Excitation transfer between the rubidium 5 2 D fine-structure levels in collisions with ground-state rubidium atoms: Experiment and theory

We report a study of fine-structure mixing Rb(5 2 D 5/2 )→Rb(5 2 D 3/2 ) in collisions with ground-state Rb atoms. In the experiment, two-photon cw laser excitation was applied to the Rb vapor cell. The measured cross section for the process was (5.8Ϯ1.9)ϫ10 Ϫ14 cm 2 . Theoretical calculations using nonadiabatic collision theory gave a value of 3.4ϫ10 Ϫ14 cm 2

Aerobic and anaerobic energy expenditure during rest and activity in montane Bufo b. boreas and Rana pipiens

The relations of standard and active aerobic and anaerobic metabolism and heart rate to body temperature ( T b ) were measured in montane groups of Bufo b. boreas and Rana pipiens maintained under field conditions. These amphibians experience daily variation of T b over 30°C and 23°C, respectively (Carey, 1978). Standard and active aerobic and anaerobic metabolism, heart rate, aerobic and anaerobic scope are markedly temperature-dependent with no broad plateaus of thermal independence. Heart rate increments provide little augmentation of oxygen transport during activity; increased extraction of oxygen from the blood probably contributes importantly to oxygen supply during activity. Development of extensive aerobic capacities in Bufo may be related to aggressive behavior of males during breeding. Standard metabolic rates of both species are more thermally dependent than comparable values for lowland relatives. Thermal sensitivity of physiological functions may have distinct advantages over thermally compensated rates in the short growing season and daily thermal fluctuations of the montane environment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47726/1/442_2004_Article_BF00348070.pd

Inelastic cross-sections and natural lifetimes for the 6

The results of an experimental study of population dynamics following excitation of $\rm 6^2D_{5/2, 3/2}$ and $\rm 8^2S_{1/2}$ states of rubidium are reported. Excitation transfer and quenching cross-sections in collisions with ground state rubidium atoms, and natural lifetimes have been measured. The experiment was performed in a vapour cell, using pulsed two-photon excitation and photon counting detection. The analysis of time dependent signals was based on a rate equation model in which transitions induced by thermal radiation have been accounted for. The measurements yielded following results: (1) $\rm 6^2D$ state J-mixing cross-section: $\rm \sigma_{6D_{5/2} \rightarrow 6D_{3/2}}^{Rb-Rb} = 9.2(2.1) \times 10^{-14} cm^2$; (2) cross-sections for $\rm 8^2S\rightarrow 6^2D$ excitation transfer process: $\sigma^{\rm Rb-Rb}_{8{\rm S}\rightarrow 6{\rm D}} = 3.4(1.2) \times 10^{-14} {\rm cm}^2$; (3) quenching cross-sections: $\sigma^{\rm Rb-Rb}_{q, 8{\rm S}} = 12.8(3.4) \times 10^{-14} {\rm cm}^2$, $\sigma^{\rm Rb-Rb}_{q, 6{\rm D}_{3/2}} = 22.8(2.9) \times 10^{-14} {\rm cm}^2$, $\sigma^{\rm Rb-Rb}_{q, 6{\rm D}_{5/2}} = 14.1(5.7) \times 10^{-14} {\rm cm}^2$; (4) radiative lifetimes: $\tau_{8\S} = 161(3)$ ns, $\tau_{\rm 6D_{3/2}} = 256(4)$ ns, $\tau_{\rm 6D_{5/2}} = 249(5)$ ns