1,121 research outputs found
Atomic Scale Fractal Dimensionality in Proteins
The soft condensed matter of biological organisms exhibits atomic motions
whose properties depend strongly on temperature and hydration conditions. Due
to the superposition of rapidly fluctuating alternative motions at both very
low temperatures (quantum effects) and very high temperatures (classical
Brownian motion regime), the dimension of an atomic ``path'' is in reality
different from unity. In the intermediate temperature regime and under
environmental conditions which sustain active biological functions, the fractal
dimension of the sets upon which atoms reside is an open question. Measured
values of the fractal dimension of the sets on which the Hydrogen atoms reside
within the Azurin protein macromolecule are reported. The distribution of
proton positions was measured employing thermal neutron elastic scattering from
Azurin protein targets. As the temperature was raised from low to intermediate
values, a previously known and biologically relevant dynamical transition was
verified for the Azurin protein only under hydrated conditions. The measured
fractal dimension of the geometrical sets on which protons reside in the
biologically relevant temperature regime is given by . The
relationship between fractal dimensionality and biological function is
qualitatively discussed.Comment: ReVTeX4 format with 5 *.eps figure
Seals at sea: modelling seal distribution in the German bight based on aerial survey data
The Wadden Sea is an important habitat for harbour seals and grey seals. They regularly haul-out on sandbanks and islands along the coast. Comparably little is known about the time seals spend at sea and how they use the remainder of the North Sea. Yet, human activity in offshore waters is increasing and information on seal distribution in the North Sea is crucial for conservation and management. Aerial line transect surveys were conducted in the German bight from 2002 to 2007 to investigate the distribution and abundance of marine mammals. Distance sampling methodology was combined with density surface modelling for a spatially explicit analysis of seal distribution in the German North Sea. Depth and distance to coast were found to be relevant predictor variables for seal density. Density surface modelling allowed for a depiction of seal distribution in the study area as well as an abundance estimate. This is the first study to use aerial survey data to develop a density surface model (DSM) for a spatially explicit distribution estimate of seals at se
On spectral scaling laws for incompressible anisotropic MHD turbulence
A heuristic model is given for anisotropic magnetohydrodynamics (MHD)
turbulence in the presence of a uniform external magnetic field B_0 {\bf {\hat
e}_{\pa}}. The model is valid for both moderate and strong and is able
to describe both the strong and weak wave turbulence regimes as well as the
transition between them. The main ingredient of the model is the assumption of
constant ratio at all scales between \add{the} linear wave period and \add{the}
nonlinear turnover timescale. Contrary to the model of critical balance
introduced by Goldreich and Sridhar [P. Goldreich and S. Sridhar, ApJ {\bf
438}, 763 (1995)], it is not assumed in addition that this ratio be equal to
unity at all scales which allows us to use the Iroshnikov-Kraichnan
phenomenology. It is then possible to recover the widely observed anisotropic
scaling law \kpa \propto \kpe^{2/3} between parallel and perpendicular
wavenumbers (with reference to B_0 {\bf {\hat e}_{\pa}}) and to obtain the
universal prediction, , for the total energy spectrum
E(\kpe,\kpa) \sim \kpe^{-\alpha} \kpa^{-\beta}. In particular, with such a
prediction the weak Alfv\'en wave turbulence constant-flux solution is
recovered and, for the first time, a possible explanation to its precursor
found numerically by Galtier et al [S. Galtier et al., J. Plasma Phys. {\bf
63}, 447 (2000)] is given
From Cavity Electromechanics to Cavity Optomechanics
We present an overview of experimental work to embed high-Q mesoscopic
mechanical oscillators in microwave and optical cavities. Based upon recent
progress, the prospect for a broad field of "cavity quantum mechanics" is very
real. These systems introduce mesoscopic mechanical oscillators as a new
quantum resource and also inherently couple their motion to photons throughout
the electromagnetic spectrum.Comment: 8 pages, 6 figures, ICAP proceedings submissio
Adaptive synchronization in delay-coupled networks of Stuart-Landau oscillators
We consider networks of delay-coupled Stuart-Landau oscillators. In these
systems, the coupling phase has been found to be a crucial control parameter.
By proper choice of this parameter one can switch between different synchronous
oscillatory states of the network. Applying the speed-gradient method, we
derive an adaptive algorithm for an automatic adjustment of the coupling phase
such that a desired state can be selected from an otherwise multistable regime.
We propose goal functions based on both the difference of the oscillators and a
generalized order parameter and demonstrate that the speed-gradient method
allows one to find appropriate coupling phases with which different states of
synchronization, e.g., in-phase oscillation, splay or various cluster states,
can be selected.Comment: 8 pages, 7 figure
THz-range free-electron laser ESR spectroscopy: techniques and applications in high magnetic fields
The successful use of picosecond-pulse free-electron-laser (FEL) radiation
for the continuous-wave THz-range electron spin resonance (ESR) spectroscopy
has been demonstrated. The combination of two linac-based FELs (covering the
wavelength range of 4 - 250 m) with pulsed magnetic fields up to 70 T
allows for multi-frequency ESR spectroscopy in a frequency range of 1.2 - 75
THz with a spectral resolution better than 1%. The performance of the
spectrometer is illustrated with ESR spectra obtained in the
2,2-diphenyl-1-picrylhydrazyl (DPPH) and the low-dimensional organic material
(CHN)CuCl.Comment: 9 pages, 9 figures. Rev. Sci. Instrum., accepte
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