Cellular function depends on diverse biomolecular interactions, often giving rise to large biomolecular assemblies and phase-separated compartments. Experimental observations of membraneless organelles (MLOs) raise a fundamental question. How do cells strike a balance between forming dynamic self-assemblies while safeguarding against deleterious effects associated with irreversible protein aggregates? Using biomolecular simulations at multiple resolutions, we investigate how phosphorylation modulates the dynamics of phase-separated FUS droplets and helps suppress amyloid-like aggregation. We then turn to the role of physical enzyme clustering in long biochemical reaction cascades, exploring how spatial organization and enzyme–enzyme interactions can influence reaction fluxes and yields. Finally, we examine signatures of protein–protein interactions in well-characterized biochemical pathways such as glycolysis, folate metabolism, and purine biosynthesis. Overall, our work highlights how molecular interactions and spatial organization govern the regulation and function of biomolecular assemblies, from controlling protein aggregation to shaping the organization and efficiency of biochemical pathways.
In this talk, we will discuss a systematic approach to gravitational waves generated by localized sources in de Sitter spacetime, starting from quadrupolar radiation and moving toward a general multipolar framework. We will first review the geometry of de Sitter spacetime and explain how it modifies the standard flat-space description of radiation. Next, we will discuss de Sitter Teukolsky waves and demonstrate their relation, through explicit gauge transformations, to other quadrupolar solutions in the literature. We will explain how a consistent truncation of the source multipole expansion can be performed while preserving stress-tensor conservation and the generalized harmonic gauge conditions, alongside its asymptotic Bondi description. Going beyond the quadrupole, we will describe the construction of the source-generated metric through octupolar order, including its electric and magnetic ($\ell=3$) sectors. Finally, we will present recent work extending this construction to arbitrary multipole order using an exact map to an auxiliary flat-space problem. The resulting framework provides a systematic starting point for studying gravitational radiation and its observables at arbitrary multipole order in an accelerating background.
Neutrino Astronomy started with the observation of Solar neutrinos
and then the Supernova neutrinos. Establishing that neutrinos are
massive through the observation of neutrino oscillations led to neutrino
physics becoming an integral part of astrophysics. The kilometer-cubed
size detector IceCube has taken the astrophysical role of neutrinos
further by detecting extremely high energy neutrinos from extra galactic
sources. This has also led to the concept of Multi-Messenger astronomy.
In this talk, I will describe some of the highlights of IceCube results and
how we hope to learn more about the universe from these results.
Physics Colloquium | Alladi Ramakrishnan Hall
Oct 29 15:30-16:30
R. Thangadurai | Harish Chandra Research Institute
A classical theorem of Kronecker states that the Mahler
measure, $M(P) = 1$ for any monic, irreducible polynomial with integer
coefficients if and only if $P$ is a $n$-th cyclotomic polynomial for
some natural number $n$. If a monic irreducible polynomial $P(x)\in
\mathbb{Z}[x]$ with $P(0)
e 0$ which is not a cyclotomic polynomial,
then $M(P) > 1$. In 1933, D. H. Lehmer posed the following problem.
Does there exist a positive constant $c$ such that $M(P) \geq 1+c$ for
all monic, polynomial $P$ with $P(0)
e 0$ and integer coefficients?
Recently, we proved the following results. Let $\mathcal{P}$ be the
collection of all monic, irreducible non-cyclotomic polynomials $P$ of
degree $d\geq 1$ with integer coefficients and $P(0)
e 0$. For a given
prime $p$, we partition $\mathcal{P} = \bigcup_{R\geq 0}
\mathcal{P}_{p,R}$. Then for a fixed $R\geq 0$, we prove Lehmer's
Problem for all primes $p$. Also, for any fixed prime $p$ and $d$ large
enough, we proved a quantitative uniform lower bound for the Lehmer's
Problem by varying $R\leq d/\log d$. We also note that Lehmer's problem
is equivalent to prove a uniform lower bound by varying $R\leq d-1$ and
for any fixed prime $p$. In this talk, we discuss the proof of a case
when $R = 1$. This is a joint work with Piyush Kumar Jha.