Magnetic-Island Contraction and Particle Acceleration in Simulated Eruptive Solar Flares

The mechanism that accelerates particles to the energies required to produce the observed high-energy impulsive emission in solar flares is not well understood. Drake et al. (2006) proposed a mechanism for accelerating electrons in contracting magnetic islands formed by kinetic reconnection in multi-layered current sheets. We apply these ideas to sunward-moving flux ropes (2.5D magnetic islands) formed during fast reconnection in a simulated eruptive flare. A simple analytic model is used to calculate the energy gain of particles orbiting the field lines of the contracting magnetic islands in our ultrahigh-resolution 2.5D numerical simulation. We find that the estimated energy gains in a single island range up to a factor of five. This is higher than that found by Drake et al. for islands in the terrestrial magnetosphere and at the heliopause, due to strong plasma compression that occurs at the flare current sheet. In order to increase their energy by two orders of magnitude and plausibly account for the observed high-energy flare emission, the electrons must visit multiple contracting islands. This mechanism should produce sporadic emission because island formation is intermittent. Moreover, a large number of particles could be accelerated in each magnetohydrodynamic-scale island, which may explain the inferred rates of energetic-electron production in flares. We conclude that island contraction in the flare current sheet is a promising candidate for electron acceleration in solar eruptions.Comment: Accepted for publication in The Astrophysical Journal (2016

Topologically decoherence-protected qubits with trapped ions

We show that trapped ions can be used to simulate a highly symmetrical Hamiltonian with eingenstates naturally protected against local sources of decoherence. This Hamiltonian involves long range coupling between particles and provides a more efficient protection than nearest neighbor models discussed in previous works. Our results open the perspective of experimentally realizing in controlled atomic systems, complex entangled states with decoherence times up to nine orders of magnitude longer than isolated quantum systems.Comment: 4 page

Gas-dynamic shock heating of post-flare loops due to retraction following localized, impulsive reconnection

We present a novel model in which shortening of a magnetic flux tube following localized, three-dimensional reconnection generates strong gas-dynamic shocks around its apex. The shortening releases magnetic energy by progressing away from the reconnection site at the Alfven speed. This launches inward flows along the field lines whose collision creates a pair of gas-dynamic shocks. The shocks raise both the mass density and temperature inside the newly shortened flux tube. Reconnecting field lines whose initial directions differ by more that 100 degrees can produce a concentrated knot of plasma hotter that 20 MK, consistent with observations. In spite of these high temperatures, the shocks convert less than 10% of the liberated magnetic energy into heat - the rest remains as kinetic energy of bulk motion. These gas-dynamic shocks arise only when the reconnection is impulsive and localized in all three dimensions; they are distinct from the slow magnetosonic shocks of the Petschek steady-state reconnection model

The TSS-1 mission: Results on satellite charging

In the present paper we first give a short account of the mission TSS-1 flown on the Shuttle sts-46 in August 1992 and its basic electrical configurations. We then show some results obtained from the experiment RETE on board the satellite which are relevant for the issue of satellite charging

Discovery of a Nearby Low-Surface-Brightness Spiral Galaxy

During the course of a search for compact, isolated gas clouds moving with anomalous velocities in or near our own Galaxy (Braun and Burton 1998 A&A, in press), we have discovered, in the data of the Leiden/Dwingeloo survey (Hartmann and Burton 1997, Atlas of Galactic Neutral Hydrogen, CUP) of Galactic hydrogen, the HI signature of a large galaxy, moving at a recession velocity of 282 km/s, with respect to our Galaxy. Deep multicolor and spectroscopic optical observations show the presence of star formation in scattered HII regions; radio HI synthesis interferometry confirms that the galaxy is rich in HI and has the rotation signature of a spiral galaxy; a submillimeter observation failed to detect the CO molecule. The radio and optical evidence combined suggest its classification as a low-surface-brightness spiral galaxy. It is located in close spatial and kinematic proximity to the galaxy NGC 6946. The newly-discovered galaxy, which we call Cepheus 1, is at a distance of about 6 Mpc. It is probably to be numbered amongst the nearest few LSB spirals.Comment: 13 page LaTeX, requires aastex, 4 GIF figures. Accepted for publication in the AJ, January 199

Efeito do manejo da água e da ração ao desmame sobre o intervalo desmame-cio fértil e o número de leitões nascidos.

bitstream/item/58891/1/CUsersPiazzonDocuments136.pd

Double-lambda microscopic model for entangled light generation by four-wave-mixing

Motivated by recent experiments, we study four-wave-mixing in an atomic double-{\Lambda} system driven by a far-detuned pump. Using the Heisenberg-Langevin formalism, and based on the microscopic properties of the medium, we calculate the classical and quantum properties of seed and conju- gate beams beyond the linear amplifier approximation. A continuous variable approach gives us access to relative-intensity noise spectra that can be directly compared to experiments. Restricting ourselves to the cold-atom regime, we predict the generation of quantum-correlated beams with a relative-intensity noise spectrum well below the standard quantum limit (down to -6 dB). Moreover entanglement between seed and conjugate beams measured by an inseparability down to 0.25 is expected. This work opens the way to the generation of entangled beams by four-wave mixing in a cold atomic sample.Comment: 11 pages, 6 figures, submitted to PR

Comportamento de suínos suplementados com ractopamina.

Projeto: 02.06.01.001