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S. L. Narasimhan

Publications and source records attributed to S. L. Narasimhan.

At least 19 recordsLinked to original sources
arXiv2019

ragamAI: A Network Based Recommender System to Arrange a Indian Classical Music Concert

South Indian classical music (Carnatic music) is best consumed through live concerts. A carnatic recital requires meticulous planning accounting for several parameters like the performers' repertoire, composition variety, musical versatility, thematic structure, the recital's arrangement, etc. to ensure that the audience have a comprehensive listening experience. In this work, we present ragamAI a novel machine learning framework that utilizes the tonic nuances and musical structures in the carnatic music to generate a concert recital that melodically captures the entire range in an octave. Utilizing the underlying idea of playlist and session-based recommender models, the proposed model studies the mathematical structure present in past concerts and recommends relevant items for the playlist/concert. ragamAI ensembles recommendations given by multiple models to learn user idea and past preference of sequences in concerts to extract recommendations. Our experiments on a vast collection of concert show that our model performs 25%-50% better than baseline models. ragamAI's applications are two-fold. 1) it will assist musicians to customize their performance with the necessary variety required to sustain the interest of the audience for the entirety of the concert 2) it will generate carefully curated lists of south Indian classical music so that the listener can discover the wide range of melody that the musical system can offer.

cs.IR↗
arXiv2019

Exclusion process on an open lattice with fluctuating boundaries

We show that the TASEP of a driven system of particles of arbitrary size, with nearest neighbor repulsive interaction, on an open lattice is equivalent to the TASEP of interacting monomers on an open lattice whose size fluctuates in response to the entry and exit of particles. We have presented the maximal current profile as a function of the interaction strength for dimers and tetramers, obtained in Monte Carlo simulation; the results agree well with the ones computed by applying a specific rod-to-monomer mapping to the steady state current and density predicted by a mean-field theory of interacting monomers which adapts a Markov Chain approach for incorporating nearest-neighbor correlations.

cond-mat.stat-mech↗
arXiv2012

HP-sequence design for lattice proteins - an exact enumeration study on diamond as well as square lattice

We present an exact enumeration algorithm for identifying the {\it native} configuration - a maximally compact self avoiding walk configuration that is also the minimum energy configuration for a given set of contact-energy schemes; the process is implicitly sequence-dependent. In particular, we show that the 25-step native configuration on a diamond lattice consists of two sheet-like structures and is the same for all the contact-energy schemes, ${(-1,0,0);(-7,-3,0); (-7,-3,-1); (-7,-3,1)}$; on a square lattice also, the 24-step native configuration is independent of the energy schemes considered. However, the designing sequence for the diamond lattice walk depends on the energy schemes used whereas that for the square lattice walk does not. We have calculated the temperature-dependent specific heat for these designed sequences and the four energy schemes using the exact density of states. These data show that the energy scheme $(-7,-3,-1)$ is preferable to the other three for both diamond and square lattice because the associated sequences give rise to a sharp low-temperature peak. We have also presented data for shorter (23-, 21- and 17-step) walks on a diamond lattice to show that this algorithm helps identify a unique minimum energy configuration by suitably taking care of the ground-state degeneracy. Interestingly, all these shorter target configurations also show sheet-like secondary structures.

cond-mat.stat-mech↗
arXiv2010

Dynamics of a stochastically driven Brownian particle in one dimension

We present a study on the dynamics of a system consisting of a pair of hardcore particles diffusing with different rates. We solved the drift-diffusion equation for this model in the case when one particle, labeled F, drifts and diffuses slowly towards the second particle, labeled M. The displacements of particle M exhibits a crossover from diffusion to drift at a characteristic time which depends on the rate constants. We show that the positional fluctuation of M exhibits an intermediate crossover regime of subdiffusion separating initial and asymptotic diffusive behavior; this is in agreement with the complete set of Master Equations that describe the stochastic evolution of the model. The intermediate crossover regime can be considerably large depending on the hopping probabilities of the two particles. This is in contrast to the known crossover from diffusive to subdiffusive behavior of a tagged particle that is in the interior of a large single-file system on an unbound real line. We discuss our model with respect to the biological phenomena of membrane protrusions where polymerizing actin filaments (F) push the cell membrane (M).

cond-mat.stat-mech↗
arXiv2010

flatIGW - an inverse algorithm to compute the Density of States of lattice Self Avoiding Walks

We show that the Density of States (DoS) for lattice Self Avoiding Walks can be estimated by using an inverse algorithm, called flatIGW, whose step-growth rules are dynamically adjusted by requiring the energy histogram to be locally flat. Here, the (attractive) energy associated with a configuration is taken to be proportional to the number of non-bonded nearest neighbor pairs (contacts). The energy histogram is able to explicitly direct the growth of a walk because the step-growth rule of the Interacting Growth Walk \cite{IGW} samples the available nearest neighbor sites according to the number of contacts they would make. We have obtained the complex Fisher zeros corresponding to the DoS, estimated for square lattice walks of various lengths, and located the $θ$ temperature by extrapolating the finite size values of the real zeros to their asymptotic value, $\sim 1.49$ (reasonably close to the known value, $\sim 1.50$ \cite{barkema}).

cond-mat.stat-mech↗
arXiv2008

A tunable solid-on-solid model of surface growth

We have performed a detailed Monte Carlo study of a diffusionless $(1+1)$-dimensional solid-on-solid model of particle deposition and evaporation that not only tunes the roughness of an equilibrium surface but also demonstrates the need for more than two exponents to characterize it. The tunable parameter, denoted by $μ$, in this model is the dimensionless surface tension per unit length. For $μ< 0$, the surface becomes increasingly spikier and its average width grows linearly with time; for $μ= 0$, its width grows as $\sqrt{t}$. On the other hand, for positive $μ$, the surface width shows the standard scaling behavior, $\la σ_m(t)\ra \sim M^αf(t/M^{α/β})$ where $M$ is the substrate size and $f(x) \to const (x^β)$ for $x$ large (small). The roughness exponent, $α= 1/2$ for $μ\leq 2$, and $ = 3/5, 4/5 & \sim 1$ for $μ= 5, 6 & 7$ respectively; the growth exponent, $β= 1/4$ for $μ\leq 2$ and $= 1/2$ for $μ> \sim 3.5$ respectively. These exponents are different from those of the height-difference correlation function,$α' = 1/2, β' = 1/4$ and $z' = 2$, for higher values of $μ$ suggesting thereby that the surface could be self-constraining.

cond-mat.stat-mech↗
arXiv2007

A growth walk model for estimating the canonical partition function of Interacting Self Avoiding Walk

We have explained in detail why the canonical partition function of Interacting Self Avoiding Walk (ISAW), is exactly equivalent to the configurational average of the weights associated with growth walks, such as the Interacting Growth Walk (IGW), if the average is taken over the entire genealogical tree of the walk. In this context, we have shown that it is not always possible to factor the the density of states out of the canonical partition function if the local growth rule is temperature-dependent. We have presented Monte Carlo results for IGWs on a diamond lattice in order to demonstrate that the actual set of IGW configurations available for study is temperature-dependent even though the weighted averages lead to the expected thermodynamic behavior of Interacting Self Avoiding Walk (ISAW).

cond-mat.stat-mech↗
arXiv2007

Flat Energy histogram version for Interacting Growth Walk

Interacting Growth Walks is a recently proposed stochastic model for studying the coil-globule transition of linear polymers. We propose a flat energy histogram version for Interacting Growth Walk. We demonstrate the algorithm on two dimensional square and triangular lattices by calculating the density of energy states of Interacting Self Avoiding Walks.

cond-mat.stat-mech↗
arXiv2007

Coil-Globule transition of a single short polymer chain - an exact enumeration study

We present an exact enumeration study of short SAWs in two as well as three dimensions that addresses the question, `what is the shortest walk for which the existence of all the three phases - coil, globule and the {\it theta} - could be demonstrated'. Even though we could easily demonstrate the coil and the globule phases from Free Energy considerations, we could demonstrate the existence of a {\it theta} phase only by using a scaling form for the distribution of gyration radius. That even such short walks have a scaling behavior is an unexpected result of this work.

cond-mat.stat-mech↗
arXiv2006

Fast Condensation in a tunable Backgammon model

We present a Monte Carlo study of the Backgammon model, at zero temperature, in which a departure box is chosen at random with a probability proportional to $(2ω- 1)k + (1 - ω)N$, where $k$ is the number of particles in the departure box and $N$ is the total number of particles (equivalently, boxes) in the system. The parameter $ω\in [0,1]$ tunes the dynamics from being slow ($ω= 1$) to being fast ($ω= 0$). This parametrization tacitly assumes a two-box representation for the system at any instant of time and $ω$ is formally related to the 'memory' parameter of a correlated binary sequence. For $ω< 1/2$, the system undergoes a fast condensation beyond a certain time that depends on $ω$ and the system size $N$. This condensation provides an interesting contrast to that studied with Zeta Urn model in that the probability that a box contains $k$ particles evolves differently in the model discussed here.

cond-mat.stat-mech↗
arXiv2005

A formalism for studying long-range correlations in many-alphabets sequences

We formulate a mean-field-like theory of long-range correlated $L$-alphabets sequences, which are actually systems with $(L-1)$ independent parameters. Depending on the values of these parameters, the variance on the average number of any given symbol in the sequence shows a linear or a superlinear dependence on the total length of the sequence. We present exact solution to the four-alphabets and three-alphabets sequences. We also demonstrate that a mapping of the given sequence into a smaller alphabets sequence (namely, a {\it coarse-graining} process) does not necessarily imply that long-range correlations found in the latter would correspond to those of the former.

cond-mat.stat-mech↗
arXiv2004

Can coarse-graining introduce long-range correlations in a symbolic sequence?

We present an exactly solvable mean-field-like theory of correlated ternary sequences which are actually systems with two independent parameters. Depending on the values of these parameters, the variance on the average number of any given symbol shows a linear or a superlinear dependence on the length of the sequence. We have shown that the available phase space of the system is made up a diffusive region surrounded by a superdiffusive region. Motivated by the fact that the diffusive portion of the phase space is larger than that for the binary, we have studied the mapping between these two. We have identified the region of the ternary phase space, particularly the diffusive part, that gets mapped into the superdiffusive regime of the binary. This exact mapping implies that long-range correlation found in a lower dimensional representative sequence may not, in general, correspond to the correlation properties of the original system.

cond-mat.stat-mech↗
arXiv2002

Interacting Growth Walk - a model for hyperquenched homopolymer glass?

We show that the compact self avoiding walk configurations, kinetically generated by the recently introduced Interacting Growth Walk (IGW) model, can be considered as members of a canonical ensemble if they are assigned random values of energy. Such a mapping is necessary for studying the thermodynamic behaviour of this system. We have presented the specific heat data for the IGW, obtained from extensive simulations on a square lattice; we observe a broad hump in the specific heat above the $θ$-point, contrary to expectation.

cond-mat.stat-mech↗
arXiv2002

Interacting Growth Walk on a honeycomb lattice

The Interacting Growth Walk (IGW) is a kinetic algorithm proposed recently for generating long, compact, self avoiding walks. The growth process in IGW is tuned by the so called growth temperature $T' = 1/(k_B β')$. On a square lattice and at $T' = 0$, IGW is attrition free and hence grows indefinitely. In this paper we consider IGW on a honeycomb lattice. We take contact energy, see text, as $ε=-|ε|=-1$. We show that IGW at $β' =\infty$ ($T'=0$) is identical to Interacting Self Avoiding Walk (ISAW) at $β=\ln 4$ ($k_B T = 1/\ln 4=0.7213$). Also IGW at $β' = 0$ ($T' = \infty$) corresponds to ISAW at $β= \ln 2$ ($k_B T= 1/ln 2 = 1.4427$). For other temperatures we need to introduce a statistical weight factor to a walk of the IGW ensemble to make correspondence with the ISAW ensemble.

cond-mat↗
arXiv2002

Protein folding simulations with Interacting Growth Walk model

We demonstrate that the recently proposed interacting growth walk (IGW) model, modified for generating self-avoiding heteropolymers, proves to be a simpler alternative to the other Monte Carlo methods available in the literature for obtaining minimum energy conformation of lattice proteins. In fact, this simple growth algorithm seems to be capable of quickly leading to low energy states for all the three dimensional bench mark HP-sequences investigated.

cond-mat.stat-mech↗
arXiv2001

Comment on "Peculiar Scaling of Self-Avoiding Walk Contacts"

We demonstrate that the recently proposed Interacting Growth Walk (cond-mat/0108097) does not have the contact-scaling behaviour of Self-Avoiding Walk (M. Baiesi, E. Orlandini and A. L. Stella, Phys. Rev. Lett. 87, 070602 (2001)) at finite temperatures.

cond-mat↗
arXiv2001

A new monte carlo algorithm for growing compact Self Avoiding Walks

We propose an algorithm based on local growth rules for kinetically generating self avoiding walk configurations at any given temperature. This algorithm, called the Interacting Growth Walk (IGW) algorithm, does not suffer from attrition on a square lattice at zero temperature, in contrast to the existing algorithms. More importantly, the IGW algorithm facilitates growing compact configurations at lower temperatures - a feature that makes it attractive for studying a variety of processes such as the folding of proteins. We demonstrate that our algorithm correctly describes the collapse transition of a homopolymer in two dimensions.

cond-mat.stat-mech↗