Doron Chelouche (University of Haifa) | Unlocking Line-Locking Phenomena in Quasars | Quasars are unique phases in the lifetime of galaxies during which their central supermassive black hole is in the process of accreting material at a high rate. This phase is accompanied by the ejection of material from the central regions of the galaxy with outflow speeds of order 10,000 km/sec, which can substantially affect the large-scale environment of the quasar. In this talk, the phenomenon of quasar outflows will be reviewed as well its connection to “big” astrophysical problems pertaining to the formation and evolution of galaxies, the enrichment of the inter-galactic medium with heavy elements, and the growth of supermassive black holes. Specifically, the largely overlooked phenomenon of line locking, which appears to be very common in quasar outflows, will be reviewed, and its physical implications for quasar- outflow physics will be discussed. It will be shown that the phenomenon of line-locking poses significant challenges to current theories of quasar outflows with implications for the physical mechanisms underlying cloud formation and acceleration, as well as for the confinement of such clouds over dynamical timescales in the interstellar medium of (active) galaxies. When: April 15, 2024 2:15 PM (Israel Standard Time). Where: delivered over zoom only.

Michael Lublinsky (Ben-Gurion University of the Negev) | Quark Gluon Plasma: from Early Universe to Heavy Ion Collisions | Quark Gluon Plasma is an exotic state of hadronic matter, which existed when the Universe was extremely hot, shortly after the Big Bang. On Earth, these conditions are recreated in heavy ion collision experiments. I will give an overview of the research program highlighting some major experimental results and theoretical ideas employed to explain them. Recording Slides When: March 6, 2024 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Erez Gilad (Ben-Gurion University of the Negev) | Reactor Physics: An essential link towards nuclear energy in Israel | Nuclear power, characterized by its reliability, safety, and minimal carbon emissions, contributes approximately 10% to the global electricity supply, with around 450 reactors operational across over 30 nations, accumulating more than 19,000 operational years since the 1960s. Israel has been exploring integrating nuclear energy into its national energy portfolio since the 1970s. Despite the clear benefits of diversifying its energy sources to include nuclear power, Israel must resolve some unique geo-political and security challenges to actualize its nuclear power ambitions. Nonetheless, Israel is preparing to transition into a newcomer state in the nuclear arena. The field of Reactor Physics deals with studying nuclear processes inside a reactor core, especially the nuclear fission chain reaction. This field is essential for understanding the neutron’s behavior in the core and improving its neutronic design. The reactor core constitutes a highly complex system involving many coupled physical, chemical, mechanical, electrical, and material science processes. This colloquium will start with a brief overview of nuclear energy, highlighting the specific considerations and challenges from an Israeli perspective. The central part of the talk will cover contemporary problems and advances in reactor physics research. This includes exploring stochastic evolutionary algorithms, specifically genetic algorithms, to optimize nuclear core performance, the application of the neutron transport equation and its adjoint for enhancing neutronic core design, and the utilization of the integral neutron transport equation to improve the accuracy of the neutron diffusion approximation. When: May 27, 2024 2PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Uri Nevo (Tel Aviv University) | Thoughts on the mechanics of our thoughts | Brain activity is a set of electrical events, setting the basis for the view of the brain as a unique binary-coded electric computer. However, neuronal activity includes multiple mechanical events. The propagating wave of depolarization includes release of heat and a wave of swelling that acts like an acoustic wave along the interface of the lipid bi-layer. Both phenomena have no place in the classical Hodgkin-Huxley model. What is the biological origin of these and of additional mechanical events? What is their physiological importance? In this lecture I will propose a new hypothesis regarding the way mechanical changes in active neurons define the phenomenon of short term memory. Specifically, we suggest that action potentials trigger an in-flow and release of Ca2+ to the cell’s cytosol. We suggest that this inflow triggers the recruitment of Myosin light chains on the cellular circumference and their phosphorylation. This may happen on a very fast time scale and increase tension that persists in activated neurons. Thus, activated neuronal circuits become a preferred route for further mechanical activations. We suggest that this is the known ‘activity-silent’ short term memory: a state-shift of the activated cells that become more susceptible to further activations relative to other cells. This view suggests that the brain is not different from other tissues that employ mechano-electric pulses to create forces and lead to actions. The potential implications extend beyond basic brain research, to the practical study of aging, neurodegenerative diseases and other brain pathologies. Recording When: February 7, 2024 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Yossef Zenati (Johns Hopkins University) | Nucleosynthesis and electromagnetic outcome from compact object mergers and their legacy | In the last decade, gravitational waves and multi-messenger time-domain astronomy provides a fresh view of the dynamic Universe and precursor of a new era in astrophysics. Notably, it sheds light on the astrophysics of compact objects, the origin of the heaviest elements, and allows for unique probes of fundamental physics. Those heavy elements produced via the rapid neutron capture process have remained a question of intense debate for many years. A fresh example event is the “kilonova” emission that accompanied GW170817 and revealed a binary neutron star merger. I will discuss recent results on the binary neutron stars simulation and how other explosive transient like the collapse of massive rotating stars “collapsars” which give rise to long GRBs and the formation of heavy elements in the universe. In particular, I will focus on two frontier research areas- neutron star mergers and collapsar (/ massive- collapsar). Also, I will highlight how multi-messenger astronomy may answer how does the Universe create the heaviest elements. Recording Slides When: January 31, 2024 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Ohad Shpielberg (The University of Haifa at Oranim) | Arrhenius Law in Interacting Systems: Unexplored Universalities, Phase Transitions and More Surprises | Protein unfolding, chemical reactions, and flashing of fireflies are all examples of thermal activation processes. In its most basic form, we will be interested in the escape rate of a particle in a potential trap, due to thermal fluctuations. The Arrhenius law famously captures the escape rate of this problem. For deep traps, Arrhenius law states that the escape rate is universal, independent of the details of the trap. Here, we revisit the escape problem for an interacting system. Unlike the single body case, known for over a century, we will show that the many-body escape problem leads to new universalities, phase transitions, and more surprises. Recording Slides When: January 10, 2024 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Ephraim Eliav (Tel Aviv University) | Benchmark electronic structure calculations at the edge of the Periodic Table | High-accuracy calculations of atomic properties of the heaviest elements are reviewed (for more details see [1]). The properties discussed include electronic structure and energetics (ionization potentials, electron affinities, excitation energies), which are associated with the spectroscopic and chemical behavior of these elements and are therefore of considerable interest. Accurate predictions of these quantities require high order inclusion of relativity, QED and electron correlation effects, as well as large, converged basis sets. The Dirac-Coulomb-Breit Hamiltonian, which includes all terms up to second order in the fine-structure constant, serves as the framework for the treatment; higher-order Lamb shift terms are considered in most cases. Electron correlation is treated by the Fock-space coupled cluster method, enhanced by the intermediate Hamiltonian scheme, allowing the use of large, converged model (P) spaces. The calculations on superheavy elements (SHE) are supported by the very good agreement with experiment obtained for the lighter homologues, usually within a few hundredths of an eV, and similar accuracy is expected for the SHEs, with Z>100, for which experimental values are scarce. Many of the properties predicted for these species differ significantly from what may be expected by straightforward extrapolation of lighter homologs, demonstrating that the structure and chemistry of SHEs are strongly affected by relativity and electron correlation. The major scientific challenge of the calculations is to find the electronic structure and basic atomic properties of a SHE and assign its proper place in the Periodic Table. The extended Periodic Table up to E174 is presented on the base of our benchmark calculations. Different unusual inclinations and irregularities of the Periodic Law at the edge of extended Periodic System are discussed. References: 1) E. Eliav, A.Borschevsky, U.Kaldor, in “Handbook of Relativistic Quantum Chemistry”,

Menachem Stern (University of Pennsylvania) | Learning in physical machines | From electrically responsive neuronal networks to the adaptive immune response, biological systems can learn to perform complex tasks. In this seminar, we explore physical learning, a framework inspired by computational learning theory and biological systems, where networks physically adapt to applied forces to adopt desired functions. Unlike traditional engineering approaches, physical learning is facilitated by physically realizable learning rules, requiring only local responses and no explicit information about the desired functionality. Our research shows that such local learning rules can be derived for broad classes of physical networks, and that physical learning is indeed physically realizable through laboratory experiments. Furthermore, we demonstrate that learning induces architectural changes in the physical network, leading to a decrease in the effective physical dimension and a realignment of its inherent coordinate system to the learned task. These effects suggest a method for discovering the task that a novel network may have been trained for. By leveraging the advances of statistical learning theory in physical machines, we propose autonomous physical learning as a promising bridge between computational machine learning and biology, with the potential to enable the development of new classes of smart metamaterials that adapt in-situ to users’ needs. When: June 7, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Yasmine Meroz (Tel Aviv University) | Plant Tropisms as a Window on Plant Computational Processes | Plants survive in a harsh and fluctuating environment, optimising their search for fluctuating nutrients, and predicting danger. They achieve this through complex response processes, such as decision-making, based on memory, or the capability to accumulate and compare past stimuli. For example, a plant shoot accumulates sensory information from various fluctuating light sources, decides which direction yields consistently most light for photosynthesis, and grows in that direction. Here we propose a reverse-engineering approach to investigating the underlying rules for the accumulation and integration of sensory inputs. Our theoretical model, based on response theory, predicts that plants respond to the sum of stimuli at short timescales, and to the difference in stimuli at longer timescales. We confirm this experimentally, and suggest that this process may be essential for navigational problem-solving capabilities of plants. I will also briefly talk about the role of art in science, giving two particular examples of collaborations with artist Liat Segal: “Tropism” and “Impossible Object” When: May 31, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

David Andelman (Tel Aviv University) | One Hundred Years of Electrified Interfaces: What’s New with the Theories of Debye and Onsager? | The Poisson-Boltzmann theory stems from the pioneering works of Debye and Onsager and is considered even today as the benchmark of ionic solutions and electrified interfaces. It has been instrumental during the last century in predicting charge distributions and interactions between charged surfaces, membranes, electrodes, macromolecules, and colloids. The electrostatic model of charged fluids, on which the Poisson-Boltzmann description rests and its statistical mechanical consequences have been scrutinized in great detail. Much less, however, is understood about its probable shortcomings when dealing with various aspects of real physical, chemical, and biological systems. After reviewing the Poisson-Boltzmann theory, I will discuss several extensions and modifications to the seminal works of Debye and Onsager as applied to ions and macromolecules in confined geometries. These novel ideas include the effect of dipolar solvent molecules, finite size of ions, ionic specificity, surface tension, and conductivity of concentrated ionic solutions. When: May 17, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Shahar Hadar (The University of Haifa at Oranim) | Resolving the Photon Ring | In the past few years, the Event Horizon Telescope has released the first close-up interferometric images of two supermassive black holes, M87* and SgrA*. It is believed that within these images is embedded a fine, yet-unresolved brightness enhancement called the photon ring. The ring is a universal consequence of extreme lensing by the black hole and thereby conveys information on its spacetime geometry, potentially providing a new independent avenue for future tests of general relativity in the strong-field regime. In the talk I will briefly review the theory of the photon ring and its corresponding spacetime region, the photon shell, which governs the universal lensing structure. I will then describe some current efforts and future prospects for resolving the ring, which include both the construction of transformative new instruments and the development of novel analysis methods. Focusing on the latter, I will discuss how source variability may be harnessed to detect the ring. In particular I will review a recently proposed observable, the 2-point correlation function of intensity fluctuations around the ring, and present its recent generalization to frequency-dependent sources. Using a simple toy model of line- emitting, orbiting sources and integrating over the image, I will argue that extreme lensing effects induce particular spectro-temporal correlations in specific flux fluctuations that could be relevant for unresolved spectrometric observations. When: May 24, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Hillel Aharoni (Weizmann Institute of Science) | Tunable Architecture of Nematic Disinclination Lines | In this talk, I will introduce a theorethical framework to tailor three-dimensional defect line architecture in nematic liquid crystals. By drawing an analogy between nematic liquid crystals and magnetostatics, I will show that: i) disclination lines connect defects with the same topological charge on opposite surfaces and ii) disclination lines are attracted to regions of maximal twist. Using these principles, I will show quantitative predictions for the connectivity and shape of defect lines in a nematic confined between two thinly spaced glass substrates. I will demonstrate experimental and numerical verification of these predictions, and identify critical parameters that tune the disclination lines’ curvature within an experimental setup, as well as non- dimensional parameters that allow matching experiments and simulations at different length scales. Our system provides both physical insight and powerful tools to induce desired shape changes of defect lines, opening opportunities to design new types of smart materials. When: May 10, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Elisabetta Boaretto (Weizmann Institute of Science) | Plants-Climate-Atmosphere: Understanding Rapid Fluctuations in Radiocarbon Recorded in Archaeology | When: May 3, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Mikhail Shifman (University of Minnesota) | 50 Years of Supersymmetry | Abstract: I present a broad non-technical review of supersymmetry in our world from its inception to the current status. Related concepts of naturalness and strongly coupled field theories will be discusses too. This colloquium will be structured in a conversational manner; questions are most welcome. When: April 19, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Boris Shapiro (Technion) | Fluctuation-induced forces: from van Der-Waals to quantum friction | Abstract: All bodies are surrounded by a fluctuating electromagnetic field, due to the random motion of charges inside a body. These fluctuating fields give rise to forces between nearby bodies. Such fluctuation-induced forces go by the names of van der-Waals, Casimir or Lifshitz, depending on the circumstances. The purpose of this talk is to review the subject, with emphasis on the recent developments related to systems out of equilibrium. Slides When: March 29, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Eran Sharon (Hebrew University of Jerusalem) | Self-Morphing of frustrated sheets – from the lab to the real world and from statics to locomotion | Abstract: Humanity spends huge amounts of time, energy and resources in the shaping of solids into desired three-dimensional shapes. Unlike (nearly) all manmade structures, which are shaped by external constraints, most natural structures shape themselves via the distribution of non-uniform active growth. Apparently, this mode of shaping can be implemented with synthetic solid structures. Solids are not necessarily passive, they can be “programmed” to shape themselves upon induction. I will briefly present the principles and status of the field of “Self-Morphing”. Then I will focus on two different projects. In the first we attempt to “export” self-morphing from the scientific community and lab scale, to the real world of architecture and design. In the second project we study the locomotion of active gel sheets on a curved fluid interface. The sheets metabolize chemical energy (“food”) from their surroundings and convert it into periodic change of their curvature and to their periodic motion along the fluid interface. We suggest that the difference between the curvature of the sheet and that of the substrate leads to forces and torques on the sheet and to its locomotion. This mechanism is likely to be relevant to the motion of cells on curved surfaces (curvotaxis) When: March 22, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Haim Diamant (Tel Aviv University) | Using entropy to study systems out of thermal equilibrium | Abstract: Thermodynamic variables such as temperature and pressure are ill-defined out of thermal equilibrium. However, the relation between entropy and the information contained in the statistical distribution of the system’s microstates is assumed to hold regardless of whether or not the system is at equilibrium. Therefore, entropy should be a useful global property for characterizing non-equilibrium behaviors. We have obtained, based on first principles, a universal inequality relating the entropy of a system at steady state and the diffusion coefficient of its constituents. The relation can be used to obtain useful bounds for the diffusion coefficient (normal or anomalous) from the calculated thermodynamic entropy or, conversely, to estimate the entropy based on measured diffusion coefficients. We demonstrate the validity and applicability of the relation in several examples. We have derived a functional which takes as input measurable pair-correlations (such as the structure factor) and gives a useful upper bound for the entropy. We use it to pin-point and characterize dynamic transitions in several experimental and computational systems, including driven and active particles. When: March 15, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Yuval Garini (Technion) | The multi-scale structure of chromatin in the nucleus | Abstract: The DNA in a human cell which is ~2 meters long is packed in a ~10 μm radius nucleus. It is immersed in a condensed soup of proteins, RNA and enzymes and it is highly dynamic, while it must stay organized to prevent chromosome entanglement and for ensuring proper genome expression. Studying this nanometer – micrometer scale structure requires to use both high spatial and temporal resolutions and we combine comprehensive live-cell and molecular methods. Diffusion-based analysis allowed us to identify complex normal and sub-diffusion modes. The results allowed us to identify lamin A as the main player in the chromatin organization mechanism. It forms chromatin loops in the whole nuclear volume thereby restricting the chromatin dynamics increasing its elasticity and rigidity. Together with other mechanisms, it takes part in controlling gene expression and provides the nucleus its rigidity that is important even for preventing cell metastasis. When: March 8, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom

Barak Kol (the Hebrew University of Jerusalem) | The flux-based statistical theory for the three- body problem | Abstract: The Newtonian three-body problem is one of the richest, deepest and longest-standing open problems in physics. It is the fertile soil that brought about the paradigm change from the clockwork universe to chaos, and it grew numerous scientific theories including perturbation theory, the symplectic formulation of mechanics, and the mathematical field of topology. The generic, non-hierarchical, three-body system is known to be chaotic. In fact, it is so chaotic that one expects that a statistical solution is the optimal solution. Yet, despite considerable progress, all extant statistical approaches displayed two flaws. First, probability was equated with phase space volume, thereby ignoring the fact that significant regions of phase space describe regular motion, including post-decay motion. Secondly and relatedly, an adjustable parameter, the strong interaction region, which is a sort of cutoff, was a central ingredient of the theory. The talk will describe a theory that is based on phase-space flux, rather than phase-space volume, which remedies these flaws. Statistical predictions for the identity of the escaper, and other measurable quantities, will be shown to agree with computerized simulations considerably better than previous theories. Moreover, the flux-based theory enables to predict the distribution of decay times. This prediction relies on the definition and determination of a regularized phase-volume for the system, and the latter led us to a second aspect of the problem, namely a decomposed formulation of it. Basically, this decomposition separates the motion of the instantanoues plane defined by the three bodies, from the motion of the bodies within the plane. Recording Slides Youtube movie of a 3 body movement Based on: Barak Kol, “Flux-based statistical prediction of three-body outcomes”, Celest. Mech. Dyn. Astron. 133 17 (2021). Viraj Manwadkar, Barak Kol,

Matan Mussel (University of Haifa) | On spikes and sound: debating the physical nature of action potentials | Abstract: Excitable cells generate a characteristic transient change in transmembrane potential that propagates along the cell membrane in response to suitable stimuli. These signals are called action potentials (APs), and are principally associated with behavioral activities of many organisms. Thus, an understanding of the mechanism of APs, as well as their actions and interactions, constitutes one of the fundamental aspects of biology. The mechanism that underlies an AP is widely considered to be electrical, and is typically interpreted through a representation of the cell membrane as an equivalent electric circuit. However, the theory relies on phenomenological equations that require many fit parameters. In addition, several experimental facts are neither readily explained nor predicted by the electrical theory. On the other hand, solitary sound waves that propagate within lipid monolayers show remarkable similarities to APs and the theory of sound can bridge some of the gaps while using zero fit parameters. An important prediction of this approach is that electricity is merely one aspect of the signal, and it is, therefore, possible that valuable information is overlooked. The talk will conclude by proposing falsifiable predictions and discussing experimental and theoretical challenges. Recording Slides When: January 4, 2023 2:00 PM (Israel Standard Time). Where: Room 223, Multipurpose Bldg. & over Zoom