The dispersion relations of normal modes in the layered constructions are studied.In the frequency region with negative permittivity,we investigate the normal modes near the air-metal and the air-matematerial interfac...The dispersion relations of normal modes in the layered constructions are studied.In the frequency region with negative permittivity,we investigate the normal modes near the air-metal and the air-matematerial interfaces and compare them.An extra bulk mode appearing in a pass band of two media is found near the air-matematerial interface,which is different from the air-metal case.Moreover,the bulk mode will be further proved by the attenuated total reflection (ATR) technique,in which the coupling between the incident electromagnetic waves and the normal modes is studied.For p-polarized incident waves,the ATR spectra based on the Otto and the Kretschmann configurations are obtained numerically,where the dips present the excitations of the surface and bulk modes.Furthermore,we also discuss the influences of the middle layer thickness,the incident angle and the damping term on the reflection in detail.It is found that the coupling frequencies and the maximum strength are strongly dependent on the above media parameters.展开更多
The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic mod...The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection(TR) method is introduced into the verification of contact models.An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity's merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.展开更多
Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in tw...Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.展开更多
INSULIN secretion was traditionally measured with biochemical and immunological methods such as enzyme linked immunosorbant assay and radio-immunoassay.However,these methods can only tell the amount of insulin secrete...INSULIN secretion was traditionally measured with biochemical and immunological methods such as enzyme linked immunosorbant assay and radio-immunoassay.However,these methods can only tell the amount of insulin secreted; they give no information about the secretion process or mechanism of exocytosis.In recent years,an imaging technique known as total internal reflection fluorescence (TIRF) microscopy has been employed to study insulin secretion.1-4 This imaging technique can explore events taking place near or on live cell membrane,such as secretory granule movement,exocytosis,vesicle content release,and membrane fusion.5-10 In the present paper,we applied TIRF microscopy to the observation of insulin exocytosis by the pancreatic β cell line Ins-1.展开更多
The propagation of elastic waves is studied in a porous solid saturated with two immiscible viscous fluids.The propagation of three longitudinal waves is represented through three scalar potential functions.The lone t...The propagation of elastic waves is studied in a porous solid saturated with two immiscible viscous fluids.The propagation of three longitudinal waves is represented through three scalar potential functions.The lone transverse wave is presented by a vector potential function.The displacements of particles in different phases of the aggregate are defined in terms of these potential functions.It is shown that there exist three longitudinal waves and one transverse wave.The phenomena of reflection and refraction due to longitudinal and transverse waves at a plane interface between an elastic solid half-space and a porous solid half-space saturated with two immiscible viscous fluids are investigated.For the presence of viscosity in pore-fluids,the waves refracted to the porous medium attenuate in the direction normal to the interface.The ratios of the amplitudes of the reflected and refracted waves to that of the incident wave are calculated as a nonsingular system of linear algebraic equations.These amplitude ratios are used to further calculate the shares of different scattered waves in the energy of the incident wave.The modulus of the amplitude and the energy ratios with the angle of incidence are computed for a particular numerical model.The conservation of the energy across the interface is verified.The effects of variations in non-wet saturation of pores and frequencies on the energy partition are depicted graphically and discussed.展开更多
We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted...We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.展开更多
A spectrometric setup to perform total internal reflection fluorescence (TIRF) and synchronous TIRF measurements at solid/liquid interfaces is presented. The combination of TIRF and synchronous fluorescence was propos...A spectrometric setup to perform total internal reflection fluorescence (TIRF) and synchronous TIRF measurements at solid/liquid interfaces is presented. The combination of TIRF and synchronous fluorescence was proposed to analyze simultaneously different components at interfaces. The TIRF excitation, emission and synchronous spectra of a watersoluble porphyrin were obtained from water/glass interface using this setup without the existence of a surfactant.展开更多
Total internal reflection fluorescence spectroscopy (TIRF) and synchronous scanning technique were combined to study the adsorption behavior of the meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) at the glass-water...Total internal reflection fluorescence spectroscopy (TIRF) and synchronous scanning technique were combined to study the adsorption behavior of the meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) at the glass-water interface without any surfactant. The pH dependence of synchronous fluorescence signal at the interface was analyzed. Both unprotonated (TPPS4-) and diprotonated (H2TPPS2-) forms of TPPS were observed at the interface. But the interface favored the adsorption of. The apparent estimated pKa2 value shifted from 5.00 in the bulk solution to 2.7 at the interface. STIRF provides a good technique to study multi-component systems at the interface.展开更多
AIM: To explore the effect of the posterior astigmatism on total corneal astigmatism and evaluate the error caused by substituting the corneal astigmatism of the simulated keratometriy(simulated K) for the total corne...AIM: To explore the effect of the posterior astigmatism on total corneal astigmatism and evaluate the error caused by substituting the corneal astigmatism of the simulated keratometriy(simulated K) for the total corneal astigmatism in age-related cataract patients.METHODS: A total of 211 eyes with age-related cataract from 164 patients(mean age: 66.8±9.0 y, range: 45-83 y) were examined using a multi-colored spot reflection topographer, and the total corneal astigmatism was measured. The power vector components J0 and J45 were analyzed. Correlations between the magnitude difference of the simulated K and total cornea astigmatism(magnitude differenceSim K-Tca), anterior J0, and absolute meridian difference(AMD) between the anterior and posterior astigmatisms were calculated. To compare the astigmatism of the simulated K and total cornea both in magnitude and axial orientation, we drew double-angle plots and calculated the vector difference between the two measures using vector analysis. A corrective regression formula was used to adjust the magnitude of the simulated K astigmatism to approach that of the total cornea.RESULTS: The magnitude differenceSim K-Tca was positively correlated with the anterior corneal J0(Spearman's rho= 0.539; P<0.001) and negatively correlated with the AMDR(Spearman's rho=-0.875, P<0.001). When the anterior J0 value was larger than 1.3 D or smaller than-0.8 D, the errors caused by determining the total corneal astigmatism with the karatometric calculation tended to be greater than 0.25 D. An underestimation by 16% was observed for against the rule(ATR) astigmatism and an overestimation by 9% was observed for with the rule(WTR) astigmatism when ignoring the posterior measurements.CONCLUSION: Posterior corneal astigmatism should be valued for more precise corneal astigmatism management, especially for higher ATR astigmatism of the anterior corneal surface. We suggest a 9% reduction in the magnitude of the simulated K in eyes with WTR astigmatism, and a 16% addition of the magnitude of the simulated K in eyes with ATR astigmatism.展开更多
Pores,microcracks and density of plasma sprayed Cr2O3 coatings before and after high-intensity pulsed ion beam(HIPIB) irradiation were investigated using the ultrasonic reflection coefficient spectroscopy(URCS).The UR...Pores,microcracks and density of plasma sprayed Cr2O3 coatings before and after high-intensity pulsed ion beam(HIPIB) irradiation were investigated using the ultrasonic reflection coefficient spectroscopy(URCS).The URCS was analyzed based on an acoustic transmission model for the multi-layered structure.The longitudinal velocity in the coatings was calculated from the experimental URCS,and the attenuation coefficient expression was deduced by comparing the experimental and numerical fitting amplitude spectral lines.The longitudinal velocity of as-sprayed Cr2O3 coating is 2 002 m/s,and increases to 2 099 and 2 148 m/s after being irradiated by HIPIB with 1 and 5 shots.Correspondingly,the factor A changes from 0.046 to 0.026 and 0.020 and n from 1.702 to 1.658 and 1.649 in the attenuation coefficient expression of α=Af n.It is observed that the surface morphology of Cr2O3 coatings changes from rough and porous to smooth and uniform with the increase of shot number,which accords with the ultrasonic analyses reasonably.The URCS seems to provide a convenient and nondestructive method to characterize surface modification of the plasma sprayed coatings.展开更多
A sensitive and selective assay of proteins is proposed based on measuring the total internal-reflected resonance light scattering（TIR-RLS） signals produced on the water/tetrachloromethane（H2O/CCl4） interface. In ...A sensitive and selective assay of proteins is proposed based on measuring the total internal-reflected resonance light scattering（TIR-RLS） signals produced on the water/tetrachloromethane（H2O/CCl4） interface. In an aqueous medium with pH value in the range of 3.29—3.78, electrostatic attraction occurs between the negatively charged Evans Blue（EB） and positively charged proteins, forming hydrophobic ion associates and resulting in EB-protein adsorption on H2O/CCl4 interface. The presence of cetyltrimethylammonium bromide prompts this adsorption, resulting in strongly enhanced TIR-RLS signals. The intensity of the enhanced TIR-RLS at 360—370 nm was found to be proportional to the concentration of proteins. For bovine serum albumin and human serum albumin, the linear range of detection is 0.07—1.2 μg/mL and the limits of detection are 6.68 and 6.30 ng/mL（3σ）, respectively, while for lysozyme, the linear range of detection is 0.06—1.0 μg/mL and the limit of detection is 6.0 ng/mL（3σ）. The content of the total albumin in a human urine sample could be directly determined by using the standard addition method with a percent recovery of 97.6%—104.1%, and the RSD ranging from 1.9% to 4.2%.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.10775055)
文摘The dispersion relations of normal modes in the layered constructions are studied.In the frequency region with negative permittivity,we investigate the normal modes near the air-metal and the air-matematerial interfaces and compare them.An extra bulk mode appearing in a pass band of two media is found near the air-matematerial interface,which is different from the air-metal case.Moreover,the bulk mode will be further proved by the attenuated total reflection (ATR) technique,in which the coupling between the incident electromagnetic waves and the normal modes is studied.For p-polarized incident waves,the ATR spectra based on the Otto and the Kretschmann configurations are obtained numerically,where the dips present the excitations of the surface and bulk modes.Furthermore,we also discuss the influences of the middle layer thickness,the incident angle and the damping term on the reflection in detail.It is found that the coupling frequencies and the maximum strength are strongly dependent on the above media parameters.
基金Project supported by the National Natural Science Foundation of China(Grant No.11872033)the Beijing Natural Science Foundation,China(Grant No.3172017)
文摘The simulation of real contact area between materials is foundationally important for the contact mechanics of mechanical structures. The Greenwood and Williamson(GW) model and the Majumdar(MB) model are the basic models in this field, which are widely accepted and proven to be valid in many experiments and engineering. Although the contact models have evolved considerably in recent years, the verifications of the models are most based on the indirect methods such as electrical conductivity and contact stiffness, because of the lack of effective methods to directly measure the variation of contact surface. In this paper, the total reflection(TR) method is introduced into the verification of contact models.An experiment system based on TR method is constructed to measure the real contact area of two PMMA specimens. The comparison analysis between the results of experiment and models suggests that the experiment result has the same trend with simulation, the MB model has better agreement with the experimental result because this method can take into account the variation of radius and the merging of asperities, while the GW model has a huge deviation because of the dependence on resolution and the lack of considering the variation of radius and asperity's merging process. Taking the interaction of asperities into account could give a better result that is closer to the experiment. Our results and analysis prove that the experimental methods in this paper could be used as a more direct and valid method to quantitatively measure the real contact area and to verify the contact models.
基金supported by the K. C. Wong Education Foundation (GJTD-2018-08)the Natural Science Foundation of China (NSFC) (Grants 11804334, 51705192)+1 种基金the China Postdoctoral Science Foundation (2017M611325)the National Postdoctoral Program for Innovative Talents (BX201600064)
文摘Although abundant research on the anisotropy of van der Waals(vd W)materials has been published,we undertake an in-depth study of their optical properties as they have an important guiding role for light control in two-dimensional(2D)nanospace.As an example,we study the reflectance of few-layered black phosphorus(BP)in the total internal reflection(TIR)mode in detail.We demonstrate that its optical anisotropy can be changed on a large scale by varying the incident angles,polarization states,and the in-plane rotation angles of the BP samples.Theoretical analysis indicates that the phenomena observed are common to all the atom-thick biaxial crystals,so these conclusions can be widely applied to other anisotropic 2D materials.This research furthers the current understanding of the properties of BP more comprehensively,and provides guidance for developing new optoelectronic applications,especially when BP and other atom-thick biaxial crystals are integrated with TIR devices.
文摘INSULIN secretion was traditionally measured with biochemical and immunological methods such as enzyme linked immunosorbant assay and radio-immunoassay.However,these methods can only tell the amount of insulin secreted; they give no information about the secretion process or mechanism of exocytosis.In recent years,an imaging technique known as total internal reflection fluorescence (TIRF) microscopy has been employed to study insulin secretion.1-4 This imaging technique can explore events taking place near or on live cell membrane,such as secretory granule movement,exocytosis,vesicle content release,and membrane fusion.5-10 In the present paper,we applied TIRF microscopy to the observation of insulin exocytosis by the pancreatic β cell line Ins-1.
基金Project supported by the Council of Scientific and Industrial Research (CSIR) of New Delhi(Nos. 09/105(0169)/2008-EMR-I and 09/105(0185)/2009-EMR-I)
文摘The propagation of elastic waves is studied in a porous solid saturated with two immiscible viscous fluids.The propagation of three longitudinal waves is represented through three scalar potential functions.The lone transverse wave is presented by a vector potential function.The displacements of particles in different phases of the aggregate are defined in terms of these potential functions.It is shown that there exist three longitudinal waves and one transverse wave.The phenomena of reflection and refraction due to longitudinal and transverse waves at a plane interface between an elastic solid half-space and a porous solid half-space saturated with two immiscible viscous fluids are investigated.For the presence of viscosity in pore-fluids,the waves refracted to the porous medium attenuate in the direction normal to the interface.The ratios of the amplitudes of the reflected and refracted waves to that of the incident wave are calculated as a nonsingular system of linear algebraic equations.These amplitude ratios are used to further calculate the shares of different scattered waves in the energy of the incident wave.The modulus of the amplitude and the energy ratios with the angle of incidence are computed for a particular numerical model.The conservation of the energy across the interface is verified.The effects of variations in non-wet saturation of pores and frequencies on the energy partition are depicted graphically and discussed.
基金Project supported by the National Natural Science Foundation of China(Grant No.11872033)the Beijing Natural Science Foundation,China(Grant No.3172017)
文摘We build an experiment system based on total reflection(TR) method to observe the evolution of real contact area of polymethyl methacrylate(PMMA) in the continual stick-slip movement. The bilateral friction is adopted to overcome the bending moment in the lateral friction movement. Besides some classical phenomena of stick-slip movement such as periodical slow increase of frictional force in sticking phase and a sudden drop when slipping, a special phenomenon that the contact area increases with the tangential force is observed, which was called junction growth by Tabor in 1959.Image processing methods are developed to observe the variation of the junction area. The results show that the center of the strongest contact region will keep sticking under the tangential force until the whole slipping, the strongest point undergoes three stages in one cycle, which are named as sticking stage, fretting stage, and cracking stage, respectively. The combined analysis reveals a physical process of stick-slip movement: the tangential force causes the increase of the real contact area, which reduces the pressure between the contact spots and finally leads to the slipping. Once slipping occurs,the real contact area drops to the original level resulting in the pressure increase to the original level, which makes the sticking happen again.
文摘A spectrometric setup to perform total internal reflection fluorescence (TIRF) and synchronous TIRF measurements at solid/liquid interfaces is presented. The combination of TIRF and synchronous fluorescence was proposed to analyze simultaneously different components at interfaces. The TIRF excitation, emission and synchronous spectra of a watersoluble porphyrin were obtained from water/glass interface using this setup without the existence of a surfactant.
文摘Total internal reflection fluorescence spectroscopy (TIRF) and synchronous scanning technique were combined to study the adsorption behavior of the meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS) at the glass-water interface without any surfactant. The pH dependence of synchronous fluorescence signal at the interface was analyzed. Both unprotonated (TPPS4-) and diprotonated (H2TPPS2-) forms of TPPS were observed at the interface. But the interface favored the adsorption of. The apparent estimated pKa2 value shifted from 5.00 in the bulk solution to 2.7 at the interface. STIRF provides a good technique to study multi-component systems at the interface.
基金Supported by the National Natural Science Foundation of China(No.81670837)the Scientific and Technological Project of Tianjin Health Bureau(No.2015KY38)
文摘AIM: To explore the effect of the posterior astigmatism on total corneal astigmatism and evaluate the error caused by substituting the corneal astigmatism of the simulated keratometriy(simulated K) for the total corneal astigmatism in age-related cataract patients.METHODS: A total of 211 eyes with age-related cataract from 164 patients(mean age: 66.8±9.0 y, range: 45-83 y) were examined using a multi-colored spot reflection topographer, and the total corneal astigmatism was measured. The power vector components J0 and J45 were analyzed. Correlations between the magnitude difference of the simulated K and total cornea astigmatism(magnitude differenceSim K-Tca), anterior J0, and absolute meridian difference(AMD) between the anterior and posterior astigmatisms were calculated. To compare the astigmatism of the simulated K and total cornea both in magnitude and axial orientation, we drew double-angle plots and calculated the vector difference between the two measures using vector analysis. A corrective regression formula was used to adjust the magnitude of the simulated K astigmatism to approach that of the total cornea.RESULTS: The magnitude differenceSim K-Tca was positively correlated with the anterior corneal J0(Spearman's rho= 0.539; P<0.001) and negatively correlated with the AMDR(Spearman's rho=-0.875, P<0.001). When the anterior J0 value was larger than 1.3 D or smaller than-0.8 D, the errors caused by determining the total corneal astigmatism with the karatometric calculation tended to be greater than 0.25 D. An underestimation by 16% was observed for against the rule(ATR) astigmatism and an overestimation by 9% was observed for with the rule(WTR) astigmatism when ignoring the posterior measurements.CONCLUSION: Posterior corneal astigmatism should be valued for more precise corneal astigmatism management, especially for higher ATR astigmatism of the anterior corneal surface. We suggest a 9% reduction in the magnitude of the simulated K in eyes with WTR astigmatism, and a 16% addition of the magnitude of the simulated K in eyes with ATR astigmatism.
基金Project(KM200710015010) supported by the Scientific Research Program of Beijing Municipal Education Commission,China
文摘Pores,microcracks and density of plasma sprayed Cr2O3 coatings before and after high-intensity pulsed ion beam(HIPIB) irradiation were investigated using the ultrasonic reflection coefficient spectroscopy(URCS).The URCS was analyzed based on an acoustic transmission model for the multi-layered structure.The longitudinal velocity in the coatings was calculated from the experimental URCS,and the attenuation coefficient expression was deduced by comparing the experimental and numerical fitting amplitude spectral lines.The longitudinal velocity of as-sprayed Cr2O3 coating is 2 002 m/s,and increases to 2 099 and 2 148 m/s after being irradiated by HIPIB with 1 and 5 shots.Correspondingly,the factor A changes from 0.046 to 0.026 and 0.020 and n from 1.702 to 1.658 and 1.649 in the attenuation coefficient expression of α=Af n.It is observed that the surface morphology of Cr2O3 coatings changes from rough and porous to smooth and uniform with the increase of shot number,which accords with the ultrasonic analyses reasonably.The URCS seems to provide a convenient and nondestructive method to characterize surface modification of the plasma sprayed coatings.
文摘A sensitive and selective assay of proteins is proposed based on measuring the total internal-reflected resonance light scattering（TIR-RLS） signals produced on the water/tetrachloromethane（H2O/CCl4） interface. In an aqueous medium with pH value in the range of 3.29—3.78, electrostatic attraction occurs between the negatively charged Evans Blue（EB） and positively charged proteins, forming hydrophobic ion associates and resulting in EB-protein adsorption on H2O/CCl4 interface. The presence of cetyltrimethylammonium bromide prompts this adsorption, resulting in strongly enhanced TIR-RLS signals. The intensity of the enhanced TIR-RLS at 360—370 nm was found to be proportional to the concentration of proteins. For bovine serum albumin and human serum albumin, the linear range of detection is 0.07—1.2 μg/mL and the limits of detection are 6.68 and 6.30 ng/mL（3σ）, respectively, while for lysozyme, the linear range of detection is 0.06—1.0 μg/mL and the limit of detection is 6.0 ng/mL（3σ）. The content of the total albumin in a human urine sample could be directly determined by using the standard addition method with a percent recovery of 97.6%—104.1%, and the RSD ranging from 1.9% to 4.2%.
