539 research outputs found
Inhibition of Na+/H+ exchange reduces Ca2+ mobilization without affecting the initial cleavage of phosphatidylinositol 4,5-bisphosphate in thrombin-stimulated platelets
AbstractStimulation of human platelets increases cytoplasmic pH (pHi) via activation of Na+/H+ exchange. We have determined the effect of inhibiting Na+/H+ exchange on (i) thrombin-induced Ca2+ mobilization and (ii) turnover of 32P-labelled phospholipids. Blocking Na+/H+ exchange by removal of extracellular Na+ or by ethylisopropylamiloride (EIPA) inhibited Ca2+ mobilization induced by 0.2 Uml thrombin, whereas increasing pHi by NH4C1 enhanced the thrombin-induced increase in cytosolic free Ca2+. The effect of EIPA was bypassed after increasing pHi by moneasin. The thrombin-induced cleavage of phosphatidylinositol 4,5-bisphosphate (PIP2) was unaffected by treatments that blocked Na+/H+ exchange or increased pHi. It is concluded that activation of Na+/H+ exchange is a prerequisite for Ca2+ mobilization in human platelets but not for the stimulus-induced hydrolysis of PIP2
Influence des collisions nucléaires sur la linéarite des détecteurs à semiconducteurs
On a déterminé le défaut de hauteur d'impulsion dans les diodes à barriÚre de surface bombardées par des ions He+, N+ et Ne + d'énergies comprises entre 30 et 150 keV. L'influence des collisions nucléaires et de la canalisation des ions est plus spécialement analysée
PULSED LASER AND ELECTRON BEAM INDUCED DIFFUSION OF ANTIMONY IN SILICON
The aim of this work is to compare the diffusion into silicon of a thin film (~ 100 Ă
) of deposited antimony induced either by a pulsed laser irradiation or electron beam and to interpret the different experimental behaviours as observed by Rutherford backscattering spectrometry, by using the calculated temperature distributions obtained by solving the heat flow equation for the two different annealing processes
PULSED ELECTRON BEAM ANNEALING OF As AND B IMPLANTED SILICON
p-type (100) silicon wafers have been implanted either by As or B ions at 20 and 200 keV energies and doses of 1016cm-2. Pulsed electron beam annealing has been performed with fluences of 1.1 and 1.4 J/cm2 using a mean electron energy of 15 keV. The pulse duration was 50 ns. The annealed layers have been investigated by Rutherford backscattering under random and channeling conditions and by S.I.M.S. profiling. Good crystal regrowth and high dopant activation occur in all cases except for the 200 keV Boron implant. Impurities redistribution is observed but no significant segregation effects appear. The experimental profiles are in good agreement with a diffusion model using a modified green function solution and taking into account dopant diffusion in liquid phase and the computed melt front location. The deduced diffusion coefficient are in the 5.10-5cm2/s range for boron and 2.10-4cm2/s range for arsenic
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
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