Journal articles: 'Vnf modeling'

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Marchetto, Guido, Riccardo Sisto, Matteo Virgilio, and Jaloliddin Yusupov. "A VNF modeling approach for verification purposes." International Journal of Electrical and Computer Engineering (IJECE) 9, no. 4 (August 1, 2019): 2627. http://dx.doi.org/10.11591/ijece.v9i4.pp2627-2636.

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Network Function Virtualization (NFV) architectures are emerging to increase networks flexibility. However, this renewed scenario poses new challenges, because virtualized networks, need to be carefully verified before being actually deployed in production environments in order to preserve network coherency (e.g., absence of forwarding loops, preservation of security on network traffic, etc.). Nowadays, model checking tools, SAT solvers, and Theorem Provers are available for formal verification of such properties in virtualized networks. Unfortunately, most of those verification tools accept input descriptions written in specification languages that are difficult to use for people not experienced in formal methods. Also, in order to enable the use of formal verification tools in real scenarios, vendors of Virtual Network Functions (VNFs) should provide abstract mathematical models of their functions, coded in the specific input languages of the verification tools. This process is error-prone, time-consuming, and often outside the VNF developers’ expertise. This paper presents a framework that we designed for automatically extracting verification models starting from a Java-based representation of a given VNF. It comprises a Java library of classes to define VNFs in a more developer-friendly way, and a tool to translate VNF definitions into formal verification models of different verification tools.

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Vladislavić, Đani, Darko Huljenić, and Julije Ožegović. "Virtual Network Resource Optimization Model for Network Function Virtualization." Wireless Communications and Mobile Computing 2021 (August 17, 2021): 1–21. http://dx.doi.org/10.1155/2021/9928210.

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Network function virtualization (NFV) is a concept aimed at achieving telecom grade cloud ecosystem for new-generation networks focusing on capital and operational expenditure (CAPEX and OPEX) savings. This study introduces empirical throughput prediction model for the virtual network function (VNF) and network function virtualization infrastructure (NFVI) architectures based on Linux kernel. The model arises from the methodology for performance evaluation and modeling based on execution area (EA) distribution by CPU core pinning. EA is defined as a software execution unit that can run isolated on a compute resource (CPU core). EAs are derived from the elements and packet processing principles in NFVIs and VNFs based on Linux kernel. Performing measurements and observing linearity of the measured results open the possibility to apply model calibration technique to achieve general VNF and NFVI architecture model with performance prediction and environment setup optimization. The modeling parameters are derived from the cumulative packet processing cost obtained by measurements for collocated EAs on the CPU core hosting the bottleneck EA. The VNF and NFVI architecture model with performance prediction is successfully validated against the measurement results obtained in emulated environment and used to predict optimal system configurations and maximal throughput results for different CPUs.

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Zeng, Zhihao, Zixiang Xia, Xiaoning Zhang, and Yexiao He. "SFC Design and VNF Placement Based on Traffic Volume Scaling and VNF Dependency in 5G Networks." Computer Modeling in Engineering & Sciences 134, no. 3 (2023): 1791–814. http://dx.doi.org/10.32604/cmes.2022.021648.

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Wei, Yifei, Yuning Jia, Jun Li, and Xiaojun Wang. "RESEARCH ON 5G NETWORK RESOURCE ORCHESTRATION ALGORITHM BASED ON NETWORK VIRTUALIZATION TECHNOLOGY." Latin American Applied Research - An international journal 52, no. 4 (September 25, 2022): 347–52. http://dx.doi.org/10.52292/j.laar.2022.970.

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With the advancement of wireless network technology to the next generation, network function virtualization (NFV) brings the advantages of centralized scheduling of virtual wireless resources and the ability to orchestrate virtual network functions. This makes it possible to dynamically deploy and manage service function chains (SFCs) in virtualized wireless networks according to changes in network load. Through the network function virtualization technology, the DU/CU separation architecture under 5G-NG-RAN is considered. Aiming at the resource orchestration problem of the 5G access network virtual protocol stack function and service function chain after deployment, an energy-aware virtualized network function instance (VNFI) orchestration algorithm is proposed. By modeling the underlying physical network and node energy consumption, the node load, resource type, tolerable delay and migration loss are included in the decision, and the state of the general server node is divided into two types: running state and sleep state. The algorithm decouples the decision-making process of VNF migration into two specific modules, namely "the VNF selection module" and "the migration destination node selection module". It is verified by simulation that compared with other energy-saving strategies, the algorithm in this paper has better performance in reducing energy consumption and reducing migration loss, and it can take into account both the reduction of the number of open server nodes and the improvement of resource utilization.

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Rafiq, Adeel, Asif Mehmood, Talha Ahmed Khan, Khizar Abbas, Muhammad Afaq, and Wang-Cheol Song. "Intent-Based End-to-End Network Service Orchestration System for Multi-Platforms." Sustainability 12, no. 7 (April 1, 2020): 2782. http://dx.doi.org/10.3390/su12072782.

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On-demand service is the main feature of the 5G network, and Network Function Virtualization (NFV) provides it by virtualizing the existing 5G network infrastructure. NFV crafts various virtual networks on a shared physical network, but one of the core challenges in future 5G networks is to automate the modeling of Virtualized Network Functions (VNFs) and end-to-end Network Service (NS) orchestration with less human interaction. Traditionally, the descriptor of VNF and NS is created manually, which requires expert-level skills. This manual approach has a big threat of human error, which can be avoided by using the Intent-Based Networking (IBN) approach. The IBN approach eliminates the requirement of expertise for designing VNFs and NS by taking users’ intentions as an input. In this paper, the proposed system presents the Intent Management System for VNF modeling and end-to-end NS orchestration for multi-platforms. This system takes the high-level information related to a specific service, configures it accordingly, and converts it into the selected platform. The proposed system is tested using Mobile Central Office Re-architected as Data Center (M-CORD) and Open-Source Management and Orchestration (OSM) orchestrators. The results section shows that the proposed system reduces the effort of the end-user in creating network slices and provides seamless end-to-end service orchestration.

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Ye, Qiang, Weihua Zhuang, Xu Li, and Jaya Rao. "End-to-End Delay Modeling for Embedded VNF Chains in 5G Core Networks." IEEE Internet of Things Journal 6, no. 1 (February 2019): 692–704. http://dx.doi.org/10.1109/jiot.2018.2853708.

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Elvidge, Christopher D., Mikhail Zhizhin, Feng Chi Hsu, Tamara Sparks, and Tilottama Ghosh. "Subpixel Analysis of Primary and Secondary Infrared Emitters with Nighttime VIIRS Data." Fire 4, no. 4 (November 7, 2021): 83. http://dx.doi.org/10.3390/fire4040083.

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Biomass burning is a coupled exothermic/endothermic system that transfers carbon in several forms to the atmosphere, ultimately leaving mineral ash. The exothermic phases include flaming and smoldering, which produce the heat that drives the endothermic processes. The endothermic components include pre-heating and pyrolysis, which produce the fuel consumed by flaming and smoldering. These components can be broadly distinguished from each other based on temperature. For several years, we have researched the subpixel analysis of two temperature phases present in fire pixels detected in nighttime VIIRS data. Here, we present the flaming subtractive method, with which we have successfully derived temperatures and source areas for two infrared (IR) emitters and a cooler background. This is developed as an add-on to the existing VIIRS nightfire algorithm version 3 (VNF v.3) which uses Planck curve fitting to calculate temperatures and source areas for a single IR emitter and background. The flaming subtractive method works with data collected in four spectral ranges: near-infrared (NIR), short-wave infrared (SWIR), mid-wave infrared (MWIR) and long-wave infrared (LWIR). With sunlight eliminated, the NIR and SWIR radiances can be fully attributed to the primary IR emitter. The analysis begins with Planck curve modeling for the primary emitter based on the NIR and SWIR radiances, yielding temperature, source area and primary emitter radiances in all spectral bands. The primary emitter radiances are subtracted from each spectral band and then the residual radiance is analyzed for a secondary IR emitter and the background. Spurious results are obtained in pixels lacking a discernable secondary emitter. These misfit pixels revert back to the single IR emitter analysis of VNF v.3. In tests run for two California megafires, we found that the primary emitters straddle the temperature ranges for flaming and smoldering, the exothermic portions of biomass burning, which are apparently commingled on the ground. The secondary emitter temperatures span 350–750 K, corresponding to pre-heating and slow pyrolysis. The natural gas flare test case had few numbers of successful secondary emitter retrievals and a wide range of secondary emitter temperatures. The flaming subtractive analysis is the key addition to VNF version 4, which will commence production later in 2021. In 2022, we will seek validation of the VNF v.4 from nighttime Landsat and other data sources.

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Baldi, Mario, and Amedeo Sapio. "Network Function Modeling and Performance Estimation." International Journal of Electrical and Computer Engineering (IJECE) 8, no. 5 (October 1, 2018): 3021. http://dx.doi.org/10.11591/ijece.v8i5.pp3021-3037.

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This work introduces a methodology for the modelization of network functions focused on the identification of recurring execution patterns as basic building blocks and aimed at providing a platform independent representation. By mapping each modeling building block on specific hardware, the performance of the network function can be estimated in termsof maximum throughput that the network function can achieve on the specific execution platform. The approach is such that once the basic modeling building blocks have been mapped, the estimate can be computed automatically for any modeled network function. Experimental results on several sample network functions show that although our approach cannot be very accurate without taking in consideration traffic characteristics, it is very valuable for those application where even loose estimates are key. One such example is orchestration in network functions virtualization (NFV) platforms, as well as in general virtualization platforms where virtual machine placement is based also on the performance of network services offered to them. Being able to automatically estimate the performance of a virtualized network function (VNF) on different execution hardware, enables optimal placement of VNFs themselves as well as the virtual hosts they serve, while efficiently utilizing available resources.

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Zhu, Haochen, Bo Hu, and Fengrui Yang. "Removal of Sulfadiazine by Polyamide Nanofiltration Membranes: Measurement, Modeling, and Mechanisms." Membranes 11, no. 2 (February 2, 2021): 104. http://dx.doi.org/10.3390/membranes11020104.

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In this study, a complete steric, electrostatic, and dielectric mass transfer model is applied to investigate the separation mechanism of typical antibiotic sulfadiazine by NF90, NF270, VNF-8040 and TMN20H-400 nanofiltration membranes. FTIR and XPS analysis clearly indicate that the membranes we used possess skin layers containing both amine and carboxylic acid groups that can be distributed in an inhomogeneous fashion, leading to a bipolar fixed charge distribution. We compare the theoretical and experimental rejection rate of the sulfadiazine as a function of the pressure difference across the nanopore for the four polyamide membranes of inhomogeneously charged nanopores. It is shown that the rejection rate of sulfadiazine obtained by the solute transport model has similar qualitative results with that of experiments and follows the sequence: RNF90>RVNF2−8040>RNF270>RTMN20H−400. The physical explanation can be attributed to the influence of the inhomogeneous charge distribution on the electric field that arises spontaneously so as to maintain the electroneutrality within the nanopore.

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Elagin, Vasily S., Alexander V. Bogachev, and Ilya A. Belozertsev. "Modeling the estimation of end-to-end packet latency for a chain of NFV nodes in 5G networks." T-Comm 16, no. 3 (2022): 23–30. http://dx.doi.org/10.36724/2072-8735-2022-16-3-23-30.

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It is expected that future communication networks will provide configurable delay-sensitive types of services (for example, streaming video, machine interaction). To support a variety of applications and use cases of servers providing various functions, you can use network function virtualization (NFV), which will be able to provide flexible implementation and placement of configuration of the necessary network functions. This article analyzes the end-to-end packet latency (E2E) for multiple traffic flows passing through the chain of embedded virtual network functions (VNF) in fifth-generation communication networks (5G). The Dominant of Generalized Resource Processing (DR-GPS) is used to distribute computing resources and transfer data between threads in each node of Network Function Virtualization (NFV) to achieve equitable distribution and utilization of available resources. The tandem queuing model is designed for incoming packets combined in several streams passing through the NFV node and its outgoing transmission channel. To analyze manageability, we separate packet processing (and transmission) of various streams in the simulation and determine the average packet processing and transmission rates of each stream as approximate service speeds.

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Asgarian, Mina, Ghasem Mirjalily, and Zhi-Quan Luo. "Trade-Off Between Efficiency and Complexity in Multi-Stage Embedding of Multicast VNF Service Chains." IEEE Communications Letters 26, no. 2 (February 2022): 429–33. http://dx.doi.org/10.1109/lcomm.2021.3132134.

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Dang-Quang, Nhat-Minh, and Myungsik Yoo. "Optimized placement of symmetrical service function chain in network function virtualization." Computer Science and Information Systems, no. 00 (2022): 6. http://dx.doi.org/10.2298/csis210920006d.

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Network function virtualization (NFV) is one of the key technology enablers for actualizing 5G networks. With NFV, virtual network functions (VNFs) are linked together as a service function chain (SFC), which provides network functionality for the customer on demand. However, how to efficiently find a suitable placement for VNFs regarding the given objectives is an extremely difficult issue. The existing approaches assume that the SFC has a simple and asymmetrical pattern that is unsuitable to modeling a real system. We address this limitation by studying a VNF placement optimization problem with symmetrical SFCs that can support both symmetric and asymmetric traffic flows. This NP-hard problem is formulated as a mixed-integer linear programming (MILP) model. An iterative greedy-based heuristic is proposed to overcome the complexity of the MILP model. Extensive simulation results show that the proposed heuristic can obtain a near-optimal solution compared to MILP for a small-scale network, and at the same time, is superior to a traditional heuristic for a large-scale network.

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Tam, Prohim, Sa Math, and Seokhoon Kim. "Priority-Aware Resource Management for Adaptive Service Function Chaining in Real-Time Intelligent IoT Services." Electronics 11, no. 19 (September 20, 2022): 2976. http://dx.doi.org/10.3390/electronics11192976.

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The growth of the Internet of Things (IoT) in various mission-critical applications generates service heterogeneity with different priority labels. A set of virtual network function (VNF) orders represents service function chaining (SFC) for a particular service to robustly execute in a network function virtualization (NFV)-enabled environment. In IoT networks, the configuration of adaptive SFC has emerged to ensure optimality and elasticity of resource expenditure. In this paper, priority-aware resource management for adaptive SFC is provided by modeling the configuration of real-time IoT service requests. The problem models of the primary features that impact the optimization of configuration times and resource utilization are studied. The proposed approaches query the promising embedded deep reinforcement learning engine in the management layer (e.g., orchestrator) to observe the state features of VNFs, apply the action on instantiating and modifying new/created VNFs, and evaluate the average transmission delays for end-to-end IoT services. In the embedded SFC procedures, the agent formulates the function approximator for scoring the existing chain performance metrics. The testbed simulation was conducted in SDN/NFV topologies and captured the average of rewards, delays, delivery ratio, and throughput as −48.6666, 10.9766 ms, 99.9221%, and 615.8441 Mbps, which outperformed other reference approaches, following parameter configuration in this environment.

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Van Rossem, Steven, Wouter Tavernier, Didier Colle, Mario Pickavet, and Piet Demeester. "VNF Performance modelling: From stand-alone to chained topologies." Computer Networks 181 (November 2020): 107428. http://dx.doi.org/10.1016/j.comnet.2020.107428.

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Darsono, Muhammad, Ahmad Ruri Wijaya, and Rommy Hartono. "Modeling and Simulation of Dual-band Yagi Antennas for Voice Communication on Microsatellite." JURNAL INFOTEL 11, no. 3 (September 30, 2019): 68–72. http://dx.doi.org/10.20895/infotel.v11i3.435.

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The design of the dual-band Yagi antenna was developed to support voice communication through voice repeaters on microsatellites in the UHF-VHV frequency from ground stations. The Yagi antenna is a type of half lambda dipole antenna that makes it easy to obtain direction and increase gain. The antenna is designed using the method of moment through a simulation with the CST microwave studio software application. The design used as an antenna element material is a type of copper pipe cylinder. The results of the Yagi antenna design in the VHF frequency consist of one driven element, one reflector element, and three director elements, while the UHF frequency consists of one reflector element and seven directors. The results of simulation parameters are obtained, such as Bandwidth of return loss below 10 dB is 4.3 MHz(VHF), and 44 MHz (UHF), VSWR (2:1) is 1.24 (VHF) and 1.36 (UHF), Gain is 9.19 dBi (VHF) and 10.5 dBi (UHF) and Beam Width is 64 degree (VHF) and 58 degree (UHF). The suitability of the antenna design target is dual-band, and Gain value in UHF is higher than VHF.

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Poikonen, Ari, and Ilkka Suppala. "On modeling airborne very low‐frequency measurements." GEOPHYSICS 54, no. 12 (December 1989): 1596–606. http://dx.doi.org/10.1190/1.1442627.

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Numerical models employed in ground VLF modeling use a normally incident (homogeneous) plane wave as a primary field. We show that these models are not directly applicable to modeling the impedance and wavetilt in the air, quantities needed in the interpretation of airborne VLF resistivity measurements. Instead, the primary field must be replaced by an inhomogeneous plane wave incident on the ground at an angle close to 90 degrees in order to provide the correct behavior of the apparent resistivities in the air. VLF magnetic polarization parameters, however, can be modeled in the air using the normally incident plane wave as a primary field. We also show that the plane‐wave analysis provides the same attenuation characteristics for the wavetilt in the air that is predicted by the Norton’s surface wave obtained by using the vertical electric dipole as a source. Use of the inhomogeneous plane wave introduces the vertical component of the electric field in the model. A 2‐D modeling technique based on the network solution is used to demonstrate the effects of the vertical electric field in the H‐polarization case. The vertical electric field generates charge distributions on the horizontal boundaries of conductors. In the case of a vertical sheet‐like conductor, these charges cause a slight asymmetry in apparent‐resistivity anomalies. Attenuation characteristics of various VLF anomalies with altitude are also presented. The H‐polarization anomalies attenuate much more rapidly in the air than those for E‐polarization due to the difference in the dominating source of EM fields in each polarization.

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Kaikkonen, P., S. P. Sharma, and S. Mittal. "3D modeling and inversion of VLF and VLF-R electromagnetic data." GEOPHYSICS 77, no. 4 (July 1, 2012): WB219—WB231. http://dx.doi.org/10.1190/geo2011-0360.1.

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Three-dimensional linearized nonlinear electromagnetic inversion is developed for revealing the subsurface conductivity structure using isolated very low frequency (VLF) and VLF-resistivity anomalies due to conductors that may be arbitrarily directed towards the measuring profiles and the VLF transmitter. We described the 3D model using a set of variables in terms of geometric and physical parameters. These model parameters were then optimized (parametric inversion) to obtain their best estimates to fit the observations. Two VLF transmitters, i.e., the [Formula: see text], [Formula: see text] (“E”) and the [Formula: see text], [Formula: see text] (“H”) polarizations, respectively, can be considered jointly in inversion. After inverting several noise-free and noisy synthetic data, the results revealed that the estimated model parameters and the functionality of the approach were very good and reliable. The inversion procedure also worked well for the field data. The reliability and validity of the results after the field data inversion have been checked using data from a shear zone associated with uranium mineralization.

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Hien, Dinh Sy. "Development of Quantum Simulator for Emerging Nanoelectronics Devices." ISRN Nanotechnology 2012 (August 28, 2012): 1–10. http://dx.doi.org/10.5402/2012/617214.

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We have developed NEMO-VN2, a new quantum device modeling tool that simulates a wide variety of quantum devices including the resonant tunneling diode, the single electron transistor, the molecular field effect transistor, the carbon nanotube field effect transistor, and the spin field effect transistor. In this work the nonequilibrium Green’s function is used to perform a comprehensive study of the emerging nanoelectronics devices. The program has been written by using graphic user interface of Matlab. NEMO-VN2 uses Matlab to solve Schrodinger equation to get current-voltage characteristics of quantum devices. In the paper, we present a short overview of the theoretical methodology using non-equilibrium Green’s function for modeling of various quantum devices and typical simulations used to illustrate the capabilities of the NEMO-VN2.

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Ramesh Babu, V., Subhash Ram, and N. Sundararajan. "Modeling and inversion of magnetic and VLF-EM data with an application to basement fractures: A case study from Raigarh, India." GEOPHYSICS 72, no. 5 (September 2007): B133—B140. http://dx.doi.org/10.1190/1.2759921.

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We present modeling of magnetic and very low frequency electromagnetic (VLF-EM) data to map the spatial distribution of basement fractures where uranium is reported in Sambalpur granitoids in the Raigarh district, Chhattisgarh, India. Radioactivity in the basement fractures is attributed to brannerite, [Formula: see text] complex, and uranium adsorbed on ferruginous matter. The amplitude of the 3D analytical signal of the observed magnetic data indicates the trend of fracture zones. Further, the application of Euler 3D deconvolution to magnetic data provides the spatial locations and depth of the source. Fraser-filtered VLF-EM data and current density pseudosections indicate the presence of shallow and deep conductive zones along the fractures. Modeling of VLF-EM data yields the subsurface resistivity distribution of the order of less than 100 ohm-m of the fractures. The interpreted results of both magnetic and VLF-EM data agree well with the geologic section obtained from drilling.

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Roy, Jean. "On: “Effect of temporal and spatial variations of the primary signal on VLF total‐field surveys” by M. A. Vallee, M. Chouteau, and G. J. Palacky (January 1992 GEOPHYSICS, p. 97‐105)." GEOPHYSICS 58, no. 5 (May 1993): 756. http://dx.doi.org/10.1190/1.1443461.

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Vallee et al. (1992) remark on the sensitivity of airborne ratio measuring VLF instruments to platform attitude stability. The authors also remind the users of VLF total field amplitude data, as produced by instruments such as the Herz TOTEM, of two problems associated with this type of data: spatial and temporal fluctuations of the VLF primary field. They recommend the use of a dense network of VLF monitoring stations and numerical modeling of field propagation to cope with these problems. These two recommendations are briefly discussed here and one alternative recommendation is made.

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Mitsis, Georgios D., Rong Zhang, Benjamin D. Levine, and Vasilis Z. Marmarelis. "Cerebral hemodynamics during orthostatic stress assessed by nonlinear modeling." Journal of Applied Physiology 101, no. 1 (July 2006): 354–66. http://dx.doi.org/10.1152/japplphysiol.00548.2005.

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The effects of orthostatic stress, induced by lower body negative pressure (LBNP), on cerebral hemodynamics were examined in a nonlinear context. Spontaneous fluctuations of beat-to-beat mean arterial blood pressure (MABP) in the finger, mean cerebral blood flow velocity (MCBFV) in the middle cerebral artery, as well as breath-by-breath end-tidal CO2 concentration (PetCO2) were measured continuously in 10 healthy subjects under resting conditions and during graded LBNP to presyncope. A two-input nonlinear Laguerre-Volterra network model was employed to study the dynamic effects of MABP and PetCO2 changes, as well as their nonlinear interactions, on MCBFV variations in the very low (VLF; below 0.04 Hz), low (LF; 0.04–0.15 Hz), and high frequency (HF; 0.15–0.30 Hz) ranges. Dynamic cerebral autoregulation was described by the model terms corresponding to MABP, whereas cerebral vasomotor reactivity was described by the model PetCO2 terms. The nonlinear model terms reduced the output prediction normalized mean square error substantially (by 15–20%) and had a prominent effect in the VLF range, both under resting conditions and during LBNP. Whereas MABP fluctuations dominated in the HF range and played a significant role in the VLF and LF ranges, changes in PetCO2 accounted for a considerable fraction of the VLF and LF MCBFV variations, especially at high LBNP levels. The magnitude of the linear and nonlinear MABP-MCBFV Volterra kernels increased substantially above −30 mmHg LBNP in the VLF range, implying impaired dynamic autoregulation. In contrast, the magnitude of the PetCO2-MCBFV kernels reduced during LBNP at all frequencies, suggesting attenuated cerebral vasomotor reactivity under dynamic conditions. We speculate that these changes may reflect a progressively reduced cerebrovascular reserve to compensate for the increasingly unstable systemic circulation during orthostatic stress that could ultimately lead to cerebral hypoperfusion and syncope.

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Palit, S., T. Basak, S. K. Mondal, S. Pal, and S. K. Chakrabarti. "Modeling of the Very Low Frequency (VLF) radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry." Atmospheric Chemistry and Physics Discussions 13, no. 3 (March 7, 2013): 6007–33. http://dx.doi.org/10.5194/acpd-13-6007-2013.

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Abstract. X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~ 60 to 100 km) in excess of what is expected from a quiet sun. Very Low Frequency (VLF) radio wave signals reflected from the D region are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the lower ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the VLF signal change. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.

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Palit, S., T. Basak, S. K. Mondal, S. Pal, and S. K. Chakrabarti. "Modeling of very low frequency (VLF) radio wave signal profile due to solar flares using the GEANT4 Monte Carlo simulation coupled with ionospheric chemistry." Atmospheric Chemistry and Physics 13, no. 18 (September 16, 2013): 9159–68. http://dx.doi.org/10.5194/acp-13-9159-2013.

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Abstract. X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km) in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF) radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.

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Beamish, David. "Three-dimensional modelling of VLF data." Journal of Applied Geophysics 39, no. 2 (June 1998): 63–76. http://dx.doi.org/10.1016/s0926-9851(98)00012-3.

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Liu, Jicheng, Curtis E. Woodcock, Rae A. Melloh, Robert E. Davis, Ceretha McKenzie, and Thomas H. Painter. "Modeling the View Angle Dependence of Gap Fractions in Forest Canopies: Implications for Mapping Fractional Snow Cover Using Optical Remote Sensing." Journal of Hydrometeorology 9, no. 5 (October 1, 2008): 1005–19. http://dx.doi.org/10.1175/2008jhm866.1.

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Abstract Forest canopies influence the proportion of the land surface that is visible from above, or the viewable gap fraction (VGF). The VGF limits the amount of information available in satellite data about the land surface, such as snow cover in forests. Efforts to recover fractional snow cover from the spectral mixture analysis model Moderate Resolution Imaging Spectroradiometer (MODIS) snow-covered area and grain size (MODSCAG) indicate the importance of view angle effects in forested landscapes. The VGF can be estimated using both hemispherical photos and forest canopy models. For a set of stands in the Cold Land Field Processes Experiment (CLPX) sites in the Fraser Experimental Forest in Colorado, the convergence of both measurements and models of the VGF as a function of view angle supports the idea that VGF can be characterized as a function of forest properties. A simple geometric optical (GO) model that includes only between-crown gaps can capture the basic shape of the VGF as a function of view zenith angle. However, the GO model tends to underestimate the VGF compared with estimates derived from hemispherical photos, particularly at high view angles. The use of a more complicated geometric optical–radiative transfer (GORT) model generally improves estimates of the VGF by taking into account within-crown gaps. Small footprint airborne lidar data are useful for mapping forest cover and height, which makes the parameterization of the GORT model possible over a landscape. Better knowledge of the angular distribution of gaps in forest canopies holds promise for improving remote sensing of snow cover fraction.

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Stanley, Bradford J., Elana S. Ehrlich, Leslie Short, Yunkai Yu, Zuoxiang Xiao, Xiao-Fang Yu, and Yong Xiong. "Structural Insight into the Human Immunodeficiency Virus Vif SOCS Box and Its Role in Human E3 Ubiquitin Ligase Assembly." Journal of Virology 82, no. 17 (June 18, 2008): 8656–63. http://dx.doi.org/10.1128/jvi.00767-08.

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ABSTRACT Human immunodeficiency virus (HIV) virion infectivity factor (Vif) causes the proteasome-mediated destruction of human antiviral protein APOBEC3G by tethering it to a cellular E3 ubiquitin ligase composed of ElonginB, ElonginC, Cullin5, and Rbx2. It has been proposed that HIV Vif hijacks the E3 ligase through two regions within its C-terminal domain: a BC box region that interacts with ElonginC and a novel zinc finger motif that interacts with Cullin5. We have determined the crystal structure of the HIV Vif BC box in complex with human ElonginB and ElonginC. This complex presents direct structural evidence of the recruitment of a human ubiquitin ligase by a viral BC box protein that mimics the conserved interactions of cellular ubiquitin ligases. We further mutated conserved hydrophobic residues in a region downstream of the Vif BC box. These mutations demonstrate that this region, the Vif Cullin box, composes a third E3-ligase recruiting site critical for interaction between Vif and Cullin5. Furthermore, our homology modeling reveals that the Vif Cullin box and zinc finger motif may be positioned adjacent to the N terminus of Cullin5 for interaction with loop regions in the first cullin repeat of Cullin5.

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Røge, Rasmus E., Kristoffer H. Madsen, Mikkel N. Schmidt, and Morten Mørup. "Infinite von Mises–Fisher Mixture Modeling of Whole Brain fMRI Data." Neural Computation 29, no. 10 (October 2017): 2712–41. http://dx.doi.org/10.1162/neco_a_01000.

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Cluster analysis of functional magnetic resonance imaging (fMRI) data is often performed using gaussian mixture models, but when the time series are standardized such that the data reside on a hypersphere, this modeling assumption is questionable. The consequences of ignoring the underlying spherical manifold are rarely analyzed, in part due to the computational challenges imposed by directional statistics. In this letter, we discuss a Bayesian von Mises–Fisher (vMF) mixture model for data on the unit hypersphere and present an efficient inference procedure based on collapsed Markov chain Monte Carlo sampling. Comparing the vMF and gaussian mixture models on synthetic data, we demonstrate that the vMF model has a slight advantage inferring the true underlying clustering when compared to gaussian-based models on data generated from both a mixture of vMFs and a mixture of gaussians subsequently normalized. Thus, when performing model selection, the two models are not in agreement. Analyzing multisubject whole brain resting-state fMRI data from healthy adult subjects, we find that the vMF mixture model is considerably more reliable than the gaussian mixture model when comparing solutions across models trained on different groups of subjects, and again we find that the two models disagree on the optimal number of components. The analysis indicates that the fMRI data support more than a thousand clusters, and we confirm this is not a result of overfitting by demonstrating better prediction on data from held-out subjects. Our results highlight the utility of using directional statistics to model standardized fMRI data and demonstrate that whole brain segmentation of fMRI data requires a very large number of functional units in order to adequately account for the discernible statistical patterns in the data.

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Singh, S. B., K. Patel, R. P. Patel, A. K. Singh, and R. P. Singh. "Modeling of VHF scintillation observed at low latitude." Journal of Physics: Conference Series 208 (February 1, 2010): 012065. http://dx.doi.org/10.1088/1742-6596/208/1/012065.

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Zoghzoghy, F. G., M. B. Cohen, R. K. Said, N. G. Lehtinen, and U. S. Inan. "Shipborne LF-VLF oceanic lightning observations and modeling." Journal of Geophysical Research: Atmospheres 120, no. 20 (October 23, 2015): 10,890–10,902. http://dx.doi.org/10.1002/2015jd023226.

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Guli, Guli, Heri Sapari Kahpi, Cecep Warman, and Fathurrohman Fathurrohman. "Peran Karakteristik Kepemimpinan dan Budaya Organisasi dalam Peningkatan Kinerja Karyawan di Mediasi oleh Variabel Motivasi." JIIP - Jurnal Ilmiah Ilmu Pendidikan 4, no. 4 (August 13, 2021): 237–47. http://dx.doi.org/10.54371/jiip.v4i4.262.

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Tujuan dari penelitian ini untuk mengujiperan motivasi dalam memediasi pengaruh karakteristik pemimpin dan budaya organisasi terhadap kinerja karyawan dengan menggunakan Structural Equation Modeling. Sampel yang diambil adalah 100 karyawan dengan menggunakan purposive sampling didasarkan pada judgment sampling. Hasil penelitian menunjukkan bahwa hasil efek tidak langsung karakteristik pemimpin terhadap kinerja melalui motivasi artinya positif dan signifikan signifikan. Budaya organisasi terhadap kinerja melalui motivasi berarti signifikan. Pengaruh total (total effect) karakteristik pemimpin terhadap kinerja melalui motivasi adalah 0,418 (0,204 + 0,214) dengan VAF sebesar 0,633 (0,418 + 0,214). Sedangkan pengaruh total (total effect) budaya organisasi terhadap kinerja melalui motivasia dalah 0,347 (0,226 + 0,121) dengan VAF sebesar 0,347 (0,347 + 0,121). Hasil VAF pengaruh karakteristik pemimpin terhadap kinerja melalui motivasi bernilai 0,633 atau 63,3% ini dikategorikan memediasi penuh, Hasil VAF pengaruh budaya orgnasisasi terhadap kinerja melalui motivasi bernilai 0,347atau 34,7% ini dikategorikan memediasi penuh.

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Dwinanda, Aldi Rivaldi, Bambang Setia Nugroho, and Aloysius Adya Pramudita. "Modeling of Cavities Detection in The Tree Stemsection Using Radar Vector Network Analyzer (VNA) Elaborating Radon Transform." Journal of Measurements, Electronics, Communications, and Systems 9, no. 1 (June 30, 2022): 29. http://dx.doi.org/10.25124/jmecs.v9i1.5370.

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Trees are one of the most useful plants for life on earth. However, trees can be harmful due to cavities in the stem sections. Rapid detection is needed to prevent several losses that may arise due to fallen trees. This research identified a hollow and non-hollow tree stem section of flamboyant tree with a sub-surface detection radar system. The sub surface detection radar system was modeled using a Vector Network Analyzer (VNA) connected to a Vivaldi antenna. VNA emitted electromagnetic waves to the tree stem section and subsequently propagated and penetrated hollow tree stem section. The propagation wave met the boundary plane between the wood and the cavity which reflected the electromagnetic waves. The reflected wave was caught by antenna and was display by the VNA as S-Parameter. This research used a Vivaldi antenna with a working frequency of 1 GHz – 10 GHz and a VNA with working frequency 300KHz - 8GHz. The difference in the amplitude of the signal could be seen from the results of cavity measurements made at one point. By implementing circular scanning method with inverse radon transformation, this research could identify a 19 cm diameter wood with a hole of 6 cm and 9.5 cm diameter filled with water, respectively. It was observed that the optimal detection was obtained by placing object between the antennas. This research has signified the application of radar modeled with VNA for detecting the cavities in tree stem section.

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Koner, S., Sumit, R. Shukla, S. K. Majumder, and S. Satapathy. "FEM modelling of magnetoelectric coupling in (2-2)LSMO/ P(VDF-TrFE) polymer composite." IOP Conference Series: Materials Science and Engineering 1248, no. 1 (July 1, 2022): 012079. http://dx.doi.org/10.1088/1757-899x/1248/1/012079.

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Abstract Strain mediated magnetoelectric (ME) coupling effect has been investigated in bilayer structure of LSMO/P (VDF-TrFE) nanocomposite in the transverse ME mode. In the transverse mode, Finite Element Method (FEM) based small signal analysis has been performed by the COMSOL Multiphysics 6.0 software. La0.7Sr0.3MnO3(LSMO)/P (VDF-TrFE) nanocomposite (2-2) has been prepared by gluing LSMO pellet with P(VDF-TrFE) polymer film. This bilayer structure shows multiferroic property at room temperature. Simulated FEM modelverifies the magneto-strictive property of LSMO layer and explained the experimental results.Experimental and simulated ME coupling coefficient are found to be very close to each other.

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Aloulou, Wala, Hajer Aloulou, Afef Attia, Sudip Chakraborty, and Raja Ben Amar. "Treatment of Tuna Cooking Juice via Ceramic Ultrafiltration Membrane: Optimization Using Response Surface Methodology." Membranes 12, no. 8 (August 22, 2022): 813. http://dx.doi.org/10.3390/membranes12080813.

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In the present work, optimized ultrafiltration conditions, using a ceramic multi tubular titania membrane (150 KDa), were investigated for the treatment of tuna cooking juice, for water reuse in the industrial process. The interactive effects of the volume concentrating factor (VCF) (1.03–4.25), feed temperature (T) (20–60 °C), and applied transmembrane pressure (ΔP) (2–5 bar) on protein removal (R protein) and permeate flux (J) were determined. A Box–Behnken experimental design (BBD) with the response surface methodology (RSM) was used for statistical analysis, modeling, and optimization of the operating conditions. The analysis of variance (ANOVA) results proved that the protein removal and permeate flux were significant and represented good correlation coefficients of 0.9859 and 0.9294, respectively. Mathematical modeling showed that the best conditions were VCF = 1.5 and a feed temperature of 60 °C, under a transmembrane pressure of 5 bar. The fouling mechanism was checked by applying a polarization concentration model. Determination of the gel concentration confirmed the results found in the mass balance calculation and proved that the VCF must not exceed 1.5. The membrane regeneration efficiency was proven by determining the water permeability after the chemical cleaning process.

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Lenshin, A. V., V. N. Tikhomirov, E. V. Shatalov, M. P. Savchenko, and N. M. Tikhomirov. "FREQUENCY SYNTHESIZERS MODERNIZATION OF VHF RADIO COMMUNICATION." T-Comm 16, no. 9 (2022): 20–27. http://dx.doi.org/10.36724/2072-8735-2022-16-9-20-27.

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Trends and prospects for the development of modern systems and complexes of radio communication, features of the use of frequency synthesizers based on the pulse-phase-locked loop in modern radio communications are analyzed. The results of the MF modernization on an integrated circuit HMC704 for transceivers of VHF radio stations are presented. The modeling of the upgraded midrange main units was carried out in the TI PLLatinumSim program. The LPF elements values and power spectral density of the output MF signal phase noise on LMX2594 IC are calculated. Due to the possibility of using a high comparison frequency in a frequency-phase detector, it was possible to improve the weight and size indicators, increase the speed and purity of the output signal spectrum of upgraded MF, which was confirmed by the results of modeling and experimental studies of the current synthesizer layout.

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Gui, Chengcheng, Xuguang Chen, Khadija Sheikh, Liza Mathews, Sheng-Fu L. Lo, Junghoon Lee, Majid A. Khan, Daniel M. Sciubba, and Kristin J. Redmond. "Radiomic modeling to predict risk of vertebral compression fracture after stereotactic body radiation therapy for spinal metastases." Journal of Neurosurgery: Spine 36, no. 2 (February 1, 2022): 294–302. http://dx.doi.org/10.3171/2021.3.spine201534.

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OBJECTIVE In the treatment of spinal metastases with stereotactic body radiation therapy (SBRT), vertebral compression fracture (VCF) is a common and potentially morbid complication. Better methods to identify patients at high risk of radiation-induced VCF are needed to evaluate prophylactic measures. Radiomic features from pretreatment imaging may be employed to more accurately predict VCF. The objective of this study was to develop and evaluate a machine learning model based on clinical characteristics and radiomic features from pretreatment imaging to predict the risk of VCF after SBRT for spinal metastases. METHODS Vertebral levels C2 through L5 containing metastases treated with SBRT were included if they were naive to prior surgery or radiation therapy, target delineation was based on consensus guidelines, and 1-year follow-up data were available. Clinical features, including characteristics of the patient, disease, and treatment, were obtained from chart review. Radiomic features were extracted from the planning target volume (PTV) on pretreatment CT and T1-weighted MRI. Clinical and radiomic features selected by least absolute shrinkage and selection operator (LASSO) regression were included in random forest classification models, which were trained to predict VCF within 1 year after SBRT. Model performance was assessed with leave-one-out cross-validation. RESULTS Within 1 year after SBRT, 15 of 95 vertebral levels included in the analysis demonstrated new or progressive VCF. Selected clinical features included BMI, performance status, total prescription dose, dose to 99% of the PTV, lumbar location, and 2 components of the Spine Instability Neoplastic Score (SINS): lytic tumor character and spinal misalignment. Selected radiomic features included 5 features from CT and 3 features from MRI. The best-performing classification model, derived from a combination of selected clinical and radiomic features, demonstrated a sensitivity of 0.844, specificity of 0.800, and area under the receiver operating characteristic (ROC) curve (AUC) of 0.878. This model was significantly more accurate than alternative models derived from only selected clinical features (AUC = 0.795, p = 0.048) or only components of the SINS (AUC = 0.579, p < 0.0001). CONCLUSIONS In the treatment of spinal metastases with SBRT, a machine learning model incorporating both clinical features and radiomic features from pretreatment imaging predicted VCF at 1 year after SBRT with excellent sensitivity and specificity, outperforming models developed from clinical features or components of the SINS alone. If validated, these findings may allow more judicious selection of patients for prophylactic interventions.

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Nakashima, Masaaki, Hirotaka Ode, Takashi Kawamura, Shingo Kitamura, Yuriko Naganawa, Hiroaki Awazu, Shinya Tsuzuki, et al. "Structural Insights into HIV-1 Vif-APOBEC3F Interaction." Journal of Virology 90, no. 2 (November 4, 2015): 1034–47. http://dx.doi.org/10.1128/jvi.02369-15.

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ABSTRACTThe HIV-1 Vif protein inactivates the cellular antiviral cytidine deaminase APOBEC3F (A3F) in virus-infected cells by specifically targeting it for proteasomal degradation. Several studies identified Vif sequence motifs involved in A3F interaction, whereas a Vif-binding A3F interface was proposed based on our analysis of highly similar APOBEC3C (A3C). However, the structural mechanism of specific Vif-A3F recognition is still poorly understood. Here we report structural features of interaction interfaces for both HIV-1 Vif and A3F molecules. Alanine-scanning analysis of Vif revealed that six residues located within the conserved Vif F1-, F2-, and F3-box motifs are essential for both A3C and A3F degradation, and an additional four residues are uniquely required for A3F degradation. Modeling of the Vif structure on an HIV-1 Vif crystal structure revealed that three discontinuous flexible loops of Vif F1-, F2-, and F3-box motifs sterically cluster to form a flexible A3F interaction interface, which represents hydrophobic and positively charged surfaces. We found that the basic Vif interface patch (R17, E171, and R173) involved in the interactions with A3C and A3F differs. Furthermore, our crystal structure determination and extensive mutational analysis of the A3F C-terminal domain demonstrated that the A3F interface includes a unique acidic stretch (L291, A292, R293, and E324) crucial for Vif interaction, suggesting additional electrostatic complementarity to the Vif interface compared with the A3C interface. Taken together, these findings provide structural insights into the A3F-Vif interaction mechanism, which will provide an important basis for development of novel anti-HIV-1 drugs using cellular cytidine deaminases.IMPORTANCEHIV-1 Vif targets cellular antiviral APOBEC3F (A3F) enzyme for degradation. However, the details on the structural mechanism for specific A3F recognition remain unclear. This study reports structural features of interaction interfaces for both HIV-1 Vif and A3F molecules. Three discontinuous sequence motifs of Vif, F1, F2, and F3 boxes, assemble to form an A3F interaction interface. In addition, we determined a crystal structure of the wild-type A3F C-terminal domain responsible for the Vif interaction. These results demonstrated that both electrostatic and hydrophobic interactions are the key force driving Vif-A3F binding and that the Vif-A3F interfaces are larger than the Vif-A3C interfaces. These findings will allow us to determine the configurations of the Vif-A3F complex and to construct a structural model of the complex, which will provide an important basis for inhibitor development.

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Zuckerman, Neil, and Noam Lior. "Impingement Heat Transfer: Correlations and Numerical Modeling." Journal of Heat Transfer 127, no. 5 (May 1, 2005): 544–52. http://dx.doi.org/10.1115/1.1861921.

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Uses of impinging jet devices for heat transfer are described, with a focus on cooling applications within turbine systems. Numerical simulation techniques and results are described, and the relative strengths and drawbacks of the k-ε,k-ω, Reynolds stress model, algebraic stress models, shear stress transport, and v2f turbulence models for impinging jet flow and heat transfer are compared. Select model equations are provided as well as quantitative assessments of model errors and judgments of model suitability.

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Kim, Hoyoung, and Vijay Harid. "Numerical Modeling of Nondestructive Testing of Various Conductive Objects inside Metal Enclosures Using ELF/VLF Magnetic Fields." Applied Sciences 11, no. 8 (April 19, 2021): 3665. http://dx.doi.org/10.3390/app11083665.

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Nondestructive evaluation of various conductive objects through metal enclosures is investigated by using ELF/VLF magnetic induction fields in detailed simulations. ELF/VLF magnetic fields (<30 kHz) have a unique ability to penetrate highly conductive or permeable shields. Using a magnetic dipole source antenna, objects hidden inside a metal enclosure are imaged via examining distortions to the field outside the enclosure. The field distortion is parametrically studied by varying the size, conductivity, and permeability of the hidden objects. Furthermore, the importance of the conductivity of the enclosure itself is investigated using both low (106 S/m) and high (108 S/m) conductivity metallic shields. It is shown that the responses are quite sensitive to the object and shield parameters; both qualitative and quantitative properties of the field distortions are described in detail. The simulation results suggest that properties of hidden conductive or permeable objects, over a relatively wide range of parameters (both geometry and material), can be inferred nondestructively using ELF/VLF magnetic induction fields.

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You, Jun, Xian-rong Wan, Zi-ping Gong, Feng Cheng, and Heng-yu Ke. "Echo Modeling and Detection Performance of Wideband VHF Radar." Journal of Electronics & Information Technology 35, no. 12 (February 23, 2014): 2795–801. http://dx.doi.org/10.3724/sp.j.1146.2013.00369.

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Rodger, Craig J., and David Nunn. "VLF scattering from red sprites: Application of numerical modeling." Radio Science 34, no. 4 (July 1999): 923–32. http://dx.doi.org/10.1029/1999rs900040.

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Rodger, Craig J., Mark A. Clilverd, and Neil R. Thomson. "Modeling of subionospheric VLF signal perturbations associated with earthquakes." Radio Science 34, no. 5 (September 1999): 1177–85. http://dx.doi.org/10.1029/1999rs900061.

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Lehtinen, Nikolai G., and Umran S. Inan. "Full-wave modeling of transionospheric propagation of VLF waves." Geophysical Research Letters 36, no. 3 (February 2009): n/a. http://dx.doi.org/10.1029/2008gl036535.

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Schmitter, E. D. "Remote sensing and modeling of lightning caused long recovery events within the lower ionosphere using VLF/LF radio wave propagation." Advances in Radio Science 12 (November 11, 2014): 241–50. http://dx.doi.org/10.5194/ars-12-241-2014.

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Abstract. On the 4 November 2012 at 3:04:27 UT a strong lightning in the midst of the North Sea affected the propagation conditions of VLF/LF transmitter radio signals from NRK (Iceland, 37.5 kHz) and GBZ (UK, 19.58 kHz) received at 5246° N 8° E (NW Germany). The amplitude and phase dips show a recovery time of 6–12 min pointing to a LOng Recovery Early VLF (LORE) event. Clear assignment of the causative return stroke in space and time was possible with data from the WWLLN (Worldwide Lightning Location Network). Based on a return stroke current model the electric field is calculated and an excess electron density distribution which decays over time in the lower ionosphere is derived. Ionization, attachment and recombination processes are modeled in detail. Entering the electron density distribution in VLF/LF radio wave propagation calculations using the LWPC (Long Wavelength Propagation Capability) code allows to model the VLF/LF amplitude and phase behavior by adjusting the return stroke current moment. The results endorse and quantify the conception of lower ionosphere EMP heating by strong – but not necessarily extremely strong – return strokes of both polarities.

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Pan, Yuyan, Jifu Guo, and Yanyan Chen. "Calibration of Dynamic Volume-Delay Functions: A Rolling Horizon-Based Parsimonious Modeling Perspective." Transportation Research Record: Journal of the Transportation Research Board 2676, no. 2 (October 20, 2021): 606–20. http://dx.doi.org/10.1177/03611981211044727.

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Volume-delay functions (VDF) are the critical building block in static traffic assignment and general demand-supply analysis. This paper aims to provide a rolling horizon-based modeling framework to establish and further calibrate dynamic VDF (DVDF) for a corridor. The development and application of classic VDF in recent traffic planning studies are first reviewed. Analytical formulas based on a rolling horizon framework are then developed to redefine critical elements in the Bureau of Public Roads (BPR) function to capture the time-dependent volume–delay relationship. Time-dependent average demand and discharge rate are used in a real-world bottleneck in oversaturated conditions. By constructing an estimate or approximate for the dynamic degree of saturation, the proposed method could (i) better interpret the underlying mechanism of the time-dependent demand–delay function; (ii) provide a valuable tool to estimate the speed for a time rolling horizon with given real-time data in practice, and (iii) analyze the correlation between a bottleneck and upstream or downstream on a road network to acquire accurate discharge rates for different situations. Experiments using corridors in Beijing and Los Angeles demonstrate that the proposed dynamic analytical methods can outperform the traditional BPR function in dynamic congestion cases. The results improve the DVDF goodness-of-fit from [Formula: see text] of 44% to 87% under different conditions, which sheds more light on future online traffic simulation applications.

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Vallée, Marc A., Michel Chouteau, and G. J. Palacky. "Effect of temporal and spatial variations of the primary signal on VLF total‐field surveys." GEOPHYSICS 57, no. 1 (January 1992): 97–105. http://dx.doi.org/10.1190/1.1443192.

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Most of the airborne and ground VLF instruments presently used measure the total‐field response in addition to field ratios. Results of surveys using these instruments are adversely affected by spatial and temporal variations in the VLF primary field. Until now, the nature of such variations has not been studied from the point of view of geophysical surveying practice. Spatial variations are analyzed using radio propagation models. The most important result is the identification of primary field minima where surveys would be unreliable. Their dependence on the transmitter location is rather complex, and modeling should be carried out before specifying VLF stations for a survey area. Spatial and temporal variations have been studied using field monitoring of the transmitted signal. The results of field experiments indicate that the nature of the received VLF fields changes significantly even over moderate distances (20–30 km) and that data cannot be reliably corrected over larger distances. This observation has a significant implication for VLF total‐field surveys, particularly airborne, in which base stations have been routinely used to monitor the primary field strength and to correct the survey data. The results of primary signal monitoring are also used to demonstrate the effect of solar flares on VLF surveys. Because of the large intensity and complex electromagnetic character of solar flares, survey data recorded during such events cannot be used for map compilation and interpretation.

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Slingsby, P. L. "Modelling tropospheric ducting effects on VHF/UHF propagation." IEEE Transactions on Broadcasting 37, no. 2 (June 1991): 25–34. http://dx.doi.org/10.1109/11.86959.

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Srećković, Vladimir A., Desanka M. Šulić, Ljubinko Ignjatović, and Veljko Vujčić. "Low Ionosphere under Influence of Strong Solar Radiation: Diagnostics and Modeling." Applied Sciences 11, no. 16 (August 4, 2021): 7194. http://dx.doi.org/10.3390/app11167194.

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Solar flares (SFs) and intense radiation can generate additional ionization in the Earth’s atmosphere and affect its structure. These types of solar radiation and activity create sudden ionospheric disturbances (SIDs), affect electronic equipment on the ground along with signals from space, and potentially induce various natural disasters. Focus of this work is on the study of SIDs induced by X-ray SFs using very low frequency (VLF) radio signals in order to predict the impact of SFs on Earth and analyze ionosphere plasmas and its parameters. All data are recorded by VLF BEL stations and the model computation is used to obtain the daytime atmosphere parameters induced by this extreme radiation. The obtained ionospheric parameters are compared with results of other authors. For the first time we analyzed physics of the D-region—during consecutive huge SFs which continuously perturbed this layer for a few hours—in detail. We have developed an empirical model of the D-region plasma density and gave a simple approximative formula for electron density.

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Havnes, O., H. Pinedo, C. La Hoz, A. Senior, T. W. Hartquist, M. T. Rietveld, and M. J. Kosch. "A comparison of overshoot modelling with observations of polar mesospheric summer echoes at radar frequencies of 56 and 224 MHz." Annales Geophysicae 33, no. 6 (June 16, 2015): 737–47. http://dx.doi.org/10.5194/angeo-33-737-2015.

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Abstract. We have compared radar observations of polar mesospheric summer echoes (PMSEs) modulated by artificial electron heating, at frequencies of 224 MHz (EISCAT VHF) and 56 MHz (MORRO). We have concentrated on 1 day of observation, lasting ~ 3.8 h. The MORRO radar, with its much wider beam, observes one or more PMSE layers all the time while the VHF radar observes PMSEs in 69% of the time. Statistically there is a clear difference between how the MORRO and the VHF radar backscatter reacts to the heater cycling (48 s heater on and 168 s heater off). While MORRO often reacts by having its backscatter level increased when the heater is switched on, as predicted by Scales and Chen (2008), the VHF radar nearly always sees the "normal" VHF overshoot behaviour with an initial rapid reduction of backscatter. However, in some heater cycles we do see a substantial recovery of the VHF backscatter after its initial reduction to levels several times above that just before the heater was switched on. For the MORRO radar a recovery during the heater-on phase is much more common. The reaction when the heater was switched off was a clear overshoot for nearly all VHF cases but less so for MORRO. A comparison of individual curves for the backscatter values as a function of time shows, at least for this particular day, that in high layers above ~ 85 km height, both radars see a reduction of the backscatter as the heater is switched on, with little recovery during the heater-on time. These variations are well described by present models. On the other hand, the backscatter in low layers at 81–82 km can be quite different, with modest or no reduction in backscatter as the heater is switched on, followed by a strong recovery for both radars to levels several times above that of the undisturbed PMSEs. This simultaneous, nearly identical behaviour at the two very different radar frequencies is not well described by present modelling.

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Barbero, R., J. T. Abatzoglou, N. K. Larkin, C. A. Kolden, and B. Stocks. "Climate change presents increased potential for very large fires in the contiguous United States." International Journal of Wildland Fire 24, no. 7 (2015): 892. http://dx.doi.org/10.1071/wf15083.

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Very large fires (VLFs) have important implications for communities, ecosystems, air quality and fire suppression expenditures. VLFs over the contiguous US have been strongly linked with meteorological and climatological variability. Building on prior modelling of VLFs (>5000 ha), an ensemble of 17 global climate models were statistically downscaled over the US for climate experiments covering the historic and mid-21st-century periods to estimate potential changes in VLF occurrence arising from anthropogenic climate change. Increased VLF potential was projected across most historically fire-prone regions, with the largest absolute increase in the intermountain West and Northern California. Complementary to modelled increases in VLF potential were changes in the seasonality of atmospheric conditions conducive to VLFs, including an earlier onset across the southern US and more symmetric seasonal extension in the northern regions. These projections provide insights into regional and seasonal distribution of VLF potential under a changing climate, and serve as a basis for future strategic and tactical fire management options.

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Basanov, B. V., N. B. Badmaev, A. V. Bazarov, and A. I. Kulikov. "Radiophysical methods for modelling frozen soils dielectric permittivity in the southern Vitim plateau (Eastern Siberia, Russia)." IOP Conference Series: Earth and Environmental Science 908, no. 1 (November 1, 2021): 012032. http://dx.doi.org/10.1088/1755-1315/908/1/012032.

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Abstract The article presents the results of applying the radiophysical method for modelling the dielectric permittivity on the example of Haplic Chernozem Molliglossic soils in the south of the Vitim plateau, depending on VHF and UHF wavelengths, temperature, and soil moisture. Depending on the heterogeneity of moisture reserves and heat content, the soil is considered as a three-layer medium with different soil characteristics. A difference in the frequency dispersion of the complex dielectric permittivity over the entire soil profile in the VHF and UHF ranges has been established.

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Journal articles on the topic 'Vnf modeling'

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