Stationary Ones Research Articles

Transient feature extraction of encoder signal for condition assessment of planetary gearboxes with variable rotational speed

This paper proposes a transient feature extraction algorithm of encoder signal for the condition assessment of planetary gearboxes under variable speed condition. In the proposed method, local polynomial fitting and sparsity based algorithm (LSA) is first constructed to extract time domain transient features from raw encoder signal and then order tracking (OT) technique is applied to convert non-stationary transient features in time domain into stationary ones in angular domain. Meanwhile, to solve the formulated local polynomial fitting and sparsity based optimization problem, a fast convergence algorithm is derived based on alternating direction method of multipliers and majorization-minimization. Additionally, an adaptive parameter selection strategy is introduced for automatically selecting appropriate parameters of the proposed method LSA-OT. With the proposed method LSA-OT, the transient features can be effectively extracted and the condition assessment of planetary gearboxes can be easily achieved. The effectiveness of LSA-OT is confirmed by simulation evaluation and case study.

Asynchronous Acoustic Localization and Tracking for Mobile Targets

Recently, acoustic-based indoor localization has attracted much attention due to its affordable infrastructure costs and high localization accuracy. However, previous work is infeasible in mobile target tracking for its long latency in obtaining sufficient beacon messages. In addition, the performance can further deteriorate due to device diversity, varying channel gains, and background noises. To this end, we propose an asynchronous acoustic localization and tracking system (AALTS), which utilizes distributed acoustic anchor nodes to locate passive off-the-shelf mobile devices. In AALTS, we propose an orthogonal chirp spread spectrum (OCSS) modulation technique, which doubles the data rate and thus mitigates the latency. We design a more robust method to capture acoustic signals which embody timestamps for localization, accounting for device diversity, varying channel gains, and the multipath effect. Finally, we incorporate an acoustic Doppler speed estimation module with a path-based particle filter framework to accurately track the moving targets. We have evaluated AALTS in an indoor testbed of size $8\times 12\,\,\text{m}^{2}$ with commodity mobile phones and customized acoustic anchors. Our evaluation results demonstrate remarkable performance: AALTS achieves 90-percentile tracking errors of 0.49 m for mobile targets and a median of 0.12 m for stationary ones with only four anchor nodes.

On low-Prandtl-number convection in an inclined layer of liquid mercury

This paper reports on a theoretical analysis of convection in an inclined layer of mercury, a common low-Prandtl-number fluid ($Pr=0.025$). The investigation is based on the standard Oberbeck–Boussinesq equations, which are explored as a function of the inclination angle $\unicode[STIX]{x1D6FE}$ and for Rayleigh numbers $R$ in the vicinity of the convection onset. Along with the conventional Galerkin methods to study convection rolls and their secondary instabilities, we employ direct numerical simulations for fluid layers with quite large aspect ratios. It turns out that, even for small inclination angles $\unicode[STIX]{x1D6FE}\lesssim 6^{\circ }$, the secondary instabilities of the basic rolls lead either to oscillatory three-dimensional patterns or to stationary ones, which appear alternately with increasing $\unicode[STIX]{x1D6FE}$. Due to the competition of these instabilities the patterns may show a complex dynamics.

Experimental investigation on ice accretion on a rotating aero-engine spinner with hydrophobic coating

Ice accretion on aero-engine inlets is a serious threat to the inflight safety. As an important part of the engine inlet components, the rotating spinner has special icing phenomena compared with the stationary ones. An experimental study is conducted to investigate the ice accretion on a rotating aero-engine spinner in the icing wind tunnel. A full-scale engine spinner model is used in the experiments operated under different conditions. The hydrophobic nanoparticle-polymer composite coating is applied to cover on the aluminum-based spinner and then to examine its anti-icing performance. The dynamic icing processes and the final ice shapes on the rotating spinner surface are captured. The experimental results reveal that the ice growth and ice shape are basically determined by the airflow temperature and slightly affected by the rotating speed when the airflow velocity and icing cloud parameters are constant. The ice fracture and shedding are greatly dependent on the rotating speed when the icicle length is large enough. The freezing delay on the hydrophobic coating is inconspicuous and there is even no effect on the ice growth. However, the ice shedding on the coating happens, especially in the mixed icing condition with a higher rotating speed, demonstrating its icephobicity. Meanwhile, the dynamic icing processes and the effects of the airflow velocity and rotating speed on the ice growth are analyzed based on the mechanism of the supercooled droplet impingement characteristics, heat and mass transfer, force analysis on the rotating surface. The surface wettability is introduced to evaluate the freezing delay and icephobicity on the hydrophobic coating.

Elliptical Gaussian beam propagation in nonlinear fibres with focusing and defocusing refractive profiles

The paper shows systematic analysis of elliptical Gaussian beam (GB) propagating in self-focusing/self-defocusing media of Kerr type with focusing/defocusing linear refractive profiles. Instead of solving commonly accepted Nonlinear Schrödinger Equation (NLS) we propose equations of geometrical optics: complex eikonal equation and complex transport one. Eikonal equation let us derive immediately the ordinary differential equations for principle widths omitting this way complicated variational process and virial theory used in nonlinear optics. From the transport equation we obtain first order ordinary differential equation for complex amplitude evolution and conservation principle for energy flux in the elliptical GB cross-section. For combined effects of diffraction, nonlinear refraction and focusing/defocusing graded-index factor we observe three types of the solutions for the elliptical radius of principle beam widths: self-focusing or self-defocusing together with diffraction widening, stationary and oscillatory ones under and without collapse effect. We prove here that principle curvatures of the wave front can introduce into our description the additional ellipticity of the beam, which can effectively limit collapse effect. Moreover, we discuss the evolution of elliptical Gaussian beam in nonlinear self-defocusing fibre with focusing refractive profile presenting conditions for existence of elliptical spatial solitons. We discuss here also the influence of initial wave front curvatures on elliptical Gaussian beam evolution in nonlinear inhomogeneous fibres of Kerr-type.

Assessment of future changes in intensity-duration-frequency curves for Southern Ontario using North American (NA)-CORDEX models with nonstationary methods

Study regionSouthern Ontario, Canada. Study focusThe evaluation of possible climate change consequence on extreme rainfall has significant implications for the design of engineering structures and socioeconomic resources development. To date, there has been no comprehensive comparison or evaluation of intensity-duration-frequency (IDF) statistics at a regional scale, considering both stationary versus nonstationary models for the future climate projection. To understand how extreme precipitation may affect future IDFs, we used an ensemble of three regional climate models (RCMs) participating in the NA-CORDEX domain over eight selected rainfall stations across Southern Ontario, one of the most densely populated and major economic regions in Canada. We modeled precipitation extremes, at different durations using extreme value distributions considering parameters that are either stationary or nonstationary, as a linear function of time. New hydrological insights for the regionExtreme precipitation intensity driven by future climate forcing shows a significant increase in intensity for 10-year events in the 2050s (2030–2070) relative to 1990s (1970–2010) baseline period across most of the locations. For longer return period (i.e., 25-year), we note detectable changes in design storm considering a nonstationary model than that of the stationary ones. Finally, the results of this study are not only limited to develop nonstationary IDFs for the future emission scenario but the proposed framework can serve as a basis to improve weather generator accounting nonstationary nature of extreme precipitation.

Steady flows and unsteady ones in pipes: models link and quasistationarity hypothesis

Models of unsteady flows and stationary ones in pipes and the requirements of their joining are considered. In this view, the problem of the description of a friction at a non-stationary flow is considered. So-called “quasi-stationarity hypothesis” is discussed. The formula for a friction coefficient generalized on a non-stationary case is offered. It is concluded that additional losses at the non-stationary mode are caused by energy consumptions for reorganization of speed chart.

Untimely Destruction: Pestilence, War and Accumulation in the Long Run

This paper analyses the effects of disease and war on the accumulation of human and physical capital. We employ an overlapping-generations frame-work in which young adults, confronted with such hazards and motivated by old-age provision and altruism, make decisions about investments in schooling and reproducible capital. A poverty trap exists for a wide range of stationary war losses and premature adult mortality. If parents are altruistic and their sub-utility function for own consumption is more concave than that for the children's human capital, the only possible steady-state growth path involves full education. Otherwise, steady-state paths with incompletely educated children may exist, some of them stationary ones. We also examine, analytically and with numerical examples, a growing economy's robustness in a stochastic environment. The initial boundary conditions have a strong influence on outcomes in response to a limited sequence of destructive shocks.

Regulatory Experience in Licensing of Alternative Supplier Fuel

At present, the diversification of nuclear fuel is ongoing at Ukrainian NPPs. The Ukrainian regulatory authority and SSTC NRS, as a technical support organization, take active part in the licensing process for introduction of new fuel assembly types. In the framework of this activity, the technical review of justification material is performed in various nuclear safety issues including a wide range of verifying calculations. Neutron kinetic, thermal-hydraulic and fuel thermal-mechanical models are developed for technical review of justification material such as safety analysis of mixed cores. The features of the developed models for safety analysis of new fuel implementation and results of their application for verifying calculations are presented in this paper. The results cover such aspects as preparation of few-group cross-section libraries with features of new FA types, calculations of transitional mixed fuel loadings up to stationary ones, verifying safety assessment for some design-basis reactivity-initiated accidents, criticality of fuel management systems and thermal-mechanical fuel behavior.

Case study of random vibration analysis of train-bridge systems subjected to wind loads

In order to reveal the independent relationship between track irregularity and wind loads, the stochastic characteristics of train-bridge coupling systems subjected to wind loads were investigated by the multi-sample calculation. The vehicle was selected as 23 degrees of freedom dynamical model, and the bridge was described by three-dimensional finite element model. It was assumed that the wind loads were random processes with strong spatial correlation, while the track irregularities were stationary random ones. As a case study, a high-speed train running on a cable-stayed bridge subjected to wind loads was studied. The effect of rail irregularities was deemed to be independent of the effect of wind excitations on the coupling system in the same wind circumstance for the same project, leading to the conclusion that the effect of wind loads and moving vehicle could be calculated separately. The variance results of the stochastic responses of vehicle-bridge coupling system under the action of wind loads and rail irregularities together were equivalent to the sum of the variance of the responses induced by each excitation. Therefore, when one of the input excitations is different, only the effect of changed loads needs to be assessed. Moreover, the new calculated results were combined with the effect of unchanged loads to present the stochastic response of coupling system subjected to the different excitations, reducing the cost of computations. The stochastic characteristics, the CFD (cumulative distribution function) of the coupling system with different wind velocities, vehicle speed, and vehicle marshalling were studied likewise.

Empirical Study on the Effects of Stationary and Mobile Student Laboratories: How Successful Are Mobile Student Laboratories in Comparison to Stationary Ones at Universities?

In the past 20 years, science education in schools has increasingly been supported by extracurricular learning opportunities. From the point of view of pupils and teachers, student laboratories mak...

Influence of the Location of Moving and Stationary Lags on Their Suppression

The precedence effect is a phenomenon characterizing the noise stability of the auditory system in localizing a sound source. This phenomenon is based on the ability of the auditory system to localize a direct sound in an environment of masking acoustic reflections coming from various surfaces. To create the precedence effect, we used two signals: the first was a direct signal (the lead) and the second one arriving at a delay relative to the onset of the lead was an echo signal (the lag). The signals were presented in the horizontal plane. Their duration was 1 s. Delays between the onset of the lag and that of the lead ranged from 1 to 40 ms. The suppression of the moving lag was compared in the study with that of the stationary lag. The movement of the lag was created along two paths located to the left from the subject’s head midline in the horizontal plane (–86°...–52° and –52°...–18°). The stationary lag was located at the ends of these two paths. The lag movement was simulated in opposite directions (either approaching or distancing from the lead signal). The lead was always stationary and located to the right from the head midline in the horizontal plane (15°). The lag suppression was estimated by echo suppression threshold values. It has been shown for the stationary lag that the nearer the lag was located to the lead the higher the lag was suppressed and the mean echo suppression threshold values increased from 5.1 to 7.1 ms. The location and the direction of movement of a travelling lag did not affect its suppression. The mean threshold values ranged from 6.2 to 6.9 ms. Individual differences between the threshold values were greater with moving signals than with stationary ones.

Elastic wave propagation in moving phononic crystals and correlations with stationary spatiotemporally modulated systems

This work presents a generalized physical interpretation of unconventional dispersion asymmetries associated with moving phononic crystals (PCs). By shifting the notion from systems with time-variant material fields to physically traveling materials, the newly adopted paradigm provides a novel approach to the elastic dispersion problem and, in the process, highlights discrepancies between moving PCs and stationary ones with dynamic material fields. Equations governing the motion of an elastic rod with a prescribed moving velocity observed from a stationary reference frame are used to predict propagation patterns and asymmetries in wave velocities obtained as a result of the induced linear momentum bias. Three distinct scenarios are presented corresponding to a moving rod with a constant modulus, a spatially varying one, and one that varies in space and time. These cases are utilized to extract and interpret correlations pertaining to directional velocities, dispersion patterns, as well as nature of band gaps between moving periodic media and their stationary counterparts with time-traveling material properties. A linear vertical shear transformation is then derived and utilized to neutralize the effect of the moving velocity on the resultant band diagrams. Finally, dispersion contours associated with the transient response of a finite moving medium are used to validate the entirety of the presented framework.

Features of Network Navigation Systems Construction for Surface Consumers Using Offshore Reference Points

The paper addresses the problem of required positioning accuracy to be provided for a marine consumer. To improve the reliability of navigation measurements, an option of system implementation comprising both stationary onshore facilities and mobile offshore ones is proposed. In order to ensure appropriate range and accuracy of navigation using surface radio navigation aids (RNA), it is proposed to employ medium-wave radiation. Specific features of navigation measures within the selected range are studied in detail, which made it possible for the authors to develop particular technical recommendations and to formulate the accuracy estimations of marine consumer positioning using the proposed solutions under different conditions.

Stationary Mahalanobis kernel SVM for credit risk evaluation

This paper proposed Mahalanobis distance induced kernels in Support Vector Machines (SVMs) with applications in credit risk evaluation. We take a particular interest in stationary ones. Compared to traditional stationary kernels, Mahalanobis kernels take into account on feature's correlation and can provide a more suitable description on the behavior of the data sets. Results on real world credit data sets show that stationary kernels with Mahalanobis distance outperform the stationary kernels with various distance measures and they can also compete with frequently used kernels in SVM. The superior performance of our proposed kernels over other classical machine learning methods and the successful application of the kernels in large scale credit risk evaluation problems may imply that we have proposed a new class of kernels appropriate for credit risk evaluations.

Epidemiological Survey of Ascosphaera apis in Small-Scale Migratory Apis mellifera iberiensis Colonies

Honey bee hives are moved yearly mainly for pollination, but also to take advantage of consecutive flowering events to get as many harvests of honey as possible and/or to find favorable sites for food sources and summer temperatures. Such movements may lead to pathogen spill-over with consequences on the honey bee health and finally on population decline. Ascosphaera apis is the causative agent of the chalkbrood disease, a pathology affecting honey bee larvae that significantly harms population growth and colony productivity. In this study, we detected the presence of A. apis in adult worker honey bees by PCR-amplification of the intergenic transcribed spacer (ITS1) of the ribosomal gene (rDNA). We first optimized the DNA extraction by testing different protocols in individual and pooled (colony level) adult honey bee samples. Subsequently, the presence of the fungus A. apis was assessed in both stationary and migratory colonies (subjected to small scale regional level movements) to determine the effect of migratory practices on the dispersal of this pathogen. Results confirmed a higher prevalence of A. apis in migratory apiaries when compared to stationary ones, indicating that migratory colonies are more likely to develop chalkbrood disease. Given these results, we suggest that beekeepers should be aware of the risks of pathogens spreading while moving beehives, even within a reduced geographic range.

Theoretical study of the system stabilization of the amplifier properties of the radio channel for units with rotating parts

Automation of ore grinding control is restrain due to the lack of sufficiently accurate systems for transferring information from rotating parts of aggregates to stationary ones. The aim of the work is a theoretical study of the system stabilization of the radio channel reinforcement properties. The work solves the problems of theoretical investigation of the stabilization of the radio channel reinforcement properties, the rationale for the radio transmitter, the radio receiving system and the automatic regulator of the amplification mode. Methods of analysis, studies of radio transmitting and radio receiving devices, discrete control systems, theory of automatic control, digital systems were used. As a result of theoretical studies it was established that the frequency stability of the radio channel is high, and the amplitude stability is low. In this radio channel, the amplitude stability takes the first problem place, which has not been solved in radio engineering yet. It is proved that the amplitude stability can be increased to the required values by setting the preset value of the radio channel gain. The gain is set by applying the reference signal and automatically adjusting in the low-frequency amplifier of the receiver by a digital controller with a relatively low error of ± 1 %. The functional nodes of the radio channel are controlled by a cyclic system. For the first time, a radio channel was created for transmitting signals from rotating parts of aggregates to fixed ones, in which high amplitude stability is achieved. An experimental verification established almost complete coincidence of the parameters of the random process at the input and output of the radio channel. The dispersion of the signals at the modulator input and the output of the radio channel, respectively, amounted to 1.8585 and 1.8489 units, the number of positive emissions for the zero level is 4, and spectral densities occupy the range from 50 to 250 Hz.

Fuel-Free Light-Powered TiO2/Pt Janus Micromotors for Enhanced Nitroaromatic Explosives Degradation.

Nitroaromatic explosives such as 2,4,6-trinitrotoluene (2,4,6-TNT) and 2,4-dinitrotoluene (2,4-DNT) are two common nitroaromatic compounds in ammunition. Their leakage leads to serious environmental pollution and threatens human health. It is important to remove or decompose them rapidly and efficiently. In this work, we present that light-powered TiO2/Pt Janus micromotors have high efficiency for the "on-the-fly" photocatalytic degradation of 2,4-DNT and 2,4,6-TNT in pure water under UV irradiation. The redox reactions, induced by photogenerated holes and electrons on the TiO2/Pt Janus micromotor surfaces, produce a local electric field that propels the micromotors as well as oxidative species that are able to photodegrade 2,4-DNT and 2,4,6-TNT. Furthermore, the moving TiO2/Pt Janus micromotors show an efficient degradation of nitroaromatic compounds as compared to the stationary ones thanks to the enhanced mixing and mass transfer in the solution by movement of these micromotors. Such fuel-free light-powered micromotors for explosive degradation are expected to find a way to environmental remediation and security applications.

One- and two-dimensional modes in the complex Ginzburg-Landau equation with a trapping potential.

We propose a new mechanism for the stabilization of confined modes in lasers and semiconductor microcavities holding exciton-polariton condensates, with spatially uniform linear gain, cubic loss, and cubic self-focusing or defocusing nonlinearity. We demonstrated that the commonly known background instability driven by the linear gain can be suppressed by a combination of a harmonic-oscillator trapping potential and effective diffusion. Systematic numerical analysis of one- and two-dimensional (1D and 2D) versions of the model reveals a variety of stable modes, including stationary ones, breathers, and quasi-regular patterns filling the trapping area in the 1D case. In 2D, the analysis produces stationary modes, breathers, axisymmetric and rotating crescent-shaped vortices, stably rotating complexes built of up to 8 individual vortices, and, in addition, patterns featuring vortex turbulence. Existence boundaries for both 1D and 2D stationary modes are found in an exact analytical form, and an analytical approximation is developed for the full stationary states.

Non-stationary statistical modeling of extreme wind speed series with exposure correction

Extreme wind speed analysis has been carried out conventionally by assuming the extreme series data is stationary. However, time-varying trends of the extreme wind speed series could be detected at many surface meteorological stations in China. Two main reasons, exposure change and climate change, were provided to explain the temporal trends of daily maximum wind speed and annual maximum wind speed series data, recorded at Hangzhou (China) meteorological station. After making a correction on wind speed series for time varying exposure, it is necessary to perform non-stationary statistical modeling on the corrected extreme wind speed data series in addition to the classical extreme value analysis. The generalized extreme value (GEV) distribution with time-dependent location and scale parameters was selected as a non-stationary model to describe the corrected extreme wind speed series. The obtained non-stationary extreme value models were then used to estimate the non-stationary extreme wind speed quantiles with various mean recurrence intervals (MRIs) considering changing climate, and compared to the corresponding stationary ones with various MRIs for the Hangzhou area in China. The results indicate that the non-stationary property or dependence of extreme wind speed data should be carefully evaluated and reflected in the determination of design wind speeds.