A Hierarchical Relationship between the Fluence Spectra and CME Kinematics in Large Solar Energetic Particle Events: A Radio Perspective

We report on further evidence that solar energetic particles are organized by the kinematic properties of coronal mass ejections (CMEs)[1]. In particular, we focus on the starting frequency of type II bursts, which is related to the distance from the Sun where the radio emission starts. We find that the three groups of solar energetic particle (SEP) events known to have distinct values of CME initial acceleration, also have distinct average starting frequencies of the associated type II bursts. SEP events with ground level enhancement (GLE) have the highest starting frequency (107 MHz), while those associated with filament eruption (FE) in quiescent regions have the lowest starting frequency (22 MHz); regular SEP events have intermediate starting frequency (81 MHz). Taking the onset time of type II bursts as the time of shock formation, we determine the shock formation heights measured from the Sun center. We find that the shocks form on average closest to the Sun (1.51 Rs) in GLE events, farthest from the Sun in FE SEP events (5.38 Rs), and at intermediate distances in regular SEP events (1.72 Rs). Finally, we present the results of a case study of a CME with high initial acceleration (~3 km s^-2) and a type II radio burst with high starting frequency (~200 MHz) but associated with a minor SEP event. We find that the relation between the fluence spectral index and CME initial acceleration continues to hold even for this minor SEP event.Comment: 11 pages, 7 figures, 1 table, to appear in Journal of Physics: Conference Series (JPCS), Proceedings of the 16th Annual International Astrophysics Conference held in Santa Fe, NM, 201

Different Power-law Indices in the Frequency Distributions of Flares with and without Coronal Mass Ejections

We investigated the frequency distributions of flares with and without coronal mass ejections (CMEs) as a function of flare parameters (peak flux, fluence, and duration of soft X-ray flares). We used CMEs observed by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) mission and soft X-ray flares (C3.2 and above) observed by the GOES satellites during 1996 to 2005. We found that the distributions obey a power-law of the form: dN/dX~X^-alpha, where X is a flare parameter and dN is the number of events recorded within the interval [X, X+dX]. For the flares with (without) CMEs, we obtained the power-law index alpha=1.98+-0.05 (alpha=2.52+-0.03) for the peak flux, alpha=1.79+-0.05 (alpha=2.47+-0.11) for the fluence, and alpha=2.49+-0.11 (alpha=3.22+-0.15) for the duration. The power-law indices for flares without CMEs are steeper than those for flares with CMEs. The larger power-law index for flares without CMEs supports the possibility that nanoflares contribute to coronal heating.Comment: 4 pages, 2 figures embedded, accepted for publication in ApJ

Quantum wells with atomically smooth interfaces

By a cleaved-edge overgrowth method with molecular beam epitaxy and a (110) growth-interrupt-anneal, we have fabricated a GaAs quantum well exactly 30 monolayers thick bounded by atomically smooth AlGaAs hetero-interfaces without atomic roughness. Micro-photoluminescence imaging of this quantum well indeed shows spatially uniform and spectrally sharp emission over areas of several tens of $\mu$m in extent. By adding a fractional GaAs monolayer to our quantum well we are able to study the details of the atomic step-edge kinetics responsible for flat interface formation.Comment: 4 pages, 3 figures, revTex

How policy changes affected cocoa sectors in sub-Saharan African countries

Structural adjustment programs in sub-Saharan African countries in the 1980s removed trade restrictions, price controls, and export taxes and abolished state-owned commodity marketing bodies. The authors studied the effects of these policy changes on the coca sector, using a global econometric model specifying major producer countries through the vintage-capital approach. They focused on Ghana and Nigeria (major cocoa producers that undertook structural adjustment programs), as well as on Cote d'Ivoire and Cameroon. The impact on world cocoa prices of structural adjustment programs in Ghana and Nigeria was relatively small. The results imply that, without structural adjustment programs in Ghana and Nigeria, world cocoa prices in the late 1980s would have been about US$1,060/ton (in 1985 constant dollars), instead of US$850/ton. So, without the structural adjustment programs, 1989-90 world prices in real terms would have been about 45 percent lower than they were in the early 1980s, compared with an actual decline of 55 percent. Much more important in depressing prices in this period was the rapid increase in production in Brazil, Cote d'Ivoire, Indonesia, and Malaysia (which together accounted for about 75 percent of the increased production in that decade). That increased production resulted largely from tree planting in response to higher world cocoa prices in the late 1970s -- and subsequent increases in productivity. The results of counterfactual simulations suggest that cocoa production in Ghana would have been at almost half its 1989-90 level if Ghana had not implemented its structural adjustment program. The producers'surplus would have been lower without the program, and the government's budget deficit would have been unsustainable. The effects of the structural adjustment program in Nigeria are mixed. The simulation results show lower cocoa production but higher government revenue without the reforms. But the program was evaluated only three years after the reforms, so the full effects on production had not been realized. The structural adjustment programs in Ghana and Nigeria had a negative effect on other cocoa-producing countries in sub-Saharan Africa and the rest of the world -- producing an estimated loss (in government revenue from cocoa exports and producer surplus) of about 15 percent in other sub-Saharan African countries. Results show that both Cote d'Ivoire and Cameroon would have been better off had they set export taxes at a higher level (closer to an estimated"optimal"level) at the same time that they depreciated the real exchange rate. Producer prices could have been sustained at their earlier higher level, or even raised, without hurting government revenues. Structural adjustment programs in Ghana and Nigeria had a negative effect on producers in other countries, but not adopting such policies would have been economically irrational, contend the authors.Environmental Economics&Policies,Economic Theory&Research,Economic Stabilization,Access to Markets,Markets and Market Access

Ground Level Enhancement in the 2014 January 6 Solar Energetic Particle Event

We present a study of the 2014 January 6 solar energetic particle (SEP) event, which produced a small ground level enhancement (GLE), making it the second GLE of this unusual solar cycle 24. This event was primarily observed by the South Pole neutron monitors (increase of ~2.5%) whereas a few other neutron monitors recorded smaller increases. The associated coronal mass ejection (CME) originated behind the western limb and had the speed of 1960 km/s. The height of the CME at the start of the associated metric type II radio burst, which indicates the formation of a strong shock, was measured to be 1.61 Rs using a direct image from STEREO-A/EUVI. The CME height at the time of GLE particle release (determined using the South Pole neutron monitor data) was directly measured as 2.96 Rs, from the STEREO-A/COR1 white-light observations. These CME heights are consistent with those obtained for the GLE71, the only other GLE of the current cycle as well as cycle-23 GLEs derived using back-extrapolation. GLE72 is of special interest because it is one of the only two GLEs of cycle 24, one of the two behind-the-limb GLEs and one of the two smallest GLEs of cycles 23 and 24

One-dimensional continuum and exciton states in quantum wires

High-quality T-shaped quantum wires are fabricated by cleaved-edge overgrowth with the molecular beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal. Characterization by micro-photoluminescence (PL) and PL excitation (PLE) spectroscopy at 5 K reveals high uniformity, a sharp spectral width, and a small Stokes shift of one-dimensional (1-D) excitons. The PLE spectrum for 1-D states shows a large peak of ground-state excitons and a small absorption band ascribed to 1-D continuum states with an onset at 11 meV above the exciton peak.Comment: 4 pages, 4 figures, RevTe

The Peculiar Behavior of Halo Coronal Mass Ejections in Solar Cycle 24

We report on a remarkable finding that the halo coronal mass ejections (CMEs) in cycle 24 are more abundant than in cycle 23, although the sunspot number in cycle 24 has dropped by about 40%. We also find that the distribution of halo-CME source locations is different in cycle 24: the longitude distribution of halos is much flatter with the number of halos originating at central meridian distance >/=60 degrees twice as large as that in cycle 23. On the other hand, the average speed and the associated soft X-ray flare size are the same in the two cycles, suggesting that the ambient medium into which the CMEs are ejected is significantly different. We suggest that both the higher abundance and larger central meridian longitudes of halo CMEs can be explained as a consequence of the diminished total pressure in the heliosphere in cycle 24 (Gopalswamy et al. 2014). The reduced total pressure allows CMEs expand more than usual making them appear as halos.Comment: 12 pages, 5 figures, accepted for publication in the Astrophysical Journal Letters, April 7, 201