252 research outputs found
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Molecular Hydrogen Formation in the Early Universe: New Implications From Laboratory Measurements
We have performed the first energy-resolved measurement of the associative detachment (AD) reaction H- + H â H2 + e-: This reaction is the dominant formation pathway for H2 during the epoch of first star formation in the early universe. Despite being the most fundamental anion-neutral chemical reaction, experiment and theory have failed to converge in both magnitude and energy dependence. The uncertainty in this rate coefficient severely limits our under- standing of the formation of the first stars and protogalaxies
Recommended from our members
Molecular Hydrogen Formation in the Early Universe: New Implications From Laboratory Measurements
We have performed the first energy-resolved measurement of the associative detachment (AD) reaction H- + H â H2 + e-: This reaction is the dominant formation pathway for H2 during the epoch of first star formation in the early universe. Despite being the most fundamental anion-neutral chemical reaction, experiment and theory have failed to converge in both magnitude and energy dependence. The uncertainty in this rate coefficient severely limits our under- standing of the formation of the first stars and protogalaxies
Assignment of resonances in dissociative recombination of HD+ ions: high-resolution measurements compared with accurate computations
The collision-energy resolved rate coefficient for dissociative recombination
of HD+ ions in the vibrational ground state is measured using the photocathode
electron target at the heavy-ion storage ring TSR. Rydberg resonances
associated with ro-vibrational excitation of the HD+ core are scanned as a
function of the electron collision energy with an instrumental broadening below
1 meV in the low-energy limit. The measurement is compared to calculations
using multichannel quantum defect theory, accounting for rotational structure
and interactions and considering the six lowest rotational energy levels as
initial ionic states. Using thermal equilibrium level populations at 300 K to
approximate the experimental conditions, close correspondence between
calculated and measured structures is found up to the first vibrational
excitation threshold of the cations near 0.24 eV. Detailed assignments,
including naturally broadened and overlapping Rydberg resonances, are performed
for all structures up to 0.024 eV. Resonances from purely rotational excitation
of the ion core are found to have similar strengths as those involving
vibrational excitation. A dominant low-energy resonance is assigned to
contributions from excited rotational states only. The results indicate strong
modifications in the energy dependence of the dissociative recombination rate
coefficient through the rotational excitation of the parent ions, and underline
the need for studies with rotationally cold species to obtain results
reflecting low-temperature ionized media.Comment: 15 pages, 10 figures. Paper to appear in Phys. Rev. A (version as
accepted
Modes of Disintegration of Solid Foods in Simulated Gastric Environment
A model stomach system was used to investigate disintegration of various foods in simulated gastric environment. Food disintegration modes and typical disintegration profiles are summarized in this paper. Mechanisms contributing to the disintegration kinetics of different foods were investigated as related to acidity, temperature, and enzymatic effect on the texture and changes in microstructure. Food disintegration was dominated by either fragmentation or erosion, depending on the physical forces acting on food and the cohesive force within the food matrix. The internal cohesive forces changed during digestion as a result of water penetration and acidic and enzymatic hydrolysis. When erosion was dominant, the disintegration data (weight retention vs. disintegration time) may be expressed with exponential, sigmoidal, and delayed-sigmoidal profiles. The different profiles are the result of competition among the rates of water absorption, texture softening, and erosion. A linear-exponential equation was used to describe the different disintegration curves with good fit. Acidity and temperature of gastric juice showed a synergistic effect on carrot softening, while pepsin was the key factor in disintegrating high-protein foods. A study of the change of carrot microstructure during digestion indicated that degradation of the pectin and cell wall was responsible for texture softening that contributed to the sigmoidal profile of carrot disintegration
Static and Dynamic Properties of a Viscous Silica Melt Molecular Dynamics Computer Simulations
We present the results of a large scale molecular dynamics computer
simulation in which we investigated the static and dynamic properties of a
silica melt in the temperature range in which the viscosity of the system
changes from O(10^-2) Poise to O(10^2) Poise. We show that even at temperatures
as high as 4000 K the structure of this system is very similar to the random
tetrahedral network found in silica at lower temperatures. The temperature
dependence of the concentration of the defects in this network shows an
Arrhenius law. From the partial structure factors we calculate the neutron
scattering function and find that it agrees very well with experimental neutron
scattering data. At low temperatures the temperature dependence of the
diffusion constants shows an Arrhenius law with activation energies which
are in very good agreement with the experimental values. With increasing
temperature we find that this dependence shows a cross-over to one which can be
described well by a power-law, D\propto (T-T_c)^gamma. The critical temperature
T_c is 3330 K and the exponent gamma is close to 2.1. Since we find a similar
cross-over in the viscosity we have evidence that the relaxation dynamics of
the system changes from a flow-like motion of the particles, as described by
the ideal version of mode-coupling theory, to a hopping like motion. We show
that such a change of the transport mechanism is also observed in the product
of the diffusion constant and the life time of a Si-O bond, or the space and
time dependence of the van Hove correlation functions.Comment: 30 pages of Latex, 14 figure
Guiding principles on the education and practice of theranostics.
The recent development and approval of new diagnostic imaging and therapy approaches in the field of theranostics have revolutionised nuclear medicine practice. To ensure the provision of these new imaging and therapy approaches in a safe and high-quality manner, training of nuclear medicine physicians and qualified specialists is paramount. This is required for trainees who are learning theranostics practice, and for ensuring minimum standards for knowledge and competency in existing practising specialists.
To address the need for a training curriculum in theranostics that would be utilised at a global level, a Consultancy Meeting was held at the IAEA in May 2023, with participation by experts in radiopharmaceutical therapy and theranostics including representatives of major international organisations relevant to theranostics practice.
Through extensive discussions and review of existing curriculum and guidelines, a harmonised training program for theranostics was developed, which aims to ensure safe and high quality theranostics practice in all countries.
The guiding principles for theranostics training outlined in this paper have immediate relevance for the safe and effective practice of theranostics
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