Microscopic-Phenomenological Model of Glass Transition and Temperature Dependence of Viscosity—Part I: Foundations of the Model

The glass transition is described as a time- and history-independent singular event, which takes place in an interval dependent on the distribution width of molecular vibration amplitudes. The intrinsic glass transition is not seen as a relaxation phenomenon, but is characterized by a fixed volumetric state at the glass temperature Tg0. The relaxation behavior of the transport properties depends on the distance to Tg0. Free volume is redefined and its generation is the result of the fluctuating transfer of thermal energy into condensed matter and the resulting combined interactions between the vibration elements. This creates vacancies between the elements which are larger than the cross-section of an adjacent element or parts thereof. Possible shifts of molecules or molecular parts through such apertures depend on the size and axis orientation and do not require further energetic activation. After a displacement, additional volume is created by delays in occupying abandoned positions and restoring the energetic equilibrium. The different possibilities of axis orientation in space result in the different diffusive behavior of simple molecules and chain molecules, silicate network formers, and associated liquids. Glass transformation takes place at a critical volume Vg0 when the cross-section of apertures becomes smaller than the cross-section of the smallest molecular parts. The glass transition temperature Tg0 is assigned to Vg0 and is therefore independent of molecular relaxation processes. Tg0 is well above the Kauzmann and Vogel temperatures, usually just a few degrees below the conventionally measured glass temperature Tg(qT). The specific volume at the two temperatures mentioned above cannot be achieved by a glass with an unordered structure but only with aligned molecular axes, i.e. in a crystalline state. Simple liquids consisting of non-spherical molecules additionally alter their behavior above Vg0 at Vglwhere the biggest gaps are as small as the largest molecular diameter. Tgl is located in the region of the crystalline melting point Tm. Both regions, above and below Tm, belong to different physical states and have to be treated separately. In the region close to Vg0 respectively Tg0, the distribution of vibration amplitudes has to be taken into account. The limiting volume Vg0 and the formation of apertures larger than the cross-section of the vibrating elements or parts thereof, in conjunction with the distribution width of molecular vibrations as Vg0 is approached, and the spatial orientation of the molecular axes is key to understanding the glass transition.

ACE2 Is an Adjacent Element of Atherosclerosis and COVID-19 Pathogenesis

COVID-19 is a highly contagious new infection caused by the single-stranded RNA Sars-CoV-2 virus. For the first time, this infection was recorded in December 2019 in the Chinese province of Wuhan. The virus presumably crossed the interspecies barrier and passed to humans from a bat. Initially, the disease was considered exclusively in the context of damage to the respiratory system, but it quickly became clear that the disease also entails serious consequences from various systems, including the cardiovascular system. Among these consequences are myocarditis, myocardial damage, subsequent heart failure, myocardial infarction, and Takotsubo syndrome. On the other hand, clinical data indicate that the presence of chronic diseases in a patient aggravates the course and outcome of coronavirus infection. In this context, the relationship between COVID-19 and atherosclerosis, a condition preceding cardiovascular disease and other disorders of the heart and blood vessels, is particularly interesting. The renin-angiotensin system is essential for the pathogenesis of both coronavirus disease and atherosclerosis. In particular, it has been shown that ACE2, an angiotensin-converting enzyme 2, plays a key role in Sars-CoV-2 infection due to its receptor activity. It is noteworthy that this enzyme is important for the normal functioning of the cardiovascular system. Disruptions in its production and functioning can lead to various disorders, including atherosclerosis.

INVESTIGATION OF LOCAL UNLOADING OF AN ELEMENT IN A FINITE ELEMENT CONTINUUM

The subcritical elastoplastic deformation and the fracturing of an element of a finite element continuum in the Ansys Workbench complex are considered. When solving the elastoplastic problem of the subcritical deformation, a finite element with the failure criterion reached is selected. In a pre-fracture state of the element, the nodal forces provided by the interaction with an adjacent element are determined using the Ansys Workbench internal procedure. The following step is the consideration of the varying stress-strain state of the body during the element destruction. The elastoplastic problem is solved in the conditions of simple unloading of the body surface adjacent to the destructible element while maintaining the external load corresponding to the destruction initiation. When implementing the local unloading, a possibility of the new plastic region formation and the partial unloading are studied. As a result, the stress-strain state of the body at the beginning of local unloading is not the same as that at the end of the process. The proposed approach differs from the “element killing” procedure when the element stiffness after the failure criterion reached is assumed to be close to zero. The paper provides solutions to the problems of deformation of elastic and elastoplastic plates with a side cut taking into account their element destruction.

Predicting forming limit diagrams for AZ31 magnesium alloy and 7050 aluminum alloy by numerical simulation

Forming limit diagram (FLD) is the most intuitive method to evaluate and analyze the forming performance of sheet metal, which is widely used in production. To examine the formability of AZ31 magnesium alloy and 7050 aluminum alloy, the simplified bulging models based on the Nakazima experiment are established by ABAQUS finite element (FE) software, and the maximum punch force criterion is adopted as the instability criterion. The forming limit diagrams of 7050 high-strength aluminum alloy at room temperature and AZ31 magnesium alloy at warm working conditions are obtained by extracting the in-plane strain of the adjacent element of the maximum strain element at the moment of instability. Compared with experimental observation shows that the Nakazima virtual model established in this paper can accurately predict FLD. In addition, the influences of lubrication conditions and virtual punching speeds on the bulging process of AZ31 and AA7050 sheet metals are also investigated. The results show that the better the lubrication environment, or the lower the punching speed, the better the formability of the sheet, and reducing the punching speed has a more significant improvement effect on the formability of AZ31 sheets.

Ultra Wide Band Multiple Input Multiple Output Antenna for Internet of Things Applications

This paper mainly gives information about a compact 4-element multiple input multiple output (MIMO) antenna which is useful for IOT applications. Advantages of the proposed antenna is that it can be easily extendable for a large size array. The array consists of 4 elements placed at an angle of 90 degree to the adjacent element. The substrate used in the design is a low loss laminate of FR4 with dielectric constant of 4.4. Based on the results obtained the antenna covers a UWB band of 2.4 GHz–13.0 GHz and the isolations also exceed 20 dB. Return loss, radiation pattern and isolation is plotted. The simulation results show that the proposed antenna can perform well for MIMO devices. The proposed antenna is much suitable for the applications of IOT and RADAR.

Rare Earth Elements – Environmental occurrence and mobilities

<p></p><p></p><p>Because the abundances of rare earth elements are strongly intercorrelated, lacking data can be estimated from adjacent element concentrations. Because Ce can be oxidized to Ce(IV) and Eu can be reduced to Eu(II), deviations from the calculated values have been defined as positive or negative anomalies. The anomalies permit conclusions of mineral weathering, transportation and adsorption.</p><p>Anomalies detected in soils did not cause respective anomalies in apple leaves, blossom leaves nor fruits, which prevents conclusions of geographical origin. In the apple plants, Ce showed negative anomalies throughout, particularly in the blossom leaves. To the contrary, Eu showed positive anomalies throughout, particularly in the green leaves, which suggests uptake similar to Ca.</p><p>In green leaves (apples) growing in the temperate climatic zone, concentrations of rare earth elements increase with age, like for other elements of low physiological interaction also, whereas nutritional and essential trace elements remain constant or decrease.</p><p> </p>

Adaptation algorithm for the finite element mesh in the problems of the fracture of solids under dynamic loads

Представлен алгоритм эрозионного разрушения, позволяющий адекватно описывать разрушение материалов в области контактного взаимодействия. В результате работы данного алгоритма в области контактного взаимодействия происходит перестроение конечно-элементной сетки и пересчет сосредоточенных масс в узлах расчетной сетки в соответствии с законом сохранения массы. Представлена методика ускорения данного алгоритма путем использования параллельных вычислений. Результаты численного моделирования качественно и количественно хорошо согласуются с экспериментальными данными. The present work suggests algorithm enabling to adequately describe fracture of materials and structures under impulse loading. The methodology of reconfiguration finite element mesh with recomputation of concentrated masses in nodes is considered. The algorithm uses all the capabilities of modern parallel computing to the full extent and can be easily scaled for all possible objectives. There are various approaches to implement surface erosion of interacting bodies under high-velocity loading. Authors used the approach for which in the case when one or several nodes of the fractured element no longer belong to the other elements, then their mass is equally distributed between the remaining nodes of this element (erosion fracture algorithm). The most time-consuming part of the algorithm of erosion fracture is searching of adjacent planes of elements. In order to accelerate data, preparation for erosion fracture algorithm searching algorithm of adjacent planes of elements was optimized. Optimization was performed using the method of sorting of all planes for all elements and their correlation with each other. The exact optimization of the algorithm includes the following steps: initially all finite element mesh is divided into N areas and searching for the adjacent plane for the element i is at first performed in the area it belongs to and then it proceeds to adjacent areas, the maximum number of areas where the search of adjacent element can be performed is 27. The areas for search were defined according to the maximum capability of an adjacent plane to get into it. Unfortunately, not the entire program code can be realized simultaneously, there are some areas which require consequent calculation, therefore, improvement of the performance with the increased number of cores is non-linear. However, along with the increase in the size of computation mesh the efficiency of using larger number of cores grows significantly. Application of erosion fracture algorithm is required for appropriate description of the processes of fracture propagation under high-velocity interaction of solid bodies. Dividing the computation mesh into areas provides significant performance improvement for erosion fracture algorithm during the data preparation stage. Decrease in the size of area results in reduced relative number of elements getting into the main area, which influences negatively the processing time. Time which the processor spends on data preparation should be taken into account, it still contributes to the total time to the less extent as compared to the iterations on searching the adjacent planes of finite elements.

Synthesis of non-uniform circular antenna arrays with multiple constraints

Synthesis of non-uniform circular antenna arrays using a hybrid invasive weed optimization is introduced in this paper. The excitation weights and positions of array elements are optimized to reduce the peak side lobe level (PSLL) of the radiation pattern. The method proposed in this paper can effectively constrain the number of the array elements, size of the array, and the angular spacing of the adjacent element simultaneously. The radiation pattern has the constraint of a fixed major lobe beamwidth. Synthesis results of three different circular antenna arrays are given. The results show the effectiveness and feasibility of the proposed synthesis method in non-uniform circular antenna arrays.

Accurate Prediction Approach of 3D Trimming Line for Auto Panel Part

It is difficult to obtain 3D trimming line using traditional prediction methods for auto panel parts. An initial geometrical development method with element layer is proposed based on one step inverse analysis theory for this problem. The flange mesh can be unfold onto the die surface layer by layer according to nodal adjacent element relation, then the above development mesh is smoothed by mesh smoothing method with sliding constraint surface in order to delete overlap and distorted mesh, the 3D initial mesh can be obtained for one step inverse analysis method. The accurate 3D trimming line of auto panel part can be achieved by plasticity iteration of one step inverse analysis. A typical real part of 3D trimming line prediction is selected to prove this method, the comparison results between the simulated and experimental values show that this method has enough precision and can handle complex parts, satisfies the engineering practical demands.