Description: This article discusses microwave absorption by an array of carbon nanotubes. Abstract: A simple model to explain microwave-induced heating of carbon nanotubes (CNTs) through transformation of electromagnetic energy into mechanical vibrations is proposed and analyzed. The model provides a way to understand recent observations of heating of CNTs exposed to microwaves in the range of 2-20 GHz. It is shown that transverse vibrations of CNTs during microwave irradiation can be associated with parametric resonance, as occurs in the analysis of acoustic experiments on forced longitudinal vibrations of a stretched elastic string. For carbon nanotubes [single wall nanotube (SWNT), double wall nanotube (DWNT), multiwall nanotube (MWNT), ropes, and strands] the resonant parameters are shown to be located in a region of instability of the Mathieu's equation. Wave equations with cubic nonlinearity were used to qualitatively describe the effects of phonon-phonon interactions and energy transfer from microwaves to CNTs at a rate much exceeding the traditional Joule heating via electron-phonon interaction.

Description: This article discusses non-Gaussian statistics of anomalous diffusion. Abstract: We adopt a non-Gaussian indicator to measure the deviation from Gaussian statistics of a diffusion process generated by dichotomous fluctuations with infinite memory. We also make analytical predictions on the transient behavior of the non-Gaussian indicator as well as on its stationary value. We then apply this non-Gaussian analysis to the DNA sequences of prokaryotes adopting a theoretical model where the "DNA dynamics" are assumed to be determined by the statistical superposition of two independent generators of fluctuations: a generator of fluctuations with no correlation and a generator of fluctuations with infinite correlation "time". We study also the influence that the finite length of the observed sequences has on the short-range fluctuation and sequence truncation. Nevertheless, under proper conditions, fulfilled by all the DNA sequences of prokaryotes that have been examined, a non-Gaussian signature remains to signal the correlated nature of the driving process.

Description: This article discusses the observation of picosecond superfluorescent pulses in rubidium atomic vapor pumped by 100-fs laser pulses. Abstract: We study the superfluorescence (SF) from a gas of rubidium atoms. The atoms of a dense vapor are excited to the 5D state from the 5S state by a two-photon process driven by 100-fx laser pulses. The atoms decay to the 6P state and then to the 5S state. The SF emission at 420 nm on the 6P-5S transition is recorded by a streak camera with picosecond time resolution. The time duration of the generated SF is tens of picoseconds, which is much shorter than the time scale of the usual relaxation processes, including spontaneous emission and atomic coherence dephasing. The dependence of the time delay between the reference input pulse and SF is measured as a function of laser power. The experimental data are described quantitatively by a simulation based on the semiclassical atom-field interaction theory. The observed change in scaling laws for the peak intensity and delay time can be elucidated by an SF theory in which the sample length is larger than the cooperation length.

Description: This article discusses nuclear lifetime of states in ⁹⁴TC and ⁹⁶TC via the pulsed-beam, direct-timing technique. Abstract: The mean lifetimes of the 333 keV level in ⁹⁴TC and the 119 and 315 keV levels in ⁹⁶TC were measured by the pulsed-beam, direct-timing technique. The values obtained for the mean lifetimes are: τ(333 keV)=2.2(-0.3)(+0.5) nsec, τ(119 keV)=37.0(-0.3)(+0.6) nsec, and τ(315 keV)=2.9(-0.2)(+0.5) nsec. The transition strengths are in agreement with those for other transitions in this mass region.

Description: This article discusses non-Markovian nonstationary completely positive open-quantum-system dynamics. Abstract: By modeling the interaction of a system with an environment through a renewal approach, we demonstrate that completely positive non-Markovian dynamics may develop some unexplored nonstandard statistical properties. The renewal approach is defined by a set of disruptive events, consisting in the action of a completely positive superoperator over the system density matrix. The random time intervals between events are described by an arbitrary waiting-time distribution. We show that, in contrast to the Markovian case, if one performs a system preparation (measurement) at an arbitrary time, the subsequent evolution of the density-matrix evolution is modified. The nonstationary character refers to the absence of an asymptotic master equation even when the preparation is performed at arbitrary long times. In spite of this property, we demonstrate that operator expectation values and operators correlations have the same dynamical structure, establishing the validity of a nonstationary quantum regression hypothesis. The nonstationary property of the dynamics is also analyzed through the response of the system to an external weak perturbation.