20 research outputs found
Fabrication of a Flexible UV Band-Pass Filter Using Surface Plasmon Metal-Polymer Nanocomposite Films for Promising Laser Applications
No full textWe introduce a strategy for the fabrication of silver/polycarbonate (Ag/PC) nanocomposite flexible films of (20 +/- 0.01) mu m thickness with different filling factor of surface plasmon metal using customized solution cast thermal evaporation method. Structural characterizations confirmed the good crystallinity with cubic phase of Ag nanoparticles in PC films. Moreover, the microstructural evolutions of nanocomposite films are investigated by transmission electron microscopy, which indicates that the metal fraction is in the form of fractals. Additionally, the surface plasmonic behavior of nanocomposite films has been explored in detail to examine the distribution of Ag nanoparticles in PC film by spectroscopic technique. Furthermore, the obtained transmittance spectral features of this nanocomposite film are suitable for the applications of band-pass filter at 320 nm UV range, which is highly desirable for a HeCd laser
High-Order Numerical Schemes for Compressible Flows
No full textHigh-order numerical methods for Computational Fluid Dynamics have undergone significant fundamental developments over the last two decades owing to combined efforts from the applied mathematics and engineering communities. Even though low-order numerical methods are still the standard in industry, the increased requirements of engineering applications have led to significant scientific interest in developing efficient and robust numerical methods. Applications that would benefit from high-order numerical methods include Direct Numerical Simulations (DNS), Large Eddy simulations (LES), Computational Aero-Acoustics (CAA) and vortex dominated flows. The objective of this thesis is to successfully implement and validate a fifth order traditional WENO scheme in a finite volume framework, for a solver currently being developed in the Aerodynamics group of TU Delft. A detailed literature study of classical numerical schemes has been performed along with a study of the traditional WENO schemes. The quality of results using the fifth order scheme is studied for a variety of test cases to study the shock capturing ability of the scheme. Implementing the finite volume WENO schemes includes the calculation of numerical flux at cell faces using Gaussian quadrature formulas. The effect of varying the number of Gaussian quadrature points while calculating the numerical flux is investigated. Also, the effect of the approximate Riemann solvers on the quality of results is studied by implementing four different Riemann solvers and studying the results for different test cases using these Riemann solvers. The test cases are governed by the inviscid Euler equations and deals with flow in the compressible regime. They involve shocks, other discontinuities and often also complicated structures in the smooth part of the solution which tests the design of the schemes to be non-oscillatory at the discontinuities and still gives a high order of accuracy in the smooth parts of the flow. Convergence tests of the error for test cases using the linear advection equation is used to study the order of accuracy of the scheme using different number of Gaussian quadrature points. The tests clearly show that the order of accuracy remains the same irrespective of the number of quadrature points used. This result is important as it allows simulation run with just one quadrature point which is less expensive, and saves memory. This result is highly relevant while running test cases for LES where very fine grids have to be used. WENO schemes have been considered to be too dissipative for LES in their traditional form. This is indeed true as seen by Kelvin-Helmholtz type small scale vortices (which are characteristic of high Reynolds number flows), even in the test cases using the inviscid Euler equations, due to the inherent dissipation in the schemes. However, this could be seen as motivation for using the WENO schemes for Implicit LES where no explicit sub-grid scale models are used to represent the unresolved scales. The different Riemann solvers exhibit different levels of dissipation and recommendations are made for the choice of Riemann solvers according to the application.Aerospace EngineeringFlight Performance and Propulsio
Some applications in laser technology
No full textThe discovery of the Photoacoustic (PA) effect was a remarkable
achievement and was relegated to the scientific footnotes of the nineteenth
century. However, after the advent of lasers and sophisticated
electronics this effect was rediscovered and it has established itself
as an important research and analytical tool in numerous areas, including
physics, chemistry, biology and medicine. Quite recently, this phenomenon
has made its impact in the field of laser technology for applications
such as the developments of highly efficient active media for
lasers, high quality optics and sensitive laser power monitoring devices.
This thesis presents the work carried out by the author in this field
during the past few years at the Department of Physics in Cochin University
of Science and Technology.
The studies discussed here are mostly based on the development
of a sensitive PA laser power meter and its various applications using
different laser systems available in the laboratory. This includes the
development of a current regulated CW C0 laser and its application
in material processing. The thesis contains seven chapters which by and large are self
contained with separate abstracts and references. The first chapter
which is divided into two parts presents an introduction to the PA effect
and its present status. Part A reviews the basic theory of laser and
gives a sum mary of various lasers and their applications. Part B presents
a brief description of PA effect and its suitability as a spectroscopic
tool followed by its applications to various branches of science and
technology.Cochin
University of Science and TechnologyDepartment of Physics, Cochin
University of Science and Technolog
New Insights into the Triton X-100 Induced Chemical Exfoliation of MoS2 to Derive Highly Luminescent Nanosheets
No full textThe exfoliation of two dimensional (2D) transition metal dichalcogenides (TMDs) into mono- or few-layers without compromising their semiconductor properties has momentous interest for both point of view; fundamental studies and further implementation in practical applications. Herein, we reported a novel and inexpensive approach for high yield nanosheets from bulk MoS2 to few layers of strong luminescent MoS2 nanosheets using Triton X-100 as a surfactant with tailoring the bulk band gap 1.2 eV to 1.79 eV of few layers of nanosheets after chemical exfoliation process, which can be easily scaled-up in large quantity. The microstructural results reveal that the exfoliated nanosheets have thickness in the range of few layers and lateral dimension in the range of few hundred nanometers. Our findings may offer a new innovative one setup chemical exfoliation process to design a few layer of MoS2 nanosheets without suppressing luminescent properties, which is highly desirable for the next generation optoelectronic devices
Examining effects of air pollution on photovoltaic systems via interpretable random forest model
No full textIn: Renewable Energy. Amsterdam : Elsevier B.V., 2024. ISSN 0960-1481. No. 232 (2024), pp. 1-10.Renewable energy plays a vital role in power generation and solar photovoltaic systems due to resource availability throughout the year. This work aims to investigate the impact of air pollutants and meteorological parameters on the performance of the photovoltaic systems locally, taking into consideration the advantages of the photovoltaic power potential of the SW part of Romania, where Craiova is located (average solar radiation intensity >1350 kWh/m2/year). This study is based on a one-year dataset provided by a sensor that monitors particulate matter concentrations, volatile organic compounds, dioxide of carbon, ozone, noise, formaldehyde and three climate parameters (temperature, pressure, and relative humidity). The research methodology applies an innovative interpretable random forest model emphasising the implications of air pollution for photovoltaic systems. The proposed machine learning model was trained to predict the particulate matter level in air based on the basic environmental variable measurements. The study presents six random forest models of varying complexity, which reach the accuracy of classification for the selected problem up to 99 %, and applies the Shapley Additive Explanations technique to interpret the decision-making model. The observation regarding the highest concentration of particulate matter occurring during cold months, which typically do not align with peak solar irradiance, underscores the importance of considering various environmental factors in solar energy planning. With its practical implications, this insight offers decision-makers valuable information about the feasibility of optimising solar energy generation despite seasonal variations in air pollution levels, directly addressing their needs and concerns
Effect of Collagen Supplementation in Broiler Feed: Influence on Productive Performance and Muscle Quality in Broiler Chicken
No full textThe Effect of Stir-Squeeze Casting Process Parameters on Mechanical Property and Density of Aluminum Matrix Composite
No full textThis present investigation focusing on preparation of Al-based hybrid composites in which Al6082 is engaged as the main alloy reinforced with two reinforcements of ZrSiO₄/TiC. The combination of the stir-squeeze process helps to make different specimen by change of four parameters such as stir speed, stir time, reinforcements, and squeeze pressure. In this process, two reinforcements are reserved as constant about 7.5 wt%. The four levels of each parameter are stir speed (300, 400, 500, and 600 rpm), stir time (10, 15, 20, and 25 min), reinforcement (2.5, 5, 7.5, and 10 wt%), and squeeze pressure (50, 60,70, and 80 MPa). According to the L16 orthogonal array Taguchi design, the specimens are created to analyze the mechanical properties of tensile strength and hardness along with porosity. In addition, the optimization technique is used to determine the optimal parameter on improving tensile strength. The optimization process can be assisted by the software namely Minitab-17 which helps to study analysis of variance, regression model, and contour plots. The observed result of ANOVA showed that stir speed (41.8%) is the maximum influenced parameter that increases TS, followed by squeeze pressure (25.7%), stir time (12.7%), and reinforcement (1.96%), and optimum tensile strength is found at the parameters of stir speed 600 rpm, stir time 10 min, reinforcement 2.5 wt%, and squeeze pressure 80 MPa. The fractured surface of tensile strength also examined by the SEM test. The combined parameters of S4-T1-R1-P4 achieve the highest TS, and it is observed that there are nearly no pore defects and good diffusion as a result of the reinforcements to be properly mixed. It is noticeable that the TiC and Al 6082 matrix, as well as the various ZrSiO4 exhibit stronger bonds
Fabrication of a Flexible UV Band-Pass Filter Using Surface Plasmon Metal–Polymer Nanocomposite Films for Promising Laser Applications
No full textWe introduce a strategy for the fabrication
of silver/polycarbonate (Ag/PC) nanocomposite flexible films of (20
± 0.01) μm thickness with different filling factor of surface
plasmon metal using customized solution cast–thermal evaporation
method. Structural characterizations confirmed the good crystallinity
with cubic phase of Ag nanoparticles in PC films. Moreover, the microstructural
evolutions of nanocomposite films are investigated by transmission
electron microscopy, which indicates that the metal fraction is in
the form of fractals. Additionally, the surface plasmonic behavior
of nanocomposite films has been explored in detail to examine the
distribution of Ag nanoparticles in PC film by spectroscopic technique.
Furthermore, the obtained transmittance spectral features of this
nanocomposite film are suitable for the applications of band-pass
filter at 320 nm UV range, which is highly desirable for a HeCd laser
High-frequency vertical profiling of meteorological parameters using AMF1 facility during RAWEX-GVAX at ARIES, Nainital
No full textAn extensive field study, RAWEX-GVAX, was carried out during a 10-month (June 2011-March 2012) campaign at ARIES, Nainital and observations on a wide range of parameters like physical and optical properties of aerosols, meteorological parameters and boundary layer evolution were made. This work presents results obtained from high-frequency (four launches per day), balloon-borne observations of meteorological parameters (pressure, temperature, relative humidity, wind speed and wind direction). These observations show wind speed as high as 84 m/s near the subtropical jet. It is shown that reanalysis wind speeds are in better agreement at 250 hPa (altitude of subtropical jet) than those above or below this value (100 hPa or 500 hPa). These observations also demonstrate that AIRS-derived temperature profiles are negatively biased in the lower altitude region, whereas they are positively biased near the tropopause. WRF simulated results are able to capture variations in temperature, humidity and wind speed profile reasonable well. WRF and AIRS-derived tropopause height, tropopause pressure and tropopause temperature also show agreement with radiosonde estimates
