bluuebunny/crossref_metadata_2025_split huggingface dataset:
A unified statistical rain‐attenuation model for communication link fade predictions and optimal stochastic fade control design using a location‐dependent rain‐statistics database
Authors: Manning Robert M. 
Published: July 2007

AbstractThe simultaneous demand for increased capacity of communication satellite channels and the demand for such systems to be designed and operate within increasingly stringent economic constraints places severe requirements on the ability to predict, achieve and maintain the reliable operation of these satellite links throughout the United States. The operating frequencies of satellite links are such that the occurrence of rain anywhere along the link will induce attenuation of the signal and is the major source of link reliability degradation. A unified model is presented that describes the relevant static and dynamic statistics of attenuation on an arbitrarily specified satellite link for any location for which there is a long‐term data record of rainfall statistics. In addition to providing accurate, location‐dependent statistical predictions of the reliability of satellite links, the generality of the model also establishes a basis for the design of optimal stochastic control algorithms used to mitigate the deleterious effects of attenuation and thus maintain link reliability. The rain statistics that are required to characterize the location of interest are derived from extreme value statistics theory. A rain‐statistics database has been compiled that allows one to apply the model anywhere in the continental United States with the resolution of 0.5° in latitude and longitude. Comparison of the model predictions is made with available experimental observations and agreement is found to be quite good.
Adaptive modulation as a fade countermeasure. An olympus experiment
Authors: Filip M. , Vilar E. 
Published: July 2007

AbstractWith the launch of the European Space Agency's Olympus‐1 satellite, a whole new era of communication experiments in the 20/30 GHz bands will start. Of particular interest will be those experiments concerned with fade countermeasures for the very small aperture terminals (VSATs). Portsmouth Polytechnic's experiment will focus on adaptive modulation as a type of fade countermeasure, and this paper introduces and describes the whole concept. Based on the assumption that the performance of a VSAT operating at 20/30 GHz band will be affected to a major extent by amplitude scintillations and rain fading, the performance of a range of combinations of earth‐station power amplifier and antenna characteristics is presented. An adaptive multi‐phase shift keying technique is then compared with conventional systems in terms of availability and data throughput. It is shown that such a fade countermeasure contributes to increasing both the overall system availability and the total data throughput of a digital communication system, while the inevitable reductions in data rate occur smoothly.
Influence of signal constellation on the performance of 16‐ary deqam transmission through a regenerative satellite link
Authors: Cheung S. W. 
Published: July 2007

AbstractThe paper presents the results of a series of computer‐simulation tests to determine the effects of non‐linear distortion and adjacent channel interference (ACI), on the tolerance to additive white Gaussian noise (AWGN) of a digital satellite modem. The modem transmits a 16‐ary differentially encoded quadrature‐amplitude‐modulated (16‐ary DEQAM) signal over a regenerative satellite link, where the high‐power amplifier (HPA) at the transmitter may introduce AM‐AM and AM‐PM conversion effects into the 16‐ary DEQAM signal. Three signal constellations are used at the transmitter, namely (1) a conventional 16‐ary DEQAM signal constellation, (2) a predistorted 16‐ary DEQAM signal constellation and (3) a prerotated 16‐ary DEQAM signal constellation. An equivalent baseband model of the transmission system is used to determine the performance of the modem under the various conditions studied, and the results are used to select the preferred modem design.
Optimization of satellite orbital positions using an objective function related to aggregate interference levels
Authors: Fortes José Mauro P. , Ribeirete Ericson C. 
Published: July 2007

AbstractAn optimization method to identify satellite orbital positions in an interference environment is proposed. Its objective function is related to the aggregate interference affecting each satellite network and is defined in terms of the isolation concept. The method is applied to two specific situations, and the resulting solutions are compared to those obtained when a minimax technique is used in a tentative manner to equalize interference. Results indicate that the use of the minimax approach may not be adequate.
The measurement of rainfall in Papua New Guinea, and its effect on microwave propagation
Authors: Harris D. J. , Milner E. 
Published: July 2007

AbstractA programme of measurement on rainfall characteristics has been commenced at Lae, Papua New Guinea, using pluviometers, tipping bucket rain‐gauges and a rapid‐response rain‐gauge. Pluviographs extending over many years have been analysed by computer to give data on general rain conditions and on the probability of rainfall intensity exceeding particular levels. The resultant distribution compares well with the empirical formula of Moupfouma, and corresponding parameters are given. Simultaneous measurements are also being made on the 12 GHz signal level variation from the Aussat television signal, and on the attenuation on a 10 GHz terrestrial link.
Prediction of attenuation due to rain: Characteristics of the 0°C isotherm in temperate and tropical climates
Authors: Ajayi Gabriel Olarere , Barbaliscia Francesco 
Published: July 2007

AbstractA detailed investigation of the vertical structure of rain and of the characteristics of the 0°C isotherm height in both rainy and non‐rainy conditions has been carried out in connection with the prediction of rain attenuation on Earth‐satellite links. Radiosonde data have been analysed for eight and nine locations in the southern and northern hemispheres, respectively. The temporal, latitudinal variations and the relationship between the 0°C isotherm height and ground meteorological parameters such as rainfall, temperature and relative humidity, are reported. The equivalent rain height measured along the Earth‐satellite link is compared with the heights obtained from meteorological data.
Ku‐band slant‐path radiometric measurements at three locations in Brazil
Authors: Pontes M. S. , Mello L. A. R. Silva , Migliora C. G. S. 
Published: July 2007

AbstractThis paper presents results of the 12 GHz propagation experiment that is being conducted in Brazil. The data obtained are useful to investigate the impairment due to rain attenuation in satellite links operating in tropical and equatorial climates. Radiometric sky noise temperature and rainfall rate are being measured at three locations. At one location, site diversity measurements are also being conducted. Cumulative distributions of sky‐noise temperature, equivalent attenuation and rainfall rate at each site are presented together with worst‐month statistics. Also, the joint‐probability distribution of equivalent attenuation at the diversity sites is shown. Finally, the measured probability distributions of attenuation are compared to those obtained from the measured rainfall rate distributions, using prediction models.
Operating aspects of new LRE/DSI DCMEs
Authors: Campanella S. Joseph , Reiser Jack H. 
Published: July 2007

AbstractDigital circuit multiplication equipment (DCME) that uses a combination of talk‐spurt interpolation and low‐rate encoding (32 kb/s ADPCM rather than the traditional 64 kb/s PCM) is about to be introduced in operating satellite systems. These DCMEs possess a number of important features that have been introduced to achieve a suitable balance between high channel multiplication ratios and high quality voice and data transmission. The methods used to accomplish this are generation of overload channels to virtually eliminate talk‐spurt clipping, establishing a limit on the fraction of channels that undergo bit reduction by use of dynamic load control, automatic routeing of trunks carrying in‐band data signals to non‐interpolated bearer channels, use of a bit‐bank approach to provide five‐bits/sample ADPCM coding for in‐band data channels and rotation of the server channels among the talk‐spurts to spread the degradation caused by bit reduction uniformly across all talk‐spurts. This paper analyses the performance of the DCME embodying the above features, and presents results in terms of the input‐to‐output channel multiplication ratio (CMR) as a function of the number of bearer channels (over a range from 4 to 61 bearer channels) and the number of input channels carrying in‐band data. Extending the operation range down to as few as four bearer channels permits evaluation of the effectiveness of multiclique operation. In addition, the influence on CMR of (a) non‐bit‐bank operation, that would be possible if an ADPCM codec capable of supporting in‐band data carriers at four‐bits/sample were used, and (b) a short‐hangover‐time speech detector are examined. Use of hangover times less than 30 ms are shown to achieve a CMR of as great as 3.3: 1.
Intelsat digital circuit multiplication equipment
Authors: Forcina G. , Oei W. S. , Oishi T. , Phiel J. F. 
Published: July 2007

AbstractThis paper illustrates the salient features and the technical structure of the digital circuit multiplication equipment (DCME) specified by INTELSAT. First, an overview of the basic DCME requirements is presented and the network applications of the DCME are discussed. Then a systematic and detailed description of the body of the technical specification is provided. Finally, the complementary activities that followed the completion of the specification are briefly addressed.
New trends in digital circuit multiplication technology
Authors: Piasetzky J. 
Published: July 2007

AbstractThis paper discusses the achievements and the unsolved problems of the first generation of Digital Circuit Multiplication Systems (DCMS)DCMS is an abbreviation for Digital Circuit Multiplication Systems. DCME is an abbreviation for Digital Channel Multiplication Equipment. Both refer to the same technique of combining digital speech interpolation and low rate encoding.
. The following summarizes proposed improvements in DCMS technology. A major improvement in DCMS gain may be achieved by implementation of facsimile demodulation. The design considerations of this technique are discussed. The CCITT activities on standardization of a 16 kb/s speech coding algorithm are reviewed. In order to adapt this algorithm to implementation in a DCMS, the operation of the algorithm has been modified to enable variable bit rate operation at rates between 12·8 and 24 kb/s. The implementation of such an algorithm in DCMS will further increase the overall compression gain. The first generation of DCMS has been implemented mainly on heavy traffic routes. A DCMS terminal which is optimized for operation on ‘thin’, or smaller, routes, using an IDR link operating at 512 kb/s, is described. Tandem operation of DCMS is becoming an increasingly important consideration on both international and national routes. The accumulation of qdu's (quantization distortion units) when two pairs of DCME/S terminals are operated in tandem can be avoided by an arrangement without ADPCM decoding/encoding in the transit terminals so that the ADPCM decoding is carried out only at the final destination DCMS terminal.
Circuit multiplication equipment
Authors: Bareyt C. , Karas A. , Salomon J. , Aboaf P. 
Published: July 2007

AbstractThis paper discusses the main issues relating to the configuration and equipment which are to be provided in earth‐stations for implementing satellite links with digital circuit multiplication (DCM). Such an implementation is possible using either FDMA/TDM/PSK (continuous) or TDMA/PSK (burst mode) carriers. The main accent will be put in the paper on earth‐stations operating with FMDA/TDM/PSK carriers (called IDR carriers by INTELSAT).As regards the RF/IF subsystem, it is shown that IDR and TDMA are very effective in terms of earth‐station equipment as compared with conventional FDM/FM operation.As regards the communication subsystem—independently of the DCM equipment proper—a compact terminal, integrating all the signal processing and baseband functions is described.
The effect of channel errors on the performance of a contention‐based tdma protocol
Authors: Liang Lung‐Sing , Chang Jin‐Fu 
Published: July 2007

AbstractA previously proposed contention‐based TDMA protocol is modified to remain operational for a channel which is not noise free. The protocol is a mixture of random accessing and time division multiplexing and is suitable for data transmission through a channel which is characterized by non‐negligible round‐trip signal propagation delay. The effect of channel errors on the performance of the protocol is studied. Through numerical calculation it is observed that for the bit‐error‐rates encountered in practice the protocol remains stable. When the channel becomes rather noisy, error correcting codes can be imbedded to improve the performance. The validity of analysis has been verified by computer simulation.
Analysis and correction techniques of doppler shift for non‐geosynchronous communication satellites
Authors: Vilar Enric , Austin John 
Published: July 2007

AbstractA theoretical and experimental study of Doppler correction strategies for elliptical orbit satellite communications is presented. Exact analytical expressions for Doppler shift and elevation angle as a function of perigee time of the ground‐station are also presented. It is shown that for a 63° inclined Molnya orbit and a U.K. observer, the Doppler shift remains below about ± 10 ppm and the Doppler rate below about 6 × 10−4 ppm/s. Various strategies for continuous Doppler correction of the on‐board oscillators are reviewed or proposed. These include a closed loop ground–satellite system and an on‐board programmable correction approach. Two detailed theoretical and experimental studies of on‐board encoded Doppler correction distribution systems are presented in the context of the UK CERS/TSAT mobile communications experiment. A frequency lock system which requires the distribution of only one signal and a phase‐lock system requiring a master reference and the time‐variant code word are described. Numerical values for a 1·5 GHz carrier are presented throughout but can be scaled to other frequencies.
Sperm count as a surrogate endpoint for male fertility control
Authors: Benda Norbert , Gerlinger Christoph 
Published: July 2007

AbstractWhen assessing the effectiveness of a hormonal method of fertility control in men, the classical approach used for the assessment of hormonal contraceptives in women, by estimating the pregnancy rate or using a life‐table analysis for the time to pregnancy, is difficult to apply in a clinical development program. The main reasons are the dissociation of the treated unit, i.e. the man, and the observed unit, i.e. his female partner, the high variability in the frequency of male intercourse, the logistical cost and ethical concerns related to the monitoring of the trial. A reasonable surrogate endpoint of the definite endpoint time to pregnancy is sperm count. In addition to the avoidance of the mentioned problems, trials that compare different treatments are possible with reasonable sample sizes, and study duration can be shorter. However, current products do not suppress sperm production to 100 per cent in all men and the sperm count is only observed with measurement error. Complete azoospermia might not be necessary in order to achieve an
acceptable failure rate compared with other forms of male fertility control. Therefore, the use of sperm count as a surrogate endpoint must rely on the results of a previous trial in which both the definitive‐ and surrogate‐endpoint results were assessed. The paper discusses different estimation functions of the mean pregnancy rate (corresponding to the cumulative hazard) that are based on the results of sperm count trial and a previous trial in which both sperm count and time to pregnancy were assessed, as well as the underlying assumptions. Sample size estimations are given for pregnancy rate estimation with a given precision. Copyright © 2007 John Wiley & Sons, Ltd.
Pilot‐plant fractionation of cottonseed: V. A preliminary cost study
Authors: Persell R. M. , Vix H. L. E. , Reuther C. G. , Pollard E. F. 
Published: July 2007

SummaryA preliminary cost study was made of a combination screw‐press extraction‐fractionation plant. The economic advantage of the combination plant over the screw‐press operation as shown here is small in comparison with the large additional investment required for the combination plant. The present value of the combination process lies in the production of two new products, a purified high‐protein meal and a concentrated pigment gland fraction and in the possibility of producing a high‐grade oil as the removal of the whole pigment gland prevents the pigment material from coming in contact with the oil. Pilot‐plant work under way indicates improvements in the process such as a higher recovery of the meal as purified meal. The development of additional and more profitable uses for the products would increase their value and provide a broader and more stable market for cottonseed.
Comparison of solvent extraction characteristics of rice bran pretreated by hot air drying, steam cooking and extrusion
Authors: Kim C. J. , Byun S. M. , Cheigh H. S. , Kwon T. W. 
Published: July 2007

AbstractRice bran was pretreated by hot air drying, steam cooking and extrusion before solvent extraction of oil. The extractions were conducted in a glass column percolator (i.d. 120 mm), packed to a depth of 90 cm and using n‐hexane at 60 C and gravity feed. Fines (defined as<0.5 mm) in raw bran were significantly reduced by steam cooking and extrusion treatments. Extruded rice bran (ERB) was pelletized and had a bulk density 1.5 times higher than the other products. Regardless of the weight of bran loaded in the percolator, extraction time to reach 1% residual oil was decreased in the order of 116, 67 and 10 min for hot air‐dried rice bran (HARB), steam‐cooked rice bran (SRB) and ERB, respectively. This was due to increases in the percolation rate of SRB by 2 times and by 9 times for ERB compared to HARB. The solvent/bran ratio for extraction to 1% residual oil was decreased by nearly half, from 3.18 for HARB and 3.12 for SRB to 1.77 for ERB.
Analysis of milkfat by HPLC
Authors: Frede Ekkehart , Thiele Herbert 
Published: July 2007

AbstractA routine method for HPLC analysis of milkfat has been developed, which takes into account the specific phenomena of this complex and far‐ranging system of triglycerides. The usual amount of injection of 1 mg has been reduced to 30 or 10 µg of fat. By this the composition of the mobile phase (acetone:acetonitrile, 35/65) and the temperature of the column (Nucleosil C18‐5 µ, 15 cm + Microspher C18‐3µ, 10 cm, in series, T=30–35 C) could be adjusted to a relatively high selectivity without inducing the high‐melting fat components to crystallize on the column. A further advantage resulting from this consisted in permitting the eluent to be recycled over long periods of time. The extremely low amounts of samples necessitated a highly sensitive detection (Δn=5 × 10−7 RI units full scale deflection) which could be realized by an interferential refractometer in connection with a thermostat to keep up a stable temperature of the whole HPLC system (ΔT<0,005 K). By this it was possible to separate milkfat into 45 to 50 different types of triglycerides. By comparing soft and hard milkfats and fractions of milkfats, every fourth peak, starting with C 42, could be attributed to saturated triglycerides; apart from this, easily recognizable qualitative features appearing in the chromatograms permitted conclusions about the feeding regimen and energy supply of the cattle. Furthermore, due to the high stability of separating conditions achieved and due to computer software developed for this purpose it was possible to obtain and compare a large number of chromatograms under the same conditions.
Lipid composition of coconut cake oil
Authors: Gopalakrishnan N. , Narayanan C. S. , Mathew A. G. , Arumughan C. 
Published: July 2007

AbstractLipid classes and fatty acids were analyzed in expeller and rotary extracted coconut oils and corresponding solvent extracted cake oils. Triacylglycerols (84.0 to 93.1%); 1,2 diacylglycerols (1.5 to 5.1%); 1,3 diacylglycerols (1.2 to 2.1%); monoacylglycerols (1.0 to 7.0%); free fatty acids (1.0 to 2.6%); phospholipids (0.03 to 0.4%) and glycolipids (0.2 to 0.35%) were present in these oils. Fatty acid composition of triacylglycerols, phospholipids and glycolipids resembled each other and differed from those of 1,2 and 1,3 diacylglycerols which in turn were similar.
Rapid quantitative HPLC analysis of polyethoxylated nonionics
Authors: Yoshimura Haruo , Sugiyama Toyoki , Nagai Toshio 
Published: July 2007

AbstractA rapid quantitative HPLC method for alkylethoxylate was studied. According to theoretical considerations based on the plate theory, it was expected that alkylethoxylate could be separated to give one chromatographic peak regardless of the carbon number distribution in hydrophobic moiety and adducted number of ethylene oxide by using a back flush technique.As expected, a single peak with good shape for quantitative use was obtained. Quantitative analytical methods were developed for (i) unconverted alkylethoxylate in alkylethoxysulfate, and (ii) alkylethoxylate nonionics formulated with anionics in detergents.As anionics generally were retained less than alkylethoxylates under the condition in which ODS‐column and a methanolic aqueous eluent were used, a single peak for alkylethoxylates was obtained by back flushing after anionics were eluted from the column. In the case of a heavy duty detergent, an additional column was needed to remove the interferences owing to co‐existing more retained species.
Time series modelling and trophic interactions: rainfall, vegetation and ungulate dynamics
Authors: Månsson Lena , Ripa Jörgen , Lundberg Per 
Published: July 2007

AbstractTime series analysis is a tool that is now commonly used when analysing the states of natural populations. This is a particularly complicated task for ungulates, since the data involved usually contain large observation errors and span short periods of time relative to the species’ life expectancies. Here we develop a method that expands on previous analyses, combining statistical state space modelling with biological mechanistic modelling. This enables biological interpretability of the statistical parameters. We used this method to analyse African ungulate census data, and it revealed some clarifying patterns. The dynamics of one group of species were generally independent of density and strongly affected by rainfall, while the other species were governed by a delayed density dependence and were relatively unaffected by rainfall variability. Dry season rainfall was more influential than wet season rainfall, which can be interpreted as indicating that adult survival is more important than recruitment in governing ungulate dynamics.