• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 1126
  • 548
  • 420
  • 178
  • 111
  • 49
  • 35
  • 28
  • 22
  • 20
  • 18
  • 18
  • 17
  • 12
  • 12
  • Tagged with
  • 3117
  • 607
  • 414
  • 279
  • 269
  • 256
  • 252
  • 205
  • 205
  • 198
  • 198
  • 183
  • 173
  • 162
  • 161
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
401

Propagation channel models for 5G mobile networks. Simulation and measurements of 5G propagation channel models for indoor and outdoor environments covering both LOS and NLOS Scenarios

Manan, Waqas January 2018 (has links)
At present, the current 4G systems provide a universal platform for broadband mobile services; however, mobile traffic is still growing at an unprecedented rate and the need for more sophisticated broadband services is pushing the limits on current standards to provide even tighter integration between wireless technologies and higher speeds. This has led to the need for a new generation of mobile communications: the so-called 5G. Although 5G systems are not expected to penetrate the market until 2020, the evolution towards 5G is widely accepted to be the logical convergence of internet services with existing mobile networking standards leading to the commonly used term “mobile internet” over heterogeneous networks, with several Gbits/s data rate and very high connectivity speeds. Therefore, to support highly increasing traffic capacity and high data rates, the next generation mobile network (5G) should extend the range of frequency spectrum for mobile communication that is yet to be identified by the ITU-R. The mm-wave spectrum is the key enabling feature of the next-generation cellular system, for which the propagation channel models need to be predicted to enhance the design guidance and the practicality of the whole design transceiver system. The present work addresses the main concepts of the propagation channel behaviour using ray tracing software package for simulation and then results were tested and compared against practical analysis in a real-time environment. The characteristics of Indoor-Indoor (LOS and NLOS), and indoor-outdoor (NLOS) propagations channels are intensively investigated at four different frequencies; 5.8 GHz, 26GHz, 28GHz and 60GHz for vertical polarized directional, omnidirectional and isotropic antennas patterns. The computed data achieved from the 3-D Shooting and Bouncing Ray (SBR) Wireless Insite based on the effect of frequency dependent electrical properties of building materials. Ray tracing technique has been utilized to predict multipath propagation characteristics in mm-wave bands at different propagation environments. Finally, the received signal power and delay spread were computed for outdoor-outdoor complex propagation channel model at 26 GHz, 28 GHz and 60GHz frequencies and results were compared to the theoretical models.
402

Sexual and asexual propagation of red elm (Ulmus rubra), grey alder (Alnus incana), and buffaloberry (Shepherdia canadensis)

Morales Rivera, Brenda Michelle January 1900 (has links)
Master of Science / Department of Horticulture, Forestry, and Recreation Resources / Charles Barden / Cheryl Boyer / Red elm (Ulmus rubra), grey alder (Alnus incana and A. incana spp. tenuifolia) and buffaloberry (Shepherdia canadensis) are considered important plants for many Native American tribes in the United States. Native Americans have used these three species for a variety of medicinal uses and ceremonial purposes. Currently, Kansas tribal leaders would like to plant more of these species on tribal land, but the plants have been difficult to propagate. While red elm is valued as a ceremonial tree, it is susceptible to Dutch Elm Disease caused by the fungus (Ophiostoma ulmi) and is not grown in many ornamental nurseries. This has led to declining tree populations. The objective of these studies were to evaluate methods to propagate red elm, grey alder and buffaloberry in order to find techniques that can lead to an increase in the production of these species commercially and enable tribes and landowners to increase the presence of these native plants on their lands. In the first study, the use of gibberellic acid (GA3) was investigated to determine the optimum concentration needed for maximum seed germination. Studies were conducted with stratified (cold, moist storage) and non-stratified red elm, grey alder, and buffaloberry seeds soaked in one of four treatments: 0, 250, 500 or 1000 ppm of GA3 in 2010, and 0, 500, 1000, 2000 ppm of GA3 in 2011. Results indicate the use of GA3 in high concentrations promoted germination of unstratified seeds of red elm, though low seed viability in grey alder and buffaloberry resulted in poor germination. In a second study, vegetative cuttings were treated with potassium indole-3-butyric acid (K-IBA) and Dip ‘N GrowTM containing indole-3-butyric acid and naphthalene acetic acid (IBA + NAA). Softwood cuttings for the three species were treated with K-IBA and Dip ‘N GrowTM (plant rooting hormones): K-IBA at 5,000 and 10,000 ppm and Dip ‘N GrowTM at 1:10 ratio solutions. Results of this study showed that only grey alder softwood cuttings had callus formation, root growth, and shoot growth while red elm and buffaloberry did not respond to cutting propagation treatments.
403

Studies on damping-off of alfalfa cuttings in the greenhouse

Addoh, Paul Gyamera. January 1961 (has links)
Call number: LD2668 .T4 1961 A33
404

OBJECT RECOGNITION BY GROUND-PENETRATING RADAR IMAGING SYSTEMS WITH TEMPORAL SPECTRAL STATISTICS

Ono, Sashi, Lee, Hua 10 1900 (has links)
International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper describes a new approach to object recognition by using ground-penetrating radar (GPR) imaging systems. The recognition procedure utilizes the spectral content instead of the object shape in traditional methods. To produce the identification feature of an object, the most common spectral component is obtained by singular value decomposition (SVD) of the training sets. The identification process is then integrated into the backward propagation image reconstruction algorithm, which is implemented on the FMCW GPR imaging systems.
405

L'utilisation des ondes de surface pour la caractérisation non intrusive des structures en béton

Weil, Fabiano January 2010 (has links)
Les méthodes de surveillance et d'inspection des structures en béton sont indispensables pour évaluer les dégradations du béton. L'étendue des dommages peut entraîner des frais considérables pour l'entretien et la réparation. Les techniques d'évaluation non destructives du béton durci aident à contrôler l'état de dégradation des structures de béton et ces résultats fournissent l'information nécessaire pour mettre en place l'entretien éventuel et les réparations nécessaires. Cette étude concerne l'utilisation des méthodes d'investigation basées sur la propagation des ondes de surface Rayleigh pour la caractérisation non intrusive des structures de béton. Des simulations numériques ont été effectuées pour examiner la propagation des ondes élastiques sur une dalle de béton afin de caractériser cette structure en utilisant la méthode MASW ( Modal Analysis of Surface Waves ). La technique MASW a été développée à l'Université de Sherbrooke pour le domaine de la géotechnique et du contrôle des infrastructures civiles. Les résultats des simulations numériques ont démontré plusieurs aspects importants dans la formation et la propagation des ondes de Rayleigh pour caractériser les couches de béton en profondeur.
406

Decoding and Turbo Equalization for LDPC Codes Based on Nonlinear Programming

Iltis, Ronald A. 10 1900 (has links)
ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / Decoding and Turbo Equalization (TEQ) algorithms based on the Sum-Product Algorithm (SPA) are well established for LDPC codes. However there is increasing interest in linear and nonlinear programming (NLP)-based decoders which may offer computational and performance advantages over the SPA. We present NLP decoders and Turbo equalizers based on an Augmented Lagrangian formulation of the decoding problem. The decoders update estimates of both the Lagrange multipliers and transmitted codeword while solving an approximate quadratic programming problem. Simulation results show that the NLP decoder performance is intermediate between the SPA and bit-flipping algorithms. The NLP may thus be attractive in some applications as it eliminates the tanh/atanh computations in the SPA.
407

High-fidelity 3D acoustic simulations of wind turbines with irregular terrain and different atmospheric profiles

Hedlund, Erik January 2016 (has links)
We study noise from wind turbines while taking irregular terrain and non-constant atmosphere into consideration. We will show that simulating the distribution of 3D acoustic waves can be done by using only low frequencies, thus reducing the computational complexity significantly.
408

ACTS Propagation Experiment and Solar/Lunar Intrusions

Gardner, Christopher S. 10 1900 (has links)
International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / In this paper are described the effects that solar and lunar intrusions have on statistical analysis of the data. The NASA ACTS experiment focuses on the 20 and 27 GHz radiometer and beacon. The experiment is currently compiling a database for the attenuation for these different channels. For the year of 1994 our sight obtained 86.5 hours of attenuation and for 1995 our sight obtained 77 hours of attenuation. The total amount of interference time for sun/lunar intrusions for 1994 and 1995 was respectively, 39 hours and 38.5 hours, which is nearly half the total amount of attenuation due to rain and cloud fades. It is clear to see why this data must be taken out for any type of statistical analysis of the data.
409

BACKWARD PROPAGATION BASED ALGORITHMS FOR HIGH-PERFORMANCE IMAGE FORMATION

Lee, Hua, Lockwood, Stephanie, Tandon, James, Brown, Andrew 10 1900 (has links)
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / In this paper, we present the recent results of theoretical development and software implementation of a complete collection of high-performance image reconstruction algorithms designed for high-resolution imaging for various data acquisition configurations.
410

MODELING OF THE SURFACE ATTENUATION EFFECTS OF RAIN ON COMPOSITE ANTENNA STRUCTURES AT KA-BAND

Borsholm, Atle 10 1900 (has links)
International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / During the NASA Ka-band propagation experiment it was discovered that rainwater on the antenna caused significant attenuation. It is necessary to estimate the losses caused by water on the antenna in order to separate these losses from the atmospheric propagation losses. A prediction model is developed for losses caused by rainwater on a satellite dish antenna. The model is based entirely on physical parameters including elevation angle, dish diameter, focal length, properties of present coating layers, feed window properties, frequency, polarization, water temperature and rain rate. The prediction model is implemented using Matlab and has been tested against experimental data.

Page generated in 0.1143 seconds