Properties of heavy quarkonia and B_c mesons in the relativistic quark model

The mass spectra and electromagnetic decay rates of charmonium, bottomonium and B_c mesons are comprehensively investigated in the relativistic quark model. The presence of only heavy quarks allows the expansion in powers of their velocities. All relativistic corrections of order v^2/c^2, including retardation effects and one-loop radiative corrections, are systematically taken into account in the computations of the mass spectra. The obtained wave functions are used for the calculation of radiative magnetic dipole (M1) and electric dipole (E1) transitions. It is found that relativistic effects play a substantial role. Their account and the proper choice of the Lorentz structure of the quark-antiquark interaction in a meson is crucial for bringing theoretical predictions in accord with experimental data. A detailed comparison of the calculated decay rates and branching fractions with available experimental data for radiative decays of charmonium and bottomonium is presented. The possibilities to observe the currently missing spin-singlet S and P states as well as D states in bottomonium are discussed. The results for B_c masses and decays are compared with other quark model predictions.Comment: 31 pages, 2 figures, minor correction

Higher order association in polyelectrolyte-micelle complexes

Langmuir681422-142

Piezo2 is the major transducer of mechanical forces for touch sensation in mice

The sense of touch provides critical information about our physical environment by transforming mechanical energy into electrical signals. It is postulated that mechanically activated cation channels initiate touch sensation, but the identity of these molecules in mammals has been elusive. Piezo2 is a rapidly adapting, mechanically activated ion channel expressed in a subset of sensory neurons of the dorsal root ganglion and in cutaneous mechanoreceptors known as Merkel-cell-neurite complexes. It has been demonstrated that Merkel cells have a role in vertebrate mechanosensation using Piezo2, particularly in shaping the type of current sent by the innervating sensory neuron; however, major aspects of touch sensation remain intact without Merkel cell activity. Here we show that mice lacking Piezo2 in both adult sensory neurons and Merkel cells exhibit a profound loss of touch sensation. We precisely localize Piezo2 to the peripheral endings of a broad range of low-threshold mechanoreceptors that innervate both hairy and glabrous skin. Most rapidly adapting, mechanically activated currents in dorsal root ganglion neuronal cultures are absent in Piezo2 conditional knockout mice, and ex vivo skin nerve preparation studies show that the mechanosensitivity of low-threshold mechanoreceptors strongly depends on Piezo2. This cellular phenotype correlates with an unprecedented behavioural phenotype: an almost complete deficit in light-touch sensation in multiple behavioural assays, without affecting other somatosensory functions. Our results highlight that a single ion channel that displays rapidly adapting, mechanically activated currents in vitro is responsible for the mechanosensitivity of most low-threshold mechanoreceptor subtypes involved in innocuous touch sensation. Notably, we find that touch and pain sensation are separable, suggesting that as-yet-unknown mechanically activated ion channel(s) must account for noxious (painful) mechanosensation