Matrix solutions of a noncommutative KP equation and a noncommutative mKP equation

Matrix solutions of a noncommutative KP and a noncommutative mKP equation which can be expressed as quasideterminants are discussed. In particular, we investigate interaction properties of two-soliton solutions.Comment: 2 figure

GITM‐Data Comparisons of the Depletion and Enhancement During the 2017 Solar Eclipse

The total solar eclipse of 21 August 2017 was simulated with the Global Ionosphere‐Thermosphere Model (GITM), and the results were compared with the total electron content (TEC) measurements provided by the Global Navigation Satellite System, as well as F2 layer peak electron density (NmF2) derived from six ionosondes. TEC decreased over North America by ~54.3% in the model and ~57.6% in measurements, and NmF2 decreased by ~20–50% in the model and ~40–60% in the measurements. GITM predicted a posteclipse enhancement of ~10% in TEC and NmF2, consistent with observations which suggested an increase of ~10–25% in TEC and ~10–40% in NmF2. GITM showed that the divergence of horizontal winds drove the increase in Oxygen after the eclipse allowing an increase in the ionization rate. The slower charge exchange due to both the decreased ion temperature and N2 density allowed an increase of O+ density in the F region also.Plain Language SummaryThe total solar eclipse of 21 August 2017 was explored with the Global Ionosphere‐Thermosphere Model, which simulates weather in space. The results were compared with ionospheric observations from the Global Navigation Satellite System and six ground‐based measurements. Both the model and data showed a decrease in ionospheric densities during the eclipse and an enhancement above what would happen without the eclipse after the passage of the moon. The analysis showed that the posteclipse enhancement in the ionosphere was caused by the enhanced neutral Oxygen density, which was driven by the horizontal winds, as well as decreased neutral N2 density, which was driven primarily by the cooling of the atmosphere.Key PointsModel‐data comparisons showed a relatively consistent depletion and enhancement in the ionosphere during and after the eclipseGITM showed that the divergence of horizontal winds drove the increased O after the eclipse allowing an increase in the ionization rateSlower charge exchange due to both the decreased ion temperature and N2 density allowed an increase of O+ density in the F region alsoPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144250/1/grl57159_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144250/2/grl57159.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144250/3/grl57159-sup-0001-2018GL077409-SI.pd

Exchange coupling in Eu monochalcogenides from first principles

Using a density functional method with explicit account for strong Coulomb repulsion within the 4f shell, we calculate effective exchange parameters and the corresponding ordering temperatures of the (ferro)magnetic insulating Eu monochalcogenides (EuX; X=O,S,Se,Te) at ambient and elevated pressure conditions. Our results provide quantitative account of the many-fold increase of the Curie temperatures with applied pressure and reproduce well the enhancement of the tendency toward ferromagnetic ordering across the series from telluride to oxide, including the crossover from antiferromagnetic to ferromagnetic ordering under pressure in EuTe and EuSe. The first and second neighbor effective exchange are shown to follow different functional dependencies. Finally, model calculations indicate a significant contribution of virtual processes involving the unoccupied f states to the effective exchange.Comment: 4 pages, 6 figure

Ionospheric response to the 2009 sudden stratospheric warming over the equatorial, low, and middle latitudes in the South American sector

The present study investigates the ionospheric total electron content (TEC) and F-layer response in the Southern Hemisphere equatorial, low, and middle latitudes due to major sudden stratospheric warming (SSW) event, which took place during January-February 2009 in the Northern Hemisphere. In this study, using 17 ground-based dual frequency GPS stations and two ionosonde stations spanning latitudes from 2.8°N to 53.8°S, longitudes from 36.7°W to 67.8°W over the South American sector, it is observed that the ionosphere was significantly disturbed by the SSW event from the equator to the midlatitudes. During day of year 26 and 27 at 14:00 UT, the TEC was two times larger than that observed during average quiet days. The vertical TEC at all 17 GPS and two ionosonde stations shows significant deviations lasting for several days after the SSW temperature peak. Using one GPS station located at Rio Grande (53.8°S, 67.8°W, midlatitude South America sector), it is reported for the first time that the midlatitude in the Southern Hemisphere was disturbed by the SSW event in the Northern Hemisphere.Fil: Fagundes, P. R.. Universidade do Vale do Paraíba; BrasilFil: Goncharenko, L. P.. Massachusetts Institute of Technology; Estados UnidosFil: De Abreu, A. J.. Universidade do Vale do Paraíba; BrasilFil: Venkatesh, K.. Universidade do Vale do Paraíba; BrasilFil: Pezzopane, M.. Istituto Nazionale Di Geofisica E Vulcanologia; ItaliaFil: De Jesus, R.. Universidade do Vale do Paraíba; BrasilFil: Gende, Mauricio Alfredo. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Coster, A. J.. Massachusetts Institute of Technology; Estados UnidosFil: Pillat, V. G.. Universidade do Vale do Paraíba; Brasi

Day-to-day variability and solar preconditioning of thermospheric temperature over Millstone Hill

We use a continuous 30 day incoherent scatter radar experiment at Millstone Hill in October 2002 to examine day-to-day thermospheric variability in exospheric temperature T[subscript ex]. Solar flux and magnetic activity influences as the main driving factors for day-to-day variability are investigated quantitatively. Solar ultraviolet flux levels are based on the TIMED/SEE space weather product, allowing for analysis of ultraviolet flux-T[subscript ex] correlation. T[subscript ex] is most sensitive to solar EUV flux with approximately a 2 day delay at wavelengths of 27–34 nm (including 30.4 nm). In particularly, a 20–60 h time delay occurs in T[subscript ex] response to EUV flux at 27–34 nm band, with shorter delays in the morning and longer delays in the afternoon and at night. The 1 ∼ 2 day delayed T[subscript ex] response to solar ultraviolet flux and associated thermospheric solar preconditioning (“memory”) are most significant in the daily mean for the 27–34 nm band, in the diurnal and semidiurnal amplitudes for the soft X-ray flux at 0.1–7 nm, and in the diurnal amplitude for longer wavelengths. An empirical model driven only by EUV flux at 27–34 nm from 2 days in advance reproduces 90% of the observed variability in the Tex daily mean. With a 2 day time delay, solar X-ray flux at 0.1–7 nm is correlated positively with T[subscript ex] diurnal amplitude and negatively with T[subscript ex] semidiurnal amplitude. Finally, magnetic activity control, as represented by the Dst index, is weaker during the day and stronger at night and is important for the semidiurnal amplitude but not important for the daily mean.National Science Foundation (U.S.) (Award AGS-1042569

Magnetic fluctuations in frustrated Laves hydrides R(Mn_{1-x}Al_{x})_{2}H_{y}

By neutron scattering, we have studied the spin correlations and spin fluctuations in frustrated Laves hydrides, where magnetic disorder sets in the topologically frustrated Mn lattice. Below the transition towards short range magnetic order, static spin clusters coexist with fluctuating and alsmost uncorrelated spins. The magnetic response shows a complexe lineshape, connected with the presence of the magnetic inhomogeneities. Its analysis shows the existence of two different processes, relaxation and local excitations, for the spin fluctuations below the transition. The paramagnetic fluctuations are discussed in comparison with classical spin glasses, cluster glasses, and non Fermi liquid itinerant magnets

Anisotropic Bose-Einstein condensates and completely integrable dynamical systems

A Gaussian ansatz for the wave function of two-dimensional harmonically trapped anisotropic Bose-Einstein condensates is shown to lead, via a variational procedure, to a coupled system of two second-order, nonlinear ordinary differential equations. This dynamical system is shown to be in the general class of Ermakov systems. Complete integrability of the resulting Ermakov system is proven. Using the exact solution, collapse of the condensate is analyzed in detail. Time-dependence of the trapping potential is allowed

GNSS Observations of Ionospheric Variations During the 21 August 2017 Solar Eclipse

An edited version of this paper was published by AGU. Copyright 2017 American Geophysical Union. Coster, A.J., Goncharenko, L., Zhang S.-R., Erickson, P.J., Rideout, W. & Vierinen, J. (2017). GNSS Observations of Ionospheric Variations During the 21 2 August 2017 Solar Eclipse. Geophysical Research Letters, 44(24), 12041-12048. https://doi.org/10.1002/2017GL075774. To view the published open abstract, go to https://doi.org/10.1002/2017GL075774.On 21 August 2017, during daytime hours, a total solar eclipse with a narrow ∼160 km wide umbral shadow occurred across the continental United States. Totality was observed from the Oregon coast at ∼9:15 local standard time (LST) (17:20 UT) to the South Carolina coast at ∼13:27 LST (18:47 UT). A dense network of Global Navigation Satellite Systems (GNSS) receivers was utilized to produce total electron content (TEC) and differential TEC. These data were analyzed for the latitudinal and longitudinal response of the TEC and for the presence of traveling ionospheric disturbances (TIDs) during eclipse passage. A significant TEC depletion, in some cases greater than 60%, was observed associated with the eclipse shadow, exceeding initial model predictions of 35%. Evidence of enhanced large‐scale TID activity was detected over the United States prior to and following the large TEC depletion observed near the time of totality. Signatures of enhanced TEC structures were observed over the Rocky Mountain chain during the main period of TEC depletion