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Investigation of different inputs and a new release policy in the proposed simulation model for wafer fabrication system
No full textThis paper investigates the effect of different inputs on selected performance metrics such as cycle time, WIP level and throughput in the processes of semiconductor wafer fab by developing a simulation model of representative but fictitious semiconductor wafer fab. The different inputs include arrival rate, arrival distribution, processing time, maintenance schedule, operator schedule, batch size, dispatching rule and release policy. Simulation results show that the relationship between inputs and system performance metrics, considered in this study, are extremely complex particularly for the inputs maintenance schedule, operator schedule and batch size. An overall result shows that dispatching rule and closed loop release policy can significamtly improve the performance of wafer fabrication system. However; major improvement comes from closed loop release policy. Accordingly, this paper presents a new closed loop release policy called as constant batch machine workload (CONSTBWL) to improve the performance of wafer fab. The behaviour of CONSTBWL is analysed in combination with dispatching rules using the proposed simulation model for wafer fab. Simulation results show that CONSTBWL policy outperformed traditional release policies in terms of the average cycle time, the work in process (WIP) level and the standard deviation of WIP level under a prescribed throughput level. Furthermore, the analysis of the results indicated that a good shop floor performance can be achieved with a right combination of closed loop release policy and simple dispatching rules with respect to the choice of performance metrics
Structural mechanism behind piezoelectric enhancement in off-stoichiometric Na0.5Bi0.5TiO3 based lead-free piezoceramics
No full textWhile studies in the past have shown that certain kinds of off-stoichiometry enhance the piezoelectric response of the lead-free piezoceramic Na0.5Bi0.5TiO3 (NBT), there is a lack of clarity regarding the mechanism associated with this interesting phenomenon from the fundamental structural perspective. In this paper, we have investigated this issue comprehensively and succeeded in establishing a mutual correspondence between off-stoichiometry, grain size, crystal structure, dielectric and piezoelectric properties in Na0.5Bi0.5TiO3 (NBT). Of the four different types of off-stoichiometric samples synthesized as per nominal formulae namely Na0.5+xBi0.5TiO3 (Na-excess Na-series), Na0.5-xBi0.5TiO3 (Na-deficient Na-series), Na0.5Bi0.5+xTiO3 (Bi-excess Bi-series), and Na0.5Bi0.5+xTiO3 (Bi-deficient Bi-series), the best piezoelectric response (d(33) similar to 100 pC/N) was obtained in the Na-deficient series with x = 0.04. We succeeded in establishing the structural link between off-stoichiometry and piezoelectricity of this series by examining the structural state of the specimens in their poled state. We show that the off-stoichiometric compositions exhibiting higher piezoelectric response contain a higher fraction of the disordered ferroelectric phase coexisting with the field stabilized long-range ferroelectric (R3c) order. Beyond the critical off-stoichiometry (x > 0.04), the dominance of the structural disorder collapses the piezoelectric response of the system. We also show that what can be achieved by off-stoichiometry can as well be achieved by reducing the grain size of stoichiometric NBT. Our results suggest that the enhanced piezoelectric response of the off-stoichiometric compositions is due to their reduced grain size as compared to the stoichiometric composition, and that the nature of the defect species has a secondary role, if any. We found the same phenomenon/mechanism to be operative in the off-stoichiometric morphotropic phase boundary composition 0.94Na(0.5)Bi(0.5)TiO(3)-0.06BaTiO(3) (NBT-6BT). While our experiments confirm the role of the surviving structural heterogeneity (after poling) as an important contributing factor which enhances the piezoelectric response of NBT-based lead-free piezoceramics, we also use dielectric dispersion as a tool to show that the off-stoichiometric composition exhibiting highest piezoelectric response is characterized by maximum suppression of the disordered phase by the poling field. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Morphology controlling of < 111 >-3C-SiC films by HMDS flow rate in LCVD
No full textMorphology of < 111 >-oriented 3C-SiC films was transformed from mosaic to whisker to cauliflower-like with the increased flow rate (f) of hexametyldisilane (HMDS) in the process of laser chemical vapor deposition (LCVD). The SiC whiskers were naturally sharp hexagonal pyramids with average height of 250 nm and an aspect ratio in the range of 5 to 10, with a density of 1.3 x 10(8) mm(-2). The influence mechanism of f on the surface morphology, as well as the growth mechanism of SiC whiskers, was discussed
A compact pitch and time representation for melodic contours in Indian art music
No full textPredominant melody offers a complete representation of melodic contours of heterophonic Indian Art Music (IAM). A compact representation of melodic contours while preserving raga characteristics is proposed. Such representations have applications in music transcription, analysis, and synthesis. Contours are quantized on a pitch-time grid after normalizing critical points with tonic and rhythmic pulse period estimates. Non-uniform quantization intervals are selected from pitch and time scales prevalent in IAM, while accommodating pitch and inter-note-interval variations on pitch-time grid. An evaluation of quantized-reconstructed contours through listening tests by trained musicians shows raga preserving capabilities of the proposed approach in spite of alterations in contour shapes. (C) 2019 Acoustical Society of America
Chiral phase transition of (2+1)-flavor QCD
No full textWe present here results on the determination of the critical temperature in the chiral limit for (2+1)-flavor QCD. We propose two novel estimators of the chiral critical temperature where quark mass dependence is strongly suppressed compared to the conventional estimator using pseudo-critical temperatures. We have used the HISQ/tree action for the numerical simulation with lattices with three different temporal extent N-tau = 6, 8, 12 and varied the aspect ratio over the range 4 <= N-sigma/N-tau <= 8. To approach the chiral limit, the light quark mass has been decreased keeping the strange quark mass fixed at its physical value. Our simulations correspond to the range of pion masses, 55 MeV <= m(pi) <= 160 MeV
Beyond nPDFs effects: Prompt J/psi and psi(2S) production in pPb and pp collisions
No full textA multi-dimensional analysis of prompt charmonia in pp and pPb collisions at root s(NN) = 5.02 TeV with the CMS detector is presented. The pPb differential cross-sections of prompt J/psi are shown in a wide kinematic region, for transverse momentum p(T) spanning from 2 to 30 GeV/c and a rapidity interval between -2.4 to 1.93 in the center of mass of the collision. The final results on prompt psi/(2S) meson production cross section in pp and pPb collisions at 5.02 TeV are also reported as a function of p(T) and rapidity, for p(T) from 4 to 30 GeV/c. The nuclear modification factor is found to be smaller than that of prompt J/psi in all measured bins, especially at low p(T) and at backward rapidity. Such a different behaviour between the ground and excited states cannot be reproduced considering nPDF effects alone
Role of CO2 methanation into the kinetics of preferential CO oxidation on Cu/Co3O4
No full textIn the present study, cobalt oxide (Co3O4) and Cu substituted Co3O4 were synthesized using sonochemical method. The role of Cu substitution was studied for CO oxidation in absence of H-2 as well as in H-2 rich conditions (PrOx). The synthesized catalysts were characterized by XRD, XPS, TEM and BET. The role of side reactions such as H-2 oxidation and CO2 methanation in inhibiting the CO oxidation reaction were discussed. H-2 - TPR and in situ FTIR were conducted to understand the reducible nature of the support and reaction mechanism. The intermediate species such as carbonates, bicarbonates, formates play an important role for CO oxidation under H-2 rich conditions. Further, the utilization of atomic hydrogen by surface CO2 species, enhanced the methane formation. A detailed reaction mechanism was proposed for both CO oxidation and PrOx conditions with the insights obtained from in situ FTIR. 3% Cu/Co3O4 showed high stability for CO oxidation under hydrogen rich conditions for 50 h at 170 degrees C as well as in methanation prone region at 200 degrees C
Light trapping in photovoltaic devices with weak dielectric absorbers: Nanostructured dielectric and metal interfaces
No full textNanostructured designs provide new possibilities to improve light absorption in thin film photovoltaic devices. However, the underlying design rules are not well established. Most thin film photovoltaic absorbers are weak dielectrics in which light trapping is a challenge, owing to lower density of admissible trapped waveguide modes. We consider a nanostructured bulk heterojunction as a representative example of the weak dielectric systems. We show using a combination of theoretical simulations and experiments that such a weak dielectric photovoltaic system built on a nanostructured transparent substrate can enhance light trapping via nano-scale morphologies at both the dielectric light entry interface and at the rear absorber-metal electrode interfaces. Our simulations predict an enhancement exceeding 80% in the photocurrent density generated per unit absorber volume, for absorber thickness in the range 100-200 nm. This thickness range appears to be optimal for most thin-film solar cells. Our experiments based on monolithic nanostructured substrates showed good agreement with the predictions of the model. Broadband enhancement in photocurrent was obtained only for thinner absorbers which allowed the formation of nanoscale interfaces on the front and rear interfaces. Further, we have studied the role of the nano-scale curvature through simulations. It was seen that the convex nano-domes result in the best optoelectronic performance with similar to 14% improvement in photocurrent and similar to 15% improvement in the fill factor leading to about 30% improvement in the power conversion efficiency. This is due to an improved absorption in conjunction with about 38% drop in the series resistance. This study shows using that in the case of weak-dielectric absorbers, it is useful to have nanoscale interfaces of optimal curvature at both the front and rear absorber contacts. The associated design rules for simultaneous improvement of optical and electrical performances are established
A Soft-Switched High-Frequency Link Single-Stage Three-Phase Inverter for Grid Integration of Utility Scale Renewables
No full textA novel single-stage high-frequency link three-phase (3 phi) inverter along with a modulation strategy is presented in this paper. The topology is targeted for grid integration of utility scale renewable and alternative energy sources like solar, fuel cell, and wind, where the power flow is unidirectional (from dc to ac). The primary side converter has a 3 phi voltage source inverter (VSI) structure along with an additional half-bridge leg. Sinusoidal pulsewidth modulation is implemented in the primary side converter. The three legs of the primary side VSI are zero voltage switched (ZVS) for most part of the line cycle. The additional half bridge leg is ZVS over the complete line cycle. The active switches in secondary side converter are line frequency switched and thus results in negligible switching loss. The converter switching process is described in detail to show the soft-switching of the primary side converter using the device capacitances and leakage inductances of the high-frequency transformers (HFTs). The HFT galvanic isolation results in high power density. A 4-kW laboratory scale hardware prototype is built and testedwith the proposed modulation strategy. The experimental results are presented to verify the converter operation