Atomic transition frequencies, isotope shifts, and sensitivity to variation of the fine structure constant for studies of quasar absorption spectra

Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, alpha, could be detected via shifts in the frequencies of atomic transitions in quasar absorption systems. Recent studies using 140 absorption systems from the Keck telescope and 153 from the Very Large Telescope, suggest that alpha varies spatially. That is, in one direction on the sky alpha seems to have been smaller at the time of absorption, while in the opposite direction it seems to have been larger. To continue this study we need accurate laboratory measurements of atomic transition frequencies. The aim of this paper is to provide a compilation of transitions of importance to the search for alpha variation. They are E1 transitions to the ground state in several different atoms and ions, with wavelengths ranging from around 900 - 6000 A, and require an accuracy of better than 10^{-4} A. We discuss isotope shift measurements that are needed in order to resolve systematic effects in the study. The coefficients of sensitivity to alpha-variation (q) are also presented.Comment: Includes updated version of the "alpha line" lis

Observing the Mpemba effect with minimal bias and the value of the Mpemba effect to scientific outreach and engagement

The Mpemba effect is the assertion that it is quicker to cool or freeze water when the initial temperature is high. We define the Mpemba effect to have been observed when two samples of water, one initially warmer than the other, are cooled and the initially hotter sample freezes or cools to a prescribed temperature in less time; this assumes that the samples are of the same mass, are at least as pure as drinking water, the cooling is delivered to both samples in the same manner and the same level of insulation is applied to both. Under this definition, we enable repeatable observations of the Mpemba effect by systematically introducing increased nucleation sites (in our case by roughening the container walls with sandpaper) within the cooling environment of the initially warmer sample. We remain able to observe the Mpemba effect when the enthalpy of cooling and freezing the initially warmer sample exceeds that of the initially cooler sample by over 50%, corresponding to a difference in the initial temperatures of around 50 °C. The context of this study, initiated by a high-school student who then carried out all of the experiments, highlights the value of the Mpemba effect as a tool for scientific learning and engagement

Detection of carbon using amplified laser-induced fluorescence

Radiative lifetimes and stimulated emission have been studied in two-photon-excited carbon atoms. A strong fluorescence enhancement was detected in the direction of the exciting laser beam. Rate equations for the energy levels involved have been calculated in order to obtain number densities from the emitted light. Lifetimes were measured for the 2p3p 3p and 3D states and for the A 3[Pi]g state of the C2 molecule

Investigations of radiative lifetimes in the 3p 5p configuration of neutral silicon

Lifetimes for the3S1,3P0, 1, 2 and3D1, 2, 3 states in the 3s23p5p configuration of silicon have been determined using stepwise dye laser excitation and time resolved detection. A comparison is made with theoretical values, calculated using multi-configuration Hartree-Fock wavefunctions. Laser-evaporation was used to produce free silicon atoms by focusing a Nd: YAG laser on a rotating silicon target

Experimental Mg I oscillator strengths and radiative lifetimes for astrophysical applications on metal-poor stars : New data for the Mg I b triplet

Original article can be found at: http://www.aanda.org/--Copyright The European Southern Observatory DOI : 10.1051/0004-6361:20066266Peer reviewe