18,491 research outputs found
Polymer Translocation Through a Long Nanopore
Polymer translocation through a nanopore in a membrane investigated
theoretically. Recent experiments on voltage-driven DNA and RNA translocations
through a nanopore indicate that the size and geometry of the pore are
important factors in polymer dynamics. A theoretical approach is presented
which explicitly takes into account the effect of the nanopore length and
diameter for polymer motion across the membrane. It is shown that the length of
the pore is crucial for polymer translocation dynamics. The present model
predicts that for realistic conditions (long nanopores and large external
fields) there are two regimes of translocation depending on polymer size: for
polymer chains larger than the pore length, the velocity of translocation is
nearly constant, while for polymer chains smaller than the pore length the
velocity increases with decreasing polymer size. These results agree with
experimental data.Comment: 14 pages, 5 figure
Exact asymptotic distribution of change-point mle for change in the mean of Gaussian sequences
We derive exact computable expressions for the asymptotic distribution of the
change-point mle when a change in the mean occurred at an unknown point of a
sequence of time-ordered independent Gaussian random variables. The derivation,
which assumes that nuisance parameters such as the amount of change and
variance are known, is based on ladder heights of Gaussian random walks hitting
the half-line. We then show that the exact distribution easily extends to the
distribution of the change-point mle when a change occurs in the mean vector of
a multivariate Gaussian process. We perform simulations to examine the accuracy
of the derived distribution when nuisance parameters have to be estimated as
well as robustness of the derived distribution to deviations from Gaussianity.
Through simulations, we also compare it with the well-known conditional
distribution of the mle, which may be interpreted as a Bayesian solution to the
change-point problem. Finally, we apply the derived methodology to monthly
averages of water discharges of the Nacetinsky creek, Germany.Comment: Published in at http://dx.doi.org/10.1214/09-AOAS294 the Annals of
Applied Statistics (http://www.imstat.org/aoas/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Applying a CART-based approach for the diagnostics of mass appraisal models
In this paper an approach for automatic detection of segments where a regression model significantly underperforms and for detecting segments with systematically under- or overestimated prediction is introduced. This segmentational approach is applicable to various expert systems including, but not limited to, those used for the mass appraisal. The proposed approach may be useful for various regression analysis applications, especially those with strong heteroscedasticity. It helps to reveal segments for which separate models or appraiser assistance are desirable. The segmentational approach has been applied to a mass appraisal model based on the Random Forest algorithm.CART, model diagnostics, mass appraisal, real estate, Random forest, heteroscedasticity
Identifying structural shocks behind loan supply fluctuations in Russia
We examine the drivers behind loan supply fluctuations in Russia using Bayesian vector autoregressive model with sign restrictions on impulse response functions. We identify two types of structural innovations: loan supply shock and monetary stance shock. We find that contractionary shocks of both types contributed significantly and in the roughly equal measure to the decrease of bank lending after the Lehman Brothers collapse.loan supply; Bayesian VAR; sign restrictions; financial crisis; Russia
Quasiparticle-vibration coupling in relativistic framework: shell structure of Z=120 isotopes
For the first time, the shell structure of open-shell nuclei is described in
a fully self-consistent extension of the covariant energy density functional
theory. The approach implies quasiparticle-vibration coupling for superfluid
systems. One-body Dyson equation formulated in the doubled quasiparticle space
of Dirac spinors is solved for nucleonic propagators in tin isotopes which
represent the reference case: the obtained energies of the single-quasiparticle
levels and their spectroscopic amplitudes are in agreement with data. The model
is applied to describe the shell evolution in a chain of superheavy isotopes
120 and finds a rather stable proton spherical shell
closure at Z = 120. An interplay of the pairing correlations and the
quasiparticle-phonon coupling gives rise for a smooth evolution of the neutron
shell gap between N = 172 and N = 184 neutron numbers. Vibrational corrections
to the alpha decay energies reach several hundred keV and can be either
positive and negative, thus also smearing the shell effects.Comment: 10 pages, 3 figure
Effects of recreational activity on Acorn Barnacle (Tetraclita squamosa rufotincta) in the Red Sea
Environmental recreation is a fast growing industry. However, in many cases the consequences for the environment are ignored. Eilat is just such a case wherein tourism is the mainstay of the city and the Red Sea is the main attraction. Most areas are developed specifically for enhancing tourism and one of the most benign of creatures, that sits permanently on rocks and seashores, is trodden upon regularly is the Acorn Barnacle (Tetraclita squamosa rufotincta). We surveyed 10 sites with the same area for the number of barnacles that were live, dead or deserted. We compared between areas frequented by recreationists, and from which, they were denied access. We found a significantly greater number of individuals, live barnacles, and fewer deserted barnacles in the restricted areas. We conclude that the Acorn Barnacles in the undisturbed areas had significantly greater probability of survival and longevity compared to those exposed to anthropogenic activity
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