3D model of magnetic fields evolution in dwarf irregular galaxies

Radio observations show that magnetic fields are present in dwarf irregular galaxies (dIrr) and its strength is comparable to that found in spiral galaxies. Slow rotation, weak shear and shallow gravitational potential are the main features of a typical dIrr galaxy. These conditions of the interstellar medium in a dIrr galaxy seem to unfavourable for amplification of the magnetic field through the dynamo process. Cosmic-ray driven dynamo is one of the galactic dynamo model, which has been successfully tested in case of the spiral galaxies. We investigate this dynamo model in the ISM of a dIrr galaxy. We study its efficiency under the influence of slow rotation, weak shear and shallow gravitational potential. Additionally, the exploding supernovae are parametrised by the frequency of star formation and its modulation, to reproduce bursts and quiescent phases. We found that even slow galactic rotation with a low shearing rate amplifies the magnetic field, and that rapid rotation with a low value of the shear enhances the efficiency of the dynamo. Our simulations have shown that a high amount of magnetic energy leaves the simulation box becoming an efficient source of intergalactic magnetic fields.Comment: 4 pages, 4 figures, to appear in Proceedings of IAU Symp. 274, Advances in Plasma Astrophysics, ed. A. Bonanno, E. de Gouveia dal Pino and A. Kosoviche

Probing colored glass via qqˉq\bar{q} photoproduction

In this paper, we calculate the cross-section for the photoproduction of quark-antiquark pairs in the peripheral collision of ultra-relativistic nuclei, by treating the color field of the nuclei within the Color Glass Condensate model. We find that this cross-section is sensitive to the saturation scale $Q_s^2$ that characterizes the model. In particular, the transverse momentum spectrum of the produced pairs could be used to measure the properties of the color glass condensate.Comment: 25 pages LaTeX document - A reference and some footnotes added (version to appear in Nucl. Phys. A

Compensation of elevation angle variations in polarimetric brightness temperature measurements from airborne microwave radiometers

This paper presents a method for compensating the elevation angle fluctuations occurring in airborne radiometry due to aircraft roll and pitch. The correction is based on a radiative transfer model, and is demonstrated by real data from conical scans over the ocean, showing good results.Peer Reviewe

Analysis of multiscale radiometric data collected during the Cold Land Processes Experiment-1 (CLPX-1)

Histograms of brightness temperatures collected at 18.7 and 37 GHz over the Fraser and North Park Meso-Scale Areas during the Cold Land Processes Experiment by the NOAA Polarimetric Scanning Radiometer (PSR/A) airborne sensor are modelled by a log-normal distribution (Fraser, forested area) and by a bi-modal distribution (North Park, patchy-snow, non-forested area). The brightness temperatures are re-sampled over a range of resolutions to study the effects of sensor resolution on the shape of the distribution, on the values of the average brightness temperatures and standard deviations. The histograms become more uniform and the spatial information in the initial distribution is lost for a resolution larger than 5000 m, in both areas. The values of brightness temperatures obtained by re-sampling the PSR-A data at 25 km resolution are consistent with those recorded by the Advanced Microwave Scanning Radiometer (AMSR-E) and Special Sensor Microwave/Imager (SSM/I) satellite radiometers at similar resolutions

Low-x QCD physics from RHIC and HERA to the LHC

We present a summary of the physics of gluon saturation and non-linear QCD evolution at small values of parton momentum fraction $x$ in the proton and nucleus in the context of recent experimental results at HERA and RHIC. The rich physics potential of low-x studies at the LHC, especially in the forward region, is discussed and some benchmark measurements in pp, pA and AA collisions are introduced.Comment: Invited overview talk at the 2nd HERA-LHC Workshop (CERN) and 4th International Conference on Quarks and Nuclear Physics (QNP06, Madrid). 7 pages, 13 figs. To appear in EPJ-

The Eruption from a Sigmoidal Solar Active Region on 2005 May 13

This paper presents a multiwavelength study of the M8.0 flare and its associated fast halo CME that originated from a bipolar active region NOAA 10759 on 2005 May 13. The source active region has a conspicuous sigmoid structure at TRACE 171 A channel as well as in the SXI soft X-ray images, and we mainly concern ourselves with the detailed process of the sigmoid eruption as evidenced by the multiwavelength data ranging from Halpha, WL, EUV/UV, radio, and hard X-rays (HXRs). The most important finding is that the flare brightening starts in the core of the active region earlier than that of the rising motion of the flux rope. This timing clearly addresses one of the main issues in the magnetic eruption onset of sigmoid, namely, whether the eruption is initiated by an internal tether-cutting to allow the flux rope to rise upward or a flux rope rises due to a loss of equilibrium to later induce tether cutting below it. Our high time cadence SXI and Halpha data shows that the first scenario is relevant to this eruption. As other major findings, we have the RHESSI HXR images showing a change of the HXR source from a confined footpoint structure to an elongated ribbon-like structure after the flare maximum, which we relate to the sigmoid-to-arcade evolution. Radio dynamic spectrum shows a type II precursor that occurred at the time of expansion of the sigmoid and a drifting pulsating structure in the flare rising phase in HXR. Finally type II and III bursts are seen at the time of maximum HXR emission, simultaneous with the maximum reconnection rate derived from the flare ribbon motion in UV. We interpret these various observed properties with the runaway tether-cutting model proposed by Moore et al. in 2001.Comment: 10 pages, 10 figures, The Astrophysical Journal, accepted July, 200

On Board Accurate Calibration of Dual-Channel Radiometers Using Internal and External References

This paper presents a method for combining internal noise injection and external reference standard looks to accurately calibrate an airborne dual-channel radiometer. The method allows real-time estimation of the correct values of the radiometer gains and offsets, even for nontemperature-stabilized radiometers and with minimum loss of measurement time spent in external load measurement. Crosstalk and leakage introduced by the noise injection circuitry is also taken into account, thus providing high gain and offset estimation accuracy. The method was implemented on a National Oceanic and Atmospheric Administration airborne instrument, the Polarimetric Scanning Radiometer, which was used to obtain an extensive set of radiometric measurements over oceanic convection during CAMEX3 in August–September 1998

Geometrical Scaling and the Dependence of the Average Transverse Momentum on the Multiplicity and Energy for the ALICE Experiment

We review the recent ALICE data on charged particle multiplicity in p-p collisions, and show that it exhibits Geometrical Scaling (GS) with energy dependence given with characteristic exponent $\lambda=0.22$. Next, starting from the GS hypothesis and using results of the Color Glass Condensate effective theory, we calculate as a function $N_{\rm ch}$ including dependence on the scattering energy $W$. We show that $< p_{\text{T}}>$ both in p-p and p-Pb collisions scales in terms of scaling variable $(W/W_{0})^{\lambda/(2+\lambda)}% \sqrt{N_{\mathrm{ch}}/S_{\bot}}$ where $S_{\bot}$ is multiplicity dependent interaction area in the transverse plane. Furthermore, we discuss how the behavior of the interaction radius $R$ at large multiplicities affects the mean $p_{\mathrm{T}}$ dependence on $N_{\rm ch}$, and make a prediction that at high multiplicity should reach an energy independent limit.Comment: 15 pages, 7 figures, in v2 one figure and one reference added, v3: version accepted in Phys. Lett. B., some modifications, references adde

Cronin Effect at Different Rapidities at RHIC

Calculations of the nuclear modification factor, R_dAu, for pi^0 production in dAu collisions at s_NN^1/2 = 200 GeV are presented. The applied pQCD-improved parton model incorporates intrinsic k_T. Nuclear multiscattering and nuclear shadowing are considered in the Au nucleus. Theoretical results are displayed for midrapidity and high pseudorapidity (eta), and compared to preliminary PHENIX and BRAHMS data.Comment: Contributed to 17th International Conference on Ultra Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland, California, 11-17 Jan 200