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On the Development of Improved Mammogram Detection System using Machine Learning Approaches
No full textIn recent years, breast cancer has become one of the most prevalent causes of death among women. Once the malignant cells are developed in the breast, it spreads to different body organs very quickly. Detection at the early stages and diagnosis is the only way to prevent mortality. Mammography, a noninvasive, non-radioactive imaging technique, has been widely used in diagnosing breast tissue abnormalities. Manual diagnosis based on visual inspection of mammograms is time-consuming, inconvenient, and necessitates skilled supervision. Thus, automated detection using modern imaging, machine learning, and deep learning approaches has become vital for quick, reliable, and correct conclusions. In the last decade, the development of automated computer-aided diagnosis/detection (CAD) models has progressed remarkably. However, there is still an opportunity for improvement in terms of automation, usability, and accuracy. This dissertation is aimed at designing automated CAD frameworks that will help radiologists validate their clinical diagnoses. This research primarily proposes various feature extraction techniques and classifiers for detecting breast tumors in mammography images. The first contribution consists of three frameworks with various feature extraction techniques like discrete wavelet transform (DWT), lifting wavelet transform (LWT), and fast curvelet transforms (FCT). For all frameworks, a combined feature reduction technique such as principal component analysis (PCA) and linear discriminant analysis (LDA) has been employed for feature vector computation. Finally, a simple and flexible learning scheme called the extreme learning algorithm (ELM), back-propagation neural network, k-nearest neighbors, and support vector machine have been used separately to obtain the classification accuracy. This contribution describes an empirical analysis of ELM with other classifiers. In the second contribution, a set of innovative hybrid classification systems proposes to reduce the bottleneck caused by extreme learning machines and contemporary meta-heuristic optimization techniques to classify mammogram images. The optimization techniques have been utilized to obtain the hidden node parameters of the ELM. Here, the same feature reduction technique is used as in the previous contribution. Different hybrid classification systems have examined the three handcrafted feature extraction techniques: DWT, LWT, and FCT. The third contribution is about designing a framework based on non-handcrafted features. Here, deep learning algorithms are used to solve the challenge of manually selecting appropriate features for mammogram classification. The different deep CNN models such as VGG-16, ResNet-50, and Inception-V3 have been utilized for feature extraction, and the same feature reduction method is applied as previous frameworks. Finally, various hybrid classifiers are used for the classification task. The final contribution involves designing a customized CNN model for multiclass mammogram images. This model is designed to extract high-level features from mammogram images automatically. End-to-end learning is facilitated by the proposed deep architectures, which aid in generating promising results. To evaluate the efficiency of each suggested CAD framework, a significant number of experiments have been conducted individually utilizing binary and multiclass mammogram classification. Various performance measurements have been used to compare the suggested CAD frameworks with existing standard techniques. Experimental results demonstrate that the proposed methodologies are superior to existing binary and multiclass breast cancer detection models. The customized CNN model removes manual handcrafted feature extraction issues and avoids feature reduction tasks. As a result, the proposed CAD frameworks are faster and can be used as an enhanced tool by clinicians to validate their diagnoses
Mechanical Behavior of Graphene Nanofiller Grafted Carbon Fiber Reinforced Polymer Composites
No full textGlobally fiber reinforced polymer (FRP) composites are drawing tremendous attention recently for their use in critical applications like structurals and bridges as a substitute for traditional metallic materials. They have an added advantage over traditional metals in terms of high corrosion resistance, greater strength and modulus. The use of carbon fiber reinforced polymer (CFRP) composites is progressively increasing in the fields of aerospace, cryogenic storage tanks, marine and so on because of their high specific strength, chemical resistance and thermal and electrical conductivity. The poor interfacial adhesion between reinforcing carbon fiber (CF) surface and polymer materials affects the interface dependent critical mechanical properties like interlaminar shear strength and flexural strength. The improvement in interfacial properties can be carried out by introducing a third phase into the composites, i.e., nanofiller. Currently, decoration of carbon fiber (CF) surface with graphene based nanofillers (GBNs) by electrophoretic deposition (EPD) route is a trend to enhance the interfacial performance of CFRP composites. The present investigation begins with assessing the improvement in the flexural and interlaminar properties of CFRP composites by surface modification of carbon fiber via EPD technique using different graphene based nanofillers like graphene (G), graphene oxide (G-O), graphene hydroxyl (G-OH) and graphene carboxyl (G-COOH) and selecting a better nanofiller out of these for further studies. The highest flexural strength and interlaminar shear strength (ILSS) were obtained for the G-COOH grafted CFRP (G-COOH/CFRP) composites, which were 9.6 % and 22.9 % higher than that of control CFRP composites, respectively. Thermo-mechanical analysis was conducted in the temperature range of 30 ºC to 180 ºC to understand the temperature dependent mechanical behavior of all the composites. FTIR analysis of nanofillers was carried out to confirm the functionalization of nano fillers. From the previous study, it was learnt that grafting G-COOH on carbon fiber surface by electrophoretic deposition (EPD) is a promising route to improve the mechanical properties of CFRP composites. Methyl violet (MV) was used in the cathodic EPD technique to maintain stability of the suspension and to impart a positive charge to the nanofillers there by facilitating the cathodic EPD. Before going for thermal annealing of decorated carbon fibers, they were washed with acetone to remove methyl violet. This step of removing MV was one of the longest time consuming step as it involves 24 hours of air drying, followed by washing with acetone. These steps might hinder the commercialization of cathodic EPD technique due to the long processing times involved. Therefore, in the current research study, an attempt was made to analyse the necessity of removing MV by washing the decorated fibers with acetone, post EPD and its effect on the mechanical behavior of the modified CFRP composite by carrying out flexural and short beam shear tests. The G-COOH/CFRP composite in which the MV was not washed has shown a decrement of 20.82 % and 4.90 % in ILSS and flexural strength respectively in comparison to neat CFRP composites. Carbon fiber surface topography was analysed using a scanning electron microscope (SEM) before and after acetone washing. Fractography analysis was carried out to understand the failure mechanism and dominant mode of failure using SEM. FTIR analysis of neat and G-COOH loaded epoxy was carried out to understand the effect of MV on the epoxy/G-COOH interface. The next objective was aimed at analysing the mechanical behavior of G-COOH/CFRP composites when they are tested in-situ at room temperature, cryogenic temperatures (CT) and elevated temperature (ET). Along with this, the effect of a prominent processing parameter, which was the nanofiller concentration in the EPD bath on the deposition morphology, and mechanical behavior of G-COOH/CFRP composites, was also studied. Experimental results showed that out of three different concentrations (0.5 g/L, 1.0 g/L, 1.5 g/L) used, composites made with 1.5 g/L bath concentration have shown the best mechanical behavior at both room temperature (RT) and cryogenic temperature (CT). At RT, improvements of 25.38 % and 17.02 % were observed in ILSS and flexural strength, respectively in comparison to neat CFRP composites. At CT, the highest improvements observed in ILSS and flexural strength were 20.78 % and 5.34 %, respectively in comparison to neat CFRP composites. Similarly, composites made with 1.5 g/L EPD bath concentration had shown a maximum improvement in energy absorbed before failure of 33.25 % at RT and 22.54 % at ET for flexural testing (flexural toughness) and in case of short beam shear tests (interlaminar toughness), improvements of 35 % at RT and 78 % at CT were observed in comparison to that of neat CFRP composites at respective test temperatures. However, at ET, modified composites exhibited lower flexural strength and interlaminar shear strength (ILSS) values in comparison to that of neat CFRP composites. Viscoelastic behavior of all composites was studied to understand bath concentration's effect on thermal behavior via dynamic mechanical thermal analysis (DMTA). Fractography of tested samples (both ET and RT) was performed utilizing a scanning electron microscope (SEM) to determine the prominent failure mode. As the next step towards a comprehensive understanding of EPD process, the effect of electrophoretic deposition time on the resultant carbon fiber surface morphology and mechanical behavior of G-COOH/CFRP composites was analysed at room temperature and elevated temperatures in this study. The laminates fabricated (both neat and modified) were subjected to short beam shear tests (SBS) at room temperature (RT) and different elevated temperatures (ET), i.e. 70 ºC, 100 ºC, 120 ºC and the role of deposition time at each testing temperature was also analysed. CFRP composites fabricated with 60 minutes of deposition time have shown an improvement of 35.0 % in ILSS, when compared to that of control specimen at RT. Modified composites showed a maximum improvement of 16 % and 13 % in ILSS values over neat CFRP composites at RT, 70 ºC and 120 ºC, respectively. However, interestingly at 100 ºC, modified composites have shown inferior shear behavior in comparison to neat CFRP composite. Scanning electron microscope (SEM) was used to observe the tested samples to find out the dominant mode of failure
Magnetic, Magnetodielectric and Lattice Dynamic Effect of Chemically Substituted Y Type Ba2Mg2Fe12O22 Hexaferrites
Get PDFIn the last few decades, multiferroic (MF) materials have attracted interesting attention due to their mutual control of electric and magnetic properties termed as magnetoelectric (ME) effect. This area of research is important in terms of potential technological applications such as spintronic devices, electronic devices, medical drug delivery, and ME sensors. Most MF materials exhibit high field control ME coupling below liquid nitrogen temperature, which is not appropriate for effective devices based on the ME effect. To realize useful devices based on the ME effect, it requires a low field control ME effect at RT. Amongst MF materials, hexaferrite is one such class of materials that exhibit low field control ME effect near or above RT. Interestingly, Y-type hexaferrite possesses a significantly low field control ME effect at RT, which has an advantage over several other single-phase MF materials. However, direct measurement of ME coupling is not an easy task as most MF materials are poor insulators. Hence, an alternative route to investigate ME coupling is to measure the influence of dielectric properties with an application of magnetic field termed as magnetodielectric (MD) effect. The Y-type Ba2Mg2Fe12O22 (BMF) hexaferrite has drawn significant attention recently due to its tuneable magnetic and ME properties upon suitable substitution at magnetic and non-magnetic sites. In this present thesis, a systematic investigation was carried out on magnetic and MD properties along with lattice dynamic effect of polycrystalline BMF sample. For the first time, a robust MD effect is reported in the BMF sample. The effect of Mn and Ni substitution following Ba2Mg2(Fe1-xMnx)12O22 (0 ≤ x ≤ 0.12) and Ba2Mg2-xNixFe12O22 (0 ≤ x ≤ 2.0) system respectively on magnetic, MD, and lattice dynamics properties were investigated in detail. Further, the effect of Sr and Mn co-doped Ba2-xSrxMg2Fe11.48Mn0.52O22 (0 ≤ x ≤ 1) on magnetic, MD, and lattice dynamics properties is also studied. All the samples were prepared using a conventional solid-state reaction route. The BMF exhibits irreversibility between ZFC and FC of magnetization below 270 K, and magnetization value decreases with lowering temperature following an anomaly at TII (170 K) and TI (25 K). The anomaly around 170 K indicates ferrimagnetic (FIM) to proper screw transition, while at 25 K denotes proper screw to longitudinal conical spin transition. Surprisingly, two distinct dielectric anomalies, near 25 K (TI) and 170 K (TII) are observed in the vicinity of magnetic spin phase transition, suggesting a strong coupling between dielectric and magnetic properties. The MD% vs. H data suggest the colossal MD% value at T > 200 K is mainly due to the Maxwell-Wagner (M-W) effect, while the butterfly loop at T < 200 K indicates the intrinsic MD effect in the sample. Further, the temperature-dependent Raman study confirms the absence of structural phase transition and the existence of possible spin-phonon coupling (SPC) in the sample. The Mn substitution modulates not only the superexchange angle near the boundary of magnetic blocks but also the magnetic transition temperature. The transition temperature TII increases from 170 K to 208 K, while TI decreases from 25 K to 15 K. The value of loss tangent decreases with increasing doping concentration at 300 K, i.e., ~60% and 180% in a decrease in 4% (BMFM4) and 8% (BMFM8) Mn-doped sample respectively as compared to BMF, suggesting the evolution of intrinsic feature. The presence of substantial intrinsic MD% (~6%) at 1.3 T at 300 K for a 4% Mn-doped sample is observed. The nature and strength of magnetoelectric coupling in BMFM4 and BMFM8 samples at 300 K is found to be biquadratic (P2M2), and the maximum strength of coupling is 3.09×10-4 emu2/g2 and 2.34×10-4 emu2/g2, respectively. Ni substitution in Ba2Mg2-xNixFe12O22 (0 ≤ x ≤ 2.0) enhances temperature TII from 170 K for x = 0 to 230 K for x = 2.0 suggesting Ni substitution progressively stabilizes the screw order. While TI increases from 25 K to 40 K with an increase doping up to x ≤ 1.0 and a sharp decrease is seen for x ≥ 1.0. The K value increases with an increase in doping up to x ≤ 1.5, and a sharp decrease is seen for x ≥ 1.5, which is due to the substitution of larger magnetic anisotropic Ni2+ ions in place of non-magnetic Mg2+. The observed contraction in few Raman modes (704 and 507 cm-1) is due to distortion produced by doping of Ni ions which is well confirmed by the decrement of lattice parameters (a, c) with an increase in Ni content. The frequency-dependent dielectric ɛrˊ´ data suggest that the M-W type conduction mechanism dominates near RT. In contrast, the Warburg-type conduction mechanism is prevalent in the low-temperature regime. The intrinsic MD
effect for the x = 1.0 sample is ~ 2 times greater than the x = 0 sample, and the range of frequency over which it is observed increases from 105 - 106 Hz to 103 - 106 Hz. Finally, the Sr and Mn co-substitution in Ba2 xSrxMg2Fe11.48Mn0.52O22 (0 ≤ x ≤ 1) enhances spin ordering transition temperature TI (TII) from 52 K (210 K) to 73 K (315 K). The presence of single cluster-glass transition at Tf1 (45 K) in the x = 0.25 sample. Interestingly, for the x > 0.25 sample, double cluster class transition is observed, one around Tf1 and the other at Tf2. The freezing temperature Tf1 decreases with an increase in x, while Tf2 increases substantially with x. The Ms value found to be decreased from 28.88 emu/g for x = 0.25 to 26.28 emu/g for x = 0.75 at 300 K. However, for x > 0.75 this value increases. Raman modes at 78, 135, 335, and 694 cm-1 show a gradual increase in Raman shift up to x = 0.75, but a drastic decrease is seen for x > 0.75. Along with enhanced magnetic properties, Sr doped sample shows better MD properties. The MD% value at RT increases with doping concentration up to x = 0.75 (MD% ~1.2); beyond that, its value decreases. The anomalous response of MD% associated with SPC is confirmed by the anomalous behavior of different Raman modes across the spin ordering transition temperatures. The H-dependent MD exhibits symmetric anomalies close to the H-induced transition indicating an exchange-striction phenomenon in the samples. Hence, the enhanced magnetic and low field control MD behavior at RT is exciting for exploring the ME devices based on hexaferrite
Secure and Reliable Energy Harvesting System Design for Sustainability in IoT for Smart Cities and Smart Villages
No full textThe Internet-of-Things (IoT) consists of a large number of different and heterogeneous devices under one umbrella. Building a typical architecture for the devices used in IoT is a challenge due to the involvement of a vast number of devices, layers, protocols, middleware, and software. The sensors in IoT have to monitor the activities regularly, making the end node devices energy hungry. Traditional fixed batteries get drained out in a limited time, requiring continuous replacement, thereby increasing the budget. Providing power to IoT things (i.e., sensors + their communications) is a challenge as batteries have a limited lifetime and maintenance, and disposal is costly and hazardous. System on chip (SoC) power requirements for IoT ultra-low-power realm are different and needs a lot of effort for the design engineers to provide uninterrupted power. The power requirements also include power conditioning in generating higher voltages on-chip, which is a massive challenge for on-chip peripherals and systems. Recently, harvesting natural energy is gaining more attention than other conventional approaches for sustainable Internet-of-Things (IoT). To face the challenges in current IoTs, the focus should also be on security and reliability in energy harvesting system (EHS) design. Security, reliability and energy consumption are the conflicting challenges in the design and operation as per the application requirements in IoT. A detailed discussion is carried out in selecting a appropriate energy source and power conditioning circuits suitable for on-chip implementation. The switched capacitor (SC) circuits are proved to be more beneficial for on-chip performance and to extract maximum power from the input. Hill-climbing and perturb & observe maximum power point tracking (MPPT) techniques are chosen due to their inherent advantages in extracting maximum power from the source. The proposed charge pump (CP) uses a two-phase clock with adiabatic-charging and charge-sharing principle, with separate body bias. The independent body bias of higher amplitude resolves the threshold voltage issues and the reverse current problem. This principle also reduces the charge transfer and charge-sharing losses. The control section monitors the load and also the recharging of the battery/super-capacitor. Low drop-out regulators (LDOs) are used to provide various regulated power to the load. In this thesis, a paradigm shift research that addresses secure self-sustainable solar energy harvesting system (EHS) with security and reliability mechanism is proposed. This design incorporates unique ID generation of a device, physically unclonable functions (PUFs) for the protection of EHS by enabling various modules along with a mechanism to detect recycled IC. Many reliability degrading factors influence the performance of EHS which includes ripples and attacks due to adversaries. The presence of ripples, intentional aging, and aggression due to hardware Trojan (A2) is addressed with proper detection and mitigation mechanisms. The secure and reliable EHS is designed in CMOS 90nm technology. The resulting output is in the range of 3 V to 3.55 V with an input 1 V to 1.5 V. The proposed EHS is consuming power under the micro-watt range that fulfills the ultra-low-power requirements of IoT smart nodes. In acquiring new skill set, a mixed-mode approach is adopted in designing the energy harvesting system that uses Verilog and Verilog-A to model the EHS. The modeled design has been implemented as a SoC for fabrication
Design and Development of a Cryogenic Decorticator Cum Grinder for Phytochemical Rich Myrobalan Fruit Powder
No full textMyrobalan (Terminalia chebula and Terminalia bellerica) fruits have many vital phytochemicals and nutraceuticals. These fruits have numerous medicinal uses in Ayurveda, Siddha, Unani, Tibetan, Chinese, and folklore medicines. Myrobalans are the essential constituents of the traditional herbal medicine named Triphala. Unit operations such as decortication and grinding are essential for proper utilization and value-addition of the myrobalan fruits. Due to lack of proper equipment, the decortication of the fruits is done manually using a hammer or stone. It is a labor-intensive and time-consuming process. It also increases the chance of contamination, making the product unsuitable for medicinal uses. After the decortication, the end products are ground to make powder. Currently, conventional methods are used for the grinding process. During the process, much heat is generated that denatures most of the heat-sensitive phytochemicals in the final product and makes it unsuitable for medicinal uses. Hence, there is a need to develop proper methods and equipment for optimum utilization of the myrobalan fruits. A new cryogenic decorticator-cum-grinding equipment was designed, developed, fabricated, and evaluated for myrobalan fruits to address the above issue. Various physical and engineering properties of the fruits, necessary for designing the equipment, were determined. Chemical and phytochemical properties were also determined. The equipment was designed using CATIA V5 (CAD, USA). It was fabricated with the support structure and contact parts made of mild steel and stainless steel (304 L). The equipment consists of a pre-cooling tunnel, decorticator, separator, and grinder. Liquid nitrogen was used in the pre-cooling tunnel, decorticator, and grinder sections to reduce the heat generated and loss of heat-sensitive phytochemicals during the operation. The performance of the equipment was evaluated, and the process parameters such as feed rate and liquid nitrogen dosage were optimized. The optimum grinding efficiency of 98.00% could be achieved at a 12.28 kg/hr feed rate and liquid nitrogen dosage of 0.72 L/kg of feed for T. chebula. Similarly, optimum grinding efficiency of 96.11% could be achieved at a feed rate of 12.86 kg/hr and liquid nitrogen dosage of 0.74 L/kg of feed for T. bellerica. The DPPH retention of the cryogenically ground powders of T. chebula and T. bellerica were 90.60 and 90.11%, respectively. The other phytochemical constituents, such as phenolic compounds, flavonoids, and tannin content, were higher in the cryogenically ground powders of T. chebula and T. bellerica than the powders obtained in the conventional method. Maximum iv retention of these phytochemicals, close to natural content, was observed. Various powder properties such as flowability, wall friction, oil and water holding indices, emulsion activities, stability, crystallinity, and surface morphology (SEM) were determined and compared. All these properties of the cryogenically ground powders were better than that of the conventionally produced powders suggesting the feasibility and proper working of the decorticator-cum-grinder. The cost economic analysis of the equipment was also done. The unit cost of the cryogenic decorticator-cum-grinder was ₹4,99,450.00 INR ($ 6,834.00 USD). The return on investment (ROI) of 911%, breakeven point (BEP) of 166 kg of powder production, and payback period (PBP) of 45 days on the initial investment cost suggested the economic feasibility and commercial viability of the equipment. The developed cryogenic decorticator-cum-grinder could be a possible solution for processing and value-addition of myrobalan fruits for increasing the income for sustainable livelihood of rural population dependent on the collection and sale of these fruits. It could also help in commercializing myrobalan fruit products for use in the herbal medicine industry
Polysaccharide-based Oil-in-water Emulsion Systems for the Prolonged Efficacy of Hydrophobic Antimicrobial Compounds
No full textPrevalence of foodborne pathogens and its associated disease outbreaks are major causes of concern for public health globally. Significant efforts have been taken to resolve this issue, among which the use of antimicrobials is a major approach. Antimicrobial compounds have been used alone or in combinations to achieve enhanced functionality within food systems. Natural antimicrobials such as essential oils used in food preservation by conventional techniques are prone to rapid depletion owing to their volatile nature, hydrophobic properties, enzymatic hydrolysis, specific interactions with surrounding food components and alteration of flavor profile at higher usage levels. One strategy for prolonged protection of antimicrobial compounds is through designing a suitable carrier vehicle. In this study, the overall goal is to design oil-in-water emulsion systems for the sustained protection of various antimicrobial compounds against targeted foodborne pathogens. The first part of the work was carried out in model testing system such as Brain heart infusion (BHI) broth, where the effective concentration of antimicrobial emulsions prepared through ultrasonication and stabilized with gum arabic were evaluated. The oil phase of formulated emulsions was constituted with geraniol and carvacrol, incorporated at various ratios of 1:0, 2:1, 1:1, 1:2, and 0:1 (v/v). These emulsion systems were characterized for mean particle diameter, polydispersity index (PDI), ζ-potential, storage stability, creaming index, and microstructural parameters (confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM)). In addition, Time-kill assay for the formulated emulsions was tested against model bacterial pathogens, Gram-positive bacteria B. cereus MTCC 430 and Gram-negative bacteria Escherichia coli MTCC 443. The results demonstrated that among all the formulations, higher stability was displayed by combined oil, geraniol: carvacrol (1:1) emulsion with no visible separation of cream. Further, the microstructural analysis confirmed the presence of stable emulsion. Analysis of time-kill assay showed prolonged antibacterial efficacy for the combined essential oil-based emulsion against both the model bacterial pathogens. In the second part of the work, the antimicrobial emulsions incorporated with geraniol and carvacrol at the selected oil phase ratios were stabilized with Tween 80 and Gum arabic (coating solution). These emulsion-based coating solutions were used to extend the shelf life of goat meat. They were characterized for mean particle diameter, PDI, ζ-potential, storage stability and creaming index, and microstructural parameters. Evaluation of the antimicrobial activity of the functional emulsions was carried out against Gram-positive bacteria B. cereus MTCC 430 and Gram-negative bacteria Escherichia coli MTCC 443. The study showed that the emulsion-entrapped formulations could prolong the antimicrobial efficacy of geraniol and carvacrol till nine days as compared to treatments performed with non-emulsion formulations on a goat meat model. The final part of the work was focused towards using two volatile essential oils, d-limonene and trans-cinnamaldehyde stabilized by Tween-20 and Starch-Octenyl Succinic Anhydride (OSA), for the preparation and characterization of oil-in-water type emulsions (coating solution). The impact of this delivery system on the antimicrobial retention was studied against the model bacterial pathogens using fresh-cut papaya as the model food. It was found that the emulsion-based coating solutions could prolong the antimicrobial efficacy of d-limonene and trans-cinnamaldehyde against both B. cereus MTCC 430 and Escherichia coli MTCC 443 on fresh-cut papaya. Overall, the emulsion-based carrier systems demonstrated effective retention of antimicrobials in the model testing system (BHI broth) and a potential application of these delivery systems to extend the shelf-life of goat meat and fresh-cut fruits was identified
Leakage Power Minimization in CMOS VLSI Circuits: Circuit level Approaches
No full textAn electronic system/appliance/portable device with high speed, low power, and feasible area has become the finest choice for the consumer. CMOS technology has been continuously scaled down to meet the increasing demand of such kind. Nonetheless, the extent of scaling is constrained by physical limitations such as short-channel effects. The problem has taken a serious turn as the scaling extends into ultra-deep-submicron (UDSM) regime. The main consequences are the leakage currents contributing to massive static power dissipation. Hence the power dissipation has become the critical issue in the design of microelectronic circuits. These unsolicited leakage currents should be minimized for the smooth functioning of the circuit. Designing of such leakage free nanoscale CMOS circuits turns to be a challenging task. In this thesis, we have focused on the leakage power minimization of CMOS VLSI circuits. We have presented three proposed circuit level techniques to minimize the static power dissipation by controlling the subthreshold leakage current. Through exploiting the stacking effect, we have proposed a circuit level leakage reduction technique named LRT (Leakage Reluctant Transistor). Another novel circuit technique is proposed based on the source biasing approach. The third proposed technique works on the principle of increasing the effective resistance of the path from the supply voltage to ground. The design methodology for the implementation and the detailed analysis of the proposed techniques are presented in the thesis. Circuit simulations are carried out at three technology nodes: 90nm, 45nm, and 22nm. The detailed comparison of the performance parameters such as power dissipation, delay, power-delay product (PDP) of CMOS inverter, NAND gate, NOR gate and a benchmark circuit with the other reported techniques is presented. Simulation results show that the three proposed approaches achieves an average leakage power saving of 72 %, 31 %, and 74 % compared to the conventional design at 22nm technology node. However, the approaches increased the delay and area. Few of the proposed designs yields better power-delay product compared to conventional designs
Genesis of Gold Mineralization in the South Kolar and Gadag Greenstone Belts, Dharwar Craton: Constraints from Hydrothermal Alteration, Tourmaline Chemistry, Fluid Inclusion and Stable Isotope Studies
No full textSouth Kolar greenstone belt (SKGB) in the Eastern Dharwar Craton (EDC) and Gadag greenstone belt (GGB) in the Western Dharwar Craton (WDC) are well known for Neoarchean orogenic gold deposits in India. Chigargunta (CG) and Bisanatham (BN) deposits with contrasting host rocks such as Champion gneiss and metabasalt respectively within the SKGB reflect almost similar steeply dipping structural attitudes (0–10/74W– 87E) that controls the emplacements of auriferous lodes. On the other hand, third generation deformations along the NW-SE were the key structural control for major gold mineralization in turbidite hosted Gadag gold field (GGF) in the GGB. Hydrothermal alteration mineral assemblages i.e., quartz + carbonate + muscovite + chlorite + sericite + tourmaline (± biotite) are common in both the SKGB and GGF deposits irrespective of their host rock compositions, deformation settings and P-T conditions of alteration. Although, mineralogically they are similar, alteration mineral chemistry and substantial mobility of elements during alteration of two contrasting lithounits from the CG (Champion gneiss) and BN (metabasalt) typically fingerprint the host rock chemistry. Abridged activity-activity [(aMg2+/aH+) vs. (aK+/aH+) and (aNa+/aH+) vs. (aK+/aH+)] diagrams corroborate the observed alteration-induced mineralogical changes, in accordance with the isocon plot and constrain the possible fluid composition. Occurrences of native gold in association with sulfides are more common in the SKGB while both invisible lattice bound refractory as well as native gold are observed in the GGF. Hydrothermally precipitated tourmalines intimately associated with/without sulfides, in the alteration zones, from the gold deposits of the CG, BN and GGF belong to dravite or oxy-dravite group. A significant fluctuation in chemical compositions (XFe, Mg, Ca) from proximal to inner zone and strong chemical zoning of tourmaline grains without changes in Na content reflect no changes in fluid salinity in the CG and suggest ore fluid evolution with multiple pulses in a cyclic fluid flow event. Such notable change in fluid chemistry is attributed to the result of fluctuation of fluid pressure during seismic fracture propagation accompanying gold mineralization event. The intra-deposit chemical fluctuation within tourmaline in the BN and GGF are insignificant. The low salinity and reduced nature of the ore fluid are consistent throughout all the deposits inferred from low to medium Na, medium to high X-site vacancy and low Fe3+/Fe2+ ratio. Detailed fluid inclusion study from the mineralized quartz-carbonate veins reveals low to medium saline (CG: 0.5–13.3 wt% NaCl equiv.; BN: 1. 6–6.4 wt% NaCl equiv; GGF: 0.04–9.6 wt% NaCl equiv.) H2O-NaCl-CO2±CH4±N2 primary fluid. Estimated P-T conditions (CG: 1.7–3.5 kbar/285–378 ℃; BN: 0.8–1.2 kbar/365405 ℃; GGF: 1.62.9 kbar/296333 ℃) by combining fluid inclusion, chlorite and arsenopyrite thermometry reflect greenschist facies conditions of alteration and mineralization at the SKGB and GGF. Alteration mineral assemblages, tourmaline chemistry and fluid inclusion study confirm that the low saline, reduced fluid transported gold as Au(HS)2 − complex and precipitated gold as a consequence of pressure drop induced phase separation as well as wall rock interaction processes rather than fluid mixing. Sulfur isotopic compositions of the ore fluid (34SH2S) (CG: –0.4 to +2.4‰, BN: +0.3 to +2.3‰ and GGF: +1.0 to +3.4‰) are indicative of average crustal sulfur source. The 34S (+1.5 to +4.5‰) values of mineralized sulfides overlap with host-rock early pyrites (–1.0 to +7.5‰) in the GGF. Thus, it can be inferred that the sulfur in the mineralizing fluid most likely have derived either by desulfidation and/or dissolution of early pyrites during the continuous fluid flux along the shear zone. Carbon (δ13CCO2) isotopic compositions of ore fluid deduced from δ13C of carbonates furnish a range from –2.4 to +3.3‰ in the CG, – 2.1 to +1.4‰ in the BN and –5.9 to +1.6‰ in the GGF. Such inferred narrow ranges signify that the carbonates in ore forming fluid could have possibly been derived by decarbonation or dissolution of marine carbonates during the metamorphic devolatilization of the greenstone belts. Hence, the metamorphic source of ore-forming fluid is postulated for the gold mineralization at the SKGB and GGF and it is comparable with other orogenic gold hosting greenstone belts in the Dharwar Craton and elsewhere in the world
Combined Density Functional Theory and Molecular Dynamics Study On the Design and Application of Super- Alkali/Halogen and Analysis of Reaction Mechanism
No full textDensity functional theory (DFT), an alternative to ab-initio wave-function based electronic structure method and Conceptual density functional theory (CDFT), a method extracted from chemically relevant concepts and principles from DFT, have been used to analyze different reaction mechanism and the properties, associated energies, stabilities of various special molecules like superalkalis, superhalogens, superacids, etc. The dynamical properties and potential application of some of these molecules were further investigated using molecular dynamics (MD) techniques. The thesis is segregated into nine chapters. Chapter 1 provides a short account of the current status of research in the area of different types of superalkalis, superhalogens, superacids, frustrated Lewis pairs (FLP), etc., and their potential applications. A brief note on the methodologies employed to design such molecules, analyze their properties, and study different reaction mechanism has been furnished. Chapter 2 deals with the design of heterocyclic superalkalis and superhalogens as well as organometallic superalkalis from the stable aromatic molecular systems like C6H6, B3N3H6, Au3 etc. Chapter 3 foretells the designing of superacids in terms of Brønsted and Lewis perspectives from the more reactive aromatic superhalogen molecules. In Chapter 4 an attempt has been made to design the frustrated Lewis pairs by replacing the ligand in Lewis acid part of popularly used FLP, tris(pentafluorophenyl) borane (TPFPB) with the superhalogen to explore its efficiency to activate the H2 molecule compared to the conventionally used FLP. Further, a new class of boron-based anion receptor for Li-ion battery (LIB) electrolytes has been designed using the superhalogen ligands. Chapter 5 unfolds the transport properties and solvent properties of some of the designed boron-based anion receptor additives and identifies their efficacy as compared to the popular anion-receptor additive, TPFPB for the use of LIB electrolyte. Chapters 6 to 9 deal with various reactions mechanism studies. The ground state and first excited state gas phase double proton transfer reaction mechanism was studied in formic acid dimer in the light of reaction force, reaction electronic flux, and its different components in Chapter 6. Chapter 7 provides a relation between pKa and activation energy for double proton transfer reaction in inorganic acid dimer. The reaction involved in the CO2 activation with the help of a small cluster B3N3 was studied extensively in Chapter 8. In Chapter 9, the chemical reaction involved in the alkylation process of Zintl cluster was analyzed with different CDFT descriptors
Effects of Processing and Composition on the Electrical, Optical and Photocatalytic Properties of Ba, Ni Modified KNbO3 Ceramics
No full textFerroelectric materials are widely used in capacitors, actuators, non-volatile memory, electro-optic materials for data storage applications and thermistors. In recent years ferroelectrics with narrow bandgap offer tremendous scope for applications in the field of photocatalysis and photovoltaics because of their efficient ferroelectric polarization-driven carrier separation which in principle can lead to better photocatalytic activity compared to conventional semiconducting oxides. However, the efficiency reported so far for conventional ferroelectrics is still too low to be considered for practical application due to wide band gap (>3 eV) of these materials. The invention of visible light absorbing semiconducting ferroelectric oxide (1-x)KNbO3-x(BaNi12Nb12O3−δ) (KBNNO) by Grinberg et al. augmented global research activity in the area of semiconducting ferroelectric. However, the synthesis of KBNNO by solid state route, require high calcination temperature (850oC) and sintering at further higher temperature (1100oC). Due to this prolonged heat treatment at high temperature, potassium volatizes which results in non-stoichiometry may have an adverse effect on densification, dielectric and optical properties. Very few reports are available on the effect of dopants on structural, electrical and optical properties. Hence, a systematic study of the effect of suitable dopant atoms in such oxide perovskite would throw light on the structure-band gap microstructure-electronic property relationship in these materials which is one of the objectives of the present work. In addition to band gap of a photocatalyst, particle size and particle morphology also have an important role on the photocatalytic activity of oxide semiconductor. Furthermore, it will be interesting to study the synthesis of KBNNO at significant lower temperature compared to solid state method. There are no reports available on the detailed study of photocatalytic mechanism in KBNNO. Coupling of narrowband gap oxide semiconductors with conventional ferroelectrics, photocatalytic efficiency can be enhanced further by preventing the charge carriers from rapid recombination and increase in visible light activity. However, there are no reports available on the formation of heterojunction composite with KBNNO. The purpose of this proposed work is focused on the preparation of KNbO3, KNb1- x/2Ni x/2O3-δ (KNNO), [KNbO3]1-x[BaNb1/2Ni1/2]xO3-δ (KBNNO) (x = 0.05, 0.1, 0.15 and 0.2) visible light absorbing ferroelectric perovskite through solid state method and characterization of their structural, dielectric, ferroelectric, electrical, optical and photocatalytic properties. XRD and Raman spectroscopy confirm the orthorhombic structure in synthesized ceramics. Ni substitution in KNbO3 showed appearance of absorption peaks in visible region. Furthermore, a shifting in absorption edge to higher wavelength was observed for Ba, Ni co-doped KNbO3. Raman spectroscopy shows weakening of long range polar order with increase in Ba-Ni doping (x>0.1). FESEM micrographs show the drastic reduction in grain size in KBNNO ceramics. Ni doping shifted the Curie temperature slightly towards the room temperature and in Ba, Ni co-doped samples, a broad hump can be observed around phase transition. From Impedance spectroscopy, the decrease in conductivity of Ba, Ni modified KNbO3 compared to Ni-doped KNbO3 may be due to the reduction of oxygen vacancies created by acceptor doping (Ni+2) in KNbO3 which in turn led to better photocatalytic activity for KBNNO ceramics. Raman, P-E hysteresis, PL, Impedance spectroscopy indicate optimum dopant concentration that is necessary to get visible absorption with retention of ferroelectricity and better photocatalytic activity in KBNNO. These results are useful in the understanding of phase evolution, bandgap tunability, electrical conductivity and photocatalysis in KNbO3 and show the potential of such materials in photocatalysis and photovoltaic application.
In order to reduce the phase formation temperature and to prepare nano structured KBNNO ceramics, solution combustion method was explored. (1-x)KNbO3-x(BaNi12Nb12O3−δ) (x = 0, 0.05, 0.1, 0.15 and 0.2) ceramics were successfully synthesized at low temperature using citrate-nitrate solution combustion method at 600oC. The fuel-to-oxidizer ratio (Φe) (0.6–1.0) has significant effect on the combustion process and phase evolution. TEM micrograph of KBNNO 0.1 shows that the particles are in nano meter range and the average particle size is around 17 nm. Raman and P-E loop indicate polar structure and photoluminescence spectroscopy displays the lowest electron-hole recombination, in KBNNO 0.1 and this may be the reason for the best photocatalytic activity. The rate constant of KBNNO 0.1 for RhB degradation is 3.17 times and 1.4 times higher than KNbO3 and P25 (commercial TiO2 based photocatalyst), respectively under similar visible light illumination. The mechanism behind photocatalytic activity and photo-stability have also been studied for the best composition. In order to further reduce the phase formation temperature and to make oriented nanostructure (nanorods/nano wires), hydrothermal method was explored. Phase pure KBNNO 0.1 were successfully synthesized via hydrothermal method at 200oC. In hydrothermal synthesis of KBNNO 0.1, the effect of KOH concentration (1M-18M) and the effect of reaction time (30min-12h) on phase evolution and powder morphology were investigated. We found that to get complete phase purity atleast 10M KOH concentration and 12h soaking time were required. The Powder morphology varies from spherical to irregular shape, to rod like nature, to cube shape when KOH concentration of the starting solution in the range of 4-6M, 8-12M and 14-18M, respectively. However, its photocatalytic properties are poorer compared to combustion derived samples and comparable to that of solid state samples. To further enhance the photocatalytic property of KBNNO 0.1, nanostructured ferroelectric/conventional semiconductor heterostructure (KBNNO-Ag2O and KBNNO-Bi2O3) has been explored. In context, a series of KBNNO-Ag2O/Bi2O3 composites with varying weight ratios (75:25, 50:50 and 25:75) by a simple precipitation technique/solid state method. Preparation method and processing temperature have significant effect on phase stability and interface formation for KBNNO-Ag2O/Bi2O3 composites. UV-Vis spectroscopy shows that the synthesized composites exhibited higher visible light absorption and PL spectroscopy indicates reduced recombination time of charge carriers than the parent materials. Photocatalytic studies shows that KBNNO:Ag2O (50:50) composite sample can completely mineralize the dye within 25 min. However, the best composition for KBNNO:Bi2O3 (25:75) can completely mineralize RhB in 45 min. Radical trapping experiment shows that O2− , h+ and .OH are the major reactive species helping in mineralization of RhB in KBNNO:Bi2O3 system and h+ and O2− are the major reactive species in KBNNO:Ag2O (50:50) system. The significant absorption in visible region and reduced recombination time of charge carriers in the composite than the parent materials were responsible for excellent photocatalytic properties. The mechanism for degradation was also studied in detail. Moreover, a reasonable degradation of 95% (on an average) was observed after 5 cycles, suggesting a good photocatalytic stability of the composites. Ag nanoparticle dispersed orthorhombic KBNNO are synthesized by photoreduction method. The photoreactivity of Ag/KBNNO nanocomposites as a function of Ag content (0.5-4 wt%) is studied toward aqueous rhodamine B degradation under visible light. The photocatalytic degradation of RhB under visible light irradiation indicates that 3wt% Ag-KBNNO has the highest rate of degradation (0.056 min-1) and can completely mineralize RhB in 60 min. However, the rate constant and degradation time is much lower than the best composition of KBNNO/Ag2O (50:50) which are 0.113 min-1 and 25 min respectively. In Ag-KBNNO, radical trapping experiments show that O2− and .OH are the major reactive species involved in photodegradation of RhB