16,624 research outputs found
Properties of the density for a three dimensional stochastic wave equation
We consider a stochastic wave equation in space dimension three driven by a
noise white in time and with an absolutely continuous correlation measure given
by the product of a smooth function and a Riesz kernel. Let be the
density of the law of the solution of such an equation at points
(t,x)\in]0,T]\times \IR^3. We prove that the mapping owns the same regularity as the sample paths of the process
\{u(t,x), (t,x)\in]0,T]\times \mathbbR^3\} established Dalang and Sanz-Sol\'e
[Memoirs of the AMS, to appear]. The proof relies on Malliavin calculus and
more explicitely, Watanabe's integration by parts formula and estimates derived
form it.Comment: 29 page
Cosmopolitan speakers and their cultural cartographies
Language learners' increased mobility and the ubiquity of virtual intercultural encounters has challenged traditional ideas of âculturesâ. Moreover, representations of cultures as consumable life-choices has meant that learners are no longer locked into standard and static cultural identities. Language learners are better defined as cosmopolitan individuals with subjective and complex socio-political and historical identities. Such models push the boundaries of current concepts in language pedagogy to new understandings of who the language learner is and a refashioning of the cultural maps they inhabit. This article presents a model for cultural understanding that draws on the theoretical framework of Beck's Cosmopolitan Vision and its related concepts of âBanal Cosmopolitanismâ and âCosmopolitan Empathyâ. Narrative accounts are used to illustrate the experience of a group of students of Arabic and Serbian/Croatian and their use of the cultural resources at their disposal to construct their own subjective cosmopolitan life-worlds. Through the analysis of learners' everyday cultural practices inside and outside the educational environment, the scope of the intercultural experience is revisited and a new paradigm for the language learner is presented. The Cosmopolitan Speaker (CS) described in this article is a subject who adopts a flĂąneur-like disposition to reflect on and scrutinise the target culture. Armed with this highly personal interpretation of reality, CSs will be able to take part in their own cultural trajectories and imagine and âfigureâ their own cartography of the world
Nonequilibrium entropic bounds for Darwinian replicators
Life evolved on our planet by means of a combination of Darwinian selection
and innovations leading to higher levels of complexity. The emergence and
selection of replicating entities is a central problem in prebiotic evolution.
Theoretical models have shown how populations of different types of replicating
entities exclude or coexist with other classes of replicators. Models are
typically kinetic, based on standard replicator equations. On the other hand,
the presence of thermodynamical constrains for these systems remain an open
question. This is largely due to the lack of a general theory of out of
statistical methods for systems far from equilibrium. Nonetheless, a first
approach to this problem has been put forward in a series of novel
developements in non-equilibrium physics, under the rubric of the extended
second law of thermodynamics. The work presented here is twofold: firstly, we
review this theoretical framework and provide a brief description of the three
fundamental replicator types in prebiotic evolution: parabolic, malthusian and
hyperbolic. Finally, we employ these previously mentioned techinques to explore
how replicators are constrained by thermodynamics.Comment: 12 Pages, 5 Figure
Efficient prime counting and the Chebyshev primes
The function \epsilon(x)=\mbox{li}(x)-\pi(x) is known to be positive up to
the (very large) Skewes' number. Besides, according to Robin's work, the
functions \epsilon_{\theta}(x)=\mbox{li}[\theta(x)]-\pi(x) and
\epsilon_{\psi}(x)=\mbox{li}[\psi(x)]-\pi(x) are positive if and only if
Riemann hypothesis (RH) holds (the first and the second Chebyshev function are
and ,
respectively, \mbox{li}(x) is the logarithmic integral, and
are the M\"obius and the Von Mangoldt functions). Negative jumps
in the above functions , and
may potentially occur only at (the set of primes). One
denotes j_p=\mbox{li}(p)-\mbox{li}(p-1) and one investigates the jumps ,
and . In particular, , and
for . Besides, for any odd p \in
\mathcal{\mbox{Ch}}, an infinite set of so-called {\it Chebyshev primes } with
partial list . We establish a few properties of the set
\mathcal{\mbox{Ch}}, give accurate approximations of the jump
and relate the derivation of \mbox{Ch} to the explicit Mangoldt formula for
. In the context of RH, we introduce the so-called {\it Riemann
primes} as champions of the function (or of the function
). Finally, we find a {\it good} prime counting function
S_N(x)=\sum_{n=1}^N \frac{\mu(n)}{n}\mbox{li}[\psi(x)^{1/n}], that is found
to be much better than the standard Riemann prime counting function.Comment: 15 pages section 2.2 added, new sequences added, Fig. 2 and 3 are ne
Extreme values of the Dedekind function
Let denote the Dedekind
function. Define, for the ratio
We prove unconditionally that for Let
be the primorial of order We prove that the statement
for is equivalent to the Riemann
Hypothesis.Comment: 5 pages, to appear in Journal of Combinatorics and Number theor
How Turing parasites expand the computational landscape of digital life
Why are living systems complex? Why does the biosphere contain living beings
with complexity features beyond those of the simplest replicators? What kind of
evolutionary pressures result in more complex life forms? These are key
questions that pervade the problem of how complexity arises in evolution. One
particular way of tackling this is grounded in an algorithmic description of
life: living organisms can be seen as systems that extract and process
information from their surroundings in order to reduce uncertainty. Here we
take this computational approach using a simple bit string model of coevolving
agents and their parasites. While agents try to predict their worlds, parasites
do the same with their hosts. The result of this process is that, in order to
escape their parasites, the host agents expand their computational complexity
despite the cost of maintaining it. This, in turn, is followed by increasingly
complex parasitic counterparts. Such arms races display several qualitative
phases, from monotonous to punctuated evolution or even ecological collapse.
Our minimal model illustrates the relevance of parasites in providing an active
mechanism for expanding living complexity beyond simple replicators, suggesting
that parasitic agents are likely to be a major evolutionary driver for
biological complexity.Comment: 13 pages, 8 main figures, 1 appendix with 5 extra figure
Large deviations for rough paths of the fractional Brownian motion
Starting from the construction of a geometric rough path associated with a
fractional Brownian motion with Hurst parameter given by
Coutin and Qian (2002), we prove a large deviation principle in the space of
geometric rough paths, extending classical results on Gaussian processes. As a
by-product, geometric rough paths associated to elements of the reproducing
kernel Hilbert space of the fractional Brownian motion are obtained and an
explicit integral representation is given.Comment: 32 page
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