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Microstructural Response of Shock-Loaded Concrete, Mortar, and Cementitious Composite Materials in a Shock Tube Setup
No full textMicrostructural changes in concrete, mortar, and cementitious composite material were investigated to determine the efficacy of these materials subjected to shock loading. An experimental methodology with the ability to generate reproducible shock waves of specified blast pressure and decay time was used to perform repeatable experiments in the range of trinitrotoluene (TNT) explosion that is unsafe for concrete columns as specified in the FEMA (Federal Emergency Management Agency) guidelines (38 kg TNT at 3.7 m). The changes in the pore volume fraction of the samples before and after shock loading were used to determine the efficacy of the materials subjected to shock loading. The study reveals that even though percentage increase in pore volume fraction before and after shock loading is highest for cementitious materials, its absolute value is low compared to that of control samples, thereby justifying the better performance of cementitious composite materials. Moreover, the size of the pores is also observed to be lower for cementitious composite samples compared to those of the and concrete samples after shock loading in comparison to the control materials in the study. The reason for the better performance of cementitious composite materials can be attributed to an increase in tensile ductility of the sample as a result of fiber addition. Apart from development of a new cementitious material for blast load mitigation, the study also demonstrates the need to consider pore size distribution in equations relating pore volume fraction to strength
Using wavelet analysis to investigate synchronization
No full textWavelet analysis is shown to be a more robust technique than previously used methods in the investigation of synchronization. The highlight of the technique is that it encompasses most of the information obtained by conventional methods into a single picture, while giving a deeper insight into the dynamics of the system. Order parameters derived from continuous wavelet transform coefficients are proposed, which can be used in the quantification of measure synchronization in Hamiltonian systems and identical synchronization in dissipative systems, irrespective of the nature of coupling, the nature of synchronization (complete or partial, quasiperiodic or chaotic), and the number of coupled subsystems
Equation of state of colloidal membranes
No full textIn the presence of a non-adsorbing polymer, monodisperse rod-like colloids assemble into one-rod-length thick liquid-like monolayers, called colloidal membranes. The density of the rods within a colloidal membrane is determined by a balance between the osmotic pressure exerted by the enveloping polymer suspension and the repulsion between the colloidal rods. We developed a microfluidic device for continuously observing an isolated membrane while dynamically controlling the osmotic pressure of the polymer suspension. Using this technology we measured the membrane rod density over a range of osmotic pressures than is wider that what is accessible in equilibrium samples. With increasing density we observed a first-order phase transition, in which the in-plane membrane order transforms from a 2D fluid into a 2D solid. In the limit of low osmotic pressures, we measured the rate at which individual rods evaporate from the membrane. The developed microfluidic technique could have wide applicability for in situ investigation of various soft materials and how their properties depend on the solvent composition
Aspects of boundary conditions for non-Abelian gauge theories
No full textThe boundary values of the time component of the gauge potential form externally specifiable data characterizing a gauge theory. We point out some of their consequences such as reduced symmetries, bulk currents for manifolds with disjoint boundaries and some nuances of how the charge algebra is realized
Evaporation driven self-assembly in a levitated nanocolloidal droplet can create a spatially varying photonic band-gap
No full textLevitated colloidal droplets can be used to dynamically assemble millimeter sized discs with a photonic bandgap in the visible spectrum. A top-down scheme is proposed to control the bottom-up kinetics of particle assembly in a bid to modulate photonic bandgap of the precipitate. Levitated drops of different colloidal compositions (specified as the number fraction of particles N) are evaporated under different fluxes of laser irradiation (H). The resulting microstructure of the precipitate is quantified using Voronoi tessellation. Micro-reflectance spectroscopy is used to validate the modulation of the photonic bandgap of the synthesized sample. The parametric control of the evaporation dynamics of the levitated droplet changes the kinetics of the microparticle aggregation as validated by Voronoi tessellation of the scanning electron micrographs of the precipitate. Reflectance microscopy of the precipitate's surface reveals a spatial shift in the Bragg's peak of reflectance. Mean variation in the ordering of the particles results in the modulation of the bandgap of the precipitate. The simplicity of self-assembly using levitated droplets is shown to be promising pathway for creating samples with spatially tunable photonic bandgap
Microstructure-corrosion property correlation in electrodeposited AlCrFeCoNiCu high entropy alloys-graphene oxide composite coatings
No full textAlCrFeCoNiCu high entropy alloys (HEA) composite coating with and without graphene oxide (GO) were electrodeposited over mild steel substrate. Potentiodynamic polarization and electrochemical impedance spectroscopy tests performed in 3.5 wt% NaCl aqueous solution showed that the corrosion resistance of the HEA-GO composite coatings was higher than the HEA coating without GO. The corrosion resistance gradually increased with increase in the GO amount in the coating. Detailed microstructural characterization performed using transmission electron microscopy technique revealed that addition of GO facilitated microstructural and compositional homogeneity which eliminated localized corrosive attack due to elemental segregation induced galvanic coupling thereby increasing the corrosion resistance for the HEA-GO composite coatings
Test System for Thin Film Transistor Parameter Extraction in Active Matrix Backplanes
No full textThin film transistor (TFT) active matrix backplanes are used in large area electronic systems, such as displays and image sensors. With backplanes being fabricated on wearable and flexible substrates, the possibilities of operational faults in backplanes have increased. These faults could either be hard faults, such as line opens or shorts or could be softer faults, such as time dependent variations in the TFT transfer characteristics. Real time diagnosis of these faults require built-in-self-test systems. While many such systems have been demonstrated to diagnose hard faults, an easily realizable system to identify soft faults, such as variations in transistor transconductance remain an open challenge. In this paper, we discuss a system that extracts the transconductance by charging and then discharging the pixel capacitor at various gate voltages for an active matrix liquid crystal display backplane. This permits a plot of the time averaged current versus the gate voltage from which the spatial variation of transconductance can be extracted. The details of the design are discussed and a proof of concept with a 3 x 4 amorphous silicon backplane is demonstrated
Design and Validation of a Novel High Sensitivity Self-Temperature Compensated Fiber Bragg Grating Accelerometer
No full textFiber Bragg Grating-based accelerometers are being used in structural health monitoring as they offer several advantages over their electrical counterparts. In this paper, the concept of a novel T-shaped cantilever-based mechanical sensor head is proposed on which the two Fiber Bragg Gratings are integrated in a differential sensing configuration to realize an optical accelerometer. This elegant design simultaneously achieves the dual goals of sensitivity enhancement, and self-temperature compensation. A mathematical model of the accelerometer is developed, and numerical simulations are carried out for three mechanical sensor head designs. A prototype is fabricated and characterized to prove the design. The sensitivity of 821 pm/g of is achieved with a linearity of 99.7%, cross-axis sensitivity of 0.3%, and natural frequency of 64 Hz; self-temperature compensation is achieved with an error of 0.07 pm/degrees C
Compatibilising action of multiwalled carbon nanotubes in polycarbonate/polypropylene (PC/PP) blends: phase morphology, viscoelastic phase separation, rheology and percolation
No full textMultiwalled carbon nanotubes were introduced into both dispersed and co-continuous polycarbonate/polypropylene blends through melt compounding in an internal mixer. Both the neat blends and blend nanocomposites showed viscoelastic phase separation process where phase in phase morphologies could be observed due to viscosity disparity and T-g differences between the component polymers. A strong compatibilising action was noticed up on the addition of a small quantity of MWCNT into both dispersed and co-continuous morphologies. Theoretical predictions based on thermodynamic considerations clearly indicated the preferential localisation of MWCNTs in the PC phase. However, because of the viscosity differences between the two polymers, we also found that some of the MWCNTs being localised at the blend interphase and in PP phase. From linear viscoelastic studies rheological percolation was observed at high concentration of the MWCNTs where carbon nanotubes formed a network-like structure leading to solid state behaviour at low frequencies