Events
Condensed Matter Seminar
Quasistatic transfer protocols for atomtronic superfluid circuits *** Zoom invitation added ***
Mr. Yehoshua Winsten
Bgu
Mon, 01 Jun 2020, 11:30
Sacta-Rashi Building for Physics (54), room 207
Abstract: This seminar will be on Zoom *only* please see the details below.
Quasi-static protocols for systems that feature a mixed phase-space with both chaos and quasi-regular regions are beyond the standard paradigm of adiabatic processes. We focus on a many-body system of atoms that are described by the Bose-Hubbard Hamiltonian, specifically a circuit that consists of bosonic sites. We consider a sweep process: slow variation of the rotation frequency of the device (time dependent Sagnac phase). The parametric variation of phase-space topology implies that the quasistatic limit is irreversible. Detailed analysis is essential in order to determine the outcome of such transfer protocol, and its efficiency.
Dganit Meidan is inviting you to a scheduled Zoom meeting.
Topic: Yehosua Winsten
Time: Jun 1, 2020 11:30 AM Jerusalem
Join Zoom Meeting
https://zoom.us/j/95221139473?pwd=aXA5YTUyRnBvT21KYTNOVks1WFNQdz09
Meeting ID: 952 2113 9473
Password: 342825
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Meeting ID: 952 2113 9473
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Particles and Fields Seminar
Catching recoiling ions from cold collisions and nuclear beta-decay
Ben Ohayon
Eth Zürich
Mon, 01 Jun 2020, 14:00
Zoom only
Abstract: Zoom only: https://zoom.us/j/95759068407
The last decade witnessed a plethora of applications of experimental methods from AMO physics to low-energy nuclear physics. These include precision laser spectroscopy of short lived or exotic atoms, penning-trap mass spectrometry, and atom-trap trace analysis. A new and promising direction is the application of charged particle imaging methods for medium energy (keV) particles recoiling from nuclear decay.
In this talk I present a new experimental scheme that combines the well-established method of velocity-map-imaging with a metastable neon MOT target. We use this MOT-VMI for obtaining the branching ratios and recoil-ion energy distributions for the penning ionization process in optical collisions of cold metastable neon, from which we extract the potential depth of the highly excited dimers, and compare with theoretical calculations [1].
In the second part of the talk I will show the design and simulation of a High-Energy MOT-VMI acting as a 'decay microscope' for short-lived neon isotopes, enabling the measurement of branching fractions to various excited states, and angular correlations between the decay products. In light of on-going and planned experiments in this field, the main opportunities to make a significant impact using trapped neon isotopes, is in searching for, or excluding, new tensor physics which is coupled to right-handed neutrinos, as well as extracting the Vud CKM matrix element for mirror and superallowed Fermi transitions [2].
[1] BO, H Rahangdale, J Chocron, Y Mishnayot, R Kosloff, O Heber, G Ron. Physical Review Letters 123 (6), 063401
[2] BO, H Rahangdale, E Parnes, G Perelman, O Heber, G Ron. Physical Review C 101 (3), 035501
Zoom only:
https://zoom.us/j/95759068407
Biological and soft-matter physics
A theory of Gap Junction Plasticity
Mr. Eyal Fishel
Dept. Of Physics, Ben-Gurion University Of The Negev
Thu, 04 Jun 2020, 12:00
ZOOM meeting ID: 919-198-85007 Password: 2q35r3
Abstract: Rhythms in the brain have been reported in relation with a wide range of cognitive tasks. Moreover, changes and modifications to the normal rhythmic activity have been linked to pathologies and mental disorders. Although the functional role of rhythmic activity in the brain is yet undecided, it is clear that rhythmic activity is abundant in the brain. Numerous theoretical studies investigated the underlying mechanisms for rhythmic activity. However, all these studies require a certain degree of fine tuning of parameters (such as the strengths of synaptic connectivity) to generate the desired rhythmic activity. This raises the question:
What possible mechanism can regulate network parameters in order to stabilize a specific rhythm?
It was suggested that a synaptic learning rule, known as spike-timing-dependent-plasticity, can provide such a mechanism. However, synaptic connectivity is not the only means of neuronal interaction. Gap junctions, intercellular channels permitting a bi-directional flow of ionic currents across paired cells, have been shown to facilitate synchronized neural activities. Moreover, it has been claimed that Gap junctions have an important role in governing rhythmic activity. Recently, experimental studies demonstrated that similar to synaptic connectivity, Gap junctions also undergo activity-dependent plasticity.
Here we study the hypothesis that Gap junction plasticity may (also) serve as a mechanism for stabilizing and regulating the desired rhythmic activity in the brain. We propose that Gap junction undergo activity dependent plastic changes that take into account the temporal and causal relations and suggest a learning rule that generalizes synaptic spike-timing dependent plasticity. We then study under what conditions does our hypothesized gap junction plasticity rule stabilize the resultant oscillations? How do the features characterizing the plasticity rule govern the rhythmic activities?
We address these questions in the framework of a modelling study. We investigate Gap junction plasticity in a model of reciprocally connected neuronal network via Gap junctions. Analyzing the rhythmic activity as function of the Gap junction couplings provides the phase diagram of the system. Assuming Gap junction plasticity occurs at a slower timescale than the rhythmic activity we use the separation of timescales and develop the Gap junction plasticity dynamics in the limit of slow learning. Thus, Gap junction plasticity induces a flow on the phase diagram of the system. Next, we analyze, analytically and numerically under what conditions can Gap junction plasticity stabilize a specific rhythmic activity, and if so, what features of the Gap junction plasticity rule govern the resultant rhythmic activity. Thus, our theory demonstrates that in principle Gap junction plasticity can provide the stabilizing mechanism for rhythmic activity. The constraints on the plasticity rule obtained from our theory, provide further predictions for the validity of our theory.
Join URL: https://zoom.us/j/91919885007?pwd=WVRtRjlqQ1lDZkJ1cmJGbEcwSW4wZz09
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