2,398 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
Cool for Cats
The iconic Schr\"odinger's cat state describes a system that may be in a
superposition of two macroscopically distinct states, for example two clearly
separated oscillator coherent states. Quite apart from their role in
understanding the quantum classical boundary, such states have been suggested
as offering a quantum advantage for quantum metrology, quantum communication
and quantum computation. As is well known these applications have to face the
difficulty that the irreversible interaction with an environment causes the
superposition to rapidly evolve to a mixture of the component states in the
case that the environment is not monitored. Here we show that by engineering
the interaction with the environment there exists a large class of systems that
can evolve irreversibly to a cat state. To be precise we show that it is
possible to engineer an irreversible process so that the steady state is close
to a pure Schr\"odinger's cat state by using double well systems and an
environment comprising two-photon (or phonon) absorbers. We also show that it
should be possible to prolong the lifetime of a Schr\"odinger's cat state
exposed to the destructive effects of a conventional single-photon decohering
environment. Our protocol should make it easier to prepare and maintain
Schr\"odinger cat states which would be useful in applications of quantum
metrology and information processing as well as being of interest to those
probing the quantum to classical transition.Comment: 10 pages, 7 figures. Significantly updated version with supplementary
informatio
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
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In search of predictive endophenotypes in addiction: insights from preclinical research.
Drug addiction is widely recognized to afflict some but not all individuals by virtue of underlying risk markers and traits involving multifaceted interactions between polygenic and external factors. Remarkably, only a small proportion of individuals exposed to licit and illicit drugs develop compulsive drug-seeking behavior, maintained in the face of adverse consequences and associated detrimental patterns of drug intake involving extended and repeated bouts of binge intoxication, withdrawal and relapse. As a consequence, research has increasingly endeavored to identify distinctive neurobehavioral mechanisms and endophenotypes that predispose individuals to compulsive drug use. However, research in active drug users is hampered by the difficulty in categorizing putatively causal behavioral traits prior to the initiation of drug use. By contrast, research in experimental animals is often hindered by the validity of approaches used to investigate the neural and psychological mechanisms of compulsive drug-seeking habits in humans. Herein, we survey and discuss the principal findings emanating from preclinical animal research on addiction and highlight how specific behavioral endophenotypes of presumed genetic origin (e.g. trait anxiety, novelty preference and impulsivity) differentially contribute to compulsive forms of drug seeking and taking and, in particular, how these differentiate between different classes of stimulant and non-stimulant drugs of abuse.The authors acknowledge funding support from the UK Medical Research Council (grants G9536855; G0701500; G0802729), the Newton-Cambridge Trust and the Wellcome Trust (grant WT109738MA). The Behavioural and Clinical Neuroscience Institute at Cambridge University is supported by a core award from the Medical Research Council (G1000183) and Wellcome Trust (093875/Z/10/Z).This is the author accepted manuscript. The final version is available from Wiley via http://dx.doi.org/10.1111/gbb.1226
Modularity measure of networks with overlapping communities
In this paper we introduce a non-fuzzy measure which has been designed to
rank the partitions of a network's nodes into overlapping communities. Such a
measure can be useful for both quantifying clusters detected by various methods
and during finding the overlapping community-structure by optimization methods.
The theoretical problem referring to the separation of overlapping modules is
discussed, and an example for possible applications is given as well
A Bose-condensed, simultaneous dual species Mach-Zehnder atom interferometer
This paper presents the first realisation of a simultaneous Rb
-Rb Mach-Zehnder atom interferometer with Bose-condensed atoms. A number
of ambitious proposals for precise terrestrial and space based tests of the
Weak Equivalence Principle rely on such a system. This implementation utilises
hybrid magnetic-optical trapping to produce spatially overlapped condensates
with a duty cycle of 20s. A horizontal optical waveguide with co-linear Bragg
beamsplitters and mirrors is used to simultaneously address both isotopes in
the interferometer. We observe a non-linear phase shift on a non-interacting
Rb interferometer as a function of interferometer time, , which we
show arises from inter-isotope scattering with the co-incident Rb
interferometer. A discussion of implications for future experiments is given.Comment: 7 pages, 5 figures. The authors welcome comments and feedback on this
manuscrip
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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