Showing papers on "TEC published in 2000"

Severe B cell deficiency in mice lacking the tec kinase family members Tec and Btk.

Abstract: The cytoplasmic protein tyrosine kinase Tec has been proposed to have important functions in hematopoiesis and lymphocyte signal transduction. Here we show that Tec-deficient mice developed normally and had no major phenotypic alterations of the immune system. To reveal potential compensatory roles of other Tec kinases such as Bruton's tyrosine kinase (Btk), Tec/Btk double-deficient mice were generated. These mice exhibited a block at the B220+CD43+ stage of B cell development and displayed a severe reduction of peripheral B cell numbers, particularly immunoglobulin (Ig)MloIgDhi B cells. Although Tec/Btknull mice were able to form germinal centers, the response to T cell–dependent antigens was impaired. Thus, Tec and Btk together have an important role both during B cell development and in the generation and/or function of the peripheral B cell pool. The ability of Tec to compensate for Btk may also explain phenotypic differences in X-linked immunodeficiency (xid) mice compared with human X-linked agammaglobulinemia (XLA) patients.

Estimates of Faraday rotation with passive microwave polarimetry for microwave remote sensing of Earth surfaces

Abstract: A technique based on microwave passive polarimetry for the estimates of ionospheric Faraday rotation for microwave remote sensing of Earth surfaces is described. Under the assumption of azimuth symmetry for the surfaces under investigation, it is possible to estimate the ionospheric Faraday rotation from the third Stokes parameter of microwave radiation. An error analysis shows that the Faraday rotation can be estimated with an accuracy of better than 1/spl deg/ with a space-based L-band system, and the residual correction errors of linearly polarized brightness temperatures can be less than 0.1 K. It is suggested that the estimated Faraday rotation angle can be further utilized to derive the ionospheric total electron content (TEC) with an accuracy of about 1 TECU=10/sup 16/ electrons-m/sup -2/ which will yield 1 mm accuracy for the estimate of an ionospheric differential delay at the Ku-band. Therefore, this technique can potentially provide accurate estimates of ionospheric Faraday rotation, TEC and differential path delay for applications including microwave radiometry and scatterometry of ocean salinity and soil moisture as well as satellite altimetry at sea surface height. A conceptual design applicable to real aperture and aperture synthesis radiometers is described for the measurements of the third Stokes parameter.

The application of GPS observations to equatorial aeronomy

Abstract: Routine observations of the ionospherically imposed propagation effects upon GPS satellite signals are available online from the International GPS Service for Geodynamics. With over 200 ground-based stations now reporting data, ionospheric studies ranging from the analysis of single-site observations to the full global network have demonstrated the geophysical science yield possible from this remarkable resource. In this paper we expand on the use of GPS data for comprehensive “regional studies” at low latitudes. Using the GPS observing sites in South America, we show how routine observations are processed to form reliable total electron content (TEC) values capable of describing the latitudinal, longitudinal, local time, and storm time behavior over the full span of the continent. To study the dominant F region structure at low latitudes, the Appleton anomaly, two indices are developed to assess its strength (Is) and asymmetry (Ia). TEC data at 30 s intervals are used to form phase fluctuation indices that capture plasma irregularity patterns at 15-min (fp) and hourly (Fp) time resolution. Tests of Fp at Atlantic and Pacific sector locations show them to reproduce accurately all known occurrence patterns for equatorial spread F (ESF). The use of the three indices (Is,Ia, and Fp) to formulate predictive capabilities for ESF on the basis of the enhancement or suppression of growth rate indicators was not particularly successful.

The increase of the ionospheric activity as measured by GPS

Abstract: The paper outlines a method allowing to compute the TEC with a precision of about 2–3 TECU and to detect Travelling Ionospheric Disturbances using GPS measurements. We describe the solar cycle dependance of the TEC and TIDs. Since the beginning of 1998, we have observed a stronger ionospheric activity due to the increasing solar activity. This ionospheric activity is characterized by larger TEC values which are regularly reaching the level of 60 TECU and by a larger number of Travelling Ionospheric Disturbances. During the winter 1999–2000, the mean daily TEC was above 45 TECU; at solar minimum the mean daily TEC is ranging from 4 TECU to 12 TECU. In January 2000 (close to solar maximum) more than 1300 events due to TID’s were detected: it is 6.5 more than in January 1996 (at solar minimum).

Fusion of the NH2-Terminal Domain of the Basic Helix-Loop-Helix Protein TCF12 to TEC in Extraskeletal Myxoid Chondrosarcoma with Translocation t(9;15)(q22;q21)

Abstract: Extraskeletal myxoid chondrosarcomas (EMCs) are characterized by recurrent t(9;22) or t(9;17) translocations resulting in fusions of the NH 2 -terminal transactivation domains of EWS or TAF2N to the entire TEC protein. We report here an EMC with a novel translocation t(9;15)(q22;q21) and a third type of TEC -containing fusion gene. The chimeric transcript encodes a protein in which the first 108 amino acids of the NH 2 -terminus of the basic helix-loop-helix (bHLH) protein TCF12 is linked to the entire TEC protein. The translocation separates the NH 2 -terminal domain of TCF12 from the bHLH domain as well as from a potential leucine zipper domain located immediately downstream of the breakpoint. These results demonstrate that the NH 2 -terminal transactivation domains of EWS or TAF2N are not unique in their ability to convert the TEC protein into an oncogenically active fusion protein, and that they may be replaced by a domain from a bHLH protein that presumably endows the fusion protein with similar functions.

Thromboembolic complications in children with nephrotic syndrome in Bulgaria (1974-1996).

Abstract: Over a period of 22 years, 447 children with nephrotic syndrome (NS) have been retrospectively studied for clinically apparent thromboembolic complications (TEC). The incidence of TEC is 2% (9/447); 16 clinically apparent TEC were registered in 9 children. The incidence of TEC was 1.5% among patients with steroid-sensitive NS and 3.8% among those with steroid-resistant NS. TEC were predominantly venous (81% venous vs. 19% arterial). The most commonly affected vessels were deep leg veins, followed by inferior vena cava (IVC). Rare locations of TEC were also observed – superior vena cava (SVC), mesenteric artery, IVC, and hepatic veins with the development of Budd-Chiari syndrome Depending on the location of the TEC, imaging techniques used were: X-ray, computed tomography, and Doppler sonography. The major iatrogenic risk factor was furosemide, administered to 7 of the 9 children with TEC. In some patients additional predisposing factors were infections, dehydration, trauma, venepuncture, and immobilization. Treatment with heparin was followed by oral anticoagulation. Fibrinolytic therapy was effective in 3 of 4 patients. No new TEC occurred under oral anticoagulant prophylaxis. The outcome was a full recovery in 6 patients and a partial recovery in 1 patient. Two children died – 1 with SVC thrombosis and the other with recurrent TEC affecting cerebral vessels. Although rare, TEC are among the most serious life-threatening complications in children with NS and require intensive care.

GPS global detection of the ionospheric response to solar flares

Abstract: This author suggests the concept of a new technology for global detection (GLOBDET) of atmospheric disturbances of natural and technogenic origin, on the basis of phase measurements of the total electron content (TEC) in the ionosphere using an international GPS network. Temporal dependencies of TEC are obtained for a set of spaced receivers of the GPS network simultaneously for the entire set of “visible” (over a given time interval) GPS satellites (up to 5–10 satellites). These series are subjected to filtering in the selected range of oscillation periods using algorithms for spatiotemporal analysis of signals of nonequidistant GPS phased antenna arrays which are adequate to the detected disturbance. An analysis is made of the possibilities of using the GLOBDET when detecting the ionospheric response of solar flares. In this case it is best to make the coherent summation of the filtered series of TEC. Powerful impulsive flares of July 29, 1999, and December 28, 1999, were chosen to illustrate the practical implementation of the proposed method.

Geomagnetic storm effects on the topside ionosphere and plasmasphere : A compact tutorial and new results

Abstract: The coupled ionosphere–thermosphere–plasmasphere system is very complex. The study of its interrelationships during geomagnetically disturbed conditions is an especially challenging task.Significant progress has been achieved during the last few years in developing comprehensive theoretical models to describe its global behaviour.Moreover, more simple, specialized numerical modelling of some specialaspects of storm behaviour and/or regional models have contributedto the progress in this field.This paper summarizes recent developments in upper ionosphereand plasmasphere storm studies and modelling.From an observational point of view the upper ionosphere/plasmasphereregion is well reflected in radio beacon measurements providing the totalelectron content (TEC). The development of space-based radio navigation systems such as GPS offersnew opportunities to derive TEC on both regional and global scale.Combining TEC with ionosonde data enables the variability of the shape of the electron density distribution during storms to be studied.We present some examples of co-ordinated investigation,made during the CEDAR storm study intervals.

Nighttime equatorial ionosphere: GPS scintillations and differential carrier phase fluctuations

Abstract: The presence of scintillation-producing irregularities in the nighttime equatorial ionosphere, in the path of Global Positioning System (GPS) signals received at an equatorial station, causes dual-frequency measurements of the differential carrier phase of GPS L1 and L2 signals to have a contribution from phase scintillations on the two signals. Dual-frequency data for fluctuations in the total electron content (TEC) along the path of GPS signals to the equatorial station Ancon (1.5° dip), sampled at a rate of 1 Hz, are used to separate this contribution from the slower TEC variations. Rapid fluctuations in the differential carrier phase, usually on timescales < 100 s, which result from diffraction, are seen to follow the pattern of intensity scintillations on the L1 signal. Intensity scintillations are also related to the variations in TEC which arise from density fluctuations associated with ionospheric irregularities. An approximate version of the transport-of-intensity equation, based on a phase screen description of the irregularities, suggests that a quantitative measure of intensity scintillations may be provided by the derivative of rate of change of TEC index (DROTI), obtained from the second derivative of TEC. This equation also yields the dependence of the scaling factor between DROTI and S4 on the Fresnel frequency. Comparison of DROTI computed from relative TEC data to corresponding S4 indices indicates that there may be lesser uncertainity in a quantitative relation between the two than between the index ROTI, introduced in recent years, and S4. Power spectral analysis of TEC fluctuations and simultaneous intensity scintillations on L1 signal, recorded at Ancon, does not indicate any simple dependence of the scaling factor between DROTI and S4 on the spectral characteristics.

The GPS global detection of the ionospheric response to solar flares

Abstract: This author suggests the concept of a new technology for global detection (GLOBDET) of atmospheric disturbances of natural and technogenic origin, on the basis of phase measurements of the total electron content (TEC) in the ionosphere using an international GPS network. Temporal dependencies of TEC are obtained for a set of spaced receivers of the GPS network simultaneously for the entire set of "visible" (over a given time interval) GPS satellites (up to 5-10 satellites). These series are subjected to filtering in the selected range of oscillation periods using algorithms for spatio-temporal analysis of signals of non-equidistant GPS phased antenna arrays which are adequate to the detected disturbance. An analysis is made of the possibilities of using the GLOBDET when detecting the ionospheric response of solar flares. In this case it is best to make the coherent summation of the filtered series of TEC. A powerful impulsive flares of July 29, 1999 and December 28, 1999 were chosen to illustrate the practical implementation of the proposed method.

Global Positioning System measurements of the ionospheric zonal apparent velocity at Cachoeira Paulista in Brazil

Abstract: Ionospheric irregularities and their zonal apparent drift were studied using Global Positioning System (GPS) measurements at Cachoeira Paulista (22.41°S, 45.00°W, −26° dip angle) in Brazil during November 6–19, 1998. Radio scintillations at the GPS L1 frequency (1.575 GHz) were monitored using four GPS receivers spaced geomagnetically east–west and north–south. Total electron content (TEC) was measured through the ionospheric advance of the GPS L1 and L2 (1.227 GHz) phases. Strong amplitude scintillations coincided with TEC fluctuations associated with spread F bubbles elongated along the magnetic field. Movement of the Presnel-scale (400 m) ionospheric irregularity layers caused the scintillation to drift, and their zonal apparent drift velocities were measured using a cross-correlation technique. Our measurements show that the apparent eastward velocity varies from 200 m/s to 150 m/s at 2000 LT, and then it decreases to 100–50 m/s at midnight. On a magnetically disturbed day, reversal of the zonal apparent drift was observed just after midnight, and the apparent westward velocities observed at early in the morning showed large variations with location in the sky. From the receivers spaced in the geomagnetic north–south direction we measured near-zero time shifts, from which we conclude that the correlation length of several-hundred-meter-scale irregularities is much larger than 70-m separation between the north and south receivers.

A study on the TEC perturbations prior to the Rei-Li, Chi-Chi and Chia-Yi earthquakes

Abstract: Three large earthquakes struck central Taiwan near the towns of Rei-Li on 17 July 1998, Chi-Chi on 20 (21 for local time) September 1999 and Chia-Yi on 22 October 1999, respectively These earthquakes severely damaged structures heavily changed landforms and disturbed geophysical environments In this paper, a procedure is introduced to derive the ionospheric total electron content (TEC) from data recorded by a network of the Global Positioning System (GPS) in Taiwan Based on the network data, the latitude-time-TEC (LTT) plots prior to the three earthquakes are constructed The plots show that during 1-4 days prior to the three earthquake onsets, the TEC values decrease and the anomaly crests move toward the equator

Porous silicon layer coupled with thermoelectric cooler: a humidity sensor

Abstract: In this work, an original humidity sensor is described. It is based on the study of the capacitance variation of a porous silicon layer (PSL) during water condensation induced by a commercial small-size thermoelectric cooler (TEC). The measurement principle is to detect the weak increase of capacitance created when water condensation occurs in a PSL stuck on a TEC. This important variation of capacitance is related to the high difference between the dielectric constant of PS ( e r e r ≅80). The dielectric constant of PS ranges from these of silicon oxide ( e r =3.9) to these of silicon ( e r =12) [H. Mathieu, Physique des semiconducteurs et des composants electroniques, Masson, 1987, p. 36]. Experimental measurements are performed in a climatic chamber for several values of relative humidity from 10% to 95% and for a TEC current equal to 0.43 A for the cooling part of the process. The analysis of the PS capacitance leads to information over the condensation formation during the TEC cooling. A quick increase of the capacitance appears after a delay time, τ , of 0.5–2 s from the start of the TEC cooling. The higher the humidity level, the faster the capacitance increase. It is possible to draw the capacitance reached after 1 s, from the start of the TEC cooling as a function of the relative humidity level.

Highly structured tropical airglow and TEC signatures during strong geomagnetic activity

Abstract: A remarkable set of all-sky images using the 630 nm airglow emission has been taken over the Arecibo Observatory in Puerto Rico. Wave-like structures at a height of about 250 km are commonly found to travel in the southwest direction at speeds ranging from 20-120 m/s. Most surprising is that geomagnetic activity seems to greatly amplify them, forming very intricate patterns of light and dark. Simultaneous observations using GPS satellite transmissions on one night reveal that dark regions are severely plasma depleted while bright regions have nighttime content as large as the full noontime ionosphere. This unexpected geomagnetic effect at mid-latitudes has implications for trans-ionospheric radiowave propagation and Space Weather.

Combined Ionospheric Campaign 1: Ionospheric tomography and GPS total electron count (TEC) depletions

Abstract: Results from the June 1998 combined ionospheric campaign (CIC) are presented. The CIC represents an attempt to focus a large number of different instruments on one interesting geophysical region. The Center for Ionospheric Research (CIR) at Applied Research Laboratories, the University of Texas at Austin (ARL:UT), has had several computerized ionospheric tomography (CIT) receivers deployed in the Caribbean region since July 1997. In this paper we compare CIT data, GPS TEC data and data from the incoherent scatter radar at Arecibo to try to obtain an understanding of the temporal and spatial distribution of ionospheric structure observed during the campaign. We use the three data sets as inputs to the 3DVAR tomography algorithm developed at CIR and present results of the 3DVAR “objectively analyzed” electron density field. An ionization wall was found near 40° latitude in agreement with previous Millstone Hill and DMSP observations in high Kp. Several elongated density depletions were also detected.

The use of the international GPS network as the global detector (GLOBDET) simultaneously observing sudden ionospheric disturbances

Abstract: We developed a new technology for global detection of ionospheric disturbances, on the basis of phase measurements of the total electron content (TEC) along the line-of-sight (LOS) between the receiver on the ground and transmitters on the GPS satellites using an international GPS networks. Temporal dependencies of TEC with the time resolution of 30 s are obtained for a set of spaced receivers of the GPS network simultaneously for the entire set of visible satellites. These series are subjected to filtering in the selected range of oscillation periods using known algorithms for spatio-temporal analysis of signals. An analysis is made of the possibilities of using the GLOBDET when detecting the ionospheric response of solar flares. In this case it is best to make the coherent summation of the filtered series of TEC. Because of a statistical independence of the background fluctuations, the signal/noise ratio, when the flare effect is detected, is increased due to a coherent processing by at least the times, where N is the number of LOS.

Structure and expression of the mouse gene encoding the orphan nuclear receptor TEC.

Abstract: Translocated in extraskeletal chondrosarcoma (TEC) is an orphan nuclear receptor involved in the control of cell proliferation and apoptosis and is expressed mainly in the mammalian central nervous...

Adhesion of immature and mature T cells induces in human thymic epithelial cells (TEC) activation of IL-6 gene trascription factors (NF-kappaB and NF-IL6) and IL-6 gene expression: role of alpha3beta1 and alpha6beta4 integrins.

Abstract: T cell precursors homed to thymus develop in close contact with stromal cells. Among them, thymic epithelial cells (TEC) are known to exert dominant roles in their survival and functional shaping. Key molecules mediating TEC/thymocytes interactions include cytokines and growth factors secreted by the two cell types and adhesion receptors mediating cell contact. Signaling events triggered in thymocytes by adhesion to epithelial cells have been extensively investigated, whereas little is known on the opposite phenomenon. We have previously investigated this issue in a co-culture system composed of TEC cultures derived from human normal thymus and heterologous thymocytes. We demonstrated that thymocytes adhere to TEC involving β1 and β4 integrins and induce the clustering of (α3β1 and α6β4 heterodimers at the TEC surface. In addition thymocyte adhesion was followed by activation of NF-κB and NF-IL6 gene transciption factors and enhanced IL-6 production. The two latter phenomena were reproduced by the cross-linking of the α3, α6, β1 and β4 integrins, thus implying that the α3β1 and α6β4 heterodimers can signal during thymocyte adhesion. We have extended our previous work investigating in the same experimental setting the inducing activity of non stimulated or activated policlonal or clonal mature T cells as representative of the more mature thymocyte subset. We found that adhesion of unstimulated T cell i) involved β1, but not β4 integrin functions at the surface ii) induced the clustering of α3β1 , but not α2β1 heterodimers at the TEC surface and iii) up-regulated the nuclear binding activity of NF-κB transcription factor and the IL-6 secretion. We propose that α3β1 and α6β4 heterodimers are induced to cluster at the TEC surface recognizing yet unknown cellular ligands differentially expressed during T cell development.

Mesoscale structure of the midlatitude ionosphere during high geomagnetic activity: Airglow and GPS observations

Abstract: On the night of November 22, 1997, the Cornell All-Sky Imager recorded a spectacular display of structure in the 630.0 nm emission over Arecibo, Puerto Rico. This event is an example of a phenomenon we have termed “intense midlatitude spread F.” In this paper we describe the stormtime geophysical conditions for the period and detail the evolution of the event. The daytime midlatitude ionosphere was disturbed for four consecutive days. The initial daytime doubling of the total electron content (TEC) was associated with equatorward propagation of a high-TEC patch that seemed to have associated composition changes. The following days had distinct diurnal double maxima (DDM). The TEC in the Caribbean was very high during the first night of the storm and was extremely structured. Airglow depletions and enhancements surged poleward, bifurcating numerous times in the process. The airglow depletions were collocated with TEC minima along similar lines of sight to Global Positioning System satellites. Eventually, four parallel and very similar airglow wave packets were visible and oriented at an angle similar to the less violent structures reported in the companion paper [Garcia et al., this issue] and moving slowly toward the southwest. We explore a number of possible explanations for these features. We are most confident that secondary instabilities of the generalized ExB process can explain the evolution of the structures once they are formed. The initial process itself remains controversial.

Interleukin-8 secretion of cortical tubular epithelial cells is directed to the basolateral environment and is not enhanced by apical exposure to Escherichia coli

Abstract: In upper urinary tract infections, tubular epithelial cells (TEC) may play a pivotal role in the initiation of the renal inflammatory response. They exert crucial immunological functions such as processing and presentation of foreign antigen, secretion of proinflammatory cytokines (interleukin-6 [IL-6] and tumor necrosis factor alpha) and chemokines (IL-8, MCP-1, ENA-78, and RANTES). Since monolayer cultures are a limited model for polarized tubular epithelial cells, we studied the side-dependent IL-8 secretion of TEC by using cell culture inserts as a basement membrane imitation. Primary cultures of proximal TEC were stimulated with differently fimbriated mutants of Escherichia coli, E. coli LPS, S-fimbria isolates, and IL-1α. IL-8 protein was measured by enzyme-linked immunosorbent assay, and IL-8-like biological activity was tested by measuring elastase release from polymorphonuclear cells in supernatants of the upper and lower compartments. IL-8 mRNA was compared by competitive PCR. IL-8 secretion by TEC into the basolateral environment was significantly higher than secretion into the apical compartment, representing the tubular lumen. However, stimulation of IL-8 secretion by TEC was restricted to IL-1α and was not inducible by E. coli mutants, S fimbriae, or lipopolysaccharide. With this in vitro model of polarized TEC, we show that luminal contact of TEC with uropathogenic E. coli does not result in enhanced IL-8 secretion. The basolaterally directed production of the neutrophil chemotactic factor IL-8 by TEC after stimulation with IL-1α might play an important role in the initiation of inflammatory cell influx into the renal parenchyma.

Comparison of total electron content obtained from GPS with IRI

Abstract: The comparison of the IRI model with TEC estimated using the continuous GPS observations of European part of IGS network is considered. The variability of a measured TEC was analyzed for the low solar activity in the period 1996–1997. We used IRI 90 version with upped height limit 2000 km and IRI 95 up to 1000 km. It is shown that the difference between model and measured TEC depends on latitude and season. Generally, IRI 95 underestimate and IRI 90 overestimate the TEC relative to GPS measurements. The relative difference may reach over 50%.

Role of Tec kinase in nuclear factor of activated T cells signaling.

Abstract: The Tec protein kinase family includes Btk, Itk, Tec, Rlk and Bmx, which are critically involved in signals mediated by various cytokines and antigen receptors Btk mutations cause severe immunodeficiencies, with defective B cell function In T cells, Tec regulates cytokine production However, the downstream targets of these Tec kinases are poorly defined Here we report that overexpression of Tec in T cells can regulate gene transcription through the nuclear factor of activated T cells (NF-AT) Using different reporter gene constructs, we establish that Tec in transfected T cells dramatically induced NF-AT-dependent gene transcription, which was prevented by a dominant-negative mutant of NF-AT or by the immunosuppressive drug cyclosporin A Tec appears to regulate NF-AT nuclear import In addition, Tec influences cytoplasmic free calcium increase Taken together, our results identify NF-AT as a major downstream target of Tec kinases that is critically involved in transcriptional gene regulation These observations highlight signaling pathways regulated by Tec kinases and provide new pharmacological targets to regulate immune functions

Study of the ionospheric TEC using GPS during the large solar flare burst on Nov. 6,1997

Abstract: Using the data from 15 global positioning system (GPS) stations scattered between 28° N—45° N and 90° W—77° E we obtained the total electron content (TEC) variations with time during a large solar flare. The results indicated that the flare makes the TEC of ionosphere increasing in a large spatial area. The amounts of the TEC enhancement are mainly determined by the local time of subionospheric point, and the largest TEC enhancement is about 2.5 TECU. It is also concluded that the TEC enhancement is not symmetrical about the local noon time, the TEC enhancement values during morning hours are larger than those of the afternoon hours.

Eye on the Ionosphere: The Correlation between Solar 10.7 cm Radio Flux and Ionospheric Range Delay

Abstract: Patricia Doherty joins the regular contributors of this column to discuss the correlation between measurements of solar 10.7 cm radio flux and ionospheric range delay effects on GPS. Mrs. Doherty has extensive experience in the analysis of ionospheric range delays from worldwide systems and in the utilization and development of analytical and theoretical models of the Earth's ionosphere. Ionospheric range delay effects on GPS and other satellite ranging systems are directly proportional to the Total Electron Content (TEC) encountered along slant paths from a satellite to a ground location. TEC is a highly variable and complex parameer that is a function of geographic location, local time, season, geomagnetic activity, and solar activity. When insufficiently accounted for, ionospheric TEC can seriously limit the performance of satellite ranging applications. Since the ionosphere is a dispersive medium, dual-frequency Global Positoning System (GPS) users can make automatic corrections for ionospheric range delay by computing the apparent difference in the time delays between the two signals. Single-frequency GPS users must depend on alternate methods to account for the ionospheric range delay. Various models of the ionosphere have been used to provide estimates of ionospheric range delay. These models range from the GPS system's simple eight-coefficient algorithm designed to correct for approximately 50% rms of the TEC, to state-of-the-art models derived from physical first principles, which can correct for up to 70 to 80% rms of the TEC but at a much greater computational cost. In an effort to improve corrections for the day-to-day variability of the ionosphere, some attempts have been made to predict the TEC by using the daily values of solar 10.7 cm radio flux (F10,7). The purpose of this article is to show that this type of prediction is not useful due to irregular, and sometimes very poor, correlation between daily values of TEC and F10.7. Long-term measurements of solar radio flux, however, have been shown to be well correlated with monthly mean TEC, as well as with the critical frequency of the inonospheric F2 region (foF2), which is proportional to the electron density at the peak of the ionospheric F2 region. © 2000 John Wiley & Sons, Inc.

Preferential Activity of Wild‐type and Mutant Tumor Necrosis Factor‐α against Tumor‐derived Endothelial‐like Cells

Abstract: Tumor-derived endothelial-like cells (tEC) were prepared by culturing human umbilical vein endothelial cells (HUVEC) in the presence of HT1080 human fibrosarcoma-conditioned medium. tEC showed higher permeability and less cell-adhesion activity than normal HUVEC (nEC). Tumor necrosis factor-alpha (TNF) is known to have tumor-vasculature disrupting activity. tEC showed higher cytotoxicity to recombinant human TNF (rhTNF) than nEC, and was not observed using HUVEC cultured with WI38 human diploid cell-conditioned medium as a medium-control. These results demonstrate that tEC acquire physiological properties of tumor-associated vasculature, and may be a useful model system for the study of the mechanisms of TNF antitumor action. The TNF-mutant RGD-V29 (code No. F4614), which has an inserted 4Arg-Gly-Asp sequence and an 29Arg-->Val replacement, was found to induce greater preferential destruction of tEC compared to rhTNF. When the preferential activities were evaluated in terms of 30% cytotoxicity (IC30) ratio (nEC/tEC), the ratio was 460 for RGD-V29 compared to 4.2 for rhTNF. RGD-V29 also exhibited cell-adhesive function and bound preferentially to the p55 TNF-receptor. Both these properties of RGD-V29 contributed to the tEC selective cytotoxicity, indicating that the RGD ligands and selective p55 receptor binding on the cells, although uncharacterized, are involved in tEC targeting. Therefore, the TNF mutant RGD-V29 may show greater selectivity toward tumor vasculature than wild-type TNF.

Quantitative Investigation of Ionospheric Density Gradients at Mid Latitudes

Abstract: The sub-auroral ionosphere, at the magnetic latitudes which characterize the northeastern United States, is subject to severe F-region ionospheric density structuring due to the space weather effects of magnetospheric disturbance electric fields. Communications and navigation systems relying on trans-ionospheric propagation must be able to compensate for the effects of the sharp changes (> 10x) in total electron content (TEC) associated with the ionospheric trough and storm-time disturbance effects at mid latitudes. An accurate characterization of these gradients and their variability is needed in the design and evaluation of navigation systems utilizing trans-ionospheric propagation in this regime. A study is underway at the MIT Haystack Observatory using the Millstone Hill incoherent scatter radar database to investigate the spatial extent and temporal evolution of TEC and density altitude/latitude structure at mid and sub-auroral latitudes as a function of solar cycle, season, and level of geomagnetic activity. The Massachusetts Institute of Technology maintains an extensive radar research facility at Millstone Hill, located 35 miles northwest of met-ropolitan Boston at 42.6° N latitude, 288.5° E longitude. Multi-megawatt UHF transmitters and a fully-steerable 46-m antenna provide wide-ranging spatial coverage, spanning >30° of latitude and 4+ hours of local time at F-region heights. The facility is situated at 54° geomagnetic latitude such that its extensive field-of-view for ionospheric observations encompasses the full extent of mid-latitude, sub-auroral, and auroral features and processes. The Millstone Hill incoherent scatter radar has been in operation through three solar cycles and its data characterize ionospheric features and response over the altitude range 100 km to 1000 km with a typical altitude/spatial resolution of 50 km. Long-term operations as a part of the international Inco-herent Scatter World Day program have built up a database of radar elevation scans which sample a span of 15° - 25° latitude with better than 1° latitude resolution and ~35 km altitude resolution. Data from each radar elevation scan is used to produce vertical TEC in the altitude range 150 km - 650 km with better than 1° latitude resolution. Density gradients associated with the deep, narrow ionospheric trough which forms during disturbed conditions are ~10 TEC units / degree latitude. Storm enhanced density (SED), the bulk redistribu-tion of F-region plasma by disturbance electric fields, can result in TEC > 100 over New England and TEC gradients of ~50 TEC / degree latitude.