325 research outputs found
How a "Hit" is Born: The Emergence of Popularity from the Dynamics of Collective Choice
In recent times there has been a surge of interest in seeking out patterns in
the aggregate behavior of socio-economic systems. One such domain is the
emergence of statistical regularities in the evolution of collective choice
from individual behavior. This is manifested in the sudden emergence of
popularity or "success" of certain ideas or products, compared to their
numerous, often very similar, competitors. In this paper, we present an
empirical study of a wide range of popularity distributions, spanning from
scientific paper citations to movie gross income. Our results show that in the
majority of cases, the distribution follows a log-normal form, suggesting that
multiplicative stochastic processes are the basis for emergence of popular
entities. This suggests the existence of some general principles of complex
organization leading to the emergence of popularity. We discuss the theoretical
principles needed to explain this socio-economic phenomenon, and present a
model for collective behavior that exhibits bimodality, which has been observed
in certain empirical popularity distributions.Comment: 17 pages, 14 figures, A version of the work is published in
Econophysics and Sociophysics: Trends and Perspectives, (eds.) Bikas K.
Chakrabarti, Anirban Chakraborti, Arnab Chatterjee; Wiley-VCH, Berlin (2006);
Chapter-15, pages: 417-44
Effects of temporal correlations on cascades: Threshold models on temporal networks
A person's decision to adopt an idea or product is often driven by the
decisions of peers, mediated through a network of social ties. A common way of
modeling adoption dynamics is to use threshold models, where a node may become
an adopter given a high enough rate of contacts with adopted neighbors. We
study the dynamics of threshold models that take both the network topology and
the timings of contacts into account, using empirical contact sequences as
substrates. The models are designed such that adoption is driven by the number
of contacts with different adopted neighbors within a chosen time. We find that
while some networks support cascades leading to network-level adoption, some do
not: the propagation of adoption depends on several factors from the frequency
of contacts to burstiness and timing correlations of contact sequences. More
specifically, burstiness is seen to suppress cascades sizes when compared to
randomised contact timings, while timing correlations between contacts on
adjacent links facilitate cascades.Comment: 9 pages, 7 figures, Published versio
The strength of strong ties in scientific collaboration networks
Network topology and its relationship to tie strengths may hinder or enhance
the spreading of information in social networks. We study the correlations
between tie strengths and topology in networks of scientific collaboration, and
show that these are very different from ordinary social networks. For the
latter, it has earlier been shown that strong ties are associated with dense
network neighborhoods, while weaker ties act as bridges between these. Because
of this, weak links act as bottlenecks for the diffusion of information. We
show that on the contrary, in co-authorship networks dense local neighborhoods
mainly consist of weak links, whereas strong links are more important for
overall connectivity. The important role of strong links is further highlighted
in simulations of information spreading, where their topological position is
seen to dramatically speed up spreading dynamics. Thus, in contrast to ordinary
social networks, weight-topology correlations enhance the flow of information
across scientific collaboration networks.Comment: 6 Pages, 6 Figures, Published version, Minor changes, Results also
verified using new weight-schem
Cosmology in a Time-Crystal Background
We investigate the effects of a Time Crystal-like Condensate on cosmological
dynamics. It is well known that quadratic gravity reduces to Einstein gravity
along with a decoupled higher derivative dynamical scalar
\cite{Alvarez-Gaume:2015rwa}. According to \cite{Chakraborty:2020ktp}, the
above scalar sector can sustain a Time Crystal-like minimum energy state, with
non-trivial time dependence. In the present work we treat the Time Crystal-like
state as the background (that replaces the classical Minkowski vacuum) and
study cosmic evolution on this ``dynamic'' ground state. In the first part we
re-derive \cite{Chakraborty:2020ktp}, in a covariant and more systematic way,
the frequencies that characterize the oscillator like Time crystalline
condensate and interpret it as a background energy-momentum tensor simulating a
matter-like effect. Importantly, no external matter is introduced here and the
condensate, consists of a combination of the metric field and is
generated due to the -term ( is the Ricci scalar) in quadratic gravity
\cite{Alvarez-Gaume:2015rwa}. In a way the spurious degrees of freedom of
-gravity turns into a useful component. The second part comprises of new
effects where the cosmology in Friedmann-Lem\^{i}atre-Robertson-Walker (FLRW)
universe is studied in presence of the energy-momentum tensor characterizing
the Time Crystal Condensate. Under certain approximations, the scale factor of
the FLRW universe is analytically obtained for any spatial geometry. We also
find that the Time Crystal Condensate contributes as a new matter candidate
having radiation-like behavior in the universe. Additionally, irrespective of
the spatial geometry of the universe, the Time Crystal condensate generates a
decelerating phase before the early acceleration starts. This is an indication
of a contracting phase of the universe before its accelerated expansion.Comment: 11 pages, 4 compound figures. Comments are welcom
Time-Varying Priority Queuing Models for Human Dynamics
Queuing models provide insight into the temporal inhomogeneity of human
dynamics, characterized by the broad distribution of waiting times of
individuals performing tasks. We study the queuing model of an agent trying to
execute a task of interest, the priority of which may vary with time due to the
agent's "state of mind." However, its execution is disrupted by other tasks of
random priorities. By considering the priority of the task of interest either
decreasing or increasing algebraically in time, we analytically obtain and
numerically confirm the bimodal and unimodal waiting time distributions with
power-law decaying tails, respectively. These results are also compared to the
updating time distribution of papers in the arXiv.org and the processing time
distribution of papers in Physical Review journals. Our analysis helps to
understand human task execution in a more realistic scenario.Comment: 8 pages, 6 figure
Contextual analysis framework for bursty dynamics
To understand the origin of bursty dynamics in natural and social processes
we provide a general analysis framework, in which the temporal process is
decomposed into sub-processes and then the bursts in sub-processes, called
contextual bursts, are combined to collective bursts in the original process.
For the combination of sub-processes, it is required to consider the
distribution of different contexts over the original process. Based on minimal
assumptions for inter-event time statistics, we present a theoretical analysis
for the relationship between contextual and collective inter-event time
distributions. Our analysis framework helps to exploit contextual information
available in decomposable bursty dynamics.Comment: 5 pages, 3 figure
Collective behavior of stock price movements in an emerging market
To investigate the universality of the structure of interactions in different
markets, we analyze the cross-correlation matrix C of stock price fluctuations
in the National Stock Exchange (NSE) of India. We find that this emerging
market exhibits strong correlations in the movement of stock prices compared to
developed markets, such as the New York Stock Exchange (NYSE). This is shown to
be due to the dominant influence of a common market mode on the stock prices.
By comparison, interactions between related stocks, e.g., those belonging to
the same business sector, are much weaker. This lack of distinct sector
identity in emerging markets is explicitly shown by reconstructing the network
of mutually interacting stocks. Spectral analysis of C for NSE reveals that,
the few largest eigenvalues deviate from the bulk of the spectrum predicted by
random matrix theory, but they are far fewer in number compared to, e.g., NYSE.
We show this to be due to the relative weakness of intra-sector interactions
between stocks, compared to the market mode, by modeling stock price dynamics
with a two-factor model. Our results suggest that the emergence of an internal
structure comprising multiple groups of strongly coupled components is a
signature of market development.Comment: 10 pages, 10 figure
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