Compressive high-frequency waves riding on an Alfv\'en/ion-cyclotron wave in a multi-fluid plasma

In this paper, we study the weakly-compressive high-frequency plasma waves which are superposed on a large-amplitude Alfv\'en wave in a multi-fluid plasma consisting of protons, electrons, and alpha particles. For these waves, the plasma environment is inhomogenous due to the presence of the low-frequency Alfv\'en wave with a large amplitude, a situation that may apply to space plasmas such as the solar corona and solar wind. The dispersion relation of the plasma waves is determined from a linear stability analysis using a new eigenvalue method that is employed to solve the set of differential wave equations which describe the propagation of plasma waves along the direction of the constant component of the Alfv\'en wave magnetic field. This approach also allows one to consider weak compressive effects. In the presence of the background Alfv\'en wave, the dispersion branches obtained differ significantly from the situation of a uniform plasma. Due to compressibility, acoustic waves are excited and couplings between various modes occur, and even an instability of the compressive mode. In a kinetic treatment, these plasma waves would be natural candidates for Landau-resonant wave-particle interactions, and may thus via their damping lead to particle heating.Comment: 15 pages, 5 figure

Multi-strand coronal loop model and filter-ratio analysis

We model a coronal loop as a bundle of seven separate strands or filaments. Each of the loop strands used in this model can independently be heated (near their left footpoints) by Alfv\'en/ion-cyclotron waves via wave-particle interactions. The Alfv\'en waves are assumed to penetrate the strands from their footpoints, at which we consider different wave energy inputs. As a result, the loop strands can have different heating profiles, and the differential heating can lead to a varying cross-field temperature in the total coronal loop. The simulation of TRACE observations by means of this loop model implies two uniform temperatures along the loop length, one inferred from the 171:195 filter ratio and the other from the 171:284 ratio. The reproduced flat temperature profiles are consistent with those inferred from the observed EUV coronal loops. According to our model, the flat temperature profile is a consequence of the coronal loop consisting of filaments, which have different temperatures but almost similar emission measures in the cross-field direction. Furthermore, when we assume certain errors in the simulated loop emissions (e.g., due to photometric uncertainties in the TRACE filters) and use the triple-filter analysis, our simulated loop conditions become consistent with those of an isothermal plasma. This implies that the use of TRACE/EIT triple filters for observation of a warm coronal loop may not help in determining whether the cross-field isothermal assumption is satisfied or not

Ray tracing of ion-cyclotron waves in a coronal funnel

Remote observations of coronal holes have strongly implicated the kinetic interactions of ion-cyclotron waves with ions as a principal mechanism for plasma heating and acceleration of the fast solar wind. In order to study these waves, a linear perturbation analysis is used in the work frame of the collisionless multi-fluid model. We consider a non-uniform background plasma describing a funnel region and use the ray tracing equations to compute the ray path of the waves as well as the spatial variation of their properties.Comment: 4 pages, 3 figures Modern Solar Facilities, Advanced Solar Science, Universitatsverlag Goettingen 200

Correlations between the proton temperature anisotropy and transverse high-frequency waves in the solar wind

Correlations are studied between the power density of transverse waves having frequencies between $0.01$ and $1$ normalized to the proton gyrofrequency in the plasma frame and the ratio of the perpendicular and parallel temperature of the protons. The wave power spectrum is evaluated from high-resolution 3D magnetic field vector components, and the ion temperatures are derived from the velocity distribution functions as measured in fast solar wind during the Helios-2 primary mission at radial distances from the Sun between 0.3~AU and 0.9~AU. From our statistical analysis, we obtain a striking correlation between the increases in the proton temperature ratio and enhancements in the wave power spectrum. Near the Sun the transverse part of the wave power is often found to be by more than an order of magnitude higher than its longitudinal counterpart. Also the measured ion temperature anisotropy appears to be limited by the theoretical threshold value for the ion-cyclotron instability. This suggests that high-frequency Alfv\'{e}n-cyclotron waves regulate the proton temperature anisotropy.Comment: Some references have been adde

Why is Price Discovery in Credit Default Swap Markets News-Specific?

Abstract: We analyse daily lead-lag patterns in US equity and credit default swap (CDS) returns. We first document that equity returns robustly lead CDS returns. However, we find that the CDSlag is due to common (and not firm-specific) news and arises predominantly in response to positive (instead of negative) equity market news. We provide an explanation for this newsspecific price discovery based on dealers in the CDS market exploiting their informational advantage vis-à-vis institutional investors with hedging demands. In support of this explanation we find that the CDS-lag and its newsspecificity are related to various firm-level proxies for hedging demand in the cross-section as well measures for economy-wide informational asymmetries over time.price discovery;CDS;hedging demand;informational asymmetries

The coronal convection

We study the hydrogen Lyman emission in various solar features - now including Lyman-alpha observations free from geocoronal absorption - and investigate statistically the imprint of flows and of the magnetic field on the line profile and radiance distribution. As a new result, we found that in Lyman-alpha rasters locations with higher opacity cluster in the cell interior, while the network has a trend to flatter profiles. Even deeper self reversals and larger peak distances were found in coronal hole spectra. We also compare simultaneous Lyman-alpha and Lyman-beta profiles. There is an obvious correspondence between asymmetry and redshift for both lines, but, most surprisingly, the asymmetries of Lyman-alpha and Lyman-beta are opposite. We conclude that in both cases downflows determine the line profile, in case of Lyman-alpha by absorption and in the case of Ly-beta by emission. Our results show that the magnetically structured atmosphere plays a dominating role in the line formation and indicate the presence of a persisting downflow at both footpoints of closed loops. We claim that this is the manifestation of a fundamental mass transportation process, which Foukal back in 1978 introduced as the 'coronal convection'.Comment: 8 pages, 5 figures, accepted for publication in Cent. Eur. Astrophys. Bul

Multi-strand coronal loop model and filter-ratio analysis

We model a coronal loop as a bundle of seven separate strands or filaments. Each of the loop strands used in this model can independently be heated (near their left footpoints) by Alfv\'en/ion-cyclotron waves via wave-particle interactions. The Alfv\'en waves are assumed to penetrate the strands from their footpoints, at which we consider different wave energy inputs. As a result, the loop strands can have different heating profiles, and the differential heating can lead to a varying cross-field temperature in the total coronal loop. The simulation of TRACE observations by means of this loop model implies two uniform temperatures along the loop length, one inferred from the 171:195 filter ratio and the other from the 171:284 ratio. The reproduced flat temperature profiles are consistent with those inferred from the observed EUV coronal loops. According to our model, the flat temperature profile is a consequence of the coronal loop consisting of filaments, which have different temperatures but almost similar emission measures in the cross-field direction. Furthermore, when we assume certain errors in the simulated loop emissions (e.g., due to photometric uncertainties in the TRACE filters) and use the triple-filter analysis, our simulated loop conditions become consistent with those of an isothermal plasma. This implies that the use of TRACE/EIT triple filters for observation of a warm coronal loop may not help in determining whether the cross-field isothermal assumption is satisfied or not

Uplink CoMP under a Constrained Backhaul and Imperfect Channel Knowledge

Coordinated Multi-Point (CoMP) is known to be a key technology for next generation mobile communications systems, as it allows to overcome the burden of inter-cell interference. Especially in the uplink, it is likely that interference exploitation schemes will be used in the near future, as they can be used with legacy terminals and require no or little changes in standardization. Major drawbacks, however, are the extent of additional backhaul infrastructure needed, and the sensitivity to imperfect channel knowledge. This paper jointly addresses both issues in a new framework incorporating a multitude of proposed theoretical uplink CoMP concepts, which are then put into perspective with practical CoMP algorithms. This comprehensive analysis provides new insight into the potential usage of uplink CoMP in next generation wireless communications systems.Comment: Submitted to IEEE Transactions on Wireless Communications in February 201

Systemic 5-fluorouracil induced lupus erythematosus: a review of the literature

Drug-induced subacute cutaneous lupus erythematosus (SCLE) is the most common subtype of drug-induced systemic lupus erythematosus and has been associated with more than 100 drugs. It presents weeks to months after initiation of the culprit medication. The eruption is typically in a photodistribution and it is marked by positive serology to anti-Ro (SSA) antibody. Systemic 5-fluorouracil (5-FU) is a less-common culprit of drug-induced SCLE and its occurrence is likely dependent on exposure to ultraviolet light. Herein, we present a review of drug-induced lupus induced by the pyrimidine analog, 5-FU, and its prodrugs, capecitabine and uracil-tegafur. The search was carried out using the following terms: (PubMed: keywords included drug-induced lupus, 5-fluorouracil, subacute cutaneous lupus erythematosus, capecitabine, uracil-tegafur, discoid lupus, systemic lupus erythematosus)

On nonlinear Alfv\'en-cyclotron waves in multi-species plasma

Large-amplitude Alfv\'en waves are ubiquitous in space plasmas and a main component of magnetohydrodynamic (MHD) turbulence in the heliosphere. As pump waves they are prone to parametric instability by which they can generate cyclotron and acoustic daughter waves. Here we revisit a related process within the framework of the multi-fluid equations for a plasma consisting of many species. The nonlinear coupling of the Alfv\'en wave to acoustic waves is studied, and a set of compressive and coupled wave equations for the transverse magnetic field and longitudinal electric field is derived for waves propagating along the mean-field direction. It turns out that slightly compressive Alfv\'en waves exert, through induced gyro-radius and kinetic-energy modulations, an electromotive force on the particles in association with a longitudinal electric field, which has a potential that is given by the gradient of the transverse kinetic energy of the particles gyrating about the mean field. This in turn drives electric fluctuations (sound and ion-acoustic waves) along the mean magnetic field, which can nonlinearly react back on the transverse magnetic field. Mutually coupled Alfv\'en-cyclotron-acoustic waves are thus excited, a nonlinear process that can drive a cascade of wave energy in the plasma and may generate compressive microturbulence. These driven electric fluctuations might have consequences for the dissipation of MHD turbulence and, thus, for the heating and acceleration of particles in the solar wind.Comment: 19 pages, accepted by Journal of Plasma Physics, in press, Link: http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=7908294&fulltextType=RA&fileId=S002237781000054