70,192 research outputs found
A dual frequency microstrip antenna for Ka band
For fixed satellite communication systems at Ka band with downlink at 17.7 to 20.2 GHz and uplink at 27.5 to 30.0 GHz, the focused optics and the unfocused optics configurations with monolithic phased array feeds have often been used to provide multiple fixed and multiple scanning spot beam coverages. It appears that a dual frequency microstrip antenna capable of transmitting and receiving simultaneously is highly desirable as an array feed element. This paper describes some early efforts on the development and experimental testing of a dual frequency annular microstrip antenna. The antenna has potential application for use in conjunction with a monolithic microwave integrated circuit device as an active radiating element in a phased array of phased array feeds. The antenna is designed to resonate at TM sub 12 and TM sub 13 modes and tuned with a circumferential microstrip ring to vary the frequency ratio. Radiation characteristics at both the high and low frequencies are examined. Experimental results including radiating patterns and swept frequency measurements are presented
Magnetic Phase Transitions in One-dimensional Strongly Attractive Three-Component Ultracold Fermions
We investigate the nature of trions, pairing and quantum phase transitions in
one-dimensional strongly attractive three-component ultracold fermions in
external fields. Exact results for the groundstate energy, critical fields,
magnetization and phase diagrams are obtained analytically from the Bethe
ansatz solutions. Driven by Zeeman splitting, the system shows exotic phases of
trions, bound pairs, a normal Fermi liquid and four mixtures of these states.
Particularly, a smooth phase transition from a trionic phase into a pairing
phase occurs as the highest hyperfine level separates from the two lower energy
levels. In contrast, there is a smooth phase transition from the trionic phase
into a normal Fermi liquid as the lowest level separates from the two higher
levels.Comment: 4 pages, 3 figures, minor revisions to text, replacement figure, refs
added and update
Ka-band MMIC microstrip array for high rate communications
In a recent technology assessment of alternative communication systems for the space exploration initiative (SEI), Ka-band (18 to 40 GHz) communication technology was identified to meet the mission requirements of telecommunication, navigation, and information management. Compared to the lower frequency bands, Ka-band antennas offer higher gain and broader bandwidths; thus, they are more suitable for high data rate communications. Over the years, NASA has played an important role in monolithic microwave integrated circuit (MMIC) phased array technology development, and currently, has an ongoing contract with Texas Instrument (TI) to develop a modular Ka-band MMIC microstrip subarray (NAS3-25718). The TI contract emphasizes MMIC integration technology development and stipulates using existing MMIC devices to minimize the array development cost. The objective of this paper is to present array component technologies and integration techniques used to construct the subarray modules
Tensor Networks for Dimensionality Reduction and Large-Scale Optimizations. Part 2 Applications and Future Perspectives
Part 2 of this monograph builds on the introduction to tensor networks and
their operations presented in Part 1. It focuses on tensor network models for
super-compressed higher-order representation of data/parameters and related
cost functions, while providing an outline of their applications in machine
learning and data analytics. A particular emphasis is on the tensor train (TT)
and Hierarchical Tucker (HT) decompositions, and their physically meaningful
interpretations which reflect the scalability of the tensor network approach.
Through a graphical approach, we also elucidate how, by virtue of the
underlying low-rank tensor approximations and sophisticated contractions of
core tensors, tensor networks have the ability to perform distributed
computations on otherwise prohibitively large volumes of data/parameters,
thereby alleviating or even eliminating the curse of dimensionality. The
usefulness of this concept is illustrated over a number of applied areas,
including generalized regression and classification (support tensor machines,
canonical correlation analysis, higher order partial least squares),
generalized eigenvalue decomposition, Riemannian optimization, and in the
optimization of deep neural networks. Part 1 and Part 2 of this work can be
used either as stand-alone separate texts, or indeed as a conjoint
comprehensive review of the exciting field of low-rank tensor networks and
tensor decompositions.Comment: 232 page
Tensor Networks for Dimensionality Reduction and Large-Scale Optimizations. Part 2 Applications and Future Perspectives
Part 2 of this monograph builds on the introduction to tensor networks and
their operations presented in Part 1. It focuses on tensor network models for
super-compressed higher-order representation of data/parameters and related
cost functions, while providing an outline of their applications in machine
learning and data analytics. A particular emphasis is on the tensor train (TT)
and Hierarchical Tucker (HT) decompositions, and their physically meaningful
interpretations which reflect the scalability of the tensor network approach.
Through a graphical approach, we also elucidate how, by virtue of the
underlying low-rank tensor approximations and sophisticated contractions of
core tensors, tensor networks have the ability to perform distributed
computations on otherwise prohibitively large volumes of data/parameters,
thereby alleviating or even eliminating the curse of dimensionality. The
usefulness of this concept is illustrated over a number of applied areas,
including generalized regression and classification (support tensor machines,
canonical correlation analysis, higher order partial least squares),
generalized eigenvalue decomposition, Riemannian optimization, and in the
optimization of deep neural networks. Part 1 and Part 2 of this work can be
used either as stand-alone separate texts, or indeed as a conjoint
comprehensive review of the exciting field of low-rank tensor networks and
tensor decompositions.Comment: 232 page
Exchange effects on electron scattering through a quantum dot embedded in a two-dimensional semiconductor structure
We have developed a theoretical method to study scattering processes of an
incident electron through an N-electron quantum dot (QD) embedded in a
two-dimensional (2D) semiconductor. The generalized Lippmann-Schwinger
equations including the electron-electron exchange interaction in this system
are solved for the continuum electron by using the method of continued
fractions (MCF) combined with 2D partial-wave expansion technique. The method
is applied to a one-electron QD case. Cross-sections are obtained for both the
singlet and triplet couplings between the incident electron and the QD electron
during the scattering. The total elastic cross-sections as well as the
spin-flip scattering cross-sections resulting from the exchange potential are
presented. Furthermore, inelastic scattering processes are also studied using a
multichannel formalism of the MCF.Comment: 11 pages, 4 figure
When resources collide: Towards a theory of coincidence in information spaces
This paper is an attempt to lay out foundations for a general theory of coincidence in information spaces such as the World Wide Web, expanding on existing work on bursty structures in document streams and information cascades. We elaborate on the hypothesis that every resource that is published in an information space, enters a temporary interaction with another resource once a unique explicit or implicit reference between the two is found. This thought is motivated by Erwin Shroedingers notion of entanglement between quantum systems. We present a generic information cascade model that exploits only the temporal order of information sharing activities, combined with inherent properties of the shared information resources. The approach was applied to data from the world's largest online citizen science platform Zooniverse and we report about findings of this case study
Wilson ratio of Fermi gases in one dimension
We calculate the Wilson ratio of the one-dimensional Fermi gas with spin
imbalance. The Wilson ratio of attractively interacting fermions is solely
determined by the density stiffness and sound velocity of pairs and of excess
fermions for the two-component Tomonaga-Luttinger liquid (TLL) phase. The ratio
exhibits anomalous enhancement at the two critical points due to the sudden
change in the density of states. Despite a breakdown of the quasiparticle
description in one dimension, two important features of the Fermi liquid are
retained, namely the specific heat is linearly proportional to temperature
whereas the susceptibility is independent of temperature. In contrast to the
phenomenological TLL parameter, the Wilson ratio provides a powerful parameter
for testing universal quantum liquids of interacting fermions in one, two and
three dimensions.Comment: 5+2 pages, 4+1 figures, Eq. (4) is proved, figures were refine
High-Q bismuth silicate nonlinear glass microsphere resonators
The fabrication and characterization of a bismuth-silicate glass microsphere resonator has been demonstrated. At wavelengths near 1550 nm, high-modes can be efficiently excited in a 179 µm diameter bismuth-silicate glass microsphere via evanescent coupling using a tapered silica fiber with a waist diameter of circa 2 µm. Resonances with Q-factors as high as were observed. The dependence of the spectral response on variations in the input power level was studied in detail to gain an insight into power-dependent thermal resonance shifts. Because of their high nonlinearity and high- factors, bismuth-silicate glass microspheres offer the potential for robustly assembled fully integrated all-optical switching devices
Artificial molecular quantum rings: Spin density functional theory calculations
The ground states of artificial molecules made of two vertically coupled
quantum rings are studied within the spin density functional theory for systems
containing up to 13 electrons. Quantum tunneling effects on the electronic
structure of the coupled rings are analyzed. For small ring radius, our results
recover those of coupled quantum dots. For intermediate and large ring radius,
new phases are found showing the formation of new diatomic artificial ring
molecules. Our results also show that the tunneling induced phase transitions
in the coupled rings occur at much smaller tunneling energy as compared to
those for coupled quantum dot systems.Comment: 10 pages, 6 figure
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