901 research outputs found
Unsuitability of the Oxidation-Reduction Potential Measurement for the Quantification of Fecal Redox Status in Inflammatory Bowel Disease
Oxidative stress is a key pathophysiological process associated with the development and progression of inflammatory bowel disease (IBD). Biomarkers for oxidative stress, however, are scarce, as are diagnostic tools that can interrogate an individualâs gut redox status. This proof- of-concept study aimed to evaluate the potential utility of an oxidation-reduction potential (ORP) measurement probe, to quantify redox status in the feces of both patients with IBD and healthy controls. Previous studies using this ORP measurement probe demonstrated promising data when comparing ORP from severely malnourished individuals with that of healthy controls. To date, ORP analyses have not been performed in the context of IBD. We hypothesized that measuring the ORP of fecal water in patients with IBD might have diagnostic value. The current study, however, did not show significant differences in ORP measurement values between patients with IBD (median [IQR] 46.5 [33.0â61.2] mV) and healthy controls (25 [8.0â52.0] mV; p = 0.221). Additionally, ORP measurements were highly unstable and rapidly fluctuated throughout time, with ORP values varying from +24 to +303 mV. Due to potential biological processes and limitations of the measuring equipment, this study was unable to reliably measure ORP. As a result, our findings indicate that ORP quantification may not be a suitable method for assessing fecal redox status and, therefore, does not currently support further exploration as a diagnostic or monitoring tool
Timing performance of the Timepix4 front-end
A characterisation of the Timepix4 pixel front-end with a strong focus on
timing performance is presented. Externally generated test pulses were used to
probe the per-pixel time-to-digital converter (TDC) and measure the time-bin
sizes by precisely controlling the test-pulse arrival time in steps of 10 ps.
The results indicate that the TDC can achieve a time resolution of 60 ps,
provided that a calibration is performed to compensate for frequency variation
in the voltage controlled oscillators of the pixel TDCs. The internal clock
distribution system of Timepix4 was used to control the arrival time of
internally generated analog test pulses in steps of about 20 ps. The analog
test pulse mechanism injects a controlled amount of charge directly into the
analog front-end (AFE) of the pixel, and was used to measure the time
resolution as a function of signal charge, independently of the TDC. It was
shown that for the default configuration, the AFE time resolution in the
hole-collecting mode is limited to 105 ps. However, this can be improved up to
about 60 ps by increasing the preamplifier bias-current at the cost of
increased power dissipation. For the electron-collecting mode, an AFE time
resolution of 47 ps was measured for a bare Timepix4 device at a signal charge
of 21 ke. It was observed that additional input capacitance from a bonded
sensor reduces this figure to 62 ps
Timing measurements with a 3D silicon sensor on Timepix3 in a 180 GeV/<i>c</i> hadron beam
Test beam measurements have been carried out with a 3D sensor on a Timepix3 ASIC and the time measurements are presented. The measurements are compared to those of a thin planar sensor on Timepix3. It is shown that for a perpendicularly incident beam the time resolution of both detectors is dominated by the Timepix3 front-end. The 3D detector is dominated by the time-to-digital conversion whereas the analog front-end jitter also gives a significant contribution for the thin planar detector. The 3D detector reaches an overall time resolution of 567 ± 6 ps compared to 683 ± 8 ps for the thin planar detector. For a grazing angle beam, however, the thin planar detector achieves a better time resolution because it has a lower pixel capacitance, and therefore suffers less from jitter in the analog front-end for the low charge signals that mainly occur in this type of measurement. Finally, it is also shown that the 3D and thin planar detector can achieve time resolutions for large clusters of about 100 ps and 250 ps, respectively, by combining many single hit measurements
Spatial resolution and efficiency of prototype sensors for the LHCb VELO Upgrade
A comprehensive study of the spatial resolution and detection efficiency of
sensor prototypes developed for the LHCb VELO upgrade is presented. Data
samples were collected at the CERN SPS H8 beam line using a hadron mixture of
protons and pions with momenta of approximately 180 GeV/c. The sensor
performance was characterised using both irradiated and non-irradiated sensors.
Irradiated samples were subjected to a maximum fluence of
, of both protons and neutrons.
The spatial resolution is measured comparing the detected hits to the position
as predicted by tracks reconstructed by the Timepix3 telescope. The resolution
is presented for different applied bias voltages and track angles, sensor
thickness and implant size.Comment: 18 pages, 15 Figure
Timing performance of the LHCb VELO Timepix3 Telescope
We performed a detailed study of the timing performance of the LHCb VELO
Timepix3 Telescope with a 180 GeV/c mixed hadron beam at the CERN SPS. A
twofold method was developed to improve the resolution of single-plane time
measurements, resulting in a more precise overall track time measurement. The
first step uses spatial information of reconstructed tracks in combination with
the measured signal charge in the sensor to correct for a mixture of different
effects: variations in charge carrier drift time; variations in signal
induction, which are the result of a non-uniform weighting field in the pixels;
and lastly, timewalk in the analog front-end. The second step corrects for
systematic timing offsets in Timepix3 that vary from -2 ns to 2 ns. By applying
this method, we improved the track time resolution from 43816 ps to
2764 ps
CH Cygni I: Observational Evidence for a Disk-Jet Connection
We investigate the role of accretion in the production of jets in the
symbiotic star CH Cygni. Assuming that the rapid stochastic optical variations
in CH Cygni come from the accretion disk, as in cataclysmic variables, we use
changes in this flickering to diagnose the state of the disk in 1997. At that
time, CH Cyg dropped to a very low optical state, and Karovska et al. report
that a radio jet was produced. For approximately one year after the jet
production, the amplitude of the fastest (time scales of minutes) variations
was significantly reduced, although smooth, hour-time-scale variations were
still present. This light curve evolution indicates that the inner disk may
have been disrupted, or emission from this region suppressed, in association
with the mass-ejection event. We describe optical spectra which support this
interpretation of the flickering changes. The simultaneous state change, jet
ejection, and disk disruption suggests a comparison between CH Cygni and some
black-hole-candidate X-ray binaries that show changes in the inner disk radius
in conjunction with discrete ejection events on a wide range of time scales
(e.g., the microquasar GRS 1915+105 and XTE J1550-564).Comment: 7 pages, 4 figures, to appear in the Ap
Resource Selection of Free-ranging Horses Influenced by Fire in Northern Canada
Free-ranging or feral horses (Equus ferus caballus) were important to the livelihood of First Nations and indigenous communities in Canada. The early inhabitants of the boreal region of British Columbia (BC) capitalized on naturally occurring wildfires and anthropogenic burning to provide forage for free-ranging horses and manage habitat for wildlife. This form of pyric herbivory, or grazing driven by fi re via the attraction to the palatable vegetation in recently burned areas, is an evolutionary disturbance process that occurs globally. However, its application to manage forage availability for free-ranging horses has not been studied in northern Canada. Across Canada, there are varying levels of governance for feral and free-ranging horses depending on the provincial jurisdiction and associated legislation. The BC Range Act (Act) allows range tenure holders to free-range horses that they own for commercial operations on Crown land. Big-game guide outfitters as range tenure holders are provided grazing licences or grazing permits under the Act with an approved range use plan. Guide outfitters and other range tenure holders have incorporated fi re ecology as part of their rangeland management in mountainous portions of the boreal forest of northeastern BC to promote mosaics of vegetation height and species composition across the landscape to meet nutritional requirements of their free-ranging horses. Using resource selection function models, we evaluated the influence of pyric herbivory on boreal vegetation and use by horse herds occupying 4 distinct landscapes. We found that horses preferentially selected recently burned areas and areas that burned more frequently when they were available. We also found that horses avoided steep slopes and forest cover types. Fire and the ecological processes associated with it, including pyric herbivory, are important considerations when managing boreal rangelands in northeastern BC. Because historical fi re regimes of the boreal region of Canada differ from the arid regions of the United States inhabited by feral horses, the role of pyric herbivory in altering horse distributions in the United States is limited
Charge collection properties of prototype sensors for the LHCb VELO upgrade
An extensive sensor testing campaign is presented, dedicated to measuring the
charge collection properties of prototype candidates for the Vertex Locator
(VELO) detector for the upgraded LHCb experiment. The charge collection is
measured with sensors exposed to fluences of up to , as well as with nonirradiated prototypes. The results are
discussed, including the influence of different levels of irradiation and bias
voltage on the charge collection properties. Charge multiplication is observed
on some sensors that were nonuniformly irradiated with 24 GeV protons, to the
highest fluence levels. An analysis of the charge collection near the guard
ring region is also presented, revealing significant differences between the
sensor prototypes. All tested sensor variants succeed in collecting the minimum
required charge of 6000 electrons after the exposure to the maximum fluence
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