Particle Cross-sectional Area Research Articles

On-Chip Multiple Particle Velocity and Size Measurement Using Single-Shot Two-Wavelength Differential Image Analysis.

Precise and quick measurement of samples’ flow velocities is essential for cell sorting timing control and reconstruction of acquired image-analyzed data. We developed a simple technique for the single-shot measurement of flow velocities of particles simultaneously in a microfluidic pathway. The speed was calculated from the difference in the particles’ elongation in an acquired image that appeared when two wavelengths of light with different irradiation times were applied. We ran microparticles through an imaging flow cytometer and irradiated two wavelengths of light with different irradiation times simultaneously to those particles. The mixture of the two wavelength transmitted lights was divided into two wavelengths, and the images of the same microparticles for each wavelength were acquired in a single shot. We estimated the velocity from the difference of its elongation divided by the difference of irradiation time by comparing these two images. The distribution of polystyrene beads’ velocity was parabolic and highest at the center of the flow channel, consistent with the expected velocity distribution of the laminar flow. Applying the calculated velocity, we also restored the accurate shapes and cross-sectional areas of particles in the images, indicating this simple method for improving of imaging flow cytometry and cell sorter for diagnostic screening of circulating tumor cells.

Variability of the Suspended Particle Cross-Sectional Area in the Bohai Sea and Yellow Sea

A cross-sectional area (CSA) is a key element in the optical properties of suspended particles. The seasonal evolution of CSA has great potential for use in mapping total suspended particles, and such mapping plays an important role in water quality monitoring. In this study, the spatiotemporal variations in CSA in the Bohai Sea and the Yellow Sea were studied using temperature, salinity and chlorophyll-a data collected by four cruises. The CSA field data covered a wide range of spatiotemporal variabilities in the Bohai Sea and the Yellow Sea. The results revealed that the largest CSA (>2 m−1) was found in the coastal area, while the CSA (≤1 m−1) on the outer shelf was much smaller. Large values of CSA (>15 m−1) were observed in winter, whereas the smallest values of CSA (0~2 m−1) were observed in summer. These results suggest that vertical mixing and ocean stratification might be important physical mechanisms that influences the CSA seasonal distribution in the surface layer. The results also showed that phytoplankton played an important role in the CSA, with an R2 value of 0.601. The seasonal patterns of CSA documented in this study provide a fundamental theory for research on optical properties, mapping transparency, and photosynthetically active radiation.

Predicting kernel processing score of harvested and processed corn silage via image processing techniques

An image processing algorithm was developed to characterize the size distribution of corn kernel particles from Whole Plant Corn Silage (WPCS). The algorithm determines particle cross sectional area and maximum inscribed circle diameter as well as cumulative undersize percent, dimensions of significance, and key characteristics of the distribution including mean particle size, skewness, and kurtosis. Kernel Possessing Score (KPS) was derived from the area-weighted cumulative undersize percent of 4.75 mm. Samples of WPCS harvested using self-propelled forage harvester with crop processing roll gap clearance of 1, 2, 3, and 4 mm were analyzed in their fresh, dry, and sieved states. Algorithm results were compared with the standard method of mechanical sieving and found to be well correlated r(23) = 0.8, p < 0.001. Additionally, analysis of particles before and after sieving indicated that sieving significantly increased KPS for 1 (t(5) = 6.6, p = 0.001), 2 (t(5) = 4.2, p = 0.01), and 3 (t(5) = 3.5, p = 0.02) mm samples. This algorithm has the potential to more accurately determine KPS in field compared to currently available methods, allowing for adjustment of kernel processing during harvest which will improve silage quality.

Study on AZ91D chip for injection molding (2nd Report, Effect of dimension on effective thermal conductivity after consolidation)

The purpose of this study is to propose an effective model to estimate the effective thermal conductivity of compacts made from magnesium alloy particles, considering the effects of particle size, temperature and pressure. In order to investigate the influence of the particle size, six kinds of particles were prepared in which the cross sectional area was different. The test particles made from AZ91D were poured into a compression vessel and then a given pressure was applied to the piston of vessel for six hours under constant temperature condition. After compression, effective thermal conductivity of compacts were measured by steady state comparative-longitudinal heat flow method. The numerical calculation considering two-dimensional steady heat conduction was also conducted by using the actual cross section of compacts. Test results showed that the effective thermal conductivity of compacts were increased with increase of applied pressure and temperature elevation. Calculation results also revealed that by considering the actual cross section of compacts, the effective thermal conductivity could be well estimated when filling fraction is lower than 0.8. However, when filling fraction is exceed 0.8, the effect of thermal contact resistance between particles on thermal conductivity is not negligible. The experimental equation of effective thermal conductivity of compacts was determined to discuss the effects of cross sectional area of particles.

Remote Sensing of Particle Cross-Sectional Area in the Bohai Sea and Yellow Sea: Algorithm Development and Application Implications

Suspended particles in waters play an important role in determination of optical properties and ocean color remote sensing. To link suspended particles to their optical properties and thereby remote sensing reflectance (Rrs(λ)), cross-sectional area is a key factor. Till now, there is still a lack of methodologies for derivation of the particle cross-sectional area concentration (AC) from satellite measurements, which consequently limits potential applications of AC. In this study, we investigated the relationship between AC and Rrs(λ) based on field measurements in the Bohai Sea (BS) and Yellow Sea (YS). Our analysis confirmed the strong dependence of Rrs(λ) on AC and that such dependence is stronger than on mass concentration. Subsequently, a remote sensing algorithm that uses the slope of Rrs(λ) between 490 and 555 nm was developed for retrieval of AC from satellite measurements of the Geostationary Ocean Color Imager (GOCI). In situ evaluations show that the algorithm displays good performance for deriving AC and is robust to uncertainties in Rrs(λ). When the algorithm was applied to satellite data, it performed well, with a coefficient of determination of 0.700, a root mean squared error of 2.126 m−1 and a mean absolute percentage error of 40.7%, and it yielded generally reasonable spatial and temporal distributions of AC in the BS and YS. The satellite-derived AC using our algorithm may offer useful information for modeling the inherent optical properties of suspended particles, deriving the water transparency, estimating the particle composition and possibly improving particle mass concentration estimations in future.

射出成形用AZ91D粒子に関する研究（第1報，圧密後のかさ密度に与える粒子寸法の影響）

The purpose of this study is to propose an effective model to estimate the filling fraction of compacts made from magnesium alloy particles, considering the effects of particle size, temperature and pressure. In order to investigate the influence of the particle size, six kinds of particles were prepared in which the cross sectional area was different. The test particles made from AZ91D were poured into a compression vessel and then a given pressure was applied to the piston of vessel for six hours under constant temperature condition. During the testing, the displacement of piston was measured to evaluate the change of bulk density of compacts, and then the filling fraction was simply calculated by the ratio of bulk density of compacts and density of AZ91D. Test results showed that the filling fraction of the largest particles was lower than that of other particles in the temperature region between 523 K and 623 K. The densification rates of compacts were increased with increase of applied pressure and temperature elevation. The experimental equation of densification rates of compacts was determined to discuss the effects of cross sectional area on densification rate. Determination results showed that the transition point to the steady creep was increased with increase of cross sectional area of particles.

Dissolution Model of Ball Milled Rice Straw Particles in 1-Ethyl-3-Methyl Imidazolium Acetate at Elevated Temperature

In Asia, rice straw residue left in fields after harvest is often burned which causes air pollution or anaerobically digested in the rice patty moist soil to yield methane a greenhouse gas. Effective and efficient process strategies are needed to convert straw into fuels and feedstock’s which do not harm the environment. As a result, this study was undertaken to liquefy Japanese rice straw (RS) an abundant agricultural residue into a liquid after pre-treatment by ball-milling at various temperatures and develop a bioprocess model. Specifically, RS was ball milled into 75-100 μm size particles at temperatures of 60°C, 25°C, and -196°C (cryogenically) and dissolved by heating in 1-ethyl-3- methylimidazolium acetate [Emim][OAc] at different temperatures between 120° 140° and 160°C to understand the interactions between the process parameters. The milled RS powder particles were characterized by FTIR, XRD, BET analyzer and dissolution follow using optical microscopy. The particle dissolution was analyzed by measuring the particle light intensity ratio and particle cross-sectional area as a function of heating time. Higher milling temperature leads to amorphization of the RS cellulose accelerating dissolution. Measurement of the particle light intensity ratio was used to estimate the rice straw particles dissolution endpoint. A particle dissolution model indicated that ball milling temperature and [Emim][OAc] heating temperature strongly interacts influencing the dissolution time. To dissolve RS in [Emim][OAc] quickly, it important to reduce the crystallinity of the cellulose and increase the particle surface area by milling at higher temperature. It is believed this model would have applications to other biomass dissolution processes.

The effect of particulate organic content on the remote sensing of marine suspended sediments

We report on the relationship between the backscattering coefficient at 665 nm and the cross sectional area of particles in suspension in the Irish Sea, Celtic Sea and English Channel. A plot of the backscattering coefficient against particle area shows two distinct trends: one for particles with high mineral content and another for particles with low mineral content. Backscattering per unit particle area (effective backscattering efficiency, Qbb) shows a continuous non-linear dependence on the ratio of mineral to total suspended solids (MSS/TSS) over the range 0.35 < MSS/TSS < 0.91. The relationship can be represented by an exponential function: Qbb = 0.000087 exp(6.9 MSS/TSS), which explains 62% of the observed variance in backscattering efficiency. Changes in particle size have no significant influence on Qbb. As the MSS/TSS ratio increases, the backscattering ratio (bb/b) also increases. The implication for the quantitative remote sensing of marine suspended sediments is that the mass specific backscattering coefficient, bb* depends on the particle area per unit mass multiplied by a function which depends on the mineral content of the particles.

Evidence that satellites sense the cross-sectional area of suspended particles in shelf seas and estuaries better than their mass

Quantitative algorithms for the remote sensing of suspended sediments in shelf seas and estuaries have traditionally sought to relate the signal sensed by the satellite radiometer to the mass of particles in suspension. In situ measurements presented in this paper, however, show that the irradiance reflection coefficient at the sea surface is more closely related to the cross-sectional area of particles in suspension than to their mass. Other optical properties (which in turbid water depend on particle area) can therefore be related directly to the reflection coefficient. To interpret satellite data in terms of mass concentration (for testing numerical models of suspended sediment transport, for example), it is necessary to know the relationship between the area and mass of the particles. For the 2008–2009 dataset presented here for western UK coastal waters, the particle cross-sectional area varies by a factor of 5 for particles of a given size and mass. The causes of this variation are currently poorly understood.

The optical efficiency of flocs in shelf seas and estuaries

A correct understanding of the way in which light interacts with suspended particles is essential for quantitative interpretation of satellite visible band imagery of turbid shelf seas and estuaries. In this paper we describe new optical observations at 90 stations in the tidally energetic waters along the south and west coasts of Britain. The cross sectional area of the particles in suspension has been measured with a LISST laser diffraction instrument. Light scattering and absorption coefficients have been determined by applying Kirk’s method to radiometric measurements at 6 wavelengths. Results show that the scattering coefficient increases linearly with particle cross sectional area A per unit volume of water with a slope (scattering efficiency) of 1.96 (standard error 0.08) at 665 nm. Particle absorption coefficients a P also increase with particle cross sectional area but at the most turbid stations, particle absorption per unit area ( a P / A) is observed to increase with the mean size of the particles in suspension. The particles are mostly mineral flocs which become more opaque as they grow larger and the photon path length through them increases. The implication of these results for remote sensing is that reflectance in the red part of the spectrum, which mainly depends on light scattering, is proportional to the cross sectional area of particles in suspension. Reflectance measurements in the green and blue parts of the spectrum, where particle absorption becomes more important, depend on the diameter of the particles as well as their cross sectional area. We show that simultaneous measurements of reflectance in the red and green parts of the spectrum can be used to derive both the area and size of the particles in suspension.

Dynamics of gas–solid fluidised beds with non-spherical particle geometry

Fluidised beds play an important role in physical and chemical engineering processing. Understanding the granular motion within these beds is essential for design, optimisation and control of such processes. Motion on the particle scale is difficult to measure experimentally, making computational simulations invaluable for determining the dynamics within such systems. Computational models which have had the greatest success at capturing the full range of dynamics are coupled discrete element model and Navier–Stokes solvers, based on a pressure-gradient-force formulation. However, most discrete element models assume spherical geometry for the particles. Particle shape in many important industrial processes, such as catalysis and pyrolysis, is often non-spherical. We present a re-formulation of the pressure-gradient force model, based on a modified pressure correction method, coupled to a discrete element model with non-spherical grains. The drag relations for the coupling are modified to take into account the grain shape and cross-sectional area relative to the local gas flow. We show that grain shape has a significant effect on the dynamics of the fluidised bed, including increased pressure gradients within the bed and lower fluidisation velocities when compared to beds of spherical particles. A model is presented to explain these effects, showing that they are due to both decreased porosity within the bed as well as the relative particle cross-sectional area creating a greater net drag over the bed. Our findings will be of interest from an applied standpoint as well as showing fundamental effects of particle shape on coupled fluid and granular flow.

Computer simulation of diffusion-limited cluster-cluster aggregation with an Epstein drag force

The motion of particles, dispersed in a medium, between collisions with each other can, in limiting situations, be either ballistic (straight line) or diffusive (random walker). The diffusive regime can be divided into two distinct subregimes. The "continuum regime" exhibits Stokes-Einstein-type diffusion (no-slip surface boundary condition) with a frictional coefficient proportional to the particle size (linear dimension). The "Epstein regime," as we shall refer to it, is characterized by a frictional coefficient proportional to the particle cross-sectional area, hence an Epstein-type diffusion (slip surface). The purpose of the current study is to illuminate the dynamics of dilute-limit aggregation in the Epstein regime. We present results from low volume fraction Monte Carlo simulations of cluster-cluster aggregation in the Epstein regime with the particle motion based on each particle's cross-sectional area. Our findings indicate that aggregates grown under Epstein conditions have a fractal dimension of approximately 1.8, similar to that of diffusion-limited cluster-cluster aggregates (DLCA) in the continuum regime. The kinetic exponent z in the Epstein regime is found to be z approximately 0.8, lower than its value for both the continuum regime DLCA (z = 1) and for the ballistic cluster aggregation regime (z approximately 2). Cluster size distribution data for Epstein systems are found to scale at large cluster sizes with exponents consistent with the kinetic data. A scaling argument for predicting the kinetic exponent and kernel homogeneity based on the mass or size dependence of the particle velocity and collision cross section is presented and is seen to give accurate results for dilute and intermediate values of particle volume fractions not only for the current study, but also for work done by other researchers with various choices for the aggregation kernel.

A Generalized Approximation for the Thermophoretic Force on a Free-Molecular Particle

A general, approximate expression is described that can be used to predict the thermophoretic force on a free-molecular, motionless, spherical particle suspended in a quiescent gas with a temperature gradient. The thermophoretic force is equal to the product of an order-unity coefficient, the gas-phase translational heat flux, the particle cross-sectional area, and the inverse of the mean molecular speed. Numerical simulations are used to test the accuracy of this expression for monatomic gases, polyatomic gases, and mixtures thereof. Both continuum and noncontinuum conditions are examined; in particular, the effects of low pressure, wall proximity, and high heat flux are investigated. The direct simulation Monte Carlo (DSMC) method is used to calculate the local molecular velocity distribution, and the force-Green's-function method is used to calculate the thermophoretic force. The approximate expression is found to predict the calculated thermophoretic force to within 10% for all cases examined. The sou...

SUSPENSOIDS IN NEW YORK CITY'S DRINKING WATER RESERVOIRS: TURBIDITY APPORTIONMENT1

ABSTRACT: The technique of individual particle analysis conducted by scanning electron microscopy interfaced with automated X‐ray microanalysis (IPA/SAX) was used to characterize suspended particulate matter in New York City's drinking water reservoirs and their tributaries. The study covered a two year period and involved analyses of more than 300 samples. The particle cross sectional area per unit volume (PAV), or area concentration, was measured to account for the observed turbidity, a representation of light scattering property of the studied medium. A simple linear model with a nearly zero intercept was able to explain more than 85 percent of the variation in the measured turbidity. Moreover, the particle assemblage was categorized into generic particle types with distinctive geochemical or geological origins. Thus, PAV compositions in terms of particle types could be apportioned into turbidity components based on the model. Inorganic tripton, dominated by aluminosilicate (clay) and silicate of nonbiological nature, was found to be the major turbidity causing constituent in most cases. With the exception of one reservoir where organic detritus was significant, the predicted inorganic particle turbidity agreed with the measured turbidity within experimental error.

Parameterization of effective ice particle size for high‐latitude clouds

AbstractA parameterization has been developed for mean effective size Dge in terms of ice water content (IWC) and temperature using in situ measurements of ice crystal spectra, cloud particle shapes and particle cross‐sectional area A from four research projects conducted in latitudes north of 45° N. The cloud microphysical measurements were made using PMS 2D optical probes, a PMS forward scattering spectrometer probe (FSSP), and Nevzorov total water and liquid water content probes. The IWCs derived from particle spectra using three different methods were compared with IWC measured with the Nevzorov probe (IWCNev). The contribution of small particles to the total mass was estimated by integrating a gamma distribution function that was fitted to match the measured FSSP concentrations. The Dge was calculated from the derived IWC and total cross‐sectional area per unit volume Ac.This analysis indicates that there are significant differences among the schemes used to derive the IWC. It was found that the IWC derived based on the Cunningham scheme and IWCNev have the highest correlation: r2 = 0.78. After considering small particles, the derived IWC almost matched the IWCNev. The average estimated contribution of small particles to the Ac was 43%. The average estimated contribution of small particles to the total IWC, however, was 20%. Since Dge is directly proportional to the ratio IWC/Ac, the addition of small particles reduced the derived Dge considerably. The largest changes in Dge associated with small particles, however, occur at the coldest temperature and at low IWC, reaching up to 45% for temperatures less than −25° C. Generally, Dge and IWC increase with increasing temperature. Good agreement between the parameterized Dge and derived Dge from measurements were found when small particles were included. Copyright © 2002 Royal Meteorological Society.

Observations and Parameterizations of Particle Size Distributions in Deep Tropical Cirrus and Stratiform Precipitating Clouds: Results from In Situ Observations in TRMM Field Campaigns

In this study, we report on the evolution of particle size distributions (PSDs) and habits as measured during slow, Lagrangian-type spiral descents through deep subtropical and tropical cloud layers in Florida, Brazil, and Kwajalein, Marshall Islands, most of which were precipitating. The objective of the flight patterns was to learn more about how the PSDs evolved in the vertical and to obtain information of the vertical structure of microphysical properties. New instrumentation yielding better information on the concentrations of particles in the size (D) range between 0.2 and 2 cm, as well as improved particle imagery, produced more comprehensive observations for tropical stratiform precipitation regions and anvils than have been available previously. Collocated radar observations provided additional information on the vertical structure of the cloud layers sampled. Most of the spirals began at cloud top, with temperatures (T) as low as -50 C, and ended at cloud base or below the melting layer (ML). The PSDs broadened from cloud top towards cloud base, with the largest particles increasing in size from several millimeters at cloud top to one centimeter or larger towards cloud base. Some continued growth was noted in the upper part of the ML. Concentrations of particles less than 1 mm in size decreased with decreasing height. The result was a consistent change in the PSDs in the vertical. Similarly, systematic changes in the size dependence of the particle cross-sectional area was noted with decreasing height. Aggregation-as ascertained from both the changes in the PSDs and evolution of particle habits as observed in high detail with the cloud particle imager (CPI) probe-was responsible for these trends. The PSDs were generally well-represented by gamma distributions of the form N = N0 gamma D microns e- lambda gamma D that were fitted to the PSDs over 1-km horizontal intervals throughout the spirals. The intercept (N0 gamma), slope (lambda gamma), and dispersion (microns) values were derived for each PSD. Exponential curves (N = N0e- lambdaD; micron = 0) were also fitted to the distributions. The lambda gamma values for given spirals varied systematically with temperature as did the values of lambda (exponential), and the data generally conformed to values found in previous studies involving exponential fits to size distributions in mid-latitude frontal and cirrus layers. Considerable variability often noted in the PSD properties during the loops of individual spirals was manifested primarily in large changes in N0 gamma and N0, but micron, lambda gamma and lambda remained fairly stable. Temperature is not found to be the sole factor controlling lambda gamma or lambda but is a primary one. Direct relationships were found between lambda gamma and N0 gamma or lambda gamma and micron for the gamma distributions and lambda and N0 for the exponential. The latter relationship was not found as distinctly in earlier studies; observed PSDs in this study had better fidelity with less scatter. The micron values changed monotonically with T over the range of temperatures and were directly related to N0 gamma or lambda gamma, thereby reducing the number of variables in the PSD functional equation to two. In the upper part of the ML, N0 and lambda continued to decrease, and in the lower part these values began to increase as the largest particles melted. We developed general expressions relating various bulk microphysical, radar, and radiative transfer-related variables to N0 gamma and lambda gamma, useful for both tropical and mid-latitude clouds. These relationships facilitate the specification of a number of bulk properties in cloud and climate models. The results presented in this paper apply best to temperatures between 0 and -40 C, for which the measured radar reflectivities fall in the range of 0 to 25 dBZe.

Rheological Behavior of Kaolin and Montmorillonite Suspensions at Low Concentrations

The rheological behavior of kaolin and montmorillonite suspensions at low concentrations in water and polymer solutions has been investigated. An influence of the polymer concentration on the viscosity of suspension for the kaolin suspension in the presence of diethylenetriaminomethylated polyacrylamide and for the montmorillonite suspension in the presence of polyacrylic acid has been demonstrated. The dependence between the shear stress and the cross-sectional area of particles and the number of particles in a unit volume of the suspension has been shown. Mathematical equations for the number of aggregates in the unit volume of suspension and the number of initial particles in aggregate at the different polymer concentrations in mixture are proposed.

Structural analysis of cloned plasma membrane proteins by freeze-fracture electron microscopy.

We have used freeze-fracture electron microscopy to examine the oligomeric structure and molecular asymmetry of integral plasma membrane proteins. Recombinant plasma membrane proteins were functionally expressed in Xenopus laevis oocytes, and the dimensions of their freeze-fracture particles were analyzed. To characterize the freeze-fracture particles, we compared the particle cross-sectional area of proteins with alpha-helical transmembrane domains (opsin, aquaporin 1, and a connexin) with their area obtained from existing maps calculated from two-dimensional crystals. We show that the cross-sectional area of the freeze-fracture particles corresponds to the area of the transmembrane domain of the protein, and that the protein cross-sectional area varies linearly with the number membrane-spanning helices. On average, each helix occupies 1.40 +/- 0.03 nm2. By using this information, we examined members from three classes of plasma membrane proteins: two ion channels, the cystic fibrosis transmembrane conductance regulator and connexin 50 hemi-channel; a water channel, the major intrinsic protein (the aquaporin 0); and a cotransporter, the Na+/glucose cotransporter. Our results suggest that the cystic fibrosis transmembrane conductance regulator is a dimer containing 25 +/- 2 transmembrane helices, connexin 50 is a hexamer containing 24 +/- 3 helices, the major intrinsic protein is a tetramer containing 24 +/- 3 helices, and the Na+/glucose cotransporter is an asymmetrical monomer containing 15 +/- 2 helices.

Alternating current magnetic properties of cores made from pressed acicular steel particles

This article describes results of magnetic testing of cores made from a composite material that yields powder metallurgically pressed compacts of high density suitable for a variety of ac magnetic applications. Small acicular steel particles are annealed, individually insulated, and uniaxially pressed using standard powder metallurgical techniques. The ac losses and permeability of the pressed compacts are strongly dependent upon particle geometry. The variations of the core loss among the different particle geometries was found to be a function of the cross sectional area of the acicular particles as well as the strain imparted to the particles during the pressing operation. The core loss, when measured at 60 Hz, exhibits a minimum at a certain cross sectional area. The shape of the curve is attributed to a decrease in eddy current loss with decreasing particle cross sectional area, while the hysteresis loss increases with decreasing particle cross sectional area. At a test frequency of 400 Hz, the eddy current component of core loss predominates, and the core loss decreases steadily with decreasing particle cross sectional area. Permeability was also found to depend upon particle geometry. The smaller the demagnetizing factor of the individual particles, the higher the permeability, while the increased strain in the smaller particles overwhelms the smaller demagnetizing factor resulting in a decrease in permeability. The net result is a maximum in permeability for the mid-sized particles.

High Albedos of Cirrus in the Tropical Pacific Warm Pool: Microphysical Interpretations from CEPEX and from Kwajalein, Marshall Islands

Abstract Recent studies suggest that extensive shields of cirrus clouds over the equatorial Pacific “warm pool” may have a significant influence on the global climate, yet details of the links between cloud microphysical properties, upper-tropospheric latent and radiative heating rates, and climate are poorly understood. This study addresses whether relatively reflective ice crystals with dimensions smaller than about 100 µm near the tops of tropical cirrus clouds, produced by deep convection when the sea surface temperature exceeds 300 K, are principally responsible for the high albedos observed in this region. In situ measurements of ice crystal size distributions and shapes, acquired during the Central Equatorial Pacific Experiment (CEPEX), are used to derive cloud ice water content (IWC), particle cross-sectional area (A), and other microphysical and optical properties from particles with sizes down to 5 µm. These measurements are needed to ascertain the microphysical properties primarily responsible ...