Silicon photomultipliers (SiPMs) are widely used in both high energy physics and medical physics due to their high gain, excellent timing resolution, low operating voltage and insensitivity to magnetic fields. This paper presents a system containing a 64 channel frontend electronics package integrated with a temperature compensation circuit and a light emitting diode (LED) driver circuit for gain stabilization and calibration. The system also has a field-programmable gate array (FPGA) programmed data acquisition system which can simultaneously read 8 frontend cards and provide a programmable high voltage (40-100 V) for the SiPMs. The system has been used in the electromagnetic calorimeter (ECAL) of the positron electron balloon spectrometer (PEBS), a collaboration between Switzerland, Germany, the USA and China with good results in a beam test at the European Organisation for Nuclear Research (CERN). The high-density, multi-channel SiPM readout system can adjust the detector operating voltage on each specific channel with a precision of up to 4 mV and the gain variance is less than 2% after adjustments. This system provides efficient utilization of SiPM in particle-track detectors and calorimeters.
Simulations of blood flows in the aorta area provide a better understanding of the hemodynamic blood flow mechanism for evaluating the risk of some cardiovascular diseases. An aorta model was reconstructed from magnetic resonance imaging (MRI) images while the blood flow and hemodynamic parameters in the ascending aorta, the descending aorta and the main peripheral arteries were measured using phase contrast MRI (PC-MRI). The boundary conditions affected the flow rate, wall shear stress, averaged wall shear stress and the oscillating shear index. The results show that simulations with zero pressure outlets, simulations with fitted input flows and zero pressure outlets, and simulations with fitted input flow and outflow discharges give quite different results. The input flow variations are mainly related to the local and average wall shear stresses and the oscillating shear index. The outlet flows are strongly related to the outlet boundary conditions.
Clinical implementation of magnetic induction hyperthermia (MIH) seeks to conformally killing tumor cells while protecting the normal tissue. Thus, the temperature distribution in the treatment area needs to be accurately simulated by the preoperative treatment planning systems (TPS) to help the surgeon make an appropriate clinical plan to ensure the safety and efficacy of the MIH therapy. Medical image open source toolkits, such as VTK and ITK, can give accurate 3-D reconstruction, visualization and segmentation of tumors and their surrounding tissue from 2-D CT images. Then, ferromagnetic thermoseeds are implanted into the tumor region. Electromagnetism and bio-heat transfer theories are used to predict the energy fields generated by the thermoseeds and the temperature distributions due to the heat diffusion in the MIH process. This conformal-hyperthermia method can be applied in magnetic induction hyperthermia treatment planning systems (MHTPS). The results show that the conformal-hyperthermia method in MHTPS can help surgeons intuitively segment tumors, accurately predict the temperature distributions in the treatment area, and make reasonable preoperative plans.
The ability of the urban canopy model (UCM) to predict meso-scale atmospheric dispersion of radioactive materials is evaluated based on the Fukushima accident using the weather research and forecasting (WRF) model coupled with the single-layer and multi-layer UCM. The deposition of the radioactive materials is compared with observations for the different UCM. The results show that the multi-layer model gives the best simulations of the wind fields. Near the source, the single-layer model gives the best predictions of the accumulated ground deposition of 137Cs, while in the area far from the source, the single-layer model performs the best for the daily deposition of 131I and the multi-layer model performs the best for the daily deposition of 137Cs.
Bench scale tests are often used to measure the thermal insulation of protective clothing. The thermal insulation is one of the main parameters controlling the clothing thermal comfort and protective performance. A bench-scale system is developed to measure the heat transfer within a multi-layer fabric using a cone calorimeter. A model is then developed to calculate the thermal insulation in hot environments. This paper presents measurements of the thermal insulation of the multi-layer fabric for low intensity thermal radiation of 1-10 kW/m2. The tests show that the total thermal insulation decreases with increasing heat flux as the local resistances of the outer shell layer, the moisture layer and the thermal barrier layer decrease, while that of the inner layer increases at first and then decreases. The influence of the thermal radiation reflectivity can be neglected for low intensity thermal radiation less than 10 kW/m2.
This paper presents a vehicle mass estimation method based on high-frequency information extraction to improve existing mass estimation methods that are susceptible to the influence of road slope with poor real-time performance. Accurate estimates are needed to accurately predict the driving force provided by the electrical drive systems. A high-pass filter is used to extract high-frequency longitudinal driving force and acceleration information. Then, a recursive least squares algorithm estimates the vehicle mass. Then, the road slope is estimated based on a combined kinematic and dynamic model. This method solves the problem that road slope estimates require an accurate vehicle dynamic model and are susceptible to acceleration sensor bias. The algorithm combines the dynamic method in a recursive least squares algorithm with a factor to neglect some previous information to estimate the road slope and a kinematic method that uses the relationship between the longitudinal vehicle acceleration and the acceleration sensor to calculate the road slope. Experimental tests show that this method is robust and can accurately estimate the vehicle mass and road slope in real-time.
For four-wheel-independent-drive electric vehicles, limited yaw moment can be generated by traction coordination and inaccurate torque control exists in the traditional electronic stability control system. A brake and traction force coordination control method is developed to alleviate this problem using model predictive control. The vehicle stability at the limiting conditions is improved by a cost function and a multi-input multi-output predictive control law. The quadratic programming method is used to solve the receding horizon problem. Simulations show that the system achieves quicker yaw response than the normal feedback control method, so the vehicle lateral stability is improved.
The vehicle initial acceleration process significantly influences the drivability and service life of dry dual clutch transmissions (DCT). Road conditions and driver intentions during the initial acceleration vary greatly, so flexible control strategies are needed to optimize transmission performance. The control strategies presented in this paper use the vehicle speed, equivalent slope, adhesion coefficient and driver intention with vehicle dynamic theory. The driver intention is recognized by a fuzzy logic model to give adaptive initial acceleration control strategies. The strategies decide the startup gear by considering the vehicle speed and adhesion coefficient and optimize the dual clutch control for the equivalent slope and driver intention. Finally, the recognition method and adaptive initial acceleration control strategies are evaluated to show that the vehicle can chose the best way to start for various road conditions and driver intentions that effectively improves the DCT startup performance.
Conventional automotive generators do not provide voltage regulation or intelligent control in real time. This paper analyzes intelligent control and multiple working modes for generators. The control system integrates the battery energy and vehicle state to improve generator voltage control in traditional fueled vehicles with reformation. Bench tests and tests on sample vehicles verify the system effectiveness for real-time online adjustments of the generator output voltage and braking energy recovery. The test results show that this intelligent control strategy reduces fuel consumption by 3.7%.
A device is developed to measure the friction torque of rolling bearings subjected to radial loads while running at steady speeds. The friction torques are measured at various speeds and radial loads for typical rolling bearings used in an engine front end accessory belt drive of a passenger vehicle. The least squares method is used to fit the friction torque and the rotational speed with the optimal function chosen according to the correlation coefficient and significance level. A set of empirical formulae are then derived for the friction torque in terms of both the rotational speed and the radial load. The expressions are more accurate than the Palmgren formula. The test method can be applied to measure the friction torque of rolling bearings used in other fields as a valuable method to characterize the torque characteristics.
Existing crash test dummies are commonly designed to work in a specific loading direction. Without validation of their responses in other directions, say with oblique forces, the use of such dummies to evaluate injury risks of occupants in complex loading conditions is questionable. This paper describes a conceptual dummy thorax structure which can function in pure frontal, pure lateral and oblique 60˚ loading directions by properly positioning spring-damper modules inside the thorax structure. The dynamic behavior of the thorax to these three different directions is simulated using lumped-mass spring damper models and by building a simplified two-dimensional finite element dummy chest model that couples all three directions. The results show that the dummy thorax model can work in multiple loading directions. The validated mathematical model is reliable, with potential to be used in thorax injury studies for multiple/complex crash loading conditions, including oblique impact.
Driver drowsiness estimates can be realized by analyses of the drivers' eye movements based on a machine vision system. However, the system requires accurate eye region recognition in the driver's facial image. Random, rapid changes of the head posture complicate locating the eye region in real driving scenarios. The active shape model (ASM) can be used to coarsely locate the eye region. This study uses a local ASM model to enhance the head posture adaptability of the ASM algorithm. Then, the average of synthetic exact filters (ASEF) algorithm and the ASM are combined to improve the eye region location precision. A single eye ASEF and a double eyes ASEF are integrated to more robustly identify the iris center location. Tests show that the algorithm has strong head posture adaptability and can robustly and accurately identify the eye region location.
Data reconciliation method is used to improve sensor fault detection, identification and data rebuilding for a high pressure feedwater heater and extraction steam pipe system in a 1 000 MW coal-ired power generation unit. The dominant factor modeling method is used to build the characteristic constraint relationships between the parameters. A case study shows that this method can efficiently detect, identify and rebuild data after sensor faults with an average relative error in the rebuilt data of 2.42%.
The film cooling effectiveness distributions on the leading edge and the pressure side of a turbine vane are tested using pressure sensitive paint (PSP) for various blowing ratios and density ratios. A uniform effectiveness distribution is obtained along the leading edge by proper arrangement of the film cooling holes. The film cooling flow distribution on the pressure side from the leading edge injections is related to the blowing ratios with higher blowing ratios given wider coverage. The coolant injections on the pressure side are supplied independently for each row of holes to conveniently and accurately control the local flow parameters. This paper presents the film cooling efficiencies for each injection row for different blowing ratios and density ratios. The film cooling performance on the pressure side is most strongly related to the blowing ratio since the injected coolant remains in good contact with the wall with this hole shape arrangement. When the coolant is injected through all the holes together, the film cooling effectiveness downstream can be predicted using Shettle superposition.
The influence of the superficial gas velocity on the residence time distributions (RTDs) of large spherical objects of different densities in the dense phase of a fluidized bed was studied using electrical capacitance tomography (ECT) tracing technique. The regularity and randomness of the motion of a large object were decided by a probabilistic statistical analysis to investigate the mechanical characteristics of an object in a bed. The results show that decreasing the fluidization velocity first slowly reduces the residence time. When the gas velocity is lower than a critical value, the residence time sharply increases until the object does not reach the low side of the air distributor. Heavier objects have higher critical gas velocities. The RTD curves are very broad due to the stochastic pressure and velocity pulsations in the fluidization bed.
Current heat transfer coefficient formulae for particles are derived from data for spheres. However, a real particle is not a sphere, but an irregular body, so the assumption that the real particle approximates a sphere is questionable in mathematical models. Fractal models, which give shapes similar to real particles, are produced by the random walk method to calculate the heat transfer coefficient of a factual particle in a low Reynolds number flow using kinetic theory and gas diffusion theory. The particle diameter is less than 5 μm. Simulations show that the spherical assumption is not suitable for the fractal particle with a maximum error of 82%. Nu is then greatly influenced by the specific area and fractal dimension.
Machine vision systems are used to analyze bottled liquid medicines. The systems detect light reflected from impurity particles in the liquid with the detection ability directly affecting the system impurity detection rate. The system is optimized here to improve the system liquid detection rate. The regularity of the optical field distribution is obtained using the light integral method and the refraction law. Then, the light distribution is decomposed into a superposition of two basic fields with the distribution optimized using the mean square error of the superposition matrix of the matrixes for the two fields. Tests show that this optimization method effectively optimizes the light distribution and improves the impurity detection rate by 26%.
When antennae are blocked by buildings or the signals are drowned by strong noise, global navigation satellite system (GNSS) receivers require both long coherent integration times and a large number of non-coherent integration operations to acquire the signal. However, navigation data bit transition during the long coherent integration results in integrator signal energy attenuation and non-coherent integration will have squared losses that limit the ability to acquire weak signals. A signal acquisition algorithm is given here based on non-coherent integration that estimates the optimal combination of navigation data bits with the maximum energy criterion to eliminate the length limit and improve the ability to acquire weak signals. Tests demonstrate that these techniques greatly increase the gain such that low signal to noise ratio (SNR) signals as low as 20 dBHz can be successfully acquired.
This article describes the trajectory planning for redundant robots for spraying the inner surface of a curved pipe. The complex inner surface constraints and the redundant robot kinematics are modeled with the inverse kinematics solved to plan the redundant robot trajectories for inner surface spraying which can apply to all types of pipes. Simulations give collision-free spraying trajectories for various conditions. Spraying tests show that the redundant robots complete the collision-free spraying operations. The coating thickness and uniformity both satisfy the requirements.
The flow and temperature distributions in a brush seal are predicted using a three-dimensional computational fluid dynamics (CFD) model with software ANSYS. The results show the effect of the number of bristles rows on the leakage and the flow and temperature distributions in the brush seal (14 rows, 0.93 mm thick). The results relate the characteristics of the flow and temperature distributions around the bristles to the clearances between bristles and the influence of various operating parameters (pressure differential, interference, linear speed) on the maximum temperature. Results show that as the bristle row number increases, the leakage first decreases exponentially, then decreases linearly and slowly, and tends to a stable value in the end. The effects of interference and linear speed on the maximum temperature are more obvious.
The gyroscope chip is the key component of micro electro mechanical system (MEMS) gyroscopes. The multi-frequency signal excitation method is used to improve the efficiency of dynamic characteristic tests of such chips. The dynamic characteristics of the linear vibration MEMS gyroscope are analyzed using electrostatic excitation and capacitive detection. A multi-frequency signal with an equivalent amplitude and a linear initial phase difference distribution is constructed to fit the maximum amplitude limit of the exciting signal. This method takes only 1.5 s to finish one modal test with 601 frequency points and 1 Hz frequency resolution around the 3 000 Hz resonance frequency. The multi-frequency method acquires almost the same amplitude-frequency and phase-frequency curves as the traditional sine wave sweep excitation method and their repeatabilities for the resonance frequency and corresponding amplitude and phase are similar. Although the testing accuracy of the multi-frequency method is a little lower than that of the sine wave sweep method, the multi-frequency method can be used to test large numbers of gyroscope chips for filtering and pairing.
The dynamic behavior of the support directly affects the dynamic behavior of a machine tool. Thus, the support joint parameters are needed for accurate dynamic models of machine tools. This paper presents a method to identify the equivalent stiffness and damping of support joints. A 3-D stiffness-damping model is used to replace the support joint of the machine tool bed in the dynamic model. The support joint parameters are identified by modal testing which shows the natural frequencies and the damping ratios of several vibration mode shapes of the machine tool bed. However, the method is unable to identify the joint parameters for all support states. To solve this problem, this model first identifies the joint parameters for a bed with a uniform mass in the symmetrical support state, and then repeats the modal testing as the normal force on the support joint is changed to relate the joint parameters to the normal force to identify the joint parameters for any support state. The results show that the stiffness and damping both increase with increasing normal force on the support joint. Finite element method (FEM) simulations are used to verify the parameters identification results with the FEM model for the support joint parameters consistent with the experimental results.
Feed-rate planning models must be accurate to improve contouring performance and efficiency. Quadrant protrusion errors caused by friction forces are an important source of contour error in high-speed contouring of complex curves. A theoretical analysis is given here to describe the relationships among the curvature, feed rate and quadrant protrusion error. Then, experiments with a wide range of parameters are used to develop a friction error model for feed-rate planning with the friction error as a constraint. Tests show that the model can accurately estimate the friction error and guarantee the contour accuracy requirements.
The influence factor of the creep rupture properties of the materials in dissimilar material joints was studied using a transition layer and weld built with the same welding parameters as for real structures with the same base and weld materials. Creep rupture tests were conducted on welded joints at different temperatures and stresses. Most fractures appeared at the fusion zones between the transition layers. Metallographic observations, micro hardness tests, chemical composition analyses and scanning electron microscope (SEM) observations show a softened layer at the fusion zone of the transition layer which causes strain concentrations and easier fracture. The large Cr gradient between the transition layers leads to carbon migration and hardness reductions that eventually result in a softened layer. In addition, the crystallization orientation between the fusion zone and other areas in the transition layer is found to differ, which will also reduce the creep rupture strength. Thus, the creep rupture properties of dissimilar joints can be improved by optimizing the weld composition and the welding process.
Methane-air turbulent premixed planar jet flames are simulated using direct numerical simulations. A fluctuating velocity field at the jet inflow boundary is generated based on a prescribed turbulent energy spectrum. The peak wavenumber in the energy spectrum is determined from the turbulent integral length scale and turbulent kinetic energy at the jet inlet. The model also gives the instantaneous distributions of the gas temperature, species concentrations, and vorticity. The results show that coherent structures in the shear layer gradually appear as the eddy sizes increase. The chemical reactions are affected by the turbulence and the instantaneous reaction surface is quite wrinkled with its area increase. The turbulent kinetic energy gradually decreases, while the root mean squares of the temperature and methane concentration fluctuations increase along the jet centerline.