64,796 research outputs found
A biomimetic nanofluidic diode based on surface-modified polymeric carbon nitride nanotubes
A controllable ion transport including ion selectivity and ion rectification across nanochannels or porous membranes is of great importance because of potential applications ranging from biosensing to energy conversion. Here, a nanofluidic ion diode was realized by modifying carbon nitride nanotubes with different molecules yielding an asymmetric surface charge that allows for ion rectification. With the advantages of low-cost, thermal and mechanical robustness, and simple fabrication process, carbon nitride nanotubes with ion rectification have the potential to be used in salinity-gradient energy conversion and ion sensor systems
Magnetic susceptibility in quasi one-dimensional Ba2V3O9: chain segmentation versus the staggered field effect
A pronounced Curie-like upturn of the magnetic susceptibility chi(T) of the
quasi one-dimensional spin chain compound Ba2V3O9 has been found recently.
Frequently this is taken as a signature for a staggered field mechanism due to
the presence of g-factor anisotropy and Dzyaloshinskii-Moriya interaction. We
calculate this contribution within a realistic structure of vanadium 3d- and
oxygen 2p-orbitals and conclude that this mechanism is far too small to explain
experimental results. We propose that the Curie term is rather due to a
segmentation of spin chains caused by broken magnetic bonds which leads to
uncompensated S=1/2 spins of segments with odd numbers of spins. Using a
finite-temperature Lanczos method we calculate their effective moment and show
that ~1% of broken magnetic bonds is sufficient to reproduce the anomalous
low-T behavior of chi(T) in Ba2V3O9.Comment: 5 pages, 5 figures, REVTeX 4, minor corrections to the text,
references adde
Finite-Element Simulations of Light Propagation through Circular Subwavelength Apertures
Light transmission through circular subwavelength apertures in metallic films
with surrounding nanostructures is investigated numerically. Numerical results
are obtained with a frequency-domain finite-element method. Convergence of the
obtained observables to very low levels of numerical error is demonstrated.
Very good agreement to experimental results from the literature is reached, and
the utility of the method is demonstrated in the investigation of the influence
of geometrical parameters on enhanced transmission through the apertures
Fast simulation method for parameter reconstruction in optical metrology
A method for automatic computation of parameter derivatives of numerically
computed light scattering signals is demonstrated. The finite-element based
method is validated in a numerical convergence study, and it is applied to
investigate the sensitivity of a scatterometric setup with respect to
geometrical parameters of the scattering target. The method can significantly
improve numerical performance of design optimization, parameter reconstruction,
sensitivity analysis, and other applications
Stochastic Simulation of a finite-temperature one-dimensional Bose-Gas: from Bogoliubov to Tonks-Girardeau regime
We present an ab initio stochastic method for calculating thermal properties
of a trapped, 1D Bose-gas covering the whole range from weak to strong
interactions. Discretization of the problem results in a Bose-Hubbard-like
Hamiltonian, whose imaginary time evolution is made computationally accessible
by stochastic factorization of the kinetic energy. To achieve convergence for
low enough temperatures such that quantum fluctuations are essential, the
stochastic factorization is generalized to blocks, and ideas from
density-matrix renormalization are employed. We compare our numerical results
for density and first-order correlations with analytic predictions.Comment: 5 pages, 3 figures;text added;accepted in Physical Review
Shuttle payload S-band communications system
The Shuttle payload S-band communications system design, operational capabilities, and performance are described in detail. System design requirements, overall system and configuration and operation, and laboratory/flight test results are presented. Payload communications requirements development is discussed in terms of evolvement of requirements as well as the resulting technical challenges encountered in meeting the initial requirements. Initial design approaches are described along with cost-saving initiatives that subsequently had to be made. The resulting system implementation that was finally adopted is presented along with a functional description of the system operation. A description of system test results, problems encountered, how the problems were solved, and the system flight experience to date is presented. Finally, a summary of the advancements made and the lessons learned is discussed
Correlation-function spectroscopy of inelastic lifetime in heavily doped GaAs heterostructures
Measurements of resonant tunneling through a localized impurity state are
used to probe fluctuations in the local density of states of heavily doped
GaAs. The measured differential conductance is analyzed in terms of correlation
functions with respect to voltage. A qualitative picture based on the scaling
theory of Thouless is developed to relate the observed fluctuations to the
statistics of single particle wavefunctions. In a quantitative theory
correlation functions are calculated. By comparing the experimental and
theoretical correlation functions the effective dimensionality of the emitter
is analyzed and the dependence of the inelastic lifetime on energy is
extracted.Comment: 41 pages, 14 figure
Pfaffian pairing wave functions in electronic structure quantum Monte Carlo
We investigate the accuracy of trial wave function for quantum Monte Carlo
based on pfaffian functional form with singlet and triplet pairing. Using a set
of first row atoms and molecules we find that these wave functions provide very
consistent and systematic behavior in recovering the correlation energies on
the level of 95%. In order to get beyond this limit we explore the
possibilities of multi-pfaffian pairing wave functions. We show that a small
number of pfaffians recovers another large fraction of the missing correlation
energy comparable to the larger-scale configuration interaction wave functions.
We also find that pfaffians lead to substantial improvements in fermion nodes
when compared to Hartree-Fock wave functions.Comment: 4 pages, 2 figures, 2 tables, submitted to PR
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