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TEC

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


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Journal ArticleDOI
TL;DR: It is demonstrated that the circles are highly sensitive to S1, mung bean and Bal 31 nucleases, and the site of sensitivity maps to the junction, which is a likely explanation for the nuclease sensitivity.
Abstract: Approximately 60,000 transposon-like elements of the Tec1 and Tec2 families excise en masse from the micronuclear genome during formation of a macronucleus in Euplotes crassus. The circular product has been shown previously to contain the element inverted repeats joined head to head. To elucidate the mechanism of Tec excision, we have further characterized the circular products. DNA sequence analysis of cloned inverted repeat junctions and of population of supercoiled Tec circles shows that the inverted repeat junctions consist of both copies of the target site duplication surrounding 10 additional bases. The 10 bp differs for each junction. We demonstrate that the circles are highly sensitive to S1, mung bean and Bal 31 nucleases, and the site of sensitivity maps to the junction. Alkaline gel electrophoresis indicates that the junction does not contain a nick or gap; thus, a likely explanation for the nuclease sensitivity is the existence of a heteroduplex DNA structure at the junction. On the basis of these results, we present a model of Tec excision and discuss the relationship of Tec excision to IES elimination and chromosome fragmentation in E. crassus.

61 citations

Journal ArticleDOI
TL;DR: In this paper, a two-step regularization algorithm was proposed to combine signals from all the satellites for a given instant and given station and estimate the vertical TEC (VTEC) values for any desired period without missing any important features in the temporal or spatial domain.

61 citations

Journal ArticleDOI
TL;DR: It is shown that the inositol 5′ phosphatases SHIP1 and SHIP2 interact preferentially with Tec, compared with other Tec family members, and four lines of evidence suggest that SHIP phosphatase are negative regulators of Tec.

60 citations

Journal ArticleDOI
TL;DR: In this article, the authors used the dispersive property of the ionosphere to correct positional measurements for ionospheric effects, and found that GPS observations at Kwajalein (9°N latitude) reported here for August 14, 1990, show severe ionosphere disruption.
Abstract: GPS satellites broadcast at two frequencies (Ll of 1575.42 MHz and L2 of 1227.6 MHz). The dispersive property of the ionosphere is frequently used to correct positional measurements for ionospheric effects. Independent measurements at the two frequencies can also be combined to form a relative ionospheric delay and a measure of the total electron content (TEC) which is uncertain by an additive constant. In a previous paper (Musman et al., 1990) estimates of this offset were utilized in constructing models of the time history of the equivalent zenith delay at Westford, Massachusetts. An ionospheric model composed of uniform shells whose electron density changes slowly in a typical diurnal pattern would produce relative ionospheric delays with a simple u-shaped or j-shaped curve. Most of the change in delay would be a result of changes in geometry between the observer and the satellite. Departures from a simple pattern are indicative of ionospheric disturbances and the influence of the protonosphere. From GPS data alone, it is ambiguous whether these disturbances are due to spatial structures, temporal changes, or some combination of the two. Equatorial spread F (ESF) refers to a variety of equatorial ionospheric disturbances, some of which are associated with rising plasma plumes having low electron density and a high degree of turbulence. This phenomenon occurs primarily between local sunset and local midnight at sites within about 15° of the magnetic equator. In some seasons, disturbances can occur during two out of three evenings, while at other times it can be much quieter. GPS observations at Kwajalein (9°N latitude) reported here for August 14, 1990, show severe ionospheric disruption. Two independent and simultaneous sets of radar observations confirm the presence of ESF and reveal quite a bit about the spatial and temporal conditions which affect the system. GPS observations on August 15, 1990, when no ESF was present are much quieter. We find that tens of minute variations in the TEC correspond to the motion of large scale features across the GPS field of view. More severe GPS effects are seen to be collocated with turbulent low density plumes which rise rapidly to high altitudes and drift west to east across the GPS line of sight. Severe disruption can occur in moderately sophisticated GPS systems during such events, at least near solar maximum.

60 citations

Journal ArticleDOI
TL;DR: In this article, a regional total electron content (TEC) mapping technique over China and adjacent areas is developed on the basis of a Kalman filter data assimilation scheme driven by Global Navigation Satellite Systems (GNSS) data from the Crustal Movement Observation Network of China and International GNSS Service.
Abstract: In this paper, a regional total electron content (TEC) mapping technique over China and adjacent areas (70 degrees E-140 degrees E and 15 degrees N-55 degrees N) is developed on the basis of a Kalman filter data assimilation scheme driven by Global Navigation Satellite Systems (GNSS) data from the Crustal Movement Observation Network of China and International GNSS Service. The regional TEC maps can be generated accordingly with the spatial and temporal resolution being 1 degrees x1 degrees and 5min, respectively. The accuracy and quality of the TEC mapping technique have been validated through the comparison with GNSS observations, the International Reference Ionosphere model values, the global ionosphere maps from Center for Orbit Determination of Europe, and the Massachusetts Institute of Technology Automated Processing of GPS TEC data from Madrigal database. The verification results indicate that great systematic improvements can be obtained when data are assimilated into the background model, which demonstrates the effectiveness of this technique in providing accurate regional specification of the ionospheric TEC over China and adjacent areas.

60 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023303
2022578
2021284
2020321
2019293
2018272