Doppler ultrasound is able to visualize blood flow by the change in frequency (Doppler shift) of sound waves that are reflected by moving blood cells inside the vessels (Doppler effect). Since hyperemia caused by vasodilation and angiogenesis can be the earliest detectable pathologic changes in the beginning of synovitis, Doppler ultrasonography can be used to assess inflammatory activity. In a...

OFDM is a multicarrier modulation technology which has efficient spectrum utilization to support the transmission of high data rates. The typical subcarrier modulation schemes used in orthogonal frequency division multiplexing (OFDM) system includes: b inary phase shift keying (BPSK), phase shift keying (PSK) and quadrature amplitude modulation (QAM). This paper analyses the comparative perform...

Within the framework of the composite surface scattering model, analytical formulas for Doppler shift and bandwidth of radar echoes backscattered from time-varying sea surface are derived in the forms of three-dimensional integrals. In our derivations, the influences of the tilt modulation (TM), the hydrodynamic modulation (HM), the shadow and the curvature of large-scale undulating waves are a...

A compact cold-atom clock based on coherent population trapping is being developed. The clock aims to ultimately achieve a timing uncertainty of a few nanoseconds per day. Here we present an initial evaluation of the three main systematic frequency shifts – the first-order Doppler shift, the light shift, and the Zeeman shift. Planned steps to reduce the size of these shifts will also be presented.

A method to separate a Doppler power spectrum into a number of flow velocity components, measured in absolute units (mm/s), is presented. A Monte Carlo software was developed to track each individual Doppler shift, to determine the probability, p(n), for a photon to undergo n Doppler shifts. Given this shift distribution, a mathematical relationship was developed and used to calculate a Doppler...

A simplified Doppler frequency shift (DFS) measurement approach based on Serrodyne optical translation is reported. sawtooth wave with high amplitude sent to one phase modulation arm of a Mach–Zehnder modulator in conjunction the transmitted signal implement translation, as well frequency-shifted carrier. The echo applied other modulator. lower first-order sidebands from are selected by an band...