430,586 research outputs found
Existence uniqueness and ratio decomposition for Gibbs states via duality
We give an elementary proof of existence and uniqueness of Gibbs states for Hölder weight systems on subshifts of finite type. This uses a notion of duality for such subshifts. The approach of Paterson [2] is used to construct a measure with a prescribed Jacobian and the duality is used to produce an invariant measure from this
Rigidity of hyperbolic sets on surfaces
Given a hyperbolic invariant set of a diffeomorphism on a surface, it is proved that, if the holonomies are sufficiently smooth, then the diffeomorphism on the hyperbolic invariant set is rigid in the sense that it is C1+ conjugate to a hyperbolic affine model
Smoothness of holonomies for codimension 1 hyperbolic dynamics
Hyperbolic invariant sets {Lambda} of C1+{gamma} diffeomorphisms where either the stable or unstable leaves are 1-dimensional are considered in this paper. Under the assumption that the {Lambda} has local product structure, the authors prove that the holonomies between the 1-dimensional leaves are C1+{alpha} for some 0 < {alpha} < 1
Teichmüller spaces and HR structures for hyperbolic surface dynamics
We construct a Teichmüller space for the C^{1+}-conjugacy classes of hyperbolic dynamical systems on surfaces. After introducing the notion of an HR structure which associates an affine structure with each of the stable and unstable laminations, we show that there is a one-to-one correspondence between these HR structures and the C^{1+}-conjugacy classes. As part of the proof we construct a canonical representative dynamical system for each HR structure. This has the smoothest holonomies of any representative of the corresponding C^{1+}-conjugacy class. Finally, we introduce solenoid functions and show that they provide a good Teichmüller space
Bouncing droplets on a billiard table
In a set of experiments, Couder et. al. demonstrate that an oscillating fluid
bed may propagate a bouncing droplet through the guidance of the surface waves.
We present a dynamical systems model, in the form of an iterative map, for a
droplet on an oscillating bath. We examine the droplet bifurcation from
bouncing to walking, and prescribe general requirements for the surface wave to
support stable walking states. We show that in addition to walking, there is a
region of large forcing that may support the chaotic bouncing of the droplet.
Using the map, we then investigate the droplet trajectories for two different
wave responses in a square (billiard ball) domain. We show that for waves which
are quickly damped in space, the long time trajectories in a square domain are
either non-periodic dense curves, or approach a quasiperiodic orbit. In
contrast, for waves which extend over many wavelengths, at low forcing,
trajectories tend to approach an array of circular attracting sets. As the
forcing increases, the attracting sets break down and the droplet travels
throughout space
High levels of cyclic di-GMP in Klebsiella pneumoniae attenuate virulence in the lung
ABSTRACT
The bacterial second messenger bis-(3′-5′)-cyclic dimeric GMP (c-di-GMP) has been shown to influence the expression of virulence factors in certain pathogenic bacteria, but little is known about its activity in the increasingly antibiotic-resistant pathogen
Klebsiella pneumoniae
. Here, the expression in
K. pneumoniae
of a heterologous diguanylate cyclase increased the bacterial c-di-GMP concentration and attenuated pathogenesis in murine pneumonia. This attenuation remained evident in mice lacking the c-di-GMP sensor STING, indicating that the high c-di-GMP concentration exerted its influence not on host responses but on bacterial physiology. While serum resistance and capsule expression were unaffected by the increased c-di-GMP concentration, both type 3 and type 1 pili were strongly upregulated. Importantly, attenuation of
K. pneumoniae
virulence by high c-di-GMP levels was abrogated when type 1 pilus expression was silenced. We conclude that increased type 1 piliation may hamper
K. pneumoniae
virulence in the respiratory tract and that c-di-GMP signaling represents a potential therapeutic target for antibiotic-resistant
K. pneumoniae
in this niche.
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Thermal cycle testing of Space Station Freedom solar array blanket coupons
Lewis Research Center is presently conducting thermal cycle testing of solar array blanket coupons that represent the baseline design for Space Station Freedom. Four coupons were fabricated as part of the Photovoltaic Array Environment Protection (PAEP) Program, NAS 3-25079, at Lockheed Missile and Space Company. The objective of the testing is to demonstrate the durability or operational lifetime of the solar array welded interconnect design within the durability or operational lifetime of the solar array welded interconnect design within a low earth orbit (LEO) thermal cycling environment. Secondary objectives include the observation and identification of potential failure modes and effects that may occur within the solar array blanket coupons as a result of thermal cycling. The objectives, test articles, test chamber, performance evaluation, test requirements, and test results are presented for the successful completion of 60,000 thermal cycles
Transport equations for the inflationary spectral index
We present a simple and efficient method to compute the superhorizon evolution of the spectral index in multifield inflationary models, using transport equation techniques. We illustrate the evolution of n(s) with time for various interesting potentials
ZEKE-PFI spectroscopy of 1:1 complexes of sodium with water and ammonia
ZEKE-PFI (zero kinetic energy pulsed field ionization) photoelectron spectra of the Na(H_2O), Na(D_2O), Na(NH_3), and Na(ND_3) complexes are reported. Spectra of all four complexes were obtained by single-photon ionization, and, for the Na(NH_3) and Na(ND_3) complexes, by two-color (1 + 1′) photoionization as well, with the Ã^2E state serving as the intermediate resonance. Improved values for the ionization energies (IE) and intermolecular vibrational frequencies of the complexes were determined. The single-photon ZEKE-PFI spectra show transitions only between states of the same vibrational symmetry, in accord with the selection rule for allowed electronic transitions. Some of the two-color ZEKE-PFI spectra, however, show strong transitions between states of different vibrational symmetry which we attribute to vibronic coupling in the intermediate state
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