82,088 research outputs found
A cusp electron gun for millimeter wave gyrodevices
The experimental results of a thermionic cusp electron gun, to drive millimeter and submillimeter wave harmonic gyrodevices, are reported in this paper. Using a "smooth" magnetic field reversal formed by two coils this gun generated an annular-shaped, axis-encircling electron beam with 1.5 A current, and an adjustable velocity ratio alpha of up to 1.56 at a beam voltage of 40 kV. The beam cross-sectional shape and transported beam current were measured by a witness plate technique and Faraday cup, respectively. These measured results were found to be in excellent agreement with the simulated results using the three-dimensional code MAGIC
Enhancement of magnetic anisotropy barrier in long range interacting spin systems
Magnetic materials are usually characterized by anisotropy energy barriers
which dictate the time scale of the magnetization decay and consequently the
magnetic stability of the sample. Here we present a unified description, which
includes coherent rotation and nucleation, for the magnetization decay in
generic anisotropic spin systems. In particular, we show that, in presence of
long range exchange interaction, the anisotropy energy barrier grows as the
volume of the particle for on site anisotropy, while it grows even faster than
the volume for exchange anisotropy, with an anisotropy energy barrier
proportional to , where is the particle volume, is the range of interaction and is the embedding dimension. These
results shows a relevant enhancement of the anisotropy energy barrier w.r.t.
the short range case, where the anisotropy energy barrier grows as the particle
cross sectional area for large particle size or large particle aspect ratio.Comment: 7 pages, 6 figures. Theory of Magnetic decay in nanosystem. Non
equilibrium statistical mechanics of many body system
Pion Superfluidity and Meson Properties at Finite Isospin Density
We investigate pion superfluidity and its effect on meson properties and
equation of state at finite temperature and isospin and baryon densities in the
frame of standard flavor SU(2) NJL model. In mean field approximation to quarks
and random phase approximation to mesons, the critical isospin chemical
potential for pion superfluidity is exactly the pion mass in the vacuum, and
corresponding to the isospin symmetry spontaneous breaking, there is in the
pion superfluidity phase a Goldstone mode which is the linear combination of
the normal sigma and charged pion modes. We calculate numerically the gap
equations for the chiral and pion condensates, the phase diagrams, the meson
spectra, and the equation of state, and compare them with that obtained in
other effective models. The competitions between pion superfluidity and color
superconductivity at finite baryon density and between pion and kaon
superfluidity at finite strangeness density in flavor SU(3) NJL model are
briefly discussed.Comment: Updated version: (1)typos corrected; (2)an algebra error in Eq.(87)
corrected; (3)Fig.(17) renewed according to Eq.(87). We thank Prof.Masayuki
Matsuzaki for pointing out the error in Eq.(87
Existence Criterion of Genuine Tripartite Entanglement
In this paper, an intuitive mathematical formulation is provided to
generalize the residual entanglement for tripartite systems of qubits [Phys.
Rev. A 61, 052306 (2000)] to the tripartite systems in higher dimension. The
spirit lies in the tensor treatment of tripartite pure states [Phys. Rev. A 72,
022333 (2005)]. A distinct characteristic of the present generalization is that
the formulation for higher dimensional systems is invariant under permutation
of the subsystems, hence is employed as a criterion to test the existence of
genuine tripartite entanglement. Furthermore, the formulation for pure states
can be conveniently extended to the case of mixed states by utilizing the
Kronecker product approximate technique. As applications, we give the analytic
approximation of the criterion for weakly mixed tripartite quantum states and
consider the existence of genuine tripartite entanglement of some weakly mixed
states.Comment: 6 pages, 2 figure
Group-level Emotion Recognition using Transfer Learning from Face Identification
In this paper, we describe our algorithmic approach, which was used for
submissions in the fifth Emotion Recognition in the Wild (EmotiW 2017)
group-level emotion recognition sub-challenge. We extracted feature vectors of
detected faces using the Convolutional Neural Network trained for face
identification task, rather than traditional pre-training on emotion
recognition problems. In the final pipeline an ensemble of Random Forest
classifiers was learned to predict emotion score using available training set.
In case when the faces have not been detected, one member of our ensemble
extracts features from the whole image. During our experimental study, the
proposed approach showed the lowest error rate when compared to other explored
techniques. In particular, we achieved 75.4% accuracy on the validation data,
which is 20% higher than the handcrafted feature-based baseline. The source
code using Keras framework is publicly available.Comment: 5 pages, 3 figures, accepted for publication at ICMI17 (EmotiW Grand
Challenge
Repeating head-on collisions in an optical trap and the evaluation of spin-dependent interactions among neutral particles
A dynamic process of repeating collisions of a pair of trapped neutral
particles with weak spin-dependent interaction is designed and studied. Related
theoretical derivation and numerical calculation have been performed to study
the inherent coordinate-spin and momentum-spin correlation. Due to the
repeating collisions the effect of the weak interaction can be accumulated and
enlarged, and therefore can be eventually detected. Numerical results suggest
that the Cr-Cr interaction, which has not yet been completely clear, could be
thereby determined. The design can be in general used to determine various
interactions among neutral atoms and molecules, in particular for the
determination of very weak forces.Comment: 15 pages, 7 figure
K+ -> pi+ nu nu(bar) and FCNC from non-universal Z' bosons
Motivated by the E787 and E949 result for K+ -> pi+ nu nu(bar) we examine the
effects of a new non-universal right-handed Z' boson on flavor changing
processes. We place bounds on the tree-level FCNC from K-K(bar) and B-B(bar)
mixing as well as from the observed CP violation in kaon decay. We discuss the
implications for K -> pi nu nu(bar), B -> X nu nu(bar) and B -> tau+ tau-. We
find that existing bounds allow substantial enhancements in the K+ -> pi+ nu
nu(bar) rate, particularly through a new one-loop Z' penguin operator.Comment: Typos corrected, references added, version to appear in PR
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Highly Stable Luminous "snakes" from CsPbX3 Perovskite Nanocrystals Anchored on Amine-Coated Silica Nanowires
CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs) are known for their exceptional optoelectronic properties, yet the material's instability toward polar solvents, heat, or UV irradiation greatly limits its further applications. Herein, an efficient in situ growing strategy has been developed to give highly stable perovskite NC composites (abbreviated CsPbX3@CA-SiO2) by anchoring CsPbX3 NCs onto silica nanowires (NWs), which effectively depresses the optical degradation of their photoluminescence (PL) and enhances stability. The preparation of surface-functionalized serpentine silica NWs is realized by a sol-gel process involving hydrolysis of a mixture of tetraethyl orthosilicate (TEOS), 3-aminopropyltriethoxysilane (APTES), and trimethoxy(octadecyl)silane (TMODS) in a water/oil emulsion. The serpentine NWs are formed via an anisotropic growth with lengths up to 8 μm. The free amino groups are employed as surface ligands for growing perovskite NCs, yielding distributed monodisperse NCs (∼8 nm) around the NW matrix. The emission wavelength is tunable by simple variation of the halide compositions (CsPbX3, X = Cl, Br, or I), and the composites demonstrate a high photoluminescence quantum yield (PLQY 32-69%). Additionally, we have demonstrated the composites CsPbX3@CA-SiO2 can be self-woven to form a porous 3D hierarchical NWs membrane, giving rise to a superhydrophobic surface with hierarchical micro/nano structural features. The resulting composites exhibit high stability toward water, heat, and UV irradiation. This work elucidates an effective strategy to incorporate perovskite nanocrystals onto functional matrices as multifunctional stable light sources
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