963 research outputs found
Non-Gaussian fluctuations in stochastic models with absorbing barriers
The dynamics of a one-dimensional stochastic model is studied in presence of
an absorbing boundary. The distribution of fluctuations is analytically
characterized within the generalized van Kampen expansion, accounting for
higher order corrections beyond the conventional Gaussian approximation. The
theory is shown to successfully capture the non Gaussian traits of the sought
distribution returning an excellent agreement with the simulations, for {\it
all times} and arbitrarily {\it close} to the absorbing barrier. At large
times, a compact analytical solution for the distribution of fluctuations is
also obtained, bridging the gap with previous investigations, within the van
Kampen picture and without resorting to alternative strategies, as elsewhere
hypothesized.Comment: 2 figures, submitted to Phys. Rev. Let
Visualization of Coherent Destruction of Tunneling in an Optical Double Well System
We report on a direct visualization of coherent destruction of tunneling
(CDT) of light waves in a double well system which provides an optical analog
of quantum CDT as originally proposed by Grossmann, Dittrich, Jung, and Hanggi
[Phys. Rev. Lett. {\bf 67}, 516 (1991)]. The driven double well, realized by
two periodically-curved waveguides in an Er:Yb-doped glass, is designed so that
spatial light propagation exactly mimics the coherent space-time dynamics of
matter waves in a driven double-well potential governed by the Schr\"{o}dinger
equation. The fluorescence of Er ions is exploited to image the spatial
evolution of light in the two wells, clearly demonstrating suppression of light
tunneling for special ratios between frequency and amplitude of the driving
field.Comment: final versio
High U(1) charges in type IIB models and their F-theory lift
We construct models with U(1) gauge group and matter with charges up to 6, in the context of type IIB compactifications. We show explicitly that models with charges up to 4 can be derived from corresponding models in F-theory by applying the Sen weak coupling limit. We derive which type IIB models should be the limit of charge 5 and 6 F-theory models. Explicit six dimensional type IIB models with maximal charge 5 and 6 are constructed on an algebraic K3 surface that is the double cover of \u2102\u2119 2 . By using type IIB results we are also able to rediscover the F-theory charge 4 model in a straightforward way
Analytical study of non Gaussian fluctuations in a stochastic scheme of autocatalytic reactions
A stochastic model of autocatalytic chemical reactions is studied both
numerically and analytically. The van Kampen perturbative scheme is
implemented, beyond the second order approximation, so to capture the non
Gaussianity traits as displayed by the simulations. The method is targeted to
the characterization of the third moments of the distribution of fluctuations,
originating from a system of four populations in mutual interaction. The theory
predictions agree well with the simulations, pointing to the validity of the
van Kampen expansion beyond the conventional Gaussian solution.Comment: 15 pages, 8 figures, submitted to Phys. Rev.
Poisson bracket in classical field theory as a derived bracket
We construct a Leibniz bracket on the space of
all differential forms over the finite-dimensional jet bundle . As
an example, we write Maxwell equations with sources in the covariant
finite-dimensional hamiltonian form.Comment: 4 page
The Immune Response to Tumors as a Tool toward Immunotherapy
Until recently cancer medical therapy was limited to chemotherapy that could not differentiate cancer cells from normal cells. More recently with the remarkable mushroom of immunology, newer tools became available, resulting in the novel possibility to attack cancer with the specificity of the immune system. Herein we will review some of the recent achievement of immunotherapy in such aggressive cancers as melanoma, prostatic cancer, colorectal carcinoma, and hematologic malignancies.
Immunotherapy of tumors has developed several techniques: immune cell transfer, vaccines, immunobiological molecules such as monoclonal antibodies that improve the immune responses to tumors. This can be achieved by blocking pathways limiting the immune response, such as CTLA-4 or Tregs. Immunotherapy may also use cytokines especially proinflammatory cytokines to enhance the activity of cytotoxic T cells (CTLs) derived from tumor infiltrating lymphocytes (TILs). The role of newly discovered cytokines remains to be investigated. Alternatively, an other mechanism consists in enhancing the expression of TAAs on tumor cells. Finally, monoclonal antibodies may be used to target oncogenes
Semi-Teleparallel Theories of Gravitation
A class of theories of gravitation that naturally incorporates preferred
frames of reference is presented. The underlying space-time geometry consists
of a partial parallelization of space-time and has properties of Riemann-Cartan
as well as teleparallel geometry. Within this geometry, the kinematic
quantities of preferred frames are associated with torsion fields. Using a
variational method, it is shown in which way action functionals for this
geometry can be constructed. For a special action the field equations are
derived and the coupling to spinor fields is discussed.Comment: 14 pages, LaTe
Generalized parallel tempering on Bayesian inverse problems
Funder: Alexander von Humboldt-Stiftung; doi: http://dx.doi.org/10.13039/100005156In the current work we present two generalizations of the Parallel Tempering
algorithm, inspired by the so-called continuous-time Infinite Swapping
algorithm. Such a method, found its origins in the molecular dynamics
community, and can be understood as the limit case of the continuous-time
Parallel Tempering algorithm, where the (random) time between swaps of states
between two parallel chains goes to zero. Thus, swapping states between chains
occurs continuously. In the current work, we extend this idea to the context of
time-discrete Markov chains and present two Markov chain Monte Carlo algorithms
that follow the same paradigm as the continuous-time infinite swapping
procedure. We analyze the convergence properties of such discrete-time
algorithms in terms of their spectral gap, and implement them to sample from
different target distributions. Numerical results show that the proposed
methods significantly improve over more traditional sampling algorithms such as
Random Walk Metropolis and (traditional) Parallel Tempering
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