6,334 research outputs found
Himalayan Hybridity and the Evolution of Ladakhi Popular Music
Historically, Ladakh in the Western Himalayas was a significant nexus of Trans-Himalayan caravan trade, and thus exhibited a significant hybridity in its material, linguistic, religious, and musical culture. In this paper, I examine the rise of Ladakhi popular music in and through these crossroads, paying attention to themes of hybridity. I look at the development of Ladakhi ethnic, political, and musical identity, and the role of government, non-governmental organizations (NGOs), and individuals with regard to the rise of new musical genres. Accompanying the historical survey of the music is as discussion of the evolutions of textual content. Changes in mass media technology and economics have had a profound effect on this remote region, and have shaped how cultural identity is negotiated by both song writers and consumers of popular music
An efficient multi-scale Green's Functions Reaction Dynamics scheme
Molecular Dynamics - Green's Functions Reaction Dynamics (MD-GFRD) is a
multiscale simulation method for particle dynamics or particle-based
reaction-diffusion dynamics that is suited for systems involving low particle
densities. Particles in a low-density region are just diffusing and not
interacting. In this case one can avoid the costly integration of microscopic
equations of motion, such as molecular dynamics (MD), and instead turn to an
event-based scheme in which the times to the next particle interaction and the
new particle positions at that time can be sampled. At high (local)
concentrations, however, e.g. when particles are interacting in a nontrivial
way, particle positions must still be updated with small time steps of the
microscopic dynamical equations. The efficiency of a multi-scale simulation
that uses these two schemes largely depends on the coupling between them and
the decisions when to switch between the two scales. Here we present an
efficient scheme for multi-scale MD-GFRD simulations. It has been shown that
MD-GFRD schemes are more efficient than brute-force molecular dynamics
simulations up to a molar concentration of . In this paper, we
show that the choice of the propagation domains has a relevant impact on the
computational performance. Domains are constructed using a local optimization
of their sizes and a minimal domain size is proposed. The algorithm is shown to
be more efficient than brute-force Brownian dynamics simulations up to a molar
concentration of and is up to an order of magnitude more
efficient compared with previous MD-GFRD schemes
A variational approach to modeling slow processes in stochastic dynamical systems
The slow processes of metastable stochastic dynamical systems are difficult
to access by direct numerical simulation due the sampling problem. Here, we
suggest an approach for modeling the slow parts of Markov processes by
approximating the dominant eigenfunctions and eigenvalues of the propagator. To
this end, a variational principle is derived that is based on the maximization
of a Rayleigh coefficient. It is shown that this Rayleigh coefficient can be
estimated from statistical observables that can be obtained from short
distributed simulations starting from different parts of state space. The
approach forms a basis for the development of adaptive and efficient
computational algorithms for simulating and analyzing metastable Markov
processes while avoiding the sampling problem. Since any stochastic process
with finite memory can be transformed into a Markov process, the approach is
applicable to a wide range of processes relevant for modeling complex
real-world phenomena
Variational approach for learning Markov processes from time series data
Inference, prediction and control of complex dynamical systems from time
series is important in many areas, including financial markets, power grid
management, climate and weather modeling, or molecular dynamics. The analysis
of such highly nonlinear dynamical systems is facilitated by the fact that we
can often find a (generally nonlinear) transformation of the system coordinates
to features in which the dynamics can be excellently approximated by a linear
Markovian model. Moreover, the large number of system variables often change
collectively on large time- and length-scales, facilitating a low-dimensional
analysis in feature space. In this paper, we introduce a variational approach
for Markov processes (VAMP) that allows us to find optimal feature mappings and
optimal Markovian models of the dynamics from given time series data. The key
insight is that the best linear model can be obtained from the top singular
components of the Koopman operator. This leads to the definition of a family of
score functions called VAMP-r which can be calculated from data, and can be
employed to optimize a Markovian model. In addition, based on the relationship
between the variational scores and approximation errors of Koopman operators,
we propose a new VAMP-E score, which can be applied to cross-validation for
hyper-parameter optimization and model selection in VAMP. VAMP is valid for
both reversible and nonreversible processes and for stationary and
non-stationary processes or realizations
Time-lagged autoencoders: Deep learning of slow collective variables for molecular kinetics
Inspired by the success of deep learning techniques in the physical and
chemical sciences, we apply a modification of an autoencoder type deep neural
network to the task of dimension reduction of molecular dynamics data. We can
show that our time-lagged autoencoder reliably finds low-dimensional embeddings
for high-dimensional feature spaces which capture the slow dynamics of the
underlying stochastic processes - beyond the capabilities of linear dimension
reduction techniques
Non-equilibrium steady states for chains of four rotors
We study a chain of four interacting rotors (rotators) connected at both ends
to stochastic heat baths at different temperatures. We show that for
non-degenerate interaction potentials the system relaxes, at a stretched
exponential rate, to a non-equilibrium steady state (NESS). Rotors with high
energy tend to decouple from their neighbors due to fast oscillation of the
forces. Because of this, the energy of the central two rotors, which interact
with the heat baths only through the external rotors, can take a very long time
to dissipate. By appropriately averaging the oscillatory forces, we estimate
the dissipation rate and construct a Lyapunov function. Compared to the chain
of length three (considered previously by C. Poquet and the current authors),
the new difficulty with four rotors is the appearance of resonances when both
central rotors are fast. We deal with these resonances using the rapid
thermalization of the two external rotors.Comment: Minor changes to reflect the published versio
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