Upper Region Research Articles

Experimental investigation of the effect of copper foam pore structure on the thermal performance of phase change material in different centrifugal force fields

In this paper, composite phase change material (PCM) was fabricated by incorporating copper foam into paraffin wax. The effects of porosity (ε = 0.93, 0.95 and 0.97) and pore density (ω =10, 20 and 40 PPI) on the thermal performance of composite PCM were experimentally investigated in positive centrifugal force field (5 g), normal gravity field (0 g) and negative centrifugal force field (-5 g), respectively. The end-state isobar and buoyancy vector are introduced for the description of the heat transfer process. The results show that there are differences in the effects of metal foam pore structure on the heat transfer process of composite PCM under different force field conditions. At 0 g and 5 g, the isotherms of all experimental conditions gradually converge to the end-state isobars, but decreasing the porosity or increasing the pore density can slow down this evolution rate. At -5 g, the evolution of isotherms is mainly influenced by the buoyancy vector, and isotherms with lower porosity or higher pore density are less influenced by buoyancy. It was also found that reducing the porosity effectively shortens the melting time lags along the heat flow flux direction for all force field conditions. However, reducing the pore density at -5 g shortens the melting time lags in both the upper and lower regions in the heat flux direction, while it only shortens that in the upper region at 0 g, and it has no significant effect on that either in upper region or lower region at 5 g. In addition, in the positive centrifugal force field, lowering the porosity can more significantly improve the heat transfer efficiency, while lowering the pore density can more effectively improve the heat transfer efficiency in the negative centrifugal force field.

Correlation mechanism of friction behavior and topological properties of the contact network during powder compaction

The effect of friction behavior on the compacted density is significant, but the relationship between the topological properties of the contact network and friction behavior during powder compaction remains unclear. Based on the discrete element method (DEM), a DEM model for die compaction was established, and the Hertz contact model was modified into an elastoplastic contact model that was more suitable for metal-powder compaction. The evolution of the topological properties of the contact network and its mechanism during powder compaction was explored using the elastoplastic contact model. The results demonstrate that the friction behavior between the particles is closely related to the topological properties of the contact network. Side wall friction results in smaller clustering coefficient (CC) and excess contact (EC) in the lower region near the side wall. Corresponding to this phenomenon, the upper region near the side wall has more high-stress particles when the major principal stress threshold was considered, and the CC and EC are significantly higher than those in the other regions. This study provides a theoretical basis for improving powder compaction behavior.

Microscopia especular das diferentes regiões da córnea de suínos - estudo ex vivo

Abstract The objective of this study was to determine the endothelial cell density (ECD) and hexagonality of the cornea in the different regions of healthy swine corneal endothelium using specular microscopy. Twenty-four eyeballs from 12 male, 6-month-old Large White pigs (Sus scrofa domesticus) were studied. Contact specular microscopy was performed in the central, superior, inferior, lateral and medial regions. The corneal parameters analysed in this study were ECD and hexagonality. The ECD in the central region was 1865 cells/mm2; in the upper region, it was 1877 cells/mm2, in the lower region, it was 1854 cells/mm2, in the lateral region, it was 1847 cells/mm2, in the medial region, it was 1831 cells/mm2. Hexagonality in the central region, was 53%; in the upper region, it was 54%, in the lower region, it was 54%, in the lateral region, it was 54%, in the medial region, it was 54%. There was no significant difference regarding to the evaluated parameters in all corneal regions evaluated. No statistically significantly differences were observed in ECD and hexagonality between the left and the right eyes. This study demonstrates that ECD and hexagonality of the central cornea area represent the entire endothelial mosaic.

EFFECT OF GEOMETRY UPON COOLING CHARACTERISTICS OF WAFER BLOCK COOLERS

The product formed after the cream is spread between the wafer sheets is called a wafer block. The wafer block can have a minimum of 3 layers (2 sheets, 1 cream) and a maximum of 9 layers (5 sheets, 4 creams). The temperature of the wafer block before entering the cooling tower is 30-35°C. After the cooling process is completed, it cannot be reduced to the outlet temperature (~16°C) and the temperature is not homogeneously distributed. Especially the middle regions are hot. In this paper, the homogeneous temperature distribution is aimed at by using the CFD method. CFD analysis of three predetermined designs was performed using Solidworks / Flow Simulation software. The first design is the one currently used. In the second design, a design improvement has been made to reduce the effect of vortices in dead zones. In the third design, a design improvement was made to positively affect the flow rate in the upper region where the evaporator and fan are located. In the second design, the temperature difference on the wafer block is reduced by 0.02°C compared to the current design. The third design decreases by 0.13°C compared to the second design.

Binder Jetting Additive Manufacturing: Spreading and Permeation of Multiple Micron Droplets in Porous Media

AbstractThe penetrating behavior of binder droplets has a substantial effect on the dimensional correctness and strength of the manufactured components. In this article, a physical model and a mathematical model of multiphase flow are created, computationally computed, and experimentally validated to predict the spreading and penetration behavior of multi‐drop binder in a powder bed. The findings indicate: 1) The spreading diameter and penetration depth of the binder increase as the number of droplets grows. However, the size of the rise reduces as the number of droplets grows. 2) The binder is spread symmetrically in the powder bed, with greater saturation in the middle area than margins on both sides, and a higher saturation in the upper region than the lower. 3) Repeated drops of binder in various areas may improve the saturation of the peripheral region while ensuring that the core area is not oversaturated. 4) It is discovered that as the number of ink jet drops rises, the size of the sample grows, and the growth in sample size reduces with the number of ink jet drops. This paper's findings provide light on the mechanics behind light‐cured binder jet additive manufacturing.

Management of whitefly, Bemisia tabaci (Gennadius) in bushy Lac host, Flemingia semialata at Thrissur, Kerala

Flemingia semialata is an established host plant of lac insects and is widely grown to promote lac cultivation in India. One of the most destructive pests that can cause significant yield loss in many crops is a sap sucking whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), which is also found to infest the Flemingia sp. They cause vast damage to the host plants during feeding by reducing the rate of photosynthesis through the excretion of honeydew and by transmitting a large number of plant pathogenic viruses. Although there are several methods to control whitefly infestation, the commonly adopted practice is the application of chemical pesticides, owing to their efficiency in whitefly control. This study focused to test the effectiveness of two chemical: Thiamethoxam 25% WG (Actara®) and Phosmet 70 % WP (Imidan®) and an organic pesticide: Neem Oil, in whitefly control on F. semialata. The experimental design consisted of two different concentrations of each pesticide i.e., Phosmet 0.5 ml/L, 1ml/L, Thiamethoxam 0.25g/L, 0.5 g/L, Neem oil 1ml/L, 2ml/L applied on 21 test plants in sets of three and also on three regions of the test plants i.e, upper, middle and lower. The number of whiteflies was counted after 6, 12 and 24 hours of pesticide application. The results revealed that, among all the treatments, Thiamethoxam 0.5mg/L was found to be the most effective with highest percentage of reduction over control in the number of whiteflies in all the time intervals. The leaves in the middle and lower regions of the test plants showed relatively higher loads of whiteflies than those in the upper region throughout the experiment. Although, Neem oil is an environment friendly natural pesticide, Thiamethoxan has negligible volatilization properties and high degradation rates in the soil and therefore could be successfully and safely applied on the lac insect host plants during the pre-inoculation stages to lessen the whitefly attack.

Numerical simulation study of the hydrodynamic regimes in large to micro fluidized beds based on a Two-Fluid Model

Although the hydrodynamic properties of fluidized bed reactors have been investigated experimentally in the macro- to micro-scale range, the measurements and diagnostic tools needed for this analysis are complex. This in turn increases the difficulties experienced when trying to account for various specific phenomena, which occur within very small, i.e. Micro-Fluidized Beds (MFBs). In the present study, a numerical approach has been used to better understand the hydrodynamic behaviour of microreactors. The influence of a reduced value of bed diameter (Dt), the value of the static bed height (Hs), and the role of changing boundary conditions on various hydrodynamic parameters, bubble behaviours and particle circulation patterns were simulated using a Two-Fluid Model (TFM), and compared with our previous experimental results. It was found that a reasonable setting of the solid volume fraction in a fixed bed (εs,0) was key to successful simulation of the onset of minimum fluidization (and minimum bubbling), which is delayed for decreasing values of Dt. Setting the specularity coefficient (ϕ) to 1 resulted in bubble and particle movements being more consistent with those observed in the MFB experiment. In the simulation, a round-nosed slug rose along the center of the bed for small values of Hs, whereas it transformed into a wall slug in the upper region at greater values of Hs, which is in good agreement with our experimental observations. In addition, the experimental phenomenon in which slug is prevented from rising upwards within the MFB was successfully reproduced in the simulation.

Stability Characteristics of Planar Rivlin–Ericksen Fluid Interface With Mass and Heat Transfer

Abstract The interface of viscous-Rivlin-Ericksen fluids is analyzed through the linear theory of stability analysis when mass and heat is transferring across the interface. The Rivlin-Ericksen fluid lies in the upper region while the lower region of the interface contains viscous fluid. The gravitational acceleration destabilizes the top-heavy arrangement and interface instability is governed by Rayleigh–Taylor instability. The two-dimensional interface is considered, and the viscous potential flow theory is employed to establish the relationship between perturbation's growth and wave number. This relationship is analyzed, and the perturbation's growth is plotted for various flow parameters. A marginal stability condition is obtained, and it is given in terms of heat transport coefficient Λ and wave number. The marginal stability criterion is analyzed using the well-known Newton–Raphson method. The heat and mass transfer phenomenon drives the unstable interface toward stability. It is pointed out that the viscoelastic coefficient λo influences the interface to be stable while the thickness of the viscoelastic fluid makes the interface unstable. Atwood numbers and Weber numbers show destabilizing behavior.

Characteristics of Underwater Acoustics in Different Habitat Types along a Natural River Channel

Fluvial biological habitat types are classified using the diversity in physical characteristics of a water channel. Recent ecological management studies have highlighted the potential of underwater sound as a quantitative indicator of habitat characteristics. We investigate the relationship between underwater acoustic characteristics and hydraulic factors of 12 habitat types in the Namdae Stream in Yangyang, Korea, namely riffles, pools, and step riffle habitats. In the riffles and pools, the underwater sound levels were measured as sound pressure levels (SPLs). SPL(RMS) and 1/3 octave band have been measured in the frequency range between 8 Hz and 20 kHz. Among riffles, high SPL corresponded to the descending level of flow velocity. Pools generally had a low SPL. Low-frequency sound waves in the upper regions are better transmitted in the deeper water. To quantitatively analyze the water depth and flow velocity, we used a regression between the observed water depth, flow velocity, and acoustic SPL. The application of this study was certificated. The correlation coefficients between SPL and flow velocity/water depth revealed specific frequency bands with very strong positive correlations between SPL and flow rate in riffles and very strong negative correlations between SPL and pool water depth. Consequently, underwater sound can be used as an alternative for evaluating biological habitats.

Impact of stellar flares on the chemical composition and transmission spectra of gaseous exoplanets orbiting M dwarfs

Context. Stellar flares of active M dwarfs can affect the atmospheric composition of close-orbiting gas giants, and can result in time-dependent transmission spectra. Aims. We aim to examine the impact of a variety of flares, differing in energy, duration, and occurrence frequency, on the composition and transmission spectra of close-orbiting, tidally locked gaseous planets with climates dominated by equatorial superrotation. Methods. We used a series of pseudo-2D photo- and thermochemical kinetics models, which take advection by the equatorial jet stream into account, to simulate the neutral molecular composition of a gaseous planet (Teff = 800 K) that orbits a M dwarf during artificially constructed flare events. We then computed transmission spectra for the evening and morning limb. Results. We find that the upper regions (i.e. below 10 μbar) of the dayside and evening limb are heavily depleted in CH4 and NH3 up to several days after a flare event with a total radiative energy of 2 × 1033 erg. Molar fractions of C2H2 and HCN are enhanced up to a factor three on the nightside and morning limb after day-to-nightside advection of photodissociated CH4 and NH3. Methane depletion reduces transit depths by 100–300 parts per million (ppm) on the evening limb and C2H2 production increases the 14 μm feature up to 350 ppm on the morning limb. We find that repeated flaring drives the atmosphere to a composition that differs from its pre-flare distribution and that this translates to a permanent modification of the transmission spectrum. Conclusions. We show that single high-energy flares can affect the atmospheres of close-orbiting gas giants up to several days after the flare event, during which their transmission spectra are altered by several hundred ppm. Repeated flaring has important implications for future retrieval analyses of exoplanets around active stars, as the atmospheric composition and resulting spectral signatures substantially differ from models that do not include flaring.

Electroosmotic effect on two immiscible (conducting–non-conducting) fluids flowing in the porous channel under magnetic field

In this article, we investigate the motion of two-phase immiscible fluids in the channel with the porous medium in the presence of a magnetic field. Depending on the different levels of permeability, the channel is classified into two regions. The lower region (region-I) consists of non-conducting modified Casson fluid and the upper region (region-II) consist of conducting Newtonian fluid. The external electric field is applied in the region-II and the electroosmotic effect is produced at the wall and the interface region. Due to the interfacial effect, the non-conducting fluid was driven by conducting fluid. To compute the flow dynamic and electric potential nature, the momentum equation and Poisson–Boltzmann equation have been solved analytically in the state of periodic vibrations. The impact of physiological parameters such as Debye–Hückel parameter, electric field, magnetic field, Darcy numbers, viscosity ratio, Casson parameter and Womersley number has been investigated and the various behaviours were characterised. Based on numerical computations performed on the aforementioned parameters, we found that the Casson parameter, Darcy numbers and electric double layer (EDL) effects are predominant features. In the velocity profiles, we identified the flow of the fluid was enhanced by the augmented values of Darcy numbers, electric field (wall zeta potential), Debye–Hückel parameter and Casson parameter. The retardation flow occurred for the higher values of the magnetic field, viscosity ratio and electric field (interface zeta potential). Based on the conditional cases, the Womersley number possesses inconsistent behaviour. The depletion nature was found in the percentage flow rate of the Casson parameter. By increasing the value of the electric field and Casson parameter, the magnitude of wall shear stress to Darcy number increases and decreases for higher values of the magnetic field, viscosity ratio and pulsatile Reynolds number. It is first noticed that for any value of M1 and M2, Darcy number (Da2) plays a dual role in the upper wall shear stress. The present study leads to the pumping effect of gas pipelines or designing the microfluidic devices which are manipulated in biosensors/biochips.

Attenuation of combustion instability in a fuel-staged dual-nozzle gas turbine combustor with asymmetric hydrogen composition

The instability attenuation mechanism of fuel staging was investigated in a CH4/H2 fueled dual-nozzle gas turbine combustor. Fuel staging was implemented using an asymmetry in fuel composition between the two nozzles. The fuel composition of the upper nozzle was varied while keeping that of the lower nozzle constant. Under these conditions, the self-excited and forced responses of fuel-staged flames were analyzed using OH* chemiluminescence imaging, OH planar laser-induced fluorescence, and particle image velocimetry. In the self-excited measurements, although strong combustion instability was exhibited in the symmetric condition, it weakened gradually with increasing asymmetry in fuel composition. The symmetric flame exhibited significant fluctuations in the heat release rate around the flame tip, which acted as the primary cause of driving combustion instability. However, in asymmetric flames, the H2 addition induced phase leads in heat release rate fluctuations at the upper region, which damped combustion instability. Thus, our observations revealed a high correlation between the phase leads and the attenuation of combustion instability. Analyses of the forced responses showed that the heat release rate fluctuations were induced by interactions between the flame and the shedding vortex released from the nozzle tip into the downstream. Although these characteristics of shedding vortices did not depend on the H2 addition, the change in the axial position of the flame caused by the H2 addition induced the relocation of the site, at which the flame interacted with the vortex. Subsequently, it induced phase leads in the heat release rate fluctuations. The phase difference of heat release rate fluctuations between the two flames due to this phase leads enlarged progressively with increasing asymmetry in fuel composition, leading to the attenuation of combustion instability in asymmetric conditions.

Crystal plasticity model of induction heating-assisted incremental sheet forming with recrystallisation simulation in cellular automata

To relate the thermomechanical behaviour and microstructural evolution of the heat-assisted incremental sheet forming (SPIF) for Ti–6Al–4 V sheet, multi-scale models based on crystal plasticity finite element model (CPFEM), representative elementary volume (RVE), and cellular automaton (CA) were established in this article. An experimental-scale CPFEM was built in advance to provide macrograin level strain, strain rate, and temperature output data, which were then used in RVE and CA as inputs to simulate the microstructural evolution throughout the SPIF process. The output results include the pole figures, dynamic recrystallisation (DRX) maps, and statistics results of the alpha (α) phase of the Ti–6Al–4 V (α-Ti) alloy from stage to stage throughout the 700 ^circ{rm C} SPIF. The obtained statistics results of dislocation density, grain orientation angles, and grain size were verified with electron backscatter diffraction (EBSD). The CA analysis of the DRX progress at the upper, centre, and lower regions of the deformed workpiece has discovered that the incremental increase of the strain rate has significant effects on the dislocation density that produced a proportional relationship to the DRX percentage. The results revealed that the strain rate has strong domination in affecting the slip of grains orientation, which overcomes the effect of temperature increase in this SPIF process. Furthermore, it was found that a large amount of DRXed grains were generated at the grain boundaries, which reduced the mean grain size and increased the DRX percentage, which produced an inversely proportional relationship to the dislocation density. The thermomechanical behaviour on the SPIF workpiece was increased incrementally, which is insufficient for DRX initiation in the upper region, and the behaviour was enhanced at the centre and lower region, which can be corresponded to the microstructural evolution throughout the process.

Raising the Roof in Cædmon's Hymn

Raising the Roof in <i>Cædmon's Hymn</i>

A Dual‐Level Magmatic System Beneath the East Pacific Rise, 9°N

AbstractData from three co‐located wide‐angle ocean‐bottom seismograph experiments were used to make a new two‐dimensional tomographic image of the East Pacific Rise at 9°N. The upper half of the crustal magmatic system has a different seismic structure than the lower half, presumably corresponding with differences in melt storage and crustal cooling. The upper region is narrow (∼4.5 km wide at 2–3 km depth bsf) and estimated to contain higher melt fractions; the lower region broadens with depth and contains lower melt fractions. The shape of the system suggests steeply‐dipping isotherms and relatively stronger hydrothermal circulation in the upper gabbroic section of the crust, with moderately flattening isotherms and less circulation in the lower gabbroic section.

Enhancement of oil repellency on hyperbolic microarrays by compressive bending of elastomeric films

Applying elastic deformation to modulate the microscale surface shapes of films is an efficient way to prepare samples with various geometric designs. Tensile stress can be applied by stretching films, and it can increase the pitches of line arrays or the diameters of pillar arrays on a film surface. However, it is difficult to apply lateral compressive stress to films because films buckle during compression. In this study, we exploit bending to apply lateral compressive stress to the surface of a film. To accomplish this, we use arrays of microhyperbolic pillars or lines that have inversely tapered shapes in the upper region and widened bottoms. By using deformation of elastomeric films and a subsequent replication process, we fabricate microhyperbolic structures with decreased pitches and increased pattern heights. In addition, the deformation of microarrays by compressive stress can enhance oil repellency by increasing the sharpness of the inversely tapered shapes. Using this concept, we demonstrate the enhancement of oil repellency on patterned surfaces prepared by compressive bending of microarrays. Furthermore, we provide selective oil repellency by modulating the compressive stress on a single line array. The concept of compressive bending can be applied widely to decrease the dimensions of arrays and modulate surface shapes for greater oil repellency.

Catalyst-scale investigation of polydispersity effect on thermophysical properties in a commercial-scale catalytic MTO fluidized bed reactor

The methanol-to-olefin (MTO) process is commercialized worldwide, yet the understanding of in-furnace phenomena is still lacking. Accordingly, this work explores the multiphase flow and thermochemical characteristics in a commercial-scale MTO fluidized bed reactor using a three-dimensional multiphase particle-in-cell model. After model validations, the intrinsic relationship of solid transportation and thermochemical properties is elucidated together with the study of the polydispersity effect on reactor performance. The non-uniform gas-solid distribution in the reactor demonstrates the turbulent fluidization regime. Heat transfer coefficients (HTCs) of about 300 and 200 W/(m2·K) are observed in the medium and upper regions, respectively. The small velocity, particle Reynolds number, temperature, and HTC correspond to those large-size catalysts in the dense region where particles are nearly close packing with a large solid volume fraction. Increasing particle size distribution (PSD) width increases the catalyst HTCs and the mass fraction of C2H4, promoting reactor performance. Besides, increasing the PSD width enlarges gas viscosity, gas specific heat capacity, and gas thermal conductivity but decreases gas density.

Abdominal pain patterns during COVID-19: an observational study

Abdominal pain and liver injury have been frequently reported during coronavirus disease-2019 (COVID-19). Our aim was to investigate characteristics of abdominal pain in COVID-19 patients and their association with disease severity and liver injury.Data of all COVID-19 patients hospitalized during the first wave in one hospital were retrieved. Patients admitted exclusively for other pathologies and/or recovered from COVID-19, as well as pregnant women were excluded. Patients whose abdominal pain was related to alternative diagnosis were also excluded.Among the 1026 included patients, 200 (19.5%) exhibited spontaneous abdominal pain and 165 (16.2%) after abdomen palpation. Spontaneous pain was most frequently localized in the epigastric (42.7%) and right upper quadrant (25.5%) regions. Tenderness in the right upper region was associated with severe COVID-19 (hospital mortality and/or admission to intensive/intermediate care unit) with an adjusted odds ratio of 2.81 (95% CI 1.27–6.21, p = 0.010). Patients with history of lower abdomen pain experimented less frequently dyspnea compared to patients with history of upper abdominal pain (25.8 versus 63.0%, p < 0.001). Baseline transaminases elevation was associated with history of pain in epigastric and right upper region and AST elevation was strongly associated with severe COVID-19 with an odds ratio of 16.03 (95% CI 1.95–131.63 p = 0.010).More than one fifth of patients admitted for COVID-19 presented abdominal pain. Those with pain located in the upper abdomen were more at risk of dyspnea, demonstrated more altered transaminases, and presented a higher risk of adverse outcomes.

Microstructure and properties of a Ni–Ti–Cr–Mo–Nb alloy fabricated in situ by dual-wire arc additive manufacturing

A Ni–Ti–Cr–Mo–Nb wall component was fabricated for the first time by dual-wire arc additive manufacturing (in situ alloying) using TA1 and Inconel 625 welding wires as feedstock for the potential application in fields characterized by low temperature environments, such as polar research and space exploration. The microstructure and properties of the as-built component were studied. The results show the as-built component consists of NiTi (B2), Cr2Ti, and Ti2Ni phases. In the upper region, Ti2Ni phase is present as nanoparticles mainly embedded in Cr2Ti phase. Cr2Ti phase is present as long oriented strips or granular precipitates. Due to the presence of secondary Cr2Ti and Ti2Ni phases, the hardness of this component is 600–650 HV0.2. The average compression strength is ∼1970 MPa and it exhibits outstanding superelasticity with a recoverable strain of 5.5%. The austenite finish temperature is −62 °C, which indicates that Ni–Ti–Cr–Mo–Nb alloy has the superelasticity at low temperature.

Analysis of microstructure, mechanical properties, and wear performance of NiTi alloy fabricated by cold metal transfer based wire arc additive manufacturing

In this work, wall-shaped NiTi components were fabricated by cold metal transfer (CMT) based wire arc additive manufacturing (WAAM) with optimized depositing speed. The microstructure, mechanical properties, and wear performance of the as-fabricated specimens along the building direction, together with their correlations were investigated in-depth. Coarse columnar grains were refined gradually with the increase of wall height. An equiaxed microstructure was obtained in the upper region. The Ni4Ti3 precipitates were distributed in the matrix. The microhardness, critical stress, and elongation increase monotonously with the increase of wall height. Plastic deformation, together with wear-induced work hardening is the main form of wear, which is mainly hindered by the superelasticity of NiTi alloys. Good homogeneity of the microstructure, mechanical properties, and wear resistance is obtained due to the CMT process with optimized depositing speed, indicating that this technique provides great potential to make novel NiTi flexible structures.