No abstract

Rain attenuation is the most dominant cause of signal degradation in satellite links operating at Ka-band. This is a particularly serious issue for ground terminal stations located in a sub-tropical region such as state of Florida. Presently, most rain compensation algorithms are based on the use of a fued, large fade margin to combat occasional deep fades. However, the use of a fmed margin, especially for a rainy region, results in an inefficient use of channel capacity for a high percentage of the time. This paper uses an adaptive rain fade counter-measure based on the effective utilization of the channel capacity for several Florida locations with links operating in the Ka-band. In order to determine the outage rates both in terms of channel capacity and BER, Manning's rain attenuation prediction model, based on the rain history of the transmitting and receiving stations has been employed. L INTRODUCTIONSatellite communications form an essential part of global telecommunication systems, carrying large amounts of data, voice and video, and offer a number of features not readily available with other means of coxnmunications. As demand for telecommunication services increases, spectrum congestion forces system planners to use higher frequencies [ 13. Currently, most satelhte W operate at C-band, but as time passes, there wdl be increased use of earth-space links operating at Ka-band.The Advanced Comunications Technology Satellite (ACTS), which was launched into orbit on September 12, 1993, has several experiments on board related to the utdization of earth-space link at Ka-band with downlink hquencies i?om 19.2 to 20.2 GHz and uplink hquencies from 29.1 to 30.0 Ghz [2]. The ACTS mobile terminal program will explore the potentials of Ka-band to meet the needs of future mobile satelhte services. The Kaband, with the promise of less congestion, may also offer increased bandwidth and, therefore, the expansion of system capacity and user services. Also, accompanying sigdicantly smaller ground terminal equipment is expected to reduce system cost [3]. However, one of the major concems of the investigators is that satellite channels at Ka-band are subject to severe performance degradations due to propagation effects that occur at this fadmg region. For a mobile satellite link, the attenuation factors involved include scintillation, shadowing, multipath fading, and the most dominant factor of all, rain attenuation. In the design of such a link maintaining a fixed, large fade margin to combat occasional deep rain fades as done in most rain compensation algorithms, results in severe reduction in communication capacity [4]. Traditional fade countermeasures concentrate on the use of power, bandwidth, and site diversity but pay very little attention to the optimum use of channel capacity. In this paper we use the adaptive rain fade counter measure, based on the effective utllization of the channel capacity proposed in [4] to study the performance of typical ACTS communication links for ground terrmnal locations in Florida. IL ...

The dust storm happens in the Middle East with very high frequency. According to the dust storm effects, it is vital to study on the dust storms in the Middle East. The first step toward the study on dust storm is the enhancement of dust storms and determination of the point sources. In this paper, a new false color composite (FCC) map for the dust storm enhancement and point sources determination in the Middle East has been developed. The 28 Terra-MODIS images in 2008 and 2009 were utilized in this study. We tried to replace the Red, Green and Blue bands in RGB maps with the bands or maps that enhance the dust storms. Hence, famous indices for dust storm detection (NDDI, D and BTD) were generated using the different bands of MODIS images. These indices with some bands of MODIS were utilized for FCC map generation with different combinations. Among the different combinations, four better FCC maps were selected and these four FCC are compared using visual interpretation. The results of visual interpretations showed that the best FCC map for enhancement of dust storm in the middle east is an especial combination of the three indices (Red: D, Green: BTD and Blue: NDDI). Therefore, we utilized of this new FCC method for the enhancement of dust storms and determination of point sources in Middle East.

AbstractWhile reactive focus on form (FonF) has been addressed extensively in the literature, preemptive FonF has not attracted the attention it deserves. To fill in part of this gap in the English-language teaching (ELT) context, the present study was conducted to examine the occurrence of preemptive focus on form episodes (FFEs) in the classes of two male and two female English-language teachers. Additionally, it aimed to explore the frequency of student-initiated and teacher-initiated FFEs as well as the uptake and no uptake moves in four classes. To address these issues, all cases of preemptive FFEs were identified in 6 h of instruction obtained from videotaping of four classes. Results confirmed that preemptive FonF does occur in the process of meaning-focused communication and that they are used by male and female teachers almost equally to deal with linguistic difficulties. The findings further showed that student-initiated and teacher-initiated FFEs occurred almost equally in four classes. As to the type of moves, no uptake move was recorded to occur more frequently in male teachers’ classes and to occur more frequently in student-initiated episodes in all classes. Results can raise the awareness of ELT teachers about the benefits of employing preemptive FonF in the context of meaning-focused communications.

We study induced representations of Hilbert modules over locally C*-algebras and their non-degeneracy. We show that if V and W are Morita equivalent Hilbert modules over locally C*-algebras A and B, respectively, then there exists a bijective correspondence between equivalence classes of non-degenerate representations of V and W .