128 research outputs found
Nonlocal description of sound propagation through an array of Helmholtz resonators
A generalized macroscopic nonlocal theory of sound propagation in
rigid-framed porous media saturated with a viscothermal fluid has been recently
proposed, which takes into account both temporal and spatial dispersion. Here,
we consider applying this theory capable to describe resonance effects, to the
case of sound propagation through an array of Helmholtz resonators whose
unusual metamaterial properties such as negative bulk moduli, have been
experimentally demonstrated. Three different calculations are performed,
validating the results of the nonlocal theory, relating to the
frequency-dependent Bloch wavenumber and bulk modulus of the first normal mode,
for 1D propagation in 2D or 3D periodic structures.Comment: 19 page
Quantum Conductance of the Single Electron Transistor
The quantum conductance of the single-electron tunneling (SET) transistor is
investigated in this paper by the functional integral approach. The formalism
is valid for arbitrary tunnel resistance of the junctions forming the SET
transistor at any temperature. The path integrals are evaluated by the
semiclassical method to yield an explicit non-perturbation form of the quantum
conductance of the SET transistor. An anomaly of the quantum conductance is
found if the tunnel resistances are much smaller than the quantum resistance.
The dependence of the conductance on the gate voltage is also discussed.Comment: 4 pages including some mathe details of cond-mat/990806
Cluster transfer matrix method for the single electron box
With the newly developed cluster transfer matrix method, we calculate the
average electron number n vs nx (the polarization charge) for varying junction
conductance and its first derivative at nx=0 for finite temperatures, and
demonstrate that the new method is as powerful as the Monte Carlo and
renormalization group methods.Comment: 11 pages including figure
Individual charge traps in silicon nanowires: Measurements of location, spin and occupation number by Coulomb blockade spectroscopy
We study anomalies in the Coulomb blockade spectrum of a quantum dot formed
in a silicon nanowire. These anomalies are attributed to electrostatic
interaction with charge traps in the device. A simple model reproduces these
anomalies accurately and we show how the capacitance matrices of the traps can
be obtained from the shape of the anomalies. From these capacitance matrices we
deduce that the traps are located near or inside the wire. Based on the
occurrence of the anomalies in wires with different doping levels we infer that
most of the traps are arsenic dopant states. In some cases the anomalies are
accompanied by a random telegraph signal which allows time resolved monitoring
of the occupation of the trap. The spin of the trap states is determined via
the Zeeman shift.Comment: 9 pages, 8 figures, v2: section on RTS measurements added, many
improvement
Charging Ultrasmall Tunnel Junctions in Electromagnetic Environment
We have investigated the quantum admittance of an ultrasmall tunnel junction
with arbitrary tunneling strength under an electromagnetic environment. Using
the functional integral approach a close analytical expression of the quantum
admittance is derived for a general electromagnetic environment. We then
consider a specific controllable environment where a resistance is connected in
series with the tunneling junction, for which we derived the dc quantum
conductance from the zero frequency limit of the imaginary part of the quantum
admittance. For such electromagnetic environment the dc conductance has been
investigated in recent experiments, and our numerical results agree
quantitatively very well with the measurements. Our complete numerical results
for the entire range of junction conductance and electromagnetic environmental
conductance confirmed the few existing theoretical conclusions.Comment: 7 pages, 3 ps-figure
Effect of the Tunneling Conductance on the Coulomb Staircase
Quantum fluctuations of the charge in the single electron box are
investigated. The rounding of the Coulomb staircase caused by virtual electron
tunneling is determined by perturbation theory up to third order in the
tunneling conductance and compared with precise Monte Carlo data computed with
a new algorithm. The remarkable agreement for large conductance indicates that
presently available experimental data on Coulomb charging effects in metallic
nanostructures can be well explained by finite order perturbative results.Comment: 4 pages, 5 figure
Strong Charge Fluctuations in the Single-Electron Box: A Quantum Monte Carlo Analysis
We study strong electron tunneling in the single-electron box, a small
metallic island coupled to an electrode by a tunnel junction, by means of
quantum Monte Carlo simulations. We obtain results, at arbitrary tunneling
strength, for the free energy of this system and the average charge on the
island as a function of an external bias voltage. In much of the parameter
range an extrapolation to the ground state is possible. Our results for the
effective charging energy for strong tunneling are compared to earlier -- in
part controversial -- theoretical predictions and Monte Carlo simulations
Charge Fluctuations in the Single Electron Box
Quantum fluctuations of the charge in the single electron box are
investigated. Based on a diagrammatic expansion we calculate the average island
charge number and the effective charging energy in third order in the tunneling
conductance. Near the degeneracy point where the energy of two charge states
coincides, the perturbative approach fails, and we explicitly resum the leading
logarithmic divergencies to all orders. The predictions for zero temperature
are compared with Monte Carlo data and with recent renormalization group
results. While good agreement between the third order result and numerical data
justifies the perturbative approach in most of the parameter regime relevant
experimentally, near the degeneracy point and at zero temperature the
resummation is shown to be insufficient to describe strong tunneling effects
quantitatively. We also determine the charge noise spectrum employing a
projection operator technique. Former perturbative and semiclassical results
are extended by the approach.Comment: 20 pages, 15 figure
Land subsidence hazard in iran revealed by country-scale analysis of sentinel-1 insar
Many areas across Iran are subject to land subsidence, a sign of exceeding stress due to the over-extraction of groundwater during the past decades. This paper uses a huge dataset of Sentinel-1, acquired since 2014 in 66 image frames of 250Ă—250km, to identify and monitor land subsidence across Iran. Using a two-step time series analysis, we first identify subsidence zones at a medium scale of 100m across the country. For the first time, our results provide a comprehensive nationwide map of subsidence in Iran and recognize its spatial distribution and magnitude. Then, in the second step of analysis, we quantify the deformation time series at the highest possible resolution to study its impact on civil infrastructure. The results spots the hazard posed by land subsidence to different infrastructure. Examples of road and railways affected by land subsidence hazard in Tehran and Mashhad, two of the most populated cities in Iran, are presented in this study
Exploring cloud-based platforms for rapid insar time series analysis
The idea of near real-time deformation analysis using Synthetic Aperture Radar (SAR) data as a response to natural and anthropogenic disasters has been an interesting topic in the last years. A major limiting factor for this purpose has been the non-availability of both spatially and temporally homogeneous SAR datasets. This has now been resolved thanks to the SAR data provided by the Sentinel-1A/B missions, freely available at a global scale via the Copernicus program of the European Space Agency (ESA). Efficient InSAR analysis in the era of Sentinel demands working with cloud-based platforms to tackle problems posed by large volumes of data. In this study, we explore a variety of existing cloud-based platforms for Multioral Interferometric SAR (MTI) analysis and discuss their opportunities and limitations
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