Zhong Chen

Bio: Zhong Chen is an academic researcher from Nanyang Technological University. The author has contributed to research in topics: Medicine & Chemistry. The author has an hindex of 80, co-authored 1000 publications receiving 28171 citations. Previous affiliations of Zhong Chen include Institute of High Performance Computing Singapore & National Institute of Education.

Development of high speed board level bend tester for drop impact applications

Abstract: Due to the widespread use of portable electronics, there is a significant increase in interest in exploring the impact reliability of electronic packaging during impact shock. Currently, the test standard used for board level drop testing is JESD 22-B111 [1], which specifies the impact pulse (i.e. 1500G at 0.5ms) as a criterion for drop testing. However, this may not mimic the actual product testing. The board level cyclic bend test standard (JESD 22-B113) [2] is subsequently developed and introduced to perform low frequency bending (1 to 3 Hz). However, cyclic bend at low frequency is not able to produce similar failure mode as drop testing because board frequency during drop impact is usually much higher. Thus in this study, a high speed bend test (>50Hz) is developed to perform strain-controlled bend testing. The strain amplitude and frequency effects on BGA and WLCSP package solder joint life on various board sizes and component layout are studied and discussed. An increase in frequency was found to result in a significant reduction in time to failure, though a shift in failure mode (from bulk solder to inter-metallic failure) and reduction in cycles to failure were not observed. Results indicated that at higher strain amplitudes, cycles to fatigue life of package significantly decreased. This study has also shown a certain extent of correlation between drop test and high speed bend test.

A General Reconstruction Method for Multidimensional Sparse Sampling Nuclear Magnetic Resonance Spectroscopy.

Abstract: Multidimensional NMR spectroscopy provides a powerful tool for structure elucidation and dynamic analysis of complex samples, particularly for biological macromolecules. Multidimensional sparse sampling effectively accelerates NMR experiments while an efficient reconstruction method is generally required for unraveling spectra. Various reconstruction methods were proposed for pure Fourier NMR (only involving chemical shifts and J couplings detection). However, reconstruction concerned with Laplace-related NMR (i.e., involving relaxation or diffusion detection) is more challenging due to its ill-posed property. The existing Laplace-related NMR sparse sampling reconstruction methods suffer from poor resolution and possible artifacts in the resulting spectra owing to the pitfalls of the optimization algorithms. Herein, we propose a general approach for fast high-resolution reconstruction of multidimensional sparse sampling NMR, including pure Fourier, mixed Fourier-Laplace, and pure Laplace NMR, benefiting from the comprehensive sparse constraint and effective optimization algorithm and thus showing the promising prospects of multidimensional NMR.

Optimization of the cooling characteristics in high-voltage LEDs

Abstract: Cooling is a critical process in the thermal designs of high-voltage light-emitting diodes (HV-LEDs), whose junction temperatures are in turn an essential criterion for evaluations of LED aging, light-color quality, and luminous efficacies. In the present work, both numerically and experimentally, we have identified two cooling-related parameters, namely thermal crowdedness and nonuniformity, that are related to the lowering of junction temperatures of 17 microchips. Based on these two parameters, we have further proposed three regimes that facilitate the optimization. In addition, great care must be taken to incorporate the difficulty of tackling the high voltage into electrical-resistance selections. The 3D transient conjugate heat transfer is simulated using the finite element package named COMSOL. Finally, we hope that the present study can provide the photonic and cooling industries with the guidance for optimizing cooling characteristics in HV-LEDs based on these two parameters and three reg...

Electrochemical nuclear magnetic resonance in-situ quantitative detection electrolytic tank

Abstract: The utility model discloses an electrochemical nuclear magnetic resonance in-situ quantitative detection electrolytic tank, and relates to an electrochemical electrolytic tank. The electrolytic tank comprises a tank body, a sample pipe rotor, connecting rods, an electrode patchplug, a fixed table, three electrodes, and nuclear magnetic sample pipes, wherein the top of the tank body is fixedly connected to the bottom of the sample pipe rotor; the three electrodes penetrate through a sample pipe cap arranged at the top of the sample pipe rotor through lead wires and are connected to coaxial cables through metal needles arranged in the electrode patchplug; the tops of the coaxial cables are fixed on the fixed table arranged at the tops of the connecting rods; the coaxial cables are externally connected with an electrochemical workstation; the five nuclear magnetic sample pipes are arranged inside the tank body; the second nuclear magnetic sample pipe is coaxially fixed inside the first nuclear magnetic sample pipe; a working electrode reaction electrolysis chamber is formed in the area between the second nuclear magnetic sample pipe and the fifth nuclear magnetic sample pipe; a porous glass sand core is embedded to the lower part of the third nuclear magnetic sample pipe to form an auxiliary electrode reaction electrolysis chamber; an isolation electrolysis chamber is formed between the third nuclear magnetic sample pipe and the first nuclear magnetic sample pipe.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Principles of Neural Science

Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Abstract: As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...