Search

Degradation modeling and remaining useful life (RUL) prediction for hard disk drives are crucial for exploring the failure mechanism, evaluating the design reliability and improving the design. Motivated by the fact that magnetic head degradation is the most prevailing failure mode, a variety of methods for head degradation problem have been proposed. For example, non-homogeneous Poisson processes were developed to deal with such problems. However, a general non-homogeneous Poisson process assumes that the mean cumulative function is deterministic. This assumption cannot be satisfied when the degradation process contains stochastic dynamics in uncertain operating environments. To solve this problem, this article proposes a non-homogeneous Poisson process with a stochastic mean cumulative function that uses Gaussian noise terms to capture the stochastic effects. Then, a nonlinear state-space model is built using the proposed model to track the dynamic degradation process and predict the RUL of magnetic head under uncertain operating conditions. To estimate and update the model parameters adaptively, a stochastic filter and a maximum likelihood estimation (smoother) based on the expectation–maximization algorithm is derived. Finally, a real case study is used to illustrate the effectiveness of the proposed method.

To simulate the price fluctuation dynamics of financial markets, a novel financial price model is developed by the voter dynamic system on the Watts-Strogtz small-world network and the random jump process. The voter system is a classical statistical physics system, which describes the dynamics of voters’ attitudes towards a certain topic in the mutual influence. The Watts-Strogtz small-world network is a special kind of complex networks, which can be used to study the transmission dynamics of different things in complex and real-world systems. The paper first attempts to use the voter dynamic system on the small-world network to reproduce the micro-mechanism of price fluctuations caused by the interaction among different investors in financial markets, where investors can potentially disseminate information and interact via additional long-distance contacts. Moreover, considering that external macro environments have the impact on price fluctuations in financial markets, this paper introduces the random jump process in the price model. The effectiveness of the proposed model can be verified by comparing price returns generated by the model with returns of several important stock indexes in terms of nonlinear fluctuation behaviors. First, some statistical behaviors of the fluctuation dynamics are explored, including distribution characteristics and autocorrelation. Moreover, based on the ensemble empirical mode decomposition method, multifractal behaviors and complexity behaviors of returns and the first three intrinsic mode functions are investigated. The empirical results show that the dynamical model can well simulate these nonlinear fluctuation behaviors of real markets.

Low-phase-noise and pure-spectrum Raman light is vital for high-precision atom interferometry by two-photon Raman transition. A preferred and prevalent solution for Raman light generation is electro-optic phase modulation. However, phase modulation inherently brings in double sidebands, resulting in residual sideband effects of multiple laser pairs beside Raman light in atom interferometry. Based on a well-designed rectangular fiber Bragg grating and an electro-optic modulator, optical single-sideband modulation has been realized at 1560 nm with a stable suppression ratio better than -25 dB despite of intense temperature variations. After optical filtration and frequency doubling, a robust phase-coherent Raman light at 780 nm is generated with a stable SNR of better than -19 dB and facilitates measuring the local gravity successfully. This proposed all-fiber single-sideband-modulated Raman light source, characterized as robust, compact and low-priced, is practical and potential for field applications of portable atom interferometry., 12 pages, 7 figures

Electro-optic modulation with a constant modulation depth plays important roles in quantum metrology, microwave photonics, and optical precision measurement and sensing, etc. To compensate the continuous drift of the half-wave voltage and maintain the modulation depth, we incidentally generated a reference laser to make intermedia optical beatings with the carrier and +1st sideband, and tightly locked the carrier to sideband ratio by extracting the relative microwave power of those intermedia beat signals using a home-made electronic control module. Experiments of the short-term test for locking bandwidth, the anti-jamming capability, and the long-term stability were demonstrated. As is verified that, the locking bandwidth was estimated up to tens of kHz, and the anti-jamming capability was confirmed despite of a strong hair-dryer agitation. The long-term stability for the modulation depth stabilization showed that the peak-to-peak relative stability for 150-minute was 5.67 × 10−6, and the Allan deviation reached a minimum of 2.19 × 10−7 at an averaging time of 400 s, which is improved by more than four orders of magnitude compared with the open-loop regime. We believe the reported method as well as the designed module is versatile and potential to precision measurement and sensing applications badly requiring a stable modulation depth, such as atom interferometry, optical interferometry and lidar detection.

Background and Objectives. Gastric cancer (GC) is one of the common gastrointestinal tumors and the third in the mortality rate among tumors. Studies have shown that the human antigen receptor (HuR) is associated with the malignant degree of GC. Methods. We performed qRT-PCR, cell cycle assay, cell migration, and mouse transplantation model analysis in our experiments. It has been clarified that HuR and microRNAs (miRNAs) have important interplays in the regulation of tumor progression. Results. This study found microRNA-133b (miR-133b), as a HuR-sponged miRNA in GC cells. Downregulation of HuR can promote the expression of miR-133b and further affect the downstream cyclin CDC5L. The expressions of miR-133b were slightly lower in GC tissues than adjacent normal tissues. Conclusion. Our studies suggest that HuR and miR-133b are involved in the development and pathological process of GC cells.

The design, fabrication, and demonstration of a planar two-dimensional-crossed reflective diffractive grating are proposed to construct a novel optical configuration, to the best of our knowledge, potentially applied for atom cooling and trapping in a magneto-optical trap. Based on the proposed single-beam single-exposure scheme by means of an orthogonal two-axis Lloyd’s mirrors interferometer, we rapidly patterned a ∼ 1 µ m period grating capable of providing a uniform intensity of the diffracted beams. The key structural parameters of the grating including the array square hole’s width and depth were determined, aiming at providing a high energy of the diffracted beams to perform the atom cooling and trapping. To guarantee the diffracted beams to be overlapped possibly, we adopted a polarized beam splitter to guide the optical path of the incident and zero-order diffracted beams. Therefore, one zero-order diffracted beam with a retroreflected mode and four first-order diffracted beams with appropriate optical path constructed a three-dimensional optical configuration of three orthogonal pairs of counterpropagating beams. Finally, three pairs of the counterpropagating cooling laser beams with 9 mm diameter and > 10 % diffraction efficiencies were achieved, and the circular polarization chirality, purity, and compensation of the desired diffracted beams are further evaluated, which preliminarily validated a high applicability for the magneto-optical trap system.

The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti2AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti2AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti2AlC. However, the electrical conductivity of the Ti2AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti2AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti2AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti2AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti2AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti2AlC MAX phase ceramic.

The present work introduced first-principles calculation to explore the substitution behavior of Ag atoms for Al or Ti atoms in the Ti2AlC MAX phase ceramic. The effect of Ag substitution on supercell parameter, bonding characteristic, and stability of the Ti2AlC was investigated. The results show that for the substitution of Ag for Al, the Al-Ti bond was replaced by a weaker Ti-Ag bond, decreasing the stability of the Ti2AlC. However, the electrical conductivity of the Ti2AlC was enhanced after the substitution because of the contribution of Ag 4d orbital electrons toward the density of states (DOS) at the Fermi level coupled with the filling of Ti d orbital electrons. For the substitution of Ag for Ti, new bonds, such as Ag-Al bond, Ag-C bond, Al-Al bond, Ti-Ti anti-bond, and C-C anti-bond were generated in the Ti2AlC. The Ti-Ti anti-bond was strengthened as well as the number of C-C anti-bond was increased with increasing the substitution ratio of Ag for Ti. Similar to the substitution of Ag for Al, the stability of the Ti2AlC also decreased because the original Al-Ti bond became weaker as well as the Ti-Ti and C-C anti-bonds were generated during the substitution of Ag for Ti. Comparing with the loss of Ti d orbital electrons, Ag 4d orbits contributed more electrons to the DOS at the Fermi level, improving the electrical conductivity of the Ti2AlC after substitution. Based on the calculation, the substitution limit of Ag for Al or Ti was determined. At last, the substitution behavior of Ag for Al or Ti was compared to discriminate that Ag atoms would tend to preferentially substitute for Ti atoms in Ti2AlC. The current work provides a new perspective to understand intrinsic structural characteristic and lattice stability of the Ti2AlC MAX phase ceramic.

The visibility graph algorithm is applied to convert the financial volatility duration series into the assortative complex network, in an attempt to investigate nonlinear scaling behaviors of volatility duration. The visibility graph maps a time series into a network, and the volatility duration describes the volatility consistently above or below a given data point in the volatility series. In order to comprehensively study the visible volatility duration series, a financial Potts market dynamics model is developed, where the Potts model is an extension of the Ising model with the integer q-state interacting spins on a two-dimensional lattice, and depicts the interaction strength among the agents. For the proposed model, we make an approach focusing on the scaling exponent analysis, including vertex degree distribution, fractal scaling and hierarchical property. The validity of the price model is verified through the comparatively empirical research with the real market data.

A financial dynamics of interaction and jump is developed and investigated by two statistical physics systems — Ising model and continuum percolation. This proposed model aiming at understanding price fluctuations needs to define a mechanism for the formation of the price, in an attempt to describe interacting micromechanism and sudden jump for stock price changes. Further, the corresponding fluctuation behaviors and various complexity properties of logarithmic returns for the financial model are investigated by some statistical and complex analyses. Then p -order multiscale autocorrelation function and q -order multiscale entropy are also introduced to study the financial model with scaled analysis methods. Moreover, the real stock market indexes are used to compare with the simulation returns from the financial model. The empirical research shows that the simulation time series exhibits the similar fluctuation patterns with real time series.

The free vibration of a fluid-conveying nanotube composed of carbon nanotube and boron nitride (BN) nanotube is studied in this paper. The nonlocal Euler-Bernoulli beam model is adopted to describe the transverse displacement of the hybrid nanotube, and the governing equation is segmented because of the material properties' change at the junction. Then the dynamic stiffness method is used to solve the governing equation, and we investigated the effects of length ratio and nonlocal parameter on the vibration behavior and stability of the fluid-conveying hybrid nanotube. It can be concluded that the instability of the nanotube is significantly dependent on the length ratio and the nonlocal parameter. The increase of length ratio or nonlocal parameter will both make the system more unstable, in particularly, the nonlocal parameter has a great effect on the second-mode divergence. And we also find that the extra support at the junction will lead a great increment to the first two order frequencies and critical flow velocity.

Single frequency fiber lasers (SFFLs) have seen increasing applications in state-of-the-art quantum technologies, which usually require precise and stable offset frequency locking (OFL). However, limited by the piezoelectric transducer bandwidth in SFFLs and the loop bandwidth of the OFL, the large-gap jumping between two locked offset frequencies will take an undesirable amount of time. In order to diminish that consuming time, we developed an agile offset frequency locking system based on a hybrid loop of a feed-forward path and a feedback path. In accordance with the experimental demonstration, we characterized the performances of the offset frequency locking system, as frequency-locking stability with an Allan deviation of 3.2 × 10−14 at 1 s averaging time and jumping agility with a duration of 0.6 ms at 1.3 GHz frequency gap, which is a factor of 60 faster than that without the feed-forward path. This mechanism can find direct applications in existing quantum metrology experiments with SFFLs where high-speed frequency jumping or sweeping is needed.

Stimulated Raman adiabatic passage (STIRAP) is an effective technique to transfer state coherently with the features of both high fidelity and robustness in the field of quantum information and quantum precise measurement. In this note, we present a simple method to generate arbitrary laser shapes for STIRAP by controlling the modulation depth of the electro-optic modulator (EOM) and the diffraction efficiency of the acoustic–optic modulator (AOM) simultaneously. The EOM and AOM are used to control the power ratio between the two Raman lasers (pumping laser and Stokes laser) and the total power, respectively. Compared with the traditional method by combining two Raman lasers separated in space, this method has the advantage of simple structure and insensitivity to the environment disturbance, which would degrade the relative phase noise between two Raman lasers.

Light shift produced by the AC Stark effect is one of the major factors limiting the accuracy and long-term stability of a cold atom interferometer. The first order light shift can be canceled by fixing the power ratio of the Raman beams at a specified value. We report here a new method to stabilize the power ratio of the two Raman lasers with ∼100 kHz locking bandwidth, suppressing the effect of the first order light shift. We first mixed the two Raman lasers (at different optical frequencies) with a reference beam and then used two Schottky diode detectors to extract the corresponding beat note signals for each beam, which are much easier to be manipulated and processed as they are in the microwave band. The stability of the power ratio is improved by three orders of magnitude from 5.84 × 10-3 to 3.51 × 10-6 at 1 s averaging time and reaches 1.59 × 10-7 at 10 000 s integrating time when the servo loop is engaged. This method can be used in other precise quantum measurement based on the stimulated Raman transition and can be applied to compact inertial sensors.

The present paper introduces a novel stochastic statistical physics financial system by combining exclusion system with compound Poisson process. The financial system is a model concerning with price fluctuations derived from dissemination of trading attitudes of financial agents and random drastic jumps caused by exogenous economic factors, respectively. Multifractal detrended cross-correlation analysis and fuzzy entropy of simulation dataset are performed. Fractional fuzzy entropy based on fuzzy entropy method and fractional calculus, is also developed to explore nonlinear complexity of the proposed model in the paper. Empirical results display that there are significant multifractality and fractal asymmetry in the proposed model, and the complexity of return series increases when λ or γ increases, correspondingly. And same analyses for actual stock market dataset are comparatively investigated. The conclusions reveal that the novel compound dynamics can reproduce various nonlinear behaviors of actual stock markets to a certain extent.

In attempt to reproduce and investigate nonlinear dynamics of security markets, a novel nonlinear random interacting price dynamics, which is considered as a Levy type process, is developed and investigated by the combination of lattice oriented percolation and Potts dynamics, which concerns with the instinctive random fluctuation and the fluctuation caused by the spread of the investors’ trading attitudes, respectively. To better understand the fluctuation complexity properties of the proposed model, the complexity analyses of random logarithmic price return and corresponding volatility series are preformed, including power-law distribution, Lempel–Ziv complexity and fractional sample entropy. In order to verify the rationality of the proposed model, the corresponding studies of actual security market datasets are also implemented for comparison. The empirical results reveal that this financial price model can reproduce some important complexity features of actual security markets to some extent. The complexity of returns decreases with the increase of parameters γ 1 and β respectively, furthermore, the volatility series exhibit lower complexity than the return series

Ocean economy plays a crucial role in the strengthening maritime safety industry and in the welfare of human beings. Electric Submersible Pumps (ESP) have been widely used in floating platforms on the sea to provide oil for machines. However, the ESP fault may lead to ocean environment pollution, on the other hand, a timely fault diagnosis of ESP can improve the ocean economy. In order to meet the strict regulations of the ocean economy and environmental protection, the fault diagnosis of ESP system has become more and more popular in many countries. The vibration mechanical models of typical faults have been able to successfully diagnose the faults of ESP. And different types of sensors are used to monitor the vibration signal for the signal analysis and fault diagnosis in the ESP system. Meanwhile, physical sensors would increase the fault diagnosis challenge. Nowadays, the method of neural network for the fault diagnosis of ESP has been applied widely, which can diagnose the fault of an electric pump accurately based on the large database. To reduce the number of sensors and to avoid the large database, in this paper, algorithms are designed based on feature extraction to diagnose the fault of the ESP system. Simulation results show that the algorithms can achieve the prospective objectives superbly.

Modal property is the crucial factor that can influence the vibration characteristics of the planetary gear system. Previous studies used time invariant mesh stiffness (TIMS) to study the natural characteristics. However, with the rotation of the gear, the meshing stiffness will change periodically which will lead to changes of modal properties. Based on these properties which are ignored in previous studies, a translational-torsional free vibration model base on time-varying mesh stiffness (TVMS) rather than time invariant mesh stiffness (TIMS) is established in this paper to study the modal properties of the planetary gear system, the effects of TVMS on the natural characteristics are investigated. The results show that the meshing phase difference and the change regulation of the time varying natural frequencies are correlated, and there is a dramatic variation of higher order natural frequencies at the contact teeth change points. Furthermore, a useful conclusion can be drawn that takes TVMS to calculate higher order frequencies has certain advantages over traditional methods.

Spark Plasma Sintering technique was applied to fabricate MoSi2 and MoSi2-bentonite coatings on molybdenum. The phase composition, morphologies and anti-oxidation properties of the coatings at 1500 °C were investigated. Penetrated cracks generated in MoSi2 coating after SPS while the composite coating was crack-free because of the reduction of CTE mismatch. Cracks existed in the silica layer of MoSi2 coating after oxidation while the silica layer of bentonite-containing coating showed dense and crack-free morphologies. Compared with MoSi2, the composite coating possessed thinner Mo5Si3 diffusion layer and silica layer, exhibiting less loss of substrate and coating with improved oxidation resistance.