Electron acceleration and parallel electric fields due to kinetic Alfvén waves in plasma with similar thermal and Alfvén speeds

We investigate electron acceleration due to shear Alfven waves in a collissionless plasma for plasma parameters typical of 4–5RE radial distance from the Earth along auroral field lines. Recent observational work has motivated this study, which explores the plasma regime where the thermal velocity of the electrons is similar to the Alfven speed of the plasma, encouraging Landau resonance for electrons in the wave fields. We use a self-consistent kinetic simulation model to follow the evolution of the electrons as they interact with a short-duration wave pulse, which allows us to determine the parallel electric field of the shear Alfven wave due to both electron inertia and electron pressure effects. The simulation demonstrates that electrons can be accelerated to keV energies in a modest amplitude sub-second period wave. We compare the parallel electric field obtained from the simulation with those provided by fluid approximations.

Squeeze flow viscoelasticity of electrorheological fluids based on microcrystalline cellulose

Dynamic viscoelasticity of electrorheological fluids based on microcrystalline cellulose/castor oil suspensions was experimentally investigated in squeeze flow. The dependence of storage modulus G' and loss modulus G" parallel to external electric field on electric fields and strain amplitudes is presented. The experiments show that, when external electric field is higher than the critical field, the viscoelasticity of the ER fluids converts from linear to nonlinear, and the ER fluids transfer from solid-like state to fluid state with the growth of strain amplitude. The influences of strain amplitude and oscillatory frequency on the nonlinearity of viscoelasticity were also studied.

Simulation of field-induced structural formation and transition in electromagnetorheological suspensions

A computer simulation method has been used to study the three-dimensional structural formation and transition of eleetromagnetorheological (EMR) suspensions under compatible electric and magnetic fields. When the fields are applied simultaneously and perpendicularly to each other, the particles rapidly arrange into single layer structures parallel to both fields. In each layer, there is a two-dimensional hexagonal lattice. The single layers then combine together to form thicker sheetlike structures. With the help of the thermal fluctuations, the thicker structures relax into three-dimensional close-packed structures, which may be face-centered cubic (fcc), hexagonal close-packed (hup) lattices, or, more probably, the mixture of them, depending on the initial configurations and the thermal fluctuations. On the other hand, if the electric field is applied first to induce the body-centered tetragonal (bct) columns in the system, and then the magnetic field is applied in the perpendicular direction, the bet to fee structure transition is observed in a very short time. Following that, the structure keeps on evolving due to the demagnetization effect and finally forms close-packed structures with fee and hcp lattice character. The simulation results are in agreement with the theoretical and experimental results.

Modeling the observed proton aurora and ionospheric convection responses to changes in the IMF clock angle: 2. Persistence of ionospheric convection

We apply a numerical model of time-dependent ionospheric convection to two directly driven reconnection pulses during a 15-min interval of southward IMF on 26 November 2000. The model requires an input magnetopause reconnection rate variation, which is here derived from the observed variation in the upstream IMF clock angle, q. The reconnection rate is mapped to an ionospheric merging gap, the MLT extent of which is inferred from the Doppler-shifted Lyman-a emission on newly opened field lines, as observed by the FUV instrument on the IMAGE spacecraft. The model is used to reproduce a variety of features observed during this event: SuperDARN observations of the ionospheric convection pattern and transpolar voltage; FUV observations of the growth of patches of newly opened flux; FUVand in situ observations of the location of the Open-Closed field line Boundary (OCB) and a cusp ion step. We adopt a clock angle dependence of the magnetopause reconnection electric field, mapped to the ionosphere, of the form Enosin4(q/2) and estimate the peak value, Eno, by matching observed and modeled variations of both the latitude, LOCB, of the dayside OCB (as inferred from the equatorward edge of cusp proton emissions seen by FUV) and the transpolar voltage FPC (as derived using the mapped potential technique from SuperDARN HF radar data). This analysis also yields the time constant tOCB with which the open-closed boundary relaxes back toward its equilibrium configuration. For the case studied here, we find tOCB = 9.7 ± 1.3 min, consistent with previous inferences from the observed response of ionospheric flow to southward turnings of the IMF. The analysis confirms quantitatively the concepts of ionospheric flow excitation on which the model is based and explains some otherwise anomalous features of the cusp precipitation morphology.

Coordinated ground-based, low altitude satellite and Cluster observations on global and local scales during a transient post-noon sector excursion of the magnetospheric cusp

On 14 January 2001, the four Cluster spacecraft passed through the northern magnetospheric mantle in close conjunction to the EISCAT Svalbard Radar (ESR) and approached the post-noon dayside magnetopause over Greenland between 13:00 and 14:00 UT During that interval, a sudden reorganisation of the high-latitude dayside convection pattern accurred after 13:20 UT most likely caused by a direction change of the Solar wind magnetic field. The result was an eastward and poleward directed flow-channel, as monitored by the SuperDARN radar network and also by arrays of ground-based magnetometers in Canada, Greenland and Scandinavia. After an initial eastward and later poleward expansion of the flow-channel between 13:20 and 13:40 UT, the four Cluster spacecraft, and the field line footprints covered by the eastward looking scan cycle of the Sondre Stromfjord incoherent scatter radar were engulfed by cusp-like precipitation with transient magnetic and electric field signatures. In addition, the EISCAT Svalbard Radar detected strong transient effects of the convection reorganisation, a poleward moving precipitation, and a fast ion flow-channel in association with the auroral structures that suddenly formed to the west and north of the radar. From a detailed analysis of the coordinated Cluster and ground-based data, it was found that this extraordinary transient convection pattern, indeed, had moved the cusp precipitation from its former pre-noon position into the late post-noon sector, allowing for the first and quite unexpected encounter of the cusp by the Cluster spacecraft. Our findings illustrate the large amplitude of cusp dynamics even in response to moderate solar wind forcing. The global ground-based data proves to be an invaluable tool to monitor the dynamics and width of the affected magnetospheric regions.

Non-Maxwellian ion velocity distributions observed using EISCAT

Recent observations from the EISCAT incoherent scatter radar have revealed bursts of poleward ion flow in the dayside auroral ionosphere which are consistent with the ionospheric signature of flux transfer events at the magnetopause. These bursts frequently contain ion drifts which exceed the neutral thermal speed and, because the neutral thermospheric wind is incapable of responding sufficiently rapidly, toroidal, non-Maxwellian ion velocity distributions are expected. The EISCAT observations are made with high time resolution (15 seconds) and at a large angle to the geomagnetic field (73.5°), allowing the non-Maxwellian nature of the distribution to be observed remotely for the first time. The observed features are also strongly suggestive of a toroidal distribution: characteristic spectral shape, increased scattered power (both consistent with reduced Landau damping and enhanced electric field fluctuations) and excessively high line-of-sight ion temperatures deduced if a Maxwellian distribution is assumed. These remote sensing observations allow the evolution of the distributions to be observed. They are found to be non-Maxwellian whenever the ion drift exceeds the neutral thermal speed, indicating that such distributions can exist over the time scale of the flow burst events (several minutes).

A new source of suprathermal O+ions near the dayside polar cap boundary

A new dayside source of O+ ions for the polar magnetosphere is described, and a statistical survey presented of upward flows of O+ ions using 2 years of data from the retarding ion mass spectrometer (RIMS) experiment on board DE 1, at geocentric distances below 3 RE and invariant latitudes above 40°. The flows are classified according to their spin angle distributions. It is believed that the spacecraft potential near perigee is generally less than +2 V, in which case the entire O+ population at energies below about 60 eV is sampled. Examples are given of field-aligned flow and of transversely accelerated “core” O+ ions; in the latter events a large fraction of the total O+ ion population has been transversely accelerated, and in some extreme cases all the observed ions (of all ion species) have been accelerated, and no residual cold population is observed (“toroidal” distributions). However, by far the most common type of O+ upflow seen by DE RIMS lies near the dayside polar cap boundary (particularly in the prenoon sector) and displays an asymmetric spin angle distribution. In such events the ions carry an upward heat flux, and strong upflow of all species is present (H+, He+, O+, O++, and N+ have all been observed with energies up to about 30 eV, but with the majority of ions below about 2 eV); hence, these have been termed upwelling ion events. The upwelling ions are embedded in larger regions of classical light ion polar wind and are persistently found under the following conditions: at geocentric distances greater than 1.4 RE; at all Kp in summer, but only at high Kp in winter. Low-energy conical ions (<30 eV) are only found near the equatorial edge of the events, the latitude of which moves equatorward with increasing Kp and is highly correlated with the location of field-aligned currents. The RIMS data are fully consistent with a “mass spectrometer effect,” whereby light ions and the more energetic O+ ions flow into the lobes and mantle and hence the far-tail plasma sheet, but lower-energy O+ is swept across the polar cap by the convection electric field, potentially acting as a source for the nightside auroral acceleration regions. The occurrence probability of upwelling ion events, as compared to those of low-altitude transversely accelerated core ions and of field-aligned flow, suggests this could be the dominant mechanism for supplying the nightside auroral acceleration region, and subsequently the ring current and near-earth plasma sheet, with ionospheric O+ ions. It is shown that the total rate of O+ outflow in upwelling ion events (greater than 10^25 s^{−1}) is sufficient for the region near the dayside polar cap boundary to be an important ionospheric heavy ion source.

A statistical evaluation of the field emission for copper oxide nanostructures

A statistical data analysis methodology was developed to evaluate the field emission properties of many samples of copper oxide nanostructured field emitters. This analysis was largely done in terms of Seppen-Katamuki (SK) charts, field strength and emission current. Some physical and mathematical models were derived to describe the effect of small electric field perturbations in the Fowler-Nordheim (F-N) equation, and then to explain the trend of the data represented in the SK charts. The field enhancement factor and the emission area parameters showed to be very sensitive to variations in the electric field for most of the samples. We have found that the anode-cathode distance is critical in the field emission characterization of samples having a non-rigid nanostructure. (C) 2007 Elsevier B.V. All rights reserved.

Static electric fields interfere in the viability of cells exposed to ionising radiation

Purpose: The interference of electric fields (EF) with biological processes is an issue of considerable interest. No studies have as yet been reported on the combined effect of EF plus ionising radiation. Here we report studies on this combined effect using the prokaryote Microcystis panniformis, the eukaryote Candida albicans and human cells. Materials and methods: Cultures of Microcystis panniformis (Cyanobacteria) in glass tubes were irradiated with doses in the interval 0.5-5kGy, using a 60Co gamma source facility. Samples irradiated with 3kGy were exposed for 2h to a 20Vcm-1 static electric field and viable cells were enumerated. Cultures of Candida albicans were incubated at 36C for 20h, gamma-irradiated with doses from 1-4kGy, and submitted to an electric field of 180Vcm-1. Samples were examined under a fluorescence microscope and the number of unviable (red) and viable (apple green fluorescence) cells was determined. For crossing-check purposes, MRC5 strain of lung cells were irradiated with 2 Gy, exposed to an electric field of 1250 V/cm, incubated overnight with the anti-body anti-phospho-histone H2AX and examined under a fluorescence microscope to quantify nuclei with -H2AX foci. Results: In cells exposed to EF, death increased substantially compared to irradiation alone. In C. albicans we observed suppression of the DNA repair shoulder. The effect of EF in growth of M. panniformis was substantial; the number of surviving cells on day-2 after irradiation was 12 times greater than when an EF was applied. By the action of a static electric field on the irradiated MRC5 cells the number of nuclei with -H2AX foci increased 40%, approximately. Conclusions: Application of an EF following irradiation greatly increases cell death. The observation that the DNA repair shoulder in the survival curve of C. albicans is suppressed when cells are exposed to irradiation+EF suggests that EF likely inactivate cellular recovering processes. The result for the number of nuclei with -H2AX foci in MRC5 cells indicates that an EF interferes mostly in the DNA repair mechanisms. A molecular ad-hoc model is proposed.

Anomalous dependence on the diffusion coefficients of the ionic relaxation time in electrolytes

We show, by using a numerical analysis, that the dynamic toward equilibrium for an electrolytic cell subject to a step-like external electric field is a multirelaxation process when the diffusion coefficients of positive and negative ions are different. By assuming that the diffusion coefficient of positive ions is constant, we observe that the number of involved relaxation processes increases when the diffusion coefficient of the negative ions diminishes. Furthermore, two of the relaxation times depend nonmonotonically on the ratio of the diffusion coefficients. This result is unexpected, because the ionic drift velocity, by means of which the ions move to reach the equilibrium distribution, increases with increasing ionic mobility.

Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory

The advent of the Auger Engineering Radio Array (AERA) necessitates the development of a powerful framework for the analysis of radio measurements of cosmic ray air showers. As AERA performs ""radio-hybrid"" measurements of air shower radio emission in coincidence with the surface particle detectors and fluorescence telescopes of the Pierre Auger Observatory, the radio analysis functionality had to be incorporated in the existing hybrid analysis solutions for fluorescence and surface detector data. This goal has been achieved in a natural way by extending the existing Auger Offline software framework with radio functionality. In this article, we lay out the design, highlights and features of the radio extension implemented in the Auger Offline framework. Its functionality has achieved a high degree of sophistication and offers advanced features such as vectorial reconstruction of the electric field, advanced signal processing algorithms, a transparent and efficient handling of FFTs, a very detailed simulation of detector effects, and the read-in of multiple data formats including data from various radio simulation codes. The source code of this radio functionality can be made available to interested parties on request. (C) 2011 Elsevier B.V. All rights reserved.

Infrared chiral anomaly at finite temperature

We study the Schwinger model at finite temperature and show that a temperature dependent chiral anomaly may arise from the long distance behavior of the electric field. At high temperature this anomaly depends linearly on the temperature T and is present not only in the two point function, but also in all even point amplitudes. (C) 2011 Elsevier B.V. All rights reserved.

Pressure-induced electrical and structural anomalies in Pb(1-x)Ca(x)TiO(3) thin films grown at various oxygen pressures by chemical solution route

Lead calcium titanate (Pb(1-x)Ca(x)TiO(3) or PCT) thin films have been thermally treated under different oxygen pressures, 10, 40 and 80 bar, by using the so-called chemical solution deposition method. The structural, morphological, dielectric and ferroelectric properties were characterized by x-ray diffraction, FT-infrared and Raman spectroscopy, atomic force microscopy and polarization-electric-field hysteresis loop measurements. By annealing at a controlled pressure of around 10 and 40 bar, well-crystallized PCT thin films were successfully prepared. For the sample submitted to 80 bar, the x-ray diffraction, Fourier transformed-infrared and Raman data indicated deviation from the tetragonal symmetry. The most interesting feature in the Raman spectra is the occurrence of intense vibrational modes at frequencies of around 747 and 820 cm(-1), whose presence depends strongly on the amount of the pyrochlore phase. In addition, the Raman spectrum indicates the presence of symmetry-breaking disorder, which would be expected for an amorphous (disorder) and mixed pyrochlore-perovskite phase. During the high-pressure annealing process, the crystallinity and the grain size of the annealed film decreased. This process effectively suppressed both the dielectric and ferroelectric behaviour. Ferroelectric hysteresis loop measurements performed on these PCT films exhibited a clear decrease in the remanent polarization with increasing oxygen pressure.

Adsorption Behavior of 5-Fluorouracil on Au(111): An In Situ STM Study

The biological effects of chemical substitution of DNA bases triggered several investigations of their physicochemical properties This paper studies the adsorption behavior of a halogenated uracil, 5-fluorouracil (5FU). at the electrochemical interface of Au(111) and sulfuric acid solution. Upon modulation of the electric field across the interface, four distinct phases could be inferred by means of cyclic voltammetry (CV) At negative potentials relative to the SCE electrode, limited by the threshold of hydrogen evolution, no molecular species could be detected by scanning tunneling microscopy (STM) at the reconstructed Au(111)-(23 x root 3) surface, indicating that any physisorbed molecules are randomly distributed Incursion into more positive potentials increases the surface population but doer not form any two-dimensional (2D) physisorbed ordered structure Instead, we observed metastable structures that are only detectable. on surfaces with high defect density At sufficiently high positive potentials. limited by gold oxidation, the molecules are chemisorbed in a (3 x 2 root 3) ordered structure. with the aromatic ring perpendicular to the surface We report the densest chemisorbed monolayer for pyrimidine-derivative molecules (area per molecule 0 14 +/- 0 04 nm(2)). A comparison of the adsorption behavior of uracil derivatives has been made based on recent results of chemical substitution and solvent effects. We propose that pi-stacking is enhanced when halogens are incorporated in the uracil structure, in a similar fashion to what is observed in then crystal structure