65,957 research outputs found
Hermitian scattering behavior for the non-Hermitian scattering center
We study the scattering problem for the non-Hermitian scattering center,
which consists of two Hermitian clusters with anti-Hermitian couplings between
them. Counterintuitively, it is shown that it acts as a Hermitian scattering
center, satisfying , i.e., the Dirac probability current
is conserved, when one of two clusters is embedded in the waveguides. This
conclusion can be applied to an arbitrary parity-symmetric real Hermitian graph
with additional PT-symmetric potentials, which is more feasible in experiment.
Exactly solvable model is presented to illustrate the theory. Bethe ansatz
solution indicates that the transmission spectrum of such a cluster displays
peculiar feature arising from the non-Hermiticity of the scattering center.Comment: 6 pages, 2 figure
Generalized-Ensemble Simulations of the Human Parathyroid Hormone Fragment PTH(1-34)
A generalized-ensemble technique, multicanonical sampling, is used to study
the folding of a 34-residue human parathyroid hormone fragment. An all-atom
model of the peptide is employed and the protein-solvent interactions are
approximated by an implicit solvent. Our results demonstrate that
generalized-ensemble simulations are well suited to sample low-energy
structures of such large polypeptides. Configurations with a root-mean-square
deviation (rmsd) to the crystal structure of less than one \AA are found.
Finally, we discuss limitations of our implicit solvent model.Comment: To appear in J. Chem. Phy
Environmental boundary tracking and estimation using multiple autonomous vehicles
In this paper, we develop a framework for environmental
boundary tracking and estimation by considering the
boundary as a hidden Markov model (HMM) with separated
observations collected from multiple sensing vehicles. For each
vehicle, a tracking algorithm is developed based on Page’s
cumulative sum algorithm (CUSUM), a method for change-point
detection, so that individual vehicles can autonomously
track the boundary in a density field with measurement noise.
Based on the data collected from sensing vehicles and prior
knowledge of the dynamic model of boundary evolvement, we
estimate the boundary by solving an optimization problem, in
which prediction and current observation are considered in the
cost function. Examples and simulation results are presented
to verify the efficiency of this approach
Resonance enhanced turbulent transport
The effect of oscillatory shear flows on turbulent transport of passive scalar fields is studied by numerical computations based on the results provided by E. Kim [Physics of Plasmas 13, 022308 (2006)] . Turbulent diffusion is found to depend crucially on the competition between suppression due to shearing and enhancement due to resonances, depending on the characteristic time and length scales of shear flow and turbulence. Enhancements in transport occur for turbulence with finite memory time either due to Doppler or parametric resonances. Scalings of turbulence amplitude and transport are provided in different parameter spaces. The results suggest that oscillatory shear flows are not only less efficient in regulating turbulence, but also can enhance the value of turbulent diffusion, accelerating turbulent transport
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