לוח שנה משולב

The innervation of peripheral targets during embryonic development is largely regulated by the levels of target-derived trophic factors. But whether additional target-derived factors act in concert with these trophic factors and their identity is largely unknown. Sensory innervation of the mammary gland is controlled by Brain derived-neurotrophic factor (BDNF), and sexually dimorphic sequestering of BDNF by the truncated form of its receptor (TrkB.T1), directs male-specific axonal pruning in mice.
In search for cues that control the innervation together with BDNF I have found specific, non-dimorphic, expression of Semaphorin family members in the mouse mammary gland, which signal through PlexinA4. PlexinA4 deletion in both female and male embryos caused developmental hyperinnervation of the gland, which could be reduced by genetic co-reduction of BDNF. Moreover, in males, PlexinA4 ablation delayed axonal pruning, independently of the initial levels of innervation.
Overall, my study shows that precise sensory innervation of the mammary gland is regulated by the balance between trophic and repulsive signaling. Upon inhibition of trophic signaling, these repulsive factors are critical to promote axonal pruning.

A few years ago, the first signs of a new emergent particle — Majorana modes — were obtained. It was an exciting development because Majoranas are predicted to show nonabelian particle-exchange statistics, which would be a first for any physical system. As if that weren’t enough, another motivation to develop this experimental observation into a controlled electronic device is that the use of topology in such systems is expected to yield unrivalled coherence in topological qubits made from Majoranas. The experimental situation is that we aren’t there yet, not because of unforeseen problems — in fact, the foreseen problems are hard enough. This talk will address where things stand, how’s the qubit, what are the challenges, and what is the future of this unconventional approach to quantum information.

Despite the importance of tissue microstructure in health and disease, its noninvasive characterization remains a formidable challenge. Signal representations (diffusion/kurtosis tensors) are unspecific while tissue modelling using ideal geometries representing different cellular components have failed when scrutinized vis-à-vis histology: axon diameter, for example, is overestimated by factors of >6. Biophysical models characterizing signal behavior in specific diffusion-weighting regimes (power law scaling in “q” or “t”) have been more recently proposed as more reliable means for characterizing tissues. In recent years, the most prevalent biophysical model for diffusion in tissues was termed the “Standard Model”, consisting of a sum of gaussian components (nearly always two), one of which with zero diffusivity (stick). In the lecture, we will present validity regimes for the standard model and provide evidence for its limits. We will then propose a few novel means for characterizing

Nuclear Pore Complex (NPC) is a biomolecular “nanomachine” that controls nucleocytoplasmic transport in eukaryotic cells. The key component of the functional architecture of the NPC is the assembly of the polymer-like intrinsically disordered proteins that line its passageway and play a central role in the NPC transport mechanism. Due to paucity of experimental methods capable to directly probe the morphology and the dynamics of this assembly in intact NPCs, much of our knowledge about its properties derives from /in vitro/ experiments interpreted through theoretical and computational modeling.
Remarkably, despite their molecular complexity, much of the behavior of these assemblies and their selective permeability with respect to cargo-carrying transport proteins can be understood based on minimal complexity models relying on the statistical physics of molecular assemblies on the nanoscale. I will present the recent insights into the architecture and the dynamics of the NPC arising from the theoretical analysis of the wide range of experimental results.

Solid-state theory has been formulated in the 20th century on the assumptions of regular crystalline lattices where linear dynamics holds at both classical and quantum levels, while dissipative effects are taken into account to perturbative order. While considerable success has been achieved in the further understanding of disorder effects on the electronic properties of solids, the same is not true for the thermal, vibrational and mechanical properties due to the difficulty of reformulating the whole body of lattice dynamics in a non-perturbative way for disordered systems. I will present a formulation of lattice dynamics extended (in a non-perturbative way) to disordered systems, called Nonaffine Lattice Dynamics (NALD), successfully tested on different systems [1-3]. I will then consider the effect of viscous dissipation on the lattice dynamics of crystalline solids and show how dissipation can lead, in perfectly ordered crystals, to effects very similar to disorder-induced effects in glasses. Theory can explain all these surprising effects in perfect crystals as a result of anharmonic damping inducing diffusive modes that compete with propagating modes [4], and also predicts similar effects resulting from low-lying soft optical phonons (experimentally confirmed). This framework may lead to a new quantitative connection between lattice/atomic parameters, electron-phonon coupling and the Tc of superconductors with the possibility, in future work, of rationalizing a variety of experimental data and to provide a more quantitative (less empirical) understanding of how Tc can be varied in conventional and perhaps also more exotic superconductors.
[1] A. Zaccone and E. Scossa-Romano, Phys. Rev. B 83, 184205 (2011). [2] R. Milkus and A. Zaccone, Phys. Rev. B 93, 094204 (2016). [3] V.V. Palyulin, C. Ness, R. Milkus, R.M. Elder, T.W. Sirk, A. Zaccone, Soft Matter 14, 8475 (2018). [4] M. Baggioli and A. Zaccone, arXiv:1810.09516v1 [cond-mat.soft].

Electrostriction is a second order electro-mechanical coupling that exists in all dielectrics. Classical electrostriction describes anharmonic perturbation of the chemical bonds in the lattice, which gives rise to changes in the average position of atoms. It was found that the mechanism of electrostriction in gadolinium doped ceria (CGO) is fundamentally different from that of classical electrostriction, in which high electrostriction goes together with a large dielectric constant. The mechanism of electrostriction in CGO is not known yet. However, the current hypothesis attributes it to rearrangement of local distortions in the fluorite lattice.
This PhD thesis presents investigation of non-classical electrostriction effect in self-supported films of gadolinium doped ceria: dependence of the electrostriction strain coefficient on frequency and magnitude of the electric field and mechanical fatigue in thin films. Using self-supported Al/Ti/CGO/Ti/Al structure, I also identified electro-chemo-mechanical effect, which was previously considered unfeasible actuation mechanism at room temperature. The processes presented in this work provide a technological basis for integrating CGO as an active material in electro-active ceramic MEMS (microelectromechanical system)-actuation devices.