7,302 research outputs found
Investigation of remote sensing techniques of measuring soil moisture
Major activities described include development and evaluation of theoretical models that describe both active and passive microwave sensing of soil moisture, the evaluation of these models for their applicability, the execution of a controlled field experiment during which passive microwave measurements were acquired to validate these models, and evaluation of previously acquired aircraft microwave measurements. The development of a root zone soil water and soil temperature profile model and the calibration and evaluation of gamma ray attenuation probes for measuring soil moisture profiles are considered. The analysis of spatial variability of soil information as related to remote sensing is discussed as well as the implementation of an instrumented field site for acquisition of soil moisture and meteorologic information for use in validating the soil water profile and soil temperature profile models
SCD Patterns Have Singular Diffraction
Among the many families of nonperiodic tilings known so far, SCD tilings are
still a bit mysterious. Here, we determine the diffraction spectra of point
sets derived from SCD tilings and show that they have no absolutely continuous
part, that they have a uniformly discrete pure point part on the z-axis, and
that they are otherwise supported on a set of concentric cylinder surfaces
around this axis. For SCD tilings with additional properties, more detailed
results are given.Comment: 11 pages, 2 figures; Accepted for Journal of Mathematical Physic
Radar cross calibration investigation TAMU radar polarimeter calibration measurements
A short pulse, 20 MHz bandwidth, three frequency radar polarimeter system (RPS) operates at center frequencies of 10.003 GHz, 4.75 GHz, and 1.6 GHz and utilizes dual polarized transmit and receive antennas for each frequency. The basic lay-out of the RPS is different from other truck mounted systems in that it uses a pulse compression IF section common to all three RF heads. Separate transmit and receive antennas are used to improve the cross-polarization isolation at each particular frequency. The receive is a digitally controlled gain modulated subsystem and is interfaced directly with a microprocesser computer for control and data manipulation. Antenna focusing distance, focusing each antenna pair, rf head stability, and polarization characteristics of RPS antennas are discussed. Platform and data acquisition procedures are described
Random Walks Along the Streets and Canals in Compact Cities: Spectral analysis, Dynamical Modularity, Information, and Statistical Mechanics
Different models of random walks on the dual graphs of compact urban
structures are considered. Analysis of access times between streets helps to
detect the city modularity. The statistical mechanics approach to the ensembles
of lazy random walkers is developed. The complexity of city modularity can be
measured by an information-like parameter which plays the role of an individual
fingerprint of {\it Genius loci}.
Global structural properties of a city can be characterized by the
thermodynamical parameters calculated in the random walks problem.Comment: 44 pages, 22 figures, 2 table
Two qubits entanglement dynamics in a symmetry-broken environment
We study the temporal evolution of entanglement pertaining to two qubits
interacting with a thermal bath. In particular we consider the simplest
nontrivial spin bath models where symmetry breaking occurs and treat them by
mean field approximation. We analytically find decoherence free entangled
states as well as entangled states with an exponential decay of the quantum
correlation at finite temperature.Comment: 10 pages, 2 figure
Non-Markovian dynamics for bipartite systems
We analyze the appearance of non-Markovian effects in the dynamics of a
bipartite system coupled to a reservoir, which can be described within a class
of non-Markovian equations given by a generalized Lindblad structure. A novel
master equation, which we term quantum Bloch-Boltzmann equation, is derived,
describing both motional and internal states of a test particle in a quantum
framework. When due to the preparation of the system or to decoherence effects
one of the two degrees of freedom is amenable to a classical treatment and not
resolved in the final measurement, though relevant for the interaction with the
reservoir, non-Markovian behaviors such as stretched exponential or power law
decay of coherences can be put into evidence.Comment: published version, 15 pages, revtex, no figure
Density-potential mappings in quantum dynamics
In a recent letter [Europhys. Lett. 95, 13001 (2011)] the question of whether
the density of a time-dependent quantum system determines its external
potential was reformulated as a fixed point problem. This idea was used to
generalize the existence and uniqueness theorems underlying time-dependent
density functional theory. In this work we extend this proof to allow for more
general norms and provide a numerical implementation of the fixed-point
iteration scheme. We focus on the one-dimensional case as it allows for a more
in-depth analysis using singular Sturm-Liouville theory and at the same time
provides an easy visualization of the numerical applications in space and time.
We give an explicit relation between the boundary conditions on the density and
the convergence properties of the fixed-point procedure via the spectral
properties of the associated Sturm-Liouville operator. We show precisely under
which conditions discrete and continuous spectra arise and give explicit
examples. These conditions are then used to show that in the most physically
relevant cases the fixed point procedure converges. This is further
demonstrated with an example.Comment: 20 pages, 8 figures, 3 table
CMB Lensing Reconstruction on the Full Sky
Gravitational lensing of the microwave background by the intervening dark
matter mainly arises from large-angle fluctuations in the projected
gravitational potential and hence offers a unique opportunity to study the
physics of the dark sector at large scales. Studies with surveys that cover
greater than a percent of the sky will require techniques that incorporate the
curvature of the sky. We lay the groundwork for these studies by deriving the
full sky minimum variance quadratic estimators of the lensing potential from
the CMB temperature and polarization fields. We also present a general
technique for constructing these estimators, with harmonic space convolutions
replaced by real space products, that is appropriate for both the full sky
limit and the flat sky approximation. This also extends previous treatments to
include estimators involving the temperature-polarization cross-correlation and
should be useful for next generation experiments in which most of the
additional information from polarization comes from this channel due to
sensitivity limitations.Comment: Accepted for publication in Phys. Rev. D; typos correcte
Two-axis bend measurement with Bragg gratings in multicore optical fiber
We describe what is to our knowledge the first use of fiber Bragg gratings written into three separate cores of a multicore fiber for two-axis curvature measurement. The gratings act as independent, but isothermal, fiber strain gauges for which local curvature determines the difference in strain between cores, permitting temperature-independent bend measurement. (C) 2003 Optical Society of America
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