423 research outputs found
Identification and critique of the citizenship notion informing the Itorero training scheme for high school leavers in post-genocide Rwanda
There is a dearth of research on citizenship education in post-genocide countries. The present article investigates the citizenship concept informing Itorero, a non-formal citizenship education platform meant for High School Leavers (hereafter HSLs) in post-genocide Rwanda. To this end, the paper engages with classical notions of citizenship (civic republicanism, liberalism and communitarianism), and modern ones (cosmopolitanism and radical democracy) in a bid to identify the notion deemed preferable to competing notions. It is revealed that the Itorero training relies heavily on the civic republican/communitarian concepts of citizenship. The paper argues that while these concepts contain constructive elements, such as fostering courage, self-sacrifice, patriotism, connectedness, and common good concern, excessive pursuit of this citizenship model might not be helpful for post-genocide Rwanda. The civic republican/communitarian paradigm â as it is practiced in Itorerotraining â is likely to produce uncritical, docile, dependent, short-sighted and child-like citizens; it encourages fanaticism.
Multiplicative Noise: Applications in Cosmology and Field Theory
Physical situations involving multiplicative noise arise generically in
cosmology and field theory. In this paper, the focus is first on exact
nonlinear Langevin equations, appropriate in a cosmologica setting, for a
system with one degree of freedom. The Langevin equations are derived using an
appropriate time-dependent generalization of a model due to Zwanzig. These
models are then extended to field theories and the generation of multiplicative
noise in such a context is discussed. Important issues in both the cosmological
and field theoretic cases are the fluctuation-dissipation relations and the
relaxation time scale. Of some importance in cosmology is the fact that
multiplicative noise can substantially reduce the relaxation time. In the field
theoretic context such a noise can lead to a significant enhancement in the
nucleation rate of topological defects.Comment: 21 pages, LaTex, LA-UR-93-210
Quantum State Diffusion and Time Correlation Functions
In computing the spectra of quantum mechanical systems one encounters the
Fourier transforms of time correlation functions, as given by the quantum
regression theorem for systems described by master equations. Quantum state
diffusion (QSD) gives a useful method of solving these problems by unraveling
the master equation into stochastic trajectories; but there is no generally
accepted definition of a time correlation function for a single QSD trajectory.
In this paper we show how QSD can be used to calculate these spectra directly;
by formally solving the equations which arise, we arrive at a natural
definition for a two-time correlation function in QSD, which depends explicitly
on both the stochastic noise of the particular trajectory and the time of
measurement, and which agrees in the mean with the ensemble average definition
of correlation functions.Comment: 16 pages standard LaTeX + 1 figure (uuencoded postscript) Numerous
minor revisions and clarifications. To appear in J. Mod. Optic
Transport and bistable kinetics of a Brownian particle in a nonequilibrium environment
A system reservoir model, where the associated reservoir is modulated by an
external colored random force, is proposed to study the transport of an
overdamped Brownian particle in a periodic potential. We then derive the
analytical expression for the average velocity, mobility, and diffusion rate.
The bistable kinetics and escape rate from a metastable state in the overdamped
region are studied consequently. By numerical simulation we then demonstrate
that our analytical escape rate is in good agreement with that of numerical
result.Comment: 10 pages, 2 figures, RevTex4, minor correction
Anomalous diffusion in a random nonlinear oscillator due to high frequencies of the noise
We study the long time behaviour of a nonlinear oscillator subject to a
random multiplicative noise with a spectral density (or power-spectrum) that
decays as a power law at high frequencies. When the dissipation is negligible,
physical observables, such as the amplitude, the velocity and the energy of the
oscillator grow as power-laws with time. We calculate the associated scaling
exponents and we show that their values depend on the asymptotic behaviour of
the external potential and on the high frequencies of the noise. Our results
are generalized to include dissipative effects and additive noise.Comment: Expanded version of Proceedings StatPhys-Kolkata V
Generalization of escape rate from a metastable state driven by external cross-correlated noise processes
We propose generalization of escape rate from a metastable state for
externally driven correlated noise processes in one dimension. In addition to
the internal non-Markovian thermal fluctuations, the external correlated noise
processes we consider are Gaussian, stationary in nature and are of
Ornstein-Uhlenbeck type. Based on a Fokker-Planck description of the effective
noise processes with finite memory we derive the generalized escape rate from a
metastable state in the moderate to large damping limit and investigate the
effect of degree of correlation on the resulting rate. Comparison of the
theoretical expression with numerical simulation gives a satisfactory agreement
and shows that by increasing the degree of external noise correlation one can
enhance the escape rate through the dressed effective noise strength.Comment: 9 pages, 1 figur
Critical dynamics of phase transition driven by dichotomous Markov noise
An Ising spin system under the critical temperature driven by a dichotomous
Markov noise (magnetic field) with a finite correlation time is studied both
numerically and theoretically. The order parameter exhibits a transition
between two kinds of qualitatively different dynamics, symmetry-restoring and
symmetry-breaking motions, as the noise intensity is changed.
There exist regions called channels where the order parameter stays for a
long time slightly above its critical noise intensity. Developing a
phenomenological analysis of the dynamics, we investigate the distribution of
the passage time through the channels and the power spectrum of the order
parameter evolution. The results based on the phenomenological analysis turn
out to be in quite good agreement with those of the numerical simulation.Comment: 27 pages, 12 figure
Ergodic directional switching in mobile insect groups
We obtain a Fokker-Planck equation describing experimental data on the
collective motion of locusts. The noise is of internal origin and due to the
discrete character and finite number of constituents of the swarm. The
stationary probability distribution shows a rich phenomenology including
non-monotonic behavior of several order/disorder transition indicators in noise
intensity. This complex behavior arises naturally as a result of the randomness
in the system. Its counterintuitive character challenges standard
interpretations of noise induced transitions and calls for an extension of this
theory in order to capture the behavior of certain classes of biologically
motivated models. Our results suggest that the collective switches of the
group's direction of motion might be due to a random ergodic effect and, as
such, they are inherent to group formation.Comment: Physical Review Focus 26, July 201
Class of self-limiting growth models in the presence of nonlinear diffusion
The source term in a reaction-diffusion system, in general, does not involve
explicit time dependence. A class of self-limiting growth models dealing with
animal and tumor growth and bacterial population in a culture, on the other
hand are described by kinetics with explicit functions of time. We analyze a
reaction-diffusion system to study the propagation of spatial front for these
models.Comment: RevTex, 13 pages, 5 figures. To appear in Physical Review
Transitions Induced by the Discreteness of Molecules in a Small Autocatalytic System
Autocatalytic reaction system with a small number of molecules is studied
numerically by stochastic particle simulations. A novel state due to
fluctuation and discreteness in molecular numbers is found, characterized as
extinction of molecule species alternately in the autocatalytic reaction loop.
Phase transition to this state with the change of the system size and flow is
studied, while a single-molecule switch of the molecule distributions is
reported. Relevance of the results to intracellular processes are briefly
discussed.Comment: 5 pages, 4 figure
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