Secretion of catecholamines from single bovine chromaffin cells in culture was elicited by brief pressure ejections from a micropipette containing nicotine, carbamoylcholine, or potassium ions or by ...mechanical stimulation. Release was monitored electrochemically with a carbon-fiber microelectrode placed adjacent to the cell. Cyclic voltammetry was used to identify secreted species, whereas constant potential amperometry was used for improved temporal resolution (millisecond range) of catecholamine detection. During secretion, brief current spikes were observed, which were shown to be due to detection of catecholamines by electrooxidation. The spikes have the physical characteristics of multimolecular packets of catecholamines released at random times and locations from the surface of the single cell. The half-width of the spikes was found to increase with an increase in cell-electrode spacing. The properties of the catecholamine spikes correlate well with expectations based on secretion from individual storage vesicles. Spikes do not occur in the absence of Ca2+in the buffer, and the majority of spikes are found to be distributed between 0.2 and 2 picocoulombs, corresponding to 1-10 attomoles of catecholamine detected. The frequency of the spikes increases with the intensity of the stimulus, but the average quantity of catecholamine in each spike is independent of the stimulus. Thus, these measurements represent time-resolved observation of quantal secretion of catecholamines and provide direct evidence for the exocytotic hypothesis.
Beam test performance of the SKIROC2 ASIC Amjad, M.S.; Anduze, M.; Augustin, J.-E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2015, Letnik:
778
Journal Article
Recenzirano
Beam tests of the first layers of CALICE silicon tungsten ECAL technological prototype were performed in April and July 2012 using 1–6GeV electron beam at DESY. This paper presents an analysis of the ...SKIROC2 readout ASIC performance under test beam conditions.
Application Specific Integrated Circuits, ASICs, similar to those envisaged for the readout electronics of the central calorimeters of detectors for a future lepton collider have been exposed to ...high-energy electromagnetic showers. A salient feature of these calorimeters is that the readout electronics will be embedded into the calorimeter layers. In this article it is shown that interactions of shower particles in the volume of the readout electronics do not alter the noise pattern of the ASICs. No signal at or above the MIP level has been observed during the exposure. The upper limit at the 95% confidence level on the frequency of fake signals is smaller than
1
×
10
−
5
for a noise threshold of about 60% of a MIP. For ASICs with similar design to those which were tested, it can thus be largely excluded that the embedding of the electronics into the calorimeter layers compromises the performance of the calorimeters.
Various structures for n-in-p planar pixel sensors have been developed at KEK in order to cope with the huge particle fluence in the upcoming LHC upgrades. Performances of the sensors with different ...structures have been evaluated with testbeam. The n-in-p devices were connected by bump-bonding to the ATLAS Pixel front-end chip (FE-I4A) and characterized before and after the irradiation to 1×1016 1MeV neq/cm2. Results of measurements with 120GeV/c momentum pion beam at the CERN Super Proton Synchrotron (SPS) in September 2012 are presented.
•Pixel sensors with two biasing and two isolation structures were evaluated.•Overall hit efficiency of 97.6% was confirmed at −1200V after 1×1016neq/cm2.•Inefficiency regions were observed in non-irradiated samples with P-spray isolation.•Inefficiency regions after high irradiation were observed under bias rail and PolySi.•The potential of the surface structure is thought to affect the charge collection.
Quantifying mechanisms underlying extracellular signaling by the neurotransmitter dopamine (DA) is a difficult task, particularly in the complex extracellular microenvironment of the intact brain. In ...this study, two methods for evaluating release and uptake from DA dynamics monitored by real-time voltammetry are described. Both are based on a neurochemical model characterizing electrically evoked levels of DA as a balance between these opposing mechanisms. The theoretical basis of what is called here nonlinear regression and single curve analyses is given. Fitting simulated data tests the reliability of the methods. The two analyses are also compared with an experimental data set describing the effects of pharmacologically inhibiting the DA transporter in the caudate-putamen (CP) and nucleus accumbens (NAc). The results indicate that nonlinear regression and single curve analyses are suitable for quantifying release and uptake mechanisms underlying DA neurotransmission. Additionally, the most important experimental finding of this technical study was the independent confirmation of high affinity (≈0.2 μM) DA uptake in the intact striatum.
Precision physics at future colliders requires highly granular calorimeters to support the particle flow approach for event reconstruction. This article presents a review of about 10-15 years of ...research and development, mainly conducted within the CALICE Collaboration, for this novel type of detector. The performance of large-scale prototypes in beam tests validates the technical concept of particle flow calorimeters. The comparison of test-beam data with simulation, of, e.g., hadronic showers, supports full detector studies and gives deeper insight into the structure of hadronic cascades than was possible previously.
Physics at the $$e^+ e^-$$ e + e - linear collider Moortgat-Pick, G.; Baer, H.; Battaglia, M. ...
The European physical journal. C, Particles and fields,
8/2015, Letnik:
75, Številka:
8
Journal Article
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