162,997 research outputs found
Half-tapering strategy for conditional simulation with large datasets
Gaussian conditional realizations are routinely used for risk assessment and
planning in a variety of Earth sciences applications. Conditional realizations
can be obtained by first creating unconditional realizations that are then
post-conditioned by kriging. Many efficient algorithms are available for the
first step, so the bottleneck resides in the second step. Instead of doing the
conditional simulations with the desired covariance (F approach) or with a
tapered covariance (T approach), we propose to use the taper covariance only in
the conditioning step (Half-Taper or HT approach). This enables to speed up the
computations and to reduce memory requirements for the conditioning step but
also to keep the right short scale variations in the realizations. A criterion
based on mean square error of the simulation is derived to help anticipate the
similarity of HT to F. Moreover, an index is used to predict the sparsity of
the kriging matrix for the conditioning step. Some guides for the choice of the
taper function are discussed. The distributions of a series of 1D, 2D and 3D
scalar response functions are compared for F, T and HT approaches. The
distributions obtained indicate a much better similarity to F with HT than with
T.Comment: 39 pages, 2 Tables and 11 Figure
On Analytic Perturbations of a Family of Feigenbaum-like Equations
We prove existence of solutions of a family of of
Feigenbaum-like equations \label{family} \phi(x)={1+\eps \over \lambda}
\phi(\phi(\lambda x)) -\eps x +\tau(x), where \eps is a small real number and
is analytic and small on some complex neighborhood of and
real-valued on \fR. The family (\ref{family}) appears in the context of
period-doubling renormalization for area-preserving maps (cf. \cite{GK}).
Our proof is a development of ideas of H. Epstein (cf \cite{Eps1},
\cite{Eps2}, \cite{Eps3}) adopted to deal with some significant complications
that arise from the presence of terms \eps x +\tau(x) in the equation
(\ref{family}). The method relies on a construction of novel {\it a-priori}
bounds for unimodal functions which turn out to be very tight. We also obtain
good bounds on the scaling parameter .
A byproduct of the method is a new proof of the existence of a
Feigenbaum-Coullet-Tresser function
The reception of Ernst Mach in the school of Brentano
This paper is about the reception of Ernst Mach by Brentano and his
students in Austria. I shall outline the main elements of this reception, starting with
Brentano’s evaluation, in his lectures on positivism, of Mach’s theory of sensations.
Secondly, I shall comment the early reception of Mach by Brentano’s pupils in Prague.
The third part bears on the close relationship that Husserl established between his
phenomenology and Mach’s descriptivism. I will then briefly examine Mach’s contribution
to the controversy on gestalt qualities. The fifth part bears on Stumpf’s debate with Mach
on psychophysical relations and I shall conclude on Husserl’s criticism of Mach’s alleged
logical psychologism
Kinetic approaches to lactose operon induction and bimodality
The quasi-equilibrium approximation is acceptable when molecular interactions
are fast enough compared to circuit dynamics, but is no longer allowed when
cellular activities are governed by rare events. A typical example is the
lactose operon (lac), one of the most famous paradigms of transcription
regulation, for which several theories still coexist to describe its behaviors.
The lac system is generally analyzed by using equilibrium constants,
contradicting single-event hypotheses long suggested by Novick and Weiner
(1957). Enzyme induction as an all-or-none phenomenon. Proc. Natl. Acad. Sci.
USA 43, 553-566) and recently refined in the study of (Choi et al., 2008. A
stochastic single-molecule event triggers phenotype switching of a bacterial
cell. Science 322, 442-446). In the present report, a lac repressor
(LacI)-mediated DNA immunoprecipitation experiment reveals that the natural
LacI-lac DNA complex built in vivo is extremely tight and long-lived compared
to the time scale of lac expression dynamics, which could functionally
disconnect the abortive expression bursts and forbid using the standard modes
of lac bistability. As alternatives, purely kinetic mechanisms are examined for
their capacity to restrict induction through: (i) widely scattered derepression
related to the arrival time variance of a predominantly backward asymmetric
random walk and (ii) an induction threshold arising in a single window of
derepression without recourse to nonlinear multimeric binding and Hill
functions. Considering the complete disengagement of the lac repressor from the
lac promoter as the probabilistic consequence of a transient stepwise
mechanism, is sufficient to explain the sigmoidal lac responses as functions of
time and of inducer concentration. This sigmoidal shape can be misleadingly
interpreted as a phenomenon of equilibrium cooperativity classically used to
explain bistability, but which has been reported to be weak in this system
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