Magnetic loop emergence within a granule

We investigate the temporal evolution of magnetic flux emerging within a granule in the quiet-Sun internetwork at disk center. We combined IR spectropolarimetry performed in two Fe I lines at 1565 nm with speckle-reconstructed G-band imaging. We determined the magnetic field parameters by a LTE inversion of the full Stokes vector using the SIR code, and followed their evolution in time. To interpret the observations, we created a geometrical model of a rising loop in 3D. The relevant parameters of the loop were matched to the observations where possible. We then synthesized spectra from the 3D model for a comparison to the observations. We found signatures of magnetic flux emergence within a growing granule. In the early phases, a horizontal magnetic field with a distinct linear polarization signal dominated the emerging flux. Later on, two patches of opposite circular polarization signal appeared symmetrically on either side of the linear polarization patch, indicating a small loop-like structure. The mean magnetic flux density of this loop was roughly 450 G, with a total magnetic flux of around 3x10^17 Mx. During the ~12 min episode of loop occurrence, the spatial extent of the loop increased from about 1 to 2 arcsec. The middle part of the appearing feature was blueshifted during its occurrence, supporting the scenario of an emerging loop. The temporal evolution of the observed spectra is reproduced to first order by the spectra derived from the geometrical model. The observed event can be explained as a case of flux emergence in the shape of a small-scale loop.Comment: 10 pages, 13 figures; accepted for Astronomy and Astrophysics; ps and eps figures in full resolution are available at http://www.astro.sk/~koza/figures/aa2009_loop

Evaluating the performance of low-energy feed forward osmosis system for desalination using impaired and saline water sources

Forward Osmosis (FO) is a natural process of treating water or wastewater due to the difference in osmotic pressures. FO is a membrane separation technology, applicable to food processing, industrial wastewater treatment and seawater or brackish water desalination. The phenomena of FO processes occur whereby water molecules are driven across a semi-permeable membrane by an osmotic pressure gradient that is generated from a higher concentrate draw solution. FO processes can recover potable water resources from wastewater streams through the flow of pure water from a lower concen-trated feed solution towards higher concentrated draw solutions leaving behind pollutants, impurities, and salts in the semi-permeable membrane. This paper assesses the design, build and testing of a laboratory scaled Feed Forward Osmosis (FFO) system for treating river water collected from the River Medway, Kent, England. The FO process was a highly effective form of river water treatment and able to treat the River Water with high rejection rates of solutes (>90%). Experimental results showed that the FFO system can achieve a better performance when the molarity of the draw solution is higher. The average solute rejection rate of the FO membrane for both inorganic and organic compounds was 94.83 %. Moreover, the operation of the forward osmosis membrane illustrated that it has a lower fouling propensity and higher solute rejection ca-pabilities. The pilot scaled FFO system has the ability for greater salt rejection and lower electronic conductivity levels which resulted from the successful desalination of river water. A sodium chloride (NaCl) or saltwater draw solution performed posi-tively in inducing higher osmotic pressures with a substantial effect of lower energy requirements for the system. Lower en-ergy consumptions of the FFO system allow similar water treatment possibilities with energy savings potential. The FFO system showed to be an environmentally viable and economically feasible river water treatment technology

Observations of ozone production in a dissipating tropical convective cell during TC4

From 13 July–9 August 2007, 25 ozonesondes were launched from Las Tablas, Panama as part of the Tropical Composition, Cloud, and Climate Coupling (TC4) mission. On 5 August, a strong convective cell formed in the Gulf of Panama. World Wide Lightning Location Network (WWLLN) data indicated 563 flashes (09:00–17:00 UTC) in the Gulf. NO2 data from the Ozone Monitoring Instrument (OMI) show enhancements, suggesting lightning production of NOx. At 15:05 UTC, an ozonesonde ascended into the southern edge of the now dissipating convective cell as it moved west across the Azuero Peninsula. The balloon oscillated from 2.5–5.1 km five times (15:12–17:00 UTC), providing a unique examination of ozone (O3) photochemistry on the edge of a convective cell. Ozone increased at a rate of 1.6–4.6 ppbv/hr between the first and last ascent, resulting cell wide in an increase of (2.1–2.5)×106 moles of O3. This estimate agrees to within a factor of two of our estimates of photochemical lightning O3 production from the WWLLN flashes, from the radar-inferred lightning flash data, and from the OMI NO2 data (1.2, 1.0, and 1.7×106 moles, respectively), though all estimates have large uncertainties. Examination of DC-8 in situ and lidar O3 data gathered around the Gulf that day suggests 70–97% of the O3 change occurred in 2.5–5.1 km layer. A photochemical box model initialized with nearby TC4 aircraft trace gas data suggests these O3 production rates are possible with our present understanding of photochemistry

Deviations from plastic barriers in Bi2_2Sr2_2CaCu2_2O8+δ_{8+\delta} thin films

Resistive transitions of an epitaxial Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ thin film were measured in various magnetic fields ($H\parallel c$), ranging from 0 to 22.0 T. Rounded curvatures of low resistivity tails are observed in Arrhenius plot and considered to relate to deviations from plastic barriers. In order to characterize these deviations, an empirical barrier form is developed, which is found to be in good agreement with experimental data and coincide with the plastic barrier form in a limited magnetic field range. Using the plastic barrier predictions and the empirical barrier form, we successfully explain the observed deviations.Comment: 5 pages, 6 figures; PRB 71, 052502 (2005

Voltage control of magnetocrystalline anisotropy in ferromagnetic - semiconductor/piezoelectric hybrid structures

We demonstrate dynamic voltage control of the magnetic anisotropy of a (Ga,Mn)As device bonded to a piezoelectric transducer. The application of a uniaxial strain leads to a large reorientation of the magnetic easy axis which is detected by measuring longitudinal and transverse anisotropic magnetoresistance coefficients. Calculations based on the mean-field kinetic-exchange model of (Ga,Mn)As provide microscopic understanding of the measured effect. Electrically induced magnetization switching and detection of unconventional crystalline components of the anisotropic magnetoresistance are presented, illustrating the generic utility of the piezo voltage control to provide new device functionalities and in the research of micromagnetic and magnetotransport phenomena in diluted magnetic semiconductors.Comment: Submitted to Physical Review Letters. Updates version 1 to include a more detailed discussion of the effect of strain on the anisotropic magnetoresistanc