21 research outputs found
Evaluation of a method for time-of-flight, wavelength and distance calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors
Accurate conversion of neutron time-of-flight (TOF) to wavelength, and its
uncertainty, is of fundamental importance to neutron scattering measurements.
Especially in cases where instruments are highly configurable, the
determination of the absolute wavelength after any change must always be
performed. Inspired by the manner with which neutron spectrometers determine
the absolute wavelength, we evaluate for the first time, in the author's
knowledge, a commonly used method for converting TOF to neutron wavelength, the
distance of a monitor from the source of neutrons and we analytically calculate
the uncertainty contributions that limit the precision of the conversion. The
method was evaluated at the V20 test beamline at the Helmholtz Zentrum Berlin
(HZB), emulating the ESS source with a pulse of 2.86 ms length and 14 Hz
repetition rate, by using a mini-chopper operated at 140 Hz, beam monitors
(BMs) and data acquisition infrastructure. The mini-chopper created
well-defined neutron pulses and the BM was placed at two positions, enabling
the average wavelength of each of the pulses created to be determined. The used
experimental setup resulted in absolute wavelength determination at the monitor
positions with a of 1.8% for
\r{A}. With a modest increase of the distance between the
reference monitor positions a of below
0.5% can be achieved. Further improvements are possible by using a thinner
monitor, smaller chopper disc openings and a higher rotational speed chopper.
The method requires only two neutron measurements and doesn't necessitate the
use of crystals or complex fitting, and could constitute a suitable addition to
imaging, diffraction, reflectometers and small angle neutron scattering
instruments, at spallation sources, that do not normally utilise fast choppers
Effects of reactive oxygen species and neutrophils on endothelium-dependent relaxation of rat thoracic aorta
Reactive oxygen species (ROS) are produced in different metabolic processes including the respiratory burst of neutrophils accompanying local inflammation. The aim of this study was to analyze the effects of N-formyl-methionyl-leucyl-phenylalanine (FMLP)-activated neutrophils, isolated from the guinea pig peritoneal cavity, on isolated rings of a large (conduit) artery, the rat thoracic aorta. FMLP-activated neutrophils enhanced the basal tension increased by α1-adrenergic stimulation. In phenylephrine-precontracted aortae, they elicited marked contraction, while in noradrenaline-precontracted rat aortal rings they caused a biphasic response (contraction-relaxation). To eliminate interaction of activated neutrophils with catecholamines, in the subsequent experiments the basal tension was increased by KCl-induced depolarization. Activated neutrophils evoked a low-amplitude biphasic response (relaxation-contraction) on the KCl-induced contraction. Not only the acetylcholine- and A23187-induced relaxations but also the catalase sensitive hydrogen peroxide (H2O2) elicited contractions were endothelium-dependent. Even though the acetylcholine-induced relaxation was changed by activated neutrophils and by the ROS studied, their effects differed significantly, yet none of them did eliminate fully the endothelium-dependent acetylcholine relaxation. The effect of activated neutrophils resembled the effect of superoxide anion radical (O2
•–) produced by xanthine/xanthine oxidase (X/XO) and differed from the inhibitory effects of Fe2SO4/H2O2-produced hydroxyl radical (•OH) and H2O2. Thus O2
•– produced either by activated neutrophils or X/XO affected much less the endothelium-dependent acetylcholine-activated relaxation mechanisms than did •OH and H2O2. In the large (conduit) artery, the effects of activated neutrophils and various ROS (O2
•–, •OH and H2O2) seem to be more dependent on muscle tension than on endothelial mechanisms
Time- and energy-resolved effects in the boron-10 based Multi-Grid and helium-3 based thermal neutron detectors
The boron-10 based Multi-Grid detector is being developed as an alternative
to helium-3 based neutron detectors. At the European Spallation Source, the
detector will be used for time-of-flight neutron spectroscopy at cold to
thermal neutron energies. The objective of this work is to investigate fine
time- and energy-resolved effects of the Multi-Grid detector, down to a few
eV, while comparing it to the performance of a typical helium-3 tube.
Furthermore, it is to characterize differences between the detector
technologies in terms of internal scattering, as well as the time
reconstruction of ~ s short neutron pulses. The data were taken at the
Helmholtz Zentrum Berlin, where the Multi-Grid detector and a helium-3 tube
were installed at the ESS test beamline, V20. Using a Fermi-chopper, the
neutron beam of the reactor was chopped into a few tens of s wide pulses
before reaching the detector, located a few tens of cm downstream. The data of
the measurements show an agreement between the derived and calculated neutron
detection efficiency curve. The data also provide fine details on the effect of
internal scattering, and how it can be reduced. For the first time, the chopper
resolution was comparable to the timing resolution of the Multi-Grid detector.
This allowed a detailed study of time- and energy resolved effects, as well as
a comparison with a typical helium-3 tube.Comment: 37 pages, 21 figure
USE OF FIBRIN GLUE AS A SUBSTRATE FOR INVITRO ENDOTHELIALIZATION OF PTFE VASCULAR GRAFTS
Evaluation of a method for time-of-flight, wavelength and neutron flight path calibration for neutron scattering instruments by means of a mini-chopper and standard neutron monitors
Accurate conversion of neutron time-of-flight (TOF) to wavelength is of fundamental importance to neutron scattering measurements in order to ensure the accuracy of the instruments and the experimental results. Equally important in these measurements is the determination of uncertainties, and with the appropriate precision. Especially in cases where instruments are highly configurable, the determination of the absolute wavelength after any change must always be performed (e.g. change of detector position). Inspired by the manner with which neutron spectrometers determine the absolute wavelength, we evaluate for the first time, in the author's knowledge, a commonly used method for converting TOF to neutron wavelength by measuring the neutron flight path length from the source of neutrons to a monitor and we proceed to analytically calculate the uncertainty contributions that limit the precision of the conversion. The method was evaluated at the V20 test beamline at the Helmholtz Zentrum Berlin (HZB), emulating the ESS source with a long pulse of 2.86 ms length and 14 Hz repetition rate, by using a mini-chopper operated at 140 Hz and two portable beam monitors (BMs), as well as accompanied data acquisition infrastructure. The mini-chopper created well-defined neutron pulses and the BM was placed at two positions, enabling the average wavelength of each of the pulses created to be determined. The used experimental setup resulted in absolute wavelength determination at the monitor positions with a δλmean / λmean of ∼1.8% for λ > 4 Å. With the use of a thinner monitor, a δλmean / λmean of ∼1% can be reached and with a modest increase of the distance between the reference monitor positions a δλmean / λmean of below 0.5% can be achieved. Further improvements are possible by using smaller chopper disc openings and a higher rotational speed chopper. The method requires only two neutron measurements and doesn't necessitate the use of crystals or complex fitting with sigmoid functions and multiple free variables, and could constitute a suitable addition to imaging, diffraction, reflectometers and small angle neutron scattering instruments, at spallation sources, that do not normally utilise fast choppers
Spectroscopic neutron imaging for resolving hydrogen dynamics changes in battery electrolytes
Die Synovialeinrichtungen des M. fibularis longus bei Katze, Hund, Schwein, Rind, Schaf und Ziege
In Situ Neutron Diffraction Analyzing Stress-Induced Phase Transformation and Martensite Elasticity in [001]-Oriented Co49Ni21Ga30 Shape Memory Alloy Single Crystals
Recent studies demonstrated excellent pseudoelastic behavior and cyclic stability under compressive loads in [001]-oriented Co–Ni–Ga high-temperature shape memory alloys (HT-SMAs). A narrow stress hysteresis was related to suppression of detwinning at RT and low defect formation during phase transformation due to the absence of a favorable slip system. Eventually, this behavior makes Co–Ni–Ga HT-SMAs promising candidates for several industrial applications. However, deformation behavior of Co–Ni–Ga has only been studied in the range of theoretical transformation strain in depth so far. Thus, the current study focuses not only on the activity of elementary deformation mechanisms in the pseudoelastic regime up to maximum theoretical transformation strains but far beyond. It is shown that the martensite phase is able to withstand about 5% elastic strain, which significantly increases the overall deformation capability of this alloy system. In situ neutron diffraction experiments were carried out using a newly installed testing setup on Co–Ni–Ga single crystals in order to reveal the nature of the stress–strain response seen in the deformation curves up to 10% macroscopic strain