Miracle-dz/UniFAR-FTUs huggingface dataset:
Theory of harmonic generation using antiferromagnets in the far-infrared

This paper considers the usefulness of antiferromagnetic materials as second-harmonic generators. Using molecular field theory and a 2-sublattice model, the second-order susceptibility of an antiferromagnetic structure is derived. The resulting nonlinear electromagnetic wave equations are then solved using a particular set of boundary conditions for the case in which the input radiation is at the material's antiferromagnetic resonance frequency. The strong absorption of the fundamental radiation at this frequency is taken into account. A method of matching the impedance of the material to that of the environment is described, wherein one face of the material is impedance matched at the frequency of the entering primary radiation, and the opposite face is impedance matched at the harmonic frequency of the emerging radiation. The theoretical results are applied to the particular case of FeF 2 . Using published results for the anisotropy, resonance frequency, and bandwidth of FeF 2 , its efficiency as a second-harmonic generator is found. This result is compared to the efficiency of KDP, a non-linear dielectric used as an harmonic generator in the optical band. It is concluded that, in the far-infrared waveband, FeF 2 , used at its resonant frequency, should be 106to 106times as efficient as KDP. In conclusion, a summary of the relative advantages and disadvantages of magnetic and dielectric materials as harmonic generators in the far-infrared is given.
Bias estimation using targets of opportunity

Fusion of data from multiple sensors can be hindered by systematic errors known as biases. Specifically, the presence of biases can lead to data misassociation and redundant tracks. Fortunately, if an estimate of the unknown biases can be obtained, the measurements and transformations for each sensor can be debiased prior to fusion. In this paper, we present an algorithm that uses targets of opportunity in the sensor field-of-view for online estimation of time-variant biases. The algorithm uses the singular value decomposition (SVD) to automatically handle the issue of parameter observability during tracking, allowing for shorter estimation windows and more accurate bias estimation. Our approach extends the novel methods proposed in the companion paper by Herman and Poore that used the SVD within a nonlinear least-squares estimator to handle the issue of parameter observability during offine estimation of time-invariant biases using truth data.
MR images denoising using DCT-based unbiased nonlocal means filter

The non-local means (NLM) filter has been proven to be an efficient feature-preserved denoising method and can be applied to remove noise in the magnetic resonance (MR) images. To suppress noise more efficiently, we present a novel NLM filter by using a low-pass filtered and low dimensional version of neighborhood for calculating the similarity weights. The discrete cosine transform (DCT) is used as a smoothing kernel, allowing both improvements in similarity estimation and computational speed-up. Experimental results show that the proposed filter achieves better denoising performance in MR Images compared to others filters, such as recently proposed NLM filter and unbiased NLM (UNLM) filter.
Adaptive color contrast enhancement for digital images

Noncanonical illumination that is too dim or with color cast induces degenerated images. To cope with this, we propose a method for color-contrast enhancement. First, intensity, chrominance, and contrast characteristics are explored and integrated in the Naka-Rushton equation to remove underexposure and color cast simultaneously. Motivated by the comparison mechanism in Retinex, the ratio of each pixel to its surroundings is utilized to improve image contrast. Finally, inspired by the two color-opponent dimensions in CIELAB space, a color-enhancement strategy is devised based on the transformation from CIEXYZ to CIELAB color space. For images that suffer from underexposure, color cast, or both problems, our algorithm produces promising results without halo artifacts and corruption of uniform areas.
Drag measurements for axisymmetric motion of a torus at low Reynolds number

Measurements are presented for the drag on a torus moving along its axis of rotational symmetry at low Reynolds number. If D is the outside diameter of the torus, and d is the thickness in the axial direction, then the measurements cover the range s0 = 1 (the closed torus) to s0 = 135, where s0≡(D/d)−1. The effect of a coaxial cylindrical boundary (diameter H) is taken into account by an empirical correlation. The values of drag obtained by extrapolating to a fluid of infinite extent are in good agreement with the exact solution obtained by Majumdar and O’Neill. When πd(s0)1/2≪H, the empirical boundary correlation is consistent with the result of Brenner for a particle of arbitrary shape. Measurements with outer boundaries of square and circular cross section indicate that the relative effect of the two boundary shapes on the drag is the same for the torus as that found by Happel and Bart for a sphere. Empirical results are presented for the case in which the torus is strongly influenced by a coaxial cyli.
Density response of neutral atmospheric layers to gravity wave perturbations

Expressions for the density response of neutral atmospheric layers to propagating waves are derived. The expressions include nonlinear effects and are used to compute the response of the mesospheric sodium layer to low-frequency internal gravity waves. The results are compared with lidar observations of the sodium layer and used to deduce gravity wave parameters. It is shown that because of the large sodium density gradients and the relatively high amplitudes of gravity waves at mesospheric heights the nonlinear components of the layer density response must be considered in interpreting sodium lidar data.
On the use of time series representations of population models

Many population models which are far from stationarity can nevertheless be written in autoregressive format, perhaps with random coefficient. It is the thesis of this paper that procedures developed for stationary time series models are a useful guide to inferential results for population processes and may indeed be directly applicable. The illustrations concentrate on estimation of the matrix of mean vital rates in an age-structured population.
Effective conductivity of periodic composites composed of two very unequal conductors

The effective conductivity tensor is calculated for a periodic composite composed of alternating rectangular blocks of two very unequal conductors. The two‐dimensional case of a checkerboard pattern of rectangles is also treated, and Gautesen’s result for it is obtained. The checkerboard of parallelograms is treated, too. The method can be applied to alternating parallelepipeds and to certain other configurations.
Near-field microscopy of light propagation in photonic crystal waveguides

A collection scanning near-field optical microscope (SNOM) is used to image the propagation of light at telecommunication wavelengths along straight and bent regions of silicon-on-insulator photonic crystal waveguides (PCWs) formed by removing a single row of holes in the triangular 410-nm-period lattice along GM direction of the irreducible Brillouin zone. High quality SNOM images of PCWs and access ridge waveguides excited in the wavelength range of 1520-1570 nm are obtained, demonstrating multimode behavior of ridge waveguides and good PCW (fundamental) mode confinement along with its low propagation loss. We analyze light intensity variations along the ridge and PCW waveguides measured with the SNOM at different distances from the sample surface. Considering the interference between a quasi-homogeneous background field and propagating mode fields and taking into account Bloch harmonics of the PCW modes, we account for spatial frequency spectra of the intensity variations and determine the dispersion of the PCW mode propagation constant. The possibilities and limitations of SNOM imaging for the characterization of PCWs as well as conventional waveguides are discussed.
Difference of multiconvex relaxation of parameterized LMIs: control applications

Relaxation of an optimization problem under parametrized LMIs (PLMIs) constraint is discussed in this paper. The relaxation methods are based on convexfication using difference of convex (d.c.) and multiconvexfication techniques, thus the relaxed problems become numerically tractable. The d.c. relaxation method is generalized and is imported into the multiconvex relaxation method, then the difference of multiconvex relaxation is naturally defined. These two relaxation methods are applied to stability and L/sub 2/ gain analysis of linear parameter varying (LPV) systems based on affine parameter-dependent Lyapunov function and are discussed from an amount of computation viewpoint. Numerical examples are illustrated for the application to show the effectiveness of these methods.
Absorbing Boundary Conditions for the Two-Dimensional Schrödinger Equation with an Exterior Potential. Part I: Construction and a priori Estimates

The aim of this paper is to construct some classes of absorbing boundary conditions for the two-dimensional Schrodinger equation with a time and space varying exterior potential and for general convex smooth boundaries. The construction is based on asymptotics of the inhomogeneous pseudodifferential operators defining the related Dirichlet-to-Neumann operator. Furthermore, \textit{a priori} estimates are developed for the truncated problems with various increasing order boundary conditions. The effective numerical approximation will be treated in a second paper.
The Structure of Positive Elements for C*-Algebras with Real Rank Zero

In this paper we give a representation theorem for the Cuntz monoid S(A) of a σ-unital C*-algebra A with real rank zero and stable rank one, which allows to prove several Riesz decomposition properties on the monoid. As a consequence, it is proved that the comparability conditions (FCQ), stable (FCQ) and (FCQ+) are equivalent for simple C*-algebras with real rank zero. It is also shown that the Grothendieck group of S(A) is a Riesz group, and lattice-ordered under some additional assumptions on A.
Design to learn: customizing services when the future matters

Internet-based customization tools can be used to design service encounters that maximize customers' utility in the present or explore their tastes to provide more value in the future, where these two goals conflict with each other. Maximizing expected customer satisfaction in the present leads to slow rates of learning that may limit the ability to provide quality in the future. An emphasis on learning can lead to unsatisfied customers that will not only forego purchasing in the current period, but, more seriously, never return if they lose trust in the service provider's ability to meet their needs. This paper describes service design policies that balance the objectives of learning and selling by characterizing customer lifetime value as a function of knowledge. The analysis of the customization problem as a dynamic program yields three results. The first result is the characterization of customization policies that quantify the value of knowledge so as to adequately balance the expected revenue of present and future interactions. The second result is an analysis of the impact of operational decisions on loyalty, learning, and profitability over time. Finally, the quantification of the value of knowing the customer provides a connection between customer acquisition and retention policies, thus enhancing the current understanding of the mechanisms connecting service customization, value creation, and customer lifetime value.
Accommodation of unknown actuator faults using output feedback‐based adaptive robust control

In this paper, we solve the problem of output tracking for linear uncertain systems in the presence of unknown actuator failures using discontinuous projection‐based output feedback adaptive robust control (ARC). The faulty actuators are characterized as unknown inputs stuck at unknown values experiencing bounded disturbance and actuators losing effectiveness at unknown instants of time. Many existing techniques to solve this problem use model reference adaptive control (MRAC), which may not be well suited for handling various disturbances and modeling errors inherent to any realistic system model. Robust control‐based fault‐tolerant schemes have guaranteed transient performance and are capable of dealing with modeling errors to certain degrees. But, the steady‐state tracking accuracy of robust controllers, e.g. sliding mode controller, is limited. In comparison, the backstepping‐based output feedback adaptive robust fault‐tolerant control (ARFTC) strategy presented here can effectively deal with such uncertainties and overcome the drawbacks of individual adaptive and robust controls. Comparative simulation studies are performed on a linearized Boeing 747 model, which shows the effectiveness of the proposed scheme. Copyright © 2011 John Wiley & Sons, Ltd.
An Electromagnetic Target Classification Method for the Target Sets with Alien Target: Application to Small-scale Aircraft Targets

The electromagnetic target classiflcation is a challenging problem since the scat- tered fleld from a target is highly dependent on operating frequency, polarization and aspect angle. In order to minimize adverse efiects of these dependencies an intelligent classifler con- taining some distinguishable target features is needed. In addition, in order to be suitable for real target applications, the properties of operating with moderate frequency bandwidth and discriminating an alien target from a target set containing friend targets are important. In this study, an electromagnetic target classiflcation method for isolated targets using noisy data in the classifler design to obtain high accuracy performance in a wider SNR range and having the ability of discrimination of an alien target without any priori information is introduced. The proposed method is mainly based on a late-time resonance region target classiflcation technique, which was reported recently to use the multiple signal classiflcation (MUSIC) algorithm and natural-resonance mechanism modeled by singularity expansion method (SEM) for target fea- ture extraction, and modifled for target sets containing alien target(s). The proposed classifler design method is demonstrated and tested for a target set of flve friend and one alien small-scale aircraft targets. According to the test result, the proposed method gives high accuracy rates for this target set.
Energy spectra and coherent structures in forced two-dimensional and beta-plane turbulence

Results from a wide range of direct numerical simulations of forced-dissipative, differentially rotating two-dimensional turbulence are presented, in order to delineate the broad dependence of flow type on forcing parameters. For most parameter values the energy spectra of simulations forced at low wavenumbers are markedly steeper than the classical k−3 enstrophy inertial-range prediction, and although k−3 spectra can be produced under certain circumstances, the regime is not robust, and the Kolmogorov constant is not universal unless a slight generalization is made in the phenomenology. Long-lived, coherent vortices form in many cases, accompanied by steep energy spectra and a higher than Gaussian vorticity kurtosis. With the addition of differential rotation (the β-effect), a small number of fairly distinct flow regimes are observed. Coherent vortices weaken and finally disappear as the strength of the β-effect increases, concurrent with increased anisotropy and decreased kurtosis. Even in the absence of coherent vortices and with a Gaussian value of the kurtosis, the spectra remain relatively steep, although not usually as steep as for the non-rotating cases. If anisotropy is introduced at low wavenumbers, the anisotropy is transferred to all wavenumbers in the inertial range, where the dynamics are isotropic. For those simulations that are forced at relatively high wavenumbers, a well resolved and very robust k−5/3 energy inertial range is observed, and the Kolmogorov constant appears universal. The low-wavenumber extent of the reverse energy cascade is essentially limited by the β-effect, which produces an effective barrier in wavenumber space at which energy accumulates, and by frictional effects which must be introduced to achieve equilibrium. Anisotropy introduced at large scales remains largely confined to the low wavenumbers, rather than being cascaded to small scales. When there is forcing at both large and small scales (which is of relevance to the Earth's atmosphere), energy and enstrophy inertial ranges coexist, with an upscale energy transfer and downscale enstrophy transfer in the same wavenumber interval, without the need for any dissipation mechanism between forcing scales.
Robust stability and stabilization of discrete-time non-linear systems: The LMI approach

The purpose of this paper is to convert the problem of robust stability of a discrete-time system under non-linear perturbation to a constrained convex optimization problem involving linear matrix inequalities (LMI). The nominal system is linear and time-invariant, while the perturbation is an uncertain non-linear time-varying function which satisfies a quadratic constraint. We show how the proposed LMI framework can be used to select a quadratic Lyapunov function which allows for the least restrictive non-linear constraints. When the nominal system is unstable the framework can be used to design a linear state feedback which stabilizes the system with the same maximal results regarding the class of non-linear perturbations. Of particular interest in this context is our ability to use the LMI formulation for stabilization of interconnected systems composed of linear subsystems with uncertain non-linear and time-varying coupling. By assuming stabilizability of the subsystems we can produce local control laws under decentralized information structure constraints dictated by the subsystems. Again, the stabilizing feedback laws produce a closed-loop system that is maximally robust with respect to the size of the uncertain interconnection terms.
Further evidence concerning the local density of red dwarfs

Recent evidence has suggested the existence of a large number of red dwarfs, highly concentrated to the galactic plane, in the solar neighborhood. These results are reexamined using photoelectrically determined B--V and (R--I)/subw/ colors for a sample of stars near the North Galactic Pole. Preliminary analysis of the data indicates that the density of the reddest stars is not nearly as great as was previously reported. (AIP)
NUMERICAL STUDIES OF AN AXIAL FLOW BLOOD PUMP WITH DIFFERENT DIFFUSER DESIGNS

Most axial flow blood pumps basically consist of a straightener, an impeller, and a diffuser. The diffuser plays a very important role in the performance of the pump to provide an adequate pressure head and to increase the hydraulic efficiency. During the development of an axial flow blood pump, irregular flow field near the diffuser hub is not desirable as it may induce thrombosis. In order to avoid this phenomenon, two approaches were adopted. In the first approach, the number of the diffuser blades was increased from three (B3, baseline model) to five (B5 model). It was observed that the flow field was improved, but the irregular flow patterns were not completely eliminated. In the second approach, we detached the blades from the diffuser hub (B3C2 model), which was integrated and rotated with the impeller hub. It was found that the rotary diffuser hub significantly improved the flow field, especially near the diffuser hub. Besides the detailed flow fields, the hydraulic and hematologic performances at various flow conditions were also estimated using computational fluid dynamics (CFD). Although each design has its own advantages and disadvantages, the B5 model was superior based on a comparative overview.
Distributional Kalman filters for Bayesian forecasting and closed form recurrences

Over the last 50 years there has been an enormous explosion in developing full distributional analogues of the Kalman filter. In this paper we explore how some of the second-order processes discovered by Kalman have their analogues in Bayesian state space models. Many of the analogues in the lierature need to be calculated using numerical methods like Markov chain Monte Carlo so they retain, or even enhance, the descriptive power of the Kalman filter, but at the cost of reduced transparency. However, if the analogues are drawn properly, elegant recurrence relationships—like those of the Kalman filter—can still be developed that apply, at least, for one‐step‐ahead forecast distributions. In this paper we explore the variety of ways such models have been built, in particular with respect to graphical time series models. Copyright (C) 2010 John Wiley & Sons, Ltd.
Controlled dewetting as fabrication and patterning strategy for metal nanostructures

Metal thin films and metal nanostructures find a key role in the actual nanotechnology revolution. They can be engineered for nanoelectronics, plasmonics, and sensing applications. However, the crucial step toward reliable technological applications of metal‐based nanodevices is the development of simple, low cost, versatile, and high‐throughout nanofabrication methodologies. In general, top‐down nanofabrication approaches allow a minimum size of the single nanostructure higher than 10 nm, a high control on spatial regularity and size of the nanostructures, but involve high cost and long processing time. In contrast, bottom‐up approaches allow a minimum size of the single nanostructure lower than 10 nm, a low control on spatial regularity and size of the nanostructures, but involve low cost and short processing time. In this paper, the controlled dewetting process of thin metal films on surfaces is reviewed as a patterning and nanofabrication method for metal‐based nanocomposites, crossing the strenghts of both approaches.
Partitioned Linear Multistep Method for Long Term Integration of the N‐Body Problem

In this paper an exponential fitted partitioned linear multistep method is developed for the long term integration of the N-body problem. The new method integrates exactly any linear combination of the functions 1, x, x2, x3 ,…, x2k–1, exp(±wx) for the coordinates and any linear combination of the functions 1, x, x2, x3,…, x2k–3, exp(±wx) for the velocities. Numerical results are produced and compared with a set of well known symplectic and single step methods. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Development of a PET detector system compatible with MRI/NMR systems

We report the development of a prototype positron emission tomography (PET) scanner compatible with clinical magnetic resonance imaging (MRI) scanners and nuclear magnetic resonance (NMR) spectrometers. This single slice PET system consists of 72 2/spl times/2/spl times/5 mm lutetium oxyorthosilicate (LSO) crystals coupled by 2 mm diameter, 4 meter long double clad optical fibers to three multi-channel photomultiplier tubes (MC-PMTs) shielded inside an aluminum closure. The ring diameter is 54 mm and the slice thickness is /spl sim/1 mm FWHM. Measurements with a point source demonstrate that this PET system has a reconstructed resolution of 2.1 mm, a coincidence time resolution of 26 ns and a typical energy resolution of 45%. Simultaneously acquired PET and MR phantom images, show no significant artifacts or distortions. We also obtained simultaneous NMR spectra and PET images from an isolated, perfused rat heart, demonstrating the power of obtaining temporally correlated PET and NMR information in biological systems. Again, no artifacts in the PET or NMR data were apparent, despite the high field strength of 9.4 T. The challenge for the future is to scale up the design to develop a high resolution, high sensitivity device that can be used in simultaneous PET and MR studies of in vivo systems.