Multiline Spectrum Research Articles

A preliminary study on generation of axle box vibration spectra for metro vehicles in China using the developed spectral synthesis method

ABSTRACT In-service metro vehicles in China exhibit diverse vibration behaviours. This study focuses on analysing the vibration characteristics of these vehicles, with a particular focus on the complex non-stationary axle box vibrations measured on-site, as they closely correlate with wheel-rail interaction dynamics. A developed PSD-based synthesis method is first proposed to quantify the axle box vibration. The axle box vibration spectra of the metro vehicles in China are then generated from the measurements for various vehicles. Furthermore, a multi-line segment flat spectrum, designed specifically for the shaker loading, has been produced. The results show that the proposed method can determine the parameters (segment number, quantile) by the energy conservation law, which avoids the empirical value selection in previous methods and can be effectively utilized to generate the vibration spectra of the axle box. In addition, a notable distinction exists between the IEC 61,373 standard spectrum and the axle box vibration spectra of Chinese metro vehicles. While the former represents a single-peak spectrum ranging from 20 ~ 100 Hz, the latter consists of a multi-peak spectrum with peak frequency bands exceeding 100 Hz. The wear condition of the wheel-rail surface has a pronounced contribution to the vibration spectral magnitude. In cases of wheel-rail surface severe wear, the vibration spectrum values in the Z direction surpass the standard spectrum values across most frequencies, with the highest spectral value notably observed within 50 ~ 200 Hz. Such observations should be thoroughly taken into account in the analysis of fatigue damage to mounted equipment.

The low frequency multi-linear spectrum vibration control study of cylindrical shell through a semi-analytical method

Dynamic vibration absorber is efficient in controlling low frequency vibration of cylindrical shell, which is meaningful for engineering practice. However, the efficiency of designing dynamic vibration absorber using traditional method is low. This paper demonstrates a semi-analytical method for designing dynamic vibration absorber of cylindrical shell. The convergence analysis presented in the research proves the accuracy of the current method when handling different edge constraints through limited truncation numbers. Additionaly, forced vibration and control of multi-line spectrum vibration of cylindrical shell have also been studied. The comparison between FEM and current method shows a significant improvement when handling equivalent mass, which is a key process when designing dynamic vibration absorbers. Finally, an intriguing relationship is discovered when controlling multiple resonance peaks through a single dynamic vibration absorber. The semi-analytical method described in this paper may be beneficial when controlling the vibration of cylindrical shell structures in the further research.

Active vibration control using nonlinear auto-regressive neural network to identify secondary channel

The power unit on board the ship generates periodic low-frequency vibration that affects the normal operation of the equipment on board, and the adaptive feedforward control algorithm can effectively suppress such harmful vibration noise. But the adaptive feedforward control algorithm needs to obtain the identification model of the secondary channels, and the frequency domain least squares method based on the linear Extended auto-regressive model (ARX) is difficult to obtain the identification model with nonlinear characteristics. The nonlinear auto-regressive model (NARX) adds nonlinear mapping layers to the topology of the ARX model to enhance the identification capability of the NARX model for complex systems. In this paper, a block diagram of the Fx-LMS feedforward control algorithm based on the NARX model is proposed, then the initial parameters of the NARX neural network are optimized using the Quantum Particle Swarm Optimization (QPSO) algorithm and the secondary channel is identified, and the identification results show that the accuracy of identifying the secondary channel using the NARX neural network is higher than that of the ARX model. The simulation and experimental results show that the vibration damping effect of the proposed method is better than the traditional Fx-LMS method for both single-line spectrum and multi-line spectrum periodic low-frequency disturbances, which provides a new method for the suppression of periodic low-frequency disturbances.

Spectrum collapse in a 7-core Yb-doped fiber laser with an array of fs-inscribed fiber Bragg gratings.

Femtosecond inscription of fiber Bragg gratings (FBGs) in each core of a cladding-pumped seven-core Yb-doped fiber enables efficient (≈70%) 1064-nm lasing in a robust all-fiber scheme with ≈33 W power, nearly the same for uncoupled and coupled cores. However, the output spectrum is quite different: without coupling, seven individual lines corresponding to the in-core FBG reflection spectra sum up into a broad (0.22 nm) total spectrum, whereas the multiline spectrum collapses into a single narrow line at strong coupling. The developed model shows that the coupled-core laser generates coherent superposition of supermodes at the wavelength corresponding to the geometric mean of the individual FBG spectra, whereas the generated laser line broadens, with a power (0.04-0.12 nm) like the single-core mode of a seven-times larger effective area.

Design method for distributed dynamic vibration absorbers of stiffened plate under different boundary constraints

A theoretical model of stiffened plate with multiple dynamic vibration absorbers under different boundary constraints is proposed in the current research. Compared with FEM, the solution efficiency of equivalent mass using model proposed in the current paper is improved by 90%. In addition, different boundary conditions and the connection relationship between stiffened plate and dynamic vibration absorbers can be easily implemented through virtual boundary spring stiffness and the introduction of auxiliary sine functions in the displacement function. The reliability of current method is confirmed by comparing with FEM, related literatures, and experiment. Based on theoretical model presented in the current research, the vibration control of stiffened plate under various edge constraints is discussed in detail. The theoretical model presented in the current research may be useful for engineering designers in the process of multi-line spectrum vibration control of stiffened plate.

A Two-DOF Active-Passive Hybrid Vibration Isolator Based on Multi-Line Spectrum Adaptive Control

In order to effectively control the low-frequency vibration of ship machinery, based on the improved multi-line spectrum adaptive control algorithm, a two-degree-of-freedom (two-DOF) active-passive hybrid vibration isolator composed of an electromagnetic actuator, rubber spring, and the hydraulic device is proposed. The dynamic model of the two-DOF vibration isolation system is established and the main control force demand of the vibration isolation system at different damping forces is analyzed. By introducing the improved wavelet packet decomposition algorithm with the Hartley block least mean square algorithm to the filter-x least mean square (FxLMS) algorithm, an improved wavelet packet Hartley block filter-x least mean square (IWPHB-FxLMS) algorithm is established. The experimental results show that the IWPHB-FxLMS algorithm has better control performance. Compared with the traditional FxLMS algorithm, the IWPHB-FxLMS control algorithm improves the convergence speed by 91.7% and the line spectrum power spectrum attenuation by 58.1%. The active-passive hybrid vibration isolator is based on multi-line spectrum adaptive control and can achieve good control effects under the excitation of multi-frequency line spectrum and constant frequency line spectrum.

Synthesis of Square Planar Cu4 Clusters.

Template-assisted synthesis of well-defined polynuclear clusters remains a challenge for [M4 ] square planar topologies. Herein, we present a tetraamine scaffold R L(NH2 )4 , where L is a rigidified resorcin[4]arene, to direct the formation of C4 -symmetric R L(NH)4 Cu4 clusters with Cu-Cu distances around 2.7 Å, suggesting metal-metal direct interactions are operative since the sum of copper's van der Waals radii is 2.8 Å. DFT calculations display HOMO to HOMO-3 residing all within a 0.1 eV gap. These four orbitals display significant electron density contribution from the Cu centers suggesting a delocalized electronic structure. The one-electron oxidized [Cu4 ]+ species was probed by variable temperature X-band continuous wave-electron paramagnetic resonance (CW-EPR), which displays a multiline spectrum at room temperature. This work presents a novel synthetic strategy for [M4 ] clusters and a new platform to investigate activation of small molecules.

Synthesis of Square Planar Cu4 Clusters

AbstractTemplate‐assisted synthesis of well‐defined polynuclear clusters remains a challenge for [M4] square planar topologies. Herein, we present a tetraamine scaffold RL(NH2)4, where L is a rigidified resorcin[4]arene, to direct the formation of C4‐symmetric RL(NH)4Cu4 clusters with Cu−Cu distances around 2.7 Å, suggesting metal‐metal direct interactions are operative since the sum of copper's van der Waals radii is 2.8 Å. DFT calculations display HOMO to HOMO‐3 residing all within a 0.1 eV gap. These four orbitals display significant electron density contribution from the Cu centers suggesting a delocalized electronic structure. The one‐electron oxidized [Cu4]+ species was probed by variable temperature X‐band continuous wave‐electron paramagnetic resonance (CW‐EPR), which displays a multiline spectrum at room temperature. This work presents a novel synthetic strategy for [M4] clusters and a new platform to investigate activation of small molecules.

Electron paramagnetic resonance proof for the existence of molecular hydrino

Quantum mechanics postulates that the hydrogen atom has a stable ground state from which it can be promoted to excited states by capture of electromagnetic radiation, with the energy of all possible states given by En = −13.598/n2 eV, in which n ≥ 1 is a positive integer. It has been previously proposed that the n = 1 state is not the true ground state, and that so-called hydrino states of lower energy can exist, which are characterized by fractional quantum numbers n = 1/p, in which 1 < p ≤ 137 is a limited integer. Electron transition to a hydrino state, H(1/p) is non-radiative and requires a quantized amount of energy, 2mE1 (m is an integer), to be transferred to a catalyst. Numerous putative hydrino-forming reactions have been previously explored and the products have been characterized by a range of analytical methods. Molecular hydrino has been predicted to be paramagnetic. Here, we give an account of an electron paramagnetic resonance (EPR) study of molecular hydrino H2(1/4) that was produced as gaseous inclusion in polymeric Ga(O)OH by a plasma reaction of atomic hydrogen with non-hydrogen bonded water as the catalyst. A sharp, complex, multi-line EPR spectrum is found, whose detailed properties prove to be consistent with predictions from hydrino theory. Molecular hydrino was also identified in gas chromatography as a compound faster than molecular hydrogen.

Passive estimation of target velocity based on cross-spectrum histogram.

In underwater acoustic target parameter estimation, the cross-spectrum method estimates the velocity of the target by the interference structure of the cross-correlated fields in two ranges. However, with the increase in interference in the marine environment, the performance of conventional cross-spectrum target velocity estimation methods gradually declines or even fails. To solve this problem, a cross-spectrum histogram method that combines the multi-line spectrum characteristics of the target is proposed in this paper. First, each frequency point of all line spectra is compensated by the cross-spectrum compensation method. Then the target velocity estimation value is obtained by performing probability distribution statistics on the velocity estimation results for all frequency points. Under different signal-to-noise ratios, simulations and experiments are carried out to verify the effectiveness of the proposed method. The results show that the proposed method is still effective in estimating the target velocity when the conventional method fails.

Research on the low-frequency multiline spectrum vibration control of offshore platforms

Abstract With the increasing scale, complexity and diversity of supporting equipment of offshore platform, the low-frequency vibration of equipment such as dynamic positioning system and the main engine is difficult to attenuate in the propagation process of the platform structure, which causes a local resonance of platform, aggravates the fatigue damage of structure and causes discomfort to the human body. Dynamic vibration absorption is widely used in the low-frequency vibration control of offshore platforms; however, there is little research about the multiline spectrum vibration control method in the local resonance region of platforms. In the current research, we first take the stiffened plate under multipoint excitation as the research object, and the effectiveness of the optimal homology design method of dynamic vibration absorption is verified. Subsequently, the low-frequency multiline spectrum vibration control method about the local resonance region of the offshore platform is proposed. Finally, a large offshore platform is chosen as the research object and the measured load of the main engine is taken as the input to calculate the vibration response of the platform. The effect of distributed dynamic vibration absorption of the resonance area verifies the effectiveness of the vibration control method presented in the article and provides a basis for the engineering application.

Multi-line spectrum feedback control algorithm for active vibration isolation

Multi-line spectrum feedback control algorithm for active vibration isolation

Fast multiline spectral reshaping algorithm for active vibration control

Multiline spectral vibration (or noise) is very common in rotating machinery like motor, gearbox, compressor, propeller, etc. Active reshaping of these vibrations is one of the most important branches for active vibration control, which may find application in fields of sound quality control, psychoacoustics, military camouflage, etc. The traditional filtered-reference LMS is the most popular structure for multiline spectral reshaping control. However, with the increase of spectral lines, vibration sources and observation points (feedback channels), the traditional structure will have extremely heavy computational complexity, especially for the system whose dynamic of secondary path is complex, since it requires two long filters for every single spectral line and secondary path to adjust the reference signals. In this study, we propose a fast-multiline spectrum reshaping algorithm for active vibration control. We first construct an equivalent system of the traditional multiline spectrum reshaping algorithm by introducing two extra control branches, which is able to improve the convergence property of the system. Then, we generate a group of pre-phase-scheduled reference signals using the phase information at certain frequencies of the secondary paths instead of using filters. Afterwards, we conduct a theoretical analysis of computational complexity of multiline spectrum reshaping and fast multiline spectrum reshaping algorithms. Finally, we carried out two case studies based on the FEMilS test-bed to verify the effectiveness of the proposed algorithm. The results show that the proposed algorithm performs an accurate residual vibration control with uniformed convergence speed and reduced computational complexity.

High-gain and low-distortion Brillouin amplification based on pump multi-frequency intensity modulation**Project supported by the National Natural Science Foundation of China (Grant No. 61605034).

Using a pump with a multi-line spectrum to broaden the Brillouin gain bandwidth is an effective way to achieve low-distortion amplification with high gain. Here, we theoretically and experimentally investigate the generation of a broadband Brillouin gain spectrum based on multi-frequency intensity modulation in an optical fiber. The arbitrary bandwidth of the Brillouin gain spectrum of stimulated Brillouin scattering (SBS) can be obtained as expected. In our experiment, a broadband Brillouin gain spectrum with a bandwidth of about 200 MHz is demonstrated. We also achieve a low-distortion amplification of a weak signal, whose maximum magnification is 65 dB for a −68-dBm input power signal.

A Three-Dimensional Target Depth-Resolution Method with a Single-Vector Sensor.

This paper mainly studies and verifies the target number category-resolution method in multi-target cases and the target depth-resolution method of aerial targets. Firstly, target depth resolution is performed by using the sign distribution of the reactive component of the vertical complex acoustic intensity; the target category and the number resolution in multi-target cases is realized with a combination of the bearing-time recording information; and the corresponding simulation verification is carried out. The algorithm proposed in this paper can distinguish between the single-target multi-line spectrum case and the multi-target multi-line spectrum case. This paper presents an improved azimuth-estimation method for multi-target cases, which makes the estimation results more accurate. Using the Monte Carlo simulation, the feasibility of the proposed target number and category-resolution algorithm in multi-target cases is verified. In addition, by studying the field characteristics of the aerial and surface targets, the simulation results verify that there is only amplitude difference between the aerial target field and the surface target field under the same environmental parameters, and an aerial target can be treated as a special case of a surface target; the aerial target category resolution can then be realized based on the sign distribution of the reactive component of the vertical acoustic intensity so as to realize three-dimensional target depth resolution. By processing data from a sea experiment, the feasibility of the proposed aerial target three-dimensional depth-resolution algorithm is verified.

Performance comparisons between semiconductor and fiber amplifier gain assistance in a recirculating frequency shifter.

Recirculating frequency shifter (RFS) loops can be used for electronically programmable, variable-spacing multiline spectrum generation, which can benefit the development of fully flexible optical communications and other frequency comb applications. Here, we report on and explain the observation of significant performance variations between chip-based gain in semiconductor optical amplifiers (SOA) and fiber-based gain in erbium-doped fiber amplifiers (EDFA) when used as the gain element in the RFS. Previously, SOAs and EDFAs have been demonstrated in different RFS experiments and studied separately from each other; thus, discussion mainly focused on the noise from amplified spontaneous emission. We show that SOA effects, including four wave mixing, can be measured, which impose limits to the wavelength spacing of the combs, and that this effect is mitigated by increasing the RF drive frequency of the RFS and operating SOA in deeper saturation.

Optimization of a Multiline Neutron Source Based on a 232Th Filter

A multiline neutron source can be produced by using a metallic 232Th filter in conjunction with a white neutron source. The multiline spectrum consists of ∼20 relatively strong intensity lines ranging from 10 to 4000 eV. It is shown that the width of each neutron line of the spectrum is strongly dependent on the absorber thickness. This neutron source is useful for accurate cross section measurements with precise neutron energies. The optimum thickness of the 232Th absorber, which was found to yield a sharp multiline spectrum throughout the above energy range, was found to be ∼14 cm.

Deformation Defects Supporting Quantum Readout of 29 Si Nuclear Spins in Si: P Deformed Crystals

High temperature (950 °C) plastic deformation of the 29Si enriched silicon crystals generates ˜10 15 cm−3 paramagnetic defects of the new type. The multiline spectrum of electron paramagnetic resonance (EPR) of the defects corresponds to S = 1 electronic spin of the clusters containing oxygen. Strong anisotropy and large linewidth of the EPR spectra (˜1 kOe) were observed. The Pake doublet split by spin-spin nuclear dipole interaction was analyzed in the nuclear magnetic resonance (NMR) spectra of the crystals. Contribution of the electron-nuclear interaction to the EPR linewidth is negligibly small, while the NMR linewidth is controlled by the dipole-dipole nuclear relaxation.

Contrasting the experimental properties of hydrogen in SnO2, In2O3, and TiO2

IR spectroscopy has been used to investigate the properties of H and D in single crystals of the transparent conducting oxides, SnO2, and In2O3. H introduces several O-H stretching lines and also the broad absorption arising from free carriers. IR spectroscopy has been used to identify the sources of n-type conductivity, its thermal stability, and the reactions of H-containing defects. The properties of OH and OD centers in TiO2, while studied for decades, reveal new surprises and properties that are in sharp contrast to the shallow, H-related donors seen in SnO2 and In2O3. Recent theory and EPR experiments find that electrons in TiO2 become self-trapped at Ti sites to form small polarons. The OD center in TiO2 shows a multiline vibrational spectrum with an unusual temperature dependence that can be explained by a small polaron model with the donor electron self-trapped at different Ti sites near the OD oscillator.

Intramolecular Transport of Charge Carriers in Trimeric Aniline upon a Three-Step Acid Doping Process

The "acid doping" of a methyl-capped aniline trimer, N-[4-(dimethylamino)phenyl]-N-(4-{[4-(dimethylamino)phenyl]imino}-2,5- cyclohexadien-1-ylidene)-amine (TANI), was performed stoichiometrically to study the nature of charge carriers induced by the acid protonation process. The redox centers in TANI were found to undergo a reversible three-step protonation with 1 equiv, 2 equiv and a large molar excess of dodecylbenzenesulfonic acid (DBSA) in chloroform, as evidenced by three different chromophores (doping levels I, II and III) observed using UV-vis-NIR. Acidity of the dopants and solvent polarity were controlling factors. As revealed by electron paramagnetic resonance spectroscopy (EPR), the doping levels I, II, and III achieved by doping 0.1 mM TANI/chloroform solutions with different amounts of DBSA exhibited relative spin densities of 1:1.2:2.2. Since the expected maximum spin population of TANI through acid doping is two spins per molecule, the reduced paramagnetism given by the doubly protonated TANI (doping level II) indicated partially coupled unpaired spins. The third protonation step (doping level III) produced almost double the unpaired spin concentration compared to the lower doping levels and a multiline EPR spectrum likely comprising two overlapping signals of similar overall line width. The hyperfine couplings contributing to the splittings in this signal were estimated by simulation incorporating 6-H and 1-N nuclei most likely from one highly localized unpaired spin on a terminal dimethylamino group, with an underlying apparent singlet arising from a delocalized unpaired spin; the diradical proposed as the species exhibiting the multiplet EPR signal is isolated by the bridging ammonium cation created by the third doping step. The phenomena suggested the stepwise evolution of partly formed diamagnetic bipolarons from polaron interactions at doping level II and the transformation to the more isolated unsymmetrical system we label "two polarons on a chain" in a triplet state at doping level III. The results provide the characterization of novel doping behaviors for a trimeric aniline molecule in organic solution.