Publications
497 results found
Zhong WX, Ho WC, Liu X, et al., 2010, Self-driven AC-DC synchronous rectifier for power applications - A direct energy-efficient replacement for traditional diode rectifier, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 994-1001
Synchronous rectification has previously been adopted in switched mode circuits for reducing the conduction losses particularly in low-voltage and high-current applications. This paper presents a generalized "self-driven" AC-DC synchronous rectification technique that can be used to develop AC-DC synchronous rectifier that behaves like a diode bridge, but with much reduced conduction losses and without control integrated circuits. This generalized concept can be extended from single-phase to multi-phase systems. Experiments based on 1kW and 2kW single-phase systems have been successfully conducted for capacitive, inductive and resistive loads. Very significant power loss reduction (over 50%) has been achieved in the rectification stage at both 110V and 220V AC mains operations. This patent-pending circuit can be regarded as a direct replacement of general-purpose diode rectifier. Due to the reduction of power loss, further reduction in the size and cost of the heatsink or thermal management for the power circuit becomes possible. ©2010 IEEE.
Hui SYR, Li SN, Tao XH, et al., 2010, A novel passive off-line light-emitting diode (LED) driver with long lifetime, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 594-600
This paper describes a patent-pending passive offline LED driver that has no semiconductor switches, electrolytic capacitors, auxiliary power supply and control board. It can provide a fairly smooth current from the ac mains to drive LED strings. The new circuit has the advantages of high input power factor, high energy efficiency and luminous efficacy, long lifetime, stable luminous output and high robustness against extreme weather conditions. In addition, over 90% of the driver material is recyclable, leading to reduction of electronic waste. It is particularly suitable public LED lighting systems such as road lighting systems. Experimental results based on a 50W system are included in the paper to confirm the validity of the proposal. Due to the circuit simplicity, an energy efficiency exceeding 93.6% has been achieved. ©2010 IEEE.
Hui SYR, Lin DY, Ng WM, et al., 2010, A "class-A2" ultra-low-loss magnetic ballast for T5 fluorescent lamps, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 1346-1351
This paper shows that magnetic ballasts for high-voltage T5 lamps are not only feasible but their luminous and ballast-loss performance can be better than those of electronic ballasts. A computer-aided design and practical implementation of an ultra-low-loss magnetic ballast system for T5 28W lamps is presented. The high-voltage & low-current features of T5 lamps imply that the copper and core losses of the magnetic ballast can be greatly reduced. Its total system power is 30W (with a ballast loss of only 2.42W) is less than the 32W upper limit specified for Class A2 of energy-efficient electronic ballast for T5 28W lamps. High luminous efficacy of 74.8 lumen/W can be achieved. This important breakthrough has the potential of reversing the existing trend of using electronic ballasts as the energy-saving technology in lighting industry. With a better luminous efficacy, lower product and maintenance costs, much longer lifetime and the use of recyclable metallic materials over its electronic counterparts, this patent-pending proposal provides a truly sustainable lighting solution to the lighting industry. ©2010 IEEE.
Choi WP, Ho WC, Liu X, et al., 2010, Bidirectional communication techniques for wireless battery charging systems & portable consumer electronics, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 2251-2257
Simultaneous power and signal transfer in a wireless/contactless system is an emerging technology for portable electronics. This paper aims at exploring simple and cost effective ways for such applications for a wide range of the portable consumer electronic devices such as mobile phones. Frequency-shift keying (FSK) and amplitude-shift keying (ASK) techniques for an inductive battery charging platform have been successfully implemented for simultaneous power and signal transfer in an 10W wireless charging system. The proposed techniques provide effective bidirectional communication between the charging platform and the loads and form the basis for load identification and battery monitoring in wireless charging system. Considerations of these methods for compatibility among a wide range of portable products are discussed. ©2010 IEEE.
Lee CK, Hui SYR, 2010, Experimental comparison of traditional and alternating winding method for planar spiral inductor, Electronics Letters, Vol: 46, Pages: 238-239, ISSN: 0013-5194
Two planar winding structures have been built to compare the characteristics of traditional and alternating winding methods. The alternating winding method reduces the potential difference of adjacent conductors, thus reducing substantially the self-capacitance in the winding. Measurements confirmed that the two inductors have similar equivalent inductance and low-frequency series resistance. However, the alternating winding method has a higher self resonant frequency. It is also evident that the reduction of self-capacitance in the winding not only increased the operating bandwidth of the device but also reduced the power losses of the inductor at high frequency. © 2010 The Institution of Engineering and Technology.
Tao X, Hui SYR, 2010, A general photo-electro-thermo-temporal theory for light-emitting diode (LED) systems, 2010 IEEE Energy Conversion Congress and Exposition, ECCE 2010 - Proceedings, Pages: 184-191
This paper presents a dynamic photo-electro-thermal theory for LED systems. In addition to photometric, electrical and thermal aspects, this theory incorporates the time domain into the generalized equations. A dynamic model for a general LED system is developed for system analysis. This theory highlights the fact that the luminous output of an LED system will decrease with time from the initial operation to the steady-state due to the rising temperature of the heatsink and the LED devices. The essential thermal time constants involved in the LED systems are explained. The time factor is critical in understanding how much the luminous output will decrease with time and is essential to the optimal designs of LED systems that are operated continuously (e.g general lighting) or momentarily (e.g. traffic lights). Experiments on several LED systems at different time frames have been conducted and the practical measurements confirm the validity of this theory. © 2010 IEEE.
Choi WP, Ho WC, Liu X, et al., 2010, Comparative Study on Power Conversion Methods for Wireless Battery Charging Platform, PROCEEDINGS OF 14TH INTERNATIONAL POWER ELECTRONICS AND MOTION CONTROL CONFERENCE (EPE-PEMC 2010)
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- Citations: 11
Tao XH, Li SN, Hui SYR, 2010, Estimation of Internal Junction Temperature & Thermal Resistance of Light-Emitting Diodes Using External Luminous Flux Measurements, 2010 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION, Pages: 179-183, ISSN: 2329-3721
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- Citations: 2
Zhong WX, Liu X, Hui SYR, 2010, Analysis on a Single-Layer Winding Array Structure for Contactless Battery Charging Systems with Free-positioning and Localized Charging Features, 2010 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION, Pages: 658-665, ISSN: 2329-3721
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- Citations: 11
Chen W, Li SN, Hui SYR, 2010, A Comparative Study on the Circuit Topologies for Offline Passive Light-Emitting Diode (LED) Drivers with Long Lifetime & High Efficiency, 2010 IEEE ENERGY CONVERSION CONGRESS AND EXPOSITION, Pages: 724-730, ISSN: 2329-3721
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- Citations: 36
Lee CK, Su YP, Hui SYR, 2009, Multilayer stacked coreless printed spiral winding inductor with wide frequency bandwidth, 2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009, Pages: 1002-1009
In this paper, three types of winding methods for the multi-layer stacked coreless printed spiral winding inductors are studied and evaluated for megahertz operation. They are traditional winding, alternating winding and partial alternating winding. The winding parasitic capacitances of different windings structures are estimated by distributed capacitance models. The electric field energy distributions in the inductors are derived from the voltage profiles to illustrate the relative magnitudes of winding parasitic capacitances. Calculated results show that partial alternating winding has a wide frequency bandwidth with reduced number of through-hole via. All calculated parameters are confirmed with measurements. The results provide useful information for the optimal design of coreless spiral or core-based planar inductors. © 2009 IEEE.
Lee LM, Hui SY, 2009, Automatic lamp detection and operation for warm-start tubular fluorescent lamps, IEEE Transactions on Power Electronics, Vol: 24, Pages: 2933-2941, ISSN: 0885-8993
The availability of T5 high-efficiency (HE) and T5 high-output (HO) fluorescent lamp families not only increases the number of commonly used tubular fluorescent lamps from 9 to 18, but more importantly, increases the chance of ballastlamp mismatch because T5 HO and T5 HE lamps have similar physical outlooks and dimensions but vastly different lamp characteristics. The large number of lamp types increases the number of specific ballast designs and users have the new inconvenience of ensuring the correct matching of the lamps and ballasts. In this paper, a survey and analysis of lamp characteristics of all commonly used T5, T8, and T12 tubular fluorescent lamps is presented. Based on the heated lamp electrodes, lamp voltage, and lamp current, a classification system that maps the lamp characteristics into various groups for automatic lamp detection is proposed. The successful implementation of this method is explained and demonstrated. © 2006 IEEE.
Yan W, Hui SYR, Chung HSH, 2009, Energy saving of large-scale high-intensity-discharge lamp lighting networks using a central reactive power control system, IEEE Transactions on Industrial Electronics, Vol: 56, Pages: 3069-3078, ISSN: 0278-0046
This paper summarizes the test results on several large-scale lighting systems based on a range of high-intensity-discharge (HID) lamps. The study focuses on the energy-saving, energy-efficiency, and dimming characteristics of magnetic-ballast-driven HID lamp systems that are suitable for public lighting networks. A central energy-saving unit that can change the input mains voltage of 220 V to a variable voltage within the range from 220 to 170 V is used to control a large lighting network. This central dimming unit offers a new freedom for users to use lighting energy when and where it is needed and to an appropriate power level. Lamp characteristics under full and reduced voltage operation for six types of HID lamps have been measured. Six large-scaled networks of ballast-lamp sets have been set up and dimmed with a central energy-saving unit with a rated power of 13.2 kVA per phase. The full load current under test was set at about 40 A per phase. The loss of the energy-saving unit on a per-lamp-set basis was measured at different voltage levels. It is found that the energy-saving unit can reduce overall system power at least 40% without causing lamp flickering. Through the controllable voltage range, there is no obvious change in color temperature. The lamp power and light output decrease almost linearly with input voltage within the range from 170 to 220 V, and the power loss of the energy-saving unit is less than 2.4% of the full power in all tests. For these large-scaled lighting networks, it is envisaged that 25%-35% of energy saving can be achieved in large public lighting applications. © 2009 IEEE.
Hui SYR, Qin YX, 2009, A General Photo-Electro-Thermal Theory for Light Emitting Diode (LED) Systems, IEEE Transactions on Power Electronics, Vol: 24, Pages: 1967-1976
Qin YX, Lin DY, Hui SYR, 2009, A simple method for comparative study on the thermal performance of light emitting diodes (LED) and fluorescent lamps, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 152-158
A simple method is proposed to measure the heat dissipation of LEDs and fluorescent lamps in an open system which allows light energy to escape. Based on this method, a comparative study on the thermal and luminous performance of high-brightness LEDs and fluorescent lamps is presented. At rated power, T5 & T8 fluorescent lamps generate about 73%-77% of their total power as heat, whilst three types of highbrightness LEDs dissipate about 87% to 90% of input power as heat. Heat dissipation is an important factor particularly for airconditioned buildings when overall energy efficiency is considered. T5 fluorescent lamps perform better than some existing LEDs in terms of luminous efficacy and heat generation in this study. © 2009 IEEE.
Hui SYR, Qin YX, 2009, A general photo-electro-thermal theory for light emitting diode (LED) systems, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 554-562
The photometric, electrical and thermal features of LED systems are highly dependent on one another. By considering all these factors together, it is possible to optimize the design of LED systems. This paper presents a general theory that links the photometric, electrical and thermal behaviors of a LED system together. The theory shows that the thermal design is an indispensible part of the electrical circuit design and will strongly influence the peak luminous output of LED systems. It can be used to explain why the optimal operating power, at which maximum luminous flux is generated, may not occur at the rated power of the LEDs. This theory can be used to determine the optimal operating point for a LED system so that the maximum luminous flux can be achieved for a given thermal design. The general theory has been verified favorably by experiments using high-brightness LEDs. ©2009 IEEE.
Lee LM, Hui SYR, 2009, Automatic lamp detection and operation for warm-start tubular fluorescent lamps, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 1518-1525
The availability of T5 high-efficiency (HE) and high-output (HO) fluorescent lamp families not only increases the number of commonly used tubular fluorescent lamps from 9 to 18, but more importantly, increases the chance of ballast-lamp mismatch because T5(HO) and T5(HE) lamps have similar physical outlooks and dimensions but vastly different lamp characteristics. The large number of lamp types increases the number of specific ballast designs and users have the new inconvenience of ensuring the correct matching of the lamps and ballasts. In this paper, a survey and analysis of lamp characteristics of all commonly used T5, T8 and T12 tubular fluorescent lamps is presented. Based on the heated lamp electrodes, lamp voltage and lamp current, a classification system that maps the lamp characteristics into various groups for automatic lamp detection is proposed. The successful implementation of this method is explained and demonstrated. ©2009 IEEE.
Su YP, Liu X, Hui SYR, 2009, Mutual Inductance Calculation of Movable Planar Coils on Parallel Surfaces, IEEE Transactions on Power Electronics, Vol: 24, Pages: 1115-1123
Tam PW, Chung HSH, Hui SY, 2009, Iterative behavioral modeling of charge-pump-based electronic ballast-fluorescent lamp system, IEEE Transactions on Power Electronics, Vol: 24, Pages: 278-287, ISSN: 0885-8993
A new behavioral model for analyzing the current-source charge-pump-based ballast with a self-oscillatory gate drive circuit is proposed in this paper. A detailed model derivation is presented and the model is applied to analyze a ballast system of a 16-W compact fluorescent lamp (CFL) as an illustration. The ballast of the CFL consists of a self-oscillatory driven inverter stage and charge pump circuitry. The iterative modeling technique links together the three mutual dependent parts of the system, namely: 1) the charge pump circuit; 2) the self-oscillatory gate drive; and 3) the lamp model, so that they can be designed and studied as an integrated system. It is shown that the model can give a comprehensive interpretation of the whole system and provide a reasonable prediction of the ballast behavior. © 2009 IEEE.
Lin D, Yan W, Zissis G, et al., 2009, A simple physical low pressure discharge lamp model, 2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009, Pages: 2051-2058
A simple physical low pressure discharge lamp model has been proposed in this paper. The new model is based on the physical processes inside a fluorescent lamp by considering the increasing rate of electron density and the ambipolar diffusion process. The model can accurately predict not only the lamp electrical terminal characteristics but also the electron density and electron temperature inside the fluorescent lamp. The results are comparable with the predictions from the complicated plasma models. The simple lamp model can accurately predict the lamp characteristics at both high and low operating frequencies, and the voltage spikes caused by arc re-ignition at each half cycle when the lamp is operated at mains frequency. This model can be easily implemented into MATLAB/Simulink as a simple, accurate and user-friendly CAD tool. © 2009 IEEE.
Qin YX, Lin DY, Chung HSH, et al., 2009, Dynamic control of a light-emitting diode system based on the general photo-electro-thermal theory, 2009 IEEE Energy Conversion Congress and Exposition, ECCE 2009, Pages: 2815-2820
This paper presents a dynamic thermal model of a LED system and a control strategy for optimal power point tracking (OPPT). The control strategy is based on the general theory which links the photometric, electric and thermal behaviors of LEDs together. The control implementation enables the optimal operating of the LED systems to be determined dynamically. By measuring the ambient temperature and the heatsink temperature of LED system, the proposed control scheme allows the LED system to operate at the optimal dynamic operating points at which maximum luminous flux is generated. Practical tests have been carried out to verify the model and the general theory. © 2009 IEEE.
Chan PKW, Chung HSH, Hui SY, 2009, A generalized theory of boundary control for a single-phase multilevel inverter using second-order switching surface, IEEE Transactions on Power Electronics, Vol: 24, Pages: 2298-2313, ISSN: 0885-8993
An extension of the use of the boundary control method using second-order switching functions for controlling single-phase multilevel inverters is presented in this paper. The time instant of switching the output voltage of the inverter bridge from one voltage level to another voltage level is governed by two second-order switching functions. The input variables of the switching functions are the input and output voltages of the inverter, reference output voltage, and output filter capacitor current. The switching functions are derived by first estimating the respective trajectories of the output voltage of the inverter with the two possible voltage levels from the inverter bridge supplying to the input of the output filter, and then formulating mathematical functions to approximate the two trajectories (one for each voltage level) that pass through the target operating point. The distinct feature of this method is that the output voltage of the inverter can reach the target operating point in two switching actions in the inverter bridge after the inverter is subjected to an external disturbance. Derivation of the switching functions and implementation of the controller will be given. Three single-phase inverter topologies, including cascaded five-level inverter, hybrid seven-level inverter, and three-level diode-clamped inverter, with the proposed control method have been built and tested. The steady-state and largesignal dynamic responses of the three inverters supplying to three different load types, including resistive, inductive, and nonlinear diode-capacitor circuits, will be discussed. © 2009 IEEE.
Lin DY, Yan W, Hui SYR, et al., 2009, An improved semi-theoretical fluorescent lamp model for dimmable applications, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 819-825
Due to the energy-saving and environmentally friendly features, dimmable magnetic ballasts will be paid more attention in the future. This make a more accurate fluorescent lamp model at different dimming levels necessary at low operating frequency. This paper presents a new method that considers the effect of tube temperature at different dimming levels in the process of the analysis of the fluorescent lamp model. The model is verified favorably by the comparison between the simulation results and experimental results. It's clear that after the effect of tube temperature at different dimming levels is considered, the model becomes more accurate and reliable than before. This model can be used to design dimmable magnetic ballast. Hence, the proposed model shows a good degree of accuracy for a large dimming range at different operating frequencies. ©2009 IEEE.
Lee CK, Chan PCF, Hui SYR, 2008, Alternating stacked inductor for Mega-Hertz power converter and filtering applications, PESC Record - IEEE Annual Power Electronics Specialists Conference, Pages: 3021-3027, ISSN: 0275-9306
In this paper, an alternating winding structure for the stacked inductor is studied for use in Mega-Hertz switching converter and filtering applications. This alternating stacked winding structure reduces the parasitic capacitance of a stacked inductor. Thus, the operating frequency range of the inductor is substantially extended. The equivalent capacitances of the alternating stacked inductors are estimated by energy consideration in an attempt to explain the relative magnitudes of the capacitances of the stacked inductors with similar but different structures. Both theoretical analysis and practical measurements have confirmed the bandwidth advantages of the alternating stacked inductors. ©2008 IEEE.
Su YP, Liu X, Hui SYR, 2008, Mutual inductance calculation of movable planar coils on parallel surfaces, PESC Record - IEEE Annual Power Electronics Specialists Conference, Pages: 3475-3481, ISSN: 0275-9306
Recent developments of wireless battery charging platform have prompted the requirements to investigate the mutual inductance between a movable planar coil and the fixed planar coil on the charging platform. The wireless battery charging platform must allow the load to be placed anywhere on the charging surface. Therefore the relative position between the movable energy-receiving coil and the energy-transmitting coils on the charging platform must be flexible. In this paper, an extended formula is proposed for the mutual inductance calculation for two coaxial or non-coaxial planar spiral windings sandwiched between two double-layer substrates. It can quickly determine the mutual coupling of two planar windings that can have different relative positions and distance between them. This new calculation method provides a new and useful tool for determining the mutual inductance of a movable planar coil and the fixed planar coil on the wireless battery charging platform. The theory has been favorably tested and compared with practical measurements and also finite-element analysis. ©2008 IEEE.
Hui SYR, Chung HSH, Qiu DY, 2008, Effective standby power reduction using non-dissipative single-sensor method, PESC Record - IEEE Annual Power Electronics Specialists Conference, Pages: 678-684, ISSN: 0275-9306
This paper presents an implementation of the "single-sensor" method for controlling a power factor correction (PFC) circuit. The method eliminates lossy resistive feedback by deriving control variables such as the input and output voltages of the power converter via the switching action of the power MOSFET of the power converter. It can be applied directly to control the PFC circuit under all conditions. A simple technique is also introduced to overcome the sensing problem under the no-load condition. This proposed scheme requires only simple modifications of existing PFC control integrated circuits (IC) and can be extended to all other PFC control ICs. Practical results of an 80W PFC system for 88V to 265V operation from no-load to 100% load conditions under both steady-state and transient conditions are included to confirm the success of such implementation. The proposed method can in principle be applied to a wide range of switched mode power electronic systems for reduction of standby power. ©2008 IEEE.
Liu X, Ng WM, Lee CK, et al., 2008, Optimal operation of contactless transformers with resonance in secondary circuits, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 645-650
Contactless transformer is an essential element in inductive power transfer systems. To improve its efficiency performance, a resonant tank is normally formed at the secondary side by adding an external capacitor in series (SS) or in parallel (SP) with the secondary winding. In this paper, a mathematical analysis based on simplified circuit model is presented. It leads to the theory of the boundary frequency which can be used to determine the optimal operating range for SS and SP mode, respectively, from the efficiency point of view. Calculated and measured results have been given to verify the theory in a case study. © 2008 IEEE.
Ho WC, Lee CK, Liu X, et al., 2008, A hybrid EMI filter with ultra-wide bandwidth, Conference Proceedings - IEEE Applied Power Electronics Conference and Exposition - APEC, Pages: 676-681
This paper describes an integrated active and passive planar electromagnetic-interference (EMI) filter structure with effective noise suppression over a very wide bandwidth. Such hybrid EMI filter pa ves the way input filter design for future mega-hertz switching power converters. This study shows that it has superior performance over traditional active filters and passive filters. Spectral results of a switching converter from 150kHz to 30MHz using various of active, passive and the proposed hybrid EMI filters have confirmed the validity and high performance of the hybrid EMI filter. © 2008 IEEE.
Su YP, Liu X, Hui SY, 2008, Extended theory on the inductance calculation of planar spiral windings including the effectof double-layer electromagnetic shield, IEEE Transactions on Power Electronics, Vol: 23, Pages: 2052-2061, ISSN: 0885-8993
Recent progress on wireless planar battery charging platform highlights a requirement that the platform must be shielded underneath so that the electromagnetic (EM) flux will not leak through the bottom of the charging platform. The presence of the EM shield will inevitably alter the flux distribution and thus the inductance of the planar windings. In this paper, a theory of inductance calculation of spiral windings is extended to determine the inductance of planar spiral windings shielded by a double-layer planar EM shield which consists of a layer of soft magnetic material and a layer of conductive material. With the generalized equations, the impedance of the planar spiral windings on double-layer shielding substrate and the optimal thickness of shielding materials can be calculated accurately without using time-consuming finite-element method. Therefore, the influence of the double-layer electromagnetic shield on the inductance of the planar spiral windings can be analyzed. Simulations and measurements have been carried out for several shielding plates with different permeability, conductivity, and thickness. Both of the simulations and measurements of the winding inductance agree well with the extended theory. © 2008 IEEE.
Qin YX, Chung HSH, Lin DY, et al., 2008, Current source ballast for high power lighting emitting diodes without electrolytic capacitor, IECON Proceedings (Industrial Electronics Conference), Pages: 1968-1973
An LED driver requiring no electrolytic capacitor in the whole power conversion process is presented. It consists of two power conversion stages. The first stage is a buck converter operating in discontinuous capacitor voltage mode, so that the input current is continuous. It is used to deliver a regulated current for the second stage. The second stage is a current-fed inverter, in which the semiconductor switches are operated at constant switching frequency and constant duty cycle of 0.5. The power supplying to the LED string is regulated by controlling the duty cycle of the main switch in the front-stage buck converter. The two stages are interconnected by an LC filter, which is designed to attenuate harmonics at double of the line frequency. Instead of using an electrolytic capacitor for the filter, a polyester capacitor of better lifetime expectancy is used. An 18W experimental prototype has been built and tested. © 2008 IEEE.
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