50175 research outputs found
Sort by
Visible light generation in the cladding of optical fibers carrying near-infrared continuous-wave lasers due to Cherenkov-phase matched harmonic conversion
No full textIn this work, we report and analyze the cause of the surprising observation of visible light generation in the cladding of silica-based continuous-wave (CW), near-infrared fiber lasers. We observe a visible rainbow of hues in a cascaded Raman fiber laser, which we attribute to second and third harmonic conversion of the different wavelength components propagating in the core of the fiber. The light in the cladding of the fiber occurs through Cherenkov-type phase matching, and a mathematical analysis is presented to estimate the power of the harmonic light generated. We then extend this theory to visible light generation in other types of fiber lasers. Specifically, we analyze the case of a CW supercontinuum generated in standard telecom fibers, and verify our theoretical predictions with experimental results through visible spectra collected
Development of a very high sensitivity magnetic field sensor based on planar Hall effect
No full textWhile planar Hall effect based magnetic field detection is a well-studied area, the sensing capabilities of �Hall cross� sensors had not improved significantly for more than a decade. Here we report a major improvement in the sensing characteristics of �cross� geometry by using pulsed laser ablation grown Permalloy as sensing material. Our sensor has two modes of operation. In the linear regime, it has a field sensitivity of 650 Ω/T with an estimated detection threshold of 5nT in open-loop condition. In switching applications, it shows a 400 output voltage swing in a range of ±0.3 mT, a value comparable with modern TMR sensors at room temperature. These values, which are the highest reported for the �cross� geometry, make it applicable in a wide range of scenarios like geomagnetic field and magnetic anomaly detection. The small size of the sensing area also makes it a desirable choice for magnetic microbead based biomolecule detection
Defect engineering of VO2 thin films synthesized by Chemical Vapor Deposition
No full textVanadium dioxide (VO2) has been a much sought after candidate for many electronics and photonics based applications. These applications demand CMOS compatibility and simple but scalable synthesis procedure. Herein we report the deposition of VO2 on CMOS compatible Si substrates via easily scalable Metal Organic Chemical Vapor Deposition (MOCVD) at different substrate temperatures between 520 and 550 °C. The morphology of the films deposited at different growth temperatures varied drastically despite retaining VO2 in the M1 phase. This was verified by XRD and Raman experiments. The thin films deposited at 535 °C showed sharp grain boundaries with a grain size of about 200 nm. Similarly, the electrical characteristics of the films deposited at 535 °C showed superior transition compared to the films deposited at other temperatures. However the films deposited at 550 °C retained the superiority in the transition strength, the transition width and the hysteresis of the transition increased at that temperatures. We understand that the reason for this observed behavior is the fraction of surface defects. It is seen from XPS measurements that vanadium was available in V3+, V4+ and V5+ oxidation states and the fractions of these individual components varied in all the thin films deposited at different temperatures. We believe that the defects fraction can give a handle to control the nature and quality of the transition in VO2
Clumped isotope geochemistry of carbonatites in the north-western Deccan igneous province: Aspects of evolution, post-depositional alteration and mineralisation
No full textCarbonatites crystallise along a wide range of solidus temperatures and are commonly affected by post-magmatic textural re-equilibration and diagenesis. Further insights into the formation and modification of carbonatites are provided using carbon, oxygen and clumped isotope (�47) data of rocks from spatially associated Amba Dongar and Siriwasan alkaline complexes in the north-western Deccan igneous province, India. We derive apparent equilibrium blocking temperatures to help constrain the thermal evolution of the different rock types found within the alkaline complexes in a petrographic context. The apparent temperatures for the carbonatites are significantly low but are consistent with reports on other global carbonatites and model predictions. Rapidly cooled Oldoinyo Lengai natrocarbonatite yielded similar low temperatures, even in the absence of bulk isotopic alteration. The isotopic proxies and petrographic observations favour both isotopic exchange reactions and diagenesis in altering �47 values in calciocarbonatites. Diagenetic reactions are however strongly favoured, as secondary calcites in nephelinites and ferrocarbonatites record much lower temperatures than in the calciocarbonatites, highlighting the effect of fluids and diagenetic reactions in 13Csbnd18O bond ordering in carbonatites. Variations in the CsbndO isotope data reveal the coupling of fractional crystallisation and post-magmatic fluid-rock interactions on bulk rock composition. After emplacement, the resetting of clumped isotope signatures in carbonatites is facilitated by post-magmatic processes in both open and closed systems. © 2020 Elsevier Lt
Synthesis and application of porous oil-sorbent microspheres: Characterization retention capacity and sorption kinetics
No full textThe article focuses on the study of oil spill cleanup in an aquatic media by comparing the oil sorption capacities of three polymeric sorbents. Styrene - dodecyl methacrylate - DVB with toluene as porogen (P3) showed a highest removal ability of 5 times its weight. However, key aspect of this research is associated with the retention capacities of the sorbents. The loss in weight measured over time was found to be numerically insignificant for all the three sorbents. Water contact angle for the sorbents i.e., P1, P2, P3 were found to be 113.3 degrees, 107.2 degrees and 97.5 degrees respectively. SEM results confirmed the entrapment of oil between the polymer molecules thereby confirming the phenomenon of sorption. The sorption kinetics of oil over the sorbent surface was followed the pseudo-second order model. The prepared sorbents can be successfully employed for the recovery of oil spills from water sources
Mesoscale Analysis of Fatigue Damage through Aggregate-Mortar Bond Cracks in Cementitious Composites
No full textA micromechanics-based model is developed to study the fatigue response of cementitious composites. Microcrack growth, which is the predominant mechanism responsible for fatigue damage, is explicitly modeled at the mesoscale. The damaged state at the macroscopic scale is determined by using energetic criterion. The dissipated energy associated with each stage of microcrack propagation is computed numerically based on the elastic solutions of the stress and displacement quantities at the mesoscale. The model is used to predict the fatigue life of plain concrete beams under fatigue load cycles. The influence of the various properties of the constituent phases on the fatigue life of the composite is investigated through a parametric study
Evolution of local flame displacement speeds in turbulence
No full textgIn this study, we assess the veracity of models for density-weighted local flame displacement speed of turbulent premixed flames. It will be shown that a combination of two models, one for the weakly stretched laminar flame state and another derived for a configuration where a curved laminar flame interacts with itself to annihilate, can describe most local realizations of a turbulent premixed flame. To that end, we have performed direct numerical simulations of a reactive mixture of hydrogen-air at atmospheric pressure using a detailed chemical reaction mechanism and analysed the dataset with recently developed flame particle tracking techniques. Forward tracking a large number of flame particles from the generating locations of the corresponding flame surfaces (given by backward tracking) to the corresponding annihilating locations, creates a manifold of local states that can represent nearly all possible states realizable for the turbulent premixed flame under consideration. With all the states of the flame accessible over time, we first assess the applicability of the two-parameter Markstein length based flame speed model. It is found that the model prediction is reasonably accurate for a significant part of the flame particles' lifetime, for turbulent premixed flames with Karlovitz number O.10 /. However, during the final stage of annihilation of the flame particles in the negatively curved trailing regions, the local structure of the flame no longer resembles a standard premixed flame, even qualitatively. A new interaction model for the flame displacement speed, during these final stages of annihilation of the flame elements, has been derived
A novel weak form quadrature element for gradient elastic beam theories
No full textA novel weak form quadrature element is proposed for non-classical strain gradient Euler-Bernoulli beam theories. The element is formulated with the aid of variational principles and has displacement as the only degree of freedom in the element domain and displacement, slope and curvature at the boundaries. All the classical and non-classical support conditions associated with the gradient beam theory are represented accurately. The Gauss-Lobatto-Legendre quadrature points are considered as element nodes and also used for numerical integration of the element matrices. Numerical examples on bending, free vibration and stability analysis of gradient beams are presented to demonstrate the efficiency and accuracy of the proposed element. To substantiate the generality of the element, beams with discontinuity in loading and geometry are examined
Gamma-irradiation induced modifications in structural and magnetic properties of nanocrystalline Mn0.5Zn0.5SmxFe2-xO4 ceramics
No full textThe changes in structure, infrared absorption and magnetic property of nanocrystalline Mn0.5Zn0.5SmxFe2-xO4 (x = 0.01, 0.03 and 0.05) ceramics were studied after different doses (0, 15 and 25 kGy) of gamma-irradiation. The samples were prepared by solution combustion route. We observed that up to the highest studied dose (25 kGy) of y-irradiation all the samples retain the cubic spinel (Fd-3m) structure as of the pristine samples, however, the lattice parameter decreases. Furthermore, we observed the metastability of Sm (and Mn) atoms at the octahedral sites. By Sm3+ doping the saturation magnetization of the pristine samples decreases, but the magnetic coercivity increases drastically, indicating enhancement of magnetic anisotropy. After gamma-irradiation the magnetic anisotropy vanishes completely and the sample behaves super-paramagnetically with a small variation in saturation magnetization. Our results are important to understand the behavior and stability of the magnetic hardness created by Sm3+ doping in soft magnetic Mn-Zn ferrite ceramics
Adaptive Dielectric Thin Film Transistors-A Self-Configuring Device for Low Power Electrostatic Discharge Protection
No full textLarge area and flexible electronic systems are widely used in applications such as displays, image sensors, wearable electronics and energy harvesting systems. A key element in many of these systems is the electrostatic discharge protection circuit. The conventional protection circuit uses large aspect-ratio diode connected thin film transistors that offer a low resistance path to the surge current but also does the same to signals during normal system operation resulting in power loss. Here we describe as well as demonstrate the feasibility of a novel idea for electrostatic discharge protection involving an adaptive dielectric thin film transistor that self-configures itself to a low resistance state during an electrostatic discharge event and a high resistance state during normal operation without external control. This results in 1000-10000 times the power savings compared to diode connected TFTs