Relativistic Time Transfer for Inter-satellite Links

Energy Technology Data Exchange (ETDEWEB)

Xie, Yi, E-mail: yixie@nju.edu.cn [Department of Astronomy, School of Astronomy and Space Sciences, Nanjing University, Nanjing (China); Shanghai Key Laboratory of Space Navigation and Position Techniques, Shanghai (China); Key Laboratory of Modern Astronomy and Astrophysics, Nanjing University, Ministry of Education, Nanjing (China)

2016-04-26

Inter-Satellite links (ISLs) will be an important technique for a global navigation satellite system (GNSS) in the future. Based on the principles of general relativity, the time transfer in an ISL is modeled and the algorithm for onboard computation is described. It is found, in general, satellites with circular orbits and identical semi-major axes can benefit inter-satellite time transfer by canceling out terms associated with the transformations between the proper times and the Geocentric Coordinate Time. For a GPS-like GNSS, the Shapiro delay is as large as 0.1 ns when the ISL passes at the limb of the Earth. However, in more realistic cases, this value will decrease to about 50 ps.

Digital optical feeder links system for broadband geostationary satellite

Science.gov (United States)

Poulenard, Sylvain; Mège, Alexandre; Fuchs, Christian; Perlot, Nicolas; Riedi, Jerome; Perdigues, Josep

2017-02-01

An optical link based on a multiplex of wavelengths at 1.55μm is foreseen to be a valuable solution for the feeder link of the next generation of high-throughput geostationary satellite. The main satellite operator specifications for such link are an availability of 99.9% over the year, a capacity around 500Gbit/s and to be bent-pipe. Optical ground station networks connected to Terabit/s terrestrial fibers are proposed. The availability of the optical feeder link is simulated over 5 years based on a state-of-the-art cloud mask data bank and an atmospheric turbulence strength model. Yearly and seasonal optical feeder link availabilities are derived and discussed. On-ground and on-board terminals are designed to be compliant with 10Gbit/s per optical channel data rate taking into account adaptive optic systems to mitigate the impact of atmospheric turbulences on single-mode optical fiber receivers. The forward and return transmission chains, concept and implementation, are described. These are based on a digital transparent on-off keying optical link with digitalization of the DVB-S2 and DVB-RCS signals prior to the transmission, and a forward error correcting code. In addition, the satellite architecture is described taking into account optical and radiofrequency payloads as well as their interfaces.

Intersatellite link application to commercial communications satellites

Science.gov (United States)

Lee, Young S.; Atia, Ali E.; Ponchak, Denise S.

1988-01-01

The fundamental characteristics of intersatellite link (ISL) systems, and their application to domestic, regional, and global satellite communications, are described. The quantitative advantages of using ISLs to improve orbit utilization, spectrum occupancy, transmission delay (compared to multi-hop links), coverage, and connectivity, and to reduce the number of earth station antennas, are also presented. Cost-effectiveness and other systems benefits of using ISLs are identified, and the technical and systems planning aspects of ISL systems implementation are addressed.

A description of QUALCOMM Automatic Satellite Position Reporting (QASPR(R)) for mobile communications

Science.gov (United States)

Ames, William G.

1990-01-01

Two satellite position reporting has been introduced into the OmniTRACS mobile satellite communication system. This system significantly improves position reporting reliability and accuracy while simplifying the terminal's hardware. The positioning technique uses the original OmniTRACS TDMA timing signal formats in the forward and return link directions plus an auxiliary, low power forward link signal through a second satellite to derive distance values. The distances are then converted into the mobile terminal's latitude and longitude in real time. A minor augmentation of the spread spectrum profile of the return link allowed the resolution of periodic ambiguities. The system also locates the two satellites in real time with fixed platforms in known locations using identical mobile terminal hardware. Initial accuracies of 1/4 mile have been realized uniformly throughout the USA using a satellite separation of 22 degrees and there are no dead zones, skywaves, or cycle slips as found in terrestrial systems like LORAN-C.

Enhanced bit rate-distance product impulse radio ultra-wideband over fiber link

DEFF Research Database (Denmark)

Rodes Lopez, Roberto; Jensen, Jesper Bevensee; Caballero Jambrina, Antonio

2010-01-01

We report on a record distance and bit rate-wireless impulse radio (IR) ultra-wideband (UWB) link with combined transmission over a 20 km long fiber link. We are able to improve the compliance with the regulated frequency emission mask and achieve bit rate-distance products as high as 16 Gbit/s·m....

Simulation and Analysis of Autonomous Time Synchronization Based on Asynchronism Two-way Inter-satellite Link

Science.gov (United States)

Fang, L.; Yang, X. H.; Sun, B. Q.; Qin, W. J.; Kong, Y.

2013-09-01

The measurement of the inter-satellite link is one of the key techniques in the autonomous operation of satellite navigation system. Based on the asynchronism inter-satellite two-way measurement mode in GPS constellation, the reduction formula of the inter-satellite time synchronization is built in this paper. Moreover, the corrective method of main systematic errors is proposed. Inter-satellite two-way time synchronization is simulated on the basis of IGS (International GNSS Service) precise ephemeris. The impacts of the epoch domestication of asynchronism inter-satellite link pseudo-range, the initial orbit, and the main systematic errors on satellite time synchronization are analyzed. Furthermore, the broadcast clock error of each satellite is calculated by the ``centralized'' inter-satellite autonomous time synchronization. Simulation results show that the epoch domestication of asynchronism inter-satellite link pseudo-range and the initial orbit have little impact on the satellite clock errors, and thus they needn't be taken into account. The errors caused by the relativistic effect and the asymmetry of path travel have large impact on the satellite clock errors. These should be corrected with theoretical formula. Compared with the IGS precise clock error, the root mean square of the broadcast clock error of each satellite is about 0.4 ns.

Effect of digital scrambling on satellite communication links

Science.gov (United States)

Dessouky, K.

1985-01-01

Digital data scrambling has been considered for communication systems using NRZ symbol formats. The purpose is to increase the number of transitions in the data to improve the performance of the symbol synchronizer. This is accomplished without expanding the bandwidth but at the expense of increasing the data bit error rate (BER). Models for the scramblers/descramblers of practical interest are presented together with the appropriate link model. The effects of scrambling on the performance of coded and uncoded links are studied. The results are illustrated by application to the Tracking and Data Relay Satellite System (TDRSS) links. Conclusions regarding the usefulness of scrambling are also given.

Evaluation strategies for midwifery education linked to digital media and distance delivery technology.

Science.gov (United States)

Fullerton, Judith T; Ingle, Henry T

2003-01-01

The goal of the teaching and learning process for health professionals is the acquisition of a fundamental core of knowledge, the demonstration of critical thinking ability, and the demonstration of competency in the performance of clinical skills. Teaching and learning in distance education programs require that the administration, teachers, and students be creative in developing evaluation strategies that can be adapted to the challenges of the cyberspace on-line educational environment. Evaluation standards for distance education programs recently have been delineated by federal agencies, private organizations, and academic accreditation associations. These standards are linked to principles of sound education practice that promote program quality, high levels of student-faculty interaction, and support effective teaching and learning in the distance education context. A growing body of evidence supports the conclusion that technology-enhanced teaching is equivalent in effectiveness compared with traditional methods when student-learning outcomes are the focus of measurement. An allied body of literature offers model approaches that can be useful to educators who must also conduct the evaluation of clinical skills, provide feedback, and promote socialization to the nurse-midwifery/midwifery role for students being educated in whole or in part through instruction delivered at a distance.

Satellite communications: possibilities and problems

International Nuclear Information System (INIS)

Hine, M.

1986-01-01

Communication links via satellites are becoming available in Europe, both as part of the development of the telephone system and as special services aimed at data traffic. They offer the possibility of speeds between 50 kb/s and 2 Mb/s, without the problems and long term commitments of long distance land lines. Such links are provided by the PTT's as circuits which can be booked for variable periods, and have error rates which can be very low and well controlled. Problems in networking can arise from the satellite delay, particularly if errors occur in the local connections, and from the leased circuit and tariff philosophies of the PTT's. (Auth.)

Effectiveness evaluation of double-layered satellite network with laser and microwave hybrid links based on fuzzy analytic hierarchy process

Science.gov (United States)

Zhang, Wei; Rao, Qiaomeng

2018-01-01

In order to solve the problem of high speed, large capacity and limited spectrum resources of satellite communication network, a double-layered satellite network with global seamless coverage based on laser and microwave hybrid links is proposed in this paper. By analyzing the characteristics of the double-layered satellite network with laser and microwave hybrid links, an effectiveness evaluation index system for the network is established. And then, the fuzzy analytic hierarchy process, which combines the analytic hierarchy process and the fuzzy comprehensive evaluation theory, is used to evaluate the effectiveness of the double-layered satellite network with laser and microwave hybrid links. Furthermore, the evaluation result of the proposed hybrid link network is obtained by simulation. The effectiveness evaluation process of the proposed double-layered satellite network with laser and microwave hybrid links can help to optimize the design of hybrid link double-layered satellite network and improve the operating efficiency of the satellite system.

A BAYESIAN APPROACH TO LOCATING THE RED GIANT BRANCH TIP MAGNITUDE. II. DISTANCES TO THE SATELLITES OF M31

Energy Technology Data Exchange (ETDEWEB)

Conn, A. R.; Parker, Q. A.; Zucker, D. B. [Department of Physics and Astronomy, Macquarie University, NSW 2109 (Australia); Ibata, R. A.; Martin, N. F. [Observatoire Astronomique, Universite de Strasbourg, CNRS, F-67000 Strasbourg (France); Lewis, G. F. [Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, Sydney, NSW 2006 (Australia); McConnachie, A. W. [NRC Herzberg Institute of Astrophysics, 5071 West Saanich Road, Victoria, British Columbia V9E 2E7 (Canada); Irwin, M. J.; Chapman, S. C. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Tanvir, N. [Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH (United Kingdom); Fardal, M. A. [University of Massachusetts, Department of Astronomy, LGRT 619-E, 710 N. Pleasant Street, Amherst, MA 01003-9305 (United States); Ferguson, A. M. N. [Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Valls-Gabaud, D. [Observatoire de Paris, LERMA, 61 Avenue de l' Observatoire, F-75014 Paris (France)

2012-10-10

In 'A Bayesian Approach to Locating the Red Giant Branch Tip Magnitude (Part I)', a new technique was introduced for obtaining distances using the tip of the red giant branch (TRGB) standard candle. Here we describe a useful complement to the technique with the potential to further reduce the uncertainty in our distance measurements by incorporating a matched-filter weighting scheme into the model likelihood calculations. In this scheme, stars are weighted according to their probability of being true object members. We then re-test our modified algorithm using random-realization artificial data to verify the validity of the generated posterior probability distributions (PPDs) and proceed to apply the algorithm to the satellite system of M31, culminating in a three-dimensional view of the system. Further to the distributions thus obtained, we apply a satellite-specific prior on the satellite distances to weight the resulting distance posterior distributions, based on the halo density profile. Thus in a single publication, using a single method, a comprehensive coverage of the distances to the companion galaxies of M31 is presented, encompassing the dwarf spheroidals Andromedas I-III, V, IX-XXVII, and XXX along with NGC 147, NGC 185, M33, and M31 itself. Of these, the distances to Andromedas XXIV-XXVII and Andromeda XXX have never before been derived using the TRGB. Object distances are determined from high-resolution tip magnitude posterior distributions generated using the Markov Chain Monte Carlo technique and associated sampling of these distributions to take into account uncertainties in foreground extinction and the absolute magnitude of the TRGB as well as photometric errors. The distance PPDs obtained for each object both with and without the aforementioned prior are made available to the reader in tabular form. The large object coverage takes advantage of the unprecedented size and photometric depth of the Pan-Andromeda Archaeological Survey

Ground-to-satellite quantum teleportation.

Science.gov (United States)

Ren, Ji-Gang; Xu, Ping; Yong, Hai-Lin; Zhang, Liang; Liao, Sheng-Kai; Yin, Juan; Liu, Wei-Yue; Cai, Wen-Qi; Yang, Meng; Li, Li; Yang, Kui-Xing; Han, Xuan; Yao, Yong-Qiang; Li, Ji; Wu, Hai-Yan; Wan, Song; Liu, Lei; Liu, Ding-Quan; Kuang, Yao-Wu; He, Zhi-Ping; Shang, Peng; Guo, Cheng; Zheng, Ru-Hua; Tian, Kai; Zhu, Zhen-Cai; Liu, Nai-Le; Lu, Chao-Yang; Shu, Rong; Chen, Yu-Ao; Peng, Cheng-Zhi; Wang, Jian-Yu; Pan, Jian-Wei

2017-09-07

An arbitrary unknown quantum state cannot be measured precisely or replicated perfectly. However, quantum teleportation enables unknown quantum states to be transferred reliably from one object to another over long distances, without physical travelling of the object itself. Long-distance teleportation is a fundamental element of protocols such as large-scale quantum networks and distributed quantum computation. But the distances over which transmission was achieved in previous teleportation experiments, which used optical fibres and terrestrial free-space channels, were limited to about 100 kilometres, owing to the photon loss of these channels. To realize a global-scale 'quantum internet' the range of quantum teleportation needs to be greatly extended. A promising way of doing so involves using satellite platforms and space-based links, which can connect two remote points on Earth with greatly reduced channel loss because most of the propagation path of the photons is in empty space. Here we report quantum teleportation of independent single-photon qubits from a ground observatory to a low-Earth-orbit satellite, through an uplink channel, over distances of up to 1,400 kilometres. To optimize the efficiency of the link and to counter the atmospheric turbulence in the uplink, we use a compact ultra-bright source of entangled photons, a narrow beam divergence and high-bandwidth and high-accuracy acquiring, pointing and tracking. We demonstrate successful quantum teleportation of six input states in mutually unbiased bases with an average fidelity of 0.80 ± 0.01, well above the optimal state-estimation fidelity on a single copy of a qubit (the classical limit). Our demonstration of a ground-to-satellite uplink for reliable and ultra-long-distance quantum teleportation is an essential step towards a global-scale quantum internet.

DISTANCE LEARNING STUDENTS’ NEED: Evaluating Interactions from Moore’s Theory of Transactional Distance

Directory of Open Access Journals (Sweden)

Rusmanizah USTATI

2013-04-01

Full Text Available This study draws on the experience from a focus group interviews under the distance learning programme known as Program Pensiswazahan Guru (PPG organized by the Malaysian Ministry of Education in collaboration with local universities and institutes of education. Its purpose is to uncover students’ perception about the platform used by International Islamic University Malaysia (IIUM which is the Learning Management System (LMS. LMS is a vital instructional medium especially for the varsity distant learners. Michael Moore’s Theory of Transactional Distance is used as the guiding framework to gain insights on learning and interactions in this e-learning setting. Teacher-student interactions are analyzed for better understanding of the phenomena under study. The findings indicate that in terms of usability LMS is perceived as a good platform to acquire information on content and to receive feedback from instructors. However, IIUM learners hope for more interactivity where learners can communicate amongst themselves beside engaging with the instructor-learner- content interactions that they currently experience via the system. This study aspires to provide insights on the significance of interactions from distance learners’ perception.

Solar array experiments on the SPHINX satellite. [Space Plasma High voltage INteraction eXperiment satellite

Science.gov (United States)

Stevens, N. J.

1974-01-01

The Space Plasma, High Voltage Interaction Experiment (SPHINX) is the name given to an auxiliary payload satellite scheduled to be launched in January 1974. The principal experiments carried on this satellite are specifically designed to obtain the engineering data on the interaction of high voltage systems with the space plasma. The classes of experiments are solar array segments, insulators, insulators with pin holes and conductors. The satellite is also carrying experiments to obtain flight data on three new solar array configurations: the edge illuminated-multijunction cells, the teflon encased cells, and the violet cells.

Improved GPS-based Satellite Relative Navigation Using Femtosecond Laser Relative Distance Measurements

Directory of Open Access Journals (Sweden)

Hyungjik Oh

2016-03-01

Full Text Available This study developed an approach for improving Carrier-phase Differential Global Positioning System (CDGPS based realtime satellite relative navigation by applying laser baseline measurement data. The robustness against the space operational environment was considered, and a Synthetic Wavelength Interferometer (SWI algorithm based on a femtosecond laser measurement model was developed. The phase differences between two laser wavelengths were combined to measure precise distance. Generated laser data were used to improve estimation accuracy for the float ambiguity of CDGPS data. Relative navigation simulations in real-time were performed using the extended Kalman filter algorithm. The GPS and laser-combined relative navigation accuracy was compared with GPS-only relative navigation solutions to determine the impact of laser data on relative navigation. In numerical simulations, the success rate of integer ambiguity resolution increased when laser data was added to GPS data. The relative navigational errors also improved five-fold and two-fold, relative to the GPS-only error, for 250 m and 5 km initial relative distances, respectively. The methodology developed in this study is suitable for application to future satellite formation-flying missions.

LERC-SLAM - THE NASA LEWIS RESEARCH CENTER SATELLITE LINK ATTENUATION MODEL PROGRAM (MACINTOSH VERSION)

Science.gov (United States)

Manning, R. M.

1994-01-01

The frequency and intensity of rain attenuation affecting the communication between a satellite and an earth terminal is an important consideration in planning satellite links. The NASA Lewis Research Center Satellite Link Attenuation Model Program (LeRC-SLAM) provides a static and dynamic statistical assessment of the impact of rain attenuation on a communications link established between an earth terminal and a geosynchronous satellite. The program is designed for use in the specification, design and assessment of satellite links for any terminal location in the continental United States. The basis for LeRC-SLAM is the ACTS Rain Attenuation Prediction Model, which uses a log-normal cumulative probability distribution to describe the random process of rain attenuation on satellite links. The derivation of the statistics for the rainrate process at the specified terminal location relies on long term rainfall records compiled by the U.S. Weather Service during time periods of up to 55 years in length. The theory of extreme value statistics is also utilized. The user provides 1) the longitudinal position of the satellite in geosynchronous orbit, 2) the geographical position of the earth terminal in terms of latitude and longitude, 3) the height above sea level of the terminal site, 4) the yearly average rainfall at the terminal site, and 5) the operating frequency of the communications link (within 1 to 1000 GHz, inclusive). Based on the yearly average rainfall at the terminal location, LeRC-SLAM calculates the relevant rain statistics for the site using an internal data base. The program then generates rain attenuation data for the satellite link. This data includes a description of the static (i.e., yearly) attenuation process, an evaluation of the cumulative probability distribution for attenuation effects, and an evaluation of the probability of fades below selected fade depths. In addition, LeRC-SLAM calculates the elevation and azimuth angles of the terminal

Scaling of Airborne Ad-hoc Network Metrics with Link Range and Satellite Connectivity

Directory of Open Access Journals (Sweden)

Kai-Daniel BÜCHTER

2018-06-01

Full Text Available In this contribution, large-scale commercial aeronautical ad-hoc networks are evaluated. The investigation is based on a simulation environment with input from 2016 flight schedule and aircraft performance databases for flight movement modelling, along with a defined infrastructure of ground gateways and communication satellites. A cluster-based algorithm is used to build the communication network topology between aircraft. Cloud top pressure data can be considered to estimate cloud height and evaluate the impact of link obscuration on network availability, assuming a free-space optics-based communication network. The effects of communication range, satellite availability, fleet equipage ratio and clouds are discussed. It is shown how network reach and performance can be enhanced by adding taps to the network in the form of high-speed satellite links. The effect of adding these is two-fold: firstly, network reach can be increased by connecting remote aircraft clusters. Secondly, larger clusters can effectively be split into smaller ones in order to increase performance especially with regard to hop count and available overall capacity. In a realistic scenario concerning communication range and with moderate numbers of high-speed satellite terminals, on average, 78% of all widebody aircraft can be reached. With clouds considered (assuming laser links, this number reduces by 10%.

Development and field testing of satellite-linked fluorometers for marine mammals

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This dataset includes telemetry data related to the development and testing of an animal-borne satellite-linked fluorometer tag, used on northern fur seals and...

Tracking and Data Relay Satellite System user impact and network compatibility study. [antenna design and telecommunication links

Science.gov (United States)

1973-01-01

The report contains data on antenna configurations for the low data rate users of the Tracking and Data Relay Satellite System (TDRSS). It treats the coverage and mutual visibility considerations between the user satellites and the relay satellites and relates these considerations to requirements of antenna beamwidth and fractional user orbital coverage. A final section includes user/TDRS telecommunication link budgets and forward and return link data rate tradeoffs.

Bird migration and avian influenza: a comparison of hydrogen stable isotopes and satellite tracking methods

Science.gov (United States)

Bridge, Eli S.; Kelly, Jeffrey F.; Xiao, Xiangming; Takekawa, John Y.; Hill, Nichola J.; Yamage, Mat; Haque, Enam Ul; Islam, Mohammad Anwarul; Mundkur, Taej; Yavuz, Kiraz Erciyas; Leader, Paul; Leung, Connie Y.H.; Smith, Bena; Spragens, Kyle A.; Vandegrift, Kurt J.; Hosseini, Parviez R.; Saif, Samia; Mohsanin, Samiul; Mikolon, Andrea; Islam, Ausrafal; George, Acty; Sivananinthaperumal, Balachandran; Daszak, Peter; Newman, Scott H.

2014-01-01

Satellite-based tracking of migratory waterfowl is an important tool for understanding the potential role of wild birds in the long-distance transmission of highly pathogenic avian influenza. However, employing this technique on a continental scale is prohibitively expensive. This study explores the utility of stable isotope ratios in feathers in examining both the distances traveled by migratory birds and variation in migration behavior. We compared the satellite-derived movement data of 22 ducks from 8 species captured at wintering areas in Bangladesh, Turkey, and Hong Kong with deuterium ratios (δD) in the feathers of these and other individuals captured at the same locations. We derived likely molting locations from the satellite tracking data and generated expected isotope ratios based on an interpolated map of δD in rainwater. Although δD was correlated with the distance between wintering and molting locations, surprisingly, measured δD values were not correlated with either expected values or latitudes of molting sites. However, population-level parameters derived from the satellite-tracking data, such as mean distance between wintering and molting locations and variation in migration distance, were reflected by means and variation of the stable isotope values. Our findings call into question the relevance of the rainfall isotope map for Asia for linking feather isotopes to molting locations, and underscore the need for extensive ground truthing in the form of feather-based isoscapes. Nevertheless, stable isotopes from feathers could inform disease models by characterizing the degree to which regional breeding populations interact at common wintering locations. Feather isotopes also could aid in surveying wintering locations to determine where high-resolution tracking techniques (e.g. satellite tracking) could most effectively be employed. Moreover, intrinsic markers such as stable isotopes offer the only means of inferring movement information from

Levels of Interaction Provided by Online Distance Education Models

Science.gov (United States)

Alhih, Mohammed; Ossiannilsson, Ebba; Berigel, Muhammet

2017-01-01

Interaction plays a significant role to foster usability and quality in online education. It is one of the quality standard to reveal the evidence of practice in online distance education models. This research study aims to evaluate levels of interaction in the practices of distance education centres. It is aimed to provide online distance…

Interaction in Distance Nursing Education

Science.gov (United States)

Boz Yuksekdag, Belgin

2012-01-01

The purpose of this study is to determine psychiatry nurses' attitudes toward the interactions in distance nursing education, and also scrunize their attitudes based on demographics and computer/Internet usage. The comparative relational scanning model is the method of this study. The research data were collected through "The Scale of Attitudes of…

An up-link power control for demand assignment International Business Satellite Communications Network

Science.gov (United States)

Nohara, Mitsuo; Takeuchi, Yoshio; Takahata, Fumio

Up-link power control (UPC) is one of the essential technologies to provide efficient satellite communication systems operated at frequency bands above 10 GHz. A simple and cost-effective UPC scheme applicable to a demand assignment international business satellite communications system has been developed. This paper presents the UPC scheme, including the hardware implementation and its performance.

LERC-SLAM - THE NASA LEWIS RESEARCH CENTER SATELLITE LINK ATTENUATION MODEL PROGRAM (IBM PC VERSION)

Science.gov (United States)

Manning, R. M.

1994-01-01

The frequency and intensity of rain attenuation affecting the communication between a satellite and an earth terminal is an important consideration in planning satellite links. The NASA Lewis Research Center Satellite Link Attenuation Model Program (LeRC-SLAM) provides a static and dynamic statistical assessment of the impact of rain attenuation on a communications link established between an earth terminal and a geosynchronous satellite. The program is designed for use in the specification, design and assessment of satellite links for any terminal location in the continental United States. The basis for LeRC-SLAM is the ACTS Rain Attenuation Prediction Model, which uses a log-normal cumulative probability distribution to describe the random process of rain attenuation on satellite links. The derivation of the statistics for the rainrate process at the specified terminal location relies on long term rainfall records compiled by the U.S. Weather Service during time periods of up to 55 years in length. The theory of extreme value statistics is also utilized. The user provides 1) the longitudinal position of the satellite in geosynchronous orbit, 2) the geographical position of the earth terminal in terms of latitude and longitude, 3) the height above sea level of the terminal site, 4) the yearly average rainfall at the terminal site, and 5) the operating frequency of the communications link (within 1 to 1000 GHz, inclusive). Based on the yearly average rainfall at the terminal location, LeRC-SLAM calculates the relevant rain statistics for the site using an internal data base. The program then generates rain attenuation data for the satellite link. This data includes a description of the static (i.e., yearly) attenuation process, an evaluation of the cumulative probability distribution for attenuation effects, and an evaluation of the probability of fades below selected fade depths. In addition, LeRC-SLAM calculates the elevation and azimuth angles of the terminal

White Rabbit Precision Time Protocol on Long-Distance Fiber Links

NARCIS (Netherlands)

Dierikx, E.F.; Dierikx, A.E.; Fordell, T.; Myyry, J.; Koponen, P.; Merimaa, M.; Pinkert, T.J.; Koelemeij, J.C.J.; Peek, H.Z.; Smets, R.

2016-01-01

The application of White Rabbit precision time protocol (WR-PTP) in long-distance optical fiber links has been investigated. WR-PTP is an implementation of PTP in synchronous Ethernet optical fiber networks, originally intended for synchronization of equipment within a range of 10 km. This paper

A Horse of a Different Color: Distance Education; Making it Effective.

Science.gov (United States)

Jakupcak, Jo; Fishbaugh, Mary Susan

This paper discusses techniques and strategies to improve the effectiveness of distance education delivered via interactive video telecommunication. Advantages and disadvantages of three types of interactive video--telephone linkage, end-to-end fiber optic digital transmission, and satellite broadcasts--are briefly discussed. Prebroadcast…

Interactions of planetary magnetospheres with icy satellite surfaces

International Nuclear Information System (INIS)

Cheng, A.F.; Haff, P.K.; Johnson, R.E.; Lanzerotti, L.J.

1986-01-01

When natural satellites and ring particles are embedded within magnetospheric plasmas, the charged particles interact with the surfaces of these solid bodies. These interactions have important implications for the surface, the atmosphere of the parent body, and the magnetosphere as a whole. Significant erosion of the surface by sputtering, as well as redeposition of sputter ejecta, can occur over geologic time. The surface can also be chemically modified. Sputter ejecta can make important contributions to the atmosphere; sputtering provides a lower limit to the atmospheric column density even for arbitrarily cold satellite surfaces. Sputter ejecta escaping from the parent body can form extensive neutral clouds within the magnetosphere. Ionization and dissociation within these neutral clouds can be dominant sources of low-energy plasma. The importance of these processes is discussed for the satellites and magnetospheres of Jupiter, Saturn and Uranus

Study of LEO-SAT microwave link for broad-band mobile satellite communication system

Science.gov (United States)

Fujise, Masayuki; Chujo, Wataru; Chiba, Isamu; Furuhama, Yoji; Kawabata, Kazuaki; Konishi, Yoshihiko

1993-01-01

In the field of mobile satellite communications, a system based on low-earth-orbit satellites (LEO-SAT's) such as the Iridium system has been proposed. The LEO-SAT system is able to offer mobile telecommunication services in high-latitude areas. Rain degradation, fading and shadowing are also expected to be decreased when the system is operated at a high elevation angle. Furthermore, the propagation delay generated in the LEO-SAT system is less pronounced than that in the geostationary orbit satellite (GEO-SAT) system and, in voice services, the effect of the delay is almost negligible. We proposed a concept of a broad-band mobile satellite communication system with LEO-SAT's and Optical ISL. In that system, a fixed L-band (1.6/1.5 GHz) multibeam is used to offer narrow band service to the mobile terminals in the entire area covered by a LEO-SAT and steerable Ka-band (30/20 GHz) spot beams are used for the wide band service. In this paper, we present results of a study of LEO-SAT microwave link between a satellite and a mobile terminal for a broad-band mobile satellite communication system. First, the results of link budget calculations are presented and the antennas mounted on satellites are shown. For a future mobile antenna technology, we also show digital beamforming (DBF) techniques. DBF, together with modulation and/or demodulation, is becoming a key technique for mobile antennas with advanced functions such as antenna pattern calibration, correction, and radio interference suppression. In this paper, efficient DBF techniques for transmitting and receiving are presented. Furthermore, an adaptive array antenna system suitable for this LEO-SAT is presented.

Introducing you to satellite operated data collection platforms (DCP).

CSIR Research Space (South Africa)

Stavropoulos, CC

1977-09-01

Full Text Available and operate in the VHF, UHF or microwave bands. By using a satellite as a repeater, large distances over land and sea can be covered with a single repeater in the sky. Trans-continental links for communication purposes have been operational for many years...

A Survey of Congestion Control Techniques and Data Link Protocols in Satellite Networks

OpenAIRE

Fahmy, Sonia; Jain, Raj; Lu, Fang; Kalyanaraman, Shivkumar

1998-01-01

Satellite communication systems are the means of realizing a global broadband integrated services digital network. Due to the statistical nature of the integrated services traffic, the resulting rate fluctuations and burstiness render congestion control a complicated, yet indispensable function. The long propagation delay of the earth-satellite link further imposes severe demands and constraints on the congestion control schemes, as well as the media access control techniques and retransmissi...

Distance learning through synchronous interactive television.

Science.gov (United States)

Hall, Janis L

2007-01-01

The advent and popularity of asynchronous online learning has somewhat obscured a standby technology developed over the last two decades. Interactive videoconferencing, sometimes called "interactive television," though not as glamorous and popular a topic at distance-learning conferences, is still alive and well at many institutions. Three or four years ago, many of us were led to believe that interactive television would go the way of the dinosaurs-everything would soon be in an asynchronous format or on individual desktops. There would no longer be any need for elaborately designed classrooms, networks, and operations staff. To date, this prediction has not come true. In fact, synchronous interactive television has experienced significant growth as newer, easier, and cheaper technologies allow institutions to reach more students with less resource investment. Faculty and students, while appreciating the convenience of asynchronous delivery, still express a need for synchronous communication. This article explores the issues involved in synchronous distance education, the current technologies and proposed future developments, and best practices in terms of classroom design, faculty use, and operational issues. It is not a research article but an anecdotal case study based on Washington State University's experiences over the last 20 years in developing and adapting to new synchronous technologies and creating the support and technical infrastructure to best deliver academic courses through this medium.

White Rabbit Precision Time Protocol on Long-Distance Fiber Links.

Science.gov (United States)

Dierikx, Erik F; Wallin, Anders E; Fordell, Thomas; Myyry, Jani; Koponen, Petri; Merimaa, Mikko; Pinkert, Tjeerd J; Koelemeij, Jeroen C J; Peek, Henk Z; Smets, Rob

2016-07-01

The application of White Rabbit precision time protocol (WR-PTP) in long-distance optical fiber links has been investigated. WR-PTP is an implementation of PTP in synchronous Ethernet optical fiber networks, originally intended for synchronization of equipment within a range of 10 km. This paper discusses the results and limitations of two implementations of WR-PTP in the existing communication fiber networks. A 950-km WR-PTP link was realized using unidirectional paths in a fiber pair between Espoo and Kajaani, Finland. The time transfer on this link was compared (after initial calibration) against a clock comparison by GPS precise point positioning (PPP). The agreement between the two methods remained within [Formula: see text] over three months of measurements. Another WR-PTP implementation was realized between Delft and Amsterdam, the Netherlands, by cascading two links of 137 km each. In this case, the WR links were realized as bidirectional paths in single fibers. The measured time offset between the starting and end points of the link was within 5 ns with an uncertainty of 8 ns, mainly due to the estimated delay asymmetry caused by chromatic dispersion.

A class-based link prediction using Distance Dependent Chinese Restaurant Process

Science.gov (United States)

Andalib, Azam; Babamir, Seyed Morteza

2016-08-01

One of the important tasks in relational data analysis is link prediction which has been successfully applied on many applications such as bioinformatics, information retrieval, etc. The link prediction is defined as predicting the existence or absence of edges between nodes of a network. In this paper, we propose a novel method for link prediction based on Distance Dependent Chinese Restaurant Process (DDCRP) model which enables us to utilize the information of the topological structure of the network such as shortest path and connectivity of the nodes. We also propose a new Gibbs sampling algorithm for computing the posterior distribution of the hidden variables based on the training data. Experimental results on three real-world datasets show the superiority of the proposed method over other probabilistic models for link prediction problem.

Optical intersatellite links - Application to commercial satellite communications

Science.gov (United States)

Paul, D.; Faris, F.; Garlow, R.; Inukai, T.; Pontano, B.; Razdan, R.; Ganz, Aura; Caudill, L.

1992-01-01

Application of optical intersatellite links for commercial satellite communications services is addressed in this paper. The feasibility of commercialization centers around basic issues such as the need and derived benefits, implementation complexity and overall cost. In this paper, commercialization of optical ISLs is assessed in terms of the services provided, systems requirements and feasibility of appropriate technology. Both long- and short-range ISLs for GEO-GEO, GEO-LEO and LEO applications are considered. Impact of systems requirements on the payload design and use of advanced technology in reducing its mass, power, and volume requirements are discussed.

Interactive Distance Learning Effectively Provides Winning Sports Nutrition Workshops.

Science.gov (United States)

Ricketts, Jennifer; Hoelscher-Day, Sharon; Begeman, Gale; Houtkooper, Linda

2001-01-01

Interactive distance-education (n=226) and face-to-face (n=129) continuing education workshops for health care and education professionals on sports nutrition were evaluated immediately and after 6 months. The well-designed distance-education format was as effective and acceptable as face to face and increased sports nutrition knowledge. (SK)

Intersatellite Link (ISL) application to commercial communications satellites. Volume 1: Executive summary

Science.gov (United States)

Young, S. Lee

1987-01-01

Based on a comprehensive evaluation of the fundamental Intersatellite Link (ISL) systems characteristics, potential applications of ISLs to domestic, regional, and global commercial satellite communications were identified, and their cost-effectiveness and other systems benefits quantified wherever possible. Implementation scenarios for the cost-effective communications satellite systems employing ISLs were developed for the first launch in 1993 to 1994 and widespread use of ISLs in the early 2000's. Critical technology requirements for both the microwave (60 GHz) and optical (0.85 micron) ISL implementations were identified, and their technology development programs, including schedule and cost estimates, were derived.

DFT Modeling of Cross-Linked Polyethylene: Role of Gold Atoms and Dispersion Interactions.

Science.gov (United States)

Blaško, Martin; Mach, Pavel; Antušek, Andrej; Urban, Miroslav

2018-02-08

Using DFT modeling, we analyze the concerted action of gold atoms and dispersion interactions in cross-linked polyethylene. Our model consists of two oligomer chains (PEn) with 7, 11, 15, 19, or 23 carbon atoms in each oligomer cross-linked with one to three Au atoms through C-Au-C bonds. In structures with a single gold atom the C-Au-C bond is located in the central position of the oligomer. Binding energies (BEs) with respect to two oligomer radical fragments and Au are as high as 362-489 kJ/mol depending on the length of the oligomer chain. When the dispersion contribution in PEn-Au-PEn oligomers is omitted, BE is almost independent of the number of carbon atoms, lying between 293 and 296 kJ/mol. The dispersion energy contributions to BEs in PEn-Au-PEn rise nearly linearly with the number of carbon atoms in the PEn chain. The carbon-carbon distance in the C-Au-C moiety is around 4.1 Å, similar to the bond distance between saturated closed shell chains in the polyethylene crystal. BEs of pure saturated closed shell PEn-PEn oligomers are 51-187 kJ/mol. Both Au atoms and dispersion interactions contribute considerably to the creation of nearly parallel chains of oligomers with reasonably high binding energies.

A modified error correction protocol for CCITT signalling system no. 7 on satellite links

Science.gov (United States)

Kreuer, Dieter; Quernheim, Ulrich

1991-10-01

Comite Consultatif International des Telegraphe et Telephone (CCITT) Signalling System No. 7 (SS7) provides a level 2 error correction protocol particularly suited for links with propagation delays higher than 15 ms. Not being originally designed for satellite links, however, the so called Preventive Cyclic Retransmission (PCR) Method only performs well on satellite channels when traffic is low. A modified level 2 error control protocol, termed Fix Delay Retransmission (FDR) method is suggested which performs better at high loads, thus providing a more efficient use of the limited carrier capacity. Both the PCR and the FDR methods are investigated by means of simulation and results concerning throughput, queueing delay, and system delay, respectively. The FDR method exhibits higher capacity and shorter delay than the PCR method.

Advanced technologies for encryption of satellite links

Science.gov (United States)

McMahan, Sherry S.

The use of encryption on satellite links is discussed. Advanced technology exists to provide transmission security for large earth station with data rates up to 50 megabits per second. One of the major concerns in the use of encryption equipment with very small aperture terminals (VSAT) is the key management issue and the related operational costs. The low cost requirement and the lack of physical protection of remote VSATs place severe constraints on the design of encryption equipment. Encryption may be accomplished by embedding a tamper proof encryption module into the baseband unit of each VSAT. VSAT networks are usually star networks where there is a single large earth station that serves as a hub and all satellite communications takes place between each VSAT and the hub earth station. The hub earth station has the secret master key of each VSAT. These master keys are used to downline load encrypted session keys to each VSAT. A more secure alternative is to use public key techniques where each embedded VSAT encryption module internally generates its own secret and public numbers. The secret number never leaves the module while the public number is sent to the hub at the time of initialization of the encryption module into the VSAT. Physical access control to encryption modules of VSAT systems can be implemented using passwords, smart cards or biometrics.

Intersatellite Link (ISL) application to commercial communications satellites. Volume 2: Technical final report

Science.gov (United States)

Young, S. Lee

1987-01-01

Intersatellite Link (ISL) applications can improve and expand communication satellite services in a number of ways. As the demand for orbital slots within prime regions of the geostationary arc increases, attention is being focused on ISLs as a method to utilize this resource more efficiently and circumvent saturation. Various GEO-to-GEO applications were determined that provide potential benefits over existing communication systems. A set of criteria was developed to assess the potential applications. Intersatellite link models, network system architectures, and payload configurations were developed. For each of the chosen ISL applications, ISL versus non-ISL satellite systems architectures were derived. Both microwave and optical ISL implementation approaches were evaluated for payload sizing and cost analysis. The technological availability for ISL implementations was assessed. Critical subsystems technology areas were identified, and an estamate of the schedule and cost to advance the technology to the requiered state of readiness was made.

Overview of the Use of Media in Distance Education. I.E.T. Paper on Broadcasting No. 220.

Science.gov (United States)

Bates, A. W.

This paper reviews the use of different audio-visual media in distance education, including terrestrial broadcasting, cable satellite, videocassettes, audiocassettes, telephone teaching, viewdata, teletext, microcomputers, and interactive video. Trends in distance education are also summarized and related to trends in media technology development.…

Interactive Distance Education: A Cognitive Load Perspective

Science.gov (United States)

Kalyuga, Slava

2012-01-01

Evidence-based approaches to the design of the next generation of interactive distance education need to take into account established multimedia learning principles. Cognitive load theory is a theory that has significantly contributed to the development of such principles. It has applied our knowledge of major features and processing limitations…

Crosstalk cancellation on linearly and circularly polarized communications satellite links

Science.gov (United States)

Overstreet, W. P.; Bostian, C. W.

1979-01-01

The paper discusses the cancellation network approach for reducing crosstalk caused by depolarization on a dual-polarized communications satellite link. If the characteristics of rain depolarization are sufficiently well known, the cancellation network can be designed in a way that reduces system complexity, the most important parameter being the phase of the cross-polarized signal. Relevant theoretical calculations and experimental data are presented. The simplicity of the cancellation system proposed makes it ideal for use with small domestic or private earth terminals.

Radiation-hard mid-power booster optical fiber amplifiers for high-speed digital and analogue satellite laser communication links

Science.gov (United States)

Stampoulidis, L.; Kehayas, E.; Stevens, G.; Henwood-Moroney, L.; Hosking, P.; Robertson, A.

2017-11-01

Optical laser communications (OLC) has been identified as the technology to enable high-data rate, secure links between and within satellites, as well as between satellites and ground stations with decreased mass, size, and electrical power compared to traditional RF technology.

Distance Learning Delivery Systems: Instructional Options.

Science.gov (United States)

Steele, Ray L.

1993-01-01

Discusses the availability of satellite and cable programing to provide distance education opportunities in school districts. Various delivery systems are described, including telephones with speakers, personal computers, and satellite dishes; and a sidebar provides a directory of distance learning opportunities, including telecommunications…

A Framework for Building an Interactive Satellite TV Based M-Learning Environment

Directory of Open Access Journals (Sweden)

Ghassan Issa

2010-07-01

Full Text Available This paper presents a description of an interactive satellite TV based mobile learning (STV-ML framework, in which a satellite TV station is used as an integral part of a comprehensive interactive mobile learning (M-Learning environment. The proposed framework assists in building a reliable, efficient, and cost-effective environment to meet the growing demands of M-Learning all over the world, especially in developing countries. It utilizes recent advances in satellite reception, broadcasting technologies, and interactive TV to facilitate the delivery of gigantic learning materials. This paper also proposed a simple and flexible three-phase implementation methodology which includes construction of earth station, expansion of broadcasting channels, and developing true user interactivity. The proposed framework and implementation methodology ensure the construction of a true, reliable, and cost effective M-Learning system that can be used efficiently and effectively by a wide range of users and educational institutions to deliver ubiquitous learning.

UAS CNPC Satellite Link Performance - Sharing Spectrum with Terrestrial Systems

Science.gov (United States)

Kerczewski, Robert J.; Wilson, Jeffrey D.; Bishop, William D.

2016-01-01

In order to provide for the safe integration of unmanned aircraft systems into the National Airspace System, the control and non-payload communications (CNPC) link connecting the ground-based pilot with the unmanned aircraft must be highly reliable. A specific requirement is that it must operate using aviation safety radiofrequency spectrum. The 2012 World Radiocommunication Conference (WRC-12) provided a potentially suitable allocation for radio line-of-sight (LOS), terrestrial based CNPC link at 5030-5091 MHz. For a beyond radio line-of-sight (BLOS), satellite-based CNPC link, aviation safety spectrum allocations are currently inadequate. Therefore, the 2015 WRC will consider the use of Fixed Satellite Service (FSS) bands to provide BLOS CNPC under Agenda Item 1.5. This agenda item requires studies to be conducted to allow for the consideration of how unmanned aircraft can employ FSS for BLOS CNPC while maintaining existing systems. Since there are terrestrial Fixed Service systems also using the same frequency bands under consideration in Agenda Item 1.5 one of the studies required considered spectrum sharing between earth stations on-board unmanned aircraft and Fixed Service station receivers. Studies carried out by NASA have concluded that such sharing is possible under parameters previously established by the International Telecommunications Union. As the preparation for WRC-15 has progressed, additional study parameters Agenda Item 1.5 have been proposed, and some studies using these parameters have been added. This paper examines the study results for the original parameters as well as results considering some of the more recently proposed parameters to provide insight into the complicated process of resolving WRC-15 Agenda Item 1.5 and achieving a solution for BLOS CNPC for unmanned aircraft.

Teleducation : Linking Continents Across Time and Space Through Live, Real-Time Interactive Classes

Science.gov (United States)

Macko, S. A.; Szuba, T.; Swap, R.; Annegarn, H.; Marjanovic, B.; Vieira, F.; Brito, R.

2005-12-01

International education is a natural extension of global economies, global environmental concerns, and global science. While faculty and student exchanges between geographic areas permit for educational experiences and cultural exchanges for the privileged few, distance learning offers opportunities for educational exchanges under any circumstance where time, expense, or location otherwise inhibit offering or taking a particular course of study. However, there are severe pedagogical limitations to traditional Web-based courses that suffer from a lack of personalized, spontaneous exchange between instructor and student. The technology to establish a real time, interactive teleducation program exists, but to our knowledge is relatively untested in a science classroom situation, especially internationally over great distances. In a project to evaluate this type of linkage, we offered a real-time, interactive class at three separate universities, which communicated instantaneously across an ocean at a distance of greater than 8,000 miles and seven time zones. The course, 'Seminar on the Ecology of African Savannas', consisted of a series of 11 lectures originating in either Mozambique (University of Eduardo Mondlane), South Africa (University of the Witwatersrand) or the United States (University of Virginia). We combined ISDN, internet and satellite linkages to facilitate the lectures and real time discussions between instructors and approximately 200 university students in the three countries. Although numerous technical, logistical, and pedagogical issues - both expected and unexpected - arose throughout the pilot year, the project can be viewed as overwhelmingly successful and certainly serves as proof-of-concept for future initiatives, both internationally and locally. This review of our experience will help to prepare other students, faculty, and institutions interested in establishing or developing international education initiatives

Testing spatial theories of plant coexistence: no consistent differences in intra- and interspecific interaction distances.

Science.gov (United States)

Vogt, Deborah R; Murrell, David J; Stoll, Peter

2010-01-01

Plants stand still and interact with their immediate neighbors. Theory has shown that the distances over which these interactions occur may have important consequences for population and community dynamics. In particular, if intraspecific competition occurs over longer distances than interspecific competition (heteromyopia), coexistence can be promoted. We examined how intraspecific and interspecific competition scales with neighbor distance in a target-neighbor greenhouse competition experiment. Individuals from co-occurring forbs from calcareous grasslands were grown in isolation and with single conspecific or heterospecific neighbors at distances of 5, 10, or 15 cm (Plantago lanceolata vs. Plantago media and Hieracium pilosella vs. Prunella grandiflora). Neighbor effects were strong and declined with distance. Interaction distances varied greatly within and between species, but we found no evidence for heteromyopia. Instead, neighbor identity effects were mostly explained by relative size differences between target and neighbor. We found a complex interaction between final neighbor size and identity such that neighbor identity may become important only as the neighbor becomes very large compared with the target individual. Our results suggest that species-specific size differences between neighboring individuals determine both the strength of competitive interactions and the distance over which these interactions occur.

ORBITAL DEPENDENCE OF GALAXY PROPERTIES IN SATELLITE SYSTEMS OF GALAXIES

International Nuclear Information System (INIS)

Hwang, Ho Seong; Park, Changbom

2010-01-01

We study the dependence of satellite galaxy properties on the distance to the host galaxy and the orbital motion (prograde and retrograde orbits) using the Sloan Digital Sky Survey (SDSS) data. From SDSS Data Release 7, we find 3515 isolated satellite systems of galaxies at z -1 . It is found that the radial distribution of early-type satellites in prograde orbit is strongly concentrated toward the host while that of retrograde ones shows much less concentration. We also find the orbital speed of late-type satellites in prograde orbit increases as the projected distance to the host (R) decreases while the speed decreases for those in retrograde orbit. At R less than 0.1 times the host virial radius (R vir,host ), the orbital speed decreases in both prograde and retrograde orbit cases. Prograde satellites are on average fainter than retrograde satellites for both early and late morphological types. The u - r color becomes redder as R decreases for both prograde and retrograde orbit late-type satellites. The differences between prograde and retrograde orbit satellite galaxies may be attributed to their different origin or the different strength of physical processes that they have experienced through hydrodynamic interactions with their host galaxies.

Periodic anti-phases. Long distance antiphase-order transformations (1961); Antiphases periodiques. Transformation antiphase-ordre a grande distance (1961)

Energy Technology Data Exchange (ETDEWEB)

Hauptman, A; Kleinberger, R; Okuzumi, H; Perio, P; Tournarie, M [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

1961-07-01

Periodic anti-phases are ordered structures in which the movable elements alternates regularly between two available sites, in one or two directions. We study in the present work two particular properties of periodic anti-phases : 1- The irrationality or the continuous variation of the periodic anti-phase. 2- The reversible transition between the anti-phase state and that of long distance order. We have calculated the distribution of the diffracted amplitudes for the 'rational statistic' model. They can easily be identified and the two types of diagram observed are presented. For the long distance anti-phase-order transformation, we propose a model in which a domain grows laterally at the expense of the other. Calculation shows that in this case certain order reflections re-appear accompanied by extra satellites whose amplitude is not proportional to that of the pure anti-phase satellites, the opposite of the case of a double diffraction. The irreversible evolution of Au{sub 3}Mn alloys is then described; in this case interactions between domains of different type occur. Finally a diagram for the alloy Au{sub 3}Mn is given; the anti-phase boundaries are made up of 130 planes. (authors) [French] Les antiphases periodiques sont des structures ordonnees dans lesquelles l'element ordonnable alterne regulierement entre deux sites disponibles, suivant une ou deux directions. Nous etudions, dans le travail presente, deux proprietes particulieres des antiphases periodiques: 1- L'irrationalite ou la variation continue de la periode d'antiphase. 2- La transition reversible entre l'etat antiphase et l'etat d'ordre a grande distance. Nous avons calcule la distribution des amplitudes diffractees pour le modele 'rationnel statistique'. Elles sont facilement identifiables et les deux types de diagrammes observes sont presentes. Pour la transformation antiphase-ordre a longue distance, nous proposons un modele de croissance laterale d'un domaine au detriment de l'autre. Le calcul

Improvement of Ka-band satellite link availability for real-time IP-based video contribution

Directory of Open Access Journals (Sweden)

G. Berretta

2017-09-01

Full Text Available New High Throughput Satellite (HTS systems allow high throughput IP uplinks/contribution at Ka-band frequencies for relatively lower costs when compared to broadcasting satellite uplinks at Ku band. This technology offers an advantage for live video contribution from remote areas, where the terrestrial infrastructure may not be adequate. On the other hand, the Ka-band is more subject to impairments due to rain or bad weather. This paper addresses the target system specification and provides an optimized approach for the transmission of IP-based video flows through HTS commercial services operating at Ka-band frequencies. In particular, the focus of this study is on the service requirements and the propagation analysis that provide a reference architecture to improve the overall link availability. The approach proposed herein leads to the introduction of a new concept of live service contribution using pairs of small satellite antennas and cheap satellite terminals.

Precise Time Synchronisation and Ranging in Nano-Satellite Swarms

Science.gov (United States)

Laabs, Martin; Plettemeier, Dirk

2015-04-01

Precise time synchronization and ranging is very important for a variety of scientific experiments with more than two nano-satellites: For synthetic aperture radar (SAR) applications, for example, the radar signal phase (which corresponds to a synchronized time) as well as the location must be known on each satellite forming synthetic antenna. Also multi-static radar systems, MIMO radar systems or radio tomography applications will take advantage from highly accurate synchronization and position determination. We propose a method for synchronizing the time as well as measuring the distance between nano-satellites very precisely by utilizing mm-wave radio links. This approach can also be used for time synchronization of more than two satellites and accordingly determinating the precise relative location of nano-satellites in space. The time synchronization signal is modulated onto a mm-wave carrier. In the simplest form it is a harmonic sinusoidal signal with a frequency in the MHz range. The distance is measured with a frequency sweep or short pulse modulated onto a different carrier frequency. The sweep or pulse transmission start is synchronized to the received time synchronization. The time synchronization transmitter receives the pulse/sweep signal and can calculate the (double) time of flight for both signals. This measurement can be easily converted to the distance. The use of a mm-wave carrier leads to small antennas and the free space loss linked to the high frequency reduces non line of sight echoes. It also allows a high sweep/pulse bandwidth enabling superior ranging accuracy. Additionally, there is also less electromagnetic interference probability since telemetry and scientific applications typically do not use mm-wavefrequencies. Since the system is working full-duplex the time synchronization can be performed continuously and coherently. Up to now the required semiconductor processes did not achieve enough gain/bandwidth to realize this concept at

Age and gender interactions in short distance triathlon performance.

Science.gov (United States)

Etter, Franziska; Knechtle, Beat; Bukowski, Arkadiusz; Rüst, Christoph Alexander; Rosemann, Thomas; Lepers, Romuald

2013-01-01

This study investigated the participation and performance trends as well as the age and gender interaction at the Olympic distance 'Zürich Triathlon' (1.5 km swim, 40 km cycle and 10 km run) from 2000 to 2010 in 7,939 total finishers (1,666 females and 6,273 males). Female triathletes aged from 40 to 54 years significantly (P distance triathlon performance increased after the age of 35 years, which appeared earlier compared to long distance triathlon as suggested by previous studies. Future investigations should compare gender difference in performance for different endurance events across age to confirm a possible effect of exercise duration on gender difference with advancing age.

Unveiling aerosol-cloud interactions - Part 1: Cloud contamination in satellite products enhances the aerosol indirect forcing estimate

Science.gov (United States)

Christensen, Matthew W.; Neubauer, David; Poulsen, Caroline A.; Thomas, Gareth E.; McGarragh, Gregory R.; Povey, Adam C.; Proud, Simon R.; Grainger, Roy G.

2017-11-01

Increased concentrations of aerosol can enhance the albedo of warm low-level cloud. Accurately quantifying this relationship from space is challenging due in part to contamination of aerosol statistics near clouds. Aerosol retrievals near clouds can be influenced by stray cloud particles in areas assumed to be cloud-free, particle swelling by humidification, shadows and enhanced scattering into the aerosol field from (3-D radiative transfer) clouds. To screen for this contamination we have developed a new cloud-aerosol pairing algorithm (CAPA) to link cloud observations to the nearest aerosol retrieval within the satellite image. The distance between each aerosol retrieval and nearest cloud is also computed in CAPA. Results from two independent satellite imagers, the Advanced Along-Track Scanning Radiometer (AATSR) and Moderate Resolution Imaging Spectroradiometer (MODIS), show a marked reduction in the strength of the intrinsic aerosol indirect radiative forcing when selecting aerosol pairs that are located farther away from the clouds (-0.28±0.26 W m-2) compared to those including pairs that are within 15 km of the nearest cloud (-0.49±0.18 W m-2). The larger aerosol optical depths in closer proximity to cloud artificially enhance the relationship between aerosol-loading, cloud albedo, and cloud fraction. These results suggest that previous satellite-based radiative forcing estimates represented in key climate reports may be exaggerated due to the inclusion of retrieval artefacts in the aerosol located near clouds.

Networks systems and operations. [wideband communication techniques for data links with satellites

Science.gov (United States)

1975-01-01

The application of wideband communication techniques for data links with satellites is discussed. A diagram of the demand assigned voice communications system is provided. The development of prototype integrated spacecraft paramps at S- and C-bands is described and the performance of space-qualified paramps is tabulated. The characteristics of a dual parabolic cylinder monopulse zoom antenna for use with the tracking and data relay satellite system (TDRSS) are analyzed. The development of a universally applicable transponder at S-band is reported. A block diagram of the major subassemblies of the S-band transponder is included. The technology aspects of network timing and synchronization of communication systems are to show the use of the Omega navigation system. The telemetry data compression system used during the Skylab program is evaluated.

Limitations in distance and frequency due to chromatic dispersion in fibre-optic microwave and millimeter-wave links

DEFF Research Database (Denmark)

Gliese, Ulrik Bo; Nielsen, Søren Nørskov; Nielsen, Søren Nørskov

1996-01-01

Chromatic dispersion significantly limits the distance and/or frequency in fibre-optic microwave and millimeter-wave links based on direct detection due to a decrease of the carrier to noise ratio. The limitations in links based on coherent remote heterodyne detection, however, are far less...

Icy Saturnian satellites: Disk-integrated UV-IR characteristics and links to exogenic processes

Science.gov (United States)

Hendrix, Amanda R.; Filacchione, Gianrico; Paranicas, Chris; Schenk, Paul; Scipioni, Francesca

2018-01-01

Combined Cassini observations obtained at similar observing geometries in the ultraviolet through infrared spectral range, along with additional ultraviolet (UV) data from Hubble Space Telescope where available, are used to study system-wide trends in spectral albedos of the inner icy Saturnian satellites (Mimas, Enceladus, Tethys, Dione, Rhea). We derive UV and visible geometric albedos and UV absorption strengths of the leading and trailing hemispheres and compare with E ring grain flux and charged particle intensities (electrons and ions of varying energies) to those hemispheres. We find that the UV absorption strength on the leading and trailing hemispheres is anti-correlated with E ring grain flux. On the trailing hemispheres, the UV absorption strength is correlated with intensity of electrons in the tens of keV range. We suggest that these relationships could imply links with the organic component of the E ring. Radiolytic processing of organics causes the products to become spectrally redder, increasing the UV absorption strength. Such processing occurs while organic-rich grains are in the E ring, and increases with exposure time in the E ring, such that grains interacting with Rhea are redder (more processed) than those impacting moons closer to Enceladus. Further processing (and associated darkening/reddening) occurs on the trailing hemispheres of the satellites, via radiolysis by electrons in the tens of keV range. Silicates and salts also redden with weathering; however because organics are present in the E ring in significantly greater abundance than salts or silicates, we suggest here that weathering of organics dominates the coloring of the inner Saturnian moons.

Propagation engineering in radio links design

CERN Document Server

Ghasemi, Abdollah; Ghasemi, Farshid

2013-01-01

Propagation Engineering in Radio Link Design covers the basic principles of radiowaves propagation in a practical manner.  This fundamental understanding enables the readers to design radio links efficiently. This book elaborates on new achievements as well as recently developed propagation models.  This is in addition to a comprehensive overview of fundamentals of propagation in various scenarios. It examines theoretical calculations, approaches and applied procedures needed for radio links design. The authors study and analysis of the main propagation phenomena and its mechanisms based on the recommendations of International Telecommunications Union, (ITU). The book has been organized in 9 chapters and examines the role of antennas and passive reflectors in radio services, propagation mechanisms related to radar, satellite, short distance, broadcasting and trans-horizon radio links, with two chapters devoted to radio noise and main  parameters of radio link design. The book presents some 278 illustration...

Interactive Distance Learning Technologies for Rural and Small Schools: A Resource Guide. ERIC Mini-Review.

Science.gov (United States)

Barker, Bruce O.

In remote and isolated schools where a certified teacher is not always available, or in small schools where limited student enrollments make hiring teachers for low incident courses cost-prohibitive, instruction via distance may be the "next best thing to being there." Several approaches are available: (1) satellite transmissions--the…

Using Linked Data to Annotate and Search Educational Video Resources for Supporting Distance Learning

Science.gov (United States)

Yu, Hong Qing; Pedrinaci, C.; Dietze, S.; Domingue, J.

2012-01-01

Multimedia educational resources play an important role in education, particularly for distance learning environments. With the rapid growth of the multimedia web, large numbers of educational video resources are increasingly being created by several different organizations. It is crucial to explore, share, reuse, and link these educational…

Interaction in Distance Education Environments: A Trend Analysis

Science.gov (United States)

Karatas, Serçin; Yilmaz, Ayse Bagriacik; Dikmen, Cemal Hakan; Ermis, Ugur Ferhat; Gürbüz, Onur

2017-01-01

The aim of this study is to determine the trend concerning interaction in distance education between the years 2011 and 2015. According to this aim, 544 articles in the databases of EBSCO, Scopus, and Web of Science were examined. The examination has been conducted on the basis of various variables including year, country, number of authors,…

Kids Interactive Telecommunications Project by Satellite (KITES): A Telecommunications Partnership To Empower Middle School Students.

Science.gov (United States)

LeBaron, John

Kids Interactive Telecommunications Project by Satellite (KITES) is a cooperative international telecommunications partnership involving the University of Lowell, Digital's corporate video network, Videostar Connections Inc. (a satellite networking broker), PanAmSat (a satellite operator), and several other public education institutions in…

Expanding Access with Satellite-Enabled Distance Education

Directory of Open Access Journals (Sweden)

Qi Wang

2006-12-01

Full Text Available Education and training became increasingly critical for citizens of every nation during the last century, and that paradigm will be no less true, throughout the 21st Century. As the world progresses fully into an information society, access to information and to a knowledge-based work force is a precondition for any country to remain competitive. Education, and increasingly distant education (DE, plays a vital role in turning human resources into knowledge workers. Information and communications technologies (ICT have provided new ways to educate and to disseminate information that is crucial for creating these competitive, knowledge-based work forces. Modern DE, enabled by ICT-based networks and the Internet tools, offers great advantages that are leveling the global playing field, in terms of providing access and opportunities for specialized training and education. Using satellite technology in DE may be imperative to developing countries, where the majority of their populations are scattered in rural and remote areas. Where the traditional brick and mortar classrooms cannot easily reach, satellite-powered DE systems can. Through literature review and rational analysis, this paper examines how satellite-assisted DE systems expand education access.

Condensing Massive Satellite Datasets For Rapid Interactive Analysis

Science.gov (United States)

Grant, G.; Gallaher, D. W.; Lv, Q.; Campbell, G. G.; Fowler, C.; LIU, Q.; Chen, C.; Klucik, R.; McAllister, R. A.

2015-12-01

Our goal is to enable users to interactively analyze massive satellite datasets, identifying anomalous data or values that fall outside of thresholds. To achieve this, the project seeks to create a derived database containing only the most relevant information, accelerating the analysis process. The database is designed to be an ancillary tool for the researcher, not an archival database to replace the original data. This approach is aimed at improving performance by reducing the overall size by way of condensing the data. The primary challenges of the project include: - The nature of the research question(s) may not be known ahead of time. - The thresholds for determining anomalies may be uncertain. - Problems associated with processing cloudy, missing, or noisy satellite imagery. - The contents and method of creation of the condensed dataset must be easily explainable to users. The architecture of the database will reorganize spatially-oriented satellite imagery into temporally-oriented columns of data (a.k.a., "data rods") to facilitate time-series analysis. The database itself is an open-source parallel database, designed to make full use of clustered server technologies. A demonstration of the system capabilities will be shown. Applications for this technology include quick-look views of the data, as well as the potential for on-board satellite processing of essential information, with the goal of reducing data latency.

Study on the Implementation of Interaction Teaching Mode in Distance Education

Science.gov (United States)

Zhou, Chunyu; Xu, Zhenhui

2015-01-01

By analyzing the learning characteristics of learners and the features of interactive teaching in distance education, this paper proposes the curriculum implementation subject of network education, namely objects multi-directional interaction teaching mode, so as to improve teaching effectiveness and achieve teaching objectives to ensure the…

Mobile satellite service communications tests using a NASA satellite

Science.gov (United States)

Chambers, Katherine H.; Koschmeder, Louis A.; Hollansworth, James E.; ONeill, Jack; Jones, Robert E.; Gibbons, Richard C.

1995-01-01

Emerging applications of commercial mobile satellite communications include satellite delivery of compact disc (CD) quality radio to car drivers who can select their favorite programming as they drive any distance; transmission of current air traffic data to aircraft; and handheld communication of data and images from any remote corner of the world. Experiments with the enabling technologies and tests and demonstrations of these concepts are being conducted before the first satellite is launched by utilizing an existing NASA spacecraft.

Interactive Distance Learning in Connecticut.

Science.gov (United States)

Pietras, Jesse John; Murphy, Robert J.

This paper provides an overview of distance learning activities in Connecticut and addresses the feasibility of such activities. Distance education programs have evolved from the one dimensional electronic mail systems to the use of sophisticated digital fiber networks. The Middlesex Distance Learning Consortium has developed a long-range plan to…

Communication schemes for olfar's inter-satellite links

NARCIS (Netherlands)

Budianu, A.; Willink-Castro, T.J.; Meijerink, Arjan; Bentum, Marinus Jan

2012-01-01

The Orbiting Low Frequency Array for Radio astronomy(OLFAR) project is aimed at developing a radio telescope in space sensitive for the 0.3–30 MHz range by using a swarm of more than 50 identical nano-satellites. The satellites will form a very large aperture, capable of capturing very weak

Local network interconnection through a satellite point-to-multipoint link. Ph.D. Thesis - Ecole Nationale Superieure des Telecommunications, 6 Jul. 1985

Science.gov (United States)

Duarte, O. Muniz Bandeira

1986-01-01

Four architectures to implement a point to multipoint satellite link protocol for communication services offered by the Telecom 1 satellite network are presented. A safe communication service with error correction and flow control facilities is described. It is shown that a time transparent communication system combines simplicity and cost advantages.

Application of a genetic algorithm in the conformational analysis of methylene-acetal-linked thymine dimers in DNA: Comparison with distance geometry calculations

International Nuclear Information System (INIS)

Beckers, Mischa L.M.; Buydens, Lutgarde M.C.; Pikkemaat, Jeroen A.; Altona, Cornelis

1997-01-01

The three-dimensional spatial structure of a methylene-acetal-linked thymine dimer present in a 10 base-pair (bp) sense-antisense DNA duplex was studied with a genetic algorithm designed to interpret NOE distance restraints. Trial solutions were represented by torsion angles. This means that bond angles for the dimer trial structures are kept fixed during the genetic algorithm optimization. Bond angle values were extracted from a 10 bp sense-antisense duplex model that was subjected to energy minimization by means of a modified AMBER force field. A set of 63 proton-proton distance restraints defining the methylene-acetal-linked thymine dimer was available. The genetic algorithm minimizes the difference between distances in the trial structures and distance restraints. A large conformational search space could be covered in the genetic algorithm optimization by allowing a wide range of torsion angles. The genetic algorithm optimization in all cases led to one family of structures. This family of the methylene-acetal-linked thymine dimer in the duplex differs from the family that was suggested from distance geometry calculations. It is demonstrated that the bond angle geometry around the methylene-acetal linkage plays an important role in the optimization

Satellites

International Nuclear Information System (INIS)

Burns, J.A.; Matthews, M.S.

1986-01-01

The present work is based on a conference: Natural Satellites, Colloquium 77 of the IAU, held at Cornell University from July 5 to 9, 1983. Attention is given to the background and origins of satellites, protosatellite swarms, the tectonics of icy satellites, the physical characteristics of satellite surfaces, and the interactions of planetary magnetospheres with icy satellite surfaces. Other topics include the surface composition of natural satellites, the cratering of planetary satellites, the moon, Io, and Europa. Consideration is also given to Ganymede and Callisto, the satellites of Saturn, small satellites, satellites of Uranus and Neptune, and the Pluto-Charon system

Handoff algorithm for mobile satellite systems with ancillary terrestrial component

KAUST Repository

Sadek, Mirette

2012-06-01

This paper presents a locally optimal handoff algorithm for integrated satellite/ground communication systems. We derive the handoff decision function and present the results in the form of tradeoff curves between the number of handoffs and the number of link degradation events in a given distance covered by the mobile user. This is a practical receiver-controlled handoff algorithm that optimizes the handoff process from a user perspective based on the received signal strength rather than from a network perspective. © 2012 IEEE.

Distance- and momentum-dependence of modern nucleon-nucleon interactions

International Nuclear Information System (INIS)

Feldmeier, Hans; Neff, Thomas; Weber, Dennis

2015-01-01

A phase-space representation of nuclear interactions, which depends on the distance r vector and relative momentum p vector of the nucleons, is presented. It visualizes in an intuitive way the non-local behavior introduced by cutoffs in momentum space or renormalization procedures that are used to adapt the interaction to low momentum many-body Hilbert spaces, as done in the unitary correlation operator method (UCOM) or with the similarity renormalization group (SRG). It allows to develop intuition about the various interactions and illustrates how the softened interactions reduce the short-range repulsion in favor of non-locality or momentum dependence while keeping the scattering phase shifts invariant. It also reveals that these effective interactions can have undesired complicated momentum dependencies at momenta around and above the Fermi momentum. Properties, similarities, and differences of the Argonne and the N3LO chiral potential, and their UCOM and SRG derivatives are discussed. (author)

Supervisor-employee power distance incompatibility, gender similarity, and relationship conflict: A test of interpersonal interaction theory.

Science.gov (United States)

Graham, Katrina A; Dust, Scott B; Ziegert, Jonathan C

2018-03-01

According to interpersonal interaction theory, relational harmony surfaces when two individuals have compatible interaction styles. Building from this theory, we propose that supervisor-employee power distance orientation incompatibility will be related to employees' experience of higher levels of relationship conflict with their supervisors. Additionally, we propose an asymmetrical incongruence effect such that relationship conflict will be highest when supervisors are high in power distance and employees are low in power distance. Furthermore, we address calls in interpersonal interaction research for more direct attention to the social context of the dyadic interaction and explore the moderating effects of supervisor-employee gender (dis)similarity on the relationship between this incompatibility and conflict. We propose that supervisor-employee gender dissimilarity (e.g., male-female or female-male pairs) acts as a conditional moderator, neutralizing the power distance incongruence effect and the asymmetrical incongruence effect. Using 259 supervisor-employee dyads in the physical therapy industry, the hypotheses were generally supported. Theoretical and practical implications regarding the unique benefits of power distance compatibility and gender diversity in supervisor-employee dyads are discussed. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Satellite-detected fluorescence reveals global physiology of ocean phytoplankton

Directory of Open Access Journals (Sweden)

M. J. Behrenfeld

2009-05-01

Full Text Available Phytoplankton photosynthesis links global ocean biology and climate-driven fluctuations in the physical environment. These interactions are largely expressed through changes in phytoplankton physiology, but physiological status has proven extremely challenging to characterize globally. Phytoplankton fluorescence does provide a rich source of physiological information long exploited in laboratory and field studies, and is now observed from space. Here we evaluate the physiological underpinnings of global variations in satellite-based phytoplankton chlorophyll fluorescence. The three dominant factors influencing fluorescence distributions are chlorophyll concentration, pigment packaging effects on light absorption, and light-dependent energy-quenching processes. After accounting for these three factors, resultant global distributions of quenching-corrected fluorescence quantum yields reveal a striking consistency with anticipated patterns of iron availability. High fluorescence quantum yields are typically found in low iron waters, while low quantum yields dominate regions where other environmental factors are most limiting to phytoplankton growth. Specific properties of photosynthetic membranes are discussed that provide a mechanistic view linking iron stress to satellite-detected fluorescence. Our results present satellite-based fluorescence as a valuable tool for evaluating nutrient stress predictions in ocean ecosystem models and give the first synoptic observational evidence that iron plays an important role in seasonal phytoplankton dynamics of the Indian Ocean. Satellite fluorescence may also provide a path for monitoring climate-phytoplankton physiology interactions and improving descriptions of phytoplankton light use efficiencies in ocean productivity models.

A Dual-Channel Acquisition Method Based on Extended Replica Folding Algorithm for Long Pseudo-Noise Code in Inter-Satellite Links.

Science.gov (United States)

Zhao, Hongbo; Chen, Yuying; Feng, Wenquan; Zhuang, Chen

2018-05-25

Inter-satellite links are an important component of the new generation of satellite navigation systems, characterized by low signal-to-noise ratio (SNR), complex electromagnetic interference and the short time slot of each satellite, which brings difficulties to the acquisition stage. The inter-satellite link in both Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS) adopt the long code spread spectrum system. However, long code acquisition is a difficult and time-consuming task due to the long code period. Traditional folding methods such as extended replica folding acquisition search technique (XFAST) and direct average are largely restricted because of code Doppler and additional SNR loss caused by replica folding. The dual folding method (DF-XFAST) and dual-channel method have been proposed to achieve long code acquisition in low SNR and high dynamic situations, respectively, but the former is easily affected by code Doppler and the latter is not fast enough. Considering the environment of inter-satellite links and the problems of existing algorithms, this paper proposes a new long code acquisition algorithm named dual-channel acquisition method based on the extended replica folding algorithm (DC-XFAST). This method employs dual channels for verification. Each channel contains an incoming signal block. Local code samples are folded and zero-padded to the length of the incoming signal block. After a circular FFT operation, the correlation results contain two peaks of the same magnitude and specified relative position. The detection process is eased through finding the two largest values. The verification takes all the full and partial peaks into account. Numerical results reveal that the DC-XFAST method can improve acquisition performance while acquisition speed is guaranteed. The method has a significantly higher acquisition probability than folding methods XFAST and DF-XFAST. Moreover, with the advantage of higher detection

A Dual-Channel Acquisition Method Based on Extended Replica Folding Algorithm for Long Pseudo-Noise Code in Inter-Satellite Links

Directory of Open Access Journals (Sweden)

Hongbo Zhao

2018-05-01

Full Text Available Inter-satellite links are an important component of the new generation of satellite navigation systems, characterized by low signal-to-noise ratio (SNR, complex electromagnetic interference and the short time slot of each satellite, which brings difficulties to the acquisition stage. The inter-satellite link in both Global Positioning System (GPS and BeiDou Navigation Satellite System (BDS adopt the long code spread spectrum system. However, long code acquisition is a difficult and time-consuming task due to the long code period. Traditional folding methods such as extended replica folding acquisition search technique (XFAST and direct average are largely restricted because of code Doppler and additional SNR loss caused by replica folding. The dual folding method (DF-XFAST and dual-channel method have been proposed to achieve long code acquisition in low SNR and high dynamic situations, respectively, but the former is easily affected by code Doppler and the latter is not fast enough. Considering the environment of inter-satellite links and the problems of existing algorithms, this paper proposes a new long code acquisition algorithm named dual-channel acquisition method based on the extended replica folding algorithm (DC-XFAST. This method employs dual channels for verification. Each channel contains an incoming signal block. Local code samples are folded and zero-padded to the length of the incoming signal block. After a circular FFT operation, the correlation results contain two peaks of the same magnitude and specified relative position. The detection process is eased through finding the two largest values. The verification takes all the full and partial peaks into account. Numerical results reveal that the DC-XFAST method can improve acquisition performance while acquisition speed is guaranteed. The method has a significantly higher acquisition probability than folding methods XFAST and DF-XFAST. Moreover, with the advantage of higher

Land-atmosphere interaction patterns in southeastern South America using satellite products and climate models

Science.gov (United States)

Spennemann, P. C.; Salvia, M.; Ruscica, R. C.; Sörensson, A. A.; Grings, F.; Karszenbaum, H.

2018-02-01

In regions of strong Land-Atmosphere (L-A) interaction, soil moisture (SM) conditions can impact the atmosphere through modulating the land surface fluxes. The importance of the identification of L-A interaction regions lies in the potential improvement of the weather/seasonal forecast and the better understanding of the physical mechanisms involved. This study aims to compare the terrestrial segment of the L-A interaction from satellite products and climate models, motivated by previous modeling studies pointing out southeastern South America (SESA) as a L-A hotspot during austral summer. In addition, the L-A interaction under dry or wet anomalous conditions over SESA is analyzed. To identify L-A hotspots the AMSRE-LPRM SM and MODIS land surface temperature products; coupled climate models and uncoupled land surface models were used. SESA highlights as a strong L-A interaction hotspot when employing different metrics, temporal scales and independent datasets, showing consistency between models and satellite estimations. Both AMSRE-LPRM bands (X and C) are consistent showing a strong L-A interaction hotspot over the Pampas ecoregion. Intensification and a larger spatial extent of the L-A interaction for dry summers was observed in both satellite products and models compared to wet summers. These results, which were derived from measured physical variables, are encouraging and promising for future studies analyzing L-A interactions. L-A interaction analysis is proposed here as a meeting point between remote sensing and climate modelling communities of Argentina, within a region with the highest agricultural and livestock production of the continent, but with an important lack of in-situ SM observations.

Sea ice-atmospheric interaction: Application of multispectral satellite data in polar surface energy flux estimates

Science.gov (United States)

Steffen, Konrad; Key, J.; Maslanik, J.; Schweiger, A.

1993-01-01

This is the third annual report on: Sea Ice-Atmosphere Interaction - Application of Multispectral Satellite Data in Polar Surface Energy Flux Estimates. The main emphasis during the past year was on: radiative flux estimates from satellite data; intercomparison of satellite and ground-based cloud amounts; radiative cloud forcing; calibration of the Advanced Very High Resolution Radiometer (AVHRR) visible channels and comparison of two satellite derived albedo data sets; and on flux modeling for leads. Major topics covered are arctic clouds and radiation; snow and ice albedo, and leads and modeling.

Accurate beacon positioning method for satellite-to-ground optical communication.

Science.gov (United States)

Wang, Qiang; Tong, Ling; Yu, Siyuan; Tan, Liying; Ma, Jing

2017-12-11

In satellite laser communication systems, accurate positioning of the beacon is essential for establishing a steady laser communication link. For satellite-to-ground optical communication, the main influencing factors on the acquisition of the beacon are background noise and atmospheric turbulence. In this paper, we consider the influence of background noise and atmospheric turbulence on the beacon in satellite-to-ground optical communication, and propose a new locating algorithm for the beacon, which takes the correlation coefficient obtained by curve fitting for image data as weights. By performing a long distance laser communication experiment (11.16 km), we verified the feasibility of this method. Both simulation and experiment showed that the new algorithm can accurately obtain the position of the centroid of beacon. Furthermore, for the distortion of the light spot through atmospheric turbulence, the locating accuracy of the new algorithm was 50% higher than that of the conventional gray centroid algorithm. This new approach will be beneficial for the design of satellite-to ground optical communication systems.

Centriolar satellites

DEFF Research Database (Denmark)

Tollenaere, Maxim A X; Mailand, Niels; Bekker-Jensen, Simon

2015-01-01

Centriolar satellites are small, microscopically visible granules that cluster around centrosomes. These structures, which contain numerous proteins directly involved in centrosome maintenance, ciliogenesis, and neurogenesis, have traditionally been viewed as vehicles for protein trafficking...... highlight newly discovered regulatory mechanisms targeting centriolar satellites and their functional status, and we discuss how defects in centriolar satellite components are intimately linked to a wide spectrum of human diseases....

Protein-protein interaction site predictions with minimum covariance determinant and Mahalanobis distance.

Science.gov (United States)

Qiu, Zhijun; Zhou, Bo; Yuan, Jiangfeng

2017-11-21

Protein-protein interaction site (PPIS) prediction must deal with the diversity of interaction sites that limits their prediction accuracy. Use of proteins with unknown or unidentified interactions can also lead to missing interfaces. Such data errors are often brought into the training dataset. In response to these two problems, we used the minimum covariance determinant (MCD) method to refine the training data to build a predictor with better performance, utilizing its ability of removing outliers. In order to predict test data in practice, a method based on Mahalanobis distance was devised to select proper test data as input for the predictor. With leave-one-validation and independent test, after the Mahalanobis distance screening, our method achieved higher performance according to Matthews correlation coefficient (MCC), although only a part of test data could be predicted. These results indicate that data refinement is an efficient approach to improve protein-protein interaction site prediction. By further optimizing our method, it is hopeful to develop predictors of better performance and wide range of application. Copyright © 2017 Elsevier Ltd. All rights reserved.

Electromagnetic distance measurement

CERN Document Server

1967-01-01

This book brings together the work of forty-eight geodesists from twenty-five countries. They discuss various new electromagnetic distance measurement (EDM) instruments - among them the Tellurometer, Geodimeter, and air- and satellite-borne systems - and investigate the complex sources of error.

Scientific analysis of satellite ranging data

Science.gov (United States)

Smith, David E.

1994-01-01

A network of satellite laser ranging (SLR) tracking systems with continuously improving accuracies is challenging the modelling capabilities of analysts worldwide. Various data analysis techniques have yielded many advances in the development of orbit, instrument and Earth models. The direct measurement of the distance to the satellite provided by the laser ranges has given us a simple metric which links the results obtained by diverse approaches. Different groups have used SLR data, often in combination with observations from other space geodetic techniques, to improve models of the static geopotential, the solid Earth, ocean tides, and atmospheric drag models for low Earth satellites. Radiation pressure models and other non-conservative forces for satellite orbits above the atmosphere have been developed to exploit the full accuracy of the latest SLR instruments. SLR is the baseline tracking system for the altimeter missions TOPEX/Poseidon, and ERS-1 and will play an important role in providing the reference frame for locating the geocentric position of the ocean surface, in providing an unchanging range standard for altimeter calibration, and for improving the geoid models to separate gravitational from ocean circulation signals seen in the sea surface. However, even with the many improvements in the models used to support the orbital analysis of laser observations, there remain systematic effects which limit the full exploitation of SLR accuracy today.

HAPS Gateway Link in the 5850-7075 MHz and Coexistence with Fixed Satellite Service

Directory of Open Access Journals (Sweden)

M. Ahmed

2013-09-01

Full Text Available Gateway link is essential to connect HAPS platform to terrestrial based networks. This crucial link is incorporated in HAPS fixed service spectrum allocation in considerably high frequencies, renders the link for more attenuations by atmospheric gases, and rain effects, especially when the regional climate is not favorable. However, under the agenda item 1.20 of World Radio Conference-2012 (WRC-12 new HAPS allocation in the 5850-7075 MHz band is proposed. Although, spectrum features are incomparably reliable, on the contrary, Fixed Satellite Service (FSS uplink transmissions will have signal levels much higher than those in HAPS systems and have the potential for causing interference at the HAPS gateway receiver. In this article a key aspect of co-channel interference phenomena is investigated to facilitate optimum frequency sharing in the band in question. By proposing mitigation techniques and statistical method this generic prediction model enhances the capability of the HAPS spectrum sharing and provides flexibility in spectrum planning for different fixed services.

SPECIAL FEATURES OF VIRTUAL PRACTICE INTERACTIVE MEDIA DISCIPLINES FOR DISTANCE LEARNING

Directory of Open Access Journals (Sweden)

M.P. Mazur

2010-08-01

Full Text Available The features of the development of interactive virtual practical training courses for distance learning are examined in the article. The authors propose their own methods of development tools such disciplines as virtual simulation or video-on labs.

Demise of faint satellites around isolated early-type galaxies

Science.gov (United States)

Park, Changbom; Hwang, Ho Seong; Park, Hyunbae; Lee, Jong Chul

2018-02-01

The hierarchical galaxy formation scenario in the Cold Dark Matter cosmology with a non-vanishing cosmological constant Λ and geometrically flat space (ΛCDM) has been very successful in explaining the large-scale distribution of galaxies. However, there have been claims that ΛCDM over-predicts the number of satellite galaxies associated with massive galaxies compared with observations—the missing satellite galaxy problem1-3. Isolated groups of galaxies hosted by passively evolving massive early-type galaxies are ideal laboratories for identifying the missing physics in the current theory4-11. Here, we report—based on a deep spectroscopic survey—that isolated massive and passive early-type galaxies without any signs of recent wet mergers or accretion episodes have almost no satellite galaxies fainter than the r-band absolute magnitude of about Mr = -14. If only early-type satellites are used, the cutoff is at the somewhat brighter magnitude of about Mr = -15. Such a cutoff has not been found in other nearby satellite galaxy systems hosted by late-type galaxies or those with merger features. Various physical properties of satellites depend strongly on the host-centric distance. Our observations indicate that the satellite galaxy luminosity function is largely determined by the interaction of satellites with the environment provided by their host.

Can technical laboratory skills be taught at a distance? An analysis of a semiconductor course taught at a distance via interactive technologies

Science.gov (United States)

Rao, Lalita

2000-10-01

This study investigated extending synchronous distance learning to teaching courses in the psychomotor domain in real-time, with immediate, direct feedback on technical skills performance from an instructor at a remote site via interactive technologies such as videoconferencing. This study focused on two research questions (1) can interactive distance learning technologies be used to teach technical and/or trouble shooting skills that fall under psychomotor domain? and, (2) to what degree can psychomotor skills be taught at a distance? A technical course, "RF Power PC 211L" from a technical and vocational institute was selected and the instructor who had no prior experience in teaching a distance learning course taught the course. Data on cognitive skills, psychomotor technical skills, attitudes and perceptions, demographics as well as boundary conditions on teaching psychomotor skills was gathered from both remote and the main campus. Instruments used for data gathering were final course grades, total points in laboratory exercise, pre and post course surveys, demographic survey and open-ended interviews with the instructor, student and review of instructor journal were used to address the two research questions. The main campus course was taught to the remote campus via distance learning technology in a distance learning format. The main technology used was videoconferencing. Both campus classrooms had the RF Trainer equipment. The rooms were set up to facilitate distance learning in the classroom. The instructor was present only at the main campus. The students on the remote campus were the experimental group. The experimental group participated in all course activities such as demonstrations, laboratory exercises, learning conceptual skills and tests only via distance. These students only had the benefit of laboratory assistant. The role of the laboratory assistant was to assist students/instructor as needed, ensure the safety of students and equipment and

Satellite fixed communications service: A forecast of potential domestic demand through the year 2000. Volume 3: Appendices

Science.gov (United States)

Kratochvil, D.; Bowyer, J.; Bhushan, C.; Steinnagel, K.; Kaushal, D.; Al-Kinani, G.

1983-09-01

Voice applications, data applications, video applications, impacted baseline forecasts, market distribution model, net long haul forecasts, trunking earth station definition and costs, trunking space segment cost, trunking entrance/exit links, trunking network costs and crossover distances with terrestrial tariffs, net addressable forecasts, capacity requirements, improving spectrum utilization, satellite system market development, and the 30/20 net accessible market are considered.

Software-type Wave-Particle Interaction Analyzer on board the Arase satellite

Science.gov (United States)

Katoh, Yuto; Kojima, Hirotsugu; Hikishima, Mitsuru; Takashima, Takeshi; Asamura, Kazushi; Miyoshi, Yoshizumi; Kasahara, Yoshiya; Kasahara, Satoshi; Mitani, Takefumi; Higashio, Nana; Matsuoka, Ayako; Ozaki, Mitsunori; Yagitani, Satoshi; Yokota, Shoichiro; Matsuda, Shoya; Kitahara, Masahiro; Shinohara, Iku

2018-01-01

We describe the principles of the Wave-Particle Interaction Analyzer (WPIA) and the implementation of the Software-type WPIA (S-WPIA) on the Arase satellite. The WPIA is a new type of instrument for the direct and quantitative measurement of wave-particle interactions. The S-WPIA is installed on the Arase satellite as a software function running on the mission data processor. The S-WPIA on board the Arase satellite uses an electromagnetic field waveform that is measured by the waveform capture receiver of the plasma wave experiment (PWE), and the velocity vectors of electrons detected by the medium-energy particle experiment-electron analyzer (MEP-e), the high-energy electron experiment (HEP), and the extremely high-energy electron experiment (XEP). The prime objective of the S-WPIA is to measure the energy exchange between whistler-mode chorus emissions and energetic electrons in the inner magnetosphere. It is essential for the S-WPIA to synchronize instruments to a relative time accuracy better than the time period of the plasma wave oscillations. Since the typical frequency of chorus emissions in the inner magnetosphere is a few kHz, a relative time accuracy of better than 10 μs is required in order to measure the relative phase angle between the wave and velocity vectors. In the Arase satellite, a dedicated system has been developed to realize the time resolution required for inter-instrument communication. Here, both the time index distributed over all instruments through the satellite system and an S-WPIA clock signal are used, that are distributed from the PWE to the MEP-e, HEP, and XEP through a direct line, for the synchronization of instruments within a relative time accuracy of a few μs. We also estimate the number of particles required to obtain statistically significant results with the S-WPIA and the expected accumulation time by referring to the specifications of the MEP-e and assuming a count rate for each detector.

An Unsupervised Anomalous Event Detection and Interactive Analysis Framework for Large-scale Satellite Data

Science.gov (United States)

LIU, Q.; Lv, Q.; Klucik, R.; Chen, C.; Gallaher, D. W.; Grant, G.; Shang, L.

2016-12-01

Due to the high volume and complexity of satellite data, computer-aided tools for fast quality assessments and scientific discovery are indispensable for scientists in the era of Big Data. In this work, we have developed a framework for automated anomalous event detection in massive satellite data. The framework consists of a clustering-based anomaly detection algorithm and a cloud-based tool for interactive analysis of detected anomalies. The algorithm is unsupervised and requires no prior knowledge of the data (e.g., expected normal pattern or known anomalies). As such, it works for diverse data sets, and performs well even in the presence of missing and noisy data. The cloud-based tool provides an intuitive mapping interface that allows users to interactively analyze anomalies using multiple features. As a whole, our framework can (1) identify outliers in a spatio-temporal context, (2) recognize and distinguish meaningful anomalous events from individual outliers, (3) rank those events based on "interestingness" (e.g., rareness or total number of outliers) defined by users, and (4) enable interactively query, exploration, and analysis of those anomalous events. In this presentation, we will demonstrate the effectiveness and efficiency of our framework in the application of detecting data quality issues and unusual natural events using two satellite datasets. The techniques and tools developed in this project are applicable for a diverse set of satellite data and will be made publicly available for scientists in early 2017.

HADRONS-94: Soft interactions at large distances

International Nuclear Information System (INIS)

Atkinson, David; Jenkovszky, Laszlo

1994-01-01

Ten years ago the Institute for Theoretical Physics (known since 1992 as the Bogolubov Institute after its founder) of the Academy of Science of the Ukraine initiated what has become a very successful series of annual meetings on strong interactions at large distances. Although sometimes overshadowed by the successes of the Standard Model isotope dilutions and the theoretical enticements of supertheories; the Hadrons series has overcome political barriers and financial chaos to bring together physicists from diverse backgrounds to discuss central physics issues. The latest workshop in the series was held from September 7-11 in Uzhgorod (Ungvar), a small university town in the westernmost reaches of the Ukraine, bordering on Hungary, Poland, Romania and Slovakia.

Long-distance multipartite quantum communication

International Nuclear Information System (INIS)

Herbst, T.

2014-01-01

This work addresses two long-distance free-space experiments based on multi-photon polarization entanglement. The highlighted measurements were performed between the Canary Islands La Palma and Tenerife, featuring a 143 km horizontal free-space quantum channel. Based on the superposition principle, quantum entanglement constitutes the key building block in quantum information sciences. Its nonclassical correlations lay the ground for exciting new protocols like quantum cryptography, quantum computation or quantum teleportation. Our first experiment targeted on the teleportation of entanglement, also known as entanglement swapping, where the entanglement from two polarization entangled photon pairs 0-1 and 2-3 is swapped onto photons 1-2 and 0-3. This feature constitutes the fundamental resource for so-called quantum repeaters. In the future such devices could be used to subdivide large distances into shorter links and finally extend the entanglement over the whole range by entanglement swapping. In the second experiment we realized four-photon entanglement in the form of a GHZ-state, named after the researchers Daniel Greenberger, Michael Horne and Anton Zeilinger. At the base station on La Palma we employed two sources for polarization-entanglement, generating photon pairs of 808 nm wavelength by spontaneous parametric down-conversion of femtosecond pulsed laser light. In both experiments one of the four photons per pulse was transmitted over a 143 km free-space link to the receiver station on Tenerife, whereas the remaining three photons were measured locally on La Palma. Long term atmospheric turbulences in the near-ground quantum channel were compensated by means of a bi-directional closed-loop tracking of the transceiver telescopes. Despite an average link attenuation of around 30 dB over the 143 km free-space channel, we successfully showed entanglement swapping with a statistical significance of more than 6 standard deviations. Moreover we faithfully

Design and Evaluation of 10-Gbps Inter-satellite Optical Wireless Communication Link for Improved Performance

Science.gov (United States)

Gupta, Amit; Nagpal, Shaina

2017-05-01

Inter-satellite optical wireless communication (IsOWC) systems can be chosen over existing microwave satellite systems for deploying in space in the future due to their high bandwidth, small size, light weight, low power and low cost. However, the IsOWC system suffers from various attenuations due to weather conditions, turbulence or scintillations which limit its performance and decreases its availability. So, in order to improve the performance, IsOWC system using directly modulated laser source is proposed in this work. The system is designed and evaluated to be suitable for high data rate transmissions up to 10 Gbps. The performance of the system is investigated in order to reduce the cost and complexity of link and improving the quality of information signal. Further the proposed IsOWC system is analysed using BER analyser, power meter and oscilloscope Visualizer.

Distance Education for the Gifted and Talented: An Interactive Design Model.

Science.gov (United States)

McKinnon, David H.; Nolan, C. J. Patrick

1999-01-01

Discusses development of an Australian distance-education cosmology course that employs an interactive design model and an extensive communication system. The way the model is used to organized, sequence, and deliver the course is explained. Discussion addresses how the model might be used to design other courses. (Author/CR)

Interactive access to LP DAAC satellite data archives through a combination of open-source and custom middleware web services

Science.gov (United States)

Davis, Brian N.; Werpy, Jason; Friesz, Aaron M.; Impecoven, Kevin; Quenzer, Robert; Maiersperger, Tom; Meyer, David J.

2015-01-01

Current methods of searching for and retrieving data from satellite land remote sensing archives do not allow for interactive information extraction. Instead, Earth science data users are required to download files over low-bandwidth networks to local workstations and process data before science questions can be addressed. New methods of extracting information from data archives need to become more interactive to meet user demands for deriving increasingly complex information from rapidly expanding archives. Moving the tools required for processing data to computer systems of data providers, and away from systems of the data consumer, can improve turnaround times for data processing workflows. The implementation of middleware services was used to provide interactive access to archive data. The goal of this middleware services development is to enable Earth science data users to access remote sensing archives for immediate answers to science questions instead of links to large volumes of data to download and process. Exposing data and metadata to web-based services enables machine-driven queries and data interaction. Also, product quality information can be integrated to enable additional filtering and sub-setting. Only the reduced content required to complete an analysis is then transferred to the user.

Using satellites and global models to investigate aerosol-cloud interactions

Science.gov (United States)

Gryspeerdt, E.; Quaas, J.; Goren, T.; Sourdeval, O.; Mülmenstädt, J.

2017-12-01

Aerosols are known to impact liquid cloud properties, through both microphysical and radiative processes. Increasing the number concentration of aerosol particles can increase the cloud droplet number concentration (CDNC). Through impacts on precipitation processes, this increase in CDNC may also be able to impact the cloud fraction (CF) and the cloud liquid water path (LWP). Several studies have looked into the effect of aerosols on the CDNC, but as the albedo of a cloudy scene depends much more strongly on LWP and CF, an aerosol influence on these properties could generate a significant radiative forcing. While the impact of aerosols on cloud properties can be seen in case studies involving shiptracks and volcanoes, producing a global estimate of these effects remains challenging due to the confounding effect of local meteorology. For example, relative humidity significantly impacts the aerosol optical depth (AOD), a common satellite proxy for CCN, as well as being a strong control on cloud properties. This can generate relationships between AOD and cloud properties, even when there is no impact of aerosol-cloud interactions. In this work, we look at how aerosol-cloud interactions can be distinguished from the effect of local meteorology in satellite studies. With a combination global climate models and multiple sources of satellite data, we show that the choice of appropriate mediating variables and case studies can be used to develop constraints on the aerosol impact on CF and LWP. This will lead to improved representations of clouds in global climate models and help to reduce the uncertainty in the global impact of anthropogenic aerosols on cloud properties.

A Primer on Satellite Equipment.

Science.gov (United States)

Doan, Michael

1992-01-01

Information provided for school districts desiring to offer distance education courses to their students describes the kind of satellite dish needed; its size, sturdiness, placement, and number of dishes needed; satellite receivers; the function of a descrambler; copyright restrictions; features of an Integrated Receiver/Descrambler; selecting a…

How to implement decoy-state quantum key distribution for a satellite uplink with 50-dB channel loss

Science.gov (United States)

Meyer-Scott, Evan; Yan, Zhizhong; MacDonald, Allison; Bourgoin, Jean-Philippe; Hübel, Hannes; Jennewein, Thomas

2011-12-01

Quantum key distribution (QKD) takes advantage of fundamental properties of quantum physics to allow two distant parties to share a secret key; however, QKD is hampered by a distance limitation of a few hundred kilometers on Earth. The most immediate solution for global coverage is to use a satellite, which can receive separate QKD transmissions from two or more ground stations and act as a trusted node to link these ground stations. In this article we report on a system capable of performing QKD in the high loss regime expected in an uplink to a satellite using weak coherent pulses and decoy states. Such a scenario profits from the simplicity of its receiver payload, but has so far been considered to be infeasible due to very high transmission losses (40-50 dB). The high loss is overcome by implementing an innovative photon source and advanced timing analysis. Our system handles up to 57 dB photon loss in the infinite key limit, confirming the viability of the satellite uplink scenario. We emphasize that while this system was designed with a satellite uplink in mind, it could just as easily overcome high losses on any free space QKD link.

How to implement decoy-state quantum key distribution for a satellite uplink with 50-dB channel loss

International Nuclear Information System (INIS)

Meyer-Scott, Evan; Yan, Zhizhong; MacDonald, Allison; Bourgoin, Jean-Philippe; Huebel, Hannes; Jennewein, Thomas

2011-01-01

Quantum key distribution (QKD) takes advantage of fundamental properties of quantum physics to allow two distant parties to share a secret key; however, QKD is hampered by a distance limitation of a few hundred kilometers on Earth. The most immediate solution for global coverage is to use a satellite, which can receive separate QKD transmissions from two or more ground stations and act as a trusted node to link these ground stations. In this article we report on a system capable of performing QKD in the high loss regime expected in an uplink to a satellite using weak coherent pulses and decoy states. Such a scenario profits from the simplicity of its receiver payload, but has so far been considered to be infeasible due to very high transmission losses (40-50 dB). The high loss is overcome by implementing an innovative photon source and advanced timing analysis. Our system handles up to 57 dB photon loss in the infinite key limit, confirming the viability of the satellite uplink scenario. We emphasize that while this system was designed with a satellite uplink in mind, it could just as easily overcome high losses on any free space QKD link.

Probability of satellite collision

Science.gov (United States)

Mccarter, J. W.

1972-01-01

A method is presented for computing the probability of a collision between a particular artificial earth satellite and any one of the total population of earth satellites. The collision hazard incurred by the proposed modular Space Station is assessed using the technique presented. The results of a parametric study to determine what type of satellite orbits produce the greatest contribution to the total collision probability are presented. Collision probability for the Space Station is given as a function of Space Station altitude and inclination. Collision probability was also parameterized over miss distance and mission duration.

Modeling and simulation of satellite subsystems for end-to-end spacecraft modeling

Science.gov (United States)

Schum, William K.; Doolittle, Christina M.; Boyarko, George A.

2006-05-01

During the past ten years, the Air Force Research Laboratory (AFRL) has been simultaneously developing high-fidelity spacecraft payload models as well as a robust distributed simulation environment for modeling spacecraft subsystems. Much of this research has occurred in the Distributed Architecture Simulation Laboratory (DASL). AFRL developers working in the DASL have effectively combined satellite power, attitude pointing, and communication link analysis subsystem models with robust satellite sensor models to create a first-order end-to-end satellite simulation capability. The merging of these two simulation areas has advanced the field of spacecraft simulation, design, and analysis, and enabled more in-depth mission and satellite utility analyses. A core capability of the DASL is the support of a variety of modeling and analysis efforts, ranging from physics and engineering-level modeling to mission and campaign-level analysis. The flexibility and agility of this simulation architecture will be used to support space mission analysis, military utility analysis, and various integrated exercises with other military and space organizations via direct integration, or through DOD standards such as Distributed Interaction Simulation. This paper discusses the results and lessons learned in modeling satellite communication link analysis, power, and attitude control subsystems for an end-to-end satellite simulation. It also discusses how these spacecraft subsystem simulations feed into and support military utility and space mission analyses.

Connecticut's Evolving Interactive Distance Learning Network in the Cable and Telecommunications Industries.

Science.gov (United States)

Pietras, Jesse John

This paper describes the state of interactive distance learning in Connecticut, particularly the current and future provision of these services by the telecommunications and cable television industries. The overview examines questions of where obligation and responsibility lie (with schools, local exchange companies, cable franchises, etc.) in…

Protein structure modelling and evaluation based on a 4-distance description of side-chain interactions

Directory of Open Access Journals (Sweden)

Inbar Yuval

2010-07-01

Full Text Available Abstract Background Accurate evaluation and modelling of residue-residue interactions within and between proteins is a key aspect of computational structure prediction including homology modelling, protein-protein docking, refinement of low-resolution structures, and computational protein design. Results Here we introduce a method for accurate protein structure modelling and evaluation based on a novel 4-distance description of residue-residue interaction geometry. Statistical 4-distance preferences were extracted from high-resolution protein structures and were used as a basis for a knowledge-based potential, called Hunter. We demonstrate that 4-distance description of side chain interactions can be used reliably to discriminate the native structure from a set of decoys. Hunter ranked the native structure as the top one in 217 out of 220 high-resolution decoy sets, in 25 out of 28 "Decoys 'R' Us" decoy sets and in 24 out of 27 high-resolution CASP7/8 decoy sets. The same concept was applied to side chain modelling in protein structures. On a set of very high-resolution protein structures the average RMSD was 1.47 Å for all residues and 0.73 Å for buried residues, which is in the range of attainable accuracy for a model. Finally, we show that Hunter performs as good or better than other top methods in homology modelling based on results from the CASP7 experiment. The supporting web site http://bioinfo.weizmann.ac.il/hunter/ was developed to enable the use of Hunter and for visualization and interactive exploration of 4-distance distributions. Conclusions Our results suggest that Hunter can be used as a tool for evaluation and for accurate modelling of residue-residue interactions in protein structures. The same methodology is applicable to other areas involving high-resolution modelling of biomolecules.

Threshold separation distance for attractive interaction between dust particles

International Nuclear Information System (INIS)

Jabdaraghi, R. Najafi; Sobhanian, S.

2008-01-01

Interaction between dust grains in a dusty plasma could be both repulsive and attractive. The Coulomb interaction between two negatively charged dust particulates and the electrostatic force between them are repulsive, while the shadowing force affecting them is attractive. We show in this paper that in some experimental conditions, there is some grain separation zone for which the attractive shadowing force is larger than the repulsive forces between them. In experimental conditions, for the grains separation distance r = 0.4 cm the shadowing force is almost equal to the electrostatic force between them and for r>0.4 cm the shadowing force exceeds the electrostatic force. So the resultant interaction force will be attractive. The possibility of dust crystal formation in this zone and also the motion of dust particles in the resultant potential of the form V = -(a/r)+(b/r 2 ) will be discussed. This form of potential comes from the combination electrostatic (F es (c/r 3 )) and shadowing (F shadow = -(d/r 2 )) forces.

Deep space optical communication via relay satellite

Science.gov (United States)

Dolinar, S.; Vilnrotter, V.; Gagliardi, R.

1981-01-01

The application of optical communications for a deep space link via an earth-orbiting relay satellite is discussed. The system uses optical frequencies for the free-space channel and RF links for atmospheric transmission. The relay satellite is in geostationary orbit and contains the optics necessary for data processing and formatting. It returns the data to earth through the RF terrestrial link and also transmits an optical beacon to the satellite for spacecraft return pointing and for the alignment of the transmitting optics. Future work will turn to modulation and coding, pointing and tracking, and optical-RF interfacing.

Long distance free-space quantum key distribution

International Nuclear Information System (INIS)

Schmitt-Manderbach, T.

2007-01-01

The aim of the presented experiment was to investigate the feasibility of satellite-based global quantum key distribution. In this context, a free-space quantum key distribution experiment over a real distance of 144 km was performed. The transmitter and the receiver were situated in 2500 m altitude on the Canary Islands of La Palma and Tenerife, respectively. The small and compact transmitter unit generated attenuated laser pulses, that were sent to the receiver via a 15-cm optical telescope. The receiver unit for polarisation analysis and detection of the sent pulses was integrated into an existing mirror telescope designed for classical optical satellite communications. To ensure the required stability and efficiency of the optical link in the presence of atmospheric turbulence, the two telescopes were equipped with a bi-directional automatic tracking system. Still, due to stray light and high optical attenuation, secure key exchange would not be possible using attenuated pulses in connection with the standard BB84 protocol. The photon number statistics of attenuated pulses follows a Poissonian distribution. Hence, by removing a photon from all pulses containing two or more photons, an eavesdropper could measure its polarisation without disturbing the polarisation state of the remaining pulse. In this way, he can gain information about the key without introducing detectable errors. To protect against such attacks, the presented experiment employed the recently developed method of using additional ''decoy'' states, i.e., the the intensity of the pulses created by the transmitter were varied in a random manner. By analysing the detection probabilities of the different pulses individually, a photon-number-splitting attack can be detected. Thanks to the decoy-state analysis, the secrecy of the resulting quantum key could be ensured despite the Poissonian nature of the emitted pulses. For a channel attenuation as high as 35 dB, a secret key rate of up to 250 bit

Long distance free-space quantum key distribution

Energy Technology Data Exchange (ETDEWEB)

Schmitt-Manderbach, T.

2007-10-16

The aim of the presented experiment was to investigate the feasibility of satellite-based global quantum key distribution. In this context, a free-space quantum key distribution experiment over a real distance of 144 km was performed. The transmitter and the receiver were situated in 2500 m altitude on the Canary Islands of La Palma and Tenerife, respectively. The small and compact transmitter unit generated attenuated laser pulses, that were sent to the receiver via a 15-cm optical telescope. The receiver unit for polarisation analysis and detection of the sent pulses was integrated into an existing mirror telescope designed for classical optical satellite communications. To ensure the required stability and efficiency of the optical link in the presence of atmospheric turbulence, the two telescopes were equipped with a bi-directional automatic tracking system. Still, due to stray light and high optical attenuation, secure key exchange would not be possible using attenuated pulses in connection with the standard BB84 protocol. The photon number statistics of attenuated pulses follows a Poissonian distribution. Hence, by removing a photon from all pulses containing two or more photons, an eavesdropper could measure its polarisation without disturbing the polarisation state of the remaining pulse. In this way, he can gain information about the key without introducing detectable errors. To protect against such attacks, the presented experiment employed the recently developed method of using additional 'decoy' states, i.e., the the intensity of the pulses created by the transmitter were varied in a random manner. By analysing the detection probabilities of the different pulses individually, a photon-number-splitting attack can be detected. Thanks to the decoy-state analysis, the secrecy of the resulting quantum key could be ensured despite the Poissonian nature of the emitted pulses. For a channel attenuation as high as 35 dB, a secret key rate of up to 250

Three-dimensional disc-satellite interaction: torques, migration, and observational signatures

Science.gov (United States)

Arzamasskiy, Lev; Zhu, Zhaohuan; Stone, James M.

2018-04-01

The interaction of a satellite with a gaseous disc results in the excitation of spiral density waves, which remove angular momentum from the orbit. In addition, if the orbit is not coplanar with the disc, three-dimensional effects will excite bending and eccentricity waves. We perform three-dimensional hydrodynamic simulations to study nonlinear disc-satellite interaction in inviscid protoplanetary discs for a variety of orbital inclinations from 0° to 180°. It is well known that three-dimensional effects are important even for zero inclination. In this work, we (1) show that for planets with small inclinations (as in the Solar system), effects such as the total torque and migration rate strongly depend on the inclination and are significantly different (about 2.5 times smaller) from the two-dimensional case, (2) give formulae for the migration rate, inclination damping, and precession rate of planets with different inclination angles in disc with different scale heights, and (3) present the observational signatures of a planet on an inclined orbit with respect to the protoplanetary disc. For misaligned planets, we find good agreement with linear theory in the limit of small inclinations, and with dynamical friction estimates for intermediate inclinations. We find that in the latter case, the dynamical friction force is not parallel to the relative planetary velocity. Overall, the derived formulae will be important for studying exoplanets with obliquity.

Investigations in Satellite MIMO Channel Modeling: Accent on Polarization

Directory of Open Access Journals (Sweden)

Karagiannidis George K

2007-01-01

Full Text Available Due to the much different environment in satellite and terrestrial links, possibilities in and design of MIMO systems are rather different as well. After pointing out these differences and problems arising from them, two MIMO designs are shown rather well adapted to satellite link characteristics. Cooperative diversity seems to be applicable; its concept is briefly presented without a detailed discussion, leaving solving particular satellite problems to later work. On the other hand, a detailed discussion of polarization time-coded diversity (PTC is given. A physical-statistical model for dual-polarized satellite links is presented together with measuring results validating the model. The concept of 3D polarization is presented as well as briefly describing compact 3D-polarized antennas known from the literature and applicable in satellite links. A synthetic satellite-to-indoor link is constructed and its electromagnetic behavior is simulated via the FDTD (finite-difference time-domain method. Previous result of the authors states that in 3D-PTC situations, MIMO capacity can be about two times higher than SIMO (single-input multiple-output capacity while a diversity gain of nearly is further verified via extensive FDTD computer simulation.

Particle-induced bit errors in high performance fiber optic data links for satellite data management

International Nuclear Information System (INIS)

Marshall, P.W.; Carts, M.A.; Dale, C.J.; LaBel, K.A.

1994-01-01

Experimental test methods and analysis tools are demonstrated to assess particle-induced bit errors on fiber optic link receivers for satellites. Susceptibility to direct ionization from low LET particles is quantified by analyzing proton and helium ion data as a function of particle LET. Existing single event analysis approaches are shown to apply, with appropriate modifications, to the regime of temporally (rather than spatially) distributed bits, even though the sensitivity to single events exceeds conventional memory technologies by orders of magnitude. The cross-section LET dependence follows a Weibull distribution at data rates from 200 to 1,000 Mbps and at various incident optical power levels. The LET threshold for errors is shown, through both experiment and modeling, to be 0 in all cases. The error cross-section exhibits a strong inverse dependence on received optical power in the LET range where most orbital single events would occur, thus indicating that errors can be minimized by operating links with higher incident optical power. Also, an analytic model is described which incorporates the appropriate physical characteristics of the link as well as the optical and receiver electrical characteristics. Results indicate appropriate steps to assure suitable link performance even in severe particle orbits

COTS low-cost 622-Mb/s free-space laser communications link for short-distance commercial applications

Science.gov (United States)

Morrison, Kenneth A.

2000-05-01

The results from a low cost 622 Mb/s, free-space laser communication link operating at 850 nm for short distance commercial applications is presented. The test results demonstrate the use of a free-space laser communications transceiver for building to building applications such as LAN, WAN and ATM operations, etc. This illustrates the potential for wide-use commercial computer network applications. The transceiver is constructed of commercial off-the-shelf materials for the development of a low-cost laser communications data link. The test system configuration utilizes standard Personal Computers with network cards and signal conversion cards for the copper to optical medical conversion. These tests precede the development of an increased data rate device operating at 2.5 Gb/s.

Land-mobile satellite excess path loss measurements

Science.gov (United States)

Hess, G. C.

1980-05-01

An experiment conducted with the ATS-6 satellite to determine the additional path loss over free-space loss experienced by land-mobile communication links is described. This excess path loss is measured as a function of 1) local environment, 2) vehicle heading, 3) link frequency, 4) satellite elevation angle, and 5) street side. A statistical description of excess loss developed from the data shows that the first two parameters dominate. Excess path loss on the order of 25 dB is typical in urban situations, but decreases to under 10 dB in suburban/rural areas. Spaced antenna selection diversity is found to provide only a slight decrease (4 dB, typically) in the urban excess path loss observed. Level crossing rates are depressed in satellite links relative to those of Rayleigh-faded terrestrial links, but increases in average fade durations tend to offset that advantage. The measurements show that the excess path loss difference between 860-MHz links and 1550-MHz links is generally negligible.

Escape of natural satellites from Mercury and Venus

Energy Technology Data Exchange (ETDEWEB)

Kumar, S S [Virginia Univ., Charlottesville (USA)

1977-09-01

It is suggested that the slow rotations of Mercury and Venus may be connected with the absence of natural satellites around them. If Mercury or Venus possessed a satellite at the time of formation, the tidal evolution would have caused the satellite to recede. At a sufficiently large distance from the planet, the Sun's gravitational influence makes the satellite orbit unstable. The natural satellites of Mercury and Venus might have escaped as a consequence of this instability.

INTERACTION BETWEEN ENTERPRISES AND UNIVERSITIES CIVIL AVIATION BASED TECHNOLOGIES OF DISTANCE EDUCATION

Directory of Open Access Journals (Sweden)

K. S. Ermakov

2015-01-01

Full Text Available Distance education based on modern information technology as a tool for interaction between universities and enterprises of civil aviation. The introduction of the learning process real needs of civil aviation, enabling an airline to use scientific potential of educational institutions for the successful implementation of scientific research aimed at solving urgent problems.

Interaction in distance learning pedagogy: the views of tutors and students

Directory of Open Access Journals (Sweden)

Erlinda Martins Batista

2016-05-01

Full Text Available This study shares the results of a survey that sought to analyze the process of interaction in a Virtual Learning Environment – VLE from the perspective of students and tutors of a distance learning course of Pedagogy offered by a Brazilian public university. Based on a critical paradigm and a qualitative methodology, this article presents a discussion on the role of interaction in distance learning courses, from the viewpoints of students and tutors. The participants´ concepts of interaction were analyzed from the dialectic and socio-historical perspective, according to which interaction is established in the social relations and mediated by the educator to promote learning. The results suggest that interaction is characterized as a form of communication that occurs especially in the virtual setting and it is strongly unidirectional and little interactional, as it occurs in only one direction, in this case, from students towards tutors as far as schoolwork is concerned. We conclude that both tutors and students need to reframe the concept of interaction, considered in the study as a process of ‘wholeness’. Within the concept of ‘wholeness’, communication occurs so that the Interacting participant is wholly involved in the communication. Their perception of communication is twofold, simultaneous, that is, they see themselves as whole, both in interaction and in the wholeness process. The dialogs in this process occur in a historical, social and dialectical way. Therefore, we support a process that goes beyond interaction, that is, wholeness to promote effective learning in DE – Distance Education. Este estudo compartilha os resultados de uma pesquisa que buscou analisar o processo de interação em ambiente virtual de aprendizagem – AVA, na visão dos estudantes, professores tutores de um curso de pedagogia a distância de uma instituição pública brasileira. Fundamentado no paradigma crítico e na metodologia qualitativa, este

Buckshot Routing with Distance Vectors in Three Application Scenarios for Wireless Sensor Networks with Unstable Network Topologies and Unidirectional Links

Directory of Open Access Journals (Sweden)

Reinhardt Karnapke

2015-02-01

Full Text Available Experiments have shown that the number of asymmetric and unidirectional links often exceeds the number of bidirectional ones, especially in the transitional area of the communication range of wireless sensor nodes. Still, most of today’s routing protocols ignore their existence or try to remove their implications. Also, links are not stable over time, and routes become unusable often, resulting in a need for new routing protocols that can handle highly dynamic links and use unidirectional links to their advantage. At SENSORCOMM' 2014, we presented BuckshotDV, a routing protocol which is resilient against link fluctuations and uses the longer reach of unidirectional links to increase its performance. Furthermore, its distance vector nature makes it scalable for large sensor networks. This paper is an extended version which adds some implementation details and the evaluation of BuckshotDV in two more application scenarios.

On the strong influence of molecular interactions over large distances

Science.gov (United States)

Pfennig, Andreas

2018-03-01

Molecular-dynamics simulations of liquid water show deterministic chaos, i.e. an intentionally introduced molecular position shift of an individual molecule increases exponentially by a factor of 10 in 0.23 ps. This is a Lyaponov instability. As soon as it reaches molecular scale, the direction of the resulting shift in molecular motions is unpredictable. The influence of any individual distant particle on an observed molecule will be minute, but the effect will quickly increase to molecular scale and beyond due to this exponential growth. Consequently, any individual particle in the universe will affect the behavior of any molecule within at most 33 ps after the interaction reaches it. A larger distance of the faraway particle does not decrease the influence on an observed molecule, but the effect reaches molecular scale only some ps later. Thus in evaluating the interactions, nearby and faraway molecules have to be equally accounted for. The consequences of this quickly reacting network of interactions on universal scale are fundamental. Even in a strictly deterministic view, molecular behavior is principally unpredictable, and thus has to be regarded random. Corresponding statements apply for any particles interacting. This result leads to a fundamental rethinking of the structure of interactions of molecules and particles as well as the behavior of reality.

Precise Determination of the Baseline Between the TerraSAR-X and TanDEM-X Satellites

Science.gov (United States)

Koenig, Rolf; Rothacher, Markus; Michalak, Grzegorz; Moon, Yongjin

TerraSAR-X, launched on June 15, 2007, and TanDEM-X, to be launched in September 2009, both carry the Tracking, Occultation and Ranging (TOR) category A payload instrument package. The TOR consists of a high-precision dual-frequency GPS receiver, called Integrated GPS Occultation Receiver (IGOR), for precise orbit determination and atmospheric sounding and a Laser retro-reflector (LRR) serving as target for the global Satellite Laser Ranging (SLR) ground station network. The TOR is supplied by the GeoForschungsZentrum Potsdam (GFZ) Germany, and the Center for Space Research (CSR), Austin, Texas. The objective of the German/US collaboration is twofold: provision of atmospheric profiles for use in numerical weather predictions and climate studies from the occultation data and precision SAR data processing based on precise orbits and atmospheric products. For the scientific objectives of the TanDEM- X mission, i.e., bi-static SAR together with TerraSAR-X, the dual-frequency GPS receiver is of vital importance for the millimeter level determination of the baseline or distance between the two spacecrafts. The paper discusses the feasibility of generating millimeter baselines by the example of GRACE, where for validation the distance between the two GRACE satellites is directly available from the micrometer-level intersatellite link measurements. The distance of the GRACE satellites is some 200 km, the distance of the TerraSAR-X/TanDEM-X formation will be some 200 meters. Therefore the proposed approach is then subject to a simulation of the foreseen TerraSAR-X/TanDEM-X formation. The effect of varying space environmental conditions, of possible phase center variations, multi path, and of varying center of mass of the spacecrafts are evaluated and discussed.

Mena–GRASP65 interaction couples actin polymerization to Golgi ribbon linking

Science.gov (United States)

Tang, Danming; Zhang, Xiaoyan; Huang, Shijiao; Yuan, Hebao; Li, Jie; Wang, Yanzhuang

2016-01-01

In mammalian cells, the Golgi reassembly stacking protein 65 (GRASP65) has been implicated in both Golgi stacking and ribbon linking by forming trans-oligomers through the N-terminal GRASP domain. Because the GRASP domain is globular and relatively small, but the gaps between stacks are large and heterogeneous, it remains puzzling how GRASP65 physically links Golgi stacks into a ribbon. To explore the possibility that other proteins may help GRASP65 in ribbon linking, we used biochemical methods and identified the actin elongation factor Mena as a novel GRASP65-binding protein. Mena is recruited onto the Golgi membranes through interaction with GRASP65. Depleting Mena or disrupting actin polymerization resulted in Golgi fragmentation. In cells, Mena and actin were required for Golgi ribbon formation after nocodazole washout; in vitro, Mena and microfilaments enhanced GRASP65 oligomerization and Golgi membrane fusion. Thus Mena interacts with GRASP65 to promote local actin polymerization, which facilitates Golgi ribbon linking. PMID:26538023

Tourists consuming distance

DEFF Research Database (Denmark)

Larsen, Gunvor Riber

The environmental impact of tourism mobility is linked to the distances travelled in order to reach a holiday destination, and with tourists travelling more and further than previously, an understanding of how the tourists view the distance they travel across becomes relevant. Based on interviews...... contribute to an understanding of how it is possible to change tourism travel behaviour towards becoming more sustainable. How tourists 'consume distance' is discussed, from the practical level of actually driving the car or sitting in the air plane, to the symbolic consumption of distance that occurs when...... travelling on holiday becomes part of a lifestyle and a social positioning game. Further, different types of tourist distance consumers are identified, ranging from the reluctant to the deliberate and nonchalant distance consumers, who display very differing attitudes towards the distance they all travel...

THE THREE-DIMENSIONAL STRUCTURE OF THE M31 SATELLITE SYSTEM; STRONG EVIDENCE FOR AN INHOMOGENEOUS DISTRIBUTION OF SATELLITES

International Nuclear Information System (INIS)

Conn, A. R.; Parker, Q. A.; Zucker, D. B.; Lewis, G. F.; Ibata, R. A.; Martin, N. F.; McConnachie, A. W.; Valls-Gabaud, D.; Tanvir, N.; Irwin, M. J.; Ferguson, A. M. N.; Chapman, S. C.

2013-01-01

We undertake an investigation into the spatial structure of the M31 satellite system utilizing the distance distributions presented in a previous publication. These distances make use of the unique combination of depth and spatial coverage of the Pan-Andromeda Archaeological Survey to provide a large, homogeneous sample consisting of 27 of M31's satellites, as well as M31 itself. We find that the satellite distribution, when viewed as a whole, is no more planar than one would expect from a random distribution of equal size. A disk consisting of 15 of the satellites is however found to be highly significant, and strikingly thin, with an rms thickness of just 12.34 +0.75 -0.43 kpc. This disk is oriented approximately edge-on with respect to the Milky Way and almost perpendicular to the Milky Way disk. It is also roughly orthogonal to the disk-like structure regularly reported for the Milky Way satellite system and in close alignment with M31's Giant Stellar Stream. A similar analysis of the asymmetry of the M31 satellite distribution finds that it is also significantly larger than one would expect from a random distribution. In particular, it is remarkable that 20 of the 27 satellites most likely lie on the Milky Way side of the galaxy, with the asymmetry being most pronounced within the satellite subset forming the aforementioned disk. This lopsidedness is all the more intriguing in light of the apparent orthogonality observed between the satellite disk structures of the Milky Way and M31.

High Bandwidth Optical Links for Micro-Satellite Support

Science.gov (United States)

Chao, Tien-Hsin (Inventor); Wilson, Keith E. (Inventor); Coste, Keith (Inventor)

2016-01-01

A method, systems, apparatus and device enable high bandwidth satellite communications. An onboard tracking detector, installed in a low-earth orbit satellite, detects a position of an incoming optical beam received/transmitted from a first ground station of one or more ground stations. Tracker electronics determine orientation information of the incoming optical beam based on the position. Control electronics receive the orientation information from the tracker electronics, and control a waveguide drive electronics. The waveguide drive electronics control a voltage that is provided to an electro-optic waveguide beam steering device. The electro-optic waveguide beam steering device steers an outgoing optical beam to one of the one or more ground stations based on the voltage.

Prediction Method for Rain Rate and Rain Propagation Attenuation for K-Band Satellite Communications Links in Tropical Areas

Directory of Open Access Journals (Sweden)

Baso Maruddani

2015-01-01

Full Text Available This paper deals with the prediction method using hidden Markov model (HMM for rain rate and rain propagation attenuation for K-band satellite communication link at tropical area. As is well known, the K-band frequency is susceptible of being affected by atmospheric condition, especially in rainy condition. The wavelength of K-band frequency which approaches to the size of rain droplet causes the signal strength is easily attenuated and absorbed by the rain droplet. In order to keep the quality of system performance for K-band satellite communication link, therefore a special attention has to be paid for rain rate and rain propagation attenuation. Thus, a prediction method for rain rate and rain propagation attenuation based on HMM is developed to process the measurement data. The measured and predicted data are then compared with the ITU-R recommendation. From the result, it is shown that the measured and predicted data show similarity with the model of ITU-R P.837-5 recommendation for rain rate and the model of ITU-R P.618-10 recommendation for rain propagation attenuation. Meanwhile, statistical data for measured and predicted data such as fade duration and interfade duration have insignificant discrepancy with the model of ITU-R P.1623-1 recommendation.

The escape of natural satellites from Mercury and Venus

International Nuclear Information System (INIS)

Kumar, S.S.

1977-01-01

It is suggested that the slow rotations of Mercury and Venus may be connected with the absence of natural satellites around them. If Mercury or Venus possessed a satellite at the time of formation, the tidal evolution would have caused the satellite to recede. At a sufficiently large distance from the planet, the Sun's gravitational influence makes the satellite orbit unstable. The natural satellites of Mercury and Venus might have escaped as a consequence of this instability. (Auth.)

Satellite switching concepts for European business services in the nineties

Science.gov (United States)

Lombard, D.; Rouffet, D.

A first generation of business communication satellites are now operational or to be launched. Increased demands for communication satellite facilities will develop, if special services, such as videoconferencing, can be provided at a reasonable cost. For such developments, it will be necessary to define a second generation of business communication satellites. The present investigation evaluates briefly the size of the expected European market for 1995. A study is conducted of the payload structure for the required satellite system, and aspects related to link budgets and power consumption are explored. It is found that system dimensioning is determined by the up-link and by technology. Critical factors are related to the output and input multiplexors for the link budget, the switching matrix, and implications for the mass budget. The best trade-off between technological, mass, and link budget limitations is achieved in connection with the employment of a hinged antennas satellite, using an intermediate number of spot beams and associated earth stations of reasonable size.

TETRA Backhauling via Satellite: Improving Call Setup Times and Saving Bandwidth

Directory of Open Access Journals (Sweden)

Anton Donner

2014-01-01

Full Text Available In disaster management scenarios with seriously damaged, not existing, or saturated communication infrastructures satellite communications can be an ideal means to provide connectivity with unaffected remote terrestrial trunked radio (TETRA core networks. However, the propagation delay imposed by the satellite link affects the signalling protocols. This paper discusses the suitability of using a satellite link for TETRA backhauling, introducing two different architectures. In order to cope with the signal delay of the satellite link, the paper proposes and analyzes a suitable solution based on the use of a performance enhancing proxy (PEP. Additionally, robust header compression (ROHC is discussed as suitable technology to transmit TETRA voice via IP-based satellite networks.

Satellite Navigation Systems: Policy, Commercial and Technical Interaction.

Science.gov (United States)

Rycroft, M.

2003-12-01

This book adopts a broad perspective on positioning and navigation systems which rely on Earth orbiting satellites for their successful operation. The first of such global systems was the US Global Positioning System (GPS), and the next the Russian GLONASS system. Now studies relating to Europe's future Galileo system are gaining momentum and other nations are planning regional augmentation systems. All such systems are discussed here, particularly relating to political, commercial, legal and technical issues. The opportunities - and also the problems - of having three similar systems in operation simultaneously are examined, and several novel applications are proposed. These range from improved vehicular transport by land, sea and air, to more accurate surveying, more efficient agricultural practices and safer operations in mountainous regions. Everyone who is challenged by these topics will find this volume invaluable. ISU WWW Server; http://www.isunet.edu. Further information on ISU Symposia may also be obtained by e-mail from symposium@isu.isunet.edu Link: http://www.wkap.nl/prod/b/1-4020-1678-6

Interactive virtual laboratory for distance education in nuclear engineering

International Nuclear Information System (INIS)

Jain, P.; Stubbins, J.; Uddin, R.

2006-01-01

A real time, distance lab module is being developed and implemented in the Dept. of Nuclear, Plasma and Radiological Engineering at the Univ. of Illinois at Urbana-Champaign. This internet based system allows remote personnel to watch the experiments, acquire data, and interact with on-site personnel. The e-lab broadcasts not only the live scenes of laboratory and experiments, but also the real time data and plots being measured and displayed in graphical and other formats. Moreover, use of LabVIEW's remote front panel feature allows communications between the local lab and remote client so that, if permitted, remote client can control part or all of the experiment in real-time. (authors)

Loss of niche-satellite cell interactions in syndecan-3 null mice alters muscle progenitor cell homeostasis improving muscle regeneration.

Science.gov (United States)

Pisconti, Addolorata; Banks, Glen B; Babaeijandaghi, Farshad; Betta, Nicole Dalla; Rossi, Fabio M V; Chamberlain, Jeffrey S; Olwin, Bradley B

2016-01-01

The skeletal muscle stem cell niche provides an environment that maintains quiescent satellite cells, required for skeletal muscle homeostasis and regeneration. Syndecan-3, a transmembrane proteoglycan expressed in satellite cells, supports communication with the niche, providing cell interactions and signals to maintain quiescent satellite cells. Syndecan-3 ablation unexpectedly improves regeneration in repeatedly injured muscle and in dystrophic mice, accompanied by the persistence of sublaminar and interstitial, proliferating myoblasts. Additionally, muscle aging is improved in syndecan-3 null mice. Since syndecan-3 null myofiber-associated satellite cells downregulate Pax7 and migrate away from the niche more readily than wild type cells, syxndecan-3 appears to regulate satellite cell homeostasis and satellite cell homing to the niche. Manipulating syndecan-3 provides a promising target for development of therapies to enhance muscle regeneration in muscular dystrophies and in aged muscle.

A Mobile Communications Space Link Between the Space Shuttle Orbiter and the Advanced Communications Technology Satellite

Science.gov (United States)

Fink, Patrick; Arndt, G. D.; Bondyopadhyay, P.; Shaw, Roland

1994-01-01

A communications experiment is described as a link between the Space Shuttle Orbiter (SSO) and the Advanced Communications Technology Satellite (ACTS). Breadboarding for this experiment has led to two items with potential for commercial application: a 1-Watt Ka-band amplifier and a Ka-band, circularly polarized microstrip antenna. Results of the hybrid Ka-band amplifier show gain at 30 dB and a saturated output power of 28.5 dBm. A second version comprised of MMIC amplifiers is discussed. Test results of the microstrip antenna subarray show a gain of approximately 13 dB and excellent circular polarization.

An Understanding Information Management System for a Real-Time Interactive Distance Education Environment

Science.gov (United States)

He, Aiguo

2009-01-01

A real-time interactive distance lecture is a joint work that should be accomplished by the effort of the lecturer and his students in remote sites. It is important for the lecturer to get understanding information from the students which cannot be efficiently collected by only using video/audio channels between the lecturer and the students. This…

Satellite Based Education and Training in Remote Sensing and Geo-Information AN E-Learning Approach to Meet the Growing Demands in India

Science.gov (United States)

Raju, P. L. N.; Gupta, P. K.

2012-07-01

One of the prime activities of Indian Space Research Organisation's (ISRO) Space Program is providing satellite communication services, viz., television broadcasting, mobile communication, cyclone disaster warning and rescue operations etc. so as to improve their economic conditions, disseminate technical / scientific knowledge to improve the agriculture production and education for rural people of India. ISRO, along with National Aeronautical and Space Administration (NASA) conducted experimental satellite communication project i.e. Satellite Instructional Television Experiment (SITE) using NASA's Advanced Telecommunication Satellite (i.e. ATS 6) with an objective to educate poor people of India via satellite broadcasting in 1975 and 1976, covering more than 2600 villages in six states of India and territories. Over the years India built communication satellites indigenously to meet the communication requirements of India. This has further lead to launch of an exclusive satellite from ISRO for educational purposes i.e. EDUSAT in 2004 through which rich audio-video content is transmitted / received, recreating virtual classes through interactivity. Indian Institute of Remote Sensing (IIRS) established in 1966, a premier institute in south East Asia in disseminating Remote Sensing (RS) and Geographical Information System (GIS), mainly focusing on contact based programs. But expanded the scope with satellite based Distance Learning Programs for Universities, utilizing the dedicated communication satellite i.e. EDUSAT in 2007. IIRS conducted successfully eight Distance Learning Programs in the last five years and training more than 6000 students mainly at postgraduate level from more than 60 universities /Institutions spread across India. IIRS obtained feedback and improved the programs on the continuous basis. Expanded the scope of IIRS outreach program to train user departments tailor made in any of the applications of Remote Sensing and Geoinformation, capacity

SATELLITE BASED EDUCATION AND TRAINING IN REMOTE SENSING AND GEO-INFORMATION: AN E-LEARNING APPROACH TO MEET THE GROWING DEMANDS IN INDIA

Directory of Open Access Journals (Sweden)

P. L. N. Raju

2012-07-01

Full Text Available One of the prime activities of Indian Space Research Organisation's (ISRO Space Program is providing satellite communication services, viz., television broadcasting, mobile communication, cyclone disaster warning and rescue operations etc. so as to improve their economic conditions, disseminate technical / scientific knowledge to improve the agriculture production and education for rural people of India. ISRO, along with National Aeronautical and Space Administration (NASA conducted experimental satellite communication project i.e. Satellite Instructional Television Experiment (SITE using NASA’s Advanced Telecommunication Satellite (i.e. ATS 6 with an objective to educate poor people of India via satellite broadcasting in 1975 and 1976, covering more than 2600 villages in six states of India and territories. Over the years India built communication satellites indigenously to meet the communication requirements of India. This has further lead to launch of an exclusive satellite from ISRO for educational purposes i.e. EDUSAT in 2004 through which rich audio-video content is transmitted / received, recreating virtual classes through interactivity. Indian Institute of Remote Sensing (IIRS established in 1966, a premier institute in south East Asia in disseminating Remote Sensing (RS and Geographical Information System (GIS, mainly focusing on contact based programs. But expanded the scope with satellite based Distance Learning Programs for Universities, utilizing the dedicated communication satellite i.e. EDUSAT in 2007. IIRS conducted successfully eight Distance Learning Programs in the last five years and training more than 6000 students mainly at postgraduate level from more than 60 universities /Institutions spread across India. IIRS obtained feedback and improved the programs on the continuous basis. Expanded the scope of IIRS outreach program to train user departments tailor made in any of the applications of Remote Sensing and

Impact of distance education via interactive videoconferencing on students' course performance and satisfaction.

Science.gov (United States)

Klibanov, Olga M; Dolder, Christian; Anderson, Kevin; Kehr, Heather A; Woods, J Andrew

2018-03-01

The impact of distance education via interactive videoconferencing on pharmacy students' performance in a course was assessed after implementation of a distance campus. Students filled out a "Student Demographic Survey" and a "Precourse Knowledge Assessment" at the start of the course and a "Postcourse Knowledge Assessment" and a "Postcourse Student Perceptions Survey" at the end of the course. The primary end point, a comparison of course grades (%) between the main and distance campuses, was examined using the two-sample t-test. We examined the relationships among demographics, campus location, course grades, grade point average, pre- and postcourse knowledge assessments, and postcourse perceptions as our secondary end points with parametric and nonparametric tests. Data from 93 students were included in the analysis [main campus ( n = 81); distance campus ( n = 12)]. Students on the main campus achieved a significantly higher final course grade (87 vs. 81%; P = 0.02). Scores on the Postcourse Knowledge Assessment were also significantly higher compared with those of students on the distance education campus (77 vs. 68%; P = 0.04). Students on both campuses reported self-perceived improvement in their knowledge base regarding various aspects of infectious diseases. Compared with the students on the distance campus, those on the main campus were more likely to subjectively perceive that they had succeeded in the course ( P = 0.04). Our study suggests that students on the main campus achieved a higher final course grade and were more likely to feel that they had succeeded in the course. Students on both campuses reported improvement in knowledge.

Estimating Effects Of Rain On Ground/Satellite Communication

Science.gov (United States)

Manning, R. M.

1992-01-01

LeRC-SLAM provides static and dynamic statistical assessment of impact of attenuation by rain on communication link established between Earth terminal and geosynchronous satellite. Program designed for use in specification, design, and assessment of satellite link for any terminal location in continental United States. IBM PC version written in Microsoft QuickBASIC, and Macintosh version written in Microsoft Basic.

Agent control of cooperating satellites

OpenAIRE

Lincoln, N.K.; Veres, S.M.; Dennis, Louise; Fisher, Michael; Lisitsa, Alexei

2011-01-01

A novel, hybrid, agent architecture for (small)swarms of satellites has been developed. The software architecture for each satellite comprises ahigh-level rational agent linked to a low-level control system. The rational agent forms dynamicgoals, decides how to tackle them and passes theactual implementation of these plans to the control layer. The rational agent also has access to aMatLabmodel of the satellite dynamics, thus allowing it to carry out selective hypothetical reasoningabout pote...

INVESTIGATION OF ADS-B MESSAGES TRAFFIC VIA SATELLITE COMMUNICATION CHANNEL

Directory of Open Access Journals (Sweden)

Volodymyr Kharchenko

2014-12-01

Full Text Available For modelling of ADS-B messages transmition with the help of low-orbit satellite complex Іrіdіumdifferent models of communication channel "Aircraft-to-Satellites-to-Ground Stations" were built using NetCrackerProfessіonal 4.1 software. Influence of aircraft and satellites amount on average link utilization and message travellingtime was studied for telecommunication channels with intersatellite link and bent-pipe architecture. The effect ofcommunication channel "saturation" during simultaneous data transmission through a satellite communicationchannel from many planes was investigated.

Advanced domestic digital satellite communications systems experiments

Science.gov (United States)

Iso, A.; Izumisawa, T.; Ishida, N.

1984-02-01

The characteristics of advanced digital transmission systems were measured, using newly developed small earth stations and a K-band and C-band communication satellite. Satellite link performance for data, facsimile, video and packet switching information transmission at bit rates ranging from 6.4 kbit/s to 6.3 Mbit/s have been confirmed, using a small K-band earth station and a demand-assignment time division multiple access system. A low-capacity omni-use C-band terminal experiment has verified a telephone channel transmission performance by spread-spectrum multiple access. Single point to multipoint transmission characteristics of the 64 kbit/s data signals from the computer center were tested, using a receive-only 4 GHz earth terminal. Basic satellite link performance was confirmed under clear-sky conditions. Precise satellite orbit and attitude keeping experiments were carried out to obtain precise satellite antenna pointing accuracy for development of K-band earth stations that do not require satellite tracking equipment. Precise station keeping accuracy of 0.02 degrees was obtained.

Satellite Communications Using Commercial Protocols

Science.gov (United States)

Ivancic, William D.; Griner, James H.; Dimond, Robert; Frantz, Brian D.; Kachmar, Brian; Shell, Dan

2000-01-01

NASA Glenn Research Center has been working with industry, academia, and other government agencies in assessing commercial communications protocols for satellite and space-based applications. In addition, NASA Glenn has been developing and advocating new satellite-friendly modifications to existing communications protocol standards. This paper summarizes recent research into the applicability of various commercial standard protocols for use over satellite and space- based communications networks as well as expectations for future protocol development. It serves as a reference point from which the detailed work can be readily accessed. Areas that will be addressed include asynchronous-transfer-mode quality of service; completed and ongoing work of the Internet Engineering Task Force; data-link-layer protocol development for unidirectional link routing; and protocols for aeronautical applications, including mobile Internet protocol routing for wireless/mobile hosts and the aeronautical telecommunications network protocol.

Leucocytes, cytokines and satellite cells

DEFF Research Database (Denmark)

Paulsen, Gøran; Mikkelsen, Ulla Ramer; Raastad, Truls

2012-01-01

uncertain. The COX enzymes regulate satellite cell activity, as demonstrated in animal models; however the roles of the COX enzymes in human skeletal muscle need further investigation. We suggest using the term 'muscle damage' with care. Comparisons between studies and individuals must consider changes......-damaging exercise', primarily eccentric exercise. We review the evidence for the notion that the degree of muscle damage is related to the magnitude of the cytokine response. In the third and final section, we look at the satellite cell response to a single bout of eccentric exercise, as well as the role...... variation in individual responses to a given exercise should, however be expected. The link between cytokine and satellite cell responses and exercise-induced muscle damage is not so clear The systemic cytokine response may be linked more closely to the metabolic demands of exercise rather than muscle...

Body Space in Social Interactions: A Comparison of Reaching and Comfort Distance in Immersive Virtual Reality

Science.gov (United States)

Iachini, Tina; Coello, Yann; Frassinetti, Francesca; Ruggiero, Gennaro

2014-01-01

Background Do peripersonal space for acting on objects and interpersonal space for interacting with con-specifics share common mechanisms and reflect the social valence of stimuli? To answer this question, we investigated whether these spaces refer to a similar or different physical distance. Methodology Participants provided reachability-distance (for potential action) and comfort-distance (for social processing) judgments towards human and non-human virtual stimuli while standing still (passive) or walking toward stimuli (active). Principal Findings Comfort-distance was larger than other conditions when participants were passive, but reachability and comfort distances were similar when participants were active. Both spaces were modulated by the social valence of stimuli (reduction with virtual females vs males, expansion with cylinder vs robot) and the gender of participants. Conclusions These findings reveal that peripersonal reaching and interpersonal comfort spaces share a common motor nature and are sensitive, at different degrees, to social modulation. Therefore, social processing seems embodied and grounded in the body acting in space. PMID:25405344

An interactive software package for validating satellite data

Digital Repository Service at National Institute of Oceanography (India)

Muraleedharan, P.M.; Pankajakshan, T.

to be highly correlated (r = 0.75) with the satellite data. Very good correlation (r = 0.80) is obtained for wind speed measured from both Moored buoy and Autonomous Weather Station. Night time SSTs are found to be closer to the satellite values for wind speed...

INVESTIGATION OF ADS-B MESSAGES TRAFFIC VIA SATELLITE COMMUNICATION CHANNEL

OpenAIRE

Volodymyr Kharchenko; Wang Bo; Andrii Grekhov; Marina Kovalenko

2014-01-01

For modelling of ADS-B messages transmition with the help of low-orbit satellite complex Іrіdіumdifferent models of communication channel "Aircraft-to-Satellites-to-Ground Stations" were built using NetCrackerProfessіonal 4.1 software. Influence of aircraft and satellites amount on average link utilization and message travellingtime was studied for telecommunication channels with intersatellite link and bent-pipe architecture. The effect ofcommunication channel "saturation" during simultaneou...

Distribution of high-dimensional entanglement via an intra-city free-space link.

Science.gov (United States)

Steinlechner, Fabian; Ecker, Sebastian; Fink, Matthias; Liu, Bo; Bavaresco, Jessica; Huber, Marcus; Scheidl, Thomas; Ursin, Rupert

2017-07-24

Quantum entanglement is a fundamental resource in quantum information processing and its distribution between distant parties is a key challenge in quantum communications. Increasing the dimensionality of entanglement has been shown to improve robustness and channel capacities in secure quantum communications. Here we report on the distribution of genuine high-dimensional entanglement via a 1.2-km-long free-space link across Vienna. We exploit hyperentanglement, that is, simultaneous entanglement in polarization and energy-time bases, to encode quantum information, and observe high-visibility interference for successive correlation measurements in each degree of freedom. These visibilities impose lower bounds on entanglement in each subspace individually and certify four-dimensional entanglement for the hyperentangled system. The high-fidelity transmission of high-dimensional entanglement under real-world atmospheric link conditions represents an important step towards long-distance quantum communications with more complex quantum systems and the implementation of advanced quantum experiments with satellite links.

Daily Social Interactions and the Biological Stress Response: Are There Age Differences in Links Between Social Interactions and Alpha-Amylase?

Science.gov (United States)

Birditt, Kira S; Tighe, Lauren A; Nevitt, Michael R; Zarit, Steven H

2017-12-12

According to the strength and vulnerability integration (SAVI) model, older people are better able to avoid negative social interactions than younger people, but when they do experience negative interactions, they are equally or more emotionally and physiologically reactive than younger people. Less is known about the links between daily negative and positive social encounters and the sympathetic adrenal medullary system (a key stress pathway) and whether there are age differences in these links. This study considers whether negative and positive social interactions are associated with diurnal alpha-amylase (a measure of the sympathetic adrenal medullary system) and whether there are differences in these links by age. Participants were from the Daily Health, Stress, and Relationship Study, which includes a random sample of 89 individuals (aged 40-95) who completed 14 days of daily diary interviews and provided saliva samples four times a day (wake, 30 min after wake, lunch, and bedtime) for four of those days that were assayed for alpha-amylase. Days in which people reported more negative interactions were associated with flatter morning declines in alpha-amylase, indicating greater stress. Links between positive interactions and diurnal alpha-amylase varied by age group. Findings are consistent with the SAVI model indicating that older adults respond differently to social stimuli than younger people. © The Author(s) 2017. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Satellite Teleconferencing in the Caribbean.

Science.gov (United States)

Sankar, Hollis C.

1985-01-01

Discusses the need for, and the development, use, and future trends of, the University of the West Indies Distance Teaching Experiment, which utilizes telephone and communications satellite technology teleconferencing to extend educational opportunities to the peoples of the Caribbean. (MBR)

Measurements of VLF-particle interactions at the South Atlantic Magnetic Anomaly on board a Brazilian geophysical satellite

International Nuclear Information System (INIS)

Gonzalez, W.D.; Pinto Junior, O.; Dutra, S.L.G.; Takahashi, H.

1988-01-01

A summary of the proposal for measurements of VLF wave-particle interactions, expected to occur at the South Atlantic magnetic anomaly, to be carried out on board a Brazilian geophysical satellite, will be presented. The expected domain of such interactions refers to electromagnetic VLF waves and to energetic-relativistic inner belt electrons, pitch angle diffusing into the atmosphere via cyclotron resonances. The detectors involve a tri-axial search coil magnetometer and a surface barrier silicon telescope. A modified and preliminary version of this proposed experiment will be carried out on board long duration balloon flights, well before the beginning of the intended satellite measurements. For the ballon flights the particle detector will be replaced by an x-ray detector, which can also monitor parameters related to the electron precipitation. (author) [pt

Aerosols, Chemistry, and Radiative Forcing: A 3-D Model Analysis of Satellite and ACE-Asia data (ACMAP)

Science.gov (United States)

Chin, Mian; Ginoux, Paul; Torres, Omar; Zhao, Xue-Peng

2005-01-01

We propose a research project to incorporate a global 3-D model and satellite data into the multi-national Aerosol Characterization Experiment-Asia (ACE-Asia) mission. Our objectives are (1) to understand the physical, chemical, and optical properties of aerosols and the processes that control those properties over the Asian-Pacific region, (2) to investigate the interaction between aerosols and tropospheric chemistry, and (3) to determine the aerosol radiative forcing over the Asia-Pacific region. We will use the Georgia TecWGoddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model to link satellite observations and the ACE-Asia measurements. First, we will use the GOCART model to simulate aerosols and related species, and evaluate the model with satellite and in-situ observations. Second, the model generated aerosol vertical profiles and compositions will be used to validate the satellite products; and the satellite data will be used for during- and post- mission analysis. Third, we will use the model to analyze and interpret both satellite and ACE- Asia field campaign data and investigate the aerosol-chemistry interactions. Finally, we will calculate aerosol radiative forcing over the Asian-Pacific region, and assess the influence of Asian pollution in the global atmosphere. We propose a research project to incorporate a global 3-D model and satellite data into

Robust cross-links in molluscan adhesive gels: testing for contributions from hydrophobic and electrostatic interactions.

Science.gov (United States)

Smith, A M; Robinson, T M; Salt, M D; Hamilton, K S; Silvia, B E; Blasiak, R

2009-02-01

The cross-linking interactions that provide cohesive strength to molluscan adhesive gels were investigated. Metal-based interactions have been shown to play an important role in the glue of the slug Arion subfuscus (Draparnaud), but other types of interactions may also contribute to the glue's strength and their role has not been investigated. This study shows that treatments that normally disrupt hydrophobic or electrostatic interactions have little to no effect on the slug glue. High salt concentrations and non-ionic detergent do not affect the solubility of the proteins in the glue or the ability of the glue proteins to stiffen gels. In contrast, metal chelation markedly disrupts the gel. Experiments with gel filtration chromatography identify a 40 kDa protein that is a central component of the cross-links in the glue. This 40 kDa protein forms robust macromolecular aggregations that are stable even in the presence of high concentrations of salt, non-ionic detergent, urea or metal chelators. Metal chelation during glue secretion, however, may block some of these cross-links. Such robust, non-specific interactions in an aqueous environment are highly unusual for hydrogels and reflect an intriguing cross-linking mechanism.

Gesture Interaction at a Distance

NARCIS (Netherlands)

Fikkert, F.W.

2010-01-01

The aim of this work is to explore, from a perspective of human behavior, which gestures are suited to control large display surfaces from a short distance away; why that is so; and, equally important, how such an interface can be made a reality. A well-known example of the type of interface that is

Mena-GRASP65 interaction couples actin polymerization to Golgi ribbon linking.

Science.gov (United States)

Tang, Danming; Zhang, Xiaoyan; Huang, Shijiao; Yuan, Hebao; Li, Jie; Wang, Yanzhuang

2016-01-01

In mammalian cells, the Golgi reassembly stacking protein 65 (GRASP65) has been implicated in both Golgi stacking and ribbon linking by forming trans-oligomers through the N-terminal GRASP domain. Because the GRASP domain is globular and relatively small, but the gaps between stacks are large and heterogeneous, it remains puzzling how GRASP65 physically links Golgi stacks into a ribbon. To explore the possibility that other proteins may help GRASP65 in ribbon linking, we used biochemical methods and identified the actin elongation factor Mena as a novel GRASP65-binding protein. Mena is recruited onto the Golgi membranes through interaction with GRASP65. Depleting Mena or disrupting actin polymerization resulted in Golgi fragmentation. In cells, Mena and actin were required for Golgi ribbon formation after nocodazole washout; in vitro, Mena and microfilaments enhanced GRASP65 oligomerization and Golgi membrane fusion. Thus Mena interacts with GRASP65 to promote local actin polymerization, which facilitates Golgi ribbon linking. © 2016 Tang et al. This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License (http://creativecommons.org/licenses/by-nc-sa/3.0).

Encryption protection for communication satellites

Science.gov (United States)

Sood, D. R.; Hoernig, O. W., Jr.

In connection with the growing importance of the commercial communication satellite systems and the introduction of new technological developments, users and operators of these systems become increasingly concerned with aspects of security. The user community is concerned with maintaining confidentiality and integrity of the information being transmitted over the satellite links, while the satellite operators are concerned about the safety of their assets in space. In response to these concerns, the commercial satellite operators are now taking steps to protect the communication information and the satellites. Thus, communication information is being protected by end-to-end encryption of the customer communication traffic. Attention is given to the selection of the NBS DES algorithm, the command protection systems, and the communication protection systems.

Jovian magnetosphere-satellite interactions: aspects of energetic charged particle loss

International Nuclear Information System (INIS)

Thomsen, M.F.

1979-01-01

Observations of energetic charged particles obtained by Pioneers 10 and 11 near the orbits of the inner Jovian satellites are reviewed with particular emphasis on the implications of these observations with regard to possible models of the access of charged particles to the satellite surfaces. The observed effects on particle pitch angle distributions and the observed energy dependence of the intensity depletions seen at the satellite orbits are compared with predictions of satellite sweepup based on several different access models. The two major uncertainties which hamper the comparisons are those associated with the satellite conductivities and the ionospheric dynamo electric field power spectrum. The satellite conductivity is important because it governs the access of the particles to the satellite surface and therefore the lifetime tau: the dynamo power spectrum is important because it controls the magnitude and energy dependence of the radial diffusion coefficient. In spite of these uncertainties we can nevertheless make the following conclusions. The electron pitch angle distributions at Io's orbit are compatible with expectations based on sweeping. The energy dependences of the observed electron depletions at all three inner satellites (Amalthea, Io, and Europa) are incompatible with expectations based on a perfect conductor model of a satellite and its flux tube but are compatible with the energy dependence expected for perfectly insulating or partially conducting satellites However, the proton losses at Io are observed to be much stronger than the electron losses, in contradiction to expectations based on sweeping. The most attractive explanation for the proton-electron discrepancy at Io is that the large proton losses at Io's orbit are principally due to enhanced pitch angle scattering in the region of higher plasma density

Satellite outreach in Asia and the Pacific.

Science.gov (United States)

1977-01-01

Communication by satellite is rapidly changing information exchange in Asia, especially for rural areas. The integrated education planned for satellite networks includes family planning as part of general development. A series of conferences has already been held successfully via satellite for family planning associations who are members of the East and Southeast Asia and Oceania Region of the International Planned Parenthood Federation. These included a conference on nursing training. In India the Satellite Instructional Television Experiment (SITE) made history during its 1-year trial. By 1981 the entire nation is to be linked by satellite. The question is whether the television education will truly change rural life or whether it will become merely a diversion. In Indonesia, satellites were chosen as the fastest way to obtain interisland communication. The Domsat system links the entire 13,000-island archipelago and is already being used for emergency communications. The system, which was developed in 1 1/2 years by the Hughes Aircraft Corporation will be used for teaching basic health, hygiene, and family planning. It will be several years before Domsat is fully operational, but it bears watching.

EPPUR SI MUOVE: POSITIONAL AND KINEMATIC CORRELATIONS OF SATELLITE PAIRS IN THE LOW Z UNIVERSE

International Nuclear Information System (INIS)

Ibata, Rodrigo A.; Famaey, Benoit; Martin, Nicolas; Lewis, Geraint F.; Ibata, Neil G.

2015-01-01

We have recently shown that pairs of satellite galaxies located diametrically opposite to each other around their host possess predominantly anti-correlated velocities. This is consistent with a scenario in which ≳50% of satellite galaxies belong to kinematically coherent rotating planar structures. Here we extend this analysis, examining satellites of giant galaxies drawn from an SDSS photometric redshift catalog. We find that there is a ∼17% overabundance (>3σ significance) of candidate satellites at positions diametrically opposite to a spectroscopically confirmed satellite. We show that ΛCDM cosmological simulations do not possess this property when contamination is included. After subtracting contamination, we find ∼2 times more satellites diametrically opposed to a spectroscopically confirmed satellite than at 90° from it, at projected distances ranging from 100 to 150 kpc from the host. This independent analysis thus strongly supports our previous results on anti-correlated velocities. We also find that those satellite pairs with anti-correlated velocities have a strong preference (∼3:1) to align with the major axis of the host whereas those with correlated velocities display the opposite behavior. We finally show that repeating a similar analysis to Ibata et al. with same-side satellites is generally hard to interpret, but is not inconsistent with our previous results when strong quality cuts are applied on the sample. This addresses all of the concerns recently raised by Cautun et al., who did not uncover any flaw in our previous analysis, but may simply have hinted at the physical extent of planar satellite structures by pointing out that the anti-correlation signal weakens at radii >150 kpc. All these unexpected positional and kinematic correlations strongly suggest that a substantial fraction of satellite galaxies are causally linked in their formation and evolution

EPPUR SI MUOVE: POSITIONAL AND KINEMATIC CORRELATIONS OF SATELLITE PAIRS IN THE LOW Z UNIVERSE

Energy Technology Data Exchange (ETDEWEB)

Ibata, Rodrigo A.; Famaey, Benoit; Martin, Nicolas [Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de l’Université, F-67000 Strasbourg (France); Lewis, Geraint F. [Sydney Institute of Astronomy, School of Physics A28, University of Sydney, NSW 2006 (Australia); Ibata, Neil G., E-mail: rodrigo.ibata@astro.unistra.fr [Trinity College, Trinity Street, Cambridge, CB2 1TQ (United Kingdom)

2015-05-20

We have recently shown that pairs of satellite galaxies located diametrically opposite to each other around their host possess predominantly anti-correlated velocities. This is consistent with a scenario in which ≳50% of satellite galaxies belong to kinematically coherent rotating planar structures. Here we extend this analysis, examining satellites of giant galaxies drawn from an SDSS photometric redshift catalog. We find that there is a ∼17% overabundance (>3σ significance) of candidate satellites at positions diametrically opposite to a spectroscopically confirmed satellite. We show that ΛCDM cosmological simulations do not possess this property when contamination is included. After subtracting contamination, we find ∼2 times more satellites diametrically opposed to a spectroscopically confirmed satellite than at 90° from it, at projected distances ranging from 100 to 150 kpc from the host. This independent analysis thus strongly supports our previous results on anti-correlated velocities. We also find that those satellite pairs with anti-correlated velocities have a strong preference (∼3:1) to align with the major axis of the host whereas those with correlated velocities display the opposite behavior. We finally show that repeating a similar analysis to Ibata et al. with same-side satellites is generally hard to interpret, but is not inconsistent with our previous results when strong quality cuts are applied on the sample. This addresses all of the concerns recently raised by Cautun et al., who did not uncover any flaw in our previous analysis, but may simply have hinted at the physical extent of planar satellite structures by pointing out that the anti-correlation signal weakens at radii >150 kpc. All these unexpected positional and kinematic correlations strongly suggest that a substantial fraction of satellite galaxies are causally linked in their formation and evolution.

Trends in mobile satellite communication

Science.gov (United States)

Johannsen, Klaus G.; Bowles, Mike W.; Milliken, Samuel; Cherrette, Alan R.; Busche, Gregory C.

1993-01-01

Ever since the U.S. Federal Communication Commission opened the discussion on spectrum usage for personal handheld communication, the community of satellite manufacturers has been searching for an economically viable and technically feasible satellite mobile communication system. Hughes Aircraft Company and others have joined in providing proposals for such systems, ranging from low to medium to geosynchronous orbits. These proposals make it clear that the trend in mobile satellite communication is toward more sophisticated satellites with a large number of spot beams and onboard processing, providing worldwide interconnectivity. Recent Hughes studies indicate that from a cost standpoint the geosynchronous satellite (GEOS) is most economical, followed by the medium earth orbit satellite (MEOS) and then by the low earth orbit satellite (LEOS). From a system performance standpoint, this evaluation may be in reverse order, depending on how the public will react to speech delay and collision. This paper discusses the trends and various mobile satellite constellations in satellite communication under investigation. It considers the effect of orbital altitude and modulation/multiple access on the link and spacecraft design.

Shadow imaging of geosynchronous satellites

Science.gov (United States)

Douglas, Dennis Michael

Geosynchronous (GEO) satellites are essential for modern communication networks. If communication to a GEO satellite is lost and a malfunction occurs upon orbit insertion such as a solar panel not deploying there is no direct way to observe it from Earth. Due to the GEO orbit distance of ~36,000 km from Earth's surface, the Rayleigh criteria dictates that a 14 m telescope is required to conventionally image a satellite with spatial resolution down to 1 m using visible light. Furthermore, a telescope larger than 30 m is required under ideal conditions to obtain spatial resolution down to 0.4 m. This dissertation evaluates a method for obtaining high spatial resolution images of GEO satellites from an Earth based system by measuring the irradiance distribution on the ground resulting from the occultation of the satellite passing in front of a star. The representative size of a GEO satellite combined with the orbital distance results in the ground shadow being consistent with a Fresnel diffraction pattern when observed at visible wavelengths. A measurement of the ground shadow irradiance is used as an amplitude constraint in a Gerchberg-Saxton phase retrieval algorithm that produces a reconstruction of the satellite's 2D transmission function which is analogous to a reverse contrast image of the satellite. The advantage of shadow imaging is that a terrestrial based redundant set of linearly distributed inexpensive small telescopes, each coupled to high speed detectors, is a more effective resolved imaging system for GEO satellites than a very large telescope under ideal conditions. Modeling and simulation efforts indicate sub-meter spatial resolution can be readily achieved using collection apertures of less than 1 meter in diameter. A mathematical basis is established for the treatment of the physical phenomena involved in the shadow imaging process. This includes the source star brightness and angular extent, and the diffraction of starlight from the satellite

A statistical rain attenuation prediction model with application to the advanced communication technology satellite project. 3: A stochastic rain fade control algorithm for satellite link power via non linear Markow filtering theory

Science.gov (United States)

Manning, Robert M.

1991-01-01

The dynamic and composite nature of propagation impairments that are incurred on Earth-space communications links at frequencies in and above 30/20 GHz Ka band, i.e., rain attenuation, cloud and/or clear air scintillation, etc., combined with the need to counter such degradations after the small link margins have been exceeded, necessitate the use of dynamic statistical identification and prediction processing of the fading signal in order to optimally estimate and predict the levels of each of the deleterious attenuation components. Such requirements are being met in NASA's Advanced Communications Technology Satellite (ACTS) Project by the implementation of optimal processing schemes derived through the use of the Rain Attenuation Prediction Model and nonlinear Markov filtering theory.

The interaction of grammatical aspect and temporal distance in motion descriptions

Directory of Open Access Journals (Sweden)

Sarah eAnderson

2013-07-01

Full Text Available Grammatical aspect is known to shape event understanding. However, little is known about how it interacts with other important temporal information, such as recent and distant past. The current work uses computer-mouse tracking (Spivey, Grosjean, & Knoblich, 2005 to explore the interaction of aspect and temporal context. Participants in our experiment listened to past motion event descriptions that varied according to aspect (simple past, past progressive and temporal distance (recent past, distant past while viewing scenes with paths and implied destinations. Participants used a computer mouse to place characters into the scene to match event descriptions. Our results indicated that aspect and temporal context interact in interesting ways. When aspect placed emphasis on the ongoing details of the event and the temporal context was recent (thus, making fine details available in memory, this match between conditions elicited smoother and faster computer mouse movements than when conditions mismatched. Likewise, when aspect placed emphasis on the less-detailed end state of the event and temporal context was in the distant past (thus making fine details less available, this match between conditions also elicited smoother and faster computer mouse movements.

Coverage Extension via Side-Lobe Transmission in Multibeam Satellite System

OpenAIRE

Gharanjik, Ahmad; Kmieciak, Jarek; Shankar, Bhavani; Ottersten, Björn

2017-01-01

In this paper, we study feasibility of coverage extension of a multibeam satellite network by providing low-rate communications to terminals located outside the coverage of main beams. Focusing on the MEO satellite network, and using realistic link budgets from O3b networks, we investigate the performance of both forward and return-links for terminals stationed in the side lobes of the main beams. Particularly, multi-carrier transmission for forward-link and single carrier transmission for re...

Don’t stand so close to me: Psychopathy and the regulation of interpersonal distance

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Joana B. Vieira

2014-01-01

Full Text Available Psychopathy is characterized by callous-unemotional traits, such as reduced empathy and remorse, and a tendency toward deviant interpersonal behaviors. It has been suggested that subtle behavioral cues in individuals with high levels of psychopathic traits may betray their personality during interpersonal interactions, but little research has addressed what these clues might be. In this study, we investigated whether psychopathic traits predict interpersonal distance preferences, which have been previously linked to amygdala functioning. Forty-six healthy participants performed a behavioral task in which the distance they preferred to maintain between themselves and an experimenter was measured across a series of trials. Psychopathic traits, including Coldheartedness, Fearless Dominance, and Self-centered Impulsivity were assessed using the Psychopathic Personality Inventory-Revised (Lilienfeld & Widows, 2005. Results demonstrated that Coldheartedness predicted preferred interpersonal distance, with more coldhearted participants preferring shorter distances. These findings suggest that interpersonal distance preferences may signal psychopathic traits, particularly callousness, supporting accounts of amygdala dysfunction in psychopathy.

Satellite tracking of threatened species

Science.gov (United States)

Williams, M.; Lunsford, A.; Ellis, D.; Robinson, J.; Coronado, P.; Campbell, W.

1998-01-01

In 1990, a joint effort of two U.S. federal agencies, NASA Goddard Space Flight Center (GSFC) and the Patuxent Wildlife Research Center, began. We initially joined forces in a project that used satellite telemetry to discover the winter home of a tiny dwindling population of Siberian Cranes. Since then several projects have emerged, and a web site was created to follow some of these activities. This web site is called the Satellite Tracking of Threatened Species and its location is http://sdcd.gsfc.nasa.gov/ISTO/satellite_tracking. It describes the overall program, and links you to three subsections that describe the projects in more detail: Satellite Direct Readout, Birdtracks, and Birdworld.

Long distance signaling using axionlike particles

International Nuclear Information System (INIS)

Stancil, Daniel D.

2007-01-01

The possible existence of axionlike particles could lead to a new type of long-distance communication. In this work, basic antenna concepts are defined and a Friis-like equation is derived to facilitate long-distance link calculations. An example calculation is presented showing that communication over distances of 1000 km or more may be possible for m a aγγ >5x10 -8 GeV -1

Experiments of 10 Gbit/sec quantum stream cipher applicable to optical Ethernet and optical satellite link

Science.gov (United States)

Hirota, Osamu; Ohhata, Kenichi; Honda, Makoto; Akutsu, Shigeto; Doi, Yoshifumi; Harasawa, Katsuyoshi; Yamashita, Kiichi

2009-08-01

The security issue for the next generation optical network which realizes Cloud Computing System Service with data center" is urgent problem. In such a network, the encryption by physical layer which provide super security and small delay should be employed. It must provide, however, very high speed encryption because the basic link is operated at 2.5 Gbit/sec or 10 Gbit/sec. The quantum stream cipher by Yuen-2000 protocol (Y-00) is a completely new type random cipher so called Gauss-Yuen random cipher, which can break the Shannon limit for the symmetric key cipher. We develop such a cipher which has good balance of the security, speed and cost performance. In SPIE conference on quantum communication and quantum imaging V, we reported a demonstration of 2.5 Gbit/sec system for the commercial link and proposed how to improve it to 10 Gbit/sec. This paper reports a demonstration of the Y-00 cipher system which works at 10 Gbit/sec. A transmission test in a laboratory is tried to get the basic data on what parameters are important to operate in the real commercial networks. In addition, we give some theoretical results on the security. It is clarified that the necessary condition to break the Shannon limit requires indeed the quantum phenomenon, and that the full information theoretically secure system is available in the satellite link application.

Kagawa Satellite “STARS” in Shikoku

Science.gov (United States)

Nohmi, Masahiro; Yamamoto, Takeshi; Andatsu, Akira; Takagi, Yohei; Nishikawa, Yusuke; Kaneko, Takashi; Kunitom, Daisuke

The Space Tethered Autonomous Robotic Satellite (STARS) is being developed in Kagawa University, and it will be launched by the H-IIA rocket by Japan Aerospace Exploration Agency (JAXA) in summer 2008. STARS is the first satellite developed in Shikoku, and its specific characteristics are: (i) mother and daughter satellites, which have basic satellite system respectively, and those are launched at the same time; (ii) large space system more than 5m by extending tether; (iii) robotic system, the daughter satellite controls its arm link and the mother satellite controls tether extension. Development of STARS in Kagawa University demonstrates space technology in local community, which has been considered to be a national project. Also, it promotes popularization, enlightenment, and understanding of space technology in local area of the Kagawa prefecture and around it.

Formation of the satellites of the outer solar system - Sources of their atmospheres

International Nuclear Information System (INIS)

Coradini, A.; Cerroni, P.; Magni, G.; Federico, C.

1989-01-01

The present account of the current understanding of regular satellite systems' origins gives attention to the essential processes leading to current satellite configurations, proceeding on the concept that the presence of atmospheres is connected with the final phases of satellite formation. Four major formation stages are envisioned: (1) the disk phase, linking the formation of the primary body to that of the satellites; (2) the formation phase of intermediate-sized bodies; (3) the collisional evolution of planatesimals; and (4) a series of evolutionary phases linking the primordial phases to currently observed states, in which the internal composition and thermal history of the satellites are key factors in satellite atmosphere formation

Safe Laser Beam Propagation for Interplanetary Links

Science.gov (United States)

Wilson, Keith E.

2011-01-01

Ground-to-space laser uplinks to Earth–orbiting satellites and deep space probes serve both as a beacon and an uplink command channel for deep space probes and Earth-orbiting satellites. An acquisition and tracking point design to support a high bandwidth downlink from a 20-cm optical terminal on an orbiting Mars spacecraft typically calls for 2.5 kW of 1030-nm uplink optical power in 40 micro-radians divergent beams.2 The NOHD (nominal ocular hazard distance) of the 1030nm uplink is in excess of 2E5 km, approximately half the distance to the moon. Recognizing the possible threat of high power laser uplinks to the flying public and to sensitive Earth-orbiting satellites, JPL developed a three-tiered system at its Optical Communications Telescope Laboratory (OCTL) to ensure safe laser beam propagation through navigational and near-Earth space.

Modern Geometric Methods of Distance Determination

Science.gov (United States)

Thévenin, Frédéric; Falanga, Maurizio; Kuo, Cheng Yu; Pietrzyński, Grzegorz; Yamaguchi, Masaki

2017-11-01

Building a 3D picture of the Universe at any distance is one of the major challenges in astronomy, from the nearby Solar System to distant Quasars and galaxies. This goal has forced astronomers to develop techniques to estimate or to measure the distance of point sources on the sky. While most distance estimates used since the beginning of the 20th century are based on our understanding of the physics of objects of the Universe: stars, galaxies, QSOs, the direct measures of distances are based on the geometric methods as developed in ancient Greece: the parallax, which has been applied to stars for the first time in the mid-19th century. In this review, different techniques of geometrical astrometry applied to various stellar and cosmological (Megamaser) objects are presented. They consist in parallax measurements from ground based equipment or from space missions, but also in the study of binary stars or, as we shall see, of binary systems in distant extragalactic sources using radio telescopes. The Gaia mission will be presented in the context of stellar physics and galactic structure, because this key space mission in astronomy will bring a breakthrough in our understanding of stars, galaxies and the Universe in their nature and evolution with time. Measuring the distance to a star is the starting point for an unbiased description of its physics and the estimate of its fundamental parameters like its age. Applying these studies to candles such as the Cepheids will impact our large distance studies and calibration of other candles. The text is constructed as follows: introducing the parallax concept and measurement, we shall present briefly the Gaia satellite which will be the future base catalogue of stellar astronomy in the near future. Cepheids will be discussed just after to demonstrate the state of the art in distance measurements in the Universe with these variable stars, with the objective of 1% of error in distances that could be applied to our closest

Satellite teleradiology test bed for digital mammography

Science.gov (United States)

Barnett, Bruce G.; Dudding, Kathryn E.; Abdel-Malek, Aiman A.; Mitchell, Robert J.

1996-05-01

Teleradiology offers significant improvement in efficiency and patient compliance over current practices in traditional film/screen-based diagnosis. The increasing number of women who need to be screened for breast cancer, including those in remote rural regions, make the advantages of teleradiology especially attractive for digital mammography. At the same time, the size and resolution of digital mammograms are among the most challenging to support in a cost effective teleradiology system. This paper will describe a teleradiology architecture developed for use with digital mammography by GE Corporate Research and Development in collaboration with Massachusetts General Hospital under National Cancer Institute (NCI/NIH) grant number R01 CA60246-01. The testbed architecture is based on the Digital Imaging and Communications in Medicine (DICOM) standard, created by the American College of Radiology and National Electrical Manufacturers Association. The testbed uses several Sun workstations running SunOS, which emulate a rural examination facility connected to a central diagnostic facility, and uses a TCP-based DICOM application to transfer images over a satellite link. Network performance depends on the product of the bandwidth times the round- trip time. A satellite link has a round trip of 513 milliseconds, making the bandwidth-delay a significant problem. This type of high bandwidth, high delay network is called a Long Fat Network, or LFN. The goal of this project was to quantify the performance of the satellite link, and evaluate the effectiveness of TCP over an LFN. Four workstations have Sun's HSI/S (High Speed Interface) option. Two are connected by a cable, and two are connected through a satellite link. Both interfaces have the same T1 bandwidth (1.544 Megabits per second). The only difference was the round trip time. Even with large window buffers, the time to transfer a file over the satellite link was significantly longer, due to the bandwidth-delay. To

Satellite communication from user to user

Science.gov (United States)

Gern, Manfred

Satellite communication systems which allow a multitude of user-to-user, point-to-point, and multipoint connections, are presented. The bit rates are 64 kbit/sec and multiples, up to 1.92 Mbit/sec. If required, the ground-stations are installed at the customer's site or at suitable locations in order to serve several customers. However, technical requirements for station location have also to be fulfulled, in order to avoid interference with terrestrial radio services. The increasing number of participants to Satellite Multi Service and INTELSAT Business Services imposes the solution of the problem of communication using cheap techniques. The changes of the German Federal Post Office also permit the economic use of satellite radio techniques for short distances.

Distance to high-voltage power lines and risk of childhood leukemia--an analysis of confounding by and interaction with other potential risk factors.

Directory of Open Access Journals (Sweden)

Camilla Pedersen

Full Text Available We investigated whether there is an interaction between distance from residence at birth to nearest power line and domestic radon and traffic-related air pollution, respectively, in relation to childhood leukemia risk. Further, we investigated whether adjusting for potential confounders alters the association between distance to nearest power line and childhood leukemia. We included 1024 cases aged <15, diagnosed with leukemia during 1968-1991, from the Danish Cancer Registry and 2048 controls randomly selected from the Danish childhood population and individually matched by gender and year of birth. We used geographical information systems to determine the distance between residence at birth and the nearest 132-400 kV overhead power line. Concentrations of domestic radon and traffic-related air pollution (NOx at the front door were estimated using validated models. We found a statistically significant interaction between distance to nearest power line and domestic radon regarding risk of childhood leukemia (p = 0.01 when using the median radon level as cut-off point but not when using the 75th percentile (p = 0.90. We found no evidence of an interaction between distance to nearest power line and traffic-related air pollution (p = 0.73. We found almost no change in the estimated association between distance to power line and risk of childhood leukemia when adjusting for socioeconomic status of the municipality, urbanization, maternal age, birth order, domestic radon and traffic-related air pollution. The statistically significant interaction between distance to nearest power line and domestic radon was based on few exposed cases and controls and sensitive to the choice of exposure categorization and might, therefore, be due to chance.

Bit Error Rate Due to Misalignment of Earth Station Antenna Pointing to Satellite

Directory of Open Access Journals (Sweden)

Wahyu Pamungkas

2010-04-01

Full Text Available One problem causing reduction of energy in satellite communications system is the misalignment of earth station antenna pointing to satellite. Error in pointing would affect the quality of information signal to energy bit in earth station. In this research, error in pointing angle occurred only at receiver (Rx antenna, while the transmitter (Tx antennas precisely point to satellite. The research was conducted towards two satellites, namely TELKOM-1 and TELKOM-2. At first, measurement was made by directing Tx antenna precisely to satellite, resulting in an antenna pattern shown by spectrum analyzer. The output from spectrum analyzers is drawn with the right scale to describe swift of azimuth and elevation pointing angle towards satellite. Due to drifting from the precise pointing, it influenced the received link budget indicated by pattern antenna. This antenna pattern shows reduction of power level received as a result of pointing misalignment. As a conclusion, the increasing misalignment of pointing to satellite would affect in the reduction of received signal parameters link budget of down-link traffic.

Characterizing SPDY over High Latency Satellite Channels

Directory of Open Access Journals (Sweden)

Luca Caviglione

2014-12-01

Full Text Available The increasing complexity ofWeb contents and the growing diffusion of mobile terminals, which use wireless and satellite links to get access to the Internet, impose the adoption of more specialized protocols. In particular, we focus on SPDY, a novel protocol introduced by Google to optimize the retrieval of complex webpages, to manage large Round Trip Times and high packet losses channels. In this perspective, the paper characterizes SPDY over high latency satellite links, especially with the goal of understanding whether it could be an efficient solution to cope with performance degradations typically affecting Web 2.0 services. To this aim, we implemented an experimental set-up, composed of an ad-hoc proxy, a wireless link emulator, and an instrumented Web browser. The results clearly indicate that SPDY can enhance the performances in terms of loading times, and reduce the traffic fragmentation. Moreover, owing to its connection multiplexing architecture, SPDY can also mitigate the transport layer complexity, which is critical when in presence of Performance Enhancing Proxies usually deployed to isolate satellite trunks.

ARTutor—An Augmented Reality Platform for Interactive Distance Learning

Directory of Open Access Journals (Sweden)

Chris Lytridis

2018-01-01

Full Text Available Augmented Reality (AR has been used in various contexts in recent years in order to enhance user experiences in mobile and wearable devices. Various studies have shown the utility of AR, especially in the field of education, where it has been observed that learning results are improved. However, such applications require specialized teams of software developers to create and maintain them. In an attempt to solve this problem and enable educators to easily create AR content for existing textbooks, the ARTutor platform was developed. It consists of a web-based application that acts as an AR authoring tool, and an accompanying mobile application that is used to access and interact with the educational AR content. In addition, the ARTutor application allows students to ask questions verbally and receive answers based on the contents of the book. This means that the system is suitable for distance learning and promotes self-study and independent learning.

EFFECTS OF VOLUNTARY WHEEL RUNNING ON SATELLITE CELLS IN THE RAT PLANTARIS MUSCLE

Directory of Open Access Journals (Sweden)

Atsushi Kojima

2009-03-01

Full Text Available This study investigated the effects of voluntary wheel running on satellite cells in the rat plantaris muscle. Seventeen 5-week-old male Wistar rats were assigned to a control (n = 5 or training (n = 12 group. Each rat in the training group ran voluntarily in a running-wheel cage for 8 weeks. After the training period, the animals were anesthetized, and the plantaris muscles were removed, weighed, and analyzed immunohistochemically and biochemically. Although there were no significant differences in muscle weight or fiber area between the groups, the numbers of satellite cells and myonuclei per muscle fiber, percentage of satellite cells, and citrate synthase activity were significantly higher in the training group compared with the control group (p < 0.05. The percentage of satellite cells was also positively correlated with distance run in the training group (r = 0.61, p < 0.05. Voluntary running can induce an increase in the number of satellite cells without changing the mean fiber area in the rat plantaris muscle; this increase in satellite cell content is a function of distance run

Datasets related to in-land water for limnology and remote sensing applications: distance-to-land, distance-to-water, water-body identifier and lake-centre co-ordinates.

Science.gov (United States)

Carrea, Laura; Embury, Owen; Merchant, Christopher J

2015-11-01

Datasets containing information to locate and identify water bodies have been generated from data locating static-water-bodies with resolution of about 300 m (1/360 ∘ ) recently released by the Land Cover Climate Change Initiative (LC CCI) of the European Space Agency. The LC CCI water-bodies dataset has been obtained from multi-temporal metrics based on time series of the backscattered intensity recorded by ASAR on Envisat between 2005 and 2010. The new derived datasets provide coherently: distance to land, distance to water, water-body identifiers and lake-centre locations. The water-body identifier dataset locates the water bodies assigning the identifiers of the Global Lakes and Wetlands Database (GLWD), and lake centres are defined for in-land waters for which GLWD IDs were determined. The new datasets therefore link recent lake/reservoir/wetlands extent to the GLWD, together with a set of coordinates which locates unambiguously the water bodies in the database. Information on distance-to-land for each water cell and the distance-to-water for each land cell has many potential applications in remote sensing, where the applicability of geophysical retrieval algorithms may be affected by the presence of water or land within a satellite field of view (image pixel). During the generation and validation of the datasets some limitations of the GLWD database and of the LC CCI water-bodies mask have been found. Some examples of the inaccuracies/limitations are presented and discussed. Temporal change in water-body extent is common. Future versions of the LC CCI dataset are planned to represent temporal variation, and this will permit these derived datasets to be updated.

Conceptual design of a synchronous Mars telecommunications satellite

Science.gov (United States)

Badi, Deborah M.; Farmer, Jeffrey T.; Garn, Paul A.; Martin, Gary L.

1989-01-01

Future missions to Mars will require a communications system to link activities on the Martian surface with each other and with mission controllers on Earth. A conceptual design is presented for an aerosynchronous communications satellite to provide these links. The satellite provides the capability for voice, data/command, and video transmissions. The mission scenario assumed for the design is described, and a description of a single aerosynchronous satellite is explained. A viable spacecraft design is then presented. Communication band selection and channel allocation are discussed. The communications system conceptual design is presented along with the trades used in sizing each of the required antennas. Also, the analyses used to develop the supporting subsystem designs are described as is the communications impact on each subsystem design.

Network Performance Evaluation of Abis Interface over DVB-S2 in the GSM over Satellite Network

Directory of Open Access Journals (Sweden)

S. B. Musabekov

2010-01-01

Full Text Available This paper deals with establishing a GSM link over Satellite. Abis interface, which is defined between Base Transceiver Station (BTS and Base Station Controller (BSC, in a GSM network is considered here to be routed over the Satellite. The satellite link enables a quick and cost-effective GSM link in meagerly populated areas. A different scenario comparison was done to understand the impact of Satellite environment on network availability comparing to terrestrial scenario. We have implemented an Abis interface over DVB S2 in NS2 and evaluated the performance over the high delay and loss satellite channel. Network performance was evaluated with respect to Satellite channel delay and DVB S2 encapsulation efficiency under different amount of user traffic and compared with the terrestrial scenario. The results clearly showed an increased amount of SDCCH and TCH channels required in the case of satellite scenario for the same amount of traffic in comparison to conventional terrestrial scenario. We have optimized the parameters based on the simulation results. Link budget estimation considering DVB-S2 platform was done to find satellite bandwidth and cost requirements for different network setups.

Peculiarities of the ionosphere monitoring from low-flying satellites

International Nuclear Information System (INIS)

Danilkin, N.P.; Denisenko, P.F.; Mal'tseva, O.A.

1998-01-01

Peculiarities of the HF-radiowave propagation between ground stations and low-flying satellites near and below the maximum of the F area are studied through the method of mathematical modeling. It is established that the signal may propagate by three trajectories. The first one is below the satellite orbit. The turn altitudes of the second and the third beams are above the satellite orbit. Availability of three trajectories leads to the three-digit dependence of the group ways on the working frequency F. The P(f) curves for different satellite distances from a reception point and its orbit altitudes for the isotropic and magnetoactive ionosphere are presented

Current Trends and Challenges in Satellite Laser Ranging

Science.gov (United States)

Appleby, Graham M.; Bianco, Giuseppe; Noll, Carey E.; Pavlis, Erricos C.; Pearlman, Michael R.

2016-12-01

Satellite Laser Ranging (SLR) is used to measure accurately the distance from ground stations to retro-reflectors on satellites and on the Moon. SLR is one of the fundamental space-geodetic techniques that define the International Terrestrial Reference Frame (ITRF), which is the basis upon which many aspects of global change over space, time, and evolving technology are measured; with VLBI the two techniques define the scale of the ITRF; alone the SLR technique defines its origin (geocenter). The importance of the reference frame has recently been recognized at the inter-governmental level through the United Nations, which adopted in February 2015 the Resolution "Global Geodetic Reference Frame for Sustainable Development." Laser Ranging provides precision orbit determination and instrument calibration and validation for satellite-borne altimeters for the better understanding of sea level change, ocean dynamics, ice mass-balance, and terrestrial topography. It is also a tool to study the dynamics of the Moon and fundamental constants and theories. With the exception of the currently in-orbit GPS constellation, all GNSS satellites now carry retro-reflectors for improved orbit determination, harmonization of reference frames, and in-orbit co-location and system performance validation; the next generation of GPS satellites due for launch from 2019 onwards will also carry retro-reflectors. The ILRS delivers weekly realizations that are accumulated sequentially to extend the ITRF and the Earth Orientation Parameter series with a daily resolution. SLR technology continues to evolve towards the next-generation laser ranging systems and it is expected to successfully meet the challenges of the GGOS2020 program for a future Global Space Geodetic Network. Ranging precision is improving as higher repetition rate, narrower pulse lasers, and faster detectors are implemented within the network. Automation and pass interleaving at some stations is expanding temporal coverage and

Plasma satellites of X-ray spectral lines of ions in a plasma of solid-state targets, heated by a picosecond laser pulse

International Nuclear Information System (INIS)

Belyaev, V.S.; Vinogradov, V.I.; Kurilov, A.S.; Matafonov, A.P.; Lisitsa, V.S.; Gavrilenko, V.P.; Faenov, A.Ya.; Pikuz, T.A.; Skobelev, I.Yu.; Magunov, A.I.; Pikuz, S.A.

2003-01-01

The results of measuring the ions X-ray spectral lines by the interaction of the picosecond laser pulses with the solid-state target are presented. The spectra of the X-ray radiation were observed on the fluorine ion line. The spectral lines satellites, testifying to the availability, are identified. The position of the satellites and the distance between them make it possible to connect them with the intensive electrostatic oscillations with the amplitude, exceeding 10 8 V/cm, and the frequency close to 7 x 10 14 s -1 , substantially lower than the laser wave frequency. The experimental results are compared with the calculated data on the multicharge ions spectra [ru

Leo satellite-based telecommunication network concepts

Science.gov (United States)

Aiken, John G.; Swan, Peter A.; Leopold, Ray J.

1991-01-01

Design considerations are discussed for Low Earth Orbit (LEO) satellite based telecommunications networks. The satellites are assumed to be connected to each other via intersatellite links. They are connected to the end user either directly or through gateways to other networks. Frequency reuse, circuit switching, packet switching, call handoff, and routing for these systems are discussed by analogy with terrestrial cellular (mobile radio) telecommunication systems.

A cosmic ray-climate link and cloud observations

Directory of Open Access Journals (Sweden)

Dunne Eimear M.

2012-11-01

Full Text Available Despite over 35 years of constant satellite-based measurements of cloud, reliable evidence of a long-hypothesized link between changes in solar activity and Earth’s cloud cover remains elusive. This work examines evidence of a cosmic ray cloud link from a range of sources, including satellite-based cloud measurements and long-term ground-based climatological measurements. The satellite-based studies can be divided into two categories: (1 monthly to decadal timescale analysis and (2 daily timescale epoch-superpositional (composite analysis. The latter analyses frequently focus on sudden high-magnitude reductions in the cosmic ray flux known as Forbush decrease events. At present, two long-term independent global satellite cloud datasets are available (ISCCP and MODIS. Although the differences between them are considerable, neither shows evidence of a solar-cloud link at either long or short timescales. Furthermore, reports of observed correlations between solar activity and cloud over the 1983–1995 period are attributed to the chance agreement between solar changes and artificially induced cloud trends. It is possible that the satellite cloud datasets and analysis methods may simply be too insensitive to detect a small solar signal. Evidence from ground-based studies suggests that some weak but statistically significant cosmic ray-cloud relationships may exist at regional scales, involving mechanisms related to the global electric circuit. However, a poor understanding of these mechanisms and their effects on cloud makes the net impacts of such links uncertain. Regardless of this, it is clear that there is no robust evidence of a widespread link between the cosmic ray flux and clouds.

Reduced arctic tundra productivity linked with landform and climate change interactions

Science.gov (United States)

Lara, Mark J.; Nitze, Ingmar; Grosse, Guido; Martin, Philip; McGuire, A. David

2018-01-01

Arctic tundra ecosystems have experienced unprecedented change associated with climate warming over recent decades. Across the Pan-Arctic, vegetation productivity and surface greenness have trended positively over the period of satellite observation. However, since 2011 these trends have slowed considerably, showing signs of browning in many regions. It is unclear what factors are driving this change and which regions/landforms will be most sensitive to future browning. Here we provide evidence linking decadal patterns in arctic greening and browning with regional climate change and local permafrost-driven landscape heterogeneity. We analyzed the spatial variability of decadal-scale trends in surface greenness across the Arctic Coastal Plain of northern Alaska (~60,000 km²) using the Landsat archive (1999–2014), in combination with novel 30 m classifications of polygonal tundra and regional watersheds, finding landscape heterogeneity and regional climate change to be the most important factors controlling historical greenness trends. Browning was linked to increased temperature and precipitation, with the exception of young landforms (developed following lake drainage), which will likely continue to green. Spatiotemporal model forecasting suggests carbon uptake potential to be reduced in response to warmer and/or wetter climatic conditions, potentially increasing the net loss of carbon to the atmosphere, at a greater degree than previously expected.

Multi-core fiber amplifier arrays for intra-satellite links

Science.gov (United States)

Kechagias, Marios; Crabb, Jonathan; Stampoulidis, Leontios; Farzana, Jihan; Kehayas, Efstratios; Filipowicz, Marta; Napierala, Marek; Murawski, Michal; Nasilowski, Tomasz; Barbero, Juan

2017-09-01

In this paper we present erbium doped fibre (EDF) aimed at signal amplification within satellite photonic payload systems operating in C telecommunication band. In such volume-hungry applications, the use of advanced optical transmission techniques such as space division multiplexing (SDM) can be advantageous to reduce the component and cable count.

Different types of interactions of links in artificial and natural ecosystems under anthropogenic pressure

Science.gov (United States)

Somova, Lydia; Pisman, Tamara; Mikheeva, Galina; Pechurkin, Nickolay

The life of organisms in an ecosystem depends not only on abiotic factors, but also on the interaction of organisms in which they come with each other. The study of mechanisms of the bioregulation based on ecological - biochemical interactions of ecosystem links is necessary to know the ecosystem development, its stability, survival of ecosystem organisms. It is of high importance as for the creation of artificial ecosystems, and also for the study of natural ecosystems under anthropogenic pressure on them. To create well-functioning ecosystems is necessary to study and consider the basic types of relationships between organisms. The basic types of interactions between organisms have been studied with simple terrestrial and water ecosystems. 1. The interaction of microbiocenoses and plants were studied in experiments with agrocenoses. Microbiocenosis proposed for increase of productivity of plants and for obtaining ecologically pure production of plants has been created taking into account mutual relationships between species of microorganisms. 2. The experimental model of the atmosphere closed «autotroph - heterotroph» system in which heterotrophic link was the mixed population of yeasts (Candida utilis and Candida guilliermondii) was studied. The algae Chlorella vulgaris was used as an autotroph link. It was shown, that the competition result for heterotrophic link depended on strategy of populations of yeast in relation to a substrate and oxygen utilization. 3. As a result of experimental and theoretical modelling of a competition of algae Chlorella vulgaris and Scenedesmus quadricauda at continuous cultivation, the impossibility of their coexistence in the conditions of limitation on nitrogen was shown. 4. Pray-predator interactions between algae (Chlorella vulgaris, Scenedesmus quadricauda) and invertebrates (Paramecium caudatum, Brachionus plicatilis) were studied in experimental closed ecosystem. This work was partly supported by the Russian Foundation for

Influence of effective electron interaction on critical current of Josephson weak links

International Nuclear Information System (INIS)

Kupriyanov, M.Yu.; Likharev, K.K.; Lukichev, V.F.

1981-01-01

On the basis of microscopic theory of superconductivity, the dc Josphson effect in weak links of the type of variable thickness bridges or high ohmic interlayer sandwiches is studied. The Isub(C)Rsub(N) product is calculatied as a function of temperature T and weak link length L for various amplitudes and both signs of effective electron-electron interaction constant lambda. If the weak link material is superconducting with critical temperature Tsub(C) > 0 (lambda > 0), the maximum value of Isub(C)Rsub(N) product (under condition of the singlevalued Isub(S)(phi) relationship) can be achieved at L approx. <= 3xisup(*) when Tsub(C) approx. <= Tsub(CS)/2, and at L=(4 / 6)xisup(*) when Tsub(C) = Tsub(CS). Electron repulsion inside the weak link (lambda < 0) results in some reduction of the Isub(C)Rsub(N) product in comparison with the case of 'really normal' weak link material (lambda = 0). (orig.)

Use of the Advanced Communications Technology Satellite to Promote International Distance Education Programs for Georgetown University

Science.gov (United States)

Bradley, Harold; Kauffman, Amy

1996-01-01

Georgetown's distance education program is designed to demonstrate to faculty and administrators the feasibility and desirability of using two-way video transmission for international education. These programs will extend the reach of Georgetown's educational offerings; enrich the curriculum and content of Georgetown's offerings by interaction with institutions in other nations; enhance the world view of the School of Business Administration; enable Georgetown to share its resources with other institutions outside of the United States; and promote Commerce within the Americas. The primary reason for this pilot program is to evaluate the effectiveness and economic viability of offering academic courses and Small Business Development training.

Laser experiments in light cloudiness with the geostationary satellite ARTEMIS

Science.gov (United States)

Kuzkov, V.; Kuzkov, S.; Sodnik, Z.

2016-08-01

The geostationary satellite ARTEMIS was launched in July 2001. The satellite is equipped with a laser communication terminal, which was used for the world's first inter-satellite laser communication link between ARTEMIS and the low earth orbit satellite SPOT-4. Ground-to-space laser communication experiments were also conducted under various atmospheric conditions involving ESA's optical ground station. With a rapidly increasing volume of information transferred by geostationary satellites, there is a rising demand for high-speed data links between ground stations and satellites. For ground-to-space laser communications there are a number of important design parameters that need to be addressed, among them, the influence of atmospheric turbulence in different atmospheric conditions and link geometries. The Main Astronomical Observatory of NAS of Ukraine developed a precise computer tracking system for its 0.7 m AZT-2 telescope and a compact laser communication package LACES (Laser Atmosphere and Communication experiments with Satellites) for laser communication experiments with geostationary satellites. The specially developed software allows computerized tracking of the satellites using their orbital data. A number of laser experiments between MAO and ARTEMIS were conducted in partial cloudiness with some amount of laser light observed through clouds. Such conditions caused high break-up (splitting) of images from the laser beacon of ARTEMIS. One possible explanation is Raman scattering of photons on molecules of a water vapor in the atmosphere. Raman scattering causes a shift in a wavelength of the photons.In addition, a different value for the refraction index appears in the direction of the meridian for the wavelength-shifted photons. This is similar to the anomalous atmospheric refraction that appears at low angular altitudes above the horizon. We have also estimated the atmospheric attenuation and the influence of atmospheric turbulence on observed results

Solar array experiments on the Sphinx satellite

Science.gov (United States)

Stevens, N. J.

1973-01-01

The Space Plasma, High Voltage Interaction Experiment (SPHINX) is the name given to an auxiliary payload satellite scheduled to be launched in January 1974. The principal experiments carried on this satellite are specifically designed to obtain the engineering data on the interaction of high voltage systems with the space plasma. The classes of experiments are solar array segments, insulators, insulators with pin holes and conductors. The satellite is also carrying experiments to obtain flight data on three new solar array configurations; the edge illuminated-multijunction cells, the Teflon encased cells and the violet cells.

Measurement of distance parameter using semiclassical model in various heavy ion interactions

Energy Technology Data Exchange (ETDEWEB)

Nasir, Tabassum [Department of Physics, Gomal University D.I. Khan (Pakistan); Khan, E U [Department of Physics, CIIT, Islamabad (Pakistan); Baluch, J J [Department of Environmental Sciences, CIIT, Abbottabad (Pakistan); Qureshi, I E [Pakistan Atomic Energy Commission, P.O. Box 1114, Islamabad (Pakistan); Sajid, M; Shahzad, M I; Khan, H A [Physics Research Division, PINSTECH, P.O. Nilore, Islamabad (Pakistan)

2008-08-15

The technique of solid state nuclear track detection was employed to collect data of elastic scattering as well as inelastic reaction channel. The elastic data of the reactions {sup 238}U+{sup 209}Bi, {sup 238}U+{sup 197}Au, {sup 208}Pb+{sup 197}Au and {sup 197}Au+{sup 197}Au were used to calculate the experimental elastic scattering cross-sections for various angular bins. The ratio of these cross-sections to Rutherford/Mott cross-sections were plotted with respect to distance d({theta}). Distance parameter d{sub 0} in all four reactions was obtained from the discontinuity of the slope following the method suggested in the semiclassical model. Partial reaction cross-sections were also obtained from the inelastic binary as well as multiprong events in the heavy ion interactions of {sup 208}Pb+{sup 197}Au and {sup 197}Au+{sup 197}Au both at 11.67 MeV/u beam energy. The higher values of partial cross-sections of two prong inelastic events as compared with {sigma}{sub 3} and {sigma}{sub 4} have been attributed to the emission of intermediate mass fragments in both the reactions.

Survey and analysis of satellite-based telemedicine projects involving Japan and developing nations: investigation of transmission rates, channel numbers, and node numbers.

Science.gov (United States)

Nakajima, I; Natori, M; Takizawa, M; Kaihara, S

2001-01-01

We surveyed interactive telemedicine projects via telecommunications satellite (AMINE-PARTNERS, Post-PARTNERS, and Shinshu University Project using Inmarsat satellites) offered by Japan as assistance to developing countries. The survey helped clarify channel occupation time and data transfer rates. Using our survey results, we proposed an optimized satellite model with VSATs simulating the number of required channels and bandwidth magnitude. For future implementation of VSATs for medical use in developing nations, design of telecommunication channels should take into consideration TCP/IP-based operations. We calculated that one hub station with 30-76 VSATs in developing nation can be operated on bandwidth 6 Mbps using with 128 Kbps videoconferencing system for teleconsultation and teleconference, and linking with Internet.

Activities of Canadian Satellite Communications, Inc.

Science.gov (United States)

1992-12-01

Canadian Satellite Communications (Cancom) has as its core business the provision of television and radio signals to cable systems in Canada, with the objective of making affordable broadcast signals available to remote and/or small communities. Cancom also provides direct-to-home services to backyard receiving dishes, as well as satellite digital data business communications services, satellite business television, and satellite network services. Its business communication services range from satellite links for big-city businesses with small branch operations located far from major centers, to a mobile messaging and tracking system for the trucking industry. Revenues in 1992 totalled $48,212,000 and net income was just over $7 million. Cancom bought 10 percent interest in Leosat Corp. of Washington, DC, who are seeking approval to operate a position locator network from low-orbit satellites. Cancom has also become a partner in SovCan Star Satellite Communications Inc., which will build an international satellite system in partnership with Russia. The first satellite in this east-west business network will be placed in a Russian orbital slot over the Atlantic by 1996, and a second satellite will follow for the Pacific region. This annual report of Cancom's activities for 1992 includes financial statements and a six year financial review.

Ecosystem-groundwater interactions under changing land uses: Linking water, salts, and carbon across central Argentina

Science.gov (United States)

Jobbagy, E. G.; Nosetto, M. D.; Santoni, C. S.; Jackson, R. B.

2007-05-01

Although most ecosystems display a one-way connection with groundwater based on the regulation of deep water drainage (recharge), this link can become reciprocal when the saturated zone is shallow and plants take up groundwater (discharge). In what context is the reciprocal link most likely? How is it affected by land use changes? Has it consequences on salt and carbon cycling? We examine these questions across a precipitation gradient in the Pampas and Espinal of Argentina focusing on three vegetation change situations (mean annual rainfall): afforestation of humid (900-1300 mm) and subhumid grassland (700-900 mm/yr of rainfall), annual cultivation of subhumid grasslands (700-800 mm/yr), and annual cultivation of semiarid forests (500-700 mm). Humid and subhumid grasslands have shallow (measurements. Groundwater contributions enhance carbon uptake in plantations compared to grasslands as suggested by aboveground biomass measurements and satellite vegetation indexes from sites with and without access to groundwater. Where rainfall is 15 m deep) and recharge under natural conditions is null. The establishment of crops, however, triggers the onset of recharge, as evidenced by vadose zones getting wetter and leached of atmospheric chloride. Cropping may cause water table raises leading to a two-way coupling of ecosystems and groundwater in the future, as it has been documented for similar settings in Australia and the Sahel. In the Pampas land use change interacts with groundwater consumption leading to higher carbon uptake (humid and subhumid grasslands) and salt accumulation (subhumid grasslands). In the Espinal (semiarid forest) land use change currently involves a one-way effect on groundwater recharge that may switch to a reciprocal connection if regional water table raises occur. Neglecting the role of groundwater in flat sedimentary plains can obscure our understanding of carbon and salt cycling and curtail our attempts to sustain soil and water resources under

The Psychology of Psychic Distance

DEFF Research Database (Denmark)

Håkanson, Lars; Ambos, Björn; Schuster, Anja

2016-01-01

and their theoretical underpinnings assume psychic distances to be symmetric. Building on insights from psychology and sociology, this paper demonstrates how national factors and cognitive processes interact in the formation of asymmetric distance perceptions. The results suggest that exposure to other countries...

IceBridge GPS L0 Raw Satellite Navigation Data

Data.gov (United States)

National Aeronautics and Space Administration — The NASA IceBridge GPS L0 Raw Satellite Navigation Data (IPUTG0) data set contains GPS readings, including latitude, longitude, track, ground speed, off distance,...

Microprocessor-controlled CAMAC data link module

International Nuclear Information System (INIS)

Potter, J.M.

1978-05-01

Communication between the central control computer and remote, satellite data-acquisition/control stations at the Clinton P. Anderson Meson Physics Facility (LAMPF) is presently accomplished through the use of CAMAC-based Data Link modules. With the advent of the microprocessor, a new philosophy for digital data communications has evolved. Data Link modules containing microprocessor controllers provide link management and communication network protocol through algorithms executed in the Data Link microprocessor. 13 figures

Interactions between two superconducting weak links in the stationary (V = 0) states

International Nuclear Information System (INIS)

Way, Y.S.; Hsu, K.S.; Kao, Y.H.

1977-01-01

Effects of interaction between two superconducting weak links (SWL) at V = 0 have been calculated using the Ginzburg-Landau theory. Variations of the critical current of one SWL affected by dc current in a neighboring SWL are found in good qualitative agreement with a recent experiment. The current-phase relation of the combined system is computed for various separations between the two SWL7's; it is shown explicitly that the system behaves as a single SWL when the spacing between links is comparable to the coherence length

Concerning the mass of the suggested sixth satellite of Uranus

International Nuclear Information System (INIS)

Steigmann, G.A.

1979-01-01

Comparison of the strength of resonances arising from the known satellites of Uranus in the vicinity of the α and γ rings, with the strengths of probable resonances at the β and delta rings, suggest that the β and delta rings might be associated with an undiscovered satellite of mass approximately 0.4 mass of Miranda. This satellite is predicted to be a 17 to 18 mag object moving in a near-circular orbit, of low inclination to the plane of the rings, at a distance of 105 221 km from Uranus. (author)

Fine-tuning satellite-based rainfall estimates

Science.gov (United States)

Harsa, Hastuadi; Buono, Agus; Hidayat, Rahmat; Achyar, Jaumil; Noviati, Sri; Kurniawan, Roni; Praja, Alfan S.

2018-05-01

Rainfall datasets are available from various sources, including satellite estimates and ground observation. The locations of ground observation scatter sparsely. Therefore, the use of satellite estimates is advantageous, because satellite estimates can provide data on places where the ground observations do not present. However, in general, the satellite estimates data contain bias, since they are product of algorithms that transform the sensors response into rainfall values. Another cause may come from the number of ground observations used by the algorithms as the reference in determining the rainfall values. This paper describe the application of bias correction method to modify the satellite-based dataset by adding a number of ground observation locations that have not been used before by the algorithm. The bias correction was performed by utilizing Quantile Mapping procedure between ground observation data and satellite estimates data. Since Quantile Mapping required mean and standard deviation of both the reference and the being-corrected data, thus the Inverse Distance Weighting scheme was applied beforehand to the mean and standard deviation of the observation data in order to provide a spatial composition of them, which were originally scattered. Therefore, it was possible to provide a reference data point at the same location with that of the satellite estimates. The results show that the new dataset have statistically better representation of the rainfall values recorded by the ground observation than the previous dataset.

Air-sea interaction over the Indian Ocean during the two contrasting monsoon years 1987 and 1988 studied with satellite data

Digital Repository Service at National Institute of Oceanography (India)

RameshKumar, M.R.; Schluessel, P.

The air-sea interaction processes over the tropical Indian Ocean region are studied using sea surface temperature data from the Advanced Very High Resolution Radiometer sensor onboard the NOAA series of satellites. The columnar water-vapour content...

Coded throughput performance simulations for the time-varying satellite channel. M.S. Thesis

Science.gov (United States)

Han, LI

1995-01-01

The design of a reliable satellite communication link involving the data transfer from a small, low-orbit satellite to a ground station, but through a geostationary satellite, was examined. In such a scenario, the received signal power to noise density ratio increases as the transmitting low-orbit satellite comes into view, and then decreases as it then departs, resulting in a short-duration, time-varying communication link. The optimal values of the small satellite antenna beamwidth, signaling rate, modulation scheme and the theoretical link throughput (in bits per day) have been determined. The goal of this thesis is to choose a practical coding scheme which maximizes the daily link throughput while satisfying a prescribed probability of error requirement. We examine the throughput of both fixed rate and variable rate concatenated forward error correction (FEC) coding schemes for the additive white Gaussian noise (AWGN) channel, and then examine the effect of radio frequency interference (RFI) on the best coding scheme among them. Interleaving is used to mitigate degradation due to RFI. It was found that the variable rate concatenated coding scheme could achieve 74 percent of the theoretical throughput, equivalent to 1.11 Gbits/day based on the cutoff rate R(sub 0). For comparison, 87 percent is achievable for AWGN-only case.

Near or far? It depends on my impression: moral information and spatial behavior in virtual interactions.

Science.gov (United States)

Iachini, Tina; Pagliaro, Stefano; Ruggiero, Gennaro

2015-10-01

Near body distance is a key component of action and social interaction. Recent research has shown that peripersonal space (reachability-distance for acting with objects) and interpersonal space (comfort-distance for interacting with people) share common mechanisms and reflect the social valence of stimuli. The social psychological literature has demonstrated that information about morality is crucial because it affects impression formation and the intention to approach-avoid others. Here we explore whether peripersonal/interpersonal spaces are modulated by moral information. Thirty-six participants interacted with male/female virtual confederates described by moral/immoral/neutral sentences. The modulation of body space was measured by reachability-distance and comfort-distance while participants stood still or walked toward virtual confederates. Results showed that distance expanded with immorally described confederates and contracted with morally described confederates. This pattern was present in both spaces, although it was stronger in comfort-distance. Consistent with an embodied cognition approach, the findings suggest that high-level socio-cognitive processes are linked to sensorimotor-spatial processes. Copyright © 2015. Published by Elsevier B.V.

Probing the earth's gravity field by means of satellite-to-satellite tracking

Science.gov (United States)

Vonbun, F. O.

1977-01-01

Two satellite-to-satellite tracking (sst) tests are described in detail: (1) the ATS-6/Geos-3 and (2) the ATS-6/Apollo-Soyuz experiment. The main purpose of these two experiments was to track via ATS-6 the Geos-3, as well as the Apollo-Soyuz and to use these tracking data to determine both of the orbits at the same time, each of the orbits alone, and to test the two sst links to study local gravity anomalies. A second purpose was to test communications, command and data transmission from the ground via ATS-6 to these spacecraft and back again to the ground.

Molecular Dynamics Insights into Polyamine-DNA Binding Modes: Implications for Cross-Link Selectivity.

Science.gov (United States)

Bignon, Emmanuelle; Chan, Chen-Hui; Morell, Christophe; Monari, Antonio; Ravanat, Jean-Luc; Dumont, Elise

2017-09-18

Biogenic polyamines, which play a role in DNA condensation and stabilization, are ubiquitous and are found at millimolar concentration in the nucleus of eukaryotic cells. The interaction modes of three polyamines-putrescine (Put), spermine (Spm), and spermidine (Spd)-with a self-complementary 16 base pair (bp) duplex, are investigated by all-atom explicit-solvent molecular dynamics. The length of the amine aliphatic chain leads to a change of the interaction mode from minor groove binding to major groove binding. Through all-atom dynamics, noncovalent interactions that stabilize the polyamine-DNA complex and prefigure the reactivity, leading to the low-barrier formation of deleterious DNA-polyamine cross-links, after one-electron oxidation of a guanine nucleobase, are unraveled. The binding strength is quantified from the obtained trajectories by molecular mechanics generalized Born surface area post-processing (MM-GBSA). The values of binding free energies provide the same affinity order, Putdistances along the series of polyamines illustrate the selectivity towards deleterious DNA-polyamine cross-link formation through the extraction of average approaching distances between the C8 atom of guanines and the ammonium group. These results imply that the formation of DNA-polyamine cross-links involves deprotonation of the guanine radical cation to attack the polyamines, which must be positively charged to lie in the vicinity of the B-helix. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cross-link guided molecular modeling with ROSETTA.

Directory of Open Access Journals (Sweden)

Abdullah Kahraman

Full Text Available Chemical cross-links identified by mass spectrometry generate distance restraints that reveal low-resolution structural information on proteins and protein complexes. The technology to reliably generate such data has become mature and robust enough to shift the focus to the question of how these distance restraints can be best integrated into molecular modeling calculations. Here, we introduce three workflows for incorporating distance restraints generated by chemical cross-linking and mass spectrometry into ROSETTA protocols for comparative and de novo modeling and protein-protein docking. We demonstrate that the cross-link validation and visualization software Xwalk facilitates successful cross-link data integration. Besides the protocols we introduce XLdb, a database of chemical cross-links from 14 different publications with 506 intra-protein and 62 inter-protein cross-links, where each cross-link can be mapped on an experimental structure from the Protein Data Bank. Finally, we demonstrate on a protein-protein docking reference data set the impact of virtual cross-links on protein docking calculations and show that an inter-protein cross-link can reduce on average the RMSD of a docking prediction by 5.0 Å. The methods and results presented here provide guidelines for the effective integration of chemical cross-link data in molecular modeling calculations and should advance the structural analysis of particularly large and transient protein complexes via hybrid structural biology methods.

Space Weather: Linking Stellar Explosions to the Human Endeavor

Science.gov (United States)

Knipp, Delores

2017-06-01

Arguably humans have flourished as a result of stellar explosions; we are, after all, stardust. Nonetheless, rapid technology advances of the last 200 years sometimes put society and individuals on a collision course with the natural variability of stellar and solar atmospheres. Human space exploration, routine satellite navigation system applications, aviation safety, and electric power grids are examples of such vulnerable endeavors. In this presentation I will outline how global society relies on ‘normal’ solar and stellar emissions, yet becomes susceptible to extremes of these emissions. The imprints of these astronomical-terrestrial interactions abound. In particular, I will highlight ways in which stellar/solar bursts link with our space-atmosphere-interaction region, producing multi-year patterns in cosmic ray detection, gorgeous aurora, and deep concern for good order and function of global community.

ACTS for distance education in developing countries

Science.gov (United States)

Kalu, A.; Ventre, G.

1995-08-01

The need for electrical energy supply in the rural communities of developing countries has been well documented. Equally well known is the potential for photovoltaic in cost effectively meeting this need. A major impediment to fulfilling the need is the lack of indigenous personnel with a knowledgeof photovoltaic systems, and the associated infrastructure required to implement project. Various delivery schemes for providing the needed training to developing countries personnel have been investigated. Various train methods and programs that have been employed to remedy the problem have had significant drawbacks in terms of cost, consistency, impact, reach, and sustainability. The hypothesis to be tested in this project posits that satellite-based distance education using ACTS technologies can overcome these impediments. The purpose of the project is to investigate the applicability of the ACTS satellite in providing distance education in photovoltaic systems to developing countries and rural communities. An evaluation of the cost effectiveness of using ACTS unique technologies to overcome identified problems shall be done. The limitations of ACTS in surmounting distance education problems in developing countries shall be investigated. This project will, furthermore, provide training to Savannah State College faculty in photovoltaic (PV) systems and in distance education configurations and models. It will also produce training materials adequate for use in PV training programs via distance education. Savannah State College will, as a consequence become well equipped to play a leading role in the training of minority populations in photovoltaic systems and other renewables through its Center for Advanced Water Technology and Energy Systems. This communication provides the project outline including the specific issues that will be investigated during the project. Also presented i the project design which covers the participations of the various components of a network

Mapping turbidity in the Charles River, Boston using a high-resolution satellite.

Science.gov (United States)

Hellweger, Ferdi L; Miller, Will; Oshodi, Kehinde Sarat

2007-09-01

The usability of high-resolution satellite imagery for estimating spatial water quality patterns in urban water bodies is evaluated using turbidity in the lower Charles River, Boston as a case study. Water turbidity was surveyed using a boat-mounted optical sensor (YSI) at 5 m spatial resolution, resulting in about 4,000 data points. The ground data were collected coincidently with a satellite imagery acquisition (IKONOS), which consists of multispectral (R, G, B) reflectance at 1 m resolution. The original correlation between the raw ground and satellite data was poor (R2 = 0.05). Ground data were processed by removing points affected by contamination (e.g., sensor encounters a particle floc), which were identified visually. Also, the ground data were corrected for the memory effect introduced by the sensor's protective casing using an analytical model. Satellite data were processed to remove pixels affected by permanent non-water features (e.g., shoreline). In addition, water pixels within a certain buffer distance from permanent non-water features were removed due to contamination by the adjacency effect. To determine the appropriate buffer distance, a procedure that explicitly considers the distance of pixels to the permanent non-water features was applied. Two automatic methods for removing the effect of temporary non-water features (e.g., boats) were investigated, including (1) creating a water-only mask based on an unsupervised classification and (2) removing (filling) all local maxima in reflectance. After the various processing steps, the correlation between the ground and satellite data was significantly better (R2 = 0.70). The correlation was applied to the satellite image to develop a map of turbidity in the lower Charles River, which reveals large-scale patterns in water clarity. However, the adjacency effect prevented the application of this method to near-shore areas, where high-resolution patterns were expected (e.g., outfall plumes).

Can you go the distance? Attending the virtual classroom.

Science.gov (United States)

Bigony, Lorraine

2010-01-01

Distance learning via the World Wide Web offers convenience and flexibility. Online education connects nurses geographically in a manner that the traditional face-to-face learning environment lacks. Delivered in both a synchronous (real time interaction) or asynchronous (delayed interaction) format, distance programs continue to provide nurses with choice, especially in the pursuit of advanced degrees. This article explores the pros and cons of distance education, in addition to the most popular platform used in distance learning today, the Blackboard Academic Suite. Characteristics of the potential enrollee to ensure a successful distance education experience are also discussed. Distance nursing programs are here to stay. Although rigorous, the ease of accessibility makes distance learning a viable alternative for busy nurses.

A Communication Process: Electronic Media in Distance Education--A Review.

Science.gov (United States)

George, Donald; And Others

1989-01-01

Reviews the current use of electronic media in distance education, emphasizing Canadian examples. Examines broadcast television, videotape, satellite, telephone, radio, audiocassette, and computer. Discusses trends in media use and institutional development, focusing on education as communication and on the importance of combining different media.…

Experimental Satellite Phase 3D before Launch

Directory of Open Access Journals (Sweden)

J. Sebesta

1999-04-01

Full Text Available To build a satellite can be a dream for many engineers. We are happy that we can participate in the AMSAT PHASE 3D project. Our responsibility is very high because one of our on-board receivers is the main one of the command link and will never be switched off. The project is also a very good opportunity for our students to meet satellite technology.

The Use of a Satellite Human Interaction System in Conjunction with a Satellite Media Distribution System. Satellite Technology Demonstration, Technical Report No. 0217.

Science.gov (United States)

Dale, Joyce B.

Satellite Technology Demonstration (STD) was designed to provide data on the use of a satellite to deliver educational programs to 56 rural-isolated schools in eight Rocky Mountain States. Three series were broadcast: (1) a junior high school career development, (2) career development for public school administrators and teachers, and (3) topical…

Does Distance to Subsidiaries affect Headquarters Value Added?

DEFF Research Database (Denmark)

Nell, Phillip C.; Beugelsdijk, Sjoerd; Ambos, Björn

2014-01-01

How does distance between MNC headquarters and their subsidiaries affect the value added generated by headquarters? Integrating theories on spatial transaction costs with the headquarter view of the MNC, we link two types of distances, geographic distance and contextual distance, with headquarters...... value added. We test our hypotheses on an original dataset of 124 manufacturing subsidiaries in Europe. We find that the relation between distance and headquarters value added is conditional on the degree of subsidiaries’ external embeddedness. We find no direct effect of distance. The value added...... of headquarters is highest for subsidiaries that are not externally embedded in the host country and that operate at a large distance. It is lowest for locally responsive subsidiaries with high external embeddedness operating at a large distance. We discuss implications for the literature on headquarters-subsidiaries...

Error resilient H.264/AVC Video over Satellite for low Packet Loss Rates

DEFF Research Database (Denmark)

Aghito, Shankar Manuel; Forchhammer, Søren; Andersen, Jakob Dahl

2007-01-01

The performance of video over satellite is simulated. The error resilience tools of intra macroblock refresh and slicing are optimized for live broadcast video over satellite. The improved performance using feedback, using a cross- layer approach, over the satellite link is also simulated. The ne...

Soviet satellite communications science and technology

Energy Technology Data Exchange (ETDEWEB)

Birch, J.N.; Campanella, S.J.; Gordon, G.D.; McElroy, D.R.; Pritchard, W.L.; Stamminger, R.

1991-08-01

This is a report by six US scientists and engineers concerning the current state of the art and projections of future Soviet satellite communications technologies. The panel members are experts in satellite stabilization, spacecraft environments, space power generation, launch systems, spacecraft communications sciences and technologies, onboard processing, ground stations, and other technologies that impact communications. The panel assessed the Soviet ability to support high-data-rate space missions at 128 Mbps by evaluating current and projected Soviet satellite communications technologies. A variety of space missions were considered, including Earth-to-Earth communications via satellites in geostationary or highly elliptical orbits, those missions that require space-to-Earth communications via a direct path and those missions that require space-to-Earth communications via a relay satellite. Soviet satellite communications capability, in most cases, is 10 years behind that of the United States and other industrialized nations. However, based upon an analysis of communications links needed to support these missions using current Soviet capabilities, it is well within the current Soviet technology to support certain space missions outlined above at rates of 128 Mbps or higher, although published literature clearly shows that the Soviet Union has not exceeded 60 Mbps in its current space system. These analyses are necessary but not sufficient to determine mission data rates, and other technologies such as onboard processing and storage could limit the mission data rate well below that which could actually be supported via the communications links. Presently, the Soviet Union appears to be content with data rates in the low-Earth-orbit relay via geostationary mode of 12 Mbps. This limit is a direct result of power amplifier limits, spacecraft antenna size, and the utilization of K{sub u}-band frequencies. 91 refs., 16 figs., 15 tabs.

Satellite Control Laboratory

DEFF Research Database (Denmark)

Wisniewski, Rafal; Bak, Thomas

2001-01-01

The Satellite Laboratory at the Department of Control Engineering of Aalborg University (SatLab) is a dynamic motion facility designed for analysis and test of micro spacecraft. A unique feature of the laboratory is that it provides a completely gravity-free environment. A test spacecraft......-axis magnetometer, three piezoelectric gyros, and four reaction wheels in a tetrahedron configuration. The operation of the spacecraft is fully autonomous. The data flow between the transducers and the onboard computer placed physically outside the satellite is provided by a radio link. The purpose...... can be implemented in the laboratory, e.g. three-axis attitude control, slew manoeuvres, spins stabilization using magnetic actuation and/or reaction wheels. The spacecraft attitude can be determined applying magnetometer measurements....

A comparison of Hipparcos parallaxes with planetary nebulae spectroscopic distances

NARCIS (Netherlands)

Pottasch, [No Value; Acker, A

1998-01-01

The Hipparcos satellite has measured the parallax of a small sample of planetary nebulae. In this paper we consider the results for 3 planetary nebulae (PN) for which spectroscopic distances have also been determined from stellar gravities. These gravities in turn have been derived from profile

High-Velocity Cloud Complex H and Weaver's "Jet": Two candidate dwarf satellite galaxies for which dark matter halo models indicate distances of ~27 kpc and ~108 kpc

Science.gov (United States)

Simonson, S. Christian

2018-04-01

Two anomalous-velocity H I features, High-Velocity Cloud Complex H (HVC H) (Blitz et al. 1999), and Weaver's "jet" (Weaver 1974), appear to be good candidates for dwarf satellites. In this work they are modeled as H I disks in dark matter halos that move in 3D orbits in the combined time-dependent gravitational fields of the Milky Way and M31. As they orbit in the Local Group they develop tidal distortions and produce debris. The current l,b,V appearance of the tidal features as they approach the Milky Way indicate distances of 27 ± 9 kpc for HVC H and 108 ± 36 kpc for Weaver's "jet". As these are within the distances to known Milky Way satellites, finding stellar components would be of interest for the star formation history of the Milky Way. This work uses recent Hubble Space Telescope results on M31 (van der Marel et al. 2012) to calculate the center-of-mass (COM) locations and the dark matter mass distributions of the Milky-Way—M31 system since the Big Bang. Time-dependent COM orbits of the satellites have been computed in 3D, along with rings of test particles representing their disks. Tidal effects that develop on these rings have been compared with published 21-cm line data from Lockman (2003) and Simonson (1975). For HVC H at l = 130.5°, b = +1.5°, V = -200 km/s, the dark matter mass (in solar masses) is estimated as 5.2 ± 3.5E8. The previously estimated H I mass is 6.4E6, or 1.2% of the newly derived satellite mass. For Weaver's "jet", which covers 2° by 7° at l = 197.3°, b = +2.1°, V = -30 to -87 km/s, the dark matter mass is estimated as 1.8 ± 0.6E9. The H I mass is 1.8 ± 1.1E8, or 6% to 12% of the satellite mass. In the case of HVC H, owing to its disk angle of 45°, tidal debris is thrown upward. This would presumably contribute to a halo star stream. In the case of Weaver's "jet", the streamer represents accreting material for the disk. I am grateful to Leo Blitz for bringing Lockman's work on HVC H to my attention and for many helpful

Satellite-Relayed Intercontinental Quantum Network.

Science.gov (United States)

Liao, Sheng-Kai; Cai, Wen-Qi; Handsteiner, Johannes; Liu, Bo; Yin, Juan; Zhang, Liang; Rauch, Dominik; Fink, Matthias; Ren, Ji-Gang; Liu, Wei-Yue; Li, Yang; Shen, Qi; Cao, Yuan; Li, Feng-Zhi; Wang, Jian-Feng; Huang, Yong-Mei; Deng, Lei; Xi, Tao; Ma, Lu; Hu, Tai; Li, Li; Liu, Nai-Le; Koidl, Franz; Wang, Peiyuan; Chen, Yu-Ao; Wang, Xiang-Bin; Steindorfer, Michael; Kirchner, Georg; Lu, Chao-Yang; Shu, Rong; Ursin, Rupert; Scheidl, Thomas; Peng, Cheng-Zhi; Wang, Jian-Yu; Zeilinger, Anton; Pan, Jian-Wei

2018-01-19

We perform decoy-state quantum key distribution between a low-Earth-orbit satellite and multiple ground stations located in Xinglong, Nanshan, and Graz, which establish satellite-to-ground secure keys with ∼kHz rate per passage of the satellite Micius over a ground station. The satellite thus establishes a secure key between itself and, say, Xinglong, and another key between itself and, say, Graz. Then, upon request from the ground command, Micius acts as a trusted relay. It performs bitwise exclusive or operations between the two keys and relays the result to one of the ground stations. That way, a secret key is created between China and Europe at locations separated by 7600 km on Earth. These keys are then used for intercontinental quantum-secured communication. This was, on the one hand, the transmission of images in a one-time pad configuration from China to Austria as well as from Austria to China. Also, a video conference was performed between the Austrian Academy of Sciences and the Chinese Academy of Sciences, which also included a 280 km optical ground connection between Xinglong and Beijing. Our work clearly confirms the Micius satellite as a robust platform for quantum key distribution with different ground stations on Earth, and points towards an efficient solution for an ultralong-distance global quantum network.

Satellite-Relayed Intercontinental Quantum Network

Science.gov (United States)

Liao, Sheng-Kai; Cai, Wen-Qi; Handsteiner, Johannes; Liu, Bo; Yin, Juan; Zhang, Liang; Rauch, Dominik; Fink, Matthias; Ren, Ji-Gang; Liu, Wei-Yue; Li, Yang; Shen, Qi; Cao, Yuan; Li, Feng-Zhi; Wang, Jian-Feng; Huang, Yong-Mei; Deng, Lei; Xi, Tao; Ma, Lu; Hu, Tai; Li, Li; Liu, Nai-Le; Koidl, Franz; Wang, Peiyuan; Chen, Yu-Ao; Wang, Xiang-Bin; Steindorfer, Michael; Kirchner, Georg; Lu, Chao-Yang; Shu, Rong; Ursin, Rupert; Scheidl, Thomas; Peng, Cheng-Zhi; Wang, Jian-Yu; Zeilinger, Anton; Pan, Jian-Wei

2018-01-01

We perform decoy-state quantum key distribution between a low-Earth-orbit satellite and multiple ground stations located in Xinglong, Nanshan, and Graz, which establish satellite-to-ground secure keys with ˜kHz rate per passage of the satellite Micius over a ground station. The satellite thus establishes a secure key between itself and, say, Xinglong, and another key between itself and, say, Graz. Then, upon request from the ground command, Micius acts as a trusted relay. It performs bitwise exclusive or operations between the two keys and relays the result to one of the ground stations. That way, a secret key is created between China and Europe at locations separated by 7600 km on Earth. These keys are then used for intercontinental quantum-secured communication. This was, on the one hand, the transmission of images in a one-time pad configuration from China to Austria as well as from Austria to China. Also, a video conference was performed between the Austrian Academy of Sciences and the Chinese Academy of Sciences, which also included a 280 km optical ground connection between Xinglong and Beijing. Our work clearly confirms the Micius satellite as a robust platform for quantum key distribution with different ground stations on Earth, and points towards an efficient solution for an ultralong-distance global quantum network.

Understanding and Analyzing Latency of Near Real-time Satellite Data

Science.gov (United States)

Han, W.; Jochum, M.; Brust, J.

2016-12-01

Acquiring and disseminating time-sensitive satellite data in a timely manner is much concerned by researchers and decision makers of weather forecast, severe weather warning, disaster and emergency response, environmental monitoring, and so on. Understanding and analyzing the latency of near real-time satellite data is very useful and helpful to explore the whole data transmission flow, indentify the possible issues, and connect data providers and users better. The STAR (Center for Satellite Applications and Research of NOAA) Central Data Repository (SCDR) is a central repository to acquire, manipulate, and disseminate various types of near real-time satellite datasets to internal and external users. In this system, important timestamps, including observation beginning/end, processing, uploading, downloading, and ingestion, are retrieved and organized in the database, so the time length of each transmission phase can be figured out easily. Open source NoSQL database MongoDB is selected to manage the timestamp information because of features of dynamic schema, aggregation and data processing. A user-friendly user interface is developed to visualize and characterize the latency interactively. Taking the Himawari-8 HSD (Himawari Standard Data) file as an example, the data transmission phases, including creating HSD file from satellite observation, uploading the file to HimawariCloud, updating file link in the webpage, downloading and ingesting the file to SCDR, are worked out from the above mentioned timestamps. The latencies can be observed by time of period, day of week, or hour of day in chart or table format, and the anomaly latencies can be detected and reported through the user interface. Latency analysis provides data providers and users actionable insight on how to improve the data transmission of near real-time satellite data, and enhance its acquisition and management.

Mobile Learning in Distance Education: Utility or Futility?

Science.gov (United States)

Koole, Marguerite; McQuilkin, Janice Letkeman; Ally, Mohamed

2010-01-01

Can mobile technology improve flexibility and quality of interaction for graduate students in distance programs? This paper reports the results of an innovative study exploring the usability, learning, and social interaction of mobile access to online course materials at a Canadian distance education university. Through a system called MobiGlam,…

Modification of the ''Coulomb'' interaction at small distances in finite quantum electrodynamics

International Nuclear Information System (INIS)

Manoukian, E.B.

1982-01-01

We investigate the ''Coulomb'' interaction in finite QED at small distances. By finite QED it is meant that we sum all photon self-energy subgraphs in renormalized QED and fix α, the renormalized fine-structure constant, as the (infinite order) zero of the Callan-Symanzik function: β(α) = 0/sup infinity/. We show that for mcVertical Barx-x 'Vertical Bar/h 1 and e 2 at x and x ', respectively, is given by V(Vertical Barx-x'Vertical Bar)approx. =(e 1 e 2 / 4πVertical Barx-x'Vertical Bar) [q 1 (α)-q 2 (α)mcVertical Barx-x'Vertical Bar / h+O(m 2 c 2 Vertical Barx-x'Vertical Bar 2 /h 2 )], where 1 1 (α) 2 (α)< infinity

Earth-Space Links and Fade-Duration Statistics

Science.gov (United States)

Davarian, Faramaz

1996-01-01

In recent years, fade-duration statistics have been the subject of several experimental investigations. A good knowledge of the fade-duration distribution is important for the assessment of a satellite communication system's channel dynamics: What is a typical link outage duration? How often do link outages exceeding a given duration occur? Unfortunately there is yet no model that can universally answer the above questions. The available field measurements mainly come from temperate climatic zones and only from a few sites. Furthermore, the available statistics are also limited in the choice of frequency and path elevation angle. Yet, much can be learned from the available information. For example, we now know that the fade-duration distribution is approximately lognormal. Under certain conditions, we can even determine the median and other percentiles of the distribution. This paper reviews the available data obtained by several experimenters in different parts of the world. Areas of emphasis are mobile and fixed satellite links. Fades in mobile links are due to roadside-tree shadowing, whereas fades in fixed links are due to rain attenuation.

L’interaction orale en présentiel et à distance : une étude de cas en classe de français

Directory of Open Access Journals (Sweden)

Gemma Delgar Farrés

2015-12-01

Full Text Available Dans cet article, nous analysons les différences qui existent entre l’interaction orale directe et l’interaction orale à distance à partir de l’enregistrement d’une tâche d’expression orale réalisée par deux groupes de deux étudiants de français d’un niveau B1 face à face et par visioconférence. Ces deux enregistrements ont été transcrits avec le logiciel CLAN du programme CHILDES et ce logiciel nous a permis de caractériser les deux types d’interaction orale au niveau des pauses, des répétitions, des reformulations, de la longueur des énoncés, de la richesse lexicale, etc. Notre objectif est l’étude de l’influence du dispositif dans la communication orale à distance en cours de français.

Congestion control and routing over satellite networks

Science.gov (United States)

Cao, Jinhua

) method and then develop a novel on-demand routing system named Cross Entropy Accelerated Ant Routing System (CEAARS) for regular constellation LEO satellite networks. By implementing simulations on an Iridium-like satellite network, we compare the proposed CEAARS algorithm with the two approaches to adaptive routing protocols on the Internet: distance-vector (DV) and link-state (LS), as well as with the original Cross Entropy Ant Routing System (CEARS). DV algorithms are based on distributed Bellman Ford algorithm, and LS algorithms are implementation of Dijkstras single source shortest path. The results show that CEAARS not only remarkably improves the convergence speed of achieving optimal or suboptimal paths, but also reduces the number of overhead ants (management packets).

Facebook Mediated Interaction and Learning in Distance Learning at Makerere University

Science.gov (United States)

Mayende, Godfrey; Muyinda, Paul Birevu; Isabwe, Ghislain Maurice Norbert; Walimbwa, Michael; Siminyu, Samuel Ndeda

2014-01-01

This paper reports on an investigation of the use of Facebook as a tool to mediate learning amongst distance learners at Makerere University, a dual-mode institution offering both conventional and distance learning programs. While conventional courses take 17 weeks in a semester, the distance learners come in for two residential sessions, each…

Probability of detecting marine predator-prey and species interactions using novel hybrid acoustic transmitter-receiver tags.

Directory of Open Access Journals (Sweden)

Laurie L Baker

Full Text Available Understanding the nature of inter-specific and conspecific interactions in the ocean is challenging because direct observation is usually impossible. The development of dual transmitter/receivers, Vemco Mobile Transceivers (VMT, and satellite-linked (e.g. GPS tags provides a unique opportunity to better understand between and within species interactions in space and time. Quantifying the uncertainty associated with detecting a tagged animal, particularly under varying field conditions, is vital for making accurate biological inferences when using VMTs. We evaluated the detection efficiency of VMTs deployed on grey seals, Halichoerus grypus, off Sable Island (NS, Canada in relation to environmental characteristics and seal behaviour using generalized linear models (GLM to explore both post-processed detection data and summarized raw VMT data. When considering only post-processed detection data, only about half of expected detections were recorded at best even when two VMT-tagged seals were estimated to be within 50-200 m of one another. At a separation of 400 m, only about 15% of expected detections were recorded. In contrast, when incomplete transmissions from the summarized raw data were also considered, the ratio of complete transmission to complete and incomplete transmissions was about 70% for distances ranging from 50-1000 m, with a minimum of around 40% at 600 m and a maximum of about 85% at 50 m. Distance between seals, wind stress, and depth were the most important predictors of detection efficiency. Access to the raw VMT data allowed us to focus on the physical and environmental factors that limit a transceiver's ability to resolve a transmitter's identity.

Support Services for Distance Education

Directory of Open Access Journals (Sweden)

Sandra Frieden

1999-01-01

Full Text Available The creation and operation of a distance education support infrastructure requires the collaboration of virtually all administrative departments whose activities deal with students and faculty, and all participating academic departments. Implementation can build on where the institution is and design service-oriented strategies that strengthen institutional support and commitment. Issues to address include planning, faculty issues and concerns, policies and guidelines, approval processes, scheduling, training, publicity, information-line operations, informational materials, orientation and registration processes, class coordination and support, testing, evaluations, receive site management, partnerships, budgets, staffing, library and e-mail support, and different delivery modes (microwave, compressed video, radio, satellite, public television/cable, video tape and online. The process is ongoing and increasingly participative as various groups on campus begin to get involved with distance education activities. The distance education unit must continuously examine and revise its processes and procedures to maintain the academic integrity and service excellence of its programs. It’s a daunting prospect to revise the way things have been done for many years, but each department has an opportunity to respond to new ways of serving and reaching students.

Linked data and user interaction

CERN Document Server

Cervone, H Frank

2015-01-01

This collection of research papers provides extensive information on deploying services, concepts, and approaches for using open linked data from libraries and other cultural heritage institutions. With a special emphasis on how libraries and other cultural heritage institutions can create effective end user interfaces using open, linked data or other datasets. These papers are essential reading for any one interesting in user interface design or the semantic web.

FORMATION OF MULTIPLE-SATELLITE SYSTEMS FROM LOW-MASS CIRCUMPLANETARY PARTICLE DISKS

International Nuclear Information System (INIS)

Hyodo, Ryuki; Ohtsuki, Keiji; Takeda, Takaaki

2015-01-01

Circumplanetary particle disks would be created in the late stage of planetary formation either by impacts of planetary bodies or disruption of satellites or passing bodies, and satellites can be formed by accretion of disk particles spreading across the Roche limit. Previous N-body simulation of lunar accretion focused on the formation of single-satellite systems from disks with large disk-to-planet mass ratios, while recent models of the formation of multiple-satellite systems from disks with smaller mass ratios do not take account of gravitational interaction between formed satellites. In the present work, we investigate satellite accretion from particle disks with various masses, using N-body simulation. In the case of accretion from somewhat less massive disks than the case of lunar accretion, formed satellites are not massive enough to clear out the disk, but can become massive enough to gravitationally shepherd the disk outer edge and start outward migration due to gravitational interaction with the disk. When the radial location of the 2:1 mean motion resonance of the satellite reaches outside the Roche limit, the second satellite can be formed near the disk outer edge, and then the two satellites continue outward migration while being locked in the resonance. Co-orbital satellites are found to be occasionally formed on the orbit of the first satellite. Our simulations also show that stochastic nature involved in gravitational interaction and collision between aggregates in the tidal environment can lead to diversity in the final mass and orbital architecture, which would be expected in satellite systems of exoplanets

Social Interaction in Self-Paced Distance Education

Science.gov (United States)

Anderson, Terry; Upton, Lorne; Dron, Jon; Malone, Judi; Poelhuber, Bruno

2015-01-01

In this paper we present a case study of a self-paced university course that was originally designed to support independent, self-paced study at distance. We developed a social media intervention, in design-based research terms, that allows these independent students to contribute archived content to enhance the course, to engage in discussions…

The gravitational law of social interaction

Science.gov (United States)

Levy, Moshe; Goldenberg, Jacob

2014-01-01

While a great deal is known about the topology of social networks, there is much less agreement about the geographical structure of these networks. The fundamental question in this context is: how does the probability of a social link between two individuals depend on the physical distance between them? While it is clear that the probability decreases with the distance, various studies have found different functional forms for this dependence. The exact form of the distance dependence has crucial implications for network searchability and dynamics: Kleinberg (2000) [15] shows that the small-world property holds if the probability of a social link is a power-law function of the distance with power -2, but not with any other power. We investigate the distance dependence of link probability empirically by analyzing four very different sets of data: Facebook links, data from the electronic version of the Small-World experiment, email messages, and data from detailed personal interviews. All four datasets reveal the same empirical regularity: the probability of a social link is proportional to the inverse of the square of the distance between the two individuals, analogously to the distance dependence of the gravitational force. Thus, it seems that social networks spontaneously converge to the exact unique distance dependence that ensures the Small-World property.

Satellite cluster flight using on-off cyclic control

Science.gov (United States)

Zhang, Hao; Gurfil, Pini

2015-01-01

Nano-satellite clusters and disaggregated satellites are new concepts in the realm of distributed satellite systems, which require complex cluster management - mainly regulating the maximal and minimal inter-satellite distances on time scales of years - while utilizing simple on-off propulsion systems. The simple actuators and long time scales require judicious astrodynamical modeling coupled with specialized orbit control. This paper offers a satellite cluster orbit control law which works for long time scales in a perturbed environment while utilizing fixed-magnitude thrusters. The main idea is to design a distributed controller which balances the fuel consumption among the satellites, thus mitigating the effect of differential drag perturbations. The underlying methodology utilizes a cyclic control algorithm based on a mean orbital elements feedback. Stability properties of the closed-loop cyclic control system do not adhere to the classical Lyapunov stability theory, so an effort is made to define and implement a suitable stability theory of noncompact equilibria sets. A state selection scheme is proposed for efficiently establishing a low Earth orbit cluster. Several simulations, including a real mission study, and several comparative investigations, are performed to show the strengths of the proposed control law.

Educating Laboratory Science Learners at a Distance Using Interactive Television

Science.gov (United States)

Reddy, Christopher

2014-01-01

Laboratory science classes offered to students learning at a distance require a methodology that allows for the completion of tactile activities. Literature describes three different methods of solving the distance laboratory dilemma: kit-based laboratory experience, computer-based laboratory experience, and campus-based laboratory experience,…

Web Transfer Over Satellites Being Improved

Science.gov (United States)

Allman, Mark

1999-01-01

Extensive research conducted by NASA Lewis Research Center's Satellite Networks and Architectures Branch and the Ohio University has demonstrated performance improvements in World Wide Web transfers over satellite-based networks. The use of a new version of the Hypertext Transfer Protocol (HTTP) reduced the time required to load web pages over a single Transmission Control Protocol (TCP) connection traversing a satellite channel. However, an older technique of simultaneously making multiple requests of a given server has been shown to provide even faster transfer time. Unfortunately, the use of multiple simultaneous requests has been shown to be harmful to the network in general. Therefore, we are developing new mechanisms for the HTTP protocol which may allow a single request at any given time to perform as well as, or better than, multiple simultaneous requests. In the course of study, we also demonstrated that the time for web pages to load is at least as short via a satellite link as it is via a standard 28.8-kbps dialup modem channel. This demonstrates that satellites are a viable means of accessing the Internet.

Small Satellite Transceiver for Launch Vehicles, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — NAL Research Corporation proposes to develop a small, light-weight, low-cost transceivers capable of establishing satellite communications links for telemetry and...

Examining Perceived Distance and Personal Authenticity as Mediators of the Effects of Ghost-Tweeting on Parasocial Interaction.

Science.gov (United States)

Cohen, Elizabeth L; Tyler, William J

2016-05-01

A number of high-profile public figures hire ghost-tweeters to post to their social media accounts on their behalf, but no research has examined how this social media practice can affect followers' feelings of connection to the public figures. College students (n = 132) participated in an online experiment to examine the effect of ghost-tweeting practices on parasocial interaction (PSI) with social media figures. Tweet authorship (use of a ghost-tweeter or not) was manipulated. Ghost-tweeting resulted in reduced PSI. Perceptions of distance, but not personal authenticity mediated this effect. However, authenticity and distance did serially mediate the relationship between ghost-tweeting and PSI. These findings shed light on the process of PSI with celebrities and other media figures on social network sites.

Satellite-to-ground radiowave propagation

CERN Document Server

Allnutt, JE

2011-01-01

This book is a follow up to the award winning first edition and is written as a comprehensive guide for those who need to obtain a working knowledge of radiowave propagation on satellite-to-ground links at frequencies above 1 GHz, and as a reference book for experts in the field.

VLBI Observations of Geostationary Satellites

Science.gov (United States)

Artz, T.; Nothnagel, A.; La Porta, L.

2013-08-01

For a consistent realization of a Global Geodetic Observing System (GGOS), a proper tie between the individual global reference systems used in the analysis of space-geodetic observations is a prerequisite. For instance, the link between the terrestrial, the celestial and the dynamic reference system of artificial Earth orbiters may be realized by Very Long O Baseline Interferometry (VLBI) observations of one or several satellites. In the preparation phase for a dedicated satellite mission, one option to realize this is using a geostationary (GEO) satellite emitting a radio signal in X-Band and/or S-Band and, thus, imitating a quasar. In this way, the GEO satellite can be observed by VLBI together with nearby quasars and the GEO orbit can, thus, be determined in a celestial reference frame. If the GEO satellite is, e.g., also equipped with a GNSS-type transmitter, a further tie between GNSS and VLBI may be realized. In this paper, a concept for the generation of a radio signal is shown. Furthermore, simulation studies for estimating the GEO position are presented with a GEO satellite included in the VLBI schedule. VLBI group delay observations are then simulated for the quasars as well as for the GEO satellite. The analysis of the simulated observations shows that constant orbit changes are adequately absorbed by estimated orbit parameters. Furthermore, the post-fit residuals are comparable to those from real VLBI sessions.

IceBridge GPS L0 Raw Satellite Navigation Data, Version 1

Data.gov (United States)

National Aeronautics and Space Administration — The NASA IceBridge GPS L0 Raw Satellite Navigation Data (IPUTG0) data set contains GPS readings, including latitude, longitude, track, ground speed, off distance,...

Two-way laser ranging and time transfer experiments between LOLA and an Earth-based satellite laser ranging station

Science.gov (United States)

Mao, D.; Sun, X.; Neumann, G. A.; Barker, M. K.; Mazarico, E. M.; Hoffman, E.; Zagwodzki, T. W.; Torrence, M. H.; Mcgarry, J.; Smith, D. E.; Zuber, M. T.

2017-12-01

Satellite Laser Ranging (SLR) has established time-of-flight measurements with mm precision to targets orbiting the Earth and the Moon using single-ended round-trip laser ranging to passive optical retro-reflectors. These high-precision measurements enable advances in fundamental physics, solar system dynamics. However, the received signal strength suffers from a 1/R4 decay, which makes it impractical for measuring distances beyond the Moon's orbit. On the other hand, for a two-way laser transponder pair, where laser pulses are both transmitted to and received from each end of the laser links, the signal strength at both terminals only decreases by 1/R2, thus allowing a greater range of distances to be covered. The asynchronous transponder concept has been previously demonstrated by a test in 2005 between the Mercury Laser Altimeter (MLA) aboard the MESSENGER (MErcury Surface, Space ENvironment, Geochemistry, and Ranging) spacecraft and NASA's Goddard Geophysical and Astronomical Observatory (GGAO) at a distance of ˜0.16 AU. In October 2013, regular two-way transponder-type range measurements were obtained over 15 days between the Lunar Laser Communication Demonstration (LLCD) aboard the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft and NASA's ground station at White Sands, NM. The Lunar Orbiter Laser Altimeter (LOLA) aboard the Lunar Reconnaissance Orbiter (LRO) provides us a unique capability to test time-transfer beyond near Earth orbit. Here we present results from two-way transponder-type experiments between LOLA and GGAO conducted in March 2014 and 2017. As in the time-transfer by laser link (T2L2) experiments between a ground station and an earth-orbiting satellite, LOLA and GGAO ranged to each other simultaneously in these two-way tests at lunar distance. We measured the time-of-flight while cross-referencing the spacecraft clock to the ground station time. On May 4th, 2017, about 20 minutes of two-way measurements were collected. The

Collocation mismatch uncertainties in satellite aerosol retrieval validation

Science.gov (United States)

Virtanen, Timo H.; Kolmonen, Pekka; Sogacheva, Larisa; Rodríguez, Edith; Saponaro, Giulia; de Leeuw, Gerrit

2018-02-01

Satellite-based aerosol products are routinely validated against ground-based reference data, usually obtained from sun photometer networks such as AERONET (AEROsol RObotic NETwork). In a typical validation exercise a spatial sample of the instantaneous satellite data is compared against a temporal sample of the point-like ground-based data. The observations do not correspond to exactly the same column of the atmosphere at the same time, and the representativeness of the reference data depends on the spatiotemporal variability of the aerosol properties in the samples. The associated uncertainty is known as the collocation mismatch uncertainty (CMU). The validation results depend on the sampling parameters. While small samples involve less variability, they are more sensitive to the inevitable noise in the measurement data. In this paper we study systematically the effect of the sampling parameters in the validation of AATSR (Advanced Along-Track Scanning Radiometer) aerosol optical depth (AOD) product against AERONET data and the associated collocation mismatch uncertainty. To this end, we study the spatial AOD variability in the satellite data, compare it against the corresponding values obtained from densely located AERONET sites, and assess the possible reasons for observed differences. We find that the spatial AOD variability in the satellite data is approximately 2 times larger than in the ground-based data, and the spatial variability correlates only weakly with that of AERONET for short distances. We interpreted that only half of the variability in the satellite data is due to the natural variability in the AOD, and the rest is noise due to retrieval errors. However, for larger distances (˜ 0.5°) the correlation is improved as the noise is averaged out, and the day-to-day changes in regional AOD variability are well captured. Furthermore, we assess the usefulness of the spatial variability of the satellite AOD data as an estimate of CMU by comparing the

Migratory herbivorous waterfowl track satellite-derived green wave index.

Directory of Open Access Journals (Sweden)

Mitra Shariatinajafabadi

Full Text Available Many migrating herbivores rely on plant biomass to fuel their life cycles and have adapted to following changes in plant quality through time. The green wave hypothesis predicts that herbivorous waterfowl will follow the wave of food availability and quality during their spring migration. However, testing this hypothesis is hampered by the large geographical range these birds cover. The satellite-derived normalized difference vegetation index (NDVI time series is an ideal proxy indicator for the development of plant biomass and quality across a broad spatial area. A derived index, the green wave index (GWI, has been successfully used to link altitudinal and latitudinal migration of mammals to spatio-temporal variations in food quality and quantity. To date, this index has not been used to test the green wave hypothesis for individual avian herbivores. Here, we use the satellite-derived GWI to examine the green wave hypothesis with respect to GPS-tracked individual barnacle geese from three flyway populations (Russian n = 12, Svalbard n = 8, and Greenland n = 7. Data were collected over three years (2008-2010. Our results showed that the Russian and Svalbard barnacle geese followed the middle stage of the green wave (GWI 40-60%, while the Greenland geese followed an earlier stage (GWI 20-40%. Despite these differences among geese populations, the phase of vegetation greenness encountered by the GPS-tracked geese was close to the 50% GWI (i.e. the assumed date of peak nitrogen concentration, thereby implying that barnacle geese track high quality food during their spring migration. To our knowledge, this is the first time that the migration of individual avian herbivores has been successfully studied with respect to vegetation phenology using the satellite-derived GWI. Our results offer further support for the green wave hypothesis applying to long-distance migrants on a larger scale.

Spatial and energy distributions of satellite-speed helium atoms reflected from satellite-type surfaces

International Nuclear Information System (INIS)

Liu, S.M.; Rodgers, W.E.; Knuth, E.L.

1977-01-01

Interactions of satellite-speed helium atoms (accelerated in an expansion from an arc-heated supersonic-molecular-beam source) with practical satellite surfaces have been investigated experimentally. The density and energy distributions of the scattered atoms were measured using a detection system developed for this study. This detection system includes (a) a target positioning mechanism, (b) a detector rotating mechanism, and (c) a mass spectrometer and/or a retarding-field energy analyzer. (Auth.)

Teaching and Learning Against all Odds: A Video-Based Study of Learner-to-Instructor Interaction in International Distance Education

Directory of Open Access Journals (Sweden)

Jean-Marie Muhirwa

2009-09-01

Full Text Available Distance education and information and communication technologies (ICTs have been marketed as cost-effective ways to rescue struggling educational institutions in developing countries, particularly in sub-Saharan Africa (SSA. This study uses classroom video analysis and follow-up interviews with teachers, students, and local tutors to analyse the interaction at a distance between learners in Mali and Burkina Faso and their French and Canadian instructors. Findings reveal multiple obstacles to quality interaction: frequent Internet disconnections, limited student access to computers, lack of instructor presence, ill-prepared local tutors, student unfamiliarity with typing and computer technology, ineffective technical support, poor social dynamics, learner-learner conflict, learner-instructor conflict, and student withdrawal and resignation. In light of the near death of the costly World Bank-initiated African Virtual University (AVU, this paper concludes by re-visiting the educational potential of traditional technologies, such as radio and video, to foster development in poor countries.

Distance-Based Tear Lactoferrin Assay on Microfluidic Paper Device Using Interfacial Interactions on Surface-Modified Cellulose.

Science.gov (United States)

Yamada, Kentaro; Henares, Terence G; Suzuki, Koji; Citterio, Daniel

2015-11-11

"Distance-based" detection motifs on microfluidic paper-based analytical devices (μPADs) allow quantitative analysis without using signal readout instruments in a similar manner to classical analogue thermometers. To realize a cost-effective and calibration-free distance-based assay of lactoferrin in human tear fluid on a μPAD not relying on antibodies or enzymes, we investigated the fluidic mobilities of the target protein and Tb(3+) cations used as the fluorescent detection reagent on surface-modified cellulosic filter papers. Chromatographic elution experiments in a tear-like sample matrix containing electrolytes and proteins revealed a collapse of attractive electrostatic interactions between lactoferrin or Tb(3+) and the cellulosic substrate, which was overcome by the modification of the paper surface with the sulfated polysaccharide ι-carrageenan. The resulting μPAD based on the fluorescence emission distance successfully analyzed 0-4 mg mL(-1) of lactoferrin in complex human tear matrix with a lower limit of detection of 0.1 mg mL(-1) by simple visual inspection. Assay results of 18 human tear samples including ocular disease patients and healthy volunteers showed good correlation to the reference ELISA method with a slope of 0.997 and a regression coefficient of 0.948. The distance-based quantitative signal and the good batch-to-batch fabrication reproducibility relying on printing methods enable quantitative analysis by simply reading out "concentration scale marks" printed on the μPAD without performing any calibration and using any signal readout instrument.

6/4 GHz band small capacity omni-use terminal satellite system

Science.gov (United States)

Masamura, T.; Inoue, T.

1983-03-01

This paper presents system outline and multiple access techniques for a domestic satellite communication system accommodating numerous small earth stations. Two kinds of earth stations are employed in this system, a small earth terminal (SET) and a master earth station (MES). There are 48 both way satellite channels using a 6/4 GHz band transponder whose e.i.r.p is about 62 dBm. The TDM (Time Division Multiplex) method is employed in the MES to SET link, and the SSMA (Spread Spectrum Multiple Access) method is used in the SET to MES link.

Problems in the links between scattering data and interaction potentials

Energy Technology Data Exchange (ETDEWEB)

Amos, K.

1995-10-01

The scattering function is of paramount importance in any approaches by which quantitative information on the interaction between colliding quantal systems of nuclear, atomic or molecular type, may be sought from measured, elastic scattering data. Therein there are two possible spectral parameters, the energy and the angular momentum. Most experimental results suggest use of fixed energy and variable angular momentum schemes. Such fixed energy data and their analyses are the subject of this report, with particular emphasis placed upon the problems of the link between data and the scattering function. 18 figs.

Problems in the links between scattering data and interaction potentials

International Nuclear Information System (INIS)

Amos, K.

1995-01-01

The scattering function is of paramount importance in any approaches by which quantitative information on the interaction between colliding quantal systems of nuclear, atomic or molecular type, may be sought from measured, elastic scattering data. Therein there are two possible spectral parameters, the energy and the angular momentum. Most experimental results suggest use of fixed energy and variable angular momentum schemes. Such fixed energy data and their analyses are the subject of this report, with particular emphasis placed upon the problems of the link between data and the scattering function. 18 figs

Distance Learning Courses on the Web: The Authoring Approach.

Science.gov (United States)

Santos, Neide; Diaz, Alicia; Bibbo, Luis Mariano

This paper proposes a framework for supporting the authoring process of distance learning courses. An overview of distance learning courses and the World Wide Web is presented. The proposed framework is then described, including: (1) components of the framework--a hypermedia design methodology for authoring the course, links to related Web sites,…

Leader-team complementarity: Exploring the interactive effects of leader personality traits and team power distance values on team processes and performance.

Science.gov (United States)

Hu, Jia; Judge, Timothy A

2017-06-01

Integrating the leader trait perspective with dominance complementarity theory, we propose team power distance as an important boundary condition for the indirect impact of leader extraversion, agreeableness, and conscientiousness on team performance through a team's potency beliefs and through relational identification with the leader. Using time-lagged, 3-source data from 71 teams, we found that leader extraversion had a positive indirect impact on team in-role and extrarole performance through relational identification, but only for high power distance teams; leader conscientiousness had a positive influence on team in-role performance through team potency, but only for high power distance teams; and leader agreeableness had a positive effect on team in-role and extrarole performance via relational identification and on team in-role performance via team potency, but only for low power distance teams. The findings address prior inconsistencies regarding the relationships between leader traits and team effectiveness, identify an important boundary condition and key team processes that bridge the links, and provide a deeper understanding of the role of leader traits in teams. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

High-speed optical feeder-link system using adaptive optics

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Arimoto, Yoshinori; Hayano, Yutaka; Klaus, Werner

1997-05-01

We propose a satellite laser communication system between a ground station and a geostationary satellite, named high- speed optical feeder link system. It is based on the application of (a) high-speed optical devices, which have been developed for ground-based high-speed fiber-optic communications, and (b) the adaptive optics which compensates wavefront distortions due to atmospheric turbulences using a real time feedback control. A link budget study shows that a system with 10-Gbps bit-rate are available assuming the state-of-the-art device performance of the Er-doped fiber amplifier. We further discuss preliminary measurement results of the atmospheric turbulence at the telescope site in Tokyo, and present current study on the design of the key components for the feeder-link laser transceiver.

Mexico and Asia-Pacific: proximities and distances of a long relationship

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José Luis León-Manríquez

2015-09-01

Full Text Available Mexico and Asia-Pacific have strong links and yet they keep their distance at a subjective level. This article analyses this complex relationship in order to identify the points of approchement and bilateral distancing from a historical perspective. The text analyses the economic, trade, political and multilateral links between Mexico and the main countries and regional organisations in the region of Asia-Pacific. It observes that, despite the economic emergence of Asia-Pacific in recent decades, Mexico alternates between periods of distancing and rapprochement. If it maintains this trend, Mexico will lose out on participating actively in the region where the most dynamic international relations in the 21st century are being formed.

Resolving the faint end of the satellite luminosity function for the nearest elliptical Centaurus A

Science.gov (United States)

Crnojevic, Denija

2014-10-01

We request HST/ACS imaging to follow up 15 new faint candidate dwarfs around the nearest elliptical Centaurus A (3.8 Mpc). The dwarfs were found via a systematic ground-based (Magellan/Megacam) survey out to ~150 kpc, designed to directly confront the "missing satellites" problem in a wholly new environment. Current Cold Dark Matter models for structure formation fail to reproduce the shallow slope of the satellite luminosity function in spiral-dominated groups for which dwarfs fainter than M_V<-14 have been surveyed (the Local Group and the nearby, interacting M81 group). Clusters of galaxies show a better agreement with cosmological predictions, suggesting an environmental dependence of the (poorly-understood) physical processes acting on the evolution of low mass galaxies (e.g., reionization). However, the luminosity function completeness for these rich environments quickly drops due to the faintness of the satellites and to the difficult cluster membership determination. We target a yet unexplored "intermediate" environment, a nearby group dominated by an elliptical galaxy, ideal due to its proximity: accurate (10%) distance determinations for its members can be derived from resolved stellar populations. The proposed observations of the candidate dwarfs will confirm their nature, group membership, and constrain their luminosities, metallicities, and star formation histories. We will obtain the first complete census of dwarf satellites of an elliptical down to an unprecedented M_V<-9. Our results will crucially constrain cosmological predictions for the faint end of the satellite luminosity function to achieve a more complete picture of the galaxy formation process.

Spin physics and inclusive processes at short distances

International Nuclear Information System (INIS)

Craigie, N.S.

1982-10-01

The following aspects of spin physics at short distances are studied: 1. the factorization theorem in perturbative QCD and helicity asymmetries in inclusive processes, 2. the effect of higher order radiative corrections on helicity asymmetries, 3. the higher order power mechanism and spin asymmetries, 4. difficulties in understanding transverse spin in perturbative QCD, 5. helicity asymmetries of short distances as a means of recognizing supersymmetric interactions. Experiments are suggested for the verification of theoretical conclusions. Although spin-physics at short distances is difficult to demonstrate experimentally it may provide a valuable tool to show how perturbative QCD operates in the presence of the non-perturbative hadronic structure. It may also prove valuable to show new interactions which might occur at very short distances

Long distance synchronization of mobile robots

NARCIS (Netherlands)

Alvarez Aguirre, A.; Nijmeijer, H.; Oguchi, T.

2010-01-01

This paper considers the long distance master-slave and mutual synchronization of unicycle-type mobile robots. The issues that arise when the elements of a robotic network are placed in different locations are addressed, specifically the time-delay induced by the communication channel linking the

Probing the earth's gravity field using Satellite-to-Satellite Tracking (SST)

Science.gov (United States)

Vonbun, F. O.

1976-01-01

Satellite-to-Satellite (SST) tests, namely: (a) the ATS-6/GEOS-3 and (b) the ATS-6/Apollo-Soyuz experiment and some of the results obtained are described. The main purpose of these two experiments was first to track via ATS-6 the GEOS-3 as well as the Apollo-Soyuz and to use these tracking data to determine (a) both orbits, that is, ATS-6, GEOS-3 and/or the Apollo-Soyuz orbits at the same time; (b) each of these orbits alone; and (c) test the ATS-6/GEOS-3 and/or Apollo-Soyuz SST link to study local gravity anomalies; and, second, to test communications, command, and data transmission from the ground via ATS-6 to these spacecraft and back again to the ground. The Apollo-Soyuz Geodynamics Experiment is discussed in some detail.

Optimization of Formaldehyde Cross-Linking for Protein Interaction Analysis of Non-Tagged Integrin β1

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Cordula Klockenbusch

2010-01-01

Full Text Available Formaldehyde cross-linking of protein complexes combined with immunoprecipitation and mass spectrometry analysis is a promising technique for analysing protein-protein interactions, including those of transient nature. Here we used integrin β1 as a model to describe the application of formaldehyde cross-linking in detail, particularly focusing on the optimal parameters for cross-linking, the detection of formaldehyde cross-linked complexes, the utility of antibodies, and the identification of binding partners. Integrin β1 was found in a high molecular weight complex after formaldehyde cross-linking. Eight different anti-integrin β1 antibodies were used for pull-down experiments and no loss in precipitation efficiency after cross-linking was observed. However, two of the antibodies could not precipitate the complex, probably due to hidden epitopes. Formaldehyde cross-linked complexes, precipitated from Jurkat cells or human platelets and analyzed by mass spectrometry, were found to be composed of integrin β1, α4 and α6 or β1, α6, α2, and α5, respectively.

Optimization of Formaldehyde Cross-Linking for Protein Interaction Analysis of Non-Tagged Integrin β1

Science.gov (United States)

Klockenbusch, Cordula; Kast, Juergen

2010-01-01

Formaldehyde cross-linking of protein complexes combined with immunoprecipitation and mass spectrometry analysis is a promising technique for analysing protein-protein interactions, including those of transient nature. Here we used integrin β1 as a model to describe the application of formaldehyde cross-linking in detail, particularly focusing on the optimal parameters for cross-linking, the detection of formaldehyde cross-linked complexes, the utility of antibodies, and the identification of binding partners. Integrin β1 was found in a high molecular weight complex after formaldehyde cross-linking. Eight different anti-integrin β1 antibodies were used for pull-down experiments and no loss in precipitation efficiency after cross-linking was observed. However, two of the antibodies could not precipitate the complex, probably due to hidden epitopes. Formaldehyde cross-linked complexes, precipitated from Jurkat cells or human platelets and analyzed by mass spectrometry, were found to be composed of integrin β1, α4 and α6 or β1, α6, α2, and α5, respectively. PMID:20634879

A study of 60 Gigahertz intersatellite link applications

Science.gov (United States)

Anzic, G.; Connolly, D. J.; Haugland, E. J.; Kosmahl, H. G.; Chitwood, J. S.

Applications of intersatellite links operating at 60 GHz are reviewed. Likely scenarios, ranging from transmission of moderate and high data rates over long distances to low data rates over short distances are examined. A limited parametric tradeoff is performed with system variables such as radiofrequency power, receiver noise temperature, link distance, data rate, and antenna size. Present status is discussed and projections are given for both electron tube and solid state transmitter technologies. Monolithic transmit and receive module technology, already under development at 20 to 30 GHz, is reviewed and its extension to 60 GHz, and possible applicability is discussed.

A study of 60 GHz intersatellite link applications

Science.gov (United States)

Anzic, G.; Connolly, D. J.; Haugland, E. J.; Kosmahl, H. G.; Chitwood, J. S.

Applications of intersatellite links operating at 60 GHz are reviewed. Likely scenarios, ranging from transmission of moderate and high data rates over long distances to low data rates over short distances are examined. A limited parametric tradeoff is performed with system variables such as radiofrequency power, receiver noise temperature, link distance, data rate, and antenna size. Present status is discussed and projections are given for both electron tube and solid state transmitter technologies. Monolithic transmit and receive module technology, already under development at 20 to 30 GHz, is reviewed and its extension to 60 GHz, and possible applicability is discussed.

A study of 60 Gigahertz intersatellite link applications

Science.gov (United States)

Anzic, G.; Connolly, D. J.; Haugland, E. J.; Kosmahl, H. G.; Chitwood, J. S.

1983-01-01

Applications of intersatellite links operating at 60 GHz are reviewed. Likely scenarios, ranging from transmission of moderate and high data rates over long distances to low data rates over short distances are examined. A limited parametric tradeoff is performed with system variables such as radiofrequency power, receiver noise temperature, link distance, data rate, and antenna size. Present status is discussed and projections are given for both electron tube and solid state transmitter technologies. Monolithic transmit and receive module technology, already under development at 20 to 30 GHz, is reviewed and its extension to 60 GHz, and possible applicability is discussed.

A study of 60 GHz intersatellite link applications

Science.gov (United States)

Anzic, G.; Connolly, D. J.; Haugland, E. J.; Kosmahl, H. G.; Chitwood, J. S.

1983-01-01

Applications of intersatellite links operating at 60 GHz are reviewed. Likely scenarios, ranging from transmission of moderate and high data rates over long distances to low data rates over short distances are examined. A limited parametric tradeoff is performed with system variables such as radiofrequency power, receiver noise temperature, link distance, data rate, and antenna size. Present status is discussed and projections are given for both electron tube and solid state transmitter technologies. Monolithic transmit and receive module technology, already under development at 20 to 30 GHz, is reviewed and its extension to 60 GHz, and possible applicability is discussed.

Tracking Climate Effects on Plant-Pollinator Interaction Phenology with Satellites and Honey Bee Hives

Science.gov (United States)

Esaias, Wayne E.; Nickeson, Jaime E.; Tan, Bin; Ma, Peter L.; Nightingale, Joanne M.; Wolfe, Robert E.

2011-01-01

Background/Question/Methods: The complexity of plant-pollinator interactions, the large number of species involved, and the lack of species response functions present challenges to understanding how these critical interactions may be impacted by climate and land cover change on large scales. Given the importance of this interaction for terrestrial ecosystems, it is desirable to develop new approaches. We monitor the daily weight change of honey bee (Apis mellifera) colonies to record the phenology of the Honey Bee Nectar Flow (HBNF) in a volunteer network (honeybeenet.gsfc.nasa.gov). The records document the successful interaction of a generalist pollinator with a variety of plant resources. We extract useful HBNF phenology metrics for three seasons. Sites currently exist in 35 states/provinces in North America, with a concentration in the Mid-Atlantic region. HBNF metrics are compared to standard phenology metrics derived from remotely sensed vegetation indices from NASA's MODIS sensor and published results from NOAA's A VHRR. At any given time the percentage of plants producing nectar is usually a sma11 fraction of the total satellite sensor signal. We are interested in determining how well the 'bulk' satellite vegetation parameters relate to the phenology of the HBNF, and how it varies spatially on landscape to continental scales. Results/Conclusions: We found the median and peak seasonal HBNF dates to be robust, with variation between replicate scale hives of only a few days. We developed quality assessment protocols to identify abnormal colony artifacts. Temporally, the peak and median of the HBNF in the Mid-Atlantic show a significant advance of 0.58 d/y beginning about 1970, very similar to that observed by the A VHRR since 1982 (0.57 d/y). Spatially, the HBNF metrics are highly correlated with elevation and winter minimum temperature distribution, and exhibit significant but regionally coherent inter-annual variation. The relationship between median of the

A flocking algorithm for multi-agent systems with connectivity preservation under hybrid metric-topological interactions.

Science.gov (United States)

He, Chenlong; Feng, Zuren; Ren, Zhigang

2018-01-01

In this paper, we propose a connectivity-preserving flocking algorithm for multi-agent systems in which the neighbor set of each agent is determined by the hybrid metric-topological distance so that the interaction topology can be represented as the range-limited Delaunay graph, which combines the properties of the commonly used disk graph and Delaunay graph. As a result, the proposed flocking algorithm has the following advantages over the existing ones. First, range-limited Delaunay graph is sparser than the disk graph so that the information exchange among agents is reduced significantly. Second, some links irrelevant to the connectivity can be dynamically deleted during the evolution of the system. Thus, the proposed flocking algorithm is more flexible than existing algorithms, where links are not allowed to be disconnected once they are created. Finally, the multi-agent system spontaneously generates a regular quasi-lattice formation without imposing the constraint on the ratio of the sensing range of the agent to the desired distance between two adjacent agents. With the interaction topology induced by the hybrid distance, the proposed flocking algorithm can still be implemented in a distributed manner. We prove that the proposed flocking algorithm can steer the multi-agent system to a stable flocking motion, provided the initial interaction topology of multi-agent systems is connected and the hysteresis in link addition is smaller than a derived upper bound. The correctness and effectiveness of the proposed algorithm are verified by extensive numerical simulations, where the flocking algorithms based on the disk and Delaunay graph are compared.

A flocking algorithm for multi-agent systems with connectivity preservation under hybrid metric-topological interactions.

Directory of Open Access Journals (Sweden)

Chenlong He

Full Text Available In this paper, we propose a connectivity-preserving flocking algorithm for multi-agent systems in which the neighbor set of each agent is determined by the hybrid metric-topological distance so that the interaction topology can be represented as the range-limited Delaunay graph, which combines the properties of the commonly used disk graph and Delaunay graph. As a result, the proposed flocking algorithm has the following advantages over the existing ones. First, range-limited Delaunay graph is sparser than the disk graph so that the information exchange among agents is reduced significantly. Second, some links irrelevant to the connectivity can be dynamically deleted during the evolution of the system. Thus, the proposed flocking algorithm is more flexible than existing algorithms, where links are not allowed to be disconnected once they are created. Finally, the multi-agent system spontaneously generates a regular quasi-lattice formation without imposing the constraint on the ratio of the sensing range of the agent to the desired distance between two adjacent agents. With the interaction topology induced by the hybrid distance, the proposed flocking algorithm can still be implemented in a distributed manner. We prove that the proposed flocking algorithm can steer the multi-agent system to a stable flocking motion, provided the initial interaction topology of multi-agent systems is connected and the hysteresis in link addition is smaller than a derived upper bound. The correctness and effectiveness of the proposed algorithm are verified by extensive numerical simulations, where the flocking algorithms based on the disk and Delaunay graph are compared.

Distributed interactive virtual environments for collaborative experiential learning and training independent of distance over Internet2.

Science.gov (United States)

Alverson, Dale C; Saiki, Stanley M; Jacobs, Joshua; Saland, Linda; Keep, Marcus F; Norenberg, Jeffrey; Baker, Rex; Nakatsu, Curtis; Kalishman, Summers; Lindberg, Marlene; Wax, Diane; Mowafi, Moad; Summers, Kenneth L; Holten, James R; Greenfield, John A; Aalseth, Edward; Nickles, David; Sherstyuk, Andrei; Haines, Karen; Caudell, Thomas P

2004-01-01

Medical knowledge and skills essential for tomorrow's healthcare professionals continue to change faster than ever before creating new demands in medical education. Project TOUCH (Telehealth Outreach for Unified Community Health) has been developing methods to enhance learning by coupling innovations in medical education with advanced technology in high performance computing and next generation Internet2 embedded in virtual reality environments (VRE), artificial intelligence and experiential active learning. Simulations have been used in education and training to allow learners to make mistakes safely in lieu of real-life situations, learn from those mistakes and ultimately improve performance by subsequent avoidance of those mistakes. Distributed virtual interactive environments are used over distance to enable learning and participation in dynamic, problem-based, clinical, artificial intelligence rules-based, virtual simulations. The virtual reality patient is programmed to dynamically change over time and respond to the manipulations by the learner. Participants are fully immersed within the VRE platform using a head-mounted display and tracker system. Navigation, locomotion and handling of objects are accomplished using a joy-wand. Distribution is managed via the Internet2 Access Grid using point-to-point or multi-casting connectivity through which the participants can interact. Medical students in Hawaii and New Mexico (NM) participated collaboratively in problem solving and managing of a simulated patient with a closed head injury in VRE; dividing tasks, handing off objects, and functioning as a team. Students stated that opportunities to make mistakes and repeat actions in the VRE were extremely helpful in learning specific principles. VRE created higher performance expectations and some anxiety among VRE users. VRE orientation was adequate but students needed time to adapt and practice in order to improve efficiency. This was also demonstrated successfully

Spatial generalised linear mixed models based on distances.

Science.gov (United States)

Melo, Oscar O; Mateu, Jorge; Melo, Carlos E

2016-10-01

Risk models derived from environmental data have been widely shown to be effective in delineating geographical areas of risk because they are intuitively easy to understand. We present a new method based on distances, which allows the modelling of continuous and non-continuous random variables through distance-based spatial generalised linear mixed models. The parameters are estimated using Markov chain Monte Carlo maximum likelihood, which is a feasible and a useful technique. The proposed method depends on a detrending step built from continuous or categorical explanatory variables, or a mixture among them, by using an appropriate Euclidean distance. The method is illustrated through the analysis of the variation in the prevalence of Loa loa among a sample of village residents in Cameroon, where the explanatory variables included elevation, together with maximum normalised-difference vegetation index and the standard deviation of normalised-difference vegetation index calculated from repeated satellite scans over time. © The Author(s) 2013.

Design and Realization of FIR Filter for Inter Satellite Link at 50-90 MHZ Frequency using FPGA

Directory of Open Access Journals (Sweden)

Yuyu Wahyu

2016-12-01

Full Text Available In this paper, design and realization of FIR filter with a bandwidth of 40 MHz at 50-90 MHz frequency has been proposed. The design was destined to be implemented on the Inter Satellite Links (ISL. This kind of filter had been selected due to a need in linear phase responseon the ISL data communication. Equiripple method was used to design the filter becauseof its reliability in minimizing the magnitude errors. The design of this FIR filter was conducted with theoretical calculation and simulation using the R2012b Matlab. For the implementation, FPGA was used with a VHDL as the programming language with a help of Xilinx ISE Design Suite 14.5. Simulation results in Matlab and Simulink indicated that the filter design could be well implemented on ISL at frequency of 50 MHz - 90 MHz with stopband of 60 db. The phase responseresult of the realized design is quite linear so that the filter is suitable for data communication on the ISL.

CAMAC based computer--computer communications via microprocessor data links

International Nuclear Information System (INIS)

Potter, J.M.; Machen, D.R.; Naivar, F.J.; Elkins, E.P.; Simmonds, D.D.

1976-01-01

Communications between the central control computer and remote, satellite data acquisition/control stations at The Clinton P. Anderson Meson Physics Facility (LAMPF) is presently accomplished through the use of CAMAC based Data Link Modules. With the advent of the microprocessor, a new philosophy for digital data communications has evolved. Data Link modules containing microprocessor controllers provide link management and communication network protocol through algorithms executed in the Data Link microprocessor

Testing the gravitational interaction in the field of the Earth via satellite laser ranging and the Laser Ranged Satellites Experiment (LARASE)

International Nuclear Information System (INIS)

Lucchesi, D M; Peron, R; Visco, M; Anselmo, L; Pardini, C; Bassan, M; Pucacco, G

2015-01-01

In this work, the Laser Ranged Satellites Experiment (LARASE) is presented. This is a research program that aims to perform new refined tests and measurements of gravitation in the field of the Earth in the weak field and slow motion (WFSM) limit of general relativity (GR). For this objective we use the free available data relative to geodetic passive satellite lasers tracked from a network of ground stations by means of the satellite laser ranging (SLR) technique. After a brief introduction to GR and its WFSM limit, which aims to contextualize the physical background of the tests and measurements that LARASE will carry out, we focus on the current limits of validation of GR and on current constraints on the alternative theories of gravity that have been obtained with the precise SLR measurements of the two LAGEOS satellites performed so far. Afterward, we present the scientific goals of LARASE in terms of upcoming measurements and tests of relativistic physics. Finally, we introduce our activities and we give a number of new results regarding the improvements to the modelling of both gravitational and non-gravitational perturbations to the orbit of the satellites. These activities are a needed prerequisite to improve the forthcoming new measurements of gravitation. An innovation with respect to the past is the specialization of the models to the LARES satellite, especially for what concerns the modelling of its spin evolution, the neutral drag perturbation and the impact of Earth's solid tides on the satellite orbit. (paper)

ALS-linked mutant SOD1 proteins promote Aβ aggregates in ALS through direct interaction with Aβ.

Science.gov (United States)

Jang, Ja-Young; Cho, Hyungmin; Park, Hye-Yoon; Rhim, Hyangshuk; Kang, Seongman

2017-11-04

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive degeneration of motor neurons. Aggregation of ALS-linked mutant Cu/Zn superoxide dismutase (SOD1) is a hallmark of a subset of familial ALS (fALS). Recently, intracellular amyloid-β (Aβ) is detected in motor neurons of both sporadic and familial ALS. We have previously shown that intracellular Aβ specifically interacts with G93A, an ALS-linked SOD1 mutant. However, little is known about the pathological and biological effect of this interaction in neurons. In this study, we have demonstrated that the Aβ-binding region is exposed on the SOD1 surface through the conformational changes due to misfolding of SOD1. Interestingly, we found that the intracellular aggregation of Aβ is enhanced through the direct interaction of Aβ with the Aβ-binding region exposed to misfolded SOD1. Ultimately, increased Aβ aggregation by this interaction promotes neuronal cell death. Consistent with this result, Aβ aggregates was three-fold higher in the brains of G93A transgenic mice than those of non Tg. Our study provides the first direct evidence that Aβ, an AD-linked factor, is associated to the pathogenesis of ALS and provides molecular clues to understand common aggregation mechanisms in the pathogenesis of neurodegenerative diseases. Furthermore, it will provide new insights into the development of therapeutic approaches for ALS. Copyright © 2017 Elsevier Inc. All rights reserved.

The organization of interaction of subjects of educational process when using platforms of distance learning

Directory of Open Access Journals (Sweden)

F. S. Mukhametzyanova

2016-01-01

Full Text Available Within research in article the special attention is paid to the organization of distance training by means of the specialized local tool information systems oriented to provision of a certain set of educational services on the Internet. On the basis of the carried-out analysis advantages of platforms of distance training are noted: availability, a personifitsirovannost, a modularity on structure, usability, etc. Characteristics «the subject - subject» interactions are described in case of remote form of education: an active position trained in the course of activities, equality of persons training and trained, the joint problem resolution, game, dialogue, work in microgroups, admissibility of coexistence and acceptance of the opposite points of view. Specifics of process of interaction of subjects of educational process in higher education institution of physical culture on the basis of use of the Moodle platform, performed with participation of students athletes, teachers, the trainer, the staff of department of information technologies, managerial control are considered. Feature of such interaction is caused by need students athletes to combine sport and training in the conditions of long sports trainings and participation in competitions in the cities remote from educational institution. The accurate list of functions of each of subjects in the scheme of interaction is provided. In tabular option the example of a matrix of elements of the training remote rate for students of different forms of education (internal, correspondence and full-time according to the individual training plan which implementation is impossible without harmonious work of all subjects involved in educational process is given. The schemes «the subject-subject» of interaction in case of distance training in higher education institution of physical culture with use of the Moodle platform are described. So for example, for students athletes of full-time courses

Mapping protein-RNA interactions by RCAP, RNA-cross-linking and peptide fingerprinting.

Science.gov (United States)

Vaughan, Robert C; Kao, C Cheng

2015-01-01

RNA nanotechnology often feature protein RNA complexes. The interaction between proteins and large RNAs are difficult to study using traditional structure-based methods like NMR or X-ray crystallography. RCAP, an approach that uses reversible-cross-linking affinity purification method coupled with mass spectrometry, has been developed to map regions within proteins that contact RNA. This chapter details how RCAP is applied to map protein-RNA contacts within virions.

Environmental Satellite Models for a Macroeconomic Model

International Nuclear Information System (INIS)

Moeller, F.; Grinderslev, D.; Werner, M.

2003-01-01

To support national environmental policy, it is desirable to forecast and analyse environmental indicators consistently with economic variables. However, environmental indicators are physical measures linked to physical activities that are not specified in economic models. One way to deal with this is to develop environmental satellite models linked to economic models. The system of models presented gives a frame of reference where emissions of greenhouse gases, acid gases, and leaching of nutrients to the aquatic environment are analysed in line with - and consistently with - macroeconomic variables. This paper gives an overview of the data and the satellite models. Finally, the results of applying the model system to calculate the impacts on emissions and the economy are reviewed in a few illustrative examples. The models have been developed for Denmark; however, most of the environmental data used are from the CORINAIR system implemented in numerous countries

Feasibility assessment of optical technologies for reliable high capacity feeder links

Science.gov (United States)

Witternigg, Norbert; Schönhuber, Michael; Leitgeb, Erich; Plank, Thomas

2013-08-01

Space telecom scenarios like data relay satellite and broadband/broadcast service providers require reliable feeder links with high bandwidth/data rate for the communication between ground station and satellite. Free space optical communication (FSOC) is an attractive alternative to microwave links, improving performance by offering abundant bandwidth at small apertures of the optical terminals. At the same time Near-Earth communication by FSOC avoids interference with other services and is free of regulatory issues. The drawback however is the impairment by the laser propagation through the atmosphere at optical wavelengths. Also to be considered are questions of eye safety for ground personnel and aviation. In this paper we assess the user requirements for typical space telecom scenarios and compare these requirements with solutions using optical data links through the atmosphere. We suggest a site diversity scheme with a number of ground stations and a switching scheme using two optical terminals on-board the satellite. Considering the technology trade-offs between four different optical wavelengths we recommend the future use of 1.5 μm laser technology and calculate a link budget for an atmospheric condition of light haze on the optical path. By comparing link budgets we show an outlook to the future potential use of 10 μm laser technology.

A Hybrid Satellite-Terrestrial Approach to Aeronautical Communication Networks

Science.gov (United States)

Kerczewski, Robert J.; Chomos, Gerald J.; Griner, James H.; Mainger, Steven W.; Martzaklis, Konstantinos S.; Kachmar, Brian A.

2000-01-01

Rapid growth in air travel has been projected to continue for the foreseeable future. To maintain a safe and efficient national and global aviation system, significant advances in communications systems supporting aviation are required. Satellites will increasingly play a critical role in the aeronautical communications network. At the same time, current ground-based communications links, primarily very high frequency (VHF), will continue to be employed due to cost advantages and legacy issues. Hence a hybrid satellite-terrestrial network, or group of networks, will emerge. The increased complexity of future aeronautical communications networks dictates that system-level modeling be employed to obtain an optimal system fulfilling a majority of user needs. The NASA Glenn Research Center is investigating the current and potential future state of aeronautical communications, and is developing a simulation and modeling program to research future communications architectures for national and global aeronautical needs. This paper describes the primary requirements, the current infrastructure, and emerging trends of aeronautical communications, including a growing role for satellite communications. The need for a hybrid communications system architecture approach including both satellite and ground-based communications links is explained. Future aeronautical communication network topologies and key issues in simulation and modeling of future aeronautical communications systems are described.

Millimeter wave propagation modeling of inhomogeneous rain media for satellite communications systems

Science.gov (United States)

Persinger, R. R.; Stutzman, W. L.

1978-01-01

A theoretical propagation model that represents the scattering properties of an inhomogeneous rain often found on a satellite communications link is presented. The model includes the scattering effects of an arbitrary distribution of particle type (rain or ice), particle shape, particle size, and particle orientation within a given rain cell. An associated rain propagation prediction program predicts attenuation, isolation and phase shift as a function of ground rain rate. A frequency independent synthetic storm algorithm is presented that models nonuniform rain rates present on a satellite link. Antenna effects are included along with a discussion of rain reciprocity. The model is verified using the latest available multiple frequency data from the CTS and COMSTAR satellites. The data covers a wide range of frequencies, elevation angles, and ground site locations.

The X-linked 1.688 Satellite in Drosophila melanogaster Promotes Specific Targeting by Painting of Fourth.

Science.gov (United States)

Kim, Maria; Ekhteraei-Tousi, Samaneh; Lewerentz, Jacob; Larsson, Jan

2018-02-01

Repetitive DNA, represented by transposons and satellite DNA, constitutes a large portion of eukaryotic genomes, being the major component of constitutive heterochromatin. There is a growing body of evidence that it regulates several nuclear functions including chromatin state and the proper functioning of centromeres and telomeres. The 1.688 satellite is one of the most abundant repetitive sequences in Drosophila melanogaster , with the longest array being located in the pericentromeric region of the X-chromosome. Short arrays of 1.688 repeats are widespread within the euchromatic part of the X-chromosome, and these arrays were recently suggested to assist in recognition of the X-chromosome by the dosage compensation male-specific lethal complex. We discovered that a short array of 1.688 satellite repeats is essential for recruitment of the protein POF to a previously described site on the X-chromosome ( PoX2 ) and to various transgenic constructs. On an isolated target, i.e. , an autosomic transgene consisting of a gene upstream of 1.688 satellite repeats, POF is recruited to the transgene in both males and females. The sequence of the satellite, as well as its length and position within the recruitment element, are the major determinants of targeting. Moreover, the 1.688 array promotes POF targeting to the roX1 -proximal PoX1 site in trans Finally, binding of POF to the 1.688-related satellite-enriched sequences is conserved in evolution. We hypothesize that the 1.688 satellite functioned in an ancient dosage compensation system involving POF targeting to the X-chromosome. Copyright © 2018 by the Genetics Society of America.

Linking hearts and minds in couple interactions: intentions, attributions, and overriding sentiments.

Science.gov (United States)

Waldinger, Robert J; Schulz, Marc S

2006-09-01

This study examined the role of emotion and relationship satisfaction in shaping attributions about a partner's intentions in couple interactions. Using video recall, participants (N = 156 couples) reported on their own and their partner's intentions and emotions during affective moments of a discussion about an upsetting event. Links were found between relationship satisfaction and factor-analytically derived intention and attribution scales. Attributions about a partner's intentions were weakly to moderately correlated with the partner's self-reported intentions. Relationship satisfaction accounted for part of the discrepancy between self-reported intentions and partner attributions. Emotions mediated the links between relationship satisfaction and attributions, suggesting that clinicians working with distressed couples should pay more attention to the emotional climate in which attributions are made. Copyright (c) 2006 APA, all rights reserved.

THE EXTRAGALACTIC DISTANCE DATABASE

International Nuclear Information System (INIS)

Tully, R. Brent; Courtois, Helene M.; Jacobs, Bradley A.; Rizzi, Luca; Shaya, Edward J.; Makarov, Dmitry I.

2009-01-01

A database can be accessed on the Web at http://edd.ifa.hawaii.edu that was developed to promote access to information related to galaxy distances. The database has three functional components. First, tables from many literature sources have been gathered and enhanced with links through a distinct galaxy naming convention. Second, comparisons of results both at the levels of parameters and of techniques have begun and are continuing, leading to increasing homogeneity and consistency of distance measurements. Third, new material is presented arising from ongoing observational programs at the University of Hawaii 2.2 m telescope, radio telescopes at Green Bank, Arecibo, and Parkes and with the Hubble Space Telescope. This new observational material is made available in tandem with related material drawn from archives and passed through common analysis pipelines.

Creating proximity across distances – Management tools to support performance and employee well-being

DEFF Research Database (Denmark)

Ipsen, Christine; Poulsen, Signe

), in satellite offices (intra-organizational work), or at the customers’ or clients’ locations (interorganizational work) (Verburg et al. 2013; Cropper et al. 2008). In inter-organizations, distance employees are employed by one company (the provider) but work at a different company (the customer) (Cropper et al...... either time or geography separate managers from their employees, it becomes more difficult to ensure both the employees psychosocial work environment and organizational performance. This paper explores distance managers’ preventive activities that ensure both employee well-being and performance across...... distances as part of their daily management. The study contributes to the discussion on management of prevention of work-related stress in the context of distance work. We applied a case study approach to explore the tools distance managers make use of to ensure employee wellbeing and organizational...

On the center of distances

Czech Academy of Sciences Publication Activity Database

Bielas, Wojciech; Plewik, S.; Walczyńska, Marta

2018-01-01

Roč. 4, č. 2 (2018), s. 687-698 ISSN 2199-675X R&D Projects: GA ČR GF16-34860L Institutional support: RVO:67985840 Keywords : Cantorval center of distances von Neumann's theorem * set of subsums Subject RIV: BA - General Mathematics OBOR OECD: Pure mathematics https://link.springer.com/article/10.1007%2Fs40879-017-0199-4

Network design consideration of a satellite-based mobile communications system

Science.gov (United States)

Yan, T.-Y.

1986-01-01

Technical considerations for the Mobile Satellite Experiment (MSAT-X), the ground segment testbed for the low-cost spectral efficient satellite-based mobile communications technologies being developed for the 1990's, are discussed. The Network Management Center contains a flexible resource sharing algorithm, the Demand Assigned Multiple Access scheme, which partitions the satellite transponder bandwidth among voice, data, and request channels. Satellite use of multiple UHF beams permits frequency reuse. The backhaul communications and the Telemetry, Tracking and Control traffic are provided through a single full-coverage SHF beam. Mobile Terminals communicate with the satellite using UHF. All communications including SHF-SHF between Base Stations and/or Gateways, are routed through the satellite. Because MSAT-X is an experimental network, higher level network protocols (which are service-specific) will be developed only to test the operation of the lowest three levels, the physical, data link, and network layers.

Function of Junk: Pericentromeric Satellite DNA in Chromosome Maintenance.

Science.gov (United States)

Jagannathan, Madhav; Yamashita, Yukiko M

2018-04-02

Satellite DNAs are simple tandem repeats that exist at centromeric and pericentromeric regions on eukaryotic chromosomes. Unlike the centromeric satellite DNA that comprises the vast majority of natural centromeres, function(s) for the much more abundant pericentromeric satellite repeats are poorly understood. In fact, the lack of coding potential allied with rapid divergence of repeat sequences across eukaryotes has led to their dismissal as "junk DNA" or "selfish parasites." Although implicated in various biological processes, a conserved function for pericentromeric satellite DNA remains unidentified. We have addressed the role of satellite DNA through studying chromocenters, a cytological aggregation of pericentromeric satellite DNA from multiple chromosomes into DNA-dense nuclear foci. We have shown that multivalent satellite DNA-binding proteins cross-link pericentromeric satellite DNA on chromosomes into chromocenters. Disruption of chromocenters results in the formation of micronuclei, which arise by budding off the nucleus during interphase. We propose a model that satellite DNAs are critical chromosome elements that are recognized by satellite DNA-binding proteins and incorporated into chromocenters. We suggest that chromocenters function to preserve the entire chromosomal complement in a single nucleus, a fundamental and unquestioned feature of eukaryotic genomes. We speculate that the rapid divergence of satellite DNA sequences between closely related species results in discordant chromocenter function and may underlie speciation and hybrid incompatibility. © 2017 Jagannathan and Yamashita; Published by Cold Spring Harbor Laboratory Press.

Representing distance, consuming distance

DEFF Research Database (Denmark)

Larsen, Gunvor Riber

Title: Representing Distance, Consuming Distance Abstract: Distance is a condition for corporeal and virtual mobilities, for desired and actual travel, but yet it has received relatively little attention as a theoretical entity in its own right. Understandings of and assumptions about distance...... are being consumed in the contemporary society, in the same way as places, media, cultures and status are being consumed (Urry 1995, Featherstone 2007). An exploration of distance and its representations through contemporary consumption theory could expose what role distance plays in forming...

A CONCEPTUAL MODEL FOR EFFECTIVE DISTANCE LEARNING IN HIGHER A CONCEPTUAL MODEL FOR EFFECTIVE DISTANCE LEARNING IN HIGHER A CONCEPTUAL MODEL FOR EFFECTIVE DISTANCE LEARNING IN HIGHER EDUCATION

Directory of Open Access Journals (Sweden)

Mehran FARAJOLLAHI

2010-07-01

Full Text Available The present research aims at presenting a conceptual model for effective distance learning in higher education. Findings of this research shows that an understanding of the technological capabilities and learning theories especially constructive theory and independent learning theory and communicative and interaction theory in Distance learning is an efficient factor in the planning of effective Distance learning in higher education. Considering the theoretical foundations of the present research, in the effective distance learning model, the learner is situated at the center of learning environment. For this purpose, the learner needs to be ready for successful learning and the teacher has to be ready to design the teaching- learning activities when they initially enter the environment. In the present model, group and individual active teaching-learning approach, timely feedback, using IT and eight types of interactions have been designed with respect to theoretical foundations and current university missions. From among the issues emphasized in this model, one can refer to the Initial, Formative and Summative evaluations. In an effective distance learning environment, evaluation should be part of the learning process and the feedback resulting from it should be used to improve learning. For validating the specified features, the opinions of Distance learning experts in Payame Noor, Shiraz, Science and Technology and Amirkabir Universities have been used which verified a high percentage of the statistical sample of the above mentioned features.

Composeable Chat over Low-Bandwidth Intermittent Communication Links

National Research Council Canada - National Science Library

Wilcox, D. R

2007-01-01

Intermittent low-bandwidth communication environments, such as those encountered in U.S. Navy tactical radio and satellite links, have special requirements that do not pertain to commercial applications...

Satellite-based empirical models linking river plume dynamics with hypoxic area andvolume

Science.gov (United States)

Satellite-based empirical models explaining hypoxic area and volume variation were developed for the seasonally hypoxic (O2 < 2 mg L−1) northern Gulf of Mexico adjacent to the Mississippi River. Annual variations in midsummer hypoxic area and ...

Interactive Links between Relational Aggression, Theory of Mind, and Moral Disengagement among Early Adolescents

Science.gov (United States)

Kokkinos, Constantinos M.; Voulgaridou, Ioanna; Mandrali, Marianna; Parousidou, Chrysoula

2016-01-01

The aim of this study was to investigate possible interactive links between theory of mind (ToM), moral disengagement and relational aggression, using a moderated mediation analysis, with gender as a moderator, in a sample of 120 Greek preadolescents. Results indicated that relational aggression was significantly positively associated with moral…

Prediction of protein conformational freedom from distance constraints

NARCIS (Netherlands)

de Groot, B.L.; van Aalten, D.M.F.; Scheek, R.M.; Amadei, A; Vriend, G.; Berendsen, H.J.C.

1997-01-01

A method is presented that generates random protein structures that fulfil a set of upper and lower interatomic distance limits, These limits depend on distances measured in experimental structures and the strength of the interatomic interaction, Structural differences between generated structures

Satellite remote sensing in epidemiological studies.

Science.gov (United States)

Sorek-Hamer, Meytar; Just, Allan C; Kloog, Itai

2016-04-01

Particulate matter air pollution is a ubiquitous exposure linked with multiple adverse health outcomes for children and across the life course. The recent development of satellite-based remote-sensing models for air pollution enables the quantification of these risks and addresses many limitations of previous air pollution research strategies. We review the recent literature on the applications of satellite remote sensing in air quality research, with a focus on their use in epidemiological studies. Aerosol optical depth (AOD) is a focus of this review and a significant number of studies show that ground-level particulate matter can be estimated from columnar AOD. Satellite measurements have been found to be an important source of data for particulate matter model-based exposure estimates, and recently have been used in health studies to increase the spatial breadth and temporal resolution of these estimates. It is suggested that satellite-based models improve our understanding of the spatial characteristics of air quality. Although the adoption of satellite-based measures of air quality in health studies is in its infancy, it is rapidly growing. Nevertheless, further investigation is still needed in order to have a better understanding of the AOD contribution to these prediction models in order to use them with higher accuracy in epidemiological studies.

Quenching of satellite galaxies at the outskirts of galaxy clusters

Science.gov (United States)

Zinger, Elad; Dekel, Avishai; Kravtsov, Andrey V.; Nagai, Daisuke

2018-04-01

We find, using cosmological simulations of galaxy clusters, that the hot X-ray emitting intracluster medium (ICM) enclosed within the outer accretion shock extends out to Rshock ˜ (2-3)Rvir, where Rvir is the standard virial radius of the halo. Using a simple analytic model for satellite galaxies in the cluster, we evaluate the effect of ram-pressure stripping on the gas in the inner discs and in the haloes at different distances from the cluster centre. We find that significant removal of star-forming disc gas occurs only at r ≲ 0.5Rvir, while gas removal from the satellite halo is more effective and can occur when the satellite is found between Rvir and Rshock. Removal of halo gas sets the stage for quenching of the star formation by starvation over 2-3 Gyr, prior to the satellite entry to the inner cluster halo. This scenario explains the presence of quenched galaxies, preferentially discs, at the outskirts of galaxy clusters, and the delayed quenching of satellites compared to central galaxies.

In-Culture Cross-Linking of Bacterial Cells Reveals Large-Scale Dynamic Protein-Protein Interactions at the Peptide Level.

Science.gov (United States)

de Jong, Luitzen; de Koning, Edward A; Roseboom, Winfried; Buncherd, Hansuk; Wanner, Martin J; Dapic, Irena; Jansen, Petra J; van Maarseveen, Jan H; Corthals, Garry L; Lewis, Peter J; Hamoen, Leendert W; de Koster, Chris G

2017-07-07

Identification of dynamic protein-protein interactions at the peptide level on a proteomic scale is a challenging approach that is still in its infancy. We have developed a system to cross-link cells directly in culture with the special lysine cross-linker bis(succinimidyl)-3-azidomethyl-glutarate (BAMG). We used the Gram-positive model bacterium Bacillus subtilis as an exemplar system. Within 5 min extensive intracellular cross-linking was detected, while intracellular cross-linking in a Gram-negative species, Escherichia coli, was still undetectable after 30 min, in agreement with the low permeability in this organism for lipophilic compounds like BAMG. We were able to identify 82 unique interprotein cross-linked peptides with cross-links occur in assemblies involved in transcription and translation. Several of these interactions are new, and we identified a binding site between the δ and β' subunit of RNA polymerase close to the downstream DNA channel, providing a clue into how δ might regulate promoter selectivity and promote RNA polymerase recycling. Our methodology opens new avenues to investigate the functional dynamic organization of complex protein assemblies involved in bacterial growth. Data are available via ProteomeXchange with identifier PXD006287.

Experimental study of the helicopter-mobile radioelectrical channel and possible extension to the satellite-mobile channel

Science.gov (United States)

Blanchetiere-Ciarletti, V.; Sylvain, M.; Lemenn, P.

1994-07-01

The use of satellite seems to be an answer to the radioelectrical covering problem for the mobile communications, particularly in the low populated areas. Frequency bands at 1.5 and 2.5 GHz have been dedicated to these future services. Satellite-mobile links will be much more affected by propagation phenomena than the existing links between satellites and fixed stations. The reasons for that are twofold: The probable use of LEO (Low-Earth-Orbit) satellites instead of GEO; such satellites will have to be received at relatively low elevation to limit their number; the use of mobile communication terminals with small and non directive antennas that must work in various environments instead of terrestrian stations located at carefully chosen places and equipped with large diameter paraboloids. These propagation phenomena mainly consist in the fading of the signal level (shadowing of the link), and a frequency selective fading due to multipath propagation. The experience run by C.R.P.E. is aimed at a better understanding of the satellite-mobile propagation channel at fixed frequency as well as on a large band. In this paper, we discuss preliminary results from a series of propagation measurements performed (by lack of any experimental satellite) on an experimental radio link at 1.45 GHz on a of 20 MHz bandwidth between a helicopter flying at a height of 2 km and a mobile receiver. The whole experiment has been run in a rural environment in Brittany (France). In a first part, we illustrate the quality of the data collected during the experiment on a typical case study and give a possible physical interpretation of the observed phenomena. Then we present statistical results concerning the various characteristics (attenuation and delay spreads) of the propagation channel. Finally, we discuss the problem of using a helicopter (flying at a height of 2 km) as a substitute for a satellite at about 1000 km and try to estimate to what extent it is possible to use the data

OWLS as platform technology in OPTOS satellite

Science.gov (United States)

Rivas Abalo, J.; Martínez Oter, J.; Arruego Rodríguez, I.; Martín-Ortega Rico, A.; de Mingo Martín, J. R.; Jiménez Martín, J. J.; Martín Vodopivec, B.; Rodríguez Bustabad, S.; Guerrero Padrón, H.

2017-12-01

The aim of this work is to show the Optical Wireless Link to intraSpacecraft Communications (OWLS) technology as a platform technology for space missions, and more specifically its use within the On-Board Communication system of OPTOS satellite. OWLS technology was proposed by Instituto Nacional de Técnica Aeroespacial (INTA) at the end of the 1990s and developed along 10 years through a number of ground demonstrations, technological developments and in-orbit experiments. Its main benefits are: mass reduction, flexibility, and simplification of the Assembly, Integration and Tests phases. The final step was to go from an experimental technology to a platform one. This step was carried out in the OPTOS satellite, which makes use of optical wireless links in a distributed network based on an OLWS implementation of the CAN bus. OPTOS is the first fully wireless satellite. It is based on the triple configuration (3U) of the popular Cubesat standard, and was completely built at INTA. It was conceived to procure a fast development, low cost, and yet reliable platform to the Spanish scientific community, acting as a test bed for space born science and technology. OPTOS presents a distributed OBDH architecture in which all satellite's subsystems and payloads incorporate a small Distributed On-Board Computer (OBC) Terminal (DOT). All DOTs (7 in total) communicate between them by means of the OWLS-CAN that enables full data sharing capabilities. This collaboration allows them to perform all tasks that would normally be carried out by a centralized On-Board Computer.

Effect of carbon nanotube dispersion on glass transition in cross-linked epoxy-carbon nanotube nanocomposites: role of interfacial interactions.

Science.gov (United States)

Khare, Ketan S; Khare, Rajesh

2013-06-20

We have used atomistic molecular simulations to study the effect of nanofiller dispersion on the glass transition behavior of cross-linked epoxy-carbon nanotube (CNT) nanocomposites. Specific chemical interactions at the interface of CNTs and cross-linked epoxy create an interphase region, whose impact on the properties of their nanocomposites increases with an increasing extent of dispersion. To investigate this aspect, we have compared the volumetric, structural, and dynamical properties of three systems: neat cross-linked epoxy, cross-linked epoxy nanocomposite containing dispersed CNTs, and cross-linked epoxy nanocomposite containing aggregated CNTs. We find that the nanocomposite containing dispersed CNTs shows a depression in the glass transition temperature (Tg) by ~66 K as compared to the neat cross-linked epoxy, whereas such a large depression is absent in the nanocomposite containing aggregated CNTs. Our results suggest that the poor interfacial interactions between the CNTs and the cross-linked epoxy matrix lead to a more compressible interphase region between the CNTs and the bulk matrix. An analysis of the resulting dynamic heterogeneity shows that the probability of percolation of immobile domains becomes unity near the Tg calculated from volumetric properties. Our observations also lend support to the conceptual analogy between polymer nanocomposites and the nanoconfinement of polymer thin films.

Interactions of cross-linked and uncross-linked chitosan hydrogels ...

African Journals Online (AJOL)

The swelling equilibrium of Chitosan and sodium tripolyphosphate (NaTPP) cross-linked chitosan hydrogels in aqueous solutions of surfactants differing in structure and hydrophobicity at 250C is reported. Anionic surfactant sodium dodecylsulfate (SDS), the cationic surfactant hexadecyltrimethylammonium bromide (HTAB) ...

MeV ion beam interaction with polymer films containing cross-linking agents

International Nuclear Information System (INIS)

Evelyn, A. L.

1999-01-01

Polymer films containing cross linking enhancers were irradiated with MeV alpha particles to determine the effects of MeV ion beam interaction on these materials. The contributed effects from the electronic and nuclear stopping powers were separated by irradiating stacked thin films of polyvinyl chloride (PVC), polystyrene (PS) and polyethersulfone (PES). This layered system allowed most of the effects of the electronic energy deposited to be experienced by the first layers and the last layers to receive most of the effects of the nuclear stopping power. RGA, Raman microprobe analysis, RBS and FTIR measured changes in the chemical structures of the irradiated films. The characterization resolved the effects of the stopping powers on the PVC, PS and PES and the results were compared with those from previously studied polymers that did not contain any cross linking agents

A Topology Control Strategy with Reliability Assurance for Satellite Cluster Networks in Earth Observation.

Science.gov (United States)

Chen, Qing; Zhang, Jinxiu; Hu, Ze

2017-02-23

This article investigates the dynamic topology control problemof satellite cluster networks (SCNs) in Earth observation (EO) missions by applying a novel metric of stability for inter-satellite links (ISLs). The properties of the periodicity and predictability of satellites' relative position are involved in the link cost metric which is to give a selection criterion for choosing the most reliable data routing paths. Also, a cooperative work model with reliability is proposed for the situation of emergency EO missions. Based on the link cost metric and the proposed reliability model, a reliability assurance topology control algorithm and its corresponding dynamic topology control (RAT) strategy are established to maximize the stability of data transmission in the SCNs. The SCNs scenario is tested through some numeric simulations of the topology stability of average topology lifetime and average packet loss rate. Simulation results show that the proposed reliable strategy applied in SCNs significantly improves the data transmission performance and prolongs the average topology lifetime.

Endurance and age : evidence from long-distance running data

NARCIS (Netherlands)

Sterken, Elmer

2001-01-01

This paper analyzes the impact of aging on long-run endurance. We analyze the determinants of running speed on distances from 5K to the marathon. We model running speed as a function of distance, age, and sex. We find evidence for interaction between age and sex, but not between distance and sex.

Dark influences: imprints of dark satellites on dwarf galaxies

NARCIS (Netherlands)

Starkenburg, T. K.; Helmi, A.

Context. In the context of the current Λ cold dark matter cosmological model small dark matter halos are abundant and satellites of dwarf galaxies are expected to be predominantly dark. Since low mass galaxies have smaller baryon fractions, interactions with these satellites may leave particularly

S-LINK, a data link interface specification for the LHC era

International Nuclear Information System (INIS)

Bij, H.C. van der; McLaren, R.A.; Boyle, O.

1996-01-01

In the Technical Proposals for ATLAS, CMS and ALICE there is a requirement for several thousand data links. Although there is an obvious need for standardization, this seems difficult to achieve as the links run at different speeds, over different distances and have various constraints of power consumption, size and radiation hardness. An additional complication is that today we cannot decide which will be the most cost effective technology for the implementation of the final links. Furthermore, we must allow designers of boards at each end of the link, for example readout electronics and input buffers, to work in parallel with the development of the links. The S-LINK is a new concept which should provide the benefits of standardization without the limitations. The S-LINK specification defines, at both ends of the link, a simple FIFO-like user interface which remains independent of the technology used to implement the physical link. The physical link provides transfer of event data and control words, error detection, optional flow control and test facilities. This paper describes the S-LINK specification and gives examples of the use of the S-LINK, the physical links being designed, and the test equipment that is being developed

Telecommunication service markets through the year 2000 in relation to millimeter wave satellite systems

Science.gov (United States)

Stevenson, S. M.

1979-01-01

NASA is currently conducting a series of millimeter wave satellite system and market studies to develop 30/20 GHz satellite system concepts that have commercial potential for the period 1980-2000. The results of the market studies to-date focusing on the overall demand forecasts and distributions by geographic location, distance, and user category are discussed. Tables are presented indicating baseline market forecast voice and video services, data service category, impacted baseline forecast, and traffic/distance distribution voice services. It is concluded that the total market and system activity will be influential in determining the potential role of millimeter wave systems in the overall transmission needs of the nation, and the amount of the total forecasted traffic suitable for millimeter wave systems.

Interactive 3D Mars Visualization

Science.gov (United States)

Powell, Mark W.

2012-01-01

The Interactive 3D Mars Visualization system provides high-performance, immersive visualization of satellite and surface vehicle imagery of Mars. The software can be used in mission operations to provide the most accurate position information for the Mars rovers to date. When integrated into the mission data pipeline, this system allows mission planners to view the location of the rover on Mars to 0.01-meter accuracy with respect to satellite imagery, with dynamic updates to incorporate the latest position information. Given this information so early in the planning process, rover drivers are able to plan more accurate drive activities for the rover than ever before, increasing the execution of science activities significantly. Scientifically, this 3D mapping information puts all of the science analyses to date into geologic context on a daily basis instead of weeks or months, as was the norm prior to this contribution. This allows the science planners to judge the efficacy of their previously executed science observations much more efficiently, and achieve greater science return as a result. The Interactive 3D Mars surface view is a Mars terrain browsing software interface that encompasses the entire region of exploration for a Mars surface exploration mission. The view is interactive, allowing the user to pan in any direction by clicking and dragging, or to zoom in or out by scrolling the mouse or touchpad. This set currently includes tools for selecting a point of interest, and a ruler tool for displaying the distance between and positions of two points of interest. The mapping information can be harvested and shared through ubiquitous online mapping tools like Google Mars, NASA WorldWind, and Worldwide Telescope.

NASA/DARPA advanced communications technology satellite project for evaluation of telemedicine outreach using next-generation communications satellite technology: Mayo Foundation participation.

Science.gov (United States)

Gilbert, B K; Mitchell, M P; Bengali, A R; Khandheria, B K

1999-08-01

To describe the development of telemedicine capabilities-application of remote consultation and diagnostic techniques-and to evaluate the feasibility and practicality of such clinical outreach to rural and underserved communities with limited telecommunications infrastructures. In 1992, Mayo Foundation (Rochester, Minn, Jacksonville, Fla, and Scottsdale, Ariz), the National Aeronautics and Space Administration, and the Defense Advanced Research Projects Agency collaborated to create a complex network of fiberoptic landlines, video recording systems, satellite terminals, and specially developed data translators linking Mayo sites with other locations in the continental United States on an on-demand basis. The purpose was to transmit data via the asynchronous transfer mode (ATM) digital communications protocol over the Advanced Communications Technology Satellite. The links were intended to provide a conduit for transmission of data for patient-specific consultations between physicians, evaluation of medical imagery, and medical education for clinical staffs at remote sites. Low-data-rate (LDR) experiments went live late in 1993. Mayo Clinic Rochester successfully provided medical consultation and services to 2 small regional medical facilities. High-data-rate (HDR) experiments included studies of remote digital echocardiography, store-and-forward telemedicine, cardiac catheterization, and teleconsultation for congenital heart disease. These studies combined landline data transmission with use of the satellite. The complexity of the routing paths and network components, immaturity of available software, and inexperience with existing telecommunications caused significant study delays. These experiments demonstrated that next-generation satellite technology can provide batch and real-time imagery for telemedicine. The first-generation of the ATM and satellite network technology used in these experiments created several technical problems and inconveniences that should

Key issues of multiple access technique for LEO satellite communication systems

Institute of Scientific and Technical Information of China (English)

温萍萍; 顾学迈

2004-01-01

The large carrier frequency shift caused by the high-speed movement of satellite (Doppler effects) and the propagation delay on the up-down link are very critical issues in an LEO satellite communication system, which affects both the selection and the implementation of a suitable access method. A Doppler based multiple access technique is used here to control the flow and an MPRMA-HS protocol is proposed for the application in LEO satellite communication systems. The extended simulation trials prove that the proposed scheme seems to be a very promising access method.

Vibration monitoring of large vertical pumps via a remote satellite station

International Nuclear Information System (INIS)

Cook, S.A.; Crowe, R.D.; Roblyer, S.P.; Toffer, H.

1985-01-01

The Hanford N Reactor is operated by UNC Nuclear Industries for the Department of Energy for the production of special isotopes and electric energy. The reactor has a unique design in which the equipment such as pumps, turbines, generators and diesel engines are located in separate buildings. This equipment arrangement has led to the conclusion that the most cost-effective implementation of a dedicated vibration monitoring system would be to install a computerized network system in lieu of a single analyzing station. In this approach, semi-autonomous micro processor based data collection stations referred to as satellite stations are located near each concentration of machinery to be monitored. The satellite stations provide near continuous monitoring of the machinery. They are linked to a minicomputer using voice grade telephone circuits and hardware and software specifically designed for network communications. The communications link between the satellite stations and the minicomputer permits data and programs to be transmitted between the units. This paper will describe the satellite station associated with large vertical pumps vibration monitoring. The reactor has four of these pumps to supply tertiary cooling to reactor systems. 4 figs

Engineering satellite-based navigation and timing global navigation satellite systems, signals, and receivers

CERN Document Server

Betz, J

2016-01-01

This book describes the design and performance analysis of satnav systems, signals, and receivers. It also provides succinct descriptions and comparisons of all the world’s satnav systems. Its comprehensive and logical structure addresses all satnav signals and systems in operation and being developed. Engineering Satellite-Based Navigation and Timing: Global Navigation Satellite Systems, Signals, and Receivers provides the technical foundation for designing and analyzing satnav signals, systems, and receivers. Its contents and structure address all satnav systems and signals: legacy, modernized, and new. It combines qualitative information with detailed techniques and analyses, providing a comprehensive set of insights and engineering tools for this complex multidisciplinary field. Part I describes system and signal engineering including orbital mechanics and constellation design, signal design principles and underlying considerations, link budgets, qua tifying receiver performance in interference, and e...

Relativistic effects on earth satellites and their measurement

International Nuclear Information System (INIS)

Bertotti, B.

1988-01-01

There are three kinds of relativistic effects on earth satellites: those due post newtonian corrections in the field of the earth; the relativistic corrections in the field of the sun; and the precession of the local frames with respect to far away bodies. The authors point out that it is not possible to eliminate the second kind by decreasing the distance of the satellite and the earth; in other words, the effect of the sun is not entirely tidal and a generalized principle of equivalence does hold exactly. Concerning the third kind, the motion of the moon and the measurements of its distance from the earth by lunar laser ranging provides a way to establish experimentally the two connections between the three fundamental frames one should consider: the local frame, determined geometrically by parallel transport; the planetary dynamical frame; and the kinematical frame defined by extragalactic radio sources. According to general relativity the first two frames are related by de Sitter's precision; the last two coincide. It shown that the connections between the first two frames and the first and third frame are already hidden in the existing data

Testing command and control of the satellites in formation flight

Science.gov (United States)

Gheorghe, Popan; Gheorghe, Gh. Ion; Gabriel, Todoran

2013-10-01

The topics covered in the paper are mechatronic systems for determining the distance between the satellites and the design of the displacement system on air cushion table for satellites testing. INCDMTM has the capability to approach the collaboration within European Programms (ESA) of human exploration of outer space through mechatronic systems and accessories for telescopes, mechatronics systems used by the launchers, sensors and mechatronic systems for the robotic exploration programs of atmosphere and Mars. This research has a strong development component of industrial competitiveness many of the results of space research have direct applicability in industrial fabrication.

The interplay between regulatory focus and temporal distance in the health context.

Science.gov (United States)

Berezowska, Aleksandra; Fischer, Arnout R H; van Trijp, Hans C M

2018-02-01

This study identifies how the interaction between temporal distance, regulatory focus, and framing of health outcomes affects individuals' intention to adopt a personalized nutrition service. A 2 (temporal distance: immediate health outcomes vs. delayed health outcomes) × 2 (regulatory focus: prevention vs. promotion) × 2 (health outcome framing: illness prevention vs. health promotion) full-factorial between-subjects design. In two experiments with samples of 236 and 242 students, regulatory focus was manipulated by asking participants to describe which academic outcomes they want to either achieve or prevent and how they aim to do this. Temporal distance and health outcome framing were manipulated by modifying descriptions of personalized nutrition services. To study the process through which temporal distance, regulatory focus, and health outcome framing affect adoption intention, measures of perceived privacy risk and perceived personalization benefit were included as mediators. The interaction between temporal distance and regulatory focus had a significant effect on adoption intention, perceived privacy risk, and perceived personalization benefit. For prevention-focused individuals' adoption intention was higher, perceived personalization benefit was higher, and perceived privacy risk was lower when health outcomes were immediate instead of delayed. These effects were not significant for promotion-focused individuals. Health outcome framing affected the interaction between temporal distance and regulatory focus, but only in Study 1. Only perceived personalization benefit served as a mediator. Tailoring temporal distance to individuals' regulatory focus increases adoption intention for personalized nutrition advice. Statement of contribution What is already known on this subject? Intention to adopt dietary recommendations results from a cognitive decision-making process. Regulatory focus and temporal distance are relevant for the adoption of dietary

R&D of a Next Generation LEO System for Global Multimedia Mobile Satellite Communications

Science.gov (United States)

Morikawa, E.; Motoyoshi, S.; Koyama, Y.; Suzuki, R.; Yasuda, Y.

2002-01-01

Next-generation LEO System Research Center (NeLS) was formed in the end of 1997 as a research group under the Telecommunications Advancement Organization of Japan, in cooperation with the telecommunications operators, manufacturers, universities and governmental research organization. The aim of this project is to develop new technology for global multimedia mobile satellite communications services with a user data rate around 2Mbps for handy terminals. component of the IMT-2000, and the second generation of the big-LEO systems. In prosecuting this project, two-phase approach, phase 1 and phase 2, is considered. Phase 1 is the system definition and development of key technologies. In Phase 2, we plan to verify the developed technology in Phase 1 on space. From this year we shifted the stage to Phase 2, and are now developing the prototype of on-board communication systems for flight tests, which will be planed at around 2006. The satellite altitude is assumed to be 1200 km in order to reduce the number of satellites, to avoid the Van Allen radiation belts and to increase the minimum elevation angle. Ten of the circular orbits with 55 degree of inclination are selected to cover the earth surface from -70 to 70 degree in latitude. 12 satellites are positioned at regular intervals in each orbit. In this case, the minimum elevation angle from the user terminal can be keep more than 20 degree for the visibility of the satellite, and 15 degree for simultaneous visibility of two satellites. Then, NeLS Research Center was focusing on the development of key technologies as the phase 1 project. Four kinds of key technologies; DBF satellite antenna, optical inter-satellite link system, satellite network technology with on-board ATM switch and variable rate modulation were selected. Satellite Antenna Technology: Development of on-board direct radiating active phased array antenna with digital beam forming technology would be one of the most important breakthroughs for the

Distance Education in Technological Age

Directory of Open Access Journals (Sweden)

R .C. SHARMA

2005-04-01

provides details on how the multi-media systems like radio, audio cassettes, telephone, video cassettes, video discs, education television and computer based education etc can be successfully adopted. There are factors like socio-political, economic, human and administrative, and economic, which manipulate the application of information communication technology in education in developing countries. The authors in their chapters on satellite communication and virtual university explain the advancements. The book also gives details of how the library services could be arranged for the distance learners in developing countries. Skills in distance teaching are crucial to the successful counseling and teaching as the learners have varied characteristics. These skills contribute to the effective distance teaching in traditional as well as online distance education settings. A major portion of the book has been dedicated to the e-learning and virtual university initiatives. Cases from YashwantRao Chawan Maharastra Open University, a project C-MODE which deals with offering education through virtual academy and application of non-broadcasting and broadcasting media technologies to distance education can be found in these chapters.Research in and research on distance education is very significant. Quality and Quantity of research in distance education has been a source of prime concern of educators. The readers can find here an overview of review and critiques of researches in the field of open and distance learning in the Indian context and what are various changing paradigms of research in distance education. The authors strongly suggest undertaking researches on pedagogy, educational media and management of distance education. The book contains useful information for the beginners in basic distance education and those who are interested in knowing what happened and what is happening in developing countries. Biodata and Adresses of Reviewer Ramesh Chandra Sharma holds a PhD in

Experimental evaluation of open-loop UpLink Power Control using ACTS

Science.gov (United States)

Dissanayake, Asoka

1995-01-01

The present investigation deals with the implementation of open-loop up-link power control using a beacon signal in the down-link frequency band as the control parameter. A power control system was developed and tested using the ACTS satellite. ACTS carries beacon signals in both up- and down-link bands with which the relationship between the up- and down-link fading can be established. A power controlled carrier was transmitted to the ACTS satellite from a NASA operated ground station and the transponded signal was received at COMSAT Laboratories using a terminal that was routinely used to monitor the two ACTS beacon signals. The experiment ran for a period of approximately six months and the collected data were used to evaluate the performance of the power control system. A brief review of propagation factors involved in estimating the up-link fade using a beacon signal in the down-link band are presented. The power controller design and the experiment configuration are discussed. Results of the experiment are discussed.

Short-term prediction of rain attenuation level and volatility in Earth-to-Satellite links at EHF band

Directory of Open Access Journals (Sweden)

L. de Montera

2008-08-01

Full Text Available This paper shows how nonlinear models originally developed in the finance field can be used to predict rain attenuation level and volatility in Earth-to-Satellite links operating at the Extremely High Frequencies band (EHF, 20–50 GHz. A common approach to solving this problem is to consider that the prediction error corresponds only to scintillations, whose variance is assumed to be constant. Nevertheless, this assumption does not seem to be realistic because of the heteroscedasticity of error time series: the variance of the prediction error is found to be time-varying and has to be modeled. Since rain attenuation time series behave similarly to certain stocks or foreign exchange rates, a switching ARIMA/GARCH model was implemented. The originality of this model is that not only the attenuation level, but also the error conditional distribution are predicted. It allows an accurate upper-bound of the future attenuation to be estimated in real time that minimizes the cost of Fade Mitigation Techniques (FMT and therefore enables the communication system to reach a high percentage of availability. The performance of the switching ARIMA/GARCH model was estimated using a measurement database of the Olympus satellite 20/30 GHz beacons and this model is shown to outperform significantly other existing models.

The model also includes frequency scaling from the downlink frequency to the uplink frequency. The attenuation effects (gases, clouds and rain are first separated with a neural network and then scaled using specific scaling factors. As to the resulting uplink prediction error, the error contribution of the frequency scaling step is shown to be larger than that of the downlink prediction, indicating that further study should focus on improving the accuracy of the scaling factor.

Short-term prediction of rain attenuation level and volatility in Earth-to-Satellite links at EHF band

Science.gov (United States)

de Montera, L.; Mallet, C.; Barthès, L.; Golé, P.

2008-08-01

This paper shows how nonlinear models originally developed in the finance field can be used to predict rain attenuation level and volatility in Earth-to-Satellite links operating at the Extremely High Frequencies band (EHF, 20 50 GHz). A common approach to solving this problem is to consider that the prediction error corresponds only to scintillations, whose variance is assumed to be constant. Nevertheless, this assumption does not seem to be realistic because of the heteroscedasticity of error time series: the variance of the prediction error is found to be time-varying and has to be modeled. Since rain attenuation time series behave similarly to certain stocks or foreign exchange rates, a switching ARIMA/GARCH model was implemented. The originality of this model is that not only the attenuation level, but also the error conditional distribution are predicted. It allows an accurate upper-bound of the future attenuation to be estimated in real time that minimizes the cost of Fade Mitigation Techniques (FMT) and therefore enables the communication system to reach a high percentage of availability. The performance of the switching ARIMA/GARCH model was estimated using a measurement database of the Olympus satellite 20/30 GHz beacons and this model is shown to outperform significantly other existing models. The model also includes frequency scaling from the downlink frequency to the uplink frequency. The attenuation effects (gases, clouds and rain) are first separated with a neural network and then scaled using specific scaling factors. As to the resulting uplink prediction error, the error contribution of the frequency scaling step is shown to be larger than that of the downlink prediction, indicating that further study should focus on improving the accuracy of the scaling factor.

Use of online interactive tools in an open distance learning context: Health studies students' perspective*

Directory of Open Access Journals (Sweden)

Kefiloe A. Maboe

2017-10-01

Full Text Available Background: Open distance learning (ODL institutions provide educational challenges with specific reference to the training of nurses. They have adopted online technologies to facilitate teaching and learning. However it is observed that most nurses do not use or minimally use tools such as a discussion forum for online interaction to facilitate teaching and learning. Objective: The purpose of this study was to determine how the discussion forum as an online interactive tool be used in an ODL institution to enhance student-to-student and student-to-lecturer online interactions. Design: Quantitative and descriptive in nature. Method: No sampling was done. An online questionnaire was sent to all 410 second and third years Health Services Management students around the world registered with a specific ODL institution during the second semester. Eighty seven students responded to the questionnaire. Data analysis was done quantitatively and descriptively in the form of diagrams. Results: The findings indicated that 84.9% of students own computers, and 100% own cellular phones, but only 3.8% participated in online discussion forum. Some students indicated that they were technologically challenged. Some lecturers interact minimally online and are not supportive to them. The institution does not give them the support they need to acquire the necessary skills to utilise these technologies. Conclusion: The article suggests that lecturers, active interaction in an online discussion forum as a way of supporting students, are fundamental to effective teaching and learning.The university should consider providing intensive mentoring to students to enable them to utilise the available technologies optimally.

Critical Points in Distance Learning System

Directory of Open Access Journals (Sweden)

Airina Savickaitė

2013-08-01

Full Text Available Purpose – This article presents the results of distance learning system analysis, i.e. the critical elements of the distance learning system. The critical points of distance learning are a part of distance education online environment interactivity/community process model. The most important is the fact that the critical point is associated with distance learning participants. Design/methodology/approach – Comparative review of articles and analysis of distance learning module. Findings – A modern man is a lifelong learner and distance learning is a way to be a modern person. The focus on a learner and feedback is the most important thing of learning distance system. Also, attention should be paid to the lecture-appropriate knowledge and ability to convey information. Distance system adaptation is the way to improve the learner’s learning outcomes. Research limitations/implications – Different learning disciplines and learning methods may have different critical points. Practical implications – The information of analysis could be important for both lecturers and students, who studies distance education systems. There are familiar critical points which may deteriorate the quality of learning. Originality/value – The study sought to develop remote systems for applications in order to improve the quality of knowledge. Keywords: distance learning, process model, critical points. Research type: review of literature and general overview.

Wireless data link for FBTR

International Nuclear Information System (INIS)

Sundararajan, M.K.; Prabhakara Rao, G.; Ilango Sambasivan, S.; Swaminathan, P.; Ramakrishna, P.V.

2004-01-01

This paper deals with the design and development of a wireless data link for transmission of block pile signals at the Fast Breeder Test Reactor (FBTR) of Indira Gandhi Center for Atomic Research (IGCAR). This link is to establish wireless connectivity, typically at RS232C rates, over distances of the order of 50 m, and is expected to operate under electrically hostile conditions. (author)

L’interaction orale en présentiel et à distance : une étude de cas en classe de français

OpenAIRE

Gemma Delgar Farrés

2015-01-01

Dans cet article, nous analysons les différences qui existent entre l’interaction orale directe et l’interaction orale à distance à partir de l’enregistrement d’une tâche d’expression orale réalisée par deux groupes de deux étudiants de français d’un niveau B1 face à face et par visioconférence. Ces deux enregistrements ont été transcrits avec le logiciel CLAN du programme CHILDES et ce logiciel nous a permis de caractériser les deux types d’interaction orale au niveau des pauses, des répétit...

Students' experiences with interactivity and learning in a high school physics multimedia distance learning course

Science.gov (United States)

Villarreal-Stewart, Irene

The purpose guiding this research has been to learn about and describe the phenomena of interactivity from the learners' perspectives and to learn which of the interactivity affordances and practices were actually used by students and why in the process of learning physics using an interactive multimedia distance learning course system. The bigger purpose behind learning about and describing interactivity has been to gain knowledge and perspective for its instructional design to benefit the learner, the school as curriculum implementer, and instructional media designers to create better products. Qualitative methodology in the interpretivist tradition was used, that is, in-depth interviews and on-site observations, to gain understanding of interactivity from the learners' perspective and to gain understanding of the student learning context impacting and shaping the students' interactivity experiences. NVivo was used to sort, organize and index data. All data were read on three levels: literally, interpretively, and reflexively; and were read comparatively to other perspectives to get descriptions and interpretations that were holistic to the implementation and had potential insight to improve practice for instructional designers, teachers, administrators, specifically to improve the learning experience for students. Site-Specific Findings: Students watched videos, resisted using phone and e-mail, and worked math problems to demonstrate learning, which resulted in very little interactivity, virtually no dialogue about physics, no physical activity, one-way communication, multifaceted dissatisfaction, student need for teacher involvement in the learning enterprise, student appreciation for interactivity, and expressed desire for a real, live teacher. I also found that some students did experience the system as interactive, did experience learner control and self-directed learning, and despite dissatisfaction, liked and appreciated the course. Wider Applications

Static and kinematic positioning using WADGPS from geostationary satellites

Science.gov (United States)

Cefalo, R.; Gatti, M.

2003-04-01

STATIC AND KINEMATIC POSITIONING USING WADGPS CORRECTIONS FROM GEOSTATIONARY SATELLITES Cefalo R. (1), Gatti M (2) (1) Department of Civil Engineering, University of Trieste, P.le Europa 1, 34127 Trieste, Italy, cefalo@dic.univ.trieste.it, (2) Department of Engineering, University of Ferrara, via Saragat 1, 44100 Ferrara, Italy, mgatti@ing.unife.it ABSTRACT. Starting from February 2000, static and kinematic experiments have been performed at the Department of Civil Engineering of University of Trieste, Italy and the Department of Engineering of University of Ferrara, Italy, using the WADGPS (Wide Area Differential GPS) corrections up linked by Geostationary Satellites belonging to the American WAAS and European EGNOS. Recently, a prototypal service by ESA (European Space Agency) named SISNet (Signal In Space through Internet), has been introduced using Internet to diffuse the messages up linked through AOR-E and IOR Geostationary Satellites. This service will overcome the problems relative to the availability of the corrections in urban areas. This system is currently under tests by the authors in order to verify the latency of the message and the applicability and accuracies obtainable in particular in dynamic applications.

Data processing in Software-type Wave-Particle Interaction Analyzer onboard the Arase satellite

Science.gov (United States)

Hikishima, Mitsuru; Kojima, Hirotsugu; Katoh, Yuto; Kasahara, Yoshiya; Kasahara, Satoshi; Mitani, Takefumi; Higashio, Nana; Matsuoka, Ayako; Miyoshi, Yoshizumi; Asamura, Kazushi; Takashima, Takeshi; Yokota, Shoichiro; Kitahara, Masahiro; Matsuda, Shoya

2018-05-01

The software-type wave-particle interaction analyzer (S-WPIA) is an instrument package onboard the Arase satellite, which studies the magnetosphere. The S-WPIA represents a new method for directly observing wave-particle interactions onboard a spacecraft in a space plasma environment. The main objective of the S-WPIA is to quantitatively detect wave-particle interactions associated with whistler-mode chorus emissions and electrons over a wide energy range (from several keV to several MeV). The quantity of energy exchanges between waves and particles can be represented as the inner product of the wave electric-field vector and the particle velocity vector. The S-WPIA requires accurate measurement of the phase difference between wave and particle gyration. The leading edge of the S-WPIA system allows us to collect comprehensive information, including the detection time, energy, and incoming direction of individual particles and instantaneous-wave electric and magnetic fields, at a high sampling rate. All the collected particle and waveform data are stored in the onboard large-volume data storage. The S-WPIA executes calculations asynchronously using the collected electric and magnetic wave data, data acquired from multiple particle instruments, and ambient magnetic-field data. The S-WPIA has the role of handling large amounts of raw data that are dedicated to calculations of the S-WPIA. Then, the results are transferred to the ground station. This paper describes the design of the S-WPIA and its calculations in detail, as implemented onboard Arase.[Figure not available: see fulltext.

DISTANCES TO DARK CLOUDS: COMPARING EXTINCTION DISTANCES TO MASER PARALLAX DISTANCES

International Nuclear Information System (INIS)

Foster, Jonathan B.; Jackson, James M.; Stead, Joseph J.; Hoare, Melvin G.; Benjamin, Robert A.

2012-01-01

We test two different methods of using near-infrared extinction to estimate distances to dark clouds in the first quadrant of the Galaxy using large near-infrared (Two Micron All Sky Survey and UKIRT Infrared Deep Sky Survey) surveys. Very long baseline interferometry parallax measurements of masers around massive young stars provide the most direct and bias-free measurement of the distance to these dark clouds. We compare the extinction distance estimates to these maser parallax distances. We also compare these distances to kinematic distances, including recent re-calibrations of the Galactic rotation curve. The extinction distance methods agree with the maser parallax distances (within the errors) between 66% and 100% of the time (depending on method and input survey) and between 85% and 100% of the time outside of the crowded Galactic center. Although the sample size is small, extinction distance methods reproduce maser parallax distances better than kinematic distances; furthermore, extinction distance methods do not suffer from the kinematic distance ambiguity. This validation gives us confidence that these extinction methods may be extended to additional dark clouds where maser parallaxes are not available.

The Application of the Technology of 3D Satellite Cloud Imaging in Virtual Reality Simulation

Directory of Open Access Journals (Sweden)

Xiao-fang Xie

2007-05-01

Full Text Available Using satellite cloud images to simulate clouds is one of the new visual simulation technologies in Virtual Reality (VR. Taking the original data of satellite cloud images as the source, this paper depicts specifically the technology of 3D satellite cloud imaging through the transforming of coordinates and projection, creating a DEM (Digital Elevation Model of cloud imaging and 3D simulation. A Mercator projection was introduced to create a cloud image DEM, while solutions for geodetic problems were introduced to calculate distances, and the outer-trajectory science of rockets was introduced to obtain the elevation of clouds. For demonstration, we report on a computer program to simulate the 3D satellite cloud images.

Minimum-link paths among obstacles in the plane

NARCIS (Netherlands)

Mitchell, J.S.B.; Rote, G.; Woeginger, G.J.

1992-01-01

Given a set of nonintersecting polygonal obstacles in the plane, thelink distance between two pointss andt is the minimum number of edges required to form a polygonal path connectings tot that avoids all obstacles. We present an algorithm that computes the link distance (and a corresponding

Dialing long distance : communications to northern operations like the MGP require sophisticated satellite networks for voice, data

Energy Technology Data Exchange (ETDEWEB)

Cook, D.

2006-04-15

Telecommunications will play a major role in the construction of the Mackenzie Gas Project due to the remoteness of its location and the volume of communication data required to support the number of people involved and the amount of construction activity. While suppliers for communications tools have not yet been identified, initial telecommunications plans call for the installation of communication equipment at all camps, major facility sites and construction locations. Equipment will be housed in self-contained, climate-controlled buildings called telecommunication service modules (TSMs), which will be connected to each other as well as to existing public communications networks. The infrastructure will support telephone and fax systems; Internet and electronic mail services; multiple channel very high frequency radios; air-to-ground communication at airstrips and helipads; ship-to-shore at barge landings; closed circuit television; satellite community antenna television; CBC radio broadcast; public address systems; security systems; and supervisory control and data acquisition (SCADA) systems. An Internet Protocol (IP) network with a voice telephone system will be implemented along with a geostationary orbit satellite network. Satellite servers and real-time data services will be used. Car kits that allow call and battery-operated self-contained telemetry devices designed to communicate via a satellite system have been commissioned for the project that are capable of providing cost-efficient and reliable asset tracking and fleet management in remote regions and assisting in deployment requirements. It was concluded that many of today's mega-projects are the driving factors behind new telecommunications solutions in remote areas. 1 fig.

A Mobile Satellite Experiment (MSAT-X) network definition

Science.gov (United States)

Wang, Charles C.; Yan, Tsun-Yee

1990-01-01

The network architecture development of the Mobile Satellite Experiment (MSAT-X) project for the past few years is described. The results and findings of the network research activities carried out under the MSAT-X project are summarized. A framework is presented upon which the Mobile Satellite Systems (MSSs) operator can design a commercial network. A sample network configuration and its capability are also included under the projected scenario. The Communication Interconnection aspect of the MSAT-X network is discussed. In the MSAT-X network structure two basic protocols are presented: the channel access protocol, and the link connection protocol. The error-control techniques used in the MSAT-X project and the packet structure are also discussed. A description of two testbeds developed for experimentally simulating the channel access protocol and link control protocol, respectively, is presented. A sample network configuration and some future network activities of the MSAT-X project are also presented.

Origin of the Local Group satellite planes

Science.gov (United States)

Banik, Indranil; O'Ryan, David; Zhao, Hongsheng

2018-04-01

We attempt to understand the planes of satellite galaxies orbiting the Milky Way (MW) and M31 in the context of Modified Newtonian Dynamics (MOND), which implies a close MW-M31 flyby occurred ≈8 Gyr ago. Using the timing argument, we obtain MW-M31 trajectories consistent with cosmological initial conditions and present observations. We adjust the present M31 proper motion within its uncertainty in order to simulate a range of orbital geometries and closest approach distances. Treating the MW and M31 as point masses, we follow the trajectories of surrounding test particle disks, thereby mapping out the tidal debris distribution. Around each galaxy, the resulting tidal debris tends to cluster around a particular orbital pole. We find some models in which these preferred spin vectors align fairly well with those of the corresponding observed satellite planes. The radial distributions of material in the simulated satellite planes are similar to what we observe. Around the MW, our best-fitting model yields a significant fraction (0.22) of counter-rotating material, perhaps explaining why Sculptor counter-rotates within the MW satellite plane. In contrast, our model yields no counter-rotating material around M31. This is testable with proper motions of M31 satellites. In our best model, the MW disk is thickened by the flyby 7.65 Gyr ago to a root mean square height of 0.75 kpc. This is similar to the observed age and thickness of the Galactic thick disk. Thus, the MW thick disk may have formed together with the MW and M31 satellite planes during a past MW-M31 flyby.

Long-term passive distance-bounded relative motion in the presence of TeX perturbations

NARCIS (Netherlands)

Chu, J.; Guo, J.; Gill, E.K.A.

2015-01-01

This paper presents closed-form solutions for the problem of long-term satellite relative motion in the presence of J2 perturbations, and introduces a design methodology for long-term passive distance-bounded relative motion. There are two key ingredients of closed-form solutions.One is the model of

CERN: Installing STELLA

Energy Technology Data Exchange (ETDEWEB)

Anon.

1980-01-15

STELLA - Satellite Transmission Experiment Linking Laboratories - is now taking shape. This interesting project will explore the possibilities of transmitting data accurately over large distances and at high speeds using the European Space Agency's 0TS-2 communications satellite launched last year. With STELLA, physics Laboratories are pioneering the use of high speed data communications by satellite in Europe.

Linking market interaction intensity of 3D Ising type financial model with market volatility

Science.gov (United States)

Fang, Wen; Ke, Jinchuan; Wang, Jun; Feng, Ling

2016-11-01

Microscopic interaction models in physics have been used to investigate the complex phenomena of economic systems. The simple interactions involved can lead to complex behaviors and help the understanding of mechanisms in the financial market at a systemic level. This article aims to develop a financial time series model through 3D (three-dimensional) Ising dynamic system which is widely used as an interacting spins model to explain the ferromagnetism in physics. Through Monte Carlo simulations of the financial model and numerical analysis for both the simulation return time series and historical return data of Hushen 300 (HS300) index in Chinese stock market, we show that despite its simplicity, this model displays stylized facts similar to that seen in real financial market. We demonstrate a possible underlying link between volatility fluctuations of real stock market and the change in interaction strengths of market participants in the financial model. In particular, our stochastic interaction strength in our model demonstrates that the real market may be consistently operating near the critical point of the system.

Galactic cosmic ray and El Nino Southern Oscillation trends in International Satellite Cloud Climatology Project D2 low-cloud properties

DEFF Research Database (Denmark)

Marsh, N.; Svensmark, Henrik

2003-01-01

[1] The recently reported correlation between clouds and galactic cosmic rays (GCR) implies the existence of a previously unknown process linking solar variability and climate. An analysis of the interannual variability of International Satellite Cloud Climatology Project D2 (ISCCP-D2) low-cloud...... a strong correlation with GCR, which suggests that low-cloud properties observed in these regions are less likely to be contaminated from overlying cloud. The GCR-low cloud correlation cannot easily be explained by internal climate processes, changes in direct solar forcing, or UV-ozone interactions...... properties over the period July 1983 to August 1994 suggests that low clouds are statistically related to two processes, (1) GCR and (2) El Nino-Southern Oscillation (ENSO), with GCR explaining a greater percentage of the total variance. Areas where satellites have an unobstructed view of low cloud possess...

Exploring the disconnections: Student interaction with support services upon commencement of distance education

Directory of Open Access Journals (Sweden)

Mark Brown

2013-08-01

Full Text Available While provision of appropriate supports in the first year of study has been found to have a positive effect on student success, supports targeting online and distance learners are often applied in a “goulash approach.” Against this backdrop, the research investigated the experiences of first-time distance learners with a view to informing the future design of supports during the early stages of the study lifecycle. The study was framed around Design-Based Research involving a mixed method approach over three phases: a stocktake of services designed to support distance learning; a pre- and post-semester survey of first-time distance learners; and a video diary phase that gathered the lived experiences of 20 students upon commencement of their study. Triangulated results of the three phases highlight a disconnection between institutional support services and the majority of first-time distance learners who demonstrated a self-sufficient, lone wolf approach to learning. .

General conditions for the generation of long-distance entanglement

International Nuclear Information System (INIS)

Kuwahara, Tomotaka

2012-01-01

We generally investigate necessary conditions for the generation of long-distance entanglement. We consider a quantum system in which a system mediates the indirect interaction between two spins, which we refer to as probe spins. Firstly, we weaken the coupling between each probe spin and the mediator system to the infinitesimal strength in order to generate the long-distance entanglement. We give two necessary conditions for the mediator system to generate the long-distance entanglement. We prove that indirect interaction cannot generate the entanglement if it is ‘classical’. We also give a necessary condition for the effective fields on the probe spins to satisfy. Secondly, we generate the long-distance entanglement by the use of only external fields. We show that external fields on the adjacent spins to the probes are necessary in addition to external fields on the probe spins. Finally, we consider the cases where the coupling strength between each probe spin and the mediator system is finite. In particular, we show two examples where the external fields on the mediator system highly enhance the long-distance entanglement. (paper)

Earth-satellite propagation above GHz: Papers from the 1972 spring URSI session on experiments utilizing the ATS-5 satellite

Science.gov (United States)

Ippolito, L. J. (Compiler)

1972-01-01

Papers are reported from the Special Session on Earth-Satellite Propagation Above 10 GHz, presented at The 1972 Spring Meeting of the United States National Committee, International Union of Radio Science, April 1972, Washington, D. C. This session was devoted to propagation measurements associated with the Applications Technology Satellite (ATS-5), which provided the first operational earth-space links at frequencies above 15 GHz. A comprehensive summary is presented of the major results of the ATS-5 experiment measurements and related radiometric, radar and meteorological studies. The papers are organized around seven selected areas of interest, with the results of the various investigators combined into a single paper presented by a principal author for that area. A comprehensive report is provided on the results of the ATS-5 satellite to earth transmissions. A complete list of published reports and presentations related to the ATS-5 Millimeter Wave Experiment is included.

Linking probabilities of off-lattice self-avoiding polygons and the effects of excluded volume

International Nuclear Information System (INIS)

Hirayama, Naomi; Deguchi, Tetsuo; Tsurusaki, Kyoichi

2009-01-01

We evaluate numerically the probability of linking, i.e. the probability of a given pair of self-avoiding polygons (SAPs) being entangled and forming a nontrivial link type L. In the simulation we generate pairs of SAPs of N spherical segments of radius r d such that they have no overlaps among the segments and each of the SAPs has the trivial knot type. We evaluate the probability of a self-avoiding pair of SAPs forming a given link type L for various link types with fixed distance R between the centers of mass of the two SAPs. We define normalized distance r by r=R/R g,0 1 where R g,0 1 denotes the square root of the mean square radius of gyration of SAP of the trivial knot 0 1 . We introduce formulae expressing the linking probability as a function of normalized distance r, which gives good fitting curves with respect to χ 2 values. We also investigate the dependence of linking probabilities on the excluded-volume parameter r d and the number of segments, N. Quite interestingly, the graph of linking probability versus normalized distance r shows no N-dependence at a particular value of the excluded volume parameter, r d = 0.2

Facial expression recognition and model-based regeneration for distance teaching

Science.gov (United States)

De Silva, Liyanage C.; Vinod, V. V.; Sengupta, Kuntal

1998-12-01

This paper presents a novel idea of a visual communication system, which can support distance teaching using a network of computers. Here the author's main focus is to enhance the quality of distance teaching by reducing the barrier between the teacher and the student, which is formed due to the remote connection of the networked participants. The paper presents an effective way of improving teacher-student communication link of an IT (Information Technology) based distance teaching scenario, using facial expression recognition results and face global and local motion detection results of both the teacher and the student. It presents a way of regenerating the facial images for the teacher-student down-link, which can enhance the teachers facial expressions and which also can reduce the network traffic compared to usual video broadcasting scenarios. At the same time, it presents a way of representing a large volume of facial expression data of the whole student population (in the student-teacher up-link). This up-link representation helps the teacher to receive an instant feed back of his talk, as if he was delivering a face to face lecture. In conventional video tele-conferencing type of applications, this task is nearly impossible, due to huge volume of upward network traffic. The authors utilize several of their previous publication results for most of the image processing components needs to be investigated to complete such a system. In addition, some of the remaining system components are covered by several on going work.

Photo-cross-linked small-molecule microarrays as chemical genomic tools for dissecting protein-ligand interactions.

Science.gov (United States)

Kanoh, Naoki; Asami, Aya; Kawatani, Makoto; Honda, Kaori; Kumashiro, Saori; Takayama, Hiroshi; Simizu, Siro; Amemiya, Tomoyuki; Kondoh, Yasumitsu; Hatakeyama, Satoru; Tsuganezawa, Keiko; Utata, Rei; Tanaka, Akiko; Yokoyama, Shigeyuki; Tashiro, Hideo; Osada, Hiroyuki

2006-12-18

We have developed a unique photo-cross-linking approach for immobilizing a variety of small molecules in a functional-group-independent manner. Our approach depends on the reactivity of the carbene species generated from trifluoromethylaryldiazirine upon UV irradiation. It was demonstrated in model experiments that the photogenerated carbenes were able to react with every small molecule tested, and they produced multiple conjugates in most cases. It was also found in on-array immobilization experiments that various small molecules were immobilized, and the immobilized small molecules retained their ability to interact with their binding proteins. With this approach, photo-cross-linked microarrays of about 2000 natural products and drugs were constructed. This photo-cross-linked microarray format was found to be useful not merely for ligand screening but also to study the structure-activity relationship, that is, the relationship between the structural motif (or pharmacophore) found in small molecules and its binding affinity toward a protein, by taking advantage of the nonselective nature of the photo-cross-linking process.

Remote Sensing of Aerosols from Satellites: Why Has It Been Do Difficult to Quantify Aerosol-Cloud Interactions for Climate Assessment, and How Can We Make Progress?

Science.gov (United States)

Kahn, Ralph A.

2015-01-01

The organizers of the National Academy of Sciences Arthur M. Sackler Colloquia Series on Improving Our Fundamental Understanding of the Role of Aerosol-Cloud Interactions in the Climate System would like to post Ralph Kahn's presentation entitled Remote Sensing of Aerosols from Satellites: Why has it been so difficult to quantify aerosol-cloud interactions for climate assessment, and how can we make progress? to their public website.

How geographic distance and political ideology interact to influence public perception of unconventional oil/natural gas development

International Nuclear Information System (INIS)

Clarke, Christopher E.; Bugden, Dylan; Hart, P. Sol; Stedman, Richard C.; Jacquet, Jeffrey B.; Evensen, Darrick T.N.; Boudet, Hilary S.

2016-01-01

A growing area of research has addressed public perception of unconventional oil and natural gas development via hydraulic fracturing (“fracking”). We extend this research by examining how geographic proximity to such extraction interacts with political ideology to influence issue support. Regression analysis of data from a fall 2013 national telephone survey of United States residents reveals that as respondents’ geographic distance from areas experiencing significant development increases, political ideology becomes more strongly associated with issue support, with the liberal-partisan divide widening. Our findings support construal level theory's central premise: that people use more abstract considerations (like political ideology) the more geographically removed they are from an issue. We discuss implications for studying public opinion of energy development as well as for risk communication. - Highlights: • Conservatives support unconventional oil and gas development (UOGD) more than liberals. • This divide widened as geographic distance from UOGD areas increased • Construal Level Theory may help explain this finding • We discuss implications for energy policy and risk communication

Collage of Saturn's smaller satellites

Science.gov (United States)

1981-01-01

This family portrait shows the smaller satellites of Saturn as viewed by Voyager 2 during its swing through the Saturnian system. The following chart corresponds to this composite photograph (distance from the planet increases from left to right) and lists names, standard numerical designations and approximate dimensions (radii where indicated) in kilometers: 1980S26Outer F-ringshepherd120 X 100 1980S1Leadingco-orbital220 X 160 1980S25TrailingTethys trojanradii: 25 1980S28Outer Ashepherdradii: 20 1980S27Inner F-ringco-orbital145 X 70 1980S3TrailingTethys trojan140 X 100 1980S13LeadingTethys trojanradii: 30 1980S6LeadingDione trojanradii: 30 These images have been scaled to show the satellites in true relative sizes. This set of small objects ranges in size from small asteroidal scales to nearly the size of Saturn's moon Mimas. They are probably fragments of somewhat larger bodies broken up during the bombardment period that followed accretion of the Saturnian system. Scientists believe they may be mostly icy bodies with a mixture of meteorite rock. They are somewhat less reflective than the larger satellites, suggesting that thermal evolution of the larger moons 'cleaned up' their icy surfaces. The Voyager project is managed for NASA by the Jet Propulsion Laboratory, Pasadena, Calif.

Relationship between Social Media and Academic Performance in Distance Education

Science.gov (United States)

Gupta, C. A. Pallavi; Singh, Bharti; Marwaha, Tushar

2013-01-01

The scope and method of imparting distance education to the learner has evolved over a period of time. Various models of distance education have been introduced over the years; the latest introduction is the use of Web 2.0 technologies to make distance learning more analytical, flexible, interactive, and collaborative for both the teacher and the…

The quasi-parallel lives of satellite cells and atrophying muscle

Directory of Open Access Journals (Sweden)

Stefano eBiressi

2015-07-01

Full Text Available Skeletal muscle atrophy or wasting accompanies various chronic illnesses and the aging process, thereby reducing muscle function. One of the most important components contributing to effective muscle repair in postnatal organisms, the satellite cells, have recently become the focus of several studies examining factors participating in the atrophic process. We critically examine here the experimental evidence linking satellite cell function with muscle loss in connection with various diseases as well as aging, and in the subsequent recovery process. Several recent reports have investigated the changes in satellite cells in terms of their differentiation and proliferative capacity in response to various atrophic stimuli. In this regard, we review the molecular changes within satellite cells that contribute to their dysfunctional status in atrophy, with the intention of shedding light on novel potential pharmacological targets to counteract the loss of muscle mass.

Linking Customer Interaction and Innovation

DEFF Research Database (Denmark)

Foss, Nicolai Juul; Laursen, Keld; Pedersen, Torben

2011-01-01

employees for sharing and acquiring knowledge, and high levels of delegation of decision rights. In this paper, six hypotheses were developed and tested on a data set of 169 Danish firms drawn from a 2001 survey of the 1,000 largest firms in Denmark. A key result is that the link from customer knowledge...

V-SIPAL - A VIRTUAL LABORATORY FOR SATELLITE IMAGE PROCESSING AND ANALYSIS

Directory of Open Access Journals (Sweden)

K. M. Buddhiraju

2012-09-01

Full Text Available In this paper a virtual laboratory for the Satellite Image Processing and Analysis (v-SIPAL being developed at the Indian Institute of Technology Bombay is described. v-SIPAL comprises a set of experiments that are normally carried out by students learning digital processing and analysis of satellite images using commercial software. Currently, the experiments that are available on the server include Image Viewer, Image Contrast Enhancement, Image Smoothing, Edge Enhancement, Principal Component Transform, Texture Analysis by Co-occurrence Matrix method, Image Indices, Color Coordinate Transforms, Fourier Analysis, Mathematical Morphology, Unsupervised Image Classification, Supervised Image Classification and Accuracy Assessment. The virtual laboratory includes a theory module for each option of every experiment, a description of the procedure to perform each experiment, the menu to choose and perform the experiment, a module on interpretation of results when performed with a given image and pre-specified options, bibliography, links to useful internet resources and user-feedback. The user can upload his/her own images for performing the experiments and can also reuse outputs of one experiment in another experiment where applicable. Some of the other experiments currently under development include georeferencing of images, data fusion, feature evaluation by divergence andJ-M distance, image compression, wavelet image analysis and change detection. Additions to the theory module include self-assessment quizzes, audio-video clips on selected concepts, and a discussion of elements of visual image interpretation. V-SIPAL is at the satge of internal evaluation within IIT Bombay and will soon be open to selected educational institutions in India for evaluation.

Modulation/demodulation techniques for satellite communications. Part 1: Background

Science.gov (United States)

Omura, J. K.; Simon, M. K.

1981-01-01

Basic characteristics of digital data transmission systems described include the physical communication links, the notion of bandwidth, FCC regulations, and performance measurements such as bit rates, bit error probabilities, throughputs, and delays. The error probability performance and spectral characteristics of various modulation/demodulation techniques commonly used or proposed for use in radio and satellite communication links are summarized. Forward error correction with block or convolutional codes is also discussed along with the important coding parameter, channel cutoff rate.

Distance to High-Voltage Power Lines and Risk of Childhood Leukemia – an Analysis of Confounding by and Interaction with Other Potential Risk Factors

DEFF Research Database (Denmark)

Pedersen, Camilla; Bräuner, Elvira V; Rod, Naja Hulvej

2014-01-01

. We used geographical information systems to determine the distance between residence at birth and the nearest 132-400 kV overhead power line. Concentrations of domestic radon and traffic-related air pollution (NOx at the front door) were estimated using validated models. We found a statistically......We investigated whether there is an interaction between distance from residence at birth to nearest power line and domestic radon and traffic-related air pollution, respectively, in relation to childhood leukemia risk. Further, we investigated whether adjusting for potential confounders alters...

U.S. dental hygiene faculty perceptions of learner outcomes in distance education courses.

Science.gov (United States)

Corum, Kathrine A; Gadbury-Amyot, Cynthia C; Johnson, Kerry; Strait, Tia M

2014-04-01

The purpose of this study was to determine perceptions of full-time, entry-level dental hygiene educators regarding the ability to achieve interaction in their distance education courses and the impact of interaction on learning outcomes. The specific interactions explored were student-instructor, student-content, and student-student. A survey was developed, pilot tested, revised, and mailed to 287 educators across the United States, generating an overall response rate of 22.3 percent. The majority of respondents perceived interaction to be achievable in their distance courses, to increase through technology, and to positively influence learning outcomes. Nearly 90 percent reported student-instructor interaction as achievable, 95.3 percent reported student-content interaction as achievable, and 79.7 percent reported student-student interaction as achievable. Learning outcomes were defined in this study as the student's achievement of course objectives and competencies at course completion. Approximately 81 percent of the respondents reported a positive influence from student-instructor interaction, 79.7 percent from student-content interaction, and 70.3 percent from student-student interaction. This study also examined which modalities were perceived as being most influential in achieving interaction. The results demonstrated a prevalence of discussion board posting in an environment in which numerous Web 2.0 tools are available and respondents were not as positive about their ability to achieve student-student interaction in the distance learning environment. The authors conclude that faculty development is critical in achieving quality outcomes in dental hygiene distance education courses.

The space between us: stereotype threat and distance in interracial contexts.

Science.gov (United States)

Goff, Phillip Atiba; Steele, Claude M; Davies, Paul G

2008-01-01

Four studies investigate the role that stereotype threat plays in producing racial distancing behavior in an anticipated conversation paradigm. It was hypothesized that the threat of appearing racist may have the ironic effect of causing Whites to distance themselves from Black conversation partners. In Study 1, participants distanced themselves more from Black partners under conditions of threat, and this distance correlated with the activation of a "White racist" stereotype. In Study 2, it was demonstrated that Whites' interracial distancing behavior was not predicted by explicit or implicit prejudice. Study 3 provides evidence that conceiving of interracial interactions as opportunities to learn may attenuate the negative consequences of threat for Whites. Study 4 found that Whites have conscious access to their experience of stereotype threat and that this awareness may mediate the relationship between threat and distance. These results are discussed within a broader discourse of racial distancing and the possibility that certain identity threats may be as important as prejudice in determining the outcomes of interracial interactions. Copyright 2008 APA, all rights reserved.

Linked-cluster formulation of electron-hole interaction kernel in real-space representation without using unoccupied states.

Science.gov (United States)

Bayne, Michael G; Scher, Jeremy A; Ellis, Benjamin H; Chakraborty, Arindam

2018-05-21

Electron-hole or quasiparticle representation plays a central role in describing electronic excitations in many-electron systems. For charge-neutral excitation, the electron-hole interaction kernel is the quantity of interest for calculating important excitation properties such as optical gap, optical spectra, electron-hole recombination and electron-hole binding energies. The electron-hole interaction kernel can be formally derived from the density-density correlation function using both Green's function and TDDFT formalism. The accurate determination of the electron-hole interaction kernel remains a significant challenge for precise calculations of optical properties in the GW+BSE formalism. From the TDDFT perspective, the electron-hole interaction kernel has been viewed as a path to systematic development of frequency-dependent exchange-correlation functionals. Traditional approaches, such as MBPT formalism, use unoccupied states (which are defined with respect to Fermi vacuum) to construct the electron-hole interaction kernel. However, the inclusion of unoccupied states has long been recognized as the leading computational bottleneck that limits the application of this approach for larger finite systems. In this work, an alternative derivation that avoids using unoccupied states to construct the electron-hole interaction kernel is presented. The central idea of this approach is to use explicitly correlated geminal functions for treating electron-electron correlation for both ground and excited state wave functions. Using this ansatz, it is derived using both diagrammatic and algebraic techniques that the electron-hole interaction kernel can be expressed only in terms of linked closed-loop diagrams. It is proved that the cancellation of unlinked diagrams is a consequence of linked-cluster theorem in real-space representation. The electron-hole interaction kernel derived in this work was used to calculate excitation energies in many-electron systems and results

Dynamical history of coplanar two-satellite systems

International Nuclear Information System (INIS)

Ruskol, E.L.; Nikolajeva, E.V.; Syzdykov, A.S.

1975-01-01

One of the possible early states of the Earth-Moon system was a system of several large satellites around the Earth. The dynamical evolution of coplanar three-body systems is studied; a planet (Earth) and two massive satellites (proto-moons) with geocentric orbits of slightly different radii. Such configurations may arise in multiple satellite systems receding from a planet due to tidal friction. The numerical integration of the equations of motion shows that initially circular Keplerian orbits are soon transformed into disturbed elliptic orbits which are intersecting. The life-time of such a coplanar system between two probable physical collisions of satellites is roughly from one day to one year for satellite systems with radii less than 20 R(Earth), and may reach 100 yr for three-dimensional systems. This time-scale is short in comparison with the duration of the removal of satellites due to tides raised on the planet, which is estimated as 10 6 -10 8 yr for the same orbital dimensions. Therefore, the life-time of a system of several proto-moons is mainly determined by their tidal interactions with the Earth. For conditions which we have considered, the most probable result of the evolution was coalescence of satellites as the consequence of the collisions. (Auth.)

ANALYSIS OF THE EFFECTS OF IMAGE QUALITY ON DIGITAL MAP GENERATION FROM SATELLITE IMAGES

Directory of Open Access Journals (Sweden)

H. Kim

2012-07-01

Full Text Available High resolution satellite images are widely used to produce and update a digital map since they became widely available. It is well known that the accuracy of digital map produced from satellite images is decided largely by the accuracy of geometric modelling. However digital maps are made by a series of photogrammetric workflow. Therefore the accuracy of digital maps are also affected by the quality of satellite images, such as image interpretability. For satellite images, parameters such as Modulation Transfer Function(MTF, Signal to Noise Ratio(SNR and Ground Sampling Distance(GSD are used to present images quality. Our previous research stressed that such quality parameters may not represent the quality of image products such as digital maps and that parameters for image interpretability such as Ground Resolved Distance(GRD and National Imagery Interpretability Rating Scale(NIIRS need to be considered. In this study, we analyzed the effects of the image quality on accuracy of digital maps produced by satellite images. QuickBird, IKONOS and KOMPSAT-2 imagery were used to analyze as they have similar GSDs. We measured various image quality parameters mentioned above from these images. Then we produced digital maps from the images using a digital photogrammetric workstation. We analyzed the accuracy of the digital maps in terms of their location accuracy and their level of details. Then we compared the correlation between various image quality parameters and the accuracy of digital maps. The results of this study showed that GRD and NIIRS were more critical for map production then GSD, MTF or SNR.

Evaluating the hydrological consistency of satellite based water cycle components

KAUST Repository

Lopez Valencia, Oliver Miguel

2016-06-15

Advances in multi-satellite based observations of the earth system have provided the capacity to retrieve information across a wide-range of land surface hydrological components and provided an opportunity to characterize terrestrial processes from a completely new perspective. Given the spatial advantage that space-based observations offer, several regional-to-global scale products have been developed, offering insights into the multi-scale behaviour and variability of hydrological states and fluxes. However, one of the key challenges in the use of satellite-based products is characterizing the degree to which they provide realistic and representative estimates of the underlying retrieval: that is, how accurate are the hydrological components derived from satellite observations? The challenge is intrinsically linked to issues of scale, since the availability of high-quality in-situ data is limited, and even where it does exist, is generally not commensurate to the resolution of the satellite observation. Basin-scale studies have shown considerable variability in achieving water budget closure with any degree of accuracy using satellite estimates of the water cycle. In order to assess the suitability of this type of approach for evaluating hydrological observations, it makes sense to first test it over environments with restricted hydrological inputs, before applying it to more hydrological complex basins. Here we explore the concept of hydrological consistency, i.e. the physical considerations that the water budget impose on the hydrologic fluxes and states to be temporally and spatially linked, to evaluate the reproduction of a set of large-scale evaporation (E) products by using a combination of satellite rainfall (P) and Gravity Recovery and Climate Experiment (GRACE) observations of storage change, focusing on arid and semi-arid environments, where the hydrological flows can be more realistically described. Our results indicate no persistent hydrological

STABILITY OF SATELLITES IN CLOSELY PACKED PLANETARY SYSTEMS

International Nuclear Information System (INIS)

Payne, Matthew J.; Holman, Matthew J.; Deck, Katherine M.; Perets, Hagai B.

2013-01-01

We perform numerical integrations of four-body (star, planet, planet, satellite) systems to investigate the stability of satellites in planetary systems with tightly packed inner planets (STIPs). We find that the majority of closely spaced stable two-planet systems can stably support satellites across a range of parameter-space which is only slightly decreased compared to that seen for the single-planet case. In particular, circular prograde satellites remain stable out to ∼0.4 R H (where R H is the Hill radius) as opposed to 0.5 R H in the single-planet case. A similarly small restriction in the stable parameter-space for retrograde satellites is observed, where planetary close approaches in the range 2.5-4.5 mutual Hill radii destabilize most satellites orbits only if a ∼ 0.65 R H . In very close planetary pairs (e.g., the 12:11 resonance) the addition of a satellite frequently destabilizes the entire system, causing extreme close approaches and the loss of satellites over a range of circumplanetary semi-major axes. The majority of systems investigated stably harbored satellites over a wide parameter-space, suggesting that STIPs can generally offer a dynamically stable home for satellites, albeit with a slightly smaller stable parameter-space than the single-planet case. As we demonstrate that multi-planet systems are not a priori poor candidates for hosting satellites, future measurements of satellite occurrence rates in multi-planet systems versus single-planet systems could be used to constrain either satellite formation or past periods of strong dynamical interaction between planets

LTE Adaptation for Mobile Broadband Satellite Networks

Directory of Open Access Journals (Sweden)

Bastia Francesco

2009-01-01

Full Text Available One of the key factors for the successful deployment of mobile satellite systems in 4G networks is the maximization of the technology commonalities with the terrestrial systems. An effective way of achieving this objective consists in considering the terrestrial radio interface as the baseline for the satellite radio interface. Since the 3GPP Long Term Evolution (LTE standard will be one of the main players in the 4G scenario, along with other emerging technologies, such as mobile WiMAX; this paper analyzes the possible applicability of the 3GPP LTE interface to satellite transmission, presenting several enabling techniques for this adaptation. In particular, we propose the introduction of an inter-TTI interleaving technique that exploits the existing H-ARQ facilities provided by the LTE physical layer, the use of PAPR reduction techniques to increase the resilience of the OFDM waveform to non linear distortion, and the design of the sequences for Random Access, taking into account the requirements deriving from the large round trip times. The outcomes of this analysis show that, with the required proposed enablers, it is possible to reuse the existing terrestrial air interface to transmit over the satellite link.

The influence of interactions between accommodation and convergence on the lag of accommodation.

Science.gov (United States)

Schor, C

1999-03-01

Several models of myopia predict that growth of axial length is stimulated by blur. Accommodative lag has been suggested as an important source of blur in the development of myopia and this study has modeled how cross-link interactions between accommodation and convergence might interact with uncorrected distance heterophoria and refractive error to influence accommodative lag. Accommodative lag was simulated with two models of interactions between accommodation and convergence (one with and one without adaptable tonic elements). Simulations of both models indicate that both uncorrected hyperopia and esophoria increase the lag of accommodative and uncorrected myopia and exophoria decrease the lag or introduce a lead of accommodation in response to the near (40 cm) stimulus. These effects were increased when gain of either cross-link, accommodative convergence (AC/A) or convergence accommodation (CA/C), was increased within a moderate range of values while the other was fixed at a normal value (clamped condition). These effects were exaggerated when both the AC/A and CA/C ratios were increased (covaried condition) and affects of cross-link gain were negated when an increase of one cross-link (e.g. AC/A) was accompanied by a reduction of the other cross-link (e.g. CA/C) (reciprocal condition). The inclusion of tonic adaptation in the model reduced steady state errors of accommodation for all conditions except when the AC/A ratio was very high (2 MA/D). Combinations of cross-link interactions between accommodation and convergence that resemble either clamped or reciprocal patterns occur naturally in clinical populations. Simulations suggest that these two patterns of abnormal cross-link interactions could affect the progression of myopia differently. Adaptable tonic accommodation and tonic vergence could potentially reduce the progression of myopia by reducing the lag of accommodation.

Satellite communication system for emergency monitoring within the Chernobyl exclusion zone

International Nuclear Information System (INIS)

Franchini, C.; Mensa, M.; Kanevsky, V.A.

1997-01-01

A Satellite Emergency Monitoring system of the Chernobyl Exclusive Zone (SEM CEZ) was designed to provide the Ukraine authorities and the neighbouring countries with updated information when an emergency situation occurs in the Exclusion Zone. This is of particular importance when environment contamination has transboundary effect. SEM system consists of mobile and fixed sensors reporting data via a dedicated satellite communications link. Mobile sensors are fitted with Global Positioning System (GPS) receivers that determine current coordinates of the sensor. Sensors data are transmitted to the Emergency Monitoring Centre equipped with PC and a satellite terminal. Both sensors data and the current position are visualized on digital maps

Alaska northern fur seal adult male satellite telemetry data, 2009-2010

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This data set is comprised of satellite-linked telemetry data collected to investigate winter migration patterns and foraging strategies of adult male northern fur...

Design and Optimization of a 3-Coil Inductive Link for Efficient Wireless Power Transmission.

Science.gov (United States)

Kiani, Mehdi; Jow, Uei-Ming; Ghovanloo, Maysam

2011-07-14

Inductive power transmission is widely used to energize implantable microelectronic devices (IMDs), recharge batteries, and energy harvesters. Power transfer efficiency (PTE) and power delivered to the load (PDL) are two key parameters in wireless links, which affect the energy source specifications, heat dissipation, power transmission range, and interference with other devices. To improve the PTE, a 4-coil inductive link has been recently proposed. Through a comprehensive circuit based analysis that can guide a design and optimization scheme, we have shown that despite achieving high PTE at larger coil separations, the 4-coil inductive links fail to achieve a high PDL. Instead, we have proposed a 3-coil inductive power transfer link with comparable PTE over its 4-coil counterpart at large coupling distances, which can also achieve high PDL. We have also devised an iterative design methodology that provides the optimal coil geometries in a 3-coil inductive power transfer link. Design examples of 2-, 3-, and 4-coil inductive links have been presented, and optimized for 13.56 MHz carrier frequency and 12 cm coupling distance, showing PTEs of 15%, 37%, and 35%, respectively. At this distance, the PDL of the proposed 3-coil inductive link is 1.5 and 59 times higher than its equivalent 2- and 4-coil links, respectively. For short coupling distances, however, 2-coil links remain the optimal choice when a high PDL is required, while 4-coil links are preferred when the driver has large output resistance or small power is needed. These results have been verified through simulations and measurements.

The Interactive Modes of Non-Native Speakers in International Chinese Language Distance Class Discussions: An Analysis of Smiling as a Facial Cue

Science.gov (United States)

Sunaoka, Kazuko

2018-01-01

The focus of this research is on an international distance discussion class carried out in Chinese between university students in Japan, China and Taiwan using videoconferencing. Smiling was used as an interactional index in an analysis of the archival footage of the recordings of the discussion between native speakers (NS) of Chinese and…

Distance education: Physics through the University of South Carolina for pre-service and in-service K-12 teachers

Science.gov (United States)

Safko, John L.; Edge, Ronald D.

1997-03-01

For the past several years (10 years for JLS, 3 years for RDE) we have been offering telecommunications-based distance education for K-12 teachers through our Office of Distance Education. In addition to practicing teachers and those majoring in science education, we also enroll students who are working on their Master's of Art in Teaching. These latter students often have an undergraduate degree in some science and are completing content and methods courses for state certification as a teacher. These courses are delivered by video cassette and written material. The courses offered are a two semester introductory physics course (by JLS) and a one semester course in physics demonstrations and experiments suitable for the elementary/middle/high school with little or no sources of equipment (by RDE). These courses will be described in the next two sections. First, a few comments on the services provided by the Office of Distance Education and Instructional Services. The University of South Carolina has been offering courses by telecommunications instruction since 1972. During that time it has developed excellent support services for the instructor. Currently the university offers courses live over satellite links and by video cassette to over 10,000 students. The office provides recording capabilities as well as taking care of distribution of video and print materials. They coordinate the receipt and return of any assignments and exams and provide student services for questions about enrollment, supplies, and other technical problems versus content questions. Keeping all of this organized is a full time job for many staff.

The influence of distance and level of care on delivery place in rural Zambia: a study of linked national data in a geographic information system.

Science.gov (United States)

Gabrysch, Sabine; Cousens, Simon; Cox, Jonathan; Campbell, Oona M R

2011-01-25

Maternal and perinatal mortality could be reduced if all women delivered in settings where skilled attendants could provide emergency obstetric care (EmOC) if complications arise. Research on determinants of skilled attendance at delivery has focussed on household and individual factors, neglecting the influence of the health service environment, in part due to a lack of suitable data. The aim of this study was to quantify the effects of distance to care and level of care on women's use of health facilities for delivery in rural Zambia, and to compare their population impact to that of other important determinants. Using a geographic information system (GIS), we linked national household data from the Zambian Demographic and Health Survey 2007 with national facility data from the Zambian Health Facility Census 2005 and calculated straight-line distances. Health facilities were classified by whether they provided comprehensive EmOC (CEmOC), basic EmOC (BEmOC), or limited or substandard services. Multivariable multilevel logistic regression analyses were performed to investigate the influence of distance to care and level of care on place of delivery (facility or home) for 3,682 rural births, controlling for a wide range of confounders. Only a third of rural Zambian births occurred at a health facility, and half of all births were to mothers living more than 25 km from a facility of BEmOC standard or better. As distance to the closest health facility doubled, the odds of facility delivery decreased by 29% (95% CI, 14%-40%). Independently, each step increase in level of care led to 26% higher odds of facility delivery (95% CI, 7%-48%). The population impact of poor geographic access to EmOC was at least of similar magnitude as that of low maternal education, household poverty, or lack of female autonomy. Lack of geographic access to emergency obstetric care is a key factor explaining why most rural deliveries in Zambia still occur at home without skilled care

The influence of distance and level of care on delivery place in rural Zambia: a study of linked national data in a geographic information system.

Directory of Open Access Journals (Sweden)

Sabine Gabrysch

Full Text Available BACKGROUND: Maternal and perinatal mortality could be reduced if all women delivered in settings where skilled attendants could provide emergency obstetric care (EmOC if complications arise. Research on determinants of skilled attendance at delivery has focussed on household and individual factors, neglecting the influence of the health service environment, in part due to a lack of suitable data. The aim of this study was to quantify the effects of distance to care and level of care on women's use of health facilities for delivery in rural Zambia, and to compare their population impact to that of other important determinants. METHODS AND FINDINGS: Using a geographic information system (GIS, we linked national household data from the Zambian Demographic and Health Survey 2007 with national facility data from the Zambian Health Facility Census 2005 and calculated straight-line distances. Health facilities were classified by whether they provided comprehensive EmOC (CEmOC, basic EmOC (BEmOC, or limited or substandard services. Multivariable multilevel logistic regression analyses were performed to investigate the influence of distance to care and level of care on place of delivery (facility or home for 3,682 rural births, controlling for a wide range of confounders. Only a third of rural Zambian births occurred at a health facility, and half of all births were to mothers living more than 25 km from a facility of BEmOC standard or better. As distance to the closest health facility doubled, the odds of facility delivery decreased by 29% (95% CI, 14%-40%. Independently, each step increase in level of care led to 26% higher odds of facility delivery (95% CI, 7%-48%. The population impact of poor geographic access to EmOC was at least of similar magnitude as that of low maternal education, household poverty, or lack of female autonomy. CONCLUSIONS: Lack of geographic access to emergency obstetric care is a key factor explaining why most rural deliveries

Characteristics of equatorial ionization anomaly (EIA) in relation to transionospheric satellite links around the northern crest in the Indian longitude sector

Science.gov (United States)

Das, A.; Paul, K. S.; Halder, S.; Basu, K.; Paul, A.

2014-02-01

The poleward gradient of the equatorial ionization anomaly (EIA) introduces more intense propagation effects on transionospheric satellite links in comparison to the equatorward gradient. Characterization of the poleward gradient was performed during March-April, August-October 2011 and March-April 2012 using GPS total electron content (TEC) recorded from a chain of stations located more or less along the same meridian (88.5° E) at Calcutta, Baharampore, Farakka and Siliguri. The poleward gradients calculated on magnetically quiet days at elevation in excess of 50° at 14:00, 15:00 and 16:00 LT were found to have a strong correlation with GPS S4 observed from Calcutta during post-sunset-to-midnight hours. A threshold value of poleward TEC gradient is calculated above which there is a probability of scintillation at Calcutta with S4 ≥ 0.4.

Characteristics of equatorial ionization anomaly (EIA in relation to transionospheric satellite links around the northern crest in the Indian longitude sector

Directory of Open Access Journals (Sweden)

A. Das

2014-02-01

Full Text Available The poleward gradient of the equatorial ionization anomaly (EIA introduces more intense propagation effects on transionospheric satellite links in comparison to the equatorward gradient. Characterization of the poleward gradient was performed during March–April, August–October 2011 and March–April 2012 using GPS total electron content (TEC recorded from a chain of stations located more or less along the same meridian (88.5° E at Calcutta, Baharampore, Farakka and Siliguri. The poleward gradients calculated on magnetically quiet days at elevation in excess of 50° at 14:00, 15:00 and 16:00 LT were found to have a strong correlation with GPS S4 observed from Calcutta during post-sunset-to-midnight hours. A threshold value of poleward TEC gradient is calculated above which there is a probability of scintillation at Calcutta with S4 ≥ 0.4.

Spontaneous Self-Distancing and Adaptive Self-Reflection Across Adolescence.

Science.gov (United States)

White, Rachel E; Kross, Ethan; Duckworth, Angela L

2015-07-01

Experiments performed primarily with adults show that self-distancing facilitates adaptive self-reflection. However, no research has investigated whether adolescents spontaneously engage in this process or whether doing so is linked to adaptive outcomes. In this study, 226 African American adolescents, aged 11-20, reflected on an anger-related interpersonal experience. As expected, spontaneous self-distancing during reflection predicted lower levels of emotional reactivity by leading adolescents to reconstrue (rather than recount) their experience and blame their partner less. Moreover, the inverse relation between self-distancing and emotional reactivity strengthened with age. These findings highlight the role that self-distancing plays in fostering adaptive self-reflection in adolescence, and begin to elucidate the role that development plays in enhancing the benefits of engaging in this process. © 2015 The Authors. Child Development © 2015 Society for Research in Child Development, Inc.

Transactional Distance and Second Life: The Effects of Video Game Experience

Science.gov (United States)

Atkinson, Mark

2013-01-01

As a subset of distance education, online learning takes place primarily in learning management systems through asynchronous interaction, that can cause transactional distance between instructor and learners. This study investigated how transactional distance may be affected by the use of Second Life, a 3-D virtual world, as a learning environment…

Performance Analysis of Space Information Networks with Backbone Satellite Relaying for Vehicular Networks

Directory of Open Access Journals (Sweden)

Jian Jiao

2017-01-01

Full Text Available Space Information Network (SIN with backbone satellites relaying for vehicular network (VN communications is regarded as an effective strategy to provide diverse vehicular services in a seamless, efficient, and cost-effective manner in rural areas and highways. In this paper, we investigate the performance of SIN return channel cooperative communications via an amplify-and-forward (AF backbone satellite relaying for VN communications, where we assume that both of the source-destination and relay-destination links undergo Shadowed-Rician fading and the source-relay link follows Rician fading, respectively. In this SIN-assisted VN communication scenario, we first obtain the approximate statistical distributions of the equivalent end-to-end signal-to-noise ratio (SNR of the system. Then, we derive the closed-form expressions to efficiently evaluate the average symbol error rate (ASER of the system. Furthermore, the ASER expressions are taking into account the effect of satellite perturbation of the backbone relaying satellite, which reveal the accumulated error of the antenna pointing error. Finally, simulation results are provided to verify the accuracy of our theoretical analysis and show the impact of various parameters on the system performance.

Helical chirality: a link between local interactions and global topology in DNA.

Directory of Open Access Journals (Sweden)

Youri Timsit

Full Text Available DNA supercoiling plays a major role in many cellular functions. The global DNA conformation is however intimately linked to local DNA-DNA interactions influencing both the physical properties and the biological functions of the supercoiled molecule. Juxtaposition of DNA double helices in ubiquitous crossover arrangements participates in multiple functions such as recombination, gene regulation and DNA packaging. However, little is currently known about how the structure and stability of direct DNA-DNA interactions influence the topological state of DNA. Here, a crystallographic analysis shows that due to the intrinsic helical chirality of DNA, crossovers of opposite handedness exhibit markedly different geometries. While right-handed crossovers are self-fitted by sequence-specific groove-backbone interaction and bridging Mg(2+ sites, left-handed crossovers are juxtaposed by groove-groove interaction. Our previous calculations have shown that the different geometries result in differential stabilisation in solution, in the presence of divalent cations. The present study reveals that the various topological states of the cell are associated with different inter-segmental interactions. While the unstable left-handed crossovers are exclusively formed in negatively supercoiled DNA, stable right-handed crossovers constitute the local signature of an unusual topological state in the cell, such as the positively supercoiled or relaxed DNA. These findings not only provide a simple mechanism for locally sensing the DNA topology but also lead to the prediction that, due to their different tertiary intra-molecular interactions, supercoiled molecules of opposite signs must display markedly different physical properties. Sticky inter-segmental interactions in positively supercoiled or relaxed DNA are expected to greatly slow down the slithering dynamics of DNA. We therefore suggest that the intrinsic helical chirality of DNA may have oriented the early

Linking macroecology and community ecology: refining predictions of species distributions using biotic interaction networks.

Science.gov (United States)

Staniczenko, Phillip P A; Sivasubramaniam, Prabu; Suttle, K Blake; Pearson, Richard G

2017-06-01

Macroecological models for predicting species distributions usually only include abiotic environmental conditions as explanatory variables, despite knowledge from community ecology that all species are linked to other species through biotic interactions. This disconnect is largely due to the different spatial scales considered by the two sub-disciplines: macroecologists study patterns at large extents and coarse resolutions, while community ecologists focus on small extents and fine resolutions. A general framework for including biotic interactions in macroecological models would help bridge this divide, as it would allow for rigorous testing of the role that biotic interactions play in determining species ranges. Here, we present an approach that combines species distribution models with Bayesian networks, which enables the direct and indirect effects of biotic interactions to be modelled as propagating conditional dependencies among species' presences. We show that including biotic interactions in distribution models for species from a California grassland community results in better range predictions across the western USA. This new approach will be important for improving estimates of species distributions and their dynamics under environmental change. © 2017 The Authors. Ecology Letters published by CNRS and John Wiley & Sons Ltd.

Introverts, Extroverts, and Achievement in a Distance Learning Environment

Science.gov (United States)

Offir, Baruch; Bezalel, Rachel; Barth, Ingrid

2007-01-01

Although difficulties that characterize distance learning (DL) clearly have differential effects on different learners, links between barrier research and individual differences remain relatively unexplored. This study examined the relationship between cognitive style, based on Jung's (1971) theory, and achievement levels among 77 university…

What does electronic conferencing afford distance education?

OpenAIRE

Barnes , Sally

2000-01-01

Pre-published, final revised version of journal article published in Distance Education, 2000, Vol. 21, No. 2, pp. 236-247; Technology is potentially offering many opportunities to extend and expand distance learning in the higher education sector. Electronic conferencing, in particular, is seen as a technique, which offers opportunities for course delivery and methods of interaction for distant learners. This paper examines the similarities and differences between face-to-face seminars and o...

Geolocation applications of the Gonets LEO messaging satellites

Science.gov (United States)

Vlasov, Vladimir N.; Ashjaee, Javad M.

Geostationary satellites carry a majority of the international telecommunications traffic not carried by transoceanic cable. However, because the radio path links to and from geostationary satellites total at least 70,000 km and because of inherent on-board spacecraft power limitations, earth stations used in conjunction with geostationary satellites are usually large and expensive. This limits their installation to areas with a well-developed industrial and economic infrastructure. This reality helps perpetuate a chicken egg dilemma for the developing countries and isolated regions. Economic integration with the developed world requires being 'networked'. But for many developing entities, even the initial price of entry exceeds their modest resources. Exclusion from the global information highways virtually assures retardation of economic growth for developing nations, remote and isolated areas. Very Small Aperture Terminal (VSAT) earth stations are often thought of as a solution for networking developing regions. But economic considerations often forecloses this option. If VSAT size and cost is to be minimized, powerful spot beams from the satellite need to be focused on relatively small regions. This is not often feasible because of the high cost of the satellite itself. To dedicate a high power spot beam to a small region is usually not economically feasible.

Building policy capacities: an interactive approach for linking knowledge to action in health promotion.

Science.gov (United States)

Rütten, Alfred; Gelius, Peter

2014-09-01

This article outlines a theoretical framework for an interactive, research-driven approach to building policy capacities in health promotion. First, it illustrates how two important issues in the recent public health debate, capacity building and linking scientific knowledge to policy action, are connected to each other theoretically. It then introduces an international study on an interactive approach to capacity building in health promotion policy. The approach combines the ADEPT model of policy capacities with a co-operative planning process to foster the exchange of knowledge between policy-makers and researchers, thus improving intra- and inter-organizational capacities. A regional-level physical activity promotion project involving governmental and public-law institutions, NGOs and university researchers serves as a case study to illustrate the potential of the approach for capacity building. Analysis and comparison with a similar local-level project indicate that the approach provides an effective means of linking scientific knowledge to policy action and to planning concrete measures for capacity building in health promotion, but that it requires sufficiently long timelines and adequate resources to achieve adequate implementation and sustainability. © The Author (2013). Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Assessing the Impact of Earth Radiation Pressure Acceleration on Low-Earth Orbit Satellites

Science.gov (United States)

Vielberg, Kristin; Forootan, Ehsan; Lück, Christina; Kusche, Jürgen; Börger, Klaus

2017-04-01

The orbits of satellites are influenced by several external forces. The main non-gravitational forces besides thermospheric drag, acting on the surface of satellites, are accelerations due to the Earth and Solar Radiation Pres- sure (SRP and ERP, respectively). The sun radiates visible and infrared light reaching the satellite directly, which causes the SRP. Earth also emits and reflects the sunlight back into space, where it acts on satellites. This is known as ERP acceleration. The influence of ERP increases with decreasing distance to the Earth, and for low-earth orbit (LEO) satellites ERP must be taken into account in orbit and gravity computations. Estimating acceler- ations requires knowledge about energy emitted from the Earth, which can be derived from satellite remote sensing data, and also by considering the shape and surface material of a satellite. In this sensitivity study, we assess ERP accelerations based on different input albedo and emission fields and their modelling for the satellite missions Challenging Mini-Satellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE). As input fields, monthly 1°x1° products of Clouds and the Earth's Radiant En- ergy System (CERES), L3 are considered. Albedo and emission models are generated as latitude-dependent, as well as in terms of spherical harmonics. The impact of different albedo and emission models as well as the macro model and the altitude of satellites on ERP accelerations will be discussed.

MultiWaveLink: An interactive data base for the coordination of multiwavelength and multifacility observations

Science.gov (United States)

Cordova, F. A.

1993-01-01

MultiWaveLink is an interactive, computerized data base that was developed to facilitate a multi-wavelength approach to studying astrophysical sources. It can be used to access information about multiwavelenth resources (observers, telescopes, data bases and analysis facilities) or to organize observing campaigns that require either many telescopes operating in different spectral regimes or a network of similar telescopes circumspanning the Earth.

Arcs électriques sur panneaux solaires de satellite

OpenAIRE

Amorim, Emmanuel

2002-01-01

Tout au long de leur durée de vie, les satellites sont en interaction constante avec l'environnement spatial. En orbite géostationnaire, les surfaces des satellites sont par exemple chargées par les particules de la magnétosphère, en particulier par les électrons. Récemment, des pertes de puissance ont été constatées sur certains satellites situés en orbite géostationnaire. Ces anomalies ont été corrélées avec des périodes d'environnement chargeant et s'expliqueraient par une décharge électro...

"Known Unknowns": Current Questions in Muscle Satellite Cell Biology.

Science.gov (United States)

Cornelison, Ddw

2018-01-01

Our understanding of satellite cells, now known to be the obligate stem cells of skeletal muscle, has increased dramatically in recent years due to the introduction of new molecular, genetic, and technical resources. In addition to their role in acute repair of damaged muscle, satellite cells are of interest in the fields of aging, exercise, neuromuscular disease, and stem cell therapy, and all of these applications have driven a dramatic increase in our understanding of the activity and potential of satellite cells. However, many fundamental questions of satellite cell biology remain to be answered, including their emergence as a specific lineage, the degree and significance of heterogeneity within the satellite cell population, the roles of their interactions with other resident and infiltrating cell types during homeostasis and regeneration, and the relative roles of intrinsic vs extrinsic factors that may contribute to satellite cell dysfunction in the context of aging or disease. This review will address the current state of these open questions in satellite cell biology. © 2018 Elsevier Inc. All rights reserved.

Space Link Extension (SLE) Emulation for High-Throughput Network Communication

Science.gov (United States)

Murawski, Robert W.; Tchorowski, Nicole; Golden, Bert

2014-01-01

As the data rate requirements for space communications increases, significant stress is placed not only on the wireless satellite communication links, but also on the ground networks which forward data from end-users to remote ground stations. These wide area network (WAN) connections add delay and jitter to the end-to-end satellite communication link, effects which can have significant impacts on the wireless communication link. It is imperative that any ground communication protocol can react to these effects such that the ground network does not become a bottleneck in the communication path to the satellite. In this paper, we present our SCENIC Emulation Lab testbed which was developed to test the CCSDS SLE protocol implementations proposed for use on future NASA communication networks. Our results show that in the presence of realistic levels of network delay, high-throughput SLE communication links can experience significant data rate throttling. Based on our observations, we present some insight into why this data throttling happens, and trace the probable issue back to non-optimal blocking communication which is sup-ported by the CCSDS SLE API recommended practices. These issues were presented as well to the SLE implementation developers which, based on our reports, developed a new release for SLE which we show fixes the SLE blocking issue and greatly improves the protocol throughput. In this paper, we also discuss future developments for our end-to-end emulation lab and how these improvements can be used to develop and test future space communication technologies.

Improve observation-based ground-level ozone spatial distribution by compositing satellite and surface observations: A simulation experiment

Science.gov (United States)

Zhang, Yuzhong; Wang, Yuhang; Crawford, James; Cheng, Ye; Li, Jianfeng

2018-05-01

Obtaining the full spatial coverage of daily surface ozone fields is challenging because of the sparsity of the surface monitoring network and the difficulty in direct satellite retrievals of surface ozone. We propose an indirect satellite retrieval framework to utilize the information from satellite-measured column densities of tropospheric NO2 and CH2O, which are sensitive to the lower troposphere, to derive surface ozone fields. The method is applicable to upcoming geostationary satellites with high-quality NO2 and CH2O measurements. To prove the concept, we conduct a simulation experiment using a 3-D chemical transport model for July 2011 over the eastern US. The results show that a second order regression using both NO2 and CH2O column densities can be an effective predictor for daily maximum 8-h average ozone. Furthermore, this indirect retrieval approach is shown to be complementary to spatial interpolation of surface observations, especially in regions where the surface sites are sparse. Combining column observations of NO2 and CH2O with surface site measurements leads to an improved representation of surface ozone over simple kriging, increasing the R2 value from 0.53 to 0.64 at a surface site distance of 252 km. The improvements are even more significant with larger surface site distances. The simulation experiment suggests that the indirect satellite retrieval technique can potentially be a useful tool to derive the full spatial coverage of daily surface ozone fields if satellite observation uncertainty is moderate.

Oil collecting bees and Byrsonima cydoniifolia A. Juss. (Malpighiaceae interactions: the prevalence of long-distance cross pollination driving reproductive success

Directory of Open Access Journals (Sweden)

MORGANA S. SAZAN

2014-03-01

Full Text Available Oil-collecting bees are the natural pollinators of oil-flower plants, but little is known about the pollination process and the effectiveness of their pollination service to the reproductive success of their host plants. In species of Byrsonima the reproductive system have been described as auto-compatible or self-incompatible. We studied the reproductive system of Byrsonima cydoniifolia, the fructification by means of short, medium and long-distance cross pollinations, the morphology and floral biology and the pollination interactions with species of oil-collecting bees. By means of controlled pollinations we found self-incompatibility caused by abortion of most self-pollinated flowers and demonstrated that the prevailing cross pollination ensuring the reproductive success of B. cydoniifolia is the long-distance cross pollination and Centridini bees; Epicharis nigrita, particularly, are the pollinators promoting the gene flow between genetically distinct populations.

The Gould's Belt Distances Survey (GOBELINS). IV. Distance, Depth, and Kinematics of the Taurus Star-forming Region

Science.gov (United States)

Galli, Phillip A. B.; Loinard, Laurent; Ortiz-Léon, Gisela N.; Kounkel, Marina; Dzib, Sergio A.; Mioduszewski, Amy J.; Rodríguez, Luis F.; Hartmann, Lee; Teixeira, Ramachrisna; Torres, Rosa M.; Rivera, Juana L.; Boden, Andrew F.; Evans, Neal J., II; Briceño, Cesar; Tobin, John J.; Heyer, Mark

2018-05-01

We present new trigonometric parallaxes and proper motions of young stellar objects in the Taurus molecular cloud complex from observations collected with the Very Long Baseline Array as part of the Gould’s Belt Distances Survey. We detected 26 young stellar objects and derived trigonometric parallaxes for 18 stars with an accuracy of 0.3% to a few percent. We modeled the orbits of six binaries and determined the dynamical masses of the individual components in four of these systems (V1023 Tau, T Tau S, V807 Tau, and V1000 Tau). Our results are consistent with the first trigonometric parallaxes delivered by the Gaia satellite and reveal the existence of significant depth effects. We find that the central portion of the dark cloud Lynds 1495 is located at d =129.5 ± 0.3 pc, while the B216 clump in the filamentary structure connected to it is at d = 158.1 ± 1.2 pc. The closest and remotest stars in our sample are located at d = 126.6 ± 1.7 pc and d = 162.7 ± 0.8 pc, yielding a distance difference of about 36 pc. We also provide a new distance estimate for HL Tau that was recently imaged. Finally, we compute the spatial velocity of the stars with published radial velocity and investigate the kinematic properties of the various clouds and gas structures in this region.

Satellite monitoring of cyanobacterial harmful algal bloom ...

Science.gov (United States)

Cyanobacterial harmful algal blooms (cyanoHABs) cause extensive problems in lakes worldwide, including human and ecological health risks, anoxia and fish kills, and taste and odor problems. CyanoHABs are a particular concern because of their dense biomass and the risk of exposure to toxins in both recreational waters and drinking source waters. Successful cyanoHAB assessment by satellites may provide a first-line of defense indicator for human and ecological health protection. In this study, assessment methods were developed to determine the utility of satellite technology for detecting cyanoHAB occurrence frequency at locations of potential management interest. The European Space Agency's MEdium Resolution Imaging Spectrometer (MERIS) was evaluated to prepare for the equivalent Sentinel-3 Ocean and Land Colour Imager (OLCI) launched in 2016. Based on the 2012 National Lakes Assessment site evaluation guidelines and National Hydrography Dataset, there were 275,897 lakes and reservoirs greater than 1 hectare in the 48 U.S. states. Results from this evaluation show that 5.6 % of waterbodies were resolvable by satellites with 300 m single pixel resolution and 0.7 % of waterbodies were resolvable when a 3x3 pixel array was applied based on minimum Euclidian distance from shore. Satellite data was also spatially joined to US public water surface intake (PWSI) locations, where single pixel resolution resolved 57% of PWSI and a 3x3 pixel array resolved 33% of

Global Broadcast Service Reach Back Via Satellite Tactical Digital Link J (S-TADIL J)

National Research Council Canada - National Science Library

Fenton, Sandra

1999-01-01

...) to deployed forces via UHF Follow On (UFO) satellites during GBS Phase Two. The concept of Smart Push provides for most of the users' needs but cannot anticipate every need or emerging needs of the user...

THEMIS satellite observations of hot flow anomalies at Earth's bow shock

Directory of Open Access Journals (Sweden)

C. Chu

2017-03-01

Full Text Available Hot flow anomalies (HFAs at Earth's bow shock were identified in Time History of Events and Macroscale Interactions During Substorms (THEMIS satellite data from 2007 to 2009. The events were classified as young or mature and also as regular or spontaneous hot flow anomalies (SHFAs. The dataset has 17 young SHFAs, 49 mature SHFAs, 15 young HFAs, and 55 mature HFAs. They span a wide range of magnetic local times (MLTs from approximately 7 to 16.5 MLT. The largest ratio of solar wind to HFA core density occurred near dusk and at larger distances from the bow shock. In this study, HFAs and SHFAs were observed up to 6.3 RE and 6.1 RE (Earth radii, respectively, upstream from the model bow shock. HFA–SHFA occurrence decreases with distance upstream from the bow shock. HFAs of the highest event core ion temperatures were not seen at the flanks. The ratio of HFA ion temperature increase to HFA electron temperature increase is highest around 12 MLT and slightly duskward. For SHFAs, (Tihfa∕Tisw/(Tehfa∕Tesw generally increased with distance from the bow shock. Both mature and young HFAs are more prevalent when there is an approximately radial interplanetary magnetic field. HFAs occur most preferentially for solar wind speeds from 550 to 600 km s−1. The correlation coefficient between the HFA increase in thermal energy density from solar wind values and the decrease in kinetic energy density from solar wind values is 0.62. SHFAs and HFAs do not show major differences in this study.

Iterative method to compute the Fermat points and Fermat distances of multiquarks

International Nuclear Information System (INIS)

Bicudo, P.; Cardoso, M.

2009-01-01

The multiquark confining potential is proportional to the total distance of the fundamental strings linking the quarks and antiquarks. We address the computation of the total string distance and of the Fermat points where the different strings meet. For a meson the distance is trivially the quark-antiquark distance. For a baryon the problem was solved geometrically from the onset by Fermat and by Torricelli, it can be determined just with a rule and a compass, and we briefly review it. However we also show that for tetraquarks, pentaquarks, hexaquarks, etc., the geometrical solution is much more complicated. Here we provide an iterative method, converging fast to the correct Fermat points and the total distances, relevant for the multiquark potentials.

Iterative method to compute the Fermat points and Fermat distances of multiquarks

Energy Technology Data Exchange (ETDEWEB)

Bicudo, P. [CFTP, Departamento de Fisica, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal)], E-mail: bicudo@ist.utl.pt; Cardoso, M. [CFTP, Departamento de Fisica, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal)

2009-04-13

The multiquark confining potential is proportional to the total distance of the fundamental strings linking the quarks and antiquarks. We address the computation of the total string distance and of the Fermat points where the different strings meet. For a meson the distance is trivially the quark-antiquark distance. For a baryon the problem was solved geometrically from the onset by Fermat and by Torricelli, it can be determined just with a rule and a compass, and we briefly review it. However we also show that for tetraquarks, pentaquarks, hexaquarks, etc., the geometrical solution is much more complicated. Here we provide an iterative method, converging fast to the correct Fermat points and the total distances, relevant for the multiquark potentials.

PERSEUS I: A DISTANT SATELLITE DWARF GALAXY OF ANDROMEDA

International Nuclear Information System (INIS)

Martin, Nicolas F.; Laevens, Benjamin P. M.; Schlafly, Edward F.; Rix, Hans-Walter; Slater, Colin T.; Bell, Eric F.; Bernard, Edouard J.; Ferguson, Annette M. N.; Finkbeiner, Douglas P.; Burgett, William S.; Chambers, Kenneth C.; Hodapp, Klaus W.; Kaiser, Nicholas; Kudritzki, Rolf-Peter; Magnier, Eugene A.; Morgan, Jeffrey S.; Tonry, John L.; Draper, Peter W.; Metcalfe, Nigel; Price, Paul A.

2013-01-01

We present the discovery of a new dwarf galaxy, Perseus I/Andromeda XXXIII, found in the vicinity of Andromeda (M31) in stacked imaging data from the Pan-STARRS1 3π survey. Located 27.°9 away from M31, Perseus I has a heliocentric distance of 785 ± 65 kpc, compatible with it being a satellite of M31 at 374 −10 +14 kpc from its host. The properties of Perseus I are typical for a reasonably bright dwarf galaxy (M V = –10.3 ± 0.7), with an exponential half-light radius of r h = 1.7 ± 0.4 arcmin or r h =400 −85 +105 pc at this distance, and a moderate ellipticity (ϵ=0.43 −0.17 +0.15 ). The late discovery of Perseus I is due to its fairly low surface brightness (μ 0 =25.7 −0.9 +1.0  mag arcsec –2 ), and to the previous lack of deep, high quality photometric data in this region. If confirmed to be a companion of M31, the location of Perseus I, far east from its host, could place interesting constraints on the bulk motion of the satellite system of M31

Reionization of the Milky Way, M31, and their satellites - I. Reionization history and star formation

Science.gov (United States)

Dixon, Keri L.; Iliev, Ilian T.; Gottlöber, Stefan; Yepes, Gustavo; Knebe, Alexander; Libeskind, Noam; Hoffman, Yehuda

2018-06-01

Observations of the Milky Way (MW), M31, and their vicinity, known as the Local Group (LG), can provide clues about the sources of reionization. We present a suite of radiative transfer simulations based on initial conditions provided by the Constrained Local UniversE Simulations (CLUES) project that are designed to recreate the Local Universe, including a realistic MW-M31 pair and a nearby Virgo. Our box size (91 Mpc) is large enough to incorporate the relevant sources of ionizing photons for the LG. We employ a range of source models, mimicking the potential effects of radiative feedback for dark matter haloes between {˜ }10^8 and 10^9 M_{⊙}. Although the LG mostly reionizes in an inside-out fashion, the final 40 per cent of its ionization shows some outside influence. For the LG satellites, we find no evidence that their redshift of reionization is related to the present-day mass of the satellite or the distance from the central galaxy. We find that fewer than 20 per cent of present-day satellites for MW and M31 have undergone any star formation prior to the end of global reionization. Approximately 5 per cent of these satellites could be classified as fossils, meaning the majority of star formation occurred at these early times. The more massive satellites have more cumulative star formation prior to the end of global reionization, but the scatter is significant, especially at the low-mass end. Present-day mass and distance from the central galaxy are poor predictors for the presence of ancient stellar populations in satellite galaxies.

SDI satellite autonomy using AI and Ada

Science.gov (United States)

Fiala, Harvey E.

1990-01-01

The use of Artificial Intelligence (AI) and the programming language Ada to help a satellite recover from selected failures that could lead to mission failure are described. An unmanned satellite will have a separate AI subsystem running in parallel with the normal satellite subsystems. A satellite monitoring subsystem (SMS), under the control of a blackboard system, will continuously monitor selected satellite subsystems to become alert to any actual or potential problems. In the case of loss of communications with the earth or the home base, the satellite will go into a survival mode to reestablish communications with the earth. The use of an AI subsystem in this manner would have avoided the tragic loss of the two recent Soviet probes that were sent to investigate the planet Mars and its moons. The blackboard system works in conjunction with an SMS and a reconfiguration control subsystem (RCS). It can be shown to be an effective way for one central control subsystem to monitor and coordinate the activities and loads of many interacting subsystems that may or may not contain redundant and/or fault-tolerant elements. The blackboard system will be coded in Ada using tools such as the ABLE development system and the Ada Production system.

The future of acoustics distance education at Penn State

Science.gov (United States)

Brooks, Karen P.; Sparrow, Victor W.; Atchley, Anthony A.

2005-04-01

For nearly 20 years Penn State's Graduate Program in Acoustics has offered a graduate distance education program, established in response to Department of Defense needs. Using satellite technology, courses provided synchronous classes incorporating one-way video and two-way audio. Advancements in technology allowed more sophisticated delivery systems to be considered and courses to be offered to employees of industry. Current technology utilizes real time video-streaming and archived lectures to enable individuals anywhere to access course materials. The evolution of technology, expansion of the geographic market and changing needs of the student, among other issues, require a new paradigm. This paradigm must consider issues such as faculty acceptance and questions facing all institutions with regard to blurring the distinction between residence and distance education. Who will be the students? What will be the purpose of education? Will it be to provide professional and/or research degrees? How will the Acoustics Program ensure it remains attractive to all students, while working within the boundaries and constraints of a major research university? This is a look at current practice and issues with an emphasis on those relevant to constructing the Acoustics Programs distance education strategy for the future.

Technology News; Distance Education Project: Extending Extension Programming via Telecommunications Technology; [and] Fax for Library Services.

Science.gov (United States)

Coyle, Larry; Spitzer, Kathleen L.

1992-01-01

Three articles discuss (1) the numbers of microcomputers installed in elementary and secondary schools; (2) a distance education project in the Minnesota Extension Service that used a satellite delivery system and integrated it with a computer information network; and (3) the use of facsimile machines for library services. (LRW)

A proposed architecture for a satellite-based mobile communications network - The lowest three layers

Science.gov (United States)

Yan, T. Y.; Naderi, F. M.

1986-01-01

Architecture for a commercial mobile satellite network is proposed. The mobile satellite system (MSS) is composed of a network management center, mobile terminals, base stations, and gateways; the functions of each component are described. The satellite is a 'bent pipe' that performs frequency translations, and it has multiple UHF beams. The development of the MSS design based on the seven-layer open system interconnection model is examined. Consideration is given to the functions of the physical, data link, and network layers and the integrated adaptive mobile access protocol.

Protocol and Topology Issues for Wide-Area Satellite Interconnection of Terrestrial Optical LANs

Science.gov (United States)

Parraga, N.

2002-01-01

Apart from broadcasting, the satellite business is targeting niche markets. Wide area interconnection is considered as one of these niche markets, since it addresses operators and business LANs (B2B, business to business) in remote areas where terrestrial infrastructure is not available. These LANs - if high-speed - are typically based on optical networks such as SONET. One of the advantages of SONET is its architecture flexibility and capacity to transport all kind of applications including multimedia with a range of different transmission rates. The applications can be carried by different protocols among which the Internet Protocol (IP) or the Asynchronous Transfer Mode (ATM) are the most prominent ones. Thus, the question arises how these protocols can be interconnected via the satellite segment. The paper addresses several solutions for interworking with different protocols. For this investigation we distinguish first of all between the topology and the switching technology of the satellites. In case of a star network with transparent satellite, the satellite protocol consists of physical layer and data layer which can be directly interconnected with layer 2 interworking function to their terrestrial counterparts in the SONET backbone. For regenerative satellites the situation is more complex: here we need to distinguish the types of transport protocols being used in the terrestrial and satellite segment. Whereas IP, ATM, MPEG dominate in the terrestrial networks, satellite systems usually do not follow these standards. Some might employ minor additions (for instance, satellite specific packet headers), some might be completely proprietary. In general, interworking must be done for the data plane on top of layer 2 (data link layer), whereas for the signaling plane the interworking is on top of layer 3. In the paper we will discuss the protocol stacks for ATM, IP, and MPEG with a regenerative satellite system. As an example we will use the EuroSkyWay satellite

Precision Viticulture from Multitemporal, Multispectral Very High Resolution Satellite Data

Science.gov (United States)

Kandylakis, Z.; Karantzalos, K.

2016-06-01

In order to exploit efficiently very high resolution satellite multispectral data for precision agriculture applications, validated methodologies should be established which link the observed reflectance spectra with certain crop/plant/fruit biophysical and biochemical quality parameters. To this end, based on concurrent satellite and field campaigns during the veraison period, satellite and in-situ data were collected, along with several grape samples, at specific locations during the harvesting period. These data were collected for a period of three years in two viticultural areas in Northern Greece. After the required data pre-processing, canopy reflectance observations, through the combination of several vegetation indices were correlated with the quantitative results from the grape/must analysis of grape sampling. Results appear quite promising, indicating that certain key quality parameters (like brix levels, total phenolic content, brix to total acidity, anthocyanin levels) which describe the oenological potential, phenolic composition and chromatic characteristics can be efficiently estimated from the satellite data.

New satellite altimetry products for coastal oceans

Science.gov (United States)

Dufau, Claire; Mercier, F.; Ablain, M.; Dibarboure, G.; Carrere, L.; Labroue, S.; Obligis, E.; Sicard, P.; Thibaut, P.; Birol, F.; Bronner, E.; Lombard, A.; Picot, N.

Since the launch of Topex-Poseidon in 1992, satellite altimetry has become one of the most essential elements of the Earth's observing system. Its global view of the ocean state has permitted numerous improvements in the environment understanding, particularly in the global monitoring of climate changes and ocean circulation. Near the coastlines where human activities have a major impact on the ocean, satellite altimeter techniques are unfortunately limited by a growth of their error budget. This quality loss is due to land contamination in the altimetric and radiometric footprints but also to inaccurate geophysical corrections (tides, high-frequency processes linked to atmospheric forcing).Despite instrumental perturbations by emerged lands until 10 km (altimeter) and 50 km (radiometer) off the coasts, measurements are made and may contain useful information for coastal studies. In order to recover these data close to the coast, the French Spatial Agency (CNES) has funded the development of the PISTACH prototype dedicated to Jason-2 altimeter processing in coastal ocean. Since November 2008, these new satellite altimeter products have been providing new retracking solutions, several state-of-the-art or with higher resolution corrections in addition to standard fields. This presentation will present and illustrate this new set of satellite data for the coastal oceans.

Why GPS makes distances bigger than they are.

Science.gov (United States)

Ranacher, Peter; Brunauer, Richard; Trutschnig, Wolfgang; Van der Spek, Stefan; Reich, Siegfried

2016-02-01

Global navigation satellite systems such as the Global Positioning System (GPS) is one of the most important sensors for movement analysis. GPS is widely used to record the trajectories of vehicles, animals and human beings. However, all GPS movement data are affected by both measurement and interpolation errors. In this article we show that measurement error causes a systematic bias in distances recorded with a GPS; the distance between two points recorded with a GPS is - on average - bigger than the true distance between these points. This systematic 'overestimation of distance' becomes relevant if the influence of interpolation error can be neglected, which in practice is the case for movement sampled at high frequencies. We provide a mathematical explanation of this phenomenon and illustrate that it functionally depends on the autocorrelation of GPS measurement error ( C ). We argue that C can be interpreted as a quality measure for movement data recorded with a GPS. If there is a strong autocorrelation between any two consecutive position estimates, they have very similar error. This error cancels out when average speed, distance or direction is calculated along the trajectory. Based on our theoretical findings we introduce a novel approach to determine C in real-world GPS movement data sampled at high frequencies. We apply our approach to pedestrian trajectories and car trajectories. We found that the measurement error in the data was strongly spatially and temporally autocorrelated and give a quality estimate of the data. Most importantly, our findings are not limited to GPS alone. The systematic bias and its implications are bound to occur in any movement data collected with absolute positioning if interpolation error can be neglected.

Orbital and Collisional Evolution of the Irregular Satellites

Science.gov (United States)

Nesvorný, David; Alvarellos, Jose L. A.; Dones, Luke; Levison, Harold F.

2003-07-01

The irregular moons of the Jovian planets are a puzzling part of the solar system inventory. Unlike regular satellites, the irregular moons revolve around planets at large distances in tilted and eccentric orbits. Their origin, which is intimately linked with the origin of the planets themselves, is yet to be explained. Here we report a study of the orbital and collisional evolution of the irregular satellites from times after their formation to the present epoch. The purpose of this study is to find out the features of the observed irregular moons that can be attributed to this evolution and separate them from signatures of the formation process. We numerically integrated ~60,000 test satellite orbits to map orbital locations that are stable on long time intervals. We found that the orbits highly inclined to the ecliptic are unstable due to the effect of the Kozai resonance, which radially stretches them so that satellites either escape from the Hill sphere, collide with massive inner moons, or impact the parent planet. We also found that prograde satellite orbits with large semimajor axes are unstable due to the effect of the evection resonance, which locks the orbit's apocenter to the apparent motion of the Sun around the parent planet. In such a resonance, the effect of solar tides on a resonant moon accumulates at each apocenter passage of the moon, which causes a radially outward drift of its orbital apocenter; once close to the Hill sphere, the moon escapes. By contrast, retrograde moons with large orbital semimajor axes are long-lived. We have developed an analytic model of the distant satellite orbits and used it to explain the results of our numerical experiments. In particular, we analytically studied the effect of the Kozai resonance. We numerically integrated the orbits of the 50 irregular moons (known by 2002 August 16) for 108 yr. All orbits were stable on this time interval and did not show any macroscopic variations that would indicate

Tele-ultrasound using ATM over a T-1 satellite connection

Science.gov (United States)

Williamson, Morgan P.; Suitor, Charles T.; de Treville, Robert E.; Freckleton, Michael W.; Kinsey, Van; Goeringer, Fred; Lyche, David K.; Hunter, Bruce; Jennings, Neal E.; Shelton, Philip D.; Marcy, Jon; Poore, Tom; North, Jack

1996-04-01

In September 1995 the United States military conducted a demonstration project to provide live ultrasound video and diagnostic DICOM still images using GTE's asynchronous transfer mode (ATM) technologies over an Orion T-1 satellite link. Still images were frame-grabbed from a Diasonics ultrasound and sent to the ALI Wide Area Network system. A group of diagnostic images was then sent in DICOM 3.0 format over a virtual ethernet satellite link from Chantilly, Virginia to Dayton, Ohio. These images came across a DICOM gateway into the Medical Diagnostic Imaging Support (MDIS) System. Live video from the ultrasound was also routed through a CLI Radiance VTC over the satellite to a VTC in Ohio. The video bandwidth was progressively narrowed with two radiologists determining the minimal acceptable bandwidth for detecting test objects in a phantom. The radiologists accepted live video ultrasound at bandwidths as low as 384 kbps from the hands of an experienced ultrasonographer located hundreds of miles away. DICOM still images were sent uncompressed and were of acceptable image quality when viewed on the MDIS system. The technology demonstrated holds great promise for both deployed U.S. Military Forces and civil uses of remote radiology. Detailed network drawings and videotapes of the ultrasound examinations at the remote site are provided.

THE PLASMA ENVIRONMENT IN COMETS OVER A WIDE RANGE OF HELIOCENTRIC DISTANCES: APPLICATION TO COMET C/2006 P1 (MCNAUGHT)

Energy Technology Data Exchange (ETDEWEB)

Shou, Y.; Combi, M.; Gombosi, T.; Toth, G. [Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI (United States); Jia, Y.-D. [IGPP, and EPSS, University of California, Los Angeles, CA 90095 (United States); Rubin, M. [Physikalisches Institut, University of Bern, Sidlerstrasse. 5, CH-3012 Bern (Switzerland)

2015-08-20

On 2007 January 12, comet C/2006 P1 (McNaught) passed its perihelion at 0.17 AU. Abundant remote observations offer plenty of information on the neutral composition and neutral velocities within 1 million kilometers of the comet nucleus. In early February, the Ulysses spacecraft made an in situ measurement of the ion composition, plasma velocity, and magnetic field when passing through the distant ion tail and the ambient solar wind. The measurement by Ulysses was made when the comet was at around 0.8 AU. With the constraints provided by remote and in situ observations, we simulated the plasma environment of Comet C/2006 P1 (McNaught) using a multi-species comet MHD model over a wide range of heliocentric distances from 0.17 to 1.75 AU. The solar wind interaction of the comet at various locations is characterized and typical subsolar standoff distances of the bow shock and contact surface are presented and compared to analytic solutions. We find the variation in the bow shock standoff distances at different heliocentric distances is smaller than the contact surface. In addition, we modified the multi-species model for the case when the comet was at 0.7 AU and achieved comparable water group ion abundances, proton densities, plasma velocities, and plasma temperatures to the Ulysses/SWICS and SWOOPS observations. We discuss the dominating chemical reactions throughout the comet-solar wind interaction region and demonstrate the link between the ion composition near the comet and in the distant tail as measured by Ulysses.

THE PLASMA ENVIRONMENT IN COMETS OVER A WIDE RANGE OF HELIOCENTRIC DISTANCES: APPLICATION TO COMET C/2006 P1 (MCNAUGHT)

International Nuclear Information System (INIS)

Shou, Y.; Combi, M.; Gombosi, T.; Toth, G.; Jia, Y.-D.; Rubin, M.

2015-01-01

On 2007 January 12, comet C/2006 P1 (McNaught) passed its perihelion at 0.17 AU. Abundant remote observations offer plenty of information on the neutral composition and neutral velocities within 1 million kilometers of the comet nucleus. In early February, the Ulysses spacecraft made an in situ measurement of the ion composition, plasma velocity, and magnetic field when passing through the distant ion tail and the ambient solar wind. The measurement by Ulysses was made when the comet was at around 0.8 AU. With the constraints provided by remote and in situ observations, we simulated the plasma environment of Comet C/2006 P1 (McNaught) using a multi-species comet MHD model over a wide range of heliocentric distances from 0.17 to 1.75 AU. The solar wind interaction of the comet at various locations is characterized and typical subsolar standoff distances of the bow shock and contact surface are presented and compared to analytic solutions. We find the variation in the bow shock standoff distances at different heliocentric distances is smaller than the contact surface. In addition, we modified the multi-species model for the case when the comet was at 0.7 AU and achieved comparable water group ion abundances, proton densities, plasma velocities, and plasma temperatures to the Ulysses/SWICS and SWOOPS observations. We discuss the dominating chemical reactions throughout the comet-solar wind interaction region and demonstrate the link between the ion composition near the comet and in the distant tail as measured by Ulysses

Cosmic rays and other space weather effects influenced on satellite operation, technologies, biosphere and people health

Science.gov (United States)

Lev, Dorman

2016-07-01

Satellite anomalies (or malfunctions), including total distortion of electronics and loose of some satellites cost for Insurance Companies billions dollars per year. During especially active periods the probability of big satellite anomalies and their loosing increased very much. Now, when a great number of civil and military satellites are continuously worked for our practice life, the problem of satellite anomalies became very important. Many years ago about half of satellite anomalies were caused by technical reasons (for example, for Russian satellites Kosmos), but with time with increasing of production quality, this part became smaller and smaller. The other part, which now is dominated, caused by different space weather effects (energetic particles of CR and generated/trapped in the magnetosphere, and so on). We consider only satellite anomalies not caused by technical reasons: the total number of such anomalies about 6000 events, and separately for high and low altitude orbit satellites (5000 and about 800 events, correspondingly for high and low altitude satellites). No relation was found between low and high altitude satellite anomalies. Daily numbers of satellite anomalies, averaged by a superposed epoch method around sudden storm commencements and solar proton event onsets for high (>1500 km) and low (railway operation (possible, through induction currents), catastrophes in long-distance electric power lines and transformators, and in other ground technologies.

Nanomechanical characterization by double-pass force-distance mapping

Energy Technology Data Exchange (ETDEWEB)

Dagdas, Yavuz S; Tekinay, Ayse B; Guler, Mustafa O; Dana, Aykutlu [UNAM Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey); Necip Aslan, M, E-mail: aykutlu@unam.bilkent.edu.tr [Department of Physics, Istanbul Technical University, Istanbul (Turkey)

2011-07-22

We demonstrate high speed force-distance mapping using a double-pass scheme. The topography is measured in tapping mode in the first pass and this information is used in the second pass to move the tip over the sample. In the second pass, the cantilever dither signal is turned off and the sample is vibrated. Rapid (few kHz frequency) force-distance curves can be recorded with small peak interaction force, and can be processed into an image. Such a double-pass measurement eliminates the need for feedback during force-distance measurements. The method is demonstrated on self-assembled peptidic nanofibers.

Nanomechanical characterization by double-pass force-distance mapping

International Nuclear Information System (INIS)

Dagdas, Yavuz S; Tekinay, Ayse B; Guler, Mustafa O; Dana, Aykutlu; Necip Aslan, M

2011-01-01

We demonstrate high speed force-distance mapping using a double-pass scheme. The topography is measured in tapping mode in the first pass and this information is used in the second pass to move the tip over the sample. In the second pass, the cantilever dither signal is turned off and the sample is vibrated. Rapid (few kHz frequency) force-distance curves can be recorded with small peak interaction force, and can be processed into an image. Such a double-pass measurement eliminates the need for feedback during force-distance measurements. The method is demonstrated on self-assembled peptidic nanofibers.

THE USE OF FACEBOOK FOR ONLINE DISCUSSIONS AMONG DISTANCE LEARNERS

Directory of Open Access Journals (Sweden)

Tina LIM

2010-10-01

Full Text Available With the advent of Web 2.0 tools, educators are looking to these new technological tools to examine its potential in enhancing teaching and learning. While its runaway success as a social networking tool is now renowned, the use of Facebook for educational purposes may be considered still at its infancy stage. This paper describes the use of Facebook as a platform for academic discussions among distance learners. It offers a glimpse into how mobile learning via SMS together with Facebook was used to support and enhance the blended learning approach at Open University Malaysia for three courses: Learning Skills for Open and Distance Learners, Company Law and Renal Nursing. Data on user interactions collected were from the “Page Insights” tools available to Page administrators for the whole duration of a course semester. Facebook interactions examined include total number of fans, total interactions, interactions per post, post quality and unique page views. Findings indicate that Facebook does have the potential to draw distance learners to engage in meaningful academic conversations but the quantity and quality of posts very much depends on the timing as well as the topics of discussion.

Energy Deposition and DPA in the Superconducting Links for the HILUMI LHC Project at the LHC Interaction Points

CERN Document Server

AUTHOR|(CDS)2092158; Broggi, Francesco; Santini, C; Ballarino, Amalia; Cerutti, Francesco; Esposito, Luigi Salvatore

2015-01-01

In the framework of the upgrade of the LHC machine, the powering of the LHC magnets foresees the removal of the power converters and distribution feedboxes from the tunnel and its location at the surface[1]. The Magnesium Diboride (MgB2) connecting lines in the tunnel will be exposed to the debris from 7+7 TeV p-p interaction. The Superconducting (SC) Links will arrive from the surface to the tunnel near the separation dipole, at about 80 m from the Interaction Point at IP1 and IP5. The Connection Box (where the cables of the SC Links are connected to the NbTi bus bar) will be close to the beam pipe. The debris and its effect on the MgB2 SC links in the connection box (energy deposition and displacement per atom) are presented. The effect of thermal neutrons on the Boron consumption and the contribution of the lithium nucleus and the alpha particle on the DPA are evaluated. The results are normalized to an integrated luminosity of 3000 fb-1, value that represents the LHC High Luminosity lifetime. The dose de...

Small Satellite Constellations for Geospace Sciences

Science.gov (United States)

Spence, H. E.

2016-12-01

The recent National Academy of Sciences Solar and Space Physics Decadal Survey (DS) identified community-consensus science priorities for the decade spanning 2013 - 2022. In this talk, we discuss the ways by which small satellite constellations are already and may soon accelerate progress toward achieving many of these science targets. The DS outlined four overarching science goals: (1) determine the origins of the Sun's activity and predict the variations in the space environment; (2) determine the dynamics and coupling of Earth's magnetosphere, ionosphere, and atmosphere and their response to solar and terrestrial inputs; (3) determine the interaction of the Sun with the solar system and the interstellar medium; and, (4) discover and characterize fundamental processes that occur both within the heliosphere and throughout the universe. These DS science goals provide the context for key science challenges in the three connected parts of the system that encompass all of solar and space physics, herein referred to as geospace: the Sun and heliosphere; the coupled solar wind-magnetosphere system; and, the coupled atmosphere-ionosphere-magnetosphere system. The DS further presented the role that small satellites play in resolving many of these science challenges, with a particular emphasis on the role that constellations of small satellites will play. While once considered by many as being "futuristic" or even "unrealizable", constellations of small satellites are already making important contributions to geospace science and with the promise for more to come. Using the DS as a guidepost, in this presentation, we outline representative small satellite constellation missions alread underway, some in development, and others notionally proposed over the next several years that employ small satellite constellations to tackle large science imperatives. Finally, we give examples of key small satellite technologies in development that will potentially enable great scientific

Thermospheric density and satellite drag modeling

Science.gov (United States)

Mehta, Piyush Mukesh

The United States depends heavily on its space infrastructure for a vast number of commercial and military applications. Space Situational Awareness (SSA) and Threat Assessment require maintaining accurate knowledge of the orbits of resident space objects (RSOs) and the associated uncertainties. Atmospheric drag is the largest source of uncertainty for low-perigee RSOs. The uncertainty stems from inaccurate modeling of neutral atmospheric mass density and inaccurate modeling of the interaction between the atmosphere and the RSO. In order to reduce the uncertainty in drag modeling, both atmospheric density and drag coefficient (CD) models need to be improved. Early atmospheric density models were developed from orbital drag data or observations of a few early compact satellites. To simplify calculations, densities derived from orbit data used a fixed CD value of 2.2 measured in a laboratory using clean surfaces. Measurements from pressure gauges obtained in the early 1990s have confirmed the adsorption of atomic oxygen on satellite surfaces. The varying levels of adsorbed oxygen along with the constantly changing atmospheric conditions cause large variations in CD with altitude and along the orbit of the satellite. Therefore, the use of a fixed CD in early development has resulted in large biases in atmospheric density models. A technique for generating corrections to empirical density models using precision orbit ephemerides (POE) as measurements in an optimal orbit determination process was recently developed. The process generates simultaneous corrections to the atmospheric density and ballistic coefficient (BC) by modeling the corrections as statistical exponentially decaying Gauss-Markov processes. The technique has been successfully implemented in generating density corrections using the CHAMP and GRACE satellites. This work examines the effectiveness, specifically the transfer of density models errors into BC estimates, of the technique using the CHAMP and

Satellite-based laser windsounder

International Nuclear Information System (INIS)

Schultz, J.F.; Czuchlewski, S.J.; Quick, C.R.

1997-01-01

This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The project''s primary objective is to determine the technical feasibility of using satellite-based laser wind sensing systems for detailed study of winds, aerosols, and particulates around and downstream of suspected proliferation facilities. Extensive interactions with the relevant operational organization resulted in enthusiastic support and useful guidance with respect to measurement requirements and priorities. Four candidate wind sensing techniques were evaluated, and the incoherent Doppler technique was selected. A small satellite concept design study was completed to identify the technical issues inherent in a proof-of-concept small satellite mission. Use of a Mach-Zehnder interferometer instead of a Fabry-Perot would significantly simplify the optical train and could reduce weight, and possibly power, requirements with no loss of performance. A breadboard Mach-Zehnder interferometer-based system has been built to verify these predictions. Detailed plans were made for resolving other issues through construction and testing of a ground-based lidar system in collaboration with the University of Wisconsin, and through numerical lidar wind data assimilation studies

GLOBALIZATION, DISTANCE EDUCATION AND HEGEMONIC FUTURES

Directory of Open Access Journals (Sweden)

Glenn RUSSELL

2007-10-01

Full Text Available ABSTRACT Consideration of the place of theory in distance education suggests that existing definitions do not adequately account for economic, cultural and historical factors. The application of the notion of hegemonic valency to distance education highlights the ways in which tools, technological systems and online environments operate in predictable ways. Historically, the imperatives of market forces and social justice have displayed a tension that is continued in contemporary contexts including virtual learning environments. A characteristic of this tension can be seen in the forces and interactions associated with globalisation and technology. These forces, in association with others, have contributed to a null curriculum in which some alternatives open to distance education practitioners remain invisible. It is likely that this situation is further compounded by the difficulty of ascertaining what distance education practices are actually operating world-wide at any identifiable time. Available options for distance educators can be understood in terms of instrumental and interpersonal axes that can potentially indicate the relative consideration that can be given to these factors. This approach is suggested as one way to understand available options at a time when there has been an apparent increase in instrumental approaches to distance education at the expense of interpersonal approaches and issues of social justice. While this problem is of concern, it is more appropriate to reflect on the unintended consequences of distance education for society and identify them than it is to uncritically oppose globalisation and its adherents.

Measurement-based perturbation theory and differential equation parameter estimation with applications to satellite gravimetry

Science.gov (United States)

Xu, Peiliang

2018-06-01

The numerical integration method has been routinely used by major institutions worldwide, for example, NASA Goddard Space Flight Center and German Research Center for Geosciences (GFZ), to produce global gravitational models from satellite tracking measurements of CHAMP and/or GRACE types. Such Earth's gravitational products have found widest possible multidisciplinary applications in Earth Sciences. The method is essentially implemented by solving the differential equations of the partial derivatives of the orbit of a satellite with respect to the unknown harmonic coefficients under the conditions of zero initial values. From the mathematical and statistical point of view, satellite gravimetry from satellite tracking is essentially the problem of estimating unknown parameters in the Newton's nonlinear differential equations from satellite tracking measurements. We prove that zero initial values for the partial derivatives are incorrect mathematically and not permitted physically. The numerical integration method, as currently implemented and used in mathematics and statistics, chemistry and physics, and satellite gravimetry, is groundless, mathematically and physically. Given the Newton's nonlinear governing differential equations of satellite motion with unknown equation parameters and unknown initial conditions, we develop three methods to derive new local solutions around a nominal reference orbit, which are linked to measurements to estimate the unknown corrections to approximate values of the unknown parameters and the unknown initial conditions. Bearing in mind that satellite orbits can now be tracked almost continuously at unprecedented accuracy, we propose the measurement-based perturbation theory and derive global uniformly convergent solutions to the Newton's nonlinear governing differential equations of satellite motion for the next generation of global gravitational models. Since the solutions are global uniformly convergent, theoretically speaking

Satellite orbits perturbed by direct solar radiation pressure: general expansion of the disturbing function

International Nuclear Information System (INIS)

Hughes, S.

1977-01-01

An expression is derived for the solar radiation pressure disturbing function on an Earth satellite orbit which takes into account the variation of the solar radiation flux with distance from the Sun's centre and the absorption of radiation by the satellite. This expression is then expanded in terms of the Keplerian elements of the satellite and solar orbits using Kaula's method (Astr. J.; 67:300 (1962)). The Kaula inclination functions are replaced by an equivalent set of modified Allan (Proc. R. Soc. A.; 288:60 (1965)) inclination functions. The resulting expression reduces to the form commonly used in solar radiation pressure perturbation studies (e.g. Aksnes, Cel. Mech.; 13:89 (1976)), when certain terms are neglected. If, as happens quite often in practice, a satellite's orbit is in near-resonance with certain of these neglected terms, these near-resonant terms can cause changes in the satellite's orbital elements comparable to those produced by the largest term in Aksnes's expression. A new expression for the solar radiation pressure disturbing function expansion is suggested for use in future studies of satellite orbits perturbed by solar radiation pressure. (author)