Observation of narrow fluorescence from doubly driven four-level atoms at room temperature

Unusually narrow fluorescence peaks are seen from Rubidium-85 atoms under the action of two driving laser fields that are in a three dimensional molasses configuration. One of the lasers is held at a fixed detuning from the "cooling" transition, while the other is scanned across the "repumping" transitions. The fluorescence peaks are split into symmetric pairs, with the seperation within a pair increasing with the detuning of the cooling laser. For large detunings additional small peaks are seen. A simple model is proposed to explain these experimental observations.Comment: 8 pages, 4 figures, needs epl.cl

Analysis of a Modified Feedback Control Technique for Suppressing Electrical Alternans in Cardiac Tissue

Alternans is an abnormal cardiac rhythm in which action potential duration alternates from beat-to-beat. In order for an implanted pacemaker to successfully seize control of the heart rhythm, its electrical stimuli have to be carefully timed relative to the firing of the heart’s specialized pacemaker cells. In this manuscript, we use mathematical techniques to analyze a novel feedback control algorithm for suppressing alternans. We model the cardiac rhythm and the effect of the controller using a system of two nonlinear difference equations. Our analysis reveals that it is often advantageous not to allow the pacemaker to intervene in every beat when attempting to control alternans

Stranded in isolation: structural role of isolated extended strands in proteins

Reasons for the formation of extended-strands (E-strands) in proteins are often associated with the formation of β -sheets. However E-strands, not part of β-sheets, commonly occur in proteins. This raises questions about the structural role and stability of such isolated E-strands. Using a dataset of 250 largely non-homologous and high-resolution (<2 Å) crystal structures of proteins, we have identified 518 isolated E-strands from 187 proteins. The two most distinguishing features of isolated E-strands from β-strands in β-sheets are the high preponderance of prolyl residues occuring in isolated E-strands and their high exposure to the surroundings. Removal of regions with polyproline conformation from the dataset did not significantly reduce the propensity of prolyl residues to occur in isolated E-strands. Isolated E-strands are often characterized by their main-chain amide and carbonyl groups involved in hydrogen bonding with polar side chains or water. They are often flanked by irregular loop structures and are less well conserved, than β-sheet forming β-strands, among homologous protein structures. It is suggested that isolated β-strands have many characteristics of loop segments but with repetitive (φ,ψ) values falling within the β-region of the Ramachandran map

The role of clefting, word order and given-new ordering in sentence comprehension: Evidence from Hindi

Two Hindi eyetracking studies show that clefting a noun results in greater processing diculty initially, due to the extra processing steps involved in encoding a clefted noun (e.g., for computing the exhaustiveness interpretation). However, this extra diffculty in encoding a clefted noun results in a processing advantage when the clefted noun needs to be retrieved later on in the sentence { the clefted noun is retrieved faster in subsequent processing compared to its non-clefted counterpart. This effect is short-lived, however; it does not last beyond the current sentence. We also show that given-new ordering yields a processing advantage over new-given order, but this is only seen after the whole sentence is processed, i.e., it is a late effect that occurs after syntactic processing is completed. Finally, following up on work on German by Hornig et al. (2005), we present evidence that non-canonical order can be processed more easily than canonical order given appropriate context