bluuebunny/crossref_metadata_2025_split huggingface dataset:
Implementation of adaptive modulation as A fade countermeasure
Authors: Filip Miodrag , Vilar Enric 
Published: July 2007

AbstractThree key problem areas associated with implementation of the concept of adaptive modulation as a fade countermeasure in a practical VSAT system are addressed in this paper. First, the heart of such a system, an adaptive modem, is described; such a device should be able to support a number of different modulation schemes, independently for modulation and demodulation. It is shown how an adaptive modulator can be built around a VLSI numerically controlled oscillator and that an adaptive demodulator is feasible once the universal carrier tracking loop is implemented with use of digital signal processing. As regards system operation, a data transfer scenario is described which highlights that it is important to expand the set of commands and responses of the data link control protocol in order to cater for the new abilities of the system. Finally, the article describes a computer simulation of system performance evaluation under dynamic rain fading propagation conditions and applied to a Ka band link. The results confirm earlier theoretical work and show great advantage over systems using fixed modulation schemes and fixed link propagation budget margins.
An architecture design approach for large satellite networks
Authors: Cotner C. , Inukai T. 
Published: July 2007

AbstractDesigning a world‐wide satellite network that consists of hundreds of user sites and thousands of circuit connections is a complex problem, which involves selecting a set of candidate satellites and satellite beams/frequency bands from among numerous existing and planned satellites, evaluation of circuit connectivity, earth‐station compatibility and sizing, and estimating transponder loading. The design process may also require assessment of the impact of a different set of satellites and modified user traffic requirements on the space segment, the earth‐station types and quantity, and the total system cost. Although a conventional design approach based on link‐by‐link and site‐by‐site analysis provides accurate results, it is time‐consuming and impractical for developing high‐level network architectures in a time‐constrained environment. A design technique is proposed which employs a set of rules for satellite network design, in combination with extensive databases of satellite parameters, earth‐station parameters and user traffic requirements, to synthesize a network architecture. The technique is particularly useful for performing high‐level trade‐offs among alternative architectures in terms of space segment requirements, the number and type of earth‐stations and overall system cost. Once the desired architecture has been selected, a detailed design may be developed using conventional methods.
Performance of A prioritized on‐board baseband switch for A multiservice multibeam satellite
Authors: Bohm S. , Elhakeem A. K. , Murthy K. M. S. , Hachicha M. 
Published: July 2007

AbstractIn this paper, we study the performance of a prioritized on‐board baseband switch in conjunction with a multibeam satellite handling integrated services. The services considered for the analysis include voice, video, file transfer and interactive data. The prioritized switch uses both input and output buffering, switch speed‐up as well as a two‐phase head‐of‐line resolution algorithm, in order to reduce the buffer loss while maintaining acceptable user delays. The minimum required buffer capacity and switch speed‐up for each service in a prioritized environment are found under uniform traffic conditions. It is shown that under uniform traffic conditions, only minimal buffering and switch speed‐up are needed even for the lowest priority users. The performance dependence on the switch size is also substantially reduced with head of line resolution and buffering even in a prioritized environment.
Performance of the GLONASS P‐code at L1 and L2 frequencies
Authors: Riley Stuart , Daly Peter 
Published: July 2007

AbstractThe transmission of satellite signals at two widely spaced frequencies allows correction of the ionospheric delay. Both GPS and GLONASS transmit such signals, and to date there have been no published dual frequency GLONASS studies. This paper shows the fundamental accuracy of the Leeds University multichannel GPS/GLONASS receiver. Details are then given of the processing methods that have been used to obtain the ionospheric group delay using GLONASS L1 and L2 P‐code measurements. Examples of the measured delay are provided and compared with the GPS model. Navigation results are shown using the P‐code phase at L1 only and with a combination of the L1 and L2 measurements. An analysis of the accuracy of the P‐code pseudorange and navigation capability is presented.
Digital sound broadcasting: Satellites or Terrestrial Networks?
Authors: Lemaire Jean 
Published: July 2007

AbstractWhen European laboratories decided to develop a digital sound broadcasting system (DSB), they specified three main conditions to fulfil:

quality improvement up to the level of ‘CD’ sound, even in difficult reception conditions (mobile vehicles, etc)
additional significant digital data transmissions in order to transform sound broadcasting into a really new service
the possibility of a common system for satellite and terrestrial transmissions.

It is on these bases that the European project ‘Eureka 147’ defined the system called DAB (digital audio broadcasting). In 1992, the ITU Conference WARC 92 allocated 40 MHz to DSB in the L‐band in the configuration of complementary terrestrial and satellite networks; nevertheless, the present state of technical possibilities makes such mixed networks almost unfeasible and the lack of available spectrum in VHF bands led a significant number of countries to envisage L‐band for T‐DAB. The situation could turn to a competition between terrestrial and satellite networks, especially because the bandwidth in L‐band is not that large!France belongs to the countries facing this problem. L‐band alone is intended to be used by T‐DAB, and broadcasters taking part in the work of ‘Club DAB’ estimated that 20 MHz would be a minimum to ensure the success of T‐DAB introduction. It is half of the DSB band. Splitting this band into two parts has already been decided by CEPT, but in the proportion of 1/3 for T‐DAB. This organization intends to arrange a European planning meeting for T‐DAB in July 1995, and, shortly after, several countries are ready to start the implementation of the terrestrial networks. At the same time, international broadcasters wonder whether satellite transmission could present an alternative to HF.
In‐orbit testing of TDMA occupied channels
Authors: Kasstan B. , Bosowski M. , Horton M. 
Published: July 2007

AbstractThe expected introduction of new TDMA earth‐stations in the EUTELSAT network with a lower diameter antenna, together with the need to ensure the high quality of services are the two principal reasons why regular review of the performance trend of TDMA links is becoming so vital. Such a review will allow overall optimization of the EUTELSAT TDMA system by ensuring that the transponders are operated at their specified points, and will make it possible to be prepared in advance in the event of a transponder gain drop to reconfigure the system with no loss of traffic.To implement these tests, EUTELSAT at its IOT facilities near Paris has installed a burst mode saturation analyser' (BMSA) developed by Hollis Electronics Company. The BMSA has been specially designed as a stand‐alone test system for testing TDMA channels in a burst mode without interrupting the operational traffic.This paper describes how the BMSA operates and in particular how the system self synchronizes in order to position the BMSA test burst correctly in the frame, and how the burst is allowed to vary in amplitude in order to characterize the channel under test. This paper also discusses how the BMSA is interfaced to the host IOT station and how the tight measurement accuracy in terms of absolute transmit e.i.r.p. and spacecraft IPFD have been met.The paper concludes by comparing results obtained by classical CW test methods with this new burst method. The conclusions also discuss the limitations of the system and suggest possible improvements.
Performance analysis of integrated‐services load‐adaptive/TDMA satellite networks
Authors: Rubin Izhak , Chang Kirk K. , Forcina Gianpero 
Published: July 2007

AbstractA load‐adaptive/TDMA multiple‐access communications system which serves to interconnect broad‐band multimedia packet streams is considered. In particular, the use of a satellite backbone communications link whose channels are dynamically assigned to network stations is investigated. Each station supports packetized voice and data message streams. Incoming streams to a station are statistically multiplexed by the station across the backbone channels currently allocated to this station. To enhance the multiplexing process, a variable bit‐rate packet‐voice encoding scheme is also employed. Stations periodically issue requests for backbone channel allocations, based upon their estimated loading status. We introduce two distinct multiple‐access algorithms for allocating the shared backbone channels to the stations. We develop analytical methods for the analysis and design of such integrated multiplexing/multiple‐access networks. Performance measures include voice and data packet delays and packet blocking probabilities. Voice stream performance is also characterized by the average number of bits per sample used by the voice encoding scheme. The effects of the propagation delay across the backbone link are especially demonstrated. Also illustrated are the performance improvements attained due to the use of the load‐adaptive/TDMA scheme. Under the example of the ’all‐voice’ traffic loading, an LA/TDMA scheme exhibits no obvious performance improvement over a fix‐assigned scheme. However, as the burstiness of the traffic loading increases in the example of the ’data‐voice’ traffic loading, a significant amount of improvement (36 per cent bandwidth savings) is realized by a LA/TDMA scheme.
A computationally efficient method of timing and phase estimation in TDMA systems using a preamble sequence
Authors: Bolding Gerald , Cowley William G. 
Published: July 2007

AbstractOptimum and near optimum methods of burst parameter estimation based on the discrete Fourier transform are presented. The methods are applicable to single sample per symbol demodulators when the burst preamble is chosen to be a discrete frequency component at one quarter of the symbol rate. The proposed methods do not require the squaring of the signal, and hence avoid the loss associated with squaring the noise components. The optimum method is shown to reach the Cramer‐Rao bound for symbol timing and carrier phase estimation for the chosen preamble, whereas the more computationally efficient method shows a loss of 1.0dB and yields information regarding the timing offset only. The performances of the two methods in the presence of carrier frequency offset and additive white Gaussian noise are analysed, and implementations are given together with a comparison of the respective computational complexities.
Distributed access algorithms for portable meshed vsat networks
Authors: Piñtar F. J. Ruiz , Fern Campo A. Ández Del , Nieto C. Miguel , Sisó L. Vidaller 
Published: July 2007

AbstractIn recent years technological evolution has made it possible to develop portable meshed VSAT networks (PMVN). Among the distinguishing features of this satellite network family we can cite the following: portable terminals, direct connectivity is allowed between any pair of network nodes (meshed topology), the network may comprise a high number of terminals, the network is intended to offer low rate voice and data communication services. For this satellite network family, the most widely used technique of resource allocation is centralized allocation. But in any network with a high number of nodes, the dependence on a single resource is a potential bottleneck of the network, in terms of flexibility, reliability and scalability of costs. In order to avoid this drawback, two distributed access algorithms are proposed in this paper. Both algorithms are based on carrier sensing (CS). In order to evaluate their performance, a model for PMVNs is proposed. This model is used to study the behaviour of the conventional access technique (central allocation) and the proposed distributed algorithms. We conclude that the use of the proposed distributed algorithms is feasible with present technology, with a performance comparable to that of the central allocation algorithm, but with the advantages associated with distributed algorithms concerning flexibility, reliability and cost.
Clustering of membrane proteins in the pre‐stimulation stage is required for signal transduction: a computer analysis
Authors: Kobayashi Hiroshi , Azuma Ryuzo , Konagaya Akihiko 
Published: July 2007

AbstractThe physiological significance of membrane protein clustering for signal transduction was examined theoretically using a Monte Carlo computer simulation. Simulation results revealed that pre‐stimulation clustering of membrane proteins enhanced signal transduction. Membrane protein clustering induced by the binding of external stimuli provided no kinetic advantage in terms of formation rate or maximum quantity of active membrane receptor complexes. These data suggested that membrane proteins associate weakly in the clustering areas of non‐stimulated cells, and that their association is strengthened upon binding of extracellular stimuli to the membrane receptor. Additionally, the number of cytosolic proteins recruited to membrane receptor complexes was not increased by the membrane complex clustering, except when cytosolic signal proteins were localized to a narrow area such as a tunnel that ran from the membrane cluster to the nucleus. Simulations were carried out on a conventional personal computer under Windows XP or 2000 operating systems. Since neither special computing hardware nor special training is required, our simulation procedure could be easily adapted for kinetic analysis of any signal transduction pathway.
A Method for Reproducibly Preparing Synthetic Nanopores for Resistive‐Pulse Biosensors
Authors: Wharton John E. , Jin Pu , Sexton Lindsay T. , Horne Lloyd P. , Sherrill Stefanie A. , Mino Warren K. , Martin Charles R. 
Published: July 2007

AbstractThere is increasing interest in using nanopores in synthetic membranes as resistive‐pulse sensors for biomedical analytes. Analytes detected with prototype artificial‐nanopore biosensors include drugs, DNA, proteins, and viruses. This field is, however, currently in its infancy. A key question that must be addressed in order for such sensors to progress from an interesting laboratory experiment to practical devices is: Can the artificial‐nanopore sensing element be reproducibly prepared? We have been evaluating sensors that employ a conically shaped nanopore prepared by the track‐etch method as the sensor element. We describe here a new two‐step pore‐etching procedure that allows for good reproducibility in nanopore fabrication. In addition, we describe a simple mathematical model that allows us to predict the characteristics of the pore produced given the experimental parameters of the two‐step etch. This method and model constitute important steps toward developing practical, real‐world, artificial‐nanopore biosensors.
Thermal polymerization of unsaturated fatty esters normal methyl linoleate
Authors: Paschke R. F. , Wheeler D. H. 
Published: July 2007

Summary

Debromination methyl linoleate has been polymerized at 290° and 300° for varying periods, and analysis has been made for monomer, dimer, trimer, normal, and conjugated linoleate.

The disappearance of normal linoleate follows a first order reaction rate with values of K=0.10 hr.−1 at 300° and 0.05 hr.−1 at 290°.

Polymerization of mixtures of normal and conjugated linoleate indicate that dimer may be formed by their reaction with each other.

The value for K, the first order reaction velocity constant for disappearance of normal linoleate, decreases to a limiting value on dilution with methyl stearate. This limiting value is about one‐fourth that obtained on undiluted linoleate.

The above facts are qualitatively explained by assuming that the mechanism of dimerization of normal linoleate is extensively: N»C relatively slow N+C→D relatively rapid.
The aldehydes produced during the autoxidation of cottonseed oil
Authors: Swift C. E. , O'Connor R. T. , Brown L. E. , Dollear F. G. 
Published: July 2007

SummarySpectrophotometric evidence was obtained that Δ2 and Δ2:4 aldehydes are produced during the autoxidation of cottonseed oil.The unsaturated carbonyls were converted into semicarbazones and 2,4‐dinitrophenylhydrazones whose characteristics indicated that the oxidation of cottonseed oil produces Δ2:4‐decadienal, Δ2‐octenal, and hexanal.Although the exact mechanism of their formation has not been established, these aldehydes are believed to result from the decomposition of the isomeric hydroperoxides of linoleic acid, the principal fatty acid constituent of cottonseed oil.
Application of spectrophotometric methods to the determination of glycerine color
Authors: Miner C. S. , Weil C. M. 
Published: July 2007

SummaryA method has been developed by which spectrophotometrically measured glycerine color can be expressed in terms of Lovibond units. The yellow and red color values are determined, by means of two statistically derived linear relationships, from optical density measurements at 440 mμ and 520 mμ, respectively. The conversion from spectrophotometric data to Lovibond color units may be done graphically and the results are at least as reliable as the results of repeated visual measurements.
Analyses of mixtures of t,tΔ9,11‐ and t,tΔ10,12‐linoleic acids by X‐ray diffraction patterns and solidification points
Authors: Witnauer Lee P. , Nichols Peter L. , Senti Frederic R. 
Published: July 2007

SummaryX‐ray diffraction and solidification point data are reported for t,tΔ9,11‐ and t,tΔ10,12‐linoleic acids and their mixtures. The long spacing of the Δ9,11‐isomer was 47.95 Å whereas that of the Δ10,12‐isomer was 44.09 Å. X‐ray diffraction patterns of binary mixtures showed the characteristic pattern of each isomer if the mixture contained not less than 25% of the t,tΔ10,12‐isomer or not less than 5% of the t,tΔ9,11‐isomer. Outside these composition limits only the pattern of the predominant isomer appeared, and solidification point data were used to define the composition. The solidification point in conjunction with the X‐ray data defined the composition of any mixture to ±3%.
Oxidation of various lipid substrates with unfractionated soybean and wheat lipoxidase
Authors: Guss P. L. , Richardson T. , Stahmann M. A. 
Published: July 2007

AbstractQuantitative determinations of lipoxidase in wheat were made on five milling fractions from four wheat varieties, including two hard red winter and two hard red spring wheats. Lipoxidase content decreased with increasing refinement and was lowest in the flour fraction. In general, the mill fractions from spring wheats exhibited slightly higher lipoxidase content than the corresponding mill fractions from winter wheats.Aqueous extracts from soybeans (variety Hawkeye) and wheat (variety Selkirk, break shorts fraction) were adjusted in concentration so that the lipoxidase activity with respect to linoleic acid was approximately the same. The diluted extracts were then tested for their ability to oxidize other lipid substrates with the necessary 1,4 pentadiene system. Soybean lipoxidase was far more reactive toward methyl linoleate and trilinolein than wheat lipoxidase. Mono‐ and dilinolein were relatively unreactive in both systems although dilinolein was a better substrate in the soybean system than in the wheat. Neither system oxidized highly unsaturated digalactosyl diglycerides alone. However the soybean extract oxidized this substrate to a small extent in the presence of catalytic amounts of linoleic acid while, under identical conditions, the wheat extract remained inactive.Polyacrylamide gel electrophoresis of the aqueous extracts of soybeans and wheat‐milling fractions coupled with a staining procedure specifically for lipoxidase indicated three to four isoenzyme bands in the soybeans and two to four isoenzyme bands in the wheat‐milling fractions. Isoenzymes may be responsible for differences in enzymatic activity on various substrates.
Eleostearic acid derivatives. I. Reactions at the carboxyl group
Authors: Thames Shelby F. , Long J. S. , Smith O. D. , Jen S. J. , Evans J. M. 
Published: July 2007

AbstractNine C1 substituted derivatives of eleostearic acid have been prepared and characterized by elemental analyses and spectrophotometric data. The preparation of two additional derivatives is indicated by infrared spectroscopy, but difficulties in purification precluded elemental analysis data. Comments are made concerning conditions for product stability and reaction environment.
A study of eleostearic acid‐containing resins
Authors: Long J. S. , Thames Shelby F. , Smith Oliver W. 
Published: July 2007

AbstractA variety of polyesters, polyurethanes, and sulfonyl‐polyurethanes containing eleostearic acid (ESA) have been prepared and evaluated. The film parameters under investigation usually included water absorption, tensile strength, elongation, density, permeability, and percentage of oxygen uptake.The incorporation of ESA into polyester resin compositions results in such film properties as decreased water absorption, oxygen uptake, elongation, and permeability with a concemitant increase in tensile strength and density. Oxidativepolymerization of the polyesters containing ESA affords advantages in that their films show good tensile strength. Elongation is quite superior to that of the non‐oxidatively polymerized ESA polyesters.As a result of the advantages gained by the incorporation of ESA into polyester resins, its use (or tung oil) is recommended in these and similar resin systems.
A review of methods for determining pesticide residues, contaminants and adulterants in fats and oils
Authors: Firestone David 
Published: July 2007

AbstractSensitive chromatographic methods are available for determining chlorinated pesticide residues and chick edema factor contaminants in fats and oils. Determination of chlorinated pesticide residues in fats and oils generally involves acetonitrile extraction, Florisil column cleanup, and analysis by electron capture gasliquid chromatography (ECGLC). However, other procedures are available including dimethyl sulfoxide extraction and sweep codistillation. Sensitive screening tests for chick edema factor involve alumina column fractionation of isolated unsaponifiable matter, sulfuric acid cleanup, and examination by ECGLC. Admixtures of animal and vegetable fats are detected by the gasliquid chromatography (GLC) of isolated sterols, and individual vegetable oils can be characterized by GLC analysis of the sterols as well as of the other unsaponiflable constituents.
The electronic identity of inductive and capacitive plasmas
Authors: BURM K. T. A. L. 
Published: July 2007

AbstractAn electronic identity relation, relating capacitively coupled plasma sources to corresponding inductively coupled plasma sources, has been derived, starting from the Maxwell relations for matter and the characteristics of a capacitor and of an inductor. Furthermore, the breakdown conditions for both capacitively coupled plasmas and for inductively coupled plasmas as well as their optimal operation frequency ranges are discussed.