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Design and development of frequency selective surfaces for wireless applications
No full textFrequency Selective Surfaces (FSSs) with multi-functional capabilities are a current research interest due to their wide range of applications, mainly in wireless communication, sensing, and radar systems. FSS plays an important role in RF systems within wireless communication networks, such as suppressing interference, enhancing transmission selectivity, improving channel quality, and directionally reflecting electromagnetic waves across various ranges. Considering current requirements, their importance becomes even more critical, especially for meeting communication bandwidth and transmission selectivity needs. This creates new opportunities and challenges to the researchers. This challenge is not just to enhance the existing structures but also adding various functionalities to the entire system keeping relatively low cost and maintaining efficiency. Various FSS designs have been extensively investigated with desirable properties like sharp roll offs, miniaturization, cost-effectiveness and reconfigurability.
This thesis primarily focuses on the design and development of Frequency Selective Surfaces (FSSs) for wireless applications. The initial part of the thesis is dedicated in developing various passive FSSs for enhancing the desirable characteristics of the structure. Various techniques have been developed to achieve additional degrees of freedom in design parameters, cost efficiency, manufacturing feasibility and reliability. The advantages of 3-D printing and other low-cost substrate material have been utilized in prototyping different types of Frequency Selective Surfaces and investigating various desirable parameters, primarily to produce multiple bandwidth channels with intervals and sharp roll-off edges, which are highly anticipated in the development of reconfigurable FSS.
The term "reconfigurable" refers to a wide range of parametric selectivity in FSS without physical changes to the structure. The reconfigurable FSS(RFSS) achieves a wider operating frequency range either tuning electrically or mechanically. In thesis work, RFSS incorporates active circuit elements, such as variable capacitors, to achieve real-time tuning of the resonating unit cells. Consequently, the development of reconfigurable FSS using active components is more challenging compared to conventional FSS. As a result, the work has been carried out in multiple stages. The desirable features of FSSs are explored and prototyping FSS using 3-D printing is a critical step, providing sufficient knowledge and data resources to finalize the design and
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implementation of reconfigurable FSS. Furthermore, the developed 3-D printed FSS and other low cost FSSs may have a wide range of applications, such as RF shields, reflectors, filters, etc.
The key milestones of the work presented in this thesis are briefly discussed below:
• The first part deals with two FSS designs to achieve higher selectivity and miniaturization characteristics. In first work, FSS is designed to exhibit filter like characteristics with flat passbands and fast roll-off edges, resulting in better frequency selectivity. Next design deals with miniaturization that led more and more unit cells to be integrated to smaller space thus saving size and space. The miniaturized FSS has been investigated using metallic vias to resonate at frequency bands of 1.24 GHz and 2.65 GHz. These works focus on achieving precise frequency control while maintaining lightweight, small and cost-effective designs.
• The operating frequency of 3-D printed FSS has been altered by incorporating the designed elevated pattern on the surface of substrate. The work exploited the unit cell design by varying substrate height and metallization patterns and leads to significant variation in operating bands. The 3-D printed FSSs have also been explored for harmonic radar applications. The harmonic radar transmits at a harmonic frequency and detects the second harmonic frequency of reflected signal. The presented works reject the frequency at 2.5 GHz while passing the second harmonic frequency at 5 GHz frequency band. Another work is presented for RF shielding applications to suppress the various signals for security reasons and prevent cross-coupling between nearby wireless channels. The work also investigated the fabrication tolerances of 3-D printed technique.
• The reconfigurable FSSs are explored for wideband tuning characteristics and beam steering applications. First work deals with dual bandstop tuning that can be individually as well as simultaneously tuned for achieving wideband characteristics. The wideband tuning with sharp roll off rejection at upper edge of frequency band is achieved by simultaneous varying the capacitance of varactor diode inserted at the top and bottom side of substrate. Effectiveness of the FSS design is tested by the fabricated prototype mounted with capacitors in order to achieve cost-effectiveness of proposed structure. Another reconfigurable bandpass FSS has been investigated to achieve desirable transmission phase for beam steering applications. The work mainly focuses on demonstrating the steering capability with extensive control over the phase distribution
Resource Mobilization by Micro, Small & Medium Enterprises in India: An Exploratory Research
No full textMicro Small Medium Enterprises (henceforth MSMEs) are the major drivers of the economies across the world. They not only are a major contributor to the GDP growth but also create employment for a major part of the population. Mobilization of resources is a key and critical strategy for MSMEs to sustain, grow and continue to contribute to the economy. However, due to limitation of their size, MSMEs face challenges of resource (human, financial, technology etc.) constraints. MSMEs also need to externally compete with Larger Enterprises (henceforth LEs) which by virtue of their vintage, market establishment, and better leverage of technology, deploy resources more effectively and efficiently.
A detailed review of literature suggests that majority of work in resource mobilization has been conducted in LE setups. MSMEs differ from LEs in terms of capabilities to develop and execute strategies to manage and deploy resources for continued growth. These differences create unique challenges for resource mobilization in MSMEs. Hence, existing theories for LEs may not fully encapsulate and explain the uniqueness and nuances of resource mobilization in MSMEs. Further, due to significant differences in economic, political and social eco-systems between emerging economies such as India and developed economies, existing MSME theories developed for advanced economies may not map to those in emerging economies. A grounded exploration of resource mobilization by MSMEs in emerging economies is thus necessary for progressing research further on how MSMEs in emerging markets deploy resources in a resource constrained environment.
This thesis aims to build a model around resource mobilization in MSMEs operating in India. We adopted an exploratory approach under which an iterative process of literature review was followed, highlighting the internal and external components and linkages of resource management and the dynamics of interaction between them. Based on literature review, we narrowed our focus to select resource management theories of Bricolage, Resource Orchestration and Social Embeddedness to build following research questions 1) How do various factors, internal and external to MSMEs, induce them towards Bricolage and what Bricolage actions do MSMEs utilize to sustain themselves? 2) How do MSMEs orchestrate resources internal and external to the organization to create competitive advantage? and 3) How do MSME leverage social network and embeddedness for mobilizing resources?
An inductive, multiple-case research design was developed for the thesis. Data was collected from 6 MSMEs in India. Selection of organizations was done through theoretical sampling method. Data was collected and triangulated through semi-structured interviews, observations collected through field visits, documents such as financial reports provided by MSMEs, and data collected through secondary sources such as company websites. Data analysis was conducted through within case analysis and cross case analysis.
The research thesis explores a hitherto less studied area of MSMEs within resource-scarce environments. This research would also assist MSME practitioners in emerging economies to plan for rapid resource mobilization and scaling up in their venture to achieve their objective of sustenance and growth under condition of resource scarcity. Finally, this research will also guide policymakers on what conducive and supportive conditions are needed to enable MSMEs to mobilize resources in emerging economies successfully
Crack Remediation in Cementitious Composites Using Self-Healing Strategies
No full textConcrete is a widely utilized construction material owing to its cost-effectiveness, adaptability and capacity to withstand substantial compressive loads. However, its limited tensile strength renders it prone to cracking. These cracks accelerate the entry of water and deleterious substances like sulphates, chloride and carbon dioxide into the concrete, resulting in the corrosion initiation of the protective passive layer of steel reinforcement. As the steel undergoes corrosion, it expands, causing the concrete cover meant to shield it from the environment to spall off, ultimately compromising the safety of the structure and its occupants. Regular maintenance and repair work is necessary to prevent such deterioration, however, conventional methods for repairing cracks often fail to match the properties of the existing material, demonstrate limited long-term effectiveness, and are not ideal for inaccessible or narrow cracks. This research investigates a sustainable, material-integrated approach by exploring chemical-assisted healing for crack-healing for closure of cracks in cementitious structures.
The study focuses on three primary strategies for chemical healing- injection-based, dipping-based, and admixture-based approaches, evaluated using various healing agents including sodium silicate (NS), calcium hydroxide (CH), calcium nitrate (CN), and their combinations. In the injection-based approach involved the direct insertion of healing agents into the cracks, enabling localized and controlled healing. In the dipping technique, the cracked specimens were immersed in the healing agent solution, facilitating capillary absorption and internal crack repair, whereas in the admixing approach, the healing agents were directly in the cementitious mix during casting without encapsulation.
These treatments were evaluated for their effectiveness in healing cracks, compatibility with the cement matrix, and suitability for field-scale applications. The research utilized different evaluation techniques, incorporating both traditional and advanced non-destructive testing (NDT) tools such as Ultrasonic Pulse Transmission (UPT) and Infrared Thermography (IRT), along with visual inspections, water permeability, sorptivity tests, recovery in compressive strength, and microstructural characterization (FESEM-EDS and XRD).
The sensitivity of ultrasonic waves to the change in the elastic properties of the medium through which it propagates is used to monitor the progressive healing of cracks in concrete. An increase in the UPT signal strength with the progression of healing in cracked concrete was
used to interpret the condition of the crack. Furthermore, the progression of healing is also effectively captured by an IRT camera, which identifies the healed zones based on surface temperature changes. Together, they provided a dual-mode real-time monitoring platform, offering a holistic understanding of the crack-healing phenomenon. Microstructural analyses revealed deposition of C-S-H gels (NS-treated) and calcite crystals (CN-treated) within cracks, confirming chemical compatibility with the host matrix.
Comparative analysis revealed that surface crack sealing was achieved more quickly with dipping methods, while injection techniques provided greater depth of penetration and targeted application, making them more effective for both extensive and localized repairs. Systems utilizing admixtures show potential for developing intelligent self-healing concretes but need further enhancement for accommodating larger crack widths.
This study not only confirms the viability of chemical-based strategies for crack healing through effective delivery methods but also underscores the dependability of advanced non-destructive testing (NDT) techniques in measuring healing effectiveness. The results from this research establish a foundation for the creation of automated crack detection and healing solutions, where real-time monitoring using UPT can initiate the controlled release of healing materials, and IRT can illustrate and verify the progress of healing. The approaches and results are adaptable for practical use in the field, such as spraying, injection, or dosing of admixtures, facilitating the development of sustainable and low-maintenance concrete infrastructure
Development of sustainable approaches for the synthesis of biologically relevant molecules
No full textSeismic Behavior Enhancement of Reinforced Concrete Structures in Hilly Terrains Using Shear Walls and Friction Dampers
No full textThis dissertation presents a comprehensive comparative study on the seismic performance of reinforced
concrete (RC) structures located in hilly terrains, focusing on three distinct design approaches: (i) a bare
frame structure without supplemental elements, (ii) a frame structure incorporating shear walls, and (iii) a
frame structure equipped with friction dampers. The primary objective of the research is to evaluate and
enhance the earthquake resistance of RC buildings using advanced modeling and analysis techniques
tailored for topographically irregular sites.
Special emphasis is placed on two common structural configurations used in hilly regions: Step-back (SB)
and Split-foundation (SF) buildings. These configurations present unique challenges due to geometric
irregularities, varying foundation levels, and eccentric mass distributions, which tend to amplify seismic
vulnerabilities. The study models both SB and SF buildings under each of the three design schemes to
accurately reflect real-world construction practices in hilly areas.
Initially, linear static and response spectrum analyses were conducted to understand the fundamental seismic
behavior of each model. The analysis revealed that the introduction of shear walls significantly improves
the lateral strength and stiffness of both SB and SF buildings, reducing displacements, drifts, and base shear
compared to bare frame configurations. However, to better capture the nonlinear dynamic response and
energy dissipation capacity, nonlinear time history analysis was employed using real earthquake records.
The incorporation of friction dampers provided further performance enhancement, particularly for splitfoundation structures, which are inherently more susceptible to torsional irregularities. Friction dampers
effectively minimized story drifts and displacements by dissipating seismic energy, outperforming both bare
frame and shear wall models across key response parameters.
The results indicate that while shear walls provide substantial improvement over bare frame structures,
friction dampers offer superior control over seismic response, especially in irregular hill buildings like SB
and SF configurations. This research underscores the necessity of integrating modern damping technologies
alongside traditional reinforcement techniques to achieve resilient and earthquake-resistant structures in
seismically active hilly terrains
Simulation and Experimental Analysis of an Electro-Hydrostatic Actuator for Next-Generation Primary Flight Control Systems
No full textThis work is directed towards model based dynamics analysis and fault identification of Electric Hydraulic Actuator (EHA) for flight control systems. It is driven by the urgent need to fulfill the rigorous demands of next-generation aircraft. Recent trends highlight the necessity for improved vibration tolerance, efficiency, fault tolerance, and power capability in EHAs. The research aims to address these requirements by focusing on various aspects of EHA technology. Firstly, it delves into the steady-state characteristics of loss coefficients in hydrostatic cylinder drives, seeking to establish relationships between these coefficients and state variables to optimize control parameters for enhanced efficiency. Additionally, diagnostic fault simulations are carried out to analyze the impact of various faults on system responses, aiding in fault detection and the refinement of valve spool motion profiles. Furthermore, the selection of control valves for local hydraulic power sources in aircraft applications is examined, considering factors such as energy loss and system dynamics to guide valve selection decisions. To improve fault prediction accuracy, a modified Particle Swarm Optimization (PSO) algorithm is proposed for predicting incipient faults in hydraulic pumps, crucial for maintaining system reliability, particularly in aviation applications where pump failures can be catastrophic. Also, fault identification in high-performance hydraulic pumps is investigated using PSO algorithms, with a focus on enhancing fault identification performance amidst nonlinearities and uncertainties inherent in hydraulic systems. This research contributes significantly to advancing EHA technology, offering vital insights into efficiency enhancement, fault detection, and optimization practices essential for the evolution of flight control systems in next-generation aircraft
Performative Activism in Social Movements: Analysis of Online and Offline Social Movements
No full textThe aim of the study was to examine the performative activism in social movements by
analysing online and offline factors of social movements. The comparative case study
approach and qualitative research design are used to investigate three contemporary
movements- The Free Palestine Movement (2021-2023), The Farmers Protest (2020-present),
and the RG KAR Medical College Case, Kolkata (2024). The study was conducted in two
phases. In phase 1, online posts on social media and data from newspapers and e-newspapers
were gathered for all three cases, while in phase 2, the farmers’ protest was the main focus
and data were collected by interviewing individuals who participated in the protest both
online and offline. To fully understand the concept of how digital engagements influence
real-world protest outcomes, Thematic and Sentimental analysis was done along with
theoretical lenses such as Social Identity Theory, Collective Action frameworks, framing
theory, and Goffman’s dramaturgy concept.
The results and findings of both phases revealed that strong collective identity, cultural
solidarity, physical presence, long-term commitment, willingness to make sacrifices and risktaking are very important for the success of the movement. All these were seen in farmers'
protest, in comparison to it, RG KAR Case and Free Plaestine movement are characterized by
viral posts, trending hashtags which were successful in grabbing the attention but failed to
mobilise people on ground for the long run. The role of mainstream media is also
controversial and criticised in spreading fake news and setting up false narratives, which
leads the protestors to rely on online or digital platforms to share the real on-ground coverage
and reality to the world.
The hybrid factor of the protest allows it to sustain momentum for a long time; social media
served as a bridge between the protestors, supporters and other individuals. The framing of
8 | Pagemainstream media is also mitigated by the social media platforms where protestors made
their own official accounts. Besides physical hardships, strategic blocking and internet
shutdown, unity, solidarity, and genuine commitment are the factors that bring success to the
movement. These insights can help future movements to avoid the hurdles and trend-driven
participation, as well as ensure that digital allyship/activism serves effective on-ground
action.
Keywords- solidarity, activism, performative activism, unity, sustainability, collective
identity, farmers, protest
Role of genetic variants in phase-II drug metabolizing genes as predictors of Drug-Induced Liver Injury (DILI) in patients on Anti-Tubercular drugs
No full textBackground: According to the World Health Organisation (WHO), Tuberculosis is the
world's leading infectious killer and is still a major health threat around the world.
Mycobacterium tuberculosis causes tuberculosis (TB), which mostly affects the lungs. It is
treated with a mix of anti-tubercular drugs like isoniazid, rifampicin, ethambutol, and
pyrazinamide. A significant number of TB patients get liver damage from the anti-TB drugs,
which is called Anti-Tuberculosis Drug-Induced Liver Injury (AT-DILI). One of the major
cause of hepatotoxicity is incomplete breakdown of the anti-TB drugs drug and build up of
toxic intermediates in the liver. N-acetyltransferase 2 (NAT2) and UDPglucuronosyltransferase 2B7 (UGT2B7) are two examples of phase-II drug-metabolizing
enzymes in the liver. Genetic variations in the genes that code for these enzymes can make
them less effective and raise the risk of liver damage.
Purpose: The goal of this study is to look into how certain genetic variants NAT2*5,
NAT2*6, NAT2*7, and UGT2B7 influence susceptibility to get AT-DILI in North Indian
population, who are on standard anti-TB treatment.
Experimental Design: The study used a case-control design, with TB patients who
developed AT-DILI (cases) and those who did not (controls), all of whom were getting
standard anti-TB treatment. We took out genomic DNA and used PCR-RFLP methods to
genotype certain SNPs in the NAT2 and UGT2B7 genes. We checked liver function (SGOT,
SGPT, bilirubin) at the start and again during follow-ups and compared them to genotypes. A
meta-analysis of 48 studies from around the world with more than 10,000 subjects was also
done to look at the overall link between NAT2 polymorphisms and AT-DILI risk in different
ethnic groups. The results showed that NAT2*5C was strongly linked to a higher risk of ATDILI under the recessive model and that there were variations in liver enzyme levels linked to
enzyme phenotype. The meta-analysis supported these results, showing that slow acetylator
genotypes have a threefold higher risk, especially in Asian and African populations. These
results show that pharmacogenetic screening could help doctors choose safer and more
effective TB treatments
