OpenMETU (Middle East Technical University)
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Surrogate model based optimization of variable stiffness composite wingbox for improved buckling load with manufacturing and failure constraints
No full textThe buckling load of a wingbox is maximized by applying different automatic fiber placement (AFP) strategies on the skins of the wing having NACA 4412 airfoil profile. Specifically, the effect of single, dual and three region application of AFP on the optimal buckling load is studied to provide an outlook on the improvement of the optimal buckling load by increasing the number of skin panels, between rib stations, over which distinct reference fiber path definitions are made. Buckling load optimizations with manufacturing and failure constraints are performed via two different metaheuristic optimization algorithms to ensure that the global optimum reference fiber paths are obtained. For computational efficiency, separate radial basis function based surrogate models are generated for the buckling and the failure analysis. Our results show that the application of AFP separately with distinct reference fiber path definitions in each skin panel between the rib stations, the buckling load can be improved compared to the application of the AFP to a larger section of the wing skin. For the wingbox studied, compared to the wing with quasi-isotropic skins, 94% increase in the local buckling load of the root panel is obtained with the three region AFP application
Nanoindentation study of PbMoO<sub>4</sub> single crystals: mechanical properties and implications for applications
No full textNanomechanical properties of lead molybdate ( PbMoO 4 ) single crystal were investigated using nanoindentation measurements. The force-dependent Young's modulus and hardness of PbMoO4 along the [ 100 ] direction was determined using the Oliver-Pharr method. As the applied force increased, hardness and young modulus values decreased. This behavior was referred to the indentation size effect ( ISE ) . The force-dependent plots were analyzed using proportional specimen resistance model and true hardness value was determined as 1.84 GPa. As a result of increasing the applied force from 5 to 100 mN, the Young modulus decreased from 81.7 to 60.2 GPa. The dependencies of plastic and elastic deformation components were also reported in the present study. It was seen that plastic deformation is the dominant component. The fi ndings suggest that PbMoO4 is relatively soft material and can be considered as a promising material for mechanical and optoelectronics applications that require revealed hardness and Young's modulus values
High-yield production of lactide isomers from depolymerization of polylactic acid in supercritical carbon dioxide
No full textChemical depolymerization of polylactic acid (PLA) was demonstrated in supercritical carbon dioxide medium. No catalyst, organic solvent or water was employed in the reaction. The primary feedstocks used in ring opening polymerization of PLA, lactide isomers, were produced with high yield. More specifically, lactides were produced as the sole nongaseous products with a 93 % yield based on the initial polymer mass at 200 °C and 310 bar in 120 min. The influences of the reaction temperature, time, and pressure on PLA depolymerization products were investigated. While the lactide yield and distribution were highly influenced by the reaction temperature and time, further improvement was attained with an increase in the pressure. The results demonstrate that supercritical CO2 can be applied as a promising reaction medium for PLA degradation, providing a high-yield production of its feedstock. The process can enable green depolymerization of polylactic acid and promote its circular economy with a closed loop production
Nanoparticle concentration and solvent exchange via organic solvent ultrafiltration
No full textDownstream processing of nanoparticles after synthesis frequently involves purification, concentration and solvent exchange steps. While these are typically done via centrifugation in lab scale, ultrafiltration is a practical and economical alternative in large scale continuous production. Treating suspensions in organic solvents via ultrafiltration requires solvent-stable membranes and in this study we present the performance of cellulose ultrafiltration membranes in the concentration and solvent exchange of hydrophilic and hydrophobized silica nanoparticles using isopropanol, water, dimethyl formamide and ethanol as solvents. Hydrophobized particles formed less permeable cake layers than hydrophilic particles during concentration. All fouling was reversible upon ultrasonication while physical cleaning via stirring could only recover the complete membrane permeance fouled with hydrophilic particles in dimethyl formamide and hydrophobic particles in isopropanol and water. Quality of nanoparticle recovery was assessed by the amount recovered in retentate and cleaning suspensions as well as the particle size after these steps. Highest recovery of hydrophilic particles was obtained in dimethyl formamide and that of hydrophobic particles in isopropanol. No agglomeration of recovered hydrophilic particles was observed, while hydrophobic particles recovered via physical cleaning partly agglomerated in isopropanol and dimethyl formamide. Finally, continuous solvent exchange from isopropanol to ethanol, water and dimethyl formamide was achieved with no performance loss throughout the process
VO<sub>2</sub>-Based Dynamic Coding Metamaterials for Terahertz Wavefront Engineering
No full textDigital coding metasurfaces (DCMS) offer a promising alternative to conventional metasurface designs for achieving common functionalities by controlling the phase of reflected or transmitted electromagnetic waves. Their simple unit cell designs allow for scalability across the THz spectrum and facilitate large-area fabrication. The true potential of DCMS lies in dynamical coding, which enables real-time reconfigurability through a tuning and/or switching mechanism. In this study, metasurfaces that achieve 1-bit dynamic coding of unit cells via thermally induced metal-insulator transition of VO2 layers are designed and fabricated. We investigate experimentally the beam splitting functionality at certain frequencies in the 0.50-0.75 THz range reflected from the stripe- and checkerboard patterned metasurface samples, and demonstrate the switching of this functionality under thermal illumination
Stories and Memories, Memories and Histories: A Cross-disciplinary Volume on Time, Narrativity, and Identity
No full textThis edited volume brings together authors from a wide variety of
disciplines in the social sciences and humanities. A historian first
investigates understudied samizdat literature, a film critic then
analyzes Balkan cinema via psychoanalysis, a psychologist examines
contemporary European border policies, and a political scientist
analyzes the Confederate-memorial debate. Philosophers consider the
space of those memorials, ethno-national narratives in India, the
Anthropocene and the mind’s historical imaginary, and the notion of
home. Literary critics examine recent developments in modes of
storytelling and images of Orientalism. What emerges is a new
understanding of history, memory, and time
Doped NaMnOx cathodes for Zn-MnO2 batteries for improved capacity and rechargeability
No full textZn-MnO2 batteries are safe, low cost, and have a high energy density comparable to Li-ion batteries. This study focuses on finding a new MnO2-based cathode composition for rechargeable mildly acidic Zn-MnO2 battery. For this purpose, a combinatorial approach was used, and thick film cathodes were deposited on nickel substrates using sputter targets MnO2, Na0.7MnO2, NiO and Bi2O3. A total of 36 cathodes were produced over a wide compositional range. The study has shown two regions of high rechargeable capacity, one centered on Bi0.02Na0.63Ni0.02Mn0.33Oxand the other on Bi0.04Na0.37Ni0.06Mn0.53Oxto be developed as cathodes using conventional slurry method
Presenting predictions and performance of probabilistic models for clinical decision support in trauma care
No full textIntroduction: Both predictions and performance of clinical predictive models can be presented with various verbal and visual representations. This study aims to investigate how different risk and performance presentations for probabilistic predictions affect clinical users' judgement and preferences. Methods: We use a clinical Bayesian Network (BN) model that has been developed for predicting the risk of Trauma Induced Coagulopathy (TIC). Three patient scenarios with different levels of TIC risk were shown to trauma care clinicians. The prediction and discriminatory performance of TIC BN were shown with each scenario using different charts in a random order. Bar charts, icon arrays and gauge charts were used for presenting the prediction. Receiver operating characteristic curves, true and false positive rate curves and icon arrays were used for presenting the performance. Risk judgement for patient scenarios, perceived accuracy for the predictions and the model, and preferences for charts were elicited using an online survey. Results: A total of 25 clinicians evaluated 75 BN predictions. The choice of risk charts was associated with the risk score in the borderline medium-risk scenario. The choice of risk and performance charts interacts with the perceived accuracy of the predictions and model in the high and low-risk scenarios, respectively. The participants had varying but persistent preferences regarding risk presentation charts. Icon arrays were preferred for performance presentations. Conclusions: The choice of presenting predictions and the performance of predictive models can affect risk and performance interpretation. Clinical predictive models should offer the flexibility of presenting predictions with different illustrations
Coupled thermo-elastic dynamics of rotating pre-twisted blades exposed to thermal shock including nonlinear rotational effects
No full textRotating blades operating under high-temperature experience intense mechanical and thermal stresses induced by centrifugal forces and thermal shock. In this research, to address this critical yet understudied topic, coupled thermo-elastic dynamics of rotating blades incorporating precise rotational effects is investigated. A comprehensive modeling approach, characterizing blade geometry in terms of pre-twist and pre-set angles is employed based on the theory of surfaces. Thermal strain-displacement field is defined based on third-order shear deformation theory in the model integrated with a third-order expansion of temperature change distribution within the blade. Rotational factors related to Coriolis, centrifugal stiffening, and rotational softening effects are considered. In the case of stiffening effects, two different modeling approaches including direct integration of centrifugal forces (DICFs), and pre-stressed dynamics about steady-state equilibrium deformations (SSEDs) are employed. When incorporating large- amplitude SSEDs in the latter, nonlinear rotational effects are incorporated into the model. To overcome the complexity arising from coupled thermo-elasticity, and rotational motion, the spectral Chebyshev technique is applied to the derived integral boundary value problems and coupled energy equations. Finally, natural frequencies, and thermal and centrifugal deformations are investigated comprehensively by including DICFs and pre-stressed dynamics. Results show that thermo-elastic dynamics of the system is highly affected by the modeling approaches used for centrifugal stiffening effects
