לוח שנה משולב

Energy transfer through the Förster mechanism, often referred to as FRET, depends critically on the overlap between the emission of the donor chromophore and the absorption of the acceptor chromophore. When photochromic molecules (molecular photoswitches) are isomerized between the two forms, the absorption spectra typically experience dramatic changes. Also, some photoswitches display emission exclusively in one isomeric form. This opens up the possibility to switch the capacity to act as both donor- and acceptor units, and hence, also to control energy transfer processes with concomitant changes in the fluorescence pattern.
In addition to the abovementioned spectral features, the rate of the FRET process is highly dependent on the distance between the donor and the acceptor. This parameter can also be varied using molecular photoswitches, in the making/breaking of supramolecular complexes, which in turn dramatically changes the donor-acceptor distance and the FRET efficiencies.
In this presentation, I will give examples of how the both these approaches can be used to tune the emissive properties of photochromic constructs. From trivial fluorescence “on-off” switching, via directional switching, to systems displaying full-color reproduction.

Individual differences are an essential property of all living things, and personality provides a unique glimpse into the biology underlying behavioral variability. And yet, because of the lack of a systematic approach to personality, most works on animal personalities still end up examining a limited subset of subjectively chosen behavioral readouts. Lately, we have shown how personality can be inferred directly and objectively from high-dimensional natural behavioral space. While this approach is not species-specific, we have demonstrated it on mice as it is one of the most common model animals. The mice were videoed over several days, and their behavior automatically analyzed in depth. Altogether, the computer identified 60 separate behaviors such as approaching others, chasing or fleeing, sharing food or keeping others away from food, exploring, or hiding. We found the mice personalities by working backward from behavior and extracting the underlying traits that differ among individuals while being stable over time and across contexts. We validated that traits found this way (which we term identity domains) were stable across social context, do not change with age, explain the variability in performance in classical tests, and significantly correlates with gene expression in brain regions related to personality. Expanding this method to human behavior, by using location and physiological data from cellphones and smartwatches, revealed a highly structured personality space which resembles that of the mice. This method allows for better informed mechanistic investigations into the biology of individual differences, systematically comparing behaviors across species, as well as develop more personalized psychiatry. Recently we have also been employing this approach to subjectively quantify wellness and welfare in both people and animals, towards the biology of happiness.

Rivers are the most effective agent of erosion on earth, transporting massive amounts of detrital and dissolved matter into depositional basins, making them a significant part of the rock cycle. To better understand the relationship between denudation of continents and the rivers that drain them, numerous studies examine the pathways of sediment transport through large drainage systems. However, due to the complex nature of sediment storage and transport dynamics in large-scale fluvial systems, the amount of time sediment spends in the sedimentary system is poorly constrained.
We measured cosmogenic 21Ne to quantify the exposure time of sediments within large-scale fluvial systems in large rivers: the modern Colorado river, the Miocene Hazeva River (~18 Ma), and the Lower Cretaceous (~130 Ma) Kurnub fluvial system. We observe that fluvial transport dynamics in large rivers are complex and that sediment transport time varies significantly and can last between very rapid (faster than our analytical measurement limitation ~103 yr) and 105 yr. To better understand the nature of fluvial transport dynamics in large rivers, we constructed a stochastic model that simulates repeated episodes of burial and exposure and examines the changes in concentrations of cosmogenic 26Al, 10Be, and 21Ne. We compared the simulated results to the concentrations measured in the Colorado River, and we predict that the total that sediment spent both buried and exposed – the residence time in large rivers is ~103-105 years. These observations suggest that the time-scales of sediment transport in large rivers have not changed significantly over the past 130 Myr and have remained significantly fast compared to other processes in the rock-cycle.

Active materials are composed of many components that can convert energy from its environment (usually in the form of chemical energy) into directed mechanical motion. Time reversal symmetry is thus locally broken, leading to a variety of novel phenomena such as motility induced phase separation, reversal of the Ostwald process and flocking. Examples of active matter are abundant and range from living matter such as bacteria, actomyosin networks and bird flocks to Janus particles, colloidal rollers and macroscale driven chiral rods. Nevertheless, in many cases experiments on active materials exhibit equilibrium like properties (e.g., sedimentation of bacteria). In the first part of the talk I will try to answer the important question: how do we know a system is `active’? And if it is, can we have generic observables as in equilibrium thermodynamics? Can we measure how far it is from equilibrium? In the second part of the talk I will focus on examples of activity in biopolymer gels, such as the cytoskeleton of living cells. I will show some of the effects of active motors with emphasis on chiral motors. The latter does not have a unique hydrodynamic description, which one can utilize to gain access to the microscopic details of the complex motors using macroscopic measurements. I will also discuss non-motor activity and demonstrate how it can result in contractility, e.g., in the process of cell division.