26 results on '"Qianping He"'
Search Results
2. Fast Method for Estimating Stain Density in Electron Microscopy of Conventionally Prepared Biological Specimens
- Author
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Guofeng Zhang, Andrea Fera, Qianping He, and Richard D. Leapman
- Subjects
Biological specimen ,Materials science ,law ,Electron microscope ,Instrumentation ,Stain ,Nuclear chemistry ,law.invention - Published
- 2021
3. Imbalanced dataset-based echo state networks for anomaly detection
- Author
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Anguo Zhang, Qianping He, Tingwen Huang, Yongduan Song, and Qing Chen
- Subjects
0209 industrial biotechnology ,Artificial neural network ,Computer science ,business.industry ,Anomaly (natural sciences) ,Echo (computing) ,Pattern recognition ,02 engineering and technology ,Function (mathematics) ,Information theory ,Field (computer science) ,020901 industrial engineering & automation ,Artificial Intelligence ,0202 electrical engineering, electronic engineering, information engineering ,020201 artificial intelligence & image processing ,Anomaly detection ,Artificial intelligence ,Echo state network ,business ,Software - Abstract
Anomaly detection is a very effective method to extract useful information from abundant data. Most existing anomaly detection methods are based on normal region or some specific algorithms, which ignore the fact that many actual datasets are mainly imbalanced, resulting in not function properly or effectively in practical, especially in the medical field. On the other hand, imbalanced dataset is also a frequently encountered problem in the learning of neural network because the lack of data in a minority class may lead to uneven classification accuracy. In this paper, inspired by these observations, a novel anomaly detection approach by using classical echo state network (ESN), a brain-inspired neural computing model, is presented. The entire dataset of the proposed method obeys an extremely imbalanced distribution, that is, anomalies are much rarer than normal data. And the training dataset has only the normal data. When the ESN is well trained, the parameters in ESN are the memory of normal data. If the normal data are added into the well-trained network, the error between the input data and the corresponding output is smaller compared with the error between abnormal input data and its corresponding output. Then anomaly behavior is detected if the error between the input data and the corresponding predictive value exceeds a certain threshold. Different from setting an invariable threshold arbitrarily for all of the data, the threshold value used in the proposed method is determined from the analysis of information theory and can be adjust adaptively according to different datasets. Experiments on abnormal heart rate detection are conducted to demonstrate and verify the effectiveness of the proposed detection algorithm and theory.
- Published
- 2018
4. Quantitative method for estimating stain density in electron microscopy of conventionally prepared biological specimens
- Author
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Qianping He, Guofeng Zhang, Andrea Fera, and Richard D. Leapman
- Subjects
Blood Platelets ,Histology ,Materials science ,Scanning electron microscope ,Analytical chemistry ,02 engineering and technology ,Focused ion beam ,Stain ,Article ,Pathology and Forensic Medicine ,law.invention ,Mice ,03 medical and health sciences ,Biological specimen ,Microscopy, Electron, Transmission ,law ,Microtome ,Animals ,Humans ,Coloring Agents ,030304 developmental biology ,Brain Chemistry ,0303 health sciences ,Histocytological Preparation Techniques ,Staining and Labeling ,Brain ,Microtomy ,021001 nanoscience & nanotechnology ,Liver ,Electron tomography ,Transmission electron microscopy ,Ultrastructure ,Electron microscope ,0210 nano-technology - Abstract
SummaryStain density is an important parameter for optimizing the quality of ultrastructural data obtained from several types of 3D electron microscopy techniques, including serial block-face electron microscopy (SBEM), and focused ion beam scanning electron microscopy (FIB-SEM). Here, we show how some straightforward measurements in the TEM can be used to determine the stain density based on a simple expression that we derive. Numbers of stain atoms per unit volume are determined from the measured ratio of the bright-field intensities from regions of the specimen that contain both pure embedding material and the embedded biological structures of interest. The determination only requires knowledge of the section thickness, which can either be estimated from the microtome setting, or from low-dose electron tomography, and the elastic scattering cross section for the heavy atoms used to stain the specimen. The method is tested on specimens of embedded blood platelets, brain tissue, and liver tissue.
- Published
- 2019
5. Optimizing Specimen Thickness by Measuring Stain Density in STEM Tomography of Cells and Tissues
- Author
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Guofeng Zhang, Richard D. Leapman, and Qianping He
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Materials science ,STEM Tomography ,Instrumentation ,Stain ,Biomedical engineering - Published
- 2020
6. STEM tomography reveals that the canalicular system and α‐granules remain separate compartments during early secretion stages in blood platelets
- Author
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Jeffrey A. Kamykowski, Jake D. Hoyne, Qianping He, Bryan C. Kuo, Andrew A. Prince, Gina N. Calco, Maria A. Aronova, Irina D. Pokrovskaya, Brian Storrie, and Richard D. Leapman
- Subjects
Blood Platelets ,Microscopy, Electron, Scanning Transmission ,0301 basic medicine ,Time Factors ,Tissue Fixation ,Population ,Biology ,Cytoplasmic Granules ,Membrane Fusion ,Article ,03 medical and health sciences ,Native state ,Humans ,Secretion ,Platelet ,Platelet activation ,education ,education.field_of_study ,Secretory Vesicles ,Cell Membrane ,Cryoelectron Microscopy ,Granule (cell biology) ,Intracellular Membranes ,Hematology ,Platelet Activation ,030104 developmental biology ,Membrane ,Biochemistry ,Hemostasis ,Biophysics - Abstract
UNLABELLED ESSENTIALS: How platelets organize their α-granule cargo and use their canalicular system remains controversial. Past structural studies were limited due to small sampling volumes or decreased resolution. Our analyses revealed homogeneous granules and a closed canalicular system that opened on activation. Understanding how platelets alter their membranes during activation and secretion elucidates hemostasis. SUMMARY BACKGROUND Platelets survey the vasculature for damage and, in response, activate and release a wide range of proteins from their α-granules. Alpha-granules may be biochemically and structurally heterogeneous; however, other studies suggest that they may be more homogeneous with the observed variation reflecting granule dynamics rather than fundamental differences. OBJECTIVES Our aim was to address how the structural organization of α-granules supports their dynamics. METHODS To preserve the native state, we prepared platelets by high-pressure freezing and freeze-substitution; and to image nearly entire cells, we recorded tomographic data in the scanning transmission electron microscope (STEM). RESULTS AND CONCLUSIONS In resting platelets, we observed a morphologically homogeneous α-granule population that displayed little variation in overall matrix electron density in freeze-substituted preparations (i.e., macro-homogeneity). In resting platelets, the incidence of tubular granule extensions was low, ~4%, but this increased by > 10-fold during early steps in platelet secretion. Using STEM, we observed that the initially decondensing α-granules and the canalicular system remained as separate membrane domains. Decondensing α-granules were found to fuse heterotypically with the plasma membrane via long, tubular connections or homotypically with each other. The frequency of canalicular system fusion with the plasma membrane also increased by about three-fold. Our results validate the utility of freeze-substitution and STEM tomography for characterizing platelet granule secretion and suggest a model in which fusion of platelet α-granules with the plasma membrane occurs via long tubular connections that may provide a spatially limited access route for the timed release of α-granule proteins.
- Published
- 2016
7. Comparison of Techniques for Fine Alignment of Image Stacks in Serial Block-Face Electron Microscopy
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Guofeng Zhang, Qianping He, R. D. Leapman, and M. Guay
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Optics ,Materials science ,law ,business.industry ,Block face ,Electron microscope ,business ,Instrumentation ,law.invention ,Image (mathematics) - Published
- 2019
8. Comparison of 3D cellular imaging techniques based on scanned electron probes: Serial block face SEM vs. Axial bright-field STEM tomography
- Author
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Jake D. Hoyne, Andrew A. Prince, Amith Rao, Irina D. Pokrovskaya, Alioscka A. Sousa, Maria A. Aronova, E.L. McBride, Qianping He, Guofeng Zhang, Gina N. Calco, Brian Storrie, Richard D. Leapman, and B.C. Kuo
- Subjects
0301 basic medicine ,Serial block-face scanning electron microscopy ,Blood Platelets ,Microscopy, Electron, Scanning Transmission ,Electron Microscope Tomography ,Materials science ,Cellular architecture ,Image processing ,Signal ,Article ,03 medical and health sciences ,030104 developmental biology ,Imaging, Three-Dimensional ,Electron tomography ,Structural Biology ,Scanning transmission electron microscopy ,Ultrastructure ,Image Processing, Computer-Assisted ,Humans ,Tomography ,Biomedical engineering - Abstract
Microscopies based on focused electron probes allow the cell biologist to image the 3D ultrastructure of eukaryotic cells and tissues extending over large volumes, thus providing new insight into the relationship between cellular architecture and function of organelles. Here we compare two such techniques: electron tomography in conjunction with axial bright-field scanning transmission electron microscopy (BF-STEM), and serial block face scanning electron microscopy (SBF-SEM). The advantages and limitations of each technique are illustrated by their application to determining the 3D ultrastructure of human blood platelets, by considering specimen geometry, specimen preparation, beam damage and image processing methods. Many features of the complex membranes composing the platelet organelles can be determined from both approaches, although STEM tomography offers a higher ∼3 nm isotropic pixel size, compared with ∼5 nm for SBF-SEM in the plane of the block face and ∼30 nm in the perpendicular direction. In this regard, we demonstrate that STEM tomography is advantageous for visualizing the platelet canalicular system, which consists of an interconnected network of narrow (∼50–100 nm) membranous cisternae. In contrast, SBF-SEM enables visualization of complete platelets, each of which extends ∼2 µm in minimum dimension, whereas BF-STEM tomography can typically only visualize approximately half of the platelet volume due to a rapid non-linear loss of signal in specimens of thickness greater than ∼1.5 µm. We also show that the limitations of each approach can be ameliorated by combining 3D and 2D measurements using a stereological approach.
- Published
- 2017
9. Improved Z-axis Resolution in Serial Block Face SEM with Dual Primary Energies and Monte Carlo Simulation of Electron Scattering
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Qianping He, D. C. Joy, Guofeng Zhang, and R. D. Leapman
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010302 applied physics ,Materials science ,Monte Carlo method ,Resolution (electron density) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Computational physics ,Dual (category theory) ,law.invention ,law ,0103 physical sciences ,Block face ,Cartesian coordinate system ,0210 nano-technology ,Instrumentation ,Electron scattering - Published
- 2018
10. Dual-Energy Serial Block Face SEM Imaging of Biological Structures at Near Isotropic Spatial Resolution
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Qianping He, David C. Joy, Richard D. Leapman, and Guofeng Zhang
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Materials science ,Optics ,Dual energy ,business.industry ,Isotropy ,Biophysics ,Block face ,business ,Image resolution - Published
- 2018
11. Improved Visualization of Structure at the Nano-Scale in Entire Eukaryotic Cells by Fine Alignment of Serial Block Face Sem Image Stacks
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Richard D. Leapman, Matthew D. Guay, Qianping He, and Guofeng Zhang
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Materials science ,business.industry ,Biophysics ,Block face ,Computer vision ,Artificial intelligence ,business ,Nanoscopic scale ,Visualization ,Image (mathematics) - Published
- 2019
12. Structure of the Ionomer Film in Catalyst Layers of Proton Exchange Membrane Fuel Cells
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David C. Joy, Qianping He, David J. Keffer, and Nethika S. Suraweera
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chemistry.chemical_classification ,Materials science ,Proton exchange membrane fuel cell ,chemistry.chemical_element ,Polymer ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,chemistry.chemical_compound ,General Energy ,Membrane ,chemistry ,Chemical engineering ,Proton transport ,Physical and Theoretical Chemistry ,Carbon ,Ionomer ,Layer (electronics) - Abstract
The nanoscale structure of the ionomer film located in the catalyst layer of polymer exchange membrane fuel cells (PEMFCs) is of vital importance to proton transport and catalyst utilization. Classical molecular dynamic simulations are conducted to explore the molecular-level structure as well as the structure–property relationships in the ionomer film. Twenty-four systems are simulated to investigate the effect of (i) hydration, (ii) ionomer film thickness, (iii) oxidation of the carbon support surface, and (iv) the presence of catalyst nanoparticles on film adhesion and morphology. The ionomer does not form a continuous film on the carbon surface; rather, the ionomer forms irregular patches through which proton transport from the catalyst to the membrane must occur. These ionomer films are not able to retain water to the same extent as bulk ionomer membranes. However, thicker films retain proportionally more water than thinner films, allowing for a larger and better connected aqueous domain required for...
- Published
- 2013
13. Nanoparticle adhesion in proton exchange membrane fuel cell electrodes
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Qianping He, David J. Keffer, and David C. Joy
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Materials science ,Renewable Energy, Sustainability and the Environment ,Inorganic chemistry ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Nanoparticle ,Proton exchange membrane fuel cell ,Adhesion ,Electrochemistry ,Catalysis ,chemistry.chemical_compound ,chemistry ,Nafion ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry ,Platinum ,Carbon - Abstract
Carbon supported platinum (Pt/C) catalyst remains among the most preferable catalyst materials for Proton Exchange Membrane (PEM) fuel cells. However, platinum (Pt) particles suffer from poor durability and encounter electrochemical surface area (ESA) loss under operation with the accompany of Pt nanoparticle coarsening. Several proposed mechanisms have involved the Pt detachment from its carbonate support as an initial step for the deactivation of Pt nanoparticles. In this study, we investigated the detachment mechanism from the nano-adhesion point of view. Classic molecular dynamics simulations are performed on systems contain Pt nanoparticles of different sizes and shapes. A thin Nafion film (1 nm) at different hydration levels is also included in the system to study the environmental effect on nanoparticle adhesion. We found that the adhesion force strengthens as the Pt size goes up. Pt nanoparticles of tetrahedral shape exhibit relatively stronger connection with the carbon substrate due to its unique ‘anchor-like’ structure. Adhesion is enhanced with the introduction of a Nafion. The humidity level in the Nafion film has a rather complicated effect on the strength of nanoparticle adhesion. The binding energies and maximum adhesive forces are reported for all systems studied.
- Published
- 2013
14. Electron beam induced radiation damage in the catalyst layer of a proton exchange membrane fuel cell
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David J. Keffer, David C. Joy, Jihua Chen, and Qianping He
- Subjects
Scanning electron microscope ,Chemistry ,Analytical chemistry ,Proton exchange membrane fuel cell ,Microstructure ,Platinum nanoparticles ,Atomic and Molecular Physics, and Optics ,Characterization (materials science) ,law.invention ,law ,Radiation damage ,Cathode ray ,Composite material ,Electron microscope ,Instrumentation - Abstract
Summary Electron microscopy is an essential tool for the evaluation of microstructure and properties of the catalyst layer (CL) of proton exchange membrane fuel cells (PEMFCs). However, electron microscopy has one unavoidable drawback, which is radiation damage. Samples suffer temporary or permanent change of the surface or bulk structure under radiation damage, which can cause ambiguity in the characterization of the sample. To better understand the mechanism of radiation damage of CL samples and to be able to separate the morphological features intrinsic to the material from the consequences of electron radiation damage, a series of experiments based on high-angle annular dark-field–scanning transmission scanning microscope (HAADF-STEM), energy filtering transmission scanning microscope (EFTEM), and electron energy loss spectrum (EELS) are conducted. It is observed that for thin samples (0.3–1 times λ), increasing the incident beam energy can mitigate the radiation damage. Platinum nanoparticles in the CL sample facilitate the radiation damage. The radiation damage of the catalyst sample starts from the interface of Pt/C or defective thin edge and primarily occurs in the form of mass loss accompanied by atomic displacement and edge curl. These results provide important insights on the mechanism of CL radiation damage. Possible strategies of mitigating the radiation damage are provided. SCANNING 36:338–346, 2014. © 2013 Wiley Periodicals, Inc.
- Published
- 2013
15. Molecular Dynamic Simulations of the Effect on the Hydration of Nafion in the Presence of a Platinum Nanoparticle
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Qianping He, David J. Keffer, Elisa M. Calvo-Muñoz, and Myvizhi Esai Selvan
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chemistry.chemical_classification ,Hydronium ,Chemistry ,Inorganic chemistry ,chemistry.chemical_element ,Electrolyte ,Sulfonic acid ,Platinum nanoparticles ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,chemistry.chemical_compound ,General Energy ,Nafion ,Molecule ,Physical and Theoretical Chemistry ,Platinum - Abstract
Platinum catalysts play a critical role in fuel cell technology. Current optimization efforts focus on reducing the amount of Pt in the system and optimizing the utilization of that which remains. The effect of the presence of Pt nanoparticles on the local structure and morphology of the polymer electrolyte membrane, water, and hydronium ions has been studied at molecular level in this work. Classical molecular dynamics simulation has been used to examine a system containing a 4 nm fcc cubic ({100} face) platinum nanoparticle at the center surrounded by Nafion polymer, water molecules, and hydronium ions at λ = 3, 6, 9, 15, and 22. The changes in density and orientation distribution of sulfonic acid groups in the side-chains, water, and hydronium as a function of distance from platinum surface are analyzed in this study. Sulfonic acid groups and hydronium ions show a very high increase in density near the platinum surface, and they approach the bulk value as they move away from the platinum surface. At lo...
- Published
- 2012
16. Comparison of 3-D Cellular Imaging Techniques using Scanned Electron Probes
- Author
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Maria A. Aronova, Matthew D. Guay, Amith Rao, Brian Storrie, Qianping He, Irina D. Pokrovskaya, E.L. McBride, Richard D. Leapman, and Guofeng Zhang
- Subjects
0301 basic medicine ,03 medical and health sciences ,030104 developmental biology ,Materials science ,Cellular imaging ,Electron ,Instrumentation ,Biomedical engineering - Published
- 2017
17. Sub-Surface Serial Block Face SEM of Biological Structures at Near Isotropic Spatial Resolution
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Guofeng Zhang, David C. Joy, Richard D. Leapman, and Qianping He
- Subjects
0301 basic medicine ,Surface (mathematics) ,03 medical and health sciences ,Crystallography ,030104 developmental biology ,Materials science ,Isotropy ,Biophysics ,Block face ,Geometry ,Image resolution - Published
- 2017
18. Scanning Transmission Electron Tomography of Blood Platelets in Thick Sections
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Brian Storrie, Alioscka A. Sousa, Maria A. Aronova, Andrew A. Prince, Irina D. Pokrovskaya, Gina N. Calco, Bryan C. Kuo, Qianping He, Guofeng Zhang, Jake D. Hoyne, Laura J. MacDonald, and Richard D. Leapman
- Subjects
0303 health sciences ,Materials science ,business.industry ,Biophysics ,law.invention ,03 medical and health sciences ,0302 clinical medicine ,Optics ,Electron tomography ,law ,Scanning transmission electron microscopy ,Micrometer ,Chromatic aberration ,Medical imaging ,Ultrastructure ,sense organs ,Platelet activation ,Tomography ,business ,030217 neurology & neurosurgery ,030304 developmental biology ,Biomedical engineering - Abstract
Electron tomography in the scanning transmission electron microscope (STEM) can be performed on sections of stained plastic-embedded tissues or cells of 1 to 2 micrometer thickness without effects of chromatic aberration because there are no imaging lenses after the specimen. By using a small STEM probe convergence angle of 1-2 mrad the geometrical broadening of the probe is restricted, which enables a spatial resolution of a few nanometers. Furthermore, by using an axial bright-field detector instead of the standard high-angle annular dark-field detector, image blurring due to multiple elastic scattering can be reduced in the lower part of the specimen. Here, we have applied STEM tomography to elucidate the 3D ultrastructure of human blood platelets, which are small anucleate blood cells that aggregate to seal leaks at sites of vascular injury and are important in the pathology of atherosclerosis and other diseases. Of particular interest are the morphological changes that occur in alpha-granules, which contain important proteins released when platelets are activated. Axial bright-field STEM electron tomographic tilt series were acquired at an accelerating voltage of 300 kV from 1.5-micrometer thick sections of platelets that had been prepared by rapid freezing and freeze-substitution; and the tomograms were reconstructed from dual-axis tilt series. The tomographic reconstructions revealed changes in ultrastructure that occurred on platelet activation including release of alpha granules through channels connecting to the plasma membrane. The research was supported by the intramural program of the National Institute of Biomedical Imaging and Bioengineering, and the research in the Storrie laboratory was supported in part by NIH grant R01 HL119393.
- Published
- 2015
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19. Choice of Specimen Thickness in Axial Bright-Field STEM Tomography of Cells
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Qianping He and Richard D. Leapman
- Subjects
0301 basic medicine ,03 medical and health sciences ,030104 developmental biology ,Materials science ,Optics ,Field (physics) ,business.industry ,02 engineering and technology ,STEM Tomography ,021001 nanoscience & nanotechnology ,0210 nano-technology ,business ,Instrumentation - Published
- 2016
20. Serial Block Face Sem of Biological Structures at Near Isotropic Spatial Resolution using Multiple Beam Energies and Monte Carlo Simulations
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Maria A. Aronova, Qianping He, Guofeng Zhang, David C. Joy, and Richard D. Leapman
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Serial block-face scanning electron microscopy ,Materials science ,Optics ,business.industry ,Resolution (electron density) ,Monte Carlo method ,Detector ,Isotropy ,Biophysics ,Electron beam processing ,business ,Image resolution ,Beam (structure) - Abstract
Serial block face scanning electron microscopy (SBF-SEM) provides nanoscale 3D ultrastructure of entire cells and tissue volumes. In SBF-SEM, an ultramicrotome built into the SEM specimen stage successively removes thin sections from a plastic-embedded, heavy metal-stained specimen. After each cut, the freshly exposed block face is imaged at a low incident electron energy using a backscattered electron detector to provide 3D ultrastructure with a resolution of approximately 5 nm in the plane of the block face and around 25 nm in the perpendicular z-direction, as limited by the slice thickness. We have explored the feasibility of improving the z-resolution in SBF-SEM by recording images at multiple primary beam energies, thus sampling different depths below the block surface.A linear relationship was found between the depth of test structures, generated by Monte Carlo simulations, and the ratio of backscattered image intensities recorded at primary beam energies between 1.4 keV and 6.8 keV. This enabled us to reconstruct the 3D model within a 25-nm surface layer at a z-resolution of around 5 nm. We used a Zeiss Sigma-VP SEM equipped with a Gatan 3View SBF system to acquire 3D data from a specimen consisting of gold spheres embedded in carbon. Experiments were also performed on embedded blocks of stained biological tissues.Although damage of the block under electron irradiation limits the signal to noise ratio, the use of multiple primary beam energies, coupled with a physics-based Monte Carlo model, provides the possibility of obtaining cellular ultrastructure at nearly isotropic 3D spatial resolution.
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- 2016
21. Bright-Field STEM Tomography of Blood Platelets in Thick Sections
- Author
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B.C. Kuo, Maria A. Aronova, Andrew A. Prince, Richard D. Leapman, Jake D. Hoyne, Brian Storrie, Laura J. MacDonald, Irina D. Pokrovskaya, Gina N. Calco, and Qianping He
- Subjects
Materials science ,Field (physics) ,Platelet ,STEM Tomography ,Instrumentation ,Biomedical engineering - Published
- 2015
22. Electron beam induced radiation damage in the catalyst layer of a proton exchange membrane fuel cell
- Author
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Qianping, He, Jihua, Chen, David J, Keffer, and David C, Joy
- Subjects
Membranes ,Radiation ,Bioelectric Energy Sources ,Microscopy, Electron, Scanning ,Electrons ,Protons ,Artifacts - Abstract
Electron microscopy is an essential tool for the evaluation of microstructure and properties of the catalyst layer (CL) of proton exchange membrane fuel cells (PEMFCs). However, electron microscopy has one unavoidable drawback, which is radiation damage. Samples suffer temporary or permanent change of the surface or bulk structure under radiation damage, which can cause ambiguity in the characterization of the sample. To better understand the mechanism of radiation damage of CL samples and to be able to separate the morphological features intrinsic to the material from the consequences of electron radiation damage, a series of experiments based on high-angle annular dark-field-scanning transmission scanning microscope (HAADF-STEM), energy filtering transmission scanning microscope (EFTEM), and electron energy loss spectrum (EELS) are conducted. It is observed that for thin samples (0.3-1 times λ), increasing the incident beam energy can mitigate the radiation damage. Platinum nanoparticles in the CL sample facilitate the radiation damage. The radiation damage of the catalyst sample starts from the interface of Pt/C or defective thin edge and primarily occurs in the form of mass loss accompanied by atomic displacement and edge curl. These results provide important insights on the mechanism of CL radiation damage. Possible strategies of mitigating the radiation damage are provided.
- Published
- 2013
23. Electron Beam Induced Radiation Damage in Nafion and the Lifetime of Fuel Cells
- Author
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Qianping He, David J. Keffer, and David C. Joy
- Subjects
chemistry.chemical_compound ,Materials science ,chemistry ,Nafion ,Radiochemistry ,Radiation damage ,Cathode ray ,Fuel cells ,Instrumentation - Abstract
Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.
- Published
- 2011
24. Impact of oxidation on nanoparticle adhesion to carbon substrates
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David J. Keffer, Qianping He, and David C. Joy
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Materials science ,General Chemical Engineering ,Nanoparticle ,chemistry.chemical_element ,Proton exchange membrane fuel cell ,General Chemistry ,Adhesion ,Electrolyte ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Nafion ,Organic chemistry ,Graphite ,Platinum ,Carbon - Abstract
Carbon supported platinum (Pt/C) catalysts are of vital importance to today's fine chemical industry. However, both Pt and its carbon support surface undergo oxidation during operation. There is a lack of information on how surface oxidation affects the durability of Pt/C catalysts. In this study, we report the impact of oxidation of Pt/C on the binding energy and nanoparticle adhesion force. Classic molecular dynamics simulations are performed on systems containing PtO nanoparticles of 4 nm and graphite surfaces oxidized with either epoxy or hydroxyl groups at several oxidation extents (10%, 25% and 50%). Appropriate for service in polymer electrolyte membrane fuel cells (PEMFC), the effect of a thin Nafion film (1 nm thick) at different hydration levels (λ = 3, 6, 9 and 15) is also included in the system to study the impact of oxidation on the interface structure of the electrolyte and the electrode. This study shows that the adhesion of both the Nafion film and the PtO nanoparticle is drastically affected by the type and degree of oxidation on the carbon surface. The oxidation with hydroxyl groups on the graphite surface enhanced the binding energy between the polymer electrolyte and the carbon electrode, while oxidation with the epoxy group beyond a certain amount caused delamination of the film. The adhesion of the PtO nanoparticle was similarly enhanced by the hydroxylated surface and diminished by the epoxidized surface. The binding energies and adhesive forces are reported for all systems studied.
- Published
- 2013
25. Nano-Particle Adhesion in PEM Fuel Cell Electrodes
- Author
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Qianping He, David C. Joy, and David J. Keffer
- Abstract
not Available.
- Published
- 2012
26. Sub-Surface Serial Block Face Scanning Electron Microscopy
- Author
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Maria A. Aronova, David C. Joy, Richard D. Leapman, Qianping He, and Guofeng Zhang
- Subjects
Serial block-face scanning electron microscopy ,Materials science ,Optics ,business.industry ,Monte Carlo method ,Resolution (electron density) ,Biophysics ,SPHERES ,Tomography ,business ,Focused ion beam ,Nanoscopic scale ,Beam (structure) - Abstract
Serial block face scanning electron microscopy (SBF-SEM) provides nanoscale 3D ultrastructure of tissue samples up to several hundred micrometers in size. In SBF-SEM, an ultramicrotome built into the SEM specimen stage successively removes thin sections from a plastic-embedded, heavy metal-stained specimen. After each cut, the freshly exposed block face is imaged at a low incident electron energy using the backscattered electron signal, which is sensitive to heavy atoms in the sample. Although the x-y resolution in the plane of the block face is approximately 5 nm, the resolution along the z-axis in SBF-SEM is limited by the minimum slice thickness of around 25 nm. We have explored the feasibility of improving the z-resolution in SBF-SEM by recording images at more than one primary beam energy, thus sampling different depths below the block surface. We used Monte Carlo simulations of SEM images from an epoxy block containing 5-nm diameter carbon spheres stained with 14% osmium positioned at different depths, as a model for small biological structures. A linear relationship was found between the depth of the spheres and the ratio of backscattered signals at primary beam energies of 1.4 keV and 6.8 keV, which allowed us to generate 3D tomograms with a depth resolution of around 5 nm. Experiments are in progress to test this technique using a Zeiss Sigma-VP SEM equipped with a Gatan 3View SBF system. Sub-surface SBF-SEM could potentially match focused ion beam (FIB) SEM in terms of z-resolution, but with the added advantage of providing higher throughput and larger tissue volumes. The research was supported by the intramural program of NIBIB.
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