Current Propagation Models Research Articles

Characterization of multi-rotor aircraft using truss support structure

Characterization of multi-rotor drone aircraft noise is vital to expanded use within the United States. To provide compatibility with current propagation and perception models, acoustic noise characterization focuses on the creation of equivalent lower hemispheres, and application of methods developed for manned aircraft for description of the noise directivity patterns. But a previous measurement determined that a refinement of these methods was required for the application to drone noise. One of these refinements was the use of a larger truss support rig, which was selected to provide sufficient clearance for the aircraft. The rig also provided regular holes where the microphones’ support arms could be mounted; the rigid structure possessed no flat faces and minimal cylindrical truss structures to minimize scattering of reflected signals. In addition to the lighting rig array, a number of additional microphones were placed along the flight path, and in-plane but outside of the measurement array for validation of the acoustic sources. With this improved array, another measurement of a multi-rotor aircraft was conducted, equivalent acoustic sources constructed, and validation performed. This measurement validates the use of the square array to characterize these types of aircraft.

Adaptive radio propagation model for maximizing performance efficiency in smart city disaster management application

Climate change poses several environmental threats like floods to urban environment; thus, effective and reliable communication of emergency information is needed during massive breakdown of network infrastructure. This paper presents a mobile adhoc network (MANETs) based effective information such as calls, image, and videos communication system that is compatible with current 3GPP and 5G communication network. Here in maintaining connectivity the information is communicated between different MANET nodes in a multi-hop manner. However, designing radio propagation is challenging considering higher local emergency request congestion at different terrain with varying speed of users. The current radio propagation model is designed without considering the effect of line-of-sight between communicating device and are not adaptive to different environment considering urban disaster management environment. This paper develops an adaptive radio propagation (ARP) model namely expressway, city and semiurban. Then, in reducing congestion and improving network performance efficiency the work introduced an adaptive medium access control (AMAC) protocol. The MAC incorporates a dynamic network controller (DNC) to optimize the contention window size in dynamic manner according to current traffic demands. The AMAC protocol achieves much improved throughput with lesser packet loss in comparison with existing MAC (EMAC) model considering different radio propagation model introduced in this work.

Review on 6G-oriented terahertz communication channel

With the large-scale commercialization of 5G mobile communication systems in the world, 6G technology is becoming a new hotspot of global information technology research. The terahertz band (300GHz to 3THz) has extremely rich frequency resources, which can support ultra-high speed wireless communication from 100Gbps to 1Tbps, improve the existing 5G peak transmission rate by one or two orders of magnitude, and meet the requirements of new applications such as ultra-high resolution holographic communication and meta-universe. An in-depth understanding of the propagation channel is crucial to the design of the communication system. This paper summarizes the research status of the terahertz channel, including its characteristics in the atmosphere, the current channel propagation model, and terahertz channel measurement. At the same time, the future research direction of terahertz communication is analyzed and prospected, and the possible challenges in the future research are discussed, which will help promote the application of terahertz communication technology to 6G communication. Due to technical limitations, terahertz channels have not been fully developed and utilized in the field of communication, and there are many technical bottlenecks that cannot be broken. In the future, new channel models may be built, and there will be opportunities for AI-assisted channel measurement.

Negative frequencies in pulse propagation equations and the double analytic signal

In recent years, the topic of negative frequencies has resurfaced in optics motivated by the optical analogue of Hawking radiation. We discuss the physical meaning of negative frequencies and the conditions under which they are relevant. We review how negative frequencies are treated in current pulse propagation models based on the electric field (EF) and the analytic signal (AS). We focus on experimentally measured signals predicted by the conservation of negative comoving frequency in the nonlinear polarization terms to advance these concepts. We propose a new formalism called the double analytic signal (DAS) which clearly separates negative frequencies from positive ones. Additionally, we reduce this new formalism to the AS to prove their equivalence. Throughout the paper, we present numerical solutions of the unidirectional pulse propagation equation to illustrate the EF, AS, and DAS formalisms and to highlight their differences.

Graph Convolutional-Based Deep Residual Modeling for Rumor Detection on Social Media

The popularity and development of social media have made it more and more convenient to spread rumors, and it has become especially important to detect rumors in massive amounts of information. Most of the traditional rumor detection methods use the rumor content or propagation structure to mine rumor characteristics, ignoring the fusion characteristics of the content and structure and their interaction. Therefore, a novel rumor detection method based on heterogeneous convolutional networks is proposed. First, this paper constructs a heterogeneous map that combines both the rumor content and propagation structure to explore their interaction during rumor propagation and obtain a rumor representation. On this basis, this paper uses a deep residual graph convolutional neural network to construct the content and structure interaction information of the current network propagation model. Finally, this paper uses the Twitter15 and Twitter16 datasets to verify the proposed method. Experimental results show that the proposed method has higher detection accuracy compared to the traditional rumor detection method.

LTE wireless network coverage optimisation based on corrected propagation model

Abstract With the development of technology, the 5th-generation mobile communication technology is becoming more and more mature, and the LTE wireless network is in the peak of application. Although the current wireless propagation model has good adaptability, the prediction accuracy of signal propagation in various specific environments is low; therefore, the wireless propagation model needs to be corrected. The LTE wireless network propagation model was optimised by using the neural network algorithm and corrected by combining with the actual geomorphic characteristics of the experimental area so as to improve the accuracy of simulation prediction of the signal in the service coverage area by the propagation model and provide reference for wireless network planning.

Genetic Drift Versus Climate Region Spreading Dynamics of COVID-19.

Background: The current propagation models of COVID-19 are poorly consistent with existing epidemiological data and with evidence that the SARS-CoV-2 genome is mutating, for potential aggressive evolution of the disease. Objectives: We looked for fundamental variables that were missing from current analyses. Among them were regional climate heterogeneity, viral evolution processes versus founder effects, and large-scale virus containment measures. Methods: We challenged regional versus genetic evolution models of COVID-19 at a whole-population level, over 168,089 laboratory-confirmed SARS-CoV-2 infection cases in Italy, Spain, and Scandinavia at early time-points of the pandemic. Diffusion data in Germany, France, and the United Kingdom provided a validation dataset of 210,239 additional cases. Results: Mean doubling time of COVID-19 cases was 6.63 days in Northern versus 5.38 days in Southern Italy. Spain extended this trend of faster diffusion in Southern Europe, with a doubling time of 4.2 days. Slower doubling times were observed in Sweden (9.4 days), Finland (10.8 days), and Norway (12.95 days). COVID-19 doubling time in Germany (7.0 days), France (7.5 days), and the United Kingdom (7.2 days) supported the North/South gradient model. Clusters of SARS-CoV-2 mutations upon sequential diffusion were not found to clearly correlate with regional distribution dynamics. Conclusion: Acquisition of mutations upon SARS-CoV-2 spreading failed to explain regional diffusion heterogeneity at early pandemic times. Our findings indicate that COVID-19 transmission rates are rather associated with a sharp North/South climate gradient, with faster spreading in Southern regions. Thus, warmer climate conditions may not limit SARS-CoV-2 infectivity. Very cold regions may be better spared by recurrent courses of SARS-CoV-2 infection.

A computational model to guide the functional decoupling of two brain regions with transcranial alternating current stimulation

Abstract Recent research has shown that cortical hyper-synchronization between frontoparietal areas in resting state could be an early biomarker of Alzheimer’s disease (AD). It is expected that reducing this synchronization could slow down the development of AD typical symptoms. In this sense, non-invasive neurostimulation techniques are candidate tools to desynchronize distant regions of the brain. In specific, transcranial Alternating Current Stimulation (tACS) can influence the oscillatory dynamics of neuronal groups in the brain specially modifying signals’ frequency and amplitude. Here we explore the possibility of using tACS to desynchronize frontoparietal brain regions: would this be possible? What frequencies would be the most suitable to minimize synchronization? Thus, we built ten personalized brain models in The Virtual Brain from magnetic resonance imaging and magnetoencephalography recordings. They are built of a structural connectivity network linking brain regions (from AAL2 atlas) and neural mass models per region to simulate electrophysiological dynamics. We applied tACS to stimulate those virtual brains areas on the parietal cortex (P3, P4 positions), using ROAST to calculate a current propagation model that determines how much electric field reaches each part of the brain. Our results show that it is possible to reduce cortical synchronization between two regions with tACS applying frequencies around the natural (i.e. in resting state) oscillation frequency of the stimulated region. These results could lead the experimental search of brain desynchronization with tACS on real subjects. Additionally, they strengthen the possibility of using that technique as an early intervention in Alzheimer’s disease. Keywords: Simulation, The virtual brain, Magnetoencephalography, tACS

IoT focused VHF and UHF propagation study and comparisons

As the market for internet of things (IoT) is growing and due to Ofcom's decision to reassign parts of the very high frequency (VHF) spectrum in the UK for IoT use, a propagation study has been conducted using the newly released VHF spectrum and the currently commercially operated ultra-high frequency (UHF) spectrum, in order to compare and contrast the suitability of the VHF spectrum for IoT use. The authors conducted their study in a number of different environments (rural, suburban, urban and dense urban), with measurement equipment deployed in a manner suitable for a portable IoT use case. Results are presented in comparison to other propagation studies available in the literature and widely used propagation models such as the Hata model. Shadowing and noise are also measured and examined. It is found that current propagation models do not provide adequate predictions within the considered use case, but found it is possible to calculate log-distance based models that provide good predictions. Path-loss is found to be constantly lower at VHF than UHF, but radio frequency noise is consistently higher. The newly released spectrum is found to be suitable for IoT deployments in all the examined environments.

Unification of engineering return stroke models

Engineering models burrow various features from transmission line theory and combine them using empirical data to create models that can predict the electromagnetic fields of lightning return strokes in space and time. At present, engineering models are the most successful in predicting the features of lightning electromagnetic fields in close agreement with the experimental data. Today, most scientists who are interested in lightning protection use engineering models in their studies. A large number of engineering return stroke models exist in the literature. Depending on the assumptions made they can be categorized as Current Propagation models (CP-models), Current Generation models (CG-models) and Current Dissipation models (CD-models). The goal of this paper is to describe the different approximations used in constructing these engineering return stroke models and to show that all these models are a special case of a more general model which we call Current model (C-model). We will show how various return stroke models can be precipitated from the C-model by neglecting different features associated with it.

Positive opinion maximization in signed social networks

Opinion maximization is a kind of optimization method, which leverages a subset of influential nodes in social networks to spread user opinions towards the target product and eventually obtains the largest opinion propagation. The current propagation models on the opinion maximization mainly focus on the activated nodes and the static opinion formation process. However, they neglect the combination between the activated nodes and the dynamic opinion formation process. Moreover, previous studies are more attentive to the positive relationships among users. In the real scenario, negative relationships among users may damage the product reputation. Therefore, in this paper, we study positive opinion maximization by using an Activated Opinion Maximization Framework (AOMF) in signed social networks. The proposed AOMF is composed of three phases: i) the selection of candidate seed nodes, ii) the activated opinion formation process and iii) the determination of seed nodes. We first use an effective heuristic rule to select candidate seed nodes. To model the activation and dynamic opinion formation process of network nodes, we devise the activated opinion formation model based on the multi-stage linear threshold model and the Degroot model. Then, we calculate the opinion propagation of each candidate seed node by using the activated opinion formation model. Based on the candidate seed nodes and the activated opinion formation process, seed nodes are further determined. Finally, experimental results on six social network datasets demonstrate that the proposed method has superior potential opinions and positive ratio than the chosen benchmarks.

Mitigation effects of trees on rockfall hazards: does rock shape matter?

Does rock shape matter to the mitigation effects of trees on rockfall hazards? This question must be resolved in order to better quantify the protective role of mountain forests against rockfall. To probe this question, we investigate a single rock-tree interaction using non-smooth, hard-contact mechanics that allows us to consider rock shape at impact. The interaction of equant shaped rocks with cylinder-like tree stems is modeled. The equant shaped rocks are close to spherical but have a certain shape variability governed by the rock’s surface area ratio and aspect ratio. This work serves as an important follow-up study to the existing investigations from Toe et al. (Landslides 14: 1603-1614, 2017), where the effects of trees on block propagation are numerically investigated using spherical shaped rocks. The objective of our simulations is to understand how and to what extent, shape will influence energy dissipation and trajectory change. The primary results include: surface area ratio plays a more important role than aspect ratio in determining the rock’s post-impact dynamics. The primary parameters governing the rock kinematics after impact (i.e., block’s energy reduction, reflected rotational speed, and trajectory change) are impact velocity, impact eccentricity, and the tree stem diameter. The latter observation aligns well with previous findings and suggests that the shape factors, at least for nearly spherical rocks, can be integrated into the current block propagation models. However, from a statistical viewpoint, the anisotropic distribution of mass and hence the asymmetric moment of inertia of non-spherical rocks leads to stronger or weaker spin effects compared to mass- and volume-equivalent spheres. Apparently, the rotational motion of an irregular object serves as a kinetic energy reservoir leading to subsequent rock-tree impacts, and therefore significant differences in energy loss and trajectory in comparison to spherical shaped rocks. This effect must be further investigated using elongated and flattened blocks and underscores the importance of measuring rockfall rotation in experimental investigations.

Some new hints on cosmic-ray propagation from AMS-02 nuclei spectra

In this work, we considered 2 schemes (a high-rigidity break in primary source injections and a high-rigidity break in diffusion coefficient) to reproduce the newly released AMS-02 nuclei spectra (He, C, N, O, Li, Be, and B) when the rigidity larger than 50 GV. The fitting results show that current data set favors a high-rigidity break at ∼ 325 GV in diffusion coefficient rather than a break at ∼ 365 GV in primary source injections. Meanwhile, the fitted values of the factors to rescale the cosmic-ray (CR) flux of secondary species/components after propagation show us that the secondary flux are underestimated in current propagation model. It implies that we might locate in a slow diffusion zone, in which the CRs propagate with a small value of diffusion coefficient compared with the averaged value in the galaxy. Another hint from the fitting results show that extra secondary CR nuclei injection may be needed in current data set. All these new hints should be paid more attention in future research.

Site Prediction Model for the over Rooftop Path in a Suburban Environment at Millimeter Wave

This paper proposes the site-specific pathloss model for a small town in a suburban environment at millimeter wave. Also, the site general characteristics are provided in the entire measurement area of the small town. The proposed pathloss model is based on the moving measurement campaign according to the distance between a transmitter and a receiver in the candidate millimeter wave band or future five-generation service. In addition, the probability characteristics of pathloss such as the cumulative density function are shown to estimate the spreading characteristics of the wideband signal with a five-hundred-MHz bandwidth. Measurement was performed for the small town in a suburban covered with low-rise commercial restaurants or houses. Transmitting signals propagate through the over rooftop of low-rise houses of average ten meters height. Their multipath signals may be arrived at a receiving station located at the below roof of the house by reflection, diffraction, and scattered mechanism. A current propagation model for the over rooftop is based on generic or geometrical optic equations in a fully non-line-of-sight environment. But, non-line-of-sight cases in a realistic suburban environment include partly the open space between houses. Therefore, the definition of the propagation model of this sight-specific case is very important so clearly as to show the difference for the over rooftop according to the different displacements of houses in a non-line-of-sight environment. Finally, we suggest the improved propagation model of pathloss that can reflect various environments in a small town.

Channel Characterization and Path Loss Modeling in Indoor Environment at 4.5, 28, and 38 GHz for 5G Cellular Networks

The current propagation models used for frequency bands less than 6 GHz are not appropriate and cannot be applied for path loss modeling and channel characteristics for frequency bands above 6 GHz millimeter wave (mmWave) bands, due to the difference of signal propagation characteristics between existing frequency bands and mmWave frequency bands. Thus, extensive studies on channel characterization and path loss modeling are required to develop a general and appropriate channel model that can be suitable for a wide range of mmWave frequency bands in its modeling parameter. This paper presents a study of well-known channel models for an indoor environment on the 4.5, 28, and 38 GHz frequency bands. A new path loss model is proposed for the 28 GHz and 38 GHz frequency bands. Measurements for the indoor line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios were taken every meter over a separation distance of 23 m between the TX and RX antenna locations to compare the well-known and the new large-scale generic path loss models. This measurement was conducted in a new wireless communication center WCC block P15a at Universiti Teknologi Malaysia UTM Johor, Malaysia, and the results were analyzed based on the well-known and proposed path loss models for single-frequency and multifrequency models and for directional and omnidirectional path loss models. Results show that the large-scale path loss over distance could be modeled better with good accuracy by using the simple proposed model with one parameter path loss exponent PLE (n) that is physically based to the transmitter power, rather than using the well-known models that have no physical base to the transmitted power, more complications (require more parameters), and lack of anticipation when explaining model parameters. The PLE values for the LOS scenario were 0.92, 0.90, and 1.07 for the V-V, V-H, and V-Omni antenna polarizations, respectively, at the 28 GHz frequency and were 2.30, 2.24, and 2.40 for the V-V, V-H, and V-Omni antenna polarizations, respectively, at the 38 GHz frequency.

Calculation of the channel discharge function for the generalized lightning traveling current source return stroke model

The generalized lightning traveling current source return stroke model (also called GTCS model) represents generalization of all engineering lightning return stroke models that is generalization of the transmission line (TL models, also called current propagation models) and traveling current source models (TCS models, also known as current generation models). The channel discharge function was introduced and calculated for special cases within the GTCS model. We applied new numerical method for the calculation of the channel discharge function. The proposed method is highly accurate, extremely efficient and relatively simple.

Modeling shock formation and propagation in high-performance jet aircraft noise

Nonlinear propagation can play an important role in both time and frequency-domain features of far-field supersonic jet noise. Many aspects of nonlinear propagation, such as waveform steepening and greater-than-expected high-frequency spectral levels, have been previously predicted for select angles and engine conditions. This paper builds on previous successes and presents a comparison of nonlinear and linear predictions for the F-35B aircraft. Results are shown over a wide spatial and angular range and over varying engine power conditions, including showing evidence of nonlinear propagation in the forward direction at the highest engine conditions. In addition, specific features, such as individual shocks, are compared between numerically propagated and measured waveforms, highlighting the successes and deficiencies of current propagation models. Weather and multi-path interference effects are also addressed and corrected using an empirical model. [Work supported by USAFRL through ORISE. Distribution A: Approved for public release; distribution unlimited; Cleared 07/10/2017; JSF17-714.]

A modification of DMVs based state space model of variation propagation for multistage machining processes

PurposeComplicated workpiece, such as an engine block, has special rough locating datum features (i.e. six independent datum features) due to its complex structure. This locating datum error cannot be handled by current variation propagation model based on differential motion vectors. To extend variation prediction fields, this paper aims to solve the unaddressed variation sources to modify current model for multistage machining processes.Design/methodology/approachTo overcome the limitation of current variation propagation model based on differential motion vectors caused by the unaddressed variation sources, this paper will extend the current model by handling the unaddressed datum-induced variation and its corresponding fixture variation.FindingsThe measurement results of the rear face with respect to the rough datum W and the pan face with respect to the hole Q by coordinate measuring machine (CMM) are −0.006 mm and 0.031 mm. The variation results for rear face and pan face predicted by the modified model are −0.009 mm and 0.025 mm, respectively. The discrepancy of model prediction and measurement is very small.Originality/valueThis paper modifies the variation propagation model based on differential motion vectors by solving the unaddressed variation sources, which can extend the variation prediction fields for some complicated workpiece and is useful in the future work for many fields, such as process monitoring, fault diagnosis, quality-assured setup planning and process-oriented tolerancing.

SAIDR: A New Dynamic Model for SMS-Based Worm Propagation in Mobile Networks

Recently, short message service (SMS) has become one of the most popular applications for mobile users. However, it provides convenience for worms to spread in mobile networks. Due to the differences between computers and smartphones, the current propagation models of computer worms cannot be employed in the mobile network directly, especially in the SMS scenario. In this paper, we propose a worm propagation model based on SMS, named susceptible-affected-infectious-suspended-recovered. To accurately predict the worm propagation via SMS, first, we add the affected state to represent the state of users who have received the messages but have not clicked the malicious links. Second, since an infected node does not always send malicious messages to others, a novel state, the suspended state, is introduced to describe this situation. Furthermore, related stabilities of the worm-free equilibrium and the endemic equilibrium are studied. The worm-free equilibrium is locally and globally asymptotically stable if the basic reproduction number ${R}_{0} , whereas the endemic equilibrium is locally asymptotically stable if $R_{0}>1$ . Finally, comprehensive experiments have been done to support our conclusions and confirm the rationality.

Design and analysis of SEIQR worm propagation model in mobile internet

The mobile Internet has considerably facilitated daily life in recent years. However, it has become the breeding ground for lots of new worms, including the Bluetooth-based worm, the SMS/MMS-based worm and the Wi-Fi-based worm. At present, Wi-Fi is widely used for mobile devices to connect to the Internet. But it exposes these devices to the dangerous environment. Most current worm propagation models aim to solve the problems of computer worms. They cannot be used directly in the mobile environment, particularly in the Wi-Fi scenario, because of the differences between computers and mobile devices. In this paper, we propose a worm propagation model in the Wi-Fi environment, called SEIQR (Susceptible-Exposed-Infectious- Quarantined-Recovered). In the model, infected nodes can be quarantined by the Wi-Fi base station, and a new state named the Quarantined state (Q) is established to represent these infected nodes. Based on this model, we present an effective method to inhibit the spread of the Wi-Fi-based worms. Furthermore, related stabilities of the worm-free and endemic equilibriums are studied based on the basic reproduction number R0. The worm-free equilibrium is locally and globally asymptotically stable if R0 < 1, whereas the endemic equilibrium is locally asymptotically stable if R0 < 1. Finally, we evaluate the performance of our model by comprehensive experiments with different infection rates and quarantine rates. The results indicate that our mechanism can combat the worms propagated via Wi−Fi.