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In the paper the properties of solids were considered as the result of various scales structures interaction. The paper presents the model of the oscillatory interaction of four-scaled structures in solids. In the model exchange of energy between structural levels is described as evolution of the dynamic system. Obviously that evolution of this dynamical system is described by various types of attractors in the four-dimensional phase space. To determine these types and their effect on the processes of self-organization and conductivity in the model visualization of attractors is provided. For this, the trajectory of the system in phase space was dissected by a three-dimensional analogue of the Poincare cross-sections specially designed by authors to solve this problem.

The paper treats Schwarzschild spaces as a model for gravity features. We study a wrapped product of metrics of Schwarzschild spaces. The paper demonstrates that there are two substantial components and coeffcients can be calculated basing on the physical considerations. We treated a phenomenon of gravitational distortion of beams, moving from periphery of the Universe to the terrestrial observer. The centers of active galactic nuclei (AGN) were selected as point sources of such quanta. The galaxies were selected as distant as possible due to the limitations on the registered distance. We defined the spatial properties of the quanta trajectories depending on the distribution of galaxies along the way of the beam.

In this paper, we clarify the duplicated electromagnetic characteristics between the proposed two-beam overmoded multi-gap structure published in the paper titled “Tractable resonant structure with two nonuniform beams for a high-power 0.22-THz extended interaction oscillator” [Bi et al., IEEE Electron Device Lett. 42(6), 931–934 (2021)] and conventional multi-gap structures from the physical concept point of view. The replacement of the TE10 mode by the TE30 mode used in the interaction gaps provides the basis for the duplicated electromagnetic field distributions and frequencies between the two structures. The concept of magnetic coupling is proposed to support the resonant condition that supports duplication of the TE30 field and the frequency of the single-gap structure into the periodic standing-wave field of the multi-gap structure. With this concept, the perturbation of different axial phase shifts across one period to the standing-wave field of the TE30-0 mode is analyzed to clarify the profiles of the dispersion curves of the TE30 mode in the overmoded structure and the TE10 mode in the conventional structure. To demonstrate the profiles, a 220-GHz overmoded and conventional structure with nine gaps is designed, and their dispersion curves are obtained by using eigenmode simulations. In addition, the effect of the difference in the boundary conditions of the geometries of these two structures on the magnetic field distribution is analyzed to demonstrate the duplication of the ohmic losses between the two structures. The physical analysis in the duplicated electromagnetic characteristics lays a foundation for the promising design of the overmoded structure with two beams for high frequency extended interaction oscillators.

We obtain the phase diagram of the hard core lattice gas with third nearest neighbor exclusion on the triangular lattice using Monte Carlo simulations that are based on a rejection-free flat histogram algorithm. In a recent paper [J. Chem. Phys. 151, 104702 (2019)], it was claimed that the lattice gas with third nearest neighbor exclusion undergoes two phase transitions with increasing density, with the phase at intermediate densities exhibiting hexatic order with continuously varying exponents. Though a hexatic phase is expected when the exclusion range is large, it has not been seen earlier in hard core lattice gases with short range exclusion. In this paper, by numerically determining the entropies for all densities, we show unambiguously that there is only a single phase transition in the system between a low-density fluid phase and a high-density ordered sublattice phase, and that a hexatic phase is absent. The transition is shown to be first order in nature and the critical parameters are determined accurately., Comment: 11 pages, 5 figures, 63 references

High-precision wind power prediction could reference the optimal dispatch and stable operation of the power system. This paper proposes an adaptive hybrid optimization algorithm that integrates decomposition and reconstruction to effectively explore the potential characteristics and related factors of wind power output and improve the accuracy of short-term wind power prediction. First, the extreme-point symmetric mode decomposition is used to analyze the periodicity, trend, and abrupt characteristics in the original wind power sequence and form multiple intrinsic mode functions with local time-domain characteristics. Then, considering the similarity of the feature sequence and the efficiency of the prediction algorithm, the permutation entropy is used to reconstruct the components with close time-domain characteristics to form subsequences that could reflect different spectral characteristics. Then, the improved maximum relevance minimum redundancy-the long short-term memory-the adaptive boosting algorithm model is used to determine the prediction model structure, parameters, and optimal feature factors of the subsequences. Finally, the prediction results of each subsequence are integrated to obtain the final wind power. Taking a wind farm in northern Shaanxi as the application object, the prediction accuracy and efficiency of the methods proposed in this paper are compared in terms of the decomposition method, prediction model, and prediction timeliness. The results show that in the 15 min to 3 h forecast periods, compared with other models, the mean absolute error and root mean square error of the proposed model are increased. At the same time, as the forecast period grows, the superiority of the proposed method is more prominent.

This paper takes the annular solar eclipse that occurred in China on June 21, 2020, as the background and conducts tests and analysis of shortwave timing sky wave signals. The test group continuously tested the signal field strength data from June 20, 2020, to June 23, 2020. The results show that the shortwave signal field strength on June 21, the day of the annular eclipse, is significantly weaker than that on two other days—before and during the annular eclipse—and there are three obvious jumps in the field strength value. (1) The first jump occurs more than one hour before the annular eclipse, and then, the field strength has an oscillatory attenuation. Between the first jump and the second jump, the overall change trend of the field strength value is an oscillatory decline one. (2) About 25 min before the beginning of the eclipse, the second jump of the field strength occurs; from the second jump to the third jump, that is, before the occurrence of the beginning of the eclipse and the transition phase from the beginning to the middle of the eclipse, the value of the field strength has an oscillatory increase. (3) During the period of 8:00–8:10, the field strength shows a third jump. Although the field strength oscillates after the third jump, it has no obvious increasing or decreasing trend. Based on the results of previous studies on the annular eclipse on that day and the analysis of the theoretical model of radio wave propagation, this paper preliminarily considers that the change in signal field strength is supposed to be caused by the impact of the outbreak of the annular eclipse on the ionosphere. When the annular eclipse occurred, the sunlight reaching the ground is blocked by the Moon, and the ionization degree of electrons in the ionosphere is reduced, resulting in an increase in the penetration factor, and the overall performance of the shortwave signal reaching the ground is weakened.

The paper [Djenidi et al., Phys. Fluids 33(3), 031703 (2021)] considers a classical issue of an anomalous scaling of velocity structure functions in a high-Reynolds number turbulent flow. The paper offers a mathematical proof of the ground-breaking result: the intermittency is an artifact of the Reynolds number finiteness. However, the proof contains a technical error that makes this conclusion ungrounded.

Laminar-to-turbulent transitional flow plays a key role in determining the overall aerodynamic performance of turbomachinery. In this paper, the physical mechanisms concerning transitional flow inside compressor cascade passages at low Reynolds number condition are investigated based on the large eddy simulations. Two categories of cascade flow simulations are conducted: one is for the quasi three-dimensional (3D) cascade flow without endwalls, i.e., the translational periodic boundary conditions are employed for hub and shroud surfaces, while the other focuses on the fully 3D cascade passage flow. Special emphasis is placed on the effect of endwalls on the laminar-to-turbulent transitional flow inside the compressor cascade passage. In addition, two levels of freestream turbulent intensity are set in these simulations. It is concluded that the endwall boundary layer flow has a non-ignorable influence on transitional flows in the lower-span region. Under the condition of low freestream turbulence intensity, the original laminar separation-induced transition pattern dominating the mid-span suction surface evolves to become natural and bypass transition flow when approaching the endwall region. With increase in the incoming turbulent intensity, the natural transitional flow disappears, and the cascade suction surface is dominated by the bypass transitional flow. Moreover, the blade loading near endwall is reduced and the aerodynamic loss on lower spanwise airfoil sections is substantially increased when compared to the cascade without endwall. The physical mechanisms concerning transitional flow described in this paper might provide some meaningful guidance toward developing advanced turbomachinery.

This contribution is to add to the timely celebration of Professor R. B. Bird's outstanding career and accomplishments. Following introductory remarks on material/fluid types, the paper reviews the concept of yield stress. Although yield stress has been studied for several decades, it is still very much a topic of current interest. This paper covers phenomenological yield stress models as well as experimental techniques to measure yield stress. It also discusses, in particular, problems associated with very low yield stress measurements that occur with bio-fluids such as blood.

The aircraft skin is an important component of the aircraft, and its integrity affects the flight performance and safety performance of the aircraft. Damage detection technology with ultrasonic nondestructive testing as the core has played an important role in aircraft skin damage detection. Due to the difficulty in aircraft skin detection, relying solely on the ultrasonic A-scan equipment has very low detection efficiency. The introduction of artificial intelligence can effectively improve the detection efficiency. This paper establishes the one-dimensional convolutional neural network and single shot multibox detector network, which is based on the SSD network and uses dilated convolution to improve the real-time tracking of the ultrasonic probe. At the same time, 1DCNN is introduced to classify the ultrasonic A-scan signal. Finally, the detection results of the two are combined to achieve the reflection of the internal conditions of the aircraft skin. After testing, the algorithm can identify skin simulation specimens, and its recognition accuracy is 96.5%, AP is 90.9%, and kappa is 0.996. Comparing the improved SSD network with networks such as SSD, YOLOv3, and Faster R-CNN, the results show that the improved network used in this paper is more excellent and effective. At the same time, the detection effects of four types of optimization algorithms and five learning rates are studied, and finally, the corresponding signal classification model adopts Adam and the learning rate of 0.0001 has the best effect.

This paper considers a pure electron plasma, with a small admixture of negative ions, confined in a Penning–Malmberg trap. When a diocotron mode is excited on the plasma, the end sheaths of the plasma are azimuthally distorted. During reflection at a distorted end sheath, an ion steps off of the surface characterizing the drift motion in the plasma interior, and this step produces transport. The diocotron mode transfers canonical angular momentum to the ions, and in response damps. These transport mechanism and associated damping are called rotational pumping. It is particularly strong when the axial bounce motion and the rotational drift motion, in the rotating frame of the mode, satisfy a resonance condition. This paper calculates the transport flux of ions and the associated damping rate of the mode in the resonant regime. Previous papers have discussed the theory and the experimental observation of rotational pumping for the special case of a diocotron mode with azimuthal wave number l = 1, and this paper extends the theory to modes with l≠1, which may sound like a trivial extension, but in fact is not.

Recently, the COVID-19 virus pandemic has led to many studies on the airborne transmission of expiratory droplets. While limited experiments and on-site measurements offer qualitative indication of potential virus spread rates and the level of transmission risk, the quantitative understanding and mechanistic insights also indispensably come from careful theoretical modeling and numerical simulation efforts around which a surge of research papers has emerged. However, due to the highly interdisciplinary nature of the topic, numerical simulations of the airborne spread of expiratory droplets face serious challenges. It is essential to examine the assumptions and simplifications made in the existing modeling and simulations, which will be reviewed carefully here to better advance the fidelity of numerical results when compared to the reality. So far, existing review papers have focused on discussing the simulation results without questioning or comparing the model assumptions. This review paper focuses instead on the details of the model simplifications used in the numerical methods and how to properly incorporate important processes associated with respiratory droplet transmission. Specifically, the critical issues reviewed here include modeling of the respiratory droplet evaporation, droplet size distribution, and time-dependent velocity profile of air exhaled from coughing and sneezing. According to the literature review, another problem in numerical simulations is that the virus decay rate and suspended viable viral dose are often not incorporated; therefore here, empirical relationships for the bioactivity of coronavirus are presented. It is hoped that this paper can assist researchers to significantly improve their model fidelity when simulating respiratory droplet transmission.

This paper examines the evolution of closing the Reynolds-averaged Navier–Stokes equations by approximating the Reynolds stresses via the second-moment transport equations themselves. This strategy first proposed by Rotta is markedly in contrast to the more usual approach of computing an effective “turbulent viscosity” to deduce the turbulent stresses as in a Newtonian fluid in laminar motion. This paper covers the main elements in the development of this approach and shows examples of applications in complex shear flows that collectively include the effects of three-dimensional straining, force fields, and time dependence that affect the flow evolution in ways that cannot be readily mimicked with an eddy viscosity model.

The extended interaction oscillator has high power and efficiency advantages for terahertz vacuum electronic devices. The ladder line is a crucial high-frequency structure with strong coupling ability and can interact with the sheet beam to significantly improve the beam-wave interaction efficiency and is widely studied and implemented. This paper presents an optimized structure, expanding the cavities on both sides based on the original ladder line structure. The TM11 mode is effectively suppressed in the optimized structure so that the sheet beam can interact with the TM31 mode, and the cavity characteristic impedance R/Q and output power are significantly improved. Based on the theoretical derivation of the original structure and the approximated analysis of the optimized structure, the change in dispersion with structure is discussed in this paper. The field distribution in the optimized structure based on the 0.22-THz frequency band is further studied and compared with the original structure by numerical calculation and particle simulation. Furthermore, the optimal operating voltage and output window parameters are analyzed using Particle-in-Cell software, and the surface loss simulation results are given. Finally, the cavity characteristic impedance R/Q is increased by 66.7%, the bandwidth is slightly increased compared with the original structure, and the output power is increased by 163.8%. The results of the preliminary processing and cold test are presented.

Vacuum leakage is extremely harmful to aircraft and needs to be discovered as soon as possible. Aiming at the problem of vacuum leakage location, this paper proposes a cross-correlation wavenumber domain imaging method. This method obtains the time-space domain information of the leakage elastic wave through the array sensor and transforms it into the frequency-wavenumber domain through the three-dimensional Fourier transform. The direction of the maximum value of the wavenumber vector represents the direction of the leakage source. In the algorithm, the cross-correlation operation is added, and the synchronous acquisition of multiple array elements is replaced by the polling scan method, which greatly improves the possibility of the realization of the algorithm. A 64-element ultrasonic sensor was fabricated and the method was verified. The results show that the method proposed in this paper can realize the continuous leakage signal direction of the planar structure and is applicable to the leakage holes of different apertures, and it has the potential for application on orbiting spacecraft and aircraft.

This paper presents further development of the new semi-classical trajectory-based formalism described in Paper I [Chistikov et al., J. Chem. Phys. 151, 194106 (2019)]. We report the results of simulation and analysis of the low-frequency collision-induced absorption (CIA) in CO2–Ar, including its true dimer component. Our consideration relies on the use of ab initio intermolecular potential energy and induced dipole surfaces for CO2–Ar calculated in an assumption of a rigid CO2 structure using the CCSD(T) method. The theory, the details of which are reported in Paper I [Chistikov et al., J. Chem. Phys. 151, 194106 (2019)], permits taking into account the effect of unbound and quasi-bound classical trajectories on the CIA in the range of a rototranslational band. This theory is largely extended by trajectory-based simulation of the true bound dimer absorption in the present paper. The spectra are obtained from a statistical average over a vast ensemble of classical trajectories restricted by properly chosen domains in the phase space. Rigorous classical theory is developed for two low-order spectral moments interpreted as the Boltzmann-weighted average of the respective dipole functions. These spectral moments were then used to check the accuracy of our trajectory-based spectra, for which both spectral moments can be evaluated independently in terms of specific integrals over the trajectory-based calculated spectral profiles. Good agreement between the spectral moments calculated as integrals over the frequency domain or the phase space largely supports the reliability of our simulated CIA spectra, which conform with the available microwave and far-infrared observations.

A recently developed mixing length model of the turbulent shearing stress has been shown to generate a universal velocity profile that provides an accurate approximation to incompressible pipe flow velocity profiles over a wide Reynolds number range [B. J. Cantwell, “A universal velocity profile for smooth wall pipe flow,” J. Fluid Mech. 878, 834–874 (2019)]. More recently, the same profile was shown to accurately approximate velocity profiles in channel flow, the zero pressure gradient boundary layer, and the boundary layer in an adverse pressure gradient [M. A. Subrahmanyam, B. J. Cantwell, and J. J. Alonso, “A universal velocity profile for turbulent wall flows,” AIAA Paper No. 2021-0061, 2021 and M. A. Subrahmanyam, B. J. Cantwell, and J. J. Alonso, “A universal velocity profile for turbulent wall flows including adverse pressure gradient boundary layers,” J. Fluid Mech. (unpublished) (2021)] The universal velocity profile is uniformly valid from the wall to the free stream at all Reynolds numbers from zero to infinity. At a low Reynolds number, the profile approaches the laminar channel/pipe flow limit. The primary measure of the Reynolds number used in this work is the friction Reynolds number Rτ=uτδ/ν. It is a little unusual to use Rτ for the boundary layer since it requires that the velocity profile be cutoff using an arbitrarily defined overall boundary layer thickness, δ. Because of the slow approach of the velocity to the free stream, different conventions used to define the thickness lead to different values of Rτ assigned to a given flow. It will be shown in this paper that, through its connection to channel/pipe flow, the universal velocity profile can be used to define a practically useful, unambiguous, measure of overall boundary layer thickness, called here the equivalent channel half height, δh. For Rτ>≈5000, the universal velocity profile defines a Reynolds number independent shape function that can be used to generate explicit expressions for the infinite Reynolds number behavior of all the usual integral boundary layer measures; displacement thickness, momentum thickness, energy thickness, overall boundary layer thickness, and skin friction. The friction coefficient Cf(Rδ2) generated by the universal velocity profile accurately approximates data over a wide range of momentum thickness Reynolds numbers collected by Nagib et al. [“Can we ever rely on results from wall-bounded turbulent flows without direct measurements of wall shear stress?,” AIAA Paper No. 2004-2392, 2004]. The universal velocity profile is used to integrate the von Kaŕman boundary layer integral equation [T. von Karman, “Uber laminaire und turbulente reibung,” Z. Angew. Math. Mech. 1, 233–252 (1921)] in order to generate the various thicknesses and friction velocity as functions of the spatial Reynolds number, Rx=uex/ν.

Strong oblique shock waves of granular flow are a steady-state solution formed when a granular free-surface flow deflects around a wedge-shaped obstacle at a supercritical speed, but they do not usually occur because their formation requires specific conditions to be satisfied downstream of the shock wave. This paper discusses the method of generating the strong oblique shock wave in a laboratory experiment and numerical simulation. The experiment is conducted on a plexiglass chute inclined at an angle to the horizontal, in which a dry granular material is released from a hopper at the top of the chute to form a channelized flow that passes a wedge at a downslope location. In order to generate a strong oblique shock wave, a second gate is established at the downstream of the wedge to control the material to flow out only at the designed time and height. Such a granular flowing process is simulated with a depth-averaged granular flow model, where the above two-gate system is mirrored into the inlet and outlet boundaries, respectively. The formation of the strong oblique shock is investigated through the transient solution of the flow field, and a good agreement is observed between the experiment and the simulation. Then, the steady-state solution of the interaction between the weak and strong oblique shocks is analyzed in the experiment and simulation. This result can be regarded as the third solution of granular shock because it can be formed by just changing the opening time of the second gate. With the dramatic change in flow thickness and velocity across the strong oblique shock, the bulk inertial number, used to quantify the rheological relation of granular materials, becomes extremely small, but it does not seem to affect the behavior of the flow discussed in this paper.

This paper deals with the investigations of the auxiliary glow discharge in the trigger unit of the pseudospark switch. The trigger unit communicates with the grounded electrode of the main high-voltage gap due to the aperture in the flat part of one of the trigger electrodes. Then, the so-called parasitic current closes to the main electrode via this aperture. This paper is mainly concentrated on the problem of the formation of the parasitic current for different regimes of the auxiliary discharge burning and for different designs of the trigger system. At a low current, the auxiliary discharge burns in the suppressed regime, and an increase in the current results in the stepwise transition to the ordinary glow discharge. The conditions of sustaining the auxiliary discharge influence on the value of the parasitic current. In the experiments, the cavity of the trigger electrode can play a role of the hollow cathode or the hollow anode, so that the negative glow plasma or the positive column plasma is generated in this hollow electrode. It is demonstrated that for both cases, the parasitic current is determined by the ion flow from the plasma boundary.

In this paper, for the first time, we have designed, simulated, and constructed an efficient air-conditioning system via a microwave plasma source to eliminate pathogens in the air, which can be found in crowded places such as hospitals and subways, and prevent the diseases' outbreak. The plasma air-conditioning system designed in this paper, besides having a high plasma density (increasing the probability of electrons collision with contaminants), uses a very high-temperature plasma (gas), which is an effective factor to eliminate any contamination. Also, to design and simulate the introduced system, COMSOL software, and its Electromagnetic Waves, Plasma, Laminar Flow, Heat Transfer in Fluids, and Bioheat Transfer modules were used; and the performance of the system has been entirely investigated. Finally, we have shown that the designed system, via an output power of 1000 W, a frequency of 2.45 GHz, and a standard airflow of 170 l/min, can destroy any microorganisms and pathogenic respiratory droplets in the air.

The single-crystal spectropolarimeter envisioned by Baronova and Stepanenko splits an incident x-ray beam into two beams with mutually orthogonal linear polarizations by using simultaneous reflections at the perfectly polarizing 45° Bragg angle on certain pairs of internal planes in hexagonal or cubic crystals. These planes intersect along a threefold symmetry axis, making a 120° angle with each other, and are typically symmetric with respect to the crystal surface. In practice, the wavelength of the diagnostic x-ray lines does not exactly satisfy Bragg's law for the crystal in the ideal polarizing orientation, so the extinction of reflections is incomplete. Accepting this limitation, this paper shows that for cubic crystals, other pairs of internal planes exist that satisfy the polarization requirements approximately. Typically, they are accessible from the perfect polarization-splitting geometry by small rotations of the crystal. This paper includes examples of such planes for cubic crystals with {110} and {211} surface cuts.

In this paper, a novel reduced order model based on a convolutional auto-encoder with self-attention (SACAE ROM) is proposed. The proposed model is a non-intrusive reduced order model, which uses a convolutional neural network and a long short-term memory network to extract temporal feature relationships from high-fidelity numerical solutions. The self-attention is introduced into the convolutional neural network to enhance the non-local information perception ability of the convolutional neural network and improve the feature extraction ability of the network. The model adopts a joint construction method, which overcomes the problem of propagating error in each process of the model. The model proposed in this paper has been verified on the problem of the flow around a cylinder. The experimental results indicate that the SACAE ROM has higher robustness and accuracy. Compared with the ROM based on a convolutional auto-encoder, the prediction error of the SACAE ROM is reduced by 42.9%. As with other ROMs based on deep neural networks, the SACAE ROM takes a long time to train. To solve this problem, the transfer and generalization ability of the model is studied in this paper. In the experiment, the flow velocity and spoiler of the flow around the cylinder were changed, and the training time of the transfer model was reduced by about 50% to 60%. This result demonstrates that the problem of too long training time can be solved by transfer learning.

This paper proposes a complementary frequency electromagnetic gyroscope. In this gyroscope, a voltage-controlled oscillator (VCO) is applied to generate complementary frequency signals and the angular rate detection is realized based on a phase-locked loop. The complementary frequency electromagnetic gyroscope can be fully realized by micro-electronic technology, which is beneficial to the miniaturization of the angular rate measurement system and has a wide application prospect. The complementary frequency electromagnetic gyroscope extends the application of the Sagnac effect and replaces the optical signal with the electromagnetic pulse signal. It can make full use of the advantages of microelectronic technology and microwave technology to realize the miniaturization of measuring components and even realize the system on a chip. In this paper, the mathematical model of the complementary frequency electromagnetic gyroscope is established and verified by simulation analysis. Theoretical analysis shows that the measured angular rate is proportional to the relative frequency difference of complementary VCO output. The simulation results indicate that the sensitivity of the complementary frequency gyroscope is 1 × 10−5 rad/s and is insensitive to noise. When the signal-to-noise ratio is lower than 0 dB, the gyroscope still has good angular rate measurement accuracy.

This paper investigates sound propagation in polydisperse heterogeneous porous composites. The two-scale asymptotic method of homogenization is used to obtain a macroscopic description of the propagation of sound in such composites. The upscaled equations demonstrate that the studied composites can be modeled as equivalent fluids with complex-valued frequency-dependent effective parameters (i.e., dynamic viscous permeability and compressibility) as well as unravel the sound energy dissipation mechanisms involved. The upscaled theory is both exemplified by introducing analytical and hybrid models for the acoustical properties of porous composites with different geometries and constituent materials (e.g., a porous matrix with much less permeable and/or impervious inclusions with simple or complex shapes) and validated through computational experiments successfully. It is concluded that the developed theory rigorously captures the physics of acoustic wave propagation in polydisperse heterogeneous porous composites and shows that the mechanisms that contribute to the dissipation of sound energy in the composite are classical visco-thermal dissipation together with multiple pressure diffusion phenomena in the heterogeneous inclusions. The results show that the combination of two or more permeable materials with highly contrasted permeabilities can improve the acoustic absorption and transmission loss of the composite. This paper provides fundamental insights into the propagation of acoustic waves in complex composites that are expected to guide the rational design of novel acoustic materials.

10.1063/5.0056530.4In this paper, we experimentally verify the phenomenon of chaotic synchronization in coupled forced oscillators. The study is focused on the model of three double pendula locally connected via springs. Each of the individual oscillators can behave both periodically and chaotically, which depends on the parameters of the external excitation (the shaker). We investigate the relation between the strength of coupling between the upper pendulum bobs and the precision of their synchronization, showing that the system can achieve practical synchronization, within which the nodes preserve their chaotic character. We determine the influence of the pendula parameters and the strength of coupling on the synchronization precision, measuring the differences between the nodes' motion. The results obtained experimentally are confirmed by numerical simulations. We indicate a possible mechanism causing the desynchronization of the system's smaller elements (lower pendula bobs), which involves their motion around the unstable stationary position and possible transient dynamics. The results presented in this paper may be generalized into typical models of pendula and pendula-like coupled systems, exhibiting chaotic dynamics.

It was of great significance to study the damage evolution mechanism of geomaterial/soil interfaces in landfill seepage control systems to evaluate the slope instability of landfill sites with high dam and large storage capacity. In this paper, the interfacial shear behaviors of geomaterial/soil were studied by drawing test. At the same time, the interface meso-test was used to analyze the change characteristics of geomaterial/soil interfaces during the drawing process. The results showed that under the synergistic action of the interface friction of geotextile/geomembrane and the reinforced shear band at the interface of geotextile/soil, the shear strength and interface stability of the composite geomaterial/soil interface not only increased but also improved. In order to describe the shear deformation and softening characteristics of the geomaterial/soil interfaces, a constitutive model of the interface was established based on the statistical damage theory to study the damage evolution mechanism of the interface under the action of drawing. The fitting results showed that the fitting correlation between the interface constitutive model established in this paper and the shear strength–drawing displacement curves obtained from the tests was greater than 0.97, which indicated that the constitutive model could better describe the shear deformation characteristics of the interface.

The use of low-emissivity coatings as an infrared (IR) stealth method for weaponry is an important guarantee for the survival of weaponry in the battlefield. The damage on low-emissivity coatings leads to a significant drop in the IR stealth performance of weaponry. Therefore, this paper carries out a research on the intelligent damage identification of low-emissivity coatings based on convolutional neural networks (CNNs). A low-emissivity coating damage dataset with the characteristics of large changes in brightness, distortion of images, and large changes in the target scale is constructed. A composite network (CompoNet) based on feature fusion is designed to extract the detailed features of damage and identify damage types. Compared with VGG16, the damage identification accuracy of CompoNet is improved by 5.49% points. The idea of specific feature extraction layers (SFELs) is proposed. Three SFELs are designed to extract the color, texture, and contour features, which are important basis for judging damage types. The SFEL accelerates the convergence of the model and increases the identification accuracy of the model by 2.02% points. The generative adversarial network is used to generate low-emissivity coating damage images, which solves the problem that the number of damage images collected is small due to practical difficulties. The final damage identification accuracy of the CompoNet fused with SFELs (CompoNet with SFELs) constructed in this paper reaches 99.17%, which is much higher than other generic CNNs.

The gas spark switch is the most used key device in pulsed power systems. As a difficult problem affecting the performance of the gas spark switch, electrode erosion has always been of wide concern and has been studied by scholars. In order to reduce electrode erosion, the erosion resistance of the electrode materials is particularly critical. At present, researchers at home and abroad mainly perform a large number of experiments to compare the erosion resistance of different electrode materials, which require a lot of time and are expensive. Based on the theoretical derivation of the erosion heat conduction process and the analysis of the molten pool movement process, a theoretical prediction model of erosion resistance of electrode materials is established in this paper. The prediction results of this model are consistent with the experimental results of most researchers in the past. In order to further verify the accuracy of this model, this paper selected six electrode materials [stainless steel, brass, RHEAs (Refractory High Entropy Alloys), 90WCu alloy, 70WCu alloy, and 50WCu alloy] tested for 10 000 times under the experimental conditions of a peak current of 30 kA, a single discharge charge transfer of 78 mC, and 2 bars dry air. The final experimental results show that the six electrode materials ranked from weak to strong in erosion resistance: brass, stainless steel, 50WCu, 70WCu, RHEAs, and 90WCu, which is consistent with the prediction results of the model.

Cathode erosion by ion sputtering is one of the primary erosion mechanisms in hollow cathode discharges. In this paper, the moving mesh approach coupling with a two-dimensional plasma fluid model was employed to simulate the cathode erosion process for 100 h in a hollow cathode arc discharge. In the numerical model, plasma transport, arc flow and heating, and cathode thermal balance were considered. In addition, the electron emission, ion bombardment, and surface radiation were taken into account on the cathode wall. The normal erosion depth on the cathode surface was defined to characterize the degree of cathode erosion. The results showed that the ion sputtering erosion was sensitive to the ion flux toward the cathode wall and the distribution of the plasma potential. The external magnetic field could mitigate the erosion process. The changes of erosion depth and position under different discharge currents, gas flow rates, and intensities of the applied magnetic field were also investigated in this paper.

In this paper, a reconfigurable one-dimensional single column plasma photonic crystal (SC-PPC) has been investigated. The SC-PPC is a glass column containing standing plasma density patterns (SPDPs) called plasma blobs, where its density varies sinusoidally along the column axis. It appears like a collinear array of the plasma blobs which is produced by having the critical combination of input RF power and gas pressure in a column. The numbers of blobs and plasma density can be controlled by RF power and gas pressure. The value of plasma density is measured for the different numbers of plasma blobs formation by using the experimental setup. These measured data are utilized in the modeling and simulation of SC-PPC for the photonic bandgap (PBG) analysis. The simulation outcomes reveal that the SC-PPC induces PBGs that can be reconfigured with plasma density, lattice constant, and numbers of plasma blobs. This paper explicitly investigates the PBG analysis by modeling two cases, where the plasma density N e = 2.45 × 10 16 m − 3 with five plasma blobs and N e = 9 × 10 16 m − 3 with six plasma blobs are considered. The obtained outcomes verify the reconfigurable characteristics of SC-PPC.

We prove a large deviation principle (LDP) and a fluctuation theorem (FT) for the entropy production rate (EPR) of the following $d$ dimensional stochastic differential equation \begin{equation*} d X_{t}=AX_{t} d t+\sqrt{Q} d B_{t} \end{equation*} where $A$ is a real normal stable matrix, $Q$ is positive definite, and the matrices $A$ and $Q$ commute. The rate function for the EPR takes the following explicit form: \begin{equation*} I(x)=\left\{ \begin{array}{ll} x\frac{\sqrt{1+\ell_0(x)}-1}{2}+\frac 12\sum\limits_{k=1}^{d} \left(\sqrt{\alpha_k^2- \beta_k^2\ell_0(x)}+\alpha_k\right) , & x\ge 0 , \\ -x\frac{\sqrt{1+\ell_0(x)}+1}{2} +\frac 12\sum\limits_{k=1}^{d} \left(\sqrt{\alpha_k^2- \beta_k^2\ell_0(x)}+\alpha_k\right) , &x, Comment: There are two reasons for replace the papers: 1. the title of the paper makes others misunderstand that the work is just a straightforward generalization of our work before; 2. the content in introduction is not comprehensive and does not indicate our main contributions, we have to make some big revisions to make this paper more readable

During the last decade, detection and manipulation of single vortex lines in bulk superconductors have been achieved experimentally. Electrodynamic response of pinned vortices in the high-frequency range is instrumental in studying specific aspects of their behavior. The present paper reviews the state of the art in studies of the oscillations of a single Abrikosov vortex in type II superconductors. The equations for free and forced oscillations of a single elastic vortex line are analyzed taking into account different forces affecting its motion: pinning, elasticity, viscosity and the Lorenz force. The equations also account for the inertial properties of a vortex due to various mechanisms of massiveness. The nature and magnitude of the vortex effective mass caused by some of the mechanisms are discussed in the paper. The roles of each force and inertia in the free oscillation spectrum are thoroughly analyzed. For the De Gennes and Matricon mode (at about a megahertz) with parabolic dispersion and the pi...

This paper discusses and analyzes the quasistatic optimal plasmonic dipole resonance of a small dielectric particle embedded in a lossy surrounding medium. The optimal resonance at any given frequency is defined by the complex valued dielectric constant that maximizes the absorption of the particle under the quasistatic approximation and a passivity constraint. In particular, for an ellipsoid aligned along the exciting field, the optimal material property is given by the complex conjugate of the pole position associated with the polarizability of the particle. In this paper, we employ the classical Mie theory to analyze this approximation for spherical particles in a lossy surrounding medium. It turns out that the quasistatic optimal plasmonic resonance is valid, provided that the electrical size of the particle is sufficiently small at the same time as the external losses are sufficiently large. Hence, it is important to note that this approximation cannot be used for a lossless medium, and which is also obvious, since the quasistatic optimal dipole absorption becomes unbounded for this case. Moreover, it turns out that the optimal normalized absorption cross sectional area of the small dielectric sphere has a very subtle limiting behavior and is, in fact, unbounded even in full dynamics when both the electrical size and the exterior losses tend to zero at the same time. A detailed analysis is carried out to assess the validity of the quasistatic estimation of the optimal resonance, and numerical examples are included to illustrate the asymptotic results.This paper discusses and analyzes the quasistatic optimal plasmonic dipole resonance of a small dielectric particle embedded in a lossy surrounding medium. The optimal resonance at any given frequency is defined by the complex valued dielectric constant that maximizes the absorption of the particle under the quasistatic approximation and a passivity constraint. In particular, for an ellipsoid aligned along the exciting field, the optimal material property is given by the complex conjugate of the pole position associated with the polarizability of the particle. In this paper, we employ the classical Mie theory to analyze this approximation for spherical particles in a lossy surrounding medium. It turns out that the quasistatic optimal plasmonic resonance is valid, provided that the electrical size of the particle is sufficiently small at the same time as the external losses are sufficiently large. Hence, it is important to note that this approximation cannot be used for a lossless medium, and which is also...

Since the publication of the Newman-Penrose (“NP”) equations in 1962 they have been regarded as simply a different version of the Einstein field equations (“EFEs”). This paper reports the fact that symmetry methods can be employed to reduce the complexity of the NP equations, reformulated in terms of the elements of the metric tensor rather than the spin coefficients, and to derive the exact solution in the reference frame of an observer who is in radial free fall through the external vacuum gravitational field of an isolated, non-rotating, spherically symmetric gravitating body. While the domain of the solution is confined to the axis along which the observer falls, it can be directly compared to the Schwarzschild solution and is shown to differ from that solution.Since the publication of the Newman-Penrose (“NP”) equations in 1962 they have been regarded as simply a different version of the Einstein field equations (“EFEs”). This paper reports the fact that symmetry methods can be employed to reduce the complexity of the NP equations, reformulated in terms of the elements of the metric tensor rather than the spin coefficients, and to derive the exact solution in the reference frame of an observer who is in radial free fall through the external vacuum gravitational field of an isolated, non-rotating, spherically symmetric gravitating body. While the domain of the solution is confined to the axis along which the observer falls, it can be directly compared to the Schwarzschild solution and is shown to differ from that solution.

In this paper, the resonant coil is used in the design of wireless power transfer (WPT) to investigate the efficiency of the system. Conventional 2 coil WPT having problem in power transfer as the distance increase the PTE decreases. Therefore, this paper analyzed the effect of adding the resonant coil to the conventional 2 coil WPT. The power transfer efficiency (PTE) is analyzed by varying the diameter of coil, thickness of coil, and adding the resonant coil at both transmitter and receiver. The coil are design and simulate by using CST software and the PTE result are calculated based on the s-parameter value. Thus, from the result and analysis, the best design of WPT is by adding the resonator with efficiency of PTE above 50% with distance of 50 cm separation between transmitter to receiver with resonant frequency consistently around 13.55MHz.

In this paper, the existence of Rayleigh waves in an anisotropic prestressed compressible elastic half space overlying by an anisotropic prestressed compressible elastic layer of arbitrary uniform thickness is discussed. The basic purpose of the paper is to derive explicit exact secular equation of the Rayleigh waves using the effective boundary conditions method. These secular equations are very useful for non-destructively finding the bounding between the layer and the half-space as well as their mechanical properties.

The paper presents the development of Magnetic Induction Tomography Setup based on eight - coil sensor array which has been designed for further non-destructive research on spatial distribution of electromagnetic parameters of tested elements. The applied method rests on time - varying magnetic field generation from excitation coil, detection of it in sensor coil due to inducted electromotive force and an impact the inserted element exerts upon the measured value by formation of eddy current in examined material. Number of coils used in the system is a trade-off between spatial resolution and complexity which effects on measurement time. The data acquisition system consists of PC computer controlling generation parameters (frequency and amplitude of signal) and acquiring of the measured values (voltage and phase shift in detecting coil) using LabVIEW graphical programming. Along with the computer there is a microcontroller responsible for completing both excitation and detection circuits by a proper pair of coils by manipulating 24 relays.The paper presents the development of Magnetic Induction Tomography Setup based on eight - coil sensor array which has been designed for further non-destructive research on spatial distribution of electromagnetic parameters of tested elements. The applied method rests on time - varying magnetic field generation from excitation coil, detection of it in sensor coil due to inducted electromotive force and an impact the inserted element exerts upon the measured value by formation of eddy current in examined material. Number of coils used in the system is a trade-off between spatial resolution and complexity which effects on measurement time. The data acquisition system consists of PC computer controlling generation parameters (frequency and amplitude of signal) and acquiring of the measured values (voltage and phase shift in detecting coil) using LabVIEW graphical programming. Along with the computer there is a microcontroller responsible for completing both excitation and detection circuits by a proper pair ...

In this paper, we present the simulations of an electrostatic quadrupole quadruplet (EQQ) lens system that will be used in a new sub-micron multi-ion beam for radiobiological studies. The new sub-micron beam will be used to carry out fine controlled irradiation of sub-cellular matrix with a variety of ions (H+, He2+, C6+) with energies up to 3 MeV/charge. Simulations using the SIMION 8.1 ® have shown that the EQQ lens system, configured with a symmetry normally used in a “Russian quadruplet”, can achieve a demagnification factor (Df) of 33 at a working distance (Dw) of ∼ 98 mm for a 3MeV/charge ion beam. Such focusing strength is comparable to the separated EQ sextuplet (EQS) lens system used in the sub-micron ion beam at Columbia university (Df ∼ 38 and Dw ∼ 126 mm) [1], but with a more compact lens design and two fewer quadrupoles. Calculations show that the chromatic and the spherical aberration of the EQQ lens system is comparable to those of the EQS lens system. This indicates that the EQQ lens system may be able to give a performance equivalent to the EQS in the Columbia University micro-ion beam when the object aperture is less than or equal to 30 µm. The compact design is expected to allow for precise alignment of the quadrupole electrodes and is intended to achieve stable micron beam spots at the target position.In this paper, we present the simulations of an electrostatic quadrupole quadruplet (EQQ) lens system that will be used in a new sub-micron multi-ion beam for radiobiological studies. The new sub-micron beam will be used to carry out fine controlled irradiation of sub-cellular matrix with a variety of ions (H+, He2+, C6+) with energies up to 3 MeV/charge. Simulations using the SIMION 8.1 ® have shown that the EQQ lens system, configured with a symmetry normally used in a “Russian quadruplet”, can achieve a demagnification factor (Df) of 33 at a working distance (Dw) of ∼ 98 mm for a 3MeV/charge ion beam. Such focusing strength is comparable to the separated EQ sextuplet (EQS) lens system used in the sub-micron ion beam at Columbia university (Df ∼ 38 and Dw ∼ 126 mm) [1], but with a more compact lens design and two fewer quadrupoles. Calculations show that the chromatic and the spherical aberration of the EQQ lens system is comparable to those of the EQS lens system. This indicates that the EQQ lens syste...

In this paper, we focus on the interdisciplinary relationship of Mathematics and Physics in the preparation of future mathematics teachers. We take into account the facts that arise from the ongoing school reform in the secondary school curriculum. Based on our years of experience, we assess their impact on the level of knowledge from the subject of Physics that a student should use in solving of the application problems related to the topic of the conic sections. Discussion about usage of the dynamic geometric software GeoGebra is included in this paper, too.

The paper introduces a new approach to magnify vibration responses of an object. In general, the higher the frequency of vibration, the lower the amplitude of displacement, so the response can be loaded by noise. The aim of this paper is to present practical application of the proposed approach in 3D digital image correlation method. This method uses two high speed cameras to measure displacements of the object. The phase-based motion magnification technique is used to magnify motion in captured image frames. Magnified frames are subsequently correlated to acquire displacement and deformation fields of the object. By this way, the amplified response is obtained. This approach also can be useful when the level of excitation is too low. The paper describes the experimental measurement that is based on the following procedure. As first the experimental modal analysis is performed and one of vibration mode is chosen for the further analysis. Thereafter, the object is excited using an acoustic exciter by harmonic signal with frequency of the chosen mode at two different amplitudes of excitation. The measurement with the higher level excitation is considered as the reference one. The responses acquired under the low level of excitation are subjected to the given procedure to magnify vibration motion. Results of both measurements are compared and commented.

This paper constructed a new high speed and power density servo motor design scheme based on magnetic pole eccentricity proposed according to the requirements of electrical performance parameters. The analytical formulae were deduced in view of the theory of thick-walled elastic cylinders and the actual model by analytical calculations and finite element calculations. The structure strength of permanent magnet was analyzed. Furthermore, comprehensively comparing and analyzing the calculation results of the two methods verify the accuracy of the analytical calculation method and the rationality of the permanent magnet structure design. In brief, this paper provides a reference for the design of high-speed motor magnetic pole eccentricity.

In paper [10], the class of sets, namely nano θ-preopen, nano θ-semiopen and nano θβ-open sets were introduced by using nano θ-open sets. Here we discuss some basic topological properties of continuous functions of the above said sets in nano topological spaces.In paper [10], the class of sets, namely nano θ-preopen, nano θ-semiopen and nano θβ-open sets were introduced by using nano θ-open sets. Here we discuss some basic topological properties of continuous functions of the above said sets in nano topological spaces.

This paper presents investigations on electron temperatures and potentials in steady and dilute plasma flows. The analysis is based on the detailed fluid model for electrons. Ionizations, normalized electron number density gradients, and magnetic fields are neglected. The transport properties are assumed as local constants. With these treatments, along an electron streamline, the partial differential equation for electron temperature simplifies as an ordinary differential equation, and two simple formulas for electron temperature and plasma potential are obtained. These formulas offer several insights, e.g., the electron temperature and plasma potential distributions along an electron streamline include several exponential functions.This paper presents investigations on electron temperatures and potentials in steady and dilute plasma flows. The analysis is based on the detailed fluid model for electrons. Ionizations, normalized electron number density gradients, and magnetic fields are neglected. The transport properties are assumed as local constants. With these treatments, along an electron streamline, the partial differential equation for electron temperature simplifies as an ordinary differential equation, and two simple formulas for electron temperature and plasma potential are obtained. These formulas offer several insights, e.g., the electron temperature and plasma potential distributions along an electron streamline include several exponential functions.

Cellular Automata have rich computational properties and provide many models in mathematical and physical processes. In this paper, We study the characterization of two dimensional linear Cellular Automata defined by the Von Neumann with neighborhood radius 2 of periodic boundary conditions over the field ℤ3. Transition rule matrix for periodic boundary condition and reversibility of Von Neumann with neighborhood cellular automata radius 2 of periodic boundary condition is studied.Cellular Automata have rich computational properties and provide many models in mathematical and physical processes. In this paper, We study the characterization of two dimensional linear Cellular Automata defined by the Von Neumann with neighborhood radius 2 of periodic boundary conditions over the field ℤ3. Transition rule matrix for periodic boundary condition and reversibility of Von Neumann with neighborhood cellular automata radius 2 of periodic boundary condition is studied.

The paper deals with homogenization of the generalized Poisson–Nernst–Planck problem stated in the disconnected domain composed of solid and pore phases. The nonlinear cross-diffusion transport equations are coupled with the Stokes flow model. At the interface between two phases, field variables are discontinuous allowing jumps, and nonlinear interface conditions describing electro-chemical reactions are taken into consideration. The first-order asymptotic corrector corresponding to the non-periodic interface data is derived rigorously and justified by residual error estimates within the homogenization procedure.The paper deals with homogenization of the generalized Poisson–Nernst–Planck problem stated in the disconnected domain composed of solid and pore phases. The nonlinear cross-diffusion transport equations are coupled with the Stokes flow model. At the interface between two phases, field variables are discontinuous allowing jumps, and nonlinear interface conditions describing electro-chemical reactions are taken into consideration. The first-order asymptotic corrector corresponding to the non-periodic interface data is derived rigorously and justified by residual error estimates within the homogenization procedure.

The paper presents basic principles of the Hyperuniverse theory and laws arising therefrom. Based on this theory, nature of gravity was explained, laws of periodic alterations in radius, velocity and acceleration of expansion (compression) of the Universe within the process of its motion on the surface of the five-dimensional torus of the Hyperuniverse were obtained, which are described in this article. Nature and multi-dimensional structure of Black Holes and Quasars is explained from the point of view of the Hyperuniverse theory. The paper describes in what way the process of exchange of matter and energy between parallel Universes is taking place. Theoretical possibility of non-destructive transfer of material objects between parallel Universes using local curvature of space is demonstrated.

Applications of the diffuse optical tomography to a thyroid cancer detection have been investigated by using the optical contrast. For the application, one needs to investigate effects of two factors (the diffusive reflection and refractive-index mismatch) at the tissue-trachea interface on light propagation in the human neck. In a previous work, the human neck was modeled as a two-dimensional circular heterogeneous medium consisting of a background medium and a circular void region, and the effects of the two factors at the medium-void interface in the simple heterogeneous medium were investigated using the time-dependent radiative transfer equation (RTE) in the time domain (TD). Nevertheless, the effects of the two factors in the continuous wave (CW) is still unclear because a crossover from the ballistic light to diffusive light in the CW differs from that in the TD. In this paper, we investigated the effects of the two factors using the steady-state RTE in the CW for the simple heterogeneous medium. The numerical results showed that the diffusive reflection dominated over the refractive-index mismatch at the medium-void interface even when the void region was located near the light source, where light is scattered anisotropically. The results in the CW were quite different from those in the TD, where the strong effects of the refractive-index mismatch were observed. The difference in the effects between the TD and CW is probably ascribed to a fact the refractive index influences in a shorter time scale compared to the time period for the average in the TD.Applications of the diffuse optical tomography to a thyroid cancer detection have been investigated by using the optical contrast. For the application, one needs to investigate effects of two factors (the diffusive reflection and refractive-index mismatch) at the tissue-trachea interface on light propagation in the human neck. In a previous work, the human neck was modeled as a two-dimensional circular heterogeneous medium consisting of a background medium and a circular void region, and the effects of the two factors at the medium-void interface in the simple heterogeneous medium were investigated using the time-dependent radiative transfer equation (RTE) in the time domain (TD). Nevertheless, the effects of the two factors in the continuous wave (CW) is still unclear because a crossover from the ballistic light to diffusive light in the CW differs from that in the TD. In this paper, we investigated the effects of the two factors using the steady-state RTE in the CW for the simple heterogeneous medium. T...

Natural convection heat sinks are still important in many industrial applications thanks to their simple design, effectiveness and noise-free operation. In this paper we present some case studies of experimental determination of the thermal characteristics of such devices, carried out using an innovative three-dimensional method of position detection for the temperature transducer (thermocouple). The three-dimensional position detection system uses acoustic waves emitted by a small grid of four loudspeakers, which simultaneously emit pseudo-random noise sequences orthogonal to one another. A small microphone samples the sounds coming from the four loudspeakers and its position in the three-dimensional space is obtained through trilateration calculations and signal analysis. Microphone and thermocouple are mounted on the same movable support, so that by measuring the position of the microphone, the position of the thermocouple is also detected. In this way it is possible to measure the temperature in a cloud of points of known position in space and obtain the three-dimensional thermal field around the heat sink. From these measurements it is possible to evaluate the thermal field around the heat sink and to easily compare different construction geometries. The position detection system has good precision and is inexpensive, allowing this type of measurement to be carried out even in low-budget situations. It also differs from thermal imaging systems such as IR cameras, in that it allows measurement of the temperature in the fluid surrounding the heat sink and not on its surface only.Natural convection heat sinks are still important in many industrial applications thanks to their simple design, effectiveness and noise-free operation. In this paper we present some case studies of experimental determination of the thermal characteristics of such devices, carried out using an innovative three-dimensional method of position detection for the temperature transducer (thermocouple). The three-dimensional position detection system uses acoustic waves emitted by a small grid of four loudspeakers, which simultaneously emit pseudo-random noise sequences orthogonal to one another. A small microphone samples the sounds coming from the four loudspeakers and its position in the three-dimensional space is obtained through trilateration calculations and signal analysis. Microphone and thermocouple are mounted on the same movable support, so that by measuring the position of the microphone, the position of the thermocouple is also detected. In this way it is possible to measure the temperature in a clo...

In this paper, a calculation of radial compressor characteristics from measured data is dealt with. The measured quantities as temperatures, pressures, working gas relative humidity, shaft rotational speed and torque are processed to obtain absolute and dimensionless parameters of the given machine. The methodology is generalized to both experimental and production machines and it deals with incorporation of any suitable equation of state. A modular and configurable in-house code is used for this purpose. It adopts the ASME performance test code for compressors scheme of measuring stations, stages, sections and machines. The theoretical background and the structure of the program are described. Benedict-Webb-Rubin equation of state for real gases is implemented. Gas humidity, orifice flowmeter, bearings mechanical losses and torquemeter measurements are covered. Various cases of measuring station calculations considering high speed and/or rotational flow based on total and static state parameters are elaborated. Polytrophic compression and the accuracy of evaluation of polytrophic efficiency are discussed in terms of various real gas corrections. Conversion of the results to comparable form is explained. The conversion involves standard gas intake state and composition and corrections to impeller rotational speed discrepancies.In this paper, a calculation of radial compressor characteristics from measured data is dealt with. The measured quantities as temperatures, pressures, working gas relative humidity, shaft rotational speed and torque are processed to obtain absolute and dimensionless parameters of the given machine. The methodology is generalized to both experimental and production machines and it deals with incorporation of any suitable equation of state. A modular and configurable in-house code is used for this purpose. It adopts the ASME performance test code for compressors scheme of measuring stations, stages, sections and machines. The theoretical background and the structure of the program are described. Benedict-Webb-Rubin equation of state for real gases is implemented. Gas humidity, orifice flowmeter, bearings mechanical losses and torquemeter measurements are covered. Various cases of measuring station calculations considering high speed and/or rotational flow based on total and static state parameters are elab...

The analysis of orbital motion and equilibrium of large structures is one of the relevant problems of space flight mechanics. The article deals with the equilibrium of extended one-dimensional objects in a circular orbit. The following properties of the objects are shown in the paper: non-Keplerian motion of the center of mass, the relative position of the center of mass and center of gravity, the nature of acting forces. The expressions for determining the axial force in the cross-sections of the structure are proposed in the framework of exact and linearized approaches. The gravitational-centrifugal load acting on an extended object is considered as a self-balanced system of forces of apparent weight with apparent acceleration variable along the local vertical. The assumptions related to the physical linearization of the problem are given. The nature and value of the microgravity acceleration acting in the cross-sections of extended objects are shown. The difference between the orbital angular velocity of the point particle and the mass center of an extended object is approximated. It is found that the position of the gravitational center relative to the center of mass depends on the squared ratio of the radius of gyration to the orbital radius.The analysis of orbital motion and equilibrium of large structures is one of the relevant problems of space flight mechanics. The article deals with the equilibrium of extended one-dimensional objects in a circular orbit. The following properties of the objects are shown in the paper: non-Keplerian motion of the center of mass, the relative position of the center of mass and center of gravity, the nature of acting forces. The expressions for determining the axial force in the cross-sections of the structure are proposed in the framework of exact and linearized approaches. The gravitational-centrifugal load acting on an extended object is considered as a self-balanced system of forces of apparent weight with apparent acceleration variable along the local vertical. The assumptions related to the physical linearization of the problem are given. The nature and value of the microgravity acceleration acting in the cross-sections of extended objects are shown. The difference between the orbital angular velocity ...