As playing a key role in high-speed railway, CTCS-3 (Chinese Train Control System - Level 3) is a typical safety-critical system. Effective testing is an important mean to improve security of ...safety-critical system. A set of test case generation method for CTCS-3 based on Colored Petri net is proposed in this paper. According to CTCS-3 technical specification, corresponding models are established, then state space of the models are generated and path to goal state is queried. The test case is generated based on the path to target state. By comparing the test case generated by Colored Petri net and the existing test case, the correctness of test case generation method based on Colored Petri net is verified, which avoids the possible ambiguity in the natural language description of traditional test case.
In situ thermal transport measurement of flowing fluid could be useful for the characterization and diagnosis of practical thermal systems such as fluid heat exchangers and thermal energy storage ...systems. Despite abundant reports on the ex-situ thermal conductivity measurement of stagnant fluids, a suitable technique for the thermal conductivity measurement of flowing fluid has been rarely reported. This paper presents the thermal conductivity measurement of flowing fluid within a pipe using a non-contact modulated photothermal radiometry (MPR) technique, where the surface of the pipe is heated by an intensity-modulated laser and the heat diffuses into the fluid with suitable modulation frequency. We design a tube section with small wall thickness suitable for the MPR measurements to maximize the sensitivity of the thermal response to the fluid properties while minimizing the lateral heat spreading effect. Intrinsic thermal conductivity of different fluids was obtained within a proper range of frequency and flow velocity where the forced convection effect is negligible. The forced convection effect became prominent at high flowing velocity and at low modulation frequency, leading to overestimated thermal conductivity of fluid. It is found that the intrinsic thermal conductivity could be obtained when the flow velocity is less than 100 mm/sec and ReD1/2Pr1/3 < 100 for DI water and Xceltherm oil under the specified experimental conditions, where Re_D is the Reynolds number and Pr is the Prandtl number.
Due to flexibility, low cost and rapid deployment, wireless sensor networks (WSNs)have been drawing more and more interest from governments, researchers, application developers, and manufacturers in ...recent years. Nowadays, we are in the age of industry 4.0, in which the traditional industrial control systems will be connected with each other and provide intelligent manufacturing. Therefore, WSNs can play an extremely crucial role to monitor the environment and condition parameters for smart factories. Nevertheless, the introduction of the WSNs reveals the weakness, especially for industrial applications. Through the vulnerability of IWSNs, the latent attackers were likely to invade the information system. Risk evaluation is an overwhelmingly efficient method to reduce the risk of information system in order to an acceptable level. This paper aim to study the security issues about IWSNs as well as put forward a practical solution to evaluate the risk of IWSNs, which can guide us to make risk evaluation process and improve the security of IWSNs through appropriate countermeasures.
Molten salts are being used or explored for thermal energy storage and conversion systems in concentrating solar power and nuclear power plants. Thermal conductivity of molten salts is an important ...thermophysical property dictating the performance and cost of these systems, but its accurate measurement has been challenging, as evidenced by wide scattering of existing data in literature. The corrosive and conducting nature of these fluids also leads to time consuming sample preparation processes of many contact-based measurements. Here, we report the measurement of thermal conductivity of molten salts using a modulated photothermal radiometry (MPR) technique, which is a laser-based, non-contact, frequency-domain method adopted for molten salts for the first time. By unitizing the advantages of front side sensing of frequency-domain measurements and the vertical holder orientation, the technique can minimize the natural convection and salt creeping effects, thus yielding accurate molten salt thermal conductivity. The MPR technique is first calibrated using standard molten materials including paraffin wax and sulfur. It is then applied on measuring pure nitrate salts (\(NaNO_3\) and \(KNO_3\)), solar salt (\(NaNO_3-KNO_3\) mixture), and chloride salt (\(NaCl-KCl-MgCl_2\)). The measurement results are compared with data from literature, especially those obtained from laser flash analysis (LFA). Our results demonstrate that the MPR is a convenient and reliable technique of measuring thermal conductivity of molten salts. Accurate thermal conductivity data of molten salts will be valuable in developing the next-generation high-temperature thermal energy storage and conversion systems.
Particle beds are widely used in various systems and processes, such as particle heat exchangers, granular flow reactors, and additive manufacturing. Accurate modeling of thermal conductivity of ...particle beds and understanding of their heat transfer mechanisms are important. However, previous models were based on a simple cubic packing of particles which could not accurately represent the actual heat transfer processes under certain conditions. Here, we examine the effect of the packing structure on thermal conductivity of particle beds. We use monodispersed silica microspheres with average article sizes ranging from 23 to 330 um as a model material. We employ a transient hot-wire technique to measure the thermal conductivity of the particle beds with packing density of 43 to 57% within a temperature range of room temperature to 500 deg. C and under N2 gaseous pressures of 20 to 760 Torr. We then use a discrete element method (DEM) to obtain the realistic packing structure of the particles, which is then fed into a finite-element model (FEM) to calculate the thermal conductivity, with the consideration of solid conduction, gas conduction, and radiation heat transfer. Our results show that the thermal conductivity model based on the more realistic random packing structure derived from the DEM shows better agreement with the experimental data compared to that based on the simple cubic packing structure. The combined DEM and FEM methodology can serve as a useful tool to predict effective thermal conductivity of particle beds and to quantify different heat transfer mechanisms under various conditions.
This paper compares the long-channel and short-channel 3300-V, 5-A silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) manufactured by GeneSiC regarding static ...characteristics and short-circuit (SC) sustaining capability. Their saturation currents were measured up to 2200-V drain bias at different gate voltages. The SC withstand times of two types of devices were measured at 2200-V drain voltage and 1S-V gate voltage. Their SC test results were compared with 1200-V SiC MOSFETs from four different manufactures, which suggested that SiC MOSFETs with longer channel length should have longer sustaining times in a SC event. In addition, the device dynamic characteristic was evaluated. A comprehensive simulation program with integrated circuit emphasis (SPICE) model was developed based on the device test results.
In oilfield distribution networks, the presence of inappropriate transformer capacity and excessively high current density in certain lines may lead to excessive distribution of reactive power in ...distribution networks; low operating power factor, increased network losses, degraded voltage quality, and Grid capacity cannot be fully utilized. In view of the above issues, based on the power flow calculation of distribution network, the maximum annual net profit of the distribution network is used as the objective function, and the voltage and capacitor capacity are the constraints to establish a mathematical model for reactive power compensation optimization. The sensitivity analysis method is used to determine the compensation. Compensate the position, determine the compensation capacity with the criterion of the optimal network loss and increase the rate, thus carry on the simple reactive power compensation. Improve equipment utilization and grid operation power factor and reduce network loss. The computation of the IEEE30-bus system verifies that the proposed reactive power optimization model and algorithm are correct and effective.
A systematic study was performed to measure the effective thermal conductivity of ceramic particle beds, a promising heat transfer and thermal energy storage media for concentrating solar power ...(CSP). The thermal conductivity of the ceramic particle beds was measured using a transient hot-wire (THW) method within a temperature range of room temperature to 700 oC, the target operating temperature of the next-generation CSP systems. Two different types of ceramic particles were examined: (1) CARBOBEAD HSP 40/70 and (2) CARBOBEAD CP 40/100 with the average particle sizes of ~ 400 {\mu}m and ~280 {\mu}m, respectively, and thermal conductivities ranging from ~0.25 W m-1 K-1 to ~0.50 W m-1 K-1 from 20 oC to 700 oC in both air and N2 gas. The gaseous pressure dependence of the thermal conductivity of the ceramic particle beds was also studied in the N2 environment to differentiate the contributions from gas conduction, solid conduction, and radiation. Calculations using the Zehner, Bauer, and Schl\"under (ZBS) model showed good agreements with the measurements. Based on the model, it is concluded that the effective thermal conductivity of the packed particle beds is dominated by the gas conduction while the solid conduction and radiation contributes to about 20% of the effective thermal conductivity at high temperature.
Accurate determination of heat transfer coefficients for flowing packed particle beds is essential to the design of particle heat exchangers and other thermal and thermochemical processes. The ...discrete nature of granular materials alters the thermal transport processes in both the near-wall and bulk regions of flowing particle beds from their stationary counterparts. Heat transfer correlations based on the stationary particle bed thermal conductivity could be inadequate for flowing particles in a heat exchanger. Thermophysical properties of the continuum were often obtained from measurements on stationary beds owing to the difficulty of flowing bed measurements. In this work, we found that the properties of a stationary bed are highly sensitive to the method of particle packing and there is a decrease in the particle bed thermal conductivity and increase in the near-wall thermal resistance, as measured by an air gap thickness, on the onset of particle flow. These variations in the thermophysical properties of stationary vs. flowing particle beds can lead to large errors in heat transfer coefficient calculations. Therefore, we modelled heat transfer coefficients for granular flows using the experimentally determined flowing particle bed thermal conductivity and near-wall air gap for ceramic particles - CARBO CP 40/100 (mean diameter=275 um), HSP 40/70 (404 um) and HSP 16/30 (956 um); at velocities of 5-15 mms-1; and temperatures of 300-650 oC. These calculations, which show good agreement with experiments in literature, can be used as a guide for heat exchanger designs.
In this paper, we present a computer vision-based system that is capable of automatically analyzing presentation videos and evaluating it according to the learned user's preference. In this system, ...different visual features indicating the effectiveness of the presentation are extracted. They include the speaker's global movement, face/head orientation distribution and motions caused by the use of hands. Given a set of user scored presentation videos, we adapt the RankBoost algorithm to learn the user's scoring preference so that the system can score a new presentation video in the future to provide the user feedback. The experiment results show that the vision processing part can reliably extract the low level features and the ranking learning part can successfully learn user's different scoring preferences and achieve an average ranking error within one level or less.
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