The Na+/H+ exchanger is involved in rat hepatic stellate cell (HSC) proliferation induced by platelet-derived growth factor (PDGF). We therefore evaluated in human HSC: (1) the mechanisms of ...intracellular pH regulation; (2) the relationship between Na+/H+ exchange activation and cell proliferation induced by PDGF, insulin-like growth factor 1 (IGF-1) and insulin.
pH(i) regulation was mainly dependent on the activity of the Na+/H+ exchanger, which was evaluated by measuring pH(i) recovery from an acute acid load. PDGF (25 ng/ml) gradually increased the activity of the Na+/H+ exchanger which peaked at 18 h and remained stable until the 24th h. IGF-1 (10 nmol/l), but not insulin (100 nmol/l), slightly but significantly increased the activity of the Na+/H+ exchanger. Amiloride (100 micromol/l) and 20 micromol/l 5-N-ethyl-N-isopropyl-amiloride completely inhibited HSC proliferation (evaluated by measurement of bromodeoxyuridine incorporation) induced by PDGF and IGF-1, but did not affect proliferation of HSC induced by insulin. Finally, IGF-1 did not modify the activity of the Na+/Ca2+ exchanger.
The Na+/H+ exchanger is involved in HSC proliferation induced by PDGF and IGF-1, whereas the proliferative effect of insulin is mediated by intracellular pathways which are Na+/H+ exchange-independent.
Various dark matter models predict annual and diurnal modulations of dark matter interaction rates in Earth-based experiments as a result of the Earth's motion in the halo. Observation of such ...features can provide generic evidence for detection of dark matter interactions. This paper reports a search for both annual and diurnal rate modulations in the LUX dark matter experiment using over 20 calendar months of data acquired between 2013 and 2016. This search focuses on electron recoil events at low energies, where leptophilic dark matter interactions are expected to occur and where the DAMA experiment has observed a strong rate modulation for over two decades. By using the innermost volume of the LUX detector and developing robust cuts and corrections, we obtained a stable event rate of 2.3\(\pm\)0.2~cpd/keV\(_{\text{ee}}\)/tonne, which is among the lowest in all dark matter experiments. No statistically significant annual modulation was observed in energy windows up to 26~keV\(_{\text{ee}}\). Between 2 and 6~keV\(_{\text{ee}}\), this analysis demonstrates the most sensitive annual modulation search up to date, with 9.2\(\sigma\) tension with the DAMA/LIBRA result. We also report no observation of diurnal modulations above 0.2~cpd/keV\(_{\text{ee}}\)/tonne amplitude between 2 and 6~keV\(_{\text{ee}}\).
LUX Trigger Efficiency Akerib, D S; Alsum, S; Araújo, H M ...
arXiv.org,
09/2018
Paper, Journal Article
Odprti dostop
The Large Underground Xenon experiment (LUX) searches for dark matter using a dual-phase xenon detector. LUX uses a custom-developed trigger system for event selection. In this paper, the trigger ...efficiency, which is defined as the probability that an event of interest is selected for offline analysis, is studied using raw data obtained from both electron recoil (ER) and nuclear recoil (NR) calibrations. The measured efficiency exceeds 98\% at a pulse area of 90 detected photons, which is well below the WIMP analysis threshold on the S2 pulse area. The efficiency also exceeds 98\% at recoil energies of \mbox{0.2 keV} and above for ER, and \mbox{1.3 keV} and above for NR. The measured trigger efficiency varies between 99\% and 100\% over the fiducial volume of the detector.
Weakly Interacting Massive Particles (WIMPs) are a leading candidate for dark matter and are expected to produce nuclear recoil (NR) events within liquid xenon time-projection chambers. We present a ...measurement of the scintillation timing characteristics of liquid xenon in the LUX dark matter detector and develop a pulse shape discriminant to be used for particle identification. To accurately measure the timing characteristics, we develop a template-fitting method to reconstruct the detection times of photons. Analyzing calibration data collected during the 2013-16 LUX WIMP search, we provide a new measurement of the singlet-to-triplet scintillation ratio for electron recoils (ER) below 46~keV, and we make a first-ever measurement of the NR singlet-to-triplet ratio at recoil energies below 74~keV. We exploit the difference of the photon time spectra for NR and ER events by using a prompt fraction discrimination parameter, which is optimized using calibration data to have the least number of ER events that occur in a 50\% NR acceptance region. We then demonstrate how this discriminant can be used in conjunction with the charge-to-light discrimination to possibly improve the signal-to-noise ratio for nuclear recoils.
The \((x, y)\) position reconstruction method used in the analysis of the complete exposure of the Large Underground Xenon (LUX) experiment is presented. The algorithm is based on a statistical test ...that makes use of an iterative method to recover the photomultiplier tube (PMT) light response directly from the calibration data. The light response functions make use of a two dimensional functional form to account for the photons reflected on the inner walls of the detector. To increase the resolution for small pulses, a photon counting technique was employed to describe the response of the PMTs. The reconstruction was assessed with calibration data including \({}^{\mathrm{83m}}\)Kr (releasing a total energy of 41.5 keV) and \({}^{3}\)H (\(\beta^-\) with Q = 18.6 keV) decays, and a deuterium-deuterium (D-D) neutron beam (2.45 MeV). In the horizontal plane, the reconstruction has achieved an \((x, y)\) position uncertainty of \(\sigma\)= 0.82 cm for events of only 200 electroluminescence photons and \(\sigma\) = 0.17 cm for 4,000 electroluminescence photons. Such signals are associated with electron recoils of energies \(\sim\)0.25 keV and \(\sim\)10 keV, respectively. The reconstructed position of the smallest events with a single electron emitted from the liquid surface has a horizontal \((x, y)\) uncertainty of 2.13 cm.
