Search results for "fission"
showing 10 items of 421 documents
Intraspecific competition affects population size and resource allocation in an ant dispersing by colony fission
2010
Intraspecific competition is a pervasive phenomenon with important ecological and evolutionary consequences, yet its effect in natural populations remains controversial. Although numerous studies suggest that in many cases populations across all organisms are limited by density-dependent processes, this conclusion often relies on correlative data. Here, using an experimental approach, we examined the effect of intraspecific competition on population regulation of the ant Aphaenogaster senilis. In this species females are philopatric while males disperse by flying over relatively long distances. All colonies were removed from 15 experimental plots, except for one focal colony in each plot, w…
Importance of mitochondrial dynamin-related protein 1 in hypothalamic glucose sensitivity in rats.
2012
International audience; AIMS: Hypothalamic mitochondrial reactive oxygen species (mROS)-mediated signaling has been recently shown to be involved in the regulation of energy homeostasis. However, the upstream signals that control this mechanism have not yet been determined. Here, we hypothesize that glucose-induced mitochondrial fission plays a significant role in mROS-dependent hypothalamic glucose sensing. RESULTS: Glucose-triggered translocation of the fission protein dynamin-related protein 1 (DRP1) to mitochondria was first investigated in vivo in hypothalamus. Thus, we show that intracarotid glucose injection induces the recruitment of DRP1 to VMH mitochondria in vivo. Then, expressio…
Transport of recoil atoms in a stream of liquid-air-cooled pure helium
1974
Abstract Pure commercial helium cooled down to the temperature of liquid air (80 K) has been used for rapid transportation of recoil atoms over distances as long as 10 m. Transport efficiencies of several tens of per cent have been obtained for recoil atoms resulting from alpha decay or from decay by fission. The angle of divergence of the beam of recoil atoms at the exit of the transport capillary is measured to be (11±2)° for particles of mass number A = 211. Experimental results are discussed in terms of thermal diffusion. The elimination of carrier vapors will probably simplify the use of the helium-jet technique in on-line mass separators.
Fission barriers of doubly charged silver clusters
1999
The monomer evaporation energies and fission barriers of doubly charged silver cluster ions in the size range 9≤n≤25 are measured by collision induced dissociation. They are compared to the dissociation energies of singly charged silver clusters. A macroscopic liquid drop model combined with empirical microscopic corrections successfully describes the measured fission barriers.
Laser spectroscopy of cooled zirconium fission fragments
2002
The first on-line laser spectroscopy of cooled fission fragments is reported. The $^{\mathrm{96}\mathrm{--}\mathrm{102}}\mathrm{Z}\mathrm{r}$ ions, produced in uranium fission, were extracted and separated using an ion guide isotope separator. The ions were cooled and bunched for collinear laser spectroscopy by a gas-filled linear Paul trap. New results for nuclear mean-square charge radii, dipole, and quadrupole moments are reported across the $N=60$ shape change. The mean-square charge radii are found to be almost identical to those of the Sr isotones and previously offered modeling of the radial changes is critically reviewed.
An on-line mass separator for fission-produced alkali isotopes
1980
Abstract The design of an on-line mass separator installed at the TRIGA reactor in Mainz is described and its performance discussed. A tungsten oven, filled with about 2 g of 235U embedded in graphite, is exposed to a flux of 1.7 × 1011 thermal neutrons (s− cm−2) near the reactor core. After diffusion out of the graphite the fission-produced alkali isotopes are surface-ionized and electromagnetically mass-separated, the resolving power being about 750. Losses during the diffusion out of the target material are discussed. Due to these losses the maximum separator efficiency is about 5%, corresponding to a source strength of about 109 particles s−1 for the most abundant isotopes. The heaviest…
Luminescence and EPR spectroscopy of neutron-irradiated single crystals of magnesium aluminium spinel
2016
Abstract Neutron irradiated single crystals of stoichiometric MgAl 2 O 4 and MgAl 2 O 4 :Mn 2+ (0.15 wt. %) were studied using the methods of luminescence spectroscopy and versions of electron paramagnetic resonance. In stoichiometric MgAl 2 O 4 :Mn 2+ single crystals, the transition of a part of manganese impurity ions from tetrahedral to octahedral coordination, caused by irradiation with fast fission neutrons, is detected using photoluminescence spectra. This fact confirms the partial inversion of a normal spinel due to neutron-irradiation. Using pulse EPR technique it is shown that an electron in the field of oxygen vacancy (i.e. from neutron-irradiation induced F + centres, which are s…
An improved system for fast, continuous chemical separations (“SISAK 2”) in nuclear spectroscopic studies
1980
Abstract An improved rapid, continuous solvent extraction system (“SISAK 2”) is described. The system is connected to a gas-jet installed at the Mainz reactor. It allows single or multistage chemical separations of liquid phases by means of specially designed centrifuges within ∼1 s per stage. The application of this system to study short-lived nuclides is exemplified for neutron-rich lanthanum and cerium isotopes produced by fission.
Characterisation of Apatites as Potential Uranium Reference Materials for Fission-track Dating by LA-ICP-MS
2015
We report homogeneity tests on large natural apatite crystals to evaluate their potential as U reference materials for apatite fission-track (AFT) thermochronology by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The homogeneity tests include the measurements of major element concentrations by electron probe microanalysis (EPMA), whereas for U concentration, isotope dilution (ID) ICP-MS and laser ablation (LA) ICP-MS were employed. Two apatite crystals are potential reference materials for LA-ICP-MS analysis: a 1 cm3 fraction of a Durango crystal (7.5 μg g−1 U) and a 1 cm3 Mud Tank crystal (6.9 μg g−1 U). The relative standard deviation (1 RSD) of the U concentrat…
Validation of matrix diffusion modeling
2010
Abstract Crystalline rock has been chosen as the host medium for repository of highly radioactive spent nuclear fuel in Finland. Radionuclide transport takes place along water-carrying fractures, and matrix diffusion has been indicated as an important retarding mechanism that affects the transport of mobile fission and activation products. The model introduced here for matrix diffusion contains a flow channel facing a porous matrix with stagnant water into which tracer molecules advected in the channel can diffuse. In addition, the possibility of a finite depth of the matrix and an initial tracer distribution (‘contamination’) in the matrix are included in the model. In order to validate th…