37 research outputs found
Forget-me-not: History-less Mobile Messaging
Text messaging has long been a popular activity, and today
smartphone apps enable users to choose from a plethora of
mobile messaging applications. While we know a lot about
SMS practices, we know less about practices of messaging
applications. In this paper, we take a first step to explore
one ubiquitous aspect of mobile messaging – messaging
history. We designed, built, and trialled a mobile messaging
application without history—named forget-me-not. The
two-week trial showed that history-less messaging no
longer supports chit-chat as seen in e.g. WhatsApp, but is
still considered conversational and more ‘engaging’.
Participants expressed being lenient and relaxed about what
they wrote. Removing the history allowed us to gain
insights into what uses history has in other mobile
messaging applications, such as planning events, allowing
for distractions, and maintaining multiple conversation
threads
On the Selection of Tuning Methodology of FOPID Controllers for the Control of Higher Order Processes
In this paper, a comparative study is done on the time and frequency domain
tuning strategies for fractional order (FO) PID controllers to handle higher
order processes. A new fractional order template for reduced parameter modeling
of stable minimum/non-minimum phase higher order processes is introduced and
its advantage in frequency domain tuning of FOPID controllers is also
presented. The time domain optimal tuning of FOPID controllers have also been
carried out to handle these higher order processes by performing optimization
with various integral performance indices. The paper highlights on the
practical control system implementation issues like flexibility of online
autotuning, reduced control signal and actuator size, capability of measurement
noise filtration, load disturbance suppression, robustness against parameter
uncertainties etc. in light of the above tuning methodologies.Comment: 27 pages, 10 figure
Anomalous fluctuation relations
We study Fluctuation Relations (FRs) for dynamics that are anomalous, in the
sense that the diffusive properties strongly deviate from the ones of standard
Brownian motion. We first briefly review the concept of transient work FRs for
stochastic dynamics modeled by the ordinary Langevin equation. We then
introduce three generic types of dynamics generating anomalous diffusion:
L\'evy flights, long-time correlated Gaussian stochastic processes and
time-fractional kinetics. By combining Langevin and kinetic approaches we
calculate the work probability distributions in the simple nonequilibrium
situation of a particle subject to a constant force. This allows us to check
the transient FR for anomalous dynamics. We find a new form of FRs, which is
intimately related to the validity of fluctuation-dissipation relations.
Analogous results are obtained for a particle in a harmonic potential dragged
by a constant force. We argue that these findings are important for
understanding fluctuations in experimentally accessible systems. As an example,
we discuss the anomalous dynamics of biological cell migration both in
equilibrium and in nonequilibrium under chemical gradients.Comment: book chapter; 25 pages, 10 figures. see
http://www.maths.qmul.ac.uk/~klages/smallsys/smallsys_rk.htm
Characterizations and simulations of a class of stochastic processes to model anomalous diffusion
In this paper we study a parametric class of stochastic processes to model
both fast and slow anomalous diffusion. This class, called generalized grey
Brownian motion (ggBm), is made up off self-similar with stationary increments
processes (H-sssi) and depends on two real parameters alpha in (0,2) and beta
in (0,1]. It includes fractional Brownian motion when alpha in (0,2) and
beta=1, and time-fractional diffusion stochastic processes when alpha=beta in
(0,1). The latters have marginal probability density function governed by
time-fractional diffusion equations of order beta. The ggBm is defined through
the explicit construction of the underline probability space. However, in this
paper we show that it is possible to define it in an unspecified probability
space. For this purpose, we write down explicitly all the finite dimensional
probability density functions. Moreover, we provide different ggBm
characterizations. The role of the M-Wright function, which is related to the
fundamental solution of the time-fractional diffusion equation, emerges as a
natural generalization of the Gaussian distribution. Furthermore, we show that
ggBm can be represented in terms of the product of a random variable, which is
related to the M-Wright function, and an independent fractional Brownian
motion. This representation highlights the -{\bf sssi} nature of the ggBm
and provides a way to study and simulate the trajectories. For this purpose, we
developed a random walk model based on a finite difference approximation of a
partial integro-differenital equation of fractional type.Comment: 25 pages, 9 figure
Synchronous Text Messaging
We have created and evaluated a novel mobile messaging app named Curtains Messenger. The app has been designed to support synchrony in messaging. It does this by requiring users to be in the app at the same time as each other in order to send, receive and read messages. This design is contrary to typical apps where messages can be sent and read asynchronously at an individual's convenience. We have conducted a field trial in which 15 users installed the app on their own devices and used it in the wild. We present a qualitative analysis of interviews with the participants following the trial. The findings address how the app was used, how synchrony affected conversational flows, how synchrony raised issues of attention and intimacy, and what issues users faced in the practical work of conducting synchronous messaging. This work demonstrates how core concepts in the study of cooperative work such as a/synchrony can be drawn upon to reconsider taken-for-granted design features of mobile applications and the lived experience of communication
Fast tensor product solvers for optimization problems with fractional differential equations as constraints
Fractional differential equations have recently received much attention within computational mathematics and applied science, and their numerical treatment is an important research area as such equations pose substantial challenges to existing algorithms. An optimization problem with constraints given by fractional differential equations is considered, which in its discretized form leads to a high-dimensional tensor equation. To reduce the computation time and storage, the solution is sought in the tensor-train format. We compare three types of solution strategies that employ sophisticated iterative techniques using either preconditioned Krylov solvers or tailored alternating schemes. The competitiveness of these approaches is presented using several examples