Frequency Shift Parameter Research Articles

Non-cooperative underwater acoustic MFSK time-frequency representation optimization method based on sparse reconstruction

The performance of the traditional non-cooperative underwater acoustic (UWA) multiple frequency shift key (MFSK) recognition and parameter estimation method based on time-frequency representation (TFR) is affected by TFR energy divergence. Herein, a sparse TFR estimation model for UWA MFSK is presented. The model exploits the properties of MFSK TFR element sparsity and row sparsity, which can effectively reduce the impact of the channel and does not require any a priori information. To achieve better TFR performance, we propose an inversion fitting method that can effectively improve the frequency resolution, while keeping the time resolution unchanged. Simulation and experimental results show that the Peak Signal to Noise Ratio (PSNR) of the proposed method reaches 21dB with the increase of Signal to Noise Ratio (SNR), indicating that the proposed method has high carrier frequency reconstruction and noise suppression performance. The proposed method can continuously reduce the value of Average Carrier Frequency Offset (ACFO) under inversion fitting method, indicating that inversion fitting method can further reduce the energy divergence and improve frequency resolution.

Nonlinear site response at liquefiable sites: Insights from downhole seismic observations

The nonlinear behavior of shallow soil plays an important role in modifying surface ground motions. We analyze the nonlinear site response at liquefiable sites using the compiled long-term ground motion data (ranging from 1992 to 2020 with over 2000 earthquake events) at four high-quality downhole arrays that have liquefied during at least one earthquake. Two nonlinear event parameters, the percentage of nonlinearity (PNL) and the frequency shift parameter (fsp), are used to quantify the modification of site response of strong events to that of weak events. Site-specific regression analyses are performed to correlate nonlinear event parameters to incident motion parameters. Results indicate that site response at liquefiable sites varies from linear to nonlinear to liquefied states as the incident motion intensity changes, and the occurrence of liquefaction could enhance the amplification of low-frequency and very-high-frequency ground motions. As strong-motion observations for liquefiable sites are very limited, the findings of this work are of significance for further study of strong-motion seismology at liquefiable sites.

Critical magnetic behavior in [Ag8/Co0.5]x64, [Ag8/Co1]x32 and [Ag16/Co1]x32 epitaxial multilayers

We investigate the low temperature magnetic behavior of three epitaxial Co/Ag multilayers, grown onto MgO (001) substrates, with a nominal content per period of either half a monolayer or one monolayer of Co, and either 8 or 16 Ag monolayers. The samples were studied by X-ray reflectivity and diffraction, transmission electron microscopy, magnetometry and ac susceptometry. The results indicated a well defined stacking sequence in the growth direction, the number of periods and of Ag monolayers per period being coincident with the nominal values for each sample. The Co layers were found to be discontinuous and corresponded to a quasi-monodisperse in-plane distribution of Co nanoparticles embedded in a Ag(001) matrix. The zero-field cooled and field cooled temperature variations of the low field magnetization indicated the presence of irreversibilities at temperatures below 20 K. The ac field frequency (f) and temperature (T) dependencies of the real part of the susceptibility (χ′) corresponded to a Vogel–Fulcher behavior in the three samples, and indicated a frequency shift parameter (Γ) of the order of 4 x 10-2. For each sample, the experimental data corresponding to the variations of the imaginary part of the ac susceptibility (χ″) with f and T were found to collapse into a single curve according to the dynamic scaling law. Taken together, these results allow us to conclude that the three multilayers experience a phase transition of the paramagnetic to superspin glass type, driven by the dipolar interactions between the Co nanoparticles. Regarding the influence of the multilayer features, we found a clear dependence of the order parameter of the transition on the nominal number of Co monolayers per period.

Variation of a signal in Schwarzschild spacetime

In this paper, the variation of a signal in Schwarzschild spacetime is studied and a general equation for frequency shift parameter (FSP) is presented. The FSP is found to depend on the gravitationally modified Doppler effects and the gravitational effects of observers. In addition, the time rates of a transmitter and receiver may differ. When the FSP is a function of the receiver time, the FSP contributed through the gravitational effect (GFSP) or the gravitationally modified Doppler effect (GMDFSP) may convert a bandlimited signal into a non-bandlimited signal. Using the general equation, the FSP as a function of receiver time is calculated in three scenarios: (a) a spaceship leaving a star at constant velocity communicating with a transmitter at a fixed position; (b) a spaceship moving around a star with different conic trajectories communicating with a transmitter at a fixed position; and (c) a signal transmitted from a fixed position in a star system to a receiver following an elliptic trajectory in another star system. The studied stars are a Sun-like star, a white dwarf, and a neutron star. The theory is illustrated with numerical examples.

7T GRE-MRI signal compartments are sensitive to dysplastic tissue in focal epilepsy

Ultra-high field magnetic resonance imaging data obtained using a multi-echo gradient echo sequence has been shown to contain information on tissue microstructure. Quantitative assessment of water fraction, relaxation time and frequency shift using multi-compartment signal modelling may help improve our understanding of diseases and disorders affecting the human brain. In this study, we explored tissue microstructure information by analysing voxel compartment water fraction and frequency shifts derived from 7 T multi-echo gradient recalled echo MRI data. We aimed to test whether the parameters of a three compartment model could distinguish the normal cortex from the cortex affected by focal cortical dysplasia. We compartmentalised normal and dysplastic cortical regions in patients diagnosed with focal cortical dysplasia. We found the frequency shift parameter of the shortest T2⁎ signal compartment to be sensitive to regions of dysplastic tissue. We conclude that mathematical modelling of echo time dependent gradient recalled echo MRI signals in patients with focal cortical dysplasia can potentially delineate cortical areas that have undergone microstructural changes in comparison to normal tissue.

A prospective evaluation of hepatic steatosis using quantitative ultrasonographic parameters using controlled attenuation parameter as the reference standard

Purpose To investigate the diagnostic performance of quantitative ultrasonography (QUS) for the assessment of hepatic steatosis in patients with chronic liver disease using controlled attenuation parameter (CAP) as the reference standard. Materials and Methods Our institutional review board approved this study, and informed consent was obtained from all of the patients. In this prospective study, we analyzed 216 patients with chronic liver disease who had reliable measurement results at both QUS and CAP. QUS parameters included center frequency shift (a slope of center frequency change according to depth) and Nakagami parameter (backscattered distribution). Correlation between QUS parameters and CAP was evaluated using the Pearson's correlation analysis. In addition, based on the cut-off value of ≥ 288 dB/m on CAP, diagnostic performance of QUS parameters for hepatic steatosis was assessed using the receiver operating characteristics (ROC) curve analysis. Multiple regression analysis was performed to determine significant independent factors for the hepatic steatosis on CAP. Intra-operator reliability (repeatability) of QUS parameter measurements was assessed with intraclass correlation coefficients (ICCs). Results Center frequency shift showed a moderate negative correlation with CAP (r = −0.66; 95% confidence interval (CI), −0.73 to −0.59; P Conclusion Quantitative ultrasonographic parameters, including center frequency shift and Nakagami parameter, were demonstrated to be well correlated with CAP and thus may provide good diagnostic performance in the assessment of hepatic steatosis, making it a promising tool for the noninvasive assessment and quantification of hepatic steatosis.

Anti-dark solitons for a variable-coefficient higher-order nonlinear Schrödinger equation in an inhomogeneous optical fiber

Investigated in this paper is a variable-coefficient higher-order nonlinear Schrödinger equation, which can describe the propagation of subpicosecond or femtosecond optical pulse in an inhomogeneous optical fiber. With a set of the Painlevé-integrable coefficient constraints, the equation is transformed into its bilinear forms. Single- and two- anti-dark soliton solutions are constructed via the Hirota method. Based on the solutions, we graphically discuss the features of the anti-dark solitons, as well as their interaction, in the inhomogeneous optical fibers. As shown in our results, the backgrounds of the anti-dark solitons are related to the gain/loss coefficients, while the third-order dispersion coefficients directly influence the propagation trajectories of the anti-dark solitons, which provide a possible way to manage these solitons in the inhomogeneous fiber. On the other hand, overtaking interaction between the two anti-dark solitons is obtained, and seen to be elastic. The frequency shift parameter has almost no effect on the solitons.

Phase and amplitude dynamics in large systems of coupled oscillators: Growth heterogeneity, nonlinear frequency shifts, and cluster states

This paper addresses the behavior of large systems of heterogeneous, globally coupled oscillators each of which is described by the generic Landau-Stuart equation, which incorporates both phase and amplitude dynamics of individual oscillators. One goal of our paper is to investigate the effect of a spread in the amplitude growth parameter of the oscillators and of the effect of a homogeneous nonlinear frequency shift. Both of these effects are of potential relevance to recently reported experiments. Our second goal is to gain further understanding of the macroscopic system dynamics at large coupling strength, and its dependence on the nonlinear frequency shift parameter. It is proven that at large coupling strength, if the nonlinear frequency shift parameter is below a certain value, then there is a unique attractor for which the oscillators all clump at a single amplitude and uniformly rotating phase (we call this a single-cluster "locked state"). Using a combination of analytical and numerical methods, we show that at higher values of the nonlinear frequency shift parameter, the single-cluster locked state attractor continues to exist, but other types of coexisting attractors emerge. These include two-cluster locked states, periodic orbits, chaotic orbits, and quasiperiodic orbits.

Simultaneous distributed strain and temperature sensing based on combined Raman–Brillouin scattering using Fabry–Perot lasers

An investigation is performed of the possibility of achieving simultaneous distributed strain and temperature sensing based on hybrid Raman–Brillouin scattering with the use of multi-wavelength optical sources such as common Fabry–Perot (FP) lasers. By employing a self-heterodyne detection scheme based on a multi-wavelength optical local oscillator, the benefits of FP lasers are fully exploited, allowing for high-power Raman intensity measurements and a simultaneous high-accuracy detection of the Brillouin frequency shift parameter for each FP longitudinal mode. Experimental results point out a significant reduction of coherent Rayleigh noise, and highlight the enhanced performance in hybrid Raman–Brillouin sensing when using FP lasers; in particular using standard FP lasers at 1550 nm results in about 12 dB (7 dB) temperature (strain) accuracy improvement at 25 km sensing distance with respect to the use of standard distributed feedback lasers.

On a necessary condition for B-spline Gabor frames

In a previous note Grochenig et al. prove that if g is a continuous function with compact support such that the translates of g form a partition of unity, then g cannot generate a Gabor frame for integer values of the frequency shift parameter b greater than 1 (Grochenig et al. in IEEE Trans Inform Theory 49:3318–3320, 2003). We give a simpler proof of this result which applies also to windows g which are neither continuous nor with compact support. Our proof is based on a necessary condition for Gabor frames due to Heil and Walnut.

Fiber-Optic Distributed Sensor Based on Hybrid Raman and Brillouin Scattering Employing Multiwavelength Fabry–PÉrot Lasers

We propose the use of standard multiwavelength Fabry–PErot (FP) lasers for distributed strain and temperature measurement in hybrid Raman- and Brillouin-based fiber-optic sensors. The multiple longitudinal modes of FP lasers allow for accurate spontaneous Raman scattering measurement and for simultaneous high-sensitivity coherent detection of the Brillouin frequency shift parameter for all longitudinal modes. Experimental results confirm great performance improvement in simultaneous strain and temperature measurement using a single optical fiber.

FOUNDATION AND RESULTS OF A COSMOLOGY WITHOUT BIG BANG ON THE BASIS OF THE PROJECTIVE UNIFIED FIELD THEORY

After a short introduction into the Projective Unified Field Theory developed by the author during the last decades this theory is applied to a closed homogenous isotropic 2-component cosmos model, based on a mixture of a mechanical particle (urparticle) gas and a photon gas. The field equations lead to three nonlinear differential equations for the temporal course of the world radius, the scalaric world function and the mechanical energy density of the cosmos. These equations were solved numerically and evaluated in detail. The results are presented for a series of important cosmological quantities: world radius, world age, cosmological frequency shift and Hubble parameter, deceleration parameter, mechanical mass density, photon mass density, mechanical pressure, electromagnetic radiation pressure, kinetic particle temperature, electromagnetic radiation (microwave background) temperature, mechanical particle number density, photon number density, etc. Specific results of the theory are: explanation of the time dependence of the Newton gravitational constant, scalaric cosmological heat production in moving celestial bodies and the numerical value of the mass of an urparticle.

Traverse shear mode piezoelectric chemical sensor

The present invention relates to a process for sensing biological or chemical changes in molecular structural shape or mass of molecules attached to the surface of a transverse shear piezoelectric oscillating molecular sensing device driven by a network analyzer. The process comprises the steps of i) exciting the sensor device at a series of predetermined frequencies, ii) collecting data to determine values for the predetermined parameters of series resonance frequency shift (fS), motional resistance (RM), motional inductance (LM), motional capacitance (CM), electrostatic capacitance (Co) and boundary layer slip parameter (α); and iii) determining relative changes in the measured parameters to detect thereby any changes in molecular structural shape or mass at sensing device surface.

Spectroscopic studies of the adsorption and reactions of chlorofluorocarbons (CFC-11 and CFC-12) and hydrochlorofluorocarbon (HCFC-22) on oxide surfaces

Raman and Fourier transform infrared (FT-IR) spectroscopy have been applied to a systematic investigation of the adsorption and decomposition of dichlorodifluoromethane (CCl 2F 2, CFC-12), fluorotrichloromethane (CCl 3F, CFC-11), chlorodifluoromethane (CHClF 2, HCFC-22) and molecular chlorine on oxide surfaces. Additionally, the effects of heating and ultraviolet photolysis of the CFC and HCFCs adsorbed on the oxide surfaces have been investigated. Spectral features for these species indicated a small wavenumber shift (1−6 cm −1) associated with the adsorbed phase. Some evidence, specifically the appearance of the Raman band at 507 cm −1, is presented to show that chlorine decomposition species are associated with these oxide surfaces. It was concluded that the new spectral feature (at ca. 507 cm −1) related with the decomposition of the CFC and HCFC molecules was an important indicator of the extent to which the reaction between the adsorbed CFC and HCFC and oxide surface has taken place. The extent of CFC-surface interaction has been quantified in terms of a maximum (Raman) frequency shift parameter ( A M). Wavenumber shifts suggest both cation-adsorbate and non-specific adsorption interactions are occurring in the internal channels of the zeolites. Slow decomposition of the adsorbed CFCs under ultraviolet-visible photolysis (at λ > 300 nm) and/or thermal treatment was observed spectroscopically. Using FT-IR spectroscopy, the formation of gas-phase products (CO, CO 2, HCl) both onyn photolysis and heating was evident. Results of these measurements are compared with the observed atmospheric reactivity of these compounds.

Discrete Gabor expansion of discrete-time signals in [formula omitted] via frame theory

This paper presents the Gabor representation for discrete-time signals in l 2( Z) . The frame theory for discrete-time signals is introduced first. In this discrete Gabor expansion, the time-shift parameter N and the frequency-shift parameter M are taken to be integers with M ⩾ N for stable reconstruction. With the assumption that the Gabor analysis function has finite length, many useful formulae can be derived from frame theory. In particular, we discuss discrete-time signal decomposition and reconstruction and an algorithm for computing the dual frame by means of frame theory and time-frequency analysis. Important features of these results is that the decomposition and reconstruction can be easily computed, and perfect reconstruction is achieved. In particular: (1) we develop a frame theory for the discrete-time Gabor decomposition and reconstruction problem in l 2( Z) and derive formulae that can be directly implemented via DSP methods (these results cannot be obtained simply from digitizing the equivalent continuous-time formulation of Daubechies);(2) there are no constraints on the time-shift parameter N and frequency-shift parameter M except M ⩾ N for stable reconstruction, i.e., the oversampling ratio R = M/ N is a rational number, while in previous work that also dealt with discrete-time functions, the oversampling ratio can only be chosen from a few numbers dependent on the signal length; (3) the computation of the dual sequence is easy and fast in terms of Eqs. (1.9) and (1.12) (moreover, the matrix equation (1.12) for solving the dual can be separated into submatrix equations (1.15) thereby significantly reducing the computing time by a factor of M); and (4) examples are provided that illustrate the computation of dual frames (analysis sequences), the relationship between the dual frame and parameters M, N, and Q, comparisons with existing results, and the achievement of perfect reconstruction.

Active Chatter Suppression in Boring Operations.

The Chatter suppression in this paper is based on the application of active dampers to a boring bar. The active damping system consists of 1) a pickup to detect chatter vibrations, 2) a driver with a computer and 3) piezoelectric actuators as a damper. In this system, the chatter vibration signals are fed to the computer. After the chatter frequency and phase shift parameter are calculated by the computer, these signals are supplied to the piezoelectric actuators with the same phase as that of the vibration velocity of the boring bar. As a result of this, the actuators can generate damping forces. If the chatter frequency changes or fluctuates, the computer, which constantly monitors the chatter vibrations, recalculates the phase shift parameter and instantly supplies the modified signals to the actuators. This boring bar system has been examined in cutting tests. It has been confirmed that the system has a great effect on the chatter suppression and adapts to change and fluctuation of the chatter frequency.

Absorber speed dependence of the coherence relaxation rate of the J=0–1 transition of N2O

The coherence relaxation rate (T2) of the J=0 –1 transition of 15N2O has been examined using microwave transient techniques. The transient decays were analyzed by a model which considers the absorber speed dependence of the collisional relaxation process [S. L. Coy, J. Chem. Phys. 73, 5531 (1980)]. The decays were also analyzed by the standard speed independent model. In the speed dependent analysis, a linear absorber speed dependence of the form k(v)=k0+k1(v−v̄), where v̄ is the Boltzmann average speed, was assumed. Values of k0=0.0300(1) μs−1 mTorr−1 and k1v̄=0.0099(4) μs−1 mTorr−1 were determined. In the speed independent analysis a relaxation rate, k=0.029 22(6) μs−1 mTorr−1, was found. This corresponds to a pressure broadening parameter 1/2πT2 of 4.65(1) MHz/Torr. A zero pressure transition frequency and pressure dependent frequency shift parameter were also determined. They are 24 274.7865(1) MHz and +30(4) kHz/Torr, respectively. The experimental uncertainties reported above are two standard errors from linear least squares fits of k, k0, k1v̄, and transition frequency, vs sample pressure. The most significant systematic error is a 1% uncertainty in the pressure calibration which contributes an additional 1% error to the slopes determined from the linear least squares fits.