2,063 research outputs found
Comparison of LANDSAT-2 and field spectrometer reflectance signatures of south Texas rangeland plant communities
The accuracy was assessed for an atmospheric correction method that depends on clear water bodies to infer solar and atmospheric parameters for radiative transfer equations by measuring the reflectance signature of four prominent south Texas rangeland plants with the LANDSAT satellite multispectral scanner (MSS) and a ground based spectroradiometer. The rangeland plant reflectances produced by the two sensors were correlated with no significant deviation of the slope from unity or of the intercept from zero. These results indicated that the atmospheric correction produced LANDSAT MSS estimates of rangeland plant reflectances that are as accurate as the ground based spectroradiometer
Tunable refraction in a two dimensional quantum metamaterial
In this paper we consider a two-dimensional metamaterial comprising an array
of qubits (two level quantum objects). Here we show that a two-dimensional
quantum metamaterial may be controlled, e.g. via the application of a magnetic
flux, so as to provide controllable refraction of an input signal. Our results
are consistent with a material that could be quantum birefringent (beam
splitter) or not dependent on the application of this control parameter. We
note that quantum metamaterials as proposed here may be fabricated from a
variety of current candidate technologies from superconducting qubits to
quantum dots. Thus the ideas proposed in this work would be readily testable in
existing state of the art laboratories.Comment: 4 pages, 2 figure
Non-linear dynamics, entanglement and the quantum-classical crossover of two coupled SQUID rings
We explore the quantum-classical crossover of two coupled, identical,
superconducting quantum interference device (SQUID) rings. We note that the
motivation for this work is based on a study of a similar system comprising two
coupled Duffing oscillators. In that work we showed that the entanglement
characteristics of chaotic and periodic (entrained) solutions differed
significantly and that in the classical limit entanglement was preserved only
in the chaotic-like solutions. However, Duffing oscillators are a highly
idealised toy model. Motivated by a wish to explore more experimentally
realisable systems we now extend our work to an analysis of two coupled SQUID
rings. We observe some differences in behaviour between the system that is
based on SQUID rings rather than on Duffing oscillators. However, we show that
the two systems share a common feature. That is, even when the SQUID ring's
trajectories appear to follow (semi) classical orbits entanglement persists.Comment: 9 pages, 4 figures. Published as part of the proceedings of the 32nd
International Workshop on Condensed Matter Theories (CMT32) Loughborough
University, 2008 (invited paper
Is a single photon's wave front observable?
The ultimate goal and the theoretical limit of weak signal detection is the
ability to detect a single photon against a noisy background. [...] In this
paper we show, that a combination of a quantum metamaterial (QMM)-based sensor
matrix and quantum non-demolition (QND) readout of its quantum state allows, in
principle, to detect a single photon in several points, i.e., to observe its
wave front.
Actually, there are a few possible ways of doing this, with at least one
within the reach of current experimental techniques for the microwave range.
The ability to resolve the quantum-limited signal from a remote source against
a much stronger local noise would bring significant advantages to such diverse
fields of activity as, e.g., microwave astronomy and missile defence.
The key components of the proposed method are 1) the entangling interaction
of the incoming photon with the QMM sensor array, which produces the spatially
correlated quantum state of the latter, and 2) the QND readout of the
collective observable (e.g., total magnetic moment), which characterizes this
quantum state. The effects of local noise (e.g., fluctuations affecting the
elements of the matrix) will be suppressed relative to the signal from the
spatially coherent field of (even) a single photon.Comment: 13 pages, 4 figure
The metaphysics of Machian frame-dragging
The paper investigates the kind of dependence relation that best portrays Machian frame-dragging in general relativity. The question is tricky because frame-dragging relates local inertial frames to distant distributions of matter in a time-independent way, thus establishing some sort of non-local link between the two. For this reason, a plain causal interpretation of frame-dragging faces huge challenges. The paper will shed light on the issue by using a generalized structural equation model analysis in terms of manipulationist counterfactuals recently applied in the context of metaphysical enquiry by Schaffer (2016) and Wilson (2017). The verdict of the analysis will be that frame-dragging is best understood in terms of a novel type of dependence relation that is half-way between causation and grounding
Mixed mode data clustering: an approach based on tectrachoric correlations
In this paper we face the problem of clustering mixedmode data by assuming that the observed binary variables aregenerated from latent continuous variables. We perform a principalcomponents analysis on the matrix of tetrachoric correlations and wethen estimate the scores of each latent variable and construct adata matrix with continuous variables to be used in fully Guassianmixture models or in the k-means cluster analysis. The calculationof the expected a posteriori (EAP) estimates may proceed by simplyconsidering a limited number of quadrature points. Results on asimulation study and on a real data set are reported
The Zero-Removing Property and Lagrange-Type Interpolation Series
The classical Kramer sampling theorem, which provides a method for obtaining orthogonal sampling formulas, can be formulated in a more general nonorthogonal setting. In this setting, a challenging problem is to characterize the situations when the obtained nonorthogonal sampling formulas can be expressed as Lagrange-type interpolation series. In this article a necessary and sufficient condition is given in terms of the zero removing property. Roughly speaking, this property concerns the stability of the sampled functions on removing a finite number of their zeros
A Bright Solitonic Matter-Wave Interferometer
We present the first realisation of a solitonic atom interferometer. A
Bose-Einstein condensate of atoms of rubidium-85 is loaded into a
horizontal optical waveguide. Through the use of a Feshbach resonance, the
-wave scattering length of the Rb atoms is tuned to a small negative
value. This attractive atomic interaction then balances the inherent
matter-wave dispersion, creating a bright solitonic matter wave. A Mach-Zehnder
interferometer is constructed by driving Bragg transitions with the use of an
optical lattice co-linear with the waveguide. Matter wave propagation and
interferometric fringe visibility are compared across a range of -wave
scattering values including repulsive, attractive and non-interacting values.
The solitonic matter wave is found to significantly increase fringe visibility
even compared with a non-interacting cloud.Comment: 6 pages, 4 figure
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