Large-scale synthesis of ZnO hexagonal pyramids was achieved by a simple thermal decomposition route of precursor at 240 oC in the presence of PEG400. The precursor was obtained by room-temperature solid-state grindin...Large-scale synthesis of ZnO hexagonal pyramids was achieved by a simple thermal decomposition route of precursor at 240 oC in the presence of PEG400. The precursor was obtained by room-temperature solid-state grinding reaction between Zn（CH3COO）2-2H2O and Na2CO3. Crystal structure and morphology of the products were analyzed and characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and high-resolution transmission electron microscopy （HRTEM）. The results of further experiments show that PEG400 has an important role in the formation of ZnO hexagonal pyramids. Difference between the single and double hexagonal pyramid structure may come from the special thermal decomposition reaction. The photoluminescence （PL） spectra of ZnO hexagonal pyramids exhibit strong near-band-edge emission at about 386 nm and weak green emission at about 550 nm. The Raman-active vibration at about 435 cm-1 suggests that the ZnO hexagonal pyramids have high crystallinity.展开更多
Growth of gallium nitride(GaN)inverted pyramids on c-plane sapphire substrates is benefit for fabricating novel devices as it forms the semipolar facets.In this work,GaN inverted pyramids are directly grown on c-plane...Growth of gallium nitride(GaN)inverted pyramids on c-plane sapphire substrates is benefit for fabricating novel devices as it forms the semipolar facets.In this work,GaN inverted pyramids are directly grown on c-plane patterned sapphire substrates(PSS)by metal organic vapor phase epitaxy(MOVPE).The influences of growth conditions on the surface morphol-ogy are experimentally studied and explained by Wulff constructions.The competition of growth rate among{0001},{1011},and{1122}facets results in the various surface morphologies of GaN.A higher growth temperature of 985 ℃ and a lowerⅤ/Ⅲratio of 25 can expand the area of{}facets in GaN inverted pyramids.On the other hand,GaN inverted pyramids with almost pure{}facets are obtained by using a lower growth temperature of 930℃,a higherⅤ/Ⅲratio of 100,and PSS with pattern arrangement perpendicular to the substrate primary flat.展开更多
A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a con-venient photo-assisted chemical （PAC） etching method. The solution concentration has an evident influe...A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a con-venient photo-assisted chemical （PAC） etching method. The solution concentration has an evident influence on the surface morphology of GaN and the optimal solution concentrations for GaN hexagonal pyramids have been identified. GaN with hexagonal pyramids have higher crystal quality and tensile strain relaxation compared with as-grown GaN. A detailed anal- ysis about evolution of the size, density and optical property of GaN hexagonal pyramids is described as a function of light intensity. The intensity of photoluminescence spectra of GaN etched with hexagonal pyramids significantly increases compared to that of as-grown GaN due to multiple scattering events, high quality GaN with pyramids and the Bragg effect.展开更多
Precise spatial control of 2D materials is the key capability of engineering their optical,electronic,and mechanical properties.However,growth of novel 2D Mo2C on Cu surface by chemical vapor deposition method was rev...Precise spatial control of 2D materials is the key capability of engineering their optical,electronic,and mechanical properties.However,growth of novel 2D Mo2C on Cu surface by chemical vapor deposition method was revealed to be seed-induced 2D growth,limiting further synthesis of complex Mo2C spatial structures.In this research,we demonstrate the controlled growth of Mo2C pyramids with numerous morphologies,which are characterized with clear terraces within the structures.The whole evolution for Mo2C pyramids in the coursed of CVD process has been detected,posing significant potential in probing growth mechanism.The formation of the Mo2C pyramids arises from the supersaturation-induced nucleation and concentration-gradient driven diffused growth of a new Mo2C layer on the edged areas of intrinsic ones,as supported by STEM imaging.This work provides a novel Mo2C-based pyramid structure and further reveals a sliding growth mechanism,which could offer impetus for the design of new 3D spatial structures of Mo2C and other 2D materials.展开更多
In this paper, a novel and reliable structure of the side passivated emitter and the rear locallydiffused（PERL） silicon light emitting diodes （LEDs） is proposed. The inverted pyramids surface, the important interf...In this paper, a novel and reliable structure of the side passivated emitter and the rear locallydiffused（PERL） silicon light emitting diodes （LEDs） is proposed. The inverted pyramids surface, the important interface in this structure, is given according to the experiment. The results show that the inverted pyramids surface has a low refection about 8%, in the anisotropic etching 70 ℃, 5% TMAH concentration, corrosion time of 90 min or 30 rain. Low refection means high light emitting rate. Most of the structure and manufacturing process can be compatible with planar CMOS technology, which makes the silicon LED greater potential for development in the future.展开更多
Selecting a site for a nuclear power plant requires extensive studies to ensure its safety and stability during its operation until its decommissioning. The 4,500-year old Egyptian pyramids at Giza are buildings to le...Selecting a site for a nuclear power plant requires extensive studies to ensure its safety and stability during its operation until its decommissioning. The 4,500-year old Egyptian pyramids at Giza are buildings to learn from. This paper tries to pin down the reasons for the survival of the Giza pyramids in order to reach a criterion for choosing sites for important buildings. It argues that the site selection and the geological properties of the area, being away from seismic effects,, floods and groundwater levels, the stability of the geometric form of the pyramid, the solidity of the structural engineering and precision of execution arguably are the reasons why the Great Pyramids of Giza are the only survivors of the seven wonders of the ancient world.展开更多
The simulation of indentations with so called “equivalent” pseudo-cones for decreasing computer time is challenged. The mimicry of pseudo-cones having equal basal surface and depth with pyramidal indenters is exclud...The simulation of indentations with so called “equivalent” pseudo-cones for decreasing computer time is challenged. The mimicry of pseudo-cones having equal basal surface and depth with pyramidal indenters is excluded by basic arithmetic and trigonometric calculations. The commonly accepted angles of so called “equivalent” pseudo-cones must not also claim equal depth. Such bias (answers put into the questions to be solved) in the historical values of the generally used half-opening angles of pseudo-cones is revealed. It falsifies all simulations or conclusions on that basis. The enormous errors in the resulting hardness H<sub>ISO</sub> and elastic modulus E<sub>r-ISO</sub> values are disastrous not only for the artificial intelligence. The straightforward deduction for possibly ψ-cones (ψ for pseudo) without biased depths’ errors for equal basal surface and equal volume is reported. These ψ-cones would of course penetrate much more deeply than the three-sided Berkovich and cube corner pyramids (r a/2), and their half-opening angles would be smaller than those of the respective pyramids (reverse with r > a/2 for four-sided Vickers). Also the unlike forces’ direction angles are reported for the more sideward and the resulting downward directions. They are reflected by the diameter of the parallelograms with length and off-angle from the vertical axis. Experimental loading curves before and after the phase-transition onsets are indispensable. Mimicry of ψ-cones and pyramids is also quantitatively excluded. All simulations on their bases would also be dangerously invalid for industrial and solid pharmaceutical materials.展开更多
Pyramids,symbols of the Ancient Egyptian civilization,are visited by tourists and studied by researchers from all around the world.However,the techniques used by Ancient Egyptians to construct the pyramid,specifically...Pyramids,symbols of the Ancient Egyptian civilization,are visited by tourists and studied by researchers from all around the world.However,the techniques used by Ancient Egyptians to construct the pyramid,specifically,how such a tall structure could have been constructed from huge blocks of stone with the limited productive forces at the time,remains a mystery to the world.Though numerous theories,such as the use of ramps,levers,pulleys,fluid buoyancy,and cast-in-place concrete,have been proposed in academia,no consensus has been reached to date.Based on mechanical principles and the productive forces available at the time,the famous Pyramid of Khufu is used as a case study in this paper to propose a theory of pit-aided construction.The main steps include the digging of the pit,the transportation of stone blocks into the pit,the layer-by-layer construction,and the layer-by-layer filling of soil until the top of the pyramid is completed.The main idea of the pit-aided construction was to use the self-weight of the stone material to achieve the transportation of stone blocks by converting potential energy to kinetic energy,thereby avoiding the large amounts of work that must be done to elevate the huge blocks of stone.The proposed theory of pit-aided construction is consistent with the cultural custom of burial that is associated with tomb construction,namely laying the deceased to rest through burial,and is also consistent with the productive forces available in Ancient Egypt at the time.展开更多
GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method.Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviole...GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method.Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination,producing submicron-sized pyramids.Hexagonal pyramids on the etched GaN with well-defined{1011}facets and very sharp tips are formed.High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality,and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN.The cathodoluminescence intensity of GaN after etching is significantly increased by three times,which is attributed to the reduction in the internal reflection,high-quality GaN with pyramids and the Bragg effect.展开更多
Hyperbolic Coxeter polytopes are defined precisely by combinatorial type. Polytopes in hyperbolic n-space with n + p faces that have the combinatorial type of a pyramid over a product of simplices were classified by T...Hyperbolic Coxeter polytopes are defined precisely by combinatorial type. Polytopes in hyperbolic n-space with n + p faces that have the combinatorial type of a pyramid over a product of simplices were classified by Tumarkin for small p. In this article we generalise Tumarkin’s methods and find the remaining hyperbolic Coxeter pyramids.展开更多
Classical facet elements do not provide an optimal rate of convergence of the numerical solution toward the solution of the exact problem in H(div)-norm for general unstructured meshes containing hexahedra and prisms....Classical facet elements do not provide an optimal rate of convergence of the numerical solution toward the solution of the exact problem in H(div)-norm for general unstructured meshes containing hexahedra and prisms.We propose two new families of high-order elements for hexahedra,triangular prisms and pyramids that recover the optimal convergence.These elements have compatible restrictions with each other,such that they can be used directly on general hybrid meshes.Moreover the H(div)proposed spaces are completing the De Rham diagram with optimal elements previously constructed for H1 and H(curl)approximation.The obtained pyramidal elements are compared theoretically and numerically with other elements of the literature.Eventually,numerical results demonstrate the efficiency of the finite elements constructed.展开更多
Monitoring physiological signals of the human body can provide extremely important information for sports healthcare,preventing injuries and providing efficient guidance for individual sports.However,the signals relat...Monitoring physiological signals of the human body can provide extremely important information for sports healthcare,preventing injuries and providing efficient guidance for individual sports.However,the signals related to human healthcare involve both subtle and vigorous signals,making it difficult for a sensor to satisfy the full-scale monitoring at the same time.Here,a novel conductive elastomer featuring homogeneously micropyramid-structured PDMS/CNT composite is used to fabricate highperformance piezoresistive sensors by a drop-casting method.Benefiting from the significant increase in the contact area of microstructure during deformation,the flexible sensor presents a broad detection range(up to 185.5 kPa),fast response/recovery time(44/13 ms),ultrahigh sensitivity(242.4 kPa–1)and excellent durability over 8,000 cycles.As a proof of concept,the as-fabricated pressure sensor can be used for body-area sports healthcare,and enable the detection of full-scale pressure distribution.Considering the fabulous sensing performance,the sensor may potentially become promising in personal sports healthcare and telemedicine monitoring.展开更多
In order to improve the quality of remote sensing image fusion,a new method combining nonsubsampled Laplacian pyramid (NLP)and bidimensional empirical mode decomposition(BEMD)is proposed.First,the high resolution panc...In order to improve the quality of remote sensing image fusion,a new method combining nonsubsampled Laplacian pyramid (NLP)and bidimensional empirical mode decomposition(BEMD)is proposed.First,the high resolution panchromatic image (PAN)is decomposed using NLP until the approximate component and the low resolution multispectral image(MS)contain features with a similar scale.Then,the approximation component and the MS are decomposed by BEMD,resulting in a number of bidimensional intrinsic mode functions(BIMF)and a residue respectively.The instantaneous frequency is computed in 4 directions of the BIMFs.Considering the positive or negative coefficients in the corresponding position,a weighted algorithm is designed for fusing the high frequency details using the instantaneous frequency and the coefficient absolute value of the BIMFs as fusion feature.The fused image is then obtained through inverse BEMD and NLP.Experimental results have illustrated the advantage of this method over the IHS,DWT andà-Trous wavelet in both spectral and spatial detail qualities.展开更多
This paper describes practical approaches on how to construct bounding pyramids and bounding cones for triangular Bezier surfaces. Examples are provided to illustrate the process of construction and comparison is made...This paper describes practical approaches on how to construct bounding pyramids and bounding cones for triangular Bezier surfaces. Examples are provided to illustrate the process of construction and comparison is made between various surface bounding volumes. Furthermore, as a starting point for the construction, we provide a way to compute hodographs of triangular Bezier surfaces and improve the algorithm for computing the bounding cone of a set of vectors. [ABSTRACT FROM AUTHOR]展开更多
Surface-enhanced Raman scattering(SERS)substrates play important roles for the enhancement of inelastic scattering signals.Traditional substrates such as roughened electrodes and colloidal aggregates suffer from well-...Surface-enhanced Raman scattering(SERS)substrates play important roles for the enhancement of inelastic scattering signals.Traditional substrates such as roughened electrodes and colloidal aggregates suffer from well-known signal reproducibility issues,whereas for current dominant two-dimensional planar systems,the hot spot distributions are limited by the zero-,one-or two-dimensional plane.The introduction of a three-dimensional(3D)system such as a pyramid geometry breaks the limitation of a single Cartesian SERS-active area and extends it into the z-direction,with the tip potentially offering additional benefits of strong field enhancement and high sensitivity.However,current 3D pyramidal designs are restricted to film deposition on prepared pyramid templates or self-assembly in pyramidal molds with spherical building blocks,hence limiting their SERS effectiveness.Here,we report on the fabrication of a new class of low cost and well-defined plasmonic nanoparticle pyramid arrays from different anisotropic shaped nanoparticles using combined top-down lithography and bottom-up self-assembly approach.These pyramids exhibit novel optical scattering properties that can be exploited for the design of reproducible and sensitive SERS substrate.The SERS intensity was found to decrease drastically in accordance with a power law function as the focal planes move from the apex of the pyramid structure towards the base.In comparison to sphere-based building blocks,pyramids assembled from anisotropic rhombic dodecahedral gold nanocrystals with numerous sharp tips exhibited the strongest SERS performance.Graphical Abstract Macroscale pyramidal array films with plasmonic tunability as a new class of SERS substrate for sensitive detection of chemicals.展开更多
Pyramidal elements are often used to connect tetrahedral and hexahedral elements in the finite element method.In this paper we derive three new higher order numerical cubature formulae for pyramidal elements.
Archaeologists(考古学家)have unearthed the remains of a Mayan city nearly 3,000 years old in northern Guatemala,with pyramids(金字塔)and monuments that showcase its significance as an important ceremonial site.The May...Archaeologists(考古学家)have unearthed the remains of a Mayan city nearly 3,000 years old in northern Guatemala,with pyramids(金字塔)and monuments that showcase its significance as an important ceremonial site.The Mayan civilization arose around 2000 BC,reaching its height between 400 AD and 900 AD in what is present-day southern Mexico and Guatemala,as well as parts of Belize,El Salvador and Honduras.展开更多
Two-dimensional endoscopic images are susceptible to interferences such as specular reflections and monotonous texture illumination,hindering accurate three-dimensional lesion reconstruction by surgical robots.This st...Two-dimensional endoscopic images are susceptible to interferences such as specular reflections and monotonous texture illumination,hindering accurate three-dimensional lesion reconstruction by surgical robots.This study proposes a novel end-to-end disparity estimation model to address these challenges.Our approach combines a Pseudo-Siamese neural network architecture with pyramid dilated convolutions,integrating multi-scale image information to enhance robustness against lighting interferences.This study introduces a Pseudo-Siamese structure-based disparity regression model that simplifies left-right image comparison,improving accuracy and efficiency.The model was evaluated using a dataset of stereo endoscopic videos captured by the Da Vinci surgical robot,comprising simulated silicone heart sequences and real heart video data.Experimental results demonstrate significant improvement in the network’s resistance to lighting interference without substantially increasing parameters.Moreover,the model exhibited faster convergence during training,contributing to overall performance enhancement.This study advances endoscopic image processing accuracy and has potential implications for surgical robot applications in complex environments.展开更多
Audio-visual scene classification(AVSC)poses a formidable challenge owing to the intricate spatial-temporal relationships exhibited by audio-visual signals,coupled with the complex spatial patterns of objects and text...Audio-visual scene classification(AVSC)poses a formidable challenge owing to the intricate spatial-temporal relationships exhibited by audio-visual signals,coupled with the complex spatial patterns of objects and textures found in visual images.The focus of recent studies has predominantly revolved around extracting features from diverse neural network structures,inadvertently neglecting the acquisition of semantically meaningful regions and crucial components within audio-visual data.The authors present a feature pyramid attention network(FPANet)for audio-visual scene understanding,which extracts semantically significant characteristics from audio-visual data.The authors’approach builds multi-scale hierarchical features of sound spectrograms and visual images using a feature pyramid representation and localises the semantically relevant regions with a feature pyramid attention module(FPAM).A dimension alignment(DA)strategy is employed to align feature maps from multiple layers,a pyramid spatial attention(PSA)to spatially locate essential regions,and a pyramid channel attention(PCA)to pinpoint significant temporal frames.Experiments on visual scene classification(VSC),audio scene classification(ASC),and AVSC tasks demonstrate that FPANet achieves performance on par with state-of-the-art(SOTA)approaches,with a 95.9 F1-score on the ADVANCE dataset and a relative improvement of 28.8%.Visualisation results show that FPANet can prioritise semantically meaningful areas in audio-visual signals.展开更多
基金Project (BK2009379) supported by the Natural Science Foundation of Jiangsu Province, ChinaProject (1006-56XNA12069) supported by the Nanjing University of Aeronautics and Astronautics Research Funding, China+3 种基金Projects (51172108, 91023020) supported by the National Natural Science Foundation of ChinaProject (IRT0968) supported by the Program for Changjiang Scholars and Innovative Research Team in University, ChinaProject (NCET-10-0070) supported by the Program for New Century Excellent Talents in University, ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions, China
文摘Large-scale synthesis of ZnO hexagonal pyramids was achieved by a simple thermal decomposition route of precursor at 240 oC in the presence of PEG400. The precursor was obtained by room-temperature solid-state grinding reaction between Zn（CH3COO）2-2H2O and Na2CO3. Crystal structure and morphology of the products were analyzed and characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, transmission electron microscopy （TEM） and high-resolution transmission electron microscopy （HRTEM）. The results of further experiments show that PEG400 has an important role in the formation of ZnO hexagonal pyramids. Difference between the single and double hexagonal pyramid structure may come from the special thermal decomposition reaction. The photoluminescence （PL） spectra of ZnO hexagonal pyramids exhibit strong near-band-edge emission at about 386 nm and weak green emission at about 550 nm. The Raman-active vibration at about 435 cm-1 suggests that the ZnO hexagonal pyramids have high crystallinity.
基金the National Key Research and Development Program(2021YFA0716400)the National Natural Science Foundation of China(62225405,62350002,61991443)+1 种基金the Key R&D Project of Jiangsu Province,China(BE2020004)the Collaborative Innovation Centre of Solid-State Lighting and Energy-Saving Electronics.
文摘Growth of gallium nitride(GaN)inverted pyramids on c-plane sapphire substrates is benefit for fabricating novel devices as it forms the semipolar facets.In this work,GaN inverted pyramids are directly grown on c-plane patterned sapphire substrates(PSS)by metal organic vapor phase epitaxy(MOVPE).The influences of growth conditions on the surface morphol-ogy are experimentally studied and explained by Wulff constructions.The competition of growth rate among{0001},{1011},and{1122}facets results in the various surface morphologies of GaN.A higher growth temperature of 985 ℃ and a lowerⅤ/Ⅲratio of 25 can expand the area of{}facets in GaN inverted pyramids.On the other hand,GaN inverted pyramids with almost pure{}facets are obtained by using a lower growth temperature of 930℃,a higherⅤ/Ⅲratio of 100,and PSS with pattern arrangement perpendicular to the substrate primary flat.
基金Project supported by the National Basic Research Program of China(Grant Nos.2011CB301900,2012CB619304,and 2010CB327504)the National High Technology Research and Development Program of China(Grant No.2011AA03A103)+1 种基金the National Nature Science Foundation of China(Grant Nos.60990311,60906025,60936004,and 61176063)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK2011010 and BK2009255)
文摘A series of experiments were conducted to systematically study the effects of etching conditions on GaN by a con-venient photo-assisted chemical （PAC） etching method. The solution concentration has an evident influence on the surface morphology of GaN and the optimal solution concentrations for GaN hexagonal pyramids have been identified. GaN with hexagonal pyramids have higher crystal quality and tensile strain relaxation compared with as-grown GaN. A detailed anal- ysis about evolution of the size, density and optical property of GaN hexagonal pyramids is described as a function of light intensity. The intensity of photoluminescence spectra of GaN etched with hexagonal pyramids significantly increases compared to that of as-grown GaN due to multiple scattering events, high quality GaN with pyramids and the Bragg effect.
文摘Precise spatial control of 2D materials is the key capability of engineering their optical,electronic,and mechanical properties.However,growth of novel 2D Mo2C on Cu surface by chemical vapor deposition method was revealed to be seed-induced 2D growth,limiting further synthesis of complex Mo2C spatial structures.In this research,we demonstrate the controlled growth of Mo2C pyramids with numerous morphologies,which are characterized with clear terraces within the structures.The whole evolution for Mo2C pyramids in the coursed of CVD process has been detected,posing significant potential in probing growth mechanism.The formation of the Mo2C pyramids arises from the supersaturation-induced nucleation and concentration-gradient driven diffused growth of a new Mo2C layer on the edged areas of intrinsic ones,as supported by STEM imaging.This work provides a novel Mo2C-based pyramid structure and further reveals a sliding growth mechanism,which could offer impetus for the design of new 3D spatial structures of Mo2C and other 2D materials.
文摘In this paper, a novel and reliable structure of the side passivated emitter and the rear locallydiffused（PERL） silicon light emitting diodes （LEDs） is proposed. The inverted pyramids surface, the important interface in this structure, is given according to the experiment. The results show that the inverted pyramids surface has a low refection about 8%, in the anisotropic etching 70 ℃, 5% TMAH concentration, corrosion time of 90 min or 30 rain. Low refection means high light emitting rate. Most of the structure and manufacturing process can be compatible with planar CMOS technology, which makes the silicon LED greater potential for development in the future.
文摘Selecting a site for a nuclear power plant requires extensive studies to ensure its safety and stability during its operation until its decommissioning. The 4,500-year old Egyptian pyramids at Giza are buildings to learn from. This paper tries to pin down the reasons for the survival of the Giza pyramids in order to reach a criterion for choosing sites for important buildings. It argues that the site selection and the geological properties of the area, being away from seismic effects,, floods and groundwater levels, the stability of the geometric form of the pyramid, the solidity of the structural engineering and precision of execution arguably are the reasons why the Great Pyramids of Giza are the only survivors of the seven wonders of the ancient world.
文摘The simulation of indentations with so called “equivalent” pseudo-cones for decreasing computer time is challenged. The mimicry of pseudo-cones having equal basal surface and depth with pyramidal indenters is excluded by basic arithmetic and trigonometric calculations. The commonly accepted angles of so called “equivalent” pseudo-cones must not also claim equal depth. Such bias (answers put into the questions to be solved) in the historical values of the generally used half-opening angles of pseudo-cones is revealed. It falsifies all simulations or conclusions on that basis. The enormous errors in the resulting hardness H<sub>ISO</sub> and elastic modulus E<sub>r-ISO</sub> values are disastrous not only for the artificial intelligence. The straightforward deduction for possibly ψ-cones (ψ for pseudo) without biased depths’ errors for equal basal surface and equal volume is reported. These ψ-cones would of course penetrate much more deeply than the three-sided Berkovich and cube corner pyramids (r a/2), and their half-opening angles would be smaller than those of the respective pyramids (reverse with r > a/2 for four-sided Vickers). Also the unlike forces’ direction angles are reported for the more sideward and the resulting downward directions. They are reflected by the diameter of the parallelograms with length and off-angle from the vertical axis. Experimental loading curves before and after the phase-transition onsets are indispensable. Mimicry of ψ-cones and pyramids is also quantitatively excluded. All simulations on their bases would also be dangerously invalid for industrial and solid pharmaceutical materials.
文摘Pyramids,symbols of the Ancient Egyptian civilization,are visited by tourists and studied by researchers from all around the world.However,the techniques used by Ancient Egyptians to construct the pyramid,specifically,how such a tall structure could have been constructed from huge blocks of stone with the limited productive forces at the time,remains a mystery to the world.Though numerous theories,such as the use of ramps,levers,pulleys,fluid buoyancy,and cast-in-place concrete,have been proposed in academia,no consensus has been reached to date.Based on mechanical principles and the productive forces available at the time,the famous Pyramid of Khufu is used as a case study in this paper to propose a theory of pit-aided construction.The main steps include the digging of the pit,the transportation of stone blocks into the pit,the layer-by-layer construction,and the layer-by-layer filling of soil until the top of the pyramid is completed.The main idea of the pit-aided construction was to use the self-weight of the stone material to achieve the transportation of stone blocks by converting potential energy to kinetic energy,thereby avoiding the large amounts of work that must be done to elevate the huge blocks of stone.The proposed theory of pit-aided construction is consistent with the cultural custom of burial that is associated with tomb construction,namely laying the deceased to rest through burial,and is also consistent with the productive forces available in Ancient Egypt at the time.
基金the National Basic Research Program of China under Grant Nos 2011CB301900,2012CB619304 and 2010CB327504the High-Technology Research and Development Program of China under Grant No 2011AA03A103+1 种基金the National Natural Science Foundation of China under Grant Nos 60990311,60906025,60936004 and 61176063the Natural Science Foundation of Jiangsu Province under Grant Nos BK2011010 and BK2009255.
文摘GaN with hexagonal pyramids is fabricated using the photo-assisted electroless chemical etching method.Defective areas of the GaN substrate are selectively etched in a mixed solution of KOH and K2S2O8 under ultraviolet illumination,producing submicron-sized pyramids.Hexagonal pyramids on the etched GaN with well-defined{1011}facets and very sharp tips are formed.High-resolution x-ray diffraction shows that etched GaN with pyramids has a higher crystal quality,and micro-Raman spectra reveal a tensile stress relaxation in GaN with pyramids compared with normal GaN.The cathodoluminescence intensity of GaN after etching is significantly increased by three times,which is attributed to the reduction in the internal reflection,high-quality GaN with pyramids and the Bragg effect.
文摘Hyperbolic Coxeter polytopes are defined precisely by combinatorial type. Polytopes in hyperbolic n-space with n + p faces that have the combinatorial type of a pyramid over a product of simplices were classified by Tumarkin for small p. In this article we generalise Tumarkin’s methods and find the remaining hyperbolic Coxeter pyramids.
文摘Classical facet elements do not provide an optimal rate of convergence of the numerical solution toward the solution of the exact problem in H(div)-norm for general unstructured meshes containing hexahedra and prisms.We propose two new families of high-order elements for hexahedra,triangular prisms and pyramids that recover the optimal convergence.These elements have compatible restrictions with each other,such that they can be used directly on general hybrid meshes.Moreover the H(div)proposed spaces are completing the De Rham diagram with optimal elements previously constructed for H1 and H(curl)approximation.The obtained pyramidal elements are compared theoretically and numerically with other elements of the literature.Eventually,numerical results demonstrate the efficiency of the finite elements constructed.
基金This work was financially supported by the National Natural Science Foundation of China(No.61801403)the Sichuan province Foundation for Distinguished Young Team(No.20CXTD0106)the Basic Research Cultivation Project(No.2682021ZTPY004).
文摘Monitoring physiological signals of the human body can provide extremely important information for sports healthcare,preventing injuries and providing efficient guidance for individual sports.However,the signals related to human healthcare involve both subtle and vigorous signals,making it difficult for a sensor to satisfy the full-scale monitoring at the same time.Here,a novel conductive elastomer featuring homogeneously micropyramid-structured PDMS/CNT composite is used to fabricate highperformance piezoresistive sensors by a drop-casting method.Benefiting from the significant increase in the contact area of microstructure during deformation,the flexible sensor presents a broad detection range(up to 185.5 kPa),fast response/recovery time(44/13 ms),ultrahigh sensitivity(242.4 kPa–1)and excellent durability over 8,000 cycles.As a proof of concept,the as-fabricated pressure sensor can be used for body-area sports healthcare,and enable the detection of full-scale pressure distribution.Considering the fabulous sensing performance,the sensor may potentially become promising in personal sports healthcare and telemedicine monitoring.
基金supported by the National Basic Research Program ofChina("973"Program)(Grant Nos.2006CB701300,2006CB701304)the China Postdoctoral Foundation(Grant No.2007041172),Hubei Natural Science Foundation(Grant No.2007ABA042)LIESMARS Special Research Fund and the Wuhan Key Scientific and Technological Project(Grant No.200810321144)
文摘In order to improve the quality of remote sensing image fusion,a new method combining nonsubsampled Laplacian pyramid (NLP)and bidimensional empirical mode decomposition(BEMD)is proposed.First,the high resolution panchromatic image (PAN)is decomposed using NLP until the approximate component and the low resolution multispectral image(MS)contain features with a similar scale.Then,the approximation component and the MS are decomposed by BEMD,resulting in a number of bidimensional intrinsic mode functions(BIMF)and a residue respectively.The instantaneous frequency is computed in 4 directions of the BIMFs.Considering the positive or negative coefficients in the corresponding position,a weighted algorithm is designed for fusing the high frequency details using the instantaneous frequency and the coefficient absolute value of the BIMFs as fusion feature.The fused image is then obtained through inverse BEMD and NLP.Experimental results have illustrated the advantage of this method over the IHS,DWT andà-Trous wavelet in both spectral and spatial detail qualities.
基金NKBRSF on Mathematics Mechanics! (grant G1998030600)the National Natural Science Foundation of China! (grants 69603009 and 1
文摘This paper describes practical approaches on how to construct bounding pyramids and bounding cones for triangular Bezier surfaces. Examples are provided to illustrate the process of construction and comparison is made between various surface bounding volumes. Furthermore, as a starting point for the construction, we provide a way to compute hodographs of triangular Bezier surfaces and improve the algorithm for computing the bounding cone of a set of vectors. [ABSTRACT FROM AUTHOR]
基金M.P.,and W.L.C.acknowledge Discovery Grants DP110100713,DP140100883,DP120100170,and DP140100052the Melbourne Centre for Nanofabrication(MCN)in the Victorian Node of the Australian National Fabrication Facility(ANFF).D.Sikdar acknowledges Engineering and Physical Sciences Research Council UK’s funding scheme EP/L02098X/1.
文摘Surface-enhanced Raman scattering(SERS)substrates play important roles for the enhancement of inelastic scattering signals.Traditional substrates such as roughened electrodes and colloidal aggregates suffer from well-known signal reproducibility issues,whereas for current dominant two-dimensional planar systems,the hot spot distributions are limited by the zero-,one-or two-dimensional plane.The introduction of a three-dimensional(3D)system such as a pyramid geometry breaks the limitation of a single Cartesian SERS-active area and extends it into the z-direction,with the tip potentially offering additional benefits of strong field enhancement and high sensitivity.However,current 3D pyramidal designs are restricted to film deposition on prepared pyramid templates or self-assembly in pyramidal molds with spherical building blocks,hence limiting their SERS effectiveness.Here,we report on the fabrication of a new class of low cost and well-defined plasmonic nanoparticle pyramid arrays from different anisotropic shaped nanoparticles using combined top-down lithography and bottom-up self-assembly approach.These pyramids exhibit novel optical scattering properties that can be exploited for the design of reproducible and sensitive SERS substrate.The SERS intensity was found to decrease drastically in accordance with a power law function as the focal planes move from the apex of the pyramid structure towards the base.In comparison to sphere-based building blocks,pyramids assembled from anisotropic rhombic dodecahedral gold nanocrystals with numerous sharp tips exhibited the strongest SERS performance.Graphical Abstract Macroscale pyramidal array films with plasmonic tunability as a new class of SERS substrate for sensitive detection of chemicals.
基金This paper was supported by The National Natural Science Foundation of China(No.10771063)Key Laboratory ofHigh performance Computation and Stochastic Information Processing,Hunan Province and Ministry of Education,Institutional Research Plan No.AV0Z 10190503,Anhui Agricultural University(yj2012-03)Grant No.IAA 100190803 of the Academy of Sciences of the Czech Republic and The Natural Sciences and Engineering Research Council of Canada.The authors are indebted to Pavel Krızek and Kevin B.Davies for their help in preparation of Figs.1 and 2,and Jan Brandts for fruitful discussions.
文摘Pyramidal elements are often used to connect tetrahedral and hexahedral elements in the finite element method.In this paper we derive three new higher order numerical cubature formulae for pyramidal elements.
文摘Archaeologists(考古学家)have unearthed the remains of a Mayan city nearly 3,000 years old in northern Guatemala,with pyramids(金字塔)and monuments that showcase its significance as an important ceremonial site.The Mayan civilization arose around 2000 BC,reaching its height between 400 AD and 900 AD in what is present-day southern Mexico and Guatemala,as well as parts of Belize,El Salvador and Honduras.
基金Supported by Sichuan Science and Technology Program(2023YFSY0026,2023YFH0004)Supported by the Institute of Information&Communications Technology Planning&Evaluation(IITP)grant funded by the Korean government(MSIT)(No.RS-2022-00155885,Artificial Intelligence Convergence Innovation Human Resources Development(Hanyang University ERICA)).
文摘Two-dimensional endoscopic images are susceptible to interferences such as specular reflections and monotonous texture illumination,hindering accurate three-dimensional lesion reconstruction by surgical robots.This study proposes a novel end-to-end disparity estimation model to address these challenges.Our approach combines a Pseudo-Siamese neural network architecture with pyramid dilated convolutions,integrating multi-scale image information to enhance robustness against lighting interferences.This study introduces a Pseudo-Siamese structure-based disparity regression model that simplifies left-right image comparison,improving accuracy and efficiency.The model was evaluated using a dataset of stereo endoscopic videos captured by the Da Vinci surgical robot,comprising simulated silicone heart sequences and real heart video data.Experimental results demonstrate significant improvement in the network’s resistance to lighting interference without substantially increasing parameters.Moreover,the model exhibited faster convergence during training,contributing to overall performance enhancement.This study advances endoscopic image processing accuracy and has potential implications for surgical robot applications in complex environments.
基金Shenzhen Institute of Artificial Intelligence and Robotics for Society,Grant/Award Number:AC01202201003-02GuangDong Basic and Applied Basic Research Foundation,Grant/Award Number:2024A1515010252Longgang District Shenzhen's“Ten Action Plan”for Supporting Innovation Projects,Grant/Award Number:LGKCSDPT2024002。
文摘Audio-visual scene classification(AVSC)poses a formidable challenge owing to the intricate spatial-temporal relationships exhibited by audio-visual signals,coupled with the complex spatial patterns of objects and textures found in visual images.The focus of recent studies has predominantly revolved around extracting features from diverse neural network structures,inadvertently neglecting the acquisition of semantically meaningful regions and crucial components within audio-visual data.The authors present a feature pyramid attention network(FPANet)for audio-visual scene understanding,which extracts semantically significant characteristics from audio-visual data.The authors’approach builds multi-scale hierarchical features of sound spectrograms and visual images using a feature pyramid representation and localises the semantically relevant regions with a feature pyramid attention module(FPAM).A dimension alignment(DA)strategy is employed to align feature maps from multiple layers,a pyramid spatial attention(PSA)to spatially locate essential regions,and a pyramid channel attention(PCA)to pinpoint significant temporal frames.Experiments on visual scene classification(VSC),audio scene classification(ASC),and AVSC tasks demonstrate that FPANet achieves performance on par with state-of-the-art(SOTA)approaches,with a 95.9 F1-score on the ADVANCE dataset and a relative improvement of 28.8%.Visualisation results show that FPANet can prioritise semantically meaningful areas in audio-visual signals.
