Observation of Postsoliton Expansion Following Laser Propagation through an Underdense Plasma

The expansion of electromagnetic postsolitons emerging from the interaction of a 30 ps, 3 x 10(18) W cm(-2) laser pulse with an underdense deuterium plasma has been observed up to 100 ps after the pulse propagation, when large numbers of postsolitons were seen to remain in the plasma. The temporal evolution of the postsolitons has been accurately characterized with a high spatial and temporal resolution. The observed expansion is compared to analytical models and three-dimensional particle-in-cell results, revealing a polarization dependence of the postsoliton dynamics.

Combined R-matrix eigenstate basis set and finite-difference propagation method for the time-dependent Schrodinger equation: The one-electron case

In this work we present the theoretical framework for the solution of the time-dependent Schrödinger equation (TDSE) of atomic and molecular systems under strong electromagnetic fields with the configuration space of the electron’s coordinates separated over two regions; that is, regions I and II. In region I the solution of the TDSE is obtained by an R-matrix basis set representation of the time-dependent wave function. In region II a grid representation of the wave function is considered and propagation in space and time is obtained through the finite-difference method. With this, a combination of basis set and grid methods is put forward for tackling multiregion time-dependent problems. In both regions, a high-order explicit scheme is employed for the time propagation. While, in a purely hydrogenic system no approximation is involved due to this separation, in multielectron systems the validity and the usefulness of the present method relies on the basic assumption of R-matrix theory, namely, that beyond a certain distance (encompassing region I) a single ejected electron is distinguishable from the other electrons of the multielectron system and evolves there (region II) effectively as a one-electron system. The method is developed in detail for single active electron systems and applied to the exemplar case of the hydrogen atom in an intense laser field.

Nonlinear propagation of electromagnetic waves in negative-refraction-index composite materials

We investigate the nonlinear propagation of electromagnetic waves in left-handed materials. For this purpose, we consider a set of coupled nonlinear Schrodinger (CNLS) equations, which govern the dynamics of coupled electric and magnetic field envelopes. The CNLS equations are used to obtain a nonlinear dispersion, which depicts the modulational stability profile of the coupled plane-wave solutions in left-handed materials. An exact (in)stability criterion for modulational interactions is derived, and analytical expressions for the instability growth rate are obtained.

Nonlinear propagation of modulated ion-acoustic plasma waves in the presence of an electron beam

Theoretical and numerical studies are presented of the amplitude modulation of ion-acoustic waves (IAWs) in a plasma consisting of warm ions, Maxwellian electrons, and a cold electron beam. Perturbations parallel to the carrier IAW propagation direction have been investigated. The existence of four distinct linear ion acoustic modes is shown, each of which possesses a different behavior from the modulational stability point of view. The stability analysis, based on a nonlinear Schrodinger equation (NLSE) reveals that the IAW may become unstable. The stability criteria depend on the IAW carrier wave number, and also on the ion temperature, the beam velocity and the beam electron density. Furthermore, the occurrence of localized envelope structures (solitons) is investigated, from first principles. The numerical analysis shows that the two first modes (essentially IAWs, modified due to the beam) present a complex behavior, essentially characterized by modulational stability for large wavelengths and instability for shorter ones. Dark-type envelope excitations (voids, holes) occur in the former case, while bright-type ones (pulses) appear in the latter. The latter two modes are characterized by an intrinsic instability, as the frequency develops a finite imaginary part for small ionic temperature values. At intermediate temperatures, both bright- and dark-type excitations may exist, although the numerical landscape is intertwined between stability and instability regions.(c) 2006 American Institute of Physics.

Nonlinear perpendicular propagation of ordinary mode electromagnetic wave packets in pair plasmas and electron-positron-ion plasmas

The nonlinear amplitude modulation of electromagnetic waves propagating in pair plasmas, e.g., electron-positron or fullerene pair-ion plasmas, as well as three-component pair plasmas, e.g., electron-positron-ion plasmas or doped (dusty) fullerene pair-ion plasmas, assuming wave propagation in a direction perpendicular to the ambient magnetic field, obeying the ordinary (O-) mode dispersion characteristics. Adopting a multiple scales (reductive perturbation) technique, a nonlinear Schrodinger-type equation is shown to govern the modulated amplitude of the magnetic field (perturbation). The conditions for modulation instability are investigated, in terms of relevant parameters. It is shown that localized envelope modes (envelope solitons) occur, of the bright- (dark-) type envelope solitons, i.e., envelope pulses (holes, respectively), for frequencies below (above) an explicit threshold. Long wavelength waves with frequency near the effective pair plasma frequency are therefore unstable, and may evolve into bright solitons, while higher frequency (shorter wavelength) waves are stable, and may propagate as envelope holes.(c) 2007 American Institute of Physics.

Clonal characteirization of sporadic cribriform-morular variant of papillary thyroid carcinoma by laser microdissection based APC mutation analysis

Cribriform-morular variant (C-MV) of papillary thyroid carcinoma (PTC) is a rare and unusual neoplasm composed of multiple histologic components, including cribriform, papillary, solid, tall columnar, and morular patterns. Analyses of gross C-MV of PTC lesions has linked adenomatous polyposis coli (APC) mutations to its pathogenesis; however, the extent of involvement of mutations in the development Of individual components is unclear We report on bidirectional sequencing of the mutation cluster region (codons 1032-1565) of the APC gene in individually laser-microdissected components of a previously unreported C-MV of PTC. A silent Thr1493Thr gene variant was found in all tumoral components, whereas a 5-base-pair frameshift deletion at codon 1309 was identified only in the morules. Neither variant was observed in matched normal thyroid tissue. These results show the histologic components of C-MV of PTC to have some common mutational background, although additional somatic mutations may be involved in the development of morular structures.

Domain Wall Propagation in Meso and Nanoscale Ferroelectrics

As part of an ongoing programme to evaluate the extent to which external morphology alters domain wall mobility in ferroelectrics, the electrical switching characteristics of single-crystal BaTiO3 nanorods and thin film plates have been measured and compared. It was found that ferroelectric nanorods were more readily switched than thin plates; increasing the shape constraint therefore appears to enhance switchability. This observation is broadly consistent with previous work, in which local notches patterned along the length of nanorods enhanced switching (McMillen et al 2010 Appl. Phys. Lett. 96 042904), while antinotches had the opposite effect (McQuaid et al 2010 Nano Lett. 10 3566). In this prior work, local enhancement and denudation of the electric field was expected at the notch and antinotch sites, respectively, and this was thought to be the reason for the differences in switching behaviour observed. However, for the simple nanorods and plates investigated here, no differences in the electric field distributions are expected. To rationalise the functional measurements, domain development during switching was imaged directly by piezoresponse force microscopy. A two-stage process was identified, in which narrow needle-like reverse domains initially form across the entire interelectrode gap and then subsequently coarsen through domain wall propagation perpendicular to the applied electric field. To be consistent with the electrical switching data, we suggest that the initial formation of needle domains occurs more readily in the nanorods than in the plates.

Hybrid image/ray-shooting UHF radio propagation predictor for populated indoor environments

A novel model for indoor wireless communication, based on a dual image and ray-shooting approach, is presented. The model, capable of improved site-specific indoor propagation prediction, considers multiple human bodies moving within the environment. In a modern office at 2.45GHz, the combined effect of pedestrian traffic and a moving receiver causes rapid temporal fading of up to 30dB.

Effects of external axial magnetic field on fast electron propagation

A scheme employing an external axial magnetic field is proposed to diagnose the intrinsic divergence of laser-generated fast electron beams, and this is studied numerically with hybrid simulations. The maximum beam radius of fast electrons increases with the initial divergence and decreases with the amplitude of the axial magnetic field. It is indicated that the intrinsic divergence of fast electrons can be inferred from measurements of the beam radius at different depth under the axial field. The proposed scheme here may be useful for future fast ignition experiments and in other applications of laser-generated fast electron beams. (C) 2011 American Institute of Physics. [doi:10.1063/1.3630925]