Theoretical analysis of the optical rotational Doppler effect under atmospheric turbulence by mode decomposition

The optical rotational Doppler effect associated with orbital angular momentum provides a new means for rotational velocity detection.In this paper,we investigate the influence of atmospheric turbulence on the rotational Doppler effect.First,we deduce the generalized formula of the rotational Doppler shift in atmospheric turbulence by mode decomposition.It is found that the rotational Doppler signal frequency spectrum will be broadened,and the bandwidth is related to the turbulence intensity.In addition,as the propagation distance increases,the bandwidth also increases.And when C_(n)^(2)≤5×10^(-15)m^(-2/3)and 2z≤2 km,the rotational Doppler signal frequency spectrum width d and the spiral spectrum width d_(0)satisfy the relationship d=2d_(0-1).Finally,we analyze the influence of mode crosstalk on the rotational Doppler effect,and the results show that it destroys the symmetrical distribution of the rotational Doppler spectrum about 2l·Ω/2π.This theoretical model enables us to better understand the generation of the rotational Doppler frequency and may help us better analyze the influence of the complex atmospheric environment on the rotational Doppler frequency.

Effect Due to the Particle Nature of the Doppler Shifted Radiation on the Dynamics of the Spherical Light Emitting Source

The Doppler effect is a phenomenon of intrinsic kinematic character. This paper analyzes the kinematic Doppler effect for the case where the source is moving and the observer is at rest in the classical limit. The particle nature properties of radiation are considered and how it affects the dynamics of the Source has been studied. The dynamical and kinematical equations have been derived by considering this effect. It has been conclusively shown that a moving light-emitting source experiences a finite recoil momentum in the direction opposite to the direction of motion and come to rest in finite time.

First spectroscopic study of HFRC plasma

An advanced spectral diagnostic system was developed to measure the electron temperature(T_(e)),electron density(N_(e)),and ion temperature(T_(i))of the Huazhong University of Science and Technology field-reversed configuration plasma.The system consists of an optic fiber spectrometer with a wide spectral band and a 670 mm focal length high throughout Czerny-Turner monochromator equipped with both a 3600 g mm^(-1)grating and a 2400 g mm^(-1)grating to measure the line spectrum.Accompanying these components is an electronmultiplying charge-coupled device camera to capture spectral data.The relative intensity of the optical fiber spectrometer was calibrated using a standard luminance source,and the wavelength calibration of the spectrometer was accomplished using a Hg/Ar lamp.This diagnostic setup was configured to measure electron density based on the Stark effect of H_γ(n=5→n=2;434.04 nm).Doppler broadening of an OⅢ(2s^(2)2p(^(2)P^(0))3p→2s^(2)2p(^(2)P^(0))3s;375.988 nm)emission line was measured and analyzed to obtain the ion temperature,and electron temperatures were estimated from the relative strength of H_(β)(n=4→n=2;486.14 nm)(D_(β))and H_(γ)(D_(γ))spectral lines when the electron density was obtained from Stark effect measurements.The initial experimental results indicate that the highest electron temperature of the formation region was approximately 8 eV,the electron density of the colliding-and-merging region was approaching 10^(20)m^(-3),and the ion temperature reached about 40 eV.

Doppler effect of the rupture process of the great M_W7.9 Wenchuan earthquake

In this study we performed a classical spectrum analysis of seismic waveforms recorded at far field stations of the great MW7.9 Wenchuan earthquake to observe the shifts of the corner frequency with azimuth due to the Doppler effect.Our results show that this damaging great earthquake had a dominating rupture propagation direction of 64.0°.The equivalent radius of the fault rupture surface was estimated to be 33 km,yielding the rupture area of about 3 500 km2.Thus the length of the rupture fault surface is about 230 km if the depth（or width） extent is 15 km.The computer program developed in this study can quickly provide the information about the source of a future large（damaging） earthquake,which could be very useful for predicting aftershocks and planning the rescue operations.

Noticeable positive Doppler effect on optical bistability in an N-type active Raman gain atomic system

We theoretically investigate the Doppler effect on optical bistability in an N-type active Raman gain atomic system inside an optical ring cavity. It is shown that the Doppler effect can greatly enhance the dispersion and thus create the bistable behaviour or greatly increase the bistable region, which has been known as the positive Doppler effect on optical bistability. In addition, we find that a positive Doppler effect can change optical bistability from the hybrid dispersion-gain type to a dispersive type.

An analytical model for cross-Kerr nonlinearity in a four-level N-type atomic system with Doppler broadening

We present an analytical model for cross-Kerr nonlinear coefficient in a four-level N-type atomic medium under Doppler broadening.The model is applied to87 Rb atoms to analyze the dependence of the cross-Kerr nonlinear coefficient on the external light field and the temperature of atomic vapor.The analysis shows that in the absence of electromagnetically induced transparency(EIT)the cross-Kerr nonlinear coefficient is zero,but it is significantly enhanced when the EIT is established.It means that the cross-Kerr effect can be turned on/off when the external light field is on or off.Simultaneously,the amplitude and the sign of the cross-Kerr nonlinear coefficient are easily changed according to the intensity and frequency of the external light field.The amplitude of the cross-Kerr nonlinear coefficient remarkably decreases when the temperature of atomic medium increases.The analytical model can be convenient to fit experimental observations and applied to photonic devices.

Coherent Phase-Coded Pulse Train with Doppler Cascade-Processing for Detection of Aircraft Target in a HF Radar

The effect of range-Doppler coupling caused by aircraft moving at very high speed makes trouble on selection of waveform parameters by using frequency-modulated interrupted continuous wave (FMICW) or frequency-coded pulse (FCP). It also limits the increasing of coherent integration time. In this paper, application of coherent phase-coded pulse train (CPCPT) solves range-Doppler coupling well. Relevant processing of CPCPT consists of three parts: Doppler preprocessing, pulse compression, and Doppler post-processing. The velocity information obtained by Doppler preprocessing is used for better pulse compression and range tracking. Doppler post-processing with range tracking could make longer coherent accumulation for better detection of target and higher velocity resolution. Finally, examples of data simulation are given to demonstrate the achievements mentioned above.

The Doppler effect induced by earthquakes:A case study of the Wenchuan MS8.0 earthquake

Seismologists have found that the first arrival frequencies of P waves at different seismic stations have different widths,that is,different periods or frequencies,and they think that this phenomenon can be used to identify whether a Doppler effect is induced by earthquakes.However,the fault rupture process of a real earthquake is so complex that it is difficult to identify a frequency shift similar to the Doppler effect.A method to identify whether a Doppler effect is induced by an earthquake is proposed here.If a seismic station is in the direction of fault rupture propagation,this station could observe a Doppler effect induced by the earthquake.The Doppler effect causes the frequency of the seismic wave to shift from low frequency to high frequency,and the high frequency amplitudes become mutually superimposed.Under the combined influences of the absorption effect,geometric spreading effect and Doppler effect,the high frequency amplitude of the seismic wave will gradually become higher than the low frequency amplitude with increasing epicentral distance.If we find that the high frequency amplitude is higher than the low frequency amplitude with increasing epicentral distance in the direction of fault rupture propagation,then there is a Doppler effect.The fault that generated the Wenchuan earthquake is a reverse fault,and its horizontal rupture propagation velocity was low.To link fault rupture propagation velocity with the Doppler effect and identify the Doppler effect more easily,we decompose three-component records into two directions:the direction of fault rupture propagation and the direction perpendicular to the fault rupture propagation along the fault plane.The initial components of the two directions are processed by wavelet transform.Several seismic stations in the direction of fault rupture propagation of the Wenchuan earthquake were selected,and it was found that with increasing epicentral distance,the high frequency amplitudes of the wavelet spectra become obviously higher than the low frequency amplitudes.It can be concluded that due to the existence of the Doppler effect,high frequency amplitudes can overcome the influences of the absorption and geometric spreading effects on seismic waves in the fault rupture propagation process.

The Modulation of Ionospheric Alfvén Resonator on Heating HF Waves and the Doppler Effect

The propagation of HF waves in IAR can produce many nonlinear effects, including the modulation effect of IAR on HF waves and the Doppler effect. To start with the dependence of the ionospheric electron temperature variations on the Alfvén resonant field, We discuss the mechanism of the modulation effect and lucubrate possible reasons for the Doppler effect. The results show that the Alfvén resonant field can have an observable modulation effect on HF waves while its mechanism is quite different from that of Schumann resonant field on HF waves. The depth of modulation of IAR on HF waves has a quasi\|quadratic relation with the Alfvén field, which directly inspires the formation of cross\|spectrum between ULF waves and HF waves and results in spectral peaks at some gyro\|frequencies of IAR. With respect to the Doppler effect during the propagation of HF waves in IAR, it is mainly caused by the motion of the high\|speed flyer and the drifting electrons and the frequency shift from the phase variation of the reflected waves can be neglected when the frequency of HF incident wave is high enough.

Experimental Studies of the Doppler Effect

Recent experimental results of the Doppler effect formula verification are reported. The moving emitters are hydrogen atoms in the excited state. The results of the work corroborate the classical not the relativistic,formula for the Doppler effect.

The Application of Prostaglandin E_1 Indirect Portal Vein Angiography and Color Doppler Ultrasound in Patients with Post－deva

The selection of proper treatment is based on identification of the causes of massive hemorrhage of gastrointestinal tract after pericardial devascularization.The combined use of prostaglandin E1 indirect portal vein angiography, DSA of celiac artery and color Doppler can provide detailed information about portal vein system,including the presence of embolism, spongioid changes and devasculization of left gastric vein and left gastric artery and the direction of blood flow. If these techniques failed to reveal the causes of digestive tract bleeding, the endoscopy may show lesions of gastric mucosa, which could be accountable for the bleeding.

Nonreciprocal negative refraction in a dense hot atomic medium

We investigate the electromagnetic properties of a four-level dense atomic gas medium with Doppler effect.It is shown that the relative permittivity and relative permeability of the medium can be negative simultaneously with low absorption in the same detuning interval on account of electromagnetically induced transparency.Furthermore,with the suitable parameters,the nonreciprocal negative refraction can be obtained due to the Doppler effect,and the nonreciprocity frequency band can be regulated by adjusting the temperature,the intensity of the control field and the atomic density in this hot atomic medium.

A Thermal Analogue of the Zel’Dovich Effect

We analyze in this work anisotropic heat conduction induced by a harmonically oscillating laser source incident on rotating conductors, exploiting an analogy with an effect discovered long ago, called the Zel’dovich effect. We re-covered the main results of a recently published paper that predicts the translational Doppler frequency shift of a thermal wave induced on a sample moving with uniform rectilinear motion. We extend then this framework to take into account the frequency shift of a thermal field propagating on a rotating platform. We show that it coincides with the rotational frequency shift which has been recently observed on surface acoustic waves and hydrodynamic surface waves, called rotational superradiance. Finally, we use an analogy with the Tolman effect to deduce a simple estimate of the average temperature gradient induced by rotation, showing the existence of a new cooling effect associated with heat torque transfer.

Elements of Time

A clear mathematical theory of time remains one of the most difficult challenges of science, which seems highly intriguing. In this work, we assume that time is the main independent attribute of nature and therefore may serve as the foundation of a comprehensive field theory. Furthermore, we assume that division algebras with the Euclidean norm are essential mathematical tools of time and the physical world in general. We use a four-dimensional normed division algebra of quaternions to describe time mathematically, as originally envisioned by Hamilton. We systematically define basic quaternion concepts related to time, such as the quaternion time interval, scalar measured time, the arrow of time, vector velocity, and quaternion frequency. We apply quaternion time concepts to the optical Doppler effect and demonstrate that our approach predicts known experimental results. Furthermore, we show that the quaternion solution of the Doppler effect enhances the relativity theory by resolving the notorious twin paradox. We identify quaternion frequency with the traditional concept of energy. We assume that quaternion energy, which is generally dependent on time and external interactions, can be used to describe dynamic properties of matter. In conclusion, we suggest that a state of matter can be represented by the eight-dimensional octonion configuration space, consisting of a quaternion time interval and a time dependent quaternion frequency. Therefore, it appears that the application of normed division algebras for the study of time and nature is highly logical, credible, and compelling.

In situ measurement on nonuniform velocity distributionin external detonation exhaust flow by analysis ofspectrum features using TDLAS

Instantaneous and precise velocity sensing is a critical part of research on detonation mechanism and flow evolution.This paper presents a novel multi-projection tunable diode laser absorption spectroscopy solution,to provide a real-time and reliable measurement of velocity distribution in detonation exhaust flow with obvious nonuniformity.Relations are established between overlapped spectrums along probing beams and Gauss velocity distribution phantom according to the frequency shifts and tiny variations in components of light-of-sight absorbance profiles at low frequencies analyzed by the fast Fourier transform.With simulated optical measurement using H2O feature at 7185.6 cm-1 carried out on a phantom generated using a simulation of two-phase detonation by a two-fluid model,this method demonstrates a satisfying performance on recovery of velocity distribution profiles in supersonic flow even with a noise equivalent absorbance up to 2×10^(-3).This method is applied to the analysis of rapidly decreasing velocity during a complete working cycle in the external flow field of an air-gasoline detonation tube operating at 25 Hz,and results show the velocity in the core flow field would be much larger than the arithmetic average from traditional tunable diode laser doppler velocimetry.This proposed velocity distribution sensor would reconstruct nonuniform velocity distribution of high-speed flow in low cost and simple operations,which broadens the possibility for applications in research on the formation and propagation of external flow filed of detonation tube.

A method of measuring micro-impulse with torsion pendulum based on multi-beam laser heterodyne

In this paper, we propose a novel method of multi-beam laser heterodyne measurement for micro-impulse. The measurement of the micro-impulse, which is converted into the measurement of the small tuning angle of the torsion pendulum, is realized by considering the interaction between pulse laser and working medium. Based on Doppler effect and heterodyne technology, the information regarding the small tuning angle is loaded to the frequency difference of the multi-beam laser heterodyne signal by the frequency modulation of the oscillating mirror, thereby obtaining many values of the small tuning angle after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, the small tuning angle can be obtained accurately and the value of the micro-impulse can eventually be calculated. Using Polyvinylchlorid＋2%C as a working medium, this novel method is used to simulate the value of the micro-impulse by MATLAB which is generated by considering the interaction between the pulse laser and the working medium, the obtained result shows that the relative error of this method is just 0.5%.

Intelligent Blind Source Separation Technology Based on OTFS Modulation for LEO Satellite Communication

In LEO(Low Earth Orbit)satellite communication system,the orbit height of the satellite is low,the transmission delay is short,the path loss is small,and the frequency multiplexing is more effective.However,it is an unavoidable technical problem of the significant Doppler effect caused by the interference between satellite networks and the high-speed movement of the satellite relative to the ground.In order to improve the target detection efficiency and system security of LEO satellite communication system,blind separation technology is an effective method to process the collision signals received by satellites.Because of the signal has good sparsity in Delay-Doppler domain,in order to improve the blind separation performance of LEO satellite communication system,orthogonal Time-Frequency space(OTFS)modulation is used to convert the sampled signal to Delay-Doppler domain.DBSCAN clustering algorithm is used to classify the sparse signal,so as to separate the original mixed signal.Finally,the simulation results show that the method has a good separation effect,and can significantly improve the detection efficiency of system targets and the security of LEO satellite communication system network.

Velocity Diagnosis of Critical Surface at Microwave Band in Laser-Induced Plasma

The velocity of critical surface at microwave band in laser-induced plasma was measured and the results are presented. The results indicate that the velocity of critical surface with low electron density is larger than that with the high one; and the velocity of critical surface increases with the laser power density.

A Study on Ionospheric HF Channel with Bitemporal Response and Scattering Function

At first the bitemporal response method is introduced to solve the scattering function of the ionospeeric channel. We can get the scattering function, as a function, of the group path time delay and Doppler frequency. Thus Doppler effect resulting from the continuous movement of the ionosphere is analyzed to study the characteristics of the various ionospheric irregularities and diturbance. many possible problems and correction are researched lastly.

A Sequential Adaptive Method for Enhancing DOA Tracking Performance

A sequential processing is presented aiming at optimizing the direction of arrival(DOA)tracking performance.Firstly,current positions and Doppler frequency are estimated and a mathematical model is derived in order to clarify the effect of Doppler frequency on the estimation.The Doppler effect is employed within subspace concept in order to refine the estimation of the target position.Secondly,a renewed weight factor that depends on target maneuver is employed in order to realize more accurate association and smoothing processes.Simulation results show that the presented method has high accuracy in DOA tracking.