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End corrections for double-tuning of the same-end inlet-outlet muffler
No full textTransmission loss spectrum of a simple expansion chamber (SEC) muffler is characterized by periodic domes. In recent years, it has been shown that by extending the inlet pipe and outlet pipe of the SEC inwards by nearly half and quarter lengths (L/2 and L/4) into the chamber, it is possible to raise three-fourths of all the IL-troughs, thereby ensuring a wide-band TL spectrum. This has been called Double-Tuning of the SEC. In practice, physical lengths of the extended inlet and extended outlet are made shorter than L/2 and L/4 by end correction in order to account for the higher-order evanescent modes at the two junctions. In this paper, making use of the three-dimensional (3-D) finite element method (FEM), general parametric expressions have been developed for the end corrections of the two junctions of the same-end inlet-outlet (SEIO) chamber, or flow-reversal chamber, in order to double-tune it on the lines of the co-axial opposite-ends inlet-outlet chamber muffler. The 3-D finite element mesh convergence has been validated against the available experimental TL spectra. This study is perhaps the first known attempt at double-tuning of the same-end inlet-outlet (SEIO) chamber muffler
Minimization of Switched Capacitor Voltage Ripple in a Multilevel Dodecagonal Voltage Space Vector Structure for Drives
No full textA multilevel dodecagonal voltage space vector generation scheme for variable-speed drive applications with single-dc-link operation requires a large value of capacitance for cascaded H-bridge (CHB) filters, when operated at lower speeds. In existing schemes, the multilevel dodecagonal structure is obtained by cascading a flying capacitor inverter with a CHB. In this paper, a new scheme has been proposed to minimize the capacitance requirement for full speed operation by creating vector redundancies using modular and equal voltage CHBs. Also, an algorithm has been developed to optimize the selection of vector redundancies among the CHBs in order to minimize the voltage ripple of the floating capacitors. The proposed algorithm considers instantaneous capacitor voltages and phase currents for optimal selection of vector redundancies. A mathematical model for capacitor voltage deviation is presented, and the effectiveness of the proposed algorithm is verified in both the simulation and the experiment
Investigation of superconducting gap structure in HfIrSi using muon spin relaxation/rotation
No full textWe have investigated the superconducting state of HfIrSi using magnetization, specific heat, muon spin rotation and relaxation (SR) measurements. Superconductivity was observed at K in both specific heat and magnetization measurements. From an analysis of the transverse-field SR data, it is clear that the temperature variation of superfluid density is well fitted by an isotropic Bardeen?Cooper?Schrieffer (BCS) type s-wave gap structure. The superconducting carrier density m(?3), the magnetic penetration depth, nm, and the effective mass, , were calculated from the TF-SR data. Zero-field SR data for HfIrSi reveal the absence of any spontaneous magnetic moments below , indicating that time-reversal symmetry (TRS) is preserved in the superconducting state of HfIrSi. Theoretical investigations suggest that the Hf and Ir atoms hybridize strongly along the c-axis, and that this is responsible for the strong three-dimensionality of this system which screens the Coulomb interaction. As a result, despite the presence of d-electrons in HfIrSi, these correlation effects are weakened, making the electron-phonon coupling more important
Controlled growth of 1D-ZnO nanotubes using one-step hot plate technique for CZTS heterojunction solar cells
No full textPresent work reports a simple, rapid, one-step hot plate technique for systematic growth transformation of highly oriented ZnO nanorods (ZNRs) into ZnO nano tubes (ZNTs). The controlled growth of ZnO nanostructures (nanorods and nanotubes) was achieved at low temperature (90 degrees C) in a short time (1hr) in a sealed weighing bottle (100 ml). It is observed that as the Zinc precursor concentration increases, a vertically grown ZnR morphology evolves into ZNT. The crystal structure of as-grown ZnO nanostructures, surface morphology, phase, and optical energy gap were respectively characterized by XRD, FESEM, Raman, XPS, CL and UV-Vis spectroscopy. Grown nanostructures are further explored for their application in CZTS based heterojunction photovoltaics
Electric field enabled manipulation of CNT alignment in epoxy matrix: Methodology and mechanical characterization
No full textThe alignment of carbon nanotubes (CNTs) in polymer matrix is an effective way to utilize their anisotropic properties. In this study, a CNT alignment methodology based on the use of a non-uniform electric field is presented. The manipulation of CNT behaviour in an epoxy matrix was accomplished based on the principle of dielectrophoresis. The effectiveness of the technique was assessed by determining the tensile strength and fracture toughness (KIC) of aligned CNT/epoxy composites samples prepared using this method. Tensile tests revealed an increase in tensile strength of nanocomposites with increasing CNT loading content up to 0.1 wt. CNT. A ~ 27 increase in tensile strength in CNT nanocomposite samples containing 0.1 wt. CNTs with respect to that of neat resin was observed. The fracture toughness values were also observed to increase with increasing CNT loading content. A ~ 50 increase in KIC value in nanocomposites containing 0.5 wt. CNTs was observed as compared to that of neat resin. The results indicate that the method can be effectively used to preferentially align CNTs in a polymer matrix. © CCM 2020 - 18th European Conference on Composite Materials. All rights reserved
Quantitative earthquake-like statistical properties of the flow of soft materials below yield stress
No full textThe flow behavior of soft materials below the yield stress can be rich and is not fully understood. Here, we report shear-stress-induced reorganization of three-dimensional solid-like soft materials formed by closely packed nematic domains of surfactant micelles and a repulsive Wigner glass formed by anisotropic clay nano-discs having ionic interactions. The creep response of both the systems below the yield stress results in angular velocity fluctuations of the shearing plate showing large temporal burst-like events that resemble seismic foreshocks-aftershocks data measuring the ground motion during earthquake avalanches. We find that the statistical properties of the quake events inside such a burst map on to the scaling relations for magnitude and frequency distribution of earthquakes, given by Gutenberg-Richter and Omori laws, and follow a power-law distribution of the inter-occurrence waiting time. In situ polarized optical microscopy reveals that during these events the system self-organizes to a much stronger solid-like state
Broadband optical single sideband generation using an ultra high shape-factor self coupled ring resonator
No full textIn this study, we realize an integrated generation of optical Single SideBand with Carrier (SSB+C) signal for microwave photonics applications. It has been achieved using a Micro Ring Modulator (MRM) combined with a cavity based wavelength selective filter. MRM, when applied with an RF input, results in a Double SideBand with Carrier (DSB+C) signal where one sideband is suppressed by applying this signal to the filter. The filter has been created using a single resonance-split self-coupled cavity with an extremely high shape factor of 0.69. The sideband suppression ratio between DSB+C and SSB+C ranges from 16 dB to 55 dB for a frequency range of 4 GHz to 20 GHz. Tunable suppression ratio of 21 dB has been achieved at a fixed frequency of 15 GHz. Dynamic range performance of the generated signal has been evaluated at a noise floor of -156 dBm. The dynamic range remains stable in the range of 1 GHz - 5 GHz at � 80 dB.Hz2�3
Magnetocaloric effect in molecular spin clusters and their assemblies: Exact and Monte Carlo studies using exact cluster eigenstates
No full textFrustrated magnetic molecules are promising alternatives to refrigerant materials for low temperature magnetic refrigeration. We investigate the magnetocaloric effect (MCE) in un-frustrated and frustrated spin clusters formed from spin chains of six sites, with site spins s=1,3/2 and 2 possessing site diagonal anisotropies and anisotropic exchange interactions, using exact diagonalization method. We also study MCE in spin clusters, on a chain, a 2-D square lattice and a 3-D cubic lattice with spin-dipolar interactions by a Monte Carlo method in spin-1 systems which uses exact eigenstates of a cluster. The magnetocaloric effect is closely related to the magnetic Grüneisen parameter �H. In this paper, we compute the magnetic Grüneisen parameter �H, and study its dependence on exchange anisotropy and spin-dipolar interaction. With increase of exchange anisotropy, the maxima in �H shifts to higher magnetic fields and becomes a sharp singularity. The singularities in �H correlate with cusps in the entropy as a function of magnetic field strength, and with crossover in the magnetization in the ground state in isolated clusters. The first maximum in �H shifts to lower fields as we increase spin-dipolar interaction. The first maximum in �H also shifts to lower magnetic field strength as the magnitude of the site spin increases. We show the dependence of �H on the dimensionality of the lattice for a fixed lattice constant
Selective Electron or Hole Conduction in Tungsten Diselenide (WSe2) Field-Effect Transistors by Sulfur-Assisted Metal-Induced Gap State Engineering
No full textFor semiconductor industry to replace silicon CMOS integrated circuits by 2-D semiconductors or transition metal dichalcogenides (TMDs), TMD-based n-FETs as well as p-FETs having performance better than Si FETs are a must. While a lot of literature demonstrates n-channel characteristics, the major roadblocks in the realization of TMD-based CMOS integrated circuit are the lack of approach to realize p-channel transistors having performance comparable to n-channel transistors, all realized over the same TMD substrate. To address this, we propose a new technique by engineering WSe2/metal interface to realize WSe2-based high-performance p-and n-channel transistors and therefore unveil its potential toward CMOS-integrated technology. The technique involves a dry process, based on the chemistry between the sulfur atom and WSe2 surface, that induces unique metal-induced gap states in the source/drain (S/D) contact area, which causes improved hole (electron) injection when Cr (Ni) as S/D metal was used. This has enabled the controlled realization of high-performance WSe2 FETs with desired polarity (N, P, or ambipolar), which solely depends on the contact metal used and contact engineering (CE)/surface engineering. Fundamental investigations on the effect of the proposed CE on metal-WSe2 interface revealed interesting and counter-intuitive facts, which very well corroborate with experimental observations
Deep Submicron Normally Off AlGaN/GaN MOSFET on Silicon with VTH > 5V and On-Current > 0.5 A mm�1
No full textA submicron gate normally off AlGaN/GaN high-electron-mobility transistor (HEMT) with a high on-current and high threshold voltage (VTH) is demonstrated. The high-performance device is realized utilizing a gate recess with a length and depth of 200 and 124 nm, respectively. The recess-etched region has a roughness of 0.7 nm. Various recess-etch depths and dielectric annealing conditions are used to tune VTH. The optimized device exhibits an on-current and VTH of 500 mA mm�1 and 5 V, respectively. The measured breakdown characteristics of the devices and their limitations are investigated using 2D-technology computer-aided design (TCAD) device simulation. The penetration of the residual electric field in most of the recess region can be the reason for the premature breakdown of deeply scaled recess-gate e-mode HEMTs