Determination of curve speed zones for mountainous freeways

Different vehicular speed limits may have an impact on the balance between safety and efficiency of travel on mountainous road corners associated with complex road conditions. Placing suitable speed limit warning signs does not merely effectively improve traffic safety but can also improve traffic efficiency. In this study, a global positioning system (GPS) terminal and Metrocount were used to collect vehicle speed data from more than 40 provincial-level curves in 8 provinces over the course of 1 year. Each road data collection time-period lasted approximately 8 hours. A descriptive statistics method was adopted by means of data screening and pretreatment. Additionally, both a velocity difference estimation model was established and a linear model of velocity differential estimation was constructed. Quantitative analysis was carried out on the safe speed, the driver’s expected speed, and the location of the speed limit warning signs. This demonstrated a positive correlation with the initial speed. When the difference in speed was greater than 15 km/h, a safety warning sign was required to limit the design speed to 80 km/h. A safety warning sign was also required when the corner radius was less than 300 m. The location of safety warning signs could be calculated based on the operating speed and taking driving safety and the visual range of drivers into consideration. The results can provide a theoretical reference for setting up appropriate safe speed limiting signs on road corners in mountainous areas

Electronic Structures of Fe3−xV_{3-x}V_x$Si Probed by Photoemission Spectroscopy

The electronic structures of the Heusler type compounds Fe$_{3-x}V$_x$Si in the concentration range between x = 0 and x = 1 have been probed by photoemission spectroscopy (PES). The observed shift of Si 2p core- level and the main valence band structres indicate a chemical potential shift to higher energy with increasing x. It is also clarified that the density of state at Fermi edge is owing to the collaboration of V 3d and Fe 3d derived states. Besides the decrease of the spectral intensity near Fermi edge with increasing x suggests the formation of pseudo gap at large x.Comment: 4 pages, 5 figures, 5 reference

Analysis and Criterion for Inherent Balance Capability in Modular Multilevel DC–AC–DC Converters

Modular multilevel dc-ac-dc converters (MMDAC) have emergedrecently for high step-ratio connectionsin medium voltage distribution systems.Extended phase-shiftmodulation has been proposed and was found to create the opportunity for inherent balance of SM capacitor voltages. This letter presents fundamentalanalysis leading toclear criterion for the inherent balancecapability in MMDAC. A sufficient and necessary condition,with associated assumptions,to guarantee this capability isestablished. Using the mathematics of circulant matrices, this condition is simplified to a co-prime criterion which gives rise to practical guidance for the design of an MMDAC. Experimentson down-scaled prototypesand simulations on full-scale examples both provide verification of the analysis and criterion for the inherent balance capability of MMDAC

Dispersion Relations for Thermally Excited Waves in Plasma Crystals

Thermally excited waves in a Plasma crystal were numerically simulated using a Box_Tree code. The code is a Barnes_Hut tree code proven effective in modeling systems composed of large numbers of particles. Interaction between individual particles was assumed to conform to a Yukawa potential. Particle charge, mass, density, Debye length and output data intervals are all adjustable parameters in the code. Employing a Fourier transform on the output data, dispersion relations for both longitudinal and transverse wave modes were determined. These were compared with the dispersion relations obtained from experiment as well as a theory based on a harmonic approximation to the potential. They were found to agree over a range of 0.9<k<5, where k is the shielding parameter, defined by the ratio between interparticle distance a and dust Debye length lD. This is an improvement over experimental data as current experiments can only verify the theory up to k = 1.5.Comment: 8 pages, Presented at COSPAR '0

Trapezoidal Current Modulation for Bidirectional High-Step-Ratio Modular DC–DC Converters

Modular dc-dc converter (MDCC) has been proposed for high step-ratio interconnection in dc grid applications. To further optimize the performance of MDCC, this paper presents a trapezoidal current modulation with bidirectional power flow ability. By giving all the sub-module (SM) capacitors an equal duty to withstand the stack dc voltage, their voltages are balanced without additional feedback control. Moreover, based on soft-switching performance and circulating current analysis, three-level and two-level operation modes featured with high efficiency conversion and large power transmission, respectively, are introduced. The control schemes of both modes are designed to minimize the conduction losses. Besides, the SM capacitor voltage ripples with different switching patterns are compared and the option for ripple minimization is presented. A full-scale case study is provided to introduce the design process and device selection of the MDCC. The experimental tests based on a downscaled prototype are finally presented to validate the theoretical analysis

IRS-Aided Uplink Security Enhancement via Energy-Harvesting Jammer

In this paper, we investigate the security enhancement by combining intelligent reflecting surface (IRS) and energy harvesting (EH) jammer for the uplink transmission. Specifically, we propose an IRS-aided secure scheme for the uplink transmission via an EH jammer, to fight against the malicious eavesdropper. The proposed scheme can be divided into an energy transfer (ET) phase and an information transmission (IT) phase. In the first phase, the friendly EH jammer harvests energy from the base station (BS) aided by IRS. We maximize the harvested energy of jammer by obtaining the closed-form solution to the phase-shift matrix of IRS. In the second phase, the user transmits confidential information to the BS while the jamming is generated to confuse the eavesdropper without affecting the legitimate transmission. The phase-shift matrix of IRS and time switching factor are jointly optimized to maximize the secrecy rate. To tackle the non-convex problem, we first decompose it into two sub-problems. The one of IRS can be approximated to convex with fixed time switching factor. Then, the time switching factor can be solved by Lagrange duality. Thus, the solution to the original problem can be obtained by alternately optimizing these two sub-problems. Simulation results show that the proposed Jammer-IRS assisted secure transmission scheme can significantly enhance the uplink security

Uplink Secure Communication via Intelligent Reflecting Surface and Energy-Harvesting Jammer

In this paper, we investigate the uplink secure communication by combining intelligent reflecting surface (IRS) and energy-harvesting (EH) jammer. Specifically, we propose an IRS-aided secure scheme for the uplink transmission via an EH jammer, to fight against the malicious eavesdropper. An energy transfer (ET) phase and an information transmission (IT) phase are proposed in this scheme. In the ET phase, we optimize the phase-shift matrix of IRS to maximize the harvested energy of jammer. In the IT phase, the phase-shift matrix of IRS and time switching factor are jointly optimized to maximize the secrecy rate. To tackle the non-convex problem, we first decompose it into two subproblems to solve by capitalizing on semi-definite relaxation (SDR) and Lagrange duality. Then, the solutions to the original problem can be obtained by alternately optimizing the two subproblems. Simulation results show that the proposed Jammer-IRS assisted secure transmission scheme can significantly enhance the uplink security