61 research outputs found
Bose-enhanced chemistry: Amplification of selectivity in the dissociation of molecular Bose-Einstein condensates
We study the photodissociation chemistry of a quantum degenerate gas of
bosonic triatomic molecules, assuming two open rearrangement channels
( or ). The equations of motion are equivalent to those of a
parametric multimode laser, resulting in an exponential buildup of macroscopic
mode populations. By exponentially amplifying a small differential in the
single-particle rate-coefficients, Bose stimulation leads to a nearly complete
selectivity of the collective -body process, indicating a novel type of
ultra-selective quantum degenerate chemistry.Comment: 5 pages, 3 figure
Design and Characterization of a Hypervelocity Expansion Tube Facility
We report on the design and characterization of a 152 mm diameter expansion tube capable of accessing a range of high enthalpy test conditions
with Mach numbers up to 7.1 for aerodynamic studies. Expansion tubes
have the potential to offer a wide range of test flow conditions as gas acceleration is achieved through interaction with an unsteady expansion wave
rather than expansion through a fixed area ratio nozzle. However, the range
of test flow conditions is in practice limited by a number of considerations
such as short test time and large amplitude flow disturbances. We present
a generalized design strategy for small-scale expansion tubes. As a starting
point, ideal gas dynamic calculations for optimal facility design to maximize
test time at a given Mach number test condition are presented, together
with a correction for the expansion head reflection through a non-simple
region. A compilation of practical limitations that have been identified for
expansion tube facilities such as diaphragm rupture and flow disturbance
minimization is then used to map out a functional design parameter space.
Experimentally, a range of test conditions have been verified through pitot
pressure measurements and analysis of schlieren images of flow over simple
geometries. To date there has been good agreement between theoretical
and experimental results
Oscillatory Dynamics of Cell Cycle Proteins in Single Yeast Cells Analyzed by Imaging Cytometry
Progression through the cell division cycle is orchestrated by a complex network of interacting genes and proteins. Some of these proteins are known to fluctuate periodically during the cell cycle, but a systematic study of the fluctuations of a broad sample of cell-cycle proteins has not been made until now. Using time-lapse fluorescence microscopy, we profiled 16 strains of budding yeast, each containing GFP fused to a single gene involved in cell cycle regulation. The dynamics of protein abundance and localization were characterized by extracting the amplitude, period, and other indicators from a series of images. Oscillations of protein abundance could clearly be identified for Cdc15, Clb2, Cln1, Cln2, Mcm1, Net1, Sic1, and Whi5. The period of oscillation of the fluorescently tagged proteins is generally in good agreement with the inter-bud time. The very strong oscillations of Net1 and Mcm1 expression are remarkable since little is known about the temporal expression of these genes. By collecting data from large samples of single cells, we quantified some aspects of cell-to-cell variability due presumably to intrinsic and extrinsic noise affecting the cell cycle
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