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Number of results: 192
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Abstract

Actuellement la linguistique arabe met en usage le terme et la notion du type “néo-arabe” afin que definer les changements structureles communs aux dialectes arabes modernes. L’analyse contrastif des categories grammaticales et de leurs paradigms montre qu’il n’est pas facile de construir un modèle commun au “Néo-arabe”. Il ne s’agit que d’une tendance commune des reductions et des innovations.
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Abstract

The central theme of this work was to analyze high aspect ratio structure having structural nonlinearity in low subsonic flow and to model nonlinear stiffness by finite element-modal approach. Total stiffness of high aspect ratio wing can be decomposed to linear and nonlinear stiffnesses. Linear stiffness is modeled by its eigenvalues and eigenvectors, while nonlinear stiffness is calculated by the method of combined Finite Element-Modal approach. The nonlinear modal stiffness is calculated by defining nonlinear static load cases first. The nonlinear stiffness in the present work is modeled in two ways, i.e., based on bending modes only and based on bending and torsion modes both. Doublet lattice method (DLM) is used for dynamic analysis which accounts for the dependency of aerodynamic forces and moments on the frequency content of dynamic motion. Minimum state rational fraction approximation (RFA) of the aerodynamic influence coefficient (AIC) matrix is used to formulate full aeroelastic state-space time domain equation. Time domain dynamics analyses show that structure behavior becomes exponentially growing at speed above the flutter speed when linear stiffness is considered, however, Limit Cycle Oscillations (LCO) is observed when linear stiffness along with nonlinear stiffness, modeled by FE-Modal approach is considered. The amplitude of LCO increases with the increase in the speed. This method is based on cantilevered configuration. Nonlinear static tests are generated while wing root chord is fixed in all degrees of freedom and it needs modification if one requires considering full aircraft. It uses dedicated commercial finite element package in conjunction with commercial aeroelastic package making the method very attractive for quick nonlinear aeroelastic analysis. It is the extension of M.Y. Harmin and J.E. Cooper method in which they used the same equations of motion and modeled geometrical nonlinearity in bending modes only. In the current work, geometrical nonlinearities in bending and in torsion modes have been considered.
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Abstract

Successful implementation of an active vibration control system is strictly correlated to the exact knowledge of the dynamic behavior of the system, of the excitation level and spectra and of the sensor and actuator’s specification. Only the correct management of these aspects may guarantee the correct choice of the control strategy and the relative performance. Within this paper, some preliminary activities aimed at the creation of a structurally simple, cheap and easily replaceable active control systems for metal panels are discussed. The final future aim is to control and to reduce noise, produced by vibrations of metal panels of the body of a car. The paper is focused on two points. The first one is the realization of an electronic circuit for Synchronized Shunted Switch Architecture (SSSA) with the right dimensioning of the components to control the proposed test article, represented by a rectangular aluminum plate. The second one is a preliminary experimental study on the test article, in controlled laboratory conditions, to compare performances of two possible control approach: SSSA and a feed-forward control approach. This comparison would contribute to the future choice of the most suitable control architecture for the specific attenuation of structure-born noise related to an automotive floor structure under deterministic (engine and road-tyre interaction) and stochastic (road-tyre interaction and aerodynamic) forcing actions.
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Abstract

In the paper, the authors discuss the numerical and experimental modal analysis of the cantilever thin-walled beams made of a carbon-epoxy laminate. Two types of beams were considered: circumferentially asymmetric stiffness (i.e., CAS) and circumferentially uniform stiffness (i.e., CUS) beams. The layer-up configurations of the laminate were chosen to get a vibration mode coupling effect in both analysed cases. The aim of the paper was to perform the numerical and experimental modal analysis of the composite structures, when a flapwise bending with torsion coupling effect or flapwise-chordwise bending coupling effect took place. Firstly, numerical studies by the finite element method was performed. The numerical simulations were carried out by the Lanczos method in the Abaqus software package. The natural frequencies and the corresponding free vibration modes were determined. Next, the experimental modal analyses of the CAS and CUS beams were performed. The test stand was consisted of a special grip, two beams with an adhered holder, the LMS Scadas III system with a modal hammer and an acceleration sensor. Finally, the results of both methods were compared.
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Abstract

The human environment consists of a large variety of mechanical and biomechanical systems in which different types of contact can occur. In this work, we consider a monopedal jumper modelled as a three-dimensional rigid multibody system with contact and simulate its dynamics using a structure preserving method. The applied mechanical integrator is based on a constrained version of the Lagrange-d’Alembert principle. The resulting variational integrator preserves the symplecticity and momentum maps of the multibody dynamics. To ensure the structure preservation and the geometric correctness, we solve the non-smooth problem including the computation of the contact configuration, time and force instead of relying on a smooth approximation of the contact problem via a penalty potential. In addition to the formulation of non-smooth problems in forward dynamic simulations, we are interested in the optimal control of the monopedal high jump. The optimal control problem is solved using a direct transcription method transforming it into a constrained optimisation problem, see [14].
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Abstract

Formation of modern landscapes of Zaporizhzhya region occurred in the Holocene period. During the Holocene wet phase changing climate fairly arid, warm - rather cold, but the average climatic indicators were close to modern. These conditions contributed to the formation of steppe zonal type of landscape. However, due to prolonged exposure to diverse steppe landscapes economic impacts associated with mismanagement of their natural potential and increasing human pressure on the natural environment has been transformed natural landscapes and change their properties. The result of this action was that the area landscapes drastically reduced. Zaporizhzhya region was the most economically mastered in all regions of Ukraine. To further study the issues to optimize environmental management of the region, the article reproduced a modern structure of landscapes area. The area characterized Zaporizhzhya region lowland class and type steppe landscapes. Three subtypes of landscapes: the north, middle and dry steppe. Each subtype is divided into land. Within North steppe subtype isolated Dniester-Dnieper and the Left-Bank Dnepr-Azov province. Medium steppe subtype is represented by the Black Sea margin, and dry steppe - Black sea-Azov. The most popular items on the optimization of environmental management are landscaped areas and areas of morphological units within them. That level reflects the nature of the landscape area inside the area landscape differentiation. Within the Zaporizhzhya region allocated 7 landscaped areas: highland Azov, highland-Dnieper south slope, Kinsko-Yalinska low-lying, low-lying Azov, the Dnieper-Molochansk low-lying, Western Azov-slope highland and lowland Prisivasko-Priazov.
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Abstract

The paper looks at an analysis of the tendency of changes in the fuel structure of electricity generation and thus resulting changes in carbon dioxide emissions. Forecasts drawn up by various institutions and organizations were selected for the analysis. Firstly, on the basis of statistical data contained in (IEA 2017a, IEA 2008) and with the use of Kay’s indicators, the impact of changes in energy intensity of the national income and energy mix on changes in carbon dioxide emissions per capita in 2006–2015 for the OECD countries and Poland were analyzed. A small effect of changes was found in the fuel mix in this period of time on the emissions. The main impact was due to changes in the energy intensity of the national income and changes in the national income per capita. Next, selected fuel scenarios for the period up to 2050 (60) were discussed – WEC, IEA, EIA, BP, Shell, with a focus on the WEC scenarios. These have been developed for various assumptions with regard to the pace of economic development, population growth, and developments of the political situation and the situation on the fuel market. For this reason, it is difficult to assess the reliability thereof. The subject of the discussion was mainly the data on the fuel structure of electricity generation and energy intensity of national income and changes in carbon dioxide emissions. The final part of the paper offers a general analysis of forecasts drawn up for Poland. These are quite diverse, with some of them being developed as part of drawing up the Energy Policy for Poland until 2050, and some covering the period up to 2035. An observation has been made that some forecasts render results similar to those characteristic of the WEC Hard Rock scenario.
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Abstract

A revision of the standard approach to characterization of thin-semiconductor-layer Hall samples has been proposed. Our results show that simple checking of I(V) curve linearity at room temperature might be insufficient for correct determination of bias conditions of a sample before measurements of Hall effect. It is caused by the nonlinear behaviour of electrical contact layers, which should be treated together with the tested layer a priori as a metal-semiconductor-metal (MSM) structure. Our approach was examined with a Be-doped p-type InAs epitaxial layer, with four gold contacts. Despite using full high-quality photolithography a significant asymmetry in maximum differential resistance (Rd) values and positions relative to zero voltage (or current) value was observed for different contacts. This suggests that such characterization should be performed before each high-precision magneto-transport measurement in order to optimize the bias conditions.
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Abstract

Social and Economic Costs of Spatial Disorder in Agriculture. The main objective of the study was the identification of the phenomena of chaos in the structure and spatial organization of agriculture, that is the agrarian fragmentation of farms, exclusion of land from agricultural production in suburban zones and the fragmentation of the agricultural landscape. These processes cause a major increase in economic and social costs, which results in the loss of resources and spatial disorder in agriculture. An attempt was made to estimate the costs of these processes in economic, social and environmental terms. The economic dimension of spatial disorder in agriculture is manifested by negative results in the production and consumption sphere related most often to high labour costs, and consequently to low incomes. The social dimension of spatial disorder in agriculture is demonstrated by the effects of de-agrarization processes and deformation of social structures. De-agrarization means the processes of agricultural area reduction, extensification and fallowing as well as an increasingly limited significance of agriculture as a workplace and a reduction in the source of income by rural residents. A conducted analysis of spatial disorder in agriculture resulting from the lack of appropriate regulation and taxation systems as well as historical factors allowed determining direct and indirect results influencing the structure and spatial organization of agriculture. Direct results include: a chessboard pattern of agricultural land, marginalization of the agricultural function in rural areas which mostly applies to suburban zones, unregulated ownership of farmland, its unjustified designation for other purposes, a decrease in biodiversity in agriculture and fragmentation of the agricultural landscape. Indirect results include: an increase in the costs of agricultural production, expensive agricultural-installation plans, loss of direct payments, easement appurtenant, the emergence of human-environment conflicts and major transformations of the agricultural landscape in a suburban zone.
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Abstract

The aim of the current study was to examine the structure of an alloy treated at various temperatures up to 2,000–2,100 °C. Among research techniques for studying alloy structure there were the electron and optical microstructure, X-ray structure, and spectral analysis, and for studying the developed furnace geometric parameters the authors employed mathematical modeling method. The research was performed using aluminum smelting gas-fired furnaces and electric arc furnaces. The objects of the study were aluminum alloys of the brand AK7p and AK6, as well as hydrogen and aluminum oxide in the melt. For determining the hydrogen content in the aluminum alloy, the vacuum extraction method was selected. Authors have established that treatment of molten aluminum alloy in contact with carbon melt at high temperatures of 2,000–2,100 °C has resulted in facilitating reduction of hydrogen and aluminum oxide content in the melt by 40-43% and 50-58%, respectively, which is important because hydrogen and aluminum oxide adversely affect the structure and properties of the alloy. Such treatment contributes to the formation of the extremely fine-grained microstructure of aluminum alloy.
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Abstract

The resistance of cast iron to abrasive wear depends on the metal abrasive hardness ratio. For example, hardness of the structural constituents of the cast iron metal matrix is lower than the hardness of ordinary silica sand. Also cementite, the basic component of unalloyed white cast iron, has hardness lower than the hardness of silica. Some resistance to the abrasive effect of the aforementioned silica sand can provide the chromium white cast iron containing in its structure a large amount of (Cr, Fe)7C3 carbides characterised by hardness higher than the hardness of the silica sand in question. In the present study, it has been anticipated that the white cast iron structure will be changed by changing the type of metal matrix and the type of carbides present in this matrix, which will greatly expand the application area of castings under the harsh operating conditions of abrasive wear. Moreover, the study compares the results of abrasive wear resistance tests performed on the examined types of cast iron. Tests of abrasive wear resistance were carried out on a Miller machine. Samples of standard dimensions were exposed to abrasion in a double to-and-fro movement, sliding against the bottom of a trough filled with an aqueous abrasive mixture containing SiC + distilled water. The obtained results of changes in the sample weight were approximated with a power curve and shown further in the study.
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Abstract

This paper presents a control concept for a single-axle mobile robot moving on the horizontal plane. A mathematical model of the nonholonomic mechanical system is derived using Hamel’s equations of motion. Subsequently, a concept for a tracking controller is described in detail. This controller keeps the mobile robot on a given reference trajectory while maintaining it in an upright position. The control objective is reached by a cascade control structure. By an appropriate input transformation, we are able to utilize an input-output linearization of a subsystem. For the remaining dynamics a linear set-point control law is presented. Finally, the performance of the implemented control law is illustrated by simulation results.
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Abstract

We apply a fluid-structure interaction method to simulate prototypical dynamics of the aortic heart-valve. Our method of choice is based on a monolithic coupling scheme for fluid-structure interactions in which the fluid equations are rewritten in the 'arbitrary Lagrangian Eulerian' (ALE) framework. To prevent the backflow of structure waves because of their hyperbolic nature, a damped structure equation is solved on an artificial layer that is used to prolongate the computational domain. The increased computational cost in the presence of the artificial layer is resolved by using local mesh adaption. In particular, heuristic mesh refinement techniques are compared to rigorous goal-oriented mesh adaption with the dual weighted residual (DWR) method. A version of this method is developed for stationary settings. For the nonstationary test cases the indicators are obtained by a heuristic error estimator, which has a good performance for the measurement of wall stresses. The results for prototypical problems demonstrate that heart-valve dynamics can be treated with our proposed concepts and that the DWR method performs best with respect to a certain target functional.
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Abstract

The aim of this paper is to compare some geometric parameters and deflections of a sandwich meta-structure with its classic, three-layer counterpart. Both structures are composed of the same materials and have the same external dimensions and mass, but their middle layers (cores) are different. The core of the sandwich meta-structure is a new spatial structure itself, consisting of there-layer bars. The core of the classic sandwich structure is a layer of the continuum. To make the comparison more general and convincing, three geometrical parameters, i.e., ratio of interfacial contact (Ric), interlayer bonding factor (Ibf) and coefficient of impact sensitivity (Cis), were introduced and applied. Deflections of the structures, simply supported at the edges and loaded in the mid-span by a static force, have been measured and are presented in the paper. Potential advantages of the new meta-structure are briefly outlined.
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Abstract

The paper presents the method and results of low-frequency noise measurements of modern mid-wavelength infrared photodetectors. A type-II InAs/GaSb superlattice based detector with nBn barrier architecture is compared with a high operating temperature (HOT) heterojunction HgCdTe detector. All experiments were made in the range 1 Hz - 10 kHz at various temperatures by using a transimpedance detection system, which is examined in detail. The power spectral density of the nBn’s dark current noise includes Lorentzians with different time constants while the HgCdTe photodiode has more uniform 1/f - shaped spectra. For small bias, the low-frequency noise power spectra of both devices were found to scale linearly with bias voltage squared and were connected with the fluctuations of the leakage resistance. Leakage resistance noise defines the lower noise limit of a photodetector. Other dark current components give raise to the increase of low-frequency noise above this limit. For the same voltage biasing devices, the absolute noise power densities at 1 Hz in nBn are 1 to 2 orders of magnitude lower than in a MCT HgCdTe detector. In spite of this, low-frequency performance of the HgCdTe detector at ~ 230K is still better than that of InAs/GaSb superlattice nBn detector.
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Abstract

The dual core bit-byte CPU must be equipped with properly designed circuits, providing interface between the two processor units, and making it possible to exploit all its advantages like versatility of the byte unit and speed of the bit unit. First of all, the interface circuits should be designed in such a way, that they don’t disturb maximally parallel operation of the units, and that the CPU as a whole works in the same manner as in a standard PLC. The paper presents hardware solutions supporting effective operation of PLC CPU-s. Possibilities of solving problems concerning data exchange between a CPU and peripheral circuits were presented, with a special stress on timers and counters, and also on data exchange between the bit unit and the byte unit. The objective of the proposed solutions is to decrease the time necessary for a CPU to access its peripheries.
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