Research and Diagnostics Laboratory of Pressure Resistive Sensors for Composites

The use of sensors prevents the shortened service life, wear and tear, and decreased accuracy due to degradation during operation. For sensors prone to inaccuracy, a “sensor-device-program” diagnostic assembly has been created. Such a circuit is capable of autonomous diagnosis, calibration and evaluation, up to and including autonomous recalibration of sensors. The diagnostic device also has a shock test function. The purpose of the operation is to deliberately increase the life and accuracy of the sensor under test. The diagnostic device is designed for testing under laboratory conditions and verifies the correctness of the diagnostic algorithm. The result of diagnostics is a report on the current state of the sensor and the changes compared to the past states. The current state includes estimates of accuracy, range, sensitivity or error parameters such as strain constant, maximum Po value and others. Thus, the degradation of selected parameters can be monitored and a mathematical calculation of the results can be applied to possibly improve/correct the sensor errors. By recording force levels, it will be known what force was applied to the sensor during the measurement and thus protects against damage from overloading. The maximized life is achieved through a combination of the accuracy control, calibration performance and error estimation. As a result, the conventional industrial sensor will be a reliable tool for industrial measurements, not just laboratory measurements.

Change of air temperature in Crimea

The article presents the results of spatial and temporal dynamics research of the air temperature fields on the territory of the Crimean Peninsula due to the change of circulation epochs and periods of the Northern Hemisphere. Average multiannual maps of air temperature on the Crimean Peninsula for each circulating epoch and period were obtained, as well as maps of temperature fields dynamics at their change. Based on the obtained analysis of the maps it was found out that change in air temperature occurred not synchronously, but had its own characteristics in different regions of the Crimean Peninsula, which is explained by the influence of local factors. Zones characterized by constant maximum air temperatures in all considered periods have been recorded. It was found that during the instrumental observations on the Crimean Peninsula the warming occurred by 1 °C. This warming was occurring during the last circulation period.

Mixing Times of Markov Chains on Degree Constrained Orientations of Planar Graphs

We study Markov chains for $\alpha$-orientations of plane graphs, these are orientations where the outdegree of each vertex is prescribed by the value of a given function $\alpha$. The set of $\alpha$-orientations of a plane graph has a natural distributive lattice structure. The moves of the up-down Markov chain on this distributive lattice corresponds to reversals of directed facial cycles in the $\alpha$-orientation. We have a positive and several negative results regarding the mixing time of such Markov chains. A 2-orientation of a plane quadrangulation is an orientation where every inner vertex has outdegree 2. We show that there is a class of plane quadrangulations such that the up-down Markov chain on the 2-orientations of these quadrangulations is slowly mixing. On the other hand the chain is rapidly mixing on 2-orientations of quadrangulations with maximum degree at most 4. Regarding examples for slow mixing we also revisit the case of 3-orientations of triangulations which has been studied before by Miracle et al.. Our examples for slow mixing are simpler and have a smaller maximum degree, Finally we present the first example of a function $\alpha$ and a class of plane triangulations of constant maximum degree such that the up-down Markov chain on the $\alpha$-orientations of these graphs is slowly mixing.

Inapproximability of the Partition Function for the Antiferromagnetic Ising and Hard-Core Models

Recent inapproximability results of Sly (2010), together with an approximation algorithm presented by Weitz (2006), establish a beautiful picture of the computational complexity of approximating the partition function of the hard-core model. Let λc($\mathbb{T}_{\Delta}$) denote the critical activity for the hard-model on the infinite Δ-regular tree. Weitz presented anFPTASfor the partition function when λ < λc($\mathbb{T}_{\Delta}$) for graphs with constant maximum degree Δ. In contrast, Sly showed that for all Δ ⩾ 3, there exists εΔ> 0 such that (unless RP = NP) there is noFPRASfor approximating the partition function on graphs of maximum degree Δ for activities λ satisfying λc($\mathbb{T}_{\Delta}$) < λ < λc($\mathbb{T}_{\Delta}$) + εΔ.We prove that a similar phenomenon holds for the antiferromagnetic Ising model. Sinclair, Srivastava and Thurley (2014) extended Weitz's approach to the antiferromagnetic Ising model, yielding anFPTASfor the partition function for all graphs of constant maximum degree Δ when the parameters of the model lie in the uniqueness region of the infinite Δ-regular tree. We prove the complementary result for the antiferromagnetic Ising model without external field, namely, that unless RP = NP, for all Δ ⩾ 3, there is noFPRASfor approximating the partition function on graphs of maximum degree Δ when the inverse temperature lies in the non-uniqueness region of the infinite tree$\mathbb{T}_{\Delta}$. Our proof works by relating certain second moment calculations for random Δ-regular bipartite graphs to the tree recursions used to establish the critical points on the infinite tree.

Using the Nonlinear Kinematic Hardening Material Model of Chaboche for Elastic–Plastic Ratcheting Analysis

Commonly used design codes for power plant components and pressure vessels include rules for ratcheting analysis that specify limits on accumulated strain. No guidance is provided on the use of the material model. The objective of the paper is to provide guidance that may be helpful to analysts. The Chaboche nonlinear kinematic (NLK) hardening material model is chosen as an appropriate model. Two methods are selected for its calibration that can determine the parameters for stainless steels. One is manual that requires no outside software and the other uses finite element software. Both are based on the monotonic stress–strain curve obtained from a tension specimen. The use of the Chaboche parameters for cases when ratcheting is caused by cyclic temperature fields is selected as the example of an application. The conclusion is that the number of allowable design cycles is far higher when using the parameters with temperature dependency than those at the constant maximum temperature that is being cycled.

On Galileo’s Tallest Column

The height at which an unloaded column will fail under its own weight was calculated for first time by Galileo for cylindrical columns. Galileo questioned himself if there exists a shape function for the cross section of the column with which it can attain a greater height than the cylindrical column. The problem is not solved since then, although the definition of the so named “constant maximum strength” solids seems to give an affirmative answer to Galileo’s question, in the form of shapes which seem to attain infinite height, even when loaded with a useful load at the top. The main contribution of this work is to show that Galileo’s problem is (i) an important problem for structural design theory of buildings and other structures, (ii) not solved by the time being in any sense, and (iii) an interesting problem for mathematicians involved in related but very different problems (as Euler’s tallest column). A contemporary formulation of the problem is included as a result of a research on the subject.

Impact of Sr on the performance of BaTi0.9Zr0.1O3–BaTiO3 dielectric powders

BaTi 0.9 Zr 0.1 O 3– Ba 1-x Sr x TiO 3 fine-powders are synthesized by two-step liquid phase method. Phase analysis and microstructure evaluation conducted by X-ray diffraction and scanning electron microscopy confirm the perovskite structure of the ceramic grain. Different Sr content is considered to optimize the density and dielectric performance. The dielectric constant increases and dielectric loss decreases with the rising of Sr content until x = 0.05. At the doping content of 5%, the dielectric constant maximum of 42,430 and excellent Y5V dielectric material can be obtained due to composition inhomogeneity and compact properties. Its dielectric properties are as follows: ε RT = 36,914, tan δ < 0.09, ΔC/C 20° C at -30° C and 80°C are -58.98% and 14.94%, respectively, and the breakdown strength Eb ≥ 5.2 kV ⋅ mm -1.

Investigation of Fatigue Crack Acceleration under Variable Amplitude Loading for a Structural Steel and Aluminium Alloy

There are currently serious doubts about the accuracy of Miners rule for designing welded structures subjected to variable amplitude loading, particularly under spectra cycling down from a constant maximum stress. The deficiency has been attributed primarily to stress interaction effects that cause crack growth acceleration. In this paper the crack growth response of a structural steel and an aluminium alloy to a loading spectrum designed to promote fatigue crack acceleration is studied and the potential mechanisms responsible are evaluated.

Terminal Area Energy Management Trajectory Planning for an Unpowered Reusable Launch Vehicle with Gliding Limitations

RLVs' gliding capability, determined by its maximum dive and maximum range, provided a significant restriction in TAEM trajectory planning in this paper. The maximum-dive trajectory was generated based on Eq.(3) for a constant maximum dynamic pressure. In the guidance, it was optimized to be Eq.(13) for the open-loop command of bank angle in HAC segment. The simplified closed-loop command of angle of attack contained errors of altitude and path angle except the controlled velocity. Energy propagating as Eq.(8) calculated the reference velocity for the speed brake to track. Finally, an illustrative example was given to confirm the efficiency of the trajectory planning algorithm and optimized command. The simulation results in Fig.2 and Fig.3 indicate the proposed trajectory planning algorithm and guidance method are useful for the gliding capability limited RLV's TAEM with initial deviations.