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Over the last decade, the systematic application of spherical neutron polarmetry (SNP) has been successfully used to investigate scientific questions which were intractable before, e.g. study of magneto-electric crystals such as L...
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Over the last decade, the systematic application of spherical neutron polarmetry (SNP) has been successfully used to investigate scientific questions which were intractable before, e.g. study of magneto-electric crystals such as LiCoPO4 and MnGeO3. Until now, the only device capable of performing routine SNP measurements at finite scattering angles was CryoPAD (cryogenic polarization analysis device), presented by Tasset et al. in 1989. Recently we demonstrated that an alternative setup named MuPAD (Mu-metal polarization analysis device) based on a zero-field environment produced by highly permeable mu-metal is also feasible. Here we present this new SNP device together with some first results. (c) 2007 Elsevier B.V. All rights reserved.
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Polarized Small Angle Neutron Scattering (SANS) is a powerful tool for studying mesoscale magnetic structures. In a recent development at the Oak Ridge National Laboratory (ORNL), a polarized neutron beam has been implemented for ...
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Polarized Small Angle Neutron Scattering (SANS) is a powerful tool for studying mesoscale magnetic structures. In a recent development at the Oak Ridge National Laboratory (ORNL), a polarized neutron beam has been implemented for the CG-2 (GP-SANS) beamline at the High Flux Isotope Reactor (HFIR). Three major components were developed to provide the polarized neutron capability: a transmission supermirror neutron polarizer, an adiabatic fast passage neutron spin flipper and a polarized He-3 filter as neutron spin analyzer. The new polarized beam SANS capability was used to investigate several magnetic samples having mesoscale structures.
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Hypercomplex polar Fourier analysis treats a signal as a vector field and generalizes the conventional polar Fourier analysis. It can handle signals represented by hypercomplex numbers such as color images. Hypercomplex polar Four...
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Hypercomplex polar Fourier analysis treats a signal as a vector field and generalizes the conventional polar Fourier analysis. It can handle signals represented by hypercomplex numbers such as color images. Hypercomplex polar Fourier analysis is reversible that means it can reconstruct image. Its coefficient has rotation invariance property that can be used for feature extraction. However in order to increase the computation speed, fast algorithm is needed especially for image processing applications like realtime systems and limited resource platforms. This paper presents fast hypercomplex polar Fourier analysis based on symmetric properties and mathematical properties of trigonometric functions. Proposed fast hypercomplex polar Fourier analysis computes symmetric points simultaneously, which significantly reduce the computation time.
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The current endeavour focuses on the notion of positive versus negative polarity preferences of verbs for their direct objects. We observed verbs with a relatively clear positive or negative polarity preference (called polar), as ...
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The current endeavour focuses on the notion of positive versus negative polarity preferences of verbs for their direct objects. We observed verbs with a relatively clear positive or negative polarity preference (called polar), as well as cases of verbs where positive and negative polarity preference is balanced (called bi-polar). These polarity preferences of verbs are induced on the basis of a large dependency-parsed corpus by means of statistical measures and a lexicon of manually curated prior noun polarities. Given (learned) polar verbs, the contextual polarity of their direct objects can be derived. We reached a lower bound of 81.97% and an upper bound of 93.34% precision in these experiments. The polarity of a noun was predicted by the majority vote of the verbs that take that noun as its direct object in our corpus. In a second experimental setting, we also considered the role of neutral nouns co-occurring with these verbs. We found that the induction of the (tripartite) prior polarity of nouns can be achieved with a precision of 75.97%.
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Polarizing supermirrors have been widely used in neutron scattering facilities where they have been employed as neutron spin filters to polarize neutron beams as well as analyze their polarization. In the past, the performance of ...
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Polarizing supermirrors have been widely used in neutron scattering facilities where they have been employed as neutron spin filters to polarize neutron beams as well as analyze their polarization. In the past, the performance of polarizing supermirrors has been limited by their small acceptance angle, which made them less suitable for use at short wavelengths or with highly divergent beams. Recent advances in supermirror coatings have led to an array of devices designed to, at least partially, overcome this limitation. V-polarizers and multi-channel polarizers have been employed in several different types of neutron scattering instruments. However, our observations in the field where these types of polarizers are in use have raised concerns about their performance. In this paper, we report on detailed Monte-Carlo simulations performed on a multi-channel polarizer used on a prototype Spin-Echo Small Angle Neutron Scattering (SESANS) instrument to better understand its performance. Our results show that careful simulations of polarizers based on mirror reflection are needed to determine whether a particular design is suitable for SESANS applications.
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Four types of polarizers are experimentally evaluated and compared for the uniformity of their transmission axis orientations and the contrast ratio and their spatial variation. Representative samples of calcite Glan-Thompson pola...
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Four types of polarizers are experimentally evaluated and compared for the uniformity of their transmission axis orientations and the contrast ratio and their spatial variation. Representative samples of calcite Glan-Thompson polarizers, polarizing beamsplitters, silver glass polarizers, and stretched polymer polarizers are characterized at 850 nm using a rotating polarizer imaging polarimeter. The sample Glan-Thompson polarizers show the highest contrast ratios and greatest uniformity of transmission axis. Silver glass polarizers and stretched polymer polarizers show intermediate contrast ratios, but all samples of both show a systematic variation of the transmission axis orientation with a magnitude of several tenths of a degree. The polarizing beamsplitter cube samples have very good uniformity of transmission axis but the smallest contrast ratios with noticeable spatial variations of contrast.
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We consider the application of the general theory of unitary matrices to problems of wave scattering involving polarized waves. Having outlined useful parameterizations of the low dimensional groups associated with these unitary m...
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We consider the application of the general theory of unitary matrices to problems of wave scattering involving polarized waves. Having outlined useful parameterizations of the low dimensional groups associated with these unitary matrices, we develop a general processing strategy, which we suggest has application in the extraction of physical information from a range of scattering matrices in optics. Examples are presented of applying the unitary matrix structure to problems of single and multiple scattering from a cloud of random particles. The techniques are best suited to characterization of depolarizing systems, where the scattered waves undergo a change of degree as well as polarization state. The degree of disorder of the system is then quantified by a scalar, the polarimetric entropy, defined from the eigenvalues of a scattering matrix that ranges from 0 for systems with zero scattering to 1 for perfect depolarizers. Further, we show that the unitary matrix parameterization can be used to extract important system information from the eigenvectors of this matrix.
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The mean state, variability, and extreme variability of the stratospheric polar vortices, with an emphasis on the Northern Hemisphere (NH) vortex, are examined using two-dimensional moment analysis and extreme value theory (EVT). ...
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The mean state, variability, and extreme variability of the stratospheric polar vortices, with an emphasis on the Northern Hemisphere (NH) vortex, are examined using two-dimensional moment analysis and extreme value theory (EVT). The use of moments as an analysis tool gives rise to information about the vortex area, centroid latitude, aspect ratio, and kurtosis. The application of EVT to these moment-derived quantities allows the extreme variability of the vortex to be assessed. The data used for this study are 40-yr ECMWFRe-Analysis (ERA-40) potential vorticity fields on interpolated isentropic surfaces that range from 450 to 1450 K. Analyses show that the most extreme vortex variability occurs most commonly in late January and early February, consistent with when most planetary wave driving from the troposphere is observed. Composites around sudden stratospheric warming (SSW) events reveal that the moment diagnostics evolve in statistically different ways between vortex splitting events and vortex displacement events, in contrast to the traditional diagnostics. Histograms of the vortex diagnostics on the 850-K (;10 hPa) surface over the 1958–2001 period are fitted with parametric distributions and show that SSW events constitute the majority of data in the tails of the distributions. The distribution of each diagnostic is computed on various surfaces throughout the depth of the stratosphere; it shows that in general the vortex becomes more circular with higher filamentation at the upper levels. The Northern and Southern Hemisphere (SH) vortices are also compared through the analysis of their respective vortex diagnostics, confirming that the SH vortex is less variable and lacks extreme events compared to the NH vortex. Finally, extreme value theory is used to statistically model the vortex diagnostics and make inferences about the underlying dynamics of the polar vortices.
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The possibility in principle of determining the circular polarization of a high-energy photon by measuring the created electron polarization in the process of triplet photoproduction γ + e ~- → e ~+ e ~- + e ~- is investigated. ...
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The possibility in principle of determining the circular polarization of a high-energy photon by measuring the created electron polarization in the process of triplet photoproduction γ + e ~- → e ~+ e ~- + e ~- is investigated. The respective event number, which depends on polarization states of the photon and the created electron, does not decrease as the photon energy increases, and this circumstance can ensure the high efficiency in such experiments. We study different double and single distributions of the created electron (or positron), which allow probing the photon circular polarization and measuring its magnitude (the Stokes parameter ξ_2) using the technique of Sudakov variables. Some experimental setups with different rules for event selection are studied and the corresponding numerical estimations are presented.
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Entangled state analysis is one of the basic techniques in quantum information processing. However, it is impossible to fully distinguish the three-photon Greenberger-Horne-Zeilinger (GHZ) states with only linear optical elements....
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Entangled state analysis is one of the basic techniques in quantum information processing. However, it is impossible to fully distinguish the three-photon Greenberger-Horne-Zeilinger (GHZ) states with only linear optical elements. Here, we propose a deterministic scheme to complete three-photon spatial-polarization hyperentangled GHZ-state analysis (HGSA) by using the giant optical Faraday rotation induced by an excess electron spin in a quantum dot inside a one-sided optical microcavity as a result of cavity quantum electrodynamics. It is divided into two steps. The first step is used to distinguish the eight three-photon GHZ states in the spatial-mode degree of freedom (DOF) without destroying the polarization states. The second step is used to distinguish the eight GHZ states in the polarization DOF. This scheme can be generalized to N-photon spatial-polarization HGSA and has useful applications in quantum communication protocols.
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