Geometric Aspect Ratio Research Articles

Flexible Single-Crystal Perovskite Photodetectors via Polymer-Controlled Transfer.

The large-sized perovskite single-crystal sheet (SCS) serves as the ideal research platform for perovskite photodetectors due to its outstanding carrier photophysics, pronounced geometric aspect ratio, and ultrahigh material utilization rate. However, its performance in flexible device applications is relatively lackluster due to the rigid and brittle nature of the three-dimensional cubic lattices. In this work, the indium tin oxide (ITO)-based multimillimeter-sized MAPbBr3 SCS is transformed into MAPbI3 SCS via ion exchange strategy. Significantly, we proposed and implemented a polymer-controlled transfer strategy─utilizing the dichloromethane (DCM) solution of poly(methyl methacrylate) (PMMA)─to nondestructively transfer the whole perovskite SCS off the ITO substrates and subsequently adhere it onto a flexible polyethylene terephthalate (PET) substrate of interdigital electrode, thereby fabricating a lateral-structured photodetector with a PMMA-SCS-Au-PET multilayer configuration. The tight self-encapsulation between the top PMMA membrane and the bottom PET substrate imparts excellent waterproof stability and concurrently excellent mechanical flexibility to these devices; additionally, the MAPbI3 device exhibits comprehensively superior performance to the MAPbBr3 one. This work represents a proactive attempt and exploration of the high-performance advancement of large-sized SCS photodetectors, undoubtedly introducing novel momentum and solutions to this domain.

Effect of aspect ratio and geometric defects on the stability performance of U-rib stiffened plates

As an important component of steel-box beams, the stability of stiffened plates is a key factor that affects the safety of bridge structures. The geometric dimensions, such as the width-to-thickness ratio of the motherboard, stiffening rib thickness, and ratio of stiffening rib area to motherboard area, of stiffened plates have been considered in existing studies. However, the impact of the aspect ratio has not been reported in the literature. This study systematically investigated the effect of the aspect ratio on the stability performance of U-rib stiffened plates. Five sets of stiffened plate specimens with different aspect ratios were designed and manufactured. After testing the initial geometric defects of the specimens, axial compressive stability tests were conducted. Rotational hinge supports were placed at both ends of the specimens in order to simulate simply supported boundary conditions. The influence of geometric defects and aspect ratio on the stability of stiffened plates was discussed through numerical simulation. The results reveal that as the width of the stiffened plate increases, the initial geometric defects are distributed in a half-wave form along both the longitudinal and transverse directions, exhibiting an overall hemispherical distribution. The instability mode of a single-rib stiffened plate is characterized by local instability, whereas multi-rib stiffened plates exhibit global instability. The buckling mode is significantly influenced by the distribution of initial geometric defects. As the aspect ratio of the specimen decreases, the average stress at instability decreases and the stiffened plate gradually undergoes a biased compression state during the compression process. Failure of the specimen typically results in pure bending deformation when the aspect ratio is relatively large, whereas when the aspect ratio is relatively small, failure may result in bending and twisting deformation. Finally, a reasonable aspect ratio recommendation value was given.

Experimentation, identification, and simulation of polymer swelling at extrusion die outlets

AbstractThe behavior of polyamide PA12 melt extrudates at die outlets is modeled to determine swelling process and rate. It is assessed as a function of imposed input parameters, process parameters, and die geometries. The modeling is carried out using Comsol Multiphysics® platform to simulate the swelling; in particular, its progression in time is investigated for different extrusion process parameters. The experimental swelling observed in extrusion lines tests is compared with the Tanner and Carreau‐Yasuda rheological models. A database is built up with all experiments carried out; the comparison between numerical and experimental results shows close agreement. A parametric analysis of the experimental and numerical swelling is performed. It confirms the important role of the die diameter on swelling rate, independently of shear rate. Increase in temperature lowers swelling rate at constant shear rates and geometric aspect ratio of the dies.Highlights Experimental and numerical study of polymer swelling at capillary die outlets. Behavior of PA12 polymer extrudate modeled to determine its swelling. Rheological models implemented to simulate the swelling phenomenon. Simulation results validated with experimental tests for two millimetric dies. Influence of die geometrical parameters investigated and justified.

Dependence of Magnetic Properties of As-Prepared Nanocrystalline Ni2MnGa Glass-Coated Microwires on the Geometrical Aspect Ratio.

We have prepared NiMnGa glass-coated microwires with different geometrical aspect ratios, ρ = dmetal/Dtotal (dmetal-diameter of metallic nucleus, and Dtotal-total diameter). The structure and magnetic properties are investigated in a wide range of temperatures and magnetic fields. The XRD analysis illustrates stable microstructure in the range of ρ from 0.25 to 0.60. The estimations of average grain size and crystalline phase content evidence a remarkable variation as the ρ-ratio sweeps from 0.25 to 0.60. Thus, the microwires with the lowest aspect ratio, i.e., ρ = 0.25, show the smallest average grain size and the highest crystalline phase content. This change in the microstructural properties correlates with dramatic changes in the magnetic properties. Hence, the sample with the lowest ρ-ratio exhibits an extremely high value of the coercivity, Hc, compared to the value for the sample with the largest ρ-ratio (2989 Oe and 10 Oe, respectively, i.e., almost 300 times higher). In addition, a similar trend is observed for the spontaneous exchange bias phenomena, with an exchange bias field, Hex, of 120 Oe for the sample with ρ = 0.25 compared to a Hex = 12.5 Oe for the sample with ρ = 0.60. However, the thermomagnetic curves (field-cooled-FC and field-heating-FH) show similar magnetic behavior for all the samples. Meanwhile, FC and FH curves measured at low magnetic fields show negative values for ρ = 0.25, whereas positive values are found for the other samples. The obtained results illustrate the substantial effect of the internal stresses on microstructure and magnetic properties, which leads to magnetic hardening of samples with low aspect ratio.

Spectral analysis of the correlation between temperature and wall-normal velocity in Rayleigh-Bénard convection at moderate Rayleigh numbers

Turbulent Rayleigh-Bénard convection holds significant scientific and engineering implications, with one of the most debated topics in convection research being the ultimate scaling of the Nusselt number at extremely high Rayleigh numbers. A widely adopted method for investigating this issue is direct numerical simulation (DNS); however, achieving the ultimate Rayleigh number with DNS can be prohibitively expensive. To overcome this limitation, one approach is to employ a small simulation domain size for high Rayleigh number cases. This study explores the impact of simulation domain size by conducting DNS with a large geometrical aspect ratio. Specifically, we perform spectral analysis on the covariance of wall-normal velocity and temperature, along with its transport equations. The results reveal that the characteristic length scale in the intermediate length-scale region linearly increases with wall-normal distance. Moreover, the spectral analysis indicates that large-scale structures play a crucial role in the dynamics of the covariance of wall-normal velocity and temperature. However, the study suggests that these large-scale structures have a minimal impact on the scaling of the Nusselt number. This is attributed to the fact that large-scale structures remain in regions away from the wall, and no processes transfer them from large to small-scale structures. As a consequence, the dynamics of the covariance of wall-normal velocity and temperature in the close vicinity of the wall experience little influence from large-scale dynamics.

Comparative analysis of nondimensionalization approaches for solving the 2‐D differentially heated cavity problem

AbstractThis work reports a numerical study on the effect of three nondimensionalization approaches that are commonly used to solve the classic problem of the 2‐D differentially heated cavity. The governing equations were discretized using orthogonal collocation with Legendre polynomials, and the resulting algebraic system was solved via Newton–Raphson method with LU factorization. The simulations were performed for Rayleigh numbers between 103 and 108, considering the Prandtl number equal to 0.71 and a geometric aspect ratio equal to 1, analyzing the convergence and the computation time on the flow lines, isotherms and the Nusselt number. The mesh size that provides independent results was 51 × 51. Approach II was the most suitable for the nondimensionalization of the differentially heated cavity problem.

Preparation and magnetic properties of MnFePSi-based glass-coated microwires

We prepared a Mn48Fe22P15Si15 glass-coated microwires (GCMWS) with metallic nucleus diameter, d = 11.2 μm and total diameter, D = 28.3 μm (geometrical aspect ratio d/D = 0.4) for the first time by using the Taylor–Ulitovsky Technique. This low-cost, single-step fabrication approach enabled the preparation of kilometers-long GCMWS from a few grams of low-cost components (Mn, Fe, P, and Si) for a variety of applications. The analysis of the magnetic measurements revealed a well-defined magnetic anisotropy in the whole temperature range. Moreover, relatively hard magnetic properties were observed for the temperature range of 5–400 K, where the average of coercivity, Hc ≈ 465 Oe. Notable magnetic field, H, and temperature dependencies of the magnetic properties were observed. Substantially irreversible magnetic behavior with a blocking temperatures Tb = 97 K at H = 1 kOe and Tb = 50 K at H = 5 kOe upon field cooling was observed. The modification in the magnetic properties of MnFePSi-glass-coated microwires is ascribed to the presence of various magnetic phases resulting from internal stresses induced by the glass coating. Moreover, the elevated Curie temperature (Tc > 400 K) observed in the investigated sample, makes this material as an appealing choice for several industrial applications.

Transition of natural convection on a cooled circular surface with heated annular extension

Transition of natural convection on a circular cooled surface with heated annular extension is investigated in the present study by numerical simulation. Flow features and regimes of natural convection on the surface are studied for which the cooling and heating Rayleigh numbers (Rac and Rah) vary from 1 to 106 with air as the working fluid (Prandtl number of 0.71) at a fixed geometrical aspect ratio of 1 (heating characteristic length/cooling characteristic length). Three steady states revealed by numerical results include steady plume flow, steady dome flow and steady crown flow, which are corresponding to different dynamic regimes: a positive buoyancy dominated regime, a transitional regime and a negative buoyancy dominated regime. Besides, the dynamics behaviors in those steady regimes are scaled and validated by numerical results. The transition route of natural convection on the cooled circular surface with heated annular extension to the unsteady flow is also characterized in the case of Rac/Rah = 1. It has been demonstrated that the steady regime is followed by the unsteady regime. The periodic puffing flow, quasi-periodic flow, and chaotic flow are present in the unsteady regime. In addition, heat transfer in different regime flows is quantified.

Hierarchical Deployment of Vortex Generators for Wake Management in Finned-Tube Heat Exchanger

While developing thermal management systems, volumetric compactness of the heat exchange module is a critical design factor. This three-dimensional computational analysis seeks to boost the thermal compactness of fin-and-tube heat exchangers by employing winglet-type vortex generators. Due to the fact that the thermo-hydraulic performance of vortex generators in such thermal systems is determined by three distinct design parameters, namely the attack angle, spatial location, and geometric aspect ratio, a concurrent parametric analysis of all three design parameters is conducted to gain a thorough understanding. In addition, regression analysis is applied to develop functional correlations that can predict the enhanced thermo-hydraulic performance of the heat exchangers. The improvements in wake-affected heat transfer brought on by the modifications are also specifically explored, along with other aspects of the augmentation mechanism. The highest thermal augmentation over the wake-affected fin is seen as 120%. Based on a thermo-hydraulic tradeoff, the friction factor increases exponentially with the attack angle, and the rate of increase is lowest for 15–30 degree range of attack angle and highest for 45–60 degree range. Certainly, there are multiple locations where winglets can be erected, and heat transfer enhancement by each potential location incurs linearized increase in the friction factor.

Free vibration analysis of sandwich structure via point interpolation meshfree method based on polynomial basic function

The stability of circular and annular sector plate structures under aerodynamic pressure in supersonic conditions is crucial for aircraft components. Conventional uniform materials lead to heavy structures, which are undesirable for aircraft. This study explores the use of functionally graded materials to enhance flutter stability. It employs a refined logarithmic shear deformation theory to describe plate displacement, classical elasticity theory for constitutive equations, and Hamilton’s principle for equations of motion. Two methods, finite element, and Meshfree radial point interpolation, are used to solve these equations and verify the results. Parameter studies are conducted to assess the effects of grading index, Biot’s coefficient, span angle, and geometrical aspect ratio, revealing unexpected adverse effects of grading material on stability.

Numerical Modeling and Simulation of Rooftop Thermal Photovoltaic Chimney for Buildings' Electrical Energy Generation and Passive Cooling

The present study consisted mainly of making the thermal and dynamic analysis of the fluid flows in mixed convection in the chimney integrated into the building with an upper-covered horizontal hybrid thermal photovoltaic collector on a slab roof. The governing equations discretized by the finite difference method resulted in the systems of tri-diagonal algebraic equations, which were solved by Thomas' algorithm and Gauss Seidel's iterative method. Numerical solutions are presented for various geometrical aspect ratios, Rayleigh, and Reynolds numbers. The results are presented in terms of streamlines, isotherms, velocity, heat transfer intensity, and PV cells’ electrical efficiency versus the governing control parameters in detail.

Pseudo-optimum geometries for 1-100 ton spool compressors with low-GWP refrigerants

Simulation models are often employed for guiding compressor prototype development, particularly for novel devices like the spool compressor. The spool compressor is a novel compressor technology that can provide competitive performance for low-pressure refrigerants (like R1234ze(E)) with a compact design. A parametric study is presented to find the optimum geometric aspect ratio for five refrigerants (CO2, R134a, R454B, R468B and R1234ze(E)) and a range of cooling capacities between 1-100 RT. A pseudo-optimum geometry is explored by varying the aspect ratio, defined by the eccentricity ratio (rotor diameter to bore diameter), and the compressor L/D ratio (axial length to bore diameter), varying from 0.75-0.8 and 0.4-3, respectively. A scaling model is developed to vary the compressor geometry and ports. A spool compressor model, developed by Bradshaw and Groll (2013), is extended and by validating the model using data from 30 RT and 40 RT prototype compressors using R134a and R1234ze(E). The model is then used to predict the performance of a spool compressor with the various geometric inputs and refrigerants. The results suggest that the volumetric and isentropic efficiencies can be maximized by using an eccentricity ratio of 0.75 and L/D ratios from 1-1.5 for various displacement volumes. The results showed that the optimum isentropic efficiency increases asymtoptically from 1 to 100 RT for most working fluids and it increases linearly for CO2. Additionally, the compressor performance becomes insensitive to the aspect ratio for large compressor sizes.

Geometric control of tilt transition dynamics in single-clamped thermalized elastic sheets.

We study the finite-temperature dynamics of thin elastic sheets in a single-clamped cantilever configuration. This system is known to exhibit a tilt transition at which the preferred mean plane of the sheet shifts from horizontal to a plane above or below the horizontal. The resultant thermally roughened two-state (up/down) system possesses rich dynamics on multiple timescales. In the tilted regime a finite-energy barrier separates the spontaneously chosen up state from the inversion-symmetric down state. Molecular dynamics simulations confirm that, over sufficiently long time, such thermalized elastic sheets transition between the two states, residing in each for a finite dwell time. One might expect that temperature is the primary driver for tilt inversion. We find, instead, that the primary control parameter, at fixed tilt order parameter, is the dimensionless and purely geometrical aspect ratio of the clamped width to the total length of the otherwise-free sheet. Using a combination of an effective mean-field theory and Kramers' theory, we derive the transition rate and examine its asymptotic behavior. At length scales beyond a material-dependent thermal length scale, renormalization of the elastic constants qualitatively modifies the temperature response. In particular, the transition is suppressed by thermal fluctuations, enhancing the robustness of the tilted state. We check and supplement these findings with further molecular dynamics simulations for a range of aspect ratios and temperatures.

Influence of the Geometrical Aspect Ratio on the Magneto-Structural Properties of Co2MnSi Microwires

This present study illustrates the strong effect of geometrical parameters on the magneto-structural properties of Co2MnSi glass-coated microwires prepared using the Taylor–Ulitovsky method. Thus, there are three samples with different geometrical aspect ratios (ρ). The XRD analysis shows a significant change by modifying the aspect ratio; for ρ = 0.42, the main peak with miller indices (220) is recognized as an A2-type disordered cubic structure. For the sample with ρ = 0.46, mixed L21 and B2 cubic structures are observed. Meanwhile, in the sample with a low aspect ratio, ρ = 0.30, the perfect L21 ordered cubic structure is attained. Magnetic characterization has been carried out at a wide range of temperatures and magnetic fields. A significant increase in coercivity and normalized reduced remanence by decreasing the aspect ratio is detected. The change in the magnetic properties is attributed to the modification in the microstructure, which is induced during the fabrication process. Such a dependence on the microstructure and magnetic properties on the ρ-ratio can be associated either with the internal stress distribution and magnitude or with different quenching rates of microwires with different aspect ratios. The current findings demonstrate the tunability of the microstructure and magnetic properties of Co2MnSi-glass-coated microwires simply via a small modification in the geometric properties during the manufacturing process and without excreting any additional post-processing. The variation in the geometric parameters of Co2MnSi glass-coated microwires allows us to tune the magnetic properties and structure, which is essentially advantageous for sensing device development.

Effect of control domains of fractures and caves on reactive transport in porous media

It is often highly difficult to predict the main flow path of reactive fluids in porous media with complexly distributed fractures and/or caves. Based on Darcy's law, this research defines the control domain of fractures/caves that represents the interference range of fractures/caves. This control domain can be used to identify the connectivity possibility between fractures/caves and predict the flow paths of reactive fluids at the optimal flow rate. Furthermore, after simplifying the geometry of fractures/caves, a threshold geometric aspect ratio of 20 is set to distinguish fractures and caves, concerning the flow mechanisms, by clarifying the ranges of control domains. Moreover, the control domain theory is combined with the two-scale continuum model for acidizing carbonate rocks to estimate the flow paths of acid in fractured-vuggy carbonate rocks at an optimal flow rate, thereby validating the accuracy of the reactive fluid main flow path estimation based on the control domain theory. The primary criterion to determine the reactive transport in porous media with complex fracture/cave distribution is the overlap degrees of control domains of adjacent isobaric bodies along their width and length directions, while the directions of isobaric bodies offer supplementary material. If the control domains of two isobaric bodies overlap with each other perpendicular to the flow direction, these isobaric bodies have higher odds of connected fluid flow.

Dielectric Roasting Induced Physical, Mechanical, and Grinding Characteristics of Black Pepper (Piper nigrum)

The present study was focused on microwave (dielectric) roasting (300-600 W, 5-15 min) on the physical, textural, color, and grinding of black pepper. The microwave roasting is a volumetric heating that causes rapid removal of moisture, and internal pressure generated inside the seed tends to change the physiology and physical attributes. An increase in roasting power and time increased the geometric mean diameter (5.216 to 6.283 mm), sphericity (0.883 to 0.927), aspect ratio (0.853 to 0.914), and surface area (85.560 to 124.262 mm2) of black pepper. Whereas the significant ( p < 0.05 ) reduction was observed in 100 grain weight (7.55 to 5.63 g), bulk density (500.97 to 251.38 kg/m3), fracturability (72.99 to 1.78 N), and hardness (63.65 to 1.61 N). Roasting led to browning, and a significant reduction was observed in the color parameters, L ∗ (22.82 to 17.76), a ∗ (2.47 to 0.56), and b ∗ (2.41 to -0.75) with a significant ( p < 0.05 ) increase in total color difference (0.96 to 5.30). Roasting also increased the particle size distribution in grounded power, and the mean particle size increased from 121.72 to 146.14 μm.

Moisture dependent postharvest physical and textural characteristics of brown sesame seed (var. TMV-4)

Physical and textural characteristics are important in design and manufacturing of harvest and post harvest machines. Some postharvest physical and textural characteristics of brown sesame seed (var. TMV-4) were determined as a function of moisture content in the range of 4.3 per cent to 20 per cent (d.b). The axial dimensions, geometric mean diameter, surface area, volume, sphericity and aspect ratio were found to be increasing linearly for all studied moisture levels. Furthermore, the thousand seed mass, true density, porosity and the angle of repose also increased linearly whereas, bulk density decreased linearly with the increase of moisture content under study. The results showed that the static coefficient of friction on four different surfaces of plywood, mild steel, galvanized iron and glass also increased linearly for all level of moisture. The initial cracking force, average rupture force and average rupture energy decreased linearly with increased moisture content of 4.3 to 20 per cent (d.b.).

Augmented Performance and Wake Management in Finned Tube Arrays Through Hierarchical Deployment of Toe-Out Winglets

Abstract Downsizing the heat exchanger without compromising its heat exchange capacity is highly desirable for containing the box volume of a thermal management system. This investigation seeks to substantially boost the thermal compactness of a widely used gas-to-liquid heat exchanger, called finned tube arrays. For that purpose, winglet-type vortex generators are adopted. The novelty of the present study lies in the fact that it uses regression analysis to develop thermo-hydraulic functional correlations corresponding to three diverse design parameters of winglet-type vortex generators: the attack angle, the location and the geometric aspect ratio. In addition, enhancement in the wake-affected heat transfer is specifically examined, followed by a proof-of-concept study by making the best design(s) of vortex generators perform under widely varying operating conditions. Based on a thermo-hydraulic assessment of the generators' attack angle, 45-degrees is the limiting value of optimal attack angle. Although multiple winglet locations are found to deliver the desired thermal augmentation, a few locations incur disproportionate flow loss whereas majority locations facilitate linearized thermal augmentation. It is encouraging to find that the relative Colburn j-factor of the modified heat exchanger increases with the Reynolds number, despite the absolute values bearing an inverse correlation. While the highest augmentation in the average Colburn j-factor equals 44.1%, it is 150.1% over the wake-affected fin surface.

An experimental study on shear resistance of austenitic and duplex stainless steel plate girders with perforated webs

Stainless steel is increasingly being used in the field of engineering as building construction materials, as it has an inherent ability to resist corrosion, as well as other environmental benefits. When used as plate girders, web perforations are often required to accommodate building services. In the literature, no experimental study has been reported that investigates the shear resistance of austenitic and duplex stainless steel plate girders with perforated webs. This issue is addressed herein. A detailed experimental program is described comprising eight stainless steel plate girders. The plates are austenitic grade EN 1.4301 and duplex grade EN 1.4462, and the depth of web is fixed as 500 mm and 700 mm. For comparison, specimens with perforated webs and solid webs were tested. Prior to shear tests, the distribution of initial geometrical imperfections was determined through three-dimensional (3D) scanning. Finite element (FE) models incorporating the material non-linearity and initial geometric imperfections were then developed. The results of FE models were validated against the experimental results. Using the validated FE models, a parametric study comprising 182 FE models was then undertaken, and variables which were examined included local geometrical imperfections, aspect ratio, end conditions, hole ratio and stainless steel grades. The results suggested that for those members with a hole diameter - web height ratio of 0.6, the shear resistance was reduced by 52% on average due to the web perforation. The design rules given in Eurocodes, American Specification and those design recommendations proposed by Chen et al. (2023) were evaluated.

High-resolution X-ray diffraction to probe quantum dot asymmetry

The symmetry of nanostructures forming an active part of optoelectronic devices severely impacts their properties. It is crucial for the design of polarization-insensitive semiconductor optical amplifiers or sources of entangled photon pairs. We show how quantum dot symmetry can be measured, including atomic force microscopy and polarization-resolved spectroscopy. We discuss the drawbacks of the typical approaches for nanostructure symmetry detection and propose a way to determine quantum dot geometrical aspect ratio based on high-resolution X-ray diffraction. The offered method provides a non-destructive insight into crystal lattice disturbances reflecting in-plane quantum dot geometrical aspect ratio.