Search

We consider the coefficient inverse problem for the 2D acoustic equation. The problem is recovering the speed of sound in the medium (which depends only on the depth) and the density (function of both variables). We describe the method, based on the Gelfand–Levitan–Krein approach, which allows us to obtain both functions by solving two sets of integral equations. The main advantage of the proposed approach is that the method does not use the multiple solution of direct problems, and thus has quite low CPU time requirements. We also consider the variation of the method for the 1D case, where the variation of the wave equation is considered. We illustrate the results with numerical experiments in the 1D and 2D case and study the efficiency and stability of the approach.

Mechanical engineering structures and structural components are often subjected to cyclic thermomechanical loading which stresses their material beyond its elastic limits well inside the inelastic regime. Depending on the level of loading inelastic strains may lead either to failure, due to low cycle fatigue or ratcheting, or to safety, through elastic shakedown. Thus, it is important to estimate the asymptotic stress state of such structures. This state may be determined by cumbersome incremental time-stepping calculations. Direct methods, alternatively, have big computational advantages as they focus on the characteristics of these states and try to establish them, in a direct way, right from the beginning of the calculations. Among the very few such general-purpose direct methods, a powerful direct method which has been called RSDM has appeared in the literature. The method may directly predict any asymptotic state when the exact time history of the loading is known. The advantage of the method is due to the fact that it addresses the physics of the asymptotic cycle and exploits the cyclic nature of its expected residual stress distribution. Based on RSDM a method for the shakedown analysis of structures, called RSDM-S has also been developed. Despite most direct methods for shakedown, RSDM-S does not need an optimization algorithm for its implementation. Both RSDM and RSDM-S may be implemented in any Finite Element Code. A thorough review of both these methods, together with examples of implementation are presented herein.

In this letter, we present a direct visual odometry (VO) using points and lines. Direct methods generally choose pixels with sufficient gradients to minimize the photometric error for the status estimation. Pixels on lines are generally involved in this process. But the collinear constraint among these points are generally ignored, which may result in less accurate depth estimation. This letter introduces the collinear constraint into the state-of-the-art direct visual odometry DSO (J. EngelI et al., 2018) to overcome this problem. The 3D lines, points and poses within a sliding window are jointly optimized. Points are generally only visible within a short time window. However, as lines are unbounded entities, they can be observed by a camera significantly longer than points. Thus, we seek to establish the long-term data association for lines among the keyframes. The 3D collinear points that are removed from the sliding window are served as collinear priors for the following windowed optimization. We prove that the prior collinear constraints of a 3D line can be compressed into six residuals in the optimization. This significantly reduces the computational complexity, and enables real-time performance for incorporating long 3D line segments into the windowed optimization. We present a new 3D line representation which reduces the four degrees of freedom (DoF) of a 3D line into two DoF by parameterizing the 3D line in the back-projection plane of its first 2D line observation. The experimental results show that our algorithm outperforms the state-of-the-art direct monocular VO algorithms.

RESUMEN: El objeto general de este trabajo es la implementación de una nueva técnica de prospección minera mediante el uso de los drones y los sensores térmicos. En primer lugar, se debe realizar un estudio del comportamiento térmico de las litologías a estudio, comprobando si existe una diferencia en el comportamiento térmico que de justificación a esta nueva metodología mediante la realización de una serie de experimentos en el laboratorio. Tras la determinación de este primer paso, a continuación, se debe proceder localizar una zona de estudio donde se procederá a realizar un vuelo fotogramétrico mediante el empleo de un dron equipado con un sensor RGB y uno térmico, para posteriormente tratar esas imágenes y obtener una ortoimagen de la zona, así como un mapa térmico de las diferentes litologías. Por último, para la validación de los resultados se debe proceder a la comparación del mapa térmico obtenido con el procesado de las imágenes térmicas del vuelo fotogramétrico con una ortoimagen de la zona del vuelo y con la cartografía de detalle de la zona realizada con la toma de puntos de contacto entre las dos litologías para verificar los resultados obtenidos. Tras esta comparación de los resultados por tres metodologías diferentes se obtiene la verificación de esta nueva metodología. La metodología propuesta es válida y tiene grandes ventajas frente a las técnicas de prospección tradicionales, las principales son su sencillez o la reducción de costes y tiempos, temporal, etc. La realización de cartografía geológica de detalle es la técnica más precisa pero también es la que consume mayores recursos. La fotointerpretación y/o fotogeología requieren que exista una diferencia cromática entre las litologías a prospectar, circunstancia que no siempre se produce. En definitiva, el empleo de sensores infrarrojos aerotransportados en plataformas UAV en actividades de prospección minera es una metodología con gran potencial. Permiten llevar un paso más allá las labores de investigación, obteniendo resultados de forma rápida y económica. Además, aplicarse en zonas complejas y de difícil acceso, haciendo más atractiva su implementación. ABSTRACT: The general objective of this work is the implementation of a new mining prospecting technique using drones and thermal sensors. First of all, a study of the thermal behaviour of the lithologies to be studied must be carried out, checking if there is a difference in the thermal behaviour that justifies this new methodology by carrying out a series of experiments in the laboratory. After determining this first step, it is then necessary to locate a study area where a photogrammetric flight will be carried out using a drone equipped with an RGB sensor and a thermal sensor, in order to subsequently process these images and obtain an orthoimage of the area, as well as a thermal map of the different lithologies. Finally, to validate the results, the thermal map obtained by processing the thermal images of the photogrammetric flight must be compared with an orthoimage of the flight area and with the detailed mapping of the area carried out by taking contact points between the two lithologies to verify the results obtained. After this comparison of the results by three different methodologies, the verification of this new methodology is obtained. The proposed methodology is valid and has great advantages over traditional prospecting techniques, the main ones being its simplicity or the reduction of costs and time, time, etc. Detailed geological mapping is the most accurate technique but it is also the most resource-intensive. Photointerpretation and/or photogeology require a chromatic difference between the lithologies to be prospected, which is not always the case. In short, the use of airborne infrared sensors on UAV platforms in mining prospecting activities is a methodology with great potential. It allows research work to be taken a step further, obtaining results quickly and economically. In addition, they can be applied in complex and difficult to access areas, making their implementation more attractive. Grado en Ingeniería de los Recursos Mineros

Informar en los estudios sobre el tamaño del efecto de una intervención o del impacto de factor(es) sobre un desenlace, permite tomar mejores decisiones para la aplicación de los resultados a la práctica clínica. En este artículo se presenta la manera de analizar el tamaño del efecto, lo cual puede ser mediante métodos estadísticos directos o indirectos. Dentro de los métodos directos, se encuentra la diferencia de promedios entre grupos y la diferencia de frecuencias absolutas o relativas. Dentro de los métodos indirectos se muestran los índices de la familia de “d” de Cohen (que se basan en valores de desviación estándar), la familia de “r y R2”, medidas de asociación (RM, RR, HR) e impacto (NNT). La decisión del uso de cualquiera de los métodos descritos, depende de los objetivos del estudio, la escala de medición usada para evaluar los resultados y la distribución de los datos. Para facilitar la comprensión, se incluyen ejemplos y se resalta la necesidad de incluir los diferentes estadísticos con su nivel de precisión (ej. intervalos de confianza), junto con los umbrales clínicos de decisión, a fin de mejorar su interpretación.

The issue of distinguishing between the same-source and different-source hypotheses based on various types of traces is a generic problem in forensic science. This problem is often tackled with Bayesian approaches, which are able to provide a likelihood ratio that quantifies the relative strengths of evidence supporting each of the two competing hypotheses. Here, we focus on distance-based approaches, whose robustness and specifically whose capacity to deal with high-dimensional evidence are very different, and need to be evaluated and optimized. A unified framework for direct methods based on estimating the likelihoods of the distance between traces under each of the two competing hypotheses, and indirect methods using logistic regression to discriminate between same-source and different-source distance distributions, is presented. Whilst direct methods are more flexible, indirect methods are more robust and quite natural in machine learning. Moreover, indirect methods also enable the use of a vectorial distance, thus preventing the severe information loss suffered by scalar distance approaches. Direct and indirect methods are compared in terms of sensitivity, specificity, and robustness, with and without dimensionality reduction, with and without feature selection, on the example of hand odor profiles, a novel and challenging type of evidence in the field of forensics. Empirical evaluations on a large panel of 534 subjects and their 1690 odor traces show the significant superiority of the indirect methods, especially without dimensionality reduction, be it with or without feature selection.

Three stage sixth-order exponentially fitted and trigonometrically fitted explicit two-derivative Runge–Kutta-type methods are proposed for solving $$u^{'''}(t) = \, f(t,u(t),u'(t)).$$ The idea of construction is based on linear composition of the set functions $$e^{\omega t}$$ and $$e^{-\omega t}$$ for exponentially fitted and $$e^{i\omega t}$$ and $$e^{-i\omega t}$$ for trigonometrically fitted with $$\omega \in \mathbb {R}$$ to integrate initial value problems. The selected coefficients of two-derivative Runge–Kutta-type method are modified to depend on the principle frequency of the numerical problems to construct exponentially fitted and trigonometrically fitted Runge–Kutta-type direct methods, denoted as EFTDRKT6 and TFTDRKT6 methods. The numerical experiments illustrate competence of the new exponentially fitted and trigonometrically fitted method compared to existing methods for solving special type third-order ordinary differential equations with initial value problems.

The multi T-beam finite element model with an initial crack was generated based on the element and direct methods. The element method was used to evaluate the bonding performance of the fibre reinf...

This paper studies the problem of fixed-time synchronization for a class of delayed complex-valued neural networks with inertial term. Two different controllers are designed, under which the addressed inertial complex-valued neural networks with different types of activation functions can achieve synchronization perfectly in a fixed time. The corresponding synchronization criteria in terms of matrix inequalities and the estimates of the settling times are derived by using separation and direct methods, respectively, which are concise and easy to verify compared with algebraic inequalities conditions. Some innovative inequalities in the complex field are fully utilized. The in-depth analysis results are an advancement of the existing research progress. Finally, in order to support the theoretical results, numerical simulations for different types of activation functions are provided.

An experimental study of the efficiency of solvers of 2D boundary value problems on subgrids of quasi-structured rectangular grids is carried out. A solver means a solution method and its software implementation. The following three solvers are considered: a direct solver (Buneman’s cyclic reduction method) and two iterative ones (the alternative direction method of Peaceman and Rachford and the successive overrelaxation method). Characteristic features of the study are as follows: 1) the subgrids have a small number of nodes, namely 8 × 8, 16 × 16, 32 × 32, and 64 × 64; 2) the efficiency is estimated not only for single calculations, but also for series of calculations; in each of them the problem is repeatedly solved with different boundary conditions on the same subgrid. Based on a series of calculations, a combined method is proposed, and recommendations on using the solvers are given.

Eliminating wellbore storage (WBS) effects inherent in pressure transient data is one of the challenges in well test analysis. The available WBS-removal techniques are either direct or time-consuming approaches. The direct methods are mostly unstable and require accurate data with almost no noise. However, well test data often have noise in both rate and pressure measurements. This work discusses the development of a stable technique to overcome the shortcomings in the available WBS-removal methods. The technique presented here takes advantage of the recently developed stable deconvolution algorithms (e.g. von Schroeter algorithm) to achieve a stable WBS-removal process. The developed approach provides longer WBS-free reservoir response signal (extended over the entire test duration) than the previous methods. In addition, the approach introduced here can remove WBS-effects in noisy data and does not require sandface rate measurements. Different simulated and field examples were used to validate the proposed approach. The examples included data with different levels of rate and pressure measurement errors and covered wide variety of well/reservoir models. The available approaches were implemented to the same examples. A comparison of the results shows the superiority of the approach presented in this paper.

All numerical and analytical methods dealing with the calculating deformation of rock mass require deformation modulus (Df) which is measured by direct or estimated by indirect approaches. Direct methods such as plate loading, flat jack, and dilatometer test have been developed, but they are generally expensive, time-consuming, and sometimes questionable. Furthermore, Df data is often limited and insufficient to estimate its statistics or not being available at all in many rock engineering projects. The empirical approach, as a practical tool, seems attractive and an alternative approach for Df determination. This experimental study presents a new empirical correlation set for the Df estimation based on 73 dilatometer tests, 27 laboratory tests, and related rock quality designation (RQD) which belonged to several dam/hydro-power projects. The statistical method and regression approach were used to analyze the data to develop a new correlation set in which about 70% of the database gathered for Df equations development and the remaining data (30%) for its validation process. Data were used to developing of the new empirical equation set; generally belong to the fair to good quality rock masses. The input data for the Df estimation consist of laboratory elasticity modulus (El), RQD, and loading level factor ( $${\text{B}}_{{\text{n}}}$$ ). The statistical analysis revealed that Df has a significant dependence on the loading level factor. Also, El and in-situ elasticity modulus ( $${\text{E}}_{{\text{f}}}$$ ) would have the best correlation if the laboratory specimen was achieved from the dilatometer test zone. The R-square ( $$R^{2}$$ = 0.91) and the mean absolute relative prediction error (MARPE about 20%) verified the new correlation set. Finally, the estimated total deformation modulus from this paper’s relation set compared with the deformation modulus achieved from two existing empirical equations, and the main cause of differences was discussed.

Model predictive control (MPC) is a control strategy that can handle state and control multi-variables at same time. To use the MPC using direct methods for solving the a dynamic optimization problem, one needs, for example, to transform the optimization problem into a nonlinear programming (NLP) problem by dividing the prediction horizon into equal time intervals. In this work, we suggest a tool and procedures for helping to choose a ‘compromise’ number of time intervals with a needed accuracy, objective cost, number of turned NLP iterations and computational time. On the other hand, we offer a simplified nonlinear program to ensure the convergence of a class of finite optimal control problem by modifying the state box constraints. In particular, a special type of box constraints were used to the constrained optimal control problem to enforce the state trajectories to reach the desired stationary point. These box constraints are characterized by some parameters that are easily optimized by our proposed nonlinear program. Our proposed tools are tested using two case studies; nonlinear continuous stirred tank reactor (CSTR) and nonlinear batch reactor.

The demand for rapid column screening, computer-assisted method development and method transfer, and unambiguous compound identification by LC/MS analyses has pushed analysts to adopt experimental protocols and software for the accurate prediction of the retention time in liquid chromatography (LC). This Perspective discusses the classical approaches used to predict retention times in LC over the last three decades and proposes future requirements to increase their accuracy. First, inverse methods for retention prediction are essentially applied during screening and gradient method optimization: a minimum number of experiments or design of experiments (DoE) is run to train and calibrate a model (either purely statistical or based on the principles and fundamentals of liquid chromatography) by a mere fitting process. They do not require the accurate knowledge of the true column hold-up volume V0, system dwell volume Vdwell (in gradient elution), and the retention behavior (k versus the content of strong solvent φ, temperature T, pH, and ionic strength I) of the analytes. Their relative accuracy is often excellent below a few percent. Statistical methods are expected to be the most attractive to handle very complex retention behavior such as in mixed-mode chromatography (MMC). Fundamentally correct retention models accounting for the simultaneous impact of φ, I, pH, and T in MMC are needed for method development based on chromatography principles. Second, direct methods for retention prediction are ideally suited for accurate method transfer from one column/system configuration to another: these quality by design (QbD) methods are based on the fundamentals and principles of solid-liquid adsorption and gradient chromatography. No model calibration is necessary; however, they require universal conventions for the accurate determination of true retention factors (for 1 < k < 30) as a function of the experimental variables (φ, T, pH, and I) and of the true column/system parameters (V0, Vdwell, dispersion volume, σ, and relaxation volume, τ, of the programmed gradient profile at the column inlet and gradient distortion at the column outlet). Finally, when the molecular structure of the analytes is either known or assumed, retention prediction has essentially been made on the basis of statistical approaches such as the linear solvation energy relationships (LSERs) and the quantitative structure retention relationships (QSRRs): their ability to accurately predict the retention remains limited within 10-30%. They have been combined with molecular similarity approaches (where the retention model is calibrated with compounds having structures similar to that of the targeted analytes) and artificial intelligence algorithms to further improve their accuracy below 10%. In this Perspective, it is proposed to adopt a more rigorous and fundamental approach by considering the very details of the solid-liquid adsorption process: Monte Carlo (MC) or molecular dynamics (MD) simulations are promising tools to explain and interpret retention data that are too complex to be described by either empirical or statistical retention models.

Tracer diffusion is one of most reliable techniques for providing basic kinetic data in solids. In the present review, selected direct methods, in particular the radiotracer measurements as a superior technique due to its high sensitivity, Secondary-Ion-Mass-Spectroscopy (SIMS) profiling, X-Ray Diffraction measurements and Rutherford Backscattering Spectrometry are presented and discussed. Special attention is put on the radiotracer technique describing the currently used sectioning techniques in detail with a focus on the experimental applications and complications. The relevant experimental results are exemplary shown. Furthermore, the most recent developments and advances related to the combined tracer/inter-diffusion measurements are highlighted. It is shown that this approach offers possibilities to provide the concentration-dependent tracer diffusion coefficients of the constituting elements in multi-component alloys in high-throughput experiments. Possibilities of estimating the tracer diffusion coefficients following different types of diffusion couple methods in binary and multicomponent systems are briefly introduced. Finally, specificity of SIMS analysis of diffusion in fine-grained materials are carefully analyzed. If applicable, a direct comparison of the results obtained by different techniques is given.

The crystal structure of linagliptin hemihydrate hemiethanolate was solved by direct methods and refined by least-squares on the basis of 3D electron diffraction data. Linagliptin is one of the lar...

Cilj modelnega posodabljanja je pridobitev izboljšanega numeričnega modela, ki je sposoben natančnega poustvarjanja odziva realne strukture. Meritev vibracij s pomočjo hitre kamere je ena od razvijajočih se alternativ klasičnemu pristopu meritev s pospeškomeri. Nekatere metode modelnega posodabljanja smo teoretično predstavili ter jih ovrednotili na podlagi sintetičnih eksperimentov ter preprostega realnega eksperimenta, ki je služil tudi primerjavi meritev s pospeškomerom ter meritev s hitro kamero. Slednje so se izkazale za obetavne, razvidne pa so bile tudi potencialne prednosti uporabe hitre kamere na geometrijsko kompleksnejših strukturah. The goal of model updating is to obtain an improved numerical model capable of accurately reproducing the response of a real structure. Vibration measurement using a high-speed camera is one of the developing alternatives to the classic approach of measuring with accelerometers. Selected methods of model updating were theoretically presented and evaluated on the basis of synthetic experiments and a simple real experiment, which also served to compare measurements with an accelerometer and measurements with a high-speed camera. The latter proved to be promising and with the potential advantages with more complex structures.

Methods based on Gaussian stochastic process (GSP) models and expected improvement (EI) functions have been promising for box-constrained expensive optimization problems. These include robust design problems with environmental variables having set-type constraints. However, the methods that combine GSP and EI sub-optimizations suffer from the following problem, which limits their computational performance. Efficient global optimization (EGO) methods often repeat the same or nearly the same experimental points. We present a novel EGO-type constraint-handling method that maintains a so-called tabu list to avoid past points. Our method includes two types of penalties for the key “infill” optimization, which selects the next test runs. We benchmark our tabu EGO algorithm with five alternative approaches, including DIRECT methods using nine test problems and two engineering examples. The engineering examples are based on additive manufacturing process parameter optimization informed using point-based thermal simulations and robust-type quality constraints. Our test problems span unconstrained, simply constrained, and robust constrained problems. The comparative results imply that tabu EGO offers very promising computational performance for all types of black-box optimization in terms of convergence speed and the quality of the final solution.

Dynamic tomography reconstructs a time activity curve (TAC) for every voxel assuming that the algebraic form of the function is known a priori. The algebraic form derived from the analysis of compartmental models depends nonlinearly on the nonnegative parameters to be determined. Direct methods apply fitting in every iteration step. Because of the iterative nature of the maximum likelihood–expectation maximization (ML–EM) reconstruction, the fitting result of the previous step can serve as a good starting point in the current step; thus, after the first iteration we have a guess that is not far from the solution, which allows the use of gradient-based local optimization methods. However, finding good initial guesses for the first ML–EM iteration is a critical problem since gradient-based local optimization algorithms do not guarantee convergence to the global optimum if they are started at an inappropriate location. This paper examines the robust solution of the fitting problem both in the initial phase and during the ML–EM iteration. This solution is implemented on GPUs and is built into the 4D reconstruction module of the TeraTomo software.

Over the last few years, a direct method known as the new auxiliary method has been shown to solve non-linear partial differential equations effectively where this method can give more exact solutions compared to the traditional direct methods. Due to these promising results, efforts are now being made to extend this method in solving the more complicated non-linear fractional partial differential equations. The new auxiliary method is a very powerful, felicitous, and effective method to get exact and traveling wave solutions of partial differential equations. Therefore, we apply the new auxiliary method to solve for the traveling wave solutions of the space-time fractional Cahn-Hilliard equation and the space-time fractional symmetric regularized long-wave equation. Furthermore, it is considered as more general method for solving that time of equations because it is shown that more exact solutions for the traveling wave on these equations will be obtained with the application of the new auxiliary method.

In this paper, the optimal control of a continuous type bioreactor with multi-input-multi-output signals is presented for the two active phases: growth and stationary. The underlying criterion to be minimized generalizes the classic quadratic forms to address some crucial objectives in controlling the bioreactor. In particular, the protection of actuators against fast switching in the controller output is considered by including a weighting term of the control signal derivatives. The direct optimal control approach is used to carry out the optimization in the presence of various limiting constraints. Direct methods are based on transcribing the infinite-dimensional problem to a finite-dimensional one. In this manuscript, direct single shooting and trapezoidal collocation methods are used for transcription, and the successive quadratic programming method is employed to solve the resulting nonlinear programming problem. It is shown that the trapezoidal method is an effective method for controlling the bioreactor in all the active phases, whereas the single shooting fails in dealing with the unstable one (i.e., growth). To analyze solutions in a more accurate manner, an auxiliary criterion is defined, and then the cheap control analysis is studied. The convergence to the lowest value of the auxiliary cost function and the effects on the optimal state and control trajectories are then examined by varying cheap parameters. Several numerical simulations support the presented theoretical formulation.

The paper introduces an approach to solve the optimal control problem applying symbolic regression methods. All known approaches to solve the optimal control problem are based on direct or indirect methods. Indirect methods may provide analytical solution but impose restrictions on the form and dimension of control object. In direct ones the optimal control problem is reduced to the nonlinear programming problem which provides general numerical solution. Also direct methods impose no restrictions on control object and have a wide range of application to complex applied problems. The approach proposed combines the advantages of both direct and indirect methods not involving the disadvantages mentioned previously. The suggested approach provides solution to the optimal control problem as a control function of time in explicit form. This approach benefits in case of applied optimal control problem requiring a solution in explicit form while indirect methods are inapplicable due to the restrictions imposed on the control system. The computational experiment of solving the optimal control problem for a mobile robot with phase constraints is presented. The results illustrate that the proposed approach finds an optimal control as a function of time which provides a mobile robot’s motion along the optimal trajectory avoiding phase constraints.

Domain switching process is a complex process and is not as simple in occurrence as appears from conceptual framework. Fortunately, the theories of nucleation and crystal growth successfully applied to switching domains help in understanding switching kinetics in ferroelectric samples. Direct methods of parameter estimation can provide only the local information of the target region while the ‘universal integrating methods’ provide domain kinetic parameters with their response proportional to the fraction of the phase grown at that time. Besides being statistical, the later is much simpler and popular in delivering more credible results. In this paper, an indirect estimation of significant microscopic parameters of optimized NaNO2-PVA ferroelectric composites is made by fitting their current transients with IGM, FGM and NLS switching models The fitting of these models into the experimental switching transient helps (i) in finding dimensionality n , characteristic time t o , nucleation rate R and domain size L and (ii) to identify whether a thin film can be considered to be an ensemble of a number of independent elementary regions switching their states independently with exponential distribution of their relaxation times. IGM model suggests that polarization switching proceeds through a continuous nucleation process. The results of FGM fitting the transients supports the points that with increase in signal-amplitude, new regions are nucleated leading to reduction of adjacent relative distance between the domains The excellent NLS fit over whole range of switching times suggests that composite film can be considered an ensemble of elementary regions individually characterized by independent relaxation times.

An efficient numerical method for the wideband scattering analysis of the freestanding large-scale finite periodic array is presented using the macro block-characteristic basis function method (MB-CBFM) and the improved frequency-independent reaction (FIR). In the MB-CBFM, the blocks (unit cells) are divided into some types of macro blocks. By analyzing the subarray with the macro blocks, the CBFs for the macro blocks will be obtained. The blocks in the same macro block share the same CBFs. Substituting the CBFs into the moment matrix equation, a reduced matrix equation whose size does not depend on the number of the blocks can be obtained and handled utilizing direct methods. When the MB-CBFM is applied for wideband analysis, the matrix needs to be recomputed. The reduced matrix can be efficiently generated by using the improved FIR, in which the matrix elements are expressed as the product of the geometrical elements and the phase factor. The geometrical elements are computed one time and reused. Only the phase factor needs to be recomputed. Several numerical examples are carried out. Simulation results show that the results of the proposed algorithm agree well with those of other numerical methods. The total CPU time is significantly reduced.

The ability to accurately and precisely measure gas volume and gas flow is a fundamental component in the safe provision of modern anaesthesia. This is vital for the delivery of gasses and monitoring of respiration. A range of techniques are used to measure gas volume and flow, both by direct and indirect measurement. Direct methods of gas volume measurement tend to be large and impractical. By using physical properties of gases indirect measurements can be made. Understanding the principles of these techniques allows interpretation of the data they produce. Descriptions of devices used in anaesthetic practice are given. These devices include the variable orifice flowmeter, differential pressure flowmeter, hot wire anemometer, mechanical flow transducer, ultrasonic flowmeter, Wright respirometer, Vitalograph and peak flowmeter.

During the manipulation of hen eggs from the farm to the consumer due to action of external forces and weak mechanical strength of shell, the eggs break. The goal of egg producers is to reduce losses when breaking eggs during the production and placement, and thus increase revenues. Each egg can be damaged by external forces whose values are greater than maximum strength of the egg shell. Direct and indirect methods are used to determine the quality of eggs and shell strength. By direct methods, strength of the shell can be determined on the basis of puncture force measurements, impact forces, quasi-static compression forces and free fall forces on a known surface. In our research, a device was constructed for the realization of experiment and a direct method for determining strength of eggs was applied on the basis of measured breaking force of the shell. The device for measuring strength of eggs by the direct method of puncture eggshell was constructed and applied at the Faculty of Technical Sciences and the Faculty of Agronomy in Čačak. Class "M" hen eggs produced on the "Grbović" farm in the vicinity of Čačak were used in the research. The laying hens are a 41-week-old Isa Brown hybrid. During the research, physical characteristics of hen eggs were determined: length, width, index of shape and weight of eggs, as well as weight of the shell, share of the shell in the total mass of eggs, thickness and puncture force of the shell. The results of research show that the length of egg is 57.00 mm, width 44.59 mm with a coefficient of variation from 2.7 to 1.4%. The thickness of egg shell is on average 0.39 mm, in range from 0.377 to 0.416 mm. The share of shell is 10.54% of average weight of eggs (62.43 g). The quality of the tested eggs was quite uniform because the puncture force of egg shell ranged from 20.35 to 23.97 N. The research results are important for cage construction, design of egg collection equipment, design of egg packaging, and applicable in selection for obtaining new genotypes of laying hens with increased resistance to egg breaking.

In this work, we have studied the asymptotic behavior of Green's function and the reciprocity relation of the far-field pattern in the stratified ocean waveguide. Moreover, two direct sampling meth...

В повседневной клинической практике стоматолог чаще всего сталкивается с необходимостью ортопедического лечения имея в анамнезе одно или несколько эндодонтических вмешательств. К сожалению, современные стандарты даже первичной механической обработки корневого канала подразумевают значительное иссечение корневого дентина. Наиболее часто применяемые для восстановления супраструктуры литые металлические культевые вкладки помимо несомненных достоинств, имеют два выраженных недостатка - эстетический фактор и самый высокий процент перелома корня зуба. В связи с этим все более популярным становится использование прямых вкладок с использованием специализированного композита. Основным преимуществом применения специализированных культевых материалов является геометрическая точность механической обработки опорного зуба, с возможностью внутриротового сканирования и изготовления виртуального слепка, т.е., переход в цифровую стоматология и CAD/CAM технологии. Кроме того, отсутствие напряжения на границе тканей зуба и реставрации улучшают прочностные характеристики культи опорного зуба и, следовательно, продлевают срок службы несъемного протеза In everyday clinical practice, the dentist most often faces the need for orthopedic treatment with a history of one or more endodontic interventions. Unfortunately, current standards of even primary root canal machining involve significant excision of root dentin. In addition to the undoubted advantages, cast metal stump inserts most often used for buildup restoration have two distinct disadvantages - the aesthetic factor and the highest percentage of tooth root fracture. In this regard, the use of direct tabs using a specialized composite is becoming increasingly popular. The main advantage of using specialized stump materials is the geometric accuracy of machining the abutment, with the possibility of intraoral scanning and manufacturing of a virtual impression, i.e., the transition to digital dentistry and CAD/CAM technology. In addition, the absence of tension at the border of the tooth tissue and restoration improve the strength characteristics of the stump of the abutment tooth and, therefore, extend the life of the fixed prosthesis

Fluid catalytic cracking unit, whose batch operations are operated in a multirate mode, is a typical continuous process with batch operations. The integrated optimization of this problem can be formulated as a hybrid parametric dynamic optimization. To obtain a high-quality solution, adaptive direct methods are usually required to solve the problem iteratively. By exploiting the decomposable structure, a novel framework is proposed in this paper, which can obtain an equivalent or better precision solution with relatively coarse discretization. In detail, by designating the batch operations as complicating variables, an optimal solution and sensitivity information about batch operations are obtained by a nonconvex sensitivity-based generalized Benders decomposition algorithm. Then the optimal continuous operations are implemented as extra closed-loop controllers by tracking the necessary conditions of optimality, while the optimal batch operations are improved by a line search method. The practical potential of the framework is demonstrated with several operation modes.

Indirect, non-destructive methods to derive biophysical parameters, such as leaf area index (LAI), are of major importance for optimal grassland growth modelling and management. In this study, we compared different methods for the estimation of LAI in permanent grassland including (i) two direct methods, (ii) two indirect optical methods (AccuPAR and LAI-2200C), (iii) a proximal (field spectrometer) and a satellite remote sensing approach using Sentinel-2 (S-2) data, both based on radiative transfer modelling (RTM) of vegetation. To consider the seasonal variability of LAI sufficiently, we performed in situ measurements weekly during the entire growing season of 2018 and 2019. The RTM-based methods showed the lowest root-mean-square error (RMSE) when compared with direct green LAI measurements, which ranged from 1.68 to 7.85. The indirect optical methods resulted in higher RMSE values but in similar high correlation coefficients (r). The comparison between the indirect optical methods showed that the AccuPAR and the LAI-2200C highly correlate with a systematic underestimation of the AccuPAR in the upper range of LAI values. As expected, S-2 and the field spectrometer showed the highest correlation (RMSE: 0.40 and r: 0.95). Generally, we observed a significant influence of the seasonal changes of the canopy structure and morphology on the estimation accuracy.

Hybrid frequency synthesizers based on direct methods of digital and analog synthesis were examined. The possibilities of applying synthesizers as heterodynes of modern spectrum analyzers built on the superheterodyne plan were studied. The possibility of using a hybrid synthesizer as the heterodyne of the first cascade of spectrum analyzers was analyzed. The requirements for heterodynes of the first cascades of the mixing of spectrum analyzers are provided. A structural diagram of a broadband heterodyne generating frequencies in the range 4000–8000 MHz with a step not exceeding 1 Hz is presented. Formulas to calculate the fundamental frequency relations in the heterodyne structure were developed. A mathematical model of the power spectrum density of phase noises as a function of the offset frequency from the carrier was developed. With the aid of the created model, the noise characteristics of the proposed layout was examined. It is shown that at offset frequencies over 1 kHz from the carrier, a hybrid synthesizer based on direct digital and analog methods of synthesis has an advantage at a phase noise level 5–30 dB over low-noise heterodynes of modern spectrum analyzers. The advantages of the suggested layout by which the hybrid synthesizer is capable of improving the technical characteristics of modern spectrum analyzers are defined.

The origin-free modulus sum function SM refines the set Φ of phases of the structure factors by maximizing the coincidence between the experimental origin-free modulus function and the calculated one in terms of the ρ(Φ)2 density function [Rius, J. (1993). Acta Cryst. A49, 406–409]. Maximization is normally achieved through the recursive application of a Fourier-based algorithm. The purpose of the present study is: (i) to show that ρ(Φ)2 can be replaced by |ρ(Φ)| in SM; (ii) to illustrate the viability of the corresponding phasing algorithm with experimental data., MINECO & FEDER (grant No. RTI2018-098537-B-C21 ); Severo Ochoa Programme for Centres of Excellence in R&D (grant No. SEV-2015-0496).

Direct methods are applied to solve linear time-varying delay systems based on vector forms of block-pulse functions (BPFs) and triangular functions (TFs). Operational matrices of integration of BPFs and TFs are applied to transform linear time-varying delay systems to a linear set of algebraic equations. Further, some numerical examples are provided to indicate reliability and the accuracy of these methods. Convergence analysis of the proposed method has been discussed.

Special features in the process of determining the coordinates of sound anomalies according to the sound series were considered. Sound anomalies have been shown to be a source of information about events, phenomena that are already occurring, or are their harbingers. It has been stated that audio interception systems complement thermal imagers and provide savings in financial and human resources when used in combination with the benefits of unmanned aerial vehicles. The methods facilitating solution of the problem of surveillance and prediction by finding coordinates of sound anomalies were presented. Indirect methods for solving problems of searching for sound anomaly coordinates with three microphones in accordance with a linear scheme of approximants and linear and quadratic approximation were proposed. Solutions were reduced to analytical complete expressions that make it possible to calculate coordinates according to the input conditions for three or four microphones. Also, a problem of finding coordinates of a sound anomaly for three and four microphones was set and solved by direct methods. Solutions were presented as expressions that make it possible to calculate coordinates of sound anomalies. Numerical experiments were performed during which coordinates of sound anomalies, the absolute error of their determination at each iteration, and total time spent for calculation were found. Systems with coordinates of microphones and sound sources almost identical or coinciding have been shown to have the greatest error. Under these conditions, for direct methods, values of the equation coefficients decreased to almost zero or turned to zero and the difference of values of the sought coordinates between iterations increased sharply which slowed down the process of solution convergence. It was shown that the application of approximate methods to the search for coordinates by solving the minimization problems with the involvement of the recurrent approximation method makes it possible to construct simple algorithms. Their implementation to solve the problems of numerical experiments has given quick and practically accurate coordinate values. It was found, that the application of algorithms to the methods of logical analysis and rules of logical inference reduces the number of iterations and the total calculation time

This paper proposes a homotopy-based method for efficiently computing and precisely determining controlling unstable equilibrium points (CUEPs) in transient stability analysis and screening using direct methods. The proposed method is intended to overcome potential numerical convergence problems associated with computing CUEPs. These convergence problems are mostly due to irregularities in the region of convergence of CUEPs which make it difficult to determine suitable initial points. The most commonly used initial points in computing CUEPs are minimum gradient points (MGPs) on the stability boundary which in turn rely on the determination of exit points (Eps—points at which sustained-fault trajectories exit system stability boundaries). However, determination of MGPs and EPs are computationally involved and sophisticated numerical methods have been introduced such as stability-boundary-following procedure and shadowing method to correct the solution trajectory. The proposed method does not depend on MGPs and also does not require accurate EPs. The proposed method maps the solution from EPs to the CUEPs. The proposed method is applied on several known systems including the NE 39 bus system and the reduced WECC system and the results are provided. The results are compared with the traditional methods such as Boundary of stability region based CUEP method (BCU method).

Estimates for small areas defined by social, demographic, and geographic variables are increasingly important for official statistics. To overcome problems of small sample sizes, statisticians usually derive model-based estimates. When aggregated, however, the model- based estimates typically do not agree with aggregate estimates (benchmarks) obtained through more direct methods. This lack of agreement between estimates can be problematic for users of small area estimates. Benchmarking methods have been widely used to enforce agreement. Fully Bayesian benchmarking methods, in the sense of yielding full posterior distributions after benchmarking, can provide coherent measures of uncertainty for all quantities of interest, but research on fully Bayesian benchmarking methods is limited. We present a flexible fully Bayesian approach to benchmarking that allows for a wide range of models and benchmarks. We revise the likelihood by multiplying it by a probability distribution that measures agreement with the benchmarks. We outline Markov chain Monte Carlo methods to generate samples from benchmarked posterior distributions. We present two simulations, and an application to English and Welsh life expectancies.

The inclusion of large numbers of renewable energy sources (RESs) can lead to the operation of electric-power systems close to their natural stability limits. To improve stability, the flexibility and fast control of RESs can be exploited. However, RESs must be “told” what to do for the sake of the “common good”. One possibility is to apply global control based on energy functions, but this requires the appropriate mathematical tools and models. In addition to the “real power feed”, the RESs’ power converters, among others, offer the functionality of a static synchronous compensator (STATCOM). Therefore, the aim of this paper was to develop energy functions for a STATCOM—the ones that consider its control strategies and limitations—that can be applied in energy-function-based methods for a transient-stability assessment and improvement. The two main contributions of this paper derive from the developed energy function (EF). The first contribution is the ability to use a direct method for the transient-stability assessment of an EPS that includes STATCOMs. The second contribution is the application of the developed EF in the control strategies of STATCOM and RES for a globally optimal, transient-stability improvement that can be used as a reference for other, simpler and more applicable control strategies. Such a reference has not existed until now. The STATCOM’s energy functions were developed as additional expressions that can be added to the already-known energy function of the electric-power system in the structure-preserving frame. The correctness of the developed energy functions was proved by applying them in a direct method for the transient-stability assessment and a comparison of these results with those obtained with a numerical simulation. Examples of the use of energy functions for the control of a STATCOM’s reactive current show how the STATCOM can improve the transient stability in a globally optimal way and can be used as a reference for a STATCOM’s simpler control strategies based on local parameters. An example of a RES’s reactive current control that is based on the developed energy functions shows that the RES can be successfully applied for a transient-stability enhancement. The paper can be seen as the first step towards a globally optimal control of the RES during transients.

In scanning probe microscopy laser interferometers are usually used for measuring the position of the probe tip with a metrological traceability. As the most of the AFM setups are designed to work under standard atmospheric conditions the changes of the refractive index of air have an influence to measured values of the length with 1.0e-4 relatively. In order to achieve better accuracies the refractive index of air has to be monitored continuously and its instantaneous value has to be used for compensating the lengths measured by all of the interferometric axes. In the presented work we developed a new concept of an electronic unit which is able to monitor the refractive index of air on basis of measurement of ambient atmospheric conditions: temperature, humidity, pressure of the air and the CO2 concentration. The data processing is based on Ciddor equation for calculating the refractive index of air. The important advantage of the unit is a very low power consumption of the electronics so the unit causes only negligible temperature effects to the measured environment. The accuracy of the indirect measuring method employed by the unit was verified. We tested the accuracy in comparison with a direct method of measuring refractive index of air based on an evacuatable cell placed at the measuring arm of a laser interferometer. An experimental setup used for verification is presented together with a set of measurements describing the performance. The resulting accuracy of the electronic unit falls to the 4.1e-7 relatively., Comment: 8 pages, 4 figures; SPIE Optical Metrology 2013, 2013, Munich, Germany

Development of damage stability as a scientific subject, specifically in damage ship hydrodynamics and, generally, flooding risk assessment, has evolved primarily by inquisitive academics with support by people with vision and passion towards maritime safety enhancement from industry and Government, the latter in the wake of serious accidents. Notwithstanding this, the subject has seen remarkable development in a short period of time in terms of understanding process, and developing methods and tools for practical implementation of such developments. The stage has now been reached where large-scale EC and industry-funded projects are bringing all requisite knowledge and experience together towards implementation by end users with the view to institutionalizing such developments. The paper critically traces and presents key developments starting from basic concepts to a complete framework for performing numerical simulations of ship survivability in operational conditions in the seaway, leading to flooding risk assessment with application potential for new and existing ships with focus on the design phase but with operation potential in ship operation, the latter involving emergencies.

To design the structure of foundations and tunnels, one of the most important parameters to be well considered is the rock tensile strength (TS). Direct methods of TS measurement, i.e., laboratory experiments, are both costly and time-consuming. Therefore, to measure the rock TS, this paper proposes two novel hybrid optimization models, i.e. relevance vector regression (RVR) optimized by the harmony search (HS) and cuckoo search (CS) algorithms. A database including 76 datasets was constructed through collecting the rock samples from a tunnel site and exposing them to different tests (Brazilian tensile strength, BTS, as output) in laboratory. The proposed models performances were assessed through some statistical metrics, e.g., determination coefficient. The results demonstrated the successful application of RVR-HS and RVR-CS models in predicting BTS. However, the performance of RVR-HS was better than RVR-CS. As a conclusion, the HS algorithm played a great role in optimizing the proposed RVR model.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.Localization and mapping technologies are of great importance for all varieties of Unmanned Aerial Vehicles (UAVs) to perform their operations. In the near future, it is planned to increase the use of micro/nano-size UAVs. Such vehicles are sometimes expendable platforms, and reuse may not be possible. Compact, mounted and low-cost cameras are preferred in these UAVs due to weight, cost and size limitations. Visual simultaneous localization and mapping (vSLAM) methods are used for providing situational awareness of micro/nano-size UAVs. Fast rotational movements that occur during flight with gimbal-free, mounted cameras cause motion blur. Above a certain level of motion blur, tracking losses exist, which causes vSLAM algorithms not to operate effectively. In this study, a novel vSLAM framework is proposed that prevents the occurrence of tracking losses in micro/nano-UAVs due to the motion blur. In the proposed framework, the blur level of the frames obtained from the platform camera is determined and the frames whose focus measure score is below the threshold are restored by specific motion-deblurring methods. The major reasons of tracking losses have been analyzed with experimental studies, and vSLAM algorithms have been made durable by our studied framework. It has been observed that our framework can prevent tracking losses at 5, 10 and 20 fps processing speeds. vSLAM algorithms continue to normal operations at those processing speeds that have not been succeeded before using standard vSLAM algorithms, which can be considered as a superiority of our study.

This paper deals with cross-kink waves in the (2+1)-dimensional KP–BBM equation in the incompressible fluid. Based on Hirota’s bilinear technique, cross-kink solutions related to KP–BBM equation are constructed. Taking the special reduction, the exact expression of different types of solutions comprising exponential, trigonometric and hyperbolic functions is obtained. Moreover, He’s variational direct method (HVDM) based on the variational theory and Ritz-like method is employed to construct the abundant traveling wave solutions of the (2+1)-dimensional generalized Hirota–Satsuma–Ito equation. These traveling wave solutions include kinky dark solitary wave solution, dark solitary wave solution, bright solitary wave solution, periodic wave solution and so on, which are all depending on the initial hypothesis for the Ritz-like method. In continuation, the modulation instability is engaged to discuss the stability of the obtained solutions. Moreover, the rational [Formula: see text] method on the generalized Hirota–Satsuma–Ito equation is investigated. The applicability and effectiveness of the acquired solutions are presented through the numerical results in the form of 3D and 2D graphs. A variety of interactions are illustrated analytically and graphically. The influence of parameters on propagation is analyzed and summarized. The results and phenomena obtained in this paper enrich the dynamic behavior of the evolution of nonlinear waves.

C(27)H(20)N(2)O(3), MW = 420, orthorhombic, Pbc2(1), a = 4.686(2), b = 16.784(8), c = 25.924(10)Å, V = 2039Å(3), d(obs) = 1.37 g cm(−3) (flotation), d(calc) = 1.369g cm(−3), Z = 4. The structure has been determined by direct methods and refined to R = 0.045 based on 1419 independent reflections. No crystallographic symmetry element is present in the dixanthylurea molecule. In fact, the molecule is considerably distorted from any possible mirror symmetry. The molecules are hydrogen bonded in an infinite chain along the a-axis. The compound is of interest because of its role in the analytical determination of urea.

We describe an algorithm to extract the complex refractive index of a material from broadband reflectance and transmittance measurements taken by spectrophotometers. The algorithm combines Kramers–Kronig analysis with an inversion of Fresnel’s equations to provide a direct method of solving for the refractive index which is accurate, even for weakly absorbing materials, and easily applicable to radiative heat transfer calculations. The algorithm is validated by extracting the complex refractive index of polydimethylsiloxane between 0.25 μm and 100 μm and comparing against existing literature. We also discuss the importance of broadband optical properties to passive radiative cooling and details of the uncertainty analysis of the algorithm.

The ascertainment of magnetic aromaticity is not necessarily straightforward, especially for large and bent systems, such as the cycloporphyrin nanorings recently synthesized by the group of Anderson. Six of these cycloporphyrin nanorings were studied here computationally. Indirect methods, based on nuclear shielding and magnetizabilities, and direct methods, based on standard quantum mechanics, were both used effectively to determine their magnetically induced current strength, which mostly confirmed Anderson’s classification. However, in the case of hexanions, and in particular for cyclohexaporphyrin hexacations, a significant cancellation of delocalized diatropic and paratropic flow occurred, showing that the resultant faint aromatic character was a result of competing aromatic and antiaromatic contributions, as also evidenced by the ipsocentric method. A warning is renewed on the use of isotropic shielding to determine the tropicity of the magnetically induced current.

Vehicle speed is a crucial input for mechanistic-based design and maintenance decision making of asphalt pavement. It can be measured using direct methods and indirect methods. Direct metho...