Showing papers on "TEC published in 1990"
TL;DR: In this article, the presence or absence of the latitudinal anomaly in TEC on a particular day depended only on the strength of the electrojet current, as determined by the difference of the horizontal magnetic field at stations on the magnetic equator and stations outside the equatorial electrojet.
Abstract: Results are presented on continuous TEC measurements, taken along a chain of stations spaced between 0 deg N and 25 deg N and aligned roughly along the same longitude sector in India, that describe the day-to-day behavior of the location of equatorial anomaly in the TEC during the period of the 1975-1976 sunspot minimum, when the ATS spacecraft was visible from India. It was found that the presence or absence of the latitudinal anomaly in TEC on a particular day depended only on the strength of the electrojet current, as determined by the difference of the horizontal magnetic field at stations on the magnetic equator and stations outside the equatorial electrojet, rather than on the horizontal magnetic field measured only at equatorial stations.
222 citations
TL;DR: In this paper, a method for approximating the peak height and scale height of the electron density profile is discussed as well as a reconstruction technique based on the multiplicative algebraic reconstruction technique algorithm and a back projection based initial guess.
Abstract: Ionospheric total electron content (TEC) measurements, obtained simultaneously at several locations, can be processed using computerized tomography (CT) algorithms to obtain two-dimensional images of ionospheric electron density. Using TEC data, computerized ionospheric tomography (CIT) reconstructs an image of the electron density structures in a vertical slice above the receiving stations. We successfully applied this technique to realistic simulations of ionospheric density variations over 16° of latitude and a height range of 50 to 1000 km. A method for approximating the peak height and scale height of the electron density profile will be discussed as well as a reconstruction technique based on the multiplicative algebraic reconstruction technique algorithm and a back projection based initial guess. The quality of reconstructions is considered for two geometries and image resolutions. In particular, the image of a mid-latitude trough with background horizontal density gradient and large-scale irregular structures has been reconstructed from TEC data generated from a model based on an incoherent scatter radar observation. The CT reconstructed image was compared with the original contour map obtained by the incoherent scatter radar. Good agreement has been achieved. The CIT technique has also been applied to a modeled ionosphere to calculate the range rate corrections for a Doppler-tracking radar.
196 citations
Journal Article•
TL;DR: This is the first report showing a protein-tyrosine kinase which may be specifically involved in the cell growth of hepatocytes or in the step of hepatocarcinogenesis.
Abstract: To identify protein-tyrosine kinases which play an important role in the process of hepatocarcinogenesis, we have screened a murine liver cDNA library with v-fps kinase domain as a probe. Using low stringency screening, we could isolate cDNAs of a putative protein-tyrosine kinase, tec (tyrosine kinase expressed in hepatocellular carcinoma). Nucleotide sequences of the cDNAs show that the C-terminal domain of its predicted protein has significant homology with that of the members of the src family. The tec gene is expressed mainly in liver and faintly in heart, kidney and ovary. Northern analysis further shows that in 2 out of 4 cell lines of human hepatocellular carcinoma (HCC) the tec gene is highly expressed compared to normal human liver. This is the first report showing a protein-tyrosine kinase which may be specifically involved in the cell growth of hepatocytes or in the step of hepatocarcinogenesis.
137 citations
TL;DR: It is concluded that elevated ICAM-1 expression on TEC increases the immune accessory cell capability of TEC bearing Ia antigens, and is resistant to down-regulation by some immunosuppressive agents.
118 citations
TL;DR: To resolve the controversy on the role of thymic epithelial cells (TEC) in tolerance induction, athymic mice were grafted with allogeneic day‐14 fetal thymuses treated with deoxyguanosine in vitro and the data indicate that the tolerogenicity of TEC varies considerably according to the antigen and the subpopulation of T cells studied.
Abstract: To attempt to resolve the controversy on the role of thymic epithelial cells (TEC) in tolerance induction, athymic mice were grafted with allogeneic day-14 fetal thymuses treated with deoxyguanosine in vitro. The data indicate that the tolerogenicity of TEC varies considerably according to the antigen and the subpopulation of T cells studies. For cytotoxic CD8 + cells responding to H-2 class I antigens, TEC induce minimal tolerance. For proliferative responses of CD4 + cells, by contrast, TEC induce significant tolerance to H-2 class II antigens but no detectable tolerance to Mls a antigens
78 citations
TL;DR: TEC appear to produce a cytokine that is functionally, biochemically, and antigenically indistinguishable from GM-CSF, suggesting that these cells may play a role in modulating the inflammatory response in the airway.
Abstract: It is unknown whether local resident cells of the upper airway are able to regulate the number and function of phagocytic cells by the secretion of cytokines. We undertook to determine if tracheal epithelial cells (TEC) produce the potent cytokine granulocyte/macrophage colony-stimulating factor (GM-CSF) and how TEC-derived GM-CSF might be regulated. Conditioned media (TEC-CM) from 7- to 21-day-old primary cultures of rat TEC contained material with bioactivity similar to GM-CSF. This bioactivity was increased in conditioned medium from lipopolysaccharide (LPS)-treated (1 microgram/ml) TEC. Molecular characterization of bioactivity revealed a molecular weight of 27 to 44 kD by gel-filtration high performance liquid chromatography (HPLC), and elution at 44 to 50% acetonitrile by reverse-phase HPLC, similar to that of authentic GM-CSF. The biologic activity of TEC-CM was completely blocked by a goat polyclonal anti-GM-CSF antibody. With in situ hybridization using a murine GM-CSF cDNA probe, more than 95% of the adherent TEC population expressed GM-CSF transcripts, and the number of transcripts was significantly increased by LPS (1 microgram/ml, 48 h). TEC appear to produce a cytokine that is functionally, biochemically, and antigenically indistinguishable from GM-CSF. The ability of TEC to produce GM-CSF suggests that these cells may play a role in modulating the inflammatory response in the airway.
58 citations
TL;DR: Several methods of constructing systematic t-error correcting/all unidirectional error-detecting codes are described, and further bounds on the word length of systematic tEC/AUED codes are derived.
Abstract: Several methods of constructing systematic t-error correcting/all unidirectional error-detecting codes are described. These codes can be constructed by adding a tail to a linear t-error correcting code, but other constructions presented are more of an ad hoc nature. These codes will often be found as suitably chosen subsets of nonsystematic tEC/AUED codes. Further bounds on the word length of systematic tEC/AUED codes are derived, and extensive tables are given. >
38 citations
TL;DR: TEC are a source of cytokines and show that TEC respond to IL1 by producing cytokines with consequences on the thymic lymphoid population, which further emphasizes the importance and complexity of paracrine molecular interactions involved in intrathymic development.
29 citations
Journal Article•
TL;DR: In this article, the authors summarized the observations and theoretical interpretations of the ionospheric effects of the previous 6 solar eclipses and showed that the optical eclipse effects on the E and F1 regions and the dynamic effect on the F2 region are all quite clear, and that the values of f0F2 on the eclipse day, comparing with those in the control day, could decrease, increase or remain unchanged.
Abstract: In this paper, the observations and theoretical interpretations of the ionospheric effects of the previous 6 solar eclipses are summarized. The ionospheric observations of solar eclipse effects are made at 18 ionospheric stations of 14 provinces in China. The first one of the 6 solar eclipses occurred, on 20 June 1955, the last one on 18 March 1988. In addition to the ionospheric observations, the observations of Faraday rotation of satellite beacons and the whistlers were made some time during the solar eclipses. They have shown that:(1)The optical eclipse effects on the E and F1 region and the dynamic effect on the F2 region are all quite clear;(2)The values of f0F2 on the eclipse day, comparing with those in the control day, could decrease, increase or remain unchanged;(3)There are either concave or non-concave outline for the curves of the TEC, the values of the TEC on the eclipse day comparing with those in the control day could increase during the solar eclipse.The dynamic characteristics of the F2 region and outer ionosphere during the solar eclipses were also discussed briefly. It is found that striking decrease of the space plasma temperature and the space plasma diffusion along magnetic field lines are main factors of the solar eclipse effects on the F2 region and outer ionosphere, and the plasma diffusion along the magnetic field line over the geomagnetic equator, the fountain effect, the thermospheric wind and position of the zone of the total (annular) solar eclipse are important factors of the ionospheric effects of the solar eclipse on the magnetic equatorial anonaly.
21 citations
TL;DR: The thermal expansion coefficient (TEC) of thin multilayers is determined by measuring the temperature dependence of the lattice mismatch with respect to the substrate as mentioned in this paper, which can be explained as for single layers having thickness of a few micrometer.
Abstract: The anisotropy of the thermal expansion coefficient (TEC) of thin multilayers is determined by measuring the temperature dependence of the lattice mismatch with respect to the substrate. The TEC of the substrate is determined by the Bond method. The elastic strain and the TEC of 8 to 90 nm thin sandwiched layers can be explained as for single layers having thickness of a few micrometer. An influence of the elastic interaction through the interfaces on the TEC is not noticeable.
Die Anisotropie des thermischen Ausdehnungskoeffizienten (TEC) dunner Vielfachschichten wird durch Messung der Temperaturabhangigkeit der Gitterfehlanpassung bezuglich des Substrats bestimmt. Die TEC des Substrats wird durch die Bond-Methode bestimmt. Die elastische Spannung und die TEC von 8 bis 90 nm dicken Sandwichstrukturen lassen sich wie fur Einfachschichten, die eine Dicke von einigen Mikrometern haben, erklaren. Ein Einflus der elastischen Wechselwirkung durch die Grenzflachen auf die TEC wird nicht festgestellt.
11 citations
TL;DR: The obtained results showed that the expression of CK polypeptides in fetal and neonatal thymus differed from the adult patterns, and a switch in their expression in the cortex was observed during the first two weeks of postnatal life.
Abstract: Ontogenetic study on the expression of cytokeratin (CK) polypeptides within particular subsets of rat thymic epithelial cells (TEC) has been performed by a large panel of anti-CK monoclonal antibodies (mAbs) using the streptavidin-biotin immunoperoxidase method Simultaneous presence of two or more CK subunits in the same TEC has been demonstrated by double immunoflouorescence labeling The obtained results showed that the expression of CK polypeptides in fetal and neonatal thymus differed from the adult patterns The main difference was observed in expression of CK10, 18, and 19 polypeptides During fetal ontogeny, CK10 and 18 are markers for most medullary TEC or a subset of medullary TEC, respectively, whereas CK19 is mainly a pan-TEC marker In the adult animals, they are localized in the cortical and a subset of medullary TEC (CK18), subcapsular/perivascular and some medullary TEC (CK19), or in a subset of medullary TEC and Hasall’s corpuscles (HC) (CK10) The switch in their expression in the cortex was observed during the first two weeks of postnatal life
03 May 1990
TL;DR: In this article, the authors compared GPS and incoherent scatter (IS) measurements of the total electron content (TEC) taken during 1-3 March 1989, and found that the IS profiles are then integrated to produce TEC measurements up to 800 km.
Abstract: GPS and incoherent scatter (IS) measurements of the total electron content (TEC) taken during 1-3 March 1989 are compared. During this period, four different GPS satellites, SV nos. 6, 9, 11, and 12, were observed. The T14100 GPS receiver at Millstone monitored these satellites continuously while they were in view. At the same time, the Millstone UHF radar was sequentially pointed in the direction of several of these satellites taking incoherent scatter measurements. The incoherent scatter measurements produce profiles of the electron density distribution. The IS profiles are then integrated to produce TEC measurements up to 800 km. The combined pseudo-range and phase data of the GPS system measure the group delay at both the L1 (1575.42 MHz) and L2 (1227.6 MHz) frequencies. This information is converted to TEC measurements along the line of sight to the satellite at 19000 km. The comparison of the GPS and incoherent scatter data gives us a new technique for estimating the number of electrons above 800 km. Our results were surprising. The 1-3 March time period was associated with interesting geophysical conditions. The experiment began during quiet geomagnetic conditions and at a time when the daily 10.7 cm solar flux values were moderatemore » (162).« less
11 Jun 1990
TL;DR: In this paper, a dual-frequency codeless Global Positioning System (GPS) receiver for measuring ionospheric delay, called GTR-2, has been developed, which uses a cross-correlation property of the P-code signals transmitted from GPS satellites to measure ionosphere total electron content (TEC).
Abstract: A dual-frequency codeless Global Positioning System (GPS) receiver for measuring ionospheric delay, called GTR-2, has been developed. Results of a feasibility study of using GTR-2 for single-frequency very-long-baseline interferometry (VLBI) experiments are presented. GTR-2 uses a cross-correlation property of the P-code signals transmitted from GPS satellites to measure ionospheric total electron content (TEC) with a measurement uncertainty of about 2*10/sup 16/ electrons/m/sup 2/ along the line of site to the satellite. Ionospheric compensation of the signal from radio stars is studied using the TEC data obtained from GTR-2. >
TL;DR: Supernatants of 5 day cultures of peripheral blood mononuclear cells (PBMC) stimulated by thyroid microsomal antigens (TMA), and liver microSomal antIGens (LMA) have been utilized to induce HLA-DR expression on human thyroid epithelial cells (TEC).
Abstract: Supernatants of 5 day cultures of peripheral blood mononuclear cells (PBMC) stimulated by thyroid microsomal antigens (TMA), and liver microsomal antigens (LMA) have been utilized to induce HLA-DR expression on human thyroid epithelial cells (TEC). The PBMC were obtained from 8 normal control persons and 13 patients with autoimmune thyroid disease (AITD) (7 Graves' disease and 6 Hashimoto's thyroiditis). The TEC HLA-DR expression was measured by an enzyme-linked immunosorbent assay (EL1SA) technique. TEC HLA-DR expression was calculated as follows: (experimental optical density -control optical density) x 103; TEC HLA-DR index: % HLA-DR expression of IFNγ 100 U/ml stimulation; and stimulation index (SI): TEC HLA-DR expression index induced by PBMC supernatants with antigen stimulation/TEC HLA-DR expression index induced by PBMC supernatants without antigen stimulation ± 100. Supernatants without antigen stimulation from both normal control subjects and patients were able to induce TEC HLA-DR expression on...
03 May 1990
TL;DR: In this paper, a first-order estimate of the shape of the electron density profile, Nsube(h), is given by the ratio of the profile's total electron content (TEC) to its peak density (Nmax).
Abstract: : A first-order estimate of the shape of the electron density profile, Nsube(h), is given by the ratio of the profile's total electron content (TEC) to its peak density (Nmax). Applications to transionospheric and hf supported propagation can be aided by models of this quantity, tab and thus the BU/AFGL slab thickness model has been developed to describe the mean variations of slab thickness. In this paper addresses the issue of ;how geomagnetic disturbances affect tab at mid-latitudes, making use of a database of two solar cycles of observations from Hamilton (Ma) and Wallops Island (Va). These results are compared with those deduced from an Italian station pair(Florence and Rome).
03 May 1990
TL;DR: In this paper, the latitudinal extent of the equatorial anomaly has been studied using a theoretical model of the ionosphere which incorporates measured values of vertical E x B drift at the earth's magnetic equator.
Abstract: : The latitudinal extent of the equatorial anomaly has been studied using a theoretical model of the ionosphere which incorporates measured values of vertical E x B drift at the earth's magnetic equator. Realistic values of neutral winds are also included. The equatorial anomaly region, typically between plus and minus 20 degrees magnetic latitude, is that part of the world where the highest values of electron density and Total Electron Content, (TEC), normally occur, and hence is very important to high frequency propagation and to trans-ionospheric propagation effects. During the daytime upward E x B drift at the magnetic equator drives the ionization across field lines to higher latitudes, causing crests in ionization to occur at approximately plus and minus 15 deg dip latitude. The latitude range over which the anomaly makes a significant difference in values of foF2 and TEC is calculated as a percent departure from the case with no equatorial electric field. Results from the model studies with different values of realistic electric fields show that the effects of the anomaly can be highly variable and widespread in latitude and local time.
03 May 1990
TL;DR: In this article, a review of the GPS P-code capability of GPS receivers using the full GPS Pcode capability, contrasted with newer, less costly, instruments which make much more limited measurements without requiring knowledge of GPSP-codes.
Abstract: : Effects of the ionosphere can be significant to modern RF systems which depend on trans-ionospheric signal propagation. Delay effects caused by ionospheric total electron content, (TEC), and scintillation effects due to small-scale ionospheric irregularities, are of particular importance since they can, for example, cause ranging errors and signal or target fades. Signals from the Global Positioning System (GPS) satellites will provide the opportunity to measure TEC and scintillation parameters on a continuous basis in several directions from anywhere on earth. GPS signals have been used since 1984 to make measurements of polar cap TEC and L-Band scintillation, at Thule, Greenland. Concurrent observations of amplitude fading at 250 MHz link these GPS measurements to a large data base of polar scintillation at that frequency. Examples of these data will be given which illustrate the extreme variability of the polar cap ionosphere, which can be a significant limitation to trans-ionospheric systems which must operate in this part of the world. This paper will also review ionospheric measurement capability of GPS receivers using the full GPS P-code capability, contrasted with newer, less costly, instruments which make much more limited measurements without requiring knowledge of the GPS P-codes.