Physics and Astronomy Calendar

Week of Monday, January 15th 2018

Monday, January 15th 2018

Tuesday, January 16th 2018
12:20 pm:
Space Physics Seminar in Tate 301-20
There will be no seminar this week.

Wednesday, January 17th 2018
1:25 pm:
Speaker: Jeff Derby (Dept. of Chemical Engineering and Materials Science, U of M)
Subject: The synergy of modeling and novel experiments for melt crystal growth research

Our understanding of crystal growth fundamentals and processes are advanced when the synergy between mathematical models and novel experiments is exploited. We present recent examples of how modeling and experiments together have enabled the identification of fundamental mechanisms important during the growth of bulk crystals from the melt.

We first discuss how microgravity experiments, carried out via sounding rockets, motivated a reexamination of classical theories for foreign particle engulfment during crystal growth. Via the development and application of rigorous numerical models, we were able, for the first time in over a decade of research on this system, to quantitatively describe data on the engulfment of SiC (silicon carbide) particles during the growth of crystalline silicon. Moreover, model results identified previously unascertained mechanisms responsible for the behavior of this system and, via this insight, provided insight for analytical derivation of a new scaling law for the dependence of critical engulfment velocity on particle size.

We finish with an overview of exciting, new research that employs neutron imaging to directly “see,” in operando, the bulk growth of scintillator crystals during a gradient-freeze process. We argue that the synergies of “seeing” via both models and neutron imaging will improve our fundamental understanding and provide for a closed-loop approach for optimizing the growth of large, single crystals from the melt.

This research was supported in part by NASA NNX10AR70G, DOE/NNSA DE-NA0002514, DOE/NNSA/DNN R&D (LBNL subcontract AC0205CH11231); no official endorsement should be inferred.

Faculty Host: Paul Crowell
3:35 pm:
To be announced.

Thursday, January 18th 2018
10:10 am:
Biophysics Seminar in PAN 120
Speaker: John Yin, University of Wisconsin
Subject: Paths to biological polymers: an insight from virus infections and origins of life

(1) Given the genome of a virus and PubMed, how well could one predict the one-step growth of the virus? Decades of biochemical and biophysical studies on bacteriophage T7, incorporated into a chemical kinetic model for template-dependent processes of transcription, translation, and genome replication, as well as particle assembly and release, enabled simulation of one-step growth behavior that recapitulated the experimentally observed kinetics of phage growth. Extension of the model and experiments to study the effects of host-cell physiology on phage growth highlighted the host cellular protein synthesis machinery as a key limiting resource for phage growth.
(2) Given amino acid monomers, but no cells, no templates and no protein synthesis machinery, how might the monomers nevertheless form polymers? The synthesis of peptide bonds between amino acids is a condensation reaction that is generally disfavored in aqueous solutions. However, we have found that for appropriate initial conditions of pH and temperature, drying of amino acids can promote their condensation to form peptides.
So what is the common insight from (1) and (2)? The often neglected “nurture” part of “nature versus nurture” can be important. The kinetics of phage growth depends on the physiological state of its host cell, and the de novo synthesis of a polypeptide species critically depends on the acidity and temperature of its initial solution. In short, we are all products of our environments.

Faculty Host: J. Woods Halley
3:35 pm:
Speaker: Harvey Brown, Philosophy of Physics, University of Oxford
Subject: Quantum Bayesianism (QBism): the way to understand the quantum world

The recent philosophy of Quantum Bayesianism, or QBism, represents an attempt to solve the traditional puzzles in the foundations of quantum theory by denying the objective reality of the quantum state. Einstein had hoped to remove the spectre of nonlocality in the theory by also assigning an epistemic status to the quantum state, but his version of this doctrine was recently proved to be inconsistent with the predictions of quantum mechanics. In this talk, I present plausibility arguments, old and new, for the reality of the quantum state, and expose what I think are weaknesses in QBism as a philosophy of science. (The talk is based on this paper:

Friday, January 19th 2018
10:10 am:
Nuclear Physics Seminar in Tate 201-20
To be announced.
12:20 pm:
Speaker: Evan Moen
Subject: Spin Transport in Superconducting Spin Valves
Speaker: No colloquium this week.
Speaker: Harvey Brown, Philosophy of Physics, University of Oxford
Subject: "How Einstein Came to Use the Action-Reaction Principle in Promoting his Theory of Gravity"
Refreshments served at 3:15 p.m.

Einstein regarded as one of the triumphs of his 1915 theory of gravity — the general theory of relativity — that it vindicated the action–reaction principle, while Newtonian mechanics as well as his 1905 special theory of relativity supposedly violated it. In this talk I examine why Einstein came to emphasise this position several years after the development of general relativity. Several key considerations are relevant to the story: the connection Einstein originally saw between Mach’s analysis of inertia and both the equivalence principle and the principle of general covariance, the waning of Mach’s influence owing to de Sitter’s 1917 results, and Einstein’s detailed correspondence with Moritz Schlick in 1920. (The talk is based on ‘Einstein, the reality of space, and the action-reaction principle’, H.R.B. and Dennis Lehmkuhl, in Einstein, Tagore and the Nature of Reality, Partha Ghose (ed.), Routledge, London and New York, 2016; pp. 9-36. arXiv:1306.4902v1.)

4:40 pm:
Speaker: Priscilla Cushman, University of Minnesota
Subject: SuperCDMS - searching for dark matter
4:40 pm:
Organizational Meeting. Time and place of seminar will resume to match class schedule next week.

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