AIM:To assess the variations in photoreceptor cell packing density(PCPD)across the retina among young healthy individuals with emmetropia,low and moderate myopia.METHODS:High-resolution adaptive optics scanning laser ...AIM:To assess the variations in photoreceptor cell packing density(PCPD)across the retina among young healthy individuals with emmetropia,low and moderate myopia.METHODS:High-resolution adaptive optics scanning laser ophthalmoscopy(AOSLO)systems were utilized for retinal imaging with a large sampling window of 700μm×700μm.The study cohort included 14 emmetropic[spherical equivalent(SE)ranged+0.5 to-0.5 D],15 low myopic(SE ranged-0.5 to-3 D)and 21 moderate myopic(SE ranged-3 to-6 D)healthy young adults.Photoreceptors at 3°temporal,6°superior and inferior 6°were captured.Statistical analysis was then performed to obtain PCPD and cell spacing.RESULTS:The average age of participants was 22.54±2.86(ranged 20–30y)with no difference among 3 groups.At 3°temporal,the emmetropic group exhibited the highest PCPD of 15186.16±2050.54 cells/mm^(2),while the low and moderate myopic groups had PCPD of 14009.15±1073.01 and 13466.92±1121.71 cells/mm2,respectively.At 3°temporal,the emmetropic group also had the smallest cell spacing at 6.66±0.26 mm,compared to 6.85±0.26 and 6.91±0.28 mm for the low and moderate myopic groups,respectively.Compared to the emmetropic group,at 3°temporal,the myopic groups showed significantly reduced PCPD(low myopia:P=0.032;moderate myopia:P=0.001).At 6°inferior,the moderate myopic group exhibited a significant decrease in PCPD(P=0.013),while at 6°superior,there were no significant statistical differences in PCPD for the low and moderate myopic groups(P>0.05).In comparison to the emmetropic group,only the moderate myopic group showed significantly increased cell spacing at all three positions(temporal 3°:P=0.011,superior 6°:P=0.046,inferior 6°:P=0.013).Correlation analysis revealed a positive correlation between PCPD and axial length changes(P<0.05).CONCLUSION:Reduced PCPD and increased cell spacing strongly correlated with refractive error in mild to moderate myopic eyes,especially at 6°inferior to the fovea and the decreased PCPD in the macular region of myopic patients may be associated with increased axial lengthinduced retinal stretching.展开更多
The propylene/propane(C_(3)H_(6)/C_(3)H_(8))separation is particularly challenging due to their highly similar physical properties,but of industrial importance.Herein,we report a bifunctional ultramicroporous metal-or...The propylene/propane(C_(3)H_(6)/C_(3)H_(8))separation is particularly challenging due to their highly similar physical properties,but of industrial importance.Herein,we report a bifunctional ultramicroporous metal-organic framework(Co-aip-pyz)with customized pore environment and selective binding sites for the challenging C_(3)H_(6)/C_(3)H_(8) separation.Co-aip-pyz exhibits a good C_(3)H_(6) uptake with an ultrahigh C_(3)H_(6) packing density(931 g/L),as well as possesses a remarkable C_(3)H_(6)/C_(3)H_(8) uptake ratio with 911% and distinguished C_(3)H_(6)/C_(3)H_(8) selectivity(>10^(4))at 298 K and 1.0 bar.Furthermore,Co-aip-pyz possesses a record high C_(3)H_(6) packing density with 859 g/L at 313 K and 1.0 bar,which is unprecedented in the C_(3)H_(6)/C_(3)H_(8) separation.Its high performance for the C_(3)H_(6)/C_(3)H_(8) separation has been further confirmed by breakthrough experiments and molecular simulations.Combined with good stability,facilely synthesized procedure by low-cost precursors,record-high C_(3)H_(6) packing density,as well as good C_(3)H_(6)/C_(3)H_(8) separation performance,it highlights Co-aip-pyz as a benchmark adsorbent to address daunting challenge for industrial C_(3)H_(6)/C_(3)H_(8) separation.This work provides valuable insights into constructing top-performing MOF materials for addressing the industrial separation challenges.展开更多
Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To ob...Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To obtain a high packing density, powders with different particle sizes, including limestone fines (LSF), superfine cement (SFC), condensed silica fume (CSF), were added to the cement paste and the resulting packing densities were measured directly by a newly-developed wet packing test. Results demonstrated that addition of powders with a finer size would more significantly improve the packing density but the powders should be at least as fine as 1/4 of the OPC to effectively improve the packing density. Packing density and voids ratio relationship showed that a small increase in packing density can significantly decrease the voids ratio, which could allow the W/P ratio to be reduced to improve the strength and durability of the concrete without compromising the flowability.展开更多
Crystal structure determines electrochemical energy storage characteristics;this is the underlying logic of material design.To date,hundreds of electrode materials have been developed to pursue superior performance.Ho...Crystal structure determines electrochemical energy storage characteristics;this is the underlying logic of material design.To date,hundreds of electrode materials have been developed to pursue superior performance.However,it remains a great challenge to understand the fundamental structure–performance relationship and achieve quantitative crystal structure design for efficient energy storage.In this review,we introduce the concept of crystal packing factor(PF),which can quantify crystal packing density.We then present and classify the typical crystal structures of attractive cathode/anode materials.Comparative PF analyses of different materials,including polymorphs,isomorphs,and others,are performed to clarify the influence of crystal packing density on energy storage performance through electronic and ionic conductivities.Notably,the practical electronic/ionic conductivities of energy storage materials are based on their intrinsic characteristics related to the PF yet are also affected by extrinsic factors.The PF provides a novel avenue for understanding the electrochemical performance of pristine materials and may offer guidance on designing better materials.Additional approaches involve size regulation,doping,carbon additives,and other methods.We also propose extended PF concepts to understand charge storage and transport behavior at different scales.Finally,we provide our insights on the major challenges and prospective solutions in this highly exciting field.展开更多
The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extractio...The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.展开更多
Particle elongation is an important factor affecting the packing properties of rod-like particles. However, rod-like particles can be easily bent into non-convex shapes, in which the effect of bending should also be o...Particle elongation is an important factor affecting the packing properties of rod-like particles. However, rod-like particles can be easily bent into non-convex shapes, in which the effect of bending should also be of concerned, To explore the shape effects of elongation and bending, together with the size and volume fraction effects on the disordered packing density of mixtures of non-convex particles, binary and polydisperse mixtures of curved spherocylinders are simulated employing sphere assembly models and the relaxation algorithm in the present work. For binary packings with the same volume, curves of the packing density versus volume fraction have good linearity, while densities are plotted as a series of equidistant curves under the condition of the same shape. The independence of size and shape effects on the packing density is verified for mixtures of curved spherocylinders. The explicit formula used to predict the density of binary mixtures, by superposing the two independent functions of the size and shape parameters, is extended to include a non-convex shape factor. A polydisperse packing with the shape factor following a uniform distribution under the condition of the same volume is equivalent to a binary mixture with certain components. The packing density is thus predicted as the mean of maximum and minimum densities employing a weighing method.展开更多
In rockfill dam engineering,particle breakage of rockfill materials is one of the major factors resulting in dam settlement.In this study,one-dimensional compression tests on a series of coarse granular materials with...In rockfill dam engineering,particle breakage of rockfill materials is one of the major factors resulting in dam settlement.In this study,one-dimensional compression tests on a series of coarse granular materials with artificially-graded particle size distributions(PSDs)were carried out.The tests focused on understanding the role of initial PSDs in the dense packing density,compressibility and crushability of coarse granular materials.The effects of fractal dimension(D)and size polydispersity(θ)of PSDs were quantitatively analyzed.Two different loading stages were identified from the logarithms of the stress-strain relationships,with the turning point marked as the yield stress.A similar effect of initial PSDs was observed on the packing density and low-pressure modulus of coarse granular materials.The packing density and low-pressure modulus increased monotonically withθ,and their peak values were attained at a D value of approximately 2.2.However,there was no unique correspondence between the dense packing density and low-pressure modulus.The particle breakage was influenced differently by the initial PSDs,and it decreased with the values of D andθ.The emergence of the unique ultimate state was also identified from both the compression curves and PSDs of the samples after the tests.The potential implications of the test results in the design of both low and high rockfill dams were also demonstrated.展开更多
Random packings of spherical particles have attracted attention for many years.An algorithm based on compression is developed to generate random packings of spherical particles in this paper.This method is different f...Random packings of spherical particles have attracted attention for many years.An algorithm based on compression is developed to generate random packings of spherical particles in this paper.This method is different from previous compression-based algorithm.In order to increase the packing density,a process of shaking is applied during packing process.The algorithm is mainly composed of three procedures:generating initial packing configuration by using random sequential adsorption(RSA),compressing packing domain,and shaking.The packing structure is characterized by packing density and coordinate number.The packing density increases with iteration number and a stable packing configuration is obtained after the iteration number is more than 34 000.The packing density is 0.85 and the average coordinate number is 3.7 in a stable packing configuration.展开更多
To guarantee the efficient and high-value reutilization of waste concrete from construction waste,the waste concrete was mechanically ground,and three degrees of fineness recycled concrete powder(RCP)were obtained by ...To guarantee the efficient and high-value reutilization of waste concrete from construction waste,the waste concrete was mechanically ground,and three degrees of fineness recycled concrete powder(RCP)were obtained by different grinding time.By analyzing the particle characteristics of RCP with different fineness,the filling-densification effect of cement-RCP cementitious material system was quantitatively investigated based on Andreasen,Fuller,and Aim-Goff models.In addition,the macroscopic mechanical properties of cement paste mixed with RCP were studied,and the influencing mechanisms of RCP on the microstructure of cement paste was revealed.Macroscopic research results show that the particle fineness of RCP after grinding is smaller than that of cement.When the RCP replaces 0%to 20%cement,the packing density based on the Aim-Goff model increases with the increase of RCP content,whereas the macro-mechanical properties first improve and then degrade with the increase of RCP content.Microscopic results show that at 5%RCP content,beneficial hydration products such as C-S-H and beneficial pore increase in cement-RCP paste;while at>15%content,beneficial products decrease and harmful substances such as Ca(OH)_(2)and harmful pore increases.These research findings suggest that the incorporation of RCP can make the cementitious system denser,and the appropriate RCP content can improve the macro-and microscopic properties of cement-based materials.展开更多
To explore mix proportion design of RAC with aggregates tightly packed,the dry and wet packing density of recycled coarse aggregates mixture system and recycled coarse and fine aggregates were tested,then the influenc...To explore mix proportion design of RAC with aggregates tightly packed,the dry and wet packing density of recycled coarse aggregates mixture system and recycled coarse and fine aggregates were tested,then the influence of replacement rate and particle size ratio on the packing density of particle system was explored,the packing density prediction model of recycled coarse aggregates based on particle morphology was constructed,and the mix proportion optimization for recycled aggregate concrete with dry-wet packing model was carried out.The experimental results show that,with the increasing of recycled aggregate replacement rate or fine-grained volume ratio,the dry packing density of recycled coarse aggregates decreases gradually.With the increasing of replacement rate,the particle gradation can be optimized by increasing coarsegrained volume ratio.There is a significant effect for particle morphology parameter K and the particle size ratio on the packing density of the binary mixed system,and the packing density prediction model of recycled coarse aggregates based on particle morphology was constructed.The maximum increase in compressive strength and tensile strength of RAC with mix proportion optimized by the dry-wet packing model are 12.94%and 11.09%,and the cementitious materials is reduced by 21.83%,then the superiority of the mix proportion optimization of RAC with the dry-wet close packing model is confirmed.The results of this paper can provide a theoretical basis for the mix proportion design of RAC.展开更多
A two-dimensional generalized Langevin equation is proposed to describe the protein conformational change, compatible to the electron transfer process governed by atomic packing density model. We assume a fractional G...A two-dimensional generalized Langevin equation is proposed to describe the protein conformational change, compatible to the electron transfer process governed by atomic packing density model. We assume a fractional Gaussian noise and a white noise through bond and through space coordinates respectively, and introduce the coupling effect coming from both fluctuations and equilibrium variances. The general expressions for autocorrelation functions of distance fluctuation and fluorescence lifetime variation are derived, based on which the exact conformational change dynamics can be evaluated with the aid of numerical Laplace inversion technique. We explicitly elaborate the short time and long time approximations. The relationship between the two-diraensional description and the one-dimensional theory is also discussed.展开更多
Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam(PBF-EB)tech-nology.In this st...Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam(PBF-EB)tech-nology.In this study,mechanical stimulation was suggested to suppress smoke of gas-atomized(GA)Ti-48Al-2Cr-2Nb powder using Al_(2)O_(3) and WC ball milling.The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribu-tion map and contact mechanics simulation.It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture.The variation of surface and electrical properties by mechanical stimulation was investigated via XPS,TEM,and Impedance analysis.The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration,despite the increased oxide film thickness,and the capacitive response disappeared in Al-60 and WC-30 via metal-insulator transition.This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation.The smoke mechanism of ball-milled powders was discussed based on the percolation theory.In the smoke experiment,smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50,respectively,despite the longer charge dissipation time.This could be due to the high probability of contact with conductive particles.For the Al-60 and WC-30 powders,smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity.We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.展开更多
An alternative model for the prediction of surface roughness length is developed. In the model a new factor is introduced to compensate for the effects of wake diffusion and interactions between the wake and roughness...An alternative model for the prediction of surface roughness length is developed. In the model a new factor is introduced to compensate for the effects of wake diffusion and interactions between the wake and roughness obstacles. The experiments are carried out by the use of the hot wire anemometry in the simulated atmospheric boundary layer in a wind tunnel. Based on the experimental data, a new expression for the zero-plane displacement height is proposed for the square arrays of roughness elements, which highlights the influence of free-stream speed on the roughness length. It appears that the displacement height increases with the wind speed while the surface roughness length decreases with Reynolds number increasing. It is shown that the calculation results based on the new expressions are in reasonable agreement with the experimental data.展开更多
The Cerrado region of Brazil,one of the fastest-growing agricultural areas in the world,is undergoing very rapid mechanization;this development is good for the country's economy but may also snowball into substant...The Cerrado region of Brazil,one of the fastest-growing agricultural areas in the world,is undergoing very rapid mechanization;this development is good for the country's economy but may also snowball into substantial loss of agricultural land and other environmental degradation if the soil susceptibility and vulnerability to compaction is not well understood.In this study we explored different techniques for estimating soil intrinsic abilities to withstand applied pressure using the prevalent Oxisols of the Cerrado region under native vegetation.Undisturbed samples were collected from three sites within the region and subjected to 1) compressibility test;2) manual penetration resistance test;3) automated penetration resistance test;and 4) packing density analysis.The four methods produced analogous results.Our results showed the significant influence of soil structure on the inherent strength and compaction susceptibility of the soils.We also established the association of soil structure with the mineralogy of the soil.It is noteworthy that the packing density which was developed from very simple and easily obtained parameters could give a picture of the tendency of the soil to compact.Thus,this approach would be useful in developing compaction susceptibility maps for the region.It could be concluded that most of the Oxisols in the Cerrado region would support mechanized agricultural production very successfully.However,there is need for careful management of the mechanization process to avert degradation.The management techniques should include conservationist practices such as no till in order to maintain as much as possible the favorable structure and drainage of these very old soils.展开更多
The calculating model for the packing degree of spherical particles system was modified. The grain grading model of cement-based materials was established and could be applied in the global grading system as well as i...The calculating model for the packing degree of spherical particles system was modified. The grain grading model of cement-based materials was established and could be applied in the global grading system as well as in the nano-fiber reinforced system. According to the grain grading model, two kinds of mortar were designed by using the global grain materials and nano-fiber materials such as fly ash, silica fume and NR powder. In this paper, the densities of two above systems cured for 90d were tested and the relationship of deleterious porosity and the total porosity of hardened mortar was discussed. Research results show that nano-fiber material such as NR powder can increase the density of cement-based materials. The relationship of deleterious porosity and the total porosity of hardened mortar accords with logarithmic curve. The deleterious porosity and the rationality of the grading can be roughly predicted through calculating the packing degree by the grain grading model of cement-based materials.展开更多
Sand textural control on SECB （shear-enhanced compaction band） formation is analyzed combining field observations, detailed material characterization and mechanical testing for poorly lithified sandstone units in Pr...Sand textural control on SECB （shear-enhanced compaction band） formation is analyzed combining field observations, detailed material characterization and mechanical testing for poorly lithified sandstone units in Provence （France）. Field observations show that SECBs are densely distributed in a coarse-grained unit with moderate porosity （27%）, whereas few SECBs are developed within the overlying fine-grained, high-porosity （39%） unit. Results from textural characterization show that the main difference between the two sand units is grain size and sorting, whereas they are similar with respect to composition and grain angularity. Packing density is introduced as an important parameter for comparing the compaction properties independent of the textural variations between the two units. Compaction experiments show a slightly faster compaction of the coarse-grained sand as compared to the fine-grained sand, and more pronounced grain crushing is observed in the coarse-grained unit. The results indicate that the preferential localization of SECBs to the coarse-grained unit is controlled by a slightly denser packing of the coarse-grained material at the time of band formation together with higher stress concentrations on grain contacts. Hence, this study emphasizes that porosity alone is an insufficient parameter for predicting deformation band evolution in sand （stone）.展开更多
The effect of ultra-fine fly ash(UFFA),steel slag(SS)and silica fume(SF)on packing density of binary,ternary and quaternary cementitious materials was studied in this paper in terms of minimum water requirement of cem...The effect of ultra-fine fly ash(UFFA),steel slag(SS)and silica fume(SF)on packing density of binary,ternary and quaternary cementitious materials was studied in this paper in terms of minimum water requirement of cement.The influence of mineral admixtures on the relative density of pastes with low water/hinder ratios was analyzed and the relationship between paste density and compressive strength of the corresponding hardened mortars was discussed.The results indicate that the incorporation of mineral admixtures can effectively improve the packing density ofcementitious materials;the increase in packing density of a composite with incorporation of two or three kinds of mineral admixtures is even more obvious than that with only one mineral admixture.Moreover,an optimal amount of mineral admixture imparts to the mixture maximum packing density.The dense packing effect of a mineral admixture can increase the packing density of the resulting cementitious material and also the density of paste with low water/binder ratio,which evidently enhances the compressive strength of the hardened mortar.展开更多
The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in ...The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in terms of packing density and coordination number （CN）. It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing den- sity of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.展开更多
Random packings of binary mixtures of spheres and spherocylinders with the same volume and the same diameter were simulated by a sphere assembly model and relaxation algorithm.Simulation results show that,independentl...Random packings of binary mixtures of spheres and spherocylinders with the same volume and the same diameter were simulated by a sphere assembly model and relaxation algorithm.Simulation results show that,independently of the component volume fraction,the mixture packing density increases and then decreases with the growth of the aspect ratio of spherocylinders,and the packing density reaches its maximum at the aspect ratio of 0.35.With the same volume particles,results show that the dependence of the mixture packing density on the volume fraction of spherocylinders is approximately linear.With the same diameter particles,the relationship between the mixture packing density and component volume fraction is also roughly linear for short spherocylinders,but when the aspect ratio of spherocylinders is greater than 1.6,the curves turn convex which means the packing of the mixture can be denser than either the sphere or spherocylinder packing alone.To validate the sphere assembly model and relaxation algorithm,binary mixtures of spheres and random packings of spherocylinders were also simulated.Simulation results show the packing densities of sphere mixtures agree with previous prediction models and the results of spherocylinders correspond with the simulation results in literature.展开更多
The existing particle packing density models each with two or more parameters accounting for certain particle interactions （the loosening effect parameter, wall effect parameter, wedging effect parameter, and compact...The existing particle packing density models each with two or more parameters accounting for certain particle interactions （the loosening effect parameter, wall effect parameter, wedging effect parameter, and compaction index, denoted by a, b, c, and K, respectively） may be classified into the 2-parameter model （with a and b incorporated）, the compressible model （with a, b, and 1（incorporated）, and the 3- parameter model （with a, b, and c incorporated）. This paper evaluates these models by comparing their respective packing density predictions with the test results published in the literature. It was found that their accuracy varies with both the size ratio and volumetric fractions of the binary mix. In general, when the size ratio is larger than 0.65, all the packing models are sufficiently accurate. However, when the size ratio is smaller than 0.65, some of them become inaccurate and the errors tend to be larger at around the volumetric fractions giving maximum packing density. Relatively, the 3-parameter model is the most accurate and widely applicable.展开更多
基金Supported by National Natural Science Foundation of China(No.82271107).
文摘AIM:To assess the variations in photoreceptor cell packing density(PCPD)across the retina among young healthy individuals with emmetropia,low and moderate myopia.METHODS:High-resolution adaptive optics scanning laser ophthalmoscopy(AOSLO)systems were utilized for retinal imaging with a large sampling window of 700μm×700μm.The study cohort included 14 emmetropic[spherical equivalent(SE)ranged+0.5 to-0.5 D],15 low myopic(SE ranged-0.5 to-3 D)and 21 moderate myopic(SE ranged-3 to-6 D)healthy young adults.Photoreceptors at 3°temporal,6°superior and inferior 6°were captured.Statistical analysis was then performed to obtain PCPD and cell spacing.RESULTS:The average age of participants was 22.54±2.86(ranged 20–30y)with no difference among 3 groups.At 3°temporal,the emmetropic group exhibited the highest PCPD of 15186.16±2050.54 cells/mm^(2),while the low and moderate myopic groups had PCPD of 14009.15±1073.01 and 13466.92±1121.71 cells/mm2,respectively.At 3°temporal,the emmetropic group also had the smallest cell spacing at 6.66±0.26 mm,compared to 6.85±0.26 and 6.91±0.28 mm for the low and moderate myopic groups,respectively.Compared to the emmetropic group,at 3°temporal,the myopic groups showed significantly reduced PCPD(low myopia:P=0.032;moderate myopia:P=0.001).At 6°inferior,the moderate myopic group exhibited a significant decrease in PCPD(P=0.013),while at 6°superior,there were no significant statistical differences in PCPD for the low and moderate myopic groups(P>0.05).In comparison to the emmetropic group,only the moderate myopic group showed significantly increased cell spacing at all three positions(temporal 3°:P=0.011,superior 6°:P=0.046,inferior 6°:P=0.013).Correlation analysis revealed a positive correlation between PCPD and axial length changes(P<0.05).CONCLUSION:Reduced PCPD and increased cell spacing strongly correlated with refractive error in mild to moderate myopic eyes,especially at 6°inferior to the fovea and the decreased PCPD in the macular region of myopic patients may be associated with increased axial lengthinduced retinal stretching.
基金financially supported by the National Natural Science Foundation of China(No.22275102)NCC Fund(No.NCC2022FH01)。
文摘The propylene/propane(C_(3)H_(6)/C_(3)H_(8))separation is particularly challenging due to their highly similar physical properties,but of industrial importance.Herein,we report a bifunctional ultramicroporous metal-organic framework(Co-aip-pyz)with customized pore environment and selective binding sites for the challenging C_(3)H_(6)/C_(3)H_(8) separation.Co-aip-pyz exhibits a good C_(3)H_(6) uptake with an ultrahigh C_(3)H_(6) packing density(931 g/L),as well as possesses a remarkable C_(3)H_(6)/C_(3)H_(8) uptake ratio with 911% and distinguished C_(3)H_(6)/C_(3)H_(8) selectivity(>10^(4))at 298 K and 1.0 bar.Furthermore,Co-aip-pyz possesses a record high C_(3)H_(6) packing density with 859 g/L at 313 K and 1.0 bar,which is unprecedented in the C_(3)H_(6)/C_(3)H_(8) separation.Its high performance for the C_(3)H_(6)/C_(3)H_(8) separation has been further confirmed by breakthrough experiments and molecular simulations.Combined with good stability,facilely synthesized procedure by low-cost precursors,record-high C_(3)H_(6) packing density,as well as good C_(3)H_(6)/C_(3)H_(8) separation performance,it highlights Co-aip-pyz as a benchmark adsorbent to address daunting challenge for industrial C_(3)H_(6)/C_(3)H_(8) separation.This work provides valuable insights into constructing top-performing MOF materials for addressing the industrial separation challenges.
文摘Adoption of a low water/powder (W/P) ratio is the key to improve the strength and durability of concrete, which relies on a high packing density because fresh concrete requires excess water to offer flowability. To obtain a high packing density, powders with different particle sizes, including limestone fines (LSF), superfine cement (SFC), condensed silica fume (CSF), were added to the cement paste and the resulting packing densities were measured directly by a newly-developed wet packing test. Results demonstrated that addition of powders with a finer size would more significantly improve the packing density but the powders should be at least as fine as 1/4 of the OPC to effectively improve the packing density. Packing density and voids ratio relationship showed that a small increase in packing density can significantly decrease the voids ratio, which could allow the W/P ratio to be reduced to improve the strength and durability of the concrete without compromising the flowability.
基金supported by the National Natural Science Foundation of China(52202327)Science and Technology Commission of Shanghai Municipality(22ZR1471300)the Key Research Program of Frontier Science,Chinese Academy of Sciences(Grant No.QYZDJ-SSW-JSC013 and KGZD-EW-T06).
文摘Crystal structure determines electrochemical energy storage characteristics;this is the underlying logic of material design.To date,hundreds of electrode materials have been developed to pursue superior performance.However,it remains a great challenge to understand the fundamental structure–performance relationship and achieve quantitative crystal structure design for efficient energy storage.In this review,we introduce the concept of crystal packing factor(PF),which can quantify crystal packing density.We then present and classify the typical crystal structures of attractive cathode/anode materials.Comparative PF analyses of different materials,including polymorphs,isomorphs,and others,are performed to clarify the influence of crystal packing density on energy storage performance through electronic and ionic conductivities.Notably,the practical electronic/ionic conductivities of energy storage materials are based on their intrinsic characteristics related to the PF yet are also affected by extrinsic factors.The PF provides a novel avenue for understanding the electrochemical performance of pristine materials and may offer guidance on designing better materials.Additional approaches involve size regulation,doping,carbon additives,and other methods.We also propose extended PF concepts to understand charge storage and transport behavior at different scales.Finally,we provide our insights on the major challenges and prospective solutions in this highly exciting field.
基金the U.S. Department of Energy (Grant No. NE TL, DE-PS26-08NT00290)in part by the National Science Foundation (ECCS-1408051, CBET1120399)
文摘The finite-difference time-domain method was employed to calculate light extraction efficiency of thin-film flip-chip In Ga N/Ga N quantum well light-emitting diodes（LEDs） with TiO2 microsphere arrays. The extraction efficiency for LEDs with microsphere arrays was investigated by focusing on the effect of the packing density,packing configuration, and diameter-to-period ratio. The comparison studies revealed the importance of having a hexagonal and close-packed monolayer microsphere array configuration for achieving optimum extraction efficiency, which translated into a 3.6-fold enhancement in light extraction compared to that for a planar LED. This improvement is attributed to the reduced Fresnel reflection and enlarged light escape cone. The engineering of the far-field radiation patterns was also demonstrated by tuning the packing density and packing configuration of the microsphere arrays.
基金This work was supported by the National Natural Science Foundation of China （Grant Nos. 11272010, 11572004 and 11602088）. Tile China Postdoctoral Science Foundation （Grant No. 2016M592484） is also acknowledged.
文摘Particle elongation is an important factor affecting the packing properties of rod-like particles. However, rod-like particles can be easily bent into non-convex shapes, in which the effect of bending should also be of concerned, To explore the shape effects of elongation and bending, together with the size and volume fraction effects on the disordered packing density of mixtures of non-convex particles, binary and polydisperse mixtures of curved spherocylinders are simulated employing sphere assembly models and the relaxation algorithm in the present work. For binary packings with the same volume, curves of the packing density versus volume fraction have good linearity, while densities are plotted as a series of equidistant curves under the condition of the same shape. The independence of size and shape effects on the packing density is verified for mixtures of curved spherocylinders. The explicit formula used to predict the density of binary mixtures, by superposing the two independent functions of the size and shape parameters, is extended to include a non-convex shape factor. A polydisperse packing with the shape factor following a uniform distribution under the condition of the same volume is equivalent to a binary mixture with certain components. The packing density is thus predicted as the mean of maximum and minimum densities employing a weighing method.
基金supported by the National Natural Science Foundation of China(Grants No.52009036,U1765205,and 51979091)the Key Project of Water Conservancy Science and Technology in Jiangxi Province(Grant No.201921ZDKT13).
文摘In rockfill dam engineering,particle breakage of rockfill materials is one of the major factors resulting in dam settlement.In this study,one-dimensional compression tests on a series of coarse granular materials with artificially-graded particle size distributions(PSDs)were carried out.The tests focused on understanding the role of initial PSDs in the dense packing density,compressibility and crushability of coarse granular materials.The effects of fractal dimension(D)and size polydispersity(θ)of PSDs were quantitatively analyzed.Two different loading stages were identified from the logarithms of the stress-strain relationships,with the turning point marked as the yield stress.A similar effect of initial PSDs was observed on the packing density and low-pressure modulus of coarse granular materials.The packing density and low-pressure modulus increased monotonically withθ,and their peak values were attained at a D value of approximately 2.2.However,there was no unique correspondence between the dense packing density and low-pressure modulus.The particle breakage was influenced differently by the initial PSDs,and it decreased with the values of D andθ.The emergence of the unique ultimate state was also identified from both the compression curves and PSDs of the samples after the tests.The potential implications of the test results in the design of both low and high rockfill dams were also demonstrated.
基金National Key Basic Research and Developing Project,China(973 program) (No. 2005CB623902)A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions,China
文摘Random packings of spherical particles have attracted attention for many years.An algorithm based on compression is developed to generate random packings of spherical particles in this paper.This method is different from previous compression-based algorithm.In order to increase the packing density,a process of shaking is applied during packing process.The algorithm is mainly composed of three procedures:generating initial packing configuration by using random sequential adsorption(RSA),compressing packing domain,and shaking.The packing structure is characterized by packing density and coordinate number.The packing density increases with iteration number and a stable packing configuration is obtained after the iteration number is more than 34 000.The packing density is 0.85 and the average coordinate number is 3.7 in a stable packing configuration.
基金Funded by the National Natural Science Foundation of China Project(Nos.52108219 and U21A20150)the Lanzhou University of Technology Hongliu Outstanding Young Talent Program,China(No.04-062407)。
文摘To guarantee the efficient and high-value reutilization of waste concrete from construction waste,the waste concrete was mechanically ground,and three degrees of fineness recycled concrete powder(RCP)were obtained by different grinding time.By analyzing the particle characteristics of RCP with different fineness,the filling-densification effect of cement-RCP cementitious material system was quantitatively investigated based on Andreasen,Fuller,and Aim-Goff models.In addition,the macroscopic mechanical properties of cement paste mixed with RCP were studied,and the influencing mechanisms of RCP on the microstructure of cement paste was revealed.Macroscopic research results show that the particle fineness of RCP after grinding is smaller than that of cement.When the RCP replaces 0%to 20%cement,the packing density based on the Aim-Goff model increases with the increase of RCP content,whereas the macro-mechanical properties first improve and then degrade with the increase of RCP content.Microscopic results show that at 5%RCP content,beneficial hydration products such as C-S-H and beneficial pore increase in cement-RCP paste;while at>15%content,beneficial products decrease and harmful substances such as Ca(OH)_(2)and harmful pore increases.These research findings suggest that the incorporation of RCP can make the cementitious system denser,and the appropriate RCP content can improve the macro-and microscopic properties of cement-based materials.
基金Funded by joint Funds of the National Natural Science Foundation of China(No.U1904188)the Key Research Project of Henan Province for Colleges and Universities(No.26A560009)+3 种基金the Jiaozuo City Science and Technology Planning Project(No.2025210099)the Henan Provincial Science and Technology Research Project(No.252102320305)the Natural Science Foundation of Henan Province(No.252300421917)the Project by Key Laboratory of Intelligent Construction and Safety Operation and Maintenance of Underground Engineering in Henan Province(No.KFKT2024-01)。
文摘To explore mix proportion design of RAC with aggregates tightly packed,the dry and wet packing density of recycled coarse aggregates mixture system and recycled coarse and fine aggregates were tested,then the influence of replacement rate and particle size ratio on the packing density of particle system was explored,the packing density prediction model of recycled coarse aggregates based on particle morphology was constructed,and the mix proportion optimization for recycled aggregate concrete with dry-wet packing model was carried out.The experimental results show that,with the increasing of recycled aggregate replacement rate or fine-grained volume ratio,the dry packing density of recycled coarse aggregates decreases gradually.With the increasing of replacement rate,the particle gradation can be optimized by increasing coarsegrained volume ratio.There is a significant effect for particle morphology parameter K and the particle size ratio on the packing density of the binary mixed system,and the packing density prediction model of recycled coarse aggregates based on particle morphology was constructed.The maximum increase in compressive strength and tensile strength of RAC with mix proportion optimized by the dry-wet packing model are 12.94%and 11.09%,and the cementitious materials is reduced by 21.83%,then the superiority of the mix proportion optimization of RAC with the dry-wet close packing model is confirmed.The results of this paper can provide a theoretical basis for the mix proportion design of RAC.
基金This work was supported by the National Natural Science Foundation of China （No.20973119 and No.21033008）.
文摘A two-dimensional generalized Langevin equation is proposed to describe the protein conformational change, compatible to the electron transfer process governed by atomic packing density model. We assume a fractional Gaussian noise and a white noise through bond and through space coordinates respectively, and introduce the coupling effect coming from both fluctuations and equilibrium variances. The general expressions for autocorrelation functions of distance fluctuation and fluorescence lifetime variation are derived, based on which the exact conformational change dynamics can be evaluated with the aid of numerical Laplace inversion technique. We explicitly elaborate the short time and long time approximations. The relationship between the two-diraensional description and the one-dimensional theory is also discussed.
基金This work was partially supported by JSPS KAKENHI(grant numbers 18H03834 and 21k14432)This research was also supported by“Materials Integration for Revolutionary Design System of Structure Materials”of the Cross-Ministerial Strategic Innovation Promotion Program(SIP)of Japan Science and Technology(JST).This work was also based on the results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization(NEDO)(JPNP14014).This work was partly supported by the Technology Research Association for Future Additive Manufacturing(TRAFAM).This work is also based on the results obtained from a project(JPNP19007)commissioned by the New Energy and Industrial Technology Development Organization(NEDO).
文摘Smoke is unexpected powder-splashing caused by electrostatic force and is one of the main problems hindering the process stability and applicability of the powder bed fusion electron beam(PBF-EB)tech-nology.In this study,mechanical stimulation was suggested to suppress smoke of gas-atomized(GA)Ti-48Al-2Cr-2Nb powder using Al_(2)O_(3) and WC ball milling.The deformation mechanism of the GA powder depending on the ball milling media was discussed based on the developed particle morphology distribu-tion map and contact mechanics simulation.It was revealed that the rapid decrement of flowability and packing density after WC ball milling owing to the formation of angular fragments by the brittle fracture.The variation of surface and electrical properties by mechanical stimulation was investigated via XPS,TEM,and Impedance analysis.The electrical resistivity of the ball-milled powders gradually decreased with increasing milling duration,despite the increased oxide film thickness,and the capacitive response disappeared in Al-60 and WC-30 via metal-insulator transition.This could be due to the accumulation of strain and defects on the oxide film via mechanical stimulation.The smoke mechanism of ball-milled powders was discussed based on the percolation theory.In the smoke experiment,smoke was more suppressed for WC-10 and WC-20 than that for Al-40 and Al-50,respectively,despite the longer charge dissipation time.This could be due to the high probability of contact with conductive particles.For the Al-60 and WC-30 powders,smoke was further restricted by the formation of a percolation cluster with metal-like electrical conductivity.We believe that this study will contribute to a better understanding of the smoke mechanism and process optimization of the PBF-EB.
基金Project supported by the Major Program of the National Natural Science Foundation of China （Grant No 10632070）.
文摘An alternative model for the prediction of surface roughness length is developed. In the model a new factor is introduced to compensate for the effects of wake diffusion and interactions between the wake and roughness obstacles. The experiments are carried out by the use of the hot wire anemometry in the simulated atmospheric boundary layer in a wind tunnel. Based on the experimental data, a new expression for the zero-plane displacement height is proposed for the square arrays of roughness elements, which highlights the influence of free-stream speed on the roughness length. It appears that the displacement height increases with the wind speed while the surface roughness length decreases with Reynolds number increasing. It is shown that the calculation results based on the new expressions are in reasonable agreement with the experimental data.
基金Project supported by the Brazilian National Council for Scientific and Technological Development and the Academy of Sciences for the Developing World (TWAS)
文摘The Cerrado region of Brazil,one of the fastest-growing agricultural areas in the world,is undergoing very rapid mechanization;this development is good for the country's economy but may also snowball into substantial loss of agricultural land and other environmental degradation if the soil susceptibility and vulnerability to compaction is not well understood.In this study we explored different techniques for estimating soil intrinsic abilities to withstand applied pressure using the prevalent Oxisols of the Cerrado region under native vegetation.Undisturbed samples were collected from three sites within the region and subjected to 1) compressibility test;2) manual penetration resistance test;3) automated penetration resistance test;and 4) packing density analysis.The four methods produced analogous results.Our results showed the significant influence of soil structure on the inherent strength and compaction susceptibility of the soils.We also established the association of soil structure with the mineralogy of the soil.It is noteworthy that the packing density which was developed from very simple and easily obtained parameters could give a picture of the tendency of the soil to compact.Thus,this approach would be useful in developing compaction susceptibility maps for the region.It could be concluded that most of the Oxisols in the Cerrado region would support mechanized agricultural production very successfully.However,there is need for careful management of the mechanization process to avert degradation.The management techniques should include conservationist practices such as no till in order to maintain as much as possible the favorable structure and drainage of these very old soils.
基金the Natural Science Foundation of Ningbo(Grant No.2007A610061)
文摘The calculating model for the packing degree of spherical particles system was modified. The grain grading model of cement-based materials was established and could be applied in the global grading system as well as in the nano-fiber reinforced system. According to the grain grading model, two kinds of mortar were designed by using the global grain materials and nano-fiber materials such as fly ash, silica fume and NR powder. In this paper, the densities of two above systems cured for 90d were tested and the relationship of deleterious porosity and the total porosity of hardened mortar was discussed. Research results show that nano-fiber material such as NR powder can increase the density of cement-based materials. The relationship of deleterious porosity and the total porosity of hardened mortar accords with logarithmic curve. The deleterious porosity and the rationality of the grading can be roughly predicted through calculating the packing degree by the grain grading model of cement-based materials.
文摘Sand textural control on SECB （shear-enhanced compaction band） formation is analyzed combining field observations, detailed material characterization and mechanical testing for poorly lithified sandstone units in Provence （France）. Field observations show that SECBs are densely distributed in a coarse-grained unit with moderate porosity （27%）, whereas few SECBs are developed within the overlying fine-grained, high-porosity （39%） unit. Results from textural characterization show that the main difference between the two sand units is grain size and sorting, whereas they are similar with respect to composition and grain angularity. Packing density is introduced as an important parameter for comparing the compaction properties independent of the textural variations between the two units. Compaction experiments show a slightly faster compaction of the coarse-grained sand as compared to the fine-grained sand, and more pronounced grain crushing is observed in the coarse-grained unit. The results indicate that the preferential localization of SECBs to the coarse-grained unit is controlled by a slightly denser packing of the coarse-grained material at the time of band formation together with higher stress concentrations on grain contacts. Hence, this study emphasizes that porosity alone is an insufficient parameter for predicting deformation band evolution in sand （stone）.
文摘The effect of ultra-fine fly ash(UFFA),steel slag(SS)and silica fume(SF)on packing density of binary,ternary and quaternary cementitious materials was studied in this paper in terms of minimum water requirement of cement.The influence of mineral admixtures on the relative density of pastes with low water/hinder ratios was analyzed and the relationship between paste density and compressive strength of the corresponding hardened mortars was discussed.The results indicate that the incorporation of mineral admixtures can effectively improve the packing density ofcementitious materials;the increase in packing density of a composite with incorporation of two or three kinds of mineral admixtures is even more obvious than that with only one mineral admixture.Moreover,an optimal amount of mineral admixture imparts to the mixture maximum packing density.The dense packing effect of a mineral admixture can increase the packing density of the resulting cementitious material and also the density of paste with low water/binder ratio,which evidently enhances the compressive strength of the hardened mortar.
文摘The random packing of tetrahedral particles is studied by applying the discrete element method （DEM）, which simulates the effects of friction, height ratio, and eccentricity. The model predictions are ana- lyzed in terms of packing density and coordination number （CN）. It is demonstrated that friction has the maximal effect on packing density and mean CN among the three parameters. The packing den- sity of the regular tetrahedron is 0.71 when extrapolated to a zero friction effect. The shape effects of height ratio and eccentricity show that the regular tetrahedron has the highest packing density in the family of tetrahedra, which is consistent with what has been reported in the literature. Compared with geometry-based packing algorithms, the DEM packing density is much lower. This demonstrates that the inter-particle mechanical forces have a considerable effect on packing. The DEM results agree with the published experimental results, indicating that the polyhedral DEM model is suitable for simulating the random packing of tetrahedral particles.
基金supported by the National Natural Science Foundation of China(Grant No.10772005)the National Basic Research Program of China(Grant Nos.2007CB714603 and 2010CB832701)
文摘Random packings of binary mixtures of spheres and spherocylinders with the same volume and the same diameter were simulated by a sphere assembly model and relaxation algorithm.Simulation results show that,independently of the component volume fraction,the mixture packing density increases and then decreases with the growth of the aspect ratio of spherocylinders,and the packing density reaches its maximum at the aspect ratio of 0.35.With the same volume particles,results show that the dependence of the mixture packing density on the volume fraction of spherocylinders is approximately linear.With the same diameter particles,the relationship between the mixture packing density and component volume fraction is also roughly linear for short spherocylinders,but when the aspect ratio of spherocylinders is greater than 1.6,the curves turn convex which means the packing of the mixture can be denser than either the sphere or spherocylinder packing alone.To validate the sphere assembly model and relaxation algorithm,binary mixtures of spheres and random packings of spherocylinders were also simulated.Simulation results show the packing densities of sphere mixtures agree with previous prediction models and the results of spherocylinders correspond with the simulation results in literature.
文摘The existing particle packing density models each with two or more parameters accounting for certain particle interactions （the loosening effect parameter, wall effect parameter, wedging effect parameter, and compaction index, denoted by a, b, c, and K, respectively） may be classified into the 2-parameter model （with a and b incorporated）, the compressible model （with a, b, and 1（incorporated）, and the 3- parameter model （with a, b, and c incorporated）. This paper evaluates these models by comparing their respective packing density predictions with the test results published in the literature. It was found that their accuracy varies with both the size ratio and volumetric fractions of the binary mix. In general, when the size ratio is larger than 0.65, all the packing models are sufficiently accurate. However, when the size ratio is smaller than 0.65, some of them become inaccurate and the errors tend to be larger at around the volumetric fractions giving maximum packing density. Relatively, the 3-parameter model is the most accurate and widely applicable.
