Integrated Calendar

Abstract: The lifetime of false vacua can be calculated by Coleman's semiclassical method. This method implicitly uses a deformation of the potential. I will discuss an alternative approach to the calculation of the
lifetime of the false vacua.

References:
Direct Approach to Quantum Tunneling
Anders Andreassen, David Farhi, William Frost, Matthew D. Schwartz
Published in Phys.Rev.Lett. 117 (2016) no.23, 231601
e-Print: arXiv:1602.01102 [hep-th]

Precision decay rate calculations in quantum field theory
Anders Andreassen, David Farhi, William Frost, Matthew D. Schwartz
Published in Phys.Rev. D95 (2017) no.8, 085011
e-Print: arXiv:1604.06090 [hep-th]

Over the past decade, fluorescence-based single-molecule studies significantly contributed
to characterizing the mechanism of RNA polymerase at different steps in transcription, especially
in transcription initiation. Transcription by bacterial DNA-dependent RNA polymerase is a
multistep process that uses genomic DNA to synthesize complementary RNA molecules. Transcription initiation is a highly regulated step in E. coli, but it has been challenging to study its
mechanism because of its stochasticity and complexity. In this talk, we will describe how single molecule approaches have contributed to our understanding of transcription and have uncovered mechanistic details that were not observed in conventional assays because of ensemble averaging.

We have performed direct numerical simulations of transient turbulence in pipe flow for Re=2,250 which is established as a threshold of an equilibrium puff. We investigate the structure of an individual puff by considering three-dimensional snapshots across a long time-period. To assimilate the velocity data, we apply a conditional sampling based on the location of the maximum energy of the transverse (turbulent) motion. Specifically, at each time instance, we follow a turbulent puff by a three-dimensional moving-window centered at that location. We collected a snapshot-ensemble of the velocity fields acquired over 10,000 time instances (snapshots) inside the moving-window. The considered fow is intermittent and transitional. The velocity field inside the puff shows the dynamics of a developing turbulence. The localized puff is about of 12-15 pipe diameters long with almost laminar trailing and leading edges. In the puff core, despite the low Reynolds number, along the moving-window, it takes the downstream short distance of several pipe diameters to form the state of developed turbulence, when the turbulence statistics becomes similar to fully-developed turbulent pipe flow; the velocity profile becomes flat in the pipe core and logarithmic near the wall. It is shown that this “fully-developed turbulent slot” is very narrow, about two pipe diameters; it is localized and moves with a puff.