The daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100 to 120 km altitude region within ±2° latitude of the dip equator. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the Horizontal (H) component between a magnetometer placed directly on the magnetic equator and one displaced 6 to 9 degrees away. The difference between these measured H values provides a direct measure of the daytime electrojet current, and in turn, the magnitude of the vertical ExB drift velocity in the F region ionosphere. This paper discusses a recent study that has established the quantitative relationship between the vertical ExB drift velocity in the ionospheric F region and the daytime strength of the equatorial electrojet in the South American (west coast) longitude sector.

Although all human ESC (hESC) lines have similar morphology, express key pluripotency markers, and can differentiate toward primitive germ layers in vitro, the lineagespecific developmental potential may vary between individual lines. In the current study, four hESC lines were cultured in the same feeder-free conditions to provide a standardized platform for interline analysis. A highthroughput, forced-aggregation system involving centrifugation of defined numbers of hESCs in V-96 plates (V-96FA) was developed to examine formation, growth, and subsequent cardiomyocyte differentiation from >22,000 EBs. Homogeneity of EBs formed by V-96FA in mouse embryo fibroblast-conditioned medium was significantly improved compared with formation in mass culture (p < .02; Levene's test). V-96FA EB formation was successful in all four lines, although significant differences in EB growth were observed during the first 6 days of differentiation (p ‫؍‬ .044 to .001; one-way analysis of variance [ANOVA]). Cardiomyocyte differentiation potential also varied; 9.5% ؎ 0.9%, 6.6% ؎ 2.4%, 5.2% ؎ 3.1%, and 1.6% ؎ 1.0% beating EBs were identified for HUES-7, NOTT2, NOTT1, and BG01, respectively (p ‫؍‬ .008; one-way ANOVA). Formation of HUES-7 V-96FA EBs in defined medium containing activin A and basic fibroblast growth factor resulted in 23.6% ؎ 3.6% beating EBs, representing a 13.1-fold increase relative to mass culture (1.8% ؎ 0.7%), consistent with an observed 14.8-fold increase in MYH6 (␣MHC) expression by real-time polymerase chain reaction. In contrast, no beating areas were derived from NOTT1-EBs and BG01-EBs formed in defined medium. Thus, the V-96FA system highlighted interline variability in EB growth and cardiomyocyte differentiation but, under the test conditions described, identified HUES-7 as a line that can respond to cardiomyogenic stimulation. STEM CELLS 2007;25:929 -938 Disclosure of potential conflicts of interest is found at the end of this article.

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The ionosphere is a highly dynamic medium that exhibits weather disturbances at all latitudes, longitudes, and altitudes, and these disturbances can have detrimental effects on both military and civilian systems. In an effort to mitigate the adverse effects, we are developing a physics‐based data assimilation model of the ionosphere and neutral atmosphere called the Global Assimilation of Ionospheric Measurements (GAIM). GAIM will use a physics‐based ionosphere‐plasmasphere model and a Kalman filter as a basis for assimilating a diverse set of real‐time (or near real‐time) measurements. Some of the data to be assimilated include in situ density measurements from satellites, ionosonde electron density profiles, occultation data, ground‐based GPS total electron contents (TECs), two‐dimensional ionospheric density distributions from tomography chains, and line‐of‐sight UV emissions from selected satellites. When completed, GAIM will provide specifications and forecasts on a spatial grid that can be global, regional, or local. The primary output of GAIM will be a continuous reconstruction of the three‐dimensional electron density distribution from 90 km to geosynchronous altitude (35,000 km). GAIM also outputs auxiliary parameters, including NmF2, hmF2, NmE, hmE, and slant and vertical TEC. Furthermore, GAIM provides global distributions for the ionospheric drivers (neutral winds and densities, magnetospheric and equatorial electric fields, and electron precipitation patterns). In its specification mode, GAIM yields quantitative estimates for the accuracy of the reconstructed ionospheric densities.

[1] The daytime equatorial electrojet is a narrow band of enhanced eastward current flowing in the 100--120 km altitude region within ±2°latitude of the dip equator. A unique way of determining the daytime strength of the electrojet is to observe the difference in the magnitudes of the horizontal (H) component between a magnetometer placed directly on the magnetic equator and one displaced 6°--9°away. The difference between these measured H values provides a direct measure of the daytime electrojet current and, in turn, the magnitude of the vertical E Â B drift velocity in the F region ionosphere. This paper discusses a recent study where 27 months of magnetometer H component observations and daytime, vertical E Â B drift velocities were obtained in the Peruvian longitude sector between August 2001 and December 2003. In order to establish the relationships between DH and E Â B drift velocities for the 270 days of observations, three approaches were chosen: (1) a linear regression analysis, (2) a multiple regression approach, and (3) a neural network approach. The neural network method gives slightly lower RMS error values compared with the other two methods. The relationships for all three techniques are validated using an independent set of E Â B drift observations from the Jicamarca incoherent scatter radar (ISR) located at Jicamarca, Peru. The techniques presented here will be incorporated into a recently developed, real-time Global Assimilation of Ionospheric Measurements (GAIM) model.

The Earth's thermosphere and ionosphere constitute a dynamic system that varies daily in response to energy inputs from above and from below. This system can exhibit a significant response within an hour to changes in those inputs, as plasma and fluid processes compete to control its temperature, composition, and structure. Within this system, short wavelength solar radiation and charged particles from the magnetosphere deposit energy, and waves propagating from the lower atmosphere dissipate. Understanding the global-scale response of the thermosphere-ionosphere (T-I) system to these drivers is essential to advanc- ing our physical understanding of coupling between the space environment and the Earth's atmosphere. Previous missions have successfully determined how the "climate" of the T-I system responds. The Global-scale Observations of the Limb and Disk (GOLD) mission will determine how the "weather" of the T-I responds, taking the next step in understanding the coupling between the space environment and the Earth's atmosphere. Operating in geostationary orbit, the GOLD imaging spectrograph will measure the Earth's emissions from 132 to 162 nm. These measurements will be used image two critical variables-thermospheric temperature and composition, near 160 km-on the dayside disk at half-hour time scales. At night they will be used to image the evolution of the low latitude ionosphere in the same regions that were observed earlier during the day. Due to the geostationary orbit being used the mission observes the same hemisphere repeatedly, allowing the unambiguous separation of spatial and temporal variability over the Americas.

Our primary goal is to construct a real-time data assimilation model for the ionosphere-plasmasphere system that will provide reliable specifications and forecasts. A secondary goal is to validate the model for a wide range of geophysical conditions, including different solar cycle, seasonal, storm, and substorm conditions. OBJECTIVES We propose to develop a software program that will provide for a Global Assimilation of Ionospheric Measurements (GAIM). GAIM will use a physics-based ionosphere-plasmasphere model as a basis for assimilating a diverse set of real-time (or near real-time) measurements. The program will provide specifications and forecasts on a specified spatial grid that can be global, regional, or local (50 km x 50 km). The specifications/forecasts will be in the form of 3-dimensional electron density distributions from 90 km to geosynchronous altitudes (35,000 km). Auxiliary plasma parameters will also be provided, such as N m F 2 , h m F 2 , N m E, h m E, and slant and vertical TEC. In its specification mode, GAIM will provide quantitative estimates for the accuracy of the reconstructed ionospheric densities. The measurements GAIM will assimilate include: (1) Slant path TECs between 80-90 ground receivers and the Global Positioning System (GPS) satellites; (2) Occultation data from a satellite constellation such as COSMIC; (3) TECs associated with the CIT network; (4) Bottomside N e profiles from digisondes associated with the Air Force DISS network; (5) In situ plasma parameters from the SSIES instrument package on the DMSP satellites; and (6) Line-of-sight UV emissions and deduced plasma parameters from the Naval Research Laboratory's SSUSI and SSULI instruments. GAIM will have a modular construction, so that new data types can be readily assimilated when they become available. APPROACH Our approach is to use a two-step process to obtain a 3-D ionospheric reconstruction. First, certain data sets will be assimilated so that the inputs (neutral parameters, electric fields, precipitation) to the physics-based ionosphere-plasmasphere model can be adjusted, within expected errors, to match observations, and then the physics-based model will be run in order to obtain a 3-D N e distribution that is consistent with the measured inputs. This first step should result in realistic ionospheric density features. Next, this simulated ionosphere-plasmasphere system will be used as a starting point for an electron density reconstruction using all of the different data types that pertain to N e and a Kalman filter assimilation technique. The use of a simulated ionosphere-plasmasphere system will provide

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