9,340 research outputs found
Substituted phenylarsonic acids; structures and spectroscopy
Full NMR and ESI-MS spectra, and differential scanning calorimeter data are presented for 15 substituted phenylarsonic acids, including two new fluoro-substituted examples. X-ray crystal structure determinations of five examples (phenylarsonic acid and the 4-fluoro-, 4-fluoro-3-nitro-, 3-amino-4-hydroxy- and 3-amino-4-methoxy-substituted derivatives) were determined and the H-bonding crystal-packing patterns analysed
Darwin\u27s Bee-Trap: The Kinetics of Catasetum, a New World Orchid
The orchid genera Catasetum employs a hair-trigger activated, pollen release mechanism, which forcibly attaches pollen sacs onto foraging insects in the New World tropics. This remarkable adaptation was studied extensively by Charles Darwin and he termed this rapid response sensitiveness. Using high speed video cameras with a frame speed of 1000 fps, this rapid release was filmed and from the subsequent footage, velocity, speed, acceleration, force and kinetic energy were computed
Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in 1-TiSe
Using time- and angle-resolved photoemission spectroscopy with selective
near- and mid-infrared photon excitations, we investigate the femtosecond
dynamics of the charge density wave (CDW) phase in 1-TiSe, as well as
the dynamics of CDW fluctuations at 240 K. In the CDW phase, we observe the
coherent oscillation of the CDW amplitude mode. At 240 K, we single out an
ultrafast component in the recovery of the CDW correlations, which we explain
as the manifestation of electron-hole correlations. Our momentum-resolved study
of femtosecond electron dynamics supports a mechanism for the CDW phase
resulting from the cooperation between the interband Coulomb interaction, the
mechanism of excitonic insulator phase formation, and electron-phonon coupling.Comment: 9 pages, 6 figure
Chaotic saddles in nonlinear modulational interactions in a plasma
A nonlinear model of modulational processes in the subsonic regime involving
a linearly unstable wave and two linearly damped waves with different damping
rates in a plasma is studied numerically. We compute the maximum Lyapunov
exponent as a function of the damping rates in a two-parameter space, and
identify shrimp-shaped self-similar structures in the parameter space. By
varying the damping rate of the low-frequency wave, we construct bifurcation
diagrams and focus on a saddle-node bifurcation and an interior crisis
associated with a periodic window. We detect chaotic saddles and their stable
and unstable manifolds, and demonstrate how the connection between two chaotic
saddles via coupling unstable periodic orbits can result in a crisis-induced
intermittency. The relevance of this work for the understanding of modulational
processes observed in plasmas and fluids is discussed.Comment: Physics of Plasmas, in pres
Amplitude dependent frequency, desynchronization, and stabilization in noisy metapopulation dynamics
The enigmatic stability of population oscillations within ecological systems
is analyzed. The underlying mechanism is presented in the framework of two
interacting species free to migrate between two spatial patches. It is shown
that that the combined effects of migration and noise cannot account for the
stabilization. The missing ingredient is the dependence of the oscillations'
frequency upon their amplitude; with that, noise-induced differences between
patches are amplified due to the frequency gradient. Migration among
desynchronized regions then stabilizes a "soft" limit cycle in the vicinity of
the homogenous manifold. A simple model of diffusively coupled oscillators
allows the derivation of quantitative results, like the functional dependence
of the desynchronization upon diffusion strength and frequency differences. The
oscillations' amplitude is shown to be (almost) noise independent. The results
are compared with a numerical integration of the marginally stable
Lotka-Volterra equations. An unstable system is extinction-prone for small
noise, but stabilizes at larger noise intensity
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