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Bipul Pandey

Publications and source records attributed to Bipul Pandey.

4 recordsLinked to original sources

Learning constructive models of emergent systems

Emergent systems - systems with multiscale interactions - arise through iteration than forward design, leaving principles for building them under-explored. Current artificial intelligence architectures, while useful for generation, provide no logic for construction. Inspired by statistical phylogenetics, we show that inferring scales of system entropy then constraining information from low to high entropic scales yields stepwise constructive models. We term this architecture the Layer-Restricted Boltzmann Machine (LRBM). Applied identically to digit images, natural language, and enzyme sequences, LRBMs follow a common hierarchical logic: lower layers encode global structure, higher layers fine-grained features. As a stringent test, we assayed 160 synthetic chorismate mutase (CM) constructive trajectories alongside 1,130 natural homologs in vivo. Designed CMs functioned up to 53% divergent from nearest natural homolog. Fold emerged at intermediate layers while function required all layers, illustrating that fold was necessary but insufficient for function. Our results demonstrate a shared, learnable logic for constructing emergent systems.

cond-mat.dis-nn

Going Beyond the Cumulant Approximation II:Power Series Correction to Single Particle Green's Function in 1D Holstein Chain

Previously, we introduced a method for systematically correcting a quasiparticle green's function via a power series expansion. Here we present an ODE based formalisms of power series correction that goes beyond the cumulant approximation and implement it to 1D Holstein chain for a wide range of coupling strengths in a scalable and inexpensive fashion at both zero and finite temperature. We show that this first differential formalism of the power series is both qualitatively and quantitatively in excellent agreement with exact diagonalization results on 1D Holstein chain with dispersive bosons for a large range of electron-boson coupling strength. We investigate carrier mass growth rate and carrier energy displacement across a wide range of coupling strength. Finally, we present a heuristic argument which predicts most of the rich satellite structure without explicit calculation.

cond-mat.mtrl-sci

Going Beyond the Cumulant Approximation: Power Series Correction to Single Particle Green's Function in Holstein System

In the context of a single electron two orbital Holstein system coupled to dispersionless bosons, we develop a general method to correct single particle Green's function using a power series correction(PSC) scheme. We then outline the derivations of various flavors of cumulant approximation through the PSC scheme and explain the assumptions and approximations behind them. Finally, we compute and compare PSC spectral function with cumulant and exact diagonalized spectral functions and elucidate three regimes of this problem - two that cumulant explains and one where cumulant fails. We find that the exact and the PSC spectral functions match within spectral broadening across all three regimes.

cond-mat.str-el

TMCI and Space Charge

Transverse mode-coupling instability (TMCI) is known to limit bunch intensity. Since space charge (SC) changes the spectra of the collective modes, it affects the TMCI threshold as well. In agreement with results of M. Blaskiewicz and V. Balbekov, we found that, when the wake is negative or it essentially negative, the instability threshold increases as fast as the space charge tune shift when the latter is large enough. In contrast, for oscillating wakes, when the oscillations are sufficiently pronounced, the threshold dependence on SC is non-monotonic; at sufficiently high SC tune shift the threshold goes inversely proportional to that.

physics.acc-ph