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Kernel sparse representation for MRI image analysis in automatic brain tumor segmentation

Frontiers of Information Technology & Electronic Engineering 2018年第4期19卷 471-480页

作者： Ji-jun TONG Peng ZHANG yu-xiang weng Dan-hua ZHU School of lnformation Science and Technology Zhejiang Sci-Tech UniversityHangzhou 310018China Department of Neurosurgery The First Affiliated HospitalSchool of MedicineZhejiang UniversityHangzhou 310003China State Key Laboratory for Diagnosis and Treatment of lnfectious Diseases Collaborative Innovation Center for Diagnosis and Treatment of Infectious DiseasesThe First Affiliated HospitalSchool of MedicineZhejiang UniversityHangzhou 310003China

The segmentation of brain tumor plays an important role in diagnosis, treatment planning, and surgical simulation. The precise segmentation of brain tumor can help clinicians obtain its location, size, and shape information. We propose a fully automatic brain tumor segmentation method based on kernel sparse coding. It is validated with 3D multiple-modality magnetic resonance imaging(MRI). In this method, MRI images are pre-processed first to reduce the noise, and then kernel dictionary learning is used to extract the nonlinear features to construct five adaptive dictionaries for healthy tissues, necrosis, edema, non-enhancing tumor, and enhancing tumor tissues. Sparse coding is performed on the feature vectors extracted from the original MRI images, which are a patch of m×m×m around the voxel. A kernel-clustering algorithm based on dictionary learning is developed to code the voxels. In the end, morphological filtering is used to fill in the area among multiple connected components to improve the segmentation quality. To assess the segmentation performance, the segmentation results are uploaded to the online evaluation system where the evaluation metrics dice score, positive predictive value(PPV), sensitivity, and kappa are used. The results demonstrate that the proposed method has good performance on the complete tumor region(dice: 0.83; PPV: 0.84; sensitivity: 0.82), while slightly worse performance on the tumor core(dice: 0.69; PPV: 0.76; sensitivity: 0.80) and enhancing tumor(dice: 0.58; PPV: 0.60; sensitivity: 0.65). It is competitive to the other groups in the brain tumor segmentation challenge. Therefore, it is a potential method in differentiation of healthy and pathological tissues.

关键词： Brain tumor segmentation Kernel method Sparse coding Dictionary learning

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Construction of the Apparatus for Two Dimensional Electronic Spectroscopy and Characterization of the Instrument

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Chinese Journal of Chemical Physics 2015年第4期28卷 -页

作者： Shuai yue Zhuan Wang Xiao-chuan He Gang-bei Zhu yu-xiang weng Laboratory of Soft Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China

This work describes the construction of a phase-stable two dimensional electronic spectrometer operating in a photon echo mode with optical heterodyne detection, where the diffractive optics were used to realize the passive phase stabilization. In addition, a high speed and sensitive EMCCD was configured for shot-to-shot measurement which effectively improved signal-to-noise ratio. Consequently, the phase stability between a pulse pair split by the diffractive optics was determined in terms of standard deviation to be λ/200 during an observation period of 30 min, while the phase stability of the photon echo signal measured with IR140 is λ/90 in 19 min. In addition, a method of phase-shift in the pump pulse is also presented, which can effectively remove the interference from scattering light in collection of pump-probe transient absorption spectrum. The phase-shift method can improve the accuracy of phase adjustment in 2D electronic spectrum of scattering samples.

关键词： Two-dimensional electronic spectroscopy Phase stability Phase adjustment

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Detection of Electronic Coherence via Two-Dimensional Electronic Spectroscopy in Condensed Phase

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Chinese Journal of Chemical Physics 2018年第2期31卷 135-151,245页

作者： yu-xiang weng Laboratory of Soft Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China

Two dimensional Fourier transforrn electronic spectroscopy （2DES） in the visible region enables direct observation of complex dynamics of molecules including quantum coherence in the condensed phase. This review aims to provide a bridge between the principles and intuitive physical description of 2DES for tutorial purpose. Special emphasis is laid upon how 2DES circumvents the restrictions from both uncertainty principle and the wave-packet collapse during the coherent detection, leading to the successful detection of the coherence in terms of energy difference between the eigenstates showing as the quantum beats; then upon the possible mixing among the pure electronic transition, single-rnode and multi-mode coupled vibronic transition leading to the observed beating phenomena. Finally, recent ad- vances in experimentally distinguishing between the electronic coherence and the vibrational coherence are briefly discussed.

关键词： Quantum coherence Uncertainty principle Wave-packet collapse Multi-rnodevibronic coupling Two dimensional electronic spectroscopy

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Thermal-induced Unfolding of β-Crystallin and Disassembly of its Oligomers Revealed by Temperature-Jump Time-Resolved Infrared Spectroscopy

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Chinese Journal of Chemical Physics 2013年第6期26卷 739-746,I0004页

作者： Shan-shan Li Ying-ying yu De-yong Li Xiao-chuan He Yong-zhen Bao yu-xiang weng Laboratory of Soft Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190China Beijing Key Laboratory of Diagnosis and Therapy of Retinal and Choroid Diseases Key Laboratory ofVision Loss and Restoration Ministry of Education Department of Ophthalmology Peking UniversityPeople's Hospital Belying 100044 China

β-Crystallins are the major structural proteins existing in the vertebrate lens, and their conformational stability is critical in maintaining the life-long transparency and refraction index of the lens. Seven subunits of β-crystallins naturally assemble into various heteroge- neous oligomers with different sizes. Here, we systematically investigated the thermal sta- bility of the different secondary structures present in β-Crystallins and then the dynamic process for the thermal-induced unfolding of β-crystallins by Fourier transform infrared spectroscopy-monitored thermal titration and temperature-jump nanosecond time-resolved IR difference absorbance spectra. Our results show that the N-terminal anti-parallel β-sheets in β-crystallin are the most unstable with a transition midpoint temperature at 36.0-2.1℃, leading to the formation of an intermediate consisting vastly of random coil structures. This intermediate structure is temporally assigned to that of the monomer generated by the thermal-induced disassembly of β-crystallin oligomers with a transition midpoint tempera- ture of 40.4-0.7℃. The global unfolding of β-crystallins that leads to denaturation and aggregation indicated by the formation of intermolecular anti-parallel β-sheets has a transi- tion midpoint temperature determined as 72.4-0.2 ℃. Temperature-jump time-resolved IR absorbance difference spectroscopy analysis further reveals that thermal-induced unfolding of β-crystallins occurs firstly in the anti-parallel β-sheets in the N-terminal domains with a time constant of 50 ns.

关键词： β-Crystallin Protein dynamical structure Temperature-jump Time-resolved IR spectrum

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Infrared Absorption Intensity Analysis as a New Tool for Investigation of Salt Effect on Proteins

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Chinese Journal of Chemical Physics 2009年第6期22卷 556-562,J0001页

作者： Heng Li Yan-yan Xu yu-xiang weng Laboratory of Soft Matter Physics Institute of Physics Chinese Academy of Sciences Beifing 100190China

The native protein structures in buffer solution are maintained by the electrostatic force as well as the hydrophobic force, salt ions play an important role in maintaining the protein native structures, and their effect on the protein stability has attracted tremendous interests. Infrared spectroscopy has been generally used in molecular structure analysis due to its fingerprint resolution for different species including macromolecules as proteins. However spectral intensities have received much less attention than the vibrational frequencies. Here we report that the spectral intensities of protein amide I band, the finger prints for the protein secondary structures, are very sensitive to the local electric field known as Onsager reaction field caused by salt ions. IR absorbance thermal titrations have been conducted for a series of samples including simple water soluble amino acids, water soluble monomeric protein cytochrome c and dimeric protein DsbC and its single-site mutant G49R. We found that at lower temperature range （10-20℃）, there exists a thermal activated salting-in process, where the IR intensity increases with a rise in the temperature, corresponding to the ions binding of the hydrophobic surface of protein. This process is absent for the amino acids. When further raising the temperature, the IR intensity decreases, this is interpreted as the thermal activated breaking of the ion-protein surface binding. Applying Van＇t Hoff plot to the thermal titration curves, the thermodynamic parameters such as AH and AS for salting-in and ion unbinding processes can be derived for various protein secondary structural components, revealing quantitatively the extent of hydrophobic interaction as well as the strength of the ion-protein binding.

关键词： Infrared intensity Salt effect Fourier transform infrared spectroscopy Secondary structure Thermodynamic constant

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Transitional Process of Ploy（N-isopropylacrylamide） in Deuterated Solution

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Chinese Journal of Chemical Physics 2009年第5期22卷 447-452,I0001页

作者： Shao-hua Zhang Yang Chen Heng Li yu-xiang weng Hefei National Laboratory for Physical Sciences at the Microscale Department of Chemical PhysicsUniversity of Science and Technology of China Hefei 230026 China Laboratory of Soft Matter Physics Institute of Physics Chinese Academy of Sciences Beijing National Laboratory of Condensed Matter Physics Beijing 100080 China

The fast phase-transitional process of ploy（N-isopropylacrylamide）（PNIPAM） in deuterated solution was studied by laser induced temperature jump technique combined with time-resolved mid-infrared absorbance difference spectroscopy on nanosecond level. The multi-peaks of amide I＇band of PNIPAM among the energy range of 1565-1700 cm^-1 was experimentally resolved to three groups （i, ii, iii） for the first time, while the distinct threestage procedure in the phase transitional process of long-chain PNIPAM was observed firstly too. Furthermore, proper assignments were also made for the three group peaks in amide I＇band and the three steps in the kinetics process of long-chain PNIPAM.

关键词： Poly(N-isopropylacrylamide) Laser induced temperature jump Kinetic Transient mid-infrared absorbance difference spectroscopy Multistage Transitional process

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An integrative mathematical model of microwave ion thruster for mHz-frequency thrust noise analysis

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Chinese Journal of Aeronautics 2024年第4期37卷 121-136页

作者： xiang NIU Hui LIU Daren yu Plasma Propulsion Laboratory Harbin Institute of TechnologyHarbin 150001China

Many high-precision space missions need thrusters to produce thrust with low noise to compensate for disturbances and ensure satellite platform stability. Microwave ion thruster is characterized with a wide thrust range and potential for these missions. A cost-effective and accurate mathematical model is crucial for mHz-frequency thrust noise analysis and feedback controller design. The Particle-In-Cell(PIC) and global models are two common simulation tools. The PIC model is characterized with high accuracy but huge computation cost, which is difficult to analyze long-time performance characteristics. Now, the global model is only used for the discharge chamber with low accuracy and cannot reflect ion extraction properties. In this paper, an integrative mathematical model is built for a 1-cm microwave ion thruster and can reflect ion beamlet divergence and impingement on the Accelerator Grid(AG). Simulation results show good agreement with experiments at 0.06 sccm. However, the model demonstrates worse consistency with experiments when the flux increases to 0.1 sccm, which may be because the influence of neutral gas on the Electron Cyclotron Resonance(ECR) is not considered in the model. A long-time(1000 s) simulation is conducted with this model under 35 μN. It takes 3 hrs, and the thrust noise reaches 1 μN/Hz^(0.5) at 1 mHz.

关键词： Electric propulsion Microwave ion thruster Integrative model Sheath property Ion beamlet divergence Thrust noise Plasma

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Microstructure and mechanical properties of a cast TRIP-assisted multiphase stainless steel

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China Foundry 2024年第3期21卷 221-228页

作者： Meng-xin Wang Zi-xiang Wu Jing-yu He xiang Chen School of Materials Science and Engineering Tsinghua UniversityBeijing 100084China Key Laboratory for Advanced Materials Processing Technology Ministry of EducationBeijing 100084China

Stainless steels are used in a wide range of complex environments due to their excellent corrosion *** stainless steels can offer an excellent combination of strength,toughness and corrosion resistance due to the coexistence of different *** microstructure and mechanical properties of a novel cast multiphase stainless steel,composed of martensite,ferrite,and austenite,were investigated following appropriate heat treatment processes:solution treatment at 1,050℃ for 0.5 h followed by water quenching to room temperature,and aging treatment at 500℃ for 4 h followed by water quenching to room *** show reversed austenite is formed by diffusion of Ni element during aging process,and the enrichment of Ni atoms directly determines the mechanical stability of *** austenite with a lower Ni content undergoes a martensitic transformation during plastic *** tensile strength of the specimen exceeds 1,100 MPa and the elongation exceeds 24%after solid solution,and further increases to 1,247 MPa and 25%after aging *** enhancement is due to the TRIP effect of austenite and the precipitation of the nanoscale G-phase pinning dislocations in ferrite and martensite.

关键词： multiphase stainless steel mechanical properties TRIP effect reversed austenite G-phase

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Reduction of unactivated alkyl chlorides enabled by light-induced single electron transfer

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Science China Chemistry 2024年第2期67卷 471-481页

作者： Lei Dai Zhao-Fei Zhang xiang-yu Chen School of Chemical Sciences University of the Chinese Academy of SciencesBeijing100049China Institute of Chemistry Chinese Academy of SciencesBeijing100190China Binzhou Institute of Technology Weiqiao-UCAS Science and Technology ParkBinzhou256606China

Alkyl chlorides are abundant and easily accessible starting ***,due to the high reduction potentials associated with unactivated alkyl chlorides,achieving their single electron reduction remains a persistent *** challenge has spurred the exploration of efficient activation methods to overcome this *** recent years,photocatalysis has emerged as a mild and potent tool for the single electron reduction of unactivated alkyl chlorides,opening up new possibilities in this *** the rapid advancements in this area,a comprehensive review that provides a conceptual understanding of this emerging field,with a specific focus on reaction design and catalytic mechanisms,would be timely and highly ***,we present an overview of various synthetic techniques for photoinduced single electron reduction of unactivated alkyl ***,we also discuss the limitations of the present methods and future directions that lie ahead in this field.

关键词： photocatalysis unactivated alkyl chlorides single electron transfer radical reactions

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Mean field game of optimal relative investment with jump risk

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Science China Mathematics 2024年第5期67卷 1159-1188页

作者： Lijun Bo Shihua Wang xiang yu School of Mathematics and Statistics Xidian UniversityXi'an 710126China School of Mathematical Sciences University of Science and Technology of ChinaHefei 230026China Department of Applied Mathematics The Hong Kong Polytechnic UniversityHong KongChina

In this paper,we study the n-player game and the mean field game under the constant relative risk aversion relative performance on terminal wealth,in which the interaction occurs by peer *** the model with n agents,the price dynamics of underlying risky assets depend on a common noise and contagious jump risk modeled by a multi-dimensional nonlinear Hawkes *** a continuum of agents,we formulate the mean field game problem and characterize a deterministic mean field equilibrium in an analytical form under some conditions,allowing us to investigate some impacts of model parameters in the limiting model and discuss some financial ***,based on the mean field equilibrium,we construct an approximate Nash equilibrium for the n-player game when n is sufficiently *** explicit order of the approximation error is also derived.

关键词： relative performance contagious jump risk mean field game with jumps mean field equilibrium approximate Nash equilibrium

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