-rate signals with wavelength conversion. We also perform Layer-2 evaluation at a line rate of 40 Gb/s by using specially developed Ether-frame media converters. Loss-free transport of encapsulated Ether-frames is demonstrated successfully over the 2-hop OBS field testbed.

Exciton Migration by Ultrafast Förster Transfer in Highly Doped Matrixes

The energy transfer between dye molecules and the mobility of the corresponding excitons are investigated in polymethyl methacrylate films highly doped with perylene bisimide dyes. The dynamics is measured by group delay corrected, femtosecond broad-band spectroscopy revealing the transfer route via absorption changes that are specific for the participating species. In films doped with 0.14 M perylene orange an ultrafast homotransfer between the dye molecules is found by analyzing the loss of the excitation-induced anisotropy. The process exhibits a stretched exponential time dependence which is characteristic for Förster energy transfer between immobilized molecules. The transfer time is 1.5 ps for an average transfer distance of 2.3 nm and results in a high mobility of the optically generated excitons. In addition, we find that the excitons move to perylene orange dimers, which have formed in low concentration during the sample preparation. The observed energy transfer time is slightly shorter than expected for a direct Förster transfer and indicates that exciton migration by multistep transfer between the monomers speeds up the transport to the dimers. In samples doped with perylene orange and perylene red heterotransfer to perylene red takes place with transfer times down to 600 fs. The mechanism is Förster transfer as demonstrated by the agreement with calculations assuming electric dipole interaction between immobilized and statistically distributed donor and acceptor units. The model predicts the correct time dependence and concentration scaling for highly doped as well as diluted samples. The results show that ultrafast exciton migration between dye molecules in highly doped matrixes is an attractive and efficient mechanism to transport and collect energy in molecular systems and organic electronic devices. Further optimization should lead to a loss-free transport over distances typical for the thickness of active layers in these systems.

Polished sapphire for ultracold-neutron guides

We show that polished sapphire allows one to efficiently reflect ultracold neutrons (UCN) at specular trajectories. The probability of specular UCN reflection at sapphire surface under typical experimental conditions was measured to be at least 99.8%. That could provide nearly loss-free transport of UCN between a source and an experimental installation at a distance of some 10 m. Polished sapphire can be used for specular neutron guides at steady and pulsed UCN sources. It can also be used in experimental installations, in particular, for building compact gravitational spectrometers and for study of the resonance transitions between neutron quantum states in the gravitational field.

Overcritical states in magnetically shielded superconductor strips

The flux-free current-carrying state of a superconductor strip with a reasonably high edge barrier against magnetic flux penetration is studied. It is shown that magnetic field conditioning by specially arranged ferromagnetic shields allows the strip to carry loss-free transport currents exceeding typical critical currents provided by pinning.

Overcritical states of a superconductor strip in a magnetic environment

A current-carrying superconducting strip partly penetrated by magnetic flux and surrounded by a bulk magnet of high permeability is considered. Two types of samples are studied: those with critical current controlled by an edge barrier dominating over the pinning, and those with high pinning-mediated critical current masking the edge barrier.It is shown for both cases that the current distribution in a central flux-free part of the strip is strongly affected by the actual shape of the magnetic surroundings. Explicit analytical solutions for the sheet current and self-field distributions are obtained which show that, depending on the geometry, the effect may suppress the total loss-free transport current of the strip or enhance it by orders of magnitude. The effect depends strongly on the shape of the magnet and its distance to the superconductor but only weakly on the magnetic permeability.

Dust in jupiter's magnetosphere: Effect on magnetospheric electrons and ions

The interaction of the Jovian energetic radiation belt electrons, and the Jovian plasma, with an ambient dust population is examined. Firstly the distribution of dust, ejected from Io, in the inner magnetosphere is calculated. Using the mass loss in submicron particles of ~13g/sec, which is required to model the intensity and shape of the Jovian ring in the model of Morfill etal. (1980b), it is possible to quantitatively calculate losses of magnetospheric ions and electrons due to direct collisions with charged dust particles as well as multiple Coulomb scattering with resultant losses in the Jovian atmosphere. It is shown that the magnitude and radial dependence of the losses are sufficient to explain the electron measurements, although the possibility that some other process may be more effective cannot be ruled out. The same dust population has, on the other hand, no significant effect on the plasma, which should therefore be transported essentially loss free, except within the Jovian ring, if there are no other processes involved. Comparison with the data shows that loss free transport outside the ring does indeed satisfy the measurement constraints.