Indian Institute of Science Bangalore
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Understanding the Long-term Impact and Mechanism of Action of Endosulfan, an Organochlorine Pesticide on Fertility, Development and Growth of Mice
No full textEndosulfan (ES) is one of the major broad-spectrum organochlorine pesticides
categorized as Class II (moderately hazardous) by WHO and Class I (highly acutely toxic) by
US Environment Protection Agency. Although the use and manufacture of Endosulfan is
banned or phased out in Europe and the US since the Stockholm Convention in 2011, it is
still used in developing countries, including most parts of India. Endosulfan is persistent in
nature due to which it bioaccumulates in food chain and its residues and metabolites are
detected in water, food, milk, tissues and human blood samples. Various epidemiological
and animal studies have reported Endosulfan and its metabolites as neurotoxic, genotoxic,
and harmful to reproductive organs. Previous studies from our laboratory have shown that
exposure to Endosulfan can cause infertility in male mice due to testicular atrophy and
reduced sperm count. Endosulfan treatment induced DNA damage, altered DNA damage
response, and promoted the error-prone DNA repair pathway called microhomologymediated
end joining (MMEJ) (Sebastian and Raghavan, 2016).
Various studies from the literature showed that the serum concentration of
Endosulfan in the affected human population is up to 547.6 μg/L and it was up to 700 μg/L
when tested after 2 h of exposure, which is much higher than that was used in our previous
study (20-25 μg/L)
Therefore, to study the effect of Endosulfan in environmentally relevant concentration, we
have treated mice with 5 mg/Kg body weight for 10 doses every alternate day. Bioavailability
analysis in mice serum revealed a concentration of ~50 μg/L. Results revealed that
Endosulfan affects the normal physiology of mice. Haematological analysis, liver function
test, and kidney function test showed a decrease in the total bilirubin, creatinine, and blood
urea nitrogen (BUN) in the treated mice. Besides an increase in neutrophils, monocytes, and
total leukocyte count and decreased lymphocyte percentage were observed in treated mice.
Furthermore, our results showed that Endosulfan treatment resulted in infertility in majority of
female and male mice. While treatment with Endosulfan resulted in infertility in 55% of male
mice, it was 62% in females.
Besides compromised fertility, exposure to Endosulfan in mice resulted in abnormal
growth and development. The progenies of the Endosulfan-treated mice were born with
multiple developmental defects like delayed fur development, delayed eye-opening,
abnormal walking patterns, difficulty in parturition, etc. A significant reduction in body weight
of new-born from treated mice was also observed, which was more prominent when both
parents were exposed to Endosulfan. The comparison of organ weights between the treated
and control mice at postnatal day 21 showed a significant reduction in size and weight of
spleen and thymus. In contrast, a significant increase in size and weight were observed in
case of kidney, lungs, and heart. A significant decrease in CD19+ B cells and CD3+ T cells in
bone marrow and thymus respectively indicates the Endosulfan-induced effects on immune
system of mice. Histopathological examination of various tissues from Endosulfan exposed
mice showed a severe effect on testis, ovary, liver, and lungs which include vacuolar
degeneration of the basal germinal epithelial cells, degradation of the interstitial matrix in
testes, reduction in number of mature Graafian follicles, mild vacuolation in hepatocytes all
over the liver, etc. Histopathological analysis of testis from postnatal day 12 mice showed a
reduction in the size and number of seminiferous tubules. Comprehensive histopathological
analysis of vital organs of post-natal day 12 mice showed that the progenies from treated
mice had severe effects on different organs such as brain, cerebellum, liver, kidney, heart,
ovary, testis, lung, spleen when compared with age matched control organs. Further,
detailed analyses through TUNEL assay revealed long-term testicular cell death, indicative
of persistent damage. Evaluation of DNA breaks using 53BP1 staining in mice testis from
postnatal day 12 showed several 53BP1 positive cells in seminiferous tubules, unlike control
animals. Consistent to the observed increase in DNA breaks in cells from reproductive
tissues, an increase in expression of DNA Ligase III was also observed, which was
consistent with previously reported elevated levels of MMEJ mediated repair. Furthermore,
transcriptome analysis of tissues from treated, control and progeny mice revealed
deregulation of several genes associated with gametogenesis and DNA repair pathways
both in the testis and ovary. We have also analysed the genes associated with learning and
memory, apoptosis, eye development, particularly from mice brain and validated by
behaviour studies in progeny mice. Contextual fear conditioning test of progenies from
treated mice revealed loss of both newly acquired memory and remote memory particularly
when both the parents were treated.
Importantly, tumor development near lung and ovary was observed post Endosulfan
treatment (12 months). Further abnormal regression of ovary, elevated skin infection etc.
were also observed in few animals over the months. The mice with developmental defects
survived only for short period while animals with normal phenotype survived just like control
animals. Similar observations like developmental delay, mental retardation, increased
incidence of cancer and infertility were reported on the people living in Endosulfan exposed
regions. Thus, by using the mice model system, we could recapitulate several
developmental defects which were observed in people living in Endosulfan exposed areas.
The persistence of Endosulfan in water is a controversial area of research. The
stability of Endosulfan in water depends on various parameters like pH and micro4
organisms. Although the half-life of Endosulfan in water is considered less, various studies
from different parts of the world have reported the detection of Endosulfan in water
resources like rivers, oceans, and underground water. Using HPLC analysis, we find that
Endosulfan remains stable for >100 days in water collected from various sources like local
pond water, rainwater, underground water collected in a container.
In conclusion, our study is relevant to the present Indian and Asian scenario where
pesticide usage is not tightly regulated even though the side effects possess significant
risk. In the present study, several characteristic features of people living in Endosulfan
exposed areas have been reported using mice model
On late stages of transition in round jets
No full textA round jet is one of the simplest canonical axisymmetric free shear flows that occur both
in engineering applications and natural phenomena. A laminar-turbulent transition process
is inherent to its development involving multiple stages of instabilities – a topic of intense
research due to its importance in mixing and noise generation. This study focuses on the
last two stages of this transition process, .i.e. instability of vortex rings and its breakdown
to turbulence. Vortex rings are subjected to two types of short wavelength azimuthal insta-
bilities: elliptic and curvature, with the former most commonly seen during the transition of
round jets. A global linear stability analysis was performed to examine elliptic instability,
and the results were compared with asymptotic theories and Direct Numerical Simulations
(DNS). The stability analysis explored two types of base flows: Gaussian and equilibrated
– a skewed Gaussian, which differ in their core vorticity distribution. The growth rates of
the stationary modes are found to be very sensitive to the vorticity distribution, in a way
not accounted for in the asymptotic theories. This is demonstrated by the equilibrated ring
results where a 9% difference in inviscid growth rates is observed for rings with the same
slenderness ratio but evolved with different Reynolds numbers, leading to slight variations
in their vorticity distribution. However, inviscid growth rates are very close to asymptotic
theory predictions if corrections for the ring radius evolution and equilibrated distribution
are considered, while for Gaussian rings, these are smaller by 19 − 33%. This difference in
Gaussian rings is attributed to the absence of a local contribution in the vorticity distribution
that comes from the deformation of the ring core due to the strain field of induced velocity,
which gets naturally included for equilibrated rings. The inclusion of viscosity reduces the
growth rates due to damping, which agree very well with those extracted from the DNS for
equilibrated rings, but there are differences for the Gaussian rings. Additionally, for viscous
cases non-zero frequency rotating modes were isolated for both the base flow types which
appeared in multiple branches, physically corresponding to both curvature and elliptic insta-
bilities.
The large-scale structures from the nonlinear evolution of elliptic instability modes were
next explored using DNS and linear stability analysis. The evolution of the most unstable
mode leads to the formation of an inner core, wrapped around by halo vorticity, which even-
tually breaks down due to nonlinear interactions, yielding a turbulent vortex ring with the
ejection of multiple hairpin vortices in the wake of the ring. The evolution of an isolated hairpin vortex was studied with other vortex structures during the transition modelled as a
background flow: a uniformly convecting stream and a uniform shear. In all the cases inves-
tigated in this work, the entire hairpin vortex moved upward due to its self-induced velocity,
and due to large curvature, its tip rose above its plane, resulting in the two legs approaching
each other upstream of the tip. Further evolution leads to the viscous vortex reconnection
process at the point of closest approach, which splits the hairpin into a vortex ring and a
second hairpin. In this study, with the addition of a background flow the reconnection plane
gets convected downstream, while three stages of the reconnection process: inviscid advec-
tion, bridging and threading, observed in other configurations, are identified. Reconnection
occurs early and at increasingly smaller timescales with an increase in Reynolds number,
while the addition of a positive and negative shear accelerates and decelerates the onset of
the reconnection process, unlike a uniformly convecting stream. The present work identifies
the vortex reconnection process as an important mechanism for the formation of small-scales
during the last stages of breakdown of a laminar vortex ring into turbulence
Developing a tunable, adaptive plasmid selection system to screen Aminoacyl-tRNA synthetase variants
No full textThe genetic code refers to a set of rules used by living organisms to translate information encoded within the genetic material (DNA/mRNA sequences) into proteins. All organisms generally encode 22 proteinogenic or canonical amino acids using the ribosomal machinery. By expanding the genetic code, it is possible to incorporate an unnatural amino acid (UAA) into proteins using the cellular translational apparatus. The incorporation of non-canonical amino acids having various functional properties into proteins has garnered significant interest in recent years. Over 200 non-canonical amino acids have been site-specifically installed into recombinant proteins, thus enabling the expansion of genetic code. Evolution of Aminoacyl tRNA-synthetases typically involves building a library with randomized residues in the amino acid binding pocket of these enzymes and subjecting them to rounds of positive and negative selection. The long-term idea here is to develop and use an ‘adaptable’ selection system for a large library of aminoacyl tRNA/synthetase pair mutants and thus get orthogonal variants specific to a particular unnatural amino acid, and aminoacylate that suppressor tRNA. Traditionally, the selection technique used contained a two-step procedure and was used to evolve the residues in the binding pocket of tyrosyl tRNA synthetase from Methanococcus jannaschii to charge a variety of amino acid substrates (O-methyl tyrosine) other than phenol side chain from tyrosine.
In the initial part of this thesis, we describe the usage of the bacteriophage λ Red recombineering system encoded in pKD46 helper plasmid to knockout the upp gene sequence from DH10B strain. The knockout strain DH10B∆upp was generated as a prerequisite for conducting the UPRT negative selection with 5-Fluorouracil on E. coli, since its essential that cellular toxicity in response to 5-FU is due to the expression of upp from the selection vector and not due to the expression of the genomic copy. Before using the UPRT negative selection system with 5-FU on E. coli, it is essential that the strain being used in the selection is itself devoid of the upp gene, in order to ensure that whatever cellular toxicity (in response to 5-FU) arises is due to the external conditions only. (From the plasmid transformed into the cells) In this case the parent strains were DH10B and KL16 and from these DH10BΔupp strain was produced (discussed in detail in this study). This study aims to describe the knockout procedure adopted in order to produce these strains. Here in E. coli, the reporter genes are CAT and UPRT- both selectable markers being expressed and regulated constitutively under T7 promoter being carried by the vector. The bacteriophage λ Red recombineering system was used (encoded in pKD46 helper plasmid) to knockout the upp gene sequence from DH10B and KL-16 strains. The upp sequence was replaced with an antibiotic cassette flanked by FRT sites in the first step, after amplifying the latter via PCR. Subsequently, with the help of another helper plasmid pCP20 that induces Flippase enzyme action, was introduced to target the FRT sites and knock out the KanR cassette, leaving a FRT scar behind. The knockout strain DH10B Δupp was thus obtained.
The second part of this report is based on the development of the selection system and optimization of the conditions for carrying the selection using CAT and UPRT as the selectable markers. Through solid media LB-Agar spot growth assays and O.D.600 monitoring experiments, we validated both positive and negative selection steps. Using this validated selection procedure, we successfully demonstrated this technique on two engineered Methanococcus jannaschii aminoacyl-3-iodo-tyrosyl tRNA-synthetase (Mj3IYRS) and aminoacyl-4-borono-phenylalanyl tRNA-synthetase (pBoFRS). We also made an improvement over the previous fused cat-uprt selection construct used to carry out enrichment and selection of PylRS variants in other reports, by designing a degradation experiment for selectively chewing away the selection plasmid, thus doing away with the conventional time-taking and laborious sequential co-transformation and harvesting the synthetase genes between two- different plasmid systems after each round of selection
Self-healing in Space Electronics Circuits
No full textSelf-healing in space electronics carries the possibility of creating a paradigm shift in engineering space systems with lesser complexity and mass. Space electronics plays a crucial role in the success of a mission as it acts as the brain, linking diverse systems and generating synergy. The possibility for the faults to develop is more in spacecraft due to long-duration exposure to operating environments of temperature, vacuum, radiation and cyclic operations. Space electronic packages consist of printed circuit boards, and they, in turn, have numerous crisscrossing copper tracks carrying crucial signals. Open interconnect faults that may occur in these tracks during the package operation plays a crucial role in the operational reliability of the mission. These damages can lead to degraded performance, progressive failures detrimental to the payload or the satellite itself.In space missions during the fault scenarios, troubleshooting and repair are almost impossible from the ground unless there is an automatic active healing system in the spacecraft itself.
The studies in this thesis can transmute space electronics with eFASH-enabled PCBs. The research work presented in this thesis also lay the foundation for further investigations, which will be beneficial for self-healed space electronics. This thesis acts as an enabler for future space technology in the facet of the emerging space economy
Electronic Photonic Circuit Design for RF Transceiver
No full textRF over fibre (RoF) based communication system combines features of mm-wave and optical fibre communication. The RoF-based system has the advantage of both optical fibre systems (such as high bandwidth, signal transparency, low-loss and lesser weight of optical fibre) and RF systems (such as mobility and distribution). This RoF transceiver can be made more efficient by combining it with beamforming techniques and reconfigurability. Spatial beamforming techniques help in minimizing the interference in the wavefront by active beam alignment in the transmit and receive paths. Even though, the realization of transceiver chip with electronics and optical circuits is very challenging, it can potentially be realized in future using silicon-photonics technology. This technology is commercially viable for mass-production, since it is compatible with matured CMOS technology. This dissertation presents different design techniques and architectures of electronic components, such as, phase-shifter, attenuator, SPDT switch and TIA, for improving the performance of RoF based phased array transceiver using CMOS/BiCMOS technologies.
The trade-offs in the beamforming architectures have been first discussed in terms of their performance, circuit design complexity and realization cost. Overview of the functionalities and implementation of each electronics and photonics component used in the RoF based phased array transceiver has been presented. The research objectives have been outlined based on the available literature and implementation strategy.
The design of a 7-bit S-band digital passive phase shifter realized using CMOS 65 nm technology is first described. This phase-shifter utilizes novel switched delay network- based topologies for 5.625 degree and 2.8 degree phase bit, along with modified switched filter topologies for other phase-bits. The experimental results of the fabricated chip have shown 7-bit performance with an average insertion loss, root mean square (RMS) phase error and RMS amplitude error of ≤ 11 dB, ≤ 2.0 degree and ≤ 0.6 dB, respectively, with S11 ≥ 7.5 dB and S22 ≥ 14.5 dB across the target frequency band of 2.6 to 3.2 GHz. In addition, design techniques for the realization of broadband switched type IF passive phase-shifter have been presented. These techniques include custom design of a two-metals inductor, a cross-coupled inductor with centre taping and setting the DC bias at RF input/output to 0 V. Design and EM simulation results of a 22.5 degree passive phase-shifter, with and without these broadband techniques, have been discussed for demonstrating their validity. The proposed topology has shown broadband phase-shifter response across 2.5-to-8.0 GHz, with RMS phase error, amplitude error and insertion loss of 9.2 dB.
The design details and simulations of an 8-bit S-band digital passive attenuator, and proposal of a bit topology selection algorithm to achieve low RMS phase error and low amplitude error have been described next. This attenuator has been designed by using new phase compensated Π−, T−and T −bridge attenuator bit topologies for 32 dB to 0.25 dB attenuator bits, and adopting the bit topology selection algorithm. This attenuator has been designed using 65 nm CMOS technology, and its performance has been characterized with the help of exhaustive post-layout simulation in 2.8 GHz to 4.0 GHz frequency band. The designed attenuator has demonstrated significant improvement in performance with 8-bit attenuation accuracy, insertion-loss of ≤ 5.1 dB, RMS amplitude error of ≤ 0.1 dB, RMS phase error of ≤ 0.78 degree, and S11/S22 > 12 dB in 2.8 GHz to 4.0 GHz frequency band.
Thirdly, the design details of a fully differential Ka-band single-pole double-throw (SPDT) switch with virtual grounding, realized using 0.13 μm SiGe BiCMOS technology, have been discussed. This SPDT switch with fully differential topology inherently offers cancellation of common-mode disturbance and has high P−1dB. Further, an asymmetri- cally tapered inductor utilization has been introduced in this SPDT switch with a normal spiral inductor to reduce the layout area of the SPDT switch. Experimental results of the fabricated differential SPDT switch with normal spiral inductor has exhibited the best insertion loss of 2.9 dB and an isolation of -39 dB in 25 GHz to 40 GHz frequency-band, with input P−1dB of 12.6 dBm at 34 GHz and 0.47 mm2 chip-area. Compact differential SPDT switch with asymmetrically tapered inductor has occupied an area of 0.11 mm^2 in the layout and demonstrated superior insertion loss of 1.8 dB and isolation of -39 dB in the same frequency-band with improved input P−1dB of 14.1 dBm at 34 GHz. For further improving the input P−1dB of this SPDT switch, a design of SPDT switch design 3 with pass-gate switch configuration has been presented next. In this design 3, pass-gate tran- sistor terminals biasing is set to 0 V through a 20 KΩ resistance for reducing variations in device parasitics. This SPDT switch has demonstrated a minimum insertion-loss of 1.29 dB, maximum isolation of 41.2 dB and S11/S22 better than 12 dB across the frequency band of operation. This SPDT switch has also shown input P1dB of 15.4 dBm with a layout area of 0.11 mm^2
Design trade-offs, mathematical analysis and circuit architecture of a new low-noise, broadband single-stage transimpedance amplifier (TIA) using 130 nm bipolar complemen- tary metal-oxide-semiconductor (BiCMOS) has been next presented in detail. This TIA is designed as a Common-emitter (CE) shunt-shunt feedback topology with active inductor peaking, and scalable bandwidth enabling better noise, gain and driving capability. The validity of the active inductive peaking and mathematical analysis has been proved with the help of simulations and measurement results. The experimental results of Ku-band TIA (10 MHz to 14 GHz) designed using this architecture have shown a transimpedance gain of 53.2 dBΩ, input-referred current noise of 16.8 pA/√Hz with power consumption of 9.8 mW. Further, another TIA covering K- and Ka-bands (10 MHz to 35 GHz) has been presented to demonstrate the architecture’s adaptability for higher bandwidth. This K-and Ka-bands TIA has demonstrated a transimpedance gain of 33.4 dBΩ, input-referred current noise of 29.4 pA/√Hz with a power consumption of 28.1 mW in the post-layout simulation results, and occupies the same chip area as that of Ku-band TIA, i.e., 0.1 × 0.21 mm^2.
Finally, the feasibility of a 35 GHz RoF communication link has been presented with the help of an experimental demonstration of a 2D integrated RoF photonic transmitter link. This demonstration has addressed the challenges associated with 2D integration. This test-jig has been assembled on a Kovar substrate using a silicon-photonics microring modulator die, driver amplifier die, and interconnected using 50 Ω transmission line. The integrated transmitter link has demonstrated the measured electro-optical (S21) band- width of 35 GHz, the maximum gain of 12.4 dB, RF matching at driver amplifier input in the range of -5 dB to -42 dB and optical matching at microring modulator input in the range of -8 dB to -21 dB for 50 Ω load across 35 GHz frequency bandwidth
Optimization of Wastewater Treatment Process in a Bioreactor Through Hydrodynamic-biokinetic Modeling and Experimental Studies
No full textMembrane bioreactor has emerged as one of the leading technologies for treating municipal and industrial wastewater due to its efficiency in producing high-quality effluents. One of the significant challenges in bioreactors is the high energy and operating costs. The diffused aeration process of a bioreactor is the most energy-intensive operation amounting to 45-75% of the plant energy costs. This study attempts to optimize the wastewater treatment (WWT) process in a bioreactor through modeling and experimental studies. The overall aim is to develop efficient models which can be used to reduce the treatment costs of the WWT process while increasing the treatment efficiency.
As a first objective, a multiphase mixture computational fluid dynamics (CFD) model was developed using k- turbulence closure equations and a discrete population balance model (PBM) add-on with specific bubble classes to predict the oxygen mass transfer in synthetic water. The validated model was extended for sensitivity analysis for a diffused aeration system in a bench-scale aeration tank. Results show that the volumetric oxygen mass transfer coefficient increased by 15 %, with a decrease in air bubble size by 10 %. In a diffuse aeration system, the air bubbles had a wider distribution, with a larger diameter near the bottom of the bioreactor, and narrow distribution, with a smaller bubble size at the top of the bioreactor.
As a second objective, an integrated model was developed by combining the multiphase CFD model, the PBM sub-model, an activated sludge submodel, and a combined extracellular polymeric substance (EPS) – soluble microbial product (SMP) (CES) submodel to investigate the oxygen uptake rate, the aeration efficiency, and treatment efficiency in bioreactors. Three different scale bioreactors, namely, i) case 1- laboratory, ii) case 2 – pilot, and iii) case 3- full-scale system, were studied. The model predictions on water quality were validated well with the experimental results. The validated model was used for sensitivity analysis to identify optimum conditions. The maximum percentage reduction in chemical oxygen demand and total nitrogen were 17 % and 18 %, respectively, for case 3. Also, a reduction of 32 % in the cost of aeration was observed when the bubble size was reduced to 5 mm (from the current value of 7 mm).
The third objective focused on developing a multiphase CFD – porous- CES model to investigate the effect of hydrodynamics on biofouling and the effect of the EPS and SMP on the cake layer formation. The developed model was validated with experimental observations from the laboratory-scale ultrafiltration hollow fiber membrane setup. Observations showed that as the filtration time increased, the transmembrane pressure (TMP) increased, and the permeate flux decreased. Furthermore, in experimental set 2 (synthetic wastewater with sludge seeding), the effect of cake deposition on TMP and permeate flux was 17% and 1.5% higher, respectively, compared to experimental set 1 (synthetic wastewater with yeast sludge). The validated model was then used to investigate the sensitivity of the CES submodel by comparing it with the sectional resistance submodel. It was observed that the sectional resistance model underpredicted the mass of cake deposited by 13 % and overpredicted the limiting flux by 4 %. The results suggest the importance of accounting for the influence of EPS and SMP on the cake layer formation and biofouling.
The fourth objective of this thesis reports a BioWin©- ASM for optimizing the biological nutrient removal (BNR) in a 55 million liters per day sewage treatment plant (STP). The proposed modification was to incorporate an intermediate virtual anoxic zone to achieve simultaneous nitrification-denitrification and total dissolved phosphorus (TDP as PO4) removal. The hydraulic residence time (HRT), dissolved oxygen (DO), and mixed liquor suspended solids (MLSS) of the bioreactor were varied to identify the optimum operating conditions. The optimum DO and MLSS levels were identified as 4 mg/L and 4000 mg/L, respectively, and the optimum HRT was found to be 2 h. in the aeration zone, 1 h. in anoxic, and 3 h. in the reaeration zone. Implementing these modifications in the STP, with minimal operational interventions and no capital costs, improved its performance as predicted by the model. The total nitrogen and TDP (as PO4) reduced from 20 mg/L to 8 mg/L and 3.5 mg/L to 0.9 mg/L, respectively, and met the revised discharge standards. This intervention gave a cost saving of approximately 5.6 million USD.
This work has demonstrated that the numerical models can be successfully used to optimize the treatment efficiency while reducing the capital (membrane replacement) costs and operating (aeration) costs of a bioreactor. The time and efforts required for identifying the optimum conditions through numerical modeling are significantly less than physically characterizing the bioreactor (and varying the conditions to optimize them)
Electronic, Magnetic and Local structure of Some Selected Strongly Correlated Systems
No full textAccording to independent electron band structure theories, transition metal oxides (TMOs) with partially filled 3d valence band are predicted to be metallic in nature. Though in reality, most of them are insulators. Mott and later Hubbard introduced electron-electron interactions in order to explain such insulating behaviors. These systems are often known as Mott-Hubbard insulators (or Mott insulators). Such systems have attracted a great deal of attention in the last several decades, not only due to the intriguing physics observed in these materials with variations in pressure, temperature, doping, etc., but also due to their diverse application potentials. The discovery of high-temperature superconductivity (high-TC) in the copper-based TMOs regenerated the interest in these systems characterized by strong electron-electron interactions; such systems are generally called strongly correlated systems (SCS) to include materials that are not necessarily insulating, but whose properties are believed to be controlled by strong electron-electron interactions. These SCS, particularly those based on the 3d TMOs, are of great importance and cover various phenomena such as metal-insulator transitions (MIT), high-TC superconductivity, and colossal magnetoresistance. All such exciting properties, shown by 3d TMOs, are fundamentally important due to the presence of a partially filled 3d valence band (VB) and to understand such properties, one needs to investigate the electronic and crystal structures of these materials. In this thesis, we have investigated the electronic, magnetic, and local geometric structures of some selected strongly correlated systems with interesting properties like MIT, and strong magnetoelectric coupling with the help of different high energy spectroscopic techniques along with dielectric and magnetic measurements.
The samples reported in this thesis were prepared by various synthetic routes, such as solid-state reaction, sol-gel method, and d.c arc melting. These samples were characterized by x-ray diffraction, magnetic susceptibility, optical absorption, dielectric constant and energy dispersive analysis of x-rays. Various spectroscopic techniques like Hard X-ray Photoemission Spectroscopy (HAXPES) and Extended X-ray Absorption Fine Structure (EXAFS) were used to probe the electronic and local structures of the samples of Nickel Oxide (NiO), La1-xCaxVO3, Ga-doped YMnO3 and La-doped SrTiO
PDMS-Based Nanocomposite for EMI Shielding application
No full textLightweight, flexible, and easy-to-integrate solutions are in great demand in electronic devices. The present work deals with the preparation of Poly dimethyl siloxane (PDMS) based nanocomposite for suppressing electromagnetic interference (EMI). This work is broadly divided into five chapters. The first chapter discusses the state-of-the-art literature on polymeric nanocomposites in general and PDMS-based composites in particular for EMI shielding applications.
The second chapter discusses the materials and methods used for the preparation of nanocomposite in this study. The third chapter discusses the synthesis and characterization of MoO3-MWCNTs conjugates and their composites with PDMS. The bulk electrical conductivity and the EMI shielding performance of the nanocomposites are discussed in this chapter. The challenges associated with the curing of PDMS are also discussed in this chapter. This filler system exhibited shielding effectiveness of SET ca. 25 dB for a 1 mm thick sample.
The fourth chapter highlights the synthesis and preparation of hybrid fillers consisting of carbonaceous fillers such as rGO and MWCNT and MoS2 using a hydrothermal technique. When incorporated in PDMS and cured using condensation curing, the composites showed SE of ca. 25 dB for a 1 mm thick sample.
In the last chapter, the EMI shielding performance of multi-layered stacking of previously prepared sheets was evaluated. The composite with the best configuration showed SET up to 40 dB for a 3 mm thick sample.
In summary, two different filler systems were explored in this thesis for the efficient absorption of EM waves. In this thesis, two different crosslinking mechanisms (addition and condensation curing) were explored based on the chemistry of the filler system. The composite was further characterized for AC conductivity, EMI shielding and UV blocking characteristics.Momentive Performance Materials PVT. LTD. and CI
Effect of As and Se substitution on the Phase Change properties of GeTe based alloys
No full textPhase-change memory (PCM) is a key enabling technology for non-volatile electrical data storage at the nanometer scale. A PCM device consists of a small active volume of phase-change material between two electrodes. In PCM, data are stored using the electrical resistance contrast between a high-conductive crystalline phase and a low-conductive amorphous phase. An appealing attribute of PCM is that the stored data is retained for a very long time (typically 10 years at room temperature). This property could enable PCM to be used for non-volatile storage such as Flash and hard disk drives, while operating almost as fast as high-performance volatile memory such as dynamic random-access memory (DRAM). Primarily, chalcogenide alloys are used as an active element in PCM devices. The device performance relies on the structural variations, thus understanding the structural modulations with variation in composition is of great importance.
Current work is focused on GeTe based alloys Ge2Sb2−xAsxTe5 ( 0 ≤ x ≤ 2.0) and GeTe1−xSex ( 0 ≤ x ≤ 1.0). The objective is to study the effect of the substitution of smaller atoms in place of larger atoms on the structural and phase change properties. The substitution of As and Se is expected to influence the ionicity and hybridization capability of GeTe based alloys to a larger extent as predicted by Littlewoods ionicity - hybridization map for group IV-VI alloys. The As substituted for Sb in Ge2Sb2Te5 (GST) samples i.e. Ge2Sb2−xAsxTe5 , crystallize at higher temperatures compared to the parent GST. During the phase change, a direct transition from amorphous to the stable hexagonal structure for x > 1.0 has been observed. A distinct two-step transition in Sb rich samples and a single step transition for As rich samples are observed in R-T measurements with a high contrast in electrical resistivity. A composition-dependent Metal-Insulator Transition (MIT) is also observed in these samples. In GeTe1−xSex alloys, it is observed that with increasing Se substitution, the structure transforms from rhombohedral to orthorhombic, supported by Rietveld refinement analysis. In GeTe1−xSex thin films the transition temperature for amorphous to crystalline phase shows an increasing trend with the Se substitution. The contrast in electrical resistivity between the amorphous and crystalline states is 104 for GeTe, and with the Se substitution, the contrast increases considerably to 106 for GeTe0.5Se0.5. Devices fabricated with thin films show that the threshold current decreases with the Se substitution indicating a reduction in the power required for WRITE operation.
The present study shows that the crystalline structure, resistivity, optical bandgap, transition temperature, data retention and threshold voltage can be effectively controlled and tuned by the substitution of Se for Te in GeTe and As for Sb in Ge2Sb2Te5, which is conducive for phase change memory applications.UG
Neural Approaches for Natural Language Query Answering over Source Code
No full textDuring software development, developers need to ensure that the developed code is bug-free and the best coding practices are followed during the code development process. To guarantee this, the developers require answers to queries about specific aspects of the code relevant to the development. Powerful code-query languages such as CodeQL have been developed for this purpose. Use of such code-query languages, however, requires expertise in writing formal queries. For each separate query, one needs to write several lines in a code-query language.
To remedy these problems, we propose to represent each query by a natural language phrase and answer such queries using neural networks. We aim to perform model training such that a single model can answer multiple queries as opposed to writing separate formal queries for each task. Such a model can answer these queries against unseen code. With this motivation, we introduce the novel NlCodeQA dataset. It includes 171,346 labeled examples where each input consists of a natural language query and a code snippet. The labels are answer spans in the input code snippet with respect to the input query. State-of-the-art BERT-style neural architectures were trained using the NlCodeQA data. Preliminary experimental results show that the proposed model achieves the exact match accuracy of 86.30%.
The proposed use of natural language query and neural models for query understanding will help increase the productivity of software developers and pave the way for designing machine learning based code analysis tools that can complement the existing code analysis systems for complex code queries that are either hard or expensive to represent using a formal query language