Convection Research Articles

Unsteady EMHD free convective second grade fluid flow past an exponentially accelerated vertical porous plate

This paper presents a detailed account of unsteady, incompressible, viscous, electrically conducting, unidirectional, free convective second grade fluid through an exponentially accelerated vertically infinite plate with both applied electric field and magnetic field being present. The equation of motion and energy manifested as nonlinear partial differential equation are represented as algebraic equations using implicit finite difference scheme and solved numerically by implementing the damped-Newton method. With the help of the momentum and energy equation, we defined the expressions for skin friction and Nusselt number. The cases n = 1(constant acceleration) and n = 0.5(variable acceleration) are also taken into consideration. The solution obtained is eventually simulated using MATLAB and the resulting graphs representing the influence of non-dimensional parameters on flow field and temperature field are discussed thoroughly. We have also validated the results obtained from the present methodology with the results obtained from already existing methodologies under some limited cases. It is interesting to note that when the plate is being cooled by free convection current, with increase in viscoelastic parameter the viscous forces are dominated by the elastic effects which results in accelerating the velocity flow profile. For comparatively smaller values of Ec the temperature distribution decreases with increasing Re as the suction propagation facilitates decrease in boundary layer thickness which consequently enhances heat transfer rate. The effect of Ec is to raise the temperature profile due to enhancement in viscous dissipation effects. Practically, the combined effects of the physical parameters are remarkably important in various engineering, medical and industrial applications.

Climate Behaviour and Plant Heat Activity of a Citrus Tunnel Greenhouse: A Computational Fluid Dynamic Study

Response to the expanding demand for high-quality citrus saplings plants requires optimisation and a deep understanding of production climate behaviour. In this context, greenhouse production is the most used technique because it allows farmers to effectively monitor plant growth through production condition control, especially climatic parameters. The current work presents an analysis of climate behaviour and plant heat activity of a citrus sapling tunnel greenhouse in the middle region of Morocco. In this regard, a computational fluid dynamic (CFD) model was developed and validated with respect to temperature and relative humidity measured values. The specificity of this model is the inclusion of a new non-grey radiative and heat transfers physical sub-models to couple the convective and radiative exchanges at the plastic roof cover and crop level. The findings showed that using a green shade net increased the greenhouse shadow, and the layering of plastic and shade net significantly reduced solar radiation inside the greenhouse by 50%. Also, the greenhouse airflow speed was deficient; it cannot exceed 0.3 ms−1, hence the dominance of the chimney effect in heat transfer. Despite the previous results, analyses of greenhouse temperature and relative humidity fields clearly showed the greenhouse climate behaviour heterogeneity, where spatial greenhouse air temperature and relative humidity difference values reached a maximum of 29.7 °C and 23%, respectively. For citrus plants, heat activity results showed that a weak fraction (1.44%) of the short wavelength radiation is converted to latent heat, which explains the low plant transpiration under these conditions. While the convective currents are the primary source of temperature and relative humidity heterogeneity inside the greenhouse, the presence of crop rows tends to homogenise the climate inside the greenhouse. We also concluded the necessity of proper condensation modelling near ground surfaces and inside the crop, and the water vapour effect on climate determination.

Geometry effect of phase change material container on waste heat recovery enhancement

Waste heat recovery from industrial exhaust gases is a key method to reduce fuel consumption and improve system energy efficiency. Phase change materials (PCMs) are one of the major media in the waste heat storing and recovering processes. The PCM container geometry is a crucial design factor but attracts less attention for its effect on the PCM melting and heat storage operation. This study simulates the melting behaviour and heat storage performance in the PCM storage containers with the same cross area but different configurations with the rectangular shape and ones with concave folded sidewalls and protruding folded sidewalls. The geometry variation on PCM containers influences both the contact area with the hot airflow and natural convection in the melting phase of PCMs. The three-dimensional transient modelling indicates that the natural convection currents enhance the PCM melting and thermal storage rates. The PCM container design angle, α, shows a remarkable impact on the natural convection strength, PCM melting time, and energy storage rate. The protruding-shaped container with α at 133.8∘ presents the least melting time of 4,645 s, reducing 24.9% of the melting time in comparison to the rectangular chamber as the baseline with α= 90 ∘. The study can inspire the design of PCM storage geometries with efficient waste heat recovery in the industrial applications.

Analysis of distillation characteristics via CFD (computational fluid dynamics) of Korean traditional 'Sojutgori' and study on structure for distillation efficiency enhancement.

The design of the Korean traditional distiller 'sojutgori' was extracted as a digital sketch, and the internal fluid flow in the distillation process was tracked through computer simulation. Based on this, a new design was derived to improve distillation efficiency and its changes were researched. The ethanol particles vaporized inside the distiller were stagnated or their discharge was accelerated according to the magnitude and frequency of vortex. If the center is narrow and the fluid rotates, the vortex decreases or changes to a regular form. To effectively control the vortex, six simple models and two materialized models were designed and the optimal design was derived. When compared with the traditional distiller, the outlet fluid speed of the final design increased by 78% and the residence time dispersion of ethanol particles decreased by 39%. Furthermore, to suppress the temperature spread of fermented wash, a streamlined blade structure that can promote convection current was added. This structure had the effect of reducing the temperature spread of fermented wash by 57%. In addition, a reflux ring structure that can control the recondensed fermented wash caused by heat loss at the inner wall of the distiller was designed and applied. The reflux ring structure minimized the temperature change of the fermented wash and decreased temperature change by 23% compared to the condition without the reflux ring structure.

Pathways to Boost Solar-to-Hydrogen Efficiencies for Z-Scheme Photocatalytic Reactors: Learnings from Equivalent Circuit and Continuum Multiphysics Models

Z-scheme semiconductor particles present in an aqueous solution with soluble redox shuttles provides a promising two-step approach to split water to produce hydrogen and oxygen using sunglight. This approach facilitates efficient utilization of the incident solar spectrum with tandem light-absorbers and promotes safe reactor operation with hydrogen and oxygen produced in physically distinct locations. Thermodynamically, these systems are projected to achieve solar-to-hydrogen (STH) efficiencies that are comparable to the electrode architectures, which are as large as 34% with idealized light absorbers and perfect reaction selectivity1. Up to 4% STH efficiencies were theoretically projected for state-of-the-art light absorbers and cocatalysts with diffusion-driven redox shuttle transport between reaction sites2. However, practical demonstrations are limited to efficiencies that are significantly smaller (less than 1%)3. Two main factors impeding actual performance in these systems include: (a) undesired reactions of any redox species, including hydrogen, oxygen, or the redox shuttle species, on the photocatalyst site; and (b) mass-transfer limitations of reactant/product species between oxygen and hydrogen evolution reaction sites. In this work, I will present materials- and device-level insights obtained from physics-based models of varying complexities. An expanded, zero-dimensional (0-D), equivalent-circuit model is developed to probe the effectiveness of semipermeable oxide coatings to achieve reaction selectivity. This model introduces powerful innovations to model parallel/competing redox reactions at the valence and conduction bands, while also accounting for mass-transfer limitations. Moreover, our framework provides a tractable approach to quantify the multidimensional dependencies of coating transport and kinetic parameters, concentration of light absorbers, and species mass-transfer rates on the STH efficiencies. At the reactor-scale, we assess the viability of natural convective currents to enhance species mixing. Temperature and concentration profiles are predicted from a two-dimensional (2-D), coupled flow, heat, and mass-transfer model of two reaction compartments separated by a membrane. Modeling predictions are compared to and validated against experimental measurements on dual-compartment reactor prototypes. Enhanced rate of species transport is predicted in the presence of thermal convection in addition to diffusion. Improved species mixing is observed for the horizontal, as compared to the vertically stacked, arrangement of reaction compartments, and is attributed to attenuation of incident sunlight by the membrane present along the optical path. With 2-cm tall reaction compartments, the minimum redox shuttle concentration needed to sustain a 10% STH efficiency decreases by 80% in the presence of natural convection as compared to diffusion. Overall, these results provide new insights and strategies to realize highly effective materials-to-device scale designs for Z-scheme photocatalytic solar fuel reactors with soluble redox shuttles. References (1) Keene, S.; Bala Chandran, R.; Ardo, S. Calculations of Theoretical Efficiencies for Electrochemically-Mediated Tandem Solar Water Splitting as a Function of Bandgap Energies and Redox Shuttle Potential. Energy Environ. Sci. 2019, 12 (1), 261–272. https://doi.org/10.1039/C8EE01828F.(2) Bala Chandran, R.; Breen, S.; Shao, Y.; Ardo, S.; Weber, A. Z. Evaluating Particle-Suspension Reactor Designs for Z-Scheme Solar Water Splitting via Transport and Kinetic Modeling. Energy Environ. Sci. 2018, 11 (1), 115–135. https://doi.org/10.1039/C7EE01360D.(3) Wang, Z.; Hisatomi, T.; Li, R.; Sayama, K.; Liu, G.; Domen, K.; Li, C.; Wang, L. Efficiency Accreditation and Testing Protocols for Particulate Photocatalysts toward Solar Fuel Production. Joule 2021, 5 (2), 344–359. https://doi.org/10.1016/j.joule.2021.01.001.

No fins attached? Numerical analysis of internal–external fins coupled PCM melting for solar applications

Thermal energy storage/sink is imperative for any type of solar energy harnessing system/technology. However, the inevitable challenge remains in developing and optimizing a thermal energy storage (TES) system suitable for long cyclic operation. This work numerically analyses the melting characteristics of phase change material (PCM; RT42)-based latent thermal energy storage (LTES) as a two-dimensional rectangular enclosure. The consequence of utilizing internal–external extended surfaces (fins) with realistic convective boundary condition is studied for photovoltaic thermal (PVT) applications. The application of internal–external fins is intended for enhancing the charging (melting) duration according to the long cyclic solar operation and better dissipation of heat after complete melting. Three kind of fins-rectangular, triangular, and Y-type- are investigated for two orientations of storage/sink enclosures-upright ( θ = 90°) and inclined ( θ = 35°). Moreover, three fin configurations are analyzed-equal, decreasing and increasing-stepped-based on the arrangement of fins along the enclosure height. Two-dimensional, transient numerical simulations are conducted for governing PCM melting, contemplating the consequences of natural convection. The performance assessment of each storage unit (orientation/fin-type/fin-arrangement) is made based on parameters such as time enhancement ratio, suppression ratio, liquid fraction, temperature distribution, melt velocity magnitude, storage capacity/rate, and enhancement in Nusselt number. The melting is delayed for triangular and Y-fins enclosures as compared to that for rectangular fins. Equal and increasing-stepped Y-fin arrangements yielded the largest time enhancement ratios of 42.38% and 29.86% for inclined and upright enclosures, respectively. Moreover, Y-fins-based enclosure produced a larger average suppression ratio as compared to other types of fins. A 2.56, 2.67, and 2.64 times enhancement in Nusselt number is observed for increasing-stepped fin arrangement of rectangular, triangular, and Y-finned upright enclosures, respectively. However, for the inclined enclosure, a 2.32 times enhancement in Nusselt number is reported for increasing-stepped Y-fin. • Internal–external fin-coupled thermal storage for cyclic solar PVT applications. • Utilization of rectangular, triangular, and Y-fins in augmenting PCM melting. • Assessment of 3 configurations/fin-immersions for intensifying convection currents. • Effect of cavity inclination on melting characteristics for long duty operation. • Maximum 2.67 times Nusselt number enhancement for increasing triangular fin.

Pore-scale phenomena in carbon geological storage (Saline aquifers—Mineralization—Depleted oil reservoirs)

The injection of CO2 into geological formations triggers inherently coupled thermo-hydro-chemo-mechanical processes. The reservoir pressure and temperature determine the CO2 density, the CO2-water interfacial tension, and the solubility of CO2 in water (hindered by salts and competing gases). The CO2-water interface experiences marked pinning onto mineral surfaces, and contact angles can range from the asymptotic advancing to receding values, in contrast to the single contact angle predicted by Young’s equation. CO2 dissolves in water to form carbonic acid and the acidified water dissolves minerals; mineral dissolution enhances porosity and permeability, triggers settlement, may couple with advection to form “wormholes”, produces stress changes and may cause block sliding and shear bands. Convective currents can emerge beneath the CO2 plume and sustain CO2 and mineral dissolution processes. On the other hand, mineralization is a self-homogenizing process in advective regimes. The crystallization pressure can exceed the tensile capacity of the host rock and create new surfaces or form grain-displacive lenses. Within the rock matrix, coupled reactive-diffusion-precipitation results in periodic precipitation bands. Adequate seal rocks for CO2 geological storage must be able to sustain the excess capillary pressure in the buoyant CO2 plume without experiencing open-mode discontinuities or weakening physico-chemical interactions. CO2 injection into depleted oil reservoirs benefits from time-proven seals; in addition, CO2 can mobilize residual oil to simultaneously recover additional oil through oil swelling, ganglia destabilization, the reduction in oil viscosity and even miscible displacement. Rapid CO2 depressurization near the injection well causes cooling under most anticipated reservoir conditions; cooling can trigger hydrate and ice formation, and reduce permeability. In some cases, effective stress changes associated with the injection pressure and cooling thermoelasticity can reactivate fractures. All forms of carbon geological storage will require large reservoir volumes to hold a meaningful fraction of the CO2 that will be emitted during the energy transition.

Evolution of IMF By induced asymmetries during substorms: Superposed epoch analysis at geosynchronous orbit

The By component of the magnetic field inside the magnetosphere is positively correlated with the By component of the Interplanetary Magnetic Field (IMF). This leads to asymmetries in aurora, plasma convection and electric currents between the northern and southern hemispheres It has been demonstrated that magnetic conjugate locations in the northern and southern ionosphere become less displaced during magnetospheric substorms, which are associated with enhanced reconnection in the near-Earth tail. Here we directly address how the average By component in the magnetotail evolves relative to substorm onset by performing a superposed epoch analysis of the magnetic field observed at nightside geosynchronous orbit during periods with dominant IMF By. The observations demonstrate that the average |By| in the magnetotail increases during the loading phase prior to onset. |By| maximizes in the expansion phase and is subsequently reduced during the remaining unloading phase. The observed trends become more pronounced using substorm onset lists that on average identify stronger substorms. Since dayside reconnection dominates over tail reconnection during the loading phase, whereas tail reconnection dominates during the unloading phase, the results demonstrate how asymmetries build up during periods with low tail reconnection and are reduced during periods with enhanced tail reconnection in agreement with previous case studies of conjugate auroral substorm features.

Numerical study of laminar natural convection in a half ellipsoid of revolution subjected to heat flux of constant density

In this article, we numerically study the natural convection in a half-eliipsoid of revolution filled with a Newtonian fluid (air). The ellipsoid wall is isothermal which is maintained at a heat flux of constant density. The equations that govern the flow and heat transfer are described by the so-called Navier-Stokes equation of motion accompanied by the so-called Fourier equation of heat. The finite element method is used to solve the system of equations. We consider the effect of the shape factor of the elliptical wall and the Grashof number on the results obtained in the form of streamlines, and mean Nusselt numbers. The Nusselt numbers for natural convection inside a system formed by a rectangular geometry and for a curved shape are comparer and analyzed each other. We find that this number is quite higher for a curved system than that of a planar shape. It shows the importance of the form factor, particularly, in circular shape which is much more advantageous compared to the straight shape.In terms of inertia, the geometry of rounded shape ensures the best distribution of energy. In fact, the half ellipsoidal greenhouse with a circular base studied during this research offers a better distribution for the flow of the convection currents from the bottom to the top of the system.

Magmatic processes recorded in plagioclase crystals of the Rio Jacaré Batholith, Sergipano Orogenic System, Northeast Brazil

Plagioclase crystallization is common in magmatic systems and are textures can provide valuable information about the physicochemical conditions present during magmatic evolution. This work presents a systematic study of textures and compositional variation in plagioclase crystals in the granites and microgranular enclaves of the Rio Jacaré Batholith (RJB) aiming to infer the magmatic processes that were recorded in these crystals. Plagioclase of the inequigranular facies has composition ranging from albite to andesine (An7-33), while in the porphyritic facies it is albite and oligoclase (An5-23). In microgranular enclaves plagioclase composition ranges from albite to labradorite (An6-51). In addition to the presence of chemical zoning in plagioclase of the RJB rocks, patchy zoning, boxy cellular texture, crystal cores showing embayed or homogeneous composition as well as inclusion zones of mafic and synneusis minerals also occur. The textures identified in the RJB rocks allowed us to infer that during the evolution of the RJB magma, there was a period of stable conditions followed by a period with injections of mafic magmas, which modified the conditions (temperature, pressure, and H2O activity) of this magmatic system and stimulated mixing between magmas. The mafic magma injections are most likely to have generated convection currents in the magmatic chamber of the RJB. In addition to this process, it is also necessary to consider the decompression of magma, caused by its rapid rise. This complex evolution of the Rio Jacaré magmatic system was registered in the textures and compositions of the plagioclase crystals and suggests at least five successive moments of resorption in these crystals.

Thermal Vibrational Convection in a Rotating Plane Layer

The influence of rotation on the thermal vibrational convection of liquid in a horizontal plane layer is studied experimentally. The convection in the layer is excited by the vibrations of circular polarization in the horizontal plane. The research is carried out in a liquid layer heated from above, under conditions of a strong stabilizing effect of gravity. In this case, the vibrational convection is excited at a relatively high intensity of vibrations and manifests itself in the development of short-wavelength convective structures in the form of beads. It is found that the rotation has a stabilizing effect and increase the vibrational convection excitation threshold. A map of convective stability is plotted on the plane of dimensionless parameters: vibrational parameter, and dimensionless velocity of rotation, for different values of the gravitational Rayleigh number. The results are compared with the classic case of gravitational convection in a rotating layer. It is shown that, similarly to the case of gravitational convection, rotation has a stabilizing effect on vibroconvective stability; the threshold value of the vibration parameter increases with the dimensionless velocity. It is found that at large negative values of the gravitational Rayleigh number, when cellular convective structures of vibroconvective nature are characterized by large wave numbers, in the studied area of the dimensionless frequency, rotation has little effect on the wave number of spatial convective structures, but changes their shape. (Clinical trials: no any clinical trials were performed).

Numerical research of characteristic mixing times of isothermal three-component steam-gas systems

Multicomponent diffusion in gases is characterized by a number of effects that are not observed in binary diffusion. Analysis of existing works shows that convective instability may occur in some systems with significantly different diffusion coefficients with certain geometric and thermophysical characteristics. Stability analysis allows determining the spectrum of parameters at which a transition from a diffusive state to a convective is possible. However, this approach does not allow the researchers to investigate the dynamics of the process. Therefore, this work aims to describe emergence and evolution of convective flows in threecomponent systems and assess the influence of the initial composition on the occurrence of concentration gravitational convection. The main part of the work presents a mathematical model describing the occurrence of convective flows based on the splitting scheme according to physical parameters. Numerical data on the concentration fields of the gas with the highest molecular weight at various time points is obtained. It is established that curvature of the isoconcentration lines of the diffusing components can be associated with instability of the mechanical equilibrium of the system. Degree of curvature is determined by the initial concentration of components of the mixture. The obtained data can be used to determine the main characteristics of mass transfer used in calculations related to combined heat and mass transfer in a wide range of thermophysical parameters.

Numerical research of characteristic mixing times of isothermal three-component steam-gas systems

Multicomponent diffusion in gases is characterized by a number of effects that are not observed in binary diffusion. Analysis of existing works shows that convective instability may occur in some systems with significantly different diffusion coefficients with certain geometric and thermophysical characteristics. Stability analysis allows determining the spectrum of parameters at which a transition from a diffusive state to a convective is possible. However, this approach does not allow the researchers to investigate the dynamics of the process. Therefore, this work aims to describe emergence and evolution of convective flows in threecomponent systems and assess the influence of the initial composition on the occurrence of concentration gravitational convection. The main part of the work presents a mathematical model describing the occurrence of convective flows based on the splitting scheme according to physical parameters. Numerical data on the concentration fields of the gas with the highest molecular weight at various time points is obtained. It is established that curvature of the isoconcentration lines of the diffusing components can be associated with instability of the mechanical equilibrium of the system. Degree of curvature is determined by the initial concentration of components of the mixture. The obtained data can be used to determine the main characteristics of mass transfer used in calculations related to combined heat and mass transfer in a wide range of thermophysical parameters.

Sensitivity analysis of design parameters for melting process of lauric acid in the vertically and horizontally oriented rectangular thermal storage units

Widespread commercialization of PCM-based latent heat storage systems is limited by the low melting and solidification rates during the phase transition process. In this study, fins are used to enhance the phase change process. A parametric study is conducted to understand the effect of fins on the thermal performance of vertically- and horizontally-oriented rectangular storage tanks. Throughout simulations, the fin volume, and thereby the mass of PCM in the tank, were kept constant. It was observed that the horizontal enclosures can take advantage of the development of strong natural convection flow until near the end of the melting process, whereas with vertical counterparts the strength of the convection currents was diminished during the shrinkage stage. The results suggest that longer and thinner fins are more beneficial for enhancing the melting rate than shorter and thicker fins. It was concluded that for horizontal enclosures with fin lengths of 25 and 35 mm, increasing the number of fins does not necessarily shorten the melting time. The maximum melting time reduction compared to the 3-fin vertical enclosure with a fin length of 25 mm (chosen as our benchmark case) was 75.1% when nine 45-mm-long fins are used in a horizontal enclosure.

Studies of the Origin and Nature of the Energetic Forces Exerted on a Torsion Pendulum by Human Subjects

These results extend what is known about the effects of a human subject sitting under a torsion pendulum. Previous results showed that subjects affected the pendulum in significant ways. Substantial shifts of the center of oscillation of the pendulum, shifts as large as 2.2 cm (7 deg) requiring a force that is equivalent to 45 mg were observed. Many new frequencies of oscillation of the pendulum were introduced when a subject was present. Dramatic changes in the amplitudes of oscillation of the pendulum were observed throughout the experiments; increasing, decreasing, and increasing again, in quasi-consistent patterns. These shifts of the center of oscillation, the new frequencies of oscillation, and the changes in amplitudes all persisted for 30-60 min after the subject has left the pendulum. These effects have been variously attributed to ‘human bioenergy,’ or to simple cranial heat convection currents. The physical nature of the forces causing these effects remains uncertain. Until now all the experiments we have performed have used ‘control subjects,’ which refers to subjects with no known abilities that would affect the pendulum in unusual ways. In this work, a subject who had 45 years of daily experience with a particular type of meditation ‘sound current meditation’ was recruited. The purpose was to see if different mental states such as a meditative state versus a non-meditative sate, would affect the pendulum differently. These results establish that they are different, both qualitatively and quantitatively, and that the effects by the experienced meditator were significantly different than those routinely seen with ‘control subjects.’ A new kind of experiment was performed by having subjects sit beside the pendulum instead of directly under it. Subjects were the ‘experienced meditator,’ and a ‘control subject.’ Effects on the pendulum with subjects sitting beside the pendulum were diminished in amplitude but were otherwise similar to subjects sitting directly under the pendulum. Although the possibility of cranial heat convection currents being able to exert these effects from a significant distance is not eliminated, the argument that cranial heat convection currents are solely responsible for subject effects on the pendulum is weakened.

Regimes of steady jetting in electrohydrodynamic jet printing

Electrohydrodynamic (EHD) jet printing is an additive manufacturing technique in which an electrified jet of functional ink is deposited on a motion-controlled substrate. Through experimental visualization of EHD jets, current measurements and scaling analysis, we show that steady EHD jetting can occur in three regimes: the cone-jet, moderately stretched jet, and thick-jet regimes. These EHD jetting regimes differ with respect to the relative importance of surface convection and bulk conduction currents downstream of the jet.

Petrographic evidences of open-system magmatic processes in the felsic rocks of the northern part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania)

Abstract Over the almost 190 years-long research of the Ditrău Alkaline Massif (Eastern Carpathians, Romania), felsic rocks have been regarded as homogeneous, uniform units of the igneous complex. Nevertheless, our detailed textural study revealed that the felsic suite (diorite–alkaline feldspar syenite and nepheline-bearing syenite–granite series) cropping out north of the Jolotca Creek valley is more heterogenous at micro-scale than previously thought. This heterogeneity partly derives from abundant mafic mineral-rich clusters; nevertheless, felsic minerals also exhibit various, remarkable textural features. Outcrop to micro-scale traits of felsic crystal settling, mafic mineral aggregates and flow fabrics along with metamorphic country rock xenoliths suggest that the studied rocks crystallized under dynamic magmatic conditions. Cumulate formation, shear flow, convection currents as well as various open-system magmatic processes (e.g., magma recharge, magma mixing and mingling, crystal or mush transfer and recycling, country rock assimilation) played a significant role in the petrogenesis of the examined felsic suite. Based on field observations as well as on the microtextural relationship of the minerals, two major groups of felsic rocks were distinguished: (1) felsic rocks (lacking or containing sparse mafic minerals) spatially associated with mafic rocks and (2) felsic rocks (with mafic minerals and clots) spatially unassociated with mafic rocks. Rocks of the former group are dominated by plagioclase, accompanied by minor alkaline feldspar, biotite and accessory titanite. Distinct structural and textural features suggest the physical accumulation of the rock-forming phases. Such textural properties can also be observed in some rocks of the second group. Isolated mafic minerals are rather scarce in the latter; nevertheless, different types of aggregates made up of either identical or various mafic phases are more common. Clustered minerals are either intact or show different stages of alteration. A detailed petrographic study of the above-mentioned peculiarities has been implemented in order to define their potential origin(s) and petrogenetic significance.

Microgravity crystallization of perdeuterated tryptophan synthase for neutron diffraction

Biologically active vitamin B6-derivative pyridoxal 5′-phosphate (PLP) is an essential cofactor in amino acid metabolic pathways. PLP-dependent enzymes catalyze a multitude of chemical reactions but, how reaction diversity of PLP-dependent enzymes is achieved is still not well understood. Such comprehension requires atomic-level structural studies of PLP-dependent enzymes. Neutron diffraction affords the ability to directly observe hydrogen positions and therefore assign protonation states to the PLP cofactor and key active site residues. The low fluxes of neutron beamlines require large crystals (≥0.5 mm3). Tryptophan synthase (TS), a Fold Type II PLP-dependent enzyme, crystallizes in unit gravity with inclusions and high mosaicity, resulting in poor diffraction. Microgravity offers the opportunity to grow large, well-ordered crystals by reducing gravity-driven convection currents that impede crystal growth. We developed the Toledo Crystallization Box (TCB), a membrane-barrier capillary-dialysis device, to grow neutron diffraction-quality crystals of perdeuterated TS in microgravity. Here, we present the design of the TCB and its implementation on Center for Advancement of Science in Space (CASIS) supported International Space Station (ISS) Missions Protein Crystal Growth (PCG)-8 and PCG-15. The TCB demonstrated the ability to improve X-ray diffraction and mosaicity on PCG-8. In comparison to ground control crystals of the same size, microgravity-grown crystals from PCG-15 produced higher quality neutron diffraction data. Neutron diffraction data to a resolution of 2.1 Å has been collected using microgravity-grown perdeuterated TS crystals from PCG-15.

Convection-induced bridging during alloy solidification

In this work, the effect of solute expansion coefficient on the natural convection and freezing front propagation is investigated by performing three-side cooled solidification experiments. Four different aqueous salt solutions, and different compositions thereof, were employed for experimentation. The mixtures were solidified to analyze the effect of solute expansion coefficients on the convection currents and the composition distribution in the bulk. The initial compositions were chosen such that all cases have the same primary solid fraction at eutectic temperature, for obtaining similar compositional changes in the bulk liquid at various stages. Similar cooling conditions were also maintained to ensure that the variation in convection strength is primarily caused by different solute expansion coefficients. A distinct observation of the free surface freezing before the bulk, termed bridging, is reported in certain cases. Further analysis revealed that the bridging could be attributed to a difference in solute convection caused by the solute expansion coefficient. Numerical simulations were performed to further ascertain the plausible initiation mechanisms for bridging. The predicted compositional and solid fraction distribution revealed lesser solute accumulation near the surface, for the lower solute expansion cases, and the resulting increase in the tendency of freezing at the top. An upper limit for the ratio of solutal to thermal Rayleigh numbers in the experimental conditions has been identified for the occurrence of bridging in high Prandtl number fluids.

Assessing the Impact of Cumulus Parameterization Schemes on Simulated Summer Wind Speed over Mainland China

Wind speed is an important meteorological parameter, whose simulation is influenced by various physical process parameterizations. However, the impact of cumulus parameterization schemes (CPSs) on wind speed simulation at the climate scale has not been sufficiently investigated in previous studies. Using the Advanced Research version of the Weather Research and Forecasting model (ARWv3) and hydrostatic wind speed change equation, we assessed the effects of four CPSs on a 10 m wind speed simulation over mainland China in the summer of 2003. In general, different CPSs can reproduce the wind speed distribution. Meanwhile, the sensitivity of wind speed simulation to CPSs was found to be the highest in East and southern China, followed by the Tibetan Plateau, and then Northwest China. We found that the main physical processes influencing wind speed (i.e., the pressure gradient (PRE), diffusion (DFN), and convection (CON) terms) vary greatly with sub-regions. CPSs mainly affect the secondary CON that regulates the balance between the dominant terms PRE and DFN, and also has a significant effect on PRE. For example, for CON, the difference index (DIF) between the Kain–Fritsch (KF) and previous KF (pKF) CPSs is larger than 20%, corresponding to a PRE DIF of about 14%. The term of local wind speed change (Vt) is significantly more sensitive to the CPSs than the other terms with a DIF of 283% over the Tibetan Plateau, suggesting high CPS sensitivity of the simulated wind speed. In addition, we explained the causes of the CPS-induced sensitivities. This work helps understand the Weather Research and Forecasting model (WRF) performance and emphasizes the importance of the CPS choice in simulating/forecasting wind speed.