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A repository of scholarly research output from the Indian Institute of Science Education and Research (IISER) Pune.
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- Theses submitted to IISER Pune in partial fulfilment of the requirements of the BS-MS dual degree, MSc. and Ph.D programmes. Also, project reports submitted by the students.
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Item type:Item, Access status: Open Access , Approach to Failures in Complex Networks and Possible Interventions(2026-09) ROY, SHAUNAK; SANTHANAM, M S; Dept. of Physics; 20172035Complex networks form the backbone of modern infrastructure, including power grids, transportation and communication systems. While failures in such systems are often associated with external shocks or deliberate attacks, they can also arise spontaneously from the intrinsic fluctuations of the processes taking place within the network. This thesis investigates how such internal fluctuations can drive a complex network from normal operation to complete and irreversible failure. The work reveals that intrinsic fluctuations alone can lead to network collapse through three distinct regimes: independent failures, cascade failures, and overload failures. A capacity-to-load ratio is the parameter characterizing these regimes, with the same qualitative behavior observed across a range of network topologies, and real-world networks. The thesis further examines network recovery through delayed repair. The analysis demonstrates that early intervention, before the onset of cascading failures, is both more effective and less resource-intensive. In addition, structural and temporal signatures of approaching failure are identified, providing potential early-warning indicators of systemic collapse. Overall, this work establishes that large-scale network failure need not require an external perturbation: intrinsic stochastic fluctuations can themselves generate cascading breakdowns. The results provide a framework for understanding, anticipating, and mitigating failure in complex networked systems.Item type:Item, Access status: Metadata only , Item type:Item, Access status: Metadata only , Simultaneous formation of peptides and RNA via prebiotic cross-catalytic enhancement(Springer Nature, 2026-09) ROY, RAYA; SAWANT, ANUPAM A.; RAJAMANI, SUDHA; Dept. of BiologyNucleoside triphosphates, cyclic monophosphates and amino acids are hypothesized to have been present together in the prebiotic milieu. Earlier studies have demonstrated the importance of their phosphorylation to result in oligomers. In this study, we characterized the cross-catalytic effect of oligomerization stemming from the simultaneous presence of nucleotide and amino acids, two biochemically important monomers, in a reaction mixture, and discuss its implications for biomolecular evolution. Intrinsically phosphorylated linear or cyclic nucleotides (ATP and cAMP, respectively), when mixed with glycine in a one-pot- reaction under prebiotically pertinent conditions, resulted in peptides and oligonucleotides.Mass spectrometry analysis indicated the formation of oligomers, with an increase in relative abundance observed in certain reaction scenarios when compared to reactions that involved only oligomerization of the individual monomer. The reason for this enhancement in case of both the oligomer types, was the formation of a reactive intermediate, an aminoacylated-AMP (AMP-aa). We extended this strategy to study amino acids with different side chains to comprehend the properties required for the formation of AMP-aa under our reaction conditions. The nonenzymatic formation of AMP-aa, which resulted in longer oligomers, indicates the plausibility of the emergence of initial steps involved in a primordial aminoacylation or single nucleotide translation system.Item type:Item, Access status: Metadata only , Gaia’s Promise to Detect Compact-object Binaries: Where We Stand with the Third Data Release(IOP Publishing, 2026-08) CHAWLA, CHIRAG; Chatterjee, Sourav; Breivik, Katelyn; Dept. of PhysicsWith its third data release (DR3), Gaia begins unveiling dormant candidate compact object (CO) binaries with luminous companions (LC) as predicted by several past theoretical studies. To date, three black hole (BH), 21 neutron star (NS), and ≈3200 white dwarf (WD) candidates have been identified with LCs in detached orbits using astrometry. We adopt an observationally motivated sampling scheme for the star formation history of the Milky Way, and initial zero-age main-sequence binary properties, and incorporate all relevant binary interaction processes during evolution to obtain a realistic present-day intrinsic population of CO–LC binaries. We apply Gaia’s selection criteria to identify the CO–LC binaries detectable using the observational cuts applicable for DR3 as well as its end-of-mission (EOM). We find that under the DR3 selection cuts, our detectable population includes no BH–LCs, approximately 10–40 NS–LCs, and around ∼4300 WD--LCs. Our predicted NS–LC population is in good agreement with the current DR3 census, both in its predicted yield and in the orbital and stellar properties, and we recover a close analogue of the Gaia NS1 candidate together with its detailed formation pathway. For WD–LC binaries, we find that a moderate natal kick of 5–15 km s−1 imparted at WD formation is required to match the observed orbital properties of WD–LC candidates in DR3. We further show that Gaia BH3–like binaries can form through standard isolated binary evolution without invoking any additional modeling assumptions, whereas reproducing Gaia BH1 and BH2 remains challenging within this framework. Looking ahead to the EOM, we predict detection of ∼30–300 BH–LC binaries, ∼1500–5000 NS-LC binaries, and ∼105–106 WD–LC binaries, primarily due to the significantly longer observational baseline.Item type:Item, Access status: Metadata only , Learning models on rooted regular trees with majority update policy: Convergence and phase transition(Cambridge University Press, 2026-08) PODDER, MOUMANTI; Sarkar, Anish; Dept. of MathematicsWe study a model of social learning on rooted regular trees. An agent is stationed at each vertex of 𝕋𝑚, the rooted tree in which each vertex has precisely m children, and at any time step 𝑡 ∈ℕ0, the agent is allowed to select one of two available technologies: B and R. Let the technology chosen by the agent at vertex v of 𝕋𝑚, at time step t, be 𝐶𝑡(𝑣). We begin with the independent and identically distributed (i.i.d.) collection {𝐶0(𝑣) : 𝑣 ∈𝕋𝑚}, where 𝐶0(𝑣) =𝐵 with probability 𝜋0. During the epoch t, the agent at vertex v performs an experiment that results in success with probability 𝑝𝐵 if 𝐶𝑡(𝑣) =𝐵, and with probability 𝑝𝑅 if 𝐶𝑡(𝑣) =𝑅. If the children of v are denoted 𝑣1,…,𝑣𝑚, the agent at v updates their technology to 𝐶𝑡+1(𝑣) =𝐵 if the number of successes among all 𝑣𝑖 (where 𝑖 ∈{1,2,…,𝑚}) with 𝐶𝑡(𝑣𝑖) =𝐵 exceeds, strictly, the number of successes among all 𝑣𝑗 (where 𝑗 ∈{1,2,…,𝑚}) with 𝐶𝑡(𝑣𝑗) =𝑅. If these two numbers are equal then the agent at v sets 𝐶𝑡+1(𝑣) =𝐵 with probability 1/2. In all other cases, 𝐶𝑡+1(𝑣) =𝑅. We show that {𝐶𝑡(𝑣) : 𝑣 ∈𝕋𝑚} is i.i.d. as well, with 𝐶𝑡(𝑣) =𝐵 with probability 𝜋𝑡, where the sequence {𝜋𝑡}𝑡∈ℕ0 converges to a fixed point 𝜋, in [0, 1], of a function 𝑔𝑚. We show that for 𝑚 ⩾3, there exists a 𝑝(𝑚) ∈(0,1) such that 𝑔𝑚 has the unique fixed point 1/2 when 𝑝 ⩽𝑝(𝑚), and three distinct fixed points, of the form 𝛼, 1/2, and 1 −𝛼, for some 𝛼 ∈[0,1/2) when 𝑝 >𝑝(𝑚). When 𝑚 =3, 𝑝𝐵 =1, and 𝑝𝑅 ∈[0,1), we show that the function 𝑔3 (i) has a unique fixed point, 1, when 𝑝𝑅 <√3 −1, (ii) has two distinct fixed points, one of which is 1, when 𝑝𝑅 =√3 −1, and (iii) has three distinct fixed points, one of which is 1, when 𝑝𝑅 >√3 −1. When 𝑔𝑚 has multiple fixed points, we also specify which of these fixed points 𝜋 equals, depending on 𝜋0. Finally, for 𝑚 =2, we describe the behaviour of 𝑔2 for all values of 𝑝𝐵 and 𝑝𝑅.