Collision frequencies and electron temperatures in the lower ionosphere

Collision frequencies and electron temperatures in lower ionospher

Observations of neutral circulation at mid-latitudes during the Equinox Transition Study

Measurements of ion drift velocity made by the Millstone Hill incoherent scatter radar have been used to calculate the meridional neutral wind velocity during the Sept. 17 to 24, 1984 period. Strong daytime southward neutral surges were observed during the magnetically disturbed days of September 19 and 23, in contrast to the small daytime winds obtained as expected during the magnetically quiet days. The surge on September 19 was also seen at Arecibo. In addition, two approaches have been used to calculate the meridional wind component from the radar-derived height of the F-layer electron density peak. Results confirm the wind surge, particularly when the strong electric fields measured during the disturbed days are included in the calculations. The two approaches for the F-layer peak wind calculations are applied to the radar-derived electron density peak height as a function of latitude to study the variation of the southward daytime surges with latitude

Quark-Gluon Plasma Fireball

Lattice-QCD results provide an opportunity to model, and extrapolate to finite baryon density, the properties of the quark-gluon plasma (QGP). Upon fixing the scale of the thermal coupling constant and vacuum energy to the lattice data, the properties of resulting QGP equations of state (EoS) are developed. We show that the physical properties of the dense matter fireball formed in heavy ion collision experiments at CERN-SPS are well described by the QGP-EoS we presented. We also estimate the properties of the fireball formed in early stages of nuclear collision, and argue that QGP formation must be expected down to 40A GeV in central Pb--Pb interactions.Comment: 10 pages, 9 postscript figures, 1 table, uses revtex, V3: introduced difference between n_f and n_s; fireball restframe energy corrected, references added. Publisched version in press Phys. Rev.

Determining the Magnetic Field Orientation of Coronal Mass Ejections from Faraday Rotation

We describe a method to measure the magnetic field orientation of coronal mass ejections (CMEs) using Faraday rotation (FR). Two basic FR profiles, Gaussian-shaped with a single polarity or "N"-like with polarity reversals, are produced by a radio source occulted by a moving flux rope depending on its orientation. These curves are consistent with the Helios observations, providing evidence for the flux-rope geometry of CMEs. Many background radio sources can map CMEs in FR onto the sky. We demonstrate with a simple flux rope that the magnetic field orientation and helicity of the flux rope can be determined 2-3 days before it reaches Earth, which is of crucial importance for space weather forecasting. An FR calculation based on global magnetohydrodynamic (MHD) simulations of CMEs in a background heliosphere shows that FR mapping can also resolve a CME geometry curved back to the Sun. We discuss implementation of the method using data from the Mileura Widefield Array (MWA).Comment: 22 pages with 9 figures, accepted for publication in Astrophys.

Relaxation and Landau-Zener experiments down to 100 mK in ferritin

Temperature-independent magnetic viscosity in ferritin has been observed from 2 K down to 100 mK, proving that quantum tunneling plays the main role in these particles at low temperature. Magnetic relaxation has also been studied using the Landau-Zener method making the system crossing zero resonant field at different rates, alpha=dH/dt, ranging from 10^{-5} to 10^{-3} T/s, and at different temperatures, from 150 mK up to the blocking temperature. We propose a new Tln(Delta H_{eff}/tau_0 alpha) scaling law for the Landau-Zener probability in a system distributed in volumes, where Delta H_{eff} is the effective width of the zero field resonance.Comment: 13 pages, 4 postscript figure

Millstone Hill measurements and TGCM simulation for the 30 May 1984 annular solar eclipse

On 30 May 1984, the Millstone Hill incoherent scatter radar was operated to gather data on the effects of the annular solar eclipse on the structure and dynamics of the ionosphere and thermosphere. The eclipse path was about 3 deg. south of Millstone which experienced a maximum obscuration of 86% at about 1705 UT. Both the zenith steerable antennas at Millstone were used in the experiment to collect data on the temporal evolution of the eclipse effects. This experiment represented the first opportunity at Millstone to collect data during an eclipse in the absence of a major magnetospheric disturbance which had previously made the unravelling of eclipse effects difficult. In addition, the configuration of the experiment and analysis of the data included a detailed examination of the effects on the neutral atmosphere. A major catalyst for this study was the opportunity to compare the results with the predictions made from the Thermospheric General Circulation Model (TGCM) at NCAR, as a calibration point for the model. The Arecibo and Sondrestrom radars also participated as part of a radar chain experiment. The analysis of the data from these stations is in progress; the initial results from Millstone Hill are presented

Efficiency Increase and Fuel Save Benefits of Combined Cycle Operation (Garri Power Plant as a Case Study)

Thermal power plants’ overall efficiency increase, and fuel consumption decrease draw worldwide researcher’s attention due to the limited resources and high cost of fossil fuel. Considering Al-Jaily power plant, the so-called Garri power plants 1 and 2 in Sudan as the case study, this paper compares overall plant efficiency and fuel save with the combined cycle and open cycle operation in which both plants could run. Evaluation of plant’s efficiency is based on the first law of thermodynamics. The results reveal advantage of the combined cycle operation mode in terms of efficiency increase, and on the other hand, in terms of fuel consumption decrease with the same amount of energy produced

A new layout optimization technique for interferometric arrays, applied to the MWA

Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21 cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed---even at the remote Australian location of the MWA (Murchison Widefield Array) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhance the PSF sidelobes and reduce the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution, and snapshot PSF for this array choice.Comment: 12 pages, 6 figures, 1 table. Accepted for publication in MNRA

Realisation of a low frequency SKA Precursor: The Murchison Widefield Array

The Murchison Widefield Array is a low frequency (80-300 MHz) SKA Precursor, comprising 128 aperture array elements distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper will focus on a brief discussion of the as-built MWA system, highlighting several novel characteristics of the instrument, and a brief progress report (as of June 2012) on the final construction phase. Practical completion of the MWA is expected in November 2012, with commissioning commencing from approximately August 2012 and operations commencing near mid 2013. A brief description of recent science results from the MWA prototype instrument is given