לוח שנה משולב

Despite being a very useful and versatile tool, Nuclear Magnetic Resonance (NMR) has a major disadvantage in the form of its inherently low signal to noise ratio (SNR) compared to other methods of spectroscopy. One approach to enhance the SNR is by increasing the initial nuclear polarization. This can be done by, among other ways, dynamic nuclear polarization (DNP), the topic of my Masters research project. In DNP the large electron polarization is transferred to nuclei by the use of MW irradiation, thereby increasing the NMR signal. In this lecture I will show experimental results from our hybrid pulsed Electron Paramagnetic Resonance and NMR DNP spectrometer, from samples of DMSO/Water and a derivative of the stable radical 2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO). I interpret the data using a quantum mechanical theoretical model that gives good agreement with the experimental results, and through other quantum mechanical simulations of DNP systems.

The ability to anticipate and prepare in advance to changes in the environment is ascribed to neuronal systems in multi-cellular organisms. Yet by means of gene expression regulatory connectivity microbes too may have evolved to "anticipate" and prepare in advance. I will present evidence for microbial Pavlovian-like conditioning and discuss the similarities and differences to conditioning in the neuronal-cognitive context.

A paradox stems from the discrepancy between the large number of protein-protein interactions (PPIs) characterized by large-scale experiments, and the comparatively smaller number of PPIs that the scientific community can make biological sense of. This paradox fuels debates around a fundamental question: what do all these interactions mean? We argue that a large number of physical PPIs may simply be nonfunctional, or promiscuous. That is, they do exist in cells, they can be detected by typical PPI assays, but they have not evolved to achieve a particular function. We will examine this question from several different perspectives.


In a first, theoretical and computational part, (i) we will see two formalisms that anticipate the existence of promiscuous interactions (Levy, JMB, 2010; Levy, Landry, Michnick, Science Signaling, 2009); (ii) furthermore, by projecting amino-acid evolutionary conservation onto protein structures, we will see that mutations likely to induce promiscuous interactions with other proteins are selected against; (iii) finally, because non-functional interactions should not be conserved across organisms, we will assess the evolutionary conservation of a particular type of PPI: kinase-substrate interactions. This will reveal that the fraction of functional interactions could in fact be smaller than the fraction of promiscuous ones (Landry, Levy, Michnick, TiGs, 2009).


In a second, experimental part, we will see (i) how we can use promiscuous interactions to our advantage to create an in-vivo PPI microarray in yeast; and (ii) how we can filter promiscuous PPIs using information on their dynamics across different growth conditions

Originating from the works of Bekenstein and Hawking on the entropy of black holes, area laws constitute a central tool for understanding entanglement and locality properties in quantum systems. Essentially, in a system that obeys an area law, the _entanglement_ entropy of a bounded region scales like its boundary
area, rather than its volume.

In 2007, in a seminal paper, Hastings proved that all 1D quantum spin systems with a constant spectral gap obey an area law in their ground state. The proof, however, uses rather involved analytical tools such as the Lieb-Robinson bounds and does not seem to be generalizable to higher dimensions. In this talk I will present a new, purely combinatorial, proof of the 1D area law for frustration-free systems. The proof gives an exponentially better bound on the entanglement entropy, and, in addition, might be generalizable to higher dimensions.

In the center of the proof lies a new tool called ``the detectability lemma'', which proves extremely useful for studying the ground states of frustration-free systems. I will describe this lemma, and also use it to present a very simple proof of another seminal result of Hastings: the exponential decay of correlations in the ground states of gapped spin systems (in any dimension).

The talk connects various works: Aharonov, Arad, Landau and Vazirani, 2008 & 2010 [3,4], as well as Hastings 2003 & 2007 [1,2].

Refs:
[1] http://arxiv.org/abs/cond-mat/0305505
[2] http://arxiv.org/abs/0705.2024
[3] http://arxiv.org/abs/0811.3412
[4] http://arxiv.org/abs/1011.3445