Level-crossings reveal organized coherent structures in a turbulent time series

In turbulent flows, energy production is associated with highly organized structures, known as coherent structures. Since these structures are three-dimensional, their detection remains challenging in the most common situation, when single-point temporal measurements are considered. While previous research on coherent structure detection from time series employs a thresholding approach, the thresholds are ad-hoc and vary significantly from one study to another. To eliminate this subjective bias, we introduce the level-crossing method and show how specific features of a turbulent time series associated with coherent structures can be objectively identified, without assigning a prior any arbitrary threshold. By using two wall-bounded turbulence time series datasets, we successfully extract through level-crossing analysis the impacts of coherent structures on turbulent dynamics, and therefore, open an alternative avenue in experimental turbulence research. By utilizing this framework further we identify a new metric, characterized by a statistical asymmetry between peaks and troughs of a turbulent signal, to quantify inner-outer interaction in wall turbulence. Moreover, a connection is established between extreme value statistics and level-crossing analysis, thereby allowing additional possibilities to study extreme events in other dynamical systems.Comment: This manuscript has 9 figures and 3 supplementary figure

Visibility network analysis of large-scale intermittency in convective surface layer turbulence

Large-scale intermittency is a widely observed phenomenon in convective surface layer turbulence that induces non-Gaussian temperature statistics, while such signature is not observed for velocity signals. Although approaches based on probability density functions have been used so far, those are not able to explain to what extent the signals' temporal structure impacts the statistical characteristics of the velocity and temperature fluctuations. To tackle this issue, a visibility network analysis is carried out on a field-experimental dataset from a convective atmospheric surface layer flow. Through surrogate data and network-based measures, we demonstrate that the temperature intermittency is related to strong non-linear dependencies in the temperature signals. Conversely, a competition between linear and non-linear effects tends to inhibit the temperature-like intermittency behaviour in streamwise and vertical velocities. Based on present findings, new research avenues are likely to be opened up in studying large-scale intermittency in convective turbulence.Comment: 4 figure

A Survey of Wireless Communication Technologies & Their Performance for High Speed Railways

High Speed Railway (HSR) provides its customers not only safety, security, comfort and on-time commuting, but also a fast transportation alternative to air travel or regular passenger rail services. Providing these benefits would not be possible without the tremendous growth and prevalence of wireless communication technologies. Due to advances in wireless communication systems, both trains and passengers are connected through high speed wireless networks to the Internet, data centers and railroad control centers. Railroad communities, academia, related industries and standards bodies, even the European Space Agency, are involved in advancing developments of HSR for highly connected train communication systems. The goal of these efforts is to provide the capabilities for uninterrupted high-speed fault-tolerant communication networks for all possible geographic, structural and weather conditions. This survey provides an overview of the current state-of-the-art and future trends for wireless technologies aiming to realize the concept of HSR communication services. Our goal is to highlight the challenges for these technologies, including GSM-R, Wi-Fi, WIMAX, LTE-R, RoF, LCX & Cognitive Radio, the offered solutions, their performance, and other related issues. Currently, providing HSR services is the goal of many countries across the globe. Europe, Japan & Taiwan, China, as well as North & South America have increased their efforts to advance HSR technologies to monitor and control not only the operations but also to deliver extensive broadband solutions to passengers. This survey determined a trend of the industry to transition control plane operations towards narrowband frequencies, i.e. LTE400/700, and to utilize concurrently other technologies for broadband access for passengers such that services of both user and train control systems are supported. With traditional technologies, a tradeoff was required and often favored train control services over passenger amenities. However, with the advances in communication systems, such as LTE-R and cognitive radios, it is becoming possible for system designers to offer rich services to passengers while also providing support for enhanced train control operations such as Positive Train Control

A Survey of Wireless Communication Technologies & Their Performance for High Speed Railways

High Speed Railway (HSR) provides its customers not only safety, security, comfort and on-time commuting, but also a fast transportation alternative to air travel or regular passenger rail services. Providing these benefits would not be possible without the tremendous growth and prevalence of wireless communication technologies. Due to advances in wireless communication systems, both trains and passengers are connected through high speed wireless networks to the Internet, data centers and railroad control centers. Railroad communities, academia, related industries and standards bodies, even the European Space Agency, are involved in advancing developments of HSR for highly connected train communication systems. The goal of these efforts is to provide the capabilities for uninterrupted high-speed fault-tolerant communication networks for all possible geographic, structural and weather conditions. This survey provides an overview of the current state-of-the-art and future trends for wireless technologies aiming to realize the concept of HSR communication services. Our goal is to highlight the challenges for these technologies, including GSM-R, Wi-Fi, WIMAX, LTE-R, RoF, LCX & Cognitive Radio, the offered solutions, their performance, and other related issues. Currently, providing HSR services is the goal of many countries across the globe. Europe, Japan & Taiwan, China, as well as North & South America have increased their efforts to advance HSR technologies to monitor and control not only the operations but also to deliver extensive broadband solutions to passengers. This survey determined a trend of the industry to transition control plane operations towards narrowband frequencies, i.e. LTE400/700, and to utilize concurrently other technologies for broadband access for passengers such that services of both user and train control systems are supported. With traditional technologies, a tradeoff was required and often favored train control services over passenger amenities. However, with the advances in communication systems, such as LTE-R and cognitive radios, it is becoming possible for system designers to offer rich services to passengers while also providing support for enhanced train control operations such as Positive Train Control

Persistence behaviour of heat and momentum fluxes in convective surface layer turbulence

The characterization of heat and momentum fluxes in wall-bounded turbulence is of paramount importance for a plethora of applications, ranging from engineering to Earth sciences. However, how the turbulent structures associated with velocity and temperature fluctuations interact to produce the emergent flux signatures, is not evident till date. In this work, we investigate this fundamental issue by studying the switching patterns of intermittently occurring turbulent fluctuations from one state to another, a phenomenon called persistence. We discover that the persistence patterns for heat and momentum fluxes are widely different. Moreover, we uncover power-law scaling and length scales of turbulent motions that cause this behavior. Furthermore, by separating the phases and amplitudes of flux events, we explain the origin and differences between heat and momentum transfer efficiencies in convective turbulence. Our findings provide new understanding on the connection between flow organization and flux generation mechanisms, two cornerstones of turbulence research

A Novel Method of Near-Miss Event Detection with Software Defined RADAR in Improving Railyard Safety

Railyards are one of the most challenging and complex workplace environments in any industry. Railyard workers are constantly surrounded by dangerous moving objects, in a noisy environment where distractions can easily result in accidents or casualties. Throughout the years, yards have been contributing 20–30% of the total accidents that happen in railroads. Monitoring the railyard workspace to keep personnel safe from falls, slips, being struck by large object, etc. and preventing fatal accidents can be particularly challenging due to the sheer number of factors involved, such as the need to protect a large geographical space, the inherent dynamicity of the situation workers find themselves in, the presence of heavy rolling stock, blind spots, uneven surfaces and a plethora of trip hazards, just to name a few. Since workers spend the majority of time outdoors, weather conditions also play an important role, i.e., snow, fog, rain, etc. Conventional sensor deployments in yards thus fail to consistently monitor this workspace. In this paper, the authors have identified these challenges and addressed them with a novel detection method using a multi-sensor approach. They have also proposed novel algorithms to detect, classify and remotely monitor Employees-on-Duty (EoDs) without hindering real-time decision-making of the EoD. In the proposed solution, the authors have used a fast spherical-to-rectilinear transform algorithm on fish-eye images to monitor a wide area and to address blindspots in visual monitoring, and employed Software-Defined RADAR (SDRADAR) to address the low-visibility problem. The sensors manage to monitor the workspace for 100 m with blind detection and classification. These algorithms have successfully maintained real-time processing delay of ≤0.1 s between consecutive frames for both SDRADAR and visual processing

5G-UCDA Multi Antenna-To-Logical Cell Circular FIFO Mapping Strategy For High-Speed Train Wireless Communications

2020 is the target year for the roll out of fifth generation wireless communication methodologies. The commercial vendors have characterized 5G as a collection of disruptive set of technologies to provide high throughput, low latency communication supporting a variety of services, i.e., machine to machine communication to next generation base stations and vehicle-to-vehicle communication to radio-over-fiber and high mobility channels. High-speed train wireless communication channels as a subset of high mobility channels have their clear advantages and disadvantages considering other vehicular channels. The speed of high-speed trains is going to reach 500km/hr and with Hyperloop it may reach 1000km/hr. LTE for railways (have) has been specified to support train to ground communication channels only up to 350km/hr and is still not future proof considering the bandwidth intensive passenger services. The next generation passenger services include conference calls, Ultra-HD video streaming, video streaming and downloads, resource intensive multimedia services for passengers comprising of gaming, personalized advertising, virtual and augmented reality, etc. Therefore, high-speed trains being next generation transportation system, the services provided to passengers on-board may suffer compared to the ground. The difference in provided services may sound significant compared to in-flight infotainment services based on satellite communication and on-board Wi-Fi. In our approach, we have investigated the 5G physical deployment scenario without disrupting or interfering with prioritized train control communication channels. The novelty of separating train control and passenger services can be observed with mapping of different planes in 5G/LTE evolution specification. The separation provides an opportunity to not to compromise passenger services, maintaining quality of service in resource sensitive bandwidth. In our study, we found out that with more number of physical small cell deployment, capacity and area spectral efficiency are biased in front of base stations. In most of the conventional architectures the reliability and bandwidth efficiency of the architecture degrade beyond according to Gaussian distribution, which is directly related to propagation distance. In our proposed architecture, we showed that with a deployment scheme of on-roof multi train antennas, physical size of small cells can be reduced further and adaptably extended based on antenna distances. The on-roof antennas connected through fiber can access small cells in First In First Out manner without any additional signaling overhead or forwarding. The scope of this adaptability reduces outage probability comparable to macro cells and achieves flexible power consumption with high area spectral efficiency. The proposed architecture can attain a 10-15-fold improvement in spectral efficiency and 95% improvement in reliability than conventional architectures. Advisor: Hamid R. Sharif-Kashan

BIOTRUST: A Novel Biologically Inspired Optimal TRusted User Social Trait-Aware Association for Wireless Proximity Services in 5G and Beyond

In the 5G and post-5G networks, the IMT-2020 demand among the devices in terms of throughput, reliability, low-latency and security can be observed. The intensive demand inside the network is imposed upon the network to obtain the required Quality-of-Service (QoS) to fulfill the demand. This leads to introduction of device-centric network configuration, where network can offload objectives for optimal resource allocation to the edge devices. The connectivity to ensure that required QoS is termed as trust in this research. Device-to-Device (D2D) communication is integrated in the next-generation wireless network, which facilitates optimal offloaded trust allocation in the network. From the network perspective, device trust is calculated centrally. But during device-to-device association, the trust value of the device is associated locally by the associating user. The distribution of the load and resource allocation among the devices thus lead to flexibly serving different network requirement based services: Ultra-Reliable Low-Latency Communication (URLLC), Enhanced Mobile Broadband (eMBB), Proximity Services (ProSe), Mission Critical Push To Talk (MCPTT), massive-Machine Type Communication (mMTC), etc. These services comprise of reliable low latency communication to high performing mobile broadband in the nodes. The reliability of these variety of services depends on optimal device-centric association for the last-mile network organization. The proposed measures take user-device mobility, socialness and behavior into account and prove the optimality in the device association. The novelty of the proposed optimal measures relies on capturing sporadic behavioral transition and ensuring associations in the network for hand-offs and maximal throughput. In this research, a novel biologically inspired definition of user-device trust-based interaction has been provided and the measures are proposed to find optimal joint user-device trust. The research proves the optimality of the proposed social-behavioral measures and achieves 50-100% more throughput and 6-100 times more probability of association retention compared to social aware algorithms. The guaranteed maximal throughput and association is obtained by achieving 200% more trust compared to conventional social-aware algorithms