Wei-chun Hsu | Massachusetts Institute of Technology (MIT) (original) (raw)

Papers by Wei-chun Hsu

Scientific reports, 2015

A new approach is introduced to significantly improve the performance of thermophotovoltaic (TPV)... more A new approach is introduced to significantly improve the performance of thermophotovoltaic (TPV) systems using low-dimensional thermal emitters and photovoltaic (PV) cells. By reducing the thickness of both the emitter and the PV cell, strong spectral selectivity in thermal emission and absorption can be achieved by confining photons in trapped waveguide modes inside the thin-films that act as thermal analogs to quantum wells. Simultaneously, photo-excited carriers travel shorter distances across the thin-films reducing bulk recombination losses resulting in a lower saturation current in the PV cell. We predict a TPV efficiency enhancement with near-field coupling between the thermal emitter and the PV cell up to 38.7% using a thin-film germanium (Ge) emitter at 1000 K and an ultra-thin gallium antimonide (GaSb) cell supported by perfect back reflectors separated by 100 nm. Even in the far-field limit, the efficiency is predicted to reach 31.5%, which is over an order of magnitude ...

Lecture Notes in Electrical Engineering, 2011

In this paper, an algorithm of Selective Block Size Decision for Intra Prediction in Video Coding... more In this paper, an algorithm of Selective Block Size Decision for Intra Prediction in Video Coding and Learning Website will be presented. The main purpose is to reduce the high complexity of video when predict in intra prediction to select the mode. Video coding decision is divided into two stages: the selective block size and reduce the prediction mode. When

The second to the fifth harmonics of a fundamental frequency are generated in a lithium tantalate... more The second to the fifth harmonics of a fundamental frequency are generated in a lithium tantalate crystal by cascaded quasi-phase-matched frequency mixing. These harmonics can be used to synthesize a train of periodic sub-femtosecond pulses.

2009 First International Workshop on Education Technology and Computer Science, 2009

In this paper, a new noise filtering, three-phase distance matrices filter (TPDMF), for restorati... more In this paper, a new noise filtering, three-phase distance matrices filter (TPDMF), for restoration of corrupted image by impulsive noise is presented. Whether images were attacked by random valued impulse or constant valued impulse, this method can restore corrupted images fast and effectively without iterative procedure. For avoiding oversmoothing after filtering, TPDMF uses distance matrices to preserve edge and detail

2005 6th International Conference on ASIC, 2005

In today's automotive industry, the issue of driver safety and comfort is of great importance. An... more In today's automotive industry, the issue of driver safety and comfort is of great importance. An automatic windshield wiper system is of great aid in such cases. It betters the driving experience and improvises the safety factor of a vehicle by converting the manual windshield wiper system into an automatic system. By taking care of the attentions drivers would have to devote to control a manual system, an automatic wiper system helps them to concentrate more on driving safely. Although, few automated windshield wiper systems are available in the automotive market, they are very costly and not very effective. This paper presents a cost effective and high performance automatic windshield wiper system developed using an Arduino Uno microcontroller and a rain intensity detection sensor. The system was programmed to use fuzzy logic to manipulate the analog data collected from the sensor, and the microcontroller controlled the wiper motor using pulse width modulation (PWM). The use of fuzzy logic allows the system to be easily reconfigurable. Such feature can be utilized to design different wiper system for different vehicles and weather conditions without any hardware modification. It was successfully connected to a commercial vehicle (Mazda Protégé) and tested for different rain conditions. The sensor data was collected using artificial rain conditions to mimic real world raining conditions and the resultant windshield wiper movement strongly resembled manual control of the wipers. In a nutshell, the developed system was not only cost effective but also highly performing.

2009 Conference on Lasers & Electro Optics & The Pacific Rim Conference on Lasers and Electro-Optics, 2009

Lecture Notes in Electrical Engineering, 2011

Motion estimation is the most important part that needs about 80% of computation in the procedure... more Motion estimation is the most important part that needs about 80% of computation in the procedure of image compression coding. So there are many fast algorithms for motion vector search proposed to reduce time consumed and keep good qualities. In this paper some traditional algorithms and algorithms using prediction values are investigated, including DS (diamond search), HEXBS (hexagonbased search) and

Optics Letters, 2009

We report the generation of the second to the sixth harmonics of a fundamental frequency covering... more We report the generation of the second to the sixth harmonics of a fundamental frequency covering two and a half octaves in a multiply-periodically poled lithium tantalate crystal by cascaded quasi-phase-matched frequency mixing. A frequency comb that is composed of these harmonics will permit the synthesis of a train of periodic subcycle subfemtosecond pulses in a compact setting.

Journal of System Design and Dynamics, 2009

This paper combines a verified interval optimization method with the FEM for designing structures... more This paper combines a verified interval optimization method with the FEM for designing structures, which is denominated as the Hybrid Interval Genetic Algorithm (HIGA). This algorithm can neglect formulated equations and interval analysis, and while determining ...

Journal of Sound and Vibration, 2009

This paper studies the dynamic response of a rotating multi-span shaft with elastic bearings subj... more This paper studies the dynamic response of a rotating multi-span shaft with elastic bearings subjected to an axially moving load. The moving load is motivated by the cutting forces in machining process. The multi-span shaft with elastic bearings models a system that a rotating shaft is mounted by the tailstock and chuck and the steady rests are installed between the

Journal of Polymer Science Part A: Polymer Chemistry, 2010

ABSTRACT Through the Stille coupling polymerization, a series of soluble acceptor/donor quinoxali... more ABSTRACT Through the Stille coupling polymerization, a series of soluble acceptor/donor quinoxaline/thiophene alternating conducting polymers with a hole-transporting moiety of carbazole as a side chain (PCPQT) has been designed, synthesized, and investigated. The UV–vis measurement of the charge-transferred type PCPQTs of different molecular weights with low polydispersity exhibits a red shifting of their absorption maximum from 530 to 630 nm with increasing chain length (Mn: from 1100 to 19,200). The HOMO and LUMO energy levels of PCPQT can be determined from the cyclic voltammetry measurement to be −5.36 and −3.59 eV, respectively. Solar cells made from PCPQT/PCBM bulk heterojunction show a high open-circuit voltage, Voc of ∼0.75 V, which is significantly higher than that of a solar cell made from conventional poly(3-hexyl thiophene)/PCBM as the active polymer PCPQT has lower HOMO level. Further improvements are anticipated through a rational design of the new low band-gap and the structurally two-dimensional donor–acceptor conducting polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1607–1616, 2010

The International Journal of Advanced Manufacturing Technology, 2011

The dynamic behavior of a ball screw under a moving grinding force and the resulting ball screw s... more The dynamic behavior of a ball screw under a moving grinding force and the resulting ball screw surface roughness are investigated. The system includes a ball screw, a headstock, a tailstock, a steady rest, a grinding wheel, and a wheel head. Equations of motion of the system are derived through Lagrangian approach combined with global assumed mode method in this study. The transient responses of the system due to a moving force are evaluated using Runge-Kutta method. Results show that the steady rest can reduce 90% vibration in a grinding process. An equation is proposed to predict the maximum response by the cutting depth. Then we simulate the grain height distribution on the grinding wheel, considering transient response on the ball screw and the grinding wheel. Lastly, the ball screw surface roughness could be simulated via calculating the depth of all working grains. The purpose of using grinding process is that the ball screw needs fine surface roughness. The ball screw surface roughness is influenced by the grain size more than the structure numbers can be.

Advanced materials (Deerfield Beach, Fla.), Jan 18, 2015

Only ten micrometer thick crystalline silicon solar cells deliver a short-circuit current of 34.5... more Only ten micrometer thick crystalline silicon solar cells deliver a short-circuit current of 34.5 mA cm(-2) and power conversion efficiency of 15.7%. The record performance for a crystalline silicon solar cell of such thinness is enabled by an advanced light-trapping design incorporating a 2D inverted pyramid photonic crystal and a rear dielectric/reflector stack.

Scientific reports, 2015

A new approach is introduced to significantly improve the performance of thermophotovoltaic (TPV)... more A new approach is introduced to significantly improve the performance of thermophotovoltaic (TPV) systems using low-dimensional thermal emitters and photovoltaic (PV) cells. By reducing the thickness of both the emitter and the PV cell, strong spectral selectivity in thermal emission and absorption can be achieved by confining photons in trapped waveguide modes inside the thin-films that act as thermal analogs to quantum wells. Simultaneously, photo-excited carriers travel shorter distances across the thin-films reducing bulk recombination losses resulting in a lower saturation current in the PV cell. We predict a TPV efficiency enhancement with near-field coupling between the thermal emitter and the PV cell up to 38.7% using a thin-film germanium (Ge) emitter at 1000 K and an ultra-thin gallium antimonide (GaSb) cell supported by perfect back reflectors separated by 100 nm. Even in the far-field limit, the efficiency is predicted to reach 31.5%, which is over an order of magnitude ...

Lecture Notes in Electrical Engineering, 2011

In this paper, an algorithm of Selective Block Size Decision for Intra Prediction in Video Coding... more In this paper, an algorithm of Selective Block Size Decision for Intra Prediction in Video Coding and Learning Website will be presented. The main purpose is to reduce the high complexity of video when predict in intra prediction to select the mode. Video coding decision is divided into two stages: the selective block size and reduce the prediction mode. When

The second to the fifth harmonics of a fundamental frequency are generated in a lithium tantalate... more The second to the fifth harmonics of a fundamental frequency are generated in a lithium tantalate crystal by cascaded quasi-phase-matched frequency mixing. These harmonics can be used to synthesize a train of periodic sub-femtosecond pulses.

2009 First International Workshop on Education Technology and Computer Science, 2009

In this paper, a new noise filtering, three-phase distance matrices filter (TPDMF), for restorati... more In this paper, a new noise filtering, three-phase distance matrices filter (TPDMF), for restoration of corrupted image by impulsive noise is presented. Whether images were attacked by random valued impulse or constant valued impulse, this method can restore corrupted images fast and effectively without iterative procedure. For avoiding oversmoothing after filtering, TPDMF uses distance matrices to preserve edge and detail

2005 6th International Conference on ASIC, 2005

In today's automotive industry, the issue of driver safety and comfort is of great importance. An... more In today's automotive industry, the issue of driver safety and comfort is of great importance. An automatic windshield wiper system is of great aid in such cases. It betters the driving experience and improvises the safety factor of a vehicle by converting the manual windshield wiper system into an automatic system. By taking care of the attentions drivers would have to devote to control a manual system, an automatic wiper system helps them to concentrate more on driving safely. Although, few automated windshield wiper systems are available in the automotive market, they are very costly and not very effective. This paper presents a cost effective and high performance automatic windshield wiper system developed using an Arduino Uno microcontroller and a rain intensity detection sensor. The system was programmed to use fuzzy logic to manipulate the analog data collected from the sensor, and the microcontroller controlled the wiper motor using pulse width modulation (PWM). The use of fuzzy logic allows the system to be easily reconfigurable. Such feature can be utilized to design different wiper system for different vehicles and weather conditions without any hardware modification. It was successfully connected to a commercial vehicle (Mazda Protégé) and tested for different rain conditions. The sensor data was collected using artificial rain conditions to mimic real world raining conditions and the resultant windshield wiper movement strongly resembled manual control of the wipers. In a nutshell, the developed system was not only cost effective but also highly performing.

2009 Conference on Lasers & Electro Optics & The Pacific Rim Conference on Lasers and Electro-Optics, 2009

Lecture Notes in Electrical Engineering, 2011

Motion estimation is the most important part that needs about 80% of computation in the procedure... more Motion estimation is the most important part that needs about 80% of computation in the procedure of image compression coding. So there are many fast algorithms for motion vector search proposed to reduce time consumed and keep good qualities. In this paper some traditional algorithms and algorithms using prediction values are investigated, including DS (diamond search), HEXBS (hexagonbased search) and

Optics Letters, 2009

We report the generation of the second to the sixth harmonics of a fundamental frequency covering... more We report the generation of the second to the sixth harmonics of a fundamental frequency covering two and a half octaves in a multiply-periodically poled lithium tantalate crystal by cascaded quasi-phase-matched frequency mixing. A frequency comb that is composed of these harmonics will permit the synthesis of a train of periodic subcycle subfemtosecond pulses in a compact setting.

Journal of System Design and Dynamics, 2009

This paper combines a verified interval optimization method with the FEM for designing structures... more This paper combines a verified interval optimization method with the FEM for designing structures, which is denominated as the Hybrid Interval Genetic Algorithm (HIGA). This algorithm can neglect formulated equations and interval analysis, and while determining ...

Journal of Sound and Vibration, 2009

This paper studies the dynamic response of a rotating multi-span shaft with elastic bearings subj... more This paper studies the dynamic response of a rotating multi-span shaft with elastic bearings subjected to an axially moving load. The moving load is motivated by the cutting forces in machining process. The multi-span shaft with elastic bearings models a system that a rotating shaft is mounted by the tailstock and chuck and the steady rests are installed between the

Journal of Polymer Science Part A: Polymer Chemistry, 2010

ABSTRACT Through the Stille coupling polymerization, a series of soluble acceptor/donor quinoxali... more ABSTRACT Through the Stille coupling polymerization, a series of soluble acceptor/donor quinoxaline/thiophene alternating conducting polymers with a hole-transporting moiety of carbazole as a side chain (PCPQT) has been designed, synthesized, and investigated. The UV–vis measurement of the charge-transferred type PCPQTs of different molecular weights with low polydispersity exhibits a red shifting of their absorption maximum from 530 to 630 nm with increasing chain length (Mn: from 1100 to 19,200). The HOMO and LUMO energy levels of PCPQT can be determined from the cyclic voltammetry measurement to be −5.36 and −3.59 eV, respectively. Solar cells made from PCPQT/PCBM bulk heterojunction show a high open-circuit voltage, Voc of ∼0.75 V, which is significantly higher than that of a solar cell made from conventional poly(3-hexyl thiophene)/PCBM as the active polymer PCPQT has lower HOMO level. Further improvements are anticipated through a rational design of the new low band-gap and the structurally two-dimensional donor–acceptor conducting polymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1607–1616, 2010

The International Journal of Advanced Manufacturing Technology, 2011

The dynamic behavior of a ball screw under a moving grinding force and the resulting ball screw s... more The dynamic behavior of a ball screw under a moving grinding force and the resulting ball screw surface roughness are investigated. The system includes a ball screw, a headstock, a tailstock, a steady rest, a grinding wheel, and a wheel head. Equations of motion of the system are derived through Lagrangian approach combined with global assumed mode method in this study. The transient responses of the system due to a moving force are evaluated using Runge-Kutta method. Results show that the steady rest can reduce 90% vibration in a grinding process. An equation is proposed to predict the maximum response by the cutting depth. Then we simulate the grain height distribution on the grinding wheel, considering transient response on the ball screw and the grinding wheel. Lastly, the ball screw surface roughness could be simulated via calculating the depth of all working grains. The purpose of using grinding process is that the ball screw needs fine surface roughness. The ball screw surface roughness is influenced by the grain size more than the structure numbers can be.

Advanced materials (Deerfield Beach, Fla.), Jan 18, 2015

Only ten micrometer thick crystalline silicon solar cells deliver a short-circuit current of 34.5... more Only ten micrometer thick crystalline silicon solar cells deliver a short-circuit current of 34.5 mA cm(-2) and power conversion efficiency of 15.7%. The record performance for a crystalline silicon solar cell of such thinness is enabled by an advanced light-trapping design incorporating a 2D inverted pyramid photonic crystal and a rear dielectric/reflector stack.