Highly stereoselective reductions of α-alkoxy-β-keto esters. Aspects of the mechanism of sodium borohydride reduction of ketones in 2-propanol

Reduction of α-alkoxy-β-keto esters with sodium borohydride in 2-propanol proceeds with high stereoselectivity via a five-membered ring chelated sodium ion.     

Pressures inside a room subjected to simulated sonic booms

The pressure variations inside a room of plaster-wood construction subjected to sonic boom loadings were investigated both analytically and experimentally to study the problems of dynamic structural response. The N-wave pressure signatures were generated in the UTIAS (University of Toronto Institute for Aerospace Studies) Travelling Wave Horn-Type Sonic Boom Simulator. The room overpressures in some cases were found to be twice as great as that in the incident sonic boom. The analysis and experimental data can be useful in assessing structural damage caused by supersonic aircraft overfligths.     

E2 nuclear resonance effects in pionic and kaonic atoms

The attenuation due to the E2 nuclear resonance effect has been measured in hadronic atoms using pions with ¹¹¹Cd and ¹¹²Cd, and for kaons with ¹²²Sn. Energies of the relevant X-ray and γ-ray transitions and of the X-ray cascade intensities have also been measured so as to give a self-consistent set of information. The results are found to be in very good agreement with theoretical calculations.     

Green's function for magnetically incoherent interacting electrons in one dimension

Using a path integral approach and bosonization, we calculate the low-energy asymptotics of the one particle Green's function for a "magnetically incoherent" one dimensional strongly interacting electron gas at temperatures much greater than the typical exchange energy but much lower than the Fermi energy. The Green's function exhibits features reminiscent of spin-charge separation, with exponential spatial decay and scaling behavior with interaction dependent anomalous exponents inconsistent with any unitary conformal field theory. We compute the tunneling density of states at low energies and find that it is a power law in energy with exponent 1/(4g)-1, where g is the Luttinger interaction parameter in the charge sector. The underlying physics is made transparent by the simplicity of the approach. Our results generalize those of Cheianov and Zvonarev [Phys. Rev. Lett. 92, 176401 (2004)]].     

Brane-World Models Emerging from Collisions of Plane Waves in 5D

We consider brane-world models embedded in a five-dimensional bulk spacetime with a large extra dimension and a cosmological constant. The cosmology in 5D possesses wave-like character in the sense that the metric coefficients in the bulk are assumed to have the form of plane waves propagating in the fifth dimension. We model the brane as the plane of collision of waves propagating in opposite directions along the extra dimension. This plane is a jump discontinuity which presents the usual Z ₂ symmetry of brane models. The model reproduces the generalized Friedmann equation for the evolution on the brane, regardless of the specific details in 5D. Model solutions with spacelike extra coordinate show the usual big-bang behavior, while those with timelike extra dimension present a big bounce. This bounce is an genuine effect of a timelike extra dimension. We argue that, based on our current knowledge, models having a large timelike extra dimension cannot be dismissed as mathematical curiosities in non-physical solutions. The size of the extra dimension is small today, but it is increasing if the universe is expanding with acceleration. Also, the expansion rate of the fifth dimension can be expressed in a simple way through the four-dimensional deceleration and Hubble parameters as – q H. These predictions could have important observational implications, notably for the time variation of rest mass, electric charge and the gravitational constant. They hold for the three (k = 0, + 1, – 1) models with arbitrary cosmological constant, and are independent of the signature of the extra dimension.