Miracle-dz/UniFAR-FTUs huggingface dataset:
Quantitative recurrence properties for group actions

We generalized Boshernitzan's quantitative recurrence theorem to general group actions. Let (X, d) be a metric space with a finite measure and G be a countable group acting on (X, d). Assume that the action of G on (X, d) is measure preserving and let Fn ⊂ G be a sequence with |Fn| ↑ ∞ and put . Then we have for almost every x, where α is the Hausdorff dimension of (X, d).
Collision Avoidance of a Multiple Degree of Redundancy Manipulator Operating Through a Window

The problem of collision-free operation of a multiple-degree-of-redundancy manipulator operating through a window is addressed. An efficient gradient projection optimization scheme is presented for the kinematic control of manipulators with multiple degrees of redundancy. This scheme was developed for dextrous robotic and telerobotic applications in space station construction as well as in congested shop floor environment. A performance criterion is defined to maximize the shortest distances between the manipulator links and the edges of the window. Effectiveness of this scheme and the validity of the performance criterion are verified through simulations of the seven-degree-of-freedom NASA Laboratory Telerobotic Manipulator.
Multiple scattering of compressional and shear waves by fiber‐reinforced composite materials

A multiple scattering formalism using a T matrix to characterize the response of a single fiber to an incident wave is presented to describe P‐ and SV‐wave propagation in a fiber‐reinforced composite. A convenient numerical procedure is then developed to compute the effective elastic moduli, attenuation, and phase velocity as a function of frequency and fiber concentration.
Distributed Estimation over Analog Fading Channels Using Constant-Gain Estimators

Abstract This paper considers the distributed estimation of an unstable target via constant-gain estimators under local communications and channel fading. The communication graph is assumed to be fixed and undirected, and the channel fading is assumed to be identical. Necessary and sufficient conditions on communication network over which the state of the unstable target can be estimated in the mean square sense are given for both continuous-time and discrete-time cases, which reveal the fundamental limitation on distributed estimation induced by local communications, channel fading, and target dynamics. In addition, our results for the case without channel fading and the case with separate communications are consistent with the results in the literature.
Constant-beamwidth antenna development

Broad-band microwave receiving and tracking systems generally require medium to high-gain antennas that have a minimum beamwidth requirement dictated by probability of intercept and acquisition time considerations. This paper discusses a technique whereby the secondary pattern beamwidth variation is decreased or eliminated over portions of the frequency band of these antennas. The antennas consist of a parabolic reflector illuminated by a ridge-loaded horn. A brief analysis, based on empirical antenna equations, is presented along with a description of a pencil-beam antenna and a very broad-band conical-scan tracking antenna that were made possible through the use of this technique.
Agrégation à poids exponentiels et estimation penalisée : Inégalités oracles

Un probleme classique en traitement du signal et des images vise a estimer un signal/image a partir de ses mesures lineaires sous-determinees et bruitees. Le probleme etant mal-pose, l'approche usuelle consiste a imposer des a priori sur les objets recherches. Dans cet article, nous presentons une analyse unifiee des garanties theoriques de performance de deux familles d'estimateurs: les estimateurs par agregation a poids exponentiels et les estimateurs penalises pour une classe d'a priori favorisant une certaine notion de simplicite/faible complexite. Plus precisement, nous montrons que les deux classes d'estimateurs satisfont des inegalites oracles fines en probabilite lorsque le bruit est gaussien ou sous-gaussien. Ces resultats sont ensuite appliques a plusieurs penalites classiques notamment les norme 1 (LASSO), 1–2 (LASSO par groupes et sa version analyse), ∞ (anti-parcimonie), et la norme nucleaire. Abstract – A classical problem in signal and image processing aims at recovering a signal/image from a set of underdetermined and noisy linear measurements. The problem is generally ill-posed and the usual approach consists in imposing prior knowledge on the set of sought-after objects. In this paper, we present an unified analysis of the theoretical performance guarantees of two classes of estimators: exponential weighted aggregation and penalized estimators for a general class of priors which promote objects complying with some notion of simplicity/low complexity. More precisely, we show that these two estimators satisfy sharp oracle inequalities in probability when the noise is Gaussian or subgaussian. These results are then applied to several popular penalties including the 1 (LASSO), the 1–2 (group LASSO and its analysis version), ∞ (anti-sparsity), and the nuclear norms.
Optimal mixing in recirculation zones

Coarse-scale mixing in a recirculation zone is described with a simple vortex model. Time-dependent forcing is employed to change the vortex motion and mixing properties. An optimal mixing problem is defined in which the flux across the recirculation region shall be maximized under the side-constraints of bounded vortex motion and bounded actuation. Concepts of control theory and chaotic advection are used to achieve this goal. In particular, controllability is proven with a transformation into flat coordinates. Thus, a feedforward law for the optimal trajectory and a feedback law for its stabilization are derived. Observability of the vortex motion is indicated by a dynamic observer. Mixing in the optimized flow is studied using Poincare maps. The low-frequency modulations to vortex motion are shown to substantially increase mixing in the average. Generalizations of the mathematical framework for mixing optimization are suggested for a larger class of models and flows.
Femtosecond ultraviolet pulse generation in β‐BaB2O4

Intracavity doubling in β‐BaB2 O4 (BBO) of femtosecond pulses into the ultraviolet with high efficiency is reported. Pulse widths down to 43 fs at a 108 Hz repetition rate and outputs as high as 20 mW per arm of the femtosecond laser on a continuous‐wave basis can be achieved. The ultraviolet pulse widths were determined through detailed cross‐correlation measurements based on sum‐frequency mixing to 210 nm in ultrathin BBO crystals.
On the local topology evolution of a high‐symmetry flow

The local topology evolution of a high‐symmetry, high resolution (effective maximum resolution of 10243 grid points, maximum wave number of 341) incompressible flow simulation having a Reynolds number (=1/ν) of 1000 is investigated. The Q–R invariants of the velocity gradient tensor Aij, the enstrophy, ΩijΩij and the mean‐square strain rate SijSij are computed at an interval when the local maximum vorticity increases drastically. All the analysis of the computations are done on the z=0 plane, where the maximum vorticity and strain are located during the evolution. In the Q–R plane, most of the collocation points evolve towards the lower right corner, a region where strain dominates over vorticity. The pressure Hessian tensor components are computed in the 0 planes. Points with very large strain and no vorticity, which are located along the boundaries separating oppositely signed vortices, are found to have a diagonal pressure Hessian tensor. It is discussed how such a Hessian tensor form can result in a s.
Diffraction enhanced imaging computed tomography (DEI-CT) at the BMIT facility at the Canadian Light Source

A synchrotron source such as available at the Canadian Light Source provides the ability to use a large number of imaging techniques. Computed tomography (CT) can be a extension of many X-ray imaging techniques. The ability to turn two dimensional projections into three dimensional structures is a powerful method of data analysis. CT also allows the user to slice the data in any desired direction without the need to cut up the sample. Diffraction enhanced imaging (analyzer based imaging) uses a crystal to measure refraction of the sample which may give significantly larger contrast than absorption alone. Measurements typically involve make images at multiple positions of the analyzer crystal and then using the images to extract the absorption, refraction components. Multiple-image radiology increases the number of images and adds the ultra-small-angle scatter. This paper will discuss the practical and technical aspects of extending diffraction enhanced imaging (DEI) to three dimensions (DEI-CT). A combination of hardware and software is used to provide a stable x-ray beam for the duration of potentially long measurement times and thus enable measurement of good quality diffraction enhanced imaging computed tomography (DEI-CT) data.
Exact quasi-soliton solutions and soliton interaction for the inhomogeneous coupled nonlinear Schrödinger equations

We consider the inhomogeneous (1+1)-dimensional coupled nonlinear Schrödinger equations from the integrability point of view. This system has potential applications in inhomogeneous birefringent fiber media or in optical communication links with variable parameters. The exact analytical multisoliton solutions are obtained by employing the simple, straightforward Darboux transformation based on the obtained 3 × 3 Lax pair. Some main propagation and interaction properties of the one- and two-soliton solutions are discussed simultaneously. Also, the interaction between two neighboring combined solitary waves is numerically discussed. Excellent agreement with analytical results are found in the case of no collision. Moreover, the stability of these solutions are discussed in detail numerically with respect to a finite perturbation.
Random Heterogeneous Materials: Microstructure and Macroscopic Properties

Motivation and overview * PART I Microstructural characterization * Microstructural descriptors * Statistical mechanics of particle systems * Unified approach * Monodisperse spheres * Polydisperse spheres * Anisotropic media * Cell and random-field models * Percolation and clustering * Some continuum percolation results * Local volume fraction fluctuation * computer simulation and image analysis * PART II Microstructure property connections * Local and homogenized equations * Variational Principles * Phase-interchange relations * Exact results * Single-inclusion solutions * Effective medium approximations * Cluster expansions * Exact contrast expansions * Rigorous bounds * Evaluation of bounds * Cross-property relations * Appendix A Equilibrium Hard disk program * Appendix B Interrelations among 2-3D moduli* References * Index
Direct Evidence that Dislocations are Non-Radiative Recombination Centers in GaN

Plan-view transmission electron microscopy (TEM) and cathodoluminescence (CL) images were taken for the same sample at exactly the same location in n-type GaN grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD). There was a clear one to one correspondence between the dark spots observed in CL images and the dislocations in TEM foils, indicating that the dislocations are non-radiative recombination centers. The hole diffusion length in n-type GaN was estimated to be neighboring 50 nm by comparing the diameters of the dark spots in thick samples used for CL and samples that were thinned for TEM observation. The efficiency of light emission is high as long as the minority carrier diffusion length is shorter than the dislocation spacing.
A conceptual model of hysteresis

A conceptual model of the capillary hysteresis phenomenon is suggested. The advantage of this model is that all scanning curves are derived with the aid of simple functions from the main drying curve and the main wetting curves solely. Like the generalized approach of Enderby (1955) the present model takes into account a reversible part of the process. A simple method of predicting the first drying curve and the scanning curves branched out of the first drying curve is also proposed. Results based on this model are compared with laboratory measurements and the general Neel-Everett independent domain model. The comparison shows that the present model is often in more satisfactory agreement with measurements for cases in which the prediction based on the Neel-Everett model is poor. The suggested method can be used for solving problems in which hysteresis plays a significant role, the difficulties associated with laboratory determination of the ψ-θ relationships in the whole domain thus being avoided.
High precision trace humidity measurements with a fibre-coupled diode laser absorption spectrometer at atmospheric pressure

Laser absorption spectroscopy offers the potential for fast and precise trace moisture detection in gases at atmospheric pressure with a small cross sensitivity towards other molecules. We report on the development and calibration of a fibre-coupled tunable diode laser absorption spectrometer operating in the 1 - 100 ppm humidity range. The spectrometer was tested at three European humidity standards laboratories. The performance of the spectrometer was characterized by monitoring constant water vapour concentrations over several hours, yielding a good long-term stability, reproducibility and accuracy. The standard deviations of the measured water vapour concentrations for values above 5 ppm were below ±2%. Comparisons of the instrument with chilled mirror hygrometers demonstrated its fast response time. The dependences of the signal upon the flow rate and temperature are discussed.
The transmission of credit risk in the Brazilian shoe supply chain

The world financial system is now undergoing a global economic crisis of staggering proportions. This evolving global and financial crisis and credit crunch afflicted developed and developing economies. In the vast majority of countries, credit concession has been deeply affected, and new and innovative ways to grant credit needed to be developed in order to reduce risk. The use of accurate information in the credit concession analysis process, where credit scores play a crucial role, became imperative. In this context, the present study brings new insights to this discussion because it aims at verifying potential transmission of credit risks among companies in the context of the Brazilian shoe supply chain. For that, the author brought supply chain concepts largely discussed in the operations arena to the credit risk analysis. The results show that when the retail link experiences a variation in the credit risk level (hereby
'Rational Overeating' in a Feast-or-Famine World: Economic Insecurity and the Obesity Epidemic

Obesity has risen dramatically in the United States since the 1980s, but incidence varies across demographic groups. We investigate the potential role of economic insecurity—defined, roughly, as the extent to which a household faces the threat of catastrophic income loss–in explaining these changes. We construct a synthetic panel of demographic groups for 1988–2016 by combining the Economic Security Index (which measures the probability of a year‐on‐year drop in adjusted household income of 25% or more) with data from the NHANES surveys. This gives us a plausibly exogenous group‐level measure of economic insecurity while allowing us to control for both individual characteristics and various interactions of group and year fixed effects. We find robust evidence of a link between economic insecurity and obesity, suggesting a nearly one‐to‐one correspondence in percentage point changes in ESI and obesity, for both men and women. We further show that if we instead measure economic insecurity based on the changing occupational exposure of each demographic group to trade with China over time, we find similar qualitative results for men, but not for women. Taken together, these results are supportive of a causal interpretation of our findings.
Iterative Bayesian Learning for Crowdsourced Regression ( Supplementary Material )

Crowdsourcing is a primary marketplace to get labels on training datasets, to be used to train machine learning models. In this section, using both semi-synthetic and real datasets, we investigate the impact of having higher quality labels on real-world machine learning tasks. We show that sophisticated regression algorithms like BI can produce high quality labels on the crowdsourced training datasets, improving the end-to-end performance of convolutional neural network (CNN) on visual object detection or human age prediction. This highlights the importance of estimator but also justifies the use of the proposed BI, in a real world system.
Early Severe Thunderstorm Forecasting and Research by the United States weather Bureau

Abstract In the early nineteenth century, fragmentary weather observing networks were established in portions of the United States, primarily to constitute a climatological history. The invention of the telegraph in 1833 and its availability to the public in 1845 eventually led to a nationwide observation network with the formation of a national weather service in 1870 within the Signal Service of the U.S. Army. While Lt. J. P. Finley of the Signal Service was developing techniques for the prediction of tornadoes, others, as Prof. Henry A. Hazen (also of the Signal Service) and the New England Meteorological Society, were studying the thunderstorm in hope of developing predictors for the forecasting of these events. The thunderstorm studies were carried over to the civilian U.S. Weather. Bureau in 1891, but interest in thunderstorm and tornado research wanted as a ban on the use of the word “tornado” in forecasts, inherited from the Signal Corps, was carried into the twentieth century. The growth of the a.
Unified Treatment of Flow Instabilities of Turbomachines

The relationship among four flow instabilities of turbomachines, namely, surge, rotating stall, cavitation surge, and rotating cavitation, is elucidated, using a unified or common model for their analysis. The simplest unifying model was employed in the analysis to focus on the characteristic features of each instability. Moreover, the concentration is on the stability criteria, and hence, the amplitudes are assumed small. Of course, the instabilities often grow to amplitudes comparable with the average value of the flow variable. Flows upstream and downstream of the impeller were assumed to be one dimensional for surge and cavitation surge and to be two dimensional for rotating stall and rotating cavitation, respectively. Viscous effects were taken into consideration in the form of cascade loss. Impeller blade geometry was incorporated in the assumption that the flow is perfectly guided. The peripheral wavelength of the disturbance was assumed to be much larger than the blade pitch.
Similarity and the Turbulent Energy Spectrum

Spherically averaged spectral densities of quantities appearing in the turbulent energy equation are assumed to be locally similar: i.e., to depend on external parameters in a similar way when referred to local scales of flux and length. Dynamical equations are given for the influence of production (including anisotropy), viscosity, buoyancy, magnetic field, and elasticity. General solutions of these equations are obtained implicitly, and the leading term in a series expansion explicitly. This similarity is shown to be a generalization of the ideas of Kolmogorov, of the modified Onsager cascade used by Corrsin, and of the formulation of Kovasznay and Shur for the influence of viscosity and buoyancy. In the case of viscosity, the prediction of a spectral cutoff by the Kovasznay formulation is seen to be misleading, and due to the retention of only the leading term in the expansion.
The Enumeration of Point Labelled Chromatic Graphs and Trees

Given n points with c1 of one colour, c2 of another colour, up to k colours, linear graphs are formed with the restriction that no line connects points of the same colour. Following fairly standard terminology, coloured graphs with this restriction will be called point chromatic graphs. Giving the points numerical labels running from 1 to ci for points of the ith colour (i = 1, 2, … , k) forms point labelled chromatic graphs. Note that this description is slightly different from assigning a label and a colour independently to each point.
Importance of level mixing on accurate [Fe II] transition rates

Context. In a very recent measurement Gurell et al. (2009, A&A, 508, 525) commented that while the theoretical lifetime of a 4 G5.5 is approximately one tenth of the lifetime of b 2 H5.5 the corresponding measurement shows this to be close to one fifth. This large discrepancy is attributed to the effect of inadequate level mixing in the theoretical calculations. Aims. The aim of this work is to make a detailed analysis of these level mixing effects on transitions from various lower levels to the a 4 G5.5 and b 2 H5.5 levels given in three previous calculations and in the present more extensive CI calculation. Methods. The CIV3 structure codes of Hibbert (1975, Comput. Phys. Commun., 9, 141) and Hibbert et al. (1991, Comput. Phys. Commun., 64, 455) are used in the present work, combined with our “fine-tuning” extrapolation process. Results. The calculated mixing between the upper levels, obtained in previous calculations, is shown to be too weak. The stronger mixing determined in our work gives rise to a calculated lifetime for b 2 H5.5 within 3% of the measured value. On the other hand our calculated lifetime for a 4 G5.5 is around 20% lower than the measured value, which has fairly wide error bars. Conclusions. Our enhanced calculations explain the difference between previous calculations of the b 2 H5.5 lifetime and the recent measured value and confirm the latter. We also suggest a somewhat higher value than experiment for the lifetime of a 4 G5.5.
CONSTRAINTS ON THE GALACTIC BULGE USING IRAS VARIABLE POINT SOURCES

A flux-limited sample of IRAS variable sources is used to probe the three-dimensional structure of the Galactic bulge. No distinct vertically extended bulge component is seen; the spatial distribution is that of a centrally concentrated disk. The two-dimensional distribution of IRAS variables on the sky is well fitted by an exponential disk with scale length a = 4.5 kpc and scale height h = 800 pc and more poorly fitted by an exponential disk plus an R 1/4 law. The combined results suggest that any bulge component is quite small and/or flattened with a vertical scale height not significantly larger than the disk itself
Improvement in Discrimination by Eliciting Properties of Echo Signals from Different Seabed Materials

To improve the discrimination ratio of seabed materials, considering that the difference in scattering style brings forth the difference in the duration time of echo signals corresponding to different materials, the product of the area intensity, which is employed in our previous method, and the effective duration time of echo signal is defined as a new time-weighted intensity, and is introduced to elicit the reflection properties with clearer differences between different materials. Three types of material, namely, crushed stone, sea sand, and mud, are measured. The distributions of two types of intensity corresponding to different materials are compared, and the comparison results show that the newly proposed intensities provide more differences between materials than the previous area intensities. Moreover, the discrimination ratio of materials is improved significantly, and all the discrimination ratios for three types of material up to more than 90% are obtained.