169 research outputs found
Attractive regular stochastic chains: perfect simulation and phase transition
We prove that uniqueness of the stationary chain, or equivalently, of the
-measure, compatible with an attractive regular probability kernel is
equivalent to either one of the following two assertions for this chain: (1) it
is a finitary coding of an i.i.d. process with countable alphabet, (2) the
concentration of measure holds at exponential rate. We show in particular that
if a stationary chain is uniquely defined by a kernel that is continuous and
attractive, then this chain can be sampled using a coupling-from-the-past
algorithm. For the original Bramson-Kalikow model we further prove that there
exists a unique compatible chain if and only if the chain is a finitary coding
of a finite alphabet i.i.d. process. Finally, we obtain some partial results on
conditions for phase transition for general chains of infinite order.Comment: 22 pages, 1 pseudo-algorithm, 1 figure. Minor changes in the
presentation. Lemma 6 has been remove
Histone Deacetylase Inhibitors Restore Cell Surface Expression of the Coxsackie Adenovirus Receptor and Enhance CMV Promoter Activity in Castration-Resistant Prostate Cancer Cells
Adenoviral gene therapy using the death receptor ligand TRAIL as the therapeutic transgene can be safely administered via intraprostatic injection but has not been evaluated for efficacy in patients. Here we investigated the efficacy of adenoviral TRAIL gene therapy in a model of castration resistant prostate cancer and found that intratumoral injections can significantly delay tumor growth but cannot eliminate established lesions. We hypothesized that an underlying cause is inefficient adenoviral delivery. Using the LNCaP progression model of prostate cancer we show that surface CAR expression decreases with increasing tumorigenicity and that castration resistant C4-2b cells were more difficult to transduce with adenovirus than castration sensitive LNCaP cells. Many genes, including CAR, are epigenetically silenced during transformation but a new class of chemotherapeutic agents, known as histone deacetylase inhibitors (HDACi), can reverse this process. We demonstrate that HDACi restore CAR expression and infectivity in C4-2b cells and enhance caspase activation in response to infection with a TRAIL adenovirus. We also show that in cells with high surface CAR expression, HDACi further enhance transgene expression from the CMV promoter. Thus HDACi have multiple beneficial effects, which may enhance not only viral but also non-viral gene therapy of castration resistant prostate cancer
Perfect Simulation Of Processes With Long Memory: a 'Coupling Into And From The Past' Algorithm
International audienceWe describe a new algorithm for the perfect simulation of variable length Markov chains and random systems with perfect connections. This algorithm, which generalizes Propp and Wilson's simulation scheme, is based on the idea of coupling into and from the past. It improves on existing algorithms by relaxing the conditions on the kernel and by accelerating convergence, even in the simple case of finite order Markov chains. Although chains of variable or infinite order have been widely investigated for decades, their use in applied probability, from information theory to bio-informatics and linguistics, has recently led to considerable renewed interest
ANALYSIS OF SUBGROUP EFFECTS IN RANDOMIZED TRIALS WHEN SUBGROUP MEMBERSHIP IS INFORMATIVELY MISSING: APPLICATION TO THE MADIT II STUDY
In this paper, we develop and implement a general sensitivity analysis methodology for drawing inference about subgroup effects in a two-arm randomized trial when subgroup status is only known for a non-random sample in one of the trial arms. The methodology is developed in the context of the MADIT II study, a randomized trial designed to evaluate the effectiveness of implantable defibrillators on survival
Quantum-Information Theoretic Properties of Nuclei and Trapped Bose Gases
Fermionic (atomic nuclei) and bosonic (correlated atoms in a trap) systems
are studied from an information-theoretic point of view. Shannon and Onicescu
information measures are calculated for the above systems comparing correlated
and uncorrelated cases as functions of the strength of short range
correlations. One-body and two-body density and momentum distributions are
employed. Thus the effect of short-range correlations on the information
content is evaluated. The magnitude of distinguishability of the correlated and
uncorrelated densities is also discussed employing suitable measures of
distance of states i.e. the well known Kullback-Leibler relative entropy and
the recently proposed Jensen-Shannon divergence entropy. It is seen that the
same information-theoretic properties hold for quantum many-body systems
obeying different statistics (fermions and bosons).Comment: 24 pages, 9 figures, 1 tabl
Chains of infinite order, chains with memory of variable length, and maps of the interval
We show how to construct a topological Markov map of the interval whose
invariant probability measure is the stationary law of a given stochastic chain
of infinite order. In particular we caracterize the maps corresponding to
stochastic chains with memory of variable length. The problem treated here is
the converse of the classical construction of the Gibbs formalism for Markov
expanding maps of the interval
Spreading lengths of Hermite polynomials
The Renyi, Shannon and Fisher spreading lengths of the classical or
hypergeometric orthogonal polynomials, which are quantifiers of their
distribution all over the orthogonality interval, are defined and investigated.
These information-theoretic measures of the associated Rakhmanov probability
density, which are direct measures of the polynomial spreading in the sense of
having the same units as the variable, share interesting properties: invariance
under translations and reflections, linear scaling and vanishing in the limit
that the variable tends towards a given definite value. The expressions of the
Renyi and Fisher lengths for the Hermite polynomials are computed in terms of
the polynomial degree. The combinatorial multivariable Bell polynomials, which
are shown to characterize the finite power of an arbitrary polynomial, play a
relevant role for the computation of these information-theoretic lengths.
Indeed these polynomials allow us to design an error-free computing approach
for the entropic moments (weighted L^q-norms) of Hermite polynomials and
subsequently for the Renyi and Tsallis entropies, as well as for the Renyi
spreading lengths. Sharp bounds for the Shannon length of these polynomials are
also given by means of an information-theoretic-based optimization procedure.
Moreover, it is computationally proved the existence of a linear correlation
between the Shannon length (as well as the second-order Renyi length) and the
standard deviation. Finally, the application to the most popular
quantum-mechanical prototype system, the harmonic oscillator, is discussed and
some relevant asymptotical open issues related to the entropic moments
mentioned previously are posed.Comment: 16 pages, 4 figures. Journal of Computational and Applied Mathematics
(2009), doi:10.1016/j.cam.2009.09.04
A simple method for the evaluation of the information content and complexity in atoms. A proposal for scalability
We present a very simple method for the calculation of Shannon, Fisher,
Onicescu and Tsallis entropies in atoms, as well as SDL and LMC complexity
measures, as functions of the atomic number Z. Fractional occupation
probabilities of electrons in atomic orbitals are employed, instead of the more
complicated continuous electron probability densities in position and momentum
spaces, used so far in the literature. Our main conclusions are compatible with
the results of more sophisticated approaches and correlate fairly with
experimental data. We obtain for the Tsallis entropic index the value q=1.031,
which shows that atoms are very close to extensivity. A practical way towards
scalability of the quantification of complexity for systems with more
components than the atom is indicated. We also discuss the issue if the
complexity of the electronic structure of atoms increases with Z. A Pair of
Order-Disorder Indices (PODI), which can be introduced for any quantum
many-body system, is evaluated in atoms. We conclude that "atoms are ordered
systems, which do not grow in complexity as Z increases".Comment: Preprint, 25 pages, 15 figures, 1 Tabl
Configuration Complexities of Hydrogenic Atoms
The Fisher-Shannon and Cramer-Rao information measures, and the LMC-like or
shape complexity (i.e., the disequilibrium times the Shannon entropic power) of
hydrogenic stationary states are investigated in both position and momentum
spaces. First, it is shown that not only the Fisher information and the
variance (then, the Cramer-Rao measure) but also the disequilibrium associated
to the quantum-mechanical probability density can be explicitly expressed in
terms of the three quantum numbers (n, l, m) of the corresponding state.
Second, the three composite measures mentioned above are analytically,
numerically and physically discussed for both ground and excited states. It is
observed, in particular, that these configuration complexities do not depend on
the nuclear charge Z. Moreover, the Fisher-Shannon measure is shown to
quadratically depend on the principal quantum number n. Finally, sharp upper
bounds to the Fisher-Shannon measure and the shape complexity of a general
hydrogenic orbital are given in terms of the quantum numbers.Comment: 22 pages, 7 figures, accepted i
Net Fisher information measure versus ionization potential and dipole polarizability in atoms
The net Fisher information measure, defined as the product of position and
momentum Fisher information measures and derived from the non-relativistic
Hartree-Fock wave functions for atoms with Z=1-102, is found to correlate well
with the inverse of the experimental ionization potential. Strong direct
correlations of the net Fisher information are also reported for the static
dipole polarizability of atoms with Z=1-88. The complexity measure, defined as
the ratio of the net Onicescu information measure and net Fisher information,
exhibits clearly marked regions corresponding to the periodicity of the atomic
shell structure. The reported correlations highlight the need for using the net
information measures in addition to either the position or momentum space
analogues. With reference to the correlation of the experimental properties
considered here, the net Fisher information measure is found to be superior
than the net Shannon information entropy.Comment: 16 pages, 6 figure
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