Hexagonal Columns Research Articles

The impact of ice particle roughness on the scattering phase matrix

The goal of this study is to explore the influence of ice particle habit (or shape) and surface roughness on the scattering phase matrix. As an example, reported here are the results for two wavelengths: 0.67 and 1.61 μm. For this effort, a database of single-scattering properties has been computed for a set of habits including hexagonal plates, hollow and solid columns, hollow and solid 3D bullet rosettes, droxtals, aggregates of solid columns, and aggregates of plates. The database provides properties for each of the habits at 101 wavelengths between 0.45 and 2.24 μm for smooth, moderately roughened, and severely roughened particles. At each wavelength, the scattering properties are provided at 233 discrete particle diameters ranging from 2 to 10,000 μm. A single particle size distribution from a very cold ice cloud sampled during the CRYSTAL-FACE field campaign ( T cld=–76 °C) is used to illustrate the influence of habit and roughness on the phase matrix. In all, four different habit mixtures are evaluated. The nonzero elements of the phase matrix are shown to be quite sensitive to the assumed habit, particularly in the case of − P 12/ P 11 that is associated with the degree of linear polarization of scattered radiation. Surface roughness is shown to smooth out maxima in the scattering phase function and in the other elements of the phase matrix, consistent with other studies. To compare with the theoretical simulations of the phase matrix for smooth and roughened particles, a full year of cloud-aerosol lidar with orthogonal polarization (CALIOP) data from 2008 is analyzed to provide global statistics on the values of P 11 and P 22/ P 11 in the backscattering direction. In a comparison of two of the habit mixtures (one used for MODIS Collection 5 and another that incorporates new habits including hollow bullet rosettes and aggregates of plates) with the CALIOP data, the values for P 11 are higher regardless of the degree of particle surface roughness, and the values for P 22/ P 11 are lower than those for CALIOP. Further investigation is warranted to better understand this discrepancy.

Modeling and optimization of foam-filled thin-walled columns for crashworthiness designs

Thin-walled columns play an important role on passenger safety in vehicular collisions for their progressive deformation patterns and large energy absorptions. A thin-walled column with a large specific energy, i.e., the ratio of energy absorption to its mass, is often desirable to the automotive industry, because such designs could enhance safety and reduce manufacturing cost. Due to the complexity of crash mechanism, obtaining such designs has been a challenge to the trial-and-error approach using physical prototype testing. To this end, combining finite element simulations with optimization methodologies has become the viable means to meet the challenge. In this paper, single- and triple-cell hexagonal columns filled with aluminum foams were optimized for maximum specific energy with simultaneous consideration of section geometry, tube thickness, and foam density. The effects of crushing forces on column designs were analyzed by comparing optimum solutions with and without constraints on the mean crushing forces. The interaction effects between the tube and foam of composite columns and the relative advantages of single- and triple-cell structures were investigated and discussed.

A LiDAR study of the effective size of cirrus ice crystals over Chung-Li, Taiwan

In this paper, we estimated the effective size of ice crystals in cirrus clouds using fall velocity derived from LiDAR (light detection and ranging) measurements at Chung-Li (24.58°N, 121.1°E), Taiwan. Nine shapes of the ice crystals, viz. hexagonal plates, hexagonal columns, rimed long columns, crystals with sector-like branches, broad-branched crystals, stellar crystal with broad arms, side planes, bullet rosettes and assemblages of planar poly-crystals of specific dimensions have been analyzed. The results show that the lidar derived most probable mean effective size of ice crystals is 340±180 μm with a dominant size range of 200–300 μm. The lidar derived mean effective size of cirrus crystals are parameterized in terms of cloud mid-height temperature as well as optical depth. The discussed method will be useful to study the most probable effective size distribution of ice crystals in cirrus cloud.

Electrochemical synthesis of ZnO coatings from water–isopropanol mixed baths: control over oriented crystallization

Electroreduction of an aqueous solution of a soluble Zn salt results in the deposition of ZnO crystallites with hexagonal columnar morphology. The crystallites grow with their long axes normal to the substrate resulting in adherent coatings with a strong c-axis orientation. This phenomenon is on account of the polarity of the 001 crystal face combined with the high dielectric constant of water. When the dielectric constant of the solvent is changed by making a mixture of water and isopropanol, there is a change in the direction of orientation of the coating. The switch takes place in the sequence [001] → [102], [103] → unoriented → [100], [110] as the isopropanol concentration is raised in a step-wise manner to 60% (v/v). The switch in orientation is caused by the tilt of the long axes of the hexagonal columns of ZnO with respect to the normal to the substrate. Above 60% isopropanol concentration, ZnO deposition is suppressed. This work demonstrates solution-mediated control over oriented crystallization.

A Theoretical Formula for Predicting the Instantaneous Folding Force of the First Fold in a Single Cell Hexagonal Honeycomb under Axial Loading

This article calculates a theoretical formula to predict the instantaneous folding force of the first fold creation in a single cell hexagonal honeycomb under axial loading. For this purpose, the sum of dissipated energy rate under bending around horizontal and inclined hinge lines and that under extensional deformations was equated to the work rate of the external force on the column. The final formula reasonably predicts the instantaneous folding force of the first fold of the thin-walled hexagonal columns during the folding progress. Finally, according to the calculated theoretical relation, the instantaneous folding force of the hexagonal column versus the axial displacement was sketched, and the comparison to the experimental results showed a good correlation.

Review of the Septibranchia (Mollusca: Pelecypoda) from the deep sea of Campos Basin, Brazil: Family Lyonsiellidae, with description of a new species

A review is made of the members of Lyonsiellidae present on the continental slope (750-2000 m) of Campos Basin (22°S), off south-eastern Brazil. A total of six taxa are recognized. Two taxa were previously unknown to science ( Lyonsiella pipoca n. sp., described herein, and Policordia sp.). Lyonsiella frielei and Policordia gemma are recorded from Brazilian waters for the first time. Lyonsiella abyssicola is distributed throughout the Atlantic Ocean, but the present record fills a gap in its distribution in the southwest Atlantic. Lyonsiella cf. formosa has a confused taxonomic status, and we believe that more than one species has been called L. formosa. Lyonsiella abyssicola, L. frielei and L. cf. formosa have the shell surface covered by small spines that typically have a hexagonal column and a stellate structure at the distal end.

Fluorescence-Enhanced Organogels and Mesomorphic Superstructure Based on Hydrazine Derivatives

New low-molecular-mass organic gelators (LMOGs) bearing hydrazine linkage and end-capped by phenyl, namely 1,4-bis[(3,4-bisalkoxyphenyl)hydrozide]phenylene (BPH-n, n = 4, 6, 8, 10), were designed and synthesized. These organogelators have shown great ability to gel a variety of organic solvents to form stable organogels with the critical gelation concentration as low as 8.7 x 10(-4) mol L(-1) (0.06 wt %). The formed gel has a high gel-sol transition temperature (T(gel)) at low gelation concentration. Aggregation-induced emission (AIE) has been observed after gelation though conventional chromophore units not incorporated in BPH-n. The fluorescence quantum yields of xerogel are 2 orders higher than that of dilute solution. In addition, the BPH-n (n = 6, 8, 10) exhibited thermotropic hexagonal column (Col(h)) mesophase, which are stable at room temperature as revealed by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD) studies.

Symmetry relations for the phase matrix of horizontally oriented particles

Seven symmetry relations, with a wide range of validity, are presented for the phase matrix of horizontally oriented particles. Three of these relations constitute a fundamental basis from which four others can be derived by making combinations. All seven relations can be used for many types of particles, including hexagonal plates and columns as well as spheroids, cylinders and cubes. Some applications are also pointed out.

ZnO Grown by Metal Organic Chemical Vapor Deposition: Effect of Substrate on Optical and Structural Properties

This paper reports the effects of the following substrates on the optical, structural and morphological properties of ZnO thin films: Si (100), Si (111), c- and r-sapphire, glass, GaAs and ZnO. The thin films were deposited by low pressure Metal Organic Chemical Vapor Deposition using diethylzinc and tertiary butanol as the zinc and oxygen sources, respectively. X-ray diffraction analysis shows that all the ZnO layers are c-axis orientated. Scanning Electron microscopy reveals similar morphology for all the substrates used, with hexagonal columns having cone shape ends being evident. The photoluminescence spectra are similar, but the various transitions have different relative intensities. It is clear that the different substrates influence neither the orientation of the films, nor the surface morphology, significantly. The photoluminescence hints at larger stacking fault densities in films grown on silicon and glass, however, as evidenced by stronger basal plane stacking fault-related luminescence at ~3.319 eV in the relevant low temperature photoluminescence spectra.

Electrochemical Deposition of ZnO Nanostructures. Mechanism of Growth

The growth kinetics of ZnO nanorods were studied by means of an electrochemical deposition process on ITO electrodes submerged in an aqueous solution of 5 mM ZCl+0.1 M KCl at 80 degrees C. The stages of the growth kinetics showed a mechanism of formation of nano-spheres which with time were transformed into hexagonal crystals of ZnO. Cathodic current densities of 0.1 to 1 mAcm2 formed hexagonal columns of 800 nm thickness while stronger currents formed a high-density layer of cylindrical nanorods 80 nm in diameter. An amorphous barrier layer was found between the surface of the electrode and the base of the nano-columns. The conditions assayed showed the possibility of adjusting the morphological characteristics of the layer in order to obtain different properties in different applications.

Morphology-selective synthesis of mesoporous SBA-15 particles over micrometer, submicrometer and nanometer scales

Mesoporous silica structures are of increasing importance as supports for enzymes and molecular organometallic catalysts. For high-surface-area, porous 3-d catalytic supports, the relationship between the exterior particle morphology and the 3-d mesopore structure is of particular significance. This paper describes the designed synthesis of selected morphologies of mesoporous SBA-15, which can be chosen from micrometer sized spheres to hundreds or tens of nanometers sized monodispersed particles such as platelets, hexagonal columns, rice-shapes, rods with tunable aspect ratios, and donuts. These are directly synthesized via control of the fundamental synthesis factors, including initial temperature, stirring rate and micelle packing parameter, rather than by the use of additives that have been generally utilized for specific morphologies in previous reports. The relationship between these basic synthesis parameters and morphologies provides insights into the formation of mesostructured materials.The SBA materials with various morphologies are expected to be useful in applications that require anisotropic or path-length-controlled diffusion.

The synthesis and mechanism investigations of morphology controllable 1-D SiCnanostructuresvia a novel approach

Single crystalline one-dimensional (1-D) β-SiC nanostructures were synthesized by the CVD (chemical vapor deposition) method using single crystal silicon wafers and detonation soot as the raw materials. The phase, morphology, crystal structure, and defects of the products were characterized by X-ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy. Within a 2 h reaction time, the morphology of the SiC nanostructures can be tuned to nanowires, hexagonal columns and nanopyramids by simply altering the reaction temperature from 1250 °C, 1300 °C to 1350 °C, respectively. Based on the VLS mechanism, we propose a model to explain the novel behavior of the temperature-dependent morphology considering the relationships between catalytic droplets and nucleation.

Parameterization of Shortwave and Longwave Radiative Properties of Ice Clouds for Use in Climate Models

AbstractClimate modeling and prediction require that the parameterization of the radiative effects of ice clouds be as accurate as possible. The radiative properties of ice clouds are highly sensitive to the single-scattering properties of ice particles and ice cloud microphysical properties such as particle habits and size distributions. In this study, parameterizations for shortwave (SW) and longwave (LW) radiative properties of ice clouds are developed for three existing schemes using ice cloud microphysical properties obtained from five field campaigns and broadband-averaged single-scattering properties of nonspherical ice particles as functions of the effective particle size De (defined as 1.5 times the ratio of total volume to total projected area), which include hexagonal solid columns and hollow columns, hexagonal plates, six-branch bullet rosettes, aggregates, and droxtals.A combination of the discrete ordinates radiative transfer model and a line-by-line model is used to simulate ice cloud radiative forcing (CRF) at both the surface and the top of the atmosphere (TOA) for the three redeveloped parameterization schemes. The differences in CRF for different parameterization schemes are in the range of −5 to 5 W m−2. In general, the large differences in SW and total CRF occur for thick ice clouds, whereas the large differences in LW CRF occur for ice clouds with small ice particles (De less than 20 μm). The redeveloped parameterization schemes are then applied to the radiative transfer models used for climate models. The ice cloud optical and microphysical properties from the Moderate Resolution Imaging Spectroradiometer (MODIS) cloud product over a granule and the collocated atmospheric profiles from the Atmospheric Infrared Sounder (AIRS) product are input into these radiative transfer models to compare the differences in CRF between the redeveloped and existing parameterization schemes. Although differences between these schemes are small in the LW CRF, the differences in the SW CRF are quite large.

Review of the Septibranchia (Pelecypoda: Mollusca) from deep sea of Campos Basin, Brazil: family Verticordiidae, with description of a new species

Despite the increase in the number of deep-sea studies, little is known about the hadal molluscs. For Brazil, only a few studies have treated the Septibranchia. This contribution is part of an effort to increase the knowledge of this group off the Brazilian coast, although it is focused only on the Campos Basin (22°S), State of Rio de Janeiro. Four species of the family Verticordiidae are recognized here. ForSpinosipella tingaSimone & Cunha, 2008, the known depth distribution is extended to 1050 m. ForVerticordia woodiiSmith, 1885, previously reported from Brazil, the known distribution is extended southwards to the Campos Basin.Verticordia quadrataSmith, 1885, is reported from Brazil for the first time. A previously unknown species,Verticordia ouricurisp. nov., is described. The presence of small spines, typically with a hexagonal column and a stellate structure at their distal end emerges as an additional taxonomic character for the verticordiids.

Single scattering from frozen hydrometeors at microwave frequencies

Scattering of electromagnetic waves from homogeneous or coated spheres can be computed in a mathematically exact way using the Mie theory. Therefore, for many approaches in remote sensing, frozen hydrometeors are parameterized as ice spheres. However, many frozen hydrometeors have non-spherical overall shapes and lack a spherically symmetric internal structure. They exist in a huge variety of shapes and exhibit different mixtures of ice, water and air. Therefore it is desirable to accurately compute scattering from non-spherical particles in order to clearly understand the effect the shape of a hydrometeor has on its scattering pattern. In this study, single scattering parameters like scattering cross section, absorption cross section, and asymmetry factor were calculated for frozen hydrometeors using the Discrete Dipole Approximation (DDA). The particles were modeled as hexagonal plates, columns, needles and dendrites by applying known dimensional relationships. The calculations were carried out over a wide range of centimeter and millimeter-wavelengths (1 GHz to 300 GHz), since millimeter-wave radiometers are highly sensitive to scattering by frozen hydrometeors in the atmosphere. The study results show that for size parameters < 1 (a ratio between wavelength and particle size) the scattering cross section of randomly orientated ice crystals is close to that of an equal volume ice sphere. Absorption cross section and asymmetry factor of non-spherical particles however are up to twice as high as that of equal volume ice spheres. Further the influence of the assumed model for the refractive index of ice at microwave wavelengths on the scattering parameters is investigated.

Temperature-sensitive supramolecules self-assembled by G-quadruplex DNA

Using guanine (G)-quadruplexes to construct supramolecular systems receives great attention because G-quadruplexes possess peculiar structural and electronic properties. In this paper, a temperature-sensitive supramolecule self-assembled by G-quadruplexes has been reported, whose structure was demonstrated to be a hexagonal column with rod-shaped G-quadruplex aggregates bundling together.

Influence of ice crystal shape on retrieval of cirrus optical thickness and effective radius: A case study

Airborne measurements of spectral upwelling radiances (350–2200 nm) reflected by cirrus using the Spectral Modular Airborne Radiation measurement sysTem (SMART)‐Albedometer were made over land and water surfaces. Based on these data, cloud optical thickness τ and effective radius Reff of the observed cirrus were retrieved. By using different crystal shape assumptions (hexagonal plates, solid and hollow columns, rough aggregates, planar and spatial rosettes, ice spheres, and a mixture of particle habits) in the retrieval, the influence of crystal shape on the retrieved τ and Reff was evaluated. With relative differences of up to 70%, the influence of particle habit on τ is larger than on Reff (up to 20% differences). Retrieved τ values agreed with values derived from concurrent lidar measurements within the measurement uncertainties.

Arctic aerosol and clouds studied by bistatic lidar technique

Aerosol and cloud studies were carried out with a polarimetric bistatic lidar setup at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) in Andenes (69°N, 16E°), Norway. The measurements were performed from 10 to 23 October 2006 and covered altitudes between 1.5 and 11 km, corresponding to scattering angles between 130 and 170°. The degree of linear polarization, PL, calculated from the experiments was compared with light scattering calculations using Lorenz‐Mie theory for spherical particles, the T‐matrix approach for nonspherical rotationally symmetric particles, and a geometric optics ray‐tracing method. Average PL values between 0.61 and 0.72 were obtained for the background aerosol under cloud‐free conditions. The aerosol results may be qualitatively reproduced by standard aerosol types if a suitable combination of coarse‐ and fine‐mode spherical particles is assumed. The PL values obtained for thin and mildly opaque clouds were in the range from 0.21 to 0.38. These results were not well described by spherical particles, and the results for relatively small prolate and oblate particles studied with the T‐matrix method tended to be slightly higher than the experimental values. Geometric optics calculations for hexagonal column ice particles with surface roughness were able to reproduce the experimental cloud data. This does not rule out contributions from other types of particles, and particle orientation effects may also have influenced the results. We conclude that the experimental results are consistent with earlier in situ studies of cirrus clouds, and the further development and application of the bistatic lidar technique is discussed.

Synthesis of nanometer-sized hexagonal disk-shaped ZnO in formic acid using a hydrothermal method and its optical properties

This study focused on the stable synthesis of nanometer-sized hexagonal disk-like ZnO, which can be utilized as the working electrode in DSSCs (dye-sensitized solar cells). Nanometer-sized zinc oxides, ZnOs, were successfully synthesized by hydrothermal treatment at 150, 200, and 250 °C for 8 h, and their morphologies were controlled by using different pHs, pH = 2, 3, and 4, with the addition of formic acid. The TEM (transmission electron microscopy) results reveal that the as-prepared particles at pH = 3 are hexagonal disk-shaped and the crystallite sizes are 40 nm measured across the diagonal. However, the shapes were different at the other pHs; nanoneedles at pH = 2 and hexagonal columns at pH = 4. The patterns of the photoluminescence (PL) spectra of the ZnOs varied according to their shapes; two types of emitting bands were observed in the case of the hexagonal nanodisks and columns at around 386–415 nm (violet) and 540–567 nm (green), respectively.

Development of a light scattering solver applicable to particles of arbitrary shape on the basis of the surface-integral equations method of Müller type I Methodology, accuracy of calculation, and electromagnetic current on the particle surface

We develop a numerical algorithm for calculating the light-scattering properties of small particles of arbitrary shape on the basis of a method involving surface integral equations. The calculation error was estimated by performing a comparison between the proposed method and the exact Mie method with regard to the extinction efficiency factor, and the results show that the error is less than 1% when four or more nodes per wavelength are set on the surface of a spherical particle. The accuracy fluctuates in accordance with the distribution of nodal points on the particle surface with respect to the direction of propagation of the incident light. From our examinations, it is shown that the polar incidence alignment yields higher accuracy than equator incidence when a "latitude-longitude" type of mesh generation is adopted. The electric currents on the particle surface and the phase functions of all scattering directions are shown for particles shaped as spheres or hexagonal columns. It is shown that the phase function for a hexagonal column has four or eight cold spots. The phase function of a randomly oriented hexagonal column shows halolike peaks with size parameters of up to 20. This method can be applied to particles with a size parameter of up to about 20 without using the symmetry characteristic of the particle.