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Droplet size distribution in a swirl airstream using in-line holography technique
Full text linkWe investigate the morphology and size distribution of satellite droplets resulting from the interaction of a freely falling water droplet with a swirling airstream of different strengths by employing shadowgraphy and deep-learning-based digital in-line holography techniques. We found that the droplet exhibits vibrational, retracting bag and normal breakup phenomena for the no swirl, low and high swirl strengths for the same aerodynamic field. In the high-swirl scenario, the disintegrations of the nodes, rim and bag-film contribute to the number mean diameter, resulting in smaller satellite droplets. In contrast, in the low-swirl case, the breakup of the rim and nodes only contributes to the size distribution, resulting in larger droplets. The temporal variation of the Sauter mean diameter reveals that for a given aerodynamic force, a high swirl strength produces more surface area and surface energy than a low swirl strength. The theoretical prediction of the number-mean probability density of tiny satellite droplets under swirl conditions agrees with experimental data. However, for the low swirl, the predictions differ from the experimental results, particularly due to the presence of large satellite droplets. Our results reveal that the volume-weighted droplet size distribution exhibits two (bi-modal) and three (multi-model) peaks for low and high swirl strengths, respectively. The analytical model that takes into account various mechanisms, such as the nodes, rim and bag breakups, accurately predicts the shape and characteristic sizes of each mode for the case of high swirl strength
A study on the seismic behavior of Shape Memory Alloy (SMA) reinforced low-rise and mid-rise concrete frames
No full textEarthquakes have created greater drift demands mainly residual drift demands on
reinforced concrete (RC) structures. Higher residual drift demands result in permanent
deformation, which poses unfavorable conditions for the occupants of building. The
rupture distance of an earthquake plays a crucial role in the seismic performance of
structures. Previous researches have explored methods like base isolation and seismic
dampers to enhance post-earthquake functionality, but their maintenance and repair
requirements have redirected attention to smart alloys such as shape memory alloys
(SMA). These alloys possess unique properties like super elasticity and shape memory
effect, enabling them to recover their original shape after unloading and exhibit high
recovery strains of approximately 7%. The objective of this study is to mitigate
residual drift demands in RC structures by utilizing SMA as reinforcement within the
plastic hinge length. The effectiveness of this approach is compared under near fault
and far fault ground motions, considering both low-rise and mid-rise RC frames. The
findings reveal that SMA demonstrates a significant improvement in reducing residual
drift demands in RC frames subjected to near fault ground motions compared to far
fault ground motions
A Stage-Stage Dead-Band Compensated Multiband RF Energy Harvester for Sensor Nodes
Full text linkThis article presents a dead-band compensated multiband stacked electromagnetic energy harvester for powering sensor nodes. It is adaptive for typical ambient radio frequency (RF) power levels found within the environment. A stage-stage feedforward technique is adopted in the proposed harvester to enhance the output voltage, in turn, harvested power and sensitivity. Moreover, a compensation circuit is included in the design for bypassing the inactive bands to avoid unexcited band rectifier diodes. A prototype is designed to cover four frequency bands GSM (900 and 1800 MHz), 4G-LTE (2.3 GHz), and Wi-Fi (2.4 GHz) and further integrated with a TI BQ25570 power converter. The analytical, simulated, and measured results show the increment in the output voltage with the frequency bands. The measured efficiency of the RF-to-dc converter is 44.2% at -20-dBm input power and 89% at 0 dBm. The efficiency is improved by 13% on average under dead-band compensation. With the multiband stacking, the harvester achieves a start-up voltage of 320 mV at -24 dBm and is found to be efficient to drive a temperature sensor STLM20 at -12-dBm input power
Modeling of geometrical stiffening in a rotating blade—A review
Full text linkThe present work reviews different approaches adopted for modeling the geometrical or centrifugal stiffening of a beam due to rotation about an axis perpendicular to its longitudinal axis. The longitudinal displacement of the beam consists of three components: the axial displacement of the neutral axis (elastic extension), displacement associated with rotation of the plane section and the displacement due to the foreshortening effect. A widely used approach for modeling the geometrical stiffening is based on the foreshortening effect, which essentially is the longitudinal shrinkage due to the transverse motion of the beam. This approach uses nonlinear strain–displacement relations. As a result, the equations of motion and associated boundary conditions are nonlinear. The geometric stiffening terms in the nonlinear models are fundamentally a linear/quadratic function of the high-frequency axial elastic deformation. Various nonlinear models are discussed and summarized based on the different approximations of the strain–displacement relation. The solution procedure of these nonlinear models is complicated and computationally expensive due to coupling between high-frequency axial and low-frequency bending modes. Simplifying the model by direct linearization of the equations of motion eliminates the geometrical stiffening term resulting in an incorrect model. Different approaches to include geometrical stiffening terms in the linear model are discussed. One of the approaches is linearizing the nonlinear terms arising from the coupled axial-transverse motion around the steady-state axial solutions. The steady-state axial equilibrium equation can be linear or nonlinear depending on the type of strain measure employed. A comparison of the solution of these different linear/nonlinear steady-state axial equilibrium equations is presented. The applicability of these models based on the steady-state axial equations is tested, and the rotation speed limit within which these models are valid is also discussed. In another approach, the equations of motion are derived using a time-independent centrifugal force. The resulting equations are equivalent to those governing the transverse vibrations of beams subject to an external axial force. Nevertheless, another approach proposed by Kane et al. (1987) uses stretch as a variable in the formulation instead of the axial displacement. The linear geometrical stiffening models are discussed in detail. Further, the effects of geometric properties of the blade, such as taper, twist angle, pre-setting angle and asymmetry in cross-section on the modal characteristics are brought out. A comparison of the different beam theories used in studying the dynamics of rotating blades is also presented
Enriched visible light absorption by Au-embedded Sm3+ doped TiO2 compact photoanode for enhanced dye-sensitized solar cell performance
Full text linkThe cooperative effect of Samarium (Sm3+)-doped TiO2 and gold nanoparticles (Au NPs) is investigated in this work to explore its potential to boost visible light absorption in dye-sensitized solar cells (DSSC). As Sm3+ exhibits PL emissions at 583 nm, 612.2 nm, 663.6 nm, and 726.3 nm, there is an overlap with the absorption region of the N719 dye and these PL emission wavelengths resulting in a rise in photocurrent density and PCE owing better UV light harvesting. Sm3+ absorption and emissions were boosted by LSPR (Localized surface plasmon resonance) of Au NPs. As a result, the Au NPs embedded Sm-doped TiO2 photoanode-based DSSC capture more visible light. Sm (0.3)-TiO2 based DSSC reports the highest PCE (η:7.2%) among a series of Sm (0.2%, 0.3%, 0.4%, and 0.5% mol) TiO2 concentrations. Further, with the addition of Au NPs into the Sm3+ -doped TiO2, the PCE is enlarged into (η: 8.33%), which is more than 60% higher than TiO2 photoanode-based DSSC (η: 5.58%)
Femtosecond nonlinear optical properties of polycyclic aromatic hydrocarbon-based Benzo[e]pyrene derivatives
Full text linkWe herein report our results on the nonlinear optical (NLO) properties of three polycyclic aromatic hydrocarbons (PAHs) based benzo[e]pyrene derivatives namely 10-phenylbenzo[e]pyrene (BP1), 13-fluoro-10-(4-fluorophenyl)benzo[e]pyrene (BP2), and 13-methoxy-10-(4 methoxyphenyl)benzo[e]pyrene (BP3). Using experimental techniques such as UV–Visible absorption, Z-scan technique, and theoretical time-dependent density functional theory (TDDFT), we have investigated the linear absorption, NLO coefficients, second hyperpolarizability, and optical limiting onset of these molecules. The ultrafast nonlinear Z-scan experiment was performed using ∼70 fs pulsed laser with 800 nm as central wavelength. Using the three-level model analysis based on rate equations, the contribution of different nonlinear processes contributing to nonlinear absorptions in these molecules is elucidated. All three molecules exhibited strong reverse saturable absorption due to mixed contribution of two-photon absorption (2PA) and three-photon absorption (3PA) with 2PA and 3PA coefficients of (1.26–1.79) × 10−11 cm/W and (6.23–7.39) × 10−5 cm3/GW2, respectively. The closed-aperture Z-scan data for all the examined molecules depicted valley-peak signature, which indicated a positive refractive index. The second hyperpolarizability was calculated with magnitude observed ∼10−32 esu. Using the TDDFT calculation, the complete optimization of the individual structure of molecules was achieved and the results matched with experimental observations
Skyrmion based 3D low complex runtime reconfigurable architecture design methodology of universal logic gate
No full textIn this study, we introduce the area efficient low complex runtime reconfigurable architecture design methodology based on Skyrmion logic for universal logic gate (ULG) i.e. NOR/NAND implementation using micromagnetic simulations. We have modelled the two input 3D device structure using bilayer ferromagnet/heavy metal where the magnetic tunnel junctions inject and detect the input and output skyrmions by exploiting the input reversal mechanism. The implementation of NOR and NAND is performed using this same device where it is reconfigured runtime with enhanced tunability by the ON and OFF state of current passing through a non magnetic metallic gate respectively. This gate acts as a barrier for skyrmion motion (additional control mechanism) to realize the required Skyrmion logic output states. To the best of authors’s knowledge the boolean optimizations and the mapping logic have been presented for the first time to demonstrate the functionalities of the NOR/NAND implementation. This proposed architecture design methodology of ULG leads to reduced device footprint with regard to the number of thin film structures proposed, low complexity in terms of fabrication and also providing runtime reconfigurability to reduce the number of physical designs to achieve all truth table entries (∼75% device footprint reduction). The proposed 3D ULG architecture design benefits from the miniaturization resulting in opening up a new perspective for magneto-logic devices
Signed spectral Turań type theorems
Full text linkA signed graph Σ=(G,σ) is a graph where the function σ assigns either 1 or −1 to each edge of the simple graph G. The adjacency matrix of Σ, denoted by A(Σ), is defined canonically. In a recent paper, Wang et al. extended the spectral bounds of Hoffman and Cvetković for the chromatic number of signed graphs. They proposed an open problem related to the balanced clique number and the largest eigenvalue of a signed graph. We solve a strengthened version of this open problem. As a byproduct, we give alternate proofs for some of the known classical bounds for the least eigenvalues of unsigned graphs. We extend the Turán's inequality for the signed graphs. Besides, we study the Bollobás and Nikiforov conjecture for the signed graphs and show that the conjecture need not be true for the signed graphs. Nevertheless, the conjecture holds for signed graphs under some assumptions. Finally, we study some of the relationships between the number of signed walks and the largest eigenvalue of a signed graph
Experimental Studies on Pullout Resistance of Overlapping Geogrids
No full textIn the present world, mechanically stabilized earth (MSE) walls are an established technology and have effectively replaced conventional gravity or semi-gravity type concrete retaining walls. The type of wall facia dictates the connection type between geogrid and facia and subsequently the arrangement of geogrid. One arrangement commonly adopted in the field is geogrid overlapped in a trapezoidal shape. In the design of such walls, however, the laboratory pullout is determined typically using ASTM D6706 which uses a single layer of geogrid and subjecting it to axial pullout. In the present study, the actual arrangement (trapezoidal shape) of polyester uniaxial geogrid layers was replicated in the laboratory pullout testing to study the axial pullout resistance of overlapping geogrids. The overlapping of geogrid layers was expressed in terms of the spread area ratio and the effect of spread area ratio on the pullout resistance of the geogrid was discussed. A significant difference in the pullout resistance was observed between single layer of geogrid and the overlapping arrangement of geogrid layers. The pullout resistance of two layers of geogrid was higher than one layer of geogrid. Additionally, the pullout resistance of the geogrids with high spread area ratio exhibited high pullout resistance. The axial pullout resistance factors ranged from 0.69 to 0.85 for one-layered geogrid, while it ranged from 0.98 to 1.74 for two-layered geogrid according to the spread area ratios of the geogrid. The proposed pullout resistance factors can help in realistic design of soil structures reinforced with geogrids overlapped in a trapezoidal shape
Hydrodynamic forces in non-uniform cantilever beam resonator
Full text linkIn this paper, we developed two dimensional and three dimensional boundary element method (BEM) to compute hydrodynamic forces due to the oscillation of non-uniform beam (NUB) in a quiescent incompressible fluid with linear and quartic varying widths. To model the fluid flow under small amplitude oscillation of thin NUB in its first mode, the linearized unsteady Stokes equation is solved using BEM. After finding the converged structural and fluid nodes in all the cases, we compute real and imaginary components of hydrodynamic function. Subsequently, damping ratio or quality factor is found from energy dissipation due to drag forces mainly because of stress jumps across the thin beam thickness. Similarly, the frequency shift is found due to virtual added mass obtained from the mean hydrodynamic thrust force. The results are validated with existing literature and further analysis is done in terms of tapering parameter and index of non-uniform beam, and the corresponding aspect ratio and frequency parameters. Based on the analysis presented, it is found that quartic converging beam provides better quality factor and least added mass effect and it can be explored to design a cantilever based resonator operating in fluid with improved performance such as AFM probes. Thus, the new model developed for non-uniform beam can be useful to drag forces in other types of 2D and 3D beams