8 research outputs found
Setagin and secretagogin-R22: Posttranscriptional modification products of the secretagogin gene
We describe two new variants of the recently identified hexa-EF-hand calcium binding protein secretagogin. The first variant (secretagogin-R22) is characterized by one single amino acid exchange (Q/R) at codon 22, most likely due to RNA editing. The second variant of secretagogin (setagin) consists of 49 amino acids. Due to a frame shift, only the first 27 amino acids are identical to secretagogin. We demonstrate that this protein truncation results in complete loss of the calcium binding capacity. Setagin expression was found in considerable amounts in the pancreas whereas secretagogin and secretagogin-R22 were also found in the central nervous system and organs containing neurendocrine cells. (c) 2005 Elsevier Inc. All rights reserved
Active magnetic levitation and 3-D position measurement for a ball viscometer
We present a new technique for 3-D position sensing and active magnetic
levitation of a steel ball for use in a levitating ball viscometer. In order
to achieve a stable levitation, a very sensitive positioning measurement
system is mandatory. For this task the differential transformer principle was
chosen to realize a 3-D position measurement. This leads to a purely magnetic
sensor and actuator system without the need for other transducer types such
as optical readout. The actuation utilizes power efficient switch-mode
electronic circuitry which opens the possibility of upscaling the device, if
demanded, for future applications. It is shown that this switch-mode
actuation can be combined directly with the position measurement when special
switching patterns are applied. A position resolution of
 ∼  100 µm in all three axial directions at a sample rate
of 476.19 Hz is achieved. For viscosity sensing, the steel ball is
magnetically driven to orbital movements of variable revolution frequency of
up to 2.5 Hz within a fluid chamber. The frequency response is analyzed
and related to the shear viscosity of the fluid under test. As a proof of
concept, measurements in various viscous liquids were performed with the
prototype, showing promising results in the range of 1–10 mPa s. The
principle may also be of interest for applications beyond viscosity sensing,
such as fluid mixers, or as actuators in microfluidic devices
Balanced torsionally oscillating pipe used as a viscosity sensor
We present a robust viscosity measurement system based on a torsionally oscillating pipe. The sensitive surface of the sensor performs periodic movements in the fluid to be sensed, generating a shear wave that penetrates the fluid. Due to this interaction, the resonance characteristic of the structure is affected, in particular the quality factor decreases with increasing viscosity. The pipe is mounted at its center where it features a nodal point of the preferred resonant mode, reducing temperature issues while simultaneously enabling high quality factors. A mathematical model is presented illustrating how different parameters influence the sensitivity of the sensor. Long-term measurements were performed to demonstrate the time stability of the sensor setup.(VLID)341185