Observation of slow and fast cylindrical soliton-like waves

Two types of soliton-like ion acoustic waves are observed simultaneously, one travelling initially faster and the other slower than a one-dimensional soliton.     

On singlet exciton fission in anthracene and tetracene at 77°K

Relative variations of prompt flourescence yield, on application of a magnetic field are studied at 77°K for anthracene and tetracene crystals excited by light with wavenumbers up to 50,000 cm^-1. The results obtained for anthacene, as compared to those previously reported at 300°K, indicate a very small temperature dependence. The variations observed for tetracene at 77°K are comparable in magnitude to those for anthracene. The singlet exciton fission process, responsible for the experimental observations, does not involve a thermally relaxed lowest bound or charge transfer singlet exciton. The possible role of upper excited vibronic states is discussed.     

Observation of long-lived muonic hydrogen in the 2S state

The kinetic energy distribution of ground state muonic hydrogen atoms mup(1S) is determined from time-of-flight spectra measured at 4, 16, and 64 hPa H2 room-temperature gas. A 0.9 keV component is discovered and attributed to radiationless deexcitation of long-lived mu p(2S) atoms in collisions with H2 molecules. The analysis reveals a relative population of about 1%, and a pressure-dependent lifetime (e.g., 30.4 +21.4/-9.7 ns at 64 hPa) of the long-lived mu p(2S) population, equivalent to a 2S quench rate in mu p(2S)+H2 collisions of 4.4 +2.1/-1.8 x 10(11) s(-1) at liquid-hydrogen density.     

The colors of polydiacetylenes: a commentary

Polydiacetylenes (PDA) can take several colors, mostly "red" and "blue", and blue-to-red color transitions are usually considered as transitions from a well ordered state to a disordered one. Recent work on single isolated PDA chains shows that this is not correct: red chains can be quasi-perfect quantum wires. The transition is between two different chain conformations, and each may, or may not, be perfectly ordered. Disorder, when it occurs, is a side-product of the transformation.