Indian Institute of Science Bangalore
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Development of A Reconfigurable Synchronous Machine Emulation Platform
No full textStudying the dynamic behaviour of non-linear complex power systems in a laboratory
is very challenging. Early experimental platforms used micro-alternators to emulate the
behaviour of fixed steam and hydro turbine models. The micro-alternator is a three-phase
synchronous generator with similar electrical constants (in per unit on machine rating) as
those typically found in alternators in large power stations. It is an electrical scaled-down
model of machines up to 1000 MW rating and is rated between 1 to 10 kVA. Researchers
used these micro-machines up to the 90s to study large electric generators’ transient and
steady-state performance. The department of electrical engineering at the Indian Institute
of Science (IISc) was also very active in experimental research in power engineering.
The department still retained two-three kVA and one ten kVA micro-machine sets, but
the control panels of these machines became obsolete as the manufacturer of these machines
Mawdsley, London, doesnt exist anymore. Advancements in simulation software
packages and real-time simulators have primarily replaced the experimental models of
electric power systems worldwide. The push for green energy technologies worldwide due
to climate concerns has increased the presence of power electronic converters in the power
grids. Reduction of overall inertia, frequent occurrence of electromechanical oscillations,
electromagnetic transients, and control interaction modes has become a concern for the
power grid operators. The need for understanding the physical insights of the oscillatory
modes introduced by fast-acting power electronic converters, the need for developing practically
feasible control algorithms for mitigating the interaction modes, and the need for
developing dispatchability and grid support features like conventional generation sources
have triggered the development of laboratory-scale experimental power grids across the
world in the past decade.
In this thesis, initially, an attempt is made to revive the old 3 kVA micro
alternator controls. An IGBT-based buck converter static excitation system has been
developed for the micro-alternator. This exciter also incorporates several limiters which
were non-existent in the old analog control panels. An under-excitation limiter, overexcitation
limiter, and V/Hz limiter as per IEEE standard 421.5 have been designed to
protect the micro-alternator during abnormal conditions such as overloading, overheating,
and over-fluxing of the machine. A digital time constant regulator (TCR) is incorporated
to modify the micro-alternator field’s time constant to mimic large synchronous machines’
dynamics as micro-machine time constants are very small. The detailed tuning procedure
of limiters and TCR is discussed to comply with IEEE STD 421.2 and IEEE STD 421.5.
Overheating of old micro-machines was observed due to the creation of multiple shortcircuit
faults. Hence, a custom 5 kVA micro-alternator is manufactured through a local
vendor having parameters like the old machines.
A single micro-alternator can represent only one large alternator dynamics,
thereby limiting the scalability of the platform. Emulating machines of different ratings
using a single micro-machine would undoubtedly boost the capabilities of experimental
platforms for investigating conventional and non-conventional source interactions in laboratories.
To the best of our knowledge, only one such attempt was made in the literature,
where a model reference control algorithm is proposed to mimic any rating alternator
dynamics using a doubly excited laboratory micro-alternator. However, doubly excited
micro-alternators are non-existent today. A reconfigurable experimental single machine
infinite bus testbed using the 5 kVA singly excited micro-alternator is developed reconfigurable
options to emulate different types of IEEE Standard excitation systems, standard
turbine governor models and different machine parameters.
A non-linear output matching control based on the dynamic inversion technique
is proposed for emulating the synchronous generators of different ratings with the IEEE
standard excitation system and governor turbine models using a single micro-alternator.
IEEE Model 1.1 is used for representing the behaviour of large alternators. The singlemachine
infinite bus (SMIB) experimental testbed has been used to validate the proposed
emulation approach. The dynamics of the synchronous generator model in per unit corresponding
to 128 MVA and 192 MVA machines have been physically emulated on the 5 kVA
laboratory micro-alternator. Good tracking performance is obtained with the proposed
approach under small and large disturbances in MATLAB simulations and experimental
evaluations. Using a systematic scaling procedure the proposed emulation approach has
been extended to evaluate the possibility of emulating the WSCC 3 machine 9 bus system
in the laboratory using MATLAB simulations. The simulation results are found to be very
promising in replicating the dynamics of WSCC system using the 5 kVA micro-machines.
Emulation of large machine dynamics with different types of turbines, governors, and excitation
controls using a singly excited micro-alternator enabling a generalized synchronous
machine emulation platform is a first-of-its-kind effort in the literature to the best of our
knowledge
Investigations on Capacitor Size Reduction and PWM Strategy for Multilevel Polygonal Space Vector Structure for Induction Motor Drives
No full textMultilevel voltage source inverter transformed conversion of DC to AC for medium to high power application. With increasing electric power demand, the multilevel converter allows high power density converters for medium to high voltage high power applications. Motor drives, high voltage DC (HVDC) transmission, renewable energy systems, and electric traction are some applications that employ multilevel converters. Conventional two-level inverters need to switch between full DC link to ground potential and require voltage blocking equal to the supply voltage. In addition, 2-level inverters require harmonic filters for filtering harmonics in the output voltage. The filters are costly and bulky and dissipate power, decreasing the system's overall efficiency. Multilevel inverters overcome the disadvantages of conventional inverters by switching intermediate voltage levels between DC link voltage and zero voltage. The higher resolution in the inverter voltage levels reduces the output voltage error compared to the required sinusoidal waveform and improves the harmonic quality. The converter's switching frequency is reduced to minimise the switching losses, thereby increasing the system efficiency. The dv/dt of the multilevel converter is less, which reduces the switching stress on the device and brings down the conductive and radiative emissions. Multilevel inverters can also utilise time-tested low voltage semiconductor technologies to build the converters, improving the system's reliability and easy component availability. Basic and most popular multilevel topologies are cascaded H-bridge inverter, neutral point clamped inverter and flying capacitor inverter. Another class of hybrid multilevel inverters is obtained by cascading basic multilevel inverter cells, which can generate high-quality output voltage waveforms with greater voltage levels. Hybrid multilevel inverters for induction motor drives are also obtained by configuring the motor as an open-end and feeding on both sides of the induction motor.
The conventional voltage source inverter generates a hexagonal space vector structure. The inverters are required to operate in the overmodulation region for maximum utilisation of the available DC-link. Operating in the overmodulation region generates lower-order harmonics in the phase voltage and causes several undesirable problems in the systems. The linear modulation range of the hexagonal space vector structure is 90.7\% of the peak fundamental voltage for the maximum modulation index. Induction motor drives using hexagonal space vector structure suffer from torque pulsations on the motor shaft, which could even lead to total system failure. The harmonics in the system affect the dynamic performance of closed-loop current control of the motor and generate significant power loss.
Various techniques have been proposed in the literature to suppress the problems caused by harmonics. Increasing the switching frequency of the converter is one such method to reduce the effect of harmonics by having lowest harmonics only at switching frequency, which is easy to filter out. High switching frequency is not a practical solution for medium and high power applications due to the high magnitude of switching loss in the device, resulting in worse electromagnetic compatibility performance. Also, the increased switching frequency is only effective for operation within the linear modulation range. Another conventional method for harmonic suppression is using passive filters. But, for variable frequency operation like in induction motor drives, filtering out lower order harmonics requires bulky filters, which increases the system's size and cost and adds to the resistive loss. Moreover, the addition of the filter to the system affects the system's dynamic performance and reduces the fundamental voltage at the output. Selective harmonic elimination (SHE) is a special pulse width modulation (PWM) to suppress the harmonics by introducing fixed notches in the output. SHE operates with a low switching frequency but suffers from low DC-link utilisation due to the introduction of the notches. Also, the method becomes complex for the elimination of multiple harmonics and has poor dynamic performance. An elegant method to eliminate harmonics in the output voltage is to realise space vector structures with inherent harmonic elimination.
Polygonal space vector structure with a higher number of sides than a hexagon, such as 12-sided polygon and 18-sided polygon, eliminates lower order harmonics. 12-sided polygon eliminates the lower order harmonics of the order 5th and 7th and has harmonics only from 11th and 13th. 18-sided polygon eliminates the harmonics up to the 13th order and only harmonics from the 17th and 19th order. The polygons with a higher number of sides are closer to a circle geometrically and have an increased linear modulation region than hexagon (6-sided) for a given DC-link voltage. Generating higher fundamental voltage inverter operations compare to hexagon for the same DC-link voltage leads to better DC-link utilisation. Schemes generating multilevel polygonal space vector structures have evolved to incorporate the advantages of multilevel converters. There are several challenges to generating multilevel polygonal structures, including the requirement of large capacitance, the complexity of PWM techniques etc. Power circuit topologies with a single DC source to generate polygonal space vector structures have evolved but suffer from the requirement of large capacitor size. This thesis proposes a capacitor size reduction methodology and a simple PWM strategy for multilevel polygonal space vector structure. Chapter 1 introduces various harmonic suppression schemes and topologies for generating multilevel inverter polygonal space vector structures.
A multilevel 12-sided polygonal voltage space vector generation scheme for variable-speed drive applications with a single DC-link operation requires an enormous capacitance value for cascaded H-bridge (CHB) filters when operated at lower speeds. The multilevel 12-sided polygonal structure is obtained in existing schemes by cascading a flying capacitor inverter with a CHB. Chapter 2 proposes a new scheme to minimise the capacitance requirement for full-speed operation by creating vector redundancies using modular and equal voltage CHBs. Also, an algorithm has been developed to optimise the selection of vector redundancies among the CHBs to minimise the floating capacitors' voltage ripple. The algorithm computes the optimal vector redundancies by considering the instantaneous capacitor voltages and the phase currents.
Chapter 3 proposes a simple unified pulse width modulation (PWM) strategy for multilevel polygonal space vector structure (SVS) partitioned into symmetric triangles for the first time. The algorithm obtains the PWM timing durations for a 2-level polygonal voltage SVS in a sampling duration using only the sampled reference values of voltages. The PWM timings obtained for a 2-level structure are then mapped to multilevel SVS. The matrices used for this mapping remain the same irrespective of the sides of the polygon. The smallest triangle encompassing the reference voltage vector in the multilevel structure is identified using this algorithm along with the PWM timings for which the voltage vectors forming the vertices of this smallest triangle are applied. The algorithm involves only operations like addition, multiplication, and logical comparisons. A general implementation scheme for an N-level, p-sided polygon is presented in this paper. A novel 5-level 18-sided SVS is also proposed in this paper. The scheme incorporates the advantages of harmonic elimination due to an 18-sided polygon and the inherent advantages of a multilevel inverter.
A multilevel variable speed induction motor drive scheme using an 18-sided polygon with a very dense voltage space vector structure (SVS) is proposed in chapter 4. The proposed SVS consists of 101 concentric layers of 18-sided polygons. The 18-sided polygonal SVS eliminates lower order harmonics 5th, 7th, 11th and 13th orders from the output voltage for the entire modulation range. The linear modulation range of the 18-sided polygon is extended to 99\% of the base speed compared to 90.7\% of the hexagonal SVS. It also has higher peak phase fundamental voltage at the output and better DC-link utilisation than conventional inverters. The SVS is generated by superposition of 5-level main hexagonal SVS of radius VDC and 5-level auxiliary hexagonal SVS of radius 0.379VDC. The dense voltage space vector structure facilitates the generation of reference by nearest vector switching in the 18-sided polygon, reducing the semiconductor devices' switching. The vector switched to realise the reference voltage in a sampling period is only one polygonal vector throughout the modulation range, drastically reducing switching loss and electromagnetic emissions.
Simulation and experimental results of the proposed drive scheme are presented to prove the effectiveness of the drive scheme. The inverter is modelled and extensively simulated using a MATLAB-SIMULINK environment. An experimental setup using inverter modules is set up to test the inverter. The semiconductor switches used are SKM75GB12T4 and IRF260N. Gate drive circuits based on opto-isolated IC M5792L from Mitsubishi and capacitive isolated IC ISO5451 from Texas Instruments are used. TMS320F28335 DSP from Texas Instruments and XC2S200 FPGA from Xilinx were used as the controllers for realising the hardware prototype. A 3-phase open-end induction motor of ratings 15 kW, 415 V, and 4-pole is used for testing the proposed drive schemes
Exploring the role of low complexity protein sequence in regulating RNA granule dynamics and translation control
No full textRNA granules are conserved membraneless mRNP complexes that play an important role in determining mRNA fate by affecting translation repression and mRNA decay. Processing bodies (P-bodies) harbor enzymes responsible for mRNA decay and proteins involved in modulating translation. Although many proteins have been identified to play a role in P-body assembly, a bonafide disassembly factor remains unknown. We observed that Sbp1 with the help of its RGG-motif promotes P-body disassembly in S. cerevisiae. This study provides an example of the role of low complexity sequence in RNA granule disassembly. We have further explored the role of human RGG-motif containing proteins in regulation of translation. Here we studied LSM14A (human homolog of Scd6) in maintaining RNA granule dynamics and regulation of mRNA. We observe that LSM14A binds to human eIF4G and plays an important role in regulating the translation of certain mRNAs in response to genotoxic stress. Overall using a combination of yeast and human cell culture system, this study provides critical insight into the role of conserved low complexity sequences
A non-classical continuum approach to study the fragmentation of brittle solids
No full textIn this thesis, a non-local continuum approach coupled with the phase-field theory and Jones-Wilkins-Lee (JWL) equation of state (EOS) is proposed to model and simulate blast-induced fracture in brittle materials. Also, we study the evolution of field variables in the underground explosion of steel fiber reinforced concrete (SFRC). For numerical implementation, we have used a non-ordinary state-based peridynamic theory coupled with a diffusive phase-field damage approach. Moreover, JWL EOS from the family of isentropes has been formed, and finally, the constitutive relations have been arrived with the help of the JWL EOS. As the conventional equation of motion cannot capture the discontinuities in the damaged portion of the material, derivative-free integro-differential equations of motion have been used in line with the peridynamics approach to overcome the limitation of the conventional equation of motion. The motivation for using non-ordinary state-based (NOSB) peridynamics (PD) over the bond-stretch-based (BSB) or bond-energy-based (BEB) models comes from the fact that the applicability of BSB and BEB models are only limited to materials with Poisson's ratio 1/4.
We have introduced a dynamic failure mechanism due to blast-induced stress wave propagation in rock media, generated due to the pressure of a high-velocity gaseous detonator. Furthermore, an expansion of stress wave in the SFRC mass due to the underground explosion of highly pressurized detonators (Iregel 1175U) has been studied in this thesis. A program-burn algorithm inside the JWL EOS has been implemented to model rock fragmentation. A predictor-corrector explicit time integration scheme has been used to update the field variables at every time step. The phase-field damage can capture well the explosive-induced fracture in rock media and damage in the SFRC medium for the underground explosion. The current numerical approach suggests a versatile physics-oriented future model for this class of problems. The formulation proposed in the thesis has been validated against two numerical benchmark tests and has shown good predictive quality
Achieving practical secure non-volatile memory system with in-Memory Integrity Verification (iMIV)
No full textRecent commercialization of Non-Volatile Memory (NVM) technology in the form of Intel Optane enables programmers to write recoverable programs. However, the data on NVM is susceptible to a plethora of data remanence attacks, which makes confidentiality and integrity protection of data essential for a secure NVM system. However, that requires computing and maintaining a large amount of security metadata (encryption counters, message authentication code (MAC), and integrity tree nodes (BMT)). Furthermore, crash consistency guarantees require the system to persist the security metadata and data atomically back to NVM, incurring high overheads. So there is a trade-off between providing complete security guarantees, the performance and recovery time of an NVM system. Our work explores the resilience of the NVM system to system crashes and malicious attacks.
To ensure the confidentiality and integrity of data, a substantial quantity of security metadata is required. Of these, persisting Bonsai Merkel Tree (BMT) nodes, which are essential for fine-grain integrity verification, add substantial cost owing to the massive amount of data that must be moved off-chip to the bandwidth-constrained NVM. Thus, prior works often make a trade-off between performance and fine-grain verifiability, or forego it entirely in favour of performance.
The goal of this work is to maintain the strongest security and verifiability guarantees while limiting the cost of BMT updates. We accomplish this by leveraging the in-memory integrity verification.
We make the fine-grain integrity verifiability realizable with a radically different approach of using in-memory computing for integrity verification. Our proposal, iMIV draws inspiration from the fact that today's commercial Optane NVM performs encryption onboard the DIMM. We argue that memory-intensive integrity verification operation should be performed near the (non-volatile) memory to avoid off-chip data movement.
In this thesis, we propose a novel and practical hardware-managed security solution called iMIV, which leverages in-memory integrity verification operations to reduce the overheads associated with integrity protection (BMT nodes computation and persistence), which is a key performance bottleneck. iMIV persists the complete security metadata (encryption counter, MAC, BMT nodes) with each data persist, providing it the ability to detect and locate the tampered data block and tampered counter block. Hence, ensuring no single point of failure due to any malicious attack. The work targets to minimize the off-chip memory transfer and mitigate the effect of the bandwidth wall. The proposed iMIV also scales to larger NVM capacity in future systems with per-DIMM BMT.
Experiments are carried out on a trace-driven cycle-accurate simulator VANS, which mimics the internal micro-architecture of Intel Optane memory DIMMs. Experimental results show that in comparison to the Baseline scheme with write-through caches and strict persistency model, which also provides complete security guarantees, iMIV reduces system runtime by 1.8x for NVM-aware workloads and 3.4x for NVM-agnostic workloads. iMIV's recovery time on system crashes is microsecond-scale without compromising on detecting tampering and fast pin-point of the unverifiable region.
iMIV brings down the performance overheads of fine-grain integrity verification on secure NVMs for NVM-aware workloads from 205% (baseline with all security operations performed at memory controller) to 55% (integrity verification operation offloaded to near the NVM)
Comparative Analysis of Topological Structures
No full textMeasuring scientific processes result in a set of scalar functions (scalar fields) which may be related temporally, be part of an ensemble, or unrelated. Overall understanding and visualization of scientific processes require the study of individual fields and, more importantly, the development of methods to compare them meaningfully. In this thesis, we focus on the problem of designing meaningful measures to compare scalar fields by comparing their abstract representations called topological structures. We emphasize on intuitive and practical measures with useful properties and applications.
The first part of the thesis deals with comparing a topological structure called the merge tree. We propose two global comparison measures, both based on tree edit distances. The first measure OTED is based on the assumption that merge trees are ordered rooted trees. Upon finding that there is no meaningful way of imposing such an order, we propose a second measure called MTED for comparing unordered rooted trees. We propose intuitive cost models and prove that MTED is a metric. We also provide various applications such as shape comparison, periodicity detection, symmetry detection, temporal summarization, and an analysis of the effects of sub-sampling /smoothing on the topology of the scalar field.
The second part deals with a local comparison measure LMTED for merge trees that supports the comparison of substructures of scalar fields, thus facilitating hierarchical or multi-scale analysis and alleviating some drawbacks of MTED. We propose a dynamic programming algorithm, prove that LMTED is a metric and also provide applications such as symmetry detection in multiple scales, a finer level analysis of sub-sampling effects, an analysis of the effects of topological compression, and feature tracking in time-varying fields.
The third part of the thesis deals with comparison of a topological structure called the extremum graph. We provide two comparison measures for extremum graphs based on persistence distortion (PDEG) and Gromov-Wasserstein distance (GWEG). Both persistence distortion and Wasserstein distance are known metrics. We analyze how the underlying
metric affects these comparison measures and present various applications such as periodicity detection to facilitate scientific data analysis and visualization.
The final part of the thesis introduces a time-varying version of extremum graphs (TVEG) with a simple comparison criterion to identify correspondences between features in successive time steps. We provide applications to tracking features in time-varying scalar fields from computational fluid dynamics.MHRD, DST/SJF/ETA-02/2015-16, JATP/RG/PROJ/2015/16, Robert Bosch Centre for Cyber Physical Systems, Mindtree Chair research grant, Tata Trust travel grant, ACM IARCS travel gran
Developing an Analytical Model to Predict Customer Churn for Customer Satisfaction (CS) and Customer Loyalty (CL) with respect to Automobile After Sales Service Centres (AASSC)
No full textCustomer Satisfaction has always been a key to success for any automobile after sales service centre (AASSC). To retain customer satisfaction (CS) and customer loyalty (CL), it is crucial for any AASSC to track the important factors and its measurement variables that influence CS and CL. From the literature, it was identified that many research studies considered only Service Quality as the factor influencing CS and CL. Further, a few studies have considered different combinations of the other factors: Belief, Brand Awareness, Product Quality, Economic Service, Convenient service, Service Capability, and Warranty Handling for understating its influence on CS and CL at AASSC. However, it appears from the analysis of the literature that there is no study considers all the unique factors mentioned in the literature together to understand its influence on CS and CL at AASSC. Moreover, every AASSC has been striving hard in identifying and prioritising the factors that have been given importance by the customers during and after services are provided.
Overall, it appears from the analysis of the literature that (a) identifying all the unique factors and its measurement variables, which are expected to strongly influence CS and CL, (b) constructing a structural / conceptual model, considering the identified factors and its measurement variable to predict the customer churning from AASSC, and (c) prioritizing the identified factors are not dealt in the literature in general, and particularly for Indian AASSC. Accordingly, this study addresses 4 research objectives : (i) To identify the factors and its measurement variables which are influencing CS and CL for AASSC and to develop a conceptual framework for CS-CL-AASSC using a rational approach : Total Interpretive Structural Modelling (TISM); (ii) To validate and finalize the proposed conceptual framework for CS-CL-AASSC; (iii) To prioritize and rank the factors involved in the proposed conceptual framework for CS-CL-AASSC, from the customer perspective, using MCDM methods : Analytical Hierarchy Process (AHP) and Best Worst Method (BWM); (iv) To develop an analytical model using the identified factors to predict the customer churn for AASSC.
From the analysis of the literature, 10 unique factors are identified, and 2 new factors are proposed from the researcher’s perspective considering their importance. For measuring these factors, 53 measurement variables are identified from the literature review, researcher's perspective and from the adaption of Caselet approach. Considering the identified factors and its measurement variables, a structural / conceptual model is developed for CS-CL-AASSC following the TISM approach. For validating the proposed conceptual framework, a descriptive research method, particularly the survey method is carried out to collect the opinion from the customers regarding the services provided by AASSC. The questionnaire developed is circulated among 226 and 228 Hyundai car owners/customers in Bangalore and Chennai based Hyundai AASSC respectively and collected the required data (called as BSC-data and CSC-data respectively). Each of the BSC-data and CSC-data is appropriately given as input to simple hypothesis testing through Structural Equation Modelling (SEM) approach and validated each of the conceptual model constructed for Bangalore and Chennai based Hyundai AASSC. Based on the validation processes, a few insignificant measurement variables for a few factors associated with each of the conceptual model constructed for Bangalore and Chennai based Hyundai AASSC are removed, and a final conceptual model are derived.
Further, by applying two MCDM methods: AHP and BWM, independently, the 10 factors considered in each of the proposed conceptual models are prioritized. Based on the processes of prioritizing the factors it is observed that the 3 factors: Product Quality, Service Quality, and Belief are found to be the most important factors for CS-CL-AASSC. Considering these 3 factors as a key input, this study developed an analytical model for predicting customer churn for each of the Bangalore and Chennai based Hyundai AASSC. This analytical model would provide insight for the service advisor to identify the profile of the customers who would be satisfied at AASSC. In addition, an advisor at AASSC can identify the important factors for AASSC from the customer's perspective.
Although the research has accomplished its planned objectives, there are certain limitations such as (i) The survey conducted in this study considers only passenger vehicles and not commercial vehicles, (ii) The required data are collected only from respondents in tier 1 cities and not from the tier 2 and tier 3 cities, and (iii) For demonstrating the workability of the MCDM methods for prioritizing the factors, the required data is collected only from six customers. In addition to addressing each of these limitations as immediate future research in this area, one can think of either modifying the proposed conceptual model or proposing a new conceptual model for CS-CL-AASSC focusing on (a) Battery Cars, and (b) two-wheelers as further research issues in this area of research
Investigating the role and regulation of Polypyrimidine tract binding protein (PTB) in isoform switching during muscle development in Drosophila melanogaster
No full textMuscles are an excellent system to dissect the development, physiology and evolution of cell heterogeneity and isoform switching. The vertebrate skeletal muscles are composed of heterogeneous muscle fibres. These fibres are classified as Type I (slow-twitch) and Type IIA and IIB (fast-twitch- oxidative & glycolytic) based on their distinct contractile and physiological properties. Fibre specific properties can be directly attributed to the differential expression of their protein isoforms. Thus, fibres can switch from one type to another based on developmental, physiological, and environmental cues by coordinated regulation of gene expression, co-integrated with protein isoform transitions. Alternative splicing is one of the major contributors to isoform transitions. Extensive investigations over the years have shown the involvement of several RNA Binding Proteins (RBPs) like MBNL, RBFOX1, PTBP, CELF etc., in establishing, refining, and maintaining fibre specific properties. However, the process by which isoform switching is fine-tuned remains largely unexplored.
In this study, we investigated the process of developmentally regulated isoform switching mediated by the polypyrimidine-tract binding protein (PTB)- an hnRNP (heterogeneous ribonucleoprotein), in the developing Indirect Flight Muscles (IFMs) of Drosophila melanogaster. In mammals, PTB proteins have been shown to affect the alternative splicing of neuronal and muscle genes and the mutations in PTB are implicated in several cancers. Nevertheless, the role and genetic interactions of PTBs in muscle development remain largely unexplored. Drosophila IFMs are an excellent model to study isoform switching as it expresses distinct isoforms of sarcomeric proteins, which give rise to their characteristic fibrillar type of muscle fibres. During IFM development, the sarcomeric genes undergo pupal adult isoform transition during 55-95 hours after puparium formation, which impart properties like stretch activation, enabling the fly to attain a wingbeat frequency of ~200 Hz. We observed that PTB is upregulated explicitly during this window of isoform switching.
To further investigate the role of PTB in isoform switching during IFM development, we adopted an RNAi based approach. PTB in Drosophila is encoded by a single gene, hephaestus (heph). Knockdown of heph in IFMs leads to loss of flight function and defective muscle fibres. We show that the sarcomere maturation phase is affected, resulting in thinning, and shortening of sarcomeres accompanied by actin blob formation at Z-discs of the sarcomeres. Through RNA sequencing analysis, we identified that heph is required for inclusion of fibrillar exons of several sarcomeric genes like Mhc (Myosin heavy chain), wupA, up (Troponin I & T) etc., Several RBPs and channel proteins have also been differentially spliced upon heph knockdown.
Subsequent bio-informatic analyses coupled with functional experiments, helped us extend our search to identify the network of other RNA Binding Proteins that work in tandem with PTB. This led to the identification of how (Held out wings) and Sm (Smooth) as potential candidates involved in the isoform switching stage. This presentation, thus, shall focus on the pathways and molecular players along with a brief mention of the role of calcium signalling in the regulation of isoform switching during Drosophila IFM development.DST, DB
Hyperspectral remote sensing for soil property estimation in the context of spectral mixtures
No full textThe implementation of sustainable agricultural, hydrological, and environmental management entails an improved understanding of soil properties and its conditions at increasingly finer resolutions. In this context, the detailed reflectance spectra provided by hyperspectral sensors can be beneficially employed in acquiring information about the topsoil. The recent availability of hyperspectral data from newly launched sensors and the advancements in techniques for handling and analyzing hyperspectral images have given rise to a wealth of new research findings in soil monitoring and mapping. Though hyperspectral imaging spectroscopy has facilitated the mapping of soil properties at large scales with finer resolutions, it is limited to only bare soil pixels. This is because the presence of non-soil cover in the form of photosynthetic or non-photosynthetic vegetation in a pixel affects the reflectance spectra by causing a “spectral mixing effect”, which in turn would affect the performance of soil property estimation models. Hence it is essential to identify the bare soil pixels in a study area and address the issue of spectral mixtures prior to soil property mapping. In this context, the reported study aimed at addressing this issue of spectral mixtures to improve the knowledge base on topsoil properties, particularly clay content, in a study area characterized by heterogeneity in terms of soil type and fertility, area under cultivation, crop type and cropping system. This work focused on the following three objectives:
To analyze the effect of different spectral reduction strategies prior to endmember extraction in a linear spectral mixture model in terms of pixel reconstruction errors.
To propose a thresholding approach for bare soil identification using pixel soil fractions obtained from spectral unmixing prior to clay content mapping and compare it with the classic method of using spectral indices
To develop a novel soil fraction-based composite mapping approach to extend the spatial coverage of predicted clay maps.
Spectral mixture modelling is one of the most important techniques for classifying hyperspectral data at sub-pixel resolution and identifying spectrally pure endmembers for estimating their corresponding abundances is an important step in spectral unmixing. The application of spectral reduction techniques prior to endmember extraction for unmixing would optimize the process by increasing the sensitivity of the algorithms to the most distinctive and informative features of the dataset. The first part of the study compared different spectral reduction techniques prior to endmember extraction on six real hyperspectral datasets, including an Airborne Visible InfraRed Imaging Spectrometer-Next Generation (AVIRIS-NG) image over Indian sub-continent. Spectral reduction of the datasets were applied using both feature extraction techniques like Principal Component Analysis (PCA), Independent Component Analysis (ICA), Minimum Noise Fraction (MNF), and a feature selection technique based on Partial Informational Correlation (PIC) measure, along with a no reduction case where all the spectral bands were used. A PIC based spectral reduction was employed for endmember extraction specifically in the context of spectral unmixing for the first time in this study. The locations of the endmembers were identified from these reduced datasets using four endmember extraction algorithms- Pixel Purity Index (PPI), N-FINDR, Automatic Target Generation Process (ATGP) and Vertex Component Analysis (VCA). The endmembers identified from the different combinations of spectral reduction and endmember extraction techniques were used for linear spectral unmixing of the original datasets. The performance of each of the combinations after unmixing were compared in terms of the pixel reconstruction errors and the computation times for each dataset. It was observed that the PIC based spectral reduction performed well in terms of reconstruction errors and computation times when combined with the N-FINDR endmember extraction algorithm. This approach could be recommended for spectral reduction in unmixing of datasets from heterogeneous study areas with similar endmember classes.
The second part of the study aimed to analyze the impact of bare soil pixel identification on clay content estimation using an airborne hyperspectral image. Two methods were tested for identifying the bare soil pixels (i) using a combination of two spectral indices, Normalized Difference Vegetation Index (NDVI) for identifying photosynthetic vegetation and Cellulose Absorption Index (CAI) for identifying non-photosynthetic vegetation and (ii) using soil fraction obtained from spectral unmixing using three endmembers: soil, photosynthetic and non-photosynthetic vegetation. The study used an AVIRIS-NG image and laboratory measured clay content of 272 soil samples acquired over an area of 300 sq. km, in the Gundlupet taluk, Karnataka, India. Two sets of bare soil pixels were identified using the two methods and partial least squares regression (PLSR) models were calibrated and validated to estimate the clay contents over the study area from each. The performances of the regression models and predicted clay content maps were analyzed and compared. It was observed that the PLSR model based on bare soil pixels identified by unmixing provided better performances (R2 of 0.61) than the one using spectral indices (R2 of 0.46) for validation, even though the area mapped was reduced by half (14.96% of the study area) as compared to the latter (30.31%). This study highlighted that an improvement in prediction performance comes at the cost of reduction in spatial coverage in mapping of clay content. Finally, the study also brought forth the need for studying other spectral perturbing factors such as rugosity (due to ploughing) which may explain the modest performances of the clay prediction models, even using a hyperspectral image characterized by high spatial and spectral resolutions.
The limited utility of imaging spectroscopy for topsoil property mapping requires approaches for maximizing the bare soil coverage so as to extend the mapped area. In this regard, a novel soil fraction-based composite mapping approach for clay content estimation from a single AVIRIS-NG image over heterogenous crop fields was proposed as the last part of this study. The approach classified the image pixels according to their soil fraction determined by spectral unmixing and assigned specific regression models to each soil fraction class to estimate clay content along with the prediction uncertainty. The composite clay map gave modest performances with R_val^2 ranging from 0.53 to 0.63 for soil fraction thresholds varying from >0.3 to >0.7 respectively and showed correct spatial pattern irrespective of the soil fraction classes. In addition, the effect of the soil fraction threshold on clay content estimation was analyzed by comparing the performances of regression models built using bare soil pixels identified from varying soil fraction thresholds. It was observed that the model performance increases with adoption of higher soil fraction thresholds in terms of an increase in R_val^2 and decrease in RMSEP values. The potential mapped area in terms of clay content in this study ranged from 10.39% to 52.81% with a soil fraction threshold of >0.7 and >0.3 respectively, and so the compositing approach allowed an extension of the mapped surface by 42.42%. The proposed approach could be adopted to extend the mapping capability of planned and current hyperspectral satellite missions where a combination of the proposed soil fraction-based thresholding and multi-temporal image compositing could significantly increase both the extent of the mapped area and associated prediction performances.
The proposed studies on combination of spectral reduction and endmember extraction techniques prior to unmixing, the bare soil identification analyses and soil fraction-based composite clay mapping approach are envisaged as a premise for future researchers to develop on. The scope of its applicability may be broadened and refined with the inclusion of more sensors, soil properties and analysis techniques. The proposed framework may thus be extended to incorporate newer study areas
Droplet, Jets, and Leaky Surfaces
No full textSurface structuring on a micro-nano scale, combined with a low surface energy coating, leads to anti-wetting properties. Such surfaces also exhibit other properties such as self-cleaning, antifouling, bacteriostatic, drag reduction, and anti-icing. Hierarchical structures with dual-scale roughness provide the superhydrophobic surface with lower droplet adhesion and better protection against failure (i.e., Wenzel transition). This understanding has led to the study of nanostructured sieves, as the sieve wires (having diameters ranging from 10 to 100 microns) provide the higher-level roughness required in dual-scale surfaces. Thus, for sieves, a single nano-structuring step leads to dual-scale rough surfaces. Further, the pores in sieves provide an additional structural feature for enabling other applications such as oil-water separation. Hence, nanostructured sieves are being investigated today for novel applications.
Studying the impact of droplets on sieves with different wettability is fascinating as their porosity leads to several exciting scenarios that can be explored for potential use. This thesis investigates the different outcomes of droplet impact on sieves and explores new possibilities. The first part of the study explores droplet impact at the low Weber number regime. The formation of different cavities and their collapse have been studied. The focusing of kinetic energy in the cavity collapse process and the associated singularity leads to the generation of a single droplet. This work reports a new kind of cavity formation phenomenon unique to sieve configurations. In contrast to cavities observed for droplet impact on solid surfaces, this cavity is formed during the droplet impact's recoil phase. Hence, it is called the recoil cavity. The cavity formation and collapse are explained using experimental results and theoretical modeling.
The collapse of the recoil cavity leads to the generation of a satellite-free single droplet underneath the sieve. Essentially this phenomenon of ejecting a single drop opens up avenues for novel applications. This thesis explores the drop-on-demand technique for material jetting and printing. Interestingly, we found that using superhydrophobic sieves could eliminate a long-standing problem of clogging in printing. We explored the clogging issue in-depth and showed our technique's unique capability in printing high mass loading and large particle size.
We report printing of ink with mass loading as high as 71% using our technique. Further, the use of this printing technique has been demonstrated for various applications. Electronic circuits and devices have been printed on flexible substrates. 3D printing has also been demonstrated using high mass loading ink. Printing of live cells and bacteria has also been achieved using this technique.
This thesis explores droplet impact at a high Weber number regime in the second part. We developed double sieve-based air-transparent surfaces capable of repelling rain droplets impacting at terminal velocities. Such air-transparent surfaces will find use in roofs and windows of homes and public places. Current understanding would point towards the use of nanostructured superhydrophobic sieves. However, liquid leaks through such superhydrophobic sieves when the dynamic pressure of the impacting droplet is larger than the anti-penetration Laplace pressure. When the droplet penetrates through the sieve, it comes out in the form of jets. Due to Rayleigh-Plateau instability, the ejected jets break into smaller droplets. This jetting dictates the outcome of the impact. Contrary to the common understanding, we explain our experimental results, which show that the jet velocity can be larger than the impact velocity. This increase in velocity of the ejected droplet makes it difficult to stop the ejected jet using a second superhydrophobic sieve. We use a combination of superhydrophilic and superhydrophobic sieves to repel raindrops impacting at the terminal velocity.
Overall, this thesis deals with the droplet interaction with sieves of different wettability. The present work evolves to innovate interesting applications and solve significant problems