Generic singular configurations of linkages

We study the topological and differentiable singularities of the configuration space C(Γ) of a mechanical linkage Γ in Rd, defining an inductive sufficient condition to determine when a configuration is singular. We show that this condition holds for generic singularities, provide a mechanical interpretation, and give an example of a type of mechanism for which this criterion identifies all singularities.     

Analytical extraction of the recombination zone location in organic light-emitting diodes from emission pattern extrema

We present an analytical method for extracting the recombination zone location from emission patterns produced by organic LEDs (OLEDs). The method is based on derivation of the closed-form expressions for OLED-radiated power developed in previous work and formulation of the analytical relations between the emitter position and the pattern extrema. The results are confirmed to be in good agreement with reported optical measurements. The resultant formulae offer insight regarding the dominant physical processes in the device and can be utilized to assess or verify the location of the recombination zone, a very important parameter in the optimization process of OLED efficiency, from standard optical measurements, otherwise a very difficult task to achieve.     

Shot-noise limited single-molecule FRET histograms: comparison between theory and experiments

We describe a simple approach and present a straightforward numerical algorithm to compute the best fit shot-noise limited proximity ratio histogram (PRH) in single-molecule fluorescence resonant energy transfer diffusion experiments. The key ingredient is the use of the experimental burst size distribution, as obtained after burst search through the photon data streams. We show how the use of an alternated laser excitation scheme and a correspondingly optimized burst search algorithm eliminates several potential artifacts affecting the calculation of the best fit shot-noise limited PRH. This algorithm is tested extensively on simulations and simple experimental systems. We find that dsDNA data exhibit a wider PRH than expected from shot noise only and hypothetically account for it by assuming a small Gaussian distribution of distances with an average standard deviation of 1.6 A. Finally, we briefly mention the results of a future publication and illustrate them with a simple two-state model system (DNA hairpin), for which the kinetic transition rates between the open and closed conformations are extracted.     

Importance of the heavier singlet neutrinos in leptogenesis

We argue that fast interactions of the lightest singlet neutrino N1 would project part of a preexisting lepton asymmetry L{p} onto a direction that is protected from N1 washout effects, thus preventing it from being erased. In particular, we consider an asymmetry generated in N2 decays, assuming that N1 interactions are fast enough to bring N1 into full thermal equilibrium. If N1 decays occur at T > or = 10{9} GeV, that is, before the muon Yukawa interactions enter into thermal equilibrium, then generically part of L{p} survives. In this case some of the constraints implied by the standard N1 leptogenesis scenario hold only if L{p} approximately 0. For T < or = 10{9} GeV, L{p} is generally erased, unless special alignment or orthogonality conditions in flavor space are realized.     

Dynamic ionization of water under extreme conditions

Raman spectroscopy in a laser heated diamond anvil cell and first principles molecular dynamics simulations have been used to study water in the temperature range 300 to 1500 K and at pressures to 56 GPa. We find a substantial decrease in the intensity of the O-H stretch mode in the liquid phase with pressure, and a change in slope of the melting line at 47 GPa and 1000 K. Consistent with these observations, theoretical calculations show that water beyond 50 GPa is "dynamically ionized" in that it consists of very short-lived (<10 fs) H2O, H3O+, and OH- species, and also that the mobility of the oxygen ions decreases abruptly with pressure, while hydrogen ions remain very mobile. We suggest that this regime corresponds to a superionic state.