10 research outputs found
Beta decay and the origin of biological chirality: New experimental results
The proposed connection between the parity-violating handedness of beta particles in radioactive decay and the sign (L) of biological chirality (the Vester-Ulbricht [V-U] hypothesis) is being investigated by measuring the theoretically predicted asymmetry in the formation of triplet positronium in amino acid enantiomers by low energy positrons under reversal of the helicity of the positrons. We find the asymmetry in leucine to be (0.8±1.0)×10 −4 , i.e. consistent with the theoretical, prediction of 10 −6 to 10 −7 . The apparatus is now sensitive enough to test the predicted asymmetry in optically active molecules which have heavy atoms at their chiral centers. The connection between these results and asymmetry in radiolysis by beta-decay electrons is made, and the implications of our limits for the V-U hypothesis discussed. Although the above limits are 10 6 times lower than direct measurements of radiolysis, they are still not small enough to allow us to rule out the V-U hypothesis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43347/1/11084_2004_Article_BF00933685.pd
Macroscopic Quantum Fluctuations in the Josephson Dynamics of Two Weakly Linked Bose-Einstein Condensates
We study the quantum corrections to the Gross-Pitaevskii equation for two
weakly linked Bose-Einstein condensates. The goals are: 1) to investigate
dynamical regimes at the borderline between the classical and quantum behaviour
of the bosonic field; 2) to search for new macroscopic quantum coherence
phenomena not observable with other superfluid/superconducting systems. Quantum
fluctuations renormalize the classical Josephson oscillation frequencies. Large
amplitude phase oscillations are modulated, exhibiting collapses and revivals.
We describe a new inter-well oscillation mode, with a vanishing (ensemble
averaged) mean value of the observables, but with oscillating mean square
fluctuations. Increasing the number of condensate atoms, we recover the
classical Gross-Pitaevskii (Josephson) dynamics, without invoking the
symmetry-breaking of the Gauge invariance.Comment: Submitte
Phase dynamics after connection of two separate Bose-Einstein condensates
We study the dynamics of the relative phase following the connection of two
independently formed Bose-Einstein condensates. Dissipation is assumed to be
due to the creation of quasiparticles induced by a fluctuating condensate
particle number. The coherence between different values of the phase, which is
characteristic of the initial Fock state, is quickly lost after the net
exchange of a few atoms has taken place. This process effectively measures the
phase and marks the onset of a semiclassical regime in which the system
undergoes Bloch oscillations around the initial particle number. These fast
oscillations excite quasiparticles within each condensate and the system
relaxes at a longer time scale until it displays low-energy, damped Josephson
plasma oscillations, eventually coming to a halt when the equilibrium
configuration is finally reached.Comment: 4 pages, 1 figure, submitted to Physical Review
Homochirality as the signature of life: The SETH Cigar
A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could be used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life