87,541 research outputs found
Global Patterns of Synchronization in Human Communications
Social media are transforming global communication and coordination. The data
derived from social media can reveal patterns of human behavior at all levels
and scales of society. Using geolocated Twitter data, we have quantified
collective behaviors across multiple scales, ranging from the commutes of
individuals, to the daily pulse of 50 major urban areas and global patterns of
human coordination. Human activity and mobility patterns manifest the synchrony
required for contingency of actions between individuals. Urban areas show
regular cycles of contraction and expansion that resembles heartbeats linked
primarily to social rather than natural cycles. Business hours and circadian
rhythms influence daily cycles of work, recreation, and sleep. Different urban
areas have characteristic signatures of daily collective activities. The
differences are consistent with a new emergent global synchrony that couples
behavior in distant regions across the world. A globally synchronized peak that
includes exchange of ideas and information across Europe, Africa, Asia and
Australasia. We propose a dynamical model to explain the emergence of global
synchrony in the context of increasing global communication and reproduce the
observed behavior. The collective patterns we observe show how social
interactions lead to interdependence of behavior manifest in the
synchronization of communication. The creation and maintenance of temporally
sensitive social relationships results in the emergence of complexity of the
larger scale behavior of the social system.Comment: 20 pages, 12 figures. arXiv admin note: substantial text overlap with
arXiv:1602.0621
Rendezvous of Two Robots with Constant Memory
We study the impact that persistent memory has on the classical rendezvous
problem of two mobile computational entities, called robots, in the plane. It
is well known that, without additional assumptions, rendezvous is impossible if
the entities are oblivious (i.e., have no persistent memory) even if the system
is semi-synchronous (SSynch). It has been recently shown that rendezvous is
possible even if the system is asynchronous (ASynch) if each robot is endowed
with O(1) bits of persistent memory, can transmit O(1) bits in each cycle, and
can remember (i.e., can persistently store) the last received transmission.
This setting is overly powerful.
In this paper we weaken that setting in two different ways: (1) by
maintaining the O(1) bits of persistent memory but removing the communication
capabilities; and (2) by maintaining the O(1) transmission capability and the
ability to remember the last received transmission, but removing the ability of
an agent to remember its previous activities. We call the former setting
finite-state (FState) and the latter finite-communication (FComm). Note that,
even though its use is very different, in both settings, the amount of
persistent memory of a robot is constant.
We investigate the rendezvous problem in these two weaker settings. We model
both settings as a system of robots endowed with visible lights: in FState, a
robot can only see its own light, while in FComm a robot can only see the other
robot's light. We prove, among other things, that finite-state robots can
rendezvous in SSynch, and that finite-communication robots are able to
rendezvous even in ASynch. All proofs are constructive: in each setting, we
present a protocol that allows the two robots to rendezvous in finite time.Comment: 18 pages, 3 figure
- …