25 results on '"Yunfeng SHI"'
Search Results
2. Localization for Almost-Periodic Operators with Power-law Long-range Hopping: A Nash-Moser Iteration Type Reducibility Approach
- Author
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Yunfeng Shi
- Subjects
Mathematics - Spectral Theory ,Mathematics - Analysis of PDEs ,FOS: Mathematics ,FOS: Physical sciences ,Statistical and Nonlinear Physics ,Mathematical Physics (math-ph) ,Dynamical Systems (math.DS) ,Mathematics - Dynamical Systems ,Spectral Theory (math.SP) ,Mathematical Physics ,Analysis of PDEs (math.AP) - Abstract
In this paper we develop a Nash-Moser iteration type reducibility approach to prove the (inverse) localization for some $d$-dimensional discrete almost-periodic operators with power-law long-range hopping. We also provide a quantitative lower bound on the regularity of the hopping. As an application, some results of \cite{Sar82, Pos83, Cra83, BLS83} are generalized to the power-law hopping case., Comment: to appear in CMP
- Published
- 2023
3. Multigrid reduced-order topology optimization scheme for structures subjected to stationary random excitations
- Author
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Bo Wang, Haodong You, Xiangtao Ma, Yunfeng Shi, Peng Hao, and Jiaxiong Zhang
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Control and Optimization ,Control and Systems Engineering ,Computer Graphics and Computer-Aided Design ,Software ,Computer Science Applications - Published
- 2023
4. Succession of Bacteria Attached to Microplastics After Transferring from a Mariculture Area to a Seagrass Meadow
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Shuai Wang, Yunfeng Shi, Hui Wang, Zhaoyang Li, and Muqiu Zhao
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Health, Toxicology and Mutagenesis ,General Medicine ,Toxicology ,Pollution - Published
- 2023
5. Dissolution kinetics of malachite in trichloroacetic acid solution
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Yunfeng Shi, Qi Zuo, Dan Liu, and Dandan Wu
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General Chemistry - Published
- 2022
6. Absence of Eigenvalues of Analytic Quasi-Periodic Schrödinger Operators on $${\mathbb {R}}^d$$
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Yunfeng Shi
- Subjects
Physics ,FOS: Physical sciences ,Duality (optimization) ,Statistical and Nonlinear Physics ,Position and momentum space ,Mathematical Physics (math-ph) ,Dynamical Systems (math.DS) ,Lambda ,Mathematics - Spectral Theory ,Combinatorics ,symbols.namesake ,Operator (computer programming) ,Energy interval ,FOS: Mathematics ,symbols ,Mathematics - Dynamical Systems ,Quasi periodic ,Spectral Theory (math.SP) ,Mathematical Physics ,Schrödinger's cat ,Eigenvalues and eigenvectors - Abstract
In this paper we study on $L^2(\mathbb{R}^d)$ the quasi-periodic Schr\"odinger operator $H=-\Delta+ \lambda V(x),$ where $V$ is a real analytic quasi-periodic function and $\lambda>0$. We first show that $H$ has no eigenvalues in \textit{low energy region}. We also provide in \textit{low energy region} the new phase transition parameter, i.e. the competition between the strength of coupling and the length for frequencies., Comment: Comments welcome, a revised version, 22 pages
- Published
- 2021
7. Localization for a class of discrete long-range quasi-periodic operators
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Yunfeng Shi and Li Wen
- Subjects
Statistical and Nonlinear Physics ,Mathematical Physics - Published
- 2022
8. Study on advection–dispersion behavior for simulation of HTO and Se transport in crushed granite
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Weigang Liu, Neng-Chuan Tien, Rong Hua, Aiming Zhang, Chuan-Pin Lee, Haoqi Yu, Yanqin Hu, Jie Kong, Yunfeng Shi, Yudan Wang, and Liu Hesheng
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Radionuclide ,Materials science ,Health, Toxicology and Mutagenesis ,Public Health, Environmental and Occupational Health ,Radioactive waste ,Sorption ,Soil science ,Pollution ,Selenate ,Analytical Chemistry ,Volumetric flow rate ,chemistry.chemical_compound ,Nuclear Energy and Engineering ,chemistry ,Deep geological repository ,Radiology, Nuclear Medicine and imaging ,Dispersion (chemistry) ,Spectroscopy ,Retardation factor - Abstract
For the safety assessement of deep geological repository for high-level radioactive waste, radionuclides transport behavior in rock systems is necessary to clairify and establish a suitable model. The advection–dispersion experiments(ADEx) was effectively designed to inadequate transport models through a calibration/validation process, and HTO, selenate (VI) and selenite (IV) migration behavior on crushed granite was studied by a high reliable and dynamic column device to obtailned retardation factor (R) and the dispersion coeffcient (D) by fitting experimental breakthrough curves (BTCs) in a various range of flow rates. Moreover, it showed the similar results between the BTCs of HTO and Se(VI) by fitting a equlibrium model due to no retardation effect. In fact, there was a relatively obvious sorption of Se(IV) in BTCs by fitting a retardation factor (R) value higher than 1. In addition, the two sites non-equilibrium model with a lowest root mean square error were applied to realize Se(IV) sorption mechanism on granite.
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- 2021
9. Safety and immunogenicity of the SARS-CoV-2 BNT162b1 mRNA vaccine in younger and older Chinese adults: a randomized, placebo-controlled, double-blind phase 1 study
- Author
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Zhenggang Wu, Xiling Guo, Li Zhu, Siyue Jia, Ruiru Ji, Özlem Türeci, Eleni Lagkadinou, Fuzhong Peng, Rong Tang, Xiang Zhang, Ugur Sahin, Zhongkui Zhu, Aimin Hui, Zhilong Ma, Yunfeng Shi, Huayue Ye, Fengcai Zhu, Hong-Xing Pan, Alexander Muik, Mei Lin, Yumei Yang, and J Li
- Subjects
0301 basic medicine ,medicine.medical_specialty ,business.industry ,Immunogenicity ,General Medicine ,Placebo ,General Biochemistry, Genetics and Molecular Biology ,law.invention ,Clinical trial ,Vaccination ,03 medical and health sciences ,030104 developmental biology ,0302 clinical medicine ,Randomized controlled trial ,Tolerability ,law ,030220 oncology & carcinogenesis ,Internal medicine ,medicine ,Young adult ,business ,Adverse effect - Abstract
An effective vaccine is needed to end the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Here, we assess the preliminary safety, tolerability and immunogenicity data from an ongoing single-center (in Jiangsu province, China), parallel-group, double-blind phase 1 trial of the vaccine candidate BNT162b1 in 144 healthy SARS-CoV-2-naive Chinese participants. These participants are randomized 1:1:1 to receive prime and boost vaccinations of 10 µg or 30 µg BNT162b1 or placebo, given 21 d apart, with equal allocation of younger (aged 18–55 years) and older adults (aged 65–85 years) to each treatment group (ChiCTR2000034825). BNT162b1 encodes the SARS-CoV-2 spike glycoprotein receptor-binding domain (RBD) and is one of several messenger RNA-based vaccine candidates under clinical investigation. Local reactions and systemic events were generally dose dependent, transient and mild to moderate. Fever was the only grade 3 adverse event. BNT162b1 induced robust interferon-γ T cell responses to a peptide pool including the RBD in both younger and older Chinese adults, and geometric mean neutralizing titers reached 2.1-fold (for younger participants) and 1.3-fold (for the older participants) that of a panel of COVID-19 convalescent human sera obtained at least 14 d after positive SARS-CoV-2 polymerase chain reaction test. In summary, BNT162b1 has an acceptable safety profile and produces high levels of humoral and T cell responses in an Asian population. Phase 1 trial results of the messenger RNA vaccine candidate BNT162b1, which encodes the receptor-binding domain of the SARS-CoV-2 spike protein, show safety and elicitation of antibody and T cell responses in both younger and older Chinese adults.
- Published
- 2021
10. Preface to Innovations in High-Entropy Alloys and Bulk Metallic Glasses in Honor of Peter K. Liaw
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Robert Maaß, Gongyao Wang, Liang Jiang, Soo Yeol Lee, Yanfei Gao, E. Wen Huang, Michael C. Gao, Xie Xie, Yunfeng Shi, and Hahn Choo
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Structural material ,Materials science ,Amorphous metal ,Mechanics of Materials ,High entropy alloys ,Honor ,Metallurgy ,Metallic materials ,Metals and Alloys ,Condensed Matter Physics - Published
- 2021
11. Machine learning-based microstructure prediction during laser sintering of alumina
- Author
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Jianan Tang, Jianhua Tong, Xiao Geng, Dongsheng Li, Yunfeng Shi, Fei Peng, and Hai Xiao
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Materials science ,Science ,02 engineering and technology ,Machine learning ,computer.software_genre ,Article ,Techniques and instrumentation ,law.invention ,Sem micrographs ,law ,020204 information systems ,0202 electrical engineering, electronic engineering, information engineering ,Theory and computation ,Multidisciplinary ,Secondary phase ,Series (mathematics) ,business.industry ,Computational science ,Function (mathematics) ,021001 nanoscience & nanotechnology ,Microstructure ,Laser ,Selective laser sintering ,Medicine ,Artificial intelligence ,0210 nano-technology ,business ,computer - Abstract
Predicting material’s microstructure under new processing conditions is essential in advanced manufacturing and materials science. This is because the material’s microstructure hugely influences the material’s properties. We demonstrate an elegant machine learning algorithm that faithfully predicts the microstructure under new conditions, without the need of knowing the governing laws. We name this algorithm, RCWGAN-GP, which is regression-based conditional generative adversarial networks with Wasserstein loss function and gradient penalty. This algorithm was trained with experimental SEM micrographs from laser-sintered alumina under various laser powers. The RCWGAN-GP realistically regenerates the SEM micrographs under the trained laser powers. Impressively, it also faithfully predicts the alumina’s microstructure under unexplored laser powers. The predicted microstructure features, including the morphology of the sintered particles and the pores, match the experimental SEM micrographs very well. We further quantitatively examined the prediction accuracy of the RCWGAN-GP. We trained the algorithm with computer-created micrograph datasets of secondary-phase growth governed by the well-known Johnson–Mehl–Avrami (JMA) equation. The RCWGAN-GP accurately regenerates the micrographs at the trained time series, in terms of the grains’ shapes, sizes, and spatial distributions. More importantly, the predicted secondary phase fraction accurately follows the JMA curve.
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- 2021
12. Single asperity friction in the wear regime
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Yongjian Yang and Yunfeng Shi
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single-asperity contact ,Materials science ,lcsh:Mechanical engineering and machinery ,friction ,Computer Science::Human-Computer Interaction ,02 engineering and technology ,Plasticity ,01 natural sciences ,Stress (mechanics) ,Computer Science::Hardware Architecture ,0103 physical sciences ,medicine ,Coupling (piping) ,lcsh:TJ1-1570 ,Attrition ,Composite material ,010306 general physics ,atomic wear ,Mechanical Engineering ,Adhesion ,021001 nanoscience & nanotechnology ,medicine.disease ,molecular dynamics ,Surfaces, Coatings and Films ,plastic wear ,Contact mechanics ,Lubrication ,0210 nano-technology ,Asperity (materials science) - Abstract
We used molecular dynamics simulation to investigate the friction of a single asperity against a rigid substrate, while generating debris. In the low wear regime (i.e., non-linear wear rate dependence on the contact stress, via atom-by-atom attrition), the frictional stress is linearly dependent on the normal stress, without any lubrication effect from the wear debris particles. Both the slope (friction coefficient) and friction at zero normal stress depend strongly on asperity-substrate adhesion. In the high wear regime (i.e., linear wear rate dependence on the contact stress, via plastic flow), the friction-normal stress curves deviate from a linear relation merging toward plastic flow of the single asperity which is independent of the interfacial adhesion. One can further link wear and friction by considering debris generation as chemical reaction, driven by both normal and frictional forces. The coupling between wear and friction can then be quantified by a thermodynamic efficiency of the debris generation. While the efficiency is less than 5% in the low wear regime, indicating poor mechanochemical coupling, it increases with normal stress toward 50% in the high wear regime.
- Published
- 2018
13. Exponential Decay of the Lengths of the Spectral Gaps for the Extended Harper’s Model with a Liouvillean Frequency
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Xiaoping Yuan and Yunfeng Shi
- Subjects
010101 applied mathematics ,Partial differential equation ,Exponential growth ,Ordinary differential equation ,010102 general mathematics ,Statistical physics ,0101 mathematics ,Exponential decay ,01 natural sciences ,Analysis ,Mathematics - Abstract
In this paper, we study the non-self dual extended Harper’s model with a Liouvillean frequency. By establishing quantitative reducibility results together with the averaging method, we prove that the lengths of the spectral gaps decay exponentially.
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- 2018
14. The local stress state of a running shear band in amorphous solids
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Jian Luo and Yunfeng Shi
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Materials science ,Amorphous metal ,Mechanical Engineering ,Condensed Matter Physics ,Condensed Matter::Disordered Systems and Neural Networks ,Amorphous solid ,law.invention ,Physics::Fluid Dynamics ,Condensed Matter::Soft Condensed Matter ,Stress (mechanics) ,Molecular dynamics ,Mechanics of Materials ,law ,Shear stress ,Forensic engineering ,General Materials Science ,Hydrostatic equilibrium ,Composite material ,Shear band - Abstract
In molecular dynamics simulations, the local stress state in the shear band is examined in six different model metallic glasses and one amorphous Si system (also has been perceived as a metallic glass analog) under different loading conditions. For all but the FeP and the amorphous Si systems, the running shear band (RSB) exhibits a liquid-like hydrostatic plus shear stress state. Our results suggest that the liquid feature of a RSB is not due to temperature rise or plastic confinement but due to the disorder driven by flow, which can be offset by strong directionality in bonding, phase segregation, or aging. The knowledge of the liquid-like stress state can be conveniently utilized in experiments to infer the local stress state of the RSB from the global tensile stress for metallic glasses.
- Published
- 2015
15. STAT1 Regulates MD-2 Expression in Monocytes of Sepsis via miR-30a
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Benquan Wu, Ding-Yun Feng, Jinmei Luo, Yunfeng Shi, Tie-Hua Li, Hui Liu, and Yan-Hong Wang
- Subjects
Lipopolysaccharide ,medicine.medical_treatment ,Immunology ,Lymphocyte Antigen 96 ,Inflammation ,Biology ,Monocytes ,Cell Line ,Sepsis ,Interferon-gamma ,chemistry.chemical_compound ,medicine ,Humans ,Immunology and Allergy ,STAT1 ,Interleukin-6 ,Critically ill ,medicine.disease ,Blot ,MicroRNAs ,STAT1 Transcription Factor ,Cytokine ,Gene Expression Regulation ,chemistry ,biology.protein ,Interleukin 19 ,medicine.symptom - Abstract
Sepsis is a major cause of morbidity and mortality in critically ill patients. MD-2 is a 25-kDa lipopolysaccharide (LPS)-binding protein that forms a heterodimer with TLR42, but its regulation in sepsis is not clear. This study aims to investigate the molecular mechanism of regulation of MD-2. Inflammation cytokines in monocytes were analyzed by real-time RT-PCR and ELISA, and it was found that IL-10 was elevated significantly in the monocytes with LPS treatment. And then, when the cells were treated with IL-10, STAT1 was activated in the monocytes using Western blotting. It was also found that STAT1 could enhance MD-2 expression on transcriptional and posttranscriptional levels. Finally, miR-30a was predicted to the molecule that may regulate STAT1 expression. It was verified that STAT1 was a new target gene of miR-30a. miR-30a could inhibit IL-10-induced cytokine release by targeting STAT1-MD-2 in monocytes. In conclusion, this study for the first time demonstrated that miR-30a inhibits MD-2 expression by targeting of STAT1 in human monocytes.
- Published
- 2014
16. Photoluminescence-enhanced CdTe quantum dots by hyperbranched poly(amidoamine)s functionalization
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Xiaoyin Zhang, Gangsheng Tong, Zongyao Wang, Sujuan Li, Xuemin Zu, Fang Guo, Yunfeng Shi, Junjie Wang, and Xiuxiu Zang
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Nanocomposite ,Materials science ,Photoluminescence ,Polymer nanocomposite ,Mechanical Engineering ,Quantum yield ,Nanotechnology ,Poly(amidoamine) ,Condensed Matter Physics ,Polymerization ,Mechanics of Materials ,Quantum dot ,Surface modification ,General Materials Science - Abstract
A new strategy using hyperbranched poly(amidoamine)s to functionalize CdTe quantum dots (QDs) has been described. Hyperbranched poly(amidoamine)s with amine terminals (HP-EDAMA1) were synthesized by one-pot polymerization via the coupled-monomer method and subsequently used to functionalize preformed CdTe QDs. Quite different from previous studies in which the photoluminescence of QDs was quenched by further functionalization with tailored ligands, the quantum yield of CdTe/HP-EDAMA1 nanocomposites was 2 times that of pure CdTe QDs without modification. With this versatile method, the photoluminescence quenching of QDs in the modification process by matrix materials can be effectively solved and new QDs/hyperbranched polymer nanocomposites with potential applications in biomedicine might be offered.
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- 2013
17. Additive Results of the Drazin Inverse for Bounded Linear Operators
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Junjie Huang, Yunfeng Shi, and Alatancang Chen
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Discrete mathematics ,Computational Mathematics ,Computational Theory and Mathematics ,Applied Mathematics ,Bounded function ,Linear algebra ,Drazin inverse ,Linear operators ,Banach space ,Operator theory ,Mathematics - Abstract
Given two bounded linear operators $$P$$ and $$Q$$ on a Banach space the formula for the Drazin inverse of $$P+Q$$ is given, under the assumptions $$P^2 Q+PQ^2=0$$ and $$P^3 Q=PQ^3=0$$ . In particular, some recent results arising in Drazin (Am Math Mon 65:506–514, 1958), Hartwig et al. (Linear Algebra Appl 322:207–217, 2001) and Castro-Gonzalez et al. (J Math Anal Appl 350:207–215, 2009) are extended.
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- 2013
18. Inhibitory effects of simvastatin on staphylococcus aureus lipoteichoic acid-induced inflammation in human alveolar macrophages
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Benquan Wu, Yan-Hong Wang, Yunfeng Shi, Jinmei Luo, Hui Liu, Tian-tuo Zhang, and Jun-Hui Ba
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Lipopolysaccharides ,Simvastatin ,Staphylococcus aureus ,Anti-Inflammatory Agents ,Inflammation ,Biology ,medicine.disease_cause ,Systemic inflammation ,General Biochemistry, Genetics and Molecular Biology ,Microbiology ,Sepsis ,Macrophages, Alveolar ,medicine ,Humans ,Cells, Cultured ,Gene Expression Profiling ,General Medicine ,medicine.disease ,Teichoic Acids ,Apoptosis ,Cytokines ,lipids (amino acids, peptides, and proteins) ,Tumor necrosis factor alpha ,Lipoteichoic acid ,medicine.symptom ,medicine.drug - Abstract
Staphylococcus aureus (S. aureus) is the most common bacterium in sepsis and pneumonia involving gram-positive bacteria. Lipoteichoic acid (LTA) is a cell wall component of gram-positive bacteria. It is a potent inducer of inflammatory mediators in human dendritic cells, human pulmonary epithelial cells, and murine macrophages. However, the effect of LTA on human alveolar macrophages (AMs) which are the major effector cells in host defense against respiratory tract infections has hardly been studied. Statins have anti-inflammatory, immunomodulatory, antioxidative, anticoagulant, and antibacterial activities. These effects may be contributed to reduce the markers of systemic inflammation. Emerging retrospective studies have demonstrated that statin use decreased the mortality of pneumonia. However, the precise mechanisms responsible for these effects are unclear. The purpose of this study is to define the role of S. aureus LTA in human AMs and the effects of simvastatin (SV) on LTA-stimulated human AMs. The results showed that LTA induced tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), IL-8 mRNA expression, and suppressed IL-10 mRNA expression in human AMs. Simultaneously, LTA induced human AMs apoptosis. These effects were parallel with the up-regulation of the expression of NF-κB-P65 protein in the LTA-stimulated human AMs. The above effects of LTA on human AMs were inhibited significantly by SV. These data indicate that S. aureus LTA induces potent pro-inflammatory and pro-apoptotic effects on human AMs and statins exert anti-inflammatory effects by mediating inhibition of NF-κB activation and cytokine mRNA expression in human AMs. These results may explain, in part, the mechanisms responsible for favorable effects of statins on pneumonia.
- Published
- 2013
19. Facile preparation of highly luminescent CdTe quantum dots within hyperbranched poly(amidoamine)s and their application in bio-imaging
- Author
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Guanqing Zhang, Jimin Du, Huan Pang, Wangchuan Xiao, Xiaoyin Zhang, Lin Liu, Yunfeng Shi, Yangyan Ou, and Hongli Zhou
- Subjects
Nanocomposite ,Materials science ,Nano Express ,Biocompatibility ,Bio-imaging ,Quantum yield ,Nanochemistry ,Nanotechnology ,CdTe quantum dots ,Poly(amidoamine) ,Condensed Matter Physics ,Fluorescence ,Cadmium telluride photovoltaics ,Hyperbranched poly(amidoamine)s ,Nanocomposites ,Materials Science(all) ,Quantum dot ,General Materials Science ,Luminescence - Abstract
A new strategy for facile preparation of highly luminescent CdTe quantum dots (QDs) within amine-terminated hyperbranched poly(amidoamine)s (HPAMAM) was proposed in this paper. CdTe precursors were first prepared by adding NaHTe to aqueous Cd2+ chelated by 3-mercaptopropionic sodium (MPA-Na), and then HPAMAM was introduced to stabilize the CdTe precursors. After microwave irradiation, highly fluorescent and stable CdTe QDs stabilized by MPA-Na and HPAMAM were obtained. The CdTe QDs showed a high quantum yield (QY) up to 58%. By preparing CdTe QDs within HPAMAM, the biocompatibility properties of HPAMAM and the optical, electrical properties of CdTe QDs can be combined, endowing the CdTe QDs with biocompatibility. The resulting CdTe QDs can be directly used in biomedical fields, and their potential application in bio-imaging was investigated.
- Published
- 2014
20. The Effects of Annealing on Fatigue Behavior in Zr-based Bulk Metallic Glasses
- Author
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Anna Llobet, Yunfeng Shi, Peng Tong, Rick Spence, Graham King, Gongyao Wang, Peter K. Liaw, Yoshihiko Yokoyama, and Despina Louca
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Amorphous metal ,Materials science ,law ,Annealing (metallurgy) ,Neutron diffraction ,Fatigue loading ,Metallurgy ,Composite material ,Neutron scattering ,Temperature measurement ,Synchrotron ,Amorphous solid ,law.invention - Abstract
The effects of annealing and fatigue on the local structure of Zr50Cu40Al10 and Zr60Cu30Al10 bulk metallic glasses (BMG) were investigated using the pair density function (PDF) analysis of synchrotron X-ray and neutron diffraction data. Our results indicate that the two compositions respond differently to annealing. The first PDF peak becomes sharper after annealing in Zr50Cu40Al10 with its intensity increasing, indicating that short-range ordering may be induced after the heat treatment. On the other hand, in Zr60Cu30Al10, the effects due to the heat treatment on the local structure are more subtle. Separately, the as-quenched and annealed alloys with the composition Zr50Cu40Al10 were subjected to fatigue loading conditions with ~ 106 compression cycles. The room temperature measurements showed changes in the local structure with fatigue especially for the annealed sample, involving the Cu-Zr correlations. Our results suggest that the physical properties of BMGs upon fatigue loading conditions may become accentuated due to the structural relaxation brought upon by annealing, leading to observable structural changes at the atomic level from fatigue.
- Published
- 2011
21. Elastic Properties of Mimetically Synthesized Model Nanoporous Carbon
- Author
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Xi Mi and Yunfeng Shi
- Subjects
Bulk modulus ,Materials science ,Graphene ,Diffusion ,Modulus ,law.invention ,Shear modulus ,Molecular dynamics ,Adsorption ,law ,medicine ,Composite material ,Activated carbon ,medicine.drug - Abstract
Activated carbon is widely used for its attractive diffusion, adsorption and reaction properties. However, its mechanical behavior has received much less attention. We present a molecular dynamics simulation study on the elastic properties of activated carbon with nanometer-sized pores. The nanoporous carbon sample is composed of curved and defected graphene sheets, which is synthesized using quench molecular dynamics (QMD) method [1]. One unique feature of the current model is the mechanical stability, thus the bulk modulus, Young’s modulus, shear modulus and Poisson’s ratio can be obtained from simulated mechanical tests. By varying the density of the nanoporous carbon model, it was further found that the bulk modulus vs. density relation follows Gibson-Ashby type power law with exponents of 2.80 at low densities and 1.65 at high densities.
- Published
- 2009
22. Molecular Dynamics Simulations of the Mechanical Response of Metallic glass/BCC Nanocomposite Materials
- Author
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Michael L. Falk and Yunfeng Shi
- Subjects
Materials science ,Nanocomposite ,Amorphous metal ,Fracture toughness ,Strain hardening exponent ,Composite material ,Ductility ,Shear band ,Stress concentration ,Amorphous solid - Abstract
This is a copy of the slides presented at the meeting but not formally written up for the volume. Bulk metallic glass (BMG) has been of intense interest recently because of its unique combination of excellent mechanical properties including high strength. One of the major drawbacks of monolithic BMG materials is the limited ductility due to strain localization. Except a few recent reports on monolithic ductile BMG, the most popular method to enhance the ductility of the BMG samples is to introduce a crystalline or quasicrystalline phase by precipitation or mixing. The composite material usually exhibits some degree of strain hardening along with significantly higher impact resistance and fracture toughness. However, the mechanism of this strain hardening is not well understood. We present simulated uniaxial compression tests on a monatomic model amorphous system embedded with body-center cubic (BCC) nanocrystals. The advantage of this model system is that intimate amorphous-crystal interfaces can be obtained. We observe that when comparing to monolithic glassy samples where a single shear band normally dominates, multiple shear bands appear in the BCC-amorphous composite samples. The plastic deformation initiates at the interfaces between nanocrystals and the glassy phase due to stress concentration. Furthermore, we demonstrate that shear along the bands results in growth of the nanocrystals.
- Published
- 2006
23. Atomic-scale simulations of strain localization in a single-component three-dimensional model amorphous solid
- Author
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Michael L. Falk and Yunfeng Shi
- Subjects
Quenching ,Molecular dynamics ,Materials science ,Nanostructure ,Shear (geology) ,Single component ,Molecular physics ,Atomic units ,Amorphous solid ,Three dimensional model - Abstract
Molecular dynamics is used to simulate model non-crystalline solids described by a single-component Dzugutov system. The solids are produced by quenching equilibrium liquids at different cooling rates. These are then tested in uniaxial compression. Samples produced at high cooling rates exhibit homogenous deformation while samples quenched at low cooling rates exhibit localized deformation. Shear bands are shown to correspond to regions of depleted short-range order as determined by a Frank-Kasper criterion.
- Published
- 2005
24. Nanocluster Epitaxy by Annealing: Ag on H-terminated Si (111) Surfaces
- Author
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J. K. Bording, Jian-Min Zuo, Boquan Li, and Yunfeng Shi
- Subjects
Crystallography ,Materials science ,Annealing (metallurgy) ,Crystallite ,Epitaxy ,Surface energy ,Nanoclusters - Abstract
We report an experimental investigation on the morphology and orientation of Ag nanoclusters by RT deposition and subsequent annealing. We show that epitaxial Ag clusters of 2 ∼ 6 nm in diameter can be synthesized in this way. The RT self-assembled Ag clusters grow as mostly single-crystal crystallites with Ag(111)//Si(111), but the in-plane orientation has a dispersion of ∼ 9° centering at Si[110] direction. Upon annealing, the Ag clusters drastically rotated to the epitaxial configuration with the in-plane orientation aligned to the Ag[110] //Si[110] direction. The rotation and epitaxy of the Ag nanoclusters are explained based on a coincident site lattice model and interface energy minimization.
- Published
- 2002
25. Strain Localization in a Molecular-Dynamics Model of a Metallic Glass
- Author
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Michael L. Falk and Yunfeng Shi
- Subjects
Length scale ,Molecular dynamics ,Amorphous metal ,Materials science ,Condensed matter physics ,Shear (geology) ,Cavitation ,Slip (materials science) ,Shear band ,Amorphous solid - Abstract
Molecular dynamics simulations of a two-dimensional amorphous solid exhibit strain localization when loaded in uniaxial tension with free boundaries. The degree of localization depends sensitively on the rate of loading and on the existence of surface defects. Regions of both dilation and contraction arise during the shear band slip process. These dilation and contraction events correspond to dynamic free-volume generation and annihilation during shear. Correlations of the dilation and contraction of the material reveal a length scale of 1–4 atomic diameters associated with this physical process. Dilation is observed to result in nanometer scale cavitation.
- Published
- 2002
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