TEC

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

TEC-family kinases: regulators of T-helper-cell differentiation

Abstract: The TEC-family protein tyrosine kinases ITK, RLK and TEC have been identified as key components of T-cell-receptor signalling that contribute to the regulation of phospholipase C-gamma, the mobilization of Ca(2+) and the activation of mitogen-activated protein kinases. Recent data also show that TEC kinases contribute to T-cell-receptor-driven actin reorganization and cell polarization, which are required for productive T-cell activation. Functional studies have implicated TEC kinases as important mediators of pathways that control the differentiation of CD4(+) T helper cells. Here, we review studies of signalling pathways that involve TEC kinases and how these pathways might contribute to the regulation of T-helper-cell differentiation and function.

Regularized estimation of vertical total electron content from Global Positioning System data

Abstract: [1] A novel regularization technique which can combine signals from all Global Positioning System (GPS) satellites for a given instant and a given receiver is developed to estimate the vertical total electron content (VTEC) values for the 24-hour period without missing any important features in the temporal domain. The algorithm is based on the minimization of a cost function which also includes a high pass penalty filter. Optional weighting function and sliding window median filter are added to enrich the processing and smoothing of the data. The developed regularized estimation algorithm is applied to GPS data for various locations for the solar maximum week of 23–28 April 2001. The parameter set that is required by the estimation algorithm is chosen optimally using appropriate error functions. This robust and optimum parameter set can be used for all latitudes and for both quiet and disturbed days. It is observed that the estimated TEC values are in general accordance with the TEC estimates from other global ionospheric maps, especially for quiet days and midlatitudes. Owing to its 30 s time resolution, the regularized VTEC estimates from the developed algorithm are very successful in representation and tracking of sudden temporal variations of the ionosphere, especially for high latitudes and during ionospheric disturbances.

Three‐dimensional waveform modeling of ionospheric signature induced by the 2004 Sumatra tsunami

Abstract: [1] The Sumatra, December 26th, 2004, tsunami produced internal gravity waves in the neutral atmosphere and large disturbances in the overlying ionospheric plasma. To corroborate the tsunamigenic hypothesis of these perturbations, we reproduce, with a 3D numerical modeling of the ocean-atmosphere-ionosphere coupling, the tsunami signature in the Total Electron Content (TEC) data measured by the Jason-1 and Topex/Poseidon satellite altimeters. The agreement between the observed and synthetic TEC shows that ionospheric remote sensing can provide new tools for offshore tsunami detection and monitoring.

A new global TEC model for estimating transionospheric radio wave propagation errors

Abstract: Space-based navigation and radar systems operating at single frequencies of <10 GHz require ionospheric corrections of the signal delay or range error. Because this ionospheric propagation error is proportional to the total electron content of the ionosphere along the ray path, a user friendly TEC model covering global scale and all levels of solar activity should be helpful in various applications. Since such a model is not available yet, we present an empirical model approach that allows determining global TEC very easily. Although the number of model coefficients and parameters is rather small, the model describes main ionospheric features with good quality. Presented is the empirical approach describing dependencies on local time, geographic/geomagnetic location and solar irradiance and activity. The non-linear approach needs only 12 coefficients and a few empirically fixed parameters for describing the broad spectrum of TEC variation at all levels of solar activity. The model approach is applied on high-quality global TEC data derived by the Center for Orbit Determination in Europe (CODE) at the University of Berne over more than half a solar cycle (1998–2007). The model fits to these input data with a negative bias of 0.3 TECU and a RMS deviation of 7.5 TECU. As other empirical models too, the proposed Global Neustrelitz TEC Model NTCM-GLis climatological, i.e. the model describes the average behaviour under quiet geomagnetic conditions. During severe space weather events the actual TEC data may deviate from the model values considerably by more than 100%. A preliminary comparison with independent data sets as TOPEX/Poseidon altimeter data reveals similar results for NeQuick and NTCM-GL with RMS deviations in the order of 5 and 11 TECU (1 TECU = 1016 electrons/m2) for low and high-solar activity conditions, respectively. The more extended data base of ionosphere information that accumulates in the coming years will help in further improving the set of coefficients of the model.

Ionosphere plasma bubbles and density variations induced by pre‐earthquake rock currents and associated surface charges

Abstract: [1] Recent ionospheric observations indicate that the total electron content (TEC) may anomalously decrease or increase up to 5–20% before the occurrence of big earthquakes. The ionospheric density variations can be caused by earth surface charges/currents produced from electric currents associated with the stressed rock. We formulate a coupling model for the stressed rock-Earth surface charges-atmosphere-ionosphere system. The stressed-rock acts as the dynamo to provide the currents for the coupling system. The electric fields and currents in the atmosphere and the lower boundary of ionosphere are obtained by solving the current continuity equation, ∇ • J = 0, where J is the current density. A three-dimensional ionosphere simulation code is then used to study the ionospheric dynamics based on the obtained electric fields and currents. The simulation results show that a current density Jrock = 0.2–10 μA/m2 in an earthquake fault zone is required to cause daytime TEC variations of 2–25%. The simulation results also show that a current density Jrock = 0.01–1 μA/m2 can lead to nighttime TEC variations of 1–30% as well as the formation of a nighttime plasma bubble (equatorial spread F) extending over the whole magnetic flux tube containing the earthquake epicenter. We suggest that observations of daytime and nighttime TEC variations and a nighttime plasma bubble within the affected region can be used as precursors for earthquake prediction.