Miracle-dz/UniFAR-FTUs huggingface dataset:
From local to global and back : a closed walk in mathematical programming and its applications

An overview of my research contributions in optimization is provided, passing through mixed-integer nonlinear optimization, nonlinear continuous local optimization and network (graph) clustering. The first chapter deals with mixed-integer nonlinear programming and deterministic global optimization, and presents contributions concerning theoretical investigations as well as applications to real-world problems. We mainly discuss about convex relaxations and automatic reformulations of mathematical programming problems, aiming at enhancing the efficiency of Branch-and-Bound algorithms. Focusing on polynomial programming, we investigate tight convex relaxations for multilinear monomials and the generation of compact relaxations of polynomial problems based on a special reformulation-linearization technique. Among applications, a special attention is devoted to real-life problems arising in Air Traffic Management. We propose new mathematical models and solution approaches from mixed-integer optimization on the one hand, and optimal control on the other hand. A few topics in nonlinear continuous optimization are described in the second chapter. Interior point methods for quadratic programming and their linear algebra kernels (KKT systems) are first discussed. The focus is on iterative methods for the KKT systems and related issues, such as preconditioning techniques and convergence properties. The other discussed topic relates, again, to air traffic problems. This concerns the mentioned optimal control-based approaches that lead to nonlinear problems. The third chapter presents my main results in the area of network clustering. The problem of identifying clusters in networks can be formulated using mathematical programming and usually leads to a combinatorial optimization problem. My contributions concern clustering criteria and corresponding clustering methods. A special attention is devoted to exact methods, used either to solve the whole optimization problem or, locally, subproblems arising in hierarchical heuristics, or to refine solutions previously obtained by other methods.
Caputo fractional differential equations with non-instantaneous impulses and strict stability by Lyapunov functions

In this paper the statement of initial value problems for fractional differential equations with noninstantaneous impulses is given. These equations are adequate models for phenomena that are characterized by impulsive actions starting at arbitrary fixed points and remaining active on finite time intervals. Strict stability properties of fractional differential equations with non-instantaneous impulses by the Lyapunov approach is studied. An appropriate definition (based on the Caputo fractional Dini derivative of a function) for the derivative of Lyapunov functions among the Caputo fractional differential equations with non-instantaneous impulses is presented. Comparison results using this definition and scalar fractional differential equations with non-instantaneous impulses are presented and sufficient conditions for strict stability and uniform strict stability are given. Examples are given to illustrate the theory.
Topological states applied to spintronics devices

LORETO, Renan Pires, D.Sc., Universidade Federal de Viçosa, April, 2018. Topological states applied to spintronics devices. Adviser: Clodoaldo Irineu Levartoski de Araújo. In this work we study three important magnetic systems extensively researched in the past decades. In the first part, the recent proposition of the use of magnetic skyrmions, which are topological particle-like excitations in ferromagnets, in racetrack memories, have attracted a lot of attention recently opening up a new field of study called skyrmionics which is an attempt to use those magnetic structures as information carriers in next generation of spintronic devices. For usage of magnetic skyrmions, in some systems is necessary to include the DzyaloshinskiiMoriya interaction (DMI) and the out-of-plane magnetic field into the system. In this work, we explore a system without these requirements. First, we propose a controlled way for the creation of magnetic skyrmions and skyrmioniums imprinted in a perpendicular magnetized ferromagnetic nanotrack. Then we investigate the detachment of the imprinted spin textures from the underneath of the nanodisk, the transport by the spin-transfer torque imposed by spin-polarized current pulses applied in the nanotrack and the detection by Tunnel Magnetoresistance (TMR). We notice that the moving structure is not a skyrmion after is detached, and by calculating how the topological charge behaves, we have called it the resonant magnetic soliton (RMS). The second part covers the generation of spin currents by Spin Pumping and Spin Seebeck effects and the conversion of this spin current to charge current in (Bi0.22Sb0.78)2Te3 topological insulators at room temperature. The spin-to-charge current conversion is attributed to the inverse Edelstein effect (IEE) made possible by the spin-momentum locking in the electron Fermi contours due to the Rashba field. The measurements by the two techniques yield the same value for the IEE parameter, showing that those methods can be an efficient way to the spin to charge current in topological insulators. In the third part, arrays of nanomagnets designed to resemble spin ice materials (disordered magnetic states) are known as artificial spin ices (ASI). Here we study, both theoretically and experimentally the thermodynamic effects on streched arrays of spin ices. The rectangular artificial spin ices (RASI) is expected do show different phase transitions by changing the geometry
Fault Diagnosis of Bearings with Adjusted Vibration Spectrum Images

In order to diagnose bearing faults under different operating state and limited sample condition, a fault diagnosis method based on adjusted spectrum image of vibration signal is proposed in this paper. Firstly, the Davies–Bouldin index (DBI) is employed to select a proper capture focus (CF) and image size, and the spectrum of vibration signal is computed via fast Fourier transformation (FFT) and adjusted according to the average rotating speed. Then, the spectrum is plotted and captured as a two-dimensional (2D) image with the optimized CF and image size. Two-dimensional principal component analysis (2DPCA) is used to reduce the dimension of images, and finally a nearest neighbour method is applied to classify the faults of bearings. Two experiments are carried out to validate the effectiveness of the proposed method. Besides, a further investigation on the effect of spectrum frequency resolution is conducted and a recommended selection method of frequency resolution is given based on the experimental performances. In our method, the training samples could be from only one operating condition, while the testing samples are from all possible operation conditions. All experiment results have demonstrated that the proposed method could achieve high classification accuracy even with very limited training samples.
Pulmonary Embolism: Imaging Modalities-V/Q Scan, Spiral (Helical) CT, and MRI

Ventilation-perfusion (V/Q) imaging has been used as the screening test for pulmonary embolism (PE) for many years with diagnostic algorithms developed as a result of the Prospective Investigation of Pulmonary Embolism Diagnosis study. The primary conclusions were that high probability V/Q scans were reliable indicators for PE and normal or near-normal scans were reliable in the exclusion of PE. With the increasing availability of spiral (helical) computed tomography (CT) and many studies showing a high degree of accuracy for PE, there is much support for the replacement of V/Q by spiral CT. This article reviews the literature concerning V/Q scanning, spiral (helical) CT, and the future potential for magnetic resonance in the diagnosis of PE.
Text image authenticating algorithm based on MD5-hash function and Henon map

In order to cater to the evidentiary requirements of the text image, this paper proposes a fragile watermarking algorithm based on Hash function and Henon map. The algorithm is to divide a text image into parts, get flippable pixels and nonflippable pixels of every lump according to PSD, generate watermark of non-flippable pixels with MD5-Hash, encrypt watermark with Henon map and select embedded blocks. The simulation results show that the algorithm with a good ability in tampering localization can be used to authenticate and forensics the authenticity and integrity of text images
Evolution from successive phase transitions to “morphotropic phase boundary” in BaTiO3-based ferroelectrics

Obtaining superior physical properties for ferroic materials by manipulating the phase transitions is a key concern in solid state physics. Here, we investigated the dielectric permittivity, piezoelectric coefficient d33, storage modulus, and crystal symmetry of (1-x)Ba(Ti0.8Zr0.2)O3-x(Ba1−yCay)TiO3 (BZT-xBCyT) systems to demonstrate the gradual evolution process from successive phase transitions in BaTiO3 to the morphotropic phase boundary (MPB) regime in BZT-xBC0.3T. Furthermore, we analysed with a Landau-type theoretical model to show that the high field-sensitive response (dielectric permittivity) originates from a small polarization anisotropy and low energy barrier at the quadruple point. Together, the intermediate orthorhombic phase regime and the tetragonal-orthorhombic and orthorhombic-rhombohedral phase boundaries constitute the MPB. Our work not only reconciles the arguments regarding whether the structural state around the MPB corresponds to a single-phase regime or a multiple-phase-coexistence regime but also suggests an effective method to design high-performance functional ferroic materials by tailoring the successive phase transitions.
On homogenized equations of filtration in two domains with common boundary

We consider an initial-boundary value problem describing the process of filtration of a weakly viscous fluid in two distinct porous media with common boundary. We prove, at the microscopic level, the existence and uniqueness of a generalized solution of the problem on the joint motion of two incompressible elastic porous (poroelastic) bodies with distinct Lamé constants and different microstructures, and of a viscous incompressible porous fluid. Under various assumptions on the data of the problem, we derive homogenized models of filtration of an incompressible weakly viscous fluid in two distinct elastic or absolutely rigid porous media with common boundary.
Lie algebroids in derived differential topology

A classical principle in deformation theory asserts that any formal deformation problem is controlled by a differential graded Lie algebra. This thesis studies a generalization of this principle to Lie algebroids, and uses this to examine the interactions between the theory of Lie algebroids and the derived geometry of moduli spaces. The first half of the thesis develops the homotopy theory of differential graded Lie algebroids over a fixed affine derived manifold. We prove that any deformation problem over such a derived manifold is controlled by a Lie algebroid, by constructing an equivalence between the homotopy theory of Lie algebroids and the homotopy theory of formal moduli problems. This equivalence furthermore extends to an equivalence between representations of Lie algebroids and quasi-coherent sheaves over formal moduli problems. In the second half of the thesis, we develop the theory of derived differential topology and apply it to study Lie algebroids arising from derived differentiable stacks. Using the results of the first half, we show that the relative tangent bundle of a derived manifold over a derived stack has a Lie algebroid structure. We then provide a criterion for maps between Lie algebroids to integrate to maps between stacks, generalizing classical theorems of Lie and Van Est. This result is applied to show that finite-dimensional L-infinity algebras can be integrated to higher Lie groups.
New Strategies in the Treatment of Dyslipidemia: Do We Know How?

The treatment of dyslipidemia is beyond doubt one of the cornerstones of cardiovascular prevention. If we want to touch and comment on at least the principal news in this broad ﬁeld, we must simplify and pay attention to only a few selected areas. The focus of this article is on hypercholesterolemia and the treatment options for elevated low-density lipoprotein (LDL)-cholesterol; it also addresses the questions of low high-density lipoprotein (HDL)-cholesterol levels and the treatment of dyslipidemia of the metabolic syndrome. In particular, statins have had accumulation of new evidence resulting in novel indications and new target groups. Modern, even more potent drugs lowering total and LDL-cholesterol levels are available (new statins, e.g., rosuvastatin, pitavastatin, cholesterol absorption inhibitor ezetimibe) More and more attention of the medical public is being paid to dyslipidemia of the metabolic syndrome (so-called lipid triad), which seems to be the greatest rival of LDL-cholesterol among lipid risk factors for cardiovascular disease. In the treatment of this dyslipidemia especially the nuclear peroxisome proliferator-activated receptor (PPAR) agonists play an important role. In particular ﬁbrates but also glithasones are noteworthy in this respect. There are fewer data for ﬁbrates than for statins, but nevertheless evidence documenting beneﬁt of this therapy is growing. A statin and ﬁbrate combination is a promising future approach not only to the treatment of metabolic syndrome. Moreover, niacin, particularly in combination with a statin, might experience a renaissance. HDL-cholesterol level modiﬁcation attracts more and more discussions; on the horizon there are new therapies of low HDL, for example, cholesterol-ester transfer protein inhibitors, which have been shown to have a potency for increasing HDL by more than 50%.
Application of Adomian Decomposition Method in Solving Second Order Nonlinear Ordinary Differential Equations

In this paper, we use Adomian Decomposition Method to numerically analyse second order nonlinear ordinary differential equations and implement the continuous algorithm in a discrete domain. This is facilitated by Maple package. And, the results from the two test problems used shows that the Adomian Decomposition Method is almost as the classical solutions.
Visual decision making in the presence of stimulus and measurement correlations

Our brains process sensory information to infer the state of the world. However, the input from our senses is noisy, which may lead to errors in perceptual judgements. A number of theoretical studies have modeled perception as a process of probabilistic inference that involves making decisions based on uncertain evidence. Bayesian optimality is a general principle of probabilistic inference that has been successfully used to build quantitative models of perception. In addition, several experimental studies show that human observers make best possible decisions, and hence exhibit close to Bayes-optimal behavior on various visual perceptual tasks such as visual search, sameness judgement, and change detection. However, the impact of structured stimuli on decision-making remains largely unexplored. Moreover, the sensory measurements can themselves be strongly correlated to produce a structured representation of the stimulus input. These measurement correlations can interact with the structure of the external input in many possible ways and should not be considered in isolation. In this work, we focus on visual search task to examine how visual perception is affected by structured input. We analyze the responses of subjects on a target detection experiment where the stimulus orientations were generated with varying strength of correlations across different experimental sessions. We fit several models to the experimental data using maximum-likelihood parameter estimation. We use rigorous model selection to find that human observers take into account stimulus correlations in detecting a target. However, they behave suboptimally in inferring the correct stimulus correlations that were used in the experiment. We
Lithospheric reflection imaging by multidimensional deconvolution of earthquake scattering coda

Seismic interferometry (SI) for body waves offers the opportunity to utilize highfrequency scattering coda from local earthquakes to obtain a detailed reflectivity image of the lithosphere. In this thesis it is demonstrated that classical SI methods are seriously affected by circumstances that are typical of field data and that multiple scattering poses a complex trade-off for SI performance. Therefore, we propose an alternative method by multidimensional deconvolution (MDD) that proves to be more resilient under realistic circumstances and properly utilizes the scattering coda: full-field MDD. The main advantage of this method over classical MDD methods is that the kernel of its governing equation is exact, which allows for an optimal use of the multiple scattering coda to obtain virtual primary reflections of the lithosphere.
Exploring Vacuum Energy in a Two-Fluid Bianchi Type I Universe

We use a dynamical systems approach based on the method of orthonormal frames to study the dynamics of a two-fluid, non-tilted Bianchi Type I cosmological model. In our model, one of the fluids is a fluid with bulk viscosity, while the other fluid assumes the role of a cosmological constant and represents nonnegative vacuum energy. We begin by completing a detailed fixed-point analysis of the system which gives information about the local sinks, sources and saddles. We then proceed to analyze the global features of the dynamical system by using topological methods such as finding Lyapunov and Chetaev functions, and finding the αand ω-limit sets using the LaSalle invariance principle. The fixed points found were a flat Friedmann-LeMâıtre-Robertson-Walker (FLRW) universe with no vacuum energy, a de Sitter universe, a flat FLRW universe with both vacuum and non-vacuum energy, and a Kasner quarter-circle universe. We also show in this paper that the vacuum energy we observe in our present-day universe could actually be a result of the bulk viscosity of the ordinary matter in the universe, and proceed to calculate feasible values of the bulk viscous coefficient based on observations reported in the Planck data. We conclude the paper with some numerical experiments that shed further light on the global dynamics of the system.
Planetary boundary layer evolution over an equatorial Andean valley: A simplified model based on balloon‐borne and surface measurements

Planetary boundary layer (PBL) evolution over a populated Andean valley east of Quito, Ecuador is investigated through an empirical model. Balloon‐borne measurements of boundary layer height (PBLh) were found to correlate strongly (R2 = 0.871) as a function of virtual temperature at the surface calculated with 10 min ground station observations. This simplified model captures slow and fast regimes of PBL growth observed from the early morning to midday, which lead to the development of either shallow or deep PBLs. Surface conditions under which different scenarios of PBL develop are discussed in light of a test performed with 2015 station data. The proposed model can be used with the purpose of interpreting air quality measurements.
MESHING STRATEGY EVALUATION FOR A SQUARE SHAPED BLUFF BODY UNDER HIGH REYNOLDS NUMBER CROSS FLOW

This work consists in the numerical evaluation of meshes employed in a twodimensional, incompressible, and transient flow, with high Reynolds numbers and forced convection that passes through a square shaped bluff body. The objective of the study is to evaluate different strategies of mesh construction to solve this type of problem, seeking to reduce the computational cost and improve the solution. The simulations were performed for Reynolds and Prandtl numbers of ReD = 22,000 and Pr = 0.71. The turbulence behavior is solved with the RANS SST–-model. The evaluation of the solutions is performed analyzing the drag coefficient (CD), Nusselt number (NuD) and Strouhal number (St). The use of an unstructured mesh with fully structured local refinement was able to validate the fluid dynamics of the case with a relative deviation of 14.95% for the velocity field, compared to the literature. The deviations for CD and St were as low as 0.43% and 0.79% respectively. For thermal verification, the deviation of the mean local Nusselt number along the bluff body (NuD) was 5.93%, and the deviation for the global Nusselt number (Nug) was as low as 0.56% compared to the literature.
SHARE: Regularization for Deep Learning

Regularization is a big issue for training deep neural networks. In this paper, we propose a new information-theory-based regularization scheme named SHARE for SHAnnon DEcay. The originality of the approach is to deﬁne a prior based on conditional entropy, which explicitly decouples the learning of invariant representations in the regularizer and the learning of correlations between inputs and labels in the data ﬁtting term. Our second contribution is to derive a stochastic version of the regularizer compatible with deep learning, resulting in a tractable training scheme. We empirically validate the efﬁciency of our approach to improve classiﬁcation performances compared to common regularization schemes on several standard architectures.
Acoustic Analysis of Monophthongs in Monguor Language

The purpose of the study is to analyze the acoustic features of Monophthongs in Monguor language. On the base of acoustic parameter database of the Monguor speech, the study discusses the differences in duration and F2 difference between short and long monophthongs in monosyllabic words and the differences in duration and F2 difference in first syllable, middle syllable(s), and last syllable for short and long monophthongs. The results show that in Monguor language, short and long vowels have the opposed relation and therefore differentiate the meanings of words.
Photonic crystals for optimal color conversion in light-emitting diodes: a semi-analytical approach

Based on effective-medium approximation, we analytically optimize the color conversion of GaN-based light-emitting p–n junctions, with respect to the size and spatial density of the used photonic crystals (PhCs), being filled with quantum dots (QDs). The model is two-dimensional and the incoherent excitation into the multiple quantum wells is mimicked by line sources of random electric and magnetic currents. Optimal operation is achieved by suppressing the radiation extraction for one visible color and simultaneously maximizing the emission for another color. For these cases, the field gets inevitably concentrated into the PhCs of QDs, where the conversion occurs, and the performance of the device is maximized. Several examples from these ultra-performing designs are provided, within which a secondary sweep can be applied by posing extra constraints related to cost or ease of fabrication.
Correlation between AC and DC transport properties of Mn substituted cobalt ferrite

The CoFe2-xMnxO4 compound is prepared by following the sol gel technique. The structural analysis through XRD and Rietveld has been confirmed for the single cubic phase having Fd3¯m space group for CoFe2-xMnxO4 and also verified it through Raman spectroscopy measurements. The tetrahedral site observed to be red shifted with increase in Mn concentration in cobalt ferrite. All the XRD patterns have been analyzed by employing the Rietveld refinement technique. The particle size was found to be in the range of 30–40 nm. The electrical properties of polycrystalline CoFe2-xMnxO4 for x = 0.00, 0.10, 0.15, and 0.2, spinel ferrite was investigated by impedance spectroscopy. The influence of doping, frequency and temperature on the electrical transport properties of the CoFe2-xMnxO4 for x = 0.00, 0.10, 0.15, and 0.20 were investigated. The magnitude of Z′ and Z″ decreases with increase in temperature. Only one semicircle is observed in each Cole Cole plot which reveals that ac conductivity is dominated by grains. T.