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Ultracold molecules are currently a topic of great interest in AMO physics. One method for forming such molecules is photoassociation, where two colliding atoms absorb a photon and are bound into an excited molecule. We examine a variation of this process in Rb2, using frequency-chirped light on the nanosecond time scale. In the case of a positive chirp, the photoassociation can be followed by stimulated emission into a high vibrational level of the lowest-lying (metastable) triplet state. We show that this two-step process can be enhanced by a judicious shape of the chirp. Quantum simulations of the molecular formation are not only in good agreement with the experimental results, but also give insight into the enhancement mechanism.

The process of self-replication is at the core of Biological systems. Therefore, understanding the constraints that act on the process of self-replication is crucial. However, little is known about the physical and evolutionary constraints that shape the observed behavior of Biological Systems. We show that molecular noise can be exploited by bacteria to spread the time-scale of self-replication. However noise is not always the underlying cause of variability in clonal cells populations. We show that the variability of self-replication times in mammalian cells is governed by a deterministic process.

The high-latitude vertical structure of temperature is poorly understood, yet is an important factor in the polar amplification of climate change. To better understand the high-latitude lapse rate and its sensitivity to various forcings, we explore two perspectives on the high-latitude temperature structure.
The first is the Lagrangian perspective of Arctic air formation. We prescribe the initial sounding of the atmosphere representing an air column starting over the ocean, then allow the air mass to evolve for two weeks in the absence of any solar heating and with a very low heat capacity surface underneath (representing the movement of the air column over high-latitude sea ice or a continental interior). Using a single-column model, we find that a low-cloud feedback slows cooling of the surface and amplifies continental warming, increasing the continental surface air temperature by roughly two degrees for each degree increase of the initial maritime surface air temperature. We discuss extension with a 2D cloud-resolving model, and applications to past and future warm climates.
The second is the Eulerian perspective of radiative-advective equilibrium. High latitude temperature profiles are generally stable to convection, with frequent surface-based inversions, especially in winter. Such profiles result from the stabilizing influences of advective heat flux convergence and atmospheric solar absorption, which dominate over the destabilizing influences of surface solar absorption and subsurface heating. We formulate an analytical model for the high-latitude temperature profile, using prescribed heat flux convergence and either gray- or windowed-gray thermal radiative transfer. We discuss how climate feedbacks in this state depend on the type of forcing, and compare temperature feedbacks in high-latitude radiative-advective equilibrium to the more familiar case of low-latitude radiative-convective equilibrium.