1,247 research outputs found
Synthesis of a protected keto-lysidine analogue via improved preparation of arabino-isocytosine nucleosides
Anhydrouridines react with aliphatic amines to give N-alkyl isocytosines, but reported procedures often demand very long reaction times and can be low yielding, with narrow scope. A modified procedure for such reactions has been developed, using microwave irradiation, significantly reducing reaction time and allowing facile access to a diverse range of novel nucleosides on the gram scale. The method has been used to prepare a precursor to a novel analogue of lysidine, a naturally occurring iminonucleoside found in (t)RNA
On a stochastic partial differential equation with non-local diffusion
In this paper, we prove existence, uniqueness and regularity for a class of
stochastic partial differential equations with a fractional Laplacian driven by
a space-time white noise in dimension one. The equation we consider may also
include a reaction term
The Continuum Directed Random Polymer
Motivated by discrete directed polymers in one space and one time dimension,
we construct a continuum directed random polymer that is modeled by a
continuous path interacting with a space-time white noise. The strength of the
interaction is determined by an inverse temperature parameter beta, and for a
given beta and realization of the noise the path evolves in a Markovian way.
The transition probabilities are determined by solutions to the one-dimensional
stochastic heat equation. We show that for all beta > 0 and for almost all
realizations of the white noise the path measure has the same Holder continuity
and quadratic variation properties as Brownian motion, but that it is actually
singular with respect to the standard Wiener measure on C([0,1]).Comment: 21 page
Weak convergence of finite element approximations of linear stochastic evolution equations with additive noise II. Fully discrete schemes
We present an abstract framework for analyzing the weak error of fully
discrete approximation schemes for linear evolution equations driven by
additive Gaussian noise. First, an abstract representation formula is derived
for sufficiently smooth test functions. The formula is then applied to the wave
equation, where the spatial approximation is done via the standard continuous
finite element method and the time discretization via an I-stable rational
approximation to the exponential function. It is found that the rate of weak
convergence is twice that of strong convergence. Furthermore, in contrast to
the parabolic case, higher order schemes in time, such as the Crank-Nicolson
scheme, are worthwhile to use if the solution is not very regular. Finally we
apply the theory to parabolic equations and detail a weak error estimate for
the linearized Cahn-Hilliard-Cook equation as well as comment on the stochastic
heat equation
Large Deviations for Stochastic Evolution Equations with Small Multiplicative Noise
The Freidlin-Wentzell large deviation principle is established for the
distributions of stochastic evolution equations with general monotone drift and
small multiplicative noise. As examples, the main results are applied to derive
the large deviation principle for different types of SPDE such as stochastic
reaction-diffusion equations, stochastic porous media equations and fast
diffusion equations, and the stochastic p-Laplace equation in Hilbert space.
The weak convergence approach is employed in the proof to establish the Laplace
principle, which is equivalent to the large deviation principle in our
framework.Comment: 31 pages, published in Appl. Math. Opti
Transport in rough self-affine fractures
Transport properties of three-dimensional self-affine rough fractures are
studied by means of an effective-medium analysis and numerical simulations
using the Lattice-Boltzmann method. The numerical results show that the
effective-medium approximation predicts the right scaling behavior of the
permeability and of the velocity fluctuations, in terms of the aperture of the
fracture, the roughness exponent and the characteristic length of the fracture
surfaces, in the limit of small separation between surfaces. The permeability
of the fractures is also investigated as a function of the normal and lateral
relative displacements between surfaces, and is shown that it can be bounded by
the permeability of two-dimensional fractures. The development of channel-like
structures in the velocity field is also numerically investigated for different
relative displacements between surfaces. Finally, the dispersion of tracer
particles in the velocity field of the fractures is investigated by analytic
and numerical methods. The asymptotic dominant role of the geometric
dispersion, due to velocity fluctuations and their spatial correlations, is
shown in the limit of very small separation between fracture surfaces.Comment: submitted to PR
Gravitationally lensed QSOs in the ISSIS/WSO-UV era
Gravitationally lensed QSOs (GLQs) at redshift z = 1-2 play a key role in
understanding the cosmic evolution of the innermost parts of active galaxies
(black holes, accretion disks, coronas and internal jets), as well as the
structure of galaxies at intermediate redshifts. With respect to studies of
normal QSOs, GLQ programmes have several advantages. For example, a monitoring
of GLQs may lead to unambiguous detections of intrinsic and extrinsic
variations. Both kinds of variations can be used to discuss central engines in
distant QSOs, and mass distributions and compositions of lensing galaxies. In
this context, UV data are of particular interest, since they correspond to
emissions from the immediate surroundings of the supermassive black hole. We
describe some observation strategies to analyse optically bright GLQs at z of
about 1.5, using ISSIS (CfS) on board World Space Observatory-Ultraviolet.Comment: 7 pages, 4 figures, Accepted for publication in Astrophysics & Space
Scienc
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