Basal Face Research Articles

Una nueva especie de cangrejo topo ciego del género Zygopa Holthuis, 1961 (Crustacea, Decapoda, Anomura) de Cuba

Se describe una nueva especie de cangrejo topo ciego del género Zygopa. La especie nueva Z. lalanai sp. nov. se diferencia de las otras dos especies del género conocidas al presentar los ojos soldados en una placa transversa con sus extremos romos; la presencia de un campo setoso dispuesto entre la zona CG-6 y el margen del carapacho; por tener un diente en el margen basal interno del dedo móvil del quelípedo izquierdo y poseer la punta de los dactilos de los pereópodos 2 y 3 romas. Z. lalanai sp. nov. es la primera especie de Zygopa para Cuba y la zona suroriental del Golfo de México. Es la tercera especie conocida a nivel mundial.

Prism and Other High-Index Faces of Ice Crystals Exhibit Two Types of Quasi-Liquid Layers

Surface melting of ice significantly governs a wide variety of phenomena in nature. We recently succeeded in directly observing the surface melting on ice basal faces (Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 1052–1055) by our advanced optical microscopy, which can detect 0.37-nm-thick elementary steps on basal faces. However, the direct observation of surface melting on the other prism and high-index faces remains an experimental challenge. To fully obtain a comprehensive understanding, we need to examine the surface melting on these faces. Here we show the appearance of two types of quasi-liquid layers (QLLs) on prism and high-index faces just below the melting point. We quickly raised the temperature of ice crystals and then observed prism and high-index faces during a roughening process. We found that with increasing temperature, round liquid-like droplets (α-QLLs) first appeared at temperatures higher than −1.4 to −0.5 °C, and then thin liquid-like layers (β-QLLs) also appeared at temperatures higher...

Structural characterization of [formula omitted] irregular-shaped twinning boundary in hexagonal close-packed metals

In deformation twinning, the twinning boundary (TB) contour usually looks elliptical. Here, the 101¯2 TB contours are investigated in AZ31, Ti and Co by using transmission electron microscopy (TEM) and high-resolution TEM, suggesting a very irregular shape. The formation of a 101¯2 irregular-shaped TB is closely related to the interface defects and basal–prismatic interfaces, which place basal and prismatic planes face to face.

When are antifreeze proteins in solution essential for ice growth inhibition?

Antifreeze proteins (AFPs) are a widespread class of proteins that bind to ice and facilitate the survival of organisms under freezing conditions. AFPs have enormous potential in applications that require control over ice growth. However, the nature of the binding interaction between AFPs and ice remains the subject of debate. Using a microfluidics system developed in-house we previously showed that hyperactive AFP from the Tenebrio molitor beetle, TmAFP, remains bound to an ice crystal surface after exchanging the solution surrounding the ice crystal to an AFP-free solution. Furthermore, these surface-adsorbed TmAFP molecules sufficed to prevent ice growth. These experiments provided compelling evidence for the irreversible binding of hyperactive AFPs to ice. Here, we tested a moderately active type III AFP (AFPIII) from a fish in a similar microfluidics system. We found, in solution exchange experiments that the AFPIIIs were also irreversibly bound to the ice crystals. However, some crystals displayed "burst" growth during the solution exchange. AFPIII, like other moderately active fish AFPs, is unable to bind to the basal plane of an ice crystal. We showed that although moderate AFPs bound to ice irreversibly, moderate AFPs in solution were needed to inhibit ice growth from the bipyramidal crystal tips. Instead of binding to the basal plane, these AFPs minimized the basal face size by stabilizing other crystal planes that converge to form the crystal tips. Furthermore, when access of solution to the basal plane was physically blocked by the microfluidics device walls, we observed enhancement of the antifreeze activity. These findings provide direct evidence that the weak point of ice growth inhibition by fish AFPs is the basal plane, whereas insect AFPs, which can bind to the basal plane, are able to inhibit its growth and thereby increase antifreeze activity.

Xe- and U-tracks in apatite and muscovite near the etching threshold

Ion irradiation of a wedge-shaped Durango apatite backed by a mica detector allows investigating ion track ranges and etching properties at different points along the tracks. Transmission profiles obtained by irradiation with 2×106cm−2 11.1MeV/amu 132Xe and 2×106cm−2 11.1MeV/amu 238U parallel to the apatite c-axis correspond to ranges calculated with SRIM (Xe: 76.3μm; U: 81.1μm). However, the measured profiles show much greater etchable track-length variations than the calculated longitudinal straggles. The probable cause is that the length deficit exhibits significant variation from track to track. The measured length deficit in muscovite is in agreement with most existing data. In contrast, the length deficit in apatite appears to be close to zero, which is in conflict with all earlier estimates. This probably results from the etching properties of the apatite basal face, which permit surface-assisted sub-threshold etching of track sections in the nuclear stopping regime. These sections are not accessible from the opposite direction, i.e. by etching towards the endpoint of the tracks or in the direction of the ion beam. This conclusion is supported by the fact that linear dislocations are revealed in apatite basal faces and by the observation of imperfect etch pits that are separated from the etched ion track channel by a section that appears unetched under the microscope.

Numerical simulation of the flow fields around falling ice crystals with inclined orientation and the hydrodynamic torque

The flow field and orientation of ice particles are fundamental information to understand cloud microphysical processes, optical phenomena, and electric-field induced orientation and to improve remote sensing of ice clouds. The purpose of this study is to investigate the flow fields and hydrodynamic torques of falling ice columns and hexagonal plates with their largest dimension inclined with respect to the airflow. The Reynolds numbers range from 2 to 70 for columns and 2 to 120 for plates. The flow fields are obtained by numerically solving the relevant Navier–Stokes equations under the assumption of air incompressibility. It was found that for the intermediate Reynolds number the streamlines around the inclined crystals exhibit less spiral rotation behind them than those around the stable posture. The vorticity magnitude was larger in the upstream side and broader in the downstream than the one without inclination. For plates, a high-pressure dome on the center of the lower basal face disappears with inclination, possibly leading to an increase of riming there. The torques acting on the crystals have a local maximum over the inclined angle and exhibit almost symmetric around 45° over the range of Reynolds numbers. The torque parameterization was performed under pressures of 300, 500, and 800hPa as a function of Reynolds number and aspect ratio. It was found that the time scale of rotation for plates is smaller than the one for columns. Furthermore, the torque formula was applied to assess alignment of crystals along electric fields. It was found that these crystals of millimeter size require 120kV/m for the electrical alignment, which agrees with previous studies.

The growth of ice particles in a mixed phase environment based on laboratory observations

This paper describes new laboratory observations about the size evolution of ice crystals and cloud droplets immersed in a mixed-phase cloud. The experiments were performed by using a cloud chamber facility for three temperatures −6°C, −10°C and −20°C, in order to explore the basic crystal growth habits (columns and hexagonal plates). The sizes of the cloud droplets, ice-columns and hexagonal ice-plates were examined for growth times between 50 and 300s. The results show evidence that after ice crystal nucleation, the cloud droplets reduce gradually their sizes by the evaporation process; while the ice crystals grow as a consequence of the water vapor diffusion process. The ice crystal growths at different temperatures were compared with the results reported by other authors. The experimental data were also compared with a theoretical model of the growth rate of ice crystals. It was observed that the numerical model provides a description of the ice columns' growth in fairly good agreement with the laboratory observations, while it predicts that the hexagonal plates evolve with maximum sizes larger than those observed in the experiments. In general, it has been noted that the results obtained from the model are very sensitive to the parameter that denotes the ratio between the condensation coefficient for the basal face and prism face. It is a critical coefficient that needs to be carefully addressed in cloud modeling.

Roles of Surface/Volume Diffusion in the Growth Kinetics of Elementary Spiral Steps on Ice Basal Faces Grown from Water Vapor

We measured velocities Vstep of lateral displacement of individual elementary steps on an ice basal face, for the first time, by advanced optical microscopy, under various bulk water vapor pressure PH2O∞. Distances L between adjacent spiral steps exhibited considerable variation under constant PH2O∞. Hence, we analyzed Vstep as functions of L and PH2O∞. Then we found that (1) under a constant PH2O∞, Vstep decreased with decreasing distances L when L ≤ 15 μm and that Vstep remained constant when L ≥ 15 μm. We named Vstep of L ≥ 15 μm (isolated steps) Vstepint and analyzed dependencies of Vstepint on PH2O∞. Then we found that (2) the slope of the Vstepint vs PH2O∞ plot gradually decreased with increasing PH2O∞. We proposed a model that took into account both the volume diffusion of water vapor molecules and the surface diffusion of water admolecules on a terrace. Our model could explain result (1) mainly by the competition of adjacent spiral steps for water admolecules diffusing on a terrace but could not explain the result (2) satisfactorily.

Best face forward: crystal-face competition at the ice-water interface.

The ice-water interface plays an important role in determining the outcome of both biological and environmental processes. Under ambient pressure, the most stable form of ice is hexagonal ice (Ih). Experimentally probing the surface free energy between each of the major faces of Ih ice and the liquid is both experimentally and theoretically challenging. The basis for the challenge is the near-equality of the surface free energy for the major faces along with the tendency of water to supercool. As a result, morphology from crystallization initiated below 0 °C is kinetically controlled. The reported work circumvents supercooling consequences by providing a polycrystalline seed, followed by isothermal, equilibrium growth. Natural selection among seeded faces results in a single crystal. A record of the growth front is preserved in the frozen boule. Crystal orientation at the front is revealed by examining the boule cross section with two techniques: (1) viewing between crossed polarizers to locate the optical axis and (2) etching to distinguish the primary-prism face from the secondary-prism face. Results suggest that the most stable ice-water interface at 0 °C is the secondary-prism face, followed by the primary-prism face. The basal face that imparts the characteristic hexagonal shape to snowflakes is a distant third. The results contrast with those from freezing the vapor where the basal and primary-prism faces have comparable free energy followed by the secondary-prism face.

Reduced embodied simulation in psychopathy

Objectives. Psychopathy is characterized by severe deficits in emotion processing and empathy. These emotional deficits might not only affect the feeling of own emotions, but also the understanding of others’ emotional and mental states. The present study aims on identifying the neurobiological correlates of social-cognitive related alterations in psychopathy. Methods. We applied a social-cognitive paradigm for the investigation of face processing, emotion recognition, and affective Theory of Mind (ToM) to 11 imprisoned psychopaths and 18 healthy controls. Functional magnetic resonance imaging was used to measure task-related brain activation. Results. While showing no overall behavioural deficit, psychopathy was associated with altered brain activation. Psychopaths had reduced fusiform activation related to face processing. Related to affective ToM, psychopaths had hypoactivation in amygdala, inferior prefrontal gyrus and superior temporal sulcus, areas associated with embodied simulation of emotions and intentions. Furthermore, psychopaths lacked connectivity between superior temporal sulcus and amygdala during affective ToM. Conclusions. These results replicate findings of alterations in basal face processing in psychopathy. In addition, they provide evidence for reduced embodied simulation in psychopathy in concert with a lack of communication between motor areas and amygdala which might provide the neural substrate of reduced feeling with others during social cognition.

Self-regulated in-plane polarity of [11¯00]-oriented GaN domains coalesced from twins grown on a SiO2-patterned m-plane sapphire substrate

In-plane polarity of [11¯00]-oriented GaN domains coalesced from twins grown on a SiO2-patterned m-plane sapphire substrate was observed to be self-regulated in such a way that basal faces of coalesced domains were mainly found to have the (0001¯) polarity only. This self-regulation behavior of in-plane polarity was explained by a computational simulation of plan-view surface morphology evolution during coalescence of twins. Based on a computational simulation, asymmetrically suppressed growth rates of twins near a SiO2 pattern were proposed to be responsible for the survival of the slower growing (0001¯) basal faces instead of the faster growing (0001) basal faces during coalescence of twins.

Double Spiral Steps on Ih Ice Crystal Surfaces Grown from Water Vapor Just below the Melting Point

During the growth of ice crystals, spiral growth is one of the important growth mechanisms that dominate their growth. However, the structure of spiral steps on ice crystal surfaces at temperatures near the melting point has not been identified. Here we show a possible model structure of spiral steps on basal and prism faces of Ih ice crystals grown from water vapor just below 0 °C. We observed in situ the coalescences of spiral steps and steps of two-dimensional (2D) islands by our advanced optical microscopy, which can visualize individual elementary steps (single-bilayer height) of 2D islands on ice basal faces. We found that both spiral steps and 2D island steps on basal and prism faces show single-bilayer heights, though Burgers’ vectors of screw dislocations on both faces need to have double-bilayer heights because of a crystallographic requirement. These results suggest that at the center of a spiral growth hillock, steps of two adjacent single bilayers coincide and then form a double-bilayer step ...

The influence of individual clay minerals on formation damage of reservoir sandstones: a critical review with some new insights

AbstractThe influence of individual clay minerals on formation damage of reservoir sandstones is reviewed, mainly through the mechanism of fine particle dispersion and migration leading to the accumulation and blockage of pore throats and significant reduction of permeability. The minerals discussed belong to the smectite, kaolinite, illite and chlorite groups respectively. These minerals usually occur in an aggregate form in reservoir sandstones and the physicochemical properties of these aggregates are reviewed in order to reach a better understanding of the factors that lead to their dispersion in aqueous pore fluids. Particularly significant properties include the surface charge on both basal and edge faces of the clay minerals and how this varies with pH, external surface area of both swelling and non-swelling clays, porosity and pore size distribution in the micro- and meso-pore size range and overall aggregate morphology. For non-swelling clays, and perhaps even for swelling clays, dispersion is thought to be initiated at the micro- or meso-pore level, where the interaction between the pore solution and the charged clay surfaces exposed on adjacent sides of slit- or wedge-shaped pores brings about expansion of the diffuse double electric layer (DDL) and an increase in hydration pressure. Such expansion occurs only in dilute electrolyte solutions in contrast to the effect of concentrated solutions which would shrink the thickness of the DDL and so inhibit dispersion. Stable dispersions are formed, particularly where the solution pH exceeds the isoelectric pH of the mineral, which is often at alkali pH values, so that both basal face and edge surfaces are negatively charged and the particles repel each other. The osmotic swelling of smectitic clays to a gel-like form, so effectively blocking pores in situ, is often invoked as an explanation of formation damage in reservoir sandstones. Such swelling certainly occurs in dilute aqueous solutions under earth surface conditions but it is uncertain that stable smectitic gels could form at the temperatures and pressures associated with deeply buried reservoir sandstones.

Water in extremely narrow planar pores with crystalline walls. 2. Thermodynamics

The free energy, entropy, and work of water vapor adsorption in planar pores with widths of 0.62 and 1.25 nm located in a silver iodide crystal parallel to its basal face have been computed at the molecular level. In contrast to adsorption on a free surface, the adsorption in the pores proceeds in three stages, i.e., the formation of molecular films on the walls, coalescence of the films, and densification of the fluid in the pore volume. At the second stage, the equilibrium between the fluid in the pore and the vapor over the pore at temperatures corresponding to normal conditions is thermodynamically unstable and accompanied by the development of a free energy barrier and the existence of metastable states. As temperature is elevated, the instability is gradually evened out; however, its signs remain preserved even at the boiling temperature of water. Extremely narrow pores with widths smaller than 1 nm are always filled with water under conditions of even a rather dry natural atmosphere. The filling of pores several nanometers wide in strongly unsaturated water vapors overcomes the free-energy barrier; however, the fluid that has filled the pore remains stable with respect to evaporation in vapors with densities lower than the density of saturated vapor by several orders of magnitude. The existence of the free-energy barrier and metastable states in nanosized breaks in crystals creates conditions for hysteresis of adsorption-desorption cycles.

Water in extremely narrow planar pores with crystalline walls. 1. Structure

Computer simulation has been employed to study the structure of water condensate filling planar pores 1.25 and 0.62 nm wide located parallel to the basal face in a silver iodide crystal at 260 K. All stages of adsorption of single molecules up to complete pore filling have been described. At an initial stage, strong clustering of molecules is observed on the walls; then, the walls are covered with a monomolecular film; and, at the final stage, molecules are adhered to the surface of the film, thus filling the internal space of the pore. First, adsorption occurs at the wall containing positive ions on the surface and, then, on the opposite wall with negative ions. On both walls, adsorbed molecules are adhered to the surface via the interaction with ions of the second crystallographic layer; given this, two types, α and β, of molecule plane orientation are realized on opposite walls. The adhesion of an adsorbed molecular film to molecules filling the interior of the pore requires the partial transition of film molecules from the α- to the β-type orientation on one wall and the inverse transition on the other wall. The deficiency of α-oriented molecules on one wall and β-oriented ones on the other is the main reason for poor wettability of the surface of the monomolecular films adsorbed on the walls. In an extremely narrow pore, molecules are simultaneously captured in the field of both walls. The forces acting from the sides of both walls result in the separation of a film into spots having structures matched to the crystalline structure of each wall, with the film being on the verge of breakage.

In-layer stacking competition during ice growth

When ice grows, the growth rates are unequal [corrected] along different growth directions and some layers contain planar defective regions. With the aim of helping to understand these phenomena, we report the molecular dynamics simulations of ice growth on the basal and prismatic faces of initial hexagonal ice, using the TIP5P-E water model. By presenting the time evolution of the two-dimensional density profiles of water molecules in each layer and the kinetics of layer formation during ice growth at the temperature of 11 K supercooling, we show that two forms of ice arrangements, hexagonal and cubic, develop competitively within the same ice layer on the basal face, whereas such in-layer stacking-competition is insignificant on the prismatic face. It is shown that, on the basal face, the occurrence of significant in-layer stacking competition in one of the layers significantly delays the layer formation in several overlying layers and explains the overall delay in ice growth on the basal face compared to that on the prismatic face. In addition, it is observed that large planar defects form on the basal face, as a consequence of the long-lasting in-layer stacking competition when the overlying layer grows rapidly.

Radiation growth of hcp crystals driven by discrete breathers

A new mechanism of radiation growth (RG) of hexag-onal close pack (hcp) crystals is proposed, which is based on the radiation-induced creation of moving ‘discrete breathers’ (DBs), i.e. large amplitude anharmonic lattice vibrations, which can propagate and transfer energy along close-packed crystallographic directions within the basal planes of and excite atoms at prismatic faces/edges. Ac-cordingly, the DB-induced vacancy emission from pris-matic faces is enhanced as compared to that from the basal faces, at which only thermally activated vacancy emission takes place. This should result in the vacancy diffusional flow from prismatic to basal faces leading to expansion along the a-directions and to contraction along the c-axis, i.e. to the radiation-induced growth. The RG rate driven by this mechanism is evaluated in the framework of a rate theory modified with account of the DB-induced vacancy emission.

The Emergence Processes of two Types of Quasi-Liquid Layer Phases with Different Morphologies on an Ice Basal Face

The Emergence Processes of two Types of Quasi-Liquid Layer Phases with Different Morphologies on an Ice Basal Face

One-pot in situ synthesized TiO2/layered double hydroxides (LDHs) composites toward environmental remediation

In this paper, a novel approach to synthesize nanostructural composite materials of TiO2/ZnAl LDH is reported for the first time. By simply mixing precursor solutions, TiO2/ZnAl LDH composite materials can be readily synthesized. The deposition of TiO2 nanoparticles on the basal face of ZnAl LDH had maintained the original layered structure of ZnAl LDH. TiO2/LDH composites exhibited a typical IV isotherm type indicating a mesopore structure. The specific surface area of TiO2/LDH composites was four times that of pristine LDH. Furthermore, the adsorption test using the typical dye (methylene blue: MB) indicated that the adsorption ability of LDH had been significantly enhanced after the incorporation of TiO2 by this strategy. Therefore, the developed TiO2/LDH composite materials with unique adsorption characteristics have great potential for diverse applications.

A comprehensive stochastic model of phyllosilicate dissolution: Structure and kinematics of etch pits formed on muscovite basal face

Accurate modeling of phyllosilicate dissolution kinetics is a complex problem involving recognition of the influence of structure, chemical composition, lattice defects, and surface topography on local and global dissolution mechanisms. Previous research has provided a wealth of experimental observations that illustrate the dominant role of etch pits in formation of the steps on the basal face of mica during the dissolution reaction. The shape of the etch pits bears important information on surface reactivity and dissolution rate anisotropy at given environmental conditions. In order to understand the influence of various kinetic factors on etch pit and step morphology, as well as the overall dissolution mechanisms, we have developed a new Kinetic Monte Carlo model simulating dissolution of these minerals. The model considers the effects of chemical composition, structural position, the number of first and second-order nearest neighbors and the steric hindrance of surface atoms on the etch pit morphology and step reactivity. We describe several complexity levels of the model which are characterized by the different ranges of the effects considered. These levels were developed in order to find the most optimal model capable of predicting experimentally observed etch pit morphologies. Our simulation results show that the models based on the sole consideration of the first coordination sphere in general can predict etch pit shape and orientation, while recognition of the site reactivity difference imposed by the steric factors helps us to explain the geometry of monolayer pit superposition. However, the distinction of the ledge and kink sites at all the experimentally observed surface steps is possible only with the use of the second-order neighbors. Based on these findings, we propose a mechanistic scheme explaining the role of the first and second-order coordination numbers in step stabilization and correct prediction of the etch pit structure.