bluuebunny/crossref_metadata_2025_split huggingface dataset:
A statistical model of FM‐TV spectra for satellite interference and distortion prediction
Authors: Böck A. M. , Carpenter D. C. , Gallois A. P. 
Published: July 2007

AbstractThe requirement for a model of FM‐TV spectra in the planning procedure of satellite communication systems is introduced. Based on long‐term measurements of live TV channels, statistical properties of video spectra are examined and probability distributions for the luminance and chrominance components are proposed.The spectrum of the frequency‐modulated signal is then derived, and signal distortion due to bandlimiting is calculated. Adjacent and cochannel interference effects are also investigated, with example cases illustrating influences of subcarrier loading and energy dispersion.The proposed model, which describes FM‐TV spectra in terms of random variables, makes it possible to examine relative effects of system parameters, and will, therefore, be of benefit in the planning of new satellite services.
The intelsat slant‐path radiowave propagation experiments in tropical regions
Authors: Allnutt J. E. , Rogers D. V. 
Published: July 2007

AbstractThe requirement for INTELSAT to operate world‐wide in a diverse range of climates has motivated a number of experiments within the INTELSAT R&D programme to identify and model propagation impairments. The effects of some propagation phenomena, such as depolarization, were anticipated. Others (e.g. ionospheric scintillation at gigahertz frequencies) were unexpected or exhibited unusual features (rain attenuation in tropical climates). This paper presents the background of the INTELSAT R&D propagation measurements, with special emphasis on those in tropical regions, and provides the principal results. Several ongoing experiments are also discussed.
Rainfall rate characteristics for microwave systems in tropical and equatorial areas
Authors: Moupfouma Fidele , Martin Louis , Spanjaard Nicolas , Hughes Kevin 
Published: July 2007

AbstractThe wave propagation at frequencies from about 10 GHz can suffer rain effects such as attenuation, scattering and depolarization. The magnitude of these effects depends on rain characteristics. This paper presents results of the propagation experiments undertaken in Douala (Cameroon) and in Brazzaville (Congo) under the auspices of the ITU (Geneva) with the collaboration of CNET (France Telecom). Data based on five months measurements of rain rates in Douala with a network of four rain‐gauges are presented with reference also to some results of a propagation campaign in Brazzaville. The rain measurement period in Douala includes all of the rainy season. The measurement data are used to investigate the rain effect characteristics of the low latitude tropical regions of Africa and are discussed in relation to the influence of rain on microwave system performances in the region.
Some aspects of tropical rainfall and their effect on microwave propagation
Authors: Ajayi G. Olalere 
Published: July 2007

AbstractSome characteristics of tropical rain rate and raindrop size distribution are briefly reported, making use of the data obtained at locations in Nigeria. Models and empirical relations have been obtained for the computation of the effects of tropical rain on radiowave propagation at centimetre and millimetre waves. Results are presented for the effect of integration time on rain rate as well as the rain‐rate duration characteristics, rain‐induced phase shift, attenuation and depolarization, in addition to the relationship between the rain rate and other rainfall parameters. Comparisons have also been made in many cases with the CCIR reports and results from other locations.
Elevation angle dependence in tropical regions
Authors: Bowthorpe B. J. , Andrews F. B. , Kikkert C. J. , Arlett P. L. 
Published: July 2007

AbstractThe variation of path attenuation with elevation angle has been generally considered to approximate a cosecant law, certainly between elevation angles of about 10° and 50°. Such a theory relies on the assumption that the attenuation layer is statiform for most of the time, and is therefore probably reasonable for temperate regions. In tropical areas however the incidence of convective rain is much higher than in temperate regions, so that during rainy periods, particularly at times of high rain rate, the assumption that the attenuating layer is stratiform is no longer valid. The cosecant law does not therefore hold in such conditions.An experiment has been carried out in the tropical rain belt of northern Australia over several years to investigate the elevation‐angle dependency. Four radiometers were co‐sited, with the same azimuth. Three of these, with a half power beamwidth of 2.2°. were elevated to 15°, 45° and 85°. The fourth. with a beamwidth of 0·6° was elevated to 45° so as to allow an investigation into aperture effects. The antennae were all orientated for horizontal polarization. Rain‐gauges were co‐sited with the radiometers and placed along the look path.The results obtained clearly indicate that, in tropical regions. the cosecant law is inappropriate for predicting the elevation angle effects of path attenuation. particularly at high rain rates. The presence of rain cells with rates exceeding 300 mm/h ensures that the assumption of a stratiform attenuating layer is invalid.
Measurements of 11 GHz attenuation using the intelsat V beacon in Indonesia
Authors: Juy M. , Maurel R. , Rooryck M. , Nugroho I. A. , Hariman T. 
Published: July 2007

AbstractA campaign of measurements in Indonesia has been carried out according to a co‐operation agreement concluded between the Indonesian and French Administrations with the aim of estimating rain attenuation on slant paths. The experiment was planned using two earth‐stations, at Cibinong and Padang, both receiving a Ku‐band beacon from an INTELSAT V satellite, coupled with rain‐rate measurements at a number of sites.Rain‐rate statistics are given for several locations in the Indonesian Archipelago. Cumulative distributions of attenuation and simultaneous rain rate, obtained at the earth‐stations, are presented. The analysis of the results has led to the proposal of an adaptation of the CCIR attenuation prediction method for low latitudes.
Conceptual design of rain radar for the tropical rainfall measuring mission
Authors: Nakamura Kenji , Okamoto Ken'Ichi , Ihara Toshio , Awaka Jun , Kozu Toshiaki , Manabe Takeshi 
Published: July 2007

AbstractSpecifications for a spaceborne rain radar for tropical rainfall measurement are described. A spaceborne rain radar has problems peculiar to rain observation from space. The radar must have a fast scanning mechanism to cover a large swath. Very weak rain echoes compared to the sea or land surface signal must be detected. These capabilities must be attained under the severe power consumption and mass limitations of the satellite bus.The fast scanning requirement forces application of an electrically scanning mechanism. This requirement also causes a severe limitation of the available number of independent samples. The requirement for weak rain echoes excludes application of the pulse compression technique, which is a very conventional technique for other active microwave sensors on board satellites.Under these constraints, a rain radar with an electrically scanning planar antenna at 13‐8 GHz is proposed.
Doppler‐shift correction by the DFT, for a QPSK satellite modem
Authors: Clark A. P. , Aftelak A. , Savjani M. , Ang C. 
Published: July 2007

AbstractThis paper describes a novel technique for the measurement and correction of the Doppler shift (frequency offset) in a received QPSK signal that has been transmitted over a satellite link. The satellite is here assumed to be in a non‐geostationary orbit, and correction of the Doppler shift is required to be achieved as soon as the satellite rises above the horizon, when the Doppler shift may be very high and the signal/noise ratio very low. The receiver now has no prior knowledge of the transmitted data, so that a non‐data‐aided system must be used, capable of operating under seriously adverse conditions.The selected technique measures the DFTs of successive blocks of samples of the received and demodulated signal, and from the DFTs it derives a control signal for the VCO, which generates the in‐phase and quadrature reference carriers for the coherent demodulator. The frequency of the latter is adjusted to reduce the residual Doppler shift in the demodulated signal to a sufficiently small value, so that correct phase synchronization of the VCO on to the received signal carrier can then be achieved by means of an appropriate conventional system (not considered here).The paper describes the new technique of Doppler shift correction, and presents the results of computer‐simulation tests to measure the time taken to correct an initial Doppler shift of 5 kHz in the received QPSK signal, at very low signal/noise ratios.
Analysis of random multiple access transmission systems
Authors: Phinainitisart N. , Wu William W. 
Published: July 2007

AbstractFor a very large number of small earth‐stations with varying transmission time and light traffic, the random multiple access (RMA) transmission system is capable of providing simultaneous access to earth‐stations by associating each station with a unique sequence of code symbols. Each information bit will be transformed into these code symbols, where each symbol is an entry in a discrete time‐frequency matrix. In this paper we propose a system model for RMA transmission systems and illustrate the application of RMA code sequences. The analysis of this transmission system, which causes interference to the desired signal, is presented. The performance parameter considered is the signal‐to‐noise ratio (SNR) at the output of a correlation detector. The analysis shows that the SNR depends on the number of users, the energy per data bit and the design of the time‐frequency matrix which determines the total numbers and values of the time‐delay units associated with any carrier.
CCITT/ANSI voice packetization protocol
Authors: Sherif M. H. , Clark R. J. , Forcina G. P. 
Published: July 2007

AbstractThis paper introduces the packetized voice protocol G.PVNP/T1.PVP which is being standardized in both the CCITT and T1Y1. At layer 2, G.PVNP/T1.PVP extends the ISDN LAPD protocol to include packetized voice, thereby potentially allowing the integration of voice and data traffic. Layer 3 specifies procedures to deal with voice‐band data traffic and to handle channel‐associated signalling.
Wideband packet technology in the integrated access and cross‐connect system (IACS)
Authors: Sherif M. H. , Malaret‐Collazo A. D. , Gruensfelder M. C. 
Published: July 2007

AbstractThe integrated access and cross‐connect system (IACS) is an AT&T product based on the wideband packet technology. The IACS has two components: the integrated access terminal (IAT) and the integrated access controller (IAC). The IAC provides centralized control, operations and maintenance for a network of IATs. An IAT provides direct digital connectivity at 1·536 Mb/s or 2·048 Mb/s to customer terminals and to circuit‐ and packet‐switched networks. It integrates voice, voiceband data, facsimile traffic, digital data, signalling, image and network control into packets of common format. It allows networking in both the circuit and packet domains, offers bandwidth on demand, and achieves graceful degradation of voice quality during congestion.
The development of an open‐network digital circuit multiplication equipment system
Authors: Kihlström Lars‐Olof , Viklund Nils , Bridgewater David 
Published: July 2007

AbstractThis paper discusses the systematization effort undertaken to generate an equipment specification of an extremely detailed and new nature for DCMEs in accordance with the INTELSAT specification IESS‐501. The main areas of importance addressed are additional to what has already been defined within the IESS‐501. A discussion of important aspects when introducing DCME into actual network conditions is also contained and results based on simulations of performance under simulated network environments are included.
Payload design for a switchboard in the sky
Authors: Berner W. , Ortwein F. 
Published: July 2007

AbstractThe architecture of an experimental payload with on‐board processing capabilities is described. Since the system is proposed as an experimental one it operates with only four beams in the 20/30 GHz frequency band. Special emphasis is put on the design of the switch and its associated control. The switch operates in a synchronous circuit‐switching manner and provides a throughput of 131 Mb/s. To derive the requirements for the on‐board controller, a process model is established. This model shows that an implementation in a finite state machine will not give enough flexibility. Therefore a microprocessor system is proposed for the controller.
The search for optimized shaping filters suitable for vsat systems
Authors: Tomlinson M. , Stevens R. , Saunders D. 
Published: July 2007

AbstractThe satellite communications industry has seen the emergence of VSAT (very small aperture terminal) systems with the promise of high growth in the next decade. The system design of the VSAT ground station has generally followed traditional satellite communication system design, namely featuring data transmission using QPSK (quadrature phase shift keying) or BPSK (binary phase shift keying) and 50 per cent raised cosine shaping filters with quasilinear transmission. Transmitter power is strictly limited and is at a premium for the VSAT transmitter which usually consists of a non‐linear solid‐state power amplifier (SSPA). Consequently it is important to operate the SSPA so that the maximum power is obtained, which means that the SSPA should be operated close to its saturation point. In so doing considerable distortion can be introduced, which leads to intersymbol interference (ISI) in the receiver and an associated degradation in error rate. Although constant envelope BPSK or QPSK solves the intersymbol interference problem and enables operation at the saturating point of the SSPA, the sinx/x spectral shape has unacceptable sidelobe levels.This paper gives results of a search for a pulse shaping filter characteristic that is bandlimited and yet has improved performance over the traditional root 50 per cent cosine roll‐off filter when used in a VSAT ground station with a SSPA. The performance improvement due to improved shaping filtering is maintained over a range of output levels of the SSPA.Performance evaluation results using computer simulation are presented.
Satellite antenna depointing originating from attitude control and station keeping specifications
Authors: Bousquet Michel , Maral Gérard 
Published: July 2007

AbstractThe paper establishes practical formulae in order to determine the depointing angle for a geostationary satellite antenna. Both satellite attitude and station‐keeping errors are considered. The attitude control and station‐keeping specifications give the amplitude of the angular motion of the satellite about its centre of mass and the amplitude of the displacement of the satellite with respect to its nominal position, respectively. The effects of these angular motions and displacements on the aiming of the satellite antenna are analysed. A set of formulae is derived which permits the calculation of the overall satellite antenna depointing angle. These formulae can be used for the estimation of the satellite antenna gain loss or interference contribution at a given location on the Earth.
Adapted packet speech interpolation
Authors: Lacovara R. C. , Vaman D. R. 
Published: July 2007

AbstractAdapted packet speech interpolation (APSI) is presented as an evolution of digital speech interpolation (DSI) techniques. The inherent overload penalties of DSI are mitigated by the use of an overload strategy which distributes the penalties uniformly across all active speech sources. A novel use of linear delta modulation (LDM) allows the system to re‐encode the input sources at various rates depending upon the total offered load to the system. The subjective performance of hardware is discussed. Two models of silence and talk‐spurt behaviour (called activity) of speech are presented: an analytic model for single speakers obtained by the application of renewal theory, and a simulation model obtained from the analytic model.
An introduction to the NASA Shuttle ground operations simulator (SGOS)
Authors: Cook R. P. 
Published: July 2007

AbstractThe Shuttle ground operations simulator (SGOS) simulation software introduced in this paper is used to train NASA ground controllers and to certify launch countdown readiness. The SGOS executive and its subsystems have been an integral component of the Shuttle Launch Safety Program for almost 30 years. It is usable (via a LAN) by over 2000 NASA employees at the Kennedy Space Center and 11 000 contractors. SGOS supports over 800 models comprised of several hundred thousand lines of code and over 1000 Model Control Procedures. Copyright © 2007 John Wiley & Sons, Ltd.
Flavor reversion in soybean oil. VI. Isolation and identification of reversion compounds in unhardened soybean oil
Authors: Stapf R. J. , Daubert B. F. 
Published: July 2007

SummaryTwo compounds possibly contributing to the reverted flavor in soybean oil have been isolated from the condensate obtained from the deodorization of soybean oils.From physical and chemical data compiled, including absorption and hydrogenation studies, the structure of the 2,4‐dinitrophenylhydrazones have been shown to correspond closely with the 2–4‐dinitrophenylhydrazones of Δ2:4 and acetaldehyde.
Biochemical modification of fats by microorganisms: A preliminary survey
Authors: Koritala S. , Hesseltine C. W. , Pryde E. H. , Mounts T. L. 
Published: July 2007

AbstractOver 100 different strains of bacteria, actinomycetes, fungi and yeasts were incubated at 28 C for five days in the presence of soybean oil. Some soybean oil was consumed by many microorganisms, and some was also hydrolyzed to free fatty acids.Aspergillus oryzae, two different strains ofAmylomyces rouxii andRhizopus oligosporus hydrolyzed the oil completely (95%). The fatty acids fromAspergillus flavus fermentation contained less linolenic acid than the original soybean oil. Lipase was found intra‐ and extracellularly when microorganisms were grown in the presence of soybean oil.
Determination of individual tocopherols by derivative spectrophotometry
Authors: Bukovits Gabriel J. , Lezerovich Alberto 
Published: July 2007

AbstractThe second order derivative UV spectra of α‐, β‐, γ‐ and σ‐tocopherols showed small differences that allowed development of a derivative spectrophotometric method for determining individual tocopherols in a mixture. The procedure consists of measuring the second derivative spectrum of the sample at four specified wavelengths and calculating each concentration by means of a method for multicomponent analysis that uses mixtures as standards. Vegetable oils and other fatty products usually require a previous clean‐up process (under study) in order to remove interfering substances.
Mechanistic considerations of polymorphic transformations of tristearin in the presence of emulsifiers
Authors: Aronhime J. Schlichter , Sarig Sara , Garti N. 
Published: July 2007

AbstractFat polymorphs influence the quality of some food and cosmetic products. Emulsifiers traditionally have been added in order to retard undesired polymorphic transformations. The present study is an attempt to understand the role of selected emulsifiers on such transformations. Tristearin was heated or aged under controlled conditions using differential scanning calorimetry (DSC) and X‐ray techniques, and the extent of transformation was evaluated in view of the possible pathways of α transforming into β. The temperature regime controls the extent of mobility of fat molecules, the local crystal imperfections and the degree of liquefaction. As a result, it dictates the kinetics of the polymorphic transformation.The surfactant added as an impurity does not have a straightforward effect, as thought previously, but rather varies with the kinetic conditions. During aging some selected solid emulsifiers will retard the α‐β transformation while others still enhance it (during heating, all of them will inhibit β form crystallization). Their effect probably is related to different crystalline organizations and the creation of imperfections. Liquid emulsifiers in any case will enhance the α‐β transformation, due probably to their weak structure compatibility with tristearin, which causes a higher mobility of triglyceride molecules.
Characterization of peanut oil tricacyglycerols by HPLC, GLC and EIMS
Authors: Singleton J. A. , Pattee H. E. 
Published: July 2007

AbstractTwenty‐three peanut oil triacylglycerols have been characterized by liquid chromatography, gas chromatography and electron impact mass spectrometry. High resolution was achieved using two 8‐cm × 6.2‐mm reverse phase columns in series, and 20 of the triacylglycerols were separated in an analysis time of less than 45 min. Triacylglycerols were identified by analyzing each liquid chromatography fraction for carbon number, fatty acid composition and mass fragmentation pattern. The combined application of these methods permitted the identification of triacylglycerols representing combinations of all of the fatty acids present in peanut oil.
Methodology for the In Vivo Measurement of the Δ9‐Desaturation of Myristic, Palmitic, and Stearic Acids in Lactating Dairy Cattle
Authors: Mosley Erin E. , McGuire Mark A. 
Published: July 2007

AbstractThere is limited methodology available to quantitatively assess the activity of the Δ9‐desaturase enzyme in vivo without chemically inhibiting the enzyme or using radioactively labeled substrates. The objective of these experiments was to develop methodology to determine the incorporation and desaturation of 13C‐labeled fatty acids into milk lipids. In a preliminary experiment, 3.7 g [1‐13C]myristic acid ([1‐13C]14:0), 19.5 g [1‐13C]palmitic acid ([1‐13C]16:0), 20.0 g [1‐13C]stearic acid ([1‐13C]18:0) were combined and infused into the duodenum of a cow over 24 h. In a following experiment, 5.0 g [1‐13C]14:0, 40.0 g [1‐13C]16:0, and 50.0 g [1‐13C]18:0 were infused into the abomasums of separate cows as a bolus over 20 min or continuously over 24 h. Milk fat was extracted using chloroform:methanol. Fatty acids were methylated, and fatty acid methyl esters (FAME) were converted to dimethyl disulfide derivatives (DMDS). The FAME and DMDS were analyzed by gas chromatography mass spectrometry. In the preliminary experiment, 13C enrichment in 14:0 but not 16:0 or 18:0 was observed. When dosage amounts were increased in the following experiment, peak enrichments from the bolus infusion were observed at 8 h. Enrichments for continuous infusion peaked at 16 h for 14:0 and 18:0, and at 24 h for 16:0. The Δ9‐desaturase products of these fatty acids were estimated to be 90% of cis‐9 14:1, 50% of cis‐9 16:1, and 59% of cis‐9 18:1. This study demonstrates that 13C‐labeled fatty acids may be utilized in vivo to measure the activity of the Δ9‐desaturase enzyme.