Autler-Townes effect in a strongly driven electromagnetically induced transparency resonance

In this paper we study the nonlinear behavior of an electromagnetically induced transparency EIT resonance subject to a coherent driving field. The EIT is associated with a three-level system where two hyperfine levels within an electronic ground state are coupled to a common excited state level by a coupling field and a probe field. In addition there is an radio-frequency rf field driving a hyperfine transition within the ground state. The paper contrasts two different situations. In one case the rf-driven transition shares a common level with the probed transition and in the second case it shares a common level with the coupled transition. In both cases the EIT resonance is split into a doublet and the characteristics of the EIT doublet are determined by the strength and frequency of the rf-driving field. The doublet splitting originates from the rf-field induced dynamic Stark effect and has close analogy with the Autler-Townes effect observed in three-level pump-probe spectroscopy study. The situation changes when the rf field is strong and the two cases are very different. One is analogous to two three-level systems with EIT resonance associated with each. The other corresponds to a doubly driven three-level system with rf-field-induced electromagnetically induced absorption resonance. The two situations are modeled using numerical solutions of the relevant equation of motion of density matrix. In addition a physical account of their behaviors is given in terms of a dressed state picture

Secondary particle size determining sedimentation and adsorption kinetics of titanate-based materials for ammonia nitrogen and methylene blue removal

The effect of the main size distribution of particles on the adsorption process for adsorbent materials has been well-recognized; however, the impact of secondary particle size (agglomerated, aggregated or hydrated ones) on adsorbent properties and performance was rarely reported so far. In this study, a series of sodium titanates (STs) and peroxide modified sodium titanates (PSTs) with different primary particle sizes, and secondary sizes are synthesized by controlling synthesis conditions and subsequently applied to batch adsorption experiment. By employing scanning electron microscopes and Laser particle size analyzers, the particle sizes of STs and PSTs are found to be closely correlated with synthesis conditions. The surface morphology and specific surface area of titanates are size-dependent, while the components of all the samples maintained constant. The sedimentation experiment and CFD simulation demonstrated that particles with larger secondary sizes tended to settle more quickly than those with a bigger size. PSTs or STs particles with smaller secondary sizes could reach equilibrium more rapidly than those with the bigger size. The fitting results from Elovich and Weber-Morris models demonstrated that the particle sizes affect kinetics mainly through the liquid film diffusion process within the initial stages

The GC Content as a Main Factor Shaping the Amino Acid Usage During Bacterial Evolution Process

Understanding how proteins evolve is important, and the order of amino acids being recruited into the genetic codons was found to be an important factor shaping the amino acid composition of proteins. The latest work about the last universal common ancestor (LUCA) makes it possible to determine the potential factors shaping amino acid compositions during evolution. Those LUCA genes/proteins from Methanococcus maripaludis S2, which is one of the possible LUCA, were investigated. The evolutionary rates of these genes positively correlate with GC contents with P-value significantly lower than 0.05 for 94% homologous genes. Linear regression results showed that compositions of amino acids coded by GC-rich codons positively contribute to the evolutionary rates, while these amino acids tend to be gained in GC-rich organisms according to our results. The first principal component correlates with the GC content very well. The ratios of amino acids of the LUCA proteins coded by GC rich codons positively correlate with the GC content of different bacteria genomes, while the ratios of amino acids coded by AT rich codons negatively correlate with the increase of GC content of genomes. Next, we found that the recruitment order does correlate with the amino acid compositions, but gain and loss in codons showed newly recruited amino acids are not significantly increased along with the evolution. Thus, we conclude that GC content is a primary factor shaping amino acid compositions. GC content shapes amino acid composition to trade off the cost of amino acids with bases, which could be caused by the energy efficiency