Integrated Calendar

Lasing during laser filamentation in the air was discovered about a decade ago. Its physical origins remain puzzling and controversial to this day. Yet, the phenomenon itself appears stubbornly robust and ubiquitous, arising experimentally under many different conditions.
In this talk I will argue that air lasing is a spectacular manifestation of lasing without inversion. In contrast to a frequent belief that lasing without inversion is a delicate, exotic, and fragile phenomenon,
this particular incarnation of it appears as inevitable and as robust as the simple fact that short intense laser pulses inevitably force nitrogen molecules in the air to align, ionize, and continue to rotate after the laser pulse is gone.
I will also point out how one can tailor the initial laser pulse to turn air lasing into lasing with real inversion. The implication is that once you fire your tailored laser pulse sequence into the air, the air might actually fire back at you, within a picosecond or so.

The ultimate purpose of sensory systems is to drive behaviour.  Yet the bulk of textbook knowledge of sensory systems comes from experiments on anaesthetised animals where the motor systems are disengaged.  The broad aim of our research is to investigate the neural basis of sensation in the behaving brain.  In this talk, I will present work that addresses two fundamental issues concerning the function of primary sensory cortex.  First, what role does Sensory Adaptation play under awake, behaving conditions?  Second, to what extent does behaviour modulate sensory processing in freely moving animals?

Visual information is transferred at the ribbon synapse – the first synapse of the visual system – from photoreceptors to bipolar cells and horizontal cells. Whereas multiple bipolar cell types form parallel channels of vertical signal transfer to ganglion cells, the output neurons of the retina, the molecular basis of horizontal function within the retinal circuitry remains enigmatic.
We have combined electrophysiology and calcium imaging with immunocytochemistry as well as single-cell RNA-sequencing and machine-learning approaches to establish a detailed map of voltage- and ligand-gated ion channels expressed by horizontal cells of the vertebrate retina. Our results provide a characteristic molecular signature of ionotropic glutamate receptors responsible for converting photoreceptor signals into postsynaptic membrane potential changes. We suggest that local information processing in horizontal cell dendrites is accompanied by cell-wide signals mediated by activation of voltage-gated calcium and sodium channels, which generate spike-like events. Comparison across different vertebrate species indicates a common theme of ion channel expression with variations based on evolutionary distance.
Correlating the spatio-temporal pattern of horizontal cell activity with the biophysical properties of ion channels and neurotransmitter receptors will provide a better understanding of early signal processing in the vertebrate retina.

A 47 years-old story that started with the discovery of an ordered organosilane monolayer that assembles itself on various polar surfaces has evolved into an ongoing “research thriller” craving explanations for a series of unusual experimental findings. Using interfacial electron beam lithography – a novel approach to chemical surface patterning that allows fabrication of hybrid inorganic-organic monolayer structures spanning nano-to-macroscale dimensions, we fabricate metal (Ag)-monolayer quasinanowires on silicon with micrometer-centimeter lengths and planned layouts that exhibit puzzling electrical conduction. Depending on the composition and structure of the quasinanowire and the nature of the silicon support, the room-temperature resistivities of such surface entities may vary between that of a practical insulator to some extremely low values. These findings defy rationalization in terms of conventional electrical conduction mechanisms. Interfacial systems with characteristic structural features akin to those of our quasinanowires have, however, been proposed in both the exciton model of high-temperature superconductivity (Little, Ginzburg, 1964-70) and that of superconductivity by the pairing of spatially separated electrons and holes (Lozovik & Yudson, 1976). While gathering additional clues that might shed light on the mystery of our thriller, these theoretical predictions spur us to seek the shining light at the end of the tunnel...

Proteins are highly dynamic biomolecules that can undergo ligand-induced
conformational changes, thus often playing a crucial role in biomolecular processes. For
an in-depth understanding of protein function, the conversion of one conformational state
into another has to be resolved over space and time. Pulsed electron-electron double
resonance spectroscopy (PELDOR/DEER) in combination with site-directed spin
labelling (SDSL) is a powerful tool for obtaining distributions of interspin distances in
proteins [1, 2]. It allows for measurements with Angstrom precision, but it cannot directly
determine the time scale and the mechanism of the conformational change. However,
coupling PELDOR with rapid freeze-quench techniques adds the time axis to the
distance distribution and thus permits studying conformational changes with temporal
resolution.
Here, we show that the combination of Microsecond Freeze-Hyperquenching (MHQ) [3]
and PELDOR resolves ligand-triggered conformational changes in proteins on the
Angstrom length and microsecond time scale. It allows taking snapshots along the
trajectory of the conformational change by rapid quenching within aging times of
82-668 μs, and it is applicable at protein amounts down to 7.5 nmol (75 μM, 100 μL) per
time point. We applied MHQ/PELDOR to the cyclic nucleotide-binding domain (CNBD)
of the MloK1 channel from Mesorhizobium loti, which undergoes a conformational
change upon binding of cyclic adenosine monophosphate (cAMP). We observed a
gradual population shift from the apo to the holo state on the microsecond time scale,
but no distinct conformational intermediates (Fig. 1a, b). [4]
Figure 1: a) Interspin distance distributions obtained at different aging times and b) the corresponding
fractions of apo and holo state. c) Free-energy profile of the ligand-induced conformational change.
Corroborated by measurements of ligand-binding kinetics and molecular dynamics (MD)
simulations, we interpret the data in terms of a dwell time distribution. The transitions
across the free-energy barriers (Fig. 1c) i.e., ligand binding and the conformational
change, are on the nanosecond time scale and thus below the time resolution of the
MHQ device. However, the dwell time of the apo state in complex with the cAMP ligand
is in the microsecond range and can be monitored by MHQ/PELDOR. [4]
Literature:
[1] A.D. Milov et al., Fiz. Tverd. Tela 1981, 23, 975-982. [2] G. Jeschke, Annu. Rev. Phys. Chem.
2012, 63, 419-446. [3] A.V. Cherepanov et al., Biochim. Biophys. Acta 2004, 1656, 1-31.
[4] T. Hett et al., J. Am. Chem. Soc. 2021, 143, 6981-6989.