In mixed systems of trapped ions and cold atoms, the ions and atoms can coexist at different temperatures. This is primarily due to their different trapping and cooling mechanisms. The key questions ...of how ions can cool collisionally with cold atoms and whether the combined system allows stable coexistence, need to be answered. Here we experimentally demonstrate that rubidium ions cool in contact with magneto-optically trapped rubidium atoms, contrary to the general experimental expectation of ion heating. The cooling process is explained theoretically and substantiated with numerical simulations, which include resonant charge exchange collisions. The mechanism of single collision swap cooling of ions with atoms is discussed. Finally, it is experimentally and numerically demonstrated that the combined ion-atom system is intrinsically stable, which is critical for future cold chemistry experiments with such systems.
We experimentally demonstrate cooling of trapped ions by collisions with cotrapped, higher-mass neutral atoms. It is shown that the lighter ^{39}K^{+} ions, created by ionizing ^{39}K atoms in a ...magneto-optical trap (MOT), when trapped in an ion trap and subsequently allowed to cool by collisions with ultracold, heavier ^{85}Rb atoms in a MOT, exhibit a longer trap lifetime than without the localized ^{85}Rb MOT atoms. A similar cooling of trapped ^{85}Rb^{+} ions by ultracold ^{133}Cs atoms in a MOT is also demonstrated in a different experimental configuration to validate this mechanism of ion cooling by localized and centered ultracold neutral atoms. Our results suggest that the cooling of ions by localized cold atoms holds for any mass ratio, thereby enabling studies on a wider class of atom-ion systems irrespective of their masses.
This study provides new data regarding the burning dynamics of a thin oil layer on a water surface with carefully controlled turbulence intensity. The turbulent water surface is generated using a ...unique experimental platform comprising an axisymmetric upward-pointing submerged jet, an approach used in studies of free-surface turbulence. The turbulence is isotropic in the horizontal plane and bulk-flow free, with turbulence intensity u′ ranging from 0.017−0.035 m/s comparable to water turbulence in calm oceans. The experiments revealed a strong dependence on the burning rate of the oil layer with the turbulence intensity of the water surface. Increasing turbulence increased the heat transfer rate at the oil-water interface, reducing the burning rate. Results were modeled using a 1-D heat transfer model, where heat loss to the turbulent water was analyzed by an experimentally determined convective heat transfer coefficient. The coupling with the gas phase heat transfer was achieved using a parameter χ representing the fraction of heat release fed back to the fuel.
As part of a study of the combustion of boxes of commodities, rates of upward flame spread during early-stage burning were observed during experiments on wide samples of corrugated cardboard. The ...rate of spread of the flame front, defined by the burning pyrolysis region, was determined by visually averaging the pyrolysis front position across the fuel surface. The resulting best fit produced a power-law progression of the pyrolysis front,
x
p
=
At
n
, where
x
p
is the average height of the pyrolysis front at time
t,
n
=
3/2, and
A is a constant. This result corresponds to a slower acceleration than was obtained in previous measurements and theories (e.g.
n
=
2), an observation which suggests that development of an alternative description of the upward flame spread rate over wide, inhomogeneous materials may be worth studying for applications such as warehouse fires. Based upon the experimental results and overall conservation principles it is hypothesized that the non-homogeneity of the cardboard helped to reduce the acceleration of the upward spread rates by physically disrupting flow in the boundary layer close to the vertical surface and thereby modifying heating rates of the solid fuel above the pyrolysis region. As a result of this phenomena, a distinct difference was observed between scalings of peak flame heights, or maximum “flame tip” measurements and the average location of the flame. The results yield alternative scalings that may be better applicable to some situations encountered in practice in warehouse fires.
A continuously operated electrostatic trap for polar molecules is demonstrated. The trap has a volume of approximately 0.6 cm3 and holds molecules with a positive Stark shift. With deuterated ammonia ...from a quadrupole velocity filter, a trap density of approximately 10(8) cm(-3) is achieved with an average lifetime of 130 ms and a motional temperature of approximately 300 mK. The trap offers good starting conditions for high-precision measurements, and can be used as a first stage in cooling schemes for molecules and as a "reaction vessel" in cold chemistry.
The interaction of laser cooled atoms with resonant light is determined by the natural linewidth of the excited state. An optical cavity is another optically resonant system where the loss from the ...cavity determines the resonant optical response of the system. The near resonant combination of an optical Fabry-Pérot cavity with laser cooled and trapped atoms couples two distinct optical resonators via light and has great potential for precision measurements and the creation of versatile quantum optics systems. Here we show how driven magneto-optically trapped atoms in collective strong coupling regime with the cavity leads to lasing at a frequency red detuned from the atomic transition. Lasing is demonstrated experimentally by the observation of a lasing threshold accompanied by polarization and spatial mode purity, and line-narrowing in the outcoupled light. Spontaneous emission into the cavity mode by the driven atoms stimulates lasing action, which is capable of operating as a continuous wave laser in steady state, without a seed laser. The system is modeled theoretically, and qualitative agreement with experimentally observed lasing is seen. Our result opens up a range of new measurement possibilities with this system.
Multiple pool fires (MPFs) is the term used to denote pool fires which occur close enough of each other to influence each other. Even though much lesser attention has been paid to the understanding ...and control of MPFs, in comparison to stand-alone pool fires (SPFs), MPFs are by no means uncommon in chemical process industries. Worse, most of the MPFs–such as the ones that occurred at Buncesfield (UK) in 2005, and Jaipur (India) in 2009–are so powerful that they defy all attempts of quenching them and continue to rage till the fuel that was feeding them gets exhausted. Such fires cause enormous damage to property, besides loss of lives as occurred at Jaipur.
Of the several factors that influence the destruction potential of the MPFs, pool size and separation distance between pools (S) to diameter (D) ratio (S/D) were expected to be the key factors. But no study has been done so far to analyse the effect of pool size and S/D ratio on MPFs and the present paper attempts to bridge this knowledge gap.
Computational fluid dynamics (CFD) was used to model the effect of pool sizes on MPFs. The model was validated with the experimental data generated earlier by Fukuda et al. (2005). The validated code was then used to simulate the burning rate of MPFs involving pools of diameters larger than the ones used by Fukuda et al. (2005).
It was observed that flame temperature, flame height, and the burning rate, all increase with an increase in the pool diameter of the participating pools in the MPFs. It was also observed that of the four S/D ratios — 0.25, 0.45, 0.66 and 1.08 — for which we have done the simulations, maximum flame height and burning rates accrues with the S/D ratio of 0.45.
•When two or more pool fires burn interactively they are termed multiple pool fires (MPF).•Past studies have shown that stand-alone pool fires are strongly influenced by the area of the fuel pool.•No previous study on the effect of pool area on MPFs exists, making this work the first of its kind.•CFD code, validated with experimental data from Fukuda, Kudo, and Ito (2005), was used for the study.•Adequate precision was achieved in simulation, enabling forecasts to be made.
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