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Results for “Doppler Effect”

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At least 37 records · Page 2Linked to original sources
PubMed2006

Doppler effect in fluorine K-Auger line produced in electron-induced core ionization of SF6.

An experimental evidence is reported on the observation of the Doppler effect in fluorine K-Auger line emitted from a core-ionized SF6 molecule under an impact of 16 keV electrons. The emitting source of the Auger line is found to acquire a kinetic energy of 4.7+/-0.3 keV. We propose that such large energy is released from the Coulomb repulsion taking place between F+ and SF5+ fragment ions under influence of an intense focusing field of the incident electrons. In the presence of the Coulomb field of these ions, the Auger line obtains a polarization P = 76%+/-7%.

Journal Article↗
PubMed1991

Acoustical imaging and processing of blood vessel and the related materials using ultrasound Doppler effect.

In the present paper a method is proposed to measure the degree of the degradation of the elasticity in natural blood vessel and the related materials by using ultrasound Doppler effect. It was found that the deformation rate and its acceleration in the radial direction of the blood vessel can be detected by acoustical imaging and processing using this method. These results were proven to correspond to the degree of the degradation of the elasticity, that is, the degree of viscoelasticity in the blood vessel from the wave versus time pattern detected and its simple analysis. This method was applied to predicting the arteriosclerosis of blood vessels of humans by acoustical imaging and processing uninvadedly, as the characteristics of viscoelasticity in blood vessels.

Algorithms↗
PubMedDate not supplied

[New applications of the Doppler effect in urology].

Ultrasound is currently the noninvasive imaging technique most commonly utilized in the clinical setting. It can be used in two ways: to obtain morphological data and to obtain dynamic information via the Doppler effect.

Adenocarcinoma↗
PubMed2004

Relativistic Doppler effect: universal spectra and zeptosecond pulses.

We report on a numerical observation of the train of zeptosecond pulses produced by the reflection of a relativistically intense femtosecond laser pulse from the oscillating boundary of an overdense plasma because of the Doppler effect. These pulses promise to become unique experimental and technological tools since their length is of the order of the Bohr radius and the intensity is extremely high proportional, variant 10(19) W/cm(2). We present the physical mechanism, analytical theory, and direct particle-in-cell simulations. We show that the harmonic spectrum is universal: the intensity of nth harmonic scales as 1/n(p) for n<4gamma(2), where gamma is the largest gamma factor of the electron fluid boundary, and p=3 and p=5/2 for the broadband and quasimonochromatic laser pulses, respectively.

Journal Article↗
PubMedDate not supplied

[Study of arterial diseases of the lower limbs using an exercise test monitored by Doppler effect ultrasonometry].

A study has been carried out using Doppler ultrasonometry on 223 cases, 191 of them suffering from occlusive or stenosing arterial illnesses and 12 with deep massive venous thrombosis, together with 68 control cases. Systolic tensions in the popliteal, dorsalis pedis and posterior tibialis arteries, both at rest and after a conveniently standardized effort, were studied every five minutes over periods of up to thirty minutes. The results are shown grouping these patients according to their clinical features and giving their different responses to the test. Special emphasis is given to cases of badly compensated recent intermittent claudication, diffused atheromatosis, asymtomatic arterial stenosis, thromboangiitis obliterans, Leriche's syndrome and hypertensive ulcers.

Adolescent↗
PubMed1978

[Extra-intracranial arterial bypasses. Evaluation of their permeability by use of the Doppler effect].

40 temporo-sylvian anastomoses were controlled using Doppler ultrasonic examination. The results are compared to post-operative arteriograms. The Doppler examination has proved to be highly accurate when compared to contrast arteriography in the survey of extra-intracranial anastomosis. This non invasive procedure can easily be repeated. However the size of the revascularized area cannot be estimated. The simultaneous isotopic studies of regional cerebral blood flow could provide a means of quantifying the results of the anastomoses.

Carotid Artery, External↗
PubMed1994

Theoretical foundation on a noninvasive estimation for viscoelastic mechanical property of blood vessels by ultrasonic Doppler effect.

The method used in this paper is developed to estimate the degree of viscoelasticity of the blood vessel wall in a noninvasive mechanical method. In this proposed method, we can obtain an output waveform connected with mechanical behavior of blood vessels by using Ultrasonic Doppler Effect Sensory (UDES). Characterizing parameters on this waveform are established to estimate the mechanical properties of blood vessels. By analyzing the characteristics of these parameters, we attempt to estimate the viscoelastic property of blood vessels. Previously, it was found that these parameters are related to viscoelastic mechanical properties of materials. In this paper, we carried out computer analysis on the mechanical viscoelastic model and compared the theoretical behavior of blood vessels with the experimental output waveform by UDES. From these results, it was proved that values of these parameters connect with the change of the viscoelastic mechanical property of blood vessels. Therefore, the characterizing parameters of experimental output waveforms can be used to estimate the viscoelastic property of blood vessels in a noninvasive method.

Animals↗
PubMed2003

Manifestation of the rotational Doppler effect by use of an off-axis optical vortex beam.

We report what is to our knowledge the first all-optical detection of the frequency beats between Gaussian and Laguerre-Gaussian LG0(1) modes in their axial superposition, caused by the rotational Doppler effect. The relation between the observable off-axis optical vortex rotation and the rotational frequency shift of the Laguerre-Gaussian component is ascertained. The results can be used as a physical basis for recognition of Laguerre-Gaussian mode spectra along their orbital angular momenta.

Journal Article↗
PubMed2005

Wave grouping of a meandering spiral induced by Doppler effects and oscillatory dispersion.

A new type of meandering spiral pattern, in which the dense waves form groups while the sparse waves keep evenly spaced, is observed in a spatial open reactor using a ferroin-catalyzed Belousov-Zhabotinsky reaction. Such a phenomenon is related to both the Doppler effect of a meandering spiral and the oscillatory dispersion relation of the system. Simulation in the two-dimensional Oregonator reaction-diffusion model with an oscillatory dispersion relation gives very similar results.

Colloids↗
PubMed2003

Doppler effect of nonlinear waves and superspirals in oscillatory media.

Nonlinear waves emitted from a moving source are studied. A meandering spiral in a reaction-diffusion medium provides an example in which waves originate from a source exhibiting a back-and-forth movement in a radial direction. The periodic motion of the source induces a Doppler effect that causes a modulation in wavelength and amplitude of the waves ("superspiral"). Using direct simulations as well as numerical nonlinear analysis within the complex Ginzburg-Landau equation, we show that waves subject to a convective Eckhaus instability can exhibit monotonic growth or decay as well as saturation of these modulations depending on the perturbation frequency. Our findings elucidate recent experimental observations concerning superspirals and their decay to spatiotemporal chaos.

Journal Article↗
PubMed2003

Reversed Doppler effect in photonic crystals.

Nonrelativistic reversed Doppler shifts have never been observed in nature and have only been speculated to occur in pathological systems with simultaneously negative effective permittivity and permeability. This Letter presents a different, new physical phenomenon that leads to a nonrelativistic reversed Doppler shift in light. It arises when light is reflected from a moving shock wave propagating through a photonic crystal. In addition to reflection of a single frequency, multiple discrete reflected frequencies or a 10 GHz periodic modulation can also be observed when a single carrier frequency of wavelength 1 microm is incident.

Journal Article↗
PubMedDate not supplied

[Reliability of the results of the ultrasonic hemodynamic recording (Doppler effect) in the diagnosis of cerebral ishemic ischemia of carotid origin].

The Doppler ultrasound diagnosis of carotid artery stenosis (asymetrical systolic and diastolic flows; elevated resistance index: ratio of flow pulse amplitude to systolic and diastolic values; flow reversal in the ophtalmic artery) is compared, in 52 patients, to the clinical, angiographic (40 patients) an surgical findings and to the peroperative measure of intra-arterial pressure and flow (30 patients). Its reliability is proved as a guide for angiographic exploration and for postoperative watching, but it is restricted to great vessels (cervical carotid artery) and is unable to detect ulcerated plate without stenosis.

Angiography↗
PubMed1981

[Spectral analysis of frequencies by conventional Doppler effect examination of the supra-aortic trunks (author's transl)].

Using a directional Doppler (4 MHz) coupled to a frequency analyser, authors investigate the supra-aortic trunks on 90 patients documented by arteriography. The analyser is made of a 16 filter bank system giving a spectrum composed of 16 frequency bands within range of 160 Hz to 4,800 Hz. Data analysis is made on a computer using the comparison means test and the discriminant analysis. Authors compare frequencies on normal common carotid arteries between a group (N = 102) with internal and external carotid arteries free of lesions on one hand, and a group (N = 75) with stenosis or occlusion of internal and/or external carotid arteries on the other hand. They don't note any significant difference for each on of the 16 frequency bands. Comparison of frequencies between normal subclavian arteries (N = 115) and subclavian arteries with proximal stenosis or occlusion (N = 24) shows a significant difference concerning the following bands : F12, F14, F15, F16 (p = 0.05), F13 (p = 0.01). Comparison of frequencies between normal internal carotid arteries (N = 108) and stenosed internal carotid arteries (N = 57) shows significant difference concerning : F11 (p = 0.05), F7, F8, F9, F12, F13, F14, F15, F16 (p = 0.01). On the other side, the discriminant function distinguishes a normal internal carotid artery from a stenosed internal carotid artery in 90% of cases, whatever the stenosis degree is. A discriminant function, added to this analyser, could obtain a frequency analysis easier and less expensive than by fast Fourier transform.

Arterial Occlusive Diseases↗
PubMedDate not supplied

[The external saphenous vein and the Doppler effect].

After medium physical exertion, twelve athletes had their venous reflux measured using a Doppler fluxometer. A rise in the speed of the blood flow was recorded. This is due to the hyperactivity of the thoraco-abdominal and cardiac pumps, whose efficiency is boosted by arteriocapillary vasodilation. In some cases, this happens only in the deep system. But in others, this "arterialization" is apparent in the superficial system too, and especially in the region of the short saphenous vein. This occurs in such a way as to suggest that the deep course becomes saturated and so the reflux is redirected along the superficial course. This hypothesis is an argument in favour of the existence of vein to vein anastomosis.

Adolescent↗