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: February 21, 2024 2:15 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", Ed. W. Liu 2015, Springer-Verlag Berlin Heidelberg, chapter 26

When: June 14, 2023 2:00 PM (Israel Standard Time).

Where: Room 223, Multipurpose Bldg. & over Zoom

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