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TUŠAR, Kaja, SERŠA, Igor. Use of nonlinear pulsed magnetic fields for spatial encoding in magnetic resonance imaging. Scientific reports. 2024, vol. 14, art. 7521, 15 str. ISSN 2045-2322. https://www.nature.com/articles/s41598-024-58229-x.

This study examines the use of nonlinear magnetic field coils for spatial encoding in magnetic resonance imaging. Existing theories on imaging with such coils share a complex reconstruction process that originates from a suboptimal signal interpretation in the spatial-frequency domain (k-space). In this study, a new solution to this problem is proposed, namely a two-step reconstruction process, in which in the first step, the image signal is converted into a frequency spectrum, and in the second step, the spectrum, which represents the distorted image, is geometrically and intensity corrected to obtain an undistorted image. The results of this study facilitate the use of simple encoding coil designs that can feature low inductance, allowing for much faster switching times and higher magnetic field gradients.

Hana Kokot, Boštjan Kokot and Iztok Urbančič (Laboratory of Biophysics, Condensed Matter Physics Department, F5) have, together with colleagues from the Faculty of Pharmacy (University of Ljubljana), published a paper titled Amphiphilic coumarin-based probes for live-cell STED nanoscopy of plasma membrane in the journal Bioorganic Chemistry.

The authors synthesized and characterized a novel amphiphilic fluorescent label SHE-2N, which enables quick and long-lasting fluorescent labeling of the outer cell membranes of living cells. This new label for fluorescence microscopy is also suitable for high-resolution STED microscopy and two-photon microscopy due to its high photostability and appropriate spectral characteristics.

Andraž Rešetič, at the invitation of the editor of Communications Chemistry, published a review article titled “Shape programming of liquid crystal elastomers,” Commun Chem 7, 56 (2024), in which he provided a brief overview of current shape programming methods for liquid crystal elastomers (LCEs). LCEs are materials that reversibly change shape when exposed to external stimuli, such as light or heat. The local arrangement of liquid crystal components in LCEs affects the complexity of the shape response, and this arrangement is programmed into the material using various processes, including mechanical deformation, external electric or magnetic fields, polarized light, and other methods. As an unavoidable part of LCE synthesis, these processes also introduce geometrical constraints and influence the final size and amount of synthesized material. Therefore, the applicability of LCEs is highly dependent on the methods used. In the article, the author explored these limiting factors and provided his perspective on the future implementation of LCEs in everyday applications.

Journal Physical Review Letters published a paper “Dynamics and Topology of Symmetry Breaking with Skyrmions”, by Jaka Pišljar, Andriy Nych, Uliana Ognysta, Andrej Petelin, Samo Kralj and Igor Muševič, from J. Stefan Institute and Institute of Physics, Kyiv. The authors showed how the formation of the half-skyrmions-vortices from the high temperature isotropic phase dramatically changes as the chiral liquid crystal sample is confined to thickness below 100 nm. They observed unusally slow fluctuations, which represent spontanoeus formation and decay of individual half-skyrmions, also shown in the accompanying figure. The rate of such dynamics is 4 orders of magnitude slower of what was expected and is explained by the mechanism of thermal hopping between states, which become energetically accessible due to the strong confinement effects. This phenomenon is interesting from the topological point of view as well, as the experiments reveal the mechanisms of  topological charge conservation at the phase transition. The paper was also highlighted in the journal Physics.

Aljaž Kavčič and doc. dr. Matjaž Humar from the Laboratory for biological and soft photonics, Department of Condensed Matter Physics, along with dr. Nerea Sebastian from the Department of Complex Matter at the “Jožef Stefan” Institute, in collaboration with colleagues from the “Max-Planck Institute for the Science of Light”, have published an article in Nature titled Tuneable entangled photon pair generation in a liquid crystal. In their work, they, for the first time, demonstrate the generation of entangled photons in liquid crystals and, with this, in any organic material. In addition to the fact that the efficiency of entangled photon generation in liquid crystals is comparable to the best existing sources, their main advantage lies in the tunability of the state of photon pairs. This tunability can be achieved by applying an electric field or by arranging the liquid crystal molecules into the appropriate configuration. The ability to tune the quantum state indicates significant practical potential for numerous quantum technologies. A summary of the research can also be viewed in a short video.