Events - Weekly
|Sunday, February 10|
|Monday, February 11|
Doug Weibel (U. Wisconsin) "Regulation of bacterial biochemistry at strained bacterial membranes"
We are exploring an evolutionarily conserved mechanism for the localization and regulation of biochemistry at strained membranes in bacteria and mitochondria. In this talk, I highlight this mechanism by discussing the regulation of the universal and widely conserved DNA-repair protein, RecA. An emerging picture of bacterial organization is that membrane curvature causes strain in the bilayer that leads to the accumulation of intrinsically curved, anionic phospholipids at the bacterial poles. We have discovered that a large fraction of RecA in Escherichia coli cells is not associated with DNA during normal growth—it is temporally localized at the cell poles through its interaction with anionic phospholipids. Fascinatingly, this interaction inhibits the ATPase activity of RecA, which turns the DNA repair activity of the protein off. When cells are stressed and DNA repair is required, RecA dissociates from the membrane, rapidly diffuses to the mid-cell where DNA is concentrated, and forms active nucleoprotein filaments. We have traced the regulation of RecA function back to the C-terminal region RecA, which forms a known autoregulatory domain.
Early studies in this field demonstrated that large amounts of RecA associate with membrane fractions during DNA damage (Garvey et al. 1985, J. Biol. Chem. 285, 18984). A fundamental unanswered question is why does RecA bind the membrane. We have pursued this question using an approach that fuses biophysics, biochemistry, and engineering. Our data supports a model in which the cell prevents unproductive RecA-DNA interactions by storing protein at a DNA-free region of the membrane when its enzymatic function is not required. These and other studies in our lab are enabling us to decode spatial and temporal control of biochemistry in bacteria and mitochondria.
Joseph Henry Room · 12:00 p.m.– 1:00 p.m.
Condensed Matter Seminar- Johnpierre Paglione, Univ of Maryland-Separation of magnetism and superconductivity in rare earth-doped CaFe2As2 by pressure
Traces of a high-Tc superconducting phase with transition temperatures approaching 50 K have been stabilized by the substitution of light rare earths for Ca atoms in the iron-pnictide material CaFe2As2 [*]. I will present our recent studies of the evolution of superconductivity and magnetism in single crystals of La-doped CaFe2As2 under both quasi-hydrostatic and hydrostatic applied pressures by means of transport, magnetic, and neutron scattering measurements. Upon pressure increase, we find evidence that the "50 K" superconducting phase is an intrinsic property of the materials. However, unlike transition metal-doped 122 iron-superconductors where superconductivity happily coexists with AFM, the little coexistence of SC and AFM appears to mimic that found in 1111 iron-superconductors, suggesting a similar phase diagram. I will discuss this unusual dichotomy between lower-Tc systems that happily coexist with AFM and the tendency for the highest-Tc systems to show phase separation.
[*] S.R. Saha et al, Phys. Rev. B 85, 024525 (2012).
PCTS Seminar Room · 1:15 p.m.– 2:30 p.m.
High Energy Theory Seminar - Tim Cohen, SLAC Stanford - "Jet Substructure by Accident"
abstract: We propose a new search strategy for high-multiplicity hadronic final states. When new particles are produced at threshold, the distribution of their decay products is approximately isotropic. If there are many partons in the final state, it is likely that several will be clustered into the same large-radius jet. The resulting jet exhibits substructure, even though the parent states are not boosted. This "accidental" substructure is a powerful discriminant against background because it is more pronounced for high-multiplicity signals than for QCD multijets. We demonstrate how to take advantage of accidental substructure to reduce backgrounds without relying on the presence of missing energy. As an example, we present the expected limits for several R-parity violating gluino decay topologies. This approach allows for the determination of QCD backgrounds using data-driven methods, which is crucial for the feasibility of any search that targets signatures with many jets and suppressed missing energy.
PCTS Seminar Room · 2:30 p.m.– 4:00 p.m.
|Tuesday, February 12|
CANCELLED Math Physics Seminar - Vojkan Jaksic, McGill University - Quantum Hypothesis Testing and Non-Equilibrium Statistical Mechanics
Since the days of Chernoff, the hypothesis testing has played an important role in theoretical and applied statistics.
In the last decade, the mathematical structure and basic results of classical hypothesis testing have been extended to the non-commutative setting and are an important branch of quantum information theory. It was recently observed that there is a close relation (almost a a parallel) between the recent developments in quantum hypothesis testing and the developments in non-equilibrium quantum statistical mechanics. In this talk we will elaborate on this relation. (The talk is based on the joint work with Y. Ogata, C.-A. Pillet and R. Seiringer.)
Jadwin A06 · 4:30 p.m.– 6:00 p.m.
|Wednesday, February 13|
Physics Group Meeting IAS - Nima Arkani-Hamed, IAS - “Locality and Unitarity from Positivity - Part 2”
Bloomberg Lecture Hall · 1:30 p.m.– 3:00 p.m.
|Thursday, February 14|
Hamilton Colloquium Series - Duncan Haldane, Princeton University - "The Entanglement Spectrum: A new tool for studying quantum states of matter"
Until recently, the von Neumann entropy and its generalizations (Renyi) were the principal quantitative characterizations of entanglement. A richer characterization, first developed here at Princeton, is becoming the tool of choice for investigating topological (and conventional) order in quantum ground states of condensed matter systems. A Schmidt decomposition that partitions the ground state between two sets of degrees of freedom can be presented as the spectrum of the reduced density matrix, characterized by symmetry quantum numbers, analogous to the spectrum of elementary excitations of a Hamiltonian. From this spectrum, a rich amount of information about the ground state, both topological and geometrical, can be extracted.
Jadwin A10 · 4:30 p.m.– 5:30 p.m.
|Friday, February 15|
High Energy Theory Seminar - IAS - Daniel Harlow, Princeton University - “Quantum Computation vs. Firewalls”
Almheiri, Marolf, Polchinski, and Sully have claimed thatunitarity of black hole evaporation is inconsistent with the existenceof a smooth horizon. I will argue that computational restrictionsprevent the type of thought-experiment which motivates their argumentfrom being done, and I will speculate about what type of theory couldmake use of this loophole to avoid their conclusion withoutintroducing new inconsistencies.
Bloomberg Lecture Hall · 1:30 p.m.– 3:00 p.m.
|Saturday, February 16|