Optical imaging has served as a primary method to collect information about biosystems across scales—from functionalities of tissues to morphological structures of cells and even at biomolecular levels.However,to ade...Optical imaging has served as a primary method to collect information about biosystems across scales—from functionalities of tissues to morphological structures of cells and even at biomolecular levels.However,to adequately characterize a complex biosystem,an imaging system with a number of resolvable points,referred to as a space-bandwidth product(SBP),in excess of one billion is typically needed.Since a gigapixel-scale far exceeds the capacity of current optical imagers,compromises must be made to obtain either a low spatial resolution or a narrow field-of-view(FOV).The problem originates from constituent refractive optics—the larger the aperture,the more challenging the correction of lens aberrations.Therefore,it is impractical for a conventional optical imaging system to achieve an SBP over hundreds of millions.To address this unmet need,a variety of high-SBP imagers have emerged over the past decade,enabling an unprecedented resolution and FOV beyond the limit of conventional optics.We provide a comprehensive survey of high-SBP imaging techniques,exploring their underlying principles and applications in bioimaging.展开更多
The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling p...The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry（PIV） technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in ＇various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics（CFD） simulations.展开更多
Conventional ptychography translates an object through a localized probe beam to widen the field of view in real space.Fourier ptychography translates the object spectrum through a pupil aperture to expand the Fourier...Conventional ptychography translates an object through a localized probe beam to widen the field of view in real space.Fourier ptychography translates the object spectrum through a pupil aperture to expand the Fourier bandwidth in reciprocal space.Here we report an imaging modality,termed synthetic aperture ptychography(SAP),to get the best of both techniques.In SAP,we illuminate a stationary object using an extended plane wave and translate a coded image sensor at the far field for data acquisition.The coded layer attached on the sensor modulates the object exit waves and serves as an effective ptychographic probe for phase retrieval.The sensor translation process in SAP synthesizes a large complex-valued wavefront at the intermediate aperture plane.By propagating this wavefront back to the object plane,we can widen the field of view in real space and expand the Fourier bandwidth in reciprocal space simultaneously.We validate the SAP approach with transmission targets and reflection silicon microchips.A 20-mm aperture was synthesized using a 5-mm sensor,achieving a fourfold gain in resolution and 16-fold gain in field of view for object recovery.In addition,the thin sample requirement in ptychography is no longer required in SAP.One can digitally propagate the recovered exit wave to any axial position for post-acquisition refocusing.The SAP scheme offers a solution for far-field sub-diffraction imaging without using lenses.It can be adopted in coherent diffraction imaging setups with radiation sources from visible light,extreme ultraviolet,and X-ray,to electron.展开更多
The growth of well-aligned carbon nanotube (CNT) arrays using a heat chemical vapor deposition system on silicon substrates is reported. The growth properties of CNT arrays are studied as a function of synthesis condi...The growth of well-aligned carbon nanotube (CNT) arrays using a heat chemical vapor deposition system on silicon substrates is reported. The growth properties of CNT arrays are studied as a function of synthesis conditions. It is found that 750°C and 10 nm Fe film are suitable conditions for the growth of well-aligned CNT arrays. CNT arrays with a uniform diameter, thick tube wall and firm cohesion to the Si substrate can be grown for C2H2 concentration of 27%. Based on the experiment, the processes of improving the alignment of CNT arrays and cohesion between CNT arrays and Si substrates are discussed.展开更多
Controlling photographic illumination in a structured fashion is a common practice in computational photography and image-based rendering. Here we introduce an incoherent photographic imaging approach, termed Fourier ...Controlling photographic illumination in a structured fashion is a common practice in computational photography and image-based rendering. Here we introduce an incoherent photographic imaging approach, termed Fourier ptychographic photography, that uses nonuniform structured light for super-resolution imaging. In this approach,frequency mixing between the object and the structured light shifts the high-frequency object information to the passband of the photographic lens. Therefore, the recorded intensity images contain object information that is beyond the cutoff frequency of the collection optics. Based on multiple images acquired under different structured light patterns, we used the Fourier ptychographic algorithm to recover the super-resolution object image and the unknown illumination pattern. We demonstrated the reported approach by imaging various objects, including a resolution target, a quick response code, a dollar bill, an insect, and a color leaf. The reported approach may find applications in photographic imaging settings, remote sensing, and imaging radar. It may also provide new insights for high-resolution imaging by shifting the focus from the collection optics to the generation of structured light.展开更多
Full-color imaging is of critical importance in digital pathology for analyzing labeled tissue sections.In our previous cover story[Sci.China:Phys.,Mech.Astron.64,114211(2021)],a color transfer approach was implemente...Full-color imaging is of critical importance in digital pathology for analyzing labeled tissue sections.In our previous cover story[Sci.China:Phys.,Mech.Astron.64,114211(2021)],a color transfer approach was implemented on Fourier ptychographic microscopy(FPM)for achieving high-throughput full-color whole slide imaging without mechanical scanning.The approach was able to reduce both acquisition and reconstruction time of FPM by three-fold with negligible trade-off on color accuracy.However,the method cannot properly stain samples with two or more dyes due to the lack of spatial constraints in the color transfer process.It also requires a high computation cost in histogram matching of individual patches.Here we report a modified full-color imaging algorithm for FPM,termed color-transfer filtering FPM(CFFPM).In CFFPM,we replace the original histogram matching process with a combination of block processing and trilateral spatial filtering.The former step reduces the search of the solution space for colorization,and the latter introduces spatial constraints that match the low-resolution measurement.We further adopt an iterative process to refine the results.We show that this method can perform accurate and fast color transfer for various specimens,including those with multiple stains.The statistical results of 26 samples show that the average root mean square error is only 1.26%higher than that of the red-green-blue sequential acquisition method.For some cases,CFFPM outperforms the sequential method because of the coherent artifacts introduced by dust particles.The reported CFFPM strategy provides a turnkey solution for digital pathology via computational optical imaging.展开更多
Polarimetric imaging provides valuable insights into the polarization state of light interacting with a sample.It can infer crucial birefringence properties of specimens without using labels,thereby facilitating the d...Polarimetric imaging provides valuable insights into the polarization state of light interacting with a sample.It can infer crucial birefringence properties of specimens without using labels,thereby facilitating the diagnosis of diseases such as cancer and osteoarthritis.In this study,we present a novel polarimetric coded ptychography(pol-CP)approach that enables high-resolution,high-throughput gigapixel birefringence imaging on a chip.Our platform deviates from traditional lens-based systems by employing an integrated polarimetric coded sensor for lensless coherent diffraction imaging.Utilizing Jones calculus,we quantitatively determine the birefringence retardance and orientation information of biospecimens from the recovered images.Our portable pol-CP prototype can resolve the 435 nm linewidth on the resolution target,and the imaging field of view for a single acquisition is limited only by the detector size of 41 mm2.The prototype allows for the acquisition of gigapixel birefringence images with a 180 mm^(2) field of view in~3.5 min,a performance that rivals high-end whole slide scanner but at a small fraction of the cost.To demonstrate its biomedical applications,we perform high-throughput imaging of malaria-infected blood smears,locating parasites using birefringence contrast.We also generate birefringence maps of label-free thyroid smears to identify thyroid follicles.Notably,the recovered birefringence maps emphasize the same regions as autofluorescence images,underscoring the potential for rapid on-site evaluation of label-free biopsies.Our approach provides a turnkey and portable solution for lensless polarimetric analysis on a chip,with promising applications in disease diagnosis,crystal screening,and label-free chemical imaging,particularly in resource-constrained environments.展开更多
Micro-endoscopes are widely used for detecting and visualizing hard-to-reach areas of the human body and for in vivo observation of animals.A micro-endoscope that can realize 3D imaging at the camera framerate could b...Micro-endoscopes are widely used for detecting and visualizing hard-to-reach areas of the human body and for in vivo observation of animals.A micro-endoscope that can realize 3D imaging at the camera framerate could benefit various clinical and biological applications.In this work,we report the development of a compact light-field micro-endoscope(LFME)that can obtain snapshot 3D fluorescence imaging,by jointly using a single-mode fiber bundle and a small-size light-field configuration.To demonstrate the real imaging performance of our method,we put a resolution chart in different z positions and capture the z-stack images successively for reconstruction,achieving 333-μm-diameter field of view,24μm optimal depth of field,and up to 3.91μm spatial resolution near the focal plane.We also test our method on a human skin tissue section and He La cells.Our LFME prototype provides epi-fluorescence imaging ability with a relatively small(2-mm-diameter)imaging probe,making it suitable for in vivo detection of brain activity and gastrointestinal diseases of animals.展开更多
In most pathology labs,clinicians diagnose diseases by examining tissue slices using a light microscope.This process typically requires clinicians to move the microscope stage to different positions and identify areas...In most pathology labs,clinicians diagnose diseases by examining tissue slices using a light microscope.This process typically requires clinicians to move the microscope stage to different positions and identify areas of interest that can be further analyzed using a higher magnification objective lens.For proper focusing of the slide,the axial position needs to be constantly adjusted by manually rotating the focus knob.As a result,the reviewing process can be easily disrupted when the clinician bumps the slide to the objective lens or switches to a different objective lens for focusing again.Although it remains the gold standard in diagnosing almost all types of cancers,manual microscopic inspection is,in general,labor-intensive and does not form a streamlined workflow in clinical practice.Furthermore,it is largely based on subjective opinions of clinicians:different clinicians may arrive at different conclusions for the same slide and the same person may give different conclusions at different time points[1].展开更多
The structures and field emission properties of multi-walled carbon nanotube arrays implanted with Zn+ by MEVVA ion implanter have been investigated.The results revealed that Zn+implantation induced structural damage ...The structures and field emission properties of multi-walled carbon nanotube arrays implanted with Zn+ by MEVVA ion implanter have been investigated.The results revealed that Zn+implantation induced structural damage and that the top of carbon nanotubes with multi-layered graphite structure were transformed into carbon nanowires with amorphous structure.Meanwhile,C:Zn solid solution was synthesized after Zn+ implantation.The turn-on field and threshold field were 0.80 and 1.31 V/μm,respectively for original multi-walled carbon nanotube arrays and were reduced to 0.66 and 1.04 V/μm due to the synthesis of C and Zn composite,in which the work function was reduced after low doses of Zn+implantation.It is indicated that low doses of Zn+implantation can improve field emission performance of multi-walled carbon nanotube arrays.Otherwise,high doses of Zn+implantation can reduce field emission properties of multi-walled carbon nanotube arrays,because radiation damage reduces the electric field enhancement factor.展开更多
A new approach for designing the Biorthogonal Wavelet Filter Bank (BWFB) for the purpose of image compression is presented in this letter. The approach is decomposed into two steps. First, an optimal filter bank is de...A new approach for designing the Biorthogonal Wavelet Filter Bank (BWFB) for the purpose of image compression is presented in this letter. The approach is decomposed into two steps. First, an optimal filter bank is designed in theoretical sense based on Vaidyanathan’s coding gain criterion in SubBand Coding (SBC) system. Then the above filter bank is optimized based on the criterion of Peak Signal-to-Noise Ratio (PSNR) in JPEG2000 image compression system, resulting in a BWFB in practical application sense. With the approach, a series of BWFB for a specific class of applications related to image compression, such as remote sensing images, can be fast designed. Here, new 5/3 BWFB and 9/7 BWFB are presented based on the above approach for the remote sensing image compression applications. Experiments show that the two filter banks are equally performed with respect to CDF 9/7 and LT 5/3 filter in JPEG2000 standard; at the same time, the coefficients and the lifting parameters of the lifting scheme are all rational, which bring the computational advantage, and the ease for VLSI implementation.展开更多
Defect engineering is in the limelight for the fabrication of electrochemical energy storage devices.However,determining the influence of the defect density and location on the electrochemical behavior remains challen...Defect engineering is in the limelight for the fabrication of electrochemical energy storage devices.However,determining the influence of the defect density and location on the electrochemical behavior remains challenging.Herein,self-organized TiO_(2)nanotube arrays(TNTAs)are synthesized by anodization,and their oxygen defect location and density are tuned by a controllable post-annealing process.TNTAs annealed at 600℃ in N2 exhibit the highest capacity(289.2 m Ah g^(-1)at 0.8 C)for lithium-ion storage,while those annealed at 900℃ in N2 show a specific capacitance of 35.6 m F cm^(-2)and stability above96%after 10,000 cycles for supercapacitor.Ex situ electron paramagnetic resonance spectra show that the surface-exposed oxygen defects increase,but the bulk embedded oxygen defects decrease with increasing annealing temperature.Density functional theory simulations reveal that a higher density of bulk oxygen defects corresponds to higher localized electrons states,which upshift the Fermi level and facilitate the lithium intercalation kinetic process.Meanwhile,differential charge density calculation indicates that the increase of surface oxygen defects in the anatase(101)plane leads to higher density excess electrons,which act as negative charge centers to enhance the surface potential for ion adsorption.This oxygen-deficient location and density tunable strategy introduce new opportunities for high-energy and high-power-density energy storage systems.展开更多
基金supported partially by the National Institutes of Health(R01EY029397,R35GM128761)the National Science Foundation(1652150)+1 种基金support from the Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(2019R1A6A3A03031505)support from the National Science Foundation(1846784)。
文摘Optical imaging has served as a primary method to collect information about biosystems across scales—from functionalities of tissues to morphological structures of cells and even at biomolecular levels.However,to adequately characterize a complex biosystem,an imaging system with a number of resolvable points,referred to as a space-bandwidth product(SBP),in excess of one billion is typically needed.Since a gigapixel-scale far exceeds the capacity of current optical imagers,compromises must be made to obtain either a low spatial resolution or a narrow field-of-view(FOV).The problem originates from constituent refractive optics—the larger the aperture,the more challenging the correction of lens aberrations.Therefore,it is impractical for a conventional optical imaging system to achieve an SBP over hundreds of millions.To address this unmet need,a variety of high-SBP imagers have emerged over the past decade,enabling an unprecedented resolution and FOV beyond the limit of conventional optics.We provide a comprehensive survey of high-SBP imaging techniques,exploring their underlying principles and applications in bioimaging.
基金supported by National Natural Science Foundation of China (Grant No. 50575017, Grant No. 50875016)
文摘The failure of a drilling pump is always due to the break of the drilling pump valve, which is one of the most important but also the weakest parts of the drilling pump. Over the decades, the degradation of drilling pump valves has been investigated extensively and various failure mechanisms have been proposed. However, no experimental test on the fluid has been successfully performed to support some of these mechanisms. In this paper, tests of the flow within the valve play are carried out to investigate the factors resulting in the failure of the valve. In the tests, particle image velocimetry（PIV） technology is employed to measure the flow field distribution of the valve play in the model. From these tests, the distributions of velocity and vorticity of fluid in ＇various valves with different valve angles and different valve lifts are obtained, from which the features of flow fields are derived and generalized. Subsequently, a general rule of the influence of valve angles and valve lifts on the flow velocity is concluded according to chart analyses of maximal velocities and mean velocities. Finally, an analysis is made on the possibility of valve failure caused by erosion and abrasion in a working valve, with the application of the failure mechanisms of drilling pump valves. PIV measurement improves the study on the failure of the drilling pump valve, and the results show good agreement with previous computational fluid dynamics（CFD） simulations.
文摘Conventional ptychography translates an object through a localized probe beam to widen the field of view in real space.Fourier ptychography translates the object spectrum through a pupil aperture to expand the Fourier bandwidth in reciprocal space.Here we report an imaging modality,termed synthetic aperture ptychography(SAP),to get the best of both techniques.In SAP,we illuminate a stationary object using an extended plane wave and translate a coded image sensor at the far field for data acquisition.The coded layer attached on the sensor modulates the object exit waves and serves as an effective ptychographic probe for phase retrieval.The sensor translation process in SAP synthesizes a large complex-valued wavefront at the intermediate aperture plane.By propagating this wavefront back to the object plane,we can widen the field of view in real space and expand the Fourier bandwidth in reciprocal space simultaneously.We validate the SAP approach with transmission targets and reflection silicon microchips.A 20-mm aperture was synthesized using a 5-mm sensor,achieving a fourfold gain in resolution and 16-fold gain in field of view for object recovery.In addition,the thin sample requirement in ptychography is no longer required in SAP.One can digitally propagate the recovered exit wave to any axial position for post-acquisition refocusing.The SAP scheme offers a solution for far-field sub-diffraction imaging without using lenses.It can be adopted in coherent diffraction imaging setups with radiation sources from visible light,extreme ultraviolet,and X-ray,to electron.
基金the National Natural Science Foundation of China (Grant No.10275005) the Bud Project of Beijing Academy of Science and Technology.
文摘The growth of well-aligned carbon nanotube (CNT) arrays using a heat chemical vapor deposition system on silicon substrates is reported. The growth properties of CNT arrays are studied as a function of synthesis conditions. It is found that 750°C and 10 nm Fe film are suitable conditions for the growth of well-aligned CNT arrays. CNT arrays with a uniform diameter, thick tube wall and firm cohesion to the Si substrate can be grown for C2H2 concentration of 27%. Based on the experiment, the processes of improving the alignment of CNT arrays and cohesion between CNT arrays and Si substrates are discussed.
文摘Controlling photographic illumination in a structured fashion is a common practice in computational photography and image-based rendering. Here we introduce an incoherent photographic imaging approach, termed Fourier ptychographic photography, that uses nonuniform structured light for super-resolution imaging. In this approach,frequency mixing between the object and the structured light shifts the high-frequency object information to the passband of the photographic lens. Therefore, the recorded intensity images contain object information that is beyond the cutoff frequency of the collection optics. Based on multiple images acquired under different structured light patterns, we used the Fourier ptychographic algorithm to recover the super-resolution object image and the unknown illumination pattern. We demonstrated the reported approach by imaging various objects, including a resolution target, a quick response code, a dollar bill, an insect, and a color leaf. The reported approach may find applications in photographic imaging settings, remote sensing, and imaging radar. It may also provide new insights for high-resolution imaging by shifting the focus from the collection optics to the generation of structured light.
基金National Natural Science Foundation of China (12104500).
文摘Full-color imaging is of critical importance in digital pathology for analyzing labeled tissue sections.In our previous cover story[Sci.China:Phys.,Mech.Astron.64,114211(2021)],a color transfer approach was implemented on Fourier ptychographic microscopy(FPM)for achieving high-throughput full-color whole slide imaging without mechanical scanning.The approach was able to reduce both acquisition and reconstruction time of FPM by three-fold with negligible trade-off on color accuracy.However,the method cannot properly stain samples with two or more dyes due to the lack of spatial constraints in the color transfer process.It also requires a high computation cost in histogram matching of individual patches.Here we report a modified full-color imaging algorithm for FPM,termed color-transfer filtering FPM(CFFPM).In CFFPM,we replace the original histogram matching process with a combination of block processing and trilateral spatial filtering.The former step reduces the search of the solution space for colorization,and the latter introduces spatial constraints that match the low-resolution measurement.We further adopt an iterative process to refine the results.We show that this method can perform accurate and fast color transfer for various specimens,including those with multiple stains.The statistical results of 26 samples show that the average root mean square error is only 1.26%higher than that of the red-green-blue sequential acquisition method.For some cases,CFFPM outperforms the sequential method because of the coherent artifacts introduced by dust particles.The reported CFFPM strategy provides a turnkey solution for digital pathology via computational optical imaging.
基金National Natural Science Foundation of China(61975254,62075175)。
文摘Polarimetric imaging provides valuable insights into the polarization state of light interacting with a sample.It can infer crucial birefringence properties of specimens without using labels,thereby facilitating the diagnosis of diseases such as cancer and osteoarthritis.In this study,we present a novel polarimetric coded ptychography(pol-CP)approach that enables high-resolution,high-throughput gigapixel birefringence imaging on a chip.Our platform deviates from traditional lens-based systems by employing an integrated polarimetric coded sensor for lensless coherent diffraction imaging.Utilizing Jones calculus,we quantitatively determine the birefringence retardance and orientation information of biospecimens from the recovered images.Our portable pol-CP prototype can resolve the 435 nm linewidth on the resolution target,and the imaging field of view for a single acquisition is limited only by the detector size of 41 mm2.The prototype allows for the acquisition of gigapixel birefringence images with a 180 mm^(2) field of view in~3.5 min,a performance that rivals high-end whole slide scanner but at a small fraction of the cost.To demonstrate its biomedical applications,we perform high-throughput imaging of malaria-infected blood smears,locating parasites using birefringence contrast.We also generate birefringence maps of label-free thyroid smears to identify thyroid follicles.Notably,the recovered birefringence maps emphasize the same regions as autofluorescence images,underscoring the potential for rapid on-site evaluation of label-free biopsies.Our approach provides a turnkey and portable solution for lensless polarimetric analysis on a chip,with promising applications in disease diagnosis,crystal screening,and label-free chemical imaging,particularly in resource-constrained environments.
基金National Natural Science Foundation of China(62071219,62025108)Natural Science Foundation of Jiangsu Province(BK20190292)。
文摘Micro-endoscopes are widely used for detecting and visualizing hard-to-reach areas of the human body and for in vivo observation of animals.A micro-endoscope that can realize 3D imaging at the camera framerate could benefit various clinical and biological applications.In this work,we report the development of a compact light-field micro-endoscope(LFME)that can obtain snapshot 3D fluorescence imaging,by jointly using a single-mode fiber bundle and a small-size light-field configuration.To demonstrate the real imaging performance of our method,we put a resolution chart in different z positions and capture the z-stack images successively for reconstruction,achieving 333-μm-diameter field of view,24μm optimal depth of field,and up to 3.91μm spatial resolution near the focal plane.We also test our method on a human skin tissue section and He La cells.Our LFME prototype provides epi-fluorescence imaging ability with a relatively small(2-mm-diameter)imaging probe,making it suitable for in vivo detection of brain activity and gastrointestinal diseases of animals.
文摘In most pathology labs,clinicians diagnose diseases by examining tissue slices using a light microscope.This process typically requires clinicians to move the microscope stage to different positions and identify areas of interest that can be further analyzed using a higher magnification objective lens.For proper focusing of the slide,the axial position needs to be constantly adjusted by manually rotating the focus knob.As a result,the reviewing process can be easily disrupted when the clinician bumps the slide to the objective lens or switches to a different objective lens for focusing again.Although it remains the gold standard in diagnosing almost all types of cancers,manual microscopic inspection is,in general,labor-intensive and does not form a streamlined workflow in clinical practice.Furthermore,it is largely based on subjective opinions of clinicians:different clinicians may arrive at different conclusions for the same slide and the same person may give different conclusions at different time points[1].
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2010CB832905)the National Natural Science Foundation of China(Grant No.10575011)the Key Scientific and Technological Project of Ministry of Education of China(Grant No.108124)
文摘The structures and field emission properties of multi-walled carbon nanotube arrays implanted with Zn+ by MEVVA ion implanter have been investigated.The results revealed that Zn+implantation induced structural damage and that the top of carbon nanotubes with multi-layered graphite structure were transformed into carbon nanowires with amorphous structure.Meanwhile,C:Zn solid solution was synthesized after Zn+ implantation.The turn-on field and threshold field were 0.80 and 1.31 V/μm,respectively for original multi-walled carbon nanotube arrays and were reduced to 0.66 and 1.04 V/μm due to the synthesis of C and Zn composite,in which the work function was reduced after low doses of Zn+implantation.It is indicated that low doses of Zn+implantation can improve field emission performance of multi-walled carbon nanotube arrays.Otherwise,high doses of Zn+implantation can reduce field emission properties of multi-walled carbon nanotube arrays,because radiation damage reduces the electric field enhancement factor.
基金Supported by the National Natural Science Foundation of China (No.60021302, No.60635050 and No.60405004).
文摘A new approach for designing the Biorthogonal Wavelet Filter Bank (BWFB) for the purpose of image compression is presented in this letter. The approach is decomposed into two steps. First, an optimal filter bank is designed in theoretical sense based on Vaidyanathan’s coding gain criterion in SubBand Coding (SBC) system. Then the above filter bank is optimized based on the criterion of Peak Signal-to-Noise Ratio (PSNR) in JPEG2000 image compression system, resulting in a BWFB in practical application sense. With the approach, a series of BWFB for a specific class of applications related to image compression, such as remote sensing images, can be fast designed. Here, new 5/3 BWFB and 9/7 BWFB are presented based on the above approach for the remote sensing image compression applications. Experiments show that the two filter banks are equally performed with respect to CDF 9/7 and LT 5/3 filter in JPEG2000 standard; at the same time, the coefficients and the lifting parameters of the lifting scheme are all rational, which bring the computational advantage, and the ease for VLSI implementation.
基金supported by the National Nature Science Foundation of China(11575025,U1832176)the Science and Technology Project of Beijing(Z171100002017008)the Fundamental Research Funds for the Central Universities。
文摘Defect engineering is in the limelight for the fabrication of electrochemical energy storage devices.However,determining the influence of the defect density and location on the electrochemical behavior remains challenging.Herein,self-organized TiO_(2)nanotube arrays(TNTAs)are synthesized by anodization,and their oxygen defect location and density are tuned by a controllable post-annealing process.TNTAs annealed at 600℃ in N2 exhibit the highest capacity(289.2 m Ah g^(-1)at 0.8 C)for lithium-ion storage,while those annealed at 900℃ in N2 show a specific capacitance of 35.6 m F cm^(-2)and stability above96%after 10,000 cycles for supercapacitor.Ex situ electron paramagnetic resonance spectra show that the surface-exposed oxygen defects increase,but the bulk embedded oxygen defects decrease with increasing annealing temperature.Density functional theory simulations reveal that a higher density of bulk oxygen defects corresponds to higher localized electrons states,which upshift the Fermi level and facilitate the lithium intercalation kinetic process.Meanwhile,differential charge density calculation indicates that the increase of surface oxygen defects in the anatase(101)plane leads to higher density excess electrons,which act as negative charge centers to enhance the surface potential for ion adsorption.This oxygen-deficient location and density tunable strategy introduce new opportunities for high-energy and high-power-density energy storage systems.
