2,439 research outputs found
A Portable Eddy Covariance System for the Measurement of Ecosystem–Atmosphere Exchange of CO2, Water Vapor, and Energy
To facilitate the study of flux heterogeneity within a region, the authors have designed and field-tested a portable eddy covariance system to measure exchange of CO2, water vapor, and energy between the land surface and the atmosphere. The combination of instrumentation used in this system allows high precision flux measurements without requiring on-site infrastructure such as prepositioned towers or line power. In addition, the system contains sensors to measure a suit of soil, climatic, and energy-related parameters that are needed to quality control the fluxes and to characterize the flux footprint. The physical design and instrument packaging used in the system allows for simple transport (fits in a standard minivan) and for rapid deployment with a minimal number of field personnel (usually less than a day for one person). The power requirement for the entire system (instruments and data loggers) is less than 35 W, which is provided by a companion solar power system.
Side-by-side field comparisons between this system and two permanent AmeriFlux sites and between the roving AmeriFlux intercomparison system are described here. Results of these comparisons indicate that the portable system is capable of absolute flux resolutions of about 61.2 mmol m22 s21 for CO2, 615 W m22 for LE, 67 W m22 for H, and 60.06 m s21 for u* between any given 30-min averaging periods. It is also found that, compared to a permanent Ameriflux site, the relative accuracy of this flux estimates is between 1% and 7%. Based on these results, it is concluded that this portable system is capable of making ecosystem flux measurements with an accuracy and precision comparable to most permanent AmeriFlux systems
Fractal Noise in Quantum Ballistic and Diffusive Lattice Systems
We demonstrate fractal noise in the quantum evolution of wave packets moving
either ballistically or diffusively in periodic and quasiperiodic tight-binding
lattices, respectively. For the ballistic case with various initial
superpositions we obtain a space-time self-affine fractal which
verify the predictions by Berry for "a particle in a box", in addition to
quantum revivals. For the diffusive case self-similar fractal evolution is also
obtained. These universal fractal features of quantum theory might be useful in
the field of quantum information, for creating efficient quantum algorithms,
and can possibly be detectable in scattering from nanostructures.Comment: 9 pages, 8 postscript figure
Chaos and isospin symmetry breaking in rotational nuclei
For nuclei with N = Z, the isospin degree of freedom is important and, for
deformed systems, rotational bands of different isospin may be expected at low
excitation energies. We have investigated, in a simple model space, the
influence of the isospin-breaking Coulomb interaction on the degree of
chaoticity of these rotational bands. The statistical measures used rely on an
analysis of level-spacing distributions, which are extremely difficult to
measure experimentally. We show, however, that the overlap intergrals between
states of similar frequency reflect well the degree of chaoticity. This
quantity is closely related to the experimentally more accessible gamma-decay
``spreading width''.Comment: 13 pages, 9 figures, Elsevie
Ultrafast geometric manipulation of electron spin and detection of the geometric phase via Faraday rotation spectroscopy
Time-resolved Faraday rotation spectroscopy is currently exploited as a
powerful technique to probe spin dynamics in semiconductors. We propose here an
all-optical approach to geometrically manipulate electron spin and to detect
the geometric phase by this type of extremely sensitive experiment. The global
nature of the geometric phase can make the quantum manipulation more stable,
which may find interesting application in quantum devices.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
Wave scattering from self-affine surfaces
Electromagnetic wave scattering from a perfectly reflecting self-affine
surface is considered. Within the framework of the Kirchhoff approximation, we
show that the scattering cross section can be exactly written as a function of
the scattering angle via a centered symmetric Levy distribution for general
roughness amplitude, Hurst exponent and wavelength of the incident wave. The
amplitude of the specular peak, its width and its position are discussed as
well as the power law decrease (with scattering angle) of the scattering cross
section.Comment: RevTeX, 4 pages including 2 figures. Submitted Phys. Rev. Let
Generalization of geometric phase to completely positive maps
We generalize the notion of relative phase to completely positive maps with
known unitary representation, based on interferometry. Parallel transport
conditions that define the geometric phase for such maps are introduced. The
interference effect is embodied in a set of interference patterns defined by
flipping the environment state in one of the two paths. We show for the qubit
that this structure gives rise to interesting additional information about the
geometry of the evolution defined by the CP map.Comment: Minor revision. 2 authors added. 4 pages, 2 figures, RevTex
Perturbative Formulation and Non-adiabatic Corrections in Adiabatic Quantum Computing Schemes
Adiabatic limit is the presumption of the adiabatic geometric quantum
computation and of the adiabatic quantum algorithm. But in reality, the
variation speed of the Hamiltonian is finite. Here we develop a general
formulation of adiabatic quantum computing, which accurately describes the
evolution of the quantum state in a perturbative way, in which the adiabatic
limit is the zeroth-order approximation. As an application of this formulation,
non-adiabatic correction or error is estimated for several physical
implementations of the adiabatic geometric gates. A quantum computing process
consisting of many adiabatic gate operations is considered, for which the total
non-adiabatic error is found to be about the sum of those of all the gates.
This is a useful constraint on the computational power. The formalism is also
briefly applied to the adiabatic quantum algorithm.Comment: 5 pages, revtex. some references adde
- …