Ren Xi-Jun

Job/Title:

Prof.

Primary Category:

Visiting Scientists

Discipline:

Condensed Matter Physics

Interests:

Atomic, Molecular and Optical Physics

Office:

Danciger B 222

Phone:

02 6586 355

E-Mail:

Upcoming Events

Yesterday

Biological Physics Seminar: "Single-cell time-resolved multiparameter fluorescence spectroscopy of phytoplankton"
- Start time: 10:00am
- End date: Wednesday, November 27th
- End time: 11:30am
- Lecturer: Eitan Lerner (HUJI) Abstract:
  
  Aquatic phytoplankton are in charge of the majority of photosynthesis on earth, and serve as the main contributors to primary productivity. Cells of these species carry molecular systems that specialize in funneling radiative energy for performing photosynthesis-related charge separation, and subsequently respiration. These systems include photosystems embedded in membranes, and light harvesting complexes on top of photosystems to optimize the funneling of radiative energy. Such well-controlled highly-efficient use of light is driven by the spatial organization of specific pigments and by the excitation energy transfer between them at different coupling regimes. As such, the autofluorescence of unicellular phytoplankton species is meaningful and therefore can be used for identifying different species and their metabolic responses to certain environmental changes. As for the control over the photosynthesis efficiency, time-resolved fluorescence can also be used.In this work I will showcase the single-cell time-resolved multiparameter fluorescence spectroscopy approach we used with our confocal-based setup, to extract multiple autofluorescence parameters, and use them to track photo-physiological changes that different phytoplankton species (i.e., cyanobacteria, dinoflagellates and red algae) undergo in response to changes in light intensity that mimic day/night cycles, as well as abrupt vertical mixing. Based on our results, we show how different species alter the function of their photosynthetic apparati differently in response to light intensity changes.In the next part of the talk, I will present some preliminary results from an experimental mimic of algal bloom rise of the Kinneret-Blooming Microcystis phytoplankton, in which we characterize the earliest stages in algal blooms before cells start to re-proliferate.In the final part of my talk, I will discuss some exotic excited-state dynamics, which suggest a unique energy trapping mechanism that exists in species of cyanobacteria with depopulation times that do not distribute exponentially.
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Nonlinear Physics seminar: "Complex bands and topology with coupled lasers"
- Start time: 12:00pm
- End date: Wednesday, November 27th
- End time: 01:30pm
- Lecturer: Nir Davidson, Dept. of Physics of Complex Systems, Weizmann Institute of Science, Rehovot, Israel Abstract:Complex coupling in periodic laser arrays leads to complex bands, where the real part corresponds to the dispersion relation of the band w(k) and the imaginary part corresponds to k-dependent loss. By precisely tuning the complex coupling and the array geometry we engineer the complex bands to generate unique topological lasing states. We demonstrate how lasing at Dirac points in a hexagonal laser lattice can lead to Klein tunneling of coherence through a barrier, how complex Hermitian coupling can generate artificial gauge fields and edge states. Finally, we characterize the effects of quenches disorder and hints to KT physic in coupled laser arrays.
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Monday, December 2nd

Physics Colloquium : "Are `analog computers' back in fashion?"
- Start time: 12:00pm
- End date: Monday, December 2nd
- End time: 01:30pm
- Lecturer: Prof. Oren Raz, Weizmann InstituteAbstract:In the last decade there have been several efforts to use physical systems as 'physical computers': D-Wave is using super-conducting qubits as an adiabatic computer, the Israeli company Light-Solver uses lasers to find optimal solutions to optimization algorithm, HP is developing `memristor computation', and companies like Toshiba and Fujitsu are commercializing products like `Bifurcation machines' and `Digital annealers'... In the talk I will review this topic, show some results, what we do and don't understand, and try to provide some intuition on what physical mechanisms are expected to give real benefits.
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Tuesday, December 3rd

Astrolunch: Cecilia Chirenti
- Start time: 05:00pm
- End date: Tuesday, December 3rd
- End time: 06:00pm
- Contact: Dima Ofengeim
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Ren Xi-Jun