Acoustic Doppler current profiler
An acoustic Doppler current profiler (ADCP or ADP) is a hydroacoustic current meter similar to a sonar, attempting to measure water current velocities over a depth range using the Doppler effect of sound waves scattered back from particles within the water column. The term ADCP is used synonymously for all kind of acoustic current meters although the abbreviation originates from the name of an instrument series by Teledyne. ADCPs have been commercially available since the late 1980s. The working frequencies range from 38 kHz to several megahertz.
Working principle
ADCPs contain piezoelectric oscillators to transmit and receive sound signals. The traveling time of sound waves gives an estimate of the distance, the red or blue shift can be converted to a velocity. To measure 3D velocities, at least three vector components have to be estimated, this is why the instrument typically has four of them.
Further components of an ADCP are an electronic amplifier, a receiver, a mixer, a clock to measure the traveling time, a temperature sensor, a compass to know the relative rotation, and a pitch/roll sensor to know the horizontal. An analog-to-digital converter and a digital signal processor are required to sample the returning signal in order to determine the Doppler shift. A micro processor evaluates the sound velocity at the instrument position using the seawater equation of state, and uses this to estimate the velocities. This procedure assumes that the same density in the water column nearby is mainly determined by temperature, i.e. that the salinity has a preconfigured constant value. Finally, the results are saved on a memory card.
Dipeptidyl peptidase-4
Dipeptidyl peptidase-4 (DPP4), also known as adenosine deaminase complexing protein 2 or CD26 (cluster of differentiation 26) is a protein that, in humans, is encoded by the DPP4 gene. DPP4 is related to attractin, FAP, DPP8 and DPP9.
Function
The protein encoded by the DPP4 gene is an antigenic enzyme expressed on the surface of most cell types and is associated with immune regulation, signal transduction and apoptosis. It is an intrinsic membrane glycoprotein and a serine exopeptidase that cleaves X-proline dipeptides from the N-terminus of polypeptides.
It is a rather indiscriminate enzyme for which a diverse range of substrates are known. The substrates of CD26/DPPIV are proline(or alanine)-containing peptides and include growth factors, chemokines, neuropeptides, and vasoactive peptides. DPP4 plays a major role in glucose metabolism. It is responsible for the degradation of incretins such as GLP-1. Furthermore, it appears to work as a suppressor in the development of cancer and tumours.
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