A Survey of Air-to-Ground Propagation Channel Modeling for Unmanned Aerial Vehicles

In recent years, there has been a dramatic increase in the use of unmanned aerial vehicles (UAVs), particularly for small UAVs, due to their affordable prices, ease of availability, and ease of operability. Existing and future applications of UAVs include remote surveillance and monitoring, relief operations, package delivery, and communication backhaul infrastructure. Additionally, UAVs are envisioned as an important component of 5G wireless technology and beyond. The unique application scenarios for UAVs necessitate accurate air-to-ground (AG) propagation channel models for designing and evaluating UAV communication links for control/non-payload as well as payload data transmissions. These AG propagation models have not been investigated in detail when compared to terrestrial propagation models. In this paper, a comprehensive survey is provided on available AG channel measurement campaigns, large and small scale fading channel models, their limitations, and future research directions for UAV communication scenarios

Flood fragility analysis for bridges with multiple failure modes

Bridges are one of the most important infrastructure systems that provide public and economic bases for humankind. It is also widely known that bridges are exposed to a variety of flood-related risk factors such as bridge scour, structural deterioration, and debris accumulation, which can cause structural damage and even failure of bridges through a variety of failure modes. However, flood fragility has not received as much attention as seismic fragility despite the significant amount of damage and costs resulting from flood hazards. There have been few research efforts to estimate the flood fragility of bridges considering various flood-related factors and the corresponding failure modes. Therefore, this study proposes a new approach for bridge flood fragility analysis. To obtain accurate flood fragility estimates, reliability analysis is performed in conjunction with finite element analysis, which can sophisticatedly simulate the structural response of a bridge under a flood by accounting for flood-related risk factors. The proposed approach is applied to a numerical example of an actual bridge in Korea. Flood fragility curves accounting for multiple failure modes, including lack of pier ductility or pile ductility, pier rebar rupture, pile rupture, and deck loss, are derived and presented in this study.ope

Efficient numerical computation and experimental study of temporally long equilibrium scour development around abutment

YesFor the abutment bed scour to reach its equilibrium state, a long flow time is needed. Hence, the employment of usual strategy of simulating such scouring event using the 3D numerical model is very time consuming and less practical. In order to develop an applicable model to consider temporally long abutment scouring process, this study modifies the common approach of 2D shallow water equations (SWEs) model to account for the sediment transport and turbulence, and provides a realistic approach to simulate the long scouring process to reach the full scour equilibrium. Due to the high demand of the 2D SWEs numerical scheme performance to simulate the abutment bed scouring, a recently proposed surface gradient upwind method (SGUM) was also used to improve the simulation of the numerical source terms. The abutment scour experiments of this study were conducted using the facility of Hydraulics Laboratory at Nanyang Technological University, Singapore to compare with the presented 2D SGUM-SWEs model. Fifteen experiments were conducted over a total period of 3059.7 hours experimental time (over 4.2 months). The comparison shows that the 2D SGUM-SWEs model gives good representation to the experimental results with the practical advantage

Socially and biologically inspired computing for self-organizing communications networks

The design and development of future communications networks call for a careful examination of biological and social systems. New technological developments like self-driving cars, wireless sensor networks, drones swarm, Internet of Things, Big Data, and Blockchain are promoting an integration process that will bring together all those technologies in a large-scale heterogeneous network. Most of the challenges related to these new developments cannot be faced using traditional approaches, and require to explore novel paradigms for building computational mechanisms that allow us to deal with the emergent complexity of these new applications. In this article, we show that it is possible to use biologically and socially inspired computing for designing and implementing self-organizing communication systems. We argue that an abstract analysis of biological and social phenomena can be made to develop computational models that provide a suitable conceptual framework for building new networking technologies: biologically inspired computing for achieving efficient and scalable networking under uncertain environments; socially inspired computing for increasing the capacity of a system for solving problems through collective actions. We aim to enhance the state-of-the-art of these approaches and encourage other researchers to use these models in their future work

Response of root explants to in vitro cultivation of marketable garlic cultivars

Garlic cultivars are sexually sterile under standard growth conditions, with direct implications for commercial production costs as well as breeding programs. Garlic is propagated commercially via bulblets, which facilitates disease transmission and virus load accumulation over vegetative generations. Tissue culture produces virus-free clones that are more productive, while keeping the desired traits of the cultivar. Consequently, this technique allows studies of garlic genetics as well as guarantees genetic conservation of varieties. We aimed at analyzing the in vitro regeneration of eight marketable cultivars of garlic using root segments as explants. For each genotype, bulblet-derived explants were isolated and introduced into MS medium supplemented with 2,4-D and 2-iP. Calli were transferred to MS medium supplemented with 8.8 mM BAP and 0.1 mM NAA (regeneration medium A), or with 4.6 mM kinetin alone (regeneration medium B). The calli were then evaluated for regeneration frequency after sixty days of in vitro cultivation. The noble cultivar 'Jonas' presented the highest rates of plant regeneration among the cultivars tested. The medium A, which contained auxin and cytokinin, induced the highest regeneration rates of all cultivars. The process described herein is simple, reproducible and can potentially be used as a tool in molecular breeding strategies for other marketable cultivars and genotypes of garlic

Anomalous ferromagnetic behaviour of Y(2)O(3) and CuO nanoparticles in YBa(2)Cu(3)O(y) superconductor

Anomalous ferromagnetic behaviour of the Y 2O 3 and CuO components in YBa 2Cu 3O y (Y123) was observed after severe reduction of particle size. The particle size reduction was performed in two ways. First, Y 2O 3, BaCO 3 and CuO were ground for different times to reduce the particle size to the nanoscale. It was found that the superconducting phase could not be obtained without heat treatment, but a weak ferromagnetic behaviour of the mixture was observed at liquid and room temperatures. Second, preheated Y123 powders were subjected to grinding for various times followed by a second sintering process. It was found that the superconducting transition temperature, T c, was strongly suppressed by increasing grinding time, and ferromagnetic behaviour at both room and liquid nitrogen temperatures was also observed. In order to understand which compound is responsible for this weak ferromagnetism, the Y 2O 3, BaCO 3 and CuO powders were separately ground and M-H loops taken at 290K. The resultsindicated that both Y 2O 3 and CuO powders showed weak ferromagnetism, but BaCO 3 showed anti ferromagnetism. It is thought that energy transfer to the powder particles by grinding results in severe plastic deformation of the particles to produce dislocations, vacancies and atomic disorder. We discuss then the observations in the context of recent studies of the magnetic properties of nanoscale oxide materials. © 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim

Capacity and Benefit-Cost Relation for Concrete Gravity and RCC Dams

The relationship between capacity and total net benefit of concrete gravity and roller compacted concrete (RCC) dams is investigated using benefit-cost analyses. The total capital cost of such dams is equal to the summation of costs of construction, engineering and consultancy services, right of way, and relocation of structures. Operation, maintenance and repair costs are considered as the annual costs during the service life of the structure. Implementation of dams may lead to the achievement of several benefits, such as meeting municipal water demand, irrigation, hydropower, navigation, flood mitigation, water quality control, wildlife and recreational facilities, and positive impacts on the environment. In a case study, benefit-cost analyses have been carried out for 144 different concrete gravity and RCC dam alternatives that can be implemented at Cine Dam site, Turkey. Stability analyses have also been conducted for the proposed alternatives. The information obtained through this study can be used in decision-making for optimum size and type of a gravity dam

Köprü Ayakları Etrafındaki Koruyucu Kaplamanın Bilgisayar Destekli Tasarımı

Akarsu geçişli köprülerde, akım alanı içerisinde kalan köprü ayakları çevresinde gelişen yerel oyulmalar, köprü emniyetini olumsuz etkilemektedir. Özellikle mevcut köprülerde, taban oyulmalarını önlemek için yapılan düzenleme yapılarının nitelikli bir şekilde tasarımı ve uygulanması ile köprülerde meydana gelen hasarların önüne geçmek mümkün olmaktadır. Bu çalışma kapsamında, köprü açıklığındaki oyulmalara karşı literatürde kabul gören kriterlere göre ayaklar etrafına yapılacak çeşitli kaplamaların tasarımı için VB.Net dilinde bir bilgisayar programı geliştirilmiştir. Programın uygulaması için Türkiye’nin Rize ilinde yer alan mevcut bir köprü projesi ele alınmış; akım, taban malzemesi ve yapısal özellikler göz önünde tutularak köprü bölgesindeki olası yatak oyulmaları belirlenmiştir. Elde edilen değerler ışığında çeşitli koruma yapısı seçenekleri arasından yapısal, zemin, hidrolik ve ekonomi gibi etmenleri göz önünde bulunduran bir seçim kriteri yardımı ile kısmi harçlı riprapın anılan köprü projesi için uygulanabilirliği teyit edilmiştir

Assessment of overtopping reliability and benefits of a flood detention dam

There is a growing tendency to assess safety levels of existing dams and to design new dams using probabilistic approaches according to project characteristics and site-specific conditions. This study is a probabilistic assessment of the overtopping reliability of a dam, which will be designed for flood detention purpose, and will compute the benefits that can be gained as a result of the implementation of this dam. In a case study, a bivariate flood frequency analysis was carried out using a five-parameter bivariate gamma distribution. A family of joint return period curves relating the runoff peak discharges to the runoff volumes at the dam site was derived. A number of hydrographs were also obtained under a joint return period of 100ayears to observe the variation of overtopping tendency. The maximum reservoir elevation and overtopping reliability were determined by performing a probabilistic reservoir routing based on Monte Carlo simulations

On the reliability based safety analysis of the Porsuk dam

Dams are large hydraulic structures constructed to meet various project demands. Their roles in both the environment and the economy of a country are so important that their design and construction should be carried out with a negligibly small risk. Conventional design approaches are deterministic, which ignore variations in the governing variables. To offset this limitation, high safety factors are considered that increase the cost of the structure. Reliability-based design approaches are probabilistic in nature since possible sources of uncertainties associated with the variables are identified using statistical information, which is incorporated into the reliability models. Risk analysis with the integration of risk management and risk assessment is a growing trend in dam safety assessment. This study deals with the probabilistic evaluation of safety of gravity dams. A computer program based on the probabilistic treatment of random loading and resistance terms will be used for the safety analysis. A case study is conducted to illustrate the use of this program