Development of High-Performance, Lightweight, Low-Cost Carbon Fibers for Sustainability

This dissertation focuses on the development of high-performance carbon fibers for light weighting automobiles to achieve sustainable developmental goals (SDG) of clean energy, climate action and infrastructure. Replacing steel and aluminum used in current day automobiles by carbon fibers leads to low-weight structures (theoretical reduction by ~70 % and 35% for steel and aluminum, respectively) with higher fuel savings and lower emissions. Two pathways were studied to design high performance carbon fibers that could have the potential for such replacement and their widespread use in the future. The first approach towards the goal involved designing porous carbon fibers with low-density and multifunctional capability using blends of poly(acrylonitrile) (PAN) with sacrificial polymers and block copolymers. The second route explored the use of low-cost precursor, asphaltene, to derive carbon fibers. Porous carbon fibers from gel-spun blends of PAN with sacrificial polymers were the initial systems studied to characterize the mechanical performance upon introduction of porosity. Orientation imparted during gel-spinning of the PAN-sacrificial polymer blends was synergistically combined with the micro-phase separation of the polymer pairs, to tailor the porous morphology of these fibers and their resultant mechanical properties. From five sacrificial polymers, three systems including poly(acrylic acid) (PAA), poly(methyl methacrylate) (PMMA), poly(styrene-co-acrylonitrile) (SAN), were selected due to their intermediate and higher degree of compatibility with PAN, discerned through UV-vis spectroscopy. Porous morphology of the different carbon fibers produced was characterized through scanning electron microscopy (SEM) and the differences shown due to the sacrificial polymers studied. The variation in pore size caused by the differences in compatibility between PAN and the sacrificial polymer was evaluated experimentally through blend rheology and theoretically using interaction parameter values. The tensile properties of porous carbon fibers from the three systems were compared to that of the non-porous PAN based carbon fibers processed under similar conditions. Specific tensile modulus of the porous carbon fibers derived from PAN-PAA and PAN-PMMA was found to be 15 to 40 % higher than that for the PAN based carbon fibers. Additionally, influence of sacrificial polymer content (5-20 wt%) on the mechanical, structural and morphological properties was studied for the PAN-SAN fiber systems with porous channeled morphology. This study showed that gel-spinning of bicomponent PAN/PMMA-b-PAN fibers provided a versatile means for tuning the mechanical and electrochemical properties of porous carbon fibers, thus allowing for their potential use as structural energy storage materials. Herein, by gel-spinning polymer precursors of poly(acrylonitrile) (PAN) and poly(methyl methacrylate)-block¬-poly(acrylonitrile) (PMMA-b-PAN), we produced a series of carbon fibers and systematically studied the morphological, mechanical, and electrochemical properties. Porous carbon fibers with block copolymer (BCP) in the sheath exhibited the best tensile properties with a strength of 1.1 GPa, modulus of ~190 GPa, and electrochemical capacitance of 11 F/g at 10 mV/s when pyrolyzed at 1315 °C under tension. Without tension and at a pyrolysis temperature of 800 °C, the fibers with BCP as both the sheath and core components achieved the highest electrochemical capacitance of 70 F/g at 10 mV/s and highest surface area of 264 m2/g. The characteristic correlation length of PMMA-b-PAN was calculated through thermodynamically governed computational method and compared with the pore size in the experimentally obtained carbon fibers. Through the second approach, conditions to gel-spin blends of low-cost precursor of asphaltene with PAN were established. Functionalization of asphaltenes with nitric acid (f-Asp) enabled their complete solubility in dimethylacetamide (DMAc) unlike the as-received asphaltene powder and further resulted in obtaining relatively homogeneous spinning solutions with PAN. Mechanical properties and structural parameters of precursor f-Asp/PAN fibers with their blend ratio ranging from 30/70 to 60/40, were studied. Carbon fibers with maximum tensile strength and modulus of 1.1 GPa and 181 GPa, were obtained from the gel-spun f-Asp/PAN blends. The study suggests that carbon fibers with reasonable mechanical properties can be derived from low-cost asphaltene through the scalable route of solution/gel-spinning. The two approaches studied in the dissertation present ways to develop high-performance carbon fibers that would have the potential to light weighting automobiles and thus, steer towards a future of achieving SDG.Ph.D

Multiple novel prostate cancer susceptibility signals identified by fine-mapping of known risk loci among Europeans

Genome-wide association studies (GWAS) have identified numerous common prostate cancer (PrCa) susceptibility loci. We have fine-mapped 64 GWAS regions known at the conclusion of the iCOGS study using large-scale genotyping and imputation in 25 723 PrCa cases and 26 274 controls of European ancestry. We detected evidence for multiple independent signals at 16 regions, 12 of which contained additional newly identified significant associations. A single signal comprising a spectrum of correlated variation was observed at 39 regions; 35 of which are now described by a novel more significantly associated lead SNP, while the originally reported variant remained as the lead SNP only in 4 regions. We also confirmed two association signals in Europeans that had been previously reported only in East-Asian GWAS. Based on statistical evidence and linkage disequilibrium (LD) structure, we have curated and narrowed down the list of the most likely candidate causal variants for each region. Functional annotation using data from ENCODE filtered for PrCa cell lines and eQTL analysis demonstrated significant enrichment for overlap with bio-features within this set. By incorporating the novel risk variants identified here alongside the refined data for existing association signals, we estimate that these loci now explain ∼38.9% of the familial relative risk of PrCa, an 8.9% improvement over the previously reported GWAS tag SNPs. This suggests that a significant fraction of the heritability of PrCa may have been hidden during the discovery phase of GWAS, in particular due to the presence of multiple independent signals within the same regio

Laughter and humour

Brief overview of theories of humor.This is an overview of theories of humor's adaptive significance

Influence of flame on graphene based flexible nanocomposite

The study aims to develop a novel composite, with a combined contribution of reduced graphene oxide, poly(dimethyl-siloxane), and sodium bentonite (organoclay), for flame protection. Thermo-gravimetric analysis revealed an outstanding thermal stability of the composite as compared to its constituents. The superior composite is demonstrated to efficiently protect a polymer layer that burns instantly upon exposure to flame. The char residue of the composite indicated the formation of a spherical structure that acted as barrier layer to the underlying material to avoid any structural damage caused due to the exposure of the flame

Molecular and Genetic Characterization of Natural HIV-1 Tat Exon-1 Variants from North India and Their Functional Implications

<div><p>Background</p><p>Designing an ideal vaccine against HIV-1 has been difficult due to enormous genetic variability as a result of high replication rate and lack of proofreading activity of reverse transcriptase leading to emergence of genetic variants and recombinants. Tat transactivates HIV-1 LTR, resulting in a remarkable increase in viral gene expression, and plays a vital role in pathogenesis. The aim of this study was to characterize the genetic variations of Tat exon-1 from HIV-1 infected patients from North India.</p><p>Methods</p><p>Genomic DNA was isolated from PBMCs and Tat exon-1 was PCR amplified with specific primers followed by cloning, sequencing and sequence analyses using bioinformatic tools for predicting HIV-1 subtypes, recombination events, conservation of domains and phosphorylation sites, and LTR transactivation by luciferase assay.</p><p>Results</p><p>Phylogenetic analysis of Tat exon-1 variants (n = 120) revealed sequence similarity with South African Tat C sequences and distinct geographical relationships were observed for B/C recombinants. Bootscan analysis of our variants showed 90% homology to Tat C and 10% to B/C recombinants with a precise breakpoint. Natural substitutions were observed with high allelic frequencies which may be beneficial for virus. High amino acid conservation was observed in Tat among Anti Retroviral Therapy (ART) recipients. Barring few changes, most of the functional domains, predicted motifs and phosphorylation sites were well conserved in most of Tat variants. dN/dS analysis revealed purifying selection, implying the importance of functional conservation of Tat exon-1. Our Indian Tat C variants and B/C recombinants showed differential LTR transactivation.</p><p>Conclusions</p><p>The possible role of Tat exon-1 variants in shaping the current HIV-1 epidemic in North India was highlighted. Natural substitutions across conserved functional domains were observed and provided evidence for the emergence of B/C recombinants within the ORF of Tat exon-1. These events are likely to have implications for viral pathogenesis and vaccine formulations.</p></div

HIV-1 sub-typing based on global subtype references.

<p><b>A</b>) The phylogenetic tree of Tat exon-1 variants with M (A to K including A1, A2, F1, and F2), N, O and P groups. <b>B</b>) The phylogenetic tree of Tat exon-1 variants with global subtype B from countries such as China (CN), France (FR), Japan (JP), Thailand (TH), United States (US), Canada (CA) and Brazil (BR) and global subtype C from countries such as Botswana (BW), Tanzania (TZ), South Africa (ZA), Zambia (ZM), Kenya (KE), Malawi (MW) and Brazil (BR) sequences. Each reference sequence was labelled with a subtype, followed by country of isolation and accession number. Filled circles represent our C variants and filled rectangles represent our B/C recombinants. The bootstrap probability (>65%, 1,000 replicates) was showed with asterisk (*) at the corresponding nodes of the tree and the scale bar represents the selection distance of 0.05 and 0.02 nucleotides per position in the sequence.</p

HIV-1 LTR Transactivation by Tat C variants and B/C Tat.

<p>HEK293 cells were co-transfected with 200 ng Tat variants (TatN12, TatD60 and TatVT6) and 50 ng of pGL3-Luc vector containing subtype B or C LTR, and pGL3-Luc B or C LTR alone was used as control. After 24 hours of transfection, cells were lysed with lysis buffer and the luciferase activity was measured in a luminometer. The relative transactivation was expressed as mean luciferase units obtained from luciferase assay. The error bar represents the standard deviation of luciferase units and the p values less than 0.05 represents the significance of luciferase activity.</p

Tat exon-1 amino acid sequence analysis.

<p><b>A</b>) Amino acid signature pattern of Tat exon-1 variants were compared with consensus Tat B sequence. <b>B</b>) Amino acid signature pattern of Tat exon-1 variants were compared with consensus Tat C sequence. The X-axis represents the amino acid consensus sequence of Tat B and C with the functional domains such as N-terminal (1–21aa), Cystine rich (22–37aa), Core (38–48aa), Arginine rich (49–57aa), Glutamine rich (58–71aa) and the Y-axis represents the amino acid frequency observed in our variants.</p