Showing papers on "TEC published in 1994"

Heat exchanger for thermoelectric cooling device

Abstract: Heat exchangers for a thermoelectric cooling (TEC) device. A heat dissipation assembly comprises an array of foil corrugations disposed in generally parallel spaced relationship with the heat dissipation plate of the TEC. The array of foil corrugations includes at least an inner and an outer bank of foil corrugations and at least one plate sandwiched therebetween and secured thereto by vacuum brazing thereacross. In this manner, heat conductivity is maximized for transfer of heat thereacross and from the TEC to the outer bank. A heat absorption assembly for use with the TEC comprises a thermal transfer plate having a teflon coated, serpentine fluid conduit therein facilitating the flow of a variety of fluids to be cooled therethrough without contamination thereof.

Molecular Cloning and Analysis of the Human Tec Protein-Tyrosine Kinase

Abstract: Mouse Tec is a non-receptor type protein-tyrosine kinase and is highly expressed in many hematopoietic cell lines. To investigate the roles of the Tec kinase in the human hematopoietic system, we isolated cDNAs encoding the human Tec kinase. The human tec cDNAs can encode a peptide of 631 amino acid residues with a calculated molecular mass of 73,624. The predicted human Tec protein is highly homologous to those of the members of the Tec family including mouse Tec type IV (94% homology), mouse Tsk/Itk (60%), and human Btk (57%). The homology between human Tec and other members of the Tec family can be observed not only in the Src homology 3 (SH3), SH2, and kinase domains, but also in the N-terminal unique domain. Northern blot analysis demonstrated that the major transcripts of tec could be detected at 2.6 kb and 3.6 kb in a wide range of human hematopoietic cell lines including myeloid, B-, and T-cell lineages. Interestingly, high expression of the tec gene could be detected in all of the three patients examined with myelodysplastic syndrome. The human tec gene was mapped by fluorescence in situ hybridization (FISH) to chromosome 4p12.

Apparatus and method for ionospheric mapping

Abstract: This invention is a unique single-site method of determining the local total electron content (TEC) of the ionosphere and its space-time variation using a global positioning system (GPS) ionospheric receiver. The TEC of the ionosphere is specified in terms of a space-time map of the local TEC in the vicinity of the receiver. Differential group and phase path data between two L-band frequencies (L1 and L2) for a plurality of the GPS satellites in view of the receiver station are analyzed by a least squares technique to extract both the ten parameters of a full second order space-time polynomial expansion for the vertical TEC (VTEC) and the differential delay biases associated with the space vehicles (SVs). The method is applicable to day and nighttime data.

Extracting Ionospheric Measurements from GPS in the Presence of Anti-Spoofing

Abstract: Line-of-sight ionospheric measurements derived from differencing dual-frequency Global Positioning System (GPS) pseudorange 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. Hardware calibration of the instrumental delay is possible for some types of receivers (e.g., Allen Osborne Associate’s Rogue SNR-8), but the satellite biases must be estimated using a remote technique. Ignoring the satellite (receiver) biases when computing line-of-sight TEC measurements from GPS observables may result in an error of +-9 (+-30) TECU (1 TEC unit = 1016 electrons/meter2 = 0.35 nanoseconds of differential delay). Using a global ionospheric shell model to fit GPS-based ionospheric delay data from a world-wide network of 50+ receivers, we can simultaneously estimate a global ionospheric map, satellite biases for the entire GPS constellation, and receiver biases for all the uncalibrated receivers. The uncertainty in the resulting estimates of the satellite biases is a dominant error source in extracting line-of-sight TEC measurements from GPS observables. We present the resuits of daily fits of satellite biases over a period spanning 20 months from Jan. 1993 through Aug. 1994. Seven separate time periods each consisting of IO- 12 consecutive days were processed. The day-to-day variability of the estimates has been computed in an effort to assess their precision. Before anti-spoofing (AS) encryption of the GPS ranging code, the estimated satellite biases exhibited a day-to-day standard deviation of 0.6 nanoseconds or 1.7 TECU. With the advent of AS encryption, the pseudorange observable exhibits a lower signal-to-noise ratio, but the day-to-day reproducibility of the biases has not changed significantly. This preliminary study indicates that AS has not had a significant impact on our estimates of the satellite biases. The current satellite bias estimates (with AS on) are consistent with the pre-AS values to a precision of 0.6 ns or 1.7 TECU.

Model‐assisted ionospheric tomography: A new algorithm

Abstract: Ionospheric tomography uses total electron content (TEC) records collected by longitudinally aligned stations, which receive a beacon satellite orbiting overhead. The electron density distribution is reconstructed for the region bounded by the satellite orbit and the line of ground receivers. A new reconstruction algorithm is describes which satisfies the TEC records, makes use of an ionospheric model, and allows the incorporation of complementary measurements. The new algorithm also accepts relative (rather than absolute) TEC as input data. A comparison of the new algorithm and one used recently shows significant improvement over early techniques, particularly when a scaled ionogram is included in the data.

A status report on applying discrete inverse theory to ionospheric tomography

Abstract: Discrete inverse theory (DIT) provides an orderly framework in which to combine measurements of total electron content (TEC) with a priori information to image the ionosphere tomographically. We have developed a DIT-based tomographic processor for use with relative TEC data. The processor's a priori information comprises the global mean of over 17,000 profiles generated from an ionospheric model, for use as a “generic background”; empirical orthogonal functions (EOFs) spanning the same model profiles, for use as vertical basis functions; and a red power-law horizontal spectrum. Relative TEC data are used to evaluate coefficients multiplying the EOFs and harmonics, thus quantifying a perturbation electron-density field. The perturbation field, which need not be small, is added to the a priori background to produce the image. We present here several images produced by employing the processor with simulated TEC data based on in situ ionospheric measurements and incoherent-scatter radar observations.©1994 John Wiley & Sons Inc

Developmentally regulated, low abundance Tec element transcripts in Euplotes Crassus—Implications for DNA elimination and transposition

Abstract: During macromolecular development in the ciliated protozoan, Euplotes crassus, > 105 Tec elements are precisely eliminated from the genome in a 2-4 h time interval, generating extrachromosomal circular forms of the elements. Various models have proposed a transposition-based mechanism for this excision. We have tested this hypothesis by determining the abundance of transcripts of Tec element open reading frames (ORFs) and the timing of their appearance. Transcripts are very low in abundance and are only detected by PCR amplification techniques. Thus, the low levels of transcripts argue against the participation of element-encoded functions in the Tec element elimination process. The element transcripts are only detected in RNA samples from mated cells, indicating that the micronucleus and/or developing macronucleus are transcriptionally active during the sexual phase of the life cycle. The transcription detected could allow a low level of germline-specific transposition for these elements.

The desflurane Tec 6 vaporizer

Abstract: A late development model of the Tec 6 vaporizer for the administration of desflurane vapour has been evaluated, It is heated electrically and has both electronic monitors of vaporizer function and alarms. The new filling system is a significant improvement over previous Tec filling systems. The vaporizer requires a warm-up period before it may be used, but when activated it provides an output that is approximately linear between 1 and 18% vapour concentrations, at flow rates between 200 ml min−1 and 10 litre min−1. (Br. J. Anaesth. 1994; 72: 470–473)

Predicted and measured total electron content at both peaks of the equatorial anomaly

Abstract: The total electron content (TEC) of the ionosphere is a parameter of great importance for the systems which use transionospheric radiowaves and for the checking of the validity of ionospheric models. It is known that the highest TEC values in the world occur at the peaks of the equatorial anomaly (EA) regions at ∼15° either side from the magnetic equator. In this paper, TEC measurements obtained with Faraday technique at three stations placed near both peaks of the EA are used to check the validity of three ionospheric models to predict TEC in these regions. The TEC data of the southern peak of the EA were obtained at Tucuman (26.9°S, 294.6°E) in 1982, and those corresponding to the northern peak were Obtained at Palehua (21.4°N, 203.2°E) in 1978 and Delhi (28.6°N, 77.2°E) in 1968. Ionosonde data from Tucuman, Delhi, and Maui, (20.8°N, 203.5°E) are also used. Two widely used models are considered, namely: the international reference ionosphere and the semiempirical low-latitude ionospheric model. The third model considered is a Chapman layer with scale height equal to atomic oxygen scale height (CHOEA). In general, the models underestimate TEC during daylight hours at Tucuman suggesting that the real electron density profiles are larger in electron density magnitudes than those given by the models. For Palehua and Delhi the models' predictions are better than those for Tucuman, and a very good agreement among calculated and measured TEC values at Palehua for some months is observed. Taking into account the simplicity of the TEC calculus with CHOEA, this model would be an adequate alternative to predict TEC at stations placed near the northern crest of the EA, at least for the considered solar activity. This model allows also to calculate TEC at the southern crest of the EA with a similar degree of accuracy of those values obtained with the other models.

Data from orbiting navigation satellites for tomographic reconstruction

Abstract: So far, orbiting navigation satellites are the only source for primary data in ionospheric tomography. Phase difference measurements give the input for tomographic reconstruction. Except for a constant, the initial phase difference value, the data can be considered to be the line integral of electron density along the straight line from the satellite to a ground based receiver (“slant electron content”). In ionospheric physics a projection onto the vertical is used: (vertical) electron content (TEC). Many investigations have been based on this quantity alone. This work discusses some of the propeties of the measured data (instrumental and “ionospheric” limitations in section II), and the role of TEC evaluation assumptions (“mean ionospheric height” and initial phase constant, in section III). Some of the problems inherent in ionospheric tomography using orbiting navigation satellites are discussed by means of model calculations (section IV). The models are mathematically defined two-dimensional electron density distributions that are used to calculate the latitude dependence of both slant and vertical TEC. Among others, the model calculations are useful in showing that strongly different electron density distributions can lead to similar electron contents. Tomographic reconstruction would probably not be able to distinguish between the different distributions, which leads to the recommendation to incorporate additional data in the reconstruction process. It is well known, and reflected in the model electron contents, that without additional data tomographic reconstruction is not accurate in height determination. Layer height variations with latitude, however, can have a strong influence on slant and vertical electron content.©1994 John Wiley & Sons Inc

Fabrication of an expanded core fiber having MFD of 40 /spl mu/m preserving outer diameter

Abstract: A thermally-diffused expanded core (TEC) fiber with the mode field diameter (MFD) of 40 /spl mu/m has been fabricated by improving the diffusion process using an electric furnace. The outer diameter of any TEC fiber is preserved and the excess loss (normal-TEC-normal) is as low as 0.1 dB. >

TEC and f0F2 comparison

Abstract: Following an investigation on the calibration of Faraday Rotation measurements by the slab thickness method, several interesting results have been obtained concerning the limits of application of TEC data in f0F2 modelling at middle latitudes.

Phase relationships between total electron content variations, Doppler velocity oscillations and geomagnetic pulsations

Abstract: The phase relationship between variations of ionospheric total electron content (TEC) and ground-level ULF geomagnetic pulsations has been examined for the advection and compression mechanisms. To determine the causal mechanism, several earlier studies have examined the phase difference between oscillations of Doppler velocity in ionospherically reflected radio waves and simultaneous ULF geomagnetic pulsations. In most instances it was found that the phase relation varied from event to event. With the application of Euler’s formula this study shows that in low geomagnetic and midgeomagnetic latitudes the phase differences between variations of TEC and ULF pulsations in the northward component of the geomagnetic field due to the advection and compression mechanisms are 0o and 180o, respectively. We also found that TEC variations tend to lead ionospheric Doppler velocity oscillations by 90o. Furthermore, it is shown that the phase relationship between ionospheric Doppler velocity oscillations and ULF pulsations of the northward component of the geomagnetic field, caused by the advection and compression mechanisms, are functions of the scale length, frequency of ULF waves, and geomagnetic dip.

Trellis excitation speech coding at low bit rates

Abstract: Trellis coded vector quantization (TCVQ) and code-excited linear prediction (CELP) coding are combined to form an efficient low-bit rate speech coding system. The resulting system uses a trellis search to select the synthesis filter excitation sequence, and is referred to as trellis excitation coding (TEC). Simulations are performed for encoding rates of 6.4 and 8 kbps. Informal listening tests indicate that the 8 kbps TEC system has quality roughly between that of 6-bit and 7-bit /spl mu/-law PCM with /spl mu/=255. The 6.4 kbps TEC system provides speech quality between 5-bit and 6-bit /spl mu/-law PCM. A subjective comparison with vector sum excited linear prediction (VSELP) indicates that the 8 kbps TEC and the VSELP reconstructed speech is about equally preferable. >

Observations of TEC fluctuations from an explosion on the Earth`s surface

Abstract: The authors report observations of perturbations in the ionosphere total electron content (TEC) caused by acoustic waves propagating from a large chemical explosion in souther New Mexico at the earth`s surface. Fluctuations in TEC were measured by two arrays of receivers that monitor the phase of the 136 MHz beacons on two geostationary satellites. One array, located in northern New Mexico, observed fluctuations in the region where acoustic waves from the blast impinged directly on the ionosphere, while the second array, in Texas, was located to observe fluctuations caused by ducted acoustic waves. The TEC disturbance at the New Mexico array had an amplitude of about 2 {times} 10{sup 14} m{sup {minus}2} (more than 10 times the array noise level), while the amplitude at the Texas array, at a range of 900 km, was only a few times the instrumental noise level. Noise background analysis shows that the probability that a comparable or larger response at the New Mexico array might have been caused by a background noise event was less than 1%. The corresponding probability for the Texas array was 3%.

Trenchless Excavation construction in Federal Contracting

Abstract: : The industry related to Trenchless Excavation Construction (TEC) is seeing wide spread expansion. Technological developments in the last twenty years have been applied to TEC and now allow the installation of underground utility lines under previously developed properties and in difficult soil conditions. Large municipalities and industrial owners have greatly benefited from projects constructed using TEC. The Naval Facilities Engineering Command (NAVFAC) is the construction and maintenance arm of the Navy and manages projects world wide. It is governed in is contracting by the Federal Acquisition Regulations (FAR) which among many things attempts to encourage fair and equitable administration of contracts. The FAR does this by restricting proprietary language and actions in government contracts and also by focusing contracts on final products versus construction methodology. Since TEC is new, unfamiliar, and is often viewed to be a methodology and not a final product, NAVFAC's specification writers have been concerned about addressing TEC in their contracts. The purpose of this research project is to give NAVFAC designers and specification writers a Guide Specification that allows for TEC, provides them a comparison project that shows how TEC may be utilized, and also to make them aware of the basic concepts of TEC via a NAVFAC magazine article.

Investigation of the ionospheric short-term variability

Abstract: : Reliable HF communications require propagation assessment. Such assessment could be facilitated with the monitoring of ionospheric characteristics by continuously available passive means, i.e, measurements of the total electron content(TEC) using satellite-emitted signals without a need for burdening the electromagnetic spectrum. With the Global Positioning System (GPS) providing instantaneous time delay, or equivalently, TEC, values when needed, an assessment of HF propagation may be available on a near realtime basis. To assess this possibility a one year study of the correlation between TEC and foF2 using GPS time delay observation taken at Matera, Italy was undertaken during 1995-1996. This is a period of minimum solar activity with sunspot numbers varying between 6-18. The observed correlation coefficient varied between 0.55 in the winter of 1996 to about 0.75-0.8 during the summer of 1995. In addition to the seasonal variability of the correlation coefficient, a diurnal variability is also present with the coefficient normally maximizing during the day and minimizing in the predawn periods. The predawn minimum may be due to the contribution of plasmaspheric electron content. The correlation coefficient appears to increase with magnetic activity, indicating that TEC and foF2 behave similarly during magnetically active periods. Distribution of errors between measured foF2 values and predicted ones using a) standard predictions algorithms and b) TEC measurements converted to foF2 from a model of slab thickness, show that the errors are reduced when using TEC observations. The errors would be further reduced if the satellite subionospheric point would approach the location of the foF2 actual measurements.

Ionospheric Corrections to Precise Time Transfer Using GPS

Abstract: The free electrons in the earth's ionosphere can retard the time of reception of GPS signals received at a ground station, compared to their time in free space, by many tens of nanoseconds, thus limiting the accuracy of time transfer by GPS. The amount of the ionospheric time delay is proportional to the total number of electrons encountered by the wave on its path from each GPS satellite to a receiver. This integrated number of electrons is called Total Electron Content, or TEC. Dual frequency GPS receivers designed by Allen Osborne Associates, Inc. (AOA) directly measure both the ionospheric differential group delay and the differential carrier phase advance for the two GPS frequencies and derive from this the TEC between the receiver and each GPS satellite in track. The group delay information is mainly used to provide an absolute calibration to the relative differential carrier phase, which is an extremely precise measure of relative TEC. The AOA Mini-Rogue ICS-4Z and the AOA TurboRogue ICS-4000Z receivers normally operate using the GPS P code, when available, and switch to cross-correlation signal processing when the GPS satellites are in the Anti-Spoofing (A-S) mode and the P code is encrypted. An AOA ICS-Z receiver has been operated continuously for over a year at Hanscom AFB, MA to determine the statistics of the variability of the TEC parameter using signals from up to four different directions simultaneously. The 4-channel ICS-4Z and the 8-channel ICS-4000Z, have proven capabilities to make precise, well calibrated, measurements of the ionosphere in several directions simultaneously. In addition to providing ionospheric corrections for precise time transfer via satellite, this dual frequency design allows full code and automatic codeless operation of both the differential group delay and differential carrier phase for numerous ionospheric experiments being conducted. Statistical results of the data collected from the ICS-4Z during the initial year of ionospheric time delay in the northeastern U.S., and initial results with the ICS-4000Z, will be presented.