Showing papers on "TEC published in 1993"

A New Method for Monitoring the Earth's Ionospheric Total Electron Content Using the GPS Global Network

Abstract: The global positioning system satellites and a world-wide network of dual-frequency GPS receivers can be used to measure ionospheric total electron content (TEC) on global scales. A new method for generating global TEC maps is described. This method uses a Kalman-type filter and random-walk process noise to generate TEC maps at time intervals of one hour or less. The maps utilize a locally-supported vertical TEC function (called “TRIN”) based on tessellation of the sphere into 1280 spherical triangles. The 642 vertices of the triangles are assigned a TEC value estimated from the data and the TEC within each tile is computed by linearly interpolating between vertex TEC values. The previous approach used a single- batch filter requiring an averaging time of 6-12 hours before a map could be obtained; the TEC data was fitted to a surface harmonic expansion which did not follow local TEC variations accurately. Both approaches use a spherical thin-shell elevation mapping function to convert all station-to-satellite TEC measurements to equivalent vertical TEC at a unique shell intersect point. The new maps follow diurnal TEC variations over a single site to within a few TECU as measured by established single-site GPS calibration techniques. In a global-scale simulation using the Bent ionosphere model, the TRIN fit reproduces the simulated data set to within 5 TECU over 70 percent of the globe. Errors exceeding 10 TECU are seen in the daytime-peak regions within the equatorial bulge. Methods for improving the accuracy of the maps are discussed.

Expression of a novel form of Tec kinase in hematopoietic cells and mapping of the gene to chromosome 5 near Kit.

Abstract: The Tec kinase was initially identified as a novel cytoplasmic protein tyrosine kinase that is preferentially expressed in the liver and is highly homologous to the Drosophila Dsrc28C src-related tyrosine kinase. In screening of interleukin 3 (IL-3)-dependent myeloid leukemia cells for protein tyrosine kinases, we observed that all cell lines examined expressed high levels of Tec transcripts. However, characterization of Tec cDNAs indicated that they differed significantly from the published sequence. Most strikingly, an insertion of 41 bp in the 5' region affects the initiation codon and results in replacing the published 13 amino acid amino-terminal sequences with 94 amino acids. Using polymerase chain reaction (PCR) analysis, only the form containing the insertion was detected in hematopoietic cells. In addition, we found an in-frame insertion of 66 bp that introduces an additional 22 amino acids into the SH3 domain. This insertion restores conserved SH3 sequences that are found in the src gene family and in the Dsrc28C gene. By PCR analysis, approximately equal levels of Tec transcripts containing the intact SH3 domain and containing the 22 amino acid deletion were found in hematopoietic cells. Lastly, by interspecies backcross analysis, we show that the Tec gene is tightly linked to the c-Kit gene on mouse chromosome 5.

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).

Light-propagation characteristics in thermally diffused expanded core fibers

Abstract: Characteristics of light propagation in thermally diffused expanded-core (TEC) fibers are analyzed. Changes in the modal-field distributions along fibers and transition losses are obtained by use of the propagating-beam method. It is found that a transition length sufficiently longer than the characteristic length is necessary to expand or reduce the field diameter with low losses. A simplified model for understanding the mechanism of light propagation in TEC fibers is presented. Transmission losses between TEC fibers having imperfect splices are measured, the results are compared with those obtained by a simple theory and an exact theory. >

Elimination of Tec elements involves a novel excision process.

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.

Diurnal double maxima patterns in the F region ionosphere: Substorm-related aspects

Abstract: Daytime double maxima (twin peaks or bite-outs) in the ionospheric total electron content (TEC) at middle and lower latitudes are found to be related to substorm signatures shown in both auroral electrojet and ring current variations. Case studies reveal that during substorm onset and recovery phases, the penetration of magnetospheric convection electric fields and their subsequent {open_quotes}overshielding{close_quotes} effects may be the major dynamical sources of these events. A theoretical low-latitude ionospheric model is used to simulate the dynamical effects of electric field disturbances on F region electron density and TEC. It is demonstrated that the diurnal double maxima in TEC can be created by a combined effect of E x B drift and altitude-dependent F region chemical loss. The required zonal electric fields are found to have greater penetration efficiency in the early evening sector and their latitudinal requirements appear to change with local time. The time scales for the modeled penetration and overshielding effects are 2-3 hours. Modeling results also show that considerable structuring in the local time variation of the ionospheric {open_quotes}equatorial anomaly{close_quotes} can occur due to the interplay of convection electric field penetration and overshielding effects. The possible cause of the midday bite-out ionospheric disturbances by themore » meridional winds associated with traveling atmospheric disturbances (TADs) is also addressed in modeling studies, but the specialized nature of the required TADs makes this a less well understood substorm-related mechanism. 64 refs., 14 figs., 3 tabs.« less

Interleukin-6 overproduction by cultured thymic epithelial cells from patients with myasthenia gravis is potentially involved in thymic hyperplasia.

Abstract: Most patients with Myasthenia Gravis (MG) present a thymic hyperplasia characterized by the presence of lymphoid follicles. The acetylcholine receptor autoantigen, as well as autoantigen specific activated T and B cells found in the thymus, strongly suggest that auto-sensitization could take place in this organ. Since IL-6 is involved in T and B cell growth and differentiation, we thought that abnormal IL-6 expression by thymic epithelial cells (TEC) could be related to thymic hyperplasia in MG. In this paper, IL-6 protein and gene expression by cultured TEC from patients with MG were examined. TEC from patients presented a dramatic IL-6 hyperproduction phenotype as compared to controls when stimulated by exogenous signals such as LPS and cytokines (IL-1 beta, TNF-alpha) alone or in combination. Moreover, we observed a similar effect with a physiological signal such as the syngeneic lympho-epithelial cell contact. Autologous thymocytes stimulated normal and MG TEC IL-6 production in a time- and dose- dependent way, and with a higher magnitude in MG TEC compared to controls. In all stimulation conditions, induction of IL-6 production required protein synthesis and was associated with increased IL-6 mRNA level expression as assessed by computer-aided quantification after in situ mRNA hybridization. In addition, recombinant IL-6 induced in vitro growth of TEC, demonstrating that IL-6 is a possible autocrine growth factor for these cells. This deregulated IL-6 production as well as the ability of TEC to use it as a growth factor may be of pathophysiological relevance in MG. It provides an explanation for morphological changes of the thymus and may have a key role in initiation, exacerbation and ongoing of the autoimmune response in MG. Therefore this study extends our current understanding of the molecular pathophysiology of MG.

A statistical characterization of local mid‐latitude total electron content

Abstract: The integrated line-of-sight electron density within the ionosphere, known as the total electron content (TEC), is commonly used to quantify ionospheric propagation effects. In order to extrapolate single-point measurements of TEC to other locations and times, some characterization of the TEC spatiotemporal variation must be available. Using a four-channel receiver tracking coded signals from the NAVSTAR Global Positioning System satellites, estimates of both the mean variation and correlation coefficient have been made for the approximately 1200-km or 1-hour local time radius ionospheric region within view of a mid-latitude station. Results were obtained for morning and midday over a 4-week period near the autumnal equinox in 1989. The derived mean variation was found to be well characterized by linear functions of the local time and latitude separation between the ground site and the ionospheric penetration point of the signal. The correlation coefficient during midday was found to decrease linearly with latitude, longitude, and time separation, with values of about 0.91 for a 1000-km separation and 0.98 for a 1-hour separation. During morning hours the longitude and time coefficients were similar to the midday values, but the latitude coefficient was found to have a nonlinear dependence, with values as small as 0.70. The combined results suggest that the decorrelation is due primarily to longer term TEC fluctuations, such as day-to-day variation in the TEC spatial dependence, rather than to transient effects such as traveling ionospheric disturbances. The analysis provides a spatiotemporal characterization of TEC that can be used to extrapolate TEC values from single-point measurements.

Remote sensing of auroral E region plasma structures by radio, radar, and UV techniques at solar minimum

Abstract: The unique capability of the Polar BEAR satellite to simultaneously image auroral luminosities at multiple ultraviolet (UV) wavelengths and to remote sense large-scale (hundreds to tens of kilometers) and small-scale (kilometers to hundreds of meters) plasma density structures with its multifrequency beacon package is utilized to probe the auroral E region in the vicinity of the incoherent scatter radar (ISR) facility near Sondrestrom. In particular, we present coordinated observations on two nights obtained during the sunspot minimum (sunspot number <10) January–February 1987 period when good spatial and temporal conjunction was obtained between Polar BEAR overflights and Sondrestrom ISR measurements. With careful coordinated observations we were able to confirm that the energetic particle precipitation responsible for the UV emissions causes the electron density increases in the E region. These E region electron density enhancements were measured by the ISR at Sondrestrom. The integrations up to the topside of these ISR electron density profiles were consistent with the total electron content (TEC) measured by the Polar BEAR satellite. An electron transport model was utilized to determine quantitatively the electron density profiles which could be produced by the particle precipitation, which also produced multiple UV emissions measured by the imager; these profiles were found to be in good agreement with the observed ISR profiles in the E region. Surprisingly large magnitudes of phase and amplitude scintillations were measured at 137 and 413 MHz in the regions of TEC enhancements associated with the particle precipitation. Steep phase spectral slopes with spectral index of 4 were found in these regions. Strength-of-turbulence computations utilizing the ISR electron density profiles and observed characteristics of phase and amplitude scintillations are interpreted in terms of an irregularity amplitude varying between 10 and 20% at a several-kilometer outer scale size in the E region extending approximately 50 km in altitude. This outer scale size is also consistent with the measured phase to amplitude scintillation ratio. An estimate of the linear growth rate of the gradient-drift instability in the E region shows that these plasma density irregularities could have been generated by this process. The mutual consistency of these different sets of measurements provides confidence in the ability of the different techniques to remote sense large- and small-scale plasma density structures in the E region at least during sunspot minimum when the convection-dominated high-latitude F region is fairly weak.

Age dependency of red blood cell deformability and density : studies in transient erythroblastopenia of childhood

Abstract: Several investigators have demonstrated that red blood cell (RBC) deformability decreases progressively with increasing cell density and proposed that reduction in deformability plays a role in the senescence process of normal RBCs. Transient erythroblastopenia of childhood (TEC) results from temporary cessation of erythropoiesis. Since no new RBCs are produced for some time, the circulating RBCs are relatively old. RBS density (phthalate-oil method) and RBC deformability (RBC elongation in a counter-rotating rheoscope) were studied in seven children with TEC and in 10 control children. The mean values of MCHC, RBC density and RBC deformation were not significantly different between TEC and control children. Compared to controls, the frequency distribution of RBC density in TEC was slightly shifted to higher values. The percentage of RBCs with extremely low densities ( 1.106 g/ml) was 6.4 +/- 2.1% in the patients and 4.9 +/- 1.8% in the controls (P > 0.10). The reduction of RBCs with low density in TEC suggests that RBCs with low density are relatively young. Since the percentage of RBCs with high density increased only slightly in TEC, we conclude that only a fraction of dense RBCs is old. In TEC, the frequency distribution of RBC elongation was slightly shifted to lower values. 5% of the RBCs studied in the control children had RBC elongation values above 0.39 (TEC 1.2%) and 5% had elongation values below 0.16 (TEC 6.7%). Thus, only a small fraction of highly deformable RBCs was diminished in TEC. These data suggest that a decrease in deformability is not a significant part of the normal ageing process of human RBCs.

Construction and performance of the L3 central tracking detector

Abstract: The L3 central tracking detector has been in operation since the start-up of LEP (Large Electron Positron collider) in 1989. This detector consists of a Time Expansion Chamber (TEC), a layer of Plastic Scintillating Fibers and a Z-chamber. The TEC gives a high spatial resolution and an excellent multi-track reconstruction capability. The fibers are designed to calibrate the drift velocity with high precision. The Z-Chamber provides TEC with accurate information about the z-coordinates of the tracks. A description of the design and the infrastructure of these three detectors, including the readout and data acquisition system, is given. The performance of the detectors during the 1990 and 1991 LEP running periods is presented.

GPS L1-L2 Bias Determination

Abstract: : The GPS satellite L1-L2 bias T sub gd is determined using data from a TI-4100 receiver operating at Millstone Hill in Westford, MA. Pseudorange L1-L2 differences are computed. This difference is a measure of the total electron content (TEC) path delay along the line of sight plus the L1-L2 satellite and receiver bias. The difference of two measurements at the same time and satellite position cancels the TEC path delay and possible receiver bias and is a measure of the difference in satellite bias of the two satellites; i.e., Sv(a)L1-L2 - Sv(b)L1-L2. such direct measurements are not often available. Therefore, measurements at the same time are converted to 'zenith' TEC values using a mapping function. These difference are used in a least squares solution to determine the difference in bias between GPS satellites. Individual bias differences are obtained with an accuracy of 0.1 ns (o.285 TEC units) or better. By choosing one satellite as the reference, the individual satellite biases can also be obtained. The stability of each satellite bias is also estimated by examining a time series of the differences.

Sub-Daily Northern Hemisphere Ionospheric Maps Using the IGS GPS Network

Abstract: Ionospheric total electron content (TEC) data derived from dual-frequency GPS signals from 30 globally distributed IGS network sites are fit to a simple ionospheric shell model, yielding, simultaneously, values for the satellite and receiver biases, and a map of the ionosphere in the northern hemisphere every 12 hours during the period of Jan. 1-15, 1993. RMS residuals of 2-3 TEC units are observed over the 20-80 degree latitude band. Various systematic errors affecting the TEC estimates are discussed. The capability of using these global maps to produce ionosphere calibrations for sites at which no GPS data are available is investigated.

Analysis of rocket beacon transmissions for computerized reconstruction of ionospheric densities

Abstract: Three methods are described to obtain ionospheric electron densities from transionospheric, rocket-beacon TEC data. First, when the line-of-sight from a ground receiver to the rocket beacon is tangent to the flight trajectory, the electron concentration can be obtained by differentiating the TEC with respect to the distance to the rocket. A similar method may be used to obtain the electron-density profile if the layer is horizontally stratified. Second, TEC data obtained during chemical release experiments may be interpreted with the aid of physical models of the disturbed ionosphere to yield spatial maps of the modified regions. Third, computerized tomography (CT) can be used to analyze TEC data obtained along a chain of ground-based receivers aligned along the plane of the rocket trajectory. CT analysis of TEC data is used to reconstruct a 2D image of a simulated equatorial plume. TEC data is computed for a linear chain of nine receivers with adjacent spacings of either 100 or 200 km. The simulation data are analyzed to provide an F region reconstruction on a grid with 15 x 15 km pixels. Ionospheric rocket tomography may also be applied to rocket-assisted measurements of amplitude and phase scintillations and airglow intensities.

New mode-field conversion technique in optical fiber using thermal relaxation of residual stress

Abstract: For lensless in-line optical devices, thermally diffused expanded- core (TEC) fibers have been proposed by Kawakami,1 and the application of the TEC technique to isolators and the low-loss splicing of high-N.A. single-mode fibers have been actively studied.8 In a TEC fiber the mode-field diameter (MFD) is gradually increased along the fiber axis with the thermal diffusion of the dopants induced by heat treatment. However, the heating process for a dopant diffusion requires either a high temperature or a long duration. In this paper we propose and demonstrate a MFD conversion technique that uses thermal relaxation of the residual stress in the core.

Regulation of M-CSF production by cultured human thymic epithelial cells.

Abstract: We have studied the regulation of M-CSF production by human thymic epithelial cells (TEC) in a continuing effort to better understand the contribution of TEC to the intrathymic cytokine network. The levels of M-CSF were measured by radioimmunoassay. Five different TEC cultures were studied and we found that all cells examined produced M-CSF constitutively. We also studied the effects of cytokines on the regulation of the M-CSF secretion profile. IL-1, which strongly induces the secretion of a number of cytokines in TEC, was found to up-regulate M-CSF levels. The effects of IL-1 were dose and time dependent suggesting a direct effect on TEC. IFN-gamma is known to up-regulate cell surface antigens, and to modulate the IL-1-induced cytokine response in TEC. IFN-gamma could induce M-CSF by itself, but the effects were less pronounced than those of IL-1. IFN-gamma did not modify the IL-1-induced M-CSF. IL-4, which has been shown to partially modulate the IL-1-induced GM-CSF in TEC, had no effect on constitutive or induced M-CSF levels. These data are discussed in the context of the regulation of myelopoietic growth factor production by thymic stromal cells.

Mechanical dilatation rather than plaque removal as major mechanism of transluminal coronary extraction atherectomy.

Abstract: Atherectomy with the transluminal extraction endarterectomy catheter (TEC) is a new approach for treatment of coronary artery disease, which continues to undergo FDA investigational studies, The major mechanism of the TEC device should be excision of plaque and its removal due to suction applied through an attached vacuum. We report about the acute results in 24 patients treated with TEC atherectomy in native vessels and the outcome of 18 patients who, until recently, underwent follow-up catheterization after 6 months. The procedure was successful (residual stenosis < 50%) in 7 of 24 patients with TEC atherectomy alone (29%); 15 of 24 patients (65%)required additional PTCA in order to achieve angiographic success (10 of 24) or to treat total occlusion (2 of 24) or distal embolization (3 of 24) following atherectomy. One TEC attempt failed due to guiding catheter problems, another major complication was a vessel perforation leading to a non-Q wave infarction. The minimal residual diameter after passage of the stenosis (prior to additional PTCA) with the 5.5Fr catheter (n = 14) nsas 1.5 ± 0.2 mm, with the 6Fr catheter (n = 9) 1.8 ± 0.4 mm, and 2.2 ± 0.2 mm using the 7Fr catheter (n = 10). The histologic findings revealed intimal cells, fibrous tissue, and homogenate with no identifiable tissue in five cases (21%), whereas in 17 patients (72%) light microscopy could only assess blood cells. Restenosis was present in 9 of 18 patients (50%), occurred in 3 of 7 patients treated with TEC alone, and in 6 of 11 patients treated with TEC + PTCA. The primary underlying mechanism of TEC atherectomy seems to be mechanical dilatation while tissue excision proved to be inadequate to explain the angiographic result. Further studies should be designed to directly compare TEC atherectomy to PTCA in specific patient subgroups (e.g., bypass grafts, intraluminal thrombus, diffuse disease), in order to define the role of this device.

LYM-type inequalities for tEC/AUED codes

Abstract: Some LYM-type inequalities are introduced to obtain a relationship between the parameters of t-error correcting/all unidirectional error-detecting codes of length n. As an application of these inequalities, new lower bounds on the redundancies of systematic tEC/AUED codes are derived and an extensive table is given. >

Two novel monoclonal antibodies reactive with different components of the rat thymic epithelium.

Abstract: Two novel monoclonal antibodies (mAbs) (PT10B7 and PT13D11) have been raised against molecules of rat thymic epithelial cells (TEC). Streptavidin-biotin immunoperoxidase staining and double immunofluorescence using these mAbs and anti-cytokeratin (CK) antibodies showed that PT10B7 and PT13D11 mAbs bound to different components of rat TEC. PT10B7 mAb reacted with cortical and a subset of medullary TEC, whereas PT13D11 mAb labeled subcapsular/perivascular and most medullary TEC, including TE-R 2.5 TEC line of medullary origin. Their staining patterns were different from those seen using mAbs to CK10, CK18 and CK19 polypeptides and other anti-rat TEC mAbs produced so far. The differences in immunoreactivity of these two mAbs on rat thymus during ontogeny and on other epithelial cells of adult rats were also seen. Namely, PT13D11 stained ectoderm-derived epithelia, whereas PT10B7 stained some cells of simple epithelia. Cumulatively, these results reveal a fine phenotypic heterogeneity within rat thymic epithelium.

A first-principle derivation of the high-latitude total electron content distribution

Abstract: Calculation of the high-latitude distribution of the vertical total electron content (TEC) is possible using a three-dimensional, time-dependent ionospheric model. Global and local comparisons may be made with observations of TEC. We compare the local diurnal variation of TEC calculated by the model with observations of TEC at Goose Bay, Labrador and Hamilton, Massachusetts. Data from the period of March 1–11, 1989, and monthly averaged data for solar maximum and solar minimum periods are examined. We extend the model to predict diurnal variations of TEC in the polar cap and compare these results with the observed TEC at Thule, Greenland, during an 8-day campaign from January 28 through February 4,1984. We propose a possible explanation for the large variability observed. We show that the “equivalent vertical content” TEC is very sensitive to horizontal F layer electron density gradients and that such “equivalent vertical” TECs may vary significantly from the true vertical TEC of the ionosphere. By incorporating these results, we calculate the vertical TEC distribution of the high-latitude ionosphere for a wide range of solar activity, seasons, and Kp variation represented by a recently completed Utah State University time-dependent ionospheric model data base. Finally, we discuss the possible uses of TEC as a diagnostic tool for testing ionospheric models.

On the construction of systematic tEC/AUED codes

Abstract: A new approach for the construction of systematic tEC/AUED codes is presented. These new constructions improve many values of the upper bound on the redundancy of the code for t=1 and 2. >

Sub-Daily Northern Hemisphere Ionospheric Maps Using a World-Wide Network of GPS Receivers

Abstract: Ionospheric total electron mapping content (TEC) data derived from dual-frequency Global Positioning System (GPS) signals from 30 globally distributed network sites are fit into a simple ionospheric shell model,...

Nocturnal disturbances of total electron content and their correlation with VHF radio wave scintillations in the Pacific‐Asia region

Abstract: We have collected 136-MHz Faraday rotation and scintillation data of signals transmitted by the satellite ETS-2 and received at 13 ground stations in the Pacific-Asia region. Using this data base, a statistical analysis has been carried out by correlating the nocturnal TEC disturbances with the amplitude scintillations. Also presented are several typical events observed simultaneously over this network. An important result in the present paper is that the occurrence of amplitude scintillations is closely associated with the wavelike disturbances in TEC with periods below 2 hours. These periods agree with the TIDs produced by atmospheric gravity waves in the ionosphere. Furthermore, simultaneous recordings at several spaced stations indicate the disturbances are traveling. It is therefore deduced that wavelike disturbances in TEC observed are manifested as the ionospheric response to gravity waves in the neutral atmosphere.

Ionospheric calibration for single frequency altimeter measurements

Abstract: This study is a preliminary analysis of the effectiveness (in terms of altimeter calibration accuracy) of various ionosphere models and the Global Positioning System (GPS) to calibrate single frequency altimeter height measurements for ionospheric path delay In particular, the research focused on ingesting GPS Total Electron Content (TEC) data into the physical Parameterized Real-Time Ionospheric Specification Model (PRISM), which estimates the composition of the ionosphere using independent empirical and physical models and has the capability of adjusting to additional ionospheric measurements Two types of GPS data were used to adjust the PRISM model: GPS receiver station data mapped from line-of-sight observations to the vertical at the point of interest and a grid map (generated at the Jet Propulsion Laboratory) of GPS derived TEC in a sun-fixed longitude frame The adjusted PRISM TEC values, as well as predictions by the International Reference Ionosphere (IRI-90), a climatological (monthly mean) model of the ionosphere, were compared to TOPEX dual-frequency TEC measurements (considered as truth) for a number of TOPEX sub-satellite tracks For a 136 GHz altimeter, a Total Electron Content (TEC) of 1 TECU 10(exp 16) electrons/sq m corresponds to approximately 0218 centimeters of range delay A maximum expected TEC (at solar maximum or during solar storms) of 10(exp 18) electrons/sq m will create 22 centimeters of range delay Compared with the TOPEX data, the PRISM predictions were generally accurate within the TECU when the sub-satellite track of interest passed within 300 to 400 km of the GPS TEC data or when the track passed through a night-time ionosphere If neither was the case, in particular if the track passed through a local noon ionosphere, the PRISM values differed by more than 10 TECU and by as much as 40 TECU The IRI-90 model, with no current ability to unseat GPS data, predicted TEC to a slightly higher error of 12 TECU The performance of PRISM is very promising for predicting TEC and will prove useful for calibrating single frequency altimeter height measurements for ionospheric path delay When adjusted to the GPS line-of-sight data the PRISM URSI empirical model predicted TEC over a day's period to within a global error of 860 TECU rms during a nighttime ionosphere and 974 TECU rms during the day When adjusted to the GPS derived TEC grid, the PRISM parametrized model predicted TEC to within an error of 847 TECU rms for a nighttime ionosphere and 1283 TECU rms during the day However, the grid cannot be considered globally due to the lack of sufficient numbers of GPS stations and large latitude gaps in GPS data It is the opinion of the authors that using the PRISM model and adjusting to the global sun-fixed TEC grid regenerated with a localized weighted interpolation offers the best possibility of meeting the 10 TECU global rms (or 2 cm at 136 GHz) ionosphere range correction accuracy requirement of TOPEX/Poseidon and should be the subject of further study However, it is clear that the anticipated requirement of 34 TECU global rms for TOPEX/Poseidon Follow-On (corresponding to the TOPEX/Poseidon performance) can not be met with any realizable combination of existing models and data assimilation schemes

Method for measuring maximum core expansion position of core-expanded optical fiber

Abstract: PURPOSE:To measure the max. core expansion position of a core-expanded optical fiber (TEC fiber) formed with a core-expanded part by partially heating the core of the optical fiber. CONSTITUTION:The center in the longitudinal direction of the heating region of the TEC fiber 4 is determined as the max. core expansion position 3. The max. detection position of leak light power is determined by measuring (photodetector 6) the light power leaking to the outside from the core-expanded part when the light is made incident on the TEC fiber 4 (light source 5). The positional relation between the max. core expansion position 3 and the max. detection position is determined from the above. The light having the same wavelength as the wavelength of the above-mentioned light is made incident on the TEC fiber 4 in the stage of producing the TEC fiber 4 and the max. detection position of the leak light power is determined. The max. core expansion position is obtd. from the positional relation obtd. in such a manner.