TEC

About: TEC is a research topic. Over the lifetime, 5119 publications have been published within this topic receiving 84696 citations.

Instrumental Biases in Ionospheric Measurements Derived from GPS Data

Abstract: Line-of-sight ionosphere measurements derived from differencing dual-frequency Global Positioning System (GPS) range data are corrupted by instrumental biases in both the receiver and GPS satellite transmitters due to hardware delays in the Ll and L2 signal paths. The line- of-sight differential delay can be modeled as the sum of a receiver bias, a satellite transmitter bias, and the line-of- sight ionospheric delay or TEC (total electron content). While the receiver bias can be calibrated directly for some types of receivers, the satellite biases must be estimated from the GPS data itself by using a model of the ionosphere. Ignoring the satellite (receiver) biases when computing TEC measurements from GPS will result in an error of 59 (k30) TECU (1 TEC unit = 1016 electrons/mete+. Using a global ionospheric shell model to fit GPS-based ionospheric delay data from a world-wide network of 30- 40 receivers, we can estimate, with a single fit, satellite biases for the entire GPS constellation and receiver biases for all the uncalibrated receivers. Current studies indicate that the estimated receiver biases agree with the hardware calibrations at the level of 1 nanosecond (ns) and the day- to-day scatter of the estimated satellite biases ranges from 0.3 to 0.5 ns. Preliminary results show our estimated satellite biases agree with other reported values only at the level of 0.7 ns (RMS difference over all satellites). Further investigation will be required to reconcile these differences. If the true accuracy is 0.5 ns, as derived from day-to-day scatter, then the total uncertainty in line-of- sight TEC measurements derived from GPS is 0.6 ns or 1.8 TECU (1 ns corresponds to 2.85 TECU).

Design optimization of thermoelectric cooling systems for applications in electronic devices

Abstract: This paper presents a generalized theoretical model for the optimization of a thermoelectric cooling (TEC) system, in which the thermal conductances from the hot and cold sides of the system are taken into account. Detailed analyses of the optimal allocation of the finite thermal conductance between the cold-side and hot-side heat exchangers of the TEC system are conducted by considering the constraint of the total thermal conductance. The analysis results show that the maximum coefficient of performance (COP) and the maximum cooling capacity of the TEC system can be obtained when the finite total thermal conductance is optimally allocated. Furthermore, the effects of the total thermal conductance and the heat capacity rate of the cooling fluid on the performance of the TEC system and the optimal thermal conductance allocation ratio are also examined.

The Role of Tec Family Kinases in Myeloid Cells

Abstract: Members of the Tec kinase family (Bmx, Btk, Itk, Rlk and Tec) are primarily expressed in the hematopoietic system and form, after the Src kinase family, the second largest class of non-receptor protein tyrosine kinases. During lymphocyte development and activation Tec kinases have important functions in signaling pathways downstream of the antigen receptors. Tec family kinases are also expressed in cells of the myeloid lineage. However, with the exception of mast cells and platelets, their biological role in the myeloid system is only poorly understood. This review summarizes the current knowledge about the function of Tec family kinases in hematopoietic cells of the myeloid lineage.

The 2009 Samoa and 2010 Chile tsunamis as observed in the ionosphere using GPS total electron content

Abstract: [1] Ground-based Global Positioning System (GPS) measurements of ionospheric total electron content (TEC) show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events: the Samoa earthquake of 29 September 2009 and the Chile earthquake of 27 February 2010. Both earthquakes produced ocean tsunamis that were destructive to coastal communities near the epicenters, and both were observed in tidal gauge and buoy measurements throughout the Pacific Ocean. We observe fluctuations in TEC correlated in time, space, and wave properties with these tsunamis using the Jet Propulsion Laboratory's Global Ionospheric Mapping software. These TEC measurements were band-pass filtered to remove ionospheric TEC variations with wavelengths and periods outside the typical range for tsunamis. Observable variations in TEC appear correlated with the tsunamis in some locations (Hawaii and Japan), but not in others (Southern California or near the epicenters). Where variations are observed, the typical amplitude tends to be ∼0.1–0.2 TEC units for these events, on the order of ∼1% of the background TEC value. These observations are compared to estimates of expected tsunami-driven TEC variations produced by Embry Riddle Aeronautical University's Spectral Full Wave Model, an atmosphere-ionosphere coupled model, and are found to be in good agreement. Significant TEC variations are not always seen when a tsunami is present, but in these two events the regions where a strong ocean tsunami was observed coincided with clear TEC observations, while a lack of clear TEC observations coincided with smaller sea surface height amplitudes. There exists the potential to apply these detection techniques to real-time GPS TEC data, providing estimates of tsunami speed and amplitude that may be useful for early warning systems.

Statistical analysis of solar activity variations of total electron content derived at Jet Propulsion Laboratory from GPS observations

Abstract: [1] We analyzed the data series of the total electron content (TEC) derived at Jet Propulsion Laboratory from Global Positioning System (GPS) observations to investigate the solar activity effects of TEC on a global scale. The daily values of the solar extreme ultraviolet (EUV) fluxes in 0.1–50 nm wavelengths, 10.7 cm radio flux F10.7, and F10.7P (the average of daily F10.7 and its 81-day mean F10.7A) are adopted to represent the solar EUV variability, respectively. The EUV fluxes are measured by the Solar EUV Monitor (SEM) spectrometer aboard Solar Heliospheric Observatory (SOHO). Three kinds of patterns (linearity, saturation, and amplification) can be detected in TEC versus F10.7P and EUV. A saturation feature exists in TEC versus F10.7 in the daytime, more pronounced at low latitudes than at middle and high latitudes. The saturation in the equatorial anomaly regions is strongest in equinoxes and weakest in the June solstice. In contrast, the amplification in TEC, as a novel feature, is mainly distributed in the northern middle, and high latitudes in the December solstice and in the Southern Hemisphere in the June solstice and the March equinox. It is the first time to determine where and when the linear, saturation, and amplification patterns are distributed in TEC. Further, the solar activity sensitivity of TEC is stronger at day than at night and more evident at lower latitudes than at higher latitudes. The solar activity dependent rates of TEC in the equatorial and low-latitude regions have a minimum around the dip equator and maxima on both sides of the dip equator (near the crest of the equatorial anomaly). This structure is roughly aligned along the dip equator, being strongest in equinoxes and weakest in the June solstice, which highlights the importance of ionospheric dynamics related with E × B drift. In addition, this analysis confirms that in a statistical sense, a quadrate polynomial can well capture the long-term solar activity dependency of TEC at specified local time.